Accepted Manuscript Title: Structural, optical and electrical properties of the Zn doped MoO3 deposited on porous silicon Authors: Taher Ghrib, Amal L. Al-Otaibi, Mody Alqahtani, Nafla A Altamimi, Afrah Bardaoui, Sami Brini PII: DOI: Article Number: S0924-4247(19)30857-X https://doi.org/10.1016/j.sna.2019.111537 111537 Reference: SNA 111537 To appear in: Sensors and Actuators A Received date: Revised date: Accepted date: 15 May 2019 31 July 2019 2 August 2019 Please cite this article as: Ghrib T, Al-Otaibi AL, Alqahtani M, Altamimi NA, Bardaoui A, Brini S, Structural, optical and electrical properties of the Zn doped MoO3 deposited on porous silicon, Sensors and amp; Actuators: A. Physical (2019), https://doi.org/10.1016/j.sna.2019.111537 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Structural, optical and electrical properties of the Zn doped MoO3 deposited on porous silicon Taher Ghrib1,2,*, Amal L. Al-Otaibi1,2, Mody Alqahtani1,2, Nafla A, Altamimi1, 2, Afrah Bardaoui3, Sami Brini1,2 1 of Department of physics, College of Science, Imam Abdulrahman Bin Faisal University, P.O. Box 1982, 31441, City Dammam, Saudi Arabia. 2 Basic and Applied Scientific Research Center, Imam Abdulrahman Bin Faisal University, P.O. Box 1982, 31441, Dammam, Saudi Arabia. 3 Laboratory of Nanomaterials and Systems of Renewable Energy (LANSER), Center for Research and Technologies of Energy, BorjCedria Technopole, Bp 95, Hammam-Lif, 2050 Tunis, Tunisia ro * Corresponding author: [email protected] 5000000 3 5 7 10 12 min min min min min room temperature ur na 4000000 lP re -p Graphical abstract Z,,(Ohm) 3000000 2000000 Jo 1000000 0 0 2000000 4000000 6000000 8000000 , Z (Ohm) 1 Highlights: In this work it was studied and presented the 5% zinc doped molybdenum oxide deposited on porous silicon prepared with different porous density by varying the etching duration (at 3, 5, 7, 10,12 min), it was denoted: Successful deposition of Zn doped MoO3 films on porous silicon Zn doped MoO3 films are predominantly amorphous in structure with small fraction of orthorhombic MoO3 will crystallized progressively with the etching time. High photocalytic effect of 5%Zn doped MoO3 nanofilm. of ro Abstract: This study presents the preparation process of porous silicon substrates and the deposed -p thin film of 5%Zn doped MoO3 on porous silicon. The first part covers many techniques used to characterize porous silicon substrates. It examines the photoluminescence spectra analysis to re study the etching time effect on the PL intensity, and the UV–vis analysis to find the band gap of the prepared porous silicon substrates with different etching time. The second part treats lP several techniques for studying the etching time effect on the structural, electrical, optical properties of the 5%Zn doped MoO3 thin film. X-ray diffraction (XRD) was used to study the structure of the samples, Fourier transform infrared spectroscopy (FTIR) was used to determine ur na the functional groups. While Photoluminescence spectra analysis, Photocatalytic activity test, and Electrochemical impedance spectroscopy (EIS) were used to study the electrical properties. By increasing the time etching, the structure crystallization was ameliorated, the band gap was decreased from 2.96 to 2.75 eV, a visible optical absorption was detected at 450 to 500nm range which increased from 88 to 92% and the electrical conductivity was increased by ten times from Jo 6.28 × 10−5 to 6.06 × 10−4 −1 . cm−1 . Keywords: Molybdenum oxide; Zinc doping; etching time; photocatalysis; electrochemical impedance spectroscopy. 2 1. Introduction Semiconductor metal oxides such as MoO3, SnO2, ZnO, In2O3, ... have been widely studied for their high thermal and chemical stability and suitability in many applications. Molybdenum trioxide belongs to the transition metal oxides, crystallizes in the orthorhombic structure and has high chemical and thermal stability and interesting physical properties that may be useful in optoelectronic apparatus. Recently, due its attractive electrical properties, the MoO3 oxide was used in many applications such as optical devices [1] , smart windows [2], medicine and agriculture [3] and it was incorporated in transistors [4], catalysts [5], electrochemical capacitors [6] and gas sensors [7-9] to improve their physical properties. of Molybdenum trioxide can be crystallized in three polymorphic phases; the stable phase α-MoO3 and two meta-stable phases β-MoO3 and h-MoO3. Also, it used different elements for the ro doping of MoO3 such as iron used by Ouyang et al. [8] who studied the facile synthesis of Fedoped MoO3 by a hydrothermal method, in which the Fe doping amount was easily adjusted to -p be 0.3, 0.6, 0.7 and 0.9 wt.% by only increasing the reaction time. Kamoun et al.[10] investigated the physical properties of MoO3 in thin films doped with europium element and an aqueous solution of ammonium Molybdate containing various concentration of Europium (0– re 2%) sprayed on a glass substrate heated at 460 °C in air. Other researchers used the Cobalt [11] , the cerium [12],… as dopant to ameliorate its physical properties. lP The MoO3 were mainly manufactured in thin films shape by using chemical or physical methods. The physical methods include magnetron sputtering [13] and pulsed laser deposition (PLD) [14], while the chemical methods include spay pyrolysis [15], chemical vapor deposition ur na (CVD) [16] and electrochemical deposition methods [17, 18]. These processes are very simple and can be operated at relatively low deposition temperature using relatively low concentrations and gave thin films in good adhesion with the substrate; demonstrating a uniform molecular distribution, excellent optical properties and high purity. The nature of the used wafer on the creation and the grains’ shape constituting the prepared thin film and its overall physical Jo properties such as the glass [12, 14], porous silicon [2, 19] and graphite [20]. This work examined the thin film of MoO3 deposited on porous silicon; which was prepared in various etching times. The prepared MoO3 thin films deposited on porous silicon were studied using the X-ray diffraction (XRD) to investigate the evolution of its structure, the scanning electron microscopy (SEM) to investigate its morphology, the UV–vis spectra and photoluminescence measurements in order to analyze the optical properties and measure the band gap, the Fourier transform infrared spectroscopy (FTIR) to analyze the existing functional 3 groups and its purity and the Electrochemical impedance spectroscopy (EIS) and Hall effect to study the evolution of its electrical properties. The photocatalytic effect of the zinc doped MoO3 deposited on porous silicon substrate on methylene blue (MB) was examinated and the obtained results were related to the optical and electrical properties behaviors. 2. Porous silicon substrate. 2.1. Preparation The used substrate as initial specimen was n-type Si with orientation (100). The Si specimen was cleaned in two steps. Firstly, by using an ethanol to remove the oxide layer from its surface. The second step was by using the HCl (10%) for 5 min to remove mineral of impurities. Thin homogenous Porous silicon (PSi) layers of different thicknesses were formed on the front surface of the substance using electrochemical (EC) method. Fig. 1 shows EC ro system, in this case the n-type silicon substrate surface emerged in a solution constituted of hydrofluoric acid and ethanol (1:1, 20% diluted). One face of the silicon wafer was in contact -p with aluminum anode plate and the other side with an electrolyte which plunged a platinum electrode (cathode) by using a current intensity of 10 mA by 3, 5, 7, 10, 12 min at room re temperature. lP Fig. 1. 2.2. Photoluminescence spectra analysis Fig. 2 offers the variation of photoluminescence spectra at room temperature using 340 ur na nm wavelength excitation, with etching duration for the porous silicon (PSi) specimens obtained at the current densities 10 mA/cm2 at 3, 5, 7, 10, 12 min. The peak of the intensity shifted to the left (blue range) and the maximum wavelength increased from 472.97 to 494.39 nm when increasing the etching duration. It is denoted that the PL intensity increased with the etching duration and then with the porosity density it became higher for the highest etching duration (12 Jo min). These results are in good agreement with Omar et al.[2] who studied the effects of electrochemical etching time on the performance of porous silicon solar cells on crystalline ntype (100) and (111). This increase of the photoluminescence intensity may be influenced by the increase in the total volume of the nano-pores and the surface of the porous silicon. Also, the blue shift of PL spectra, as shown in fig. 2, may be attributed to the quantum confinement effect between electrons in the conduction band and the holes in the valence band. The confinement number increases with photons number trapped inside the porous silicon. This 4 trapping of photons will increase with density and the volume of the generated pores. The variation PL spectra confirm that the specimens have a different porous layer and pore diameter. Because when the etching duration increases, the pores size increases and the Pl intensity will decrease; but in our case, it increased. This increase may be interpreted by the apparition of new pores inside the first created pores. Therefore, the increase in the etching time is attributed to the apparition of pores with double wells whose inside is of nano-size and favors charge carrier quantum confinement. The probability of recombination of e and h is higher in very small structures (quantum confinement effects), leading to higher emissions. The pores quantum dimensions of the structure in the sample favorites the PL shift towards shorter wavelengths. of The interfacial complexes in the form of non-bridging oxygen hole centers are also possible sources of PL in PSi such as Si-O coming from the oxidation of the surface atoms. The FWHM ro of the photoluminescence maximum decreased when the etching time increased as indicated in table 1. The width of the photoluminescence peak is a good indicator of material quality, -p because the photoluminescence peak may easily be broadened by structural defects or impurities. re Fig. 2. and Table 1. lP 2.3. UV–vis analysis Fig. 3 shows the optical absorption of the Psi n-type (100) samples prepared under current density 10 mA/cm2, with different etching times 3, 5, 7, 10 and 12min. UV-vis reflectance ur na spectra of Psi substrates prepared are measured in the range of 400-800 nm. It is denoted that there was a small increase in the optical absorption when the etching time increased. The increase in the optical absorption can be interpreted by the confinement and trapping of photons inside the pores and after a multi-reflection which minimizes their optical reflection by the PSi material, and they will be absorbed. The highest effective absorption of the PS layer was Jo recorded at 12 min etching duration, which clearly reduced light reflection and increased lighttrapping at wavelengths ranging from 400 to 1000 nm, compared with the non-etched Si sample and the other etched samples. Fig. 3. It is well-known that the silicon is an indirect transition semiconductor, the absorption coefficient and the band gap energy Eg are related by the Tauc relationship[21](αhυ)2=A(hυEg), where hυ is the photons excitation energy. In fig.4, the band gaps (Eg) values are found to 5 be increased in all samples and their values are 2.091, 2.095, 2.104, 2.109 and 2.131 eV respectively for 3, 5, 7, 10, 12 min etching time as presented in table 1. It is denoted from these Eg values that the band gap increases versus the etching process out of the increase in the pores density and volume leading the Si wafer to an insulator behavior due to the vacuum created inside. These results are in good agreement with some other works. Hussein et al.[19], for instance, studied the effect of current density and etching time on photoluminescence and energy band gap of p-type porous silicon. Also Douri et al.[22] examined the Etching time affect on optical properties of porous silicon for solar cells fabrication. It fits the absorption curve between 1and 2.4 eV with this formula and estimates the energy gap Eg. of Fig. 4. ro 3. Properties of 5% Zn doped MoO3thin film deposited on porous silicon 3.1. Preparations procedures -p At first, MoO3 in powder shape was prepared by a hydrothermal method [23]. Ammonium heptamolybdate tetrahydrate (AHM; (NH4)6Mo7O24·4H2O), and nitric acid (HNO3) were used re as precursors. The AHM was dropped gradually in 30 ml distilled water under uniform stirring at room temperature until the saturation. The resulting solution was acidified with nitric acid lP (2.2 M) to a total volume of 70 ml, made in a stainless steel autoclave and heated for 40 hours at 180 ° C. The precipitate was washed with deionized water several times and dried in the oven ref-K. SI. 1700 S for 7h at 70°C. The dried product of yellowish color was calcined for 5 h at ur na 600°C giving a fine MoO3 powder. Secondly , to get 5% Zn doped MoO3, the zinc nitrate (Zn(NO3)2·6H2O) powder was added to previously prepared powder (MoO3 pure) in appropriate fractions to obtain a final solid solution of 1:20 portions (5 wt. % Zn and 95 wt. % MoO3) denoted Z5M. After that, the mixture was grinded in an agate mortar and transferred into a 50 mL stainless steel autoclave for 25 h at Jo 200°C. After being washed repeatedly with distilled water, the obtained white powder was dried for 12 h at 80°C. Finally the Z5M powder was dissolved in a hydrogen peroxide (H2O2) solution. Then, it was spread on a well cleaned PSi substrate (2×2cm size), which was placed on the substrate holder of a spin coating unit and spun at 2000 rpm. The coated MoO3 films of 200 nm thickness deposited on different etched silicon substrates were annealed from 900 °C for 1h and characterized by the following analysis. 6 3.2. X-ray diffraction analysis X-ray diffraction (XRD) patterns of the prepared samples were depicted from 10° to 80° with an incident X-ray angle 2° and evaluated according to JCPDS card No. 0050508. Fig. 5-a gives the XRD patterns for all samples at an incident angle of 2ᵒ with two broad diffraction peaks at around 2=22ᵒ and 62ᵒ angles corresponding to (110) and (430) respectively. These are related to the orthorhombic structure implying that the Zn doped MoO3 deposited on PSi starts with an amorphous structure and tends progressively towards a crystalline structure of orthorhombic -MoO3 phase. Fig. 5-b shows the SEM image of the Zn doped MoO3 deposited on porous Si etched at 10 min which demonstrates randomly distributed pores on the surface of filled with the film with various sizes ranging from about 60 nm to 85 nm. ro Fig. 5 -p 3.3. FTIR Analysis Fig. 6 shows the Fourier transform infrared (FTIR) spectrum of MoO3 deposited on porous silicon measured in the range of 400–3000 cm-1. The spectrum offers two peaks at 809 re cm−1 assigned to the stretching mode of oxygen in Mo–O–Mo bonds inter-molecular and 1092 cm−1 assigned to the terminal Mo=O stretching intra-molecular vibration [24, 25]. These two lP peaks correspond to a layered orthorhombic α-MoO3 phase in accordance with the result obtained with the XRD study. Also, it shows a broad peak at 1208 cm−1conforming to the bending vibration of Si–O–Si asymmetric stretching modes of a SiO2 [26] thin film formed on ur na the porous silicon surface after etching. Also, 2254 cm-1 belongs to the residual of CO2 present in the surrounding air [27]. The peak obtained at 470 cm−1 provides the Zn-O finger print related to the stretching vibration in the MoO3 structure [27]. This general form of these curves indicates no formation of new bonds or apparition of alternative contamination after deposition Jo on the silicon wafers. Fig. 6 3.4. Photoluminescence spectra analysis Usually the origin of photoluminescence (PL) can be attributed to four facts which are the nano-crystals surface states, the quantum confinement, the specific defects and the phase 7 disorder in structures. Related to these facts, the surface and interfacial properties can also influence it. The prepared materials revealed an amorphous phase, and this means in practice that the quantum size effect does not play the crucial role in PL properties of the prepared samples. But the morphology of the quantum pores on the silicon has a slight effect on PL active structures. Photoluminescence spectra of MoO3 deposition on porous silicon are shown in fig. 7 in the 200–700 nm range. Four samples with silicon etched at 3min, 5min, 7min, and 10min show two emission peaks in photoluminescence spectra centered at 310 and 380 nm while the sample with silicon substrate etched for 12min present another peak centered at 420 nm. The two peaks, 380 nm and 420 nm, can be attributed to the blue emission which gives to of the samples etched at 12 min and seems to be the best one for the luminescence in a visible range [28]. The origin of this major difference in the observed PL intensity is related to the ro difference in temperature and etching time. These emissions can be related to band transitions due to the presence of Mo, O and Zn interstitial sites as well as the surface defects which are -p correlated to the density of defaults. These results are useful for the development of advanced optoelectronic and nano devices based on a wide band gap luminescent metal oxide like MoO3. Future work will be focused on the wavelength dependent emission properties MoO3 and to see re the possibilities to enhance the visible emission. lP Fig. 7 3.5. Photocatalytic activity test ur na Fig. 8 shows the UV-vis absorption spectra of the MB solution at the same reaction time 1h for all samples MoO3/porous silicon catalyst. The MB solution is constituted of an MB powder dissolved in hydrogen peroxide solvent. This figure shows the variation of the optical absorption of the methyl blue (MB) after its degradation with the prepared samples. The photocatalytic activity of the samples was evaluated by the degradation of MB solution under a Jo visible light irradiation [29, 30]. It exhibits the UV–vis absorption spectroscopy recording the absorption behavior of the solution after treatment by comparing it with the characteristic light absorption of MB. Initially, the maximum absorption peak of MB is located at 667 nm, accompanied by a shoulder peak at 618 nm [31]. It is obvious that both absorption peaks have not shifted with the etching time but just subjected a decreasing in their intensities, indicating that MB has been effectively degraded. Also, it is brightly seen that the intensity of characteristic peak for MB remarkably decreases with treatment at 3 min and reaches about zero 8 after 12 min etching time, suggesting the high photocalytic effect of the 5%Zn doped MoO3 nanofilm. Fig. 8 3.6. UV–vis analysis Fig.9 shows the absorbance spectra of MoO3 deposited on PSi for five different etching times at 3, 5, 7, 10 and 12 min at a heat treatment of 900ᵒC. UV-vis spectra of these prepared samples are measured in the range of 300-1000 nm. It is denoted that there was an overall decrease in the optical absorption with the wavelength for all the etching times and pass by one of maximum absorption in the range centered at about 330nm and another broad peak at the visible range centered at 450 to 500nm. Also, there was an increase in the optical absorption with the ro etching time which can be attributed to the enhancement in the pores volume and density; which can fill more material of MoO3:Zn and increase the absorption of the photons trapped -p inside. In fig.10, (αhν)2 was plotted as a function of photon energy (hν). For various etching times, it is denoted that the band gap value is affected by the etching time. From 3 min to 12 re min, the band gap increases 2.78, 2.96, 2.90, 2.84, 2.75eV respectively which are summarized in table 2. 3.7. Electrical properties. lP Fig. 9 and Fig. 10 ur na Electrochemical impedance spectroscopy (EIS) is a nondestructive technique that can study the chemical and physical properties in solids. Also, it can study the electrical properties of materials. The results of the impedance measurement can be presented by the complex plane plot of the opposite of the imaginary part - Z" versus the real part Z' of the complex impedance Z. Each point on the complex plane plot represents the impedance at a certain frequency [32]. Jo For the Nyquist plot as obtained from the prepared specimen in fig. 11, the equivalent impedance of these elements may be arranged in parallel or in series. Through the Nyquist form, when it takes a semicircle, the equivalent circuit can be constituted of two elements; one resistor (R1) in series with another element constituted of resistor (R2) in parallel with capacitor C1 as shown in Fig. 11 [33]. R1 is an ohmic resistance obtained at a high frequency; which is related to deposited thin film (5%Zn doped MoO3) and R2 is the diameter of the semicircle which indicates the interfacial resistance between the thin film and the porous silicon substrate. 9 Fig. 11 The total equivalent impedance in series is given by the sum of the impedance values of each individual element: 𝑍𝑒𝑞 = 𝑅1 + 𝑍𝑅2 ||𝐶1 In parallel circuit, the impedance is given by the reverse of the impedance fraction sum for each element: 1 𝑍𝑅2 𝐶1 = 1 𝑅2 + 1 𝑍𝐶1 1 Where 𝑍𝐶 1= 𝑗𝐶 is the capacitor impedance and j the imaginary number defined as j2=-1, ω is 1 1 𝑅2 𝑍𝑅2𝐶 = + 𝑗𝐶1 = 1+𝑗𝑅2 𝐶1 𝑅2 𝑅2 1+𝑗𝑅2 𝐶1 𝑅2 (1−𝑗𝑅2 𝐶1 ) 1+(𝑅2 𝐶1 )2 = 𝑅1 + 𝑅2 1+(𝑅2 𝐶1 ) −𝑗 2 𝑅22 𝐶1 1+(𝑅2 𝐶1 )2 lP = 𝑅1 + 𝑅2 1 + 𝑗𝑅2 𝐶1 re 𝑍𝑒𝑞 = 𝑅1 + ro 𝑍 𝑅2 𝐶 = -p 1 of angular frequency. ur na = 𝑍 ′ + 𝑗 Z'' It can be denoted that, at high frequencies, the second and third terms in the fraction will go to zero and only 𝑅1 is observed. When the frequency is decreased even further the denominator will go to a value of one, because 𝑅2 𝐶1 tends to zero and the imaginary part will be infinitely small; only R1+R2 will then be observed. At a medium frequency the peak of the semicircle will be observed when the value for the frequency is equal to 1/𝑅2 𝐶1 ; then the total Jo impedance will be: 𝑍𝑒𝑞 = 𝑅1 + 𝑅2 𝑅2 −𝑗 2 2 The Nequist impedance spectra of MoO3/PSi under darkness are shown in fig.12. These spectra are characterized by a semicircular shape. The radius of these semicircles and the resulting resistance show an etching time dependency; it decreases when the etching time is increasing (from 3 min to 12 min); leading to the improvement in the electrical properties of the prepared 10 material [34]. The decrease in the curvature radius estimates the evolution of the effective electron lifetime, the effective electron chemical diffusion coefficient and the effective electron diffusion length and mobility in the prepared thin film; which gives the material the electrical properties that lead to a high photovoltaic efficiency. The decrease in the semicircle radius implies a decrease in the electron lifetime leading to a decrease in the volume charge Nb and surface charge Ns densities in the conduction band; which can vanish the overall photovoltaic efficiency. The decrease in the electron lifetime appears clearly in the PL measurement of fig. 7 which increases due to the charge recombination of the electron lifetime. Also, the decrease in the curative radius is accompanied by a decrease in the resistance R1and the resistance R2; of which facilitates the electron migration from the thin film to the silicon substrate and diminishes the lifetime. ro Fig. 12 -p These results are in good agreement with those obtained by Hall Effect measurement summarized in table 2; which clearly shows a decrease in the volume and surface charge re densities with the etching time and an increase in the charge mobility µ and the electrical Table 2 ur na Conclusion lP conductivity σ. These materials can be used with good performance in photovoltaic cells. This work studied the effect of deposition 5%Zn doped MoO3 on porous silicon etched with various times on the evolution of their electrical, optical and structural properties. It was observed that the porous silicon substrates have a band gap from 1.5 to 1.6 eV which increases Jo versus the etching time. Also, it was denoted that the PL intensity increases with the etching duration. For the study of the etching time effect on the electrical, structural, optical properties of the 5% Zn doped MoO3 thin film; it used the XRD which shows that the sample present amorphous structure will be crystallized for the highest etching time giving an orthorhombic phase. PL spectra show two emission peaks centered respectively at 310 and 380 nm; which are attributed to UV and blue emissions, the band gap energy decreases from 2.96 to 2.75 eV. The 11 etching time improves strongly the photocatalytic effect towards the methyl blue and the electrical properties. Acknowledgements The authors gratefully acknowledge use of the services and facilities of the Basic and Jo ur na lP re -p ro of Applied Scientific Research Center at Imam Abdulrahman Bin Faisal University. 12 References Jo ur na lP re -p ro of [1] C. Dwivedi, T. Mohammad, V. Dutta, Creation of Au nanoparticles decorated MoO3 nanorods using CoSP and the application as hole transport layer (HTL) in plasmonic-enhanced organic photovoltaic devices, Solar Energy, 176 (2018) 22-29. [2] K.A. Salman, K. Omar, Z. Hassan, The effect of etching time of porous silicon on solar cell performance, Superlattices and Microstructures, 50 (2011) 647-658. [3] T. He, J. Yao, Photochromism in composite and hybrid materials based on transition-metal oxides and polyoxometalates, Progress in Materials Science, 51 (2006) 810-879. [4] N. Kumar, B.P.A. George, H. Abrahamse, V. Parashar, J.C. Ngila, Sustainable one-step synthesis of hierarchical microspheres of PEGylated MoS2 nanosheets and MoO3 nanorods: Their cytotoxicity towards lung and breast cancer cells, Applied Surface Science, 396 (2017) 818. [5] S.E. Al Garni, A.F. Qasrawi, Design and characterization of MoO3/CdSe heterojunctions, Physica E: Low-dimensional Systems and Nanostructures, 105 (2019) 162-167. [6] C.I. Fernandes, S.C. Capelli, P.D. Vaz, C.D. Nunes, Highly selective and recyclable MoO3 nanoparticles in epoxidation catalysis, Applied Catalysis A: General, 504 (2015) 344-350. [7] L. Zhu, W. Zeng, Y. Li, J. Yang, Enhanced ethanol gas-sensing property based on hollow MoO3 microcages, Physica E: Low-dimensional Systems and Nanostructures, 106 (2019) 170175. [8] Q.-Y. Ouyang, L. Li, Q.-S. Wang, Y. Zhang, T.-S. Wang, F.-N. Meng, Y.-J. Chen, P. Gao, Facile synthesis and enhanced H2S sensing performances of Fe-doped α-MoO3 microstructures, Sensors and Actuators B: Chemical, 169 (2012) 17-25. [9] H.M.M. Munasinghe Arachchige, D. Zappa, N. Poli, N. Gunawardhana, E. Comini, Gold functionalized MoO3 nano flakes for gas sensing applications, Sensors and Actuators B: Chemical, 269 (2018) 331-339. [10] O. Kamoun, A. Boukhachem, M. Amlouk, S. Ammar, Physical study of Eu doped MoO3 thin films, Journal of Alloys and Compounds, 687 (2016) 595-603. [11] A. Boukhachem, M. Mokhtari, N. Benameur, A. Ziouche, M. Martínez, P. Petkova, M. Ghamnia, A. Cobo, M. Zergoug, M. Amlouk, Structural optical magnetic properties of Co doped α-MoO3 sprayed thin films, Sensors and Actuators A: Physical, 253 (2017) 198-209. [12] P. Dumrongrojthanath, A. Phuruangrat, S. Thipkonglas, B. Kuntalue, S. Thongtem, T. Thongtem, Synthesis and characterization of Ce-doped MoO3 nanobelts for using as visiblelight-driven photocatalysts, Superlattices and Microstructures, 120 (2018) 241-249. [13] M. Morales-Luna, S.A. Tomás, M.A. Arvizu, M. Pérez-González, E. Campos-Gonzalez, The evolution of the Mo5+ oxidation state in the thermochromic effect of MoO3 thin films deposited by rf magnetron sputtering, Journal of Alloys and Compounds, 722 (2017) 938-945. [14] O. Hussain, K. Srinivasa Rao, K. Madhuri, C. Ramana, B. Naidu, S. Pai, J. John, R. Pinto, Growth and characteristics of reactive pulsed laser deposited molybdenum trioxide thin films, ApPhA 75 (2002) 417–422. [15] F. Chandoul, A. Boukhachem, F. Hosni, H. Moussa, M.S. Fayache, M. Amlouk, R. Schneider, Change of the properties of nanostructured MoO3 thin films using gamma-ray irradiation, Ceramics International, 44 (2018) 12483-12490. [16] D. Barreca, G.A. Rizzi, E. Tondello, A chemical vapour deposition route to MoO3–Bi2O3 thin films, Thin Solid Films, 333 (1998) 35-40. [17] T.V. Sviridova, A.S. Logvinovich, D.V. Sviridov, Electrochemical growing of Ni-MoO3 nanocomposite coatings via redox mechanism, Surface and Coatings Technology, 319 (2017) 611. 13 Jo ur na lP re -p ro of [18] X. Cheng, Y. Li, L. Sang, J. Ma, H. Shi, X. Liu, J. Lu, Y. Zhang, Boosting the electrochemical performance of MoO3 anode for long-life lithium ion batteries: Dominated by an ultrathin TiO2 passivation layer, Electrochimica Acta, 269 (2018) 241-249. [19] M.J. Hussein, W.M.M. Yunus, H.M. Kamari, A. Zakaria, H.F. Oleiw, Effect of current density and etching time on photoluminescence and energy band gap of p-type porous silicon, Optical and Quantum Electronics, 48 (2016) 194. [20] X.-Y. Yue, X.-L. Li, J.-K. Meng, X.-J. Wu, Y.-N. Zhou, Padding molybdenum net with Graphite/MoO3 composite as a multi-functional interlayer enabling high-performance lithiumsulfur batteries, Journal of Power Sources, 397 (2018) 150-156. [21] M. Salem, S. Akir, T. Ghrib, K. Daoudi, M. Gaidi, Fe-doping effect on the photoelectrochemical properties enhancement of ZnO films, Journal of Alloys and Compounds, 685 (2016) 107-113. [22] Y. Al-Douri, N. Badi, C.H. Voon, Etching time effect on optical properties of porous silicon for solar cells fabrication, Optik, 147 (2017) 343-349. [23] A. L. Al-Otaibi, T. Ghrib, M. Alqahtani, M. A. Alharbi, R. Hamdi, I. Massoudi, Structural, optical and photocatalytic studies of Zn doped MoO3 nanobelts, Chemical Physics 525 (2019) 110410. [24] T. Chiang, H. Yeh, The synthesis of α-MoO3 by ethylene glycol, Materials, 6 (2013) 46094625. [25] L.G. Pereira, L.E.B. Soledade, J.M. Ferreira, S.J.G. Lima, V.J. Fernandes, A.S. Araújo, C.A. Paskocimas, E. Longo, M.R.C. Santos, A.G. Souza, I.M.G. Santos, Influence of doping on the preferential growth of α-MoO3, Journal of Alloys and Compounds, 459 (2008) 377-385. [26] Q. Hu, H. Suzuki, H. Gao, H. Araki, W. Yang, T. Noda, High-frequency FTIR absorption of SiO2/Si nanowires, Chemical Physics Letters 378 (2003) 299–304. [27] S. J. Ranan, M. I. Qadirn, O. Nur, M. Willander, Naturally oxidized synthesis of ZnO dahlia-flower nanoarchitecture, Ceramics International 40 (2014) 13667–13671. [28] A. Boukhachem, O. Kamoun, C. Mrabet, C. Mannai, N. Zouaghi, A. Yumak, K. Boubaker, M. Amlouk, Structural, optical, vibrational and photoluminescence studies of Sn-doped MoO3 sprayed thin films, Materials Research Bulletin, 72 (2015) 252-263. [29] Y. Li, L. Huang, J. Xu, H. Xu, Y. Xu, J. Xia, H. Li, Visible-light-induced blue MoO3–C3N4 composite with enhanced photocatalytic activity, Materials Research Bulletin, 70 (2015) 500505. [30] Y. Ma, Y. Jia, Z. Jiao, L. Wang, M. Yang, Y. Bi, Y. Qi, Facile synthesize α-MoO3 nanobelts with high adsorption property, Materials Letters, 157 (2015) 53-56. [31] Y. Jin, N. Li, H. Liu, X. Hua, Q. Zhang, M. Chen, F. Teng, Highly efficient degradation of dye pollutants by Ce-doped MoO3 catalyst at room temperature, Dalton Transactions, 43 (2014) 12860-12870. [32] Z. He, F. Mansfeld, Exploring the use of electrochemical impedance spectroscopy ( EIS ) in microbial fuel cell studies, 2 (2009) 215-219. [33] H. Cesiulis, N. Tsyntsaru, A. Ramanavicius, G. Ragoisha, The Study of Thin Films by Electrochemical Impedance Spectroscopy, in: I. Tiginyanu, P. Topala, V. Ursaki (Eds.) Nanostructures and Thin Films for Multifunctional Applications: Technology, Properties and Devices, Springer International Publishing, Cham, 2016, pp. 3-42. [34] S. Ebrahim, Impedance spectroscopy and equivalent circuits of heterojunction solar cell based on n-Si/polyaniline base, Polymer Science Series A, 53 (2011) 1217-1226. 14 Author Biography Taher Hcine Ghrib is currently an associate professor and aggregated teacher in physic, at the College of Sciences of Dammam of Imam Abdul Rahman bin Faisal University-Saudi Arabia. He obtained his habilitation in Physics at the science college of Carthage-UniversityTunisia on 2017. He prepared his thesis in Tunisia that of covers “investigation of the thermally treated steel by the Photothermal Deflection Technique” and presented on 2008. He obtained his aggregation in ro Physics and Chemistry at the preparatory institute for scientific and technical studies of El Marsa on 2001 of Tunisia. He worked as a course teacher of physics. He worked on steel and -p metal alloys in his thesis; he demonstrated a very practical method for measuring the mechanical properties of steels such as hardness by measuring the thermal conductivity by means of mathematical models and experimental nondestructive measurements. Almost all of re his work is published in numerous publications in various journals and books. lP Now he is specialized in nano and porous materials and thin films of metals, perovskites and alloys. He is involved in the project ETRERA (Empowering Tunisian Renewable Energy Research Activities) which object is to realize a fuel cell of high electrical performance and he ur na has led many scientific projects in Saudi Arabia. And he is the principle investigator of the Jo nanomaterials technology unit. 15 Figure captions Fig. 1. Schematic diagram of the porous silicon anodization circuit. Fig. 2. Variation of photoluminescence peaks for porous silicon specimens prepared under current density 10 mA/cm2, with different etching time 3, 5, 7, 10 and 12 min. Fig. 3. Solid state UV–vis spectrum of porous silicon at 3, 5, 7, 10, 12 min under current density 10 mA/cm2. of Fig. 4. Band gap of PSi samples prepared under current density 10 mA/cm2, with different ro etching time 3, 5, 7, 10 and 12 min. Fig. 5. XRD patterns of 5%Zn doped MoO3 deposited on n-type porous silicon prepared under of the obtained specimen for 10min etching time. -p current density 10 mA/cm2, with different etching time 3, 5, 7, 10 and 12 min and SEM image 10, 12 min and annealed at 900 ᵒC. re Fig. 6. FTIR absorbance of 5%Zn doped MoO3 deposited on porous silicon etched at 3, 5, 7, min and annealed at 900 ᵒC. lP Fig. 7. PL spectra of 5%Zn doped MoO3 deposited on porous silicon etched at 3, 5, 7, 10, 12 Fig. 8. UV-vis absorption spectra of MB solution over 5%Zn doped MoO3 on porous silicon ur na etched at 3, 5, 7, 10, 12 min and annealed at 900 ᵒC. Fig. 9. Optical absorbance of 5%Zn doped MoO3 deposited on porous silicon wafers prepared under current density 10 mA/cm2, with different etching time 3, 5, 7, 10 and 12 min and Jo annealed at 900 ᵒC. Fig. 10. Tauc plots of the specimens 5%Zn doped MoO3 deposited on Psi wafers prepared with different etching time 3, 5, 7, 10 and 12 min and annealed at 900 ᵒC. Fig. 11. Equivalent circuit model employed in analysis of electrochemical impedance data for the 5%Zn doped MoO3 deposited on porous silicon and annealed at 900 ᵒC. Fig. 12. The Nequist impedance spectra of 5%Zn doped MoO3 deposited on Psi wafers etched at 3, 5, 7, 10 and 12 min and annealed at 900 ᵒC, under darkness at room temperature. 16 Jo ur na lP -p re Fig. 1. ro of Figures list: 17 9 8 3 min 5 min 7 min 10 min 12 min 7 of 6 5 ro 4 3 -p 2 1 0 -1 500 700 600 wavelength(nm) lP 400 re photoluminescence intensity (a.u) 10 Jo ur na Fig. 2. 18 800 900 0.90 0.80 0.75 0.60 0.55 400 3min 5min 7min 10 m i n 12 m i n 500 ro 0.65 of 0.70 -p Absorbance (a.u.) 0.85 600 700 800 re wavelength (nm) Jo ur na lP Fig. 3. 19 900 1000 14 12 10 (h ev) 3min 5min 7min 10min 15min 8 6 of 4 0 0.5 1.0 1.5 2.0 2.5 3.0 4.0 Jo ur na lP re Fig. 4. 3.5 -p hev) ro 2 70 60 ity (a.u.) 50 40 (110) 3 min 5 min 7 min 10 min 12 min (b) (a) (430) 20 of ro -p re lP ur na Jo Fig. 5. 21 2.5 1092 3 min 5 min 7 min 10 min 12 min Absorbance (a.u.) 2.0 1.5 1208 470 2341 809 1.0 0.5 500 1000 1500 2000 2500 3000 3500 4000 -1 ro Wavenumber (cm ) Jo ur na lP re -p Fig. 6. 22 of 0.0 600 3 min 5 min 7 min 10 min 12 min 300 of Pl intensity(a.u.) 900 0 200 400 600 Jo ur na lP re Fig. 7. 23 800 -p Wave lenght(nm) ro 0 MB 3 min 5 min 7 min 10 m i n 12 m i n 0.2 of absorption 0.4 500 550 600 650 700 Jo ur na lP re Fig. 8. 24 750 -p n m) ro 0.0 800 0.90 of 3 min 5 min 7 min 10 min 12 min 0.85 0.80 300 400 500 600 700 Jo ur na lP re Fig. 9. 25 800 -p Wavelength (nm) ro Absorbance (a.u.) 0.95 900 24 22 20 18 14 10 3 min 5 min 7 min 10 min 12 min 8 6 4 2 0 3 4 re heV) -p 2 Jo ur na lP Fig. 10. 26 of 12 ro 2 hu) (eV) 2 16 5 Equivalent circuit Nyquist plot 2000000 room temperature lP Z,,(Ohm) 3000000 min min min min min -p 4000000 3 5 7 10 12 re 5000000 ro of Fig. 11. ur na 1000000 0 Jo 0 2000000 4000000 6000000 8000000 , Z (Ohm) Fig. 12. 27 Table captions Table 1. Show the FWHM of photoluminescence peaks with different etching time 3, 5, 7, 10 and 12 min. Table 1. PSi Band Gap FWHM from Pl 3 min 2.091 0.663 5 min 2.095 0.633 7 min 2.104 0.607 10 min 2.109 0.557 12 min 2.131 ro of Etching time -p 0.500 Table 2. lP 3, 5, 7, 10 and 12 min and annealed at 900ᵒC. re Table 2. Electrical properties of5%Zn doped MoO3 deposited on porous silicon at different etching time NS [/cm2] µ[cm2/Vs] σ[/Ohm.cm] Band Gap [ eV ] −1.460 × 1014 −5.839 × 109 2.685 6.279 × 10−5 2.78 Z5M/PSi5 −1.267 × 1013 −5.066 × 108 1.285 × 102 2.607 × 10−4 2.96 Z5M/PSi7 −7.977 × 1013 −4.387 × 109 2.964 × 102 3.788 × 10−4 2.90 Z5M/PSi10 −2.275 × 1012 −1.138 × 108 1.493 × 103 5.444 × 10−4 2.84 Z5M/PSi12 −1.239 × 1012 −6.194 × 107 3.052 × 103 6.057 × 10−4 2.75 Nb [/cm3] Z5M/PSi3 Jo ur na Sample 28