a-CNx Thin Films Research Articles

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.

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.

Increasing the Efficiency of Amino Acids Detection by Electrochemical Methods on Amorphous Carbon Nitride a-CNx Electrodes

Amorphous carbon nitride a-CNx thin films were elaborated on transparent and conductive glass/indium-tin oxide (ITO) wafers to improve the electroanalytical detection of transthyretin peptide (PN) and specific amino acids (AA) from its sequence which constitutes a great challenge for the diagnosis of transthyretin-related familial amyloïd polyneuropathy (ATTR). The naphthalene-2,3-dicarboxyaldehyde (NDA) label was used for the derivatization reaction of AAs to form N-2-substituted-1-cyanobenz-[f]-isoindole derivatives (CBI) which are both fluorescent and electroactive. The charge transfer resistance for all CBI derivatives permits to distinguish one AA from others, while no discrimination could be obtained using cyclic voltammetry where the peak potentials oxidation are too close enough.

Characterization of a-CNx Thin Films Prepared by RF-PECVD Technique for Humidity Sensor

In this work, amorphous carbon nitride (a-CNx) thin films were deposited by radio frequency (RF) plasma enhanced chemical vapor deposition (RF-PECVD) technique. The RF power and gas mixture of methane (CH4) and nitrogen (N2) flow was kept constant, while the electrode distance was varied from 1 to 6 cm. The effect of electrode distance on the chemical bonding, morphology and humidity sensing responses of the films were investigated. Fourier transform infra-red spectroscopy (FTIR) studies showed a systematic change in the spectra and showed three main peaks namely the G and D-peak, C≡N triple bonds and C-H/O-H groups. Uniform and porous morphology was observed for films deposited at smallest distance followed by non-porous cubicle-like grain as electrode distance increased. Subsequently formation of vertically aligned nanostructures apparent both from its surface and cross section images by increasing of electrode distance to the fullest. The humidity sensing property has been studied by recording their resistance response to relative humidity (RH) at room temperature. It was found that the resistance value decreases from 15.4 to 3.6 kΩ with the increase in RH from 9 to 85%, with the highest sensitivity of 77% for film deposited at smallest distance of 1 cm.

Influence of Deposition Time on Bonding and Morphology of Amorphous Carbon Nitride Thin Films

Amorphous carbon nitride (a-CNx) is a well-known material that can be used in various applications such as coating for hard disk, wear resistant, humidity sensor and others. In this research, a-CNx thin films have been deposited by using radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD) with the mixing of pure methane (CH4) and nitrogen (N2). The gas ratio of CH4/N2, electrode distance, pressure and temperature of deposition is kept constant while deposition time is allowed to vary from 30 to 150 minutes. Raman spectroscopy and field emission scanning electron microscopy (FESEM) have been used to study the bonding and morphology of these films respectively. An increase in deposition time resulted with thedecrease in sp2 content in the a-CNx thin films. Theincrease in the Id/Ig intensity ratio with the increase in deposition time can be explained by the reducing size of graphitic cluster. Long deposition time retarded the growth rate of a-CNx thin films due to etching effects. Longer exposure to the etching effect resultingin the creation of small graphitic cluster with the formation of spongy-like porous features.

Effect of RF Power on the Chemical Bonding and Humidity Sensing Properties of a-CN<sub>x</sub> 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.

Structural and optical properties of boron-doped amorphous carbon nitride thin films synthesized by microwave electron cyclotron resonance-plasma chemical vapor deposition

The structural and optical properties of boron (B)-doped amorphous carbon nitride (a-CNx) thin films with a B content of less than 10 at. % were investigated. The B-doped a-CNx thin films were synthesized by electron cyclotron resonance (ECR)-plasma chemical vapor deposition (CVD) by varying the substrate temperature and flow rate ratio of the source gases (BCl3/CH4/N2/Ar). An increase in the B content and a decrease in the Cl content were observed with increasing substrate temperature. The Tauc energy gap of the B-doped a-CNx thin films increased with decreasing C–N sp2 bond fraction and increasing B content. The photoluminescence (PL) peak position showed larger blue shifts and a tendency of increased integrated PL intensity was observed with increasing B content. These PL results suggest an increase in PL-active B-related sp2 C–C bond cluster density.

Optimizing rf Power for Preferential C≡N Bond Formation in a-CNx Thin Films Prepared by rf-PECVD Technique

Effects of rf power on the chemical bonding in carbon nitride films deposited using radio-frequency (rf) plasma enhanced chemical vapor deposition in pure methane and nitrogen gas mixtures were investigated. The rf power was varied from 60 to 100 W. The deposition rate of the films increased constantly with increasing rf power up to 80W, before saturating with further increase in rf power. Fourier transform infra-red spectroscopy (FTIR) studies showed a systematic change in the spectra and revealed three main peaks namely the G-peak, D-peak and C≡N triple bond. This work showed that rf power has significant effects on the chemical bonding of the a-CNx films and the optimum rf power for the high C≡N absorption intensity is 80 W.

Change in Surface States of Amorphous Carbon Nitride Films after Exposure to Oxygen Plasma

Amorphous carbon nitride (a-CNx) thin films were deposited by rf-reactive sputtering method using a graphite target, and after deposition the films were exposed to oxygen plasma. The effect of the oxygen plasma exposure on the morphology and chemical bonding states of the film surface has been studied. Film composition and the chemical bonding states were analyzed by X-ray photoelectron spectroscopy (XPS). Film surface was observed by atomic force microscopy (AFM). AFM observations have revealed that the as-deposited film surface is uniformly covered with particle-like features in the early stage of deposition and the surface changes to be covered with broccoli-like features with increasing the deposition time and correspondingly the surface roughness increases, while after exposure to oxygen plasma, the film surface was etched selectively and the surface roughness increases with the plasma exposure time. It should be noted that the etching behavior depends on the film deposition temperatures. XPS studies have shown that after exposure to oxygen plasma the change in the bonding states in the films prepared at 853 K is different from that in the films prepared at RT.

Effect of oxygen plasma treatment on bonding states for columnar structured a-CNx thin films prepared by reactive sputtering

Amorphous carbon nitride (a-CN) thin films were deposited on silicon single crystal substrates by rf-reactive sputtering method using a graphite target and nitrogen gas. The substrate temperature was varied from room temperature (RT) to 853K. After deposition, the effect of oxygen plasma treatment on bonding structures of the film surface has been studied by using an oxygen discharge at 16Pa and rf power of 85W. The chemical bonding states and film composition were analyzed by X-ray photoelectron spectroscopy (XPS), while film thickness was obtained from scanning electron microscopy (SEM) and ellipsometer. XPS study revealed that the films have NO2 and NO3 bonding structures when the films are deposited at temperatures higher than 673K. After exposure to oxygen plasma, carbon in the film surface was etched selectively and this phenomenon was observed in all films. In contrast, the surface concentration of nitrogen was ket at constant values before and after oxygen plasma treatment. The NO3 bonding state had dramatically increased after oxygen plasma treatment for films deposited at higher deposition temperatures. The film surfaces have been observed to change the function from hydrophobic to hydrophilic after oxygen plasma treatment.

Studies on optical and photoluminescence properties of a-CNx thin films

Amorphous carbon nitride (a-CNx) thin films of different thicknesses were deposited by radio frequency plasma enhanced chemical vapour deposition technique by varying the deposition times. The refractive index, film thickness and optical energy gap were obtained from the optical transmission spectrum of the film in visible wavelength region. The photoluminescence emission intensity and wavelength due to ultraviolet excitation were studied and analysed. The effects of deposition time and film thickness on these properties were investigated. The deposition rate decreased with increasing deposition time to a stable saturation value. The optical energy gap decreased with increasing film thickness which is attributed to increase in presence of sp2 bonding clusters in the film structure. Photoluminescence emission intensity and wavelength also showed dependence on film thickness.

Sp2 and sp3 bonding configurations in low nitrogen content a-CNx thin films

The results of an electron spectroscopy study carried out on a set of pulsed laser deposited CNx films are reported. A progressive degree of graphitization, deduced from the continuous increase in the sp2 bond fraction, has been found for x values up to 25%. The mass density values, deduced by a proper treating of both the x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy data, are consistent with a material made up by two phases, namely a sp2 threefold (graphite-like) and a sp3 fourfold (diamond-like) coordinated one. The behaviour of the density of the samples as a function of the N content does not show any abrupt change in going from lower to higher nitrogen concentrations as found by other authors, this certainly being due to differences in the starting sp3/sp2 ratio of the films at zero N concentration and to their different preparation parameters.

Irradiation Effect of Nitrogen Ion Beam on Carbon Nitride Thin Films

ABSTRACTIrradiation effect of low-energy nitrogen ion beam on amorphous carbon nitride (a-CNx) thin films has been investigated. The a-CNx films were prepared on silicon single crystal substrates by hot carbon-filament chemical vapor deposition (HFCVD). After deposition, the CNx films were irradiated by a nitrogen ion beam with energy from 0.1 to 2.0 keV. Irradiation effect on the film microstructure and composition was studied by SEM and XPS, focusing on the effect of nitrogen ion beam energy. Surface and cross sectional observations by SEM reveal that the as-deposited films show a densely distributed columnar structure and the films change to be a sparsely distributed cone-like structure after irradiation. It is also found that 2.0 keV ions skeltonize the films more clearly than 0.1 kev ions. Depth profiles of nitrogen in the films observed by XPS show that nitrogen absorption into films is more prominent after irradiation by 0.1 keV nitrogen ions than 2.0 keV ions.

Chemical analysis of a-CNx thin films synthesized by nanosecond and femtosecond pulsed laser deposition

Chemical analysis of a-CNx thin films synthesized by nanosecond and femtosecond pulsed laser deposition

Characterization of nitrogen in a-CNx thin films by gas effusion spectroscopy

The evolution and characterization of nitrogen N2 in amorphous CNx (a-CNx) have been studied by using gas effusion spectroscopy. In gas effusion spectra for a-CNx thin films, N2 evolution peaks are found near 200, 400, 600 and 700°C. The N2 peak near 200°C disappears after hydrogen plasma treatment. In the gas effusion spectrum of H2 for a sample treated by hydrogen plasma, a very small shoulder would be found near the temperature of the H2 evolution peak in chemical vapor deposited diamond. By ultra-violet irradiation, the amplitudes of the N2 evolution peaks above 400°C increase and the x=N/C ratio obtained by X-ray photo-electron spectroscopy increases from 0.5 to 0.7. From these results and comparison with other works, the origin of the N2 evolution peaks near 200 and 400°C could be estimated as N2 related to a graphite-like structure and N2 from CN, respectively, and either N2 evolution near 600°C or near 700°C, or both, could be related to CN bonds.