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Enhancement of thermoelectric performance of n-type In2(Te0.94Se0.06)3 thin films by electronic excitations
Journal Pre-proofs Full Length Article Enhancement of thermoelectric performance of n-type In2(Te0.94Se0.06)3 thin films by electronic excitations Pandian Mannu, Matheswaran Palanisamy, Gokul Bangaru, Sathyamoorthy Ramakrishnan, Meena Ramcharan, Chung-Li Dong, Asokan Kandasami PII: DOI: Reference:
S0169-4332(19)32931-9 https://doi.org/10.1016/j.apsusc.2019.144115 APSUSC 144115
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Applied Surface Science
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Please cite this article as: P. Mannu, M. Palanisamy, G. Bangaru, S. Ramakrishnan, M. Ramcharan, C-L. Dong, A. Kandasami, Enhancement of thermoelectric performance of n-type In2(Te0.94Se0.06)3 thin films by electronic excitations, Applied Surface Science (2019), doi: https://doi.org/10.1016/j.apsusc.2019.144115
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Enhancement of thermoelectric performance of n-type In2(Te0.94Se0.06)3 thin films by electronic excitations Pandian Mannu a, Matheswaran Palanisamy a*, Gokul Bangaru a, Sathyamoorthy Ramakrishnan a, Meena Ramcharan b, Chung-Li Dong c, Asokan Kandasami b* a Department of Physics, Kongunadu Arts and Science College, Coimbatore, Tamilnadu, 641029, India b Materials
Science Division, Inter University Accelerator Centre, New Delhi - 110067, India
c Research
Center for X-ray Science & Department of Physics, Tamkang University,
Tamsui 25137, Taiwan. * email addresses: [email protected], [email protected] Abstract Thermoelectric properties of metal chalcogenide based materials exhibit a great suitability in the field of energy sustainability. This study reports the thermoelectric properties of In2(Te0.94Se0.06)3films prepared by thermal evaporation after the electronic excitations produced by 120 MeV Au ions. The Seebeck coefficient value for pristine sample is found to be ~196µVK-1 and it is enhanced to ~347 µVK-1 at the higher fluence of 1×1013 ions/cm2 at 400 K. The negative value of Seebeck coefficient and the Hall effect measurements confirm the n-type conductivity in the pristine and irradiated In2(Te0.94Se0.06)3 samples. The power factor value of thin films irradiated at the fluence of 1×1013 ions/cm2is ~3.80W/K2m, as compared to pristine sample ~1.28W/K2m.The change in image contrast in FESEM is due to grain fragmentation with increase in ion fluence in comparison to the pristine sample. It is evident that the electrical resistivity and power factor values are higher for irradiated samples as compared to that of pristine samples. Moreover, presence of high density of nanoscale grain boundaries created by ion irradiations lead to the enhancement in thermoelectric properties of In2(Te0.94Se0.06)3 thin films. Keywords: Metal chalcogenide, thermal evaporation, SHI irradiation, Seebeck coefficient and thermoelectric power
1
I. Introduction The application of ion beam in solid state materials has become an important topic in the scientific point of view, to understand the ion beams interaction of surface and interface modifications through the optical, electrical, morphological and optoelectronic properties [1-4]. Swift heavy ion beam irradiation (SHI) in a solid state system induced the formation of nanostructures on the surface and it was introduced a few decades ago [5]. In addition to that, investigations of radiation induced defects in metal chalcogenide semiconducting materials have been an important task for the new technological improvement in device fabrication. The extent of radiation damage models which depends strongly energy, mass and additionally, its fluence target density. On property modification like interfacial atoms, displacement spike or thermal spike and vacant lattice sites have been reported by many research groups [3-5].The high energy deposition on the target materials promotes the production of defects and morphological changes, so that when SHI traversing into the target material, most of it energy loses by exciting electron or ionization of atoms. Se-Te based chalcogenides materials have the large impact on the performance of thermoelectric devices in the field of energy sustainability for the present fast-growing generation. The energy conversion of thermal to electrical energy in these chalcogenide materials has the intensive role to tailoring the thermoelectric performance of the devices. Considering these facts, the efficiency of thermoelectric materials is evaluated by a dimensionless figure of merit, ZT =
S2T k
[6][7] (where S, , T, and k are Seebeck coefficient, electrical conductivity,
absolute temperature at which figure of merit is measured and thermal conductivity respectively). Thermoelectric properties can also determined by well known expression called power factor (PF) as PF= S2. Generally, the best thermoelectric material should have a greater value of S and , a low value for k is necessary. In general, grain boundary scattering has an important role to determine the electrical transport properties of chalcogenide based materials and especially, nanostructured chalcogenide thermoelectric materials can also improve the S and , which enhance the thermoelectric device performance [8-10]. Lattice vibrations (phonons) are responsible for the transport of thermal energy in chalcogenide semiconductors [11]. Therefore, introducing efficient phonon scattering centers through high density of grain boundaries in 2
nanosized grains is best known process to reduce thermal energy. Enormous effort has been made to enhance the thermoelectric performance by introducing nanostructure in chalcogenide based materials with different techniques [12][13]. SHI irradiation on the semiconducting materials induces many interesting phenomena like grain fragmentation, grain alignment, surface, and morphological changes [14-16].This ion irradiation induces electronic excitation and phonon contributions due to the scattering processes through grain fragmentation/grain alignment. Ion beam irradiation on these chalcogenide materials can improve the electrical transport properties to enhance the thermoelectric performance. Therefore, metal chalcogenide based materials have been used for a long time to the fabrication of electronic devices such as phase change memory, optoelectronic, and thermoelectric devices [17-19]. Among all these chalcogenide materials, only few authors reported the thermoelectric performance of metal chalcogenide based materials, namely Tahereh Talebi et al. performed thermoelectric performance of p-type Bi2Te3 thin films and the Seebeck coefficient value was about ~239V/K [20]. Transition of p-type and n-type conductivity behavior with the addition of Bismuth in to BixSb2-xTey thin film have been reported by Jiwon Kim et al.[21], showed good enhancement in both Seebeck coefficient and thermal conductivity. In addition, 25% enhancements in Seebeck coefficient for PbTe thin film by Ag ion implantation have been reported by Bala et al[22]. Srashti Gupta et al. reported 100 MeV Ag7+ ion irradiated PbTe thin film which showed ~40 % increase in thermo power compared to the pristine and it was explained by carrier scattering due to the defects present in the material or density of state [23]. Recently, Chia-Hua chien et al. studied the enhancement in thermoelectric properties of Bi-Sb-Te nanowire by Gallium ion irradiation revealed large number of phonon scattering of defects created during the irradiation leads to the reduction in thermal conductivity and subsequently performed size dependent Seebeck coefficient and Figure of merit (ZT) [24]. Ashoka Bali et al. reported a maximum power factor of ~25 W cm-1K-2 for In and I doped PbTe bulk samples. Further, they have shown a maximum zT of 1.12 for In doped and 1.1 for Indium and Iodine doped samples [25]. In2(Te1xSex)3
is a layered compound belongs to AIII2BII3 semiconductors having disordered structure
with cation vacancies will be a promising candidate for near room temperature (300-400 K) thermoelectric devices. Moreover, electronic excitation induced by the ion beam irradiation on 3
thermoelectric properties of In-Se-Te materials is not so far investigated to the best of our knowledge. Hence, in this study, the focus is on the thermoelectric properties of Au9+ (120 MeV) ions irradiated In2(Te1-xSex)3 system. The structural and thermoelectric properties are studied and results suggest that ion beams as a promising technique to manipulate the thermoelectric performance of metal chalcogenide thin films. 2. Materials and methods In2(Te1-xSex)3thin film of thickness 800 nm were deposited on a cleaned glass substrate by thermal evaporation under Ar atmosphere at a reduced pressure 2×10-6mbar. The elements of In, Se and Te (5N- purity) with desired composition 40%:6%:54% were taken into the quartz tube and quartz ampoules were fused at a reduced 2x10-5 mbar pressure, subsequently the sealed quartz tube were annealed at 950 °C for 12 hours in rotating furnace. The temperature of the furnace was raised slowly at a rate of 2-3 °C per minute and constantly rocked by rotating the ceramic rod to get the In2(Te0.94Se0.06)3 stoichiometric alloys compound. The molten state samples were quenched to room temperature and quenched materials were taken out by breaking the quartz tube. The ingots were grained to make In2(Te0.94Se0.06)3 fine powder for the film deposition. The structural studies were performed by X-ray diffraction (XRD) using Bruker AXS (D-8 advanced, Germany) diffractometer model in the scanning range 20-80° (2ϴ) with the wavelength of 1.5406 Å. The surface morphology and elemental composition of the samples were recorded using MIRA TESCAN model scanning electron microscopy (SEM) and atomic force microscopy (AFM) on Nanoscope IIIa digital instruments at IUAC, New Delhi. Using four probes and bridge methods, the electrical resistivity (ρ) and Seebeck coefficient of the samples were measured [26]. The prepared thin film samples were irradiated with 120 MeV Au9+ ions for the fluence of 1×1011 to1×1013 ions/cm2 at a current of 0.50 pnA (particle nano Ampere) using 15 UD Pelletron at Inter University Accelerator Center (IUAC), New Delhi, the projected ions were scanned over the targets using the electrostatic scanner. For the Au9+ ion irradiation, the value of the electronic energy loss (Se-due to elastic collision) and nuclear energy loss (Sn-due to inelastic collision) is calculated using SRIM-08 and is about 1911 eV/ Å and 39.54 eV/ Å respectively. The projected range of 120 MeV Au9+ ion in the films was also calculated and is 12.11 µm, 4
which is greater than the film thickness (800 nm). Thus, the bombarding Au ions pass through the whole sample and deposited in the glass. 3. Results and discussion 3.1 Structural analysis Fig.1 (a) represents the XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films at different fluencies: 1×1011, 1×1012 and 1×1013 ions/cm2. The low and high intensity peaks from the pristine samples at 2=23.10°, 27.30°, 40.66°, 67.20° and 77.10° correspond to (2 15), (1 0 5), (2114), (12 4 4) and (11 9 5) plane of In2(Te.Se)3, In2Se3 and In2Te3 phase [JCPDS: 76 – 1182, 71 – 0250, 23 – 0294 and 33 – 1488]. It is observed that no peak shifts in the irradiated samples and shows variation in the peak intensities only that reveals the good radiation stability of In2(Te.Se)3 system. For the low fluence of 1×1011 ions/cm2, the peak intensity decreases which indicate the grain fragmentation of the samples. Further, increase in ion fluences to 1×1012 ions/cm2 and 1×1013 ions/cm2 show similar trends as the intensity of the peaks found to decrease with ion fluence. Fig.1. (b & c) depicts the variations in peak intensity of XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films at different ion fluences. As evident, the intensity of the predominant peak at 2 = 27.30° is found to decrease with increase in the ion fluences in comparison to the pristine sample (see Fig.1.1 (b)). The other dominant peak at 2 = 40.66° also shows similar decrease in intensity with ion fluences especially at the highest ion fluence of 1×1013 ions/cm2. This is attributed to the grain fragmentation of the samples due to deposition of electronic energy induced by swift heavy ions. The essential structural parameters, grain size (D) [26], Dislocation density () [28], Strain (ε) [29] were estimated by the following equations; D = kλ / β.cosθ (nm) = 1/ D2 Lines/m2
5
ε = βcosθ/4 (dyn/cm2) Where, the constant ‘k’ is the shape factor = 0.94, ‘λ’ is the wavelength of X-rays (1.5406 nm for CuK), ‘’ is the Bragg’s angle and ‘β’ is the full width at half maximum of diffraction peak measured in radians. The calculated structural parameters for pristine and irradiated In2(Te0.94Se0.06)3samples are presented in Table.1. The average crystallite size is estimated and is about ~33.08 nm for pristine sample. For the sample irradiated at 1×1011 and 1×1012 ions/cm2 fluence, the average crystallite size is found to reduce to ~24.42 nm and ~19.61 nm respectively. Further, increase in ion fluence to 1×1013 ions/cm2 also reduces the crystallite size to ~16.89 nm, which evidently reveals the occurrence of grain fragmentation/recrystallization process in the material. The prominent decrease in the grain size with the rise in fluence is due to the irradiation induced lattice defects in the material. In general, the grain growth or grain fragmentation occurred in polycrystalline samples can be due to the spread of energy loss by SHI irradiation. In other words, this reduction in grain size can be attributed to the strain induced grain fragmentation of crystallites as well. The irradiation induced defects/strain in the crystallites can be explained by thermal spike model [5, 30] and Coulomb explosion model [31, 32]. Generally, SHI passes through the target deposits a large energy in the electronic sub-system of the material creating defects in case of thermal spike. This energy is excited by electron-electron coupling and transferred to the lattice atoms. Therefore, SHI irradiation through the system or target might produce a large increase in lattice temperature, which obviously leads to strain in the crystallite. In the case of coulomb explosion model, the ionized zone of the positive charged particle is extremely generated through the path of the incident ion by dominant electrostatic repulsive force which eventually induces strain in the system inside. Thus, existence or presence of strain may promote the fragmentation in the crystallites and grains. The induced strain in the films by SHI irradiation mostly produces grain fragmentation. In the case of dislocation density (), the value of increase with ion fluence clearly represents the more grain boundaries after irradiation. The significant increase in indicates the notable damage in the surface also, and is more consistent with the observed grain fragmentation from morphological studies. 6
3.2 Surface morphological analysis The high energy SHI irradiation induced effect in the surface modifications of pristine and at different fluence for In2(Te0.94Se0.06)3 system recorded using FESEM and AFM instruments. The pristine FESEM image shows the consistent distributions of spherically shaped grains throughout the entire surface of the sample and the change in the surface morphology with irradiation is denoted in Fig.2 (a-d). The large spherical shaped grains are split into smaller size grain with the initial fluence of 1×1011 ions/cm2 i.e. pristine sample undergoes grain fragmentation with SHI irradiation. Further increase in fluence to 1×1012 and 1×1013 ions/cm2 produces much smaller size grains or closely packed grains compared to pristine samples. The observed grains are very denser with increase in ion fluence. It is very clear that increase in ion fluence lead to large increase in density of grain boundaries that could be the presence of more defects, which can be attributed to increase in electrical resistivity of the materials. Increase in ion fluences assist the grain fragmentation that confirms enormous electronic energy was deposited in the material by Au9+ ion. Thus, mostly reduces the crystallite size which is comparatively well inline with the XRD studies. The films investigated in this study are of polycrystalline in nature. The XRD results provide the crystallite size which is generally calculated using the Scherrer formula. While XRD gives information about the crystallite size, the SEM image provides details of the grains. In general, grains are composed of many crystallites. In the present case, the estimated crystallite size from the XRD pattern is 33.08 nm. As evident in Fig.2 (a) of SEM image, the observed grain size is about ~150 nm. This implies that these grains observed in SEM are composed of many crystallites with sizes ~30 nm. The significant change in the surface morphology by Au9+ ion irradiation might influence the electrical transport properties of the present system to enhance the thermoelectric properties. Fig.3 represents EDS spectra of pristine and irradiated In2(Te0.94Se0.06)3 samples. The sharp peaks in the spectra corresponding to the presence of In, Se, and Te elements in the samples and listed in the Table.2.Variation in the irradiated samples has been observed in comparison to the pristine sample, it could be the irradiation induced high energy deposition in the materials by Au ions beam. 7
The 2D, 3D AFM micrograph images of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin film was recorded and is shown in Fig.4 (a, b). The appearance of spherically shaped grains in the pristine and irradiated samples shows a very similar to that of FESEM image of the samples. The evaluated value of average grain size from the 2D image for pristine sample is about ~45 nm. The irradiated samples grain size are about ~35 nm, ~25 nm, and ~15 nm corresponding to the ion fluence of 1×1011, 1×1012 and 1×1013 ions/cm2 respectively. The average values of surface roughness (Ra)and root mean square (RMS) Rq value are found to be ~15.54and ~19.13 nm for pristine sample. However, it is reduced to ~14.53 and ~18.14 nm with initial ion fluence of1×1011 ions/cm2. At 1×1012 ions/cm2, the roughness of the film reduced to 14.10 (Ra) and 17.38 nm (Rq) respectively. At 1×1013 ions/cm2, the Ra and Rq values are further reduced to 9.36 and 12.01 nm. The significant decrease in Ra and Rq values with increase in ion fluence reveals SHI induced surface smoothening process in the material [33, 34]. Moreover, the grains are very closely packed with irradiation that confirms melting followed by recrystallization. Hence, the decrease in grain size may be due to ion beam induced fragmentation or recrystallization process in the material. 3.3 Electrical transport properties Fig.5 shows the exponential increase in resistivity () with ion fluence (1×1011, 1×1012 and 1×1013 ions/cm2) and it exhibits higher resistivity compared to pristine sample. The resistivity of the pristine and irradiated samples decreases as a function of temperature confirming the semiconducting behavior in the films [35]. It is observed that, the nature of ρ plot increases significantly for the irradiated In2(Te0.94Se0.06)3 samples as compared to that of pristine sample. This behavior in ρ curve may be attributed to induced surface modification by ion beam irradiation through the creation of impurities, grain boundaries, defects etc. Hence, this leads to reduce the carrier mobility in the material caused by point defect scattering and ionised impurity scattering. Both the carrier concentration (n) and mobility (µ) are important factors for the contribution of electrical resistivity which is correlated by the relation: ρ=1/neµ. ByAu9+ ion beam irradiation, defects or impurities rises the value of n with increase in ion fluence. Additionally, the reduction in the µ value has been noted on the other side. Thus, ρ increases for the irradiated films. The high value of resistivity for irradiated sample has been observed from 8
the plot of resistivity versus temperature (shown in Fig.5); it shows increase in resistivity with increase in ion fluence. This could be due to the defects created on the surface by SHI irradiation at different ion fluence that may lead to reduce mobility of charge carriers as evident from the Hall measurement (shown in Fig.5 (inset)). Fig.5 (inset) shows the linear increase in the carrier concentration with increase in the ion fluences. The resistivity, carrier concentration and Hall mobility of the pristine and irradiated samples are presented in Table.3.The carrier concentration for the pristine sample is found to 9.151018cm-3. The carrier concentration at different ion fluence of 1×1011, 1×1012 and 1×1013ions/cm2 are found to about 14.881018, 26.361018, and44.081018cm-3 respectively (shown in Fig.5 (inset)). The enhancement in carrier concentration with rise in the ion fluence could be due to the increase in defects like vacancies or interstitial defects. The mobility of charge carriers decreased for the irradiated samples in comparison to the pristine sample that might be the only possible reason for the high resistivity value in the irradiated samples. Additionally, the carrier concentration also increases with the ion fluences. The carrier concentrations are higher at room temperature for the irradiated films as compared to the pristine sample, which leads to increase in electrical resistivity of the irradiated samples due to the decrease in the mobility of the charge carriers. Generally, ion beam irradiation enhances the resistivity due to the creation of defects. Hence, irradiated samples show higher resistivity and reveal the presence of higher carrier concentration and minimum carrier mobility that may be as a result of grain fragmentation as evident from the morphological studies. The higher carrier concentration in the irradiated samples also confirms the presence of more defects. The temperature dependent Seebeck coefficient (S) was measured in the temperature range from 300 K to 420 K and is represented inFig.6. The Seebeck coefficient values for pristine and irradiated In2(Te0.94Se0.06)3 sample are in negative that confirms n-type conductivity in the material which is consistent with Hall effect measurement. The Seebeck coefficient value for the pristine sample is found to ~196 µVK-1 at 400 K. The observed Seebeck coefficient is temperature dependent that confirms nature the semiconducting behavior. At 1×1011 ions/cm2, an improvement in Seebeck value has been observed and is found to ~246 µVK-1.The Seebeck value are further enhanced to ~309 µVK-1 and 347 µVK-1with increase in the ion fluence of 1×1012 and 1×1013 ions/cm2 respectively. Therefore, sample irradiated at higher fluence (1×1013 9
ions/cm2) enhances the Seebeck coefficient value of almost 80% greater than the pristine sample. The Seebeck coefficient behavior in the present material is consistent with the earlier report on n-type Indium Selenium and Bi2Te3-In2Te3 nanocomposites [36, 37]. Though, the observed results are consistent with earlier investigation, not many work reported on In2(Te0.94Se0.06)3 material especially by ion beam irradiation. Since, it will be difficult to compare the present results to the literature. However, increase in ion fluence shows a significant increase in S value that may be due to the SHI induced defects in the material. The carrier concentration is not only the major reason for the variation in the S value. Additionally, charge scattering in grain boundaries may also determine the electrical transport properties of the materials. From Fig.6 (inset), power factor (PF) value for pristine In2(Te0.94Se0.06)3 sample is found to ~1.28W/K2m. PF values are found to increase about ~1.91W/K2m and ~2.85W/K2m at the ion fluence of 1×1011and 1×1012ions/cm2respectively. At the higher fluence of 1×1013 ions/cm2, PF value further increased to~3.80W/K2m (shown in Fig.6). The power factor values are found to exponentially increase with the ion fluence that shows significant enhancement in the irradiated samples as compared to that of pristine sample. Evidently, the higher value of Seebeck coefficient leads to increase the power factor values for the irradiated samples in comparison to the pristine sample. The high thermo power value for the irradiated sample as compared to pristine sample is mostly because of grain fragmentation of large nanograins into tiny nanograins as evidenced from FESEM analysis. Therefore, the effect grain boundary scattering in the material could lead to influence the electrical transport properties [8]. The presence of high density of nanoscale grain boundaries might lead to the enhancement in thermoelectric properties of In2(Te0.94Se0.06)3 thin films. The observed results are consistent with the earlier reports and suggest that phonon scattering through nanoscale grain boundary results significant enhancement in thermoelectric [33, 38-40]. Moreover, Au9+ ion irradiation in the present system show better enhancement in the thermoelectric power, which could be attributed to SHI induced defects in the material as evident from the morphological studies. Generally, the small grain contains more grain boundaries that scatter electrons lightly and this lead to increase in electrical resistivity of the sample [41]. The significant image contrast in surface morphology at different ion fluence shows the smaller grain boundary in the sample 10
due to grain fragmentation by SHI irradiation denotes scattering of minimum electrons through the boundary region leads to increase the electrical resistivity of the material. In other words, reduced value for grain size and increase in carrier concentration may lead to the dramatic increase in electrical resistivity as compared to that of pristine sample. The electrical resistivity of the sample is found to increase with ion fluence and this might be the presence of larger grain boundary due to grain fragmentation, which has more scattering center in the film. Therefore, the number of scattering center leads to the rapid increase in the electrical resistivity. Hence, the enhancement in thermo power for the irradiated sample can be attributed to charge scattering due to the grain boundary [42, 43]. Additionally, point defects also could be one of the deciding factors of impurity scattering results enhancement in thermo power. The high thermo power value for the irradiated sample as compared to pristine sample is mostly because of contrast in charge scattering due to the grain boundary. 3.4 Optical properties From
Fig.9,
the
estimated
band
gap
energy
(Eg)
value
for
the
pristine
In2(Te0.94Se0.06)3sample is found to 0.71 eV. The Eg value for the sample irradiated at different ion fluence of 1×1011, 1×1012 and 1×1013 ions/cm2 are found to 0.73, 0.75 and 0.78 eV respectively. Therefore, the Eg value increases significantly with increase in ion fluence confirm the SHI irradiation induced defects in the material as evident from the morphological studies. It is well known that SHI irradiation can produce latent tracts in the central core region (high temperature zone), where the electronic energy loss is greater in number than the threshold value [44]. When the temperature raised above melting temperature of the target is mostly formed molten phase and is subsequently quenched under high cooling rate. Mostly, this could be the only reason to produce strain and frozen into the present material. Hence, this may induce a shift in energy levels correlates increase in the energy band gap [45]. Further, the temperature difference in the untrapped track region and the surrounding region is dissimilar, which can promote defect annealing in the material. Therefore, SHI irradiation induced defects levels in the system get annealed under the irradiation process and this leads to separation of conduction band and valence band tails states. Obviously, this is the only possible reason for the increased band
11
gap energy values of irradiated samples, concludes the influence of electronic energy loss in the present material. 4. Summary Above study reported an enhancement in thermoelectric properties of the Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films. The pristine and irradiated films show negative value of Seebeck and Hall coefficient that confirms the n-type conductivity in the films. The Seebeck coefficient value for pristine sample is found to ~196 µVK- at 400 K1 and it is enhanced to ~347 µVK-1 at high fluence of 1×1013 ions/cm2, shows almost 80% higher than the pristine sample value. At 1×1013 ions/cm2 ion fluence, the PF value was found to about ~3.80W/K2m denotes 3 times greater value as compared to that of pristine sample value of ~1.28W/K2m. The morphology studies show significant change in surface due to grain fragmentation with increase in ion fluences. Additionally, the enhancement of thermopower in the present material could be due to induced defects by ion beam irradiation as evident from the morphological studies. Moreover, presence of high density of nanoscale grain boundaries that may also lead to the enhancement in thermoelectric properties of In2(Te0.94Se0.06)3 thin films. Acknowledgement The authors (P.M and M.P) greatly acknowledge the Inter University Accelerator Centre (IUAC) New Delhi, for providing financial support through the project UFR-57306. One of the authors (Pandian) acknowledges Tamkang University for providing the opportunity to visit Research Center for X-ray Science & Department of Physics and the financial support by MOST under project number MoST 107-2112-M-032-004-MY3. Reference [1]
A.I. Ryazanov, A.E. Volkov, S. Klaumünzer, Model of track formation, Phys. Rev. B. 51 (1995) 12107.
[2]
R.C. Birtcher, S.E. Donnelly, S. Schlutig, Nanoparticle ejection from Au induced by single Xe ion impacts, Phys. Rev. Lett. 85 (2000) 4968-4971.
[3]
S. Habenicht, W. Bolse, K.P. Lieb, K. Reimann, U. Geyer, Nanometer ripple formation 12
and self-affine roughening of ion-beam-eroded graphite surfaces, Phys. Rev. B Condens. Matter Mater. Phys. 60 (1999) R2200-R2203. [4]
P.C. Srivastava, V. Ganesan, O.P. Sinha, AFM studies of swift heavy ion-irradiated surface modification in Si and GaAs, in: Radiat. Meas., 36 (2003) 671 – 674.
[5]
M. Toulemonde, C. Dufour, E. Paumier, Transient thermal process after a high-energy heavy-ion irradiation of amorphous metals and semiconductors, Phys. Rev. B. 46 (1992) 14362-14369.
[6]
D. Kraemer, B. Poudel, H.P. Feng, J.C. Caylor, B. Yu, X. Yan, Y. Ma, X. Wang, D. Wang, A. Muto, K. McEnaney, M. Chiesa, Z. Ren, G. Chen, High-performance flat-panel solar thermoelectric generators with high thermal concentration, Nat. Mater. 10 (2011) 532–538.
[7]
Masashi Komabayashi, Ken-ichi Hijikata and Shunji Ido, Effects of Some Additives on Thermoelectric Properties of FeSi2 Thin Films, Japan Society of Applied Physics, 30 (1991)331-334.
[8]
I. Sanyal, K. K. Chattopadhyay, S. Chaudhuri, and A. K. Pal, Grain boundary scattering in CuInSe2 films, J. Appl. Phys. 70(1991) 841.
[9]
Xin Bo, Aiyue Tang, Meiling Dou, Zhilin Li, Feng Wang, Controllable electrodeposition and mechanism research of nanostructured Bi2Te3thin films with high thermoelectric properties, Applied Surface Science, 486 (2019) 65-71.
[10] Hye Jin Im, Bokun Koo, Min-Soo Kim, Ji Eun Lee, Solvothermal synthesis of Sb2Te3 nanoplates under various synthetic conditions and their thermoelectric properties,Applied Surface Science, 475 (2019) 510-514. [11] L.-D. Zhao, C. Chang, G. Tan, and M. G. Kanatzidis, SnSe: A remarkablenew thermoelectric material, Energy Environ. Sci. 9(2016) 3044. [12] Dong-Hyeon Kim, Dong-Hoon Lee, Effect of irradiation on the surface morphology of nanostructured superhydrophobic surfaces fabricated by ion beam irradiation,477 (2019)154-158. [13] Lijuan Zhao,Yi He,Huan Zhang,Longfei Yi,Jinrong Wu, Enhancing the thermoelectric property of Bi2Te3 through a facile design of interfacial phonon scattering,Journal of Alloys and Compounds, 768 (2018) 659-666. 13
[14] D. Mohanta, N.C. Mishra, A. Choudhury, SHI-induced grain growth and grain fragmentation effects in polymer-embedded CdS quantum dot systems, Mater. Lett. 58 (2004) 3694– 3699. [15] R.Panda,M.Panda,H.Rath,B.N.Dash,K.Asokan,U.P.Singh,R.Naik,N.C.Mishra, Structural and morphological modifications of AgInSe2 and Ag2Se composite thin films on 140 MeV Ni ion irradiation,Applied Surface Science, 479 (2019) 997-1005. [16] A.S. El-Said, R.A. Wilhelm, S. Facsko, C. Trautmann, Surface nanostructuring of LiNbO3by high-density electronic excitations, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 315 (2013) 265-268. [17] Y.T. Huang, C.W. Huang, J.Y. Chen, Y.H. Ting, K.C. Lu, Y.L. Chueh, W.W. Wu, Dynamic observation of phase transformation behaviors in indium(iii) selenide nanowire based phase change memory, ACS Nano. 8 (2014) 9457–9462. [18] A. Thakur, G. Singh, G.S.S. Saini, N. Goyal, S.K. Tripathi, Optical properties of amorphous Ge20Se80and Ag6(Ge0.20Se0.80)94thin films, Opt. Mater. (Amst). 30 (2007) 565570. [19]
S.R.Alharbi,K.A.Aly,Electrical and thermoelectric properties of ternary Cu-Ge-Te films,Journal of Alloys and Compounds, 797 (2019) 710-716.
[20]
T. Talebi, R. Ghomashchi, P. Talemi, S. Aminorroaya, Thermoelectric performance of electrophoretically deposited p-type Bi2Te3film, Appl. Surf. Sci. 477 (2019) 27-31.
[21]
J. Kim, J.-H. Lim, N. V. Myung, Composition- and crystallinity-dependent thermoelectric properties of ternary Bi x Sb 2-x Te y films, Appl. Surf. Sci. 429 (2018) 158-163.
[22]
M. Bala, A. Bhogra, S.A. Khan, T.S. Tripathi, S.K. Tripathi, D.K. Avasthi, K. Asokan, Enhancement of thermoelectric power of PbTe thin films by Ag ion implantation, J. Appl. Phys. 121 (2017) 215301.
[23]
S. Gupta, D.C. Agarwal, S.K. Tripathi, S. Neeleshwar, B.K. Panigrahi, A. Jacquot, B. Lenoir, D.K. Avasthi, Superiority of ion irradiation over annealing for enhancing the thermopower of PbTe thin films, Radiat. Phys. Chem. 86 (2013) 6-9.
[24]
C.H. Chien, P.C. Lee, W.H. Tsai, C.H. Lin, C.H. Lee, Y.Y. Chen, In-situ Observation of Size and Irradiation Effects on Thermoelectric Properties of Bi-Sb-Te Nanowire in FIB Trimming, Sci. Rep. 6 (2016) 23672. 14
[25]
A. Bali, R. Chetty, A. Sharma, G. Rogl, P. Heinrich, S. Suwas, D.K. Misra, P. Rogl, E. Bauer, R.C. Mallik, Thermoelectric properties of in and i doped PbTe, J. Appl. Phys. 120 (2016) 175101.
[26]
T.S. Tripathi, M. Bala, K. Asokan, An experimental setup for the simultaneous measurement of thermoelectric power of two samples from 77 K to 500 K, Rev. Sci. Instrum. 85 (2014) 085115.
[27]
D.N. Bose, S. De Purkayastha, Dielectric and photoconducting properties of Ga2Te3 and In2Te3 crystals, Mat. Res. Bull. 16 (1981) 635–642.
[28]
V. Riede, H. Neumann, H. Sobotta, A.R. Miedema, Infrared optical properties of InTe InTe, Solid State Commun. 38 (1981) 71–73.
[29]
R. Rousina, G.K. Shivakumar, Electron diffraction study of vacuumm deposited In2Te3 thin films, Surf. Coatings Technol. 38 (1989) 353–358.
[30]
Z.G. Wang, C. Dufour, E. Paumier, M. Toulemonde, The Sesensitivity of metals under swift-heavy-ion irradiation: A transient thermal process, J. Phys. Condens. Matter. 6 (1994) 6733-6750.
[31]
E.M. Bringa, R.E. Johnson, Coulomb Explosion and Thermal Spikes, Phys. Rev. Lett. 88 (2002) 165501.
[32]
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.
[33]
H. Narayan, S.B. Samanta, H.M. Agrawal, R.P.S. Kushwaha, D. Kanjilal, S.K. Sharma, A. V. Narlikar, An SEM and STM investigation of surface smoothing in 130 MeV Siirradiated metglass MG2705M, J. Phys. Condens. Matter. 11 (1999) 2679–2687.
[34]
V. Kumar, R.G. Singh, L.P. Purohit, F. Singh, Effect of swift heavy ion on structural and optical properties of undoped and doped nanocrystalline zinc oxide films, Adv. Mater. Lett. 4 (2013) 423-427.
[35]
H.M. Pathan, S.S. Kulkarni, R.S. Mane, C.D. Lokhande, Preparation and characterization of indium selenide thin films from a chemical route, Mater. Chem. Phys. 93 (2005) 16–20.
[36]
J. H. Yim, H. H. Park, H. W. Jang, M. J. Yoo, D. S. Paik, S. Baek and J. S. Kim, Thermoelectric properties of indium-selenium nanocomposites prepared by mechanical
15
alloying and spark sintering, J. Elect. Mater. 41 (2012)1354-1359.doi:10.1007/s11664012-1940-x. [37]
D. Liu, X. Li, P.M. Borlido, S. Botti, R. Schmechel and M. Rettenmayr, Anisotropic layered Bi2Te3-In2Te3composites: control of interface density for tuning of thermoelectric properties, Sci. Rep. 7 (2017) 43611.
[38]
H. Wu, J. Carrete, Z. Zhang, Y. Qu, X. Shen, Z. Wang, L. D. Zhao, J. Q. He, Strong Enhancement of Phonon Scattering through Nanoscale Grains in Lead Sulfide Thermoelectrics. NPG Asia Mater.6 (2014) e108.
[39]
B. Poudel, Q. Hao, Y. Ma, Y. Lan, A. Minnich, B. Yu, X. Yan, D. Wang, A. Muto, D. Vashaee, X. Chen, J. Liu, M. S. Dresselhaus, G. Chen and Z. Ren, Highthermoelectric performance of nanostructured bismuth antimony telluride bulk alloys. Science 320 (2008) 634–638.
[40]
Y. Lan, B. Poudel, Y. Ma, D. Wang, M. S. Dresselhaus, G. Chen, and Z. Ren, Structure study of bulk nanograined thermoelectric bismuth antimony telluride. Nano Lett. 9 (2009) 1419-1422.
[41]
A. Khan, M. Saleemi, M. Johnsson, L. Han, N.V. Nong, M. Muhammed, M.S. Toprak, Fabrication, spark plasma consolidation, and thermoelectric evaluation of nanostructured CoSb3,J. Alloys Compd. 612 (2014) 293-300.
[42]
J. Martin, L. Wang, L. Chen, G.S. Nolas, Enhanced Seebeck coefficient through energybarrier scattering in PbTe nanocomposites, Phys. Rev. B - Condens. Matter Mater. Phys. 79 (2009) 115311.
[43]
A. Popescu, L.M. Woods, J. Martin, G.S. Nolas, Model of transport properties of thermoelectric nanocomposite materials, 79 (2009) 205302.
[44]
S.K. Srivastava, D.K. Avasthi, Swift heavy ion-induced mixing, Def. Sci. J. 59 (2009) 425-435.
[45]
D.K. Avasthi, G. Mehta, Swift Heavy Ions for Material Engineering and Nanostructuring, Springer Publication, 2011 (Chapter 6).
16
Fig.1 (a) XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films
Fig.1 (b&c) XRD pattern of variation in the peak intensities of In2(Te0.94Se0.06)3thin films 17
Fig.2 (a-d) FESEM image of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thinfilms
18
Fig.3 EDS spectra of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films
Fig.4 (a, b) 2D and 3D AFM image of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films 19
Fig.5Electrical resistivity (ρ) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 thin films. Inset shows the results from the Hall effect measurements
20
Fig.6 Seebeck coefficient (S) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 films. Inset shows the S2.
21
Fig.7 Tau’s plot of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin film
22
Table.1. Structural Parameters of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films Sample In2(Te1-xSex)3
2Ѳ (degree) 23.11 27.65
Pristine 40.555 67.08 23.14 1×1011 ions/cm2
27.59 40.64 67.08 23.14
1×1012 ions/cm2
27.59 40.64 67.08 23.14
1×1013 ions/cm2
27.59 40.64 67.08
Phase & Orientation (hkl)
Average Crystalline Size (nm)
In2(Se.Te)3 (215) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4) In2Te3 (333) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4) In2Te3 (333) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4) In2Te3 (333) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4)
33.08
24.42
19.61
16.89
23
Dislocation Strain FWHM Density (ε) (β) Lines/m2 2 (degree) dyn/cm (1015) 0.00105
0.0644
0.263
0.00042
0.0407
0.168
0.0006
0.109
0.429
0.0122
0.219
1.053
0.0016
0.079
0.326
0.0018
0.085
0.354
0.0015
0.082
0.377
0.0119
1.030
1.04
0.0018
0.114
0.436
0.0013
0.081
0.334
0.0040
0.125
0.537
0.0121
0.218
1.05
0.0034
0.101
0.473
0.0012
0.991
0.287
0.039
0.393
1.679
0.0121
0.218
1.05
Table.2 Elemental compositions of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin film In2(Te1-xSex)3
Elemental composition (wt.%) In
Te
Se
Pristine
43.70
50.40
5.90
1×1011 ions/cm2
38.91
54.14
6.95
1×1012 ions/cm2
35.93
58.80
5.27
1×1013 ions/cm2
37.89
53.92
6.19
Table.3 Hall effect measurement of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin film Carrier concentration
Resistivity
Hall mobility
( Ω-cm)
μH (cm3/V.s)
Pristine
0.982
259.20
9.15 1018
1×1011 ions/cm2
1.255
105.91
14.88 1018
1×1012 ions/cm2
1.580
22.89
26.36 1018
1×1013 ions/cm2
1.804
7.14
44.08 1018
In2(Te1-xSex)3
NH (cm-3)
Table.4 Band gap energy of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Samples Bandgap Energy (eV)
Pristine 0.71
1×1011
1×1012
1×1013
ions/cm2
ions/cm2
ions/cm2
0.73
0.75
0.78
24
Figure captions Fig.1 (a) XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films, (b & c) XRD pattern of variation in the peak intensities of In2(Te0.94Se0.06)3 thin films Fig.2 (a-d) FESEM image of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Fig.3 EDS spectra of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Fig.4 (a, b) 2D and 3D AFM images of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Fig.5 Electrical resistivity (ρ) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 thin films. Inset shows the results from the Hall effect measurements Fig.6 Seebeck coefficient (S) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 films. Inset shows the S2. Fig.7 Tau’s plot of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films
Table caption Table.1 Structural Parameters of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films Table.2 Elemental compositions of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films Table.3 Hall effect measurement of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films, Table.4 Band gap energy of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films
25
S0169-4332(19)32931-9 https://doi.org/10.1016/j.apsusc.2019.144115 APSUSC 144115
To appear in:
Applied Surface Science
Received Date: Revised Date: Accepted Date:
10 July 2019 14 September 2019 19 September 2019
Please cite this article as: P. Mannu, M. Palanisamy, G. Bangaru, S. Ramakrishnan, M. Ramcharan, C-L. Dong, A. Kandasami, Enhancement of thermoelectric performance of n-type In2(Te0.94Se0.06)3 thin films by electronic excitations, Applied Surface Science (2019), doi: https://doi.org/10.1016/j.apsusc.2019.144115
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Enhancement of thermoelectric performance of n-type In2(Te0.94Se0.06)3 thin films by electronic excitations Pandian Mannu a, Matheswaran Palanisamy a*, Gokul Bangaru a, Sathyamoorthy Ramakrishnan a, Meena Ramcharan b, Chung-Li Dong c, Asokan Kandasami b* a Department of Physics, Kongunadu Arts and Science College, Coimbatore, Tamilnadu, 641029, India b Materials
Science Division, Inter University Accelerator Centre, New Delhi - 110067, India
c Research
Center for X-ray Science & Department of Physics, Tamkang University,
Tamsui 25137, Taiwan. * email addresses: [email protected], [email protected] Abstract Thermoelectric properties of metal chalcogenide based materials exhibit a great suitability in the field of energy sustainability. This study reports the thermoelectric properties of In2(Te0.94Se0.06)3films prepared by thermal evaporation after the electronic excitations produced by 120 MeV Au ions. The Seebeck coefficient value for pristine sample is found to be ~196µVK-1 and it is enhanced to ~347 µVK-1 at the higher fluence of 1×1013 ions/cm2 at 400 K. The negative value of Seebeck coefficient and the Hall effect measurements confirm the n-type conductivity in the pristine and irradiated In2(Te0.94Se0.06)3 samples. The power factor value of thin films irradiated at the fluence of 1×1013 ions/cm2is ~3.80W/K2m, as compared to pristine sample ~1.28W/K2m.The change in image contrast in FESEM is due to grain fragmentation with increase in ion fluence in comparison to the pristine sample. It is evident that the electrical resistivity and power factor values are higher for irradiated samples as compared to that of pristine samples. Moreover, presence of high density of nanoscale grain boundaries created by ion irradiations lead to the enhancement in thermoelectric properties of In2(Te0.94Se0.06)3 thin films. Keywords: Metal chalcogenide, thermal evaporation, SHI irradiation, Seebeck coefficient and thermoelectric power
1
I. Introduction The application of ion beam in solid state materials has become an important topic in the scientific point of view, to understand the ion beams interaction of surface and interface modifications through the optical, electrical, morphological and optoelectronic properties [1-4]. Swift heavy ion beam irradiation (SHI) in a solid state system induced the formation of nanostructures on the surface and it was introduced a few decades ago [5]. In addition to that, investigations of radiation induced defects in metal chalcogenide semiconducting materials have been an important task for the new technological improvement in device fabrication. The extent of radiation damage models which depends strongly energy, mass and additionally, its fluence target density. On property modification like interfacial atoms, displacement spike or thermal spike and vacant lattice sites have been reported by many research groups [3-5].The high energy deposition on the target materials promotes the production of defects and morphological changes, so that when SHI traversing into the target material, most of it energy loses by exciting electron or ionization of atoms. Se-Te based chalcogenides materials have the large impact on the performance of thermoelectric devices in the field of energy sustainability for the present fast-growing generation. The energy conversion of thermal to electrical energy in these chalcogenide materials has the intensive role to tailoring the thermoelectric performance of the devices. Considering these facts, the efficiency of thermoelectric materials is evaluated by a dimensionless figure of merit, ZT =
S2T k
[6][7] (where S, , T, and k are Seebeck coefficient, electrical conductivity,
absolute temperature at which figure of merit is measured and thermal conductivity respectively). Thermoelectric properties can also determined by well known expression called power factor (PF) as PF= S2. Generally, the best thermoelectric material should have a greater value of S and , a low value for k is necessary. In general, grain boundary scattering has an important role to determine the electrical transport properties of chalcogenide based materials and especially, nanostructured chalcogenide thermoelectric materials can also improve the S and , which enhance the thermoelectric device performance [8-10]. Lattice vibrations (phonons) are responsible for the transport of thermal energy in chalcogenide semiconductors [11]. Therefore, introducing efficient phonon scattering centers through high density of grain boundaries in 2
nanosized grains is best known process to reduce thermal energy. Enormous effort has been made to enhance the thermoelectric performance by introducing nanostructure in chalcogenide based materials with different techniques [12][13]. SHI irradiation on the semiconducting materials induces many interesting phenomena like grain fragmentation, grain alignment, surface, and morphological changes [14-16].This ion irradiation induces electronic excitation and phonon contributions due to the scattering processes through grain fragmentation/grain alignment. Ion beam irradiation on these chalcogenide materials can improve the electrical transport properties to enhance the thermoelectric performance. Therefore, metal chalcogenide based materials have been used for a long time to the fabrication of electronic devices such as phase change memory, optoelectronic, and thermoelectric devices [17-19]. Among all these chalcogenide materials, only few authors reported the thermoelectric performance of metal chalcogenide based materials, namely Tahereh Talebi et al. performed thermoelectric performance of p-type Bi2Te3 thin films and the Seebeck coefficient value was about ~239V/K [20]. Transition of p-type and n-type conductivity behavior with the addition of Bismuth in to BixSb2-xTey thin film have been reported by Jiwon Kim et al.[21], showed good enhancement in both Seebeck coefficient and thermal conductivity. In addition, 25% enhancements in Seebeck coefficient for PbTe thin film by Ag ion implantation have been reported by Bala et al[22]. Srashti Gupta et al. reported 100 MeV Ag7+ ion irradiated PbTe thin film which showed ~40 % increase in thermo power compared to the pristine and it was explained by carrier scattering due to the defects present in the material or density of state [23]. Recently, Chia-Hua chien et al. studied the enhancement in thermoelectric properties of Bi-Sb-Te nanowire by Gallium ion irradiation revealed large number of phonon scattering of defects created during the irradiation leads to the reduction in thermal conductivity and subsequently performed size dependent Seebeck coefficient and Figure of merit (ZT) [24]. Ashoka Bali et al. reported a maximum power factor of ~25 W cm-1K-2 for In and I doped PbTe bulk samples. Further, they have shown a maximum zT of 1.12 for In doped and 1.1 for Indium and Iodine doped samples [25]. In2(Te1xSex)3
is a layered compound belongs to AIII2BII3 semiconductors having disordered structure
with cation vacancies will be a promising candidate for near room temperature (300-400 K) thermoelectric devices. Moreover, electronic excitation induced by the ion beam irradiation on 3
thermoelectric properties of In-Se-Te materials is not so far investigated to the best of our knowledge. Hence, in this study, the focus is on the thermoelectric properties of Au9+ (120 MeV) ions irradiated In2(Te1-xSex)3 system. The structural and thermoelectric properties are studied and results suggest that ion beams as a promising technique to manipulate the thermoelectric performance of metal chalcogenide thin films. 2. Materials and methods In2(Te1-xSex)3thin film of thickness 800 nm were deposited on a cleaned glass substrate by thermal evaporation under Ar atmosphere at a reduced pressure 2×10-6mbar. The elements of In, Se and Te (5N- purity) with desired composition 40%:6%:54% were taken into the quartz tube and quartz ampoules were fused at a reduced 2x10-5 mbar pressure, subsequently the sealed quartz tube were annealed at 950 °C for 12 hours in rotating furnace. The temperature of the furnace was raised slowly at a rate of 2-3 °C per minute and constantly rocked by rotating the ceramic rod to get the In2(Te0.94Se0.06)3 stoichiometric alloys compound. The molten state samples were quenched to room temperature and quenched materials were taken out by breaking the quartz tube. The ingots were grained to make In2(Te0.94Se0.06)3 fine powder for the film deposition. The structural studies were performed by X-ray diffraction (XRD) using Bruker AXS (D-8 advanced, Germany) diffractometer model in the scanning range 20-80° (2ϴ) with the wavelength of 1.5406 Å. The surface morphology and elemental composition of the samples were recorded using MIRA TESCAN model scanning electron microscopy (SEM) and atomic force microscopy (AFM) on Nanoscope IIIa digital instruments at IUAC, New Delhi. Using four probes and bridge methods, the electrical resistivity (ρ) and Seebeck coefficient of the samples were measured [26]. The prepared thin film samples were irradiated with 120 MeV Au9+ ions for the fluence of 1×1011 to1×1013 ions/cm2 at a current of 0.50 pnA (particle nano Ampere) using 15 UD Pelletron at Inter University Accelerator Center (IUAC), New Delhi, the projected ions were scanned over the targets using the electrostatic scanner. For the Au9+ ion irradiation, the value of the electronic energy loss (Se-due to elastic collision) and nuclear energy loss (Sn-due to inelastic collision) is calculated using SRIM-08 and is about 1911 eV/ Å and 39.54 eV/ Å respectively. The projected range of 120 MeV Au9+ ion in the films was also calculated and is 12.11 µm, 4
which is greater than the film thickness (800 nm). Thus, the bombarding Au ions pass through the whole sample and deposited in the glass. 3. Results and discussion 3.1 Structural analysis Fig.1 (a) represents the XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films at different fluencies: 1×1011, 1×1012 and 1×1013 ions/cm2. The low and high intensity peaks from the pristine samples at 2=23.10°, 27.30°, 40.66°, 67.20° and 77.10° correspond to (2 15), (1 0 5), (2114), (12 4 4) and (11 9 5) plane of In2(Te.Se)3, In2Se3 and In2Te3 phase [JCPDS: 76 – 1182, 71 – 0250, 23 – 0294 and 33 – 1488]. It is observed that no peak shifts in the irradiated samples and shows variation in the peak intensities only that reveals the good radiation stability of In2(Te.Se)3 system. For the low fluence of 1×1011 ions/cm2, the peak intensity decreases which indicate the grain fragmentation of the samples. Further, increase in ion fluences to 1×1012 ions/cm2 and 1×1013 ions/cm2 show similar trends as the intensity of the peaks found to decrease with ion fluence. Fig.1. (b & c) depicts the variations in peak intensity of XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films at different ion fluences. As evident, the intensity of the predominant peak at 2 = 27.30° is found to decrease with increase in the ion fluences in comparison to the pristine sample (see Fig.1.1 (b)). The other dominant peak at 2 = 40.66° also shows similar decrease in intensity with ion fluences especially at the highest ion fluence of 1×1013 ions/cm2. This is attributed to the grain fragmentation of the samples due to deposition of electronic energy induced by swift heavy ions. The essential structural parameters, grain size (D) [26], Dislocation density () [28], Strain (ε) [29] were estimated by the following equations; D = kλ / β.cosθ (nm) = 1/ D2 Lines/m2
5
ε = βcosθ/4 (dyn/cm2) Where, the constant ‘k’ is the shape factor = 0.94, ‘λ’ is the wavelength of X-rays (1.5406 nm for CuK), ‘’ is the Bragg’s angle and ‘β’ is the full width at half maximum of diffraction peak measured in radians. The calculated structural parameters for pristine and irradiated In2(Te0.94Se0.06)3samples are presented in Table.1. The average crystallite size is estimated and is about ~33.08 nm for pristine sample. For the sample irradiated at 1×1011 and 1×1012 ions/cm2 fluence, the average crystallite size is found to reduce to ~24.42 nm and ~19.61 nm respectively. Further, increase in ion fluence to 1×1013 ions/cm2 also reduces the crystallite size to ~16.89 nm, which evidently reveals the occurrence of grain fragmentation/recrystallization process in the material. The prominent decrease in the grain size with the rise in fluence is due to the irradiation induced lattice defects in the material. In general, the grain growth or grain fragmentation occurred in polycrystalline samples can be due to the spread of energy loss by SHI irradiation. In other words, this reduction in grain size can be attributed to the strain induced grain fragmentation of crystallites as well. The irradiation induced defects/strain in the crystallites can be explained by thermal spike model [5, 30] and Coulomb explosion model [31, 32]. Generally, SHI passes through the target deposits a large energy in the electronic sub-system of the material creating defects in case of thermal spike. This energy is excited by electron-electron coupling and transferred to the lattice atoms. Therefore, SHI irradiation through the system or target might produce a large increase in lattice temperature, which obviously leads to strain in the crystallite. In the case of coulomb explosion model, the ionized zone of the positive charged particle is extremely generated through the path of the incident ion by dominant electrostatic repulsive force which eventually induces strain in the system inside. Thus, existence or presence of strain may promote the fragmentation in the crystallites and grains. The induced strain in the films by SHI irradiation mostly produces grain fragmentation. In the case of dislocation density (), the value of increase with ion fluence clearly represents the more grain boundaries after irradiation. The significant increase in indicates the notable damage in the surface also, and is more consistent with the observed grain fragmentation from morphological studies. 6
3.2 Surface morphological analysis The high energy SHI irradiation induced effect in the surface modifications of pristine and at different fluence for In2(Te0.94Se0.06)3 system recorded using FESEM and AFM instruments. The pristine FESEM image shows the consistent distributions of spherically shaped grains throughout the entire surface of the sample and the change in the surface morphology with irradiation is denoted in Fig.2 (a-d). The large spherical shaped grains are split into smaller size grain with the initial fluence of 1×1011 ions/cm2 i.e. pristine sample undergoes grain fragmentation with SHI irradiation. Further increase in fluence to 1×1012 and 1×1013 ions/cm2 produces much smaller size grains or closely packed grains compared to pristine samples. The observed grains are very denser with increase in ion fluence. It is very clear that increase in ion fluence lead to large increase in density of grain boundaries that could be the presence of more defects, which can be attributed to increase in electrical resistivity of the materials. Increase in ion fluences assist the grain fragmentation that confirms enormous electronic energy was deposited in the material by Au9+ ion. Thus, mostly reduces the crystallite size which is comparatively well inline with the XRD studies. The films investigated in this study are of polycrystalline in nature. The XRD results provide the crystallite size which is generally calculated using the Scherrer formula. While XRD gives information about the crystallite size, the SEM image provides details of the grains. In general, grains are composed of many crystallites. In the present case, the estimated crystallite size from the XRD pattern is 33.08 nm. As evident in Fig.2 (a) of SEM image, the observed grain size is about ~150 nm. This implies that these grains observed in SEM are composed of many crystallites with sizes ~30 nm. The significant change in the surface morphology by Au9+ ion irradiation might influence the electrical transport properties of the present system to enhance the thermoelectric properties. Fig.3 represents EDS spectra of pristine and irradiated In2(Te0.94Se0.06)3 samples. The sharp peaks in the spectra corresponding to the presence of In, Se, and Te elements in the samples and listed in the Table.2.Variation in the irradiated samples has been observed in comparison to the pristine sample, it could be the irradiation induced high energy deposition in the materials by Au ions beam. 7
The 2D, 3D AFM micrograph images of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin film was recorded and is shown in Fig.4 (a, b). The appearance of spherically shaped grains in the pristine and irradiated samples shows a very similar to that of FESEM image of the samples. The evaluated value of average grain size from the 2D image for pristine sample is about ~45 nm. The irradiated samples grain size are about ~35 nm, ~25 nm, and ~15 nm corresponding to the ion fluence of 1×1011, 1×1012 and 1×1013 ions/cm2 respectively. The average values of surface roughness (Ra)and root mean square (RMS) Rq value are found to be ~15.54and ~19.13 nm for pristine sample. However, it is reduced to ~14.53 and ~18.14 nm with initial ion fluence of1×1011 ions/cm2. At 1×1012 ions/cm2, the roughness of the film reduced to 14.10 (Ra) and 17.38 nm (Rq) respectively. At 1×1013 ions/cm2, the Ra and Rq values are further reduced to 9.36 and 12.01 nm. The significant decrease in Ra and Rq values with increase in ion fluence reveals SHI induced surface smoothening process in the material [33, 34]. Moreover, the grains are very closely packed with irradiation that confirms melting followed by recrystallization. Hence, the decrease in grain size may be due to ion beam induced fragmentation or recrystallization process in the material. 3.3 Electrical transport properties Fig.5 shows the exponential increase in resistivity () with ion fluence (1×1011, 1×1012 and 1×1013 ions/cm2) and it exhibits higher resistivity compared to pristine sample. The resistivity of the pristine and irradiated samples decreases as a function of temperature confirming the semiconducting behavior in the films [35]. It is observed that, the nature of ρ plot increases significantly for the irradiated In2(Te0.94Se0.06)3 samples as compared to that of pristine sample. This behavior in ρ curve may be attributed to induced surface modification by ion beam irradiation through the creation of impurities, grain boundaries, defects etc. Hence, this leads to reduce the carrier mobility in the material caused by point defect scattering and ionised impurity scattering. Both the carrier concentration (n) and mobility (µ) are important factors for the contribution of electrical resistivity which is correlated by the relation: ρ=1/neµ. ByAu9+ ion beam irradiation, defects or impurities rises the value of n with increase in ion fluence. Additionally, the reduction in the µ value has been noted on the other side. Thus, ρ increases for the irradiated films. The high value of resistivity for irradiated sample has been observed from 8
the plot of resistivity versus temperature (shown in Fig.5); it shows increase in resistivity with increase in ion fluence. This could be due to the defects created on the surface by SHI irradiation at different ion fluence that may lead to reduce mobility of charge carriers as evident from the Hall measurement (shown in Fig.5 (inset)). Fig.5 (inset) shows the linear increase in the carrier concentration with increase in the ion fluences. The resistivity, carrier concentration and Hall mobility of the pristine and irradiated samples are presented in Table.3.The carrier concentration for the pristine sample is found to 9.151018cm-3. The carrier concentration at different ion fluence of 1×1011, 1×1012 and 1×1013ions/cm2 are found to about 14.881018, 26.361018, and44.081018cm-3 respectively (shown in Fig.5 (inset)). The enhancement in carrier concentration with rise in the ion fluence could be due to the increase in defects like vacancies or interstitial defects. The mobility of charge carriers decreased for the irradiated samples in comparison to the pristine sample that might be the only possible reason for the high resistivity value in the irradiated samples. Additionally, the carrier concentration also increases with the ion fluences. The carrier concentrations are higher at room temperature for the irradiated films as compared to the pristine sample, which leads to increase in electrical resistivity of the irradiated samples due to the decrease in the mobility of the charge carriers. Generally, ion beam irradiation enhances the resistivity due to the creation of defects. Hence, irradiated samples show higher resistivity and reveal the presence of higher carrier concentration and minimum carrier mobility that may be as a result of grain fragmentation as evident from the morphological studies. The higher carrier concentration in the irradiated samples also confirms the presence of more defects. The temperature dependent Seebeck coefficient (S) was measured in the temperature range from 300 K to 420 K and is represented inFig.6. The Seebeck coefficient values for pristine and irradiated In2(Te0.94Se0.06)3 sample are in negative that confirms n-type conductivity in the material which is consistent with Hall effect measurement. The Seebeck coefficient value for the pristine sample is found to ~196 µVK-1 at 400 K. The observed Seebeck coefficient is temperature dependent that confirms nature the semiconducting behavior. At 1×1011 ions/cm2, an improvement in Seebeck value has been observed and is found to ~246 µVK-1.The Seebeck value are further enhanced to ~309 µVK-1 and 347 µVK-1with increase in the ion fluence of 1×1012 and 1×1013 ions/cm2 respectively. Therefore, sample irradiated at higher fluence (1×1013 9
ions/cm2) enhances the Seebeck coefficient value of almost 80% greater than the pristine sample. The Seebeck coefficient behavior in the present material is consistent with the earlier report on n-type Indium Selenium and Bi2Te3-In2Te3 nanocomposites [36, 37]. Though, the observed results are consistent with earlier investigation, not many work reported on In2(Te0.94Se0.06)3 material especially by ion beam irradiation. Since, it will be difficult to compare the present results to the literature. However, increase in ion fluence shows a significant increase in S value that may be due to the SHI induced defects in the material. The carrier concentration is not only the major reason for the variation in the S value. Additionally, charge scattering in grain boundaries may also determine the electrical transport properties of the materials. From Fig.6 (inset), power factor (PF) value for pristine In2(Te0.94Se0.06)3 sample is found to ~1.28W/K2m. PF values are found to increase about ~1.91W/K2m and ~2.85W/K2m at the ion fluence of 1×1011and 1×1012ions/cm2respectively. At the higher fluence of 1×1013 ions/cm2, PF value further increased to~3.80W/K2m (shown in Fig.6). The power factor values are found to exponentially increase with the ion fluence that shows significant enhancement in the irradiated samples as compared to that of pristine sample. Evidently, the higher value of Seebeck coefficient leads to increase the power factor values for the irradiated samples in comparison to the pristine sample. The high thermo power value for the irradiated sample as compared to pristine sample is mostly because of grain fragmentation of large nanograins into tiny nanograins as evidenced from FESEM analysis. Therefore, the effect grain boundary scattering in the material could lead to influence the electrical transport properties [8]. The presence of high density of nanoscale grain boundaries might lead to the enhancement in thermoelectric properties of In2(Te0.94Se0.06)3 thin films. The observed results are consistent with the earlier reports and suggest that phonon scattering through nanoscale grain boundary results significant enhancement in thermoelectric [33, 38-40]. Moreover, Au9+ ion irradiation in the present system show better enhancement in the thermoelectric power, which could be attributed to SHI induced defects in the material as evident from the morphological studies. Generally, the small grain contains more grain boundaries that scatter electrons lightly and this lead to increase in electrical resistivity of the sample [41]. The significant image contrast in surface morphology at different ion fluence shows the smaller grain boundary in the sample 10
due to grain fragmentation by SHI irradiation denotes scattering of minimum electrons through the boundary region leads to increase the electrical resistivity of the material. In other words, reduced value for grain size and increase in carrier concentration may lead to the dramatic increase in electrical resistivity as compared to that of pristine sample. The electrical resistivity of the sample is found to increase with ion fluence and this might be the presence of larger grain boundary due to grain fragmentation, which has more scattering center in the film. Therefore, the number of scattering center leads to the rapid increase in the electrical resistivity. Hence, the enhancement in thermo power for the irradiated sample can be attributed to charge scattering due to the grain boundary [42, 43]. Additionally, point defects also could be one of the deciding factors of impurity scattering results enhancement in thermo power. The high thermo power value for the irradiated sample as compared to pristine sample is mostly because of contrast in charge scattering due to the grain boundary. 3.4 Optical properties From
Fig.9,
the
estimated
band
gap
energy
(Eg)
value
for
the
pristine
In2(Te0.94Se0.06)3sample is found to 0.71 eV. The Eg value for the sample irradiated at different ion fluence of 1×1011, 1×1012 and 1×1013 ions/cm2 are found to 0.73, 0.75 and 0.78 eV respectively. Therefore, the Eg value increases significantly with increase in ion fluence confirm the SHI irradiation induced defects in the material as evident from the morphological studies. It is well known that SHI irradiation can produce latent tracts in the central core region (high temperature zone), where the electronic energy loss is greater in number than the threshold value [44]. When the temperature raised above melting temperature of the target is mostly formed molten phase and is subsequently quenched under high cooling rate. Mostly, this could be the only reason to produce strain and frozen into the present material. Hence, this may induce a shift in energy levels correlates increase in the energy band gap [45]. Further, the temperature difference in the untrapped track region and the surrounding region is dissimilar, which can promote defect annealing in the material. Therefore, SHI irradiation induced defects levels in the system get annealed under the irradiation process and this leads to separation of conduction band and valence band tails states. Obviously, this is the only possible reason for the increased band
11
gap energy values of irradiated samples, concludes the influence of electronic energy loss in the present material. 4. Summary Above study reported an enhancement in thermoelectric properties of the Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films. The pristine and irradiated films show negative value of Seebeck and Hall coefficient that confirms the n-type conductivity in the films. The Seebeck coefficient value for pristine sample is found to ~196 µVK- at 400 K1 and it is enhanced to ~347 µVK-1 at high fluence of 1×1013 ions/cm2, shows almost 80% higher than the pristine sample value. At 1×1013 ions/cm2 ion fluence, the PF value was found to about ~3.80W/K2m denotes 3 times greater value as compared to that of pristine sample value of ~1.28W/K2m. The morphology studies show significant change in surface due to grain fragmentation with increase in ion fluences. Additionally, the enhancement of thermopower in the present material could be due to induced defects by ion beam irradiation as evident from the morphological studies. Moreover, presence of high density of nanoscale grain boundaries that may also lead to the enhancement in thermoelectric properties of In2(Te0.94Se0.06)3 thin films. Acknowledgement The authors (P.M and M.P) greatly acknowledge the Inter University Accelerator Centre (IUAC) New Delhi, for providing financial support through the project UFR-57306. One of the authors (Pandian) acknowledges Tamkang University for providing the opportunity to visit Research Center for X-ray Science & Department of Physics and the financial support by MOST under project number MoST 107-2112-M-032-004-MY3. Reference [1]
A.I. Ryazanov, A.E. Volkov, S. Klaumünzer, Model of track formation, Phys. Rev. B. 51 (1995) 12107.
[2]
R.C. Birtcher, S.E. Donnelly, S. Schlutig, Nanoparticle ejection from Au induced by single Xe ion impacts, Phys. Rev. Lett. 85 (2000) 4968-4971.
[3]
S. Habenicht, W. Bolse, K.P. Lieb, K. Reimann, U. Geyer, Nanometer ripple formation 12
and self-affine roughening of ion-beam-eroded graphite surfaces, Phys. Rev. B Condens. Matter Mater. Phys. 60 (1999) R2200-R2203. [4]
P.C. Srivastava, V. Ganesan, O.P. Sinha, AFM studies of swift heavy ion-irradiated surface modification in Si and GaAs, in: Radiat. Meas., 36 (2003) 671 – 674.
[5]
M. Toulemonde, C. Dufour, E. Paumier, Transient thermal process after a high-energy heavy-ion irradiation of amorphous metals and semiconductors, Phys. Rev. B. 46 (1992) 14362-14369.
[6]
D. Kraemer, B. Poudel, H.P. Feng, J.C. Caylor, B. Yu, X. Yan, Y. Ma, X. Wang, D. Wang, A. Muto, K. McEnaney, M. Chiesa, Z. Ren, G. Chen, High-performance flat-panel solar thermoelectric generators with high thermal concentration, Nat. Mater. 10 (2011) 532–538.
[7]
Masashi Komabayashi, Ken-ichi Hijikata and Shunji Ido, Effects of Some Additives on Thermoelectric Properties of FeSi2 Thin Films, Japan Society of Applied Physics, 30 (1991)331-334.
[8]
I. Sanyal, K. K. Chattopadhyay, S. Chaudhuri, and A. K. Pal, Grain boundary scattering in CuInSe2 films, J. Appl. Phys. 70(1991) 841.
[9]
Xin Bo, Aiyue Tang, Meiling Dou, Zhilin Li, Feng Wang, Controllable electrodeposition and mechanism research of nanostructured Bi2Te3thin films with high thermoelectric properties, Applied Surface Science, 486 (2019) 65-71.
[10] Hye Jin Im, Bokun Koo, Min-Soo Kim, Ji Eun Lee, Solvothermal synthesis of Sb2Te3 nanoplates under various synthetic conditions and their thermoelectric properties,Applied Surface Science, 475 (2019) 510-514. [11] L.-D. Zhao, C. Chang, G. Tan, and M. G. Kanatzidis, SnSe: A remarkablenew thermoelectric material, Energy Environ. Sci. 9(2016) 3044. [12] Dong-Hyeon Kim, Dong-Hoon Lee, Effect of irradiation on the surface morphology of nanostructured superhydrophobic surfaces fabricated by ion beam irradiation,477 (2019)154-158. [13] Lijuan Zhao,Yi He,Huan Zhang,Longfei Yi,Jinrong Wu, Enhancing the thermoelectric property of Bi2Te3 through a facile design of interfacial phonon scattering,Journal of Alloys and Compounds, 768 (2018) 659-666. 13
[14] D. Mohanta, N.C. Mishra, A. Choudhury, SHI-induced grain growth and grain fragmentation effects in polymer-embedded CdS quantum dot systems, Mater. Lett. 58 (2004) 3694– 3699. [15] R.Panda,M.Panda,H.Rath,B.N.Dash,K.Asokan,U.P.Singh,R.Naik,N.C.Mishra, Structural and morphological modifications of AgInSe2 and Ag2Se composite thin films on 140 MeV Ni ion irradiation,Applied Surface Science, 479 (2019) 997-1005. [16] A.S. El-Said, R.A. Wilhelm, S. Facsko, C. Trautmann, Surface nanostructuring of LiNbO3by high-density electronic excitations, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 315 (2013) 265-268. [17] Y.T. Huang, C.W. Huang, J.Y. Chen, Y.H. Ting, K.C. Lu, Y.L. Chueh, W.W. Wu, Dynamic observation of phase transformation behaviors in indium(iii) selenide nanowire based phase change memory, ACS Nano. 8 (2014) 9457–9462. [18] A. Thakur, G. Singh, G.S.S. Saini, N. Goyal, S.K. Tripathi, Optical properties of amorphous Ge20Se80and Ag6(Ge0.20Se0.80)94thin films, Opt. Mater. (Amst). 30 (2007) 565570. [19]
S.R.Alharbi,K.A.Aly,Electrical and thermoelectric properties of ternary Cu-Ge-Te films,Journal of Alloys and Compounds, 797 (2019) 710-716.
[20]
T. Talebi, R. Ghomashchi, P. Talemi, S. Aminorroaya, Thermoelectric performance of electrophoretically deposited p-type Bi2Te3film, Appl. Surf. Sci. 477 (2019) 27-31.
[21]
J. Kim, J.-H. Lim, N. V. Myung, Composition- and crystallinity-dependent thermoelectric properties of ternary Bi x Sb 2-x Te y films, Appl. Surf. Sci. 429 (2018) 158-163.
[22]
M. Bala, A. Bhogra, S.A. Khan, T.S. Tripathi, S.K. Tripathi, D.K. Avasthi, K. Asokan, Enhancement of thermoelectric power of PbTe thin films by Ag ion implantation, J. Appl. Phys. 121 (2017) 215301.
[23]
S. Gupta, D.C. Agarwal, S.K. Tripathi, S. Neeleshwar, B.K. Panigrahi, A. Jacquot, B. Lenoir, D.K. Avasthi, Superiority of ion irradiation over annealing for enhancing the thermopower of PbTe thin films, Radiat. Phys. Chem. 86 (2013) 6-9.
[24]
C.H. Chien, P.C. Lee, W.H. Tsai, C.H. Lin, C.H. Lee, Y.Y. Chen, In-situ Observation of Size and Irradiation Effects on Thermoelectric Properties of Bi-Sb-Te Nanowire in FIB Trimming, Sci. Rep. 6 (2016) 23672. 14
[25]
A. Bali, R. Chetty, A. Sharma, G. Rogl, P. Heinrich, S. Suwas, D.K. Misra, P. Rogl, E. Bauer, R.C. Mallik, Thermoelectric properties of in and i doped PbTe, J. Appl. Phys. 120 (2016) 175101.
[26]
T.S. Tripathi, M. Bala, K. Asokan, An experimental setup for the simultaneous measurement of thermoelectric power of two samples from 77 K to 500 K, Rev. Sci. Instrum. 85 (2014) 085115.
[27]
D.N. Bose, S. De Purkayastha, Dielectric and photoconducting properties of Ga2Te3 and In2Te3 crystals, Mat. Res. Bull. 16 (1981) 635–642.
[28]
V. Riede, H. Neumann, H. Sobotta, A.R. Miedema, Infrared optical properties of InTe InTe, Solid State Commun. 38 (1981) 71–73.
[29]
R. Rousina, G.K. Shivakumar, Electron diffraction study of vacuumm deposited In2Te3 thin films, Surf. Coatings Technol. 38 (1989) 353–358.
[30]
Z.G. Wang, C. Dufour, E. Paumier, M. Toulemonde, The Sesensitivity of metals under swift-heavy-ion irradiation: A transient thermal process, J. Phys. Condens. Matter. 6 (1994) 6733-6750.
[31]
E.M. Bringa, R.E. Johnson, Coulomb Explosion and Thermal Spikes, Phys. Rev. Lett. 88 (2002) 165501.
[32]
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.
[33]
H. Narayan, S.B. Samanta, H.M. Agrawal, R.P.S. Kushwaha, D. Kanjilal, S.K. Sharma, A. V. Narlikar, An SEM and STM investigation of surface smoothing in 130 MeV Siirradiated metglass MG2705M, J. Phys. Condens. Matter. 11 (1999) 2679–2687.
[34]
V. Kumar, R.G. Singh, L.P. Purohit, F. Singh, Effect of swift heavy ion on structural and optical properties of undoped and doped nanocrystalline zinc oxide films, Adv. Mater. Lett. 4 (2013) 423-427.
[35]
H.M. Pathan, S.S. Kulkarni, R.S. Mane, C.D. Lokhande, Preparation and characterization of indium selenide thin films from a chemical route, Mater. Chem. Phys. 93 (2005) 16–20.
[36]
J. H. Yim, H. H. Park, H. W. Jang, M. J. Yoo, D. S. Paik, S. Baek and J. S. Kim, Thermoelectric properties of indium-selenium nanocomposites prepared by mechanical
15
alloying and spark sintering, J. Elect. Mater. 41 (2012)1354-1359.doi:10.1007/s11664012-1940-x. [37]
D. Liu, X. Li, P.M. Borlido, S. Botti, R. Schmechel and M. Rettenmayr, Anisotropic layered Bi2Te3-In2Te3composites: control of interface density for tuning of thermoelectric properties, Sci. Rep. 7 (2017) 43611.
[38]
H. Wu, J. Carrete, Z. Zhang, Y. Qu, X. Shen, Z. Wang, L. D. Zhao, J. Q. He, Strong Enhancement of Phonon Scattering through Nanoscale Grains in Lead Sulfide Thermoelectrics. NPG Asia Mater.6 (2014) e108.
[39]
B. Poudel, Q. Hao, Y. Ma, Y. Lan, A. Minnich, B. Yu, X. Yan, D. Wang, A. Muto, D. Vashaee, X. Chen, J. Liu, M. S. Dresselhaus, G. Chen and Z. Ren, Highthermoelectric performance of nanostructured bismuth antimony telluride bulk alloys. Science 320 (2008) 634–638.
[40]
Y. Lan, B. Poudel, Y. Ma, D. Wang, M. S. Dresselhaus, G. Chen, and Z. Ren, Structure study of bulk nanograined thermoelectric bismuth antimony telluride. Nano Lett. 9 (2009) 1419-1422.
[41]
A. Khan, M. Saleemi, M. Johnsson, L. Han, N.V. Nong, M. Muhammed, M.S. Toprak, Fabrication, spark plasma consolidation, and thermoelectric evaluation of nanostructured CoSb3,J. Alloys Compd. 612 (2014) 293-300.
[42]
J. Martin, L. Wang, L. Chen, G.S. Nolas, Enhanced Seebeck coefficient through energybarrier scattering in PbTe nanocomposites, Phys. Rev. B - Condens. Matter Mater. Phys. 79 (2009) 115311.
[43]
A. Popescu, L.M. Woods, J. Martin, G.S. Nolas, Model of transport properties of thermoelectric nanocomposite materials, 79 (2009) 205302.
[44]
S.K. Srivastava, D.K. Avasthi, Swift heavy ion-induced mixing, Def. Sci. J. 59 (2009) 425-435.
[45]
D.K. Avasthi, G. Mehta, Swift Heavy Ions for Material Engineering and Nanostructuring, Springer Publication, 2011 (Chapter 6).
16
Fig.1 (a) XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films
Fig.1 (b&c) XRD pattern of variation in the peak intensities of In2(Te0.94Se0.06)3thin films 17
Fig.2 (a-d) FESEM image of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thinfilms
18
Fig.3 EDS spectra of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films
Fig.4 (a, b) 2D and 3D AFM image of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films 19
Fig.5Electrical resistivity (ρ) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 thin films. Inset shows the results from the Hall effect measurements
20
Fig.6 Seebeck coefficient (S) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 films. Inset shows the S2.
21
Fig.7 Tau’s plot of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin film
22
Table.1. Structural Parameters of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films Sample In2(Te1-xSex)3
2Ѳ (degree) 23.11 27.65
Pristine 40.555 67.08 23.14 1×1011 ions/cm2
27.59 40.64 67.08 23.14
1×1012 ions/cm2
27.59 40.64 67.08 23.14
1×1013 ions/cm2
27.59 40.64 67.08
Phase & Orientation (hkl)
Average Crystalline Size (nm)
In2(Se.Te)3 (215) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4) In2Te3 (333) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4) In2Te3 (333) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4) In2Te3 (333) In2Se3 (105) In2(Se.Tex)3 (2114) In2Te3 (12 4 4)
33.08
24.42
19.61
16.89
23
Dislocation Strain FWHM Density (ε) (β) Lines/m2 2 (degree) dyn/cm (1015) 0.00105
0.0644
0.263
0.00042
0.0407
0.168
0.0006
0.109
0.429
0.0122
0.219
1.053
0.0016
0.079
0.326
0.0018
0.085
0.354
0.0015
0.082
0.377
0.0119
1.030
1.04
0.0018
0.114
0.436
0.0013
0.081
0.334
0.0040
0.125
0.537
0.0121
0.218
1.05
0.0034
0.101
0.473
0.0012
0.991
0.287
0.039
0.393
1.679
0.0121
0.218
1.05
Table.2 Elemental compositions of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin film In2(Te1-xSex)3
Elemental composition (wt.%) In
Te
Se
Pristine
43.70
50.40
5.90
1×1011 ions/cm2
38.91
54.14
6.95
1×1012 ions/cm2
35.93
58.80
5.27
1×1013 ions/cm2
37.89
53.92
6.19
Table.3 Hall effect measurement of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin film Carrier concentration
Resistivity
Hall mobility
( Ω-cm)
μH (cm3/V.s)
Pristine
0.982
259.20
9.15 1018
1×1011 ions/cm2
1.255
105.91
14.88 1018
1×1012 ions/cm2
1.580
22.89
26.36 1018
1×1013 ions/cm2
1.804
7.14
44.08 1018
In2(Te1-xSex)3
NH (cm-3)
Table.4 Band gap energy of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Samples Bandgap Energy (eV)
Pristine 0.71
1×1011
1×1012
1×1013
ions/cm2
ions/cm2
ions/cm2
0.73
0.75
0.78
24
Figure captions Fig.1 (a) XRD pattern of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films, (b & c) XRD pattern of variation in the peak intensities of In2(Te0.94Se0.06)3 thin films Fig.2 (a-d) FESEM image of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Fig.3 EDS spectra of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Fig.4 (a, b) 2D and 3D AFM images of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films Fig.5 Electrical resistivity (ρ) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 thin films. Inset shows the results from the Hall effect measurements Fig.6 Seebeck coefficient (S) of pristine and Au ion irradiated In2(Te0.94Se0.06)3 films. Inset shows the S2. Fig.7 Tau’s plot of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3 thin films
Table caption Table.1 Structural Parameters of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films Table.2 Elemental compositions of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films Table.3 Hall effect measurement of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films, Table.4 Band gap energy of pristine and Au9+ ion irradiated In2(Te0.94Se0.06)3thin films
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