摘要:

The production of periodic ripple or wavelike structure by Si+, Ne+, Ar+and Xe+high‐fluence ion bombardment at 20 and 30 keV of Si at 45° incidence angle and at target temperatures from 120 K to room temperature and observed by scanning electron and atomic force microscopy is described. Different species exhibit different behaviors at different temperatures with Xe+producing transverse wave structures at room temperature and below, Ar+producing more patchy ripple structures, and Ne+and Si+only producing wave structures at low temperatures. Possible reasons for the different behavior include implant ion incorporation which mediates flow and stress relief in the amorphized near‐surface layer. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359931

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We show experimentally that the positional uncertainty in long‐term images of a microparticle in a Paul trap in air can be reduced to the optical limit, and below the pseudopotential limit. For this damped system, far below any Mathieu instability, the particle’s thermally induced positional noise is extremely sensitive to the phase of the driving field. Accumulating images strobed at the proper phase produces a long‐term optical image which is essentially free of thermally induced positional noise. Although noise squeezing theory does not apply at such large dissipation, our results may be understood through recent theory of the Brownian parametric oscillator. Use of this theory coupled with our observations suggests that the extreme reduction in spatial variance observed by using our technique results from working in a low Reynolds number regime. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359932

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a model for the shape evolution of a thin metal film due to the bulk diffusion of vacancies. High‐temperature Al sputter deposition and postdeposition annealing are currently becoming significant (very large scale integrated circuit metallization processes. The attractiveness of these processes lies in the ability to fill and planarize high‐aspect‐ratio vias and contacts with very few process steps. Previous attempts to model these processes have not fully emphasized the role played by bulk diffusion and three‐dimensional curvature. We present the differential equation and boundary conditions that describe the flow of vacancies in metal films. An approximate method of solution for this equation system is presented and incorporated into the thin‐film deposition simulatorSIMBAD(simulation of ballistic deposition). This simulator is then used to present results pertaining to both postdeposition annealing and high‐temperature sputter deposition. Particular emphasis is placed upon determining the effects of via and contact geometries, wetting angles and deposition rate during sputtering. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.360708

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Conducting tubes filled with neutral gas at pressures between 0.001 and 0.1 Torr can be used to transport, to center, and to reduce the transverse oscillations of high current (≳10 kA) electron beams. Electron impact ionization of the gas leads to partial neutralization of the beam space charge allowing self‐focused beam transport and phase‐mix damping of injected beam oscillations. In addition, the presence of conducting walls helps center the beam in the transport tube. High current beams, transported through a 1.3 m long tube, were centered to within one‐tenth of the beam radius and input transverse oscillations were damped to submillimeter values without significant current loss or emittance growth. Beam transport properties are examined as a function of injected current, gas pressure, and cell geometry. Experimental results are compared with a theoretical model.

ISSN:0021-8979    

DOI:10.1063/1.359933

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

PassiveQswitching of an Er:glass laser with the pulse width varying between 14 and 80 ns has been demonstrated, using three resonator vanadium‐dioxide‐coated (VO2) mirror samples with temperature‐dependent reflectivity and differing in the reflectivity contrast. The reflectivity changes because of a phase transition from a semiconductor to a metallic state. Broad band operating characteristics of VO2mirrors provideQswitching over a wide range of wavelengths. In addition, mode‐locked pulses with much shorter time scales have been observed, due to exciton formation and recombination. A simple criterion is derived for the allowable ambient temperatures at which theQswitching operates effectively. A simple relation has also been found relating the duration of theQ‐switched pulse to the contrast in reflectivities of the two mirror phases. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359934

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We investigate the possibility of constructing nanostructure waveguides using Si‐based materials. For this purpose we evaluate the dielectric function of strain‐symmetrized (Si)10−n/(Ge)nstrained‐layer superlattices (SLS’s) withn=3, 5 and 7, and (Si)6/(Ge)4SLS coherently grown on a Si(001) surface, as well as that for bulk Si1−n/10Gen/10alloys withn=3, 5 and 7, and bulk Si. In particular we explore the possibility of constructing waveguides using the materials (Si)6/(Ge)4SLS, coherently grown on a Si(001) surface, and bulk Si. We investigate the case of planar waveguide structure, giving results concerning the propagation and penetration of the transverse magnetic modes. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359935

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The spontaneous emission from an InGaAs/GaAs single‐quantum well surrounded by AlAs/GaAs distributed Bragg reflectors (DBR) under the near‐resonance condition between the exciton level and the confined optical mode is investigated. Under such conditions, on‐axis spontaneous emission enhancement at the cavity resonant wavelength is clearly identified. The strength and character of the interaction of the exciton with the confined optical mode is determined by the dependence of photoluminescence spectra on the reflectivity of the DBR. Temperature dependence of the enhanced spontaneous emission shows the cavity resonant wavelength shifts at 0.85 A˚/°C around room temperature. An increase of emission intensity at the cavity resonant wavelength with increasing temperature is also observed, which can be related to the increase of the interaction between excitonic emission and cavity mode. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359936

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe our measurements of linewidths of the twoJ=2‐1 transitions (232.24 and 236.25 A˚) and theJ=0‐1 transition (196.20 A˚) of Ne‐like germanium soft x‐ray laser in slab targets. The high resolution spectral measurement was performed using a grazing incidence spectrometer with an x‐ray CCD camera. Time integrated linewidths, the full width at half maximum, of the twoJ=2‐1 lasing lines are about 20(±4) mA˚ when the gain‐length product (GL) is ∼8. The linewidth of theJ=0‐1 line is measured to be 25 mA˚ as the GL is ∼5. The measured linewidths of the 236.25 A˚ line are slightly narrower than those of 232.24 A˚ in the same shot, reflecting their different intrinsic linewidths. For theJ=2‐1 transitions, the thermal Doppler broadening (43 mA˚ inhomogeneous) has been obtained by one‐dimensional hydrodynamic simulation of the plasma expansion, and the collisional broadening (15 mA˚ homogeneous) has been considered with all inelastic electron collisional rates among the transition levels in the plasma. The predicted 52 mA˚ Voigt profile intrinsic linewidth for the 236.25 A˚ line has been used to calculate linewidth narrowing by the one‐dimensional model of amplified spontaneous emission. The experimental data are in agreement with the model calculation in the short targets. Spectral narrowing is not evident in the long targets. We examined soft x‐ray propagation in the plasma by ray‐trace calculation. It is shown that refraction is an important factor affecting the spectral narrowing of soft x‐ray lasers. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359937

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A channel waveguide on an erbium‐doped phosphate laser glass was fabricated by a dry silver‐film ion exchange technique, and its gain properties were studied experimentally. The propagation loss of the fabricated waveguide was 0.63 dB/cm at 1.3 &mgr;m. Er3+concentration of 1×1020ions/cm3was chosen so that no concentration quenching occurred. This was confirmed by measuring a fluorescence lifetime of 8.4 ms at 1.54 &mgr;m. Gain of the fabricated waveguide was measured by using a Ti:sapphire laser at a wavelength of 980 nm and a laser diode of 1.532 &mgr;m producing pump and signal beams, respectively. The signal wavelength used for the experiments was shorter than the emission peak, and the measured gain of the 1.8 cm waveguide was comparable to the total loss. However, the model showed that lasing is expected at the emission peak with a 3.6 cm long waveguide fabricated in a similar manner. Calculation results showed that the potential gain of 8.8 dB can be realized with 250 mW pump power, and a 7.2 cm long waveguide provided that mode overlap can be increased by 20% and propagation loss can be reduced by 50%. No significant upconversion effect was observed up to 1.1×106W/cm2pump intensity. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359938

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report here a direct measurement of the spatially resolved atomic hydrogen concentration profiles during hot‐filament‐assisted chemical‐vapor deposition (HFCVD) of diamond films. The ground‐state hydrogen (1s 2S1/2) atoms generated in this process are monitored by an optical four‐wave‐mixing technique, third‐harmonic generation (THG). For THG, a 364.6 nm dye laser beam is focused into the HFCVD reactor and the third‐harmonic radiation near resonant with the Lyman‐&agr; (2p 2P0j↔1s 2S1/2) transition in atomic hydrogen at 121.6 nm is observed. The resultant THG intensity and THG peak shift with respect to the Lyman‐&agr; transition are both dependent on hydrogen atom concentration. Titration experiments based on the reaction NOCl+H→HCl+NO were conducted to obtain absolute hydrogen atom concentrations from the relative concentrations determined in the THG experiment. Spatially resolved molecular hydrogen temperature and concentration profiles obtained by coherent anti‐Stokes Raman scattering in a similar HFCVD reactor are reported. The observed H atom concentrations exceed computed equilibrium concentrations based on the measured gas temperatures. Transport of the atomic hydrogen from the hot filament surfaces is discussed and diffusion is shown to be the principal mechanism controlling the H atom distribution.

ISSN:0021-8979    

DOI:10.1063/1.359939

出版商:AIP    

年代:1995

数据来源: AIP