Abstract
The rutile TiO2 of nanoparticles and microrods were simultaneously grown on FTO glass slide using a one-step hydrothermal process. CdS semiconducting nanocrystals were deposited on the surface of TiO2 surface using SILAR method. Moreover, the SEM micrograph studies, TiO2 nanorods were almost uniformly explored on FTO glass slide pattern. The photovoltaic performances, as-prepared semiconductor sensitized solar cells (SSSCs) were studied and the maximum efficiency of FTO/TiO2/CdS-8/ZnS-2 sample was 0.78% were confirmed by sun solar simulator, overall the solar cell efficiency was determined with an increasing pattern of CdS deposition is reported in detail.
Keywords: Semiconductor, Counter electrode, Rutile TiO2, TiO2 microrods, CdS sensitizer, Raman spectrum, Solar cell.
Received: 8 January 2019 / Revised: 12 February 2019 / Accepted: 15 March 2019/ Published: 3 April 2019
Contribution/ Originality
In this work, contribute to the development of Ti02 unidirectional growth nanorods on FTO glass slide and its act as a photoanode was prepared hydrothermal method. The semiconductor (CdS) quantum dots were prepared using SILAR method. These quantum dots acts as dye molecule for the fabrication solarcell. In the present studies gives an idea of semiconductor sensitized solar cells (SSSCs).
1. INTRODUCTION
In the past few years, semiconductor sensitized solar cells (SSSCs) had a great deal of attention as a candidate for third generation photovoltaic devices for the modern electronic era [1]. The focusing of (SSSCs) is similarly like dye-sensitized solar cells (DSSCs), but it was replaced with semiconductor nanocrystals as a sensitizer for light harvesting process [2]. Likely, metal oxide nanostructured were unique properties like tunable bandgap high extinction coefficient and multiple electron-hole pair generation per incident photon, among these terms are increasing the overall performance of solar cell activities [3]. Mostly, metal chalcogenides such as CdS, CdSe, PbS and CdTe, have been investigated as a sensitizing material for SSSCs [2]. Among them CdS has been a most effective sensitizer because of the suitable bandgap, simple fabrication, long lifetimes and excellent stability also reported apparently [3, 4]. In such case, (SSSCs), photoanode is also one of the main components similarly to the sensitizer. However, the TiO2, SnO2 and ZnO nanoparticles have been used as a photoanode materials likely, the power conversion efficiency (PCE) of solar cell depends on size and structure of photoanode matrix [3]. In recent research is focused on the mixing larger grain size of 2D nanostructures like nanorod, nanoflower, dendritic microsphere, microrod, nanowires, etc., Furthermore, TiO2 nanoparticles to increasing better light harvesting and higher electron transport studies in DSSCs and now in this work, extending this idea to prepare SSSCs applications [5]. Before discussion, Buatong, et al. [6] group has grown the three-dimensional flower-like TiO2 structure on array of TiO2 nanorod using double-step by hydrothermal method Buatong, et al. [6]. Cheng, et al. [7] well developed by hydrothermally to construct the structure of photoanode was hierarchical micro-corollas layer upon the nanoforest layer (HTCF) which coronal structures, on the surface of high density and long branched Cheng, et al. [7]. Park and Dhayal [5] has reported simultaneous growth of rutile TiO2 of 1D/3D-nanorod/nanoflower structure on FTO was constructed in one-step hydrothermal process eventually Park and Dhayal [5]. Sun, et al. [8] also highlighted the dendritic microsphere was deposited on the surface of one-dimensional (1-D) nanowire, TiO2 nanostructures was also prepared using one-step process on FTO plate [8]. Similarly, Ramalingam, et al. [9] have synthesized CdSe nanorods have been synthesized by the solvothermal method employing cheaper chemicals and easy process, and with better control over the morphology and crystalline quality.
More specifically, Liu, et al. [10] was described the TiO2 films with trilayer structure (microflowers, nanorod array and compact nanoparticulate) are grown on FTO substrate by one-step hydrothermal approach [10]. In this work, nanoparticles or microrods were simultaneously grown on FTO glass slide as a TiO2 photoanode by one-step hydrothermal method as per previous literature. Earlier there was no report based on this SILAR method, we are the one first time will be reporting based on the CdS semiconducting nanocrystals were deposited on the surface of TiO2 using SILAR technique, Moreover, the performances of fabricated solar cells were studied extensively.
2. EXPERIMENTAL SECTION
2.1. Materials
Tetrabutyltitanate [Ti(CH2CH2CH2CH3)4], fluorine doped tin oxide coated glass slide (FTO, Surface resistivity), hydrochloric acid (HCL), sodium sulfide hydrate (Na2S. xH2O) and Sulfur (S) were purchased from Sigma Aldrich. Absolute ethanol (C2H2OH) was obtained from Merck, India. Cadmium nitrate tetrahydrate [Cd(NO3)2. 4H2O] cupric nitrate trihydrate [(Cu(NO3)2. 3H2O] and zinc acetate dihydrate [(Zn(CH3OO)2. 2H2O] and methanol (CH3 OH) were purchased from SRL, India. All reagents were used as received without further purification. In the entire synthesis process deionized water was used as a universal solvent.
2.2. Preparation of Tio2 Thin Film
In stage one, the synthesis of TiO2 thin film on conducting the surface of FTO glass slide via hydrothermal method. In this process, 1:1 ratio of water (H2O) and hydrochloric acid (HCL) was taken in the capacity of 40 ml of both the mixture and kept it at uninterrupted stirring for 20 min at room temperature. After that 1.5 ml of tetrabutyltitanate was added into above solution for 15 min stirring. In this reaction the milky white color was tuned into transparent solution respectively. In stage two, FTO glass slide were taken and washed with 1:1 ratio of methanol and acetone for 20 min using probe type sonicator. Finally, as-prepared precursor (stage one) has been transferred into Teflon coated autoclave, the FTO glass slide was kept under the bottom of autoclave. The entire reaction undergoes by hydrothermal treatment at 160 ˚C for 14 hrs. The autoclave was cooled naturally to reach room temperature and rinsed with deionized water. Finally, the sample were calcined at 500 ˚C for 15 min and labelled it as FTO/TiO2.
2.3. Deposition of CdS Sensitizer
Cadmium sulfide (CdS) were deposited on the surface of TiO2 by successive ionic layer adsorption and reaction (SILAR) method. In First stage, the FTO/TiO2 thin film was dipped in cationic ethanol solution of 0.4 M of cadmium nitrate tetrahydrate for 4 min and rinsed with ethanol. In second stage, the rinsed film was dipped into anionic methanol solution of 0.4 M sodium sulfide hydrate and rinsed with methanol solution. The objective of the above two processes was defined as one cycle and repeated several times. The prepared sample was called as TiO2/CdS-4 and TiO2/CdS-8 for 8 SILAR method [11].
2.4. Deposition of Passive Layer
ZnS passive layer was deposited by using SILAR method. Very firstly, the FTO/TiO2/CdS thin film was dipped in 0.1 M of cationic aqueous zinc acetate dehydrate solution for 4 min and 0.1 M of anionic aqueous sodium sulfide hydrate solution for 4 min, then rinsed with ethanol and using dryer to dry the sample and it follow SILAR reaction. The photoelectrodes were so-called as FTO/TiO2/CdS-4/ZnS-2 and FTO/TiO2/CdS-8/ZnS-2. Finally, all the samples were annealed at 80 ˚C (1 hrs) to remove the solvent as well to make crystallinity of the sample [12].
2.5. Counter Electrode Preparation
In the typical synthesis, 2 M of cupric nitrate trihydrate is taken in 10 ml of de-ionized water and 2 M sodium sulfide hydrate with 10 ml of water. Mix both precursors together and stirred it well for 5 min and keep it stable for 2h at room temperature. Finally, it was centrifuged with ethanol, collected as a nanopowder, and dry it at 100 ˚C for 3h [13]. 0.0025 g of prepared CuS power was taken in 10 ml ethanol and sonicated it 30 min. It was filled in spray container and sprayed it on FTO glass slide with substrate temperature was 70 ˚C for 20 min. Finally, the resultant sample was annealed at 80˚C for 30 min.
2.6. Device Assembly
In this work, solar cell fabrication procedure was followed by the literature [14] and detailed process was given below. The photosensitizing anode and counter electrode was sandwich together using a scotch tape spacer with binder clip and few drop of polysulfide electrolyte was injected in between them. The polysulfide electrolyte solution makes 2 M of sodium sulfide hydrate and 2 M of sulfur in water-methanol (7:3, v/v) solution. A black mask on the photoanode with a window of 0.25 cm2 was used to select photo active area of the cell [15].
2.7. Characterization Studies
The crystal phases of the films were studied by the help of X-ray Diffraction (XRD, PANalyticalX’pert Pro) with Cu kα and 2θ range from 10˚ to 80˚. The morphologies were examined by scanning electron microscopy (SEM, VEGA 3 TESCAN) with energy dispersive X-ray (EDX) spectrum (Bruker). The optical properties of the as-prepared samples were performed by UV-Vis-NIR Spectrophotometer (Ocean optics HR 2000). The Photovoltaic studies (J-V curves) of CdS sensitized solar cells were measured using Agilent B2901A precision source/measure meter under one sun solar LED simulator (Royal Enterprises, Chennai, Model:100L). The intensity of the simulator was setup to 100 mW/cm2 condition using standard silicon reference cell.
3. RESULT AND DISCUSSION
3.1. XRD Analysis
The XRD patterns of FTO/TiO2 and FTO/TiO2/CdS-8 thin film samples system were recorded at 2θ range between 10˚ to 80˚ as shown in Figure 1. The diffraction peaks are located at 27.8°, 36.3°, 41.4°, 54.5°, 56.7°, 62.8°, 65.6°, 68.9° and 69.8° with respective plane of indices as (110), (101), (111), (211), (220), (002), (221), (301) and (112). The observed peak of synthesized samples confirms the tetragonal phase of rutile TiO2 and its followed the JCPDS file (Card No: 65-0192) [16]. The diffraction peaks located at 25.1° and 43.9° with indices as (100) and (110) corresponding to CdS sensitizer phase (JCPDS Card No: 65–3414) as shown in the Figure 1b [17]. Further this reveals that the diffraction peaks of CdS phase were absent, because most of the peaks are very near to SnO2 peaks. Further there is no other unwanted peak observed in presented sample.
Figure-1. XRD patterns of (a) FTO/TiO2 thin film and (b) FTO/TiO2/ CdS-8 thin film.
Source: OriginPr8.
3.2. Raman Spectroscopy Studies
The Raman Spectra of FTO/TiO2 and FTO/TiO2/CdS film were shown in the Figure 2. In the spectrum of FTO/TiO2 thin film, the peaks at 235, 441 and 607 cm-1 are typical rutile TiO2 bands and these can be corresponding to the two-photo scattering, Eg and A1g modes in Figure 2a [18, 19]. The strong peak found at 298 cm-1 which can be recognized to the first-order LO phonon vibrational modes of CdS in FTO/TiO2/CdS-8 sample [20, 21]. So, the results from Raman spectra confirm that TiO2 have in rutile phase with CdS crystal and are in good agreement with the XRD result.
Figure-2. Raman spectra of (red curve) FTO/TiO2 thin film and (black curve) FTO/TiO2/ CdS-8 thin film.
Source: OriginPr8.
3.3. Morphological Studies
Figure 3a-c, shows the SEM micrographsof FTO/TiO2 thin film with different magnification. In these SEM micrographs, microrods as well as nanoparticles of rutile TiO2 are grown on FTO glass slide in one-spot hydrothermal process. In Figure 3c, TiO2 nanoparticles are uniformly deposited on the conducting surface of FTO glass slide with diameter is approximately 200 nm. In Figure 3b, gives the novel exploration of TiO2 microrods taken place on FTO glass slide is almost uniformed manner. The diameter and length of the microrods is 50 nm and 30 nm. The thin layer of CdS nanocrystals were deposited on the surface of microrods and nanoparticles as shown in Figure 4a-c. The Figure 4d&e, gives the EDX spectra of FTO/TiO2/CdS-8 to study the compositional details of the sample. In EDX studies, CdS crystals were deposited more on microrods surface compare to nanoparticles, because of TiO2 microrods have high surface area. The EDX results give agreement with both Raman spectra and XRD results.
Figure-3. SEM images of FTO/TiO2 thin film.
Source: Jpeg image.
Figure-4. SEM and EDX images of FTO/TiO2/CdS-8 thin film.
Source: Jpeg image.
3.4. Optical Studies
The absorption spectra of FTO/TiO2 and FTO/TiO2/CdS-8 thin film is shown in Figure 5. From these spectra, FTO/TiO2/CdS-8 thin film has higher absorption intensity in the visible region compare to FTO/TiO2. The absorption spectra of FTO/TiO2 thin film shows broad absorption band and absorption edge is 408 nm and corresponding bandgap of ~3.4 eV. After deposition of CdS sensitizer on FTO/TiO2, the absorption edge was shifted (red shift) from 408 to 521 nm in visible range and its corresponding bandgap of 2.7 eV (521). The band gap of bulk CdS is ~2.42 eV from the literature [9]. The bandgap of FTO/TiO2/CdS-8 is higher than bulk, so it’s indicated that CdS nanocrystals are obey the quantum confinement effect [22].
Figure-5. UV-Vis spectrum of a) FTO/TiO2 thin film, and b) FTO/TiO2/CdS-8 thin film.
Source: OriginPr8.
A schematic diagram of CdS sensitized solar cell structure with expected pathway of charge transfer as shown in the Figure 6. The solar cell consists of semiconducting TiO2 on FTO, CdS sensitizer, ZnS passive layer, polysulfide electrolyte (Sn2-/S2-), and CuS Counter electrode (CEs) on FTO. The advantage of ZnS passive layer is to improve the cell performance, because of reduced charge recombination. The conduction band of ZnS is higher when compare to CdS, so the generated charge carrier have quantum electrical confinement effect [23]. During cell working process, CdS sensitizer with ZnS passive layer absorbs the photons to create electron-hole pairs and these pairs are separated into electrons and holes intermediate between semiconductor (TiO2) and sensitizers. The electrons are travel into the semiconducting TiO2 and then to FTO substrate and finally enter the external circuit. These electrons passed through the counterpart and then, enter the electrolyte and the process is repeated.
Figure-6. Performance of CdS sensitized solar cell based on CuS Counter electrode.
Source: Jpeg image.
3.5. J-V Characterization Studies
Figure 7 shows the photocurrent density - photovoltage (J-V) performance of fabricated CdS sensitized solar cell module under solar simulator with one sun radiation. The short circuit current density (Jsc), open circuit voltage (Voc), Fill Factor (FF) and efficiency are the solar cell parameters for fabricated SSSCs which are summarized in Table 1. The FTO/TiO2/CdS-8 solar cell has fill factor(FF) and efficiency about 32.9% and 0.49%. From the Table 1, as prepared CdS sensitized solar cell efficiency depends on the increasing layer of CdS deposition. In ZnS passivation layer on FTO/TiO2/CdS-8, the efficiency increased from 0.49 to 0.78%, because of greatly eliminated interfacial charge recombination to improve the efficiency of the solar cell [4]. In comparison, it is concluded that from the entire four samples, the FTO/TiO2/CdS-8/ZnS-2 sample have greater efficiency in the active area of 0.25 cm2.
Figure-7. J-V curve of as-prepared CdS sensitized solar cell.
Source: OriginPr8.
Table-1. Solar cell parameter of as prepared samples.
Sample code |
Voc(V) |
Jsc(mA/ cm2) |
FF% |
Ƞ% |
FTO/TiO2/CdS-4 |
0.304 |
2.01 |
30 |
0.18 |
FTO/TiO2/CdS-4/ZnS-2 |
0.478 |
3.2 |
23.7 |
0.36 |
FTO/TiO2/CdS-8/ |
0.402 |
3.7 |
32.9 |
0.49 |
FTO/TiO2/CdS-8/ZnS-2 |
0.44 |
6.21 |
28.7 |
0.78 |
Source: MS office word doc.
4. CONCLUSION
In this summary, the successful growth of nanoparticles and microrods simultaneously on FTO glass slide as a TiO2 photoanode by one-step hydrothermal method is achieved. The CdS was deposited on TiO2/FTO glass slide to sensitize the film in visible region. The SEM results confirmed that, the TiO2 microrods were explored on FTO glass slide uniformly. The efficiency of fabricated cell increased due to increase in the layer of deposition of CdS on TiO2/FTO. The efficiency of FTO/TiO2/CdS-8 sample was increased from 0.49% to 0.78% due to the deposition of ZnS passive layer (FTO/TiO2/CdS-8/ZnS-2).
| Funding: This work was fully supported by under DST-SERB (File No: EEQ/2016/198) Govt. of India project. The corresponding author (Dr.G.Ramalingam) acknowledges the Instrumentation facility used under RUSA 2.0 grant No.F.24-51/2014-U, Policy (TNMulti-Gen) Govt. of India projects. |
| Competing Interests: The authors declare that they have no competing interests. |
| Contributors/Acknowledgement: All authors contributed equally to the conception and design of the study. |
REFERENCES
[1] L. Yi, Z. Jun, C. Hui, W. Junfeng, and L. Feng, "BiVO4 semiconductor sensitized solar cell," Science China Chemistry, vol. 9, pp. 1489-1493, 2015.
[2] S. K. Kokate, C. V. Jagtap, P. K. Baviskar, S. R. Jadkar, H. M. Pathan, and K. C. Mohite, "CdS sensitized cadmium doped ZnO solar cell: Fabrication and characterizations," Optik, vol. 157, pp. 628-634, 2018. Available at: https://doi.org/10.1016/j.ijleo.2017.11.098.
[3] S. Mali, S. Desai, D. Dalavi, C. Betty, P. Bhosale, and P. Patil, "CdS-sensitized TiO2 nanocorals: Hydrothermal synthesis, characterization, application," Photochemical & Photobiological Sciences, vol. 10, pp. 1652-1658, 2011. Available at: https://doi.org/10.1039/c1pp05084b.
[4] Y. Li, L. Wei, X. Chen, R. Zhang, X. Sui, Y. Chen, J. Jiao, and L. Mei, "Efficient PbS/CdS co-sensitized solar cells based on TiO 2 nanorod arrays," Nanoscale Research Letters, vol. 8, p. 67, 2013. Available at: https://doi.org/10.1186/1556-276x-8-67.
[5] K.-H. Park and M. Dhayal, "Simultaneous growth of rutile TiO2 as 1D/3D nanorod/nanoflower on FTO in one-step process enhances electrochemical response of photoanode in DSSC," Electrochemistry Communications, vol. 49, pp. 47-50, 2014. Available at: https://doi.org/10.1016/j.elecom.2014.09.011.
[6] N. Buatong, I.-M. Tang, and W. Pon-On, "Quantum dot-sensitized solar cells having 3D-TiO 2 flower-like structures on the surface of titania nanorods with CuS counter electrode," Nanoscale Research Letters, vol. 10, p. 146, 2015. Available at: https://doi.org/10.1186/s11671-015-0844-0.
[7] P. Cheng, Y. Liu, P. Sun, S. Du, Y. Cai, F. Liu, J. Zheng, and G. Lu, "Hydrothermally growth of novel hierarchical structures titanium dioxide for high efficiency dye-sensitized solar cells," Journal of Power Sources, vol. 268, pp. 19-24, 2014. Available at: https://doi.org/10.1016/j.jpowsour.2014.05.118.
[8] Z. Sun, J. H. Kim, Y. Zhao, D. Attard, and S. X. Dou, "Morphology-controllable 1D–3D nanostructured TiO 2 bilayer photoanodes for dye-sensitized solar cells," Chemical Communications, vol. 49, pp. 966-968, 2013. Available at: https://doi.org/10.1039/c2cc37212f.
[9] G. Ramalingam, N. Melikechi, P. D. Christy, S. Selvakumar, and P. Sagayaraj, "Structural and optical property studies of CdSe crystalline nanorods synthesized by a solvothermal method," Journal of Crystal Growth, vol. 311, pp. 3138-3142, 2009. Available at: https://doi.org/10.1016/j.jcrysgro.2009.03.017.
[10] M. Liu, H. Wang, C. Yan, G. Will, and J. Bell, "One-step synthesis of titanium oxide with trilayer structure for dye-sensitized solar cells," Applied Physics Letters, vol. 98, pp. 113-133, 2011. Available at: https://doi.org/10.1063/1.3573799.
[11] C.-H. Chang and Y.-L. Lee, "Chemical bath deposition of CdS quantum dots onto mesoscopic Ti O 2 films for application in quantum-dot-sensitized solar cells," Applied Physics Letters, vol. 91, p. 053503, 2007. Available at: https://doi.org/10.1063/1.2768311.
[12] Y.-S. Lee, C. V. Gopi, A. E. Reddy, C. Nagaraju, and H.-J. Kim, "High performance of TiO 2/CdS quantum dot sensitized solar cells with a Cu–ZnS passivation layer," New Journal of Chemistry, vol. 41, pp. 1914-1917, 2017. Available at: https://doi.org/10.1039/c6nj03898k.
[13] S. Riyaz, A. Parveen, and A. Azam, "Microstructural and optical properties of CuS nanoparticles prepared by sol–gel route," Perspectives in Science, vol. 8, pp. 632-635, 2016. Available at: https://doi.org/10.1016/j.pisc.2016.06.041.
[14] P. B. Nima, V. González-Pedro, P. P. Boix, S. Chavhan, R. Tena-Zaera, G. P. Demopoulos, and I. Mora-Seró, "Colloidal PbS and PbSeS quantum dot sensitized solar cells prepared by electrophoretic deposition," The Journal of Physical Chemistry C, vol. 116, pp. 16391-16397, 2012. Available at: https://doi.org/10.1021/jp3056009.
[15] Z. Du, Z. Pan, F. Fabregat-Santiago, K. Zhao, D. Long, H. Zhang, Y. Zhao, X. Zhong, J.-S. Yu, and J. Bisquert, "Carbon counter-electrode-based quantum-dot-sensitized solar cells with certified efficiency exceeding 11%," The Journal of Physical Chemistry Letters, vol. 7, pp. 3103-3111, 2016. Available at: https://doi.org/10.1021/acs.jpclett.6b01356.
[16] S. Feng, J. Yang, M. Liu, H. Zhu, J. Zhang, G. Li, J. Peng, and Q. Liu, "CdS quantum dots sensitized TiO2 nanorod-array-film photoelectrode on FTO substrate by electrochemical atomic layer epitaxy method," Electrochimica Acta, vol. 83, pp. 321-326, 2012. Available at: https://doi.org/10.1016/j.electacta.2012.07.130.
[17] Y. Hu, B. Wang, J. Zhang, T. Wang, R. Liu, J. Zhang, X. Wang, and H. Wang, "Synthesis and photoelectrochemical response of CdS quantum dot-sensitized TiO 2 nanorod array photoelectrodes," Nanoscale Research Letters, vol. 8, p. 222, 2013. Available at: https://doi.org/10.1186/1556-276x-8-222.
[18] M. S. Abbas and Z. Hassan, "Structural and photoluminescence studies of rutile TiO2 prepared by CBD method on Si substrate," American Journal of Materials Science, vol. 5, pp. 16-20, 2015.
[19] S. F. Shaikh, R. S. Mane, B. K. Min, Y. J. Hwang, and O.-s. Joo, "D-sorbitol-induced phase control of TiO 2 nanoparticles and its application for dye-sensitized solar cells," Scientific Reports, vol. 6, p. 20103, 2016. Available at: https://doi.org/10.1038/srep20103.
[20] Z. Dai, J. Zhang, J. Bao, X. Huang, and X. Mo, "Facile synthesis of high-quality nano-sized CdS hollow spheres and their application in electrogenerated chemiluminescence sensing," Journal of Materials Chemistry, vol. 17, pp. 1087-1093, 2007. Available at: https://doi.org/10.1039/b614203f.
[21] J. Kim, H. Kim, H. Rho, Y. Choi, and J. Park, "Resonant and polarized Raman scattering from single CdS/CdSe core–shell nanowires," Journal of Physics D: Applied Physics, vol. 47, p. 135104, 2014. Available at: https://doi.org/10.1088/0022-3727/47/13/135104.
[22] S. Ali, M. Aslam, W. Farooq, A. Fatehmulla, and M. Atif, "Assembly of CdS quantum dots onto hierarchical TiO2 structure for quantum dots sensitized solar cell applications," Materials, vol. 8, pp. 2376-2386, 2015. Available at: https://doi.org/10.3390/ma8052376.
[23] M. Ganjian, M. Kolahdouz, A. Aletayeb, M. Norouzi, P. Ebrahimi, S. Pourjafari, and M. S. S. Mousavi, "ZnS shell-like CdS quantum dot-sensitized solar cell grown by SILAR approach; effect of electrolyte, counter electrode, and shell thickness," Vacuum, vol. 146, pp. 548-553, 2017. Available at: https://doi.org/10.1016/j.vacuum.2017.02.007.
Views and opinions expressed in this article are the views and opinions of the author(s), International Journal of Chemistry and Materials Research shall not be responsible or answerable for any loss, damage or liability etc. caused in relation to/arising out of the use of the content. |