6 research outputs found
Shuttle Mission STS-50: Orbital Processing of High-Quality CdTe Compound Semiconductors Experiment: Final Flight Sample Characterization Report
The Orbital Processing of High-Quality Doped and Alloyed CdTe Compound Semiconductors program was initiated to investigate, quantitatively, the influences of gravitationally dependent phenomena on the growth and quality of bulk compound semiconductors. The objective was to improve crystal quality (both structural and compositional) and to better understand and control the variables within the crystal growth production process. The empirical effort entailed the development of a terrestrial (one-g) experiment baseline for quantitative comparison with microgravity (mu-g) results. This effort was supported by the development of high-fidelity process models of heat transfer, fluid flow and solute redistribution, and thermo-mechanical stress occurring in the furnace, safety cartridge, ampoule, and crystal throughout the melting, seeding, crystal growth, and post-solidification processing. In addition, the sensitivity of the orbital experiments was analyzed with respect to the residual microgravity (mu-g) environment, both steady state and g-jitter. CdZnTe crystals were grown in one-g and in mu-g. Crystals processed terrestrially were grown at the NASA Ground Control Experiments Laboratory (GCEL) and at Grumman Aerospace Corporation (now Northrop Grumman Corporation). Two mu-g crystals were grown in the Crystal Growth Furnace (CGF) during the First United States Microgravity Laboratory Mission (USML-1), STS-50, June 24 - July 9, 1992
Emulating Bilingual Synaptic Response Using a Junction-Based Artificial Synaptic Device
Excitatory
and inhibitory postsynaptic potentials are the two fundamental
categories of synaptic responses underlying the diverse functionalities
of the mammalian nervous system. Recent advances in neuroscience have
revealed the co-release of both glutamate and GABA neurotransmitters
from a single axon terminal in neurons at the ventral tegmental area
that can result in the reconfiguration of the postsynaptic potentials
between excitatory and inhibitory effects. The ability to mimic such
features of the biological synapses in semiconductor devices, which
is lacking in the conventional field effect transistor-type and memristor-type
artificial synaptic devices, can enhance the functionalities and versatility
of neuromorphic electronic systems in performing tasks such as image
recognition, learning, and cognition. Here, we demonstrate an artificial
synaptic device concept, an ambipolar junction synaptic devices, which
utilizes the tunable electronic properties of the heterojunction between
two layered semiconductor materials black phosphorus and tin selenide
to mimic the different states of the synaptic connection and, hence,
realize the dynamic reconfigurability between excitatory and inhibitory
postsynaptic effects. The resulting device relies only on the electrical
biases at either the presynaptic or the postsynaptic terminal to facilitate
such dynamic reconfigurability. It is distinctively different from
the conventional heterosynaptic device in terms of both its operational
characteristics and biological equivalence. Key properties of the
synapses such as potentiation and depression and spike-timing-dependent
plasticity are mimicked in the device for both the excitatory and
inhibitory response modes. The device offers reconfiguration properties
with the potential to enable useful functionalities in hardware-based
artificial neural network