Surface-phase-transition

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

Second-Order Integral Equations for Associating Fluids As mentioned above in Sec. II A, the second-order theory consists of simultaneous evaluation of the one-particle (density profile) and two-particle distribution functions. Consequently, the theory yields a much more detailed description of the interfacial phenomena. In the case of confined simple fluids, the PY2 and HNC2 approaches are able to describe surface phase transitions, such as wetting and layering transitions, in particular see, e.g.. Ref. 84. 

It is well known that the catalytic oxidation of CO on certain Pt surfaces exhibits oscillatory behavior, within a restricted range of pressures and temperatures, which are coupled with adsorbate-induced surface phase transitions [16,17]. In fact, in their clean states the reconstructed surfaces of some crystallographic planes, e.g. Pt(lOO) and Pt(llO), are... 

D. P. Landau, K. Binder. Monte Carlo study of surface phase transitions in the three-dimensional Ising model. Phys Rev B 47 4633-4645, 1980. 

For the reduction of NO with propene, the catalyst potential dependence of the apparent activation energies does not show a step change and is much less pronounced than it is for the CO+O2 and NO+CO systems. There is persuasive evidence [20] that the step change is associated with a surface phase transition - the formation or disruption of islands of CO. It is reasonable to assume that this phenomenon cannot occur in the NO+propene case, since there is no reason to expect that large amounts of chemisorbed CO can be present under any conditions. That there should be a difference in this respect between CO+O2/CO+NO on the one hand, and NO+propene on the other hand, is therefore understandable however, the chemical complexity of the adsorbed layer in the NO+-propene precludes any detailed analysis of the Ea(VwR> effect. 

Pozniak B, Scherson DA. 2003. Dynamics of a surface phase transition as monitored by in situ second harmonic generation. J Am Chem Soc 125 7488-7489. 

Cox MP, Ertl G, Imbihl R, Riistig J. 1983. Non-equilibrium surface phase transitions during the catalytic oxidation of CO on Pt(lOO). Surf Sci 134 L517. 

Campbell and coworkers269 also published a kinetics study of the reverse water-gas shift over Cu(110) in 1992, and the results were cast in terms of the redox mechanism (reverse of Scheme 60, left side). A hydrogen-induced surface phase transition was suggested to impact the rate at high H2/C02 ratios, as the rate was found to exhibit a saturation-like behavior with increasing P(H2) when 5 Torr of C02 was used, but continued on a log-linear trend when 150 Torr of C02 was... 

J.C. Shelton, H.R. Patil, J.M. Blakely, Equilibrium segregation of carbon to a nickel (111) surface A surface phase transition, Surface Science, 43 (1974) 493-520. 

The strength of the lattice instability near the Fermi vector depends on the magnitude of the electron-phonon coupling and on the phase space available for electron-hole pair excitation around 2kf. Thus, a reconstructive surface phase transition has to fulfill the following requirements in order to be ascribed to an electronically driven lattice instability ... 

This paper addresses two different sets of observations on the anisotropy of wetting of Pb crystals by its own melt and by Ga-Pb alloys. The observed anisotropies in these cases are due to the anisotropy of the surface free energy of solid Pb and to the intervention of surface phase transitions. 

COUPLED CHEMICAL AND FACETING SURFACE PHASE TRANSITIONS... 

Figure 2d shows the crystal after further cooling to 225°C. In addition to 111, 100 and 227) facets, new facets have appeared at 110 orientations, and the formation ofthose facets is also accompanied by higher Bi and Ni surface concentrations at those regions (about 30 at%Bi and 20 at%Ni). At this temperature, the 100 facets are also found to have undergone the compositional surface phase transition, and display surface compositions similar to those ofthe 110 surfaces. 

Erikson, J.S., Sundaram, S., Stebe, K.J. (2000). Evidence that the induction time in the surface pressure evolution of lysozyme solutions is caused by a surface phase transition. Langmuir, 16, 5072-5078. 

The studies of Ertl and co-workers showed that the reason for self-oscillations [142, 145, 185-187] and hysteresis effects [143] in CO oxidation over Pt(100) in high vacuum ( 10 4 Torr) is the existence of spatio-temporal waves of the reversible surface phase transition hex - (1 x 1). The mathematical model [188] suggests that in each of the phases an adsorption mechanism with various parameters of CO and 02 adsorption/desorption and their interaction is realized, and the phase transition is modelled by a semi-empirical method via the introduction of discontinuous non-linearity. Later, an imitation model based on the stochastic automat was used [189] to study the qualitative characteristics for the dynamic behaviour of the surface. 

More recently, Miranda et al. [81] have shown that this family of polyelectrolytes also present a second surface phase transition at surface pressures that depend on the quaternization degree and on the length of the alkyl side chain. Similar results have been presented by Davis et al. [84],... 

Formulation of the temporal variations of the coverages of CO, NO, and O in terms of three coupled differential equations (the recombination of 2Nad and desorption of N, is much faster than the other processes and can hence be left without explicit consideration) leads indeed to oscillatory solutions without the need for additional inclusion of a surface-phase transition step. The physical reason lies in the fact that dissociation of adsorbed NO (step g) needs another free adsorption site and is inhibited if the total coverage exceeds a critical value [The adsorptive properties of... 

S-NDR Systems Involving a Surface Phase Transition of Organic Adsorbates. 145... 

The existence of bistability in the //under conditions under which chemical variable, on which the current depends, exhibits bistability as a function of DL. Thus, in S-NDR systems we have to require that the dynamic equations contain a chemical autocatalysis. As set forth below, m takes the role of the negative feedback variable. The positive feedback might be due to chemical autocatalytic reaction steps as is the case in Zn deposition [157, 158] or CO bulk oxidation on Pt [159], S-shaped current-potential characteristics may also arise in systems with potential-dependent surface phase transitions between a disordered (dilute) and an ordered (condensed) adsorption state due to attractive interactions among the adsorbed molecules. 

S-shaped current potential curves emerge when a surface phase transition of an organic adsorbate is coupled with a faradaic reaction of some electroactive species. As a representative of such a system, the periodate reduction on Au(lll) single crystal electrodes in the presence of camphor was studied [160], Camphor adsorbed on Au(lll) electrodes exhibits two first-order phase transitions upon variation of the electrode potential [161]. In a cyclic voltammogram, the phase transition manifests itself in a pair of needle-like peaks (Fig. 28 (A)). Between the peak pairs, a condensed, well-ordered camphor film exists. At more negative potentials, the camphor coverage is low, while the state of the adsorbate at positive potentials beyond the second phase transition is not yet known. The small hystereses between the respective anodic and cathodic peaks are caused by the finite nucleation rate of the respective thermodynamically stable phase. 

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