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Wang, J., Xu, C., Nilsson, A. M., Fernandes, D. L. A. & Niklasson, G. A. (2019). A novel phase function describing light scattering of layers containing colloidal nanospheres. Nanoscale, 11(15), 7404-7413
Open this publication in new window or tab >>A novel phase function describing light scattering of layers containing colloidal nanospheres
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2019 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 15, p. 7404-7413Article in journal (Refereed) Published
Abstract [en]

Light scattering from small particles exhibit unique angular scattering distributions, which are strongly dependent on the radius to wavelength ratio as well as the refractive index contrast between the particles and the surrounding medium. As the concentration of the particles increases, multiple scattering becomes important. This complicates the description of the angular scattering patterns, and in many cases one has to resort to empirical phase functions. We have measured the angle dependence of light scattering from a polymer layer containing sub-micron metallic and dielectric particles. The samples exhibited strongly forward and backward peaked scattering patterns, which were fitted to a number of empirical approximative phase functions. We found that a novel two-term Reynolds-McCormick (TTRM) phase function gave the best fit to the experimental data in all cases. The feasibility of the TTRM approach was further validated by good agreement with numerical simulations of Mie single scattering phase functions at various wavelengths and sizes, ranging from the Rayleigh scattering regime to the geometrical optics regime. Hence, the widely adaptable TTRM approach is able to describe angular scattering distributions of different kinds of nanospheres and nanocomposites, both in the single scattering and multiple scattering regimes.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-383188 (URN)10.1039/c9nr01707k (DOI)000465315900034 ()30938744 (PubMedID)
Funder
Swedish Research Council, 2016-03713
Available from: 2019-07-25 Created: 2019-07-25 Last updated: 2019-07-25Bibliographically approved
Granqvist, C. G., Arvizu, M. A., Qu, H.-Y., Wen, R.-T. & Niklasson, G. (2019). Advances in electrochromic device technology: Multiple roads towards superior durability. Paper presented at 61st Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), MAY 05-10, 2018 , Orlando, FL, USA.. Surface & Coatings Technology, 357, 619-625
Open this publication in new window or tab >>Advances in electrochromic device technology: Multiple roads towards superior durability
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2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 357, p. 619-625Article in journal (Refereed) Published
Abstract [en]

Most electrochromic (EC) devices must have a service lifetime of many years, and this is particularly so for“smart windows” in buildings with good energy efficiency and indoor comfort. The central part of oxide-based EC devices contains thin films based on W oxide and Ni oxide together with an interposed electrolyte. Depending on operating conditions, these films may show degradation at a slower or faster pace, and means to prevent or reverse this phenomenon, or as a minimum allow reliable lifetime prediction, have been sought ever since the beginnings of EC technology. Here we survey recent endeavors related to EC films of W oxide and Ni oxide and show that (i) electrochemical pretreatment of films in a liquid electrolyte can significantly improve durability, (ii)electrochemical posttreatment in a liquid electrolyte can rejuvenate degraded films, (iii) mixed oxides can have better durability and optical performance than corresponding pure oxides, and (iv) lifetime prediction is possible.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Materials Chemistry
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-369882 (URN)10.1016/j.surfcoat.2018.10.048 (DOI)000455691100083 ()
Conference
61st Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), MAY 05-10, 2018 , Orlando, FL, USA.
Funder
EU, European Research Council, 267234
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-02-05Bibliographically approved
Cindemir, U., Topalian, Z., Granqvist, C. G., Österlund, L. & Niklasson, G. (2019). Characterization of nanocrystalline-nanoporous nickel oxide thin films prepared by reactive advanced gas deposition. Materials Chemistry and Physics, 227, 98-104
Open this publication in new window or tab >>Characterization of nanocrystalline-nanoporous nickel oxide thin films prepared by reactive advanced gas deposition
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2019 (English)In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 227, p. 98-104Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Nickel oxide, Advanced gas deposition, EXAFS, Atomic structure, Gas sensor
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-387223 (URN)10.1016/j.matchemphys.2019.01.058 (DOI)000466617800013 ()
Funder
EU, FP7, Seventh Framework Programme, 267234
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Qiu, Z., Tai, C.-W., Niklasson, G. & Edvinsson, T. (2019). Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting. Energy & Environmental Science, 12(2), 572-581
Open this publication in new window or tab >>Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting
2019 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 12, no 2, p. 572-581Article in journal (Refereed) Published
Abstract [en]

Earth-abundant transition metal-based compounds are of high interest as catalysts for sustainable hydrogen fuel generation. The realization of effective electrolysis of water, however, is still limited by the requirement of a high sustainable driving potential above thermodynamic requirements. Here, we report dynamically self-optimized (DSO) NiFe layered double hydroxide (LDH) nanosheets with promising bi-functional performance. Compared with pristine NiFe LDH, DSO NiFe LDH exhibits much lower overpotential for the hydrogen evolution reaction (HER), even outperforming platinum. Under 1 M KOH aqueous electrolyte, the bi-functional DSO catalysts show an overpotential of 184 and -59 mV without iR compensation for oxygen evolution reaction (OER) and HER at 10 mA cm(-2). The material system operates at 1.48 V and 1.29 V to reach 10 and 1 mA cm(-2) in two-electrode measurements, corresponding to 83% and 95% electricity-to-fuel conversion efficiency with respect to the lower heating value of hydrogen. The material is seen to dynamically reform the active phase of the surface layer during HER and OER, where the pristine and activated catalysts are analyzed with ex situ XPS, SAED and EELS as well as with in situ Raman spectro-electrochemistry. The results show transformation into different active interfacial species during OER and HER, revealing a synergistic interplay between iron and nickel in facilitating water electrolysis.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:uu:diva-379268 (URN)10.1039/c8ee03282c (DOI)000459741700005 ()
Funder
Swedish Energy AgencySwedish Research Council, VR-2016-03713Swedish Research Council Formas, 2016-00908Knut and Alice Wallenberg Foundation
Available from: 2019-03-18 Created: 2019-03-18 Last updated: 2019-03-29Bibliographically approved
Arvizu, M. A., Qu, H.-Y., Cindemir, U., Qiu, Z., Rojas González, E. A., Primetzhofer, D., . . . Niklasson, G. (2019). Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment. Journal of Materials Chemistry A, 7(6), 2908-2918
Open this publication in new window or tab >>Electrochromic WO3 thin films attain unprecedented durability by potentiostatic pretreatment
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 6, p. 2908-2918Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-378529 (URN)10.1039/c8ta09621j (DOI)000457893400054 ()
Funder
EU, European Research Council, 267234Swedish Research Council, 821-2012-5144Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2019-03-22 Created: 2019-03-22 Last updated: 2019-03-22Bibliographically approved
Niklasson, G., Qiu, Z., Bayrak Pehlivan, I. & Edvinsson, T. (2019). Impedance spectroscopy of water splitting reactions on nanostructured metal-based catalysts. In: Functional Materials and Nanotechnologies (FM&NT 2018): . Paper presented at 12th International Scientific Conference on Functional Materials and Nanotechnologies (FM&NT), OCT 02-05, 2018, Riga, Latvia. Institute of Physics Publishing (IOPP), Article ID 012005.
Open this publication in new window or tab >>Impedance spectroscopy of water splitting reactions on nanostructured metal-based catalysts
2019 (English)In: Functional Materials and Nanotechnologies (FM&NT 2018), Institute of Physics Publishing (IOPP), 2019, article id 012005Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Hydrogen production by water splitting using nanomaterials as electrocatalysts is a promising route enabling replacement of fossil fuels by renewable energy sources. In particular, the development of inexpensive non-noble metal-based catalysts is necessary in order to replace currently used expensive Pt-based catalysts. We report a detailed impedance spectroscopy study of Ni-Mo and Ni-Fe based electrocatalytic materials deposited onto porous and compact substrates with different conductivities. The results were interpreted by a critical comparison with equivalent circuit models. The reaction resistance displays a strong dependence on potential and a lower substrate dependence. The impedance behaviour can also provide information on the dominating reaction mechanism. An optimized Ni-Fe based catalyst showed very promising properties for applications in water electrolysis.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019
Series
IOP Conference Series-Materials Science and Engineering, ISSN 1757-8981 ; 503:1
National Category
Engineering and Technology Physical Chemistry
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-369729 (URN)10.1088/1757-899X/503/1/012005 (DOI)000471150800005 ()
Conference
12th International Scientific Conference on Functional Materials and Nanotechnologies (FM&NT), OCT 02-05, 2018, Riga, Latvia
Funder
Swedish Research Council, VR-2016-03713Swedish Research Council, VR-2015-03814EU, Horizon 2020
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-08-01Bibliographically approved
Vargas, W. E., Clark, N., Munoz-Rojas, F., Azofeifa, D. E. & Niklasson, G. (2019). Optical, charge transport and magnetic properties of palladium retrieved from photometric measurements: approaching the quantum mechanics background. Physica Scripta, 94(5), Article ID 055101.
Open this publication in new window or tab >>Optical, charge transport and magnetic properties of palladium retrieved from photometric measurements: approaching the quantum mechanics background
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2019 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 94, no 5, article id 055101Article in journal (Refereed) Published
Abstract [en]

A parametric Drude-Lorentz (DL) model is used to describe the spectral variation of the dielectric functions of bulk palladium samples at low and room temperature. In addition to the contribution of conduction electrons, the contribution of holes is also explicitly accounted for in the model. A simulated annealing method is applied to obtain the optimized values of the parameters involved in the model: volume plasma frequency of conduction electrons, high frequency dielectric constant, collision frequency of holes and corresponding relaxation time, and two additional parameters from which the effective mass of holes and collision frequency of conduction electrons are evaluated. Oscillatior strengths, resonance frequencies, and widths entering in the Lorentz contribution to the dielectric function are also optimized. Renormalization of the oscillator strengths requires the introduction of a new parameter in the context of the DL model: the ratio between number density of conduction electrons and number density of metal atoms, whose optimized value fits very well with its evaluation from band structure calculations and from independent measurements. Inclusion of this parameter in the framework allows us to evaluate additional quantities related to the charge-carrier transport: average effective masses, Fermi energies and electronic densities of states at the corresponding Fermi energies, intrinsic electrical resistivity, intrinsic mean free paths, heat capacities, mobilities, as well as paramagnetic and diamagnetic susceptibilities, for both electrons and holes. The optimized resonance frequencies are compared with energy differences between plausible interband transitions, in accordance with reported band structure diagrams and with our own band structure obtained from density functional theory calculations.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
simulated annealing, palladium, Drude-Lorentz model, metal thin films, density functional theory
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-380417 (URN)10.1088/1402-4896/ab07ee (DOI)000461447700001 ()
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-04-02Bibliographically approved
Qu, H.-Y., Rojas González, E. A., Granqvist, C. G. & Niklasson, G. (2019). Potentiostatically pretreated electrochromic tungsten oxide films with enhanced durability: Electrochemical processes at interfaces of indium–tin oxide. Thin Solid Films, 682, 163-168
Open this publication in new window or tab >>Potentiostatically pretreated electrochromic tungsten oxide films with enhanced durability: Electrochemical processes at interfaces of indium–tin oxide
2019 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 682, p. 163-168Article in journal (Refereed) Published
Abstract [en]

Recent work has shown that electrochromic WO3 films, backed by In2O3:Sn (ITO) and immersed in a lithium-ion-conducting electrolyte, can attain unprecedented electrochemical cycling durability after potentiostatic pretreatment at high voltage. Here we demonstrate that this intriguing feature is associated with changes in the properties of the ITO film. Specifically, we studied thin films of ITO and WO3/ITO immersed in an electrolyte of LiClO4 in propylene carbonate at potentials up to 6.0 V vs. Li/Li+ by cyclic voltammetry and impedance spectroscopy and present evidence that electrochemical reactions occur under these conditions. X-ray photoemission spectroscopy indicated that the ITO film was partly dissolved at high voltages and that the dissolution reaction promoted diffusion of In and Sn into the WO3 film.

Keywords
Indium-tin oxide, Electrochemistry, Dissolution reaction, Tungsten oxide, Electrochromism
National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-385819 (URN)10.1016/j.tsf.2019.02.027 (DOI)
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-19Bibliographically approved
Rojas González, E. A. & Niklasson, G. (2019). Setup for simultaneous electrochemical and color impedance measurements of electrochromic films: Theory, assessment, and test measurement. Review of Scientific Instruments, 90(8), Article ID 085103.
Open this publication in new window or tab >>Setup for simultaneous electrochemical and color impedance measurements of electrochromic films: Theory, assessment, and test measurement
2019 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 90, no 8, article id 085103Article in journal (Refereed) Published
Abstract [en]

Combined frequency-resolved techniques are suitable to study electrochromic (EC) materials. We present an experimental setup for simultaneous electrochemical and color impedance studies of EC systems in transmission mode and estimate its frequency-dependent uncertainty by measuring the background noise. We define the frequency-dependent variables that are relevant to the combined measurement scheme, and a special emphasis is given to the complex optical capacitance and the complex differential coloration efficiency, which provide the relation between the electrical and optical responses. Results of a test measurement on amorphous WO3 with LED light sources of peak wavelengths of 470, 530, and 810 nm are shown and discussed. In this case, the amplitude of the complex differential coloration efficiency presented a monotonous increase down to about 0.3 Hz and was close to a constant value for lower frequencies. We study the effect of the excitation voltage amplitude on the linearity of the electrical and optical responses for the case of amorphous WO3 at 2.6 V vs Li/Li+, where a trade-off should be made between the signal-to-noise ratio (SNR) of the optical signal and the linearity of the system. For the studied case, it was possible to increase the upper accessible frequency of the combined techniques (defined in this work as the upper threshold of the frequency region for which the SNR of the optical signal is greater than 5) from 11.2 Hz to 125.9 Hz while remaining in the linear regime with a tolerance of less than 5%. (C) 2019 Author(s).

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2019
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-394164 (URN)10.1063/1.5115119 (DOI)000483885600066 ()31472623 (PubMedID)
Funder
Swedish Research Council, VR-2016-03713
Available from: 2019-10-09 Created: 2019-10-09 Last updated: 2019-10-09Bibliographically approved
Coll, M., Fontcuberta, J., Althammer, M., Bibes, M., Boschker, H., Calleja, A., . . . Granozio, F. M. (2019). Towards Oxide Electronics: a Roadmap. Applied Surface Science, 482, 1-93
Open this publication in new window or tab >>Towards Oxide Electronics: a Roadmap
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2019 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 482, p. 1-93Article in journal (Refereed) Published
Abstract [en]

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-382804 (URN)10.1016/j.apsusc.2019.03.312 (DOI)000464940900001 ()
Available from: 2019-05-08 Created: 2019-05-08 Last updated: 2019-05-08Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-8279-5163

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