Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

7C/2005G201

Improvement of XANAM apparatus for chemical mapping
Shushi SUZUKI*1, 3, Motohiro NAKAMURA1, Kumiko KINOSHITA1, Yuichiro KOIKE1, Keisuke
11, 32
1
FUJIKAWA , Wang Jae CHUN , Masaharu NOMURA , and Kiyotaka ASAKURA
1
Catalysis Research Center, Hokkaido University, Sapporo, 001-0021, Japan
2
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan
3
Japan Science and Technology Agency, Core Research for Evolutional Science and Technology,Saitama 332-0012, JapanIntroduction
Since the invention of the scanning probe microscopy,
atomic-level spatial resolution of conductive andinsulating material surfaces has been achieved. Recently
many efforts have been done to obtain chemical
information by developing techniques based on thesemicroscopes. However, it is still difficult to obtain achemical mapping directly. In this study, we report anovel phenomenon, which will provide a basic concept
for a new elemental analysis at the atomic level based on
the non-contact atomic force microscopy (NC-AFM).
Recent investigations on the NC-AFM imaging
mechanism show that the forces between a cantilever anda surface atom are not only physical forces such as vander Waals force and electrostatic force but also chemicalbonding force, which may depend on the electron densityof bonding and anti-bonding orbitals. If the electron
density of these orbitals can be controlled by X-ray
excitation of core level electron, one may control theinteraction between the surface atom and the cantilever.
The core electron has a binding energy specific toelements and their chemical state. Thus one can get achemical mapping using the NC-AFM aided by X-ray
irradiation. We named the methodology as ”X-ray Aided
Non-contact Atomic force Microscopy (XANAM)” [1].
We demonstrated X-ray could affect the force between
the surface and the AFM tip apex at the X-ray absorption
edge. In this paper we report improvement of thisapparatus for more reproducible and higher signal tonoise (S/N) ratio measurements.
Experimental
The experiments were performed with an UHV NCAFM chamber equipped with 4 axes remote control
movement system to the X-ray beam direction. A piezothin film AFM cantilever (NIKON) was used with atypical resonance frequency of 114.8 kHz. We replaced
our original SPM controller with that produced byNanonis. A Au-covered Si wafer sample was prepared byvacuum evaporation. After NC-AFM observations of thesample surface, we fixed the cantilever with keeping thecantilever-sample interaction force constant. The distance
Z as a function of X-ray energy around the Au L3
absorption edge was measured.

Results and Discussions
By improvement of scan control system, we haveobtained clearer Z distance dependency spectra on the Xray energy than the previous data, as shown in Fig. 1(a).
Figure 1(b) is a Au adsorption spectrum of a Au foil
measured separately. Consequently, we found a peak(indicated by an arrow) in Z variation at the Au L3
adsorption edge energy, which reproduced our previous
result [1]. But the S/N ratio is much improved. We think
the XANAM system has high enough to observe thenanoscale chemical image on the surface. We areplanning to try making chemical map on a sample surface
with mixed elements.
This work is supported by Grant-in-Aid for young
scientists (B) of JSPS and the Japan Science andTechnology Corporation (JST).

Fig. 1 Z distance signal recorded as a function of Xray energy around the Au L3 absorption edge (a), Xray absorption spectrum of Au foil (b).
References[1] S. Suzuki, Y. Koike, K. Fujikawa, W.-J. Chun, M.
Nomura, and K. Asakura, Chem.Lett. 33, (5), 636-637(2004).
*szk@cat.hokudai.ac.jp

Users' Report73