Zinc oxide is a widely explored semiconductor material in the fields of nanoelectronics, biosensors, and energy storage, owing to its wide band gap and tunable excitonic and optical properties. In addition to various technological applications, free-standing films are ideal for understanding the properties of ultra-thin films without the effect of supporting substrates. In this work, we establish a simple method for realizing large-scale free-standing ZnO films based on atomic layer deposition (ALD). Following the atomic layer deposition of ZnO on planar and micro-structured sacrificial polymer surfaces, the sacrificial layer is dissolved to release free-standing ZnO films. The thickness of the free-standing films can be precisely controlled down to 1 nm. The free-standing films can be transferred to arbitrary surfaces and TEM grids for further investigation. The transferred thin films retained their planar or structural configuration, evidencing the excellent mechanical stability of the free-standing structures. In-situ ellipsometry measurements and atomic force microscopy revealed the preserved thickness and surface morphology of the ZnO films after their release from the sacrificial surface. We have studied the mechanical properties of ultra-thin ZnO films using strain-induced elastic buckling instability for mechanical measurements, after transferring them to compliant polymer substrates. In conclusion, we introduce a facile method for achieving large-scale, free-standing, ultra-thin ZnO films and demonstrate their excellent mechanical stability.

Ultra-thin, free-standing atomic layer deposited ZnO films

ACS Spring 2022

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