C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6

. sc iencedi rec t . com

ava i lab le a t www

journal homepage: www.elsevier .com/ locate /carbon

In situ oxygen-assisted field emission treatmentfor improving the uniformity of carbon nanotubepixel arrays and the underlying mechanism

Yu Zhang, M.X. Liao, S.Z. Deng *, Jun Chen, N.S. Xu

State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Province Key Laboratory of Display Material and Technology,

School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, People’s Republic of China

A R T I C L E I N F O

Article history:

Received 15 October 2010

Accepted 4 April 2011

Available online 9 April 2011

0008-6223/$ - see front matter � 2011 Elsevidoi:10.1016/j.carbon.2011.04.006

* Corresponding author: Fax: +86 20 84037855E-mail address: stsdsz@mail.sysu.edu.cn

A B S T R A C T

An oxygen-assisted field emission treatment is introduced for improving field emission

uniformity of carbon nanotube (CNT) pixel arrays. Oxygen gas is added during the field

emission process, and the uniformity of both emission area and brightness of a CNT pixel

array are dramatically improved by 83% and 90%, respectively, without reducing emission

stability. The underlying physical mechanism for the improvements is attributed to the fact

that the oxygen oxidizes the highly emitting CNTs, resulting in their burning out. As a

result, the emitting CNTs having a too high current are removed and more and more emit-

ting CNTs with weak current can be stimulated at a higher field, leading finally to a balance

of emission from each pixel in the array.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Carbon nanotube (CNT) has been considered as excellent cold

cathode material, due to its superior field emission character-

istics such as low turn-on and threshold fields and large sus-

tainable emitting current density [1,2]. Application of CNT

cold cathode in vacuum devices has been widely investigated.

For instance, Choi et al. demonstrated several prototypes of

CNT field emission display (FED) [3–5]. We reported first flat

panel light source earlier [6] and recently a high brightness

thin film transistor liquid crystal display using this kind of

backlight source [7]. Kim et al. also demonstrated the field

emitters with lateral gate and mesh structures for backlight

unit [8,9]. The CNT pixel lighting element was also shown to

have performance meeting the requirements of outdoor large

display panels [10–12]. More recently, many progresses have

been made on CNT field emission X-ray tubes [13–15].

However, the progress to flat panel application has been

hampered by lack of control of the field emission uniformity

of large area CNTs. Devices such as FED and flat panel

er Ltd. All rights reserved

.(S.Z. Deng).

backlight source cannot work without a CNT pixel array with

satisfying field emission uniformity. There are at least two ba-

sic requirements that should be met; i.e. to grow uniform CNT

pixel array and to have a post treatment to obtain field emis-

sion uniformity. However, there still remain some technical

problems to achieve the growth uniformity of CNT cathode

arrays large enough for flat panel application. Thus, various

post treatment techniques have been developed, such as di-

rect current [16] or alternating current [17] electrical treat-

ment, electrical discharge machining [18], laser irradiation

surface treatment [19,20], plasma treatment [21,22] and ion

irradiation [23]. Oxygen was used as the reaction gas in plas-

ma treatments. Oxygen ions in plasma can bombard the CNT

and are reported to improve the properties of CNT. The oxida-

tion of CNT in vacuum was also adapted to reduce the diam-

eter distribution of CNT [24]. However, oxygen plasma will

also cause damages to all the CNTs subjected to bombard-

ment, and may not be able to improve the uniformity. So

far, the above post treatments are still needed to improve to

achieve both large area uniformity and high efficiency.

.

3300 C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6

Kim et al. reported the oxygen trimming method [25] by intro-

ducing oxygen into field emission and obtained a uniform

and stable emission from printed CNT.

In this paper, we report a simple technique similar to the

oxygen trimming method: the in situ oxygen-assisted field

emission treatment, and to further understand the change

of CNT in the treatment and its underlying physical mecha-

nism the experiments are carried out. A very small amount

of oxygen gas is inlet into the vacuum gap while a CNT pixel

array undergoes field emission. The oxygen causes more oxi-

dation to the highly emitting CNTs, including the higher CNTs

and the byproduct of defected CNTs, which has more signifi-

cant Joule heating. This can result in the burning-out of these

CNTs. The oxygen forms C–O bonds with CNTs, but does not

change the work function and stability. The oxidation effect

changes the morphology of CNTs and decreases the field

enhancement factor. As a result, the emitting CNTs having

too high current are removed and more and more emitting

CNTs with weak current in each pixel can be stimulated at

higher field and a uniform emission from each pixel in the ar-

ray can be achieved. The effect of oxygen on the field emis-

sion of CNT is investigated and physical and chemical

processes are found to involve in the treatment.

2. Experimental

Typical CNT cathode sample is an array of 12 · 12 pixels, each

of which has a diameter of 200 lm. The arrays were grown on

silicon substrate using Ni–Cr catalyst by thermal chemical va-

por deposition (CVD). The growth was carried out at 700 �C for

10 min in a mixed gas of acetylene and hydrogen and argon

with a ratio of flow rate of 20:200:200(sccm).

The experimental set-up for the in situ field emission post

treatment is illustrated in Fig. 1. The CNT array was placed on

the cathode electrode. An indium tin oxide glass was used as

anode for collecting emission electron and for generating vis-

ible light on electron impact. They were separated by 250 lm-

thick ceramic spacers. The pressure of the vacuum chamber

could be adjusted by introducing oxygen gas through a pin

valve to vary from 1.0 · 10�5 to 1.0 · 10�2 Pa. To increase the

treatment efficiency, lower oxygen pressure is adopted to in-

let more oxygen molecular to participate in the treatment;

however, under the pressure lower than 1.0 · 10�2 Pa arc

Fig. 1 – Illustration of the post treatment set-up.

discharge easily appears and destroys the CNT array. Thus,

the best oxygen pressure in process should be 1.0 · 10�2 Pa.

Before the treatment, the vacuum chamber was pumped to

1.0 · 10�5 Pa, and the field emission current–voltage (IV) char-

acteristics were measured and the field emission image was

recorded by camera. Then, during the field emission, the oxy-

gen gas was constantly introduced to the vacuum chamber to

start the treatment. The chamber pressure was maintained at

1.0 · 10�2 Pa. During the treatment, the field emission image

dynamically changed, and was monitored. The treatment

process was regularly interrupted to check if the effect has

reached the desirable result. This was done by repumping

the vacuum chamber to 1.0 · 10�5 Pa. At this point, the I–V

characteristics and field emission image were recorded again.

The total emission current, oxygen pressure and process time

were key parameters for obtaining a best result. Especially,

excess process time would damage most of the CNTs and de-

crease the number of emission sites. Excess current and oxy-

gen pressure would easily cause arc discharge and destroy the

CNT array in large area. The uniformity of CNT array degrades

when the CNT array is over treated. Therefore, it is important

to inspect the dynamic change of uniformity and optimize the

parameters. Based on the above procedure, the treatment is

also suitable for improving the uniformity of screen printed

CNT array in glass substrate.

The resultant changes of CNTs after treatment were stud-

ied by scanning electron microscopy (SEM), transmission

electron microscopy (TEM), Raman spectroscopy and X-ray

photoelectron spectroscopy (XPS). The burning process of

the CNTs was also investigated by thermogravimetric (TG)

analysis.

3. Results and discussion

Fig. 2 compares the field emission images recorded before and

after treatment. The emission current was set at 1.5 mA for

recording all the three images. The image before the treat-

ment is obviously not uniform. Some pixels do not emit and

the brightness of the pixels is not uniform either. After 1 h

treatment, all the pixels emit while the brightness is still

not uniform. After 2 h treatment, the brightness of pixels

and the emission area of pixels become much more uniform.

In order to evaluate the uniformity of a CNT cathode array,

two main factors should be considered: the pixel emission

area and brightness. To evaluate the uniformity of emission

area of pixels, the emission area of each pixel is measured

from the field emission image, and their space distribution

is shown in the histogram of Fig. 2d–f. Then the uniformity

is calculated by using the following equation [26]:

U ¼ 1� r

N

� �100%

where r represents the standard deviation of the area of the

pixels, N represents the average area of the pixels. The U

parameter reveals the area distribution uniformity of all the

pixels. The larger the value of U, the better the emission area

uniformity is.

The brightness of pixels could be indirectly measured from

the emission image too. The brightness of each pixel is con-

verted into the gray level signal by image processing software

Fig. 2 – Field emission image of the 12 · 12 CNTs array, and the corresponding pixel emission area distribution histogram and

pixel brightness distribution histogram, (a, d and g) before treatment, (b, e, and h) after 1 h treatment, and (c, f, and i) after 2 h

treatment.

C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6 3301

and divided into 255 levels, while 0 means black and 255

means white. The brightness level distribution histograms

are shown in Fig. 2g–i. The uniformity parameter of pixel

brightness is calculated by using the equation above too.

The uniformity analysis results of the CNT array before

and after the treatment is given in Table 1. The uniformity

is dramatically improved after the in situ oxygen assisted

field emission treatment. Before the treatment, the number

of emitting pixels is 131, and the emission area and bright-

ness uniformity are as low as 19% and 53%, respectively.

The histogram in Fig. 2d shows that the emission area of

pixels is dramatically different from each other. The bright-

Table 1 – Comparison of uniformity of a typical CNT array befor

Sample process Emitting pixel number Emi

Before treatment 131After 1 h treatment 144After 2 h treatment 144

ness distribution histogram in Fig. 2g shows that the bright-

ness is distributed from 20 to 200 in a wide range. After 1 h

treatment, all pixels emitted, but the brightness uniformity

is still not high. After 2 h treatment, the emission area and

brightness uniformity reaches 83% and 90%, respectively, of

which the improvements are 4.3 times and 2 times compared

to those of untreated CNT array. The emission area distribu-

tion histogram in Fig. 2f shows that the emission area of pix-

els is close to each other. The brightness distribution

histogram in Fig. 2i shows that the brightness is in a narrow

range from 140 to 180. The brightness uniformity is obviously

improved.

e and after treatment.

ssion area uniformity (%) Brightness uniformity (%)

19 5325 7983 90

3302 C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6

Fig. 3a and b shows the field emission IV characteristics

and their corresponding Fowler–Nordheim (FN) plot before

and after treatment. The threshold field (the field correspond-

ing to a current density of 10 mA/cm2) is increased from 4.0 to

6.25 V/lm after 1 h treatment, and to 8.2 V/lm after 2 h treat-

ment. The reason may be that the taller CNTs are burnt out

during treatment. Therefore, stronger electric field is re-

quired. The slopes of FN plot are increased too and the phys-

ical reason will be discussed later. The current stability test

(Fig. 3c) showed that the field emission stability after treat-

ment was good. The current stayed at around 0.98–1.05 mA

lasting for 30 h, and the fluctuation of current was 6%. It

showed that the oxygen adhesion also did not influence in

the field emission stability.

In order to find out the underlying physical mechanism of

in situ oxygen-assisted field emission treatment on the CNTs,

we carried out various investigations.

The effects of the oxygen assisted field emission on the

morphology and the microstructure of the CNTs can be seen

from the SEM and TEM images shown in Fig. 4. The taller

CNTs were cut off during the process. Fig. 4a shows that be-

fore the treatment, some CNTs are taller than the others.

While after the treatment in Fig. 4b, the taller CNTs almost

disappeared, leaving the others having the similar height.

The average thickness of CNT layer in the pixel also decreased

during the treatment and the thickness of all CNT pixels be-

Fig. 3 – (a) IV curve and (b) FN plot of CNT array before and after t

the voltage was set at 2.4 kV, (d) simulation result of the tempe

came close to each other after the treatment. It is believed

that this is the most benefit result for improving the unifor-

mity of CNT arrays.

The shortening of CNT is attributed to the oxidation of

CNT tips in high temperature. The taller CNTs emit electrons

under electric field, and the tips of CNTs generate Joule heat

and undergo a self-heating [27]. When the oxidation temper-

ature is reached, the CNT quickly burns out in oxygen

atmosphere. We use Huang’s model [28] to estimate the

temperature of the tip. We consider that Joule heat generates

in the CNT and dissipate by heat conduction to the flat

substrate, also by radiation from the wall and tip of CNT. It

expresses as the following heat equation [28],

pr2k@2Tx

@x2dx� 2prdxrðT4

x � T40Þ þ I2RðTxÞL�1dx ¼ 0

where r is the radius of CNT, k is the heat conduction coeffi-

cient, Tx is the temperature along the CNT, T0 is the ambient

temperature, r is the Stefan–Boltzmann constant, I is the

emission current, L is the length of CNT. R(Tx) is the resistance

of CNT, which strongly depends on temperature described as

follows,

RðTÞ ¼ R0ð1� aTþ bT3=2Þ

where a and b are the coefficients of temperature which are

chosen to match with experimental data. The boundary con-

he treatment, (c) current stability in 30 h after the treatment,

rature of CNT tip in functions of emission current.

Fig. 4 – The SEM and TEM images of the CNTs (a and c)

before and (b and d) after the treatment, respectively. The

TEM scale bars are 20 nm and 50 nm.

C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6 3303

dition is related to the tip of CNT and the substrate. The heat

loss by radiation from the tip apex of CNT is determined by

@TA

@x¼ �rk�1ðT4

A � T40Þ

where TA is the temperature of tip apex of CNT. The flat sub-

strate is assumed to be a heat sink, and the temperature at

the bottom of CNT is fixed at TB = T0. Solve the heat equation

with two boundary condition expressions, the tip tempera-

ture TA can be determined by the emission current. Here we

choose a typical CNT of r = 20 nm and L = 20 lm to carry on

the calculation. The parameters of CNT are the same with

Ref. [27] and they are k = 100 W/mK, r = 1, q = 3.26 · 10�5

Xsm, a = 8.5 · 10�4 K�1, b = 9.8 · 10�6 K�1, T0 = 300 K. The re-

sult in Fig. 3d showed that the tip temperature raise quickly

with the increase of emission current.

According to our previous report [28], the CNTs do not run

to vacuum breakdown under 1700 K, thus the effect of accel-

eration of CNT shortening needs the oxidation in lower tem-

perature. TG analysis in Fig. 5a shows that the weights of CNT

begins to loss and quickly decrease at around 770 K. There-

fore, in the treatment, the tip of CNT emitting a current larger

than 4.4 lA would reach and exceed the oxidation tempera-

ture of 770 K, and burn out quickly in the oxygen atmosphere.

The addition of oxygen increases the efficiency of the

treatment.

The oxygen seriously affects the surface of the long

CNTs. From the TEM pictures of Fig. 4c and d, the CNTs

have smooth surface before the treatment, while the sur-

face of the CNTs become rough with some piece of frag-

ment on the surface after the treatment. It is believed

that the oxygen reacts with the outer wall of the CNTs in

high temperature during the process, and turns the outer

surface of CNTs into amorphous carbon. The longer CNT

with more layers is damaged strongly in the treatment, be-

cause it is over the average height and catches more oxida-

tion. In addition, some kind of by-product, such as defect

and transpolyacetylene [29], also burn out during the treat-

ment. Raman scattering spectrum analysis in Fig. 5b shows

that the D peak is near 1350 cm�1, and the G peak is near

1590 cm�1. The intensity ratio of D peak to G peak ID/

IG = 0.792 before the treatment, while ID/IG = 0.798 after the

treatment. There is only little change of the ratio which

means the crystallinity of CNT does not change. However,

in the spectrum of near 1150 cm�1 in the left side of D

peak, a small peak appeared before the treatment, and dis-

appeared after the treatment (pointed by arrow in Fig. 5b).

According to the other authors [29–31], it is attributed to

the appearance of transpolyacetylene, which is the out-

growth of CNT during CVD growth. It can be easily decom-

posed in air in 870 K. During the treatment, heat and

oxygen can burn out transpolyacetylene and defective

CNT. The disappearance of by-product is beneficial to the

field emission stability of the CNT arrays due to the

improvement of unique CNT properties.

As for the other CNTs which were not damaged in the

treatment, the effect of oxygen exposure on them was also

analysed by XPS. The XPS spectra of C1s region between 278

and 298 eV before and after treatment are shown in Fig. 5c.

Both of the binding energy of C1s peak before and after treat-

ment is 285 eV. The notable change of the spectra after treat-

ment is the increasing intensity of the peak in the binding

energy range of 286–290 eV. The peak analysis result (Fig. 5d)

shows that there are two peaks at 286.3 and 288.9 eV corre-

sponding to the increasing peak region. According to the ref-

erence of XPS studies [32–35], the peaks in the range of 286–

290 eV are related to the following carbon-based chemical

bonds, C–O (286.4 eV), C–Cl (287.0 eV), C–F (287.8 eV), C@O

(287.8 eV), –COOR (288.9 eV). Among them, C–Cl and C–F never

exist in CNTs. Therefore, we can assign the peak at 286.3 eV to

C–O, at 288.9 eV to –COOH. The C@O at 287.8 eV is too weak to

be identified. It means that oxygen forms the chemical bond

with CNTs.

This oxygen bonding may result in the change of the work

function of the CNTs. We introduced the Seppen–Katamuki

(SK) chart analysis [36–38] to reveal the relative changes of

the work function / and voltage-local field enhancement fac-

tor b. The SK chart is a two dimensional diagram, of which ab-

scissa and ordinate are the intercept and the slope of FN plot,

respectively. The details are discussed by other authors earlier

[36–38]. According to the FN theory, the FN plot shows the

relation of

logðI=V2Þ ¼ aþ b � 1=V;

and the intercept a and slope b are

a ¼ logð1:4� 10�6ab2=/Þ þ 4:26=/1=2

b ¼ �2:82� 107/3=2=b

Fig. 5 – (a) TG and DSC plots of the CNTs heated in oxygen atmosphere. (b) Raman spectra of CNT before and after the

treatment. (c) C1s peak scan XPS spectra of the CNTs before and after treatment. (d) peak analysis of C1s peak region which

can divided into three peaks, they are C1s, C–O and –COOR.

Fig. 6 – Change of field emission character before and after

the treatment in the SK chart.

3304 C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6

a represents the effective emitting area which is related with

the b and / by the relation of a ¼ a0 expð�9:74� 107cb/1=2Þ,where a0 is the emitting area, c is the effect constant of emit-

ter shape, which are introduced from Gomer’s semi-empirical

assumptions [39]. In this calculation, a0 is 4.52 · 10�3 cm2 and

c is 7.9 · 10�13 according to the experimental data fitting and

other reports [38,40]. So, the two variables / and b decide

the intercept and slope. If we substitute the equation of b

and a into the equation of a, we can obtain the equi-work

function line and equi-field enhancement factor line by using

numerical calculation. The work function of CNT before treat-

ment was assumed to be 5 eV according to the other reports

[38,40]. As shown in Fig. 61, the solid and broken lines repre-

sent the equi-work function line and equi-field enhancement

factor line, respectively.

The slope and intercept of FN plots of CNT array before and

after the treatment are derived from the FN plot in Fig. 3b, and

marked in the SK chart in Fig. 6. The three green, red and blue

points represent the sample states before, after 1 h and after

2 h treatment. The positions are distributed along the same

equi-work function line in 5 eV from upper left to lower right.

That means, according to the interpretation above, that the

work function is not changed, while the field enhancement

1 For interpretation of color in Fig. 6, the reader is referred to the w

factor decreases dramatically after the treatment. Field

enhancement factor is related with the aspect ratio and the

apex radius of CNTs. As described above, during the

treatment, the taller CNTs are cutting off to improve the

eb version of this article.

C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6 3305

uniformity, so the aspect ratio of CNTs decreases. It is the rea-

son that the field enhancement factor reduced and the

threshold field increased. As for the invariable work function

of CNTs, it is suggested that the oxygen adhesion CNTs have

the similar work function as untreated CNTs. The C–O bonds

on the surface of CNTs have no significant influence on the

work function of CNTs.

4. Conclusions

We have developed an oxygen-assisted field emission post

treatment to improve the field emission uniformity of CNT ar-

rays. In this treatment, oxygen is introduced into the field

emission to accelerate the burning out the protrusive CNTs.

The oxygen causes more oxidation to the highly emitting

CNTs, resulting in their removing and more and more emit-

ting CNTs with weak current can be stimulated at higher field.

Thus, a final balance can be achieved of emission from each

pixel in the array. After the treatment, the emission area

and brightness uniformity of CNT array were improved to

83% and 90%, which can meet the basic requirements of flat

panel display and backlight source. Although Raman and

XPS analysis shows that the action of oxygen slightly changes

the crystallinity of CNTs and can react with the surface of

CNT to form chemical bonds, these do not affect field emis-

sion current stability. SK chart analysis also reveals that the

work function of CNT remains the same while its field

enhancement factor decreases. In conclusion, the in situ oxy-

gen-assisted field emission post treatment is an important

method for the preparation of high quality CNT cathode ar-

rays for vacuum electron devices.

Acknowledgements

The authors gratefully acknowledge the financial support of

the project from the National Natural Science Foundation of

China (Grant Nos. U0634002, 50725206), National Basic Re-

search Program of China (Grant Nos. 2010CB327703,

2007CB935501), the Science and Technology Department of

Guangdong Province, the Economic and Information Industry

Commission of Guangdong Province, and the Science & Tech-

nology and Information Department of Guangzhou City.

R E F E R E N C E S

[1] Rao AM, Jacques D, Haddon RC, Zhu W, Bower C, Jin S. In situ-grown carbon nanotube array with excellent field emissioncharacteristics. Appl Phys Lett 2001;76:3813–5.

[2] Xu NS, Huq S. Novel cold cathode materials and applications.Mater Sci Eng R 2005;48:47–189.

[3] Choi WB, Chung DS, Kang JH, Kim HY, Jin YW, Han IT, et al.Fully sealed, high-brightness carbon-nanotube field-emission display. Appl Phys Lett 1999;75:3129–31.

[4] Kim JM, Choi WB, Lee NS, Jung JE. Field emission from carbonnanotubes for displays. Diam Relat Mater 2000;9(3–6):1184–9.

[5] Chi EJ, Chang CH, Park JH, Lee CG, Lee CH, Yoo SJ, et al.Recent improvements in brightness and color gamut ofcarbon nanotube field emission display. SID Int Symp DigestTech Papers 2006;37:1841–4.

[6] Chen J, Liang XH, Deng SZ, Xu NS. Flat-panel luminescentlamp using carbon nanotube cathodes. J Vac Sci Technol B2003;21:1727–9.

[7] Zhang Y, Deng SZ, Chen J, Xu NS. A fully sealed carbonnanotube flat-panel light source and its application as thinfilm transistor–liquid-crystal display backlight. J Vac SciTechnol B 2008;26:1033–7.

[8] Kim YC, Yoo EH. Printed carbon nanotube field emittersfor backlight applications. Jpn J Appl Phys2005;44:L454–6.

[9] Kim YC, Kang HS, Cho E, Kim DY, Chung DS, Kim IH, et al.Building a backlight unit with lateral gate structure based oncarbon nanotube field emitters. Nanotechnology2009;20:095204-1–7.

[10] Deng SZ, Qian F, Chen J, Xu NS. The frequency characteristicsof a lighting element using carbon nanotube-basedcomposite cold-cathode. IEEE Trans Electron Dev2005;52:1504–7.

[11] Croci M, Arfaoui I, Stockli T, Chatelain A, Bonard JM. A fullysealed luminescent tube based on carbon nanotube fieldemission. Microelectron J 2004;35:329–36.

[12] Saitoa Y, Uemura S. Field emission from carbon nanotubesand its application to electron sources. Carbon2000;38:169–82.

[13] Liu Z, Yang G, Lee YZ, Bordelon D, Lu J, Zhou O. Carbonnanotube based microfocus field emission X-ray source formicrocomputed tomography. Appl Phys Lett 2006;89:103111-1–3.

[14] Kita S, Watanabe Y, Ogawa A, Ogura K, Sakai Y, Matsumoto Y,et al. Field-emission-type X-ray source using carbon-nanofibers. J Appl Phys 2008;103:064505-1–7.

[15] Heo SH, Ihsan A, Cho SO. Transmission-type microfocus X-ray tube using carbon nanotube field emitters. Appl Phys Lett2007;90:183109-1–3.

[16] Liang XH, Deng SZ, Xu NS, Chen J, Huang NY, She JC. Onachieving better uniform carbon nanotube field emission byelectrical treatment and the underlying mechanism. ApplPhys Lett 2006;88:111501-1–3.

[17] Baik CW, Lee J, Chung DS, Jun SC, Choi JH, Song BK, et al.Improvement of field-emission characteristics of carbonnanotubes by post electrical treatment. IEEE Trans ElectronDev 2007;54(9):2392–402.

[18] Ok JG, Kim BH, Sung WY, Chu CN, Kim YH. Uniformityenhancement of carbon nanofiber emitters via electricaldischarge machining. Appl Phys Lett 2007;90:003117-1–3.

[19] Cheng CW, Chen CM, Lee YC. Laser surface treatment ofscreen-printed carbon nanotube emitters for enhanced fieldemission. Appl Surf Sci 2009;255(11):5770–4.

[20] Zhao WJ, Kawakami N, Sawada A, Takai M. Field emissionfrom screen-printed carbon nanotubes irradiated by tunableultraviolet laser in different atmospheres. J Vac Sci Technol B2003;21(4):1734–7.

[21] Kyung SJ, Park JB, Voronko M, Lee JH, Yeom GY. The effect ofatmospheric pressure plasma treatment on the fieldemission characteristics of screen printed carbon nanotubes.Carbon 2007;45:649–54.

[22] Kyung SJ, Park JB, Park BJ, Lee JH, Yeom GY. Improvement ofelectron field emission from carbon nanotubes by Ar neutralbeam treatment. Carbon 2008;46(10):1316–21.

[23] Kim DH, Kim CD, Lee HR. Effects of the ion irradiation ofscreen-printed carbon nanotubes for use in field emissiondisplay applications. Carbon 2004;42:1807–12.

[24] Borowiak-Palen E, Pichler T, Liu X, Knupfer M, Graff A, Jost O,et al. Reduced diameter distribution of single-wall carbonnanotubes by selective oxidation. Chem Phys Lett2002;363:567–72.

[25] Kim YC, Nam JW, Hwang MI, Kim IH, Lee CS, Choi YC, et al.Uniform and stable field emission from printed carbon

3306 C A R B O N 4 9 ( 2 0 1 1 ) 3 2 9 9 – 3 3 0 6

nanotubes through oxygen trimming. Appl Phys Lett2008;92:263112-1–3.

[26] Choi YC, Jeong KS, Han IT, Kim HJ, Jin YW, Kim JM, et al.Double-gated field emitter array with carbon nanotubesgrown by chemical vapor deposition. Appl Phys Lett2006;88:263504-1–3.

[27] Purcell ST, Vincent P, Journet C, Binh VT. Hot nanotubes:stable heating of individual multiwall carbon nanotubes to2000 K induced by the field-emission current. Phys Rev Lett2002;88:105502-1–4.

[28] Huang NY, She JC, Chen J, Deng SZ, Xu NS, Bishop H, et al.Mechanism responsible for initiating carbon nanotubevacuum breakdown. Phys Rev Lett 2004;93:075501-1–4.

[29] Ferrari AC, Robertson J. Origin of the 1150-cm�1 Ramanmode in nanocrystalline diamond. Phys Rev B2001;63:121405-1–4.

[30] Lopez-Rios T, Sandre E, Leclercq S, Sauvain E. Polyacetylenein diamond films evidenced by surface enhanced Ramanscattering. Phys Rev Lett 1996;76:4935–8.

[31] Yan Y, Zhang SL, Zhao XS, Han YS, Hou L. Raman spectralresearch on MPCVD diamond film. Chin Sci Bull2003;48:2562–3.

[32] Crist BV. Handbook of monochromatic XPS spectra: theelements and native oxides. New York: John Wiley & Sons;2000. p. 45–50.

[33] Okpalugo T, Papakonstantinou P, Murphy H, McLaughlin J,Brown N. High resolution XPS characterization of chemical

functionalized MWCNTs and SWCNTs. Carbon2005;43:153–61.

[34] Lee WH, Kim SJ, Lee WJ, Lee JG, Haddon RC, Reucroft PJ. X-rayphotoelectron spectroscopic studies of surface modifiedsingle-walled carbon nanotube material. Appl Surf Sci2001;181:121–7.

[35] Yu RQ, Chen LW, Liu QP, Lin J, Tan KL, Ng SC, et al. Platinumdeposition on carbon nanotubes via chemical modification.Chem Mater 1998;10:718–22.

[36] Gotoh Y, Nagao M, Matsubara M, Inoue K, Tsuji H, Ishikawa J.Relationship between effective work functions and noisepowers of emission currents in nickel-deposited fieldemitters. Jpn J Appl Phys 1996;35:1297–300.

[37] Gotoh Y, Nagao M, Nozaki D, Utsumi K, Inoue K, Nakatani T,et al. Electron emission properties of Spindt-type platinumfield emission cathodes. J Appl Phys 2004;95:1537–49.

[38] Baik CW, Lee J, Choi JH, Jung I, Choi HR, Jin YW, et al.Structural degradation mechanism of multiwalled carbonnanotubes in electrically treated field emission. Appl PhysLett 2010;96:023105-1–3.

[39] Gomer R. Filed emission and filedionization. Cambridge: Harvard University Press; 1961. p.10–31.

[40] Bonard JM, Croci M, Arfaoui I, Noury O, Sarangi D, ChatelainA. Can we reliably estimate the emission field and fieldenhancement factor of carbon nanotube film field emitters?Diam Relat Mater 2002;11:763–8.