Concentration profiles during films deposition from a low-energy ion beam

An ion beam is described in the diffusion approximation, and a mathematical model of thin-film deposition process is developed. The volume profiles of concentration of components during nickel film deposition on a copper substrate are calculated for ion energies of 100, 200, and 400 eV and ion flux densities I = 10¹⁵, 10¹⁶, and 10¹⁷cm⁻²·s⁻¹. The deposition model parameters are estimated using programs SUSPRE and SRIM. The concentration profiles of the components are compared for the corresponding numerical values of the model parameters. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 27–34, March, 2007.     

The characteristics of high current amorphous silicon diodes

Amorphous siliconp−n junctions with various doping profiles have been prepared by the glow discharge technique and the effect of the barrier profile on electrical properties investigated. Current densities of up to 40 A cm⁻² with rectification ratios of 10⁴–10⁵ were obtained withn ⁺−ν−p ⁺ structures. The diode quality factor has also been investigated, both in the dark and under illumination.     

Polarization and thickness effects in Mössbauer spectroscopy

The lattice sites of positive pions in gold have been determined as a function of temperature by means of π⁺/μ ⁺ channelling experiments. A blocking pattern in the <100> direction at low temperatures indicates that only octahedral interstitial sites are occupied. The vanishing of this pattern and the reduction of muon flux enhancement observed in <110> ifT is raised above the Debye temperature (165 K) may be interpreted in terms of muon dechannelling owing to the thermal vibrations of the lattice atoms. Time-differential π⁺/μ ⁺ channelling studies on α-iron showed between 20 K and 70 K a strong dependence of the channelling profiles on the time the pions spent in the sample. The ‘young’ pions are well localized on O- or T-sites whereas the ‘old’ pions either become delocalized or occupy sites with strongly reduced symmetry. A model accounting for these observations is suggested. It is argued that there is a close relationship to earlierμ ⁺ SR experiments.     

Phosphorus distribution profiles in 100-silicon using a spin-on source at low temperatures

 Incorporation of phosphorus into silicon from a spin-on dopant layer (SOD) at 400 ^°C is described. Annealing experiments were carried out with SOD films deposited on (100) silicon substrates by using the spin-on technique. Conventional heating on a hotplate in normal atmosphere and a temperature range up to 400 ^°C was used to study the dopant incorporation. After removing the SOD-films one part of the silicon substrates was annealed at higher temperatures. Investigations were carried out by SIMS, SAM, XPS, HTEM, stripping Hall and Van der Pauw measurements before and after the high temperature annealing. Chemical phosphorus concentration profiles obtained from low temperature annealed samples showed diffusion depths of 60–80 nm (extrapolated to a substrate doping level of 10¹⁶ cm^-3) and surface concentrations of 10¹⁹–10²⁰ cm^-3. Electron concentration profiles exhibiting maximum values around 2⋅10¹⁹ cm^-3 could be measured on high temperature annealed samples only. Received: 28 March 1996/Accepted: 19 August 1996     

The effect of the scale factor on the focusing properties of a vortex gas flow

An experimental study is carried out to investigate a bilateral direct-flow vortex tube of small (0.3–3.0)·10⁻² m) size and to compare its optical properties with those characteristics of vortex tubes of a larger ((3–16)\10⁻² m) scale. A model is suggested for forming transverse profiles of the intensity of laser beams with an intensity hole in the center and of annular beams. Translated from Zhural Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 386–389, May–June, 1997     

High-vacuum time-resolved laser-induced incandescence of flame-generated soot

We have measured time-resolved laser-induced incandescence of flame-generated soot under high-vacuum conditions (4.1×10⁻⁶ mbar) at an excitation wavelength of 532 nm with laser fluences spanning 0.06–0.5 J/cm². We generated soot in an ethylene/air diffusion flame, introduced it into the vacuum system with an aerodynamic lens, heated it using a pulsed laser with a spatially homogeneous and temporally smooth laser profile, and recorded LII temporal profiles at 685 nm. At low laser fluences LII signal decay rates are slow, and LII signals persist beyond the residence time of the soot particles in the detection region. At these fluences, the temporal maximum of the LII signal increases nearly linearly with increasing laser fluence until reaching a plateau at ∼0.18 J/cm². At higher fluences, the LII signal maximum is independent of laser fluence within experimental uncertainty. At these fluences, the LII signal decays rapidly during the laser pulse. The fluence dependence of the vacuum LII signal is qualitatively similar to that observed under similar laser conditions in an atmospheric flame but requires higher fluences (by ∼0.03 J/cm²) for initiation. These data demonstrate the feasibility of recording vacuum LII temporal profiles of flame-generated soot under well-characterized conditions for model validation.     

Photofragment space distribution in the photodissociation of NaI in the spectral range 315–370 nm: the role of molecular axis rotation

The first determination of translational anisotropy parameters β in the photodissociation of NaI molecules in the spectral range 315–370 nm is reported. The anisotropy parameters were determined by the analysis of Doppler resolved absorption profiles of Na(²S_1/2) atoms produced in the photodissociation of NaI by linearly polarized light. The profiles were recorded for two orientations of the photolysis light: parallel and perpendicular to the direction of the probe beam. The value of the parameter β was obtained from a simultaneous fit of the profiles. The role of the rotation of the parent molecules on the branching ratio between parallel and perpendicular transitions in NaI during dissociation is discussed.     

Shape transformation transitions in a model of fixed-connectivity surfaces supported by skeletons

A compartmentalized surface model of Nambu and Goto is studied on triangulated spherical surfaces by using the canonical Monte Carlo simulation technique. One-dimensional bending energy is defined on the skeletons and at the junctions, and the mechanical strength of the surface is supplied by the one-dimensional bending energy defined on the skeletons and junctions. The compartment size is characterized by the total number L^′ of bonds between the two-neighboring junctions and is assumed to have values in the range from L^′ = 2 to L^′ = 8 in the simulations, while that of the previously reported model is characterized by L^′ = 1, where all vertices of the triangulated surface are the junctions. Therefore, the model in this paper is considered to be an extension of the previous model in the sense that the previous model is obtained from the model in this paper in the limit of L^′↦1. The model in this paper is identical to the Nambu-Goto surface model without curvature energies in the limit of L^′↦∞ and hence is expected to be ill-defined at sufficiently large L^′. One remarkable result obtained in this paper is that the model has a well-defined smooth phase even at relatively large L^′ just as the previous model of L^′↦ 1. It is also remarkable that the fluctuations of surface in the smooth phase are crucially dependent on L^′; we can see no surface fluctuation when L^′≤ 2, while relatively large fluctuations are seen when L^′≥ 3.     

Σ- atoms and the ΣN interaction

It is shown that among four models of the Nijmegen baryon-baryon interaction only model F --which leads to a repulsive potential felt by the Σ hyperon inside the nucleus-- is consistent both with the analysis of Σ^- atoms and of the (K ^-,π) reactions. The Nijmegen models are used to determine the strong complex single-particle (s.p.) potential of Σ^-, and to calculate the strong-interaction shifts and widths of the lowest observed levels of Σ^- atoms. The results obtained with model F are in best agreement with the experimental data. Received: 15 January 2002 / Accepted: 14 March 2002     

Residual strain measurements in InGaAs metamorphic buffer layers on GaAs

This work deals with the strain relaxation mechanism in InGaAs metamorphic buffers (MBs) grown on GaAs substrates and overgrown by InAs quantum dots (QD). The residual strain is measured by using Raman scattering and X-ray diffraction, both in Reciprocal Space Map and in single ω-2θ scan modes (ω and θ being the incidence angles on the sample surface and on the scattering planes, respectively). By relating the GaAs-like longitudinal optical phonon frequency ω^LO of InGaAs MBs to the in-plane residual strain ε measured by means of photoreflectance (PR), the linear ε-vs.-ω^LO working curve is obtained. The results of Raman and XRD measurements, as well as those obtained by PR, are in a very satisfactory agreement. The respective advantages of the techniques are discussed. The measurements confirm that strain relaxation depends on the thickness t of the buffer layer following a ~t^-1/2 power law, that can be explained by an energy-balance model.     

Molecular oxygen detection in low pressure flames using cavity ring-down spectroscopy

Cavity ring down spectroscopy is used for measurement of the concentration profiles of oxygen in the low pressure (30 Torr) methane/nitrogen/oxygen flames. Three different equivalence ratios are used: 0.8, 1.0 and 1.17. Molecular oxygen concentration is monitored via rotational spectrum of b¹ Σ _g ⁺←X³ Σ _g ^- (v^′=0-v^′′=0) transition, also known as atmospheric A band, located near 750 nm. The P(15)P(15) line is used for concentration measurements. The sensitivity reached is 2.2×10^-8 cm^-1. The concentration profiles are in a good agreement with the ones calculated using GRI-3.0 mechanism. PACS 33.20.Kf; 33.70.Fd; 42.60.Da     

Monitoring of the Proton Electrochemical Gradient in Reconstituted Vesicles: Quantitative Measurements of Both Transmembrane Potential and Intravesicular pH by Ratiometric Fluorescent Probes

Proteoliposomes carrying reconstituted yeast plasma membrane H⁺-ATPase in their lipid membrane or plasma membrane vesicles are model systems convenient for studying basic electrochemical processes involved in formation of the proton electrochemical gradient (Δμ_H ⁺) across the microbial or plant cell membrane. Δψ- and pH-sensitive fluorescent probes were used to monitor the gradients formed between inner and outer volume of the reconstituted vesicles. The Δψ-sensitive fluorescent ratiometric probe oxonol VI is suitable for quantitative measurements of inside-positive Δψ generated by the reconstituted H⁺-ATPase. Its Δψ response can be calibrated by the K⁺/valinomycin method and ratiometric mode of fluorescence measurements reduces undesirable artefacts. In situ pH-sensitive fluorescent probe pyranine was used for quantitative measurements of pH inside the proteoliposomes. Calibration of pH-sensitive fluorescence response of pyranine entrapped inside proteoliposomes was performed with several ionophores combined in order to deplete the gradients passively formed across the membrane. Presented model system offers a suitable tool for simultaneous monitoring of both components of the proton electrochemical gradient, Δψ and ΔpH. This approach should help in further understanding how their formation is interconnected on biomembranes and even how transport of other ions is combined to it.     

Muon channeling in Ge: Evidence for pionium formation

In a recent experiment observing muon channeling from the decay of positive pions implanted in high-purity Ge single crystals, the pion decay site is found to be sensitive to the concentration of excess charge carriers produced by photon absorption. Distinctly different channeling profiles are observed in Ge at 100 K for illuminated samples (high carrier concentration) as compared to unilluminated samples (low carrier concentration). From these data we conclude that different electronic states of the pion in a semiconductor host lattice must account for the observed changes in the pion location. Furthermore we suggest that the pion exists in the solid both as the bare entity π⁺ and as pionium (π⁺ e⁻), i.e., a hydrogen-like atom with a mesonic nucleus.     

SU(3) coupling schemes for odd-odd nuclei in the interacting boson – fermion – fermion model with both odd proton and odd neutron in natural parity orbits

The SU^BFF(3) dynamical symmetry limits of interacting boson – fermion – fermion model are identified and they are appropriate for heavy deformed odd – odd nuclei for configurations with both the odd proton and odd neutron occupying all the natural parity orbits in the corresponding valence shells. There are three symmetry limits and their correspondence with two quasi-particle (proton-neutron) Nilsson configurations is established; one of the limits mixes both Nilsson n_z's and Λ's and other two limits mix only Nilsson Λ's. The ¹⁹¹Ir (d,t) ¹⁹⁰Ir single nucleon transfer spectroscopic strengths are well described by one of the symmetry limits that mixes only Nilsson Λ's. Received: 22 June 1998     

Rapidity dependence of multiplicity fluctuations and correlations in high-energy nucleus–nucleus interactions

The multiplicity fluctuations of the produced pions were studied using scaled variance method in ¹⁶O–AgBr interactions at 2.1 AGeV, ²⁴Mg–AgBr interactions at 4.5 AGeV, ¹²C–AgBr interactions at 4.5 AGeV, ¹⁶O–AgBr interactions at 60 AGeV and ³²S–AgBr interactions at 200 AGeV at two different binning conditions. In the first binning condition, the rapidity interval was varied in steps of one centring about the central rapidity until it reached 14. In the second case, the rapidity interval was increased in steps of 1.6 up to 14.4. Multiplicity distributions and their scaled variances were presented as a function of the dependence on the rapidity width for both the binning conditions. Multiplicity fluctuations were found to increase with the increase of rapidity interval and later found to saturate at larger rapidity window for all the interactions and in both the binning conditions. Multiplicity fluctuations were found to increase with the energy of the projectile beam. The values of the scaled variances were found to be greater than one in all the cases in both the binning conditions indicating the presence of correlation during the multiparticle production process in high-energy nucleus–nucleus interactions. Experimental results were compared with the results obtained from the Monte Carlo simulated events for all the interactions. The Monte Carlo simulated data showed very small values of scaled variance suggesting very small fluctuations for the simulated events. Experimental results obtained from ¹⁶O–AgBr interactions at 60 AGeV and ³²S–AgBr interactions at 200 AGeV were compared with the events generated by Lund Monte Carlo code (FRITIOF model). FRITIOF model failed to explain the multiplicity fluctuations of pions emitted from ¹⁶O–AgBr interactions at 60 AGeV for both the binning conditions. However, the experimental data agreed well with the FRITIOF model for ³²S–AgBr interactions at 200 AGeV.     

Fluorescent Properties of a Hybrid Cadmium Sulfide-Dendrimer Nanocomposite and its Quenching with Nitromethane

A fluorescent hybrid cadmium sulphide quantum dots (QDs) dendrimer nanocomposite (DAB-CdS) synthesised in water and stable in aqueous solution is described. The dendrimer, DAB-G5 dendrimer (polypropylenimine tetrahexacontaamine) generation 5, a diaminobutene core with 64 amine terminal primary groups. The maximum of the excitation and emission spectra, Stokes’ shift and the emission full width of half maximum of this nanocomposite are, respectively: 351, 535, 204 and 212 nm. The fluorescence time decay was complex and a four component decay time model originated a good fit (χ = 1.20) with the following lifetimes: τ ₁ = 657 ps; τ ₂ = 10.0 ns; τ ₃ = 59.42 ns; and τ ₄ = 265 ns. The fluorescence intensity of the nanocomposite is markedly quenched by the presence of nitromethane with a dynamic Stern-Volmer constant of 25 M⁻¹. The quenching profiles show that about 81% of the CdS QDs are located in the external layer of the dendrimer accessible to the quencher. PARAFAC analysis of the excitation emission matrices (EEM) acquired as function of the nitromethane concentration showed a trilinear data structure with only one linearly independent component describing the quenching which allows robust estimation of the excitation and emission spectra and of the quenching profiles. This water soluble and fluorescent nanocomposite shows a set of favourable properties to its use in sensor applications.     

Distribution and heat-treatment migration studies of Cr implanted GaAs by SIMS

Depth profiles of 190 keV Cr implanted-GaAs have been measured by SIMS analysis. The as-implanted Cr profiles are approximately Gaussian with good agreement between theory and experiment on the projected range. A fast migration of Cr is observed after heat treatment under encapsulation, and even as soon as the silicon nitride film is deposited. There is no evidence for Cr precipitation, even in the case of the largest implanted dose (10¹⁵ cm⁻²).     

Relationships between a microscopic parameter and the stochastic equations for interface's evolution of two growth models

The relationship between a microscopic parameter p, that is related to the probability of choosing a mechanism of deposition, and the stochastic equation for the interface's evolution is studied for two different models. It is found that in one model, that is similar to ballistic deposition, the corresponding stochastic equation can be represented by a Kardar-Parisi-Zhang (KPZ) equation where both λ and ν depend on p in the following way: ν(p) = νp and λ(p) = λp ^3/2. Furthermore, in the other studied model, which is similar to random deposition with relaxation, the stochastic equation can be represented by an Edwards-Wilkinson (EW) equation where ν depends on p according to ν(p) = νp ². It is expected that these results will help to find a framework for the development of stochastic equations starting from microscopic details of growth models. Received 26 August 2002 / Received in final form 20 November 2002 Published online 6 March 2003 RID="a" ID="a"e-mail: ealbano@inifta.unlp.edu.ar