In situ, STM, and AFM

In the following, we proceed to several new aspects regarding molecular resolution of adsorbed metalloproteins. In Section 5.3, we first show that close to molecular resolution of the interfacial ET patterns of some two-centre proteins is within reach. The number of intermetallic interactions and resulting microscopic reduction potentials and rate constants in metalloproteins with more than two centres is, however, prohibitively large for such resolution. In Section 5.4 we address molecular and supramolecu-lar adsorption. We show here that in situ STM and AFM, indeed do hold exciting new perspectives for this important and central structural aspect of proteins at surfaces. 

Our discussion of scanning probe approaches to metalloproteins at surfaces indicates, first that in situ STM and AFM mapping of metalloproteins with molecular (rather than atomic) resolution is definitely feasible. In addition, submolecular detail is possibly within reach. This is interesting as proteins constitute a class of soft materials. It is also comforting as aqueous solution is otherwise the natural functional medium for proteins. 

Protein mobility and aggregation are inherent problems in the in situ STM and AFM characterization. This can, however, also be turned to the better and brought to open other new perspectives for mapping of molecular and collective protein dynamics such as phase transitions, heterophase fluctuations etc. 

Principally two other classes of materials have been studied by in-situ STM and AFM the III-V compounds and layered materials. In-situ atomic resolution has been obtained on p-InSe by Uosaki and Kuomina [22]. Semiconductor oxides have not been studied since the early work of Itaya and Tomita on Ti02 [42] and ZnO [43]. STS [63, 64] and atomic resolution [64] have however been recently reported in air on Ti02. Kepler and Gewirth [21] could resolve in-situ individual atoms on Ge(lll) and (110) electrodes. That in-situ atomic resolution was obtained by AFM on Ge [21] and InSe [22] opens new possibilities for electrochemical studies since the sample bias is less subject to constraints of polarization. Photoeffects, induced by the laser beam need nevertheless being avoided. 

Recently, combined electrochemical and in situ STM and AFM measurements in many Me UPD systems gave direct evidence for the participation of first order phase transitions involving 2D nucleation and growth. For example, experimental in situ STM results in the system AgQikt)/Ph, CIO4 show that at relatively low supersaturations zFlAE - A l a first order phase transition occurs exclusively via 2D nucleation and growth at monatomic steps [3.179, 3.187]. 

A knowledge of the kinetics of 2D island formation and growth processes is of great importance for a better understanding of phase transitions in 2D Me UPD overlayers. However, in situ STM and AFM techniques do not allow dynamic measurements over wide time and frequency ranges at the present state of development. 

In situ STM and AFM investigations represent a powerful tool for obtaining structural and morphological information on bare substrates and 2D Meads overlayers including phase transitions and their localization on the substrate surface. 

The third part treats surface modification by underpotential deposition (UPD) of metals. Physical nature, thermodynamics, structural aspects, kinetics, as well as surface alloy formation are discussed. Experimental support is given based on classical electrochemical investigations as well as on some recent results from modern in situ surface analytical studies including atomic imaging by in situ STM and AFM. 

The transition from the initial nucleation stages of metal deposition to 3D compact bulk deposits is described in the sixth part. Nanoscale structuring and modification of solid state surfaces by in situ STM and AFM are also considered. 

Early in situ STM (and AFM) of nucleobases focused on adenine and guanine on molybdenum disulfide and highly oriented pyrolytic graphite [131-133]. Other early studies addressed all the nucleobases and Au(lll) electrode surfaces. The bases were concluded to form planar hydrogen-bonded networks on the surfaces... 

Friis, E.P., Andersen, J.E.T., Madsen, L.L., Moller, P., and Ulstrup, J. (1997) In situ STM and AFM of the copper protein Pseudomonas aeruginosa azurin. Journal of Electroanalytical Chemistry,... 

Local structuring and modification of solid-state surfiices by electrodeposition of metals are of great practical importance. However, the realization of these processes requires an exact knowledge of UPD and OPD of Me at an atomic level. At present, first attempts have been started to develop appropriate polarization routines for a defined nanostructuring or nanomodification of solid-state siufaces (metals, semiconductors, superconductor films) using in-situ STM and AFM. 

Endres, R Borisenko, N. El Abedin, S.Z. Hayes, R. Addn, R., The interface ionic liquid(s)/ electrode(s) In situ STM and AFM measurements, Faraday Dsicuss., 2012,154, 221-233. Lassfegues, J.-C. Grondin, J. Talaga, D., Lithium solvation in bis(trifluoromethanesulfonyl) imide-based ionic liquids, Phys. Chem. Chem. Phys., 2006, 8,5629-5632. 

The EQCM should always be used as an addition tool, in combination with common electrochemical techniques (such as EIS, chrono-coulometry, electromodulated reflectance spectroscopy, FTIR spectroscopy, and in situ STM and AFM techniques, as may be appropriate), not replacing them. 

In this chapter, attention is focused on in-situ STM and AFM, and recent advances of in-situ SPM in surface electrochemistry and nanoelectrochemistry are introduced, with applications that include surface characterization, nanostructuring, and molecular electronics. First, a brief discussion of the principles and features of STM and AFM is provided, and this is followed by some selected examples of the capabilities of both techniques in the study of surface and nanoelectrochemistry, mostly acquired in recent studies conducted by the present author s group. Emphasis is placed on the roles of in-situ STM and AFM from a methodological point of view. Finally, the prospects for the further development of in-situ SPM are reviewed. 

The section on the structure of passive layers has shown the application of in situ STM and AFM and synchrotron methods like XAS and GIXD for the analysis of the structure of passivated surfaces at the atomic scale and at the nanoscale. These techniques provide... 

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