Electrical and Computer Engineering ETDs

Publication Date

Summer 5-6-2017


Study and prediction of classical and non-classical mechanical properties of GaN is crucial due to the potential application of GaN nanowires (NWs) in piezoelectric, probe-based nanometrology, and nanolithography areas. GaN is mainly grown on sapphire substrates whose lattice constant and thermal expansion coefficient are significantly different from GaN. These discrepancies cause mechanical defects and high residual stresses and strains in GaN, which reduce its quantum efficiency.

Specifically, for nanoscale applications, the mechanical properties of materials differ significantly compared to the bulk properties due to size-effects. Therefore, it is essential to investigate the mechanical properties of GaN NWs using the non-classical solid mechanic theories, modified couple stress theory (MCST) and modified strain gradient theory (MSGT).

Experimentally the GaN NWs were prepared by using top-down approach to etch c-plane GaN layer grown in Metal Organic Chemical Vapor Deposition (MOCVD) chamber to achieve high aspect ratio NWs with high uniformity. An Atomic Force Microscope (AFM) was used to apply an infinitesimal deflection on the top of clamped-free NWs while monitoring the lateral and normal forces.

According to the MCST, the Young’s modulus, shear modulus and length scale were measured to be 323 GPa, 133 GPa and 13 nm, respectively, and according to the MSGT, they were measured to be 319 GPa, 132 GPa and 8 nm, respectively. Furthermore, a quantum mechanics based approached was conducted to estimate the classical and non-classical mechanical properties of the GaN NWs as well.


GaN nanowires, Modified Couple Stress Theory, Modified Strain Gradient Theory, Mechanical Properties

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Dr. Tito Busani

Second Committee Member

Dr. Yu-Lin Shen

Third Committee Member

Dr. Francesca Cavallo