Hot-wall Vapor Research Articles

Temperature dependence of Raman and photoluminescence spectra of pure and high-quality MoO3 synthesized by hot wall horizontal thermal evaporation

In this work, a novel system for the hot wall evaporation of MoO3 in a horizontal furnace and at low vacuum atmosphere was settled. Pure MoO3 material was obtained without the presence of other phases and with a strong preferential orientation, as revealed by electron microscopy, micro-Raman spectroscopy and x-ray diffraction. Photoluminescence and Raman spectra were measured as a function of temperature. As a result, the first-order temperature coefficient of the fifteen measured vibrational modes is reported and compared with the scarce literature data available. The relation of these coefficients with the thermal expansion coefficient is discussed in the framework of the Grüneisen model. Moreover, for the first time, the temperature dependence of the different contributions of photoluminescence spectra for MoO3 is reported, and an anomalous increase in PL intensity of all transitions is observed in the range of 40–140 K, followed by a normal quenching at high temperatures. The Shibata model was used to interpret the origin of this anomalous effect.

Epitaxial Tetrathiafulvalene–Tetracyanoquinodimethane Thin Films on KCl(100): New Preparation Methods and Observation of Interface-Mediated Thin Film Polymorph

Combining organic compounds of complementary ionization potential and electron affinity allows fabrication of charge-transfer complexes that exhibit remarkable properties, resulting, for example, in very high conductivity. Though the bulk properties of the prototypical organic conductor tetrathiafulvalene–tetracyanoquinodimethane (TTF-TCNQ) have been studied in detail, the influence of defects and crystallite size on the resulting electronic properties, as well as an integration of these materials in organic thin film devices, is barely explored. One important requirement for such a comprehension is the precise control over crystallite size and quality. In this study, we report on different strategies to prepare crystalline TTF-TCNQ thin films and compare their structural quality. While conventional organic molecular beam deposition of TTF-TCNQ onto KCl(100) substrates enables the growth of epitaxial thin films with grain dimensions of up to 2 μm, further enhancement of the crystallite dimensions by raising the growth temperature is thermally limited by vanishing sticking and onset of vaporization. Using more sophisticated methods like hot wall evaporation, however, allows one to overcome these limitations and yields crystalline islands with extensions enhanced by 2 orders of magnitude. Furthermore, we identify and provide a full structure solution of a yet unknown interface-mediated thin film polymorph of TTF-TCNQ, which is adopted in films of thicknesses below 1 μm.

Structural, optical and electrical characterization of hot wall grown 9,10-dibromoanthracene films for light emitting applications

For this study thin films of 9,10-dibromoanthracene (DiBrAn) were prepared by hot wall evaporation technique onto the glass substrate under different experimental conditions for light emitting applications. These films were systematically characterized for structural, optical and electrical studies by x-ray diffraction, atomic force microscope, scanning electron microscope, Fourier transform infrared spectroscopy, UV-Vis spectroscopy, and photoluminescence investigations. On examination, crystallinity, electrical conductivity and optical band gap of the DiBrAn films were found to increase with increase in substrate temperature. The wide optical band gap and strong blue emission of DiBrAn make this material an efficient blue emitter.

Large-Area Crystalline Microcolumnar LaBr$_{3}$:Ce for High-Resolution Gamma Ray Imaging

Novel fabrication methods for cost-effective and large-volume production of important lanthanide halide scintillators are currently being explored. Here we report on the growth of LaBr :Ce scintillator films in a novel light conserving morphology known as Crystalline Microcolumnar StructureTM (CMSTM), using Hot Wall Evaporation (HWE) technique. This method produces specimens which preserve the response uniformity over the area of the film, and low attenuation of light throughout its thickness. Using this approach, we have produced LaBr :Ce film samples measuring 3-7 cm in diameter and approaching 2 cm in thickness, with densely packed microcolumns averaging ~15 μm in diameter. Some of these films show bright light emissions compared to their crystalline counterparts, demonstrating energy resolution of ~9.4% at 122 keV ( Co emission) and uniformity in light response across the area of the scintillator. Imaging data acquired using the University of Arizona Bazooka SPECT detector incorporating our CMS LaBr :Ce film demonstrated m spatial resolution ~138 μm at 122 keV in single-photon counting imaging mode. This technique permits fabrication of thick films that can simultaneously provide the high absorption efficiency and high spatial resolution required for small-animal SPECT imaging and other medical and non-medical applications.

Electrical Properties of Polycrystalline α-HgI2 Detector

Potentially low cost and large-area polycrystalline mercuric iodide (α-HgI2) is one of the preferred materials for the fabrication of room temperature X-ray and gamma-ray detectors. In this paper, polycrystalline α-HgI2 films have been grown through combining vertical deposition method with hot wall vapor phase deposition (HWPVD) method. X-ray diffraction (XRD), scan electron microscopes (SEM) and Raman spectrum were used to characterization the HgI2 films obtained, and I-V characteristics was also tested. Using the polycrystalline α-HgI2 films, we get the detector. According to the detector, on the one hand, a dark current test is made by using KEITHL EY 485 picoammeter; on the other hand, the Agilent 4294A precision impedance analyzer is taken to test the characteristic curve of its capacitor frequency.

Growth Time Influence on Polycrystalline α-HgI<sub>2</sub> Films

Polycrystalline α-HgI2 films have been grown on TFT substrates using hot-wall vapor phase deposition (HWPVD) with the different growth times. The influence of different growth times (1 hour, 2 hours, 3 hours, 4 hours) on the structural and electrical properties of the polycrystalline α-HgI2 films is investigated. Metallurgical microscope, scan electron microscopes (SEM) and X-ray diffraction (XRD) characterization and the electric transport properties were investigated by the I-V characteristics. The polycrystalline α-HgI2 films growth by 3 hours show more better performance than others. So we use it preparation a detector.Finally, capacitance frequency characteristics analysis showed the detector have good performance.

Hot Wall Evaporation of High-Sensitivity, High-Resolution CeBr$_{3}$ Scintillator

Research related to fabrication of novel lanthanide halide scintillators in large physical sizes, using time- and cost-efficient methods, has been an ongoing process. The principal emphasis is on fabrication to derive novel light-conserving morphologies that are required for room-temperature radioisotope identification and other demanding spectrographic and imaging applications. Our fabrication technique addresses each of the many serious limitations of current growth methods, allows rapid large-volume synthesis at a substantially reduced cost versus current techniques, and is equally effective for manufacturing other advanced inorganic and solid state semiconductor materials. Here we report on the growth of CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> scintillator using hot wall evaporation. Under favorable deposition conditions, this material could be grown in polycrystalline form suitable for spectroscopic applications, or even in the microcolumnar form desirable for high spatial resolution gamma ray imaging. The work carried out so far shows that films produced using this approach are self-activated and possess all of the excellent properties of their melt-grown crystal counterparts. The scintillation properties discussed in this report are relative light yield, energy resolution, spectroscopic emission, light emission uniformity and detection of alphas using as-deposited CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> specimen. This paper will further discuss fabrication technique and its advantages.

Highly oriented polycrystalline α-HgI2 films grown through combined vertical deposition and HWPVD methods

Different α-HgI2 seed layers were prepared by vertical deposition method through varying reactive solution concentrations. Polycrystalline α-HgI2 films were grown on the α-HgI2 seed layer by the hot wall vapor phase deposition (HWPVD) method. The orientation along the (001) direction and compactness of the polycrystalline α-HgI2 films are significantly enhanced as compared to that without a seed layer. The polycrystalline α-HgI2 films grown on a three-deposit seed layer show improved electrical properties.

Research on Thermal Stress of Slab Heating Process Based on Transient Non-Linear Analysis

Polycrystalline α-HgI2 films have been grown through combining vertical deposition method with hot wall vapor phase deposition (HWPVD) method. The influence of the α-HgI2 seed layers on the structural and electrical properties of the polycrystalline α-HgI2 films was investigated. It is found that the α-HgI2 seed layers play an important role in reducing the grain sizes, increasing the density improving the crystallographic orientation and electrical properties of the polycrystalline α-HgI2 films.

Effect of Seed Layers Prepared by Vertical Deposition Method on the Growth and Properties of Oriented Polycrystalline α-HgI&lt;sub&gt;2&lt;/sub&gt; Films

Polycrystalline α-HgI2films have been grown through combining vertical deposition method with hot wall vapor phase deposition (HWPVD) method. The influence of the α-HgI2seed layers on the structural and electrical properties of the polycrystalline α-HgI2films was investigated. It is found that the α-HgI2seed layers play an important role in reducing the grain sizes, increasing the density improving the crystallographic orientation and electrical properties of the polycrystalline α-HgI2films.

Growth and Characterization of Polycrystalline Lanthanide Halide Scintillators.

We are exploring a novel time- and cost-efficient approach to produce robust, large-volume polycrystalline lanthanide halide scintillators using a hot wall evaporation (HWE) technique. To date, we have fabricated LaBr3:Ce and LaCl3:Ce films (slabs) measuring up to 7 cm in diameter and 7+ mm in thickness (20 to 25 cm3 in volume) on quartz substrates. These polycrystalline scintillators exhibit very bright emissions approaching those exhibited by their melt-grown crystal counterparts. Scanning electron micrographs (SEMs) and X-ray diffraction analyses confirm polycrystalline growth with columnar structures, both of which help in light piping, thereby contributing to the observed high light yields. The new scintillators also exhibit good energy resolution for γ-rays over the tested range of 60 keV (241Am) to 662 keV (137Cs), although they have not yet reached that of the corresponding crystals. The measured response linearity over the same energy range is comparable for both our HWE synthesized films and melt-grown commercially-available reference crystals. Similar consistency in response is also observed in terms of their decay time and afterglow behaviors. The data collected so far demonstrate that our HWE technique permits the rapid creation of scintillators with desired structural and compositional characteristics, without the introduction of appreciable defects, and yields material performance equivalent to or approaching that of crystals. Consequently, the deposition parameters may be manipulated to tailor the physical and scintillation performance of the resulting structures, while achieving a cost per unit volume that is substantially lower than that of crystals. In turn, this promises to allow the use of these novel scintillation materials in such applications as SPECT, PET, room-temperature radioisotope identification and homeland security, where large volumes of materials in a wide variety of shapes and sizes are needed. This paper describes our growth and testing of polycrystalline LaBr3:Ce scintillators and provides comparative characterizations of their performance with crystals.

Pressure Dependence of Aluminum Doping in SiC Vapor Phase Epitaxy

AbstractThe dependence of the aluminum incorporation on the total pressure in a hot wall vapor phase reactor for SiC homoepitaxial growth has been investigated. It was found that in the doping concentration range from 1·1017 cm−3 to 1·1019 cm−3 the incorporated aluminum concentration varies by the factor 3 to 4, when the reactor pressure is changed from 150 mbar to 250 mbar. Lower reactor pressure gives lower aluminum concentration. Periodically changing reactor pressure results in aluminum concentration periodically changing with depth in the epilayer. All results were measured electrically by capacitance-voltage measurements on nickel Schottky contacts. Additional experiments have been performed for n-type nitrogen doped SiC epilayers for comparison. The nitrogen doping concentration was found to be independent of the reactor pressure within the accuracy of the applied C-V measurements and the doping profile analysis method.

52.4: The High Deposition Rate and High Material Yield Evaporation Method for OLED Layers

AbstractFor reducing the manufacturing cost of Organic Light Emitting Diode (OLED) display, it has been necessary to develop new fabricating method such as the mass production equipment with higher throughput, higher material yield and good film thickness uniformity for larger substrates. In order to satisfy these requirements, a new marvelous technology, we call as “Hot‐Wall evaporation method”, was introduced. This method could achieve deposition rate of 20 Å/s, material yield of 70%, and film thickness uniformity of ±4% for both a 400mm width and a 100 mm square substrate. As a result we established the possibility of manufacturing the new mass production equipments which fabricate OLED at lower cost.

Synthesis of wurtzite GaN films by reactive hot wall vapour deposition technique: fabrication of Au/GaN Schottky diode

Wurtzite GaN films were synthesised on p-Si(1 0 0) and n-Si(1 0 0) substrates by plasma assisted hot wall vapour deposition technique without using any buffer layer. The films were characterised by electrical and optical measurements while the microstructural information was obtained from atomic force microscopy (AFM) and X-ray diffraction (XRD) studies. The compositional study for the GaN film was carried out using SIMS. Photoluminescence (PL) measurement at room temperature exhibited near band edge (BE) emission at ∼363 nm (3.4 eV) along with a broad yellow band. The bonding environment in the film was revealed from FTIR studies. Schottky diode (Au/GaN), fabricated with hexagonal GaN film on n-Si substrate, was characterised by I– V and C– V analysis.

Hexagonal GaN films deposited by reactive hot wall evaporation technique

Gallium nitride (GaN) films were deposited by reactive hot wall evaporation technique onto fused silica (quartz) substrates at different substrate temperatures (573–773 K). The films were characterized by measuring microstructural, optical and electrical properties. The GaN films were predominantly hexagonal. The band gap (∼3.4 eV) refractive index (1.42–2.52) and surface roughness (10–46 nm) could be evaluated from the optical absorption spectra. The variation of AC conductivity σ( ω) with frequency ( ω) at different temperatures (134–300 K) indicated a dependence σ( ω)= Aω s with s varying within 0.85–0.97 having a weak temperature dependence. Elliot's model was utilized to interpret the conductivity data of GaN, which indicated the density of localized states to be ∼4.5×10 18 cm −3.

ホットウォール法によるＺｎドープＩｎＳｅ薄膜の作製と評価

ホットウォール法によるＺｎドープＩｎＳｅ薄膜の作製と評価

Towards Imaging with Polycrystalline Mercuric Iodide Semiconductor Detectors

AbstractPreparation of polycrystalline mercuric iodide very thin (1 μm) films using laser ablation and thick films (100–600μm), using hot pressing, hot wall vapor deposition and screen printing methods, fabricated as radiation detector plates are briefly described. X-ray diffraction, photoluminescence and optical microscopic measurements as well as response to nuclear radiation will be given. Finally, recent results obtained with a large area imaging pixel detector will be shown.

Photoconductivity of CdTe films

CdTe films were deposited at different substrate temperatures (423–573 K) using the hot wall evaporation technique. The films were polycrystalline in nature with varying grain size (0.06-0.18 μm). Dark and photo-conductivities in the films were measured in the temperature range 90–300 K. The conductivity data at low temperatures ( < 155 K) were analysed by using the quantum mechanical tunnelling of carrier through the grain boundary barrier model. The relatively large conductivity at the higher temperature region (> 155 K) was explained by the possible thermionic emission of the carrier over the grain boundary potential barrier. The influence of the modulated grain boundary barrier height (at high temperature) and width (at low temperature) with different illumination levels could explain the overall conductivity of CdTe films.

Preparation of CuInSe2 films by hot-wall evaporation technique

Cu-In-Se films have been deposited by a hot-wall evaporation technique using CuCl and In2Se3 as source materials. The composition of films was severely dependent on the substrate temperature. In the present study, near-stoichiometric CuInSe2 films were deposited on the substrate heated to about 440°C when CuCl and In2Se3 were respectively sublimed from two sources heated to 260 and 560°C. X-ray diffraction measurement detected no additional second phase and the film exhibited low resistivity and p-type conduction.

ZnSe films: preparation and properties

ZnSe films were prepared by the hot wall evaporation technique onto glass, NaCl and KCl substrates at different substrate temperatures during deposition. The effect of deposition parameters on the grain growth, grain distribution and surface roughness were studied. Information on their optical properties was also obtained. Strength of grain boundary scattering in these films was critically studied and it was observed that the films are partially depleted of carriers. The density of trap states at the grain boundaries decreased for films deposited at higher substrate temperatures while an increase in carrier concentration was observed for films deposited at higher substrate temperatures. The films deposited at higher deposition temperature contained less stress than those deposited at lower temperatures.