Electrochemistry of bismuth interlayers in (Bi2)m(Bi2Te3)n superlattice

Aliaksei Bakavets,Alexander Mazanik,Henrikas Cesiulis,Yauhen Aniskevich,Genady Ragoisha,Eugene Streltsov,Natalia Tsyntsaru

doi:10.1007/s10008-021-05068-9

Abstract

Selective electrochemical transformations of bismuth interlayers in (Bi2)m(Bi2Te3)n superlattices can be of interest as a means of thermoelectric materials design based on bismuth telluride. In this work, the interlayers in the electrodeposited (Bi2)m(Bi2Te3)n superlattice structures formed by pulse potential controlled electrodeposition were characterized with electrochemical microgravimetry on quartz crystal electrodes, cyclic voltammetry, potentiodynamic electrochemical impedance spectroscopy (PDEIS), and in situ Raman spectroscopy. The oxidation potential of bismuth in the interlayers is in between the potentials of metallic bismuth and bismuth telluride anodic oxidation, which allows electrochemical detection and selective anodic dissolution of the interlayer bismuth. Microgravimetry and cyclic voltammetry have provided monitoring of bismuth interlayer dissolution and the subsequent underpotential deposition (upd) of bismuth adatoms onto Bi2Te3 layers in the electrochemically created slits. PDEIS provided separate monitoring of the interfacial charge transfer, spatially restricted diffusion, capacitance of faradaic origin, and double-layer capacitance, which disclosed different variations of the electrochemical interface area in the superlattices with initial bismuth content below and above that of Bi4Te3. In situ Raman spectroscopy has monitored the removal of bismuth interlayers and distinguished different locations of Bi adatoms in two stages of Bi upd. The electrochemically created slits of molecular dimension have a potential of being used as sieves, e.g., to provide selective accessibility of the electrochemically created centers inside them to molecules and ions in multi-component solutions.

Highlights

(Bi2)m(Bi2Te3)n superlattices formed by alternation of elementary five-atomic layer fragments of Bi2Te3 crystal structure (Bi2Te3 quintuples) and bismuth biatomic layers
The goal of this work is the examination of anodic oxidation of bismuth interlayers in the electrodeposited (Bi2)m(Bi2Te3)n by four potentiodynamic methods: microgravimetry on quartz crystal electrodes, cyclic voltammetry (CV), potentiodynamic electrochemical impedance spectroscopy (PDEIS), and Raman spectroscopy applied in the potentiodynamic mode
Electrode mass change monitoring with Quartz Crystal Microbalance (QCM) has proved to be helpful for Figure 3a, b show variation of mass and current in a cyclic potential scan of Au QCM electrode in the electrolyte solution used for electrodeposition of (Bi2)m(Bi2Te3)n superlattices with bismuth bilayers at “low” bismuth content

Summary

Introduction

(Bi2)m(Bi2Te3)n superlattices formed by alternation of elementary five-atomic layer fragments of Bi2Te3 crystal structure (Bi2Te3 quintuples) and bismuth biatomic layers. “low bismuth content” refers to (Bi2)m(Bi2Te3)n with m ≤ n, contrary to “high bismuth content” which refers to (Bi2)m(Bi2Te3)n with bismuth content higher than in Bi4Te3. Bismuth interlayers of both kinds are distinguished from metallic bismuth by significantly higher anodic oxidation potential. Bi2Te3 framework of (Bi2)m(Bi2Te3)n superlattice oxidizes at higher potential, and this provides the opportunity of selective anodic oxidation of bismuth interlayers in (Bi2)m(Bi2Te3)n superlattice structures. The selective anodic oxidation and dissolution of bismuth from interlayers in the superlattices with low bismuth content is of special interest, as it was shown by XRD analysis to proceed with preservation of the original superlattice structure [19] (Fig. 1). The non-destructive oxidative dissolution of bismuth interlayers may provide a way for bismuth substitution by other elements in a design of more complex superlattice structures

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