Search results for "CONDUCTIVITY"

1993

Langmuir-Blodgett films from a polymer with triphenylene moieties in the side groups deposited on a quartz substratum with aluminium and gold electrodes show a dark conductivity in the plane of the Langmuir-Blodgett film. This dark conductivity is increased using gold electrodes as compared with aluminium electrodes. It depends in a superlinear way upon the applied electric field and is not enhanced by oxygen. The dark conductivity can be enhanced by doping the Langmuir-Blodgett films with iodine but it is not influenced by doping the Langmuir-Blodgett films with 2,4,7-trinitro-9-fluorenone. Upon excitation in the absorption band of the triphenylene moiety an in-plane photocurrent, which is…

Electron tunneling from colloidal CdSe quantum dots to ZnO nanowires studied by time-resolved luminescence and photoconductivity experiments

2015

CdSe quantum dots (QDs) with different organic linker molecules are attached to ZnO nanowires (NWs) to study the luminescence dynamics and the electron tunneling from the QDs to the nanowires in time-resolved photoluminescence (PL) and photoconductivity measurements. The PL transients of the QD luminescence indicate two different recombination channels: the direct recombination inside the QD core and the recombination via QD surface defect states. After linking the QDs to the ZnO NW surface, photo-induced electron tunneling from an excited state of the QD into the conduction band of the nanowire becomes visible by a clear decrease of the PL decay time. Efficient electron tunneling is confir…

Photoconductivity of Germanium Nanowire Arrays Incorporated in Anodic Aluminum Oxide

2007

Photoconductivity of germanium nanowire arrays of 50 and 100 nm diameter incorporated into Anodic Aluminum Oxide (AAO) membranes illuminated with visible light is investigated. Photocurrent response to excitation radiation with time constants faster than 10−4 s were governed by absorption of incident light by nanowires, while photokinetics with time constants of the order of 10−3 s originates from the photoluminescence of the AAO matrix. Possible applications of nanowire arrays inside AAO as photoresistors are discussed.

Erroneous p-type assignment by Hall effect measurements in annealed ZnO films grown on InP substrate

2013

We report on incorrect carrier type identification achieved by Hall effect measurements performed on ZnO films grown by pulsed laser deposition on InP substrates and subsequently annealed for 1 h at 600 C in air. While Hall measurements, after post-growth annealing, reveal a change in the electrical properties of the films, from n-type to p-type, both photocurrent-based and standard C V measurements performed on the same samples show no change in the native n-type doping of the ZnO films. A possible interpretation of the two results is reported. In particular, p-type conductivity observed by Hall effect may be ascribed to a highly conductive thin layer formed during the annealing process at…

High-sensitive switchable photodetector based on BiFeO3 film with in-plane polarization

2015

A high-sensitive and fast-response photodetector based on BiFeO3 (BFO) ferroelectric thin film is fabricated using coplanar electrode configuration. A large photocurrent/dark current ratio is found up to two orders of magnitude at 1 V bias. Enhanced photocurrent and rectification behavior of the photodetector are observed after applying high voltage pulses to the BFO film. The short-circuit current varies systematically with the poling process and increases linearly with the light density. On the contrary, the open-circuit voltage keeps as a constant during the measurements. We attribute these behaviors to the depolarization field and the interfacial fields at the film-electrode interfaces.…

Effects of Oxygen Plasma on the Chemical, Light-Emitting, and Electrical-Transport Properties of Inorganic and Hybrid Lead Bromide Perovskite Nanocry…

2018

We show that oxygen plasma affects in different ways the structural, chemical, optical, and electrical properties of methylammonium and cesium lead bromide nanocrystals. Hybrid organic–inorganic nanocrystals were severely and quickly degraded by oxygen plasma at 50 W. Their photoluminescence was quenched with almost 100% loss of the initial quantum yield, which is linked to decomposition of the nanocrystals. Inorganic nanocrystals were more resistant to oxygen plasma in the same conditions. Despite a moderate loss of photoluminescence and electrical conductivity, oxygen plasma had a positive impact, removing unbound ligands and resulting in more ohmic behavior of the film. This paves the wa…

Interlayer exciton dynamics in van der Waals heterostructures

2019

Atomically thin transition metal dichalcogenides can be stacked to van der Waals heterostructures enabling the design of new materials with tailored properties. The strong Coulomb interaction gives rise to interlayer excitons, where electrons and holes are spatially separated in different layers. In this work, we reveal the time- and momentum-dependent elementary processes behind the formation, thermalization and photoemission of interlayer excitons for the exemplary MoSe2–WSe2 heterostructure. We identify tunneling of holes from MoSe2 to WSe2 on a ps timescale as the crucial process for interlayer exciton formation. We also predict a drastic reduction of the formation time as a function of…

Hole transporting materials based on benzodithiophene and dithienopyrrole cores for efficient perovskite solar cells

2018

The development of highly efficient hole transporting materials (HTMs) for perovskite solar cells (PSCs) is still one of the most thrilling research subjects in the development of this emerging photovoltaic technology. Inner ring engineering of the aromatic core of new HTMs – consisting of three fused rings endowed with four triarylamine units – reveals major performance effects over the fabricated devices. In particular, substitution of the central pyrrole ring in dithienopyrrole (DTP) by a benzene ring – benzodithiophene (BDT) – allows enhancing the power conversion efficiency from 15.6% to 18.1%, in devices employing mixed-perovskite (FAPbI3)0.85(MAPbBr3)0.15 (MA: CH3NH3+, FA: NHCHNH3+) …

Can we use time-resolved measurements to get Steady-State Transport data for Halide perovskites?

2018

Time-resolved, pulsed excitation methods are widely used to deduce optoelectronic properties of semiconductors, including now also Halide Perovskites (HaPs), especially transport properties. However, as yet, no evaluation of their amenability and justification for the use of the results for the above-noted purposes has been reported. To check if we can learn from pulsed measurement results about steady-state phototransport properties, we show here that, although pulsed measurements can be useful to extract information on the recombination kinetics of HaPs, great care should be taken. One issue is that no changes in the material are induced during or as a result of the excitation, and anothe…

Theory of quantum-circuit refrigeration by photon-assisted electron tunneling

2017

We focus on a recently experimentally realized scenario of normal-metal-insulator-superconductor tunnel junctions coupled to a superconducting resonator. We develop a first-principles theory to describe the effect of photon-assisted electron tunneling on the quantum state of the resonator. Our results are in very good quantitative agreement with the previous experiments on refrigeration and heating of the resonator using the photon-assisted tunneling, thus providing a stringent verification of the developed theory. Importantly, our results provide simple analytical estimates of the voltage-tunable coupling strength and temperature of the thermal reservoir formed by the photon-assisted tunne…