Resistive switching control for conductive Si-nanocrystals embedded in Si/SiO2 multilayers.

In this paper, we report on the enhanced control of resistive switching in multilayer Si/SiO2 structures, which permit the formation of Si nanocrystals with a typical size of 5.88 nm and overall good shape homogeneity. The deposition of a different number of Si and SiO2 bilayers (6, 8 and 10) allowed control of SET/RESET voltages in negative bias ranges 4.5-10 V and 6.3-13 V for six- and ten-bilayer devices, respectively. The corresponding resistance ratio between ON/OFF states varied in the ranges 107-105 for the aforementioned number of bilayers. Based on the result of XPS measurements, we suggest that the resistive switching in the studied system occurs due to the formation and annihilation of Si-Si and Si-O bonds, which serve as conductive pathways and isolating material, respectively.

Fluorescence properties of Yb3+-Er3+ co-doped phosphate glasses containing silver nanoparticles.

Er3+-Yb3+ co-doped phosphate glasses containing silver nitrate (SN), were fabricated. Transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analyses were used to evidence the nucleation and presence of silver nanoparticles (SNP). The basic parameters of the glasses were inspected by means of absorption and fluorescence spectra, and fluorescence lifetimes under excitation at 916 nm (in-band of Yb3+), and at 406 nm (in-band of surface plasmon resonance given by the presence of SNP). The spectra as well as estimates for the basic parameters defining the lasing/amplifying potential of the glasses were studied as a function of SN concentration. The experimental results indicate that by increasing the SN content an enhancement of Er3+/Yb3+ fluorescence takes place.

Physical properties of inulin and inulin-orange juice: physical characterization and technological application.

In this work two systems based on a carbohydrate polymer were studied: inulin as model system and inulin-orange juice as complex system. Both system were stored at different water activity conditions and subsequently characterized. Water adsorption isotherms type II were fitted by the GAB model and the water monolayer content was determined for each system. From thermal analyzes it was found that at low water activities (aw) systems were fully amorphous. As aw increased, crystallinity was developed. This behavior was corroborated by X-ray diffraction. In the inulin-orange juice system, crystallization appears at lower water activity caused by the intensification of the chemical interaction of the low molecular weight species contained in orange juice. Glass transition temperature (Tg), determined by modulated differential scanning calorimeter, decreased with aw. As water is adsorbed, the physical appearance of samples changed which could be observed by optical microscopy and effectively related with the microstructure found by scanning electron microscopy.

Glass transition study in model food systems prepared with mixtures of fructose, glucose, and sucrose.

The glass transition temperature of model food systems prepared with several glucose/fructose/sucrose mass fractions was studied using differential scanning calorimetry (DSC). A distance-based experimental design for mixtures of 3 components was used to establish the proportion of sugars of the model systems. Thus, 32 compositions including individual sugars and sugar mixtures, both binary and ternary were prepared and analyzed. Thermograms showing the complete process of heating-cooling-reheating were used to determine the precise glass transition temperature during cooling (T(g)(c)) or reheating (T(g)(H) in amorphous sugars. The Scheffe cubic model was applied to experimental results to determine the influence of sugar composition on the glass transition temperature (P < 0.05). The final model proved to be appropriate (R(2) > 0.97, CV < 9%, model significance <0.0001) to predict the T(g) values of any dry mixture of amorphous fructose, glucose, and sucrose.