flow rate (F

CH ₄ -flow-rate-dependent Structural, Optical, and Electrical Characteristics of CVD-grown Graphene

Ju Hwan Kim · Sung Kim · Suk-Ho Choi ^∗

Department of Applied Physics, Kyung Hee University, Yongin 446-701, Korea (Received 8 August 2013 : revised 8 October 2013 : accepted 11 December 2013)

Single-layer graphene is grown on Cu foils in a chemical vapor deposition (CVD) apparatus with the CH

4

flow rate (F

R

) varied from 10 to 30 sccm, is chemically separated from the Cu foils, and is transferred to SiO

2

/Si on a quartz substrate. The graphene is shown to be composed of polycrystalline domains with boundaries by using atomic force microscopy. At F

R

= 20 sccm, the size of domains is largest, and the graphene’s surface is cleanest. The D, G, and 2D Raman peaks are observed at ∼1350, ∼1600, and ∼2680 cm

⁻¹

, respectively, for all the specimens. The G-to-2D and the D-to-G intensity ratios are smallest at F

R

= 20 sccm, indicating thickness- and defect- minimized growth of graphene, consistent with its having the smallest sheet resistance, the largest transmittance, and the highest electron/hole mobilities at the same F

R

. These results suggest that the properties of graphene are strongly affected by variations in the domain size and the boundary portion (i.e., the defect density) that result from changes in the CH

4

flow rate.

PACS numbers: 61.48.Gh, 78.67.Wj, 78.30.-j, 72.80.Vp

Keywords: Graphene, Methane, Polycrystal, Flow rate, Domain size, Boundary, Defect density

×

D] K ¡ M V ê s ” Ö «Y c l0 n É; c 8 ýA 0 < gX c l” X ¢ § Ž7 0ä à Å8 ý CH ⁴ – ¥S ë s; c   \ ¥  Œ ºX ì Ä, ° Ë Ñ] K ¡X ì Ä, õ m Í

 ¹

ÅM X ì Ä — ¤V R Ë Ž ì ŏ Œ



™ »® £Z 9  ·  ™ ») ç  · L |) o ‡ Ú ^∗

 â

 B@ /† < Ɠ § 6 £ x6   xÓ ü t o † < Æõ , 6   x“   446-701

(2013¸   8 Z 4 8{ 9  ~ à Î6 £ §, 2013¸   10 Z 4 8{ 9  à º& ñ ‘ : r ~ à Î6 £ §, 2013¸   12 Z 4 11{ 9  > F  S X ‰& ñ )

Cu foil 0 A\   o† < Æ l  © œ 7 £ x ‚ à ÌZ O `  ¦ s 6   x # Œ CH

⁴

Ä »| ¾ Ó`  ¦ 10 \ " f 30 sccm t     or v €  " f é ß –8 £ x Õ ª A

— 2 ;`  ¦ + þ A$ í ô  Ç Ê ê, Cu 8 ú ¤ B  l ó ø ÍÜ ¼– РÒ'  ì  r o  % i Ü ¼ 9, SiO

2

/Si ~ à Ì} Œ •õ  $ 3 % ò l ó ø Í 0 A\  „    % i  .

"

é

¶   j Ë µ ‰ & ³p  â Ü ¼– Ð Õ ªA — 2 ;_  ³ ð€  `  ¦ ì  r$ 3 ô  Ç   õ , Õ ªA — 2 ;“ É r  € ª œô  Ç ß ¼l _  • ¸B j“  õ   â > 8 £ x`  ¦ ° ú   H



  & ñ ½ ¨› ¸e ” `  ¦ S X ‰ “   % i  . : £ ¤ y  Ä »| ¾ Ós  20 sccm\ " f Õ ªA — 2 ;_  • ¸B j“   ß ¼l   © œ ( Ž Ü ¼ 9 L :  F M ô  Ç

³

ð€  s  › ' a ¹ 1 Ï÷ &% 3  . Õ ªA — 2 ;õ  › ' aº   ) a D (∼1350 cm

⁻¹

), G (∼1600 cm

⁻¹

) x 9  2D (∼2680 cm

⁻¹

)  ë ß – þ

j“ ¦& h [ þ t _  [ jl _  q _  ì  r$ 3 \  _ K  Ä »| ¾ Ós  20 sccm\ " f Õ ªA — 2 ;_  ¿ ºa   © œ · û ªÜ ¼€  " f• ¸   † < Ês 

 © œ & h “ É r  כ `  ¦ S X ‰ “   % i  . s  Qô  Ç   õ   H ° ú  “ É r Ä »| ¾ Ó\ " f €  $ † ½ Ós   © œ ± ú “ ¦ È Òõ • ¸ x 9  „   /& ñ / B N s

1 l x • ¸  © œ Z  }    H  z  ´[ þ t õ  B Ä º  ҽ + ˝ ) a  . s  Qô  Ç CH

4

Ä »| ¾ Ó\    É r Õ ªA — 2 ;_  : £ ¤$ í    o  H Ò q t

$ í

 ) a Õ ªA — 2 ;_  • ¸B j“   ß ¼l  x 9  Õ ª\    É r  â > 8 £ x q Ö  ¦ (7 £ ¤,   † < Êx 9 • ¸)_     oü < x 9 ] X ô  Ç › ' aº  s  e ” 6 £ §

` 

¦ _ p ô  Ç .

1301

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License

(http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any

medium, provided the original work is properly cited.

ƒ

 $ í , x 9  ’  » ¡ ¤$ í 1 p x \ " f B Ä º „ à Ì Z 4ô  Ç : £ ¤$ í `  ¦ ˜ Ðs l  M : ë

 H \   _  — ¸Ž  H › ' aº   ƒ  ½ ¨ ì  r  \ " f  © œ › ' a d ” `  ¦ ~ à ΍  H Ó

ü t| 9 s  ÷ &% 3   [1]. Õ ªA — 2 ;_  ¢ ¸   É r B § 4 “ É r Ä ºÃ ºô  Ç Ó ü t

$ í

õ   8Ô  ¦ # Q q “ §& h  6   x s  >  Õ ªA — 2 ;`  ¦ % 3 `  ¦ à º e ”    H

 כ

s  . Õ ªA — 2 ;“ É r < É Êƒ  \ " f l > & h  ~ à Ìo Z O  (mechanical exfoliation, { 9 " î Û ¼ u _ …{ 9 Z O )Ü ¼– Ð % ƒ6 £ § ì  r o ÷ &% 3 Ü ¼
 s

 ~ ½ ÓZ O _  é ß –& h “   B Ä º ± ú “ É r à ºÖ  ¦ – Ð “  K " f ™ è 6 £ x6   x \ 

#

Q 9¹ ¡ § s  e ”    H  כ s  . s \  ¦ F G4 Ÿ ¤ l  0 Aô  Ç ~ ½ ÓZ O Ü ¼– Ð

"

f \ x × þ ˜r  (epitaxy) ½ + Ë$ í Z O , Õ ªA — 2 ; í ß – oÓ ü t _  ¨ 8 Š " é ¶ x 9  í

ß – oZ O `  ¦ s 6   x ô  Ç  o† < Æ& h  ½ + Ë$ í Z O  [2,3],  o† < Æ l  © œ 7 £ x ‚ à ÌZ O  (chemical vapor deposition, CVD) [1, 4] 1 p x s  ] jî ß –÷ &% 3  Ü

¼ 9, Õ ª ü @\ • ¸  € ª œô  Ç Õ ªA — 2 ; ] j Œ •Z O [ þ t s  ™ è> h÷ &“ ¦ e ” 



. þ j   H CVD Z O `  ¦ s 6   x ô  Ç Õ ªA — 2 ;_  @ /€  & h  $ í  © œ_  z  ´

‰

&

³“ É r Õ ªA — 2 ; ƒ  ½ ¨_  D h– Ðî  r  © œ`  ¦ \ P % 3  “ ¦ K • ¸ õ ƒ  s 



m  . Õ ªA — 2 ;_  @ /€  & h  $ í  © œs  s À Ò# Qt €  " f z  ´6   x& h 

“

  ™ è 6 £ x6   x ƒ  ½ ¨  Ö ¸ µ 1 Ïy  s À Ò# Qt “ ¦ e ” Ü ¼ 9,  € ª œô  Ç

“

 ] X ì  r  _  ƒ  ½ ¨ [ þ t _  ‚ à Ð# Œ  Ö ¸ µ 1 Ïy  s À Ò# Qt l  r  Œ • Ù þ

¡ . CVD $ í  © œZ O `  ¦ s 6   x # Œ Õ ªA — 2 ;`  ¦ $ í  © œ l  0 AK 

"

f  H Ä º‚  , Ni, Cu, Pt 1 p x õ  ° ú  “ É r ò ø ͙ è\  ¦ ¸ ú ˜ f  ¨ ‚ Ã Ì   H

„

 s F K5 Å q 8 ú ¤ B 8 £ x`  ¦ l ó ø ÍÜ ¼– Ð  6   x “ ¦ “ ¦“ : r \ " f CH 4 ü <

H 2 _  ™ D ¥ ½ + ËÛ ¼\  ¦ & h { © œô  Ç q Ö  ¦ – Ð Å Ò{ 9 ô  Ç . “ ¦“ : r \ " f Å Ò { 9

 ) a ™ D ¥ ½ + ËÛ ¼\ " f ò ø ͙ è 8 ú ¤ B  8 £ x õ  ì ø Í6 £ x ô  Ç Ê ê\  / å LÏ Ÿ 

>  ÷ &€   8 ú ¤ B – РÒ'  ò ø ͙ è b  # Q4 R
š ¸€  " f ³ ð€  \  Õ

ªA — 2 ;s  $ í  © œ >   ) a  . $ í  © œ  ) a Õ ªA — 2 ;“ É r # Œ Q t     Ã

º\  _ K  Õ ªA — 2 ;_  : £ ¤$ í õ  ¿ ºa \  ¦   & ñ >   ) a  . s  Q ô

 Ç   à º[ þ t – Ѝ  H CH 4 Ä »| ¾ Ó (flow rate), H 2 Ä »| ¾ Ó, $ í  © œ“ : r • ¸, x 9

 Í ‰ ty Œ •5 Å q • ¸ 1 p x s  e ”  . : £ ¤ y  Õ ªA — 2 ; $ í  © œ\  e ” # Q CH 4 _ 

€

ª œ“ É r Õ ªA — 2 ;_  : £ ¤$ í õ  ¿ ºa \   © œ  H % ò † ¾ Ó`  ¦ p u   H כ ¹

™

è ×  æ _  
s  .

‘

: r  7 Hë  H \ " f  H CVDZ O Ü ¼– Ð $ í  © œ“ : r • ¸, Í ‰ ty Œ •5 Å q • ¸, H 2 Ä »

|

¾ Ó, ì ø Í6 £ x l  · ú š§ 4  1 p x`  ¦ “ ¦& ñ “ ¦ CH 4 Ä »| ¾ Ó`  ¦ › ¸] X  # Œ  

€

ª œô  Ç 7 á x À Ó_  Õ ªA — 2 ;`  ¦ $ í  © œ % i  . s X O >  ] j Œ •  ) a Õ ªA 

—

2 ;_  ½ ¨› ¸& h , F  g † < Æ& h , x 9  „  l & h  : £ ¤$ í `  ¦ q “ §ô  Ç   õ , þ j

&

h  o  ) a é ß –8 £ x Õ ªA — 2 ;_  ] j Œ • › ¸| `  ¦ • ¸Ø  ¦ ½ + É Ã º e ” % 3 Ü ¼ 9 z 

´+ « >  õ \  ¦  „ ½ ÓÜ ¼– Ð › ' aº   B j& m 7 £ § \  @ /K " f  7 H _ ô  Ç .

∗

E-mail: [email protected]

t

 Í ‰ ty Œ •r †   . s X O >  ½ ¨o   ñ{ 9 0 A\  $ í  © œ ) Õ ªA — 2 ;` ¦ Poly methyl methacrylate (PMMA)\  ¦ s 6   x # Œ Õ ªA — 2 ;

³

ð€  \  Û ¼— 2 ; ïh A† < ÊÜ ¼– Ð+ ‹ t t } Œ •`  ¦ + þ A$ í r †   Ê ê 0.1 M ammonium persulfate 6   xÓ  o\ " f ½ ¨o   ñ{ 9 `  ¦ d ” y Œ • “ ¦ [1, 6] PMMA/ Õ ªA — 2 ;`  ¦ 300 nm SiO 2 /Si ¢ ¸  H $ 3 % ò l ó ø Í0 A

\

 „   r v “ ¦ PMMA  H  [ j— : r`  ¦ s 6   x # Œ ] j  % i 



 [5,6]. ] j Œ •  ) a Õ ªA — 2 ;“ É r " é ¶   j Ë µ ‰ & ³p  â (atomic force micro scopy, AFM) x 9  Raman ì  rF  g l \  ¦  6   x # Œ ½ ¨› ¸

&

h

 : £ ¤$ í `  ¦ ì  r$ 3  % i  .  ü @‚  -r  F  g‚   ì  rF  gZ O `  ¦ s 6   x

# Œ Õ ªA — 2 ;_  $ í  © œ› ¸| \    É r È Òõ • ¸\  ¦ 8 £ ¤& ñ % i  .

³

ðï  r Ÿ íž Ðo ™ èÕ ªA x  / B N& ñ `  ¦ : Ÿ x # Œ „  > ´ òõ à Ô ½ ™t Û ¼ '

 (Field effect transistor, FET)\  ¦ ] j Œ • # Œ „  l & h  : £ ¤

$ í

[ þ t`  ¦ › ¸  % i  . ¢ ¸ô  Ç Van der Pauw ~ ½ ÓZ O `  ¦ s 6   x 

#

Œ Õ ªA — 2 ;_  €  $ † ½ Ó`  ¦ 8 £ ¤& ñ % i  .

III. + s ÇÊ Ý õ m Í À X Ø8 ý

Figure 1“ É r CH 4 _  Ä »| ¾ Ó`  ¦ 10  Ò'  30 sccm t     or  v

€  " f ] j Œ •ô  Ç Õ ªA — 2 ;\ " f › ' a ¹ 1 Ï  ) a AFM _  t + þ A s p t  (topographic image) s  . Fig. 1(a)-(d)\ " f% ƒ! 3   € ª œô  Ç CH 4 Ä »| ¾ Ó\ " f ] j Œ •  ) a CVD Õ ªA — 2 ;“ É r • ¸B j“    â >  (do- main boundary)\  ¦ t   H    & ñ Ü ¼– Ð › ' a ¹ 1 Ï  ) a  . AFM _

 ì  r$ 3 \  _  # Œ • ¸Ø  ¦ ) a ¨ î ç  H& h “   • ¸B j“  _  ¨ î ç  H ß ¼l \  ¦ Fig. 1(e) \  7 á x ½ + Ë % i  . CH 4 Ä »| ¾ Ós  10\ " f 20 sccmÜ ¼

–

Ð 7 £ x † < Ê\    " f • ¸B j“  _  ¨ î ç  H ß ¼l  3.6 µm\ " f 26.5 µm Ü ¼– Ð 7 £ x  t ë ß – Õ ª s  © œ_  CH 4 Ä »| ¾ Ó\ " f  H y Œ ™

™

èô  Ç . • ¸B j“  õ  • ¸B j“    s _   â > \ " f  H     Ô  ¦ { 9

u  l  M :ë  H \  Õ ªA — 2 ;_    † < Ês  Ò q t$ í  ) a   [7,8]. 7 £ ¤, • ¸ B

j“  _  ß ¼l  7 £ x † < Ê\    " f é ß –0 A€  & h { © œ • ¸B j“    â

>

8 £ x s  t    H q Ö  ¦“ É r y Œ ™™ è >  ÷ &# Q" f Õ ªA — 2 ;_    

†

< ʓ É r y Œ ™™ è >  | ¨ c  כ s  . AFM_    õ \ " f% ƒ! 3  CH ₄ Ä »

|

¾ Ós  20 sccm\ " f ] j Œ •  ) a Õ ªA — 2 ;\ " f   † < Ês   © œ ± ú `  ¦

 כ

Ü ¼– Ð l @ /  ) a  .

Figure 2(a)  H CH 4 _  Ä »| ¾ Ó`  ¦ › ¸] X  # Œ ] j Œ •ô  Ç Õ ªA — 2 ;

\

 532 nm (∼2, 33 eV)_  Y Us $  F  g " é ¶`  ¦ › ¸  # Œ › ' a ¹ 1 Ï

Fig. 1. (Color online) AFM topographic images of graphene sheets for flow rate of CH 4 : (a) 10, (b) 15, (c) 20, and (d) 30 sccm. (e) Domain size as a function of CH 4 flow rate.

ô

 Ç  ë ß – Û ¼& 7 ˜à Ô! 3 s  . Õ ªA — 2 ;_   ë ß – Û ¼& 7 ˜à Ô! 3 \ " f 



© œ Ì º§  ô  Ç þ j“ ¦& h  (peak)“ É r 1590 cm ⁻¹ Â Ò   H _  G þ j“ ¦& h  õ

 2690 cm ⁻¹ Â Ò   H _  2D þ j“ ¦& h Ü ¼– Ð+ ‹ „  + þ A& h “   Õ ªA 

—

2 ;_  Å Òכ ¹  ë ß – þ j“ ¦& h [ þ t s   [9]. s ü < † < Êa  1350 cm ⁻¹ Â

Ò   H \  D þ j“ ¦& h s  › ' a ¹ 1 Ï÷ &  H X <, s   H Õ ªA — 2 ;_    † < Ê\  _

 # Œ › ' a ¹ 1 Ï÷ &  H  כ Ü ¼– Ð · ú ˜ 94 R e ”   [9]. Fig. 2(b)  H  

€

ª œô  Ç CH ₄ Ä »| ¾ Ó\ " f ] j Œ •  ) a r « Ñ[ þ t _   ë ß – þ j“ ¦& h _  0 A u

\  ¦
  · p . CH ⁴ Ä »| ¾ Ós  10\ " f 20 sccmÜ ¼– Ð 7 £ x † < Ê

\

   " f G þ j“ ¦& h “ É r 1583 \ " f 1587 cm ⁻¹ – Ð, 2D þ j“ ¦

&

h

“ É r 2690 \ " f 2685 cm ⁻¹ – Ð, y Œ •y Œ • 4ü < 5 cm ⁻¹ m ”  ' õ AÒ  o…  ; s

 (blueshift) ¢ ¸  H & h Ò  o…  ;s  (redshift) ô  Ç . Õ ª Q
 B j ò

ø Í Ä »| ¾ Ós  25 sccm s  © œÜ ¼– Ð 7 £ x  >  ÷ &€   G þ j“ ¦& h “ É r

&

h

Ò  o…  ;s  “ ¦ 2D þ j“ ¦& h “ É r ' õ AÒ  o…  ;s  ô  Ç . Õ ªA — 2 ;_  G ü

< 2D  ë ß – þ j“ ¦& h [ þ t _     o  H Õ ªA — 2 ;_  ½ ¨› ¸& h “      o

\

   É r Ÿ í 7 H x 9  „   _   © œ  ñ Œ •6   x _     oü < x 9 ] X ô  Ç › ' aº   s

 e ”   [10,11].

Figure 2(c)  H CH 4 _  Ä »| ¾ Ó\     ] j Œ •ô  Ç Õ ªA — 2 ;_ 



ë ß – þ j“ ¦& h [ þ t _  [ jl  q  (G ü < 2D þ j“ ¦& h _  [ jl  q ,

Fig. 2. (Color online) (a) Raman spectra of graphene for various CH 4 flow rates. (b) The 2D and G band shifts as functions of CH 4 flow rate. (c) The intensity ratios of the D to G and G to 2D bands as functions of CH ₄ flow rate.

Fig. 3. (Color online) Optical transmittance spectra of graphene in the visible range for various CH ₄ flow rates.

The inset shows transmittance as a function of CH ₄ flow rate.

I(G/2D) ü < Dü < G þ j“ ¦& h _  [ jl  q , I(D/G))\  ¦ 7 á x ½ + Ë 

%

i  . { 9 ì ø Í& h Ü ¼– Ð Õ ªA — 2 ;\ " f  ë ß – [ jl _  q , I(G/2D)



 H Õ ªA — 2 ;_  8 £ x à º\  ¦
 ? / 9 s  ° ú כs  0.5˜ Ð   Œ •`  ¦ M : é ß –

 

& ñ é ß –8 £ x Õ ªA — 2 ;\  ¾ ú š  [12]. I(D/G)  H   † < Ê_  q \  ¦

  · p  [13]. Fig. 2(c)\ " f CH ⁴ Ä »| ¾ Ós  20 sccm{ 9  M : I(G/2D)  H ∼0.45 – Ð" f é ß –  & ñ é ß –8 £ x Õ ªA — 2 ;\   î  r ° ú כ

`

 ¦ t  9,   † < Ê_  q  þ j™ è  ) a  . 7 £ ¤, AFM   õ \ " f

˜

Г    ü < ° ú  s  CH 4 _  Ä »| ¾ Ós  20 sccm\ " f • ¸B j“  _  ¨ î ç

 H ß ¼l   © œ  H € ª œ| 9 _  é ß –8 £ x Õ ªA — 2 ;s  ] j Œ •÷ &  H  כ `  ¦

· ú

˜ à º e ”  . s  © œ_    õ \ " f CH 4 Ä »| ¾ Ós  20 sccm{ 9  M :



ë ß – : £ ¤$ í [ þ t s    ¨ 8 Š& h `  ¦ t   H X < s   H Õ ªa Ë > 1_  AFM ì

 r$ 3    õ ü < B Ä º Â Ò½ + Ëô  Ç .

Figure 3“ É r CH 4 Ä »| ¾ Ó    o\    É r È Òõ • ¸ Û ¼& 7 ˜à Ô! 3 

`

 ¦
  · p . { 9 ì ø Í& h Ü ¼– Ð s  © œ& h “   é ß –  & ñ é ß –8 £ x Õ ªA — 2 ; _

 È Òõ • ¸  H ∼97.7% – Ð" f ¿ ºa  7 £ x   
   & ñ $ í s  y

Œ

™™ è† < Ê\    " f È Òõ • ¸  H y Œ ™™ èô  Ç  [14]. Fig. 3\  ¶ ú š{ 9 

Fig. 4. Sheet resistance of graphene as a functions of CH 4 flow rate.

 )

a Õ ªa Ë >\ " f% ƒ! 3  r  F  g% ò % i “   550 nm\ " f Õ ªA — 2 ;_  È Ò õ

• ¸  H CH 4 _  Ä »| ¾ Ós  20 sccm\ " f  © œ ß ¼ 9, Õ ª ° ú כs  96.7% – Ð" f s  © œ& h “   é ß –8 £ x Õ ªA — 2 ;_  È Òõ • ¸\   © œ   î

 r  כ `  ¦ · ú ˜ à º e ”  .

Figure 4  H  € ª œô  Ç CH ₄ Ä »| ¾ Ó\ " f ] j Œ •  ) a Õ ªA — 2 ;[ þ t _ 

€

 $ † ½ Ó`  ¦
  · p . CVD Õ ªA — 2 ;\ " f • ¸B j“  _  ß ¼l 

7

£

x † < Ê\    " f €  $ † ½ Ó_  y Œ ™™ è\  ¦ l @ /½ + É Ã º e ”   H X < [15],

‘

: r ƒ  ½ ¨  õ \ " f• ¸ • ¸B j“  _  ¨ î ç  H ß ¼l   © œ 9 þ t M : (CH ₄ Ä »| ¾ Ó = 20 sccm) Õ ªA — 2 ;_  €  $ † ½ ӓ É r 405 ± 30Ω/sq

–

Ð" f  © œ  Œ •“ É r  כ `  ¦ · ú ˜ à º e ”  .

Figure 5  H CH 4 _  Ä »| ¾ Ó\    É r Õ ªA — 2 ; FET_  × ¼Y U“  -

™

èÛ ¼ „  À Ó (I SD )- > s à Ô „  · ú š (V G ) / B G‚  õ  n | à ̄  · ú š/s  1

l

x • ¸_     o\  ¦
  · p . V ^G   H -100  Ò'  100 V t    



o % i Ü ¼ 9 ™ èÛ ¼ü < × ¼Y U“    s \  „  · ú š“ É r 10 mV\  ¦ “  

 % i  . Fig. 5(a)\  ˜ Г    ü < ° ú  s  CH ⁴  30 sccm{ 9  M

:\  ¦ ] jü @ô  Ç — ¸Ž  H r « Ñ_  I SD − V _G / B G‚  “ É r n | Ã Ì „  · ú š`  ¦ l

ï  r Ü ¼– Ð  _  @ /g A& h “   / B G‚  s  › ' a ¹ 1 Ï  ) a  . { 9 ì ø Í& h Ü ¼– Ð I SD − V G / B G‚  \ " f s  © œ& h “   é ß –8 £ x Õ ªA — 2 ;“ É r n | Ã Ì „  · ú š s

 0 Vs   [16]. CH 4 Ä »| ¾ Ós  20 sccm{ 9  M : ] j Œ •  ) a Õ ªA 

—

2 ;“ É r n | Ã Ì „  · ú šs  6 V– Ð" f s  © œ& h “   é ß –8 £ x Õ ªA — 2 ;\  



© œ  î  r ° ú כ`  ¦ ”   . ¢ ¸ô  Ç Õ ªA — 2 ;_  I SD − V _G / B G‚  Ü ¼

–

РÒ'  „   ü < & ñ / B N _  s 1 l x • ¸\  ¦ í ß –Ø  ¦ ½ + É Ã º e ” Ü ¼ 9,  € ª œ ô

 Ç CH 4 Ä »| ¾ Ó\    É r s 1 l x • ¸\  ¦ Fig. 5(b) \  כ ¹€  • % i  .

„

   x 9  & ñ / B N _  s 1 l x • ¸  H  6 £ § õ  ° ú  “ É r d ” \  _ K " f Ä »• ¸

 ) a   [16].

µ = 1 c g

dσ dV g

, C g = 1.15 × 10 ⁻⁸ F cm ⁻² (1)

#

Œl " f C g   H > s à Ô_  „  l 6   x | ¾ Ó, σ  H Õ ªA — 2 ;_  „  • ¸• ¸, V g   H > s à Ô „  · ú š`  ¦ y Œ •y Œ •
  · p . s  © œ& h “   é ß –8 £ x Õ ª

Fig. 5. (Color online) (a) I _SD − V G curves of graphen e FETs for various CH ₄ flow rates. (b) Electron and hole mobilities as functions of CH ₄ flow rate.

A

— 2 ;_  „   î  r ì ø Í _  s 1 l x • ¸[ þ t“ É r >200,000 cm ² /Vs Ü ¼– Ð B

Ä º ß ¼ . Õ ª Q
, CVD Õ ªA — 2 ;_  s 1 l x • ¸  H  € ª œô  Ç ß ¼l  _

 • ¸B j“    â > 8 £ x M :ë  H \  „    ¢ ¸  H & ñ / B N[ þ t s    † < Ê\  à Ô ê

Á œ (trap)÷ & 
 í ß –ê ø Í # Œ s 1 l x • ¸\  ¦ y Œ ™™ èr †    [7]. Õ ª Q Ù

¼– Ð ‰ & ³F  t  CVD Õ ªA — 2 ;_  s 1 l x • ¸[ þ t“ É r 200 \ " f 2500 cm ⁻² /Vs _  # 3 0 A\ " f › ' a ¹ 1 Ï÷ &“ ¦ e ”   [17–19]. ‘ : r ƒ  ½ ¨\ 

"

f  6   x ) a CVD Õ ªA — 2 ;“ É r CH 4 _  Ä »| ¾ Ós  20 sccm{ 9  M :

„

   x 9  & ñ / B N _  s 1 l x • ¸  H y Œ •y Œ • 2500õ  1800 cm ² /Vs Ü ¼– Ð þ

j@ / ÷ & 9, s  Ä »| ¾ Ә Ð  7 £ x   
 y Œ ™™ è >  ÷ &€   s  1

l

x • ¸[ þ t“ É r & h  & h Ü ¼– Ð y Œ ™™ èô  Ç . s      õ [ þ t“ É r CH 4 _  Ä

»| ¾ Ós  20 sccm\ " f • ¸B j“  [ þ t _  ß ¼l  þ j@ / ÷ &“ ¦ Õ ª

–

Ð “   # Œ „   î  r ì ø Í _  s 1 l x • ¸ þ j@ /  ) a    H  כ `  ¦ _

p ô  Ç .

IV. + s Ç Â ] Ø

‘

: r ƒ  ½ ¨\ " f  H CVDZ O Ü ¼– Ð CH ⁴ _  Ä »| ¾ Ó`  ¦    or v €  

"

f Õ ªA — 2 ;`  ¦ ] j Œ • # Œ Õ ª ½ ¨› ¸& h , F  g † < Æ& h , x 9  „  l & h  : £ ¤$ í

`

 ¦    o\  ¦ ì  r$ 3  % i  . Õ ªA — 2 ;“ É r ´ ú §“ É r • ¸B j“  [ þ t • ¸ ½ ¨$ í

 )

a    & ñ e ” `  ¦ S X ‰ “   % i Ü ¼ 9 Õ ª ß ¼l ü < Õ ª\    É r  â > 

8

£

x _   © œ@ /& h “   q Ö  ¦ s  Ä »| ¾ Ó\  ß ¼>  _ ” > r % i  . CH 4 _  Ä

»| ¾ Ós  20 sccm{ 9  M : • ¸B j“  s  ] j{ 9  & " f  â > 8 £ x s  þ j™ è



o H † d Ü ¼– Ð+ ‹ Õ ªA — 2 ;_    † < ʕ ¸ þ j™ è o  ) a    H  כ `  ¦ AFM,



ë ß – 1 p x _  ì  r$ 3 \  _ K  S X ‰ “   % i Ü ¼ 9 s \     È Ò" î • ¸ x 9

 s 1 l x • ¸ 1 p x _  F  g † < Æ& h  x 9  „  l & h  : £ ¤$ í • ¸ ° ú  “ É r Ä »| ¾ Ó\ 

"

f  © œ Ä ºÃ º    H  כ `  ¦ È Òõ • ¸, €  $ † ½ Ó, x 9  FET_  „   À

Ó-„  · ú š : £ ¤$ í 8 £ ¤& ñ Ü ¼– Ð { 9 7 £ x % i  .

P

c p 8 ý ò k >

‘

: r ƒ  ½ ¨  H  â  B@ /† < Ɠ § 2012† < Ƹ  • ¸ “ §q ƒ  ½ ¨q  (õ ] j



   ñ: 20130104)\  _ K  t " é ¶ ÷ &% 3 Ü ¼ 9 s \  y Œ ™ × ¼w n m 



.

REFERENCES

[1] K. S. Kim, Y. Zhao, H. Jang, J. Y. Choi and B. H.

Hong et al., Nature 457, 706 (2009).

[2] I. K. Moon, J. H. Lee, R. S. Ruoff and H. Y. Lee, Nat. Commun. 1, 73 (2010).

[3] S. Pei and H. M. Cheng, Carbon 50, 3210 (2012).

[4] X. Li, W. Cai, J. An, S. Kim and J. Na et al., Science 324, 1312 (2009).

[5] X. Li, Y. Zhu, W. Cai, L. Colombo and R. S. Ruoff et al., Nano Lett. 9, 4359 (2010).

[6] M. Zheng, K. Takei, B. Hsia, H. Fang and X. Chang et al., Appl. Phys. Lett. 96, 063110 (2010).

[7] O. V. Yazyev and S. G. Louie, Nat. Mater. 9, 806 (2010).

[8] Q. Yu, L. A. Jauregui, W. Wu, S. S. Pei and Y. P.

Chen et al., Nat. Mater. 10, 443 (2011).

[9] A. C. Ferrari, J. C. Meyer, V. Scardaci, S. Roth and A. K. Geim, Phys. Rev. Lett. 97, 187401 (2006).

[10] D. Yoon, H. Moon and H. Cheong, J. Korean Phys.

Soc. 55, 1299 (2009).

[11] Y. Hao, Y. Wang, L. Wang, Z. Shen and J. T. L.

Thong et al., Small 6, 195 (2010).

[12] S. Chen, W. Cai, R. D. Piner, J. Kang and R. S.

Ruoff et al., Nano Lett. 11, 3519 (2011).

[13] A. Reina, X. Jia, J. Ho, M. S. Dresselhaus and J.

Kong et al., Nano Lett. 9, 30 (2009).

[14] R. R. Nair, P. Blake, A. N. Grigorenko, K. S.

Novoselov and T. J. Booth et al., Science 320, 1308 (2008).

[15] D. L. Duong, G. H. Han, S. M. Lee, J. Y. Choi and Y. H. Lee et al., Nature 490, 235 (2012).

[16] C. R. Dean, A. F. Young, I. Meric, K. L. Shepard and J. Hone, Nat. Nanotechnol. 5, 722 (2010).

[17] J. Kedzierski, L. P. Hsu, A. Reina, P. Wyatt and C.

Keast, IEEE Electron Device Lett. 30, 745 (2009).

[18] A. Avsar, T. Y. Yang, S. Bae, B. Beschoten and B.

Ozyilmaz, Nano Lett. 11, 2363 (2011).

[19] Y. G. Lee, C. G. Kang, U. J. Jung, R. Choi and B.

H. Lee et al., Appl. Phys. Lett. 98, 183508 (2011).