摘要:

The electrode temperature rise during the starting of an arc discharge lamp has been measured using the temperature‐dependent reflection coefficient of He‐Ne laser light from metal surfaces. Lock‐in techniques permit temporal resolution of about 3 ms, which is adequate to resolve 60‐Hz phenomena such as electrode heating during the ac cycle. Calibration curves obtained by pyrometric measurements of constant‐current tungsten ribbon lamps were used to relate the observed signal during electrode heating to its temperature. The technique described affords a nonintrusive method for measuring transient electrode temperature in an optically clustered environment with an accuracy of about 20%.

ISSN:0021-8979    

DOI:10.1063/1.345314

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An aluminum plasma is produced by an anodic vacuum arc (25 A, 17 V) with a consumable anode. The plasma expands from the anode to the walls and is investigated by Langmuir probes, a quadrupole mass spectrometer, a retarding field ion energy analyzer, and a quartz‐crystal oscillator for mass flow detection. The electron density ranges within 2×1015–3×1017m−3and the electron temperature within 0.4–0.9 eV. At a target, ion fluxes of 1.5×1019–8×1020m−2 s−1and total particle fluxes of 3×1020–4×1021m−2 s−1are measured. The ions are accelerated in the expanding plasma towards the target and gain a few eV. By a simple collisionless transport model of the expanding plasma, the plasma potential and floating potential are calculated and compared with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.345315

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this paper the results of a simple experiment designed to study refraction‐induced distortion of images of narrow‐band‐light‐emitting regions in a laser‐produced plasma are described. Source regions were formed by relaying the image of a backlit pinhole array into the plasma (25 &mgr;m‐diam. pinhole; 30‐ps, 0.25‐&mgr;m backlighter beam). Images of these source regions were recorded on film and compared with and without plasma present. Refraction effects, evidenced by translation of the apparent pinhole locations and blurring of the pinhole spots, are compared for different plasma sizes and for different delays of the backlighter pulse with respect to the plasma‐production laser pulse. These results were then compared with expectations based on numerical raytraces through a plasma‐density profile derived from a hydrodynamic simulation of our exploding‐foil plasma. The significance of these results in the imaging of harmonic and half‐harmonic light as a plasma‐density diagnostic is discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W‐7405‐ENG‐48.

ISSN:0021-8979    

DOI:10.1063/1.345316

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The behavior of CF2radicals in CF4/O2plasmas has been studied as a function of the oxygen partial pressure in an rf reactor with 13.56 MHz, 30 W, and 40 mTorr total pressure. The CF2ground and excited states were detected by the CF2(A‐X) band spectra applying laser‐induced fluorescence and optical emission spectroscopy, respectively. Adding oxygen to the CF4feed gas, the intensity of the CF2signals in both spectra showed similar decrease. No evidence is found for a simple correlation between the neutral CF2densities and the CF+2ions measured by quadrupole mass spectrometry. Electron densities and temperatures were evaluated to be slightly above 8×109cm−3and ∼5 eV, respectively. A simplified model, which takes into account different excitation paths, suggests that direct electron impact of the CF2ground state species was the dominant mechanism for the population of the electronically excited state. Absolute CF2and O concentrations depending on the oxygen feed could be estimated. We obtained CF2densities between 2×1013and 2×1012cm−3, when the oxygen concentration increases from 2% to 23%. The corresponding O densities varied from 1012to 6×1013cm−3.

ISSN:0021-8979    

DOI:10.1063/1.345317

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report mass spectroscopic measurements of the charged particle, neutral, and excited neutral species emitted from the irradiation of single‐crystal cyclotrimethylene‐trinitramine (RDX) with 248‐nm, 20‐ns laser pulses. At laser fluences above 5 mJ/cm2we observe RDX decomposition products of relatively small mass in both neutral and ionic states. With increasing fluence we see clear etching of the crystal, an increase in kinetic energy of the products, and the appearance of an intense, excited neutral species which we identify as NO in an energetic, long‐lived electronic excited state. Evidence is also presented for a sustained decomposition reaction ignited by the laser pulse.

ISSN:0021-8979    

DOI:10.1063/1.345318

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The thermal neutron reactionn+10B→4He+7Li is utilized to measure the boron concentration on the surface of silicon wafers. This neutron depth profiling measurement technique requires no sample preparation. Boron is determined on the as‐received wafers at a level of 1012to 1013atoms/cm2. A boron level of about 2×1012atoms/cm2is found at the wafer surface after oxidation or epitaxial or polycrystalline silicon deposition. Ambient air appears to be one source of the boron. Secondary‐ion mass spectroscopy performed on wafers with polysilicon provides additional support for an atmospheric source of boron.

ISSN:0021-8979    

DOI:10.1063/1.345319

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The Curie temperature relaxation behavior in two amorphous ferromagnetic alloys (Fe10Co55Ni35)78Si8B14and Fe40Ni40P14B6(Metglas 2826) subjected to annealing at pressures up to 2 GPa is investigated. A comparison of the relaxed amounts ofTCdue to isothermal and isochronal annealings at 0, 1, and 2 GPa shows a delaying effect on the relaxation process during high‐pressure annealing, while the concomitant kinetics of the processes remains unchanged. The pressure‐induced percentage reductions inTCrelaxation are estimated to be 8% and 12% per GPa, respectively. The reversible relaxation behavior was found still present during high‐pressure annealing, but with a reduced amplitude. By annealing between high and low pressures at fixed temperature, some regenerative relaxation behavior was observed after every completion of the cyclic pressures. The obtained results may be explained by pressure‐induced narrowing of regions in the amorphous structure. It is suggested that these extended regions are the main locations where the compositional short‐range ordering contributed toTCrelaxation.

ISSN:0021-8979    

DOI:10.1063/1.345320

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Understanding of the static internal stress in supported thin layers can be aided by the use of dynamic mechanical analysis, with emphasis on internal friction measurements for the detection of defects susceptible to stress‐induced ordering. In addition to the bending‐bilayer and vibrating‐reed methods used for separate measurements of internal stress and internal friction, a new vibrating‐membrane method is described that enables both quantities to be measured concurrently on the same sample. Structural relaxation, solute sorption, orientational ordering, and surface reaction are identified as four general phenomena affecting the internal stress, and experimental results are given for each of these categories. The bending‐bilayer method has been used to observe stress changes associated with structural relaxation in amorphous SiO films, and with the sorption and orientational ordering of oxygen in Nb films. The vibrating‐membrane method has been used to study stress changes in boron‐doped Si membranes, resulting from either hydrogen sorption or high‐temperature oxidation. Hydrogen sorption leads to the appearance of a new internal friction peak located near 130 K, which is governed by an activation energy of 0.23 eV.

ISSN:0021-8979    

DOI:10.1063/1.345321

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We derived equations for the target‐strength term used in the modified hydrodynamic model that describes long rod penetration into ceramic targets. Since ceramics have tensile strengths that are usually an order of magnitude lower than their compressive strength, this model allows for tensile cracking. In addition, our model includes the effect of pressure‐dependent shear strength.

ISSN:0021-8979    

DOI:10.1063/1.345322

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Undoped GaAs single crystals with ⟨123⟩ orientation are compressed at different strain rates in the temperature range between 730 and 900 °C, using the liquid encapsulation technique to prevent As loss. The resulting stress‐strain curves are characterized by five deformation stages, as is known for other semiconductors. From the lower yield point, at high strain rates, an activation energy of 1.37 eV and a stress exponent of 3.6 are deduced; these parameters nearly agree with those obtained earlier at lower temperatures and under a protective atmosphere of argon. At low strain rates deviations occur, whose origin is discussed. The analysis of the first stage of dynamical recovery (stage III), which shows a uniform behavior over the whole temperature and strain‐rate range, yields an activation energy of 2.3 eV and a stress exponent of 4.2. These values are discussed in terms of a diffusion‐controlled recovery mechanism. The second recovery stage (stage V) probably is governed by cross slip; the cross over of both recovery regimes takes place near 550 °C. The deformation behavior of GaAs is compared to that observed in other semiconductors.

ISSN:0021-8979    

DOI:10.1063/1.345323

出版商:AIP    

年代:1990

数据来源: AIP