Cross-sectional transmission electron microscopy observations on the Berkovich indentation-induced deformation microstructures in GaN thin films

Abstract

Nanoindentation-induced mechanical deformation in GaN thin films prepared by metal-organic chemical-vapour deposition was investigated using the Berkovich diamond tip in combination with the cross-sectional transmission electron microscopy (XTEM). By using focused ion beam milling to accurately position the cross-section of the indented region, the XTEM results demonstrate that the major plastic deformation was taking place through the propagation of dislocations. The present observations are in support of attributing the pop-ins that appeared in the load–displacement curves to the massive dislocation activities occurring underneath the indenter during the loading cycle. The absence of indentation-induced new phases might have been due to the stress relaxation via the substrate and is also consistent with the fact that no discontinuity was found upon unloading.

Mechanical responses of single-crystal ZnO

“…3(b) and (c)). We note that these features are also in contrast to that observed in GaN [29,30] and Al 0.16 Ga 0.84 N films [5], albeit similar Berkovich indenter tip was applied and crystal structure is the same wurzite structure.…”

Berkovich nanoindentation on InP

“…It clearly shows that multiple pop-ins (discontinuities) in load-displacement curve occur during loading and reflects the process of plastic deformation in the material. The phenomena are usually attributed to dislocation nucleation and propagation during loading as have been observed in a wide variety of materials [14,17], or micro-cracking [18] event. This observation is in contrast to that reported in the previous studies of InP [12,19], where only single "pop-in" event was observed.…”

“…Prior to milling, the FIB was used to deposit an ∼1 m thick layer of Pt to protect sample surface. The details of FIB produces in preparing XTEM sample can be found elsewhere [14]. The XTEM lamella was examined in a FEI TECNAI G 2 TEM operating at 200 kV.…”

“…However, they are inadequate to distinguish the phase changes inside the deformed zone along the direction of the concentrated applied stress. The focused ion beam (FIB) miller, which is now widely used for a range of material characterization applications [14], can be applied to readily image and prepare the cross-sections of materials. FIB can also be used in the preparation of lamella TEM sample, especially for samples which have been locally deformed.…”

Morphological, structural, and mechanical characterizations of InGaN thin films deposited by MOCVD

“…Among these methods, the nanoindentation technique plays a key role in understanding nanomechanical properties of thin films. Nanoindentation has been proven to be a powerful technique in providing information on mechanical properties (hardness and elastic modulus) of the investigated materials and variation of these properties with the penetration depth based on analysis of the load-displacement curves [10][11][12][13][14][15][16][17][18][19]. The most important advantage of nanoindentation is to obtain, nondestructively, the films properties without being affected by its substrate.…”