Microwave Surface Wave Plasma CVD Research Articles

Multilayer graphene/amorphous carbon hybrid films prepared by microwave surface-wave plasma CVD: synthesis and characterization

Hybrid films of multilayer graphene (MG) containing amorphous carbon (a-C) were synthesized on Al substrates by microwave surface-wave plasma chemical vapor deposition. Raman scattering and surface transmission electron microscopy showed that the carbon films contained a large quantity of MG when a radio frequency (RF) substrate bias was not applied. Amorphization of graphene in the carbon film was promoted by applying an RF bias, which generated Ar+ in the plasma. The bandgaps of the films were found to increase as the Raman intensity ratios between the 2D-band (at 2700 cm−1) and D-band (at 1350 cm−1) decreased, indicating the formation of a-C. The MG/a-C all-sp2 phase of carbon hybrid films exhibited an increase in current density under 5 mW/cm2 of AM1.5G solar simulated irradiation as the RF bias increased because of Ar+-induced amorphization of the graphene. Copyright © 2016 John Wiley & Sons, Ltd.

Few layers isolated graphene domains grown on copper foils by microwave surface wave plasma CVD using camphor as a precursor

Few layers isolated graphene domains were grown by microwave surface wave plasma CVD technique using camphor at low temperature. Graphene nucleation centers were suppressed on pre-annealed copper foils by supplying low dissociation energy. Scanning electron microscopy study of time dependent growth reveals that graphene nucleation centers were preciously suppressed, which indicates the possibility of controlled growth of large area single crystal graphene domains by plasma processing. Raman spectroscopy revealed that the graphene domains are few layered which consist of relatively low defects.

Low Temperature Growth of Carbon Nanomaterials on the Polymer Substrate Using Ion Assisted Microwave Plasma CVD

In this study, the successful growth of carbon nanotubes and few-layered graphene sheets on the silicon and polyimide substrates at relatively low temperature of 230-260°C by microwave surface wave plasma CVD technique has been demonstrated. Graphite-encapsulated Ni nanoparticles have been used as the catalyst for growing carbon nanomaterials (CNMs) in NH3/CH4 plasma. The results of high-resolution transmission electron microscope(TEM) analysis show the effect of substrate on the structure of CNMs.

Optical band gap of nitrogenated amorphous carbon thin films synthesized by microwave surface wave plasma CVD

Nitrogenated amorphous carbon (a-C:N) thin films were prepared on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition system, aiming to control optical band gap ( E g) of the films for photovoltaic solar cells application. For films deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor dissolved with ethyl alcohol (3:7) and acetylene. The E g of the films has been decreased from 4.1 to 2.4 eV and 2.2 to 1.6 eV with alcohol plus camphor and acetylene source gases respectively by nitrogen doping. The E g of the a-C:N films can be tuned from 2.4 to 0.95 eV by thermal annealing treatment. These results show that it is possible to control the E g by nitrogen doping with different carbon source gases and by post growth annealing of the films.

Effects of ethylene gas flow rate on optoelectrical properties of nitrogenated thin amorphous carbon films grown by microwave surface wave plasma CVD

We report on the effects of ethylene gas (C 2H 4) on the electrical and optical properties of amorphous carbon (a-C) thin films grown on silicon, indium tin oxide (ITO) and quartz substrates by microwave surface wave plasma chemical vapor deposition (MW SWP CVD) at low temperature (< 100 °C). For film deposition, we used argon gas with ethylene composition as plasma source. The influence of the nitrogen incorporation on the optical and structural properties of the carbon films were investigated using different spectroscopic techniques. The nitrogen has been incorporated into a-C: N films which was confirmed by the x-ray photoelectron spectroscopy (XPS) measurement. The results indicate that the increasing flow of source (C 2H 4) has microstructure consisting of atomic sp 2/C phase, cross linked by sp 3/C which is very similar to the properties of a-C: N. It was found that the optical gap was shifted from 2.1 to 2.6 eV with increasing flow of source.

Effect of substrate bias voltage on the properties of diamond-like carbon thin films deposited by microwave surface wave plasma CVD

Diamond-like carbon (DLC) thin films were deposited on silicon and ITO substrates with applying different negative bias voltage by microwave surface wave plasma chemical vapor deposition (MW SWP-CVD) system. The influence of negative bias voltage on optical and structural properties of the DLC film were investigated using X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. Optical band gap of the films decreased from 2.4 to 1.7 with increasing negative bias voltage (0 to − 200 V). The absorption peaks of sp 3 C H and sp 2 C H bonding structure were observed in FT-IR spectra, showing that the sp 2/sp 3 ration increases with increasing negative bias voltage. The analysis of Raman spectra corresponds that the films were DLC in nature.

The role of pressure on thin amorphous carbon films deposited using microwave surface wave plasma CVD

We report the effects of gas composition pressure (GCP) on the optical, structural and electrical properties of thin amorphous carbon (a-C) films grown on p-type silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition (MW SWP CVD). The films, deposited at various GCPs ranging from 50 to 110 Pa, were studied by UV/VIS/NIR spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and current–voltage characteristics. The optical band gap of the a-C film was tailored to a relatively high range, 2.3–2.6 eV by manipulating GCPs from 50 to 110 Pa. Also, spin density strongly depended on the band gap of the a-C films. Raman spectra showed qualitative structured changes due to sp 3/sp 2 carbon bonding network. The surfaces of the films are found to be very smooth and uniform (RMS roughness < 0.5 nm). The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm 2) show that short-circuit current density, open-circuit voltage, fill factor and photo-conversion efficiency of the film deposited at 50 Pa were 6.4 μA/cm 2, 126 mV, 0.164 and 1.4 × 10 − 4 % respectively.

Electrical conductivity improvement by iodine doping for diamond-like carbon thin-films deposited by microwave surface wave plasma CVD

We report the effects of iodine (I) doping on the optical and structural properties, and electrical conductivity of diamond-like carbon (DLC) thin-films grown on silicon, glass and quartz substrates by microwave surface wave plasma chemical vapor deposition at low temperature (< 100 °C). For film deposition, we used argon and methane as plasma source gases. The films were characterized by UV/VIS/NIR spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and current–voltage ( I– V) characteristics. The optical band gap of the films decreased from 3.5 to 1.9 eV corresponding to non-doping to I-doping conditions. The XPS results confirm the successful doping of I in the films. The FTIR result shows the effect of I-doping on reduction of sp 3-bonded carbon in the film. The I– V measurement shows I-doping induced electrical conductivity of the DLC film.

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C 10H 16O) dissolved with ethyl alcohol (C 2H 5OH), methane (CH 4), ethylene (C 2H 4) and acetylene (C 2H 2). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10 − 4 Ω − 1 cm − 1 ) and under the light illumination (i.e. 9.9 × 10 − 4 Ω − 1 cm − 1 ). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10 − 3 mA/cm 2. The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10 − 4 % and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.

Optical and structural properties of amorphous carbon thin films deposited by microwave surface-wave plasma CVD

Nitrogen doped amorphous carbon (a-C : N) thin films were deposited on silicon and quartz substrates by microwave surface-wave plasma chemical vapor deposition technique at low temperature (< 100 °C). We used argon (Ar), camphor dissolved in alcohol and nitrogen (N) as carrier, source and dopant gases, respectively. Optical band gap ( E g) decreased from 4.1 to 2.4 eV when the N gas concentration increased from 0 to 4.5%. The films were annealed at different temperatures ranging from 150 to 450 °C in Ar gas environment to investigate the optical and electrical properties of the films before and after annealing. Both E g and electrical resistivity ( ρ) decreased dramatically to 0.95 eV and 5.7 × 10 4 (Ω-cm) at 450 °C annealing. The structural modifications of the films leading to more graphite as a function of the annealing temperature was confirmed by the characterization of Raman spectra.

Bonding defects and optical band gaps of DLC films deposited by microwave surface-wave plasma CVD

The effects of CH 4 / C 2H 4 flow ratio and annealing temperature on the defect states and optical properties of diamond-like carbon (DLC) films deposited by novel microwave surface-wave plasma chemical vapour deposition (MW SWP CVD) are studied through UV/VIS/NIR measurements, atomic force microscopy, Raman spectroscopy and electron spin resonance analysis. The optical band gap of DLC has been tailored between a relatively narrow range, 2.65–2.5 eV by manipulating CH 4 / C 2H 4 flow ratio and a wide range, 2.5–0.95 by thermal annealing. The ESR spin density varied between 10 19 to 10 17 spins/cm 3 depending on the CH 4 / C 2H 4 flow ratio (1 : 3 to 3 : 1). The defect density increased with increasing annealing temperature. Also, there is a strong dependence of spin density on the optical band gap of the annealed-DLC films, and this dependency has been qualitatively understood from Raman spectra of the films as a result of structural changes due to sp 3/sp 2 carbon bonding network. The surfaces of the films are found to be very smooth and uniform (RMS roughness < 0.5 nm).

Nitrogen incorporated diamond-like carbon films by microwave surface wave plasma CVD

Nitrogen incorporated diamond like carbon films have been deposited by microwave surface wave plasma chemical vapor deposition (MW-SWP-CVD), using methane (CH 4) as the source of carbon and with different nitrogen flow rates (N 2 / CH 4 flow ratios between 0 and 3). The influence of the nitrogen incorporation on the optical, structural properties and surface morphology of the carbon films were investigated using different spectroscopic techniques. The nitrogen has been incorporated into DLC:N films which was confirmed by the X-ray photoelectron spectroscopy (XPS) measurement. Moreover, the nitrogen incorporation was accompanied by a variation in the optical gap, which was attributed to the removal or creation of band tail states.

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage ( V oc) of 168.8 mV and a short-circuit current density ( J sc) of 8.4 μA/cm 2 under light illumination (AM 1.5 100 mW/cm 2). The energy conversion efficiency and fill factor were found to be 3.4 × 10 − 4 % and 0.238 respectively.

Effects of iodine doping on optoelectronic properties of diamond-like carbon thin films deposited by microwave surface wave plasma CVD

We report the effects of iodine (I) doping on the electrical and optical properties of diamond-like carbon (DLC) thin films grown on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition at low temperature (<100 °C). For film deposition, we used argon gas with methane or camphor dissolved with ethyl alcohol composition as plasma source. The optical gap and photoconductivity measurements of the samples were carried out before and after the iodine doping. The results show that optical gap dropped from 3.4 to 0.9 eV corresponding to nondoping to iodine-doping conditions, respectively. The photovoltaic measurements show that the open-circuit voltage ( V oc) and short-circuit current density ( J sc) of I-doped DLC film deposited on n-type silicon substrate under light illumination (AM1.5, 100 mW/cm 2) were approximately 177 mV and 1.15 μA, respectively, and the fill factor was found to be 0.217.