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NANO EXPRESS

Open Access

Nanoindentation of GaSe thin films Sheng-Rui Jian1*, Shin-An Ku2, Chih-Wei Luo2 and Jenh-Yih Juang2

Abstract The structural and nanomechanical properties of GaSe thin films were investigated by means of X-ray diffraction (XRD) and nanoindentation techniques. The GaSe thin films were deposited on Si(111) substrates by pulsed laser deposition. XRD patterns reveal only the pure (000 l)-oriented reflections originating from the hexagonal GaSe phase and no trace of any impurity or additional phases. Nanoindentation results exhibit discontinuities (so-called multiple ‘pop-in’ events) in the loading segments of the load–displacement curves, and the continuous stiffness measurements indicate that the hardness and Young’s modulus of the hexagonal GaSe films are 1.8 ± 0.2 and 65.8 ± 5.6 GPa, respectively. Keywords: GaSe thin films, XRD, Nanoindentation, Hardness

Background The most unique structural feature of the family of IIIVI semiconductors is the existence of layers within which the atomic bonds are mainly covalent with a certain degree of ionic component. GaSe is a layered III-VI chalcogenide semiconductor with a number of interesting properties for electrical and nonlinear optics applications, such as compound semiconductor heterostructure devices [1], IR detectors [2], and solar cells [3]. However, while most of the previous researches have been concentrated on its electrical and optical characteristics for device applications, researches on the mechanical properties have not drawn equal attention. A quadruple layer of GaSe building block consists of two Ga and two Se sub-layers with the stacking sequence of Se-Ga-Ga-Se, where the Se-Ga and Ga-Ga bonds are covalent within the quadruple layers and the Se-Se bond between adjacent quadruple layers is due to van der Waal forces [4]. As a result, significant differences as compared to most III-V and II-VI semiconductors are expected and accurate measurements of the mechanical properties of GaSe thin films are required, since such parameters are critical for making structural elements as well as functional devices.

* Correspondence: [email protected] 1 Department of Materials Science and Engineering, I-Shou University, Main Campus No.1, Sec. 1, Syuecheng Rd., Dashu District, Kaohsiung 84001, Taiwan Full list of author information is available at the end of the article

Due to its high sensitivity, excellent resolution, and easy operation, nanoindentation has been widely used for characterizing the mechanical properties of various nanoscale materials [5,6] and thin films [7-9]. Among the mechanical properties of interest, hardness, Young’s modulus, and elastic/plastic deformation behaviors can be readily obtained from nanoindentation measurements. Through the analyses on the load–displacement curves obtained during the nanoindentation, the hardness and Young’s modulus of the test material can be easily obtained following the methods proposed by Oliver and Pharr [10]. However, in the case of thin films, the responses after certain penetration dep