Photocatalytic TiO(2) deposition by chemical vapor deposition

Dip-coating, spray-coating or spin-coating methods for crystalline thin film deposition require post-annealing process at high temperature. Since chemical vapor deposition (CVD) process is capable of depositing high-quality thin films without post-annealing process for crystallization, CVD method was employed for the deposition of TiO(2) films on window glass substrates. Post-annealing at high temperature required for other deposition methods causes sodium ion diffusion into TiO(2) film from window glass, resulting in the degradation of photocatalytic efficiency. Anatase-structured TiO(2) thin films were deposited on window glass by CVD, and the photocatalytic dissociation rates of benzene with CVD-grown TiO(2) under UV exposure were characterized. As the TiO(2) film deposition temperature was increased, the (112)-preferred orientations were observed in the film. The (112)-preferred orientation of TiO(2) thin film resulted in a columnar structure with a larger surface area for benzene dissociation. Obviously, benzene dissociation rate was maximum when the degree of the (112) preferential orientation was maximum. It is clear that the thin film TiO(2) should be controlled to exhibit the preferred orientation for the optimum photocatalytic reaction rate. CVD method is an alternative for the deposition of photocatalytic TiO(2).     

Plasma-assisted chemical vapor deposition processes and their semiconductor applications

When plasmas are used to assist chemical vapor deposition processes little thought is given to the nature of the electrical discharge that creates the plasma or the interaction between the plasma and the chamber. In this paper, some of the phenomena essential to the understanding of plasma behavior are reviewed. At the same time, some new reactor concepts that may offer improvements over traditional production reactors will be discussed.     

Relevance of thermodynamic and kinetic parameters of chemical vapor deposition precursors

We have studied various metallorganic and organometallic compounds by simultaneous nonisothermal thermogravimetric and differential thermogravimetric analyses to confirm their volatility and thermal stability. The equilibrium vapor pressures of the metallorganic and organometallic compounds were determined by horizontal dual arm single furnace thermoanalyzer as transpiration apparatus. Antoine coefficients were calculated from the temperature dependence equilibrium vapor pressure data. The model-fitting solid-state kinetic analyses of Al(acac)3, (acac = acetylacetonato), Cr(CO)6, Fe(Cp)2, (Cp-cyclopentadienyl), Ga(acac)3, Mn(tmhd)3, and Y(tmhd)3 (tmhd = 2,2,6,6,-tetramethyl-3,5-heptanedionato) revealed that the processes follow diffusion controlled, contracting area and zero order model sublimation or evaporation kinetics. The activation energy for the sublimation/evaporation processes were calculated by model-free kinetic methods. Thin films of nickel and lanthanum-strontium-manganite (LSM) are grown on silicon substrate at 573 K using selected metallorganic complexes of Ni[(acac)2en], La(tmhd)3, Sr(tmhd)2 and Mn(tmhd)3 as precursors by plasma assisted liquid injection chemical vapor deposition (PA-LICVD). The deposited films were characterized by scanning electron microscopy and energy dispersive X-ray analysis for their composition and morphology.     

Initiated chemical vapor deposition of poly(2-hydroxyethyl methacrylate) hydrogels

Initiated chemical vapor deposition (iCVD), a low temperature variant of hot-wire chemical vapor deposition (HWCVD) is a solvent-free polymerization technique. It was used to synthesize thick, free-standing films of the hydrogel poly(2-hydroxyethyl methacrylate) (PHEMA). In this work, we show that the iCVD technique can yield PHEMA which is free from residual entrained monomer, has low non-specific protein adsorption and is capable of supporting good cell adhesion and proliferation.     

Structural and electrical characterization of bi(2)se(3) nanostructures grown by metal-organic chemical vapor deposition

We characterize nanostructures of Bi(2)Se(3) that are grown via metal-organic chemical vapor deposition using the precursors diethyl selenium and trimethyl bismuth. By adjusting growth parameters, we obtain either single-crystalline ribbons up to 10 μm long or thin micrometer-sized platelets. Four-terminal resistance measurements yield a sample resistivity of 4 mΩ·cm. We observe weak antilocalization and extract a phase coherence length l(?) = 178 nm and spin-orbit length l(so) = 93 nm at T = 0.29 K. Our results are consistent with previous measurements on exfoliated samples and samples grown via physical vapor deposition.     

Towards controlled synthesis of 2D crystals by chemical vapor deposition (CVD)

The emergence of two-dimensional (2D) materials has captured the imagination of researchers since graphene was first exfoliated from graphite in 2004. Their exotic properties give rise to many exciting potential applications in advanced electronic, optoelectronic, energy and biomedical technologies. Scalable growth of high quality 2D materials is crucial for their adoption in technological applications the same way the arrival of high quality silicon single crystals was to the semiconductor industry. A huge amount of effort has been devoted to grow large-area, highly crystalline 2D crystals such as graphene and transition metal dichalcogenides (TMDs) through various methods. While CVD growth of wafer-scale monolayer graphene and TMDs has been demonstrated, considerable challenges still remain. In this perspective, we advocate for the focus on the crystal growth morphology as an underpinning for understanding, diagnosing and controlling the CVD process and environment for 2D material growth. Like snowflakes in nature, 2D crystals exhibit a rich variety of morphologies under different growth conditions. The mapping of crystal shapes in the growth parameter space “encodes” a wealth of information, the deciphering of which will lead to better understanding of the fundamental growth mechanism and materials properties. To this end, we envision a collective effort by the 2D materials community to establish the correlation between crystal shapes and the intrinsic thermodynamic and kinetic parameters for CVD reactions through integrated crystal growth experiment, database development and machine learning assisted predictive modeling, which will pave a robust path towards controlled synthesis of 2D materials and heterostructures.     

Low temperature chemical vapor deposition of TaB2

Crystalline TaB₂ was deposited using the chemical vapor deposition reaction of TaCl₅ and B₂H₆ in the temperature range 773–1200 K. Thermodynamic calculations were made which compared the use of both B₂H₆ and BCl₃ as boron source gases. The deposits obtained with B₂H₆ had an extremely small crystal size and contained amorphous boron when the deposition temperature was below approximately 873 K but were substoichiometric in boron above this temperature. Carbon analysis indicated that carbon may be substituting for boron and thereby stabilizing the diboride structure at high deposition temperatures. The microhardness of the coatings decreased with increasing atomic ratio of boron to tantalum and decreasing crystal size.     

Combinatorial initiated chemical vapor deposition (iCVD) for polymer thin film discovery

Initiated chemical vapor deposition (iCVD) is a technique used to synthesize polymer thin films and coatings from the vapor phase in situ on solid substrates via free-radical mechanisms. It is a solventless, low-temperature process capable of forming very thin conformal layers on complex architectures. By implementing a combinatorial approach that examines five initiation temperatures simultaneously, we have realized at least a five-fold increase in efficiency. The combinatorial films were compared to a series of blanket films deposited over the same conditions to ensure the combinatorial system provided the same information. Direct synthesis from the vapor phase allows for in situ control of film morphology, molecular weight and crosslinking, and the combinatorial system decreases the time required to find the relationship between these interrelated properties. Some coatings were tested for antimicrobial performance against E. coli and B. subtilis.     

Initiated chemical vapor deposition (iCVD) of copolymer thin films

Initiated chemical vapor deposition (iCVD) represents a novel hot-wire CVD variant for producing copolymer thin films. iCVD copolymerization was characterized by a conventional liquid-phase free radical copolymerization equation when applied to methacrylic acid copolymers. FTIR peak shifts with changing comonomer ratios in the copolymers further supported a copolymerization mechanism. Crosslinked methacrylic acid copolymers provided pH-dependent swelling behavior that enabled an enteric release of active core material when the copolymer was used as an encapsulation coating.     

Superlattice formation of (Ba,Sr)TiO3 prepared by metal-organic chemical vapor deposition

Dielectric superlattices of (Ba_0.5Sr_0.5)TiO₃ (BST) grown by a metal-organic chemical vapor deposition (MOCVD) have been studied by transmission electron microscopy (TEM). A selected area of electron diffraction patterns clearly show satellite spots that indicate the formation of superlattice of BST film. A superlattice distance is 6.75Å, that is, 2.4 times of (110) BST plane distance. A high-resolution TEM study revealed that the superlattices were induced by the periodic composition modulation of Ba and Sr atoms. A possible atomic arrangement model of the superlattice was proposed by a simulation with a national center for electron microscopy simulation system (NCEMSS).     

Metal organic chemical vapor deposition (MOCVD) of oxides and ferroelectric materials

The electrical properties of thin-film oxides span a tremendous range from insulating to superconducting. As a consequence, they are now finding an increasing number of applications in electronics and opto-electronics, both as stand-alone layers and for the provision of added functionality to electronic circuits, especially silicon. The modified precursor delivery technologies (e.g. aerosol or liquid delivery or injection techniques) coupled with improved precursors, and better engineering of the deposition kit, have transformed the prospects for the deposition of these materials by MOCVD. It is now possible to exploit the many traditional advantages of MOCVD, especially over other routes to thin-film oxide deposition. A wide range of oxides and particularly complex ferroelectric oxides are being produced on substrates of up to 200 mm in diameter. This paper highlights the progress and real advantages that MOCVD has for thin-film oxide deposition, including the design of improved precursors. Examples of the deposition of dielectric layers and lead-based ferroelectric layers for uncooled thermal imaging, and MEMS actuation applications are presented.     

定向碳纳米管的化学气相沉积制备法

报道了一种简便有效的合成定向碳纳米管 (CNTs)的化学气相沉积 (CVD)制备方法。以铁为催化剂 ,乙炔为碳源 ,采用单一反应炉 ,直接在石英基底上沉积催化剂颗粒薄膜 ,成功合成了定向性好、管径均匀的高质量大密度的碳纳米管     

Initiated chemical vapor deposition of pH responsive poly(2-diisopropylamino)ethyl methacrylate thin films

Poly(2-(diisopropylamino)ethyl methacrylate) (PDPAEMA) thin films were deposited on low temperature substrates by initiated chemical vapor deposition (iCVD) method using tertbutyl peroxide as an initiator. Very high deposition rates up to 38 nm/min were observed at low filament temperatures due to the use of the initiator. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy show the formation of PDPAEMA films with high retention of tertiary amine functionality which is responsible for pH induced changes in the wetting behavior of the surfaces. As-deposited PDPAEMA thin films on flat Si surface showed a reversible switching of water contact angle values between 87° and 28°; after successive treatments of high and low pH water solutions, respectively. Conformal and non-damaging nature of iCVD allowed to functionalize fragile and rough electrospun poly(methyl methacrylate) fiber mat surfaces by PDPAEMA, which creates a surface with a switching behavior between superhydrophobic and approaching superhydrophilic with contact angle values of 155 ± 3°and 22 ± 5°, respectively.     

Kinetics of SiHCl3 chemical vapor deposition and fluid dynamic simulations

Though most of the current silicon photovoltaic technology relies on trichlorosilane (SiHCl3) as a precursor gas to deposit Si, only a few studies have been devoted to the investigation of its gas phase and surface kinetics. In the present work we propose a new kinetic mechanism apt to describe the gas phase and surface chemistry active during the deposition of Si from SiHCl3. Kinetic constants of key reactions were either taken from the literature or determined through ab initio calculations. The capability of the mechanism to reproduce experimental data was tested through the implementation of the kinetic scheme in a fluid dynamic model and in the simulation of both deposition and etching of Si in horizontal reactors. The results of the simulations show that the reactivity of HCl is of key importance in order to control the Si deposition rate. When HCl reaches a critical concentration in the gas phase it starts etching the Si surface, so that the net deposition rate is the net sum of the adsorption rate of the gas phase precursors and the etching rate due to HCl. In these conditions the possibility to further deposit Si is directly related to the rate of consumption of HCl through its reaction with SiHCl3 to give SiCl4. The proposed reaction mechanism was implemented in a 3D fluid dynamic model of a simple Siemens reactor. The simulation results indicate that the proposed interpretation of the growth process applies also to this class of reactors, which operate in what can be defined as a mixed kinetic-transport controlled regime.     

A comparison of microcrystalline silicon prepared by plasma-enhanced chemical vapor deposition and hot-wire chemical vapor deposition: electronic and device properties

The optoelectronic properties of undoped μc-Si : H have been investigated, with emphasis on the states close to the edges of the band gap. The usefulness of the constant photocurrent method (CPM) for the determination of the absorption coefficient, α(E), is critically described. Combined with carefully evaluated photothermal deflection spectroscopy data, CPM spectra yield valuable information on the transport and dynamics of photo-generated carriers. By comparing photoluminescence and Raman spectra on high-quality samples prepared by plasma-enhanced and hot-wire chemical vapor deposition, with different silane concentrations in the gas stream, a correlation between the microstructure and photoluminescence energy is obtained. It is proposed that the density of band tail states is reduced with increasing silane concentration, leading to an increase in the photoluminescence energy and in the open-circuit voltages of solar cells.     

Selective ultrathin gold deposition by organometallic chemical vapor deposition onto organic self-assembled monolayers (SAMs)

We demonstrate a selective deposition of ultrathin gold layers via OMCVD (organometallic chemical vapor deposition) onto self-assembled dithiols. Dithiols have been self-assembled to produce a thiolated surface. The gold layer deposited from a gold precursor, present in the vapor around the sample, is bound to the exposed thiol groups. We demonstrate that it is possible to deposit gold only onto the areas where the binding thiol groups are located, and investigate the growth process with spontaneous desorption time-of-flight mass spectrometry, Rutherford backscattering spectroscopy, atomic absorption spectroscopy and atomic force microscopy.     

Alumina microtubes prepared via template-directed pulsed chemical vapor deposition (pulsed CVD)

Bundles of alumina microtubes were prepared by depositing alumina onto bundles of “endless” carbon fibers via pulsed chemical vapor deposition and subsequent removal of the fibers. Thin alumina films were deposited onto “endless” carbon fibers at 77 °C by gas phase exposures to sequential pulses of trimethylaluminum and water vapor, respectively. The carbon fibers were selectively removed using thermal oxidation in air at temperatures exceeding 550 °C. The length of the tubes was primarily limited by the dimension of the used furnace. The longest tubes thus had a length of 30 cm. Scanning electron microscopic (SEM) images of the microtubes revealed that each individual tube was separated from its neighbors and that the tubes had an almost uniform wall thickness. SEM and transmission electron microscopic (TEM) images indicate that the inner side of the wall has the same morphology as the fiber template. As deposited, the alumina films have a predominantly amorphous structure; this is transformed into a polycrystalline structure during thermal oxidation. At low thermal oxidation temperatures, such as 550 °C, the alumina microtubes still comprise a substantial fraction of amorphous structure, at higher oxidation temperatures, 900 °C or above, a dominating polycrystalline structure (with bigger grains) is formed. This transformation gives rise to grain boundaries. These grain boundaries might facilitate oxygen diffusion and thus oxidative removal of the fiber templates.