摘要:

Ceramics in the Al2O3‐WO3system have been produced by laser irradiation. Examination of the products by scanning electron microscopy showed that a cell structure had formed in the specimens. A comparison of the properties of the samples synthesized by laser and by conventional sintering methods showed that the laser technique can produce new materials with some unique properties such as the linear decrease in resistivity of Al2O3‐50 mol % WO3specimens with increasing temperature over the range of 10–150 °C. X‐ray photographic powder analysis indicated that the conducting phase in the specimen is a nonequilibrium product: AlxWO3tungsten bronze.

ISSN:0021-8979    

DOI:10.1063/1.354810

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

X,Y, andZcrystalline cut LiNbO3crystals were implanted by 1.0 MeV F ions with a dose of 1×1015ions/cm.2The virgin and implanted LiNbO3crystals were investigated using the Rutherford backscattering/channeling technique. The obtained minimum yields of virgin crystals were 4%, 8%, and 6% forX‐,Y‐, andZ‐cut LiNbO3crystals, respectively, because of their different arrangements of lattice sites in channeling direction. The measured damage profiles are also influenced by the arrangement of lattice sites in channeling measurements. The damage profiles ofX‐cut LiNbO3crystal induced by 1.0 MeV F+at a fluence range of 1×1014–3×1015ions/cm2have been studied and compared with the Transport of Ions in Matter, version 1990 calculation. It has been found that not only the nuclear energy deposition but also the electronic energy deposition influences the defect production.

ISSN:0021-8979    

DOI:10.1063/1.354811

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The annealing behavior of the reverse bias current‐voltage curves of 1 MeV electron irradiated In0.53Ga0.47As photodiodes has been measured at 300 K. The observed decay is shown to be correlated with the reduction of theE2 peak height with time, as measured by deep level transient spectroscopy. The reverse current is found to decay with a logarithmic time dependence, which can be explained by a model in which the annealing of theE2 defects is controlled by a distribution of thermal energy barriers.

ISSN:0021-8979    

DOI:10.1063/1.354812

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Vacancy‐type defects produced by implantation of MeV doses of Si ions (1011–1015atoms/cm2) at room temperature have been probed using depth‐resolved positron annihilation spectroscopy. The defect (divacancy) concentration increases linearly with dose for low doses (<1012Si/cm2).Insituisochronal annealing was followed for oxygen‐containing Si (10 ppm) and oxygen‐‘‘free’’ Si implanted to doses (5×1012and 5×1014Si/cm2). Two main annealing stages were observed at the same temperatures in the studied samples in spite of significant differences in doses and oxygen content. In the first stage (∼200 °C) a significant fraction of divacancies was observed to form large vacancy clusters. These clusters were removed in the second stage (∼675 °C) after which the oxygen‐free samples returned to pre‐irradiation conditions, whereas oxygen‐defect complexes were formed in the oxygen‐containing samples.

ISSN:0021-8979    

DOI:10.1063/1.354813

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A rate‐dependent constitutive model for the dynamic deformation of ductile materials is developed. The model introduces a physical length scale into the equations governing the progressive failure of materials due to void growth. Consequently, mesh sensitivity or localization problems inherent to rate‐independent models are precluded. The model is implemented into an explicit, finite‐difference computer code. The insensitivity of the model to changes in the mesh size is demonstrated. Comparisons are provided between numerical simulations and data for uniaxial impact experiments. Excellent agreement is established between the final porosity levels and the width of the damage zone. Also, excellent agreement is provided for the stress histories, including the peak stress values and the spall signal.

ISSN:0021-8979    

DOI:10.1063/1.354814

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The artificial viscosity method was originally introduced by Von Neuman and Richtmeyer [R. D. Rchtmeyer and K. W. Morton, inDifferenceMethodsforInitialValueProblem(Interscience, New York, 1967)] to spread the shock over several cells of the mesh. This method is useful if the physical phenomena present in the shock front are not of interest. In some cases, such as polymer, the amount of viscosity is large enough to spread the front shock naturally. In our problem, pseudoviscosity is ignored. A stability analysis shows that the time step restrictions for stability can be less stringent than with pseudoviscosity.

ISSN:0021-8979    

DOI:10.1063/1.354815

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report on the calculation of the total scattering rate in finite barrier GaAs/AlGaAs quantum wires based on the interaction Hamiltonian of confined longitudinal optical (LO) phonon and surface (SO) phonon modes. With multisubband processes being properly taken into account, our calculation indicates that for GaAs type of phonons the high‐frequency symmetric (s+) branch plays an important role among all the other SO phonon branches; it can even dominate over confined LO phonons in highly confined quantum wires as observed by K. W. Kim, M. A. Stroscio, A. Bhatt, R. Mickevicius, and V. V. Mitin [J. Appl. Phys.70, 319 (1991)]. Our results also demonstrate that the total contributions of confined LO and SO phonon scattering resemble closely to GaAs bulk LO phonon scattering. Selection rules between intersubband transitions for SO modes suggest the possibility of a bottle‐neck effect for carrier relaxation in square wires compared with rectangular wires.

ISSN:0021-8979    

DOI:10.1063/1.354816

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Energy‐dispersive x‐ray‐diffraction studies were carried out on the III‐V compound BP to megabar pressures using diamond‐anvil techniques and a high‐energy synchrotron x‐ray source. The BP sample remained stable in its zinc‐blende phase to at least 110 GPa, the upper pressure limit of this experiment. The equation‐of‐state and Birch coefficients of BP were obtained from this experiment. The measured bulk modulus of BP is slightly lower than the value obtained in recent theoretical calculations based on the total energy pseudopotential method within the local‐density approximation.

ISSN:0021-8979    

DOI:10.1063/1.354817

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Reactive magnetron sputtering in a mixed Ar/CH4discharge has been used to deposit 3C‐SiC films on (111)‐oriented Si substrates. The carbon content as well as the crystalline structure was found to depend on both the CH4and Ar pressures. At a total pressure of 3 mTorr and a CH4partial pressure of 0.6 mTorr, epitaxial stoichiometric films were obtained at growth temperatures as low as 850 °C. The epitaxial nature of the films was established by x‐ray diffraction using a combination of reciprocal space maps, texture scans, and 360° &fgr; scans. Based on these analyses it could also be concluded that double‐positioning domains rotated 60° to one another as well as other defects, giving rise to a mosaic broadening in the reciprocal space maps, were present in the films. Furthermore, based on plasma probe measurements and determination of the electron energy distribution functions in the near‐substrate vicinity, the low growth temperature of 850 °C is suggested to be a consequence of an effective decomposition of CH4molecules in the plasma.

ISSN:0021-8979    

DOI:10.1063/1.354818

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effects of 2 MeV H+, B+, O++, and Au++ion irradiation on the adhesion energy of thin Cu films deposited on sapphire has been investigated. Adhesion energy was measured by the observation of the resultant laterally segregated Cu particle shape after vacuum annealing. Film/substrate adhesion is shown to increase with increasing ion dose and exhibits saturation behavior at high fluences. The adhesion energy is shown to be a linear function of the electronic stopping over the entire ion mass range—suggesting a purely electronic mechanism for the adhesion enhancement in this ion energy regime.

ISSN:0021-8979    

DOI:10.1063/1.354819

出版商:AIP    

年代:1993

数据来源: AIP