Atmospheric Chemical Vapor Deposition Research Articles

Experimental study of fractal clusters formation from nanoparticles synthesized by atmospheric pressure plasma-enhanced chemical vapor deposition

This paper presents the experimental results from the fractal structures formation from nanoparticles of silicone dioxide deposited on the silicon substrate surface. Nanoparticles are synthesized by atmospheric pressure plasma-enhanced chemical vapor deposition with the use of capacitively coupled radio frequency (13.56 MHz) discharge sustained in helium atmosphere. Tetraethoxysilane is chosen as the test precursor. Correlation between the morphology of obtained deposits and the process parameters is found. The capability of nanoparticles movement along the deposit surface in local near-surface electric field is demonstrated. The empirical model that satisfactorily explained the mechanism of fractal clusters formation from nanoparticles on the substrate surface is developed. The model indicates that the dynamics of deposit morphology variations is determined by two competing processes: electrical charge transfer by nanoparticles to the deposit surface and electrical charge running off over the surface under conditions of changeable conductivity of the deposit surface.

A combination of “top-down” and “bottom-up” approaches in the fabrication of “nano bridges”

We describe a two step vertical growth of silicon nanowires (SiNWs) and the lateral growth of a bridging network of carbon nanotubes (CNTs) across the SiNWs. SiNWs were formed by an electro-less chemical bath deposition technique using silver nano particles as a virtual mask. Subsequently, the silver nano particles present on the side walls of SiNWs were used as a catalyst in the growth of CNTs by atmospheric chemical vapor deposition technique, forming “nano bridges”. A reduced reflectance of 65 % for the “nano bridge” samples compared to the SiNW samples was obtained suggesting a potential use in anti-reflection coatings.

Structural, electrical, and optical properties of CoxNi1-xO films grown by metalorganic chemical vapor deposition

Thin films of cobalt-nickel oxide (CoxNi1-xO, x=0.01, 0.02, 0.08, 0.17, 0.22, 0.35, 0.56, 0.72) were grown on Al2O3 substrate by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD). The effect of the cobalt composition on the structural, morphological, optical, and electrical properties of the films was investigated. X-ray diffraction (XRD) analysis revealed that all of the films grew with a preferred orientation towards [111]NiO and a twinned structure. Cobalt was well dispersed in the NiO structure up to x=0.08. CoxNi1-xO alloys were formed from x=0.17 to x=0.22, while phase-separated NiO and CoxNi1−xO formed when x≥0.35. The bandgap of the CoxNi1−xO film was found to decrease with increasing cobalt composition. Four-point probe measurements showed that the resistivity of the film also decreased with increasing cobalt composition, reaching a minimum of 0.006Ωcm. Hall measurements of the films revealed n-type conductivity. The correlation between the presence of cobalt in different ionization states and the observed decrease in resistivity as well as the type of conductivity in CoxNi1−xO is discussed.

Efficiency improvement of GaN-based ultraviolet light-emitting diodes with reactive plasma deposited AlN nucleation layer on patterned sapphire substrate.

The flip chip ultraviolet light-emitting diodes (FC UV-LEDs) with a wavelength of 365 nm are developed with the ex situ reactive plasma deposited (RPD) AlN nucleation layer on patterned sapphire substrate (PSS) by an atmospheric pressure metal-organic chemical vapor deposition (AP MOCVD). The ex situ RPD AlN nucleation layer can significantly reduce dislocation density and thus improve the crystal quality of the GaN epitaxial layers. Utilizing high-resolution X-ray diffraction, the full width at half maximum of the rocking curve shows that the crystalline quality of the epitaxial layer with the (RPD) AlN nucleation layer is better than that with the low-temperature GaN (LT-GaN) nucleation layer. The threading dislocation density (TDD) is estimated by transmission electron microscopy (TEM), which shows the reduction from 6.8 × 107 cm−2 to 2.6 × 107 cm−2. Furthermore, the light output power (LOP) of the LEDs with the RPD AlN nucleation layer has been improved up to 30 % at a forward current of 350 mA compared to that of the LEDs grown on PSS with conventional LT-GaN nucleation layer.

Threefold atmospheric-pressure annealing for suppressing graphene nucleation on copper in chemical vapor deposition

Chemical vapor deposition (CVD) is a promising method of producing a large single-crystal graphene on a catalyst, especially on copper (Cu), and a further increase in domain size is desirable for electro/optic applications. Here, we report on threefold atmospheric-pressure (ATM) annealing for suppressing graphene nucleation in atmospheric CVD. Threefold ATM annealing formed a step and terrace surface of the underlying Cu, in contrast to ATM annealing. Atomic force microscopy and Auger electron mapping revealed that Si-containing particles existed on threefold-ATM- and ATM-annealed surfaces; particles on Cu had a lower density after threefold ATM annealing than after ATM annealing. The formation of a step and terrace surface and the lower density of particles following the threefold ATM annealing would play a role in reducing graphene nucleation. By combining threefold ATM annealing and electropolishing of Cu, the nucleation of graphene was effectively suppressed, and a submillimeter-sized hexagonal single-crystal graphene was successfully obtained.

Numerical Study of Turbulent Confined Jets Impinging on a Heated Substrate for Thin Film Deposition

This paper reports on the study of confined jets and jets interaction in terms of increasing chemical transport. The context of this study is the atmospheric pressure plasma-enhanced chemical vapor deposition, higher thin film growth rate being desired, while maintaining total flow rate as low as possible. Turbulence mixing and enhanced heat transfer are the physical mechanisms identified as being capable of increasing the growth rate at atmospheric pressure. A numerical study of jets impinging on a heated substrate was carried out using quasicompressible Reynolds-Averaged Navier–Stokes (RANS) equations. Abe–Kondoh–Nagano (AKN) low-Reynolds k-ε and standard k-ε models were tested using an unconfined impinging jet at Reynolds number Re = 23,750 for jet diameter to plate-spacing ratios of H/d = 2 and H/d = 6. Results were compared with experimental data from the literature. Based on numerical results and in accordance with existing findings, the AKN low-Reynolds k-ε was shown to be reasonably accurate and was thus chosen for the numerical study. The effects of flow rate, hole diameter and length, jet-to-jet spacing, confinement width, and jet number were investigated numerically for inline jets confined between two vertical planes for jet Reynolds numbers between 810 and 5060. The configurations with the greatest turbulent intensity were studied, with the addition of diluted species transport and consumption. A laminar flow setup with a slot jet (Re = 79.5) was compared to two injection designs consisting of a simple set of 12 impinging gas jets (Rej = 2530; H/d = 3) with and without the adjunction of a wire to break the jets (Rej = 1687; H/d = 2). The two turbulent injection methods improved growth rate by 15%, which mainly resulted from a larger gas heating by the surface due to turbulent heat exchange in the jet impact zone.

Nitride passivation reduces interfacial traps in atomic-layer-deposited Al2O3/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al2O3. This AlN passivation incorporated nitrogen at the Al2O3/GaAs interface, improving the capacitance-voltage (C–V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C–V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (Dit). The Dit was reduced over the entire GaAs band gap. In particular, these devices exhibited Dit around the midgap of less than 4 × 1012 cm−2eV−1, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

Performance enhancement of GaN-based flip-chip ultraviolet light-emitting diodes with a RPD AlN nucleation layer on patterned sapphire substrate

In this work, flip-chip ultraviolet light-emitting diodes (FCUV-LEDs) on patterned sapphire substrate (PSS) at 375 nm were grown by an atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). A specialized reactive plasma deposited (RPD) AlN nucleation layer was utilized on the PSS to enhance the quality of the epitaxial layer. By using high-resolution X-ray diffraction, the full-width at half-maximum of the rocking curve shows that the FCUV-LEDs with RPD AlN nucleation layer had better crystalline quality when compared to conventional GaN nucleation samples. From the transmission electron microscopy (TEM) image, it can be observed that the tip and incline portion of the pattern was smooth using the RPD AlN nucleation layer. The threading dislocation densities (TDDs) are reduced from 7 × 107 cm−2 to 2.5 × 107 cm−2 at the interface between the u-GaN layers for conventional and AlN PSS devices, respectively. As a result, a much higher light output power was achieved. The improvement of light output power at an injection current of 20 mA was enhanced by 30%. Further photoluminescence measurement and numerical simulation confirm such increase of output power can be attributed to the improvement of material quality and light extraction.

High performance 380-nm ultraviolet light-emitting-diodes with 3% efficiency droop by using free-standing GaN substrate manufacturing from GaAs substrate

We investigated the influence of free-standing GaN (FS-GaN) substrates on the performance of ultraviolet light-emitting-diodes (UV-LEDs) grown on top by atmospheric pressure metal-organic chemical vapor deposition. High-resolution double-crystal x-ray diffraction (HRDCXD) analysis demonstrated high-order satellite peaks and clear fringes between them for UV-LEDs grown on the FS-GaN substrate, from which the interface roughness was estimated. In addition, the full width at half maximum of the HRDCXD rocking curve in the (0002) and the (101¯2) reflections were reduced to below 90 arc sec. The Raman results indicated that the GaN-based epilayer of strain free was grown. Additionally, the effect of the FS-GaN substrate on the crystal quality of the UV-LEDs was examined in detail by transmission electron microscopy (TEM). The TEM characterizations revealed no defects and V-pits were found in the scanned area. Based on the results mentioned above, the light output power of UV-LEDs on the FS-GaN substrate can be enhanced drastically by 80% and 90% at 20 and 100 mA, respectively. Furthermore, an ultralow efficiency degradation of about 3% can be obtained for the UV-LEDs on the FS-GaN substrate at a high injection current. The use of an FS-GaN substrate is suggested to be effective for improving the emission efficiency and droop of UV-LEDs grown thereon.

Cover Picture: Atmospheric pressure chemical vapor deposition (APCVD) grown bi‐layer graphene transistor characteristics at high temperature (Phys. Status Solidi RRL 7/2014)

A low-cost and simple atmospheric chemical vapor deposition (APCVD) based double-layer graphene is used to study its transport phenomena at temperature as high as 250 °C. Beyond this temperature the fabricated graphene transistor fails to function, indicating areas of improvements related to dielectric engineering and device isolation. At the same time, it is interesting to note that such low band gap graphene operated fully even at gate current densities as high as 1 A/cm2 and channel current densities as high as 1 MA/cm2 at 250 °C. The study by Ramy M. Qaisi et al. (pp. 621–624) can be a cornerstone to explore graphene as an alternate low-cost material in place of traditional GaN and SiC based power devices for harsh environment application.

Growth behaviors and film properties of zinc oxide grown by atmospheric mist chemical vapor deposition

We evaluated the characteristics of ZnO grown by atmospheric mist chemical vapor deposition at temperatures ranging from 200°C to 300°C as a function of the water in the solvent. We also utilized ZnO thin films as an active layer of thin film transistors (TFTs) using the mist CVD process. The mobility measured in the thin-film transistor (TFT) increased with increasing water concentration in the solvent and increasing temperature. We believe that the fact that hydrogen is incorporated in ZnO due to the function of water in the solvent plays an important role in determining the transistor characteristics. The higher deposition temperature functions to increase oxygen vacancies which influences the mobility.

Atmospheric pressure chemical vapor deposition (APCVD) grown bi‐layer graphene transistor characteristics at high temperature

AbstractWe report the characteristics of atmospheric chemical vapor deposition grown bilayer graphene transistors fabricated on ultra‐scaled (10 nm) high‐κ dielectric aluminum oxide (Al2O3) at elevated temperatures. We observed that the drive current increased by >400% as temperature increased from room temperature to 250 °C. Low gate leakage was maintained for prolonged exposure at 100 °C but increased significantly at temperatures >200 °C. These results provide important insights for considering chemical vapor deposition graphene on aluminum oxide for high temperature applications where low power and high frequency operation are required. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of glow DBD modulation on gas and thin film chemical composition: case of Ar/SiH4/NH3 mixture

In recent years, atmospheric pressure plasma-enhanced chemical vapour deposition has been identified as a convenient way to deposit good quality thin films. With this type of process, where the gas mixture is injected on one side of the electrodes, the chemical composition of the gas evolves with the gas residence time in the plasma. The consequence is a possible gradient in the chemical composition over the thickness of in-line coatings. The present work shows that the modulation of the plasma with a square signal significantly reduces this gradient while the drawback of low growth rate is avoided by increasing the discharge power. This study deals with plane/plane glow dielectric barrier discharges (DBDs) in an Ar/NH3/SiH4 gas mixture to make thin films. The 50 kHz discharge power of the glow DBD was varied by increasing voltage and modulating excitation. The impact on (i) the plasma development was observed through emission spectroscopy and (ii) the thin film coating through Fourier transform infrared measurements. It is shown that the modulation significantly decreases the time and the energy needed to achieve stable chemistry, enhances secondary chemistry and limits disturbance induced by impurities because of a slower decrease of SiH4 concentration and thus a higher ratio of SiH4/impurities, all very important points for in-line AP-PECVD development. When the growth rate is limited by diffusion, coating growth continues when the discharge is off, so long as there is a precursor gradient between the surface and the gas bulk. A higher discharge power steepens this gradient, which enhances diffusion from the bulk and thus growth rate.

Atmospheric plasma synthesized PEG coatings: non-fouling biomaterials showing protein and cell repulsion

The role of a protein-repelling coating, such as plasma-polymerized poly(ethylene glycol) (pp-PEG), is to limit the interaction between a device and its physiological environment, which could lead to undesired inflammatory reactions or in a loss of the efficiency of an implant. We developed two original methods to obtain such coatings at atmospheric pressure, in which tetra(ethylene glycol) dimethyl ether (tetraglyme) is injected either as a liquid or as a vapor, in the post-discharge of a RF torch. These are referred to as atmospheric pressure plasma liquid deposition (APPLD) and atmospheric pressure plasma-enhanced chemical vapor deposition (APPECVD). In both cases, the resulting material appears to be smooth, non-water soluble and adheres properly on the substrates (Si wafers). A systematic evaluation of the non-fouling properties of the resulting material with respect to plasma power (from 30W to 80W) and the deposition method is presented. The plasma coatings are tested by exposing them to proteins (bovine serum albumin and human fibrinogen) and cells (mouse fibroblasts (L929 and MEF)) and controlling the adsorption using X-ray photoelectron spectroscopy (proteins) and scanning electron microscopy (cells). Depending on the synthesis conditions (method and plasma power), we could highlight a very impressive reduction of protein adsorption (over 90% for the APPLD PEG (30–80W) and for the APPECVD PEG (30W)). In the same direction, cell adhesion can be reduced and avoided over the assessed areas, after 24hours of culture, showing that the generated material can be a potentially good candidate for biocompatible purposes.

Inline atmospheric pressure metal-organic chemical vapour deposition for thin film CdTe solar cells

A detailed study has been undertaken to assess the deposition of CdTe for thin film devices via an inline atmospheric pressure metal-organic chemical vapour deposition (AP-MOCVD) reactor. The precursors for CdTe synthesis were released from a showerhead assembly normal to a transparent conductive oxide (TCO)/glass substrate, previously coated with a CdZnS window layer using a conventional batch AP-MOCVD reactor with horizontal flow delivery. Under a simulated illumination with air mass coefficient 1.5 (AM1.5), the initial best cell conversion efficiency (11.2%) for such hybrid cells was comparable to a reference device efficiency (~13%), grown entirely in the AP-MOCVD batch reactor. The performance and structure of the hybrid and conventional devices are compared for spectral response, CdTe grain morphology and crystal structure. These preliminary results reported on the transfer from a batch to an inline AP-MOCVD reactor which holds a good potential for the large-scale production of thin film photovoltaics devices and related materials.

Lithium electrochromic properties of atmospheric pressure plasma jet-synthesized tungsten/molybdenum-mixed oxide films for flexible electrochromic device

An investigation is conducted into the enhanced lithium electrochromic performance of flexible tungsten/molybdenum-mixed oxide (WMo x O y C z ) films deposited onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates, using a low temperature (~23 °C) atmospheric pressure plasma-enhanced chemical vapor deposition with an atmospheric pressure plasma jet at various substrate distances. The rapid synthesis of flexible WMo x O y C z films is performed by injecting the mixed hexacarbonyl and precursors W(CO)6 and Mo(CO)6 into an air plasma jet and exposing the substrate in the plasmas for short exposure durations (19–34 s) at various substrate distances. The flexible WMo x O y C z films possess the remarkable Li+ ion electrochromic performance, even though after being bent 360° around a 2.5-cm diameter rod for 1,000 cycles and tested for 200 cycles of reversible Li+ ion intercalation and deintercalation in a 1-M LiClO4-propylene carbonate electrolyte, respectively, by a potential sweep switching at the scan rates of ±50 mV/s from the potential of −1 to 1 V and a potential step switching at the potentials of −1 and 1 V. Significant optical modulation and optical density change of up to 71.2 % and 0.73 at a wavelength of 622 nm are respectively achieved.

Effect of band alignment on photoluminescence and carrier escape from InP surface quantum dots grown by metalorganic chemical vapor deposition on Si

A detailed analysis of photoluminescence (PL) from InP quantum dots (QDs) grown on Si has been carried out to understand the effect of substrate/host material in the luminescence and carrier escape process from the surface quantum dots. Such studies are required for the development of monolithically integrated next generation III-V QD based optoelectronics with fully developed Si microelectronics. The samples were grown by atmospheric pressure metalorganic chemical vapor deposition technique, and the PL measurements were made in the temperature range 10–80 K. The distribution of the dot diameter as well as the dot height has been investigated from atomic force microscopy. The origin of the photoluminescence has been explained theoretically. The band alignment of InP/Si heterostructure has been determined, and it is found be type II in nature. The positions of the conduction band minimum of Si and the 1st excited state in the conduction band of InP QDs have been estimated to understand the carrier escape phenomenon. A blue shift with a temperature co-efficient of 0.19 meV/K of the PL emission peak has been found as a result of competitive effect of different physical processes like quantum confinement, strain, and surface states. The corresponding effect of blue shift by quantum confinement and strain as well as the red shift by the surface states in the PL peaks has been studied. The origin of the luminescence in this heterojunction is found to be due to the recombination of free excitons, bound excitons, and a transition from the 1st electron excited state in the conduction band (e1) to the heavy hole band (hh1). Monotonic decrease in the PL intensity due to increase of thermally escaped carriers with temperature has been observed. The change in barrier height by the photogenerated electric-field enhanced the capture of the carriers by the surface states rather than their accumulation in the QD excited state. From an analysis of the dependence of the PL intensity, peak position, and line width with temperature and excitation source, the existence of free and bound excitonic recombination together with e1 → hh1 transitions in the QDs is established.

A simple and scalable approach towards the preparation of superhydrophobic surfaces – importance of the surface roughness skewness

A simple and easily up-scalable approach towards the preparation of fluorine-free superhydrophobic surfaces is proposed. Surfaces with water contact angle (WCA) as high as 170° and contact angle hysteresis (CAH) down to 5° are obtained on industrial metallic foils (cold-rolled aluminium foils and electrodeposited copper foils) coated thanks to an atmospheric pressure plasma-enhanced chemical vapour deposition method. Nano- and micro-scale roughness characterisation of the surface, performed by atomic force microscopy (AFM) and confocal microscopy, provided evidence for the substrate surface skewness as the major parameter influencing the WCA for identical nano-rough plasma-polymerised PDMS coatings. A symmetric height distribution, Rskm = 0, is shown to be more desirable to achieve superhydrophobic surfaces.

Highly-branched vertically-oriented graphene nanosheets with dense open graphitic edge planes as Pt support for methanol oxidation

Vertically-oriented graphene (VG) with predominantly edge plane structure is considered as a promising catalyst support candidate for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). Inspired by the fact that catalyst nanoparticles are spontaneously attached to the exposed graphene edges, a novel highly-branched vertically-oriented graphene (HBVG) based catalyst support is proposed in the current work. With employing atmospheric normal glow discharge (ANGD) and microwave plasma-enhanced chemical vapor deposition (PECVD) methods, HBVG and maze-like VG (MVG) are synthesized on the surface of carbon paper (CP), respectively. Pt nanoparticles are deposited on pristine CP, HBVG-CP, and MVG-CP with the same route of repeated double-potential pulse electrodeposition (RDPE). Experimental results show that HBVG-CP with dense open graphitic edge planes can desirably provide a considerable number of nuclei sites for the fast nucleation and well dispersion of Pt nanoparticles. Meanwhile, a certain amount of oxygen-containing functional groups on the HBVG surface will benefit the rapid removal of CO and accumulated carbonaceous species. Based on the electrochemical measurements on Pt utilization efficiency, catalytic activity, CO tolerance, and long-term stability, Pt/HBVG-CP is demonstrated to be able to present enhanced catalytic performance over the Pt/CP and Pt/MVG-CP counterparts, holding a great potential for fuel cell applications.

Fabrication of Titanium-Based Hard Coatings by Atmospheric Microplasma-Metal Organic Chemical Vapor Deposition Using Titanium Tetraisopropoxide

The atmospheric microplasma metal organic chemical vapor deposition (AP-MOCVD) using titanium (IV) tetraisopropoxide (TTIP) as a metal alkoxide titanium source was investigated for depositing TiC and TiN hard coatings on stainless steel rods for improving the tool life of electroplated diamond tools. The components and morphology of the coating deposited by microplasma AP-MOCVD with several gas sources and different processes was observed and analyzed. The titanium-based hard coatings composed of TiC, TiN, and TiO2 was successfully obtained by microplasma AP-MOCVD using TTIP as a metal alkoxide titanium source with mixed gases (CH4, N2, H2, and Ar). For the fabrication of titanium-based coatings (TiC, TiN) by microplasma AP-MOCVD, it is important that the carbon and oxygen content, which are components of TTIP, are reduced. The addition of hydrogen gas in the microplasma AP-MOCVD process, followed by nitriding effectively reduces the carbon and oxygen content in the coating.