Plasma Enhanced Chemical Vapor Deposition Research Articles

Deposition of carbon nanolayers by PECVD on ceramic substrates

Graphene layers and nanostructures were deposited on silicon dioxide (SiO2/Si) and silicon carbide (SiC) substrates at low gas pressure (1 – 5 torr) by microwave discharge PECVD (Plasma Enhanced Chemical Vapor Deposition). The advantage of this method is the relatively low temperature (600-700°C) of the substrate in the deposition process. The diffusion processes of hydrocarbon radicals on the surface of the substrates have a significant effect on the homogeneity of deposited structures. The deposited graphene nanotubes on SiC were analyzed by scanning electron microscope (SEM) and Raman spectroscopy is applied for characterization of the graphene layers. The deposited carbon layers on SiO2 were analyzed by atomic force microscope and their thickness (12-20 nm) were determined.

Deposition of vertical carbon nanostructures by microwave plasma source on nickel and alumina

Vertical carbon nanostructures on metal and ceramic substrates are deposited successfully using planar microwave plasma source at frequency of 2.45 GHz. The PECVD (Plasma Enhanced Chemical Vapor Deposition) with microwave surface wave discharge is applied because it produces a dense plasma providing efficient decomposition of the methane and creation of a large number of reactive particles which results in lower substrate temperature for graphene deposition compared to CVD method. Optimization of the gas mixture of H2, Ar and CH4, and the gas pressure in the chamber results in a homogeneous graphene structures deposition on the substrates of Ni-foil, Ni-foam and alumina ceramics at substrate temperatures ∼600 °C. The plasma parameters of surface wave discharge such as gas temperature, electron temperature and density are obtained by measuring OH-band and Ar-lines using optical emission spectroscopy. The morphology of the vertical carbon structures is obtained using SEM analysis and the characteristics of the graphene layers were determined by Raman spectroscopy.

Characterization of a Heterojunction Silicon Solar Cell by Means of Impedance Spectroscopy.

Impedance spectroscopy provides relevant knowledge on the recombination and extraction of photogenerated charge carriers in various types of photovoltaic devices. In particular, this method is of great benefit to the study of crystalline silicon (c-Si)-based solar cells, a market-dominating commercial technology, for example, in terms of the comparison of various types of c-Si devices. This study investigates the dark and light electrophysical characteristics of a heterojunction silicon solar cell fabricated using plasma-enhanced chemical vapor deposition. The measurements are performed at various applied biases, enabling the determination of complex resistance, characteristic time, capacitive response and impurity concentration within the semiconductor junction and to correlate them with the device performance. In addition, the impedance spectra of the studied cell were investigated as a function of temperature. Studies of the frequency and temperature dependences of capacitance do not reveal a significant presence of thermally activated centers of free carrier capture, concomitant with a very small value of the activation energy extracted from an Arrhenius-type analysis. This leads to a conclusion that these centers are likely not impactful on the device operation and efficiency.

Effect of C2H2 flow rate on microstructure, properties, and application in micro-drilling of a-C:H films deposited by PECVD

The drilling of printed circuit board (PCB) using micro-drills is an important processing method in modern industry. A protective film with good lubricating and anti-wear properties is generally applied to improve the processing problems of micro-drills during operation. In this study, the effects of C2H2 flow rate on the microstructure, mechanical, and tribological properties of a-C:H films deposited by plasma enhanced chemical vapor deposition (PECVD) technique were investigated. The results showed that when the C2H2 flow rate was low, varying the flow rate had little effect on the microstructure of the prepared a-C:H films. However, when the C2H2 flow rate was greater than 210 sccm, the increase in flow rate caused large particles of carbon clusters to aggregate on the surface of a-C:H films, which resulting in an increase Ra value. Not only did it reduce the adhesion between the film and the substrate, but it also deteriorated the mechanical and tribological properties of the a-C:H film produced. In addition, a-C:H films were also deposited on the micro-drill, and were used for drilling tests on the PCBs to evaluate its servce capability. The optimal parameters of a-C:H film deposited on the micro-drill surface were obtained by observing the morphology of the micro-drill surface after drilling and the hole accuracy statistics. The results showed that a-C:H film deposited on the surface of the micro-drill showed the best machining performance when the C2H2 flow rate was 180 sccm. The surface wear of micro-drill was minimal, the entanglement of tangled chips was minimal. The value of the process capability index (CPK) after 500, 1000, and 2000 drilling of PCB boards was 5.95, 4.33, and 3.15 respectively, which showed the highest drilling accuracy. This is mainly attributed to the better overall properties of the a-C:H films prepared at C2H2 flow rate of 180 sccm, such as lower surface roughness, lowest residual stress, higher hardness, better adhesion, and lower friction coefficient.

Corrosion behavior of Si-DLC film in simulant solutions containing CO2-H2S-Cl−

Tubing and casing failure due to corrosion is a common problem in the oil industry. The Si-DLC film deposited by plasma enhanced chemical vapor deposition (PECVD) technology is expected to protect the pipeline during oil and gas exploitation. Corrosion tests were carried out in different Na2S·9H2O concentrations and temperatures in order to evaluate the corrosion resistance and stability of Si-DLC film. The results show that the Si-DLC film significantly improves the corrosion resistance of the SS304 substrate. There is no significant change on the surface of Si-DLC film with the increase of temperature, and the XPS spectrum and Raman spectrum of DLC film after corrosion possess no obvious change, which indicates that Si-DLC film possesses a great high temperature stability. The Si-DLC film is denser and it possesses excellent protective effect on the substrate compared to the corrosion product layer. The as-deposited Si-DLC film possesses excellent corrosion resistance in CO2-H2S-Cl− environment and this study provides a promising protective material for the inner surface of the pipeline during oil and gas exploitation.

Anti-fogging surfaces produced by plasma polymerization of acrylic acid

In this paper, plasma enhanced chemical vapor deposition (PECVD) of acrylic acid (AA) was employed as a one-step and solvent-free technique to prepare durable organic anti-fogging coatings on mirror and glass surfaces. The effects of important PECVD parameters including substrate temperature and plasma power on the deposition kinetics, as well as on the structural and morphological properties of the as-deposited films were investigated. Employing a low substrate temperature (5 °C) and a high plasma power (30 W) combination resulted in the highest observed deposition rate of 27.7 nm/min. Fourier-transform infrared (FTIR) spectroscopy showed high structural resemblance between PECVD-PAA and reference poly(acrylic acid) (PAA). The PAA-deposited surfaces showed excellent and durable anti-fogging performance without any loss in their optical transparencies. Successive antifogging tests showed that the PAA thin film exhibited high functional durability without delamination, indicating that it can be used in real-world applications.

All-Nitrogen Energetic Material Cubic Gauche Polynitrogen: Plasma Synthesis and Thermal Performance.

Numerous theoretical calculations have demonstrated that polynitrogen with an extending polymeric network is an ultrahigh-energy all-nitrogen material. Typical samples, such as cubic gauche polynitrogen (cg-N), have been synthesized, but the thermal performance of polynitrogen has not been unambiguously determined. Herein, macroscopic samples of polynitrogen were synthesized utilizing a coated substrate, and their thermal decomposition behavior was investigated. Polynitrogen with carbon nanotubes was produced using a plasma-enhanced chemical vapor deposition method and characterized using infrared, Raman, X-ray diffraction X-ray photoelectron spectroscopy and transmission electron microscope. The results showed that the structure of the deposited polynitrogen was consistent with that of cg-N and the amount of deposition product obtained with coated substrates increased significantly. Differential scanning calorimetry (DSC) at various heating rates and TG-DSC-FTIR-MS analyses were performed. The thermal decomposition temperature of cg-N was determined to be 429 °C. The apparent activation energy (Ea) of cg-N calculated by the Kissinger and Ozawa equations was 84.7 kJ/mol and 91.9 kJ/mol, respectively, with a pre-exponential constant (lnAk) of 12.8 min-1. In this study, cg-N was demonstrated to be an all-nitrogen material with good thermal stability and application potential to high-energy-density materials.

Nanoengineered micro-supercapacitors based on graphene nanowalls for self-powered wireless sensing system

This work presents a comprehensive investigation of micro-supercapacitors (MSCs) based on graphene nanowalls (GNWs), covering core material synthesis, device fabrication, evaluation, and application demonstrations. Three-dimensional hierarchical GNWs structures are grown successfully by a microwave plasma-enhanced chemical vapor deposition (MPECVD), with detailed descriptions of the synthesis process and underlying mechanisms. The structural and morphological properties of the GNWs are thoroughly analyzed. Several types of MSCs are reported, ranging from thin-film to three-dimensional (3D) MSCs, as well as symmetric to asymmetric MSCs. Thin-film MSC is developed by a novel micromachining process for one-step fabricating GNWs-Ni core-shell composite microstructures. A solid-state MSC utilizing 3D hierarchical electrode is created by a fully micro electro mechanical system (MEMS)-compatible process. This involves depositing GNWs-RuOx hybrid nanostructures onto microstructure scaffolds formed using deep reactive ion etching (deep RIE). Additionally, another 3D MSC utilizes GNWs-PANI electrode material deposited on silicon nanowires generated through metal-assisted chemical etching (MACE) method. To enhance MSCs performance, asymmetric MSC is proposed and realized, incorporating GNWs-MnO2 acting as the positive electrode and carbon black serving as the negative electrode. Furthermore, the successfully combination of the fabricated MSCs with an energy harvesting system is demonstrated. The self-powered sensing system driven by solar energy, with the harvested energy stored in MSCs, is effectively showcased, opening up new possibilities for futuristic MSCs to accumulate and store harvested energy as usable electricity. This demonstration has significant potential in fields such as self-powered wireless IoT sensing systems, offering valuable contributions towards sustainable and autonomous energy solutions.

Low-frequency noise in InSnZnO thin film transistors with high-quality SiO2 gate oxide stacks

Low-frequency noise (LFN) in InSnZnO (ITZO) thin-film-transistors (TFT) with high-quality SiO2 gate oxide (GO) stacks is studied. This stack is fabricated by the plasma enhanced chemical vapor deposition (PECVD) and comprises two single layers. One layer is deposited by a SiH4 source (SiH4–SiO2), and the other uses a tetraethyl-orthosilicate precursor (TEOS-SiO2). The drain current noise power spectral densities follow the typical 1/f rule, and the main origin of LFN changes with the variation of drain current intensities. At low drain current intensities, LFN is affected by grain boundaries in the channel. As the drain current intensities increase, LFN originates from the carrier number fluctuations in devices with single TEOS-SiO2 GOs and from the carrier number with correlated mobility fluctuations in devices with SiO2 stacks GOs. At extremely high drain current intensities, the contact noise acts as a significant source of LFN in devices with SiO2 GO stacks. According to the carrier number with correlated mobility fluctuation (ΔN−Δμ) model, the devices with optimal stacks GOs exhibit a relatively low trap density near the ITZO/SiO2 interface. Additionally, these devices have a lower border trap density in GOs compared to those with single compositions. It demonstrates that high-quality SiO2 stacks reduce traps near the SiO2/ITZO interface, leading to enhanced devices performance. This work provides a precise and efficient method to evaluate the quality of GOs in metal oxide TFTs.

Highly enhanced and stable field emission performance of CNT – Dielectric (Si3N4) hybrids

In the present study, vertically aligned carbon nanotubes (CNTs) were grown onto Si substrates using a simple thermal chemical vapour deposition (TCVD) technique. Subsequently, the dielectric layer of Si3N4 was coated over the pristine CNTs using the Plasma Enhanced CVD (PECVD) method. Various characterizations were carried out on the as-deposited samples to study the structural properties, surface morphology, elemental composition, and electronic structure. The field emission measurements executed on CNT – Si3N4 samples showed an enhanced current density of 8.28 mA/cm2 compared to the 2.85 mA/cm2 current density of the pristine CNTs. A detailed study reveals that, apart from the basic conventional field emission parameters, the electronic structure of the CNTs, along with the presence of disordered carbon atoms and the presence of the dielectric material, are responsible for enhancing the current density and temporal stability of the CNT – Si3N4 hybrids. The study aids in exploring CNT-dielectric hybrids for better field emission properties with improved stability for field emission applications.

Optoelectronic Properties of Cold Plasma-Deposited, Oxidized Sn-C Thin Films.

We report on investigating the structural and electronic properties of semiconducting and insulating layers produced in a process resembling percolation in a unique cold plasma fabrication method (plasma-enhanced chemical vapor deposition-PECVD). Amorphous carbon-tin films (Sn-C) produced from tetramethyl tin (TMT) with an acoustic-frequency glow discharge in a three-electrode reactor were investigated. The layers, after air exposure, oxidized to SnO2/Sn-C. Depending on the coupling capacitance applied to the plasma reactor, the films could be obtained in the form of an amorphous semiconductor or an amorphous insulator. We assume that the semiconductor consists of an internal network of channels auto-organized during deposition. The insulator does not demonstrate any internal structure features. An investigation on conductive filaments creating low-dimensional (LD) nanojunctions in the semiconductor and the location of energetic levels in the insulator was performed. The main parameters of the electronic band structure of the insulating film, such as the transport gap EG (5.2 eV), optical gap Eopt (3.1 eV), electron affinity Χ (2.1 eV), and ionization potential J (7.3 eV), were determined. We have demonstrated a simple approach for developing a catalyst candidate consisting of amorphous semiconductor-insulator nanojunctions for (photo)catalytic hydrogen evolution or CO2 reduction.

Evaluation of vertical alignment in carbon nanotubes: A quantitative approach

An automated quantitative study of the alignment of vertically aligned carbon nanotubes (VA-CNTs) from scanning electron microscopy (SEM) images has been demonstrated. It is based on the fact that the image gradient (directional change in intensity or color) at every pixel in the image contains the information about the anisotropy at that particular pixel i.e., the local alignment is maintained in the orthogonal direction to the gradient. Structure tensor metrics are formulated demonstrating to be able to summarize the distribution of gradient directions within the neighborhood of any pixel within a two-dimensional domain (surface). An image analysis is presented that evaluates the alignment in desired regions of interest (ROIs) in SEM images of VA-CNTs. This method has been exploited to study the alignment of two different kinds of VA-CNTs: one grown via the thermal chemical vapor deposition (T-CVD) method and the second synthesized via the plasma enhanced chemical vapor deposition (PE-CVD) method.

Fabrication of highly conductive phosphorous-doped nc-SiCx:H thin film on PET

Plasma enhanced chemical vapor deposition (PECVD) method has been utilized to fabricate phosphorous-doped hydrogenated nanocrystalline silicon carbide (P-doped nc-SiCx:H) thin films on polyethylene terephthalate (PET) substrate. With the aim at obtaining highly conductive thin films, H2/Ar mixed dilution has been applied for creating plasma during deposition, and the variation of structural, electrical and optical properties with H2/Ar flow ratio RH have been systemically investigated through a series of characterizations. Results show that the highly crystallized P-doped nc-SiCx:H thin film can be prepared while the properties are controllable through adjusting RH. In the case of RH = 0.75, the maximum dark conductivity (6.42 S cm−1) and a wide optical bandgap (1.93 eV) are attained. Finally, detail discussion has been made to illustrate the growth mechanism of the flexible P-doped nc-SiCx:H thin films.

Long-term antifouling surfaces for urinary catheters.

The presence of a variety of bacteria is an inevitable/indispensable part of human life. In particular, for patients, the existence and spreading of bacteria lead to prolonged treatment period with many more complications. The widespread use of urinary catheters is one of the main causes for the prevalence of infections. The necessity of long-term use of indwelling catheters is unavoidable in terms of the development of bacteriuria and blockage. As is known, since a permanent solution to this problem has not yet been found, research and development activities continue actively. Herein, polyethylene glycol (PEG)-like thin films were synthesized by a custom designed plasma enhanced chemical vapor deposition (PE-CVD) method and the long-term effect of antifouling properties of PEG-like coated catheters was investigated against Escherichia coli and Proteus mirabilis. The contact angle measurements have revealed the increase of wettability with the increase of plasma exposure time. The antifouling activity of surface-coated catheters was analyzed against the Gram-negative/positive bacteria over a long-term period (up to 30 days). The results revealed that PE-CVD coated PEG-like thin films are highly capable of eliminating bacterial attachment on surfaces with relatively reduced protein attachment without having any toxic effect. Previous statements were supported with SEM, XPS, FTIR spectroscopy, and contact angle analysis.

All-fiberized amorphous carbon nitride (a-CNx) based passive Q-switcher

This research presents the first-ever demonstration of a passively Q-switched fiber laser in the 1.5 μm wavelength region using amorphous carbon nitride (a-CNx) as a saturable absorber (SA) in an all-fiber configuration. The a-CNx thin film was prepared using plasma-enhanced chemical vapor deposition. The laser operation showed remarkable stability, achieving a repetition rate of 57.99 kHz and a pulse duration of 1.36 μs at maximum input pump power. The peak power and pulse energy reached 100.56 mW and 136.77 nJ, respectively. The utilization of a-CNx as an SA offers potential benefits such as a simpler and more flexible cavity design, making it an attractive candidate for various applications, including material processing and medical laser equipment. This work contributes to the advancement of fiber lasers and expands the possibilities for utilizing carbon nitride-based SAs in practical laser systems.

Tailoring the active phase of CoO-based thin-film catalysts in order to tune selectivity in CO2 hydrogenation.

In this study, we prepared CoO-based thin films deposited on Kanthal steel wire gauze meshes by plasma-enhanced chemical vapor deposition. X-ray photoelectron spectroscopy (XPS) analysis revealed a structure characterized by a combination of cobalt oxide and metallic cobalt embedded within a carbon matrix. Our primary objective was to gain insights into the roles of Co0 and CoO in CO2 hydrogenation reactions. To achieve this, the performance of the thin-film CoO-based catalyst with an initial atomic ratio of CoO/Co0 at 10.2 was compared with two series of the thin-film catalysts that underwent pre-reduction processes at 350 °C for durations of 30 and 60 minutes, resulting in atomic ratios of CoO/Co0 at 3.1 and 1.1, respectively. Subsequently, catalytic tests were conducted in a continuous flow stirred tank reactor operating at temperatures ranging from 250 °C to 400 °C. Our findings indicate that CoO plays a significant role in activating the CO2 methanation reaction which can be due to the high hydrogen coverage of CoO, while Co0 is the active phase in the reverse water-gas shift reaction. Results highlight the importance of oxidized cobalt for hydrogen adsorption and dissociation in CO2 hydrogenation for CH4 formation.

Experimental studies and COMSOL 1-D simulation in Ar capacitively coupled plasmas

This work systematically studies a capacitively coupled plasma (CCP) source using experiments and 1-D COMSOL simulations relevant to Ar plasmas. Two radio frequency compensated Langmuir probes (LPs) and optical emission spectroscopy (OES) were purposefully used to measure the plasma parameters, and the experimental results were compared with those of simulations. We studied the axial variation of plasma parameters using an axial LP between the power and ground electrodes of the CCP at various operating pressures ranging from 10 to 150 mTorr. The electron density showed a gradual increase in its value with rising pressures. In addition, we employed a radial LP at the axial location L = 4 cm from the surface of the power electrode to measure the plasma parameters and compare these data with those of the axial LP and simulations. The variations of plasma potential measured by the radial LP showed an opposite trend of variation to those of simulations and the axial LP at pressures 10–60 mTorr, which is attributed to the plasma diffusion at low pressures. LP and OES measurements and simulation data suggest stochastic heating that generates high electron temperatures at low pressures. In addition, data revealed that the high-density plasma generation at high pressures could be due to the effects of both collisional heating and stochastic heating. Analysis showed that electrons could gain energy from the strong field regime of the sheath closed to the electrodes, which has a similar variation to electron temperature. The results of simulations have shown excellent agreement with experiments, and this work has the basis for plasma applications like plasma-enhanced chemical vapor deposition.

Refractive index and thickness analysis of planar interfaces by prism coupling technique

Since 2022, various foundries are offering the manufacture of integrated photonic structures for the visible spectrum. As this technology continues to enter the market, there will be an increasing demand for accurate optical and dimensional characterization of these structures. To meet this demand, we have developed a highly precise optical characterization system based on the prism coupling technique, also known as m-lines spectroscopy, to investigate the optical properties of hydrogenated amorphous silicon nitride planar waveguides deposited by plasma-enhanced chemical vapor deposition. In this work, by combining visible spectroscopy with the prism coupling technique to excite modes that propagate resonantly in the waveguide via frustrated total internal reflection, using either parallel or perpendicularly polarized light beams, we were able to analyze the waveguide properties of silicon nitride thin films with an interfacial oxide layer. Furthermore, through numerical simulation of the bilayer structure, we calculate the waveguide’s refractive index and thickness, and determine the characteristics of the interfaces in terms of refractive index and thickness.

Fabrication of Double Antireflection Layer of SiO2/SiNx via Spin Coating and Brush Painting for Enhanced Performance of Silicon Solar Cells

This research investigates the optical, structural, and photovoltaic attributes of a dual antireflection (AR) layer deposition on crystalline silicon (c–Si) solar cells using second SiO2 layer on SiNx AR. The second SiO2 AR layer on a SiNx AR-based c–Si solar cell was fabricated utilizing both spin coating and brush painting techniques, resulting in a unique double (SiO2/SiNx) AR layer. The initial SiNx AR layer was deposited on the c–Si solar cell through plasma-enhanced chemical vapor deposition (PECVD), while the SiO2 layer was subsequently applied using two different methods such as spin coating at 5000 rpm for 20 s and brush painting, separately, on Si solar cell. The double (SiO2/SiNx) AR layer on the Si wafer exhibited a substantial reduction in average reflectance, approximately 6.02% through spin coating and 5.17% through brush painting, within the wavelength range of 400–1000 nm when compared to a textured silicon wafer. The fabricated solar cell featuring the double (SiO2/SiNx) AR layer, achieved a power conversion efficiency of 15.21% and 17.57% for spin coating and brush painting, respectively. The utilization of the double (SiO2/SiNx) AR layer through brush painting on the Si solar cell not only provided low reflectance but also demonstrated excellent surface properties, making it a promising candidate for the cost-effective fabrication of high-performance Si solar cells.

Enhancing thermal transport of epoxy composites with vertically aligned graphene in situ grown on the thermal interface.

The escalating demands for miniaturization, integration, and portability in electronic devices have underscored the criticality of efficient heat dissipation. The utilization of high-performance thermal interface materials (TIMs) to fill the gaps between contacting surfaces holds significant potential for enhancing heat transfer efficiency. Herein, we successfully enhance the thermal properties of the epoxy composite TIM by integrating in situ grown vertically aligned graphene on the metal surface using radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD). To investigate the effect of vertical graphene on epoxy, the sandwich structure of copper/vertical graphene-epoxy/copper (Cu/VG-EP/Cu) is fabricated by incorporating epoxy resin. The experimental results demonstrate that the thermal conductivity of VG-EP reaches 2.06 W m-1 K-1 and achieves an impressive 1215% maximum enhancement. Furthermore, the numerical simulation findings show that vertical graphene consistent with the temperature gradient exhibits the highest heat transfer efficiency. This work presents an in-depth study of vertically aligned graphene within the epoxy resin, highlighting the advantages of vertically aligned fillers and offering novel perspectives for the advancement of TIMs.