@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} } @inproceedings{SokolowskiTintenBlomeDietrichetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Dietrich, Clemens and Blums, Juris and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Squier, Jeff A. and Kammler, Martin}, title = {Structural dynamics in laser-excited solids investigated with femtosecond x-ray diffraction}, series = {2002 Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 19-24 May 2002, Long Beach, CA, USA}, booktitle = {2002 Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 19-24 May 2002, Long Beach, CA, USA}, publisher = {IEEE}, doi = {10.1109/QELS.2002.1031182}, pages = {115 -- 116}, abstract = {Summary form only given. Ultrashort x-ray pulses offer a unique combination of atomic-scale spatial and temporal resolution, which permits direct measurements of structural transients on an ultrafast time scale. Using time-resolved X-ray diffraction with femtosecond, multi-keV X-ray pulses we have studied transient lattice dynamics in optically excited semiconductors.}, language = {en} } @article{SokolowskiTintenBlomeDietrichetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Dietrich, Clemens and Tarasevitch, A. and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Squier, Jeff A. and Kammler, Martin}, title = {Femtosecond x-ray measurement of ultrafast melting and large acoustic transients}, series = {Physical review letters}, volume = {87}, journal = {Physical review letters}, publisher = {APS}, doi = {10.1103/PhysRevLett.87.225701}, abstract = {Time-resolved x-ray diffraction with ultrashort ( approximately 300 fs), multi-keV x-ray pulses has been used to study the femtosecond laser-induced solid-to-liquid phase transition in a thin crystalline layer of germanium. Nonthermal melting is observed to take place within 300-500 fs. Following ultrafast melting we observe strong acoustic perturbations evolving on a picosecond time scale.}, language = {en} } @article{SokolowskiTintenBlomeDietrichetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Dietrich, Clemens and Tarasevitch, A. and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Squier, Jeff A. and Kammler, Martin}, title = {Femtosecond time-resolved X-ray diffraction study of ultrafast structural dynamics in laser-excited solids}, series = {International Conference on Ultrafast Phenomena, 12 May 2002, Vancouver Canada}, volume = {71}, journal = {International Conference on Ultrafast Phenomena, 12 May 2002, Vancouver Canada}, publisher = {Optica Publishing Grou}, doi = {10.1007/978-3-642-59319-2_10}, pages = {36 -- 38}, abstract = {Time-resolved x-ray diffraction with sub-300 fs, multi-keV x-ray pulses was used to study ultrafast lattice dynamics in laser-irradiated germanium and bismuth. In bismuth strong excitation of optical phonons is observed prior to disordering of the material.}, language = {en} } @unpublished{TringidesConradMenzeletal.2002, author = {Tringides, Michael C. and Conrad, E. H. and Menzel, Andreas and Voss, Neil R. and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Dynamics of atomic steps on Si(001) studied by temporal LEED spectroscopy [Poster]}, year = {2002}, abstract = {While surface kinetics measurements for single atom diffusion have proliferated, little work exists attempting to measure surface dynamics under equilibrium conditions. We will present our recent work on developing Temporal LEED Spectroscopy (TLS) as a dynamic probe of surfaces capable of kinetics measurements at both high temperatures and surface coverages. By tuning the diffraction to specific structural entities such as steps, islands, etc., and monitoring the diffracted signal as a function of time, dynamics information about these structures can be obtained. As an example we will present TLS results for the dynamics of step fluctuations on Si(001) [1]. We have measured activation energies and identified step-edge diffusion as the rate limiting process for 950K < T < 1130K. Although this result is in apparent disagreement with earlier work, a careful analysis, considering crossover temperatures between different microscopic processes, can reconcile the differences. 1. M. Kammler, et al., Phys. Rev. B (in press).}, language = {en} } @article{HornvonHoegenMeyerzuHeringdorfKammleretal., author = {Horn-von Hoegen, Michael and Meyer zu Heringdorf, Frank-Joachim and Kammler, Martin and Schaeffer, C. and Reinking, D. and Hofmann, K. R.}, title = {Bi surfactant mediated epitaxy of Ge on Si(111)}, series = {Thin Solid Films}, volume = {343-344}, journal = {Thin Solid Films}, publisher = {Elsevier}, doi = {10.1016/S0040-6090(98)01659-9}, pages = {579 -- 582}, abstract = {We have tested Bi for the surfactant mediated epitaxy of Ge on Si(111). Islanding of Ge is prevented and a 2D layer growth of smooth and continuous Ge films is observed. The lattice mismatch is accommodated by a periodic array of dislocations confined to the Si/Ge interface. The large covalent radius of Bi reduces the binding energy, allowing Very efficient segregation and low doping levels even at low growth temperatures. Unfortunately, this results also in a high Bi desorption flux limiting the possible growth temperatures below 600 degrees C. Consequently the Ge films show a high defect density in the order of 10(8) cm(-2) for stacking faults and 10(9) cm(-2) for dislocations which limit electron Hall mobility to values below 700 cm(2)/V s at room temperature.}, 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{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 T{\´o}th, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Kammler, Martin}, title = {Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures}, series = {International Conference on Ultrafast Phenomena , 9 July 2000, Charleston}, journal = {International Conference on Ultrafast Phenomena , 9 July 2000, Charleston}, publisher = {Optica}, 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{SidersCavalleriSokolowskiTintenetal., author = {Siders, C. W. and Cavalleri, Andrea and Sokolowski-Tinten, Klaus and T{\´o}th, Csaba and Guo, T. and Kammler, Martin and Horn-von Hoegen, Michael and Wilson, K. R. and von der Linde, D. and Barty, C. P. J.}, title = {Detection of nonthermal melting by ultrafast X-ray diffraction}, series = {Science}, volume = {286}, journal = {Science}, number = {5443}, doi = {10.1126/science.286.5443.1340}, pages = {1340 -- 1342}, abstract = {Using ultrafast, time-resolved, 1.54 angstrom x-ray diffraction, thermal and ultrafast nonthermal melting of germanium, involving passage through nonequilibrium extreme states of matter, was observed. Such ultrafast, optical-pump, x-ray diffraction probe measurements provide a way to study many other transient processes in physics, chemistry, and biology, including direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place.}, language = {en} } @article{ReinkingKammlerHoffmannetal., author = {Reinking, D. and Kammler, Martin and Hoffmann, N. and Horn-von Hoegen, Michael and Hofmann, K. R.}, title = {Fabrication of high-mobility Ge p-channel MOSFETs on Si substrates}, series = {Electronics Letters}, volume = {35}, journal = {Electronics Letters}, number = {6}, publisher = {IET}, doi = {10.1049/el:19990349}, pages = {503 -- 504}, abstract = {The first fabrication of Ge p-channel MOSFETs (p-MOSFETs) on Si substrates is reported. A CMOS compatible process based on relaxed Ge layers grown on Si(111) substrates by surfactant mediated epitaxy (SME) was used. The non-optimised low temperature process yielded normally-off Ge p-MOSFETs with record channel drift mobilities of 430 cm2/Vs}, language = {en} } @article{SidersCavalleriSokolowskiTintenetal., author = {Siders, C. W. and Cavalleri, Andrea and Sokolowski-Tinten, Klaus and T{\´o}th, Csaba and Guo, T. and Kammler, Martin and Horn-von Hoegen, Michael and Wilson, K. R. and von der Linde, D. and Barty, C. P. J.}, title = {Direct Observation of Ultrafast Non-thermal Melting by Ultrafast X-ray Diffraction}, series = {Ultrafast Phenomena XII}, volume = {66}, journal = {Ultrafast Phenomena XII}, publisher = {Springer}, doi = {10.1007/978-3-642-56546-5_80}, pages = {276 -- 280}, abstract = {Ultrafast nonthermal melting of femtosecond laser-irradiated germanium was observed directly for the first time using sub-picosecond, 1.54-angstrom x-ray diffraction. Such measurements allow the study of transient atomic motion fundamental to many processes in physics, chemistry, and biology.}, language = {en} } @incollection{SokolowskiTintenvonderLindeSidersetal., author = {Sokolowski-Tinten, Klaus and von der Linde, D. and Siders, C. W. and Cavalleri, Andrea and T{\´o}th, Csaba and Guo, T. and Wilson, K. R. and Barty, C. P. J. and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Lattice dynamics of femtosecond laser-excited semiconductors probed by ultrafast x-ray diffraction}, series = {Applications of High Field and Short Wavelength Sources VIII}, booktitle = {Applications of High Field and Short Wavelength Sources VIII}, publisher = {Optica}, doi = {10.1364/HFSW.1999.PD3}, abstract = {The present knowledge of the atomic structure of matter is to a large extent due to x-ray spectroscopies.}, language = {en} } @article{SchmidtKroegerFlegeetal., author = {Schmidt, Thomas and Kr{\"o}ger, Roland and Flege, Jan Ingo and Horn-von Hoegen, Michael and Clausen, T. and Falta, J. and Janzen, Andreas and Zahl, P. and Kury, P. and Kammler, Martin}, title = {Less strain energy despite fewer misfit dislocations: the impact of ordering}, series = {Physical review letters}, volume = {96}, journal = {Physical review letters}, number = {6}, publisher = {APS}, doi = {10.1103/PhysRevLett.96.066101}, abstract = {The average strain state of Ge films grown on Si(111) by surfactant mediated epitaxy has been compared to the ordering of the interfacial misfit dislocation network. Surprisingly, a smaller degree of average lattice relaxation was found in films grown at higher temperature. On the other hand, these films exhibit a better ordered dislocation network. This effect energetically compensates the higher strain at higher growth temperature, leading to the conclusion that, apart from the formation of misfit dislocations, their ordering represents an important channel for lattice-strain energy relaxation.}, 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{HanischBlicharskiJanzenKrenzeretal., author = {Hanisch-Blicharski, Anja and Janzen, Andreas and Krenzer, Boris and Wall, S. and Klasing, Friedrich and Kalus, Annika and Frigge, Tim and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Ultra-fast electron diffraction at surfaces: from nanoscale heat transport to driven phase transitions}, series = {Ultramicroscopy}, volume = {127}, journal = {Ultramicroscopy}, publisher = {Elsevier}, doi = {10.1016/j.ultramic.2012.07.017}, pages = {2 -- 8}, abstract = {Many fundamental processes of structural changes at surfaces occur on a pico- or femtosecond time scale. In order to study such ultra-fast processes, we have combined modern surface science techniques with fs-laser pulses in a pump-probe scheme. Reflection high energy electron diffraction (RHEED) with grazing incident electrons ensures surface sensitivity for the probing electron pulses. Utilizing the Debye-Waller effect, we studied the cooling of vibrational excitations in monolayer adsorbate systems or the nanoscale heat transport from an ultra-thin film through a hetero-interface on the lower ps-time scale. The relaxation dynamics of a driven phase transition far away from thermal equilibrium is demonstrated with the In-induced (8×2) reconstruction on Si(111). This surface exhibits a Peierls-like phase transition at 100K from a (8×2) ground state to (4×1) excited state. Upon excitation by a fs-laser pulse, this structural phase transition is driven into an excited (4×1) state at a sample temperature of 20K. Relaxation into the (8×2) ground state occurs after more than 150 ps.}, language = {en} } @article{MenzelKammlerConradetal., author = {Menzel, Andreas and Kammler, Martin and Conrad, E. H. and Yeh, V. and Hupalo, Myron and Tringides, Michael C.}, title = {Kinetics measurements of Pb island growth on Si(111)}, series = {Physical Review B}, volume = {67}, journal = {Physical Review B}, number = {16}, publisher = {American Physical Society}, doi = {10.1103/PhysRevB.67.165314}, abstract = {We present the results of kinetics experiments on quantum-size-effects (QSE) Pb islands formed on Si(111). We have looked at the evolution of seven-layer Pb islands from five-layer Pb islands due to the transport of Pb atoms from the interisland region, overcoming a barrier at the island edges, and moving to the island tops. By analyzing low-energy electron-diffraction and scanning-tunneling microscopy data, we have estimated the barrier for layer formation in this system to be ∼0.32eV. This energy is much larger than that expected from QSE electronic contributions alone.}, language = {en} } @inproceedings{KammlerHornvonHoegenVossetal., author = {Kammler, Martin and Horn- von Hoegen, Michael and Voss, N. and Tringides, Michael C. and Menzel, Andreas and Conrad, E. H.}, title = {Surface Dynamics of Stepped Si(001) Studied by Temporal Leed Spectroscopy}, series = {Collective Diffusion on Surfaces: Correlation Effects and Adatom Interactions (NATO Science Series II: Mathematics, Physics and Chemistry}, volume = {29}, booktitle = {Collective Diffusion on Surfaces: Correlation Effects and Adatom Interactions (NATO Science Series II: Mathematics, Physics and Chemistry}, publisher = {Springer}, doi = {10.1007/978-94-010-0816-7_3}, pages = {23 -- 32}, abstract = {We present the first demonstration of Temporal LEED Spectroscopy's ability to measure surface dynamics as shown by a study of step dynamics on vicinal Si(001). While we measure activation energies consistent with other work, the observed microscopic mechanism driving the fluctuations is inconsistent with previous claims. We exclude evaporation/condensation of atoms from the steps as the rate limiting kinetics in the temperature range of this experiment. Possible reasons for these differences are discussed.}, language = {en} } @article{StreubuehrKalusZhouetal., author = {Streub{\"u}hr, C. and Kalus, Annika and Zhou, Ping and Ligges, Manuel and Hanisch-Blicharski, Anja and Kammler, Martin and Bovensiepen, U. and Horn-von Hoegen, Michael and von der Linde, D.}, title = {Comparing ultrafast surface and bulk heating using time-resolved electron diffraction}, series = {Applied Physics Letters}, volume = {104}, journal = {Applied Physics Letters}, publisher = {American Institute of Physics}, doi = {10.1063/1.4872055}, pages = {1 -- 3}, abstract = {From measurements of the transient Debye-Waller effect in Bismuth, we determine the buildup time of the random atomic motion resulting from the electronic relaxation after short pulse laser excitation. The surface sensitive reflection high energy electron diffraction and transmission electron diffraction yield a time constant of about 12 ps and 3 ps, respectively. The different energy transfer rates indicate relatively weak coupling between bulk and surface vibrational modes. (C) 2014 AIP Publishing LLC.}, language = {en} } @inproceedings{ShymanovichNicoulLuetal., author = {Shymanovich, Uladzimir and Nicoul, Matthieu and Lu, Wei and Tarasevitch, A. and Kammler, Martin and Horn-von Hoegen, Michael and von der Linde, D. and Sokolowski-Tinten, Klaus and Phipps, Claude}, title = {Coherent acoustic and optical phonons in laser-excited solids studied by ultrafast time-resolved X-ray diffraction}, series = {AIP Conference Proceedings}, booktitle = {AIP Conference Proceedings}, number = {1}, publisher = {AIP}, doi = {10.1063/1.3507146}, pages = {558 -- 566}, abstract = {We apply ultrafast time-resolved X-ray diffraction to directly study coherent acoustic and optical phonons in laser-excited materials. In Au the ps acoustic response has been investigated with the particular goal to clarify the interplay of electronic and thermal pressure contributions. In Bi the extreme softening of the coherently excited A 1 g optical phonon presents strong indication that upon intense laser-excitation the Peierls-transition which determines the equilibrium structure of Bi can be reversed. In FeRh we studied the lattice response after a fast laser-induced anti-ferromagnetic to ferromagnetic phase transition.}, 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} } @inproceedings{ZhouStreubuehrKalusetal., author = {Zhou, Ping and Streub{\"u}hr, C. and Kalus, Annika and Frigge, Tim and Wall, S. and Hanisch-Blicharski, Anja and Kammler, Martin and Ligges, Manuel and Bovensiepen, U. and von der Linde, D. and Horn-von Hoegen, Michael}, title = {Ultrafast time resolved reflection high energy electron diffraction with tilted pump pulse fronts}, series = {EPJ Web of Conferences - XVIIIth International Conference on Ultrafast Phenomena}, volume = {41}, booktitle = {EPJ Web of Conferences - XVIIIth International Conference on Ultrafast Phenomena}, publisher = {EPJ}, doi = {10.1051/epjconf/20134110016}, abstract = {We present time-resolved RHEED from a laser excited Pb(111) surface using a pulse front tilter for the compensation of the velocity mismatch of electrons and light. The laser pulses with tilted fronts were characterized by a spatially resolving cross correlator. The response of the surface upon excitation was observed to be less than 2 ps.}, language = {en} } @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} } @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} }