摘要:

Time‐resolved detection of the surface acoustic waves (SAW) generated upon relaxation of energy optically absorbed in surface films has been used to measure surface absorption spectra and laser‐induced desorption cross sections. This new background‐free spectroscopic technique is shown to be highly sensitive to the details of the film/substrate bonding. Minimum detectable molecular surface densities of 2×1011cm−2over an area of 10−3cm2have been demonstrated for rhodamine‐590 dye on a crystal quartz substrate using a pulsed laser source and an edge‐bonded SAW detector.

ISSN:0003-6951    

DOI:10.1063/1.94264

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Enhancement of the photoacoustic signal from condensed materials by several folds is achieved by the introduction of a liquid with high vapor pressure in the photoacoustic cell. The enhancement is especially marked for low absorption coefficients and high chopping frequencies. Typically the enhancement is two to nine times in the presence of diethyl ether at 293 K. A linear relationship is observed between the enhancement and the vapor pressure of the liquid.

ISSN:0003-6951    

DOI:10.1063/1.94265

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The output from a low‐beam‐divergence KrF ultraviolet laser has been used to simultaneously trigger two multimegavolt gas‐filled switches emersed in a water dielectric. Focusing 55 mJ of laser energy into the interelectrode gap of each switch has produced simultaneity jitter of ≤1.7 ns for closure of both 2.40‐MV self‐breakdown voltage (SBV) switches. Both switches have displayed essentially identical switching behavior, with individual switch jitter ≲2.3 ns. The triggering delay to switch closure after laser irradiation of the switch has exhibited linear dependence upon switch voltage in the 60%–90% SBV region.

ISSN:0003-6951    

DOI:10.1063/1.94266

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We have developed a method for measuring the thickness of thin films that is nondestructive, noncontact and that can make measurements with 2‐&mgr;m spatial resolution (i.e., 2‐&mgr;m spot size) on both optically opaque as well as optically transparent films. With this method, which is based on the use of high‐frequency thermal waves, thicknesses of Al and SiO2films on Si substrates have been measured in the 500–25 000‐A˚ range.

ISSN:0003-6951    

DOI:10.1063/1.94267

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Time‐resolved reflectivity and transmission measurements of crystalline silicon films reveal lattice heating through the temperature dependence of the complex index of refraction. The temperature rise, which is much higher than derived by others from Raman scattering experiments, occurs in a surface layer of 100‐nm thickness.

ISSN:0003-6951    

DOI:10.1063/1.94268

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A general formula for calculating the Freedericksz transition of twisted nematic liquid crystal cells has been derived by taking into consideration the following factors: unequal elastic constants and arbitrary dielectric anisotropy for the liquid crystal medium, and a general form of the anisotropic liquid crystal‐to‐substrate interfacial potential with negligible pretilt angle. The numerical computation of the threshold voltage as a function of the anchoring anisotropy has been demonstrated for two nematic mixtures. Increasing the degree of multiplexing of twisted nematic cells seems feasible using certain nematic mixtures with weak anchoring anisotropy.

ISSN:0003-6951    

DOI:10.1063/1.94269

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Surface photovoltage and Auger electron spectroscopy studies of ultrahigh vacuum cleaved (110) and chemically treated (110) InP reveal direct optical transitions to and from surface states in the band gap for a wide variety of surface conditions. These states correlate with reported Fermi level pinning behavior but cannot account for the unique reduction in surface recombination velocity at KAg(CN)−2treated surfaces. This reduction is identified instead with formation of a surface layer which excludes ambient‐induced recombination states.

ISSN:0003-6951    

DOI:10.1063/1.94270

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Raman microprobe measurements of stress have been performed on a laser‐recrystallized, seeded, lateral epitaxial silicon film on an oxidized silicon wafer. The direction‐averaged, planar tensile stress increased from 2×109dyn/cm2in the seed region to 5×109dyn/cm2in the silicon‐on‐insulator region at distances greater than 20 &mgr;m from the seed/silicon‐on‐insulator boundary. Grain‐boundary nucleation observed by optical Nomarski microscopy occurred approximately 11 &mgr;m from the seed edge in this film. Depth variations of the stress were observed by comparing measurements using 457‐nm and 514.5‐nm excitation wavelengths.

ISSN:0003-6951    

DOI:10.1063/1.94271

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The HgTe‐CdTe superlattice is found to exhibit properties superior to those of the (Hg, Cd)Te alloy as an infrared detector material. A calculation shows that the superlattice tunneling length is shorter than that of the alloy with the same band gap. For a given cutoff wavelength tolerance, we find that less fractional precision is needed in the superlattice control parameter (layer thicknesses) than in the alloy control parameter (composition). Also,p‐side diffusion currents are expected to be reduced due to the larger superlattice electron effective mass.

ISSN:0003-6951    

DOI:10.1063/1.94272

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Synchrotron‐radiation photoemission experiments directly demonstrate that the creation of an inversion layer is a common feature of the PbTe‐Al, PbTe‐In, and PbTe‐Ge interface formation processes. This phenomenon is interpreted in terms of the experimentally observed adatom‐Pb exchange reactions.

ISSN:0003-6951    

DOI:10.1063/1.94273

出版商:AIP    

年代:1983

数据来源: AIP