Yasser Khan

Abstract: Efficacy of using vertically grown ZnO nanorod array in enhancing electromagnetic field intensity and serving as the top contact layer (transparent electrodes) for solar cells was investigated.

Abstract:

Abstract: While researchers strives to increase internal quantum efficiency of solar cells, there exists a huge scope to increase overall quantum yield of these energy harvesting devices by researching into light trapping. Transparent conducting oxides have been studied extensively in display and photovoltaic devices. But, incorporating light trapping capability and transparent electrode characteristics in the same layer hasnʼt been explored extensively, which may increase overall quantum efficiency significantly. In this work, we investigate the efficacy of using vertically grown ZnO nanorod arrays for enhancing electromagnetic field intensity, and at the same time serve as the top contact layer as transparent electrodes. FDTD simulation, optical measurements, sheet resistance measurements, and SEM micrographs shows boost in adequate characteristics that can enhance overall quantum yield of solar cells.

Abstract: In scanning tunneling microscopy, sharper tips offer higher performance. Consistence in tip shape and reproducibly are extremely important for both commercial applications and research. In this work, electronic current shutoff time for conventional DC �drop-off� technique is reduced to ~36ns; static DC etching results in undesirable variability tip shapes, so �dynamic etching,� where electrolyte level moves up and down during etching, was introduced, resulting smooth controllable cone angles. It has been observed that natural potential difference between counter electrode and the W tip causes tip blunting even after fast current shut off, reverse biasing after �drop-off,� takes care of the mentioned issue. In this paper, we present a facile and robust approach that incorporates synergy of �drop-off� method, dynamic electrochemical etching, and reverse biasing after �drop-off� yielding highly reproducible tips with controllable cone angles. Reproducibility was confirmed by scanning electron microscopy, and 5-40 nm radius tungsten probe tips were produced with more than 80% success rate.

Abstract: This paper will explore the possibilities of implementing a wireless embedded control system for atomically precise manufacturing. The manufacturing process, similar to Scanning Tunneling Microscopy, takes place within an Ultra High Vacuum (UHV) chamber at a pressure of 10-10 torr. In order to create vibration isolation, and to keep internal noise to a minimum, a wireless link inside the UHV chamber becomes essential. We present a MATLAB simulation of the problem, and then demonstrate a hardware scheme between a Gumstix computer and a Linux based laptop for controlling nano-manipulators with three degrees of freedom.

Abstract: In scanning tunneling microscopy, sharper tips offer higher performance. Consistence in tip shape and reproducibly are extremely important for both commercial applications and research. In this work, electronic current shutoff time for conventional DC �drop-off� technique is reduced to ~36ns. Static DC etching results in undesirable variability tip shapes, so �dynamic etching,� where electrolyte level moves up and down during etching, was introduced, resulting smooth controllable cone angles. It has been observed that natural potential difference between counter electrode and the W tip causes tip blunting even after fast current shut off, reverse biasing after �drop-off,� takes care of the mentioned issue. In this work, we present a facile and robust approach that incorporates synergy of �drop-off� method, dynamic electrochemical etching, and reverse biasing after �drop-off� yielding highly reproducible tips with controllable cone angles. Reproducibility was confirmed by scanning electron microscopy, and 5-40 nm radius tungsten probe tips were produced with more than 80% success rate.