摘要:

Photoluminescence spectra of Hg1−xZnxTe layers with compositions ofx=0.226 and 0.248 grown by liquid phase epitaxy on CdZnTe substrates were studied between 12 and 250 K. The annealedx=0.248 sample exhibits two unresolved lines, 15 meV apart, attributed to band‐to‐band and band to‐acceptor transitions. The temperature dependence of the photoluminescence peak energy and of the energy gap, based on infrared transmission measurements, are similar. The linewidth varies with temperature with a slope of 1.6–1.7kBsuggesting transitions obeying thekconservation rule. The measured carrier concentration versus temperature curve reveals a carrier freezeout at low temperatures. The carrier lifetime measured by the photoconductive recovery technique indicates the recombination by the Shockley–Read recombination mechanism. The observed total luminescence intensity exhibits a maximum in this temperature range. The temperature dependence of the quantum efficiency, evaluated from the calculated radiative and the observed total lifetime, was found to agree with that of the total luminescence intensity.

ISSN:0021-8979    

DOI:10.1063/1.346319

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The first‐order Raman spectra of individual 8‐&mgr;m‐diam PAN‐derived carbon fibers which had been annealed at five temperatures from 1700 to 2800 °C are measured as a function of incident laser power from 1 to 140 mW. In all fibers studied, the Raman frequencies of the graphiteGband at ca. 1580 cm−1and the disordered‐inducedDband at ca. 1360 cm−1shift to lower frequency with increasing laser power. The largest shifts observed before the fiber is physically damaged are about 13 cm−1at a laser power of 30 mW. The band positions decrease further at higher laser power, up to a maximum of about 20 cm−1at 40 mW, and at powers above 30 mW the linewidths and theID/IGintensity ratio change irreversibly as the fiber begins to erode. The irreversible changes extend several hundred &mgr;m away from the 2‐&mgr;m spot illuminated by the laser. The effects are attributed to laser heating. To quantify the degree of laser heating the temperature dependence of the Raman shift (Gband) in pure bulk, highly oriented pyrolytic graphite (HOPG) is measured. To study the heating effect in more detail, a Raman imaging experiment is carried out in which a 0.1‐mm spot on a fiber is heated by a focused laser while the fiber is illuminated for Raman characterization along a 1.6 mm length by a low power probe laser. The spatially resolved Raman shifts obtained in this way are combined with the HOPG frequency‐temperature calibration to obtain theinsitutemperature profile of the laser heated fiber. The measured temperature profile along the fiber is in excellent agreement with a simple convective heat‐transfer model. Assuming that the temperature dependence of theG‐band position is the same in the fibers as in bulk graphite, the present experiments show that a laser power of 30 mW heats an 8 &mgr;m fiber to 330 °C and that above 330 °C irreversible changes are produced by erosion of the fiber. Unperturbed room‐temperature Raman frequencies for the five groups of fibers are obtained by extrapolating to zero laser power.

ISSN:0021-8979    

DOI:10.1063/1.346320

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The interaction of strontium overlayers with atomically clean Si(100) surface has been studied by x‐ray photoelectron spectroscopy. Also studied were the effects of Sr overlayers on the oxidation of silicon at different Sr coverage (0≤&thgr;≤1.85) and different oxygen exposure. It is found that at low coverage, &thgr;≤1 monolayer (ML), Sr interacts with the Si(100) surface to form a strong ionic bond. Also, Sr is found to significantly increase the oxidation of the Si(100) surface. Silicon oxidation increased with increasing Sr coverage to a maximum at &thgr;≊1 ML. Above 1‐ML Sr coverage, the rate of Si oxidation decreased with increasing coverage.

ISSN:0021-8979    

DOI:10.1063/1.346321

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

TFE (thermal field emission) properties of LaB6⟨100⟩ and ⟨310⟩ single crystals were investigated by emission pattern observation. It was found that field evaporation with the tip temperature held at ∼1500 °C is very useful to get a clean pattern of fourfold symmetry. Each of four bright spots in the clean pattern was presumed to correspond to ⟨310⟩ emission. It is proposed, as the most appropriate operating condition, to use the ⟨310⟩LaB6tip at a temperature ∼1000 °C in vacuum of 10−9 Torr region, promising a new TF emitter of high brightness and stability for practical use.

ISSN:0021-8979    

DOI:10.1063/1.346322

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Cu thin films have been deposited on Si(111) substrate using partially ionized deposition technique in which the self‐ions, i.e., the ions derived from the depositing materials themselves, are being used to concurrently bombard the substrate surface during thin film growth. The ion percentage in the deposition beam is in the range from 0% to 5% with the ion energy varying between a few eV and several keV. The Si(111) substrates are chemically cleaned by a RCA cleaning process before loading into the vacuum chamber of deposition. Noinsitucleaning of the substrate surface is performed prior to deposition. A reduction of impurities such as oxygen, carbon, and hydrogen at the Cu/Si interface is observed as a function of the ion bombardment parameters using secondary‐ion mass spectrometry. The estimates of the sputtering cross section of oxygen, carbon and hydrogen at the Cu/Si interface by Cu ions and their energy dependence are discussed in the framework of mechanisms of the impurity sputtering by low‐energy ions.

ISSN:0021-8979    

DOI:10.1063/1.346323

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A spontaneous pattern was found on the corroded surface of 1Cr18Ni9Ti stainless steel which was subjected to a crude oil containing naphthenic acid at temperature about 330 °C. The high regularity, the periodicity, and SO2symmetry of the pattern imply that a spontaneous dissipative structure arose in this corrosion system. It was also found that the distribution of chemical elements on the corroded surface was in accordance with the morphologic pattern. A new theory, which is based on the linear perturbation method and in which the shift of boundary is considered, is proposed to characterize the formation of the large‐scale spontaneous pattern, reveal the mechanism, and explain this phenomenon in the corrosion system.  

ISSN:0021-8979    

DOI:10.1063/1.346324

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Electron‐beam (EB)‐induced pattern etching of AlxGa1−xAs (0≤x≤0.7) is described. An ultra‐thin GaAs oxide at the surface of a GaAs/AlGaAs heterostructure wafer is used as a resist film. The GaAs oxide resist can be selectively removed by EB irradiation in a Cl2ambient, which results in pattern etching of GaAs/AlGaAs. The etch rate of AlGaAs is examined as functions of substrate temperature, AlAs mole fraction, and EB flux. The results indicate that pattern etching is realized in the AlAs mole fraction range of 0≤x≤0.7

ISSN:0021-8979    

DOI:10.1063/1.346325

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Plasma nitridation of thin oxides has been investigated at a temperature of 950 °C for 10 min–6 h and within an rf power of between 400 and 1100 W. The nitrogen composition in these films has been characterized in sputter depth Auger experiments. The sensitivity of this technique has been widely improved by the use of the sequential layer sputtering model. This model allows the actual nitrogen distribution in the film to be determined by taking into account the sputtering effect and by the escape depth of oxygen and nitrogen electrons. The results are observed to be independent of the oxide thickness in the range of 10–60 nm. Rapid thermal nitridation of 16‐nm‐thick oxides at 950 °C for 300 s and at 1150 °C for 15–300 s has also been studied by this method. Comparison of the results obtained using both techniques is made with a view to microelectronic applications.

ISSN:0021-8979    

DOI:10.1063/1.346326

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report the temperature dependence of lattice constants for a NdGaO3single crystal grown by the Czochralski method and thermal expansion coefficients which were obtained for the first time. Lattice mismatch between the NdGaO3substrate and YBa2Cu3Oxsuperconducting film is 0.27% at elevated temperatures and the appropriate expansivities are similar. The crystalline quality of deposited YBa2Cu3Oxfilms on NdGaO3by the laser ablation method was extremely good. NdGaO3is, therefore, an excellent candidate forepitaxialhigh‐Tcsuperconducting films.

ISSN:0021-8979    

DOI:10.1063/1.346327

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Integral equations are derived which describe free molecular flow and simultaneous film deposition in long rectangular trenches. The equations apply to flow in the absence of deposition and to both low‐pressure chemical vapor deposition (LPCVD) and physical vapor deposition (PVD), i.e., over the full range of reactant sticking coefficient from zero to unity. A steady‐state assumption is implicit in the formulation. In the absence of film deposition, the flux to the surface is spatially uniform. Analytical expressions are presented for the initial deposition profiles along the trench sides and bottom for PVD (unity sticking coefficient). Numerical inversion of the integral equations provides initial deposition profiles for LPCVD (low sticking coefficient). The calculated initial deposition profiles are consistent with empirical results which typically show poor uniformity in PVD and high uniformity in LPCVD, and also compare well with Monte Carlo based simulations of deposition processes.

ISSN:0021-8979    

DOI:10.1063/1.346328

出版商:AIP    

年代:1990

数据来源: AIP