| 1. |
- Jian, Jingxin, et al.
(författare)
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Cubic SiC Photoanode Coupling with Ni:FeOOH Oxygen-Evolution Cocatalyst for Sustainable Photoelectrochemical Water Oxidation
- 2020
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Ingår i: Solar RRL. - : WILEY-V C H VERLAG GMBH. - 2367-198X. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- As an efficient water oxidation cocatalyst, the Earth-abundant nickel-iron oxyhydroxide (Ni:FeOOH) is introduced to coat on the cubic silicon carbide (3C-SiC) photoanode surface for improving the photoelectrochemical (PEC) water oxidation performance. The FeOOH is prepared on the 3C-SiC photoanode surface by hydrothermal deposition, followed by a photoassisted electrodeposition of NiOOH. It is shown that the Ni:FeOOH layer is composed of the beta-FeOOH nanorods with a conformal coating of the amorphous NiOOH. Under AM1.5G 100 mW cm(-2) illumination, the 3C-SiC/Ni:FeOOH photoanode exhibits a very low onset potential of 0.2 V versus reversible hydrogen electrode (V-RHE) and a high photocurrent density of 1.15 mA cm(-2) at 1.23 V-RHE, distinctly outperforming the 3C-SiC and the 3C-SiC/FeOOH counterparts. Open-circuit potential and impedance spectroscopy results demonstrate that the nanostructured Ni:FeOOH layer on the 3C-SiC surface increases the photovoltage and promotes the charge transfer toward the electrolyte, thus significantly improving the PEC water-splitting performance. These results provide new insights for the development of photoanodes toward efficient solar-fuel generation.
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| 2. |
- Jian, Jingxin, et al.
(författare)
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Nanoporous Cubic Silicon Carbide Photoanodes for Enhanced Solar Water Splitting
- 2021
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:3, s. 5502-5512
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Tidskriftsartikel (refereegranskat)abstract
- Cubic silicon carbide (3C-SiC) is a promising photoelectrode material for solar water splitting due to its relatively small band gap (2.36 eV) and its ideal energy band positions that straddle the water redox potentials. However, despite various coupled oxygen-evolution-reaction (OER) cocatalysts, it commonly exhibits a much smaller photocurrent (<similar to 1 mA cm(-2)) than the expected value (8 mA cm(-2)) from its band gap under AM1.5G 100 mW cm(-2) illumination. Here, we show that a short carrier diffusion length with respect to the large light penetration depth in 3C-SiC significantly limits the charge separation, thus resulting in a small photocurrent. To overcome this drawback, this work demonstrates a facile anodization method to fabricate nanoporous 3C-SiC photoanodes coupled with Ni:FeOOH cocatalyst that evidently improve the solar water splitting performance. The optimized nanoporous 3C-SiC shows a high photocurrent density of 2.30 mA cm(-2) at 1.23 V versus reversible hydrogen electrode (V-RHE) under AM1.5G 100 mW cm(-2) illumination, which is 3.3 times higher than that of its planar counterpart (0.69 mA cm(-2) at 1.23 V-RHE). We further demonstrate that the optimized nanoporous photoanode exhibits an enhanced light-harvesting efficiency (LHE) of over 93%, a high charge-separation efficiency (Phi(sep)) of 38%, and a high charge-injection efficiency (Phi(ox)) of 91% for water oxidation at 1.23 V-RHE, which are significantly outperforming those its planar counterpart (LHE = 78%, Phi(sep) = 28%, and Phi(ox) = 53% at 1.23 V-RHE). All of these properties of nanoporous 3C-SiC enable a synergetic enhancement of solar water splitting performance. This work also brings insights into the design of other indirect band gap semiconductors for solar energy conversion.
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| 3. |
- Kaushik, Priya Darshni, et al.
(författare)
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Structural Modifications in Epitaxial Graphene on SiC Following 10 keV Nitrogen Ion Implantation
- 2020
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Modification of epitaxial graphene on silicon carbide (EG/SiC) was explored by ion implantation using 10 keV nitrogen ions. Fragments of monolayer graphene along with nanostructures were observed following nitrogen ion implantation. At the initial fluence, sp(3) defects appeared in EG; higher fluences resulted in vacancy defects as well as in an increased defect density. The increased fluence created a decrease in the intensity of the prominent peak of SiC as well as of the overall relative Raman intensity. The X-ray photoelectron spectroscopy (XPS) showed a reduction of the peak intensity of graphitic carbon and silicon carbide as a result of ion implantation. The dopant concentration and level of defects could be controlled both in EG and SiC by the fluence. This provided an opportunity to explore EG/SiC as a platform using ion implantation to control defects, and to be applied for fabricating sensitive sensors and nanoelectronics devices with high performance.
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| 4. |
- Kaushik, Priya Darshni, et al.
(författare)
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Surface functionalization of epitaxial graphene using ion implantation for sensing and optical applications
- 2020
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Ingår i: Carbon. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0008-6223 .- 1873-3891. ; 157, s. 169-184
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Tidskriftsartikel (refereegranskat)abstract
- Surface functionalization has been shown to allow tailoring of graphene lattice thus making it suitable for different applications like sensing, supercapacitance devices, drug delivery system and memory devices. In this work, surface functionalization of epitaxial graphene on SiC (EG/SiC) was done by ion beam technology (30 keV Ag- ions at fluences ranging from 5 x 10(12) ions/cm(2) to 5 x 10(14) ions/cm(2)), which is one of the most precise techniques for introducing modifications in materials. Atomic force microscopy showed presence of nanostructures in ion implanted samples and Photoluminescence and X-ray photoelectron spectroscopy revealed that these are probably silicon oxy carbide. High-resolution transmission electron microscopy (HRTEM) showed decoupling of buffer layer from SiC substrate at many places in ion implanted samples. Further, HRTEM and Raman spectroscopy showed amorphization of both graphene and SiC at highest fluence. Fluence dependent increase in absorbance and resistance was observed. Gas sensors fabricated on pristine and ion implanted samples were able to respond to low concentration (50 ppb) of NO2 and NH3 gases. Detecting NH3 gas at low concentration further provides a simple platform for fabricating highly sensitive urea biosensor. We observed response inversion with increasing fluence along with presence of an optimal fluence, which maximized gas sensitivity of EG/SiC. (C) 2019 Elsevier Ltd. All rights reserved.
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| 5. |
- Kazemi, Amin, et al.
(författare)
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The effect of Cl- and N-doped MoS2 and WS2 coated on epitaxial graphene in gas-sensing applications
- 2021
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Ingår i: SURFACES AND INTERFACES. - : ELSEVIER. - 2468-0230. ; 25
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Tidskriftsartikel (refereegranskat)abstract
- In this study, epitaxial graphene (EG) was grown on a 6H-SiC (0001) substrate via the thermal decomposition of SiC. Undoped and Cl- or N-doped molybdenum disulfide (MoS2) and tungsten disulfide (WS2) ultrathin films were spin-coated on the graphene surface. The scanning electron microscopy (SEM) images and topological atomic force microscopy (AFM) analysis showed good distribution of thin MoS2 and WS2 flakes on the EG surface. The X-ray photoelectron spectroscopy (XPS) confirmed the presence of Mo-related peaks of 3d(5/2) and 3d(3/2) at similar to 232.2 eV and 235.1 eV, respectively. It also represented peaks of W 4f(7/2) and 5p(5/2) at around 36.1 eV and 37.9 eV, respectively. Moreover, XPS results showed peaks at around 167.4 eV and 168.4 eV corresponding to S 2p for MoS2 and WS2, respectively. The XPS results also confirmed the presence of dopant elements in MoS2 and WS2 flakes. We fabricated sensors using undoped and chlorine- or nitrogen-doped MoS2 and WS2 ultrathin films for gas-sensing applications. These sensors were surveyed for ammonia (NH3) and nitrogen dioxide (NO2) gas sensing. As in NO2, both undoped sensors react with a decrease in relative sensor responses to NH3, hence showing n-type behavior. Doping MoS2 and WS2 with chlorine led to a higher response vis-a-vis the nitrogendoped sensors. The absolute relative response of Cl-doped WS2 and MoS2 was about 3.5 and 1.8 times more than that of their undoped counterparts toward NH3. A change of direction with a slightly smaller response (approximately x 0.8), however, could also be observed in the doping of MoS2 and WS2 with nitrogen. When exposed to NO2, the Cl-doped WS2 sensor response was 1.2 more than the N-doped one, while for MoS2 these values changed in the range of 1.2 - 1.6 for different flows of gas.
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| 6. |
- Li, Hao, et al.
(författare)
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Atomic-Scale Tuning of Graphene/Cubic SiC Schottky Junction for Stable Low-Bias Photoelectrochemical Solar-to-Fuel Conversion
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 14:4, s. 4905-4915
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Tidskriftsartikel (refereegranskat)abstract
- Engineering tunable graphene-semiconductor interfaces while simultaneously preserving the superior properties of graphene is critical to graphene-based devices for electronic, optoelectronic, biomedical, and photoelectrochemical applications. Here, we demonstrate this challenge can be surmounted by constructing an interesting atomic Schottky junction via epitaxial growth of high-quality and uniform graphene on cubic SiC (3C-SiC). By tailoring the graphene layers, the junction structure described herein exhibits an atomic-scale tunable Schottky junction with an inherent built-in electric field, making it a perfect prototype to systematically comprehend interfacial electronic properties and transport mechanisms. As a proof-of-concept study, the atomic-scale-tuned Schottky junction is demonstrated to promote both the separation and transport of charge carriers in a typical photoelectrochemical system for solar-to-fuel conversion under low bias. Simultaneously, the as-grown monolayer graphene with an extremely high conductivity protects the surface of 3C-SiC from photocorrosion and energetically delivers charge carriers to the loaded cocatalyst, achieving a synergetic enhancement of the catalytic stability and efficiency.
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| 7. |
- Maryam, A., et al.
(författare)
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Preparation and application of LiSiC-oxide for low temperature solid oxide fuel cells
- 2021
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Ingår i: Digest Journal of Nanomaterials and Biostructures. - : VIRTUAL CO PHYSICS SRL. - 1842-3582. ; 16:2, s. 501-508
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductors are well known as excellent materials in the field of exploring novel avenues which combine various fields in electronics, electrochemistry, etc for new functional device concepts. Lithium silicon carbide (LiSiC) is a well-known electrode material for Lithium ion batteries but relatively new for solid oxide fuel cells (SOFCs) and electrolyte-layer free fuel cells (EFFCs). In the present work, we have explored three categories of fuel cells based on mixed LiSiC-SDC (samarium doped ceria) in SOFC and LiSiC as a single component material with type (I) and without coating of a layer of 3C-SiC as EFFC type (II). All of three cells are sandwiched between Ni foams coated with NCAL (Ni0.8Co0.15Al0.05Li-oxide). The electrochemical performances of as prepared fuel cells are tested at 550 degrees C, which is substantially lower than in conventional fuel cell materials. The LiSiC based EFFC type (II) demonstrates better performance because of less ohmic resistance as compared to type (I) have more layers. This indicates that the LiSiC-SDC system has potential for fuel cell development in accordance with energy band structure and alignment.
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| 8. |
- Rasheed, M. N., et al.
(författare)
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Enhanced electrical properties of nonstructural cubic silicon carbide with graphene contact for photovoltaic applications
- 2020
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Ingår i: Digest Journal of Nanomaterials and Biostructures. - Bucharest, Romania : S.C. Virtual Company of Phisics S.R.L. - 1842-3582. ; 15:3, s. 963-972
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Tidskriftsartikel (refereegranskat)abstract
- Cubic silicon carbide (3C-SiC) is successfully synthesized through a simple solid-state reaction technique at a comparatively low temperature without using any catalyst. The XRD data is also used to study other structural parameters of synthesized sample by using different method. Raman peak at 796 cm(-1) supports the XRD results. Si-C vibrational mode observed at 788 cm-1 in the FTIR spectrum further confirms the growth of 3C-SiC. UV-Vis spectroscopy is used to measure optical bandgap energy (E-g = 2.36 eV). Other optical parameters such as dielectric constant and refractive index of grown sample are also studied. Electrical performance is analyzed by using graphene contact with further evaluation of dark and light IV-measurements. The use of graphene contact establishes the enhancement of electrical conductivity of as-grown samples particularly when they are exposed to light. These findings indicate that the grown sample has comparatively better transport properties than conventional metal contacts under the illuminated conditions.
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| 9. |
- Sarfraz, Amina, et al.
(författare)
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Catalytic Effect of Silicon Carbide on the Composite Anode of Fuel Cells
- 2021
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 4:7, s. 6436-6444
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Tidskriftsartikel (refereegranskat)abstract
- High efficiency, fuel flexibility, and sustainable energy conversion make fuel cells attractive compared to conventional energy systems. The direct ethanol fuel cells have attracted much attention because of the direct utilization of ethanol fuel. Anode materials are required to enhance the catalytic activity of the liquid fuel, which oxidize the fuel at lower operating temperature. Therefore, the catalytic effect using silicon carbide has been investigated in the LiNiO2-delta anode. The material has been characterized, and it is found that SiC shows a cubic structure and LiNiO2-delta exhibits a hexagonal structure, while the LiNiO2-delta-SiC composite exhibits a mixed cubic and hexagonal phase. Scanning electron microscopy depicts that the material is porous. The Fourier transform infrared spectroscopy analysis shows the presence of Si-O-Si, Si-C, C=O, and Si-OH bonding. The LiNiO2-delta-SiC composite (1:0.3) exhibited a maximum electrical conductivity of 1.34 S cm(-1) at 650 degrees C with an electrical band gap of 0.84 eV. The fabricated cell with the LiNiO2-delta-SiC anode exhibits a power density of 0.20 W cm(-2) at 650 degrees C with liquid ethanol fuel. The results show that there is a promising catalytic activity of SiC in the fuel cell anode.
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| 10. |
- Shi, Yuchen, et al.
(författare)
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A patterning-free approach for growth of free-standing graphene nanoribbons using step-bunched facets of off-oriented 4H-SiC(0 0 0 1) epilayers
- 2020
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 53:11
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Tidskriftsartikel (refereegranskat)abstract
- The tunable electronic structure of graphene nanoribbons (GNRs) has attracted much attention due to the great potential in nanoscale electronic applications. Most methods to produce GNRs rely on the lithographic process, which suffers from the process-induced disorder in the graphene and scalability issues. Here, we demonstrate a novel approach to directly grow free-standing GNRs on step-bunched facets of off-oriented 4H-SiC epilayers without any patterning or lithography. First, the 4H-SiC epilayers with well-defined bunched steps were intentionally grown on 4 degree off-axis 4H-SiC substrates by the sublimation epitaxy technique. As a result, periodic step facets in-between SiC terraces were obtained. Then, graphene layers were grown on such step-structured 4H-SiC epilayers by thermal decomposition of SiC. Scanning tunneling microscopy (STM) studies reveal that the inclined step facets are about 13-15 nm high and 30-35 nm wide, which gives an incline angle of 23-25 degrees. LEEM and LEED results showed that the terraces are mainly covered by monolayer graphene and the buffer layer underneath it. STM images and the analysis of their Fourier transform patterns suggest that on the facets, in-between terraces, graphene is strongly buckled and appears to be largely decoupled from the surface.
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