TY - JOUR
AB - SiGe islands move laterally on a Si(001) substrate during in situ postgrowth annealing. This surprising behavior is revealed by an analysis of the substrate surface morphology after island removal using wet chemical etching. We explain the island motion by asymmetric surface-mediated alloying. Material leaves one side of the island by surface diffusion, and mixes with additional Si from the surrounding surface as it redeposits on the other side. Thus the island moves laterally while becoming larger and more dilute.
AU - Denker, Ulrich
AU - Rastelli, Armando
AU - Stoffel, Mathieu
AU - Tersoff, Jerry
AU - Georgios Katsaros
AU - Costantini, Giovanni
AU - Kern, Klaus
AU - Jin-Phillipp, Neng Y
AU - Jesson, David E
AU - Schmidt, Oliver G
ID - 1741
IS - 21
JF - Physical Review Letters
TI - Lateral motion of SiGe islands driven by surface-mediated alloying
VL - 94
ER -
TY - JOUR
AB - The effects of substrate temperature, growth rate, and postgrowth annealing on the composition of Ge islands grown on Si(001) were investigated with a combination of selective wet chemical etching and atomic force microscopy. A simple kinetic model comprising only surface diffusion processes can explain all the experimentally observed compositional profiles for pyramid and dome islands grown in the 560-620°C range. From this model three-dimensional compositional maps were extracted. By performing annealing experiments a change in the composition of the domes was observed. This could be explained as the result of the islands' movement induced by alloying-driven energy minimization. Also in this case kinetically hindered bulk diffusion processes are not needed to explain the experimental observations.
AU - Georgios Katsaros
AU - Costantini, Giovanni
AU - Stoffel, Mathieu
AU - Esteban, Rubén
AU - Bittner, Alexander M
AU - Rastelli, Armando
AU - Denker, Ulrich
AU - Schmidt, Oliver G
AU - Kern, Klaus
ID - 1742
IS - 19
JF - Physical Review B - Condensed Matter and Materials Physics
TI - Kinetic origin of island intermixing during the growth of Ge on Si (001)
VL - 72
ER -
TY - JOUR
AB - Laterally aligned multilayer GeSiSi islands grown on a patterned Si (001) substrate are disclosed by selective etching of Si in a KOH solution. This procedure allows us to visualize the vertical alignment of the islands in a three-dimensional perspective. Our technique reveals that partly coalesced double islands in the initial layer do not merge together, but instead gradually reproduce into well-separated double islands in upper layers. We attribute this effect to very thin spacer layers, which efficiently transfer the strain modulation of each island through the spacer layer to the surface. The etching rate of Si is reduced in tensile strained regions, which helps to preserve sufficient Si between the stacked islands to form a periodic array of freestanding and vertically modulated heterostructure pillars.
AU - Zhong, Zheyang
AU - Georgios Katsaros
AU - Stoffel, Mathieu
AU - Costantini, Giovanni
AU - Kern, Klaus
AU - Schmidt, Oliver G
AU - Jin-Phillipp, Neng Y
AU - Bauer, Günther
ID - 1743
IS - 26
JF - Applied Physics Letters
TI - Periodic pillar structures by Si etching of multilayer GeSi/Si islands
VL - 87
ER -
TY - JOUR
AB - This paper presents optical duobinary and dicode signalling, as alternatives to the binary format, in order to improve the transmission performance in the presense of non-linear effects in a dense wavelength division multiplex (WDM) optical system. Duobinary signalling is applied to an optical system to explore the reduction of stimulated Brillouin scattering (SBS) effects. Duobinary signalling suppresses the SBS effects, and an eye-opening improvement of 0.25 to 1.2 dB is achieved relative to binary transmission over a range of input power levels. An experimental study demonstrates that duobinary modulation suppresses the four wave mixing (FWM) products of a dense WDM system by a maximum of 3 dB. The suppression is maintained over a range of channel spacings. An investigation of the impact of fibre dispersion on FWM products under binary, duobinary and dicode modulation in a dense WDM system is then performed, with interchannel spacing and optical power variation. This leads to the development of a set of guidelines for the application areas, in which it is appropriate to use duobinary or dicode modulation in WDM systems as a means of mitigating the impact of FWM.
AU - Georgios Katsaros
AU - Darwazeh, Izzat Z
AU - Lane, Phil M
ID - 1744
IS - 6
JF - IEE Proceedings - Optoelectronics
TI - Non linear transmission effects in duobinary and dicode optical systems
VL - 152
ER -
TY - JOUR
AB - Background: Murine leukemia virus (MLV) vector particles can be pseudotyped with a truncated variant of the human immunodeficiency virus type 1 (HIV-1) envelope protein (Env) and selectively target gene transfer to human cells expressing both CD4 and an appropriate co-receptor. Vector transduction mimics the HIV-1 entry process and is therefore a safe tool to study HIV-1 entry. Results: Using FLY cells, which express the MLV gag and pol genes, we generated stable producer cell lines that express the HIV-1 envelope gene and a retroviral vector genome encoding the green fluorescent protein (GFP). The BH10 or 89.6 P HIV-1 Env was expressed from a bicistronic vector which allowed the rapid selection of stable cell lines. A codon-usage-optimized synthetic env gene permitted high, Rev-independent Env expression. Vectors generated by these producer cells displayed different sensitivity to entry inhibitors. Conclusion: These data illustrate that MLV/HIV-1 vectors are a valuable screening system for entry inhibitors or neutralizing antisera generated by vaccines.
AU - Sandra Siegert
AU - Thaler, Sonja
AU - Wagner, Ralf
AU - Schnierle, Barbara S
ID - 1795
IS - 1
JF - AIDS Research and Therapy
TI - Assessment of HIV-1 entry inhibitors by MLV/HIV-1 pseudotyped vectors
VL - 2
ER -
TY - JOUR
AB -
Complex I of respiratory chains plays a central role in bioenergetics and is implicated in many human neurodegenerative diseases. An understanding of its mechanism requires a knowledge of the organization of redox centers. The arrangement of iron-sulfur clusters in the hydrophilic domain of complex I from Thermus thermophilus has been determined with the use of x-ray crystallography. One binuclear and six tetranuclear clusters are arranged, maximally 14 angstroms apart, in an 84-angstrom-long electron transfer chain. The binuclear cluster N1a and the tetranuclear cluster N7 are not in this pathway. Cluster N1a may play a role in the prevention of oxidative damage. The structure provides a framework for the interpretation of the large amounts of data accumulated on complex I.
AU - Hinchliffe, Philip
AU - Leonid Sazanov
ID - 1962
IS - 5735
JF - Science
TI - Biochemistry: Organization of iron-sulfur clusters in respiratory complex I
VL - 309
ER -
TY - BOOK
AB - Harold Davenport was one of the truly great mathematicians of the twentieth century. Based on lectures he gave at the University of Michigan in the early 1960s, this book is concerned with the use of analytic methods in the study of integer solutions to Diophantine equations and Diophantine inequalities. It provides an excellent introduction to a timeless area of number theory that is still as widely researched today as it was when the book originally appeared. The three main themes of the book are Waring's problem and the representation of integers by diagonal forms, the solubility in integers of systems of forms in many variables, and the solubility in integers of diagonal inequalities. For the second edition of the book a comprehensive foreword has been added in which three prominent authorities describe the modern context and recent developments. A thorough bibliography has also been added.
AU - Davenport, Harold
AU - Timothy Browning
ID - 210
T2 - Analytic methods for diophantine equations and diophantine inequalities
TI - Analytic methods for diophantine equations and diophantine inequalities
ER -
TY - JOUR
AB - Let f ∈ ℤ[x] be a polynomial of degree d. The paucity of non-trivial positive integer solutions to the equation f(x1)+f(x 2)=f(x3)+f(x4) is established, provided that d ≤ 7$. Also the corresponding situation is investigated for equal sums of three like polynomials.
AU - Timothy Browning
ID - 211
IS - 6
JF - Bulletin of the London Mathematical Society
TI - Equal sums of like polynomials
VL - 37
ER -
TY - JOUR
AB - For any n ≧ 2, let F ∈ ℤ [ x 1, … , xn ] be a form of degree d≧ 2, which produces a geometrically irreducible hypersurface in ℙn–1. This paper is concerned with the number N(F;B) of rational points on F = 0 which have height at most B. For any ε > 0 we establish the estimate N(F; B) = O(B n− 2+ ε ), whenever either n ≦ 5 or the hypersurface is not a union of lines. Here the implied constant depends at most upon d, n and ε.
AU - Timothy Browning
AU - Heath-Brown, Roger
ID - 212
IS - 584
JF - Journal fur die Reine und Angewandte Mathematik
TI - Counting rational points on hypersurfaces
ER -
TY - JOUR
AB - Given an absolutely irreducible ternary form F, the purpose of this paper is to produce better upper bounds for the number of integer solutions to the equation F=0, that are restricted to lie in very lopsided boxes. As an application of the main result, a new paucity estimate is obtained for equal sums of two like powers.
AU - Timothy Browning
AU - Heath-Brown, Roger
ID - 214
IS - 2
JF - Mathematische Zeitschrift
TI - Plane curves in boxes and equal sums of two powers
VL - 251
ER -