| 1. |
- Atak, Gamze, et al.
(författare)
-
Durability studies of annealed electrochromic tungsten oxide films
- 2021
-
Ingår i: EMRS Fall Meeting 2021.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In electrochromic (EC) applications, annealing is a crucial parameter not only for an individual layer but also for a full device. For the fabrication of a complete EC device, indium tin oxide (ITO) is often preferred as a transparent conductor layer. ITO films with high transparency and low electrical resistance are usually obtained by sputtering at high substrate temperatures. Consequently, the effect of high temperature on the EC layers can be very significant during sputtering of the ITO top layer for EC devices consisting of five sputtered layers on a single substrate. The role of annealing of a single layer of WO3 may also be important for EC performance. In the present work, we studied the effects of annealing on the durability of WO3 films. Thin films of WO3 were deposited by reactive DC magnetron sputtering in a mixture of Ar and O2 gases using an oxygen to argon ratio of 0.15. The total gas pressure was set to 4.0 Pa, and the sputtering power was 200 W. The WO3 films were deposited onto (i) unheated glass plates, (ii) such plates pre-coated with transparent and electrically conducting ITO with a sheet resistance of 60 Ω/square, and (iii) glass plates pre-coated with fluorine-doped tin oxide (FTO) with a sheet resistance of 14 Ω/square. Film thicknesses were 300±10 nm. After deposition of the films, the samples were annealed at 150, 300, 450, and 600 °C in ambient air for one h using a heating rate of 10 °C min-1. Cyclic voltammetry (CV) was performed for up to 500 cycles between 2.0 and 4.0 V vs. Li/Li+ at a scan rate of 20 mV s–1. Annealing at temperatures at and above 300 °C resulted in deteriorated electrochromic properties of the WO3 films i.e., a decreased transmittance variation. Charge density and coloration efficiency changes during extended electrochemical cycling were also observed as a function of cycle number and annealing temperature. It was found that the maximum optical transmittance modulation at a wavelength of 528 nm after 500 CV cycles was 69.3% for the film annealed at 150 °C.
|
|
| 2. |
- Atak, Gamze, et al.
(författare)
-
Electrochromic performance of WO3 films with different ITO layers
- 2019
-
Ingår i: EMRS Spring Meeting 2019..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Electrochromic (EC) materials are able to change their optical properties such as transmission, absorption and reflection reversibly by application of an external voltage. EC metal oxides are divided into two groups: cathodic (coloring under ion insertion) and anodic (coloring under ion extraction). Tungsten oxide (WO3) is a well-known cathodic EC material and has been intensively studied in the last 30 years. EC materials and devices have been developed as an alternative to passive coating materials for light and heat management. Conventionally, an EC device is a construction with five-layers: transparent conducting oxide (TCO)/cathodic EC/ion conducting layer (liquid, gel or solid)/anodic EC/TCO, either all on one substrate or positioned between two substrates in a laminated configuration. Indium-tin oxide (ITO) coated substrates are used as a TCO electrode in EC applications due to their high conductivity and transparency.In this study, we deposited WO3 films onto ITO coated glass substrates with different sheet resistances (15, 30, 60 and 1000 Ω/□) by using DC magnetron sputtering technique. Optical and structural properties of ITO films were investigated. For durability studies, cyclic voltammetry data was recorded for up to 500 cycles between 2.0 and 4.0 V versus Li/Li+ at a scan rate of 20 mV s−1. Chronoamperometry measurements of the WO3 films were also performed. We measured the inserted and extracted charges as well as bleaching and coloring times of WO3 films with different ITO layer properties. Generally, ITO with low resistivity is preferred for the electrochemical measurements while absorption is low in the near-infrared region for ITO with higher resistivity. In this study, it is observed that the ITO with 60 Ω/□ sheet resistance is very suitable for optical and electrochromic measurements.
|
|
| 3. |
- Atak, Gamze, et al.
(författare)
-
Electrochromic tungsten oxide films prepared by sputtering : Optimizing cycling durability by judicious choice of deposition parameters
- 2021
-
Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 367
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films of W oxide were prepared by reactive DC magnetron sputtering (5 cm-diameter W target), and their electrochromic (EC) properties were investigated in an electrolyte of LiClO4 in propylene carbonate. The purpose of the study was to elucidate the role of critical deposition parameters-oxygen/argon gas flow ratio for the sputter plasma Gamma, total pressure in the sputter plasma p(tot) , and sputtering power P-s - on the EC performance with foci on electrochemical cycling durability and optical modulation range Delta T. Specifically, we used 0.15 <= Gamma <= 0.90, 5 <= p(tot) <= 30 mTorr, and 200 <= P-s <= 400 W and studied cycling durability for up to 500 voltammetric cycles in the range 2.0-4.0 V vs. Li/Li+ together with optical properties at a wavelength of 528 nm. Most significantly, we discovered that a judicious choice of deposition parameters could yield films with superior cycling durability. Thus a similar to 300 nm-thick film prepared at Gamma = 0.90, p(tot) = 10 mTorr, and P-s = 200 W showed Delta T approximate to 65% after an initial "training" during similar to 100 voltammetric cycles; higher values of p(tot), on the other hand, yielded films whose Delta Ts degraded by similar to 10% during the cycling, and a lower value of p(tot) led to dark films with only marginal electrochromism. Hence our work delineates a pathway towards W oxide films with excellent durability of the EC properties.
|
|
| 4. |
- Atak, Gamze, et al.
(författare)
-
Electrochromism of nitrogen-doped tungsten oxide thin films
- 2020
-
Ingår i: Materials Today. - : Elsevier BV. - 2214-7853. ; 33:6, s. 2434-2439
-
Tidskriftsartikel (refereegranskat)abstract
- Tungsten-oxide-based thin films were prepared by reactive DC magnetron sputtering in the presence ofoxygen and nitrogen. Nitrogen contents up to 12 at.% were documented by Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis. Optical and electrochemical measurements showed that films with up to 4 at.% of nitrogen were as transparent as undoped tungsten oxide films and displayed enhanced electrochromic properties manifested in an increase in the coloration efficiency by as much as 20%.
|
|
| 5. |
- Atak, Gamze, et al.
(författare)
-
Nitrogen doped W oxide films for electrochromic applications
- 2019
-
Ingår i: EMRS Spring Meeting 2019.
-
Konferensbidrag (refereegranskat)abstract
- Electrochromic (EC) materials are able to change their optical properties such as transmission, absorption and reflection reversibly by application of an external voltage. EC metal oxides are divided into two groups: cathodic (coloring under ion insertion) and anodic (coloring under ion extraction). W oxide is a well-known cathodic EC material and its color changes from transparent to dark blue when ions are inserted.A desirable electrochromic material must have and maintain a high optical modulation, high coloration efficiency, fast coloration/bleaching switching kinetics and a stable charge/ discharge reversibility. In this study, W oxide films with different nitrogen levels were deposited by using reactive DC sputtering onto glass and ITO coated glass in Ar+O2+N2 atmosphere. For all films, the total gas pressure was set to 4.0 Pa, the Ar flow rate was kept at 50 ml/min, and the O2+N2 flow rate was kept at 7.5 ml/min. The optical, structural and electrochromic properties of undoped and N-doped W oxide films were investigated. The optical studies revealed that the average optical transmittance and band gap decreased (from 3.43 to 3.08 eV) due to N doping. It is shown that a small amount of nitrogen has promising effects on the EC performance (i.e. charge/discharge reversibility, optical modulation, coloration efficiency) of the WO3 films. It is observed that CE values increased by increasing N2 flow rate and its maximum value was 33.8 cm2/C. The maximum ΔT at 537 nm was 73.6% for an optimized N doped W oxide film.
|
|
| 6. |
- Atak, Gamze, et al.
(författare)
-
The role of oxygen to argon gas flow ratio on the durability of sputter-deposited electrochromic tungsten oxide films
- 2021
-
Ingår i: EMRS Fall Meeting 2021.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Materials that are able to vary their transparency and coloration reversibly when they are subjected to an electrical current or voltage are referred to as “electrochromic” (EC). High optical transmittance modulation and long service lifetime are apparent requirements for EC materials used in smart windows technology. An extended service lifetime is provided by the long-term durability of the materials. One important aspect of durability is the ability to sustain charge transport between the EC film and electrolyte, or between the two EC films in a device, for many hundreds or thousands of cycles without any significant changes in the performance such as optical modulation and inserted-extracted charge. The purpose of this study is to clarify the effects of the oxygen-argon gas flow ratio during sputter deposition on the durability of WO3 films. In this study, the oxygen to argon gas-flow ratio was modulated by setting the O2 flow rate to 7.5, 15.0, 22.5, and 45.0 ml min-1 and using a fixed Ar flow rate of 50 ml min-1. Thus, the oxygen to argon gas-flow ratio was varied from 0.15 to 0.90. The pressure in the sputter plasma was set as 30 mTorr and the sputter power was maintained at 200 W. For durability studies, cyclic voltammetry data were recorded for up to 500 cycles between 2.0 and 4.0 V versus Li/Li+ at a scan rate of 20 mV s-1. High oxygen to argon gas ratio was found to have a positive effect on the EC properties of the films. When the long-term performance of the films was examined, it was seen that all the samples displayed a slow decline of the colored-state transmittance due to ion accumulation in the host material. After 500 color-bleach cycles, the maximum optical transmittance modulation between colored and bleached states at a wavelength of 528 nm was 63.6% when the oxygen to argon gas-flow ratio was 0.90.
|
|
| 7. |
- Baba, Elbruz Murat, et al.
(författare)
-
Light-induced breathing in photochromic yttrium oxyhydrides
- 2020
-
Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 4:2
-
Tidskriftsartikel (refereegranskat)abstract
- When exposed to air, metallic yttrium dihydride YH2 films turn into insulating and transparent yttrium oxyhydride (YHO). The incorporation of oxygen causes the lattice expansion of YH2 and the emergence of photochromic properties, i.e., YHO darkens reversibly when illuminated with light of adequate energy and intensity. However, the adequate bleaching of the photodarkened samples once the illumination has stopped is much faster in air than in inert atmosphere. According to this experimental evidence, the photochromic mechanism has to be related to an oxygen diffusion and exchange process. Since this process is accompanied by a lattice expansion/contraction, it can be said that YHO "breathes" when subjected to illumination/darkness cycling. Another interesting side effect of the breathing is the unexpected enhancement of the hydrophobicity of the YHO samples under illumination. A theoretical model able to explain the breathing in YHO is presented, together with the discussion of other alternative explanations.
|
|
| 8. |
- Baba, Elbruz Murat, et al.
(författare)
-
Preferential Orientation of Photochromic Gadolinium Oxyhydride Films
- 2020
-
Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 25:14
-
Tidskriftsartikel (refereegranskat)abstract
- We report preferential orientation control in photochromic gadolinium oxyhydride (GdHO) thin films deposited by a two-step process. Gadolinium hydride (GdH2-x) films were grown by reactive magnetron sputtering, followed by oxidation in air. The preferential orientation, grain size, anion concentrations and photochromic response of the films were strongly dependent on the deposition pressure. The GdHO films showed a preferential orientation along the [100] direction and exhibited photochromism when synthesized at deposition pressures of up to 5.8 Pa. The photochromic contrast was larger than 20% when the films were deposited below 2.8 Pa with a 0.22 H-2/Ar flow ratio. We argue that the relation of preferential orientation and the post deposition oxidation since oxygen concentration is known to be a key parameter for photochromism in rare-earth oxyhydride thin films. The experimental observations described above were explained by the decrease of the grain size as a result of the increase of the deposition pressure of the sputtering gas, followed by a higher oxygen incorporation.
|
|
| 9. |
|
|
| 10. |
- Felsberg, Michael, 1974-, et al.
(författare)
-
The Thermal Infrared Visual Object Tracking VOT-TIR2016 Challenge Results
- 2016
-
Ingår i: Computer Vision – ECCV 2016 Workshops. ECCV 2016.. - Cham : SPRINGER INT PUBLISHING AG. - 9783319488813 - 9783319488806 ; , s. 824-849
-
Konferensbidrag (refereegranskat)abstract
- The Thermal Infrared Visual Object Tracking challenge 2016, VOT-TIR2016, aims at comparing short-term single-object visual trackers that work on thermal infrared (TIR) sequences and do not apply pre-learned models of object appearance. VOT-TIR2016 is the second benchmark on short-term tracking in TIR sequences. Results of 24 trackers are presented. For each participating tracker, a short description is provided in the appendix. The VOT-TIR2016 challenge is similar to the 2015 challenge, the main difference is the introduction of new, more difficult sequences into the dataset. Furthermore, VOT-TIR2016 evaluation adopted the improvements regarding overlap calculation in VOT2016. Compared to VOT-TIR2015, a significant general improvement of results has been observed, which partly compensate for the more difficult sequences. The dataset, the evaluation kit, as well as the results are publicly available at the challenge website.
|
|
