摘要:

Spatial distribution of electric field strength in the cathode fall region of an analytical glow discharge in helium and helium-hydrogen mixture is determined from the Stark splitting and shifting of three visible helium lines and their forbidden components. For this diagnostic technique the basic theory is outlined. The results in gas mixture agree well with electric fields determined from the shape ofH&bgr;line. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118606

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two-photon absorption cross sections of two dye molecules, doped in thin films of polymethylmethacrylate, are measured by comparing fluorescence intensities induced by single- and two-photon excitations. Ratio of the single- and two-photon absorption cross sections is related to the ratio of the single- and two-photon pumped fluorescence intensities. Using this sensitive and background-free detection technique, dispersion of the nonlinearity is measured over a wavelength range of 700–800 nm. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118638

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A low temperature process(350 °C<T<500 °C) for nanocrystalline diamond film growth by microwave plasma-enhanced chemical vapor deposition has been developed that yields high rates (up to 2.5&mgr;m/h) at relatively low plasma powers (0.5 kW). In contrast to the widely used H2-rich mixtures of CH4or CO and H2that exhibit monotonic decreases in the diamond growth rate asTis reduced from 800 to400 °C, CO-rich mixtures of CO and H2exhibit an increase and sharp maximum asTis reduced. The results suggest a different diamond growth mechanism from the CO-rich mixtures. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118607

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have characterized bias-assisted chemical vapor deposition diamond using the nondestructive technique of confocal Raman spectroscopy to investigate the interfacial structures and the variation in structure and quality with depth. The spectral depth profiles of oriented diamond showed that a band centered at 1210cm−1and the diamond peak at 1332cm−1coexisted at the interface between the oriented diamond and Si substrate. The relative intensity of the 1210cm−1band compared to that of the diamond peak varied with depth. The intensity of the band decreased and that of the diamond peak increased from the interface to the diamond surface. The quality of the oriented diamond improved with the growth time. In contrast, for the case of a randomly oriented diamond, a band centered at 1550cm−1was observed, the diamond peak was shifted between −6 and 6cm−1from the single crystal diamond peak at 1332.5cm−1,and the spectral profile did not change with depth. No band at 1210cm−1was seen in this case. We conclude that a nondiamond phase with a Raman band at 1210cm−1and a diamond phase coexist at the interface between the oriented diamond and the Si substrate, and that this 1210cm−1phase is therefore a characteristic feature of the nature of the diamond-substrate bonding in oriented films. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118608

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The purpose of this letter is to observe voids at the SiC–Si interface beneath the SiC layers grown by chemical vapor deposition at high temperature. It is shown in this letter that the volume of the voids per unit area is proportional to the oxygen concentration in the Si substrate over seven orders of magnitude.In situdynamical reflectivity measurements show that the voids are formed during the carbonization step and especially when the carbon, which has diffused deeply into the Si substrate, diffuses back toward the SiC layer just completed at the substrate surface. This back diffusion is due to the inversion of the carbon concentration gradient sign at that moment. It is accompanied by the formation of CO, resulting either from the reduction of SiO orSiO2dissolved in the Si substrate. Diffusion of carbon in silicon might improve the methods of purification for the removal of oxygen which remains the main impurity of the purest silicon material. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118609

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Field induced deformations of the bookshelf geometry in electroclinic liquid crystals are investigated by means of spatially resolved phase retardation experiments. It is found that the triangular deformation model does not adequately describe the optical data, and underestimates the achievable device contrast ratios. To more correctly model the smectic layer deformation, it is necessary to consider a distribution of molecular directors within a stripe domain. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118610

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of H on the local structure of N-containing amorphous diamondlike films(a-CNx:H)is reported. The samples were prepared by rf sputtering of graphite in aN2,Ar, andH2atmosphere. The chemical bonding of C and N atoms was inferred by analyzing theC 1sandN 1selectronic core-level by x-ray photoelectron spectroscopy. Hydrogen free films presentN 1speaks with a “doublet”, located at 398.2–400.5 eV. When H is introduced in the preparation chamber, the doublet evolves to a single wider band located at 399.1 eV. This new band becomes dominant when increasingH2partial pressure, completely hiding the original structure. HighH2partial pressure interrupts the growing network formed by N and C due to the attachment of H to N and/or C. Furthermore, the experimental results suggest that the possibility of formation of theC3N4phaselike is inhibited by the presence of hydrogen. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118611

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A method for (111) oriented diamond film synthesis has been developed using controlled seeding of micron-sized diamond particles by electrophoresis. Different sizes of diamond powders (0.25 and 5&mgr;m) were electrophoretically seeded on silicon substrates using diamond suspensions in organic solvents (acetone, methanol, and ethanol). The seeded samples were then consolidated by the hot filament chemical vapor deposition process. Diamond suspension in acetone was found to be the most suitable for obtaining uniform diamond seeding in electrophoresis. A preferred (111) orientation was obtained for a monolayer of 5 &mgr;m seeds. However, when smaller seeds (<1 &mgr;m) were used, randomly oriented films were obtained. The surface morphology, crystal orientation, and quality of diamond films were investigated using scanning electron microscopy, x-ray diffractometry, and Raman spectroscopy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118612

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A nondestructive method for structural imaging is proposed. The method is based on direct measurements of phase and amplitude changes in a two-dimensional x-ray image. A standing wave is formed between two separated crystals allowing high-resolution imaging of the complex refractive index. A comprehensive analysis of the amplitude-phase contrast is possible because of the precisely controlled variation of the phases between the reference and reflected beams from a crystalline mirror. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118613

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a technique to measure the lateral stiffness of the nanometer-sized contact formed between a friction force microscope tip and a sample surface. Since the lateral stiffness of an elastic contact is proportional to the contact radius, this measurement can be used to study the relationship between friction, load, and contact area. As an example, we measure the lateral stiffness of the contact between a silicon nitride tip and muscovite mica in a humid atmosphere (55&percent; relative humidity) as a function of load. Comparison with friction measurements confirms that friction is proportional to contact area and allows determination of the shear strength. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118639

出版商:AIP    

年代:1997

数据来源: AIP