Mechanical elasticity of vapour–liquid–solid grown GaN nanowires

Abstract

Mechanical elasticity of hexagonal wurtzite GaN nanowires with hexagonal cross sections grown through a vapour-liquid-solid (VLS) method was investigated using a three-point bending 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 spring constant, profiles were recorded over the entire length of end-supported GaN nanowires and compared to the classic elastic beam models. Profiles reveal that the bending behaviour of the smallest nanowire (57.0 nm in diameter) is as a fixed beam, while larger nanowires (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 GaN nanowires. The GaN nanowire of 57.0 nm diameter displays the lowest stiffness (0.98 N m(-1)) and the highest elastic 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 or meets the literature values for bulk single crystal and GaN nanowires with triangular cross sections from other investigators. The present results together with further tests on plastic and fracture processes will provide fundamental information for the development of GaN nanowire devices.

Tensile measurement of single crystal gallium nitride nanowires on MEMS test stages

“…[13] AFM 3-point bending on other c-axis GaN NWs found E 3 = 218-400 GPa, with a possible observation of diameter dependence of Young's modulus. [31] Elastic properties of GaN thin films and bulk crystals have been widely reported. Nanoindentation of epitaxially-grown GaN films with unspecified orientation found Young's modulus values in the range of 210-295 GPa.…”

Extracting nanowire mechanical properties from three-point bendig test

“…The so-called one dimensional (1D) nanostructures [1], such as micro/nanotube [2,3,4], nanobelt [5] and nanowire [6,7,8,9,10,11] are important types of materials used in gas sensor, high-frequency resonator, nanoscale light-emitting diodes, high resolution tip for atomic force microscope (AFM), scanning tunneling microscopes (STM) and photovoltaics etc. The mechanical properties of these 1D mi-cro/nanomaterials are of interest for both technical and theoretical reasons.…”

“…Due to its high spatial resolution and the accuracy/sensitivity of direct force measurement, bending test with AFM is commonly used for those mechanical characterizations. The 1D micro/nanomaterials in test are first suspended over either a pore of porous material [2,3,4,6], or a strip [5], or an etched hole [7], or a trench [8,9,10,11]. The AFM tip then exerts a concentrated force on some place of the suspended section to form a typical three-point bending test [7].…”

“…Here k is the effective spring stiffness of the beam and AFM measures the force-displacement ( mp F z ) curves [5,7,8,9,10,11]. F is the concentrated load exerted at the center of the beam; mp z is the beam midpoint displacement, which is also the maximum one for a clamped-clamped (C-C) beam and a hinged-hinged (H-H) beam with the load at its center.…”

“…We are fully aware that the Ag nanowires from different groups are fabricated/processed differently, which can significantly change the nanowire material properties. However, Chen et al [8,9] pointed out that the single point measurements as those done in references [2,3,4,5,6,7,10] may have the largest drawback of assuming wrong boundary conditions. The same contradicting experimental observations on other type of nanowire Young's modulus measurements are also noticed by Park and Klein [16].…”