摘要:

Few monolayers thick hydrogenated carbon films doped with boron (C/B:H) were prepared and investigated in an ultrahigh‐vacuum environment by high‐resolution electron energy loss, Auger electron, electron energy loss, and thermal desorption/decomposition spectroscopies with specific emphasis on their chemical erosion behavior as compared to their undoped C:H counterparts. Films of thicknesses ranging from 1 to about 10 monolayers, with a maximum B/C ratio of 0.5, were grown by ion‐beam deposition at room temperature on a carrier consisting of a Pt(100) single‐crystal surface covered with a graphite monolayer. The process gas used was a mixture of ethane and trimethylboron of varied compositions. While at zero boron concentration the films exhibit a graphiticlike structure with about equal amounts of carbon atoms in thesp2andsp3hybridization state, with increasing boron concentration the film structure becomes increasinglysp3dominated. This is evidenced by decreasing HREELS loss intensities of the vibrational modes related to graphitic hydrogenated carbon, i.e., C=C,sp2CH stretches, and aromatic CH deformations, but enhanced C–C andsp3CHnstretch mode intensities. No BH vibrational modes have been observed at any doping level. In accordance with these observations, the C‐272 eV Auger peak line shape underwent a change characteristic for asp3‐dominated network upon B doping. The &pgr;‐plasmon energy was found to shift toward lower energies at C/B:H films which also is in line with a decrease of the carbonsp2concentration, giving further support for a change to a less graphitic structure. The observed enhanced capacity for hydrogen in the films was found to correlate in a linear fashion with the increase of the fraction of carbon atoms in thesp3configuration. The relative hydrogen content of the films, H/C, starting at 0.4 at zero boron content, was observed to increase, saturating at 0.75 for boron concentrations greater than 10%.This in turn coincides with a substantial growth of the film hydrogen capacity, as judged from the amount of H2desorbing from the films between 500 and 1100 K upon thermal decomposition of the films. Although hydrogen originating fromsp3CH groups increased significantly, the amount of chemically eroded species, monitored by CnHmproduction in the thermal decomposition spectra, was unaffected by boron doping. However, the desorption maxima for either species, hydrogen and hydrocarbons, shift to lower temperatures at boron doped films. As reasons for the effect of B doping on the chemical constitution of C/B:H films and the resulting chemical erosion behavior, the capability of B to block the formation of aromatic structures is proposed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359185

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The behavior of anLCR(inductance‐capacitance‐resistance) circuit with a movable ferromagnetic core is discussed. The core is attracted by a magnetic field generated by an electric current resulting from the discharge of a capacitor in the closedLCRcircuit. An unusual increase in recharge voltage, which was dependent on the magnetic configuration of the coil, was observed. This voltage increase does not conform to the mathematical simulation of the system. The possibility that a positive electromotive force was involved in this effect is discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359520

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Effects of the gate dielectric nitridation on the flicker (1/f) noise characteristics of submicron metal oxide semiconductor field effect transistors (MOSFETs) are reported. Low‐frequency (1/f) noise measurements on nitrided and non‐nitrided gate oxide MOSFETs of the same geometry have been carried out, showing different noise behavior with respect to the flicker noise amplitude and bias dependence. It is found that gate oxide nitridation not only increases the flicker noise amplitude, but also enhances the correlated mobility noise mechanism. The two orders of magnitude higher noise measured in nitrided structures is consistent with the approximately two orders of magnitude increase of the nitrided gate conductance reported in the literature. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359186

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The noise characteristics of symmetrical double barrier resonant tunneling structures were measured in two samples with a fixed well width of 50 A˚ and barrier thicknesses ofLB=8 monolayer and 10 ML, respectively. The measurement was done in the frequency range of 1 Hz–100 kHz and temperature range of 77–300 K. The noise due to the excess current in the valley region, observed in both devices, was associated with defect assisted tunneling which is a two‐step process: generation‐recombination noise due to the trapping and detrapping mechanism, and 1/fnoise due to the scattering by phonons. The current dependence of 1/fnoise contribution was investigated in the resonant tunneling and valley regions. The frequency exponent of the 1/fnoise component was found to vary between 0.9–1.1 for double barrier resonant tunneling diode (DBRTD) withLB=8 ML and 1.1–1.2 for DBRTD withLB=10 ML. This noise investigation implies that there is a difference in the physics governing the transport between DBRTD withLB=8 ML and DBRTD withLB=10 ML. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359187

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Cesium telluride (Cs2Te) photocathodes, with quantum efficiencies (QEs) of 15%–18% at 251 nm, were fabricated by vapor deposition of Te and Cs onto a Mo substrate and used as an electron source for the Los Alamos Advanced Free‐Electron Laser. In the fabrication chamber, the spectral response from 251 to 578 nm was measured before and after a controlled exposure of several photocathodes to air. The 251‐nm QE dropped by about a factor of 20 when exposed to 2×10−4Torr of air for 1 h. Heating degraded photocathodes to 150–200 °C partially rejuvenated their QEs to about 60% of the value before air exposure. The performance of Cs2Te as a source of electrons for accelerators was evaluated in the photoinjector stage of the Advanced Free‐Electron Laser. The response time, saturation level, and dark current of cesium telluride photocathodes and the emittance and energy spread of the resulting electron beam were determined to be sufficient for free electron laser applications. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359188

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the thermochromic order‐disorder phase transitions in two superionic conducting compounds, Ag2HgI4and Cu2HgI4, using capacitance dilatometry to determine the relative volume change, &Dgr;V/V, at the transitions. We find an average &Dgr;V/Vof 9.6×10−3for Ag2HgI4at a transition temperature of 48.75 °C and an average &Dgr;V/Vof 4.0×10−3for Cu2HgI4at a transition temperature of 63 °C. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359189

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on Raman scattering by phonon pairs in GaN films grown on sapphire substrates by plasma‐enhanced molecular beam epitaxy. The first order data are consistent with results obtained from GaN bulk crystals of the wurtzite structure. TheA1and the much weakerE2symmetry components of the second order scattering have been identified. Two‐phonon spectra are dominated by contributions due to longitudinal optical phonons. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359190

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ag3Ni3and Ag4Ni4multilayers have been analyzed by electron induced x‐ray emission spectroscopy. Changes observed on the density of valence states in the Ni layers, with respect to the bulk, are correlated with the variation of the lattice parameter deduced from x‐ray diffraction experiments. In the Ag layers no change in the density of valence states is observed and the lattice parameter is almost unchanged. These behaviors are explained by an electronic effect due to the low dimensionality of the multilayers. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359191

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The essential role played by the physics of Zener tunneling of electrons from the barrier to the drain in finding the solutions to the field, energy‐balance, and quantum transport equations in AlGaSb/InAs/AlGaSb double‐barrier structures is pointed out. It is shown that the self‐consistent physical consideration on these equations is crucial in obtaining interesting and realistic novel hysteresis phenomena of the trapped hole charge in an AlGaSb barrier. There exist solutions to the above equations which do not incorporate the physics of Zener tunneling, which are therefore physically untenable.

ISSN:0021-8979    

DOI:10.1063/1.359192

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Laser induced damage threshold values are reported for two metal‐organic complex crystals, zinc tris(thiourea) sulfate, and bis(thiourea) cadmium chloride. These crystals have single shot and multiple shot damage thresholds which are the highest among the solution grown crystals. The damage morphology, obtained by irradiating with fluences close to the threshold, reflects the symmetry of the face of the test site. At higher fluences the damage leads to stress‐induced fracture or thermo‐chemical degradation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359127

出版商:AIP    

年代:1995

数据来源: AIP