STM Configurations

C2 = nanoparticle/substrate capacitance). Reprinted with permission from Ref. [37] ( 2007, Elsevier. 

One advantage of STM/STS measurements is, that the individual duster can be imaged and analyzed spectroscopically in one single experiment, which ensures that reliable data are acquired from individual dusters. 

The first investigations on SET events in metal nanopartides, using the above-described STM configuration, date back to the 1990s. One of the earliest examples was an STM investigation of approximately 4nm gold nanopartides, obtained by 

Vset = — 1.5 V, /set = 0.2 nA). The lower curve shows the fitting result to the charging peaks of the experimental data by the orthodox theory based mode at 78 K. Parameters are  

12 edges of the cubo-octahedron and six Cl atoms (violet) located in the center of the six square faces ofthe Au core. A comparison of (a) and (b) shows that the STM resolves the CeHs rings. Spectroscopic data were acquired at the two distinct locations marked in panel (a). Reprinted with permission from Ref. [44]  

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Using the unique four-electrode STM described above, Bard and coworkers (Lev, 0. Fan, F-R.F. Bard, A.J. J. Electroanal. Chem.. submitted) have obtained the first images of electrode surfaces under potentiostatic control. The current-bias relationships obtained for reduced and anodically passivated nickel surfaces revealed that the exponential current-distance relationship expected for a tunneling-dominated current was not observed at the oxide-covered surfaces. On this basis, the authors concluded that the nickel oxide layer was electrically insulating, and was greater than ca. 10 A in thickness. Because accurate potential control of the substrate surface is difficult in a conventional, two-electrode STM configuration, the ability to decouple the tip-substrate bias from... 

A second method of tip-directed synthesis involves a two-electrode STM configuration to form small clusters of metals, polymers, and semiconductors on graphite surfaces immersed in a dilute electrolyte [13,532-535]. Initially, the material to be deposited (i.e., Ag) is concentrated by... 

Fig. 2. (a) IETS configuration vs. (b) STM configuration. The former measures a macro-... 

The role of redox metal centres in the in situ STM configurations... 

Figure 4. EC-STM configuration. (A) Electt onic (bipo-tentiostat) circuiby. (B) Four-elecb ode experimental set-up.

Figure 7-19. Energy level diagram for tunneling in an STM configuration involving a redox active molecule. The energy levels involved are shown the Fermi levels of the substrate (Cs, left) and the tip (stip, right) and the energy levels corresponding to the oxidised and rednced state of the redox active molecule (8qx and 8re

Figure 8-6. In situ STM configuration, schematic. In this four-electrode configuration the working electrode potential is controlled relative to the electrochemical reference electrode ( gate ) and the (coated) tip potential relative to the working electrode potential. The counter electrode enables recording of electrochentical processes on the working electrode by the independently controlled tip electrode.

The chapters in this volume offer overviews of electronic properties, electron transfer and electron-proton coupled charge transfer of biological molecules and macromolecules both in the natural aqueous solution environment and on metallic electrode surfaces, where the electrochemical potential controls biomolecular function. Redox metalloproteins and DNA-based molecules are primary targets, but amino acid and nucleobase building blocks are also addressed. Novel enviromnents where proteins and DNA-based molecules are inserted in metallic nanoparticle hybrids or in situ STM configurations are other focus areas. 

Figure 5.25 (a) General scheme of the STM configuration for the investigation of SET on individual metal nanoparticles ... 

Figure 5.33 (a) Monolayer-protected nanoparticle in an electrochemical in situ STM configuration (b) Sequential charging events observed in DPV (red) and /,(r ) tunneling spectroscopy (black) at constant Vbias = 0.05 V (/°et = 0.05 nA). Inset Abundance distribution... 

The planar geometry implied by the assumption that transmission depends only on the energy of the motion parallel to the tunneling direction, as well as the explicit form of Eq. (14) are not vahd for a typical STM configuration that involves a tip on one side and a structured surface on the other. To account for these structures, Tersoff and Hamman[103] have applied Bardeen s formalism [104], which is a perturbative approach to tunneling in arbitrary geometries. Bardeen s formula for the tunneling current is... 

Figure 7.1 STM working principle, (a) Schematics of a typical STM configuration.

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