Much effort has been devoted to the development of cold cathodes in field emission flat panel display and vacuum microelectronic devices. Electron field emission from various nanostructure materials has drawn significant attention of the industrial and scientific communities over world wide. One of the cold cathodes is zinc oxide (ZnO). ZnO-based nanostructure materials have attracted great interest recently due to their potential applications such as ultraviolet nanowire nanolasers

gas sensors

solar cells and field emission (FE) devices. 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 O

2

. 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

2

V

2

/Φ

d

2

)exp(-

B

Φ

3/2

d

/β

V

)

where

J

is the current density

A

and

B

are constants with values of

A

=1.56×10

-10

A·V

-2

·eV

B

=6.8×10

3

V·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/μm 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.