Local electrode atom probe analysis of silicon nanowires grown with an aluminum catalyst.

Local electrode atom probe (LEAP) tomography of Al-catalyzed silicon nanowires synthesized by the vapor­liquid­solid method is presented. The concentration of Al within the Al-catalyzed nanowire was found to be 2 × 10(20) cm(-3), which is higher than the expected solubility limit for Al in Si at the nanowire growth temperature of 550°C. Reconstructions of the Al contained within the nanowire indicate a denuded region adjacent to the Al catalyst/Si nanowire interface, while Al clusters are distributed throughout the rest of the silicon nanowire.

Fabrication and electrical properties of si nanowires synthesized by Al catalyzed vapor-liquid-solid growth.

The synthesis of epitaxially oriented Si nanowires at high growth rates (>1 microm/min) was demonstrated on (111) Si substrates using Al as the catalyst. The use of high H(2) and SiH(4) partial pressures was found to be effective at reducing problems associated with Al oxidation and nanowire nucleation, enabling growth of high aspect ratio structures at temperatures ranging from 500 to 600 degrees C with minimal tapering of the diameter. Because of the high growth rate observed, the Al catalyst is believed to be in the liquid state during the growth. Four-point resistance measurements and back-gated current-voltage measurements indicate that the wires are p-type with an average resistivity of 0.01 +/- 0.004 Omega-cm. These results suggest that Al is incorporated into the Si nanowires under these conditions at concentrations higher than the solubility limit (5-6 x 10(18) cm(-3)) for Al in Si at 550 degrees C. This work demonstrates that Al can serve as both an effective catalyst and p-type dopant for the growth of Si nanowires.

Mimicking Neurotransmitter Release in Chemical Synapses via Hysteresis Engineering in MoS2 Transistors.

Neurotransmitter release in chemical synapses is fundamental to diverse brain functions such as motor action, learning, cognition, emotion, perception, and consciousness. Moreover, improper functioning or abnormal release of neurotransmitter is associated with numerous neurological disorders such as epilepsy, sclerosis, schizophrenia, Alzheimer's disease, and Parkinson's disease. We have utilized hysteresis engineering in a back-gated MoS2 field effect transistor (FET) in order to mimic such neurotransmitter release dynamics in chemical synapses. All three essential features, i.e., quantal, stochastic, and excitatory or inhibitory nature of neurotransmitter release, were accurately captured in our experimental demonstration. We also mimicked an important phenomenon called long-term potentiation (LTP), which forms the basis of human memory. Finally, we demonstrated how to engineer the LTP time by operating the MoS2 FET in different regimes. Our findings could provide a critical component toward the design of next-generation smart and intelligent human-like machines and human-machine interfaces.

Selective plating for junction delineation in silicon nanowires.

The in situ growth of p-n junctions in silicon nanowires enables the fabrication of a variety of nanoscale electronic devices. We have developed a method for selective coating of Au onto n-type segments of silicon nanowire p-n junctions. Selective plating allows for quick verification of the position of p-n junctions along the nanowire using electron microscopy and allows for measurement of segment length.