Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

The structural relaxation of pure amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) materials, that occurs during thermal annealing experiments, has been analysed by Raman spectroscopy and differential scanning calorimetry. Unlike a-Si, the heat evolved from a-Si:H cannot be explained by relaxation of the Si-Si network strain, but it reveals a derelaxation of the bond angle strain. Since the state of relaxation after annealing is very similar for pure and hydrogenated materials, our results give strong experimental support to the predicted configurational gap between a-Si and crystalline silicon.Comment: 15 pages, 3 figures, 1 table to be published in Applied Physics Letter

Can the crystallization rate be independent from the crystallization enthalpy? The case of amorphous silicon

The crystallization enthalpy measured in a large series of amorphous silicon (a-Si) materials varies within a factor of 2 from sample to sample (Kail et al 2011 Phys. Status Solidi RRL 5 361). According to the classical theory of nucleation, this variation should produce large differences in the crystallization kinetics leading to crystallization temperatures and activation energies exceeding 550 C and 1.7 eV, respectively, the ‘standard’ values measured for a-Si obtained by self-implantation. In contrast, the observed crystallization kinetics is very similar for all the samples studied and has no correlation with the crystallization enthalpy. This discrepancy has led us to propose that crystallization in a-Si begins in microscopic domains that are almost identical in all samples, independently of their crystallization enthalpy. Probably the existence of microscopic inhomogeneities also plays a crucial role in the crystallization kinetics of other amorphous materials and glasses

The configurational energy gap between amorphous and crystalline silicon

The crystallization enthalpy of pure amorphous silicon (a-Si) and hydrogenated a-Si was measured by differential scanning calorimetry (DSC) for a large set of materials deposited from the vapour phase by different techniques. Although the values cover a wide range (200-480 J/g), the minimum value is common to all the deposition techniques used and close to the predicted minimum strain energy of relaxed a-Si (240 ± 25 J/g). This result gives a reliable value for the configurational energy gap between a-Si and crystalline silicon. An excess of enthalpy above this minimum value can be ascribed to coordination defects

"Solid Phase Crystallized Silicon Thin Films Deposited by High Rate Electron Beam Evaporation: improvedstructural and electrical properties"

International audienc

Odd electron diffraction patterns in silicon nanowires and silicon thin films explained by microtwins and nanotwins

International audienc

Odd electron diffraction patterns in silicon nanowires and silicon thin films explained by microtwins and nanotwins

Odd electron diffraction patterns (EDPs) have been obtained by transmission electron microscopy (TEM) on silicon nanowires grown via the vapour-liquid-solid method and on silicon thin films deposited by electron beam evaporation. Many explanations have been given in the past, without consensus among the scientific community: size artifacts, twinning artifacts or, more widely accepted, the existence of new hexagonal Si phases. In order to resolve this issue, the microstructures of Si nanowires and Si thin films have been characterized by TEM, high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning transmission electron microscopy. Despite the differences in the geometries and elaboration processes, the EDPs of the materials show great similarities. The different hypotheses reported in the literature have been investigated. It was found that the positions of the diffraction spots in the EDPs could be reproduced by simulating a hexagonal structure with c/a = 12(2/3) 1/2, but the intensities in many EDPs remained unexplained. Finally, it was established that all the experimental data, i.e. EDPs and HRTEM images, agree with a classical cubic silicon structure containing two microstructural defects: (i) overlapping Σ3 microtwins which induce extra spots by double diffraction, and (ii) nanotwins which induce extra spots as a result of streaking effects. It is concluded that there is no hexagonal phase in the Si nanowires and the Si thin films presented in this work. © Cyril Cayron et al. 2009

Clin Drug Investig

Background and Objectives Non-interventional studies are a valuable source of evidence that is complementary to traditional randomised, blinded and controlled clinical trials, for evaluating antidepressants in a real-world setting. The aim of the present study was to document the use of agomelatine in current medical practice and evaluate its effectiveness and safety in outpatients prescribed agomelatine to treat their current depressive episode. Methods This 12-month observational French study included patients initiating agomelatine treatment. The intensity and severity of depression were assessed using the 17-item Hamilton Depression Rating Scale (HAM-D17) total score and the Clinical Global Impression-Severity of Illness (CGI-S) scale. Patients’ quality of life and functioning were measured using the Quality of Life in Depression Scale and the Sheehan Disability Scale, respectively. The safety measures included emergent adverse events and biological samplings, with a focus on liver acceptability. Results A total of 1484 patients (70% of women; 49.6 ± 15.4 years of age) were enrolled in the study. Most patients (62.3%) were treated with agomelatine for at least 6 months and 28.8% were treated for at least 1 year. Mean HAM-D17 total score and mean CGI-S scores decreased by 13.6 ± 8.1 and 2.1 ± 1.5 points, respectively, from baseline to last visit on agomelatine. Rates of responders (i.e. with a decrease in HAM-D17 total score by at least 50%) and remitters (HAM-D total score < 7) at the last visit were 90.7% and 56.0%, respectively. The mean HAM-D total score decreased after agomelatine withdrawal (− 4.1 ± 6.7) until the last visit. The quality of life and daily functioning of patients improved, while the numbers of days lost and underproductive days decreased over the follow-up period. Safety findings were in accordance with the known information regarding agomelatine. Conclusion In the current medical practice, this study confirms the effectiveness and good tolerability of agomelatine administered for a treatment period in agreement with guideline recommendations

The configurational energy gap between amorphous and crystalline silicon

The crystallization enthalpy of pure amorphous silicon (a-Si) and hydrogenated a-Si was measured by differential scanning calorimetry (DSC) for a large set of materials deposited from the vapour phase by different techniques. Although the values cover a wide range (200-480 J/g), the minimum value is common to all the deposition techniques used and close to the predicted minimum strain energy of relaxed a-Si (240 ± 25 J/g). This result gives a reliable value for the configurational energy gap between a-Si and crystalline silicon. An excess of enthalpy above this minimum value can be ascribed to coordination defects