Quantitative current measurements using scanning magnetoresistance microscopy

We have demonstrated the capability of scanning magnetoresistance microscope (SMRM) to be used for quantitative current measurements. The SMRM is a magnetic microscope that is based on an atomic force microscope (AFM) and simultaneously measures the localized surface magnetic field distribution and surface topography. The proposed SMRM employs an in-house built AFM cantilever equipped with a miniaturized magnetoresistive (MR) sensor as a magnetic field sensor. In this study, a spin-valve type MR sensor with a width of 1 microm was used to measure the magnetic field distribution induced by a current carrying wire with a width of 5 microm and a spacing of 1.6 microm at room temperature and under ambient conditions. Simultaneous imaging of the magnetic field distribution and the topography was successfully performed in the DC current ranging from 500 microA to 8 mA. The characterized SV sensor, which has a linear response to magnetic fields, offers the quantitative analysis of a magnetic field and current. The measured magnetic field strength was in good agreement with the result simulated using Biot-Savart's law.     

Coaxial arrangement of a scanning probe and an X-ray microscope as a novel tool for nanoscience

We report on the design and first tests of a novel instrument aimed at combining the benefits of scanning force microscopy with those of X-ray spectroscopy. For this we built an instrument combining a scanning transmission X-ray microscope with a beam-deflection atomic force microscope in a coaxial geometry. This allows to combine X-ray absorption spectroscopy and high resolution topography in-situ. When replacing the conventional scanning probe tip by a coaxially shielded tip the instrument will allow detection of the photoelectrons produced by resonant X-ray absorption. This could yield spectroscopic information with a spatial resolution approaching the values achievable with atomic force microscopy.     

The conversion of a field-emission scanning electron microscope to a high-resolution,high-performance scanning transmission electron microscope,while maintaining original functions

Recently, the reliability of field-emission electron guns has increased. In addition, the cost of computer systems for on-line processing has dropped. Hence, we should now consider the use of scanning transmission electron microscopy (STEM) for routine work, especially, in the field of biology where one may expect to utilize digital image processing techniques. An STEM has been constructed, without disturbing the original functions, by converting a commercial scanning electron microscope equipped with a fieldemission gun. The STEM is generally operated at accelerating voltage 30 kV, focal length 7.5 mm, and beam current 1?2 × 10^?10 A. Several improvements have been incorporated for removing the effects of vibration, contamination, and stray magnetic fields. Also, an adjustable detector aperture was utilized. The modified instrument was connected to an on-line digital image processing system for utilizing the information obtained from STEM images. The advantages of the modified system were studied from various viewpoints.     

Mid-infrared scanning near-field optical microscope resolves 30 nm

We explore the performance of a scanning near-field infrared microscope, which works by scattering tightly focused CO2 laser radiation (lambda = 10 microm) from the apex of a metallized atomic force microscope tip. The infrared images of test samples prove a spatial resolution of 30 nm and are free of topographical and inertial artefacts, thus they should be of great interest for practical applications. We also observe that the infrared contrast vanishes when the input beam polarization is orthogonal to the tip axis, in accordance with theoretical expectations for a mechanism of longitudinal field interaction.     

A nanopositioner for scanning probe microscopy: the KoalaDrive

We present a new type of piezoelectric nanopositioner called KoalaDrive which can have a diameter less than 2.5 mm and a length smaller than 10 mm. The new operating principle provides a smooth travel sequence and avoids shaking which is intrinsic to nanopositioners based on inertial motion with sawtooth driving signals. In scanning probe microscopy, the KoalaDrive can be used for the coarse approach of the tip or sensor towards the sample. Inserting the KoalaDrive in a piezo tube for xyz-scanning integrates a complete scanning tunneling microscope (STM) inside a 4 mm outer diameter piezo tube of <10 mm length. The use of the KoalaDrive makes the scanning probe microscopy design ultracompact and accordingly leads to a high mechanical stability. The drive is UHV, low temperature, and magnetic field compatible. The compactness of the KoalaDrive allows building a multi-tip STM as small as a single tip STM.     

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.     

Fluctuation microscopy in the STEM

Fluctuation electron microscopy is a technique for studying medium-range order in disordered materials. We present an implementation of fluctuation microscopy using nanodiffraction in a scanning transmission electron microscope (STEM) at a spatial resolution varying from 0.8 to 5.0 nm. Compared to conventional TEM (CTEM), the STEM-based technique offers a denser scattering vector sampling at a reduced sample dose and easier access to variable resolution information. We have reproduced results on amorphous silicon previously obtained by CTEM-based fluctuation microscopy, and report initial variable-resolution measurements on amorphous germanium.     

Scanning superconducting quantum interference device on a tip for magnetic imaging of nanoscale phenomena

We describe a new type of scanning probe microscope based on a superconducting quantum interference device (SQUID) that resides on the apex of a sharp tip. The SQUID-on-tip is glued to a quartz tuning fork which allows scanning at a tip-sample separation of a few nm. The magnetic flux sensitivity of the SQUID is 1.8 μΦ(0)/Hz and the spatial resolution is about 200 nm, which can be further improved. This combination of high sensitivity, spatial resolution, bandwidth, and the very close proximity to the sample provides a powerful tool for study of dynamic magnetic phenomena on the nanoscale. The potential of the SQUID-on-tip microscope is demonstrated by imaging of the vortex lattice and of the local ac magnetic response in superconductors.     

Magnetic characterization of microscopic particles by MO-SNOM

This paper reports on the development of a magneto‐optical scanning near‐field optical microscope and the experimental near‐field study of the domain structure for a model magnetic particle of 16 × 16 µm² of a Co_70.4Fe_4.6Si₁₅B₁₀ amorphous thin film, deposited on a silicon substrate. We present the topographic, optical and magneto‐optical differential susceptibility (MODS) images of the particle. Imaging by using the local MODS reveals the domain structure. These images are also used for positioning the tip in order to acquire local hysteresis loops, with submicrometre spatial resolution.     

Femtosecond near-field scanning optical microscopy

We have developed an instrument for optically measuring carrier dynamics in thin-film materials with approximately 150 nm lateral resolution, approximately 250 fs temporal resolution and high sensitivity. This is accomplished by combining an ultrafast pump-probe laser spectroscopic technique with a near-field scanning optical microscope. A diffraction-limited pump and near-field probe configuration is used, with a novel detection system that allows for either two-colour or degenerate pump and probe photon energies, permitting greater measurement flexibility than that reported in earlier published work. The capabilities of this instrument are proven through near-field degenerate pump-probe studies of carrier dynamics in GaAs/AIGaAs single quantum well samples locally patterned by focused ion beam (FIB) implantation. We find that lateral carrier diffusion across the nanometre-scale FIB pattern plays a significant role in the decay of the excited carriers within approximately 1 microm of the implanted stripes, an effect which could not have been resolved with a far-field system.     

交流励磁三维定位系统中磁传感器设计

交流励磁定位系统可以对介入式微型医疗装置在人体内的三维位置实现非接触式遥测。在定位系统中，为了测量磁场分布范围宽、下限磁场微弱的交变磁场，本文设计开发了感应线圈式磁传感器。根据电磁感应原理，感应线圈先将交变的磁信号转换为电信号，再通过后级信号处理电路在强大的噪声背景中提取出有用的电信号，结合传感器的输入输出特性，即获得待测磁场大小。实验结果表明：磁传感器能准确测量微弱交变磁场，且具有宽测量范围、高分辨率、高稳定性和高精度的优点。磁传感器还能适用于一切非导磁环境中跨度大的交变磁场的测量，具有通用性。     

Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy

By example of a Permalloy particle (40 × 40 μm(2) size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cause a change of contrast and an image deformation of the particles geometry (curvature of its edge). The magnetic stray fields are calculated from a deformation of the X-ray magnetic circular dichroism (XMCD) images taken after the magnetic field pulse in a 1 ns interval. These measurements reveal a decrease of magnetic stray fields with time. An estimate of the lower limit of the domain wall velocity yields about 2 × 10(3) m s(-1).     

Ultrahigh vacuum, variable temperature, dual scanning tunneling microscope system operating under high magnetic field

We present a dual scanning tunneling microscope (DSTM) system operating between 2.2 K and room temperature, in a split-coil superconducting magnetic field up to 12 T and in ultrahigh vacuum. The DSTM consists of two compact STMs, each having x, y, and z coarse positioning piezoelectric steppers with embedded capacitive positioning sensor for navigation. Each STM can be operated independently and can achieve atomic resolution. The DSTM and the sample is configured in a way that allows the magnetic field orientation to be varied continuously from normal to parallel to the sample surface. Together with the sample, the DSTM can form a nanometer scale three terminal setup for transport measurement.     

Demonstration of magnetoelectric scanning probe microscopy

A near-field room temperature scanning magnetic probe microscope has been developed using a laminated magnetoelectric sensor. The simple trilayer longitudinal-transverse mode sensor, fabricated using Metglas as the magnetostrictive layer and polyvinylidene fluoride as the piezoelectric layer, shows an ac field sensitivity of 467+/-3 microV/Oe in the measured frequency range of 200 Hz-8 kHz. The microscope was used to image a 2 mm diameter ring carrying an ac current as low as 10(-5) A. ac fields as small as 3 x 10(-10) T have been detected.     

扫描力显微镜中的点衍射干涉现象及其应用

本文论述了扫描力显微镜中的点衍射干涉现象,论证了硅微探针可以作为后向点衍射板并用于检测微探针变位的光学原理。根据这一原理设计了一种新型灵巧的扫描力显微镜,它具有更好的抗干扰能力,稳定优质的光电信号。理论分析及实测表明,该扫描力显微镜具有０．０１ｍｍ 的纵向分辩率、５ｎｍ 左右的横向分辨率。     

Application of photon scanning tunneling microscope to measure optical near field for atom manipulation

Photon scanning tunneling microscope has been employed to measure the three-dimensional evanescent optical field of an atom funnel. A 3.8 neV repulsive optical potential has been estimated by a 300 microm long probe with a tip radius of curvature of 21 nm. We have estimated limiting conditions for cold Rb atoms to reflect from the atom funnel. A two-dimensional doughnut-shaped optical near field has also been investigated. An aperture fiber probe is used to profile a focussed TEM(01) beam at the minimum beam waist and measure a dark center of about 10 microm while it is focussed by a converging lens of focal length 8 cm.     

软X射线显微术和光谱显微术

X射线显微术可直接在水环境中对胶体颗粒尺寸范围内的颗粒进行高分辨率成像,将该项技术与高分辨率光谱相结合,还可用于光谱显微研究。其中,常用的两种X射线显微镜是透射显微镜和扫描透射显微镜,文中示出了它们的装置图。由于X射线显微镜能迅速拍下一物体的高分辨率图像,所以,作为一种分析仪器,扫描X射线显微镜更适合作光谱显微研究。作为形态学目视化的一个示例,本文用一台透射X射线显微镜拍摄了粘土和土壤样品的图像。根据X射线图像进行的低温层析实验所获得的图像得到了有关细菌构成的显微生存环境以及其它土壤胶状体的3D结构信息。对扫描透射X射线显微镜拍摄的一系列图像进行分析,得到了土壤样品的形貌特性和化学特性。     

Nondestructive evaluation of a crack on austenitic stainless steel using a sheet type induced current and a Hall sensor array

Austenitic stainless steels (hereafter A-STS) such as STS304 and STS316 are paramagnetic metals. However, a small amount of partial magnetization is generated in A-STS because of the imperfect final heat treatment and mechanical processing. Surface cracks on paramagnetic metal with a partially magnetized region (hereafter PMR) are difficult to inspect. In this paper, we propose a method for high speed inspection and evaluation of a crack on A-STS. Cracks can be inspected with high speed by using 64 arrayed Hall sensors (HSA) with 3.5 mm spatial resolution and a sheet type induced current (STIC). Then, a crack can be evaluated quantitatively by using the detailed distribution of the magnetic field obtained by using single Hall sensor scanning (SSS) around the inspected crack area. Several cracks on A-STS with partially magnetized areas were examined and the experimental formulas were derived.     

Effect of tip shape on capacitance determination accuracy in scanning capacitance microscopy

We present an analysis of the measurement error caused by the stray field of scanning capacitance microscope probes of various shapes. Cylindrical islands and wells of varying radius and height or depth, in both conducting surfaces and structures containing dielectric films, were used as test features for modelling. The results show that high accuracy and good contrast of small details are contradictory requirements. Probes with small radius of curvature of the tip apex yield smaller errors on features with small diameter but larger ones on features with large diameter than tips with large radius of curvature. The stray electrostatic field causes large errors, which are exceptionally severe with microfabricated probes. Contrary to general belief, differential measurements, based on modulation of the probe/sample separation or of the width of depletion layer in semiconductors, do not reduce the effect of the stray field significantly. For best results, the probe should be shielded as close to the tip apex as possible. In the case of microfabricated probes, at least the side of the cantilever facing the sample should be shielded.     

Scanning electron microscopy of two-dimensional magnetic stray fields

Methods used in metrology of two-dimensional magnetic microfields and based on direct interaction of the electron beam of scanning electron microscope (SEM) with the studied fields are described. An analytical expression for calculating the value of the field is presented. The errors and applicability of the methods have been estimated. The concepts discussed are illustrated by the experimental results of the measurements of some types of statistical and dynamic stray fields.