A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18–20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

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.

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