Influence of Post-Annealing on the Structural and Nanomechanical Properties of Co Thin Films.

Yeong-Maw Hwang,Ying-Xu Lu,Cheng-Tang Pan,Huang-Wei Chang,Sheng-Rui Jian,Jenh-Yih Juang

doi:10.3390/mi11020180

Abstract

The correlations between the microstructure and nanomechanical properties of a series of thermal annealed Co thin films were investigated. The Co thin films were deposited on glass substrates using a magnetron sputtering system at ambient conditions followed by subsequent annealing conducted at various temperatures ranging from 300 °C to 800 °C. The XRD results indicated that for annealing temperature in the ranged from 300 °C to 500 °C, the Co thin films were of single hexagonal close-packed (hcp) phase. Nevertheless, the coexistence of hcp-Co (002) and face-centered cubic (fcc-Co (111)) phases was evidently observed for films annealed at 600 °C. Further increasing the annealing temperature to 700 °C and 800 °C, the films evidently turned into fcc-Co (111). Moreover, significant variations in the hardness and Young’s modulus are observed by continuous stiffness nanoindentation measurement for films annealed at different temperatures. The correlations between structures and properties are discussed.

Highlights

Cobalt (Co) thin films have been subjected to extensive studies owing to their essential importance in spintronic devices [1,2], such as multilayers giving rise to giant magnetoresistance effect [3,4] and spin valves [5,6]
The “pop-in” behavior has been interpreted as the manifestations of the dislocation activity [16,17,18], while in some materials it was attributed to either nanoindentation-induced phase transformation [19,20] or to the crack/delamination phenomena of the interface of films and substrates [23,24]
The microstructural and nanomechanical characterizations of annealed Co thin films are investigated by X-ray diffraction (XRD) and nanoindentation, respectively

Summary

Introduction

Cobalt (Co) thin films have been subjected to extensive studies owing to their essential importance in spintronic devices [1,2], such as multilayers giving rise to giant magnetoresistance effect [3,4] and spin valves [5,6]. Since the manufacturing and packaging processes are inevitably involving contact loading, it is necessary to fully recognize the mechanical characteristics of Co thin films, especially in the nanoscale regime To this respect, nanoindentation stands out as one of the most efficient tools for obtaining the basic mechanical characteristics, such as the hardness and elastic modulus, at small length scales of various thin films [7,8,9,10] or micro/nano-sized materials [11,12,13,14,15] owing to its advantages of high sensitivity, good resolution and easy operation. It has been ubiquitously identified that the materials often exhibit a characteristic feature called the “pop-in” phenomenon during loading It manifests as a sudden displacement burst at a nearly constant indentation load, signifying the onset of plastic deformation. We estimated the number of indentation-induced dislocation loops formed at the initial stage of nanoscale deformation in Co thin films using the classical dislocation theory [33]

Materials and Methods

Findings

Conclusions