摘要:

Highly oriented pyrolytic graphite samples have been implanted at elevated temperature (450 °C) with57Fe species at high fluence (2×1017cm−2) and a bombarding energy of 35 keV. Under these conditions of implantation, materials with ferromagnetic properties have been synthesized, as demonstrated by magnetization measurements using a superconducting quantum interference device magnetometer. It is further shown that the samples exhibit ferromagnetic, paramagnetic, and diamagnetic contributions to the total magnetization. The value of the measured coercive force and a comparison of scanning electron microscopy studies of the sample surface with the calculation of the saturation ferromagnetic moment suggest that fine iron particles are created on the surface. A mechanism is proposed to explain these observations. Complementary Rutherford backscattering spectroscopy and Raman measurements indicate that the lattice is not completely amorphized under these implantation conditions.

ISSN:0021-8979    

DOI:10.1063/1.340489

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The laser‐assisted chemical vapor deposition of metals is modeled. The case of pyrolytic deposition induced by a continuous laser source is considered. The heat transfer in the solid substrate is considered to be transient, while the gas‐phase heat and mass transfer are assumed to be in the quasi‐steady state. The model accommodates the use of temperature‐dependent physical properties and the occurrence of irregularly shaped deposits. The modeling equations are solved by a finite element approach which is briefly described. Volcanolike deposits are predicted under certain conditions of gas pressure and laser intensity. Model predictions show that depletion effects and adsorption‐desorption phenomena are major factors in influencing the occurrence of volcanolike deposits.

ISSN:0021-8979    

DOI:10.1063/1.340490

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The polycrystalline Pd surface of a hydrogen sensitive palladium‐silicon dioxide‐silicon [Pd‐MOS (metal‐oxide‐semiconductor)] structure has been exposed to small unsaturated hydrocarbons in the temperature range 300–500 K. Apart from the hydrogen response of the Pd‐MOS structure also work function (&Dgr;&Fgr;) and electron energy‐loss studies were performed. At 500 K the hydrocarbons dissociate completely upon adsorption and produce a surface with atomically adsorbed carbon. The Pd‐MOS structure can be used to observe both the dehydrogenation of the hydrocarbon molecules and the process of carbon adsorbing on the palladium surface. The sticking coefficient at this temperature for all hydrocarbons is close to unity. Furthermore, the hydrogen sensitivity of the structure is not drastically reduced by the adsorbed carbon. If the hydrocarbon adsorption is performed at 300 K there is still, at least on the initially clean surface, a large dehydrogenation. The dissociation is, however, not at all complete and there are considerable amounts of hydrocarbon species adsorbed for each gas. The induced work function shifts due to the different hydrocarbons vary from −1.0 to −1.7 eV. The hydrogen sensitivity of the Pd‐MOS structure is reduced for growing hydrocarbon coverages and disappears completely for work function shifts of −1.7 eV.

ISSN:0021-8979    

DOI:10.1063/1.340492

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

This paper describes the current development of a noncryogenic gravity gradiometer for future use on board the tethered satellite system (TSS). The paper also proposes a way of testing a single‐axis prototype of such an instrument that makes use of the free‐fall technique in vacuum. This gravity gradiometer has a design sensitivity of the order of 10−2EU (1 EU =Eo¨tvo¨s Unit=10−9ms−2/m) in 10‐s integration time. Because of the small size and light weight, a noncryogenic gravity gradiometer is a valid candidate to fit the limited accommodation capability of the TSS deployed from the shuttle and maintained, for several days, at an altitude of 120–130 km. This unique capability improves the resolution and accuracy achievable in reconstructing the earth gravity field, in particular at short wavelengths. A preliminary analysis of the dynamics of the TSS satellite indicates the potential of such satellite as a low‐altitude research platform for gravity gradiometry.

ISSN:0021-8979    

DOI:10.1063/1.340493

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We present an exact solution for a single‐carrier injection current in a perfect insulator with arbitrary field at the injecting boundary.

ISSN:0021-8979    

DOI:10.1063/1.340494

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Surface structures of the high‐Tcsuperconductor YBa2Cu3Oxhave been investigated with a scanning tunneling microscope. Four typical features are revealed, e.g., (i) flat area of the size up to 0.2×0.2 &mgr;m2, (ii) step structures with the height of the step from tens to hundreds of angstroms, (iii) regular arrays of subgrains having the width down to 100 A˚, and (iv) a complex formed by these features. The sharp surface corrugations suggest strong local fluctuations in the elastic and electronic properties of this material.

ISSN:0021-8979    

DOI:10.1063/1.340495

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

For Hg1−xCdxTe, in the range ofx&bartil;0.2–0.3, the optical dispersion parameters (single‐oscillator energyE0,dispersion energyEd, and lattice‐oscillator energyE1) and the fitting parameter of the exponential optical absorption (steepness factor &sgr;) were analyzed using the data by Finkman and co‐workers [J. Appl. Phys.50, 4356 (1979); J. Appl. Phys.56, 2896 (1984)]. For Hg1−xCdxTe the values ofE0,Ed, and &sgr; in this composition range are smaller than those for CdTe, andE1is larger than that for CdTe. The results suggest that the chemical bonding of Hg1−xCdxTe in the range ofx&bartil;0.2–0.3 is smaller than that of CdTe.

ISSN:0021-8979    

DOI:10.1063/1.340496

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

I‐Vcharacteristics of two‐terminaln+‐p‐n+devices fabricated by planar technology are studied theoretically and experimentally. A quasi‐two‐dimensional (2D) model is used to interpret the experimental results. The results suggest that the 2D effects are a very likely candidate to explain the difference in our results and those obtained with the conventional 1D BARRIT diodes.

ISSN:0021-8979    

DOI:10.1063/1.340497

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An accurate analysis of optical waveguides made by Na‐K ion exchange in glass is presented. A strict correlation between surface index change, guide birefringence, surface stress, and relaxation as a function of time and temperature is demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.340498

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The formation of PtSi is studied in the presence of W and Al using the Al/W/Pt/Si structure, with 1000‐A˚ W acting as the barrier layer. The PtSi layer formed stays intact at 400 °C, starts to react with Al around 450 °C, and is completely converted to PtAl2at 500 °C, with the released Si migrating to the surface. In contrast, using the W/Pt/Si structure without an Al layer, the PtSi formed remains little changed up to about 600 °C. The W‐Pt interface of the binary W/Pt structure shows no interaction up to at least 600 °C. The results are compared with those using the Al/Pt/Si structure, and their relation to contact metallurgies is discussed.

ISSN:0021-8979    

DOI:10.1063/1.340504

出版商:AIP    

年代:1988

数据来源: AIP