摘要:

Materials scientists have struggled for a while to find a process which can be used to engineer individual grain boundaries separating two adjacent grains. Considerable effort has also been devoted to finding a technique that can control the orientation of individual grains. A temperature gradient applied during the chemical vapor deposition of thin copper films provides an effect such that chains of grains oriented in the same direction are produced at chosen positions in the film. As a result of an interaction between defect migration and crystal growth, interconnected grains, oriented in the ⟨110⟩ direction and separated by twin grain boundaries, form chains along contours of equal temperature. When the temperature gradient is small, low-angle tilt boundaries, low-energy coincidence-site boundaries, and twin boundaries are observed. For a sharp temperature gradient, all boundaries are coherent twin boundaries. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120043

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have characterized by transmission electron microscopy (TEM) defect structures in GaN films grown selectively in hydride vapor-phase epitaxy (HVPE). In this experiment, growth was achieved onSiO2-stripe-patterned GaN layers that had been grown by metalorganic vapor-phase epitaxy (MOVPE) on sapphire substrates. Cross-sectional TEM revealed unambiguously that most of the dislocations, which originated from threading dislocations vertically aligned in the MOVPE-grown layer, propagated laterally around theSiO2mask in the HVPE-grown film before the film thickness amounted to about 5 &mgr;m. This change of the propagation direction prevented the dislocations from crossing the film to the surface region and thus principally led to a drastic reduction in the threading dislocation density in thicker films. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120044

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The photoelectron spectra ofSiO2on silicon powder is measured with and without the addition of carbon black. Samples without carbon black show significant charging and peak deformation due to photoelectron emission. Samples containing carbon black show no evidence of charging. Furthermore, the contribution from carbon black can be subtracted from the overall signal in the valence band region to give valence band spectra of insulating powders. It is suggested that mixing carbon black with nonconducting powders may be an effective way to eliminate surface charging effects while at the same time providing a useful calibration standard. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120045

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Monolayer and multilayer ultrathin films comprised of nanosized iron oxide(Fe3O4)particles and polyimide molecules have been fabricated on single crystal silicon and quartz substrates by a novel layer-by-layer electrostatic self-assembly process. This process involves the alternate dipping of a substrate into an aqueous solution of anionic polyimide precursor (polyamic acid salt, PAATEA), followed by dipping into an aqueous solution of polycation polydiallyldimethylammonium chloride (PDDA) which coats on nanoscaleFe3O4particles as a stabilizer. The growth process and the structure have been characterized using UV-vis spectroscopy, contact angle, and ellipsometry measurements. The results suggest that well-ordered uniform monolayer and multilayer magnetic films have been formed on silicon and silica surfaces. A recently developed highly sensitive fiber optic magnetic field sensor was used to probe the small magnetic field intensity produced by the multilayer films. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120046

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A study is reported of the codoping of SrS:Ce by Ag and Cu in order to achieve charge compensation of the trivalent Ce atom. Both Ag and Cu codoping produced a blue shift in the photoluminescence spectra and much higher electroluminescent device performance. These improvements were attributed to the substitutional incorporation of Ag and Cu onto the Sr lattice site which minimized the vacancy formation and provided charge compensation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120047

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A method to prepare silicon nitride nanoscale rods using carbon nanotube as a template has been presented in this letter. The products of the reaction of carbon nanotubes with a mixture of Si andSiO2powder in nitrogen atmosphere are&bgr;-Si3N4,&agr;-Si3N4, andSi2N2Onanorods. The sizes of the nanorods are 4–40 nm in diameter and up to several microns in length. The formation mechanism of the nanorods has also been discussed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120550

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Side chain orientation of polyimide (PI) films for liquid crystal alignment has been studied by surface second-harmonic generation (SHG). SHG from two interfaces of the film was separately observed using thick films, in which SH light from the rear interface was almost absorbed in the film. For as-coated films, the average tilt angle of the side chain at the air-PI interface is smaller than that of the other interface. Rubbing action caused in-plane anisotropy only for the air-PI interface. The distribution function of the side chain of the rubbed PI film was also discussed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120048

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The atomic configurations of segregated B atoms on a highly B-doped Si(001) surface is investigated with scanning tunneling microscopy (STM) observation and first-principle cluster calculation, on which characteristic comb-shape step structures are observed. The characteristic features in the STM image are (1) dark regions in the occupied state, and (2) paired protrusions in the unoccupied state. The calculation shows that models of a B dimer on the top surface and B atoms bonded to two neighboring Si atoms in a dimer row can reproduce STM images well for (1) and (2), respectively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120049

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Structure–property relationship studies have been performed in the La-modified lead zirconate titanate (PLZT) solution as a function of quenched La impurity content and Zr/Ti ratio. For Zr/Ti ratios of90/10and85/15,an incommensurate antiferroelectric state was found to be stabilized with increasing La content. Temperature-dependent investigations demonstrated that the incommensurate structure becomes pinned into long-time metastable states, rather than transforming to a commensurate phase. Also, the modulation wavelength (&lgr;) was found to increase significantly with the decreasing Zr/Ti ratio and decreasing La content. The results of this study clearly demonstrate that the incommensurately modulated polar structures of PLZT are dependent on the relative antiferroelectric/ferroelectric phase stability, and the concentration of quenched La impurities. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120050

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The structure of GaN films grown by hydride vapor phase epitaxy on sapphire substrates has been studied by x-ray diffraction, transmission electron microscopy (TEM), and atomic force microscopy. Films, 15–80 &mgr;m thick, were grown onc-plane sapphire that were either pretreated with GaCl or contained a ZnO sputter deposited layer. The defect density, for both types of films, was found by plan view TEM to range between mid-107to mid-108 dislocations/cm2despite very different structural defects at the film/substrate interface. Nanovoids were found; however, no cracks were observed in the films that were investigated by TEM. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120051

出版商:AIP    

年代:1997

数据来源: AIP