- Email: [email protected]
Decomposition mechanism of indium oxide nanoparticles sandwiched between zinc oxide layers by energetic ions
Available online at www.sciencedirect.com
CERAMICS INTERNATIONAL
Ceramics International 42 (2016) 2846–2853 www.elsevier.com/locate/ceramint
Decomposition mechanism of indium oxide nanoparticles sandwiched between zinc oxide layers by energetic ions Subodh K. Gautama,n, Fouran Singha,n, S. Ojhaa, R.G. Singhb, V.V. Siva Kumara a Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India Department of Physics, Bhagini Nivedita College, Delhi University, Delhi 110043, India
b
Received 19 October 2015; received in revised form 4 November 2015; accepted 5 November 2015 Available online 12 November 2015
Abstract Decomposition of indium oxide nanoparticles (IONPs) sandwiched between zinc oxide (ZnO) thin films by energetic ions is reported. Multilayers thin films were deposited using RF magnetron sputtering at room temperature, consisting two thin indium oxide layers sandwiched between three ZnO layers. Films exhibit very high transparency in the visible region. A sharp near band edge absorption with exciton absorption peak in the film annealed at the highest temperature was also observed. The structural and optical properties reveal that the as-deposited films show the formation of IONPs around the interface, which further grow upon increasing in annealing temperature. However, irradiation induces the decomposition of IONPs for the possible formation of single phase indium doped ZnO (IZO). The mechanism of the decomposition of IONPs is understood by the creation of ion tracks in IO. The track radius (Re) of 5.9 nm is calculated in the framework of thermal spike model. Therefore, the IONPs with diameter r2Re decomposed or amorphized between the crystalline ZnO layers; while the IONPs with diameter 42Re show reduction in size by the electronic sputtering from the IONPs surface under the thermo-elastic effects. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Indium oxide nanoparticles (IONPs); Energetic ions; Thermal spike model; Thermo-elastic effects
1. Introduction In recent years, the exploration of Transparent Conducting Oxides (TCOs) is an active area of research due to their multifunctional uses for the development of various optoelectronic device applications; such as solar cells, flat panel displays, transparent electrodes, diodes, etc. [1–4]. The important properties of TCO materials like transparency and conductivity are heavily dependent on crystalline phase and lattice defects. The composition of thin multilayers or superlattices can even affects the thermal (Kaptiza) resistance of interface [5], which can be controlled by the thermal annealing in controlled environment or by energetic ion irradiation [6–9]. It may be noted that the energetic ion irradiation induced defects in similar oxides has been used for better understanding of the n
Corresponding authors. E-mail addresses: [email protected] (S.K. Gautam), [email protected] (F. Singh). http://dx.doi.org/10.1016/j.ceramint.2015.11.020 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
evolution of Raman phonon modes and even semiconductor to metal transition as reported in our previous works [10–13]. Thus, the modifications in multilayer systems are liable to develop nanocomposite materials with superior properties. The most of the nanocomposite films show the characteristic of formation of metal oxide phases and metallic clusters by the treatment of thermal annealing, which affect the physical properties of the system. In such cases, the main issue is to dissolve these secondary metal or metal oxide nanoparticles (NPs) completely in the host system and to substitute them as metal cations at the proper metal site, as required for the development of spintronic devices and/or to enhance the conductivity of the host metal oxides. Generally, the decomposition of such NPs is difficult to achieve by thermal annealing [14]. However, energetic ion irradiations have proven to be as an unique tool to dissolve the NPs inside the host matrices to develop the single phase material [9]. Role of energetic ion irradiation in various undoped, doped, bilayer and/or multilayer thin system has been reported to
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
modify or control the structural, optical, and electrical properties by depositing large electronic energy via inelastic collisions [12,13,15–17]. The deposited energy is confined to a nano-cylinder along the ion trajectory. These high densities of electronic excitation in target materials are liable to perturb the atomic structure and induced various modifications such as damage creation at high electronic excitation [18–21] and track formation/sputtering [22–24]. Energetic ions can also enable mixing of bilayer or multilayer thin films around the interface by the inter-diffusion of elements across at the interface/s [25]. It is reported that the mixing of metal–semiconductor and metal–metal multilayer system increases with the increase in irradiation fluence and electronic energy loss value [26,27]. The mixing of ZnO/SiO2 at the interface has also been reported due to inter-diffusion during transient melt phase [28]. So, the energetic ions have been proven to be as an effective tool to the decomposition of NPs for the development of stable single phase materials. Therefore, the present study reports the experimental results on the effect of energetic ions on RF magnetron sputtering deposited multi-layer metal-oxide (ZnO/In2O3/ZnO/In2O3/ ZnO) thin films which induces interface mixing through the decomposition of indium oxide (IO) NPs inside the ZnO thin films. The size dependence of the decomposition of IONPs with respect to the track size and their effect on the structural and optical properties are investigated under the framework of thermal spike and thermo-elastic models [20,21]. 2. Experimental details Multi-layers thin films of thickness around 350 nm consists of two thin indium oxide layers of thickness around 20 nm sandwiched between three zinc oxide layers (ZnO/In2O3/ZnO/ In2O3/ZnO) of thickness around 100 nm were deposited using RF magnetron sputtering at room temperature. The substrates were cleaned in acetone then rinsed by hydrofluoric acid and deionized water followed by drying in nitrogen gas before loading into the deposition chamber. ZnO target with 99.99% purity and a commercially available metallic indium target of 50 mm diameter from Semi Wafer Inc., Taiwan were used as sputtering targets. The chamber was evacuated down to a base pressure of 5.5 10 5 mbar before introducing the gas into the chamber. Both the ZnO and In2O3 layers were deposited in the presence of oxygen and argon gas environment. The mixture of Arþ O2 gas was kept at a constant flow of standard cubic centimeter per minute (sccm) or ratio (70%þ 30%), respectively using the MKS mass flow meters. During the deposition, base pressure was maintained at 50 mTorr, RF power was fixed at 150 W, substrates were at room temperature and the distance between target to substrate was kept at 5.5 cm. Post annealing of the samples were carried out using Nabertherm (GERO) tubular furnace with alumina tube at different temperature ranging from 500 1C to 850 1C in oxygen ambient for time 1 h for improving the stoichiometry and crystalline nature of the films. The oxygen gas flow was maintained as one bubble per second and the ramp rate of temperature rise was kept at 3 1C/min. As-deposited, 500 1C
2847
and 850 1C annealed films were irradiated by 120 MeV Ag ions for fluence of 3 1013 ions/cm2 using the 15 UD Pelletron Accelerator available at Inter University Accelerator Centre (IUAC), New Delhi. The structure of the films is investigated by Grazing Incidence X-ray Diffraction (GIXRD) measurements, carried out using Bruker D8 advanced diffractometer equipped with Copper anode with scan speed of 0.51 per minute and with step size of 0.021. The elemental composition, thickness and the interfacial diffusion behavior of indium atoms in ZnO layers of as-deposited, annealed and irradiated samples were studied by Rutherford Backscattering Spectrometry (RBS) measurement using 2 MeV He þ ions at scattering angle of 1701. The samples were tilted by 71 to avoid the channeling of He þ ions during the backscattering measurement and the analysis of the RBS data is performed using the RUMP simulation code [29]. Field Emission Scanning Electron Microscopy (FE-SEM) along with Energy Dispersive X-ray (EDX) analysis was also carried out using MIRA\\TESCAN FE-SEM system. The UV–visible studies on films were carried out using Hitachi UV3300 double beam spectrophotometer. All the measurements were performed at room temperature (RT) using facilities at IUAC, New Delhi. 3. Results GIXRD patterns of as-deposited and annealed multilayer thin films are shown in Fig. 1(a) and the schematic of the same is shown in Fig. 1(b). The diffraction peaks corresponding to (100), (002) and (101) planes in GI-XRD patterns indicate that the films posses polycrystalline nature with hexagonal wurtzite crystal structure of ZnO [JCPDS 79-0206]. The intensity of (002) diffraction peak is relatively more intense as compared to (100) peak, indicates a texturing along the c-axis perpendicular to the substrate surface. A broad peak observed at 2θ¼ 30.4981 is assigned to the (222) diffraction peak of IONPs [JCPDS 741990]. The (222) diffraction peak of IONPs and (002) diffraction peak of ZnO get pronounced with increase in annealing temperature. The average crystallite size of both ZnO and IONPs are calculated by using the Scherrer's formula [30,31]. D¼
0:9λ β cos θ
where D is the average size, λ is the wavelength (1.5404 Å) of Cu Kα line, θ is the Bragg angle and β is full width at half maximum (FWHM) in radians of (002) and (222) diffraction peaks of ZnO and IONPS, respectively. The calculated average size of ZnO and IONPs are cited in Table 1. It is clearly evident from this table that the average size is growing with increase in annealing temperature. The diffraction peak position of ZnO corresponding to (002) and (101) are shifting towards the higher 2θ value and attain a value equivalent to the stress free ZnO at 500 1C and get more pronounced when the films were annealed at 850 1C. The annealing at 850 1C, induces a shift towards higher 2θ value with large increase in the size. Similar results are observed for (222) peak of IONPs, which also shifts to higher 2θ value of 30.691 from their bulk position (30.571). The observation reveals that as-deposited films may not be highly
2848
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
Fig. 1. (a) GIXRD patterns of as deposited, annealed films, (b) schematic diagram of multilayer arrangement, and (c) growth with annealing treatment.
Table 1 Average size estimated using Scherer’s formula for the pristine and irradiated films. Annealing temperature
As-deposited 500 1C 850 1C
ZnO (002) peak (bulk peak at 34.420)
In2O3 (222) peak (bulk peak at 30.5770)
Pristine
After Irradiation
Pristine
After Irradiation
2θ (deg.)
Av. size (nm)
2θ (deg.)
Av. size (nm)
2θ (deg.)
Av. size (nm)
2θ (deg.)
Av. size (nm)
34.26 34.43 34.51
8.5 11.1 23.0
34.27 34.42 34.43
14.3 12.7 20.8
30.50 30.58 30.69
6.5 8.5 31.3
– – 30.66
– – 15.3
stoichiometric for their respective phases of ZnO and IO. The stoichiometry of ZnO and IO phase of the films gradually improves with increasing annealing temperature. It means that the sub-stoichiometric IONPs transforms to stoichiometric phase by the presence of oxygen at interfaces and remaining Indium atoms start to diffuse inside the ZnO layers. It may ascribe to the faster migration velocity of Indium atoms as compared to Zn and O atoms in the ZnO lattice, due to the weak binding energy (or bond enthalpy) of In–O bond than Zn–O bond [31]. Moreover, it is also known that the value of diffusion coefficient (D0) for Indium and Zinc in ZnO lattice is 2.5 102 cm2 s 1and 1.7 10 3 cm2 s 1, respectively. The value of activations energy for In and Zn in ZnO is found to be 3.16 and 2.66 eV, respectively. Thus, it is better to remark that the diffusion of Indium atoms to the substitutional sites of Zn lattice leads to the formation of single phase IZO, besides the formation of IO phase. The diffusion of Indium atoms is further confirmed by the RBS study (which will be discussed in next section), reveals
that the percentage of In atoms increases in the top layer of ZnO for the films annealed at 850 1C. It may also be noted that a very large IONPs are formed at 850 1C, as shown schematically in Fig. 1(c). The shifting of (002) peak of ZnO to higher theta value can be ascribed due to the incorporation of Indium atom on substitutional sites of ZnO lattice and formation of IONPs in the ZnO lattice on defects sites (since, it is well known that defect sites act as good nucleation centers). The observed peak shifting to higher theta value and correspondingly decrease in lattice spacing reveals a compressive stress in the films. It is known that the ionic radii of In3 þ (94 pm) is about 7% larger than the ionic radii of Zn2 þ (88 pm), which is not favorable. However, the partial substitution at high temperature is expected to induced compressive stress, as experimentally observed. Similarly, the observed shifting in (222) peak of IONPs might be due to the compressive stress put by the ZnO lattice. Fig. 2(a) and (b) shows the cross section FE-SEM and EDX spectra to study the morphology, thickness, film quality and
IZO-An850
(110) ZnO
(440) In O
IZO-An850-IRR
(431) In O (102) ZnO
(400) In O
3 2
(222) In O
(100) ZnO
Intensity (a. u.)
2849
(101) ZnO
(002) ZnO
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
IZO-An500-IRR IZO-An500 IZO-AD-IRR IZO-AD
25
30
35
40
45
50
55
60
2θ (Degree)
Fig. 3. GIXRD pattern of pristine and films irradiated using 120 MeV Ag ions.
Fig. 2. FESEM images in planer and cross section along EDX spectra for elemental analysis.
compositional analysis. The cross section FE-SEM shows that total thickness of the film is 390 nm. It can be remarked that films are free of voids etc and but the different layers are not well resolved. In such a situation a high quality cross sectional scanning transmission electron microscopy (STEM) images would be better. Nevertheless, IO is very sensitive for the damage by high energy electron beam; hence any such investigations are not even reported in literature to best of our knowledge. However, the basic objective of manuscript will not change much, as the GIXRD and RBS studies are able to clearly show the diffusion and substitution of Indium atom in the ZnO lattice. It would be better to note that the RBS is well capable for the concentration and diffusion depth of indium atoms along the cross sectioned films, as reported in the present manuscript. Moreover, the diffusion of Indium metal is also confirmed by EDX study, as the spot for EDX measurements were taken much far away from the interface. XRD pattern of the pristine (as-deposited, 500 1C and 850 1C annealed) and irradiated films for 3 1013 ions/cm2 fluence are shown in Fig. 3. The 2θ position and the calculated crystallite size in the pristine and irradiated films are also cited in Table 1. As-deposited film also shows that the size of ZnO crystallites increases from 8 nm to 14.3 nm, while the films annealed at 500 1C and 850 1C do not exhibit any significant change in ZnO crystallite size after irradiation. The (222) diffraction peak of IONPs disappears for fluence of
3 1013 ions/cm2 in as-deposited and 500 1C annealed irradiated films. However, 850 1C annealed film shows that the average size of IONPs decreases from 30.2 nm to 15.3 nm and exhibits a shift towards lower diffraction angle in (002) and (101) peak upon irradiation. RBS measurements on multilayer films were carried out to determine the thickness, elemental composition and diffusion of indium atoms around the interface of films. Experimental and simulated spectra along with simulated depth profiles of pristine (as-deposited, and annealed at 850 1C) and irradiated films are shown in Fig. 4(a) and (b). Simulated results confirm that the overall measured thickness (Δt) of deposited film is around 400 nm, which is in agreement with cross sectional SEM results. The simulated spectra of as-deposited films shows that two thin of IO layers of each about 25 nm are sandwiched between the three ZnO layers and having diffused interface with ZnO layers on either side of the IO layers. It also shows 15 nm thin IO layer with 40 nm diffused interface with ZnO layers, where simulation of diffusion is taken as linear gradient concentration of indium atomic fraction from 30 at.% to nil in ZnO layers on either sides of the IO layers. The thickness of IO layer increases upto 26 nm and the length of the diffused interface layer increases with increasing in annealing temperature to 850 1C. Around 1% IO is also observed on the top ZnO layer of 850 1C annealed film. There is a shift in Indium edge from channel no. 1620 to channel no. 1700 (proper position of indium edge) is observed after annealing of as-deposited film to 850 1C, which can be ascribed to diffusion of indium atoms onto the top layer of ZnO. The irradiation of as-deposited film shows the ion beam mixing at the interfaces by the diffusion of Indium atoms in ZnO layers as the fraction of indium atoms increases from 28 to 40% in ZnO layer around interface at same 45 nm length after dissolving complete 15 nm IO layers. However, the irradiation of 850 1C annealed film shows decrement of IO layers down to 15 nm with improvement in the diffusion of atomic indium around the 55 nm on either side of the IO layers. In other words, the RBS results show the ion beam mixing around the interfaces by inter-diffusion of Indium followed by the dissolution or decomposition of IONPs [26].
2850
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
Energy (MeV)
Energy (MeV) 0.5
0.5
1.5
O Si
Normalized Yield
In
Zn Zn
60
In
Zn Zn 40
O Si 20
20
0
0 500
1000
500
1500
1000
1500
Channel
Channel 1.1
1.1 O Zn In Si
0.9
0.8
In2O3
0.7 0.6
Si Substrate
0.5 Zn/O
Zn/O
0.4
O Zn In Si
1.0 0.9
In2O3
0.8
IZO-AD
Zn/O
0.3
IZO-AD-IRR
0.7 0.6 Si Substrate
0.5 Zn/O
0.4
Zn/O
Zn/O
0.3 0.2 0.1
0.0
In
0.1
In
In
In
0.2
Concentration
1.0
Concentration
1.5
IZO-AD-IRR Simulated
80
60
40
1.0
Zn+In
Zn+In
IZO-AD Simulated
80
Normalized Yield
1.0
0.0 0
50
100 150 200 250 300 350 400 450 500
0
50
100 150 200 250 300 350 400 450 500
Thickness (nm)
Thickness (nm)
Energy (MeV) 0.5
Energy (MeV)
1.0
1.5
0.5
80
Zn+In
IZO-An850 Simulated
1.0
1.5
Zn+In
IZO-An850-IRR Simulated
80
40
Zn
20
Zn In
Normalized Yield
Normalized Yield
60
O
60
Zn
O
20
Si
Si
0
0 500
1000
500
1500
1000
1500
Channel
Channel 1.0
1.0
0.5
SiO Zn/O
0.4
2
Zn/O
Zn/O
Substrate
0.3 0.2
Concentration
0.7
0.6
IZO-An850-IRR In2O3
0.8 In2O3
0.7
O Zn In Si
0.9
In2O3
0.8
IZO-An850 In2O3
O Zn In Si
0.9
Concentration
In
Zn
40
0.6 0.5 0.4
SiO
2
Zn/O
Zn/O
Substrate
Zn/O
0.3 0.2 0.1
0.0
In
In
Zn
In
In
0.1
Zn
0.0 0
100
200
300
Thickness (nm)
400
500
0
100
200
300
400
500
Thickness (nm)
Fig. 4. Experimental and RUMP simulated RBS spectra of (a) as-deposited and irradiated and (b) 850 1C annealed and irradiated films.
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
IZO-Ad IZO-Ad-IRR IZO-An850 IZO-An850-IRR
80 60 40
(αh ν) (cm eV)
Transmittance (%)
100
20 0 300
400
500
600
700
800
Wavelength (nm)
Fig. 5. Transmittance spectra of as-deposited, annealed and irradiated films. Inset shows the Tauc's plot for estimating the band gap.
Optical absorption and transmission spectra of multilayer IZO films were also measured in the wavelength range 200– 850 nm and are shown in Fig. 5. It shows that there is almost no optical absorption in the visible region. The annealed sample shows sharpening of near band edge (NBE) absorption and improvement in exciton absorption peak by increasing annealing temperature. A sharp and strong exciton absorption peak is observed in the films annealed at 850 1C. The observation of exciton peak and the sharpening of NBE absorption confirm the improvement in the quality of ZnO crystallites. Moreover, the irradiation for a fluence of 3 1013 ions/cm2 unable to induce any significant change in NBE absorption but shows some deterioration in the peak corresponds to exciton absorption. It is known that a metal rich film usually exhibited less transparency. Hence, the decrease in optical transmittance in doped samples might be due to the increase in metal to oxygen ratio, (Zn þ In)/O. The large decrease in transmittance in the UV region may be due to the free-carrier absorption. This could be related to the oxygen and metal charge transfer or due to electron transfer to the conduction band [8]. The absorption edge of the IZO thin films corresponds to electron transitions from valence band to conduction band and this edge can be used to calculate the optical band gap of the IZO thin films. The optical band gap was determined by applying the Tauc's relationship [32]: n αhυ ¼ C hυ Eg where, C is a constant, hυ is the photon energy and Eg is the optical band gap. The value of n is equal to 2 and ½ for indirect and direct bandgap semiconductors, respectively. The value of n is taken as ½, as ZnO is a direct bandgap semiconductor. An extrapolation of the linear region of a plot of (αhυ)2 on the y-axis versus photon energy (hυ) on the x-axis gives the value of the optical band gap (Eg) for annealed and irradiated films as shown as inset in Fig. 5. The value of αhυ should be zero for determining the bandgap and thus the value of constant C will not influence the bandgap value determined
2851
using the above equation. It is better to mention that Tauc's relationship may not be suitable for multi-phase materials. However, this can be used to monitor the relative variation in bandgap for such multi-phase materials. The estimated bandgap is around 3.32 eV and 3.25 eV for the as-deposited and annealed films, respectively. This small change in bandgap can be attributed the change in density and stoichiometry of the film. The transmission spectra of films show the interference fringe with high transmittance of 70–85% in whole visible spectral region. The observation of interference fringes in the transmittance curves also reveals that the film surface is highly reflecting and free from scattering or absorption losses in the films. However, the transmission spectra of the annealed and irradiated films show that the amplitude of the fringe pattern became flatter and the average transmittance is reduced with the increasing in the annealing temperature or irradiation fluence. This can be attributed to the diffusion of indium in ZnO lattice as already confirmed by RBS and EDX measurements. 4. Discussion The decomposition processes of IONPs between the ZnO layers by energetic ion irradiation can be understood by fundamental ion solid interaction mechanism. Energetic ion losses or transfer their energy to target by two processes: (a) nuclear energy loss by elastic collisions with target atoms leads to lattice displacement, dominant in the low energy regime, and (b) electronic energy loss by inelastic collision process leads to electronic excitation and ionization in target atoms, dominant in high energy regime. In present study of 120 MeV Ag ions irradiation on ZnO, the electronic energy loss (Se, energy transferred to the target electrons by incident ions) is 21.68 keV/nm, where as nuclear energy loss (Sn) is 0.105 keV/nm and in IO, Se ¼ 22.9 KeV/nm, Sn ¼ 0.118 KeV/ nm as determined by SRIM2008 code [33]. The range of 120 MeV Ag ions in IZO film (thickness 400 nm) is more than 10 μm, so the Se remain almost constant throughout the film thickness and ions penetrate deep inside the substrate and finally get implanted inside substrate. The Se is dominating effect to induce modification in the films, as it is order of magnitude higher than Sn. However, the effects of Sn cannot be completely ignored, but difficult to evaluate quantitatively for this kind of modifications. In this dominant regime of Se, the projectile ion energy is transferred to the target electronic subsystem in a time less than 10 16 s, and gives rise to highly non-equilibrium thermal condition. The energy of electronic sub system is dissipated to atomic subsystem by electron– phonon (e-ph) coupling within a time of about 10 14 and 10 12 s. The relaxation or transfer of excess energy to lattice gave rise to increase in the transient temperature limited to a localized zone of few nanometers (known as ion track) along the ion path. The track formation and the size of latent track depend on the property of target material and the Se deposited by ions. If Se Z Seth, where Seth is the threshold electronic energy loss to form a cylindrical region of track of few nm. The Seth value of
2852
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
the material depends on many parameters such as density ρ, average specific heat c, initial width of the thermal spike a0, and electron–phonon coupling efficiency g, and can be determined using following equation [34]: Seth ¼
πρca ð0ÞT 0 g 2
ð1Þ
where T0 ¼ Tm-Tirr, temperature of thermal spike to reach the melting point and a0 is the band gap (Eg) dependent parameter and for insulators it is almost constant. The value of a(0) is define by an expression; a(0) ¼ b þ c(Eg) 1/2, where b and c are the approximation constant for ion induced thermal spike width and Eg is the bandgap of semiconductor. The value of a (0) is determined using Eg ¼ 3.7 eV for IO from the plot of (Eg)-1/2 versus a(0) and the value of a(0) found to be 6.2 nm [35]. The Seth value for IO and ZnO are calculated using above equation by substituting their suitable thermodynamic values. Indium oxide has material density (ρ¼ 7.31 g cm 3), melting temperature (Tm ¼ 2183 K), average specific heat (c¼ 0.3550 J g 1 K 1) at the irradiation temperature (296 K) [36], and electron–phonon coupling efficiency (g), which depends on the ion velocity is taken to be 0.4 [35]. Similarly for ZnO the values are taken as ρ ¼ 7.31 g cm 3, Tm ¼ 2183 K, c ¼ 0.3550 Jg 1 k 1 at Tirr (296 K) [37], and g value is 0.4 similar as in IO. Therefore the estimated Seth values are found to be 9.24 keV /nm and 10.25 keV/nm for IO and ZnO, respectively. The track size in IO and ZnO layers is calculated by using the following expression [34]: R2e ¼ a2 ð0ÞlnðSe =Seth Þ ¼ ½ða2 ð0Þ=2:7ðSe =Seth Þ
1 r Se =Seth r 2:7
ð2Þ
Se =Seth 42:7
ð3Þ
For IO, the calculated SSethe ratio is 2.47, which is less than 2.7, thus Eq. (2) is used and the track radius (Re) is found as 5.9 nm. Similarly, in term of ZnO, SSethe ratio is 2.11, less than the 2.7 and calculated track radius using Eq. (2) is 5.3 nm. According to calculated values, the estimate Seth of ZnO is slightly higher than in IO and the track radius is found to be almost similar to the value in IO. However, in our previous findings, it is clearly reported that ZnO structure remains stable even at very high irradiation dose 4 1013 ions/cm2 with high Se value 20 keV/nm [10,11]. Therefore, the latent track formation is only possible in IO, not in ZnO layers of film. Thus, the complete process of track formation and decomposition of In2O3 NPs can be well explained by Thermal spike model [20,38–40]. According to this model the IONPs with diameter r 2 Re goes to molten state and lead to the formation of solid solution of indium. It means, the IONPs having size smaller than the track diameter completely decomposed. Therefore, the IONPs in as-deposited and 500 1C annealed films completely dissolve and diffuse in the ZnO lattice since the size of IONPs is smaller than track diameter [41–43]. However, the diameter of IONPs in the film annealed at 850 1C is larger than the track diameter, which may not be completely decomposed, but decreases in size due to the electronic sputtering from their surface by and thermo-elastic
effects as reported to for such nanocomposites [21] and lead to the diffusion of Indium in the ZnO lattice [44]. 5. Conclusions The development of high quality multilayers with very high transparency in the visible region using RF sputtering is reported. The structural and compositional studies confirm the decomposition of indium oxide nanoparticles by energetic ion irradiation, which is not possible by conventional thermal annealing. The track radius (Re) of 5.9 nm is calculated in the framework of thermal spike model. Thus, the IONPs with diameterr2Re decomposed or amorphized between the crystalline layers of ZnO; while the IONPs with diameter42Re show reduction in size by the electronic sputtering from the IONPs surface under the thermo-elastic effects and is used for understanding the decomposition of IONPs followed by the diffusion of indium in the lattice. Therefore, these preliminary experiments show that energetic ion irradiation could be useful for the formation of doped single phase metal oxide film with high transparency for their possible optoelectronic applications. Acknowledgments Authors are grateful to the Director (IUAC), and Dr. D. K. Avasthi for their encouragement and moral support. Authors are also thankful to Dr. S.A. Khan for experimental support in SEM investigations, Pelletron group of IUAC for providing the stable ion beam during irradiation experiment and Dr. S. Nath (IUAC) for improving the English of the manuscript. SKG acknowledged CSIR, India for providing Senior Research Fellowship [09/760(0024)/2011-EMR-I]. DST, Govt. of India is gratefully acknowledged for providing FE-SEM through nano-mission project and for granting Science and Engineering Research Board (SERB) project (SB/EMEQ-122/2013). References [1] D.S. Ginley, C. Bright, Transparent conducting oxides, MRS Bull. 25 (2000) 15–18, http://dx.doi.org/10.1557/mrs2000.256. [2] M. Thambidurai, J.Y. Kim, C. Kang, N. Muthukumarasamy, H.-J. Song, J. Song, et al., Enhanced photovoltaic performance of inverted organic solar cells with In-doped ZnO as an electron extraction layer, Renew. Energy 66 (2014) 433–442, http://dx.doi.org/10.1016/j.renene.2013.12.031. [3] G.C. Park, S.M. Hwang, S.M. Lee, J.H. Choi, K.M. Song, H.Y. Kim, et al., Hydrothermally grown In-doped ZnO nanorods on p-GaN films for color-tunable heterojunction light-emitting-diodes, Sci. Rep. 5 (2015) 10410, http://dx.doi.org/10.1038/srep10410. [4] V.K. Jain, P. Kumar, D. Bhandari, Y.K. Vijay, Growth and characterization of transparent conducting nanostructured zinc indium oxide thin films, Thin Solid Films 519 (2010) 1082–1086, http://dx.doi.org/10.1016/j.tsf.2010.08.048. [5] X. Liang, M. Baram, D.R. Clarke, Thermal (Kapitza) resistance of interfaces in compositional dependent ZnO-In2O3 superlattices, Appl. Phys. Lett. 102 (2013) 223903, http://dx.doi.org/10.1063/1.4809784. [6] C. Huang, M. Wang, Z. Deng, Y. Cao, Q. Liu, Z. Huang, et al., Effects of hydrogen annealing on the structural, optical and electrical properties of indium-doped zinc oxide films, J. Mater. Sci. Mater. Electron. 21 (2010) 1221–1227, http://dx.doi.org/10.1007/s10854-009-0050-x. [7] P.M.R. Kumar, C.S. Kartha, K.P. Vijayakumar, Doping of spray-pyrolyzed ZnO thin films through direct diffusion of indium: Structural optical and
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853 electrical studies, J. Appl. Phys. 98 (2005) 1–7, http://dx.doi.org/10.1063/1.1985967. [8] Y. Huang, D. Li, J. Feng, G. Li, Q. Zhang, Transparent conductive tungsten-doped tin oxide thin films synthesized by sol–gel technique on quartz glass substrates, J. Sol–Gel Sci. Technol. 54 (2010) 276–281, http://dx.doi.org/10.1007/s10971-010-2182-0. [9] R. Kumar, F. Singh, B. Angadi, J.-W. Choi, W.-K. Choi, K. Jeong, et al., Single phase formation of Co-implanted ZnO thin films by swift heavy ion irradiation: optical studies, J. Appl. Phys. 100 (2006) 113708, http://dx.doi.org/10.1063/1.2399893. [10] F. Singh, R.G. Singh, V. Kumar, S.A. Khan, J.C. Pivin, Softening of phonons by lattice defects and structural strain in heavy ion irradiated nanocrystalline zinc oxide films, J. Appl. Phys. 110 (2011) 083520, http://dx.doi.org/10.1063/1.3651638. [11] F. Singh, P.K. Kulriya, J.C. Pivin, Origin of swift heavy ion induced stress in textured ZnO thin films: an in situ X-ray diffraction study, Solid State Commun. 150 (2010) 1751–1754, http://dx.doi.org/10.1016/j.ssc.2010.07.026. [12] S.K. Gautam, F. Singh, I. Sulania, R.G. Singh, P.K. Kulriya, E. Pippel, MicroRaman study on the softening and stiffening of phonons in rutile titanium dioxide film: competing effects of structural defects, crystallite size, and lattice strain, J. Appl. Phys. 115 (2014) 143504, http://dx.doi.org/10.1063/1.4868079. [13] F. Singh, B. Chaudhary, V. Kumar, R.G. Singh, S. Kumar, A. Kapoor, Disorder induced semiconductor to metal transition and modifications of grain boundaries in nanocrystalline zinc oxide thin film, J. Appl. Phys. 112 (2012) 073101, http://dx.doi.org/10.1063/1.4755795. [14] N. Tripathi, S. Rath, V. Ganesan, R.J. Choudhary, Growth dynamics of pulsed laser deposited indium oxide thin films: a substrate dependent study, Appl. Surf. Sci. 256 (2010) 7091–7095, http://dx.doi.org/10.1016/j.apsusc.2010.05.033. [15] A.M. Stoneham, N. Itoh, Materials modification by electronic excitation, Appl. Surf. Sci. 168 (2000) 186–193, http://dx.doi.org/10.1016/S0169 -4332(00)00587-0. [16] C.P. Race, D.R. Mason, M.W. Finnis, W.M.C. Foulkes, A.P. Horsfield, A.P. Sutton, The treatment of electronic excitations in atomistic models of radiation damage in metals, Rep. Prog. Phys. 73 (2010) 116501, http://dx.doi.org/10.1088/0034-4885/73/11/116501. [17] S.K. Gautam, R.G. Singh, V.V. Siva Kumar, F. Singh, Giant enhancement of the n-type conductivity in single phase p-type ZnO:N thin films by intentionally created defect clusters and pairs, Solid State Commun. 218 (2015) 20–24, http://dx.doi.org/10.1016/j.ssc.2015.05.011. [18] C. Dufour, Z.G. Wang, E. Paumier, M. Toulemonde, Transient thermal process induced by swift heavy ions: Defect annealing and defect creation in Fe and Ni, Bull. Mater. Sci. 22 (1999) 671–677. [19] A. Meftah, F. Brisard, J.M. Costantini, M. Hage-Ali, J.P. Stoquert, F. Studer, et al., Swift heavy ions in magnetic insulators: a damagecross-section velocity effect, Phys. Rev. B 48 (1993) 920–925, http://dx.doi.org/10.1103/PhysRevB.48.920. [20] M. Toulemonde, C. Dufour, A. Meftah, E. Paumier, Transient thermal processes in heavy ion irradiation of crystalline inorganic insulators, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 166 (2000) 903–912, http://dx.doi.org/10.1016/S0168-583X(99)00799-5. [21] F. Singh, J.P. Stoquert, J.C. Pivin, Study of classical thermo-mechanical equations in ultrafast thermo-elastic domain: electronic sputtering from metal–dielectric nanocomposites, J. Phys. D Appl. Phys. 46 (2013) 325305, http://dx.doi.org/10.1088/0022-3727/46/32/325305. [22] H. Dammak, D. Lesueur, A. Dunlop, P. Legrand, J. Morillo, Phenomenological model of damage creation by high electronic excitations in pure metals, Radiat. Eff. Defects Solids 126 (1993) 111–114, http://dx.doi.org/10.1080/10420159308219689. [23] P. Kluth, C.S. Schnohr, O.H. Pakarinen, F. Djurabekova, D.J. Sprouster, R. Giulian, et al., Fine structure in swift heavy ion tracks in amorphous SiO2, Phys. Rev. Lett. 101 (2008) 1–4, http://dx.doi.org/10.1103/ PhysRevLett.101.175503. [24] M. Toulemonde, W. Assmann, C. Trautmann, F. Grüner, Jetlike component in sputtering of LiF induced by swift heavy ions, Phys. Rev. Lett. 88 (2002) 057602, http://dx.doi.org/10.1103/PhysRevLett.88.057602. [25] S. Bagchi, F. Singh, D.K. Avasthi, N.P. Lalla, Thickness dependent effect of swift heavy ion irradiation in W/Ni superlattice multilayers, J. Phys. D Appl. Phys. 42 (2009) 145414, http://dx.doi.org/10.1088/0022-3727/42/14/145414.
2853
[26] S. Kumar, R.S. Chauhan, D.C. Agarwal, M. Kumar, A. Tripathi, W. Bolse, et al., Swift heavy ions induced mixing in metal/semiconductor system, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 266 (2008) 1759–1763, http://dx.doi.org/10.1016/j.nimb.2008.01.068. [27] B. Schattat, W. Bolse, Fast heavy ion induced interface mixing in thin-film systems, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 225 (2004) 105–110, http://dx.doi.org/10.1016/j.nimb.2004.04.183. [28] S. Kraft, B. Schattat, W. Bolse, S. Klaumünzer, F. Harbsmeier, A. Kulinska, et al., Ion beam mixing of ZnO/SiO[sub 2] and Sb/Ni/Si interfaces under swift heavy ion irradiation, J. Appl. Phys. 91 (2002) 1129, http://dx.doi.org/10.1063/1.1425439. [29] L.R. Doolittle, A semiautomatic algorithm for rutherford backscattering analysis, Nucl. Instruments Methods Phys. Res. B Beam Interact. Mater. Atoms 15 (1986) 227–231, http://dx.doi.org/10.1016/0168-583X(86)90291-0. [30] A.L. Patterson, The Scherrer formula for I-Ray particle size determination, Phys. Rev. 56 (1939) 978–982, http://dx.doi.org/10.1103/PhysRev.56.978. [31] B.D. Cullity, in: Elements of X-ray Diffraction, 2nd ed., AddisonWesley Publishing Company Inc., US, 1978. [32] J. Tauc, R. Grigorov, a Vancu, Optical properties and electronic structure of amorphous germanium, Phys. Status Solidi 15 (1966) 627–637, http://dx.doi.org/10.1002/pssb.19660150224. [33] J.F. Ziegler, M.D. Ziegler, J.P. Biersack, SRIM – the stopping and range of ions in matter (2010), Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 268 (2010) 1818–1823, http://dx.doi.org/10.1016/j.nimb.2010.02.091. [34] G. Szenes, General features of latent track formation in magnetic insulators irradiated with swift heavy ions, Phys. Rev. B 51 (1995) 8026–8029, http://dx.doi.org/10.1103/PhysRevB.51.8026. [35] G. Szenes, Comparison of two thermal spike models for ion-solid interaction, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 269 (2011) 174–179, http://dx.doi.org/10.1016/j.nimb.2010.11.009. [36] E.H.P. Cordfunke, E.F. Westrum, The heat capacity and derived thermophysical properties of In2O3 from 0 to 1000 K, J. Phys. Chem. Solids 53 (1992) 361–365, http://dx.doi.org/10.1016/0022-3697(92)90169-E. [37] A. Seko, F. Oba, A. Kuwabara, I. Tanaka, Pressure-induced phase transition in ZnO and ZnO–MgO pseudobinary system: a firstprinciples lattice dynamics study, Phys. Rev. B Condens. Matter Mater. Phys. 72 (2005) 1–10, http://dx.doi.org/10.1103/PhysRevB.72.024107. [38] R.L. Fleischer, P.B. Price, R.M. Walker, Ion explosion spike mechanism for formation of charged‐particle tracks in solids, J. Appl. Phys. 36 (1965) 3645–3652. [39] F. Singh, S. Mohapatra, J.P. Stoquert, D.K. Avasthi, J.C. Pivin, Shape deformation of embedded metal nanoparticles by swift heavy ion irradiation, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 267 (2009) 936–940. [40] F. Singh, J.C. Pivin, D. Dimova-Malisnovska, J.P. Stoquert, Swift heavy ion interaction with silver–silica nanocomposites: an experimental surface plasmon resonance study, J. Phys. D Appl. Phys. 44 (2011) 325101, http://dx.doi.org/10.1088/0022-3727/44/32/325101. [41] R.G. Singh, F. Singh, I. Sulania, D. Kanjilal, K. Sehrawat, V. Agarwal, et al., Electronic excitations induced modifications of structural and optical properties of ZnO–porous silicon nanocomposites, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 267 (2009) 2399–2402. [42] H. Amekura, N. Okubo, N. Ishikawa, D. Tsuya, K. Mitsuishi, Y. Nakayama, et al., Swift heavy ion irradiation of ZnO nanoparticles embedded in silica: Radiation-induced deoxidation and shape elongation, Appl. Phys. Lett. 103 (2013) 203106. [43] D.C. Agarwal, D.K. Avasthi, S. Varma, F. Kremer, M.C. Ridgway, D. Kabiraj, Phase transformation of ZnMoO4 by localized thermal spike, J. Appl. Phys. 115 (2014) 163506. [44] F. Singh, S.K. Gautam, P.K. Kulriya, J.C. Pivin, In situ X-ray diffraction study of the growth of silver nanoparticles embedded in silica film by ion irradiation: the effect of volume fraction, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 311 (2013) 5–9 http://dx.doi.org/10.1016/j.nimb.2013.06.011.
CERAMICS INTERNATIONAL
Ceramics International 42 (2016) 2846–2853 www.elsevier.com/locate/ceramint
Decomposition mechanism of indium oxide nanoparticles sandwiched between zinc oxide layers by energetic ions Subodh K. Gautama,n, Fouran Singha,n, S. Ojhaa, R.G. Singhb, V.V. Siva Kumara a Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067, India Department of Physics, Bhagini Nivedita College, Delhi University, Delhi 110043, India
b
Received 19 October 2015; received in revised form 4 November 2015; accepted 5 November 2015 Available online 12 November 2015
Abstract Decomposition of indium oxide nanoparticles (IONPs) sandwiched between zinc oxide (ZnO) thin films by energetic ions is reported. Multilayers thin films were deposited using RF magnetron sputtering at room temperature, consisting two thin indium oxide layers sandwiched between three ZnO layers. Films exhibit very high transparency in the visible region. A sharp near band edge absorption with exciton absorption peak in the film annealed at the highest temperature was also observed. The structural and optical properties reveal that the as-deposited films show the formation of IONPs around the interface, which further grow upon increasing in annealing temperature. However, irradiation induces the decomposition of IONPs for the possible formation of single phase indium doped ZnO (IZO). The mechanism of the decomposition of IONPs is understood by the creation of ion tracks in IO. The track radius (Re) of 5.9 nm is calculated in the framework of thermal spike model. Therefore, the IONPs with diameter r2Re decomposed or amorphized between the crystalline ZnO layers; while the IONPs with diameter 42Re show reduction in size by the electronic sputtering from the IONPs surface under the thermo-elastic effects. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Indium oxide nanoparticles (IONPs); Energetic ions; Thermal spike model; Thermo-elastic effects
1. Introduction In recent years, the exploration of Transparent Conducting Oxides (TCOs) is an active area of research due to their multifunctional uses for the development of various optoelectronic device applications; such as solar cells, flat panel displays, transparent electrodes, diodes, etc. [1–4]. The important properties of TCO materials like transparency and conductivity are heavily dependent on crystalline phase and lattice defects. The composition of thin multilayers or superlattices can even affects the thermal (Kaptiza) resistance of interface [5], which can be controlled by the thermal annealing in controlled environment or by energetic ion irradiation [6–9]. It may be noted that the energetic ion irradiation induced defects in similar oxides has been used for better understanding of the n
Corresponding authors. E-mail addresses: [email protected] (S.K. Gautam), [email protected] (F. Singh). http://dx.doi.org/10.1016/j.ceramint.2015.11.020 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
evolution of Raman phonon modes and even semiconductor to metal transition as reported in our previous works [10–13]. Thus, the modifications in multilayer systems are liable to develop nanocomposite materials with superior properties. The most of the nanocomposite films show the characteristic of formation of metal oxide phases and metallic clusters by the treatment of thermal annealing, which affect the physical properties of the system. In such cases, the main issue is to dissolve these secondary metal or metal oxide nanoparticles (NPs) completely in the host system and to substitute them as metal cations at the proper metal site, as required for the development of spintronic devices and/or to enhance the conductivity of the host metal oxides. Generally, the decomposition of such NPs is difficult to achieve by thermal annealing [14]. However, energetic ion irradiations have proven to be as an unique tool to dissolve the NPs inside the host matrices to develop the single phase material [9]. Role of energetic ion irradiation in various undoped, doped, bilayer and/or multilayer thin system has been reported to
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
modify or control the structural, optical, and electrical properties by depositing large electronic energy via inelastic collisions [12,13,15–17]. The deposited energy is confined to a nano-cylinder along the ion trajectory. These high densities of electronic excitation in target materials are liable to perturb the atomic structure and induced various modifications such as damage creation at high electronic excitation [18–21] and track formation/sputtering [22–24]. Energetic ions can also enable mixing of bilayer or multilayer thin films around the interface by the inter-diffusion of elements across at the interface/s [25]. It is reported that the mixing of metal–semiconductor and metal–metal multilayer system increases with the increase in irradiation fluence and electronic energy loss value [26,27]. The mixing of ZnO/SiO2 at the interface has also been reported due to inter-diffusion during transient melt phase [28]. So, the energetic ions have been proven to be as an effective tool to the decomposition of NPs for the development of stable single phase materials. Therefore, the present study reports the experimental results on the effect of energetic ions on RF magnetron sputtering deposited multi-layer metal-oxide (ZnO/In2O3/ZnO/In2O3/ ZnO) thin films which induces interface mixing through the decomposition of indium oxide (IO) NPs inside the ZnO thin films. The size dependence of the decomposition of IONPs with respect to the track size and their effect on the structural and optical properties are investigated under the framework of thermal spike and thermo-elastic models [20,21]. 2. Experimental details Multi-layers thin films of thickness around 350 nm consists of two thin indium oxide layers of thickness around 20 nm sandwiched between three zinc oxide layers (ZnO/In2O3/ZnO/ In2O3/ZnO) of thickness around 100 nm were deposited using RF magnetron sputtering at room temperature. The substrates were cleaned in acetone then rinsed by hydrofluoric acid and deionized water followed by drying in nitrogen gas before loading into the deposition chamber. ZnO target with 99.99% purity and a commercially available metallic indium target of 50 mm diameter from Semi Wafer Inc., Taiwan were used as sputtering targets. The chamber was evacuated down to a base pressure of 5.5 10 5 mbar before introducing the gas into the chamber. Both the ZnO and In2O3 layers were deposited in the presence of oxygen and argon gas environment. The mixture of Arþ O2 gas was kept at a constant flow of standard cubic centimeter per minute (sccm) or ratio (70%þ 30%), respectively using the MKS mass flow meters. During the deposition, base pressure was maintained at 50 mTorr, RF power was fixed at 150 W, substrates were at room temperature and the distance between target to substrate was kept at 5.5 cm. Post annealing of the samples were carried out using Nabertherm (GERO) tubular furnace with alumina tube at different temperature ranging from 500 1C to 850 1C in oxygen ambient for time 1 h for improving the stoichiometry and crystalline nature of the films. The oxygen gas flow was maintained as one bubble per second and the ramp rate of temperature rise was kept at 3 1C/min. As-deposited, 500 1C
2847
and 850 1C annealed films were irradiated by 120 MeV Ag ions for fluence of 3 1013 ions/cm2 using the 15 UD Pelletron Accelerator available at Inter University Accelerator Centre (IUAC), New Delhi. The structure of the films is investigated by Grazing Incidence X-ray Diffraction (GIXRD) measurements, carried out using Bruker D8 advanced diffractometer equipped with Copper anode with scan speed of 0.51 per minute and with step size of 0.021. The elemental composition, thickness and the interfacial diffusion behavior of indium atoms in ZnO layers of as-deposited, annealed and irradiated samples were studied by Rutherford Backscattering Spectrometry (RBS) measurement using 2 MeV He þ ions at scattering angle of 1701. The samples were tilted by 71 to avoid the channeling of He þ ions during the backscattering measurement and the analysis of the RBS data is performed using the RUMP simulation code [29]. Field Emission Scanning Electron Microscopy (FE-SEM) along with Energy Dispersive X-ray (EDX) analysis was also carried out using MIRA\\TESCAN FE-SEM system. The UV–visible studies on films were carried out using Hitachi UV3300 double beam spectrophotometer. All the measurements were performed at room temperature (RT) using facilities at IUAC, New Delhi. 3. Results GIXRD patterns of as-deposited and annealed multilayer thin films are shown in Fig. 1(a) and the schematic of the same is shown in Fig. 1(b). The diffraction peaks corresponding to (100), (002) and (101) planes in GI-XRD patterns indicate that the films posses polycrystalline nature with hexagonal wurtzite crystal structure of ZnO [JCPDS 79-0206]. The intensity of (002) diffraction peak is relatively more intense as compared to (100) peak, indicates a texturing along the c-axis perpendicular to the substrate surface. A broad peak observed at 2θ¼ 30.4981 is assigned to the (222) diffraction peak of IONPs [JCPDS 741990]. The (222) diffraction peak of IONPs and (002) diffraction peak of ZnO get pronounced with increase in annealing temperature. The average crystallite size of both ZnO and IONPs are calculated by using the Scherrer's formula [30,31]. D¼
0:9λ β cos θ
where D is the average size, λ is the wavelength (1.5404 Å) of Cu Kα line, θ is the Bragg angle and β is full width at half maximum (FWHM) in radians of (002) and (222) diffraction peaks of ZnO and IONPS, respectively. The calculated average size of ZnO and IONPs are cited in Table 1. It is clearly evident from this table that the average size is growing with increase in annealing temperature. The diffraction peak position of ZnO corresponding to (002) and (101) are shifting towards the higher 2θ value and attain a value equivalent to the stress free ZnO at 500 1C and get more pronounced when the films were annealed at 850 1C. The annealing at 850 1C, induces a shift towards higher 2θ value with large increase in the size. Similar results are observed for (222) peak of IONPs, which also shifts to higher 2θ value of 30.691 from their bulk position (30.571). The observation reveals that as-deposited films may not be highly
2848
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
Fig. 1. (a) GIXRD patterns of as deposited, annealed films, (b) schematic diagram of multilayer arrangement, and (c) growth with annealing treatment.
Table 1 Average size estimated using Scherer’s formula for the pristine and irradiated films. Annealing temperature
As-deposited 500 1C 850 1C
ZnO (002) peak (bulk peak at 34.420)
In2O3 (222) peak (bulk peak at 30.5770)
Pristine
After Irradiation
Pristine
After Irradiation
2θ (deg.)
Av. size (nm)
2θ (deg.)
Av. size (nm)
2θ (deg.)
Av. size (nm)
2θ (deg.)
Av. size (nm)
34.26 34.43 34.51
8.5 11.1 23.0
34.27 34.42 34.43
14.3 12.7 20.8
30.50 30.58 30.69
6.5 8.5 31.3
– – 30.66
– – 15.3
stoichiometric for their respective phases of ZnO and IO. The stoichiometry of ZnO and IO phase of the films gradually improves with increasing annealing temperature. It means that the sub-stoichiometric IONPs transforms to stoichiometric phase by the presence of oxygen at interfaces and remaining Indium atoms start to diffuse inside the ZnO layers. It may ascribe to the faster migration velocity of Indium atoms as compared to Zn and O atoms in the ZnO lattice, due to the weak binding energy (or bond enthalpy) of In–O bond than Zn–O bond [31]. Moreover, it is also known that the value of diffusion coefficient (D0) for Indium and Zinc in ZnO lattice is 2.5 102 cm2 s 1and 1.7 10 3 cm2 s 1, respectively. The value of activations energy for In and Zn in ZnO is found to be 3.16 and 2.66 eV, respectively. Thus, it is better to remark that the diffusion of Indium atoms to the substitutional sites of Zn lattice leads to the formation of single phase IZO, besides the formation of IO phase. The diffusion of Indium atoms is further confirmed by the RBS study (which will be discussed in next section), reveals
that the percentage of In atoms increases in the top layer of ZnO for the films annealed at 850 1C. It may also be noted that a very large IONPs are formed at 850 1C, as shown schematically in Fig. 1(c). The shifting of (002) peak of ZnO to higher theta value can be ascribed due to the incorporation of Indium atom on substitutional sites of ZnO lattice and formation of IONPs in the ZnO lattice on defects sites (since, it is well known that defect sites act as good nucleation centers). The observed peak shifting to higher theta value and correspondingly decrease in lattice spacing reveals a compressive stress in the films. It is known that the ionic radii of In3 þ (94 pm) is about 7% larger than the ionic radii of Zn2 þ (88 pm), which is not favorable. However, the partial substitution at high temperature is expected to induced compressive stress, as experimentally observed. Similarly, the observed shifting in (222) peak of IONPs might be due to the compressive stress put by the ZnO lattice. Fig. 2(a) and (b) shows the cross section FE-SEM and EDX spectra to study the morphology, thickness, film quality and
IZO-An850
(110) ZnO
(440) In O
IZO-An850-IRR
(431) In O (102) ZnO
(400) In O
3 2
(222) In O
(100) ZnO
Intensity (a. u.)
2849
(101) ZnO
(002) ZnO
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
IZO-An500-IRR IZO-An500 IZO-AD-IRR IZO-AD
25
30
35
40
45
50
55
60
2θ (Degree)
Fig. 3. GIXRD pattern of pristine and films irradiated using 120 MeV Ag ions.
Fig. 2. FESEM images in planer and cross section along EDX spectra for elemental analysis.
compositional analysis. The cross section FE-SEM shows that total thickness of the film is 390 nm. It can be remarked that films are free of voids etc and but the different layers are not well resolved. In such a situation a high quality cross sectional scanning transmission electron microscopy (STEM) images would be better. Nevertheless, IO is very sensitive for the damage by high energy electron beam; hence any such investigations are not even reported in literature to best of our knowledge. However, the basic objective of manuscript will not change much, as the GIXRD and RBS studies are able to clearly show the diffusion and substitution of Indium atom in the ZnO lattice. It would be better to note that the RBS is well capable for the concentration and diffusion depth of indium atoms along the cross sectioned films, as reported in the present manuscript. Moreover, the diffusion of Indium metal is also confirmed by EDX study, as the spot for EDX measurements were taken much far away from the interface. XRD pattern of the pristine (as-deposited, 500 1C and 850 1C annealed) and irradiated films for 3 1013 ions/cm2 fluence are shown in Fig. 3. The 2θ position and the calculated crystallite size in the pristine and irradiated films are also cited in Table 1. As-deposited film also shows that the size of ZnO crystallites increases from 8 nm to 14.3 nm, while the films annealed at 500 1C and 850 1C do not exhibit any significant change in ZnO crystallite size after irradiation. The (222) diffraction peak of IONPs disappears for fluence of
3 1013 ions/cm2 in as-deposited and 500 1C annealed irradiated films. However, 850 1C annealed film shows that the average size of IONPs decreases from 30.2 nm to 15.3 nm and exhibits a shift towards lower diffraction angle in (002) and (101) peak upon irradiation. RBS measurements on multilayer films were carried out to determine the thickness, elemental composition and diffusion of indium atoms around the interface of films. Experimental and simulated spectra along with simulated depth profiles of pristine (as-deposited, and annealed at 850 1C) and irradiated films are shown in Fig. 4(a) and (b). Simulated results confirm that the overall measured thickness (Δt) of deposited film is around 400 nm, which is in agreement with cross sectional SEM results. The simulated spectra of as-deposited films shows that two thin of IO layers of each about 25 nm are sandwiched between the three ZnO layers and having diffused interface with ZnO layers on either side of the IO layers. It also shows 15 nm thin IO layer with 40 nm diffused interface with ZnO layers, where simulation of diffusion is taken as linear gradient concentration of indium atomic fraction from 30 at.% to nil in ZnO layers on either sides of the IO layers. The thickness of IO layer increases upto 26 nm and the length of the diffused interface layer increases with increasing in annealing temperature to 850 1C. Around 1% IO is also observed on the top ZnO layer of 850 1C annealed film. There is a shift in Indium edge from channel no. 1620 to channel no. 1700 (proper position of indium edge) is observed after annealing of as-deposited film to 850 1C, which can be ascribed to diffusion of indium atoms onto the top layer of ZnO. The irradiation of as-deposited film shows the ion beam mixing at the interfaces by the diffusion of Indium atoms in ZnO layers as the fraction of indium atoms increases from 28 to 40% in ZnO layer around interface at same 45 nm length after dissolving complete 15 nm IO layers. However, the irradiation of 850 1C annealed film shows decrement of IO layers down to 15 nm with improvement in the diffusion of atomic indium around the 55 nm on either side of the IO layers. In other words, the RBS results show the ion beam mixing around the interfaces by inter-diffusion of Indium followed by the dissolution or decomposition of IONPs [26].
2850
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
Energy (MeV)
Energy (MeV) 0.5
0.5
1.5
O Si
Normalized Yield
In
Zn Zn
60
In
Zn Zn 40
O Si 20
20
0
0 500
1000
500
1500
1000
1500
Channel
Channel 1.1
1.1 O Zn In Si
0.9
0.8
In2O3
0.7 0.6
Si Substrate
0.5 Zn/O
Zn/O
0.4
O Zn In Si
1.0 0.9
In2O3
0.8
IZO-AD
Zn/O
0.3
IZO-AD-IRR
0.7 0.6 Si Substrate
0.5 Zn/O
0.4
Zn/O
Zn/O
0.3 0.2 0.1
0.0
In
0.1
In
In
In
0.2
Concentration
1.0
Concentration
1.5
IZO-AD-IRR Simulated
80
60
40
1.0
Zn+In
Zn+In
IZO-AD Simulated
80
Normalized Yield
1.0
0.0 0
50
100 150 200 250 300 350 400 450 500
0
50
100 150 200 250 300 350 400 450 500
Thickness (nm)
Thickness (nm)
Energy (MeV) 0.5
Energy (MeV)
1.0
1.5
0.5
80
Zn+In
IZO-An850 Simulated
1.0
1.5
Zn+In
IZO-An850-IRR Simulated
80
40
Zn
20
Zn In
Normalized Yield
Normalized Yield
60
O
60
Zn
O
20
Si
Si
0
0 500
1000
500
1500
1000
1500
Channel
Channel 1.0
1.0
0.5
SiO Zn/O
0.4
2
Zn/O
Zn/O
Substrate
0.3 0.2
Concentration
0.7
0.6
IZO-An850-IRR In2O3
0.8 In2O3
0.7
O Zn In Si
0.9
In2O3
0.8
IZO-An850 In2O3
O Zn In Si
0.9
Concentration
In
Zn
40
0.6 0.5 0.4
SiO
2
Zn/O
Zn/O
Substrate
Zn/O
0.3 0.2 0.1
0.0
In
In
Zn
In
In
0.1
Zn
0.0 0
100
200
300
Thickness (nm)
400
500
0
100
200
300
400
500
Thickness (nm)
Fig. 4. Experimental and RUMP simulated RBS spectra of (a) as-deposited and irradiated and (b) 850 1C annealed and irradiated films.
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
IZO-Ad IZO-Ad-IRR IZO-An850 IZO-An850-IRR
80 60 40
(αh ν) (cm eV)
Transmittance (%)
100
20 0 300
400
500
600
700
800
Wavelength (nm)
Fig. 5. Transmittance spectra of as-deposited, annealed and irradiated films. Inset shows the Tauc's plot for estimating the band gap.
Optical absorption and transmission spectra of multilayer IZO films were also measured in the wavelength range 200– 850 nm and are shown in Fig. 5. It shows that there is almost no optical absorption in the visible region. The annealed sample shows sharpening of near band edge (NBE) absorption and improvement in exciton absorption peak by increasing annealing temperature. A sharp and strong exciton absorption peak is observed in the films annealed at 850 1C. The observation of exciton peak and the sharpening of NBE absorption confirm the improvement in the quality of ZnO crystallites. Moreover, the irradiation for a fluence of 3 1013 ions/cm2 unable to induce any significant change in NBE absorption but shows some deterioration in the peak corresponds to exciton absorption. It is known that a metal rich film usually exhibited less transparency. Hence, the decrease in optical transmittance in doped samples might be due to the increase in metal to oxygen ratio, (Zn þ In)/O. The large decrease in transmittance in the UV region may be due to the free-carrier absorption. This could be related to the oxygen and metal charge transfer or due to electron transfer to the conduction band [8]. The absorption edge of the IZO thin films corresponds to electron transitions from valence band to conduction band and this edge can be used to calculate the optical band gap of the IZO thin films. The optical band gap was determined by applying the Tauc's relationship [32]: n αhυ ¼ C hυ Eg where, C is a constant, hυ is the photon energy and Eg is the optical band gap. The value of n is equal to 2 and ½ for indirect and direct bandgap semiconductors, respectively. The value of n is taken as ½, as ZnO is a direct bandgap semiconductor. An extrapolation of the linear region of a plot of (αhυ)2 on the y-axis versus photon energy (hυ) on the x-axis gives the value of the optical band gap (Eg) for annealed and irradiated films as shown as inset in Fig. 5. The value of αhυ should be zero for determining the bandgap and thus the value of constant C will not influence the bandgap value determined
2851
using the above equation. It is better to mention that Tauc's relationship may not be suitable for multi-phase materials. However, this can be used to monitor the relative variation in bandgap for such multi-phase materials. The estimated bandgap is around 3.32 eV and 3.25 eV for the as-deposited and annealed films, respectively. This small change in bandgap can be attributed the change in density and stoichiometry of the film. The transmission spectra of films show the interference fringe with high transmittance of 70–85% in whole visible spectral region. The observation of interference fringes in the transmittance curves also reveals that the film surface is highly reflecting and free from scattering or absorption losses in the films. However, the transmission spectra of the annealed and irradiated films show that the amplitude of the fringe pattern became flatter and the average transmittance is reduced with the increasing in the annealing temperature or irradiation fluence. This can be attributed to the diffusion of indium in ZnO lattice as already confirmed by RBS and EDX measurements. 4. Discussion The decomposition processes of IONPs between the ZnO layers by energetic ion irradiation can be understood by fundamental ion solid interaction mechanism. Energetic ion losses or transfer their energy to target by two processes: (a) nuclear energy loss by elastic collisions with target atoms leads to lattice displacement, dominant in the low energy regime, and (b) electronic energy loss by inelastic collision process leads to electronic excitation and ionization in target atoms, dominant in high energy regime. In present study of 120 MeV Ag ions irradiation on ZnO, the electronic energy loss (Se, energy transferred to the target electrons by incident ions) is 21.68 keV/nm, where as nuclear energy loss (Sn) is 0.105 keV/nm and in IO, Se ¼ 22.9 KeV/nm, Sn ¼ 0.118 KeV/ nm as determined by SRIM2008 code [33]. The range of 120 MeV Ag ions in IZO film (thickness 400 nm) is more than 10 μm, so the Se remain almost constant throughout the film thickness and ions penetrate deep inside the substrate and finally get implanted inside substrate. The Se is dominating effect to induce modification in the films, as it is order of magnitude higher than Sn. However, the effects of Sn cannot be completely ignored, but difficult to evaluate quantitatively for this kind of modifications. In this dominant regime of Se, the projectile ion energy is transferred to the target electronic subsystem in a time less than 10 16 s, and gives rise to highly non-equilibrium thermal condition. The energy of electronic sub system is dissipated to atomic subsystem by electron– phonon (e-ph) coupling within a time of about 10 14 and 10 12 s. The relaxation or transfer of excess energy to lattice gave rise to increase in the transient temperature limited to a localized zone of few nanometers (known as ion track) along the ion path. The track formation and the size of latent track depend on the property of target material and the Se deposited by ions. If Se Z Seth, where Seth is the threshold electronic energy loss to form a cylindrical region of track of few nm. The Seth value of
2852
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853
the material depends on many parameters such as density ρ, average specific heat c, initial width of the thermal spike a0, and electron–phonon coupling efficiency g, and can be determined using following equation [34]: Seth ¼
πρca ð0ÞT 0 g 2
ð1Þ
where T0 ¼ Tm-Tirr, temperature of thermal spike to reach the melting point and a0 is the band gap (Eg) dependent parameter and for insulators it is almost constant. The value of a(0) is define by an expression; a(0) ¼ b þ c(Eg) 1/2, where b and c are the approximation constant for ion induced thermal spike width and Eg is the bandgap of semiconductor. The value of a (0) is determined using Eg ¼ 3.7 eV for IO from the plot of (Eg)-1/2 versus a(0) and the value of a(0) found to be 6.2 nm [35]. The Seth value for IO and ZnO are calculated using above equation by substituting their suitable thermodynamic values. Indium oxide has material density (ρ¼ 7.31 g cm 3), melting temperature (Tm ¼ 2183 K), average specific heat (c¼ 0.3550 J g 1 K 1) at the irradiation temperature (296 K) [36], and electron–phonon coupling efficiency (g), which depends on the ion velocity is taken to be 0.4 [35]. Similarly for ZnO the values are taken as ρ ¼ 7.31 g cm 3, Tm ¼ 2183 K, c ¼ 0.3550 Jg 1 k 1 at Tirr (296 K) [37], and g value is 0.4 similar as in IO. Therefore the estimated Seth values are found to be 9.24 keV /nm and 10.25 keV/nm for IO and ZnO, respectively. The track size in IO and ZnO layers is calculated by using the following expression [34]: R2e ¼ a2 ð0ÞlnðSe =Seth Þ ¼ ½ða2 ð0Þ=2:7ðSe =Seth Þ
1 r Se =Seth r 2:7
ð2Þ
Se =Seth 42:7
ð3Þ
For IO, the calculated SSethe ratio is 2.47, which is less than 2.7, thus Eq. (2) is used and the track radius (Re) is found as 5.9 nm. Similarly, in term of ZnO, SSethe ratio is 2.11, less than the 2.7 and calculated track radius using Eq. (2) is 5.3 nm. According to calculated values, the estimate Seth of ZnO is slightly higher than in IO and the track radius is found to be almost similar to the value in IO. However, in our previous findings, it is clearly reported that ZnO structure remains stable even at very high irradiation dose 4 1013 ions/cm2 with high Se value 20 keV/nm [10,11]. Therefore, the latent track formation is only possible in IO, not in ZnO layers of film. Thus, the complete process of track formation and decomposition of In2O3 NPs can be well explained by Thermal spike model [20,38–40]. According to this model the IONPs with diameter r 2 Re goes to molten state and lead to the formation of solid solution of indium. It means, the IONPs having size smaller than the track diameter completely decomposed. Therefore, the IONPs in as-deposited and 500 1C annealed films completely dissolve and diffuse in the ZnO lattice since the size of IONPs is smaller than track diameter [41–43]. However, the diameter of IONPs in the film annealed at 850 1C is larger than the track diameter, which may not be completely decomposed, but decreases in size due to the electronic sputtering from their surface by and thermo-elastic
effects as reported to for such nanocomposites [21] and lead to the diffusion of Indium in the ZnO lattice [44]. 5. Conclusions The development of high quality multilayers with very high transparency in the visible region using RF sputtering is reported. The structural and compositional studies confirm the decomposition of indium oxide nanoparticles by energetic ion irradiation, which is not possible by conventional thermal annealing. The track radius (Re) of 5.9 nm is calculated in the framework of thermal spike model. Thus, the IONPs with diameterr2Re decomposed or amorphized between the crystalline layers of ZnO; while the IONPs with diameter42Re show reduction in size by the electronic sputtering from the IONPs surface under the thermo-elastic effects and is used for understanding the decomposition of IONPs followed by the diffusion of indium in the lattice. Therefore, these preliminary experiments show that energetic ion irradiation could be useful for the formation of doped single phase metal oxide film with high transparency for their possible optoelectronic applications. Acknowledgments Authors are grateful to the Director (IUAC), and Dr. D. K. Avasthi for their encouragement and moral support. Authors are also thankful to Dr. S.A. Khan for experimental support in SEM investigations, Pelletron group of IUAC for providing the stable ion beam during irradiation experiment and Dr. S. Nath (IUAC) for improving the English of the manuscript. SKG acknowledged CSIR, India for providing Senior Research Fellowship [09/760(0024)/2011-EMR-I]. DST, Govt. of India is gratefully acknowledged for providing FE-SEM through nano-mission project and for granting Science and Engineering Research Board (SERB) project (SB/EMEQ-122/2013). References [1] D.S. Ginley, C. Bright, Transparent conducting oxides, MRS Bull. 25 (2000) 15–18, http://dx.doi.org/10.1557/mrs2000.256. [2] M. Thambidurai, J.Y. Kim, C. Kang, N. Muthukumarasamy, H.-J. Song, J. Song, et al., Enhanced photovoltaic performance of inverted organic solar cells with In-doped ZnO as an electron extraction layer, Renew. Energy 66 (2014) 433–442, http://dx.doi.org/10.1016/j.renene.2013.12.031. [3] G.C. Park, S.M. Hwang, S.M. Lee, J.H. Choi, K.M. Song, H.Y. Kim, et al., Hydrothermally grown In-doped ZnO nanorods on p-GaN films for color-tunable heterojunction light-emitting-diodes, Sci. Rep. 5 (2015) 10410, http://dx.doi.org/10.1038/srep10410. [4] V.K. Jain, P. Kumar, D. Bhandari, Y.K. Vijay, Growth and characterization of transparent conducting nanostructured zinc indium oxide thin films, Thin Solid Films 519 (2010) 1082–1086, http://dx.doi.org/10.1016/j.tsf.2010.08.048. [5] X. Liang, M. Baram, D.R. Clarke, Thermal (Kapitza) resistance of interfaces in compositional dependent ZnO-In2O3 superlattices, Appl. Phys. Lett. 102 (2013) 223903, http://dx.doi.org/10.1063/1.4809784. [6] C. Huang, M. Wang, Z. Deng, Y. Cao, Q. Liu, Z. Huang, et al., Effects of hydrogen annealing on the structural, optical and electrical properties of indium-doped zinc oxide films, J. Mater. Sci. Mater. Electron. 21 (2010) 1221–1227, http://dx.doi.org/10.1007/s10854-009-0050-x. [7] P.M.R. Kumar, C.S. Kartha, K.P. Vijayakumar, Doping of spray-pyrolyzed ZnO thin films through direct diffusion of indium: Structural optical and
S.K. Gautam et al. / Ceramics International 42 (2016) 2846–2853 electrical studies, J. Appl. Phys. 98 (2005) 1–7, http://dx.doi.org/10.1063/1.1985967. [8] Y. Huang, D. Li, J. Feng, G. Li, Q. Zhang, Transparent conductive tungsten-doped tin oxide thin films synthesized by sol–gel technique on quartz glass substrates, J. Sol–Gel Sci. Technol. 54 (2010) 276–281, http://dx.doi.org/10.1007/s10971-010-2182-0. [9] R. Kumar, F. Singh, B. Angadi, J.-W. Choi, W.-K. Choi, K. Jeong, et al., Single phase formation of Co-implanted ZnO thin films by swift heavy ion irradiation: optical studies, J. Appl. Phys. 100 (2006) 113708, http://dx.doi.org/10.1063/1.2399893. [10] F. Singh, R.G. Singh, V. Kumar, S.A. Khan, J.C. Pivin, Softening of phonons by lattice defects and structural strain in heavy ion irradiated nanocrystalline zinc oxide films, J. Appl. Phys. 110 (2011) 083520, http://dx.doi.org/10.1063/1.3651638. [11] F. Singh, P.K. Kulriya, J.C. Pivin, Origin of swift heavy ion induced stress in textured ZnO thin films: an in situ X-ray diffraction study, Solid State Commun. 150 (2010) 1751–1754, http://dx.doi.org/10.1016/j.ssc.2010.07.026. [12] S.K. Gautam, F. Singh, I. Sulania, R.G. Singh, P.K. Kulriya, E. Pippel, MicroRaman study on the softening and stiffening of phonons in rutile titanium dioxide film: competing effects of structural defects, crystallite size, and lattice strain, J. Appl. Phys. 115 (2014) 143504, http://dx.doi.org/10.1063/1.4868079. [13] F. Singh, B. Chaudhary, V. Kumar, R.G. Singh, S. Kumar, A. Kapoor, Disorder induced semiconductor to metal transition and modifications of grain boundaries in nanocrystalline zinc oxide thin film, J. Appl. Phys. 112 (2012) 073101, http://dx.doi.org/10.1063/1.4755795. [14] N. Tripathi, S. Rath, V. Ganesan, R.J. Choudhary, Growth dynamics of pulsed laser deposited indium oxide thin films: a substrate dependent study, Appl. Surf. Sci. 256 (2010) 7091–7095, http://dx.doi.org/10.1016/j.apsusc.2010.05.033. [15] A.M. Stoneham, N. Itoh, Materials modification by electronic excitation, Appl. Surf. Sci. 168 (2000) 186–193, http://dx.doi.org/10.1016/S0169 -4332(00)00587-0. [16] C.P. Race, D.R. Mason, M.W. Finnis, W.M.C. Foulkes, A.P. Horsfield, A.P. Sutton, The treatment of electronic excitations in atomistic models of radiation damage in metals, Rep. Prog. Phys. 73 (2010) 116501, http://dx.doi.org/10.1088/0034-4885/73/11/116501. [17] S.K. Gautam, R.G. Singh, V.V. Siva Kumar, F. Singh, Giant enhancement of the n-type conductivity in single phase p-type ZnO:N thin films by intentionally created defect clusters and pairs, Solid State Commun. 218 (2015) 20–24, http://dx.doi.org/10.1016/j.ssc.2015.05.011. [18] C. Dufour, Z.G. Wang, E. Paumier, M. Toulemonde, Transient thermal process induced by swift heavy ions: Defect annealing and defect creation in Fe and Ni, Bull. Mater. Sci. 22 (1999) 671–677. [19] A. Meftah, F. Brisard, J.M. Costantini, M. Hage-Ali, J.P. Stoquert, F. Studer, et al., Swift heavy ions in magnetic insulators: a damagecross-section velocity effect, Phys. Rev. B 48 (1993) 920–925, http://dx.doi.org/10.1103/PhysRevB.48.920. [20] M. Toulemonde, C. Dufour, A. Meftah, E. Paumier, Transient thermal processes in heavy ion irradiation of crystalline inorganic insulators, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 166 (2000) 903–912, http://dx.doi.org/10.1016/S0168-583X(99)00799-5. [21] F. Singh, J.P. Stoquert, J.C. Pivin, Study of classical thermo-mechanical equations in ultrafast thermo-elastic domain: electronic sputtering from metal–dielectric nanocomposites, J. Phys. D Appl. Phys. 46 (2013) 325305, http://dx.doi.org/10.1088/0022-3727/46/32/325305. [22] H. Dammak, D. Lesueur, A. Dunlop, P. Legrand, J. Morillo, Phenomenological model of damage creation by high electronic excitations in pure metals, Radiat. Eff. Defects Solids 126 (1993) 111–114, http://dx.doi.org/10.1080/10420159308219689. [23] P. Kluth, C.S. Schnohr, O.H. Pakarinen, F. Djurabekova, D.J. Sprouster, R. Giulian, et al., Fine structure in swift heavy ion tracks in amorphous SiO2, Phys. Rev. Lett. 101 (2008) 1–4, http://dx.doi.org/10.1103/ PhysRevLett.101.175503. [24] M. Toulemonde, W. Assmann, C. Trautmann, F. Grüner, Jetlike component in sputtering of LiF induced by swift heavy ions, Phys. Rev. Lett. 88 (2002) 057602, http://dx.doi.org/10.1103/PhysRevLett.88.057602. [25] S. Bagchi, F. Singh, D.K. Avasthi, N.P. Lalla, Thickness dependent effect of swift heavy ion irradiation in W/Ni superlattice multilayers, J. Phys. D Appl. Phys. 42 (2009) 145414, http://dx.doi.org/10.1088/0022-3727/42/14/145414.
2853
[26] S. Kumar, R.S. Chauhan, D.C. Agarwal, M. Kumar, A. Tripathi, W. Bolse, et al., Swift heavy ions induced mixing in metal/semiconductor system, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 266 (2008) 1759–1763, http://dx.doi.org/10.1016/j.nimb.2008.01.068. [27] B. Schattat, W. Bolse, Fast heavy ion induced interface mixing in thin-film systems, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 225 (2004) 105–110, http://dx.doi.org/10.1016/j.nimb.2004.04.183. [28] S. Kraft, B. Schattat, W. Bolse, S. Klaumünzer, F. Harbsmeier, A. Kulinska, et al., Ion beam mixing of ZnO/SiO[sub 2] and Sb/Ni/Si interfaces under swift heavy ion irradiation, J. Appl. Phys. 91 (2002) 1129, http://dx.doi.org/10.1063/1.1425439. [29] L.R. Doolittle, A semiautomatic algorithm for rutherford backscattering analysis, Nucl. Instruments Methods Phys. Res. B Beam Interact. Mater. Atoms 15 (1986) 227–231, http://dx.doi.org/10.1016/0168-583X(86)90291-0. [30] A.L. Patterson, The Scherrer formula for I-Ray particle size determination, Phys. Rev. 56 (1939) 978–982, http://dx.doi.org/10.1103/PhysRev.56.978. [31] B.D. Cullity, in: Elements of X-ray Diffraction, 2nd ed., AddisonWesley Publishing Company Inc., US, 1978. [32] J. Tauc, R. Grigorov, a Vancu, Optical properties and electronic structure of amorphous germanium, Phys. Status Solidi 15 (1966) 627–637, http://dx.doi.org/10.1002/pssb.19660150224. [33] J.F. Ziegler, M.D. Ziegler, J.P. Biersack, SRIM – the stopping and range of ions in matter (2010), Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 268 (2010) 1818–1823, http://dx.doi.org/10.1016/j.nimb.2010.02.091. [34] G. Szenes, General features of latent track formation in magnetic insulators irradiated with swift heavy ions, Phys. Rev. B 51 (1995) 8026–8029, http://dx.doi.org/10.1103/PhysRevB.51.8026. [35] G. Szenes, Comparison of two thermal spike models for ion-solid interaction, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 269 (2011) 174–179, http://dx.doi.org/10.1016/j.nimb.2010.11.009. [36] E.H.P. Cordfunke, E.F. Westrum, The heat capacity and derived thermophysical properties of In2O3 from 0 to 1000 K, J. Phys. Chem. Solids 53 (1992) 361–365, http://dx.doi.org/10.1016/0022-3697(92)90169-E. [37] A. Seko, F. Oba, A. Kuwabara, I. Tanaka, Pressure-induced phase transition in ZnO and ZnO–MgO pseudobinary system: a firstprinciples lattice dynamics study, Phys. Rev. B Condens. Matter Mater. Phys. 72 (2005) 1–10, http://dx.doi.org/10.1103/PhysRevB.72.024107. [38] R.L. Fleischer, P.B. Price, R.M. Walker, Ion explosion spike mechanism for formation of charged‐particle tracks in solids, J. Appl. Phys. 36 (1965) 3645–3652. [39] F. Singh, S. Mohapatra, J.P. Stoquert, D.K. Avasthi, J.C. Pivin, Shape deformation of embedded metal nanoparticles by swift heavy ion irradiation, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 267 (2009) 936–940. [40] F. Singh, J.C. Pivin, D. Dimova-Malisnovska, J.P. Stoquert, Swift heavy ion interaction with silver–silica nanocomposites: an experimental surface plasmon resonance study, J. Phys. D Appl. Phys. 44 (2011) 325101, http://dx.doi.org/10.1088/0022-3727/44/32/325101. [41] R.G. Singh, F. Singh, I. Sulania, D. Kanjilal, K. Sehrawat, V. Agarwal, et al., Electronic excitations induced modifications of structural and optical properties of ZnO–porous silicon nanocomposites, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 267 (2009) 2399–2402. [42] H. Amekura, N. Okubo, N. Ishikawa, D. Tsuya, K. Mitsuishi, Y. Nakayama, et al., Swift heavy ion irradiation of ZnO nanoparticles embedded in silica: Radiation-induced deoxidation and shape elongation, Appl. Phys. Lett. 103 (2013) 203106. [43] D.C. Agarwal, D.K. Avasthi, S. Varma, F. Kremer, M.C. Ridgway, D. Kabiraj, Phase transformation of ZnMoO4 by localized thermal spike, J. Appl. Phys. 115 (2014) 163506. [44] F. Singh, S.K. Gautam, P.K. Kulriya, J.C. Pivin, In situ X-ray diffraction study of the growth of silver nanoparticles embedded in silica film by ion irradiation: the effect of volume fraction, Nucl. Instrum. Methods Phys. Res. B Beam Interact. Mater. Atoms 311 (2013) 5–9 http://dx.doi.org/10.1016/j.nimb.2013.06.011.