Advanced Materials Research Vol. 829

Abstract: The micro GEM is a position sensitive gas electron multiplier detector with high-density and regular arrangement of holes inside a insulation foil The new idea for decreasing the applied voltage with the same electric field and also get rid of the complexity of producing regular arrangement of micro holes, is the dimension reduction of the GEM to the range of nanometer. The proposed method for producing this nanostructure is anodization of the aluminium. The simulation results show that although the nanoGEM has typically less gain in comparison to micro GEM, but with applied voltages in order of few Volts, high gains can be achieve by multiple nanoGEMs. This novel idea which can be used for production of low voltage and portable position sensitive detectors has higher spatial resolution in comparison to commercial ones.

Abstract: The unique geometry of micro 3D semiconductor detectors, presents several advantages over conventional planar silicon detectors. But, manufacturing these kind of detectors requires high technology. The novel idea to achieve a high performance and low cost semiconductor detector is using the nanopattern of anodized aluminium as a mask to create nano3D detectors. The simulation results show that this novel nano3D radiation hard semiconductor detector with collection time less than 10 ps and full depletion voltage less than one volt can become increasingly important for possible future upgrades of 3D detectors of the Large Hadron Collider (LHC) at CERN and also medical imaging applications.

Abstract: Thermoelectric (TE) devices are an interested family of energy harvesters which could convert the thermal energy into electricity. However, the temperature drops at interface between thermoelectric materials and heat source, heat sink and electrodes reduce efficiency of thermoelectric devices. As a solution, thermal interface materials (TIM) which have high thermal conductance and low thermal interface resistance with adjacent materials are added to the device. In this paper, the organic material is considered as the base material for a TE energy harvester device. Also, carbon nanotube (CNT) is applied as TIM, because of its high one dimentional electrical and thermal conductance. A finite element analysis is carried out in order to investigate the role of thermal contact resistance on heat transfer at TE device. To do this, a thermoelectric leg is simulated with two structure consist of (a) TE material and electrodes in direct contact (b) TE material and electrodes with CNT interface and the results are compared. It is shown that CNT layer reduces heat dissipation at the interface and so the temperature difference at the both sides of polymer is increased, which finally results the enhancement of device output voltage.

Abstract: Piezoelectric nanogenerator (NG) made of nanowires (NWs) is a suitable device for harvesting ambient mechanical energy, applicable for self-powered electronic systems and nanodevices that operate at low power. The coupled piezoelectric and semiconducting characteristics of the zinc oxide (ZnO) NW cause an output voltage generation that made it interesting to use as an energy harvesting device in nanoscale. In this paper, the piezoelectric potential distribution in a bent ZnO NW is investigated, numerically. To do this, a three-dimensional finite element simulation of the device is performed and the results are analyzed and discussed. It is found that the output piezoelectric potential, for a constant nanowire length, is decreased as the diameter of ZnO NW increases. Study on the effect of NW diameters shows the potential will remain constant for nanowire with aspect ratio below 15. Further, the NWs are considered with an inclination of 20 degree relative to the substrate to study by applying force in different directions. The latter indicates an improvement on the output piezoelectric potential. The obtained results show that the ZnO NW can be used as a good energy harvester device by considering a suitable diameter, length and with a justified inclination angle.

Abstract: One of the most marvelous applications of GEM is hard X-ray imaging. For increasing the detection efficiency, a photoconverter is usually required. In this work a novel nanostructure photo converter is proposed. Simulation results show that the combination of fast position sensitive gas detector with nanophoto converter can be improved the detection efficiency by one order of magnitude in comparison to the bulk one, which is more benefic for hard X-ray medical imaging applications.

Abstract: This study deals with the frequency analysis of Nano-sandwich-structure with nonlocal effect. The model takes into account the flexibility of the sandwich core while the faces are treat as beams. The different stiffness of core will impart different vibration characteristic of the structure. To examine free vibrations of Nano-sandwich-structure, nonlocal elasticity theory has been applied. In this paper an investigation is carried out to understand the small-scale effects in the free vibration. The boundary conditions of simply-supported conditions are described here. Further the effects of scale coefficient and stiffness parameter are studied in this manuscript.

Abstract: Among nonomaterial with different geometric shapes, nanotubes and nanowires received special attentions with increasing applications in electronic industry and nanorobotic due to their unique properties. Therefore, in order to study the fundamental properties of nanotubes/wires, in this paper we will focus on modeling the melting of different crystal surface of metallic materials. Although there are different models in literature based on change of cohesion energy or coordination number at nanoscale, here we present a generalized thermodynamics model which considers layer by layer melting of nanotubes/wires. This model considered the surface energy of solid-gas, liquid-gas and solid-liquid along with the effect of fcc, bcc and hcp crystallography of different metals and their different surface crystal plane orientations. During the analytical simulation of surface melting, different run have been performed for variable size of tubes/wires in order to involve the size effect at nanoscale. Calculation results of model will be presented for some metallic systems such as: Ni, Pb, Fe and Zn. Results of our calculations show good agreement with experimental results and other theoretical predictions in literatures. Our model provides a powerful tool to analysis melting phenomena of metallic nanotubes/wires at different crystal structures and surface plane orientations for various sizes at nanoscale.

Abstract: Porous metal organic framework (MOF) {Zn₂(1,4-bdc)₂(dabco)}_n synthesized under solvothermal conditions. The MOF was used as the carrier matrices for drug delivery system. The ibuprofen as analgesic and anti-inflammatory drug with 0.6 nm molecule size as a model was entrapped into this new carrier with pores distribution of 1.85 nm. The ibuprofen loading efficiency was obtained by thermogravimetric analysis. The ibuprofen loading efficiency of 22% (w/w) was obtained for this MOF. The entrapped ibuprofen was released over several days by soaking the sample in the simulated body fluid (pH 7.4) at 37 °C. The ibuprofen concentrations were analyzed using UV-vis Spectrophotometer at a wavelength of 260 nm. The result of release reveals that this {Zn₂(1,4-bdc)₂(dabco)}_n is suitable as drug delivery system.

Abstract: This study has focused on mesoporous silica nanoparticles as a drug delivery system of insulin, which was synthesized via a hydrothermal process. The morphology and composition of the silica nanoparticles were characterized by different analytical techniques such as Scanning Electron Microscope (SEM), X-Ray Diffraction Analysis (XRD), Fourier Transform Infrared spectroscopy (FTIR) and BrunauerEmmettTeller (BET). The percentage of drug loading and the in vitro drug release properties of the mesoporous silica nanoparticles in gastrointestinal tract were investigated in simulated gastrointestinal conditions by ultraviolet-visible spectroscopy. The results showed the amorphous structure of SBA-15 in mesoporous silica particles has a narrow pore size distribution. Also, particles shape was nearly wheat-like with almost homogeneous size distribution. Furthermore, it was revealed that the mesoporous silica nanoparticles have a high insulin loading and release capacity. These prominent behaviors make mesoporous silica nanoparticles promising material as a drug carrier for insulin delivery.

Abstract: Poly (lactic acid)/hydroxyapatite (PLA/HAP) nanocomposites were made via solution casting method and subjected to gamma irradiation at doses of 30 and 50 kGy. FTIR spectra of the nanocomposites displayed structural changes in the crystalline phase of PLA upon irradiation. The PLA/HAP nanocomposites of 6 and 10 pph HAP irradiated at 30 kGy showed higher tensile strengths. This was attributed to radiation-induced crystallinity that verified by DSC crystallinity measurements. Using triallyl isocyanurate (TAIC) as a multifunctional monomer promoted radiation-induced crosslinking reactions in PLA that was manifested by improvements in the tensile strength of the nanocomposites. Optimum values for TAIC, irradiation dose and HAP content were found as 1 pph, 30 kGy and 10 pph respectively. Raising the irradiation dose from 30 to 50 kGy prompted chain scission reactions that had adverse effects on tensile properties.