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Ascorbic acid (AA), known as vitamin C, is a vital bioactive compound that plays a crucial role in several metabolic processes, including the synthesis of collagen and neurotransmitters, the removal of harmful free radicals, and the uptake of iron by cells in the human intestines. As a result, there is an absolute need for a highly selective, sensitive, and economically viable sensing platform for AA detection. Herein, we demonstrate a Pt-decorated MoS2 for efficient detection of an AA biosensor. MoS2 hollow rectangular structures were synthesized using an easy and inexpensive chemical vapor deposition approach to meet the increasing need for a reliable detection platform. The synthesized MoS2 hollow rectangular structures are characterized through field effect scanning electron microscopy (FESEM), energy-dispersive spectroscopy elemental mapping, Raman spectroscopy, and x-ray photoelectron spectroscopy. We fabricate a chemiresistive biosensor based on Pt-decorated MoS2 that measures AA with great precision and high sensitivity. The experiments were designed to evaluate the response of the Pt-decorated MoS2 biosensor in the presence and absence of AA, and selectivity was evaluated for a variety of biomolecules, and it was observed to be very selective towards AA. The Pt-MoS2 device had a higher response of 125% against 1 mM concentration of AA biomolecules, when compared to that of all other devices and 2.2 times higher than that of the pristine MoS2 device. The outcomes of this study demonstrate the efficacy of Pt-decorated MoS2 as a promising material for AA detection. This research contributes to the ongoing efforts to enhance our capabilities in monitoring and detecting AA, fostering advancements in environmental, biomedical, and industrial applications. [ABSTRACT FROM AUTHOR]

We report significantly enhanced sensitivity of AlGaN/GaN-based high electron mobility transistor (HEMT) sensor by the targeted synthesis of IT and 2H coexisting phase MoS2 and applying the gate bias voltage. The HEMT structures on Si (111) substrates were used for the detection of Hg2+ ions. The optimum sensitive regime in terms of V GS and V DS of the sensor was investigated by keeping the drain source voltage V DS constant at 2 V and by only varying the gate bias voltage V GS from 0 to 3 V. The strongest sensing response obtained from the device was around 0.547 mA ppbâˆ'1 at V GS = 3 V, which is 63.7% higher in comparison to the response achieved at 0 V which shows a sensing response of around 0.334 mA ppbâˆ'1. The current response depicts that the fabricated device is very sensitive and selective towards Hg2+ ions. Moreover, the detection limit of our sensor at 3 V was calculated around 6.21 ppt, which attributes to the strong field created between the gate electrode and the HEMT channel due to the presence of 1T metallic phase in synthesized MoS2, indicating that the lower detection limits are achievable in adequate strong fields. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (A1g) and in-plane () 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 A1g mode, is very strong and well resolved at low temperature. We observe that A1g mode shows the splitting at low temperature, while mode is split even at room temperature, which suggests a prominent role of A1g 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. [ABSTRACT FROM AUTHOR]

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 (A1g) and in-plane () 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 A1g mode, is very strong and well resolved at low temperature. We observe that A1g mode shows the splitting at low temperature, while mode is split even at room temperature, which suggests a prominent role of A1g 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. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA), known as vitamin C, is a vital bioactive compound that plays a crucial role in several metabolic processes, including the synthesis of collagen and neurotransmitters, the removal of harmful free radicals, and the uptake of iron by cells in the human intestines. As a result, there is an absolute need for a highly selective, sensitive, and economically viable sensing platform for AA detection. Herein, we demonstrate a Pt-decorated MoS 2 for efficient detection of an AA biosensor. MoS 2 hollow rectangular structures were synthesized using an easy and inexpensive chemical vapor deposition approach to meet the increasing need for a reliable detection platform. The synthesized MoS 2 hollow rectangular structures are characterized through field effect scanning electron microscopy (FESEM), energy-dispersive spectroscopy elemental mapping, Raman spectroscopy, and x-ray photoelectron spectroscopy. We fabricate a chemiresistive biosensor based on Pt-decorated MoS 2 that measures AA with great precision and high sensitivity. The experiments were designed to evaluate the response of the Pt-decorated MoS 2 biosensor in the presence and absence of AA, and selectivity was evaluated for a variety of biomolecules, and it was observed to be very selective towards AA. The Pt-MoS 2 device had a higher response of 125% against 1 mM concentration of AA biomolecules, when compared to that of all other devices and 2.2 times higher than that of the pristine MoS 2 device. The outcomes of this study demonstrate the efficacy of Pt-decorated MoS 2 as a promising material for AA detection. This research contributes to the ongoing efforts to enhance our capabilities in monitoring and detecting AA, fostering advancements in environmental, biomedical, and industrial applications., (© 2024 IOP Publishing Ltd.)

We report significantly enhanced sensitivity of AlGaN/GaN-based high electron mobility transistor (HEMT) sensor by the targeted synthesis of IT and 2H coexisting phase MoS 2 and applying the gate bias voltage. The HEMT structures on Si (111) substrates were used for the detection of Hg 2+ ions. The optimum sensitive regime in terms of V GS and V DS of the sensor was investigated by keeping the drain source voltage V DS constant at 2 V and by only varying the gate bias voltage V GS from 0 to 3 V. The strongest sensing response obtained from the device was around 0.547 mA ppb -1 at V GS  = 3 V, which is 63.7% higher in comparison to the response achieved at 0 V which shows a sensing response of around 0.334 mA ppb -1 . The current response depicts that the fabricated device is very sensitive and selective towards Hg 2+ ions. Moreover, the detection limit of our sensor at 3 V was calculated around 6.21 ppt, which attributes to the strong field created between the gate electrode and the HEMT channel due to the presence of 1T metallic phase in synthesized MoS 2 , indicating that the lower detection limits are achievable in adequate strong fields., (© 2022 IOP Publishing Ltd.)

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 MoS 2 /Ge heterojunction, we have deposited a wafer-scale highly crystalline few atomic layers MoS 2 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 MoS 2 /Ge heterojunction expose the presence of highly crystalline few atomic layer MoS 2 on top of Ge substrate. Interestingly, we found a type-II band alignment at the MoS 2 /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 MoS 2 /Ge heterojunction interface. Moreover, to demonstrate the practicability of the fabricated heterostructure, we explored the suitability of our device for broadband photodetection applications., (© 2021 IOP Publishing Ltd.)

We report a MoS 2 /GaN heterojunction-based gas sensor by depositing MoS 2 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 MoS 2 on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS 2 /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 MoS 2 /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 MoS 2 /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.

Here, we demonstrate improved NO 2 gas sensing properties based on reduced graphene oxide (rGO) decorated V 2 O 5 thin film. Excluding the DC sputtering grown V 2 O 5 thin film, rGO was spread over V 2 O 5 thin film by the drop cast method. The formation of several p-n heterojunctions was greatly affected by the current-voltage relation of the rGO-decorated V 2 O 5 thin film due to the p-type and n-type nature of rGO and V 2 O 5 , respectively. Initially with rGO decoration on V 2 O 5 thin film, current decreased in comparison to the pristine V 2 O 5 thin film, whereas depositing rGO film on a glass substrate drastically increased current. Among all sensors, only the rGO-decorated V 2 O 5 sensor revealed a maximum NO 2 gas sensing response for 100 ppm at 150 °C, and it achieved an approximately 61% higher response than the V 2 O 5 sensor. The elaborate mechanism for an extremely high sensing response is attributed to the formation and modulation of p-n heterojunctions at the interface of rGO and V 2 O 5 . In addition, the presence of active sites like oxygenous functional groups on the rGO surface enhanced the sensing response. On that account, sensors based on rGO-decorated V 2 O 5 thin film are highly suitable for the purpose of NO 2 gas sensing. They enable the timely detection of the gas, further protecting the ecosystem from its harmful effects.

We demonstrate a highly selective and reversible NO 2 resistive gas sensor using vertically aligned MoS 2 (VA-MoS 2 ) flake networks. We synthesized horizontally and vertically aligned MoS 2 flakes on SiO 2 /Si substrate using a kinetically controlled rapid growth CVD process. Uniformly interconnected MoS 2 flakes and their orientation were confirmed by scanning electron microscopy, x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy. The VA-MoS 2 gas sensor showed two times higher response to NO 2 compared to horizontally aligned MoS 2 at room temperature. Moreover, the sensors exhibited a dramatically improved complete recovery upon NO 2 exposure at its low optimum operating temperatures (100 °C). In addition, the sensing performance of the sensors was investigated with exposure to various gases such as NH 3 , CO 2 , H 2 , CH 4 and H 2 S. It was observed that high response to gas directly correlates with the strong interaction of gas molecules on edge sites of the VA-MoS 2 . The VA-MoS 2 gas sensor exhibited high response with good reversibility and selectivity towards NO 2 as a result of the high aspect ratio as well as high adsorption energy on exposed edge sites.

2D materials are a promising new class of materials for next generation optoelectronic devices owing to their appealing optical and electrical properties. Pristine molybdenum disulfide (MoS 2 ) is widely used in next generation photovoltaic and optoelectronic devices, but its low photo-dark current ratio prevents its use in highly efficient photo detection applications. Here, we decorated crumpled reduced graphene oxide (rGO) particles on a large-area vertically aligned MoS 2 flake network to enhance the performance of the MoS 2 -based photodetector by forming multiple nanoscale p-n heterojunctions. The rGO/MoS 2 device exhibited a significantly improved photoresponsivity of ∼2.10 A W -1 along with a good detectivity of ∼5 × 10 11 Jones (Jones = cm Hz 1/2 /W) compared to that of the pristine MoS 2 photodetector in ambient atmosphere. Moreover, the rGO/MoS 2 photodetector showed a fast response of ∼18 ms with excellent stability and reproducibility in ambient air even after three months. The high performance of the photodetector is attributed to enhanced photoexcited carrier density and suppressed photo generated electron-hole recombination due to the strong local built-in electric field developed at the rGO/MoS 2 interface. Our results showed that integration of rGO with MoS 2 provides an efficient platform for photo detection applications.

Semiconductor quantum dots have attracted tremendous attention owing to their novel electrical and optical properties as a result of their size dependent quantum confinement effects. This provides the advantage of tunable wavelength detection, which is essential to realize spectrally selective photodetectors. We report on the fabrication and characterization of a high performance narrow band ultraviolet photodetector (UV-B) based on Indium oxide (In 2 O 3 ) nanocrystals embedded in aluminium oxide (Al 2 O 3 ) matrices. The In 2 O 3 nanocrystals are synthesized in an Al 2 O 3 matrix by sequential implantation of In + and [Formula: see text] ions and post-implantation annealing. The photodetector exhibits excellent optoelectronic performances with high spectral responsivity and external quantum efficiency. The spectral response shows a band-selective nature with a full width half maximum of ∼60 nm, and a responsivity reaching up to 70 A W -1 under 290 nm at 5 V bias. The corresponding rejection ratio to visible region was as high as 8400. The high performance of this photodetector makes it highly suitable for practical applications such as narrow-band spectrum-selective photodetectors. The device design based on ion-synthesized nanocrystals could provide a new approach for realizing a visible-blind photodetector.