| dc.contributor.advisor | Pundt, Astrid Prof. Dr. | |
| dc.contributor.author | Tyagi, Anshu | |
| dc.date.accessioned | 2023-07-13T16:19:05Z | |
| dc.date.available | 2023-07-20T00:50:10Z | |
| dc.date.issued | 2023-07-13 | |
| dc.identifier.uri | http://resolver.sub.uni-goettingen.de/purl?ediss-11858/14777 | |
| dc.identifier.uri | http://dx.doi.org/10.53846/goediss-10003 | |
| dc.format.extent | XX Seiten | de |
| dc.language.iso | eng | de |
| dc.rights.uri | http://creativecommons.org/licenses/by/4.0/ | |
| dc.subject.ddc | 530 | de |
| dc.title | Interlayer effect on the hydrogen uptake in Vanadium films: Stress development, surface topography and optical behavior changes | de |
| dc.type | doctoralThesis | de |
| dc.contributor.referee | Volkert, Cynthia A. Prof. Dr. | |
| dc.date.examination | 2022-10-10 | de |
| dc.subject.gok | Physik (PPN621336750) | de |
| dc.description.abstracteng | The purpose of this study is to investigate hydrogen absorption-related properties changes of nanocrystalline thin films by varying the elastic constraints condition. The elastic constraint condition is varied by using different interface layers (interlayers) that affect the adhesion between the substrate and the film. Different interlayers of polycarbonate (PC), palladium (Pd), and patterns of PC and Pd (mixed-adhesion sample) were used. Vanadium is chosen as a model film system. Vanadium films of 30 nm, 50 nm, and 70 nm thickness were sputter deposited onto varying interlayers coated glass substrates and protected against oxidation by Pd cap layers. Hydrogen loading was done by the electrochemical method (for optical, EMF, and stress measurements) and the gas phase method ( for STM measurements).
The samples were studied by using the hydrogenography method which is a combination of electrochemical hydrogen loading and optical microscopy, allowing for simultaneous measurement of electromotive force (EMF). Hydrogenography offers the possibility to study the lateral hydrogen distribution in V-H thin film systems on the micrometer scale. The optical transmission and reflection were recorded during hydrogen absorption in the film and transmission is related to the hydrogen concentration, in accordance with Lambert-Beer’s law. Reflection images were used to monitor the sample conditions and found to visualize the presence of film buckles. Transmission images mainly give the local hydrogen concentration. It was shown in this work, that this transmission signal can be easily misinterpreted when film thickness changes are neglected. Accompanying mechanical stress measurements were done using the substrate curvature method during electrochemical hydrogen loading. The compressive stress state of the V-H system was found to be strongly affected by the current density used for hydrogen loading. Different stress release processes occurred with varying current densities.
The film changes induced by hydrogen loading were also studied by using scanning tunneling microscopy (STM). These V-films were capped with Pd layers of different thicknesses, to also observe the nanocrystalline V-film surface topography. A very symmetrical surface topography is observed in the as-prepared film, having height variations below 2 nm, and being bordered by grooves that are related to grain boundaries. Upon hydrogen loading, the film surface topography develops drastic changes of about 15 nm in height accompanied by lateral grain size broadening. The related stress measurements show hydrogen-induced ultrahigh mechanical stress in the GPa range. This strong surface topography change cannot be assigned to linear elastic film expansion or plastic deformation by dislocation movement in the film. Alternatively, grain sliding is suggested to happen in the nanocrystalline V-films adhering to the substrates. Combining this with the EMF and mechanical stress measurement results allows explaining the optical behavior of hydrogen-loaded vanadium thin films in the presence of different interface layers. Thickness changes and the local hydrogen concentration depend on the adhesion condition modified by the interface layer. This combination leads to different optical transmission.
Slightly different H-H interaction energies were calculated from the EMF-curves of V-films on different interlayers, by using the distribution of site energies model (DOS). They range from -15 kJ/mol to -13 kJ/mol, depending on the different interlayers. | de |
| dc.contributor.coReferee | Kirchheim, Reiner Prof. Dr. | |
| dc.contributor.thirdReferee | Pundt, Astrid Prof. Dr. | |
| dc.contributor.thirdReferee | Hofsäss, Hans Prof. Dr. | |
| dc.contributor.thirdReferee | Seibt, Michael Prof. Dr. | |
| dc.contributor.thirdReferee | Wenderoth, Martin PD Dr. | |
| dc.subject.eng | vanadium | de |
| dc.subject.eng | thin film | |
| dc.subject.eng | nanocrystalline | |
| dc.subject.eng | hydrogen | |
| dc.subject.eng | grain structure | |
| dc.subject.eng | Interlayer | |
| dc.subject.eng | STM | |
| dc.subject.eng | Stress | |
| dc.subject.eng | optical measurements | |
| dc.subject.eng | transmission | |
| dc.subject.eng | reflection | |
| dc.subject.eng | adhere | |
| dc.subject.eng | buckle | |
| dc.subject.eng | hydrogenography | |
| dc.subject.eng | EMF | |
| dc.identifier.urn | urn:nbn:de:gbv:7-ediss-14777-2 | |
| dc.affiliation.institute | Fakultät für Physik | de |
| dc.description.embargoed | 2023-07-20 | de |
| dc.identifier.ppn | 1852750952 | |
| dc.notes.confirmationsent | Confirmation sent 2023-07-13T19:45:01 | de |