Shin-ichi Kitamura

Reprint of: Atmospheric scanning electron microscope observes cells and tissues in open medium through silicon nitride film.

Direct observation of subcellular structures and their characterization is essential for understanding their physiological functions. To observe them in open environment, we have developed an inverted scanning electron microscope with a detachable, open-culture dish, capable of 8 nm resolution, and combined with a fluorescence microscope quasi-simultaneously observing the same area from the top. For scanning electron microscopy from the bottom, a silicon nitride film window in the base of the dish maintains a vacuum between electron gun and open sample dish while allowing electrons to pass through. Electrons are backscattered from the sample and captured by a detector under the dish. Cells cultured on the open dish can be externally manipulated under optical microscopy, fixed, and observed using scanning electron microscopy. Once fine structures have been revealed by scanning electron microscopy, their component proteins may be identified by comparison with separately prepared fluorescence-labeled optical microscopic images of the candidate proteins, with their heavy-metal-labeled or stained ASEM images. Furthermore, cell nuclei in a tissue block stained with platinum-blue were successfully observed without thin-sectioning, which suggests the applicability of this inverted scanning electron microscope to cancer diagnosis. This microscope visualizes mesoscopic-scale structures, and is also applicable to non-bioscience fields including polymer chemistry.

Robust and photocontrollable DNA capsules using azobenzenes.

Various three-dimensional structures have been created on a nanometer scale using the self-assembly of DNA molecules. However, ordinary DNA structures breakdown readily because of their flexibility. In addition, it is difficult to control them by inputs from environments. Here, we construct robust and photocontrollable DNA capsules using azobenzenes. This provides a method to construct DNA structures that can survive higher temperatures and can be controlled with ultraviolet irradiation.

High resolution imaging of contact potential difference using a novel ultrahigh vacuum non-contact atomic force microscope technique

An ultrahigh vacuum scanning Kelvin probe force microscope (UHV SKPM) based on the gradient of electrostatic force was developed using the technique of a UHV non-contact atomic force microscope (NC-AFM) capable of atomic level imaging, and used for simultaneous observation of contact potential difference (CPD) and NC-AFM images. The CPD images with a potential resolution of less than 10 meV were observed in the UHV SKPM, demonstrating an atomic level resolution. The change of potential corresponding to the charges on the insulated surface of polypropylene have been observed in UHV SKPM. We also demonstrated a reliable method to obtain the CPD from the bias voltage dependence curves of the frequency shift in all of the scanning area. The results are consistent with comparing the barrier height images in that the work functions of adatoms are greater than the work function of corner holes.

Atomic-scale variations in contact potential difference on Au/Si(111) 7 × 7 surface in ultrahigh vacuum

Abstract The results of contact potential difference (CPD) imaging on Au-deposited p-type and n-type Si(111) 7×7 surfaces are discussed. The scanning Kelvin probe microscopy (SKPM) technique based on the gradient of the electrostatic force was used under ultrahigh vacuum (UHV) conditions to acquire the data presented. The CPD images of Au deposited on the Si(111) 7×7 surface show virtually identical features, irrespective of whether the Si is n- or p-type. In these images, it is believed that the atomically resolved potential difference does not originate from the intrinsic work function of the materials but reflects the local electron density on the surface. On the other hand, the average potentials corresponding to the DC levels in each CPD image reflects the work function value on the surface. The work function of p-type Si(111) 7×7 is found to be higher than that of n-type by about 0.45 eV, where both samples had the same resistivity of about 0.5 Ω cm and the same Au coverage. If the Au coverage is increased, the work function increases.

An ultrasmall amplitude operation of dynamic force microscopy with second flexural mode

Selective detection of short-range interaction forces was carried out with the second flexural mode of a commercially available dynamic mode cantilever. A higher mode has a higher spring constant and a lower mechanical quality factor, which are suitable for the small amplitude operation in dynamic force microscopy. With 0.70A amplitude of the second flexural mode, atomically resolved constant frequency shift images of the Si(111)−7×7 reconstructed surface were obtained. The ultrasmall amplitude operation enabled imaging with high stability, due to the detection of the interaction force gradients at relatively long distances from the sample surface, and is an effective way to observe reactive surfaces while avoiding modifications and damaging of the tip and the sample.

Dynamic lateral force microscopy with true atomic resolution

We present frequency modulation dynamic lateral force microscopy with true atomic resolution. Torsional resonance mode of a commercially available rectangular cantilever was used to detect interaction lateral force gradients caused between the tip and the sample surface. A slight negative frequency shift of the torsional resonance frequency was observed before contact to the silicon surface. Individual adatoms in a unit cell of the Si(111)-7×7 reconstructed surface were imaged with the constant frequency shift mode. Two sets of the neighboring corner adatoms and one set of the center adatoms on the dithering direction of the tip were connected on the image. This method has a great potential to observe friction between single atoms.

An ultrahigh vacuum dynamic force microscope for high resonance frequency cantilevers

We present the design of an ultrahigh vacuum dynamic force microscope incorporating a heterodyne Doppler interferometer and a superheterodyne circuit with an intermediate frequency of 10.7MHz. The method allowed the use of a low-noise narrow-band analog phase-locked loop with a voltage controlled crystal oscillator for demodulating the frequency shifts caused by the interaction force gradients between the tip and the sample at the intermediate frequency. The system could be used for a conventional cantilever operating in its fundamental and higher modes, as well as for small or stiff cantilevers with high resonance frequency up to 100MHz. A preliminary measurement was demonstrated by the observation of the Si(111)−7×7 reconstructed surface with the second resonance of 1.6MHz with subangstrom amplitudes.

Scanning Tunneling Microscopy Study of the 16-Structure Appearing on a Si(110) Surface

High-resolution scanning tunneling microscopy (STM) was applied to observe the 16-structure appearing on a Si(110) surface. It was reaffirmed that the 16-structure coexisting with a facet structure was not found and could not be explained by the vicinal surface model. Bright and faint zigzag chains consisting of spheres, and the repetition of the upper and the lower layers with the height difference of 2.0 A were observed. Based on the above result, a structure model was proposed.

Observation of surface reconstruction and nano-fabrication on silicon under high temperature using a UHV-STM

Abstract In this paper we discuss three experiments on silicon (100) and (111) surface at high temperature obtained with an ultra-high-vacuum scanning tunneling microscope (UHV-STM). First, the initial stage of the crystalization process has directly been investigated on the Si(111) surface at a phase transition temperature of about 860°C. (7 × 7) domains nucleated from the step edges and expanded towards inner regions of the terraces, and the steps become straight [ 1 ¯ 1 ¯ 2 ] steps. Second, the high-temperature nano-fabrication method has been applied to Si surfaces. We succeeded in creating a hexagonal pyramid and a crater on the Si(111) surface, and a quadrangular pyramid on the Si(100) surface at 600°C. (5 × 5) domains can be observed on narrow terraces due to the relaxation of surface energy. Finally, we attempted to deposit gold (Au) atoms on silicon surfaces. Au atoms deposited on a high-temperature silicon surface migrated to the observation area while forming 5 × 1 structures. Then the Au atoms diffused into the bulk structure of silicon, and silicon (7 × 7) domains covered the surface again.

Round-robin measurements of 100- and 60-nm scales among a deep-ultraviolet laser diffractometer, a scanning electron microscope and various atomic force microscopes

An intercomparison of nanometric lateral scales, which are special one-dimensional (1D) grating standards with sub-hundred-nanometre pitches, among a deep-ultraviolet (DUV) laser diffractometer, a critical dimension scanning electron microscope (CD-SEM) and different types of atomic force microscope (AFM) was performed. The reference value and its expanded uncertainty were provided by the National Metrology Institute of Japan (NMIJ) using an atomic force microscope with differential laser interferometers (DLI-AFM). The consistency of the measurement results obtained using the DUV laser diffractometer, CD-SEM and some AFMs was satisfactory; however, that in the measurement results obtained using other AFMs was unsatisfactory. An improvement in AFM calibration technology using nanometrological standards is required for both AFM manufacturers and AFM users, including metrology institutes.