Faculty Profiles - AOKI Takaaki

Low-temperature formation of perovskite PbTiO3 films by O-2 cluster ion-assisted deposition Reviewed

M Akizuki, J Matsuo, W Qin, T Aoki, M Harada, S Ogasawara, K Yodoshi, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 255 - 257 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The formation of PbTiO3 films on Pt films using O-2 cluster ions, Pb and Ti(i-OC3H7)(4), was examined. Perovskite-PbTiO3 films could be formed at a substrate temperature of 400 degrees C, which was about 100 degrees C lower than that which is possible with CVD and sol-gel methods. An acceleration energy of 1 keV was sufficient to form the perovskite structure. These films were obtained owing to a high oxidant Aux to the surface and high-density energy deposition during growth. Another feature of the O-2 cluster ion assisted deposition was that no pyrochlore structure was observed at lower substrate temperatures. This might be due to surface reactions in the high vacuum (3 X 10(-5) Torr). (C) 1998 Elsevier Science S.A. All rights reserved.

Energy dependence of a single trace created by C-60 ion impact Reviewed

T Seki, T Aoki, M Tanomura, J Matsuo, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 143 - 146 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Cluster ion beams provide new surface modification processes, because of the unique interaction between cluster atoms and surface atoms. In order to reveal cluster-surface interaction, single traces formed by C-60 ion impact on solid surfaces were investigated using scanning tunneling microscopy. Large hill shape traces and crater shape traces were observed on a highly oriented pyrolitic graphite surface irradiated by C-60 ions. The crater formation by the C-60 impact is an effect of high-density energy deposition and multiple-collision between cluster atoms and surface atoms. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0254-0584(98)00097-2

Cluster ion bombardment on atomically flat Au(111) solid surfaces Reviewed

D Takeuchi, T Seki, T Aoki, J Matsuo, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 76 - 79 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Energetic cluster ion bombardment shows unique and complicated interactions between constituents of the cluster and atoms of the target surface. Scanning tunneling microscopy (STM) observation is one of the most powerful methods to investigate the cluster ion-solid surface interaction. We have observed crater-shape traces on highly oriented pyrolitic graphite (HOPG) surface bombarded by energetic Ar cluster ions. However, STM images of HOPG surfaces are influenced by special electronic surface states. In this paper, Ar monomer and cluster ions are bombarded on Au( iii) surfaces on mica to observe ion traces by STM. In addition, the relationship between the parameters of cluster ion beams and the features of ion traces are discussed. The STM observation showed that Ar cluster ion bombardment had circular crater-like shapes, and their diameters were proportional to the cubic root of ion energy. These indicate that the kinetic energy of cluster ions is deposited on the surface isotropically. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0254-0584(98)00052-2

Size Dependence of Bombardment Characteristics Produced by Cluster Ion Beams

Takaaki Aoki

MRS Proceedings Vol. 504 page： 93 - 98 1998.2

Cluster Ion Implantation and Device Processes

Isao Yamada, Jiro Matsuo, Noriaki Toyoda, Takaaki Aoki

Shinku/Journal of the Vacuum Society of Japan Vol. 41 ( 11 ) page： 932 - 939 1998

Gas cluster ion beam processing Reviewed

Yamada, I, J Matsuo, N Toyoda, T Aoki, E Jones, Z Insepov

SIMILARITIES AND DIFFERENCES BETWEEN ATOMIC NUCLEI AND CLUSTERS ( 416 ) page： 310 - 329 1998

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Unique characteristics of gas cluster ion beam processing are reviewed. Cluster ion beams consisting of a few hundreds to thousands of atoms have been generated from various kinds of gas materials. Multi-collisions during the impact of accelerated cluster ions upon the substrate surfaces produce fundamentally low energy bombarding effects in a range of a few eV to hundreds of eV per atom at very high density. These bombarding characteristics can be applied to shallow ion implantation high yield sputtering and smoothing, surface cleaning and low temperature thin film formation.

Molecular dynamics simulation of damage formation by cluster ion impact Reviewed

T Aoki, J Matsuo, Z Insepov, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 121 ( 1-4 ) page： 49 - 52 1997.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The irradiation of a surface with a cluster ion beam is known to give superior surface modification effects compared with monomer ions. Surface smoothing processes and sputtering yield are both better off. The irradiation process by cluster ions has proved to be quite different from that by monomer ions. We have examined the process of cluster impacts on a solid surface by molecular dynamics simulation to investigate these differences. We simulated an Ar cluster, with size from 13 to 3000 atoms, impacting on a Si(100) substrate, with acceleration energies from 0.5 keV to 55 keV. The Ar cluster atoms penetrate into the Si substrate keeping the cluster state, and the penetration depth is deeper than that of a monomer ion of the same velocity. Si atoms around the Ar cluster are displaced, some of them recover, and the Ar atoms of the cluster are reflected back into the vacuum. Consequently, the displaced Si atoms concentrate in a shallow surface area, and crater-like damage remains. The radius and the depth of the crater are almost the same and are proportional to the cube root of the acceleration energy of the cluster ion. This means that the peculiar damage formation process, created by a cluster ion impact, is caused by an isotropic energy transportation through many interactions between cluster and surface atoms.

STM observation of HOPG surfaces irradiated with Ar cluster ions Reviewed

T Seki, T Kaneko, D Takeuchi, T Aoki, J Matsuo, Z Insepov, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 121 ( 1-4 ) page： 498 - 502 1997.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Cluster ion beams offer new surface modification processes because of their unique interaction between cluster atoms and solid surfaces, For example, surface smoothing and shallow implantation by cluster ion beam have been demonstrated. Ln order to reveal such cluster-surface interaction, a single trace formed by a cluster ion impact on a solid surface has been investigated using Scanning Tunneling Microscopy (STM).
STM images of Highly Oriented Pyrolitic Graphite (HOPG) surfaces, were obtained after irradiation with 150 keV Ar cluster or 1.5 keV monomer ions. The 150 keV cluster ions, with a size of about 100 atoms, were used in comparison with 1.5 keV monomer ion. The velocity of an atom in each case was the same. In spite of these equal velocities, large craters with diameter of about 180 Angstrom were observed in the STM image of cluster-irradiated HOPG surface, while only small hills were observed in monomer-irradiated surface.

DOI： 10.1016/S0168-583X(96)00557-5

Non-linear effects in high energy cluster ion implantation International journal

Takeuchi D, Aoki T, Matsuo J, Yamada I

APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY - PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL CONFERENCE, PTS 1 AND 2 ( 392 ) page： 491 - 494 1997

Range and damage distribution in cluster ion implantation International journal

Yamada I, Matsuo J, Jones EC, Takeuchi D, Aoki T, Goto K, Sugii T

MATERIALS MODIFICATION AND SYNTHESIS BY ION BEAM PROCESSING Vol. 438 page： 363 - 374 1997

Non-linear effects in high energy cluster ion implantation Reviewed

D Takeuchi, T Aoki, J Matsuo, Yamada, I

APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY - PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL CONFERENCE, PTS 1 AND 2 ( 392 ) page： 491 - 494 1997

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP PRESS

Cluster ion implantation realizes ultra-shallow (<50nm) junction formation. Cluster ions can provide a low-energy and high-current beam, because each constituent atom in the cluster, with sizes of a few thousands, has an energy of only a few eV. Non-linear effects of high energy cluster ion implantation caused by multiple-collisions and high-density energy deposition within a local surface region, have been investigated. Decaborane (B(10)G(14)), C-60 and large A cluster ions with sizes of from 100 to 3000 were implanted into Si and sapphire substrates at energies up to 300keV. The number of disordered substrate atoms per atom in a cluster ion was much larger than the damage done by a monomer ion with the same velocity. Single traces of cluster ions on solid surfaces were observed by STM and AFM to investigate the mechanism of the non-linear effects. Those of large At cluster ions looked like crater shapes where the crater diameter was proportional to one-third of the cluster ion energy.