Search

The crystal and electronic structure, as well as the energy characteristics of seventeen polymorphic varieties of graphene layers functionalized by hydrogen, were calculated ab initio by the density functional theory method in the generalized gradient approximation. Polymorphic varieties of graphane were theoretically modeled as a result of chemical adsorption of hydrogen on the surface of graphene layers L6, L4-8, L3-12, L4-6-12 and L5-7. On the basis of each of these varieties of graphene, it is possible to form five, six, one, three and two structural types of graphane, respectively. Out of the 17 theoretically constructed graphane polymorphs, 16 have a stable structure. The structure of the СH-L4-8-T3 layer collapsed during geometry optimization. The structure of graphane layers differs by a different degree of deformation, characterized by the Def parameter. The minimum value of this parameter is 10.95° (СH-L6-T1 layer) maximum is 92.51° (СH-L4-8-T2 layer). The sublimation energy of graphane layers varies in the range from 10.70 to 11.48 eV/(CH). A linear dependence of the sublimation energy on the degree of deformation of the layer structure is observed: the less the layer is deformed, the higher its sublimation energy. The electronic structure of all studied graphane polymorphs has a band gap at the Fermi energy level. The width of the band gap varies from 4.76 (СH-L6-T1 layer) to 6.46 (СH-L4-8-T2 layer) eV. A clear dependence of the electronic characteristics on the values of the structural parameters for graphane layers could not be established. [ABSTRACT FROM AUTHOR]

The initial stages of deposition of graphene-like thin films have been studied by X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy and ellipsometry. The deposition process has been performed by sublimation of amorphous carbon on 330 nm SiO2/(001) Si substrates with surface area of 15× 15 mm². The sublimation process was carried out in a quartz tube having an internal diameter of 25 mm at a temperature of 1050°C in which samples were placed in an argon flow of about 1 cm³/s for 3 to 15 minutes. As a source of amorphous carbon, modified carbon blacks SPHERON 5000 were used. We established that an amorphous carbon film with thickness up to 3-6 nm is always deposited on the SiO2 after 3-5 min deposition and the deposition of a few-layered defected graphene as well as nano-sized graphite occurs after 5-6 min on the surface of substrate. Further on, after 8-10min deposition a non-continuous carbon film is formed and after 12-13 min the substrate is covered by a smooth and continuous carbon film. The film has extremely low resistivity (ρ= 2.8 × 10−6Ω.m) and consists of predominantly sp² hybridized carbon with a Raman spectrum similar to those of nano-sized graphene. [ABSTRACT FROM AUTHOR]

Thin films of energetic materials enable a diverse range of characterization measurements: structure, surface energy and adhesion, and even reactivity. Here we describe growth of thin films by a physical vapor deposition method (sublimation) using a dedicated instrument which can operate at ultra-high vacuum. The approach enables fabrication of thin films of energetic materials that are otherwise difficult to process by traditional methods, for example because of their low solubility. The intention is to use this instrument as a platform for studying pure materials and co-deposited materials grown either as multi-layers or as co-crystals. Examples of TATB and LLM-105 film morphologies grown using this technique are presented. [ABSTRACT FROM AUTHOR]

Numerical modelling and optimization of the gas flow and isotope separation in the Iguasu gas centrifuge (GC) for uranium enrichment have been performed for different lengths of the rotor. The calculations show that the specific separative power of the GC reduces with the length of the rotor. We show that the reduction of the specific separative power is connected with the growth of the pressure in the optimal regime and corresponding growth of temperature to prevent the working gas sublimation. The specific separative power remains constant with the growth of the rotor length provided that the temperature of the gas is taken to be constant. [ABSTRACT FROM AUTHOR]

We synthesized very pure dimer phase of coronene by simple heat-treatment and subsequent sublimation purification. It was found that the dimer phase emits very bright red light under the irradiation of low energy ultra-violet light. [ABSTRACT FROM AUTHOR]

Vanadium pentoxide nanostructured thin films (NSTs) have been studied to analyze the effect of plasma on nanostructures grown and morphology of films deposited using sublimation process. Nanostructured thin films were deposited on glass substrates, one in presence of oxygen plasma and other in oxygen environment (absence of plasma). Films were characterized using XRD, Raman spectroscopy, SEM and HRTEM. XRD studies revealed α-V2O5 films (orthorhombic phase) with good crystallinity. However, film deposited in presence of plasma have higher peak intensities as compared to those deposited in absence of plasma. Raman studies also support these finding following same trends of considerable increase in intensity in case of film deposited in presence of plasma. SEM micrographs makes the difference more visible, as film deposited in plasma have well defined plate like structures whereas other film have not-clearly-defined petal-like structures. HRTEM results show orthorhombic phase with 0.39 nm interplanar spacing, as reported by XRD. Results are hereby in good agreement with each other. [ABSTRACT FROM AUTHOR]

In this report, the effect of plasma voltage on plasma assisted sulfurization (PAS) of vertically aligned molybdenum trioxide (α- MoO3) nanoflakes (NFs) on glass substrates has been studied systematically. MoO3 NFs were deposited using plasma assisted sublimation process. These nanoflakes were subjected to H2S/Ar plasma at two different plasma voltages 600 and 1000 volts; to study the effect of plasma ionization on degree of sulfurization of MoO3 into MoS2. XRD and Raman analysis show that film sulfurized at 1000 volts have relatively higher degree of conversion into MoS2, as more intense peaks of MoS2 and MoO2 are obtained than that sulfurized at 600 volts. HRTEM of sulfurized film shows that outer surface of nanoflake has been converted into MoS2 (4-5 monolayers). Meanwhile, MoO3 was reduced into MoO2 as confirmed by XRD and Raman results. All the observed results are well in consonance with each other. [ABSTRACT FROM AUTHOR]

In the present paper, we reported the role of substrate locations relative to source on the growth of MoO3 films deposited on Ni coated glass substrates using plasma assisted sublimation process (PASP). According to the XRD and SEM results, substrate location is very crucial factor to control the morphology of MoO3 films and the best nanostructure growth (in terms of alignments and features) is obtained in case of Sample B (in which substrate is placed on source). The structural results point out that all films exhibit only orthorhombic phase of molybdenum oxide (i.e. α-MoO3)but the most preferential growth is recorded in Sample B due to the presence of intense peaks crossponding to only (0 k 0) family of crystal planes ( k = 2, 4,6..).The Raman analysis again confirms the orthorhombic nature of MoO3 NFs and details of vibrational bondsin Sample B have been given in the present report. The MoO3NFs show intense PL emission in wavelength range of 300-700 nm with three peaks located at 415, 490, and 523 nm in accordance to the improved crystallinity in Sample B. [ABSTRACT FROM AUTHOR]

In this work, we report the growth of α-V2O5 (orthorhombic) nanoplates on glass substrate using plasma assisted sublimation process (PASP) and Nickel as catalyst. 100 nm thick film of Ni is deposited over glass substrate by thermal evaporation process. Vanadium oxide nanoplates have been deposited treating vanadium metal foil under high vacuum conditions with oxygen plasma. Vanadium foil is kept at fixed temperature growth of nanoplates of V2O5 to take place. Samples grown have been studied using XPS, XRD and HRTEM to confirm the growth of α-phase of V2O5, which revealed pure single crystal of α- V2O5 in orthorhombic crystallographic plane. Surface morphological studies using SEM and TEM show nanostructured thin film in form of plates. Uniform, vertically aligned randomly oriented nanoplates of V2O5 have been deposited. [ABSTRACT FROM AUTHOR]

The paper covers the evolution of the liquid phase formed under heating metal conductors by a pulse of current with the density of j ~ 106/108 A/cm². Following the theoretical assessment and experimental data' it was shown that the two-phase state (condensed phase - gas) during the early expansion of products of electric explosion of wires can be caused by the development of density fluctuations in the liquid phase of the metal. The density fluctuation formation is caused by the destruction of liquid phase clusters of short-range order. The study demonstrated the absence of the complete transition of the semiconductor matter into gas after the injection of energy exceeding the energy of sublimation Es. [ABSTRACT FROM AUTHOR]

Unsteady behavior of Io's atmosphere caused by condensation and sublimation of SO2 (the main atmospheric component) during and after eclipse is studied on the basis of kinetic theory. A deterministic computation for a model Boltzmann equation by means of a finite-difference method is performed to obtain the time evolution of the profiles of macroscopic quantities (density, flow velocity, and temperature) in high resolution. As a result, the transient wave motion and oscillatory behavior in the profiles are clarified. To concentrate on the dominant effect of the noncondensable gas (SO or O2), other effects in the real atmosphere (e.g., plasma impingement, chemical reactions, etc.) are all omitted in the present analysis. Despite those simplifications, the overall behavior of the atmospheric column is similar to the more realistic result of the previous DSMC analysis in C. H. Moore et al., Icarus 201, 585 (2009). [ABSTRACT FROM AUTHOR]

Cadmium sulfide (CdS) thin films of different thicknesses were deposited on corning glass by closed space sublimation (CSS) technique in a vacuum. Structural, electrical, optical, Fourier transform infrared (FTIR) with Raman spectrometric properties were investigated. X-rays diffraction used to identify the preferred orientation of CdS thin films as well as crystalline size, dislocation density and strain vs thickness was estimated. The electrical properties like resistivity, mobility vs thickness was calculated at room temperature. Optical properties were investigated from UV-VIS-NIR ranges which were used to calculate band gap, thickness of the films, also samples were placed at different angles in spectrophotometer to investigate the effect of angles variation on %T and band gap. Raman spectroscopy for identification of vibration modes in thin films by varying thickness. [ABSTRACT FROM AUTHOR]

Despite the widespread use of positron technology the efficiency of positron utilization is less than 1 %. The low efficiency is primarily due to positron destruction during moderation. Emitted positrons must be filtered through a moderator material to restrict the re-emitted positrons to a useable and defined energy range. The quantum mechanical nature of solidified hydrogen holds the potential to increase the moderator efficiency an order of magnitude over solid neon-the current leader in moderator efficiency. However the characteristics of solid hydrogen as a positron moderator have never been investigated. This paper discusses the design of an experimental cryostat to create solid hydrogen targets for positron beam studies. The design is constrained by the sublimation pressure of the solid hydrogen target exceeding the vacuum pressure of the positron accelerator, and the ability to control hydrogen crystal growth and quality. Thermal control calculations of the test section and heat exchangers are presented. [ABSTRACT FROM AUTHOR]

The use of physical vapor deposition is an attractive technique to produce microenergetic samples to study sub-millimeter explosive behavior. Films of the high explosive PETN (pentaerythritol tetranitrate) were deposited through vacuum thermal sublimation. Deposition conditions were varied to understand the effect of substrate cooling capacity and substrate temperature during deposition. PETN films were characterized with surface profilometry and scanning electron microscopy. Detonation velocity versus PETN film thickness was analyzed using a variation of the standard form for analysis of the diameter effect. Results were compared with previous work conducted on PETN films deposited with lower substrate cooling capacity. Seemingly subtle variations in PETN deposition conditions led to differences in detonation behaviors such as critical thickness for detonation, detonation velocity at "infinite" thickness, and the shape of the critical thickness curves. [ABSTRACT FROM AUTHOR]

Using optical techniques, we analyzed an impact of non-intentional Al mpurity and twin boundaries to photoelectrical properties of sublimation-grown 3C heterostructures. Differential transmission techniques revealed Al related contribution to probe beam absorption with cross-section σAl = (1.8±0.5)×10-17 cm2 at 1064 nm, being four times stronger that the free-carrier absorption cross-section at given wavelength. Temperature dependent carrier recombination rates provided trap activation energy of 170 and 210 meV in two samples with different Al concentration. Saturation of probe beam absorption with excitation allowed determination of electrically active Al concentration, not gettered at grain boundaries. Increase of room-temperature mobility with injection in the highly defective layer and the corresponding lifetime decrease pointed out contribution of point and structural defects to carrier scattering. [ABSTRACT FROM AUTHOR]

We report on carbon doping of cubic GaN by CBr4 using plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. The samples consist of a 70 nm thick GaN buffer followed by a 550 nm thick GaN:C layer. Carbon doping is realized with a home-made carbon tetrabromide sublimation source. The CBr4 beam equivalent pressure was established by a needle valve and was varied between 2×10-9 mbar and 6×10-6 mbar. The growth was controlled by in-situ reflection high energy electron diffraction. The incorporated carbon concentration is obtained from secondary ion mass spectroscopy. Capacitance voltage characteristics were measured using metal-insulator-semiconductor structures. Capacitance voltage measurements on nominally undoped cubic GaN showed n-type conductivity with ND-NA = 1×1017 cm-3. With increasing CBr4 flux the conductivity type changes to p-type and for the highest CBr4 flux NA-ND = 4·5×1018 cm-3 was obtained. [ABSTRACT FROM AUTHOR]

Although the growth of 6H and 4H-SiC polytypes seem to be almost solved, it is somewhat different for the cubic 3C-SiC polytype. This latter still is a highly challenging and exciting scientific issue, mainly because of the discrepancy between the stability range of this polytype and the operating conditions of the available bulk growth processes. Despite many previous attempts along the last decades, it is only very recently that some works have paved the way to a real 3C-SiC bulk growth development. Among the key results is the demonstration of 3C-SiC growth using a variant of the sublimation method, thereby demonstrating that the high temperatures are not necessarily a lock to the growth of 3C. Another example is the achievement of a stable growth front over a very long time in a top seeded solution growth process. Both approaches have shown a real potential for growing high structural quality 3C-SiC crystals. The current state of the art of these two processes will be presented and compared with respect to the problems of size or density of extended defects. Their respective strengths will also be discussed considering their future development. [ABSTRACT FROM AUTHOR]

Epitaxial 3C-SiC layers have been grown on 6H-SiC substrate via sublimation growth in a RF induction heated reactor. The growth process was carried out at a source temperature 2000° C under vacuum condition at temperature gradient in the range of 5-8° C/mm. The morphological investigation by optical microscope with Nomarski interference contrast in transmission mode reveals 100% inclusion free 3C-SiC for the layer grown at temperature gradient of 8° C/mm. 2Theta-omega scan shows 0006 and 111 peaks coming from the substrate and the layer, respectively. The higher intensity of 3C-SiC 111 peak for the layer grown at temperature gradient of 8° C/mm is due to continuous nature of 3C-SiC domains compared to that grown at lower temperature gradient. The influence of the temperature gradient on the morphology of layers investigated by Atomic Force Microscopy (AFM) is discussed. [ABSTRACT FROM AUTHOR]

In this work we have analyzed the possibility of upscaling the growth of 3C-SiC. The growth was done at different temperatures to find limiting mechanisms of the growth rate and to examine the morphology of grown layers. Coverage by 3C-SiC increases when increasing temperature, however more twins appeared. Activation energy of the growth is 130 kcal/mol-showing that growth rate limiting mechanism is sublimation of the source. We discuss the influence of large area 6H-SiC wafers on the formation of 3C-SiC, in which the change in basal plane orientation could also influence the growth of 3C-SiC. [ABSTRACT FROM AUTHOR]

Epitaxial p-type 3C-SiC layers have been grown on 6H-SiC substrates by means of the sublimation epitaxy method. The growth process was conducted at a source temperature of 2000° C under vacuum conditions (<10-5 mbar). The source material was polycrystalline sintered SiC. The p-type doping was achieved by adding an AlN source. Two samples have been sequentially grown using the same source. Schottky contacts have been prepared and the samples have been characterized by means of current-voltage (I-V) measurements, capacitance-voltage (C-V) analysis, deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS). The results show that boron has been incorporated during the growth. The boron related D-center was found in the DLTS spectra taken on several contacts on both samples. Furthermore, the samples reveal an inhomogeneous distribution of extended defects, which are electrically active and visible in the DLTS spectra. [ABSTRACT FROM AUTHOR]

We report on carbon doping of cubic GaN by CBr4 using plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. The samples consist of a 70 nm thick GaN buffer followed by a 550 nm thick GaN:C layer. Carbon doping is realized with a home-made carbon tetrabromide sublimation source. The CBr4 beam equivalent pressure was established by a needle valve and was varied between 2×10-9 mbar and 6×10-6 mbar. The growth was controlled by in-situ reflection high energy electron diffraction. The incorporated carbon concentration is obtained from secondary ion mass spectroscopy. Capacitance voltage characteristics were measured using metal-insulator-semiconductor structures. Capacitance voltage measurements on nominally undoped cubic GaN showed n-type conductivity with ND-NA = 1×1017 cm-3. With increasing CBr4 flux the conductivity type changes to p-type and for the highest CBr4 flux NA-ND = 4·5×1018 cm-3 was obtained. [ABSTRACT FROM AUTHOR]

The present study investigates local heat/mass transfer characteristics on blade tip surface with squealer rim. A linear cascade experimental setup consists of three large scale airfoils was used. The axial chord length and turning angle of test blade are 237 mm and 126°, respectively. Heat/mass transfer coefficients were measured with three different rim heights (3%, 6% and 9% of axial chord length) and fixed tip clearance (2% of axial chord length). Main flow Reynolds number based on axial chord length is 1.5×105. Naphthalene sublimation method is used to measure the detailed mass transfer coefficient on the blade tip surface. The heat/mass transfer results show that as the rim height increases, the peak values on the upstream region of the tip surface decreases and moves to the suction side rim. At the downstream region of the tip surface, the pitch-wise averaged heat/mass transfer coefficients increases as the rim height increases. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is emerging as a viable desalination technology because of its low energy requirements that can be provided from low-grade, waste heat and because it causes less fouling. In MD, desalination is accomplished by transporting water vapour through a porous hydrophobic membrane. The vapour transport process is governed by the vapour pressure difference between the two sides of a membrane. A variety of configurations have been tested to impose this vapour pressure gradient, however, the air-gap membrane distillation (AGMD) has been found to be the most efficient. The separation mechanism of AGMD and its overall efficiency is based on vapour-liquid equilibrium (VLE). At present, little knowledge is available about the optimal design of such a transmembrane VLE-based evaporation, and subsequent condensation processes. While design parameters for MD have evolved mostly through experimentations, a comprehensive mathematical model is yet to be developed. This is primarily because the coupling and non-linearity of the equations, the interactions between the flow, heat and mass transport regimes, and the complex geometries involved pose a challenging modelling and simulation problem. Yet a comprehensive mathematical model is needed for systematic evaluation of the processes, design parameterization, and performance prediction. This paper thus presents a coupled fluid flow, heat and mass transfer model to investigate the main processes and parameters affecting the performance of an AGMD. [ABSTRACT FROM AUTHOR]

A new scenario of planetesimal formation is proposed. The key process is sublimation and condensation of H2O ice resulting in the splitting of icy dust aggregates. Fragments produced by the splitting accumulate in the solar nebula and the dust surface density increases enough to trigger gravitational instability of the dust layer. We show results of numerical simulations of the dust aggregate splitting and the evolution of the dust surface density which support this scenario. [ABSTRACT FROM AUTHOR]

One dimensional direct simulation Monte Carlo (DSMC) simulations are used to examine the effect of a trace non-condensable species on the freeze-out dynamics of Io’s sulfur dioxide sublimation atmosphere during eclipse and egress. Due to finite ballistic times, essentially no collapse occurs during the first 10 minutes of eclipse at altitudes above ∼100 km, and hence immediately after ingress auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. In the absence of a non-condensable species the sublimation SO2 atmosphere will freeze-out (collapse) during eclipse as the surface temperature drops. However, rapid collapse is prevented by the presence of even a small amount of a perfect non-condensable species due to the formation of a static diffusion layer several mean free paths thick near the surface. The higher the non-condensable mole fraction, the longer the collapse time. The effect of a weakly condensable gas species (non-zero sticking/reaction coefficient) was examined since real gas species may not be perfectly non-condensable at realistic surface temperatures. It is found that even a small sticking coefficient dramatically reduces the effect of the diffusion layer on the dynamics. If the sticking coefficient of the non-condensable exceeds ∼0.25 the collapse dynamics are effectively the same as if there was no non-condensable present. This sensitivity results because the loss of non-condensable to the surface reduces the effective diffusion layer size and the formation of an effective diffusion layer requires that the layer be stationary which does not occur if the surface is a sink. As the surface temperature increases during egress from eclipse the sublimating SO2 gas pushes the non-condensable diffusion layer up to higher altitudes once it becomes dense enough to be collisional. This vertical species stratification should alter the auroral emissions after egress. [ABSTRACT FROM AUTHOR]

We have measured the spectra of multi-bubble sonoluminescence from aqueous LiCl, NaCl, MgCl2, CaCl2, CuSO4 solutions, saturated with argon, at the frequency 22 kHz. The spectra were collected at different hydrostatic pressures for all salts and in the ambient temperature range of 1–20 °C for NaCl solutions. Total absorbed ultrasonic power was 41 W. The results show that line emission from exited state metal atoms grows rapidly with the increase of hydrostatic pressure and at low ambient temperature. In all cases the increase of the intensity of underlying continuum and OH-radical emission was much lower than that of atomic emission at the same experimental conditions. The observed effects can be explained assuming higher temperature inside the cavitation bubbles during collapse in case of increased static pressure or decreased vapor pressure. [ABSTRACT FROM AUTHOR]

Titanium evaporation in a reactive atmosphere of ammonia has been chosen to deposit thin (up to 10 nm) protective surface layers containing titanium nitride and titanium oxinitrides which suppress secondary electron emission. The coating procedure, applied by the author in DESY (Hamburg) for TESLA couplers anti-multipactor protection, has been recently implemented in The Andrzej Soltan Institute for Nuclear Studies (IPJ) where a new coating device is used, equipped with a special titanium sublimation setup in a 100 1 vacuum chamber. Several arrays of cylindrical and coaxial RF coupler windows have been coated so far after optimizing the processing parameters. A check of the obtained surface layers ability to attenuate secondary electron emission has been performed; measurements of the secondary electron yield from TiN layers deposited on alumina samples were done in IPJ on as-delivered coated samples, then after vacuum bake-out and finally after additional electron bombardment of their surfaces. Also chemical composition of the surface layers has been studied using XPS in the Institute of Physical Chemistry (IChF). [ABSTRACT FROM AUTHOR]

A basic study was carried out on the CO2 solid-gas two phase flow with particle sublimation. The CO2 two phase flow is achieved by liquid CO2 expansion process throughout the CO2 triple point. A cryogenic refrigeration below -56.6 °C is possible from the CO2 solid particle sublimation in the two phase fluid flow. An experiment was conducted in order to investigate some basic points related to the liquid CO2 expanding into the solid-gas fluid flow, which reveals the CO2 particle size and so on. Based on the primary experiment, a new refrigeration method is introduced by using the CO2 solid-gas two phase flow with particle sublimation. A CO2 heat pump, which can achieve a cryogenic refrigeration below -56.6 °C is designed, constructed and tested. In the paper, details of the CO2 heat pump system are presented and the obtained results show that a continuous operation is possible with CO2 solid-gas flow in the closed loop of the heat pump system. Furthermore, the performance of the new CO2 heat pump system is also presented in this paper, which utilize the flow dynamic of liquid CO2 expanding into the solid-gas fluid. [ABSTRACT FROM AUTHOR]

We study the generation of radiation at the 5P3/2-4S1/2 transition of potassium vapor under excitation of the 4S1/2-6S1/2 two-photon resonance. The model consists of the coupled Maxwell-Bloch equations for a four-level configuration of Potassium atom including states 4S, 4P, 5P and 6S, which is numerically solved. Previous experimental studies have shown the emission of Parametric Four-Wave Mixing (PFWM) radiation near the 5P3/2-4S1/2 transition at low vapor pressures (P<1014 atoms/cm3) which is also shown in the case of the model studied. [ABSTRACT FROM AUTHOR]

Growth of bulk hexagonal SiC crystals by Physical Vapor Transport relies on sublimation / condensation of a solid SiC charge performed in a semi-closed crucible at 2200–2400 °C. The gradual loss of silicon-rich vapor results in the shift of crystal stoichiometry from silicon to carbon rich and associated change of nitrogen dopants. The thermal gradients during growth induce stresses sometimes in excess of critical resolved shear stress reduced by high growth temperatures. This results in plastic deformation of the growing boules through the activation of <11–20>(0001) slip system. SiC epitaxial layers are deposited by Chemical Vapor Deposition process performed at 1500–1700 °C using silane and propane in hydrogen carrier gas. Since the polytype nucleating at these temperature is 3C-SiC, the layers are grown on off-cut substrates in step flow mode. Approaches to epitaxy producing layers suitable for high voltage power devices i.e. with low defect density (<1 cm-2), low doping (1×1015 cm-3), and long carrier lifetimes (>1 μs) are described. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

For complex heat and mass transfer during freeze-drying, the shape and the moving rate of sublimation interface have not been clearly recognized yet. In this paper, Micro-CT scanner was used to follow the moving interface during sublimation. Apple slices cut into 16mm in diameter and 8mm in thickness were used as experimental samples, they were scanned every two hours during sublimation. The scanning images were analyzed and measured, then variation curves of grey value and curves of sublimation rate in two directions were obtained. The moving rates of sublimation interface under various precooling rates and primary drying temperatures were compared. The results show that, heat and mass transfer happens both at the upper and the under surface of the sample. Also it happens at the side surface to some extent. The interface shows as a three-dimensional moving mode, contracts to the geometric centre of the sample and presents an approximately spheral shape. Apple samples frozen at low rate sublimated more quickly than those by high rate. While drying temperature was higher, the sublimation interface moved more quickly. Under slow precooling condition, the sublimation rate rose quickly near the end of sublimation not only in vertical direction, but in horizontal direction. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The research effort at Teledyne Energy Systems, Inc., which has been aimed at improving the performance of the currently used thermoelectric (TE) materials has identified a number of improved formulations for the standard n-type PbTe and p-type TAGS. The preliminary test results appear to indicate nearly 50% higher thermal to electric energy conversion efficiency for these new PbTe and TAGS formulations. Effort is continuing to confirm the preliminary test results and validate the materials fabrication processes. Multiple batches of the newly developed TE materials will be prepared and characterized for thermoelectric properties. The selected TE materials will be subjected to degradation analysis and life modeling to determine any deterioration in the TE properties as a function of time and operating temperatures. This effort also includes measurement of sublimation rates as a function of temperature for the selected materials. The results for the initial sublimation tests are quite encouraging and show appreciable reduction in sublimation rate for TAGS 80 and the modified TAGS alloys. Future effort will include determination of effect of sublimation on TE characteristics for the selected TE materials. Microanalysis technique such as optical and electron microscopy, XRD and EDSX will be used to determine the microstructural characteristics of the TE materials at various stages of their simulated operating life. Based on the results of these studies the n-type and p-type materials with the highest power conversion efficiency and the lowest degradation rate will be selected for use in fabrication of future thermoelectric devices. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Infinitely Thin Plate (ITP) method has been used to determine the parameters of first-order phase transitions. Experiments and main estimates were performed in a one-dimensional approximation. The method was validated for high-temperature materials with known melting parameters, namely, Zr, Ti, Ta, W for P∼105 Pa. Furthermore, the fusion temperature of W for P∼107 Pa and carbon sublimation temperature for P= 5·104 Pa were also measured. Experiments proved the ITP method to be useful for investigating the random component of the “time-temperature” curve. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this report, we synthesize vertically aligned molybdenum trioxide (ɑ-MoO3) nanoflakes (NFs) with high aspect ratio (height/thickness >15) on the cobalt coated glass substrates by the plasma assisted sublimation process, employing Mo metal strip as a sublimation source. The effect of substrate temperature, nature of substrate as well as the geometry of the sublimation source (Mo-strip) have been investigated on the morphological, structural and optical properties of the grown NFs, keeping plasma parameters as fixed. The surface morphology, crystalline structure and optical properties of MoO3 NFs have been studied systematically by using scanning electron microscope (SEM), transmission electron microscope (TEM) with selected area electron diffraction (SAED), X-ray diffractometer, and IR- spectroscopy. The experimental observations endorse that the characteristics of MoO3 NFs are strongly depend on substrate temperature, substrate nature as well as geometry of Mo-strip. All the observed results are well in consonance with each other. [ABSTRACT FROM AUTHOR]

Multi-heterojunction Organic solar cells based on small molecule have been deposited in vacuum by sublimation. The heart of the cell consists in a three superposed multilayers structure. A blend Cu-phthalocyanine:fullerene (Cu-Pc:C60) or CuPc:perylene derivative (CuPc:PTCBI) deposited by co-evaporation is sandwiched between a CuPc and a C60 (or PTCBI) layers. The anode is an ITO film deposited onto glass, while the cathode is an Al layer deposited by evaporation. In order to achieve good carrier collection efficiency by the electrode, buffer layers have been introduced between the electrodes and the organic materials. An ultra-thin gold film has been deposited onto the ITO anode to have a good band matching between the work function of the anode and the highest occupied molecular orbital (HOMO) of the electron donor, the CuPc. The bathocuproine (BCP) is used as exciton blocking layer at the interface between the electron acceptor (C60) and the Al cathode. The effect of the substrate temperature during deposition onto the solar cells performance as been studied, using the electron acceptor as parameter. It is shown that when C60 is used, that is to say when a spherical molecule is used, there is no improvement of the efficiency of the cells when the substrate is heated during deposition. On the contrary, when a planar molecule is used, such as PTCBI, there is a significant improvement of the solar cell efficiency, when the substrate is heated. This behaviour can be attributed to a higher order of the planar molecule in the film due to substrate heating during deposition. [ABSTRACT FROM AUTHOR]

Copper 2, 9, 16, 23-tetra-tert-butyl-29H, 31H-phthalocyanine (CuTTBPc) thin films have been prepared by vacuum sublimation technique. The films were annealed at 50 to 250°c for 1 hr. The optical, electrical and morphological properties have been investigated as a function of different annealing temperature. The optical measurements have been carried out in the ultraviolet and visible region. The analysis of the spectral behaviour of the absorption coefficient in the absorption region near fundamental edge reveals direct transitions. The energy band gap is investigated. The d.c electrical conductivity is carried out as a function of temperature to investigate the electronic structure of CuTTBPc thin films and to understand the conduction mechanism. The morphology of the films are studied using Scanning Electron Microscopy (SEM). [ABSTRACT FROM AUTHOR]

The dynamics of a single qubit, encoded in the charge states of a singly ionized phosphorus atom embedded in silicon bulk material are studied. For the simulation of the system a suitably modified version of the MATLAB package SCHRODINGER was used. Preliminary results were in agreement with previously published work regarding single qubit rotations. For the Hadamard Gate, the duration of the pulse T was computed as a function of input parameters the results produced outputs of the order of 9×10-10 sec. [ABSTRACT FROM AUTHOR]

Highly oriented and uniformly distributed molybdenum oxide nanoplates have been deposited on to Cobalt coated glass substrate by sublimation route in presence of reactive oxygen plasma. During entire experiments molybdenum strip is taking as a sublimation source. The possible growth process for the formation of MoO3 nanoplates has been modeled by the three step process. The morphological, structural, optical properties of nanoplates have been investigated systematically using scanning electron microscopy, x-ray diffraction, IR spectroscopy. [ABSTRACT FROM AUTHOR]