摘要:

The sheath zone near a plane probe inmersed in an electronegative plasma is analyzed. A theoretical model for the sheath zone was used to derive a new expression for the Bohm criterion. The new expression holds at any negative probe potential. Solving the model equations allows one to obtain a wealth of information including the spatial distribution of various quantities (electric field, potential, and particle densities), the sheath thickness, and the floating potential. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358709

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Nanocrystalline TiN thin films were synthesized by Xe+ion‐beam‐enhanced deposition at room temperature. X‐ray diffraction was used to study different samples prepared by different energy Xe+ions. The results indicated that different ion energies can introduce different phases. Two metastable phases (Ti2N) can be formed at higher Xe+energies than 40 keV. The crystalline phases are dependent on the temperatures in the collision cascades, which are induced by Xe+ion bombardment with different energies. The films were always composed of nanocrystallites. Therefore a lot of surface and interface structures are in the film. The grain sizes grow with the increase of the bombarding ion energy. The effect is caused by the increase of cascade size and local temperature. The lattice parameters are found to increase with the rise of defect concentration and to decrease with the increase of surface structure. These films often have preferential orientation. The relationship between preferential orientation and process parameters is discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358710

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Single crystals of lithium niobate (LiNbO3) withy‐cut orientation were irradiated at GANIL with 5.17 MeV/amu155Gd ions at a fluence ranging from 1.5×1011to 6.0×1011ions cm−2. After irradiation the samples were implanted with europium ions of 70 keV energy at a fixed fluence of 5×1016ions cm−2. Both irradiations and implantations were performed at room temperature. Thermal treatments in air, in the range 300–1100 °C, were applied to investigate the influence of the preirradiation damage on the thermal evolution of Eu implanted LiNbO3crystals. Transmission electron microscopy micrographs exhibit the amorphous track formed by high‐energy irradiations. Rutherford backscattering spectrometry results show that these amorphous tracks enhance the europium diffusion in depth of the LiNbO3. A diffusion coefficient and an activation energy were estimated to be about 4.2×10−15cm2 s−1and 0.42 eV, respectively. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358711

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Fibrous and crystal structures of a helical polymer, poly‐L‐lactic acid (PLLA), were analyzed by using x‐ray diffraction experiments. It was confirmed that the molecular residues were arranged on a nonintegral 10/3 helix as De Santis and Kovacs [Biopolymers6, 299 (1968)] reported. The atomic positions in a monomeric unit, which were proposed by Hoogsteen, Postema, Pennings, ten Brinke, and Zugenmaier [Macromolecules23, 634 (1990)], were validated. However, the previous reports on the positions of the two helical chains were found to be in error. The correct positions were determined. The second helical chain shifts from the base center by 0.45, 0.25, and 0.61 A˚ alonga,b, andcaxes. Besides, the second chain rotates by 2.46° with respect to the first. Distribution function of the crystallites in various drawn fibers were determined as a function of spiral angle. Optical gyrations of PLLA and poly‐D‐lactic acid fibers were successfully measured by using high accuracy universal polarimeter, as functions of temperature and drawing ratio. By using x‐ray data of the change of the fibrous structure by drawing treatments, the gyration tensor components of PLLA could be calculated. It is of great interest that gyration tensor componentg33along the helical axis is extremely large, ∼(3.85±0.69)×10−2, which corresponds to a rotatory power of (9.2±1.7)×103°/mm, about two orders of magnitude larger than those of ordinary crystals. This is the first experimental evidence that helical polymers will produce enormous optical activity in the solid state. Helical polymers will be important for the elucidation of gyro‐optical properties of solids and promising for new optical applications utilizing their large optical activity. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358712

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The lattice parameters of heavily boron doped silicon homoepitaxial layers before and after rapid thermal annealing at different temperatures (800–1100 °C) are characterized by x‐ray double crystal diffraction. The results illustrate that although the strain relaxation occurs after the rapid thermal annealing (RTA) treatment, the improvement of the crystalline quality of epitaxial layers are observed at RTA temperatures higher than 1000 °C. The proportional relationship between the lattice mismatch and the substitutional boron concentration with the lattice contract coefficient &bgr;=5.3 (in units 10−24cm3) is valid up to the concentration of 3×1020cm−3. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358713

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

High‐dose carbon‐ion‐implanted Si samples have been analyzed by infrared spectroscopy, Raman scattering, and x‐ray photoelectron spectroscopy (XPS) correlated with transmission electron microscopy. Samples were implanted at room temperature and 500 °C with doses between 1017and 1018C+/cm2. Some of the samples were implanted at room temperature with the surface covered by a capping oxide layer. Implanting at room temperature leads to the formation of a surface carbon‐rich amorphous layer, in addition to the buried implanted layer. The dependence of this layer on the capping oxide suggests this layer to be determined by carbon migration toward the surface, rather than surface contamination. Implanting at 500 °C, no carbon‐rich surface layer is observed and the SiC buried layer is formed by crystalline &bgr;‐SiC precipitates aligned with the Si matrix. The concentration of SiC in this region as measured by XPS is higher than for the room‐temperature implantation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358714

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The deep level transient spectroscopy technique has been used to study the EL2 defect inn‐type semiconducting GaAs subjected to 1 MeV fast neutrons at room temperature. After neutron irradiation, the EL3 defect which is usually detected between 180 and 210 K disapperared and the EL2 defect measured between 280 and 320 K was found to remain single exponential (Ec−0.820 eV) despite the creation of a broadUband measured between 100 and 270 K. From this result, together with our earlier reports on the double exponential capacitance transient of the EL2 defect after 1 MeV electron irradiation [Lai, Nener, Faraone, Nassibian, and Hotchkis, J. Appl. Phys.73, 640 (1993)] and the behavior of the electron irradiated EL2 defect upon isochronal annealing [Lai and Nener, J. Appl. Phys.75, 2354 (1994)], we observe a difference in the behavior of the EL2 defect after neutron and electron irradiation. The results of the present study indicate that the EL2‐B level reported in an earlier work is not due to any interaction of the stable EL2 (or EL2‐A) level with either theU‐band or EL6 defect. The EL2 defect is likely to be a complex defect which can manifest itself as a number of different defect levels depending on the particular details of the irradiation used. TheUband is likely to be a cluster defect caused by the large number of atoms displaced from lattice sites by the fast neutrons, and is not likely to be due to any interaction mechanism between the EL2 and EL6 defects. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358715

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Distribution of light‐induced defect states in undoped amorphous silicon has been studied by using the modulated photoconductivity spectroscopy technique. The experimental results show that a large increase of the neutral defect states occurs, and the positively charged defect states grow particularly in the midgap energy range. The qualitative features of the measured energy distribution agree well with the theoretical prediction from the current defect formation model, although a quantitative comparison with respect to the magnitude of density‐of‐states reveals a discrepancy between theory and experiment. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358716

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effect of energetic particle bombardment during sputter deposition on the physical (magnetoresistance and interlayer coupling) and microstructural (roughness and interface thickness) properties of exchange‐biased spin‐valve multilayers is investigated. An increasing pressure leads, through enhanced stopping of energetic particles by collisions with the background gas, to a decrease of the interfacial intermixing by collisions during growth, and to a more rough, void‐rich structure. These microstructural changes lead to an increase of the transmissivity of the interfaces for conduction electrons, as well as to an increase of the ferromagnetic interlayer coupling with increasing pressure. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359565

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Amorphization of 6H‐SiC with 200 keV Ge+ions at room temperature and subsequent ion‐beam‐induced epitaxial crystallization (IBIEC) with 300 keV Si+ions at 480 °C have been studied by Rutherford backscattering spectrometry/channeling and transmission electron microscopy analysis. Experimental results on amorphous layer thicknesses have been compared withtrimcalculations in association with the critical energy density model. Density changes during amorphization have been observed by step height measurements. Particular attention has been directed to the crystal quality and a possible polytype transformation during the IBIEC regrowth. The IBIEC process consists of two stages and results in a multilayer structure. In the initial phase an epitaxial growth of 6H‐SiC has been obtained. With increasing IBIEC dose the epitaxial growth changes to columnar growth and is stopped by polycrystallization of 3C polytype in the near‐surface region. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358649

出版商:AIP    

年代:1995

数据来源: AIP