Pressure-Induced Structural Transformations of ZnO Nanowires Probed by X-ray Diffraction

As an important wide band gap semiconductor (Eg = 3.37 eV), ZnO has a wide range of applications, such as in piezoelectric transducers, chemical sensors, optical coatings, photovoltaics, and ceramics. 3 In contrast to the corresponding bulk counterparts, nanostructured ZnO has enhanced electronic, and photoconducting properties. Because of the unique crystal quality and photonic properties, in particular, 1D ZnO nanomaterials have been used as functional units in the fabrication of electronic, piezoelectronic, electrochemical, and highly sensitive gas sensors with nanoscale dimensions. 8 Therefore, an increasing research effort has been focused on nanostructured ZnO, especially in exploring new structures, properties, as well as synthetic methods. In addition to the traditional synthetic and fabrication routes, external pressure can provide an alternative effective driving force to tune the structures and thus the properties of the nanostructured materials. Therefore, investigations of the structural and phase transformations of nanomaterials under high pressure represent a prevailingmaterials research frontier. One of the most interesting observations in those studies is that the compressed nanomaterials behave significantly differently than their corresponding bulk counterparts under pressure. For example, our previous studies on 1D nanomaterials (e.g., SnO2 nanowires and nanobelts, GaN nanowires, and BN nanotubes) have demonstrated profound implications for producing controlled structures by combined pressure morphology tuning. Under ambient conditions, ZnO has a wurtzite-type (B4) structure (space group P63mc) regardless of themorphologies. 14 17