@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{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{CheeKammlerGrahametal., author = {Chee, See Wee and Kammler, Martin and Graham, Jeremy and Gignac, Lynne and Reuter, Mark C. and Hull, Robert and Ross, Frances M.}, title = {Directed Self-Assembly of Ge Quantum Dots Using Focused Si2+ Ion Beam Patterning}, series = {scientific reports}, volume = {8}, journal = {scientific reports}, publisher = {Nature}, doi = {10.1038/s41598-018-27512-z}, pages = {1 -- 10}, abstract = {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.}, language = {en} } @article{KammlerChidambarraoSchwarzetal., author = {Kammler, Martin and Chidambarrao, D. and Schwarz, K. W. and Black, C. T. and Ross, Frances M.}, title = {Controlled nucleation of dislocations by a spatially localized stress field}, series = {Applied Physics Letters}, volume = {87}, journal = {Applied Physics Letters}, number = {13}, publisher = {AIP}, doi = {10.1063/1.2061862}, abstract = {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.}, language = {en} } @article{CheeKammlerBalasubramanianetal., author = {Chee, See Wee and Kammler, Martin and Balasubramanian, Prabhu and Reuter, Mark C. and Hull, Robert and Ross, Frances M.}, title = {Microstructural changes in silicon induced by patterning with focused ion beams of Ga, Si and Au}, series = {Ultramicroscopy}, volume = {127}, journal = {Ultramicroscopy}, publisher = {Elsevier}, doi = {10.1016/j.ultramic.2012.07.004}, pages = {126 -- 131}, abstract = {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.}, language = {en} } @article{SokolowskiTintenHornvonHoegenvonderLindeetal., author = {Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Kammler, Martin}, title = {Transient lattice dynamics in fs-laser-excited semiconductors probed by ultrafast X-ray diffraction}, series = {Journal de Physique IV}, volume = {11}, journal = {Journal de Physique IV}, number = {Pr2}, publisher = {EDP}, doi = {10.1051/jp4:2001290}, pages = {473 -- 477}, abstract = {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.}, language = {en} } @article{SokolowskiTintenCavalleriSidersetal., author = {Sokolowski-Tinten, Klaus and Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Kammler, Martin and Horn-von Hoegen, Michael and von der Linde, D. and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R.}, title = {Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures}, series = {Chemical Physics}, volume = {66}, journal = {Chemical Physics}, publisher = {Springer}, doi = {10.1007/978-3-642-56546-5_81}, pages = {281 -- 283}, abstract = {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.}, language = {en} } @article{CavalleriSidersBrownetal., author = {Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D. and Kammler, Martin}, title = {Anharmonic lattice dynamics in germanium measured with ultrafast x-ray diffraction}, series = {Physical review letters}, volume = {85}, journal = {Physical review letters}, number = {3}, publisher = {APS}, doi = {10.1103/PhysRevLett.85.586}, pages = {586 -- 589}, abstract = {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.}, language = {en} } @article{HullGrayKammleretal., author = {Hull, Robert and Gray, J. L. and Kammler, Martin and Vandervelde, T. and Kobayashi, Takeshi and Kumar, P. and Pernell, T. and Bean, J. C. and Floro, J. A. and Ross, Frances M.}, title = {Precision placement of heteroepitaxial semiconductor quantum dots}, series = {Materials Science and Engineering: B}, volume = {101}, journal = {Materials Science and Engineering: B}, number = {1-3}, publisher = {Elsevier}, doi = {10.1016/S0921-5107(02)00680-3}, pages = {1 -- 8}, abstract = {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 ({\^A}/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.}, language = {en} } @article{PayerKleinAcetetal., author = {Payer, Thomas and Klein, C. and Acet, M. and Ney, V. and Kammler, Martin and Meyer zu Heringdorf, Frank-Joachim and Horn-von Hoegen, Michael}, title = {High-quality epitaxial Bi(111) films on Si(111) by isochronal annealing}, series = {Thin Solid Films}, volume = {520}, journal = {Thin Solid Films}, number = {23}, publisher = {Elsevier}, doi = {10.1016/j.tsf.2012.06.004}, pages = {6905 -- 6908}, abstract = {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\%.}, 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{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{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} } @article{KleinNabbefeldHattabetal., author = {Klein, C. and Nabbefeld, T. and Hattab, H. and Meyer, D. and Jnawali, G. and Kammler, Martin and Meyer zu Heringdorf, Frank-Joachim and Golla-Franz, A. and M{\"u}ller, B. H. and Schmidt, Thomas and Henzler, M. and Horn-von Hoegen, Michael}, title = {Lost in reciprocal space? Determination of the scattering condition in spot profile analysis low-energy electron diffraction}, series = {Review of scientific instruments}, volume = {82}, journal = {Review of scientific instruments}, number = {3}, publisher = {American Institute of Physics}, doi = {10.1063/1.3554305}, abstract = {The precise knowledge of the diffraction condition, i.e., the angle of incidence and electron energy, is crucial for the study of surface morphology through spot profile analysis low-energy electron diffraction (LEED). We demonstrate four different procedures to determine the diffraction condition: employing the distortion of the LEED pattern under large angles of incidence, the layer-by-layer growth oscillations during homoepitaxial growth, a G(S) analysis of a rough surface, and the intersection of facet rods with 3D Bragg conditions.}, language = {en} } @article{CheeKammlerGrahametal., author = {Chee, See Wee and Kammler, Martin and Graham, Jeremy and Ross, Frances M. and Hull, Robert}, title = {Direct Imaging of Microstructural Changes in Si Induced by FIB-Patterning with Si ++ and Ga + Ions}, series = {Microscopy and Microanalysis}, volume = {17}, journal = {Microscopy and Microanalysis}, number = {S2}, publisher = {Cambridge University Press}, doi = {10.1017/S1431927611004156}, pages = {656 -- 657}, language = {en} }