Chlorine adlattice

Fig. 3. A sequence of 75 nm x 75 nm images revealing the movement of a domain boundary in the chlorine adlattice across the Cu(100) surface at -0.250 V vs. Cu/Cu with Ftip= 0.056 V,...

Fig. 4. A continous sequence of 50 nm x 50 nm images revealing the effects of stepping the potential between -0.25 and -0.65 V vs. Cu/Cu in 10 mmol/1 HCl with tip = 0.050 V, /t = 9 nA and frame time of 22 s The black horizontal line in images (d), (i), (p) and (t) correspond to the instant vvhen the potential was stepped between the two values. A (V2 x /2)R45 chlorine adlattice is stable at -0.25 V whereas the adlattice is reductively disrupted at -0.65 V. For images (a) - (d) E =-0.25 V, (d) -(i) E—0.65 V, (i) - (p) =-0.25 V, (p) - (t) E—0.65 V and (t) - (x) E=-0.25 V. The rapid movement and development of step curvature in images (d) - (i) and (p) - (t) corresponds to the reductive disruption and desorption of the chloride adlattice. The images, which take 18 s to collect were obtained over a period of 8 min this reveals the remarkable effects of surface rearrangement associated with the adsorption/desorption process.

This argument is supported by our STM observations. Immersion of Cu(100) in 10 mmol/1 HCl followed by polarization at -0.250 V vs. Cu/Cu results in the formation of a stable chlorine adlattice as described previously. In the presence of a dilute cuprous... 

A crystal supporting preadsorbed Cl adlattices formed with HC1 gas, as described previously, was immersed in water for one minute to investigate the stability of the Cl adlayers. Subsequent examination of the emersed (removed) crystal evidenced a partial loss of chlorine, about 1/3, and uptake of oxygen on both Cu(lll) and Cu(llO). There was no detectable oxygen uptake on the Cu(100) surface. 

Summary. An STM study has been initiated to investigate the various processes associated with electrodeposition of Cu-Ni multilayers on Cu(100). The substrates were prepared by electropolishing in phosphoric acid followed by immersion in 10 mmol/1 HCl. A (V2 x V2)R45° adlattice of oxidatively adsorbed chlorine is formed under these conditions. The adlayer stabilizes the surface steps in the <100> direction which corresponds to the close packed direction of the chloride adlattice. In dilute (millimolar) solutions of cuprous ion, reduction occurs under mass transport control with the electrocrystallization reaction proceeding by step flow in the <100> direction. At more negative potentials chloride is partially desorbed. Coincidentally, the highly kinked metal steps become Mzzy and move towards adopting the close-packed <110> orientation of the metal lattice. Preliminary experiments on heteroepitaxial nickel deposition reveal regions where electrocrystallization on Cu(100) occurs via step flow in the <110> direction. 

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