| 1. |
- Granqvist, Claes-Göran, 1946-, et al.
(författare)
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Electrochromics and thermochromics for energy efficient fenestration : Functionalities based on nanoparticles of In2O3:Sn and VO2
- 2014
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 559, s. 2-8
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Tidskriftsartikel (refereegranskat)abstract
- Windows incorporating electrochromic (EC) and thermochromic (TC) materials are of great interest for today's and tomorrow's buildings and can create energy efficiency jointly with indoor comfort. This paper summarizes several recent studies and shows that nanoparticles of transparent conducting oxides-specifically In2O3: Sn (ITO) and thermochromic VO2-can lead to desirable functionalities. We consider three examples: (i) the use of ITO nanoparticles in conventional polaronic EC devices in order to suppress near-infrared solar transmittance, (ii) performance limits for plasmonic EC devices based on ITO nanoparticles, and (iii) ITO-VO2-based nanocomposites combining low thermal emittance with TC properties. We also consider Mg doping of VO2 to enhance the luminous transmittance and Al2O3/VO2 double layers with improved durability. Both experimental and theoretical results are reported. (C) 2013 Elsevier B. V. All rights reserved.
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| 2. |
- Ji, Yu-Xia, et al.
(författare)
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Durability of thermochromic VO2 thin films under heating and humidity : Effect of Al oxide top coatings
- 2014
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 562, s. 568-573
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Tidskriftsartikel (refereegranskat)abstract
- An explorative study was performed on sputter-deposited thermochromic (TC) VO2 films exposed to heat treatment under dry and humid conditions. The ambient conditions were harsh and 80-nm-thick VO2 films were rapidly converted to non-TC V2O5. It was found that a 30-nm-thick sputter-deposited Al oxide top coating provided good protection and delayed the oxidation for more than one day upon heating in dry air at 300 degrees C and that protection occurred for several days at 95% relative humidity and 60 degrees C. The thickness of the Al oxide was important and, expectedly, increased thickness yielded enhanced protection. Our results are important for TC fenestration as well as for other technical applications.
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| 3. |
- Laaksonen, Katri, et al.
(författare)
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Nanoparticles of TiO2 and VO2 in dielectric media : Conditions for low optical scattering, and comparison between effective medium and four-flux theories
- 2014
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Ingår i: Solar Energy Materials and Solar Cells. - : Saunders Elsevier. - 0927-0248 .- 1879-3398. ; 130:SI, s. 132-137
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Tidskriftsartikel (refereegranskat)abstract
- Spectral transmittance and reflectance in the 300 to 2500 nm solar-optical wavelength range were calculated for nanoparticles of titanium dioxide and vanadium dioxide with radii between 5 and 100 nm embedded in transparent dielectric media. Both of the materials are of large importance in green nanotechnologies: thus TiO2 is a photocatalyst that can be applied as a porous film or a nanoparticle composite on indoor or outdoor surfaces for environmental remediation, and VO2 is a thermochromic material with applications to energy-efficient fenestration. The optical properties, including scattering, of the nanoparticle composites were computed from the Maxwell–Garnett effective-medium theory as well as from a four-flux radiative transfer model. Predictions from these theories approach one another in the limit of small particles and in the absence of optical interference. Effects of light scattering can be modeled only by the four-flux theory, though. We found that nanoparticle radii should be less than ~20 nm in order to avoid pronounced light scattering.
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| 4. |
- Li, Shu-Yi, et al.
(författare)
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Bandgap widening in thermochromic Mg-doped VO2 thin films : Quantitative data based on optical absorption
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:16, s. 161907-
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Tidskriftsartikel (refereegranskat)abstract
- Thermochromic Mg-doped VO2 films were deposited by reactive direct current magnetron sputtering onto heated glass and carbon substrates. Elemental compositions were inferred from Rutherford backscattering. Optical bandgaps were obtained from spectral transmittance and reflectance measurements-from both the film side and the back side of the samples-and ensuing determination of absorption coefficients. The bandgap of Mg-doped films was found to increase by 3.9 +/- 0.5 eV per unit of atom ratio Mg/(Mg + V) for 0 < Mg/(Mg + V) < 0.21. The presence of similar to 0.45 at. % Si enhanced the bandgap even more.
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| 5. |
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| 6. |
- Li, Shu-Yi, et al.
(författare)
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Thermochromic undoped and Mg-doped VO2 thin films and nanoparticles : Optical properties and performance limits for energy efficient windows
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:5, s. 053513/1-/10
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Tidskriftsartikel (refereegranskat)abstract
- Undoped and Mg-doped thermochromic VO2 films with atom ratios z equivalent to Mg/(Mg + V) of 0 <= z < 0.21 were deposited by reactive DC magnetron sputtering onto heated glass and carbon substrates. Elemental compositions were found by Rutherford backscattering spectrometry. Optical constants were determined from transmittance and reflectance measurements and were used for modeling the optical properties of thin films and dilute nanoparticle composite layers below and above the critical temperature for thermochromic switching between a low-temperature infrared transparent state and a high-temperature infrared reflecting or absorbing state. Mg-doped films showed superior luminous transmittance T-lum and solar transmittance modulation Delta T-sol compared to undoped VO2 films, and both of these parameters could be further enhanced by anti-reflection. VO2-containing nanocomposites had much larger values of T-lum and Delta T-sol than VO2-based films. Mg-doping was found to erode the properties of the nanocomposites. Approximate performance limits are given on T-lum and Delta T-sol for thermochromic VO2 films, with and without Mg doping and antireflection coating, and also for VO2-containing dilute nanocomposites.
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| 7. |
- Lykissa, Iliana, et al.
(författare)
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Electronic density-of-states of amorphous vanadium pentoxide films : Electrochemical data and density functional theory calculations
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:18, s. 183701/1-/5
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of V2O5 were prepared by sputter deposition onto transparent and electrically conducting substrates and were found to be X-ray amorphous. Their electrochemical density of states was determined by chronopotentiometry and displayed a pronounced low-energy peak followed by an almost featureless contribution at higher energies. These results were compared with density functional theory calculations for amorphous V2O5. Significant similarities were found between measured data and computations; specifically, the experimental low-energy peak corresponds to a split-off part of the conduction band apparent in the computations. Furthermore, the calculations approximately reproduce the experimental band gap observed in optical measurements.
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| 8. |
- Niklasson, Gunnar A., 1953-, et al.
(författare)
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Thermochromic vanadium oxide thin films : Electronic and optical properties
- 2014
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Ingår i: INERA Workshop. - : Institute of Physics Publishing (IOPP). ; 559:012001, s. 012001/1-012001/8
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Konferensbidrag (refereegranskat)abstract
- Vanadium dioxide, VO2, is a widely studied thermochromic material with potential applications in energy efficient window technology. It undergoes a first-order metal-to-insulator transition, accompanied by a crystal structure transformation from monoclinic to tetragonal rutile, at a critical temperature of 68 oC. Below this temperature, VO2 is semiconducting and infrared transmitting whereas it is metallic and infrared reflecting above the transition temperature. However, in order to achieve significant thermochromic switching, the luminous transmittance of thin films will be less than 0.5 . Here we report on recent research to improve the luminous transmittance as well as the transmittance change at the transition temperature. We systematically evaluate the effect of antireflection coatings, doping with Mg and the performance of coatings comprising thermochromic nanoparticles in a transparent matrix. The last option is shown to give the best performance and holds great promise for practical applications.
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| 9. |
- Topalian, Zareh, et al.
(författare)
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Resistance noise at the metal-insulator transition in thermochromic VO2 films
- 2015
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 117:2, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Thermochromic VO2 films were prepared by reactive DC magnetron sputtering onto heated sapphire substrates and were used to make 100-nm-thick samples that were 10 lm wide and 100 lm long. The resistance of these samples changed by a factor similar to 2000 in the 50T-c. These exponents can be reconciled with the Pennetta-Trefan-Reggiani theory [Pennetta et al., Phys. Rev. Lett. 85, 5238 (2000)] for lattice percolation with switching disorder ensuing from random defect generation and healing in steady state. Our work hence highlights the dynamic features of the percolating semiconducting and metallic-like regions around T-c in thermochromic VO2 films. (C) 2015 AIP Publishing LLC.
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