Local probe method

Central to all SPMs (or local probe methods , or local proximal probes as they are sometimes called) is the presence of a tip or sensor, typically of less than 100 mn radius, that is rastered in close proximity to—or in contact with—tire sample s surface. This set-up enables a particular physical property to be measured and imaged over the scaimed area. Crucial to the development of this family of teclmiques were both the ready availability of piezoelements, with which the probe can be rastered with subnanometre precision, and the highly developed computers and stable electronics of the 1980s, without which the operation of SPMs as we know them would not have been possible. 

Consequently, a quantitative analysis of current transients or impedance data requires not only highly precise charge measurement and the knowledge of Qcd - 4 ep( =0), which can be obtained from q E) or from the fXE) isotherms, but also an exact knowledge of the substrate surface morphology and the local mechanism of Me UPD depending on AE. Information on the defect structure (step distribution) of a substrate surface on an atomic level can only be obtained by in situ local probe methods. 

The results obtained in the system k x hkl)/Cv , where 2D Me UPD phenomena occur followed by a Stranski-Krastanov growth mechanism in the OPD range, show that electrochemical 3D Me phase formation processes can be used for structuring and modification of metal single crystal surfaces in the nanometer range. Local electrochemical processes are initiated by in situ local probe methods using appropriate polarization routines. 

Twenty five years after the birth of SPMs (the local-probe methods) there can be no doubt that this techniques have marked the beginning of a novel field of nanometer scale science and technology, which will offer new opportunities to electrochemistry in the 2T century. 

Nanocrystal and cluster science is the study of the chemical synthesis and physical properties of individual nanocrystals and nanotubes. It seeks to understand the evolution of molecular properties into solid state properties with increasing size. Methods include so-called bottom-up chemical synthesis of nanocrystals, nanowires, and very large species, as well as physical molecular beam approaches. Advanced physical characterization of single nano-objects by local probe methods and optics is critical here. The area is intrinsically interdisciplinary at the junction of physics, chemistry, and materials science. Outstanding chemical research in nanocrystal science is often found in a wide variety of science and engineering departments. 

Summary. Electrochemical nanotechnology and its analytical and preparative aspects using local probe techniques such as STM and AFM are described. Typical examples for in-situ application of local probe methods in different electrochemical systems are discussed UPD and OPD of metals and nanostructuring of metal, semiconductor, and superconductor surfeces. 

A number of methods exist for the study of surface diffusion ex-situ [11-13]. The STM noise method, discussed above, has its own advantages (or shortcomings) as the local probe method. However, for the electrochemical interface it seems to be unique. (The impedance measurements [14] may not always be unambiguously interpreted, and nor do they give the local information about the surface.) We thus expect that the STM noise method will be widely used for in-situ study of surface diffusion, as long as the resolution of the high frequency noise measurements improves. Then the maps of local adatom difflisivity on metal electrodes will become a reality. 

The development of local probe techniques such as Scanning Tunneling Microscopy (STM) or Atomic Force Microscopy (AFM) and related methods during the past fifteen years (Nobel price for physics 1986 to H. Rohrer and G. Binning) has opened a new window to locally study of interface phenomena on solid state surfaces (metals, semiconductors, superconductors, polymers, ionic conductors, insulators etc.) at an atomic level. The in-situ application of local probe methods in different systems (UHV, gas, or electrochemical conditions) belongs to modem nanotechnology and has two different aspects. 

First, local probe methods are applied to characterize thermodynamic, stractural, and dynamic properties of solid state surfaces and interfaces and to investigate local surface reactions. These investigations represent the analytical aspect of nanotechnology. 

The discussed models have been developed for liquid electrodes, as mentioned previously. On solid surfaces, due to the presence of atomic steps and crystal defects different atomic sites exist which differ in energy. Specific adsorption then is expected to occur preferentially at certain sites rather than uniformly. Site specific adsorption phenomena can in principle be studied with local probe methods such as the STM, but their discussion is beyond the scope of this book. 

Our proposed mechanism of lithium reversible storage in both alloying and non-alloying metal nanofilms on surface metal-oxygen bonds and in grain boundaries should be sustained by further evidences by local probe methods and first principles of computational approaches. 

The most recent approach to reductive nanofabrication that can indeed constmct nanoscale stmctures and devices uses microscopic tools (local probes) that can build the stmctures atom by atom, or molecule by molecule. Optical methods using laser cooling (optical molasses) are also being developed to manipulate nanoscale stmctures. 

We have not included Atom Probe Microanalysis in this scheme. It constitutes the ultimate in local analysis - in that individual atoms can be selected and identified by TOF spectroscopy. Chapter 1 gives an account of the range of applications of the technique at the present time the development in atom-probe methods has allowed the continuing increase of both the volume of material that can be mapped at the atomic scale and the quality of the data obtained. 

The diagrams in Fig. llc-f can be measured by the force probe method, when the amplitude and phase are measured as the tip approaches and retracts the surface vertically. In the non-contact range, both the amplitude and the phase retain their constant values (Fig. llc,e). When the tip enters the intermittent contact range (Zphase reduces almost linearly on approaching the surface. The deviation of the amplitude signal from a certain set-point value As is used by a feedback loop to maintain the separation Zc between the tip and sample constant, and hereby visualise the surface structure. When the surface composition is uniform, the amplitude variation is mainly caused by the surface topography. However, if the surface is heterogeneous, the variation in the amplitude can be affected by local differences in viscoelasticity [108-110 ] and adhesion [111] of the sample (Sect. 2.2.2). 

Further, the above methods measure the equivalent global corrosion rate of a large area. Corrosion in reality is often local, i.e., takes place only at tiny areas of the surface. It is necessary to have a local probe, not only of the rate, but of the mechanical properties. Something about this approach will be given in the discussion of local corrosion (Section 12.5). 

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