摘要:

Results are presented for the radiation‐induced transient darkening of thin organic polymer films normally used as Cerenkov light emissions sources. The radiation source is a 27‐MeV, 10‐&mgr;C, 200‐ns electron beam generated by the PHERMEX accelerator. The typical dose for a single pulse is 5 Mrad. At this dose, the broadband time‐resolved percent transmission above 520 nm was measured for four common polymers: polyimide (Kapton‐H), polyethylene terephthalate (Mylar), cellulose acetate, and high‐density polyethylene. Kapton was found to darken the most and polyethylene darkened the least. The recovery time to normal transmission for Kapton was found to be greater than 10–20 &mgr;s. The radiation‐induced attenuation coefficient is shown to depend on electronic band energy separation. The results show that Kapton is not the material of choice for a Cerenkov light source.

ISSN:0021-8979    

DOI:10.1063/1.337594

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Gallium arsenide single‐crystal layers, doped with119Sn‐enriched tin, have been prepared by liquid‐phase epitaxy and characterized by119Sn Mo¨ssbauer spectroscopy (MS) and Hall measurements. Two Sn sites are observed by MS, and the population of one of these (site A) matches the carrier concentration in as‐grown material, therefore allowing the MS parameters of this site to be positively identified as those of the SnGadonor in GaAs, and thereby showing no evidence for compensation. The population of the second type of Sn (site B) increases with the total Sn concentration, and this site is clearly electrically inactive. The site B MS parameters are similar to those of Sn3As2, SnAs, and &bgr;‐Sn, thereby demonstrating that microprecipitates of these phases may often exist in heavily Sn‐doped liquid‐phase‐epitaxial GaAs. Site B could also be due to clusters of Sn and/or Sn‐As that are precursors to the formation of distinct precipitates of Sn3As, SnAs, or &bgr;‐Sn. Annealing experiments yield a Sn‐related acceptor that is very likely of the form SnGaVGa. In addition, precise MS parameters are reported for the intermetallic phases SnAs and Sn3As2.

ISSN:0021-8979    

DOI:10.1063/1.337595

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The internal friction (IF) background of gold is studied in the kHz frequency range. Systematic measurements of IF as a function of frequency, strain amplitude, and temperature show that the IF is due to the superposition of two contributions: the thermoelastic effect and a dislocation effect. The thermoelastic effect is responsible for the IF background observed when the strain amplitude tends to zero. It is the only contribution to the IF background which is strain amplitude independent. On the contrary, the dislocation effect contributes only to the strain amplitude‐dependent IF background. This effect is proportional to the strain amplitude. In particular, it is zero when the strain amplitude tends to zero. Furthermore, the dislocation contribution is frequency independent. The experimental results show that the dislocation effect cannot be explained by a viscous damping of dislocation motion, but must be related to an hysteretic and athermal motion of dislocations.

ISSN:0021-8979    

DOI:10.1063/1.337596

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The pressure dependence of the refractive index of argon has been measured in a diamond anvil cell up to 15 GPa. We describe in detail the novel technique used, which offers considerably higher accuracy than the others previously utilized. Our results on Ar agree with previous results at lower pressures and are compared with theoretical calculations at high pressure.

ISSN:0021-8979    

DOI:10.1063/1.337597

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An effective technique for maximizing the explosive charge that a given container can safely handle is to fill the space between the charge and the container walls with a porous medium or a powder. Using the wrong powder, however, can be worse than using no powder at all. Moreover, a powder‐filled container that performs very well with a small charge may also be worse than a powderless system when the charge is increased. An analysis of this problem is developed with the aim of identifying appropriate buffer material properties and the conditions under which breakdown occurs. The results are compared with various experiments performed with graphite powder, coke chunks, granular salt, snow, and vermiculite.

ISSN:0021-8979    

DOI:10.1063/1.337598

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

At a sufficiently large liquid undercooling, the solidification of fine Bi droplet samples at ambient pressure yields a metastable phase instead of the stable structure. The metastable Bi phase is observed to melt at 174 °C at ambient pressure. Thermal analysis measurements on droplet samples subjected to hydrostatic pressures ranging up to 400 MPa demonstrate that the melting temperature of the metastable Bi phase increases by 20.8 K/GPa with pressure, while that of the stable Bi phase decreases by 38.8 K/GPa. The trend of the measured melting temperature of the metastable Bi phase joins smoothly to the melting curve of the Bi(II) high‐pressure phase. Differential scanning‐calorimetry measurements on a liquid Bi droplet sample at undercoolings up to 220 °C support the identification of the metastable Bi phase as the Bi(II) high‐pressure phase with a heat of fusion 5.98 kJ/g‐at. A shift of the nucleation temperature under pressure, which follows the trend of the melting temperature, characterizes the nucleation onset of both Bi(I) and Bi(II) phases and provides information on the kinetic competition controlling phase selection.

ISSN:0021-8979    

DOI:10.1063/1.337599

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Secondary‐ion‐mass spectrometry, Hall‐effect measurements, and dcI‐Vcharacteristics of 1‐&mgr;m Ga0.47In0.53As‐Al0.48In0.52As high‐electron mobility transistor structures indicate that significant diffusion of Si can occur in these layers. The source of the Si is both the intentional Si used for modulation doping of the devices, and Si which is an unintentional impurity in the Fe‐doped InP substrates on which the layer is grown. Preannealing and polishing the substrates can lessen the effect.

ISSN:0021-8979    

DOI:10.1063/1.337600

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Trapping of ion‐implanted deuterium (D) by irradiation defects and He bubbles in Mo was investigated through nuclear‐reaction profiling of the D during linear ramping of temperature. Resulting data were analyzed using transport theory to obtain trap strengths. Nanometer‐size He bubbles were found to trap the D with a binding enthalpy of 1.15±0.15 eV relative to the solution site, consistent with two independent predictions based, respectively, on effective‐medium theory and thermodynamic analysis. Implantation damage trapped the D with three different binding enthalpies, 1.15, 1.03, and 0.80 eV, attributed, respectively, to vacancy clusters, monovacancies with low D occupancy, and monovacancies with high D occupancy. The two latter values are in good agreement with effective‐medium theory.

ISSN:0021-8979    

DOI:10.1063/1.337601

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The crystallographic quality and the surface morphology of ZnS films on (100) Si substrates by molecular‐beam epitaxy are profoundly dependent on the substrate temperatureTs. When theTswas below 300 °C, single crystalline films with twins grew along ⟨100⟩ directions in the initial stage of growth. However, when the film thickness was increased, the growth orientation changed from ⟨100⟩ to two ⟨511⟩ directions of the Si substrate. Namely, the relation of growth orientations between overgrowth and substrate is ZnS(111)∥Si(511). When theTswas set between 340 and 370 °C, the grown films were single crystal with twins appearing initially and grew with a ⟨100⟩ orientation, but decreased with increasing film thickness. Especially in the case ofTs=340 °C, the ZnS film became best crystallized and exhibited the twin‐free streaky pattern in the reflection high‐energy electron diffraction pattern with a smooth surface morphology.

ISSN:0021-8979    

DOI:10.1063/1.337602

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The dielectric functions of InP, In0.53Ga0.47As, and In0.75Ga0.25As0.5P0.5epitaxial layers have been measured using a polarization‐modulation spectroscopic ellipsometer in the 1.5 to 5.3 eV region. The oxide removal procedure has been carefully checked by comparing spectroscopic ellipsometry and x‐ray photoelectron spectroscopy measurements. These reference data have been used to investigate the structural nature of metalorganic chemical‐vapor deposition grown In0.53Ga0.47As/InP and In0.75Ga0.25As0.5P0.5/InP heterojunctions, currently used for photodiodes and laser diodes. The sharpness of the interfaces has been systematically compared for the two types of heterojunctions: In1‐xGaxAsy/InP and InP/In1‐xGaxAsyP1‐y. The sharpest interface is obtained for InP growth on In0.75Ga0.25As0.5P0.5where the interface region is estimated to be (10±10) A˚ thick. The importance of performinginsituSE measurements is emphasized.

ISSN:0021-8979    

DOI:10.1063/1.337603

出版商:AIP    

年代:1986

数据来源: AIP