摘要:

Methyl radicals from a methane electron cyclotron resonance plasma are measured quantitatively at the sample position by ionization-threshold mass spectrometry (ITMS). The absolute fluxes are determined by calibrating theCH3ITMS results with those of methane, taking into account the published energy-dependent cross sections for the ionization ofCH3andCH4,respectively. The measuredCH3radical fluxes are on the order of some1015 cm−2 s−1, which is in accordance with recent modeling results. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121713

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report the measured phonon density of states of a bulk GaN powder by time-of-flight neutron spectroscopy. The observed one-phonon excitation spectrum consists of two broad bands centered at about 23 and 39 meV corresponding to the acoustic and the first group of optical phonons; two sharp bands of upper optic modes at about 75 and 86 meV; and a gap of 45–65 meV. The phonon dispersion curves, lattice specific heat, and Debye temperature are calculated from fitting the data with a rigid-ion model. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121714

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The phenomenological model based on the Ginsburg–Devonshire equation has been applied to investigate the size effect in thinSrTiO3andBaxSr1−xTiO3films. The size effect is caused by two phenomena: spatial correlation of the polarization and boundary conditions for the ferroelectric polarization on electrodes. The experimental data obtained by different groups were used to investigate the boundary conditions. The most remarkable result was found for theSrRuO3/BaxSr1−xTiO3/SrRuO3structure which is characterized by free boundary conditions for the ferroelectric polarization. Such boundary conditions provide the highest value of the effective dielectric constant of a dielectric layer in the sandwich structure. The strain dependence of the dielectric permittivity ofSrTiO3at finite temperatures was taken into account as well. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121715

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have utilized the tip of a scanning tunneling microscope to perturb a specific local structure (the C defect) of Si(100) at 80 K, and observed the dynamical symmetric⇔buckled transition of the surrounding dimers. The observed large-scale transition implies that the configuration of the dimers is determined by a detailed balance among many elastic long-range forces generated by the surrounding C defects. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121716

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The stress evolution of sputter deposited Mo/Si multilayers of possible application as extreme ultraviolet light mirrors has been investigated byin situsubstrate curvature measurements using a multiple parallel laser beam technique. Our preliminary results show well-defined stress modulation concurrent with the deposition of Mo and Si layers in the multilayer structure. Large changes in substrate curvature were measured during the early stages of deposition of the individual layers, with Mo exhibiting apparent tension and Si exhibiting apparent compression. The magnitudes of these curvature changes partially offset each other, resulting in an average compressive stress of −350 MPa in the multilayer. Possible stress generating mechanisms during growth of these multilayers as well as single layer films of Mo and Si will be discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121717

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The electron emission yields (&ggr;) from conductive (B doped) and undoped chemical vapor deposited diamond caused by light (protons) and heavy (argon) ion impact were measured as functions of ion dose and energy (40–300 keV). Very large values of &ggr; are obtained for the case of B doped diamond for both ions. Whereas the emission due to Ar is found to decay very rapidly towards the low &ggr; value measured for graphite, it remains persistently very high(&ggr;∼25)for the case of protons, indicating possible application of diamond as a sensitive detector for light ions. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121718

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

InAs quantum dots inserted at the middle of a GaAs quantum well structure have been investigated by transmission electron microscopy and scanning transmission electron microscopy. We find that the growth condition of the overlayer on the InAs dots can lead to drastic changes in the structure of the dots. We attribute the changes to a combination of factors such as preferential growth of the overlayer above the wetting layers because of the strained surfaces and to the thermal instability of the InAs dots at elevated temperature. The result suggests that controlled sublimation, through suitable manipulation of the overlayer growth conditions, can be an effective tool to improve the structure of the self-organized quantum dots and can help tailor their physical properties to any specific requirements of the device applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121719

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electrical activation and dopant diffusion in Zn-implanted InP after rapid thermal annealing have been investigated. For an as-implanted Zn concentration of∼4×1019 cm−3,only ∼7&percent; of the implanted Zn atoms formed electrically active shallow acceptors following a 950 °C/5 s annealing cycle. The low activation was the result of rapid Zn out-diffusion—only ∼14&percent; of the implanted dopant was retained after annealing. A significant enhancement in electrical activation and a reduction in Zn loss were achieved inZn+Pco-implanted samples which yielded a net hole concentration of⩽6×1018 cm−3and >50&percent; Zn retention. The saturation of the free hole concentration inZn+Pco-implanted samples was attributed to the formation of Zn interstitial donors and Group-V-related donor-type native defects. For comparison,Zn+AlandZn+Al+Pco-implanted samples were also examined to distinguish the relative influences of implantation-induced disorder and nonstoichiometry on electrical activation and dopant diffusion. For the given implant conditions, we found that nonstoichiometry was the dominant influence. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121720

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A Ni/GaAs/Si(001) structure was used to investigate solid-phase reactions of Ni with GaAs and Si. Cross-sectional transmission electron microscopy and secondary-ion-mass-spectrometry depth profile data reveal that a Ni/GaAs/Si(001) structure converts to a crystalline GaAs/amorphous NiSi/Si(001) after low temperature (⩽350 °C) annealing. We demonstrate that the reaction is driven by the decomposition of aNixGaAsintermediate which is induced by the proximity of the Si substrate. Two models are suggested to explain the mechanism of a crystalline GaAs layer nucleated fromNixGaAson the amorphous NiSi layer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121721

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Imaging of the surface of a cleavedBi2Sr2CaCu2O8+&dgr;(BSCCO) single crystal with a scanning tunneling microscope reveals a series of repeating terraces, whose separations are then used to identify the atomic planes which are exposed. On each of the exposed planes, the incommensurate modulation is also clearly resolved with atomic resolution. The measured separations between the terraces lead to the deduction that any atomic layer can be exposed by mechanical cleavage of BSCCO. We, therefore, suggest that the identity of atomic planes, and the direction of tunneling, should always be taken into consideration when interpreting tunneling spectra obtained on such cleaved BSCCO crystals. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121722

出版商:AIP    

年代:1998

数据来源: AIP