摘要:

Changes in polymer viscoelastic properties have been monitored using polymer‐coated surface acoustic wave (SAW) devices. Glass transitions induced by temperature changes and absorption of gas phase species have been observed. The changes in wave propagation velocity and attenuation which accompany these transitions are explained using a Maxwell model to describe the viscoelastic properties of the film.

ISSN:0003-6951    

DOI:10.1063/1.104043

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker‐reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker‐reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 °C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda‐lime glass both before and after heat treatment confirms our interpretation of the strong contrast.

ISSN:0003-6951    

DOI:10.1063/1.104019

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A wide area vacuum ultraviolet (VUV) lamp employs a ring‐shaped cold cathode to produce an electron beam excited plasma of disk geometry. When excited by the soft vacuum electron beam, molecular hydrogen, nitrogen, and atomic helium emit strong atomic resonance radiation at 121.6, 120, and 58 nm, respectively. The VUV optical power emitted on the atomic resonance line is typically 6–10% of the total applied discharge power. The spatial uniformity of the VUV emission intensity at a discharge input power level of 30 W approaches 6% across the entire disk diameter, up to a maximum of 20 cm.

ISSN:0003-6951    

DOI:10.1063/1.104020

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Particles generated in an argon plasma and suspended at the plasma/sheath boundary are localized by lateral trapping fields. In the commercial rf etching reactor used in this work, the particles and their motion in real time are observed by laser light scattering with the laser beam rapidly rastered in a plane parallel to the rf electrode. Repulsion between individual, relatively large particles is observed, verifying that there is significant negative charge on the particles. Two types of trapping regions are commonly seen: rings of particles around the outside edge of silicon wafers, and domes of particles over the centers of the wafers. It is shown that these effects are influenced by the topography of the electrode. In addition, particle densities >107cm−3for particles of diameter 0.2 &mgr;m are inferred from transmission studies for certain plasma conditions.

ISSN:0003-6951    

DOI:10.1063/1.104021

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Conducting and transparent thin films of tin oxide were prepared by the laser evaporation of an undoped powder‐pressed polycrystalline tin oxide target onto unheated substrates. After characterizing these films, the results reveal that the films are highly oriented and with a grain size ∼0.2 &mgr;m. The nearly stoichiometric deposition of tin oxide films with deposition rates exceeding 24 A˚ per pulse was obtained by this method. The lowest resistivity obtained is 3.0×10−3&OHgr; cm. The visible transmittance (between 4000 and 7000 A˚) is above 75%.

ISSN:0003-6951    

DOI:10.1063/1.103998

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Numerical inversion of the Hankel–Laplace transform has been performed for the case of ultrasonic displacements in an infinite, homogeneous, isotropic plate which is excited thermoelastically by a laser pulse. Values for the elastic moduli and the plate thickness may be extracted when the calculated displacements are compared directly to those obtained experimentally. Previous authors have demonstrated methods for determining the elastic modulus in thick plates; this letter shows that using a different method for the development of the theory allows similar modulus determinations to be made for thin as well as thick plates.

ISSN:0003-6951    

DOI:10.1063/1.103999

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

By employing an electron cyclotron resonance plasma‐enhanced chemical vapor deposition technique, we report the successful growth of cubic boron nitride films on single‐crystal (100) silicon wafer without external rf or dc substrate biasing. Ammonia and boron trifluoride gases were used for the deposition of cubic boron nitride. The substrate temperature during deposition was about 675 °C. The films were characterized by infrared spectroscopy and ellipsometry. The existence of cubic boron nitride was identified by the characteristic boron nitride infrared signal at 1110 cm−1. The film thickness was about 1000 A˚, with a growth rate of 100 A˚/min.

ISSN:0003-6951    

DOI:10.1063/1.104000

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Delta doping in quantum well structures has been studied. The quantum wells consist of a strained InGaAs layer sandwiched between two GaAs layers. The layers were undoped except for a sheet of Si dopants deposited in the middle of the quantum well. Structures with various doses and quantum well thicknesses were studied and compared. Capacitance voltage measurements were carried out to determine the carrier distribution. A very narrow carrier profile with a full width at half maximum of only 12 A˚ has been achieved. This is the narrowest carrier profile ever reported for any growth technique.

ISSN:0003-6951    

DOI:10.1063/1.104001

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In small particles of chemical vapor deposited (CVD) diamond and polycrystalline thin films composed of the particles, the recombination radiation of free excitons and bound excitons associated with multiple phonons has been observed using cathodoluminescence. The bound excitons are due to neutral acceptors of boron in the diamonds. The cathodoluminescence imaging reveals that the recombinations of free excitons are located at {100} sectors. The crystal perfection and purity is high in {100} sectors compared with {111} sectors formed in the CVD process.

ISSN:0003-6951    

DOI:10.1063/1.104002

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The recombination leakage current induced by planar isolation ofn‐p+AlGaAs graded heterojunction area with oxygen ion implantation followed by annealing at 500–650 °C has been investigated. The recombination leakage current is smaller than that induced by conventional isolation with hydrogen ion implantation; specifically, it is about one order of magnitude smaller after the higher temperature (600–650 °C) annealing. The main origin of the remaining recombination leakage current is probably not oxygen deep levels but rather recombination centers related to the ion implantation damage that remains after annealing. A point‐defect complex level, which may be related to the recombination center, is detected at an activation energy of around 0.8 eV by deep level transient spectroscopy.

ISSN:0003-6951    

DOI:10.1063/1.104003

出版商:AIP    

年代:1990

数据来源: AIP