Page 319 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 5 CHARACTERIZATION METHODS FOR NANOSTRUCTURE OF MATERIALS
and scattering of photoelectrons in the vicinity of the temperature. As the factor determining wetting or
surface [5]. This new technique is expected to non-wetting systems is an atomistic interaction
develop into a method for simultaneous determina- between atoms composing liquid and those compos-
tion of the electronic structures and the surface fine ing solid, it is important for us to understand wettabil-
structures. ity as microscopic and/or nanoscopic phenomena by
Finally, major features and limits of the XPS tech- approaching in atomistic theory.
nique are summarized as follows. Wettability of solid by liquid depends not only on a
liquid drop size as mentioned in 1.5 but also on a
1. XPS is routinely used to measure: crystal structure of solid surface and surface adsorp-
tion at a solid surface.
• the elemental compositions (qualitative and
quantitative measurements) It is well known that the factors affecting the wet-
• the chemical state identification of one or tability are:
more elements of interest
2. Sensitivities and limitations of measurements: 1. Atmosphere (especially, partial pressure of
• Depth sensitivity of analysis: 0.3–3 nm (pho- oxygen).
toelectron escape depth, depth profiling via 2. Chemical reaction at the interface between solid
angular variation of electron collection) and liquid and formation of reaction layer.
• Detectable elements: All elements with 3. Mutual solubility.
atomic number larger than or equal to 3 4. Surface morphology of solid (surface rough-
• Detection limits: 0.1–1.0 atomic% ness, crystal orientation, adsorption, and strain
3. Analysis area and depth-analysis limitations: induced by working.
• Minimum analysis area:
9 m 5. Temperature.
• Depth-profile capabilities: several tens of 6. Thermodynamical stability of solid and liquid.
nanometers to several micrometers in depth 7. Others (like impurities and additives).
(sputter-depth profiling)
The wettability of solid by liquid is determined by
above factors, but it is difficult to conclude which fac-
tor is the most dominant, since the most effective fac-
References tor depends on a combination of liquid and solid.
The wettability is generally evaluated by a contact
[1] L.C. Feldman, J.W. Mayer: Fundamentals of Surface and angle of a liquid drop on a plane solid surface as
Thin Film Analysis, Elsevier Science, North-Holland, shown in Fig. 5.3.26. It is called “wetting system”
NY and Amsterdam (1986). when the contact angle is smaller than 90 (see
[2] K. Siegbahn: ESCA, Atomic, Molecular and Solid State Fig. 5.3.26a) and “non-wetting system” when the
Structures Studied by Means of Electron Spectroscopy, contact angle is larger than 90 (see Fig. 5.3.26b). It is
Almquist and Wiksells, Uppsala (1967). usually impossible to expect whether an objective
[3] G. Somerjai: Chemistry in Two Dimensions: Surfaces,
Cornel University Press, Ithaca, NY (1981).
(a)
[4] T. Sato, H. Matsui and T. Takahashi: Oyo Buturi, 74,
1305–1315 (2005).
[5] Y. Nihei, M. Nojimai: Oyo Buturi, 74, 1341–1344 (2005).

5.3.5 Wettability
As we often observe wetting phenomena in our daily
life, in this meaning, it can be considered that the wet- (b)
ting phenomena are macroscopic ones. From a view
point of material science, many phenomena in manu-
facturing and processing of materials are influenced
by wettability of solid by liquid. Accordingly, a lot of
the wettability measurements have been conducted
and reported in aqueous solution and solid systems at Figure 5.3.26
low temperature and in melt and solid systems at high Liquid drop shape on solid.

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