| 1. |
- Khairy, Kholida Tul, et al.
(författare)
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Thermochromic properties of vanadium oxide thin films prepared by reactive magnetron sputtering at different oxygen concentrations
- 2023
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- Vanadium dioxide (VO2) is a thermochromic (TC) material, exhibits a reversible transmittance change in the near-infrared (NIR) region upon heating above a critical temperature tic, due to an insulator-to-metal phase transition. Numerous studies on the V-O system can be found in the literature, including the synthesis of VO2 films. The phase diagram of the V-O system involves complicated suboxide phases that prevent pure VO2 for-mation and obscures quantitative analysis. Here, VO2 thin films were systematically prepared with various ox-ygen flow ratios (r) using reactive magnetron sputtering. Thin films prepared with r = 4.1% show dominant VO2 phase and the highest TC performance. The r -range producing dominant VO2 phase is found to be narrow: 3.7% < r<4.2%. At lower and higher r, TC characteristics are shown to be accompanied, as expected, by electrical conductivity changes, but also by microstructure transformations. The latter producing textured films that gradually develop upon cycling around tic. In particular, a change of texture, yielding oriented VO2 crystallites, is observed by in-situ XRD around tic. Our results shed light on the VO2 formation and associated structural, chemical and electrical properties under various oxidizing conditions during magnetron sputtering, which calls for careful preparation and strategies to stabilize the VO2 phase.
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| 2. |
- Kim, Shin, et al.
(författare)
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Development of boron doped diamond electrodes material for heavy metal ion sensor with high sensitivity and durability
- 2023
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Ingår i: JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY. - : Elsevier BV. - 2238-7854 .- 2214-0697. ; 23, s. 1375-1385
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Tidskriftsartikel (refereegranskat)abstract
- We report on the optimized substrate pretreatment and deposition process conditions for boron-doped diamond (BDD) electrodes fabricated by hot-filament chemical vapor deposition (HFCVD). The optimized BDD electrode with a doping concentration of 8000 ppm showed high accuracy and precision in detecting Cd(II), Pb(II), and Cu(II) ions. In addition, this demonstrates excellent selectivity against external metal ions under the optimized stripping voltammetry measurement conditions. The detection limits of the target ions of Cd(II), Pb(II), and Cu(II) were 0.55 (+/- 0.05), 0.43 (+/- 0.04), and 0.74 (+/- 0.06) mg/L (S/N = 3), respectively. In real samples spiked with 100 mg/L Cd(II), Pb(II), and Cu(II), both the accuracy and precision of the BDD electrode were within 5%; the interference with organic matter was also negligible. The excellent selectivity and long-term stability indicate that the BDD electrode developed in this study are potentially useful for online water environment monitoring systems.
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| 3. |
- Kim, Seohan, et al.
(författare)
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Embedded Oxidized Ag-Pd-Cu Ultrathin Metal Alloy Film Prepared at Low Temperature with Excellent Electronic, Optical, and Mechanical Properties
- 2022
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:13, s. 15756-15764
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Tidskriftsartikel (refereegranskat)abstract
- Most transparent conducting materials are based on Sn:In2O3 (ITO). When applied onto flexible substrates, ITO can be prepared in an oxide-metal-oxide (OMO) configuration, typically ITO/Ag/ITO, where the ductility of the embedded metal layer is intended to reduce the mechanical brittleness and improve the electrical conductivity of the OMO multilayer. Hitherto, the lower limit of the thickness of the Ag layer has been limited by the percolation threshold, which limits the Ag layer to be thicker than similar to 10 nm to avoid agglomeration and to ensure conductivity and structural stability. Metal layers of thicknesses below 10 nm are, however, desirable for obtaining OMO coatings with better optical properties. It is known that agglomeration of the metal layer can, to some extent, be suppressed when substituting Ag by an Ag-Pd-Cu (APC) alloy. APC-based OMO films exhibit excellent optical and electrical properties, but still continuous APC films well below 10 nm thickness cannot be achieved. In this work we demonstrate that controlled oxidation of APC results in smooth, ultrathin APC:O continuous coatings (of thickness similar to 5 nm) on ITO-coated PET substrates. Moderate oxidation yields superficial PdOx formation, which suppresses Ag agglomeration, while still maintaining excellent conductivity. On the other hand, extensive oxidation of APC leads to extensive Pd oxide nucleation deteriorating the conductivity of the film. The ITO/APC:O/ITO films exhibit low resistivity, attributed to a high Hall mobility associated with suppressed agglomeration, good stability in high humidity/temperature environments, superior transmittance in the visible and infrared region, and excellent mechanical bending properties, thus providing new opportunities for fabricating superior transparent conducting coatings on polymer substrates.
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| 4. |
- Kim, Seohan, et al.
(författare)
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Hydrogen-driven surface amorphization of the transparent oxide semiconductor thin-films for photovoltaic applications
- 2021
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 555
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Tidskriftsartikel (refereegranskat)abstract
- Crystalline transparent conductive oxides are promising candidates as front electrodes in electronic devices due to the high electron mobility and good optical transparency in the visible region. However, the rough surface morphology resulting from the grain growth during the deposition and post-annealing process triggers severe drawbacks in their thin-film applications. Here, we demonstrate the hydrogen-driven surface amorphization of the crystalline In?Sn?O (c-ITO) thin film. By introducing hydrogen gas during the deposition process, the surface of the c-ITO thin film is selectively amorphized, allowing for the smooth surface morphology while preserving the advantages of the crystalline thin film. The progressive surface amorphization of c-ITO thin film offers the tunability of the work function, leading to the improved power conversion efficiency of the thin-film solar cell. Our work provides a facile method to realize the smooth surface morphology of the c-ITO thin films, which can be further utilized for a wide range of crystalline thin films for optoelectronic applications.
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| 5. |
- Park, Sungmin, et al.
(författare)
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Hydrogen-driven dramatically improved mechanical properties of amorphized ITO-Ag-ITO thin films
- 2021
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 11:6, s. 3439-3444
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Tidskriftsartikel (refereegranskat)abstract
- An oxide/metal/oxide (OMO) multi-structure, which has good electrical, optical, and mechanical stability, was studied as a potential replacement of polycrystalline In-Sn-O (ITO). However, the degradation of mechanical properties caused by the polycrystalline structure of the top layer forming on the polycrystalline metal layer needs to be improved. To address this issue, we introduced hydrogen in the oxide layers to form a stabilized amorphous oxide structure despite it being deposited on the polycrystalline layer. An ITO/Ag/ITO (IAI) structure was used in this work, and we confirmed that the correct amount of hydrogen introduction can improve mechanical stability without any deterioration in optical and electrical properties. The hydrogen presence in the IAI as intended was confirmed, and the assumption was that the hydrogen suppressed the formation of microcracks on the ITO surface due to low residual stress that came from decreased subgap level defects. This assumption was clearly confirmed with the electrical properties before and after dynamic bending testing. The results imply that we can adjust not only IAI structures with high mechanical stability due to the right amount of hydrogen introduction to make stabilized amorphous oxide but also almost all oxide/metal/oxide structures that contain unintended polycrystalline structures.
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