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.     

用于纳米计量的双元扫描隧道显微镜

研制了用于纳米计量的双元扫描隧道显微镜 ,介绍了双元扫描隧道显微镜的原理和仪器系统 ,利用该系统对原子晶格图象进行扫描 ,验证了纳米计量的可行性 ,给出了部分被测样品的纳米计量结果     

Biological structures imaged in a hybrid scanning transmission electron microscope and scanning tunneling microscope

A hybrid scanning transmission electron microscope (STEM) and scanning tunneling microscope (STM) is described which allows simultaneous imaging of biological structures adsorbed to electron-transparent specimen supports in both modes of scanning microscopy, as demonstrated on uncoated phage T4 polyheads. We further discuss the reproducibility and validity of height data obtained from STM topographs of biomacromolecules and present raw data from topographs of freeze-dried, metal-coated nuclear envelopes from Xenopus laevis oocytes.     

Automatic bias-reduction controller for a scanning tunneling microscope

In order to protect the sample and the tip against current transients in a scanning tunneling microscope, which in most cases damages the scanned surface and the tip, when using a bias higher than 1V, we have designed a simple and low-cost circuit that limits the tunneling current. During the evolution of the current transient, when the current exceeds a pre-determined value, a fast feedback control mechanism immediately reduces the bias and prevents the current transient from developing. In addition, we designed a fast pre-amplifier that works with this controller. We have shown that this mechanism provides a better scanning image compared to a system without such a mechanism.     

Construction of a versatile ultralow temperature scanning tunneling microscope

We constructed a dilution-refrigerator (DR)-based ultralow temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 30 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR-based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in an UHV environment to a STM head keeping low temperature and UHV conditions. After then, the system can be cooled back to near the base temperature within 3 h. Due to these capabilities, it has a variety of applications not only for cleavable materials but also for almost all conducting materials. The present ULT-STM has also an exceptionally high stability in the presence of magnetic field and even during field sweep. We describe details of its design, performance, and applications for low temperature physics.     

Haptic-STM: a human-in-the-loop interface to a scanning tunneling microscope

The operation of a haptic device interfaced with a scanning tunneling microscope (STM) is presented here. The user moves the STM tip in three dimensions by means of a stylus attached to the haptic instrument. The tunneling current measured by the STM is converted to a vertical force, applied to the stylus and felt by the user, with the user being incorporated into the feedback loop that controls the tip-surface distance. A haptic-STM interface of this nature allows the user to feel atomic features on the surface and facilitates the tactile manipulation of the adsorbate/substrate system. The operation of this device is demonstrated via the room temperature STM imaging of C(60) molecules adsorbed on an Au(111) surface in ultra-high vacuum.     

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.     

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.     

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.     

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.     

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。     

Self-navigation of a scanning tunneling microscope tip toward a micron-sized graphene sample

We demonstrate a simple capacitance-based method to quickly and efficiently locate micron-sized conductive samples, such as graphene flakes, on insulating substrates in a scanning tunneling microscope (STM). By using edge recognition, the method is designed to locate and to identify small features when the STM tip is far above the surface, allowing for crash-free search and navigation. The method can be implemented in any STM environment, even at low temperatures and in strong magnetic field, with minimal or no hardware modifications.     

A scanner for an ultrahigh-vacuum low-temperature scanning tunneling microscope

A scanner for an ultrahigh-vacuum low-temperature scanning tunneling microscope is described. It has a high resonance frequency (>30 kHz) and a small thermal-drift rate (≤1 nm/°C) at room temperature. The scanner feeds the tip to the sample at a distance of up to 3 mm and positions it in the sample plane on a 4 × 4-mm area. These characteristics of the scanner allow one to study atomic structures at temperature variations from 5 to 300 K with objects under study remaining in view of the microscope. The scanner has a horizontal attachment for a sample with a size of up to 6 × 6 × 3mm and ensures a scanning field of 4.8 × 4.8 × 0.6 μm at 300 K and 0.8 × 0.8 × 0.1 μm at 5 K, as well as the possibility of heating to 150°C and easily replacing the sample and tip with vacuum manipulators.     

In-vivo observation of cells with a combined high-resolution multiphoton-acoustic scanning microscope

We present a combined multiphoton-acoustic microscope giving collocated access to the local morphological as well as mechanical properties of living cells. Both methods relay on intrinsic contrast mechanisms and dispense with the need of staining. In the acoustic part of the microscope, a gigahertz ultrasound wave is generated by an acoustic lens and the reflected sound energy is detected by the identical lens in a confocal setup. The achieved lateral resolution is in the range of 1 mum. Contrast in the images arises mainly from the local absorption of sound in the cells related to viscose damping. Additionally, acoustic microscopy can access the sound speed as well as the acoustic impedance of the cell membrane and the cell shape, as it is an intrinsic volume scanning technique. The multiphoton image formation bases on the detection of autofluorescence due to endogenous fluorophores. The nonlinearity of two-photon absorption provides submicron lateral and axial resolution without the need of confocal optical detection. In addition, in the near-IR cell damages are drastically reduced in comparison with direct excitation in the visible or UV. The presented setup was aligned with a dedicated procedure to ensure identical image areas. Combined multiphoton/acoustic images of living myoblast cells are discussed focusing on the reliability of the method.     

Fabrication of silver tips for scanning tunneling microscope induced luminescence

We describe a reliable fabrication procedure of silver tips for scanning tunneling microscope (STM) induced luminescence experiments. The tip was first etched electrochemically to yield a sharp cone shape using selected electrolyte solutions and then sputter cleaned in ultrahigh vacuum to remove surface oxidation. The tip status, in particular the tip induced plasmon mode and its emission intensity, can be further tuned through field emission and voltage pulse. The quality of silver tips thus fabricated not only offers atomically resolved STM imaging, but more importantly, also allows us to perform challenging "color" photon mapping with emission spectra taken at each pixel simultaneously during the STM scan under relatively small tunnel currents and relatively short exposure time.     

Photon scanning tunneling microscope,now and in the future

The concept of photon tunneling and the principle of the photon scanning tunneling microscope (PSTM) are described. The history of the PSTM and its development in China are reviewed. The principal problem in the recent development of the PSTM, together with its solution, is discussed. The distinguishing features and the future of the PSTM are described.     

Versatile optical access to the tunnel gap in a low-temperature scanning tunneling microscope

We developed a setup that provides three independent optical access paths to the tunnel junction of an ultrahigh vacuum low temperature (4.2 K) scanning tunneling microscope (STM). Each path can be individually chosen to couple light in or out, or to image the tunnel junction. The design comprises in situ adjustable aspheric lenses to allow tip exchange. The heat input into the STM is negligible. We present in detail the beam geometry and the realization of lens adjustment. Measurements demonstrate the characterization of a typical light source exemplified by emission from tip-induced plasmons. We suggest employing the Fourier transforming properties of imaging lenses and polarization analysis to obtain additional information on the light emission process. Performance and future potential of the instrument are discussed.     

A cryogenic Quadraprobe scanning tunneling microscope system with fabrication capability for nanotransport research

We describe the development and the capabilities of an advanced system for nanoscale electrical transport studies. This system consists of a low temperature four-probe scanning tunneling microscope (STM) and a high-resolution scanning electron microscope coupled to a molecular-beam epitaxy sample preparation chamber. The four STM probes can be manipulated independently with subnanometer precision, enabling atomic resolution STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. Additionally, an integrated energy analyzer allows for scanning Auger microscopy to probe chemical species of nanostructures. Some testing results are presented.     

High-resolution photon scanning tunneling microscopic investigations of NaCl crystal surfaces

Cleaved NaCl crystal surfaces were investigated with a photon scanning tunneling microscope. Steps 4 nm high and 3 nm wide could be resolved. The lateral resolution is coupled to the step height by the steepest measured slopes of about 50°. The measured stepwidth at shallow steps is noise-and slope-limited to 3 nm. The mapping of the decay coefficient of the evanescent field shows spatial inhomogeneities often coupled to the crystalline structure.     

Highly controllable fabrication of fiber probe for photon scanning tunneling microscope

A selective chemical etching was used to fabricate fiber probes for the photon scanning tunneling microscope (PSTM). The cladding diameter of the fiber probe was controlled by varying the first-step etching time. The cone angle of the fiber probe tip was controlled by varying the doping ratio of the fiber and the composition of the etching solution. A cladding diameter of 8 μm and a tip diameter of about 3 nm were fabricated. The smallest cone angle was 14°.