LAMINATE COMPOSITE AND METHOD FOR MAKING SAME |
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申请号 | US13300228 | 申请日 | 2011-11-18 | 公开(公告)号 | US20120126920A1 | 公开(公告)日 | 2012-05-24 |
申请人 | Arthur J. Epstein; Chi-Yueh Kao; Yong G. Min; | 发明人 | Arthur J. Epstein; Chi-Yueh Kao; Yong G. Min; | ||||
摘要 | An organic-based magnet is formed by molecular layer deposition (MLD) of a first compound and MLD of a second compound. The first or second compound containing a metal-containing compound. The first and second compounds being reactive with each other to form a first layer organic-based magnet. A laminate composite includes a first monolayer including a metal bonded to a magnet forming organic compound. A second monolayer may be in direct contact with the first monolayer. One of the first monolayer and the second monolayer having an induced magnetization when exposed to a magnetic field. A device includes the laminate composite and a nonmagnetic film thereon. A method of making an organic magnet on a substrate in a vacuum chamber includes depositing a first layer of metal-containing compound on the substrate by MLD. | ||||||
权利要求 | What is claimed is: |
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说明书全文 | This application claims priority to U.S. Provisional Patent Application Ser. No. 61/415,280 filed Nov. 18, 2010, the disclosure of which is incorporated by reference herein in its entirety. The present invention generally relates to magnets, and more specifically, organic-based magnets and methods for making such magnets and in particular, laminates of organic magnets. Spintronics or spin electronics represent a new generation of electronic, solid-state devices that utilize an intrinsic spin and magnetic moment of an electron, as well as the electron's charge. It is anticipated that spintronic devices will be smaller, more versatile, and have superior properties compared to their semiconductor counterparts. These properties may include reduced power consumption due to their inherent nonvolatility, more rapid switching speed, and a larger number of carriers. Giant magnetoresistance (GMR) structures represent one known spintronic device that consists of magnetic films separated by a nonmagnetic layer. An applied magnetic field produces huge changes in the electric resistance of the magnetic films essentially turning on or turning off electron flow through the device. In this regard, GMR devices operate by switching the magnetization direction in the magnetic films by means of an external magnetic field in close proximity to the device. By switching the magnetic field, the electrical resistance of the device can be changed dramatically. This effect is exploited in some recording devices, such as, in computer hard disks. There are other devices that utilize this characteristic. For example, a magnetic version of a random access memory (RAM) device may utilize a similar effect. Unlike many current RAM devices, a magnetic random access memory device would be nonvolatile, no information is lost when the power is switched off. One structure of this device includes two magnetic films separated by an insulating metal-oxide film. The electrons may tunnel through the metal-oxide layer when the magnetization of each of the magnetic films is properly oriented. Still another device may include magnetic films that sandwich a semiconductor material layer, like a silicon layer. This construction may form a hybrid device that may behave like a conventional transistor to be used in computing. The pursuit of spintronics, however, has been hampered by poor properties and manufacturing methods. For example, in semiconductor spintronics, there have been intensive efforts to develop room-temperature magnetic semiconductors and carbon-based materials as spin-transporting channels, with only limited success. In particular, there is a focus on organic-based magnets, because organic-based magnets allow chemical tuning of the electronic and magnetic properties of the magnetic films. However, to incorporate these materials, quality thin films of the material must be made and, as yet, are generally unavailable. In this regard, there remains a need for organic-based magnetic films with improved performance and methods for making such films, which are both cost effective and scalable. In one embodiment of the invention, an organic-based magnet is formed by molecular layer deposition of a first compound and molecular layer deposition of a second compound, the first compound or the second compound including a metal-containing compound. The first compound and the second compound are reactive with each other to form a first layer organic-based magnet. In one embodiment, a second layer organic magnet deposited by molecular layer deposition on the first layer organic-based magnet. In one embodiment, a laminate composite comprises a first monolayer including a first metal bonded to a first magnet forming organic compound. The composite further comprises a second monolayer in direct contact with the first monolayer. The second monolayer includes a second metal bonded to a second magnet forming organic compound. The first monolayer and the second monolayer form a film having an induced magnetization when exposed to a magnetic field. In one embodiment, the first monolayer and/or the second monolayer is about one metal-organic molecule thick. In one embodiment, a device comprises the laminate composite and a nonmagnetic film on the laminate composite. In one embodiment, a laminate composite on a substrate comprises a first monolayer on the substrate including a first metal from a first metal-containing compound reacted with a first organic compound from a first organic-containing compound. The laminate composite further comprises a second monolayer on the first monolayer. The second monolayer includes a second metal from a second metal-containing compound reacted with a second organic compound from a second organic-containing compound. The first monolayer and the second monolayer having an induced magnetization when exposed to a magnetic field. In one embodiment, a method of making an organic magnet on a substrate in a vacuum chamber comprises depositing a first layer of metal-containing compound on the substrate by molecular layer deposition. The method further comprises depositing a magnet forming organic-containing compound by molecular layer deposition of the first layer. The organic of the organic-containing compound bonds with the metal of the metal-containing compound. The metal of the metal-containing compound adheres to the substrate and a portion of the metal-containing compound evolves prior to or during the depositing of the organic-containing compound. The bonded metal-organic compound forms a monolayer on the substrate. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, with the general description given above, together with the detailed description given below, serve to explain various aspects of the invention. With reference to To that end, in general, in one embodiment and as depicted in With continued reference to In one embodiment, the substrate 14 may be cut to size and cleaned prior to depositing the layer 22 thereon. For example, the substrate 14 may be cleaned with a solvent, such as, acetone, isopropanol, and/or deionized water. The substrate 14 may be exposed to UV-ozone cleaning followed by rinsing with deionized water. After rinsing, the substrate 14 may be dried with nitrogen gas. In addition, the surface of the substrate 14 may be subject to preprocessing. By way of example, a silica layer may be deposited on a silicon substrate in an argon-filled environment before being rinsed with deionized water. Furthermore, cleaning in a level-1000 clean room may facilitate subsequent deposition of the layers 22 and 24. Referring to Specifically with regard to the layer 22, the metal of the metal-containing compound deposited on the substrate 14 may include a transition metal, for example, vanadium (V), iron (Fe), nickel (Ni), manganese (Mn), chromium (Cr), and/or cobalt (Co). Other transition metals may include those identified in Groups 3 to 12 (IUPAC designation) of the Period Table, including the Lanthanides and the Actinides, and may preferably include electron-rich transition metals, for example, Group 3 to 10 transition metals. Alternatively, or in addition to transition metals, the metal may include rare earth metals. During deposition, during a subsequent reaction, or as a result of decomposition, a metal from the layer 22 may bond or adhere to the substrate 14. By way of example, in this regard, vanadium may be deposited as a vanadium-containing compound. The vanadium-containing compound may decompose during the deposition process, during a subsequent process, or during a reaction such that elemental vanadium resides on the substrate 14. In one embodiment, the vanadium-containing compound may be vanadium hexacarbonyl (e.g., V(CO)6), which may form a vanadium carbonyl-containing layer on the substrate 14. The carbonyl may subsequently decompose leaving residual, elemental vanadium on the substrate 14. Other transition metal carbonyls may be similarly deposited and contain the metal of the metal carbonyl. Alternatively, for example, benzene complexes of transition metals, such as, V(C6H6)2, may be deposited via MLD. Following deposition of the layer 22, the organic-containing compound may be deposited to form layer 24 on the layer 22, as shown in Advantageously, while not being bound by theory, the deposition and reaction between the layers 22 and 24 may be self-limiting. This self-limiting nature is thought to allow the thickness of the laminate composite 10 to be precisely controlled. In addition, this feature may also provide a mechanism by which the laminate composite 10 may be smooth and pinhole free even on substrates with very high aspect ratios, for example, greater than about 10. With reference to However, any additional layer 22, 24 may be of a different metal and/or a different organic compound. In this regard, the laminate composite 10 may include a plurality of monolayers 12 of different metal-organic compounds. Thus, the chemical composition may vary by monolayer. This feature allows precise control over the composition of the laminate composite 10 and the variation of the composition through the thickness of the laminate composite 10. By way of example, a cobalt-containing compound and TCNE may form subsequent layers 28 and 30, respectively, to provide a monolayer 32 of Co[TCNE]x on a previously formed V[TCNE]x monolayer. The laminate composite 10 would thus be a lamination of individual monolayers of Co[TCNE]x and V[TCNE]x. Each monolayer may have a discrete chemical composition specific to the layers used to form the monolayer 12, 32. In one embodiment, additional layers, such as, layers 34 and 36 may be deposited in accordance with previously deposited layers 22 and 24 and/or layers 28 and 30. Layers 34 and 36 may include the same or different transition metals and organic compounds as any preceding layer 22, 24, 28, or 30 or a combination thereof. Layers 34 and 36 may form a monolayer 38. Accordingly, the laminate composite 10 may include multiple monolayers of different metal-organic compounds. For example, a combination of Co, Ni, Fe, and/or V[TCNE]x compounds each formed by a self-limiting reaction between adjacent, deposited layers, for example, between layers 22 and 24, between layers 28 and 30, and/or between layers 34 and 36. The laminate composite 10 may, therefore, be a lamination of three or more different metal-organic monolayers. In this manner, the thickness of the laminate composite 10 may be built up through multiple individual layers 22 and 24, 28 and 30, and/or 34 and 36 forming discrete monolayers 12, 32, 38 of one or different metal-organic compounds, as set forth above. By the MLD process, the monolayers 12 have a thickness or dimension of about one metal-organic molecule, for example, the monolayer 12 may be about one V[TCNE]x molecule thick. With subsequent depositions or cycles, a composite laminate of individual, single monolayers of V[TCNE]x and/or other metal-organic compound monolayers may be formed. In this regard, the thickness of the laminate composite 10 may be depend on the number of deposition cycles performed, that is, on the number of combined cycles for depositing layers 22 and 24, layers 28 and 30, and/or layers 34 and 36. By way of example, for a V[TCNE]x laminate composite, the thickness may be on the order of 50 nm for about 50 cycles (i.e., about 50 paired cycles of layers 22 and 24). Thinner composite laminates may also be achieved with fewer cycles while thicker composite laminates may be achieved with additional cycles. The properties of the laminate composite 10, as set forth above, exceed those measured from other deposition processes. The laminate composite 10 may exhibit a magnetization when exposed to a magnetic field. By way of example, the coercivity of the laminate composite 10 may be from about 80 Oe to about 190 Oe. The temperature dependence of the laminate composite 10, as measured with a superconducting quantum interference device (SQUID) may be up to 400 K before any significant drop in the magnetization is observed, which suggests that embodiments of the laminate composite are more thermally stable than films made via CVD and PVD, for example. The time-dependent resistance, measured over a period of five days, indicates that the laminate composite 10 may be more air stable than CVD films. In addition to layers 22 and 24, an optional layer 26 may be interposed between layers 22 and 24 or on top of layer 24, as shown in As set forth above, the laminate composite 10 may form all or a portion of the device 16 ( Because of the advantageous properties set out above, including air stability, high temperature, high magnetic performance, flexibility, and the chemical tuning of those properties, the laminate composite 10 may be uniquely suited for use in spintronics generally, as set out above, including in security applications, such as, in terahertz imaging Imaging/Sensing; in spin-thermolelectric generators; in spin-organic photovoltaic cell applications; in spin-thin film transistor applications; in spin-light emitting diode applications; in electromagnetic interference shielding applications; in spin-torque transfer RAM (SPRAM); in magnetoresistive random access memory (MRAM) applications; and in photonic-controlled spintronics. By way of example only, laminate composite organic magnet compositions suitable for use in thermolelectric devices may include: V[TCNE]x, V[TCNQ]x, V[TCNB]x, V[HCBD]x, V[TCEP]x, Co[TCNQ]x, Co[TCNB]x, Co[HCBD]x, Co[TCEP]x, Fe[TCNQ]x, Fe[TCNB]x, Fe[HCBD]x, Fe[TCEP]x, Cr[TCNE]x, Mn[TCNE]x, Ni[TCNE]x, and other metal-organic layers plus any other organic metallic materials since there is no requirement on magnetic performance beyond the amount of unpaired spin per each metal site and each organic site. It will be appreciated that it is advantageous for thermoelectric applications due to their higher density of states around the Fermi level. By way of example only, laminate composite organic magnet compositions suitable for use in Spin-OPV devices may include: V[TCNE]x, V[TCNQ]x, V[TCNB]x, V[HCBD]x, V[TCEP]x, Co[TCNQ]x, Co[TCNB]x, Co[HCBD]x, Co[TCEP]x, Fe[TCNQ]x, Fe[TCNB]x, Fe[HCBD]x, Fe[TCEP]x, Cr[TCNE]x, Mn[TCNE]x, Ni[TCNE]x, among others, plus a material, which has functions as a magnet and has certain band gaps for harvesting light from different spectral bands, for example, in the infrared, visible, and ultraviolet bands. By way of example only, laminate composite organic magnet compositions suitable for use in MRAM/SPRAM devices may include: V[TCNE]x, V[TCNQ]x, V[TCNB]x, V[HCBD]x, V[TCEP]x, Co[TCNQ]x, Co[TCNB]x, Co[HCBD]x, Co[TCEP]x, Fe[TCNQ]x, Fe[TCNB]x, Fe[HCBD]x, Fe[TCEP]x, Cr[TCNE]x, Mn[TCNE]x, Ni[TCNE]x, among others, plus other organic metallic materials, which have strong magnetic performance, for example, high magnetic ordering temperature (above about 100° C.) and significant coercive magnetic field at room temperature (greater than above 15 Oe). By way of example only, laminate composite organic magnet compositions suitable for use in EMI Shielding devices may include: V[TCNE]x, V[TCNQ]x, V[TCNB]x, V[HCBD]x, V[TCEP]x, Co[TCNQ]x, Co[TCNB]x, Co[HCBD]x, Co[TCEP]x, Fe[TCNQ]x, Fe[TCNB]x, Fe[HCBD]x, Fe[TCEP]x, Cr[TCNE]x, Mn[TCNE]x, Ni[TCNE]x, and other metallic materials, plus any other metallic and semi-metallic materials, including conducting polymers, since electrical conductivity is required but magnetic properties are not. By way of example, the electrical conductivity of the laminate may be provided by layers incorporating electrically conducting polymers, such as, dope polyaniline, doped polypyrrole, and doped polythiophene and their derivatives. By way of example only, laminate composite organic magnet compositions suitable for use in Security: THz Imaging/Sensing devices may include: V[TCNE]x, V[TCNQ]x, V[TCNB]x, V[HCBD]x, V[TCEP]x, Co[TCNQ]x, Co[TCNB]x, Co[HCBD]x, Co[TCEP]x, Fe[TCNQ]x, Fe[TCNB]x, Fe[HCBD]x, Fe[TCEP]x, Cr[TCNE]x, Mn[TCNE]x, Ni[TCNE]x, etc. plus a mixture with inorganic materials such as, GaAs, Si wafer, etc. Because of the combined electrical and magnetic properties, sufficiently thick films of these materials will be good absorbers of electromagnetic radiation encompassing a very broad spectral range, for instance, from the infrared frequencies through the ultraviolet frequencies and including the terahertz frequencies. By way of example only, laminate composite organic magnet compositions suitable for use in Spin-LED devices may include: V[TCNE]x, V[TCNQ]x, V[TCNB]x, V[HCBD]x, V[TCEP]x, Co[TCNQ]x, Co[TCNB]x, Co[HCBD]x, Co[TCEP]x, Fe[TCNQ]x, Fe[TCNB]x, Fe[HCBD]x, Fe[TCEP]x, Cr[TCNE]x, Mn[TCNE]x, Ni[TCNE]x, etc., plus any magnetic materials and their mixture with organic based materials. By combining one embodiment of the invention with a LED material, the spin transport property allows the device to generate electroluminescence with circular polarization. In order to facilitate a more complete understanding of the embodiments of the invention, the following non-limiting examples are provided. A V[TCNE]x laminate composite was formed on Si(111) wafers. A MLD device was utilized to deposit the laminate composite. The organic compound was TCNE from Sigma-Aldrich which was purified by sublimation with activated carbon before deposition. The metal-containing compound was V(CO)6 which was synthesized according to known principles. Both compounds were stored in air-tight containers in an inert environment in a refrigerator at a temperature of about 40° C. During deposition, the base pressure in the main chamber was about 10−5 torr as a result of pumping the chamber overnight. The deposition was started by opening a shut-off valve between the main chamber and a precursor cell that contained the V(CO)6. The substrate was exposed to V(CO)6 for about 50 s to deposit V(CO)6. During V(CO)6 deposition, the pressure was permitted to rise to about 0.5 to 1 torr. Following V(CO)6 deposition, the chamber was evacuated to remove excess V(CO)6 and reaction by-products, like CO, and to reduce the pressure in the main chamber. The chamber was evacuated for about 100 s. A layer of TCNE was then deposited on the previously deposited layer. The wafers were exposed to TCNE for about 300 s. Following deposition of the TCNE, the chamber was again evacuated, though for about 150 s. During deposition, growth was monitored by a quartz crystal microbalance (QCM) (a XTM/2 by Inficon with crystals purchased from Kurt J. Lesker Company). The growth is depicted in the plot of After depositing, the chamber, which contained the laminate composite formed, was disconnected from the pumping line and moved into a glove box that was filled with inert gas, Ar. The chamber was then opened inside the Ar-filled box and the V[TCNE]x laminate composite was removed for examination of film thickness, roughness, chemical and physical properties. Chemical composition was determined by X-ray photoelectron spectroscopy (XPS), the data obtained is shown in A Co[TCNE]x laminate composite was deposited on Si(111) wafers in a similar sequence with the same MLD device to that of Example 1. In Co[TCNE]x deposition, Co2(CO)8 was used. After the deposition, the chamber was then transferred into the Ar-filled glove box for measurement. The growth process was monitored by QCM and the result is shown in A V-Co-TCNE laminate composite was deposited on Si(111) wafers in a similar sequence with the same MLD device to that of Example 1. In V-Co-TCNE deposition both Co2(CO)8 and V(CO)6 were used. The sequence for deposition was V(CO)6, TCNE, Co2(CO)8, TCNE, V(CO)6, TCNE, Co2(CO)8, TCNE, and so on. After the deposition, the chamber was then transferred into the Ar-filled glove box for measurement. The growth process was monitored by QCM and the results are shown in By comparison, it has been observed that layers deposited by chemical vapor deposition (CVD) and physical vapor deposition (PVD) are defective in one way or another. As such, it was found that the properties of layers deposited by such processes are insufficient for use in spintronics devices generally. For instance, CVD and PVD layers are relatively thin and may contain pinholes or other defects that inhibit the use of layers formed from CVD or PVD in spintronic applications. Similarly, depositing layers by CVD and PVD is difficult to control and may not be scalable for commercial purposes. In contrast, it has been observed with regard to MLD that the thickness of layers 22, 24 and, consequently, the thickness and uniformity of the monolayer 12 formed therefrom may be controlled more precisely. In this regard, the monolayer 12 may be pinhole free. As such, the properties of the laminate composite 10 made via MLD are improved over composites of similar materials made by CVD or PVD. For example, MLD deposited layers may be characterized by a higher density (about 1.5 times higher), a higher conductivity (about 105 times higher), and a higher curie temperature (Tc) of magnetic ordering of greater than about 400 K than similarly composed CVD layers. In addition, the laminate composite 10 deposited via MLD may have greater stability in air and better surface uniformity and fewer pinholes at comparable thicknesses than similarly composed CVD layers. A comparison of the coercivity for V-TCNE polymeric complexes deposited via CVD, from a solution with a powder, via PVD, and via MLD and measured at specific temperatures is provided in Table 1. Table 1 also provides a comparison of the measured magnetic order temperature for each of the same materials. While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept. |