Adsorption on semiconductor electrodes

Electrodeposition of Bi Thin Films on n-GaAs(111)B. I. Correlation between the Overpotential and the Nucleation Process

“…It is widely known that semiconductor electrodes are more complex than metal electrodes due to the particular electronic structure of the former. Besides the conduction (CB) and valence bands (VB), which introduce two possible paths for electron transfer, the semiconductor surface has surface states that strongly influence the kinetics of chemical and electrochemical processes that occur on the electrode surface. , Surface states can be classified into intrinsic and extrinsic. , The former are surface states with short relaxation times (τ = 10 –6 –10 –3 s), associated with dangling bonds present at the ideal surface (“truncated bulk”), i.e., only dependent on the crystallographic orientation of the surface. , Due to the 2D symmetry of the surface, the dangling bonds give rise to surface bands located in the energy band gap of the semiconductor that can partially overlap with the CB or the VB depending on the charge character of the dangling bond. Extrinsic surface states are assigned to surface imperfections, i.e., perturbations of the ideal surface.…”

“…Although the energy band diagram of the SEI (Figure ) assists in the interpretation of the nucleation process of the Bi films and its evolution with the SEI overpotential, some effects have not been considered. On the other hand, the energy distribution of surface states can be altered during the nucleation process due to ion adsorption or to the formation of chemical bonds . Consequently, some states disappear, whereas new states called adsorbate-induced gap states (AIGS) or metal-induced gap states (MIGS) are formed.…”

“…We have chosen the (111)B orientation since it provides Bi films with a slightly better morphology and higher out-of-plane crystal quality than those obtained onto GaAs(110) . In Part I of this work we study the effect of the overpotential on the nucleation process that is dependent on the kinetics of Bi­(III) ion reduction and on the onset of concurrent processes such as H + reduction or ion adsorption, e.g., H + or OH – , which play an important role in the overall process . We have analyzed the current density transients obtained during the nucleation process by a procedure developed by Palomar-Pardavé et al that allows the deconvolution of the overall current into its individual contributions. − In the literature there are several works that report the use of this formalism to study the nucleation of metallic deposits onto metallic surfaces. ,− However, to our best knowledge, there are rather few works in which this procedure has been used to analyze the nucleation of metallic films onto semiconducting surfaces. , In view of our results we can conclude that the nucleation process is directly related to the distribution of states in the energy band diagram of the semiconductor–electrolyte interface (SEI).…”

“…On the other hand, the energy distribution of surface states can be altered during the nucleation process due to ion adsorption or to the formation of chemical bonds. 27 Consequently, some states disappear, whereas new states called adsorbate-induced gap states (AIGS) or metal-induced gap states (MIGS) are formed. Due to the complexity of these effects, we do not consider them in our model.…”

Electrodeposition of Bi Thin Films on n-GaAs(111)B. II. Correlation between the Nucleation Process and the Structural and Electrical Properties

“…The competition of Bi(III) ion reduction with H + adsorption and reduction is complex because reduction reactions occur via energy bands, sometimes with the assistance of extrinsic surface states, 3 whereas adsorption processes take place only via surface states. 4,5 Consequently, the correlation between the nucleation process and the overpotential is rather complex and is directly related to the energy band diagram of the SEI.…”