Pulsed Chemical Vapor Deposition Research Articles

The growth behavior of GaN NWs on Si(1 1 1) by the dispersion of Au colloid catalyst using pulsed MOCVD

We report on the growth of self-assembled GaN nanowires (NWs) on Si(1 1 1) substrates via pulsed metal-organic chemical vapor deposition (MOCVD) technique. Au colloid nanoparticles dispersed on Si(1 1 1) substrate were used as catalyst to conduct the GaN NWs growth. The size of the GaN NWs can be tailored by an easy and simple method of optimizing the Au colloids catalyst using Ga pre-deposition. The pulsed MOCVD growth mode was used to grow GaN NWs in which the group III and group V precursors were introduced alternately in the sequence. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL). The XRD pattern confirmed the hexagonal structure of GaN NWs. The experimental results indicated that the GaN NW diameter depended on the size of Au+Ga droplets. The pulsed method combined with growth temperature considerably affected the shape and density of the GaN NWs.

Growth of Titanium Dioxide Nanorods in 3D-Confined Spaces

Three-dimensional (3D) nanowire (NW) networks are promising architectures for effectively translating the extraordinary properties of one-dimensional objects into a 3D space. However, to uniformly grow NWs in a 3D confined space is a serious challenge due to the coupling between crystal growth and precursor concentration that is often dictated by the mass flow characteristic of vapor or liquid phase reactants within the high-aspect ratio submicrometer channels in current strategies. We report a pulsed chemical vapor deposition (CVD) process that successfully addressed this issue and grew TiO(2) nanorods uniformly covering the entire inner surface of highly confined nanochannels. We propose a mechanism for the anisotropic growth of anatase TiO(2) based on the surface-reaction-limited CVD process. This strategy would lead to the realization of NW-based 3D nanoarchitectures from various functional materials for the applications of sensors, solar cells, catalysts, energy storage systems, and so forth.

Transport properties of two-dimensional electron gas in lattice-matched InAlN/GaN and InAlN/AlN/GaN materials

The lattice-matched InAlN/GaN structure is one kind of emerging material with high conductivity and used in GaN-based high electron mobility transistors (HEMTs). The transport properties of lattice-matched InAlN/GaN structure and InAlN/AlN/GaN structure are studied. The samples are grown using pulsed metal organic chemical vapor deposition on sapphire substates. Both structures show temperature-dependent Hall mobilities with a typical behavior of two-dimensional electron gas (2DEG). Theoretical analysis of the temperature dependence of mobility is carried out based on the comprehensive consideration of various scattering mechanisms such as acoustic deformation-potential, piezoelectric, polar optic phonon, dislocation, alloy disorder and interface roughness scattering. It is found that the dominant scattering mechanisms are the interface roughness scattering and the polar optic phonon scattering for both structures at room temperature. The insertion of AlN spacer layer into InAlN/GaN interface exempts 2DEG from alloy disorder scattering, more importantly results in a better interface, and restrains greatly interface roughness scattering. The influence of sheet density on 2DEG mobility is also considered, and the upper limit of density-dependent 2DEG mobility is given for lattice-matched InAlN/GaN and InAlN/AlN/GaN structures and compared with many reported experimental data.

Novel combination of hydrophilic/hydrophobic surface for large wettability difference and its application to liquid manipulation

This paper reports a novel combination of hydrophilic/hydrophobic materials for the evolution of liquid manipulation. Droplet generation based on a hydrophilic/hydrophobic mechanism is a promising method for highly accurate liquid manipulations. Although several droplet manipulation devices utilizing hydrophilic/hydrophobic patterns have been reported, it has been difficult to split fluid into droplets solely through hydrophilic/hydrophobic patterns in a microchannel. In this study, a material combination for fabricating hydrophilic/hydrophobic patterns was investigated and their wettability difference was enhanced for droplet generation. To improve hydrophilicity, we attempted to increase the surface area of silicon oxide through pulsed plasma chemical vapor deposition (PPCVD). To improve hydrophobicity, the damage to the hydrophobic patterns in the fabrication process was reduced. We successfully enhanced the difference in contact angles from 54.3° to 86.6° by combining the developed hydrophilic material and hydrophobic material. The developed material combination could successfully split fluid into a quantitative droplet of 14.1 nL in a microfluidic chip. Because the developed hydrophilic/hydrophobic combination enables the formation of a droplet with desirable shape in microchannels, the developed hydrophilic/hydrophobic combination is a promising component for lab-on-a-chip applications.

Unusual enhancement in electrical conductivity of tin oxide thin films with zinc doping

Electrical conductivity of SnO(2)-based oxides is of great importance for their application as transparent conducting oxides (TCO) and gas sensors. In this paper, for the first time, an unusual enhancement in electrical conductivity was observed for SnO(2) films upon zinc doping. Films with Zn/(Zn + Sn) reaching 0.48 were grown by pulsed spray-evaporation chemical vapor deposition. X-Ray diffraction (XRD) shows that pure and zinc-doped SnO(2) films grow in the tetragonal rutile-type structure. Within the low doping concentration range, Zn leads to a significant decrease of the crystallite size and electrical resistivity. Increasing Zn doping concentration above Zn/(Zn + Sn) = 0.12 leads to an XRD-amorphous film with electrical resistivity below 0.015 Ω cm at room temperature. Optical measurements show transparencies above 80% in the visible spectral range for all films, and doping was shown to be efficient for the band gap tuning.

Chemical vapor deposition and characterization of high-k BaHf1−xTixO3 dielectric layers for microelectronic applications

Possibilities to grow high-k BaHf1−xTixO3 layers were investigated by pulsed liquid injection metal-organic chemical vapor deposition technique. Ba(thd)2 (thd=2,2,6,6-tetramethylheptane-3,5-dionate), Hf(thd)4, and Ti(OiPr)2(thd)2 were used as precursors, toluene as solvent, and Si(100) as substrate. The influence of solution composition and deposition temperature on crystallization and elemental and phase compositions of Ba–Hf–Ti–O layers was investigated. BaHf1−xTixO3 layers with x∼0–0.5 may be obtained at 600–650 °C, whereas the lower deposition temperature (500–550 °C) resulted in crystallization of the dominating orthorhombic BaCO3 phase in deposited films. Films were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Electrical measurements were performed for deposited thin films in view of storage capacitor applications of BaHf1−xTixO3 films in dynamic random access memories.

Plasma deposited stability enhancement coating for amorphous ketoprofen

A hydrophobic fluorocarbon coating deposited onto amorphous ketoprofen via pulsed plasma-enhanced chemical vapor deposition (PPECVD) significantly prolonged the onset of recrystallization compared to uncoated drug. Rapid freezing (RF) employed to produce amorphous ketoprofen was followed by PPECVD of perfluorohexane. The effect of coating thickness on the recrystallization and dissolution behavior of ketoprofen was investigated. Samples were stored in open containers at 40 °C and 75% relative humidity, and the onset of recrystallization was monitored by DSC. An increase in coating thickness provided enhanced stability against recrystallization for up to 6 months at accelerated storage conditions (longest time of observation) when compared to three days for uncoated ketoprofen. Results from XPS analysis demonstrated that an increase in coating thickness was associated with improved surface coverage thus enabling superior protection. Dissolution testing showed that at least 80% of ketoprofen was released in buffer pH 6.8 from all coated samples. Overall, an increase in coating thickness resulted in a more complete drug release due to decreased adhesion of the coating to the substrate.

High quality InAlN/GaN heterostructures grown on sapphire by pulsed metal organic chemical vapor deposition

High quality InAlN/GaN heterostructures are successfully grown on the (0 0 0 1) sapphire substrate by pulsed metal organic chemical vapor deposition. The InAlN barrier layer with an indium composition of 17% is observed to be nearly lattice matched to GaN layer, and a smooth surface morphology can be obtained with root mean square roughness of 0.3 nm and without indium droplets and phase separation. The 50 mm InAlN/GaN heterostructure wafer exhibits a mobility of 1402 cm 2/V s with a sheet carrier density of 2.01×10 13 cm −2, and a low average sheet resistance of 234 Ω/cm 2 with a sheet resistance nonuniformity of 1.22%. Compared with the conventional continual growth method, PMOCVD reduces the growth temperature of the InAlN layer and the Al related prereaction in the gas phase, and consequently enhances the surface migration, and improves the crystallization quality. Furthermore, indium concentration of InAlN layer can be controlled by adjusting the pulse time ratio of TMIn to TMAl in a unit cycle, the growth temperature and pressure, as well as the InAlN layer thickness by the number of unit cycle repeats.

Formation of Iron Carbide Nanorod by Pulsed Plasma Chemical Vapor Deposition

Iron carbide nanorods were produced on the surface of pure iron sheet by means of pulsed plasma chemical vapor deposition. Hydrogen plasma was used in the initial state, varied from 10 to 60 minute, for the purpose of cleaning and preparing nanoparticles. The formation was done under methane atmosphere, varied from 2 to 30 minute. X-ray diffraction (XRD) patterns analysis showed that iron carbide was found on all of these experiment conditions. By field emission scanning electron micro spectroscopy (FESEM) observation, iron carbide nanorods, however, were found neatly only on the methane plasma treating at 10 minute.

The properties of fluorine-containing diamond-like carbon films prepared by pulsed DC plasma-activated chemical vapour deposition

Diamond-like carbon films containing up to 23.1 at. % of fluorine (F-DLC), were deposited onto silicon substrates by low-frequency, pulsed DC, plasma-activated, chemical vapour deposition (PACVD). The influence of fluorine on plasma current density, deposition rate, composition, bonding structure, surface energy, hardness, stress and biocompatibility was investigated and correlated with the fluorine content. X-ray photoelectron spectroscopy (XPS) analysis revealed the presence C–C, C–CF and C–F for F-DLC films with a low fluorine concentration (1.5–12.1 at. %), however for films with a higher fluorine content (23.0 at. %) an additional peak due to CF 2 bonding was detected. The addition of fluorine into the DLC film resulted in lower stress and hardness values. The reduction in these values was attributed to the substitution of strong C=C by weaker C–F bonds which induces a decrease in hardness. Ion scattering spectrometery (ISS) measurements revealed the presence of fluorine atoms in the outmost layer of the F-DLC films and there was no evidence of surface oxygen contamination. The water contact angle was found to increase with increasing fluorine content and has been attributed to the change of the bonding nature in the films, in particularly increasing CF and CF 2 bonds . Biocompatibility tests performed using MG-63 osteoblast-like cell cultures indicated homogeneous and optimal tissue integration for both the DLC and the F-DLC surfaces. This pulsed-PACVD technique has been shown to produce biocompatible DLC and F-DLC coatings with a potential for large area applications.

CVD of Ru, Pt and Pt-based alloy thin films using ethanol as mild reducing agent

Noble metal thin films (Pt and Ru) were grown at 250 °C, using commercially available precursors, by the pulsed spray evaporation chemical vapor deposition (PSE-CVD) technique. The growth process relies on the thermally activated reaction of ethanol with the metal acetylacetonate precursors. The synthesized polycrystalline films are pure metal phase and crystallize in hexagonal (Ru) and cubic (Pt) structures. The formation of an interfacial silicide phase was noticed in the case of the Pt growth on silicon substrates. The films are smooth, continuous and show a steady growth without any noticeable incubation time. The single-step growth of Pt-based alloys, Pt–Co and Pt–Cu, with controlled composition was performed by simply adjusting the composition of the liquid feedstock.

Growth of RuO2 Thin Films by Pulsed-Chemical Vapor Deposition Using RuO4 Precursor and 5% H2 Reduction Gas

RuO2 thin films were grown on thermal SiO2(100 nm) and Ta2O5(4 nm)/SiO2(100 nm) substrates at 230 °C by pulsed-chemical vapor deposition using a RuO4 precursor dissolved in blend of chosen organic ...

Up-scaling of a Low Temperature PACVD Process for the Deposition of α/γ-Nanocrystalline Alumina Coated Tools for Thixocasting of 1.2208 steel

An industrial-scale pulsed plasma-assisted chemical vapor deposition (PACVD) process for crystalline alumina growth was developed. To obtain a homogeneous coating thickness distribution over complex geometries and large dimensions, a suitable gas injection system was designed. A phase formation diagram for alumina coatings as a function of pulse length and cathode voltage has been compiled, allowing for the deposition of dense α/γ-Al2O3 coatings at a substrate temperature of 590 °C. Moulds coated with an α/γ-Al2O3 coating were utilized in steel thixocasting at temperatures of ∼1400 °C. The coatings were intact after thixocasting and showed significantly improved chemical wear resistance compared to plain steel moulds.

Growth of polar axis oriented tetragonal Pb(Zr,Ti)O 3 films on CaF 2 substrates with transparent (La 0.07Sr 0.93)SnO 3

Epitaxial (La 0.07Sr 0.93)SnO 3 [LSSO] films were deposited on CaF 2 substrates by pulse laser deposition. The (1 0 0) c orientation of LSSO films was observed only on (1 1 0)CaF 2, whereas (1 1 0) c orientation was found on (1 1 1)CaF 2 and (1 0 0)CaF 2. (0 0 1) polar axis oriented tetragonal Pb(Zr 0.35Ti 0.65)O 3 films were grown on the fabricated (1 0 0) c LSSO∥(1 1 0)CaF 2 by pulsed metal organic chemical vapor deposition. The (0 0 1)Pb(Zr 0.35Ti 0.65)O 3∥(1 0 0)cLSSO∥(1 1 0)CaF 2 stack structure exhibited about 70% transparency with an adsorption edge of approximately 330 nm.

Optical characterization of quaternary AlInGaN epilayer and multiple quantum wells grown by a pulsed metalorganic chemical vapor deposition

The optical properties of quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by a pulsed metalorganic chemical vapor deposition have been investigated by means of photoluminescence (PL) and time-resolved PL measurements. The PL emission peaks in both AlInGaN epilayers and MQWs show a blueshift with increasing excitation power density. The PL intensities of MQWs are much stronger (∼3–4 times) than that of the epilayer. The PL emission intensities ( I emi) of both AlInGaN epilayers and MQW samples increase superlinearly with increasing excitation power density ( I exc), following a power-law form, I emi ⧜ I exc β . The PL decay times of MQWs are longer than that of epilayer. The longer PL decay times may be due to a stronger localization effect of carriers/excitons at band tail states and wave function separation caused by the quantum confined Stark effect. These results indicate that AlInGaN/AlInGaN MQWs grown by a PMOCVD are promising materials for ultraviolet light emitting diode (LED) applications similar to the InGaN/InGaN system for blue LED applications.

Self-limiting growth of anatase TiO 2: A comparison of two deposition techniques

Self-limiting deposition of titanium dioxide thin films was accomplished using pulsed plasma-enhanced chemical vapor deposition (PECVD) and plasma-enhanced atomic layer deposition (PEALD) at low temperatures ( T < 200 °C) using TiCl 4 and O 2. TiCl 4 is shown to be inert with molecular oxygen at process conditions, making it a suitable precursor for these processes. The deposition kinetics were examined as a function of TiCl 4 exposure and substrate temperature. The quality of the anatase films produced by the two techniques was nominally identical. The key distinctions are found in precursor utilization and conformality. Pulsed PECVD requires 20 times less TiCl 4, while PEALD must be used to uniformly coat complex topographies.

Characteristics of Ge-Sb-Te Films Prepared by Cyclic Pulsed Plasma-Enhanced Chemical Vapor Deposition

Ge-Sb-Te (GST) thin films were deposited on TiN, SiO2, and Si substrates by cyclic-pulsed plasma-enhanced chemical vapor deposition (PECVD) using Ge{N(CH3)(C2H5)}, Sb(C3H7)3, Te(C3H7)3 as precursors in a vertical flow reactor. Plasma activated H2 was used as the reducing agent. The growth behavior was strongly dependent on the type of substrate. GST grew as a continuous film on TiN regardless of the substrate temperature. However, GST formed only small crystalline aggregates on Si and SiO2 substrates, not a continuous film, at substrate temperatures > or = 200 degrees C. The effects of the deposition temperature on the surface morphology, roughness, resistivity, crystallinity, and composition of the GST films were examined.

Anomalous magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films

We report on large external magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films on MgO(001). The application of a 1 T field during the growth process significantly increases the saturation magnetization of magnetite by 150%–220% at a deposition temperature of 550 and 600 °C, while the enhancement of the remanent magnetization is even larger. This anomalous magnetic field effect does not drastically alter the crystalline texture, surface morphology, and film thickness of magnetite, but is explained by a suppression of antiphase-boundary formation during film growth.

Thin film composites of nanocrystalline ZrO2 and diamond-like carbon: Synthesis, structural properties and bone cell proliferation

We report on the synthesis of thin composites of diamond-like carbon (DLC) and nanocrystalline ZrO(2) deposited using pulsed direct current plasma-enhanced chemical vapor deposition at low temperatures (<120 degrees C). Films containing up to 21at.% Zr were prepared (hydrogen was not included in the calculation) and their structural and surface properties were determined using a number of spectroscopic methods and contact angle measurements. Bone cell adhesion to the films was studied using a 3 day cell culture with osteoblasts. These nanocomposites (DLC-ZrO(2)) consist of tetragonal ZrO(2) nanocrystals with an average size of 2-5 nm embedded in an amorphous matrix consisting predominantly of DLC. The surface water contact angle of the films increased from approximately 60 degrees to 80 degrees as the Zr content increased from 0 to 21at.%. The cell culture study revealed that although the cell counts were not significantly different, the morphology of the osteoblasts growing on the DLC-ZrO(2) nanocomposites was markedly different from that of cells growing on DLC alone. Cells growing on the DLC-ZrO(2) surfaces were less spread out and had a smaller cell area in comparison with those growing on DLC surfaces. In some areas on the DLC-ZrO(2) surfaces, large numbers of cells appeared to coalesce. It is postulated that the difference in cell morphology between osteoblasts on DLC-ZrO(2) surfaces and DLC surfaces is related to the presence of very small tetragonal nanocrystals of ZrO(2) in the composite film.

Carbon nanotube junctions obtained by pulsed liquid injection chemical vapour deposition

The effect of substrate surface roughness on the synthesis of carbon nanotube (CNT) junctions is studied. CNTs were obtained by a pulsed liquid injection chemical vapour deposition system (PLICVD) and grown on quartz substrates with different roughnesses. Nickel particles were used as catalyst and acetone as the carbon precursor. Results shown that CNTs growth depend strongly on the substrate irregularity. When roughness is present, the presence of CNT junctions are increased. On the quartz surface, without any modification of roughness, CNTs are not obtained. Thus, a growth mechanism for CNT junctions, based on the substrate roughness is suggested. This method represents an important alternative to produce CNTs for applying them in nanoelectronic devices.