摘要:

Recent experiments have identified the microstructure of amorphic diamond with a model of packed nodules of amorphous diamond expected theoretically. However, this success has left in doubt the relationship of amorphic diamond to other noncrystalline forms of carbon. This work reports the comparative examinations of the microstructures of samples of amorphic diamond,i‐C, and amorphous carbon. Four distinct morphologies were found that correlated closely with the energy densities used in preparing the different materials.

ISSN:0021-8979    

DOI:10.1063/1.352168

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Time‐of‐flight (TOF) direct recoiling (DR) studies of borazine (B3N3H6) decomposition on the Si(100) surface between 100 and 850 °C are reported. The DR method with a grazing incidence angle directly detects the diffusion of light adsorbate elements into sites below the first Si layer, and this migration process is examined here as a function of temperature (T). Submonolayer coverages of coadsorbed B and N atoms (from B3N3H6) occupy subsurface sites after annealing above 550 °C. The B + N results are compared with the well‐studied N atom (from NH3) case and limited data for boron from B10H14. The atomic composition of the initial growth surface during thermal chemical vapor deposition (CVD) of boron nitride (BN) from B3N3H6is surveyedinsituas a function ofTusing DR in a B3N3H6flux of 4×1016molecules cm−2 s−1. Desorption of surface hydrogen plays a central role in controlling both the submonolayer diffusion effects and thermal CVD growth of BN.

ISSN:0021-8979    

DOI:10.1063/1.352169

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Porous layers formed inn‐type silicon are characterized by pores of square cross section oriented perpendicular to the (100) plane. The pore walls are defined by the {011} planes in the [100] zone with secondary pores propagating from the main pores in the ⟨010⟩ and ⟨001⟩ directions. The pores are located in an array with a characteristic spacing. The characteristic pore morphology during stable pore propagation is explained in terms of a tunneling mechanism due to a high‐field region created by the curvature at the pore front. The pore spacing is determined by the distance at which the region between the pores becomes fully depleted.

ISSN:0021-8979    

DOI:10.1063/1.352123

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Bipolar membranes consist of a layered ion‐exchange structure composed of a cation selective membrane joined to an anion selective membrane. They are analogous to semiconductorp‐ndevices as both of them present current‐voltage curves exhibiting similar rectification properties. In this article, we present some current‐voltage curves obtained for different bipolar membranes at several temperatures. The results can be interpreted in terms of a simple model for ion transport and field‐enhanced water dissociation previously developed. The mechanism responsible for water splitting is assumed to be a catalytic proton transfer reaction between the charged groups and the water at the membrane interface. The effects of temperature are taken into account by introducing an Arrhenius‐type relationship for the dependence of the forward rate constant of the reaction on temperature. Finally, comparison between theory and experiments provides reasonable values for the parameters introduced in the theoretical model. The analysis aims at developing a better physical understanding of a process in which chemical reactions and transport phenomena are coupled in such a way that the potential technological applications depend strongly on this coupling.

ISSN:0021-8979    

DOI:10.1063/1.352124

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A closed‐form solution is developed for the induction heating of an infinitely long cylindrical load by periodic circular current sheets. The wave equation is solved and various field quantities are obtained. An equivalent surface current is defined that enables studying the axial distribution of the induced current in the load. The power loss in the conducting load is derived and its dependence on different coil‐load configurations and characteristics is shown. The problem of multicoil systems, where coils can be of different sizes and carry different currents and frequencies, is addressed.

ISSN:0021-8979    

DOI:10.1063/1.352125

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In an attempt to pattern microbridges in a superconducting line by focused ion beam milling, we have obtained a very high critical current density: 6 × 108A/cm2at 77 K. Direct focused ion milling leads to microbridge structures as narrow as 200 nm. Ultrahigh current densities have already been reported by H. Jiang [Phys. Rev. Lett.66, 1785 (1991)] in such ‘‘nanobridges.’’ We have also measured size‐dependent critical current densities. We take into account the electrical field criterion and give a very simple interpretation of our experimental results based on the possibility of strong pinning in a very narrow bridge and the inhomogeneity of our films at a submicronic scale.

ISSN:0021-8979    

DOI:10.1063/1.352126

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We discuss the characteristics of impurity band conduction detectors prepared from epitaxial Si:Sb. These detectors are sensitive to infrared light at wavelengths between 2.5 and 40 &mgr;m and outperform the current state‐of‐the‐art Ge:Be photoconductors for this wavelength range by a combination of a peak responsivityR=32 A/W, low noise equivalent power (NEP) =1.1×10−15W/Hz1/2(at a flux of 1012ph/cm2 s), inherently low sensitivity to cosmic ray particles, and freedom from the anomalous behavior observed in photoconductors.

ISSN:0021-8979    

DOI:10.1063/1.352127

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Si delta‐doped In0.15Ga0.85As/GaAs strained quantum wells are demonstrated by atmospheric pressure metalorganic chemical vapor deposition. The samples were characterized by variable temperature Hall effect, high magnetic field magnetoresistance, quantum Hall effect, capacitance‐voltage measurements (C‐V), and secondary‐ion mass spectroscopy. TheC‐Vprofile showed a full width at half maximum as narrow as 15 A˚. Two‐dimensional electron gas transport was verified by observing step‐like structures in the quantum Hall effect in samples containing sheet densities less than 5×1012cm−2. Sheet densities as high as 1.0×1013cm−2were achieved. C and O contamination were not observed during the Si delta‐doping process.

ISSN:0021-8979    

DOI:10.1063/1.352128

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We investigated a band gap shrinkage in both lattice‐matched and compressive strained GaInAs/GaInAsP/InP multi‐quantum well lasers. The band gap shrinkage is obtained from the broadening of the low energy side in the spectrum by considering effects of an intraband scattering and a fundamental band edge. It amounts to 20–25 meV at sheet carrier densities of above 1012cm−2, and showsn1/1.3dependence at low carrier densities andn1/3dependence at higher densities. These dependencies agree well with theoretical predictions in the quantum well.

ISSN:0021-8979    

DOI:10.1063/1.352129

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The effects of hydrogen dilution on the properties and structure of silicon nitride films deposited by plasma‐enhanced chemical vapor deposition from NH3/SiH4mixtures were studied. The addition of relatively small amounts of hydrogen at a fixed NH3/SiH4ratio increased the excess Si in the film with a corresponding increase in the Si—H/N—H bonding ratio. At higher dilution [H2/(NH3+SiH4)] the films became more stoichiometric with significant changes in the hydrogen bonding. Decreases in the etch rate and refractive index with increasing hydrogen flow are discussed in terms of the changes in bonding structure and were found to be well correlated to changes in the Si—N bond density.

ISSN:0021-8979    

DOI:10.1063/1.352130

出版商:AIP    

年代:1992

数据来源: AIP