Infrared Absorption Study of Zn–S Hybrid and ZnS Ultrathin Films Deposited on Porous AAO Ceramic Support

Maksymilian Włodarski,Matti Putkonen,Małgorzata Norek

doi:10.3390/coatings10050459

Maksymilian Włodarski, Matti Putkonen + Show 1 more

Open Access

https://doi.org/10.3390/coatings10050459

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Abstract

Infrared (IR) spectroscopy is a powerful technique to characterize the chemical structure and dynamics of various types of samples. However, the signal-to-noise-ratio drops rapidly when the sample thickness gets much smaller than penetration depth, which is proportional to wavelength. This poses serious problems in analysis of thin films. In this work, an approach is demonstrated to overcome these problems. It is shown that a standard IR spectroscopy can be successfully employed to study the structure and composition of films as thin as 20 nm, when the layers were grown on porous substrates with a well-developed surface area. In contrast to IR spectra of the films deposited on flat Si substrates, the IR spectra of the same films but deposited on porous ceramic support show distinct bands that enabled reliable chemical analysis. The analysis of Zn-S ultrathin films synthesized by atomic layer deposition (ALD) from diethylzinc (DEZ) and 1,5-pentanedithiol (PDT) as precursors of Zn and S, respectively, served as proof of concept. However, the approach presented in this study can be applied to analysis of any ultrathin film deposited on target substrate and simultaneously on porous support, where the latter sample would be a reference sample dedicated for IR analysis of this film.

Highlights

Thin-film materials are becoming increasingly important in many technological fields, such as electronics, optics and biotechnology [1,2,3]
It was demonstrated that ultrathin films (20–60 nm) can be successfully investigated by standard IR spectroscopy when deposited on porous substrates with a well-developed surface
Hybrid Zn–S-1,5-pentanedithiol and ZnS thin films were analyzed which were investigated by standard IR spectroscopy when deposited on porous substrates with a deposited on flat Si and porous AAO substrates

Summary

Introduction

Thin-film materials are becoming increasingly important in many technological fields, such as electronics, optics and biotechnology [1,2,3]. The broad application of thin films has become possible thanks to the constant development of deposition techniques which have enabled the fabrication of thin films with controllable thickness, composition and structure. One of the most advanced methods to fabricate thin films is atomic layer deposition (ALD), which is distinguished from other techniques by its high conformability. Thanks to the self-limiting reaction at the surface between gaseous precursor molecules and chemical groups at a substrate [4,5], uniform layers can be grown on a high aspect ratio and three dimensionally structured materials. The ALD technique allows the film thickness and architecture to be controlled down to the molecular level. Ultrathin films play a major role in devices such as microelectronic components, solar cells, LED displays, and sensors [6,7,8,9]

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