Field emission property from Al:ZnO whiskers modified by amorphous carbon and related films

 

 

A new type of the ceramic field emitter was designed using the chemical vapor deposition process.  There are two major features on the materials that construct the emitter: electrically conductive Al:ZnO whisker with extremely sharp tip and amorphous carbon and related coating with relatively low electron affinity at the tip region. Some aggregations of whiskers were synthesized as a function of the radius of curvature at the whisker tip.  In addition, four types of amorphous coatings were provided for this experiment: C:H, CNx:H with C-H and N-H terminations, CNx:H with N-H termination and CNx films.  The field emission property was influenced by not only the radius of curvature at the tip but also the termination structure of the amorphous carbon and related films. 

 

 

 Al:ZnO whiskers were prepared using an atmospheric CVD apparatus that was previously employed in obtaining ZnO whiskers.  The reactants, Zn(C5H7O2)2 (Soekawa Chemical Co., quoted purity of 99.9%) and Al(C5H7O2)3 (Soekawa Chemical Co., quoted purity of 99.9%), were loaded into a vaporizer and vaporized at 115 .  The inside temperature of the vaporizer measured using a K-type thermocouple is defined as the vaporizing temperature.  The reactant vapor was first carried by nitrogen gas flowing at a rate of 1.2 dm3/min and then sprayed from the metallic nozzle directly onto the n-type Silicon (Shin-etsu Semiconductor Co., resistivity of 2.00~50.0 cm) substrate mounted on the electric heater.  The substrate was heated to 550C using the electric heater.  The surface temperature measured using the K-type thermocouple is defined as the substrate temperature.  The reactants, Zn(C5H7O2)2 and Al(C5H7O2)3, were immediately decomposed by the heat from the substrate heater to form whiskers.  The distance between the nozzle and the substrate was maintained at 15 mm throughout the experiments. 

The amorphous carbon and related films were prepared by several chemical-vapor deposition (CVD) methods. The a-C:H film was deposited using an electron cyclotron resonance (ECR) plasma-enhanced CVD apparatus with a gas mixture of CH4+H2.  The a-CNx:H and a-CNx films were deposited using a microwave plasma CVD apparatus.13)  CH3CN (nacalai tesque, quoted purity of 99.5%) and BrCN (nacalai tesque, quoted purity of 95%) were provided as the source material. These materials initially possess a little amount of water. Hydrogen in a-CNx:H film was offered from water in the source material.  Two types of a-CNx:H films, with and without CH terminations, were synthesized. When a-CNx film was formed, water was removed from reactant using P2O5 powder. 

 

Figures show two typical photographs of the heart-type and RGB displays operated by the cold emitter formed with the Al:ZnO whisker coated a-CNx:H film.  The Y2O3:(Eu, Tb, Tm) red, green and blue phosphors were deposited on the anode electrode using an atmospheric CVD apparatus and excited by the field emitted electrons at an operating voltage of ~600 V, implying the electric field of 2 V/mm. Very strong luminescence was observed entirely the area in which phosphor was deposited.

 

References

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