摘要:

We present an inverse scattering algorithm that makes possible the inversion of experimental thermal wave images of planar subsurface defects. The method is based on a Green’s function technique. It significantly improves the spatial resolution and removes the blurring which is otherwise characteristic of thermal wave images. The method has been applied to materials ranging from plastics (diffusivity ∼0.001 cm2/s) to aluminum alloys (diffusivity ∼0.5 cm2/s), and for depths ranging up to a few mm.

ISSN:0021-8979    

DOI:10.1063/1.354202

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Cobalt oxide thin films (thickness 2000 A˚) with different stoichiometries were deposited by reactive rf sputtering. The variation of the oxygen partial pressure lead to films with compositions varying from metallic cobalt to CO3O4, as determined by x‐ray diffraction and x‐ray photoelectron spectroscopy. The electrochromic properties of the films were investigated in aqueous electrolytes (0.1 M KOH). The initial electrochemical behavior of the films is strongly dependent on the film deposition conditions, but after cycling the electrochemical/electrochromic characteristics of the different deposits were quite similar. Transmittance changes and electrochromic efficiency are discussed.

ISSN:0021-8979    

DOI:10.1063/1.354203

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Soft x‐ray photoemission has been utilized to investigate the chemisorption and subsequent reaction of diethylsilane on Si(111) and (100) surfaces. We show that diethylsilane chemisorbs dissociatively to form Si‐CH2CH3surface species on Si(111) and Si(100) at room temperature. These species are identified by two very sharp peaks observed in the valence band spectra of both surfaces, positioned at 17.9 and 14.3 eV binding energy. Si 2pand C 1score level spectra were measured following exposures of Si(100) and (111) substrates as a function of surface temperature. C 1sdata show that carbon, in some form, exists on the Si surface following exposures at every temperature from room temperature to about 600 °C. While only –CH2CH3ethyl groups are observed on the surface at room temperature, these species appear to partially dehydrogenate above 300 °C producing a mixture of –CH2CH3groups and other intermediate carbonaceous species. At a growth temperature of about 400 °C for the technologically important (100) surface, the intermixing of elemental carbon with Si begins. At higher temperatures, we observe the continued degradation of diethylsilane to produce a Si+C alloy on the surface at 600 °C. Our results indicate that diethylsilane has potential as a candidate for SiC formation by chemical vapor deposition techniques.

ISSN:0021-8979    

DOI:10.1063/1.354176

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The negative terminal capacitance at high frequencies (usuallyf≫106Hz) in ZnO‐Bi2O3–based varistor systems is attributed to two possible sequential and/or combined sources: (a) piezoelectric grain resonance; and (b) electrode‐lead or contact impedance. These sources are examined using a variation in the geometry of the varistor material and its electrode‐lead configuration. The approximate values of the resonating parameters, designated by an equivalent series lumped inductance‐capacitance‐resistance (Lr‐Cr‐Rr) circuit in parallel with materials’ characteristic capacitanceC0, are extracted employing lumped parameter/complex plane analysis technique for these ac electrical data. At the resonating frequency, the lumped reactance of this series circuit nullifies yielding a resistanceRrreferred to the lumped ZnO grains.

ISSN:0021-8979    

DOI:10.1063/1.354177

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A transmission line consisting of a parallel connection of shunted Josephson junctions is one of the base elements in the new Rapid Single Flux Quantum (RSFQ) logic. When an additional bias current is applied to the edge junction of the transmission line it generates and injects series of flux quanta on the line. This kind of pulse generators have important applications for testing RSFQ devices at high frequencies. In such experiments unwanted steps always show up in theI‐Vcurve of the generator junction. This problem has been experimentally and numerically investigated for parallel arrays of identical junctions. Steps with extremely low differential resistance are found to be due to the self‐induced magnetic field produced by the edge current. The underlying mechanism is that the non‐uniform field divides the array into domains consisting of several (unit) cells each containing the same number of flux quanta. The influence of an applied homogeneous external magnetic field and a uniformly distributed bias current is also considered.

ISSN:0021-8979    

DOI:10.1063/1.354178

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Direct comparison of the characteristics of a Si metal‐oxide‐semiconductor device provided by Monte Carlo simulation and experimental results is rare. This paper appraises the degree of agreement between simulated and experimental results of drain current versus drain voltage (Id‐Vd). It also derives the impact ionization rate formula inversely by comparing the simulated and experimental dependence of the substrate current (Isub) on the gate voltage (Vg). We found that (1) forId‐Vdcharacteristics, the agreement in the linear region was off, but overall agreement was fairly good, and (2) the simulatedIsub‐Vgcharacteristics were in fairly good agreement with the experimental characteristics when the modified Keldish formulaPii=P0[(E−1.12)/1.12]nwith annof 7 andP0of 2.8×1011s−1was used as the formula for the impact ionization rate.

ISSN:0021-8979    

DOI:10.1063/1.354157

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Electron spin resonance ofPbcenters is used to probe the dielectric/silicon interface in NH3‐nitrided oxide (NO) and reoxidized nitrided oxide (RNO) dielectrics. ThePbspectra observed in the NO and RNO systems differ from Si/SiO2systems only in the value ofg⊥; the &Dgr;g⊥suggests that the average value of the local strainatthedefectsitedecreases upon nitridation, and is little changed by subsequent reoxidation. The relaxation of thePbcenter structure appears to coincide with a reduction of compressive stress in the dielectric and an increase of tensile stress in the silicon substrate. These results suggest that differences in atomic scale strain due to nitrogen incorporation may be involved in the reduced radiation‐ and hot carrier‐induced interface state generation that NO and RNO dielectrics exhibit.

ISSN:0021-8979    

DOI:10.1063/1.354158

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Giant magnetoresistance (GMR) is reported in Ag1−xCox(x=0.26–0.53) films cosputtered on Si at 28–354 °C from separate Ag and Co targets. GMR ratios (10 kOe maximum field) as high as 0.55 and 0.24 at 5 and 295 K, respectively, are achieved for the Ag0.67Co0.33films deposited at a substrate temperature,Ts, of 125 °C. The GMR ratio increases slightly when theTsincreases from 28 to &bartil;125 °C, and decreases substantially atTs≳175 °C. The resistivity of these films decreases monotonically with increasingTsand levels off to a value &bartil;3× of Ag atTs≥250 °C. The films deposited at lowerTsconsist of essentially a metastable Ag‐Co solid solution, while those deposited at higherTsconsist of separate fcc Ag and fcc Co. The coercivity of these films increases rapidly atTs≫125 °C, consistent with the growth of single‐domain ferromagnetic Co particles in thisTsrange. TheTsdependence of GMR ratios is interpreted based on spin‐dependent interfacial scattering arising from theTsdependence of the size and number of ferromagnetic Co particles within the electron mean free path.

ISSN:0021-8979    

DOI:10.1063/1.354159

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It is shown that the forward voltage of heterostructure transistors can be modified by varying the thickness of the undoped GaAs layer beneath the gate or by low energy ion implantation of a surface layer. This suggests that the effective barrier height can be controlled by either technique.

ISSN:0021-8979    

DOI:10.1063/1.354160

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It is shown that an annular electron beam may carry six times as much current as a pencil beam for the same beam breakup (BBU) growth. This finding suggests that the rf magnetic field of the breakup mode is far more important than the rf electric field in the excitation of BBU. A proof‐of‐principle experiment is suggested, and the implications explored.

ISSN:0021-8979    

DOI:10.1063/1.354161

出版商:AIP    

年代:1993

数据来源: AIP