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Copyright copy 2010 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 10 2741ndash2745 2010

XPS Analysis by Exclusion of a-Carbon Layer onSilicon Carbide Nanowires by a GoldCatalyst-Supported Metal-OrganicChemical Vapor Deposition Method

Sang-Hun Nam Myoung-Hwa Kim Jae-Sung HyunYoung Dok Kimlowast and Jin-Hyo Boolowast

Department of Chemistry Sungkyunkwan University Suwon 440-746 Korea

Silicon carbide (SiC) nano-structures would be favorable for application in high temperature highpower and high frequency nanoelectronic devices In this study we have deposited cubic-SiCnanowires on Au-deposited Si(001) substrates using 13-disilabutane as a single molecular precur-sor through a metal-organic chemical vapor deposition (MOCVD) method The general depositionpressure and temperature were 30times10minus6 Torr and 1000 C respectively with the deposition carriedout for 1 h Au played an important role as a catalyst in growing the SiC nanowires SiC nanowireswere grown using a gold catalyst with amorphous carbon surrounding the final SiC nanowire Thusthe first step involved removal of the remaining SiO2 followed by slicing of the amorphous carboninto thin layers using a heating method Finally the thinly sliced amorphous carbon is perfectlyremoved using an Ar sputtering method As a result this method may provide more field emis-sion properties for the SiC nanowires that are normally inhibited by the amorphous carbon layerTherefore exclusion of the amorphous carbon layer is expected to improve the overall emissionproperties of SiC nanowires

Keywords Silicon Carbide XPS Nanowires MOCVD a-Carbon

1 INTRODUCTION

One-dimensional nanoscale building blocks such asnanobelts nanorods nanotubes and nanowires have beenthe focus of considerable interest given their potentialapplication in fabrication of nanoscale electronic devicesThey also provide an ideal model system to experimen-tally investigate the physical phenomena of dimensionalityand the space-confine effect Among the one-dimensionalnanostructures the nanowire which distinctly differs fromhollow nanotubes and solid nanowires has been success-fully fabricated recently1 One-dimensional semiconduc-tor nanomaterials including nanowires of Si2 C3 Au4

ZnO5 a GaN6 have been synthesized by various methodssuch as chemical vapor deposition (CVD) oxide-assistedgrowth physical evaporation and those methods basedon the self-assembling of molecular templates Siliconcarbide has many superior properties including a largeenergy band gap (23sim34 eV) high thermal conductivity

lowastAuthors to whom correspondence should be addressed

(32sim49 WCm K) high electron mobility (1000 cm2Vs)and good physical and chemical resistance Several groupshave successfully synthesized SiC nanowires (or nanorods)by a variety of techniques For example Dai et al synthe-sized SiC nanorods through a carbon nanotube confininggrowth route7 while Hu et al reported the prepara-tion of 3C-SiC nanowires by a reduction-carburizationapproach8 Zhang et al prepared SiCSiO2 core-sheetnanowires through a chemical vapor deposition route9 andWang et al synthesized side-by-side biaxially structuredsilicon carbide-silica nanowires at sim1500 C10 Salamaet al prepared a carbon-rich 4H-SiC nanoribbon het-erostructure using a laser direct-write method11 In thispaper we employed a metal-organic chemical vapor depo-sition method (MOCVD) to synthesize one-dimensionalSiC nanowires X-ray photoelectron spectroscopy (XPS)is an excellent technique for characterizing SiC nano-structures The XPS analysis of the C (1s) peak is oftenmodified by the presence of residual carbon Si and Oin the SiC nanowire The closeness of the binding energyin the SiC nanowire C (1s) peaks with other peaks can

J Nanosci Nanotechnol 2010 Vol 10 No 4 1533-48802010102741005 doi101166jnn20101384 2741

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XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires Nam et al

be attributed to SindashC CndashO CndashOndashH and C C of theC (1s) peak Waite and Shah12 observed a single peak at abinding energy of 28575 eV attributed to diamond whileSiC and graphite that are formed together with diamondare observed at 2830 and 2846 eV respectively Beltonet al13 attributed the 2843 2827 and 2851 eV peaksto diamond SiC and adventitious carbon respectivelyArezzo et al14 suggested that the binding energies of dia-mond and graphite are 2850 and 2842 eV The deconvo-lution of the C (1s) spectrum yields peak values of 2844and 2852 eV that have been assigned to these 2 types ofatoms1415 giving a separation of about 08 eV betweenthe sp2 and sp3 contributions Leung et al16 assigned the2848 eV peak to the sp2-binding configuration in theirDLC films while the peak at 2857 eV was attributed tothe sp3 component Residual carbon in the SiC nanowiresreduces its field emission properties and as such thereexists a need to establish a method to exclude the residualcarbon In this study we firstly deposited SiC nanowireson gold-covered Si(100) substrates using a single molec-ular precursor at a deposition temperature of 1000 C bya high vacuum metal-organic chemical vapor deposition(MOCVD) method Research about a method to excludethe amorphous carbon layer using various methods suchas thermal heating oxygen atmosphere and Ar sputteringwas also carried out

2 EXPERIMENTAL DETAILS

21 SiC Nanowires Growth

The silicon carbide nanowires were grown in a homemadehigh vacuum metal organic chemical vapor deposition sys-tem The p-type 001 orientated silicon wafer was cutinto rectangle pieces 40times 8 mm2 and used as a basesubstrate for the growth of the silicon carbide nanowiresin this work Prior to their growth the substrate surfacewas degreased accordingly 10 min in an ultrasonic cleanercontaining acetone dipped in DI water for 10 min dippedin 10 wt HF solution for 15 s rinsed with DI waterand flushed in a nitrogen flow We also prepared metalcatalyst-coated Si(001) substrates The gold (Au) catalyst

Table I XPS experimental conditions for the exclusion of the amor-phous carbon layer

ExclusionNumber method Conditions

1 Thermal heating 900 C 10times10minus9 Torr2-1 Heating in 600 C 10times10minus6 Torr

atmosphere O2

2-2 Heating in 900 C 10times10minus6 Torratmosphere O2

3-1 Ar sputtering 05 KeV 5 min 15 A 10times10minus6 Torr3-2 Ar sputtering 05 KeV 10 min 243 A 10times10minus6 Torr3-3 Ar sputtering 10 KeV 10 min 266 A 10times10minus6 Torr3-4 Ar sputtering 10 KeV 10 min 832 A 50times10minus6 Torr

was deposited on the substrate using a thermal evapora-tion method The general growth conditions were a highvacuum pressure of 30times 10minus6 Torr and a temperature of1000 C The 13-disilabutane was employed as a singlesource for the growth of the silicon carbide nanowireswhich were grown directly onto the substrate gold metalcatalyst deposited onto Si(001) surface

(b)

(c)

20

(a)

30 40 50

2 Theta

Inte

nsity

(a

u)

Si(2

00)

SiC

(220

)

SiC

(200

)S

iC(1

11)

Si(4

00)

SiC

(311

)

60 70 80

Fig 1 (a) XRD pattern of SiC nanowires growth on AuSi(100) sub-strates using 13-disilabutane at a pressure of 30times10minus6 Torr at 1000 CFigures (b) and (c) show an SEM image and TEM image of the samesample

2742 J Nanosci Nanotechnol 10 2741ndash2745 2010

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Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

22 Exclusion of Amorphous Carbon inSiC Nanowires

In this study three exclusion methods for the amorphouscarbon in the SiC nanowire were attempted thermal heat-ing heating in oxygen atmosphere and Ar sputtering Thethermal heating method involves technology that breaksdown the binding energy of the amorphous carbon at ahigh temperature 900 C Heating in an oxygen atmo-sphere targets amorphous carbon exclusion through theCndashO interaction at high temperatures such as 600 and900 C Finally Ar sputtering is a method of amorphouscarbon layer removal using an Ar ion or radical generatedby plasma The experimental conditions of these methodswere developed in ultra high vacuum system Table IThe as-grown SiC nanowires were characterized by

X-ray Diffraction (XRD) Scanning Electron Microscopy(SEM) and Transmission electron microscopy (TEM)In addition exclusion of amorphous carbon experimentswere analyzed using X-ray photoelectron spectroscopy(XPS) through which the chemical characteristic of theexclusion amorphous carbon layer were confirmed

Fig 2 (a) XPS results of the SiC nanowire for the exclusion of the amorphous carbon layer using the thermal heating method Figure (b) shows theXPS results of the same sample using the thermal heating method in atmosphere oxygen

3 RESULTS AND DISCUSSION

31 Characterizations of SiC Nanowires

Figure 1(a) shows the XRD patterns of the -SiCnanowires grown at a deposition pressure of 30 times10minus6 Torr for 1 h under the deposition temperature of1000 C using a gold catalyst The XRD pattern exhibitscharacteristic peaks of -SiC at 2 = 356 414 600and 718 which refer to the diffraction of -SiC (111)(200) (220) and (311) planes To compare the JCP cardindex with Figure 1(a) we can conclude that the growthproduct has a zinc-blend structure (-SiC) In additionsince there are four peaks in Figure 1(a) a polycrystallineSiC nanowire has been obtained in our study Conclu-sively -SiC nanowires on metal catalyst-coated Si(001)substrates deposited at 1000 C are polycrystalline andalso exhibit a zinc-blend structureFigure 1(b) shows a typical SEM image of the obtained

-SiC nanowire with a specific thickness and length(such as 30 and 250 nm) grown on a gold (Au) cata-lyst at 1000 C Gold catalyst-deposited SiC nanowiresFigure 1(b) show that the thin and shorter likely SiC

J Nanosci Nanotechnol 10 2741ndash2745 2010 2743

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XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires Nam et al

Fig 3 XP spectra of SiC nanowire grown on AuSi(100) substrate at 1000 C obtained beforeafter Ar sputtering (a) high-resolution XP spectra ofSi(2p) and (b) high-resolution XP spectra of C (1s)

nanorods are straight-grown on the substrate at a highdensityTo investigate in greater depth the structure of

as-deposited -SiC nanowires transmission electronmicroscopy (TEM) combined with energy dispersiveX-ray (EDX) analyses were performed For the TEMexperiments the -SiC nanowires grown using gold (Au)catalyst at 1000 C for 1 h were prepared Figure 1(c)shows the typical TEM image obtained from a -SiCnanowire where the grown -SiC nanowire is wrappedwith an amorphous layer with a thickness of approxi-mately 2 nm We can confirm that this layer is amorphouscarbon through electron diffraction (ED) data (see inset ofFig 1(c)) Because the metal-organic source used in thisexperiment contains carbon atoms we speculated that thisamorphous carbon layer originated from the precursor Theinset image (right) in Figure 1(c) shows the correspond-ing selected area electron diffraction (ED) pattern obtainedfrom the same nanowire indicating a circular form of apolycrystalline nature

Fig 4 2-step process schematic diagram for exclusion of the amorphous carbon layer

32 Exclusion Analysis of the AmorphousCarbon Layer by XPS

Figure 2(a) shows the high-resolution spectra of Si(2p)and C (1s) obtained beforeafter the thermal heating High-resolution XP spectra show that the SiO2 peak appearingat 1034 eV decreased and that the SiC peak at 2824 eVincreased when the substrate temperature increased to900 C indicating that desorption of CO or CO2 was com-bined by amorphous carbon and SiO2Figure 2(b) shows high-resolution spectra of Si(2p) and

C (1s) measured after thermal heating at 600 and 900 Crespectively in an oxygen atmosphere to remove residualSiO2 From the experiment at 600 C we confirmed theSiO2 as the source of the material remaining behind on theSiC nanowire surface that was perfectly removed by com-bination with amorphous carbon indicating that an oxygeneffect plays an important role in removal of the SiO2 in anoxygen atmosphere In addition both Si (2p) and C (1s)peak intensities decreased when heated at 900 C denoting

2744 J Nanosci Nanotechnol 10 2741ndash2745 2010

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Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

that the surface of the amorphous carbon layer becomessmooth and that the number of electrons decrease whichis detected as a result of a decrease in thickness thin-ning As a result the CndashC bonding combination peakthat appears at 2839 eV was not removed under condi-tions of the thermal heating method However this methodperfectly removed the remaining SiO2 and made thin andsmooth the amorphous carbon surfaceFigure 3 shows the high-resolution (HR) XPS data

indicating the reduction in the residual amorphous car-bon from the Ar sputtering method The Si(2p) peak didnot show change in the sample conditions of 31sim33but intensity increases in the condition of 34 as well aschanges in binding energy from 1009 eV to 1003 eVThe C (1s) peak showed that intensity decreases and shiftsby lower binding energies in the condition of 34 simi-larly in Figure 3(b) indicating that the surface of the SiCnanowire appeared perfectly to the exterior as the amor-phous carbon is perfectly removed in the condition of 34

4 CONCLUSION

We have grown -SiC nanowires on gold-catalyzedSi(001) substrates using single molecular precursors of13-disilabutane at temperatures below 1000 C by athermal MOCVD method In the case of gold as a cata-lyst deposited SiC nanowires show that thin and shorterSiC nanorods are straightly grown on the substrates at ahigh density TEM analysis results show the grown -SiCnanowires wrapped with an amorphous carbon layer witha thickness of approximately 2sim3 nm We proposed amethod for removal of the amorphous carbon layer enclos-ing the SiC nanowire Figure 4 The first step involvesremoval of the remaining SiO2 followed by cutting theamorphous carbon layer into thin slices using a heatingmethod Finally the thin amorphous carbon slices wereperfectly removed using an Ar sputtering method As aresult this method may yield forth more potential field

emission properties of nanowires previously inhibited bythe amorphous carbon layer

Acknowledgment This work was supported by theKorea Research Foundation Grant funded by the KoreanGovernment (MOEHRD) (KRF-2005-005-J11902) aswell as by the Korea Science and Engineering Founda-tion (project No R01-2006-000-10396-0) In addition theXPS experiments at Pohang Accelerator Laboratory (PAL)were supported in part by the MOST and POSTECHThis paper was supported by Samsung Research FundSungkyunkwan University 2008

References and Notes

1 G Xi Y Peng S Wan T Li W Yu and Y Qian J Phys Chem B108 20102 (2004)

2 H Pan S Lim C Poh H Sun X Wu Y Feng and J LinNanotechnology 16 417 (2005)

3 J D Holmes Science 287 1471 (2000)4 M Diaz J L Costa-Kramer E Medina A Hasmy and P A

Serena Nanotechnology 14 113 (2003)5 X Sun H Zhang J Xu Q Zhao R Wang and D Yu Solid State

Commun 129 803 (2004)6 L Yang C Xue C Wang and H Li Nanotechnology 14 50 (2003)7 H Dai E W Wong Y Z Lu S Fan and C M Lieber Nature

375 769 (1995)8 J Q Hu Q Y Lu K B Tang B Deng R R Jiang Y T Qian

W C Yu G E Zhou X M Liu and J X Wu J Phys Chem B104 5251 (2000)

9 H F Zhang C M Wang and L S Wang Nano Lett 2 941 (2002)10 Z L Wang Z R Dai R P Gao Z G Bai and J L Gole Appl

Phys Lett 77 3349 (2000)11 I A Salama N R Quick and A Kar J Appl Phys 93 9275 (2003)12 M M Waite and S I Shah Appl Phys Lett 60 2344 (1992)13 D N Belton S J Harris S J Schmieg A M Weiner and T A

Perry Appl Phys Lett 54 416 (1989)14 F Arezzo N Zacchetti and W Zhu J Appl Phys 75 5375 (1994)15 P Merel M Tabbal M Chaker S Moisa and J Margot Appl Surf

Sci 136 105 (1998)16 T Y Leung W F Man P K Lim W C Chan F Gaspari and

S Zubotynski J Non-Cryst Solids 254 156 (1999)

Received 7 December 2008 Accepted 20 January 2009

J Nanosci Nanotechnol 10 2741ndash2745 2010 2745

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires Nam et al

be attributed to SindashC CndashO CndashOndashH and C C of theC (1s) peak Waite and Shah12 observed a single peak at abinding energy of 28575 eV attributed to diamond whileSiC and graphite that are formed together with diamondare observed at 2830 and 2846 eV respectively Beltonet al13 attributed the 2843 2827 and 2851 eV peaksto diamond SiC and adventitious carbon respectivelyArezzo et al14 suggested that the binding energies of dia-mond and graphite are 2850 and 2842 eV The deconvo-lution of the C (1s) spectrum yields peak values of 2844and 2852 eV that have been assigned to these 2 types ofatoms1415 giving a separation of about 08 eV betweenthe sp2 and sp3 contributions Leung et al16 assigned the2848 eV peak to the sp2-binding configuration in theirDLC films while the peak at 2857 eV was attributed tothe sp3 component Residual carbon in the SiC nanowiresreduces its field emission properties and as such thereexists a need to establish a method to exclude the residualcarbon In this study we firstly deposited SiC nanowireson gold-covered Si(100) substrates using a single molec-ular precursor at a deposition temperature of 1000 C bya high vacuum metal-organic chemical vapor deposition(MOCVD) method Research about a method to excludethe amorphous carbon layer using various methods suchas thermal heating oxygen atmosphere and Ar sputteringwas also carried out

2 EXPERIMENTAL DETAILS

21 SiC Nanowires Growth

The silicon carbide nanowires were grown in a homemadehigh vacuum metal organic chemical vapor deposition sys-tem The p-type 001 orientated silicon wafer was cutinto rectangle pieces 40times 8 mm2 and used as a basesubstrate for the growth of the silicon carbide nanowiresin this work Prior to their growth the substrate surfacewas degreased accordingly 10 min in an ultrasonic cleanercontaining acetone dipped in DI water for 10 min dippedin 10 wt HF solution for 15 s rinsed with DI waterand flushed in a nitrogen flow We also prepared metalcatalyst-coated Si(001) substrates The gold (Au) catalyst

Table I XPS experimental conditions for the exclusion of the amor-phous carbon layer

ExclusionNumber method Conditions

1 Thermal heating 900 C 10times10minus9 Torr2-1 Heating in 600 C 10times10minus6 Torr

atmosphere O2

2-2 Heating in 900 C 10times10minus6 Torratmosphere O2

3-1 Ar sputtering 05 KeV 5 min 15 A 10times10minus6 Torr3-2 Ar sputtering 05 KeV 10 min 243 A 10times10minus6 Torr3-3 Ar sputtering 10 KeV 10 min 266 A 10times10minus6 Torr3-4 Ar sputtering 10 KeV 10 min 832 A 50times10minus6 Torr

was deposited on the substrate using a thermal evapora-tion method The general growth conditions were a highvacuum pressure of 30times 10minus6 Torr and a temperature of1000 C The 13-disilabutane was employed as a singlesource for the growth of the silicon carbide nanowireswhich were grown directly onto the substrate gold metalcatalyst deposited onto Si(001) surface

(b)

(c)

20

(a)

30 40 50

2 Theta

Inte

nsity

(a

u)

Si(2

00)

SiC

(220

)

SiC

(200

)S

iC(1

11)

Si(4

00)

SiC

(311

)

60 70 80

Fig 1 (a) XRD pattern of SiC nanowires growth on AuSi(100) sub-strates using 13-disilabutane at a pressure of 30times10minus6 Torr at 1000 CFigures (b) and (c) show an SEM image and TEM image of the samesample

2742 J Nanosci Nanotechnol 10 2741ndash2745 2010

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IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

22 Exclusion of Amorphous Carbon inSiC Nanowires

In this study three exclusion methods for the amorphouscarbon in the SiC nanowire were attempted thermal heat-ing heating in oxygen atmosphere and Ar sputtering Thethermal heating method involves technology that breaksdown the binding energy of the amorphous carbon at ahigh temperature 900 C Heating in an oxygen atmo-sphere targets amorphous carbon exclusion through theCndashO interaction at high temperatures such as 600 and900 C Finally Ar sputtering is a method of amorphouscarbon layer removal using an Ar ion or radical generatedby plasma The experimental conditions of these methodswere developed in ultra high vacuum system Table IThe as-grown SiC nanowires were characterized by

X-ray Diffraction (XRD) Scanning Electron Microscopy(SEM) and Transmission electron microscopy (TEM)In addition exclusion of amorphous carbon experimentswere analyzed using X-ray photoelectron spectroscopy(XPS) through which the chemical characteristic of theexclusion amorphous carbon layer were confirmed

Fig 2 (a) XPS results of the SiC nanowire for the exclusion of the amorphous carbon layer using the thermal heating method Figure (b) shows theXPS results of the same sample using the thermal heating method in atmosphere oxygen

3 RESULTS AND DISCUSSION

31 Characterizations of SiC Nanowires

Figure 1(a) shows the XRD patterns of the -SiCnanowires grown at a deposition pressure of 30 times10minus6 Torr for 1 h under the deposition temperature of1000 C using a gold catalyst The XRD pattern exhibitscharacteristic peaks of -SiC at 2 = 356 414 600and 718 which refer to the diffraction of -SiC (111)(200) (220) and (311) planes To compare the JCP cardindex with Figure 1(a) we can conclude that the growthproduct has a zinc-blend structure (-SiC) In additionsince there are four peaks in Figure 1(a) a polycrystallineSiC nanowire has been obtained in our study Conclu-sively -SiC nanowires on metal catalyst-coated Si(001)substrates deposited at 1000 C are polycrystalline andalso exhibit a zinc-blend structureFigure 1(b) shows a typical SEM image of the obtained

-SiC nanowire with a specific thickness and length(such as 30 and 250 nm) grown on a gold (Au) cata-lyst at 1000 C Gold catalyst-deposited SiC nanowiresFigure 1(b) show that the thin and shorter likely SiC

J Nanosci Nanotechnol 10 2741ndash2745 2010 2743

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

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XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires Nam et al

Fig 3 XP spectra of SiC nanowire grown on AuSi(100) substrate at 1000 C obtained beforeafter Ar sputtering (a) high-resolution XP spectra ofSi(2p) and (b) high-resolution XP spectra of C (1s)

nanorods are straight-grown on the substrate at a highdensityTo investigate in greater depth the structure of

as-deposited -SiC nanowires transmission electronmicroscopy (TEM) combined with energy dispersiveX-ray (EDX) analyses were performed For the TEMexperiments the -SiC nanowires grown using gold (Au)catalyst at 1000 C for 1 h were prepared Figure 1(c)shows the typical TEM image obtained from a -SiCnanowire where the grown -SiC nanowire is wrappedwith an amorphous layer with a thickness of approxi-mately 2 nm We can confirm that this layer is amorphouscarbon through electron diffraction (ED) data (see inset ofFig 1(c)) Because the metal-organic source used in thisexperiment contains carbon atoms we speculated that thisamorphous carbon layer originated from the precursor Theinset image (right) in Figure 1(c) shows the correspond-ing selected area electron diffraction (ED) pattern obtainedfrom the same nanowire indicating a circular form of apolycrystalline nature

Fig 4 2-step process schematic diagram for exclusion of the amorphous carbon layer

32 Exclusion Analysis of the AmorphousCarbon Layer by XPS

Figure 2(a) shows the high-resolution spectra of Si(2p)and C (1s) obtained beforeafter the thermal heating High-resolution XP spectra show that the SiO2 peak appearingat 1034 eV decreased and that the SiC peak at 2824 eVincreased when the substrate temperature increased to900 C indicating that desorption of CO or CO2 was com-bined by amorphous carbon and SiO2Figure 2(b) shows high-resolution spectra of Si(2p) and

C (1s) measured after thermal heating at 600 and 900 Crespectively in an oxygen atmosphere to remove residualSiO2 From the experiment at 600 C we confirmed theSiO2 as the source of the material remaining behind on theSiC nanowire surface that was perfectly removed by com-bination with amorphous carbon indicating that an oxygeneffect plays an important role in removal of the SiO2 in anoxygen atmosphere In addition both Si (2p) and C (1s)peak intensities decreased when heated at 900 C denoting

2744 J Nanosci Nanotechnol 10 2741ndash2745 2010

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RESEARCH

ARTIC

LE

Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

that the surface of the amorphous carbon layer becomessmooth and that the number of electrons decrease whichis detected as a result of a decrease in thickness thin-ning As a result the CndashC bonding combination peakthat appears at 2839 eV was not removed under condi-tions of the thermal heating method However this methodperfectly removed the remaining SiO2 and made thin andsmooth the amorphous carbon surfaceFigure 3 shows the high-resolution (HR) XPS data

indicating the reduction in the residual amorphous car-bon from the Ar sputtering method The Si(2p) peak didnot show change in the sample conditions of 31sim33but intensity increases in the condition of 34 as well aschanges in binding energy from 1009 eV to 1003 eVThe C (1s) peak showed that intensity decreases and shiftsby lower binding energies in the condition of 34 simi-larly in Figure 3(b) indicating that the surface of the SiCnanowire appeared perfectly to the exterior as the amor-phous carbon is perfectly removed in the condition of 34

4 CONCLUSION

We have grown -SiC nanowires on gold-catalyzedSi(001) substrates using single molecular precursors of13-disilabutane at temperatures below 1000 C by athermal MOCVD method In the case of gold as a cata-lyst deposited SiC nanowires show that thin and shorterSiC nanorods are straightly grown on the substrates at ahigh density TEM analysis results show the grown -SiCnanowires wrapped with an amorphous carbon layer witha thickness of approximately 2sim3 nm We proposed amethod for removal of the amorphous carbon layer enclos-ing the SiC nanowire Figure 4 The first step involvesremoval of the remaining SiO2 followed by cutting theamorphous carbon layer into thin slices using a heatingmethod Finally the thin amorphous carbon slices wereperfectly removed using an Ar sputtering method As aresult this method may yield forth more potential field

emission properties of nanowires previously inhibited bythe amorphous carbon layer

Acknowledgment This work was supported by theKorea Research Foundation Grant funded by the KoreanGovernment (MOEHRD) (KRF-2005-005-J11902) aswell as by the Korea Science and Engineering Founda-tion (project No R01-2006-000-10396-0) In addition theXPS experiments at Pohang Accelerator Laboratory (PAL)were supported in part by the MOST and POSTECHThis paper was supported by Samsung Research FundSungkyunkwan University 2008

References and Notes

1 G Xi Y Peng S Wan T Li W Yu and Y Qian J Phys Chem B108 20102 (2004)

2 H Pan S Lim C Poh H Sun X Wu Y Feng and J LinNanotechnology 16 417 (2005)

3 J D Holmes Science 287 1471 (2000)4 M Diaz J L Costa-Kramer E Medina A Hasmy and P A

Serena Nanotechnology 14 113 (2003)5 X Sun H Zhang J Xu Q Zhao R Wang and D Yu Solid State

Commun 129 803 (2004)6 L Yang C Xue C Wang and H Li Nanotechnology 14 50 (2003)7 H Dai E W Wong Y Z Lu S Fan and C M Lieber Nature

375 769 (1995)8 J Q Hu Q Y Lu K B Tang B Deng R R Jiang Y T Qian

W C Yu G E Zhou X M Liu and J X Wu J Phys Chem B104 5251 (2000)

9 H F Zhang C M Wang and L S Wang Nano Lett 2 941 (2002)10 Z L Wang Z R Dai R P Gao Z G Bai and J L Gole Appl

Phys Lett 77 3349 (2000)11 I A Salama N R Quick and A Kar J Appl Phys 93 9275 (2003)12 M M Waite and S I Shah Appl Phys Lett 60 2344 (1992)13 D N Belton S J Harris S J Schmieg A M Weiner and T A

Perry Appl Phys Lett 54 416 (1989)14 F Arezzo N Zacchetti and W Zhu J Appl Phys 75 5375 (1994)15 P Merel M Tabbal M Chaker S Moisa and J Margot Appl Surf

Sci 136 105 (1998)16 T Y Leung W F Man P K Lim W C Chan F Gaspari and

S Zubotynski J Non-Cryst Solids 254 156 (1999)

Received 7 December 2008 Accepted 20 January 2009

J Nanosci Nanotechnol 10 2741ndash2745 2010 2745

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

22 Exclusion of Amorphous Carbon inSiC Nanowires

In this study three exclusion methods for the amorphouscarbon in the SiC nanowire were attempted thermal heat-ing heating in oxygen atmosphere and Ar sputtering Thethermal heating method involves technology that breaksdown the binding energy of the amorphous carbon at ahigh temperature 900 C Heating in an oxygen atmo-sphere targets amorphous carbon exclusion through theCndashO interaction at high temperatures such as 600 and900 C Finally Ar sputtering is a method of amorphouscarbon layer removal using an Ar ion or radical generatedby plasma The experimental conditions of these methodswere developed in ultra high vacuum system Table IThe as-grown SiC nanowires were characterized by

X-ray Diffraction (XRD) Scanning Electron Microscopy(SEM) and Transmission electron microscopy (TEM)In addition exclusion of amorphous carbon experimentswere analyzed using X-ray photoelectron spectroscopy(XPS) through which the chemical characteristic of theexclusion amorphous carbon layer were confirmed

Fig 2 (a) XPS results of the SiC nanowire for the exclusion of the amorphous carbon layer using the thermal heating method Figure (b) shows theXPS results of the same sample using the thermal heating method in atmosphere oxygen

3 RESULTS AND DISCUSSION

31 Characterizations of SiC Nanowires

Figure 1(a) shows the XRD patterns of the -SiCnanowires grown at a deposition pressure of 30 times10minus6 Torr for 1 h under the deposition temperature of1000 C using a gold catalyst The XRD pattern exhibitscharacteristic peaks of -SiC at 2 = 356 414 600and 718 which refer to the diffraction of -SiC (111)(200) (220) and (311) planes To compare the JCP cardindex with Figure 1(a) we can conclude that the growthproduct has a zinc-blend structure (-SiC) In additionsince there are four peaks in Figure 1(a) a polycrystallineSiC nanowire has been obtained in our study Conclu-sively -SiC nanowires on metal catalyst-coated Si(001)substrates deposited at 1000 C are polycrystalline andalso exhibit a zinc-blend structureFigure 1(b) shows a typical SEM image of the obtained

-SiC nanowire with a specific thickness and length(such as 30 and 250 nm) grown on a gold (Au) cata-lyst at 1000 C Gold catalyst-deposited SiC nanowiresFigure 1(b) show that the thin and shorter likely SiC

J Nanosci Nanotechnol 10 2741ndash2745 2010 2743

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires Nam et al

Fig 3 XP spectra of SiC nanowire grown on AuSi(100) substrate at 1000 C obtained beforeafter Ar sputtering (a) high-resolution XP spectra ofSi(2p) and (b) high-resolution XP spectra of C (1s)

nanorods are straight-grown on the substrate at a highdensityTo investigate in greater depth the structure of

as-deposited -SiC nanowires transmission electronmicroscopy (TEM) combined with energy dispersiveX-ray (EDX) analyses were performed For the TEMexperiments the -SiC nanowires grown using gold (Au)catalyst at 1000 C for 1 h were prepared Figure 1(c)shows the typical TEM image obtained from a -SiCnanowire where the grown -SiC nanowire is wrappedwith an amorphous layer with a thickness of approxi-mately 2 nm We can confirm that this layer is amorphouscarbon through electron diffraction (ED) data (see inset ofFig 1(c)) Because the metal-organic source used in thisexperiment contains carbon atoms we speculated that thisamorphous carbon layer originated from the precursor Theinset image (right) in Figure 1(c) shows the correspond-ing selected area electron diffraction (ED) pattern obtainedfrom the same nanowire indicating a circular form of apolycrystalline nature

Fig 4 2-step process schematic diagram for exclusion of the amorphous carbon layer

32 Exclusion Analysis of the AmorphousCarbon Layer by XPS

Figure 2(a) shows the high-resolution spectra of Si(2p)and C (1s) obtained beforeafter the thermal heating High-resolution XP spectra show that the SiO2 peak appearingat 1034 eV decreased and that the SiC peak at 2824 eVincreased when the substrate temperature increased to900 C indicating that desorption of CO or CO2 was com-bined by amorphous carbon and SiO2Figure 2(b) shows high-resolution spectra of Si(2p) and

C (1s) measured after thermal heating at 600 and 900 Crespectively in an oxygen atmosphere to remove residualSiO2 From the experiment at 600 C we confirmed theSiO2 as the source of the material remaining behind on theSiC nanowire surface that was perfectly removed by com-bination with amorphous carbon indicating that an oxygeneffect plays an important role in removal of the SiO2 in anoxygen atmosphere In addition both Si (2p) and C (1s)peak intensities decreased when heated at 900 C denoting

2744 J Nanosci Nanotechnol 10 2741ndash2745 2010

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

that the surface of the amorphous carbon layer becomessmooth and that the number of electrons decrease whichis detected as a result of a decrease in thickness thin-ning As a result the CndashC bonding combination peakthat appears at 2839 eV was not removed under condi-tions of the thermal heating method However this methodperfectly removed the remaining SiO2 and made thin andsmooth the amorphous carbon surfaceFigure 3 shows the high-resolution (HR) XPS data

indicating the reduction in the residual amorphous car-bon from the Ar sputtering method The Si(2p) peak didnot show change in the sample conditions of 31sim33but intensity increases in the condition of 34 as well aschanges in binding energy from 1009 eV to 1003 eVThe C (1s) peak showed that intensity decreases and shiftsby lower binding energies in the condition of 34 simi-larly in Figure 3(b) indicating that the surface of the SiCnanowire appeared perfectly to the exterior as the amor-phous carbon is perfectly removed in the condition of 34

4 CONCLUSION

We have grown -SiC nanowires on gold-catalyzedSi(001) substrates using single molecular precursors of13-disilabutane at temperatures below 1000 C by athermal MOCVD method In the case of gold as a cata-lyst deposited SiC nanowires show that thin and shorterSiC nanorods are straightly grown on the substrates at ahigh density TEM analysis results show the grown -SiCnanowires wrapped with an amorphous carbon layer witha thickness of approximately 2sim3 nm We proposed amethod for removal of the amorphous carbon layer enclos-ing the SiC nanowire Figure 4 The first step involvesremoval of the remaining SiO2 followed by cutting theamorphous carbon layer into thin slices using a heatingmethod Finally the thin amorphous carbon slices wereperfectly removed using an Ar sputtering method As aresult this method may yield forth more potential field

emission properties of nanowires previously inhibited bythe amorphous carbon layer

Acknowledgment This work was supported by theKorea Research Foundation Grant funded by the KoreanGovernment (MOEHRD) (KRF-2005-005-J11902) aswell as by the Korea Science and Engineering Founda-tion (project No R01-2006-000-10396-0) In addition theXPS experiments at Pohang Accelerator Laboratory (PAL)were supported in part by the MOST and POSTECHThis paper was supported by Samsung Research FundSungkyunkwan University 2008

References and Notes

1 G Xi Y Peng S Wan T Li W Yu and Y Qian J Phys Chem B108 20102 (2004)

2 H Pan S Lim C Poh H Sun X Wu Y Feng and J LinNanotechnology 16 417 (2005)

3 J D Holmes Science 287 1471 (2000)4 M Diaz J L Costa-Kramer E Medina A Hasmy and P A

Serena Nanotechnology 14 113 (2003)5 X Sun H Zhang J Xu Q Zhao R Wang and D Yu Solid State

Commun 129 803 (2004)6 L Yang C Xue C Wang and H Li Nanotechnology 14 50 (2003)7 H Dai E W Wong Y Z Lu S Fan and C M Lieber Nature

375 769 (1995)8 J Q Hu Q Y Lu K B Tang B Deng R R Jiang Y T Qian

W C Yu G E Zhou X M Liu and J X Wu J Phys Chem B104 5251 (2000)

9 H F Zhang C M Wang and L S Wang Nano Lett 2 941 (2002)10 Z L Wang Z R Dai R P Gao Z G Bai and J L Gole Appl

Phys Lett 77 3349 (2000)11 I A Salama N R Quick and A Kar J Appl Phys 93 9275 (2003)12 M M Waite and S I Shah Appl Phys Lett 60 2344 (1992)13 D N Belton S J Harris S J Schmieg A M Weiner and T A

Perry Appl Phys Lett 54 416 (1989)14 F Arezzo N Zacchetti and W Zhu J Appl Phys 75 5375 (1994)15 P Merel M Tabbal M Chaker S Moisa and J Margot Appl Surf

Sci 136 105 (1998)16 T Y Leung W F Man P K Lim W C Chan F Gaspari and

S Zubotynski J Non-Cryst Solids 254 156 (1999)

Received 7 December 2008 Accepted 20 January 2009

J Nanosci Nanotechnol 10 2741ndash2745 2010 2745

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires Nam et al

Fig 3 XP spectra of SiC nanowire grown on AuSi(100) substrate at 1000 C obtained beforeafter Ar sputtering (a) high-resolution XP spectra ofSi(2p) and (b) high-resolution XP spectra of C (1s)

nanorods are straight-grown on the substrate at a highdensityTo investigate in greater depth the structure of

as-deposited -SiC nanowires transmission electronmicroscopy (TEM) combined with energy dispersiveX-ray (EDX) analyses were performed For the TEMexperiments the -SiC nanowires grown using gold (Au)catalyst at 1000 C for 1 h were prepared Figure 1(c)shows the typical TEM image obtained from a -SiCnanowire where the grown -SiC nanowire is wrappedwith an amorphous layer with a thickness of approxi-mately 2 nm We can confirm that this layer is amorphouscarbon through electron diffraction (ED) data (see inset ofFig 1(c)) Because the metal-organic source used in thisexperiment contains carbon atoms we speculated that thisamorphous carbon layer originated from the precursor Theinset image (right) in Figure 1(c) shows the correspond-ing selected area electron diffraction (ED) pattern obtainedfrom the same nanowire indicating a circular form of apolycrystalline nature

Fig 4 2-step process schematic diagram for exclusion of the amorphous carbon layer

32 Exclusion Analysis of the AmorphousCarbon Layer by XPS

Figure 2(a) shows the high-resolution spectra of Si(2p)and C (1s) obtained beforeafter the thermal heating High-resolution XP spectra show that the SiO2 peak appearingat 1034 eV decreased and that the SiC peak at 2824 eVincreased when the substrate temperature increased to900 C indicating that desorption of CO or CO2 was com-bined by amorphous carbon and SiO2Figure 2(b) shows high-resolution spectra of Si(2p) and

C (1s) measured after thermal heating at 600 and 900 Crespectively in an oxygen atmosphere to remove residualSiO2 From the experiment at 600 C we confirmed theSiO2 as the source of the material remaining behind on theSiC nanowire surface that was perfectly removed by com-bination with amorphous carbon indicating that an oxygeneffect plays an important role in removal of the SiO2 in anoxygen atmosphere In addition both Si (2p) and C (1s)peak intensities decreased when heated at 900 C denoting

2744 J Nanosci Nanotechnol 10 2741ndash2745 2010

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

that the surface of the amorphous carbon layer becomessmooth and that the number of electrons decrease whichis detected as a result of a decrease in thickness thin-ning As a result the CndashC bonding combination peakthat appears at 2839 eV was not removed under condi-tions of the thermal heating method However this methodperfectly removed the remaining SiO2 and made thin andsmooth the amorphous carbon surfaceFigure 3 shows the high-resolution (HR) XPS data

indicating the reduction in the residual amorphous car-bon from the Ar sputtering method The Si(2p) peak didnot show change in the sample conditions of 31sim33but intensity increases in the condition of 34 as well aschanges in binding energy from 1009 eV to 1003 eVThe C (1s) peak showed that intensity decreases and shiftsby lower binding energies in the condition of 34 simi-larly in Figure 3(b) indicating that the surface of the SiCnanowire appeared perfectly to the exterior as the amor-phous carbon is perfectly removed in the condition of 34

4 CONCLUSION

We have grown -SiC nanowires on gold-catalyzedSi(001) substrates using single molecular precursors of13-disilabutane at temperatures below 1000 C by athermal MOCVD method In the case of gold as a cata-lyst deposited SiC nanowires show that thin and shorterSiC nanorods are straightly grown on the substrates at ahigh density TEM analysis results show the grown -SiCnanowires wrapped with an amorphous carbon layer witha thickness of approximately 2sim3 nm We proposed amethod for removal of the amorphous carbon layer enclos-ing the SiC nanowire Figure 4 The first step involvesremoval of the remaining SiO2 followed by cutting theamorphous carbon layer into thin slices using a heatingmethod Finally the thin amorphous carbon slices wereperfectly removed using an Ar sputtering method As aresult this method may yield forth more potential field

emission properties of nanowires previously inhibited bythe amorphous carbon layer

Acknowledgment This work was supported by theKorea Research Foundation Grant funded by the KoreanGovernment (MOEHRD) (KRF-2005-005-J11902) aswell as by the Korea Science and Engineering Founda-tion (project No R01-2006-000-10396-0) In addition theXPS experiments at Pohang Accelerator Laboratory (PAL)were supported in part by the MOST and POSTECHThis paper was supported by Samsung Research FundSungkyunkwan University 2008

References and Notes

1 G Xi Y Peng S Wan T Li W Yu and Y Qian J Phys Chem B108 20102 (2004)

2 H Pan S Lim C Poh H Sun X Wu Y Feng and J LinNanotechnology 16 417 (2005)

3 J D Holmes Science 287 1471 (2000)4 M Diaz J L Costa-Kramer E Medina A Hasmy and P A

Serena Nanotechnology 14 113 (2003)5 X Sun H Zhang J Xu Q Zhao R Wang and D Yu Solid State

Commun 129 803 (2004)6 L Yang C Xue C Wang and H Li Nanotechnology 14 50 (2003)7 H Dai E W Wong Y Z Lu S Fan and C M Lieber Nature

375 769 (1995)8 J Q Hu Q Y Lu K B Tang B Deng R R Jiang Y T Qian

W C Yu G E Zhou X M Liu and J X Wu J Phys Chem B104 5251 (2000)

9 H F Zhang C M Wang and L S Wang Nano Lett 2 941 (2002)10 Z L Wang Z R Dai R P Gao Z G Bai and J L Gole Appl

Phys Lett 77 3349 (2000)11 I A Salama N R Quick and A Kar J Appl Phys 93 9275 (2003)12 M M Waite and S I Shah Appl Phys Lett 60 2344 (1992)13 D N Belton S J Harris S J Schmieg A M Weiner and T A

Perry Appl Phys Lett 54 416 (1989)14 F Arezzo N Zacchetti and W Zhu J Appl Phys 75 5375 (1994)15 P Merel M Tabbal M Chaker S Moisa and J Margot Appl Surf

Sci 136 105 (1998)16 T Y Leung W F Man P K Lim W C Chan F Gaspari and

S Zubotynski J Non-Cryst Solids 254 156 (1999)

Received 7 December 2008 Accepted 20 January 2009

J Nanosci Nanotechnol 10 2741ndash2745 2010 2745

Delivered by Ingenta toSung Kyun Kwan University

IP 11514520978Sat 08 May 2010 082542

RESEARCH

ARTIC

LE

Nam et al XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires

that the surface of the amorphous carbon layer becomessmooth and that the number of electrons decrease whichis detected as a result of a decrease in thickness thin-ning As a result the CndashC bonding combination peakthat appears at 2839 eV was not removed under condi-tions of the thermal heating method However this methodperfectly removed the remaining SiO2 and made thin andsmooth the amorphous carbon surfaceFigure 3 shows the high-resolution (HR) XPS data

indicating the reduction in the residual amorphous car-bon from the Ar sputtering method The Si(2p) peak didnot show change in the sample conditions of 31sim33but intensity increases in the condition of 34 as well aschanges in binding energy from 1009 eV to 1003 eVThe C (1s) peak showed that intensity decreases and shiftsby lower binding energies in the condition of 34 simi-larly in Figure 3(b) indicating that the surface of the SiCnanowire appeared perfectly to the exterior as the amor-phous carbon is perfectly removed in the condition of 34

4 CONCLUSION

We have grown -SiC nanowires on gold-catalyzedSi(001) substrates using single molecular precursors of13-disilabutane at temperatures below 1000 C by athermal MOCVD method In the case of gold as a cata-lyst deposited SiC nanowires show that thin and shorterSiC nanorods are straightly grown on the substrates at ahigh density TEM analysis results show the grown -SiCnanowires wrapped with an amorphous carbon layer witha thickness of approximately 2sim3 nm We proposed amethod for removal of the amorphous carbon layer enclos-ing the SiC nanowire Figure 4 The first step involvesremoval of the remaining SiO2 followed by cutting theamorphous carbon layer into thin slices using a heatingmethod Finally the thin amorphous carbon slices wereperfectly removed using an Ar sputtering method As aresult this method may yield forth more potential field

emission properties of nanowires previously inhibited bythe amorphous carbon layer

Acknowledgment This work was supported by theKorea Research Foundation Grant funded by the KoreanGovernment (MOEHRD) (KRF-2005-005-J11902) aswell as by the Korea Science and Engineering Founda-tion (project No R01-2006-000-10396-0) In addition theXPS experiments at Pohang Accelerator Laboratory (PAL)were supported in part by the MOST and POSTECHThis paper was supported by Samsung Research FundSungkyunkwan University 2008

References and Notes

1 G Xi Y Peng S Wan T Li W Yu and Y Qian J Phys Chem B108 20102 (2004)

2 H Pan S Lim C Poh H Sun X Wu Y Feng and J LinNanotechnology 16 417 (2005)

3 J D Holmes Science 287 1471 (2000)4 M Diaz J L Costa-Kramer E Medina A Hasmy and P A

Serena Nanotechnology 14 113 (2003)5 X Sun H Zhang J Xu Q Zhao R Wang and D Yu Solid State

Commun 129 803 (2004)6 L Yang C Xue C Wang and H Li Nanotechnology 14 50 (2003)7 H Dai E W Wong Y Z Lu S Fan and C M Lieber Nature

375 769 (1995)8 J Q Hu Q Y Lu K B Tang B Deng R R Jiang Y T Qian

W C Yu G E Zhou X M Liu and J X Wu J Phys Chem B104 5251 (2000)

9 H F Zhang C M Wang and L S Wang Nano Lett 2 941 (2002)10 Z L Wang Z R Dai R P Gao Z G Bai and J L Gole Appl

Phys Lett 77 3349 (2000)11 I A Salama N R Quick and A Kar J Appl Phys 93 9275 (2003)12 M M Waite and S I Shah Appl Phys Lett 60 2344 (1992)13 D N Belton S J Harris S J Schmieg A M Weiner and T A

Perry Appl Phys Lett 54 416 (1989)14 F Arezzo N Zacchetti and W Zhu J Appl Phys 75 5375 (1994)15 P Merel M Tabbal M Chaker S Moisa and J Margot Appl Surf

Sci 136 105 (1998)16 T Y Leung W F Man P K Lim W C Chan F Gaspari and

S Zubotynski J Non-Cryst Solids 254 156 (1999)

Received 7 December 2008 Accepted 20 January 2009

J Nanosci Nanotechnol 10 2741ndash2745 2010 2745