| 1. |
- Zhang, Guobin, et al.
(författare)
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Thermal Analysis of AlGaN/GaN High-Electron-Mobility Transistors with Graphene
- 2018
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 18:11, s. 7578-7583
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Tidskriftsartikel (refereegranskat)abstract
- A thermal analysis of AlGaN/GaN high electron mobility transistors (HEMTs) with Graphene is investigated using Silvaco and Finite Element Method. Two thermal management solutions are adopted; first of all, graphene is used as dissipation material between SiC substrate and GaN buffer layer to reduce thermal boundary resistance of the device. At the same time, graphene is also used as a thermal spread material on the top of the source contacts to reduce thermal resistance of the device. The thermal analysis results show that the temperature rise of device adopting graphene decreases by 46.5% in transistors operating at 13.86 W/mm. Meanwhile, the thermal resistance of GaN HEMTs with graphene is 6.8 K/W, which is much lower than the device without graphene, which is 18.5 K/W. The thermal management solutions are useful for integration of large-scale graphene into practical devices for effective heat spreading in AlGaN/GaN HEMT.
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| 2. |
- Abadikhah, Marie, 1992, et al.
(författare)
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Effect of anode material and dispersal limitation on the performance and biofilm community in microbial electrolysis cells
- 2023
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Ingår i: Biofilm. - 2590-2075. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- In a microbial electrolysis cell (MEC), the oxidization of organic compounds is facilitated by an electrogenic biofilm on the anode surface. The biofilm community composition determines the function of the system. Both deterministic and stochastic factors affect the community, but the relative importance of different factors is poorly understood. Anode material is a deterministic factor as materials with different properties may select for different microorganisms. Ecological drift is a stochastic factor, which is amplified by dispersal limitation between communities. Here, we compared the effects of three anode materials (graphene, carbon cloth, and nickel) with the effect of dispersal limitation on the function and biofilm community assembly. Twelve MECs were operated for 56 days in four hydraulically connected loops and shotgun metagenomic sequencing was used to analyse the microbial community composition on the anode surfaces at the end of the experiment. The anode material was the most important factor affecting the performance of the MECs, explaining 54–80 % of the variance observed in peak current density, total electric charge generation, and start-up lag time, while dispersal limitation explained 10–16 % of the variance. Carbon cloth anodes had the highest current generation and shortest lag time. However, dispersal limitation was the most important factor affecting microbial community structure, explaining 61–98 % of the variance in community diversity, evenness, and the relative abundance of the most abundant taxa, while anode material explained 0–20 % of the variance. The biofilms contained nine Desulfobacterota metagenome-assembled genomes (MAGs), which made up 64–89 % of the communities and were likely responsible for electricity generation in the MECs. Different MAGs dominated in different MECs. Particularly two different genotypes related to Geobacter benzoatilyticus competed for dominance on the anodes and reached relative abundances up to 83 %. The winning genotype was the same in all MECs that were hydraulically connected irrespective of anode material used.
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| 3. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
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Microwave characterization of Ti/Au-graphene contacts
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:17, s. 173111-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report on a microwave characterization of the interface between Ti/Au contacts and chemical vapor deposition graphene using structures of Corbino geometry, with primary focus on extracting and modeling the capacitance associated with the contact region. It is found that with the current contact resistivity, ρc∼10^−6 Ωcm2, the contact capacitance, on the order Cc∼1 μF/cm2, has a negligible effect on microwave transmission through the contact below ∼100 GHz. Finally, a parallel plate capacitance model for the contact is presented.
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| 4. |
- Buron, J. D., et al.
(författare)
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Graphene Conductance Uniformity Mapping
- 2012
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 12:10, s. 5074-5081
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a combination of micro four-point probe (M4PP) and non-contact terahertz time-domain spectroscopy (THz-TDS) measurements for centimeter scale quantitative mapping of the sheet conductance of large area chemical vapor deposited graphene films. Dual configuration M4PP measurements, demonstrated on graphene for the first time, provide valuable statistical insight into the influence of microscale defects on the conductance, while THz-TDS has potential as a fast, non-contact metrology method for mapping of the spatially averaged nanoscopic conductance on wafer-scale graphene with scan times of less than a minute for a 4-in. wafer. The combination of M4PP and THz-TDS conductance measurements, supported by micro Raman spectroscopy and optical imaging, reveals that the film is electrically continuous on the nanoscopic scale with microscopic defects likely originating from the transfer process, dominating the microscale conductance of the investigated graphene film.
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| 5. |
- Deng, Liying, et al.
(författare)
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Can fluorophlogopite mica be used as an alkali metal ion source to boost the growth of two-dimensional molybdenum dioxide?
- 2023
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 612
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Tidskriftsartikel (refereegranskat)abstract
- Everyone familiar with two-dimensional (2D) materials is aware of fluorophlogopite mica (FM), which has an atomic-level flat surface that provides an ideal platform for the growth of 2D materials. Since it has been demonstrated that the alkali metal ions (AMI) can aid in the growth of large-sized 2D materials by chemical vapor deposition (CVD) in recent years, it became a major mystery whether FM which contains AMI benefits from them in the preparation of 2D materials by CVD, too. In this article, we dispelled this ambiguity and discovered that temperature is the key for FM as an AMI source to boost the growth of large-sized 2D materials. We carried out variable temperature experiments and found that FM can indeed be incorporated into the growth of large-sized 2D materials as an AMI source at high temperatures and successfully obtained the highly crystalline MoO2 with a larger size compared to those without FM. This finding is of great importance to the understanding of the growth mechanism of FM for 2D materials by CVD and to better exploit its role in the growth of 2D materials.
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| 6. |
- Dong, Y. B., et al.
(författare)
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High Light Extraction Efficiency AlGaInP LEDs With Proton Implanted Current Blocking Layer
- 2016
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 37:10, s. 1303-1306
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Tidskriftsartikel (refereegranskat)abstract
- Improving light extraction efficiency is the key issue for light-emitting diodes (LEDs). Nowadays, a vertical structure design dominates LEDs. However, the light from the active region just below the p-electrode is severely blocked by the metal contact. In this letter, we use proton implantation with a depth all the way to the active region to turn the part beneath the p-pad insulating, which constitutes the most-effective-ever current blocking method. Earlier particle implantation studies never reached the device active region. Our experimental results show that the H+-implanted LEDs improve the light output power by 75% compared with non-implanted counterparts and the light intensity increases by 64.48%. By virtue of indium tin oxide current spreading film, the increase in working voltage is negligible. Analyzing the reverse leakage current, the side effect associated with the implantation is limited to an acceptable range. Numerical simulation is performed to support the experiment. Our results represent a new and simple method for solving the light blocking problem in vertical LEDs, without introducing the seemingly existing severe implantation damage to the device structure.
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| 7. |
- Dong, Y. B., et al.
(författare)
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The growth of graphene on Ni–Cu alloy thin films at a low temperature and its carbon diffusion mechanism
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2 /Si substrate at a low temperature (~600◦ C).
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| 8. |
- Dong, Y. B., et al.
(författare)
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Transfer-free, lithography-free, and micrometer-precision patterning of CVD graphene on SiO 2 toward all-carbon electronics
- 2018
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- A method of producing large area continuous graphene directly on SiO 2 by chemical vapor deposition is systematically developed. Cu thin film catalysts are sputtered onto the SiO 2 and pre-patterned. During graphene deposition, high temperature induces evaporation and balling of the Cu, and the graphene "lands onto" SiO 2 . Due to the high heating and growth rate, continuous graphene is largely completed before the Cu evaporation and balling. 60 nm is identified as the optimal thickness of the Cu for a successful graphene growth and μm-large feature size in the graphene. An all-carbon device is demonstrated based on this technique.
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| 9. |
- Dong, Yibo, et al.
(författare)
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In Situ Growth of CVD Graphene Directly on Dielectric Surface toward Application
- 2020
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Ingår i: ACS Applied Electronic Materials. - : American Chemical Society (ACS). - 2637-6113. ; 2:1, s. 238-246
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Tidskriftsartikel (refereegranskat)abstract
- A technique for the in situ growth of patterned graphene by CVD has been achieved directly on insulating substrates at 800 degrees C. The graphene growth is catalyzed by a Ni-Cu alloy sacrificial layer, which integrates many advantages such as being lithography-free, and almost wrinkle-free, with a high repeatability and rapid growth. The etching method of the metal sacrificial layer is the core of this technique, and the mechanism is analyzed. Graphene has been found to play an important role in accelerating etching speeds. The Ni-Cu alloy exhibits a high catalytic activity, and thus, high-quality graphene can be obtained at a lower temperature. Moreover, the Ni-Cu layer accommodates a limited amount of carbon atoms, which ensures a high monolayer ratio of the graphene. The carbon solid solubility of the alloy is calculated theoretically and used to explain the experimental findings. The method is compatible with the current semiconductor process and is conducive to the industrialization of graphene devices.
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| 10. |
- Dong, Yibo, et al.
(författare)
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Transfer-free, lithography-free and fast growth of patterned CVD graphene directly on insulators by using sacrificial metal catalyst
- 2018
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Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 29:36
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Tidskriftsartikel (refereegranskat)abstract
- Chemical vapor deposited graphene suffers from two problems: transfer from metal catalysts to insulators, and photoresist induced degradation during patterning. Both result in macroscopic and microscopic damages such as holes, tears, doping, and contamination, translated into property and yield dropping. We attempt to solve the problems simultaneously. A nickel thin film is evaporated on SiO2 as a sacrificial catalyst, on which surface graphene is grown. A polymer (PMMA) support is spin-coated on the graphene. During the Ni wet etching process, the etchant can permeate the polymer, making the etching efficient. The PMMA/graphene layer is fixed on the substrate by controlling the surface morphology of Ni film during the graphene growth. After etching, the graphene naturally adheres to the insulating substrate. By using this method, transfer-free, lithography-free and fast growth of graphene realized. The whole experiment has good repeatability and controllability. Compared with graphene transfer between substrates, here, no mechanical manipulation is required, leading to minimal damage. Due to the presence of Ni, the graphene quality is intrinsically better than catalyst-free growth. The Ni thickness and growth temperature are controlled to limit the number of layers of graphene. The technology can be extended to grow other two-dimensional materials with other catalysts.
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