摘要:

We have investigated an oxygen gas-pulsed plasma in conjunction with the enhancement of atomic oxygen radicalO*flux and its application. The measured meanO*flux of5.9×1015atoms/cm2 sfrom the gas-pulsed plasma with a duty cycle of 50&percent; (periodically opened for 0.3 s and closed for 0.3 s) at 32 sccm is 1.6 times enhanced compared to that of a continuous wave plasma and is in good agreement with the increment obtained with the time averaged value of transient optical emission profiles ofO*at777.6 nm. The generation of a higherO*flux was interpreted by the mitigation of a recombinative reaction process through the interruption of gas flow injections in the gas pulsed plasma. As a preliminary application, an increase in critical temperature of superconductingYBa2Cu3O7−xthin films was achieved by the gas-pulsed plasma oxidation with a duty cycle of 50&percent;. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364263

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The sheath potential &fgr;Mis calculated from the difference between the plasma potential and the floating potential. The plasma potential has been measured by using a retarding field analyzer with an entrance slit located in front of it. The electron temperatureTeand ion temperatureTiare also measured with the same analyzer in an electron cyclotron resonance plasma. Comparing the normalized sheath potential,−e&fgr;M/kTe, with the different theoretical values, it is found that the secondary electron emission could not be neglected in our experiment and is noncritical. The critical emission corresponds to zero electric field at the emitter. The various calculations have shown that the thermionic electron emission need not be required to be taken into consideration. The total energy transmission factors&dgr;T(=W/FTe, whereWis the energy flux from the plasma,Fis the ion flux, andTeis the electron temperature at the sheath edge) for hydrogen, nitrogen, and argon plasmas are calculated from the estimated secondary electron emission coefficient and the sheath potential, respectively. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364264

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Laser-induced fluorescence was used to characterize the fluorocarbon plasma that was used to modify the wettability of hexatriacontane (HTC), a polymer model. The plasma volume downstream from a microwave plasma source was examined by monitoring the CF2concentration as well as the CF2decay rate (in the afterglow of a pulsed discharge) during treatment of the polymer surface (in 20–100 mTorr CF4). In parallel, the behavior of F atoms was monitored by means of actinometric optical emission. Pulsed modulation of the discharge allowed the effects of variations in the loss and production rates for CF2to be distinguished, in the presence of hexatriacontane. Our observations are consistent with enhanced production of CF2, possibly by an ion-assisted surface mechanism, in the presence of HTC. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364255

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A simple Langmuir probe technique has been used to measure the electron density, electron temperature, and plasma potential in the late stages (>5 &mgr;s) of a laser ablated plasma plume. In the plasma, formed following 248 nm laser irradiation of a copper target, in vacuum at a laser fluence of 2.5 J cm−2, electron densities of ∼1018m−3and temperatures of ∼0.5 eV were measured. These values are comparable with those reported previously using Faraday cup detectors and optical emission spectroscopy, respectively. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364265

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

First-principles atomic cluster calculations have been carried out in the local density approximation to understand the segregation behavior and strengthening effects of boron in Ni3Al. The binding energy of boron is calculated in lattice fragment clusters representing the perfect crystal, as well as various defect sites. The agreement between trends in energetics determined for small clusters and periodic supercells indicates the dominant role of boron’s interaction with nearest-neighbors of the host. The stereochemical factor underlying boron’s preferential bonding to nickel atoms in four-fold planar coordination (i.e.,sp3hybridization) suggests a mechanism for the boron-effect in Ni3Al: increased cohesion provides a driving force for B segregation to open sites, such as at Ni-enriched grain boundary sites, and the strengthening is a result of strong localized Ni–B covalent bond formation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364266

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A semi-kinematic approach to x-ray diffraction of real crystals with small defects is proposed by incorporating an extinction function into the kinematic diffraction formula. The effect of multiple reflections is described by the extinction coefficient which can be calculated by Darwin’s recursion relations. In this approach the intensity of the coherent scattering is related to the static Debye–Waller factor E, while the intensity of diffuse scattering is determined by the correlation function of the distortion field. When E=1, i.e., for perfect crystals, it gives exactly the same result as Darwin’s theory does. The feasibility of this approach is demonstrated by investigating the reciprocal space mapping and the crystal truncation rod of a GaAs crystal. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364285

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The size distribution of Pb inclusions formed by high-dose ion implantation in crystalline Si has been studied with a variety of experimental techniques. Results obtained from small angle x-ray scattering, transmission electron microscopy, and low-temperature magnetic moment measurements are compared. For samples implanted at room temperature, the results depend on which technique has been used, due to the amorphization of the silicon. The experiments on the samples implanted at an elevated temperature yield compatible results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364267

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new method has been developed to determine the surface anchoring strengthWand the tilt &thgr;tof the nematic director from the normal to a curved nematic–air interface. This method is based on the comparison of interference textures obtained by polarization microscopy experiments to numerical simulations of nematic liquid crystals within partially filled cylindrical tubes enforcing homeotropic anchoring. For the nematic liquid-crystal mixture ZLI 2860, we obtain &thgr;t=7°±1°,W=(1.5±0.5)×10−6J/m2at the nematic–tube andW>10−5J/m2at the nematic–air interface. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364268

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A method is described for obtaining ultrahigh time-resolution vibrational spectra of shocked polycrystalline materials. A microfabricated shock target array assembly is used, consisting of a polymer shock generation layer, a polymer buffer layer, and a thin sample layer. A near-IR pump pulse launches the shock. A pair of delayed visible probe pulses generate a coherent anti-Stokes Raman (CARS) spectrum of the sample. High-resolution Raman spectra of shocked crystalline anthracene are obtained. From the Raman shock shift, the shock pressure is determined to be 2.6 GPa. The rise time of shock loading is 400 ps. This rise time is limited by hydrodynamics of the shock generation layer. The shock velocity in the buffer layer is found to be 3.7 (±0.5) km/s, consistent with the observed shock pressure. As the shock propagates through a few &mgr;m of buffer material, the rise time and pressure can be monitored. The rise time decreases from ∼800 to ∼400 ps over the first 6 &mgr;m of travel, and the pressure begins to decline after about 12 &mgr;m of travel. The high-resolution CARS method permits detailed analysis of the vibrational line shape. Simulations of the CARS spectra show that when the shock front is in the crystal layer the spectral linewidths are inhomogeneously broadened by the distribution of pressures in the layers. When the crystal layer is behind the front, the spectral linewidth can be used to estimate the temperature. The increase of the spectral width from the ambient 4 to ∼6.5 cm−1is consistent with the expected temperature increase of ∼200°. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364269

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fluorinated Ti dioxide films were made by reactive sputtering. The mobility of Li, Na, and K in this host was studied by electrochemical techniques. Chronopotentiometry suggested that the cations occupy one type of site for cation/Ti ratios below 0.5, and that other sites are populated at higher ratios. Li and Na intercalation appeared to progress without major structural changes, whereas the intercalation of the larger K ions caused structural rearrangement. Impedance spectra were interpreted within a Randles circuit with a finite length Warburg element from which chemical diffusion coefficients were obtained at different intercalation levels and temperatures. The ion diffusion could be understood in detail from the classical Anderson–Stuart model [O. L. Anderson and D. A. Stuart, J. Am. Ceram. Soc.37, 573 (1954)] as long as the structure remained unchanged, i.e., for the Li and Na intercalation, whereas K intercalation, expectedly, could not be reconciled with this model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364232

出版商:AIP    

年代:1997

数据来源: AIP