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Viloan, R. P., Gu, J., Boyd, R., Keraudy, J., Li, L. & Helmersson, U. (2019). Bipolar high power impulse magnetron sputtering for energetic ion bombardment during TiN thin film growth without the use of a substrate bias. Thin Solid Films
Open this publication in new window or tab >>Bipolar high power impulse magnetron sputtering for energetic ion bombardment during TiN thin film growth without the use of a substrate bias
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2019 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731Article in journal (Refereed) In press
Abstract [en]

The effect of applying a positive voltage pulse (Urev = 10–150 V) directly after the negative high power impulse magnetron sputtering (HiPIMS) pulse (bipolar HiPIMS) is investigated for the reactive sputter deposition of TiN thin films. Energy-resolved mass spectroscopy analyses are performed to gain insight in the effect on the ion energy distribution function of the various ions. It is demonstrated that the energy of a large fraction of the ions can be tuned by a reverse target potential and gain energy corresponding to the applied Urev. Microscopy observations and x-ray reflectometry reveal densification of the films which results in an increase in the film hardness from 23.9 to 34 GPa as well as an increase in compressive film stress from 2.1 GPa to 4.7 GPa when comparing conventional HiPIMS with bipolar HiPIMS (Urev = 150 V).

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
High power impulse magnetron sputtering, Bipolar HiPIMS, Ion energy distribution function tuning, Titanium nitride
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-158296 (URN)10.1016/j.tsf.2019.05.069 (DOI)2-s2.0-85067028388 (Scopus ID)
Available from: 2019-06-28 Created: 2019-06-28 Last updated: 2019-08-08Bibliographically approved
Ekeroth, S., Münger, P., Boyd, R., Ekspong, J., Wågberg, T., Edman, L., . . . Helmersson, U. (2018). Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma. Nano letters (Print), 18(5), 3132-3137
Open this publication in new window or tab >>Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma
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2018 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 5, p. 3132-3137Article in journal (Refereed) Published
Abstract [en]

Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 mu m thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H-2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm(2).

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
Keywords
Nanotrusses; nanowires; nanoparticles; iron; electrocatalysis; pulsed sputtering
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-148107 (URN)10.1021/acs.nanolett.8b00718 (DOI)000432093200055 ()29624405 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, KAW 14.0276
Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2019-09-06
Elofsson, V., Almyras, G., Lü, B., Garbrecht, M., Boyd, R. & Sarakinos, K. (2018). Structure formation in Ag-X (X = Au, Cu) alloys synthesized far-from-equilibrium. Journal of Applied Physics, 123(16)
Open this publication in new window or tab >>Structure formation in Ag-X (X = Au, Cu) alloys synthesized far-from-equilibrium
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2018 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 16Article in journal (Refereed) Published
Abstract [en]

We employ sub-monolayer, pulsed Ag and Au vapor fluxes, along with deterministic growth simulations, and nanoscale probes to study structure formation in miscible Ag-Au films synthesized under far-from-equilibrium conditions. Our results show that nanoscale atomic arrangement is primarily determined by roughness build up at the film growth front, whereby larger roughness leads to increased intermixing between Ag and Au. These findings suggest a different structure formation pathway as compared to the immiscible Ag-Cu system for which the present study, in combination with previously published data, reveals that no significant roughness is developed, and the local atomic structure is predominantly determined by the tendency of Ag and Cu to phase-separate.

Place, publisher, year, edition, pages
New York: A I P Publishing LLC, 2018
National Category
Inorganic Chemistry Other Physics Topics Atom and Molecular Physics and Optics Condensed Matter Physics Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-147730 (URN)10.1063/1.5018907 (DOI)000431147200150 ()
Note

Funding agencies: Linkoping University via the "LiU Research Fellows Program"; Linkoping University via the "LiU Career Contract" [Dnr-LiU-2015-01510]; Swedish Research Council [VR-2011-5312, VR-2015-04630]

Available from: 2018-05-08 Created: 2018-05-08 Last updated: 2019-06-28Bibliographically approved
Elofsson, V., Almyras, G., Lu, B., Boyd, R. & Sarakinos, K. (2016). Atomic arrangement in immiscible Ag-Cu alloys synthesized far-from-equilibrium. Acta Materialia, 110, 114-121
Open this publication in new window or tab >>Atomic arrangement in immiscible Ag-Cu alloys synthesized far-from-equilibrium
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2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 110, p. 114-121Article in journal (Refereed) Published
Abstract [en]

Physical attributes of multicomponent materials of a given chemical composition are determined by atomic arrangement at property-relevant length scales. A potential route to access a vast array of atomic configurations for material property tuning is by synthesis of multicomponent thin films using vapor fluxes with their deposition pattern modulated in the sub-monolayer regime. However, the applicability of this route for creating new functional materials is impeded by the fact that a fundamental understanding of the combined effect of sub-monolayer flux modulation, kinetics and thermodynamics on atomic arrangement is not available in the literature. Here we present a research strategy and verify its viability for addressing the aforementioned gap in knowledge. This strategy encompasses thin film synthesis using a route that generates multi-atomic fluxes with sub-monolayer resolution and precision over a wide range of experimental conditions, deterministic growth simulations and nanoscale micro structural probes. Investigations are focused on structure formation within the archetype immiscible Ag-Cu binary system, revealing that atomic arrangement at different length scales is governed by the arrival pattern of the film forming species, in conjunction with diffusion of near-surface Ag atoms to encapsulate 3D Cu islands growing on 2D Ag layers. The knowledge generated and the methodology presented herein provides the scientific foundation for tailoring atomic arrangement and physical properties in a wide range of miscible and immiscible multinary systems. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2016
Keywords
Ag-Cu thin films; MD simulations; Modulated vapor fluxes; Nonequilibrium synthesis; Immiscible alloys
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-128722 (URN)10.1016/j.actamat.2016.03.023 (DOI)000374810400012 ()
Note

Funding Agencies|Linkoping University [Dnr-LiU-2015-01510]; Swedish Research Council [VR 621-2011-5312]; AForsk through the project "Towards Next Generation of Energy Saving Windows"

Available from: 2016-06-01 Created: 2016-05-30 Last updated: 2019-06-28
Magnfält, D., Fillon, A., Boyd, R., Helmersson, U., Sarakinos, K. & Abadias, G. (2016). Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films. Journal of Applied Physics, 119(5), 055305
Open this publication in new window or tab >>Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 5, p. 055305-Article in journal (Refereed) Published
Abstract [en]

Intrinsic stresses in vapor deposited thin films have been a topic of considerable scientific and technological interest owing to their importance for functionality and performance of thin film devices. The origin of compressive stresses typically observed during deposition of polycrystalline metal films at conditions that result in high atomic mobility has been under debate in the literature in the course of the past decades. In this study, we contribute towards resolving this debate by investigating the grain size dependence of compressive stress magnitude in dense polycrystalline Mo films grown by magnetron sputtering. Although Mo is a refractory metal and hence exhibits an intrinsically low mobility, low energy ion bombardment is used during growth to enhance atomic mobility and densify the grain boundaries. Concurrently, the lateral grain size is controlled by using appropriate seed layers on which Mo films are grown epitaxially. The combination of in situ stress monitoring with ex situ microstructural characterization reveals a strong, seemingly linear, increase of the compressive stress magnitude on the inverse grain size and thus provides evidence that compressive stress is generated in the grain boundaries of the film. These results are consistent with models suggesting that compressive stresses in metallic films deposited at high homologous temperatures are generated by atom incorporation into and densification of grain boundaries. However, the underlying mechanisms for grain boundary densification might be different from those in the present study where atomic mobility is intrinsically low. (C) 2016 AIP Publishing LLC.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-125810 (URN)10.1063/1.4941271 (DOI)000369900600028 ()
Note

Funding Agencies|COST Action "Highly Ionized Pulsed Plasmas" [MP0804]; Swedish Research Council VR [621-2014-4882]; Linkoping University via the "LiU Research Fellows" program.

The previous status of this article was Manuscript and the working title was Atom insertion into grain boundaries generates compressive intrinsic stress in polycrystalline thin films.

Available from: 2016-03-08 Created: 2016-03-04 Last updated: 2017-11-30Bibliographically approved
Boyd, R., Gunnarsson, R., Pilch, I. & Helmersson, U. (2014). Characterisation of Nanoparticle Structure by High Resolution Electron Microscopy. In: Electron Microscopy and Analysis Group Conference  (EMAG2013): . Paper presented at Conference of the Electron-Microscopy-and-Analysis-Group (EMAG) (pp. 012065). Institute of Physics Publishing (IOPP), 522(012065)
Open this publication in new window or tab >>Characterisation of Nanoparticle Structure by High Resolution Electron Microscopy
2014 (English)In: Electron Microscopy and Analysis Group Conference  (EMAG2013), Institute of Physics Publishing (IOPP), 2014, Vol. 522, no 012065, p. 012065-Conference paper, Published paper (Refereed)
Abstract [en]

Whilst the use of microscopic techniques to determine the size distributions of nanoparticle samples is now well established, their characterisation challenges extend well beyond this. Here it is shown how high resolution electron microscopy can help meet these challenges. One of the key parameters is the determination of particle shape and structure in three dimensions. Here two approaches to determining nanoparticle structure are described and demonstrated. In the first scanning transmission electron microscopy combined with high angle annular dark field imaging (HAADF-STEM) is used to image homogenous nanoparticles, where the contrast is directly related to the thickness of the material in the electron beam. It is shown that this can be related to the three dimensional shape of the nano-object. High resolution TEM imaging, combined with fast Fourier transform (FFT) analysis, can determine the crystalline structure and orientation of nanoparticles as well as the presence of any defects. This combined approach allows the physical structure of a significant number of nano-objects to be characterised, relatively quickly.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
Series
Journal of Physics Conference Series, ISSN 1742-6588 ; 522
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-110717 (URN)10.1088/1742-6596/522/1/012065 (DOI)000340969200065 ()
Conference
Conference of the Electron-Microscopy-and-Analysis-Group (EMAG)
Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2014-11-05Bibliographically approved
Elofsson, V., Saraiva, M., Boyd, R. & Sarakinos, K. (2014). Double in-plane alignment in biaxially textured thin films. Applied Physics Letters, 105(23), 233113
Open this publication in new window or tab >>Double in-plane alignment in biaxially textured thin films
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 23, p. 233113-Article in journal (Refereed) Published
Abstract [en]

The scientific interest and technological relevance of biaxially textured polycrystalline thin films stem from their microstructure that resembles that of single crystals. To explain the origin and predict the type of biaxial texture in off-normally deposited films, Mahieu et al. have developed an analytical model [S. Mahieu et al., Thin Solid Films 515, 1229 (2006)]. For certain materials, this model predicts the occurrence of a double in-plane alignment, however, experimentally only a single in-plane alignment has been observed and the reason for this discrepancy is still unknown. The model calculates the resulting in-plane alignment by considering the growth of faceted grains with an out-of-plane orientation that corresponds to the predominant film out-of-plane texture. This approach overlooks the fact that in vapor condensation experiments where growth kinetics is limited and only surface diffusion is active, out-of-plane orientation selection is random during grain nucleation and happens only upon grain impingement. Here, we compile and implement an experiment that is consistent with the key assumptions set forth by the in-plane orientation selection model by Mahieu et al.; a Cr film is grown off-normally on a fiber textured Ti epilayer to pre-determine the out-of-plane orientation and only allow for competitive growth with respect to the in-plane alignment. Our results show unambiguously a biaxially textured Cr (110) film that possesses a double in-plane alignment, in agreement with predictions of the in-plane selection model. Thus, a long standing discrepancy in the literature is resolved, paving the way towards more accurate theoretical descriptions and hence knowledge-based control of microstructure evolution in biaxially textured thin films.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113499 (URN)10.1063/1.4903932 (DOI)000346266000086 ()
Note

Funding Agencies|Linkoping University

Available from: 2015-01-19 Created: 2015-01-19 Last updated: 2017-12-05
Magnfält, D., Fillon, A., Boyd, R. D., Helmersson, U., Sarakinos, K. & Abadias, G.Atom insertion into grain boundaries generates compressive intrinsic stress in polycrystalline thin films.
Open this publication in new window or tab >>Atom insertion into grain boundaries generates compressive intrinsic stress in polycrystalline thin films
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-105789 (URN)
Available from: 2014-04-07 Created: 2014-04-07 Last updated: 2017-01-16
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6602-7981

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