Carbon Thin Films Research Articles

Influence of Si atoms on the structure and electronic properties of amorphous DLC films

The paper considers the effect of silicon on the formation of the structure and properties of amorphous diamond-like carbon (DLC) films. Thin films of silicon-modified amorphous diamond-like carbon (DLC:Si) were synthesized by magnetron ion-plasma co-sputtering of a combined target. Studies of the structure and properties of amorphous DLC:Si films were carried out in the range of silicon concentrations up to 6.75 at.%. A change in the formation of the film structure is shown using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) revealed a significant change in the local structure of amorphous DLC:Si films. Which, in turn, leads to a change in the density of states of π-electrons in the band and, as a rule, to a change in the electronic properties.

Mechanisms of Lithium-Ion Transport in Solid-State Electrolyte and Cathode Materials Prepared By PVD

Conventional liquid-state lithium-ion batteries are currently limited in their energy density, lifetime, thermal stability, and safety. The design of viable solid-state batteries shows promise to improve upon the shortcomings of liquid cells. Removal of organic electrolytes increases the lifetime while making these batteries more environmentally friendly and safe. Solid-state batteries also have the potential to demonstrate higher energy density and provide ultrafast charging. However, these desirable properties require significant efforts to uncover and utilize the chemical, morphological, and electrochemical properties of solid-state electrolytes and cathode nanocomposites. This study addresses physical vapor deposition (PVD) technology for design of solid-state material architectures with the properties needed to create high-performance electrochemical cells. The PVD process allows cathodes and electrolytes to be deposited as dense films, thereby increasing their energy density and electrochemical performance. Furthermore, this process results in excellent adhesion between dissimilar materials allowing for increased electrical and ionic conductivity. This work uses lithium oxyhalide electrolytes and eco-friendly lithium iron phosphate cathodes, which were both deposited in vacuum using radio frequency power and magnetron sputtering sources. A co-deposition technique was used to successfully deposit thin film layers of cathode, electrolyte, cathode/electrolyte mixture, and carbon thin films in a single process. Electrochemical cells with different functional layers deposited by PVD (~7 mm) were compared to the cells with commercial LFP cathodes (~32 mm thick). The electrochemical cells created by PVD showed lower charge transfer resistances and high electrochemical stability at ultra-high (10C) charging rates. Significant improvements in performance are expected to continue as the process is improved in terms of ionic and electronic transport at cathode-electrolyte interfaces. The authors acknowledge financial support from the DOD Navy SBIR Phase II project (N68335-18-C-0021), the NSF IUCRC program for supporting the “Center for solid-state electric power storage” (#2052631), and the South Dakota “Governor’s Research Center for electrochemical energy storage”. Figure 1

Investigation of Vacuum Arc-Deposited ta-C and ta-C:N Thin Films on Silicon and Stainless-Steel Foil Substrates Using Raman Spectroscopy

In this paper, we investigated the vacuum arc-deposited tetrahedral amorphous carbon (ta-C) and nitrogen-doped ta-C (ta-C:N) thin films grown on silicon and stainless-steel foil substrates by the visible Raman Spectroscopy. We found that carbon films grown on silicon surfaces prefer more sp3 hybridized carbon compared to the stainless-steel foil, which prefer more sp2 hybridized carbon even though the films are grown concurrently under the same conditions. The impact energy of plasma ions modifies the interfacial layer formation, giving a strong dependence of the sp2/sp3 ratio with the substrate bias, behaving differently for different substrates. However, nitrogen doping in amorphous carbon thin films helps to increase sp2 contents uniformly on both the surfaces for a fixed substrate bias. Understanding such interfaces are of interest for many electronic, optoelectronic, and energy storage devices as these interfaces get buried and can influence the properties significantly.

Deposited layer substrate (DeLaS)-A module for radiation measurement.

Infrared Imaging Video Bolometer (IRVB) measures the radiation from plasma in two-dimensions. IRVB uses a few micrometer thick metal foil as a radiation absorber. The foil being ultra-thin has several limitations. A new radiation absorbing module is proposed here that can effectively overcome the shortcomings of the foils used in IRVB. This module is developed by depositing carbon and metal thin films on an infrared transmitting substrate using magnetron sputtering. This patented module is termed Deposited Layer on a Substrate. A prototype is developed and laboratory tests are carried out using a laser source to demonstrate its feasibility as a radiation detector. The advantages of this module over conventional foils, its development, and experimental results validating the concept are discussed in this article.

Discrimination of different amorphous carbon by low fluence laser irradiation

Carbon thin film depositions were carried out with femtosecond laser ablation from two different sp 2 -bonded carbon targets, namely highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC). Femtosecond laser deposition is generally known as a means of generating nanoparticles. To our knowledge, Raman spectroscopy is not able to directly discriminate the as-deposited amorphous films which may contain different sp 2 carbon nanoclusters while still showing similar Raman spectra. Moreover, these films are not easily distinguishable from each other by transmission electron microscopy observation due to their amorphous structure. In this work, we show that controlled laser irradiation of thin films at low fluence is an interesting approach to reveal the existence of structural differences for amorphous films deposited from sp 2 carbon targets (HOPG and GC).

Features of Carbon and Silicon Thin Films Reflection Spectra in the Visible Region

The article is devoted to the reflection of visible light from a thin absorbing film. For a number of reasons, thin films have recently been the subject of close study. As part of the work, several non-metal films were fabricated on a glass substrate: silicon films (by resistive evaporation) and carbon films (using laser evaporation). The resulting films have an optical thickness in the range of 1 μm (that is, the actual layer thickness is in the range of 0.2-0.4 μm) and at the same time noticeably absorb the light flux. The films were processed according to the standard method in the visible region using a USB4000 spectrometer. Reflection spectra for each of the films were plotted for several different points on the surface. The spectra look similar when differences in numerical values are not considered. The contribution of the interference of rays reflected from the front and rear boundaries is significant at long wavelengths (in the red region), whereas the interference practically disappears against the background of instrument noise in the short wavelength region (violet part of the spectrum). The reason for this is that absorption during propagation of the short-wavelength part inside the film significantly reduces the intensity of the beam reflected from the rear surface of the film.

Manufacture of porous carbon thin films for energy storage

In the present work, a technique to generate pores in Vulcan VCX-72 and VCX-72R commercial coal through the Hummers method and the elaboration of membranes is shown. The product obtained through the process was cleaned and dried, then SEM microscopy in which the generation of pores in the coal was observed. Membranes were elaborated using the material and were placed in an electrochemical cell in a set up of three electrodes immersed in an acid solution of H2SO4. Autolab® potentiostat and the Nova® software were used to carry out electrochemical tests that showed capacitive properties in the Hummers method’s coal.

Electrochemical investigation of ion-beam sputter-deposited carbon thin films for Li-ion batteries

The C-rate capability of 230 nm- and 16 nm-thin ion-beam sputter-deposited amorphous carbon films, an interesting class of carbonaceous material for lithium-ion batteries, was investigated up to Li-platting. Stepwise ascending and descending constant Li+ currents after each fifth cycle, followed by hundreds of cycles with the highest current were applied. The carbon films show similar cycling with irreversible losses during the first five cycles, followed by reversible cycling with a capacity close to that of graphite. The capacity is significantly lower at high currents; however, it is restored for subsequent cycling again at low currents. Differential charge and differential capacity curves reveal three Li+ uptake and three Li+ release peaks located between 0 and 3 V. Irreversible as well as reversible Li bonding can be associated with all these peaks. Irreversibly bonded Li can be found at the surface (solid electrolyte interphase) and in the bulk of the carbon films (Li trapping). Reversible Li bonding might be possible inside the carbon films in graphite-like nano-domains and at defects. The thinner film reveals a more pseudo-capacitive cycling behavior, pointing to enhanced Li kinetics.Graphical abstract

Electrochemical Generation of Hot Electrons in Fully Aqueous Solutions at Tetrahedral Amorphous Carbon Thin Film Electrodes and Electrochemiluminescence Immunoassay of Serum Amyloid A

AbstractElectrochemistry of hot electrons in fully aqueous solutions at tetrahedral amorphous carbon thin film electrodes is discussed. The generation of these highly reducing chemical species was confirmed by normal pulse voltammetry and several electrochemiluminescent systems. Electron transfer into pre‐existing solvent cavities was observed at approximately −2.65 V vs. Ag/AgCl (sat.). Electrogenerated hot electrons were utilized as chemiluminescent mediators in heterogeneous sandwich immunoassay of Serum Amyloid A. The calibration curve was linear over four orders of magnitude and the detection limit was 85 ng L−1 that demonstrates the efficiency of hot electron generation at this electrode material.

Structure and Phase Composition Study of Heavy Doped with Carbon Thin Films of TiO2 : C Deposited by RF Magnetron Sputtering

Structure and Phase Composition Study of Heavy Doped with Carbon Thin Films of TiO2 : C Deposited by RF Magnetron Sputtering

Structure and oxygen-sensitive properties of thin films of natural carbon

Thin film carbon nanomaterials are widely studied and used as functional, conductive, reflective, and sensor coatings. In this work, films of natural graphene-based carbon are studied as a sensitive material for a gas sensor operating close to room temperature. The structural features of the films were studied by scanning electron microscopy and Raman spectroscopy. It has been found that the deposition of natural carbon on substrates with a conductive coatings of indium oxide and of indium tin oxide allows to obtain a thin films, represented by homogeneous carbon nets, in the nodes of which are globular nano-sized particles. Microwave conductivity measurements were carried out using a λ/4 coaxial resonator based on a symmetric two-wire line. The results demonstrated that films on substrates with deposited indium oxide and indium tin oxide desorb oxygen from various structural levels of graphene-based carbon.

The correlation between external magnetic field and multifractal characteristics of PLD deposited DLC films

The present study explores the application of the multifractal method in examining the surface characteristics of the diamond-like carbon (DLC) thin films deposited onto substrates of silicon through a magnetically-assisted pulsed laser deposition (MAPLD) method at room temperature (RT). Multifractal spectra f(α), obtained from atomic force microscopy (AFM) analysis, is adopted to investigate the surface morphology of the produced samples. The relationship between the applied magnetic field and multifractal characteristics of the obtained samples is examined as well. The findings attest to the apparent effect of the magnetic field on the quality of surface morphology and the multifractal spectrum width. Our results reveal that the root-mean-square (RMS) and average surface roughness are enhanced by applying and intensifying the magnetic field. Furthermore, the findings suggest that both the non-uniformity of the height distributions and the singularity spectrum width of the samples fabricated in this study increases with applying and intensifying the magnetic field. Further, Multifractal spectra f(α) demonstrate the multifractality nature of all the obtained samples, including conventionally and magnetically processed DLC thin films. Besides, the multifractality strength of thin films rises with increasing the magnetic field.

Higher-order structure of barley chromosomes observed by electron tomography

The higher order structure of the metaphase chromosome has been an enigma for over a century and several different models have been presented based on results obtained by a variety of techniques. Some disagreements in the results between methods have possibly arisen from artifacts caused during sample preparation such as staining and dehydration. Therefore, we treated barley chromosomes with ionic liquid to minimize the effects of dehydration. We also observed chromosomes on a film with holes to keep pristine chromosome structure from being flattened as seen when placed on a continuous support film. A chromosome placed over a hole in a thin carbon film was mounted on a tomography holder, and its structure was observed in three dimensions (3D) using electron tomography. We found that there are periodic structures with 300–400 nm pitch along the axis in barley chromosomes. The pitch sizes are larger than those observed in human chromosomes.

Profundity study on structural and optical properties of heavy oil fly ash (HOFA) doped calcium carbonate (CaCO3) nanostructures and thin films for optoelectronic applications

The present study was concerned with the synthesis of thin films and nano samples from heavy oil fly ash (HOFA) doped-calcium carbonate (CaCO3) with different contents (x = 0, 1, 2, 3, 4, and 5 wt%.). The motivation of this study was to benefit from fly ash resulting from heavy oil combustion in power plants in optoelectronic applications rather than as an environmental problem with repercussions including global warming, etc. The nano- and thin-film samples with a thickness of 200 nm were controlled and tuned by the monitor device and were prepared by the spin coating method on pre-clean glass substrates. The structural analysis was carried out using XRD and SEM techniques. Both techniques were proven on the crystallinity of the studied samples, and the structural parameters were calculated, such as grain size, which was affected by the increase in calcium carbonate. Furthermore, SEM images of thin-film surfaces revealed a more packed structure with a lower number of pores in the thin film containing nano-CaCO3. According to the optical spectra (transmittance T, reflectance, R), the optical absorption coefficient was calculated. Then, the related optical parameters (Tauc energy Eg, Urbach energy Eu), optical constants (an extinction coefficient kex., a reflective index n), and dispersion parameters (a single oscillator energy Eo, a dispersion energy Ed) were determined. It was clear that these layers have the great potential to be used as a window layer in solar cells and other optoelectronic applications due to the high energy range of the optical bandgap. In addition, all-optical properties were affected and improved by increasing the calcium carbonate content. This improvement in the optical properties along with the improvement of the structural properties makes the thin films and the nanoscaled samples very suitable for various applications.

(Invited) Single Walled Carbon Nanotube (SWNT) Atomic Structure and Thin Film Color during the Floating Catalyst Chemical Vapor Deposition (FC-CVD) Synthesis

We discuss the FC-CVD synthesis of SWNTs, especially the tuning of tube atomic structure i.e. (n,m) distributions and subsequently the thin film color. By introducing various amount of CO2 with CO as the carbon source and in-situ ferrocene decomposition generated Fe catalyst nanoparticles, we directly produced SWNT films with tunable (n,m) i.e. helicity distribution as well as tunable colors. When operating the FC-CVD reactor at the ambient pressure and at 850 oC temperature with 0.25 and 0.37 volume percent of added CO2, the SWNT films display green and brown colors, respectively. We ascribed various colors to suitable diameter and narrow (n,m) distributions, which were determined in detail using the electron diffraction. We calculate the color maps for all SWNT (n,m) structures.N. Wei et al. Adv. Mater. 2021, 33, 2006395.

(Digital Presentation) Cold Plasma-Enhanced N-Doped Carbon Coating over MOF Endorsed Metal Oxide Nano Seed Embedded Carbon Fabric for Ultra-Long Life Flexible Energy Storage Application

The deformable electronic devices such as flexible, foldable, bendable, wearable, etc., are deemed the future of portable electronics, which could only be realized through the proper design of an energy storage unit that could power them. Herein, we report the conception of an ultrastable, binderless flexible electrode/substrate configuration that can be implemented in various energy storage applications such as supercapacitors, lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and alike. Firstly, the conductive carbon fabric was electrochemically deposited with nickel nanospheres; then the ZIF-67 metal-organic framework (MOF) promoted metal hydroxide nanostructures were grown over the Ni-CCF substrate. As grown nanostructures were then embedded inside the CCF through a meticulous optimization process varying the calcination temperature and gas concentrations. The metal seed embedded CCF was then coated with the hydrocarbons, the precursors of which are generally known volatile organic compounds and pollutants such as C2H4, CH4, CO2, and NH3 through the dielectric barrier discharge (DBD) plasma at atmospheric pressure and temperature. The carbonization of the final product results in the ultra-robust flexible electrode with metal-oxide nano seeds embedded CCF, coated with ~20nm nitrogen-doped carbon thin film which will be an excellent electrode material for an ultra-long life flexible energy storage system. Figure 1

Thermal stability of the magnetic moment in amorphous carbon thin film - An experimental and ab-initio study

The effect of vacuum annealing on the microstructure and its consequence on the thermal stability of magnetic moment in amorphous carbon (a-C) thin film is studied. The magnetic a-C thin film of thickness 8 nm is vacuum annealed for 2 h at 523 K and 923 K. Microstructural and chemical characterization using Raman spectroscopy and x-ray photoelectron spectroscopy, respectively, reveals that with increasing annealing temperature, the sp2 fraction in the film increases. The magnetic measurement carried out at room temperature (RT) using SQUID-VSM reveals a weak ferromagnetic signal in the film due to the interaction between the unpaired sp2 sites, which prevails till 923 K. In the as-deposited sample, an isolated sp2 atom surrounded by sp3 atom results in the paramagnetic contribution, and an sp2-sp2 atom with twisted π-orbitals results in weak ferromagnetic coupling. Compared with the as-deposited case, initially, the saturation magnetization increases when the sample is annealed at 523 K and later decreases when annealed at 923 K. Subsequently, the ab-initio molecular dynamics calculation predicts that due to the increase in sp2 fraction, the net magnetization of the system increases from 300 K to 523 K. π-Orbital Axis Vector (POAV) analysis shows that further annealing to 923 K enhances π-orbital overlapping, which leads to the annihilation of moments sites. The present study differentiates between the two structures that contribute to the magnetism in a-C in terms of their thermal stability. Our simulation indicates that the twisted π-orbitals structure is thermodynamically more stable than the structure where sp3 surrounds sp2 hybridized atom.

Red Carbon Thin Film: A Carbon–Oxygen Semiconductor with Tunable Properties by Amine Vapors and Its Carbonization toward Carbon Thin Films

AbstractThe requirements for organic semiconductor materials and new methods for their synthesis at low temperature have risen over the last decades, especially due to concerns of sustainability. Herein, the synthesis of a carbon/oxygen molecular semiconductor thin film, which is promptly reactive toward amines, is presented. This allows for tuning the semiconductor properties and application as amine vapor sensors for a scope of analogous amines. The gas‐to‐solid phase reaction causes a significant change of the films’ optical properties, blue‐shifting the absorption and the photoluminescence spectra from the red to the near UV spectral range. The irreversible chemical reaction between the thin film and the amine vapor is also exploited for the preparation of nitrogen‐containing thin carbon films. The herein presented materials and methods will be of interest for gas sensing applications as well as for the development of tunable semiconductors and heteroatom‐doped thin films.

Synthesis of Carbon thin films using Aerosol-Assisted Chemical Vapour Deposition (AACVD)

Aerosol-assisted chemical vapour deposition (AACVD) technique was used to produce carbon thin films. The synthesised films have been deposited using chloroform solvent as a single source precursor at 550 °C. Raman spectroscopy, powder X-Ray diffraction (p.XRD), and scanning electron microscope (SEM) were used to characterize the thin films and the result shows that carbon thin films successfully have been prepared. Carbon thin films were produced from chloroform solvent as a single source precursor therefore, this work recommends to avoid using chloroform as a solvent in AACVD technique when the deposition carried out at high temperatures (above 500 ºC), to keep the deposited materials pure from high level of carbon contamination.

Transfer- and lithography-free CVD of N-doped graphenic carbon thin films on non-metal substrates

Although CVD is a very promising approach to the synthesis of nitrogen-doped graphenic carbon thin films (N-GCTFs), the vast majority of methods require the use of a metal catalyst, and a post-deposition transfer process, which complicates the technology, as well as damages and contaminates the films. Here, we described a simple, low-cost and scalable approach for the completely direct (transfer- and lithography-free) deposition of N-GCTFs on dielectric substrates through pyrolysis of acetonitrile (CH3CN). GCTFs are defined as multi-layer graphene films with few-nm thickness. The N/C ratio is about 2–3%, and nitrogen is mainly contained in the graphitic form. Raman spectroscopy and TEM indicate a nanocrystalline structure of the films. The values of transmittance and sheet resistance are found significantly depending on the synthesis temperature and time. The films can be grown selectively on the e-beam pre-patterned areas of the substrates. We demonstrate this by lithography-free growing of N-GCTF microstructure.