Advanced Materials Research Vols. 622-623

Abstract: We present the study of the growth of ZnO nanorods on p-Si (100) using MBE. Various characterization techniques such as Fourier transform infra-red (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and capacitance – voltage (C-V) measurements were employed to analyze and assess the grown ZnO nanorods. AFM clearly demonstrated the growth of vertically aligned nanorods, however, they get diffused as the thickness of the layer is increased beyond 1 µm. C-V measurements in particular, justified p-n junction between Si/ZnO nanorods. The junction showed n-type conductivity with carrier concentration 1×10¹⁵ cm^-3. The source of this n-type conductivity was Zn-interstitials and the presence of Zn-interstitials was confirmed by EDAX and Raman spectroscopy. Experimental detail and results were presented that help in furtherance of our understanding of the material issues and its potential as required for the practical devices.

Abstract: In this paper, a batch of M- type strontium hexaferrite samples with nominal composition of SrFe_12-xCo_xO₁₉(where x= 0- 2), have been synthesized via sol- gel method. In the synthesis of samples, first a precursor gel was prepared, and then dry- gel was calcined at 1000°C for 2 hours to obtain the nano- SrFe_12-xCo_xO₁₉. The XRD results revealed that for SrFe12-xCoxO19 samples with x≤0.5, all of them have single- phase hexaferrite structure and also this data suggests that the F ³⁺ ions are substituted by Co²⁺ ions in the crystallography sites of the SrFe_12-xCo_xO₁₉, but for the samples with x>0.5, the second phase of CoFe2O4 is appeared and suggests that the Co²⁺ ions also make a distinct phase in the samples. The magnetic properties, such as saturation magnetization (Ms), magnetic remanence (Mr), magnetic coercivity (Hc), squareness ratio (Mr/Ms), crystalline anisotropy field (Ha), energy product [(BH)max] and the susceptibility χ as the derivative of M with respect to H of the upper branch of the hysteresis loop were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). The magnetic measurements revealed that the coercively (Hc) values of all the samples decrease with increasing dopant contents.

Abstract: In this study, Photosan (PS) was loaded onto hollow silica nanospheres using one-step wet chemical-based synthetic route method. Polydispersive index of the Photosan-loaded hollow Silica Nanospheres (PS-loaded NSs) is 0.121±0.01. The photobiological activity of the PS-loaded NSs was evaluated on human cholangiocarcinoma QBC939 cells. Cells were incubated with free PS or PS-loaded NSs for 2 h and then washed with phosphate-buffered saline. Culture medium was added to the wells containing the cells. Finally, the cells were exposed to red light (630 nm) with a light dose of 10J/cm². The cellular viability was determined after 24 h of incubation. PS-loaded NSs and free PS eliminated about 96.4%±2.0% and 54.7%±1.9% of QBC939 cells, respectively. The phototoxicity was time dependent up to 2 h and concentration dependent at 1-7.5 mg/l. The cells viability decreased with the increase of the light dose in the range of 5-15 J/cm². In conclusion, PS-loaded NSs are the release systems that promise photodynamic therapy use.

Abstract: In this paper, a solid-state dye sensitized solar cell (DSSC) based on carbon nanotubes by inserting N719 dye molecules has been designed for operating at 300oK and 330oK temperatures. The role of carbon nanotubes as hole and electron conducting agents and dye molecules as absorber of solar radiation and hole-electron pair producing agents has been discussed. After inserting N719 dye, parameters of the cell such as absorption coefficient of both layers (ZNO+SWNT, P3HT+SWNT), current density of solar cell , internal and external quantum efficiency of P3HT+SWNT layer have been obtained at 300oK and 330oK, numerically. Then, improvement value of energy conversion efficiency of the cell has been compared after inserting carbon nanotubes.

Abstract: The present study describes metal-metal bonding process using mixture of CuO nanoparticles and Ag₂O nanoparticles (Ag2O/CuO mixed particles). The leaf-like aggregates with a longitudinal size of 1116 nm and a lateral size of 460 nm composed of CuO nanoparticles with a size of ca. 10 nm and the Ag₂O nanoparticles with a size of 20.6 nm were fabricated with a salt-base reaction. Metal-metal bonding could be successfully performed by using the mixed particles as a filler sandwiched between metallic discs and pressurizing the discs at 1.2 MPa for 5 min under annealing in H2 gas at 400oC. The mixed particles bonded not only metallic Cu discs but also metallic Ag discs strongly; The shear strengths were as large as 17.3 and 22.4 MPa for the Cu discs and the Ag discs, respectively.

Abstract: Nanocrystallization of anatase phase was established in BaO-TiO2-B2O3 glass system. Crystallization kinetics of anatase phase in these glasses were investigated using non-isothermal differential scanning calorimetry (DSC) at three different heating rates (10, 20 & 30 K/min). Scanning Electron Microscopy (SEM) carried out on heat treated (at 920 K) glasses confirmed bulk nucleation and three-dimensional growth. Johnson-Mehl-Avarami model could not be applied for this system suggesting considerable overlap of the nucleation and growth involving complex transformation process. However, modified Kissinger and Ozawa models were used to calculate the effective activation energy associated with anatase crystallization. The kinetic exponent n was found to be temperature dependent indicating the change in the crystallization mechanism. This was attributed to the high entropy fusion of anatase phase, fast crystallization rate and nano dimension of the anatase phase.

Abstract: Lithium ion battery prefers an electrode consist of small particles so as to allow giving short Li+ diffusion pathway. In order to obtain small particles of LiCoO², which has been commonly used as cathode for lithium battery, the ball-milling is applied to LiCoO2 prepared through a sol-gel method. By the ball-milling, the particle size of LiCoO2 can be reduced from 400 to 250 nm. The discharge capacity of milled LiCoO2 under high current density of 5C is about 100 mA h g-1, that is much higher than non-milled LiCoO2 (60 mA h g-1). It is concluded that the small LiCoO2 prepared by the ball-milling possess superior performance due to short Li+ diffusion length.

Abstract: This paper studies the thermal effect on dynamic stability of single-walled carbon nanotubes (SWCNTs) embedded in polymer matrix in low and high temperatures under impact loads. To this end, we present a nonlocal elastic shell model including thermal and small-size effects. Further, numerical calculations are presented for SWCNTs. Results show that the increasing in temperature field has the effect of increasing the dynamic buckling loads at low or room temperature. However, this effect leads to decrease the dynamic buckling loads at high temperature. In addition, it is observed that nonlocal dynamic buckling loads increase by an increase in the Neperian frequency.

Abstract: In this work, the synthesis of nano-crystalline molybdenum via mechanical activation and subsequent heat treatment using graphite as the reducing agent has been studied. XRD analysis showed that in a 50 hours milled sample, the first step of the reduction took place and MoO₃ reduced to nano-crystalline MoO₂ with a mean crystallite size of 34 nm. The resultant MoO₂ converted to molybdenum when the 20 hours milled sample was heat treated at 1000 °C for 1 hour. FESEM images confirmed the formation of uniform particles of molybdenum after heat treatment.

Abstract: High purity nanoporous silica was fabricated using Shirasu volcanic ash as a starting material. The starting materials were placed into a platinum crucible and were melted at 1400°C. A mother glass was formed by quenching the melt in pure water. Leaching was performed by immersing the mother glass into an HCl solution. Nonsilica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure and had pore size smaller than 2 nm. In order to control the pore size, post heat treatment was performed. The pore size could be controlled from 3.1 to 21.7 nm by changing the post treatment temperature.