摘要:

Using a silver grating of variable groove depth overcoated by a thin film of copper phthalocyanine, we measured an increase of the Raman efficiency of 104as compared to the flat case (copper phthalocyanine on a flat silver surface). This effect is due to the resonant excitation of delocalized surface plasmons. The value of 104corresponds to an optimum groove depth of the grating which acts as a high gain directive antenna when surface plasmons resonance is achieved at the Stokes frequency. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113852

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Volume contraction in bulk silicon crystals is observed on excitation with femtosecond visible optical pulses. The surface deformation and generated acoustic strain are measured using detection based on both probe beam reflectivity changes and probe beam deflection. The contraction is explained by the dominant electronic contribution to the strain from excitation of electron‐hole pairs, which swamps the thermoelastic expansion. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113853

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

High‐power rf oscillations are obtained in a resistive load installed in the external electrical circuit of a low‐pressure magnetic‐field‐free hollow‐cathode discharge. These intense rf oscillations have been shown to be due to a collisionless instability of the cathode sheath. A very simple device based on this effect is shown to serve as a convenient and powerful rf oscillator. Typical results first achieved without any optimization, for frequencies of 20–30 MHz and load resistances of several tens of ohms, are as follows: power of about 5 kW and efficiency ∼25%. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113854

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report experimental measurements of a high brightness electron beam produced by a ferroelectric cathode. Up to 36 A of current (10 A/cm2) were obtained at a voltage of 22.5 kV. Electron beam emission was obtained with a dc voltage held between the cathode and anode, and a gate pulse of 1–2 kV applied across the sample. The beam normalized emittance was measured at 10 kV to be 5 mm mrad with a normalized beam brightness of 1.2×1011A/m2 rad2. This value of beam brightness exceeds that of thermionic cathodes. The ferroelectric cathode emission is found to exceed that of a thermionic cathode using the same geometry. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113855

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A very hard and conducting form of carbon has been obtained from pure C60fullerenes, as well as its mixture with aluminium at nonhydrostatic pressures of 2.6–3 GPa and a temperature of 700 °C. The hardness of the material is more than 4000 kg/mm2. Its electrical conductivity is about 100 &OHgr;−1cm−1and is weakly dependent on temperature in the range 4.2–300 K. X‐ray diffraction and Raman measurements show lack of the long‐range crystalline order in the transformed material. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113856

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects of high pretilt angle are investigated on the polar anchoring energy of the nematic liquid crystal (NLC), 5CB, on rubbed polyimide (PI) films containing trifluoromethyl moieties. The pretilt angle of 5CB rapidly increases up to about 45° with the rubbing strength (RS). Also, the polar anchoring energy of 5CB initially increases with the RS for weak rubbing and then decreases. From these results, we determined the relationship between the pretilt angle and the anchoring energy on rubbed PI films. We suggest that the polar anchoring energy of 5CB with a high pretilt angle is very small because of the combination of the microsurface excluded volume effect and the van der Waals interaction between the LC molecules and the substrate surface on weakly rubbed PI films containing trifluoromethyl moeities. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113236

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new method has been developed to measure exo‐electron emissions stimulated by frictional heating for a ball‐on‐disk sliding where a tungsten carbide was biased at +15 V dc to collect exo‐electrons emitted from a &ggr;‐irradiated hot‐pressed alumina disk. Exo‐electron emission’s signals were detected above a certain critical velocity when the contact surface was frictionally heated to a critical temperature of 250 °C and emitted exo‐electrons. Sliding temperatures at any conditions of load and velocity were thus estimated using the temperature calculation program M. F. Ashby, J. Abulawi, and H. S. Kong [T‐MAPSBackgroundReadingandUserManual, Cambridge University Engineering Department (Cambridge University, London, 1992); Tribology Trans.34, 577 (1991)]. This method provides a versatile method of measuring the sliding temperature of ceramics. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113237

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have carried out structural studies of nonluminescent areas developed by current injection in ZnMgSSe alloy‐based II–VI blue light emitting diodes by electroluminescence topography and transmission electron microscopy. The nonradiative regions, which spread out in the ⟨100⟩ direction during current injection, consist of a high density of dislocation dipoles and dislocation loops. The source of these defects is the preexisting stacking faults originating at the substrate/epilayer interface. The dipoles themselves are aligned along both of the ⟨110⟩ directions lying in the {111} plane. Their Burgers vectors were of the type (a/2)⟨011⟩ inclined at 45° to the (001) junction plane. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113238

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Infrared reflectivity was measuredinsitufrom single phase layers of Rb1C60with a thickness of about 4 &mgr;m on a {111} face and of about 0.5 &mgr;m on a {100} face of C60single crystals. The fcc→orthorhombic phase transition was traced by a splitting of theF1u(4) mode into three lines within a temperature range of 2° at 404/415 K for a cooling/heating cycle, respectively. The reflectivity spectra remained unchanged after exposing the orthorhombic Rb1C60to air. Even the fcc phase appears to be vibrationally stable in air up to at least 450 K. The conductivity of the orthorhombic phase shows a weakly activated temperature dependence. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113239

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The evolution of microstructure in Al and Cu thin film lines during electromigration has been studied using a transmission electron microscopy. Grain boundary migration was found to be critically involved in the electromigration induced hillock formation that can be described as a three‐dimensional growth of a single grain. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113240

出版商:AIP    

年代:1995

数据来源: AIP