Amorphous Carbon Nitride Films Research Articles

Effect of air post contamination on mechanical properties of amorphous carbon nitride thin films

We report in this study the mechanical, structural and compositional characteristics of amorphous carbon nitride films (a-CN x ) deposited on Si(100) using RF magnetron sputtering of graphite targets in pure nitrogen and under different RF powers. The properties of the films were determined in their as deposited state using nuclear reaction analysis (NRA), elastic recoil detection (ERDA), infrared (IR) absorption and Raman spectroscopy. The mechanical properties were obtained combining nanoindentation and residual stress measurements. The presence of various types of C–N bonds, as well as the post-deposition contamination of the deposited films by oxygen and water (voids) is revealed. The measured hardness and Young modulus were 0.9–2.03 and 23–27 GPa, respectively. These results have been analysed in term of the matrix flexibility which results from the nitrogen content and the porous character of the films, which can affect deeply the estimation of the physical–mechanical properties of the films.

THE PROPERTIES OF AMORPHOUS CARBON NITRIDE THIN FILMS SYNTHESIZED BY PULSED LASER DEPOSITION WITH VARIOUS PREPARATION CONDITIONS

Surface morphology, deposition rate, bonding composition, structural, optical and electrical properties of XeCl excimer pulsed laser deposited amorphous carbon nitride ( a-CN x) films using camphoric carbon ( C 10 H 16 O ) target in 0.8 Torr nitrogen ( N ) gas ambient as a function of laser fluences (LF) (from 2.8 to 5.2 J/cm2) with fixed target-to-substrate distances (TSD) at 45 mm and substrate temperatures (ST) at 20°C; TSD (from 25 to 45 mm) with fixed LF at 3.4 J/cm2 and ST at 20°C; and ST (from 20 to 500°C) with fixed LF at 3.4 J/cm2 and TSD at 45 mm are reported. At fixed TSD and ST, the surface roughness, particle density, deposition rate and N content increase, whereas the particle size decreases with higher LF. When the LF and ST are fixed, decreasing TSD results in an increase in the irregular small particle size, particle density, surface roughness, deposition rate, N content. On the other hand, when the LF and TSD are fixed, the surface roughness, particle density and particle size increase, whereas the deposition rate decreases with higher ST. The N content increases with ST up to 400°C and decreases thereafter. We found that the amorphous structure of a-CN x films and the ratio of sp2 trihedral component to sp3 tetrahedral component are strongly dependent on the LF, TSD and ST. The a-CN x films with high N content have relatively high electrical resistivity.

Infrared spectra of amorphous carbon based materials

The IR absorption in amorphous carbon and carbon nitride films is discussed in terms of a phenomenological model based on similar absorptions occurring in doped polyconjugated polymers. It is proposed that the strong IR absorption band observed in the 1800–900 cm − 1 region arises from changes in the electronic structure in the micro-domains of the sp 2 clusters due to long and short range charge fluxes. These charge fluxes are enhanced by the increase in the Csp 2 fraction and/or the increase in the nitrogen content (with the subsequent formation of sp 2 and sp 1 sites) since both induce clustering of the sp 2 phase and delocalization of π electrons.

Field emission property improvement of ZnO nanowires coated with amorphous carbon andcarbon nitride films

In this paper, we report an approach to prepare a new type of field emitter made up ofZnO nanowires coated with an amorphous carbon (a-C) or carbon nitride film(a-CNx). The coated ZnO nanowires form coaxial nanocables. The best fieldemission properties, which showed a very low turn-on electric field of1.5 V µm−1 and an emission currentdensity of 1 mA cm−2 (enough toproduce a luminance of 300 cd m−2 from a VGA FED with a typical high-voltage phosphor screen efficacy of9 lm W−1) under the field ofonly 2.5 V µm−1, have beenobtained from the a-CNx coated ZnO nanowire field emitter among three kinds of emitters: a-C coated ZnO nanowires,a-CNx coated ZnO nanowires and uncoated ZnO nanowires. Microstructures and crystalconfiguration were investigated by scanning electron microscopy, x-ray diffraction andtransmission electron microscopy. Band edge transition without any significantphotoluminescence peak relating to intrinsic defects has been observed byphotoluminescence measurement. The superior properties of the field emission areattributed to the low work function of the coated carbon nitride film and goodelectron transport property of the ZnO nanowires with an extremely sharp tip.

THE BONDING PROPERTIES OF AMORPHOUS CARBON NITRIDE FILMS BY THE MEANS OF X-RAY PHOTOELECTRON SPECTROSCOPY STUDIES

Amorphous carbon nitride films (a -CN x) were deposited by pulsed laser deposition of camphoric carbon target at different substrate temperatures (ST). The influence of ST on the bonding properties of a -CN x films was investigated. The nitrogen to carbon (N/C) atomic ratio and oxygen to carbon (O/C) atomic ratio, bonding state and microstructure of the deposited a -CN x films were characterized by X-ray photoelectron spectroscopy and confirmed by other standard measurement techniques. The bonding states between the C and N, and C and O in the deposited films are found significantly influenced by the ST during deposition process. The N/C and O/C atomic ratio of the a -CN x films reached the maximum value at 400°C. The ST of 400°C was proposed to promote the desired sp3-hybridized C and the C 3 N 4 phase. The C–N bonding of C–N, C=N and C–N were observed in the deposited a -CN x films.

X-RAY PHOTOELECTRON SPECTROSCOPY STUDIES ON THE BONDING PROPERTIES OF AMORPHOUS CARBON NITRIDE FILMS SYNTHESIZED BY PULSED LASER DEPOSITION WITH DIFFERENT SUBSTRATE TEMPERATURES

Amorphous carbon nitride films ( a-CN x) were deposited by pulsed laser deposition of camphoric carbon target with different substrate temperatures (ST). The influence of ST on the synthesis of a-CN x films was investigated. The nitrogen-to-carbon (N/C) and oxygen-to-carbon (O/C) atomic ratios, bonding state, and microstructure of the deposited a-CN x films were characterized by X-ray photoelectron spectroscopy and were confirmed by other standard measurement techniques. The bonding states between C and N , and C and O in the deposited films were found to be significantly influenced by ST during the deposition process. The N/C and O/C atomic ratios of the a-CN x films reached the maximum value at 400°C. ST of 400°C was proposed to promote the desired sp 3-hybridized C and the C 3 N 4 phase. The C–N bonding of C–N , C=N and C≡N were observed in the films.

Improvement and characterization of the electrochemical reactivity of amorphous carbon nitride electrodes

Amorphous carbon nitride films prepared by magnetron sputtering technique display, as-prepared, a moderate reactivity. When electrochemically activated, they acquire a quasi-metallic behavior. This behavior has been assessed both by EIS and by scanning electrochemical microscopy which showed that the surface is shared between active and inactive sites. X-ray photoelectron spectroscopy analysis indicated that electrochemical activation is accompanied by a decrease of the number of superficial nitrogen atoms involved in C–Nsp 3 bonds.

Growth and characterisation of polymeric amorphous carbon and carbon nitride films from propane

In this work, we report about the deposition of a-C(N):H films by electron–cyclotron–resonance using propane as a carbon precursor. The films generally present high H contents (up to 61 at.%) and large optical gaps. The maximum N content we obtained is 13 at.%. In nitrogenated films, we observed a strong decrease of the stretching intensity of the infrared spectra of the hydrocarbon (CH n) vibrations, even at very low nitrogen content, the H content being still comparable to that of pure a-C:H. The various phenomena that can lead to such an effect are discussed: (i) different type of hydrogen bonding (CH n and NH n) in presence and in absence of nitrogenation; (ii) weakening of the cross-section of the CH n groups in presence of nitrogen; (iii) large presence of non-bonded hydrogen meaning, with this, either the presence of molecular H2 or unbounded hydrogen. In addition, the residual amount of IR absorption due to C–H vibrations shows that, in a-CN:H, C–H bonded and non-bonded hydrogen does coexist.

NEXAFS study and electrical properties of nitrogen-incorporated tetrahedral amorphous carbon films

Tetrahedral amorphous carbon nitride (ta-C:N) films obtained by filtered cathodic vacuum arc deposition have been investigated by Near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The C K (carbon K) edge NEXAFS spectra clearly revealed the increase of C N bonds with the increase of nitrogen concentration. The C K edge NEXAFS analysis further showed that the content of the surface defect (mainly C–H bonds) decreased with the increase of nitrogen in the films. As the nitrogen concentration increased a pronounced change in the π* features were observed at the N K (nitrogen K) edge. The origin of the N K edge π* peaks are mainly due to the formation of C N bonds and nitrogen substitution in the graphite network. Polarization dependent NEXAFS measurements showed an angular distribution of CN bonds. The electrical resistivity of the ta-C:N films decreased at higher nitrogen concentration and this may be from the development of graphite-like structures in these films. The electrical measurements were confirmed further with electrochemical measurements.

Effects of deposition gas pressure on the properties of hydrogenated amorphous carbon nitride films grown by surface wave microwave plasma chemical vapor deposition

The hydrogenated amorphous carbon nitride films (a-CN:H) films have been grown by a surface wave microwave chemical vapor deposition (SWMP-CVD) method at various deposition gas pressures. The effects of deposition gas pressure on the bonding, optical and electrical properties were studied through X-ray photoelectron spectroscopy, UV-visible spectroscopy and temperature dependence of electrical measurements of as-grown and annealed of the a-CN:H films at 500 °C in Argon gas ambient for 30 min. The optical absorption coefficients were obtained for the as-grown a-CN:H films, which is found to increase upon increase of deposition gas pressures and annealing temperatures. The temperature dependence measurement has shown the electrical conductivity is observed not to follow the simple activated form. Study of activation energy suggests that the Fermi level of the a-CN:H films is moved from valence band edge to nearer to the conduction band edge through mid gap. The variation of conductivity is in good agreement with the activation energy analyses. The XPS measurement also has shown the deposition gas pressure and annealing temperature has affected the properties of a-CN:H films. The results obtained are discussed and also compared with carbon films prepared by other deposition techniques in the literature.

Study on amorphous carbon nitride film prepared by facing target sputtering

Amorphous carbon nitride films were prepared by facing target sputtering at different N 2/Ar gas flow rate ratios. The films were characterized using X-ray photoelectron spectroscopy (XPS), atomic force microscopy, Raman scattering, ellipsometric spectroscopy and temperature dependent resistance tests. As the N 2/Ar ratio varies from 0 to 40%, the nitrogen to carbon ratio in the deposited films increases from 0 to 0.28. Curve fitting of the C 1s and N 1s XPS spectra shows that the C–C sp 3 fraction decreases with an increase in nitrogen content and that the nitrogen atoms are mainly bonded in sp 2 C–N bonds. All films exhibit a clean and smooth surface morphology with a root mean square roughness less than 0.25 nm over an area of 1 μm 2. The Raman spectra show a G peak ranging from 1555 to 1565 cm −1 and a D peak from 1390 to 1425 cm −1 for sp 2 C–C bonds, a weak peak for sp 1 C–N bond at approximately 2210 cm −1. As the N/C ratio increases, both G-peak and D-peak positions shift to low wave number, the I D/I G intensity ratio increases from 1.75 to 1.95, and the Tauc optical band gap decreases from 2.1 to 1.4 eV.

Nanomechanical and nanotribological properties of carbon based films

Submicrometer-thick hard amorphous carbon (a-C) and carbon nitride (CN x ) films were deposited on Si and stainless steel (SS) substrates by rf magnetron sputtering (MS) and reactive MS, respectively. a-C films were synthesized by either sputtering alternating ultrathin layers of soft and hard a-C on Si or by using a Cr interlayer between a-C and SS substrate. The main purpose of this work is to investigate and to compare the nanomechanical, adhesion and nanotribological properties of the CN x and a-C films. Hardness ( H) and elastic modulus ( E) were obtained from indentation experiments performed with a nanoindenter using the continuous stiffness method. The H of a-C films was found to be equal to ∼25 GPa, and the corresponding values of a single-layer amorphous CN x films were found to be equal to ∼12 GPa. Nanoscratch tests of the films were performed by a Nano Indenter XP system with a lateral force measuring attachment. Ultralow load scratch tests were performed in the load range from 2 to 20 mN. Below 5 mN, nanoscratching showed mainly elastic behavior of the CN x and a-C films, while above 10 mN, a mixed elastic-plastic behavior was identified. Testing under a normal load of 20 mN resulted in local grooving at the film surface; however, in situ profiling of the scratch trace showed no evidence of film failure. The coefficient of friction was found to vary in the range 0.15–0.3, being lower for a-C films. The higher elastic properties, no permanent damage and higher elastic recovery under the same normal load imply that a-C films grown on both SS and Si substrates sustain higher scratch-induced stresses and can be more effective as protective coating material.

The structure of amorphous carbon nitride films using a combined study of NEXAFS, XPS and Raman spectroscopies

The nature of bonding in tetrahedral amorphous carbon nitride (ta-C:N) films deposited by filtered cathodic vacuum arc (FCVA) technique was studied with near edge X-ray absorption fine structure (NEXAFS), X-ray photoelectron and Raman spectroscopies. The interpretation and interrelation of these spectra are discussed. The changes in the local structure were systematically studied as a function of nitrogen content. Deconvolution of the C 1 s and N 1 s XPS spectra shows that the sp 3–C fraction decreases with an increase in nitrogen content. The π* peak at the C K (carbon K) and at the N K (nitrogen K) edges were systematically studied. Comparison of intensities of the π* peak confirms the formation of CN bond at the expense of CC bond. Analysis of NEXAFS spectra at N K edge revealed as the nitrogen concentration in the films increases, the π*/ σ* intensity ratio increases, indicating that there is an increase of the amount of C N bond relative to the C–N bonds. Raman parameters, such as G peak width, I D/ I G ratio, skewness of the G line ( Q), were critically analysed in terms of N content and sp 2 content of the films. We demonstrate that the combined study of normalised Raman, XPS and NEXAFS spectra is very useful in determining the role of nitrogen incorporation in the structure of ta-C films. The hardness values, measured by nanoindentation technique reduced at higher (>7 at.%) N content films.

Microstructure and electronic investigations of carbon nitride films deposited by RF magnetron sputtering

The analysis of the relationship between the local microstructure evolution versus nitrogen content and electrical properties of amorphous carbon nitride films (a-CN x ) deposited by radio frequency (RF) magnetron sputtering is reported. Combined TRIM code, XPS measurements and Raman scattering spectroscopy are used to investigate the microstructure of a-CN x , films, in their as-deposited state, in terms of surface processes, nitrogen incorporation within the films and the Csp 2 content. These experiments were completed by dark electrical conductivity measurements performed at room temperature in coplanar configuration. A good correlation is observed between the local microstructure and the conductivity at different amounts of nitrogen.

Effects of energetic species during the growth of nitrogenated amorphous carbon thin films on their nanomechanical properties

Amorphous carbon nitride (CN x ) films are promising materials either as wear-resistant or as solid-lubricant coatings, depending on their mechanical and tribological behavior. In this work, we produced amorphous CN x films by reactive magnetron sputtering, and we varied independently the film density, sp 3/sp 2 content and [N] concentration. The morphology, density and hybridization state of the CN x films were studied ex situ by X-ray reflectivity (XRR). Also, the effects of energetic species (mainly N + or Ar +) on their microstructure and composition were investigated. Using the assumptions of the subplantation model and the results of SRIM simulations, we correlated the density of the films and [N] with the N + ion energy. The nanomechanical and tribological properties of CN x films were studied by nanoindentation and nanoscratch tests. While both adhesion and ploughing mechanisms contribute to the friction behavior in the intermediate and high load ranges, the dominant friction mechanism in the low-load range was attributed to adhesion of the film to the substrate. CN x films grown without ion bombardment (IBD), depending on the normal load, will deform either elastically or elastically–plastically, and may even delaminate. For loads below 5 mN, nanoscratching showed mainly elastic behavior of the film, while above 5 mN, a mixed elastic–plastic behavior was identified. However, the scratch and friction response of the films grown under high-energy ion bombardment (IBD) during ion beam assisted deposition showed a load-dependent transition. The results will be discussed in detail.

Optical and electronic properties of plasma-deposited hydrogenated amorphous carbon nitride and carbon oxide films

A comparative investigation of the nanostructural vs. electronic properties of DECR plasma deposited carbon nitride and carbon oxide alloys provides new insights in the changes of the sp 2-clusters and sp 3 matrix resulting from the decrease in the average coordination number, as N and O atoms are increasingly incorporated. This review emphasizes the similar incorporation efficiency of N and O atoms in the carbon matrix as a function of the gas phase mixture (C 2H 2, N 2) or (C 2H 2, O 2), the decrease in the alloy density deduced from Nuclear Reaction Analysis and optical measurements, and the better ordering of the sp 2-hybridized carbon phase evidenced by Raman studies. Opposite variations in the ohmic conductivity σ( T), apparent activation energy E ACT and hopping transport parameters (related to the localization parameter N( E F) γ −3) are found as a function of the (N/N+C) and (O/O+C) stoichiometries. This surprising result gives evidence of some competition between the improved ordering of the sp 2 phase shown by Raman spectra in both alloys (stronger in a-C 1− x N x :H with a large influence of aromatic clusters) and the increasing polymer-like character of the sp 3 matrix, dominant in a-C 1− x O x :H films where the weaker connectivity of the sp 3 matrix is attributed to two-fold bonded oxygen atoms C–O–C and terminating C O groups. The role of π and π* states localization is discussed in the context of bandtail hopping conductivity.

THE INFLUENCE OF METHANE GAS PRESSURE ON THE OPTICAL, ELECTRICAL AND STRUCTURAL PROPERTIES OF NITROGENATED AMORPHOUS CARBON FILMS GROWN BY SURFACE WAVE MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

The influence of methane gas ( CH 4) pressure on the optical, electrical and structural properties of the nitrogenated amorphous carbon nitride ( a - C : N ) films grown by microwave surface wave plasma chemical vapor deposition (SWP-CVD) on quartz and silicon (100) substrates have been studied. The a - C : N films are deposited with varying CH 4 gas ranging from 5 to 20 ml/min. To incorporate nitrogen in the film, we have introduced nitrogen gas ( N ) at 5 ml/min in the chamber. The effects of CH 4 gas pressure on the surface morphology, composition, structure, and electrical properties of the N -incorporated camphoric carbon thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), UV-visible spectroscopy and four-probe resistance measurement. We have succeed in growing a - C : N thin films using SWP-CVD at room temperature and found that the amorphous structure of a - C films can be changed and is strongly dependent on the CH 4 gas source.

Effect of pressure on the deposition of hydrogen-free amorphous carbon and carbon nitride films by the pulsed cathodic arc discharge method

Hydrogen-free amorphous carbon (a-C) and carbon nitride (a-C:N) films were deposited using the pulsed cathodic arc discharge at different argon and nitrogen pressures. The surface and mechanical properties of these films were found to strongly depend on the gas pressure. The tetrahedral amorphous carbon and hard a-C:N films with smooth surfaces (rms roughness: 0.15nm) were prepared at lower gas pressures (<6×10−2Pa). Incorporation of an increasing amount of nitrogen in a-C:N films caused a decrease in film hardness. All the films were covered with the thin (0.3–2nm) graphite-like surface layers. The film hardness was correlated to the soft surface layer thickness, and the films with thinner surface layers exhibit higher hardness. The mean energies of pulsed plasma beams were measured as the functions of argon and nitrogen pressures. The mean energies of plasma beams decrease in an exponential fashion with increasing gas pressure due to the carbon ion collisions with the neutral gas species. The effects of mean energies of deposited species on the film deposition were explained in terms of the thermal spike migration of surface atoms. The formation of graphite-like surface layers is associated with the low-energy deposition process. The low-energy (<1–3eV) species diffusing on film surface lead to the formation of graphite-like a-C films with plenty of grains. The higher-energy (>10eV) species may produce the strong thermal spike at film surface, and contribute to the formation of sp3 bonded structure at a sp3 bonded matrix.

Nanomechanical properties through nanoindentation method of amorphous carbon and carbon nitride films synthesized by shielded arc ion plating

Amorphous carbon (a-C) and carbon nitride (a-CNx) films were deposited by means of shielded arc ion plating (SAIP) with an arc current of 60 A operated in a gas pressure of 1 Pa. A bias voltage in the range from 0 to −500 V was applied to a substrate during film deposition. Nanomechanical properties of the films were measured by a nanoindentation interfaced with an atomic force microscopy (AFM) using a diamond tip. The nanoindentation was also applied to evaluate wear resistant behavior of the films in nm scale. The a-C film prepared at a substrate bias voltage ( V b) of −100 V was hardest in the present study so as to show a hardness of 43±3 GPa. This a-C film was most wear resistant as well. The a-CNx film prepared at V b of −300 V possessed the maximum hardness of 14±1 GPa among the prepared a-CNx films. Independently of V b, all of the a-CNx films showed better wear-resistance characteristics than sapphire and quartz. Although the wear-resistance of the films was not directly correlated to its hardness, elastic modulus, elastic recovery, plastic deformation energy, these properties were certainly govern the wear-resistance of the film.

Highly photoconductive amorphous carbon nitride films prepared by cyclic nitrogen radical sputtering

We report on the growth of amorphous carbon nitride films (a-CNx) showing the highest conductivity to date. The films were prepared using a layer-by-layer method (a-CNx:LL), by the cyclical nitrogen radical sputtering of a graphite radical, alternated with a brief hydrogen etch. The photosensitivity S of these films is 105, defined as the ratio of the photoconductivity σp to the dark conductivity σd and is the highest value reported thus far. We believe that the carriers generated by the monochromatic light (photon energy 6.2eV) in the a-CNx:LL films are primarily electrons, with the photoconductivity shown to increase with substrate deposition temperature.