Mechanical elasticity of vapour–liquid–solid grown GaN nanowires

Abstract

Mechanical elasticity of hexagonal wurtzite GaN nanowires with hexagonal cross sectionsgrown through a vapour–liquid–solid (VLS) method was investigated using a three-pointbending method with a digital-pulsed force mode (DPFM) atomic force microscope (AFM).In a diameter range of 57–135 nm, bending deflection and effective stiffness, or springconstant, profiles were recorded over the entire length of end-supported GaN nanowires andcompared to the classic elastic beam models. Profiles reveal that the bending behaviourof the smallest nanowire (57.0 nm in diameter) is as a fixed beam, while largernanowires (89.3–135.0 nm in diameter) all show simple-beam boundary conditions.Diameter dependence on the stiffness and elastic modulus are observed for these GaNnanowires. The GaN nanowire of 57.0 nm diameter displays the lowest stiffness(0.98 N m−1) and the highestelastic modulus (400 ± 15 GPa). But with increasing diameter, elastic modulus decreases, while stiffness increases.Elastic moduli for most tested nanowires range from 218 to 317 GPa, which approaches ormeets the literature values for bulk single crystal and GaN nanowires with triangular crosssections from other investigators. The present results together with further tests on plasticand fracture processes will provide fundamental information for the development of GaNnanowire devices.