Rahul Kumar
@pdpu.ac.in
Assistant Professor
Pandit Deendayal Energy University
RESEARCH, TEACHING, or OTHER INTERESTS
Electrical and Electronic Engineering, Engineering, Pollution, Electronic, Optical and Magnetic Materials
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Neeraj Goel, Utkarsha, Aditya Kushwaha, Monika Kwoka, Rahul Kumar, and Mahesh Kumar
Royal Society of Chemistry (RSC)
The recent advances in the field of gas sensing technology by the introduction of van der Waals (vdW) heterostructures have attracted worldwide attention.
Aditya Kushwaha, Rahul Kumar, and Neeraj Goel
Elsevier BV
Deepak Sharma, Rahul Kumar, Ayan Pal, Neha Sakhuja, and Navakanta Bhat
American Chemical Society (ACS)
Hamid Reza Ansari, Ali Mirzaei, Hooman Shokrollahi, Rahul Kumar, Jin-Young Kim, Hyoun Woo Kim, Mahesh Kumar, and Sang Sub Kim
Royal Society of Chemistry (RSC)
Flexible/wearable gas sensor technology is gaining huge interest in the current era of the Internet of Things for its applications in personal environmental monitoring, healthcare, and safety.
Rahul Kumar, Neeraj Goel, Deepak Kumar Jarwal, Yinhua Hu, Jun Zhang, and Mahesh Kumar
Royal Society of Chemistry (RSC)
Recent advances in gas detection at room temperature using chemical vapor deposition (CVD) grown different nanostructures including 0D, 1D, 2D, and 3D of emerging two-dimensional (2D) materials (such as graphene, transition metal dichalcogenides) are reviewed.
Neha Sakhuja, Rahul Kumar, Prateek Katare, and Navakanta Bhat
American Chemical Society (ACS)
Xianghong Liu, Wei Zheng, Rahul Kumar, Mahesh Kumar, and Jun Zhang
Elsevier BV
Deepu Kumar, Rahul Kumar, Mahesh Kumar, and Pradeep Kumar
Royal Society of Chemistry (RSC)
A detailed and comparative temperature-dependent photoluminescence study was carried out to understand the optical properties in few-layer vertically and horizontally aligned MoS2.
Deepu Kumar, Vivek Kumar, Rahul Kumar, Mahesh Kumar, and Pradeep Kumar
American Physical Society (APS)
Probing phonons, quasi-particle excitations and their coupling has enriched our understanding of these 2D materials and proved to be crucial for developing their potential applications. Here, we report comprehensive temperature, 4-330 K, and polarization-dependent Raman measurements on mono and bilayer MoSe2. Phonon’s modes up to fourth-order are observed including forbidden Raman and IR modes, understood considering Fröhlich mechanism of exciton-phonon coupling. Most notably, anomalous variations in the phonon linewidths with temperature pointed at the significant role of electron-phonon coupling in these systems, especially for the out-of-plane ( 1g A ) and shear mode ( 2 2g E ), which is found to be more prominent in the narrow-gaped bilayer than the large gapped monolayer. Via polarization-dependent measurements, we deciphered the ambiguity in symmetry assignments, especially to the peaks around ~ 170 cm and ~ 350 cm. Temperature-dependent thermal expansion coefficient, an important parameter for the device performance, is carefully extracted for both mono and bilayer by monitoring the temperaturedependence of the real-part of the phonon self-energy parameter. Our temperature-dependent indepth Raman studies provide a pave for uncovering the deeper role of phonons in these 2D layered materials from a fundamental as well as application point of view. E-mail: deepu7727@gmail.com *E-mail: pkumar@iitmandi.ac.in 2
Neeraj Goel, Rahul Kumar, and Mahesh Kumar
IOP Publishing
The visualization of band alignment for designing heterostructures between transition metal dichalcogenides and germanium plays a vital role in a deeper understanding of carrier dynamics at the heterointerface. Here, to study the band alignment across the MoS2/Ge heterojunction, we have deposited a wafer-scale highly crystalline few atomic layers MoS2 film via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The Raman and XRD spectra of as-fabricated MoS2/Ge heterojunction expose the presence of highly crystalline few atomic layer MoS2 on top of Ge substrate. Interestingly, we found a type-II band alignment at the MoS2/Ge heterointerface having valence band, and conduction band offset values of 0.88 and 0.21 eV, which can provide very efficient recombination through spatially confining charge carriers. The calculation of band offset parameters offers a promising way for device engineering across the MoS2/Ge heterojunction interface. Moreover, to demonstrate the practicability of the fabricated heterostructure, we explored the suitability of our device for broadband photodetection applications.
Deepu Kumar, Birender Singh, Rahul Kumar, Mahesh Kumar, and Pradeep Kumar
IOP Publishing
Abstract We present comprehensive temperature dependent Raman measurements for chemical vapor deposition grown horizontally aligned layered MoS2 in a temperature range of 4–330 K under a resonance condition. Our analysis of temperature dependent phonon frequency shift and linewidth suggests a finite role of three and four phonon anharmonic effect. We observe Davydov splitting of the out-of-plane (A 1g ) and in-plane ( E 2 g 1 ) modes for both three layer (3L) and few layer (FL) systems. The number of Davydov splitting components are found more in FL compared to 3L MoS2, which suggests that it increases with an increasing number of layers. Further, Davydov splitting is analyzed as a function of temperature. Temperature evaluation of the Raman spectra shows that the Davydov splitting, especially for A 1g mode, is very strong and well resolved at low temperature. We observe that A 1g mode shows the splitting at low temperature, while E 2 g 1 mode is split even at room temperature, which suggests a prominent role of A 1g mode in the interlayer interaction at low temperature. Further, an almost 60-fold increase in the intensity of the phonon modes at low temperature clearly shows the temperature dependent tuning of the resonance effect.
Huaping Wang, Jianmin Ma, Jun Zhang, Yuezhan Feng, Mani Teja Vijjapu, S. Yuvaraja, S. Surya, K. Salama, C. Dong, Yude Wang,et al.
Gas sensor technology is widely utilized in various areas ranging from home security, environment and air pollution, to industrial production. It also hold great promise in non-invasive exhaled breath detection and an essential device in future internet of things. The past decade has witnessed giant advance in both fundamental research and industrial development of gas sensors, yet current efforts are being explored to achieve better selectivity, higher sensitivity and lower power consumption. The sensing layer in gas sensors have attracted dominant attention in the past research. In addition to the conventional metal oxide semiconductors, emerging nanocomposites and graphene-like two-dimensional materials also have drawn considerable research interest. This inspires us to organize this comprehensive 2020 gas sensing materials roadmap to discuss the current status, state-of-the-art progress, and present and future challenges in various materials that is potentially useful for gas sensors.
Neeraj Goel, Jayanta Bera, Rahul Kumar, Satyajit Sahu, and Mahesh Kumar
Institute of Electrical and Electronics Engineers (IEEE)
Over the past several decades, metal oxide based gas sensors are widely used for hydrogen gas sensing applications. However, their poor sensitivity and very high value of operating temperature (> 300 °C) pose a severe threat over hydrogen detection due to its highly flammable nature. In recent years, a few strategies have been explored by the researchers to address these formidable challenges faced by the sensing technology. Here, we present MoS2/ZnO hybrid exhibiting higher molecular detection at low operating temperature. The ZnO film was grown using the magnetron sputtering technique, while MoS2-PVP nanocomposites (MoS2-PVP NCs) were synthesized through organic polymer assisted liquid exfoliation process. We examined the sensing performance of various MoS2/ZnO hybrids prepared by the decoration of different concentration MoS2-PVP NCs over the ZnO surface. The decoration of ZnO film through MoS2-PVP NCs increases the effective surface area and the number of active sites for the hydrogen molecules to get adsorbed, hence improved the surface reactivity to gas molecules. Interestingly, a 5 mg/mL MoS2-PVP NCs decorated ZnO sensor showed an improvement of $\\sim 8$ times in sensing response as compared to the pristine ZnO based sensor upon 50 ppm hydrogen exposure. The improvement in sensing ability is primarily ascribed to electronic sensitization and spillover effects. Our results establish that the MoS2/ZnO hybrid exhibit superior hydrogen sensing behavior indicating the prominent role of MoS2-PVP NCs in hydrogen detection.
Rahul Kumar, Neeraj Goel, Ramesh Raliya, Govind Gupta, Pratim Biswas, Jun Zhang, and Mahesh Kumar
Institute of Electrical and Electronics Engineers (IEEE)
The possibility to synergise two-dimensional (2D) materials with 0D nanoparticles has sparked a surge in high performance futuristic electronic devices. Here, we decorated plasmonic Au nanoparticles on surface of chemical vapor deposition (CVD) grown 2D MoS<sub>2</sub> nanosheet and demonstrated bifunctional sensing behaviour within a single device. The plasmonic Au nanoparticles functionalized MoS<sub>2</sub> device showed about ~5 times higher sensitivity to NO<sub>2</sub> than that of pristine MoS<sub>2</sub> at room temperature. The enhanced gas sensing performance was attributed to a combination of Schottky barriers modulation at Au/MoS<sub>2</sub> nanointerfaces and catalytic effects upon exposing the gas analyte. In addition, the device also exhibited enhanced photoresponse with a high photo-responsivity of ~17.6 A/W and a moderate detectivity of ~<inline-formula> <tex-math notation="LaTeX">${6.6} \\times {10}^{11}$ </tex-math></inline-formula> Jones due to enhanced local plasmonic effects. Finally, photons and gas molecules are detected in sequence, which proved that only a single Au-MoS<sub>2</sub> device exhibited remarkable bifunctional sensing characteristics. Such excellent bifunctional sensing ability of a single Au-MoS<sub>2</sub> device paves the way to integrate the 2D material with plasmonic nanostructures for developing an advanced multifunctional sensor.
Md Tawabur Rahman, Rahul Kumar, Mahesh Kumar, and Qiquan Qiao
Elsevier BV
Surajit Das, Rahul Kumar, Jitendra Singh, and Mahesh Kumar
Institute of Electrical and Electronics Engineers (IEEE)
Here, an ultrafast direct laser patterning technique to fabricate a low-cost microsensor and its application for formaldehyde detection are reported. The patterns of microheater and interdigitated electrodes (IDEs) were realized using laser micromachining techniques by ablation of gold thin film on alumina substrate. The thin film of gold microheater showed good stability up to 300 °C with a fast response time of 80 s and temperature coefficient of resistance (TCR) was calculated as $1.37\\times 10^{-{3}}/^{\\circ }\\text{C}$ . Moreover, gold microheater exhibited long-term reliability under self-heating mode with a negligible resistance drift < 0.5% over a period of 330 h at 250 °C through consuming low power with a heating efficiency of 0.23 °C/mW. Thermal imaging camera revealed the uniform temperature distribution with negligible heat gradient profile over the whole microsensor platform. To state-of-the-art gas sensing application of this coplanar sensing platform, a nanostructured SnO2 was deposited on IDE, which exhibited high sensitivity (13.96% ppm $^{-{1}}$ ) to formaldehyde even to detect sub-ppm concentrations with fast response (32 s) and recovery kinetics (72 s). Moreover, the microsensor was also used on-site rapid screening for the detection and quantification of formaldehyde concentration in formalin-treated fish sample.
Rahul Kumar and Mahesh Kumar
Springer Science and Business Media LLC
Rahul Kumar, Xianghong Liu, Jun Zhang, and Mahesh Kumar
Springer Science and Business Media LLC
AbstractRoom-temperature gas sensors have aroused great attention in current gas sensor technology because of deemed demand of cheap, low power consumption and portable sensors for rapidly growing Internet of things applications. As an important approach, light illumination has been exploited for room-temperature operation with improving gas sensor’s attributes including sensitivity, speed and selectivity. This review provides an overview of the utilization of photoactivated nanomaterials in gas sensing field. First, recent advances in gas sensing of some exciting different nanostructures and hybrids of metal oxide semiconductors under light illumination are highlighted. Later, excellent gas sensing performance of emerging two-dimensional materials-based sensors under light illumination is discussed in details with proposed gas sensing mechanism. Originated impressive features from the interaction of photons with sensing materials are elucidated in the context of modulating sensing characteristics. Finally, the review concludes with key and constructive insights into current and future perspectives in the light-activated nanomaterials for optoelectronic gas sensor applications.
Abhay V. Agrawal, R. Kumar, Guang Yang, Jiming Bao, Mahesh Kumar, and Mukesh Kumar
Elsevier BV
Rahul Kumar, Neeraj Goel, Mirabbos Hojamberdiev, and Mahesh Kumar
Elsevier BV
Neeraj Goel, Rahul Kumar, and Mahesh Kumar
IEEE
In this work, we demonstrate an economical NO2 gas sensor having promising attributes including working at low temperature. Our sensor showed very good sensitivity and reversibility upon adsorption and desorption of NO2. To synthesize a wafer-scale MoSe2 film, we reported a facile strategy using DC sputtering combined with a post-selenization process. The FE-SEM and Raman characterization confirm the growth of uniform and highly crystalline MoSe2 film. Our proposed approach exposed that MoSe2 can potentially be used for high-performance gas sensors.
Rahul Kumar, Neeraj Goel, Abhay Vivek Agrawal, Ramesh Raliya, Saravanan Rajamani, Govind Gupta, Pratim Biswas, Mukesh Kumar, and Mahesh Kumar
Institute of Electrical and Electronics Engineers (IEEE)
A design of an advanced sensing material, such as MoS2, is imperative to enhance the sensing performance of a sensor. Because their usage alone for developing a practical sensor is impeditive owing to low gas response and slow response/recovery kinetics. Here, we report a high-performance NO2 gas sensor using a hybrid of temperature-assisted sulfur vacancy within the edge-oriented vertically aligned MoS2 (Sv-MoS2) and crumpled reduced graphene oxide (rGO) particles. Interestingly, the Sv-MoS2 functionalized by optimized rGO concentration exhibited a significant enhancement of response to NO2 (approximately three times higher than that of pristine vertically aligned MoS2) with fast response (< 1 min) and complete recovery. Such a large improvement in the sensing performance could be attributed to controlled electrical/chemical sensitization level of MoS2 through controllable vacancy and interface engineering. The vacancy engineering offers abundant active sites through creating sulfur vacancy in additionally rich edge active sites of vertically oriented MoS2 for more electronic interaction with gas molecules. While interfacing of p-type rGO particles with n-type MoS2 leads to multiple out-of-plane vertical nano-heterojunctions as a sensitizing configuration for boosting the performance of the sensor. This paper opens up a new approach towards improving the sensing activity of a 2D material via a synergistic vacancy and interface engineering.
Neeraj Goel, Rahul Kumar, Shubhendra Kumar Jain, Saravanan Rajamani, Basanta Roul, Govind Gupta, Mahesh Kumar, and S B Krupanidhi
IOP Publishing
We report a MoS2/GaN heterojunction-based gas sensor by depositing MoS2 over a GaN substrate via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The microscopic and spectroscopic measurements expose the presence of highly crystalline and homogenous few atomic layer MoS2 on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS2/GaN interface under the reverse biased condition, thus resulting in high sensitivity. Our results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature (25–150 °C). For a deeper understanding of carrier dynamics at the heterointerface, we visualized the band alignment across the MoS2/GaN heterojunction having valence band and conduction band offset values of 1.75 and 0.28 eV. The sensing mechanism was demonstrated based on an energy band diagram at the MoS2/GaN interface in the presence and absence of hydrogen exposure. The proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes.
Neeraj Goel, Rahul Kumar, and Mahesh Kumar
IEEE
MoO3 is a well-known multifunctional material which can be potentially used in a distinct gas-sensing applications. In this study, we grow the large-scale nanonetwork composed of α-MoO3 nanosheets by using conventional chemical vapor deposition method. The microscopic and spectroscopic characterizations confirm the continuity and crystallinity of the deposited MoO3 film. The dynamic response resistance of the device reveals a high sensitivity of 53% for 1% hydrogen at 180 °C. A detailed gas-sensing mechanism was explained by the depletion-layer modulation process.
Rahul Kumar, Neeraj Goel, and Mahesh Kumar
IEEE
The anisotropic bonding in layered materials crystallize to form different structure such as smooth films, nanotubes, and fullerene-like nanoparticles. Here, the growth of different microstructure of MoS<inf>2</inf> via chemical vapor deposition (CVD) method through controlled processing parameters is reported. Scanning electron microscopy and Raman spectroscopy ascertained the MoS<inf>2</inf> on insulating substrate (SiO<inf>2</inf>/Si). It was observed that poor sulfur environment and slow vapor flow were unable to induce complete transition from MoO<inf>3</inf>-x to MoS<inf>2</inf> and formed intermediate MoO<inf>2</inf>.The MoS<inf>2</inf> and MoO<inf>2</inf>/MoS<inf>2</inf> heterostructure were synthesized via single step. In addition, by adjustment of heating rate with temperature of centre zone and vapor flow, flower like structure of MoS<inf>2</inf> was achieved.