四针氧化锌制备及其场致发射特性

Synthesis of Tetrapod-like Zinc Oxide and Its Field Emission Characteristic

采用了VS(Vapor-Solid)的方法制备了四针状ZnO,以此作为场致电子发射的冷阴极材料。并对材料进行了扫描电镜(SEM)和X射线粉末衍射(XRD)测试分析,揭示其表面形态和晶体结构。同时将阴极与印刷有荧光粉的阳极板组装成二极管结构场致发射显示屏,并进行了场致发射特性实验。该二极管结构的开启电压为3.6V/μm,其阈值电压为6.6V/μm,相应的电流密度为0.2mA/cm2,并且具有稳定的电流密度和均匀的显示效果。实验证明ZnO是一种优良的场致发射冷阴极材料,具有广阔的应用前景。

Zinc oxide is a Ⅱ-Ⅳ compound semiconductor with a direct wide bandgap （3.37 eV） and large exciton binding energy （60 meV）. Several methods have been reported for the synthesis of one-dimensional （1D） ZnO nanostructures such as nanowires, nanorods, and nanobelts. Comparing to carbon-based materials, the ZnO nanostructure has a unique advantage. Using carbon-based materials, we have to encounter a strict requirement on vacuum. If not, it will be oxidized with the growth of vacuum and temperature. ZnO nanostructure would last longer under the same vacuum for carbon-based FE device. The tetrapod-like zinc oxide synthesized by Vapor-Solid method was applied to the field emission display as the cold cathode material. Our ZnO nanostructures were prepared by oxidizing Zn vapor in a horizontal tube furnace. The source material was Zn （99.9%） powder, which was loaded in a horizontal quartz tube placed in the constant temperature zone of the tube furnace. Ar at a flow rate of 300 sccm was used first to purge the reactor for 30 min. Then the furnace was heated to 850 ℃ at a heating rate of 25 ℃/min and kept at 850 ℃ for 30 min at a flow rate of 70 sccm Ar and 40 sccm 02. Finally, after cooling down the furnace naturally to room temperature under the protection of an Ar flow, the fluffy, white ZnO was collected from the quartz tube. We introduced SEM and XRD to show the morphology and structure of the tetrapod-like zinc oxide. The field emission characteristics are evaluated by the simplified Fowler-Nordheim （FN） equation J=A（β^2V^2/φd^2^）exp（-Bφ^3/2d/βV）where J is the current density, A and B are constants with values of A =1.56×10^-10A·V^-2·eV,B=6.8×10^3V·eV^-3/2·μm^-1,respectively,β is a field enhancement factor which quantifies the field enhancement due to microstructure roughness,φ is the work function of ZnO（5.3 eV）,d is a distance between the anode and cathode and V is the applied voltage. The characteristic of the diode structure was researched and the anode display image was presented. The turn-on field was 3.6 V ·μm ^-1 and the threshold field was 6.6 V/l^m with the current density of 0.2 mA · cm ^-2. From the stable field emission and uniform display image, we can conclude that the tetrapod-like zinc oxide is an excellent cold cathode material for field emission and has a potential application in the vacuum nano-electronics.