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Vol. 129 (2016) ACTA PHYSICA POLONICA A No. 6
Structural and Optical Propertiesof Nanostructured Fe-Doped SnO2
S.A. Saleha,b, A.A. Ibrahimc and S.H. Mohameda,aPhysics Department, Faculty of Science, Sohag University, Sohag 82524, Egypt
bPhysics Department, College of Science and Arts, Najran University, P.O. 1988 Najran, KSAcChemistry Department, College of Science and Arts, Najran University, P.O. 1988 Najran, KSA
(Received July 21, 2015; revised version February 13, 2016; in final form March 11, 2016)Nanocrystalline Sn1xFexO2 (where x = 0, 0.01, 0.02, 0.03 and 0.04) powders have been successfully syn-
thesized by the hydrothermal method followed by sintering at 1000 C for 3 h. The morphology and structure ofthe samples have been analyzed by field emission scanning electron microscope and X-ray diffraction, respectively.X-ray diffraction results revealed that all diffraction peaks positions agree well with the reflection of a tetrago-nal rutile structure of SnO2 phase without extra peaks. The formation of a tetragonal rutile structure of SnO2nanostructures was further supported by the Raman spectra. The band gap of Fe-doped SnO2 nanoparticles wasestimated from the diffuse reflectance spectra using the KubelkaMunk function and it was decreasing slightly withthe increase of Fe ion concentration from 3.59 to 3.52 eV. The variation in band gap is attributed predominantlyto the lattice strain and particle size. The presence of chemical bonding was confirmed by the Fourier transforminfrared spectra.
DOI: 10.12693/APhysPolA.129.1220PACS/topics: 81.07.b, 61.05.C, 78.20.e
In last over two decades nanoscale semiconducting ox-ides have significant interest due to their applications insensing, optoelectronic devices, or catalysis . Thesematerials combining high optical transparency with goodelectrical conductivity have many different applicationsin contemporary and emerging technology such as in op-toelectronic devices for emissive and nonemissive infor-mation display [2, 3].
Presently, significant attention is given to nanostruc-tures made of SnO2 and SnO2-based optoelectronic mate-rials because of the high transparency in the visible lightrange, high reflectance in the infrared (IR) region andhigh absorbance in the ultraviolet region and high electricconductivity besides the advantages of inorganic oxidessuch as high rigidity, excellent chemical inertness, etc.The coexistence of tin interstitials and oxygen vacanciesin SnO2 provide a unique combination of optical and elec-trical properties .
In view of its large number of applications, it is inter-esting to study and modify the properties of tin dioxide.Doping is widely used to modify properties of nanoscalesemiconducting oxides; it offers the possibility of vary-ing their lattice parameters, band gap, conductivity type,carrier concentration, and other properties . Accord-ingly, it becomes important to understand the interplaybetween the nanoscale structure and optical propertiesof tin dioxide. This is essential for incorporating this
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system into technological applications that required tun-able energy gaps including solar cells and optoelectronicdevices . Tuning the optical properties by controllingthe band gap is a great challenge since attention shouldalso be directed to avoid the interfacial defects and stresswhich may occur due to lattice mismatches between thetwo materials .
Noteworthy, the crystal structure of SnO2 plays an im-portant role in its optoelectronic performance. Further-more, the optical transparency in the visible region to-gether with electronic conductivity is accomplished by in-troducing nonstoichiometry and/or appropriate dopantsin wide band-gap oxides. Of course, optimal operationalperformance requires materials with well-defined physi-cal parameters that can be modified and tuned by dopingwith suitable foreign atoms. It is well known that theintroduction of dopants not only results in interestingnew effects but also presents, on occasion, an opportu-nity to acquire knowledge of the host material itself whichwould be almost impossible to obtain otherwise. More-over, SnO2, one of the first transparent conductors ,is a degenerate n-type semiconductor because of intrin-sic defects (O vacancies or Sn interstitials)  and itsproperties can be highly tailored with suitable dopant el-ements. Many results have shown that several dopants(Co, Fe, and Cu) can lead to an increase of surface areaof SnO2 by reducing the grain size and crystallinity . Thus, the final properties of impurity doped SnO2nanoparticles are related to both composition and pro-cessing method.
It is known that the optoelectronic properties ofnanoparticles sensitively depend on their shapes and sizethat are mainly determined by the physico-chemical pa-rameters of the synthesis method. Among the synthetic
Structural and Optical Properties of Nanostructured Fe-Doped SnO2 1221
techniques, hydrothermal route  is much preferred forits simplicity and controllability of grain size, morphologyand degree of crystallinity by changing the experimentalparameters . Moreover, it has been recognized as anenvironmentally friendly process because it uses wateras a reaction medium and reaction is carried out in anautoclave, which is an enclosed system .
In this study, a very simple and efficient method for thesynthesis of SnO2 nanoparticles is described. The effectof Fe concentration on various structural, morphologicaland optical properties of SnO2 nanoparticles was stud-ied. The Raman spectroscopy in addition to the X-raydiffraction (XRD) and field emission scanning electronmicroscopy (FESEM) were used to study the structureof pure and doped SnO2 nanostructure while UV-Visibleand the Fourier transform infrared (FTIR) spectropho-tometry were used for optical studies.
2. Experimental detailsAll the chemicals utilized for the synthesis of SnO2 and
Fe-doped SnO2 were purchased from Sigma-Aldrich andused without further purifications. Well-crystalline SnO2was prepared using a conventional hydrothermal methodusing tin nitrate Sn(NO3)2 (0.1 M) in 100 ml of deionizedwater under continuous stirring for one hour. After stir-ring, few drops of ammonium hydroxide (NH4OH) wereadded in the resultant solution to maintain the pH at 10.The final solution was vigorously stirred for one houragain and consequently transferred to teflon lined auto-clave, sealed and heated up to 130 C for 8 h. After thattime, the autoclave was allowed to cool at room temper-ature. Finally, a white precipitate was obtained whichwas washed extensively several times with ethanol, deion-ized water and acetone, sequentially and dried at roomtemperature. The dried powder was calcinated for 3 hat 1000 C with gradual elevation of temperature, thencharacterized in detail in terms of their morphological,structural, compositional and optical properties. To syn-thesize the Fe-doped SnO2, we repeated the above pro-cess with adding Fe(NO3)3 6H2O at different concen-trations (0.010.04 M) to obtain 1%, 2%, 3%, and 4%Fe-doped SnO2.
Powder XRD patterns of the prepared samples weretaken by a two-circle (2 ) X-ray powder diffractome-ter (PANalytical XPertPRO) at room temperature usingCu K radiation ( = 0.15406 nm). The scan was takenbetween 2 of 20 and 2 of 80 at increments of 0.02with a count time of 4 second for each step. The mor-phology and microstructure were examined using FE-SEM (JEOL JSM-7600F). Elemental analysis of the pre-pared samples was performed by taking a spectrum ofenergy dispersive spectroscopy (EDS) attached to theFESEM. Raman spectra of the samples were recordedat room temperature with Perkin Elmer (Raman sta-tion 400) Raman spectrometer in the wave number region1000100 cm1 at 4 cm1. The resolution and excitationwavelengths were provided by an Ar+ Spectra-PhysicsLaser with exciting wavelength of 514.5 nm. Room tem-perature diffusion reflection spectra were recorded on
a UVVis spectroscopy (Perkin Elmers LAMBDA 950spectrophotometer) through the KubelkaMunk func-tion. The presence of functional groups in nanoparticleswere analyzed by FTIR spectrometer (Model: Spectrum-100: Perkin Elmer) in the wave number ranges from 400to 4000 cm1. The samples used for this measurementare in the form of pellets prepared by mixing the nanopar-ticles with KBr at 1 wt%.
3. Results and discussions
The morphologies and microstructures of the pure andFe-doped SnO2 powders were characterized by FESEM.Representative FESEM images of undoped and Fe-dopedSnO2 samples were depicted in Fig. 1. The data implythat the synthesized samples are composed of uniformlydistributed particles of almost similar size. The averagesize of the particles decreases markedly as the Fe dopinglevel increases suggesting that Fe plays vital role in thegrowth inhibition of the SnO2 material. This can be at-tributed to the increased nucleation sites resulted fromhigher stacking fault energy due to Fe incorporation inthe SnO2 material .
Fig. 1. FESEM images of (a) 0%, (b) 1% Fe, and(c) 2% Fe.
1222 S.A. Saleh, A.A. Ibrahim, S.H. Mohamed
Fig. 2. X-ray diffraction patterns of Sn1xFexO2 withvarious Fe concentrations.
XRD analysis was carried out to identify the crystalstructure and phase purity of the samples. The index-ing of XRD patterns presented in Fig. 2 revealed thatthe structure is typical for the tetragonal rutile struc-ture of the cassiterite SnO2 phase with space groupP42/mnm (136) (JCPDS file no. 41-1445). No alienphases have been observed confirming that SnO2 withtetragonal cassiterite structure is the only crystallinephase appearing in both undoped and Fe-doped SnO2nanoparticles.
The mean grain si