摘要:

Large area field effect structures with thin catalytic metal gates can be used to generate two dimensional images of the response of the metal to gas mixtures. This is done by using a scanning light pulse technique to determine polarization changes occurring in the thin metal film due to chemical reactions on the metal. Such images appear to be a new concept in chemical sensing. The present contribution is a first attempt to predict the shape of these images. We show that the occurrence of maxima in the response at certain points on the surface is most likely due to temperature dependent chemical rate constants and to the consumption of molecules on the catalytic metal surface. Experimental results of the detection of methanol, ethanol, and hydrogen on palladium and platinum, with a temperature gradient along the metals, are used to support the theoretical arguments.

ISSN:0021-8979    

DOI:10.1063/1.355045

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The ArF laser photodissociation dynamics of dimethylzinc at 193 nm have been studied, and their implications for the growth of ZnSe thin films are discussed. A broadband, vacuum ultraviolet argon plasma emission has been used to acquire time‐resolved absorption profiles from ground‐state Zn atoms and methyl radicals. Time‐resolved fluorescence from excited CH radicals has also been studied. The results indicate that the Zn concentration remains constant from 100 ns to 2 ms after the dissociating ArF pulse, indicating that this system is a good source for free Zn atoms. The CH3radicals are formed immediately after the dissociation pulse and recombine within several hundred microseconds to form ethane. There was no indication of monomethylzinc (MMZn) formation, and the detected CH radical is likely to combine with H2to form CH3within several microseconds. This implies that the major sources for carbon contamination in the growth process (CH3, MMZn, CH) are unlikely to reach the growth surface.

ISSN:0021-8979    

DOI:10.1063/1.355046

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Dependence of the electron multiplication factor on the bias voltage was considered for the blocked impurity band (BIB) detector. We found that in high gain BIB detectors multiplication factor self‐stabilization can be achieved. When bias voltageVBincreases, the multiplication factor curve flattens, starting at a certain valueVB. This can be explained by the presence of an electric field and electron current in the neutral region of the BIB detector infrared‐active layer. The influence of this behavior on the performance characteristics of BIB detectors is briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.355047

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In this article, we propose and demonstrate a novel punchthrough heterojunction phototransistor (HPT). The base of the transistor is lightly doped and completely depleted under the operating condition. The collector bias current can be applied without the base terminal. The transistors exhibit optical conversion gain as high as 1240 at an incident optical power as low as 0.5 &mgr;W, and the gain changes less than 15% over a 20 dB range of incident optical power. The transient measurements showed that the transistor has a high response speed than that of conventional two or three terminal HPTs. This represents the best performance of HPTs with similar dimensions. The results of simulation showed that the punchthrough HPTs have much lower noise characteristics than conventional HPTs. The principle reported here can be applied to HPTs made from other material systems, such as AlGaSb/GaSb and InP/InGaAs, for long wavelength optical communications.

ISSN:0021-8979    

DOI:10.1063/1.355048

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The diffuse reflectivity of polyimide during pulsed 193‐nm excimer laser irradiation has been compared to the specular reflectivity of the material over the fluence range 0.6–190 mJ/cm2. Diffuse reflectivity is observed to decrease with increasing fluence by a factor of ∼3 over the intensity range, and remains a roughly constant fraction (0.3–0.4) of total target reflectivity. These results indicate that appreciable scattering of reflected laser radiation out of the specular direction does not occur under ablation conditions, and therefore cannot account for the specularly reflected pulse truncation observed previously.

ISSN:0021-8979    

DOI:10.1063/1.355049

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A model used to approximate the measured response of a Bi‐Sr‐Ca‐Cu‐O detector to both microwave frequency and HeNe laser light over a temperature range from zero up to the critical transition temperature of the superconductorTcis reported. The nonbolometric (microwave) response model is based on microwave enhancement of a thermal fluctuation voltage occurring in the networks of inherent Josephson junctions. Modeling the film as a distribution of granular connections with varying critical currents and temperatures yields results similar to those observed in recent microwave response measurements. These results may be useful when optimizing the nonbolometric response for detector applications.

ISSN:0021-8979    

DOI:10.1063/1.355050

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It is shown that the full isothermal crystallization analysis of Fe80B20amorphous alloy must include not only a crystal nucleation‐and‐growth process but also a grain‐growth process and that these two processes are separated in time during isothermal annealing. The parameters characterizing the grain‐growth process have been found by the fitting calorimetrical signal with the one expected from the normal grain‐growth theory. Transmission electron microscopy and selected area electron diffraction seem to confirm our results since they show that there is a good agreement between the average grain radius of crystallization products seen in the micrograph and the one calculated from the obtained parameters.

ISSN:0021-8979    

DOI:10.1063/1.355051

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Erbium doped GaAs was grown by metal‐organic chemical vapor deposition using a novel liquid precursor: tris(n‐butylcyclopentadienyl)erbium [Er(C4H9C5H4)3]. The morphology was excellent at growth temperatures near 620 °C. Based on a simple model for the excitation dependence of the emission, the nonradiative Auger‐type process was estimated to be nearly five times that of the energy transfer process from bound excitons to the Er3+ions that subsequently resulted in the Er‐related light emission. Temperature induced quenching of the emission was found to be dominated by transitions with an activation energy of 74 meV.

ISSN:0021-8979    

DOI:10.1063/1.355052

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Photoluminescence (PL) of type III (high‐purity wet synthetic) silica excited by a XeCl excimer laser (h&ngr;=4 eV) is reported. Time‐resolved spectra show that a PL band peaked at 1.9 eV can be induced by the XeCl laser irradiation. This band exhibits a fast rise time (<20 ns) but a decay time of several microseconds. The possible mechanisms of photogeneration and photoexcitation of the defects related to this emission are discussed.

ISSN:0021-8979    

DOI:10.1063/1.355053

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The optical model to incorporate the effect of scattering is improved by using the energy dependent optical potential that is determined by experimental data on hot electrons. Using this model, theI−Vcharacteristic of a resonant tunneling diode is calculated, and the calculated result explains experiments well. From this analysis it turns out that the valley current of the resonant tunneling diode is intimately related to the scattering rate of hot electrons in the well. As this model is easy to use and simple to interpret, it is quite suitable for simulation of device characteristics.

ISSN:0021-8979    

DOI:10.1063/1.355054

出版商:AIP    

年代:1993

数据来源: AIP