Large-area profile transformation of inkjet-printed PD precursor films by slit-nozzle humidification and redrying for PdO nanofilm field emitters

The authors have developed a new system to improve the uniformity of the width and shape of inkjet-printed PdO nanofilms on large-area substrates for emitters in field-emission imaging devices. The system consists of the inkjet printing apparatus, a vacuum drying chamber, and a shape readjustment apparatus with two slit nozzles for humidification and drying. First, inkjet-printed Pd precursor ink droplets are quickly dried in vacuum drying, resulting in Pd precursor films having ringlike profiles and uniform widths. Next, in the readjustment apparatus, the films are moved and dissolved while maintaining their in-plane sizes under a linear downflow of humidified air through one slit nozzle, and then redried under a downflow of N₂ through the other slit nozzle. As a result, nonuniform profiles of films were successfully transformed into uniform profiles with the same in-plane size. After annealing, PdO nanofilms having the same profiles were obtained over the entire area of a large-area substrate.