摘要:

Shock waves of the order of hundreds of kilobars are produced in a tin foil 50 &mgr;m thick by a Nd:YAG laser system with a wavelength of 1.06 &mgr;m, pulse width of 7 ns [full width at half-maximum (FWHM)] and irradiance in the range(1.4–2.4)×1013 W/cm2,focused to a spot of 200 &mgr;m. Off-axis holographic measurements of the target, after 0.5 and 1 &mgr;s from the shock arrival, are reported. The hologram is produced by backscattering of a pulse, 6.5 ns (FWHM) of green laser light, from the ejected material from the target. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120411

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A reliable procedure for controlled vertical transfer of single CO molecules between a Cu(111) surface and a scanning tunneling microscope tip and vice versa is demonstrated. It is shown that with a tip having a single CO molecule at its apex, chemical contrast is achieved allowing distinction of adsorbed CO molecules and oxgen atoms, which look very similar to the bare metal tip. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119503

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The plasma-enhanced chemical vapor deposition system was used to grow amorphous hydrogenated carbon films deposited on silicon substrates. Extracts of the films were obtained by treatment with boiling cyclohexane solvent. The absorption spectra of these extracts showed the existence of small quantities of fullerenes. Using the molar extinction coefficient ofC60in cyclohexane, the mass of fullerenes in the films was estimated to be about 0.019 mg.C60induced fluorescence quenching of anthracene was also observed. Additional evidence for the presence of fullerenes was based on their capability to accelerate the photo-oxidation of anthracene through the generation of singlet oxygen with a high quantum yield under ultraviolet irradiation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119504

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We use electron microscopy and x-ray diffraction to study the microstructure of TiN deposited on Al. In contrast to previous work, we show that the TiN has a large (≈1 &mgr;m) grain size arising from its epitaxial orientation on the underlying Al. Within a single grain, the TiN has a heavily voided columnar structure that closely mimics the appearance of fine grains. The within-grain columnar structure arises from the usual shadowing mechanism for sputtered films, and has a weak dependence on the deposition temperature. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119525

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The orientational elastic constants of free-standing films in a tilted smectic phase are directly measured in absolute units with a new experimental method similar to light scattering in the heterodyne regime. Basically, the amplitude of the thermodynamically excited orientational fluctuations, which modulate polarized light, is measured in the direct space by means of a microscope and a video camera connected to a microcomputer. Then, with a Fourier transform, we go into the reciprocal space and deduce the two-dimensional bend and splay elastic constants of the film in a range of wave vectors simultaneously. The method, which only needs light experimental means, is simple, fast, and accurate. It can be particularly helpful in the ferroelectric smecticC*liquid crystals for determining the elastic constants and indirectly the ferroelectric polarizations, without problems for orienting the samples. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119505

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This letter describes a noncontact, automated means for nondestructively measuring the physical (elastic, thermal, electronic, optical) properties of bulk samples, surfaces, supported or unsupported thin films, and multilayer assemblies. The method, which is based on the transient grating technique, uses specially constructed beam-shaping optics to manipulate excitation and probe laser beams for initiating and detecting motions in a sample. We illustrate the approach by determining the thicknesses and mechanical properties of metal films commonly used in microelectronics. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119506

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Transient characteristics of organic light-emitting diodes with Langmuir–Blodgett films of quinquethiophene as the emitting material have been studied. Field and thickness dependence of the response time have been studied. From the time lag between the voltage pulse and the first appearance of electroluminescence emission, the mobility parallel to the chain of the molecules has been calculated. In thicker films, anisotropy in mobility has been observed when compared with previous results obtained from field-effect studies. The interfaces have been found to play an important role in thinner films. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119917

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies have been carried out at 6 K on the1540 nm4I13/2→4I15/2emission ofEr3+in Er-implanted films of GaN grown by metalorganic chemical vapor deposition. The PLE spectra exhibit several broad below-gap absorption bands, which excite three distinct site-selectiveEr3+PL spectra. The excitation of two of the site-selective Er PL bands involves optical absorption by defects or background impurities, rather than direct intra-fshell absorption, with subsequent nonradiative transfer of the energy to nearbyEr3+luminescence centers. The characteristics of the PLE spectrum of the third site-selective PL band suggest that an exciton bound at an Er-related trap is involved in the excitation mechanism. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119507

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on memory effects in the optical properties of GaN and AlN epitaxial-films grown by atmospheric pressure metal organic chemical vapor deposition. After exposing selected areas of particular samples with He–Cd laser light (3.8 eV), we observed a persistent and marked decrease in the near band edge photoluminescence (PL) intensity emitted from these areas. This effect has been observed in epitaxial films that typically have a pyramidlike hillock surface. This ability to modulate PL emission intensity at individual points in these materials can be exploited as a method for optical data storage. A means of erasing information stored using this effect has also been investigated using lower energy (∼2 eV). ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120414

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structure and interface state density of thin Si and Si/Ge heterolayers on sulphur passivated GaAs (110) were studied by capacitance–voltage measurements, x-ray scattering, and x-ray absorption with synchrotron radiation. The results show that the reduction of interfacial state density by utilizing Si or Si/Ge thin heterolayers on sulphur passivated GaAs (110) correlates better with the short-range electronic structure at the interface than the commonly believed long-range atomic abruptness. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119508

出版商:AIP    

年代:1997

数据来源: AIP