| 1. |
- Alvi, Sajid Ali, et al.
(författare)
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Adaptive nanolaminate coating by atomic layer deposition
- 2019
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 692
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Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposition (ALD) was used to deposit ZnO/Al2O3/V2O5 nanolaminate coatings to demonstrate a coating system with temperature adaptive frictional behaviour. The nanolaminate coating exhibited excellent conformity and crack-free coating of thickness 110 nm over Inconel 718 substrate. The ALD trilayer coating showed a hardness and elastic modulus of 12 GPa and 193 GPa, respectively. High-temperature tribology of the nanolaminate trilayer was tested against steel ball in dry sliding condition at 25 °C (room temperature, RT), 200 °C, 300 °C, and 400 °C. It was found that the nanolaminate coating showed a low coefficient of friction (COF) and wear rate at RT and 300 °C. The trilayer coating was found intact and stable at all temperatures during the friction tests. The adaptability of nanolaminate coating with the temperature was verified by performing the cyclic friction test at 300 °C and RT. The low COF and wear rate had been attributed to the (100) and (002) basal plane sliding of ZnO top layer, and the interlayer sliding of weakly bonded planes parallel to (001) plane in V2O5 bottom layer. Furthermore, even after the removal of ZnO coating during the tribotest, the bottom V2O5 layer coating stabilized the COF and wear rate at RT and 300 °C.
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| 2. |
- De Melo, C., et al.
(författare)
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Local Structure and Point-Defect-Dependent Area-Selective Atomic Layer Deposition Approach for Facile Synthesis of p-Cu2O/n-ZnO Segmented Nanojunctions
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:43, s. 37671-37678
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Tidskriftsartikel (refereegranskat)abstract
- Area-selective atomic layer deposition (AS-ALD) has attracted much attention in recent years due to the possibility of achieving accurate patterns in nanoscale features, which render this technique compatible with the continuous downscaling in nanoelectronic devices. The growth selectivity is achieved by starting from different materials and results (ideally) in localized growth of a single material. We propose here a new concept, more subtle and general, in which a property of the substrate is modulated to achieve localized growth of different materials. This concept is demonstrated by selective growth of high-quality metallic Cu and semiconducting Cu2O thin films, achieved by changing the type of majority point defects in the ZnO underneath film exposed to the reactive species using a patterned bilayer structure composed of highly conductive and highly resistive areas, as confirmed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The selective growth of these materials in a patterned ZnO/Al-doped ZnO substrate allows the fabrication of p-Cu2O/n-ZnO nanojunctions showing a nonlinear rectifying behavior typical of a p-n junction, as confirmed by conductive atomic force microscopy (C-AFM). This process expands the spectra of materials that can be grown in a selective manner by ALD and opens up the possibility of fabricating different architectures, taking advantage of the area-selective deposition. This offers a variety of opportunities in the field of transparent electronics, catalysis, and photovoltaics.
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| 3. |
- de Melo, Claudia, et al.
(författare)
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Semi-Transparent p‑Cu2O/n-ZnO Nanoscale-Film Heterojunctions for Photodetection and Photovoltaic Applications
- 2019
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 2:7, s. 4358-4366
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Tidskriftsartikel (refereegranskat)abstract
- Transparent nanoscale-film heterojunctions based on Cu2O and ZnO were fabricated by atomic layer deposition and reactive magnetron sputtering. The constitutive layers exhibit high crystalline quality and a local epitaxial relation between Cu2O and ZnO was achieved with [110] Cu2O || [001] ZnO and [001] Cu2O || [010] ZnO as evidenced by high resolution transmission electron microscopy and. Cu2O films show very low resistivity and high mobility values of 9–150 Ω cm and 19 cm2/V s, respectively. The Cu2O/ZnO heterojunctions exhibit a nonlinear rectifying behavior characteristic of a p–n junction, self-powered photoresponse under 1 Sun illumination and an average transmittance of 73% in the visible region of the electromagnetic spectrum. These results are promising for all-oxide transparent electronics, photodetection and photovoltaic applications.
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| 4. |
- de Melo, Claudia, et al.
(författare)
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Tunable Localized Surface Plasmon Resonance and Broadband Visible Photoresponse of Cu Nanoparticles/ZnO Surfaces
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:47, s. 40958-40965
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic Cu nanoparticles (NP) were successfully deposited on ZnO substrates by atomic layer deposition (ALD) owing to the Volmer–Weber island growth mode. An evolution from Cu NP to continuous Cu films was observed with an increasing number of ALD cycles. Real and imaginary parts of the NP dielectric functions, determined by spectroscopic ellipsometry using an effective medium approach, evidence a localized surface plasmon resonance that can be tuned between the visible and near-infrared ranges by controlling the interparticle spacing and size of the NP. The resulting Cu NP/ZnO device shows an enhanced photoresponse under white light illumination with good responsivity values, fast response times, and stability under dark/light cycles. The significant photocurrent detected for this device is related to the hot-electron generation at the NP surface and injection into the conduction band of ZnO. The possibility of tuning the plasmon resonance together with the photoresponsivity of the device is promising in many applications related to photodetection, photonics, and photovoltaics.
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| 5. |
- Dobryden, Illia, et al.
(författare)
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Nanoscale characterization of an all-oxide core-shell nanorod heterojunction using intermodulation atomic force microscopy (AFM) methods
- 2021
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 3:15, s. 4388-4394
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Tidskriftsartikel (refereegranskat)abstract
- The electrical properties of an all-oxide core-shell ZnO-Co3O4nanorod heterojunction were studied in the dark and under UV-vis illumination. The contact potential difference and current distribution maps were obtained utilizing new methods in dynamic multifrequency atomic force microscopy (AFM) such as electrostatic and conductive intermodulation AFM. Light irradiation modified the electrical properties of the nanorod heterojunction. The new techniques are able to follow the instantaneous local variation of the photocurrent, giving a two-dimensional (2D) map of the current-voltage curves and correlating the electrical and morphological features of the heterostructured core-shell nanorods.
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| 6. |
- Donarelli, Maurizio, et al.
(författare)
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Anomalous gas sensing behaviors to reducing agents of hydrothermally grown α-Fe2O3 nanorods
- 2018
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 273, s. 1237-1245
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Tidskriftsartikel (refereegranskat)abstract
- α-Fe2O3 nanorods have been grown by hydrothermal method, dispersed in ethanol and drop casted on a pre-patterned alumina substrate with Pt electrodes. Their morphology, crystalline and electronic properties have been investigated by Scanning Electron Microscopy, Raman and X-ray Photoelectron Spectroscopies and X-ray Diffraction. The so-fabricated devices have been used for hydrogen gas sensing, showing their ability to detect H2 at operating temperatures > 200 °C, at relative humidity values comprised from 0% to 50%. The sensing behavior of α-Fe2O3 nanorods is compatible with an n to p conductivity transition when the operating temperature is increased up to 300 °C. Outstanding p-type hydrogen sensing performances of α-Fe2O3 have been observed and reported. Besides H2 detection, the α-Fe2O3 nanorods-based device is a good humidity sensor, at room temperature (n-type) and at 400 °C (p-type). CO and ethanol sensing performances have been investigated at different operating temperatures and relative humidity values. CO and ethanol anomalous acceptor-like behaviors at 200 °C in humid air has been explained by the interactions of these target gases with the water molecules adsorbed on the metal oxide surfaces. An explanation of the n–p behavior transition at T > 200 °C in terms of band bending is reported.
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| 7. |
- Ghamgosar, Pedram, 1979-
(författare)
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Advanced Nanostructured Transition Metal Oxide Semiconductors for Solar Energy Applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing energy consumption and its environmental impacts make it necessary to look for alternative energy sources. Solar energy as huge energy source that can cover the terms sustainability is considered as a favorable alternative. Optoelectronic devices like solar cells and photoelectrochemical cells are in very high interest to provide the energy that we need. They can convert solar energy, as a sustainable energy source, to electricity and fuel. Transition metal oxides (TMOs) due to high chemical stability, abundance, facile production and low cost are favorable materials to be used in these optoelectronic applications. In TMOs, d orbitals electrons contribute in forming bonds that gives special magnetic, electronic and geometric characteristics to these materials. They can be synthesized with different types of chemical and physical deposition methods.The electronic properties of TMOs varies from metallic characteristics to electrical insulators. Transition metal oxide semiconductors (TMOSs) are mostly used in optoelectronic devices. Tuning the properties of TMOSs like, composition, morphology, dimensions, crystal structure, improves the performance of the optoelectronic devices. The light absorption, charge carrier mobility, the time scale between charge injection, regeneration and recombination processes are some of the properties critical to exploitation of TMOSs in solar cells and solar fuel technology.In this thesis, we explore the use of nanostructured TMOSs in all-oxide solar cells, photodetectors and photoelectrochemical cells. 1-dimentional heterojunctions of n-type transparent semi-conductive metal oxides (ZnO and TiO2) in conjunction to p-type light absorbing semi-conductive metal oxides (Cu2O and Co3O4) have been tested in all-oxide photodetectors and solar cells. It is shown that the 1-dimentional nanostructured geometry (nanowires, nanotubes) improves the charge separation and charge transport properties. Increasing the surface to volume aspect ratio in nanowires and nanotubes improves the light absorption compare to the thin film geometry. Our ZnO-Cu2O core-shell nanowire photodetector is the fastest visible light photodetector reported till now. Mesoporous NiO photocathode, sensitized with a biomimetic FeFe-catalyst and coumarin C343 dye, was tested in a photoelectrochemical cell for hydrogen production. This system is the first solar fuel device based on a biomimetic FeFe-catalyst and it shows a Faradic efficiency of 50% in hydrogen production. Cobalt catalysts have higher Faradic efficiency but their performance due to hydrolysis in low pH condition is limited. Nanostructured hematite/magnetite film as a photoanode was tested in a photoelectrochemical cell for water splitting. This hybrid electrode improved the photoactivity of the photoelectrochemical cell for water splitting. The main mechanism for the improvement of the functional properties relies with the role of the magnetite phase, which improves the charge carrier mobility of the composite system, compared to pure hematite, which acts as good light absorbing semiconductor.
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| 8. |
- Ghamgosar, Pedram, 1979-, et al.
(författare)
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Self-Powered Photodetectors Based on Core-Shell ZnO-Co3O4 Nanowire Heterojunctions
- 2019
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:26, s. 23454-23462
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Tidskriftsartikel (refereegranskat)abstract
- Self-powered photodetectors operating in the UV–visible–NIR window made of environmentally friendly, earth abundant, and cheap materials are appealing systems to exploit natural solar radiation without external power sources. In this study, we propose a new p–n junction nanostructure, based on a ZnO–Co3O4 core–shell nanowire (NW) system, with a suitable electronic band structure and improved light absorption, charge transport, and charge collection, to build an efficient UV–visible–NIR p–n heterojunction photodetector. Ultrathin Co3O4 films (in the range 1–15 nm) were sputter-deposited on hydrothermally grown ZnO NW arrays. The effect of a thin layer of the Al2O3 buffer layer between ZnO and Co3O4 was investigated, which may inhibit charge recombination, boosting device performance. The photoresponse of the ZnO–Al2O3–Co3O4 system at zero bias is 6 times higher compared to that of ZnO–Co3O4. The responsivity (R) and specific detectivity (D*) of the best device were 21.80 mA W–1and 4.12 × 1012 Jones, respectively. These results suggest a novel p–n junction structure to develop all-oxide UV–vis photodetectors based on stable, nontoxic, low-cost materials.
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| 9. |
- Ghamgosar, Pedram, 1979-, et al.
(författare)
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ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors
- 2018
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 51, s. 308-316
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD). The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 °C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 °C), with energy gap of 2.48 eV. The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0 V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0 V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.
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| 10. |
- Khasevani, Sepideh G., et al.
(författare)
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The beauty of being complex: Prussian blue analogues as selective catalysts and photocatalysts in the degradation of ciprofloxacin
- 2022
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Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 410, s. 307-319
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the performance of four Prussian blue analogues (PBAs) as catalysts for the selective degradation of ciprofloxacin in water, under both dark and illumination conditions. We show that no light is actually needed to induce a selective degradation of the molecular target, while light irradiation spurs the process, without, however, resulting in the commonly reported photolysis-supported breaking down. We present a systematic characterization of the PBAs aiming at interpreting the catalytic outcomes in the light of a classic coordination chemistry analysis, empowered by the most recent findings in literature. We show that varying the transition metal binding the N atom of the cyanide bridge is key to promote photoinduced charge generation and transfer, which effectively disrupts the molecular target. The analysis of the materials before and after the irradiation with solar simulated light results in a change of the lattice parameters, indicating the possibility of a light-induced spin cross-over.
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