摘要:

We demonstrate nondestructive optoacoustic generation and detection of acoustic pulses of 1‐ns duration in condensed matter. Such optoacoustic pulses are at least one order of magnitude shorter than those previously reported. These narrow acoustic pulses find new application for thin‐film pulse measurements, which are not possible with conventional transducer techniques. Round trip echo times are measured to 1% accuracy for stainless steel films of 12‐&mgr;m thickness. This provides a new high accuracy thickness measurement in a pulsed mode. Ultrasonic attenuation for the narrow acoustic pulses is very large and is also measured.

ISSN:0003-6951    

DOI:10.1063/1.95296

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

In order to accelerate intense ion beams, we heat the anode of a pinch‐reflex diode with a CO2laser. At laser power densities of 1010W/cm2over a 2‐mm focal spot, we demonstrate that gap closure is avoided and that ion efficiency is increased by at least a factor 3 over diode operation without the laser.

ISSN:0003-6951    

DOI:10.1063/1.95297

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The concept of a thermal wave phase shifter for photothermal studies of weakly absorbing samples is described. Both sample and reference are excited simultaneously, but their respective photothermal signals reach the detector subsequently. Depending on the phase shift photothermal absorption or transmission spectra can be recorded readily with the same sample. The versatility of this technique is demonstrated by spectroscopic studies of neodymium oxide doped poly(methyl methacrylate) film. At energy fluences in the order of 10 mJ/cm2sensitivities of 1014molecules/cm2are achieved with conventional, unstabilized light sources. The quantum yield for nonradiative decay is determined to be 90% throughout the entire visible spectrum.

ISSN:0003-6951    

DOI:10.1063/1.95298

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The surfaces of epitaxial CaF2layers grown on (100) and (111) Si by molecular beam epitaxy have been studied using scanning electron microscopy. The (111) surface exhibits small triangular hillocks, while the (100) surface exhibits a columnar structure. This latter structure can be accounted for by the prohibitively large free energy of the (100) surface. A dipole moment exists perpendicular to this surface which causes the electrostatic energy to diverge. This phenomenon explains the inferior (100) growth as compared to (111) and has important implications for possible applications of group II‐A fluoride/semiconductor epitaxial structures.

ISSN:0003-6951    

DOI:10.1063/1.95299

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

By utilizing the quenching effect of the deep EL2 defect in semi‐insulating GaAs in different optical measurements, it has been possible to show that the 0.635‐eV photoluminescence band is not related to EL2. The previously observed ‘‘EL2 behavior’’ of this luminescence band is shown to be only an indirect effect where the EL2 level acts as an intermediate step in the excitation process. Evidence is also given that the sharp below‐band‐gap photoluminescence excitation peak (1.50 eV) which has been regarded as an EL2 feature is actually not related to EL2. A new photoluminescence excitation band with a threshold at ∼1.1 eV is also observed.

ISSN:0003-6951    

DOI:10.1063/1.95300

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Epitaxial CrSi2has been successfully grown on (111)Si. Substrate heating at 300 or 400 °C during Cr deposition was found to be more effective than two‐step annealing in promoting the growth and improving the quality of epitaxial CrSi2. The best epitaxy was obtained when sample substrates were heated at 300 or 400 °C followed by 1000–1100 °C annealing for 1 h. The orientation relationships were found to be (0001) CrSi2//(111)Si, (224¯0)CrSi2//(224¯)Si, (202¯0)CrSi2//(202¯)Si, and [12¯13]CrSi2//[101]Si. Dislocations present in the regular interfacial dislocation network were found to be of edge or 60° type with (1)/(6) <112> Burgers vectors. The average dislocation spacings were measured to be 270–320 A˚. The discrepancy of the measured and theoretically expected value of dislocation spacing was attributed to the difference in the thermal expansion coefficients of CrSi2and Si.

ISSN:0003-6951    

DOI:10.1063/1.95301

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Titanium silicide films were grown under roughing vacuum on single crystal silicon wafers using high power quartz‐halogen tungsten lamps to provide the thermal driving force. After processing for various time intervals, ranging from 5 to 25 s, the samples were characterized by measuring their sheet resistance. Major phases were detected with x‐ray diffractometry. Elemental composition and film thickness were measured using Rutherford backscattering and Auger electron spectroscopy. These techniques consistently indicated that silicide formation was completed after 10–12 seconds processing time. The quality of these films and its potential usefulness are evidenced by their low resistivity of 21 &mgr;&OHgr; cm.

ISSN:0003-6951    

DOI:10.1063/1.95302

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The microstructural and tribological effects of ion implanting C into Ti‐implanted, Fe‐based alloys are examined and compared to the influence of C introduced by vacuum carburization during Ti implantation alone. The amorphous surface alloy formed by Ti implantation of pure Fe increases in thickness when additional C is implanted at depths containing Ti but beyond the range of carburization. Pin‐on‐disc tests of 15‐5 PH stainless steel show that implantation of both Ti and C reduces friction significantly under conditions where no reduction is obtained by Ti implantation alone; wear depths are also less when C is implanted. All available experimental results can be accounted for by consideration of the thickness and Ti concentration of the amorphous Fe‐Ti‐C alloy. The thicker amorphous layer on samples implanted with additional C extends tribological benefits to more severe wear regimes.

ISSN:0003-6951    

DOI:10.1063/1.95303

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A simple capless annealing process for post‐implantation annealing of InP material is described. The technique incorporates a simple boat design and uses InP+Sn as the source of phosphorus overpressure. Using this process, Si‐implanted (4×1012cm−2dose) InP layers show mobilities at room temperature and 77 K in the range of 3200 and ∼10 000 cm2/Vs, respectively. Dopant depth profiles with peak donor densities of 2×1017cm−3and minimal redistribution of impurities were obtained. Depletion‐mode InP metal‐insulator‐semiconductor field‐effect transistors fabricated with 4‐&mgr;m gate lengths using ion‐implanted channel and source‐drain regions, show channel mobilities of 2500 cm2/Vs.

ISSN:0003-6951    

DOI:10.1063/1.95304

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Epitaxial layers of GaAs and AlxGa1−xAs (0.2≤x≤0.5) have been grown directly on single‐crystal Si (100) substrates, without an intermediate Ge layer, by molecular beam epitaxy (MBE). To improve nucleation, after being chemically cleaned the Si substrates were preheated in the MBE system to reduce surface contamination and achieve ordered surface reconstruction prior to growth. Reflection electron diffraction, Rutherford backscattering channeling, and photoluminescence measurement were used to characterize the epitaxial layers. The AlGaAs layers were found to be superior to the GaAs layers.

ISSN:0003-6951    

DOI:10.1063/1.95305

出版商:AIP    

年代:1984

数据来源: AIP