Extra Plane Research Articles

Stable p-Type Conduction from Sb-Decorated Head-to-Head Basal Plane Inversion Domain Boundaries in ZnO Nanowires

We report that Sb-decorated head-to-head (H-H) basal plane inversion domain boundaries (b-IDBs) lead to stable p-type conduction in Sb-doped ZnO nanowires (NWs) due to Sb and O codoping. Aberration-corrected Z-contrast scanning transmission electron microscopy shows that all of the Sb in the NWs is incorporated into H-H b-IDBs just under the (0001) NW growth surfaces and the (0001) bottom facets of interior voids. Density functional theory calculations show that the extra basal plane of O per H-H b-IDB makes them electron acceptors. NWs containing these defects exhibited stable p-type behavior in a single NW FET over 18 months. This new mechanism for p-type conduction in ZnO offers the potential of ZnO NW based p-n homojunction devices.

Repeatable switching of the bending direction of ZnO nanoneedles by ion beams

We studied the ion beam bending of ZnO nanoneedles to find the dependence of their bending direction on the ion beam energy and to clarify the bending mechanism. Through gallium focused ion beam (FIB) bending, the stems of the nanoneedles were found to be bent to the direction of the ion beam source for ion beam energies of 30 keV whereas they were bent in the opposite direction at ion energies lower than 20 keV. We found for the first time that the bending direction of ZnO nanoneedles could be changed by repeated switching of the ion beam energy between lower and higher energy levels, and that the thin tip parts of the nanoneedles were bent toward to the ion beam source like the higher energy bending mode during the process of lower energy bending below 20 keV. Through high resolution transmission electron microscopy (HRTEM) observations of the microstructure of a nanoneedle, bent by 30 keV higher energy ion beams, based on the atomic scale, we found that more edge dislocations were created in the rear side, deeper than the central plane of the nanoneedle, than the front side and that each edge dislocation added an extra lattice plane in this region. These observations clearly showed that the bent nanoneedles were plastically deformed by the edge dislocations created by the ion beams.

Convex Piecewise-Linear Modeling Method for Circuit Optimization via Geometric Programming

This paper presents a new method for fitting a convex piecewise-linear function to a given set of data, which can serve as an empirical modeling framework for circuit optimization via geometric programming. The method iteratively solves a series of linear optimization problems to minimize the fitting error. To reduce the fitting error in each iteration, an extra plane is added in the region where the largest error occurs. For verification, we apply the method to create transistor-level models in 90-nm complementary metal-oxide-semiconductor technology. Numerical results indicate that the proposed method can generate process-dependent transistor-level models with reasonable modeling accuracy.

Numerical reconstruction and twin-image suppression using an off-axis Fresnel digital hologram

In this work we proposed a novel approach for the numerical reconstruction of digital holography that uses only an off-axis Fresnel digital hologram and can easily be carrying out in a personal computer. From the presented off-axis holographic principle, the reference wave accompanies to the numerically reconstructed image, also makes the separation to the zero-order and twin images. Therefore, the concept can be applied to suppress the blurring of numerical reconstruction by adding the extra reconstruction plane and the formularized numerically reference wave in the reconstruction procedure. As expected, the blurring images can be separated out and removed from the reconstructed image. Then, by performing the back propagating to the exact reconstruction plane, one can obtain the pure object image without the blurring. In contrast to the temporal phase-shifting digital holographic-based scheme that employs multiple exposures the technique can be more effectively and easily overcome the blurring problem, also provide the practical feasibility in the digital holographic application.

Core-level Interaction between Edge/Screw Dislocation and Misfit Dislocation: A Molecular Dynamics Study

We have investigated the interaction between dislocation cores of misfit dislocation on a semi-coherent interface and edge/screw dislocations gliding in a mono-lattice, by using molecular dynamics simulations. Edge dislocations, of which extra plane lies on the same side of that of misfit dislocation (same sign), bring about new dislocations from orthogonal line of misfit dislocation network to the cross-slip plane, keeping its Burgers vectors. Edge dislocations with opposite sign react with misfit dislocations, resulting in a new dislocation on the conjugate slip plane (parallel collision) or dislocation locks at the cross-sectional points (cross collision). Screw dislocations bounce at the interface by cross slip if they bump into misfit dislocation in parallel. On the other hand, a zig-zag dislocation is formed on the interface by crisscross cutting, due to the coincidence of Burgers vectors of screw and misfit (edge) dislocations. Then the zig-zag line is straightened with the line tension.

The termination of the α-Al 2O 3 (0001) surface: a LEED crystallography determination

We have performed a tensor low-energy electron diffraction (TLEED) determination of 10 diffracted beams at off-normal incidence from the (0001) surface of α-Al 2O 3 produced by oxygen plasma cleaning/annealing cycles. Structures with single domain O- or Al-terminated surface layers give a poor agreement (Pendry R-factor=0.42). Such domains are related by steps in the (11 2 ̄ 0) direction that produce an extra plane of symmetry in the LEED pattern. Allowing a mixture of domains due to steps produces a good agreement. An optimized mixture of 2:1 O/Al-terminated domains lowers the R-factor to 0.26 with an inner potential of 19.2 eV. At the R-factor minimum, we find that in both domains, the outermost atomic layer relaxes outward, with some twisting and relief of buckling in deeper layers. An outward relaxation of the top layer is in disagreement with theoretical predictions. However, such predictions are for vacuum-cleaved surfaces that are not realistic descriptions of the surface used in our experiment.

Radiation of electromagnetic waves from edge dislocations moving in ionic crystal

The emission of electromagnetic waves by a straight edge dislocation moving in ionic crystals with a NaCl-type lattice has been investigated theoretically. It is shown that the motion of a dislocation in the ionic lattice results in the appearance of a specific alternative polarization current, generated by uncompensated valence bonds along the edge of the extra plane of a dislocation. For a dislocation moving with a constant average velocity V, the frequency of this current is of the order of ω ~ 2πV/b, where b is Burgers vector. The fax of electromagnetic energy in the far field and the radiation friction force acting per unit length of the dislocation line are calculated. The emission of electromagnetic waves by an edge dislocation oscillating in the glide plane as well as by dislocation moving with a constant average acceleration is studied.

The H-FeCo interaction in BCC structure: an ASED-MO approach

The semiempirical atom superposition and electron delocalization molecular orbital (ASED-MO) theory was used to study the H-FeCo interaction. Calculations were carried out using clusters of the type Fe 45Co 16 and Fe 39Co 14 for normal and dislocated structures respectively, simulating both the adsorption and absorption of a hydrogen atom on/in the (100) face and in the (100) dislocation. The results indicate that in general the H-FeCo interaction is stronger for the dislocated structure. The available volume for the atomic H is greater as a consequence of the extra plane of atoms. The relative stability of this configuration was also compared for clusters representing normal and dislocated FeCo structures and with Co vacancies.

Substrate Engineering With Plastic Buffer Layers

The advantage that epitaxy offers the electronics and optoelectronics industries is that it allows the possibility of producing precisely controlled layers of very high crystal quality. Heteroepitaxy of different materials offers the promise of tailoring device layers in clever ways that nature did not intend. However unlike fruit juices, nature has made it difficult to epitaxially combine different materials. As the preceding articles have clearly pointed out, it is very difficult to obtain smooth epitaxial layers that are free both of defects and strain when there is a lattice mismatch between the layers and their substrates.As already discussed in this issue, a uniform network of dislocations at the interface between a flat, uniform epitaxial layer and its substrate can completely relieve strain in the majority of the epitaxial layer. This would be a satisfactory situation for many devices so long as the active region of the device could be kept away from the interface. The problem is how to introduce the dislocations in an appropriate way. When an epitaxial layer has a larger lattice parameter than the underlying substrate, a misfit dislocation running along the interface represents a plane of atoms that has been removed from the epitaxial layer. (One would insert a plane of atoms if the epitaxial lattice parameter was smaller. For simplicity however we will continue to assume that the epitaxial layer has a larger lattice parameter.) It is not possible for a whole half plane of atoms, bounded by the dislocation at the interface and the substrate edges along the two sides, to be removed at once. The boundary between where the extra plane of atoms has been removed and where the epitaxial layer has not relaxed yet will represent a threading dislocation. This threading dislocation would continue to move as the size of the misfit dislocation along the interface grows. Ideally it moves all the way out to the substrate edge and vanishes there while the misfit dislocation along the interface would end up extending from one side of the substrate to the other. However other dislocations and other kinds of defects can effectively pin the threading dislocation resulting in an epitaxial layer with many threading dislocations. Unfortunately these threading dislocations are generally detrimental to most kinds of devices. It is precisely this high density of threading dislocations that limits applications of many heteroepitaxial layers.

0.32 μm gate length InP-channel MODFETS with f t above 90 GHz

The fabrication and characterisation of high performance InAlAs/InP modulation-doped field-effect transistors (MODFETs) with 0.32 mu m gate lengths are reported. Devices have been fabricated on two different delta-doped heterostructures with one having an extra delta-doping plane just below the cap layer. The extra doping resulted in devices with lower source and drain parasitic resistances. Extrinsic DC transconductances g/sub m/as high as 805 mS/mm and unity current-gain cutoff frequency f/sub t/ as high as 92 GHz obtained for these devices at a drain-to-source voltage V/sub ds/ of 2V are attributed to the low parasitics. Also, the devices exhibited an f/sub t/ of at least 75 GHz up to a V/sub ds/ of 4 V.

Transmission electron microscope investigation of dislocation loops in Si-doped GaAs crystals

Dislocation loops in Si-doped GaAs crystals have been studied by conventional transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM). In addition to the prismatic dislocation loops lying on (110) planes and the faulted loops lying on (111) planes, the existence of prismatic dislocation loops lying on (111) planes with 1/2 (110) Burgers vectors and of interstitial character was identified for the first time. Some of the dislocation loops exhibited partly faulted and partly prismatic characteristics. This observation indicates that the prismatic dislocation loops lying on (111) planes may be converted from faulted loops by the generation and movement of two 1/6 (112) Shockley partial dislocations across the stacking fault. Because all the dislocation loops studied by HRTEM have an extra plane, it was concluded that interstitials are responsible for the formation of dislocation loops.

Recombination-generation behaviour of decorated defects in silicon

Presents a study of the electrical properties of deep states in silicon containing oxidation-induced stacking faults and dislocations. In general the electrical activity of stacking faults is associated with the Frank partial dislocation bounding it rather than the extra plane of the fault itself. In addition, the deep states associated with the partials of very clean stacking faults are rather ineffective as either generation or recombination centres. The authors have studied the effect of annealing oxidation-induced stacking faults in nitrogen and of decorating them with silver. After low-level decoration the defect states increase in concentration and the electron binding energy changes, tending to move the states towards the middle of the gap (hence increasing their effectiveness as generation centres). This level of decoration is not detectable with present-day TEM techniques. However, if the level of decoration is increased further, precipitates can be observed (using TEM) but the concentration of deep states decreases as does their electron binding energy. During this precipitative phase the intensity of the photoluminescence D lines is also seen to decrease substantially. These factors have a very considerable significance in relation to the imaging of extended defects using techniques which rely on recombination-generation effects and imply that the visibility of such defects is crucially dependent on the level of decoration.

Dislocation structure in melt-textured YBa2Cu3O7-x

Presently, there is considerable interest in the microstructure of melt-textured YBa2Cu3O7-x (MT-Y123) and its influence on flux pinning. Precipitates of Y2BaCuO5 are a common feature of the microstructure. In addition, the stacking faults associated with the insertion of an extra CuO plane may contribute to flux pinning. Thus far, the stacking faults reported have been isolated, i.e. not forming a network. There is reason to believe that an array of stacking faults would be beneficial in increasing the flux pinning, thus increasing the critical current density of MT-Y123.The material studied was prepared by CPS Superconductor Inc. by holding a mixture of YBa2Cu3O7-X and Y2BaCuO5 Just above the peritectic temperature for 1 hour and quenching to just below the peritectic for 15 hours. Samples were then subjected to an oxygen annealing. It has large, highly textured grains which measure as much as 1cm in the a-b plane. TEM samples were cut parallel and perpendicular to the caxis. The samples were polished, dimpled and ion milled at 13° in a liquid nitrogen cold stage. A Philips CM30 microscope, operated at 300kV, was used in this study.

Determination of the Formation of the 1/6[031] Extrinsic Stacking Faults in Deformed YBa2Cu3O7−δ

AbstractMechanial deformation of the YBa2Cu3O7−δ high temperature superconductor under a number of different processing conditions resulted in the formation of <100> and <110> edge dislocations, both having a (001) slip plane. Subsequent high temperature annealing at 900°C resulted in the formation of extrinsic stacking faults with a large separation of the partial dislocations, up to 0.35 μm, suggesting a very low minimum stacking fault energy of 1.2 × 10−2 J/m2. High resolution transmission electron microscopy (HRTEM) in conjunction with image simulations revealed that the stacking faults were comprised of an extra CuO plane between the Ba layers with an offset of b/2. The stacking fault vector of 1/6[031] requires some separation of the <010> Burgers vectors into the c-axis direction. A model in which [010] separates into 1/6[031] + 1/[031] is consistent with the observed stacking faults.

Electron microscope observation of lattice defects in the FeCr σ-phase

The lattice image of the FeCr σ-phase was observed by high-resolution electron microscopy with the c axis of the tetragonal cell parallel to the incident beam. It was found that bright dots of the observed image correspond to the positions of atoms in the z = ± 1 4 planes of the σ-phase structure. Sequence faults were found in the irregular part of the lattice image. The analysis of the faults shows that an extra plane of 1 2 a 0 width is inserted into the regular structure and one side of the fault is slightly shifted parallel to the fault plane with respect to the other side, which is consistent with the model proposed by Frank and Kasper. A unit cell step of the sequence faults was found and a model of the step was proposed.

Kinetic Theory of Dislocation Climb. I. General Models for Edge and Screw Dislocations

General kinetic models are established for the climb of edge and screw dislocations. The climb of a straight unconstrained edge dislocation is considered in terms of the diffusion of nonequilibrium point defects to (or from) the line and their absorption (emission) and destruction (creation) at the line. The climb is nucleated by the formation of short rows of defects which are attached to the edge of the extra plane and are bounded by jog pairs. Climb occurs by the growth of these aggregates until they destroy each other by mutual collisions. No a priori assumptions are made about the ability of either the dislocation or the jogs to maintain local point defect equilibrium during climb, and account is taken of rapid defect diffusion along the core. Effects of nonequilibrium defects in perturbing the jog population are also included. Equations describing this edge dislocation climb are developed but are left in a general form. Complete solutions are worked out in a following paper (Part II). Complications which arise when geometrical constraints and line curvature are present are discussed, and a description of the relationships between curvature, macroscopic line tension, and jog density is given. It is concluded that the results for the unconstrained climb model can be used in many such cases over a considerable range of conditions. The treatment of screw dislocation climb focuses attention on the climb of an initially straight dislocation into a multi-turned helix. The detailed mechanisms are found to depend strongly upon the geometry and mobility of point defects and point defect aggregates on the core, and therefore only a qualitative theory is given. It is suggested that in many crystals vacancies largely dissociate into kinks when they enter the core, and that the helical turns build up rather uniformly along the line by the aggregation of ordered arrangements of these kinks.

Effect of Dislocations on Ultrasonic Wave Attenuation in Metals*

The causes of energy dissipation and mechanical instabilities of the elastic constants in metals can usually be traced to the presence of an imperfection in the crystal lattice called a dislocation. Edge dislocations are regions in the lattice where an extra plane of atoms has been added or subtracted from an otherwise perfect crystal. Such dislocations can move through the crystal under the application of shearing stresses or because of thermal agitation. It is shown that the primary causes of energy dissipation in a metal are dislocation loops pinned at irregular intervals by impurity atoms. At very low temperatures these dislocations lie along minimum energy positions but at higher temperatures they can be displaced to the next minimum energy position. In going to the next position, the dislocation meets an energy barrier determined by the energy required to overcome the limiting shearing stress T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">130</inf> and the energy to stretch the dislocation. This barrier causes a relaxation effect for which the dislocations lag behind the applied stress and abstract energy from the mechanical vibrations. By measuring the position and height of the relaxation peak as a function of frequency and temperature, evidence is obtained for the value of the limiting shearing stress, the number of dislocations per square cm., and the average loop length. The values obtained agree with other methods for measuring these quantities. At higher temperatures thermal agitation causes the loops to break away from their pinning impurity atoms. In the process, it is shown that a loss occurs which is independent of frequency and amplitude but which varies exponentially with the temperature. The activation energy found agrees with the calculated value for the binding energy of an impurity atom. Dislocations also occur at the boundaries between grains in the metal and produce a peak in the measured attenuation of a polycrystal which reaches a maximum at high temperatures and low frequencies. The activation energy for this process is determined by the energy required for a vacancy to diffuse

LXXXVII. Theory of dislocations in germanium

Abstract Dislocations have a large effect on the electrical properties of germanium. Experiments show that dislocations act as acceptor centres. This paper discusses a simple model (due to W. Shockley) which identifies dislocation acceptors with the dangling unpaired electrons on the edge of the extra atomic plane of a dislocation having some edge component. In n-type germanium the line of acceptors along a dislocation accepts electrons and becomes negatively charged. The electrostatic energy in the resulting space charge region is found and shown to be a dominant factor in determining the occupation of dislocation acceptors. Formulas are given for the temperature variation of the average electron concentration in n-type material that has been lightly deformed by plastic bending. Experiments are suggested to test the theory and determine exactly the energy level of the dislocation acceptors.

Improving the Performance of a Littrow-type Infra-Red Spectrometer

IN a recent communication in Nature, A. Walsh1 suggested a means of improving the performance of a commercial infra-red spectrometer by adding extra plane mirrors so that the radiation traverses the prism four times instead of twice, and then chopping the partly dispersed radiation so that only the wanted radiation is interrupted and consequently measured. The advantages claimed are that the instrument is in effect converted into a double-monochromator with improved resolution and complete freedom from stray light even at 15 μ.