Amorphous Hydrogenated Carbon Films Research Articles

Thin amorphous hydrogenated carbon layers on polylactic acid and polyhydroxybutyrate biopolymers - influence of substrate chemistry on interlayer formation

Polymers are often modified by plasma treatment to adapt them to new applications. During the deposition of an amorphous hydrogenated (a-C:H) layer, a mixed phase (interlayer) of the polymer substrate and the deposited layer often forms. The interlayer is responsible among others for a good adhesion between the layer and the substrate. In this study, amorphous hydrogenated carbon films were deposited on the structurally similar biopolymers polylactic acid (PLA) and polyhydroxybutyrate (PHB) using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). In an industrially established process, layer thicknesses of up to 50 nm were produced in 10 nm steps. The surface morphology of each layer was investigated by ex situ atomic force microscopy. Chemical composition was explored first with surface sensitive synchrotron X-ray-based techniques such as X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure. Subsequently, IR measurements were performed for a more detailed analysis of the functional groups contained. Based on the data obtained (e.g. sp2/sp3 ratio, grain formation on the surface), it was possible to determine the transition of polymer to a-C:H layer and therefore the thickness of the interlayer dimension formed during coating. For PLA, the thickness is about 40 nm, for PHB 20 nm.

Numerical calculation of temperature, velocity, and species concentration distributions in a hot filament chemical vapor deposition in a reactor using a CH4/H2 mixture

This study is a numerical modeling of transport phenomena occurring in the reaction chamber during diamond or amorphous hydrogenated carbon films growth by a hot filament chemical vapor deposition (HFCVD) technique. A two-dimensional model was adopted to study the HFCVD reactor. The equations of heat, momentum, and mass transfer were solved numerically; the simulation was performed using a program in FORTRAN language. All temperature, velocity, and species concentration distributions were similar at the filaments and they were also similar between the filaments. The results show that the gas temperature increases when the number of filaments increases from three to four filaments. We also noted an increase in the production of CH3 and C2H5 radicals near the surface; there was also an increase in the growth rate of the thin film. The concentrations of C2H6, C2H4, and C2H5 were very high. Temperature and concentrations were affected by the distance between filaments and the distance filaments-substrates.

Probing the ultra-low friction mechanism of hydrogenated carbon films with controllable fullerene-like nano-structures grown with different bias voltage

Tribological properties of hydrogenated amorphous carbon films (HACFs) are strongly affected by external atmospheres stimulus. This greatly limited its applications in fields that require special trans-atmospheric environments. Here, a unique fullerene-like (FL) nanostructure was designed to embed in amorphous carbon matrix to improve the friction behavior of HACFs in ambient air. High-frequency pulsed plasma-enhanced chemical vapor deposition was employed to deposit the films. The HACFs with fullerene-like (FL) characteristics are fabricated with the ‘amorphous to FL’ evolutions. At bias voltage of − 950 V, HACF has the highest odd ring fraction (57.3%) and exhibit the lowest coefficient of friction (0.039) and wear rate (2.2 ×10−8 mm3/Nm) in ambient air. This may provide potential strategies for HACFs to expand the tribology application environments.

Synchrotron-based spectroscopic study of plasma generated amorphous hydrogenated carbon films (a-C:H) post-functionalized using photochemically active ruthenium-polypyridyl complexes

Amorphous hydrogenated carbon (a-C:H) films were firstly deposited on Si-substrates via plasma enhanced chemical vapor deposition. Subsequent functionalization of the carbon surface was achieved via UV-irradiation using photochemically active binuclear Ru-polypyridyl-complexes. Three differently substituted Ru-complexes {[μ-1,2-di(2,2′-bipyridin-4-yl)-diazene-1κ2N,2κ2N]-bis[bis(4,4′-R-2,2′-bipyridine-κ2N)ruthenium(II)]}(PF6)4 (R= t-Bu, (OMe), Br) were studied. Modified a-C:H films were analyzed by synchrotron-based X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy revealing the successful covalent attachment of mononuclear Ru-polypyridyl fragments.

Surface treatment of biopolymer films Polylactic acid and Polyhydroxybutyrat with angular changing oxygen plasma ‒ More than just gradual purification

Bio-based and biodegradable polymers such as polylactic acid (PLA) and polyhydroxybutyrat (PHB) are developing into increasingly important raw materials. Especially when it comes to replacing conventional polymers in order to save resources and reduce environmental impact. Such biopolymers often conform to mechanical requirements of industry, but inappropriate surface characteristics such as poor barrier properties and increased degradation limit their application. Appropriate surface modification, such as the deposition of thin amorphous hydrogenated carbon films (a-C:H) produced by low-temperature mediated radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) can provide a remedy here. Prior to this, the surfaces are mostly cleaned/activated with oxygen plasma to enable better deposition of the subsequent a-C:H layer. It has been noticed that the O2 treatment, strongly changes the surface properties. It is now to be determined how a change in the O2 plasma treatment geometry affects the surface properties and whether this can be used accordingly. Surface morphology was analyzed by AFM, surface free energy (SFE) was determined using a contact angle goniometer, and changed barrier properties were investigated via the water vapor transmission rate. Top surfaces were studied by synchrotron supported X-ray spectroscopy, revealing angle-dependent changes in C and O content and binding conditions. The present angle-dependent O2 treatment not only changed the surface roughness and its chemical composition, but also, contrary to expectations, improved the barrier properties of PLA up to 18% at highest value, while the transmittance of PHB increased by more than 10%. A similar change in the mobility of the contact angle hysteresis is observed for both materials.

Electrical Conduction Properties of Hydrogenated Amorphous Carbon Films with Different Structures.

Hydrogenated amorphous carbon (a-C:H) films have optical and electrical properties that vary widely depending on deposition conditions; however, the electrical conduction mechanism, which is dependent on the film structure, has not yet been fully revealed. To understand the relationship between the film structure and electrical conduction mechanism, three types of a-C:H films were prepared and their film structures and electrical properties were evaluated. The sp2/(sp2 + sp3) ratios were measured by a near-edge X-ray absorption fine structure technique. From the conductivity–temperature relationship, variable-range hopping (VRH) conduction was shown to be the dominant conduction mechanism at low temperatures, and the electrical conduction mechanism changed at a transition temperature from VRH conduction to thermally activated band conduction. On the basis of structural analyses, a model of the microstructure of a-C:H that consists of sp2 and sp3-bonded carbon clusters, hydrogen atoms and dangling bonds was built. Furthermore, it is explained how several electrical conduction parameters are affected by the carrier transportation path among the clusters.

Thermal Conductivity Enhancement in Ion-Irradiated Hydrogenated Amorphous Carbon Films.

Amorphous solids are traditionally assumed to set the lower bound to the vibrational thermal conductivity of a material due to the high degree of structural disorder. Here, were demonstrate the ability to increase the thermal conductivity of amorphous solids through ion irradiation, in turn, altering the bonding network configuration. We report on the thermal conductivity of hydrogenated amorphous carbon implanted with C+ ions spanning fluences of 3 × 1014-8.6 × 1014 cm-2 and energies of 10-20 keV. Time-domain thermoreflectance measurements of the films' thermal conductivities reveal significant enhancement, up to a factor of 3, depending upon the preirradiation composition. Films with higher initial hydrogen content provide the greatest increase, which is complemented by an increased stiffening and densification from the irradiation process. This enhancement in vibrational transport is unique when contrasted to crystalline materials, for which ion implantation is known to produce structural degradation and significantly reduced thermal conductivities.

Effect of Water Adsorption on the Frictional Properties of Hydrogenated Amorphous Carbon Films in Various Relative Humidities.

The tribological properties of hydrogenated amorphous carbon (a-C:H) films in ambient air were investigated from the microstructural point of view. a-C:H films with various microstructures (polymer-like, diamond-like, and graphite-like structures) were prepared, and the thickness of water adsorption layers on the films was measured. The adsorption behavior of water molecules on a-C:H films could be expressed with the Brunauer-Emmett-Teller (BET) isotherm, while the thicknesses of icelike and liquidlike water layers adsorbed on the films could be determined using the BET parameters C and nma. The polymer-like films exhibited the thickest icelike and liquidlike water adsorption layers, which decreased as the film structure changed to a diamond-like or a graphite-like structure. A strong relationship was observed between the thickness of water adsorption layers and the surface oxidation of the a-C:H films. The friction coefficient of the films in ambient air can be well explained by the surface oxidation and the thickness of water adsorption layers. Polymer-like films showed high friction coefficients due to the formation of a thick water layer on the films originated from the high surface oxidation of the film surface, whereas the graphite-like film exhibited a low friction coefficient due to low oxidation and a thin water adsorption layer. Furthermore, friction tests between the a-C:H films with different microstructures under ambient air were performed to determine the lowest friction pair in various relative humidities (RHs).

Hydrogenated Amorphous Carbon Films from Palmyra Sugar

A simple, highly reproducible, and environmentally friendly method is a considered approach in generating renewable energy materials. Here, hydrogenated amorphous carbon (a-C) films have been successfully prepared from palmyra liquid sugar, employing spin-coating and spraying methods. Compared with the former method, the latter shows a significance in producing a better homogeneity in particle size and film thickness. The obtained films have a thickness of approximately 1000 to 100 nm and contain an sp2 hexagonal structure (~70%) and sp3 tetrahedral configuration (~30%) of carbons. The introduction of boron (B) and nitrogen (N) as dopants has created the local structural modification of bonding, inducing a slight change of electrical conductivity, electronic energy bandgap, and optical transparency near-infrared region. The obtained a-C film features a “green” semiconducting material.

Hydrogenated Amorphous Carbon Film Deposited by Plasma on Recycled Polypropylene as a Functional Barrier to Hazardous Migrants

Hydrogenated Amorphous Carbon Film Deposited by Plasma on Recycled Polypropylene as a Functional Barrier to Hazardous Migrants

Multiscale Surface Microtexture Analysis of CuNPs@a-C:H Thin Films

The sputtered copper nanoparticles (Cu NPs) on amorphous hydrogenated carbon films (CuNPs@a-C:H) were deposited on a glass substrate by the codeposition method of radio-frequency (RF)-sputtering an...

Electrodeposition and biocompatibility of palladium and phosphorus doped amorphous hydrogenated carbon films

Diamond like carbon (DLC) films are considered as exciting candidates for biomaterials owing to high hardness and chemical inertness. However, the high resistivity of pure DLC films limited further applications in bioelectronic field. The palladium and phosphorus doped DLC film was fabricated by electrochemical deposition from the ethanol solution of Tetrakis (triphenylphosphine) platinum. The structure of the film was composed of CP, CP, CH, sp2–C, sp3–C bonds and Pd nanoparticles. The resistivity was evidently reduced due to the introduction of palladium and phosphorus, and the biocompatibility simultaneously enhanced. It will open up a new application direction for bioelectronic devices.

Refinement of Sustainable Polybutylene Adipate Terephthalate (PBAT) with Amorphous Hydrogenated Carbon Films (a-C:H) Revealing Film Instabilities Influenced by a Thickness-Dependent Change of sp2/sp3 Ratio

The increasing use of polymers is related to a growing disposal problem. Switching to biodegradable polymers such as polybutylene adipate terephthalate (PBAT) is a feasible possibility, but after industrial production of commercially available material PBAT is not suitable for every application. Therefore, surface refinements with amorphous hydrogenated carbon films (a-C:H) produced by plasma-assisted chemical vapor deposition (PE-CVD) changing the top layer characteristics are used. Here, 50 µm-thick PBAT films are coated with a-C:H layers up to 500 nm in 50 nm steps. The top surface sp2/sp3 bonding ratios are analyzed by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) both synchrotron-based. In addition, measurements using diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) were performed for detailed chemical composition. Surface topography was analyzed by scanning electron microscopy (SEM) and the surface wettability by contact angle measurements. With increasing a-C:H layer thickness not only does the topography change but also the sp2 to sp3 ratio, which in combination indicates internal stress-induced phenomena. The results obtained provide a more detailed understanding of the mostly inorganic a-C:H coatings on the biodegradable organic polymer PBAT via in situ growth and stepwise height-dependent analysis.

Surface-enhanced Raman scattering (SERS) of Methyl Orange on Ag-DLC nanoparticles

In the present study, Ag nanoparticles were synthesized in amorphous hydrogenated carbon films on glass substrates by RF-PECVD and RF-sputtering co-deposition method at the room temperature. Methyl orange was utilized as an analyte with different concentrations on Ag nanoparticles that were embedded in diamond-like carbon (DLC). Ultraviolet–visible (Uv–vis) spectroscopy, XRD analysis, Raman spectroscopy, Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM) were performed to characterize films. Ag-DLC with an average size of less than 14 nm was the active site for surface-enhanced Raman scattering (SERS). Sensitivity of measurements in SERS spectra was increased by these types of thin films. This method of nano-particle synthesis is cost-effective and just requires a one-step synthesis. Such substrates can be used for several times. Moreover, they are useful for biosensors because of their hardness and other properties that may be subsequently referred.

Double plasmon resonance in hybrid structures of silver nanoparticles with amorphous hydrogenated carbon

ABSTRACTIn this work, double plasmon resonances in hybrid structures comprising Ag nanoparticles (NPs) and amorphous hydrogenated carbon films (a-C:H) have been studied. Granulated silver films with a gravimetric thickness of 10 nm were thermally deposited on top or underneath a-C:H films fabricated by plasma-assisted chemical vapour deposition on a quartz substrate. Two plasmon bands with comparable intensities have been observed in the hybrid structures optical density spectrum after annealing at 200°C. On the other hand, in the absence of the amorphous hydrogenated carbon film the short-wavelength peak in the optical density spectrum of the same Ag film is hardly observable. In addition, plasmon-enhanced photoluminescence of the a-C:H film being excited close to the spectral dip at the wavelength of 405 nm was observed. The nature of double plasmon resonance spectra were discussed and explained by the resonance interaction of plasmons excited in Ag NPs with excitons in a-C:H.

Electrical and Optical Characterization of Acetylene RF CCP for Synthesis of Different Forms of Hydrogenated Amorphous Carbon Films

We present an electrical and spectroscopic characterization of Acetylene plasma used for deposition of different forms of hydrogenated amorphous carbon (a-C:H) films at different discharge powers. Asymmetric radio frequency capacitively coupled plasma source driven by 13.56 MHz used for generation of the discharge. Fast Fourier transformation of the experimentally measured discharge current waveforms shows several harmonics of the driving frequency, the number and amplitude of these harmonics depends on the experimental conditions. The plasma series resonance (PSR) oscillations generated such harmonics leading to an enhancement of ionization process. Optical emission spectroscopy results showed strong emissions intensities from C4H2+ which varied with both power and pressure, the presence of these emissions attributed to the PSR effect. The formation and transformation of the films from polymeric a-C:H to graphitic a-C:H at different discharge powers was confirmed by Raman, FTIR and optical absorption spectroscopy. For the first time we constructed a ternary phase diagram of the a-C:H films based on the relative intensity ratio of [I(C4H2+)/I(CH)] to provide quantitative information about the types of the deposited films. We pointed out that the C4H2+ ionic species play the major role in the films formation and transformation process.

Effects of Ion Bombardment Energy Flux on Chemical Compositions and Structures of Hydrogenated Amorphous Carbon Films Grown by a Radical-Injection Plasma-Enhanced Chemical Vapor Deposition

Hydrogenated amorphous carbon (a-C:H) films have attracted much attention, because of their excellent physical and chemical properties, such as high mechanical hardness, chemical robustness, a wide variety of optical bandgaps, and so forth. Although an ion bombardment energy has been regarded as essential in the well-know subplantation model, it alone is inadequate especially in complicated reactions of a plasma-enhanced chemical vapor deposition process. In this study, an ion bombardment energy flux (ΓEi) was proposed as a crucial factor to determine chemical compositions and structures of a-C:H films. To obtain the amounts of ΓEi, electron densities, hydrogen (H) excitation temperatures, and negative direct current (DC) self-bias voltage (-VDC) were measured. The deposition rate increased, and sp2-C clusters incorporation was induced by the ΓEi. With increasing ΓEi, photoluminescence (PL) backgrounds in Raman spectra decreased, while spin densities in electron spin resonance (ESR) measurements increased. These results suggested the H content of a-C:H film decreased depending on the amount of ΓEi. The ΓEi is one of the crucial factors to determine the properties of the a-C:H films.

Relaxation of the Energy of Optically Excited States in the Carbon Quantum Dots

Recently, in connection with the achievement of new technological opportunities for fabrication nanostructured carbon-containing objects, namely, carbon quantum dots (CQDs) and clusters, studies of their various physical properties have been intensively carried out. Investigation of the photoluminescence (PL) properties of these objects have revealed a number of unique features: a wide structureless band of the radiation in the ultraviolet and visible regions of the spectrum, the fluorescent kinetics of the luminescence decay, and the independence of the longwavelength edge of the band on the excitation quantum energy. Similar features of PL are observed early in the different nanostructured carbon-containing materials. A common structural feature of the different nanostructured carbon-containing materials, such as CQD, liquid and solid aromatic hydrocarbons, amorphous hydrogenated carbon films, natural biopolymer – collagen is the existence of carbon sextets-aromatic rings connected by Van der Waals forces. This representation of the structure made it possible in the present work to develop a dimer-excimer model of radiative processes in the CQD. The studies are related to the prospects of application due to the unique combination of a number of key properties including tunable photoluminescence, important for the development of tunable lasers, biomedical applications where photostability, biocompatibility, molecular dimensions are essential to allow chemical connection with any biomolecule without compromising its functions. Further development of the theory of PL mechanisms in the CQD can help to identify other important features of the studied objects that will be of fundamental and practical importance.

Bias effects on wear and corrosion behavior of amorphous hydrogenated carbon films with zirconia interlayer

This paper describes bias voltage effects during the deposition of amorphous hydrogenated carbon (a-C:H) on an interlayer of zirconia doped with silicon. The a-C:H film was synthesized using a microwave chemical vapor deposition (MPCVD) system. The interlayer was deposited via R.F. sputtering. The a-C:H and the interlayer were deposited on Ti6Al4V titanium alloy, AISI 316 L stainless steel, and silicon wafer. A mixture of methane and hydrogen (CH4 + H2) as a feed gas was needed to grow the a-C:H film. The interlayer was grown using a ZrO2 target stabilized with yttrium (8%) and placed silicon cubes in the greatest erosion zone. The chemical compositions of the a-C:H and the interlayer were determined using energy dispersive X-ray spectroscopy, and the chemical structure was analyzed using Raman spectroscopy on the a-C:H and X-ray diffraction on ZrO2 interlayer. The morphology, surface, and cross section were studied with atomic force microscopy and field emission scanning electron microscopy. The effect of bias voltage variation on the microstructure, mechanical properties, wear, corrosion resistance, and coefficient of friction was studied. The behavior under different normal loads and sliding speeds in the wear test was analyzed. Wear mechanism transitions, wear rate variations, and coefficients were recorded for each bias value applied. The best performance against wear and corrosion was achieved for the film deposited with a bias voltage of −300 V, due the wear rate is reduced as well as the current density compared to lower negative bias voltage values.

The effect of initial pressure on growth of FeNPs in amorphous carbon films

Iron nanoparticles in amorphous hydrogenated carbon films (FeNPs@a-C:H) were prepared with RF-sputtering and RFPECVD methods by acetylene gas and Fe target. In this paper, deposition and sputtering process were carried out under influence of different initial pressure gas. The morphology and roughness of surface of samples were studied by AFM technique and also TEM images show the exact size of FeNPs and encapsulated FeNPs@a-C:H. The localized surface plasmon resonance peak (LSPR) of FeNPs was studied using UV–vis absorption spectrum. The results show that the intensity and position of LSPR peak are increased by increasing initial pressure. Also, direct energy gap of samples obtained by Tauc law is decreased with respect to increasing initial pressure.