Search results

1

STM Observations of Ferromagnetic Clusters

100%

Wawro A., Kasuya A.

Acta Physica Polonica A

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1998

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vol. 93

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issue 2

443-448

EN

Co, Fe and Ni clusters of nanometer size, deposited on silicon and graphite (highly oriented pyrolytic graphite), were observed by a scanning tunneling microscope. Deposition as well as the scanning tunneling microscope measurements were carried out in an ultrahigh vacuum system at room temperature. Detailed analysis of Co cluster height was done with the scanning tunneling microscope equipped with a ferromagnetic tip in the magnetic field up to 70 Oe. It is found that bigger clusters (few nanometers in height) exhibit a dependence of their apparent height on applied magnetic field. We propose that such behaviour originates from the ferromagnetic ordering of cluster and associate this effect to spin polarized tunneling.

2

STM Imaging of Magnetic Dots with Ferromagnetic Tip

100%

Wawro A., Kasuya A.

Acta Physica Polonica A

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2000

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vol. 97

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issue 3

547-550

EN

We report on imaging of isolated, few nanometers in size, magnetic dots (Co, Ni) by the use of a scanning tunneling microscope equipped with a ferromagnetic Co tip in the presence of external magnetic field. The dependence of apparent height of dots as a function of magnetic field takes a hysteresis-like shape. We discuss possible mechanisms of the scanning tunneling microscope tip interactions with dots.

3

STM/STS Studies of Self-Organized Growth of Iron Silicide Nanocrystals on Vicinal Si(111) Surface

81%

Wawro A., Suto S., Czajka R., Kasuya A.

Acta Physica Polonica A

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2003

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vol. 104

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issue 3-4

303-319

EN

The evolution of iron silicide structure grown by solid state epitaxy on Si(111) vicinal surface was investigated by scanning tunnelling microscopy. The reactions, which occur on the surface, are compared for two various Fe coverages: 0.33 and 2 monolayers. The annealing at 250˚C does not enable substantial recovery of the surface ordering, deteriorated by Fe deposition at room temperature. The onset of 2×2 surface reconstruction is observed upon annealing at 400˚C. A three-dimensional growth tendency of iron silicide crystallites on a bare Si(111) 7×7 surface was found at 700˚C. In the case of 2 monolayer coverage crystallites nucleate along the edges of substrate terraces forming a regular array of nanometer size dots. Basing on atomically resolved spectroscopic effects and statistical considerations, structure of iron silicide nanocrystallites as well as Schottky-like character of the barrier at the interface between metallic crystallite and semiconducting substrate is deduced.

4

STM-Induced Luminescence for Alkanethiol Films on Au(111) Surface

71%

Nishitani R., Tateishi Y., Arakawa H., Kasuya A., Sumiyama K.

Acta Physica Polonica A

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2003

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vol. 104

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issue 3-4

269-279

EN

STM-induced luminescence spectra for organic molecule adsorbed Au(111) surfaces were studied, and the influence of STM-tip alloy material on the emission spectra was measured. We observed the STM-tip dependent emission spectra of Au(111). The characteristics of the spectra with Pt-Ir alloy(20%) tip are interpreted in terms of the one-mode type and two-mode type depending on the composition rates. We measured the emission spectra for two different types of molecules, decanethiol and octanedithiol, which have different adsorption structures. The emission spectra for the octanedithiol films were compared with the spectra from clean gold films and the decanethiol films. A spectral change of Au(111) due to adsorption of octanedithiol molecules on Au(111) was observed in the spectral range from 700 through 780 nm while not for the adsorption of decanethiol molecules. The spectral change due to adsorption of octanedithiol molecules is compared with the STS measurements.

5

STM and STS Investigations of Bi_2Te_3 Surface

61%

Winiarz S., Czajka R., Suto S., Lośtak P., Szuba S., Kasuya A.

Acta Physica Polonica A

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2003

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vol. 104

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issue 3-4

389-395

EN

We carried out scanning tunneling microscopy/spectroscopy studies of Bi_2Te_3 surface, which, to the best of our knowledge, had not been attempted so far. We got images of surface of the material in many scales from micrometers to nanometers, which showed a layered structure of Bi_2Te_3, with many monoatomic terraces. We found agreement between measured heights and corresponding bulk crystal structure derived from X-ray data. In nanoscale we obtained an atomic resolution. Using scanning tunneling spectroscopy we carried out examination of the electronic structure. We observed different I-V characteristics and contrast on current imaging tunneling spectroscopy maps on non equivalent terraces. The dI/dV (~ density of states) curves referred to those terraces were compared with theoretically calculated by Larson et al. density of states derived from Bi p and Te-1 p orbitals. The analysis of our results allowed us to distinguish bismuth from tellurium planes.

6

Variable Temperature STM/STS Investigations of Ag Nanoparticles Growth on Semiconductor Surfaces

52%

Suto S., Czajka R., Szuba S., Shiwa A., Winiarz S., Nagashima H., Kato H., Yamada T., Kasuya A.

Acta Physica Polonica A

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2003

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vol. 104

|

issue 3-4

289-302

EN

We have investigated the growth of Ag nanoparticles deposited on Si(111), H/Si(111)-(1×1) and Bi_2Te_3 substrates using a variable temperature scanning tunneling microscopy. These substrates are different as regards the model system for cluster and islands growth at the nanometer scale. Ag was evaporated onto the sample mounted at the scanning tunneling microscopy stage in vacuum of 10^{-10} Torr range during evaporation. The substrates were kept at different temperatures: -150˚C, room temperature, and 300˚C during the deposition process. In general, we have observed 3D growth mode up to several ML coverage. The density of clusters and their size were functions of the substrate's temperature during the deposition process - a higher density and a smaller size at -150˚C were in opposition to the 300˚C results - a lower density and a larger size. Low temperature depositions led to continuous layers above 10 ML coverage but the surface was covered by small Ag clusters of 1-2 nm in heights and 2-3 nm in diameters. The log-log graphs of height and projected diameter of Ag clusters revealed different slopes indicating different growth mechanisms at low and high temperatures. We obtained the value of n=0.25±0.02, typical of the so-called droplet model of cluster growth, only at 300˚C. Scanning tunneling spectroscopy measurements revealed clearly different I-V (and dI/dV vs. bias voltage) curves measured above clusters and directly above the substrate. In discussion, we compared our results to theoretically calculated density of states from other papers, finding conformity for partial density of states.

7

Chemical Reactions and Electronic Functions of Carbon Cluster Arrays Studied by Scanning Tunneling Spectroscopy and High-resolution Electron Energy Loss Spectroscopy

52%

Kasuya A., Hu C., Suto S., Tohji K., Takahashi H., Czajka R., Wawro A., Nishina Y.

Acta Physica Polonica A

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1998

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vol. 93

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issue 2

317-322

EN

Novel nanometer scale structures have been produced by thermal heating or laser irradiation on the surface of single- and multi-layers of C_{60} and C_{84} on Si. These structures were examined by combined measurements of scanning tunneling spectroscopy and high resolution electron energy loss spectroscopy. The results show specific chemical reactions of substrate with carbon clusters having single- and double-bonded network. Covalent bonds are formed in some of these chemical reactions.

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STM Observations of Ferromagnetic Clusters

STM Imaging of Magnetic Dots with Ferromagnetic Tip

STM/STS Studies of Self-Organized Growth of Iron Silicide Nanocrystals on Vicinal Si(111) Surface

STM-Induced Luminescence for Alkanethiol Films on Au(111) Surface

STM and STS Investigations of Bi_2Te_3 Surface

Variable Temperature STM/STS Investigations of Ag Nanoparticles Growth on Semiconductor Surfaces

Chemical Reactions and Electronic Functions of Carbon Cluster Arrays Studied by Scanning Tunneling Spectroscopy and High-resolution Electron Energy Loss Spectroscopy