摘要:

A model has been developed to explain the greatly reduced reflectivities of Ge samples implanted to doses 1.25–1.5×1018O/cm2with 45‐keV O+ions, which have reflectivity values close to zero at 0.7 &mgr;m. The model divides the inhomogeneous implanted layer into a series of homogeneous sublayers with different volume fraction and thickness for each sublayer. The complex refractive indexes for every sublayer are calculated using the Maxwell Garnett (MG) and Persson–Liebsch (PL) theories. Using the expressions for the reflectivity of an absorbing multilayer layer systems, the reflectivities have been calculated. The reflectivity curve calculated in the PL approximation is closer to the experimental observations than is the MG approximation over the wavelength range 0.2–3.0 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.346135

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The authors report time‐resolved measurements of the emission of positive and negative charge from Si and Ge surfaces irradiated with 248‐nm KrF excimer laser pulses. With pulse energies both below and above the melting threshold, the time evolution of the emission currents is complex and strikingly different for Si and Ge. The positive ion emission signal from Ge persists only for the duration of the laser pulse (<60 ns), but in sharp contrast, the signal from Si continues for several microseconds. A tentative suggestion is made that the positive ions encounter a Knudsen layer created just above the surface of the Si target. More refined experiments, coupled with a theoretical effort, are proposed.

ISSN:0021-8979    

DOI:10.1063/1.346136

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ultraviolet laser irradiation of surfaces, in the course of photoemission or surface photochemical studies, often produce copious electron emission, up to 1000’s of A/cm2. The time‐dependent fields produced by these electrons accelerate some of the electrons up to 5.4 times their initial energies. The steady‐state fields return most of the emitted electrons to the surface. We discuss and illustrate both phenomena with theoretical simulations and experiment, and discuss possible implications.

ISSN:0021-8979    

DOI:10.1063/1.346137

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Examination with x‐ray photoelectron spectroscopy (XPS) of CF4plasma etched GaAs(100) wafers unveils a residual surface reaction layer composed of Ga‐fluoride and Ga‐oxide. Efficient removal of this contamination layer by a brief immersion in a dilute NH4OH wet etch is demonstrated. The formation of a thin native oxide upon exposure to atmosphere of the clean substrate surface cannot be avoided, however. Prospective replacement of this wet etch processing byinsituthermal annealing in hydrogen was investigated. The recorded XPS spectra show almost complete desorption of fluorine after annealing at 200 °C, whereas a temperature of ∼600 °C is required for entire removal of residual surface Ga‐oxide. Heat treatment in H2also compares favorably with vacuum annealing, for which a noticeable reduction of the surface contamination layer was found only after annealing at 600 °C. The cleaning efficiency of hydrogen processing may be attributed to the reactive nature of this ambient.

ISSN:0021-8979    

DOI:10.1063/1.346138

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A study of chemical etching and chemo‐mechanical polishing of Hg0.8Cd0.2Te (MCT) with bromine‐methanol has been carried out. It was found that the etch rate could be controlled down to 0.1 nm/s when 0.001% of bromine‐methanol was used. Surface analysis using x‐ray photoelectron spectroscopy indicated that differential etching of the constituents and accumulation of elemental tellurium occurred even when only a few monolayers were etched from a stoichiometric MCT surface. The relative etch rates were determined to be Cd≫ Hg≳Te. Nevertheless, it was found that chemo‐mechanical polishing could produce smooth surfaces with no significant accumulation of elemental tellurium. The production of such surfaces, however, required a balance of chemical etching and mechanical lapping. Furthermore, quick quenching of chemical etching was o required after chemo‐mechanical polishing in order to prevent further surface degradation.

ISSN:0021-8979    

DOI:10.1063/1.346139

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Focused ion beam stimulated deposition of aluminum from trimethylamine alane, a white solid, and triethylamine alane, a colorless liquid, is reported. Initiation of growth on Si and SiO2substrates is enhanced byinsitusputter cleaning of the surface with the Ga+beam prior to introduction of the metallo‐organic. Alternatively gas phase chemical activation with a silane coupling agent can enhance nucleation. Uniform nucleation on Al surfaces does not require any pretreatment. The Al features are electrically conducting, but incorporation of C and N from the amines leads to a resistivity approximately 300 times that of bulk Al. A qualitative model is presented that describes the balance condition for net material deposition as opposed to sputtering in terms of precursor flux and sticking probability as well as ion beam current density and beam scanning parameters. Film morphology and composition are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.346140

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The composition of the reaction gases in a hot‐filament reactor for chemical vapor deposition of diamond films was analyzed using a gas chromatograph coupled with a quartz microprobe. Concentrations of several hydrocarbons were determined as functions of filament temperature (FT) and the position of the probe relative to the filament for two feed gases, methane/hydrogen and acetylene/hydrogen. The diamond growth rate was measured as a function of FT in both feed gases. The major chemical process in these reaction systems is found to be conversion between methane and acetylene with ethane and ethylene as reaction intermediates. For FT≤1800 °C, the chemical reactivity is low, and no diamond deposition is observed. For FT≥1900 °C, nearly identical chemical composition near the filament is obtained from both feed gases (indicating possible attainment of thermodynamic equilibrium in the gas mixtures), and the measured diamond growth rates are similar. A substantial depletion of carbon in the reaction gases near the filament is observed and is shown to be due to thermal diffusion. Downstream of the filament, a nonequilibrium state is observed, possibly caused by slow methane/acetylene conversion and/or fast diffusion. The trend of the diamond growth rate, which increases with increasing FT from 1900 to 2200 °C, correlates well with the concentration profile of acetylene but not that of methane.

ISSN:0021-8979    

DOI:10.1063/1.346141

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The formation of a vitreous silica surface in the presence of water vapor is investigated through the molecular dynamics simulation technique. Three‐body potentials are employed to describe the interatomic interactions. The structure of the reconstructed surface is analyzed with respect to the concentration and type of defects. Comparison between surfaces created in the presence of water and those created in a vacuum indicate that H2O‐surface reactions substantially reduce the number of topological (two‐ , three‐ , and four‐membered rings) and bonding defects (under‐ and overcoordinated species) incurred during the relaxation process. Due to the dissociation of water molecules, the wet surface contains excess oxygen with a concentration of 3.1±0.6 silanols per 100 A˚2, involving approximately 13% geminal sites.

ISSN:0021-8979    

DOI:10.1063/1.346142

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The self‐developing mechanism of nitrocellulose is studied by means of low‐temperature infrared spectroscopy. It is found that 150‐keV A+beams with fluences ranging from 1013ions cm−2to 6×1013ions cm−2induce atomic bond breaks leading to absorption bands at 2344, 2138, 1868, 1750, and 1590 cm−1, corresponding, respectively, to CO2, CNH, CO, CHO, and NO vibrations. At low temperature and under vacuum, intensity measurements of the CO2absorption band versus ion fluences are performed. Carbylamine formation, cyclic anhydride of five carbon atom formation, and denitration are observed. A theoretical model, based upon those three mechanisms is presented which partially explains the self‐development of the ion irradiated nitrocellulose.

ISSN:0021-8979    

DOI:10.1063/1.346143

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The conditions and mechanism of bonding a tungsten sheet directly onto a Si80Ge20alloy by hot pressing have been studied. It was found that W/Si80Ge20bonds are formed only at relatively high temperatures. The pressure and time required for bonding decrease with increasing temperature. In the initial stage, the W/Si80Ge20reaction follows a parabolic kinetics, suggesting it is a diffusion‐controlled process. The activation energy is 4.9 eV, and the parabolic rate constant is given byKp=(4.2±0.1)×1018 exp[−(5.7±0.1)×104/T] (&mgr;m2/ min) A bonding mechanism is proposed based on scanning electron microscopic observations and chemical analyses of the interface. Selective reaction between silicon and tungsten leaves a Ge‐rich layer at the W/Si80Ge20interface, thus reducing the melting temperature. When the silicon content in the interfacial layer becomes sufficiently low, the layer melts at the hot‐press temperature. Molten materials fill in voids and microcracks by the capillary effect, resulting in an intimate contact and a strong bond. A mathematical model of Si diffusion is proposed. Solving the equation by the finite‐difference method, silicon composition profiles were obtained and the silicon diffusion coefficient was estimated.

ISSN:0021-8979    

DOI:10.1063/1.346144

出版商:AIP    

年代:1990

数据来源: AIP