高技术陶瓷材料点缺陷化学和物理

无机材料点缺陷的研究具有基础性和前沿性特色,是当前高技术陶瓷发展中的一个新兴的技术支撑,具有诱人的应用前景,甚为世人瞩目.点缺陷结构与高技术陶瓷的物理和化学性能密切相关.本文就点缺陷能量、生成、缔合、点缺陷和界面间的互作用等化学和物理机制,点缺陷的电子学以及点缺陷工程研究中的最新进展等方面进行了综述.本文还就点缺陷对改善高技术陶瓷的电、磁、光、力和生物等性能所提供的美好前景进行了评述,以期有助于今后我国在无机材料领域原创性和开拓性研究的深入发展.     

Direct Visualization of Exciton Transport in Defective Few-Layer WS2 by Ultrafast Microscopy

As defects usually limit the exciton diffusion in 2D transition metal dichalcogenides (TMDCs), the interaction knowledge of defects and exciton transport is crucial for achieving efficient TMDC-based devices. A direct visualization of defect-modulated exciton transport is developed in few-layer WS₂ by ultrafast transient absorption microscopy. Atomic-scale defects are introduced by argon plasma treatment and identified by aberration-corrected scanning transmission electron microscopy. Neutral excitons can be captured by defects to form bound excitons in 7.75–17.88 ps, which provide a nonradiative relaxation channel, leading to decreased exciton lifetime and diffusion coefficient. The exciton diffusion length of defective sample has a drastic reduction from 349.44 to 107.40 nm. These spatially and temporally resolved measurements reveal the interaction mechanism between defects and exciton transport dynamics in 2D TMDCs, giving a guideline for designing high-performance TMDC-based devices.     

Defect-free switchable phase grating

Liquid-crystal-filled polymer structure devices offer a very low cost switchable spatial phase modulator. The phase profile set by the polymer structure may be varied or switched on/off with an applied field. Defects have been observed in some devices giving rise to spurious diffraction peaks. Computational modeling of the liquid-crystal director profile suggests that these defects might be suppressed if the dimensions of the liquid-crystal region are small. Experimental measurements confirm that this approach is effective in controlling the defects. This provides a route to fabrication of low-cost switchable complex diffractive devices.     

Defects in GaAs

A comprehensive review of defects in GaAs with focus on native point defects and dislocations is given. The effects of these defects on devices are also considered. It is pointed out that a unified point defect model cannot at present be drawn from the available information. The importance of including anti-site defects in the point defect models which have hitherto only considered vacancies and interstitials is stressed. Attention is drawn to the need for understanding the dominant equilibrium native defects in GaAs both from fundamental and technological considerations. In this respect new experimental techniques are suggested to understand and control the defect structure. The current understanding of dislocations in GaAs is very much in its infancy compared to that in elemental semiconductors. Both theoretical work and careful experiments are wanting. This is essential since dislocations have been directly implicated in the degradation of GaAs devices.     

Perfecting Imperfection—Designer Defects in Colloidal Photonic Crystals

Current progress in the exciting and burgeoning field of functional defects in colloidal photonic crystals (CPCs) is reported. After a brief introduction into the importance and nature of defects in CPCs the state‐of‐the‐art in fabricating point, line, and planar defects is described. Measurement and characterization techniques as well as the corresponding theory are discussed. Besides normal, passive defects, the recent development of reversibly tunable defects adds important functionality. In particular, the addition of chemical functionality is demonstrated to open a path to a wide range of color readout devices for ultrasensitive optical detection of biomolecules and pharmaceuticals.     

MicroRaman study of bulk inclusions in SiC crystals

The growth of defect-free SiC substrates is of primary importance for the development of devices based on this material, since defects such as micropipes and crystalline inclusions limit the performance of SiC-based devices. The analysis of these defects is crucial for the improvement of these crystals. MicroRaman spectroscopy provides structural and electronic information with micrometric spatial resolution. We present herein a microRaman study of different solid inclusions in 4H-SiC; the results are discussed in terms of the polytype structure, crystal orientation in relation to the matrix, and local electron concentration and mobility around the solid inclusions.     

Nanoscale defects and microwave properties of (BaSr)TiO<Subscript>3</Subscript> ferroelectric thin films

Thin film ferroelectrics may have important applications in microwave devices but in general have significantly worse properties than bulk material. This is principally because of secondary and point defects. The natures of the defects are reviewed and strategies to study and remove them outlined.     

A system architecture solution for unreliable nanoelectronic devices

The shrinking of electronic devices will inevitably introduce a growing number of defects and even make these devices more sensitive to external influences. It is, therefore, likely that the emerging nanometer-scale devices will eventually suffer from more errors than classical silicon devices in large scale integrated circuits. In order to make systems based on nanometer-scale devices reliable, the design of fault-tolerant architectures will be necessary. Initiated by von Neumann, the NAND multiplexing technique, based on a massive duplication of imperfect devices and randomized imperfect interconnects, had been studied in the past using an extreme high degree of redundancy. In this paper, this NAND multiplexing is extended to a rather low degree of redundancy, and the stochastic Markov nature in the heart of the system is discovered and studied, leading to a comprehensive fault-tolerant theory. A system architecture based on NAND multiplexing is investigated by studying the problem of the random background charges in single electron tunneling (SET) circuits. It might be a system solution for an ultra large integration of highly unreliable nanometer-scale devices.     

Characterization of defects in gallium arsenide

It is well-known that the properties of semiconductor materials including gallium arsenide are controlled by defects and impurities. The characterization of these defects is important not only for better understanding of the solid state phenomena but also for improved reliability and performance of electronic devices. We have been investigating the defects in gallium arsenide for several years using deep level transient spectroscopy, photoconductivity, transient photoconductivity, photoluminescence etc. Results drawn from our recent studies are presented here to illustrate some of the problems concerning transition metal impurities, process-induced defects, occurrence of intracentre transitions and metastability of deep levels in gallium arsenide.     

Structural defects as a result of Zn diffusion into CdTe single crystals

The presence of defects in CdZnTe crystals is detrimental for optoelectronic devices fabrication and therefore should be minimized. In this paper we present the characterization of structural defects on the surface and the cross-section of CdTe single crystals that were subjected to high temperature (up to 950 °C) diffusion of Zn. The defects were characterized by various X-ray techniques, optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Quantitative data are obtained, a practical solution for reducing the defects is suggested and some implementations are discussed. Further effort is currently being made to investigate the lattice sites which are involved with the diffused Zn atoms near the surface and in the bulk.     

Filament-Free Bulk Resistive Memory Enables Deterministic Analogue Switching

Digital computing is nearing its physical limits as computing needs and energy consumption rapidly increase. Analogue-memory-based neuromorphic computing can be orders of magnitude more energy efficient at data-intensive tasks like deep neural networks, but has been limited by the inaccurate and unpredictable switching of analogue resistive memory. Filamentary resistive random access memory (RRAM) suffers from stochastic switching due to the random kinetic motion of discrete defects in the nanometer-sized filament. In this work, this stochasticity is overcome by incorporating a solid electrolyte interlayer, in this case, yttria-stabilized zirconia (YSZ), toward eliminating filaments. Filament-free, bulk-RRAM cells instead store analogue states using the bulk point defect concentration, yielding predictable switching because the statistical ensemble behavior of oxygen vacancy defects is deterministic even when individual defects are stochastic. Both experiments and modeling show bulk-RRAM devices using TiO_2-X switching layers and YSZ electrolytes yield deterministic and linear analogue switching for efficient inference and training. Bulk-RRAM solves many outstanding issues with memristor unpredictability that have inhibited commercialization, and can, therefore, enable unprecedented new applications for energy-efficient neuromorphic computing. Beyond RRAM, this work shows how harnessing bulk point defects in ionic materials can be used to engineer deterministic nanoelectronic materials and devices.     

Point defects in silicon, first-principles calculations

Native defects, vacancies and self-interstitials, play a fundamental role in determining mechanical and electronic properties of silicon materials used for electronics devices. The important phenomena include diffusion of dopant impurities and formation of extended defects. First-principles calculations of electronic and ionic structures of the native defects have turned out to be very demanding. In this paper, results of recent pseudopotential-plane-wave calculations within the supercell approximation are reviewed. Vacancies, self-interstitials as well as common dopant impurities are dealt with.     

Effect of oxygen annealing on the ultraviolet photoresponse of P-NiO-nanoflower/n-ZnO-nanowire heterostructures

A transparent ultraviolet (UV) sensor using nanoheterojunctions (NHJs) composed of p-type NiO nanoflowers (NFs) and n-type ZnO nanowires (NWs) was prepared through a sequential low-temperature hydrothermal-growth process. The devices that were annealed in an oxygen (O2) ambient exhibited better rectification behavior (I forward/I reverse = 427), a lower forward threshold voltage (V(th) = 0.98 V), a lower leakage current (1.68 x 10(-5) A/cm2), and superior sensitivity (I uv/I dark = 57.8; I visible/I dark = 1.25) to UV light (lambda = 325 nm) than the unannealed devices. The remarkably improved device performances and optoelectronic characteristics of the annealed p-NiO-NF/n-ZnO-NW NHJs can be associated with their fewer structural defects, fewer interfacial defects, and better crystallinity. A stable and repeatable operation of dynamic photoresponse was also observed in the annealed devices. The excellent sensitivity and repeatable photoresponse to UV light of the hydrothermally grown p-NiO-NF/n-ZnO-NW NHJs annealed in a suitable O2 ambient indicate that they can be applied to nano-integrated optoelectronic devices.     

Effect of defects on electrical properties of 4H-SiC Schottky diodes

Most of power electronic circuits use power semiconductor switching devices which ideally present infinite resistance when off, zero resistance when on, and switch instantaneously between those two states. Switches and rectifiers are key components in power electronic systems, which cover a wide range of applications, from power transmission to control electronics and power supplies.

Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has properties that allow devices with high power voltage rating and high operating temperatures. The technology overcomes some crystal growth obstacles, by using the hydrogen in the fabrication of 4H-SiC wafers.

The presence of structural defects on 4H-SiC wafers was shown by different techniques such as optical microscopy and scanning electron microscopy. The presence of different SiC polytypes inclusions was found by Raman spectroscopy. Schottky diodes were realized on investigated wafers in order to obtain information about the correlation between those defects and electrical properties of the devices. The diodes with voltage breakdown as 600 V and ideality factor as 1.05 were obtained and characterized after packaging.     

浸渍阴极的真空预处理技术

本文总结了用于真空微波电子器件的浸渍阴极的蒸发规律,通过分析提出了浸渍阴极预处理工艺,建立了超高真空装置.在超高真空环境下,将浸渍阴极灯丝加热,使阴极温度升高到1100～1200℃,保持1～200h(温度和时间依不同微波管型而定).预处理工艺解决了浸渍阴极发射与蒸发的矛盾,现已建立数十台、几十个工位的浸渍阴极预处理设备...     

On the evaluation of scaling of QCA devices in the presence of defects at manufacturing

In this paper, we evaluate scaling of quantum-dot cellular automata (QCA) devices (majority voter and inverter) in the presence of defects due to process variations in QCA manufacturing. Simulation results using the two engines of QCADesigner are provided and compared to show the defect tolerance of these devices.     

Effects of fluid flow shear rate and surface roughness on the calcification of polymeric heart valve leaflet

Surface defects, blood flow shear rates and mechanical stresses are contributing factors in the calcification process of polymeric devices exposed to the blood flow. A number of experiments were performed to evaluate the effect of surface defects such as roughness and cracks and flow shear rate on the calcification process of a polyurethane material used in the design of prosthetic heart valves. Results showed that polyurethane surface gets calcified and the calcification is more pronounced at the lower shear rates. Roughness and cracks both increase the calcification levels. The results also suggest very little diffusion of calcium to the subsurface indicating that calcification of a polyurethane material, is a surface phenomenon. Based on a simple peeling test, the bond strength between the calcified layer and polyurethane was found to be extremely weak, suggesting that the bonding is in the form of Van-der-Waals. A limited set of experiments with polycarbonate showed that polycarbonate is less prone to calcification compared to polyurethane (p values less than 0.05), indicating its potential application in medical devices exposed to blood flow.     

Crystalline quality of the trigonal piezoelectric materials and effects of the extended defects

Many frequently used or promising piezoelectric materials belong to crystal classes 32 or 3m. Among them are α quartz and its crystallographic analogs (AlPO(4), GaPO(4), α-GeO(2), etc.), the numerous materials of the langasite (La-(3)Ga(5)SiO,sub>14) family and also lithium tantalate (LiTaO,sub>3) and lithium niobate (LiNbO 3). In this paper we study the present state of the art for these materials, indicate their principal point and extended defects, and present methods to reduce the dislocation density. Large concentrations of intrinsic point defects often exist in crystal grown at very high temperatures. The point defects (intrinsic or related to impurities) modify the constants and can increase the acoustic losses. This is the case for the alkali ions and the OH that induce severe losses in different temperature intervals. The extended defects also affect the performances of the piezoelectric devices. Some, such as twins, ferroelectric domains, or large solid or liquid inclusions, have very detrimental effects. Dislocations, growth bands, and planar defects are more difficult to avoid and affect the devices in a more subtle manner. In quartz and its analogs, dislocations seem to increase the nonlinear elastic effects and have a collective effect on the vibration modes, particularly in energy trapping resonators. Growth bands and stacking faults also produce similar effects.     

CVD Polymers for Devices and Device Fabrication

Chemical vapor deposition (CVD) polymerization directly synthesizes organic thin films on a substrate from vapor phase reactants. Dielectric, semiconducting, electrically conducting, and ionically conducting CVD polymers have all been readily integrated into devices. The absence of solvent in the CVD process enables the growth of high‐purity layers and avoids the potential of dewetting phenomena, which lead to pinhole defects. By limiting contaminants and defects, ultrathin (<10 nm) CVD polymeric device layers have been fabricated in multiple laboratories. The CVD method is particularly suitable for synthesizing insoluble conductive polymers, layers with high densities of organic functional groups, and robust crosslinked networks. Additionally, CVD polymers are prized for the ability to conformally cover rough surfaces, like those of paper and textile substrates, as well as the complex geometries of micro‐ and nanostructured devices. By employing low processing temperatures, CVD polymerization avoids damaging substrates and underlying device layers. This report discusses the mechanisms of the major CVD polymerization techniques and the recent progress of their applications in devices and device fabrication, with emphasis on initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.     

纳米电子器件呼唤真空化学研究

纳米电子器件是微电子器件发展的下一代 ,现有微电子器件的主要材料是极纯的硅、锗和镓砷等晶体半导体。纳米电子器件有可能是以有机或有机 /无机复合晶体薄膜为主要材料 ,要求纯度更高 ,结构更完善。真空制备的清洁环境 ,有希望加工组装出纳米电子器件所要求的结构。故本文建议开展真空化学研究