Imaging of granular high-Tc thin films using a scanning tunnelling microscope with large scan range

STM images are presented in the micron scale, taken in UHV with a single-tube scanner STM with SEM control of the tip position. For calibration, a carbon grid was used from which the coupling of x and y scan axes has been determined as well as the piezo-sensitivity factors. Images taken of a YBa₂Cu₃O_7-δ, film display the granular structure of the crystallites formed during the post-evaporation annealing. A direct comparison of STM scans with SEM micrographs was made which demonstrates the complementary information obtained by the two methods. The obtained resolution is compared to the tip shape which becomes crucial for the imaging of corrugated surfaces on the micron scale. With a simple geometric model, an attempt has been made to reconstruct the surface topography from STM scans based on the knowledge of the tip shape.     

Design and operation of a variable temperature scanning tunnelling microscope

A new variable temperature STM has been developed which utilizes two concentric piezoelectric tubes; an inner scanning tube, and an outer thermal compensation tube which also provides for inertial translation of the sample into tunnelling range. With this design, continuously variable temperature operation is demonstrated for the first time in an STM. Also, by eliminating all mechanical components such as springs, levers and gears, which normally couple directly to the tunnelling gap in other designs, atomic resolution operation is demonstrated in which no vibration isolation is necessary. During operation, the inside of the scanning tube is maintained at ground potential while the feedback signal is electronically summed to the scanning voltages applied to the outer quadrants. In addition to shielding the sensitive tunnelling circuit, this mode of operation enables one to electronically balance out mechanical imperfections of the scanning tube. To date, this new STM has been operated over the 77–400 K temperature range with the observed thermal drift as low as 1 Å/h and 10 Å/K. Another useful feature of this new design is the ability to reposition a sample to within 200 Å of the same location after it has been translated macroscopic distances (several mm) out of tunnelling range.     

A combined scanning tunnelling and field ion microscope

The construction of a combined scanning tunnelling and field ion microscope allowing the in situ preparation and analysis of the tunnelling tip is described. The apparatus is based on the Besocke type STM and includes a fast, automated sample approach, a sample transfer manipulator and a tip-cooling mechanism for the FIM operation mode. The design is simple and needs a mechanical feedthrough only for sample transfer. A method has been developed to produce sharp tungsten tips with small clusters on the apex plane. Test-run results of FIM and STM operation modes are discussed.     

Photon emission experiments with the scanning tunnelling microscope

We have detected the light emitted from an STM at both ultraviolet (9·5 eV) and optical (1–4 eV) energies. We show that this light contains spectroscopic information on the sample surface comparable to conventional inverse photoelectric spectroscopy, but with nearly atomic spatial resolution. At optical energies we found sufficiently high intensities to allow spatial imaging of the emission probability. We propose that the high quantum efficiency is due to resonance phenomena, and present fluorescence spectra of the emitted light that support this view. We believe that atomic resolution inverse photoemission microscopy and spectroscopy will provide an important new dimension to surface studies.     

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.     

A scanning tunnelling microscope for operation in air

In this paper a scanning tunnelling microscope for operation in air is described with emphasis on the coarse and fine sample positioning mechanism, piezoelectric scanner and vibration isolation. Line scan (amplitude modulation), top view (brightness modulation) and combined shaded topographical images of the surface of highly orientated pyrolitic graphite are shown.     

A graphite study with a new air operating scanning tunnelling microscope

A scanning tunnelling microscope working in air with good atomic resolution is described. Atomic corrugation of graphite samples cleaved in air has been observed with a lateral resolution considerably less than 1 Å. The height of the potential barrier is measured as a function of the time the system tip-sample is exposed to air. An explanation for the observed giant corrugation is given.     

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.     

A scanning near-field optical microscope having scanning electron tunnelling microscope capability using a single metallic probe tip

A new microscope system that has the combined capabilities of a scanning near-field optical microscope (SNOM) and a scanning tunnelling microscope (STM) is described. This is achieved with the use of a single metallic probe tip. The distance between the probe tip and the sample surface is regulated by keeping the tunnelling current constant. In this mode of operation, information about the optical properties of the sample, such as its refractive index distribution and absorption characteristics, can be disassociated from the information describing its surface structure. Details of the surface structure can be studied at resolutions smaller than the illumination wavelength. The performance of the microscope is evaluated by analysing a grating sample that was made by coating a glass substrate with gold. The results are then compared with the corresponding SNOM and STM images of the grating.     

PHOEBE,a prototype scanning laser-feedback microscope for imaging biological cells in aqueous media

Based on the principle of laser-feedback interferometry (LFI), a laser-feedback microscope (LFM) has been constructed capable of providing an axial (z) resolution of a target surface topography of ～ 1 nm and a lateral (x, y) resolution of ～ 200 nm when used with a high-numerical-aperture oil-immersion microscope objective. LFI is a form of interferometry in which a laser's intensity is modulated by light re-entering the illuminating laser. Interfering with the light circulating in the laser resonant cavity, this back-reflected light gives information about an object's position and reflectivity. Using a 1-mW He–Ne (λ = 632·8 nm) laser, this microscope (PHOEBE) is capable of obtaining 256 × 256-pixel images over fields from (10 μm × 10 μm) to (120 μm × 120 μm) in ～ 30 s. An electromechanical feedback circuit holds the optical pathlength between the laser output mirror and a point on the scanned object constant; this allows two types of images (surface topography and surface reflectivity) to be obtained simultaneously. For biological cells, imaging can be accomplished using back-reflected light originating from small refractive-index changes (> 0·02) at cell membrane/water interfaces; alternatively, the optical pathlength through the cell interior can be measured point-by-point by growing or placing a cell suspension on a higher-reflecting substrate (glass or a silicon wafer). Advantages of the laser-feedback microscope in comparison to other confocal optical microscopes include: the simplicity of the single-axis interferometric design; the confocal property of the laser-feedback microscope (a virtual pinhole), which is achieved by the requirement that only light that re-enters the laser meeting the stringent frequency, spatial (TEM₀₀), and coherence requirements of the laser cavity resonator mode modulate the laser intensity; and the improved axial resolution, which is based on interferometric measurement of optical amplitude and phase rather than by use of a pinhole as in other types of confocal microscopes.     

An entirely enclosed scanning tunnelling microscope capable of being fully immersed in liquid helium

We present an ultrahigh‐vacuum (UHV)‐sealed high‐stability scanning tunnelling microscope (STM) that can be entirely immersed in liquid helium and readily used in a commercial Dewar or superconducting magnet. The STM head features a horizontal microscanner that can become standalone and ultrastable when the coarse approach inertial motor retracts. Low voltage is enough to operate the STM even at low temperature owing to the powerful motor. It is housed in a tubular chamber of 49 mm outer diameter, which can be pumped via a detachable valve (DV), UHV‐sealed and remain sealed after the DV is removed. The entire so‐sealed chamber can then be inserted into liquid helium, where in situ sample cleavage is done via vacuum bellow. This allows sample cleavage and STM measurements to take place in better UHV with higher cooling power. Quality atomic resolution images of graphite and charge density wave on 1T‐TiSe₂ taken in ambient and 14 K conditions, respectively, are presented.     

In situ fabrication and regeneration of microtips for scanning tunnelling microscopy

Progress in STM, in particular for the interpretation of the tunnel signals of corrugated surfaces, is related to the possibility of sharpening and regenerating in situ reproducible tips for use as the probe. We proposed two techniques for the production of tips with controlled geometry at the atomic level. These two techniques are based on the production of tips with equilibrium profiles obtained under heat treatments in vacuum and in the presence of an electric field. Based on the pseudo-stationary profile principle, the microtips can be sharpened in situ and in a reproducible manner, either from initial cylindrical (111)-W wire, or from breakdown tips; in both cases without the need for heavy control devices (like FIM for example).     

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     

共聚焦激光扫描荧光显微镜扫描系统研制

为适应三维光学微细加工及三维光学信息存储研究的需要,研制了共聚焦激光扫描荧光显微镜的工作台式扫描系统,扫描范围138μm×138μm.工作台采用压电陶瓷驱动器( PZT actuator)驱动的方式来获得高分辨率的位移,采用带柔性铰链的杠杆放大装置来获得较大的位移范围.描述了工作台的工作原理,并对其静态和动态性能进行了测试,实验表明这一扫描系统能很好的应用于共聚焦激光扫描荧光显微镜系统.     

Finite element analysis of PZT tube scanner motion for scanning tunnelling microscopy

This article is a presentation of the results of a finite element method analysis of piezoelectric tube scanners of the type presently in wide use in scanning tunnelling microscopes. The tube scanner moves a tunnelling tip by bending sideways when unsymmetrical voltages are applied to longitudinal stripes of metallization on its walls. It also can be extended and contracted in length by application of symmetrical voltages. One wishes to know the characteristics and magnitudes of the resulting three-dimensional motion. We divided a model tube into radially polarized elements, and constructed a computer program to perform electromechanical stress calculations. The results show the dependence of motion upon applied voltage, tube material, and tube dimensions.     

A fully automated, ‘thimble-size’ scanning tunnelling microscope

A novel, fully automated high-stability, high-eigenfrequency scanning tunnelling microscope (STM) has been developed. Its key design feature is the application of two piezoelectric ceramic tubes, one for the x-y-z motion of the tip and one for a linear motor (‘nano-worm’) used for the coarse positioning of the tip relative to the specimen. By means of the nano-worm, the tip can be advanced in steps between 16 and 0·2 nm. The walking distance is >2 mm, with a maximum speed of 2000 steps/s. The nano-worm positioning implies that this STM is fully controlled by electronic means, and that no mechanical coupling is needed, which makes operation of the STM extremely convenient. The axial-symmetry construction is rigid, small and temperature-compensated, yielding reduced sensitivity to mechanical and acoustic vibrations and temperature variations. The sample is simply placed on a piece of invar which surrounds the scanner tube and the nano-worm and is held by gravity alone. This allows for easy sample mounting. The performance of the microscope has been tested in air by imaging a variety of surfaces, including graphite and biological samples.     

Imaging of hydrogen-induced Si(111) surface with the scanning tunnelling microscope

We have directly observed the hydrogen-induced changes of the Si(111)7times7 surface using a scanning tunnelling microscope (STM). The 7times7 reconstructed atomic structure was formed on a clean surface of Si(111). But when the clean surface was dosed with typically 1–2 L [1 L (Langmuir) = 1·33 times 10^?4 Pa. sec] hydrogen, the 7 times 7 image was gradually smeared out and then a 1 times 1 unreconstructed pattern appeared. After dosing with 5–10 L hydrogen, the STM image exhibited a new long-periodic structure together with the 1times1 structure underneath. These experimental results may be ascribed to the chemisorption of hydrogen atoms on clean Si surfaces.     

Multiplexing optical fiber low coherence and high coherence interferometric system with large range and high resolution for on-line measurement

A novel optical fiber sensing system multiplexing low coherence interferometry and high coherence interferometry that is endowed with large range and high resolution and is stabilized for on-line measurement is presented. An optical fiber Michelson interferometer performing measurement task in the system works in both modes of low coherence interferometry and high coherence interferometry simultaneously by employing a broadband light source and a fiber Bragg grating as an in-fiber reflective mirror. The amplitude of the measurand is determined by the low coherence interferometry while the value of the measurand is measured by the high coherence interferometry. Another optical fiber Michelson interferometer which is incorporated with the one performing measurement task stabilizes the sensing system for on-line measurement by exploiting an electronic feedback loop to reduce the influences that are resulted from environmental disturbances. The measurement range is 6 mm and the measurement uncertainty is less than 2 nm.     

A real‐time image dynamic range compensation for scanning electron microscope imaging system

This paper presents the development and implementation of a real‐time dynamic range compensation system for scanning electron microscope (SEM) imaging applications. Compared with conventional automatic brightness contrast compensators that are based on the average image or pixel intensity level, the proposed system utilizes histogram‐profiling techniques to compensate continuously the dynamic range of the processed video signal. The algorithms are implemented in software with a frame grabber card forming the front‐end video capture element. The proposed technique yields better image compensation compared with conventional methods.