# US 10,312,081 B2 · Synthesis of metal oxide surfaces and interfaces with crystallographic control using solid-liquid-vapor etching and vapor-liquid-solid growth

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- Number: US 10,312,081 B2
- Document ID: US10312081B2
- Status: Granted
- Kind: B2
- Application number: 15/370,041
- Filed: 2016-12-06
- Published: 2018-01-18
- Granted: 2019-06-04
- Earliest claimed: 2016-07-15
- Assignees: University of Kentucky Research Foundation
- Applicants: University of Kentucky Research Foundation
- Inventors: Beth S. Guiton; Lei Yu
- Web page: https://patentgrep.com/patent/US10312081B2

## CPC

- H10P 14/3462: {Nanowires}
- C30B 1/00: Single-crystal growth directly from the solid state (unidirectional demixing of eutectoid materials C30B3/00; under a protective fluid C30B27/00)
- C30B 11/12: Vaporous components, e.g. vapour-liquid-solid-growth
- C30B 29/16: Oxides
- C30B 29/60: characterised by shape
- H10F 71/00: Manufacture or treatment of devices covered by this subclass (patterning processes to connect thin photovoltaic cells in integrated devices, or assemblies of multiple devices, having photovoltaic cells H10F19/33; manufacture or treatment of encapsulations or containers for integrated devices, or assemblies of multiple devices, having photovoltaic cells H10F19/80; manufacture or treatment of integrated devices, or assemblies of multiple devices, comprising at least one element in which radiation controls the flow of current H10F39/00)
- H10P 14/271: {characterised by the preparation of substrate for selective deposition}
- H10P 14/274: {using seed materials}
- H10P 14/279: {Vapour-liquid-solid growth}
- H10P 14/2905: {Silicon, silicon germanium or germanium}
- H10P 14/2918: {being semiconductor metal oxides (Group IIB-VIA materials H10P14/2913)}
- H10P 14/2921: {being crystalline insulating materials}
- H10P 14/2925: {Surface structures}
- H10P 14/2926: {Crystal orientations}
- H10P 14/3426: {Oxides}
- H10P 14/3402: {characterised by the chemical composition}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- C30B: SINGLE-CRYSTAL GROWTH (by using ultra-high pressure, e.g. for the formation of diamonds, B01J3/06); UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL (zone-refining of metals or alloys C22B); PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE (casting of metals, casting of other substances by the same processes or devices B22D; working of plastics B29; modifying the physical structure of metals or alloys C21D, C22F); SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE (for producing semiconductor devices or parts thereof H10); APPARATUS THEREFOR
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

The present invention provides integrated nanostructures comprising a single-crystalline matrix of a material A containing aligned, single-crystalline nanowires of a material B, with well-defined crystallographic interfaces are disclosed. The nanocomposite is fabricated by utilizing metal nanodroplets in two subsequent catalytic steps: solid-liquid-vapor etching, followed by vapor-liquid-solid growth. The first etching step produces pores, or “negative nanowires” within a single-crystalline matrix, which share a unique crystallographic direction, and are therefore aligned with respect to one another. Further, since they are contained within a single, crystalline, matrix, their size and spacing can be controlled by their interacting strain fields, and the array is easily manipulated as a single entity—addressing a great challenge to the integration of freestanding nanowires into functional materials. In the second, growth, step, the same metal nanoparticles are used to fill the pores with single-crystalline nanowires, which similarly to the negative nanowires have unique growth directions, and well-defined sizes and spacings. The two parts of this composite behave synergistically, since this nanowire-filled matrix contains a dense array of well-defined crystallographic interfaces, in which both the matrix and nanowire materials convey functionality to the material. The material of either one of these components may be chosen from a vast library of any material able to form a eutectic alloy with the metal in question, including but not limited to every material thus far grown in nanowire form using the ubiquitous vapor-liquid-solid approach. This has profound implications for the fabrication of any material intended to contain a functional interface, since high interfacial areas and high quality interfacial structure should be expected. Technologies to which this simple approach could be applied include but are not limited to p-n junctions of solar cells, battery electrode arrays, multiferroic materials, and plasmonic materials.

## Claims

### Claim 1

A method for synthesizing a nanocomposite of aligned nanowires within a crystalline matrix comprising:
(a) depositing at least two metal nanodroplets on a surface of a metal oxide single crystalline matrix;
(b) etching negative nanowires into the surface of the crystalline matrix by solid-liquid-vapor etching with the metal nanodroplets; and
(c) filling the negative nanowires from (b) by vapor-liquid-solid growth with a metal oxide reactant vapor and the metal nanodroplets to form nanowires within the crystalline matrix, wherein the reactant vapor is a second material to the metal oxide of the crystalline matrix.

### Claim 2 (depends on 1)

The method of claim 1, further comprising removing the metal nanodroplets after step (c).

### Claim 3 (depends on 1)

The method of claim 1, wherein the crystalline matrix is selected from the group consisting of SnO2, ZnO, MgO, Ga2O3, TiO2, In2O3, Fe2O3, Fe3O4, CdO, γ-Al2O3, CaO, NiO, MnO, Eu2O3, and Sm2O3.

### Claim 4 (depends on 1)

The method of claim 1, wherein the metal nanodroplets comprise a metal selected from the group consisting of gold, gallium, silver, copper and platinum.

### Claim 5 (depends on 1)

The method of claim 1, wherein the reactant vapor is selected from the group consisting of SnO2, ZnO, MgO, Ga2O3, TiO2, In2O3, Fe2O3, Fe3O4, CdO, γ-Al2O3, CaO, NiO, MnO, Eu2O3, Sm2O3 and elements contained therein.

### Claim 6 (depends on 1)

The method of claim 1, wherein the reactant vapor comprises a group IV or group 14 element, a III-V material or a II-VI material.

### Claim 7 (depends on 1)

The method of claim 1, wherein the etched negative nanowire is etched vertically with respect to the surface of the crystalline matrix.

### Claim 8 (depends on 1)

The method of claim 1, wherein the etched negative nanowire is etched horizontally along the surface of the crystalline matrix.

### Claim 9 (depends on 1)

The method of claim 1, wherein the etched negative nanowire is etched at an angle with respect to the surface of the crystalline matrix.

### Claim 10 (depends on 1)

The method of claim 1, further comprising continuing growth of the nanowire such that it protrudes above the surface of the crystalline matrix.

### Claim 11 (depends on 1)

The method of claim 1, wherein growth of the nanowire is discontinued such that the nanowire only partially fills the negative nanowire.

### Claim 12 (depends on 1)

The method of claim 1, wherein the metal nanodroplets are embedded into the crystalline matrix in (b) at the base of the etched negative nanowire.

### Claim 13 (depends on 1)

The method of claim 1, wherein the negative nanowire in (b) is etched to a depth to provide an adhesive force between the metal nanodroplet and walls of the negative nanowire.

### Claim 14 (depends on 1)

The method of claim 1, wherein the formed nanowires are contained within the crystalline matrix.

### Claim 15 (depends on 1)

The method of claim 1, wherein the formed nanowires extend beyond the surface of the crystalline matrix.

### Claim 16 (depends on 1)

The method of claim 1, wherein the nanodroplets reside at the tip of the formed nanowires.