摘要:

While the widely used electrodynamic quadrupole traps are based on the dynamic stabilization around a field minimum, we demonstrate here the trapping of charged particles close to a maximum of the electric field. In the experiment charged steel spheres are trapped in the monopole potential of a tip electrode using a combination of static and alternating voltages. As a periodically driven nonlinear oscillator this system might show chaotic dynamics. A period doubling bifurcation was observed experimentally. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366407

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Reflective twisted nematic liquid crystal displays consisting of just one input polarizer, a liquid crystal cell, and a rear reflector are discussed. We first show that all such display modes reported in the literature can be depicted systematically in a series of parameter space diagrams. Then by making use of such diagrams as a guide, we show that other new high quality reflective display modes can be obtained. The three parameters that are varied are the input polarizer angle &agr;, the liquid crystal twist angle &fgr;, and the cell gap–liquid crystal birefringence productd&Dgr;n.A full numerical simulation which takes into account of the liquid crystal director deformation under the application of an electric field was used to optimize such displays. Experimental results agree well with the theoretical predictions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366408

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Light-induced absorption spectroscopy, the decay process of light-induced absorption, and its temperature dependence were investigated to study the properties of the photorefractive impurity levels in dopedBaTiO3.Light-induced absorption spectra in one Rh-doped and two Ce-dopedBaTiO3crystals from 0.7 to 3.0 &mgr;m were measured and it was found that the light-induced absorption of all these crystals approached zero above∼1.3 &mgr;m.A two-shallow-level model is proposed to explain the biexponential behavior of the decay of the induced absorption inBaTiO3:Ce.The activation energies are deduced to be 0.72 eV for the single-shallow level inBaTiO3:Rh,0.50 and 0.66 eV for the two shallow levels in the 8 ppm Ce-dopedBaTiO3,and 0.50 and 0.74 eV for that in the 30 ppm Ce-dopedBaTiO3.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366294

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The importance of diffraction losses in etched air/GaAs Bragg mirrors in waveguides is theoretically evaluated. A complete three-dimensional resolution of the Maxwell equations by a finite element method is performed, and shows the great importance of diffraction into the substrate. Two cases are distinguished: the weak guiding case, where the index contrast between waveguide and substrate is low (example: GaAs/AlAs), and the strong guiding case where this contrast is high, thanks to the use of lower refractive index substrates, such as oxidized AlAs. The latter solution is found to be very promising since the diffraction losses into the substrate are practically eliminated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366295

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A theoretical and experimental analysis of the finite laser beam size effects in thermal wave interferometry has been reported. The limits of the heat transfer one-dimensional approximation, that is usually employed in this measuring method, have been discussed. This study has been performed by considering the actual three-dimensional temperature distribution induced by gaussian laser heating. Measurements on yttria partially stabilized zirconia coatings plasma-sprayed onto two different metallic substrates were carried out for different values of the heating beam dimension. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366296

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Low pressure(<10s mTorr),high plasma density(>1011 cm−3)reactors are rapidly becoming the tool of choice for etching during microelectronics fabrication. Although gas injection and pumping are well characterized process parameters in higher pressure systems, the impact of the symmetry of gas injection and pumping on the uniformity of reactant fluxes to the substrate are less well known in low pressure systems. In this article, results from a three-dimensional plasma equipment model are used to investigate the consequences of asymmetric gas pumping on reactive fluxes in inductively coupled plasma reactors operating inCl2.We find that for typical conditions (10 mTorr, 150 sccm, 400 W) the azimuthal symmetry of ion density and ion fluxes are little affected by, for example, side pumping. This results from the dominance of ambipolar electric fields which are largely determined by the uniformity of ion sources and shape of the chamber. Neutral reactant fluxes do suffer azimuthal asymmetries due to pumping, however the variations are typically<10&percent;–15&percent;over a pressure range of 5–20 mTorr. The magnitude of the side-to-side variations is largely determined by the relative rates of loss of reactant species to surfaces compared to pumping. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366297

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Laser-induced fluorescence spectroscopy has been employed for the measurements of the ground-state CF andCF2radical densities in low-pressure and high-densityCF4plasmas generated by helicon wave discharges. In the pulsed operation (5 Hz, 10 ms duration), the radial profiles of the CF andCF2densities were hollow shape in the discharge phase, which indicates that both radicals were desorbed from the wall and were lost in the plasma column. In the continuous-wave operation, roughly uniform radial profiles were observed for both radicals. Therefore the desorbed radicals in the pulsed discharge seem to originate from the adsorbed species in the afterglow of the previous discharge. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366298

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article, the results on N and Al implantations into undoped high-resistance and vanadium doped semi-insulating bulk 6H-SiC are reported for the first time. The N implants were performed at 700 °C and the Al implants at 800 °C to createn- andp-type layers, respectively. For comparison, implants were performed into epitaxial layers at the above temperatures and, for N, also at room temperature. The implanted/annealed material was characterized by van der Pauw Hall, secondary ion mass spectrometry, and Rutherford backscattering (RBS) measurements. After annealing, the room temperature N implantation gave similar electrical and RBS results as the 700 °C implantation for a total implant dose of8×1014 cm−2which corresponds to a volume concentration of2×1019 cm−3.The Al implant redistributed in the bulk crystals during annealing, resulting in a shoulder formation at the tail of the implant profile. Lower implant activation was obtained in V-doped material compared to the undoped bulk and epitaxial layers, but the results were promising enough to use implantation technology for making planar high frequency devices in the bulk V-doped substrates, especially as the quality of the substrates continue to improve. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366299

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Low-power pulsed-laser annealing was applied toZn+-implanted InP samples. In order to avoid surface oxidation during the treatment, the laser irradiation was carried out in inert ambient of nitrogen at different pressures. The analytical techniques used include Rutherford backscattering spectroscopy, reflection high energy electron diffraction, and electrical measurements. The highest carrier activation, about 80&percent;, was achieved at the same laser power density(6.5 MW/cm2)at which the best crystal recovery was obtained. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366300

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Defects introduced in epitaxially grown cubic silicon carbide (3C-SiC) by implantation of nitrogen(N2+)and aluminum ions(Al+)at a wide temperature range from room temperature to 1200 °C were studied using electron spin resonance (ESR), photoluminescence (PL), and positron annihilation spectroscopy (PAS). It is found that while hot-implantation reduces paramagnetic defects and improves the crystallinity of implanted layers, it causes the simultaneous formation of vacancy clusters. These results can be explained in terms of the migration and combination of point defects during hot-implantation. The formation and reduction of defects by hot-implantation are discussed in connection with implantation temperature, dose, and ion species. Postimplantation annealing of the defects in hot-implanted 3C-SiC was also examined by the ESR, PL, and PAS technique. The influence of residual defects on the electrical properties of implanted 3C-SiC layers is also discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366301

出版商:AIP    

年代:1997

数据来源: AIP