Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

7C/2003G301

A Challenge to XANAM- a New Nanoscale Chemical Mapping Microscopy
Shushi SUZUKI*1, Yuichiro KOIKE1, Keisuke FUJIKAWA1, Nobuaki MATSUDAIRA1,Motohiro NAKAMURA1, Wang Jae CHUN1, Masaharu NOMURA2 and Kiyotaka. ASAKURA1
1
Catalysis Research Center, Hokkaido University, Sapporo, 001-0021, Japan
2KEK-PF, Tsukuba, Ibaraki 305-0801, Japan

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| Normalized Frequency s hift | / a .u.

Experimental
The experiments were performed with an UHV NCAFM chamber, which is equipped with 4 axes remote
movable system from outside of the X-ray beam hatch. Apiezo-thin film AFM cantilever (NIKON) was used with atypical resonance frequency of 88 kHz. A partially Aucovered sample was prepared by vacuum evaporation ofAu on a Si substrate through a 1000 L Ni mesh put on thesubstrate. After NC-AFM observations of the sample
surface, we put the cantilever above the Au island, andstopped the scan feedback routine of the cantilever.
Frequency shift as a function of X-ray energy around theAu L3 absorption edge was measured. The frequency
shift signal was normalized by incident X-ray intensity.
For comparison, we carried out the same experiment on
the bare Si surface in the same energy range.

Results and Discussions
Figure 1(a) and 1(b) show a series of frequency
dependency spectra on the X-ray energy near the Au L3
absorption edge energy above the Au islands and the bareSi regions, respectively. Consequently, we only found asudden frequency shift of the NC-AFM cantilever justabove the Au L3 X-ray absorption edge, as shown in Fig.
1. Although the detailed mechanism and physics areunclear at the moment, the phenomenon suggested that
NC-AFM could distinguish Au from Si under the X-ray
irradiation tuned at the absorption edge energy. Although
we found the phenomena occurred repeatedly, their signal
change was very small and was often interfered byaccidental noises in the experimental halls.
We are improving signal-to-noise ratio in thefrequency dependency spectra on the X-ray energy formore precise measurements by replacing a preamplifier
and a feedback instrument and after the long shutdown of
Photon Factory in 2005 spring we will get the nanoscalechemical image and establish the XANAM.
This work is supported by Grant-in-Aid for young
scientists (B) of JSPS and the Japan Science andTechnology Corporation (JST).
| Normalized Frequen cy shift | / a.u.

Introduction
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 reported anovel phenomenon, which will be a basic concept for a
new elemental analysis at the atomic level based on thenon-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 have 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 thereproducibility of this phenomenon.

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Figure 1 Frequency shift spectra normalized by I0 on both Au (a)and Si (b) regions with X-ray scanning around the Au L3
absorption edge region.

References[]] 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

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