Hydrothermal synthesis of MoS2 nanosheets for multiple wavelength optical sensing applications
Introduction
Graphene is the rising material in the field of nanotechnology and it has provided researchers with skills and tools to forward studies of other two-dimensional (2D) layered materials. In a 2D layered material, there is a strong covalent bonds interaction between the atoms of crystalline lattice structure and atoms interact with weak van der Waals forces between the layers of layered material. As compared to graphene, transition metal dichalcogenides (TMDs) possess remarkable electrical, optical and electronic properties [[1], [2], [3]]. MoS2 comes from the family of layered TMD’s (MX2, M = Mo, W; X = S, Se, Te). Its atomic structure is a hexagonal arrangement of Mo and S atoms that layered on top of each other and form a trigonal prismatic arrangement. The layered spacing of MoS2 nanosheets is 6.5 Å [4]. Bulk MoS2 is an indirect bandgap semiconductor with a bandgap of 1.29 eV, whereas monolayered MoS2 has a direct bandgap of 1.8 eV due to quantum confinement effect and hybridization change in d orbital of Mo atoms and pz of S-atom [5]. Thus, 2D MoS2 is an optically active and interesting material for device applications such as chemical sensors, electronic device, photodetectors etc. [[6], [7], [8], [9], [10]].
In this work, MoS2 nanosheets were prepared by a facile hydrothermal method. This method is far better than other conventional and non-conventional process of synthesis due to its low cost, simplicity and lesser number of precursors [11]. In hydrothermal process, sample is directly precipitated from the solution, thus regulated rate and uniformity of nucleation, control over growth, ageing, size of the nanoparticles and morphology is achieved that is not possible with many other synthesis routes [12,13]. It is reported that this method can be hybridized with other processes and do not need any catalyst, seed, expensive and harmful surfactant or template, promising for large scale production with quality crystals [[12], [13], [14]]. The unique temperature-pressure interaction of the hydrothermal solution allows the preparation of different phases of MoS2 [14].
In the present work, deep and comprehensive study is carried out on MoS2 nanosheets for optical sensing applications as a function of laser wavelength and power. Different lasers were used as an illumination source with wavelengths (λex): 440 nm (indigo); 460 nm (blue); 550 nm (green); 570 nm (yellow); 635 nm (red) and 785 nm (infra-red). The optical sensing parameter viz. photoresponsivity is evaluated for all laser sources. Researchers reporting studies on optical sensing, have so far calculated photoresponsivity only for selected wavelength of 650 nm by W. Zhang et al., and for 405 nm by Caiyun Chen et al. [15,16] with no measurement over wide spectra of light [[17], [18], [19]]. This work is to find the applicability of the MoS2 nanosheets based optical sensor in the visible light of spectrum and its sensing activity as a function of power density. The photoresponse was studied as a function of power density (0.88–3.53 mW/mm2) for fixed laser wavelength of 635 nm. The dependence of photoresponsivity over power density was used to study power law and it signifies the complex process of electron–hole generation, trapping, recombination rate trap states as well as the efficient quantum efficiency which is the significance of conducting the experiment [[20], [21], [22], [23], [24], [25]]. The reported optical sensor produced a large value of photo-to-dark current ratio with high switching speed. The optical sensing response is tested for number of cycles to confirm the reproducibility and stability of the optical sensor.
Section snippets
Chemicals/materials
All the chemicals used in the work were of analytical grade and used without further purification. Sodium molybdate (Na2MoO4·2H2O with 99% purity) was purchased from Fisher Scientific, thioacetamide (CH3CSNH2 with 99% purity) and silicontungstic acid were purchased from CDH (Central Drug House) Ltd.
Synthesis of nanosheets
Fig. 1 shows the schematic of the synthesis of MoS2 nanosheets by facile hydrothermal method. MoS2 nanosheets with good crystalline nature and morphology are synthesized by optimization of
Results and discussion
The morphology of synthesized MoS2 nanosheets is illustrated in Fig. 2. Sample is assembled as nanoflakes of MoS2 with diverse lateral size of 100 nm shown in Fig. 2(a). SEM image estimated to have high yield of nanoflakes of MoS2, which are slightly curved in shape.
HRTEM further elucidate the morphology of synthesized MoS2 nanosheets. Detection of the edge area is a direct method to count the number of layers present in the sample. Fig. 2(b & c) shows TEM results for MoS2 nanosheets and its
Conclusion
MoS2 nanosheets are successfully synthesised by hydrothermal method and characterised using TEM, SEM, XRD, UV–vis, FTIR, XPS and Raman spectroscopy. A deep and comprehensive study is done using six laser sources onto the optical sensor. The maximum photoresponsivity 23.8 μA/W is obtained for red illumination at 1.41 mW/mm2 optical power density. The mechanism for photoresponsivity is proposed to explain the observed photoresponsivity curve and correlated with the bandgap of MoS2 nanosheets.
Acknowledgement
The author NC is thankful to Department of Science and Technology, New Delhi, India for awarding Inspire fellowship and this work by supported by University Grant Commission, New Delhi, India, project (No.F.4-5(201 FRP)/2015(BSR) and Science & Engineering Research Board (SERB) New Delhi, India, project (No. ECR/2017/001222). A very thankful remark for Dr. Govind Gupta, Principal Scientist & Associate Professor, CSIR-National Physical Laboratory, New Delhi, India for XPS measurements.
Nahid Chaudhary has received the Master of Technology in Nanoscience and Nanotechnology at Indraprastha University, Dwarka, New Delhi, India in 2014, and she is currently pursuing Ph.D. in Nanotechnology from Centre for Nanoscience and Nanotechnology, Jamia Millia Islamia (Central University), Delhi. She has been awarded Inspire fellowship from Department of Science and Technology (DST), New Delhi, for pursuing her doctorate degree. Her area of research is focused on investigation of
References (62)
- et al.
Electronic structure of a single MoS2 monolayer
Solid State Commun.
(2012) - et al.
Preparation of MoS2 nanoparticles by a modified hydrothermal method and the photo-catalytic activity of MoS2/TiO2 hybrids in photo-oxidation of phenol
Chem. Eng. J.
(2008) - et al.
Hydrothermal synthesis of ZnO nanowires and nanobelts on a large scale
Mater. Chem. Phys.
(2007) - et al.
Characterization and optical property of ZnO nano-, submicro-and microrods synthesized by hydrothermal method on a large-scale
Superlattices Microstruct.
(2012) - et al.
Hydrothermal synthesis of molybdenum disulfide nanosheets as supercapacitors electrode material
Electrochim. Acta
(2014) - et al.
Understanding of the effect of synthesis temperature on the crystallization and activity of nano-MoS2 catalyst
Appl. Catal. B: Environ.
(2015) - et al.
Synthesis of bilayer MoS2 nanosheets by a facile hydrothermal method and their methyl orange adsorption capacity
Mater. Res. Bull.
(2014) - et al.
Hydrothermal synthesis of MoS2 nanosheets films: microstructure and formation mechanism research
Mater. Lett.
(2016) - et al.
Hydrothermal synthesis and characterization of MoS 2 nanorods
Mater. Lett.
(2010) - et al.
A three-dimensionally interconnected carbon nanotube/layered MoS2 nanohybrid network for lithium ion battery anode with superior rate capacity and long-cycle-life
Nano Energy
(2015)
Electrical control of optical properties of monolayer MoS2
Solid State Commun.
Transition Metal Dichalcogenides, Preparation and Crystal Growth of Materials With Layered Structures
Electronic properties of MoS2 nanoparticles
J. Phys. Chem. C
The lattice vibrations of the MoS2 structure
Philos. Mag.
Synthesis and optical properties of MoS2 and isomorphous nanoclusters in the quantum confinement regime
J. Appl. Phys.
Single-layer MoS2 transistors
Nat. Nanotechnol.
The role of solid lubricants for brake friction materials
Lubricants
CVD-grown monolayered MoS2 as an effective photosensor operating at low-voltage
2D Mater.
Detailed photocurrent spectroscopy of the semiconducting group VIB transition metal dichalcogenides
J. Phys. Chem.
High-performance chemical sensing using Schottky-contacted chemical vapor deposition grown monolayer MoS2 transistors
ACS Nano
Controlled synthesis and characterization of large-scale, uniform Dy (OH)3 and Dy2O3 single-crystal nanorods by a hydrothermal method
Nanotechnology
Highly responsive MoS2 photodetectors enhanced by graphene quantum dots
Sci. Rep.
CVD-grown monolayered MoS2 as an effective photosensor operating at low-voltage
2D Mater.
High‐gain phototransistors based on a CVD MoS2 monolayer
Adv. Mater.
High‐detectivity multilayer MoS2 phototransistors with spectral response from ultraviolet to infrared
Adv. Mater.
Single-layer MoS2 phototransistors
ACS Nano
High responsivity, large-area graphene/MoS2 flexible photodetectors
ACS Nano
Low temperature electrical and photo-responsive properties of MoSe2
Appl. Phys. Lett.
Charge trapping at the MoS2-SiO2 interface and its effects on the characteristics of MoS2 metal-oxide-semiconductor field effect transistors
Appl. Phys. Lett.
Photoresponse properties of CdSe single‐nanoribbon photodetectors
Adv. Funct. Mater.
Nanowire ultraviolet photodetectors and optical switches
Adv. Mater.
Cited by (98)
3D-printed MoS<inf>2</inf>/Ni electrodes with excellent electro-catalytic performance and long-term stability for dechlorination of florfenicol
2024, Journal of Environmental Sciences (China)An insight into the dual role of MoS2-based nanocarriers in anticancer drug delivery and therapy
2024, Acta BiomaterialiaHydrothermal synthesis of MoS<inf>2</inf> with tunable band gap for future nano-electronic devices
2024, Inorganic Chemistry CommunicationsStructural, optical and temperature dependent electric modulus property of few layer MoS<inf>2</inf> nanosheets
2023, Physica B: Condensed MatterA temperature-responsive drug release system based on MoS<inf>2</inf> nanosheets and 1-tetradecanol
2023, Colloids and Surfaces A: Physicochemical and Engineering AspectsSurface engineering of mesoporous-TiO<inf>2</inf> electron transport layer for improved performance of organic-inorganic perovskite solar cells via suppressing interface defects, enhancing charge extraction and boosting carrier transport
2023, Colloids and Surfaces A: Physicochemical and Engineering Aspects
Nahid Chaudhary has received the Master of Technology in Nanoscience and Nanotechnology at Indraprastha University, Dwarka, New Delhi, India in 2014, and she is currently pursuing Ph.D. in Nanotechnology from Centre for Nanoscience and Nanotechnology, Jamia Millia Islamia (Central University), Delhi. She has been awarded Inspire fellowship from Department of Science and Technology (DST), New Delhi, for pursuing her doctorate degree. Her area of research is focused on investigation of photoconductive response of semiconductor nanostructure for the application of optical sensor.
Dr. Manika Khanuja has obtained her M.Sc (Physics) and Ph.D. (Physics) from Indian Institute of Technology Delhi, India. She worked as a Guest-Scientist in University of Duisburg-Essen, Germany. Her area of research includes thin film deposition, nanomaterials synthesis by physical and chemical routes for various applications including photocatalysis, photocatalytic water splitting, hydrogen sensors and fuel cells.