The optical properties of twinned single crystals of YBa2(Cu12xNix)3O61y have been determined for a nominally pure system and for Ni concentrations of x50.0075 and 0.014 with oxygen dopings of y50.60 ~underdoped! and 0.95 ~optimal! over a wide frequency range above and below Tc . The optical conductivity of the twinned materials shows a rapid increase in the residual conductivity at low frequen...

The structural and thermoelectric properties of rare-earth (Sm)-substituted Ruddlesden­Popper-type Sr3Fe2O7, Sr31xSmxFe2O7 (SSFO, x = 0, 0.1, 0.15), were investigated by measuring the temperature dependence of its crystallographic parameters, electrical conductivity, and Seebeck coefficient (S). A sharp increase in electrical conductivity (·) up to 60 S/cm (log · = 1.78 S/cm) at 400­500°C occur...

– In the conventional theory of hopping transport the positions of localized electronic states are assumed to be fixed, and thermal fluctuations of atoms enter the theory only through the notion of phonons. On the other hand, in 1D and 2D lattices, where fluctuations prevent formation of long-range order, the motion of atoms has the character of the large scale diffusion. In this case the pictu...

the ac electrical behaviour of nano porous silicon (psi) with tio2 thin films was examined over the range of frequency 102 to 105 hz. porous silicon (psi) layers were obtained by electrochemical etching in hf solution and tio2 thin films were deposited on psi substrates by using electron beam evaporation technique at room temperature. the porosity of psi layer was found by using the gravimetric...

We describe how to obtain electronic transport properties of disordered graphene, including the tight binding model and nearest neighbor hopping. We present a new method for computing, electronic transport wave function and Greens function of the disordered Graphene. In this method, based on the small rectangular approximation, break up the potential barriers in to small parts. Then using the f...

During cxposurc of thin amorphous WO, films to UV light, both the optical absorptivity and thc electrical conductibity increase, Using optically excited surface plasmons. we were ablc to mcnsure even subtle changes of the absorpt~vity of 10 ntn thtck films simuFtaneously with their electrical resistivity a t varivus temperatuscs. Our measurements show that the temperature dependence and thc dcp...

Alternating current ~ac! and direct current ~dc! conductivities have been measured in polymer-nanotube composite thin films. This was carried out for a range of concentrations of multiwall nanotubes in two polymer hosts, poly~m-phenylenevinylene-co-2,5-dioctyloxyp-phenylenevinylene! ~PmPV! and polyvinylalcohol ~PVA!. In all cases the dc conductivity sDC was ohmic in the voltage range studied. I...

Carbon nanotubes (CNTs) are often used as conductive fillers in composite materials, but electrical conductivity is limited by the maximum filler concentration that is necessary to maintain composite structures. This paper presents further improvement in electrical conductivity by precipitating gold nanoparticles onto CNTs. In our composites, the concentrations of CNTs and poly (vinyl acetate) ...

Graphene oxide (GO) contains several chemical functional groups that are attached to the graphite basal plane and can be manipulated to tailor GO for specific applications. It is now revealed that the reaction of GO with ozone results in a high level of oxidation, which leads to significantly improved ionic (protonic) conductivity of the GO. Freestanding ozonated GO films were synthesized and u...

Electric transport in semiconductor superlattices is dominated by pronounced negative differential conductivity. In this report the standard transport theories for superlattices, i.e. miniband conduction, Wannier-Stark-hopping, and sequential tunneling, are reviewed in detail. Their relation to each other is clarified by a comparison with a quantum transport model based on nonequilibrium Green ...