Abstract
We explore how crystallographic order and orientation affect the tribological (friction and wear) performance of gallium nitride (GaN), through experiments and theory. Friction and wear were measured in every direction on the c-plane of GaN through rotary wear experiment. This revealed a strong crystallographic orientation dependence of the sliding properties of GaN; a 60° periodicity of wear rate and friction coefficient was observed. The origin of this periodicity is rooted in the symmetry presented in wurtzite hexagonal lattice structure of III-nitrides. The lowest wear rate was found as 0.6 × 10−7 mm3/Nm with <1bar{1}00>, while the wear rate associated with <1bar{2}10> had the highest wear rate of 1.4 × 10−7 mm3/Nm. On the contrary, higher friction coefficient can be observed along <1bar{1}00> while lower friction coefficient always appeared along <1bar{2}10>. We developed a simple molecular statics approach to understand energy barriers associated with sliding and material removal; this calculated change of free energy associated with sliding revealed that there were smaller energy barriers sliding along <1bar{2}10> as compared to the <1bar{1}00> direction.
Highlights
Performance of gallium nitride (GaN), through experiments and theory
Knowing its wear performance is critical for understanding its processing[22,23,24,25] and machinability as well as the durability of GaN-based devices exposed to harsh environments, e.g., space and desert, as well as in high-frequency microelectromechanical systems (MEMS)
It is important to note that the lattice of GaN has a 30° rotation from sapphire substrate in order to minimize the strain[27,28], this means that the flat edge corresponds to the m-plane (1100) of the GaN film
Summary
Friction and wear were measured in every direction on the c-plane of GaN through rotary wear experiment This revealed a strong crystallographic orientation dependence of the sliding properties of GaN; a 60° periodicity of wear rate and friction coefficient was observed. For HCP crystal like sapphire, wear rate on basal plane along [1120] was lower than [1010]5 After these pioneering works on anisotropic friction and wear properties, more efforts have been made in exploring directionality of tribological properties for various kind of materials[8,9,10,11,12,13,14,15,16,17]. This model simulated the free energy variation when dragging wear cluster around the surface
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