Surface phase diagram

The surface phase diagram of vanadium oxides on Rh(l 11) has been investigated in a series of papers of our group [4, 18, 19, 90, 101-103]. It is characterized by pronounced polymorphism and many different oxide structures have been detected as a function of coverage and growth temperature. The vanadium oxide structures for coverages up to the completion of the first monolayer formed on Rh(l 11) under the different preparation conditions may be subdivided into highly oxidized phases... 

S. H. Overbury, P. A. Bertrand, and G. A. Somorjai, The surface composition of binary systems Prediction of surface phase diagram of solid solutions, Chem. Rev. 75, 547—560 (1975). 

Construct a surface phase diagram for H atoms adsorbed on Cu(100) as a function of temperature and H2 pressure by comparing the relative stability of ordered overlayers of H with coverages of 1, and of a mono-layer. You could also consider situations where H atoms are present in the interstitial sites underneath the topmost layer of surface atoms. 

Fig. 7 Surface phase diagram indicating the most stable surface structures for Cu-Ag bimetallic surface as a function of the Cu surface content and oxygen chemical potential. Reprinted figure with permission from Piccinin et al. Physical Review B, 2008, 77, 075426. American Physical Society.

Although somewhat speculative, the presence of two (or perhaps three) Li UPD/stripping features is consistent with information derived from LEED for K, Cs, and on a more preliminary basis Li, adsorbed on Ni(lll) in UHV [26], from which the surface phase diagram shows at least two ordered phases as a function of 0 for 0 < 1/3. 

Fig. 28. Averaged order parameter profiles cf>av(Z,x) plotted vs the scaled distance Z=z/2 b from the left wall at z=0 for four different scaled times T after the quench as indicated, for a scaled distance D =D/2 b=60. Choosing a rescaled distance L /2 b=600, and a discretization AX=1.5, Ax=0.05, the resulting equations are solved by the cell-dynamics method. The results shown are for parameters h1=y=4, g =-4, and averaged over 2000 independent initial conditions, corresponding to random fluctuations in a state with J( )av(Z,0)dZ=0. The parameters Iq and g were chosen such that both walls prefer A but one is still in the non-wet region of the equilibrium surface phase diagram of the corresponding semi-infinite system. From Puri and Binder [145]...

Measuring Surface Tension of Thin FoUs by Laser Interferometer First Step in Generating Surface Phase Diagrams... 

The use of surface phase diagrams to control the solid surface phase[s] represents a powerful in-situ technique for use in heterogeneous catalytic studies. Knowledge of the surface phase composition allows the catalytic properties of specific metallic phases to be evaluated. This type of a-priori control is not possible with other in-situ analytical techniques... 

Surface Elemental Composition and Surface Phase Diagrams... 

Figure 7. Surface phase diagram (atomic% of Pt at die outermost layer versus atomic% of Pt in the bulk) of die Pt-Co films after annealing at 1000 K for 30 minutes.

Figure 8. FEED patterns of the annealed Pt-Co alloys at points in the surface phase diagram where (a) the outermost layer is predominantly PtsCo, and (b) the topmost layer is essentially pure Pt. 

In order to compare stabilities of different oxygen overlayers and evaluate the electrochemical surface phase diagram of Pt(l 11) in contact with an aqueous electrolyte, we performed periodic DFT calculations on the energetics and stractures of oxygen adsorption at different coverages. Since the electrode is present in the solid phase, we assume the temperature and activity dependence of G to be small, and the contributions from configurational and... 

The enormous variety of possible surface reactions still reveals many open questions regarding exact reaction pathways, kinetics, and/or structural iirformation. The seemingly simple water formation reaction from H2 and O2 over a Pt-catalyst already shows many different reaction pathways. Regarding this reaction, we have performed periodic DFT calculations and thermodynamic considerations to evaluate the corresponding (a,7 ,A(zi)-surface phase diagram for Pt(lll) on contact with an aqueous electrolyte. Our work determined that below 0.95 V no stable and ordered oxygen overlayer forms, and that between 0.95 and 1.20 V the... 

Reuter K, Scheffler M (2003) First-principles atomistic thermodynamics for oxidation catalysis surface phase diagrams and catalytically interesting regions. Phys Rev Lett 90(4) 046103... 

The Cahn approach describing simple fluid mixtures has been adopted by a mean field theory developed for polymer mixtures by Nakanishi and Pincus [61] and Schmidt and Binder [15] and is presented in the next section. The mean field theory and its various extensions [7] have been successfully used to describe much of the experimental segregation isotherm z (())<, ) data obtained so far [16, 92,120,145,165-167,169-175]. It allows us not only to distinguish isotherms z (J characteristic for partial and complete (first and second order) wetting but also to determine surface free energy parameters useful in predicting surface phase diagrams for the studied mixtures. 

The final implication of the temperature variation of (-dfs/d( ))s concerns the nature of the surface phase diagram and the location of the wetting transition point Tw For further discussion we use the Cahn construction drawn in Fig. 20b for the highest (T=184 °C) and lowest (T=99 °C) studied temperature. While the... 

Standard theoretical approaches, using the graphical Cahn construction [8, 153,176,221] or its numerical analogs [15,162,187] to analyze the surface phase diagram, have assumed that the parameters of the bare surface energy fs are... 

Fig. 5.13. DFT-GGA surface phase diagram of stable surface structures at a Pd(lOO) surface in constrained equilibrium with an O2 and CO environment. The stability range of bulk PdO is the same as the one shown in Fig. 5.12. Phases involving the (. 5 X. 5)R27° surface oxide exhibit a largely increased stability range, which now comprises gas phase conditions representative of technological CO oxidation catalysis (po2 = Pco = 1 atm. and 300 K < T < 600 K, marked by the black line, as in Fig. 5.12) (from [46])...

Lower irv-x surface phase diagram where data for upper curve containing point a are obtained from F-F of the 7r-A isotherm lower curve containing point b is obtained from G-G of the 7r—A isotherm. At any value of ttV7 condensed film at point a (x = x(c)) is in equilibrium with vapor film at point a (x-x(v)). 

Figure 6. irv-x surface phase diagrams for lipid mixtures on water, pH 5.8 at 24.5°C. Dotted line represents ideal mixing. 

Fig. 55. Surface phase diagram in the plane of variables g, and <)> for three values of g. The region where the surface is non-wet (at small gj is separated from the wet region by a phase boundary which describes the wetting transition. For > (second-order wetting) this is just the straight line giril = — g(l—) The region of first order wetting is shown for symmetrical mixtures with Na = NB = N = 10 and N = 100, respectively, and the first-order transitions are shown by dash-dotted curves. In this regime metastable wet and non wet phases are possible up to the stability limits ( surface spinodals ) denoted by dashed curves. Assuming that g, and g are essentially independent of temperature T, variation of T essentially means variation of <)>, . From Schmidt and Binder [125],...

Fig. 55. Surface phase diagram in the plane of variables p, and for three values of g. The region...

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