Noble metal alloy thin films by atomic layer deposition and rapid Joule heating

Yuanyuan Guo,Shuzhou Li,Yiming Zou,Riko I Made,Ronn Goei,Leyan Wang,Alfred Iing Yoong Tok,Kwan Wee Tan,Chunyu Cheng

doi:10.1038/s41598-022-06595-9

Abstract

Metal alloys are usually fabricated by melting constituent metals together or sintering metal alloy particles made by high energy ball milling (mechanical alloying). All these methods only allow for bulk alloys to be formed. This manuscript details a new method of fabricating Rhodium–Iridium (Rh–Ir) metal alloy films using atomic layer deposition (ALD) and rapid Joule heating induced alloying that gives functional thin film alloys, enabling conformal thin films with high aspect ratios on 3D nanostructured substrate. In this work, ALD was used to deposit Rh thin film on an Al2O3 substrate, followed by an Ir overlayer on top of the Rh film. The multilayered structure was then alloyed/sintered using rapid Joule heating. We can precisely control the thickness of the resultant alloy films down to the atomic scale. The Rh–Ir alloy thin films were characterized using scanning and transmission electron microscopy (SEM/TEM) and energy dispersive spectroscopy (EDS) to study their microstructural characteristics which showed the morphology difference before and after rapid Joule heating and confirmed the interdiffusion between Rh and Ir during rapid Joule heating. The diffraction peak shift was observed by Grazing-incidence X-ray diffraction (GIXRD) indicating the formation of Rh–Ir thin film alloys after rapid Joule heating. X-ray photoelectron spectroscopy (XPS) was also carried out and implied the formation of Rh–Ir alloy. Molecular dynamics simulation experiments of Rh–Ir alloys using Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) were performed to elucidate the alloying mechanism during the rapid heating process, corroborating the experimental results.

Highlights

Metal alloys are usually fabricated by melting constituent metals together or sintering metal alloy particles made by high energy ball milling
Conventional methods used to fabricate metal alloys typically result in bulk alloys; even with methods like mechanical alloying[9,10] which give nanostructured bulk alloys that have drawbacks like precisely control of chemical composition, thickness and microstructure
We demonstrate for the first time a novel strategy consisting of Atomic Layer Deposition (ALD) to fabricate alternating layers of nanometer-thin constituent Ir and Rh films on the basis of crystallographic similarity, and subsequent rapid EJH treatment to alloy & sinter these Rh–Ir films into an alloy

Summary

Introduction

Metal alloys are usually fabricated by melting constituent metals together or sintering metal alloy particles made by high energy ball milling (mechanical alloying). After ALD, the multilayered structure was alloyed by EJH at 1080 °C for 5 s to obtain Rh–Ir alloy thin film (Fig. 1).

Results

Conclusion