Hofsäss, Hans Christian

[["dc.bibliographiccitation.firstpage","1176"],["dc.bibliographiccitation.issue","9"],["dc.bibliographiccitation.journal","Optical Materials Express"],["dc.bibliographiccitation.lastpage","1185"],["dc.bibliographiccitation.volume","2"],["dc.contributor.author","Gruber, John B."],["dc.contributor.author","Burdick, Gary W."],["dc.contributor.author","Vetter, Ulrich"],["dc.contributor.author","Mitchell, Brandon"],["dc.contributor.author","Dierolf, Volkmar"],["dc.contributor.author","Hofsäss, Hans"],["dc.date.accessioned","2012-08-09T12:54:24Z"],["dc.date.accessioned","2021-10-11T11:26:10Z"],["dc.date.available","2012-08-09T12:54:24Z"],["dc.date.available","2021-10-11T11:26:10Z"],["dc.date.issued","2012"],["dc.description.abstract","The crystal-field and Zeeman splittings of the energy levels of Nd3+(4f3) 2S+1LJ in hexagonal phase AlN have been investigated. The multiplet manifolds of Nd3+(4f3) analyzed include the ground state, 4I9/2, and excited states 4I11/2, 4I13/2, 4F3/2, 4F5/2, 2H(2)9/2, 4F7/2, 4S3/2, 4G5/2, and 2G7/2. Experimental energy levels were obtained from analyses of the 12 K cathodoluminescence spectra from Nd3+-implanted films of AlN, and from the 15 K photoluminescence excitation spectra and the site-selective combined excitation-emission spectra (CEES) recently reported for in situ Nd-doped hexagonal AlN grown by plasma-assisted molecular beam epitaxy (PA-MBE). CEES results identify a main site and two minority sites for Nd3+ in both samples. Transition line strengths attributed to the ion in minority sites are relatively stronger in Nd:AlN than in Nd:GaN. The 15 K experimental Zeeman splitting of Nd3+ are analyzed in the PA-MBE grown AlN samples and compared with the Zeeman splitting observed in Nd:GaN. The crystal-field and Zeeman splittings were modeled using a parametrized Hamiltonian consisting of atomic and crystal-field terms. We considered possible site distortion due to the size of the implanted Nd ion that would reduce the site symmetry from C3v to C3 or C1h. However, no significant improvement was obtained using these lower symmetry models, leading us to conclude that C3v symmetry is a reasonable approximation for the main site Nd3+ ions in AlN."],["dc.description.sponsorship","Open-Access-Publikationsfonds 2012"],["dc.identifier.doi","10.1364/OME.2.001176"],["dc.identifier.isi","000308598300001"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/7850"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/90544"],["dc.language.iso","en"],["dc.notes.intern","Migrated from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Optical Soc Amer"],["dc.relation.issn","2159-3930"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.access","openAccess"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.subject","Atomic and molecular physics : Zeeman effect; Physical optics : Luminescence; Physical optics : Stark effect"],["dc.title","Crystal field and Zeeman splittings for energy levels of Nd3+ in hexagonal AlN"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","653"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Applied Physics A"],["dc.bibliographiccitation.lastpage","664"],["dc.bibliographiccitation.volume","111"],["dc.contributor.author","Hofsaess, H."],["dc.contributor.author","Zhang, K."],["dc.contributor.author","Pape, A."],["dc.contributor.author","Bobes, Omar"],["dc.contributor.author","Broetzmann, Marc"],["dc.date.accessioned","2018-11-07T09:25:02Z"],["dc.date.available","2018-11-07T09:25:02Z"],["dc.date.issued","2013"],["dc.description.abstract","We investigate the ripple pattern formation on Si surfaces at room temperature during normal incidence ion beam erosion under simultaneous deposition of different metallic co-deposited surfactant atoms. The co-deposition of small amounts of metallic atoms, in particular Fe and Mo, is known to have a tremendous impact on the evolution of nanoscale surface patterns on Si. In previous work on ion erosion of Si during co-deposition of Fe atoms, we proposed that chemical interactions between Fe and Si atoms of the steady-state mixed FexSi surface layer formed during ion beam erosion is a dominant driving force for self-organized pattern formation. In particular, we provided experimental evidence for the formation of amorphous iron disilicide. To confirm and generalize such chemical effects on the pattern formation, in particular the tendency for phase separation, we have now irradiated Si surfaces with normal incidence 5 keV Xe ions under simultaneous gracing incidence co-deposition of Fe, Ni, Cu, Mo, W, Pt, and Au surfactant atoms. The selected metals in the two groups (Fe, Ni, Cu) and (W, Pt, Au) are very similar regarding their collision cascade behavior, but strongly differ regarding their tendency to silicide formation. We find pronounced ripple pattern formation only for those co deposited metals (Fe, Mo, Ni, W, and Pt), which are prone to the formation of mono and disilicides. In contrast, for Cu and Au co-deposition the surface remains very flat, even after irradiation at high ion fluence. Because of the very different behavior of Cu compared to Fe, Ni and Au compared to W, Pt, phase separation toward amorphous metal silicide phases is seen as the relevant pro-cess for the pattern formation on Si in the case of Fe, Mo, Ni, W, and Pt co-deposition."],["dc.description.sponsorship","Deutsche Forschungsgemeinschaft [HO1125/20-1,2]"],["dc.identifier.doi","10.1007/s00339-012-7285-8"],["dc.identifier.fs","596144"],["dc.identifier.isi","000319064800046"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10293"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/29976"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Springer"],["dc.relation.issn","0947-8396"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.title","The role of phase separation for self-organized surface pattern formation by ion beam erosion and metal atom co-deposition"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["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.firstpage","131"],["dc.bibliographiccitation.issue","1-3"],["dc.bibliographiccitation.journal","HYPERFINE INTERACTIONS"],["dc.bibliographiccitation.lastpage","139"],["dc.bibliographiccitation.volume","181"],["dc.contributor.author","Roeder, J."],["dc.contributor.author","Herden, C."],["dc.contributor.author","Gardner, J. A."],["dc.contributor.author","Becker, K. D."],["dc.contributor.author","Uhrmacher, Michael"],["dc.contributor.author","Hofsaess, H."],["dc.date.accessioned","2018-11-07T11:20:03Z"],["dc.date.available","2018-11-07T11:20:03Z"],["dc.date.issued","2008"],["dc.description.abstract","In conventional perturbed angular correlation (PAC)-spectroscopy huge amounts of events are processed by fast electronics. Modern digital signal processing devices and the improvement in the computer technology in recent years allow today digital PAC-spectrometer setups capable to perform software-based data processing with all the benefits of storage, repeatable data analysis under different limits, and easy switching between different isotopes. In this paper we discuss experiences and concepts of a first realized digital PAC-spectrometer, which will be rebuild at ISOLDE/CERN/Geneva."],["dc.description.sponsorship","DFG [SPP 1136]"],["dc.identifier.doi","10.1007/s10751-008-9704-y"],["dc.identifier.isi","000260281100019"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?goescholar/3586"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/55440"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Springer"],["dc.relation.issn","0304-3843"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.access","openAccess"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.subject.ddc","530"],["dc.title","Actual concepts of digital PAC-spectroscopy"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["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"]]