(4bd) Semiconductor Nanostructures: Diffusion, Impurities, and Nanowire Fabric
Developments in materials synthesis over the past decade have enabled the large-scale production of a wide variety of semiconductor nanostructures that have historically been available only in small quantities. These advances have led to the creation of a new class of materials and devices that utilize macroscopic quantities of nanomaterials. For example, solution-liquid-solid (SLS) and supercritical fluid-liquid-solid (SFLS) growth allow Si and Ge nanowires to be produced on the gram-scale. Recently, these processes were used to develop the first Si and Ge nanowire fabrics – free-standing, flexible ceramics (up to 100 cm2 in area) made entirely of single-crystalline semiconductor nanowires. These new semiconductor fabrics are promising for future battery materials, as well as for applications requiring light harvesting and conversion.
In many cases, the physical properties of nanoscale semiconductors are drastically different from their bulk counterparts. Reducing the dimensions of a semiconductor to the nanoscale can lead to dramatic effects in optical, electrical, and mechanical properties. For example, semiconductor nanocrystals exhibit size-tunable absorption and fluorescence, with applications in bioimaging, solar energy, and display technology. Likewise, many semiconductor nanowires are incredibly flexible, exhibiting extremely high bending strengths and very large strength-to-weight ratios, unlike their brittle bulk counterparts. Phase transitions and impurity diffusion can also be quite different in nanoscale semiconductors.
Atomic impurities are particularly important in semiconductor technology. They introduce charge carriers that are used to tune electrical properties in devices such as transistors, light-emitting diodes, and lasers, and they are used to store energy in electrochemical devices like Li-ion batteries. On the nanoscale, even single atomic impurities can drastically change the optical, electrical, and magnetic properties of the material. In situ transmission electron microscopy (TEM) experiments can be used to address the dynamics of impurity diffusion and solid-state reactions in semiconductor nanostructures, but many challenges exist in the controlled incorporation and characterization of impurities in these systems.
Future research plans will be discussed in addition to the above topics.
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