Experimental observation of moving intrinsic localized modes in germanium

Deep level transient spectroscopy shows that defects created by alpha irradiation of germanium are annealed by low energy plasma ions up to a depth of several thousand lattice units. The plasma ions have energies of 2-8eV and therefore can deliver energies of the order of a few eV to the germanium atoms. The most abundant defect is identified as the E-center, a complex of the dopant antimony and a vacancy with and annealing energy of 1.3eV as determined by our measurements. The inductively coupled plasma has a very low density and a very low flux of ions. This implies that the ion impacts are almost isolated both in time and at the surface of the semiconductor. We conclude that energy of the order of an eV is able to travel a large distance in germanium in a localized way and is delivered to the defects effectively. The most likely candidates are vibrational nonlinear wave packets known as intrinsic localized modes, which exist for a limited range of energies. This property is coherent with the fact that more energetic ions are less efficient at producing the annealing effect.Comment: 20 pages, 10 figure

Rate theory of acceleration of the defect annealing driven by discrete breathers

Novel mechanisms of defect annealing in solids are discussed, which are based on the large amplitude anharmonic lattice vibrations, a.k.a. intrinsic localized modes or discrete breathers (DBs). A model for amplification of defect annealing rate in Ge by low energy plasma-generated DBs is proposed, in which, based on recent atomistic modelling, it is assumed that DBs can excite atoms around defects rather strongly, giving them energy $\gg k_BT$ for $\sim$100 oscillation periods. This is shown to result in the amplification of the annealing rates proportional to the DB flux, i.e. to the flux of ions (or energetic atoms) impinging at the Ge surface from inductively coupled plasma (ICP)Comment: 18 pages, 11 figures. arXiv admin note: text overlap with arXiv:1406.394

Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV

The interplay of intrinsic and extrinsic bounded noises in genetic networks

After being considered as a nuisance to be filtered out, it became recently clear that biochemical noise plays a complex role, often fully functional, for a genetic network. The influence of intrinsic and extrinsic noises on genetic networks has intensively been investigated in last ten years, though contributions on the co-presence of both are sparse. Extrinsic noise is usually modeled as an unbounded white or colored gaussian stochastic process, even though realistic stochastic perturbations are clearly bounded. In this paper we consider Gillespie-like stochastic models of nonlinear networks, i.e. the intrinsic noise, where the model jump rates are affected by colored bounded extrinsic noises synthesized by a suitable biochemical state-dependent Langevin system. These systems are described by a master equation, and a simulation algorithm to analyze them is derived. This new modeling paradigm should enlarge the class of systems amenable at modeling. We investigated the influence of both amplitude and autocorrelation time of a extrinsic Sine-Wiener noise on: $(i)$ the Michaelis-Menten approximation of noisy enzymatic reactions, which we show to be applicable also in co-presence of both intrinsic and extrinsic noise, $(ii)$ a model of enzymatic futile cycle and $(iii)$ a genetic toggle switch. In $(ii)$ and $(iii)$ we show that the presence of a bounded extrinsic noise induces qualitative modifications in the probability densities of the involved chemicals, where new modes emerge, thus suggesting the possibile functional role of bounded noises

Bistability and Oscillations in Gene Regulation Mediated by Small Noncoding RNAs

The interplay of small noncoding RNAs (sRNAs), mRNAs, and proteins has been shown to play crucial roles in almost all cellular processes. As key post-transcriptional regulators of gene expression, the mechanisms and roles of sRNAs in various cellular processes still need to be fully understood. When participating in cellular processes, sRNAs mainly mediate mRNA degradation or translational repression. Here, we show how the dynamics of two minimal architectures is drastically affected by these two mechanisms. A comparison is also given to reveal the implication of the fundamental differences. This study may help us to analyze complex networks assembled by simple modules more easily. A better knowledge of the sRNA-mediated motifs is also of interest for bio-engineering and artificial control

Gene switching rate determines response to extrinsic perturbations in the self-activation transcriptional network motif

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Spectroscopic observation of the TDD0 in silicon

The electronic transitions of 16 neutral thermal double donors (TDD1-TDD16) and of nine positively charged species (TDD1-TDD9) were observed previously in infrared absorption spectra. An earlier species (TDD0) was detected, however, only in persistent photoconductivity and Hall effect studies. In the present work, lines related to the electronic transitions from the ground to excited states in both neutral and singly ionized charge states of the TDD0 have been identified by infrared absorption and bistability of the defect has been confirmed. (C) 2003 Elsevier B.V. All rights reserved

Local vibrational modes of the oxygen-vacancy complex in germanium

Infrared absorption of n- and p-Ge crystals enriched with O-16 and/or O-18 isotopes was studied after irradiation with 6-MeV electrons. Absorption spectra were measured at 10 and 300 K. Along with known bands characteristic of oxygen-containing defects, new lines at 669, 944, and 990 cm(-1) were detected. These bands are annealed at temperatures of 120-140degreesC; the band at 621 cm(-1), previously related to the vacancy-oxygen complex in Ge, is simultaneously annealed. The bands at 621 and 669 cm(-1) showed identical temperatures (10 --> 300 K) and oxygen isotope (O-16 --> O-18) shifts. These bands were found to correspond to various charge states of a defect with an energy level near E-v = 0.25 +/- 0.03 eV. It is assumed that such a defect is the vacancy-oxygen complex (A center). The weak bands at 944 and 990 cm(-1) were identified as combinations of asymmetric stretching modes at 621 and 669 cm(-1) with a symmetric one at 320 cm(-1) for neutral and negative charge states of the A center, respectively