Highly oriented pyrolytic graphite steps

An STM probe has been used to isolate individual MS (M = Cd, Pb) particles and to measure electronic phenomena (55,56,81). The MS films were prepared either by exposure of metal ion/fatty acid films to H2S (55,56) or by transfer of a compressed DDAB-complexed CdS monolayer (81). All the films were transferred onto highly oriented pyrolytic graphite (HOPG) for the STM measurements. A junction was created at an individual CdS particle with the STM tip as one electrode and the graphite as the other, and the current/voltage characteristics of the panicles were measured. For the particle prepared in the fatty acid films the I/V curves exhibit step-like features characteristic of monoelectron phenomena. In the case of the DDAB-coated CdS particles the I/V measurements demonstrated n-type semiconductor behavior. The absence of steps in this system is probably a reflection of the larger size of the particles in the DDAB films (8 nm by AFM) compared to the 2-nm particle size typically found for MS particles formed in fatty acid films. 

Figure 4 Schematic illustrating the orientated growth of Api-40 fibrils along the hydrophilic step edges of highly orientated pyrolytic graphite (HOPG) in preference to assembly on the hydrophobic basal plane surface. Copyright (Losic, Martin et al., 2006). Reprinted with permission of John Wiley Sons, inc.

Figure 20.2 Ex situ atomic force microscopy (AFM) image of the basal plane of highly oriented pyrolytic graphite (HOPG). Wide terraces separated by steps can be seen.

The manufacture of heterogeneous catalysts from pre-prepared nanometal colloids as precursors via the so-called precursor concept ll has attracted industrial inter-est.l l An obvious advantage of the new mode of preparation compared with the conventional salt-impregnation method is that both the size and the composition of the colloidal metal precursors can be tailored for special applications independently of the support. In addition, the metal particle surface can be modified by lipophilic or hydrophilic protective shells, and covered with intermediate layers, e.g. of oxide. The addition of dopants to the precursor is also possible. The second step of the manufacture of the catalyst consists in the simple adsorption of the pre-prepared particles by dipping the supports into organic or aqueous precursor solutions at ambient temperature. This has been demonstrated, e.g., for charcoal, various oxidic support materials, even low-surface materials such as quartz, sapphire, and highly oriented pyrolytic graphite. A subsequent calcination step is not required (see Fig. 1). 

Boxley, C. J. White, H. S. 2003. Electrochemical deposition and reoxidation of Au at highly oriented pyrolytic graphite. Stabilization of Au nanoparticles on the upper plane of step edges. J. Phys. Chem. B 107 451 58. 

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