Effect of microwave power on diamond-like carbon films deposited using electron cyclotron resonance chemical vapor deposition

Diamond-like carbon (DLC) films have been deposited using electron cyclotron resonance chemical vapor deposition (ECR-CVD) under various microwave power conditions. Langmuir probe measurement and optical emission spectroscopy (OES) were used to characterize the ECR plasma, while the films were characterized using Raman and infrared (IR) spectroscopies, hardness and optical gap measurements. It was found that the ion density and all signal peaks in the optical emission (OE) spectra increased monotonously following the increase in microwave power. Raman spectra and optical gap measurements indicate that the films become more graphitic with lower content of sp³-hybridized carbon atoms as the microwave power was increased. IR and hardness measurements indicate a reduction in hydrogen content and decrease in hardness for the film produced at relatively high microwave powers. A deposition mechanism is described which involved the ion bombardment of film surfaces and hydrogen–surface interactions. The deposition rate of DLC film is correlated to the ion density and CH₃ density.     

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.     

Surface morphology of PECVD fluorocarbon thin films from hexafluoropropylene oxide, 1,1,2,2‐tetrafluoroethane,and difluoromethane

Atomic force microscopy (AFM) measurements have been made on a series of fluorocarbon films deposited from pulsed plasmas of hexafluoropropylene oxide (HFPO), 1,1,2,2‐tetrafluoroethane (C₂H₂F₄), and difluoromethane (CH₂F₂). All of the films give images showing nodular growth (cauliflower‐like appearance), with the size and distribution of the nodules dependent on both the precursor, the degree of surface modification to which the growing film is exposed, and the substrate surface. Films deposited from C₂H₂F₄ showed clusters of smaller nodules around larger nodules, whereas films deposited from CH₂F₂ were characterized by a uniform distribution of smaller nodules, and films deposited from HFPO had the largest observed nodules. Movchan and Demchishin's structure zone model was applied to the observed films, which were all found to be zone 1 structures, indicating that film growth is dominated by shadowing effects. Increased substrate temperature and incident power per nm of film deposited results in decreased rms roughness, consistent with greater atomic mobility during deposition. Larger nodules in the fluorocarbon films developed on silicon wafer substrates than on rougher Al‐coated substrates. Advancing contact angles for all of the films were found to be higher than that of PTFE (108°), indicating both hydrophobic and rough surfaces. Specifically, contact angles of films deposited from HFPO were found to increase with pulse off‐time, the same trend observed for both the CF₂ fraction of the film and the rms roughness. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2439–2447, 1999     

Field emission properties of carbon nanotubes synthesized by capillary type atmospheric pressure plasma enhanced chemical vapor deposition at low temperature

Carbon nanotubes (CNTs) were grown using a modified atmospheric pressure plasma with NH₃(210 sccm)/N₂(100 sccm)/C₂H₂(150 sccm)/He(8 slm) at low substrate temperatures (?500 °C) and their physical and electrical characteristics were investigated as the application to field emission devices. The grown CNTs were multi-wall CNTs (at 450 °C, 15-25 layers of carbon sheets, inner diameter: 10-15 nm, outer diameter: 30-50 nm) and the increase of substrate temperature increased the CNT length and decreased the CNT diameter. The length and diameter of the CNTs grown for 8 min at 500 °C were 8 μm and 40 ± 5 nm, respectively. Also, the defects in the grown CNTs were also decreased with increasing the substrate temperature (The ratio of defect to graphite (I_D/I_G) measured by FT-Raman at 500 °C was 0.882). The turn-on electric field of the CNTs grown at 450 °C was 2.6 V/μm and the electric field at 1 mA/cm² was 3.5 V/μm.     

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.     

Comparisons on properties and growth mechanisms of carbon nanotubes fabricated by high-pressure and low-pressure plasma-enhanced chemical vapor deposition

Effects of plasma pressure and the presence of nitrogen on growth of carbon nanotubes (CNTs) and their properties were studied by using microwave plasma chemical vapor deposition (MPCVD) (pressure=600–3300 Pa) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) (pressure=0.3–0.6 Pa) systems. CH₄/H₂ and CH₄/N₂ were used as source gases, and Co as the catalyst. The structures and properties of CNTs were characterized by using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectra, and field emission I–V measurements. The results show that CNTs made by higher plasma pressure system have a higher growth rate (typically 1–3 μm/min), smaller tube diameter, better field emission properties, and better tube quality. The growth rate is related to the availability of carbon source. The morphology change from spaghetti-like to well-aligned CNTs is discussed in terms of directed ions. The change in field emission properties is reasoned in terms of geometric enhancement factor and screening effect for different tube morphologies. The presence of nitrogen plasma can have the following effects: increasing tube diameter, increasing straightness of CNTs, forming of bamboo-like CNTs, deterioration of field emission properties, and shifting of Raman peak toward lower-frequency side (or increasing residual tensile stress).     

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     

Field emission from patterned carbon nanotube emitters produced by microwave plasma chemical vapor deposition

Large area carbon nanotube patterns were fabricated by microwave plasma chemical vapor deposition. The carbon nanotubes were grown on pre-patterned catalyst films. Scanning electron microscopy and Raman spectroscopy were used to characterize the structure of the carbon nanotubes. The carbon nanotubes were very uniform and approximately 100 nm in diameter. The Raman spectrum shows a good graphitization for the carbon nanotubes. Aligned growth was found on the pattern line area. Field emission characteristics of the patterns were characterized. A threshold field of 2.0 V/μm and emission current density of 1.1 mA/cm² at 3.6 V/μm were achieved. A clear and stable image showing the patterns were obtained.     

One-step growth process of carbon nanofiber bundle-ended nanocone structure by microwave plasma chemical vapor deposition

In this work, we report a simple one-step growth process to synthesize a novel and distinct carbon nanostructure, called a carbon nanofiber bundle-ended nanocone (CNFNC) structure, by using microwave plasma chemical vapor deposition (MPCVD) method with CH₄ and H₂ as source gases and Fe catalyst. The nanostructures and their properties after each processing step were characterized by FESEM, HRTEM, ED, AES, and Raman spectroscopy. The preliminary results have demonstrated that the CNFNC structures exhibit excellent field emission properties. The results also show that the favored conditions to form the CNFNC structures include a combination of lower CH₄/H₂ flow ratio, higher substrate negative bias, and proper working pressure and deposition time. The possible growth mechanism of the CNFNC structures is proposed.     

Numerical modeling of SiC by low-pressure chemical vapor deposition from methyltrichlorosilane

The development of functional relationships between the observed deposition rate and the experimental conditions is an important step toward understanding and optimizing low-pressure chemical vapor deposition (LPCVD) or low-pressure chemical vapor infiltration (LPCVI). In the field of ceramic matrix composites (CMCs), methyltrichlorosilane (CH₃SiCl₃, MTS) is the most widely used source gas system for SiC, because stoichiometric SiC deposit can be facilitated at 900℃-1300℃. However, the reliability and accuracy of existing numerical models for these processing conditions are rarely reported. In this study, a comprehensive transport model was coupled with gas-phase and surface kinetics. The resulting gas-phase kinetics was confirmed via the measured concentration of gaseous species. The relationship between deposition rate and 24 gaseous species has been effectively evaluated by combining the special superiority of the novel extreme machine learning method and the conventional sticking coefficient method. Surface kinetics were then proposed and shown to reproduce the experimental results. The proposed simulation strategy can be used for different material systems.     

High quality double wall carbon nanotubes with a defined diameter distribution by chemical vapor deposition from alcohol

We have synthesized double wall carbon nanotubes (DWNTs) with few defects and little amorphous carbon by hot wall chemical vapor deposition (CVD) of alcohol. Catalysts for the DWNT growth were made from cobalt and molybdenum acetates. Scanning electron microscopy, transmission electron microscopy, multi frequency resonance Raman spectroscopy and optical absorption spectroscopy were used for characterization of the product with regard to DWNT yield, the nanotube diameter distribution, defect concentration and amorphous carbon content. Base pressures lower than 1 × 10⁻⁵ mbar in the CVD reactor considerably suppress defects in the DWNTs. Optimized growth conditions for DWNT formation are presented.     

Improved biocompatibility of parylene‐C films prepared by chemical vapor deposition and the subsequent plasma treatment

The purpose of this study is to prepare the thin film of C‐type parylene (C‐type polyxylylene, parylene‐C) with improved biocompatibility for the biomedical applications, since in spite of the popularity, the parylene‐C has been known to have the less biocompatibility than the N‐type or D‐type parylene. To prepare the well‐designed parylene films through the chemical vapor deposition (CVD) process and the subsequent plasma surface treatment, the parameters of deposition and surface modification were controlled to obtain optimized physical and surface properties. Using CVD, the thin films of parylene‐C as thick as 5 μm were prepared under different deposition pressures. When increasing the deposition rate of parylene film or the deposition pressure, the tensile strength of film increased, whereas the properties such as the surface contact angle and permeability, and the elongation decreased. The deposition rate could be controlled to optimize the physical and physiochemical properties of films. The hydrophilicity of the parylene‐C film increased after plasma surface treatment by showing the larger water contact angle than untreated one. When the radio frequency power was above 100 W in the plasma process, the thin film obtained reveals an excellent cytotropism. It shows the improved biocompatibility with living cells. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Growth and characterization of fluorocarbon thin films grown from trifluoromethane (CHF3) using pulsed‐plasma enhanced CVD

Trifluoromethane (CHF₃) was used as a precursor gas in pulsed‐plasma enhanced CVD to deposit fluorocarbon films onto Si substrates. The film composition, as measured by X‐ray photoelectron spectroscopy (XPS) of the C1s peak, was observed to change as the plasma duty cycle was changed by varying the plasma off‐time; this offers a route to control the molecular architecture of deposited films. FTIR results indicate that the film is primarily composed of CF_x components, with little or no C H incorporation into the film. The rms roughness of the films is extremely low, approaching that of the Si substrate; the low growth rate and consequent high‐power input/thickness is believed to be partly responsible. CHF₃ produces films with higher % CF₂ compared to other hydrofluorocompound (HFC) monomers (CH₂F₂ and C₂H₂F₄). However, the deposition kinetics for all three HFC gases display similar trends. In particular, at a fixed on‐time of 10 ms, the deposition rate per pulse cycle reaches a maximum at an off‐time of approximately 100 ms. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 842–849, 2000     

Fast preparation of (111)‐oriented β‐SiC films without carbon formation by laser chemical vapor deposition from hexamethyldisilane without H2

(111)‐oriented β‐SiC films were prepared by laser chemical vapor deposition using a diode laser (wavelength: 808 nm) from a single liquid precursor of hexamethyldisilane (Si(CH₃)₃–Si(CH₃)₃, HMDS) without H₂. The effects of laser power (P_L), total pressure (P_tot) and deposition temperature (T_dep) on the microstructure, carbon formation and deposition rate (R_dep) were investigated. β‐SiC films with carbon formation and graphite films were prepared at P_L ≥ 170 W and P_to ≥ 1000 Pa, respectively. Carbon formation strongly inhibited the film growth. β‐SiC films without carbon formation were obtained at P_tot = 400‐800 Pa and P_L = 130‐170 W. The maximum R_dep was about 50 μm·h^?1 at P_L = 170 W, P_tot = 600 Pa and T_dep = 1510 K. The investigation of growth mechanism shows that the photolytic of laser played an important role during the depositions.     

Thermodynamics of amorphous SiN(O)H dielectric films synthesized by plasma‐enhanced chemical vapor deposition

Thin films of amorphous SiNH (a‐SiNH) and amorphous SiNOH (a‐SiNOH) synthesized by plasma‐enhanced chemical vapor deposition (PECVD) are used extensively in the semiconductor industry, but little is known regarding their thermodynamic stability, and there are several long‐term reliability issues for these materials. To address the stability issues, a detailed thermodynamic investigation has been conducted on a series of a‐SiNH, and a‐SiNOH dielectric films. High‐temperature oxidative drop‐solution calorimetry in molten sodium molybdate solvent at 1075 K was utilized to determine the formation enthalpies from the elements and from crystalline counterparts/gaseous products. Together with entropy data derived from cryogenic heat capacity measurements, we confirmed that the incorporation of more hydrogen and oxygen leads to more negative enthalpies and Gibbs free energies of formation from elements. Coupled with FTIR structural analysis, the thermochemical data suggest that the Si–H₂ chain structure and Si–O–Si bonding configurations provide the system with extra thermodynamic stability. However, the Gibbs free energies of formation from crystalline constituents and gaseous products are either positive or nearly zero, indicating that these amorphous films are not stable against decomposition, which may cause problems in high‐temperature applications.     

Hydrogenation of low‐molar‐mass,OH‐telechelic polybutadienes. II. Nuclear magnetic resonance and infrared spectrometric determination of hydroxyl end groups before and after hydrogenation by diimide

¹H nuclear magnetic resonance (¹H‐NMR), ¹³C‐NMR, and infrared spectroscopies were used to determine concentrations (c_OH, in mmol/g) of the secondary hydroxyl end groups in the low‐molar‐mass, OH‐telechelic polybutadienes, and their hydrogenated analogs. Mean OH‐functionality (f_OH ≤ 2), that is, an average number of OH groups per one polymer chain, was calculated from c_OH for each sample and each method, and the results were compared with those obtained by a conventional acetic anhydride titration method. It has been found that with molar masses of the samples studied (2310 to 3410 g/mol), the differences between individual spectrometric methods are usually not higher than approximately 10%, which corresponds to an expected relative experimental error. Certain differences in f_OH between individual methods are discussed. No systematic change of f_OH after virtually total hydrogenation of the olefinic double bonds of the polymeric substrate by diimide was observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3214–3224, 1999     

Structural study of β‐SiC(001) films on Si(001) by laser chemical vapor deposition

β‐SiC thin films have been epitaxially grown on Si(001) substrates by laser chemical vapor deposition. The epitaxial relationship was β‐SiC(001){111}//Si(001){111}, and multiple twins {111} planes were identified. The maximum deposition rate was 23.6 μm/h, which is 5‐200 times higher than that of conventional chemical vapor deposition methods. The density of twins increased with increasing β‐SiC thickness. The cross section of the films exhibited a columnar structure, containing twins at {111} planes that were tilted 15.8° to the surface of substrate. The growth mechanism of the films was discussed.     

Micro‐nanostructured silicone‐carbon composite coatings with superhydrophobicity and photoluminescence prepared by oxidative chemical vapor deposition

Transparent, superhydrophobic, and colored silicone–carbon composite coatings were prepared by oxidative chemical vapor deposition (oCVD) of bulk silicone at ambient pressure. The colors, wettability, morphologies, and transparency of the coatings can be easily varied via changing both the concentration of gaseous oxygen and the deposition temperature. Typically, the black, brown, and yellow silicone–carbon composite coatings with different superhydrophobicity and transparency were achieved under oxygen‐deficient atmospheres. Furthermore, the colored samples showed photoluminescence when they were excited by ultraviolet (UV) light, which is due to the fluorescence of carbons embedded inside the as‐prepared coatings. In addition, more regular papillae and nanofibers with excellent superhydrophobicity were obtained at higher deposition temperatures. Our method was believed to develop a new strategy for fabricating multifunctional silicone–carbon composite coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40400.     

Synthesis and visible‐light‐derived photocatalysis of titania nanosphere stacking layers prepared by chemical vapor deposition

BACKGROUND: In this study, visible‐light‐derived photocatalytic activity of metal‐doped titanium dioxide nanosphere (TS) stacking layers, prepared by chemical vapor deposition (CVD), was investigated. The as‐grown TS spheres, having an average diameter of 100–300 nm, formed a layer‐by‐layer stacking layer on a glass substrate. The crystalline structures of the TS samples were of anatase‐type. RESULTS: Ultraviolet (UV) absorption confirmed that metallic doping (i.e. Co and Ni) shifted the light absorption of the spheres to the visible‐light region. With increasing dopant density, the optical band gap of the nanospheres became narrower, e.g. the smallest band gap of Co‐doped TS was 2.61 eV. Both Ni‐ and Co‐doped TS catalysts showed a photocatalytic capability in decomposing organic dyes under visible irradiation. In comparison, Co‐doped TiO₂ catalyst not only displays the adsorption capacity, but also the photocatalytic activity higher than the N‐doped TiO₂ catalyst. CONCLUSION: This result can be attributed to the fact that the narrower band gap easily generates electron–hole pairs over the TS catalysts under visible irradiation, thus, leading to the higher photocatalytic activity. Accordingly, this study shed some light on the one‐step efficient CVD approach to synthesize metal‐doped TS catalysts for decomposing dye compounds in aqueous solution. Copyright © 2010 Society of Chemical Industry