Analysis of Energy Quantization Effects on Single-Electron Transistor Circuits

In this paper, the effects of energy quantization on different single-electron transistor (SET) circuits (logic inverter, current-biased circuits, and hybrid MOS-SET circuits) are analyzed through analytical modeling and Monte Carlo simulations. It is shown that energy quantization mainly increases the Coulomb blockade area and Coulomb blockade oscillation periodicity, and thus, affects the SET circuit performance. A new model for the noise margin of the SET inverter is proposed, which includes the energy quantization effects. Using the noise margin as a metric, the robustness of the SET inverter is studied against the effects of energy quantization. An analytical expression is developed, which explicitly defines the maximum energy quantization (termed as “ quantization threshold”) that an SET inverter can withstand before its noise margin falls below a specified tolerance level. The effects of energy quantization are further studied for the current-biased negative differential resistance (NDR) circuit and hybrid SETMOS circuit. A new model for the conductance of NDR characteristics is also formulated that explains the energy quantization effects.      

A novel SET/MOSFET hybrid static memory cell design

In this paper, a single electron transistor (SET)/metal-oxide-semiconductor field effect transistor (MOSFET)-based static memory cell is proposed. The negative differential conductance (NDC) characteristics of the SET block help us establish the static memory cell circuits more compactly than those in conventional technologies. The proposed memory cell consists of one MOSFET and two back-to-back connected SET blocks exhibiting the NDC. The peak-to-valley current ratio of the SET block is above four with C/sub G/=5.4C/sub T/ (C/sub T/=0.1 aF) at T=77K. The read and write operations of the proposed memory cell were validated with SET/MOSFET hybrid simulations at T=77 K. Even though the fabrication process that integrates MOSFET devices and SET blocks with NDC is not yet available, these results suggest that the proposed SET/MOSFET hybrid static memory cell is suitable for a high-density memory system.     

Generalized Surface-Area-Difference model for cohesive energy of nanoparticles with different compositions

The Surface-Area-Difference (SAD) model has been generalized to account for the cohesive energy of nanoparticles with different compositions (NDC) in different shape, where the particle shape is described by the shape factor. It is found that the cohesive energy of NDC depends on the particle size, the particle shape and the atomic percent of each composition, which can be simply regarded as mathematical mean values of the cohesive energies of all the compositions.     

Intercomparison exercise within a distributed-dosimetry network

The results of an intercomparison exercise within the US Navy dosimetric network (USN-DN) are presented and discussed. The USN-DN uses a commercially available LiF:Mg,Cu,P thermoluminescent dosemeter (TLD) model Harshaw 8840/8841 and TLD reader model Harshaw 8800 manufactured by Thermo Fisher Scientific. The USN-DN consists of a single calibration facility and 16 satellite dosimetry reading facilities throughout the world with ～ 40 model 8800 TLD readers and in excess of 350 000 TLD cards in circulation. The Naval Dosimetry Center (NDC) is the primary calibration site responsible for the distribution and calibration of all TLD cards and their associated holders. In turn, each satellite facility is assigned a subpopulation of cards, which are utilised for servicing their local customers. Consistency of the NDC calibration of 150 dosemeters (calibrated at NDC) and 27 locally calibrated remote readers was evaluated in the framework of this intercomparison. Accuracy of TLDs' calibration, performed at the NDC, was found to be <3 % throughout the entire network. Accuracy of the readers' calibration, performed with the NDC issued calibration dosemeters at remote sites, was found to be better than 4 % for most readers. The worst performance was found for reader Channel 3, which is calibrated using the thinnest chip of the Harshaw 8840/8841 dosemeter. The loss of sensitivity of this chip may be caused by time-temperature profile that has been designed for all four chips without consideration of chip thickness.     

Realization of multiple valued logic and memory by hybrid SETMOS architecture

A novel complimentary metal-oxide-semiconductor (CMOS) single-electron transistor (SET) hybrid architecture, named SETMOS, is proposed, which offers Coulomb blockade oscillations and quasi-periodic negative differential resistance effects at much higher current level than the traditional SETs. The Coulomb blockade oscillation characteristics are exploited to realize the multiple valued (MV) literal gate and the periodic negative differential resistance behavior is utilized to implement capacitor-less multiple valued static random access memory (MV SRAM) cell. The SETMOS literal gate is then used to build up other MV logic building blocks, e.g., transmission gate, binary to MV logic encoder, and MV to binary logic decoder. Analytical SET model simulations are employed to verify the functionalities of the proposed MV logic and memory cells for quaternary logic systems. SETMOS MV architectures are found to be much faster and less temperature-sensitive than previously reported hybrid CMOS-SET based MV circuits.     

Sb-mediated Ge quantum dots in Ti–oxide–Si diode: negative differential capacitance

Abstract

The negative differential capacitance (NDC) effect is observed on a titanium–oxide–silicon structure, formed on n-type silicon with embedded germanium quantum dots (QDs). The Ge QDs were grown by an Sb-mediated technique. The NDC effect was observed for temperatures below 200 K. We found that approximately six to eight electrons can be trapped in the valence band states of Ge QDs. We explain the NDC effect in terms of the emission of electrons from valence band states in the very narrow QD layer under reverse bias.     

Comparison of two contact models in the simulation of friction stir welding process

Two contact models are used to simulate the thermo-mechanical interaction process in friction stir welding. Comparison shows that the classical Coulomb friction model can be accurate enough for the simulation of friction stir welding in lower angular velocity. But in higher angular velocity, the classical Coulomb friction model fails to work due to the increase of the dynamic effect of the welding tool. Because the shear failure of material is considered in modified Coulomb friction model, the increase of the frictional stress on the tool–plate interface is limited by the shear failure. So, this model can keep valid even when the angular velocity of the welding tool is increased to a high level.     

Positive and negative Coulomb drag in vertically integrated one-dimensional quantum wires

Electron interactions in and between wires become increasingly complex and important as circuits are scaled to nanometre sizes, or use reduced-dimensional conductors such as carbon nanotubes, nanowires and gated high-mobility two-dimensional electron systems. This is because the screening of the long-range Coulomb potential of individual carriers is weakened in these systems, which can lead to phenomena such as Coulomb drag, where a current in one wire induces a voltage in a second wire through Coulomb interactions alone. Previous experiments have demonstrated Coulomb electron drag in wires separated by a soft electrostatic barrier of width ?80?nm (ref.?12), which was interpreted as resulting entirely from momentum transfer. Here, we measure both positive and negative drag between adjacent vertical quantum wires that are separated by ～15?nm and have independent contacts, which allows their electron densities to be tuned independently. We map out the drag signal versus the number of electron sub-bands occupied in each wire, and interpret the results both in terms of momentum-transfer and charge-fluctuation induced transport models. For wires of significantly different sub-band occupancies, the positive drag effect can be as large as 25%.     

Effect of negative differential conductance in carbon nanotubes

Measurements of transport at high electric fields in metallic single-walled carbon nanotubes (CNTs) have shown either saturation of the current or a region of negative differential conductance (NDC) characterized by the current, after reaching a maximum, decreasing with further increase in voltage. We point out that both types of behavior are characteristic of NDC, but the NDC is masked in samples showing current saturation due to generation of space charge, leading to a nonuniform electric field. We derive the relation between the carrier concentration, the electric field at which the drift velocity peaks, and the length of the sample that is required for the NDC to be manifest as saturation.     

Negative differential conductance of quasi-one-dimensional contacts

The negative differential conductance (NDC) with an S-shaped static current-voltage characteristic is investigated in quasi-one-dimensional microcontacts. It is shown that NDC can be caused by the space charge of the carriers in a channel with narrowings. Pis’ma Zh. Tekh. Fiz. 24, 40–44 (June 12, 1998)     

Imaging a single-electron quantum dot

Images of a single-electron quantum dot were obtained in the Coulomb blockade regime at liquid He temperatures using a cooled scanning probe microscope (SPM). The charged SPM tip shifts the lowest energy level in the dot and creates a ring in the image corresponding to a peak in the Coulomb-blockade conductance. Fits to the line shape of the ring determine the tip-induced shift of the energy of the electron state in the dot. SPM manipulation of electrons in quantum dots promises to be useful in understanding, building, and manipulating circuits for quantum information processing.     

Room-temperature Coulomb staircase in semiconducting InP nanowires modulated with light illumination

Detailed electron transport analysis is performed for an ensemble of conical indium phosphide nanowires bridging two hydrogenated n(+)-silicon electrodes. The current-voltage (I-V) characteristics exhibit a Coulomb staircase in the dark with a period of ～ 1 V at room temperature. The staircase is found to disappear under light illumination. This observation can be explained by assuming the presence of a tiny Coulomb island, and its existence is possible due to the large surface depletion region created within contributing nanowires. Electrons tunnel in and out of the Coulomb island, resulting in the Coulomb staircase I-V. Applying light illumination raises the electron quasi-Fermi level and the tunneling barriers are buried, causing the Coulomb staircase to disappear.     

Carbonization and oxidation of metal–organic frameworks based on 1,4-naphthalene dicarboxylates

Three new isostructural metal–organic frameworks (MOFs), [V(OH)(NDC)] (1), [Cr(OH)(NDC)] (2), and [Ga(OH)(NDC)] (3) have been synthesized hydrothermally using 1,4-naphthalene dicarboxylate (NDC) as the linker. These MOFs (1, 2 and 3) have been used as a template for the synthesis of metal-oxide-inserted nanoporous carbon materials. The newly synthesized MOFs and the resulting porous carbon hybrid functional materials have been characterized using powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopic analysis. Results show that compounds 2 and 3 form their respective metal oxide nanoparticles on the surface of the carbon materials during carbonization at 800 °C. The gas sorption properties of the new MOFs and their corresponding carbon frameworks have been reported.     

A new generic timed Petri net model for design and performance analysis of a dual kanban FMS

A new generic black token timed Petri net (PN) model of FMS based on the process plan is presented. The model allows modelling the FMS configuration, determining the optimal work in process, the number of kanban cards and the required capacity for a given maximum production rate. The lead-time and utilization of each station can be determined. Each station can have multiple identical servers. The approach is based on modelling the FMS as an event graph with part circuits, kanban circuits and sequencing circuits. The part circuits contain tokens that represent parts with attached kanban cards. In the kanban circuits there will be places containing tokens that represent kanban Move Cards (MC) and Production Cards (PC). Circuits called sequencing circuits will model the sequencing of the parts on each station. The tokens in these sequencing circuits represent the number of identical servers. The optimal solution of the model is obtained in three steps. The first step is the initial marking of the PN. The second step involves determination of the invariants of the PN. The third is solving a linear programming model.     

An Innovation‐Based Fluid Mechanics Design and Fabrication Laboratory

As part of a four‐week fluid mechanics laboratory, Mechanical Engineering students were challenged to design and manufacture the least restrictive flow nozzle for a standard test condition within several design constraints. The Nozzle Design Challenge (NDC) combined analysis, design, manufacturing, and experimentation. The positive student responses to the NDC were overwhelming. Formal evaluation of the NDC included the measured nozzle flow rates and the amount of time spent in the laboratory. The highest flow rate nozzle allowed substantially more flow than the nozzle with a 1‐inch diameter hole used for demonstration. Every group spent more time in the laboratory than was scheduled, which may indicate high levels of motivation for the project. The examination scores covering the principles learned in this laboratory were compared to the previous semester's students who did not perform the innovation‐based design and fabrication project. After blocking out the effects of GPA, the results indicate that the students who undertook the design experience performed significantly better on the examination.     

Superconducting and Insulating Behavior in One-Dimensional Josephson Junction Arrays

Experiments on one-dimensional small capacitance JosephsonJunction arrays are described. The arrays have a junctioncapacitance that is much larger than the stray capacitance ofthe electrodes, which we argue is important for observation ofCoulomb blockade. The Josephson energy can be tuned in situand an evolution from Josephson-like to Coulomb blockadebehavior is observed. This evolution can be described as asuperconducting to insulating, quantum phase transition. Inthe Coulomb blockade state, hysteretic current-voltagecharacteristics are described by a dynamic model which is dualto the resistively shunted junction model of classicalJosephson junctions.     

Non-linear characteristics of lipid monolayers in relation to the ability to self-organize

It is known that electrostatic interactions strongly influence the growth of condensed phase domains at the main phase transition of lipid membranes. It is demonstrated in this paper that the inclusion of electrostatic interactions into the pressure-area-temperature equation of state provides a much better fit to the observed equilibrium behaviour than the classical van der Waals form. Both of these equations of state predict a region of negative differential compressibility (NDC), which is not described on long time scales because of a competing first-order phase transition. It is shown in this paper that dynamic NDC can account for most of the features of the observed oscillatory behaviour of monolayers at the oil-water interface. Such behaviour may be related to self-organization of spatiotemporal structures in living organisms.     

Single molecular orientation switching of an endohedral metallofullerene

The single molecular orientation switching of the Tb@C82 endohedral metallofullerene has been studied by using low-temperature ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). An octanethiol self-assembled monolayer (SAM) was introduced between Tb@C82 and the Au111 substrate to control the thermal rotational states of Tb@C82. Scanning tunneling spectroscopy (STS) of Tb@C82 on an octanethiol SAM at 13 K demonstrated hysteresis including negative differential conductance (NDC). This observed hysteresis and NDC is interpreted in terms of a switching of the Tb@C82 molecular orientation caused by the interaction between its electric dipole moment and an external electric field.     

Tunneling into 1D and Quasi-1D Conductors and Luttinger-Liquid Behavior

The paper addresses the problem whether and how it is possible to detect the Luttinger-liquid behavior from the IV curves for tunneling to 1D or quasi-1D conductors. The power-law non-ohmic IV curve, which is usually considered as a manifestation of the Luttinger-liquid behavior, can be also deduced from the theory of the Coulomb blockaded junction between 3D conductors affected by the environment effect. In both approaches the power-law exponents are determined by the ratio of the impedance of an effective electric circuit to the quantum resistance. Though two approaches predict different power-law exponents (because of a different choice of effective circuits), the difference becomes negligible for a large number of conductance channels.     

Two-band mechanism of superconductivity in dimeric hubbard models

In the two-chain Hubbard model the on-site Coulomb repulsion generates a remarkably large pair-transfer coupling constant between bonding and antibonding orbitals of a dimer made of the two sites lying on the opposite chains and linked by a transfer energy. It leads to a pair-transfer interaction between two bands composed of these orbitals, promoting superconductivity (SC). Since it is found to be as large as intraband Coulomb coupling constants, our previous work suggests that SC can occur in this model. In fact we have obtained a clear indication of SC in restricted-size systems carrying out the exact-diagonalization with 6 electrons and a variational diagonalization with up to 14. The SC occurs in suitable band situations for a wide range of on-site Coulomb energies. We also obtained such an SC indication in a two-dimensional Hubbard model. We mention some candidate materials substantiating the present mechanism and suggest it to be quite general.