摘要:

High resolution electron microscopy has been applied to characterize the structure of &bgr;-GaN epilayers grown on (001) GaAs substrates by plasma-assisted molecular-beam epitaxy. An rf plasma source was used to promote chemically active nitrogen. An exposure of the layer surface to the As flux during the growth of the first few monolayers was shown to result in remarkably flat GaN–GaAs interface. The best quality GaN layers were achieved by near-stoichiometric nucleation with optimal Ga-to-N ratio. Deviation from these nucleation conditions leads to interface roughening and formation of the wurtzite phase within the GaN layer. All the layers contained a high density of stacking faults near the interface which sharply decreases toward the surface. Stacking faults were anisotropically distributed within the GaN layer probably due to different properties of &agr; compared to &bgr; dislocations in cubic GaN. The majority of stacking faults intersect the interface along lines parallel to the major flat of the GaAs wafer. The stacking faults are often associated with atomic steps at the GaN–GaAs interface. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120219

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A simple technique for size-controllable nanostructure array formation has been developed, using self-assembled polystyrene beads whose diameters can be arbitrarily reduced by reactive ion etching. We have produced a hole array of 83 and 157 nm diameter with 200 nm pitch on Si substrate. This technique can find potential applications in many areas of science and technology. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120220

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed a procedure for atomic scale alignment with respect to macroscopic objects. Metallic and etched registration marks on clean reconstructed Si surfaces are used to guide the tip of a scanning tunnelling microscope. The metallic marks are formed from Ta and can withstand thermal cycling up to 1500 K. These procedures have been used to investigate the interaction of Ag with a patterned fullerene multilayer deposited on Si(111)-7×7.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120221

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Surfactant stabilized gold clusters have been deposited on graphite and studied with scanning tunneling microscopy in vacuum. Cluster layers with a superlattice constant of≈31 Åwere found, extending over several micrometers. The clusters form a hexagonal lattice which is ordered over distances of about 100 Å. At low sample biases(<0.75 V)the clusters are not imaged, consistent with a Coulomb blockade effect. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120222

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of electron beam irradiation on morphology of plasma deposited amorphous hydrogenated carbon-germanium films produced from tetramethylgermanium in a three-electrode af reactor has been studied. It has been found that the insulating films are insensitive to this treatment, whereas a crystalline phase occurs in the semiconducting films. Although the molar content of germanium in these films amounts only to about 0.2, the crystalline phase is composed of pure germanium nanocrystals which contain about 70&percent; of the whole amount of germanium existing in the films. The nanocrystals are agglomerated in globules of 50–500 nm in diameter. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120223

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The microstructure of phased-in Cr–Cu/Cu/Au multilayer thin films and their solderability with high Pb-content PbSn solder(95/5&percent;)and eutectic PbSn solder(37/63&percent;)were studied by using cross-sectional transmission electron microscopy and scanning electron microscopy. We found that the phased-in Cr–Cu layer is intermixed and grains of both Cr and Cu are elongated along the growth direction. This special compositionally graded or functionally graded microstructure presents a lock-in effect of the Cr and Cu grains. It has succeeded in preventing the spalling ofCu3Snin solder joints formed using the95/5&percent;solder, but failed in preventing the spalling ofCu6Sn5in those formed using the eutectic solder. We suggest that the difference may be due to the different dissolution rates of the two compounds in the solders. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120224

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate a technique for experimentally determining stresses in crystalline thin films without any knowledge of the elastic properties of the thin film material. The results are obtained from interplanar spacing versussin2 &PSgr;plots for different stress states. The interplanar spacings are measured by non-symmetric x-ray diffraction. The different stress states are produced by annealing the thin film/substrate samples at elevated temperatures in air and by cooling them in liquid nitrogen. Poisson’s ratio for isotropic films or a similar quantity for anisotropic films can be found through the use of this technique. An extension of this technique also permits the measurement of the coefficient of thermal expansion without removing the film from the substrate. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120225

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Biaxially aligned praseodymium oxide(Pr6O11)thin films were prepared by ion-beam assisted laser deposition on mechanically polished metal alloy substrates. A low divergence rf plasma source was used as an assisting source. Deposited films showed (001) oriented film growth with a strong biaxial alignment in the film plane. The degree of in-plane orientation dependent on ion-to-atom ratio and ion bombardment angle was studied. Planar ion channeling along the {110} planes is used to explain the observed alignment features. At an ion-to-atom ratio of 0.17 and an ion incident angle of 60°, in-plane orientations of 16° full width at half-maximum were obtained. Due to the low lattice mismatch (0.3&percent;) toYBa2Cu3Oxfilms, the material could be an alternative to theYSZ/CeO2buffer layer system currently used for high critical current carrying superconducting tapes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120226

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the growth of in-plane textured (100) MgO on amorphousSi3N4substrates by ion beam assisted deposition (IBAD). The textured MgO can be used as a structural template for subsequent epitaxial thin film deposition. The results are compared with IBAD of (100) and (111) yttria-stabilized-zirconia (YSZ). Based on transmission electron microscopy (TEM) andin situreflection high energy-electron diffraction (RHEED), we find that MgO texturing is a nucleation-controlled process and the alignment is a function of nuclei size and density. This differs greatly from the evolutionary-type texturing process observed for IBAD (100) YSZ. Consequently, we are able to make 100 Å thick MgO films with 7° in-plane alignment, whereas IBAD (100) YSZ films need to be thicker than 5000 Å to achieve in-plane alignment better than 13°. This has important implications for the economical application of IBAD induced alignment in real manufacturing processes, including highTcsuperconductor (i.e., YBCO) coated tapes, photovoltaics, magnetic thin films, and semiconductor devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120227

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The split-gate concept has been applied to dual-gate high electron mobility structures for room-temperature operation. The gates are configured so that the second gate is in close proximity to the gap defined by the split-gate electrodes. This allows both gates to control the carrier density in the same region of the device, so that it is possible to control the threshold voltage for either gate by altering the bias at which the other gate is held. The effect of changing the gate configuration is demonstrated. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120228

出版商:AIP    

年代:1997

数据来源: AIP