Institute for Materials Physics

Bad Münster am Stein-Ebernburg, Germany

Institute for Materials Physics

Bad Münster am Stein-Ebernburg, Germany

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Galinski H.,ETH Zurich | Ryll T.,ETH Zurich | Schlagenhauf L.,ETH Zurich | Gauckler L.J.,ETH Zurich | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The stability of metal thin films on a dielectric substrate is conditioned by the magnitude of the interactive forces at the interface. In the case of a nonreactive interface and weak adhesion, the minimization of the free surface energy gives rise to an instability of the thin film. In order to study these effects, Pt thin films with a thickness of 50 nm were deposited via ion-beam sputtering on yttria-stabilized zirconia single crystals. All Pt films were subjected to heat treatments up to 973 K for 2 h. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy, atomic force microscopy, and standard image analysis techniques. Three main observations have been made: (i) The deposition method has a direct impact on the morphological evolution of the film during annealing. Instead of hole formation, which is typically observed as a response to a thermal treatment, anisotropic pyramidal-shaped hillocks are formed on top of the film. (ii) It is shown by comparing the hillocks' aspect ratio with finite element method simulations that the hillock formation can be assigned to a stress relaxation process inside the thin film. (iii) By measuring the quasiequilibrium shapes and the shape fluctuations of the formed Pt hillocks the anisotropy of the step free energy and its stiffness have been derived in addition to the anisotropic kink energy of the hillocks' edges. © 2012 American Physical Society.


Spasova B.,Leibniz University of Hanover | Wurz M.C.,Leibniz University of Hanover | Ruffert C.,Leibniz University of Hanover | Norpoth J.,Institute for Materials Physics | And 2 more authors.
IEEE Transactions on Magnetics | Year: 2010

Magnetic shape memory (MSM) materials present a new class of alloys, which can be used for creating electromagnetic microactuators facilitating a linear motion. The concept of the hybrid MSM microactuator pursued is using a pair of discrete MSM strips sandwiched between microstators. For the microstator fabrication, MEMS technology is applied. The two MSM strips are elongated alternatively, with one strip showing strain when exposed to a magnetizing field, while the other one is mechanically collapsed by its elongating counterpart, and vice versa. For inducing the elongation in the MSM strips, a critical field strength Hcrit has to be exceeded in vertical direction within the MSM strip. For analyzing what magnetic field strength is reached by the microstators and if it is greater than the critical field strength Hcrit required to inducing a reorientation of the twin variants in the MSM material, magneto-optical measurements were carried out. © 2006 IEEE.


Bibicu I.,Institute for Materials Physics | Lorinczi A.,Institute for Materials Physics | Popescu M.,Institute for Materials Physics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Tin chalcogenides SnX2 and SnX, where X = S, Se and Te present a particularly interest for their electronic properties and applications in gas sensors. The state of tin in these materials is important for understanding of the sensing effect and improvement of the sensor performances. Mössbauer spectroscopy is a widely used technique for the analysis of the local electronic structure or chemical bonding in solids. In this paper we applied Mössbauer technique for the investigation of bulk and thin films of SnSe2 chalcogenide. The films of SnSe2 chalcogenide were obtained by the methods: PLD ("Pulsed laser deposition") and PED ("Pulsed electron deposition"). Mössbauer measurements were performed by transmission (TMS), respectively conversion electron spectroscopy (CEMS). By CEMS spectroscopy surfaces, coatings and thin films containing Sn can be studied on substrates and to various depths up to 1000 nanometers. © 2010 SPIE.


Tal-Gutelmacher E.,Institute for Materials Physics | Gemma R.,Institute for Materials Physics | Nikitin E.,Institute for Materials Physics | Pundt A.,Institute for Materials Physics | Kirchheim R.,Institute for Materials Physics
Materials Science Forum | Year: 2010

Titanium and its conventional alloys reveal a high affinity for hydrogen, being capable to absorb up to 60 at.% hydrogen at 600°C, and even higher contents can be alloyed with titanium at lower temperatures. Hydrogen exhibits a low solubility in the low-temperature hexagonal closed-packed (hcp) α phase and a very high solubility (up to 50 at.%) in the high temperature body-centered cubic (bcc) β phase. The presence of hydrogen in the amount exceeding 200 ppm leads to formation of hydrides in α and α + β titanium alloys. While the aforementioned hydrogen behavior within bulk titanium has been well-established and reviewed, this is not the case with titanium thin films. The interpretation of results in these nanosized systems is complicated because the exact determination of the hydrogen concentration is difficult. However, using electrochemical hydrogen loading technique under the proper conditions, the hydrogen concentration can be accurately determined via Faraday's law. In this study the thermodynamics of the titanium films during hydrogen absorption were investigated by electromotive force (EMF) measurements. Titanium films of different thicknesses were prepared on sapphire substrates in an UHV chamber with a base pressure of 10-8 mbar, using ion beam sputter deposition under Ar-atmosphere at the pressure of 1,5·10 -4 mbar. The crystal structure was investigated by means of X-Ray diffraction using a Co-Kα radiation. For electrochemical hydrogen loading, the films were covered by a 30 nm thick layer of Pd in order to prevent oxidation and facilitate hydrogen absorption. The samples were step-by-step loaded with hydrogen by electrochemical charging, which was carried out in a mixed electrolyte of phosphoric acid and glycerin (1:2 in volume). An Ag/AgCl (sat.) and Pt wires were used as the reference and the counter electrode, respectively. XRD measurements were performed before and after hydrogenation in order to investigate the effect of hydrogen loading on the films microstructure. The role of varying thicknesses on the main characteristics of hydrogen's absorption behavior, as well as hydrogen-induced microstructural changes in titanium thin films, are discussed in detail. © (2010) Trans Tech Publications.


Tal-Gutelmacher E.,Institute for Materials Physics | Pundt A.,Institute for Materials Physics | Kirchheim R.,Institute for Materials Physics
Journal of Materials Science | Year: 2010

Titanium films of different thicknesses were prepared on sapphire substrates in an UHV chamber, by means of ion beam sputter deposition at room temperature, under Ar-atmosphere at the pressure of 1.5•10 E-4 mbar. For electrochemical hydrogen loading, the films were covered by a 30-nm thick layer of Pd in order to prevent oxidation and facilitate hydrogen absorption. In situ stress measurements were conducted during step-by-step electrochemical hydrogen charging of the films. XRD measurements using a Phillips X-Pert diffractometer with a Co-Kα radiation were performed before and after hydrogenation in order to investigate the effect of hydrogen loading on the microstructure. The phase boundaries, as well as the stress and strain development during hydrogen absorption, depend strongly on the thickness of the films. The main characteristics of absorption behavior of hydrogen, as well as the thermodynamics and phase boundaries of titanium-hydrogen thin films are discussed in detail with specific emphasis on the influence of films thickness. The obtained results are also compared to literature data on the widely studied titanium-hydrogen bulk system. Shifted phase boundaries and narrowed two-phase field appear in Ti-H film system, which are mainly attributed to the microstructural contribution, as well as to the large stresses in the GPa-range that built up between the films and their substrate. © 2010 The Author(s).

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