, Hamide Eskandari Torbaghan,
Volume 11, Issue 3 (2-2011)
Abstract
This study presents the electric behavior of sandwich devices based on porous silicon (PS) thin films with Au/Ps/Si/Cu structure when the material’s surface is exposed to different gases. PS thin films were fabricated by the electrochemical anodization method of Si–c (100) substrates with resistivity 1.4-2.6 Ωcm. Samples were anodized in a solution of HF (48%), C2H5OH (99.98%) and distilled water with different current densities, etching time(t) and anodization length(L). They exhibit a different behavior after anodization process. This behavior can be explained by band gap measurement on graph. In this research, measurement of I-V and I-T characteristics were carried out at different conditions, in the presence of O2, N2 and Co2 gases for gas sensing construction. The best response to gas exposure belonged to these parameters: current density= 20 mA/cm2 ،t = 1800 S ، PH = 1.869 and L = 4 cm.
Amir Eskandari, F Masoudi, N Farahkhah,
Volume 12, Issue 2 (11-2012)
Abstract
In this research, based on spatial distribution and size of crystals, the role of physical processes affecting formation of the igneous rocks such as kinetics of crystallization (nucleation and growth of crystals), dynamics of magmatic systems (e.g. mixing and convection currents) and equilibrium processes such as textural coarsening are investigated.
To this end, the spatial distribution pattern (SDP) of plagioclase, amphibole and quartz crystals were quantified in the microdiorite-quartz diorites and results were combined with petrography to discuss the factors affecting plagioclase packing arrangements and physical processes operated during formation of these rocks. The study area is located in 120 Km southeast of Birjand. The 8 thin sections of rocks were processed and geometrical features e.g. length, width and centre of 3098 crystals were measured. Then, R values (a descriptive value) were measured using nearest neighbor distance method with BigR and ArcGIS software's and the data were plotted against porosity (modal abundance of other phases in igneous rocks.) Results show that crystals have clustered SDP. The degree of plagioclases clustering is different in sections with change of crystal sizes and shapes. The origin of crystal clusters is likely to involve heterogeneous nucleation, textural coarsening and overgrowth of crystals.
