The Evaluation of the Perturbations Induced By Ionic Bombardment on Surfaces: A Challenge for Interfacial Electrochemistry
Authors: Aureau Damien , Bouttemy Muriel , Frégnaux Mathieu , Vigneron Jacky , Etcheberry Arnaud , Gonçalves Anne-Marie 
Published: February 2020

The electrochemical response of a material used as electrode is a very efficient and quantitative tool to provide information about its properties particularly its surface characteristic. When any surface is submitted to perturbation as plasma treatment, ionic bombardment, thermal annealing, etc., analysis of electrochemical response is very relevant to discuss the current level of disturbance induced by the treatments. Electrode materials are metals (M) or Semiconductors (SC) and the analysis of modifications of the electrochemical responses are very rich and sensitive due to the high number of parameters that govern the interfacial electrochemistry of the SC or M//electrolyte interface and for which well established data are available. Indeed, accurate analysis of electrochemical responses before and after the treatments gives rise to quantitative information about the electrical, chemical and structure evolutions of the modified surface and consequently on the amplitude of the perturbations. It is also a very efficient tool for estimation of the initial property recovery when additional treatments performed ex situ but also in situ, are carried on the treated surfaces. Comparing the degrees of modification can be used to evaluate the deepness of the perturbation inside de the material. When the electrochemical approach is linked to chemical surface analysis using X-Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) characterizations or to crystallographic analysis using Electron Back Scattering Diffraction (EBSD) the description of the modified surface becomes quantitative and complete at each stage of the treatment processes.

In this contribution, attention will be focused on the evaluation of the perturbation induced on SC by different ionic bombardment conditions. The SC are mono-crystalline InP (n & p type) wafers with (001) or (111) orientations. Ionic bombardment is performed using an Argon MAGCIS dual ion source which provides accelerated Ar+ monoatomic ions or clusters (Arn)+. Controlling the nature, the acceleration, the exposure time, for the beam/SC interaction it is possible to study the consequences of the ion/InP interaction toward a large set of electrochemical parameters. We will present how open circuit rest potential measured in the dark or under illumination are progressively modified. A second important feature concerns the current-potential J(V) responses in the dark or under illumination which a obviously transformed (without current domains, water molecules or protons reduction over-potentials, photo-current anodic (or cathodic) threshold potential, photocurrent saturation domains, etc). Moreover reactivity toward redox species (Ce4+, Fe(CN)6
3-, etc ) can be also impacted depending on the strength of the imposed ionic interaction. The key question of the interface energy diagram through the flat band potential position determination, using for example capacitance measurements is also a main interfacial parameter which is very interesting to follow in term of surface modification.

A very important characteristic of SC interfacial electrochemistry is its availability to generate in situ anodic dissolution with nano-metric control of the material releasing or transformation. Using this possibility it is possible to recover partially or totally the initial properties of the SC/solution interface. So the deepness of the perturbed region can be quantitatively determined. Considered alone the electrochemical characterization can be auto-sufficient for an evaluation of the induced perturbation. Coupled to the XPS analysis the electrochemical responses are now associated directly to surface chemical information as: loss of stoichiometry, Ar+ implantation, surface modification of the Fermi Energy level position, etc. As example of our experimental methodology, the evolution of the XPS core level modification (here P2p) and the associated modification of the Mott Schottky response are reported in figure 1. Both present correlated modifications that can be eliminated using anodic dissolution of the perturbed amount of material in surface. This experimental sequence illustrated the power of the electrochemical tool for a quantitative evaluation of ionic beam induced perturbation of InP surfaces in this study.

Figure 1Variation of the Mott-Shottky Plots induced by ionic bombardment on n-InP_H2SO4 (0.5M) electrolyte. Insert: variations of the XPS response on P2p of n-InP induced by ionic bombardment.

Figure 1