Radio-frequency Plasma-enhanced Chemical Vapor Deposition Research Articles

Ethanol-Precursor-Mediated Growth and Thermochromic Applications of Highly Conductive Vertically Oriented Graphene on Soda-Lime Glass.

Direct growth of vertically oriented graphene (VG) nanowalls on soda-lime glass has practical significance in extending the application of graphene to daily-life-related areas, such as gas sensors and conductive electrodes, via combining their complementary properties and applications. However, VG films derived by low-temperature deposition (e.g., on glass) usually present relatively low conductivity and optical transparency. To tackle this issue, an ethanol-precursor-based, radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) route for the synthesis of VG nanowalls is developed in this research, at around the softening temperature of soda-lime glass (∼600 °C) templates. The average sheet resistance, i.e., ∼2.4 kΩ·sq-1 (at transmittance ∼81.6%), is only one-half of that achieved by a traditional methane-precursor-based PECVD route. Based on the highly conductive and optically transparent VG/glass, as well as its scalable size up to 25 in. scale, high-performance reversible thermochromic devices were successfully constructed using VG/glass as transparent heaters. Hereby, this work should propel the scalable synthesis and applications of highly conductive VG films on glass in next-generation transparent electronics and switchable windows.

Advanced fractal analysis of nanoscale topography of Ag/DLC composite synthesized by RF-PECVD

ABSTRACTWe present an advanced image analysis study of the 3D surfaces of silver/diamond-like carbon nanocomposite films prepared by radio-frequency plasma-enhanced chemical vapour deposition. Atomic force microscopy data were analysed, with the goal to provide image analysis tools allowing for a better understanding of the structure–property correlation, with specific case for the present material. While the samples' fractal dimension decreased and the roughness increased with increasing deposition time, fractal succolarity showed no significant difference and relatively high values, describing high percolation, and fractal lacunarity decreased, in agreement with topographic entropy, which revealed uniformity in height distribution. In conclusion, the samples' microtexture shows a nearly uniform surface with a homogenous distribution of nanoparticles, due to the fabrication process and the emerging fractal nature of the nanocomposite, at all the considered deposition times. Fractal lacunarity and succolarity, currently not provided by commercial image analysis programmes, can be useful in advanced surface image characterization.

Titanium(IV) isopropoxide as a source of titanium and oxygen atoms in carbon based coatings deposited by Radio Frequency Plasma Enhanced Chemical Vapour Deposition method

This paper presents properties of TiOx-DLC (titanium oxides incorporated diamond like carbon) coatings deposited by RF PECVD (Radio Frequency Plasma Enhanced Chemical Vapour Deposition) method using combination of methane (CH4) and titanium(IV) isopropoxide (Ti[OCH(CH3)2]4) atmospheres. The obtained results show that the deposition process of TiOx-DLC coatings is strongly affected by the concentration of TTIP (titanium (IV) isopropoxide) precursor in working atmosphere. The proposed technology allows to obtain TiOx-DLC coatings with Ti concentration up to 10 at.%. Higher concentrations of Ti in the coating (5 and 10 at.%) result in twice the concentration of oxygen. As the results of the investigation it was noticed, stable TiOx-DLC coatings showing acceptable hardness and residual stress, as well as good optical properties contain up to 1.5 at.% of Ti and can be deposited at 400 V of the negative self-bias using 0.05 of TTIP partial pressure ratio.

3_D surface stereometry of Ag/DLC nanocomposite prepared by RF-PECVD

In this study, a stereometric analysis of the three-dimensional (3-D) surfaces of the Ag/diamond-like carbon (DLC) nanocomposite films was done. The nanocomposite thin films were fabricated by Radio Frequency Plasma-Enhanced Chemical Vapour Deposition (RF-PECVD). The 3-D surface microtexture was studied by high-resolution Atomic Force Microscopy (AFM) records combined with statistical analyses. More detailed information about surface statistical parameters and topographic features of analyzed samples were performed. The statistical parameters relating to the segmented motifs consistent with ISO 25178-2: 2012 have been generated using MountainsMap® Premium software. The analysis was performed by modeling Ag/DLC nanocomposite surface microtexture based on motif analysis (detection of essential characteristics in terms of surface dimensions, volume, curvature, shape) to be included in computer interactive simulation algorithms.

The effect of bias voltage and methane concentration on chemical structure and breakdown strength of polymer-like hydrogenated carbon (PLCH) dielectric films

The purpose of this study was to determine the effect of bias voltage and methane-to-argon gas ratio on molecular structure and dielectric breakdown strength of polymer-like hydrogenated carbon (PLCH) thin films deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). This study was one of several efforts to find a dielectric material suitable for fabricating very high energy density thin film capacitors. The highest energy density (Ue = 4.13 J/cm3) and breakdown strength (7.2 MV/cm) were measured on capacitors fabricated using a PLCH dielectric deposited at 100 V bias and 50% methane concentration. It was found that energy density is due to the high concentration of sp3 carbons and aromatic sp2 carbons in the films.

Experimental evidence of photonic band gap in hybrid Si/SiNOCH multilayer structure at the infrared range

Hybrid one dimensional photonic crystal (1D PC) based on alternating layers of inorganic materials, the silicon (Si), grown by radiofrequency magnétron sputtering and organic compound, HMDSO mixed with nitrogen N2 (HMDSO+N2), deposited by radiofrequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) for different N2/HMDSO flow rate at a fixed power of 200W. As the refractive index of silicon (Si) is n=3.4, to obtain a good contrast index between the inorganic and organic layers leading to appearance of large photonic band gap, we have varied the flow of the mixed gaz (HMDSO+N2) for having a lower refractive index 1.7 corresponding to a layer with the same chemical composition element of the SiNOCH material as confirmed by IR measurement. After optimization of the Si and SiNOCH thickness layers with respect to the Bragg low, we have measured the photonic band gap (PBG) of Si/SiNOCH photonic structure through transmission and reflection spectra. The PBG appears after 5 periods of alternating layers with a width of 740 nm in the near infrared (NIR) region centered at 1500 nm. Our experimental results are interpreted successfully by a theoretical model based on the transfer matrix method (TMM).

Gas permeation properties and preparation of carbon membrane by PECVD method using indene as precursor

This work could demonstrate a new approach to the fabrication of gas separation membrane using indene as polymeric precursor for low pressure PECVD system. Membrane characterization was done by taking Scanning Electron Microscopy (SEM) and FTIR measurements. For membrane performance testing, permeability and selectivity of the membrane were evaluated with pure gases of H2, N2, and CO2 using a differential permeation technique. PECVD-derived polyindene membrane showed selectivities of 8.2 and 4.0 for H2/CO2 and H2/N2, respectively, at room temperature. Polyindene (PIn) membrane was successfully fabricated onto a zeolite 5A substrate via radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at room temperature.

Optical Transmission of p-Type a-Si:H Thin Film Deposited by PECVD on ITO-Coated Glass

A p-type thin film of hydrogenated amporphous silicon (a-Si:H) has successfully been fabricated by radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD) technique. Substrate used in the deposition process is indium tin oxide (ITO) layer coated having size of 10 x10 cm2 and being cleaned with 97% alcohol using ultrasonic bath. According to Atomic Force Microscope (AFM) observation, the layer thickness of p-type a-Si: H film was 150 nm. The Transmission spectrum at room temperature obtained from UV-Vis measurement demonstrates a large period modulation, which is due to the interference within the film. At wavelength longer than 1000 nm (or energy <1 eV), the interference modulation in the transmission spectrum of the film is seen to broaden. It is shown in a zoomed - scale around the related band gap area that one may find an exciton structure.

Fabrication of Amorphous Carbon Thin Film from CH<sub>4</sub> Using PEVCD

Thin films of amorphous carbon have successfully been fabricated by radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD). Carbon film fabrication with a methane gas (CH4) source has been fabricated with deposition parameters: 15 Watt of RF power, 13.5 MHz of frequency, 100 °C of substrate temperature, 450 m Torr of pressure and 120 minutes of deposition time. Methane gas flows were 40, 60, 80 sccm, respectively. Thin film can be in the form of DLC, Graphite or Amorphous Carbon depending on the ratio of hybridized orbitals of sp3, sp2 and sp. The X-ray diffractrometry (XRD) show the amorphous phase of the thin film has been formed. Further analysis using Fourier transform infrared (FTIR) combined with synchrotron photoemission spectroscopy (PES) showed that the sp3 hybridization was more dominant than sp2. This gives an indication that as fabricated thin films are tetrahedrally amorphous carbon (ta-C). Keywords: Amorphous carbon, methane gas, thin film.

Optical detection of CO gas by the surface-plasmon resonance of Ag nanoparticles and nanoclusters synthesized on a hydrogenated amorphous carbon (a-C:H) film

Ag nanoparticles were deposited on a hydrogenate amorphous carbon (a-C:H) thin film as a host by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) for various deposition times. We observed that as the sputtering time increases, the particle shape of the deposited nanostructures changes to a cluster shape. AFM images show that the accumulation of the nanoparticles on each other leads to the vertical growth of the nanoclusters. According to X-ray diffraction patterns, the crystalline structure is formed for the nanocluster shape. The Fourier-transform infrared (FTIR) spectroscopy showed that bonds are formed between Ag ions and free hands of carbons on the surface of the a-C:H film. The peak related to carbide structures is seen around 2100cm^-1. UV-Vis spectroscopy demonstrates that the formation of Ag nanoclusters leads to the appearance of a sharp plasmonic peak, shifted towards longer wavelengths. The plasmonic peak of Ag was used for detecting CO gas in the ambient air. The adhesion of CO molecules to the Ag particles makes a significant change in the plasmonic peak. In the presence of CO gas flow, the localized surface plasmon resonance (LSPR) of Ag nanoclusters moves to a longer wavelength (red-shift) and the LSPR intensity increases. The sample with a nanocluster structure is a better adsorber for CO molecules due to its larger specific surface area.

Preparation, Characterization, and Performance Control of Nanographitic Films.

Using methane as a carbon source, low-dimensional carbon nanomaterials were obtained in this work. The films were deposited directly on glass substrates by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD). The configuration and compositions of this nanographite films were identified by X-ray photoelectron spectroscopy (XPS) as carbon in sp2 bonding form. Raman spectral characterization verified the configuration of the films to be hexatomic ring of carbon atoms. As a result, they were found to be nanographite films (NGFs). Also, the atomic force microscopy (AFM) topography and Raman spectra of different areas demonstrated the diversity of the films at the nano scale. The high light-transmitting and electron mobility indicated that the NGFs possessed excellent optic-electronic properties and could be used as good photoelectrical function materials. Furthermore, the physical and chemical growth mechanism of NGFs were analyzed by PECVD. NGFs could be obtained in a controlled process by modulating the growth conditions. In this work, the complicated transfer process commonly used for optoelectronic devices could be avoided. Also, by growing the films directly on a glass substrate, the quality degradation of the film was not a problem. This work can further promote the development of next-generation electronic or optoelectronic function materials, especially for their application in transparent conductive electrode fields.

Transparent Electrothermal Heaters Based on Vertically-Oriented Graphene Glass Hybrid Materials.

Transparent heating devices are widely used in daily life-related applications that can be achieved by various heating materials with suitable resistances. Herein, high-performance vertically-oriented graphene (VG) films are directly grown on soda-lime glass by a radio-frequency (rf) plasma-enhanced chemical vapor deposition (PECVD) method, giving reasonable resistances for electrothermal heating. The optical and electrical properties of VG films are found to be tunable by optimizing the growth parameters such as growth time, carrier gas flow, etc. The electrothermal performances of the derived materials with different resistances are thus studied systematically. Specifically, the VG film on glass with a transmittance of ~73% at 550 nm and a sheet resistance of ~3.9 KΩ/□ is fabricated into a heating device, presenting a saturated temperature up to 55 °C by applying 80 V for 3 min. The VG film on the glass at a transmittance of ~43% and a sheet resistance of 0.76 KΩ/□ exhibits a highly steady temperature increase up to ~108 °C with a maximum heating rate of ~2.6 °C/s under a voltage of 60 V. Briefly, the tunable sheet resistance, good adhesion of VG to the growth substrate, relative high heating efficiency, and large heating temperature range make VG films on glass decent candidates for electrothermal related applications in defrosting and defogging devices.

Effect of Seed Layer and Thermal Annealing on Structural and Optical Properties of Silicon Layers Deposited by PECVD

Hydrogenated silicon (Si:H) layers have been deposited on crystalline silicon substrate by radiofrequency plasma-enhanced chemical vapor deposition technique (rf-PECVD) from SiH4/H2 gas mixture using different deposition times and after a seed layer with thickness of 70 nm (to improve the nucleation of nanocrystallites). The effect of the deposition time on the as-deposited and annealed layers was investigated. Ultraviolet–visible–infrared (UV–Vis–IR) spectroscopy was used to determine the thickness of the layers. Before annealing, the layer thickness showed a linear variation with deposition time in the range from 450 s to 1500 s. On the other hand, for deposition times of 450 s, 600 s, and 1500 s, the layers showed an x-ray diffraction (XRD) peak corresponding to the (111) crystal plane of Si. Raman spectroscopy confirmed the appearance of the crystalline phase in these layers. Raman scattering studies showed that, when using the short deposition time for the top layer, the crystalline peak dominated. We deduce that insertion of a seed layer improves the crystallinity of the top layer. In addition, the crystallinity increased slightly with the deposition time. The structural properties of the layers annealed at 900°C were studied by Raman spectroscopy and XRD analysis. We noted an increase in the crystalline volume fraction and the appearance of (111) crystal plane of silicon, confirming the transition from amorphous to nanocrystalline phase for all the annealed films.

Crystallization of hydrogenated amorphous silicon thin film on glass by using ns-pulsed fiber laser operating at 1064 nm

A nanosecond pulsed, Ytterbium doped optical fiber laser, operating at 1064 nm, has been used for laser induced crystallization (LIC) of a standard recipe-hydrogenated amorphous silicon (a-Si:H) thin film, deposited in a radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) reactor. Despite relatively lower photon energy of 1.165 eV, the crystallization of the a-Si:H sample with the Tauc gap of 1.70 eV was succeeded. The optical energy density impinging on the sample surface was adjusted by the treatment parameters: average output power, repetition frequency and scanning speed. The laser spot energy density was varied mainly from 7.1 to 49.5 J/cm2. By using Raman scattering, scanning electron microscopy (SEM) and Fourier-Transform infrared (FTIR) spectroscopy, the LIC of the sample was investigated both quantitatively and qualitatively. Depending on the magnitude of the spot energy density, the crystal fraction of the sample could be adjusted between 16% and 99%. We have suggested a threshold spot energy density of 21.2 J/cm2, for a large crystal volume fraction of 60%. For smaller energy densities, sub-micrometer sized crystal structures were formed. The nano-scaled silicon grains of 3.05 nm has been reached by decreasing the laser energy density to 7.1 J/cm2. Since the crystallization of large fractions, as much as 99%, is possible with the increase of the laser spot energy density, the nanosecond pulsed 1064 nm laser is a possible candidate to produce crystal silicon on glass (CSG), for photovoltaic applications.

Role of Hydrogen Flow Rate on Microstructure of a-Si:H(n) Films: Spectroscopic Ellipsometry Studies

The influence of hydrogen flow rate on the microstructure and optical properties of phosphorous doped hydrogenated amorphous silicon (a-Si:H(n)) films is studied through spectroscopic ellipsometry (SE). A series of a-Si:H(n) films were deposited using radio frequency plasma enhanced chemical vapour deposition (RFPECVD) technique by varying the hydrogen flow rate (HFR) in the range of 30–80 SCCM. The SE measurements showed a shift in peak position of pseudo dielectric function of these films from 3.6 eV (for pure a-Si:H) to 4.1 eV with a shoulder peak at 3.4 eV (nanocrystallites embedded a-Si:H) as the hydrogen flow rate was increased. A systematic increase in crystalline fraction along with a decrease in void fraction was observed as HFR was increased up to 70 SCCM during deposition. The results confirm that hydrogen dilution helps in improving the microstructure of films and favours the formation of strong Si–H bonds. Beyond 70 SCCM of HFR, a large flux of hydrogen resulted in an increase in void fraction and disorder in the films.

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.

Stability of hydrogenated amorphous carbon thin films for application in electronic devices

In this study, hydrogenated amorphous carbon (a-C:H) films are investigated for electronic applications as an insulating layer. a-C:H films were deposited using Radio Frequency-Plasma Enhanced Chemical Vapour Deposition (RF-PECVD) technique at room temperature. For the first time, the properties of a-C:H films as a function of annealing temperature is investigated, with a focus on their electrical and optical properties. This study shows that a-C:H films are stable up to 450 °C. This investigation will facilitate the use of a-C:H films as an insulating layer where the semiconductor active layers are deposited at higher temperatures (e.g. amorphous silicon deposited around 300 °C for thin film transistor TFTs). In addition to understanding the electrical and optical properties of annealed a-C:H films, we have further explored and studied its suitability in Flash-type memory devices. Various forms of diamond-like carbon are considered to have a high chemical resistance; no extensive data are available in the literature on this subject. The stability of a-C: H thin films with variousreactive chemicals, commonly used in organic/printable electronic devices, is also investigated in this work. The findings may provide opportunities for adoption/integration of a-C:H in hybrid organic-inorganic electronic devices.

Structure and electrical properties of boron doped hydrogenated mixed-phase silicon films for uncooled microbolometer

Boron doped hydrogenated silicon films used as thermo-sensing layers in infrared detectors or uncooled micro-bolometers are prepared by radio-frequency plasma-enhanced chemical vapor deposition (PECVD). In this work, we investigated TCR (higher the better) and sheet resistance, Rsheet (lower the better), which are important factors for thermos-sensing layer used in uncooled microbolometer. The crystalline volume fraction (Xc) of films is controlled to get silicon films that satisfy the characteristics of high TCR and low Rsheet. Through the control, amorphous, mixed- and microcrystalline phases were identified. As a result, the best TCR and Rsheet were obtained in the mixed-phase. For the films, TRC is around 1–3%/K, Rsheet is around 3–61.4 MΩ/□ and Xc is around 7–17%. The 1/f noise is measured for various phases. It is found that 1/f noise of boron doped hydrogenated mixed-phase silicon (BMP-Si:H) is smaller than that of the amorphous phase. The results of BMP-Si:H films show that they are more suitable as thermos-sensing layers than boron doped hydrogenated amorphous silicon films.

Composition dependent microstructure and optical properties of boron carbide (BxC) thin films deposited by radio frequency-plasma enhanced chemical vapour deposition technique

BxC thin films were deposited on silicon (100) and sodalime glass substrates using Radio Frequency Plasma Enhanced Chemical Vapour Deposition (RF-PECVD) technique, at different substrate self-bias varying from -100V to -250V. Optical property, structure and stoichiometry of the films were determined by spectrophotometry, X-ray diffraction and proton elastic backscattering spectrometric measurements respectively to investigate the effect of film composition on microstructure and optical properties. Film refractive index at a typical wavelength of 400 nm increased from 1.87 to 1.97 on account of increasing packing density of the films with substrate self- bias. Decrease in direct and indirect optical band gap with increasing substrate self-bias, has been explained on the basis of compositional variation i.e. boron/carbon stoichiometric ratio. Finally, soft X-ray reflectivity in the wavelength range of 40 Å–360 Å has been measured to explore its potential for application as optical material in this region of electromagnetic spectrum.

Effect of Plasma Oxidation-Treated TiOx Film on Early Osseointegration.

To develop a TiOx film with high wettability using plasma oxidation methodology and to evaluate the effect of such surface modification on new bone formation and early osseointegration. Twenty sandblasted and acid-etched (SLA) titanium implants layered with a TiOx film layer were modified by plasma oxidation using a Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RFPECVD) system. Twenty SLA implants without any treatment were employed as the control group. Scanning electron microscopy was used to evaluate surface morphology of the coating. X-ray photoelectron spectroscopy (XPS) was utilized to identify the chemical composition of the implant surface, and the wettability was tested with the help of the contact angle calculation. All implants were randomly inserted into the proximal tibia of 20 rats with a split-plot design. Four weeks after implantation, early osseointegration of the two groups was analyzed by a removal torque test and histologic analysis. The surface characteristics showed that both SLA and plasma oxidization-treated SLA (PO-SLA) surfaces displayed similar typical isotropic irregular indentations. As revealed by the XPS analyses, both TiO2 and Ti2O3 were coexistent in the PO-SLA surface. The contact angle measurement revealed that the super-hydrophilic surface was created out in the PO-SLA surface. Four weeks after implantation, a higher removal torque value was observed in the group of implants with the PO-SLA surface compared with the control group (12.68 ± 1.07 vs 9.95 ± 1.42 Ncm, P < .05), and a higher rate of bone-to-implant contact was also detected in the same group of implants with the PO-SLA surface (47.79% ± 9.59% vs 39.41% ± 9.00%, P < .05). The bone area ratio was also higher in the PO-SLA surface group than the control group (39.10% ± 10.01% vs 29.01% ± 7.24%, P < .05). It was indicated that the PO-SLA surface has combined the effect of high wettability and micro/nano-structures to notably increase early bone apposition.