பொருள் அறிவியல் & பொறியியல் இதழ்

The influence of a thermoannealing on electrical conduction of silicon monocrystals doped by cobalt has been studied. Also, analysis of sequence of the impurity nanoinclusion’s disinteration under influence of thermoannealing has been carried out by the method of electron-probe microanalysis.

The electrochemical control of molecular concentrations in liquids is quite challenging because of the small ratio of interacting sites between the electrode surface and the number of molecules in the volume. Here we review our recent works aiming the control of proton concentration combining redox self-assembled monolayers with a modified platform. We used Aminothiolphenol, to obtain coatings with quasi-reversible redox states able to exchange protons with the electrolyte at low voltages using different polymerization methods. We studied their charge exchange during different cycles, which would provide us the possibility to use different cycles of reactions controlled by acidity. We achieved the control of proton concentration over the liquid with an efficient design of the microfluidic device to control the diffusion of protons avoiding the reduction of hydrogen at the counter electrode and providing long lasting stability to carry control of chemical reactions during several tenths of minutes. The experiments were carried out in aqueous environment using a pH fluorescence marker to track the pH that allowed us to monitor the proton concentration down to pH 5, where the fluorescence molecule lost its sensitivity, while calculations indicate that the pH can be below 1.

We report systematic investigation of thickness dependent surface topography, magnetic properties and magnetic domain structures of amorphous Fe₈₀Ta₈C₁₂ (x nm) films with x=5–100 nm. All the as-deposited films fabricated directly on thermally oxidized Si substrate at ambient temperature using magnetron sputtering technique exhibit amorphous structure. The structural studies reveal that island-like structure in ultra-thin films transforms into continuous one with increasing x>10. In addition, the average surface roughness increases with increasing x, but without any systematic dependency on x. Room temperature magnetic properties illustrate that the paramagnetic nature observed for films with x<10 changes into ferromagnetic one with rectangular loops having high remanence ratio (M_R/M_S>97%), low coercivity (H_C<1.77 kA/m), low saturation field (H_S<2.2 kA/m) and simple magnetization reversal behavior for x up to 40 nm. Upon increasing x ≥ 50, the loop shape again changes into transcritical one with increased H_C (>3.5 kA/m) and H_S (>40 kA/m) and reduced M_R/M_S (<45%). The magnetic domain studies not only reveal that the domains change from in-plane magnetization to dense stripe domain pattern with increasing x due to enhancement of effective magnetic anisotropy caused by stress quenched in during deposition, but also confirm that films with 12<x<40 exhibit in-plane magnetization with uniaxial anisotropy. High temperature thermomagnetization reveal a clear magnetic phase transition from ferromagnetic to paramagnetic state at relatively higher temperature of about 530 K. The observed results are elucidated on the basis of enhanced effective magnetic anisotropy, change in the magnetic domain structure and magnetic disorder with increasing FeTaC film thickness.

Wound dressing has remained challenging for some life-threatening wounds such as burning. Researchers have been engaged in looking for better solutions. This review paper depicted the ideal wound dressing based on the mechanism of human skins, compared traditional wound dressing methods to modern methods, and reviewed the use of polymers and biopolymers as advanced materials for wound dressing.

While 2D culture models have been used extensively to elucidate the cell-to-cell communication, they do not recapitulate fully the 3D characteristics of microenvironment in vivo, e.g., polarized cell attachment and generally confer a considerably stiffer substrate than the endogenous extracellular matrix. Development of fibrous scaffolds that can better mimic the native microenvironment and improve the spatial arrangement of seeded cells should foster experimental strategies to monitor and determine the 3D cell-to-cell communication. In this study, poly(ε- caprolactone) (PCL) fibers were fabricated in different sizes using a microfluidic platform and spatially arranged to create a suitable 3D microenvironment in order to investigate the cell viability and calcium signaling in mouse astrocytes. A powerful algorithm, referred to as wavelet transform coherence (WTC), was applied to establish the correlation between astrocytes that were seeded on the PCL fiber. As expected, two astrocytes that appeared to be in physical contact showed high correlation, whereas two astrocytes seeded within a few cell lengths but not in physical contact showed negligible correlation. The WTC correlation analysis of a cluster of six astrocytes seeded on a single PCL fiber led to surprising results that the cells can communicate over many cell lengths without being in physical contact. More systematic studies using spatially controlled 3D microenvironment will likely help unravel the intricate cell communication mechanisms.

Although several theories have been proposed, the mechanism of complex photoluminescence in carbon dots (CNDs) is a central quest till date. This report presents pH dependent steady state and time resolved spectroscopy study which identifies a possible origin of the complex photoluminescence in CNDs. The multiple emissive species created by the excited state protonation-deprotonation reaction at certain pH gives rise to inhomogeneous broadening and consequently excitation dependent multicolour emission. The origin of the excited state dynamics is attributed to the significant change of the proton dissociation between ground and excited state. We present a new model on protonation dynamics and show how it affects the emissive states in CNDs.