Dislocation Energetics and Pop-Ins in AlN Thin Films by Berkovich Nanoindentation.

Sheng-Rui Jian,Yu-Chin Tseng,I-Ju Teng,Jenh-Yih Juang

doi:10.3390/ma6094259

Sheng-Rui Jian, Yu-Chin Tseng + Show 2 more

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https://doi.org/10.3390/ma6094259

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Abstract

Nanoindentation-induced multiple pop-ins were observed in the load-displacement curves when the mechanical responses of AlN films grown on c-plane sapphire substrates were investigated by using Berkovich indenters. No evidence of phase transformation is revealed by cross-sectional transmission electron microscopy (XTEM) and selected area diffraction (SAD) analyses. Instead XTEM observations suggest that these “instabilities” resulted from the sudden nucleation of dislocations propagating along the slip systems lying on the {0001} basal planes and the pyramidal planes commonly observed in hexagonal compound semiconductors. Based on this scenario, an energetic estimation of dislocation nucleation is made.

Highlights

Nanoindentation has been widely employed as an important tool to study the mechanical characteristics, including the measurement of hardness and elastic modulus [1,2,3,4,5,6], creep resistance [7]and fracture behaviors [8,9] of various nano-scale materials and thin films
It is evident that there exist plastic deformation irregularities along the load-displacement curve, which are characterized by multiple discontinuities occurring at certain penetration depths, referred to as multiple “pop-ins”
Thin films is similar to phenomena previously seen in other compound semiconductor materials with hexagonal crystal structure [3,5], wherein the multiple slip systems available for indentation-induced dislocation nucleation and propagation have been identified as the primary reason giving rise to the observed multiple pop-in phenomena

Summary

Introduction

Nanoindentation has been widely employed as an important tool to study the mechanical characteristics, including the measurement of hardness and elastic modulus [1,2,3,4,5,6], creep resistance [7]. The initial segment in the nanoindentation load-displacement curve usually manifests the elastic behavior of the material under. Materials 2013, 6 test, whereas the onset of plastic deformation is generally associated with a displacement discontinuity, i.e., pop-in event, during the loading process [10]. It is the difference between the elastic and plastic deformation that allows one to extract prominent information about the mechanical behaviors of the material under investigation by analyzing various segments of the load-displacement curves obtained. The pop-in behaviors and mechanical characteristics of AlN thin films derived from nanoindentation with a Berkovich indenter are discussed in conjunction with the observations of cross-sectional transmission electron microscopy (XTEM). The correlation between the observed Berkovich nanoindentation-induced dislocation nucleation and propagation on AlN thin films and the number of dislocation loops formed in the pop-in phenomenon are estimated based on the classical dislocation theory [19]

Experimental Details

Results and Discussion

Conclusions