β-C3N4 Phase Research Articles

Applications insight into the plasmochemical state and optical properties of amorphous CNx films deposited by gas injection magnetron sputtering method

This manuscript reports the results of carbon nitride (CNx) film deposition carried out using the gas injection magnetron sputtering method. In this experiment, a pulsed gas injection was used to arrange the varying neon/nitrogen (Ne/N2) plasma discharge. This approach influences on the transition between two excitation mechanisms of plasma particles, which changed from Penning ionization to electron impact excitation, as the share of N2 pressure was increased in the range of 0.05–0.45 Pa. In relation to that outcome, the CNx (0.04 ≤ x ≤ 0.21) films presented a smoothly fluctuated chemical state, which varied from bonds hybridized in the sp1 (N ≡ C) nitrile groups, sp2 (N = C) graphite sheets, to disordered sp3 (N – C) chain structures as proved by the study of the N1s and C1s core-level spectra. These were tied up in amorphous structure arrangement, and consisted of either oxidized graphitic sheet or β-C3N4 phase, as revealed in the fast Fourier transform analysis. In conclusion, on the basis of an investigation of indiscrete optical band gap (E1g < 1.1 eV and 3.2 < E2g < 4.3 eV), the CNx were emphasized as a highly transparent (~90%) film, proving its application potential for the near-infrared devices.

Influence of the nitrogen content on the optical properties of CNx films

Polycrystalline carbon nitride thin films were prepared by electrolysis of methanol-urea solution at different concentrations of urea to methanol and applied voltage 800volts for 10h. Grazing incidence X-ray diffraction (GIXRD) revealed that the crystalline structure of carbon nitride films at moderate nitrogen content changed from amorphous phase to polycrystalline α-C3N4, and β-C3N4 phases. The optical transmission analysis of the films revealed that the band gap value for indirect allowed transitions increased with increasing nitrogen content, while the associated phonon energy value showed the opposite behavior. The refractive index and the extinction coefficient of the samples deposited with different concentrations were determined as a function of wavelength. The refractive index decreases with increasing both nitrogen content and crystallinity. The refractive index dispersion for the investigated samples is discussed in terms of the single oscillator model and oscillator parameters.

Crystalline carbon nitride films prepared by microwave plasma chemical vapour deposition

Crystalline carbon nitride films have been synthesized on Si (100) substrates by a microwave plasma chemical vapour deposition technique, using mixture of N2, CH4 and H2 as precursor. Scanning electron microscopy shows that the films consisted of hexagonal bars, tetragonal bars, rhombohedral bars, in which the bigger bar is about 20 μm long and 6 μm wide. The X-ray photoelectron spectroscopy suggests that nitrogen and carbon in the films are bonded through hybridized sp2 and sp3 configurations. The x-ray diffraction pattern indicates that the films are composed of α-, β-, pseudocubic and cubic C3N4 phase and an unidentified phase. Raman spectra also support the existence of α- and β-C3N4 phases. Vickers microhardness of about 41.9 GPa measured for the films.

Deposition of nanostructured Si–C–N superhard coatings by rf magnetron sputtering

Systematic investigation on the deposition of thin silicon-carbon-nitride films by reactive rf magnetron sputtering from SiC–C composite target in nitrogen-argon atmosphere was studied. The significant effect of deposition pressures on the hardness of the deposited SiCN films was found, which varied between 4.7 and 44GPa. The films were found to be amorphous from x-ray diffraction analysis but localized crystallization was noticed during atomic force microscopy (AFM) studies on these deposited films. The AFM studies also suggested that the increased hardness was due to reduction in particle size and localized formation of β-C3N4 and β-Si3N4 phase in the films. The x-ray photoelectron spectroscopy analyses showed the formation of C–N and Si–N bonds for the harder film. The increased nitrogen concentration in the sputtering gas mixture to 99% resulted in large particle growth and graphitic phase formation, which exhibited a low hardness value of 4.7GPa. The high C content and low Si content in the deposited films facilitated the graphitic phase formation.

Structural characterisation of crystalline carbon nitride thin films synthesised by electrolysis of urea–methanol solution

Polycrystalline carbon nitride thin films were deposited on Si(400) and ITO coated glass substrates by electrolysis of methanol–urea solution under high voltage, at atmospheric pressure and at temperatures below 350 K. Fourier transform infrared spectroscopy (FTIR) measurements of the films deposited on Si suggested the existence of single, double and triple carbon–nitrogen bonds in the films. A maximum N/C atomic ratio of 0·81 was achieved in the films as measured by C/H/N analysis. X-ray diffraction spectra of the films grown with different urea concentrations showed various peaks for different d values, which could be assigned to different crystalline carbon nitride phases. Selected area electron diffraction patterns measured by transmission electron microscopy (TEM) showed a number of concentric sharp rings, corresponding to various planes of theoretically predicted β-C3N4 phase. Scanning electron microscopy (SEM) images of the films indicated the existence of grains, the number density and size of which were dependent on the solute concentration. Optical transmission measurements of the films on ITO coated glass substrates revealed a band gap value of around 2·87 eV for direct transition. The hardness of the films on Si substrates was as high as 28 GPa.

Synthesis of Crystalline Carbon Nitride by Microwave Plasma Chemical Vapor Deposition

Carbon nitride films were grown on Si substrates by a microwave plasma chemical vapor deposition method, using mixture of N2, CH4 and H2 as precursor. Scanning electron microscopy shows that the films consisted of a large number of hexagonal crystallites. The dimension of the largest crystallite is about 3 µm. The X-ray photoelectron spectroscopy suggests that nitrogen and carbon in the films are bonded through hybridized sp2 and sp3 configurations. The X-ray diffraction pattern indicates that the major part of the films is composed of α-, β-, pseudocubic C3N4 and graphitic C3N4. The Raman peaks match well with the calculated Raman frequencies of α- and β-C3N4, revealing the formation of the α- and β-C3N4 phase.

Irradiation effect of low energy nitrogen-ion beam during pulsed laser deposition process on the structural and bonding properties of carbon–nitride thin films

Carbon–nitride thin films were deposited by pulsed laser ablation of graphite with assistance of low energy nitrogen-ion-beam irradiation. The nitrogen to carbon (N/C) atomic ratio, bonding state, microstructure, surface morphology, and electrical property of the deposited carbon–nitride films were characterized by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, micro-Raman spectroscopy, x-ray diffraction (XRD), atomic force microscopy, and four-probe resistance. The irradiation effect of low energy nitrogen-ion beam on the synthesis of carbon–nitride films was investigated. The N/C atomic ratio of the carbon–nitride films reached the maximum at the ion energy of ∼200 eV. The energy of ∼200 eV was proposed to promote the desired sp3-hybridized carbon and the C3N4 phase. Electrical resistivity of the deposited films was also influenced by the low energy nitrogen-ion-beam irradiation. However, the low energy irradiation had little effect on the surface morphology of the films. XRD results revealed the coexistence of the α- and β-C3N4 phases in the deposited thin films.

STRUCTURAL CHARACTERIZATION OF C3N4 THIN FILMS SYNTHESIZED BY MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

Crystalline carbon nitride films have been synthesized on Si substrates by microwave plasma chemical vapor deposition technique, using a gas mixture of nitrogen and methane. Scanning electron microscopy shows that the film consisted of hexagonal crystalline rods. X-ray diffraction and transmission electron microscopy indicate the films are mainly composed of α-and β-C3N4, and these results match more closely with α-C3N4 than with β-C3N4 phase. Fourier transform infrared (FTIR) and Raman spectra of carbon nitride were calculated through Hooke's law. The observed FTIR and Raman spectra support the existence of α- and β-C3N4 in the films.

X-Ray photoelectron spectroscopy reference data for identification of the C3N4 phase in carbon–nitrogen films

Abstract The β-C3N4 phase should have a tetrahedral (sp3-bonded) structure resulting in C1s and N1s XPS peaks with only one feature at a position defined by the electronegativity of four CN bonds. In this work we determined the binding energy of the C1s and N1s XPS peaks in melamine (C3N6H6). In this compound the carbon atoms have four bonds with nitrogen atoms (double and two single); the nitrogen atoms have two chemical states: CNC and CNH2. Since the total number of chemical bonds in this compound is the same as in the hypothetical β-C3N4 compound, this compound is more suitable as a C1s XPS reference for the β-C3N4 phase. The binding energy of the C1s and N1s XPS peaks in melamine was determined to be equal to 287.9 and 399.1 eV, respectively. The binding energies were determined relative to the C1s XPS peak for carbon contamination (adventitious carbon).

Characterization and tribological evaluation of duplex treatment by depositing carbon nitride films on plasma nitrided Ti-6Al-4V

Carbon nitride (CNX) films (with N/C ratio of 0.5) were deposited on both untreated and plasma nitrided Ti-6Al-4V substrates by D.C. magnetron sputtering using a graphite target in nitrogen plasma. TEM and XPS analysis revealed the formation of both amorphous CNX structure and crystalline β-C3N4 phases in the deposited coatings. Nano-indentation tests showed that the film hardness was about 18.36 GPa. Both the scratch tests and indentation tests showed that compared with CNX film deposited directly on Ti-6Al-4V, the load bearing capacity of CNX film deposited on plasma nitrided Ti-6Al-4V was improved dramatically. Ball-on-disk wear tests under both dry sliding and lubricated conditions (with simulated body fluids) were performed to evaluate the friction and wear characteristics of the deposited coatings. Results showed that under both dry and lubricated conditions, the duplex treated system (i.e., with CNX film deposited on plasma nitrided Ti-6Al-4V substrate) was more effective in maintaining a favorable low and stable coefficient of friction and improving wear resistance than both individual plasma nitriding and CNX films on Ti-6Al-4V substrate. Under dry sliding conditions, the generated wear debris of spalled films were accumulated on the wear track, mechanically alloyed and graphitized, thus significantly reducing the coefficient of friction and preventing wear of the substrate. However, under lubricated conditions, due to the flowing of the fluids, the lubricating wear debris was taken away by the fluids, and therefore, the direct contact of two original surfaces resulted in high coefficient of friction and extensive abrasive wear of the substrate for CNX films deposited on Ti-6Al-4V substrate. Also when there was some small-area spallation of CNX films, the fluids could seep into the interface between the film and substrate, thus degrading the interfacial adhesion and resulting in a large area spallation.

Low-energy plasma beam deposition of carbon nitride layers with β-C3N4-like fractions

Carbon nitride films have been generated on Si(100) substrates by low-energy plasma beam deposition with a mixed N2+–N+/Ne+-beam at an ion energy of 120 eV. The nitrogen concentration in the CNx-films, measured by MCs+-mass spectrometry, varies between 25 and 41 at%. From an analysis of the C1s and N1s XPS-peak structures, two C–N binding configurations in the CNx-layers were identified. One phase has C3N4-stoichiometry and is referred to as a β-C3N4-like phase. The other configuration with x between 0.2 and 0.8 is identified as a carbon-rich sp2-bonded structure. The results are compared with CNx-films which were previously deposited with N+/N2+–Ar+-plasma beams. A strong correlation of the N+/N2+-ratio in the plasma beam with the binding configuration and the optical band gap was found. For a maximum N+/N2+-ratio the tetrahedrally bonded component of the films and the optical band gap achieve their highest values. Transmission electron diffraction displays three diffuse diffraction rings which can be matched with the calculated lattice structure of the β-C3N4 phase.

Electron spectroscopic study of C–N bond formation by low-energy nitrogen ion implantation of graphite and diamond surfaces

The effect of 500 eV N2+ irradiation of graphite and diamond surfaces has been investigated by in situ electron spectroscopies (Auger electron spectroscopy and x-ray photoelectron spectroscopy). The chemical state of the implanted nitrogen and carbon have been studied as a function of: (i) implantation temperature in the room temperature (RT) to 800 K range, (ii) annealing of the RT implanted layer up to 800 K, (iii) and ion dose. It is concluded that the implanted nitrogen is present in three different bonding states, denoted as α, β, and γ, for all implantation conditions. The distribution of these states was found to be affected by the substrate nature as well as by the temperature of implantation and annealing process. A chemical interconvertion model is proposed to explain the changes in population of the carbon–nitrogen bonding states as a function of annealing and implantation temperature. It is suggested that the β state includes nitrogen atoms in threefold configurations and may be related to an almost unpolarized carbon–nitrogen chemical bond, which is expected to be present in β-C3N4 phase. A predominant population of this state has been achieved in the case of nitrogen ion implantation into diamond. It has been demonstrated that hot nitrogen implantation results in the formation of the least polarized carbon–nitrogen bonding state [the β state which possess higher N(1s) binding energy] in all studied systems. The structure of the nitrogen implanted layers has been assessed by the analysis of the C(KVV) Auger line shape. Partial conservation of the initial substrate structure has been observed after hot nitrogen implantation of the diamond and graphite surfaces. Our model investigation of carbon nitride formation by low energy ion implantation strongly suggests that it is impossible to populate only one particular carbon–nitrogen bonding state in which carbon is in sp3 and nitrogen in sp2 hybridization state in the frame of the studied experimental conditions. However, this state was found to be formed among a variety of possible other carbon–nitrogen bonding states. The results presented in this work are of importance for understanding the fundamental processes involved in the formation of carbon nitride thin films by ion beam deposition methods.

Nano-carbon nitride synthesis from a bio-molecular target for ion beam sputtering at low temperature

Abstract Nano-crystalline carbon nitride has been successfully synthesized at a temperature below 100 °C from an adenine(C5N5H5) target sputtered by an Ar ion beam. Because adenine possesses a ring structure similar to the hypothetical β-C3N4 phase, the use of this bio-molecular compound as the target is believed to reduce the energy barrier of carbon-nitride growth. The effect of Ar ion-sputtering voltage on the film growth and the effect of extra-N-atom incorporation on the carbon-nitride film growth are examined in this study. Only a carbon film is formed with an ion energy of 500 V. For the ion-beam energy above 750 V, carbon nitride films are deposited, and there is some hydrogen incorporation in the films. The N/C composition ratio in the films could reach 1:1 and is independent on the ion beam voltage. The nitrogen is bonded with carbon within the films, as determined by the IR and XPS measurements. However, the films deposited at a higher ion voltage could possess some original functional groups of adenine. A strong and broad peak at a d-spacing of 0.32 nm, comparable to the calculated d-spacing of the β-C3N4(110), is observed in the XRD spectra of the carbon nitride films. The TEM results indicated that the film contained nano-crystalline grains. Several d values are also in good agreement with those of adenine and the calculated values of β-C3N4. The C/N ratios of the films are still kept at almost 1:1 with N atoms added during deposition. The XRD spectra and IR spectra of these films are all similar to the film deposited without nitrogen source.

Process controlled microstructural and binding properties of hard physical vapor desposition films

The influence of the ion-to-atom flux ratio and the ion energy on the texture development and the grain size is exemplified for well controlled ion beam assisted and plasma beam deposition of TiN films. The dependence of the atomic binding configuration in hard carbon and nitride films on the energy input during film growth is also addressed with special emphasis on a possible synthesis of the hypothetical β-C3N4 phase.

STUDIES OF CNx FILMS DEPOSITED BY MEANS OF MICROWAVE PLASMA CVD METHOD

CNx films deposited on Si substrates with microwave plasma chemical vapor deposition method are measured and analyzed using Raman scattering,X-ray photoelectron spectrum,X-ray diffraction and scanning electron microscopy techniques.The result of Raman spectrum shows the amorphous graphite peak around 1600cm-1 with the flow ratio of CH4 and N2 below 1∶8.As the flow ratio is equal to 1∶8,a characteristic peak around 2190cm-1 exists,which represents C≡N bond.According to the XPS results,the binding pattern of C and N are seen to be of C—N bond and C≡N bond.There is no diffraction peaks corresponding to β-C3N4 phase in the XRD pattern.The gas pressure has influence on the deposited rate of the film.

Deposition of carbon nitride via hot filament assisted CVD and pulsed laser deposition

Bias-assisted hot filament chemical vapour deposition (HFCVD) and ion-assisted pulsed laser deposition (IA-PLD) have been employed to deposit carbon nitride films. Crystalline C-N films composed of α- and βC3N4, as well as some unpredicted C-N solids have been synthesized on Ni(100) substrates via HFCVD using a gas mixture of nitrogen and methane. The crystal constants of the α- and β-C3N4 phases, obtained via X-ray diffraction, coincide well with those predicted theoretically; additionally, cone-shaped crystals are observed on the Si(100) substrates. Similarly, high density cone-shaped (Si)-C-N crystals have been obtained on Si(100) substrates via ion-assisted pulsed laser ablation of a carbon (graphite) target intersecting a nitrogen ion beam. Amorphous C-N films were also produced using this method.

Formation of Carbon Nitride Films by Helicon Wave Plasma Enhanced DC Sputtering

Carbon nitride films have been synthesized on Si(100) substrates by using DC sputtering assisted with a high density m=0 mode helicon wave-excited plasma in Ar and N2 mixture. The composition, structure and bonding state of the films were investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy. From the XPS analysis it was found that the nitrogen to carbon (N/C) ratio in the films could be controlled over a wide range of 0.2–0.9 by changing the target voltage and nitrogen mixing rate via the production of a high density plasma of 1012–1013 cm-3. FT-IR spectroscopy indicated the appearance of an absorption band near 2200 cm-1 corresponding to C≡N covalent bonding. The XPS analysis also suggested the existence of a β-C3N4 phase with sp3 bonding correlated with the variation of the film microhardness.

Structure and mechanical properties of dual-ion-beam deposited CNxTiy/TiN multilayers

CN x Ti y /TiN multilayers have been synthesized using dual-ion-beam deposition. X-ray photoelectron spectra of C 1s, Ti 2p, N 1s, and Si 2p electrons were investigated against the depth from the film surface. The results confirm the layered structure of the films. The Ti atoms contained in a CNxTiy layer sandwiched between two TiN layers are expected to come from interlayer diffusion of Ti atoms enhanced by ion beam irradiation during deposition. As a consequence, a CNxTiy layer contains a C–N phase, a Ti–N phase, and a T–C phase. The C–N phase contains 27 at. % nitrogen, less than the level required to form the hypothetical β-C3N4 phase, indicating that the multilayer structure containing TiN layers does not favor for increasing N content in the C–N phase of the CNxTiy layers. The Ti–N and Ti–C phases are about stoichiometric. The TiN layers comprise mainly a Ti–N phase, and a small fraction of the Ti–C phase, which are both stoichiometric. However, the bonding between C and N is weak. The hardness H and elastic modulus E of the films were investigated by nanoindentation experiments. The single-layer CN0.3 is the softest (H=11.4 GPa), and the single-layer TiN is the hardest (H=22 GPa) among the samples in the series. H and E increase with increasing TiN volume fraction, as well as the number of interfaces. They also increase with increasing substrate temperature, possibly due to stronger interlayer diffusion of Ti atoms at higher temperature.

Structural studies of reactive pulsed laser-deposited CNx films by X-ray photoelectron spectroscopy and infrared absorption

The changes in the structure of reactive pulsed laser-deposited (RPLD) CNx films with nitrogen content from 3.6–22 at% have been investigated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and Fourier transform–infrared (FT–IR) absorption. The films were found to be amorphous, and to consist of a network of rings. The rings that were composed solely of carbon atoms gave rise to an XPS peak located between 284.3 and 284.8 eV (C1 component). The rings containing nitrogen led to another peak located between 285.5 and 286.4 eV (C2 component). When the nitrogen content increased, the relative intensity of the C1 component fell, while that of the C2 component rose, indicating that some carbon atoms in the rings were replaced by nitrogen atoms. C≡N bonds also contributed to the C2 component. The FT–IR data were consistent with this interpretation. No evidence for the existence of a β-C3N4 phase was found in RPLD CNx films.

Structure, Optical and Electrical Properties of Pulsed Laser Deposited and Ion Beam Deposited CNx Films

ABSTRACTCNx films were deposited using pulsed laser deposition (PLD) and ion beam deposition (IBD). The PLD films deposited at substrate temperature Ts = 25°C and high N2 partial pressure have the highest N content (fN) and polymerlike structure, accompanied by large band gap (Eg) and low electrical conductivity (σroom). The rise in Ts lowers fN and induces graphitization of the film structure, so Eg reduces and σroom increases. IBD (with and without N2+ assist) films are graphitic. Higher Ts further enhances the graphitization of the film structure, such that the conduction and valence bands overlap, and σroom approaches to that of graphite. No evidence was found to show successful formation of the hypothetical β-C3N4 phase in the films.