Showing papers on "Plasma-enhanced chemical vapor deposition published in 2015"

Low‐Temperature Synthesis of Large‐Scale Molybdenum Disulfide Thin Films Directly on a Plastic Substrate Using Plasma‐Enhanced Chemical Vapor Deposition

Abstract: By plasma-enhanced chemical vapor deposition, a molybdenum disulfide (MoS2 ) thin film is synthesized directly on a wafer-scale plastic substrate at below 300 °C. The carrier mobility of the films is 3.74 cm(2) V(-1) s(-1) . Also, humidity is successfully detected with MoS2 -based sensors fabricated on the flexible substrate, which reveals its potential for flexible sensing devices.

Low temperature critical growth of high quality nitrogen doped graphene on dielectrics by plasma-enhanced chemical vapor deposition.

Abstract: Nitrogen doping is one of the most promising routes to modulate the electronic characteristic of graphene. Plasma-enhanced chemical vapor depostion (PECVD) enables low-temperature graphene growth. However, PECVD growth of nitrogen doped graphene (NG) usually requires metal-catalysts, and to the best of our knowledge, only amorphous carbon–nitrogen films have been produced on dielectric surfaces by metal-free PECVD. Here, a critical factor for metal-free PECVD growth of NG is reported, which allows high quality NG crystals to be grown directly on dielectrics like SiO2/Si, Al2O3, h-BN, mica at 435 °C without a catalyst. Thus, the processes needed for loading the samples on dielectrics and n-type doping are realized in a simple PECVD, which would be of significance for future graphene electronics due to its compatibility with the current microelectronic processes.

FORMATION OF SiN THIN FILMS

Abstract: Methods of forming silicon nitride thin films on a substrate in a reaction space under high pressure are provided The methods can include a plurality of plasma enhanced atomic layer deposition (PEALD) cycles, where at least one PEALD deposition cycle comprises contacting the substrate with a nitrogen plasma at a process pressure of 20 Torr to 500 Torr within the reaction space In some embodiments the silicon precursor is a silyly halide, such as H 2 SiI 2 In some embodiments the processes allow for the deposition of silicon nitride films having improved properties on three dimensional structures For example, such silicon nitride films can have a ratio of wet etch rates on the top surfaces to the sidewall of about 1:1 in dilute HF

Direct low-temperature synthesis of graphene on various glasses by plasma-enhanced chemical vapor deposition for versatile, cost-effective electrodes

Abstract: Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art displays However, systematic study within this promising research field has remained scarce thus far Herein, we report the direct growth of graphene on various glasses using a low-temperature plasma-enhanced chemical vapor deposition method Such a facile and scalable approach guarantees the growth of uniform, transfer-free graphene films on various glass substrates at a growth temperature range of 400–600 °C The morphological, surface wetting, optical, and electrical properties of the obtained graphene can be tailored by controlling the growth parameters Our uniform and high-quality graphene films directly integrated with low-cost, commonly used glasses show great potential in the fabrication of multi-functional electrodes for versatile applications in solar cells, transparent electronics, and smart windows

High-efficiency amorphous silicon solar cells: Impact of deposition rate on metastability

Abstract: Hydrogenated amorphous silicon (a-Si:H) films, used for light absorbers of p-i-n solar cells, were deposited at various deposition rates (Rd) ranging over two orders of magnitude (Rd ∼ 2 × 10−3–3 × 10−1 nm/s) by using diode and triode plasma-enhanced chemical vapor deposition (PECVD). The impact of varying Rd on the light-soaking stability of the solar cells has been investigated. Although a reduction of Rd mitigates the light-induced degradation in the typical range of Rd (>10−1 nm/s), it remains present even in the very low Rd (<10−2 nm/s), indicating that the metastable effect persists in a-Si:H regardless of Rd. The best performing cell, whose a-Si:H absorber is characterized by low amount of metastable defect and high bandgap, can be obtained at Rd of ∼1–3 × 10−2 nm/s by triode PECVD. By applying such a-Si:H in the improved p-i-n devices, we demonstrate two record independently confirmed stabilized efficiencies of 10.22% for single-junction and 12.69% for a-Si:H/hydrogenated microcrystalline silicon ...

High-efficiency microcrystalline silicon solar cells on honeycomb textured substrates grown with high-rate VHF plasma-enhanced chemical vapor deposition

Abstract: The potential of high-rate growth of high-quality microcrystalline silicon (µc-Si:H) films for solar cell applications is investigated by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) under a high-pressure SiH4 depletion condition. It is found that the morphology of textured substrates plays an important role in not only light trapping but also µc-Si:H film growth. A high conversion efficiency of 11.1% is attained in a substrate-type µc-Si:H cell on a substrate with honeycomb textures, which has rounded concaves in a honeycomb arrangement with an appropriate period. It is also clarified that ZnO:B films grown by metal organic chemical vapor deposition (MOCVD) are beneficial in terms of carrier collection compared with the standard In2O3:Sn (ITO) film grown by sputtering. On the basis of these findings, a new world-record µc-Si:H cell with a certified conversion efficiency of 11.8% is developed with a relatively high deposition rate of 1 nm/s.

Constructing Fe2O3/TiO2 core–shell photoelectrodes for efficient photoelectrochemical water splitting

Abstract: In this study, plasma enhanced chemical vapor deposition (PECVD) was utilized to co-axially modify hydrothermally grown Fe2O3 nanorod arrays by depositing a TiO2 overlayer to create Fe2O3/TiO2 core–shell photoelectrodes. Comprehensive structural (XRD, SEM, TEM) and compositional (XPS) analyses were performed to understand the effects of the TiO2 shell on the PEC activities of the Fe2O3 core. It was revealed that the heterojunction structure formed between TiO2 and Fe2O3, significantly improved the separation efficiency of photo-induced charge carriers and the oxygen evolution kinetics. A maximum photocurrent density of ∼900 μA cm−2 at 0.6 V vs. saturated calomel electrode (SCE) was obtained for the Fe2O3/TiO2 photoelectrodes, which was 5 and 18 times higher when compared to that of hydrothermally synthesized Fe2O3 and PECVD synthesized TiO2 electrodes, respectively. Moreover, the Fe2O3/TiO2 core–shell nanorod arrays displayed superior stability for PEC water splitting. During 5000 s PEC measurements, a steady decrease of the photocurrent was observed, mainly attributed to the evolution of oxygen bubbles adsorbed on the working electrodes. This observation was verified by the complete recovery of the PEC performance demonstrated for a second 5000 s PEC measurement carried out after a brief time interval (10 min) that allowed the electrode surface to regenerate.

Copper-Assisted Direct Growth of Vertical Graphene Nanosheets on Glass Substrates by Low-Temperature Plasma-Enhanced Chemical Vapour Deposition Process

Abstract: Vertical graphene (VG) nanosheets are directly grown below 500 °C on glass substrates by a one-step copper-assisted plasma-enhanced chemical vapour deposition (PECVD) process. A piece of copper foil is located around a glass substrate as a catalyst in the process. The effect of the copper catalyst on the vertical graphene is evaluated in terms of film morphology, growth rate, carbon density in the plasma and film resistance. The growth rate of the vertical graphene is enhanced by a factor of 5.6 with the copper catalyst with denser vertical graphene. The analysis of optical emission spectra suggests that the carbon radical density is increased with the copper catalyst. Highly conductive VG films having 800 Ω/□ are grown on glass substrates with Cu catalyst at a relatively low temperature.

The influence of different silicon adhesion interlayers on the tribological behavior of DLC thin films deposited on steel by EC-PECVD

Abstract: Diamond-like carbon (DLC) is a hydrogenated amorphous carbon (a-C:H) thin film material owing to its unique tribological properties that may open great opportunities for new applications. However, DLC presents low chemical affinity with metallic alloys and high intrinsic stress, prompting film delamination and poor adherence on the substrate. In the present work, we performed a systematic study about structural and tribological properties of a-C:H thin films grown on steel by introducing adhesive silicon-containing interlayers deposited at different processing temperatures and times. The studied bi-layers were deposited by electrostatic confinement plasma enhanced chemical vapor deposition (EC-PECVD) and were characterized by several techniques. The results showed that the adhesive interlayers produced from tetramethylsilane are chemically structured as a non-stoichiometry hydrogenated amorphous silicon carbide alloy (a-SiC x :H). Its structure, chemical composition and thickness are very dependent on deposition conditions. The thickness of the interlayers increases with deposition time and decreases with deposition temperature. The interlayer contains less hydrogen and silicon atoms at higher deposition temperatures, with enhanced formation of Si–C bonds in its structure. This last chemical event is correlated with the rise in the critical load values found for a-C:H film delamination when the a-SiC x :H interlayers are deposited from 573 K to 823 K. On the other hand, the interlayer contains less carbon atoms at higher deposition times, decreasing the critical load values for a-C:H film delamination when the a-SiC x :H interlayers are deposited from 5 min to 10 min.

Plasma deposition of silver nanoparticles on ultrafiltration membranes: antibacterial and anti-biofouling properties

Abstract: A novel and versatile plasma reactor was used to modify polyethersulphone commercial membranes. The equipment was applied to: (i) functionalize the membranes with low-temperature plasmas, (ii) deposit a film of poly(methyl methacrylate) (PMMA) by Plasma Enhanced Chemical Vapor Deposition (PECVD) and, (iii) deposit silver nanoparticles (SNP) by gas flow sputtering. Each modification process was performed in the same reactor consecutively, without exposure of the membranes to atmospheric air. Scanning electron microscopy and transmission electron microscopy were used to characterize the particles and modified membranes. SNP are evenly distributed on the membrane surface. Particle fixation and transport inside membranes were assessed before- and after-washing assays by X-ray photoelectron spectroscopy depth profiling analysis. PMMA addition improved SNP fixation. Plasma-treated membranes showed higher hydrophilicity. Anti-biofouling activity was successfully achieved against Gram-positive (Enterococcus faecalis) and -negative (Salmonella) Typhimurium bacteria. Therefore, disinfection by ultrafiltration showed substantial resistance to biofouling. The post-synthesis functionalization process developed provides a more efficient fabrication route for anti-biofouling and anti-bacterial membranes used in the water treatment field. To the best of our knowledge, this is the first report of a gas phase condensation process combined with a PECVD procedure in order to deposit SNP on commercial membranes to inhibit biofouling formation.

Controlled MoS2 layer etching using CF4 plasma

Abstract: A few-layered molybdenum disulfide (MoS2) thin film grown by plasma enhanced chemical vapor deposition was etched using a CF4 inductively coupled plasma, and the possibility of controlling the MoS2 layer thickness to a monolayer of MoS2 over a large area substrate was investigated. In addition, damage and contamination of the remaining MoS2 layer surface after etching and a possible method for film recovery was also investigated. The results from Raman spectroscopy and atomic force microscopy showed that one monolayer of MoS2 was etched by exposure to a CF4 plasma for 20 s after an initial incubation time of 20 s, i.e., the number of MoS2 layers could be controlled by exposure to the CF4 plasma for a certain processing time. However, XPS data showed that exposure to CF4 plasma induced a certain amount of damage and contamination by fluorine of the remaining MoS2 surface. After exposure to a H2S plasma for more than 10 min, the damage and fluorine contamination of the etched MoS2 surface could be effectively removed.

Sensing Properties of Multiwalled Carbon Nanotubes Grown in MW Plasma Torch: Electronic and Electrochemical Behavior, Gas Sensing, Field Emission, IR Absorption

Abstract: Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 µm were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT‑modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures.

PECVD low stress silicon nitride analysis and optimization for the fabrication of CMUT devices

Abstract: Two technological options to achieve a high deposition rate, low stress plasma-enhanced chemical vapor deposition (PECVD) silicon nitride to be used in capacitive micromachined ultrasonic transducers (CMUT) fabrication are investigated and presented. Both options are developed and implemented on standard production line PECVD equipment in the framework of a CMUT technology transfer from R & D to production. A tradeoff between deposition rate, residual stress and electrical properties is showed.The first option consists in a double layer of silicon nitride with a relatively high deposition rate of ~100 nm min−1 and low compressive residual stress, which is suitable for the fabrication of the thick nitride layer used as a mechanical support of the CMUTs. The second option involves the use of a mixed frequency low-stress silicon nitride with outstanding electrical insulation capability, providing improved mechanical and electrical integrity of the CMUT active layers. The behavior of the nitride is analyzed as a function of deposition parameters and subsequent annealing. The nitride layer characterization is reported in terms of interfaces density influence on residual stress, refractive index, deposition rate, and thickness variation both as deposited and after thermal treatment. A sweet spot for stress stability is identified at an interfaces density of 0.1 nm−1, yielding 87 MPa residual stress after annealing. A complete CMUT device fabrication is reported using the optimized nitrides. The CMUT performance is tested, demonstrating full functionality in ultrasound imaging applications and an overall performance improvement with respect to previous devices fabricated with non-optimized silicon nitride.

A low cost, green method to synthesize GaN nanowires.

Abstract: The synthesis of gallium nitride nanowires (GaN NWs) by plasma enhanced chemical vapor deposition (PECVD) are successfully demonstrated in this work. The simple and green synthesis route is to introduce gallium oxide (Ga2O3) and nitrogen (N2) for the growth of nanowires. The prepared GaN nanowires have a single crystalline wurtzite structure, which the length of some nanowires is up to 20 μm, with a maximum diameter about 140 nm. The morphology and quantity of the nanowires can be modulated by the growth substrate and process parameters. In addition, the photoluminescence and field emission properties of the prepared GaN nanowires have been investigated, which were found to be largely affected by their structures. This work renders an environmentally benign strategy and a facile approach for controllable structures on nanodevice.

Low temperature synthesis of graphite on Ni films using inductively coupled plasma enhanced CVD

Abstract: Controlled synthesis of graphite at low temperatures is a desirable process for a number of applications. Here, we present a study on the growth of thin graphite films on polycrystalline Ni films at low temperatures, about 380 °C, using inductively coupled plasma enhanced chemical vapor deposition. Raman analysis shows that the grown graphite films are of good quality as determined by a low ID/IG ratio, ∼0.43, for thicknesses ranging from a few layers of graphene to several nanometer thick graphitic films. The growth of graphite films was also studied as a function of time, precursor gas pressure, hydrogen concentration, substrate temperature and plasma power. We found that graphitic films can be synthesized on polycrystalline thin Ni films on SiO2/Si substrates after only 10 seconds at a substrate temperature as low as 200 °C. The amount of hydrogen radicals, adjusted by changing the hydrogen to methane gas ratio and pressure, was found to dramatically affect the quality of graphite films due to their dual role as a catalyst and an etchant. We also find that a plasma power of about 50 W is preferred in order to minimize plasma induced graphite degradation.