Chemical Vapor Deposition For Applications Research Articles

Lattice Reconstruction in MoSe2–WSe2 Heterobilayers Synthesized by Chemical Vapor Deposition

Vertical van der Waals heterostructures of semiconducting transition metal dichalcogenides realize moiré systems with rich correlated electron phases and moiré exciton phenomena. For material combinations with small lattice mismatch and twist angles as in MoSe2-WSe2, however, lattice reconstruction eliminates the canonical moiré pattern and instead gives rise to arrays of periodically reconstructed nanoscale domains and mesoscopically extended areas of one atomic registry. Here, we elucidate the role of atomic reconstruction in MoSe2-WSe2 heterostructures synthesized by chemical vapor deposition. With complementary imaging down to the atomic scale, simulations, and optical spectroscopy methods, we identify the coexistence of moiré-type cores and extended moiré-free regions in heterostacks with parallel and antiparallel alignment. Our work highlights the potential of chemical vapor deposition for applications requiring laterally extended heterosystems of one atomic registry or exciton-confining heterostack arrays.

Review of the Chosen Methods of Producing Front Contacts to Transparent Conductive Oxides Layers in Photovoltaic Structures

It is well known that PV thin films can be deposited by an extensive range of more or less expensive and complicated techniques (such as sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), pulsed laser deposition, atomic layer deposition (ALD)). The present paper focuses on TCO layers applied by chosen techniques, including mainly the ALD and CVD methods. Thin layers of transparent conductive oxides constitute a well-known group of materials with unique properties. Oxides such as ZnO, SnO2, and In2O3 are the most significant materials of this type; some of them are discussed in the paper. From the application point of view in the photovoltaic industry, the goal is to apply a method that will provide the highest value of electric charge conductivity while maintaining the minimum value of absorption in the layer and a reduced value of the reflection coefficient. The implementation of significant achievements in the coming decade is for developing guidelines for metallization processes and TCO layers deposited by the ALD method. The work contains chosen engineering processes, including the fabrication of transparent conductive oxides (TCO) thin films applied to silicon substrates by ALD and CVD for application as emitter conductive coatings in photovoltaic structures and the fabrication front metallization of solar cell using different techniques, including among others laser techniques. Moreover, the work also contains predictions about solar cells, which will be among the most prevalent solar cells in mass production using thin- and thick-film technology.

Growth of Nanostructured Diamond Films on Glass Substrates by Low-Temperature Microwave Plasma-Enhanced Chemical Vapor Deposition for Applications in Nanotribology

Low-temperature fabrication of superior nano-/microcrystalline diamond (NCD/MCD) films is a major thrust in diamond technology. The widely used seeding techniques applied on the substrate surface are usually harsh, lead to defect formation, and suffer from the lack of reproducibility in maintaining homogeneity and uniformity over nano-/microdimensions. Low-temperature growth of a significant diamond phase on purely untreated glass substrates is indeed a challenging task. Using CO2 as the supplementary gas-phase constituent included in the (CH4 + H2)-plasma and a specific shadow-mask assembly to generate the diffuse plasma environment above the growth zone, the present experiment succeeds in the spontaneous growth of nanocrystalline diamond (NCD), including microcrystalline diamond (MCD) of an average crystal size of ∼0.9–1.2 μm at ∼300 °C on glass substrates, without any seeding pretreatment. In the plasma, the shadow mask establishes a virtual remote plasma configuration in setting the diffuse plasma, protects the growth surface from a direct bombardment of energetic ions, generates negative self-bias on the substrate, and, importantly, promotes significant gas-phase nucleation dominant over typical solid-state nucleation. The incubation of diamond embryo clusters onto the untreated glass substrates under the shadow-mask structure and its growth evolution through the efficient transport of the preferential carbonaceous precursors proceed within the diffuse plasma. In the course of network modification under the diffuse plasma, atomic O remains instrumental for efficient etching of the a-C overlayer on a diamond embryo and atomic H, with its small physical dimension, conveniently penetrates within the diamond network and promotes crystallization via transferring its moderate chemical energy to the diamond lattice. The low-temperature-grown nanostructured diamond films are up-and-coming for applications in nanotribology.

Synthesis and Investigation of a Photoswitchable Copolymer Deposited via Initiated Chemical Vapor Deposition for Application in Organic Smart Surfaces

The deposition of well-defined photochromic thin films is highly attractive but challenging when it comes to practical applications. In conventional wet chemistry methods, the choice of potential m...

Investigation of silicon nanoparticles produced by centrifuge chemical vapor deposition for applications in therapy and diagnostics

Porous silicon (PSi) is a biocompatible and biodegradable material, which can be utilized in biomedical applications. It has several favorable properties, which makes it an excellent material for building engineered nanosystems for drug delivery and diagnostic purposes. One significant hurdle for commercial applications of PSi is the lack of industrial scale production of nanosized PSi particles. Here, we report a novel two-step production method for PSi nanoparticles. The method is based on centrifuge chemical vapor deposition (cCVD) of elemental silicon in an industrial scale reactor followed by electrochemical post-processing to porous particles. Physical properties, biocompatibility and in vivo biodistribution of the cCVD produced nanoparticles were investigated and compared to PSi nanoparticles conventionally produced from silicon wafers by pulse electrochemical etching. Our results demonstrate that the cCVD production provides PSi nanoparticles with comparable physical and biological quality to the conventional method. This method may circumvent several limitations of the conventional method such as the requirements for high purity monocrystalline silicon substrates as starting material and the material losses during the top-down milling process of the pulse-etched films to porous nanoparticles. However, the electroless etching required for the porosification of cCVD-produced nanoparticles limited control over the pore size, but is amenable for scaling of the production to industrial requirements.

TiO2 Coated ZnO Nanorods by Mist Chemical Vapor Deposition for Application as Photoanodes for Dye-Sensitized Solar Cells.

In this study, a mist chemical vapor deposition method was applied to create a coating of titanium dioxide particles in order to fabricate ZnO/TiO2 core–shell nanostructures. The thin layers of titanium dioxide on the zinc oxide nanorods were uniform and confirmed as pure anatase phase. The morphological, structural, optical and photoluminescence properties of the ZnO/TiO2 core–shell structures were influenced by coating time. For instance, the crystallinity of the titanium dioxide increased in accordance with an increase in the duration of the coating time. Additionally, the thickness of the titanium dioxide layer gradually increased with the coating time, resulting in an increased surface area. The transmittance of the arrayed ZnO/TiO2 core–shell structures was 65% after 15 min of coating. The obtained ZnO/TiO2 core–shell nanostructures demonstrated high potentiality to serve as photoanodes for application in dye-sensitized solar cells.

Substrate with Si Nanoparticles Prepared by Low Pressure Chemical Vapor Deposition for Application in Si Solar Cells

Nanostructure strategies are frequently used to enhance the light absorption in solar cells. For improving the efficiency of absorption in solar cells, an industrial-feasible processing technique, i.e. low-pressure chemical vapor deposition was used to form a substrate with large-area silicon nanoparticles (Si-NPs). It was shown that the density and size of Si-NPs can be modulated by controlling the flow of pure SiH4, the deposition temperature and the deposition time. The substrate with large-area Si-NPs can be applied in photovoltaic devices since they can increase the effective absorption path of the incident sunlight.

Carbon Deposition Using Various Solid Fuels for Ironmaking Applications

In this paper, we describe an innovative process involving iron reduction through chemical vapor deposition for applications in the ironmaking industry. In our experiment, we produced tar vapors from pyrolysis of various solid fuels, including high-grade bituminous coal (HGC), low-grade lignite coal (LGC), and biomass palm kernel shell (PKS), and decomposed these vapors into gases, carbon, and light hydrocarbon. Carbon was deposited within the pores of pisolite ore (low-grade ore), which became porous during the dehydration process at 450 °C. We determined that the amount of tar produced during pyrolysis strongly affected carbon deposition, and HGC produced the highest carbon deposition because of its large tar product. In addition to tar amount, surface area and pore volume also played important roles in this process. PKS had the highest ratio of deposited carbon because it produced the smallest quantities of reacted tar and, consequently, the largest numbers of vacant pores. The amount of carbon deposition decreased at higher temperatures because tar was easily converted to a gaseous phase. The deposited carbon within iron ore showed potential as a reducing agent because it was highly reactive and reduced at lower temperatures. Carbon deposited within iron pores dramatically reduced the contact distance between the iron ore and carbon. Thus, these results show that our proposed methodology could have important applications as an alternative low-energy approach for producing metallic iron using low-grade materials.

Formation of a single In(Ga)As/GaAs quantum dot embedded in a site-controlled GaAs nanowire by metalorganic chemical vapor deposition for application to single photon sources

ABSTRACTWe report the formation and optical properties of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition for application to single photon sources. InAs/GaAs QD-in-NWs with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μeV are observed. Light emission from the single QD-in-NW shows photon antibunching which evidences single photon emission from high-quality QD-in-NWs.

Conducting boron-doped single-crystal diamond films for high pressure research

Epitaxial boron-doped diamond films were grown by microwave plasma chemical vapor deposition for application as heating elements in high pressure diamond anvil cell devices. To a mixture of hydrogen, methane and oxygen, diborane concentrations of 240–1200 parts per million were added to prepare five diamond thin-film samples. Surface morphology has been observed to change depending on the amount of diborane added to the feed gas mixture. Single-crystal diamond film with a lowest room temperature resistivity of 18 mΩ cm was fabricated and temperature variation of resistivity was studied to a low temperature of 12 K. The observed minima in resistivity values with temperature for these samples have been attributed to a change in conduction mechanism from band conduction to hopping conduction. We also present a novel fabrication methodology for monocrystalline electrically conducting channels in diamond and present preliminary heating data with a boron-doped designer diamond anvil to 620 K at ambient pressure.

Low temperature deposition of crystalline silicon on glass by hot wire chemical vapor deposition

Although the deposition of crystalline silicon on a glass substrate has been pursued using hot wire chemical vapor deposition or plasma enhanced chemical vapor deposition for applications in flat panel displays and solar cells, the process has been only partly successful because of the inevitable formation of an amorphous incubation layer on a glass substrate. Currently, the crystalline silicon films are prepared by depositing an amorphous silicon film on a glass substrate and then crystallizing it by excimer laser annealing (ELA), metal induced crystallization or rapid thermal annealing (RTA). Here we report a new process, which can remove the amorphous incubation layer and thereby deposit crystalline silicon directly on glass using HCl. The intrinsic crystalline silicon film has a conductivity of 3.7×10 −5 Scm −1 and the n-type doped crystalline silicon film has the Hall mobility of 15.8 cm 2V −1 s −1, whose values are comparable to those prepared by ELA and RTA, respectively.

Control of the Properties of Carbon Nanotubes Synthesized by CVD for Application in Electrochemical Biosensors

Interest in carbon nanotubes (CNT) has grown at a very rapid rate in the last decade. Their interesting physical and chemical properties open attractive possibilities in many application areas. These properties depend on the process conditions during synthesis and on subsequent purification steps. Recent studies have demonstrated that CNT can promote the electron transfer of biomolecules. These exceptional properties make them attractive for use in electrochemical biosensors. Multi walled nanotubes have been synthesized by the Chemical Vapor Deposition (CVD) method using methane as a carbon source and Ni–Al2O3–SiO2 as the catalyst. The influence of the variation of certain reaction parameters such as feed gas composition, catalyst mass, temperature and reaction time in the yield of the CVD process has been established. In addition, the structural and chemical characteristics of the CNTs have been studied and a purification process to eliminate the catalyst and amorphous carbon has been developed that involves a gaseous oxidative process and acid treatment. The efficiency of the purification step has been determined by analytical techniques. Atomic force microscopy, Raman scattering, thermogravimetric analysis, inductively coupled plasma atomic spectroscopy are the characterization techniques employed in this work.

Optical defect centers and surface morphology of isotopically enriched diamond layers in designer diamond anvils

We have studied optical defect centers and surface morphology of isotopically enriched layers grown on diamond anvils by microwave plasma chemical vapor deposition for applications as designer diamond anvils in high-pressure diamond anvil cell devices. Various mixtures of methane isotopes were used to grow homoepitaxial diamond with C13 molar fractions of 0.01, 0.41, 0.83, and 0.99 as determined from Raman spectroscopy. Defect centers were studied at temperatures between 80 and 320K using micro-photoluminescence (PL) spectroscopy with an argon ion and krypton laser excitation source. The defect spectra were dominated by zero phonon lines (ZPL) from nitrogen-related defect centers at nominal energies of 1.945eV (640nm defect) and 2.156eV (575nm defect), especially for the non-(100) surfaces. Polished (100) surfaces fluoresced weakly. ZPL’s at 1.77 and 1.68eV are observed, but not for all isotopically mixed samples. The 1.77eV ZPL appears to be associated from the original diamonds, while the 1.68eV ZPL is known to originate with silicon-based defects. Atomic force microscopy of as-grown isotopically enriched layers show rough growth steps in areas with surface roughness of hundred nanometers and smooth areas with surface roughness of few nanometers. Our studies indicate that (100) polished surfaces of isotopically enriched designer diamonds with low concentration of nitrogen defect centers can be fabricated for a variety of applications in high pressure research.

Development of P-Doped SiO[sub 2] as Proton Exchange Membrane for Microfuel Cells

Phosphorus-doped silicon dioxide PSG thin films with improved ionic conductivity were deposited via plasma-enhanced chemical vapor deposition for application as a thin-film proton exchange membrane PEM in microfabricated fuel cells. More than three orders of magnitude improvement in the ionic conductivity is obtained by P doping of low-temperature deposited SiO2. The area resistance of 3 m thick film of PSG is comparable to a 200 m thick film of Nafion. Application of these PSG films as PEM in microfuel cells yielded more than one order of magnitude improvement in power density compared to low-temperature, undoped SiO2 membranes. © 2005 The Electrochemical Society. DOI: 10.1149/1.2050587 All rights reserved.

Preparation of ZnO Thin Films Deposited by Plasma Chemical Vapor Deposition for Application to Ultraviolet-cut Coating

ZnO thin films coated on plastic materials were investigated for their use in the protection against solar ultraviolet (UV) radiation. Using diethylzinc (DEZ) as the organic source material, we attempted to deposit ZnO thin films on polycarbonate (PC) resin at room temperature by the cathode deposition technique of the capacitive-coupled radio frequency chemical vapor deposition (RFCVD) method. It was found that the ZnO films obtained were amorphous, and contained small quantities of CO and hydrocarbons, which decreased in the substrate temperature range above 75°C. In a xenon arc weatherability test, the ZnO-coated PC plates exhibited outstanding characteristics of UV protection, as they remained smooth and uncolored even after 1000 h of UV irradiation.

X-ray diffraction analysis of SiGe/Si heterostructures on sapphire substrates

Si/Si 1−x Ge x heterostructures on improved silicon-on-sapphire substrates were grown epitaxially by ultrahigh vacuum chemical vapor deposition for application as p-channel field effect transistors. High-resolution triple-axis x-ray diffraction was used to analyze these structures quantitatively and to evaluate their thermal stability. Outdiffusion of Ge from the strained Si1−xGex quantum well was observed after annealing at 850 °C. The amount of outdiffusion was comparable to that observed in Si1−xGex structures on bulk Si wafers.

Analysis Of Sige Fet Device Structures On Silicon-on-sapphire Substrates by X-Ray Diffraction

AbstractSi/Si1-xGex, heterostructures on improved silicon-on-sapphire substrates were grown epitaxially by ultra-high vacuum chemical vapor deposition for application as p-channel field effect transistors. High-resolution triple-axis x-ray diffraction was used to analyze these structures quantitatively and to evaluate the effects of device fabrication processes on them. Out-;diffusion of Ge from the Si1-xGex, quantum well was observed after fabrication as was the change in thickness of the Si cap layer due to wafer cleaning and gate oxidation at 875 °C

W-Re composite tube fabricated by chemical vapor deposition for application in an 1800 °C high thermal efficiency fuel-processing furnace

Chemically vapor-deposited rhenium was selected as the muffle material for an 1800 °C high thermal efficiency fuel-processing furnace. The muffle is exposed to high vacuum on the heater-insulation-instrumentation side and to a flowing Ar-8vol.%H 2 gas mixture at a pressure of 1 atm on the load volume side. During operation the muffle cycles from room temperature to 1800 °C and back to room temperature once every 24 h. Its operational life is dependent on its resistance to thermal fatigue during the high temperature exposure. For a prototype furnace the muffle has an inner diameter of approximately 13 cm and is 40 cm in length. A small (about half-size) rhenium closed-end tube overcoated with tungsten was used to evaluate the concept. The fabrication and testing of the composite W-Re tube and prototype rhenium muffle are described.