Electrical Scanning Probe Microscopy: Investigating the Inner Workings of Electronic and Optoelectronic Devices

Semiconductor electronic and optoelectronic devices such as transistors, lasers, modulators, and detectors are critical to the contemporary computing and communications infrastructure. These devices have been optimized for efficiency in power consumption and speed of response. There are gaps in the detailed understanding of the internal operation of these devices. Experimental electrical and optical methods have allowed comprehensive elaboration of input–output characteristics, but do not give spatially resolved information about currents, carriers, and potentials on the nanometer scale relevant to quantum heterostructure device operation. In response, electrical scanning probe techniques have been developed and deployed to observe experimentally, with nanometric spatial resolution, two-dimensional profiles of the electrical resistance, capacitance, potential, and free carrier distribution, within actively driven devices. Experimental configurations for the most prevalent electrical probing techniques based on atomic force microscopy are illustrated with considerations for practical implementation. Interpretation of the measured quantities are presented and calibrated, demonstrating that internal quantities of device operation can be uncovered. Several application areas are examined: spreading resistance and capacitance characterization of free carriers in III-V device structures; acquisition of electric potential and field distributions of semiconductor lasers, nanocrystals, and thin films; scanning voltage analysis on diode lasers—the direct observation of the internal manifestations of current blocking breakdown in a buried heterostructure laser, the effect of current spreading inside actively biased ridge waveguide lasers, anomalously high series resistance encountered in ridge lasers—as well as in CMOS transistors; and free-carrier measurement of working lasers with scanning differential spreading techniques. Applications to emerging fields of nanotechnology and nanoelectronics are suggested.     

Uniform distribution of projection data for improved reconstruction quality of 4D EPR imaging

In continuous wave (CW) electron paramagnetic resonance imaging (EPRI), high quality of reconstruction in a limited acquisition time is a high priority. It has been shown for the case of 3D EPRI, that a uniform distribution of the projection data generally enhances reconstruction quality. In this work, we have suggested two data acquisition techniques for which the gradient orientations are more evenly distributed over the 4D acquisition space as compared to the existing methods. The first sampling technique is based on equal solid angle partitioning of 4D space, while the second technique is based on Fekete points estimation in 4D to generate a more uniform distribution of data. After acquisition, filtered backprojection (FBP) is applied to carry out the reconstruction in a single stage. The single-stage reconstruction improves the spatial resolution by eliminating the necessity of data interpolation in multi-stage reconstructions. For the proposed data distributions, the simulations and experimental results indicate a higher fidelity to the true object configuration. Using the uniform distribution, we expect about 50% reduction in the acquisition time over the traditional method of equal linear angle acquisition.     

Investigation of some Chinese jade artifacts (5000 BC to 771 BC) by confocal laser micro‐Raman spectroscopy and other techniques

The study on material properties of ancient stone or jade artifacts is essential to trace the trade routes of raw materials, the tools used to making them, and moreover the social function of the artifacts. In present research, we focused on 23 intact samples that were made of versatile rocks. These samples dated from 5000 bc to 771 bc were unearthed from the Yellow River and Yangtze River basins in China. Based on the analytical results of confocal laser micro‐Raman spectroscopy, 14 minerals consisted of these rocks such as muscovite, antigorite, calcite, quartz, diopside, turquoise, corundum, and sillimanite were identified. The obtained scientific information about their primary material properties helps us to better understand their social functions and technologically related issues. Copyright © 2015 John Wiley & Sons, Ltd.     

The Non-Destructive Analysis of Some Ancient Jade Artifacts Unearthed from Henan Province by a Variety of Optical TechniquesSCIEI北大核心CSCD

A total of 14 pieces of ancient jade artifact unearthed from Henan Province were non-destructively analyzed by means of a portable X-ray fluorescence spectrometer (pXRF), laser Raman spectroscopy (portable and mobile) and optical coherence tomography (OCT) technology, comprehensively. The raw materials of ancient jade artifacts could be determined accurately through the combination of pXRF and portable Raman spectrometer in a short time. With the advantages of small size and easy-operation, these two instruments are suitable to in situ non-destructive analysis of ancient jade artifacts. The results of the pXRF shows that these ancient jade artifacts can be divided into 6 categories such as rich in Si Al K, rich in Ca, rich in Si Ca, rich in Si Mg, rich in Si, rich in Ca P. Their main phases have been successfully identified by the portable Raman spectrometer. In the lab, the mobile confocal laser Raman spectrometer, which help us find the Raman vibration peak of [OH] in the tremolite jade, is used to make up the disadvantages of the portable Raman spectrometer such as lower spectral resolution, lower accuracy and narrower measuring range. We can use the OCT to analyze the transparency, fiber fineness and inclusion etc. of the jade artifacts. The confocal laser Raman spectroscopy combined with OCT is used to analyze 2 containing inclusion of tremolite jade samples. OCT image can visually display the distribution characteristics of the inclusion in these 2 samples. Confocal laser Raman spectroscopy can accurately locate the sample surface of inclusion, then we can observe the micro morphology and analyze its phase. The results show that the black inclusion is graphite. This work is very significant to study the geographical origin of jade. Through the study we find, the use of OCRF, laser Raman spectroscopy (portable and mobile) and OCT can be achieved on the identification and analysis of cultural relic's phase composition and texture feature and meet the basic requirements of field archaeological work analysis.     

Improved reduction of motion artifacts in diffusion imaging using navigator echoes and velocity compensation

Navigator echoes provide a means with which to remove motion artifacts from diffusion-weighted images obtained using any multishot imaging technique. However, residual motion artifact is often present in the corrected images rendering the technique unreliable. It is shown that velocity-compensated diffusion sensitization when used in tandem with a navigator echo further reduces the degree of residual motion artifacts present in the corrected images and improves the reliability and clinical utility of the technique. This is demonstrated by applying a method for quantification of motion artifact to brain images of healthy volunteers scanned using both conventional (Stejskal-Tanner) and velocity-compensated gradient sensitization. Other factors affecting the efficacy of the navigator echo technique, such as brain pulsatile motion, gradient b factor, and navigator echo signal-to-noise ratio, are also discussed.     

Development of a technique based on multi-spectral imaging for monitoring the conservation of cultural heritage objects

A new approach for monitoring the state of conservation of cultural heritage objects surfaces is being developed. The technique utilizes multi-spectral imaging, multivariate analysis and statistical process control theory for the automatic detection of a possible deterioration process, its localization and identification, and the wavelengths most sensitive to detecting this before the human eye can detect the damage or potential degradation changes occur. A series of virtual degradation analyses were performed on images of parchment in order to test the proposed algorithm in controlled conditions. The spectral image of a Dead Sea Scroll (DSS) parchment, IAA (Israel Antiquities Authority) inventory plate # 279, 4Q501 Apocryphal Lamentations B, taken during the 2008 Pilot of the DSS Digitization Project, was chosen for the simulation.     

Beam localization in HIFU temperature measurements using thermocouples, with application to cooling by large blood vessels

Experimental studies of thermal effects in high-intensity focused ultrasound (HIFU) procedures are often performed with the aid of fine wire thermocouples positioned within tissue phantoms. Thermocouple measurements are subject to several types of error which must be accounted for before reliable inferences can be made on the basis of the measurements. Thermocouple artifact due to viscous heating is one source of error. A second is the uncertainty regarding the position of the beam relative to the target location or the thermocouple junction, due to the error in positioning the beam at the junction. This paper presents a method for determining the location of the beam relative to a fixed pair of thermocouples. The localization technique reduces the uncertainty introduced by positioning errors associated with very narrow HIFU beams. The technique is presented in the context of an investigation into the effect of blood flow through large vessels on the efficacy of HIFU procedures targeted near the vessel. Application of the beam localization method allowed conclusions regarding the effects of blood flow to be drawn from previously inconclusive (because of localization uncertainties) data. Comparison of the position-adjusted transient temperature profiles for flow rates of 0 and 400 ml/min showed that blood flow can reduce temperature elevations by more than 10%, when the HIFU focus is within a 2 mm distance from the vessel wall. At acoustic power levels of 17.3 and 24.8 W there is a 20- to 70-fold decrease in thermal dose due to the convective cooling effect of blood flow, implying a shrinkage in lesion size. The beam-localization technique also revealed the level of thermocouple artifact as a function of sonication time, providing investigators with an indication of the quality of thermocouple data for a given exposure time. The maximum artifact was found to be double the measured temperature rise, during initial few seconds of sonication.     

Pitfalls and Their Remedies in Time-Resolved Fluorescence Spectroscopy and Microscopy

Time-resolved fluorescence spectroscopy and microscopy in both time and frequency domains provide very useful and accurate information on dynamic processes. Good quality data are essential in obtaining reliable parameter estimates. Distortions of the fluorescence response due to artifacts may have disastrous consequences. We provide here a concise overview of potential difficulties encountered under daily laboratory circumstances in the use of time- and frequency-domain equipment as well as practical remedies against common error conditions, elucidated with several graphs to aid the researcher in visual inspection and quality-control of collected data. A range of artifacts due to sample preparation or to optical and electronic pitfalls are discussed, as are remedies against them. Also recommended data analysis strategies are described.     

多金属物体CT图像的金属伪影校正

针对多金属伪影的校正问题,本文通过仿真实验分析了多金属伪影的成因,并提出了一种基于投影校正的多金属伪影校正方法.该方法首先直接从投影域分割出金属区域,然后建立对金属区域投影值的校正模型,最后通过调整模型参数达到校正目的.模型以重建图像的灰度熵为目标函数,采用单纯形法迭代求解使熵最小时的校正参数.仿真和实际数据的实验结果表明,本文算法对多金属伪影的校正起到了良好的效果,且校正后的图像质量优于插值校正法.     

颅脑梯度回波成像:呼吸伪影和导航回波矫正

梯度回波序列是磁共振成像中常用的脉冲序列,然而梯度回波对主磁场波动非常敏感,呼吸等生理运动引起的信号波动会导致图像伪影.该文报道了采用导航回波技术获取呼吸运动导致的局部磁场波动,用以矫正图像回波中随时间变化的相位波动,并将该技术应用于三维多回波梯度回波成像和T2*定量图研究.研究结果显示:矫正前,相位波动幅度随回波时间增长而增大,模图和T2*定量图在相位编码方向有明显伪影,并且男女呼吸伪影水平有显著性差异;矫正后,相位波动幅度大幅下降,图像伪影水平有显著性下降.