AI Insight
Researchers successfully grew aluminum-scandium nitride (AlScN) nanowires with varying scandium content using molecular beam epitaxy on conductive titanium nitride substrates and integrated them into piezoelectric nanogenerators. The nanowire-based devices achieved piezoelectric charge coefficients of up to 8.5 pC/N at 32% scandium content, nearly double that of pure aluminum nitride. Despite lower charge response compared to thin films, the nanowire-polymer composite architecture demonstrated higher voltage output and comparable energy harvesting efficiency due to reduced dielectric permittivity.
Why it matters
This work advances the development of nanoscale energy harvesting devices that can convert mechanical vibrations into electricity, with potential applications in self-powered sensors, wearable electronics, and Internet of Things devices. The study also provides design principles for optimizing nanowire-based piezoelectric generators, identifying device architecture as the key factor limiting performance.
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Abstract: We study the molecular beam epitaxy of self-assembled Al$mathrm{_{1-x}}$Sc$mathrm{_{x}}$N nanowires on conductive TiN layers and demonstrate their application in piezoelectric nanogenerators. Wurtzite Al$mathrm{_{1-x}}$Sc$mathrm{_{x}}$N nanowires with uniform Sc incorporation are grown across a wide composition range (0<x<0.35). At substrate temperatures below 700 $^circ{}$C, these nanowires exhibit an inversely tapered morphology, whereas higher temperatures favor the nucleation of additional branches due to a phase separation of Al$mathrm{_{1-x}}$Sc$mathrm{_{x}}$N into wurtzite AlN and rock-salt ScN. Phase-pure Al$mathrm{_{1-x}}$Sc$mathrm{_{x}}$N nanowires are integrated into vertical nanogenerators, where the metallic TiN substrate serves as bottom electrode. The fabricated polymer-nanowire composite devices achieve effective piezoelectric charge coefficients of up to 8.5 pC N$^{-1}$ at x=0.32, thus exceeding the piezoelectric response of bulk AlN by nearly a factor of two. Although the charge response remains lower compared to Al$mathrm{_{1-x}}$Sc$mathrm{_{x}}$N thin films, the reduced effective dielectric permittivity of the nanowire-polymer composites compensates the reduction in piezoelectric charge coefficient, eventually yielding a higher voltage response and comparable energy harvesting efficiency. Finally, effective medium modeling reveals that the device architecture is the primary factor limiting performance, providing general design principles for highly efficient nanowire-based piezoelectric energy harvesters.