a-CNx Films Research Articles

Temporary change in NEXAFS spectra of amorphous carbon nitride films with photoinduced deformation by visible light irradiation

Amorphous carbon nitride (a-CNx) films, prepared by reactive radio frequency magnetron sputtering, exhibit unique characteristics under visible light irradiation, referred to as photoinduced deformation. This phenomenon represents an energy conversion system wherein photon energy transforms into kinetic energy. The chemical bonding structure of a-CNx films was analyzed using near-edge x-ray absorption fine structure (NEXAFS) at the NewSUBARU synchrotron facility of the University of Hyogo, Japan. This analysis aimed to elucidate the mechanisms behind the photoinduced deformation observed in a-CNx films. Three variants of a-CNx films, displaying varying degrees of photoinduced deformation, were deposited using a graphite target and nitrogen gas under different deposition temperatures. The NEXAFS spectra of the a-CNx films with substantial photoinduced deformation showed changes under light irradiation from a Xe lamp (directed through an optical window within the NEXAFS chamber). Specifically, the peaks corresponding to the 1s to π* transition related to C—C and 1s to σ* transition related to C—N bonds exhibited high sensitivity to visible light irradiation. Simultaneously, the N K-edge spectra associated with the 1s to π* transition, attributed to the N—C bond, exhibited a slight intensity decrease. Conversely, the C K-edge spectrum in the a-CNx films displaying minimal photoinduced deformation remained unchanged under visible light irradiation. The N K-edge spectra maintained a consistent shape under both visible light and dark conditions.

Deposition of amorphous carbon nitride thin films using pressure-gradient RF magnetron sputtering and their chemical bonding structures

Amorphous carbon nitride (a-CNx) thin films were deposited through radio frequency (RF) magnetron sputtering under increasing nitrogen gas pressure around a graphite target to provide nitrogen radicals at high concentrations. The basic properties of the films, mainly chemical bonding structures, were evaluated using X-ray photoelectron spectroscopy (XPS), soft X-ray emission spectroscopy (SXES), and near-edge X-ray absorption fine structure (NEXAFS), and compared with other films deposited through the common sputtering mode, i.e., at a uniform gas pressure in the chamber. To increase the gas pressure around the graphite target, the deposition rate was slightly increased, and the chemical bonding structure of the a-CNx films was changed. However, the nitrogen content in the a-CNx films obtained from XPS analysis did not increase when the nitrogen gas pressure around the graphite target was increased. The effect of nitrogen incorporation on the a-CNx films was comparatively more effective at higher RF powers. The intensity ratio of sp3-σ and sp2-σ in the SXES spectra of the films increased with increasing RF power, from 85 W to 130 W, then decreased with a further increase in the RF power. This trend was confirmed by the peaks in the C K-edge of the NEXAFS spectra.

Electronic properties, bonding structure and mechanical behaviours of a-CNx: Si (: B) thin films

The electronic properties, bonding structure and mechanical behaviours of amorphous carbon nitride (a-CNx), silicon doped a-CNx (a-CNx:Si) and boron doped a-CNx (a-CNx:B) thin films alloys were studied by the C K-edge, N K-edge x-ray absorption near edge structure (XANES) and valence band photoelectron spectroscopy (VB-PES). The a-CNx:Si and a-CNx:B shows higher Young’s modulus compare to a-CNx thin film that are due to increase of carbon sp3-hybridized cluster in C and N K-edge XANES spectra. We have observed from the C and N K-edge XANES spectra that the formation of different carbon, nitrogen, silicon and boron bonding with carbon in the a-CNx:Si(:B) film structure. VB-PES spectra showed that the p-σ band became more intense than the p-π band upon the addition of silicon and boron in a-CNx film structure, which confirmed the role played by the σ bonds in controlling the electronic structure of a-CNx films and hence their mechanical behaviour. These films could be very useful in the surface coating technology.

Water electrolysis system based on a lithium cation-exchange membrane

The electronic properties, bonding structure and mechanical behaviours of amorphous carbon nitride (a-CNx), silicon doped a-CNx (a-CNx:Si) and boron doped a-CNx (a-CNx:B) thin films alloys were studied by the C K-edge, N K-edge x-ray absorption near edge structure (XANES) and valence band photoelectron spectroscopy (VB-PES). The a-CNx:Si and a-CNx:B shows higher Young’s modulus compare to a-CNx thin film that are due to increase of carbon sp3-hybridized cluster in C and N K-edge XANES spectra. We have observed from the C and N K-edge XANES spectra that the formation of different carbon, nitrogen, silicon and boron bonding with carbon in the a-CNx:Si(:B) film structure. VB-PES spectra showed that the p-σ band became more intense than the p-π band upon the addition of silicon and boron in a-CNx film structure, which confirmed the role played by the σ bonds in controlling the electronic structure of a-CNx films and hence their mechanical behaviour. These films could be very useful in the surface coating technology.

Visible light irradiation effects on chemical bonding structure of amorphous carbon nitride thin films using synchrotron radiation infrared rays

Using high-intensity infrared (IR) rays from the SPring-8 synchrotron radiation, we investigated the relationship between the photo-induced deformation and the in-plane distribution of the chemical bonding state of amorphous carbon nitride (a-CNx) thin films prepared via reactive sputtering. The film deposited at 573 K has the largest amount of photo-induced deformation and the film deposited at 873 K shows no photoresponse. When the beam diameter was reduced to a few micrometers, the films were irradiated with IR rays to obtain the IR spectra at each point on the film surface. Consequently, it was discovered that the chemical bonding state of the a-CNx thin films was not uniform in the plane, and that the spectral intensity in the range of 1100–1800 cm−1 was stronger or weaker depending on the location. When irradiated with a visible light laser, the absorption band spectral intensity was assigned based on a sixfold ring structure containing nitrogen and the CN chain increased by 8%–10% in a film that underwent photo-induced deformation. In the a-CNx film with no photo-induced deformation, no IR spectral irradiation change was observed.

Electrochemical Detection of Micro-RNAs on an Amorphous Carbon Nitride a-CNx Working Electrode in a Microfluidic Chip

Introduction Polymerase Chain Reaction (PCR) is the most common method for DNA detection. Based on DNA amplification at high temperature, it is hour lasting and not reliable for short DNA strands. Recently, on-chip electrochemistry has been used for direct quantification of nucleic acids, peptides and proteins, without chemical amplification unlike PCR protocol. Instead of integrating gold electrodes in microfluidic devices, carbon materials have demonstrated their performances such as carbon nanotubes or graphene. For instance, amorphous carbon nitride (a-CNx) films are widely used as electrode materials due to a large potential window (3V-4V) [1]. The a-CNx is a polarizable material with a chemical surface composition dependent on the atomic percentage of nitrogen incorporated during the deposition [2][3]. These properties are interesting for a microfluidic chip integrating a-CNx as working microelectrode for an electrochemical detection of microRNAs. In this communication, we will present the integration, activation and functionalization of a-CNx as a working microelectrode in a microfluidic chip for a 30 minutes detection of a 23 basis RNA sequence with a limit of detection of 10-18 M. Microfluidic Chip Fabrication The microfluidic chip is composed of an a-CNx working microelectrode (30 μm x 300 μm) and a platinum counter electrode (2 mm x 300 μm). To optimize the adherence and the conductivity of the a-CNx, a titanium/ platinum (20 nm/200 nm) underlayer is evaporated on a glass wafer. Then, the a-CNx (x=0.12) layer is deposited on the working microelectrode by DC magnetron sputtering (time: 20 min, power: 200 W, thickness: 200 nm) with a graphite target under a nitrogen flow (Ptot=0.4 Pa and PN2/Ptot=3 %). The microelectrodes were patterned by photolithography and lift-off processes in cleanroom. Then, the microfluidic chip is closed off with PDMS (ratio 1:10), patterned with a SU-8 mold and sealed by O2 plasma bonding. Method The a-CNx working microelectrodes in the microfluidic chip are electrochemically pre-treated by cyclic voltammetry between -1V and 0V with a scan rate of 50 mV/s during 7 minutes, in a 0.5 M sulfuric acid solution at a flow of 0.5 μL/s. The microelectrodes can then be individually functionalized by loading a DNA probe at 10-6 M. The COOH-modified probe sequence is activated by a 2.10-7 M EDC and NHS protocol in the microfluidic chip. Then, to stabilize the self-assembled monolayer a 0.5 M NaCl solution is loaded in the chip for 30 minutes. The targeted microRNA can then be loaded in the microfluidic chip at ultra-low concentration (10-18 M) at a low 0.02 μL/s flow rate for 30 minutes. The detection of the hybridization is done electrochemically by cyclic voltammetry around 0V at a 50 mV/s scan rate and electrochemical impedance spectroscopy between 1 MHz and 100 mHz in an equimolar 3 mM ferro/ferricyanide as the redox probe and 10-8 M methylene blue solution. Results and Conclusions The methylene blue acts as an intercalator in between the strands of the DNA duplex [4]. The electrons move from the a-CNx working electrode to the intercalated methylene blue before to be reduced by the ferrocyanate in solution. It implies a current level measurements more important for a double stranded DNA than a single stranded DNA. For a non-complementary microRNA target, the same protocol shows a decreased current. Thus, the electrochemical properties of a-CNx films are interesting for the development of a microfluidic chip for an electrochemical detection of microRNAs. Indeed, an attomolar detection in 30 minutes of a microRNA has been reached, as well as a specific recognition of the microRNA hybridized on the microelectrode surface.

(Invited) Microfabrication and Electrochemical Activation of Amorphous Carbon Nitride a-CNx Working Electrode Integrated in Microfluidic Chip

a-CNx films are well-known polarizable interface materials with a large potential window (3 V-4 V [1]) interesting electrochemical reactivity [2] and tunable chemical surfacic composition [3]. Indeed, the surface structure, surface properties, number of grafting sites available are tunable according to the atomic percentage of nitrogen in the a-CNx [4]. High surface reactivity are highly dependent on the surface state and can be affected by synthesis (by varying the Csp3/sp2 ratio), and by pre-treatment (electrochemical or plasma). In this work, we elaborated a microfluidic chip integrating a-CNx as working microelectrodes. In brief, a titanium/ platinum (50/500 Å) underlayer was first deposited on the glass wafer and patterned as working microelectrodes for the future thin film a-CNx adhesion and conductivity. On the top of the working electrode, a 220 nm a-CNx (x=0.12), layer was deposited with DC magnetron sputtering (time =20 min, power=200 W) with a graphite target under a flow of nitrogen (PN2/Ptot =3%, Ptot =0.4 Pa). Then, a classical PDMS fluidic circuit was microfabricated and pre-treated with nitrogen plasma to favor its adhesion onto the glass slide containing the Ti/Pt/ a-CNx microelectrodes. The a-CNx microelectrodes were also electrochemically pre-treated in galvanostatic mode using 0.1 M KOH solution (anodic pre-treatment). The hydrodynamic properties of the fluidic channel a-CNx microelectrodes (as-grown and pre-treated) were screened with the [Fe(III)(CN)6]3−/[Fe(II)(CN)6]4− redox couple by cyclic voltammetry and impedance spectroscopy to provide a basis for further investigations such as the influence of a-CNx electrode pre-treatment on the DNA probe density issues in order to enhance the hybridization reaction efficiency with its specific DNA target. [1]. A. Lagrini, C. Deslouis, H. Cachet, M. Benlahsen, and S. Charvet. Elaboration and electrochemical characterization of nitrogenated amorphou scarbon films, Electrochem. commun., 6(3) (2004) 245–248. [2]. G Adamopoulos, C Godet, C Deslouis, H Cachet, A Lagrini, and B Saidani. The electrochemical reactivity of amorphous hydrogenated carbon nitrides for varying nitrogen contents: the role of the substrate. Diam. Relat. Mater.,12 (2003) 613– 617. [3]. R A Medeiros, A Benchick, R C Rocha-Filho, O Fatibello-Filho, B Saidani, C Debiemme-Chouvy, and C Deslouis. Simultaneous detection of ascorbic acid and dopamine with electrochemically pretreated carbon nitride electrodes: Comparison with boron-doped diamond electrodes. Electrochem. commun., 24 (2012) 61–64. [4]. M Faure, F Billon, A M Haghiri-Gosnet, B Tribollet, C Deslouis, A Pailleret, and J. Gamby. Influence of the atomic nitrogen content in amorphous carbon nitride thin films on the modulation of their polarizable interfaces properties. Electrochim. Acta, 280 (2018) 238-247.

Effect of Radio Frequency Power on a-CNx Film Properties and Its Performance as Humidity Sensors

A series of amorphous carbon nitride (a-CNx) thin films were deposited on silicon (111) substrates using a home-built radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) system. The a-CNx thin films were deposited from a mixture of a fixed flow-rate of ethane (C2H6, 20 sccm) and nitrogen (N2, 47 sccm) gases with varying RF power. A higher ratio of C to H (C to H ratio is 1:3) atoms in C2H6 as compared to the ratio in methane (CH4) gas (C to H ratio is 1:4) is expected to produce an interesting effect to the film properties as humidity sensor. The characterization techniques used to determine the morphology and chemical bonding of the thin films are field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The variation of morphology and the existence of nitrile band in these samples are correlated with the electrical properties of a-CNx thin films. Using humidity sensing system, the sensing performance of the samples was examined. It was found that the response of sensors towards the percentage of relative humidity (% RH) change is good resistive responses and good repeatability. The sensitivity of the prepared a-CNx thin films is significantly higher (up to 79%) as compared to previous studies using CH4 or acetylene as precursor gas. Based on these results, the properties and the sensitivity of the a-CNx thin films towards humidity can be tailored by using an appropriate precursor gases and deposition parameters.

Non-uniform Excitation States in Photoinduced Deformation of Amorphous Carbon Nitride Films

Amorphous carbon nitride (a-CNx) films prepared via reactive radio frequency magnetron sputtering deform under on–off visible light illumination. We investigate the relationship between photoinduced deformation and surface electrical states via scanning electron microscopy with Ar+ laser irradiation (SEM-L). Two samples with different levels of photoinduced deformation are prepared. For the film with small photoinduced deformation, uniform secondary electron emission is observed on the film surface, regardless of whether the laser is on or off. On the a-CNx film, which has fifty times larger photoinduced deformation than the previous film, light and dark patches, similar to a speckle pattern, appear on the film surface in SEM-L images. This anomalous phenomenon indicates non-uniformity of the electrical states excited by laser light irradiation. A size of the patches is well correlated with an inhomogeneous distribution of sp3C and sp2C, Isp3C/Isp2C, obtained using soft X-ray emission spectroscopy (SXES). Simultaneously, temporal decrease in the sp3C component under illumination is obtained via SXES.

Soft X-ray emission spectroscopy study of characteristic bonding states and its distribution of amorphous carbon-nitride (a-CNx) films.

Soft X-ray emission spectroscopy based on electron microscopy was applied to investigate bonding electron states of amorphous carbon nitride (a-CNx) films with different nitrogen contents of x. Carbon K-emission spectrum showed characteristic intensity distribution of not only sp2 bonding but also sp3 bonding. The a-CNx film with lager x, which has a larger macroscopic electric resistivity, shows a larger content of the carbon sp3: C-C bonding signal. Furthermore, the dependence of spectral intensity distribution on x suggests the presence of sp2: C-N and sp3: C-N bonding. Those results show that the relation between macroscopic electrical resistivity of a-CNx film and its nitrogen content is because of the decrease of sp2: C-C bonding and the formation of sp2: C-N and sp3: C-C and C-N bonding conformation induced by an introduction of nitrogen atoms. Spatial variation of a signal ratio of sp3/sp2 was visualized and was confirmed as a relation between sp3 boding amount and nitrogen content x.

Deposition of amorphous carbon nitride films on flexible substrates by reactive sputtering for applications in light-driven active devices

Amorphous carbon nitride (a-CNx) thin films deposited by reactive sputtering have great potential for driving source applications of light-driven active devices. We demonstrate, for the first time, the photoinduced deformation of a-CNx deposited on flexible substrates, namely, poly(ethylene naphthalate) (PEN) films and transparent cellulose nanopaper. a-CNx films without delamination were obtained on both substrates. By decreasing the thickness of PEN films, the photoinduced deformation became extremely large. A light-driven pump was fabricated using a-CNx-coated PEN films, and then the pumping motion was observed up to 10 Hz. When a He–Ne laser traced the surface of a-CNx films deposited on the nanopaper, the sample moved to the opposite side of the laser spot. The motion involved repeated expansions and contractions similar to the motion of caterpillars occurring owing to the temporary photoinduced deformation of a-CNx films.

The effects of nitrogen partial pressure on the microstructure of amorphous carbon nitride films

ABSTRACTThe amorphous carbon nitride (a-CNx) films with varying nitrogen content were deposited on Si (100) wafers substrates using radio frequency magnetron sputtering (RFMS) from graphite target at different nitrogen partial pressure. The influence of nitrogen partial pressure on the microstructure and phase composition of a-CNx films were researched systematically. The films were characterized by atom force spectroscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). AFM results showed cluster structure in a range of tens to hundreds namometers existed on the surface of the films and the surface roughness increased with the increase of nitrogen partial pressure. Ratio of ID/IG increased with the nitrogen partial pressure, while the sp3 phase content from fitting results of XPS displayed reverse trend. The nanohardness of a-CNx films characterized by nanoindentation test decreased with the increase of nitrogen partial pressure, which consisted with the results of Raman and XPS. Thus high nitrogen partial pressure caused the mechanical properties of a-CNx films decrease.

Effects of anode layer linear ion source on the microstructure and mechanical properties of amorphous carbon nitride films

In order to study the effects of anode layer linear ion source(ALLIS)on the microstructure and mechanical properties of amorphous carbon nitride (a-CNx) films, a-CNx films were deposited by the ALLIS assisted radio frequency magnetron sputtering (RFMS) deposition condition changing the ion source power from 0 to 200W. The growth rate, structural morphology, surface roughness, nanohardness as well as the bonding states of deposited a-CNx films were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), nanoindentation, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. The H/E and hardness increased relatively with increasing the ion source power up to 100W. From the Micro Raman analysis, the content of sp3 carbon in sp3/sp2 ratio was increased with increasing the ion source power. The cross-sectional SEM images demonstrated that the ion source enhanced the growth rate of a-CNx films. Meanwhile, the roughness was increased with the ion source power above 100W. Therefore, the optimum ion source power is considered to be around 100W in these experimental conditions.

Interface features of carbon nitride films deposited on Si substrate

One kind of super-hard a-CNx film was deposited on Si substrate by the ion-beam assist magnetron sputtering. A clear interfacial layer with homogeneous thickness was found in the as-deposited film. The a-CNx layer spontaneous spalled along the interfacial defect, which indicated a high internal stress, resulting in adhesion failure. After thermal treatment, the interfacial layer between Ti layer and Si substrate seem to present a coherent or semi-coherent type with some misfit at the Si/SiOx grain boundaries. This mismatch relaxed the strain of the interface defects, and the high internal stress of the film was induced with a 3–5 atom-thick strained layer on Si substrate.

Contribution of nitrogen to the photoinduced deformation of amorphous carbon nitride films

Amorphous carbon nitride (a-CNx) films show photoinduced deformation under visible light illumination. To investigate the effect of nitrogen on this deformation, we compared the deformation of a-CNx films with that of nitrogen-free amorphous carbon films. The films were deposited on a rectangular ultrathin Si substrate to obtain the amount of deformation estimated from the bending curvature of the substrate. The amount of photoinduced deformation was increased by nitrogen incorporation. In the case of a nitrogen concentration (N/C) of 0.3, the deformation was under the detection limit of our apparatus. By detailed analysis of chemical bonding states, the amount of deformation was found to increase with increasing N/C ratio and N–sp3C/N–sp2C ratio, which increased with increasing nitrogen content. Furthermore, from the results of Fourier transform infrared spectroscopy, it is found that the photoinduced deformation occurred through the formation of triple bonds as the termination structures related to nitrogen and chain bonds.

Long-term irradiation effects of visible light on amorphous carbon nitride films

The effect of long-term visible-light irradiation on the photo-induced deformation of amorphous carbon nitride (a-CNx) films was investigated. a-CNx films were deposited on SiO2 substrates (30×2×0.05mm3) using reactive radio frequency magnetron sputtering. Deformation of the a-CNx films was measured using continuous wave (CW) or pulsed monochromatic light with a wavelength of 470nm. Pulsed light irradiation was applied for a total of 60min with an on/off pulse period of 60s, while CW light irradiation was performed for 120, 190, and 759min with different light intensities so that the total photon flux remained constant. In all cases, the extent of photo-induced deformation of the a-CNx films before and after irradiation did not change. The chemical bonding states determined from X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses indicated no significant changes after illumination. In addition, electron spin resonance (ESR) spectroscopy measurements indicated that there was no increase in the defect density after illumination. The long-term stability of a-CNx films is one of the main advantages for their use in light-driven microactuator systems.

Structural, electrical, and optical properties of amorphous carbon nitride films prepared using a hybrid deposition technique

Amorphous carbon nitride (a-CNx) thin films were prepared using a hybrid deposition technique (HDT), which is a combination of RF and DC magnetron co-sputtering of a graphite target. We varied the nitrogen gas flow ratio (GFR, N2/N2+Ar) during deposition to prepare a-CNx films with various nitrogen concentrations. The film properties were characterized using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The optical and electrical properties were also investigated. For 0.3<GFR<1, the optical band gap and resistivity increased with increasing nitrogen concentration (x=N/C) and sp3 C–N bonding fraction in the films. Compared to carbon nitride films with a comparable nitrogen content prepared by RF and DC sputtering, the optical band gap and resistivity of a-CNx films prepared by HDT were narrower and lower, respectively.

Low-temperature growth of low friction wear-resistant amorphous carbon nitride thin films by mid-frequency, high power impulse, and direct current magnetron sputtering

The potential of different magnetron sputtering techniques for the synthesis of low friction and wear resistant amorphous carbon nitride (a-CNx) thin films onto temperature-sensitive AISI52100 bearing steel, but also Si(001) substrates was studied. Hence, a substrate temperature of 150 °C was chosen for the film synthesis. The a-CNx films were deposited using mid-frequency magnetron sputtering (MFMS) with an MF bias voltage, high power impulse magnetron sputtering (HiPIMS) with a synchronized HiPIMS bias voltage, and direct current magnetron sputtering (DCMS) with a DC bias voltage. The films were deposited using a N2/Ar flow ratio of 0.16 at the total pressure of 400 mPa. The negative bias voltage, Vs, was varied from 20 to 120 V in each of the three deposition modes. The microstructure of the films was characterized by high-resolution transmission electron microscopy and selected area electron diffraction, while the film morphology was investigated by scanning electron microscopy. All films possessed an amorphous microstructure, while the film morphology changed with the bias voltage. Layers grown applying the lowest substrate bias of 20 V exhibited pronounced intercolumnar porosity, independent of the sputter technique. Voids closed and dense films are formed at Vs ≥ 60 V, Vs ≥ 100 V, and Vs = 120 V for MFMS, DCMS, and HiPIMS, respectively. X-ray photoelectron spectroscopy revealed that the nitrogen-to-carbon ratio, N/C, of the films ranged between 0.2 and 0.24. Elastic recoil detection analysis showed that Ar content varied between 0 and 0.8 at. % and increased as a function of Vs for all deposition techniques. All films exhibited compressive residual stress, σ, which depends on the growth method; HiPIMS produces the least stressed films with values ranging between −0.4 and −1.2 GPa for all Vs, while CNx films deposited by MFMS showed residual stresses up to −4.2 GPa. Nanoindentation showed a significant increase in film hardness and reduced elastic modulus with increasing Vs for all techniques. The harder films were produced by MFMS with hardness as high as 25 GPa. Low friction coefficients, between 0.05 and 0.06, were recorded for all films. Furthermore, CNx films produced by MFMS and DCMS at Vs = 100 and 120 V presented a high wear resistance with wear coefficients of k ≤ 2.3 × 10−5 mm3/Nm. While all CNx films exhibit low friction, wear depends strongly on the structural and mechanical characteristics of the films. The MFMS mode is best suited for the production of hard CNx films, although high compressive stresses challenge the application on steel substrates. Films grown in HiPIMS mode provide adequate adhesion due to low residual stress values, at the expense of lower film hardness. Thus, a relatively wide mechanical property envelope is presented for CNx films, which is relevant for the optimization of CNx film properties intended to be applied as low friction and wear resistant coatings.

Effect of RF Power on the Chemical Bonding and Humidity Sensing Properties of a-CN&lt;sub&gt;x&lt;/sub&gt; Thin Films

Amorphous carbon nitride (a-CNx) thin films were deposited using radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique. A set of a-CNx thin films were prepared using pure methane (CH4) gas diluted with nitrogen (N2) gas. The rf power was varied at 50, 60, 70, 80, 90 and 100 W. The characterization techniques used were Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscope (FESEM). Humidity sensing properties of the a-CNx thin films were investigated by recording their electrical response to relative humidity (RH) at room temperature. Chemical bonding analysis clearly showed the presence of nitrile bands in the deposited films. The FESEM images of the films show a porous, granule-like and dendritic morphology. The average resistance of the a-CNx thin film is changed from 23.7 kΩ to 5.8 kΩ in the range of 5 to 95%RH. The films show a good response and repeatability as a humidity sensing materials. This work showed that rf power has a significant effects on the chemical bonding, morphology and electrical properties of the a-CNx films.

Spectroscopic analysis of photo-induced deformation of amorphous carbon nitride films

Reversible photo-induced deformation of amorphous carbon nitride (a-CNx) films was investigated. The films were deposited at 400 and 600 °C on a rectangular shaped ultrathin SiO2 substrate by reactive radio frequency magnetron sputtering with graphite target and pure N2 gas. The amount of deformation change was estimated from bending curvature of a-CNx/SiO2 bimorph structure. For the film deposited at 400 °C, it bent toward the film side under illumination. Photo-induced deformation of the film estimated from the bending angle was observed in the excitation energy of 1.77 to 3.35 eV. The maximum deformation was observed under illumination of 2.6 eV which corresponds with π-π* bond of carbon nitride. In contrast, the deformation was hardly observed in the films deposited at 600 oC.The difference in these two films was probably due to difference in sp2 bonding and termination structures.