| 1. |
- Aijaz, Asim, et al.
(författare)
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Deposition of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Vanadium dioxide exhibits a reversible phase transition from semiconducting state (monoclinic structure) to a metallic state (tetragonal structure) at ~68 oC. This so-called metal-insulator transition (MIT) entails thermochromic behavior manifested by large changes in optical properties, such as high infrared transmittance modulation in thin films, thereby making VO2-based films a suitable candidate for optical switching applications such as self-tunable infrared filters. Thermochromic VO2 thin films have been widely investigated for optical applications, but high growth temperatures (> 400 oC) required for synthesizing crystalline VO2 thin films, high MIT temperature (68 oC) as well as low visible transmittance (typically ~50%) limit their applicability for example for energy efficient smart windows. Synthesis of metal-oxide thin films using highly ionized vapor fluxes has been shown to facilitate low-temperature film growth as well as control over phase formation and resulting film properties. In the present work, we synthesize VO2 thin films by use of highly ionized vapor fluxes that are generated by high power impulse magnetron sputtering (HiPIMS). In order to establish a correlation between the plasma and film properties, we investigate the discharge characteristics by analyzing the discharge current-voltage characteristics under varied process parameters such as peak-power, pulse-width and gas phase composition and grow VO2 thin films under suitable process conditions. We investigate the effect of growth temperature (room temperature to 500 oC), energy of the deposition flux (controlled by substrate bias potential) and type of substrate (Si, glass, ITO-coated glass) on crystallinity, phase formation and on optical properties (visible transmittance and infrared modulation) of the resulting thin films. For reference, the discharge characteristics and properties of films deposited by pulsed direct current magnetron sputtering are also studied.
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| 2. |
- Alm, Oscar, et al.
(författare)
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Tungsten oxide nanoparticles synthesised by laser assisted homogeneous gas-phase nucleation
- 2005
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 247:1-4, s. 262-267
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten oxide nanoparticles were generated by excimer (ArF) laser assisted chemical vapor deposition from WF6/H2/O2/Ar gas mixtures. The deposited particles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The deposition rate as a function of the partial pressures of the reactants and of the laser fluence was measured by X-ray fluorescence spectroscopy. The mean diameter of the deposited tungsten oxide particles varied with the experimental parameters and was typically 23 nm. Particles with a higher degree of crystallinity were observed at a laser fluence exceeding 130 mJ/cm2, and X-ray amorphous particles were obtained below 110 mJ/cm2. The amorphous tungsten oxide had a stoichiometry ranging from WO2.7 to WO3. Deposits were formed only when hydrogen was present in the gas mixture.
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| 3. |
- Aroutiounian, V., et al.
(författare)
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Fluctuation-enhanced gas sensing
- 2009
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Ingår i: Procedia Chemistry. - : Elsevier BV. - 1876-6196.
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Konferensbidrag (refereegranskat)abstract
- The sensitivity of gas sensors was earlier measured by classical method-comparison the resistance of sensors in gas media and air. Here we reported results of the study of low-frequency noise characteristics of sensors. We compare data for different Figaro TGS sensors as well as our sol-gel H-2 tin dioxide and porous silicon sensors. The study was performed in dry air and in a mix of dry air with carbon monoxide, hydrogen and alcohol of different concentrations. Higher sensitivity of spectral dependence of noise (SDN) to gas concentration in comparison with classical method of the measurements of gas sensing by a change in the Ohmic resistance part of current-voltage characteristics of samples allows using such SND powerful method for determination of gas concentration in the air or environment.
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| 4. |
- Aroutiounian, Vladimir M., et al.
(författare)
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Noise spectroscopy of gas sensors
- 2008
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Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 8:5-6, s. 786-790
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Tidskriftsartikel (refereegranskat)abstract
- We study current-voltages and low-frequency noise characteristics of the metal-porous silicon-silicon single crystal-metal structure with 50% and 73% porosity of porous silicon. The study is performed in dry air and in a mix of dry air with carbon monoxide of different concentrations. The Hooge noise parameter alpha(H) and the parameter gamma in the frequency dependence of the noise voltage spectral density S-U (f) were determined from experimental data. High sensitivity of spectral dependence of noise to gas concentration allows offering powerful method for determination of gas concentration in the air or environment.
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| 5. |
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| 6. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochemical pretreatment of electrochromic WO3 films gives greatly improved cycling durability
- 2018
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 653, s. 1-3
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic WO3 thin films have important applications in devices such as smart windows for energy-efficient buildings. Long-term electrochemical cycling durability of these films is essential and challenging. Here we investigate reactively sputter-deposited WO3 films, backed by indium-tin oxide layers and immersed in electrolytes of LiClO4 in propylene carbonate, and demonstrate unprecedented electrochemical cycling durability after straight-forward electrochemical pretreatments by the application of a voltage of 6 V vs. Li/Li+ for several hours.
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| 7. |
- Arvizu, Miguel A., et al.
(författare)
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Electrochromic dc sputtered W1-x-y Moy Tix O3 thin films: : Optical properties and durability.
- 2016
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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).
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| 8. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochromic W(1-x-y)Ti(x)lo(y)O(3) Thin Films Made by Sputter Deposition : Large Optical Modulation, Good Cycling Durability, and Approximate Color Neutrality
- 2017
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 29:5, s. 2246-2253
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten oxide thin films are used in electrochromic devices such as variable-transmittance "smart windows" for energy efficient buildings with good indoor comfort. Two long-standing issues for WO3 thin films are their limited durability under electrochemical cycling and their blue color in transmission. Here, we show that both of these problems can be significantly alleviated by additions of titanium and molybdenum. We found that similar to 300 nm-thick films of sputter deposited W1-x-yTixMoyO3 are able to combine a midluminous transmittance modulation of 0.4 similar to 70% with good color neutrality and durability under extended electrochemical cycling. The Ti content should be similar to 10 at. % in order to achieve durability without impairing transmittance modulation significantly, and the Mo content preferably should be no larger than 6 at. % in order to maintain durability. Hence, our results give clear guidelines for making three-component mixed-oxide thin films that are suitable for electrochromic "smart windows".
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| 9. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment
- 2019
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 7:6, s. 2908-2918
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic windows and glass facades are able to impart energy efficiency jointly with indoor comfort and convenience. Long-term durability is essential for practical implementation of this technology and has recently attracted broad interest. Here we show that a simple potentiostatic pretreatment of sputterdeposited thin films of amorphous WO3-the most widely studied electrochromic material-can yield unprecedented durability for charge exchange and optical modulation under harsh electrochemical cycling in a Li-ion-conducting electrolyte and effectively evades harmful trapping of Li. The pretreatment consisted of applying a voltage of 6.0 V vs. Li/Li+ for several hours to a film backed by a transparent conducting In2O3: Sn layer. Associated compositional and structural modifications were probed by several techniques, and improved durability was associated with elemental intermixing at the WO3/ITO and ITO/glass boundaries as well as with carbonaceous solid-electrolyte interfacial layers on the WO3 films. Our work provides important new insights into long-term durability of ion-exchange-based devices.
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| 10. |
- Arvizu, Miguel A., et al.
(författare)
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Electrochromism in DC sputtered W1-yMoyO3 thin films
- 2015
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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.
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| 11. |
- Arvizu, Miguel A, et al.
(författare)
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Electrochromism in sputter-deposited W-Ti oxide films : Durability enhancement due to Ti
- 2014
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 125, s. 184-189
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of W-Ti oxide were prepared by reactive DC magnetron sputtering and were characterized by Rutherford bathcattering spectrometry, X-ray diffraction, scanning electron microscopy and atomic force microscopy. The electrochromic properties were studied by cyclic voltammetry in an electrolyte of lithium perchlorate in propylene carbonate and by optical transmittance measurements. The addition of Ti significantly promoted the amorphous nature of the films and stabilized their electrochemical cycling performance and dynamic range for electrochromism. (C) 2014 Elsevier B.V. All rights reserved.
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| 12. |
- Arvizu, Miguel, et al.
(författare)
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Galvanostatic ion de-trapping rejuvenates oxide thin films
- 2015
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 7:48, s. 26387-26390
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Tidskriftsartikel (refereegranskat)abstract
- Ion trapping under charge insertion-extraction is well-known to degrade the electrochemical performance of oxides. Galvano-static treatment was recently shown capable to rejuvenate the oxide, but the detailed mechanism remained uncertain. Here we report on amorphous electrochromic (EC) WO3 thin films prepared by sputtering and electrochemically cycled in a lithium-containing electrolyte under conditions leading to severe loss of charge exchange capacity and optical modulation span. Time-of-flight elastic recoil detection analysis (ToF-ERDA) documented pronounced Li+ trapping associated with the degradation of the EC properties and, importantly, that Li+ detrapping, caused by a weak constant current drawn through the film for some time, could recover the original EC performance. Thus, ToF-ERDA provided direct and unambiguous evidence for Li+ detrapping.
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| 13. |
- Atak, Gamze, et al.
(författare)
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Durability studies of annealed electrochromic tungsten oxide films
- 2021
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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.
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| 14. |
- Atak, Gamze, et al.
(författare)
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Electrochromic tungsten oxide films prepared by sputtering : Optimizing cycling durability by judicious choice of deposition parameters
- 2021
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 367
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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.
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| 15. |
- Atak, Gamze, et al.
(författare)
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Nitrogen doped W oxide films for electrochromic applications
- 2019
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Ingår i: EMRS Spring Meeting 2019.
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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.
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| 16. |
- Atak, Gamze, et al.
(författare)
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The role of oxygen to argon gas flow ratio on the durability of sputter-deposited electrochromic tungsten oxide films
- 2021
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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.
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| 17. |
- Avendano, Esteban, et al.
(författare)
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Coloration Mechanism in Proton-Intercalated Electrochromic Hydrated NiOy and Ni1-xVxOy Thin Films
- 2009
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 156:8, s. p132-p138
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic (EC) films of nickel oxide, with and without vanadium, were prepared by reactive dc magnetron sputtering. They were characterized by electrochemical and optical measurements and studied by X-ray photoelectron spectroscopy (PES) using synchrotron radiation. The films were analyzed under as-deposited conditions and after bleaching/coloration by insertion/extraction of protons from a basic solution and ensuing charge stabilization. Optical measurements were consistent with a coloration process due to charge-transfer transitions from Ni2+ to Ni3+ states. The PES measurements showed a higher concentration of Ni3+ in the colored films. Moreover, two peaks were present in the O 1s spectra of the bleached film and pointed to contributions of Ni(OH)(2) and NiO. The changes in the O 1s spectra upon coloration treatment indicate the presence of Ni2O3 in the colored film and necessitated an extension of the conventional model for the mechanism of EC coloration. The model involves not only proton extraction from nickel hydroxide to form nickel oxyhydroxide but also participation of NiO in the coloration process to form Ni2O3.
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| 18. |
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| 19. |
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| 20. |
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| 21. |
- Avendano, Esteban, et al.
(författare)
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Sputter Deposited Electrochromic Films and Devices Based on These : Progress on nickel-oxide-based films
- 2007
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5107 .- 1873-4944. ; 138:2, s. 112-117
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces electrochromic (EC) devices, capable of changing their optical absorption under charge insertion/extraction, and some of the required materials. Special attention is given to EC nickel-oxide-based films, for which we discuss sputter deposition and ensuing optical and structural properties. The paper is concluded with some recent results for practical foil-based devices.
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| 22. |
- Avendaño Soto, Esteban Damián, 1975-
(författare)
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Electrochromism in Nickel-based Oxides : Coloration Mechanisms and Optimization of Sputter-deposited Thin Films
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrochromic properties of sputter-deposited nickel-based oxide films have been studied with a two-fold goal. From a practical point of view, the optical switching performance has been improved by optimizing the deposition conditions and film stoichiometry with respect to oxygen and hydrogen, and further by adding Mg, Al, Si, Zr, Nb or Ta to the films. From a theoretical point of view, details of the coloration mechanism have been studied by means of electrochemical intercalation (CV, GITT), optical measurements (UV, VIS, NIR and MIR), RBS, XRD, XPS and EXAFS. Optimization of deposition conditions has been illustrated by the example of films made by sputtering of a non-magnetic Ni(93)V(7) % wt. target in an atmosphere of Ar/O2/H2. The optimized films exhibit transmittance modulation between 20% and 75 % at 18 mC/cm2 charge intercalation. The remaining problem with nickel oxide and nickel vanadium oxide films is their residual yellow-brown color tint in the bleached state, which disappears as the short-wavelength transmittance increases upon addition of Mg, Al, Zr or Ta. Optimization of deposition conditions by co-sputtering from two targets and the film composition for mixed oxide films has been illustrated by the example of nickel aluminium oxide. The mechanisms of coloration upon electrochemical charge insertion and ozone exposure have been investigated. In the beginning of the electrochemical cycling, first, a reconstruction and crystallization is observed with the outer most part of the grain surface being transformed from oxygen rich nickel oxide into nickel oxy-hydroxide and hydroxide by transfer of H+ and OH- groups. After the charge capacity has been stabilized, only a transfer of H+ occurs with two reversible reactions involved: the first one from Ni(OH)2 to NiOOH and the second one from NiO and Ni(OH)2 to Ni2O3. Ozone coloration is described by a similar reaction scheme. The ozone molecule is split on the surface and dehydrogenates Ni(OH)2 into NiOOH. Further dehydrogenation produces Ni2O3 as in the electrochemical coloration.
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| 23. |
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| 24. |
- Backholm, Jonas, et al.
(författare)
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Iridium-based oxides: Recent advances in coloration mechanism, structural and morphological characterization
- 2008
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 92:2, s. 91-96
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Tidskriftsartikel (refereegranskat)abstract
- Films of iridium-tantalum oxide and iridium oxide have been prepared by sputtering and studied regarding their structure and electrochemical properties. X-ray diffraction and transmission electron microscopy showed an average grain size of 3-4 nm for both films. Point energy dispersive X-ray spectrometry showed an inhomogeneous distribution of iridium and tantalum indicating that the iridium-tantalum oxide may be a mixture of small IrO2 and Ta2O5 grains, which is consistent with the determined composition IrTa1.4O5.6. X-ray photoelectron spectroscopy gave valuable information on the stabilization process of the as-deposited films involving an uptake of oxygen, and on a coloration mechanism only including protons.
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| 25. |
- Baloukas, Bill, et al.
(författare)
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Galvanostatic Rejuvenation of Electrochromic WO3 Thin Films : Ion Trapping and Detrapping Observed by Optical Measurements and by Time-of-Flight Secondary Ion Mass Spectrometry
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:20, s. 16996-17002
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic (EC) smart windows are able to decrease our energy footprint while enhancing indoor comfort and convenience. However, the limited durability of these windows, as well as their cost, result in hampered market introduction. Here, we investigate thin films of the most widely studied EC material, WO3. Specifically, we combine optical measurements (using spectrophotometry in conjunction with variable-angle spectroscopic ellipsometry) with time-of-flight secondary ion mass spectrometry and atomic force microscopy. Data were taken on films in their as-deposited state, after immersion in a Li-ion-conducting electrolyte, after severe degradation by harsh voltammetric cycling and after galvanostatic rejuvenation to regain the original EC performance. Unambiguous evidence was found for the trapping and detrapping of Li ions in the films, along with a thickness increase or decrease during degradation and rejuvenation, respectively. It was discovered that (i) the trapped ions exhibited a depth gradient; (ii) following the rejuvenation procedure, a small fraction of the Li ions remained trapped in the film and gave rise to a weak short-wavelength residual absorption; and (iii) the surface roughness of the film was larger in the degraded state than in its virgin and rejuvenated states. These data provide important insights into the degradation mechanisms of EC devices and into means of achieving improved durability.
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| 26. |
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| 27. |
- Barrios, David, et al.
(författare)
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Simulation of the thickness dependence of the optical properties of suspended particle devices
- 2015
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Ingår i: Solar Energy Materials and Solar Cells. - 0927-0248 .- 1879-3398. ; 143, s. 613-622
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Tidskriftsartikel (refereegranskat)abstract
- Suspended particle devices (SPDs) constitute an electrically powered chromogenic technology, in which the active layer quickly are able to rapidly switches from a dark bluish-black dark color state to a clear greyish color appearance when an AC electric field is applied. Two-flux and four-flux models were used to derive refractive indices and extinction coefficients, as well as scattering and absorption coefficients, of the particle-containing active layer. These entities were used in model calculations to predict the direct, total and diffuse components of the transmittance andthe reflectance, together along with the color appearance and haze, as a function of the thickness of the active layer. An optimum thickness for the optical contrast of the SPD was determined in this way and was found to be in the range of 200 to 300 nm. The SPDdevices device exhibits a significant reflectance haze particularly in reflection.
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| 28. |
- Barrios, David, et al.
(författare)
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Toward a quantitative model for suspended particle devices : Optical scattering and absorption coefficients
- 2013
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 111, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- Suspended particle devices (SPDs) allow rapid voltage-controlled modulation of their optical transmittance and are of interest for solar-energy-related and other applications. We investigated the spectral total and diffuse transmittance of an SPD, including its angular dependence. The optical modulation was large for visible light but almost nil in the infrared, and the devices had noticeable haze. A theoretical two-flux model was formulated and provided a quantitative description of the absorption and scattering coefficients and thereby of the detailed optical performance. This analysis gives a benchmark for assessing improvements of the SPD technology as well as for comparing it with alternative technologies for optical modulation.
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| 29. |
- Bayrak Pehlivan, I., et al.
(författare)
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A polymer electrolyte with high luminous transmittance and low solar throughput : Polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide with In2O3:Sn nanocrystals
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:24, s. 241902-
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Tidskriftsartikel (refereegranskat)abstract
- Chemically prepared similar to 13-nm-diameter nanocrystals of In2O3:Sn were included in a polyethyleneiminelithium bis(trifluoromethylsulfonyl) imide electrolyte and yielded high haze-free luminous transmittance and strong near-infrared absorption without deteriorated ionic conductivity. The optical properties could be reconciled with effective medium theory, representing the In2O3:Sn as a free electron plasma with tin ions screened according to the random phase approximation corrected for electron exchange. This type of polymer electrolyte is of large interest for opto-ionic devices such as laminated electrochromic smart windows.
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| 30. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Bifunctional solar electrocatalytic water splitting using CIGS solar modules and WO3-based electrolyzers
- 2019
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Ingår i: EMRS Spring Meeting 2019.
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Konferensbidrag (refereegranskat)abstract
- Using energy from the sun to produce a fuel and finally obtaining only water as an exhaust is a promising future technology for renewable energy and environmental sustainability. Solar driven water splitting is a method to produce hydrogen from solar energy. Coupling a solar cell with an electrolyzer is the approach with highest technological readiness. CuInxGa1-xSe2 (CIGS) is here a promising solar cell material for water splitting because it is possible to tune the band gap between 1.0 and 1.7 eV by changing the ratio between Ga and In, thus enabling maximum power point matching with an electrolyzer. Tungsten oxide is known as a photocatalytic material and mainly used for the oxygen evolution reaction in a water splitting process. However, WO3 films also show electrochromic activity together with hydrogen evolution. This result is interesting because it shows that WO3 films can be used as bifunctional materials for both hydrogen and oxygen evolution in water splitting, and provide additional functionalities to the system. In this study, WO3 films coated at different sputtering conditions on Ni foam and indium tin oxide substrates were investigated in the potential range of the hydrogen evolution reaction. The best overpotential of 164 mV vs. RHE at 10 mA/cm2 was obtained for WO3 films on Ni foam in 0.5 M H2SO4. The lowest potential needed for 10 mA/cm2 was measured 1.768 V for the electrolyzers consisting WO3 films on Ni foam as the cathode and non-coated Ni foam as the anode. Optimum solar-to-hydrogen (STH) efficiency of the CIGS solar cell modules and the electrolyzers was examined for different band gaps of the CIGS modules and sputtering conditions of WO3 films. Operation points of the combined system were calculated from the intersection of the voltage-current density curves for the CIGS modules and the electrolyzers. The results showed that the detailed sputtering conditions were not very critical to obtain high STH efficiency, indicating that the system could be robust and easily manufactured. The best-matched band gap of the CIGS was 1.19 eV and the highest STH efficiency of the CIGS driven WO3-based electrolyzers was 12.98 %.
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| 31. |
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| 32. |
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| 33. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Bayrak Pehlivan, İlknur
(författare)
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Functionalization of polymer electrolytes for electrochromic windows
- 2013
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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.
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| 38. |
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| 39. |
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| 40. |
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| 41. |
- Bayrak Pehlivan, Ilknur, et al.
(författare)
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Ion conduction of branched polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide electrolytes
- 2011
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 57, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- Ionic conductivity of polymer electrolytes containing branched poly (ethylene imine) (BPEI) and lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) was measured between temperatures of 20 and 70◦C and molar ratios of 20:1 and 400:1. The electrolytes were characterized by impedance spectroscopy, differential scanning calorimetry, and viscosity measurements. At room temperature, the maximum conductivity was 2×10−6 S/cm at a molar ratio of 50:1. The molar conductivity of the electrolytes displayed first a minimum and then a maximum upon increasing salt concentration. A proportionality of molar conductivity to segmental mobility was seen from glass transition temperature and viscosity measurements. Analysis of the Walden product and isoviscosity conductivity showed that the percentage of ions bound in ion pairs increased at low concentrations below 0.1 mol/kg. The average dipole moment decreased with salt concentration. The temperature dependence of the ionic conductivity showed an Arrhenius behavior.
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| 42. |
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| 45. |
- Bittencourt, C., et al.
(författare)
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Evaporation of WO3 on Carbon Nanotube Films : a new hybrid film
- 2006
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Ingår i: Smart materials and structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 15:6, s. 1555-1560
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid WO3-CNT ( carbon nanotube) films were prepared in two steps: in the first step, the drop coating method was employed for coating silicon substrates with a MWCNT (multiwalled CNT) film prepared with oxygen plasma functionalized MWCNTs; in the second step, a layer of WO3 nanoparticles was deposited over the MWCNT film by using an advanced gas deposition unit. The WO3 nanoparticles are formed by condensation. SEM images show that the morphology of the hybrid films is characterized by an overlayer formed from WO3 particles anchored at the surface of a well-dispersed MWCNT underlayer. TEM images show that the hybrid films are composed of a WO3 matrix supported through a dispersed mesh of CNTs-the CNTs act as internal pillars. This morphology increases the surface area for gas interaction.
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| 46. |
- Chen, Hsien-Pu, et al.
(författare)
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Do Electromagnetic Waves Exist in a Short Cable at Low Frequencies? : What Does Physics Say?
- 2014
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Ingår i: Fluctuation and Noise Letters. - 0219-4775 .- 1793-6780. ; 13:2, s. 1450016-
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Tidskriftsartikel (refereegranskat)abstract
- We refute a physical model, recently proposed by Gunn, Allison and Abbott (GAA) [http://arxiv.org/pdf/1402.2709v2.pdf], to utilize electromagnetic waves for eavesdropping on the Kirchhoff-law-Johnson-noise (KLJN) secure key distribution. Their model, and its theoretical underpinnings, is found to be fundamentally flawed because their assumption of electromagnetic waves violates not only the wave equation but also the second law of thermodynamics, the principle of detailed balance, Boltzmann's energy equipartition theorem, and Planck's formula by implying infinitely strong blackbody radiation. We deduce the correct mathematical model of the GAA scheme, which is based on impedances at the quasi-static limit. Mathematical analysis and simulation results confirm our approach and prove that GAA's experimental interpretation is incorrect too.
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| 47. |
- Chen, Hsien-Pu, et al.
(författare)
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On The "Cracking" Scheme in The Paper "A Directional Coupler Attack Against the Kish Key Distribution System" by Gunn, Allison And Abbott
- 2014
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Ingår i: METROLOGY AND MEASUREMENT SYSTEMS. - : Polish Academy of Sciences Chancellery. - 0860-8229 .- 2300-1941. ; 21:3, s. 389-400
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Tidskriftsartikel (refereegranskat)abstract
- Recently, Gunn, Allison and Abbott (GAA) [http://arxiv.org/pdf/1402.2709v2.pdf] proposed a new scheme to utilize electromagnetic waves for eavesdropping on the Kirchhoff-law-Johnson-noise (KLJN) secure key distribution. We proved in a former paper [Fluct. Noise Lett. 13 (2014) 1450016] that GAA's mathematical model is unphysical. Here we analyze GAA's cracking scheme and show that, in the case of a loss-free cable, it provides less eavesdropping information than in the earlier (Bergou)-Scheuer-Yariv mean-square-based attack [Kish LB, Scheuer J, Phys. Lett. A 374:2140-2142 (2010)], while it offers no information in the case of a lossy cable. We also investigate GAA's claim to be experimentally capable of distinguishing-using statistics over a few correlation times only-the distributions of two Gaussian noises with a relative variance difference of less than 10(-8). Normally such distinctions would require hundreds of millions of correlations times to be observable. We identify several potential experimental artifacts as results of poor KLJN design, which can lead to GAA's assertions: deterministic currents due to spurious harmonic components caused by ground loops, DC offset, aliasing, non-Gaussian features including non-linearities and other non-idealities in generators, and the time-derivative nature of GAA's scheme which tends to enhance all of these artifacts.
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| 48. |
- Cindemir, Umut, 1986-, et al.
(författare)
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Characterization of nanocrystalline-nanoporous nickel oxide thin films prepared by reactive advanced gas deposition
- 2019
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Ingår i: Materials Chemistry and Physics. - : ELSEVIER SCIENCE SA. - 0254-0584 .- 1879-3312. ; 227, s. 98-104
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline-nanoporous Ni oxide is of much interest for gas sensors and other applications. Reactive advanced gas deposition (AGD) stands out as a particularly promising technique for making thin films of this material owing to the techniques ability to separate between the growth of individual nanoparticles and their subsequent deposition to create a consolidated material on a substrate. Here we report on the characterization of Ni oxide films, made by reactive AGD, by several methods. X-ray diffractometry showed that the films had a face centered cubic NiO structure, and scanning electron microscopy indicated a compact nanoparticulate composition. X-ray photoelectron spectroscopy showed the presence of Ni3+ and demonstrated that these states became less prominent upon heat treatment in air. Extended x-ray absorption fine structure analysis elucidated the local atomic structure; in particular, data on interatomic distances and effects of annealing on local disorder showed that the Ni oxide nanoparticles crystallize upon annealing while maintaining their nanoparticle morphology, which is a crucial feature for reproducible fabrication of Ni oxide thin films for gas sensors. Importantly, several techniques demonstrated that grain growth remained modest for annealing temperatures as high as 400 degrees C for 1700-nm-thick films. The present article is a sequel to an earlier one [U. Cindemir et al., Sensors and Actuators B 242 (2017) 132-139] in which we reported on fluctuation-enhanced and conductometric gas sensing with Ni oxide films prepared by AGD.
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| 49. |
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| 50. |
- Cindemir, Umut, et al.
(författare)
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Fluctuation-enhanced and conductometric gas sensing with nanocrystalline NiO thin films : A comparison
- 2017
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 242, s. 132-139
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline thin films of NiO were prepared by advanced reactive gas deposition, and their responses to formaldehyde, ethanol and methane gases were studied via fluctuation-enhanced and conductometric methods Thin films with thicknesses in the 200–1700-nm range were investigated in as-deposited form and after annealing at 400 and 500◦C. Morphological and structural analyses showed porous deposits with NiO nanocrystals having face-centered cubic structure. Quantitative changes in frequency-dependent resistance fluctuations as well as in DC resistance were recorded upon exposure to formaldehyde, ethanol and methane at 200◦C. The response to formaldehyde was higher than that to ethanol while the response to methane was low, which indicates that the NiO films exhibit significant selectivity towards different gaseous species. These results can be reconciled with the fact that formaldehyde has a nucleophilic group, ethanol is an electron scavenger, and methane is hard to either reduce or oxidize. The gas-induced variations in DC resistance and resistance fluctuations were in most cases similar and consistent.
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