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  • 1.
    Cindemir, Umut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Calavia, R.
    Llobet, E.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ionescu, R.
    Gold Nanoparticle Thin Film Sensors for Formaldehyde Detection2014Conference paper (Refereed)
  • 2.
    Cindemir, Umut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnar, Niklasson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Porous Nickel Oxide Film Sensor for Formaldehyde2014In: INERA Workshop: Transition Metal Oxides as Functional Layers in Smart windows and Water Splitting Devices / Parallel session of the 18th International School on Condensed Matter Physics, 2014, p. UNSP 012012-Conference paper (Refereed)
    Abstract [en]

    Formaldehyde is a volatile organic compound and a harmful indoor pollutant contributing to the "sick building syndrome". We used advanced gas deposition 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 and structure of the films were investigated with scanning electron microscopy and X-ray diffraction. Porosity was determined by nitrogen adsorption isotherms with the Brunauer-Emmett-Teller method. Gas sensing measurements were performed to demonstrate the resistive response of the sensors with respect to different concentrations of formaldehyde at 150 degrees C.

  • 3.
    Cindemir, Umut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Porous Nickel Oxide Sensor for Formaldehyde Detection2014In: European Materials Society (E-MRS) Spring Meeting, Lille, France, May 26-30, 2014.: Symposium B: Advanced functional materials for environmental monitoring and applications., 2014Conference paper (Other academic)
    Abstract [en]

    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.

  • 4. Espinosa, E H
    et al.
    Ionescu, R
    Llobet, E
    Felten, A
    Bittencourt, C
    Sotter, E
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Heszler, Peter
    Granqvist, Claes G
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Pireaux, J J
    Correig, X
    Highly Selective NO2 Gas Sensors made of MWCNTs and WO3 Hybrid Layers2006In: Proc. E-MRS, 2006Conference paper (Other academic)
  • 5. Espinosa, E. H.
    et al.
    Ionescu, R.
    Llobet, E.
    Felten, A.
    Bittencourt, C.
    Sotter, E.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Heszler, Péter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pireaux, J. J.
    Correig, X.
    Highly Selective NO2 Gas Sensors made of MWCNTs and WO3 Hybrid Layers2007In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 154, no 5, p. J141-J149Article in journal (Refereed)
    Abstract [en]

    Hybrid gas sensors were fabricated by means of multiwalled carbon nanotubes (MWCNTs) covered by W O3 deposited by an advanced reactive gas deposition method. In order to increase the dispersion of nanotubes and attach functional groups to their surface so as to enhance their compatibility with other compounds, the MWCNTs were functionalized in two different radio-frequency plasmas (oxygen or hydrogen) under different operating conditions. X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy were employed to analyze the composition and morphology of the hybrid films. Gas sensors based on such films were found to be very selective to N O2 when operated at room temperature. No cross-sensitivity was found to other hazardous gases such as N H3 or CO.

  • 6.
    Granqvist, Claes Göran
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Green, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Jonsson, E K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Marsal, Roser
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Roos, Arne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Azens, A
    Georen, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gustavsson, G
    Karmhag, R
    Smulko, J
    Kish, L B
    Electrochromic foil-based devices: Optical transmittance and modulation range, effect of ultravioled irradiation, and quality assessment by 1/f current noise2008In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 17, p. 5921-5926Article in journal (Refereed)
    Abstract [en]

    We introduce electrochromic (EC) technology for modulating the transmittance of visible light and solar radiation in window apertures, with focus on recent work on foil-type devices embodying sputter deposited WO3 and NiO films joined by a polymer electrolyte. The purpose of this paper is to present a number of new and preliminary results showing that (i) double-sided antireflection coatings based on dip coating can enhance the transmittance significantly, (ii) tandem foils can yield a ratio between bleached-state and colored-state transmittance exceeding fifty, (iii) solar irradiance onto the EC device can enhance its charge insertion dynamics and thereby its optical modulation, and (iv) electromagnetic noise spectroscopy may serve as quality assessment of EC devices.

  • 7.
    Ionescu, Radu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cindemir, Umut
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Welearegay, Tesfalem Geremariam
    Calavia, Raul
    Haddi, Zouhair
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Llobet, Eduard
    Fabrication of ultra-pure gold nanoparticles capped with dodecanethiol for Schottky-diode chemical gas sensing devices2017In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 239, p. 455-461Article in journal (Refereed)
    Abstract [en]

    Ultra-pure monolayer-capped gold nanoparticles for chemical gas sensing devices were prepared by a novel two-step process: a physical vapour deposition technique was first employed to make dispersed ultra-pure size-controlled gold nanoparticles, and this step was followed by a coating process for functionalization of the gold nanoparticles with an organic ligand, specifically dodecanethiol. X-ray photoelectron spectroscopy proved that the nano-assemblies had high purity. Chemical sensing devices based on these nano-assemblies showed Schottky-diode behaviour. We believe this is the first observation of Schottky-diodes fabricated from nanomaterials based on metallic nanoparticles. Gas sensing experiments demonstrated that these devices were suitable for detecting volatile organic compounds.

  • 8.
    Jensen, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Ion Physics.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Martin, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Surpi, A
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Topalian, Z
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Yousef, H
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Sanz, R
    Damage formation in TiO2 by heavy ions: consequences for micro- and nano-struring2008In: 7th International Symposium on Swift Heavy Ions in Matter (SHIM2008), Lyon, France, 2008Conference paper (Refereed)
  • 9.
    Karimipour, Masoud
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Mageto, Maxwel Joel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Etefagh, Reyhaneh
    Azhir, Elahe
    Mwamburi, Mghendi
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Room temperature magnetization in Co-doped anatase phase of TiO22013In: European Physical Journal: Applied physics, ISSN 1286-0042, E-ISSN 1286-0050, Vol. 61, no 1, p. 10601-Article in journal (Refereed)
    Abstract [en]

    CoxTi1-xO2 films were deposited by spray pyrolysis technique on Si(1 0 0) substrates at 475 degrees C. A hydro-alcoholic solution containing titanium (iv) isopropoxide and Co(NO3)(2) with various Co doping levels from x = 0-0.015 in solution was used as spray solution. Grazing incident angle of X-ray diffraction illustrates that the CoxTi1-xO2 films are single phase and polycrystal with mixed orientations. Study of surface morphology of the films by atomic force microscope reveals that the annealing atmosphere does not significantly affect the grain size and the microstructure of the films. This study provides further insight into the importance of annealing atmosphere on magnetization of the films. Room temperature magneto-optical Kerr measurement was employed in polar mode. A hysteresis loop and a paramagnetic behavior have been recorded for samples annealed in H-2 ambient gas and air, respectively. Chemical composition analysis by X-ray photo-electron spectroscopy showed that Co atoms are bounded to oxygen and no metallic clusters are present. Moreover, it indicates the formation of high spin Co2+ for the sample x = 0.008 annealed in H-2 ambient gas. The origin of magnetization can be attributed to the contribution of oxygen vacancies in the spin polarization of the structure.

  • 10.
    Lentka, Lukasz
    et al.
    Gdansk Univ Technol, Fac Elect Telecommun & Informat, Narutowicza 11-12, PL-80233 Gdansk, Poland.
    Kotarski, Mateusz
    Gdansk Univ Technol, Fac Elect Telecommun & Informat, Narutowicza 11-12, PL-80233 Gdansk, Poland.
    Smulko, Janusz
    Gdansk Univ Technol, Fac Elect Telecommun & Informat, Narutowicza 11-12, PL-80233 Gdansk, Poland.
    Cindemir, Umut
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Calavia, Raul
    Rovira & Virgily Univ, Dept Elect, Tarragona 43006, Spain.
    Ionescu, Radu
    Rovira & Virgily Univ, Dept Elect, Tarragona 43006, Spain.
    Fluctuation-enhanced sensing with organically functionalized gold nanoparticle gas sensors targeting biomedical applications2016In: Talanta: The International Journal of Pure and Applied Analytical Chemistry, ISSN 0039-9140, E-ISSN 1873-3573, Vol. 160, p. 9-14Article in journal (Refereed)
    Abstract [en]

    Detection of volatile organic compounds is a useful approach to non-invasive diagnosis of diseases through breath analysis. Our experimental study presents a newly developed prototype gas sensor, based on organically-functionalized gold nanoparticles, and results on formaldehyde detection using fluctuation-enhanced gas sensing. Formaldehyde was easily detected via intense fluctuations of the gas sensor's resistance, while the cross-influence of ethanol vapor (a confounding factor in exhaled breath, related to alcohol consumption) was negligible.

  • 11.
    Luyo, C
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ionescu, R
    Reyes, L. F.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Estrada, W
    Llobet, E
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Heszler, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gas Sensing Response of NiO Nanoparticle Films Made by Reactive Gas Deposition2009In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 138, no 1, p. 14-20Article in journal (Refereed)
    Abstract [en]

    Nanocrystalline films comprised of NiO particles were prepared by advanced reactive gas evaporation and were investigated for gas sensing applications, specifically for detecting reducing (H2S) and oxidizing (NO2) species. The films were studied in as-deposited state and after annealing at temperatures up to 400,C, and the sensors were operated   from room temperature to 325 degrees C. The optimal operating temperature was in the 150-162 degrees C range for H2S and in the 100-125 degrees C range for NO2. We believe that this is the first report of high-sensitivity detection of H2S with NiO-based sensors, as well as the first proof that such sensors can work at room temperature.

  • 12.
    Makra, P.
    et al.
    Dept of Experimental Physics, University of Szeged, Ungern.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kish, L. B.
    Dept of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA.
    Kwan, C.
    Signal Processing Inc, Rockville, MD, USA.
    Accuracy versus speed in fluctuation-enhanced sensing2012In: Fluctuation and Noise Letters, ISSN 0219-4775, E-ISSN 1793-6780, Vol. 11, no 2, p. 1250010-Article in journal (Refereed)
    Abstract [en]

    Fluctuation-enhanced sensing (FES) comprises the analysis of the stochastic component of the sensor signal and the utilization of the microscopic dynamics of the interaction between the agent and the sensor. We study the relationship between the measurement time window and the statistical error of the measurement data in the simplest case, when the output is the mean-square value of the stochastic signal. This situation is relevant at any practical case when the time window is finite, for example, when a sampling of the output of a fluctuation-enhanced array takes place; or a single sensor's activation (temperature, etc.) is stepped up; or a single sensor's output is monitored by sampling subsequently in different frequency windows. Our study provides a lower limit of the relative error versus data window size with different types of power density spectra: white noise, 1/f (flicker, pink) noise, and 1/f(2) (red) noise spectra.

  • 13.
    Nisar, Jawat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    De Sarkar, Abir
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    TiO2‑Based Gas Sensor: A Possible Application to SO22013In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, no 17, p. 8516-8522Article in journal (Refereed)
    Abstract [en]

    Fixation of SO2 molecules on anatase TiO2 surfaceswith defects have been investigated by first-principles densityfunctional theory (DFT) calculations and in situ Fourier transforminfrared (FTIR) surface spectroscopy on porous TiO2 films. Intrinsicoxygen-vacancy defects, which are formed on TiO2(001) andTiO2(101) surfaces by ultraviolet (UV) light irradiation and atelevated temperatures, are found to be most effective in anchoringthe SO2 gas molecules to the TiO2 surfaces. Both TiO2(101) andTiO2(001) surfaces with oxygen vacancies are found to exhibit higherSO2 adsorption energies in the DFT calculations. The adsorptionmechanism of SO2 is explained on the basis of electronic structure,charge transfer between the molecule and the surface, and the oxidation state of the adsorbed molecule. The theoretical findingsare corroborated by FTIR experiments. Moreover, the (001) surface with oxygen vacancies is found to bind SO2 gas moleculesmore strongly, as compared to the (101) surface. Higher concentration of oxygen vacancies on the TiO2 surfaces is found tosignificantly increase the adsorption energy. The results shed new insight into the sensing properties of TiO2-based gas sensors

  • 14.
    Smulko, J
    et al.
    Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Polen.
    Kotarski, M
    Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Polen.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kish, L B
    Dept of Electrical Engineering, Texas A&M University, College Station, USA.
    Fluctuation-enhanced gas sensing in practice2011Conference paper (Refereed)
    Abstract [en]

    The technique of fluctuation-enhanced sensing (FES) in resistive gas sensors was proposed a few years ago. The method improves the selectivity and sensitivity of gas detection. This was confirmed in numerous laboratory experiments. Some of the latest results obtained for practical applications of the FES method are presented (toxic gases detection; problems of detection repeatability; detection of essential oils intensity during aromatherapy, biological agent detection). Additionally, a new prototype nanoparticle gas sensor was introduced with an additional potential of gas detection using noise induced by UV irradiations.

  • 15.
    Stefanov, B. I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Acetaldehyde Adsorption and Condensation on Anatase TiO2: Influence of Acetaldehyde Dimerization2014In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed)
  • 16.
    Stefanov, Bozhidar I
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization2014In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed)
    Abstract [en]

    Conversion of acetaldehyde to crotonaldehyde on anatase TiO2 films was studied by in situ Fourier transform infrared spectroscopy (FTIR) and by density functional theory (DFT) calculations. In situ FTIR showed that acetaldehyde adsorption is accompanied by the appearance of a hitherto non-assigned absorption band at 1643 cm−1, which is shown to be due to acetaldehyde dimers. The results were supported by DFT calculations. Vibrational frequencies calculated within a partially relaxed cluster model for molecular acetaldehyde and its dimer, and for the corresponding adsorbed species on the anatase (101) surface, were in good agreement with experimental results. A kinetic model was constructed based on the combined FTIR and DFT results, and was shown to explain the essential features of the acetaldehyde condensation reaction.

  • 17.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Adsorbtion and reaction of acetaldehyde on pristine and SO2 modified anatase TiO22013Conference paper (Refereed)
  • 18.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Li, Shu-Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kish, Laszlo B.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Resistance noise at the metal-insulator transition in thermochromic VO2 films2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 2, p. 1-7, article id 025303Article in journal (Refereed)
    Abstract [en]

    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 50<T-s<70 degrees C range of temperature T-s around the "critical" temperature T-c between a low-temperature semiconducting phase and a high-temperature metallic-like phase of VO2. Power density spectra S(f) were extracted for resistance noise around T-c and demonstrated unambiguous 1/f behavior. Data on S(10 Hz)/R-s(2) scaled as R-s(x), where R-s is sample resistance; the noise exponent x was -2.6 for T-s< T-c and +2.6 for T-s>T-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.

  • 19.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Li, S-Y
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, CG
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kish, Laszlo B
    Percolation noise at the metal-insulator transition of nanostructured VO2 films2015In: Extended Abstracts, 2015Conference paper (Refereed)
  • 20.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Spectroscopic study of the photofixation of SO2 on anatase TiO2 thin films and their oleophobic properties2012In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 2, p. 672-679Article in journal (Refereed)
    Abstract [en]

    Photoinduced SO2 fixation on anatase TiO2 films was studied by in situ Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The TiO2 films were prepared by reactive DC magnetron sputtering and were subsequently exposed to 50 ppm SO2 gas mixed in synthetic air and irradiated with UV light at substrate temperatures between 298 and 673 K. Simultaneous UV irradiation and SO2 exposure between 373 and 523 K resulted in significant sulfur (S) deposits on crystalline TiO2 films as determined by XPS, whereas amorphous films contained negligible amounts of S. At substrate temperatures above 523 K, the S deposits readily desorbed from TiO2. The oxidation state of sulfur successively changed from S4+ for SO2 adsorbed on crystalline TiO2 films at room temperature without irradiation to S6+ for films exposed to SO2 at elevated temperatures with simultaneous irradiation. In situ FTIR was used to monitor the temporal evolution of the photoinduced surface reaction products formed on the TiO2 surfaces. It is shown that band gap excitation of TiO2 results in photoinduced oxidation of SO2, which at elevated temperatures become coordinated to the TiO2 lattice through interactions with O vacancies and form sulfite and sulfate surface species. These species makes the surface acidic, which is manifested in nondetectable adherence of stearic acid to the modified surface. The modified films show good chemical stability as evidenced by sonication and repeated recycling of the films. The results suggest a new method to functionalize wide band gap oxide surfaces by means of photoinduced reactions in reactive gases at elevated substrate temperatures. In the case of anatase TiO2 in reactive SO2 gas, we here show that such functionalization yields surfaces with excellent oleophobic properties, as probed by adhesion of stearic acid.

  • 21.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Photo-Fixation of SO2 in Nanocrystalline TiO2 Films Prepared by Reactive DC Magnetron Sputtering2009In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 518, no 4, p. 1341-1344Article in journal (Refereed)
    Abstract [en]

    We report on photo-fixation of SO2 onto nanostructured TiO2 thin films prepared by reactive DC magnetron sputtering. The films were exposed to 50 PPM SO2 gas mixed in synthetic air and illuminated with UV light at 298 and 473 K. The evolution of the adsorbed SOx species was monitored by in situ Fourier transform infrared specular reflection spectroscopy. Significant photo-fixation occurred only in the presence of UV illumination. The SO2 uptake was dramatically enhanced at elevated temperatures and then produced strongly bonded surface-coordinated SO, complexes. The total SO, uptake is consistent with Langmuir adsorption kinetics. The sulfur doping at saturation was estimated from X-ray photoelectron spectroscopy to be similar to 2.2 at.% at 473 K These films were pale yellowish and had an optical absorption coefficient being similar to 3 times higher than in undoped film. The S-doped films exhibit interesting oleophobic properties, exemplified by the poor adherence of stearic acid. Our results suggest a new method for sulfur doping of TiO2 to achieve combined anti-grease and photocatalytic properties.

  • 22.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Smulko, J M
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Granqvist, Claes G
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Fasta tillståndets fysik.
    Resistance Noise in TiO2-Based Thin Film Gas Sensors under Ultraviolet Irradiation2007Conference paper (Refereed)
  • 23.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Stefanov, Bozhidar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling2013In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 307, p. 265-274Article in journal (Refereed)
    Abstract [en]

    Adsorption and photocatalytic oxidation of acetaldehyde have been investigated on TiO2 and sulfate-modified TiO2 films (denoted SO4TiO2). In situ Fourier transform infrared spectroscopy was used to study surface reactions as a function of time and number of experimental cycles. Spectral analysis and micro-kinetic modeling show that crotonaldehyde formation occurs spontaneously on TiO2 but is impeded on SO4TiO2, where instead acetaldehyde desorption is significant. Photo-oxidation yields significant amounts of formate on TiO2 and was identified as the rate-determining step and associated with site blocking. Significantly smaller amounts of formate were observed on SO4TiO2, which is due to the acidity of this surface resulting in weaker bonding of aldehyde and carboxylate intermediate species. Our results are of considerable interest for applications to photocatalytic air purification and to surfaces with controlled wettability.

  • 24. Valizadeh, Sima
    et al.
    Coleman, Victoria
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Strömberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Welch, Ken
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Focused ion beam fabricated nanowire based electrodes for transport studies of biomolecules and nanoparticles2007In: IVC-17/ICSS-13 and ICN+T 2007, 2007Conference paper (Refereed)
  • 25.
    Österlund, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Z.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Characterization of Oleophobic and Photocatalytic TiO2 Thin Films Prepared by Surface Functionalization with Reactive Sulfur Dioxide Gas2011In: Abstracts 2nd European Symp. Photocatalysis (JEP 2011), 2011Conference paper (Refereed)
  • 26.
    Österlund, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Photocatalytic oxide films in the built environment2014In: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices / [ed] Assoc. Prof. Dr.Tatyana Ivanova, Prof. DSc Kostadinka Gesheva, Prof. DSc Hassan Chamatti, Assoc. Prof. Dr. Georgi Popkirov, Institute of Physics (IOP), 2014, p. 012009-Conference paper (Refereed)
    Abstract [en]

    The possibility to increase human comfort in buildings is a powerful driving force for the introduction of new technology. Among other things our sense of comfort depends on air quality, temperature, lighting level, and the possibility of having visual contact between indoors and outdoors. Indeed there is an intimate connection between energy, comfort, and health issues in the built environment, leading to a need for intelligent building materials and green architecture. Photocatalytic materials can be applied as coatings, filters, and be embedded in building materials to provide self-cleaning, antibacterial, air cleaning, deodorizing, and water cleaning functions utilizing either solar light or artificial illumination sources – either already present in buildings, or by purposefully designed luminaries. Huge improvements in indoor comfort can thus be made, and also alleviate negative health effects associated with buildings, such as the sick-house syndrome. At the same time huge cost savings can be made by reducing maintenance costs. Photocatalytic oxides can be chemical modified by changing their acid-base surface properties, which can be used to overcome deactivation problems commonly encountered for TiO2 in air cleaning applications [2, 3]. In addition, the wetting properties oxides can be tailored by surface chemical modifications and made e.g. oleophobic and water repellent [5]. Here we show results of surface acid modified TiO2 coatings on various substrates. In particular, we show that advanced surface treatment of photocatalytic cement yields surfaces with beneficial self-cleaning properties by means of photo-fixation of surface sulfate groups. We propose that such approaches are feasible for a number of applications in the built environment, including windows, tiles, sheet metals, plastics, etc.

  • 27.
    Österlund, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Photocatalytic oxide films in the built environment2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 559, no 1, p. 012009-Article in journal (Refereed)
1 - 27 of 27
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