| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | July 1, 2003 |
| PATENT TITLE |
Semiconducting oxide nanostructures |
| PATENT ABSTRACT |
Nanostructures and methods of fabricating nanostructures are disclosed. A representative nanostructure includes a substrate having at least one semiconductor oxide. In addition, the nanostructure has a substantially rectangular cross-section. A method of preparing a plurality of semiconductor oxide nanostructures that have a substantially rectangular cross-section from an oxide powder is disclosed. A representative method includes: heating the oxide powder to an evaporation temperature of the oxide powder for about 1 hour to about 3 hours at about 200 torr to about 400 torr in an atmosphere comprising argon; evaporating the oxide powder; and forming the plurality of semiconductor oxide nanostructures. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | January 8, 2002 |
| PATENT REFERENCES CITED |
Pan, Dai and Wang; Lead Oxide Nanobelts and Phase Transformation Induced by Electron Beam Irradiation, Aug., 2001; pp. 1-13. Pan, Dai and Wang; Nanobelts of Semiconducting Oxides; Mar. 9, 2001; pp. 1947-1949. Ginley and Bright; Transparent Conducting Oxides; Aug., 2000; pp. 15-18. Coutts, Young and Li; Characterization of Transparent Conducint Oxides; Aug., 2000; pp. 58-65. Lewis and Paine; Applications and Processing of Transparent Conducting Oxides; Aug., 2000; pp. 22-26. Gordon; Criteria for Choosing Transparent Conductors; Aug., 2000; pp. 52-57. Kawazoe, Yanagi; Ueda, and Hosono; Transparent p-Type Conducting Oxides; Design and Fabrication of p-n Heterojunctions; Aug., 2000; pp. 28-35. Minami; New n-Type Transparent Conducting Oxides; Aug., 2000; p. 38-43. Wang; Semiconducting Oxides Prepared in the Form of Nanobelts; Aug., 2001; pp. 603-604 |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
Therefore, having thus described the invention, at least the following is claimed: 1. A nanostructure, comprising: a free standing semiconductor oxide nanostructure having a substantially rectangular cross-section, wherein the nanostructure is within the range of: about 20 nanometers to about 6000 nanometers in width, about 5 nanometers to about 100 nanometers in height, and about 100 nanometers to about 3 millimeters in length. 2. The nanostructure of claim 1, wherein the semiconductor oxide is chosen from oxides of zinc, cadmium, mercury, gallium, indium, tellurium, germanium, tin, and lead. 3. The nano structure of claim 2, wherein the at least one semiconductor oxide is a doped semiconductor oxide, wherein the doped semiconductor oxide includes the at least one semiconductor oxide and at least one dopant, wherein the at least one dopant is chosen from aluminum, gallium, boron, yttrium, indium, scandium, silicon, germanium, titanium, zirconium, hafnium, antimony, tin, nitrogen, and fluorine. 4. The nano structure of claim 1, wherein the nanostructure is single crystalline, defect-free, dislocation-free, and structurally uniform. 5. The nanostructure of claim 1, wherein the nanostructure has a width-to-height ratio of about 5 to about 35. 6. The nanostructure of claim 1, wherein the nanostructure is about 20 nanometers to about 3000 nanometers in width, about 5 nanometers to about 50 nanometers in height, and about 100 nanometers to about 3 millimeters in length. 7. The nanostructure of claim 1, wherein the nanostructure has a substantially uniform width along the length of the substrate. 8. The nanostructure of claim 1, wherein the semiconductor oxide is a binary compound. 9. The nanostructure of claim 1, wherein the semiconductor oxide is a ternary compound. 10. A nanostructure comprising: a free standing semiconductor oxide nanostructure having a top, a bottom, a right side, and a left side, wherein the top and the bottom have the same width and wherein the right side and the left side have the same height, and wherein the nanostructure is within the range of: about 20 nanometers to about 6000 nanometers in width, about 5 nanometers to about 100 nanometers in height, and about 100 nanometers to about 3 millimeters in length. 11. The nano structure of claim 10, wherein the at least one semiconductor is chosen from oxides of zinc, cadmium, mercury, gallium, indium, tellurium, germanium, tin, and lead. 12. The nanostructure of claim 11, wherein if the at least one semiconductor is the oxide of lead the top and the bottom have .+-.(201) surfaces and the left and the right sides have .+-.(101) surfaces. 13. The nanostructure of claim 11, wherein if the at least one semiconductor is the oxide of gallium the top and the bottom have .+-.(100) surfaces and the left and right sides have .+-.(010) surface. 14. The nanostructure of claim 11, wherein if the at least one semiconductor is the oxide of gallium the top and bottom surfaces have .+-.(201) and left and right sides have .+-.(101) surface. 15. The nanostructure of claim 11, wherein if the at least one semiconductor is the oxide of zinc the top and the bottom have .+-.(21 10) surfaces and the left and right sides have .+-.(01 10). 16. The nanostructure of claim 11, wherein if the at least one semiconductor is the oxide of zinc the bottom surfaces surfaces have .+-.(21 10) and the left and right sides have .+-.(0001). 17. The nanostructure of claim 11, wherein if the at least one semiconductor is the oxide of tin the top and the bottom have .+-.(101) surfaces and the left and the right sides have .+-.(010) surfaces. 18. The nano structure of claim 11, wherein if the at least one semiconductor is the oxide of indium the top and the bottom have .+-.(100) surfaces and the left and the right sides have .+-.(010) surfaces. 19. The nanostructure of claim 11, wherein if the at least one semiconductor is the oxide of cadmium the top and the bottom have .+-.(001) surfaces and the left and the right sides have .+-.(010) surfaces. 20. The nanostructure of claim 10, wherein the nanostructure has a width-to-height ratio of about 5 to about 10. |
| PATENT DESCRIPTION |
TECHNICAL FIELD The present invention is generally related to nanostructures and, more particularly, is related to semiconductive oxide nanostructures and fabrication thereof. BACKGROUND Binary semiconducting oxides often have distinctive properties and can be used as transparent conducting oxide (TCO) materials and gas sensors. Current studies of semiconducting oxides have been focused on two-dimensional films and zero-dimensional nanoparticles. For example, fluorine-doped tin oxide films are used in architectural glass applications because of their low emissivity for thermal infrared heat. Tin-doped indium oxide (ITO) films can be used for flat panel displays (FPDs) due to their high electrical conductivity and high optical transparency; and zinc oxide can be used as an alternative material for ITO because of its lower cost and easier etchability. Tin oxide nanoparticles can be used as sensor materials for detecting leakage of several inflammable gases owing to their high sensitivity to low gas concentrations. In contrast, investigations of wire-like semiconducting oxide nano structures can be difficult due to the unavailability of nanowire structures. Wire-like nano structures have attracted extensive interest over the past decade due to their great potential for addressing some basic issues about dimensionality and space confined transport phenomena as well as related applications. In geometrical structures, these nanostructures can be classified into two main groups: hollow nanotubes and solid nanowires, which have a common characteristic of cylindrical symmetric cross-sections. Besides nanotubes, many other wire-like nanomaterials, such as carbides, nitrides, compound semiconductors, element semiconductors, and oxide nanowires have been successfully fabricated. However, the nanostructures discussed above can have a variety of deficiencies. For example, often it is difficult to control the structure and morphology of many nanostructures. Further, many nanostructures are not defect and/or dislocation free. These deficiencies can cause problems such as, for example, uncontrolled properties due to uncontrolled structure and/or morphology, scattering from dislocations in electric transport applications, and degraded optical properties. Thus, a heretofore unaddressed need exists in the industry to address at least the aforementioned deficiencies and/or inadequacies. SUMMARY OF THE INVENTION Briefly described, the present invention provides for new types of nanostructures. A representative nanostructure includes a substrate having at least one semiconductor oxide. In addition, the nanostructure has a substantially rectangular cross-section. The present invention also involves a method of preparing a plurality of semiconductor oxide nanostructures that have a substantially rectangular cross-section from an oxide powder. A representative method includes: heating the oxide powder to an evaporation temperature of the oxide powder for about 1 hour to about 2 hours at about 200 torr to about 400 torr in an atmosphere comprising argon; evaporating the oxide powder; and forming the plurality of semiconductor oxide nanostructures. Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. FIG. 1 includes schematics that illustrate a perspective view, a top view, a side view, and, an end view of a nanobelt. FIG. 2 includes schematics that illustrate a perspective view, a top view, a side view, and, an end view of a nanosheet. FIG. 3 is a schematic that illustrates an apparatus that can be used to fabricate the nanobelt and/or the nanosheet shown in FIGS. 1 and 2. FIG. 4 is a flow diagram illustrating a representative method for fabricating nanostructures as shown in FIGS. 1 and 2. DETAILED DESCRIPTION The present invention provides for nanostructures and methods of fabrication thereof. The nanostructures have substantially rectangular cross-sections that may be defect free, dislocation free, and/or structurally uniform. In addition, the nanostructure can be structurally controlled as well as morphology controlled, while the surfaces of the nanostructure are specific crystallographic planes. In this manner, the nanostructures may overcome some of the deficiencies described above. In general, the nanostructures can be nanobelts, nanosheets, or nanodiskettes that have a substantially rectangular cross-section. FIG. 1 illustrates a perspective view (A), a top view (B), a side view (C), and an end view (D) of a nanobelt 10. The perspective view (A) illustrates a top 12, a side 14, and an end 16 of the nanobelt 10. The top view (B), side view (C), and the end view (D) illustrate the top 12, the side 14, and the end 16 of the nanobelt 10. FIG. 2 illustrates a perspective view (A), a top view (B), a side view (C), and an end view (D) of a nanosheet 20. The perspective view (A) illustrates a top 22, a side 24, and an end 26 of the nanosheet 20. The top view (B), the side view (C), and the end view (D) illustrate the top 22, the side 24, and the end 26 of the nanosheet 20. Nanobelts 10 can be characterized as "ribbon-like" structures, while the nanosheets 20 can take the form of a variety of polygonal shapes such as, for example, a rectangle, a square, a triangle, etc. Nanodiskettes (not shown) are similar to nanosheets 20 except that nanodiskettes are "coin-shaped" structures. This disclosure does not describe in any definite dimensions the difference between nanobelts 10, nanosheets 20, and nanodiskettes. For clarity, this disclosure refers to nanobelts 10, nanosheets 20, and nanodiskettes as "nanostructures." The nanostructures are fabricated of at least one semiconductor oxide and/or at least one doped semiconductor oxide. The semiconductor oxide includes oxides of zinc, cadmium, mercury, gallium, indium, tellurium, germanium, tin, and lead. The nanostructure fabricated of at least one semiconductive oxide can be, for example, a binary or a ternary complex of the semiconductor oxide. The doped semiconductor oxide includes at least one semiconductive oxide that can be doped with at least one dopant that may be chosen from aluminum, gallium, boron, yttrium, indium, scandium, silicon, germanium, titanium, zirconium, hafnium, antimony, tin, nitrogen, and fluorine. The nanostructure can be fabricated of at least one doped semiconductor oxide, for example, a binary or a ternary complex of the doped semiconductor oxide. The size (e.g. length, width, and height) of the nanostructure can vary within a type of semiconductor oxide and among each of the semiconductor oxides. The size of the nanostructure can be controlled to fit certain criteria for a particular application. However, in general, the nanostructures can be about 20 nanometers to about 6000 nanometers in width, about 5 nanometers to about 100 nanometers in height, and about 100 nanometers to about 3 millimeters in length. The nanostructures can have a width-to-height ratio of about 5 to about 15. In addition to the dimensions described above, the following examples describe illustrative sizes of the nanostructures for some of the semiconductor oxides. The methods for fabricating nanostructures can be based on thermal evaporation of oxide powders under controlled conditions that can be performed on the apparatus 30 shown in FIG. 3. The apparatus 30 includes a horizontal tube furnace 32 that has an alumina tube 36 therein and is wrapped in a heating coil 34. Inside the alumina tube 36 are one or more alumina plates 38 and an alumina crucible 40, which contains the oxide powder 42 and/or other chemicals used to fabricate the nanostructures. To measure the temperature at various locations in the furnace 32, a thermocouple 44 or other temperature measuring device can be moved within the furnace 32. The apparatus 30 is also equipped with input 46 and output tubes 48 to introduce and pump-out a flow gas such as Argon (Ar). Additional features known by one skilled in the art are also included in the apparatus such as vacuum pumps, vacuum manifolds, reactant gas inputs, reactant gas manifolds, etc., and will not be discussed here. In practice, the desired oxide powder is placed in the aluminum crucible 40 in the center of an alumina tube 36. The temperature, pressure, and evaporation time are controlled. Typically, the evaporation is performed without a catalyst. Except for the evaporation temperature that can be determined based on the melting point of the oxides used, the following parameters are typically kept constant: evaporation time (e.g., 2 hours), alumina tube 36 pressure (e.g., 300 Torr), and flow gas flow rate (e.g., Argon flowed at approximately 50 standard cubic centimeter per minute (sccm)). During evaporation, the products of the evaporation are deposited onto the alumina plates 38 located at the downstream end of the alumina tube 36. Typically, the as-deposited products can be characterized and analyzed by x-ray diffraction (XRD) (Philips PW 1800 with Cu K.alpha. radiation), scanning electron microscopy (SEM) (Hitachi S800 FEG), transmission electron microscopy (TEM) (Hitachi HF-2000 FEG at 200 kV and JEOL 4000EX high resolution TEM (HRTEM) at 400 kV), and energy dispersive x-ray spectroscopy (EDS). Reference will now be made to the flow diagram of FIG. 4. FIG. 4 illustrates a representative method of preparing a plurality of semiconductor oxide nanostructures having a substantially rectangular cross-section from an oxide powder. Initially, the oxide powder is heated to an evaporation temperature of the oxide powder for about 1 hour to about 3 hours at about 200 torr to about 400 torr in an atmosphere comprising Argon, as shown in block 42. Then, the oxide powder is evaporated, as shown in block 44. Thereafter, the plurality of semiconductor oxide nanostructures is formed, as shown in block 46. Having summarized the nanostructures and methods of fabrication thereof above, reference will now be made in detail to six illustrative examples of the semiconductor oxide nanostructures. While the invention is described in connection with these examples, there is no intent to limit the invention to the following examples. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention |
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