摘要:

The birefringence (&Dgr;n) of ZnGeP2has been measured directly from polarized light interference spectra obtained in transmittance over the 0.66–12 &mgr;m wavelength range from samples of six different thicknesses. The &Dgr;nvalues were determined from the positions of fringe maxima (&Dgr;n=k&lgr;/t) and then compared to previously published data which were obtained by a different technique. It was found that the interference fringe method results in values of &Dgr;naccurate to ±0.00005. The data are shown to exhibit much less scatter as a function of wavelength than previous results and can lead to more accurate calculations of phase‐matching angles for second‐harmonic generation applications. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359175

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An emission band that appears in the high energy side of the photoluminescence spectra of a modulation doped multiple quantum well structure was investigated by means of magneto‐photoluminescence and photoluminescence excitation spectroscopy. We show that this emission band is related to the Al0.36Ga0.64As layers of the structure. We analyze the data within the framework of the configuration coordinate model and attribute this photoluminescence band to the recombination of electrons trapped to a new deep center in the alloy and the photogenerated holes. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359176

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Picosecond time‐resolved coherent Raman spectroscopy (ps CARS) is used to study photothermal ablation, induced by 150 ps duration near‐infrared optical pulses, of poly‐(methyl methacrylate) (PMMA) thin films doped with a small amount of near‐infrared absorbing dye. The pressure and temperature shifts of a PMMA transition at ≊808 cm−1were calibrated in staticPandTexperiments. Dynamic frequency shifting of the PMMA transition is used to determine temperature and pressure in the ablating thin film, and to investigate the dynamics of fast thin‐film volume expansion. When the ablation pulse intensity is varied, ps CARS measurements ofTandPare shown to be consistent with the results of conventional measurements below threshold, but near and above threshold picosecond time scale data show noticeable differences. Picosecond time scale ablation involves solid‐state shock waves, which are not produced by longer duration ablation pulses. A pressure jump, often several kbar, is produced when the film is heated faster than a characteristic hydrodynamic volume relaxation time &tgr;h. Pressure release occurs by shock rarefaction wave propagation. When the rarefaction wave reaches the substrate, a tensile force is exerted on the thin film, causing it to break away from the substrate. The pressure in the thin film at ablation threshold,Pabl≊0.5 GPa, is found to be generated by roughly equal contributions from shock and thermochemical polymer decomposition processes. Therefore the picosecond time scale ablation process is termed shock‐assisted photothermal ablation. The value ofPablis interpreted to be the nanosecond time scale dynamic tensile strength of the thin film under conditions of ultrafast heating. It is found to be about one order of magnitude greater than the static strength of PMMA. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359177

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Effects of cumulative ablation on the ejection of particulates and molecular species in pulsed‐laser deposition are studied by Mie scattering and laser‐induced fluorescence spectroscopy, respectively. When a fresh target is ablated, a large amount of particulates are ejected during several initial shots and rapidly decreased within the first ten shots of ablation. This is due to the ejection of powder residues which are struck on the target surface during the polishing process. After this period, ejection of particulates increased gradually and almost saturated after 200 shots. The saturation characteristic is empirically formulated as a function of the number of cumulative ablations. On the other hand, ejection of molecular species rapidly decreases during the initial 500 ablations and afterwards decreases more slowly with further ablation. The effects of cumulative ablation on the particle ejection are discussed in conjunction with the structural modification of the ablated surface observed by the scanning electron microscope. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359178

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Single‐crystal rods and fibers of Bi12SiO20were grown directly from a rod of mixed Bi2O3and SiO2powders in a floating zone device heated by an infrared source with a special light shutter. The source rod was pressed from the mixed powders at room temperature; to avoid possible contamination, hot pressing and melting with die or crucible were not employed. The following are the main results: (a) The length of the stable molten zone is an increasing function of the diameter of the grown crystal rod. (b) Non‐transparency is a major defect in a small diameter crystal rod or fiber. The growth velocity should be less than the critical transparent velocity (the critical value below which the grown crystal is transparent throughout). For growth of a large diameter crystal rod (diameter ≥3 mm), the growth velocity should be less than both the critical transparent velocity and the critical cracking velocity (the critical value below which the grown crystal is free of cracks). In general, both the critical transparent and critical cracking velocities are decreasing functions of the diameter of the grown crystal rod. (c) Use of a single crystal with high thermal conductivity (e.g., Al2O3) as a seed can dramatically increase both the critical transparent and critical cracking velocities for growth of a single crystal of diameter larger than 3 mm. (d) The pulling down floating zone method is more suitable than the pedestal growth method because of the low surface tension and high density of the Bi12SiO20melt. (e) The grown Bi12SiO20crystal is a pure body‐centered cubic &ggr; phase and has a good infrared transmission spectrum. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359179

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Effect of high temperature annealing in the temperature range of 600–900 °C on the electrical properties and microstructure of tantalum pentoxide (Ta2O5) thin film deposited by plasma‐enhanced chemical vapor deposition (PECVD) was studied. Leakage characteristics of the Ta2O5thin film annealed at 600 °C were found to be the best in this study. However, it was observed that the leakage current in the polycrystalline Ta2O5thin film decreased with increasing the annealing temperature above 800 °C after a peak for 700 °C annealing. The dielectric constant of the annealed Ta2O5thin film was 26 after annealing at 600 °C, and decreased with the same tendency as the leakage current characteristics. Transmission electron microscopy (TEM) and x‐ray diffraction (XRD) analysis indicated that the microstructure of the Ta2O5thin film annealed above 800 °C was of &dgr;‐Ta2O5with hexagonal crystal structure. Furthermore, TEM and AES observations revealed that Ta–O–Si transition layers were formed between the annealed Ta2O5thin film and Si substrate. The electrical properties of the Ta2O5films are discussed in terms of interface modification and film densification due to rapid thermal annealing treatment. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359180

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Micromorphology of ZnO varistors made with seed grains shows that there are two kinds of combinations of ZnO grains. Two different micromodels of ZnO varistors are put forward according to their micromorphology. The relation between ZnO grains’ mean diameter and the amount of seed grains has been deduced from the micromodels. The relation between the electric fieldE1mA/cm2, nonlinear coefficient, and breakdown energy density of ZnO varistors and the amount of ZnO seed grains has been explained by means of micromodels. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359181

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dynamics of the interaction of electron‐cyclotron‐resonance (ECR) plasmas with the surface of GaAs substrates are studied by real‐time optical reflection spectroscopy. Analysis with a three‐phase ambient/overlayer/substrate model yields information on the time‐dependent composition of the near‐surface region, such as the thickness, degree of amorphization, and oxide and void fraction in the overlayer. Using this technique, it is observed that the thickness of the damaged layer formed by the impact of energetic ions increases linearly with the ion energy during argon ECR sputter etching. Furthermore, the dynamics of a cleaning process with a hydrogen ECR plasma have been studied. At temperatures between 300 and 500 °C this cleaning can be characterized by a two‐step process. During the first few seconds of exposure, the oxide layer is removed; in the second step, the GaAs is etched gently, which leads to a surface region with little damage to the crystal. At lower temperatures, cleaning is not successful and a thick damaged overlayer is formed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359182

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Lithium niobate [LiNbO3(LN)] thin films with good surface morphology and crystallinity have been epitaxially grown on lithium tantalate [LiTaO3(LT)] substrates by chemical‐vapor deposition using lithium dipivaloylmethane [Li(C11H19O2)] and niobium pentaethoxide [Nb(OC2H5)5] without postannealing. The Li/Nb ratio of LN thin films was easily controlled by adjusting the Nb source temperature, and it is possible to prepare LN thin films with stoichiometric composition (Li/Nb=1). The crystallinity of LN thin films greatly depends on substrate temperature and surface orientation of the LT substrate. It becomes better with increasing substrate temperature and is equivalent to a single crystal at 700 °C. It also becomes better in the order of (012), (110), and (001) planes of the LT substrate. The properties of surface acoustic wave propagation can be improved by preparing the LN thin film on the LT substrate. The electromechanical coupling factork2of LN/(012)LT is 0.52%, and is greater than that of the (012)LT substrate alone, 0.081%. The sound velocity of LN/(012)LT calculated from the central resonant frequency is 3200 m/s, and this value is greater than that of the (012)LT substrate by itself, 3140 m/s. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359183

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Effects of dopant additions on interface stability in zone‐melting recrystallization (ZMR) of silicon thin films have been investigated through computer simulation and experiments. The computer simulation has shown that a critical scanning speedV* exists such that the critical wavelength &lgr;* of the solidifying interface increases with scanning speed belowV* due to radiative supercooling, while &lgr;* decreases with scanning speed aboveV* due to constitutional supercooling. Experiments determined thatV* decreased with additions of B and P, which was expected from the results of the computer simulation. The primary defect spacings after ZMR was found to increase with the addition of dopants prior to ZMR. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359184

出版商:AIP    

年代:1995

数据来源: AIP