Backward Voltage Research Articles

Correlation between in Situ Raman Scattering and Electrical Conductance for an Individual Double-Walled Carbon Nanotube

In situ Raman scattering is performed on an individual semiconducting double-walled carbon nanotube (DWNT) in a field-effect transistor (FET) geometry, while the transfer characteristics of the DWNT-FET are measured. Through studying the Raman spectra with response to forward and backward gate voltage (V(gs)) sweeping, respectively, we observe hysteresis loops in the curves of G(-) peak frequency and the intensity ratio of G(-) to G(+) (I(G(-))/I(G(+))) as a function of V(gs). These loops correlate very well with the hysteretic transfer characteristics of the device. The clear correlations suggest that G(-) peak line width and I(G(-))/I(G(+)) increase with the carrier concentration in the DWNT induced by V(gs). In addition, unique G(-) peak line width variations with V(gs) can be attributed to interband electron transitions between the energy bands of two concentric shells of the DWNT excited by G phonons.

Investigating DNA migration in pulsed fields using a miniaturized FIGE system

PFGE is a well-established technique for fractionation of DNA fragments ranging from kilobases to megabases in length. But many of these separations require an undesirable combination of long experiment times (often approaching tens of hours) and application of high voltages (often approaching tens of kV). Here, we present a simple miniaturized FIGE apparatus capable of separating DNA fragments up to 32.5 kb in length within 3 h using a modest applied potential of 20 V. The device is small enough to be imaged under a fluorescence microscope, permitting the migrating DNA bands to be observed during the course of the separation run. We use this capability to investigate how separation performance is affected by parameters including the ratio of forward and backward voltage, pulse time, and temperature. We also characterize the dependence of DNA mobility on fragment size N, and observe a scaling in the vicinity of N(-0.5) over the size range investigated. The high speed, low power consumption, and simple design of this system may help enable future studies of DNA migration in PFGE to be performed quickly and inexpensively.

Transient Hole Trapping in Individual GeSi Quantum Dot Grown on Si(001) Studied by Conductive Atomic Force Microscopy

Electrical properties of individual self-assembled GeSi quantum dots grown on Si substrates are investigated by using conductive atomic force microscopy at room temperature. By controlling the bias voltage sweep in a certain fast sweep rate range, a novel current peak is observed in the current–voltage characteristics of the quantum dots. The current peaks are detectable only during the backward voltage sweep immediately after a forward sweep. The current peak position and intensity are found to depend strongly on the voltage sweep conditions. This kind of current–voltage characteristic under fast sweep is very different from the ordinary steady state current behaviour of quantum dots measured previously. The origin of this phenomenon can be attributed to the transient hole trapping in the potential well formed by the quantum dot sandwiched between the native oxide layer and the bottom Si substrate.

Electronic characteristics of n-type nanocrystalline/p-type crystalline silicon heterostructure

A heterojunction of ultrathin phosphorus-doped hydrogenated nanocrystalline silicon with p-type crystalline silicon was fabricated to investigate carrier information and conduction behaviour. The temperature-dependent carrier information of holes and electrons as well as the two-dimensional electron gas were identified. The forward conduction can be ascribed to tunnelling-aided carrier emission recombination while the reverse transport can be divided into different mechanisms within different reverse bias ranges. The reverse current can be assigned to minority carrier tunnelling through the space charge region within the backward bias voltage from 0 to about −10 V. With decreasing negative applied voltage from −10 V to around −22 V, the reverse current can be attributed to the tunnelling-assisted Poole–Frenkel emission. With further reduction of the reverse bias voltage from −22 V to about −38 V under 100 K, the reverse current staircases can be allocated to sequential resonant tunnelling; otherwise it can be due to the thermic effect at higher temperature. The main origin of short transient time for the fabricated device can be due to the tunnelling mechanism.

Study of complex behavior in a time-delayed van der Pol’s electromagnetic system (Ⅱ)——Pattern dynamics in spatiotemporal chaos

Based on a simple infinite dimensional electromagnetic system consisting of a linear lossless transmission line in combination with a nonlinear boundary condition, the local map of backward voltage wave is established by using the traveling wave theory. The numerical simulation results show rich spatiotemporal nonlinear phenomena in the voltage wave on the lossless transmission line. The pattern dynamics in spatiotemporal chaos of the voltage wave on the lossless transmission line are qualitatively analyzed by depicting space-amplitude plot and space-time diagram. A good model with solution is established to study and understand the spatiotemporal chaos.

A new power flow method for radial distribution systems including voltage dependent load models

This paper presents a simple and efficient method to solve the power flow problem in radial distribution systems. The proposed method takes into account voltage dependency of static loads, and line charging capacitance. The method is based on the forward and backward voltage updating by using polynomial voltage equation for each branch and backward ladder equation (Kirchoff's Laws). Convergence ability and reliability of the method is compared with the Ratio-Flow method, which is based on classical forward–backward ladder method, for different loading conditions, R/ X ratios and different source voltage levels, under the wide range of exponents of loads. Results demonstrate that the proposed power flow algorithm has a robust convergence ability when compared with the improved version of the classical forward-backward ladder method, i.e., Ratio-Flow.

Current–voltage characteristics of aAg:Y Ba2Cu3O7−δ/Nb-dopedSrTiO3 bilayer structure

A Ag:Y Ba2Cu3O7−δ/SrNb0.01Ti0.99O3 bilayer structure was fabricated by pulsed-laser deposition. Current–voltage(I–V) dependence measurements of the bilayer were carried out in the temperature range5–250 K with variation of magnetic field from 0 to 50 kOe. Schottky junction behaviour wasobserved at temperatures higher than the critical temperature of superconductivity(Tc) due to the n-typesemiconductor SrNb0.01Ti0.99O3 and themetallic conductivity of Y Ba2Cu3O7−δ.At temperatures lower than Tc, the bilayer becomes a degenerate heterostructure p–n junction. TheI–V characteristic shows a sequence of current steps at forward voltage andan oscillation character at backward voltage. Energy diagrams of theAg:Y Ba2Cu3O7−δ/SrNb0.01Ti0.99O3 bilayer structure have been proposed to explain the peculiarI–V characteristics.

Fabrication of a novel vacuum microelectronic pressure sensor

By combining silicon dry corrosion, wet corrosion, oxidizing sharpening and vacuum bonding techniques, and the theoretic calculation of elastic membranes and the distance from the catelectrode to the anode, a novel vacuum microelectronic pressure senor with overload protection is developed. The density of the field emission catelectrode array is about 24,000/mm2. The starting emission voltage is 0.5 to 1.5 V; backward voltage is higher than 25 V. When the forward voltage is 5 V, pressure sensitivity is 30.1 mV/kPa. The temperature error is 0.5% between 20 and 122°C.

2.5-Dimensional Multi-Signal Large-Signal Analysis of Helix TWTs

A computer model (SUNRAY-3D) for the 2.5-dimensional multi-signal large-signal analysis of helix TWTs has been developed based on the approach developed earlier by the author for the one-dimensional large-signal modelling of helix and coupled-cavity TWTs. Some of the features of O'Malley's work for three-dimensional modelling of coupled-cavity TWTs were incorporated successfully for the modelling of helix TWTs. The present model is capable for the analysis of multiple input signals together with their higher order harmonics and inter-modulation products. The expressions for the circuit field and the induced current at a plane were derived from the electric field in a helical slow-wave structure instead of using the conventional equivalent circuit approach. The program analyses TWTs with arbitrary variations in the helix pitch and rf loss (including sever and tip loss) along the slow-wave structure. Induced backward voltage components and reflected voltage components due to mismatches at the terminations of the helix were included. The program has been shown to be accurate and self-consistent for drive powers from 60dB below saturation to well above saturation. The energy balance factor is satisfied to better than ±0.1% even at and above saturation. The CPU time to compute the performance of a typical TWT for a single drive power with 96 rings and 16 steps per wavelength is less than one minute on a DEC-ALPHA computer and is much less than 20 seconds on an IBM-P-IV.

Bifurcations and chaos in transmission lines

In this article we present some examples of bifurcations and chaotic phenomena theoretically observed in a simple electromagnetic system. The system consists of a linear lossless, or Heaviside distorsionless, transmission line connected to a linear resistor at one end (active branch) and to a nonlinear resistor at the other end (passive branch). The time dynamics of the backward voltage wave evaluated across the nonlinear resistor are described by a one-dimensional non linear mapping. A uniqueness theorem and the discussion of a problem with more than one solution complete the paper.

Single-Shunt Fault Diagnosis through Terminal Attenuation Measurement and Using Fibonacci Numbers

A method is proposed of single-shunt fault diagnosis in an N-section recurrent resistive ladder through terminal voltage attenuation measurement and using the Fibonacci number. The fault value is proportional to the forward and backward voltage attenuations in the ladder and some fixed Fibonacci numbers dependent on the number of sections of the ladder, thus making the evaluation very accurate. The fault location is then identified from the fault value and a single Fibonacci number, which is, in turn, related to the difference between the forward and a specified backward voltage attenuation. This unique nature of discrimination by this method, particularly of the fault section, allows a large tolerance in the attenuation measurement. Experimental results have been given along with pertinent discussions.

Piezoelectric Effects in Selenium Rectifiers

Piezoelectric effect and inverse piezoelectric effect of a selenium rectifier, which are induced by ac strain and ac voltage, respectively, are studied. The piezoelectric effect changes with backward bias voltage, but the inverse effect is rather independent of the bias voltage. These effects are ascribed to the piezoelectricity of selenium crystals and the ordering of polycrystals at a barrier layer of the rectifier. The piezoelectric effect is more useful for the detection of ac strain of high frequency than the piezoresistive effect of semiconductor diodes.

A p-n JUNCTION IN SILICON WHISKERS GROWN BY VLS METHODS

The preparation of a p-n junction in a Si whisker grown by VLS methods from gold-silicon alloys is described. The junction formed was identified by etching and by scanning electron microscopy. Characteristics of the junction were a backward breakdown voltage of about 19 V and a forward breakdown voltage of about 0.5 V.