Resolution enhancing using cantilevered tip-on-aperture silicon probe in scanning near-field optical microscopy

Scanning near-field optical microscopy (SNOM) achieves a resolution beyond the diffraction limit of conventional optical microscopy systems by utilizing subwavelength aperture probe scanning. A problem associated with SNOM is that the light throughput decreases markedly as the aperture diameter decreases. Apertureless scanning near-field optical microscopes obtain a much better resolution by concentrating the light field near the tip apex. However, a far-field illumination by a focused laser beam generates a large background scattering signal. Both disadvantages are overcome using the tip-on-aperture (TOA) approach, as presented in previous works. In this study, a finite difference time domain analysis of the degree of electromagnetic field enhancement is performed to verify the efficiency of TOA probes. For plasmon enhancement, silver is deposited on commercially available cantilevered SNOM tips with 20nm thicknesses. To form the aperture and TOA in the probes, electron beam-induced deposition and focused ion beam machining were applied at the end of the sharpened tip. The results show that cantilevered TOA probes were highly efficient for improvements of the resolution of optical and topological measurement of nanostructures.     

Measurements of field enhancement introduced by a local electrode.

Direct measurements of field enhancement introduced by a local electrode have been carried out on a scanning atom probe (SAP). The results show that an enhancement factor of more than 2 can be obtained simply by reducing the specimen-to-electrode distance from 1.5 mm to 10 microm. Further enhancement can be achieved if the electrode has a smaller aperture. This suggests that a specimen with tip radius of approximately 200 nm, which usually is too blunt to be analysed in a standard atom probe, could now be analysed by SAP. The capability of analysing blunt tips will expand the applicability of SAP to a much broader range of materials.     

The role of tip plasmons in near-field Raman microscopy

The enhancement in electric field strength in the vicinity of a metal tip, through the excitation of plasma modes in the tip, is investigated using the finite difference time domain method; such tip enhancement has significant potential for application in scanning near-field Raman microscopy. To represent an experimentally realistic geometry the near-field probe is described by a conical metal tip with a spherical apex, with radii 20 nm and 200 nm considered, in close proximity to a glass substrate. Illumination through the substrate is considered, both at normal incidence and close to the critical angle, with the polarization in the plane of incidence. By modelling the frequency dependent dielectric response of the metal tip we are able to highlight the dependence on the scattering geometry of the nature of the electromagnetic excitations in the tip. In particular, the strongest electric field enhancement with the greatest confinement occurs for the excitation of modes localized at the tip apex, excited only for off-normal incidence. Bulk modes excited in the tip also produce enhancement, although over a larger area and with significantly less enhancement than that of the localized modes; however, the excitation of bulk modes is independent of the angle of incidence.     

Efficient heating with a controlled microwave field

To uncover the intriguing non-thermal microwave effect, an experiment was conducted using an amplifier rather than an oscillator as the radiation source, which was injected into an applicator with strong electromagnetic field enhancement. The characteristics of the applicator are discussed and the enhancement of the microwave field is illustrated and explained. Thermal distribution is simulated based on the calculated microwave field profile. It was demonstrated that the proposed system heated a SiC susceptor to a temperature of 637 °C with the input power of 60 W. The reasons for such an efficient heating are discussed.     

Apertureless near-field optical microscopy via local second-harmonic generation

We describe an apertureless scanning near-field optical microscope (SNOM) based on the local second-harmonic generation enhancement resulting from an electromagnetic interaction between a probe tip and a surface. The imaging mechanisms of such apertureless second-harmonic SNOM are numerically studied. The technique allows one to achieve strongly confined sources of second-harmonic light at the probe tip apex and/or surface area under the tip. First experimental realization of this technique has been carried out using a silver-coated fibre tip as a probe. The experiments reveal a strong influence of the tip–surface interaction as well as polarization of the excitation light on images obtained with apertureless second-harmonic SNOM. The technique can be useful for studying the localized electromagnetic excitations on surfaces as well as for visualization of lateral variations of linear and nonlinear optical properties of surfaces.     

外加电磁场对金属材料摩擦副摩擦学性能影响的研究进展

外加电磁场是改善摩擦副摩擦学性能的途径之一。从外加电磁场对位错运动的促进、接触表面氧化的增强和磨屑的细化氧化3个方面,综述了电磁场对金属材料摩擦副摩擦学性能改善的机理,介绍了外加电磁场类型、磁场强度、磁场施加方向、磁场频率以及摩擦副材料的磁导率大小及差异、外加磁性颗粒尺度对摩擦副摩擦磨损的影响,指出了未来电磁场抗磨减摩的研究方向。     

Tip-enhanced near-field Raman spectroscopy with a scanning tunneling microscope and side-illumination optics

Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensitivity due to the optical diffraction limit and small interaction cross sections. It has been reported that a highly localized and significantly enhanced electromagnetic field could be generated in the proximity of a metallic tip illuminated by a laser beam. In this study, a tip-enhanced RS system was developed to both improve the resolution and enhance the detection sensitivity using the tip-enhanced near-field effects. This instrument, by combining RS with a scanning tunneling microscope and side-illumination optics, demonstrated significant enhancement on both optical sensitivity and spatial resolution using either silver (Ag)-coated tungsten (W) tips or gold (Au) tips. The sensitivity improvement was verified by observing the enhancement effects on silicon (Si) substrates. Lateral resolution was verified to be below 100 nm by mapping Ag nanostructures. By deploying the depolarization technique, an apparent enhancement of 175% on Si substrates was achieved. Furthermore, the developed instrument features fast and reliable optical alignment, versatile sample adaptability, and effective suppression of far-field signals.     

电磁复合处理降低焊接残余应力增益效应的初步研究

通过外加磁场和通过脉冲电流改善材料的力学性能是两种新型的处理方法,研究表明这两种方法对材料残余应力有一定作用。在这两种处理方法研究的基础上,提出同时耦合脉冲磁场和脉冲电流的复合处理方式,并发现该处理方法在降低残余应力上有不同于磁处理及电处理的增益效应。试验采用16Mn平板焊接试样,通过X射线应力测定仪测量同一位置沿焊缝和垂直焊缝两个方向处理前后的残余应力的大小,并进行比较。试验结果表明,磁处理后残余应力下降10%左右,电处理后应力上升大约20%,而相同参数下同时耦合脉冲磁场、脉冲电流进行复合处理后,应力下降超过50%。对于其中出现的增益效应,初步分析是由于与残余应力相关的位错结构在脉冲磁场与电流复合作用下发生较大迁移,导致了应力的松弛。     

电子设备中吸波材料位置与尺寸的优化设计初探

为提高电子设备的电磁屏蔽能力,在其内部加贴吸波材料是一条有效途径.在材料等本身参数一定的情况下,贴装位置与尺寸对屏蔽效果有明显影响,特别对复杂结构,需要同时考虑对散热的影响.文中提出了一种优化设计模型,通过某实际机箱的数值优化,说明了模型与方法的有效性.     

电路第四基本元件—忆阻器的探索与研究

本文从理论方面,对电学界新发现——忆阻器的电路特性进行探索与分析,同时,还对忆阻器的一些新特性从电磁场学的角度进行了相应的解释,为忆阻器的原理及应用进行了初步的探索与研究。     

金铜双金属表面增强拉曼散射基底的制备及应用

双金属材料结合了两种金属的特性从而获得远超单一金属的性能,因而在材料应用领域获得了广泛关注。如何以低成本获得高性能功能性材料是双金属推广应用的关键。以Cu30Mn70合金片材为前驱体,采用自由腐蚀和化学电镀两步法制备了金包铜纳米多孔基底(Au@NPC)。金包覆层在有效抑制铜在空气中氧化的同时,减小了韧带间孔径距离,进一步增大了紧邻韧带间的电磁耦合效应,使Au@NPC具有更强的局域电磁场增强特性,表现出优于纳米多孔铜的表面增强拉曼散射活性。金铜双金属材料可用作表面拉曼增强散射基底,具有优异的稳定性和较低的成本。     

转子静偏心状态下机床电主轴电磁力有限元分析

电磁振动是电磁直驱型机床电主轴不可回避的振动来源,为了抑制电磁振动需要探讨其电磁力的频谱特征。推导了三相异步电主轴的电磁力波计算公式,重点分析了转子偏心状态下的电磁力波特点。基于Ansoft电磁场计算软件,建立了某国产电主轴的电磁场有限元分析模型,获得了电主轴的运行特性曲线。研究了转子在不偏心和偏心状态下的电磁力频谱变化规律,结果表明,静偏心会使电磁力力波成分更为丰富; 偏心的增加不会影响电磁力的阶次和频率分布,但与不平衡磁拉力的幅值和低阶力波幅值成正相关关系,将加剧电主轴的振动。     

A deep neural networks-based image reconstruction algorithm for a reduced sensor model in large-scale tomography system

Image reconstruction for soft-field tomography is a highly nonlinear and ill-posed inverse problem. Owing to the highly complicated nature of soft-field, the reconstructed images are always poor in quality. One of the factors that affect image quality is the number of sensors in a tomography system. It is commonly assumed that increasing the number of sensors in a tomography system will improve the ill-posed condition in image reconstruction and hence improve image quality. However, as the number of sensors increases, challenges such as more complicated and expensive hardware, slower data acquisition rates, longer image reconstruction times, and larger sensitivity matrices will arise, resulting in a greater ill-posed condition. Since deep learning (DL) is capable of expressing complex nonlinear functions, the majority of research efforts have been directed toward developing a robust DL-based inverse solver for image reconstruction. However, no study has been conducted to solve the inverse problem and improve the quality of the reconstructed image using a reduced sensor model for a large-scale tomography system. This paper proposed an image reconstruction algorithm based on Deep Neural Networks (DNN) to investigate its feasibility in solving the ill-posed inverse problem caused by the reduced sensor model for a large-scale tomography system. The proposed DNN model is based on a supervised, feed-forward, fully connected, backpropagation network. It comprises an input layer, three hidden layers and an output layer. Also, it was trained using large data samples obtained from COMSOL simulation. The relationship between the scattered electromagnetic field measurement and the corresponding true electromagnetic field distribution vector is determined. During the image reconstruction process, the untrained scattered electromagnetic field measurement samples are used as inputs to the trained DNN model, and the model output is an estimate of the electromagnetic field distribution. The results show that the proposed DNN can accurately describe the distribution of electromagnetic field and boundary shape of phantom compared to traditional algorithms (LBP, FBP, Noser and Tikhonov), regardless of the size and number of phantoms within the monitoring area. Hence, the proposed DNN is more robust and has a high degree of generalization.     

Current-sensing scanning near-field optical microscopy using a metal probe for nanometre-scale observation of electrochromic films

A novel technique for scanning near‐field optical microscopy capable of point‐contact current‐sensing was developed in order to investigate the nanometre‐scale optical and electrical properties of electrochromic materials. An apertureless bent‐metal probe was fabricated in order to detect optical and current signals at a local point on the electrochromic films. The near‐field optical properties could be observed using the local field enhancement effect generated at the edge of the metal probe under p‐polarized laser illumination. With regard to electrical properties, current signal could be detected with the metal probe connected to a high‐sensitive current amplifier. Using the current‐sensing scanning near‐field optical microscopy, the surface topography, optical and current images of coloured WO₃ thin films were observed simultaneously. Furthermore, nanometre‐scale electrochromic modification of local bleaching could be performed using the current‐sensing scanning near‐field optical microscopy. The current‐sensing scanning near‐field optical microscopy has potential use in various fields of nanometre‐scale optoelectronics.     

Exposure of biological preparations to radiofrequency electromagnetic fields under low gravity

There is interest as to whether the electromagnetic fields used in mobile radiotelephony might affect biological processes. Other weak fields such as gravity intervene in a number of physical and biological processes. Under appropriate in vitro conditions, the macroscopic self-organization of microtubules, a major cellular component, is triggered by gravity. We wished to investigate whether self-organization might also be affected by radiotelephone electromagnetic fields. Detecting a possible effect requires removing the obscuring effects triggered by gravity. A simple manner of doing this is by rotating the sample about the horizontal. However, if the external field does not also rotate with the sample, its possible effect might also be averaged down by rotation. Here, we describe an apparatus in which both the sample and an applied radiofrequency electromagnetic field (1.8 GHz) are stationary with respect to one another while undergoing horizontal rotation. The electromagnetic field profile within the apparatus has been measured and the apparatus tested by reproducing the in vitro behavior of microtubule preparations under conditions of weightlessness. Specific adsorption rates of electromagnetic energy within a sample are measured from the initial temperature rise the incident field causes. The apparatus can be readily adapted to expose samples to various other external fields and factors under conditions of weightlessness.     

电磁热效应止裂效果与电流通路尺寸关系的研究

从理论、试验和数值模拟三方面研究利用电磁热效应技术对具有单边裂纹的导体进行止裂时，由于裂纹尺寸不同使得导体中电流通路尺寸不同，从而导致裂纹尖端的温度场、温度梯度场分布状态的不同。理论分析、试验研究和数值模拟结果均表明：由于电流产生的焦耳热源的作用，能够在裂纹尖端处很小的范畴内熔化形成焊口，遏制裂纹的扩展；导体中裂纹的长度（即导体中电流通路尺寸）是影响裂纹尖端温度场和温度梯度场的主要因素。     

电磁轴承力学特性的有限元分析

利用有限元法对轴向电磁轴承的磁场分布进行了数值模拟分析，并通过对某一实际电磁轴承的轴向轴承磁场分布及电磁力的分析计算，得出了轴向电磁轴承的承载力工作范围和静态刚度曲线，所得结果可作为轴向电磁轴承实际设计的准则。     

电控喷油器的一种新型磁路结构

为提高喷油器的动态响应性能,以某款电控喷油器为研究对象,通过在其铁芯与导向管之间增加由不导磁材料制成的隔磁环开发了一种新型磁路结构。通过电磁场仿真分析了改进前后喷油器电磁性能的变化特点以及轭铁厚度对电磁性能的影响规律。结果表明：增加隔磁环能加快电磁力的上升速度,有效缩短喷油器的开启滞后时间,但饱和电磁力增大,造成落座滞后时间延长;适当减小轭铁厚度基本不影响电磁力的上升速度,但减小轭铁厚度会使磁阻增大,饱和电磁力降低,这样可有效缩短落座滞后时间。根据以上分析结果对喷油器进行了综合优化,并通过实验对其改进效果进行了验证,结果表明：优化后与优化前相比,喷油器的开启滞后时间缩短了0.25ms,落座滞后时间缩短了0.3ms。     

Modeling and calculation of field emission enhancement factor for carbon nanotubes array

To estimate the apex field enhancement factor associated with carbon nanotubes (CNTs) array on a planar cathode surface, the image model of floated sphere between parallel anode and cathode plates was proposed. Firstly, the field enhancement factor of individual CNT was given as the following expression, beta0=h/rho+3.5, where h is the height and rho is the radius of CNTs. Then the field enhancement factor of CNTs array was discussed and the above expression was modified to be beta=h/rho+3.5-W, in which W is the function of the intertube distance R and represents the coulomb field interaction between the CNTs. All results show that the intertube distance of CNTs array critically affects the field emission. When the intertube distance is less than the height of tube, the field enhancement factor will decrease rapidly with decreasing the intertube distance. According to the calculated results and considering the field emission current density, the filed emission is optimal theoretically when the intertube distance is comparable with the height of CNTs.     

方兴未艾的太赫兹生物医学传感器

太赫兹生物医学传感器在当前研究中属于一个热点,其工作原理主要依托人工周期性电磁媒介或二维材料构建电磁亚波长结构,与入射的太赫兹波相互作用时,引发类似表面等离子体共振现象,产生的局域电磁场增强效应对周围的介电环境敏感,从而改变太赫兹光谱中共振的品质因子与谐振频率,实现对生物分子的高灵敏度检测和分析。围绕近几年的研究现状,从生物传感器的类型及其在生物医学等领域的应用分别加以阐述,讨论了太赫兹生物医学传感器所面临的挑战和发展前景,旨在提供一些有价值的建议。