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Nov 1, 2014 - Thin films of Copper Oxide were prepared by radio frequency ..... to the reported cathode electrodes, e.g. vanadium nitride (15 mFcm. −2. ) ...
ISSN 2321-807X SUPERCAPACITIVEPERFORMANCE OF COPPER OXIDE THIN FILMS B. Purusottam Reddy, K.Sivajee Ganesh, K. Jayanth babu and O.M.Hussain* *

Thin Film Lab., Department of Physics, S.V.University, Tirupati-517 502, India

E-mail address: [email protected] ABSTRACT: Thin films of Copper Oxide were prepared by radio frequency magnetron sputtering on steel substrates maintained at 0 -3 350 C under different RF powers ranging from 100 W to 300 W by keeping the sputtering pressure at 5.7x10 mbar and O2:Ar ratio of 1:11.The structure was determined by using XRD and the modes of vibrations are analysed from Raman studies. Morphological studies of thin films reveals that the grain size and roughness was increased with increase in RFpower from 100W to 250W and then decreases with increasing RF power. The films prepared at 250 W exhibited Cu 2O phase. The cyclic voltammetry (CV), charge–discharge cycling (CP) and electrochemical impedance spectroscopy (EIS) studies of the electrodes were studied in a three-electrode configuration in PBS solution. The highest areal capacitance of -2 -1 30 mFcm at 5mVs was observed for the films deposited at RF power of 250 W. A high rate pseudocapacitance of 302 −2 -2 mFcm at 1 mAcm was obtained for the Cu2O thin films prepared at RF power of 250W.

Key words: Copper Oxide thin films; sputtering; structural; optical and electrical properties.

Council for Innovative Research Peer Review Research Publishing System

Journal: Journal of Advances in Chemistry Vol. 10, No. 8 [email protected] www.cirjac.com 2978 | P a g e

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ISSN 2321-807X 1. INTRODUCTION: Electrochemical capacitors or super capacitors are well-established class of energy storage devices and have been the subject of intense interest in view of their application towards high power energy storage devices due to their high specific power density and fast recharge capabilities. Depending upon the charge transfer mechanisms (i.e weather non - Faradic or Faradic), supercapacitors are classified into electrical double layer capacitors (EDLCs) and pseudo capacitors [1]. In EDLCs, the charge is stored in electric double layer that is formed in the interface between the electrode and electrolytic solution. Carbon structures like activated carbon, carbon nano sheets are extensively used in developing EDLCs. While,in pseudocapacitors, the charge storage processes uses faradic redox reactions at the electrode surface. The fast and the reversible faradic process along with non-faradic electric double layer formation allows pseudo capacitors to store high energy than that of EDLCs. The performance of the pseudo capacitors mainly relies on microstructure, phase, specific surface areaand the electrical conductivity. Due to their high theoretical capacity and high electrical conductivity, the Transition Metal Oxides (TMOs), such as ruthenium oxide, nickel oxide, cobalt oxide and manganese oxide are widely used as electrode materials in pseudo capacitors [2-5].Among all TMOs under study, a high value of quasi metallic conductivity and pseudocapacitance have been reported for ruthenium oxides.However, the high cost and toxicity of the compound has placed huge obstacles for its large scale manufacture [6]. Therefore, it is of great importance to study alternative electrode materials for pseudocapacitors. Among all TMOs, copper oxides has been of research interest, due to its low cost, non-toxic, abundant -1 resources. The predicted hightheoretical capacity value of 1800 Fg [7] of copper oxides, which is very close to theoretical capacity of ruthenium oxides, has been attracted as a promising electrode material for pseudocapacitors. Yu et. al. [8] prepared 3D porous gear-like CuO nanostructure on a Cu substrate via wet-chemical process with specific capacitance of -1 -1 348 Fg at a discharge current density of 1 Ag . Krishnamoorthy et. al. [9] investigated the pseudo capacitance of -1 Hierarchical CuO nanostructures grown on Cu foil by oxidation process and reported a Specific capacitance of 94 Fg with -1 a scan rate of 5 mVs . Endut et al. [10] synthesized vertical nano flakes of copper oxide electrodes using chemical bath −1 −2 oxidation technique and reported a specific capacity of 190 Fg in 1.0M KOH electrolyte at 2 mAcm current density. −1 Wang et al. [11] prepared CuO nanosheet arrays which exhibit a specific capacitance of 569 Fg , with columbic efficiency higher than 93%.Although, studies indicated that copper oxidesare potential electrode materials for supercapacitors, the difficulty in formation of single phase and the low electrical conductivity of copper oxides, the practically achievable specific capacitance of copper oxides is still much lower than the other transition metal oxides which restricts their application towards supercapacitors. To meet this challenge, copper oxide electrodes with single phase, high surface area and high electrical conductivity needs to be emerged. Copper oxide thin films were prepared via thermal evaporation, electron beam evaporation, electro deposition, spray pyrolysis, chemical vapour deposition, pulsed laser deposition, molecular beam epitaxy, plasma evaporation and DC and RF magnetron sputtering [8-21]. Among these thin film deposition methods, RF-Magnetron sputtering is one of the most favorable and industrially viable techniques since it facilitates the formation of homogeneous films with definite phase along with good adhesion.The microstructural and electrochemical properties of RF sputtered thin films principally depend on the process parameters such as substrate temperature, sputtering pressure, source to substrate distance, oxygen partial pressure and sputtering power. For instance, Pierson et.al. [19] prepared various phases of copper oxide thin films by using RF magnetron sputtering. Pham et.al. [20] reported reactively sputtered p-type copper oxide thin films with high resistivity using Cu2O target by varying Ar partial pressure from 4-30 mTorr. Li et.al. [21]reportedsingle Cu2O phase by 3 3 maintaining oxygen flow rate in between 3.8 to 4.4 cm /min and Ar flow rate as 40 cm /min keeping RF power at 100 W o and substrate temperature at 300 C. Most of the previous studies on copper oxide thin films prepared by RF sputtering are profound to study the dependence process parameters for formation of different phases of copper oxides and less emphasis on the possibility of using copper oxide films as an electrode for supercapacitor. However, the possibility of using copper oxide films as an electrode for supercapacitor is mainly depends upon the microstructure and the oxidation state which in turn controlled by RF power maintained during sputtering. Hence, in present work copper oxide thin films were prepared at different RF powers onto stain less steel substrates using sputtering technique and their pesudocapacitive properties were studied.

2. EXPERIMENTAL: Thin films of Copper oxide were prepared by using RF- Magnetron sputtering using 3" circular copper target of 99.99% purity on to the glass substrates and Stainless Steel Substratesin the presence of Ar and O 2 gas mixture.After -6 creating a base pressure of 5x10 mbar using turbo molecular pump backed by a rotary pump, the target was presputtered for 10 min by introducing argon gas into the chamber. All the depositions were carried by admitting the oxygen and argon in to the chamber through mass flow controllers having 0.1 sccm accuracy, keeping substrate 0 -3 temperature at 250 C, sputtering pressure constantly at 9.1 x 10 mbar, source to substrate distance at 8.0 cm. The O2 : Ar ratio was fixed at 1:11 for obtaining single phase copper oxide (Cu 2O) films. In order to study the effect of RF power on the pseudo capacitive performance of copper oxide thin films, the sputtering was carried by varying RF Power from 100W to 300W. The structural properties were studied by the X-ray diffraction technique (Siefert computerized X-ray diffractometer, model 3003 TT) in Ɵ - 2 Ɵ configuration using CuKα1 radiation (λ=1.54056 Å).Raman spectroscopy (Labram-HR 800 confocal Raman spectrometer with He-Ne 632 nm as exiting wavelength) was used to determine the modes of vibration and phases present in the prepared thin films. The surface morphological studies of the thin films were carried out by using NT-MDT Solvernext Atomic Force Microscope. The pseudocapacitive performance of prepared thin films was tested on CHI 600C electrochemical work station using three electrode system with platinum as reference

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ISSN 2321-807X electrode with phosphate buffer solution (PBS) of pH 7.0 as electrolyteand is operated in the cut-off voltage between 0.0 V and -1.0 V.

3. RESULTS AND DISCUSSION: Figure 1 shows XRD spectra of copper oxide thin films deposited at different RF powers ranging from 100 W – 300 W. The absence of Bragg peaks in the XRD pattern for the films prepared atlower RF powers reveals the amorphous nature of thinfilms.The XRD pattern of copper oxide thin films deposited at RF power of 180 W exhibited a weak diffraction 0 at 2Ɵ =35.55 indexed to the Fig 1: XRD spectra of copper oxide thin films deposited at different RF Powers

(1 1 1) orientation of monoclinic CuO phase (JCPDS Card No: 89-5897)while at higher RF powers of 200W – 300 W, the 0 0 XRD spectra reflected two diffraction peaks at 2 Ɵ = 36.44 and at 2 Ɵ = 42.24 corresponding to the (111) and (200) planes of cubic Cu2O(JCPDS Card No: 78-2076)

Table 1. Variation of Grain size and Roughness Parameters Crystallite Size from XRD (nm)

Grain Size from AFM(nm)

RMS Roughness (nm)

150W

-

20.6

16.019

180W

8

30.4

35.782

200W

11

48.9

93.118

220W

15

63

113.586

250W

29

72

121.627

280W

17

39.7

50.295

RF power

respectively. As the RF power increases from 200 W to 250 W the intensity of (111) orientation was increased and then decreased with further increase in RF power from 250 W to 300 W. This may be ascribed to the fact that as sputtering power increases the mobility and surface diffusion length of sputtered atoms increases leading to an increase in the probability of ad atom diffusion from the landing sites to the dense lattice plane (1 1 1) resulting the enhancement of (1 1 1) crystal plane which is in good agreement with the Zoolfakar et. al. [22].While at larger RF powers, the sputtered particles acquire high kinetic energies and eventually resputtering takes place resulting decrement in the peak intensity. It is also observed that the ratio of (1 1 1) peak intensity to (2 0 0) peak intensity increases as the RF power increase from 220 W to 250 W and then decreases with further increase in RF power which indicates that the films grown at 250 W, the RF power facilitates to grow more thermodynamically stable(1 1 1) planes [23].The crystallite size of the prepared copper oxide thin films as estimated from the Scherrere quation are given in Table I. The observed crystallite size of the copper oxide thin films measured from scherrer formula tends to increase as the RF power increased from 150 W to 250 W and

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ISSN 2321-807X further increase in RF power results in decrease of crystallite size. For better understanding of the phase and vibrational modes, the thin films are characterized by Raman spectroscopy. Fig 2: Raman spectra of copper oxide thin films deposited at different RF Powers

Figure 2 shows the Raman spectra of copper oxide thin films prepared at various RF powers in the wave number -1 -1 range 100 cm - 800 cm . The Raman spectra of the prepared thin films exhibits characteristic peaks correspond to CuO, Cu2O and Cu4O3 phases in Cu-O binary system. The Raman spectra of the copper oxide thin films prepared at 150 W −1 shows a strong peak at 298 cm corresponding to Ag Raman-allowed mode of CuO phase. Apart from that, the spectra −1 −1 exhibits two feeble peaks centered at 347 cm and 625 cm corresponds to the Bg mode. The Raman spectra −1

of thin films prepared at 200 W – 280 W range exhibit characteristic peak of Cu 2O phase located at 511 cm −1 corresponding to T2g Raman allowed mode. The peak at 218 cm originated from the second-order Eu Raman-allowed −1 mode of the Cu2O crystals. The peak at 148 cm may be attributed to Raman scattering from phonons of T1u symmetry of −1 Cu2O. The weak peak at 612 cm is attributed to the infrared-allowed mode of Cu2O phase. The presence of strong peak -1 at 535 cm for the films prepared at 180 W indicates the presence of Cu4O3 phase [24-27]. In addition, the Raman spectrum of copper oxide thin films prepared at 180 W reveals the coexistence of all the three phases CuO, Cu 2O and Cu4O3 of copper oxide which were not appeared in XRD spectrum. Raman spectra of copper oxide thin films reveals that the FWHM values of the Raman peaks decreases with increasing RF power from 150 W to 250 W indicating the betterment of the crystalline quality of films. Further increase in RF power results in decrement of Raman peak intensity which corresponds to decrease in crystallinty of the film which was in good agreement with XRD results.

The surface morphology of copper oxide thin films deposited at different RF powers are shown in Figure3. The AFM results reveals that the texture of the films have uniformly distributed spherical grains. The grain size of the films increases as the RF power increases from 150W to 250W and then a further increment in RF power decreases the grain size of the particles which is in good correspondence with the XRD results. As the sputtering power increased, the kinetic energy of particles arriving at the substrate increased. As a result, the probability of sputtered particles overcoming the barrier potential of the substrate surface increases which results in greater possibility of ad atom diffusion. Thus, by increasing RF power the sputtered particles become more mobile on substrate surface which facilitates the formation of larger grains. At larger RF powers, the kinetic energies of the species reaching the substrate increases as a result the time to dissipate the kinetic energy on the substrate surface decreases. Hence the probability of escaping the sputtered particles from the substrate potential barrier increases which results in decrease in grain size. The AFM results indicate that the surface roughness of the thin films increases as RF power increases up to 250 W and then decreases with increase in RF power.

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Fig 3: AFM images of copper oxide thin films deposited at various RF Powers (a) 150W (b) 180W (c) 200W (d) 250W (e) 280W

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Fig 4: Cyclic voltammetry profiles for copper oxide thin films deposited at various RF powers (a) 150 W (b)180 W (c) 200 W (d) 220 W (e) 250 W (f) 280 W at different scan rates

3.1 Electrochemical Studies: The copper oxide thin films were tested for pseudo capacitance using cyclic voltammetry (CV) in a PBS aqueous solution with a three-electrode system. Figure4 shows the cyclic voltammograms (CVs) recorded in the scan range of −0.1 V to 0.0 V with respect to Platinum reference electrode in an aqueous PBS electrolyte at 2 mV/sec, 5 mV/sec and 10 mV/sec.The disappearance of redox peaks in cyclic voltammograms for the copper oxide electrodes prepared at 150W indicates that the specific capacitance of the electrode is arising due to electrical double layer capacitance.

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ISSN 2321-807X Fig 5: Variation of areal capacitance as a function of RF power at different scan rates

Copper oxide electrodes prepared in the range of180W to250W, exhibited two quasi-reversible electron transfer processes in CV curves indicating that the capacity mainly results from the pseudo capacitance. It is observed that as the sweep rate is increased, the anodic peak potential and cathodic peak potential shift in more anodic and cathodic directions, respectively. The variation of areal capacitance with RF power at different scan rates are depicted in Figure5. -2 -1 The highest areal capacitance of 30 mFcm at 5mVs was observed for the films deposited at RF power of 250 W and is −2 comparable to the reported cathode electrodes, e.g. vanadium nitride (15 mFcm ), manganese oxide, molybdenum oxide −2 and ruthenium oxide films (17–38 mFcm ) [28]. From the CV reports of copper oxides in alkaline electrolytes, the redox reactions can be summerised in the following reactions [29-31]. 𝐶𝑢𝑂 + 𝐻2 𝑂 ⟺ 2𝐶𝑢(𝑂𝐻)2 ---------------- (1) 𝐶𝑢2 𝑂 + 2𝑂𝐻 − ⟺ 2𝐶𝑢𝑂 + 𝐻2 𝑂 + 2𝑒 − ---------------- (2) 𝐶𝑢𝑂 + 𝑂𝐻 − ⟺ 𝐶𝑢𝑂2− + 𝐻2 𝑂 + 𝑒 −

---------------- (3)

The CV of the copper oxide thin films prepared at 150 W and 180 W RF powers show only one anodic peak at 0.65V and cathodic peak at -0.35V corresponding to the formation of Cu(OH)2 which governed by the equation (1). As the species are nonconductive and insoluble,the peak current corresponding to Cu(OH)2 formation is very less indicating non suitability for their use in supercapacitor application. While thefilms prepared at higher RF powers show two distinct anodic peaks at -0.45V and -0.85V and two cathodic peaks at -0.1V and -0.4V corresponding to the Cu(I)/Cu(II) redox couple and the reduction of CuO to Cu(III) species governed by the equations (2) and (3). The XRD and CV results revealed that the films with intense (1 1 1) planes exhibits high areal capacity. With increase in RF power from 220 W to 250 W, the observed decrement in peak intensity of (2 0 0) plane with respect to (1 1 1) plane of Cu 2O thin films results in decrement of anodic peak current corresponding to CuO/Cu(OH)2 couple. From the first principles studies on Cu2O, it is reported that the Cu2O [1 1 1] planes are most stable owing to their less surface energy compared to Cu 2O [1 0 0] planes which are more active [23, 32]. In aqueous solutions, the Cu2O (1 0 0) planes are more robustive and oxidize to from CuO2 and when voltage is applied it converts to non reducible CuO. Whereas the Cu2O (1 1 1) are stable and converts to reducible CuO on the application of voltage.As a result, the [1 0 0] planes become non conductive and ion diffusion becomes difficult thus reduces the active sites for polarization and in consequence the capacity decreases. The copper oxide thin films with predominent (1 1 1) planes offer less resistance to ion diffusion, and hence the films exhibit high areal capacitance. Thus, it is clear from CV results that the copper oxide thin films prepared at RF power of 250 W with predominant (1 1 1) orientation exhibits highest areal capacitancecompared to all other electrodes.

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ISSN 2321-807X The galvanostatic charge and discharge (CP) studieswere carried out for further study of copper oxide thin films. -2 Figure 6 shows the galvanostatic charge and discharge profiles of copper oxide thin films at different 0.5 mAcm . The specific capacitance of the thin films were calculated by using the formula [33] 𝐶𝑠 =

𝐼𝑚𝑎𝑥 ∆𝑉 ∆𝑡 𝑤

---------------- (4)

-2

Where ‗Cs‘ is the specific capacitance in ‗Fcm ‘, ‗Imax‘ is the peak current in ‗A‘, ‗∆V‘ is the potential drop during 2 discharge in volts, ‗∆t‘ is the total discharge time in ‗sec‘, and ‗w‘ is the active area of the material in ‗cm ‘. The measured specific capacitance values of copper oxide thin film electrodes prepared at 150 W, 180 W, 200 W, 220 W, 250 W, and -2 −2 −2 −2 −2 −2 280W at a current density of 0.5mAcm are 22mFcm , 137 mFcm , 143 mFcm , 357 mFcm , 552 mFcm and 310 −2 mFcm respectively. In addition to this, the charge/discharge duration of electrodes prepared at 150 W and 180 W was minimum compare to the other electrode materials which may be due to the large amount of CuO which results in the formation of Cu(OH)2species. The poor charge/discharge for electrodes prepared at 220 W, 280 W may be due to less crystallite size and less surface roughness of the electrodes which decreases the effective utilization area of the electrode. Copper oxide thin films prepared at 250 W exhibits high charge/discharge duration that as these electrodes possesses high surface area with good crystallinity which favours Cu(I)/Cu(II) redox reaction.Figure7represents the galvanostatic charge–discharge measurements of Cu2O electrode prepared at 250 W carried out at different current densities. The discharging profiles ofthe films are curvilinearindicating the pseudocapacitance contribution from Cu2O. The calculated -2 -2 -2 -2 −2 −2 −2 values of specific capacity at 0.5mAcm , 1mAcm , 2mAcm and 5mAcm are 552 mFcm , 302 mFcm , 214 mFcm −2 and 135 mFcm respectively. The decrease in specific capacitance with increase of discharge current density may be due to large potential drop and less utilization of active material. It is observed from CV and CP that the capacitance of Cu xO films notonlyoriginatefromthedoublelayercapacitance but also from the pseudo-capacitivenature which depends on thestructureand roughness oftheactivematerial which in turn depends on the RF-power maintained during growth of thin films.

Fig 6: Potential Vs Time profiles while charging and discharging of copper oxide thin films deposited at different -2 RF Powers at current density of 0.5mA/cm

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ISSN 2321-807X Fig 7: Galvano static charge and Discharge profile of copper oxide thin films at different current densities

Fig 8: Nyquist plots of copper oxide electrodes prepared at different RF powers in PBS solution

The electrochemical impedance spectroscopic (EIS) measurements were carried out in the frequency range from 0.01Hz to 1MHz, was shown in Figure8. The series resistance (Rct) from the Nyquist plot was found to be decreases as the RF power increases from 150 W to 250 W and then increases with further increase in RF power. This may be because of the availability of effective surface area for the electrolyte. With increase in RF power, the semi-circle at high frequencies are observed to be depressed which accounts to a decrease in charge transfer resistance. At lower frequencies the films exhibits a nonlinear branch corresponding to diffusion resistance. Even though the films prepared at 220 W, 250 W, 280 W offers low charge transfer resistance the diffusion resistance offered for the ions which influences the specific capacity of the films. A high value of diffusion resistance was observed for the films prepared at 220 W and 280 W which may be due to the presence of (2 0 0) planes. The films prepared at 250W exhibits lower imaginary part of impedance values even at higher frequencies compared to the films prepared at 220 W and 280 W due to the availability of more number of thermodynamically stable (1 1 1) planes. This result is in good agreement with the XRD, Raman and CV studies.

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ISSN 2321-807X -2

-2

The cycling stability of copper oxide thin film electrodes prepared at 250W RF power at 0.5 mAcm , 1 mAcm -2 and 5mAcm current densities are shown in Figure9. A continuous degradation in specific capacity of thin film was -2 observed when the films was tested under 5 mAcm current density.The large capacitive decay observed during early cycles may be due to the loss of active material and increasing electrode resistance. After 150 cycles the thin films -2 -2 exhibited a discharge specific capacity of 225 mFcm at 1mAcm and retains 85% of its initial capacity even after 1000cycles. The large specific capacity of electrodes prepared under 250W results from less diffusion resistance and less charge transfer resistance of the electrode with respect to electrolyte. Thus from galvanostatic charge and discharge studies we can say that the RF power plays an important role in controlling the parameters, electrode resistance, grain size and roughness, which in turn controls the specific capacitance of the RF sputtered copper oxide thin films.

Fig 9: Dependences of the discharge specific capacitance of copper oxide thin films on the charge/discharge -2 -2 -2 cycle numbers at 0.5 mAcm , 1 mAcm , and 5 mAcm current densities.

4. CONCLUSIONS: Copper oxide thin films were prepared using RF - magnetron sputtering technique at various RF powers on stainless steel substrates. The Raman and XRD studies confirms single phase Cu2O with predominant (1 1 1) orientationof copper oxide thin films prepared at 250 W RF power. The AFM results indicate that the films have high surface roughness with well defined grains. The CV results indicate that these films favours very much for Cu(I)/Cu(II) redox couple which results -2 -1 in superior capacity.The highest areal capacitance of 30 mFcm at 5mVs was observed for the films deposited at RF power of 250 W.The charge discharge profile of copper oxide thin films reveals that the films exhibits superior specific −2 -2 capacitance values 302mFcm under 1mA/cm current density. It is also observed that 85% of the specific capacity is retained after 1000 cycles for the thin filmsprepared at 250W RF power. The observed that the large specific capacitance of electrodes may be due to lower diffusion and charge transfer resistances of the electrode with respect to electrolyte as observed from EIS studies.

ACKNOWLEDGEMENTS: This research work was supported by DST under Promotion of University in Research Science and Excellence (PURSE) programme.

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ISSN 2321-807X [28] Liu, C., Li, Z., Zhang, Z., 2013. MoOx thin films deposited by magnetron sputtering as an anode for aqueous microsupercapacitors. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 14 065005. [29] Jayalakshmi, M., Balasubramanian, K., 2008. Cyclic Voltammetric Behavior of Copper Powder Immobilized on Paraffin Impregnated Graphite Electrode in Dilute Alkali Solution. Int. J. Electrochem. Sci. 3, 1277 - 1287. [30] Bellakhal, N., Draou, K., Brisset, J.L., 1997. Electrochemical investigation of copper oxide films formed by oxygen plasma treatment. Journal of Applied Electrochemistry 27, 414-421. [31] Li, Q., Xu, P., Zhang, B., Tsai, H., Zheng, S., Wu, G., Wang, H.-L., 2013. Structure-Dependent Electrocatalytic Properties of Cu2O Nanocrystals for Oxygen Reduction Reaction. The Journal of Physical Chemistry C 117, 1387213878. [32] Zheng, Z., Huang, B., Wang, Z., Guo, M., Qin, X., Zhang, X., Wang, P., Dai, Y., 2009. Crystal Faces of Cu2O and Their Stabilities in Photocatalytic Reactions. The Journal of Physical Chemistry C 113, 14448-14453. [33] Dubal, D.P., Gund, G.S., Holze, R., Jadhav, H.S., Lokhande, C.D., Park, C.-J., 2013. Surfactant-assisted morphological tuning of hierarchical CuO thin films for electrochemical supercapacitors. Dalton Transactions 42, 6459-6467.

Author’ biography with Photo B.Purusottam Reddy received Bachelor of Science (2005) and Master of Science (2007)degrees from Sri Venkateswara University, Tirupati, India. He is currently undertaking his candidature for a Ph.D.in Department of Physics, Sri Venkateswara University. His research interests include preparation and characterization of metal oxide thin films, supercapcitors, batteries and bio sensors.

K. Sivajee Ganesh obtained his M.Sc. degree in physics in 2010 from SriVenkateswaraUniversity, Tirupati, India. At present he is pursuing his doctoral degree at department of physics, SriVenkateswaraUniversity. He is currently working in the area of transition metal oxide thin film cathodes for micro-battery applications. His research interests include solar cells and supercapacitors.

Jayanth Babu Karnam, He completed his doctoral degree from Sri Venkateswara University, India in 2013. Currently he is working as a Post-Doctoral fellow in University of Coimbra, Portugal under FCT programme. His area of research interests include Synthesis, Growth and Characterization of Metal Oxide Thin Films for Energy Storage and Conversion Devices Applications and Tribological applications.He has published more than 15 research papers in various reputed National and international Journals.

Dr. O. Mahammad Hussain is a professor and Dean, University Development at Sri Venkateswara University, Tirupati, India. He received his Ph.D.degree in Physics from S.V. University 1990 and laterworked as Post-Doctoral Fellow during 1991-92 in Universite Pierre et Marie Curie, Paris, France. He joined as a faculty member in 1992 in the Department of Physics, S.V.University. He has been recognized as ―Teacher of Excellence‖ in 2009 from S.V. University.So far, he has guided 10 Ph.D. students and 07 M.Phil. students and published about 140 research articles in peer reviewed journals. He is life member of several academic bodies viz IAPT, IPTA, SSI etc. and Associate Fellow for AP Akademi of Sciences. He has successfully completed several major research projects sponsored by UGC, DST andDRDO. His research interests include the synthesis of metal oxide thin films by PVD techniques (sputtering, electron Beam, PLD) and characterization for applications in micro batteries, supercapcitors, electrochromic windows and sensors.

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