SnO2 micro/nano fibers in the rutile structure were synthesized using electrospinning and metallorganic decomposition techniques. Fibers were electrospun using two different precursor solutions, one based on SnCl4 and the other on C22H44O4Sn. The fibers were sintered in air for two hours at 400, 500, 600, 700 and 800ºC. SEM, AFM, XRD, XPS and Raman microspectrometry were used to characterize the sintered fibers. The results showed that the fibers were composed of SnO2 and that the SnCl4 precursor led to better results in terms of uniformity/continuity of the fibers

Aponte, M.

Furlan, Rogerio

Leon, N.

Pinto, N.

Ramos, Idalia

Santiago-Aviles, Jorge J

Wang, Yu

English

ScholarlyCommons@Penn

University of PennsylvaniaScholarlyCommonsDepartmental Papers (ESE) Department of Electrical & Systems EngineeringFebruary 2006Tin oxide micro/nano fibers from electrostaticdepositionYu WangUniversity of PennsylvaniaM. AponteRutgers UniversityN. LeonUniversity of Puerto RicoIdalia RamosUniversity of Puerto RicoRogerio FurlanUniversity of Puerto RicoSee next page for additional authorsFollow this and additional works at: http://repository.upenn.edu/ese_papersReprinted from Revista Mexicana de Física, Volume 52, Issue 2, February 2006, pages 42-44.This paper is posted at ScholarlyCommons. http://repository.upenn.edu/ese_papers/310For more information, please contact repository@pobox.upenn.edu.Recommended CitationYu Wang, M. Aponte, N. Leon, Idalia Ramos, Rogerio Furlan, N. Pinto, and Jorge J. Santiago-Aviles, "Tin oxide micro/nano fibers fromelectrostatic deposition", . February 2006.Tin oxide micro/nano fibers from electrostatic depositionAbstractSnO2 micro/nano fibers in the rutile structure were synthesized using electrospinning and metallorganicdecomposition techniques. Fibers were electrospun using two different precursor solutions, one based onSnCl4 and the other on C22H44O4Sn. The fibers were sintered in air for two hours at 400, 500, 600, 700 and800ºC. SEM, AFM, XRD, XPS and Raman microspectrometry were used to characterize the sintered fibers.The results showed that the fibers were composed of SnO2 and that the SnCl4 precursor led to better results interms of uniformity/continuity of the fibers.Keywordstin oxide, nanofibers, electrospinningCommentsReprinted from Revista Mexicana de Física, Volume 52, Issue 2, February 2006, pages 42-44.Author(s)Yu Wang, M. Aponte, N. Leon, Idalia Ramos, Rogerio Furlan, N. Pinto, and Jorge J. Santiago-AvilesThis journal article is available at ScholarlyCommons: http://repository.upenn.edu/ese_papers/310REVISTA MEXICANA DE F´ISICA S 52 (2), 42–44 FEBRERO 2006Tin oxide micro/nano fibers from electrostatic depositionY. Wang1,a, M, Aponte2,b, N. Leo´n2, I. Ramos2, R. Furlan2, N. Pinto2, J.J. Santiago-Avile´s11Dept of Electrical & Systems Engineering, Univ of Pennsylvania,Philadelphia, PA 19104, USA.2Dept of Physics & Electronics, Univ of Puerto Rico at Humacao,CUH Station, Humacao, PR 00791.Recibido el 27 de octubre de 2004; aceptado el 26 de mayo de 2005SnO2 micro/nano fibers in the rutile structure were synthesized using electrospinning and metallorganic decomposition techniques. Fiberswere electrospun using two different precursor solutions, one based on SnCl4 and the other on C22H44O4Sn. The fibers were sintered inair for two hours at 400, 500, 600, 700 and 800◦C. SEM, AFM, XRD, XPS and Raman microspectrometry were used to characterize thesintered fibers. The results showed that the fibers were composed of SnO2 and that the SnCl4 precursor led to better results in terms ofuniformity/continuity of the fibers.Keywords: Tin oxide; nanofibers; electrospinning.Micro/nano fibras de SnO2 rutilo se sintetizaron con electrospinning y te´cnicas de descomposicio´n metalo-orga´nicas. Las fibras se produjeronutilizando dos soluciones precursoras distintas basadas en una mezcla de SnCl4 y otra de C22H44O4Sn. Las fibras se quemaron en aire por doshoras a temperaturas de 400, 500, 600, 700 y 800◦C y se analizaron utilizando SEM, AFM, XRD, XPS y microscopı´a Raman. Los resultadosmuestran que las fibras producidas con ambos precursores esta´n compuestas de SnO2 y que la solucio´n precursora con SnCl4produce fibrasma´s uniformes y continuas.Descriptores: ´Oxido de estan˜o; nanofibras; electrospinning.PACS: 81.16.Be; 81.15.Pq; 61.82.Fk1. IntroductionTin oxide, SnO2 is an n-type semiconductor with a largebandgap (Eg=3.6eV at 300K). The use of SnO2 thin filmsas chemical sensors for environmental and industrial applica-tions has been studied intensively [1-3]. SnO2 in the form offibers is expected to have improved chemical sensing char-acteristics [4]. The effective surface area for sensor applica-tions depends on the total grain boundary (GB) area in theSnO2 sensing element. The GB area-to-volume ratio will in-crease with the reduction in grain size. If we can fabricatethe element in the form of fibers with their diameter on thenano scale, the grain size will be reduced due to restrictionthe grain growth along the cross-section of the fibers, andfibers are expected to be more sensitive than a thin film. Ef-forts to synthesize the structures include the development ofnanofibers, nanowires, nanorods, and nanobelts [5-10]. Ofthe methods used to produced the nanostructures, electro-spinning is especially interesting in that it is easy and costeffective [6,8,9].As the active element in chemical or biological sensors,the tin oxide nanofibers can be configured either as resis-tors whose conductance is altered by charge-transfer pro-cesses occurring at their surfaces, or as field-effect transis-tors whose properties can be controlled by applying an ap-propriate potential to their gate [11]. The conductivity of theSnO2 semiconductor is modulated by the chemisorbed oxy-gen molecules on its surface. The absorbed oxygen, receiv-ing electrons from the conduction band, produces an electrondepletion layer under the absorbing surface and a potentialbarrier between particles, and thus decreases the conductiv-ity of the SnO2 [4]. This makes SnO2 a good candidate as agas sensor whose conductivity will increase sharply when ex-posed to a reducing gas. Sensors based on SnO2 wires usingthe conductance or field effect transistor configuration havebeen reported [10-12] with good electrical and photoconduc-tion properties.2. Formation processFibers were electrospun from two simple precursor solutions.For both solutions, the viscosity was controlled using a solu-tion of poly(ethylene oxide) (PEO) [-CH2CH2O-]n (molecu-lar weight 900,000 Aldrich) and chloroform (CHCl3 Sigma).The SnCl4 solution [8] was prepared using anhydroustin(IV) chloride (SnCl4 ACROS Organics), deionized wa-ter, propanol (C3H7OH, Fischer Scientifics), and isopropanol(2-C3H7OH, Fischer Scientifics) SnCl4:H2O:C3H7OH:2-C3H7OH in the following molar ratio: 1:9:9:6. Thenthe SnCl4 solution was combined with the viscous solu-tion (200 mg PEO/10 ml CHCl3) at a volume ratio of1:1.25. The C22H44O4Sn solution [9] was made using liq-uid dimethyldineodecanoate tin combined with the viscoussolution (100 mg PEO/10 ml CHCl3) at a volume ratio of2:1. The fibers were produced using a simple electrospinningsetup, described in more detail elsewhere [13], followed bysintering using a resistance furnace with a Sentry 2.0 digitaltemperature controller made by Paragon Industries, Inc.TIN OXIDE MICRO/NANO FIBERS FROM ELECTROSTATIC DEPOSITION 433. CharacterizationSEM and SPM observations revealed that the horizontal di-ameter of sintered fibers ranges from 60 nm to 10µm. Fig-ure 1 shows a typical image of a single fiber. Figure 2 showsthe SPM apparent average cross-section profile. It is a distor-tion of the actual profile because the tip not only has its owncone shape and size, but also cannot trace the lower part ofthe fiber. However, the vertical dimension (diameter) of 100nm is not distorted and is therefore accurate. The SEM andSPM analysis indicates that the SnCl4 precursor led to betterresults in terms of uniformity/continuity of the fibers.Figure 3 shows the XRD spectra for fibers electrospunusing the SnCl4 precursor. After sintering at 400◦C, 110,101 and 211 XRD peaks of rutile structure SnO2 appear, in-dicating the formation of its recipient lattice. These peaksbecome more distinct and an additional 200, 220 and 310peaks showed up after sintering at 600◦C, indicating the de-velopment of a more integral rutile lattice between 400◦C and600◦C. Up to 800◦C, all peaks are still identified as SnO2peaks, suggesting the following overall chemical reactions:Sn(OH)nCl4−n + (4− n)H2O→ SnO2 + 2H2O + (4− n)HCl, (1)[−CH2CH2O−]n + (5n/2)O2 → 2nCO2 + 2nH2O, (2)and n = 0, 1, 2, 3, 4.For sintering temperatures of 400, 600 and 800◦C, therelative intensities of the diffraction peaks are consistent withthose reported in Ref. [14].Typical Raman micro-scattering spectra are presented inFig. 4. After sintering at 400◦C, a peak around 631cm−1shows up, whereas another weak peak centered around774cm−1 begins to appear. The two peaks become moredistinct after sintering between 600 and 800◦C, whereasthe third peak appears around 474 cm−1 after sintering at800◦C. The SnO2 rutile structure belongs to the space groupFIGURE 1. SEM micrograph of a single fiber sintered at 600◦C for2 hours.FIGURE 2. SPM apparent average cross-section profile of a singlefiber sintered at 600 ◦C for 2 hours.FIGURE 3. XRD Spectra for SnCl4-based fibers at different tem-peratures.P42/mnm [15]. Its normal lattice vibration at the Γ point ofthe Brillouin zone isΓ = 1A1g + 1A2g + 1A2u + 1B1g + 1B2g + 2B1u+1Eg + 3Eu. (3)Of the 11 optical phonons of symmetry, A1g , B1g, B2g, andEg are Raman active with the strongest Raman intensity at631.3cm−1 for mode A1g, followed by the mode B2g at774.4cm−1 and the mode Eg at 474.0cm−1 (B1g peak is cen-tered at 87±2cm−1). The peak position and relative intensityof A1g, B2g and Eg modes are in agreement with those ob-served in a large (∼1cc) natural cassiterite crystal [15] or syn-thesized SnO2 nanorods [5]. It is noteworthy that after sinter-ing at 800◦C, two peaks appear around 605 and 708 cm−1.They cannot be attributed to any mode of lattice vibration inrutile SnO2, implying a subtle structure change that XRD isnot so sensitive to detect.Rev. Mex. Fı´s. S 52 (2) (2006) 42–4444 Y. WANG et al.FIGURE 4. Raman micro-spectra of Si substrate and SnCl4-basedmats sintered at different temperatures.FIGURE 5. Sintering temperature dependence of the atomic con-centration of SnCl4-based fibers.The XPS spectra indicated the existence of elements Sn,O, C and Cl, as well as Si in sintered mat samples [16]. TheXPS spectra for the Sn, O, C and Cl regions give the relativeintensity of the elements as a function of the binding energyfor mats sintered at 400, 500, 600, 700 and 800◦C. Using theatomic sensitivity factor, the relative atomic concentrations ofSn, O, C and C were analyzed semi-quantitatively and theirdependence on the sintering temperature is shown in Fig. 5.Upon sintering at 400◦C, Cl almost disappears; C concentra-tion decreases sharply from 36.4% to 5-8%, whereas O con-centration increases to more than 50%, and Sn concentrationincreases to 38%.The drastic decrease of carbon concentra-tion and the regular shift of the XPS C1s peak caused by sin-tering suggest that the carbon is a residual element rather thanan adventitious extrinsic impurity. We are currently investi-gating the properties of the sintered tin oxide fibers and theirdependence on the preparation conditions and shall report theresults in a coming paper.4. ConclusionTin oxide (SnO2) fibers, in the rutile phase with diame-ters ranging from 60nm to several microns were synthe-sized using two different precursor solutions. The first wasa mixture of C22H44O4Sn, and the second a mixture ofSnCl4 sol. In both cases the viscocity was controlled us-ing a poly(ethylene oxide) (molecular weight 900,000)/chlo-roform solution. The fibers were fabricated using electro-spinning and metallorganic decomposition techniques. Scan-ning electron microscopy, scanning probe microscopy, x-ray diffraction, Raman microspectrometry and x-ray photo-electron spectroscopy were used to characterize the sinteredfibers. The results showed that a series of chemical reactionsresulted in SnO2 fibers in rutile structure at sintering temper-atures between 400 and 700◦C, and that the SnCl4 precursorled to better results in terms of uniformity/continuity of thefibers.AcknowledgementsThis work was supported by NSF-DMR-353730 and NSF-SBE-0123654.a. Current address: Dept of Electrical and Computer Engineering,Univ of California, Davis, CA, 95616.b. Current address: Dept of Materials and Ceramics Engineering,Rutgers Univ, NJ, USA.1. J. Watson, Sensors and Actuators 5 (1984) 29.2. W. Gopel and K.D. Schierbaum, Sensors and Actuators B 26(1995) 1.3. A. Tang et al., Sensors and Actuators B 43 (1997) 161.4. S. Seal and S. Shukla, Journal of Metals 54 (2002) 35.5. C. Xu, G. Xu, Y. Liu, X. Zhao, and G. Wang, Scriptia Materi-alia, 46 (2002) 789.6. D. Li, Y. Wang and Y. Xia, Nano Letters 3 (2003) 1167.7. M. Law, J. Goldberger and P. Yang, Annu. Rev. Mater. Res. 34(2004) 83.8. Y. Wang et al., Journal of the American Ceramics Society(2005) in press.9. Y. Wang et al., Semicond. Sci. Techn. 19 (2004) 1057.10. E. Comini et al., Applied Physics Letters 81 (2002) 1869.11. A. Kolmakov and M. Moskovits, Annu. Rev. Mater. Res. 34(2004) 151.12. P. Candeloro et. al., Microelectronic Engineering 78 (2005)178.13. Y. Wang, R. Furlan, I. Ramos and J.J. Santiago-Avile´s, AppliedPhysics A 78 (2004) 1043.14. JCPDS Card No. 41-1445.15. J.F. Scott, J. Chem Phys 53 (1970) 852.16. J.F. Moulder et al., Handbook of X-Ray Photoelectron Spec-troscopy, Jill Chastain, (by Perkin-Elmer Corporation, PhysicalElectronics Division, Minnesota, USA, 1992).Rev. Mex. Fı´s. S 52 (2) (2006) 42–44

Tin oxide micro/nano fibers from electrostatic deposition

Kosmopolis

University of Pennsylvania
ScholarlyCommons
Departmental Papers (ESE) Department of Electrical & Systems Engineering
February 2006
Tin oxide micro/nano fibers from electrostatic
deposition
Yu Wang
University of Pennsylvania
M. Aponte
Rutgers University
N. Leon
University of Puerto Rico
Idalia Ramos
University of Puerto Rico
Rogerio Furlan
University of Puerto Rico
See next page for additional authors
Follow this and additional works at: http://repository.upenn.edu/ese_papers
Reprinted from Revista Mexicana de Física, Volume 52, Issue 2, February 2006, pages 42-44.
This paper is posted at ScholarlyCommons. http://repository.upenn.edu/ese_papers/310
For more information, please contact repository@pobox.upenn.edu.
Recommended Citation
Yu Wang, M. Aponte, N. Leon, Idalia Ramos, Rogerio Furlan, N. Pinto, and Jorge J. Santiago-Aviles, "Tin oxide micro/nano fibers from
electrostatic deposition", . February 2006.
Tin oxide micro/nano fibers from electrostatic deposition
Abstract
SnO2 micro/nano fibers in the rutile structure were synthesized using electrospinning and metallorganic
decomposition techniques. Fibers were electrospun using two different precursor solutions, one based on
SnCl4 and the other on C22H44O4Sn. The fibers were sintered in air for two hours at 400, 500, 600, 700 and
800ºC. SEM, AFM, XRD, XPS and Raman microspectrometry were used to characterize the sintered fibers.
The results showed that the fibers were composed of SnO2 and that the SnCl4 precursor led to better results in
terms of uniformity/continuity of the fibers.
Keywords
tin oxide, nanofibers, electrospinning
Comments
Reprinted from Revista Mexicana de Física, Volume 52, Issue 2, February 2006, pages 42-44.
Author(s)
Yu Wang, M. Aponte, N. Leon, Idalia Ramos, Rogerio Furlan, N. Pinto, and Jorge J. Santiago-Aviles
This journal article is available at ScholarlyCommons: http://repository.upenn.edu/ese_papers/310
REVISTA MEXICANA DE FÍSICA S52 (2), 42–44 FEBRERO 2006
Tin oxide micro/nano fibers from electrostatic deposition
Y. Wang1,a, M, Aponte2,b, N. León2, I. Ramos2, R. Furlan2, N. Pinto2, J.J. Santiago-Avilés1
1Dept of Electrical & Systems Engineering, Univ of Pennsylvania,
Philadelphia, PA 19104, USA.
2Dept of Physics & Electronics, Univ of Puerto Rico at Humacao,
CUH Station, Humacao, PR 00791.
Recibido el 27 de octubre de 2004; aceptado el 26 de mayo de 2005
SnO2 micro/nano fibers in the rutile structure were synthesized using electrospinning and metallorganic decomposition techniques. Fibers
were electrospun using two different precursor solutions, one based on SnCl4 a d the other on C22H44O4Sn. The fibers were sintered in
air for two hours at 400, 500, 600, 700 and 800◦C. SEM, AFM, XRD, XPS and Raman microspectrometry were used to characterize the
sintered fibers. The results showed that the fibers were composed of SnO2 and that the SnCl4 precursor led to better results in terms of
uniformity/continuity of the fibers.
Keywords:Tin oxide; nanofibers; electrospinning.
Micro/nano fibras de SnO2 rutilo se sintetizaron con electrospinning y técnicas de descomposición metalo-orǵanicas. Las fibras se produjeron
utilizando dos soluciones precursoras distintas basadas en una mezcla de SnCl4 y otra de C22H44O4Sn. Las fibras se quemaron en aire por dos
horas a temperaturas de 400, 500, 600, 700 y 800◦C y se analizaron utilizando SEM, AFM, XRD, XPS y microscopı́a Raman. Los resultados
muestran que las fibras producidas con ambos precursores están compuestas de SnO2 y que la solucíon precursora con SnCl4produce fibras
más uniformes y continuas.
Descriptores:Óxido de estãno; nanofibras; electrospinning.
PACS: 81.16.Be; 81.15.Pq; 61.82.Fk
1. Introduction
Tin oxide, SnO2 is an n-type semiconductor with a large
bandgap (Eg=3.6eV at 300K). The use of SnO2 thin films
as chemical sensors for environmental and industrial applica-
tions has been studied intensively [1-3]. SnO2 in the form of
fibers is expected to have improved chemical sensing char-
acteristics [4]. The effective surface area for sensor applica-
tions depends on the total grain boundary (GB) area in the
SnO2 sensing element. The GB area-to-volume ratio will in-
crease with the reduction in grain size. If we can fabricate
the element in the form of fibers with their diameter on the
nano scale, the grain size will be reduced due to restriction
the grain growth along the cross-section of the fibers, and
fibers are expected to be more sensitive than a thin film. Ef-
forts to synthesize the structures include the development of
nanofibers, nanowires, nanorods, and nanobelts [5-10]. Of
the methods used to produced the nanostructures, electro-
spinning is especially interesting in that it is easy and cost
effective [6,8,9].
As the active element in chemical or biological sensors,
the tin oxide nanofibers can be configured either as resis-
tors whose conductance is altered by charge-transfer pro-
cesses occurring at their surfaces, or as field-effect transis-
tors whose properties can be controlled by applying an ap-
propriate potential to their gate [11]. The conductivity of the
SnO2 semiconductor is modulated by the chemisorbed oxy-
gen molecules on its surface. The absorbed oxygen, receiv-
ing electrons from the conduction band, produces an electron
depletion layer under the absorbing surface and a potential
barrier between particles, and thus decreases the conductiv-
ity of the SnO2 [4]. This makes SnO2 a good candidate as a
gas sensor whose conductivity will increase sharply when ex-
posed to a reducing gas. Sensors based on SnO2 wires using
the conductance or field effect transistor configuration have
been reported [10-12] with good electrical and photoconduc-
tion properties.
2. Formation process
Fibers were electrospun from two simple precursor solutions.
For both solutions, the viscosity was controlled using a solu-
tion of poly(ethylene oxide) (PEO) [-CH2CH2O-]n (molecu-
lar weight 900,000 Aldrich) and chloroform (CHCl3 Sigma).
The SnCl4 solution [8] was prepared using anhydrous
tin(IV) chloride (SnCl4 ACROS Organics), deionized wa-
ter, propanol (C3H7OH, Fischer Scientifics), and isopropanol
(2-C3H7OH, Fischer Scientifics) SnCl4:H2O:C3H7OH:2-
C3H7OH in the following molar ratio: 1:9:9:6. Then
the SnCl4 solution was combined with the viscous solu-
tion (200 mg PEO/10 ml CHCl3) at a volume ratio of
1:1.25. The C22H44O4Sn solution [9] was made using liq-
uid dimethyldineodecanoate tin combined with the viscous
solution (100 mg PEO/10 ml CHCl3) at a volume ratio of
2:1. The fibers were produced using a simple electrospinning
setup, described in more detail elsewhere [13], followed by
sintering using a resistance furnace with a Sentry 2.0 digital
temperature controller made by Paragon Industries, Inc.
TIN OXIDE MICRO/NANO FIBERS FROM ELECTROSTATIC DEPOSITION 43
3. Characterization
SEM and SPM observations revealed that the horizontal di-
ameter of sintered fibers ranges from 60 nm to 10µm. Fig-
ure 1 shows a typical image of a single fiber. Figure 2 shows
the SPM apparent average cross-section profile. It is a distor-
tion of the actual profile because the tip not only has its own
cone shape and size, but also cannot trace the lower part of
the fiber. However, the vertical dimension (diameter) of 100
nm is not distorted and is therefore accurate. The SEM and
SPM analysis indicates that the SnCl4 precursor led to better
results in terms of uniformity/continuity of the fibers.
Figure 3 shows the XRD spectra for fibers electrospun
using the SnCl4 precursor. After sintering at 400◦C, 110,
101 and 211 XRD peaks of rutile structure SnO2 appear, in-
dicating the formation of its recipient lattice. These peaks
become more distinct and an additional 200, 220 and 310
peaks showed up after sintering at 600◦C, indicating the de-
velopment of a more integral rutile lattice between 400◦C and
600◦C. Up to 800◦C, all peaks are still identified as SnO2
peaks, suggesting the following overall chemical reactions:
Sn(OH)nCl4−n + (4− n)H2O
→ SnO2 + 2H2O + (4− n)HCl, (1)
[−CH2CH2O−]n + (5n/2)O2 → 2nCO2 + 2nH2O, (2)
andn = 0, 1, 2, 3, 4.
For sintering temperatures of 400, 600 and 800◦C, the
relative intensities of the diffraction peaks are consistent with
those reported in Ref. [14].
Typical Raman micro-scattering spectra are presented in
Fig. 4. After sintering at 400◦C, a peak around 631cm−1
shows up, whereas another weak peak centered around
774cm−1 begins to appear. The two peaks become more
distinct after sintering between 600 and 800◦C, whereas
the third peak appears around 474 cm−1 after sintering at
800◦C. The SnO2 rutile structure belongs to the space group
FIGURE 1. SEM micrograph of a single fiber sintered at 600◦C for
2 hours.
FIGURE 2. SPM apparent average cross-section profile of a single
fiber sintered at 600◦C for 2 hours.
FIGURE 3. XRD Spectra for SnCl4-based fibers at different tem-
peratures.
P42/mnm [15]. Its normal lattice vibration at theΓ point of
the Brillouin zone is
Γ = 1A1g + 1A2g + 1A2u + 1B1g + 1B2g + 2B1u
+1Eg + 3Eu. (3)
Of the 11 optical phonons of symmetry, A1g, B1g, B2g, and
Eg are Raman active with the strongest Raman intensity at
631.3cm−1 for mode A1g, followed by the mode B2g at
774.4cm−1 and the mode Eg at 474.0cm−1 (B1g peak is cen-
tered at 87±2cm−1). The peak position and relative intensity
of A1g, B2g and Eg modes are in agreement with those ob-
served in a large (∼1cc) natural cassiterite crystal [15] or syn-
thesized SnO2 nanorods [5]. It is noteworthy that after sinter-
ing at 800◦C, two peaks appear around 605 and 708 cm−1.
They cannot be attributed to any mode of lattice vibration in
rutile SnO2, implying a subtle structure change that XRD is
not so sensitive to detect.
Rev. Mex. F́ıs. S52 (2) (2006) 42–44
44 Y. WANG et al.
FIGURE 4. Raman micro-spectra of Si substrate and SnCl4-based
mats sintered at different temperatures.
FIGURE 5. Sintering temperature dependence of the atomic con-
centration of SnCl4-based fibers.
The XPS spectra indicated the existence of elements Sn,
O, C and Cl, as well as Si in sintered mat samples [16]. The
XPS spectra for the Sn, O, C and Cl regions give the relative
intensity of the elements as a function of the binding energy
for mats sintered at 400, 500, 600, 700 and 800◦C. Using the
atomic sensitivity factor, the relative atomic concentrations of
Sn, O, C and C were analyzed semi-quantitatively and their
dependence on the sintering temperature is shown in Fig. 5.
Upon sintering at 400◦C, Cl almost disappears; C concentra-
tion decreases sharply from 36.4% to 5-8%, whereas O con-
centration increases to more than 50%, and Sn concentration
increases to 38%.The drastic decrease of carbon concentra-
tion and the regular shift of the XPS C1s peak caused by sin-
tering suggest that the carbon is a residual element rather than
an adventitious extrinsic impurity. We are currently investi-
gating the properties of the sintered tin oxide fibers and their
dependence on the preparation conditions and shall report the
results in a coming paper.
4. Conclusion
Tin oxide (SnO2) fibers, in the rutile phase with diame-
ters ranging from 60nm to several microns were synthe-
sized using two different precursor solutions. The first was
a mixture of C22H44O4Sn, and the second a mixture of
SnCl4 sol. In both cases the viscocity was controlled us-
ing a poly(ethylene oxide) (molecular weight 900,000)/chlo-
roform solution. The fibers were fabricated using electro-
spinning and metallorganic decomposition techniques. Scan-
ning electron microscopy, scanning probe microscopy, x-
ray diffraction, Raman microspectrometry and x-ray photo-
electron spectroscopy were used to characterize the sintered
fibers. The results showed that a series of chemical reactions
resulted in SnO2 fibers in rutile structure at sintering temper-
atures between 400 and 700◦C, and that the SnCl4 precursor
led to better results in terms of uniformity/continuity of the
fibers.
Acknowledgements
This work was supported by NSF-DMR-353730 and NSF-
SBE-0123654.
a. Current address: Dept of Electrical and Computer Engineering,
Univ of California, Davis, CA, 95616.
b. Current address: Dept of Materials and Ceramics Engineering,
Rutgers Univ, NJ, USA.
1. J. Watson,Sensors and Actuators5 (1984) 29.
2. W. Gopel and K.D. Schierbaum,Sensors and Actuators B26
(1995) 1.
3. A. Tanget al., Sensors and Actuators B43 (1997) 161.
4. S. Seal and S. Shukla,Journal of Metals54 (2002) 35.
5. C. Xu, G. Xu, Y. Liu, X. Zhao, and G. Wang,Scriptia Materi-
alia, 46 (2002) 789.
6. D. Li, Y. Wang and Y. Xia,Nano Letters3 (2003) 1167.
7. M. Law, J. Goldberger and P. Yang,Annu. Rev. Mater. Res.34
(2004) 83.
8. Y. Wang et al., Journal of the American Ceramics Society
(2005) in press.
9. Y. Wanget al., Semicond. Sci. Techn.19 (2004) 1057.
10. E. Cominiet al., Applied Physics Letters81 (2002) 1869.
11. A. Kolmakov and M. Moskovits,Annu. Rev. Mater. Res.34
(2004) 151.
12. P. Candeloroet. al., Microelectronic Engineering78 (2005)
178.
13. Y. Wang, R. Furlan, I. Ramos and J.J. Santiago-Avilés,Applied
Physics A78 (2004) 1043.
14. JCPDS Card No. 41-1445.
15. J.F. Scott,J. Chem Phys53 (1970) 852.
16. J.F. Moulderet al., Handbook of X-Ray Photoelectron Spec-
troscopy,Jill Chastain, (by Perkin-Elmer Corporation, Physical
Electronics Division, Minnesota, USA, 1992).
Rev. Mex. F́ıs. S52 (2) (2006) 42–44


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Tin oxide micro/nano fibers from electrostatic deposition

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