Hofsäss, Hans Christian

[["dc.bibliographiccitation.artnumber","115410"],["dc.bibliographiccitation.issue","11"],["dc.bibliographiccitation.journal","PHYSICAL REVIEW B"],["dc.bibliographiccitation.volume","65"],["dc.contributor.author","Hofsass, H."],["dc.contributor.author","Feldermann, H."],["dc.contributor.author","Eyhusen, S."],["dc.contributor.author","Ronning, Carsten"],["dc.date.accessioned","2018-11-07T10:31:08Z"],["dc.date.available","2018-11-07T10:31:08Z"],["dc.date.issued","2002"],["dc.description.abstract","Boron nitride film growth from B and N ion deposition is studied. We observe growth of the cubic phase (c-BN) between 75 eV and 5 keV and a transition to sp(2)-bonded BN growth between 5 and 10 keV, as predicted by the cylindrical spike model. Atomic rearrangements in thermal spikes are identified as the mechanism responsible for c-BN formation and suppression of defect accumulation. The onset of defect accumulation eventually enhances the growth of sp(2)-bonded BN. The results highlight the fundamental role of the balance between thermal spikes and defect accumulation in ion deposition processes."],["dc.identifier.doi","10.1103/PhysRevB.65.115410"],["dc.identifier.isi","000174548400116"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/44033"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","American Physical Soc"],["dc.relation.issn","1098-0121"],["dc.title","Fundamental role of ion bombardment for the synthesis of cubic boron nitride films"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","083507"],["dc.bibliographiccitation.issue","8"],["dc.bibliographiccitation.journal","Journal of Applied Physics"],["dc.bibliographiccitation.volume","103"],["dc.contributor.author","Zhang, K."],["dc.contributor.author","Uhrmacher, Michael"],["dc.contributor.author","Hofsaess, H."],["dc.contributor.author","Krauser, Johann"],["dc.date.accessioned","2018-11-07T11:16:04Z"],["dc.date.available","2018-11-07T11:16:04Z"],["dc.date.issued","2008"],["dc.description.abstract","Ripple patterns created by sputter erosion of iron thin films induce a correlated magnetic texture of the surface near region. We investigated the magnetic anisotropy as a function of the residual film thickness and determined the thickness of the magnetically anisotropic layer as well as the magnitude of the magnetic anisotropy using by magneto-optical Kerr effect (MOKE) and Rutherford backscattering spectroscopy measurements. Ripple patterns were created by sputter erosion with 5 keV Xe ions under grazing incidence of 80 degrees with respect to the surface normal. For ion fluences of above 1x10(16) cm(-2), the formation of ripples, with wavelengths between 30 and 80 nm oriented parallel to the ion beam direction, is observed. MOKE measurements reveal a pronounced uniaxial magnetic anisotropy of the surface region of the films with orientation parallel to the ripple orientation and the ion beam direction. We find a layer thickness of 12 +/- 3 nm, in accordance with the average grain size. The magnetic anisotropy within this layer varies from about 25% for thick residual films toward 100% for films with less than 30 nm thickness. The magnitude of the magnetic anisotropy is determined by the shape anisotropy of the rippled surface as well as the interface roughness. We have demonstrated that sputter erosion yields highly anisotropic magnetic thin films and can be used to fabricate nanorods and nanowires with pronounced uniaxial magnetic anisotropy. (c) 2008 American Institute of Physics."],["dc.identifier.doi","10.1063/1.2905324"],["dc.identifier.isi","000255456200038"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/54510"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Inst Physics"],["dc.relation.issn","0021-8979"],["dc.title","Magnetic texturing of ferromagnetic thin films by sputtering induced ripple formation"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1398"],["dc.bibliographiccitation.issue","8-9"],["dc.bibliographiccitation.journal","NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS"],["dc.bibliographiccitation.lastpage","1402"],["dc.bibliographiccitation.volume","267"],["dc.contributor.author","Hofsaess, H."],["dc.contributor.author","Zhang, K."],["dc.contributor.author","Zutz, Hayo"],["dc.date.accessioned","2018-11-07T08:30:31Z"],["dc.date.available","2018-11-07T08:30:31Z"],["dc.date.issued","2009"],["dc.description.abstract","Nanostructured surface layers of titanium carbide and tungsten carbide were prepared on tetrahedral amorphous carbon (ta-C) films using the surfactant sputtering technique. Surfactant sputtering is a novel ion beam erosion technique, which utilizes the steady state coverage of a substrate surface with foreign atoms simultaneously during sputter erosion by combined ion irradiation and atom deposition. These foreign atoms act as surfactants, which strongly modify the substrate sputtering yield on atomic to macroscopic length scales. The novel technique allows smoothing of surfaces, the generation of novel surface patterns and nanostructures, controlled shaping of surfaces on the nanometer scale and the formation of ultra-thin compound surface layers. We have sputter eroded ta-C films using 5 keV Xe ions under continuous deposition of either tungsten or titanium surfactants. This leads to the steady state formation of a W(x)C or a TiC/a-C nanocomposite surface layer of few nm thickness. Depending on the ion angle of incidence the layer is either smooth or nanostructured with a ripple- or dot-like surface topography. We have analyzed the surface topography, the composition and microstructure of the metal-carbon nanocomposites, and compare coverage dependent sputtering yields with SRIM and TRIDYN simulations. (C) 2009 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.nimb.2009.01.053"],["dc.identifier.isi","000266519900047"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/16908"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.publisher.place","Amsterdam"],["dc.relation.conference","16th International Conference on Ion Beam Modification of Materials"],["dc.relation.eventlocation","Dresden, GERMANY"],["dc.relation.issn","0168-583X"],["dc.title","Nanostructured carbide surfaces prepared by surfactant sputtering"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","025011"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Journal of Micromechanics and Microengineering"],["dc.bibliographiccitation.volume","22"],["dc.contributor.author","Schulte-Borchers, Martina"],["dc.contributor.author","Vetter, Ulrich"],["dc.contributor.author","Koppe, Tristan"],["dc.contributor.author","Hofsaess, H."],["dc.date.accessioned","2018-11-07T09:13:54Z"],["dc.date.available","2018-11-07T09:13:54Z"],["dc.date.issued","2012"],["dc.description.abstract","We report on a new method of three-dimensional structuring by means of proton beam writing in p-type gallium arsenide. While up to now vertical features have been created by varying the proton beam energy during irradiation which changes the proton penetration depth and thereby the depth of the material modification, we manufactured 3D structures with a single beam energy but different proton doses supplemented by a subsequent controlled electrochemical etching process. This new approach could simplify 3D structuring in semiconductors and the usage of proton beam writing for the manufacturing of micro electromechanical devices with high aspect ratios and smooth sidewalls."],["dc.description.sponsorship","University of Melbourne"],["dc.identifier.doi","10.1088/0960-1317/22/2/025011"],["dc.identifier.isi","000299959000011"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/27276"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Iop Publishing Ltd"],["dc.relation.issn","0960-1317"],["dc.title","3D microstructuring in p-GaAs with proton beam writing using multiple ion fluences"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","art. no."],["dc.bibliographiccitation.journal","MRS INTERNET JOURNAL OF NITRIDE SEMICONDUCTOR RESEARCH"],["dc.bibliographiccitation.lastpage","W11.44"],["dc.bibliographiccitation.volume","5"],["dc.contributor.author","Ronning, Carsten"],["dc.contributor.author","Hofsass, H."],["dc.contributor.author","Stotzler, A."],["dc.contributor.author","Deicher, M."],["dc.contributor.author","Carlson, E. P."],["dc.contributor.author","Hartlieb, P. J."],["dc.contributor.author","Gehrke, T."],["dc.contributor.author","Rajagopal, P."],["dc.contributor.author","Davis, R. F."],["dc.date.accessioned","2018-11-07T11:11:57Z"],["dc.date.available","2018-11-07T11:11:57Z"],["dc.date.issued","2000"],["dc.description.abstract","Single crystalline (000l) gallium nitride layers, capped with a thin epitaxial aluminum nitride Laver, were implanted with magnesium and subsequently annealed in vacuum to 1150-1300 degreesC for 10-60 minutes. Photoluminescence (PL) measurements showed the typical donor acceptor pair (DAP) transition at 3.25 eV after annealing at high temperatures, which is related to optically active Mg accepters in GaN. After annealing at 1300 degreesC a high degree of optical activation of the implanted Mg atoms was reached in the case of low implantation doses. Electrical measurements, performed after removing the AlN-cap and the deposition of Pd/Au contacts, showed no p-type behavior of the GaN samples due to the compensation of the Mg accepters with native n-type defects."],["dc.identifier.isi","000090103600100"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/53551"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Materials Research Society"],["dc.publisher.place","Warrendale"],["dc.relation.conference","Symposium on GaN and Related Alloys Held at the MRS Fall Meeting"],["dc.relation.eventlocation","BOSTON, MASSACHUSETTS"],["dc.relation.issn","1092-5783"],["dc.title","Photoluminescence characterization of Mg implanted GaN"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","209"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","EUROPHYSICS LETTERS"],["dc.bibliographiccitation.lastpage","215"],["dc.bibliographiccitation.volume","50"],["dc.contributor.author","Habenicht, S."],["dc.contributor.author","Bolse, W."],["dc.contributor.author","Feldermann, H."],["dc.contributor.author","Geyer, U."],["dc.contributor.author","Hofsass, H."],["dc.contributor.author","Lieb, Klaus-Peter"],["dc.contributor.author","Roccaforte, F."],["dc.date.accessioned","2018-11-07T11:02:29Z"],["dc.date.available","2018-11-07T11:02:29Z"],["dc.date.issued","2000"],["dc.description.abstract","The ripple topography of ion-beam-eroded surfaces offers a novel method to determine the shape of collision cascades and the distribution of deposited energy From the energy dependence of the ripple spacing of Ar+ and Xe+-irradiated graphite surfaces at ion energies between 2 and 50 keV, the relations between mean depth, longitudinal and lateral straggling of the damage cascade were obtained. Their evolution with the ion energy was found to follow power laws for both ion masses and implies an energy-independent lateral spread of the damage cascade, while depth and longitudinal spread scale with the ion energy. This can be explained by the nuclear stopping power being nearly independent of energy in the observed region. High-resolution micrographs of single-ion impacts support this interpretation, as the hillock-shaped surface defects found in the experiments show a lateral extension being independent of the ion energy."],["dc.identifier.doi","10.1209/epl/i2000-00256-8"],["dc.identifier.isi","000086644400012"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/51393"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0295-5075"],["dc.title","Ripple topography of ion-beam-eroded graphite: A key to ion-beam-induced damage tracks"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","782"],["dc.bibliographiccitation.issue","5-6"],["dc.bibliographiccitation.journal","Diamond and Related Materials"],["dc.bibliographiccitation.lastpage","784"],["dc.bibliographiccitation.volume","20"],["dc.contributor.author","Vetter, Ulrich"],["dc.contributor.author","Mueller, Sven"],["dc.contributor.author","Broetzmann, Marc"],["dc.contributor.author","Hofsaess, Hans"],["dc.contributor.author","Gruber, John B."],["dc.date.accessioned","2018-11-07T08:56:18Z"],["dc.date.available","2018-11-07T08:56:18Z"],["dc.date.issued","2011"],["dc.description.abstract","We report on the effective reduction of AlN host lattice defect cathodoluminescence by high dose ion implantation of light elements such as fluorine as well as chlorine and neon with peak concentrations of 1 at.%. In order to distinguish between luminescence suppression in the visible to luminescence quenching due to radiation damage, all samples were additionally implanted with europium at fluences of 1.10(13) ions/cm(2). After annealing the samples at 1373 K under vacuum conditions cathodoluminescence spectra were recorded at room temperature (300 K) and at cryogenic temperature (12 K). These investigations reveal that different light ion species have different influences on the defect luminescence of the AlN host lattice which is likely due to selective passivation of these defects. The best ratio of defect luminescence suppression to radiation damage induced luminescence quenching is achieved in the case of fluorine co-doping. (C) 2011 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.diamond.2011.03.038"],["dc.identifier.isi","000291775700027"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/23111"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Sa"],["dc.relation.issn","0925-9635"],["dc.title","Effective reduction of AlN defect luminescence by fluorine implantation"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","234304"],["dc.bibliographiccitation.issue","23"],["dc.bibliographiccitation.journal","Journal of Applied Physics"],["dc.bibliographiccitation.volume","116"],["dc.contributor.author","Bradley, R. Mark"],["dc.contributor.author","Hofsaess, Hans"],["dc.date.accessioned","2018-11-07T09:31:09Z"],["dc.date.available","2018-11-07T09:31:09Z"],["dc.date.issued","2014"],["dc.description.abstract","We modify the Sigmund model of ion sputtering so that the distribution of deposited energy is in better accord with the results of molecular dynamics simulations. For a flat target surface, the model gives a sputter yield that displays a maximum as the angle of ion incidence is increased, as observed experimentally. The model also predicts that for sufficiently high angles of incidence, the curvature dependence of the crater function tends to destabilize the solid surface. (C) 2014 AIP Publishing LLC."],["dc.description.sponsorship","National Science Foundation [DMR-1305449]"],["dc.identifier.doi","10.1063/1.4904438"],["dc.identifier.isi","000346634500035"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31476"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Inst Physics"],["dc.relation.issn","1089-7550"],["dc.relation.issn","0021-8979"],["dc.title","A modification to the Sigmund model of ion sputtering"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1"],["dc.bibliographiccitation.journal","Microscopy and Microanalysis"],["dc.bibliographiccitation.lastpage","10"],["dc.contributor.author","Hennessy, Michael"],["dc.contributor.author","O'Connell, Eoghan N."],["dc.contributor.author","Auge, Manuel"],["dc.contributor.author","Moynihan, Eoin"],["dc.contributor.author","Hofsäss, Hans"],["dc.contributor.author","Bangert, Ursel"],["dc.date.accessioned","2022-07-01T07:34:43Z"],["dc.date.available","2022-07-01T07:34:43Z"],["dc.date.issued","2022"],["dc.description.abstract","In recent years, atomic resolution imaging of two-dimensional (2D) materials using scanning transmission electron microscopy (STEM) has become routine. Individual dopant atoms in 2D materials can be located and identified using their contrast in annular dark-field (ADF) STEM. However, in order to understand the effect of these dopant atoms on the host material, there is now the need to locate and quantify them on a larger scale. In this work, we analyze STEM images of MoS 2 monolayers that have been ion-implanted with chromium at ultra-low energies. We use functions from the open-source TEMUL Toolkit to create and refine an atomic model of an experimental image based on the positions and intensities of the atomic columns in the image. We then use the refined model to determine the likely composition of each atomic site. Surface contamination stemming from the sample preparation of 2D materials can prevent accurate quantitative identification of individual atoms. We disregard atomic sites from regions of the image with hydrocarbon surface contamination to demonstrate that images acquired using contaminated samples can give significant atom statistics from their clean regions, and can be used to calculate the retention rate of the implanted ions within the host lattice. We find that some of the implanted chromium ions have been successfully integrated into the MoS 2 lattice, with 4.1% of molybdenum atoms in the transition metal sublattice replaced with chromium."],["dc.description.sponsorship"," Volkswagen Foundation http://dx.doi.org/10.13039/501100001663"],["dc.description.sponsorship"," Irish Research Council http://dx.doi.org/10.13039/501100002081"],["dc.description.sponsorship"," Irish Research Council http://dx.doi.org/10.13039/501100002081"],["dc.identifier.doi","10.1017/S1431927622000757"],["dc.identifier.pii","S1431927622000757"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/112000"],["dc.language.iso","en"],["dc.notes.intern","DOI-Import GROB-581"],["dc.relation.eissn","1435-8115"],["dc.relation.issn","1431-9276"],["dc.rights.uri","https://www.cambridge.org/core/terms"],["dc.title","Quantification of Ion-Implanted Single-Atom Dopants in Monolayer MoS 2 via HAADF STEM Using the TEMUL Toolkit"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1203"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Journal of Applied Physics"],["dc.bibliographiccitation.lastpage","1207"],["dc.bibliographiccitation.volume","93"],["dc.contributor.author","Gerhards, Inga"],["dc.contributor.author","Ronning, Carsten"],["dc.contributor.author","Hofsass, H."],["dc.contributor.author","Seibt, M."],["dc.contributor.author","Gibhardt, Holger"],["dc.date.accessioned","2018-11-07T10:41:39Z"],["dc.date.available","2018-11-07T10:41:39Z"],["dc.date.issued","2003"],["dc.description.abstract","Amorphous carbon thin films containing 0-50 at. % Cu have been grown by mass selected ion beam deposition in order to synthesize isolated Cu nanoparticles within a diamond-like matrix. Raman spectroscopy and x-ray photoelectron spectroscopy show that the sp(3) content of the matrix decreases with increasing Cu content. Simultaneously, the mean particle size of the embedded Cu nanocrystals increases, as x-ray diffraction and transmission electron microscopy analysis reveal. There is apparently no dependence of the matrix structure on the Cu+ ion energy, while the Cu content is strongly influenced by this deposition parameter. (C) 2003 American Institute of Physics."],["dc.identifier.doi","10.1063/1.1531211"],["dc.identifier.isi","000180134200065"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46593"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Inst Physics"],["dc.relation.issn","0021-8979"],["dc.title","Ion beam synthesis of diamond-like carbon thin films containing copper nanocrystals"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]