Characterization of defect removal in hydrogenated and deuterated amorphous silicon thin film transistors

Thin film transistors (TFTs) utilizing an hydrogenated amorphous silicon (a-Si:H) channel layer exhibit a shift in the threshold voltage with time under the application of a gate bias voltage due to the creation of metastable defects. These defects are removed by annealing the device with zero gate bias applied. The defect removal process can be characterized by a thermalization energy which is, in turn, dependent upon an attempt-to-escape frequency for defect removal. The threshold voltage of both hydrogenated and deuterated amorphous silicon (a-Si:D) TFTs has been measured as a function of annealing time and temperature. Using a molecular dynamics simulation of hydrogen and deuterium in a silicon network in the H2 * configuration, it is shown that the experimental results are consistent with an attempt-to-escape frequency of (4.4 ± 0.3) × 1013 Hz and (5.7 ± 0.3) × 1013 Hz for a-Si:H and a-Si:D respectively which is attributed to the oscillation of the Si-H and Si-D bonds. Using this approach, it becomes possible to describe defect removal in hydrogenated and deuterated material by the thermalization energies of (1.552 ± 0.003) eV and (1.559 ± 0.003) eV respectively. This correlates with the energy per atom of the Si-H and Si-D bonds. © 2006 Elsevier B.V. All rights reserved.

EBSD characterisation of Y2Ba4CuUOx phase in melttextured YBCO with addition of depleted uranium oxide

Melt-textured YBCO samples processed with added Y2O3 and depleted uranium oxide (DU) contain nano-particles, which have been identified previously as Y2Ba4CuUOx (U-411). This phase has a cubic unit cell, which is clearly distinct from the orthorhombic Y-123 and Y-211 phases within the YBCO system. In samples with a high amount of DU addition (0.8 wt-% DU), U-2411 particles have sizes between 200 nm and several νm, so identification of the Kikuchi patterns of this phase becomes possible. Together with a parallel EDX analysis, the particles embedded in the Y-123 matrix can be identified unambiguously. In this way, a three-phase EBSD scan becomes possible, allowing also the identification of nanometre-sized particles in the sample microstructure. © 2006 IOP Publishing Ltd.

Dissecting Arabidopsis thaliana DICER function in small RNA processing, gene silencing and DNA methylation patterning.

Small RNAs have several important biological functions. MicroRNAs (miRNAs) and trans-acting small interfering RNAs (tasiRNAs) regulate mRNA stability and translation, and siRNAs cause post-transcriptional gene silencing of transposons, viruses and transgenes and are important in both the establishment and maintenance of cytosine DNA methylation. Here, we study the role of the four Arabidopsis thaliana DICER-LIKE genes (DCL1-DCL4) in these processes. Sequencing of small RNAs from a dcl2 dcl3 dcl4 triple mutant showed markedly reduced tasiRNA and siRNA production and indicated that DCL1, in addition to its role as the major enzyme for processing miRNAs, has a previously unknown role in the production of small RNAs from endogenous inverted repeats. DCL2, DCL3 and DCL4 showed functional redundancy in siRNA and tasiRNA production and in the establishment and maintenance of DNA methylation. Our studies also suggest that asymmetric DNA methylation can be maintained by pathways that do not require siRNAs.