Abstract
Metastable phase in tungsten film is of great interests in recent years due to its giant spin Hall effects,however,little information has been known on its nucleation,growth and phase transformation.In this paper,a 900 nm-thick tungsten film with double-layer structure (α-W underlayer and β-W above it) was produced on SiO2/Si substrate by high vacuum magnetron sputtering at room temperature.The structural properties of β-W were systemically investigated by X-ray diffraction,transmission electron microscopy,thermodynamic calculation,first-principle and phase-field simulations.It is found that the β-W nucle-ation is energetically favoured on the SiO2 surface compared to the α-W one.As the film thickening pro-ceeds,β-W[211]turns to be preferred direction of growth owing to the elastic strain energy minimiza-tion,which is verified by phase-field simulations.Moreover,the β→α phase transformation takes place near the film-substrate interface while the rest of the film keeps the β-W phase,leading to a double-layer structure.This localized phase transition is induced by lower Gibbs free energy of α-W phase at larger grain sizes,which can be confirmed by thermodynamic calculation.Further in-situ heating TEM analysis of the as-deposited film reveals that the β→α phase transformation is fulfilled by α/β inter-face propagation rather than local atomic rearrangements.Our findings offer valuable insights into the intrinsic properties of metastable phase in tungsten.
基金项目
National Natural Science Foundation of China(51904015)
National Natural Science Foundation of China(51534009)
General Program of Science and Technology Develop-ment Project of Beijing Municipal Education Commission(KM202010005008)
National Natural Science Fund for Innova-tive Research Groups(51621003)
Beijing Municipal Great Wall Scholar Training Plan Project(CIT&TCD20190307)
NETL
NSTL
万方数据