Nörthemann, Kai

[["dc.bibliographiccitation.artnumber","014105"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Physical Review. B"],["dc.bibliographiccitation.volume","78"],["dc.contributor.author","Nörthemann, Kai"],["dc.contributor.author","Pundt, Astrid"],["dc.date.accessioned","2018-11-07T11:13:46Z"],["dc.date.available","2018-11-07T11:13:46Z"],["dc.date.issued","2008"],["dc.description.abstract","Nucleation and growth in thin films are studied by using niobium-hydrogen (Nb-H) as model system. Hydride precipitation in thin films results in local surface topography changes that can be monitored by scanning tunneling microscopy. The local film expansion can be used to detect hydride precipitates, to study their growth, to gain information about their shape and their lattice coherency. With the help of theoretical calculations, it will be shown that cylindrical Nb-H precipitates evolve in early stages. These precipitates are coherent to the matrix as long as the film is thin and the hydride size is below a critical volume. Above this critical volume, a coherent-to-semi-coherent transition occurs. The critical size is controlled by the balance between the elastic energy stored in the coherent precipitate and the energy needed for the formation of dislocations. Consequently, films below 26 nm thickness keep coherency for all hydride precipitate volumes and never get semi-coherent."],["dc.identifier.doi","10.1103/PhysRevB.78.014105"],["dc.identifier.isi","000258190000038"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/53972"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.relation.issn","1098-0121"],["dc.relation.orgunit","Institut für Materialphysik"],["dc.title","Coherent-to-semi-coherent transition of precipitates in niobium-hydrogen thin films"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","549"],["dc.bibliographiccitation.journal","Journal of Alloys and Compounds"],["dc.bibliographiccitation.lastpage","554"],["dc.bibliographiccitation.volume","446"],["dc.contributor.author","Pundt, Astrid"],["dc.contributor.author","Nörthemann, Kai"],["dc.contributor.author","Schmidt, Soenke"],["dc.date.accessioned","2018-11-07T10:57:36Z"],["dc.date.available","2018-11-07T10:57:36Z"],["dc.date.issued","2007"],["dc.description.abstract","Nano-wire arrays of Niobium were produced by small angle sputtering on facetted sapphire, using the self shadowing effect of the facets. A wire width of about 80 nm was adjusted, the mean (maximum) wire height was about 20 nm (30 nm), the length can be in the cm range. Meander-film morphologies of 20 nm mean (26 run maximum) thickness were produced by conventional sputtering onto smooth sapphire substrates at elevated temperatures. The morphology of the wires was investigated with atomic force microscopy (AFM), using contact mode. Meander-films were studied by scanning tunnelling microscopy (STM). Hydrogen loading was performed by instantaneously increasing the hydrogen gas pressure above the solubility limit. Thus, an elongated hydride could be monitored in an about 30 nm thick wire. STM studies on meander-films show the presence of cylindrical hydrides. Local out-of-plane and in-plane expansion can be explained by the formation of hydrides, being coherent with the matrix. This was verified by finite-element calculations. The surface morphology modification associated with these coherent hydrides disappears reversibly, as soon as the hydrogen gas pressure is reduced. This indicates that plastic deformation does not occur in thin wires and meander films. (C) 2007 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.jallcom.2007.01.137"],["dc.identifier.isi","000250822900117"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/50292"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Sa"],["dc.publisher.place","Lausanne"],["dc.relation.conference","10th International Symposium on Metal-Hydrogen Systems, Fundamentals and Applications"],["dc.relation.eventend","2006-10-06"],["dc.relation.eventlocation","Lahaina, USA"],["dc.relation.eventstart","2006-10-01"],["dc.relation.issn","0925-8388"],["dc.relation.orgunit","Institut für Materialphysik"],["dc.title","Hydrogen-related surface modifications of 20 nm thin straight-sided niobium nano-wires and niobium meander-films"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1890"],["dc.bibliographiccitation.issue","14"],["dc.bibliographiccitation.journal","ChemPhysChem"],["dc.bibliographiccitation.lastpage","1904"],["dc.bibliographiccitation.volume","20"],["dc.contributor.author","Wagner, Stefan"],["dc.contributor.author","Klose, Philipp"],["dc.contributor.author","Burlaka, Vladimir"],["dc.contributor.author","Nörthemann, Kai"],["dc.contributor.author","Hamm, Magnus"],["dc.contributor.author","Pundt, Astrid"],["dc.date.accessioned","2020-12-10T14:05:59Z"],["dc.date.available","2020-12-10T14:05:59Z"],["dc.date.issued","2019"],["dc.identifier.doi","10.1002/cphc.201900247"],["dc.identifier.eissn","1439-7641"],["dc.identifier.issn","1439-4235"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/69734"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-354"],["dc.relation.orgunit","Institut für Materialphysik"],["dc.title","Structural Phase Transitions in Niobium Hydrogen Thin Films: Mechanical Stress, Phase Equilibria and Critical Temperatures"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","155420"],["dc.bibliographiccitation.issue","15"],["dc.bibliographiccitation.journal","Physical Review. B"],["dc.bibliographiccitation.volume","83"],["dc.contributor.author","Noerthemann, Kai"],["dc.contributor.author","Pundt, Astrid"],["dc.date.accessioned","2018-11-07T08:57:04Z"],["dc.date.available","2018-11-07T08:57:04Z"],["dc.date.issued","2011"],["dc.description.abstract","The kinetics of hydride precipitation in epitaxial Nb films are studied by means of scanning tunneling microscopy (STM) using hydrogen gas loading. Due to the clamped state of thin films, hydride formation results in strong unidirectional out-of-plane film expansion that can be easily detected with STM. Hydrides are found to initially form with cylindrical morphology, leading to typical surface topographies. Their localized expansion allows the analysis of the hydride lattice matching, which is coherent (H1) at the initial stages and semicoherent (H2) at later stages. The volume fraction of H1 and H2 precipitates changes with time. At initial stages, the coherent precipitates dominate, while at later stages semicoherent precipitates become the dominant ones. The relative occurrence of H1 and H2 is bimodal. A maximum occurrence of 30-40 nm sized H1 hydrides is found, which is related to coherency stress between the hydride and the Nb matrix hindering a further hydride growth. It is further demonstrated that for Nb-H films adhered to substrates, the system can be locked in the two-phase region of the phase diagram (here at 10(-4) Pa at about 50% of hydride). This is different from bulk Nb-H, where the complete sample transforms into a hydride when the hydride formation equilibrium pressure is exceeded. Impact parameters on the lateral hydride arrangement are studied. The impact of the Pd-island surface coating and the intrinsic dislocation network on the precipitation density and arrangement appear to be negligible. However, the substrate miscut and, thus, the surface roughness exhibit a strong influence on hydride nucleation. The H1 hydride arrangement along (111) and the directed H2 hydride growth along ( 111) are governed by the elastically soft matrix lattice orientations."],["dc.description.sponsorship","Deutsche Forschungsgemeinschaft [SFB 602, A9, B12]"],["dc.identifier.doi","10.1103/PhysRevB.83.155420"],["dc.identifier.isi","000289350500008"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/23300"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.relation.issn","1550-235X"],["dc.relation.issn","1098-0121"],["dc.relation.orgunit","Institut für Materialphysik"],["dc.title","Double-locked nucleation and growth kinetics in Nb-H thin films"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]