Gallium nitride nanowires (GaN-NWs) are systems of interest for mechanical resonance-based sensors due to their small mass and, in the case of c-axis NWs, high mechanical quality (Q) factors of 10,000100,000. We report on singly-clamped NW mechanical cantilevers of roughly 100nm diameter and 15m length that resonate near 1MHz and describe the behavior of GaN-NW resonant frequencies and Q factors following coating with various materials deposited by atomic layer deposition (ALD), including alumina (Al2O3), ruthenium (Ru), and platinum (Pt). Changes in the GaN-NW resonant frequencies with ALD deposition clearly distinguish conformal film growth versus island film growth. Conformal films lead to a stiffening of the NW and typically increase resonant frequency, whereas island films simply increase the NW mass and cause decreased resonant frequencies. We find that conformal growth of ALD alumina leads to stiffening of ∼4 kHz per nm of alumina, in agreement with previously measured material properties. Conformal growth of Ru and Pt, respectively, qualitatively confirm our analytical predictions of positive and negative resonant frequency shifts. Island growth of ALD Ru has demonstrated a decrease in resonant frequency consistent with mass loading of ∼0.2 fg for a 150 ALD-cycle film, also consistent with analytical predictions. Resonant Q factors are found to decrease with ALD film growth, offering the additional possibility of studying mechanical dissipation processes associated with the ALD-NW composite structures.
Citation: Sensors and Actuators A-Physical
Pub Type: Journals
Atomic layer deposition, Crystal resonators, Gallium compounds, Molecular beam epitaxial growth Nanoelectronics, Nanowires, Piezoelectric oscillations, Piezoelectric semiconductors, Q factor Resonators, Wide band gap semiconductors, IIIV semiconductorsnanoelectronics, nanowires, piezoelectric oscillations, piezoelectric semiconductors, Q factor, wide band gap semiconductors, resonators