Initial surface topography changes during divalent dissolution of silicon electrodes

• Published in: Electrochimica acta 2003-12, Vol.49 (1), p.137-146
• Main Authors: Jakubowicz, J., Jungblut, H., Lewerenz, H.J.
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Chemistry; Divalent dissolution; Electrochemistry; Electrodeposition; Exact sciences and technology; General and physical chemistry; Pit formation; Silicon; Study of interfaces; Synchrotron radiation photoelectron spectroscopys
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2003.06.001

The changes of the surface topography of float zone (FZ) n-Si(1 1 1) upon conditioning of the electrodes at potentials slightly anodic of the rest potential are monitored with atomic force microscopy (AFM) in the contact mode. The influence of the composition of the used 0.1 and 0.2 M NH 4F electrolyte at pH 4, of the potential and of the charge passed on the topography is investigated. The dissolution charges Q diss ranged from 0.28 to 10.6 mC cm −2 corresponding to ∼0.5 and ∼21 bilayers (BL), respectively. The root mean square roughness R q changes from R q=0.2 nm for the H-terminated surface to 2.9 nm for a charge passed of 10.6 mC cm −2 at an electrode potential of 0.1 V positive of the rest potential. The evaluation of height, deflection and line scan AFM data shows pitting to originate at edges of 〈1 1 2〉 oriented steps which separate atomically smooth terraces. Upon increased dissolution charge, island-type smooth and rather circular features form. Only for the highest Q diss, these islands are beginning to show corrosion. An exponential relation between R q and Q diss is found by evaluation of the three-dimensional roughness. The slope, i.e. the increase of ln R q with Q diss depends on the composition of the electrolyte and is higher for the 0.1 M NH 4F solution. From these data, a branching of the dissolution reaction between charge going into terrace removal or pit formation is obtained. Synchrotron radiation photoelectron spectroscopy (SRPES) is used to identify chemical products of the dissolution process. Comparison of data obtained at 0.15 V anodic of the electrode rest potential with an elaborate model of Gerischer and coworkers (which, however, only describes terrace dissolution) yields partial agreement with the predictions.