Research Group for Nanoscale Structure and Function of Advanced Materials
Group Leader : Katsuyuki Fukutani
Members : Wataru Higemoto, Yuki Fukaya, Takashi U. Ito, Satoshi Yasuda, Shin-ichi Shamoto,
Masahiro Yano, Tomoo Terasawa, Shinichi Machida, Takeshi Okazawa

Macroscopic properties of matter based on local states could beunderstood by investigating a nanoscale region of a sample. An
experimental technique that can be used to selectively
investigate a surface, bulk, impurity/defect, or ultrathin film can(a)

(b)

20nm

20nm

extend the field of materials research. Existing technicaldevelopments enable us to efficiently produce high-intensity
beams, especially beams of synchrotron light, electrons,neutrons, muons, and positrons, which are useful for studying
various atomic structures and dynamics of functional materials
at the length scale of advanced beams. In addition, experimental
techniques that can obey local states such as surface, interface,
and impurity have been developed as well, and they can be used
to obtain new scientific insights. Our objective is to developthese new advanced measurement technologies and study thenanoscale structures of functional devices and materials in orderto clarify the essential properties of matter.
Uniform Si nano-dot fabrication using reconstructedstructure of Si(110) [1]
We investigated the Si nano-dot (ND) formation on Si(110)by using scanning tunnelling microscope (STM). The Si-NDs
are Si crystals continuously grown from the substrate during thethermal decomposition of thin oxide layer on Si(110). The NDs
fabricated on the flat surface of the Si(110)-1 × 1 structure aresurrounded by four types of facets with almost identicalappearance probabilities, as shown in Fig. 1(a). Moreover, anincrease in the size of the NDs leads to the variety of its
morphology due to the increase of the number of facets. In
contrast, most Si-NDs fabricated at the domain boundary ofstraight-stepped Si(110)-16 × 2 reconstructed structure have
uniformed shape, which has three (17, 15, 1) facets and one (17,15, 3) facet, as shown in Fig. 1(b). The base line of the (17, 15,1) facet corresponds to the step of the 16 × 2 reconstructedstructure, suggesting that the reconstructed structure determines
the direction of the facet’s base line. This also suggests that thereconstructed structure dominates the facet structure, because
each direction of the base line has only one type of stable facetstructure. Therefore, the Si(110)-16 × 2 reconstructed structure
can be the template of uniform-structured NDs, leading new
fabrication technique of the NDs to realize the novel functionaldevices.
Fig. 1 STM images of the typical Si NDs on (a) the 1 × 1 structure and(b) 16×2 reconstructed structure. The red, blue and green linesaround the NDs indicate base lines of the facets along the crystal
directions of <112>, <332>, <552>, respectively.

Development of µSR spectrometer for ultra slow muon [2]At J-PARC muon science facility (MUSE), we are advancing
material researches by using muons. A muon belongs to Lepton
particle and used as a sensitive probe of magnetic fields insidematerials. This method is known as “muon spin relaxation(µSR)”. At MUSE, “ultra slow muon” (USM) beam isdeveloping at U1 beam line. USM is low energy muons (0.2-30keV), generated by using intense 4 MeV positive muon beamand lasers. The corresponding muon range for implantation is
0~200 nm deep for the case of copper, where we cancontinuously investigate properties of specimen from nearsurface to bulk region.
At the U1A area in the downstream of the USM beamline, wehave installed µSR spectrometer with MUSE group. The entire
spectrometer assembly including a cryostat, positron detectors,

magnets, other electronic devices and their power supplies iscontained in a large metallic cage that is on an electricallyisolated stage. The beam implantation energy is varied by tuning
electrostatic potential of the stage over a range of 0-30 kV thatserves to decelerate USMs at the entry section of thespectrometer. The required features for the USM µSR
spectrometer are common to those for conventional ones, except
sample environment which must be compatible with ultra-highvacuum condition. Moreover, cares must be taken to minimize
thermal radiation for controlling sample temperature without
beam windows and radiation shields that interrupt the USM
implantation. The spectrometer is furnished with a set ofHelmholtz coils for applying an external magnetic field up to0.14 Tesla along beam direction. As positron counters,“Kalliope” developed by KEK were installed.
This spectrometer is already working and commissioning of
the total USM system is going on. USM µSR spectrometer will
be used for researches of surface, interface and bulk states andunique scientific results will be obtained.
Fig. 2 µSR spectrometer for ultra slow muon at J-PARC MUSE.
References[1] M. Yano, Y. Uozumi, S. Yasuda, and H. Asaoka, Jpn. J.
Appl. Phys. 57, 06HD04 (2018).
[2] W. Higemoto, R. Kadono, N. Kawamura, A. Koda, K. M.
Kojima, S. Makimura, S. Matoba, Y. Miyake, K.
Shimomura and P. Strasser, Quantum Beam Sci. 1(1), 11(2017).