Thickness Of Carbon Coatings Research Articles

Thickness-controllable coating on graphite surface as anode materials using glucose-based suspending solutions for lithium-ion battery

Surface-passivation is an effective way to allow the anode materials can deliver long-term superior electrochemical performance for lithium-ion batteries (LIBs). Herein, we develop a simple solution suspension-coating method to prepare thickness-controllable nano‑carbon layer (NCL) on a synthesis graphite-mesocarbon microbeads (MCMB) using aqueous glucose solutions with a surfactant-triton X-100 at 25 °C. This simple process can control the thickness of the NCL on MCMB with a range of 1.5–20 nm with various glucose concentrations. The as-formed NCL can reduce the defect sites on MCMB surface and create slightly porous structures within NCL. For electrochemical performance in LIB, we observed that the carbon-coating thickness at around 4 nm shows better reversible capacity (from 295 to 347 mAh g−1), lower Li+ diffusion resistance, stable cycle-life, and superior C-rate performance. As our results, we provide a simple method to stabilize surface properties of MCMB and show better electrochemical performance in LIB. Moreover, this method can be easily exploited in the industrial with a massive production.

Formation of diamond like carbon films on materials for medical application

The aim of this experimental work is to identify how the surfaces of materials that are most often used inmedical implants and prostheses, affect the properties of the deposited amorphous carbon films. The DLCfilms were formed on the stainless steel, aluminium, polyetheretherketone (PEEK) and polycaprolactone(PCL) surfaces by PECVD method using C2H2 gas plasma and their properties was compared with the filmsdeposited on silicon. The differences of the films properties were determined by a null-ellipsometry and Ramanspectroscopy. It was found that the thicknesses of the carbon coatings deposited on metallic substratesare larger than on the silicon when the deposition conditions were the same. When the films are formed athigh bias voltage the refractive index of the DLC films deposited on stainless steel are lower compared tothe coatings on silicon but the extinction coefficients are higher. Raman spectra shows that sp2 bonds concentrationis higher in this case. When the ion energy is lowest (bias voltage -400 V), Raman spectroscopyshows that D peak isn’t observed on the Si-deposited carbon coating, while the typical carbon amorphouscoating is formed on the Al substrate. The thickness of amorphous carbon coatings deposited on the polymersdepends on the bias voltage, and the optical properties depend on the type of polymer. The coatingsdeposited on PCL have a much higher refractive index than on PEEK. Key words: amorphous carbon films, steel, aluminum, polyetheretherketone, polycaprolactone, Ramanspectroscopy.

Thickness of carbon coatings on silicon materials determined by hard X-ray photoelectron spectroscopy at multiple photon energies.

Hard X-ray photoelectron spectroscopy at multiple photon energies is used to investigate the surface structure of carbon coatings on silicon materials destined for use as negative electrodes in lithium-ion batteries. The photoelectron intensity from the carbon coatings decreases with an increase in the kinetic energy of the photoelectron. By fitting the photoelectron intensity versus energy to numerically derived curves, the thickness and coverage of the carbon coatings can be obtained. The results are in agreement with the values suggested by the cross-sectional secondary-electron microscopy images of the carbon coatings, although the thickness should be corrected by accounting for the rectangular parallelepiped structure of the silicon material.

Hierarchical Fe3O4@NC composites: ultra-long cycle life anode materials for lithium ion batteries

The composites of N-doped carbon-coated Fe3O4 nanoclusters (Fe3O4@NC) were prepared by a facile preparation process. The microwave-assisted solvothermal method was first employed to obtain Fe3O4 nanoclusters, and then using dopamine as carbon sources, the N-doped carbon-coated Fe3O4 nanoclusters were obtained by calcining in vacuum. By changing the amount of dopamine and calcination temperature, a series of products with different carbon-coating thickness and crystallinity were obtained. The composite synthesized by adding 0.08 g dopamine hydrochloride and calcining at 500 °C exhibits ultra-long cycle life and good rate capability, its reversible capacity can retain at 445 mAh g−1 after 2000 cycles even at a current density of 2 A g−1. The results indicate that the hierarchical Fe3O4@NC composites are promising high-performance anode materials for lithium ion batteries.

A Mathematical Model for Determining Carbon Coating Thickness and Its Application in Electron Probe Microanalysis.

In electron probe microanalysis where materials are coated with a thin conductive carbon coat before analysis, the X-ray intensity detected from a specimen may be affected to various degrees by the thickness of the carbon coating. Differences in the carbon film thickness between specimens and standards may lead to errors in analytical results, particular for lower energy X-rays. In this study, we demonstrate that the location and the distance of the specimen relative to the carbon tip in the coating chamber can affect the thickness of the carbon film produced on the specimen surface during carbon coating. The closer the specimen is to the carbon tip contacting point, the thicker is the carbon film deposited. A mathematical model to calculate the carbon film thickness at different locations on the coater plate is established, based on the assumption that carbon atoms evaporate from the carbon tip equally in all directions during the coating process. In order to reduce the differences in the carbon coating thickness, we suggest moving the carbon rod to a higher position, moving the thinner samples to the center and thicker samples to the edge of the coater plate, and using a rotating circular coater plate during coating.

One-Pot Synthesis of Carbon-Coated SnO2 Nano-Composite Using Hydrothermal Method for Lithium Ion Battery Application

Carbon-coated SnO2 nano-composite was synthesized by using a hydrothermal method in a one step process with sizes of 1 to 3 microm. The carbon-coated SnO2 nano-composite was easily obtained by changing firing atmosphere from air to argon (600 degrees C for 3 hours). The carbon-coating thickness and size of the SnO2 nanoparticles in carbon-coated SnO2 nano-composite were confirmed through a high-resolution transmission electron microscopy (HRTEM) as 40 and 5 nm, respectively. Carbon-coating and particle size affect to the capacity retention property. Carbon-coated and non carbon-coated samples were investigated as anode materials. It was confirmed that the non carbon-coated SnO2 nano-composite had a 718 mA h/g initial charge capacity, 91% reached to theoretical value of SnO2 (790 mA h/g), while the carbon-coated SnO2 nano-composite had an excellent capacity retention of 89.6% after 70 cycles (10.88% for non carbon-coated SnO2 nano-composite).

Carbon coatings on silica glass optical fibers studied by reflectance Fourier-transform infrared spectroscopy and focused ion beam scanning electron microscopy

Carbon coatings applied on optical fibers via chemical vapor deposition were characterized by a resistance technique, focused ion beam/scanning electron microscopy (FIB/SEM), and reflectance Fourier-transform infrared spectroscopy (FTIR). The resistance technique measures the thickness of carbon film by measuring the resistance over a section of optical fiber, and backing out the film thickness. The FIB/SEM system was used to remove a cross section of the optical fiber and carbon coating and using a scanning transmission electron detector the thickness was measured. The FTIR approach is based on the fact that the wavelength of the light in the mid-infrared region (~10μm) is significantly larger than the typical thickness of the carbon coatings (<0.1μm) which makes the coating “semi-transparent” to the infrared light. Carbon coating deposition results in significant transformations of the band profiles of silica in the reflectance spectra that were found to correlate with the carbon coating thickness for films ranging from 0.7nm to 54.6nm. The observed transformations of the reflectance spectra were explained within the framework of Fresnel reflection of light from a dual-layer sample. The advantage of this approach is a much higher spatial resolution in comparison with many other known methods and can be performed more quickly than many direct measurement techniques.

Impact of the Carbon Coating Thickness on the Electrochemical Performance of LiFePO4 / C Composites

Porous, well crystalline composites with different amounts of carbon have been prepared by a sol-gel technique. The thickness of carbon coatings (paintings) has been determined by high-resolution transmission electron microscopy. It is shown that carbon coating thickness can be controlled by the amount of carbon and it has an impact on the obtained reversible capacity. Furthermore, it is shown that atomic ratio of nonactive Fe(III) phase (presumably in as-synthesized composites depends on the amount of carbon in the composite. Using Mössbauer spectroscopy, we have confirmed that the nonactive Fe(III) remains nearly unchanged in the composite during cycling. The lowest amount of carbon in composites obtained from citrate anion as a gelling agent was 3.2 wt % and this particular amount corresponds to the carbon coating thickness of about 1-2 nm. The reversible capacity obtained from the above-mentioned composite delivers close to 80% of the theoretical capacity at room temperature with a current density of 170 mA/g (C/1 rate). © 2005 The Electrochemical Society. All rights reserved.

Determination of Ultra-Thin Carbon Coating Thickness by X-ray Fluorescence Technique

AbstractA tcchniquc for high-precision measurement of carbon thin-film thickness using X-ray fluorescence (XRF) is described. A quadratic calibration procedure is used for carbon thin films on silicon. Measurement of carbon-film thickness in a double-layer structure of carbon and CoCrX alloy is complicated by interference effects from the underlying layer. The dependence of the relative precision in measuring thickness (σT/T) on the counting time has been derived. It shows that a precision of 2% for a 25-nm carbon coating can be obtained using a W/C crystal and counting time of 4 minutes. Intensity and resolution advantages provided by the recently developed Ni/C and V/C multilayer synthetic crystals are also described.