CA2451882A1 - Nanofabrication - Google Patents

Abstract

Pathways to rapid and reliable fabrication of three-dimensional nanostructures are provided. Simple methods are described for the production of well-ordered, multilevel nanostructures. This is accomplished by patterning block copolymer templates with selective exposure to a radiation source. The resulting multi-scale lithographic template can be treated with post-fabrication steps to produce multilevel, three-dimensional, integrated nanoscale media, devices, and systems.

Description

NANOFABRICATTON
Government Rights This invention was made with govenunent support under U.S. Department of Energy Grant No. DE-FG02-96ERA45612, U.S. National Science Foundation Grant No. DMR-9809365, and U.S. National Science Foundation Grant No. CTS-9871782.
The government has certain rights in this invention.
Technical Field The invention relates to fabrication of nanoscopic structures. W particular, the invention relates to functionalized nanoscopic structures on surfaces.
Bacl~ground The fabrication of useful nanoscale devices has proved difficult. Approaches based on porous aluminum oxide (AnoporeTM), ion-tracl~-etched polycarbonate (NucleporeTM), ion-tracl~-etched mica, and other approaches, have been attempted.
Examples of these are disclosed by Mitchell et al., in "Template-Synthesized Nanomaterials in Electrochemistry", Electroanalytical C7zeTfZistny, A. J. Bard and I.
Rubinstein, Eds., 21, (1999), 1-74; Strijl~ers et al., in "Structure and Magnetization of Arrays of Electrodeposited Co Wires in Anodic Alumina," J. App. Plays., 86, (1999), 5141; Han et aL, in "Preparation of Noble Metal Nanowires Using Hexagonal Mesoporous Silica SBA-15," CheJn. Mater., 12, (2000), 2068-2069; Whitney et al., in "Fabrication and Magnetic Properties of Arrays of Metallic Nanowires,"
Science, 261, (1993), 1316; and in United States Patent No. 6,185,961 for "Nanopost arrays and process for malting same," to Tonucci et al.; and United States Patent No.
6,187,165 for "Arrays of semi-metallic bismuth nanowires and fabrication techniques therefor,"
to Chien et al. These approaches result in materials which can be very difficult or impossible to pattern laterally and/or integrate. Other devices which can be prepared are macroscopic in scale, as disclosed in Uuted States Patent No. 6,187,164 for a "Method for creating and testing a combinatorial array employing individually addressable electrodes," to Warren et al.

Recently, companies such as Samsung and Hitachi have used carbon nanotubes as field emission sources to make prototype field emission (FE) displays.
FE devices based on carbon nanotube materials are disclosed in "Flat panel display prototype using gated carbon nanotube field emitters," by Wang et al., App.
Phys.
Lett., 78, (2001) 1294, and can provide acceptable field emission, but can be difficult to fabricate.
Serial writing processes can be used to pattern magnetic media, as disclosed in "Writing and reading perpendicular magnetic recording media patterned by a focused ion beam," by Lohau et al., App. Plays. Lett., 78, (2001), 990, and "Magnetic block array for patterned magnetic media" by Koilce, et al., App. Phys. Lett., 78, (2001), 784. Researchers at IBM Almaden Research Center have utilized a fabrication scheme that resulted in patterned media having storage density of 100 Gb/in2, as described in Lohau et al. This scheme used a focused Ga ion beam to cut trenches in granular Co~oCr18Pt12 film media. These processes tend to be slow, and are not well suited to high tluoughput manufacture.
The efficiency of thermoelectric (TE) cooling devices has not increased significantly during the last 40 years, and currently, the figure-of merit (ZT) of the best materials is less than one. Semimetal materials such as Bi and Bi2Te3 have the highest ZT values and are ctnTently used in commercial TE devices manufacttued by companies such as Marlow and Melcor.
Summary By laterally patterning nanoscale arrays, a pathway to a rapid and reliable fabrication of three-dimensional nanostructures is provided. A simple method is described herein for the production of well-ordered, multilevel nanostructtues. This is accomplished by patterning blocl~ copolymer templates with selective exposure to a radiation source. The resulting multi-scale lithographic template can be treated with post-fabrication steps to produce multilevel, three-dimensional, integrated nanoscale media, devices, and systems.
W one aspect, the invention provides a method of preparing a laterally patterned array. The method includes coating some of conducting or semiconducting substrate (for example, a metal, such as gold) with a bloclc copolymer film (for example, a block copolymer of methylmethacrylate and styrene), where one component of the copolymer forms nanoscopic cylinders in a matrix of another component of the copolymer; placing a conducting layer on top of the copolyner to form a composite structure; vertically orienting the composite structure;
removing some of the first component fiom some of the structure to form nanoscopic pores in that region of the second component; cross-lining the second component; and at least partially filling some of the nanoscopic pores with a material.
The substrate can include conducting and non-conducting regions, which can be lithographically patterned. In such cases, a first component can be removed from some of the structure which is at least partially overlaying a conducting poution of the substrate. The structure can be vertically oriented by heating with an electric field, for example, for at least one hour. Some of the first compoizent can be removed by exposing some of the structure to ultraviolet radiation, an electron beam, or ozone.
Some of the first component can be removed by degrading the component and treating some of the stmcture with an agent that selectively removes the degraded component. Some of the nanoscopic pores can be filled by electrochemical deposition. Some of the nanoscopic pores and surface of the second component can be wetted with a surfactant prior to filling with material. Electrical current can be controlled to determine the amount of material deposited in the pores.
In another aspect, the invention provides an array manufactured by the methods described herein. The array can include a substrate, a polymer film on the substrate, and at least one set of parallel metallic (for example, gold, copper or nickel) or semi-metallic cylinders in the film, and arranged perpendicular to the substrate.
The cylinders can include a magnetic material, such as cobalt or nickel. The magnetic arrays can be used to malce a magnetic storage medium, or a magnetoresistance device, or a giant magnetoresistive device. Non-magnetic metals can be used in such arrays to make, for example, a field emission device. W some embodiments of these arrays, at least one set of cylinders includes n-type material and at least another set of cylinders includes p-type material. Such an array can be used to create a thermoelectric cooler. The cylinders can also include alternating layers of magnetic and non-magnetic material, whether the layers alterlate substantially regularly along the length of the cylinders or not. hi such arrays, the sets of cylinders can be configured in substantially regular geometrical shapes, such as circles or triangles. Of course, irregular shapes can also fmd application in the devices disclosed herein. In some of the arrays, one type of cylinder has a given magnetization direction, and another type has an opposite magentization direction. Il some embodiments, at least one set of cylinders is in electrical contact with another set of cylinders, for example, by a conductive contact on top of the film.
As used herein, the term "vertically-oriented," when referring to a copolymer film means a film that has cylindrical pores with the axis of the pores substantially normal to the surface with which the hlm is associated, or substantially normal to the film surface itself. The new materials can have cylindrical pores that are vertically oriented, or oriented at an angle to vertical, as long as the cylinders are oriented in substantially the same direction, e.g., in parallel. These cylinders can have various shapes and can, but need not, have a circular diameter cross-section.
As used herein, the term "nanoscale" refers to a characteristic size range, for example, of arrays, that is attained using the methods of self assembly of copolymer molecules described herein. For example, the pore diameter, the wire diameter, the wire lengths and the period of the array can be in the nanoscale range, that is, within a range of about a manometer to over a thousand manometers. As used herein the teen "nanowire" refers to nanoscale material created in an array pore. The term does not imply that the aspect ratio of the material need be high, and in some embodiments, the material to be deposited in an array can have a low aspect ratio. "Nanowires"
can also refer to material that is not necessarily electrically conductive; but is nevertheless.
useful when present in nanoscale arrays.
As used herein, the term "multilevel" refers to structL~res that can be constructed by multiple, independent levels of lithography, with at least one level created with a laterally-patterned diblocl~ copolymer film. As used herein, the teen "multilayering" refers to a structlual element within a single layer of lithography that contains more than one material. As used herein, the term "wire" refers to conductive material having width and length, where the aspect ratio (that is the ratio of length to width) is at least 2:1. This term is distinguishable from the term "dot,"
which refers to conductive material with Iower aspect ratios.
Unless otherwise defned, all techiucal and scientific terms used herein have the same meaning as coimnonly understood by one of ordinary slcill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. W addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
The techniques and systems described herein include many advantages. For example, the extremely high density of the magnetic cylinders in the new films offers the capability of using this system for next-generation magnetic data storage applications, with potential data storage densities in excess of 1000 Gbit/in2. The well-controlled size and separation distance of the magnetic metals on the metal, e.g., gold, film also offer the means to engineer next-generation giant-magnetoresistance magnetic-field-sensing devices.
The processes are parallel, scaleable, and not subj ect to the speed limitations experienced in nanofabrication techniques based on serial writing. The techniques are amenable to manufacture, in that they are simple, fast, and cost-effective.
They are readily adoptable by industry and compatible with other fabrication processes.
The techniques described herein significantly advance the general utility of nanofabrication by self assembling copolymer templates. The nanofabrication techniques are amenable to manufacture, in that they are simple, fast, and cost-effective. They are readily adoptable by industry and compatible with other industrial microfabrication processes. For example, lateral patterning offers the capability of using such systems for the manufacture of electronic circuits on clops. The integration of nanostriictures within chips and the interfacing of the stntctures with other chip elements in arbitrary locations is made possible through the methods disclosed herein.

For example, these three-dimensional structures offer the means to engineer electronic field-emission arrays. The arrays can be used in flat panel displays that are brighter, higher-resolution, less expensive, thimler, and more flexible than those currently available. Other field emission electron devices are possible, such as transistor-life devices, spin-polarized electron emitters, and other lmown devices based on field emission.
For example, the tluee-dimensional structures also offer the means to engineer solid-state thermoelectric cooling devices, including those with multistage cooling.
Other applications include magnetoresistive sensors, high-capacity magnetic data storage, smart media, spintronics, chemical-sensing devices, biomolecular diagnostic sensor arrays, designer "micromagnetic" media, and molecular electronics, for example.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims Brief Description of the Drawings Fig. 1 is a schematic diagram of an exposure process that can be used to create a nanoporous array, and subsequently can be used to create an array of nanowires.
Fig. 2a is a side view schematic diagram of a selective exposure process that can be used to create a laterally patterned diblocl~ copolymer film.
Fig. 2b is an overhead view schematic diagram of a selective exposure process that can be used to create a laterally patterned diblocl~ copolymer film, in this case, a triangle pattern.
Fig. 3 is a schematic diagram of a selective exposwe process that can be used to create a laterally patterned diblocl~ copolymer film, and subsequently can be used to create a laterally patterned nanostructure, in this case, a triaxlgle shaped nanostructure.
Fig. 4 is a perspective view schematic diagram of a multilevel nanostmctLUe created from laterally patterned dibloclc copolymer film.
Fig. 5 is an overhead view schematic diagram of a multilevel nanostnuctme created from laterally patterned diblocl~ copolymer film.

Fig. 6 is a perspective view schematic diagram of a field emission array created from laterally patterned diblocl~ copolymer film, including two sets of nanowires.
Fig. 7 is an overhead view schematic diagram of a field emission array created from laterally patterned diblocl~ copolymer fihn, including four individually-addressable sets of nanowires.
Fig. 8a is an overhead view optical image (at SX) of a sample showing an electrode pattern with a vertically-oriented diblocl~ copolymer film covering the surface.
Fig. 8b is an overhead view optical image (at SX) of the sample frolll Fig. 8a after electron beam patterning and removal of a copolymer component to form nanopores.
Fig. 8c is an overhead view optical image (at SX) of the sample from Fig. 8b after nanowires are electrodeposited on the sample.
Fig. 8d is a closeup overhead view optical image (at SX) of the sample from Fig. 8c.
Fig. 9 is a perspective view schematic diagram of a single-stage thermoelectric cooler created from laterally patterned diblocl~ copolymer film.
Fig. 10 is a perspective view schematic diagram of a four-wire, giant magnetoresistive (GMR) device created from laterally patterned dibloclc copolymer film.
Fig. l la is an overhead view optical image (at 10X) of a four-wire magnetoresistive device created from laterally patterled dibloclc copolyrner fihll before nanowire electrodeposition.
Fig. l 1b is an overhead view optical image (at 10X) of a four-wire mag~letoresistive device created from laterally patterned dibloclc copolymer film after nanowire electrodeposition.
Fig. 12a is a graph of giant magnetoresistance measurements of a fom-wire device as depicted in Fig.' 1 1b, as a function of device temperature.

Fig. 12b is a scanning electron micrograph SEM image of vertically oriented nanowires created from laterally patterned diblocl~ copolymer film.
Fig. 13a is a side view schematic diagram of a particular configuration of a magneto-electronic transport nanodevice created from laterally patterned dibloclc copolymer film, where the "current in" and "current out" electrodes are both on the substrate level.
Fig. 13b is a perspective view schematic diagram of a further particular configuration of a magneto-electronic transport nanodevice created from laterally patterned diblocl~ copolymer film, where the "current in" electrode is on the substrate level, and the "current out" electrode is on an upper intercoimect level.
Fig. 13 c is a side view schematic diagram of three distinct types of magneto-electronic nanoelements used in the devices of Figs. 13a and 13b.
Fig. 14a is an overhead view schematic diagram of a particular example of patterned media, showing patterned perpendicular media.
Fig. 14b is an overhead view schematic diagram of a fiu-ther particular example of patterned media, showing customized patteiTied perpendicular media.
Fig. 15a-a is a schematic depiction of a method of interfacing metal electrodes with the button and top of nanostmctures made by a nanoscale diblocl~
copolymer template.
Figs. 16a-c is a series of graphs of magnetoresistance measurements for the device depicted in Fig. l 1b, talcen a various magnetic field orientations.
Fig. 17 is a microscope photograph of a device constricted as shown in Fig.
13.
Fig. 18 is a graph of magnetoresistance measurement of electron transport through the device shown in Fig. 17.
Fig. 19 is a microscope photograph of a field emission test sample from a device constructed as depicted in Fig. 6.
Fig. 20 is a graph of electronic field emission measurements made from an array of cobalt wires in vacuum, from the device shown in Fig. 19.

Fig. 21 is a microscope photograph of particular field emission test samples from Fig. 19, but magnified to 50x.
Fig. 22 is a plot of normalized MR response (%) at 0 field versus temperaW re, in the perpendicular orientation.
Detailed Description Described herein is a process technology for the fabrication of tluee-dimensional devices using laterally-patterned blocl~ copolymer templates. In this method, copolymer films are patterned laterally by selective-area exposure to radiation sources. This produces a mufti-scale lithographic template, that is, a regular array of nanoscale pores with an overall lateral extent confined to an arbitrary and desired design. The dimensions of the lateral design can range from the nanoscale to the microscale. The patterned array template is combined with appropriately tailored pre- and post-fabrication steps to produce multilevel, tluee-dimensional integrated nanoscale media, devices, and systems. The method introduces the ability to integrate nanoscale functional elements in arbitrary and desired locations on a chip and to integrate the functional elements with other chip components in a practical mamer.
The general utility of self assembled copolymer templates is thereby significantly advanced.
General Preparative Teclniictue The methods described here axe based on the formation of regular arrays of material on surfaces. For example, diblocl~ copolymers, comprised of two chemically distinct polymers covalently lined end-to-end, can be self assembled into well-ordered arrays of spheres, cylinders or lamellae, depending on the volume fraction of the components comprising the polymer chain. Directed self assembly, carried out with an external field (for example an electric or magnetic field, or a temperature or concentration gradient), can result in useful films, with orientation sufficiently long-raazged to allow the production of extended arrays of nanowires having aspect ratios of at least 2:1 or 3:1. Vertically-oriented, cylindrical phase diblocl~
copolymer films are created. Among many suitable diblocl~ copolymers that can be use, a 70/30 (by volume fraction) polystyrene-polylnethylmethacrylate dibloclc copolymer can be exemplified. Other cylinder constituents of the copolymer can be, for example, polybutadienes, polycaprolactones, and other materials that can be solubihized in solvents. Other matrix constituents can include polybutadienes and other materials which are not reactive with agents used to remove the cylinder constituents.
A blocl~ copolymer is first deposited, e.g., spun-cast from solution onto a substrate, such as a metallic, semiconducting, or insulating substrate. The substrate can be rigid or flexible. Of particular interest are: substrates at least partially coated with a thin film of metal; semiconducting substrates; and semiconducting substrates at least partially coated with a lithographically-designed th111 f111n 111etah electrode pattern. Suitable substrates include: silicon, such as silicon wafers or chips; and polymeric substrates, such as I~apon, each of which can be made conducting or semiconducting by coating at least a portion of the substrate surface with a conducting or semiconducting material. Among metal substrates, for particular applications, the oxidation of the metal should not be as rapid as the deposition rate of materials to be deposited.
For example, substrates for use in the devices and techniques described herein may be a coating or a non-continuous surface layer on an underlying material that need not be conducting. The amount of substrate used can be any amount that allows the substrate to function as an electrode, when electrodeposition is used to deposit functional material. If other methods of material deposition are employed, the natw-e and amount of substrate is not limited. The substrate, in embodiments in which it is present as a coating or surface layer, can be applied to an underlying substrate by conventional lithographic techniques, or other 1~110W11 111ethOdS Of depOSlt111g conducting materials on surfaces.
In some embodiments, the substrate can include metals, for example, gold. In other embodiments, the substrate can have gold coated or deposited on an underlying material. In some embodiments, the substrate can be a semi-metal oxide, including for example, silicon oxide. Particular preparation methods are not required, although in some embodiments, washing the substrate with water, followed by rinsing with mild acid and/or base can be carried out.
to Diblocl~ copolymers, comprised of two chemically distinct polymers covalently liW~ed end-to-end, can be self assembled into well-ordered arrays of spheres, cylinders or lamellae, depending on the volume fraction of the components comprising the polyrner chain. If the volume fraction of a major component is about 0.7 (e.g., from about 0.65 to about 0.80), any copolymer will self assemble into a hexagonal array of cylinders of the minor component embedded in a matrix of the major component. The mole ratio of the minor component of the diblocl~
copolymer can range from about 0.20 to about 0.35 to permit the formation of microphases such as will result in cylinder formation. If the volume fraction of the major component is about 0.9, the minor component will form spheres, which can be elongated into very thin cylinders when an orienting field, e.g., an electric field, is applied.
A mixture of dibloclc copolymers, such as A-B and A-C dibloclc copolymers, can be used to create cylinders of different types, for example B and C
cylinders.
Higher block copolymers, such as A-B-C tTiblocl~ copolymers can also be used.
The molecular weight of the copolymer can be varied to achieve differing cylinder diameters. For example, a molecular weight copolymer in the range of about 1.5 million molecular weight emits (Daltons) can result in a cylinder diameter of about 70 mn. A molecular weight in the range of about 20,000 Daltons can result in a cylinder diameter of about 14 nm. A molecular weight of about 4 million Daltons results in cylinders with a diameter of about 100 nm, while a molecular weight of about l~ilodaltons results in a diameter of about 1.0 nm.
For some embodiments, the use of a block copolymer including a component that can be crosslinl~ed is desirable. This component can be crossliu~ed before or during removal of another component, and can therefore add structural integrity to the copolymer. This component can be referred to as the matrix component. W some embodiments, the matrix component will be the major component of a copolymer, by volume. Suitable matrix components include polystyrene, polybutadiene, polydimethylsiloxane, and other polymers. The component that is to be removed can be called the core component. W some embodiments, the core component will be a minor component of a copolymer, by vohune. Suitable core components include polynethylinethacrylate, polybutadiene, polycaprolactone or a photoresist.

Generally, core components are materials that can be degraded or decomposed differentially than the matrix material.
W other embodiments, block copolymers of styrene and methyhnethacrylate ca~i be used. In some embodiments, the methyhnethacrylate block constitutes a minor component. For example, a 70/30 (by volume) dibloclc copolymer of polystyrene/polymethylmethacrylate can be employed. AiZy bloclc copolymers can be used, such as allcyl/allcyl, alkyl/aryl, aryl/aryl, hydrophilic/hydrophilic, hydrophilic/hydrophobic, hydrophobic/hydrophobic, positively or negatively cl2arged/positively or negatively charged, uncharged/positively or negatively charged, or uncharged/uncharged. The film thicl~ness can vary as desired, for example, from about 0.5 mn to about 10 cm, or from about 1 mn to about 1 cm, or fr0111 about S mn to about 1000 nm. In some preferred embodiments, film thiclmesses can vary from between about 10 nm to about 200 microns, or from about 1 micron to 200 microns, or up to about 25 mil.
Orientation of the copolymers can be carried out using directed self assembly, that is, self assembly which is directed by an external field, for example an electric field, a magnetic field, a thermal gradient or a concentration gradient.
Vertical orientation of the cylinders can be accomplished by, for example, electric field aligmnent under annealing conditions, or, for example, self orientation using controlled interfacial conditions.
For electric field-induced orientation, the different chemical constitutions of the blocks of the copolymer can result in a difference in the dielectric constants of the copolymer domains. A difference of about 0.1% in the dielectric constants can result in a specific, e.g., vertical, orientation. W an electric field, the orientation dependent polarization energy associated with the cylinders, dielectric bodies that are anisotropic in shape, will align the cylinders in parallel to the electric field lines, for example, as described in Morkved, et al., "Local control of microdomain orientation in dibloclc copolymer thin films with electric fields," Science, 273, (1996), 931; Thurn-Albrecht, et al., "Overcoming Interfacial Interactions with Electric Fields,"
Macromolecules, 33, (2000) 3250-53; Amundson, et al., "Aligmnent of lamellas block-copolymer microstructure in an electric-field. 1. Aligmnent kinetics," Macromolecules 26, (1993), 2698; and Amundson, et al., "Aligmnent of lamellar block-copolymer microstructure in an electric-field. 2. Mechanisms of aligrunent,"
Macromolecules 27, (1994), 6559.
Under strong enough fields parallel to the substrate, any surface induced alignment of the morphology can be overcome, producing cylindrical microdomains oriented in parallel with the fields, which can be normal to the substrate, that extend completely through a one-micron-thick sample. Scattering experiments are ail easy means to characterize the orientation of the microphase stmcture in a thin film. When viewed fiom the side, a cylindrical structure oriented normal to the substrate is laterally periodic. Consequently, the scattering pattern measured at a finite incidence angle is strongly anisotropic, consisting of two equatorial Bragg peaks.
W some embodiments employing an electrical field to orient the polyner film, a removable conducting layer is placed on top of the copolymer film, sandwiching the film between two electrodes. For example, a conducting layer can be deposited by spin coating and then, after annealing, be removed by etching, e.g., by solvent chemical, or physical etching. Alternatively, a "spin-on" sacrificial layer can be applied, followed by a metal layer that is evaporated, sputtered, or spun-on.
After annealing, the sacrificial layer can be removed by solvent, chemical, or physical etching. This conducting layer can be metal, or semiconducting material, and can optionally be in contact with the entire film surface. For example, aluminum, copper, gold or other metal can be used as the conducting layer on the copolymer f1I111.
Metallized layers, such as ahuninized KAPT~N~ can also be used.
Metallized layers can promote the formation of a uniform film surface as orientation, e.g., vertical orientation, is carried out. For example, in some embodiments, the use of a metal conducting layer alone, in direct contact with the copol~nner film, can result in damage to the copolymer layer as the conducting layer is removed, due to sticking and/or tearing. Aluminized KaptonOO is a layer of aluminum in register with a layer of KaptonOO , in which the KaptonOO layer is directly in contact with the copolymer film.
The KaptonOO layer must not be so thick as to interfere with an electric field established between the ahuninum layer and the substrate on the other side of the film. Other metals and other polymeric materials can be used to create metallized layers for electric field-induced vertical orientation.
To mobilize the molecules in the copolymer, the smdwich stmctlue can be heated above the glass transition temperatL~re of the copolymer. Voltage is then applied between the substrate and the conducting layer to create an electric field through the mobilized copolymer film. The electric field strengths are at least 5 Vhmn, for example, at least 10 Vhmn.
After holding the film in this state for a sufficient time to allow the copolymers to self assemble, for example, over 30 minutes, over 60 minutes, over 1.5, IO over 2, or over 3 hours, the copolymer film assembly is cooled to a temperature below the glass transition temperature of the copolymer. The orienting field, e.g., electric field, is desirably turned off after the cooling has tal~en place. At this point the conducting layer, and any associated additional layer, is removed from the polpner film. The film now includes an ordered array of cylinders of one copolymer 15 component embedded in a matrix of another copolymer component. pelf assembly results in parallel orientation of the bloclcs, such that one component forms cylinders with the cylinder axis substantially in parallel to each other, e.g., all normal to the surface of the substrate, or substantially normal to the film surface itself.
The cylinders desirably extend substantially from the substrate surface to the surface of the 20 film. The cylinders have diameters ranging from about 5 urn to about 100 urn. The periodicity (L) of the cylindrical domains in the film is the distance between the central axes of the cylinders, and is proportional to the molecular weight of the copolymer (to the 2/3 power). In embodiments in which the mole fraction of the minor component is from 0.2 to 0.35, and the cylinders are hexagonally pacl~ed, the 25 periodicity defines the diameter of the cylinders. Periodicity can range, for example, from about 1.0 to about 70 urn, but can be outside this range.
fiz other embodiments, methods other than heating are used to malce the molecules of the copolymer mobile. For example, rather than heating the copolymer to its glass transition temperature, one cal, in effect, lower the glass transition 30 temperature, by any of a number of ways. For example, one can add a plasticizes, a solvent, or a supercritical fluid, such as supercritical CO~, to the copolymer to mobilize the molecules and allow them to move and self assemble. An orienting field is applied, and the plasticizes, solvent, or supercritical fluid is removed to immobilize the molecules. Thereafter, the orienting field is removed, but the immobilized molecules maintain their orientation.
Orientation using electric field allows a wide range of film thiclmesses to be prepared, and thereby a wide range of nanowire aspect ratios to be produced.
Nanowire aspect ratios can range, for example, from about 0.05:1 to about 10,000:1;
or about 0.1:1 to about 5,000:1; or about 1:1 to about 500:1; or about 2:1 to about 10,000:1 or about 2:1 to about 5,000:1, or about 2:1 to about 500:1; or about 2:1 to about 100:1. Such large aspect ratio wires in an extended array are useful for creating sufficiently large magnetic coercivity though shape anisotropy, for example.
Orientation using controlled interfacial interaction is well suited for relatively thin diblocl~ films. For example, less than about 100nm, or less than about ~Ontn, or less than about 40mn thicl~. According to such methods, a substrate is pre-treated so that it presents a "neutral" surface to a copolymer diblocl~ film. Hydrogen-passivated silicon, or silicon coated with a random-copolymer brush, are suitable exemplary neutral surfaces. Thin diblocl~ films can be spun-cast atop this surface and annealed.
The cylinders will self orient vertically without directed self assembly from an external field in sufficiently thin diblocl~ films, for example, films of less than abOLlt 1 OOmn.
Such methods result in a very flat film swface and simplify manufactwe, since the application and subsequent removal of a top electrode are not strictly required.
Ultra-high density magnetic data storage can be achieved if magnetic materials having larger intrinsic anisotropies than cobalt are used. (Feet for example.) High pattern resolution on thin films is possible using an electron beam for lateral patterning.
The surface of the copolymer film obtained after orientation can be used as formed foi: a number of applications. For some applications, the swface of the vertically oriented copolymer film is desirably substantially smooth. Such anays and tecluuques for producing substantially flat surfaces are described in Uuted States Provisional Patent Application Serial No. 60/191,340, filed March 22, 2000, titled "Magnetic Arrays;" and United States Patent Application Serial No. 09/814,891, filed March 22, 2001, titled "Nanocylinder Arrays," and each application is incorporated herein by reference in its entirety. For example, for magnetic data storage applications, in which a reading device passes rapidly over a magnetic array, the surface is desirably smooth. Any application in which a read or write head passes over an array can require high smoothness. Smoothness of a magnetic array for data storage and retrieval applications desirably ranges from about 0.5 to about 5.0 mn.
The surfaces of vertically oriented copolymer films can be made smooth with the use of an additional material, such as an elastomer or a crosslin~ed elastomer applied to the conducting layer before vertical orientation steps are undertaken. For example, an additional material, such as a crossliu~ed silicone, including crossliu~ed-polydialkylsiloxanes, -polydiarylsiloxanes, or -polyalkyl-arylsiloxanes, including, for example, crosslinked-polydimethylsiloxane, can be applied to a conducting layer, or in some embodiments, to an additional layer, as described above. The conducting layer, and/or any associated additional layer, is coated with the additional elastomeric material, and the layers placed in contact with the copolymer film. Vertical orientation is carried out, as described above, and the layers removed from the surface of the vertically oriented copolymer hlm. The surface can be made thereby smoother than surfaces created without the additional elastomeric material.
Next, the minor component (or in some embodiments the major component) of the substrate-associated copolymer is removed (either component of a diblock copolymer can be "minor" or "major," and the components can also be equally present). Removal of the minor component is achieved, e.g., by exposure to radiation (ultraviolet light, x-ray radiation, gannna radiation, visible light, heat, or an electron beam or any other radiation source which selectively degrades the minor component).
Degradation or decomposing agents such as reactive oxygen species, including for example, ozone, or solvents such as ethanol, caxi also be used. Ultraviolet light can be used to degrade, for example, polymethylmethacrylate as a core component.
Ethanol can be used to degrade, for example, polybutadiene.
Tlus treatment can be followed by a chemical rinse to remove the decomposition by-product, and typically results in porous material having pore sizes in the tens of nanometer range. A step to remove any residual component can include treatment with a liquid, including washing with a solvent, or a material that reacts preferentially with the residual component, such as an acid or a base. W some embodiments, the material used to react with residual degraded component can be, for example, a dilute form of acetic acid. The volume formerly filled by a now removed copolymer component now comprises cylindrical spaces extending tluough the thiclmess of the film. The remaining volume is occupied by the remainder copolpner component and is referred to as the matrix.
In some embodiments, it may be desirable to optionally cross-lint a component of the copolymer film. Cross-lining of a component that is not degraded by an energy source or agent can add stnictural strength to the film. W some embodiments, a copolymer component is crosslinlced simultaneously with the degradation of another copolymer component. The radiation can optionally and desirably crossliW~ and substantially immobilize the matrix component of the diblocl~
copolymer, so that the matrix maintains the allay stilicture even after the cylindrical voids are created. A nanoporous array template is the resulting overall stmctwe. For example, in the case of polymethylmethacrylate (PMMA) cylinders in a polystyrene (PS) matrix, ultraviolet radiation degrades the PMMA while crossliW~ing the PS. It is desirable that the initial morphology of the copolymer be retained tluoughout the entire process of degradation. Other methods of removing one or the other component (e.g., chemical methods) can be used. Either the "minor" or "major"
component can be removed or be remaining. The dimensions of the pores generally are the same as those of the cylindrical domains of the veutically oriented copolymer film, and as such, the pore diameters can range from about 5 mm to about 100 mm or more, and the periodicity can range from about 5.0 to 70 mm.
Subsequently, the resulting pores are at least partially filled with, for example, metallic, metalloid, semiconductor, and/or magnetic materials. Deposition of functional material can be carried out by, for example, electrodeposition, chemical vapor deposition, electroless deposition, surface chemistry, chemical adsorption, and chemically driven layer-by-layer deposition. For deposition of material in pores that have depths of more than about 30 mm, electrodeposition is a desirable method, since it provides a driving force for the deposition of material into the bottoms of the pores.

For example electrodeposition within the pores of a nanoscale template derived fiom films of diblock copolymers provides a convenient means of filling the large aspect-ratio pores in a highly controlled manner to provide an array of nanowires.
For those applications relying on magnetic propel-ties of the anay, the nanowires include at least some magnetic material. Magnetic materials include cobalt, nickel, iron, and alloys which contain one or more of these materials, and includes those materials wluch are measurably magnetic. For those applications relying on magnetic properties of the array, the nanowires include at least some magnetic material. Magnetic materials are those materials that are measurably magnetic, and can include magnetic metals, such as cobalt, nickel, iron, rare-earth magnetic materials, and alloys that contain one or more of these materials (such as iron-platinum alloys, or PERMALLOYO, an alloy of iron and nickel, with a stoichiometry of Ni$lFel~), as well as magnetic non-metals, including ceramic materials such as strontium or barium in combination with iron oxide. Organic magnets, such as tetracyanoethylene, can also be employed as magnetic materials.
Magnetic systems can also contain materials that are non-magnetic, including non-magnetic metals, such as copper, gold, silver, and the like.
Magnetic materials can also be prepared as magnetic nanowires by deposition of alternating layers of magnetic metals and non-magnetic materials. SL1C11 alternating layers can be optionally and, for some embodiments desirably, regularly alternating, and the regularity can include regularly alternating amounts of such materials. For example, a magnetic nanowire can include at least tluee layers of material altelmating as: magnetic metal, non-magnetic material, magnetic metal; or non-magnetic material, magnetic metal, non-magnetic material. The alternating layers can be optionally, and in some embodiments desirably, non-regltlarly alternating.
More details are given in "Magnetic Multilayers and Giant Magnetoresistance Fundamentals and Industrial Applications (Springer Series in SL~rface Sciences, No 37)," Uwe Hal-tmann (editor), 370 pages, (Springer-Verlag, 2000), which is incorporated herein by reference. Cobalt/copper alternating multilayers have been found to be useful.

Magnetic materials can be generally chosen to have a selected magnetic coercivity, which will depend on the desired application. For example, by L1S111g~LlSt cobalt (Co) nanowires, the coercivity can range from about 7000 Oe, to any lower number. Under appropriate fabrication conditions, the perpendicular coercivity of a cobalt nanowire array can exceed 1.71~0e at 300K; due to the cylindrical shape anisotropy and nanowires having diameters smaller than the size of a single magnetic domain. The coercivity can be tuned to smaller values by selecting specific electrodeposition conditions, pore diameter, and additives. For example, using the techniques described herein (applied field perpendicular to the substrate and parallel to wire axis), one can establish perpendicular coercivity of about 800 Oe at room temperature. Higher coercivities can be obtained by depositing rare earth magnetic materials.
Magnetic materials can also have their magnetoresistive behavior tuned by adjusting the thiclaress of the magnetic sections, the thiclmess of the normal metal sections, and the diameter of the multilayered nanowires. These devices are so-called "giant" ma~,metoresistive devices, which are sensitive magnetic field sensors, in that the resistance changes dramatically with a change in magnetic field. One can also intentionally mane "two-state" devices using non-regular multilayering. For example, a thiclc magnetic layer, followed by a thin normal metal layer, and then followed by a thin magnetic layer can be deposited in nanowires to form an array useful to design a two-state device.
hi other embodiments, one can reverse the magnetization state of the smaller magnetic layer by increasing the current through the device. A spin-polarized electron current leaves the larger magnetic region and is injected into the smaller mag~let. This cuurent exerts a torque on the magnetization in the smaller magilet and can reverse the direction of magnetization. The change in magnetization is typically accompanied by a discrete change in measured resistance. This results in a way to "write and read" using current. One can "write" with a larger eLn-rent, and "read" with a smaller current. These concepts are discussed in Katine et al., "Current-driven magnetization reversal and spin-wave excitations in Co/Cu/Co pillars," P7iyr.
Rev.
Lett., 84, (2000), 3149. Optimal electrodeposition of magnetic material can involve the alignment of the magnetic axis of the material normal to the surface upon which the magnetic material is deposited.
For those applications which do not rely on magnetic properties of arrays, any other material which can be electrodeposited can be employed, including metals generally, semi-metals (including, for example, Bi and BiTe), and certain semiconducting materials that can be electrodeposited. Optimal electrodeposition of magnetic material can involve the alignment of the magnetic axis of the material substantially, parallel or slew normal to the surface upon which the magnetic material is deposited.
The technique described above is generally depicted in Fig. 1, which shows an oriented dibloclc copolymer film on a substrate. The darl~ areas on the substrate represent one of the components of the diblocl~ copolymer, and the adjacent lighter areas represent the other component of the diblocl~ copolymer. The upper surface of the copolymer film is here shown perfectly flat. This condition can be preferable for some applications, although this is not a requirement for the technique generally.
Those applications which desirably involve the production of substantially flat film surfaces can utilize methods which use a further polpner on top of the copolymer film. For example, polydimethylsiloxane can be deposited across the surface of the copolymer film to produce a substantially flat surface on the copolymer film.
For particular applications, the matrix material is desirably removed from the substrate surface after deposition of functional material. In other applications, the matrix material is desirably present subsequent to deposition to provide stnictmal stability to the array of nanowires, or to allow further post-fabrication lithographic steps. Removal of matrix material can be achieved by treating the array with an agent that selectively degrades the matrix material with respect to the nanowires as described above.
Selective Exposure The methods of certain embodiments described herein are based on the selective exposure of the diblocl~ copolymer template to a radiation source which removes material fiom the polymer film, to create three-dimensional nanoscale elements in a multilevel integrative technology. Special multilevel processing steps, specifically tailored to each particular device configuration, are used to achieve the complex integration. A simple product may require patterned dibhock level of lithography only, while a complex integrated product may also require pre- and post-fabrication lithographic steps. The common technique to all cases of nanostructure fabrication is the selective copolymer patterning technique.
The process involves the selective alteration of specific areas or location of a nanoporous copolymer template, e.g., by exposure to a radiation source.
Suitable radiation sources for the selective degradation of a copolymer component include, for example, ultraviolet (W) light, electron beams, or other sources of radiation that can efficiently degrade a component of a diblochc copolymer. The process is depicted generally in Fig. 2a, which shows a side view of a vertically oriented diblocl~
copolymer film on a surface, with radiation impinging on the copolymer film.
The radiation removes material from the film to create cylinders, and since the exposure is selective, there are areas of the film that contain cylinders, and areas which do not.
Fig. 2b is an overhead view of the same film, showing explicitly that, in this case, a triangular shape has been imposed on the film surface, resulting in an area where electrodeposition can potentially be can-ied out, depending on the characteristics of the underlying surface. Fig. 3 depicts the same process and resulting template, with the matrix component of the film deleted in Fig. 3 for clarity.
For applications involving the use of UV light, a W mask or UV projection can be used for spatial selectivity across the surface of the aiTay. For applications involving electron beams, a focused electron beam writer or other electron beam sowce can be used for spatial selectivity. The exposure pattern imposed on the surface can be related to, or dictated by, underlying feat-~.ues in the film or on an underlying surface, or can be unrelated to such feaW res. For example, when the underlying surface includes an electrode patteun, specific ahigmnent of portions of the diblocl~ exposure pattern with portions of the electrode pattern can be a requirement for device manufacture. The resulting array is referred to as being laterally patterned.

Once a patterned nanoporous array template is created, surface-selective materials deposition methods can be used to locate desired materials into the pores to create nanoscale elements. Nanowires will be present only in areas which are the union of areas exposed to radiation, and areas containing an electrode underlying the surface of the copolymer film.
Novel use of electrochemical deposition methods, for example, enables several applications. Other surface-selective materials deposition tec1111iques can be used, including chemical vapor deposition, electroless deposition, surface chemistry, chemical adsorption, and chemically driven layer-by-layer deposition, for example.
In the case of electrochemical deposition, different electrodes can be held at differing voltages during the electrochemical deposition to allow or prevent deposition at chosen electrodes, and this technique can be referred to as "programmed deposition."
Specifically, since the underlying electrodes are separately addressable, one electrode (or group of electrodes) can be held at a potential appropriate for deposition of one material, while other electrodes are held at potentials which do not allow depositions of that material. This method offers expanded materials versatility, in that different types of nanowires can be deposited on the salve chip.
An example of this type of nanofabrication is depicted in Fig. 4, which is a schematic diagram of a multilevel structure created using tile concepts described above. In Fig. 4, the matrix component of the copolymer is deleted from view for clarity. The substrate includes thlll film electrodes in, or on, its surface, which can be created by conventional lithography, for example. Lateral patterning can be carried out in registry with the underlying electrode pattern as desired, followed by elechodeposition of a first material, results in the creation of first nanowires, as ShOWIl. Subsequent electrodeposition of a second material, at an electrode potential different from that used for the electrodeposition of the first material results in the creation of second nanowires, as shown. First and second materials can differ in characteristics, particularly in characteristics which are relevant to the functional aspects of the devices. The first and second materials can be metals or semi-metals, so that characteristics, such as reduction potential, semi-metal type (for example, "n"-or "p"-type semi-metal, metalloid or semiconducting materials), reduction potential, and other useful characteristics can be varied in different locations of the film.
Alternatively, lateral patterning, followed by electrodeposition of a first material creates first nanowires as shown. Another lateral patterning step, in a different location, followed by electrodeposition of a second material, at any electrode potential, results in the creation of second nanowires. Subsequent lithography, also lmown as electrodeposited post-level connections, on the surface of the film creates colmections between sets of nanowires, and allows the creation of simple or complex circuits. Fig. 5 shows an overhead view of another example of such a tluee dimensional structure, emphasizing the relationship between electrical colmectlons underlying (level #1), through (level #2), and overlying (level #3) the matrix component of the dibloclc copolymer to create electrical colmections in registry with components on these differing levels.' In solve applications, it is desirable to use subsequent upper levels of lithography for intercolmection and integration purposes. Such embodiments are depicted in Figs. 13a, and 13b, which show two basic configlxrations of magneto electronic transport nanodevices. Figs. 13a and 13b depict magneto-electronic device configurations that utilize transport current through the nanowires. These devices utilize anisotropic magnetoresistance, giant magnetoresistance, or spin-polarized current switching magnetoresistance, as discussed in I~atine et al., "Current-driven magnetization reversal and spin-wave excitations in Co/Cu/Co pillars," Playr.
Rev.
Lett., 84, (2000), 3149, for magnetic sensing and "spintronic" purposes. They are relevant to magnetic data storage read head technology, magnetic RAM, and magnetic sensing applications. Fig. 13a shows a first configuration, in which the "current in"
and "current out" electrodes are on the substrate level, and the intercolmection between these two electrodes is on the upper intercomiect level. Fig. 13b shows a second configuration, in which the "current in" electrode is on the substrate Ieve1 and the "current out" electrode is on the upper intercolmect level. Particular combinations of these configurations will be readily apparent to those designing circuits.
A device of the constl-uction depicted in Fig. 13 has been made, and a microscope photograph of this device is shown in Fig. 17. The patterned blacl~

regions are the locations of the nanowires. Magnetoresistance measurements of electron transport through the device depicted in Fig. 17 have been carried out, and are shown in Fig. 18.
W addition, the nanowires themselves can be multilayered, using pulsed electrodeposition in a two-component bath, for example, to create CuCo multilayers, or by sequential electrodeposition. Some embodiments of multilayered nanowires are depicted in Fig. 13c. Magnetic nanowires are, as discussed above created using magnetic materials, principally including cobalt, nicl~el, iron, and alloys containing these metals, and are useful for anisotropic magnetoresistance applications.
Multilayered magiletic nanowires are created using substantially regularly alternating layers of magnetic materials and non-magnetic materials within individual nanowires (for example, Co/Cu alternating layers), and are useful for giant magnetoresistance applications. Asmmetric mag~letic heterostnictures are made using substantially 110111egLllarly alternating layers of magnetic and non-magnetic materials, useful for spin-polarized current switching magnetoresistance.
Immediately after the selective area exposure, the polymer film contains polymer in three distinct states: 1) the degradation by-products; 2) the insoluble component; and 3) the virgin, oriented diblocl~ copolymer in the unexposed regions.
The coexistence of these tluee states offers additional fabrication versatility. By choice of solvent or radiation, one can choose to remove only the exposed cylinders, or alternatively, the exposed cylinders and the unexposed regions of dibloclc copolymer. For example, acetic acid can be used to remove degraded polymer fragments from the exposed area, but will not affect the matrix component. An agent such as acetic acid will also not remove material from the virgin, wexposed diblocl~
copolymer. If desired, the removal of material from virgin regions can be achieved by treatment with another agent, for example, toluene. If desired, the removal of the unexposed diblocl~ copolymer can be chosen to occL~r at a separate stage of processing, for example, after nanowires have been fabricated in the pores.
It is also relevant to note that for high-dosage over-exposures, both polymer blocl~s will crosslin~, rendering a solid insoluble film that can also be used for fabrication purposes. hl such embodiments, neither component of the diblocl~

copolymer can be removed. Such areas can be used as robust barners, which protect the underlying substrate from further solvent processing. The use of different combinations of exposure and solvent protocols greatly advance tile general utility of the general procedures described herein for the fabrication of nanostnlctures.
In data storage applications, patterning of magnetic arrays can be used to create patterned perpendicular magnetic media, as shown in Fig. 14a. Each set of nanowires is separated from other sets of nanowires by unexposed diblocl~
copolymer.
All individual nanowires within a given set of nanowires have the same magnetization direction, either up or down, corresponding to a data bit of either "1" or ''0."
In other applications in which the magnetic switching behavior of magnetic arrays can be exploited, the laterally patterned arrays described herein are of utility.
The magnetization switching field of a magnetic nanowire can be modified substantially by the magnetic Bipolar interactions it experiences due to neighboring nanowires, and consequently depends on whether the nanowire is found in a circle, triangle, cross- or star-shape, or other shape which tends to maximize or minimize the exposure of nanowires to each other or non-magnetic areas of the film. The lateral extent and shape of an array of magnetic nanowires will 111f111e11Ce 1tS
SWltChlllg behavior dramatically. This can be observed in the magnetic hysteresis curve (magnetization versus applied field) and in the magnetoresistance of a device using such wires. Using the patterned dibloclc templates we can create "designer micromagnetic media." Tlus designer media can be used in magneto-transport device technologies that require discontinuous changes at specific threshold fields or for other applications that utilize step-wise changes in magnetic field. Some of Sllch embodiments are exemplified in Fig. 14b, which show both triangular and circular sets of nanowires. The discontinuous switching behavior of designed devices can be e1W arced for particular applications.
Auplications The three dimensional nanostrllctured arrays described herein can be used in of technologies, including: display technology, cooling technology, magneto-electTOnic technology, data storage technology, sensor technology, biomolecular array technology, molecular electronic technology, waveguide technology, and other technologies. The techniques presented here are general and provide advances to a variety of research materials systems.
Field Emission A~~lications Field emission displays (FEDs) offer high brighW ess, low power consumption, and flat-panel design. The displays can include an addressable aiTay of field emitters and a phosphorescent screen. Efficient field emission displays require high-aspect-ratio nanoscale metal tips (for example, from about 20:1, or about 35:1, or about 50:1 to about 10,000:1) to enable electronic field emission at low tlueshold voltages. To achieve a sufficiently large current density, the emitters are desirably arranged into a high-density array. To define display pixels, the array is desirably patterned laterally into sets of nanowires, with each pixel electronically addressable.
These sets can include from one to 10, 20, 30, or more nanowires, depending on the desired application.
The present invention offers simplified processing and the ability to male tip arrays with improved orientation.
The ultra-high density, laterally patterned aiTays created by the methods described herein can be successfully used for high-resolution, low power, thin and flexible display devices. The high aspect ratio of nanowires created by the techniques described herein allow the threshold voltage for emission to be sufficiently low so that power consumption for such field emission devices is correspondingly lowered.
The devices are useful for television and video screens, computer monitor screen, and many other display devices such as on watches, GPS devices, and any other devices currently using LED or LCD displays . The thinness of such field emission aiTays allows the design of such devices to be far thimler than devices available currently.
Display devices made with the technology described herein are also much brighter for a given level of energy consumption than those cmTenthy available. The possibility of using a flexible substrate further expands the utility of display devices made with the techniques described herein. Differing display applications will have differing priorities as regards operating characteristics; for example, an outdoor display caxl require high brightness, and a video display can require lugh resolution.
An example of a field emission array created according to the methods described herein is shown in Fig. 6, which is a perspective view of a diagram of such an array. The substrate has electrodes in or on its surface, created by conventional lithography. Diblocl~ copolymer is deposited on the substrate, as described above, for example, by spin-bonding. Vertical orientation, selective irradiation, chemical treatment, and electrodeposition follow to create sets of nanowires, in this case, deposited on two distinct electrodes. For field emission applications, the ends of the nanowires are desirably at or near the film surface. This can be achieved by either growing (that is, electrodepositing) the wires to substantially the full film thiclmess, or by growing them to a lesser extent (for example, 90% of the film thiclmess), followed by removal of a portion of the surface of the film, by means l~nown to those of skill in the aut (including, for example, reactive ion etching by oxygen plasma).
Again, the matrix component is deleted from Fig. 6 for clarity.
A device according to the constriction of Fig. 6 was made, and microscope photographs of this device are shovnnn in Fig. 19. The dibloclc template is shown patterned into a circular region at 20x magnification in the upper left of Fig. 19. The same region is shown after 250 mn cobalt nanowires have been grovcm at-1V into the circular region, but before electrical measurements were made at 20x mag~lification in the upper right of Fig. 19. The same region is shown after electrical measurements were made and then having brought up the emission current to the point at which the sample was destroyed in the lower part of Fig. 19 (lower left at Sx magnification, lower right at 20x magnification). Fig. 20 shows a graph of electronic field emission measurements made from the array shown in Fig. 19. A large current density and a low threshold was achieved. Fig. 21 is a close up of the images from Fig. 19, upper right and lower left, before and after destroying the sample, respectively.
The electrodes are individually addressable, in this .case, with voltages V ~
and V2. These applied voltages are independently varied as desired to control (that is, tum "on" and "off') the emission cu3Tent from each nanowire set. A phosphor screen can be placed above the nanowire sets to create a display. Fig. 7 shows an overhead view of a similar device, but with four individually addressable sets of nanowires.
It is important to note that nanowires are deposited only on the substrate where: 1) the copolymer is exposed to irradiation that degrades a component of the copolymer down to the substrate surface; 2) the residue of degraded component is removed from the substrate surface; and 3) the substrate surface has an electrical contact allowing electrodeposition.
Thermoelectric CooliyApplications Solid-state cooling devices can also be designed utilizing the tecln~ology described herein. At present, the best commercially available thermoelectric cooling devices have thernoelectric figimes of merit of approximately 0.1. The techniques described herein can produce devices which have thermoelectric figimes of merit approaching or exceeding 2.0, e.g., devices having a figure of unit of 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.7, 1.8, 1.11, 2.0 or greater.
Fig. 9 is a diagram of a single-stage thermoelectric cooler which can be made according to the methods described herein. The substrate has electrodes pre-patterned in or on its surface. A patterned diblocl~ copolymer layer is created on the substrate, as described herein. Again, the matrix component of the copolymer is deleted in Fig.
9 for clarity. Nanowires of two types are deposited by programmed electrodeposition.
In the depicted example, "n-type" nanowires, made from ''n-type" materials, well la~own in the ant, are deposited at one electrode, and "p-type" nanowires, made from "p-type" materials, also well lmovv~m in the art, are deposited at another electrode. A
top-layer metal interconnect is then deposited electrochemically. The device operates through the application of current through the device, so that the top plate becomes cold and the electrodes and substrate become warn. The top plate can be used as a heat sinlc for use in electronic devices, for example. Multistage coolers can also be made by this fabrication method. Heating devices are also made possible by the simple adaptation of the device for such proposes.

Magnetic Data Storage Applications Next generation magnetic data storage technologies will likely utilize perpendicular magnetic media to store data. Present technologies use lateral magnetic media in which the magnetic storage elements lie along the surface of the substrate.
W the effort of packing more elements per unit area, the size of the basic elements must be reduced. This introduces a problem, however, since as the scale of these regions is reduced, so is the bloclcing temperature which marks the onset of superparamagnetism. The blocking temperature must be kept large, otherwise the stored magnetization state of each element will decay and data will be lost.
One way to reduce the size scale of a magnetic media element without substantially reducing the blocking temperature is to utilize shape and volume, that is, to make small cylindrically-shaped objects of high aspect ratio (for example, from about 20:1, or about 35:1 or about 50:1 to about 10,000:1). All other considerations being equal, a cylindrically-shaped magnet of diameter 10 nm and length of 500 nm will have a much higher blocking temperature than that of a spherical magnet of 10 nna diameter. The highest spatial packing density of magnetic cylinders occurs for cylinders in a vertical hexagonal closed-packed arrangement.
W the bulk, pure cobalt is a soft ferromagnet of relatively low coercivity and not necessarily an ideal material for magnetic data storage. However, certain cobalt alloys have "designer" magnetic properties including engineered coercivity which malces them useful for present-day magnetic media applications. These cobalt alloys can be electro-deposited from a specific plating bath containing the relevant ions.
The techniques described herein can be used to create arrays useful for the next generation of magnetic data storage. Since the surface smoothness of such arrays can be important, it is considered desirable to utilize an auxiliary pol5nner to produce highly smooth films on substrate surfaces. Highly smooth films can be created by depositing polydimethylsiloxane on a diblock copolymer film, as described in copending United States Patent Application Serial No. 09/814,891, filed March 22, 2001, titled "Nanocylinder Arrays." The application is incorporated herein by reference in its entirety.

Engineered MaQ;netoresistance Applications Magneto-electronic devices can be used for magnetic sensing applications (e.g., magnetic data storage) and for "spintronics" (e.g.,.MRAM).
Appropriately chosen nanoscale magnetic architectures can result in improved perfomnance since magnetic interactions can be tuned at the manometer scale. The techniques described herein can be used to create devices in a variety of useful magneto-electronic configurations.
Materials have been developed over the last ten years that are now used for magnetic sensing by utilizing their giant magnetoresistive (GMR) properties.
These materials have various architectures, but in general are muhtilayered materials with layers of non-magnetic metals in contact with layers of magnetic metals. The magnetic interlayer-exchange-coupling and electron spin-dependent scattering leadJto the sensitivity of resistance with respect to magnetic field. Tuning the stricture of these systems by materials engineering allows mag~letoresistive properties to be optimized for applications. GMR read heads in hard-dislc drive teclmology is one important commercial application. These engineered materials systems are expected to advance with better materials and new material architectures.
The magnetic arrays made using techniques described herein show GMR type behavior. However, the architecture of these arrays is significantly different than others that have been produced. The important consideration for GMR device design is that there be electrical contact between the substrate and the magnetic~nanowires, not whether the wires are embedded in the template or not. Therefore, the wires can be grown (that is, electrodeposited) to less than the film thichmess for GMR
devices without a need to remove matrix material prior to operability.
Of l~ey importance to optimal performance of GMR devices is the ability to form a regular array of very small dimensions, for example, an aiTay of 25.4 manometer period made of cylinders 11 manometers in diameter. Furthermore the fabrication processes described herein permit the well-controlled height of the cylinders, and the ability to muhtilayer the cylinder material as it is grown.
These new processing considerations have allowed the creation of new geometrical archutectures at size scales that have not been achieved using h~nown fabrication processes.
By tuning material structure in the fabrication processes described herein, a new breed of GMR materials is possible.
A particular embodiment of a GMR device is shown in Fig. 10. The device is created by fabricating a magnetic nanoarray as described herein on a substrate patterned with an electrode. This particular magnetoresistive device is in a "lateral transport" configuration (the transport current is affected by the presence of the magnetic nanowires, but is not configured to pass through the wire along its length).
Again, the matrix component of the copolymer is deleted fiom Fig. 10 for clarity.
The nanowires for such a device are desirably asyzrnnetric magnetic heterostnuctures, as described above with respect to Fig. 13c. Fig. 13c does not imply that in a given set of nanowires, all three types are used, rather that any one of the types can be employed in a set.
Smart Media Applications "Smaz-t media" are media that sense this enviromnent in a particular way, and create a measurable response. This could be, for example, a chemical sensor in which the device produces an electrical current when the presence of a particular type of molecule in solution is detected. Any electrical version of patterned smart media could be integrated with other signal processing on the same chip. Another example is a sensing medizun that changes color upon sensing a change in chemical environment, temperature environment, optical stimulus, or other type of stimulus.
Since the diblocl~ systems are laterally patterned, arrays with large munbers of distinct sensing elements are fabricated. Each element is a localized transducer that is integrated into an on-chip circuit.
Presently, the techniques described herein can be used to produce nanowire az~ays with a nanoelement density of approximately 1.2 x 1012 elements/in2.
This ultimately enables data storage technologies with storage capacities exceeding a terabit/in2. Patterned versions of high-density media in which one bit of data is encoded in the magnetization of a group of magnetic nanowires are created. The pattez-ned diblocl~-derived devices described herein provide a simple fabrication route to lugh storage densities.

Electrochemical Sensor Applications These sensors are used in a wide range of applications, including portable glucose detection for people with diabetes. The nanoporous templates disclosed herein are used conveniently to malce devices for electrochemical sensing as an array of "microelectrodes." In the electrochemistry literature the term "microelectrode"
refers to a conf guration of electrode that induces oadial diffusion of an electrochemically-active species toward the electrode. The behavior of a microelectrode differs dramatically from that of a planar electrode. A
nanoporous polyner template nanoelectrode array as described herein offers fast response, lower detection limits, and the possibility for molecular selectivity based on size or molecular interactions with the template. The lateral-patterning invention advances the use of nanoporous templates for this purpose because several distinct microelectrodes arrays are configured onto the same chip using patterned diblocl~
templates atop a pre-patterned thin-film electrode set.
Biomolecule ArrayApplications Combinatorial chips are configured for DNA gene expression studies and other diagnostic applications. The nanoporous polymer templates described herein are patterned and filled with metals or silicon oxide that are used to attach biomolecules that will enable new types of biomolecular research capabilities.
Patterned versions of such structures are of far greater usefulness. Another application for lateral patterning is to create structures for sorting molecules in nanoscales.
Molecular Electronics Applications Specific types of molecules and small colloidal clusters are used as electroW
c devices. The goal is to "design in" electronic functionality (e.g., rectification, switclung, negative differential resistance) by synthesizing molecules using certain types of end groups, aromatic rings and side groups. Interfacing these molecules for electrical characterization using lmown techniques is extremely challenging.

However, new patterned nanoporous templates can be used as a practical host substrate for the characterization of specific types of electroncally relevant molecules. The diblocl~ template is patterned in regions atop pre-patterned gold electrodes. The molecules axe adsorbed to the gold at the bottom.of each pore using a thiol-gold interaction. This results in a self assembled monolayer of the electronic molecules at the bottom of each pore. A counter electrode is deposited electrochemically atop the molecular layer and contacted using the patterned interconnections described above. This fabrication scheme enables convenient electrical characterization of candidate molecules.
Photonic-bandgap Structure Applications A photonic-bandgap crystal is a optical material that has periodically modulating dielectric constant. As a consequence of the periodic stnictme, the transmission properties become dependent on the incident light frequency such that certain frequencies, there is no transmission (the dispersion relation ~ (h) is non-linear and has derivative of zero at Brillouin zone boundaries, l~ _ ~/a, where a is the crystal lattice period). Using these materials, a range of devices can be configured in analogy to electronic devices. Once dibloclc copolymer systems can be made with a sufficiently long-range array order, they can be patterned in specific shapes to fabricate planar photonic-crystal waveguides and other photonic-crystal devices.
Photonic waveguides are able to have much smaller twn radius as compared to optical fiber. Such waveguides can be used to intercormect on-chip optical components.
Electrical hltercomlections to Nanowires Electrical interconnections can be made to nanowires made by patterned diblocl~ copolymer templates. This is achieved by integrating the templating process with other pre- and post-processing steps.
Am important step in utilizing electrical nanostmctures is malting appropriate electrical interfaces to these nanostructures. hl Figure 15, one embodiment of the present invention is realized. First, electrodes are prepattemed onto the substrate by a suitable lithographic technique. Secondly, a diblocl~ copolymer film is deposited.
Next, a metal layer is deposited. Finally, a conventional (photo- or e-beam-) resist is deposited. The cylinders of the diblocl~ copolymer can be oriented by the techniques described herein. The resulting structure is shown in Fig. 15a.
Selected areas of the top resist are exposed lithographically and removed by chemical development. Subsequently the exposed metal layer (#2) is removed by a metal etch. At tlus point the diblocl~ filin is exposed to ultraviolet (LTV) light or an electronic beam, if it has not been exposed in a prior step. ThIS St111CtL1Te 1S ShOWll 111 Fig. 15b.
The diblocl~ film is now chemically developed with acetic acid or another suitable developer to result in a nanoporous template. If desired, the surface of the nanoporous template can be cleaned using a reactive ion etch with oxygen. This structure is shown in Fig. 15c.
Nanowires or other suitable nanostructures are now deposited into the pores of the nanoporous template. To achieve top electrical contact, the deposition can continue until electrical connection is made with the top layer. As discussed herein, a range of different desired nanostructures~ can be deposited in the pores, depending on the target application. This structure is shown in Fig. 15d.
In some applications, such as field emissions arrays, electrical contact to the top layer is not desired. Rather, the isolated top metal layer would be used as an electrical gate in a triode field emission device configuration. In other applications, metal contact #2 can be replaced over the deposited nanowires to complete contact t1>1 ough the wires, as shown in Fig. 15 e.
The integration scheme described in Figure 15 represents only one out of several schemes for integration and interfacing nanostllictures made by patterned nanoporous templates. Nanofabrication via patterned diblocl~ copolymers can be combined easily with other (pre- and post-) process steps, and done so such that the pattern is made in registry with previous lithographic pattelms.
Another fabrication scheme can be described as follows. First, electrodes are prepatterned onto the substrate by a suitable lithographic technique.
Secondly, a diblocl~ copolymer film is deposited. The diblocl~ cyclinders are then oriented , exposed lithographically in a desired pattern, and then developed into a nanoporous template. Nanowires or other suitable nanostructures are now deposited into the pores of the nanoporous template.
, To achieve top electrical contact, or top non-contact electrodes, a suitable lithographic exposure and development, a ion etch performed to remove degraded portions (for example, oxide) from the top of the nanowires, and then deposition of metal electrodes in the contact areas.
The following examples do not limit the scope of the invention described in the claims.
EXAMPLES
The following examples illustrate particular properties and advantages of some of the embodiments.
Example 1: A Prototype of a Field Emission Array Figs. 8a-8d are 10X optical images of a prototype of a field emission array built by the inventors. In Fig. 8a, the silicon substrate was gold patterned with conventional lithography with a 1 micrometer thicl~, vertically oriented dibloclc copolymer film (polystyrene/pol5nnethylmethacrylate, 70/30 by volume) covering the entire surface (the film is optically transparent). Fig. 8b is an image of the same sample after electron-beam patterning in the shape of a square, and acetic acid development. The inner square was a patterned nanoporous template. The outer square was a solid film of crosslinl~ed polystyrene/polylnethyhnethacrylate made by intentional overexposure to radiation. Fig. 8c is an ianage of the same sample after 500 mn length cobalt wires were electrodeposited in the template. The cobalt is blacl~
in the image. Fig. 8d is a close-up of the electrodeposited area. It is important to note that the nanowires deposit only in the nanoporous template regions with metal underneath.

Example 2: A Prototype Ma~netorasistive Device Figs. l la and l 1b are lOX optical images of a prototypical four-wire magnetoresistive device made by the inventors. An array of vertical magnetic nanowires stands atop a thin-film of gold pre-patterned into a four-probe resistor pattern. This device is used to investigate spin-dependent scattering in a "current-in-plane" (CIP) geometry where the scattering interface is geometrically periodic on the scale of tens of manometers. Fig. 1 la is an image of a substrate with a patterned electrode underlayer covered with an optically transparent dibloclc copolymer film layer prepared as described in Example 1.
The four probe resistor pattern was created as 2 X1,111 111 Wldth alld 1 OO
~,L111 111 length, by standard electron beam lithography using a PMMA resist on a silicon substrate. The thin-film resistor includes a 20 nm thicl~ gold layer on top of a 1 lnn Cr adhesion layer. A 1.1 ~,m thicl~ film of poly(styrene-(3-methylmethacrylate) diblocl~
copolymer denoted P(S-(3-MMA) having 30% by volume polylnethylmethacrylate (PMMA) with molecular weight of 42,000 Daltons was spun coated onto the patterned surface of substrate. This copolymer microphase separates into a hexagonal array of PMMA cylinders in a polystyrene (PS) matrix. Almealing thin films at 180°C, above the glass transition temperature under an applied electric field, orients the PMMA cylinders rionnal to the fihn surface, enabling the fabrication of nanostructures with large aspect ratios. The sample was then exposed to an electron beam impinging on the sample in the shape of a square (area dose of 50 ~,C/cmz, with beam energy and current used is 20 l~V and 2000 pA, respectively. Generally, for such dibloclc films of about 1 micron, the exposure dose can range from about 20 to about 200 ~.C/cm2, with accelerating voltages and beam currents as described above.
Optimal doses have been found to be about 80 ~,C/cln2. The sample was then chemically developed with acetic acid. The original copolymer remains in the unexposed areas.
Cobalt nanowires were deposited in the pores on top of the gold pattern from an aqueous deposition bath, prepared by mixing 96 grams of CoS04~7Hz0 and 13.5 grams H3B03 in 300 ml pure HZO, with 60 ml of methanol added as surfactant, resulting in an electrolyte pH of 3.7. The Co was electroplated at a reduction potential of -1.OV with respect to a saturated calomel reference electrode. The nanowires were 500 nm in length. Fig. l 1b is an image of the same sample after nanowire electrodeposition.
Structural information was obtained by performing small angle X-ray scattering (SAXS) and field emission scanning electron microscopy (FESEM). The SAXS data confirms a perpendicular nanowire orientation with a period of 21.7 mn.
The sample was cleaved in two, and FESEM used to examine a cross-section of the nanowire array. The diameter of the nanowires was found to be approximately 11 mn, with a period of 21.8 lnn. At this scale, the individual magnetic naazowires should be single-domain in equilibrium, and show interesting magnetoresistance (MR) effects, since the interwire spacing is less than the spin diffusion length.
Example 3: Giant Ma~letoresistance Device and Measurements The four-wire magnetoresistive device prepared in Example 2 was used for 1S measurement. The magnetic cobalt nanowire array is composed of 14 mn diameter wires, each 500 lnn long, arranged in a hexagonal lattice With a period of 24 mn. The structure of the device was verified by shall-angle X-ray scattering measurements.
The magnetic field direction is parallel to the nanowire axis. A cross sectional scamling electron micrograph (SEM) image of such an array is shown in Fig.
12b.
The GMR ratio as a fimction of temperature between 2I~ and 300I~ 1S ShOWTI 111 Fig.
12a. The data tal~en at 2K shows the largest amplitude curve, and that taken at 300K
shows the smallest amplitude curve, with intermediate temperatures having intermediate values, with amplitudes in line with the ordering of the temperature.
Other GMR ratios, as a function of orientation of magnetic field and temperature are shown in Figs. 16a-c. The magnetoresistance is defined as [R(H) -R(501~0e)/R(50 lcOe)]. Again, the data taken at 2I~ shows the largest amplitude curve, and that tal~en at 300K shows the smallest amplitude curve, with intermediate temperatures having intermediate values, with amplitudes in line with the ordering of the temperature. In the "perpendicular" orientation '(fig. 16a), the field is normal to the plane of the Au film (parallel to the Co nanowires) and the current direction. For the "transverse" orientation (Fig. 16b) and "longitudinal" orientation (Fig.
16c), the field is in the plane of the gold film (perpendicular to the Co wires), but perpendicular or parallel to the current direction, respectively. The, different shapes and values for the MR curves for the three orientations provide evidence for the coexistence of anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR) scattering mechanisms in this system.
MR behavior of the Co nanowires was also investigated as a ft111Ct~o11 Of gold film thiclcness and Co nanowire length. Gold films of 7.5, 10 and 20 inn thiclmess were studied with Co nanowires of 500 nm. Also, samples of Co nanowire lengths of 100 and 500 nm were prepared having gold film thiclmess of 20 inn. MR behavior was found to depend principally on nanowire length. A plot of normalized MR",aX for a perpendicular orientation at 0 field versus temperature for various gold filin thiclcn.esses and Co nanowire lengths is shown in Fig. 22. The characteristics clearly indicate that the temperature dependence of MR is strongly dependent on the Co nanowire length, but not so strongly on the gold film thiclmess. Each data set is I S normalized to its 2K value for comparison.
OTHER EMBODIMENTS
It is to be understood that while the invention has been described in conjwction with the detailed description thereof, that the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

Claims (34)

What is claimed is:

1. A multilayer nanostructure comprising:
a substrate surface, at least a portion of which is conductive or semiconductive; and at least one set of nanowires extending from the conductive or semiconductive substrate surface, wherein one end of the nanowires is in electrical communcation with the conductive or semiconductive surface.

2. The multilayer nanostructure of claim 1, further comprising at least one conductive or semiconductive layer contacting an opposite end of at least some of the nanowires in the set, wherein the conductive or semiconductive layer is in electrical communication with at least some of the nanowires in the set.

3. The multilayer nanostructure of claim 1, wherein the set comprises nanowires having substantially the same length.

4. The multilayer nanostructure of claim 3, wherein the set comprises nanowires having length of at least 20 nm.

5. The multilayer nanostructure of claim 4, wherein the set comprises nanowires having length of at least 100 mn.

6. The multilayer nanostructure of claim 1, wherein the substrate is lithographically patterned, having a plurality of independently conductive or semiconductive surface regions.

7. The multilayer nanostructure of claim 6, wherein at least one set is in electrical communication with a plurality of independently conductive or semiconductive surface regions.

8. The multilayer nanostructure of claim 6, wherein at least some independently conductive or semiconductive surface regions are each in electrical communication with an individual set of nanowires.

9. The multilayer nanostructure of claim 2, wherein the substrate is lithographically patterned, having a plurality of independently conductive or semiconductive surface regions.

10. The multilayer nanostructure of claim 9, wherein at least one set is in electrical communication with a plurality of independently conductive or semiconductive surface regions.

11. The multilayer nanostructure of claim 9, wherein at least some independently conductive or semiconductive surface regions are each in electrical communication with individual sets of nanowires.

12. The multilayer nanostructure of claim 11, wherein the conductive or semiconductive layer is in electrical communication with at least some of the nanowires in a plurality of sets.

13. The multilayer nanostructure of claim 2, comprising a plurality of the conductive or semiconductive layers.

14. The multilayer nanostructure of claim 13, wherein at least some conductive or semiconductive layers are each in electrical communication with at least some nanowires in a plurality of sets.

15. The multilayer nanostructure of claim 11, wherein at least some sets comprise nanowires made of material distinct from that of other sets.

16. The multilayer nanostructure of claim 15, wherein nanowires differ in their reduction potential.

17. The multilayer nanostructure of claim 15, wherein nanowires differ in their semi-metal type.

18. The multilayer nanostructure of claim 1, wherein at least some nanowires comprise magnetic material.

19. The multilayer nanostructure of claim 1, wherein at least some nanowires are multilayered.

20. The multilayer nanostructure of claim 19, wherein at least some nanowires are multilayered.

21. The multilayer nanostructure of claim 11, wherein at least some sets can be modified to have magnetic properties distinct from those of other sets.

22. The multilayer nanostructure of claim 21, wherein the magnetic properties comprise magnetization direction.

23. A field emission display device comprising: an addressable array of field emitters comprising a multilayer nanostructure of claim 12; and a phosphorescent screen.

24. A thermoelectric cooling device comprising: a multilayer nanostructure of claim 17, comprising nanowires of "n-" and "p-" types.

25. A magnetic data storage device comprising: a multilayer nanostructure of claim 21, wherein the nanowires have an aspect ratio of at least 20:1.

26. A magneto-electronic device comprising: a multilayer nanostructure of claim 12, wherein the nanowires comprise magnetic material.

27. The magneto-electronic device of claim 26, wherein the nanowires comprise asymmetric magnetic heterostructure.

28. A method of interfacing an electrical connection with a multilayer nanostructure, the method comprising:
preparing a diblock copolymer on a substrate surface, at least a portion of which is conductive or semiconductive;
depositing a metal layer on at least a portion of the diblock copolymer layer;
orienting the diblock copolymer to form nanoscopic cylinders parallel to each other and vertically oriented with respect to the surface;
removing at least a portion of one component from the oriented copolymer to form a patterned array of nanopores in the copolymer; and at least partially filling at least some of the nanopores with a material.

29. The method of claim 28, further comprising depositing a resist layer on at least a portion of the metal layer prior to orienting the copolymer.

30. The method of claim 28, wherein the removal of at least a portion of one component from the oriented copolymer is performed by exposure to radiation.

31. The method of claim 2,8, wherein the material used to at least partially fill at least some of the nanopores comprises magnetic material.

32. A magnetotransfer device comprising:
a substrate surface comprising at least one electrode;
an array of magnetic nanowires extending vertically from the surface in electrical communication with at least one electrode, wherein the array of nanowires is periodic on the tens of manometers scale.

33. The device of claim 32, wherein the interwire spacing in the array is substantially regular.

34. The device of claim 33, wherein the interwire spacing is less than the spin diffusion length.