Cyclotron Resonance Chemical Vapor Deposition Research Articles

Diamond-like Carbon Thin Film Coating for Application on Heterojunction Solar Cells by ECR-CVD System

Diamond-like Carbon (DLC) film has the ability to change the refractive index value achieved high transmittance for potential applications of antireflection coating. DLC films were deposited on heterojunction solar cells by the ECR-CVD (Electron Cyclotron Resonance Chemical Vapor Deposition) method using Acetylene (C2H2) and Argon (Ar) gases. DLC coating affects ITO (Indium tin oxide), causing the electrical and resistivity of heterojunction solar cell vary according to the coating time. The surface and thickness of the DLC films was measured with an atomic force microscope. Illuminated I-V characteristic was investigated by photo-I–V measurements. The suitable acetylene anti-reflection deposition time at 0.40 minutes. Therefore, heterojunction solar cell was fabricated on a substrate using the optimized DLC films as an anti-reflection coating and it obtained an increase efficiency of about 1%.

Electrochemical properties of vertically aligned graphenes: tailoring heterogeneous electron transfer through manipulation of the carbon microstructure.

The electrochemical response of different morphologies (microstructures) of vertically aligned graphene (VG) configurations is reported. Electrochemical properties are analysed using the outer-sphere redox probes Ru(NH3)62+/3+ (RuHex) and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), with performances de-convoluted via accompanying physicochemical characterisation (Raman, TEM, SEM, AFM and XPS). The VG electrodes are fabricated using an electron cyclotron resonance chemical vapour deposition (ECR-CVD) methodology, creating vertical graphene with a range of differing heights, spacing and edge plane like-sites/defects (supported upon underlying SiO2/Si). We correlate the electrochemical reactivity/response of these novel VG configurations with the level of edge plane sites (%-edge) comprising their structure and calculate corresponding heterogeneous electron transfer (HET) rates, k0. Taller VG structures with more condensed layer stacking (hence a larger global coverage of exposed edge plane sites) are shown to exhibit improved HET kinetics, supporting the claims that edge plane sites are the predominant source of electron transfer in carbon materials. A measured k0eff of ca. 4.00 × 10−3 cm s−1 (corresponding to an exposed surface coverage of active edge plane like-sites/defects (% θedge) of 1.00%) was evident for the tallest and most closely stacked VG sample, with the inverse case true, where a VG electrode possessing large inter-aligned-graphene spacing and small flake heights exhibited only 0.08% of % θedge and a k0eff value one order of magnitude slower at ca. 3.05 × 10−4 cm s−1. Control experiments are provided with conventional CVD (horizontal) grown graphene and the edge plane of highly ordered pyrolytic graphite (EPPG of HOPG), demonstrating that the novel VG electrodes exhibit ca. 3× faster k0 than horizontal CVD graphene. EPPG exhibited the fastest HET kinetics, exhibiting ca. 2× larger k0 than the best VG. These results are of significance to those working in the field of 2D-carbon electrochemistry and materials scientists, providing evidence that the macroscale electrochemical response of carbon-based electrodes is dependent on the edge plane content and showing that a range of structural configurations can be employed for tailored properties and applications.

Graphitic solid core carbon nanorods grown on silica sands using electron cyclotron resonance chemical vapor deposition as a highly efficient and green sorbent for removal of phenol derivatives from water sources

AbstractIn this study, graphitic solid core carbon nanorods (GSCNRs) were, for the first time, anchored to the surface of silica sands through the electron cyclotron resonance chemical vapor deposition method to provide coated silica sands as a new, low‐cost, green, and efficient adsorbent for the removal of organic pollutants such as phenol and 2,4‐dichlorophenol (2,4‐DCP) from aqueous mediums. The characteristics of GSCNRs/SiO2 were confirmed through Fourier‐transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy techniques. After the optimization of several parameters, the removal efficiency of phenol and 2,4‐DCP using 1 g of adsorbent amount, the initial concentration of pollutants (10 mg/L phenol and 15 mg/L 2,4‐DCP), a contact time of 10 min (phenol) and 20 min (2,4‐DCP), and pH = 7 were 69 and 89%, respectively. The adsorption isotherm models of Langmuir and Freundlich, as well as pseudo‐first‐order and pseudo‐second‐order kinetic models, were examined under optimal conditions. Eventually, GSCNRs/SiO2 was regenerated five times for the removal of phenol and 2,4‐DCP. The removal efficiency of the tested contaminants from inlet raw water of a water treatment plant using the proposed adsorbent was investigated.

Hydrogenated amorphous silicon films deposited by electron cyclotron resonance chemical vapor deposition at room temperature with different radio frequency chuck powers

In this work, we present the morphological and electrical characterization of hydrogenated amorphous siliconfilms, which were deposited at room temperature on a n+-type silicon substrate using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique. To study the hydrogen incorporation into the films, radio-frequency (RF) chuck powers of 1 W, 3 W and 5 W in the silicon substrates were applied during the ECR-CVD depositions. The deposited films were p+ doped using boron ion implantation (B+ I/I) and annealed at 1273 K, using a Rapid Thermal Annealing (RTA) process for dopant activation. The hydrogen concentration, the crystalline level, the surface roughness were obtained by, respectively, Fourier-transform infrared spectroscopy of the as-deposited films; Raman spectroscopy and atomic force microscopy of the films, after the B+ I/I and RTA. The Fourier-transform infrared and Raman spectra were deconvoluted as gaussian curves to extract the molecular bond concentration between silicon and hydrogen and their vibrational modes, respectively. These analyses indicated that: the H concentration is reduced with the increase of RF chuck powers, and, the films changed from totally amorphous to partially crystalline, respectively, when are compared the structures, before and after the B+ I/I and RTA. Diodes with three p+ a-Si/n++c-Si structures were fabricated with aluminun electrodes and current-voltage curves were extracted, indicating that the devices, with films deposited with 5 W, presented the best results, with ideality factor of 1.1.

Process-dependent mechanical and optical properties of nanostructured silicon carbonitride thin films

Amorphous hydrogenated silicon carbonitride (a-SiCN:H) thin films were grown using electron cyclotron resonance chemical vapour deposition using a mixture of methane, nitrogen, and silane as precursors. The origin of the variation of macroscopic properties such as hardness (H), elastic modulus (E), photoluminescence (PL), and the optical band gap was investigated through their correlation with the microscopic features of a-SiCN:H thin films as a function of the process parameters, including the deposition temperature and methane gas flow rate. From a microstructural perspective, the thin films were investigated using x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection, transmission electron microscopy, and x-ray diffraction. It is verified that an increase of the substrate temperature resulted in the substitution of hydrogen atoms mainly by carbon atoms, causing the density of the silicon carbide-related structures to increase in the amorphous structure of the a-SiCN:H thin films. Hardness and elastic modulus were found to increase with the deposition temperature and decreased with an increase of the methane gas flow during the deposition, resulting in higher carbon content in the films. The observed changes are ascribed to the reduced density of the weak hydrogen terminated bonds and the variation of the relative bond density of Si–C to Si–N bonds. In addition, the thin films were depth profiled using a slow positron beam to investigate the role of vacancies. The observed increase of the positronium formation with increasing deposition temperature was found to correlate with the variation of PL, where an enhancement of the visible emission originating from carbon-related defects was observed. A set of optimized process parameters to fabricate a-SiCN:H thin films with improved visible emission and hardness properties is suggested.

Microstructure, mechanical and tribological properties of DLC/Cu-DLC/W-DLC composite films on SUS304 stainless steel substrates

Besides their direct use as functional coatings, metal doped diamond-like carbon (Me-DLC) films are also adopted as buffer layers of DLC films to help reducing residual stress or improving adhesion to the substrates. However, single Me-doped buffer layer often deteriorates some of the inherent excellent mechanical properties of DLC films. In this paper, composite DLC films with double buffer layer based on W-DLC and Cu-DLC thin films were deposited on stainless steel (SS) substrates using microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) method combined with magnetron sputtering method, forming a film structure of DLC/Cu-DLC/W-DLC/SS. The composite films with this film structure show very smooth surface morphology, and possess high hardness (35 GPa) and low friction coefficient (0.14, friction pair: GCr15, HRC60) at the same time. It was also shown in this work that the sputtering current of the W target when depositing the most inner W-DLC layer can affect the formation of the sp3 bond in the composite film, which has great influence on the mechanical properties of the composite films. With different sputtering current, the hardness of the composite films can go up to 35 GPa, or go down to 14 GPa, resulting in different wear resistance against GCr15 friction pair.

Low-Temperature CVD Graphene Nanostructures on Cu and Their Corrosion Properties.

Chemical vapor deposition (CVD) graphene is reported to effectively prevent the penetration of outer factors and insulate the underneath metals, hence achieving an anticorrosion purpose. However, there is little knowledge about their characteristics and corresponding corrosion properties, especially for those prepared under different parameters at low temperatures. Using electron cyclotron resonance chemical vapor deposition (ECR-CVD), we can successfully prepare graphene nanostructures on copper (Cu) at temperatures lower than 600 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and potentiodynamic polarization measurements were used to characterize these samples. In simulated seawater, i.e., 3.5 wt.% sodium chloride (NaCl) solution, the corrosion current density of one graphene-coated Cu fabricated at 400 °C can be 1.16 × 10−5 A/cm2, which is one order of magnitude lower than that of pure Cu. Moreover, the existence of tall graphene nanowalls was found not to be beneficial to the protection as a consequence of their layered orientation. These correlations among the morphology, structure, and corrosion properties of graphene nanostructures were investigated in this study. Therefore, the enhanced corrosion resistance in selected cases suggests that the low-temperature CVD graphene under appropriate conditions would be able to protect metal substrates against corrosion.

Magnetic Field Resonance and Pressure Effects on Epitaxial Thin Film Deposition and In Situ Plasma Diagnostics

This study demonstrated the use of quadrupole mass spectrometry and optical emission spectrometry in diagnosing the plasma in the electron cyclotron resonance chemical vapor deposition (ECRCVD) process. The effects of adjusting the main magnetic coil current and process pressure on chemical composition of the plasma and the characteristics of the epitaxial thin film in the ECRCVD system were investigated. When the main magnetic coil current increased, the deposition rate of thin film increased, with no major effect on thin film crystallization. However, when the process pressure was higher, both the deposition rate and crystallization of epitaxial thin film increased.

The nanostructure and microstructure of SiC surface layers deposited by MWCVD and ECRCVD

Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to investigate ex-situ the surface topography of SiC layers deposited on Si(100) by Microwave Chemical Vapour Deposition (MWCVD) -S1,S2 layers and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) – layers S3,S4, using silane, methane, and hydrogen. The effects of sample temperature and gas flow on the nanostructure and microstructure have been investigated. The nanostructure was described by three-dimensional surface roughness analysis based on digital image processing, which gives a tool to quantify different aspects of surface features. A total of 13 different numerical parameters used to describe the surface topography were used. The scanning electron image (SEM) of the microstructure of layers S1, S2, and S4 was similar, however, layer S3 was completely different; appearing like grains. Nonetheless, it can be seen that no grain boundary structure is present in the AFM images.

Luminescent Si-Based Nanostructures Fabricated By Plasma Enhanced Chemical Vapour Deposition Techniques

In order for Si-based materials to be used in solid-state lighting (SSL) schemes it is necessary to have precise control of the emission from these materials. This can be accomplished through the use of rare earth dopants such as Ce, Tb, and Eu to obtain blue, green, and red emissions, respectively. This talk will focus on the luminescence of various silicon-based nanostructures (such as silicon oxides, nitrides, and carbides) and the effect of rare earth doping of such systems. We have demonstrated very high, optically active concentrations of the rare earths by using in-situ doping processes, using electron cyclotron resonance chemical vapour deposition (ECR-CVD) or inductively coupled plasma (ICP) CVD as low thermal budget processes for film deposition. I will describe the salient features of the deposition systems and correlate important process parameters with the observed luminescence. Finally, I will discuss some of the challenges in developing electrically driven lighting cells suitable for SSL and in particular, the development of white light emitters from rare earth doped Si-based materials.

Thin SiO2/a-Si:H/SiO2 multilayer insulators obtained by electron cyclotron resonance chemical vapor deposition at room temperature for possible application in non-volatile memories

In this work we present electrical and morphological characterization of thin multilayer structures, SiO2/a-Si:H/SiO2, with possible applications in non-volatile memories devices. All films were obtained by Electron Cyclotron Resonance Chemical Vapor Deposition technique at room temperature. To induce structural changes in the amorphous silicon layer, the gate stacks were subjected to high temperature furnace annealing at 800°C and 1100°C.Three-layer MOS structures were patterned by lithography and subjected to a sintering process in forming gas for 20min. The structures annealed at high temperature present a memory window in their capacitance-voltage dependencies, which means that these structures could have a possible application as gate insulators in non-volatile memory devices. The morphology of the amorphous layers was studied by atomic force microscopy and scanning electron microscopy which revealed increase of the surface roughness and modifications in the a-Si:H layer after the high temperature process.

Deposition of Intrinsic a-Si:H by ECR-CVD to Passivate the Crystalline Silicon Heterointerface in HIT Solar Cells

We have deposited intrinsic amorphous silicon (a-Si:H) using the electron cyclotron resonance (ECR) chemical vapor deposition technique in order to analyze the a-Si:H/c-Si heterointerface and assess the possible application in heterojunction with intrinsic thin layer (HIT) solar cells. Physical characterization of the deposited films shows that the hydrogen content is in the 15–30% range, depending on deposition temperature. The optical bandgap value is always comprised within the range 1.9–2.2 eV. Minority carrier lifetime measurements performed on the heterostructures reach high values up to 1.3 ms, indicating a well-passivated a-Si:H/c-Si heterointerface for deposition temperatures as low as 100 oC. In addition, we prove that the metal–oxide–semiconductor conductance method to obtain interface trap distribution can be applied to the a-Si:H/c-Si heterointerface, since the intrinsic a-Si:H layer behaves as an insulator at low or negative bias. Values for the minimum of D it as low as 8 × 1010 cm-2⋅eV-1 were obtained for our samples, pointing to good surface passivation properties of ECR-deposited a-Si:H for HIT solar cell applications.

Electrical Characterization of Amorphous Silicon MIS-Based Structures for HIT Solar Cell Applications.

A complete electrical characterization of hydrogenated amorphous silicon layers (a-Si:H) deposited on crystalline silicon (c-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) was carried out. These structures are of interest for photovoltaic applications. Different growth temperatures between 30 and 200 °C were used. A rapid thermal annealing in forming gas atmosphere at 200 °C during 10 min was applied after the metallization process. The evolution of interfacial state density with the deposition temperature indicates a better interface passivation at higher growth temperatures. However, in these cases, an important contribution of slow states is detected as well. Thus, using intermediate growth temperatures (100–150 °C) might be the best choice.

Nanocrystalline diamond films growth by microwave ECR CVD: Studies of structural and photoconduction properties

We report studies on growth of nanocrystalline diamond films by electron cyclotron resonance chemical vapour deposition (ECR CVD) and their structural and photoconduction properties. Bias enhanced nucleation (BEN) under higher methane partial pressure has been used to grow diamond nanocrystals with sp2 carbon clusters at grain boundaries in an amorphous carbon matrix. Structural studies indicate the size of diamond nanocrystals decreased and sp2 content increased in the films with increase in methane partial pressure, which is explained using subplantation model. Current- Voltage (I-V) measurements under dark and deep ultraviolet (DUV) light illumination conditions showed higher photocurrent in films with smaller sized diamond nanocrystals (3 nm–8 nm) compared to films having diamond nanocrystals of larger size (∼15 nm). The results indicates that the photocurrent generated in the films has major contributions from photoexcited electrons in diamond nanocrystals and sp2 carbon nanoclusters, with minor contribution from amorphous carbon phase.

Strain-Controlled of Compressive/Tensile Ge Epilayers on Si by Electron Cyclotron Resonance Chemical Vapor Deposition

In this study, we use electron cyclotron resonance chemical vapor deposition to investigate the strain behavior in Ge epilayers grown on silicon at a low temperature of 220°C. The strain in the Ge epilayers is transformed from compressive (−0.567%) to tensile (0.15%) as the process pressure decreases and main coil current increases. This tensile strain is due to intrinsic stress in the Ge epilayers at high process pressure and low main coil current. Besides, the Ge atoms have higher kinetic energy and shorter mean free path at low process pressure and high main coil current, which causes atomic bombardment effect on the Ge surfaces frequently. Thus, the intrinsic stress in Ge epilayers become compressive. The absorption coefficient of tensile and compressive strain in Ge films are measured using a UV–VIS-NIR spectrophotometer. The results show the absorption coefficients of the tensile strain Ge epilayer has a redshift condition on the absorption edge compare with compressive strain Ge epilayers. Finally, the structure information of the Ge epilayers is identified by atomic force microscopy and transmission electron microscopy. This strain control technology is modulated by film growth parameter, which can adjust the Ge bandgap for the device requirement.

High Quality GaAs Epilayers Grown on Si Substrate Using 100 nm Ge Buffer Layer

We present high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers. The thin Ge buffer layers were modulated by hydrogen flow rate from 60 to 90 sccm to improve crystal quality by electron cyclotron resonance chemical vapor deposition (ECR-CVD) at low growth temperature (180°C). The GaAs and Ge epilayers quality was verified by X-ray diffraction (XRD) and spectroscopy ellipsometry (SE). The full width at half maximum (FWHM) of the Ge and GaAs epilayers in XRD is 406 arcsec and 220 arcsec, respectively. In addition, the GaAs/Ge/Si interface is observed by transmission electron microscopy (TEM) to demonstrate the epitaxial growth. The defects at GaAs/Ge interface are localized within a few nanometers. It is clearly showed that the dislocation is well suppressed. The quality of the Ge buffer layer is the key of III–V/Si tandem cell. Therefore, the high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers is suitable to develop the low cost and high efficiency III–V/Si tandem solar cells.

The Dependence of ECR-CVD Processing Parameters on Deposition Uniformity of Hydrogenated Amorphous Silicon (a-Si:H) Films

The uniformity improvement of high deposition rate in hydrogenated amorphous silicon (a-Si:H) film deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) is very essential for a large substrate in PV solar industry. In order to improve the uniformity in depositing thin film in large area, the auxiliary magnetic coils were designed and installed in ECR-CVD to modify the distribution of magnetic field. In addition, the dependence of the other ECR-CVD processing parameters such as resonance position, microwave power, working pressure, and substrate temperature were investigated. The results indicated that more uniform a-Si:H film could be obtained when working pressure was decreased. By using finite element analysis, it was found that location of turbo pump would impact gas flow field and this effect would become more significant at high pressure. Increasing microwave power, increasing horizontal gradient of the magnetic field to the substrate, and forming Cusp magnetic field could enhance ECR-CVD deposition uniformity greatly. However, the plasma location and substrate temperature were not major factors affecting a-Si:H film uniformity in ECR-CVD process. Finally, the optimal and the best 3.8% in uniformity could be achieved in 150mm diameter when the ratio of magnetic field strength at wafer edge to wafer center is 215%, working pressure is 1.5 mtorr, microwave power density is 4W/cm2, and substrate temperature is 180°C.

Influence of substrate on nucleation and growth of vertical graphene nanosheets

The present study reports the role of substrate on nucleation and growth of vertical graphene nanosheets (VGNs) under electron cyclotron resonance chemical vapor deposition (ECR-CVD). The VGNs are grown on Pt, Ni, Au, Cu, Si(100), Si(111), SiO2 and quartz substrates simultaneously. The morphology of VGNs is found to vary significantly with substrate. VGNs on Pt have the highest aerial density of vertical sheets while quartz have the lowest. The structural defects in VGNs vary with substrate as evidenced from Raman spectroscopy. The observation of defect related Raman bands such as D″ and D* at 1150 and 1500cm−1, respectively revealed the existence of pentagon–heptagon rings or carbon onions in VGNs. Formation of such defects at early stage of nucleation dictates the growth mechanism and hence the morphology. A phenomenological four-stage model is discussed, to substantiate the nucleation and growth mechanism of VGNs on different substrates, by evoking substrate–plasma interaction during growth.

Investigation of Electron Cyclotron Resonance Chemical Vapor Deposition Process for a-Si:H Deposition, Film Characterization and In Situ Plasma Diagnostics

We present the application of quadrupole mass spectrometry (QMS) with threshold ionization mass spectrometry (TIMS), optical emission spectroscopy (OES) with an actinometry method, and Langmuir probe (LP) as an integrated technique for in situ plasma characterization of the electron cyclotron resonance chemical vapor deposition (ECR-CVD) of hydrogenated amorphous silicon (a-Si:H). The main aim of this study was to determine the relationship among the process parameters, plasma characteristics, and thin film properties, including the microstructure parameter (R*), hydrogen content (CH), and a-Si:H film growth rate. The physical properties of plasma, such as the electron density (Ne), electron energy (Te), and sheath potential (Vs), were studied using an LP and OES. In addition to the general plasma properties, the ion density (Ni) and plasma electronegativity were examined. The results indicate the ECR plasma source has high potential for producing a high-quality a-Si:H film because of the availability of few high silanes (SinH2n+2, n > 2); furthermore, the results indicate an obvious difference in the QMS analysis results between plasma and gas. Therefore, the consumption of parent molecules must be considered. The TIMS method was applied to estimate the relative concentration of ground-state silane radicals (SiHx, x < 4) and consumption of SiH4. The results indicate that, in addition to the degree of ionization, the consumption of SiH4 and Vs are key factors affecting the thin film growth rate. When microwave power density increases, the values of Ni, Ne, and Vs increase considerably, but the plasma electronegativity remains unchanged. Furthermore, we compared our results with the TIMS analysis reported by other authors and found that the ratio of SiH2 to SiH3 obtained using QMS and TIMS can be considered an indicator of film quality for R* in the ECR-CVD process.

On the use of new oxidized Co–Cr–Pt–O catalysts for vertically-aligned few-walled carbon nanotube forest synthesis in electron cyclotron resonance chemical vapor deposition

A new class of the multi-element catalysis system, Co–Cr–Pt–O, is used for vertically-aligned few-walled carbon nanotube (CNT) forest synthesis by a sandwich-growth technology in electron cyclotron resonance chemical vapor deposition. The effect of catalyst compositions on the resulting particle sizes after pretreatment, and the influence of process parameters on the CNT forest heights and diameters are investigated. Results show that a plasma pretreatment step reduces the metal oxides present in the as-deposited Co–Cr–Pt–O catalyst to their metallic states or to mixed metallic/oxidic states, and the co-catalytic synergistic effect during the reduction process thus leads to the production of uniformly small particles with a size of 3.3–3.9nm over the substrate. Moreover, with CH4 as the carbon source, vertically-aligned CNT forests of ∼12μm in height are achieved, and further characterizations indicate that the forests consist of dominant triple-walled nanotubes with an average inner tube diameter of 3.2–3.7nm mostly. Additionally, field emission measurements show that the turn-on field of the CNT-forest emitters is below 2.6V/μm, and the emission current density can reach 110mA/cm2 at 4.5V/μm. High reproducibility of field emission characteristics and Raman signals suggests the regularity of the CNT forests in structure and size.