Effects Of Chemical Vapor Deposition Research Articles

Structural and Synthetic Modification of Graphitic Foams and Dendritic Graphitic Foams for Thermal Management

The performances of porous graphitic foams in flexible electronic, electrochemical, and thermal management devices can be enhanced by increasing the interfacial charge or heat transport between the 3D graphitic network and the functional materials filled into the pore space. Herein, an investigation of the effects of chemical vapor deposition (CVD) conditions on the structure and thermal conductivities of both graphitic foams grown from reticular Ni foams and dendritic graphitic foams (DGFs) synthesized from electrodeposited dendritic Ni foams is reported. A room‐temperature solid thermal conductivity () up to 800 W m−1 K−1 is obtained from the graphitic foams (GF) with less than 1% volume fraction. In comparison, the DGFs, which provide a large increase of the specific surface area for enhanced interfacial heat transfer, achieve an effective thermal conductivity of 2.5 ± 0.2 W m−1 K−1 because of an enhanced volume fraction to about 5% despite a compromised around 200 W m−1 K−1 due to the increased defect density. Through systematical variations of the catalyst template morphology and CVD conditions, this work reveals the distinct roles of catalyst surface curvature and graphitic strut thickness in controlling the properties of GFs and DGFs for thermal management.

Enhanced Surface Energetics of CNT-Grafted Carbon Fibers for Superior Electrical and Mechanical Properties in CFRPs.

Surface enhancement of components is vital for achieving superior properties in a composite system. In this study, carbon nanotubes (CNTs) were grown on carbon fiber (CF) substrates to improve the surface area and, in turn, increase the adhesion between epoxy-resin and CFs. Nickel (Ni) was used as the catalyst in CNT growth, and was coated on CF sheets via the electroplating method. Surface energetics of CNT-grown CFs and their work of adhesion with epoxy resin were measured. SEM and TEM were used to analyze the morphology of the samples. After the optimization of surface energetics by catalyst weight ratio (15 wt.% Ni), CF-reinforced plastic (CFRP) samples were prepared using the hand lay-up method. To validate the effect of chemical vapor deposition (CVD)-grown CNTs on CFRP properties, samples were also prepared where CNT powder was added to epoxy prior to reinforcement with Ni-coated CFs. CFRP specimens were tested to determine their electrical resistivity, flexural strength, and ductility index. The electrical resistivity of CNT-grown CFRP was found to be about 9 and 2.3 times lower than those of as-received CFRP and CNT-added Ni-CFRP, respectively. Flexural strength of CNT-grown Ni-CFRP was enhanced by 52.9% of that of as-received CFRP. Interestingly, the ductility index in CNT-grown Ni-CFRP was 40% lower than that of CNT-added Ni-CFRP. This was attributed to the tip-growth formation of CNTs and the breakage of Ni coating.

Effects of CVD Carbon on the Erosion Behavior of 5D Carbon-Carbon Composite in a Solid Rocket Motor

An experimental study was conducted to study the effects of chemical vapor deposition (CVD) carbon content on the erosion behavior of 5 direction (5D) carbon-carbon (C/C) composite in a solid rocket motor (SRM). A small SRM, which can compare the erosion performance of two samples under the same working conditions, was designed and tested. The erosion of the carbon-carbon composite ablative morphology at macroscale and microscale was obtained and analyzed. Results show that the average erosion rates of 1# and 2# samples are 0.35 mm/s and 0.45 mm/s, respectively, which means the erosion rate of the sample with high CVD carbon content is 22.2% times lower than the one with low CVD carbon content. During SRM operation, the fibers within fiber bundles and carbon rods are in a dispersive and integral state, respectively, thus carbon rods have a better anti-ablation capability, followed by fiber bundles and matrix in turn. As a result, a carbon rod will be positioned higher than the matrix and fiber bundles around. Furthermore, the ablation of fibers within fiber bundles and carbon rods, although they have significant differences in the ablation process, can both be described as a single fiber ablation. The oxidizing species react with the matrix, then with the CVD carbon and the fiber within a fiber bundle in turn, while they react with the matrix, the CVD carbon and the fiber within a carbon rod simultaneously. This shows that the increase in CVD carbon content will improve the ablation performance of C/C composite by protecting the fibers within the fiber bundles. The present study provides a fundamental understanding of the effect of CVD carbon on the ablation performance of C/C composite, serving as a reference for further design and optimizations of C/C composite.

The effect of MoW interlayer thickness on diamond growth on steel substrates

Abstract

Effect of Chemical Vapor Deposition of Graphite on the Mechanical Strength of a Graphite/Metal Bilayer Film

Effect of Chemical Vapor Deposition of Graphite on the Mechanical Strength of a Graphite/Metal Bilayer Film

Temperature-dependent piezotronic effect of MoS2 monolayer

Molybdenum disulfide (MoS2) monolayer is one of the most promising materials for next-generation electronic/optoelectronic devices because of its prominent piezoelectric property that can modulate Schottky barrier height and control transport behaviors without applying any external gate bias. In this work, we systematically investigated temperature dependence of piezotronic effect of chemical vapor deposition grown MoS2 monolayer by measuring transport behaviors under strains from 0% to 0.3% with various sample temperatures ranging from 270 K to 320 K. It was found that piezoelectric effect in MoS2 monolayer significantly depends on sample temperature. Due to less screening effect of piezoelectric potential generated in MoS2 with a mechanical strain at low temperature, the piezotronic effect is significantly enhanced when the sample temperature is decreased from 320 K to 270 K, revealing that the piezoelectric effect becomes stronger at lower temperature.

Improvement of chemical, physical, and electrical properties of parylene-D deposited by chemical vapor deposition by controlling the parameters process

The effect of chemical vapor deposition (CVD) parameters on the surface morphology and the molecular structure of parylene-D (also called poly-dicloro-xylylene or PPX D) films were investigated. Relevant process parameters are defined by the sublimation temperature, pyrolysis temperatures, growth rate, and time of the deposition process. The sublimation temperatures strongly affects the layer growth rate which increases by a factor of about 4 as the temperature increases from 120 to 160 °C. The sublimation temperature at which the parylene-D cannot be deposit is estimated to be 105 °C. The present CVD experimental parameters have shown that appropriate sublimation temperatures can yield a controlled growth of the layer thickness ranging from tens of nanometers up to at least 8 μm with a good control of the amorphous and the crystalline amounts. Nearly amorphous parylene-D is obtained when sublimation temperatures are height. However, the crystallinity is increased considerably when the dimer Tsub is decreased. A decrease in the surface roughness is achieved by reducing the Tsub and the deposition rate. These experimental conditions giving rise to dense and transparent parylene-D films. The pyrolysis temperatures favorite growing of globules at the surface compared to the sublimation temperatures. The size of the globules increases from 1.3 μm for Tpyr. = 650 °C to 13.7 μm for Tpyr. = 690 °C. It inferred also that the crystallinity content and the crystalline size decrease by increasing the pyrolysis temperatures. Electrical properties are very influenced by the CVD-processing parameters especially by modifying the pyrolysis temperature. Using these optimized conditions, state-of-the-art parylene-D films with promising properties are reproducibly processed. These results significantly expand the range of processing variables compatible with large applications domains.

Effect of chemical vapor deposition of Si3N4, BN and B4C coatings on the mechanical and dielectric properties of porous Si3N4 ceramic

The mechanical properties of porous Si 3 N 4 ceramic are noticeably improved after chemical vapor deposition (CVD) of Si 3 N 4 , BN and B 4 C coatings. The dielectric constant and loss of porous Si 3 N 4 ceramic remain almost unchanged after CVD of BN, increase slightly after CVD of Si 3 N 4 , but increase greatly after CVD of B 4 C. Overall, CVD of Si 3 N 4 performs better than CVD of BN and B 4 C in improving the mechanical properties and keeping the low dielectric constant and loss of porous Si 3 N 4 ceramic.

In situ control of the catalyst efficiency in chemical vapor deposition of vertically aligned carbon nanotubes on predeposited metal catalyst films

Premature termination of growth, presumably because of catalyst deactivation, is an undesirable side effect of chemical vapor deposition of vertically aligned carbon nanotubes on predeposited metal catalyst films. The addition of ferrocene, an effective precursor for in situ Fe formation, was found to enhance carbon nanotube growth rates and extend growth to 3.25 mm thick carbon nanotube films. Ferrocene was introduced into the gas stream by thermal evaporation concurrently with acetylene using a specially constructed source. The key factor facilitating the growth of thick carbon nanotube films was the independent and precise control of the ferrocene amount in the feedstock. The carbon nanotube films were characterized by scanning and transmission electron microscopy, and Raman spectroscopy. The temperature dependence of the carbon nanotube growth with ferrocene exhibits a steep drop at high substrate temperatures and a loss of vertical alignment at 900 °C. The negative temperature coefficient of the growth rate suggests that the reaction mechanism of vertically aligned carbon nanotube growth is governed by a heterogeneous intermediate step.