Flame annealing

The pc-Au/propylene carbonate (PC) + NaC104 interface has been studied by Nguyen Van Huong.481 A flame-annealed (02 + H2) pc-Au sphere was used. Before each experiment the pc-Au electrode was cleaned in an NaC104 aqueous solution by a few potential cycles involving oxidation-reduction of the surface until the i,E and C,E curves exhibited stable character. The C,E curves were recorded in the interval 15 150... 

Over the past 10 years it has been demonstrated by a variety of in situ and ex situ techniques187,188 485 487 488 534 that flame-annealed Au faces are reconstructed in the same way as the surfaces of samples prepared in UHV,526-534 and that the reconstructed surfaces are stable even in contact with an aqueous solution if certain precautions are taken with respect to the potential applied and the electrolyte composition 485,487,488 A comprehensive review of reconstruction phenomena at single-crystal faces of various metals has been given by Kolb534 and Gao etal.511,513... 

A freshly prepared flame-annealed Au(100) surface has been found to be reconstmcted188,487,534,538 and the surface atoms exhibit a hexagonal close-packed structure to yield the (hex)-stmcture. One-directional long-range corrugation of 1.45 nm periodicity and 0.05 nm height has been found on the Au( 100) surface.188,488 When the reconstruction is lifted due to specific adsorption of SO - anions at more positive , the surface changes to a (1 x 1) structure.538... 

Some measurements with Pt single-crystal faces have been published recently.140,210,773 Iwasita and Xia210 prepared platinum single crystals according to the method of Clavilier et a/.186 773 After flame annealing and cooling in an H2 + Ar mixture, the electrode was protected... 

Flade potential, 247 Flame-annealed gold surfaces and the work of Kolb, 81 Flat band potential, 483 Fluctuations asymmetrical and unstable systems, 255 controlling progress in pitting, 299 in pitting dissolution, 251 and corrosion processes, 217 during dissolution, 252 at electrodes, theory, 281 during film breakdown, 233 and mathematical expressions thereof, 276... 

Lebedeva NP, Koper MTM, Eeliu JM, van Santen RA. 2000b. The effect of the cooling atmosphere in the preparation of flame-annealed Pt(l 11) electrodes on CO adlayer oxidation. Electrochem Commun 2 487-490. 

Clavilier J. 1999. Flame-annealing and cleaning techruque. In Wieckowski A, ed. Interfacial Electrochemistry Theory, Experimenfi and Applications. New York Marcel Dekker. 

For metals and crystals, cleavage can attempt similar feats, but the results are not as good. Metal surfaces formed by cleavage are usually not atomically flat. When an Au wire is flame-annealed in a hydrogen-air flame, the Au(lll) face is formed preferentially, since it has a lower surface energy than the Au(100) or Au(110) faces, but these Au(lll) faces resemble New Mexico mesas the atomically flat region may be only 50 x 50 nm, and is surrounded by one- or two-atom steps leading down to the plain, and then on to the next mesa. 

Clavilier method for crystal preparation and flame annealing has been improved since 1980 and is employed as a standard procedure for singlecrystal electrode experiments using Pt, Pt metals, and Au. 

Clavilier s currently recommended procedure is as follows. Two cooling processes of the crystal after flame-annealing treatment are carried out between steps (a) and (b) in Fig. 1 i.e., air cooling until the temperature of the crystal becomes 200-300°C and cooling in pure water under an H2 -I- Ar stream. The transfer of the crystal into the cell in step (c) of Fig. 1 with a droplet of H2 + Ar-saturated pure water on the crystal face is important for protecting the crystal surface from impurities in air. Then the crystal surface is exposed to the solution by the dipping method of Fig. 1. 

An alternative or additional step to flame annealing is electrochemical or chemical polishing. The fundamental aspects of electropolishing were reviewed recently [185], and a list of polishing procedures and parameters is available [185,186]. This method has been successfully applied to the preparation of gold, silver, and copper electrodes for STM studies [177,180,188]. It is important to note that different mesoscopic structures may arise according to the specific preparation procedures. For example, electropolishing a mechanically prepared Au(lOO) surface followed by... 

It is noteworthy that prior to the advent of scanning probe microscopy electrochemically driven reconstruction phenomena had been identified and studied using traditional macroscopic electrochemical measurements [210,211], However, STM studies have provided insight as to the various atomistic processes involved in the phase transition between the reconstructed and unreconstructed state and promise to provide an understanding of the macroscopically observed kinetics. An excellent example is provided by the structural evolution of the Au(lOO) surface as a function of potential and sample history [210,211,216-223], Flame annealing of a freshly elec-tropolished surface results in the thermally induced formation of a dense hexagonal close-packed reconstructed phase referred to as Au(100)-(hex). For carefully annealed crystals a single domain of the reconstructed phase... 

Fig. 23. Significant coarsening of the domain structure did not occur, at least for the time scale investigated. Thus, charge-induced reconstruction in sulfuric acid results in a much smaller domain size than that associated with a freshly flame-annealed crystal. The domain boundaries act as preferred nucleation sites for subsequent (hex) (1 X 1) transformation, which occurs much more rapidly than for a freshly flame-annealed sample. Studies of this nature have provided keen insight into aging effects that would be difficult to assess by other means.

Shankar K, Paulose M, Mor GK, Varghese OK, Grimes CA (2005) A study on the spectral photoresponse and photoelectrochemical properties of flame annealed titania nanotuhe arrays. J Phys D Appl Phys 38 3543-3549. 

Fig. 5.20 FESEM images of nanotube array top surface, anodized at 25 V, (a) before and (b) after flame annealing.

An XPS scan of flame annealed nanotubes revealed the presence of carbon in all samples and a summary of the carbon content and carbon state information is provided in Table 5.5 [98], Fluorine was... 

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