A Magnetically Guided Slow Positron Beam for Defect Studies

Anwand, W.; Kissener, H.R.; Bräuer, G.

doi:10.12693/aphyspola.88.7

Cited by 87 publications

(40 citation statements)

References 1 publication

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“…SPIS studies were performed on the magnetically guided slow positron beam "SPONSOR" [6] with positron energy adjustable from 0.03 to 36 keV. Doppler broadening of the annihilation line was evaluated using the S and W line shape parameters, which were always normalized to the bulk values S 0 and W 0 determined in the reference Pd sample.…”

Section: Methodsmentioning

confidence: 99%

Structural Studies of Nanocrystalline Thin Pd Films Electrochemically Doped with Hydrogen

Čı́žek

Vlček

Lukáč

et al. 2012

DDF

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Abstract. Hydrogen absorption in Pd causes a significant volume expansion. In free-standing bulk Pd, the hydrogen-induced volume expansion is isotropic. However, the situation becomes more complicated in thin Pd films. Contrary to bulk samples, thin films are clamped to an elastically stiff substrate, which prevents in-plane expansion. Hence, the volume expansion of a thin film is strongly anisotropic because it expands in the out-of-plane direction only. Internal stresses introduced by absorbed hydrogen may become so high that detachment of a film from the substrate is energetically favorable and buckles of various morphologies are formed. In the present work, we studied hydrogen-induced buckling in a nanocrystalline thin Pd film deposited on a sapphire substrate. Slow positron implantation spectroscopy (SPIS) was employed as a principal tool for the characterization of defects and investigation of defect interactions with hydrogen. SPIS studies were combined with X-ray diffraction and direct observations of buckling by light microscopy. It was found that buckling of thin Pd film occurs at hydrogen concentrations x H > 0.1 and is accompanied by a strong increase of dislocation density. IntroductionHydrogen dissolved in interstitial sites in a host metal lattice causes a volume expansion, which is isotropic in free standing bulk samples. However, in thin films, in-plane expansion is hindered by clamping of the film to the substrate. This makes hydrogen-induced expansion strongly anisotropic: the in-plane expansion is suppressed, while the out-of-plane expansion is remarkably larger than in a free standing bulk metal. As a consequence, high compressive bi-axial in-plane stresses up to several GPa occur in thin films loaded with hydrogen [1]. These hydrogen-induced stresses grow with increasing hydrogen content and may cause local or global detachment of the loaded film from the surface, which results in formation of buckles with various morphologies [2][3][4]. Understanding of hydrogen-induced buckling is highly important since this process may cause catastrophic adhesion failure in many thin film systems or coatings exposed to hydrogen.Hydrogen-induced buckling occurs when the stored elastic strain energy overcomes the adhesion energy to the surface. Since the formation of buckles represents an irreversible change of film shape (i.e. plastic deformation) one can expect that new defects are introduced during buckling process. Although the morphology of buckles was investigated in a number of works [2][3][4], there is still a lack of information about defect evolution in buckled films. In the present work slow positron implantation spectroscopy (SPIS) was employed for characterization of development of defects in thin Pd films loaded with hydrogen. Defect studies by SPIS were combined with X-ray diffraction (XRD) and direct observations of buckles by light microscopy.

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Section: Methodsmentioning

confidence: 99%

Structural Studies of Nanocrystalline Thin Pd Films Electrochemically Doped with Hydrogen

Čı́žek

Vlček

Lukáč

et al. 2012

DDF

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“…The SPIS studies of thin films were performed at the magnetically guided positron beam facility ''SPONSOR'' [7] with a positron energy adjustable from 0.03 to 36 keV. Doppler broadening of the annihilation line was measured by an HPGe detector with an energy resolution of (1.09 AE 0.01) keV at 511 keV and characterized in terms of the S parameter.…”

Section: Methodsmentioning

confidence: 99%

Defect studies of hydrogen-loaded nanocrystalline Gd films

Čı́žek

Procházka

Vlach

et al. 2008

Applied Surface Science

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“…For the clarification of the layer properties SPIS measurements were carried out with the monoenergetic positron beam "SPONSOR" at Rossendorf, which is described in detail in [3]. About 4.5 × 10 5 events per spectrum were accumulated.…”

Section: Methodsmentioning

confidence: 99%

Structural Changes in Flash Lamp Annealed Amorphous Si Layers Probed by Slow Positron Implantation Spectroscopy

et al. 2008

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Flash lamp annealing was applied to the modification of thin amorphous Si layers on SiO 2 and glass. Slow positron implantation spectroscopy was used for the characterisation of the microstructure before and after flash lamp annealing. Changes in the structure down to a depth of some micrometres below the surface observed with slow positron implantation spectroscopy will be presented and discussed.

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A Magnetically Guided Slow Positron Beam for Defect Studies

Cited by 87 publications

References 1 publication

Structural Studies of Nanocrystalline Thin Pd Films Electrochemically Doped with Hydrogen

Structural Studies of Nanocrystalline Thin Pd Films Electrochemically Doped with Hydrogen

Defect studies of hydrogen-loaded nanocrystalline Gd films

Structural Changes in Flash Lamp Annealed Amorphous Si Layers Probed by Slow Positron Implantation Spectroscopy

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