Observation of Metastable and Stable Energy Levels of EL2 in Semi-insulating GaAs

By using combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in the light of the recently proposed models for stable and metastable configurations of EL2 in GaAs

A Hybrid model for the origin of photoluminescence from Ge nanocrystals in SiO2_2 matrix

In spite of several articles, the origin of visible luminescence from germanium nanocrystals in SiO$_2$ matrix is controversial even today. Some authors attribute the luminescence to quantum confinement of charge carriers in these nanocrystals. On the other hand, surface or defect states formed during the growth process, have also been proposed as the source of luminescence in this system. We have addressed this long standing query by simultaneous photoluminescence and Raman measurements on germanium nanocrystals embedded in SiO$_2$ matrix, grown by two different techniques: (i) low energy ion-implantation and (ii) atom beam sputtering. Along with our own experimental observations, we have summarized relevant information available in the literature and proposed a \emph{Hybrid Model} to explain the visible photoluminescence from nanocrystalline germanium in SiO$_2$ matrix.Comment: 23 pages, 8 figure

A microscopic complex potential description of elastic, inelastic cross section in the Coulomb nuclear interference region in the 28Si on 28Si system

Elastic and inelastic angular distribution and excitation functions were measured for the 28Si + 28Si system in the vicinity of the Coulomb barrier. While the elastic data could be described very well by using fully microscopic complex potential, the inelastic cross sections were found to be more sensitive to small variations in the potential. In particular the Coulomb nuclear interference dip observed in the inelastic excitation functions could not be fitted satisfactorily with calculation. Inclusion of an energy dependent term of Gaussian shape to the associated matrix element with the reorientation coupling in the phenomenological calculations leads to a better fit the inelastic excitation functions. © 1998 Elsevier Science B.V

How to increase technology transfers to developing countries: a synthesis of the evidence

The existing United Nations Framework Convention on Climate Change (UNFCCC) has failed to deliver the rate of low-carbon technology transfer (TT) required to curb GHG emissions in developing countries. This failure has exposed the limitations of universalism and renewed interest in bilateral approaches to TT. Gaps are identified in the UNFCCC approach to climate change TT: missing links between international institutions and the national enabling environments that encourage private investment; a non-differentiated approach for (developing) country and technology characteristics; and a lack of clear measurements of the volume and effectiveness of TTs. Evidence from econometric literature and business experience on climate change TT is reviewed, so as to address the identified pitfalls of the UNFCCC process. Strengths and weaknesses of different methodological approaches are highlighted. International policy recommendations are offered aimed at improving the level of emission reductions achieved through TT

Visual tool for estimating the fractal dimension of images

This work presents a new Visual Basic 6.0 application for estimating the fractal dimension of images, based on an optimized version of the box-counting algorithm. Following the attempt to separate the real information from noise, we considered also the family of all band-pass filters with the same band-width (specified as parameter). The fractal dimension can be thus represented as a function of the pixel color code. The program was used for the study of paintings cracks, as an additional tool which can help the critic to decide if an artistic work is original or not. In its second version, the application was extended for working also with csv files and three-dimensional images.Comment: A new version was accepted to Computer Physics Communications doi:10.1016/j.cpc.2009.12.00

Mechanistic details of the formation and growth of nanoscale voids in Ge under extreme conditions within an ion track

The formation of nanoscale voids in amorphous-germanium (a-Ge), and their size and shape evolution under ultra-fast thermal spikes within an ion track of swift heavy ion, is meticulously expatiated using experimental and theoretical approaches. Two step energetic ion irradiation processes were used to fabricate novel and distinct embedded nanovoids within bulk Ge. The 'bow-tie' shape of voids formed in a single ion track tends to attain a spherical shape as the ion tracks overlap at a fluence of about 1 x 10(12) ions cm(-2). The void assumes a prolate spheroid shape with major axis along the ion trajectory at sufficiently high ion fluences. Small angle x-ray scattering can provide complementary information about the primary stage of void formation hence this technique is applied for monitoring simultaneously their formation and growth dynamics. The results are supported by the investigation of cross-sectional transmission and scanning electron micrographs. The multi-time-scale theoretical approach corroborates the experimental findings and relates the bow-tie shape void formation to density variations as a result of melting and resolidification of Ge within the region of thermal spike generated along an ion track, plus non-isotropic stresses generated towards the end of the thermal spike.Peer reviewe