Hydrogen-induced stress in Nb single layers

Laudahn, U.; Pundt, Astrid; Bicker, M.; Hülsen, U. von; Geyer, U.; Wagner, T.; Kirchheim, R.

doi:10.1016/s0925-8388(99)00471-5

Cited by 88 publications

(77 citation statements)

References 12 publications

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“…On the other hand, the inplane expansion of thin film is prevented by clamping on the elastically hard substrate suggesting that film expansion in the in-plane direction is very small (if any). XRD studies of the hydrogen-loaded thin films turned out that the out-of-plane expansion is substantially larger than in a free-standing bulk sample [10]. It can be seen from Fig.…”

Section: Resultsmentioning

confidence: 69%

Defect studies of hydrogen-loaded thin Nb films

Čı́žek

Procházka

Bräuer

et al. 2006

Applied Surface Science

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Hydrogen interaction with defects in thin niobium (Nb) films was investigated using slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thin Nb films on Si substrates were prepared using cathode beam sputtering at room temperature. Initially, the microstructure of the virgin (hydrogen-free) films was characterized. Subsequently, the films were step-by-step electrochemically charged with hydrogen and the evolution of the microstructure with increasing hydrogen concentration was monitored. Hydrogen loading leads to a significant lattice expansion which was measured by XRD. Contrary to free-standing bulk metals, thin films are highly anisotropic. The in-plane expansion is prevented because the films are clamped on the elastically hard substrate. On the other hand, the out-of-plane expansion is substantially higher than in the bulk samples. Moreover, an enhanced hydrogen solubility in the a-phase was found in nanocrystalline Nb films. It was found that most of positrons in the films are trapped at open-volume defects at grain boundaries (GBs). These defects represent trapping sites also for hydrogen atoms. Hydrogen trapping at vacancy-like defects like GBs leads to a local increase of the electron density and is reflected by a pronounced decrease of the S parameter in the hydrogen-loaded samples. In addition, it was found that new defects are introduced at higher concentrations of hydrogen due to the formation of NbH (b-phase) particles. #

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Section: Resultsmentioning

confidence: 69%

Defect studies of hydrogen-loaded thin Nb films

Čı́žek

Procházka

Bräuer

et al. 2006

Applied Surface Science

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“…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].…”

Section: Introductionmentioning

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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“…1 Im Rahmen dieser Arbeit durchgeführte Untersuchungen von Laudahn et al [LAU99] und Pundt et al [PUN01a] an Nb-Schichten bestätigen das linear elastische Verhalten von Schichten bei geringen H-Konzentrationen. 2 Es handelt sich hier um 'Isothermen', bei denen der H 2 -Patialdruck als Funktion der Gitterausdehnung dargestellt sind.…”

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Nanoskalige Metall- Wasserstoff- Systeme

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2005

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Hydrogen-induced stress in Nb single layers

Cited by 88 publications

References 12 publications

Defect studies of hydrogen-loaded thin Nb films

Defect studies of hydrogen-loaded thin Nb films

Structural Studies of Nanocrystalline Thin Pd Films Electrochemically Doped with Hydrogen

Nanoskalige Metall- Wasserstoff- Systeme

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