Techniques for forming nanostructured materials are provided. In one aspect of the invention, a method for forming nanotubes on a buried insulator includes the steps of: forming one or more fins in a SOI layer of an SOI wafer, wherein the SOI wafer has a substrate separated from the SOI layer by the buried insulator; forming a SiGe layer on the fins; annealing the SiGe layer under conditions sufficient to drive-in Ge from the SiGe layer into the fins and form a SiGe shell completely surrounding each of the fins; and removing the fins selective to the SiGe shell, wherein the SiGe shell which remains forms the nanotubes on the buried insulator. A nanotube structure and method of forming a nanotube device are also provided.

Techniques for forming nanostructured materials are provided. In one aspect of the invention, a method for forming nanotubes on a buried insulator includes the steps of: forming one or more fins in a SOI layer of an SOI wafer, wherein the SOI wafer has a substrate separated from the SOI layer by the buried insulator; forming a SiGe layer on the fins; annealing the SiGe layer under conditions sufficient to drive-in Ge from the SiGe layer into the fins and form a SiGe shell completely surrounding each of the fins; and removing the fins selective to the SiGe shell, wherein the SiGe shell which remains forms the nanotubes on the buried insulator. A nanotube structure and method of forming a nanotube device are also provided.

A cold cathode field emission electron source capable of emission at levels comparable to thermal sources is described. Emission in excess of 6 A/cm.sup.2 at 7.5 V/m is demonstrated in a macroscopic emitter array. The emitter has a monolithic and rigid porous semiconductor nanostructure with uniformly distributed emission sites, and is fabricated through a room temperature process which allows for control of emission properties. These electron sources can be used in a wide range of applications, including microwave electronics and x-ray imaging for medicine and security.