Semiconductor nanowires for novel one-dimensional devices

Low-dimensional semiconductors offer interesting physical phenomena but also the possibility to realize novel types of devices based on, for instance, 1D structures. By using traditional top-down fabrication methods the performance of devices is often limited by the quality of the processed device structures. In many cases damage makes ultra-small devices unusable. In this work we present a recently developed method for bottom-up fabrication of epitaxially nucleated semiconductor nanowires based on metallic nanoparticle-induced formation of self-assembled nanowires. Further development of the vapor–liquid–solid growth method have made it possible to control not only the dimension and position of nanowires but also to control heterostructures formed inside the nanowires. Based on these techniques we have realized a series of transport devices such as resonant tunneling and single-electron transistors but also optically active single quantum dots positioned inside nanowires displaying sharp emission characteristics due to excitons.     

On the mechanism of the pseudocatalatic degradation of hydrogen peroxide by lactoperoxidase/iodide

Hydrogen peroxide is catalytically disproportionated by lactoperoxidase in the presence of iodide ions, Km = 55 microM in 100 mM sodium phosphate, pH 7.00, 25 degrees C. Products formed are water and molecular oxygen. The reaction is competitively inhibited by hydrogen sulfite, Ki = 0.24 mM in 100 mM sodium phosphate, pH 7.00, 25 degrees C. The stoichiometry of the reaction is identical with the corresponding catalase reaction but the mechanism differs. A mechanistic model for lactoperoxidase-iodide dismutation of hydrogen peroxide is discussed.     

Weak magnetism in chiral quark models

We discuss symmetry breaking in the weak magnetism form factors for the semileptonic octet baryon decays. In the chiral quark model, the symmetry breaking can be accounted for in the masses and the quark spin polarizations can take on more general values due to Goldstone boson depolarization. Here we clarify some features of the chiral quark model prediction for the weak magnetism and compare to the corresponding result of the chiral quark soliton model. Received: 29 June 1999 / Revised version: 15 September 1999 / Published online: 8 December 1999     

Coherent transient data-rate conversion and data transformation

Temporal compressions of optical pulses and pulse trains have been performed by the photon-echo process in Tm-doped YAG at 793 nm. Single-pulse temporal compression by almost a factor of 500 from 10 micros to 22 ns and pulse train compression by a factor of 14 from 5micros to 350 ns with a high-speed frequency-tunable external-cavity diode laser are demonstrated. It is suspected that significantly higher compression could be obtained by improved control of the laser frequency and laser frequency chirps. Theoretically, Tm-doped YAG should be capable of compressing single pulses by almost a factor of 10(7).     

Non-standard interactions using the OPERA experiment

We investigate the implications of non-standard interactions on neutrino oscillations in the OPERA experiment. In particular, we study the non-standard interaction parameter ε _{μ τ} . We show that the OPERA experiment has a unique opportunity to reduce the allowed region for this parameter compared with other experiments such as the MINOS experiment, mostly due to the higher neutrino energies in the CNGS beam compared to the NuMI beam. We find that OPERA is mainly sensitive to a combination of standard and non-standard parameters and that a resulting anti-resonance effect could suppress the expected number of events. Furthermore, we show that running OPERA for five years each with neutrinos and anti-neutrinos would help in resolving the degeneracy between the standard parameters and ε _{μ τ} . This scenario is significantly better than the scenario with a simple doubling of the statistics by running with neutrinos for ten years.