Ar Gas Flow Research Articles

Crystallography of Bcc/T1/T2 Three-Phase Microstructure in the Directionally Solidified Mo-Nb-Si-B Alloy

ABSTRACTIn the present study, the crystallographic features of bcc/T1/T2 three-phase microstructure in a directionally solidified Mo–32.2Nb–19.5Si–4.7B (at.%) alloy have been examined by electron back-scattering diffraction (EBSD) analysis. The alloy was directionally solidified using an optical floating zone (OFZ) furnace in a flowing Ar gas atmosphere at a constant growth rate of 10 mm/hour. The microstructure of the directionally solidified alloy is characterized by an elongated T2 phase surrounded by inclusions of bcc and T1 phases with an interwoven morphology. The T2 grains are faceted on the (001) planes and elongated along the [110] direction. The T2 phase has an orientation relationship of (001)T2 // (011)bcc and [130]T2 // [2${\rm{\bar 1}}$1]bcc with the bcc phase, whereas any particular orientation relationships of T1 phase with bcc and T2 phases have not been found. These crystallographic features of bcc/T1/T2 three-phase microstructure suggest that the primary T2 phase crystallizes and grows along the [110] direction in liquid phase, followed by nucleation of the bcc phase on the interface between T2 and liquid phases, resulting in bcc/T1 two-phase eutectic reaction surrounding the elongated T2 phase.

Evaluation of high temperature resistance of white Si–O–C(–H) ceramics in an inert atmosphere

Two kinds of white Si–O–C(–H) ceramic powders, named S900 and S1100, were prepared from cross-linked polysiloxane particles with an average diameter of 6μm. S900 was the product obtained in a hydrogen gas flow at 900°C with a holding time of 1h, whereas S1100 was the product obtained at 1100°C with a holding time of 3h. Heat stability of these ceramic powders in graphite boats were examined within the temperature range of 1200–1600°C in an Ar gas flow. The powder substantially began to degrade beyond 1400°C, which was accompanied by mass loss, fusing of particles and partial cristobalite precipitation. The color of S900, however, became black after the heat treatment at 1400°C before the substantial mass loss, whereas the color of S1100 showed small change to light gray after the heat treatment at 1400°C. The apparent color change of the samples during the heat treatment possibly corresponded to defect incorporation in the Si–O–C(–H) network, whereas the change in chemical composition was minor. At high temperature region, SiO and CO were evolved as a result of SiC–SiO2 reaction, although SiC and SiO2 were defined as virtual phases in the Si–O–C(–H) amorphous.

Inactivation of Escherichia coli using atmospheric-pressure plasma jet

An atmospheric-pressure argon (Ar) plasma jet was applied to the inactivation of Escherichia coli. The Ar plasma jet was generated at a frequency of 10 kHz, an applied voltage of 10 kV, and an Ar gas flow rate of 10 L/min at atmospheric pressure. E. coli cells seeded on an agar medium in a Petri dish were inactivated by Ar plasma jet irradiation for 1 s. Scanning electron microscopy (SEM) revealed that E. coli cells were killed because their cell wall and membrane were disrupted. To determine the causes of the disruption of the cell wall and membrane of E. coli, we performed the following experiments: the measurement of the surface temperature of an agar medium using a thermograph, the analysis of an emission spectrum of a plasma jet obtained using a multichannel spectrometer, and the determination of the distribution of the concentration of hydrogen peroxide (H2O2) generated on an agar medium by plasma jet irradiation using semiquantitative test strips. Moreover, H2O2 solutions of different concentrations were dropped onto an agar medium seeded with E. coli cells to examine the contribution of H2O2 to the death of E. coli. The results of these experiments showed that the cell wall and membrane of E. coli were disrupted by electrons in the plasma jet, as well as by electroneutral excited nitrogen molecules (N2) and hydroxyl (OH) radicals in the periphery of the plasma jet.

Optical detection of argon gas flow based on vibration-induced change in photoluminescence of a semiconducting single-walled carbon nanotube bundle.

In this work, we demonstrate that Ar gas flow can be optically detected using mechanical vibration of a semiconducting single-walled carbon nanotube (SWCNT) bundle as a platform. A change in the photoluminescence (PL) intensity was induced by out-of-focusing of the SWCNT bundle of interest due to vibration caused by the introduced gas stream, for which a gas flow control system was installed in an optical microscope. The PL intensity was found to change systemically with the Ar flow rates in a range of relatively large flow rate intervals [0.70 to 3.0 standard cubic liters per minute (SLM) with 0.1-0.5 SLM intervals] with a noticeable hysteresis. It was, however, difficult to obtain a detectable PL change in a range of very small flow rate intervals (0.67 to 0.70 SLM with a 0.01 SLM interval). The detailed results and underlying mechanism are discussed in detail.

Graphene treatment using a very low energy Ar+ ion beam for residue removal.

The effect of Ar+ ion energy on the removal of the polymethyl methacrylate (PMMA) residue remaining on the chemical vapor deposited (CVD) graphene surface without damaging the graphene surface was investigated. Stable and low energy Ar+ ion beams having a mono-energetic energy distribution with a peak energy of 7.5 eV or 11.5 eV could be formed by using a two-grid magnetically enhanced ICP ion gun with and without the application of 25 Gauss axial magnetic field, respectively, while controlling the Ar gas flow rate. When the CVD graphene treatment was performed with the Ar+ ions having the ion energy peak at 7.5 eV (with the magnetic field) and 11.5 eV (without the magnetic field), the blue shift of Raman G peak from p-type doped to intrinsic graphene indicating the removal of residue on the graphene surface could be observed for both conditions, however, the graphene treated at 11.5 eV (without the magnetic field) showed the increase of the defect while that treated at 7.5 eV (with the magnetic field) showed no significant change of the defect. It is believed that, for the treatment of CVD graphene, possibly due to the low binding energy area such as grain boundaries and domains in the CVD graphene, low energy ions with less than the energy of 10 eV is required not to damage the graphene surface, and a magnetically enhanced ICP ion gun which can provide stable and low energy Ar+ ions with a mono-energetic ion energy distribution with a peak of 7.5 eV can be applicable to the residue removal on the graphene surface.

Size-selected TiO₂ nanocluster catalysts for efficient photoelectrochemical water splitting.

Nanoclusters (NCs) are of great interest because they provide the link between the distinct behavior of atoms and nanoparticles and that of bulk materials. Here, we report precisely controlled deposition of size-selected TiO2 NCs produced by gas-phase aggregation in a special magnetron sputtering system. Carefully optimized aggregation length and Ar gas flow are used to control the size distribution, while a quadrupole mass filter provides precise in situ size selection (from 2 to 15 nm). Transmission electron microscopy studies reveal that NCs larger than a critical size (∼8 nm) have a crystalline core with an amorphous shell, while those smaller than the critical size are all amorphous. The TiO2 NCs so produced exhibit remarkable photoelectrochemical water splitting performance in spite of a small amount of material loading. NCs of three different sizes (4, 6, and 8 nm) deposited on H-terminated Si(100) substrates are tested for the photoelectrochemical catalytic performance, and significant enhancement in photocurrent density (0.8 mA/cm(2)) with decreasing NC size is observed with a low saturation voltage of -0.22 V vs Ag/AgCl (0.78 V vs RHE). The enhanced photoconductivity could be attributed to the increase in the specific surface area and increase in the number of active (defect) sites in the amorphous NCs. The unique advantages of the present technique will be further exploited to develop applications based on tunable, size-selected NCs.

Van der Waals epitaxial growth of topological insulator Bi2−xSbxTe3−ySey ultrathin nanoplate on electrically insulating fluorophlogopite mica

We report the growth of high quality Bi2−xSbxTe3−ySey ultrathin nanoplates (BSTS-NPs) on an electrically insulating fluorophlogopite mica substrate using a catalyst-free vapor solid method. Under an optimized pressure and suitable Ar gas flow rate, we control the thickness, the size, and the composition of the BSTS-NPs. Raman spectra showing systematic change indicate that the thicknesses and compositions of the BSTS-NPs are indeed accurately controlled. Electrical transport demonstrates a robust Dirac cone carrier transport in the BSTS-NPs. Since the BSTS-NPs provide superior dominant surface transport of the tunable Dirac cone surface states with negligible contribution of the conduction of the bulk states, the BSTS-NPs provide an ideal platform to explore intrinsic physical phenomena as well as technological applications of 3-dimensional topological insulators in the future.

Structure of heat-treated mesoporous carbon and its electrochemical lithium intercalation behavior

Mesoporous carbon (MPC) was synthesized via the thermal decomposition of magnesium citrate in a flow of Ar gas, followed by dissolution of MgO nanoparticles in the carbonaceous pyrolysis product. The MPC was then heated at 1800, 2000, 2200, 2400, 2500, 2700 and 3000 °C for 30 min. The MPC samples heated at 1800 and 2000 °C having a mesopore structure with graphitized carbon walls exhibited an enhanced rate capability as a composite anode for lithium ion batteries. Heat treatment of the MPC from 2200 to 2700 °C led to a partial collapse of micropores and mesopores, which decreased the charge/discharge capacity. The MPC samples heated at 2700 and 3000 °C having thick graphitized carbon layers and a mesopore structure with graphitized carbon walls showed charge/discharge curves with three lithium intercalation potential plateaus at approximately 0.2, 1.0, and 1.5 V vs. Li/Li+. The MPC sample heated at 3000 °C was the best anode material for lithium ion batteries among the MPC samples evaluated in this study because of its low irreversible capacity, high columbic efficiency, and high rate capability.

Materials Exploration in Na-Fe-S-O System: Synthesis and Electrochemistry

The current Li ion batteries which employ layered oxides such as LiCoO2, spinel LiMn2O4, and olivine LiFePO4as cathode materials have dominated global markets of secondary batteries. However, rapid expansion of their application has triggered the growing concerns on scarcity and rising costs of Li resources. As one of the most realistic alternatives, Na ion batteries re-attract massive attention owing to its abundance, lower cost, and sustainable production. In this pursuit, Na-Fe-S-O systems are one of the most desirable systems, which are consisted only by earth-abundant and geographically distributed elements. Especially, sulfate compounds are very cheap, being a byproduct of coal power plant, or petrochemical industries.During the exploration of in the Na2O-FeO-SO3 ternary phase diagrams, we identified some materials with a totally new composition and crystal structure [1]. The target cathode material was obtained via classical solid-state synthesis by ball-milling Na2SO4 and anhydrous FeSO4 followed by annealing the mixed precursors at elevated temperature under an Ar gas flow. The electrode property of as-synthesized cathode material was examined with no special effort for decreasing particle size or carbon coating. The working electrode was formulated by mixing 85 wt% active material, 10 wt% carbon black (Ketjen Black, ECP), and 5 wt% polytetrafluoro- ethylene (PTFE) binder. Figure 1 shows an example of galvanostatic charging and discharging curves measured at a rate of C/10. The initial charging capacity of 98 mAhg- 1 was retained over 10 cycles with small polarization. An average potential of 3.6 V (vs. Na/Na+) is the highest-ever Fe3+/Fe2+redox potential among all known Na-ion cathode materials. The smooth sloppy charging and discharging curves suggests a single-phase reaction mechanism, which is generally favorable from the perspective of homogeneity and kinetics of the reaction.Details on the compositions and their synthetic conditions will be disclosed in the poster.

Porous SiOC beads by freeze-drying polycarbosilane emulsions

Porous silicon oxycarbide (SiOC) beads were prepared by freeze-drying of water-in-oil (w/o) emulsion, containing water and polycarbosilane (PCS) dissolved p-xylene in the presence of sodium xylenesulfonate (SXS) as an emulsifier. The emulsion was frozen by being dropped onto a liquid N2 bath, which resulted in 1–2mm sized beads. After curing at 200°C for 1h in air and subsequent pyrolysis at 800°C for 1h in an Ar gas flow, porous SiOC beads were obtained. Freeze-dried beads showed lamellae-shaped macro-pore structures at a moderate freezing rate due to a phase separation behavior of PCS during freezing, while no lamellae pores were formed at a very high freezing rate. Lamellae-shaped pores developed along the freezing direction. Water droplets that were formed in w/o emulsion converted to spherical pores after drying. The combined processes of producing PCS emulsion and freeze-drying of emulsion resulted in two types of macro-pores: lamellae-shaped and spherical pores. Meso-pores, of which specific surface area and average pore size were 71.5m2g−1 and 4.85nm, respectively, were formed inside the SiOC strut.

Chromium thin film deposition on ITO substrate by RF sputtering

To obtain a suitable ohmic contact with the lowest resistivity, chromium (Cr) thin films were deposited on transparent conductive oxide indium tin oxide (ITO) by RF sputtering method in argon atmosphere and its electrical properties were optimized. The deposition of Cr thin film has been performed for the layers with thickness of 150, 300 and 600 nm in constant Ar gas flow of 30 SCCM. Results show that the lowest contact resistivity belongs to the layer with 600 nm thickness. Furthermore, Cr/ITO has been studied for five different RF powers of 100, 150, 200, 250 and 300 W. Experimental results show that specific contact resistance of Cr/ITO contact decreases in condition of depositing chromium thin films on ITO at higher RF powers. Analysis of SEM has been performed on the samples. The SEM micrographs show Cr thin films have smaller grains at RF power of 150 W, in comparison with other RF powers. The lowest specific contact resistivity for Cr/ITO has been obtained 4.7 × 10−2 Ω cm2 at RF power of 150 W with 600 nm thickness of chromium thin films.

태양전지용 규소 결정 성장 기술 개발의 현황

태양전지용 규소에는 단결정, 다결정, mono-like의 세 가지 재료가 사용 중에 있다. 첫 번째로, 단결정은 수율향상의 과제에 집중되고 있으며, 이것은 고액 계면의 형상이 주요 요인으로 알려지고 있다. 이에 대한 연구가 전산모사 등으로 집중되고 있다. 또한 결정과 도가니의 회전 속도가 고액 계면의 형상에 영향을 미치는 것이 확인 되었다. 다결정의 경우에는 결정립계의 역할이 매우 중요하므로 이에 대한 연구가 진행되는데, 이들을 특히 전기적으로 비활성적인 쌍정 입계로 전환하는 연구가 진행되고 있다. 성장 조건을 변경시켜 쌍정 입계로 바꾸어서 재료의 전기적 성질을 향상시키는 결과를 확인하였다. 또한 성장 공정에서 발생될 수 있는 오염을 줄이기 위한 노력은 상부의 Ar 가스의 흐름을 상향 조절하여 불순물의 용입을 줄임이 확인되었다. 다음으로 mono-like인 경우에는 측면으로부터 성장 되어 들어오는 다결정이 단결정의 분율을 저하 시키는 주요 요인이 되고 있다. 이에 대한 해결책으로 하부의 냉각 속도를 높이고 상부와 측면에 단열재를 보강하는 방안이 제시되고 있고, 하부에 놓는 seed의 orientation을 조절하여 측면으로부터 성장 되어 들어오는 다결정을 억제하는 방안이 효과가 있음이 확인 되고 있다. Three kinds of crystalline silicon have been used for the solar cell grade. First of all, single crystalline silicon is the main subject to enhance the production yield. Most of the efforts are focused on the control of the melt-crystal interface shape affected by the crystal-crucible rotation rate. The main subject in the multi-crystalline silicon ingot is the contamination control. Faster Ar gas flow above the melt surface will lower the carbon contamination in the crystal. And also, twin boundary electrically inactive is found to be more effective than grain boundary for the improvement of the MCLT. In the case of mono-like silicon material, propagation of the multi-crystalline silicon growing from the inner side crucible is the problem lowering the portion of the single crystalline part at the center of the ingot. Crystal growing apparatus giving higher cooling rate at the bottom and lower cooling rate at the side crucible was suggested as the optimum solution obtaining higher quality of the mono-like silicon ingot. Proper application of the seeds at the bottom of the crucible would be one of the solutions.

High Selectivity in Dry Etching of Silicon Nitride over Si Using a Novel Hydrofluorocarbon Etch Gas in a Microwave Excited Plasma for FinFET

The SiNx gate spacer formation is one of the key processes in the miniaturized MISFETs, because the thickness of the gate spacer and the Si recess after the gate spacer formation etching have large impacts on the electrical properties of MISFETs [1,2]. High selectivity of SiNx over Si is strongly required in MISFETs such as extremely thin silicon on insulator (ETSOI) device and 3 dimensional (3D) MOSFET for the reduction of the series resistance [1,2]. Various etching gases were evaluated in order to obtain high selectivity of SiNx over Si[3-6]. It is considered that a plasma source and etching gases are important in order to obtain high selectivity dry etching of SiNxover Si. We consider that the plasma source with low electron temperature is advantageous in the improvement of selectivity, because it prevents excessive dissociation of the etching gas. The difference of the chemical structures of etching gas with the plasma source can make a difference of the selectivity. In this work, we utilized the microwave excited plasma source that has the characteristic of low electron temperature and a novel gas (SSY525 made by ZEON) [7].Figure 1 shows the selectivity of SiNx to poly Si as a function of O2 flow rate. The flow rate of SSY525 and CH3F are 8 sccm and 10 sccm, respectively. The microwave power, the RF power of bottom electrode and the Ar gas flow rate were 1000 W, 60 W and 200 sccm, respectively. SiNx films were deposited by PECVD and LPCVD. Si/N ratio and density of SiNx by PECVD was lower than those by LPCVD [8]. In the case of SSY525, a higher selectivity of SiNx by PECVD and LPCVD to poly Si was obtained with O2 flow rate from 0 to 50 sccm to CH3F. Low etch rate of poly Si less than 0.3 nm/min and high selectivity of SiNx to Si over 50 were obtained with O2 flow rate of 0 sccm and more than 30 sccm. Figure 2 shows the analysis of poly Si surface by XPS after dry etching using SSY525. A high intensity of C 1s was obtained with O2 flow rate of 0 sccm. It is considered that high selectivity of SiNx to poly Si was obtained due to carbon deposition on poly Si surface. The intensity of C 1s decreases and the intensity of O 1s increases as the O2 flow rate increases. It is considered that High selectivity of SiNx to poly Si is obtained with O2 flow rate more than 30 sccm due to an oxidation of poly Si surface. Figure 3 (a) shows the schematic of 3D-MISFET structure. Figure 3 (b)-(d) show the cross-section SEM images from A to B in Fig. 3 (a) with various SSY525 flow rate. A 40 nm-thick SiNx was overetched at (b) 8 sccm, (c) 12 sccm and (d) 15 sccm. Si near the SiNx sidewall was etched with SSY525 of 8 sccm. It was not etched with SSY525 more than 12 sccm. About 5 nm-thick film containing carbon was deposited on the Si surface with 15 sccm. In the cases of (c) and (d), high selectivity of SiNx over Si was obtained. It is confirmed that SSY525 is effective in order to form the SiNxgate spacer in the miniaturized MISFET.

Defect induced ferromagnetism in undoped ZnO nanoparticles

Undoped ZnO nanoparticles (NPs) with size ∼12 nm were produced using forced hydrolysis methods using diethylene glycol (DEG) [called ZnO-I] or denatured ethanol [called ZnO-II] as the reaction solvent; both using Zn acetate dehydrate as precursor. Both samples showed weak ferromagnetic behavior at 300 K with saturation magnetization Ms = 0.077 ± 0.002 memu/g and 0.088 ± 0.013 memu/g for ZnO-I and ZnO-II samples, respectively. Fourier transform infrared (FTIR) spectra showed that ZnO-I nanocrystals had DEG fragments linked to their surface. Photoluminescence (PL) data showed a broad emission near 500 nm for ZnO-II which is absent in the ZnO-I samples, presumably due to the blocking of surface traps by the capping molecules. Intentional oxygen vacancies created in the ZnO-I NPs by annealing at 450 °C in flowing Ar gas gradually increased Ms up to 90 min and x-ray photoelectron spectra (XPS) suggested that oxygen vacancies may have a key role in the observed changes in Ms. Finally, PL spectra of ZnO showed the appearance of a blue/violet emission, attributed to Zn interstitials, whose intensity changes with annealing time, similar to the trend seen for Ms. The observed variation in the magnetization of ZnO NP with increasing Ar annealing time seems to depend on the changes in the number of Zn interstitials and oxygen vacancies.

Measurement of Reactive Hydroxyl Radical Species Inside the Biosolutions During Non-thermal Atmospheric Pressure Plasma Jet Bombardment onto the Solution

Non-thermal atmospheric pressure plasma jet could generate various kinds of radicals on biosolution surfaces as well as inside the biosolutions. The electron temperature and ion density for this non-thermal plasma jet have been measured to be about 0.8~1.0 eV and 1 × 1013 cm−3 in this experiment, respectively, by atmospheric pressure collisional radiative model and ion collector current. In this context, the hydroxyl OH radical density inside the biosolutions has been also investigated experimentally by ultraviolet absorption spectroscopy when the Ar non-thermal plasma jet has been bombarded onto them. It is found that the emission and absorption profiles for the other reactive oxygen species such as NO (226 nm) and O2*− (245 nm) are shown to be very small inside the biosolution in comparison with those for the OH radical species. It is found that the densities of OH radical species inside the biosolutions are higher than those on the surface in this experiment. The densities of the OH radical species inside the deionized water, Dulbecco’s modified eagle medium, and phosphate buffered saline are measured to be about 2.1 × 1016, 1.1 × 1016, and 1.0 × 1016 cm−3, respectively, at 2 mm downstream from the surface under optimized Ar gas flow of 200 sccm. It is also found that the critical hydroxyl OH radical density for the lung cancer H460 cells to experience an apoptosis is observed to be around 0.3 × 1016 cm−3 under 1 min plasma exposure in this experiment.

Effects of gas flow rate on structural features of ZnO nanowire arrays fabricated on silicon substrate

Arrays of single-crystal zinc oxide (ZnO) nanowires have been synthesized on silicon substrates by vapor–liquid–solid growth techniques. The effect of growth conditions including the substrate temperature and Ar gas flow rate on the growth properties of ZnO nanowire arrays were studied. Structural and optical characteristics were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. The XRD measurements showed that the single-crystal nanowires exhibited growth in the (002) direction. SEM images of the ZnO nanowire arrays grown at various Ar gas flow rates indicated that the alignment and structural features of the ZnO nanowires were affected by the gas flow rate. The PL of the ZnO nanowire arrays exhibited strong UV emission at 380 nm and weak green emission at approximately 510 nm. A blue shift and broadening of the UV emission were observed with increasing Ar gas flow rate.

Investigation on the bonding behavior of the interface within the supersonic plasma sprayed coating system based on the fractal theory

In order to investigate the relationship between the interfacial morphology of the coating system and its adhesion strength, the supersonic plasma spraying equipment is employed to fabricate Fe-based alloy coating. The (Ni, Al) coating is prepared as the undercoating with different flow of Ar gas, aiming at obtaining various rough morphologies. Interfacial morphologies of the coating system are quantificationally characterized by fractal dimension(FD). The pull-off method is used to test the adhesion strength. Result shows that the adhesion strength is obviously improved by fabricating an undercoating, and the FD of the interfacial morphology decreases with the increase of the flow rate of Ar gas, while the adhesion strength will be raised at the first beginning and then decreased to a certain value.

Postdeposition Annealing Effect on Cu2ZnSnS4Thin Films Grown at Different Substrate Temperature

Cu2ZnSnS4(CZTS) thin films were deposited on top of Molybdenum (Mo) coated soda lime glass (SLG) substrates using a single target rf magnetron sputtering technique. The sputtering parameters such as base pressure, working pressure, rf power, argon (Ar) gas flow rate, and deposition time were kept consistent throughout the experiment. The effect of different substrate temperatures, for example, room temperature (RT), 300°C, 350°C, 370°C, 400°C, and 450°C, was analyzed by studying their structural, electrical, and optical properties. As-sputtered films were then annealed at 460°C. X-ray diffraction (XRD) measurement revealed the structure to be kesterite with peak of (112) plane in both annealed and as-sputtered CZTS thin films. The crystallinity of the films improved with the increasing substrate temperature until 370°C. Secondary phases of MoS2,CuxMoSx,CuxSnSx,CuxS, and Cu6MoSnS8(hemusite) were also observed in the annealed CZTS films. Scanning electron microscopy (SEM) shows crystallite size of deposited CZTS thin film to be proportionally related to deposition temperature. The highest surface roughness of 67.318 nm is observed by atomic force microscopy (AFM). The conductivity type of the films was found to be p-type by Hall effect measurement system.

Graphene Grown on Ion-Implanted 4H-SiC and an Effect of Pre-Plasma Treatment

ABSTRACT4H-SiC substrates were annealed at 1500 °C for 30 min in 0.01 MPa Ar gas flow to make a graphene film. To clarify the effect of Al ion implantation and pre-plasma treatment, the graphene was fabricated on four different kinds of SiC substrates: without plasma treatment, with plasma treatment, Al ion-implanted without plasma treatment and Al ion-implanted with plasma treatment. The graphene films were analyzed by AFM and Raman spectroscopy. The Al ion implanted sample, which was then processed by CF4 plasma, showed small surface roughness of 3.49 nm (RMS), while the sample without CF4 plasma treatment showed large surface roughness of 8.41nm. Similar results were also observed for SiC samples without Al ion implantation. In Raman spectra, strong D-band, G-band and 2D-band signals were detected on both ion-implanted samples after annealing at 1500 °C, but weak D-band were observed on both samples without Al ion implantation. Raman mapping (2D-FWHM) showed that the graphene on ion-implanted SiC treated with CF4 plasma was more homogeneous than the one without CF4 plasma treatment. Hall measurements for SiC without Al ion implantation showed that graphene on SiC treated with CF4 plasma has higher mobility (389 cm2/Vs) than that without plasma treatment (136 cm2/Vs). Additionally, p-type graphene can be fabricated on Al ion-implanted SiC by CF4 plasma treatment.

Enhanced visible-light photocatalytic activity of g-C3N4/TiO2 films

Enhanced photocatalytic degradation of methylene blue (MB) using graphitic carbon nitride/titanium dioxide (g-C3N4/TiO2) catalyst films has been demonstrated in this present work. The g-C3N4/TiO2 composites were prepared by directly heating the mixture of melamine and pre-synthesized TiO2 nanoparticles in Ar gas flow. The g-C3N4 contents in the g-C3N4/TiO2 composites were varied as 0, 20, 50 and 70wt%. It was found that the visible-light-induced photocatalytic degradation of MB was remarkably increased upon coupling TiO2 with g-C3N4 and the best degradation performance of ∼70% was obtained from 50wt%g-C3N4 loading content. Results from UV–vis absorption study, Electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy suggest that the improved photoactivity is due to a decrease in band gap energy, an increased light absorption in visible light region and possibly an enhanced electron–hole separation efficiency as a result of effective interfacial electron transfer between TiO2 and g-C3N4 of the g-C3N4/TiO2 composite film. Based on the obtained results, the possible MB degradation mechanism is ascribed mainly to the generation of active species induced by the photogenerated electrons.