For many optical semiconductor fields of study, the high photoconductivity of amorphous organic semiconductors has strongly been desired, because they make the manufacture of high-performance devices easy when controlling charge carrier transport and trapping is otherwise difficult. This study focuses on the correlation between photoconductivity and bulk state in amorphous organic photorefractive materials to probe the nature of the performance of photoconductivity and to enhance the response time and diffraction efficiency of photorefractivity. The general cooling processes of the quenching method achieved enhanced photoconductivity and a decreased filling rate for shallow traps. Therefore, sample processing, which was quenching in the present case, for photorefractive composites significantly relates to enhanced photorefractivity.
We investigated the Raman, nuclear magnetic resonance (NMR), and transport characteristics of 13C-enriched single-walled carbon nanotubes (13CNTs). Systematic Raman spectroscopy measurements show that the 13C content of 13CNT can be controlled by the 13C source. Full width at half maximum of Raman spectra show a broad peak around 50% of 13C while G/D ratio remains almost constant. 13C NMR measurements indicate that the spin-lattice relaxation consists of two mechanisms and spin-spin relaxation time is of order of sub-millisecond. In transport measurement, we demonstrate that 13CNT shows quantum-dot features at low temperatures.
Quantum dots have been fabricated in an individual single-wall carbon nanotube, and their single electron transport has been measured at low temperatures with magnetic field up to 5T. The Coulomb diamonds have shown two and four electron periodicities in different gate voltage ranges. The results can be understood by the two- or four-electron shell filling model. In magnetic fields, the Zeeman splitting of single particle levels has been observed. This means that the single spin polarization is realized when an odd number of electrons are in the dot. The experimental observation suggests an important step for realization of the spin qubit.
Our effort to form reliable tunnel barriers in single and multi-wall carbon nanotubes is presented. As well as the standard method which uses a simple deposition of contact metal on nanotubes, we use a narrow SiO2 deposition and Ar ion beam irradiation to form the tunnel barrier in nanotubes. Such devices as a single electron transistor, double coupled quantum dots and a single electron inverter have been fabricated. Their performance has been measured from 20 mK up to liquid helium temperature. The unique microwave response of coupled quantum dots is also presented. We show that the carbon nanotubes are attractive material for the building block of quantum-dot based nanodevices with extremely small dimensions, and our method may be useful to realize the devices and cirucits.