research article self-catalytic growth of tin oxide...

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 712361 7 pageshttpdxdoiorg1011552013712361

Research ArticleSelf-Catalytic Growth of Tin Oxide Nanowires byChemical Vapor Deposition Process

Bongani S Thabethe12 Gerald F Malgas12 David E Motaung1

Thomas Malwela1 and Christopher J Arendse2

1 DSTCSIR Nanotechnology Innovation Centre National Centre for Nanostructured MaterialsCouncil for Scientific and Industrial Research PO Box 395 Pretoria 0001 South Africa

2 Department of Physics University of the Western Cape Private Bag X17 Bellville 7535 South Africa

Correspondence should be addressed to Gerald F Malgas gmalgascsircoza and David E Motaung dmotaungcsircoza

Received 20 February 2013 Accepted 10 June 2013

Academic Editor Rakesh Joshi

Copyright copy 2013 Bongani S Thabethe et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

We report on the synthesis of tin oxide (SnO2) nanowires by a chemical vapor deposition (CVD) process Commercially bought

SnO nanopowders were vaporized at 1050∘C for 30 minutes with argon gas continuously passing through the system The as-synthesized products were characterized using UV-visible absorption spectroscopy X-ray diffraction (XRD) scanning electronmicroscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) The band gap of the nanowires determinedfrom UV-visible absorption was around 37 eV The SEM micrographs revealed ldquowool-likerdquo structure which contains nanoribbonsand nanowires with liquid droplets at the tips Nanowires typically have diameter in the range of 50ndash200 nm and length 10ndash100 120583mThese nanowires followed the vapor-liquid-solid (VLS) growth mechanism

1 Introduction

One-dimensional (1D)metal oxides semiconductor nanoma-terials have attracted great interest as CO gas sensors due totheir novel electronic and optical properties in nanodevicesand because of their active sites to adsorb gas molecules andcatalytic reactions [1ndash7] These sensors play an essential rolein the fields of industrial processing environmental protec-tion and medical treatment However many problems needto be solved to further improve the selectivity sensitivityand stability of the sensors Among them SnO

2 an n-type

semiconductorwith awide direct band gap energy of 36 eV isa particularmaterial of interest because of its unique electricalproperties optical properties small size high sensitivitygood chemical stability high electron mobility fast responseand recovery speed [4 8ndash10] Tin oxide thin films find thebest use in chemical sensorswhich are commercially availablefor detecting fuel gas carbon monoxide combustible gasesammonia water vapour and numerous other gases andvapors [11]

Due to the enhanced surface-to-volume ratio of 1D struc-tures tin oxide nanowires have been shown to have excellentsensing performance which is comparable to or even betterthan the thin film sensors [12ndash14] These structures with ahigh aspect ratio (ie size confinement in two coordinates)offer better crystallinity higher integration density and lowerpower consumption [15] It has been reported by severalauthors that the performances of gas sensors can be enhancedby increasing the specific surface area by way of achievingnanoparticles [16 17] and by incorporation of noble metals[18] such as platinum or gold SnO

2nanowires have been

synthesized by different methods such as laser ablation [19]solution [20] template-based method [21] chemical vapordeposition [22] and thermal evaporation [23] In the last yeara great effort has been put into understanding and controllingthe growth process for the preparation of high quality quasione-dimensional nanostructures In this study we reporton the self-catalytic growth of SnO

2nanowires using a

chemical vapor deposition processThe optical and structural

2 Journal of Nanomaterials

properties of the as-grown nanowires at room temperatureare also studied

2 Experimental Details

Tin oxide nanowires were grown on a silicon substrate and atthe end of the tube by a CVDprocess using about one gram ofmonotin oxide (SnO) (purity 90) at a growth temperatureof 1050∘CThe SnOwas placed into a quartz boat and insertedinto the centre of a quartz tube (radius = 5 cm length= 20 cm)at a distance of about 1-2 cm from the Si substrateThe furnacetemperature was increased from room temperature (25∘C)to 1050∘C for 30min The annealing was made in an argonatmosphere at atmospheric pressure After cooling down afluffy layer of deposition could be collected from inside thetube wall ends in the lower end temperature zone or on theSilicon substrate

UV-visible absorption measurements were carried outon the SnO nanopowders and the SnO

2nanowires using a

Perkin Elmer spectrophotometer in a range between 200 and900 nm The morphology of the product was examined byfield-emission scanning electron microscopy (Auriga ZeissSEM) with a beam energy of 3 keV The crystal structure ofthe as-synthesized product was analysed by X-ray diffraction(XRD) analysis using a Phillips X-ray diffractometer Ahigh-resolution transmission electronmicroscope (HRTEM-JEOL-2000) was used to examine the internal structure ofthe as-synthesized product The chemical compositions weredetermined using an energy dispersive X-ray spectrometer(EDS) attached to the HRTEM instrument

3 Results and Discussion

The optical band gap of commercially bought SnO and SnO2

nanowires was investigated using the UV-visible absorptionspectrometer Figure 1 shows the UV-vis spectra of thecommercially bought SnO powder and as-synthesized SnO

2

nanowires at 1050∘C for 30min in argon gas Both sampleswere dissolved in isopropanol for UV-vis analysis A weakband edge absorption in the spectrum is observed around the375 nm wavelength The optical transition of SnO

2crystals

is known to be a direct type [24] where the absorptioncoefficient 120572 can be expressed as [25]

(120572ℎ])2prop (ℎ] minus 119864

119892) (1)

where ℎ] is the photon energy119864119892is the apparent optical band

gap and 120572 is the absorption coefficient Plots of (120572ℎ])2 versusℎ] can be derived from the absorption data in Figure 1 asshown in the inset Therefore the band gap can be obtainedby extrapolation of the previous relation in the inset ofFigure 1 The intercept of the tangent to the plot gives a goodapproximation of the band gap energy of direct band gapmaterials The calculated energy band gap values are sim37 eVfor SnO

2nanowires and sim364 eV for commercially bought

SnOpowder respectivelyThese values are slightly larger thanthat of bulk SnO

2(362 eV) and might be due to the quantum

size effect [26ndash28]

Table 1 Quantitative analysis of the SnO2 nanowires

Element Atomic WeightO 6453- 2078-Sn 3042 plusmn 027 7268 plusmn 064

Cu 271 plusmn 021 347 plusmn 027

Zn 233 plusmn 027 307 plusmn 036

Figure 2 shows the scanning electron microscopy (SEM)micrographs of Figure 2(a) commercially bought SnO pow-der and Figures 2(b) and 2(c) fluffy gray SnO

2product that

was collected on the wall of the inner quartz tube afterit was synthesized at a growth temperature of 1050∘C for30min It is evident that the as-synthesized products aredominated by ldquowire-likerdquo structures whose diameter variesfrom 50 to 200 nm The length of the wires ranges fromseveral tens to several hundredmicrometers Figures 3(a) and3(b) show high magnification images of the nanowires It isobserved that spherical particles are attached to the ends ofthe nanowires Energy-dispersive X-ray spectroscopy (EDS)analysis (Figure 4 and Table 1) extracted at four differentspots showed that the tip of the nanowires consists of tin(Sn) and oxygen (O) only The Cu and Zn peaks presentin the EDS spectra are from the brass stubs used in thesample preparation The result reveals that the products arethe coexistence of Sn andOwith amolar ratio of 3321 6664which is consistent with the composition of SnO

2and is in

good agreement with the XRD results (Figure 5)The X-ray diffraction analyses of the tin oxide precursor

were carried out as shown in Figure 5(a) All the diffractionpeaks can be attributed to the tetragonal tin oxide (SnO)(JCPDS 006-0395) with lattice constants of 119886 = 119887 = 3802 Aand 119888 = 4836 A Figure 5(b) shows the X-ray diffractionpattern for the synthesized tin oxide nanowires and ribbonsFrom the diffraction patterns the as-synthesized SnO

2

nanowires have a good crystallinity with the tetragonal tinoxide SnO

2structure The structure of the nanowires was

further characterized by transmission electron microscopyand selected area electron diffraction (SAED) patternsFigures 6(a) and 6(b) show a low and high magnificationTEM image of a single SnO

2nanowire respectively

with uniform diameter It is evident that the diameter ofnanowiresnanobelts varies from 50 to 200 nm with a fewSn droplets on the nanowires The observed tip morphologyon top of the SnO

2nanowires is consistent with the SEM

analysis The SAED pattern of the tip and the tail of thenanowires are shown in Figures 6(c) and 6(d) respectivelyThe patterns clearly confirm the polycrystalline nature of thenanowires It should be pointed out that nometal catalyst wasused during the growth of the nanowires Therefore basedon these findings we can conclude that the SnO

2nanowires

follow the vapor liquid-solid (VLS) growth mechanismThe growth mechanism of nanowires in thermal evap-

oration [29] can be explained by either vapour-liquid-solid(VLS) [30] and or vapour-solid (VS) [31] Vapor-liquid-solid(VLS)mechanism is a catalyst-assisted growth process wheremetal nanoclusters or nanoparticles are used as the nucle-ation seeds These nucleation seeds determine the interfacial

Journal of Nanomaterials 3

350 400 450 500 550 600Wavelength (nm)

03

04

05

06

07

08

Abso

rban

ce (a

u)

Pure SnOSnO2 nanowires

0300600900

12001500

20 25 30 35 40 45 50

(120572h )

2

Photon energy (eV)

Figure 1 UV-visible absorption spectra of commercially bought SnO powder and SnO2nanowiresThe inset shows the (120572ℎ])2 versus photon

energy curve

10120583m

(a)

20120583m

(b)

10120583m

(c)

Figure 2 SEM micrographs of (a) pure commercially bought SnO powders and (b) and (c) SnO2nanowire networks synthesized at 1050∘C

for 30min


2120583m

(a)

300nm

(b)

Figure 3 (a) SEM images of the synthesized SnO2nanowires and (b) a high magnification image of a single nanowire with a tip

2 4 6 8 100

2000

4000

6000

CuZnCuSn

Sn

Sn

Sn

OInte

nsity

(au

)

Energy (keV)

Spot1Spot2

Spot3Spot4

Figure 4 EDS spectra of four different spots of tin oxide nanowires The inset shows the SEM images and the different spots analyzed

10 20 30 40 50 60 70

0

5000

10000

15000

20000

25000

30000

35000

40000

(102

)(001

)

(103

)

(211

)(112

)(2

00)

(002

)(1

10)

(101

)

Inte

nsity

(au

)

Pure SnO

2120579 (degrees)

(a)

10 20 30 40 50 60 70

0

1000

2000

3000

4000

5000

6000

Inte

nsity

(au

)

2120579 (degrees)

SnO2

(310

)Sn

O2

(002

)

SnO2

(220

)Sn

O2

(210

)

SnO2

(111

)Sn

O2

(200

)

SnO2

(101

)

SnO2

(110

)

SnO2 synthesized at 1050∘C

(b)

Figure 5 X-ray diffraction patterns of (a) pure SnO and (b) the as-synthesized SnO2nanowires at a growth temperature of 1050∘C for 30min


05 120583m

(a)

100nm

(b)

5 1nm

(c)

5 1nm

(d)

Figure 6 (a) and (b) Bright-field TEM images of SnO2nanowires and the corresponding diffraction patterns of (c) tip and (d) tail of the

nanowires

energy growth direction and diameter of the final 1D metaloxide nanostructures Briefly the following chemical reactionwill take place during the thermal evaporation process [29]

2SnO (g) 997888rarr Sn (l) + SnO2(s) (2)

It is believed that tin oxide (SnO) vaporwill be transferredby the argon gas (Ar) or is naturally spread out by thermaldiffusion to the deposition area Because SnO is metastableit will decompose into Sn and SnO

2above 600∘C forming Sn

droplets as shown from the previous equation According tothis mechanism a metal catalyst is needed for Sn-metal alloydroplets by the reaction with the metal catalyst particles Atthe same time these droplets can provide the energeticallyfavored sites for adsorption of SnO vapor Subsequently thedecomposition of SnOwill result in the precipitation of SnO

2

and this leads to the formation of SnO2nanostructures [32]

However in this process no catalyst was used and thereforethe growth of the nanowires is not consistent with the VLSmodel but governed by the VS mechanism Therefore thenanonuclei necessary for theVLS growth of nanowires which

used to be obtained by adding an adscititious metal catalystcan also be created through internal chemical reactions ofprecursors which are considered to be a self-catalytic growthwhich is in good agreement with the results obtained by theEDS analysis

4 Conclusions

SnO2nanowires have been successfully synthesized using

a quartz tube-based CVD reactor at a growth temperatureof 1050∘C for 30 minutes The microstructures and surfacecompositions of the nanowires were characterized by SEM-EDS XRD and TEMThe SEMmicrographs revealed ldquowool-likerdquo structures with a network of nanowires ribbons andbelts The nanowires follow the vapor-liquid-solid growthmechanismwhich is evident because of the liquid droplets onthe tip of the nanowires They serve as transporting mediumas the nanowires develop as a result of the precipitationprocess No metal catalyst was used in the synthesis ofthese nano wires which proves that the tin oxide is self-catalytic during the synthesis process EDX analysis showed


that the samples are purely Sn and O with a 1 2 weight ratioNanowires have diameters in the range of 50ndash200 nm andlength 10ndash100120583m X-ray diffraction analysis confirmed thatthe as-synthesized materials are highly crystalline The bandgap value of the SnO

2nanowires obtained by UV-vis was

around 37 eV

Acknowledgments

The authors would like to acknowledge the financial supportof the Council for Scientific and Industrial Research (CSIR)South Africa (Project no HGER27S) and the Department ofScience and Technology

References

[1] S Y Li C Y Lee and T Y Tseng ldquoCopper-catalyzed ZnOnanowires on silicon (1 0 0) grown by vapor-liquid-solid proc-essrdquo Journal of Crystal Growth vol 247 no 3-4 pp 357ndash3622003

[2] J XWangD F Liu XQ Yan et al ldquoGrowth of SnO2nanowires

with uniform branched structuresrdquo Solid State Communica-tions vol 130 no 1-2 pp 89ndash94 2004

[3] ZW Pan Z R Dai L Xu S T Lee and Z LWang ldquoTempera-ture-controlled growth of silicon-based nanostructures by ther-mal evaporation of SiO powdersrdquo Journal of Physical ChemistryB vol 105 no 13 pp 2507ndash2514 2001

[4] K D Schierbaum U Weimar and W Gopel ldquoSchottky-barri-er and conductivity gas sensors based upon PdSnO

2and Pt

TiO2rdquo Sensors and Actuators B vol 4 no 1-2 pp 87ndash94 1992

[5] D E Williams ldquoSemiconducting oxides as gas-sensitive resis-torsrdquo Sensors and Actuators B vol 57 no 1ndash3 pp 1ndash16 1999

[6] W Fliegel G Behr J Werner and G Krabbes ldquoPreparationdevelopment of microstructure electrical and gas-sensitiveproperties of pure and doped SnO

2powdersrdquo Sensors and Actu-

ators B vol 19 no 1ndash3 pp 474ndash477 1994[7] G Korotcenkov ldquoMetal oxides for solid-state gas sensors what

determines our choicerdquo Materials Science and Engineering Bvol 139 no 1 pp 1ndash23 2007

[8] G Korotcenkov V Brynzari and S Dmitriev ldquoSnO2films for

thin film gas sensor designrdquoMaterials Science and EngineeringB vol 63 no 3 pp 195ndash204 1999

[9] N Yamazoe Y Kurokawa and T Seiyama ldquoEffects of additiveson semiconductor gas sensorsrdquo Sensors andActuators vol 4 pp283ndash289 1983

[10] G Zhang and M Liu ldquoEffect of particle size and dopant onproperties of SnO

2-based gas sensorsrdquo Sensors and Actuators B

vol 69 no 1 pp 144ndash152 2000[11] K J Albert N S Lewis C L Schauer et al ldquoCross-reactive

chemical sensor arraysrdquo Chemical Reviews vol 100 no 7 pp2595ndash2626 2000

[12] M Meyyappan and M S Sunkara Inorganic Nanowires CRCBoca Raton Fla USA 2009

[13] Z Ying QWan Z T Song and S L Feng ldquoSnO2nanowhiskers

and their ethanol sensing characteristicsrdquo Nanotechnology vol15 no 11 pp 1682ndash1684 2004

[14] V V Sysoev B K Button K Wepsiec S Dmitriev and AKolmakov ldquoToward the nanoscopic ldquoelectronic noserdquo hydrogenvs carbon monoxide discrimination with an array of individual

metal oxide nano- and mesowire sensorsrdquo Nano Letters vol 6no 8 pp 1584ndash1588 2006

[15] J G Lu P Chang and Z Fan ldquoQuasi-one-dimensional metaloxide materialsmdashsynthesis properties and applicationsrdquoMate-rials Science and Engineering R vol 52 no 1ndash3 pp 49ndash91 2006

[16] N-L Wu S-Y Wang and I A Rusakova ldquoInhibition of crys-tallite growth in the sol-gel synthesis of nanocrystalline metaloxidesrdquo Science vol 285 no 5432 pp 1375ndash1377 1999

[17] YWang X Jiang andY Xia ldquoA solution-phase precursor routeto polycrystalline SnO

2nanowires that can be used for gas sens-

ing under ambient conditionsrdquo Journal of the American Chemi-cal Society vol 125 no 52 pp 16176ndash16177 2003

[18] M Yuasa T Masaki T Kida K Shimanoe and N YamazoeldquoNano-sized PdO loaded SnO

2nanoparticles by reverse micelle

method for highly sensitive CO gas sensorrdquo Sensors and Actua-tors B vol 136 no 1 pp 99ndash104 2009

[19] M H Huang Y Wu H Feick N Tran E Weber and P YangldquoCatalytic growth of zinc oxide nanowires by vapor transportrdquoAdvanced Materials vol 13 no 2 pp 113ndash116 2001

[20] J D Holmes K P Johnston R C Doty and B A KorgelldquoControl of thickness and orientation of solution-grown siliconnanowiresrdquo Science vol 287 no 5457 pp 1471ndash1473 2000

[21] J S Jeong J Y Lee C J Lee S J An andGC Yi ldquoSynthesis andcharacterization of high-quality In

2O3nanobelts via catalyst-

free growth using a simple physical vapor deposition at lowtemperaturerdquo Chemical Physics Letters vol 384 no 4ndash6 pp246ndash250 2004

[22] M J Zheng L D Zhang G H Li X Y Zhang and X F WangldquoOrdered indium-oxide nanowire arrays and their photolumi-nescence propertiesrdquo Applied Physics Letters vol 79 p 8392001

[23] N G Patel K K Makhija C J Panchal D B Dave and V SVaishnav ldquoFabrication of carbon tetrachloride gas sensors usingindium tin oxide thin filmsrdquo Sensors andActuators B vol 23 no1 pp 49ndash53 1995

[24] D Frohlich and R Kenklies ldquoBand-gap assignment in SnO2by

two-photon spectroscopyrdquo Physical Review Letters vol 41 no25 pp 1750ndash1751 1978

[25] G Mill Z G Li and D Merisel ldquoPhotochemistry and spectro-scopy of colloidal arsenic sesquisulfiderdquoThe Journal of PhysicalChemistry vol 92 no 3 pp 822ndash828 1988

[26] S Luo P K Chu W Liu M Zhang and C Lin ldquoOriginof low-temperature photoluminescence from SnO

2nanowires

fabricated by thermal evaporation and annealed in differentambientsrdquo Applied Physics Letters vol 88 Article ID 183112 3pages 2006

[27] A L Efros and A L Efros ldquoInterband absorption of light in asemiconductor sphererdquo Soviet Physics Semiconductors vol 16pp 772ndash775 1982

[28] L Brus ldquoA simple model for the ionization potential electronaffinity and aqueous redox potentials of small semiconductorcrystallitesrdquo Journal of Chemical Physics vol 79 no 11 p 55661983

[29] B Wang Y H Yang C X Wang and G W Yang ldquoNanos-tructures and self-catalyzed growth of SnO

2rdquo Journal of Applied

Physics vol 98 no 7 Article ID 073520 5 pages 2005[30] R SWagner andW C Ellis ldquoVapor-liquid-solid mechanism of

single crystal growthrdquoApplied Physics Letters vol 4 no 5 p 891964


[31] G Gundiah A Govindaraj and C N R Rao ldquoNanowiresnanobelts and related nanostructures of Ga

2O3rdquo Chemical

Physics Letters vol 351 no 3-4 pp 189ndash194 2002[32] A Kolmakov Y Zhang G Cheng and M Moskovits ldquoDetec-

tion of CO and O2using tin oxide nanowire sensorsrdquo Advanced

Materials vol 15 no 12 pp 997ndash1000 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Polymer ScienceInternational Journal of



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NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


properties of the as-grown nanowires at room temperatureare also studied

2 Experimental Details

Tin oxide nanowires were grown on a silicon substrate and atthe end of the tube by a CVDprocess using about one gram ofmonotin oxide (SnO) (purity 90) at a growth temperatureof 1050∘CThe SnOwas placed into a quartz boat and insertedinto the centre of a quartz tube (radius = 5 cm length= 20 cm)at a distance of about 1-2 cm from the Si substrateThe furnacetemperature was increased from room temperature (25∘C)to 1050∘C for 30min The annealing was made in an argonatmosphere at atmospheric pressure After cooling down afluffy layer of deposition could be collected from inside thetube wall ends in the lower end temperature zone or on theSilicon substrate

UV-visible absorption measurements were carried outon the SnO nanopowders and the SnO

2nanowires using a

Perkin Elmer spectrophotometer in a range between 200 and900 nm The morphology of the product was examined byfield-emission scanning electron microscopy (Auriga ZeissSEM) with a beam energy of 3 keV The crystal structure ofthe as-synthesized product was analysed by X-ray diffraction(XRD) analysis using a Phillips X-ray diffractometer Ahigh-resolution transmission electronmicroscope (HRTEM-JEOL-2000) was used to examine the internal structure ofthe as-synthesized product The chemical compositions weredetermined using an energy dispersive X-ray spectrometer(EDS) attached to the HRTEM instrument

3 Results and Discussion

The optical band gap of commercially bought SnO and SnO2

nanowires was investigated using the UV-visible absorptionspectrometer Figure 1 shows the UV-vis spectra of thecommercially bought SnO powder and as-synthesized SnO

2

nanowires at 1050∘C for 30min in argon gas Both sampleswere dissolved in isopropanol for UV-vis analysis A weakband edge absorption in the spectrum is observed around the375 nm wavelength The optical transition of SnO

2crystals

is known to be a direct type [24] where the absorptioncoefficient 120572 can be expressed as [25]

(120572ℎ])2prop (ℎ] minus 119864

119892) (1)

where ℎ] is the photon energy119864119892is the apparent optical band

gap and 120572 is the absorption coefficient Plots of (120572ℎ])2 versusℎ] can be derived from the absorption data in Figure 1 asshown in the inset Therefore the band gap can be obtainedby extrapolation of the previous relation in the inset ofFigure 1 The intercept of the tangent to the plot gives a goodapproximation of the band gap energy of direct band gapmaterials The calculated energy band gap values are sim37 eVfor SnO

2nanowires and sim364 eV for commercially bought

SnOpowder respectivelyThese values are slightly larger thanthat of bulk SnO

2(362 eV) and might be due to the quantum

size effect [26ndash28]

Table 1 Quantitative analysis of the SnO2 nanowires

Element Atomic WeightO 6453- 2078-Sn 3042 plusmn 027 7268 plusmn 064

Cu 271 plusmn 021 347 plusmn 027

Zn 233 plusmn 027 307 plusmn 036

Figure 2 shows the scanning electron microscopy (SEM)micrographs of Figure 2(a) commercially bought SnO pow-der and Figures 2(b) and 2(c) fluffy gray SnO

2product that

was collected on the wall of the inner quartz tube afterit was synthesized at a growth temperature of 1050∘C for30min It is evident that the as-synthesized products aredominated by ldquowire-likerdquo structures whose diameter variesfrom 50 to 200 nm The length of the wires ranges fromseveral tens to several hundredmicrometers Figures 3(a) and3(b) show high magnification images of the nanowires It isobserved that spherical particles are attached to the ends ofthe nanowires Energy-dispersive X-ray spectroscopy (EDS)analysis (Figure 4 and Table 1) extracted at four differentspots showed that the tip of the nanowires consists of tin(Sn) and oxygen (O) only The Cu and Zn peaks presentin the EDS spectra are from the brass stubs used in thesample preparation The result reveals that the products arethe coexistence of Sn andOwith amolar ratio of 3321 6664which is consistent with the composition of SnO

2and is in

good agreement with the XRD results (Figure 5)The X-ray diffraction analyses of the tin oxide precursor

were carried out as shown in Figure 5(a) All the diffractionpeaks can be attributed to the tetragonal tin oxide (SnO)(JCPDS 006-0395) with lattice constants of 119886 = 119887 = 3802 Aand 119888 = 4836 A Figure 5(b) shows the X-ray diffractionpattern for the synthesized tin oxide nanowires and ribbonsFrom the diffraction patterns the as-synthesized SnO

2

nanowires have a good crystallinity with the tetragonal tinoxide SnO

2structure The structure of the nanowires was

further characterized by transmission electron microscopyand selected area electron diffraction (SAED) patternsFigures 6(a) and 6(b) show a low and high magnificationTEM image of a single SnO

2nanowire respectively

with uniform diameter It is evident that the diameter ofnanowiresnanobelts varies from 50 to 200 nm with a fewSn droplets on the nanowires The observed tip morphologyon top of the SnO

2nanowires is consistent with the SEM

analysis The SAED pattern of the tip and the tail of thenanowires are shown in Figures 6(c) and 6(d) respectivelyThe patterns clearly confirm the polycrystalline nature of thenanowires It should be pointed out that nometal catalyst wasused during the growth of the nanowires Therefore basedon these findings we can conclude that the SnO

2nanowires

follow the vapor liquid-solid (VLS) growth mechanismThe growth mechanism of nanowires in thermal evap-

oration [29] can be explained by either vapour-liquid-solid(VLS) [30] and or vapour-solid (VS) [31] Vapor-liquid-solid(VLS)mechanism is a catalyst-assisted growth process wheremetal nanoclusters or nanoparticles are used as the nucle-ation seeds These nucleation seeds determine the interfacial


350 400 450 500 550 600Wavelength (nm)

03

04

05

06

07

08

Abso

rban

ce (a

u)


0300600900

12001500

20 25 30 35 40 45 50

(120572h )

2

Photon energy (eV)


energy curve

10120583m

(a)

20120583m

(b)

10120583m

(c)


for 30min


2120583m

(a)

300nm

(b)


2 4 6 8 100

2000

4000

6000

CuZnCuSn

Sn

Sn

Sn

OInte

nsity

(au

)

Energy (keV)

Spot1Spot2

Spot3Spot4


10 20 30 40 50 60 70

0

5000

10000

15000

20000

25000

30000

35000

40000

(102

)(001

)

(103

)

(211

)(112

)(2

00)

(002

)(1

10)

(101

)

Inte

nsity

(au

)

Pure SnO

2120579 (degrees)

(a)

10 20 30 40 50 60 70

0

1000

2000

3000

4000

5000

6000

Inte

nsity

(au

)

2120579 (degrees)

SnO2

(310

)Sn

O2

(002

)

SnO2

(220

)Sn

O2

(210

)

SnO2

(111

)Sn

O2

(200

)

SnO2

(101

)

SnO2

(110

)


(b)



05 120583m

(a)

100nm

(b)

5 1nm

(c)

5 1nm

(d)


nanowires






2




4 Conclusions






around 37 eV

Acknowledgments


References






2and Pt






































2nanowires










2O3rdquo Chemical











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




350 400 450 500 550 600Wavelength (nm)

03

04

05

06

07

08

Abso

rban

ce (a

u)


0300600900

12001500

20 25 30 35 40 45 50

(120572h )

2

Photon energy (eV)


energy curve

10120583m

(a)

20120583m

(b)

10120583m

(c)


for 30min


2120583m

(a)

300nm

(b)


2 4 6 8 100

2000

4000

6000

CuZnCuSn

Sn

Sn

Sn

OInte

nsity

(au

)

Energy (keV)

Spot1Spot2

Spot3Spot4


10 20 30 40 50 60 70

0

5000

10000

15000

20000

25000

30000

35000

40000

(102

)(001

)

(103

)

(211

)(112

)(2

00)

(002

)(1

10)

(101

)

Inte

nsity

(au

)

Pure SnO

2120579 (degrees)

(a)

10 20 30 40 50 60 70

0

1000

2000

3000

4000

5000

6000

Inte

nsity

(au

)

2120579 (degrees)

SnO2

(310

)Sn

O2

(002

)

SnO2

(220

)Sn

O2

(210

)

SnO2

(111

)Sn

O2

(200

)

SnO2

(101

)

SnO2

(110

)


(b)



05 120583m

(a)

100nm

(b)

5 1nm

(c)

5 1nm

(d)


nanowires






2




4 Conclusions






around 37 eV

Acknowledgments


References






2and Pt






































2nanowires










2O3rdquo Chemical











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




2120583m

(a)

300nm

(b)


2 4 6 8 100

2000

4000

6000

CuZnCuSn

Sn

Sn

Sn

OInte

nsity

(au

)

Energy (keV)

Spot1Spot2

Spot3Spot4


10 20 30 40 50 60 70

0

5000

10000

15000

20000

25000

30000

35000

40000

(102

)(001

)

(103

)

(211

)(112

)(2

00)

(002

)(1

10)

(101

)

Inte

nsity

(au

)

Pure SnO

2120579 (degrees)

(a)

10 20 30 40 50 60 70

0

1000

2000

3000

4000

5000

6000

Inte

nsity

(au

)

2120579 (degrees)

SnO2

(310

)Sn

O2

(002

)

SnO2

(220

)Sn

O2

(210

)

SnO2

(111

)Sn

O2

(200

)

SnO2

(101

)

SnO2

(110

)


(b)



05 120583m

(a)

100nm

(b)

5 1nm

(c)

5 1nm

(d)


nanowires






2




4 Conclusions






around 37 eV

Acknowledgments


References






2and Pt






































2nanowires










2O3rdquo Chemical











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




05 120583m

(a)

100nm

(b)

5 1nm

(c)

5 1nm

(d)


nanowires






2




4 Conclusions






around 37 eV

Acknowledgments


References






2and Pt






































2nanowires










2O3rdquo Chemical











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






around 37 eV

Acknowledgments


References






2and Pt






































2nanowires










2O3rdquo Chemical











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





2O3rdquo Chemical











CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article self-catalytic growth of tin oxide...

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