摘要:

In SF6gas at 5–30 Torr, self‐breakdown spark discharges starting in a constricted phase expanded spatially when the discharge current decayed to a critical value. The strength of the electric field increased from 400 to 2×103Td inE/N, where 1 Td=10−21V m2, whereEis the electric field andNis the neutral gas number density. At the same time, the optical emission from the spark increased in strength and ionization instabilities started to grow. In the decay phase of SF6spark discharge, negative ions strongly enhanced electron diffusion in the multipolar diffusion that resulted in the expansion and the excitation of ionization instabilities.

ISSN:0021-8979    

DOI:10.1063/1.354874

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Self‐consistent nonequilibrium fluid models of both the two‐dimension (2D) and one‐dimension (1D) are presented. In the 2D simulations, the models evaluate the quantitative effects of both radial and axial flow dynamics inside a cylindrically symmetric parallel‐plate geometry. The 1D model assumes that the radius of the electrode is much larger than the electrode gap and the moment distributions are uniform along the radial direction. The models are based on the first three moments of the Boltzmann equation and Poisson’s equation. Radio frequency (rf) glow discharge simulations from those two fluid models are presented and compared in this study. The comparisons are presented in terms of plasma density, electric field, mean energy, and ionization rate. Results of the 1D fluid model are close to those at the center of the reactor from the 2D simulations. Nonuniform profiles along the radial direction are obtained from the 2D simulations due to the radial dynamics. Higher electron mean energy in the middle region of the radial sheath is observed. The maximum ionization rate is located in the radial sheath region and agrees with the experimental observation.

ISSN:0021-8979    

DOI:10.1063/1.354875

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

With the use of both a movable magnetic filter and a plasma grid, plasma parameters (H2‐CH4or Ar‐CH4plasmas) are spatially well controlled. At any filter position, plasma parameters change steeply across the magnetic filter. Then, a plasma source is divided into the two parts, i.e., the source plasma region (high density plasma with energetic electrons) and the diffused plasma region (low density and low‐temperature plasma without energetic electrons). Plasma parameters in the diffused plasma are well controlled by changing the plasma grid potential. The role of the magnetic filter (i.e., preferential reflection of energetic electrons) is well clarified by computer simulation. The relation between plasma parameters and some species of neutral radicals is also briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.354876

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Large particles (tens of nm to tens of &mgr;m in diameter) are problematic in low‐pressure (<1 Torr) plasma processing (etching, deposition) discharges because they can contaminate the product and can perturb electron transport. Although the source of these particles has been studied by a number of groups, a definitive explanation is still lacking. In this paper, we theoretically investigate the role of negative ions in the formation of large clusters, the precursors to particles, in low‐pressure plasmas. We find that the formation of particles requires a critically large cluster. Forming the critically large cluster requires longer residence times in the plasma than is usually possible if clustering involves only neutral particles. We propose that negatively charged intermediates, which are trapped in electropositive plasmas, increase the average residence time of clusters to allow the growth of critically large clusters.

ISSN:0021-8979    

DOI:10.1063/1.354877

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The temporal behavior of the cathode sheath in 30 kHz 0.4–1 Torr H2discharges has been investigated by optical emission spectroscopy. Analysis of the Stark splitting of plasma‐induced H Balmer delta emission was used to measure the electric field with spatial and temporal resolution in the instantaneous cathode sheath. The location of the plasma/sheath boundary was determined from the position of the maximum of the H2d 3&Pgr;u→a 3&Sgr;g+(0,0)Q1emission at 622.5 nm. Both methods showed that the sheath width increases as the cathode voltage becomes more negative, whereas the width remains constant as the applied voltage drops off. Analysis of the electric‐field profile provided information on the time evolution of the ion density close to the electrode during the cathode half‐cycle, in agreement with recent numerical calculations. At the beginning of the anodic half‐cycle an intense flash of plasma‐induced emission was observed, localized within 3 mm from the electrode.

ISSN:0021-8979    

DOI:10.1063/1.354878

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Swift heavy ion irradiation‐induced defects have been studied inn‐type germanium at room temperature using deep level transient spectroscopy. Several electron traps have been observed after irradiation. The corresponding energies have been determined to be atEc−0.22,Ec−0.275,Ec−0.29,Ec−0.32, andEc−0.465 eV. The isochronal annealing behavior of these traps has been studied in detail between room temperature and 200 °C. Comparison of our results with previously published ones allowed an identification of these defects with complexes like divacancies or associations of vacancies with impurities.

ISSN:0021-8979    

DOI:10.1063/1.354879

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

X‐ray photoelectron spectroscopy has been used to study the surface composition and chemistry of two perovskites: SrTiO3and Pb(Zr,Ti)O3(commonly known as PZT). It is seen that ion bombardment, which is a common surface modification technique, can cause substantial changes in these oxides. The PZT surface undergoes surface depletion of lead along with chemical reduction of the Pb2+ion to its metallic state. The Zr/(Ti+Zr) ratio also changes with sputtering, but the total oxygen to cation ratio is unchanged. On the other hand, the surface stoichiometry of SrTiO3is almost unaffected by ion bombardment. In all the perovskites, irrespective of whether the composition changes or not, a substantial amount of surface Ti is reduced to a lower valency state on sputtering. Most of this component is restored back to the original Ti4+state when Ni is evaporated on these surfaces, indicating that the reduced state is associated with a damaged outermost surface that can be repaired with an adsorbate. The implication of these results to the bonding properties of these materials have been discussed.

ISSN:0021-8979    

DOI:10.1063/1.354880

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Hollow glass fibers can guide x rays because glancing‐angle collisions with a smooth glass surface are highly reflective. Surface roughness decreases this reflectivity. We have developed relatively simple expressions for the effects of surface roughness on x‐ray scattering, and we relate our results to the theoretical efficiency of x‐ray lenses formed from bundles of hollow glass fibers.

ISSN:0021-8979    

DOI:10.1063/1.354881

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Positron lifetime spectroscopy and two‐dimensional angular correlation of annihilation radiation have been used to investigate grown‐in vacancy structures in synthetic crystalline &agr;‐SiO2, synthetic fused quartz, and in a 60‐&mgr;m‐thick chemical‐vapor‐deposited amorphous SiO2film. For &agr;‐SiO2a ∼300 ps lifetime component suggests trapping by either silicon monovacancies or by oxygen divacancies (or both). The vacancies are neutral and present at a concentration level of 1017/cm3. The positron bulk lifetime for &agr;‐SiO2is estimated to be ∼238 ps in good agreement with semiempirical predictions. In the fused quartz significant positronium formation is found (80%) and the remaining positrons annihilate in voids yielding a lifetime of ∼500 ps. The amorphous SiO2film contains a mixture of small vacancy clusters and voids and ∼30% of the positrons form positronium. Heat treatment above 950 °C results in a substantial reduction in defect concentration, but up to 1100 °C a small vacancy cluster contribution persists. The positron data indicate that positronium formation in the fused quartz and in the amorphous film takes place in the voids.

ISSN:0021-8979    

DOI:10.1063/1.354882

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Thin amorphous Si1−xBxfilms, withx0ranging from 0 to 0.5, were coevaporated onto preoxidized (100) Si wafers and quartz substrates, by using a dual‐electron‐gun high‐vacuum system. In order to study how the structural and optical properties depended on concentration and annealing temperature, heat treatments of the films were carried out at temperatures from 400 up to 1000 °C. The films were characterized by means of transmission electron microscopy, Auger electron spectroscopy, and spectrophotometry. It is shown that: (i) An amorphous Si1−xBxalloy can exist up to very high temperatures (≥1000 °C), whenxis larger than ∼0.4; (ii) at 400 °C the optical band gap of an amorphous Si1−xBxalloy has the maximum value (1.59 eV) forx0=0.02 and then decreases to lower values for higher concentrations (e.g., 1.18 eV forx0=0.3); (iii) the measured optical band gap of amorphous Si1−xBxincreases gradually with increasing annealing temperature up to 700–900 °C, and then increases rapidly when annealed at a higher temperature by about 0.5 eV. These changes can be associated with microstructural alterations. The stable amorphous Si1−xBxalloy withx0=0.3 has, for instance, a measured band gap of 1.23 and 1.74 eV after annealing at 800 and 900 °C, respectively. The relationship between the microstructure and the band gap of the films is discussed.

ISSN:0021-8979    

DOI:10.1063/1.354883

出版商:AIP    

年代:1993

数据来源: AIP