Developments of scanning probe microscopy with stress/strain fields

An innovative stress/strain fields scanning probe microscopy in ultra high vacuum (UHV) environments is developed for the first time. This system includes scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM). Two piezo-resistive AFM cantilever probes and STM probes used in this system can move freely in XYZ directions. The nonoptical frequency shift detection of the AFM probe makes the system compact enough to be set in the UHV chambers. The samples can be bent by an anvil driven by a step motor to induce stress and strain on their surface. With a direct current (dc) power source, the sample can be observed at room and high temperatures. A long focus microscope and a monitor are used to observe the samples and the operation of STM and AFM. Silicon(111) surface in room temperature and silicon(001) surface in high temperature with stress were investigated to check the performance of the scanning probe microscope.     

Variable-temperature independently driven four-tip scanning tunneling microscope

The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface.     

Development of probe-to-probe approach method for an independently controlled dual-probe scanning tunneling microscope

We developed a method of fast probe-to-probe approach for an independently controlled dual-probe scanning tunneling microscope (STM), which is essential to measure the transport property of nanostructures, without scanning electron microscopy (SEM). In the approach method, inchworm motors are used as the coarse positioning devices, which are controlled with a personal computer. The method enables an automatic approach of the probe to the other probe within a short time (typically 30 min). After the approach, a real distance between contact points of each probe tip to a sample can be measured from the overlapped part of the STM images obtained with individual probe. The approach method without SEM is also useful to measure the charge transport in the atmosphere, which will be essential for measurement of the bio molecules.     

Hybrid scanning transmission electron/scanning tunnelling microscope system for the preparation and investigation of biomolecules

A hybrid scanning transmission electron/scanning tunnelling microscope vacuum system is introduced, which allows freeze drying and metal coating of biological samples and their simultaneous observation by scanning transmission electron microscopy and scanning tunnelling microscopy (STM). Different metal coatings and STM tips were analysed to obtain the highest possible resolution for such a system. Bovine liver catalase was used as a test sample and the STM results are compared to a molecular scale model.     

Nanomanipulation and nanofabrication with multi-probe scanning tunneling microscope: from individual atoms to nanowires

The wide variety of nanoscale structures and devices demands novel tools for handling, assembly, and fabrication at nanoscopic positioning precision. The manipulation tools should allow for in situ characterization and testing of fundamental building blocks, such as nanotubes and nanowires, as they are built into functional devices. In this paper, a bottom-up technique for nanomanipulation and nanofabrication is reported by using a 4-probe scanning tunneling microscope (STM) combined with a scanning electron microscope (SEM). The applications of this technique are demonstrated in a variety of nanosystems, from manipulating individual atoms to bending, cutting, breaking carbon nanofibers, and constructing nanodevices for electrical characterizations. The combination of the wide field of view of SEM, the atomic position resolution of STM, and the flexibility of multiple scanning probes is expected to be a valuable tool for rapid prototyping in the nanoscience and nanotechnology.     

扫描隧道显微镜系统的优化研究

对扫描隧道显微镜(STM)系统进行了优化研究,实现了对环境振动的隔绝和电噪声的屏蔽,并在此基础上,设计并完成CCD显微监测系统,实现了对样品—探针逼近过程的实时临控。对整个系统进行了联合调试,成功获得高定向热解石墨和金表面的结构图像。     

Development of an ion beam alignment system for real-time scanning tunneling microscope observation of dopant-ion irradiation

An ion beam alignment system has been developed in order to realize real-time scanning tunneling microscope (STM) observation of "dopant-ion" irradiation that has been difficult due to the low emission intensity of the liquid-metal-ion-source (LMIS) containing dopant atoms. The alignment system is installed in our original ion gun and STM combined system (IG/STM) which is used for in situ STM observation during ion irradiation. By using an absorbed electron image unit and a dummy sample, ion beam alignment operation is drastically simplified and accurized. We demonstrate that sequential STM images during phosphorus-ion irradiation are successfully obtained for sample surfaces of Si(111)-7x7 at room temperature and a high temperature of 500 degrees C. The LMIS-IG/STM equipped with the developed ion beam alignment system would be a powerful tool for microscopic investigation of the dynamic processes of ion irradiation.     

Surface investigations with a combined scanning electron–scanning tunneling microscope

We have combined a scanning tunneling microscope (STM) with a scanning electron microscope (SEM) for surface investigations of atomically flat surfaces, ultrathin adsorbate films, and material surfaces. The mechanical stability of the hybrid instrument allows high-resolution SEM of samples mounted on the STM stage and atomic resolution with the STM. Experimental results of combined SEM/STM investigations on textured material surfaces, submicron structures, and atomically flat conducting surfaces are presented. An example is given for surface machining with the STM under SEM control.     

Ultra compact multitip scanning tunneling microscope with a diameter of 50 mm

We present a multitip scanning tunneling microscope (STM) where four independent STM units are integrated on a diameter of 50 mm. The coarse positioning of the tips is done under the control of an optical microscope or scanning electron microscopy in vacuum. The heart of this STM is a new type of piezoelectric coarse approach called KoalaDrive. The compactness of the KoalaDrive allows building a four-tip STM as small as a single-tip STM with a drift of less than 0.2 nm/min at room temperature and lowest resonance frequencies of 2.5 kHz (xy) and 5.5 kHz (z). We present as examples of the performance of the multitip STM four point measurements of silicide nanowires and graphene.     

Analytical scanning electron microscopy for solid surface

A scanning electron microscope of ultra-high-vacuum (UHV-SEM) with a field emission gun (FEG) is operated at the primary electron energies of from 100 eV to 3 keV. The instrument can form the images that contain information on surface chemical composition, chemical bonding state (electronic structure), and surface crystal structure in a microscopic resolution of several hundred angstroms (Å) using the techniques of scanning Auger electron microscope, scanning electron energy loss microscope, and scanning low-energy electron diffraction (LEED) microscope. A scanning tunneling microscope (STM) also has been combined with the SEM in order to obtain the atomic resolution for the solid surface. The instrumentation and examples of their applications are presented both for scanning LEED microscopy and STM.     

Active mechanical noise cancellation scanning tunneling microscope

We present the design and performance of an active mechanical noise cancellation scanning tunneling microscope (STM). This system features two key parts: a "twin-tip" scanner and an active mechanical noise cancellation algorithm. The twin-tip scanner functions as two independent STMs which share nearly the same mechanical transfer function, allowing both STMs to sense nearly identical background mechanical noise. Based on an adaptive digital signal processing technique, the active mechanical noise cancellation algorithm applies the noise sensed by the first STM to concurrently cancel the noise in the second STM and hence allows the second STM to acquire spectroscopy with a significantly improved signal to noise ratio. This system demonstrates long-term stability of the tip-sample tunnel junction and improved spectroscopy measurement in a mechanically noisy environment.     

Scanning tunneling microscope combined with scanning electron microscope

A scanning tunneling microscope (STM) has been installed in a usual scanning electron microscope (SEM) with a vacuum of 10⁻⁶ Torr. The STM image is displayed on the cathode ray tube of the SEM, 512 × 512 pixels, with a scanning rate of 80 s/picture. The spatial resolution of the STM is about 1 Å, while that of the SEM is several tens of ångströms. The combined scanning microscope covers a wide magnification range from 10 to 10⁷, where STM covers the high magnification region from 10⁵ to 10⁷.     

Scanning probe microscopy of biological samples and other surfaces

Scanning probe microscopes derived from the scanning tunnelling microscope (STM) offer new ways to examine surfaces of biological samples and technologically important materials. The surfaces of conductive and semiconductive samples can readily be imaged with the STM. Unfortunately, most surfaces are not conductive. Three alternative approaches were used in our laboratory to image such surfaces. 1. Crystals of an amino acid were imaged with the atomic force microscope (AFM) to molecular resolution with a force of order 10^?8 N. However, it appears that for most biological systems to be imaged, the atomic force microscope should be able to operate at forces at least one and perhaps several orders of magnitude smaller. The substitution of optical detection of the cantilever bending for the measurement by electron tunnelling improved the reliability of the instrument considerably. 2. Conductive replicas of non-conductive surfaces enabled the imaging of biological surfaces with an STM with a lateral resolution comparable to that of the transmission electron microscope. Unlike the transmission electron microscope, the STM also measures the heights of the features. 3. The scanning ion conductance microscope scans a micropipette with an opening diameter of 0·04-0·1 μm at constant ionic conductance over a surface covered with a conducting solution (e.g., the surface of plant leaves in saline solution).     

A scanning tunneling microscope (STM) for biological applications: design and performance

The design of a scanning tunneling microscope (STM) for biological applications, operating at ambient pressure, is described. The STM is combined with an "auxiliary" light microscope to facilitate finding and identifying specimen areas of interest. The performance of the STM has been tested with evaporated gold films and with graphite. We have evaluated evaporated carbon and platinum/carbon films deposited on glass or mica to be used as specimen supports. First applications to biological material coated with a conducting film of platinum/carbon are described.     

一种高稳定性扫描隧道显微镜的设计与应用

报道自行研制的一种隔振能力强、能在大气和液体中工作的高稳定性扫描隧道显微镜。它通过一个多级齿轮减速器和一个杠杆机构实现并完成探针粗进给到达压电陶瓷管的扫描和平移范围的运动。介绍了电子控制系统的组成，讨论了热漂移及其抑制方法，给出了该仪器在高序定向热裂解石墨(HOPG)、猪脾DNA分子、奥氏体晶界的观测以及石墨表面纳米级加工等方面的应用与研究结果。     

In situ cleavage mechanism for semiconductor single crystals for ultrahigh-vacuum scanning tunneling microscope

A tecnique for cleaving semiconductor single crystals under ultrahigh-vacuum conditions is proposed. A system for in situ cleavage of samples for ultrahigh-vacuum scanning tunneling microscope (STM) has been developed. STM studies of the surfaces of InAs single crystals with n and p-type bulk conduction have been performed on an Omicron ultrahigh-vacuum facility.     

Imaging biological macromolecules by STM: quantitative interpretation of topographs

Methods are discussed which permit the calibration of x-, y-, z-sensitivities, non-linearities and frequency responses of the scanning device of a scanning tunneling microscope (STM) either by interferometry or directly from STM topographs. A technique is presented to measure the frequency response of the complete STM feedback unit and to derive a maximum speed in z direction which allows one to estimate the maximum scanning speed still permitting one to track surface corrugations. The signal transfer characteristics of a STM are evaluated in a direct comparison with high resolution transmission electron microscopy on an identical specimen area. The various effects of contaminants between tip and specimen and the finite tip radius receive special attention.     

Antenna-based ultrahigh vacuum microwave frequency scanning tunneling microscopy system

The instrumental synthesis of high resolution scanning tunneling microscopy (STM) with the ability to measure differential capacitance with atomic scale resolution is highly desirable for fundamental metrology and for the study of novel physical characteristics. Microwave frequency radiation directed at the tip-sample junction in an STM system allows for such high-resolution differential capacitance information. This ability is particularly critical in ultrahigh vacuum environments, where the additional parameter space afforded by including a capacitance measurement would prove powerful. Here we describe the modifications made to a commercial scanning tunneling microscope to allow for broad microwave frequency alternating current scanning tunneling microscopy (ACSTM) in ultrahigh vacuum conditions using a relatively simple loop antenna and microwave difference frequency detection. The advantages of our system are twofold. First, the use of a removable antenna on a commercial STM prevents interference with other UHV processes while providing a simple method to retrofit any commercial UHV-STM with UHV-ACSTM capability. Second, mounting the microwave antenna on a translator allows for specific tuning of the system to replicate experimental conditions between samples, which is particularly critical in sensitive systems like organic thin films or single molecules where small changes in incident power can affect the results. Our innovation therefore provides a valuable approach to give nearly any commercial STM, be it an ambient or UHV system, the capability to measure atomic-scale microwave studies such as differential capacitance or even single molecule microwave response, and it ensures that experimental ACSTM conditions can be held constant between different samples.     

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.     

The STM learning curve and where it may take us*

The scanning tunnelling microscope (STM) has proved to be an extraordinary method to investigate surfaces in vacuum, air and liquid environments. Several issues regarding the use of the STM for atomic resolution studies are discussed. These include electronic contributions to STM images, the role of the tip in resolution and spectroscopy, as well as the need for complementary information about chemical composition or sub-surface structure.