Atomic spatial resolution

The category of simple liquids is sometimes used to establish the complementary category of complex liquids (Barrat and Hansen, 2003). Another and a broad view of complex liquids is that they are colloid, polymer, and liquid crystalline solutions featuring a wide range of spatial length scales - sometimes called soft matter (de Gennes, 1992). Planting ourselves at an atomic spatial resolution, the models analyzed for those complex liquids are typically less detailed and less realistic on an atomic scale than models of atomic liquids. 

While the macroscopic concepts of hardness, adhesion, friction, and slide have evolved over the last two centuries, atomic level understanding of the mechanical properties of surfaces eluded researchers. The discovery of the atomic force microscope in recent years promises to change this state of affairs. Being able to measure forces as small as 10 newton or as large as 10 newton [5] over a very small surface area (few atoms) and by simultaneously providing atomic spatial resolution, this technique permits the study of deformation (elastic and plastic), hardness, and friction on the atomic scale. The buried interface between moving solid surfaces can be studied with spectroscopic techniques on the molecular level. Study of the mechanical properties of interfaces is, again, a frontier research area of surface chemistry. 

AFM/SPM Atomic Force Microscopy Scanning Probe Microscopy Surface imaging with near atomic spatial resolution Atomic scale morphology 0.1 A 50 A... 

Wang, Z., A. Pakoulev, et al. (2002). Watching vibrational energy transfer in liquids with atomic spatial resolution. Science 296, 2201. 

The atomic force microscope (ATM) provides one approach to the measurement of friction in well defined systems. The ATM allows measurement of friction between a surface and a tip with a radius of the order of 5-10 nm figure C2.9.3 a)). It is the tme realization of a single asperity contact with a flat surface which, in its ultimate fonn, would measure friction between a single atom and a surface. The ATM allows friction measurements on surfaces that are well defined in tenns of both composition and stmcture. It is limited by the fact that the characteristics of the tip itself are often poorly understood. It is very difficult to detennine the radius, stmcture and composition of the tip however, these limitations are being resolved. The AFM has already allowed the spatial resolution of friction forces that exlribit atomic periodicity and chemical specificity [3, K), 13]. 

The combination of atomic force microscopy (AFM) and Raman spectroscopy is another approach to attain high spatial resolution. AFM also employs a sharp tip close to a sample surface. When the tip is made of metal and light is irradiated onto the tip and surface, Raman scattering is largely enhanced. In this way, a spatial resolution of 15 nm is achieved [2]. 

Consequently, the lateral force between the tip and sample can be significantly reduced (Fig. 6.2B). Traditionally, contact mode typically could provide higher resolution, but recent advances in noncontact techniques have led to spatial resolution up to the atomic level in vacuums and liquids (Fukuma et al., 2005 Giessibl, 2003 Sugimoto et ah, 2007). Therefore, dynamic mode is preferred for soft and unstable samples. 

The spatial resolution in quantitative analysis is defined by how large a particle must be to obtain the required analytical accuracy, and this depends upon the spatial distribution of X-ray production in the analysed region. The volume under the incident electron beam which emits characteristic X-rays for analysis is known as the interaction volume. The shape of the interaction volume depends on the energy of the incident electrons and the atomic number of the specimen, it is roughly spherical, as shown in Figure 5.7, with the lateral spread of the electron beam increasing with the depth of penetration. 

NRA is a powerful method of obtaining concentration versus depth profiles of labelled polymer chains in films up to several microns thick with a spatial resolution of down to a few nanometres. This involves the detection of gamma rays produced by irradiation by energetic ions to induce a resonant nuclear reaction at various depths in the sample. In order to avoid permanent radioactivity in the specimen, the energy of the projectile is maintained at a relatively low value. Due to the large coulomb barrier around heavy nuclei, only light nuclei may be easily identified (atomic mass < 30). 

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