T. Kirkpatrick

Hot electron effect in nanoscopically thin photovoltaic junctions

The open circuit voltage in ultrathin amorphous silicon solar cells is found to increase with light energy (frequency), due to extraction of hot electrons. The ultrathin nature of these junctions also leads to large internal electric fields, yielding reduced recombination and increased current. A simple phenomenological argument provides a qualitative understanding of these effects and gives guidelines for designing future, high-efficiency, hot electron solar cells.

Ultrasensitive chemical detection using a nanocoax sensor.

We report on the design, fabrication, and performance of a nanoporous, coaxial array capacitive detector for highly sensitive chemical detection. Composed of an array of vertically aligned nanoscale coaxial electrodes constructed with porous dielectric coax annuli around carbon nanotube cores, this sensor is shown to achieve parts per billion level detection sensitivity, at room temperature, to a broad class of organic molecules. The nanoscale, 3D architecture and microscale array pitch of the sensor enable rapid access of target molecules and chip-based multiplexing capabilities, respectively.

Direct-write, focused ion beam-deposited, 7 K superconducting C–Ga–O nanowire

We have fabricated C–Ga–O nanowires by gallium focused ion beam-induced deposition from the carbon-based precursor phenanthrene. The electrical conductivity of the nanowires is weakly temperature dependent below 300 K and indicates a transition to a superconducting state below Tc=7 K. We have measured the temperature dependence of the upper critical field Hc2(T) and estimate a zero temperature critical field of 8.8 T. The Tc of this material is approximately 40% higher than that of any other direct write nanowire, such as those based on C–W–Ga, expanding the possibility of fabricating direct-write nanostructures that superconduct above liquid helium temperatures.