Structural, optical and electrical properties of the Zn doped MoO3 deposited on porous silicon

Accepted Manuscript
Title: Structural, optical and electrical properties of the Zn
doped MoO3deposited on porous silicon
Authors: Taher Ghrib, Amal L. Al-Otaibi, Mody Alqahtani,
Nafla A Altamimi, Afrah Bardaoui, Sami Brini
PII: S0924-4247(19)30857-X
DOI: https://doi.org/10.1016/j.sna.2019.111537
Article Number: 111537
Reference: SNA 111537
To appear in: Sensors and Actuators A
Received date: 15 May 2019
Revised date: 31 July 2019
Accepted date: 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
MoO3deposited on porous silicon, Sensors and amp; Actuators: A. Physical (2019),
https://doi.org/10.1016/j.sna.2019.111537
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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
1Department of physics, College of Science, Imam Abdulrahman Bin Faisal University, P.O. Box 1982,
31441, City Dammam, Saudi Arabia.
2Basic and Applied Scientific Research Center, Imam Abdulrahman Bin Faisal
University, P.O. Box 1982, 31441, Dammam, Saudi Arabia.
3Laboratory of Nanomaterials and Systems of Renewable Energy (LANSER), Center for Research and
Technologies of Energy, BorjCedria Technopole, Bp 95, Hammam-Lif, 2050 Tunis, Tunisia
* Corresponding author: [email protected]
Graphical abstract
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12 m i n
Z,,(Ohm)
Z,(Ohm)

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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.
Abstract:
This study presents the preparation process of porous silicon substrates and the deposed
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
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
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
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
  to  .
Keywords: Molybdenum oxide; Zinc doping; etching time; photocatalysis; electrochemical
impedance spectroscopy.

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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.
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
doping of MoO3 such as iron used by Ouyang et al. [8] who studied the facile synthesis of Fe-
doped MoO3 by a hydrothermal method, in which the Fe doping amount was easily adjusted to
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–
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.
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
(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
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

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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
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
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
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
temperature.
Fig. 1.
2.2. Photoluminescence spectra analysis
Fig. 2 offers the variation of photoluminescence spectra at room temperature using 340
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
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 n-
type (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