Rustam E. Siregar

μSR study of electron radical dynamics in regio-regular polythiophene

We have carried out longitudinal field (LF) muon-spin-relaxation (μSR) measurements in polythiophene based polymers of Poly(3-hexylthiophene-2,5-diyl) with regio-regular structure to elucidate the intra- and inter-chain hopping mechanisms. The LF dependent muon-spin depolarization rate indicates the occurrence of dimensional crossover from 1 dimensional intra-chain spin diffusion to 3 dimensional inter-chain spin diffusion at 25 K.

Charge Carrier Dynamics of Active Material Solar Cell P3HT:ZnO Nanoparticles Studied by Muon Spin Relaxation (μSR)

Poly (3-hexylthiohene) (P3HT) has attracted much attention due to their chemical and thermal stability as well as their potential to be used as an active material in solar cells. Recently, hybrid solar cell has been developed due to the combining advantages of organic material (P3HT) and inorganic material such as nanoparticle zinc oxide (ZnO). ZnO is an inorganic material with high electron mobility and easy to prepare as electron acceptor to dissociate excitons formed in conjugated polymer as the active material of solar cells. ZnO also can be prepared as a nanoparticle that can resolve a problem of small exciton diffusion length of P3HT. However, the clearly explanation about the effect of ZnO to the charge carrier dynamics in P3HT is not fully understanding yet. We have studied charge carrier dynamics in active material of solar cell P3HT:ZnO along and perpendicular to the chain by means of longitudinal field (LF) muon-spin-relaxation (μSR) method to elucidate the intra and inter-chain charge carrier in polymer hybrid P3HT:ZnO. We found the charge carrier transport changes from intra-chain to inter-chain diffusion. One dimensional intra-chain diffusion is observed in the samples at low temperatures, while three dimensional inter-chain is observed at high temperatures.

An Effect of the Supercell Calculation on Muon Positions and Local Deformations of Crystal Structure in La2CuO4

Muon positions in La2CuO4 were examined by using the density functional theory. Potential minimum positions near apical and plane oxygen have been determined as possible initial muon stopping positions. We found that final muon stopping positions were different from those initial positions due to effects of the local deformation of crystal structure which was induced by injected muons. This means that injected muons relax their positions deforming local crystal structures and minimizing the total energy of the system. We also found that the estimation of those final muon positions had to be done in the large scale area as a supercell which contained 27 unit cells in order to achieve realistic situations of the system with the muon as a dilute impurity.

The optical band gap investigation of PVP-capped ZnO nanoparticles synthesized by sol-gel method

ZnO Nanoparticles (NPs) has unique natures on their crystal structure, direct band gap and high exciton binding energy, consequently applied in optoelectronic devices such as solar cells, optical wave guide and light emitting diodes (LED). However the drawback was ZnO NPs tend to agglomerate and turn to nano-structured materials with poor properties. Effort to avoid agglomerations generally resolved by surface modification of ZnO NPs to obtain well-dispersed suspension. However changes in the surface of ZnO NPs may change the electronic structure and density of states of ZnO NPs, in turn may change the optical band gap. Thus, the objective of current research is investigation of optical band gap of ZnO NPs due to surface modification by capping agent of poly-4-vinylpyrrolidone (PVP) molecules. Uncapped and PVP-capped ZnO nanoparticles were prepared by sol-gel method. The characteristics of surface modifications were investigated by UV-Vis and Photo Luminescence spectroscopy and Transmission Electron Micro...

Effect of Nb2O5 Addition to the Electrical Properties of Fe2TiO5 Ceramics-Based NTC Thermistor

The aims of this research is to identify the effect of Nb2O5 addition on the electrical properties of Fe2TiO5 ceramics-based NTC thermistor.The concentration of Fe2O3 and TiO2 was proportional to Fe2TiO5, whereas the concentration value of Nb2O5 were 0, 0.5 and 1.0 mole %, respectively. Within two hours, the mixed powder was pressed at 4 ton/cm2 to form pellets and sintered at 1300 °C in air. It can perceived from the XRD data that the sintered ceramics had single phase of Fe2TiO5, pseudobrookite. From SEM data, it is found that addition of Nb2O5 decreases the grain size. The addition of Nb2O5 increases thermistor constant, activation energy and electrical resistance of Fe2TiO5 ceramics. The values of thermistor constant of Nb2O5 added-Fe2TiO5 ceramics were relatively large, indicated that the ceramics were aplicable as the NTC thermistor.

Field and temperature dependent charge transport characteristics in regio-regular Poly(3-octylthiophene-2,5-diyl) studied by Muon Spin relaxation

Spin dynamic of regio-regular Poly(3-octylthiophene-2,5-diyl) has been investigated with longitudinal field (LF) muon-spin-relaxation (μSR) techniques. The LF dependent muon-spin depolarization rate indicates the occurrence of dimensional crossover from one-dimensional intra-chain spin diffusion to three-dimensional inter-chain spin diffusion at 50 K.

Effect of light exposure on the μSR asymmetry of graphene oxide film

Graphene has received a lot of attention due to its promising properties for electronic devices application such as energy storage device. Due to the amount needed for application, graphene oxide is widely used as a precursor to obtain graphene-like material. The GO film is thermally reduced or photoreduced to obtain graphene-like that known as reduced graphene oxide (rGO). We intend to measure microscopic intrinsic charge carrier motion of GO film by means of muon spin rotation relaxation (μSR). We prepared thick film of GO by stacking a lot of GO sheets using 4 mg/ml GO-water dispersion. The rGO material was obtained by thermally reduced GO film at 200°C for 2 hours under argon flowing. We measured zero field (ZF) μSR measurements of GO and rGO from 10 K and 300 K. During the μSR measurement we exposed the light into the samples. We discuss the effect of light exposure on the μSR asymmetry and compare to μSR asymmetry of rGO sample.

Self-Assembly of ZnO-Nanorods and Its Performance in Quasi Solid Dye Sensitized Solar Cells

Zinc oxide (ZnO) nanorods (NRs) were successfully prepared by self-assembly methods using zinc nitrate hexahydrate and hexamethylenetetramine as raw materials. ZnO-NRs were grown on FTO/ZnO seed layer and to enhance dye adsorption it was continued by deposition of titania (TiO2) paste by screen printing method. Deposition time of ZnO-NRs were varied, for 120, 150 and 180 minutes and subsequently stacked with one layer of TiO2 mesoporous. The resulting heterojunction layers of FTO/ZnO-Nrs/TiO2 was then applied as a photoanode in quasi-solid dye sensitized solar cell (QS- DSSC) with polymer gel electrolyte (PGE) as a hole conductor. UV-Vis spectrometer was used to investigate the changes of dye adsorption in photoanode with/without inserting titania mesoporous. Characterizations of scanning electron microscopy (SEM) and X-ray diffraction was carried out and the results shows that increasing the deposition time produces a smaller average grain size, diameter and denser layer of ZnO-nanorods. From current-voltage measurement, higher efficiency (η = 2.53%) was obtained for 120 min ZnO nanorods with short circuit current density (Jsc ) of 2.84 mA/cm2 and open circuit voltage (Voc) of 0.7 V. The combination of TiO2 and ZnO-NRs shows a better performance in solar cells characteristics due to increases of dye adsorption on photoanode and high photogenerated electron transport rate. This work emphasizes an optimum condition of ZnO-NRs in combination with TiO2 mesoporous as an alternative photoanode in QS-DSSC.

Thermal Reduction Study of Graphene Oxide Paper

We report the preparation, reduction and characterization of GO paper that obtained by assembly of individual GO sheets. The free standing GO paper was prepared from 4 mg/ml GO dispersed in water, and following by evaporation of water and then detach from the petri dish. In order to obtained graphene-like film, the free-standing GO film then thermally reduced by heating the samples at 250°C at varied heating time. Characteristic and properties of the thermally reduced GO paper was measured by means of infrared spectroscopy, X-ray diffraction and EDS.

The Effect of Sintering Atmosphere on Electrical Characteristics of Fe2TiO5 Pellet Ceramics Sintered at 1200°C for NTC Thermistor

Fabrication of Fe2TiO5 pellet ceramics using powder metallurgy technique for NTC thermistor has been carried out, in order to know the effect of sintering atmosphere (Oxygen, Air and Argon Gas) on the characteristic especially the electrical characteristic of Fe2TiO5 ceramics with high working temperature. X-ray diffraction analyses (XRD) was done to know crystal structure and phases formation. A SEM analysis was carried out to know microstructure of pellets. Electrical properties characterization was done through measurement of electrical resistance at various temperatures (room temperature to 250oC). The XRD data showed that the pellets crystallize in orthorhombic. The presence of second phase could not be identified from the XRD analyses. The SEM images showed that the grains size of the ceramic sintered in oxygen gas is smaller than that of the ceramic sintered in air and argon gas. Electrical data showed that the pellet ceramics sintered in oxygen gas had the largest room temperature resistance (RRT), thermistor constant (B), activation energy (Ea) and sensitivity (α) compared to those sintered in air and argon gas. From the electrical characteristics data, it was known that the electrical characteristics of the Fe2TiO5 pellet ceramics followed the NTC characteristic. The value of B and RRT of the produced Fe2TiO5 ceramics namely B = 4389-6149 K and Rrt = 342-26548kQ, fitted market requirement and can be used for temperature sensor.