Dot Contact Research Articles

Conductance of correlated many-fermion systems from charge fluctuations

We put forward a relation between the static charge fluctuations and the conductance of correlated many-fermion systems at zero temperature, avoiding the use of time-dependent fluctuations as in the fluctuation-dissipation theorem. Static charge fluctuations can efficiently be computed for low-dimensional systems using tensor network approaches, while the conductance is often significantly more difficult to obtain, requiring a challenging low-frequency linear response computation or an explicit time evolution. We put this relation to the test for quantum dot and quantum point contact setups, where in limiting cases exact results are known. Our study includes systems in which the one-dimensional reservoirs are interacting.

The electron transfer properties of an open double quantum dot based on a quantum point contact

We theoretically study the electron transfer properties of a double quantum dot system in dissipative and pure dephasing environments based on a quantum dot contact detector. Theoretical results show that in the dissipative environment, the decoherence caused by the detector would increase the stable value of the average current and Fano factor as functions of time. Meanwhile, we find the existence of the quantum Zeno effect during the process of dynamical evolution. In the case of symmetric DQD, the relaxation caused by the dissipative environment would decrease the amplitude of the average current with time evolution and increase the value of the Fano factor in the long time limit. In the case of asymmetric DQD, the relaxation reduces the peak value of Fano factor over time. In the pure dephasing environment, we find that the frequent measurement would hinder the switch between different current channels during the cotunneling process. This results in a high value of Fano factor. In the case of symmetric DQD, increasing the pure dephasing rate would improve the value of Fano factor. In the case of asymmetric DQD, the dynamical evolution with time is not sensitive to the pure dephasing rate. In addition, it is indicated that the transfer probability of electron in the detector is only affected by the coupling between QPC and DQD. The environments have no effect on the transfer of a single electron in the detector. Our theoretical results provide theoretical references for experimental researchers to study the electron transport properties.

Review of Theory of Mesocopic Systems

In the framework of this work an overview of the theory of mesoscopic systems is made. The main effects of mesoscopic systems are noted. It is determined that the macroscopic characteristics of the system are significantly fluctuating within the mesoscopic level. The basic indicators of coherence of the quantum phase are determined and the mechanisms of influence are outlined. Six effects of mesoscopic systems are characterized with detailed justification. The theory of mesoscopic systems is based on the following mesoscopic effects: the Aaronov-Bohm effect; the effect of the integral quantum output; fractional quantum Hall effect; universal fluctuations of conduction; quantum conductivity quantum dot contact; DC currents in mesoscopic rings.Prospects for further developments in this area of research are based on a detailed study of mesoscopic effects based on the growing tendency for the production and research of materials containing the smallest structures and have low-dimensional features, which leads to the mesoscopic regime.

Breaking the electrical barrier between copper and carbon nanotubes.

Improving the interface between copper and carbon nanotubes (CNTs) offers a straightforward strategy for the effective manufacturing and utilisation of Cu-CNT composite material that could be used in various industries including microelectronics, aerospace and transportation. Motivated by a combination of structural and electrical measurements on Cu-M-CNT bimetal systems (M = Ni, Cr) we show, using first principles calculations, that the conductance of this composite can exceed that of a pure Cu-CNT system and that the current density can even reach 1011 A cm-2. The results show that the proper choice of alloying element (M) and type of contact facilitate the fabrication of ultra-conductive Cu-M-CNT systems by creating a favourable interface geometry, increasing the interface electronic density of states and reducing the contact resistance. In particular, a small concentration of Ni between the Cu matrix and the CNT using either an "end contact" and or a "dot contact" can significantly improve the electrical performance of the composite. Furthermore the predicted conductance of Ni-doped Cu-CNT "carpets" exceeds that of an undoped system by ∼200%. Cr is shown to improve CNT integration and composite conductance over a wide temperature range while Al, at low voltages, can enhance the conductance beyond that of Cr.

Investigation on cornering brake stability of a heavy-duty vehicle based on a nonlinear three-directional coupled model

A nonlinear three-directional coupled lumped parameters (TCLP) model is proposed for a heavy-duty vehicle to investigate the longitudinal, lateral and vertical dynamics of vehicles simultaneously. The nonlinear property of suspension damping is described by a fitted exponent model from experimental data. The nonlinear tire forces in different directions are modeled by the nonlinear Gim model and the vertical single dot contact model with square nonlinearity. The system responses are calculated by numerical integration and compared with the Functional Virtual Prototyping (FVP) model and the test data, so as to verify the validity of this new vehicle model. With Lateral-Load Transfer Ratio (LTR) and yaw rate as evaluation indexes, the influences of system parameters on cornering brake stability are analyzed. The critical vehicle speed table is also obtained. The study shows that high vehicle running speed, large front wheel steering angle, large tire cornering stiffness or small braking moment is harmful to yaw stability and roll stability. Road surface frictional coefficient mainly influences yaw stability, and vertical tire stiffness and road surface roughness mainly influence roll stability.

Control of surface wettability for inkjet printing by combining hydrophobic coating and plasma treatment

We have obtained a wide range of surface wettabilities of PI substrate for inkjet printing by combining hydrophobic solution coating and O2 or Ar plasma treatments. Experiments were conducted to investigate the variation in inkjet-printed dot diameters with different surface treatments. The change in chemical and physical characteristics of treated surfaces was evaluated using static contact angle measurements, field emission scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Only hydrophobic coated surface produces the smallest dot diameter and the largest contact angle. Dot diameter increases and contact angle decreases as the plasma treatment time increases. Since the removal of hydrophobic layer from the surface occurs due to the etching effect of O2 and Ar plasma during the plasma treatments, F/C ratio decreases with increasing the plasma treatment time. Surface roughness variations are also observed after plasma treatments. The ranges of printed dot sizes for O2 and Ar plasma treatments are 38μm–70μm and 38μm–92μm, respectively. Ar plasma treatment shows a wider range of surface wettability because of higher removal rate of the hydrophobic layer. This combination of hydrophobic coating and plasma treatment can offer an effective way to obtain a wide range of surface wettabilities for high quality inkjet-printed patterns.

Electrostatic effects in coupled quantum dot-point contact-single electron transistor devices

We study the operation of a system where quantum dot (QD) and point contact (PC) defined in a two-dimensional electron gas of a high-mobility GaAs/AlGaAs heterostructure are capacitively coupled to each other and to metallic single electron transistor (SET). The charge state of the quantum dot can be probed by the point contact or single electron transistor. These can be used for sensitive detection of terahertz radiation. In this work, we explore an electrostatic model of the system. From the model, we determine the sensitivity of the point contact and the single electron transistor to the charge excitation of the quantum dot. Nearly periodic oscillations of the point contact conductance are observed in the vicinity of pinch-off voltage. They can be attributed to Coulomb blockade effect in a quasi-1D channel because of unintentional formation of small quantum dot. The latter can be a result of fluctuations in GaAs quantum well thickness.

Improvement of the Quality of Digital Printing Using Conditional Halftoning Function

Printed images usually suffer to halftone dot contacts and thus lose their tone details where that contact takes place. Dot contacts should be avoided by means of certain technical approaches as early as image processing stages. This paper begins with the mathematical analysis of the mechanism of dot contact regarding different dot shapes of round, square and diamond. Then experiments were carried out to verify theoretical results derived through outputting single-color chips (20 mm×20 mm) using HP indigo 3550 press with paralyzing its dot gain compensation function. Chips under research were designed with dot area percentages varying from 25% to 80%, and two levels of resolution (600 and 1200 dpi) were used respectively for each dot area percentage. The theoretical analysis showed that dot contacts happened in case of dot area percentage 78.5% for the round dots, 50% for the square dots, 35% (first contact) and 65% (second contact) for the diamond dots, respectively. Jumps in dot density were employed to determine whether the dot contact happened or not. It was observed that halftone dot contacts occurred at the dot area percentage 71% for the round dots, 47% for the square dots, 34% (first contact) and 62% (second contact) for the diamond dots, all lower than their corresponding theoretical values. A conditional halftoning function was designed on the basis of experimental results, which was programmed using the PostScript language. The averaged density difference tested at the 34% of dot area percentage was 0.026, 47% was 0.025, 62% was 0.034 and 71% was 0.041, where the normal halftoning technology was used. In contrast, the averaged density difference was reduced to 0.005 at the 34%, 0.012 at the 47%, 0.016 at the 62% and 0.019 at the 71%, in the case of using conditional halftoning function. These results indicate that the conditional halftoning function is useful for diminishing halftone dot contacts. This study provides a promising halftoning method to improve the quality of digital printing that is subject to the negative effect of halftone dot contacts.

Chaotic Behavior in the Magneto-Resistance of Quantum Dot and Quantum Point Contact

We have investigated quantum structures, such as narrow wires, single or coupled quantum dots (QDs), and quantum point contact (QPC), in order to clarify the origin of the chaotic and fractal behavior in their transport properties. Chaotic behavior in the electrical transport in QD and QPC has been studied in the low temperature magneto-resistance (MR), and by use of scanning gate microscopy (SGM). The quantum structures are fabricated using hetero-junction semiconductors. The low temperature MR has been measured using a 3He cryostat or dilution refrigerator with magnetic fields up to 8 T. We discuss the relation between the narrow constrictions in these structures and chaotic scatterings observed in the MR and SGM.

Spin-Polarized Light-Emitting Diodes with Mn-Doped InAs Quantum Dot Nanomagnets as a Spin Aligner

We have fabricated and characterized surface-emitting, spin-polarized light-emitting diodes with a Mn-doped InAs dilute magnetic quantum dot spin-injector and contact region grown by low-temperature molecular beam epitaxy, and an In(0.4)Ga(0.6)As quantum dot active region. Energy-dispersive X-ray and electron energy loss spectroscopies performed on individual dots indicate that the Mn atoms incorporate within the dots themselves. Circularly polarized light is observed up to 160 K with a maximum degree of circular polarization of 5.8% measured at 28 K, indicating high-temperature spin injection and device operation.

Electrostatic cross-talk between quantum dot and quantum point contact charge read-out in few-electron quantum dot circuits

We investigate by numerical simulation the effect of electrostatic coupling between a quantum point contact (QPC) detector of various geometries and a planar double quantum dot in a few-electron quantum dot circuit. Our simulation is based on solving coupled Kohn-Sham and Poisson equations self-consistently by the finite element method. We use the Slater formula to determine the first electron charging bias point of the plunger gate, and give the corresponding variation of the QPC conductance as a function of the QPC gate bias at that particular point, which we interpret as the detector sensitivity. For all QPC designs, we show that the charging bias point of the plunger gate decreases with increasing QPC gate bias. This effect is enhanced for designs wherein large QPC detection sensitivity is found.

Account of Thermal Flow Through Metal-Semimetal BiSb Contact Boundary for Determination of EHF Detector Volt-Watt Sensitivity

Bismuth, antimony and its alloys are the typical representatives of a class of semimetals, which electric conductance is lower in 102-103 times, than of usual well conducting an electrical current metals. The alloys bismuth with antimony have semi-conductor properties in wide area of compositions at temperatures below 77 °K. The semimetals are rather perspective materials from the point of view of their probable application in various devices [1,2,3].In present time the semimetal alloys BiSb have wide application in thermoelectric generators and refrigerators. In work [3] the opportunity of use of semimetals BiSb with percentage content of Bi and Sb from 8 % up to 25 % was shown as high-sensitivity and of small inertion indicators of the mm range radiation where thermoelectric effect is used. The principle of action of such indicators is based on occurrence of temperature gradient in a semimetal crystal BiSb that has two contacts of the various area with flowing electrical current. Basic element of such device is the dot contact metal - semimetal. One of the main characteristics is volt-watt sensitivity of metal-semimetal BiSb contact which calculating is shown in present work.

XtalView/Xfit—A Versatile Program for Manipulating Atomic Coordinates and Electron Density

Xfit is a model-building and map viewing program in XtalView that is used by the structural biology community including researchers in the fields of crystallography, molecular modeling, and electron microscopy. Among its distinguishing features are built-in fast Fourier transforms that allow users flexibility in map calculations including the creation of OMIT maps and the updating of structure factors to reflect model changes from within the program. Written in C and using the freely available XView toolkit, it is highly portable to almost any X-windows based workstation including Intel-based LINUX systems. Its user interface is designed to aid in facile model-building and contains a semiautomated fitting system that allows the user to interactively and rapidly build chainde novointo an electron density map. The program is highly optimized to allow such features as interactive contour levels and map calculations to be completed within a few seconds. Features in the latest version including phase-combination, solvent-flattening, automated water addition, and small-probe dot contact surfaces, as well as basic design features, are discussed.

Formulation of Power Loss Equation for an Emitter with Dot Contacts and Proposal of an Improved Emitter Structure in Silicon Solar Cells

A new two-dimensional emitter power-loss equation was formulated for a cell with a dot contact and verified numerically. Based on this formulation, the current crowding that occurs in two-dimensional geometry was evaluated. We propose a solar cell structure with line-shaped heavily diffused emitters under the dot contacts. The effectiveness of the proposed emitter geometry was verified by both calculation and measurement, and the formulation was found to be valid.

Formation of ohmic contacts to p-ZnTe

Formation and temperature stability of sputter deposited gold ohmic contacts to molecular beam epitaxially grown p-type ZnTe (doped with nitrogen to a free hole concentration of ≈3 × 1018 cm3) have been studied using current-voltage (I-V), Auger electron spectroscopy, secondary ion mass spectrometry, and optical and scanning electron microscopy. The I-V characteristics of ≈1500A Au/p-ZnTe contacts were measured as-deposited and after heat treatments at 150, 200, 250, and 350°C for 15 min intervals up to 90 min. As deposited, the contacts were poor Schottky contacts, but became ohmic after 15 min at all temperatures. There was an increased resistance at t>15 min for T≤250°C, and a very large resistance increase upon heat treatment for all times at 350°C. The interface between the metallization and ZnTe was initially very planar, and remained planar upon formation of the ohmic contact. Upon heating at T>250°C, Au diffused into ZnTe. The ohmic behavior of the Au/p-ZnTe contacts is attributed to this diffusion which created a highly doped near-surface region in the ZnTe. Microscopy showed that Au also migrated across the ZnTe surface forming an extended reaction zone (≈100 μm) around the dot contact at T≥250°C.