A method for suppressing impurities in GaN thin films grown via plasma-enhanced atomic deposition (PEALD) through the in situ pretreatment of Si (100) substrate with plasma was developed. This approach leads to a superior GaN/Si (100) interface. After pretreatment, the thickness of the interfacial layer between GaN films and the substrates decreases from 2.0 to 1.6 nm, and the oxygen impurity content at the GaN/ Si (100) interface reduces from 34 to 12%. The pretreated GaN films exhibit thinner amorphous transition GaN layer of 5.3 nm in comparison with those nonpretreated of 18.0 nm, which indicates the improvement of crystallinity of GaN. High-quality GaN films with enhanced density are obtained because of the pretreatment. This promising approach is considered to facilitate the growth of high-quality thin films via PEALD.

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The discovery of two-dimensional (2D) materials has gained worldwide attention owing to their extraordinary optical, electrical, and mechanical properties. Due to their atomic layer thicknesses, the emerging 2D materials have great advantages of enhanced interaction strength, broad operating bandwidth, and ultralow power consumption for optoelectromechanical coupling. The van der Waals (vdW) epitaxy or multidimensional integration of 2D material family provides a promising platform for on-chip advanced nano-optoelectromechanical systems (NOEMS). Here, we provide a comprehensive review on the nanomechanical properties of 2D materials and the recent advances of 2D-materials-integrated nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS). By utilizing active nanophotonics and optoelectronics as the interface, 2D active NOEMS and their coupling effects are particularly highlighted at the 2D atomic scale. Finally, we share our viewpoints on the future perspectives and key challenges of scalable 2D-materials-integrated active NOEMS for on-chip miniaturized, lightweight, and multifunctional integration applications.

The growth of high-quality epitaxial gallium nitride (GaN) thin films is achieved by using a baking and plasma pretreatment of the substrate prior to the GaN plasma-enhanced atomic layer deposition (PE-ALD). It is found that such pretreatment makes the GaN films grow coherently on sapphire substrates, following a layer-by-layer growth mechanism. The deposited GaN film shows high crystalline quality, a sharp GaN/sapphire interface, and a flat surface. The possibility of growing high-quality GaN epilayers in this way broadens the range of applications for PE-ALD in GaN-based devices.