Structure of copolymer films created by plasma enhanced chemical vapor deposition

The interface structure in copolymer films made using plasma enhanced chemical vapor deposition (PECVD) has been probed for the first time using X-ray reflectivity. Copolymer films made from comonomers benzene (B), octafluorocyclobutane (OFCB), and hexamethyldisiloxane (HMDS) show extremely sharp interfaces and scattering length density depth profiles that are uniform with depth, making them useful for optical applications. The polymer/air interface has an rms roughness (∼5 Å) that is only slightly larger than that of the supporting substrate (∼3 Å). Addition of either benzene or HMDS as a comonomer in the deposition of OFCB alters a transient deposition behavior at the silicon oxide interface that occurs when using only OFCB. For the B-OFCB copolymer films, a facile control of refractive index with monomer feed composition is achieved. A nonlinear variation in the X-ray scattering length density with composition for the HMDS-OFCB copolymer films is consistent with the nonlinear visible light refractive index (632.8 nm) variation reported earlier.     

Correlation of morphology and barrier properties of thin microwave plasma polymer films on metal substrate

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ?, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10⁻¹⁴ cm² s⁻¹ shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces.     

Stages in the catalyst-free InP nanowire growth on silicon (100) by metal organic chemical vapor deposition

Catalyst-free InP nanowires were grown on Si (100) substrates by low-pressure metal organic chemical vapor deposition. The different stages of nanowire growth were investigated. The scanning electron microscopy images showed that the density of the nanowires increased as the growth continued. Catalyzing indium droplets could still be fabricated in the nanowire growing process. X-ray diffraction showed that the nanowires grown at different stages were single crystalline with <111 > growth direction. The photoluminescence studies carried out at room temperature on InP nanowires reveal that the blueshift of photoluminescence decreased as the growing time accumulates, which is related to the increase in the diameter, rather than the length. Raman spectra for nanowires at different growing stages show that the quality of the nanowire changes. The growth of InP nanowires at different growing stages is demonstrated as a dynamic process.     

Microwave plasma enhanced chemical vapor deposition of diamond in silicon pores

In this work, the feasibility of growing boron-doped diamond coatings, approximately 0.3 μm thick, on thin silicon substrates that have 50-μm diameter pores etched 125 μm deep has been demonstrated using deep reactive ion etching (DRIE) in combination with chemical–mechanical polishing (CMP). Using a microwave plasma enhanced chemical vapor deposition (MPECVD) cyclic growth process consisting of carburization, bias-enhanced nucleation, diamond growth and boron-doped diamond growth, uniform diamond coatings throughout the pores have been obtained. The coatings were characterized by Raman spectroscopy and scanning electron microscopy and the secondary electron emission coefficients were found to increase from 4 to 10 between 200 and 1000 V, in agreement with reported values for thicker polycrystalline diamond films grown under similar conditions.     

Growth of graphene on Cu by plasma enhanced chemical vapor deposition

The growth of graphene on Cu substrates by plasma enhanced chemical vapor deposition (PE-CVD) was investigated and its growth mechanism was discussed. At a substrate temperature of 500 °C, formation of graphene was found to precede the growth of carbon nanowalls (CNWs), which are often fabricated by PE-CVD. The growth of graphene was investigated in various conditions, changing the plasma power, gas pressures, and the substrate temperature. The catalytic nature of Cu also affects the growth of monolayer graphene at high substrate temperatures, while the growth at low temperatures and growth of multilayer graphene are dominated mostly by radicals generated in the plasma.     

Characteristics of aluminum films prepared by metalorganic chemical vapor deposition using dimethylethylamine alane on the plasma-pretreated TiN surfaces

Aluminum films were prepared on H₂-plasma pretreated TiN substrates at deposition temperatures of 60-250 °C by metallorganic chemical vapor deposition using dimethylethylamine alane as a precursor. The films were highly pure and the growth rates were 3-50 nm/min, where the lowest deposition temperature was 60 °C. The resistivity was as low as 2.8 μΩcm. High substrate temperatures tended to favor a low resistivity and smooth surface morphology of the films, compared to films with a low temperature at a given thickness. Numerous empty pores appeared in the Al films deposited at a temperature below 150 °C when the film thickness exceeded 200 nm. The number of these pores tended to increase with decrease in temperature. However, in films deposited at temperatures above 200 °C, there were no pores and the large grains were interconnected to a high degree. Higher deposition temperatures yielded a greater preference of the (111) orientation of Al films.     

Characteristics of La2O3 thin films deposited using metal organic chemical vapor deposition with different oxidant gas

La₂O₃ films were deposited using O₃ and the structural and electrical properties were investigated and compared with those of La₂O₃ films deposited using O₂. The deposition temperature of the La₂O₃ films using O₃ was slightly reduced compared to that of the La₂O₃ films generated using O₂. After a post-annealing process at 600 and 900 °C, the crystallinity of the La₂O₃ films using O₃ were smaller than that using O₂. The leakage current density increased after annealing at 600 °C due to densification and then decreased after annealing at 900 °C due to interfacial layer growth. The effective dielectric constant of the La₂O₃ films deposited using O₃ decreased at 900 °C due to interfacial layer growth. The La₂O₃ films deposited using O₃ showed better structural and electrical properties in this study.     

Oxygen barrier coating deposited by novel plasma‐enhanced chemical vapor deposition

We report the use of a novel plasma‐enhanced chemical vapor deposition chamber with coaxial electrode geometry for the SiO_x deposition. This novel plasma setup exploits the diffusion of electrons through the inner most electrode to the interior samples space as the major energy source. This configuration enables a gentle treatment of sensitive materials like low‐density polyethylene foils and biodegradable materials. SiO_x coatings deposited in the novel setup were compared with other state of the art plasma coatings and were found to possess equally good or better barrier properties. The barrier effect of single‐layer coatings deposited under different reaction conditions was studied. The coating thickness and the carbon content in the coatings were found to be the critical parameters for the barrier property. The novel barrier coating was applied on different polymeric materials, and it increased the barrier property of the modified low‐density polyethylene, polyethylene terephthalate, and polylactide by 96.48%, 99.69%, and 99.25%, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Interface structure of photonic multilayers prepared by plasma enhanced chemical vapor deposition

The structures of substrate/layer, layer/layer, and layer/air interfaces in optical multilayers made using plasma enhanced chemical vapor deposition (PECVD) have been probed for the first time using X-ray reflectivity and neutron reflectivity. From the point of view of optical applications the interfaces are extremely sharp, sharper than is often achievable with the self-assembly of block copolymers or deposition techniques in which the polymer layers contact while in a fluid state. The average interface width, a_I, between layers made from different precursors is about 40 Å (16 Å rms). The layer/layer interfaces are generally 2-3 times broader than the layer/air interfaces. Polymeric fluorocarbon films deposited on a Si substrate using PECVD with octafluorocyclobutane (OFCB) monomer show uniform scattering length density with depth except for a region of molecular thickness immediately adjacent to the substrate. Films made from deuterated benzene show uniform density throughout the film thickness.     

Palladium catalyzed formation of carbon nanofibers by plasma enhanced chemical vapor deposition

A dc plasma enhanced chemical vapor deposition process is used to obtain vertically aligned carbon nanofibers (CNFs) from palladium catalysts using an ammonia-acetylene process gas mixture. Transmission electron microscopy is used to elucidate the microstructure of the as-grown fibers revealing different growth anomalies such as a new secondary growth phenomenon which we term hybrid tip growth. Also included in our analysis are conventional tip growth derived structures. In a few instances, the conventional tip growth derived structures possess elongated catalyst particles that impart small cone angles to the carbon nanofiber microstructure. Detailed microchemical analysis reveals that hybrid tip grown CNFs using thick Pd films are partially filled with Pd. Analysis of these growth phenomenon and implications for potential use as on-chip interconnects are discussed.     

A plasma enhanced chemical vapor deposition process to achieve branched carbon nanotubes

Vertically aligned carbon nanotubes (CNTs) have been grown on silicon substrates using nickel as the catalyst layer, acetylene as the carbon source, and hydrogen as the carrier gas. The quality of the CNTs has been examined using transmission and scanning electron microscopy and a tip-growth mechanism with an inner tube diameter of 5–8 nm was observed. The effect of plasma hydrogenation as a post-growth treatment was shown to lead to total or partial removal of the nickel seeds from the CNT tips. Using sequential hydrogenation and growth, it has been possible to achieve tree-like nanostructures.     

Synthesis of carbon nanosheets by inductively coupled radio-frequency plasma enhanced chemical vapor deposition

An ultrathin sheet-like carbon nanostructure, carbon nanosheet, has been effectively synthesized with CH₄ diluted in H₂ by an inductively coupled radio-frequency plasma enhanced chemical vapor deposition. Nanosheets were obtained without catalyst over a wide range of deposition conditions and on a variety of substrates, including metals, semiconductors and insulators. Scanning electron microscopy shows that the sheet-like structures stand on edge on the substrate and have corrugated surfaces. The sheets are 1 nm or less in thickness and have a defective graphite structure. Raman spectra show typical carbon features with D and G peaks at 1350 and 1580 cm⁻¹, respectively. The intensity ratio of these two peaks, I(D)/I(G), increases with methane concentration or substrate temperature, indicating that the crystallinity of the nanosheets decreases. Infrared and thermal desorption spectroscopies reveal hydrogen incorporation into the carbon nanosheets.     

Biased enhanced growth of nanocrystalline diamond films by microwave plasma chemical vapor deposition

Smooth nanocrystalline diamond thin films with rms surface roughness of ∼17 nm were grown on silicon substrates at 600°C using biased enhanced growth (BEG) in microwave plasma chemical vapor deposition (MPCVD). The evidence of nanocrystallinity, smoothness and purity was obtained by characterizing the samples with a combination of Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy and Auger electron spectroscopy. The Raman spectra of the films exhibit an intense band near 1150 cm⁻¹ along with graphitic bands. The former Raman band indicates the presence of nanocrystalline diamond. XRD patterns of the films show broad peaks corresponding to inter-planar spacing of (111) and (220) planes of cubic diamond supporting the Raman results. Auger line shapes closely match with the line shape of diamond suggesting high concentration of sp³ carbon on the surfaces of the films. The growth of dominantly sp³ carbon by BEG in the MPCVD system at the conditions used in the present work can be explained by the subsurface implantation mechanism while considering some additional effects from the high concentration of atomic hydrogen in the system.     

Growth of nanocrystalline diamond films by biased enhanced microwave plasma chemical vapor deposition

Nanocrystalline diamond (NCD) films were grown using biased enhanced growth (BEG) in microwave plasma chemical vapor deposition on mirror polished silicon substrates at temperatures in the range from 400 to 700°C. The films were characterized by Raman spectroscopy, X-ray diffraction (XRD), Auger electron spectroscopy and atomic force microscopy (AFM). Hardness of the films was measured by nano-indentor. Apart from graphitic D and G bands in the films, the Raman spectra exhibit NCD features near 1140 cm⁻¹. The relative intensity of the NCD to graphitic G band in the Raman spectra of the films is negligible in the films grown at 400°C. It increases with temperature and attains a maximum at 600°C following a sharp decrease in the films grown at higher temperatures. XRD results also indicate a maximum concentration of NCD in the film grown at 600°C. Average hardness of the films increases with temperature from ∼5 GPa to ∼40 GPa up to 600°C followed by a decrease (∼24 GPa) in the film grown at 700°C. Substrate temperature seems to play a crucial role in the growth of NCD in BEG processes. An increase in growth temperature may be responsible for evolving bonded hydrogen and increasing mobility of carbon atoms. Both factors help in developing NCD in the films grown at 500 and 600°C with a combination of subplantation mechanism, due to biasing, and a high concentration of H atoms in the gas-phase, typical of CVD diamond process. At 700°C the implanted carbon atoms may be migrating back to the surface resulting in domination of surface processes in the growth, which in turn should result in increase in graphitic content of the films at such a high methane concentration and continuous biasing used in the present study.     

Vapor deposition polymerization of synthetic rubber thin film in a plasma enhanced chemical vapor deposition reactor

Rubber is one of the most commonly used industrial materials worldwide. However, there is a gap in the literature on the production of rubber thin films in nanoscale. When the rubber thin films are produced in nanoscale, they can be used in high-tech applications where bulk rubbers have never been used before. This study is one of the first investigations to focus on the vapor-based production of the polyisoprene (PI), which is an important member of the synthetic rubber class. For this purpose, a single-step, rapid and environmentally friendly method based on plasma enhanced chemical vapor deposition (PECVD) was employed to produce PI thin films using 2-methyl-1,3-butadiene (isoprene). The high-vapor pressure of isoprene makes it a promising monomer for the production of chemical vapor deposition polymers. The effect of plasma processing parameters on the PI deposition rate was investigated. The deposition rate of PI thin film as high as 40 nm/min was achieved and the contact angle of PI coated bamboo surface was found to be 146.8°. The mechanical durability and laundering tests of PI thin films were performed. Based on this study results, PI thin films produced by PECVD can be used in a number of potential applications.     

流化床化学气相沉积法制备近化学计量比的Ti N粉体

传统气-固反应工艺制备Ti N粉体存在难以逾越的内扩散控制过程,导致制备高纯、正化学计量比的Ti N粉体至今存在巨大困难。提出了流态化化学气相沉积工艺(FBCVD)制备高质量TiN粉体,即基于TiCl₄-N₂-H₂体系,在往复运动的TiN种子粉体上沉积新生高质量TiN粉体的新方法。实验发现,当TiN种子粉体粒径大于52.95μm时,即使在1000℃沉积2 h也不会失流,同时在TiN种子粉体上获得了亚微米级的结节状新生TiN颗粒。通过氧氮分析仪和XRD分析发现,新方法显著提升了粉体的氮含量,获得了近化学计量比的TiN0.96,且氧含量下降了约40%。此外,流化床中气相沉积TiN的生长模式为岛状生长模式,为工业中制备高质量TiN粉体提供了一种新的方法。     

Narrow multi-walled carbon nanotubes produced by chemical vapor deposition using graphene layer encapsulated catalytic metal particles

The use of graphene layer encapsulated catalytic metal particles for the growth of narrower multi-walled carbon nanotubes (MWCNTs) has been studied using plasma-enhanced chemical vapor deposition and conventional thermal CVD. Ni–C or Fe–C composite nanoclusters were fabricated using the dc arc discharge technique with metal–graphite composite electrodes carrying a current of 100–200 A in a stainless-steel chamber filled with He and CH₄ mixture gas at 27 kPa. Nano-sized grains with diameters less than 10 nm were fabricated and deposited on a Si substrate, and were used as a catalyst for MWCNT growth. Structural analyses of the composite nanoclusters and MWCNTs were carried out using transmission electron microscopy. The results show that the diameters of the MWCNTs were reduced from 50–100 nm for a conventional Ni thin film-evaporated Si substrate to a minimum of roughly 2–4 nm in the present study.     

Nitrogenated amorphous carbon films synthesized by electron cyclotron resonance plasma enhanced chemical vapor deposition

Nitrogenated amorphous carbon (a-CN_x:H) films were investigated as protective overcoats for industrial applications. Thin a-CN_x:H films have been deposited on silicon by electron cyclotron resonance plasma-enhanced chemical vapor deposition. The substrate bias was found to play an important role in determining the chemical compositions and mechanical properties of the films. The surface roughness and hardness of the films can reach 1.4 Å and 20 GPa, respectively. The influence of mechanical properties by hydrogen was studied. A correlation exists between the background slope of Raman spectra and the hydrogen content as determined by elastic recoil detection analysis.     

Influence of nitrogen plasma post-treatment on diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

DLC films were synthesized by RF plasma enhanced chemical vapor deposition and the effects of nitrogen plasma post-treatment at different pressures on the structure and properties of DLC films were investigated. Higher roughness was obtained after plasma post-treatment at higher pressures (0.3 and 0.9 torr) and plasma post-treatment at a lower pressure (0.15 torr) resulted in lower roughness than that of original films. The hardness of DLC films decreased with the decrease of post-treatment pressure, which is consistent with the Raman results of I_D/I_G ratio and G peak position. Compared to the original DLC film, the residual stress after plasma post-treatment decreased slightly due to the relatively thin region involved in the plasma post-treatment.     

Pulsed plasma deposition from 1,1,2,2‐tetrafluoroethane by electron cyclotron resonance and conventional plasma enhanced chemical vapor deposition

Pulsed electron cyclotron resonance (ECR) plasmas from 1,1,2,2‐C₂H₂F₄ are used to deposit fluorocarbon films. The deposited films have a F : C ratio of 1, with only slight variations in % CF_x as the deposition pressure is decreased. The optical emission (OES) spectra of the pulsed C₂H₂F₄ plasmas show high intensity peaks for H, C₂, and C₃, with lower intensity CF₂ and F peaks. The dominant OES peak shifts from H_α to C₂ when the pressure is reduced, most likely a result of the increased electron temperature at the lower pressure. Gas‐phase recombination reactions may be occurring between the OES sampling region and the deposition substrate (～ 8‐in. distance), producing fluorocarbon molecular deposition species, thus accounting for the high degree of fluorination in the deposited films. Parallel plate plasma deposited films from C₂H₂F₄ show less fluorination than their ECR counterparts, as well as vastly different OES spectra, with CF₂ peaks dominating the spectra versus H and C₂. The presence of ion bombardment in the parallel plate system tends to defluorinate the depositing films, and thus can account for the less fluorinated films deposited in the parallel plate versus ECR systems. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2084–2092, 2001