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Despite their wide use in the oil refining process, little is known about the distribution of aluminium and silicon atoms in amorphous aluminosilicates (ASAs). In this paper, we report the synthesis of both Al/SiO2 and Si/Al2O3 AS...
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Despite their wide use in the oil refining process, little is known about the distribution of aluminium and silicon atoms in amorphous aluminosilicates (ASAs). In this paper, we report the synthesis of both Al/SiO2 and Si/Al2O3 ASAs by grafting aluminium and silicon alkoxides on silica respectively alumina under various conditions. For both supports, we evidence the central roles of the precursor molecule size and reactivity in the grafting yield and the deposit structure. Unless hydrolysis of the alkoxy groups by water and/ or thermal decomposition occurs, deposition is saturated at a monolayer of precursor molecules on the support oxide surface. Additional species can be deposited by repeating the grafting process provided that hydroxyl groups of the top layer are recovered after calcination. ~(27)Al NMR indicates the presence of five-coordinated aluminium species on Al/SiO2 materials prepared by two successive grafting steps. Transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirm the controlled deposition of species by selecting the appropriate synthesis conditions. Homogeneous and regular deposition is favoured in anhydrous condition and at low temperature, while water addition during synthesis leads to inhomogeneous deposits. In case of Al/SiO2 grafting in aqueous conditions, alumina nanoparticles form. The accurate knowledge of the surface structure of these ASAs opens the way to a better understanding of the origin of their Bronsted acidity.
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A suitable deposition method of CdS is necessary for the high performance CdS-sensitized ZnO electrodes. In this paper, chemical bath deposition (CBD) and sequential chemical bath deposition (S-CBD) methods were used to deposit Cd...
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A suitable deposition method of CdS is necessary for the high performance CdS-sensitized ZnO electrodes. In this paper, chemical bath deposition (CBD) and sequential chemical bath deposition (S-CBD) methods were used to deposit CdS on ZnO mesoporous films for ZnO/CdS electrodes. The analysis results of XRD patterns and UV-vis spectroscopy indicated that CBD deposition method leaded to the dissolving of ZnO mesoporous films in deposition solution and thickness reduction of ZnO/CdS electrodes. Absorption in visible region by the ZnO/CdS electrodes with CdS deposition by S-CBD was enhanced as deposition cycles increased due to the stability of ZnO mesoporous films in the S-CBD deposition solutions. The results of photocurrent-voltage (I-V) measurement showed that the performance of ZnO/CdS electrodes with CdS deposition by CBD first increased and then decreased as deposition time increased, and the greatest short-circuit current (J_(sc)) was obtained at the deposition time of 4 min. The performance of ZnO/CdS electrodes with CdS deposition by S-CBD increased as deposition cycles increased, and both open-circuit voltage (V_(oc)) and J_(sc) were greater than those electrodes with CdS deposition by CBD when the deposition cycles of S-CBD were 10 or greater. These results indicated that S-CBD is a more suitable method for high performance ZnO/CdS electrodes.
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The effects of deposition gas pressure and H_2 dilution ratio (H_2/SiH_4 + CH_4 + H_2), generally considered two of dominant parameters determining crystallinity in β-SiC thin films prepared by catalytic chemical vapor deposition...
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The effects of deposition gas pressure and H_2 dilution ratio (H_2/SiH_4 + CH_4 + H_2), generally considered two of dominant parameters determining crystallinity in β-SiC thin films prepared by catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD method, on the films properties have been systematically studied. As deposition gas pressure increase from 40 to 1000 Pa, the crystallinity of the films is improved. From the study of H_2 dilution ratio, it is considered that H_2 plays a role as etching gas and modulating the phases in β-SiC thin films. On the basis of the study on the parameters, nanocrystalline β-SiC films were successfully synthesized on Si substrate at a low temperature of 300℃. The Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) spectra show formation of β-SiC. Moreover, according to Sherrer equation, the average grain size of the films estimated is in nanometer-size.
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Selective diamond films on roughened Si(100) substrates with patternings have been achieved by microwave plasma chemical vapor deposition (MP-CVI)). The films have been characterized by scanning electron microscopy (SEM) and Raman...
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Selective diamond films on roughened Si(100) substrates with patternings have been achieved by microwave plasma chemical vapor deposition (MP-CVI)). The films have been characterized by scanning electron microscopy (SEM) and Raman spectra. The influence of substrate temperature on the selective deposition of diamond films has been discussed in detail: the diamond nucleation density on the SiO_2 mask increased with substrate temperature while the effect of the selective deposition of diamond films deteriorated; the optimized deposition temperature conditions have been concluded.
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Bioresorbable polymers such as poly(ε-caprolactone) (PCL) have a multitude of potential biomaterial applications such as controlled-release drug delivery and regenerative tissue engineering. For such biological applications, the ...
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Bioresorbable polymers such as poly(ε-caprolactone) (PCL) have a multitude of potential biomaterial applications such as controlled-release drug delivery and regenerative tissue engineering. For such biological applications, the fabrication of porous three-dimensional bioresorbable materials with tunable surface chemistry is critical to maximize their surface-to-volume ratio, mimic the extracellular matrix, and increase drug-loading capacity. Here, two different fluorocarbon (FC) precursors (octofluoropropane (C_3F_8) and hexafluoropropylene oxide (HFPO)) were used to deposit FC films on PCL scaffolds using plasma-enhanced chemical vapor deposition (PECVD). These two coating systems were chosen with the intent of modifying the scaffold surfaces to be biononreactive while maintaining desirable bulk properties of the scaffold. X-ray photoelectron spectroscopy showed high-CF_2 content films were deposited on both the exterior and interior of PCL scaffolds and that deposition behavior is PECVD system specific. Scanning electron microscopy data confirmed that FC film deposition yielded conformal rather than blanket coatings as the porous scaffold structure was maintained after plasma treatment. Treated scaffolds seeded with human dermal fibroblasts (HDF) demonstrate that the cells do not attach after 72 h and that the scaffolds are noncytotoxic to HDF. This work demonstrates conformal FC coatings can be deposited on 3D polymeric scaffolds using PECVD to fabricate 3D bio-nonreactive materials.
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Intrinsic bismuth sulfide deposited on indium thin films (similar to 20nm) change to n-type when annealed in air or nitrogen atmosphere. As deposited bismuth sulfide on the In films is amorphous and electrically very resistive, An...
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Intrinsic bismuth sulfide deposited on indium thin films (similar to 20nm) change to n-type when annealed in air or nitrogen atmosphere. As deposited bismuth sulfide on the In films is amorphous and electrically very resistive, Annealing the films in air at 200, 300, and 400 degrees C results in the formation of In2O3 as observed in the X-ray diffraction patterns of the films. The dark conductivity of the In + bismuth sulfide films nitrogen-annealed at 300 degrees C attains a value of 600 Ohm(-1) cm(-1), which is an improvement by more than eight orders of magnitude compared with as-prepared films. This improvement is attributed to amorphous-crystalline transformation and the presence of metallic bismuth and In2O3 in the annealed films. An etching test in 1 M solution of HCl indicates that these films are rather stable in acid medium. (C) 1998 Academic Press. [References: 13]
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Chemical vapor deposited monolayer graphene is transferred onto atomically fl at and ultra-thin muscovite mica to study the transport characteristics of graphene with a test structure of mica-based graphene fi eld effect transisto...
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Chemical vapor deposited monolayer graphene is transferred onto atomically fl at and ultra-thin muscovite mica to study the transport characteristics of graphene with a test structure of mica-based graphene fi eld effect transistor (GFET). The transfer curve of the 24 nm mica-based GFET shows an effective carrier mobility of 2748 cm~2 /Vs and a transconductance of 3.36 μS, a factor of 2 and 7 larger than those values obtained from 40 nm SiO_2 based GFET, respectively. The results demonstrate that mica is an excellent gate dielectric material due to its high dielectric constant, high dielectric strength, and atomically fl at surface.
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Summary. — The state of the art of Chemical Vapor Deposition (CVD) diamond detector technology is reviewed and its applications in several fields, such as high-energy physics, radiotherapy and nuclear fusion reactors, are describ...
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Summary. — The state of the art of Chemical Vapor Deposition (CVD) diamond detector technology is reviewed and its applications in several fields, such as high-energy physics, radiotherapy and nuclear fusion reactors, are described. The impact of the newest front-end electronics design is discussed. Finally, recent innovative developments using laser techniques are also illustrated together with very recent results.
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It was our aim to explore the growth of Mg,,Zni epilayerson ZnO substrates using CVD at substrate temperaturesaround 650 °C which is considerably lower than necessary forthe MOCVD growth which requires substrate temperaturesabove...
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It was our aim to explore the growth of Mg,,Zni epilayerson ZnO substrates using CVD at substrate temperaturesaround 650 °C which is considerably lower than necessary forthe MOCVD growth which requires substrate temperaturesabove 900 °C. Metallic precursors (Zn, Mg) were used to-gether with NO2 as oxygen precursor. The Mg content wasdetermined from the shift of longitudinal optical phonon line as a function of the Mg composition. The properties of thefilms were investigated by low temperature photolumines-cence. Epitaxial MgrZni ,0 films with ,fixed Mg composi-tions required an individual adjustment of the Mg reservoirtemperature. We, therefore, explored the possibility of acombinatorial growth i.e. achieving a Mg gradient within onesample.
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