Accepted Manuscript Effect of In doping on the properties and antibacterial activity of ZnO films prepared by spray pyrolysis C. Manoharan, G. Pavithra, S. Dhanapandian, P. Dhamodharan PII: DOI: Reference:
S1386-1425(15)00607-1 http://dx.doi.org/10.1016/j.saa.2015.05.019 SAA 13686
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
5 December 2014 6 March 2015 5 May 2015
Please cite this article as: C. Manoharan, G. Pavithra, S. Dhanapandian, P. Dhamodharan, Effect of In doping on the properties and antibacterial activity of ZnO films prepared by spray pyrolysis, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.05.019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of In doping on the properties and antibacterial activity of ZnO films prepared by spray pyrolysis C. Manoharan, G. Pavithra*, S. Dhanapandian and P.Dhamodharan Department of Physics, Annamalai University, Annamalai Nagar – 608 002, Tamilnadu, India Abstract Pure and In-doped ZnO thin films were deposited onto glass substrates by spray pyrolysis technique. XRD results showed that all films were polycrystalline in nature with the wurzite structure. A change in preferential orientation from (002) to (101) plane was observed with increase in content of Indium. A reduce in crystallite size was observed with increase of In content. The small sized grains with the porous nature of the film was observed from SEM analysis. AFM study depicted polycrystalline nature and uniformly distributed grains with small pores in the doped film. A decrease in band gap was noticed with increase in In content. The absence of green emission in PL spectra indicated the decreased oxygen defects.The decrease in the resistivity with increase of Hall mobility was noted for the doped film. A better antibacterial activity was observed against Staphylococcus aureus by doped ZnO thin film. Key words: Indium doped ZnO, Thin films, Spray pyrolysis technique, Antibacterial activity. *
Corresponding author
E-mail:[email protected] Tel: +91- 9487966397
1
1. Introduction In the field of materials science, Zinc oxide (ZnO) holds a very important position because it is piezoelectric, transparent in the visible range with wide band gap and become conducting with appropriate dopants. However, ease in doping by suitable impurity atoms (dopants) can make it n-type semiconductor which can tune the properties of ZnO, in order to enhance the material as a most promising candidates for optoelectronic devices such as lightemitting diodes, laser diodes, UV photo detectors [1,2], gas sensor devices, transparent electrodes, and piezoelectric devices [3]. Pure zinc oxide is unstable due to modification in the surface conductance under oxygen chemisorptions and adsorptions [4]. Its electrical and optical properties can be enhanced by doping the elements such as Al, B, In, Ga and F. By doping, metal dopants (Al, B, In, Ga) into ZnO thin films make them as highly conducting material which could be the alternative as less expensive transparent conducting layers in several applications such as transparent display devices, and solar cells [5]. Also, ZnO thin films are stable under moderate temperature ranges (250–400ºC) in the presence of air [6]. Andrea Gracia Cuevas et al., 2013 [7] stated that zinc oxide a promising material for the prevention of the food forms from being affected by food pathogens such as E. coli and S. aureus in the packed foods, applied to treat different skin conditions, in products like baby powder and creams against diaper rashes, antiseptic ointments, anti-dandruff shampoos, and as a component in tape (called “Zinc oxide tape”) used by athletes as a bandage to prevent soft tissue damage during workouts. Many techniques have been used to deposit ZnO films onto glass substrate, such as Sol-gel [8], Sputtering [9], Spray pyrolysis [10] etc. Among these techniques, spray pyrolysis is one of the most commonly used method for the preparation of metal oxide thin films due to its simplicity, affordable with uniform coating, non-vacuum system of deposition and has large area coating with device quality. In the present study it is aimed to enhance the optical and electrical properties of ZnO by doping of indium. Spray pyrolysis deposition technique has been used since it is easy and low cost equipment deposition technique. Also an attempt has been made to study the antibacterial activity against the test organisms for pure and In-doped ZnO thin films. 2. Experiment
2
ZnO : In thin films were obtained by spray pyrolysis in air atmosphere from aqueous solutions in which the atomic ratio of In in the spray solution was varied from 0, 2, 4, 6 and 8 at.%. The substrates were well cleaned by soap solution followed by HCl, acetone and distilled water. Finally, the cleaned substrates were dried in oven. The experimental set-up used for the spraying process consists of a spray head and heater which was kept inside a chamber with an exhaust fan which could remove the gaseous byproducts and solvent vapor. The substrate temperature was achieved with the help of heater which was controlled by an automatic temperature controller with an accuracy of ±5°C. The uniform growth of the film was obtained by moving the spray head in the X - Y direction which was able to scan an area of 200 x 200 mm with the flow rate of the solution, 3ml/min.The diameter of the spary nozzle is 0.45 mm. The carrier gas used in this experiment was air and the pressure of the carrier gas was maintained with the help of mechanical gauge. The entire unit was connected to computer with the help of a serial port to store the spray parameters.The spray solution was prepared by dissolving 0.1M of Zn (acac) in ethanol and Indium (III) chloride was added to the solution as a dopant. The prepared solution was sprayed onto glass substrate at the substrate temperatrure of 400°C.The grown films were annealed at 500 °C in air for an hour. 2.1 Characterization technique The structural characterization of the deposited films were carried out by X-ray diffraction technique on SHIMADZU-6000 (monochromatic Cu-Kα radiation, λ=1.5406 Ǻ). The surface morphology was studied by using SEM (JEOL-JES-1600). Optical absorption spectrum was recorded in the range of 300-1200 nm using JASCO V-670 spectrophotometer. The photoluminescence spectrum (PL) was studied at room temperature using prolog 3HORIBAJOBINYVON with an excitation source wavelength of 375 nm. The surface topological studies were carried out using Atomic force Microscope (Nano surf Easy scan2) AGILENTN9410A-5500. The electrical resistivity, carrier concentration and mobility were measured by automated Hall Effect measurement (ECOPIA HMS - 2000) at room temperature in a van der Pauw (VDP) four - point probe configuration. 2.2 Antibacterial activity Preparation of test solution and disc
3
The test solution was prepared with known weight of fractions in 10 mg/mL, and dissolved in 5 percent dimethyl sulphoxide (DMSO). Sterile discs Himedia Ltd., Mumbai. (6 mm) were impregnated with 20 µl of the ZnO and In doped ZnO (corresponding to 100, 200 and 300 mg/mL) allowed to dry at room temperature. Disc diffusion method The agar diffusion method was followed for antibacterial susceptibility test. Petri plates were prepared by pouring 20 mL of Mueller Hinton Agar allowed to solidify for the use in susceptibility test against bacteria respectively. Plates were dried and
0.1 mL of standardized
inoculums suspension was poured and uniformly spread. The excess inoculums were drained and the plates were allowed to dry for 5 minutes. After drying, the discs with ZnO and In-doped ZnO were placed on the surface of the plate with sterile forceps and gently pressed to ensure contact with the agar surface. Gentamycin (30 mg/disc) were used as the positive controls and 5 per cent DMSO was used as blind control in these assays. Finally, the inoculated plates were incubated at 37 °C for 24 h. The zone of inhibition was observed and measured in millimeters. 3. Results and Discussion 3.1. Structural Studies Fig.1. shows the XRD pattern of pure and In-doped ZnO thin films. XRD patterns confirm the formation of polycrystalline with hexagonal wurzite structure of ZnO with the absence of other peaks such as indium oxide and In-Zn compounds. The pure ZnO thin film exhibits a strong intensity to (002) plane which indicates the film is preferentially oriented along c-axis. The c-axis orientation of pristine ZnO is because of the minimal of internal stress and surface energy and by high atomic density which leads to the easy growth of the crystallites towards the c-axis direction [11]. A decrease in intensity of (002) plane and an increase in intensity of (101) plane is noticed for 2 at.% of In. However, there is no significant change in peak position of (002), (101) and (100) plane while doping indium, which shows the absence of new phase [12]. Further increase in intensity of (101) plane than the (002) plane and increase in intensity of (100) plane for 4 at.% of In, indicates the change in growth orientation from c-axis to isotropic growth. The similar change of orientation is observed for Aldoped ZnO by Yaodong Liu et al., [13]. The change of growth orientation from (002) to (101) is 4
due to the change in diffusion rate of Zn and O at surface during deposition, when presence of In3+ ions is excess in ZnO. At 4 at.% of In, the film exhibits a strong orientation along (101) plane is noticed. The lower concentration of In does not affect the preferential orientation along (002) as In incorporates into the lattice. The change in preferential orientation is noticed for higher concentration of In as the solubility limit is reached and this prevents the preferential growth.The intensity of (101) plane is gradually decreased with further increase of In content (6 at.%). The higher concentration of indium detorited the crystallinity of the films is because of the stress produced by the difference in ion size between indium and zinc are also due to segregation of dopants in grain boundaries [12,14].
The crystallite size ‘D’ is calculated by well known Debye–Scherrer formula D = where λ is the wavelength of CuKα radiation, k is the shape factor, β is the full width half maximum ( FWHM) intensity.The enhancement of density of nucleation center is the reason for the decrease of crystallites size in the doped films [15]. The calculated strain (ε) and dislocation density (δ) are tabulated in Table 1. It is observed that the strain and dislocation density increases with increase of In content, which is because of the difference in the ionic radius of zinc and indium. The formation of stress in these films is found to be compressive and indicates a negative sign which is slightly increased due to the change in the morphology of the film while doping [16]. The preferential growth orientation is determined using texture coefficient, TC(hkl) by following relation. /
TC = / ∑
/
----------1
where I(hkl) is the measured relative intensity of a plane (hkl), Io(hkl) is the standard intensity of the plane (hkl) taken from the JCPDS data, and n is the number of diffraction peaks. The increased texture coefficient (TC(hkl)>1) of the pure and 2 at.% In doped films show the preferential orientation of the crystallites along (002) plane. The observed TC(hkl)~1 for the film deposited 4 at.% of In, shows the change of preferential orientation to be random [17]. The lattice parameters a and c for the hexagonal structure can be calculated by the following equation
=
!
"!"
#
$+
&
'
----------2
The lattice constants calculated for pure and In-doped ZnO thin films are shown in Table 1. The ‘a’ and ‘c’ values are in concordance with the standard values of ZnO single crystals (a = 3.250 and c = 5.207) which indicate that the quality of ZnO films is well crystallized. The lattice 5
parameters a and c are less than the bulk value which is strong indication of compressive stress in the films [18]. It is noted that the lattice constant ‘c’ increases and ‘a’ decreases significantly, may probably be related to the some kind of defects such as interstitial In atoms, which leads to the appearance of the crystal growth orientation along (100) and (101) planes as shown in the Fig.1 The similar trend in the lattice constants was observed for Al-doped ZnO [19]. 3.2. Surface morphology analysis The morphology of pure and In-doped ZnO thin films is analyzed by scanning electron microscopy. The micrograph of Fig 2(a) depicts that the grains are uniformly distributed covering the entire surface area of the substrate and resembles the granular surface. The morphology of Fig 2(b) shows the uniform distribution of spherical grains with compact structure. Fig 2 (c) clearly evidences the small sized grains with the porous nature which is useful for the photovoltaic applications. The Fig 2 (d) depicts the hierarchical characteristics of small sized grains, whereas in the Fig 2(e) the segregation of grains take place and this is due to the excess of In content. Therefore it can be concluded that In plays a vital role in controlling the morphology of the film. The AFM images of pure and 4 at.% In-doped ZnO thin films are shown in the Fig. 3a and 3b. The Fig 3a, exhibits granular morphology with a regular arrangement of hexagonal micro crystals for pure ZnO film. From Fig 3b, it is clear that In doped film is in polycrystalline nature and uniformly distributed grains with small pores. The columnar growth of grains is seen in 3D image, (Fig 3a) shows the growth along the c-axis direction perpendicular to the substrate surface for the pure ZnO. This is in agreement with the XRD results with preferential orientation along (002) plane. The formation of island structure is observed in 3D image of the doped film (4 at.% of In-doped ZnO film), indicates the change of growth orientation as seen in XRD results. The particle size of pure (undoped) and doped films are 20 nm and 15 nm respectively. The observed roughness value of the undoped and doped films are 7.6 and 3.2 nm. The decreased surface roughness indicates that dopant plays a role in controlling the particle size and the roughness of the films. 3.3. Optical properties Fig.4 shows UV-Vis transmittance spectra of pure and In-doped ZnO thin films with different doping concentration in steps of 2 at.% In respect to zinc oxide. The transmittance of pure ZnO 6
is nearly 80%. A slight decrease in transmittance with increase of In content, may be due to the scattering of pores and other defects present in the films [20]. The optical band gap energy Eg was determined by , using the relation (αhν) = A(hν – Eg)n ----------3 where Eg is the optical band gap of the films and A is a constant. In Fig.5, the optical band gap decreases from 3.20 to 3.09 eV with increasing In content. This decrease in band gap with increasing In concentration is attributed to a shift in energy of the valence and conduction bands resulting from electron-impurity and electron-electron scattering. These two effects together decide the change in optical energy band gap [21]. The change in film density and increase in grain size are also the reason for the decrease in band gap of the doped films. The optical constants extinction coefficient (k) and refractive index (n) are calculated !+,/-
using k = )π and n = .+,/- respectively. In the Fig.6, the extinction coefficient decreases with αλ
increase of wavelength. The decrease of extinction for the doped films indicate the homogeneity of the doped film at higher concentration of In [22]. The increase of refractive index with increasing doping concentration of In may be related to an increase of the compactness of the films. (Fig. 7) The obtained results show that the refractive index is slightly greater than the refractive index of the bulk ZnO (2.0) and then become nearly constant with increasing wavelength [23]. The refractive index of the doped film shows the variation upto 2.64 in the visible region which is preferred for antireflection coating materials. 3.4. Photoluminescence Photoluminescence spectra (Fig. 8) show a strong near band edge emission (NBE) for all the films. A shift of peak position towards higher wavelength is observed in NBE emission for the doped films with increasing concentration of In [24]. The UV emission band originated from the free exciton recombination. The increased intensity of UV emission band with 2 at.% In doping content shows the improvement of crystallinity [25]. The increased intensity of NBE emission is observed for 2 at.% In-doped ZnO comes from lesser defects or (002) orientation [26]. The decrease in PL intensity > 2at.% of In doped ZnO reflects the possible lattice
7
distortion or the formation of impure phases due to In doping [27]. The improved crystallinity with decreased oxygen vacancies is evident from the absence of green emission [25]. 3.5. Electrical properties Hall measurements of pure and 4 at.% In-doped ZnO thin films are measured in order study their electrical properties. It illustrates that ZnO is a n-type semiconducting material due to the presence of oxygen vacancies and interstitial zinc atoms [16]. The pure ZnO film exhibits a resistivity of 1.27x102 Ωcm and a carrier concentration of 7.25 x 1014 cm-3 . The resistivity of In-doped ZnO film decreases as the In3+ ions which replaces a fraction of Zn2+ ions, releases one electron into the lattice which in turn increases the carrier concentration [12]. The resistivity and carrier concentration of 4 at.% of In-doped ZnO film is 6.86 x101 Ωcm and 1.97 x1017cm-3 respectively. The observed Hall mobility of the undoped and 4 at.% of In - doped ZnO films are 91.05cm2/Vs and 133.60 cm2/Vs respectively. Therefore, the conductive characteristics of ZnO:In thin films are mostly dominated by the electrons coming from the substitution of Zn2+ by In3+ [8] and favors for the potential transparent electrode for thin film solar cell [9]. 3.6. Antibacterial activity Fig. 9. (1, 2) shows the antibacterial activity of the ZnO and 4 at.% In-doped ZnO film. The antibacterial activity of pure ZnO in different concentrations against bacteria (Staphylococcus aureus, Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus mirabilis and Bacillus subtilis) is observed. The mean zone of inhibition ranges between 8 mm and 12 mm is observed in Staphylococcus aureus. Gentamycin is a positive control, for which the zone of inhibition is ranges from 13 mm to 29 mm. The highest mean zone of inhibition (12 mm) is recorded for pure ZnO against Staphylococcus aureus, 9 mm is observed for 300 mg/mL of pure ZnO against Klebsiella pneumonia and 8 and 10 mm of inhibition zone is observed for 200 mg/mL and 300 mg/mL respectively whereas there is no zone formation which is represented as NZ against the Pseudomonas aeruginosa and Proteus mirabilis (Table.2). The maximum antibacterial activity of ZnO is against Staphylococcus aureus. This is because of the firm attachment of ZnO particles to the outer cell wall membrane of the bacteria. ZnO particles begin to release the reactive species such as H2O2, OH-, O2 , Zn2+ into the medium (bacteria). These reactive species inhibit the growth of the cell which leads to the distortion and leakage of the cell and finally leads to the cell death, whereas it is observed that the moderate effect of antibacterial activity is shown by Klebsiella pneumonia (300 mg/mL) and Bacillus subtilis (200 mg/mL and 8
300 mg/mL) which is because of the weak attachment of the ZnO particles towards the cell wall membrane of the bacteria which results in the minimization of the formation of the reactive oxygen species (ROS) such as H2O2 which are responsible for the inhibition of the building elements of the bacteria [28]. The antibacterial activity of 4 at. % In-doped ZnO in different concentrations against bacteria (Staphylococcus aureus, Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus mirabilis and Bacillus subtilis) is noted. The mean zone of inhibition ranged between 9.5 mm and 12.9 mm is noticed in Staphylococcus aureus. The highest mean zone of inhibition (12.9 mm) is recorded against Staphylococcus aureus by 4 at. % In -doped ZnO are presented in Table 3. This indicates that in the doped film, In induces to deliver the high rate of generation of surface oxygen species such as H2O2 , OH-, O2 , Zn2+ from ZnO into the medium which finally leads to the death of the bacteria (Deepu Thomas et al., 2014) [29]. Ragupathy et al [30] have reported that small particles of Sn-doped ZnO have a tendency to slow down the bacterial growth. As the number of ZnO powder particle per unit volume increases with decrease of particle size, the concentration of free radicals H2O2 is generated from the surface of ZnO increases. The free radicals penetrate the inner cell membrance and created serious disruption of internal contents and cause harm to bacteria. In the present study, the decrease of particle size with the increase in In concentration may be one of the reason for the improved antibacterial activity 4. Conclusion Transparent and conductive ZnO:In thin films were deposited by the spray pyrolysis technique. XRD study revealed that the deposited films were preferentially oriented along c-axis for lower concentration of In and changed its orientation towards the isotropic growth at higher concentration of In. SEM micrograph of the films revealed that they were dense with uniform surface coverage on the substrate except for 4 at.% of In.The AFM image showed spherical nature (random orientation) for the doped films with the decrease in surface roughness of doped film (3.2 nm) than undoped film (7.6 nm). Narrowing of bandgap was noticed with increasing In content.The absence of green emission showed that the concentration of oxygen vacancy related defects which were lower in pure and In-doped ZnO. The carrier concentration and Hall mobility was increased for doped film which favored for the potential applications such as optoelectronic devices and window layers in solar cells. Furthermore, results of antibacterial 9
activity indicated that 4 at.% of In–doped ZnO yielded the better antibacterial activity against the food pathogen, Staphylococcus aureus which indicates that, the In –doped ZnO thin films would help to the prevent food forms from being affected by food pathogens by surface coating in food packages. Acknowledgement The authors thank the University Grants commission, New Delhi, India for the financial support through research Grant no. 42-860/2013. References [1] A. Chakraborty, T. Mondal, S.K. Bera, S.K. Sen, R. Ghosh, G.K. Paul, Mater. Chem. Phys. 112 (2008) 162 -166. [2] A. Souissi, A. Boukhachem, Y. Ben Taher, A. Ayadi, A. Mefteh, M. Ouesleti, S. Guermazi M. Amlouk, Optik. 125 (2014) 3344 -3349. [3] F.Paraguay D, J. Morales, W. Estrada L, E. Andrade, M. Miki-Yoshida, Thin Solid Films. 366 (2000) 16-27. [4] S.S. Shinde, A.P. Korade, C.H. Bhosale, K.Y. Rajpure, J. Alloys Comp. 551 (2013) 688-693. [5] P. Sagar, M.Kumar, R.M. Mehra, Materials Science -Poland, 23 (2005) [7] Andrea Gracia Cuevas, Kryssa Balangcod, Teodora Balangcod, Alladin Jasmin, Procedia Engineering 68 ( 2013 ) 537 – 543 [6] L. Castaneda, A. Garcia-Valenzuela, E.P. Zironi, J. Canetas-Ortega, M. Terrones, A. Maldonado, Thin Solid Films. 503 (2006) 212- 218. [8] E.J. Luna-Arredondo, A. Maldonado, R. Asomoza, D.R. Acosta, M.A. Melendez-Lira,M. de la L. Olvera, Thin Solid Films. 490 (2005) 132-136. [9] K. Djessas, I. Bouchama, J.L. Gauffier, Z. Ben Ayadi, Thin Solid Films. 555 (2014) 28-32. [10] Said Benramache, Boubaker Benhaoua, Superlattices and Microstructures 52 (2012) 10621070. [11] R.Jayakrishnan, K. Mohanachandran, R. Sreekumar, C. Sudha kartha, K.P. Vijayakumar, Mater. Sci. Semicond. Process. 16 (2013) 326-331. [12] L. Castaneda, A. Maldonado, J.Vega Perez,M.de la L.Olvera, C.Torres –Torres, Mater. Sci. Semicond. Process. 26 (2010) 288-293. [13] Yaodong Liu . Jianshe Lian, Appl. Surf. Sci. 253 (2007) 3727-3730. [14 ] Wen Chen, Jing Wang, Min-rui Wang, Vacuum. 81 (2007) 894-898. 10
[15] C.S.Prajapati, P.P.Sahay, Mater. Sci. Semicond. Process.16 (2013) 200-210. [16] T. Prasada Rao, M.C. Santhosh Kumar, A. Safarulla, V. Ganesan, S.R. Barman, C. Sanjeeviraja, Phys. B 405 (2010) 2226-2231. [17] R. Mariappan, V. Ponnuswamy, P. Suresh, Superlattices and Microstrucutres. 52 (2012) 500-513. [18] C.M. Muiva, T.S.Sathiaraj, K. Maabong, Ceram. Inter. 37 (2011) 555-560. [19] Jin Zhang,WenxiuQue, Solar Energy Materials & Solar Cells 94 (2010) 2181-2186. [20] S.Shankar, M.Saroja , M.Venkatachalama, M.Balachander , V.Kumar, J. Nano sci. Nanotechnol. 2 (2014) 769-772. [21] G.C. Xie, L. Fang, L.P. Peng, G.B. Liu, H.B. Ruan, F. Wu, C.Y. Kong, Physics Procedia 32 ( 2012 ) 651-657. [22] G. Shanmuganathan, I.B. Shameem Banu, S. Krishnan, B. Ranganathan, J. Alloy. Comp. 562 ( 2013) 187-193. [23] M.A. Kaid, A. Ashour, Appl. Surf. Sci. 253 (2007) 3029-3033. [24] Xu Zi-qiang, Deng Hong, Li Yan, Cheng Hang, Mater. Sci. Semicond. Process. 9 (2006) 132-135. [25] R. Anandhi, K. Ravichandran, R. Mohan; Mater. Sci. Eng. B 178 (2013) 65-70. [26] K.J. Chen, F.Y. Hung, S.J. Chang, Z.S. Hu, Appl. Surf. Sci. 255 (2009) 6308-6312. [27] Xiuxian He, Wen Dong, Fengang Zheng,Liang Fang, Mingrong Shen; Mater. Chem. Phy. 123 (2010) 248-288. [28] D. Jesuvathy Sornalatha, S. Bhuvaneswari, S. Murugesan, P. Murugakoothan, Optik 126 (2015) 63–67 [29] Deepu Thomas, Jyothi Abraham, Sunil C. Vattappalam, Simon Augustine, Dennis Thomas, Indo American Journal of Pharmaceutical Research, 2014, ISSN NO: 2231-6876 [30] K.R.Ragupathi, R.T.Koodali, A.C.Manna, Langmuir 27 (2011) 4020-4028.
Figure caption Fig.1. XRD pattern of pure ZnO and In doped ZnO films.
11
Fig.2. SEM images of (a) undoped ZnO, (b) 2 at% (c) 4 at% (d) 6at%, and (e) 8at% of In doped ZnO thin films. Fig.3. AFM images of (a) undoped and (b) 4 at. % In doped ZnO thin films. Fig.4. Optical transmittance of In doped ZnO thin films. Fig.5. Variation of (αhν)2 vs hν of the In doped ZnO thin films. Fig.6. The variation of extinction coefficient of the ZnO and In doped ZnO thin films with wavelength. Fig.7. The variation of refractive index of the ZnO and In doped ZnO thin films with wavelength. Fig.8. PL spectra of undoped and In doped ZnO thin films. Fig.9. Antibacterial activity of 1) ZnO 2) 4 at % of In doped ZnO thin films with g) positive control, c) negative control, a ) 100 mg/ml, b) 200 mg/ml and d) 300 mg/ml of Staphylococcus aureus.
Table caption Table.1.Variation of crystallite size (D), dislocation density (δ), strain (ε), stress (σstress), texture coefficient (TC) and lattice parameters (a and c) for pure ZnO and In doped ZnO thin films. Table.2. Antibacterial activity of Zinc oxide. Table.3. Antibacterial activity of In doped Zinc oxide.
12
Fig.1. XRD pattern of pure ZnO and In doped ZnO films.
13
Fig.2. SEM images of (a) undoped ZnO, (b) 2 at% (c) 4 at% (d) 6at%, and (e) 8at% of In doped ZnO thin films.
14
Fig.3. AFM images of (a) undoped and (b) 4 at. % In doped ZnO thin films.
Fig.4. Optical transmittance of In doped ZnO thin films.
15
Fig.5. Variation of (αhν)2 vs hν of the In doped ZnO thin films.
Fig.6. The variation of extinction coefficient of the ZnO and In doped ZnO thin films with wavelength.
16
Fig.7. The variation of refractive index of the ZnO and In doped ZnO thin films with wavelength.
Fig.8. PL spectra of undoped and In doped ZnO thin films.
17
Fig.9. Antibacterial activity of 1) ZnO 2) 4 at % of In doped ZnO thin films with g) positive control, c) negative control, a ) 100 mg/ml, b) 200 mg/ml and d) 300 mg/ml of Staphylococcus aureus.
18
Table.1.Variation of crystallite size (D), dislocation density (δ), strain (ε), stress (σstress), texture coefficient (TC) and lattice parameters (a and c) for pure ZnO and In doped ZnO thin films. sample
δx1014
D (nm)
εx10-3
σstress
lines/m2 ZnO
38.8208
TC
Lattice parameters
(GPa)
a
c
6.6353
0.8920
-1.155
1.769
3.244
5.201
2 at% In
31.1692
10.2931
1.1121
-2.1930
1.792
3.248
5.157
4 at% In
24.1657
17.1238
1.4344
-0.4644
0.937
3.248
5.216
6 at% In
13.8215
52.3467
2.507
-1.3052
2.575
3.248
5.218
8 at% In
7.9696
157.4443 4.3494
-0.0134
1.903
3.247
5.206
Table.2. Antibacterial activity of Zinc oxide organisms
Control
Gentamycin
Zone of inhibition
30 mg
(mg/mL) 100
200
300
Staphylococcus aureus
NZ
29
8
11
12
Klebsiella pneumonia,
NZ
18
NZ
NZ
9
Pseudomonas aeruginosa,
NZ
13
NZ
NZ
NZ
Proteus mirabilis
NZ
21
NZ
NZ
NZ
Bacillus subtilis
NZ
21
NZ
8
10
NZ- No Zone
19
Table.3. Antibacterial activity of In doped Zinc oxide organisms
Control
Gentamycin
Zone of inhibition
30 mg
(mg/mL) 100
200
300
Staphylococcus aureus
NZ
29
9.5
11.9
12.9
Klebsiella pneumonia,
NZ
18
NZ
NZ
NZ
Pseudomonas aeruginosa,
NZ
13
NZ
NZ
NZ
Proteus mirabilis
NZ
21
NZ
NZ
NZ
Bacillus subtilis
NZ
21
NZ
NZ
NZ
NZ- No Zone
20
Graphical Abstract
Zincacetylacetonate+ Indium chloride Ethanol
Spray Pyrolysis Technique
Antibacterial Activity
Films
Topological
21
Highlights Films with preferential orientation (002) have been deposited onto glass substrates using spray pyrolysis technique. The change of preferential orientation from (002) to (101) while doping In. The decline of transmittance with narrowing of the band gap while doping In. The decreased resistivity and improved mobility was observed for In-doped ZnO films. A better antibacterial activity was observed against Staphylococcus aureus by doped film.
22
S1386-1425(15)00607-1 http://dx.doi.org/10.1016/j.saa.2015.05.019 SAA 13686
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
5 December 2014 6 March 2015 5 May 2015
Please cite this article as: C. Manoharan, G. Pavithra, S. Dhanapandian, P. Dhamodharan, Effect of In doping on the properties and antibacterial activity of ZnO films prepared by spray pyrolysis, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.05.019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of In doping on the properties and antibacterial activity of ZnO films prepared by spray pyrolysis C. Manoharan, G. Pavithra*, S. Dhanapandian and P.Dhamodharan Department of Physics, Annamalai University, Annamalai Nagar – 608 002, Tamilnadu, India Abstract Pure and In-doped ZnO thin films were deposited onto glass substrates by spray pyrolysis technique. XRD results showed that all films were polycrystalline in nature with the wurzite structure. A change in preferential orientation from (002) to (101) plane was observed with increase in content of Indium. A reduce in crystallite size was observed with increase of In content. The small sized grains with the porous nature of the film was observed from SEM analysis. AFM study depicted polycrystalline nature and uniformly distributed grains with small pores in the doped film. A decrease in band gap was noticed with increase in In content. The absence of green emission in PL spectra indicated the decreased oxygen defects.The decrease in the resistivity with increase of Hall mobility was noted for the doped film. A better antibacterial activity was observed against Staphylococcus aureus by doped ZnO thin film. Key words: Indium doped ZnO, Thin films, Spray pyrolysis technique, Antibacterial activity. *
Corresponding author
E-mail:[email protected] Tel: +91- 9487966397
1
1. Introduction In the field of materials science, Zinc oxide (ZnO) holds a very important position because it is piezoelectric, transparent in the visible range with wide band gap and become conducting with appropriate dopants. However, ease in doping by suitable impurity atoms (dopants) can make it n-type semiconductor which can tune the properties of ZnO, in order to enhance the material as a most promising candidates for optoelectronic devices such as lightemitting diodes, laser diodes, UV photo detectors [1,2], gas sensor devices, transparent electrodes, and piezoelectric devices [3]. Pure zinc oxide is unstable due to modification in the surface conductance under oxygen chemisorptions and adsorptions [4]. Its electrical and optical properties can be enhanced by doping the elements such as Al, B, In, Ga and F. By doping, metal dopants (Al, B, In, Ga) into ZnO thin films make them as highly conducting material which could be the alternative as less expensive transparent conducting layers in several applications such as transparent display devices, and solar cells [5]. Also, ZnO thin films are stable under moderate temperature ranges (250–400ºC) in the presence of air [6]. Andrea Gracia Cuevas et al., 2013 [7] stated that zinc oxide a promising material for the prevention of the food forms from being affected by food pathogens such as E. coli and S. aureus in the packed foods, applied to treat different skin conditions, in products like baby powder and creams against diaper rashes, antiseptic ointments, anti-dandruff shampoos, and as a component in tape (called “Zinc oxide tape”) used by athletes as a bandage to prevent soft tissue damage during workouts. Many techniques have been used to deposit ZnO films onto glass substrate, such as Sol-gel [8], Sputtering [9], Spray pyrolysis [10] etc. Among these techniques, spray pyrolysis is one of the most commonly used method for the preparation of metal oxide thin films due to its simplicity, affordable with uniform coating, non-vacuum system of deposition and has large area coating with device quality. In the present study it is aimed to enhance the optical and electrical properties of ZnO by doping of indium. Spray pyrolysis deposition technique has been used since it is easy and low cost equipment deposition technique. Also an attempt has been made to study the antibacterial activity against the test organisms for pure and In-doped ZnO thin films. 2. Experiment
2
ZnO : In thin films were obtained by spray pyrolysis in air atmosphere from aqueous solutions in which the atomic ratio of In in the spray solution was varied from 0, 2, 4, 6 and 8 at.%. The substrates were well cleaned by soap solution followed by HCl, acetone and distilled water. Finally, the cleaned substrates were dried in oven. The experimental set-up used for the spraying process consists of a spray head and heater which was kept inside a chamber with an exhaust fan which could remove the gaseous byproducts and solvent vapor. The substrate temperature was achieved with the help of heater which was controlled by an automatic temperature controller with an accuracy of ±5°C. The uniform growth of the film was obtained by moving the spray head in the X - Y direction which was able to scan an area of 200 x 200 mm with the flow rate of the solution, 3ml/min.The diameter of the spary nozzle is 0.45 mm. The carrier gas used in this experiment was air and the pressure of the carrier gas was maintained with the help of mechanical gauge. The entire unit was connected to computer with the help of a serial port to store the spray parameters.The spray solution was prepared by dissolving 0.1M of Zn (acac) in ethanol and Indium (III) chloride was added to the solution as a dopant. The prepared solution was sprayed onto glass substrate at the substrate temperatrure of 400°C.The grown films were annealed at 500 °C in air for an hour. 2.1 Characterization technique The structural characterization of the deposited films were carried out by X-ray diffraction technique on SHIMADZU-6000 (monochromatic Cu-Kα radiation, λ=1.5406 Ǻ). The surface morphology was studied by using SEM (JEOL-JES-1600). Optical absorption spectrum was recorded in the range of 300-1200 nm using JASCO V-670 spectrophotometer. The photoluminescence spectrum (PL) was studied at room temperature using prolog 3HORIBAJOBINYVON with an excitation source wavelength of 375 nm. The surface topological studies were carried out using Atomic force Microscope (Nano surf Easy scan2) AGILENTN9410A-5500. The electrical resistivity, carrier concentration and mobility were measured by automated Hall Effect measurement (ECOPIA HMS - 2000) at room temperature in a van der Pauw (VDP) four - point probe configuration. 2.2 Antibacterial activity Preparation of test solution and disc
3
The test solution was prepared with known weight of fractions in 10 mg/mL, and dissolved in 5 percent dimethyl sulphoxide (DMSO). Sterile discs Himedia Ltd., Mumbai. (6 mm) were impregnated with 20 µl of the ZnO and In doped ZnO (corresponding to 100, 200 and 300 mg/mL) allowed to dry at room temperature. Disc diffusion method The agar diffusion method was followed for antibacterial susceptibility test. Petri plates were prepared by pouring 20 mL of Mueller Hinton Agar allowed to solidify for the use in susceptibility test against bacteria respectively. Plates were dried and
0.1 mL of standardized
inoculums suspension was poured and uniformly spread. The excess inoculums were drained and the plates were allowed to dry for 5 minutes. After drying, the discs with ZnO and In-doped ZnO were placed on the surface of the plate with sterile forceps and gently pressed to ensure contact with the agar surface. Gentamycin (30 mg/disc) were used as the positive controls and 5 per cent DMSO was used as blind control in these assays. Finally, the inoculated plates were incubated at 37 °C for 24 h. The zone of inhibition was observed and measured in millimeters. 3. Results and Discussion 3.1. Structural Studies Fig.1. shows the XRD pattern of pure and In-doped ZnO thin films. XRD patterns confirm the formation of polycrystalline with hexagonal wurzite structure of ZnO with the absence of other peaks such as indium oxide and In-Zn compounds. The pure ZnO thin film exhibits a strong intensity to (002) plane which indicates the film is preferentially oriented along c-axis. The c-axis orientation of pristine ZnO is because of the minimal of internal stress and surface energy and by high atomic density which leads to the easy growth of the crystallites towards the c-axis direction [11]. A decrease in intensity of (002) plane and an increase in intensity of (101) plane is noticed for 2 at.% of In. However, there is no significant change in peak position of (002), (101) and (100) plane while doping indium, which shows the absence of new phase [12]. Further increase in intensity of (101) plane than the (002) plane and increase in intensity of (100) plane for 4 at.% of In, indicates the change in growth orientation from c-axis to isotropic growth. The similar change of orientation is observed for Aldoped ZnO by Yaodong Liu et al., [13]. The change of growth orientation from (002) to (101) is 4
due to the change in diffusion rate of Zn and O at surface during deposition, when presence of In3+ ions is excess in ZnO. At 4 at.% of In, the film exhibits a strong orientation along (101) plane is noticed. The lower concentration of In does not affect the preferential orientation along (002) as In incorporates into the lattice. The change in preferential orientation is noticed for higher concentration of In as the solubility limit is reached and this prevents the preferential growth.The intensity of (101) plane is gradually decreased with further increase of In content (6 at.%). The higher concentration of indium detorited the crystallinity of the films is because of the stress produced by the difference in ion size between indium and zinc are also due to segregation of dopants in grain boundaries [12,14].
The crystallite size ‘D’ is calculated by well known Debye–Scherrer formula D = where λ is the wavelength of CuKα radiation, k is the shape factor, β is the full width half maximum ( FWHM) intensity.The enhancement of density of nucleation center is the reason for the decrease of crystallites size in the doped films [15]. The calculated strain (ε) and dislocation density (δ) are tabulated in Table 1. It is observed that the strain and dislocation density increases with increase of In content, which is because of the difference in the ionic radius of zinc and indium. The formation of stress in these films is found to be compressive and indicates a negative sign which is slightly increased due to the change in the morphology of the film while doping [16]. The preferential growth orientation is determined using texture coefficient, TC(hkl) by following relation. /
TC = / ∑
/
----------1
where I(hkl) is the measured relative intensity of a plane (hkl), Io(hkl) is the standard intensity of the plane (hkl) taken from the JCPDS data, and n is the number of diffraction peaks. The increased texture coefficient (TC(hkl)>1) of the pure and 2 at.% In doped films show the preferential orientation of the crystallites along (002) plane. The observed TC(hkl)~1 for the film deposited 4 at.% of In, shows the change of preferential orientation to be random [17]. The lattice parameters a and c for the hexagonal structure can be calculated by the following equation
=
!
"!"
#
$+
&
'
----------2
The lattice constants calculated for pure and In-doped ZnO thin films are shown in Table 1. The ‘a’ and ‘c’ values are in concordance with the standard values of ZnO single crystals (a = 3.250 and c = 5.207) which indicate that the quality of ZnO films is well crystallized. The lattice 5
parameters a and c are less than the bulk value which is strong indication of compressive stress in the films [18]. It is noted that the lattice constant ‘c’ increases and ‘a’ decreases significantly, may probably be related to the some kind of defects such as interstitial In atoms, which leads to the appearance of the crystal growth orientation along (100) and (101) planes as shown in the Fig.1 The similar trend in the lattice constants was observed for Al-doped ZnO [19]. 3.2. Surface morphology analysis The morphology of pure and In-doped ZnO thin films is analyzed by scanning electron microscopy. The micrograph of Fig 2(a) depicts that the grains are uniformly distributed covering the entire surface area of the substrate and resembles the granular surface. The morphology of Fig 2(b) shows the uniform distribution of spherical grains with compact structure. Fig 2 (c) clearly evidences the small sized grains with the porous nature which is useful for the photovoltaic applications. The Fig 2 (d) depicts the hierarchical characteristics of small sized grains, whereas in the Fig 2(e) the segregation of grains take place and this is due to the excess of In content. Therefore it can be concluded that In plays a vital role in controlling the morphology of the film. The AFM images of pure and 4 at.% In-doped ZnO thin films are shown in the Fig. 3a and 3b. The Fig 3a, exhibits granular morphology with a regular arrangement of hexagonal micro crystals for pure ZnO film. From Fig 3b, it is clear that In doped film is in polycrystalline nature and uniformly distributed grains with small pores. The columnar growth of grains is seen in 3D image, (Fig 3a) shows the growth along the c-axis direction perpendicular to the substrate surface for the pure ZnO. This is in agreement with the XRD results with preferential orientation along (002) plane. The formation of island structure is observed in 3D image of the doped film (4 at.% of In-doped ZnO film), indicates the change of growth orientation as seen in XRD results. The particle size of pure (undoped) and doped films are 20 nm and 15 nm respectively. The observed roughness value of the undoped and doped films are 7.6 and 3.2 nm. The decreased surface roughness indicates that dopant plays a role in controlling the particle size and the roughness of the films. 3.3. Optical properties Fig.4 shows UV-Vis transmittance spectra of pure and In-doped ZnO thin films with different doping concentration in steps of 2 at.% In respect to zinc oxide. The transmittance of pure ZnO 6
is nearly 80%. A slight decrease in transmittance with increase of In content, may be due to the scattering of pores and other defects present in the films [20]. The optical band gap energy Eg was determined by , using the relation (αhν) = A(hν – Eg)n ----------3 where Eg is the optical band gap of the films and A is a constant. In Fig.5, the optical band gap decreases from 3.20 to 3.09 eV with increasing In content. This decrease in band gap with increasing In concentration is attributed to a shift in energy of the valence and conduction bands resulting from electron-impurity and electron-electron scattering. These two effects together decide the change in optical energy band gap [21]. The change in film density and increase in grain size are also the reason for the decrease in band gap of the doped films. The optical constants extinction coefficient (k) and refractive index (n) are calculated !+,/-
using k = )π and n = .+,/- respectively. In the Fig.6, the extinction coefficient decreases with αλ
increase of wavelength. The decrease of extinction for the doped films indicate the homogeneity of the doped film at higher concentration of In [22]. The increase of refractive index with increasing doping concentration of In may be related to an increase of the compactness of the films. (Fig. 7) The obtained results show that the refractive index is slightly greater than the refractive index of the bulk ZnO (2.0) and then become nearly constant with increasing wavelength [23]. The refractive index of the doped film shows the variation upto 2.64 in the visible region which is preferred for antireflection coating materials. 3.4. Photoluminescence Photoluminescence spectra (Fig. 8) show a strong near band edge emission (NBE) for all the films. A shift of peak position towards higher wavelength is observed in NBE emission for the doped films with increasing concentration of In [24]. The UV emission band originated from the free exciton recombination. The increased intensity of UV emission band with 2 at.% In doping content shows the improvement of crystallinity [25]. The increased intensity of NBE emission is observed for 2 at.% In-doped ZnO comes from lesser defects or (002) orientation [26]. The decrease in PL intensity > 2at.% of In doped ZnO reflects the possible lattice
7
distortion or the formation of impure phases due to In doping [27]. The improved crystallinity with decreased oxygen vacancies is evident from the absence of green emission [25]. 3.5. Electrical properties Hall measurements of pure and 4 at.% In-doped ZnO thin films are measured in order study their electrical properties. It illustrates that ZnO is a n-type semiconducting material due to the presence of oxygen vacancies and interstitial zinc atoms [16]. The pure ZnO film exhibits a resistivity of 1.27x102 Ωcm and a carrier concentration of 7.25 x 1014 cm-3 . The resistivity of In-doped ZnO film decreases as the In3+ ions which replaces a fraction of Zn2+ ions, releases one electron into the lattice which in turn increases the carrier concentration [12]. The resistivity and carrier concentration of 4 at.% of In-doped ZnO film is 6.86 x101 Ωcm and 1.97 x1017cm-3 respectively. The observed Hall mobility of the undoped and 4 at.% of In - doped ZnO films are 91.05cm2/Vs and 133.60 cm2/Vs respectively. Therefore, the conductive characteristics of ZnO:In thin films are mostly dominated by the electrons coming from the substitution of Zn2+ by In3+ [8] and favors for the potential transparent electrode for thin film solar cell [9]. 3.6. Antibacterial activity Fig. 9. (1, 2) shows the antibacterial activity of the ZnO and 4 at.% In-doped ZnO film. The antibacterial activity of pure ZnO in different concentrations against bacteria (Staphylococcus aureus, Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus mirabilis and Bacillus subtilis) is observed. The mean zone of inhibition ranges between 8 mm and 12 mm is observed in Staphylococcus aureus. Gentamycin is a positive control, for which the zone of inhibition is ranges from 13 mm to 29 mm. The highest mean zone of inhibition (12 mm) is recorded for pure ZnO against Staphylococcus aureus, 9 mm is observed for 300 mg/mL of pure ZnO against Klebsiella pneumonia and 8 and 10 mm of inhibition zone is observed for 200 mg/mL and 300 mg/mL respectively whereas there is no zone formation which is represented as NZ against the Pseudomonas aeruginosa and Proteus mirabilis (Table.2). The maximum antibacterial activity of ZnO is against Staphylococcus aureus. This is because of the firm attachment of ZnO particles to the outer cell wall membrane of the bacteria. ZnO particles begin to release the reactive species such as H2O2, OH-, O2 , Zn2+ into the medium (bacteria). These reactive species inhibit the growth of the cell which leads to the distortion and leakage of the cell and finally leads to the cell death, whereas it is observed that the moderate effect of antibacterial activity is shown by Klebsiella pneumonia (300 mg/mL) and Bacillus subtilis (200 mg/mL and 8
300 mg/mL) which is because of the weak attachment of the ZnO particles towards the cell wall membrane of the bacteria which results in the minimization of the formation of the reactive oxygen species (ROS) such as H2O2 which are responsible for the inhibition of the building elements of the bacteria [28]. The antibacterial activity of 4 at. % In-doped ZnO in different concentrations against bacteria (Staphylococcus aureus, Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus mirabilis and Bacillus subtilis) is noted. The mean zone of inhibition ranged between 9.5 mm and 12.9 mm is noticed in Staphylococcus aureus. The highest mean zone of inhibition (12.9 mm) is recorded against Staphylococcus aureus by 4 at. % In -doped ZnO are presented in Table 3. This indicates that in the doped film, In induces to deliver the high rate of generation of surface oxygen species such as H2O2 , OH-, O2 , Zn2+ from ZnO into the medium which finally leads to the death of the bacteria (Deepu Thomas et al., 2014) [29]. Ragupathy et al [30] have reported that small particles of Sn-doped ZnO have a tendency to slow down the bacterial growth. As the number of ZnO powder particle per unit volume increases with decrease of particle size, the concentration of free radicals H2O2 is generated from the surface of ZnO increases. The free radicals penetrate the inner cell membrance and created serious disruption of internal contents and cause harm to bacteria. In the present study, the decrease of particle size with the increase in In concentration may be one of the reason for the improved antibacterial activity 4. Conclusion Transparent and conductive ZnO:In thin films were deposited by the spray pyrolysis technique. XRD study revealed that the deposited films were preferentially oriented along c-axis for lower concentration of In and changed its orientation towards the isotropic growth at higher concentration of In. SEM micrograph of the films revealed that they were dense with uniform surface coverage on the substrate except for 4 at.% of In.The AFM image showed spherical nature (random orientation) for the doped films with the decrease in surface roughness of doped film (3.2 nm) than undoped film (7.6 nm). Narrowing of bandgap was noticed with increasing In content.The absence of green emission showed that the concentration of oxygen vacancy related defects which were lower in pure and In-doped ZnO. The carrier concentration and Hall mobility was increased for doped film which favored for the potential applications such as optoelectronic devices and window layers in solar cells. Furthermore, results of antibacterial 9
activity indicated that 4 at.% of In–doped ZnO yielded the better antibacterial activity against the food pathogen, Staphylococcus aureus which indicates that, the In –doped ZnO thin films would help to the prevent food forms from being affected by food pathogens by surface coating in food packages. Acknowledgement The authors thank the University Grants commission, New Delhi, India for the financial support through research Grant no. 42-860/2013. References [1] A. Chakraborty, T. Mondal, S.K. Bera, S.K. Sen, R. Ghosh, G.K. Paul, Mater. Chem. Phys. 112 (2008) 162 -166. [2] A. Souissi, A. Boukhachem, Y. Ben Taher, A. Ayadi, A. Mefteh, M. Ouesleti, S. Guermazi M. Amlouk, Optik. 125 (2014) 3344 -3349. [3] F.Paraguay D, J. Morales, W. Estrada L, E. Andrade, M. Miki-Yoshida, Thin Solid Films. 366 (2000) 16-27. [4] S.S. Shinde, A.P. Korade, C.H. Bhosale, K.Y. Rajpure, J. Alloys Comp. 551 (2013) 688-693. [5] P. Sagar, M.Kumar, R.M. Mehra, Materials Science -Poland, 23 (2005) [7] Andrea Gracia Cuevas, Kryssa Balangcod, Teodora Balangcod, Alladin Jasmin, Procedia Engineering 68 ( 2013 ) 537 – 543 [6] L. Castaneda, A. Garcia-Valenzuela, E.P. Zironi, J. Canetas-Ortega, M. Terrones, A. Maldonado, Thin Solid Films. 503 (2006) 212- 218. [8] E.J. Luna-Arredondo, A. Maldonado, R. Asomoza, D.R. Acosta, M.A. Melendez-Lira,M. de la L. Olvera, Thin Solid Films. 490 (2005) 132-136. [9] K. Djessas, I. Bouchama, J.L. Gauffier, Z. Ben Ayadi, Thin Solid Films. 555 (2014) 28-32. [10] Said Benramache, Boubaker Benhaoua, Superlattices and Microstructures 52 (2012) 10621070. [11] R.Jayakrishnan, K. Mohanachandran, R. Sreekumar, C. Sudha kartha, K.P. Vijayakumar, Mater. Sci. Semicond. Process. 16 (2013) 326-331. [12] L. Castaneda, A. Maldonado, J.Vega Perez,M.de la L.Olvera, C.Torres –Torres, Mater. Sci. Semicond. Process. 26 (2010) 288-293. [13] Yaodong Liu . Jianshe Lian, Appl. Surf. Sci. 253 (2007) 3727-3730. [14 ] Wen Chen, Jing Wang, Min-rui Wang, Vacuum. 81 (2007) 894-898. 10
[15] C.S.Prajapati, P.P.Sahay, Mater. Sci. Semicond. Process.16 (2013) 200-210. [16] T. Prasada Rao, M.C. Santhosh Kumar, A. Safarulla, V. Ganesan, S.R. Barman, C. Sanjeeviraja, Phys. B 405 (2010) 2226-2231. [17] R. Mariappan, V. Ponnuswamy, P. Suresh, Superlattices and Microstrucutres. 52 (2012) 500-513. [18] C.M. Muiva, T.S.Sathiaraj, K. Maabong, Ceram. Inter. 37 (2011) 555-560. [19] Jin Zhang,WenxiuQue, Solar Energy Materials & Solar Cells 94 (2010) 2181-2186. [20] S.Shankar, M.Saroja , M.Venkatachalama, M.Balachander , V.Kumar, J. Nano sci. Nanotechnol. 2 (2014) 769-772. [21] G.C. Xie, L. Fang, L.P. Peng, G.B. Liu, H.B. Ruan, F. Wu, C.Y. Kong, Physics Procedia 32 ( 2012 ) 651-657. [22] G. Shanmuganathan, I.B. Shameem Banu, S. Krishnan, B. Ranganathan, J. Alloy. Comp. 562 ( 2013) 187-193. [23] M.A. Kaid, A. Ashour, Appl. Surf. Sci. 253 (2007) 3029-3033. [24] Xu Zi-qiang, Deng Hong, Li Yan, Cheng Hang, Mater. Sci. Semicond. Process. 9 (2006) 132-135. [25] R. Anandhi, K. Ravichandran, R. Mohan; Mater. Sci. Eng. B 178 (2013) 65-70. [26] K.J. Chen, F.Y. Hung, S.J. Chang, Z.S. Hu, Appl. Surf. Sci. 255 (2009) 6308-6312. [27] Xiuxian He, Wen Dong, Fengang Zheng,Liang Fang, Mingrong Shen; Mater. Chem. Phy. 123 (2010) 248-288. [28] D. Jesuvathy Sornalatha, S. Bhuvaneswari, S. Murugesan, P. Murugakoothan, Optik 126 (2015) 63–67 [29] Deepu Thomas, Jyothi Abraham, Sunil C. Vattappalam, Simon Augustine, Dennis Thomas, Indo American Journal of Pharmaceutical Research, 2014, ISSN NO: 2231-6876 [30] K.R.Ragupathi, R.T.Koodali, A.C.Manna, Langmuir 27 (2011) 4020-4028.
Figure caption Fig.1. XRD pattern of pure ZnO and In doped ZnO films.
11
Fig.2. SEM images of (a) undoped ZnO, (b) 2 at% (c) 4 at% (d) 6at%, and (e) 8at% of In doped ZnO thin films. Fig.3. AFM images of (a) undoped and (b) 4 at. % In doped ZnO thin films. Fig.4. Optical transmittance of In doped ZnO thin films. Fig.5. Variation of (αhν)2 vs hν of the In doped ZnO thin films. Fig.6. The variation of extinction coefficient of the ZnO and In doped ZnO thin films with wavelength. Fig.7. The variation of refractive index of the ZnO and In doped ZnO thin films with wavelength. Fig.8. PL spectra of undoped and In doped ZnO thin films. Fig.9. Antibacterial activity of 1) ZnO 2) 4 at % of In doped ZnO thin films with g) positive control, c) negative control, a ) 100 mg/ml, b) 200 mg/ml and d) 300 mg/ml of Staphylococcus aureus.
Table caption Table.1.Variation of crystallite size (D), dislocation density (δ), strain (ε), stress (σstress), texture coefficient (TC) and lattice parameters (a and c) for pure ZnO and In doped ZnO thin films. Table.2. Antibacterial activity of Zinc oxide. Table.3. Antibacterial activity of In doped Zinc oxide.
12
Fig.1. XRD pattern of pure ZnO and In doped ZnO films.
13
Fig.2. SEM images of (a) undoped ZnO, (b) 2 at% (c) 4 at% (d) 6at%, and (e) 8at% of In doped ZnO thin films.
14
Fig.3. AFM images of (a) undoped and (b) 4 at. % In doped ZnO thin films.
Fig.4. Optical transmittance of In doped ZnO thin films.
15
Fig.5. Variation of (αhν)2 vs hν of the In doped ZnO thin films.
Fig.6. The variation of extinction coefficient of the ZnO and In doped ZnO thin films with wavelength.
16
Fig.7. The variation of refractive index of the ZnO and In doped ZnO thin films with wavelength.
Fig.8. PL spectra of undoped and In doped ZnO thin films.
17
Fig.9. Antibacterial activity of 1) ZnO 2) 4 at % of In doped ZnO thin films with g) positive control, c) negative control, a ) 100 mg/ml, b) 200 mg/ml and d) 300 mg/ml of Staphylococcus aureus.
18
Table.1.Variation of crystallite size (D), dislocation density (δ), strain (ε), stress (σstress), texture coefficient (TC) and lattice parameters (a and c) for pure ZnO and In doped ZnO thin films. sample
δx1014
D (nm)
εx10-3
σstress
lines/m2 ZnO
38.8208
TC
Lattice parameters
(GPa)
a
c
6.6353
0.8920
-1.155
1.769
3.244
5.201
2 at% In
31.1692
10.2931
1.1121
-2.1930
1.792
3.248
5.157
4 at% In
24.1657
17.1238
1.4344
-0.4644
0.937
3.248
5.216
6 at% In
13.8215
52.3467
2.507
-1.3052
2.575
3.248
5.218
8 at% In
7.9696
157.4443 4.3494
-0.0134
1.903
3.247
5.206
Table.2. Antibacterial activity of Zinc oxide organisms
Control
Gentamycin
Zone of inhibition
30 mg
(mg/mL) 100
200
300
Staphylococcus aureus
NZ
29
8
11
12
Klebsiella pneumonia,
NZ
18
NZ
NZ
9
Pseudomonas aeruginosa,
NZ
13
NZ
NZ
NZ
Proteus mirabilis
NZ
21
NZ
NZ
NZ
Bacillus subtilis
NZ
21
NZ
8
10
NZ- No Zone
19
Table.3. Antibacterial activity of In doped Zinc oxide organisms
Control
Gentamycin
Zone of inhibition
30 mg
(mg/mL) 100
200
300
Staphylococcus aureus
NZ
29
9.5
11.9
12.9
Klebsiella pneumonia,
NZ
18
NZ
NZ
NZ
Pseudomonas aeruginosa,
NZ
13
NZ
NZ
NZ
Proteus mirabilis
NZ
21
NZ
NZ
NZ
Bacillus subtilis
NZ
21
NZ
NZ
NZ
NZ- No Zone
20
Graphical Abstract
Zincacetylacetonate+ Indium chloride Ethanol
Spray Pyrolysis Technique
Antibacterial Activity
Films
Topological
21
Highlights Films with preferential orientation (002) have been deposited onto glass substrates using spray pyrolysis technique. The change of preferential orientation from (002) to (101) while doping In. The decline of transmittance with narrowing of the band gap while doping In. The decreased resistivity and improved mobility was observed for In-doped ZnO films. A better antibacterial activity was observed against Staphylococcus aureus by doped film.
22
