摘要:

The growth kinetics of diamond films deposited at low substrate temperatures (600–400 °C) from the carbon–hydrogen gas system have been studied. When the substrate temperature alone was varied, independently of all other process parameters in the microwave plasma reactor, an activation energy in the order of 7 kcal/mol was observed. This value did not change with different carbon concentrations in hydrogen. It is supposed that growth kinetics in this temperature range are controlled by a single chemical reaction, probably the abstraction of surface bonded hydrogen by gas phase atomic hydrogen. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118348

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have combined computer simulations and atomic-resolution tunneling microscopy to investigate the kinetics of defect migration during annealing of ion implanted Si(111)-7×7. Using atomically-clean and flat surfaces as sinks for bulk point defects introduced by the irradiation, we observe distinct, temperature-dependent surface arrival rates for vacancies and interstitials, and we demonstrate that the distinct kinetics of each type of bulk point defect govern their surface segregation kinetics. A combination of simulation tools provides a detailed description of the processes that underlie the observed temperature-dependence of defect migration. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118349

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thick films of polycrystalline GaN were grown at low pressures by direct reaction of atomic nitrogen with liquid Ga without the presence of a substrate. The crystals were confirmed to be wurtzitic GaN by x-ray diffraction, transmission electron microscopy, Raman spectroscopy, and elemental analysis. Photoluminescence spectra showed near band edge peaks and broad yellow band emission at both 298 and 10 K. The results show that atomic nitrogen is an attractive alternative to high pressureN2for the saturation of liquid gallium with nitrogen for the synthesis of bulk GaN. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118350

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

During ion beam sputter deposition besides the deposited atoms, which reach the substrate with kinetic energies in the 10 eV range, a certain amount of energetic particles also hit the substrate. These particles which have been reflected or sputtered at the target represent only a small fraction of the atoms reaching the substrate, but have energies of the order of the sputtering beam. The influence of these particles on the island formation of Pt films on a Pt(111) surface has been examined by variation of the deposition geometry, the primary ion energy, and the substrate temperature. It is demonstrated that the main effect is a dramatic increase in island density. The experimental results are in quantitative agreement with the results of a newly developed computer code. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118351

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Diamond growth was studied by injecting thermally decomposed Cl atoms intoCH4/H2orC2H2/H2. Owing to the extremely short residence time (25 &mgr;s) and low gas temperature (<1000 °C) in the decomposition system, the gas reaction is insignificant. Therefore, the carbon species near the substrate surface can be nearly identical to the input carbon source. With 0.3&percent;CH4being the input carbon source,CH4remained the dominant carbon species near the surface (only 2.5&percent;C2H2was formed), and an almost continuous diamond film was deposited after 2 h growth. Raman spectra confirmed the formation of diamond. With 0.15&percent;C2H2being the input carbon source,C2H2remained the dominant carbon species near the surface (10&percent;CH4was formed), but only a few very small particles were deposited. Therefore, we conclude thatCH3radicals seem the only diamond growth precursor under the Cl-rich conditions, whereasC2H2is not efficient to grow diamond. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118352

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nuclear magnetic resonance of29Si is used to study structural properties of porous silicon and siloxene. Evidence for changes in the chemical shift of porous silicon due to quantum confinement could not be observed. A hydride phase exhibiting a chemical shift of −75 ppm versus tetramethyl silane (TMS) is found in both porous silicon and siloxene. In as-prepared Wo¨hler siloxene, a chemical shift of −83 ppm versus TMS is assigned to threefold coordinated Si atoms forming a planar polysilane. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118199

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a nuclear-magnetic-resonance (NMR) study of the structure of porous silicon. Cross-polarization–magic-angle-spinning29Si NMR shows that the silicon crystalline structure is preserved in porous silicon and that there are three protonated silicon species at the surface, which are tentatively identified as belonging to different faces. The occurrence of different environments for the surface protons is supported by the heterogeneous1H NMR line. HF andSiF62−species were detected by19F NMR in the electrolyte left in the pores. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118382

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Previous treatments of void shape evolution during electromigration have been restricted to nonsingular void surfaces. We consider the lateral spreading of a void when its leading surface is a singular facet. The facet may nucleate at the leading surface of a void migrating within one grain or may develop when a singular surface is exposed by impingement of the void at a (transverse) grain boundary. Advance of the facet requires a source of steps that we assume to be absent; void spreading results. A stationary void shape is possible when a dimensionless parameter is less than a critical value (estimated), whereas above this value the void spreads indefinitely. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118353

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The stability and electronic properties of compositeBxCyNznanotube heterojunctions were studied using bothab initioand semi-empirical approaches. C/BN andBC2N/BNsuperlattices or isolated junctions were investigated as specific examples of the wide variety of electronic devices that can be realized using such nanotubes. The characteristics of these junctions are predicted to be largely independent of the radius, helicity, multiplicity, or degree of perfection of the constituting nanotubes. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118354

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A technique of carbon film synthesis based on an electrochemical process was developed. A solution of acetylene in liquid ammonia was employed as the electrolyte. Films were deposited at the metallic anode. Two types of films were produced. Films of type I are transparent and fragile, whereas those of type II are black and plastic. The films were investigated by the electron diffraction method and Raman spectroscopy. The electron diffraction data for type I films demonstrate the films’ high degree of crystallinity. Values of lattice plane spacings agree with data on cubic diamond modifications. The Raman spectrum of type I films shows a line at 1334cm−1(full width at half-maximum equal to 15cm−1),inherent in that of diamond and an essentially amorphous carbon component. Spectra of the type II films do not feature the Raman peak of diamond. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118355

出版商:AIP    

年代:1997

数据来源: AIP