We present the first results from a high sampling rate, multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with

SynopsisThe results of measurements of the optical absorption spectra, IR absorption spectra, thermogravimetric analysis, and elementary analysis of pyrolyzed polyacrilonitrile are presented as a function of the pyrolysis temperature T, and of the duration of pyrolysis. At T, -2WC, an intermediate phase was discovered, containing conjugated CN sequences and a completely unreacted carbon backbone. The optical absorption data imply that the resulting polymer is a semiconductor with a delocalized Pelectron system and an energy gap E, 2 2.5 eV. For T, > 260°C. the weight loss rapidly increases, and the absorption edge gradually broadens and shifts to lower energies. The resulting polymer (after higher-temperature pyrolysis) contains CN and C = M conjugation sequences, but appears to be a complex structure consisting of a mixture of different chemical species.

A significantly large thermoelectric “figure of merit” in a bipolar semiconductor is achieved by converting it, by doping, into an essentially monopolar semiconductor. We show here, that for a bipolar semiconductor film, having a thickness smaller than the screening length, there is an alternative to doping to obtain a practically monopolar semiconductor. The electric-field effect (EFE) or the ferroelectric-field effect can be used to quench the concentration of one type of charge carriers. We show that this method is particularly suited for narrow-gap semiconductors and for semimetals, having sufficiently high dielectric permittivity. We also show that this “EFE doping” is free from the drawbacks of conventional doping. Our analysis demonstrates that increased values of the figure of merit are feasible. We present here the theory and the figure-of-merit calculation for typical cases of the bipolar semiconductor thermoelectric film under EFE doping. Numerical results for a film of the PbTe type are presented.

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We describe the preparation of high-temperature PbTe diodes. Satisfactory rectification was observed up to 180-200 K. Two types of diodes, based on a p-PbTe single crystal, were prepared: (1) by In ion-implantation, and (2) by thermodiffusion of In. Measurements were carried-out from ~ 10 K to ~ 200 K. The ion-implanted diodes exhibit a satisfactorily low saturation current up to a reverse bias of ~ 400 mV, and the thermally diffused junctions up to ~ 1 V. The junctions are linearly graded. The current-voltage characteristics have been fitted using the Shockley model. Photosensor parameters: zero-bias-resistance x area product, the R0C time constant and the detectivity D* are presented