1 2 Mn-doped ZnO nanoparticles: Preparation, characterization, and calculation 3 of electronic and magnetic properties 4 Pirot Moontragoon ⇑ Q1 , Supree Pinitsoontorn, Prasit Thongbai 5 Integrated Nanotechnology Research Center (INRC), Department of Physics, Khon Kaen University, Khon Kaen, 40002, Thailand 6 Nanotec-KKU Center of Excellence on Advanced Nanomaterials for Energy Production and Storage, Thailand Q2 7 8 10 article info 11 Article history: 12 Available online xxxx 13 Keywords: 14 Diluted magnetic semiconductor 15 Mn-doped ZnO 16 Spintronics 17 18 abstract 19 In this work, Zn 1x Mn x O nanoparticles were prepared by PEG sol–gel method. Structure and morpholo- 20 gies of Zn 1x Mn x O nanoparticles were investigated by using transmission electron microscope. Magnetic 21 properties were measured by using a vibrating sample magnetometer (VSM). In calculation, electronic 22 structure and magnetic properties for pure ZnO and Zn 1x Mn x O have been investigated by means of 23 the first principle calculations based on local density approximation (LDA) and LDA+U scheme, packaged 24 in the ABINIT code. The calculation was performed using self-consistent projected augmented plane wave 25 (PAW). The zinc oxide was modeled using 2 2 2 super-cell (totally containing 32 atoms) in ideal hex- 26 agonal wurtzite structure. A 9 9 5 Monkhorst–Pack k–point mesh was used for the super cell calcu- 27 lation and a plane wave cutoff energy of 16 Hartree was used to assure convergent results. The results 28 indicate that ZnO has energy band-gap about 1.97 eV which is underestimated when compared to exper- 29 iments. The magnetic dipole moments of the Zn 1x Mn x O when the manganese contents (x) are 0.0000, 30 0.0625, 0.1250 and 0.1875 equal 0.00l b , 3.83l b , 7.78l b and 10.37l b , respectively. The doped manganese 31 atoms seem to play an important role for the appearance of ferromagnetism. 32 Ó 2013 Published by Elsevier B.V. 33 34 35 1. Introduction 36 Since the discovery of ferromagnetism in diluted magnetic 37 semiconductors (DMSs), such as Mn doped GaAs, InAs or Ge, they 38 are continuously attracting research attention as promising spin- 39 tronics semiconductors with prospective applications in semicon- 40 ductor devices. A new technology which shows the potential to 41 use the spin of electron instead of the charge of electron for read- 42 ing, writing data and transferring the information to integrate with 43 traditional semiconductor technology. Therefore, this technology 44 needs ferromagnetic materials at high temperature, especially at 45 room temperature. In the early effort toward spintronic technol- 46 ogy, many researchers have been interested in the preparation 47 and characterization of manganese doped III–V and II–VI materials, 48 due to a proposed and measured Curie temperature above room 49 temperature. In the recent years, however, the diluted magnetic 50 oxides, such as TiO 2 , CeO 2 and SnO 2 doped with various transition 51 metals, such as Co, Fe, Ni and Mn, are immensely investigated, in 52 both theories and experiment, to predict magnetic properties of 53 these oxides which are doped with various transition metals 54 [1,2]. Among diluted magnetic oxide, Mn-doped ZnO materials 55 are considered as the most promising candidates because it is more 56 easy to fabricate than other oxide materials, widely use in the 57 optoelectronic devices and indicates room temperature ferromag- 58 netism. The Mn-doped ZnO compounds can be syntisised in several 59 forms, such as thin film, bulk and nanoparticles, and by several 60 methods such as RF sputtering, pulsed laser deposition (PLD), 61 chemical vapor deposition (CVD) and simple sol–gel method [3– 62 7]. In this research, experimentally, the nanoparticle of Mn-doped 63 was preparated by sol–gel method, charcterized and the magnetic 64 properties were measured. Moreover, the optical, electronic and 65 magnetic properties were studied by the first principle calculation 66 in order to study an effect of the Mn doping on the ferromagnetism 67 on ZnO. 68 2. Experimental details 69 2.1. Synthesis details 70 In this work, Zn 1x Mn x O(x = 0, 0.005, 0.01, 0.02 and 0.03) 71 powders were prepared using a polyethylene glycol (PEG) sol–gel 72 method. Zn(NO 3 ) 2 xH 2 O (99.999%, Sigma–Aldrich), Mn(NO 3 ) 2 xH 2 O 73 (99.99%, Aldrich), ethanol, and PEG (M w = 1000) were used as start- 74 ing raw materials. Firstly, 1.5 g of PEG was dissolved in ethanol 75 (30 mL) with constant stirring at room temperature until a trans- 76 parent solution was formed. Second, stoichiometric amounts of 77 Zn(NO 3 ) 2 xH 2 O and Mn(NO 3 ) 2 xH 2 O were dissolved in the solution 0167-9317/$ - see front matter Ó 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.mee.2013.01.061 ⇑ Corresponding author at: Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand. Tel.: +66 87 5149482; fax: +66 43 202374. E-mail address: [email protected](P. Moontragoon). Microelectronic Engineering xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee MEE 8806 No. of Pages 5, Model 5G 20 February 2013 Please cite this article in press as: P. Moontragoon et al., Microelectron. Eng. (2013), http://dx.doi.org/10.1016/j.mee.2013.01.061
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Microelectronic Engineering xxx (2013) xxx–xxx
MEE 8806 No. of Pages 5, Model 5G
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Contents lists available at SciVerse ScienceDirect
Microelectronic Engineering
journal homepage: www.elsevier .com/locate /mee
Mn-doped ZnO nanoparticles: Preparation, characterization, and calculationof electronic and magnetic properties
Pirot Moontragoon ⇑, Supree Pinitsoontorn, Prasit ThongbaiIntegrated Nanotechnology Research Center (INRC), Department of Physics, Khon Kaen University, Khon Kaen, 40002, ThailandNanotec-KKU Center of Excellence on Advanced Nanomaterials for Energy Production and Storage, Thailand
19202122232425
a r t i c l e i n f o
Article history:Available online xxxx
Keywords:Diluted magnetic semiconductorMn-doped ZnOSpintronics
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0167-9317/$ - see front matter � 2013 Published byhttp://dx.doi.org/10.1016/j.mee.2013.01.061
⇑ Corresponding author at: Department of Physics, FUniversity, Khon Kaen 40002, Thailand. Tel.: +66 87 5
Please cite this article in press as: P. Moontrago
a b s t r a c t
In this work, Zn1�xMnxO nanoparticles were prepared by PEG sol–gel method. Structure and morpholo-gies of Zn1�xMnxO nanoparticles were investigated by using transmission electron microscope. Magneticproperties were measured by using a vibrating sample magnetometer (VSM). In calculation, electronicstructure and magnetic properties for pure ZnO and Zn1�xMnxO have been investigated by means ofthe first principle calculations based on local density approximation (LDA) and LDA+U scheme, packagedin the ABINIT code. The calculation was performed using self-consistent projected augmented plane wave(PAW). The zinc oxide was modeled using 2 � 2 � 2 super-cell (totally containing 32 atoms) in ideal hex-agonal wurtzite structure. A 9 � 9 � 5 Monkhorst–Pack k–point mesh was used for the super cell calcu-lation and a plane wave cutoff energy of 16 Hartree was used to assure convergent results. The resultsindicate that ZnO has energy band-gap about 1.97 eV which is underestimated when compared to exper-iments. The magnetic dipole moments of the Zn1�xMnxO when the manganese contents (x) are 0.0000,0.0625, 0.1250 and 0.1875 equal 0.00lb, 3.83lb, 7.78lb and 10.37lb, respectively. The doped manganeseatoms seem to play an important role for the appearance of ferromagnetism.
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1. Introduction
Since the discovery of ferromagnetism in diluted magneticsemiconductors (DMSs), such as Mn doped GaAs, InAs or Ge, theyare continuously attracting research attention as promising spin-tronics semiconductors with prospective applications in semicon-ductor devices. A new technology which shows the potential touse the spin of electron instead of the charge of electron for read-ing, writing data and transferring the information to integrate withtraditional semiconductor technology. Therefore, this technologyneeds ferromagnetic materials at high temperature, especially atroom temperature. In the early effort toward spintronic technol-ogy, many researchers have been interested in the preparationand characterization of manganese doped III–V and II–VI materials,due to a proposed and measured Curie temperature above roomtemperature. In the recent years, however, the diluted magneticoxides, such as TiO2, CeO2 and SnO2 doped with various transitionmetals, such as Co, Fe, Ni and Mn, are immensely investigated, inboth theories and experiment, to predict magnetic properties ofthese oxides which are doped with various transition metals[1,2]. Among diluted magnetic oxide, Mn-doped ZnO materialsare considered as the most promising candidates because it is more
Elsevier B.V.
aculty of Science, Khon Kaen149482; fax: +66 43 202374.n).
on et al., Microelectron. Eng. (
easy to fabricate than other oxide materials, widely use in theoptoelectronic devices and indicates room temperature ferromag-netism. The Mn-doped ZnO compounds can be syntisised in severalforms, such as thin film, bulk and nanoparticles, and by severalmethods such as RF sputtering, pulsed laser deposition (PLD),chemical vapor deposition (CVD) and simple sol–gel method [3–7]. In this research, experimentally, the nanoparticle of Mn-dopedwas preparated by sol–gel method, charcterized and the magneticproperties were measured. Moreover, the optical, electronic andmagnetic properties were studied by the first principle calculationin order to study an effect of the Mn doping on the ferromagnetismon ZnO.
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2. Experimental details
2.1. Synthesis details
In this work, Zn1�xMnxO (x = 0, 0.005, 0.01, 0.02 and 0.03)powders were prepared using a polyethylene glycol (PEG) sol–gelmethod. Zn(NO3)2�xH2O (99.999%, Sigma–Aldrich), Mn(NO3)2�xH2O(99.99%, Aldrich), ethanol, and PEG (Mw = 1000) were used as start-ing raw materials. Firstly, 1.5 g of PEG was dissolved in ethanol(30 mL) with constant stirring at room temperature until a trans-parent solution was formed. Second, stoichiometric amounts ofZn(NO3)2�xH2O and Mn(NO3)2�xH2O were dissolved in the solution
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of PEG and ethanol with constant stirring at 150 �C until a viscousgel was formed. Viscous gel was dried at 350 �C for 30 min. To ob-tain Zn1�xMnxO powders, the resulting dried porous precursorswith various doping ions of Mn were ground into powder and cal-cined in air at 600 �C for 6 h.
2.2. Characterizations
The phase composition and morphologies of Zn1�xMnxO nano-composites were characterized by X-ray diffraction (XRD)(PW3040 Philips; Eindhoven, the Netherlands) and transmissionelectron microscopy (TEM) (FEI Tecnai G2, Eindhoven, theNetherlands), respectively. The magnetic properties of the calcinedZn1�xMnxO powders were examined at room temperature (293 K)using a vibrating sample magnetometer (VSM 7403, Lake Shore,USA).
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2θ (Degree)
Fig. 2. XRD patters of MnxZn1�xO when (a) x = 0.000, (b) x = 0.005, (c) x = 0.010,(d) x = 0.020 and (e) x = 0.030.
3. Computational details
Electronic and magnetic properties for Mn-doped zinc oxide(ZnO) have been investigated by first principle methods based onlocal density approximation (LDA) and LDA+U scheme, with cou-lomb interaction Ueff of Zn and Mn are 9.0 and 3.0 eV respectively,using the ABINIT code [8]. The calculation was performed using
Fig. 1. The crystal structures of Mn-doped zinc oxide (MnxZn(1�x)O) (a) x = 0.0000, (b)represents O atoms and light blue represents Mn atoms. (For interpretation of color in
Please cite this article in press as: P. Moontragoon et al., Microelectron. Eng. (
self-consistent pseudo-potential projected augmented plane wavewith LSDA+U formalism and the parametrization of Perdew andWang [9] to explore the possibility of ferromagnetism as observed
x = 0.0625, (c) x = 0.1250 and (d) x = 0.1875 when pink represents Zn atoms, redthis figure, the reader is referred to the web version of this article.)
Fig. 3. TEM images of MnxZn1�xO when (a) x = 0.000, (b) x = 0.005, (c) x = 0.010, (d) x = 0.020 and (e) x = 0.030.
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in recent experiments The Mn-doped zinc oxide (MnxZn(1�x)O)with Mn content x = 0.0000, 0.0625, 0.1250 and 0.1875 were mod-eled using a 2 � 2 � 2 supercell in the hexagonal wurtzite struc-ture (space group P63mc) with the lattice parameters of thesupercell, analysed from the result of the X-ray diffraction patternin the experimental part of this research (a = 6.494 Å andc = 10.410 Å, containing 32 atoms) without structural optimization,as shown in Fig. 1. A 9 � 9 � 5 Monkhorst–Pack k–point mesh was
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used for the zinc oxide super cell calculation. A projected aug-mented plane wave (PAW) with cutoff energy of 16 Hartree wasused to assure convergent results.
4. Results and discussion
Structure and phase formation of Zn1�xMnxO were investigatedby using XRD technique. The XRD patterns of the prepared
Fig. 4. The specific magnetization as a function of field measured at roomtemperature of MnxZn1�xO when x = 0.000, x = 0.005, x = 0.010, x = 0.020, andx = 0.030.
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Zn1�xMnxO were demonstrated in Fig. 2. All the detectable peakscan be indexed as the ZnO with hexagonal structure correspondingto the standard data JCPDS No. 36–1451. The Zn1�xMnxO samples
Fig. 5. The isosurface of difference between spin up electron density and spin down elec(c) x = 0.1250 and (d) x = 0.1875.
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consisted of a pure ZnO phase with no possible impurities. The val-ues of lattice parameters of Zn1�xMnxO samples were calculatedand found to be a = 3.247 and c = 5.205 Å, a = 3.243 andc = 5.188 Å, a = 3.243 and c = 5.190 Å, a = 3.247 and c = 5.202 Å,and a = 3.252 and c = 5.207 Å for x = 0.000, 0.005, 0.010, 0.020and 0.030, respectively. These values are comparable to the valuesreported in literature (a = 3.242 and c = 5.195 Å) [4] and JCPDS cardNo. 36–1451 (a = 3.249 and c = 5.206 Å).
The morphologies of Zn1�xMnxO nanopowders are shown inFig. 3. Obviously, Mn doping ions have a remarkable effect on theparticle size of Zn1�xMnxO samples. The particle size tends to de-crease with increasing Mn doping content. Particle size of pureZnO sample is in the range of 50–120 nm; while, the particle sizesof the Mn0.02Zn0.98O and Mn0.03Zn0.97O samples are in the range of20–50 nm. The decrease in particles size of the Zn1�xMnxO systemmay be due to the ability of Mn ions to inhibit the crystal growthrate of ZnO. Substitution of Mn ions into ZnO lattice can producesome defects. Therefore, variation in defect concentration cancause a change in the rate of crystal growth.
The magnetic properties of all Zn1�xMnxO powders were exam-ined at room temperature using a VSM technique. As shown inFig. 4, the linear relationship between the magnetization and ap-plied magnetic field can be observed. The linearity of the VSM re-sult indicates to the paramagnetic behavior because of their Curietemperature could lower than room temperature. The magnetiza-
tron density (spin up – spin down) of MnxZn1�xO when (a) x = 0.0000, (b) x = 0.0625,
Fig. 6. Partial density of states (PDOS) and total density of states (DOS) of pure zincoxide and Mn-doped ZnO.
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tions of the Zn1�xMnxO nanoparticles at applied magnetic field�5370 Oe were found to be 0.0321, 0.0403, 0.0413, 0.0435 and0.0337 emu/g for x = 0.000, 0.005, 0.010, 0.020 and 0.030, respec-tively. The magnetization of Zn1�xMnxO nanoparticles increaseswith increasing Mn doping concentration.
The magnetic properties of the Mn-doped zinc oxide are de-scribed as follows. According to the LSDA+U calculation, the mag-netisation of pure ZnO, Mn0.0625Zn0.9375O, Mn0.1250Zn0.8750O andMn0.1875Zn0.8125O have magnetic moments of 0.00lb, 3.83 lb,7.78 lb and 10.37 lb respectively. In the case of pure zinc oxide,this can be explained as the fact that the electrons in the zincatoms and oxygen atoms are pair electrons (spin up and spindown) in the 3d orbital and the 2p orbital, respectively, whereasthere are five unpair electrons in the 3d orbital of Mn atom. There-fore, the total net spin of pure zinc is zero, but not in Mn-dopedZnO. Whereas the appearance ferromagnetism in Mn-doped ZnOcan be described as superexchange theory which the exchangeinteraction happens only on the Mn and O side, not on Zn and Oside. Therefore, there are still four unpair electrons (spin up elec-trons or spin down electrons) located in the 3d orbital of Mn atoms,as shown in Fig. 5.
According to the density of states (DOS), shown in Fig. 6, calcu-lated by LSDA+U, it indicates that pure ZnO has energy band-gapabout 1.97 eV, which is in good agreement with the other calcula-tion. However, the energy band gap is still under-estimated whencompared with the experimental value (a direct wide-band gap of3.3 eV [10]) due to the local density approximation. There are also
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states occurring between the conduction band and the valenceband (intermediate band; IB) when doped with Manganese.
5. Conclusion
In conclusion, we have prepared Zn1�xMnxO nanoparticles byusing PEG sol–gel method. The XRD result revealed that the ZnOand Zn1�xMnxO samples are pure ZnO phase with hexagonal struc-ture. Nanoparticles of the Zn1�xMnxO samples were characterizedby TEM technique. It was found that particle size of the Zn1�xMnxOsamples decreased with increasing the Mn doping content. Elec-tronic structure and magnetic properties for manganese-dopedzinc oxide have been investigated by means of the first principlecalculations based on local spin density approximation+U(LSDA+U) scheme, packaged in the ABINIT code. The results indi-cate that zinc oxide, has energy gap 1.97 eV and the manganese-doped atoms play important role in magnetic behavior of ZnO.There are also intermediate band in ZnO when the Zn atoms weresubstituted by Mn metal ions which is not only change the bandgap but also change the transient property of the photon absorp-tion, enhancing photo-absorbed and photocatalytic activities un-der visible light which is the main part of the solar spectrum.Therefore, it could be applied to the proposed concept of anintermediate-band solar cell [11].
Acknowledgments
Funding for this work is provided by Integrated Nanotechnol-ogy Research Center (INRC), Khon Kaen University, Thailand, theNanotechnology Center (NANOTEC), NSTDA, Ministry of Scienceand Technology, Thailand, through its program of Center of Excel-lence Network.
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