Investigations on the Electrochemical Atomic Layer Growth of Bi₂Se₃ and the Surface Limited Deposition of Bismuth at the Silver Electrode.

Walter Giurlani,Giovanni Zangari,Maurizio Passaponti,Andrea Giaccherini,Nicola Calisi,Massimo Innocenti,Emanuele Salvietti,Stefano Caporali

doi:10.3390/ma11081426

Abstract

The Electrochemical Atomic Layer Deposition (E-ALD) technique is used for the deposition of ultrathin films of bismuth (Bi) compounds. Exploiting the E-ALD, it was possible to obtain highly controlled nanostructured depositions as needed, for the application of these materials for novel electronics (topological insulators), thermoelectrics and opto-electronics applications. Electrochemical studies have been conducted to determine the Underpotential Deposition (UPD) of Bi on selenium (Se) to obtain the Bi2Se3 compound on the Ag (111) electrode. Verifying the composition with X-ray Photoelectron Spectroscopy (XPS) showed that, after the first monolayer, the deposition of Se stopped. Thicker deposits were synthesized exploiting a time-controlled deposition of massive Se. We then investigated the optimal conditions to deposit a single monolayer of metallic Bi directly on the Ag.

Highlights

Bismuth (Bi) and antimony chalcogenides, where the chalcogenide is selenium (Se) or tellurium (Te), exhibit excellent thermoelectric properties, achieving thermoelectric figure of merit (ZT) values of about 1 [1]
The anion is reduced and stripped out with a conventional overpotential deposition. It seems that the SEBALD process occurs even if we want to avoid the chalcogenide electrodesorption. The morphology of this kind of deposit is crystalline, ordered and oriented as we demonstrated, with Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) images, in a previous study [31]
The amount of Bi 4f (42%) and Se 3s (58%) in the sample are compatible with the stoichiometry (2:3) of the desired compound, confirming the electrochemical results (Figure 5)

Summary

Introduction

Bismuth (Bi) and antimony chalcogenides, where the chalcogenide is selenium (Se) or tellurium (Te), exhibit excellent thermoelectric properties, achieving thermoelectric figure of merit (ZT) values of about 1 [1]. These materials commonly crystallize in a rhombohedral structure and exhibit semiconducting behavior (band gap ~0.3 eV). Beyond thermoelectric behavior, these materials show an insulating response in the bulk material while exhibiting metallic conductivity at grain boundaries or surfaces; surface states in particular, are protected via time reversal symmetry, such that electron scattering does not occur [2]. In this study we evaluate the possibility to exploit the Electrochemical Atomic Layer

Methods

Results

Conclusion