The company of my PhD colleagues Rinky Sha, Arthi Gopalakrishnan contributed immensely to my personal and professional development at IIT Hyderabad. I also express my heartfelt thanks to my sister-in-law Sanju Sahatiya for her support and love.
Introduction
Functional 2D nanomaterials such as MoS2, graphene and 1D materials such as carbon nanotubes and metal oxides are promising candidates for the development of flexible electronic devices and sensors due to their high mobility, high thermal conductivity, high Young's modulus, etc.
Review of status in research and development in the subject
Material Review
To further expand the scope of applications offered by pristine nanomaterials, hybrids of MoS2, CNTs and graphene with various metal oxides and metal chalcogenides have been synthesized and used in energy storage, electrochemical sensors, photodetectors etc. Furthermore, transition metal oxides such as vanadium oxides family find wide applications in electronics because of their reversible phase transitions from metals to semiconductors.
Substrate
The combination of 2D MoS2 with 1D V2O5 will be a step forward in the fabrication of new flexible electronic devices with potential applications in broadband photodetectors. Most of the above polymer substrates are also compatible with microfabrication and the devices can be fabricated using sophisticated cleanroom techniques that offer immense applications in the production of reliable flexible electronic devices.
Research Objective
The objective of this work is to use external strain modulation in heterojunctions to increase the responsivity of broadband photodetectors by modulating the Schottky barrier of fabricated heterojunctions. Further electrical characterization in terms of IV, CV was performed to understand the electrical properties of the fabricated devices.
Organization of Thesis
Study the morphology and electrical characterization of these devices and then use them for sensing applications. Finally, the fabricated devices were tested for various sensing applications such as broadband photodetector, pressure and voltage.
Optimization in terms of process parameters was done to produce uniform trilayer MoS2 on cellulose paper. ZnS played the dual role of absorbing in UV and in generating local electric fields, thus increasing the sensitivity of the sensor.
Introduction
Here, we report the fabrication of a new paper-based broadband photodetector using ZnS-MoS2 hybrids. To the best of our knowledge, this is the first report on paper-based broadband photodetector with ZnS-MoS2 hybrids as active sensing materials.
Results and Discussion
The peak indicating the E12g mode of MoS2 could be suppressed due to the growth of ZnS on the MoS2 layer. During light illumination, we observed an increase in the current in relation to the intensity of the illuminated light, which can be attributed to the increased number of photogenerated electrons.
Conclusion
Experimental Section
The MoS2 paper was immersed in a seed solution consisting of equimolar concentrations of ZnCl2 and CH4N2S in DI water for 60 min. The as-grown ZnS-MoS2 paper was cut to a dimension of 2 cm × 0.5 cm and electrical contacts were established using silver (Ag) paste.
Sodium molybdate, zinc chloride, and thiourea were purchased from Sigma Aldrich and used as received to grow ZnS-MoS2 hybrids. Schematic of the two-step hydrothermal process for the fabrication of a ZnS-MoS2 broadband photodetector.
Introduction
The combination of 2D MoS2 with 1D V2O5 would be a step forward in the production of new broadband photodetectors that not only broadens the absorption range in the electromagnetic spectrum, but also increases the responsivity of the photodetector. Here we demonstrate for the first time the fabrication of flexible broadband photodetector (UV-NIR) using novel 2D MoS2-1D V2O5 heterostructure in which MoS2 was grown directly on Al foil using hydrothermal method followed by spin coating of electrospun V2O5.
Results and Discussions
This can be attributed to the fact that both MoS2 and V2O5 have absorption in the visible region, thus creating more photogenerated carriers under visible illumination. The observed responsivity under NIR illumination was much lower, which can be attributed to the fact that most of the MoS2 is covered by the V2O5 nanowires, so the absorbance process occurs in the limited exposed part of the MoS2.
Conclusion
There are reports of various devices based on 2D ZnO on 2D Graphene [4], 2D Graphene-2D MoS2 [29], ZnS nanospheres on 2D MoS2 [3] for improved optoelectronic performance. 31] Most reports on 2D material hybrids produce heterojunctions that can improve response in a particular region of the electromagnetic spectrum (UV, visible, or NIR), but there are fewer reports that study detection over a broad range of the spectrum. electromagnetic.
Experimental Section
The presented strategy is an important step forward in the fabrication of broadband photodetectors that find potential applications in the fields of optoelectronic devices, security, and medical healthcare applications.
One-step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of high performance supercapacitor. The absorption of CQDs in the UV region, combined with the broadband absorption of MoS2 in the visible and NIR regions, broadens the absorbance range.
Introduction
In this work, we report the fabrication of flexible broadband photodetector based on 2D MoS2-CQD hybrids on cellulose paper. 2D MoS2 has been grown directly on cellulose paper using a simple cost-effective hydrothermal method.
Results and Discussions
The results show excellent repeatability of the sensor, where the photodetector regained its initial resistance value upon "turning off" the illumination. It should be noted that even though CQDs are deposited on MoS2, the responsivity and EQE values are larger for visible light illumination due to the discrete distribution of CQDs on MoS2.
Conclusion
Experimental Section
Carbon dots were synthesized by one-step pyrolytic treatment of chia seeds. Briefly, 500 mg of chia seeds were loaded into a ceramic pot and carbonized at 350 °C for 6 h.
Inset shows the distribution of diameter d) High magnification TEM image of CQD e) Elemental mapping of MoS2/CQD showing discrete distribution of CQD on MoS2. Schematic showing the energy band diagram of MoS2/CQD and charge transport under UV, visible and NIR illumination.
Introduction
Recently, 2D ZnO nanostructures have attracted much interest due to their outstanding properties such as high anisotropy, large surface area, high surface charge density, lower charge transfer resistance, and better separation of electrons and holes [14-15]. Strain-induced piezopolarization charges in 2D ZnO have been used to effectively modulate an optoelectronic process such as charge separation in a 2D Gr/ZnO p-n junction.
Results and Discussions
The temporal response of the strained 2D Gr/ZnO device under fixed illumination (both UV and visible) was studied and is as shown in Figure 5.5c and Figure 5.5d, respectively. As shown in the figure, different voltages ranging from 5% to 30% were applied to the 2D Gr/ZnO PD and a significant improvement in current was observed.
Conclusion
In addition, the negative piezopotential is mainly distributed over the 2D ZnO surface, which is favorable for effective charge separation at the Gr/ZnO interface [31]. The results provide insight into the functionality of 2D Gr/ZnO for broadband photodetection in the UV to visible range.
Experimental Section
Inset is the tauc plot of 2D ZnO where the optical band gap of 2D ZnO is calculated to be 2.8 eV. Expanding the depletion region improves the separation of photogenerated carriers and increases the diode performance under both visible and NIR illumination.
Introduction
Most reports of synthesis of MoS2 are carried out in vacuum or by thermolysis [15]. The work paves the way for future flexible piezotronic devices in which the external stimuli can modulate the properties of the device which has tremendous applications in the field of communication, signal processing, human machine interface, etc.
Results and Discussions
The improvement in the photocurrent and the change in the depletion capacitance of the piezotronic diode can be well understood from the energy band diagram of MoS2/CuO as shown in Figure 6.6. Also under load, due to the expansion of the depletion region, the depletion capacitance of the diode decreases under reverse bias.
Conclusion
Experimental Section
Spin-coating was performed several times to ensure uniform coverage of CuO nanoparticles over MoS2. Chemicals of analytical grade (Sodium molybdate, Thiourea and copper acetate) were purchased from Sigma Aldrich and used without further purification for the production of MoS2-CuO piezotronic diode.
Synthesis of MoS2 and MoO2 for their applications in H2 generation and Li-ion batteries: a review. The scale factor of the strain sensor was calculated to be 2.4, which is comparable to and even better than most strain and pressure sensors.
Introduction
Also, most reports are either about the feeling of pressure or strain using natural rubber which is not suited to the purpose of artificial leather applications. This excellent interfacial bonding between the MWCNTs and the rubber substrate is the key to the recovery of the sensor under deformation.
Results and Discussions
As the length of the eraser increases, the change in length (∆L) decreases, decreasing the total strain produced in the MWCNTs film. The graph shows the similarity in the values of the normalized resistance when the sensor is under compression and tensile loading.
Conclusion
The pressure sensing mechanism of the artificial e-skin is related to the capacitive variations of the eraser with MWCNT applied on the top and bottom sides. The measured spatial distribution is very consistent with the shape and weight distribution of the object, which proves the excellent response of artificial skin to external pressures.
Experimental Section
The scale factor of the strain sensor was calculated to be 2.4, which is comparable to a strain sensor fabricated with complex fabrication steps. The sensing mechanism of the eraser-based MWCNT strain sensor was attributed to the tunneling effect rather than geometrical deformations.
The resistance of the rubber-based sensor varied with the width and length of the MWCNTs deposited on the rubber and can be found in the supplementary information (SI) as fig S1. The schematic of the complete fabrication process is as shown in Figure 1. Information about materials and characterization tools can be found in the SI.
Conclusion
