Papers by Keyword: Electron Transport

Abstract: Graphene-Zinc Oxide (Gr-ZnO) nanocomposites films were successfully synthesized via facile electrodeposition method in an aqueous solution under Gr concentration conditions. Gr, as a highly conductive carbon, acts as an anchor for ZnO nanosheets and plays a substantial role in controlling the degree of dispersion of ZnO nanosheets onto indium-doped tin oxide (ITO) substrate to form Gr-ZnO nanocomposite. Atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM) analysis of Gr-ZnO nanocomposite samples confirmed that the presence of ZnO nanosheets with a high degree of dispersity and crystallinity which is well linked to the thin layer of Gr nanoparticle on ITO substrate. The surface roughness of the films found increased to ~270 nm on Gr-ZnO as compared to Gr ~44 nm and ZnO ~3 nm. Further, the x-ray diffraction spectroscopy (XRD) analysis showed the result is in good agreement with Raman spectroscopy study. The cyclic voltammetry (CV) of Gr-ZnO nanocomposite revealed that the effect of electron-hole recombination process was increased and the presence of Gr in ZnO photoanode provides the fastest redox reaction and hence offers the fastest electron transfer in photoanode.

Abstract: We theoretically investigate the thermoelectric properties of twisted armchair graphene nanoribbons (TAGNR) with various rotation angles. We find that the twist engineering applied to AGNR can alter the thermoelectric transport properties by modifying the electronic structures and phonon dispersion relations. With twist angle increasing , the thermal conductance tend to decrease, and the can tunable with different twist angle. Our calculation results suggests a possible route to increase the ZT values of AGNR-N for potential thermoelectric applications.

Abstract: The carrier velocity is measured as a function of electric field in as-grown and H-intercalaed epitaxial graphene grown on semi-insulating 4H-SiC in order to estimate the low field carrier mobility as a function of temperature. The mobility is also measured on the same samples as a function of temperature in a liquid Helium (He) cooled cryostat. The two temperature dependent measurements are compared in order to deduce the dominant carrier scattering mechanisms in both materials. In as-grown material, acoustic phonon scattering and impurity scattering both contribute, while impurity scattering dominates in H-intercalated material.

Abstract: The electrical properties of nanocomposite SiO₂(Si) films containing Si nanoclusters have been investigated. The films were formed by oxide assisted growth that included ion plasma sputtering (IPS) of Si target and following high temperature annealing. It was determined that electrical conductivity of the films correspond to the mechanism of hopping conductivity with variable hopping length through the traps near the Fermi level (Mott mechanism) due to the large number of silicon dangling bonds in the dielectric matrix. The peculiarities of charge capture in nanocomposite SiO₂(Si) films for their application as the medium for charge storage in memory cells have been investigated by C-V method. The good charge storage possibility of SiO₂(Si) films formed by IPS deposition with followed temperature annealing has been observed. The negative differential capacitance has been revealed in conditions of semiconductor surface accumulation. The physical model for explanation of the negative differential capacitance of MIS structures with nanocomposite SiO₂(Si) films as the dielectric has been proposed. The model is based on the parallel conjunction of the oxide capacitance and nanocrystals capacitance.

Abstract: TiO₂ films, which are often sintered at 450°C for 30 or 60 minutes for application in dye-sensitized solar cells (DSSCs), show no appreciable connectivity between the TiO₂ particles. The present work deals with connectivity between TiO₂ particles and its effect on electron diffusion and short circuit current density (J_sc) of DSSCs made from TiO₂ films sintered at lower temperature for longer time (450°C, 550°C, 650°C for 60 minutes) and higher temperature for shorter time (450°C for 60 min followed by 700°C and 800°C for 10 and 20 minutes). TiO₂ films sintered at higher temperature (700°C) but for shorter time (10 min) exhibited better connectivity between the particles with slight reduction in surface area. This caused faster transport of electron through the films sintered at 700°C/10 min than 450°C/60 min and 550°C/60 min and hence, resulted in highest J_sc (~ 7 mA/cm²). Films sintered at 650°C/60 min and 700°C/20 min showed better interparticle connectivity but had significantly lower surface area, dye loading and therefore, despite faster diffusion of electron in these films J_sc was measured to be lower. Sintering at 700°C/10 min following 450°C/60 min could be considered the best in terms of dye loading, electron transport and efficiency.

Abstract: 3C-SiC (n) / Si (p) heterostructures were obtained and investigated in a wide temperature range. It was shown, the main mechanisms of charge transport diffusion and recombination. The properties of silicon substrate were determining the working temperature range of investigated diodes. Therefore the rectifying properties of 3С-SiC(n)/Si(p) diodes were stable only up to 473 K. Two sites with different activation energies were observed on the Jrev(1/T) curves at fixed voltage: 0,32 eV which, characterized states on the SiC/Si interface, Е2 ≈ 0,55 eV which corresponds to the middle of silicon bandgap and defines existence of reverse current generation component.

Abstract: The influence from the dense film coverings generated during the post treatment of TiCl₄ on the photoelectric conversion efficiency of the dye-sensitized solar cells (DSSCs) is investigated in the present paper. The effect of TiCl₄ treatment can be concluded into the following two points: 1. Covering TiO₂ nanoparticles with dense films and protecting the active Ti³⁺ can enhance the electron transport. 2. The dense TiO2 is an ideal conducting film to cover the neck of nanoparticles, reduce the electron scattering and strengthen the electron transport. Acceleration of the electron transport can increase the short circuit current of the DSSCs as to obtain higher photoelectric conversion efficiency.

Abstract: The electron transport behavior of a short graphene nanoribbon sandwiched between two gold(111) electrodes is investigated using density functional theory calculations and nonequilibrium Green’s function technique. The calculated current-voltage characteristic of the graphene nanoribbon junction shows an obvious negative differential resistance (NDR) phenomenon. The mechanism of this NDR behavior of graphene nanoribbon is discussed in terms of the evolution of the molecular energy levels, the spatial distribution of frontier molecular orbitals, and the electron transmission spectra under various applied biases. It is found that the changes of the spatial distribution of molecular orbitals near Fermi level with the applied bias lead to such NDR behavior.

Abstract: The singular nature of the Boltzmann transport equation leads to the boundary layer structure around the virtual source in nano-scale device structures. We show that the boundary layer is a key concept to understand the physical mechanism behind quasi-ballistic transport in nano-scale devices. The self-consistent 3D Monte Carlo device simulator is constructed by accurately including the full Coulomb interaction. It is explicitly shown that the Coulomb interaction is indeed a key ingredient for any reliable predictions of device characteristics.

Abstract: The nonequilibrium Green’s function approach in combination with density-functional theory is used to perform ab inito quantum-mechanical calculations of the electron transport properties of porphyrin oligomers sandwiched between two gold electrodes. The results show that porphyrin oligomers are good candidates for long-range conduction wires. In particular, the decay of conductance of porphyrin oligomers does not follow the exponential relation. The electron transport behavior was analyzed from the molecular projected self-consistent Hamiltonian states and the electron transmission spectra of the molecular junctions.