Supplementary Information
Highly Flexible and Robust N-doped SiC Nanoneedle Field Emitters
Shanliang Chen1,2, Pengzhan Ying2, Lin Wang1, Guodong Wei1, Fengmei Gao1, Jinju
Zheng1, Minhui Shang1, Zuobao Yang1, Weiyou Yang1,* and Tom Wu3,
1
2
Institute of Materials, Ningbo University of Technology, Ningbo City, 315016, P.R. China.
School of Material Science and Engineering, China University of Mining and Technology, Xuzhou
City, 221116, P.R. China.
3
Physical Sciences and Engineering Division, King Abdullah University of Science and Technology,
Thuwal 23955-6900, Saudi Arabia.
Corresponding authors. E-mails: weiyouyang@tsinghua.org.cn (W. Yang) and tao.wu@kaust.edu.sa (T.
Wu)
1
Figure S1. Molecular structure of the precursors polysilazane (PSN).
2
Figure S2. Typical SEM images of the carbon fiber substrate before (a) and after (b) growing SiC
nanostructures of sample S1. (c) The SAED pattern recorded from the SiC nanoneedle. (d) Element
mapping of N dopants within the body of SiC nanoneedle.
3
Figure S3. (a) A typical SEM image of the obtained quasialigned SiC nanowires arrays of sample S2. (b)
A typical TEM image showing the tip of an individual SiC nanowire. (c-d) Corresponding SAED
pattern and HRTEM image recorded from the marked area of A in (b). (e) A representative element
mapping of N dopants within the SiC nanowire.
4
Figure S4. Typical SEM images of the obtained sample S3 under different magnifications.
5
Figure S5. A representative EDS spectrum recorded from the catalytic particle of sample S2 (marked
area of B in Figure S3b).
6
Proposed Mechanism for Doping Controlled Growth of SiC Nanowires
The growth of the SiC nanowires could be briefly described by the step-by-step schematics shown
in Figure S4(a): i) PSN polymeric precursors are converted into SiCN(O) amorphous ceramics when
heated up to 1000 °C1 and the vapor phases such as SiO and CO are released as the temperature
continues to rise (shown as step I);2 ii) With the further increase of the temperatures, the vapor phases
would react with the molten catalyst, leading to the formation of Co catalyst alloy droplets on the
substrate surface (shown as step II); iii) During the decrease of the pyrolysis temperatures, the
continuous dissolution and precipitation of vapor phases within the liquid catalytic droplets would
initiate the nucleation and growth of SiC nanowires (shown as step III-V). Meanwhile, the N atoms
coming from the gas mixtures would undergo the similar dissolution and precipitation process, which
leads to the incorporation of N into the crystal lattice via the formations of substitutional solid solutions
and/or interstitial solid ones (shown as Figure S4(b)).3 The correlation between the N doping levels of
~4.39, 5.78 and 7.32 at% and the morphologies of the samples S1, S2 and S3 implies that a higher
concentration of N2 within the N2/Ar gas mixture could favor a bigger catalyst droplet and higher N
doping level in SiC nanostructures. These could be attributed to two main reasons. One is the different
physical properties between N2 and Ar (e.g., the respective thermal conductivities of N2 and Ar at room
temperature is 0.02475 and 0.01795 W (mk)-1). For the growth of SiC nanostructures based on the VLS
process, the catalyst droplets cannot be considered as an adiabatic or isothermal system, because of the
radiative losses and conductive heat transfer between the droplets and surrounding vapors.4 The higher
N2 content with a higher thermal conductivity around the catalyst droplets would facilitate the heat
transfer (shown as Figure S4(c)) and makes the droplet temperature drops faster, which allows the
7
droplet temperature closer to that of the furnace, thus weakening the thermal evaporation and resulting
in the grown SiC nanowires with a larger catalyst droplet and body diameter. The other fact is that a
higher N2 bias pressure could makes more N atoms dissolved into the liquid catalyst droplets, and in
turn, resulting in a higher N doping levels and a bigger size of the liquid catalyst droplets, which leads
to the growth of the SiC nanostructure with bigger catalytic droplets and nanowires diameters (Figure 1,
3 and Figure S2 and S3). These results clearly suggest that the gas mixture compositions with various
ratios of N2:Ar play a profound role on the growth of flexible quasialigned SiC nanoarrays, in which the
morphologies and N-doping levels can be tailored by adjusting the gas mixture compositions.
Figure S6. Schematic illustration for doping controlled VLS growth of SiC nanostructures.
8
Figure S7. Schematic diagram of the experimental setup used for the measurement of field emission
properties of SiC field emitters.
9
Figure S8. (a-c) The typical SEM images of N-doped SiC nanoneedles after FE operation of sample S1,
S2-1 and S3-1.
10
Table S1. Turn-on and threshold fieldsa of typical nanostructured flexible emitters.
Emitters
Turn-on fields
(V/μm)
Threshold fields
(V/μm)
Ref.
n-type SiC nanoneedles flexible emitters
1.11-1.38
1.55-1.79
this work
Oriented CuO nanoknife arrays
0.9
--
5
SnO2 nanowires arrays
3.3
4.5
6
N-doped 3C-SiC nanoneedles
~1.1
--
7
Patterned carbon nanotube arrays
0.4
0.84
8
Tapered SiC Nanowires
~1.2
--
9
Carbon nanoparticles
1.33
2.8 (10 mA/ cm2)
10
Highly wrinkled graphene
1.18
1.43 (0.2 mA/ cm2)
11
Tungsten oxide nanowires
--
4.3 (10 mA/ cm2)
12
B-doped 3C-SiC nanowires
1.35
1.70
13
N-doped nanoporous SiC
4.4-9.6
--
14
Well-aligned SiC nanowires arrays
1.3
2.2
15
Al2O3-decorated tubular SiC
2.4
5.37 (10 mA/ cm2)
16
Tubular β-SiC
5
10 (10 mA/ cm2)
17
Aligned SiC porous nanowires
2.3-2.9
--
18
β-SiC nanowires
--
4
19
β-SiC nanoarchitectures
12
--
20
Bamboo-like β-SiC nanowires
10.1
--
21
SiC nanowires/nanorods
3.33
5.77 (10 mA/ cm2)
22
Nonaligned SiC nanowires
3.1-3.5
--
23
Core-shell SiC-SiO2 nanowires
3.3-4.5
--
24
Vertically aligned LaB6 nanowires arrays
1.82
2.48
25
Conical shape GaN nanorods
3.35
--
26
SnO2 nanowires
3.5
4.63
27
WO3 nanowires
1.8
3.3
28
Typical
flexible
emitters based
on carbon
fabric
substrates
Typical SiC
nanostructured
field emitters
on rigid
substrates
11
Ultrathin BN nanosheets
1.9
4.65 (10 mA/ cm2)
29
Typical
Single-crystalline CdS nanobelts
3.7
9.3
30
inorganic
Ordered CdS nanostructure arrays
12.2
15.7 (0.1 mA/ cm2)
31
semiconductor
Single-crystalline PrB6 nanorods
0.95-2.80
3.55-6.99
32
nanostructured
Ultrafine ZnS nanobelts
3.47
--
33
emitters
ZnS nanobelts quasi-arrays
3.55
--
34
Si nanowires
--
0.7
35
Aligned untralong ZnO nanobelts
1.3
2.9
36
Si-doped AlN nanoneedle array
1.8
4.6 (10 mA/ cm2)
37
TaSi2 nanowires
4-4.5
6 (10 mA/ cm2)
38
Co5Ge7 nanowire and nanobelts arrays
1.6
--
39
a
The turn-on and threshold fields required to generate an emission current density of 10 μA/cm2 and 1 mA/cm2,
respectively. If other values are used, it will be mentioned separately.
References
1
Dhamne, A., Xu, W., Fookes, B. G., Fan, Y., Zhang, L., Burton, S., Hu, J., Ford, J. & An, L. Polymer-ceramic
conversion of liquid polyaluminasilazanes for SiAlCN ceramics. J. Am. Ceram. Soc. 88, 2415-2419 (2005).
2
Li, Y., Liang, Y. & Hu, Z. Formation and characterization of α-Si3N4 whiskers from laser synthesized nano
amorphous Si-N-C powders. Ceram Int. 21, 59-64 (1995).
3
He, Z., Wang, L., Gao, F., Wei, G., Zheng, J., Cheng, X., Tang, B. & Yang, W. Synthesis of n-type SiC nanowires
with tailored doping levels. CrystEngComm 15:2354-2358 (2013).
4
Zhang, D., Alkhateeb, A., Han, H., Mahmood, H., McIlroy, D. N. & Norton, M. G. Silicon carbide nanosprings.
Nano Lett. 3, 983-987 (2003).
5
Das, S., Saha, S., Sen, D., Ghorai, U. K., Banerjee, D. & Chattopadhyay, K. K. Highly oriented cupric oxide
nanoknife arrays on flexible carbon fabric as high performing cold cathode emitter. J. Mater. Chem. C 2,
1321-1330 (2014).
6
Deng, K., Lu, H., Shi, Z., Liu, Q. & Li, L. Flexible three-dimensional SnO2 nanowire arrays: atomic layer
12
deposition-assisted synthesis, excellent photodetectors, and field emitters. ACS Appl. Mater. Inter. 5, 7845-7851
(2013).
7
Zhang, X., Chen, Y., Liu, W., Xue, W., Li, J. & Xie, Z. Growth of n-type 3C-SiC nanoneedles on carbon fabric:
toward extremely flexible field emission devices. J. Mater. Chem. C 1, 6479-6486 (2013).
8
Liu, N., Fang, G., Zeng, W., Zhou, H., Long, H. & Zhao, X. Enhanced field emission from three-dimensional
patterned carbon nanotube arrays grown on flexible carbon cloth. J. Mater. Chem. 22, 3478-3484 (2012).
9
Wu, R., Zhou, K., Wei, J., Huang, Y., Su, F., Chen, J. & Wang, L. Growth of tapered SiC nanowires on flexible
carbon fabric: toward field emission applications. J. Phys. Chem. C 116, 12940-12945 (2012).
10 Yuan, L., Tao, Y., Chen, J., Dai, J., Song, T., Ruan, M., Ma, Z., Gong, L., Liu, K., Zhang, X., Hu, X., Zhou, J. &
Wang, Z. Carbon nanoparticles on carbon fabric for flexible and high-performance field emitters. Adv. Funct.
Mater. 21, 2150-2154 (2011).
11 Maiti, U., Maiti, S., Thapa, R. & Chattopadhyay, K. Flexible cold cathode with ultralow threshold field designed
through wet chemical route. Nanotechnology 21, 505701 (2010).
12 Zhang, X., Gong, L., Liu, K., Cao, Y., Xiao, X., Sun, W., Hu, X., Gao, Y., Chen, J., Zhou, J. & Wang, Z. Tungsten
oxide nanowires grown on carbon cloth as a flexible cold cathode. Adv. Mater. 22, 5292-5296 (2010).
13 Yang, Y., Yang, H., Wei, G., Wang, L., Shang, M., Yang, Z., Tang, B. & Yang, W. Enhanced field emission of
p-type 3C-SiC nanowires with B dopants and sharp corners. J. Mater. Chem. C 2, 4515-4520 (2014).
14 Kang, M. G., Lezec, H. J. & Sharifi, F. Stable field emission from nanoporous silicon carbide. Nanotechnology 24,
065201 (2013).
15 Wu, R., Zhou, K., Qian, X., Wei, J., Tao, Y., Chorng Haur, S., Wang, L. & Huang Y. Well-aligned SiC nanoneedle
arrays for excellent field emitters. Mater. Lett. 91, 220-223 (2013).
16 Cui, H., Gong, L., Yang, G., Sun, Y., Chen, J. & Wang, C. Enhanced field emission property of a novel Al2O3
nanoparticle-decorated tubular SiC emitter with low turn-on and threshold field. Phys. Chem. Chem. Phys. 13,
985-990 (2011).
17 Cui, H., Sun, Y., Yang, G., Chen, J., Jiang, D. & Wang, C. Template-and catalyst-free synthesis, growth
mechanism and excellent field emission properties of large scale single-crystalline tubular β-SiC. Chem. Commun.
6243-6245 (2009).
18 Yang, Y., Meng, G., Liu, X., Zhang, L., Hu, Z., He, C. & Hu, Y. Aligned SiC porous nanowire arrays with
excellent field emission properties converted from si nanowires on silicon wafer. J. Phys. Chem. C 112,
20126-20130 (2008).
19 Kim, D. W., Choi, Y, J., Choi, K. J., Park, J. G., Park, J. H., Pimenov, S. M., Frolov, V. D., Abanshin, N. P.,
Gorfinkel, B. I., Rossukanyi, N. M. & Rukovishnikov, A. I. Stable field emission performance of
SiC-nanowire-based cathodes. Nanotechnology 19, 225706 (2008).
20 Shen, G., Bando, Y. & Golberg, D. Self-assembled hierarchical single-crystalline β-SiC nanoarchitectures. Cryst.
Growth Des. 7, 35-38 (2007).
21 Shen, G., Bando, Y., Ye, C., Liu, B. & Golberg, D. Synthesis, characterization and field-emission properties of
13
bamboo-like β-SiC nanowires. Nanotechnology 17, 3468 (2006).
22 Deng, S., Li, Z., Wang, W., Xu, N., Zhou, J., Zheng, X., Xu, H., Chen, J. & She, J. Field emission study of SiC
nanowires/nanorods directly grown on SiC ceramic substrate. Appl. Phys. Lett. 89, 023118-023118-3 (2006).
23 Zhou, W., Wu, Y., Kong, E. S. W., Zhu, F. & Hou, Z. Zhang Y. Field emission from nonaligned SiC nanowires.
Appl. Sur. Sci. 253, 2056-2058 (2006).
24 Ryu, Y., Tak, Y. & Yong, K. Direct growth of core-shell SiC-SiO2 nanowires and field emission characteristics.
Nanotechnology 16, S370 (2005).
25 Xu, J., Hou, G., Li, H., Zhai, T., Dong, B., Yan, H., Wang Y., Yu B., Bando, Y. & Golberg D. Fabrication of
vertically aligned single-crystalline lanthanum hexaboride nanowire arrays and investigation of their field
emission. NPG Asia Mater. 5, e5 (32013).
26 Nabi, G., Cao, C., Hussain, S., Khan, W. S., Sagar, R., Ali, Z., Butt, F. K,. Usman, Z. & Yu D. Synthesis,
photoluminescence and field emission properties of well aligned/well patterned conical shape GaN nanorods.
CrystEngComm 14, 8492-8498 (2012).
27 Fang, X., Yan, J., Hu, L., Liu, H., Lee, P. S. Thin SnO2 nanowires with uniform diameter as excellent field
emitters: a stability of more than 2400 minutes. Adv. Funct. Mater. 22, 1613-1622 (2012).
28 Li, L., Zhang, Y., Fang, X., Zhai, T., Liao, M., Sun, X., Koide, Y., Bando, Y. & Golberg D. WO3 nanowires on
carbon papers: electronic transport, improved ultraviolet-light photodetectors and excellent field emitters. J. Mater.
Chem. 21, 6525-6530 (2011).
29 Chen, Z. G. & Zou, J. Field emitters: ultrathin BN nanosheets protruded from BN fibers. J. Mater. Chem. 21,
1191-1195 (2011).
30 Li, L., Wu, P., Fang, X., Zhai, T., Dai, L., Liao, M., Koide, Y., Wang, H., Bando, Y. & Golberg D.
Single-crystalline CdS nanobelts for excellent field-emitters and ultrahigh quantum-efficiency photodetectors. Adv.
Mater. 22, 3161-3165 (2010).
31 Zhai, T., Fang, X., Bando, Y., Liao, Q., Xu, X., Zeng, H., Ma, Y., Yao, J. & Golberg, D. Morphology-dependent
stimulated emission and field emission of ordered CdS nanostructure arrays. ACS Nano 3, 9-959 (2009).
32 Zhang, Q. Y., Xu, J. Q., Zhao, Y. M., Ji, X. H. & Lau, S. P. Fabrication of large-scale single-crystalline PrB6
nanorods and their temperature-dependent electron field emission. Adv. Funct. Mater. 19, 742-747 (2009).
33 Fang, X., Bando, Y., Shen, G., Ye, C., Gautam, U. K., Costa, P. M., Zhi, C., Tang, C. & Golberg, D. Ultrafine ZnS
nanobelts as field emitters. Adv. Mater. 19, 2593-2596 (2007).
34 Fang, X., Bando, Y., Ye, C. & Golberg, D. Crystal orientation-ordered ZnS nanobelt quasi-arrays and their
enhanced field-emission. Chem. Commun. 3048-3050 (2007).
35 Zeng B, Xiong, G., Chen, S., Wang, W., Wang, D. & Ren, Z. Field emission of silicon nanowires grown on carbon
cloth. Appl. Phys. Lett. 90, 033112 (2007).
36 Wang, W. Z., Zeng, B. Q., Yang, J., Poudel, B., Huang, J., Naughton, M. J.& Ren Z. Aligned ultralong ZnO
nanobelts and their enhanced field emission. Adv. Mater. 18, 3275-3278 (2006).
14
37 Tang, Y., Cong, H., Wang, Z. & Cheng, H. M. Catalyst-seeded synthesis and field emission properties of
flowerlike Si-doped AlN nanoneedle array. Appl. Phys. Lett. 89, 253112—3 (2006).
38 Chueh, Y. L., Ko, M. T., Chou, L. J., Chen, L. J., Wu, C. S. & Chen, C. D. TaSi2 nanowires: a potential field
emitter and interconnect. Nano Lett. 6, 1637-1644 (2006).
39 Yoon, H., Seo, K., Bagkar, N., In, J., Park, J., Kim, J. & Kim, B. Vertical epitaxial Co5Ge7 nanowire and nanobelt
arrays on a thin graphitic layer for flexible field emission displays. Adv. Mater. 21, 4979-4982 (2009).
15