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Hultman, Lars, ProfessorORCID iD iconorcid.org/0000-0002-2837-3656
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Publications (10 of 617) Show all publications
Magnuson, M., Schmidt, S., Hultman, L. & Högberg, H. (2017). Electronic properties and bonding in ZrHx thin films investigated by valence-bandx-ray photoelectron spectroscopy. Physical Review B Condensed Matter, 96(19), Article ID 195103.
Open this publication in new window or tab >>Electronic properties and bonding in ZrHx thin films investigated by valence-bandx-ray photoelectron spectroscopy
2017 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 96, no 19, 195103Article in journal (Refereed) Published
Abstract [en]

The electronic structure and chemical bonding in reactively magnetron sputtered ZrHx (x = 0.15, 0.30, 1.16)thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level,and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significantreduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H1s–Zr 4d hybridization region at ∼6 eV below the Fermi level. For low hydrogen content (x = 0.15, 0.30), thefilms consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ-ZrHx(CaF2-type structure) phases, while for x = 1.16, the films form single-phase ZrHx that largely resembles thatof stoichiometric δ-ZrH2 phase. We show that the cubic δ-ZrHx phase is metastable as thin film up to x = 1.16,while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated ZrH1.16film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4p3/2 and 3d5/2peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifiesa charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemicalshifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affectsthe conductivity by charge redistribution in the valence band.

Place, publisher, year, edition, pages
College Park, United States: American Physical Society, 2017
Keyword
Metal Hydrides; X-ray Photoelectron Spectroscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-142743 (URN)10.1103/PhysRevB.96.195103 (DOI)000414133500003 ()
Note

Funding agencies: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Swedish Energy Research [43606-1]; Swedish Foundation for Strategic Research (SSF) through synergy grant FUNCASE [RMA11-0029]; Ca

Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2017-11-29Bibliographically approved
Serban, A., Palisaitis, J., Junaid, M., Tengdelius, L., Högberg, H., Hultman, L., . . . Hsiao, C.-L. (2017). Magnetron Sputter Epitaxy of High-Quality GaN Nanorods on Functional and Cost-Effective Templates/Substrates. Energies, 10(9), Article ID 1322.
Open this publication in new window or tab >>Magnetron Sputter Epitaxy of High-Quality GaN Nanorods on Functional and Cost-Effective Templates/Substrates
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2017 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 9, 1322Article in journal (Refereed) Published
Abstract [en]

We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB2/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology.

Place, publisher, year, edition, pages
Basel, Switzerland: MDPI AG, 2017
Keyword
GaN, nanorods, Si, SiC, Ti, Mo, TiN and ZrB2 templates, magnetron sputtering, epitaxy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-141597 (URN)10.3390/en10091322 (DOI)000411225200078 ()2-s2.0-85029362447 (Scopus ID)
Note

Funding agencies: Swedish Research Council (VR) [621-2012-4420, 621-2013-5360, 2016-04412]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program; Swedish Foundation for Strategic Research (SSF) through the Resea

Available from: 2017-10-02 Created: 2017-10-02 Last updated: 2017-11-29Bibliographically approved
Schmidt, S., Czigany, Z., Wissting, J., Greczynski, G., Janzén, E., Jensen, J., . . . Hultman, L. (2016). A comparative study of direct current magnetron sputtering and high power impulse magnetron sputtering processes for CNX thin film growth with different inert gases. Diamond and related materials, 64, 13-26.
Open this publication in new window or tab >>A comparative study of direct current magnetron sputtering and high power impulse magnetron sputtering processes for CNX thin film growth with different inert gases
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2016 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 64, 13-26 p.Article in journal (Refereed) Published
Abstract [en]

Reactive direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS) discharges of carbon in different inert gas mixtures (N-2/Ne, N-2/Ar, and N-2/Kr) were investigated for the growth of carbon-nitride (CNX) thin films. Ion mass spectrometry showed that energies of abundant plasma cations are governed by the inert gas and the N-2-to-inert gas flow ratios. The population of ion species depends on the sputter mode; HiPIMS yields approximately ten times higher flux ratios of ions originating from the target to process gas ions than DCMS. Exceptional are discharges in Ne with N-2-to-Ne flow ratios <20%. Here, cation energies and the amount of target ions are highest without influence on the sputter mode. CNX thin films were deposited in 14% N-2/inert gas mixtures at substrate temperatures of 110 degrees C and 430 degrees C. The film properties show a correlation to the substrate temperature, the applied inert gas and sputter mode. The mechanical performance of the films is mainly governed by their morphology and composition, but not by their microstructure. Amorphous and fullerene-like CN0.14 films exhibiting a hardness of similar to 15 GPa and an elastic recovery of similar to 90% were deposited at 110 degrees C in reactive Kr atmosphere by DCMS and HiPIMS.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2016
Keyword
Magnetron sputtering; Inert gases; Plasma analysis; Langmuir probe measurement; CNX film stress; CNX hardness
National Category
Inorganic Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-128146 (URN)10.1016/j.diamond.2016.01.009 (DOI)000374608100003 ()
Note

Funding Agencies|Carl Tryggers Foundation for Scientific Research; Hungarian Academy of Sciences

Available from: 2016-05-19 Created: 2016-05-19 Last updated: 2017-11-30
Tholander, C., Birch, J., Tasnádi, F., Hultman, L., Palisaitis, J., Persson, P. O., . . . Zukauskaitè, A. (2016). Ab initio calculations and experimental study of piezoelectric YxIn1-xN thin films deposited using reactive magnetron sputter epitaxy. Acta Materialia, 105, 199-206.
Open this publication in new window or tab >>Ab initio calculations and experimental study of piezoelectric YxIn1-xN thin films deposited using reactive magnetron sputter epitaxy
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2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 105, 199-206 p.Article in journal (Refereed) Published
Abstract [en]

By combining theoretical prediction and experimental verification we investigate the piezoelectric properties of yttrium indium nitride (YxIn1-xN). Ab initio calculations show that the YxIn1-xN wurtzite phase is lowest in energy among relevant alloy structures for 0≤x≤0.5. Reactive magnetron sputter epitaxy was used to prepare thin films with Y content up to x=0.51. The composition dependence of the lattice parameters observed in the grown films is in agreement with that predicted by the theoretical calculations confirming the possibility to synthesize a wurtzite solid solution. An AlN buffer layer greatly improves the crystalline quality and surface morphology of subsequently grown YxIn1-xN films. The piezoelectric response in films with x=0.09 and x=0.14 is observed using piezoresponse force microscopy. Theoretical calculations of the piezoelectric properties predict YxIn1−xN to have comparable piezoelectric properties to ScxAl1-xN.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
YInN, Thin films, Sputter deposition, Piezoelectricity, Ab initio calculations
National Category
Condensed Matter Physics Materials Chemistry Inorganic Chemistry Other Materials Engineering Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:liu:diva-125918 (URN)10.1016/j.actamat.2015.11.050 (DOI)000370086500023 ()
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2017-11-30Bibliographically approved
Sangiovanni, D., Mei, A. B., Hultman, L., Chirita, V., Petrov, I. & Greene, J. E. (2016). Ab Initio Molecular Dynamics Simulations of Nitrogen/VN(001) Surface Reactions: Vacancy-Catalyzed N-2 Dissociative Chemisorption, N Adatom Migration, and N-2 Desorption. The Journal of Physical Chemistry C, 120(23), 12503-12516.
Open this publication in new window or tab >>Ab Initio Molecular Dynamics Simulations of Nitrogen/VN(001) Surface Reactions: Vacancy-Catalyzed N-2 Dissociative Chemisorption, N Adatom Migration, and N-2 Desorption
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2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 23, 12503-12516 p.Article in journal (Refereed) Published
Abstract [en]

We use density-functional ab initio molecular dynamics to investigate the kinetics of N/VN(001) surface reactions at temperatures ranging from 1600 to 2300 K. N adatoms (N-ad) on VN(001) favor epitaxial atop-V positions and diffuse among them by transiting through 4-fold hollow (FFH) sites, at which they are surrounded by two V and two N surface atoms. After several atop-V -amp;gt; FFH -amp;gt; atop-V jumps, isolated N adatoms bond strongly with an underlying N surface (N-surf) atom. Frequent N-ad/N-surf pair exchange reactions lead to N-2 desorption, which results in the formation of an anion surface vacancy. N vacancies rapidly migrate via in-plane (110) jumps and act as efficient catalysts for the dissociative chemisorption of incident N-2 molecules. During exposure of VN(001) to incident atomic N gas atoms, N-ad/N-ad recombination and desorption is never observed, despite a continuously high N monomer surface coverage. Instead, N-2 desorption is always initiated by a N adatom removing a N surface atom or by energetic N gas atoms colliding with N-ad or N-surf atoms. Similarities and differences between: N/VN(001) vs. previous N/TiN(001) results, discussed on the basis of temperature-dependent ab initio electronic structures and chemical bonding, provide insights for controlling the reactivity of NaCl-structure transition-metal nitride (001) surfaces via electron-concentration tuning.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2016
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-130283 (URN)10.1021/acs.jpcc.6b02652 (DOI)000378196200021 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation (Isotope Project) [2011.0094]; Swedish Research Council (VR) Linkoping Linnaeus Initiative LiLi-NFM [2008-6572, 2014-5790, 2013-4018]; Swedish Government Strategic Research Area Grant in Materials Science on Advanced Functional Materials (through Swedens innovation agency VINNOVA) [MatLiU 2009-00971]

Available from: 2016-08-01 Created: 2016-07-28 Last updated: 2017-11-28
Beshkova, M., Hultman, L. & Yakimova, R. (2016). Device applications of epitaxial graphene on silicon carbide. Vacuum, 128, 186-197.
Open this publication in new window or tab >>Device applications of epitaxial graphene on silicon carbide
2016 (English)In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 128, 186-197 p.Article, review/survey (Refereed) Published
Abstract [en]

Graphene has become an extremely hot topic due to its intriguing material properties allowing for ground-breaking fundamental research and applications. It is one of the fastest developing materials during the last several years. This progress is also driven by the diversity of fabrication methods for graphene of different specific properties, size, quantity and cost. Graphene grown on SiC is of particular interest due to the possibility to avoid transferring of free standing graphene to a desired substrate while having a large area SiC (semi-insulating or conducting) substrate ready for device processing. Here, we present a review of the major current explorations of graphene on SiC in electronic devices, such as field effect transistors (FET), radio frequency (RF) transistors, integrated circuits (IC), and sensors. The successful role of graphene in the metrology sector is also addressed. Typical examples of graphene on SiC implementations are illustrated and the drawbacks and promises are critically analyzed. (C) 2016 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2016
Keyword
Graphene FET; RF-transistors; IC; Graphene sensors; Detectors; Quantum Hall resistance
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-129150 (URN)10.1016/j.vacuum.2016.03.027 (DOI)000376052500026 ()
Note

Funding Agencies|European Union [604391]; Swedish Research Council [VR 621-2014-5805]; LiU Linnaeus Grant

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2017-11-28
Ektarawong, A., Simak, S., Hultman, L., Birch, J., Tasnádi, F., Wang, F. & Alling, B. (2016). Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics. Journal of Chemical Physics, 144(13), Article ID 134503.
Open this publication in new window or tab >>Effects of configurational disorder on the elastic properties of icosahedral boron-rich alloys based on B6O, B13C2, and B4C, and their mixing thermodynamics
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2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 13, 134503Article in journal (Refereed) Published
Abstract [en]

The elastic properties of alloys between boron suboxide (B6O) and boron carbide (B13C2), denoted by (B6O)1−x(B13C2)x, as well as boron carbide with variable carbon content, ranging from B13C2 to B4C are calculated from first-principles. Furthermore, the mixing thermodynamics of (B6O)1−x(B13C2)x is studied. A superatom-special quasirandom structure approach is used for modeling different atomic configurations, in which effects of configurational disorder between the carbide and suboxide structural units, as well as between boron and carbon atoms within the units, are taken into account. Elastic properties calculations demonstrate that configurational  disorder in B13C2, where a part of the C atoms in the CBC chains substitute for B atoms in the B12 icosahedra, drastically increase the Young’s and shear modulus, as compared to an atomically ordered state, B12(CBC). These calculated elastic moduli of the disordered state are in excellent agreement with experiments. Configurational disorder between boron and carbon can also explain the experimentally observed almost constant elastic moduli of boron carbide as the carbon content is changed from B4C to B13C2. The elastic moduli of the (B6O)1−x(B13C2)x system are also practically unchanged with composition if boron-carbon disorder is taken into account. By investigating the mixing thermodynamics of the alloys, in which the Gibbs free energy is determined within the mean-field approximation for the configurational entropy, we outline the pseudo-binary phase diagram of (B6O)1−x(B13C2)x. The phase diagram reveals the existence of a miscibility gap at all temperatures up to the melting point. Also, the coexistence of B6O-rich as well as ordered or disordered B13C2-rich domains in the material prepared through equilibrium routes is predicted.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-122425 (URN)10.1063/1.4944982 (DOI)000374527900023 ()27059576 (PubMedID)
Note

Funding agencies:Swedish Research Council (VR) [621-2011-4417, 330-2014-6336, 2011-42-59]; CeNano at Linkoping University; Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISiS" [K3-2014-049]; LiLi-

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2017-12-01Bibliographically approved
Sangiovanni, D., Hultman, L., Chirita, V., Petrov, I. & Greene, J. E. (2016). Effects of phase stability, lattice ordering, and electron density on plastic deformation in cubic TiWN pseudobinary transition-metal nitride alloys. Acta Materialia, 103, 823-835.
Open this publication in new window or tab >>Effects of phase stability, lattice ordering, and electron density on plastic deformation in cubic TiWN pseudobinary transition-metal nitride alloys
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2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 103, 823-835 p.Article in journal (Refereed) Published
Abstract [en]

We carry out density functional theory calculations to compare the energetics of layer glide, as well as stress vs. strain curves, for cubic Ti0.5W0.5N pseudobinary alloys and reference B1-structure TiN. Irrespective of the degree of ordering on the metal sublattice, the hardness and stiffness of Ti0.5W0.5, as estimated by stress strain results and resistance to layer glide, are comparable to that of the parent binary TiN, while ductility is considerably enhanced. After an initial elastic response to an applied load, the pseudobinary alloy deforms plastically, thus releasing accumulated mechanical stress. In contrast, stress continues to increase linearly with strain in TiN. Layer glide in Ti0.5W0.5N is promoted by a high valence-electron concentration which enables the formation of strong metallic bonds within the slip direction upon deformation. [1111-oriented Ti0.5W0.5N layers characterized by high local metal-sublattice ordering exhibit low resistance to slip along < 110 > directions due to energetically favored formation of (111) hexagonal stacking faults. This is consistent with the positive formation energy of < 111 >-ordered Tio.5W0.5N with respect to mixing of cubic-BI TiN and hexagonal WC-structure WN. In the cubic pseudobinary alloy, slip occurs parallel, as well as orthogonal, to the resolved applied stress at the interface between layers with the lowest friction. We suggest that analogous structural metastability (mixing cubic and hexagonal TM nitride binary phases) and electronic (high valence electron concentration) effects are responsible for the enhanced toughness recently demonstrated experimentally for cubic single-crystal pseudobinary V0.5W0.5N and V0.5MocoN epitaxial layers. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2016
Keyword
Nitrides; Toughness Phase stability; Density functional theory (DFT); Electronic structure
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-124462 (URN)10.1016/j.actamat.2015.10.039 (DOI)000367630500081 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation [2011.0094]; Swedish Research Council (VR) Linkoping Linnaeus Initiative LiLi-NFM [2008-6572, 2014-5790, 2013-4018]; Swedish Government Strategic Research Area Grant in Materials Science on Advanced Functional Materials through Swedens innovation agency VINNOVA [2009-00971]

Available from: 2016-02-02 Created: 2016-02-01 Last updated: 2017-11-30
Tengdelius, L., Broitman, E., Lu, J., Eriksson, F., Birch, J., Nyberg, T., . . . Högberg, H. (2016). Hard and elastic epitaxial ZrB2 thin films on Al2O3(0001) substrates deposited by magnetron sputtering from a ZrB2 compound target. Acta Materialia, 111, 166-172.
Open this publication in new window or tab >>Hard and elastic epitaxial ZrB2 thin films on Al2O3(0001) substrates deposited by magnetron sputtering from a ZrB2 compound target
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2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 111, 166-172 p.Article in journal (Refereed) Published
Abstract [en]

Zirconium diboride (ZrB2) exhibits high hardness and high melting point, which is beneficial for applications in for e.g. metal cutting. However, there is limited data on the mechanical properties of ZrB2 films and no data on epitaxial films. In this study, ZrB2(0001) thin films, with thicknesses up to 1.2 μm, have been deposited on Al2O3(0001) substrates by direct current magnetron sputtering from a compound target. X-ray diffraction and transmission electron microscopy show that the films grow epitaxially with two domain types exhibiting different in-plane epitaxial relationships to the substrate. The out-of-plane epitaxial relationship was determined to ZrB2(0001)|Al2O3(0001) and the in-plane relationships of the two domains to ZrB2[100]‖Al2O3[100] and ZrB2[110]‖Al2O3[100]. Mechanical properties of the films, evaluated by nanoindentation, showed that all films exhibit hardness values above 45 GPa, a reduced Young's modulus in the range 350–400 GPa, and a high elastic recovery of 70% at an applied load of 9000 μN.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Borides, Epitaxial growth, Mechanical properties, Nanoindentation, Sputter deposition
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-128612 (URN)10.1016/j.actamat.2016.03.064 (DOI)000375812100018 ()
Note

Funding agencies: Swedish Research Council (VR) [621-2010-3921]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Knut and Alice Wallenberg Foundation

Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2017-11-30Bibliographically approved
Broitman, E., Tengdelius, L., Hangen, U. D., Lu, J., Hultman, L. & Högberg, H. (2016). High-temperature nanoindentation of epitaxial ZrB2 thin films. Scripta Materialia, 124, 117-120.
Open this publication in new window or tab >>High-temperature nanoindentation of epitaxial ZrB2 thin films
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2016 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 124, 117-120 p.Article in journal (Refereed) Published
Abstract [en]

We use in-situ heated nanoindentation to investigate the high-temperature nanomechanical properties of epitaxial and textured ZrB2 films deposited by magnetron sputtering. Epitaxial films deposited on 4H-SiC(0001) show a hardness decrease from 47 GPa at room temperature to 33 GPa at 600 °C, while the reduced elastic modulus does not change significantly. High resolution electron microscopy (HRTEM) with selected area electron diffraction of the indented area in a 0001-textured film reveals a retained continuous ZrB2 film and no sign of crystalline phase transformation, despite massive deformation of the Si substrate. HRTEM analysis supports the high elastic recovery of 96% in the films.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Sputtering; Borides; Ceramic thin film; Nanoindentation; Transmission electron microscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-130917 (URN)10.1016/j.scriptamat.2016.06.033 (DOI)000383294200027 ()
Note

Funding agencies: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Swedish Research Council (VR) [621-2010-3921]

Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2017-11-21Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-2837-3656

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