@inproceedings{LuNicoulShymanovichetal., author = {Lu, Wei and Nicoul, Matthieu and Shymanovich, Uladzimir and Tarasevitch, A. and Kammler, Martin and Horn-von Hoegen, Michael and von der Linde, D. and Sokolowski-Tinten, Klaus}, title = {Transient reversal of a Peierls-transition: Extreme phonon softening in laser-excited Bismuth}, series = {International Conference on Ultrafast Phenomena, Snowmass}, booktitle = {International Conference on Ultrafast Phenomena, Snowmass}, number = {ME41}, publisher = {Optica Publishing Group}, doi = {10.1364/UP.2010.ME41}, abstract = {Laser-excited coherent optical phonons in Bismuth were investigated using time-resolved X-ray diffraction. The observed extreme softening of the excited A1g-mode presents strong indication that the Peierls-distortion defining the equilibrium structure of Bismuth is transiently reversed.}, language = {en} } @inproceedings{GabrielWittmannHackeretal., author = {Gabriel, Christian and Wittmann, Christoffer and Hacker, B. and Mauerer, Wolfgang and Huntington, E. and Sabuncu, M. and Marquardt, Christoph and Leuchs, Gerd}, title = {A high-speed secure quantum random number generator based on vacuum states}, series = {IEEE/OSA Conference on Lasers and Electro-Optics (CLEO), 06-11 May 2012, San Jose CA USA}, booktitle = {IEEE/OSA Conference on Lasers and Electro-Optics (CLEO), 06-11 May 2012, San Jose CA USA}, publisher = {Optical Society of America}, abstract = {A high-speed continuous-variable quantum random bit generator with an expected effective bit generation rate of up to 10 GBit/s is presented. The obtained bit sequences are truly random and unique, i.e. they cannot be known by an adversary.}, language = {en} } @article{PortavoceKammlerHulletal., author = {Portavoce, A. and Kammler, Martin and Hull, Robert and Reuter, Mark C. and Copel, M. and Ross, Frances M.}, title = {Growth of nanostructures by locally modified surface reactivity}, series = {Materials Science in Semiconductor Processing}, volume = {12}, journal = {Materials Science in Semiconductor Processing}, number = {1-2}, publisher = {Elsevier}, doi = {10.1016/j.mssp.2009.07.001}, pages = {25 -- 30}, abstract = {The chemical vapor deposition (CVD) of Si and Ge on Si(0 0 1) substrates covered by 1 monolayer of Ga has been studied. Ga modifies surface reactivity and surface atom mobility. We show that islanding occurs during Ga-mediated CVD even in the absence of strain, allowing for the formation of islands without a wetting layer or with a thinner wetting layer. The morphology of the grown layer is highly dependent on kinetic parameters, i.e. growth temperature and growth pressure, that control Si and Ge deposition and Ga desorption. Si Ga-mediated CVD promotes the formation of self-assembled epitaxial Si islands exhibiting {1 1 3} facets. Ge islands grown by Ga-mediated CVD present reduced lateral sizes and an increased surface density compared to non Ga-mediated CVD. The growth morphology (particularly island size and density) can be understood by considering a qualitative model in which atoms are deposited only on sites whose dangling bonds are not passivated by Ga. We suggest that modification of surface reactivity during surfactant-mediated CVD can thus provide a new degree of freedom for quantum dot fabrication.}, language = {en} } @article{PortavoceKammlerHulletal., author = {Portavoce, A. and Kammler, Martin and Hull, Robert and Reuter, Mark C. and Ross, Frances M.}, title = {Mechanism of the nanoscale localization of Ge quantum dot nucleation on focused ion beam templated Si(001) surfaces}, series = {Nanotechnology}, volume = {17}, journal = {Nanotechnology}, number = {17}, publisher = {IOP}, doi = {10.1088/0957-4484/17/17/028}, pages = {4451 -- 4455}, abstract = {We investigate the fundamental mechanism by which self-assembled Ge islands can be nucleated at specific sites on Si(001) using ultra-low-dose focused ion beam (FIB) pre-patterning. Island nucleation is controlled by a nanotopography that forms after the implantation of Ga ions during subsequent thermal annealing of the substrate. This nanotopography evolves during the annealing stage, changing from a nanoscale annular depression associated with each focused ion beam spot to a nanoscale pit, and eventually disappearing (planarizing). The correspondence of Ge quantum dot nucleation sites to the focused ion beam features requires a growth surface upon which the nanotopography is preserved. A further key observation is that the Ge wetting layer thickness is reduced in patterned regions, allowing the formation of islands on the templated regions without nucleation elsewhere. These results provide routes to the greatly enhanced design and control of quantum dot distributions and dimensions.}, language = {en} } @article{RossKammlerReuteretal., author = {Ross, Frances M. and Kammler, Martin and Reuter, Mark C. and Hull, Robert}, title = {In-situ observations of self-assembled island nucleation on patterned substrates}, series = {Philosophical Magazine}, volume = {84}, journal = {Philosophical Magazine}, number = {25-26}, publisher = {Taylor \& Francis}, doi = {10.1080/14786430410001671430}, pages = {2687 -- 2702}, abstract = {We compare in-situ electron microscopy observations of Ge island growth on Si surfaces modulated by different techniques. Si(001) substrates were patterned either using a focused Ga ion beam or lithographically to produce similar feature sizes. In the case of the focused-ion-beam patterned substrates, chemical or strain effects caused by low Ga doses control the positions at which islands nucleate. Nucleation on topographically modulated substrates, with the pattern produced either by high-dose sputtering or lithographically, is controlled by the nature of the side walls of topographic features. The two patterning approaches have different benefits in creating arrays of islands for device applications.}, language = {en} } @article{MenzelConradTringidesetal., author = {Menzel, Andreas and Conrad, E. H. and Tringides, Michael C. and Kammler, Martin and Horn- von Hoegen, Michael}, title = {Finite collection time effects in autocovariance function measurements}, series = {Journal of Applied Physics}, volume = {93}, journal = {Journal of Applied Physics}, number = {4}, publisher = {AIP Publishing}, doi = {10.1063/1.1537466}, pages = {2229 -- 2235}, abstract = {In this paper we discuss how finite data sets influence experimental measurements of the autocovariance function. Autocovariance estimators are biased, meaning that the expectation value for any measured autocovariance function is not identical to the actual autocovariance function. In this work we show that the measured autocovariance function for a finite length time series must become negative for some lag times. We derive analytic corrections to these finite time errors for different types of correlated random sequences. Our results explain the apparent anticorrelated noise observed in experimental observations.}, language = {en} } @article{KammlerHullReuteretal., author = {Kammler, Martin and Hull, Robert and Reuter, Mark C. and Ross, Frances M.}, title = {Lateral control of self-assembled island nucleation by focused-ion-beam micropatterning}, series = {Applied Physics Letters}, volume = {82}, journal = {Applied Physics Letters}, number = {7}, doi = {10.1063/1.1542680}, pages = {1093 -- 1095}, abstract = {We demonstrate that the nucleation sites of nanoscale, self-assembled Ge islands on Si(001) can be controlled by patterning the Si surface in situ with a focused ion beam. At low doses of 6000 Ga+ ions per <100 nm spot, the selective growth is achieved without modifying the initial surface topography. At larger doses, topographic effects produced by sputtering and redeposition control the selective nucleation sites. Islands grown on irradiated spots are smaller with higher aspect ratio than islands grown on clean Si(001), suggesting a strong surfactant effect of Ga.}, language = {en} } @article{SokolowskiTintenBlomeBlumsetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Blums, Juris and Shymanovich, Uladzimir and Nicoul, Matthieu and Cavalleri, Andrea and Tarasevitch, A. and Horn-von Hoegen, Michael and Kammler, Martin and von der Linde, D.}, title = {Ultrafast X-ray diffraction}, series = {Ultrafast Phenomena XIV}, volume = {79}, journal = {Ultrafast Phenomena XIV}, publisher = {Springer}, doi = {10.1007/3-540-27213-5_53}, pages = {170 -- 174}, abstract = {In the last few years the generation of femtosecond pulses in the X-ray regime has become possible. These ultrashort X-ray pulses have enabled femtosecond time- resolution to be extended to X-rays.}, language = {en} } @article{KammlerHullPortavoceetal., author = {Kammler, Martin and Hull, Robert and Portavoce, A. and Reuter, Mark C. and Ross, Frances M.}, title = {In-Situ Focused Ion Beam Micropatterning of Ge Islands}, series = {Microscopy and Microanalysis}, volume = {9}, journal = {Microscopy and Microanalysis}, number = {S02}, publisher = {Microscopy Society of America}, doi = {10.1017/S1431927603441214}, pages = {132 -- 134}, language = {en} } @inproceedings{FinckhZilch, author = {Finckh, Wolfgang and Zilch, Konrad}, title = {Shear capacity of flexural strengthened reinforced concrete structures with CFRP materials}, series = {Advances in FRP Composites in Civil Engineering - Proceedings of the 5th International Conference on FRP Composites in Civil Engineering (CICE 2010), Sep 27-29, 2010, Beijing, China}, booktitle = {Advances in FRP Composites in Civil Engineering - Proceedings of the 5th International Conference on FRP Composites in Civil Engineering (CICE 2010), Sep 27-29, 2010, Beijing, China}, editor = {Ye, Lieping and Feng, Peng and Yue, Qingrui}, publisher = {Springer}, address = {Berlin ; Heidelberg}, isbn = {978-3-642-17486-5}, doi = {10.1007/978-3-642-17487-2_175}, abstract = {By enlarging the flexural capacity of reinforced concrete structures with externally bonded CRFP materials the shear behavior is also affected. To evaluate this effect shear tests on flexural strengthened reinforced concrete beams were carried out. Half of the tests were done with externally bonded CFRP-strips and the other half with near surface mounted reinforcement. Based on these tests and the EC2 approach for the shear force was checked.}, language = {en} } @inproceedings{AltenbergerNosterNallaetal., author = {Altenberger, Igor and Noster, Ulf and Nalla, Ravi K. and Ritchie, Robert O. and Scholtes, Berthold}, title = {Residual stress relaxation in fatigue of mechanically surface treated materials}, series = {Proceedings 132nd Annual TMS Meeting, March 2-6, 2003, San Diego, California}, booktitle = {Proceedings 132nd Annual TMS Meeting, March 2-6, 2003, San Diego, California}, pages = {312}, language = {en} } @article{FritzReisAdamsetal., author = {Fritz, D. M. and Reis, D. A. and Adams, B. and Akre, R. A. and Arthur, J. and Blome, Christian and Bucksbaum, P. H. and Cavalieri, A. L. and Engemann, S. and Fahy, S. and Falcone, R. W. and Fuoss, P. H. and Gaffney, K. J. and George, M. J. and Hajdu, J. and Hertlein, M. P. and Hillyard, P. B. and Horn-von Hoegen, Michael and Kammler, Martin and Kaspar, J. and Kienberger, R. and Krejcik, P. and Lee, S. H. and Lindenberg, A. M. and McFarland, B. and Meyer, D. and Montagne, T. and Murray, E. D. and Nelson, A. J. and Nicoul, Matthieu and Pahl, R. and Rudati, J. and Schlarb, H. and Siddons, D. P. and Sokolowski-Tinten, Klaus and Tschentscher, Th and von der Linde, D. and Hastings, J. B.}, title = {Ultrafast bond softening in bismuth: mapping a solid's interatomic potential with X-rays}, series = {Science}, volume = {315}, journal = {Science}, number = {5812}, publisher = {AAAS}, doi = {10.1126/science.1135009}, pages = {633 -- 636}, abstract = {Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high excitation densities, the interatomic forces that bind solids and determine many of their properties can be substantially altered. Here, we present the detailed mapping of the carrier density-dependent interatomic potential of bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques that use a high-brightness linear electron accelerator-based x-ray source with pulse-by-pulse timing reconstruction for femtosecond resolution, allowing quantitative characterization of the interatomic potential energy surface of the highly excited solid.}, language = {en} } @article{LaunhardtWoerzLodereretal., author = {Launhardt, M. and W{\"o}rz, A. and Loderer, A. and Laumer, Tobias and Drummer, Dietmar and Hausotte, Tino and Schmidt, Michael}, title = {Detecting surface roughness on SLS parts with various measuring techniques}, series = {Polymer Testing}, volume = {53}, journal = {Polymer Testing}, publisher = {Elsevier}, address = {Amsterdam}, isbn = {0142-9418}, issn = {1873-2348}, doi = {10.1016/j.polymertesting.2016.05.022}, pages = {217 -- 226}, abstract = {Selective Laser Sintering (SLS) is an additive manufacturing technique whereby a laser melts polymer powder layer by layer to generate three-dimensional parts. It enables the fabrication of parts with high degrees of complexity, nearly no geometrical restrictions, and without the necessity of a tool or a mold. Due to the orientation in the building space, the processing parameters, and the powder properties, the resulting parts possess an increased surface roughness. In comparison to other manufacturing techniques, e.g. injection molding, the surface roughness of SLS parts results from partially melted powder particles on the surface layer. The actual surface roughness must thus be characterized with respect to the part's eventual application. At the moment, there is no knowledge regarding which measuring technique is most suitable for detecting and quantifying SLS parts' surface roughness. The scope of this paper is to compare tactile profile measurement methods, as established in industry, to optical measurement techniques such as Focus Variation, Fringe Projection Technique (FPT), and Confocal Laser Scanning Microscope (CLSM). The advantages and disadvantages of each method are presented and, additionally, the effect of tactile measurement on a part's surface is investigated.}, language = {en} }