Al2O3 and Pt Atomic Layer Deposition for Surface Modification of NiTi Shape Memory Films

David Vokoun,Narmatha Koothan,Jaromír Kopeček,Jan Duchoň,Yo-Shane Yu,Aliaksei Vetushka,Jan Racek,Ladislav Klimša,Chi-Chung Kei,Jan Drahokoupil

doi:10.3390/coatings10080746

Abstract

Pt coatings on NiTi film micro-actuators and/or sensors can add some useful properties, e.g., they may improve the NiTi anticorrosion and thermomechanical characteristics or activate surface properties beneficial for a specific application (e.g., functionalized surfaces for biomedical applications). Pt coatings prepared via atomic layer deposition (ALD) may help reduce cost due to the nanometric thickness. However, no authors have reported preparation of Pt ALD coatings on NiTi films, perhaps due to the challenge of the concurrent NiTi film oxidation during the Pt ALD process. In the present study, Al2O3 and Pt ALD coatings were applied to NiTi thin films. The ALD coating properties were studied using electron and atomic force microscopies and X-ray photoelectron spectroscopy (XPS). Potential structural changes of NiTi due to the ALD process were evaluated using electron microscopy and X-ray diffraction. The presented ALD process resulted in well-controllable preparation of Pt nanoparticles on ultrathin Al2O3 seed layer and a change of the transformation temperatures of the NiTi films.

Highlights

Atomic layer deposition (ALD) is a kind of chemical vapor deposition (CVD) technique that typically uses two precursor gas reactants sent into the reaction zone in an alternating sequence of precisely controlled pulses
The discussion is separated into three parts related to (i) properties of Pt coating on samples Pt100 and Pt200, (ii) properties of Al2 O3 coating on samples Alu10, Pt100, Pt200 and (iii) the effect of the Pt and Al2 O3 ALD processes on the properties of the NiTi layer
As for the Pt NP size range and the Pt NP areal density on sample Pt100, there is a fair agreement between the results obtained from the scanning electron microscope (SEM) (Figure 1) and atomic force microscope (AFM) images (Figure 5c)

Summary

Introduction

Atomic layer deposition (ALD) is a kind of chemical vapor deposition (CVD) technique that typically uses two precursor gas reactants sent into the reaction zone in an alternating sequence of precisely controlled pulses. Any excessive amount of unreacted precursors in the deposition chamber is purged with an inert gas. This purging results in the self-limiting character of the surface chemical reactions on the substrate and in this way not more than one precursor monolayer is left on the surface after purging. Due to low deposition rates (100–300 nm/h [1,10] depending on the size of the deposition chamber and the aspect ratio of the substrate), the ALD is suitable mainly for nanometric coatings.

Methods

Results

Discussion

Conclusion