Charging Diagram Research Articles

Improvement quantum capacitance in supercapacitors using vacancy-defected BC3 monolayer

In present research, we aimed to assess effectiveness of employing defected BC3 monolayer in supercapacitors as an electrode through DFT computations. Our focus was on single and double-vacancy BC3 monolayer. We studied stored charge diagrams, integrated quantum capacitance (CQ), and density of state (DOS) for both pristine and vacancy-modified defected BC3 monolayer structures. According to findings, applying vacancy-modified defected structures between −0.80 and 0.80 V leads to greater CQ value in comparison to pristine BC3 monolayer. Single and double vacancies may be employed as positive and negative electrodes, and are considered as a semiconductor. Computations reveal that stored charge in vacancy-modified defected structures is more than pristine BC3 monolayer between 0 and 0.8 V. Moreover, DV-modified defected structure stores more charge than both SV structures and BC3 monolayer. Our findings suggest that DV BC3 monolayer shows potential as a material for high-performance supercapacitors.

Effect of alloying elements on the interface of fcc-Fe/Ni3Al by first principle calculations

The effect of alloying element segregation on the interface properties of the fcc-Fe/Ni3Al was investigated using the first-principles approach based on density functional theory, revealing the element segregation mechanisms from the perspectives of atoms and electrons. The results show that the alloying elements tend to replace position 1 on the interface of fcc-Fe phase side, and the order of stability after replacement is Ti, Nb, Mo, Cr and Mn. The state density diagrams show that the 4d orbital electrons of Mo and Nb contribute to increase the peak of Al atom 2p orbital at −5 eV, while the 3d orbital electrons of Cr and Ti tend to weaken the peak of Fe atom 3d orbital at 1 eV. The degrees of electron cloud enrichment and consumption increase between interface atoms of the difference charge diagrams indicate that the bonding strength increases and the interface stability is improved. The result of bond population is consistent with the differential charge density diagram. The study has a certain guiding significance for interfacial segregation behavior of alloying elements in heat-resistant steels.

Multipolar Fano resonances in concentric semi-disk ring cavities

The plasmon properties of the concentric cavity consisting of a semi-disk inside a thin ring are theoretically investigated by the finite difference time domain and plasmon hybridization methods. According to the simulated absorption and scattering spectra, electric field distributions and charge diagrams, multiplar Fano resonances are successfully generated, mainly due to the coupling between the dark multipolar modes and the bright dipolar mode originating from the hybridization between the primitive modes of the semi-disk and the ring. Moreover, the intensities and spectral positions of the Fano resonances can be manipulated by modifying the geometric parameters of the cavity. The cavity for potential use as a multi-wavelength biochemical sensor is evaluated with the refractive index sensitivity and figure of merit.

Excitation spectroscopy of few-electron states in artificial diatomic molecules

We study the excitation spectroscopy of few-electron, parallel coupled double quantum dots (QDs). By applying a finite source drain voltage to a double QD (DQD), the first excited states observed in nonequilibrium charging diagrams can be classified into two kinds in terms of the total effective electron number in the DQD, assuming a core filling. When there are an odd (even) number of electrons, one (two)-electron antibonding (triplet) state is observed as the first excited state. On the other hand, at a larger source drain voltage we observe higher excited states, where additional single-particle excited levels are involved. Eventually, we identify the excited states with a calculation using the Hubbard model and, in particular, we elucidate the quadruplet state, which is normally forbidden by the spin blockade caused by the selection rule.

Laboratory measurements of charge separation in low liquid water content conditions and low impact velocity

A laboratory investigation of the electric charge separated in collisions between vapor‐grown ice crystals and a target growing by riming is presented in this work, with the goal of studying the performance of the noninductive mechanism under microphysical conditions similar to some of those which occur in the stratiform regions of the mesoscale convective systems. A series of experiments were conducted by using a target of 2 mm in diameter, for ambient temperatures between −7°C and −13°C, effective liquid water content between 0.05 and 0.5 g m−3, and air speeds between 1 and 3 m s−1. Charge diagrams of the sign of the electric charge transfer on the rimer as a function of the ambient temperature and the effective liquid water content for each velocity are presented. The results show that the riming target charges positive for temperatures above −10°C. For temperatures below −10°C, the charging is positive for high liquid water content and negative for low liquid water content. The magnitude of the charge transfer per collision under the studied conditions ranges from 0.01 to 0.2 fC. The implications of these results to the electrification processes are discussed.

Platinum single-electron transistors with tunnel barriers made by atomic layer deposition

The fabrication and measurements of platinum single-electron transistors (SETs) employing high quality insulating barriers produced by atomic layer deposition (ALD) of alumina (Al2O3) are reported. The G-Vds, Coulomb blockade oscillations, and the charging diagram of the SET at 300 mK were successfully measured. The ALD technique provides atomic accuracy and precise control of the tunnel barriers and greatly expands the choice of materials suitable for SET fabrication (both electrodes and island materials as well as barrier dielectrics). This fabrication method is targeted toward large scale production of SETs, which will accelerate their adoption into practical applications.

Application of negative differential conductance in Al/AlOx single-electron transistors for background charge characterization

Negative differential conductance (NDC) is reported in the charging diagram of a normal state metal-metal oxide single electron transistor (SET) fabricated on a quartz substrate. We discuss the physical origin and cause of the observed effect. Using a simple electrostatic model we simulated SET charging diagrams and found excellent correlation between experiment and theory. We also found that the charging pattern associated with trap charging remains the same after warming the sample to room temperature (though position in Vg coordinates changes) and suggest to use these distinct features (such as NDC) as markers to characterize background charge in SETs.

Nonlinear transport in coupled quantum dots: A stationary probability approach

The stationary tunneling current and differential conductance of the coupled quantum dots system with split-gates are calculated by generalizing the Beenaker’s linear response theory for the description of the Coulomb-blockade oscillations of the conductance in the single quantum dot. The calculation of the charging diagram in parallel through the double dot as function of the two side-gate voltages shows a remarkable agreement with the recent experimental results by Hatano et al. (Science, 2005, 309: 268–271)

Observation of anti-bonding excited state in charging diagram of a few-electron double dot

We fabricated a unique hybrid vertical–lateral double dot device with two dots coupled in parallel to study the excitation energy spectra with the number of electrons in each dot and inter-dot level detuning as parameters. We measured the charging diagram for a finite bias voltage and observed the tunnel-coupled bonding state and anti-bonding state. The separation between the two states is a direct measure of the inter-dot tunnel coupling energy. We use this energy and other characteristic energies derived from the charging diagram to characterize the exchange interaction energy.

Topological Hunds rules and the electronic properties of a triple lateral quantum dot molecule

We analyze theoretically and experimentally the electronic structure and charging diagram of three coupled lateral quantum dots filled with electrons. Using the Hubbard model and real-space exact diagonalization techniques we show that the electronic properties of this artificial molecule can be understood using a set of topological Hunds rules. These rules relate the multielectron energy levels to spin and the interdot tunneling $t$, and control charging energies. We map out the charging diagram for up to $N=6$ electrons and predict a spin-polarized phase for two holes. The theoretical charging diagram is compared with the measured charging diagram of the gated triple-dot device.

Charge separation in updraft of convective regions of thunderstorm

The experiments described in this work are concerned with ice‐crystal graupel interactions. The influence of the impact velocity on charge separation during collisions is analyzed for three different velocities: 6, 8 and 11 m s−1. The ambient temperature was varied in the range −5 to −30°C and the effective water content between 0 to 2 g m−3. Charge diagrams of the sign of the electric current on the graupel as a function of the ambient temperature and the effective liquid water content for each velocity are presented. The results indicate that increasing the velocity leads to negative particle charging during riming at higher velocity and the implications of these findings to non‐severe thunderstorm are discussed.

Few-electron spin and charge configurations in circular and rectangular vertical quantum dot mesas in a magnetic field: Experiment and full three-dimensional self-consistent simulations

We explore the spin and charge properties as the shape of a single vertical quantum dot mesa is changed from being circular to rectangular. The magnetic field dependence of the electrochemical potentials of both mesa geometries is measured and compared with a full three-dimensional multi-scale self-consistent approach without any prior assumptions about the shape and strength of the dot confinement potential. The calculated zero field electron addition energies are in good agreement with experimental data for both mesa geometries. Few-electron charging diagrams in a magnetic field are also computed. Consistent with the experimental data, the charging curves for the rectangular mesa dot in a magnetic field are “flatter” and exhibit less features than for a circular mesa dot.

Fano interference in mesoscopic rings with quantum dots

AbstractWe propose a general formalism for describing the coexistence of coherent and resonant transport in hybrid mesoscopic structures. The approach is based on Landauer‐Büttiker formula for the electronic transmittance and on an old formula of Feshbach. The latter gives the complete Green function of coupled subsystems in terms of effective Green functions of the disconnected parts and provides informations about the individual contributions of each subsystem to transport. Motivated by the experiments of Kobayashi et al.(Phys. Rev. Lett. 88, 256806 (2002)) and Holleitner et al. (Phys. Rev. Lett. 87, 256802 (2001)) we apply the formalism to study transport in Aharonov‐Bohm interferometers (ABI) containing one or two coupled two‐dimensional quantum dots (QD). In the single dot case, we reproduce and explain the magnetic field control of the Fano interference and investigate the interaction effects in a self‐consistent approach. In the double dot case, we obtain the charging diagrams and establish precise criteria for the observation of mesoscopic Fano effect and AB oscillations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Variable electrostatic transformer: controllable coupling of two charge qubits.

We propose and investigate a novel method for the controlled coupling of two Josephson charge qubits by means of a variable electrostatic transformer. The value of the coupling capacitance is given by the discretized curvature of the lowest energy band of a Josephson junction, which can be positive, negative, or zero. We calculate the charging diagram of the two-qubit system that reflects the transition from positive to negative through vanishing coupling. We also discuss how to implement a phase gate making use of the controllable coupling.

Variable coupling in n-type silicon–germanium double quantum dots

We report low-temperature electron transport behavior of trench-isolated silicon–germanium (SiGe) double quantum dots. By sweeping the potentials on side gates, we find a hexagonal charging diagram in the conductance measurements. It is also found that the gates allow the parameters of individual tunnel barriers to be changed over a wide range. Charging effects may therefore be observed in different coupling regimes, for example, the two dots that comprise the double dot can be induced to merge together yielding a large single dot.

Single-electron tunneling effects in a metallic double dot device

We report on differential conductance measurements on a gold double-dot structure at 4.2 K. The two dots were connected in series by tunnel junctions formed by atomic force microscopy manipulation of nanodisks. The tunnel junctions were made strongly asymmetric. The characteristic honeycomb-shaped charging diagram separating different Coulomb blockade regions of well-defined occupancy of electrons was observed and the cells in the charging diagram were found to be skewed by the asymmetry of the tunnel junctions. In addition, a double-dot Coulomb staircase structure, with steps of varying width, was observed and was studied for varying gate voltage. The occupancy of electrons on the two dots was determined as a function of both drain source and gate voltages.

Simultaneous operation of two adjacent double dots in silicon

We have studied the electrical transport through two adjacent double dot structures realized in Si-on-insulator material. The small dimensions of dots and the distance between the centers of the dots, here 100 nm, allow for dc measurements at 4.2 K. We demonstrate that although the structures are entirely doped, we are able to operate both double dot structures simultaneously in the double dot regime. Clear Coulomb blockade characteristics with a Coulomb blockade region of 20 mV are observed in both structures. Using gates, the number of electrons on each individual dot can be manipulated simultaneously. From the measured charging diagrams the capacitances between the gates and the dots are determined.

Charge transfer during Crystal‐Graupel Collisions for two different cloud droplet size distributions

Laboratory experiments of graupel charging during ice crystal collisions reveal a charge sign dependence on temperature, liquid water concentration as well as the size distribution of the cloud droplets used for riming. The measurements were performed with an impact velocity of 8.5 m s−1, the ambient temperature was varied in the range −5 to −30°C and the effective water content up to 4 g m−3. Charge diagrams of the sign of the electric current on the graupel as a function of the ambient temperature (Ta) and the effective liquid water content (EW) for each of the two cloud droplet spectra used are presented. The results indicate that broadening the droplet spectrum leads to negative graupel charging and the implications of these findings to thunderstorm electrification are discussed.

Towards quantum cellular automata operation in silicon: transport properties of silicon multiple dot structures

The transport properties of two adjacent double dots, realized in silicon is studied by DC-measurements at a temperature of 4.2 K. From the measured charging diagrams the capacitances within the structure are estimated and using this information as input for a simple electrostatic model the energy scales for electron transitions between two dots are calculated. The change of energy in one pair introduced by an interdot electron transition in the other, the basic transition for the operation of quantum cellular automata, is shown to be less than the thermal energy under the present conditions. Adding an extra electron into the system causes larger energy changes in the double dots and for such transitions a clear correlation in electron transport for both double dots can be observed. The size of this effect complies with our model and the estimated capacitances and can therefore be used as a base for future cell design.

Single-electron charging in doped silicon double dots

We have fabricated and characterized a uniformly n-doped silicon double-dot structure. The electrical behaviour could be changed between that of a multiple tunnel junction and that of a double dot by applying appropriate gate voltages. The double-dot characteristics observed can be attributed to the geometry of the structure, and it is shown that the influence of the multiple tunnel junctions can be entirely eliminated. In the double-dot regime, characteristic charging diagrams were obtained by independently sweeping two sidegate voltages. Using a classical capacitance equivalent circuit the hexagonal lattice of the conductance resonances in the charging diagram was modelled and single-electron charging in the geometrical double dot is concluded from the match between model and experimental data.