Hierarchical Field Emission Devices - Hierarchical Nanostructures for Energy Devices - page 235

Table 10.1 Critical performance parameters of hierarchical field emitters reported
in the literature.

Turn-on field
(V mm 1 )[at
10 mAcm 2 ]

Stability:
testing time
- fluctuation Ref.

Enhancement
factor, b

d n 3 r 4 n g | 0

Hierarchical FE cathode

Single-wall CNTs on Si
microprotrusions

1.2 — — 9

Single-wall CNTs on Ag
microparticles

3.1 3641 — 10

Single-wall CNT hairpin arrays
on Si

— 2091 — 11

Multi-wall CNTs on Si pyramids 1.95 6980 — 12

Carbon nanowalls on Si
microcones

0.9 3533 90 h - 15% 13

Graphene on Si microcones 2.3 1604 90 h - 5% 14

Graphene nanostructures on
carbon fibers

0.41 24 065 2 h - 5% 15

Graphene on ZnO nanowires 1.8 10 179 2 h - 4% 16

ZnO nanosleeve-fishes 1.3 3010 — 17

ZnO tips on ZnO nanorods 5.6 2300 — 18

ZnO nanoscrewdrivers 8 — — 19

6-fold symmetrical hierarchical
ZnO nanostructures

6.1 1351 — 20

ZnO hexagonal towers 2.37 2691 — 21

Zn/ZnO hierarchical arrays 8.5 3490 — 22

ZnO/MWCNT array 1.5 — 5 h - 2% 23

Branched TiO 2 hierarchical
nanostructures

2.76 7440 — 24

TiO 2 nanostructures on carbon
fibers

2.72 5438 2 h - 3% 25

.

MoO 2 nanowires with
nanoprotrusions

0.2 42 991 1 h - 15% 26

SnO 2 sallow-like hierarchical
nanostructures

1.88 3028 2 h - 5% 27

WO 3 nanowires on carbon fibers 1.8 6900 12 h - 5% 28

Fe 2 O 3 hierarchical columnar
arrays

17.8 463 3 h - 50% 29

AlN hierarchical nanostructures 2.5 — 2 h - 7% 30

AlN multitipped nanowires 3.8 950 — 31

WS 2 nanotubes on Si microcones 1.1 3526 18 h - 15% 32

Flowerlike In-doped SnS 2 7.5 — — 33

AgTCNQ nanowire on carbon
fibers

1.72 1165 2 h -10% 34

enhancement of each CNT. Finally, novel SWCNT micro tip arrays with a
hairpin structure were fabricated on a patterned silicon wafer via tailoring
cross-stacked SWCNT sheets with a focused laser beam. 11 By using an ad-
hesive tape to modify the hairpin tip (Figure 10.2a), CNT field emitters can
provide 150 mA intrinsic emission currents with low beam noise. Such a good
field emission was ascribed to the Joule-heating-induced desorption
adsorbents off the emitter surface, the high temperature annealing effect,
and the surface morphology.