|A light-conducting silica nanowire wraps a beam of light around a strand of human hair. The nanowires are flexible and can be as slender as 50 nanometers in width, about one-thousandth the width of a hair.|
Credit: Limin Tong/Harvard University
Inorganic materials cover the entire span of the periodic table. Examples range from elemental semiconductors (silicon, germanium), metals (copper, aluminum), to compounds such as gallium arsenide, and all kinds of oxides and nitrides. In the last three decades, these inorganic materials have been successfully grown in the form of thin films with a film thickness as small as 1 nm and as high as several microns.
Thin films are ubiquitous in products all around us, including computers, CDs, DVDs, cell phones, iPODs, lasers (used in supermarket scanners as well as eye surgery), solar panels, and flat panel TVs. Recently there is interest in growing these same materials in the form of one dimensional nanowires rather than as two dimensional thin films.
|A schematic illustration of a "bottle-brush" structure shows nanowires arranged around a fiber. Microfibers coated with gold (yellow) scrub uncoated microfibers to produce electricity via a coupled piezoelectric-semiconducting process.|
Credit: Image courtesy of Z.L. Wang and X.D. Wang, Georgia Institute of Technology
Inorganic nanowires may have diameters of 1-50 nm and any desirable length, perhaps up to a micrometer. They offer interesting electronic, optical and other properties, and may be used in the future to link tiny components into small scale circuits. The properties of nanowires are projected to allow improved performance in existing products as well as development of new products.
Nanowires of silicon and germanium are useful in making future generation computer chips and memory devices. A variety of oxides such as zinc oxide, tin oxide, and indium tin oxide are now grown in the form of nanowires. Zinc oxide is being considered for ultraviolet (UV) lasers and light emitting diodes (LEDs). A variety of nitrides such as gallium nitride and aluminum nitride find applications in solid state lighting that may replace the inefficient filament light bulbs we use today.