Emitech (United States)

The effect on the gas sensitivity of point heterocontact between single walled nanotubes (SWNTs) and a gold microwire is demonstrated for the first time. Au-SWNT heterocontact sensors exhibit high sensitivity to NH3 and NO2 vapors with fast response and relaxation and demonstrate that these two gases can be distinguished based on the direction of charge transfer between the analyte and the SWNTs. The mechanism of sensing is associated with formation of a thin conductive channel between Au and SWNT, but the sign of the resistance change is controlled by the SWNT.

Solar cells based on organic and inorganic materials are an emerging technology for a new generation of photovoltaics (PV). Hybrid solar cells, which use both organic and inorganic components, have advantages such as cost-effective processing and the ability to fabricate devices on flexible substrates. The combination of organic materials with semiconductor nanostructures allows enhancement of the conversion efficiency due to the fast electron transport in semiconductors and a high interface area between organic and inorganic components. In our work, anodized porous Si (PSi) was chosen as a host matrix filled with Copper Phthalocyanine (CuPC) molecules. The resulting nanocomposite can yield high performance novel materials for solar cells. The fabrication of PSi was completed using electrochemical etching of Si in diluted hydrofluoric acid (HF). Also, this process, with some modifications, can be applied to produce free-standing PSi films of desired thickness. PSi layer was filled with CuPC dissolved in concentrated sulfuric acid. The top contact was made by sputtering of Au or ITO. A power conversion efficiency (PCE) of 3% (33 mW/cm²) was obtained for 12 um thick n-type pSi layer with pore sizes of approximately 15 nm filled with CuPC. The electrochemical etching of Si under different conditions was carried out to optimize the photovoltaic parameters. A detailed investigation of the solar cell performance depending on porous layer thicknesses and pore sizes is presented. The use of free-standing films of PSi can lead to the fabrication of novel PV solar cells on flexible substrates with high conversion efficiency.

The photoconductive response of single-walled carbon nanotubes (SWNTs) has been studied under CW illumination in the NIR (900-1800 nm) and far-IR (9-10 /spl mu/m) range. SWNTs were coated onto patterned gold electrodes with spacing which was varied from 5 to 300 nm. SWNT samples exhibit absorption NIR bands that are typical for semiconducting nanotubes with a diameter distribution of 0.8-1.1 nm and band at /spl sim/10 /spl mu/m in the far-IR range. A clear correlation between current and IR exposure has been observed. The detection of photoconductivity requires instrumentation with a high dynamic range due to a significant dark current. The photocurrent exhibits a linear response with light intensity and with bias voltage. Possible mechanisms of photoconductivity in SWNT films and applications of this new photosensitive material are discussed.

Phil Missing, Emitech, Ltd