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ABSTRACT: Molecular movement induced by an electric field was observed by scanning tunneling microscopy. The observed feature of the molecular lines of liquid crystal 4‐hexyl‐4’‐cyanobiphenyl on graphite appeared to change drastically in 2 min after the polarity inversion of the bias voltage, together with small shifts in the lateral arrangement of individual molecules. The rearrangements took place at the bias voltage at around 2 V and the process was found to be reversible. When a bias voltage less than -2.8 V was applied to the tip, an irreversible process, the deposition of molecules, occurred. The minimum deposition size was about 20 nm and was found to be determined by the tip shape.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 04/1991; · 1.34 Impact Factor
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ABSTRACT: Voltage‐dependent images of liquid crystals on graphite were observed in air by scanning tunneling microscopy (STM). Molecular rows of liquid crystals and the atomic pattern of the graphite substrate were imaged with high (above 1 V) and low (below 0.1 V) bias voltages, respectively. Patterns of molecules, grain boundaries, and distinguishable defects of the liquid crystal arrangement were reproduced even after imaging the substrate in the same area. This indicates that the graphite lattice can be seen by STM without touching or disturbing the adsorbed molecules on it. A resonant tunneling model is proposed to explain the phenomenon.
Applied Physics Letters 06/1990; · 3.84 Impact Factor
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ABSTRACT: Adsorbed molecules of copper phthalocyanine (CuPc) and liquid crystals on graphite were measured by scanning tunneling microscopy (STM) and spectroscopy (STS) in air. The islands of molecules of CuPc were detected by STM. Tunneling spectra taken simultaneously with STM showed characteristic peaks correlated with local topographic features. In the observation of a nematic liquid crystal on graphite, one reproducible molecular pattern was found, for which a model of molecular ordering is proposed. Ordinary spectroscopy was found to be difficult due to a large polarization current caused by the liquid surrounding the tip. Bias voltage dependent images of the molecules which demonstrate electronic structure effects were obtained.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 02/1990; · 1.25 Impact Factor
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ABSTRACT: Simultaneous measurements of scanning tunneling spectroscopy (STS) and scanning tunneling microscopy (STM) are performed on HOPG and 2H–NbSe 2 in air. In order to see the distribution of local density of states related to different atomic sites and species STS images of normalized differential conductance are mapped. Correlation function between the STS images and corrugation in corresponding STM image is obtained as a function of the tip bias voltage.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 04/1988; · 1.25 Impact Factor
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S. Okayama,
M. Komuro,
W. Mizutani,
H. Tokumoto,
M. Okano,
K. Shimizu,
Y. Kobayashi,
F. Matsumoto,
S. Wakiyama, M. Shigeno,
F. Sakai,
S. Fujiwara,
O. Kitamura,
M. Ono,
K. Kajimura
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ABSTRACT: A small‐size scanning tunnel microscope (STM) developed to provide an easy operation for both tip and sample setting is applied to three‐dimensional topographic measurements of microlithography patterns. The patterns having a grid structure with 160 nm in periodicity, 20–30 nm in groove width, and 40–50 nm in groove depth are fabricated on Si substrates using a technique of enhanced chemical etching by focused ion beam. The STM images are compared with two‐dimensional scanning electron microscope images. Fairly good resolution of topographic maps for a large area is obtained for the fine groove structures. The large‐area images are further processed to correct the piezoscanners’ nonlinearity, which becomes conspicuous for large‐area scanning.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 04/1988; · 1.25 Impact Factor
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ABSTRACT: We have constructed a very stable STM operable in air, and concentrate our study on one of the remaining problems of STM - the probing tips. In this paper we present an example of distorted atomic images of graphite and an experimental technique to extract the information of the probing tip from the images. It became clear that the images are affected by the surface structure of the tip. The distortion originated from the sample is also mentioned.
http://dx.doi.org/10.1051/jphyscol:1987612.
