Precisely positioned nanowhiskers and nanowhisker arrays and method for preparing them

1. A method for producing a structure including at least one nanowhisker on a substrate, the method comprising:

providing the substrate of a predetermined material,

providing at least one mass of a catalytic material on a surface of the substrate at a predetermined position on the surface,

applying heat and introducing at least one material in gaseous form such as to create a catalytic seed particle from each said mass, and to grow, from the catalytic seed particle, epitaxially, a nanowhisker of a predetermined material,

wherein each said mass is such that during the formation of the catalytic seed particle, forces causing the mass to migrate across said surface are less than a holding force across a wetted interface on the substrate surface,

wherein each said mass comprises a first region of a catalytic material, and a second region of an alloying material for forming said catalytic seed particle; and

wherein the mass comprises first and third layers of said catalytic material, with an intervening second layer of said alloying material.

2. A method for producing a structure including at least one nanowhisker on a substrate, the method comprising:

providing a substrate of a predetermined material

providing at least one mass of a catalytic material on a surface of the substrate at a predetermined position on the surface,

applying heat and introducing at least one material in gaseous form such as to create a catalytic seed particle from each said mass, and to grow, from the catalytic seed particle, epitaxially, a nanowhisker of a predetermined material, and

wherein:

each said mass is such that during the formation of the catalytic seed particle, forces causing the mass to migrate across said surface are less than a holding force across a wetted interface on the substrate surface,

said at least one mass is formed by a nanoimprint lithography process, employing a stamp defining the catalytic mass regions, and

the stamp is formed by an array of nanowhiskers on a substrate, whereby to permit an arbitrary diameter:height ratio for the masses of catalytic material.

3. A method for producing an array of more than about 1000 nanowhiskers on a substrate to form a photonic band gap array, the method comprising: providing a substrate of a predetermined material, providing an array of masses of a catalytic material on a surface of the substrate masses of catalytic material in a predetermined configuration, each mass being in a respective predetermined location on the surface, applying heat and introducing sequentially a plurality of materials in gaseous form such as to grow from each catalytic mass, a nanowhisker comprising segments of different materials, with sharp heterojunctions between the segments wherein nanowhisker growth conditions are regulated such as to maintain the nanowhisker sited within an accuracy from its predetermined site of 10% of the distance from its nearest neighbor;

wherein each nanowhisker comprises a series of alternating segments of two different materials, and oxidising said nanowhiskers whereby to form from said segments, alternating regions of different refractive index; and

wherein:

(a) said two different materials are Si and Al, and the regions are formed of Silica and Sapphire; or

(b) said two different materials are Si and Ge, and the regions are formed of Silica and GeO x .

4. A method according to claim 3 , wherein said two different materials are Si and Al, and the regions are formed of Silica and Sapphire.

5. A method according to claim 3 , wherein said two different materials are Si and Ge, and the regions are formed of Silica and GeO x .

6. A method according to claim 3 , wherein said segments provide a quantum dot LED structure, and providing electrical contacts to one or more selected nanowhiskers to enable operation of the LED structure.