摘要:

The structural sensitivity of x‐ray photoelectron diffraction is greatly enhanced by the acquisition of a full hemispherical diffraction pattern of chemically shifted core levels. Complex systems can be studied resolving the local order per element and per chemical environment. This technique is applied to study the earliest stages of hydrogenated diamondlike carbon film deposition on Si(001). Effects of the sample temperature and ion dose on the structure of deposited layers are discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363110

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A series of diamond films have been grown, all atTsub=1110 K and atomic H concentrations [H]=3×10−10mol/cm3. The acetylene and methyl radical concentrations at the substrate surface were varied independently by factors of up to 4 and 10, respectively, by adjusting the pressure and the input methane concentration, and the effects of these variations on the Raman spectra were examined. The linewidth of the 1332 cm−1diamond feature, thesp2nondiamond carbon feature, and the luminescence yields all increased with increased [CH3]sub, but varying the [C2H2] had no observable impact. A quantitative relationship is provided between thesp2content and [CH3]sub. The luminescence peak, which is the most sensitive feature to [CH3]sub, is due to an impurity from the filament. Using micro‐Raman spectroscopy, large variations are found in the Raman spectra of adjacent crystals and within a single crystal. We attribute these fluctuations to inhomogeneous and anisotropic strains. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363111

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this article, experimental results are presented for the homoepitaxial deposition of a GaN overlayer onto a bulk single‐crystal GaN substrate using molecular beam epitaxy. Transmission electron microscopy shows a superior structural quality of the deposited GaN overlayer when compared to heteroepitaxially grown layers. Photoluminescence shows narrow excitonic emission (3.467 eV) and the very weak yellow luminescence, whereas the bulk substrate luminescence is dominated by this deep level emission. These results show that homoepitaxy of GaN can be used to establish benchmark values for the optoelectronic properties of GaN thin films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363112

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The evolution of surface roughness in epitaxial Si0.7Ge0.3alloys grown on Si(001) as a function of temperature (200–600 °C), thickness (t=7.5–100 nm), and substrate miscut were investigated by atomic force microscopy and quantified in terms of the height‐difference correlation functionG(&rgr;), in which &rgr; is lateral distance and [G(&rgr;→∞)]1/2is proportional to the surface width. The films were deposited by ultrahigh vacuum ion‐beam sputter deposition at 0.1 nm s−1. Strain‐induced surface roughening was found to dominate in alloys grown on singular Si(001) substrates atTs≳450 °C where [G(&rgr;→∞)]1/2initially increases with increasingtthrough the formation of coherent islanding. The islands are preferentially bounded along ⟨100⟩ directions and exhibit 105 faceting. This tendency is enhanced, with much better developed ⟨100⟩ islands separated by deep trenches—of interest for growth of self‐assembled nanostructures—in films grown on Si(001)‐4°[100]. Increasing the film thickness above critical values for strain relaxation leads to island coalescence and surface smoothening. At very low growth temperatures (Ts≤250 °C), film surfaces roughen kinetically, due to limited adatom diffusivity, but at far lower rates than in the higher‐temperature strain‐induced regime. Si0.7Ge0.3alloy surfaces are smoother, while the films exhibit larger critical epitaxial thicknesses, than those of pure Si films grown in this temperature regime. There is an intermediate growth temperature range, however, over which the alloy film surfaces remain extremely smooth even at thicknesses near critical values for strain relaxation. This latter result is of potential importance for device fabrication. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363113

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report the experimental studies ofinsitukinetic thermal annealing process by Raman scattering obtained from very short period Si/Ge superlattices grown on two types of vicinal Si(100) substrates. The experimental results show that the samples grown on double‐stepped vicinal Si(100) substrates have well‐defined in‐plane strain in the epilayers and rather perfect interfaces. The samples grown on single‐stepped vicinal Si(100), on the other hand, appear to have strain‐relaxed and imperfect interfaces. The former is also thermodynamically more stable than the latter, and a suggested explanation is given. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363051

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The annealing behavior of amorphous, hydrogenated silicon carbide films in the range 400–900 °C was studied by optical characterization methods,15N hydrogen profiling, and defect profiling using a variable energy positron beam. The films were deposited in an electron cyclotron resonance chemical vapor deposition system using ditertiary butyl silane [SiH2(C4H9)2] as the monosource for silicon and carbon. As‐deposited films were found to contain large concentrations of hydrogen, both bonded and unbonded. Under rapid thermal annealing in a N2atmosphere, the bonded hydrogen effuses giving rise to additional Si–C bond formation and to film densification. After annealing at high temperatures in N2, a marked decrease in the total hydrogen content is observed. After annealing in vacuum, however, the hydrogen effusion promotes void formation in the films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363049

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Supramolecular self‐assembly of polystyrene–poly(vinylpyridine) diblock copolymers adsorbed from a selective solvent onto smooth substrates was used to create surfaces with regularly varying chemical composition. Well‐ordered arrays of localized chemical reaction sites are formed on such surfaces with sizes and intersite distances of molecular length scales. We demonstrate site‐specific complex formation with transition metal salts resulting in a nanoscopic ordered array of metal salt–polymer complexes. Selective etching of the metal‐loaded microdomains is shown. The effect of block copolymer molecular architecture on the supramolecular structure of these ‘‘chemically functionalized’’ surfaces was studied. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363114

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thin Fe2O3layers (44 and 55 nm) were deposited by pulsed excimer laser ablation on single‐crystal alumina (&agr;‐Al2O3) substrates heated at 675 °C. The ion beam mixing of these &agr;‐Fe2O3/&agr;‐Al2O3couples was carried out using 300 keV Kr3+ions at a fluence of 2×1016ions/cm2. The mixing effect was followed by Rutherford backscattering spectrometry (RBS), conversion electron Mo¨ssbauer spectroscopy, and grazing incidence x‐ray diffraction method. RBS spectra do not show any evidence of mixing at the interface, whereas the data obtained with the two other techniques display phases like oxygen deficient Fe3O4, Fe3−yAlyO4, and Fe1+xAl2−xO4. For this last phase,xis determined as being equal to about 0.5. It is shown that ion beam mixing is more efficient for the thinner Fe2O3layer, in accordance with the projected range of the Kr3+ions. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363115

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Using nonlocal empirical pseudopotentials, we compute the band structure and shear deformation potentials of strained Si, Ge, and SiGe alloys. Fitting the theoretical results to experimental data on the phonon‐limited carrier mobilities in bulk Si and Ge, the dilatation deformation potential &Xgr;dis found to be 1.1 eV for the Si &Dgr; minima, −4.4 eV for the GeLminima, corresponding to a value for the valence band dilatation deformation potentialaof approximately 2 eV for both Si and Ge. The optical deformation potentiald0is found to be 41.45 and 41.75 eV for Si and Ge, respectively. Carrier mobilities in strained Si and Ge are then evaluated. The results show a large enhancement of the hole mobility for both tensile and compressive strain along the [001] direction, but only a modest enhancement (approximately 60%) of the electron mobility for tensile biaxial strain in Si. Finally, from a fit to carrier mobilities in relaxed SiGe alloys, the effective alloy scattering potential is determined to be about 0.7 eV for electrons, 0.9±0.1 eV for holes, and the low‐field mobilities in strained alloys can be evaluated. The results show that alloy scattering completely cancels any gain expected from the lifting of the valleys/bands degeneracy caused by the strain. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363052

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

New upper and lower bounds are constructed for the macroscopic conductivity of polycrystals with random microstructure, given the principal conductivities of the constituent crystals (and the volume fractions of phases in case of a multiphase polycrystal). The new bounds lie inside the well‐known Hashin–Shtrikman ones. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363053

出版商:AIP    

年代:1996

数据来源: AIP