Seminar Emilien LEFEBVRE 16.06.2026

Engineering of surface traps in ZnO nanowires for piezoelectric devices

PhD student, Emilien Lefebvre

LMGP, Université Grenoble Alpes, CNRS, Grenoble INP, France

Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, France

Abstract

ZnO nanowire arrays are promising building blocks for a wide variety of applications, including piezoelectric devices and optoelectronics. [1] Owing to its low temperature (< 100 °C), the use of water molecules as solvent, and the non-toxicity of the two main reagents, the chemical bath deposition (CBD) technique has regularly been described as a safe and eco-friendly chemical route for the growth of ZnO nanostructures, in contrast to high-temperature deposition techniques such as metal-organic chemical vapour deposition, thermal evaporation, and spray pyrolysis. However, the use of HMTA molecules in the CBD process has recently been pointed out as incompatible with green chemistry. [2] Moreover, the high density of free electrons in the bulk of CBD-grown ZnO nanowires (~ 10¹⁹ cm^-3) as well as the high density of surface traps (~ 10¹² cm^-2) strongly limit the piezoelectric and optoelectronic properties of ZnO nanowires-based devices. [3-4]

In this seminar, an original CBD technique more compatible with green chemistry is presented by using a Good’s buffer. Based on thermodynamic computations and X-ray absorption near edge structure (XANES) measurements using synchrotron radiation, the physicochemical processes in the chemical bath are investigated in detail. The crystallisation and the structural properties of ZnO nanowires and nanostructures are shown by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and cathodoluminescence spectroscopy at 5K. The benefits and limits of the present CBD process with respect to green chemistry are discussed.

Then, the issue of surface traps in ZnO nanowires is assessed via two different routes. First, the surface passivation effect of hydrogen plasma treatments is deeply studied by cathodoluminescence spectroscopy in both continuous and time-resolved modes and from cryogenic to room temperature. Efforts are particularly placed on the explanation of optical properties such as the strong enhancement of UV luminescence intensity by two orders of magnitude observed. Surface effects of plasma treatments are also investigated by X-ray photoelectron spectroscopy. Second, the synthesis of ZnO/Ga-based oxides core-shell nanowire heterostructures is achieved by combining chemical bath deposition and atomic layer deposition methods for the purpose of integration into piezoelectric nanogenerators. The structural morphology of heterostructures is investigated using scanning and transmission electron microscopy, as well as X-ray diffraction and Raman spectroscopy. The chemical composition of the shell is assessed by X-ray photoelectron spectroscopy, while the optical properties along with their surface properties are measured by 5K cathodoluminescence spectroscopy. The piezoelectric potential in core shell ZnO nanowire heterostructures is carefully determined by piezoelectric force microscopy measurements.

[1] J. Briscoe et al., Nano Energy 14, 15-29 (2015).

[2] A. Baillard et al., Nanomaterials 15, 1574 (2025).

[3] J. Villafuerte al., Nano Energy 114, 108599 (2023).

[4] R. Tao et al., Advanced Electronic Materials 4, 1700299 (2018).

Short Bio/CV

I am a third-year PhD student at the LMGP and Institut Néel labs with a background in materials science. As part of the ANR IMINEN project, my research focuses on the development of ZnO nanowires for piezoelectric applications via chemical synthesis techniques, with a special interest in monitoring the surface effects of nanostructures