Search results for "Elementary charge"
showing 10 items of 20 documents
Tuning the hole injection barrier in the intermolecular charge-transfer compoundDTBDT-F4TCNQ at metal interfaces
2014
Molecular monolayers of the charge-transfer salt dithienobenzodithiophene-tetrafluorotetracyanoquinodimethane (DTBDT-F${}_{4}$TCNQ) have been deposited on C(R$15\ifmmode\times\else\texttimes\fi{}3$)/W(110), Co/W(110), and hcp Co(0001) using molecular beam epitaxy in an ultrahigh vacuum. The integrity of the deposited molecules has been confirmed by scanning tunneling microscopy. Scanning tunneling spectroscopy has been used to determine the energetic positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital of acceptor and donor in the pure and in the mixed phase. The mixed charge transfer phase exhibits a new HOMO close to the Fermi edge depicting a charge tra…
Revisiting the electronic properties of Molecular Semiconductor – Doped Insulator (MSDI) heterojunctions through impedance and chemosensing studies
2015
Abstract The core activity of this work was to give a new interpretation of the electronic behavior of Molecular Semiconductor – Doped Insulator heterojunctions (MSDI), a new organic device combining two molecular materials with very different electronic properties. We focused on understanding the phenomenon occurring at the interface of fluorinated and non-fluorinated phthalocyanines that appears to be a determining factor for the electronic charge transport in the two-component thin film and ultimately deciding the nature of gas sensing, as illustrated with ozone and ammonia chosen as examples of accepting and donating gases. The impedance measurements showed that the Schottky contact bet…
Formation of linear Ni nanochains inside carbon nanotubes: Prediction from density functional theory
2013
Abstract First principles calculations have been performed to investigate the ground state properties of monoperiodic single-walled carbon nanotubes (CNTs) containing nanochain of aligned Ni atoms inside. Using the PBE exchange-correlation functional ( E xc ) within the framework of density functional theory (DFT) we predict the clusterization of Ni filaments in ( n ,0) CNTs for n ⩾ 9 and for ( n , n ) CNTs for n ⩾ 6. The variations in formation energies obtained for equilibrium defective nanostructures allow us to predict the most stable Ni@CNT compositions. Finally, the electronic charge redistribution has been calculated in order to explore intermolecular properties leading to stronger…
Non-adiabatic quantized charge pumping with tunable-barrier quantum dots: a review of current progress.
2014
Precise manipulation of individual charge carriers in nanoelectronic circuits underpins practical applications of their most basic quantum property --- the universality and invariance of the elementary charge. A charge pump generates a net current from periodic external modulation of parameters controlling a nanostructure connected to source and drain leads; in the regime of quantized pumping the current varies in steps of $q_e f$ as function of control parameters, where $q_e$ is the electron charge and $f$ is the frequency of modulation. In recent years, robust and accurate quantized charge pumps have been developed based on semiconductor quantum dots with tunable tunnel barriers. These de…
Magnetic field enhanced robustness of quantized current plateaus in single and double quantum dot non-adiabatic single charge pumps
2010
We compare the robustness of the quantized current plateaus of semiconductor non-adiabatic quantized charge pumps consisting of a single quantum dot (SQD) and two QDs connected in series (DQD). For the SQD application of a perpendicular magnetic field leads to an enhanced robustness of the first current plateau I = ef, with f the pumping frequency and e the elementary charge. In contrast for the DQD a comparably enhanced robustness of the plateau I = 2ef is found. These findings might allow generation of higher currents without compromising quantization accuracy by optimizing the device geometry.
Ultrafast sequential charge transfer in a double quantum dot
2010
We use optimal control theory to construct external electric fields which coherently transfer the electronic charge in a double quantum-dot system. Without truncation of the eigenstates we operate on desired superpositions of the states in order to prepare the system to a localized state and to coherently transfer the charge from one well to another. Within a fixed time interval, the optimal processes are shown to occur through several excited states. The obtained yields are generally between 99% and 99.99% depending on the field constraints, and they are not dramatically affected by strict frequency filters which make the fields (e.g., laser pulses) closer to experimental realism. Finally …
Computational study of dimethyl- and trimethyl-tin(IV) complexes of porphyrin derivatives
2001
The molecular geometry, energetics and electronic charge distribution of diorgano- and triorgano-tin(IV) complexes of [protoporphyrin-IX] and [meso-tetra(4-carboxyphenyl)porphine] derivatives were determined at semi-empirical and ab initio levels. To study the molecular details of the complexes, simpler molecule models were calculated by the ab initio pseudo-potential method. The molecular properties of these complexes are essentially independent of the presence of the peripheral tin atoms. Agreement was always found among the results of the different computational approaches, as well as between the theoretical and the experimental findings on the molecular geometry of the hypothesized comp…
First Principles Calculations of Oxygen Vacancy Formation and Migration in Ba1−xSrxCo1−yFeyO3−δPerovskites
2011
Based on first principles DFT calculations, we analyze oxygen vacancy formation and migration energies as a function of chemical composition in complex multicomponent (Ba,Sr)(Co,Fe)O3−δ perovskites which are candidate materials for SOFC cathodes and permeation membranes. The atomic relaxation, electronic charge redistribution and energies of the transition states of oxygen migration are compared for several perovskites to elucidate the atomistic reason for the exceptionally low migration barrier in Ba0.5Sr0.5Co0.8Fe0.2O3−δ that was previously determined experimentally. The critical comparison of Ba1−xSrxCo1−yFeyO3−δ perovskites with different cation compositions and arrangements shows that …
Correlation between the Ionicity Character and the Charge Density in Semiconductors
1994
Using the electronic charge densities obtained by the empirical pseudopotential method for tetrahedrally bonded semiconductors, an ionicity scale is established that is in good agreement with the Phillips ionicity scale.
Hydrogenation of light hydrocarbons on palladium: theoretical study of the local surface arrangements
2001
Abstract Quantum mechanical calculations at HF, MP2 and DFT levels were used to rationalise the surface effects of the hydrocarbon lateral interactions occurring on single planar metal surfaces or on different adjacent surfaces during the hydrogenation on palladium catalyst. The different values of electronic charge, found in the different atoms of palladium clusters, were suggested as a possible explanation of the non-homogeneous behaviour already inferred for catalyst surface sites having non-isotropic local arrangement.