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CSME 2018/02
Volume 39 No.1
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1-9
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Effects of Annealing on Nanoindentation Behaviour and Compounds Formation of Ti/GaAs Thin Film
Woei-Shyan Leea and Chung-Chia Loa
aDepartment of Mechanical Engineering, National Cheng Kung University
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Abstract:
The mechanical properties of as-deposited Ti/GaAs thin films and Ti/GaAs thin films annealed at a temperature of 490ºC for 36 minutes are investigated by means of nanoindentation tests performed to a depth of 200 nm under room temperature (RT) conditions. The microstructures of the as-deposited and annealed Ti/GaAs films are examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman scattering spectroscopy. In the nanoindentation tests, a pop-in event is observed in the loading-depth curve of the as-deposited specimen. By contrast, the loading-depth curve of the annealed specimen is continuous and smooth. The TEM results suggest that the pop-in event in the as-deposited specimen is the result of the formation of dislocations in the indented microstructure, which leads to a plastic deformation mode. Dislocation structures are also observed in the annealed specimen even though no pop-in event occurs in the loading-depth curve (i.e., the sample undergoes elastic deformation). In this case, the dislocations are thought to be related to the density of the native defects in the GaAs substrate and the difference in doping. The nanoindentation test results show that the as-deposited film has a hardness and Young’s modulus of 8.90 GPa and 124.01 GPa, respectively. For the annealed specimen, the hardness and Young’s modulus values increase slightly to 10.44 GPa and 124.3 GPa, respectively. The TEM observation results show that Ti2Ga3 and TiAs layers are formed at the interface between the Ti thin film and the GaAs substrate during the annealing process. The Raman spectroscopy analysis results show that the Raman spectrum for the as-deposited specimen has a prominent peak associated with the GaAs substrate at 268 cm-1. By contrast, the Raman spectrum for the annealed sample shows a prominent peak associated with the Ti2Ga3 layer at 455 cm-1.
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Keywords: Nanoindentation, GaAs, Microstructural evolution, Annealing, Thin films.
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©
2018
CSME , ISSN 0257-9731
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