| 1. |
- Cindemir, Umut, et al.
(författare)
-
Porous Nickel Oxide Sensor for Formaldehyde Detection
- 2014
-
Ingår i: European Materials Society (E-MRS) Spring Meeting, Lille, France, May 26-30, 2014..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Formaldehyde is a volatile organic compound, which is a harmful indoor pollutant, causing sick building syndrome (SBS) and is released from household and building materials. Since higher concentrations of formaldehyde are considered to be carcinogenic, monitoring them indoors is of great importance. Advanced gas deposition has here been used to fabricate highly porous nickel oxide (NiO) thin films for formaldehyde sensing. The films were deposited on Al2O3 substrates with prefabricated comb-structured electrodes, and a resistive heater at the opposite face. The morphology of the films was investigated with scanning electron microscopy, and the porosity was determined by nitrogen adsorption isotherms with the Brunauer-Emmett-Teller method. The particle size was found to be less than 10 nm, as determined by x-ray diffraction. X-ray photoelectron spectroscopy of the NiO films was also done. Gas sensing measurements were done using a total gas flow rate of 200 ml/min. Resistivity values of sensors were recorded with formaldehyde diluted in synthetic air. Sensor resistances were recorded at 50 ppm, 25ppm, 10ppm and 5 ppm formaldehyde concentration. NiO films showed promising formaldehyde gas sensing properties implying lower levels of detection limit.
|
|
| 2. |
- Bayrak Pehlivan, İlknur
(författare)
-
Functionalization of polymer electrolytes for electrochromic windows
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Saving energy in buildings is of great importance because about 30 to 40 % of the energy in the world is used in buildings. An electrochromic window (ECW), which makes it possible to regulate the inflow of visible light and solar energy into buildings, is a promising technology providing a reduction in energy consumption in buildings along with indoor comfort. A polymer electrolyte is positioned at the center of multi-layer structure of an ECW and plays a significant role in the working of the ECW.In this study, polyethyleneimine: lithium (bis(trifluoromethane)sulfonimide (PEI:LiTFSI)-based polymer electrolytes were characterized by using dielectric/impedance spectroscopy, differential scanning calorimetry, viscosity recording, optical spectroscopy, and electrochromic measurements.In the first part of the study, PEI:LiTFSI electrolytes were characterized at various salt concentrations and temperatures. Temperature dependence of viscosity and ionic conductivity of the electrolytes followed Arrhenius behavior. The viscosity was modeled by the Bingham plastic equation. Molar conductivity, glass transition temperature, viscosity, Walden product, and iso-viscosity conductivity analysis showed effects of segmental flexibility, ion pairs, and mobility on the conductivity. A connection between ionic conductivity and ion-pair relaxation was seen by means of (i) the Barton-Nakajima-Namikawa relation, (ii) activation energies of the bulk relaxation, and ionic conduction and (iii) comparing two equivalent circuit models, containing different types of Havriliak-Negami elements, for the bulk response.In the second part, nanocomposite PEI:LiTFSI electrolytes with SiO2, In2O3, and In2O3:Sn (ITO) were examined. Adding SiO2 to the PEI:LiTFSI enhanced the ionic conductivity by an order of magnitude without any degradation of the optical properties. The effect of segmental flexibility and free ion concentration on the conduction in the presence of SiO2 is discussed. The PEI:LiTFSI:ITO electrolytes had high haze-free luminous transmittance and strong near-infrared absorption without diminished ionic conductivity. Ionic conductivity and optical clarity did not deteriorate for the PEI:LiTFSI:In2O3 and the PEI:LiTFSI:SiO2:ITO electrolytes.Finally, propylene carbonate (PC) and ethylene carbonate (EC) were added to PEI:LiTFSI in order to perform electrochromic measurements. ITO and SiO2 were added to the PEI:LiTFSI:PC:EC and to a proprietary electrolyte. The nanocomposite electrolytes were tested for ECWs with the configuration of the ECWs being plastic/ITO/WO3/polymer electrolyte/NiO (or IrO2)/ITO/plastic. It was seen that adding nanoparticles to polymer electrolytes can improve the coloring/bleaching dynamics of the ECWs.From this study, we show that nanocomposite polymer electrolytes can add new functionalities as well as enhancement in ECW applications.
|
|
| 3. |
- Stefanov, Bozhidar, et al.
(författare)
-
Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films : Effect of <001> preferential orientation, surface temperature and humidity
- 2016
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 335, s. 187-196
-
Tidskriftsartikel (refereegranskat)abstract
- We present a systematic in situ study of the environmental reaction conditions on the photocatalytic activity of sputter deposited anatase TiO2 films with controlled amounts of preferential <001> orientation. In particular, the effects of relative humidity (RH) and substrate temperature ( ) are investigated. It is found that {001} facets, which are present in higher abundance on highly oriented samples, exhibit an order of magnitude higher reactivity for gas-phase photocatalytic oxidation of the indoor air pollutant acetaldehyde (CH3CHO) than {101} facets do, and a functional dependence of the reaction rate on facet orientation is determined. It is proposed that water adsorbed on the film contributes with two counteracting effects on the photocatalytic activity: (i) It provides hole acceptors to complete the photo-induced redox cycle and subsequent OH– radical formation for pollutant degradation, and (ii) it creates a diffusion barrier between the catalyst interface and pollutant molecules adsorbed in the water layer. As a consequence, increasing at high RH has the beneficial effect of removing excess water and reducing the diffusion barrier, thereby improving the photocatalytic activity. A comparison is also made with a commercial anatase TiO2 film, with less developed surface crystallinity and random facet distribution, where the improvement is even more pronounced. Films with a higher degree of orientation exhibit much more stable performance over a range of operating conditions, which suggests that it is possible to tune the effects of water and exposed facet orientation to achieve optimum activity and making TiO2 films amenable to a larger (RH, ) parameter space for practical applications.
|
|
| 4. |
- Gugole, Marika, 1993, et al.
(författare)
-
High-Contrast Switching of Plasmonic Structural Colors: Inorganic versus Organic Electrochromism
- 2020
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 7:7, s. 1762-1772
-
Tidskriftsartikel (refereegranskat)abstract
- Plasmonic structural colors have recently received a lot of attention. For many applications there is a need to actively tune the colors after preparing the nanostructures, preferably with as strong changes in the optical response as possible. However, to date, there is a lack of systematic investigations on how to enhance contrast in electrically induced color modulation. In this work we implement electrochromic films with plasmonic metasurfaces and compare systematically organic and inorganic materials, with the primary aim to maximize brightness and contrast in a reflective color display. We show nanostructures with good chromaticity and high polarization-insensitive reflectivity (-90%) that are electrochemically stable in a nonaqueous solvent. Methods are evaluated for reliable and uniform electropolymerization of the conductive polymer dimethylpropylenedioxythiophene (PProDOTMe2) on gold. The resulting organic films are well-described by Lambert-Beer formalism, and the highest achievable contrast is easily determined in transmission mode. The optical properties of the inorganic option (WO3) require full Fresnel models due to thin film interference, and the film thickness must be carefully selected in order to maintain the chromaticity of the metasurfaces. Still, the optimized fully inorganic device reaches the highest contrast of approximately 60% reflectivity change for all primary colors. The switching time is about an order of magnitude faster for the organic films (hundreds of ms). The bistability is very long (hours) for the inorganic devices and comparable for the polymers, which makes the power consumption essentially zero for maintaining the same state. Finally, we show that switching of the primary colors in optimized devices (both organic and inorganic) provides almost twice as high brightness and contrast compared to existing reflective display technologies with RGB subpixels created by color filters.
|
|
| 5. |
- Aijaz, Asim, et al.
(författare)
-
Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
- 2016
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 149, s. 137-144
-
Tidskriftsartikel (refereegranskat)abstract
- Thermochromic (TC) vanadium dioxide thin films provide means for controlling solar energy throughput and can be used for energy-saving applications such as smart windows. One of the factors limiting the deployment of VO2 films in TC devices is the growth temperature tau(s). At present, temperatures in excess of 450 degrees C are required, which clearly can be an impediment especially for temperature-sensitive substrates. Here we address the issue of high tau(s) by synthesizing VO2 thin films from highly ionized fluxes of depositing species generated in high power impulse magnetron sputtering (HiPIMS) discharges. The use of ions facilitates low-temperature film growth because the energy of the depositing species can be readily manipulated by substrate bias. For comparison, films were also synthesized by pulsed direct current magnetron sputtering. Structural and optical characterization of VO2 thin films on ITO-coated glass substrates confirms previous results that HiPIMS allows tau(s) to be reduced from 500 to 300 degrees C. Importantly, we demonstrated that HiPIMS permits the composition and TC response of the films to be tuned by altering the energy of the deposition flux via substrate bias. An optimum ion energy of 100 eV was identified, which points at a potential for further reduction of tau(s) thereby opening new possibilities for industrially-relevant applications of VO2-based TC thin films. Weak TC activity was observed even at tau(s) approximate to 200 degrees C in HiPIMS-produced films.
|
|
| 6. |
- Arvizu, Miguel A., et al.
(författare)
-
Electrochromic dc sputtered W1-x-y Moy Tix O3 thin films: : Optical properties and durability.
- 2016
-
Konferensbidrag (refereegranskat)abstract
- The key component in an electrochromic (EC) device is its primary EC thin film. The outstanding intrinsic ECproperties of tungsten oxide (WO3) make this material the best option available for the cathodic layer in an ECdevice. Nevertheless much research remains in order to optimize WO3 with regard to optical properties, durability,etc. It is well known that addition of titanium (Ti) into the matrix of WO3 increases significantly the resistance of the film to electrochemical cycling both under norma loperation and during accelerated aging in extended voltage ranges [1]. On the other hand, using molybdenum (Mo) as an additive in small concentrations helps to improve the color rendering by shifting th eposition of the maximum of the coloration band to higher energies [2]. The present work reports our recent investigations on thin films of mixed oxides with a focus on ways to optimize tungsten oxide thin films regarding both their durability and color by the addition of Ti and Mo. The films were deposited by reactive DC cosputtering from Mo and W-Ti alloy targets. Cyclic voltammetry, in a three-electrode system consisting of the film and lithium foils, was performed in a solution 1 MLiClO4 in propylene carbonate (Li–PC) as electrolyte. Insitu and ex-situ optical characterization was done for the EC films, and the transmittance switching and coloration efficiency were determined. Durability was studied by analyzing how the charge density evolved and how rapidly the transmittance modulation deteriorated during cycling for the different concentrations of Mo and Ti .References[1] M.A. Arvizu, C.A. Triana, B.I. Stefanov, C.G.Granqvist , G.A. Niklasson, “Electrochromism in SputterdepositedW-Ti Oxide Films: Durability Enhancement dueto Ti”, Solar Energy Materials & Solar Cells 125 (2014)184-189 (and references therein).[2] M.A. Arvizu, C.G. Granqvist and G.A. Niklasson,“Electrochromism in sputter deposited W1–yMoyO3 thinfilms”, Journal of Physics: Conference Series 682 (2016)012005 (and references therein).
|
|
| 7. |
- Arvizu, Miguel A., et al.
(författare)
-
Electrochromism in DC sputtered W1-yMoyO3 thin films
- 2015
-
Ingår i: INERA Conference 2015. - : Institute of Physics (IOP).
-
Konferensbidrag (refereegranskat)abstract
- Electrochromic (EC) properties of tungsten–molybdenum oxide (W1–yMoyO3) thin films were investigated. The films were deposited on indium tin oxide covered glass by reactive DC sputtering from tungsten and molybdenum targets. Elemental compositions of the W1–yMoyO3 films were determined by Rutherford back scattering. Voltammetric cycling was performed in an electrolyte of 1 M LiClO4 in propylene carbonate. The increase in molybdenum content in the EC films caused both a shift towards higher energies and a quenching of the value of the maximum of the coloration band, as compared with WO3 EC films. Durability was also diminished for W1–yMoyO3 EC films.
|
|
| 8. |
- Arvizu, Miguel A, et al.
(författare)
-
Rejuvenation of degraded electrochromic MoO3 thin films made by DC magnetron sputtering : Preliminary results
- 2016
-
Ingår i: Journal of Physics: Conference Series. - : Institute of Physics Publishing (IOPP).
-
Konferensbidrag (refereegranskat)abstract
- Molybdenum oxide thin films were deposited by reactive DC magnetron sputtering and were subjected to voltammetric cycling in an electrolyte comprised of lithium perchlorate in propylene carbonate. The films were heavily degraded during 20 voltammetric cycles in an extended voltage range. The films were subsequently rejuvenated by use of potentiostatic treatments under different voltages during 20 hours. Optical changes were recorded during the electrochemical degradation and ensuing rejuvenation.
|
|
| 9. |
- 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.
|
|
| 10. |
|
|
