Defect-Enhanced Field Emission from WO₃ Nanowires for Flat-Panel X-ray Sources

Achieving high current emission from one-dimensional nanowire (NW) field emitters is essential for their application as X-ray sources. In this study, field emission (FE) from tungsten trioxide NWs (WO3 NWs) was studied, and defects were found to be responsible for the high electron emission current density. A high current density of 13.75 mA/cm2 was achieved from large area, uniformly patterned, and defect-rich monoclinic WO3 NWs, which were grown directly on indium tin oxide (ITO) glass. Comparative investigations were carried out on the field emission properties of individual NWs with different defect concentrations. The results indicated that defect-related electrical transport was the source of such high emission current. This conclusion was further confirmed by a theoretical calculation that considered both defect-related electrical transport and Joule heating in the FE process. The conductivity induced by the defects increases with rising temperature, and this mechanism regulated the Joule heating during emission and helped to achieve high current density. Furthermore, a flat panel X-ray source device using as-grown defect-rich WO3 NWs as a cold cathode was fabricated and used to image various objects. Clear X-ray images with a spatial resolution of approximately 25 μm were obtained.