TY - JOUR A1 - Fritz, D. M. A1 - Reis, D. A. A1 - Adams, B. A1 - Akre, R. A. A1 - Arthur, J. A1 - Blome, Christian A1 - Bucksbaum, P. H. A1 - Cavalieri, A. L. A1 - Engemann, S. A1 - Fahy, S. A1 - Falcone, R. W. A1 - Fuoss, P. H. A1 - Gaffney, K. J. A1 - George, M. J. A1 - Hajdu, J. A1 - Hertlein, M. P. A1 - Hillyard, P. B. A1 - Horn-von Hoegen, Michael A1 - Kammler, Martin A1 - Kaspar, J. A1 - Kienberger, R. A1 - Krejcik, P. A1 - Lee, S. H. A1 - Lindenberg, A. M. A1 - McFarland, B. A1 - Meyer, D. A1 - Montagne, T. A1 - Murray, E. D. A1 - Nelson, A. J. A1 - Nicoul, Matthieu A1 - Pahl, R. A1 - Rudati, J. A1 - Schlarb, H. A1 - Siddons, D. P. A1 - Sokolowski-Tinten, Klaus A1 - Tschentscher, Th A1 - von der Linde, D. A1 - Hastings, J. B. T1 - Ultrafast bond softening in bismuth: mapping a solid's interatomic potential with X-rays JF - Science N2 - 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. Y1 - 2007 U6 - https://doi.org/10.1126/science.1135009 VL - 315 IS - 5812 SP - 633 EP - 636 PB - AAAS ER - TY - JOUR A1 - Portavoce, A. A1 - Kammler, Martin A1 - Hull, Robert A1 - Reuter, Mark C. A1 - Copel, M. A1 - Ross, Frances M. T1 - Growth of nanostructures by locally modified surface reactivity JF - Materials Science in Semiconductor Processing N2 - 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. KW - UHV TEM KW - UHV CVD KW - Epitaxial growth KW - Si KW - Ge KW - Surfactant Ga Y1 - 2009 U6 - https://doi.org/10.1016/j.mssp.2009.07.001 VL - 12 IS - 1-2 SP - 25 EP - 30 PB - Elsevier ER - TY - JOUR A1 - Chee, See Wee A1 - Kammler, Martin A1 - Graham, Jeremy A1 - Gignac, Lynne A1 - Reuter, Mark C. A1 - Hull, Robert A1 - Ross, Frances M. T1 - Directed Self-Assembly of Ge Quantum Dots Using Focused Si2+ Ion Beam Patterning JF - scientific reports N2 - We show that templating a Si surface with a focused beam of Si2+ or Si+ ions can create suitable nucleation sites for the subsequent growth of self-assembled Ge quantum dots by chemical vapor deposition. To determine the mechanism of patterning we use atomic force microscopy to show that, similar to Ga+ patterning, the formation of a surface pit is required to enable control over Ge quantum dot locations. We find that relatively high implantation doses are required to achieve patterning, and these doses lead to amorphization of the substrate. We assess the degree to which the substrate crystallinity can be recovered by subsequent processing. Using in situ transmission electron microscopy heating experiments we find that recrystallization is possible at the growth temperature of the Ge quantum dots, but defects remain that follow the pattern of the initial implantation. We discuss the formation mechanism of the defects and the benefits of using Si ions for patterning both defects and quantum dots on Si substrates. KW - ARRAYS KW - AU KW - DAMAGE KW - GROWTH KW - IMPLANTATION KW - NUCLEATION KW - RECOVERY KW - silicon KW - TECHNOLOGY Y1 - 2018 U6 - https://doi.org/10.1038/s41598-018-27512-z VL - 8 SP - 1 EP - 10 PB - Nature ER - TY - JOUR A1 - Kammler, Martin A1 - Chidambarrao, D. A1 - Schwarz, K. W. A1 - Black, C. T. A1 - Ross, Frances M. T1 - Controlled nucleation of dislocations by a spatially localized stress field JF - Applied Physics Letters N2 - We analyze the nucleation of dislocations in silicon at spatially localized stress fields generated by silicon nitride pads having a high intrinsic stress. The nucleation and final configuration of the dislocations were studied using hot-stage transmission electron microscopy and were compared with dislocation simulations based on calculations of the stress fields around the pads. We find that the simulated configurations match well with the experimental data, and we show that the dislocation configuration can be controlled by the pad size. Y1 - 2005 U6 - https://doi.org/10.1063/1.2061862 VL - 87 IS - 13 PB - AIP ER - TY - JOUR A1 - Chee, See Wee A1 - Kammler, Martin A1 - Balasubramanian, Prabhu A1 - Reuter, Mark C. A1 - Hull, Robert A1 - Ross, Frances M. T1 - Microstructural changes in silicon induced by patterning with focused ion beams of Ga, Si and Au JF - Ultramicroscopy N2 - We use focused beams of Ga(+), Au(+) and Si(++) ions to induce local microstructural changes in single crystal silicon. The ions were delivered as single spot pulses into thin Si membranes that could subsequently be imaged and annealed in situ in a transmission electron microscope. For each ion, the focused ion beam implantation created an array of amorphous regions in the crystalline membrane. Annealing causes solid phase epitaxial regrowth to take place, but we show that the resulting microstructure depends on the ion species. For Ga(+) and Au(+), precipitates remain after recrystallization, while for Si(++), dislocation loops form around the periphery of each implanted spot. We attribute these loops to defects formed during solid phase epitaxial regrowth, with controlled placement of the loops possible. KW - dislocation engineering KW - focused ion beam KW - In situ electron microscopy KW - solid phase epitaxial regrowth Y1 - 2013 U6 - https://doi.org/10.1016/j.ultramic.2012.07.004 VL - 127 SP - 126 EP - 131 PB - Elsevier ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Cavalleri, Andrea A1 - Siders, C. W. A1 - Brown, F. L. H. A1 - Leitner, D. M. A1 - Tóth, Csaba A1 - Squier, Jeff A. A1 - Barty, C. P. J. A1 - Wilson, K. R. A1 - Kammler, Martin T1 - Transient lattice dynamics in fs-laser-excited semiconductors probed by ultrafast X-ray diffraction JF - Journal de Physique IV N2 - A study of lattice dynamics in fs-laser-excited crystalline bulk Ge and Ge/Si-heterostructures, using time-resolved x-ray diffraction, was presented. Fast energy transport deep into the bulk of the material, coherent acoustic phonon dynamics, lattice anharmonicity, and vibrational transport across a buried interfaces were observed. Graphs showing time-dependent shifts of the centroid of the measured rocking curves in the Ge-overlayer and in the Si-substrate for different fluences, were presented. Y1 - 2001 U6 - https://doi.org/10.1051/jp4:2001290 VL - 11 IS - Pr2 SP - 473 EP - 477 PB - EDP ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Cavalleri, Andrea A1 - Siders, C. W. A1 - Brown, F. L. H. A1 - Leitner, D. M. A1 - Tóth, Csaba A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Squier, Jeff A. A1 - Barty, C. P. J. A1 - Wilson, K. R. T1 - Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures JF - Chemical Physics N2 - Using time-resolved x-ray diffraction the ultafast strain dynamics in fs-laserexcited Ge/Si-heterostructures has been studied. A fluence dependent, anharmonic damping of the impulsively generated acoustic phonons and vibrational transport across the buried Ge/Si-interface are observed. Y1 - 2001 U6 - https://doi.org/10.1007/978-3-642-56546-5_81 VL - 66 SP - 281 EP - 283 PB - Springer ER - TY - JOUR A1 - Cavalleri, Andrea A1 - Siders, C. W. A1 - Brown, F. L. H. A1 - Leitner, D. M. A1 - Tóth, Csaba A1 - Squier, Jeff A. A1 - Barty, C. P. J. A1 - Wilson, K. R. A1 - Sokolowski-Tinten, Klaus A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Kammler, Martin T1 - Anharmonic lattice dynamics in germanium measured with ultrafast x-ray diffraction JF - Physical review letters N2 - Damping of impulsively generated coherent acoustic oscillations in a femtosecond laser-heated thin germanium film is measured as a function of fluence by means of ultrafast x-ray diffraction. By simultaneously measuring picosecond strain dynamics in the film and in the unexcited silicon substrate, we separate anharmonic damping from acoustic transmission through the buried interface. The measured damping rate and its dependence on the calculated temperature of the thermal bath is consistent with estimated four-body, elastic dephasing times (T2) for 7-GHz longitudinal acoustic phonons in germanium. Y1 - 2000 U6 - https://doi.org/10.1103/PhysRevLett.85.586 VL - 85 IS - 3 SP - 586 EP - 589 PB - APS ER - TY - JOUR A1 - Hull, Robert A1 - Gray, J. L. A1 - Kammler, Martin A1 - Vandervelde, T. A1 - Kobayashi, Takeshi A1 - Kumar, P. A1 - Pernell, T. A1 - Bean, J. C. A1 - Floro, J. A. A1 - Ross, Frances M. T1 - Precision placement of heteroepitaxial semiconductor quantum dots JF - Materials Science and Engineering: B N2 - We describe two new approaches to the patterning of Si(1 0 0) surfaces for controlled nucleation of heteroepitaxial Ge semiconductor clusters. In the first method, a Ga ' -focused ion beam in situ to the growth chamber is used to create local regions of enhanced Ga ' concentration and surface topography. It is shown that at low ion doses (Â/10 14 cm (2), implanted Ga causes local nucleation of Ge clusters upon the implanted region. At higher doses (]/10 15 cm (2), a complex surface topography localizes nucleation of Ge clusters. This approach can be used to seed complex patterns of Ge clusters with diameters of tens of nanometers and positional accuracy of sub-100 nm. The second method employs self-assembly of complex strain-stabilized ''quantum quadruplet'' and ''quantum fortress'' structures, whereby cooperative island nucleation around shallow strain-relieving pits is identified during Ge x Si 1(x /Si(1 0 0) heteroepitaxy. These configurations are kinetically limited structures that exist over a range of compositions, growth temperatures, and growth rates, but which are destabilized by strain relaxation (e.g. by the introduction of misfit dislocations) and by growth conditions which provide high adatom surface mobilities. Both methods have broad potential application to nanoelectronic device architectures. 2003 Elsevier Science B.V. All rights reserved. KW - Strained layer epitaxy KW - Strain relaxation KW - Quantum fortress KW - Molecular beam epitaxy KW - Controlled nucleation Y1 - 2003 U6 - https://doi.org/10.1016/S0921-5107(02)00680-3 VL - 101 IS - 1-3 SP - 1 EP - 8 PB - Elsevier ER - TY - JOUR A1 - Payer, Thomas A1 - Klein, C. A1 - Acet, M. A1 - Ney, V. A1 - Kammler, Martin A1 - Meyer zu Heringdorf, Frank-Joachim A1 - Horn-von Hoegen, Michael T1 - High-quality epitaxial Bi(111) films on Si(111) by isochronal annealing JF - Thin Solid Films N2 - Bi(111) films grown on Si(111) at room temperature show a significantly higher roughness compared to Bi films grown on Si(100) utilizing a kinetic pathway based on a low-temperature process. Isochronal annealing steps of 3 min duration each with temperatures up to 200 °C cause a relaxation of the Bi films' lattice parameter toward the Bi bulk value and yield an atomically flat Bi surface. Driving force for the relaxation and surface reordering is the magic mismatch of 11 Bi atoms to 13 Si atoms that emerges at annealing temperatures above 150 °C and reduces the remaining strain to less than 0.2%. KW - Epitaxy KW - Strain KW - Annealing KW - Bismuth KW - Silicon Y1 - 2012 U6 - https://doi.org/10.1016/j.tsf.2012.06.004 VL - 520 IS - 23 SP - 6905 EP - 6908 PB - Elsevier ER - TY - JOUR A1 - Portavoce, A. A1 - Kammler, Martin A1 - Hull, Robert A1 - Reuter, Mark C. A1 - Ross, Frances M. T1 - Mechanism of the nanoscale localization of Ge quantum dot nucleation on focused ion beam templated Si(001) surfaces JF - Nanotechnology N2 - 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. Y1 - 2006 U6 - https://doi.org/10.1088/0957-4484/17/17/028 VL - 17 IS - 17 SP - 4451 EP - 4455 PB - IOP ER - TY - JOUR A1 - Ross, Frances M. A1 - Kammler, Martin A1 - Reuter, Mark C. A1 - Hull, Robert T1 - In-situ observations of self-assembled island nucleation on patterned substrates JF - Philosophical Magazine N2 - 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. Y1 - 2004 U6 - https://doi.org/10.1080/14786430410001671430 VL - 84 IS - 25-26 SP - 2687 EP - 2702 PB - Taylor & Francis ER -