FUNDAMENTAL AND APPLIED SPECTROSCOPY: Second International Spectroscopy Conference, ISC 2007
935(2007); http://dx.doi.org/10.1063/1.2795425View Description Hide Description
In this work we shall present the overview of our work to study trapped quantum gases in terms of global thermodynamic variables, as well as in terms of coherent modes excitation and investigation of critical phenomena within a condensate. Using cold Na atoms we have produced a sample of Bose‐Einstein condensate atoms, with which we have performed the first experiments to establish an equation of state using global thermodynamic variables. In our system using Rb, we are working to continue on this direction as well as to implement and study the excitation of coherent modes on the confining potential.
935(2007); http://dx.doi.org/10.1063/1.2795399View Description Hide Description
The manipulation of cold atoms with optical fields is a very promising technique for a variety of applications ranging from laser cooling and trapping to coherent atom transport and matter wave interferometry. Optical fields have also been proposed as interesting tools for quantum information processing with cold atoms. In this paper, we present a theoretical study of the dynamics of a cold atomic cloud falling in the gravity field in the presence of two crossing dipole guides. The cloud is either deflected or split between the two branches of this guide. We explore the possibilities of optimization of this device and present preliminary results obtained in the case of zero‐temperature dilute Bose‐Einstein condensates.
935(2007); http://dx.doi.org/10.1063/1.2795412View Description Hide Description
Appearent luminescent centers in silica are the red luminescence R (650 nm, 1.9 eV) of the non‐bridging oxygen hole center (NBOHC), the blue band B (460 nm, 2.7 eV) and the ultraviolet luminescence UV (290 nm, 4.3 eV) both related commonly to oxygen deficient centers (ODC). In the present work we will enhance or replace either the first or second constituent of i.e. silicon or oxygen, isoelectronically by additional implantation of neighboring ions of the IVth group (C, Si) and of the VIth group (O, S). Implantation doses up to produce an atomic dopant fraction of about 4 at.% at the half depth of the layers. Very surprisingly, the cathodoluminescence spectra of oxygen and sulfur implanted layers show besides characteristic bands a sharp and intensive multimodal structure beginning in the green region at 500 nm up to the near IR. The energy step differences of the sublevels amount in average 120 meV and indicate vibration associated electronic states, probably of interstitial molecules.
Raman and SERS Studies of Single‐walled Carbon Nanotubes and Nanotubes/Conjugated Polymers Composites935(2007); http://dx.doi.org/10.1063/1.2795423View Description Hide Description
In this paper, we recall the main characteristics of Raman spectra of single‐walled carbon nanotubes. We illustrate our studies by results obtained on HiPCO samples on one hand, and “arc electric” samples on the other hand by using two different excitation wavelengths. We focus on the peculiarity of observing separately semi‐conducting and metallic tubes. We emphasize also the role played by the radial breathing modes whose frequency depends on the tube diameter and on the need to take into account the interactions between tubes when they are in bundles in order to determine accurately the tube diameter distribution. Finally we demonstrate briefly the evidence of using the SERS (surface enhanced Raman scattering) spectroscopy to study reactions at interfaces or between components in nanotubes/conjugated polymers composites.
935(2007); http://dx.doi.org/10.1063/1.2795424View Description Hide Description
Tin sulphide SnS thin films were deposited on glass substrates using the chemical bath deposition technique (CBD). By investigating the influence of triethanolamine (TEA) concentration on the properties of deposited films, we obtained the optimum deposition parameter. These films were characterized with X‐ray diffraction (XRD), scanning electron microscopy (SEM) analysis and spectrophotometric measurements. The obtained thin films exhibit the orthorhombic structure and the direct band gap energy is found to be about 1.65 eV, for films prepared at TEA concentration films equal to 13.5 M.
935(2007); http://dx.doi.org/10.1063/1.2795426View Description Hide Description
Indium sulphide thin films were deposited at on glass and /glass substrates using the chemical bath deposition technique (CBD). Thin films were grown on different substrates at various time depositions in the range (60–90) min. The optical transmission T(λ) and reflectivity R(λ) varies in the visible region respectively in the domains [67–78%] and [7–14%]. Analysis of the optical absorption data of indium sulphide thin films revealed an optical direct band gap around 1.94 eV and 2.05 eV respectively for layer deposited for equal to 90 min on glass and /glass substrate. The surface study of the refractive index n and the extinction coefficient k as a function of point surface coordinate (x,y) of indium sulphide thin films were studied too.
X‐photoelectron spectroscopy study of physico‐chemical properties of perovskite‐type oxides: Effect of substitution level on the surface properties in the methane combustion reaction.935(2007); http://dx.doi.org/10.1063/1.2795427View Description Hide Description
The objective of this work is to study the effect of lanthanum substitution by calcium on the physico‐chemical properties of solid solutions with a particular attention to the importance of the surface properties.
XPS analysis reveal a significant changes in the La3d,4d; Ca2p; O1s and Mn2p characteristics as well as the excess of concentration with respect to the bulk resulting from the incorporation of Ca in La sublattice. The surface manganese deficit, which is systematically found for any substitution level x, is comparatively low for and particularly important for solids with high amount of calcium.
All these properties are correlated with surface catalytic performances in the methane combustion reaction. The best activities are observed with While the difference is barely perceptible for the samples with a particular positive effect on the catalytic performances is found for
935(2007); http://dx.doi.org/10.1063/1.2795428View Description Hide Description
Submicron and nano‐magnetic particles have been attracting interest both from academic and industrial fields. More information concerning their structure and magnetic properties are needed for extensive development of these small particles to high‐density recording media. In this work, the growth and the magnetic behaviour of cobalt on porous silicon are studied as a function of substrate preparation. We show that rinsing the porous silicon (PS) substrates with ethanol leads to an oxidation of the layer that offers a three dimensional growth. The magnetic behaviour of Co particles grown on PS substrates is rather different than the conventional one and may exhibit a superparamagnetic effect.
935(2007); http://dx.doi.org/10.1063/1.2795429View Description Hide Description
In this work, we report the theoretical and experimental results of cathodoluminescence (CL) from GaN layers with thickness (1–3) micron grown at 800 °C by MOVPE on silicon substrate. The CL measurements were performed in a digital scanning electron microscope DSM 960 at room temperature. The CL spectra recorded at room temperature (RT) show the main UV peak at 3.42 eV of the fundamental transition and a broad yellow band at 2.2 eV attributed the intrinsic defects and extrinsic dopants and impurities. The simulation of the CL excitation and intensity is developed using consistent 2‐D model based on the electron beam energy dissipation and taking into account the effects of carrier diffusion, internal absorption and the recombination processes in GaN. Then, we have investigated the evolution of the CL intensity from GaN as a function the electron beam energy in the range A comparative study between experimental and simulated CL spectra at room temperature is presented.
935(2007); http://dx.doi.org/10.1063/1.2795430View Description Hide Description
In this paper we present a description of the chirp induced in a direct modulated DFB laser. Our study is follows two different approaches. The first approach is based on a resolution of the rate equations of laser; the second, on a simulation of a heterodyne system with the Optisystem software. This study enables us to visualize the chirp in the RF field. We also characterize it according to the injection current parameters, such as the amplitude and the frequency of the modulation. The aim of our study is to choose the appropriate values of these parameters, in order to use the direct modulated DFB laser as an optical tunable source for Coherent Optical Frequency Domain Reflectometry technique (C‐OFDR). We demonstrate that the optical frequency of these lasers can be controlled via the injection current and it can be linearly swept (chirped) over some tens of gigahertz.
935(2007); http://dx.doi.org/10.1063/1.2795431View Description Hide Description
The present work is devoted to a numerical modeling of the Raman scattering in pure amorphous silicon. Using the vacancy model, paracrystalline atomistic models with crystalline volume fraction of have been generated. Using the anharmonic Keating model as interatomic potential, vibrational eigenmodes have been computed in the harmonic approximation. The density of vibrational states, the photon‐phonon coupling coefficient and the reduced Raman spectrum have been calculated for each structural model. Comparison with Raman scattering measurements has been made from which more insights into the local microstructure of amorphous silicon have been inferred.
935(2007); http://dx.doi.org/10.1063/1.2795432View Description Hide Description
The optical properties of ultra thin anodic silicon layers containing silicon nanocrystals were investigated by photoluminescence spectroscopy and Fourier transform infrared absorption spectroscopy. The films were grown by electrochemical dissolution of bulk crystalline silicon at the early stages of anodization using short monopulses of anodic currents ranging from the regime of porous silicon formation to the transition regime between porosification and electropolishing. The conditions for obtaining light emitting films and the origin of light emission will be discussed.
935(2007); http://dx.doi.org/10.1063/1.2795433View Description Hide Description
Several methods of calculation can be used to establish the potential and the field generated in the space by a charge distribution. This present work deals with one of them called the electrostatic image method. We provide a general technique to efficiently calculate the electrostatic potential in dielectric media separated by plane interfaces. The same methodology can be applied to the case of a conducting spherical interface. The basic idea of the method is to take advantage of the properties of the image operator self inverse by a plane or conducting spherical interfaces. The successive image charges due to the neighbouring interfaces are obtained recurrently for the N dielectric media (vector approach). In each media, the electrostatic potential and the field is the one due to the set of successive image charges.
935(2007); http://dx.doi.org/10.1063/1.2795397View Description Hide Description
The fundamental aspects of charge trapping in electron irradiated insulators have been investigated by means of a scanning electron microscope (SEM). The technique commonly used to perform charge injection, their transport and trapping ability is based on the absorbed current method and the SEM mirror effect. In this work, we have studied the influence of temperature on the charge trapping/diffusion during injection time at industrial porcelain samples given by S.T.E.G (Tunisian Society of Electricity and Gas).
Back‐scattering Raman Spectroscopy and Near Normal FTIR Reflection Spectroscopy Investigation of Neodymium Oxide Nanosized Particles Synthesized by Low Temperature Co‐precipitation Technique935(2007); http://dx.doi.org/10.1063/1.2795398View Description Hide Description
In this work we have reported the effects of the near zero degree centigrade temperature performance of the cop‐precipitation on the grain size, agglomeration amount and molecular structure of nano‐sized neodymium oxide powders. The SEM results show that adding the precipitator to the mother salt which was kept at 0 °C has much less agglomeration in comparison with the samples prepared by the room temperature standard co‐precipitation method. Also the recorded spectra of the back scattering Raman spectroscopy of the samples reveal much better molecular structure of the nano‐sized neodymium oxide powders produced by this new modified method.
The Effects of Temperature and Catalyst Grain Sizes on The Properties and Characterization of CCVD Grown CNTs Investigated by Micro‐Raman Spectroscopy935(2007); http://dx.doi.org/10.1063/1.2795400View Description Hide Description
In order to investigate the optimum growth mechanism, carbon naotubes (CNTs) were grown on the Si(100) substrates by catalytic chemical vapor deposition (CCVD) using as the carbon source. Various growth conditions were employed for the synthesis of vertically aligned CNTs by controlling the temperature of the CCVD reactor and also the grain sizes of the catalytic. The used catalytic was in three categories of sizes. In this study, we used at fixed optimum pressure and temperature for the growth of CNTs. Carrier gases consisting of Ar and were used for the transport of the carbon source. The process involves passing a hydrocarbon vapor, typically for 5 minutes, through a tube furnace in which material on Si surface was present at sufficiently high temperature (850 °C) to decompose the hydrocarbon. powders with different nano‐grain sizes were prepared by using co‐precipitation technique. Raman scattering measurements showed that uniform CNTs with different dimensions were grown on the Si faces and the relative intensity and the position of some Raman peaks can be controlled by modulating the size of the catalytic particles in the thermal CVD. Effects of catalyst composition on morphology of CNTs were also studied by Raman spectroscopy. Our results shows that better quality CNTs can be achieved with smaller sizes of catalysts. The growing mechanism of CNTs was not totally clear in the process, what can be pictured is the crucial effect of catalyst on the initial stage of carbon atom deposition. The present results provide useful information for achieving diameter‐controlled growth of CNTs. Nevertheless, it is still hard to control nanotube diameter or chirality, which is the ultimate issue to resolve if we are to maximize their potential as one‐dimensional nanowire.
The Back Scattering Micro‐Raman Spectroscopy of Different Crystalline Phases of Nanoparticles Produced by Sol‐Gel Technique935(2007); http://dx.doi.org/10.1063/1.2795401View Description Hide Description
is known to be one of the best photocatalysts among the semiconductors. In order to improve its photocatalytic features, it is necessary to be able to control factors such as the mean particle size, nanocrystalline system, grain shapes and diffraction. Nanocrystalline sample powders were produced using and as precursor materials and their above features were then characterized by using XRD, Raman spectroscopy and SEM. The grain size was calculated using the Debye Scherrer formula for anatase phase, 15 nm, which is in agreement with the value obtained by SEM imaging. was added dropwise to a very ice‐cold solution of under intensive stirring. This immediately yielded a red solution which was shortly followed by a strong exothermic reaction due to the unstable nature of the reaction at this stage. This process also involved rigorous giving off of and butyl alcohol. A yellow transparent peroxo‐polytitanic (PPT) acid gel was thus prepared. This gel was then heated at 150 °C for 5 hours and was transformed into amorphous The produced yellow powder was heated at 250 °C, 350 °C and 450 °C for one hour with a ramping up speed of 5 °C/min heating rate. It was later calcined at 550 °C, 750 °C and 950 °C for 30 minutes. By investigating the Raman spectra typically shown in figure 1 and also XRD patterns, it was confirmed that the anatase phase nanocrystalline powder, which is well known for its application as photocatalysts, was produced at the first three lower treatment temperatures mentioned above.
Raman Back‐Scattering Spectroscopy of KDP Crystal Doped by at Low Temperatures in the Lower Hydrogen Bonds Region935(2007); http://dx.doi.org/10.1063/1.2795402View Description Hide Description
Single crystals of KDP, potassium dihydrogen phosphate, were grown from supersaturated solutions containing different trivalent metallic ions as dopants. The growth rates of (100) and (101) faces were faster than other faces. Some especial dopants commonly affect the growth rate of crystal. Such impurities can be metallic ions such as or There are many studies concerning the effect of dopants on the growth rate of KDP single crystals. Impurities produce a variety of crystals of different apparent shapes. The mechanism of crystal growth with different dopants was successfully explained by many researches. However, there is a clear lack of experimental data at low temperature Raman spectroscopy. Accordingly, the objective of this study is to show the effects of metallic ions in KDP crystal growth from a saturated solution doped by The behavior of the Raman scattering spectra at lower temperatures down to 10 K of the grown KDP crystals with doping at spectral region up to has been considered. The main emphasis of this paper will be concentrated on the modes behavior related to hydrogen bond modes and also soft modes under the effect of doping. The overall results reveal that that some of these Raman active peaks shift in frequency and they become much more intense at low temperatures.
935(2007); http://dx.doi.org/10.1063/1.2795403View Description Hide Description
Recently, we have presented the column instability under rectilinear oscillatory shear, and we have found the following facts: (a) By varying the shear frequency at fixed amplitude we have observed the quantification of the wave length distortion modes by the sample thickness. (b) By increasing the amplitude we provoke the undulation instability. In this work, we present the undulation of the structure, when the Hexagonal columnar liquid crystal (HCLC) is submitted to alternating shear excitation. We observe for the first time the wavelength modes using Rayleigh scattering. We discuss the obtained results in comparison with the mecano‐optic measurements of the band structure. These experiments give an accurate way to measure the spatial periodicity and the temporal frequency.