Multi-objective Optimal Design of High Frequency Probe for Scanning Ion Conductance Microscopy

Scanning ion conductance microscopy（SICM） is an emerging non-destructive surface topography characterization apparatus with nanoscale resolution. However, the low regulating frequency of probe in most existing modulated current based SICM systems increases the system noise, and has difficulty in imaging sample surface with steep height changes. In order to enable SICM to have the capability of imaging surfaces with steep height changes, a novel probe that can be used in the modulated current based bopping mode is designed. The design relies on two piezoelectric ceramics with different travels to separate position adjustment and probe frequency regulation in the Z direction. To fiarther improve the resonant frequency of the probe, the material and the key dimensions for each component of the probe are optimized based on the multi-objective optimization method and the finite element analysis. The optimal design has a resonant frequency of above 10 kHz. To validate the rationality of the designed probe, microstructured grating samples are imaged using the homebuilt modulated current based SICM system. The experimental results indicate that the designed high frequency probe can effectively reduce the spike noise by 26% in the average number of spike noise. The proposed design provides a feasible solution for improving the imaging quality of the existing SICM systems which normally use ordinary probes with relatively low regulating frequency.

A Novel Method for Determining the Void Fraction in Gas-Liquid Multi-Phase Systems Using a Dynamic Conductivity Probe

Conventional conductivity methods for measuring the void fraction in gas-liquid multiphase systems are typically affected by accuracy problems due to the presence of fluid flow and salinity.This study presents a novel approach for determining the void fraction based on a reciprocating dynamic conductivity probe used to measure the liquid film thickness under forced annular-flow conditions.The measurement system comprises a cyclone,a conductivity probe,a probe reciprocating device,and a data acquisition and processing system.This method ensures that the flow pattern is adjusted to a forced annular flow,thereby minimizing the influence of complex and variable gas-liquid flow patterns on the measurement results;Moreover,it determines the liquid film thickness solely according to circuit connectivity rather than specific conductivity values,thereby mitigating the impact of salinity.The reliability of the measurement system is demonstrated through laboratory experiments.The experimental results indicate that,in a range of gas phase superficial velocities 5–20 m/s and liquid phase superficial velocities 0.079–0.48 m/s,the maximum measurement deviation for the void fraction is 4.23%.

Laboratory and field experiment on measurement of soil thermal conductivity by probe method

The authors presented a new measuring method of the soil thermal conductivity,the probe method,which is designed and made based on the theory of line heat source. This method is used to measure thermal conductivity of coarse sand,fine sand and silty clay in different water contents. The results that measured by the probe method are well consistent with those of QTM-D_2. The soil thermal conductivity increases in different levels with the increase of the water content. Compared the soil thermal conductivity measured by the probe method in laboratory with in-situ experiment,it shows that the measuring gap gradually increases with the increase of the depth. The reason is that the in-situ measuring thermal conductivity can reflect the actual situation of the soil mass.

Direct measurements of conductivity and mobility in millimeter-sized single-crystalline graphene via van der Pauw geometry

We report the direct measurements of conductivity and mobility in millimeter-sized single-crystalline graphene on SiO2/Si via van der Pauw geometry by using a home-designed four-probe scanning tunneling microscope（4P-STM）. The gate-tunable conductivity and mobility are extracted from standard van der Pauw resistance measurements where the four STM probes contact the four peripheries of hexagonal graphene flakes, respectively. The high homogeneity of transport properties of the single-crystalline graphene flake is confirmed by comparing the extracted conductivities and mobilities from three setups with different geometry factors. Our studies provide a reliable solution for directly evaluating the entire electrical properties of graphene in a non-invasive way and could be extended to characterizing other two-dimensional materials.

Measurement of electrical conductivity of micron-scale metallic wires

Electrical conductivities of micron-scale aluminum wires were quantitatively measured by a four-point atomic force microscope (AFM) probe. This technique is a combination of the principles of the four-point probe method and standard AFM. This technique was applied to the 99.999% aluminum wires with 350 nm thickness and different widths of 5.0, 25.0 and 50.0μm. Since the small dimensions of the wires, the geometrical effects were discussed in details. Experiment results show that the four-point AFM probe is mechanically flexible and robust. The four-point AFM probe technique is capable of measuring surface topography together with local electrical conductivity simultaneously. The repeatable measurements indicate that this technique could be used for fast in-situ electrical properties characterization of sensors and microelectromechanical system devices.

AN APPARATUS FOR MEASURING THERMAL CONDUCTIVITY OF LIQUIDS UNDER HIGH PRESSURE

We have reported a method for measuring the thermal conductivity of liguids un-der high pressure previously [1,2].Such data are necessary for improving thetechnologies such like processing as acidity,pressure cracking,thermal exploitation ofpetroleum,etc. An apparatus has thus been constructed,as shown schematically in Fig.1,tomeasure the thermal conductivity of liquids under pressure up to 25 MPa and temperatureranging from 150 to 250℃.The thermal conductivity cell is cylindrical in from,35mmin length and 25mm in inner diameter.The sample is poured into the cell through

Determination of Work Function for p-and n-Type 4H-SiC Single Crystals via Scanning Kelvin Probe Force Microscopy

Silicon carbide(SiC) is a promising platform for fabricating high-voltage, high-frequency and high-temperature electronic devices such as metal oxide semiconductor field effect transistors in which many junctions or interfaces are involved. The work function(WF) plays an essential role in these devices. However, studies of the effect of conductive type and polar surfaces on the WF of SiC are limited. Here, we report the measurement of WFs of Si-and C-terminated polar surfaces for both p-type and n-type conductive 4H-SiC single crystals by scanning Kelvin probe microscopy(SKPFM). The results show that p-type SiC exhibits a higher WF than n-type SiC.The WF of a C-terminated polar surface is higher than that of a Si-terminated polar surface, which is further confirmed by first-principles calculations. By revealing this long-standing knowledge gap, our work facilitates the fabrication and development of SiC-based electronic devices, which have tremendous potential applications in electric vehicles, photovoltaics, and so on. This work also shows that SKPFM is a good method for identifying polar surfaces of SiC and other polar materials nondestructively, quickly and conveniently.

Comparison of Three Methods for Determination of Root Hydraulic Conductivity of Maize(Zea mays L.)Root System

Three techniques of root pressure probe, pressure chamber and high pressure flow meter were used to measure the hydraulic conductivities （Lpr） of whole root systems of young maize （Zea mays L.） seedlings grown hydroponically under either drought or normal water conditions. Compared to normal water conditions, drought stress simulated by polyethylene glycol 6 000 （osmotic potential =-0.2 MPa） reduced Lpr in the root system by over 50%. It indicated that water permeability in the roots decreased significantly when plants suffered from water shortages. Moreover, there was no significant difference （P〈 0.05） on the Lpr values in the root systems developed under a given water stress regime among the three techniques used. Therefore, all three methods are acceptable to study the hydraulic conductivity of maize seedling root systems. We have also highlighted some of the technical limitations of each method. It can be inferred that the root pressure probe is preferable for young maize seedlings because it is subtle and has the additional ability to determine solute transport properties, but the method is time consuming. Other advantages and disadvantages of each technique are discussed in order to acquaint researchers with basic information that could contribute to their choice of an appropriate technique for future studies.

Measurement of thermal conductivity of materials using single-side TPS technique

Based on the traditional measurement theory of transient plane source (TPS) technique, single-side TPS method is proposed for measuring the thermal conductivity of single specimen. The problem of transient heat conduction in a semi-infinite boundary condition is studied and the theoretical formula of single-side TPS method is deduced. During the measurement, the influence of the probe heat capacity on the results is analyzed and the corresponding mathematical compensation model is established, and a series of experiments on different materials are conducted by hot disk probe at normal temperature and pressure. The results show that the relative error with the single-side TPS method is less than 5% and the relative standard deviation is no greater than 3%. This method has high accuracy and good reproducibility, which provides a feasible measuring method for single material that does not meet the requirements of the standard TPS theory.

Conductivity of K_ (11)[Sm(AlW_ (11)O_ 39H_2)_2]·21H_2O Treated by Chemistry-Heated Diffusion of Mixed Rare Earth Ce and La Permeation

The title compound was prepared and treated by high temperature gaseous mix rare earth permeation. ICP, IR, TG-DTA, XPS, XRD were used to characterize the title compound and the treated sample. The results confirm that Ce and La can be permeated into the body of the title compound. Four-probe method was used to measure the conductivities. A novel result that the conductivity of the permeated compound (δ=9.2×10 -3 S·cm -1)improved by 7.1×106 times than that of the title compound(δ=1.29×10 -9 S·cm -1) is received.

双针热脉冲测定冻土热特性的数值模拟方法

使用双针热脉冲(dual probe heat pulse, DPHP)测定冻土热特性时施加热脉冲后会导致加热探针周围的冰融化,使用目前常用的仅考虑热传导(忽略融化相变、冰水两相分界面)的解析解处理DPHP温度数据,会导致在-5℃至0℃温度范围内无法准确测量热导率(λ)和比热(C_(v))。为了能够准确测定冻土的λ和C_v,有必要考虑DPHP加热过程中引起的冰融化的相变潜热。该研究基于COMSOL仿真软件模拟了考虑相变潜热、相变区间以及移动冰水界面的DPHP测量过程,采用随温度非线性变化的真实冻土热特性进行模拟,并与真实冻土的DPHP测量数据对比。结果表明:1)COMSOL仿真在不考虑相变条件下与无限线性热源模型结果完全吻合(R^(2)=0.998 9);2)当土壤初始温度低于-5℃时,考虑相变发生的COMSOL仿真能够准确模拟试验结果,表现出较高的相关性(R^(2)> 0.93),在-1~0℃的土壤初始温度范围内,无限线性热源模型的结果与试验测量显著偏离(R^(2) <0.001 3);3)在不同土壤初始温度下,相变温度为-1.5~-0.5℃的仿真结果与试验数据具有较高的相关性(R^(2)> 0.7)。该研究结果检验了有限元仿真用于真实冻土DPHP研究的可行性,可为准确预测冻土热特性的研究提供方法。

系列小分子液体中α弛豫与探针离子电导行为的对比

液体中平动和转动的耦合性是凝聚态物理长期关注的问题之一,本文采用介电谱方法同时获得了系列小分子液体中α弛豫的弛豫时间和探针离子的电导率.样品包括具有不同分子形状和官能团的碳原子数跨度在3—14范围内的15种一元和二元小分子液体.分析结果表明平动和转动的耦合性与液体分子的官能团并没有直接的对应关系,对分子形状、大小和离子大小也不是十分敏感,但是液体的微观结构是影响平动和转动耦合性的重要因素.也就是,无论在一元还是二元体系中,液体的微观结构没有改变时电导率的倒数和弛豫时间与温度的依赖关系具有一致性,这也为弛豫时间的测量提供了一种方法.研究结果还表明,液体中自身携带的杂质离子与定量掺入离子的电导率的温度依赖关系相同,为电解质溶解度低的有机小分子液体中离子电导率行为的研究提供了思路.本文中单羟基醇的实验结果也与单羟基醇中α弛豫而非Debye弛豫对应于体系结构弛豫的观点相一致.

加热光纤法同步测定土壤水热参数误差分析

土壤水热参数是研究土壤水热传输的基本物理参数。当前热脉冲探针法(HPP)可同步测定土壤水热参数,但该方法仅限于在点尺度下测定。与其具有相同理论基础的加热光纤法(SPHP-DTS),可将测定尺度增大至田间千米尺度,但其测定精度尚未得到有效验证。为了探知SPHP-DTS法的误差,本研究进行了SPHP-DTS法与HPP法测定土壤水热参数的对比试验。结果表明,以HPP为标准,加热光纤法测定热导率的精度RMSE为0.13 W×m^(-1)×℃^(-1)。SPHP-DTS法测定的热导率显著高于HPP法,主要原因在于加热光纤时产生的温度效应。通过热导率法测定土壤含水率时,在热导率测定误差的影响下,SPHP-DTS法的测定精度明显低于HPP法。SPHP-DTS法测定土壤水热参数的其他误差来源包括光纤与土壤之间多个界面的接触热阻、光纤的温度敏感性、噪音干扰以及温度梯度驱动下的水分迁移。本研究可为SPHP-DTS法提升土壤水热参数测定精度提供理论参考。

棒束子通道空泡份额及相界面浓度分布特性实验研究

棒束通道相态分布特性对反应堆内传热传质及流动阻力具有重要影响。本文对5×5棒束通道空气水两相流开展实验研究,采用四头电导探针测量了子通道内部的空泡份额、相界面浓度、气泡直径、气泡速度等相界面参数的局部分布。结果表明,气泡受横向作用力的影响,在子通道内会形成两种典型分布,随液相流速升高和气相流速降低,轴峰分布逐渐转变为壁峰分布;不同类型子通道空泡分布不均匀,中心子通道受壁面影响较小,气泡数量最多,边通道和角通道几乎被液相占据;本实验工况下,现有的空泡份额和相界面浓度计算关系式预测性能良好,平均最小误差分别为±18.2%与±12.2%。

实验室传导发射电磁环境噪声超标案例分析

试验场地传导发射电流法环境噪声测试时出现了尖峰毛刺、鼓包等骚扰信号。根据排查流程,从被试品的辐射和传导耦合路径入手进行分析,显示器电源适配器使用滤波器组插排时,测试数据正常,骚扰源定位在显示器电源适配器。进一步验证发现,不接滤波器组插排,分别更换为笔记本电脑适配器、ViewSonic显示器,也能消除骚扰信号。问题的分析思路、分析方法可供试验室人员解决类似试验场地电磁环境噪声问题时参考。

热针法测量材料导热系数研究

研究了可测量软性材料导热系数的热探针法 ,所用热探针由 2 0匝直径为 0 .0 2 mm的漆包铜丝紧密封进外径为 0 .3 m m的不锈钢针管制成 ,铜丝同时起加热和测温元件作用 .理论和实验研究表明 ,采用适当延迟测量时间可以克服因热针壁厚引起的误差 .测量误差估计小于± 3 %

多层桨搅拌槽内的宏观混合特性

在直径为0.476 m的搅拌槽内,采用电导法测定搅拌槽内单层桨和多层桨体系的混合时间。对于单层桨体系,在相同的搅拌输入功率下,不同类型的径向流桨和轴向流桨具有相同的混合时间。对于窄叶翼型CBY搅拌桨,在相同的搅拌输入功率下,单层、双层以及三层CBY搅拌桨的混合时间基本相同;而对于六直叶涡轮桨DT-6,在相同的搅拌输入功率下其混合时间随桨叶层数的增加而加长;多层CBY桨的混合时间远低于多层DT-6搅拌桨的混合时间。

多针热脉冲技术测定土壤热导率误差分析

土壤热导率是研究土壤热传输、水热耦合运移的基本物理参数。为了探知多针热脉冲技术的误差,该研究以能够准确测定热导率的单针法作为参比,在4种质地土壤上,对多针热脉冲技术在不同体积质量、含水率和气压条件下测定的热导率进行了分析。结果表明,多针热脉冲技术的热导率结果与单针法总体符合较好,其热导率测定值的平均误差为0.074W/(m·K)。干土热导率随气压增大呈现对数增长,这是由于气体分子平均自由程下降的原因。多针热脉冲技术的测定误差主要出现在中等含水率区域,关键问题是加热针的温度升高偏大,促进了水汽潜热传输。另外,土壤与探针之间的热接触阻力、探针导致的土壤体积质量改变、温度梯度引起的液水流也影响测定结果的准确性。该研究可为农业水土工程中的土壤热导率模拟提供依据。

掺杂对定形相变材料导热系数的影响

通过在定形相变材料中加添加剂改进定形相变材料的导热系数,用热针法对改性后的试样进行了测量,对添加剂种类和含量对定形相变材料导热系数的影响进行了定量分析。实验结果表明,石墨添加剂可以显著提高定形相变材料的导热系数。通过对实验数据的拟合,得到了石墨添加质量分数与材料有效导热系数间的拟合公式。

南海西沙海槽地区的海底热流测量

为了解南海西沙海槽区的地热特征，利用Ewing型地热探针在该区开展了地热测量，并利用TK04热导率仪测量了相关站位表层沉积物样品的热导率，获得了7个站位的热流数据。结果表明，研究区7个站位的热导率变化范围为0．88～1．06W／m·K，平均为0．96W／m·K，地温梯度变化范围为85～120℃／km，热流值变化范围为83～112mW／m^2，平均达到95mW／m^2。分析表明测量结果与20世纪80年代中美合作在西沙海槽的地热测量结果一致性较好，说明研究区仍具有高热流特征，推测高热流特征可能与本区高热背景、莫霍面埋深较浅、断裂发育、晚期岩浆活动和基底起伏等有关。