Dr. Abdus Salam Sarkar | Stevens Institute of Technology (original) (raw)

Papers by Dr. Abdus Salam Sarkar

arXiv (Cornell University), May 27, 2024

MRS bulletin, Jun 25, 2024

IEEE Open Journal of Nanotechnology

We present the observations of Aharonov-Bohm (AB) oscillations in chemical vapor deposition (CVD)... more We present the observations of Aharonov-Bohm (AB) oscillations in chemical vapor deposition (CVD)-grown graphene rings via magnetotransport measurements at 4 K under out-of-plane external magnetic fields up to +/-2.1 T. Incorporating a baseline subtraction of the original conductance data allowed us to observe two-terminal conductance oscillations with a spacing of ΔBAB of 3.66 to 32.9 mT from the ring with an inner radius of 200 nm and arm-width of 400 nm, and spacing of ΔBAB from 2.1 mT to 8.2 mT from the ring with an inner radius of 400 nm and an arm-width of 400 nm. The fast-Fourier transform (FFT) data showed AB oscillation periods, with the interval of the h/e fundamental mode given by 30/T to 273/T for the ring with the inner radius of 200 nm and arm-width of 400 nm, and 122/T to 488/T for the ring with the inner radius of 400 nm. The broad spreading of FFT peaks is due to the aspect ratio of the inner radius r1 and the width w of the ring, r/w ∼ 1. Systematic numerical simulations were performed to elucidate the relation between the AB oscillation frequency and the geometry of the ring. This work shows AB oscillations in CVD-grown graphene rings at an elevated temperature (4 K).

Advanced Optical Materials, May 1, 2022

Optics Letters

Tin (II) monosulfide (SnS) has attracted considerable attention in emerging photonics and optoele... more Tin (II) monosulfide (SnS) has attracted considerable attention in emerging photonics and optoelectronics because of high carrier mobility, large absorption coefficient, anisotropic linear and nonlinear optical properties, and long-time stability. In this Letter, we report third-order nonlinear absorption and refraction of SnS quantum dots (QDs). Under excitation with 800-nm femtosecond pulses, QDs exhibit saturable absorption (saturation intensity ∼ 47.69 GW/cm2) and positive refractive nonlinearity (nonlinear refraction coefficient ∼ 1.24 × 10-15 cm2/W). Nonetheless, we investigate charge carrier dynamics using femtosecond transient absorption spectroscopy and propose the presence of midgap defect states which not only dictate carrier dynamics but also give rise to nonlinear optical properties in SnS QDs.

Advanced Science

Recent advances in atomically thin two dimensional (2D) anisotropic group IVA‐VI metal monochalco... more Recent advances in atomically thin two dimensional (2D) anisotropic group IVA‐VI metal monochalcogenides (MMCs) and their fascinating intrinsic properties and potential applications are hampered due to an ongoing challenge of monolayer isolation. Among the most promising MMCs, tin (II) sulfide (SnS) is an earth‐abundant layered material with tunable bandgap and anisotropic physical properties, which render it extraordinary for electronics and optoelectronics. To date, however, the successful isolation of atomically thin SnS single layers at large quantities has been challenging due to the presence of strong interlayer interactions, attributed to the lone‐pair electrons of sulfur. Here, a novel liquid phase exfoliation approach is reported, which enables the overcome of such strong interlayer binding energy. Specifically, it demonstrates that the synergistic action of external thermal energy with the ultrasound energy‐induced hydrodynamic force in solution gives rise to the systemati...

Advanced Optical Materials

Two‐dimensional (2D) tin(II) sulfide (SnS) crystals belong to a class of orthorhombic semiconduct... more Two‐dimensional (2D) tin(II) sulfide (SnS) crystals belong to a class of orthorhombic semiconducting materials with remarkable properties, such as in‐plane anisotropic optical and electronic response, and multiferroic nature. The 2D SnS crystals exhibit anisotropic response along the in‐plane armchair (AC) and zigzag (ZZ) crystallographic directions, offering an additional degree of freedom in manipulating their behavior. Here, advantage of the lack of inversion symmetry of the 2D SnS crystal, that produces second harmonic generation (SHG), is taken to perform polarization‐resolved SHG (P‐SHG) nonlinear imaging of the in‐plane anisotropy. The P‐SHG experimental data are fitted with a nonlinear optics model, allowing to calculate the AC/ZZ orientation from every point of the 2D crystal and to map with high resolution the AC/ZZ direction of several 2D SnS flakes belonging in the same field of view. It is found that the P‐SHG intensity polar patterns are associated with the crystallogr...

arXiv (Cornell University), Jun 20, 2021

Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive build... more Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive building block for electronic devices due to its highly anisotropic response. Two-dimensional (2D) SnS has shown to exhibit in-plane anisotropy in optical and electrical properties. However, the limitations in growing ultrasmall structures of SnS hinder the experimental exploration of anisotropic behavior in low dimension. Here, we present an elegant approach of synthesizing highly crystalline nanometer-sized SnS sheets. Ultrasmall SnS exhibits two distinct valleys along armchair and zigzag directions due to in-plane structural anisotropy like bulk SnS. We show that in such SnS nanosheet dots, the band gaps corresponding to two valleys are increased due to quantum confinement effect. We particularly observe that SnS quantum dots (QDs) show excitation energy dependent photoluminescence (PL), which originates from the two nondegenerate valleys. Our work may open up an avenue to show the potential of SnS QDs for new functionalities in electronics and optoelectronics.

Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive build... more Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive building block for electronic devices due to its highly anisotropic response. Two-dimensional (2D) SnS has shown to exhibit in-plane anisotropy in optical and electrical properties. However, the limitations in growing ultrasmall structures of SnS hinder the experimental exploration of anisotropic behavior in low dimension. Here, we present an elegant approach of synthesizing highly crystalline nanometer-sized SnS sheets. Ultrasmall SnS exhibits two distinct valleys along armchair and zig-zag directions due to in-plane structural anisotropy like bulk SnS. We show that in such SnS nanosheet dots, the band gaps corresponding to two valleys are increased due to quantum confinement effect. We particularly observe that SnS quantum dots (QDs) show excitation energy dependent photoluminescence (PL), which originates from the two nondegenerate valleys. Our work may open up an avenue to show the potent...

arXiv: Optics, 2018

Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven ... more Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven to be a phosphorene analogue. However, difficulty in isolating very thin layer of SnS pose challenges in practical utilization. Here, we prepare ultrathin SnS via liquid phase exfoliation. With transmission electron microscopy, we identify the buckled structure of 2D SnS. We employ temperature dependent Raman spectroscopy to elucidate electron-phonon interactions, which reveals a linear phonon shifts. The active Raman modes of ultrathin SnS exhibit higher sensitivity to temperature than other 2D materials. Moreover, we demonstrate strong light-matter interaction in ultrathin SnS using Z-scan and ultrafast spectroscopy. Rich exciton-exciton and coherent exciton-photon interactions arising from many-particle excited effects in ultrathin SnS eventually enhances the nonlinear optical properties. Our findings highlight the prospects for the synthesis of ultrathin anisotropic SnS towards the b...

Scientific Reports, 2020

Tailoring the photoluminescence (PL) properties in two-dimensional (2D) molybdenum disulfide (MoS... more Tailoring the photoluminescence (PL) properties in two-dimensional (2D) molybdenum disulfide (MoS2) crystals using external factors is critical for its use in valleytronic, nanophotonic and optoelectronic applications. Although significant effort has been devoted towards enhancing or manipulating the excitonic emission in MoS2 monolayers, the excitonic emission in few-layers MoS2 has been largely unexplored. Here, we put forward a novel nano-heterojunction system, prepared with a non-lithographic process, to enhance and control such emission. It is based on the incorporation of few-layers MoS2 into a plasmonic silver metaphosphate glass (AgPO3) matrix. It is shown that, apart from the enhancement of the emission of both A- and B-excitons, the B-excitonic emission dominates the PL intensity. In particular, we observe an almost six-fold enhancement of the B-exciton emission, compared to control MoS2 samples. This enhanced PL at room temperature is attributed to an enhanced exciton–pla...

Advanced Science, 2020

The family of emerging low‐symmetry and structural in‐plane anisotropic two‐dimensional (2D) mate... more The family of emerging low‐symmetry and structural in‐plane anisotropic two‐dimensional (2D) materials has been expanding rapidly in recent years. As an important emerging anisotropic 2D material, the black phosphorene analog group IVA–VI metal monochalcogenides (MMCs) have been surged recently due to their distinctive crystalline symmetries, exotic in‐plane anisotropic electronic and optical response, earth abundance, and environmentally friendly characteristics. In this article, the recent research advancements in the field of anisotropic 2D MMCs are reviewed. At first, the unique wavy crystal structures together with the optical and electronic properties of such materials are discussed. The Review continues with the various methods adopted for the synthesis of layered MMCs including micromechanical and liquid phase exfoliation as well as physical vapor deposition. The last part of the article focuses on the application of the structural anisotropic response of 2D MMCs in field ef...

npj 2D Materials and Applications, 2020

Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven ... more Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven to be a phosphorene analog. However, difficulty in isolating a very thin layer of SnS poses challenges in practical utilization. Here, we prepare ultrathin SnS via liquid-phase exfoliation. With transmission electron microscopy, we identify the buckled structure of 2D SnS. We employ temperature dependent Raman spectroscopy to elucidate electron–phonon interactions, which reveals a linear phonon shifts. The active Raman modes of ultrathin SnS exhibit higher sensitivity to temperature than other 2D materials. Moreover, we demonstrate strong light-matter interaction in ultrathin SnS using Z-scan and ultrafast spectroscopy. Rich exciton–exciton and coherent exciton–photon interactions arising from many-particle excited effects in ultrathin SnS eventually enhances the nonlinear optical properties. Our findings highlight the prospects for the synthesis of ultrathin anisotropic SnS towards the ...

Organic Electronics, 2018

Photon harvesting by the active layers of bulk heterojunction (BHJ) polymer solar cells (PSCs) gr... more Photon harvesting by the active layers of bulk heterojunction (BHJ) polymer solar cells (PSCs) greatly influences the power conversion efficiency (PCE) of the devices. Inclusion of novel metal nanostructures in photoactive layers is one of the effective ways to enhance light trapping without increasing the device thickness. Here, we demonstrate a dramatic enhancement (up to 43%) of the power conversion efficiency (PCE) by exploiting gold nanostructures (AuNSs)-embedded graphene oxide (GO) as the hole transporting layer (HTL) in BHJ PSCs. The enhancement of the device performance could be attributed to the increase in both short circuit current density (J sc) and fill factor (FF). The increased FF is most likely the result of the enhanced charge collection through modified HTL and anode contact. Furthermore, the optical properties of the photovoltaic devices suggest that AuNSs cause light trapping via plasmonic effects resulting enhanced J sc .

ACS Omega, 2017

The heterojunctions of organic/two-dimensional transition metal dichalcogenides (TMDs) have the p... more The heterojunctions of organic/two-dimensional transition metal dichalcogenides (TMDs) have the potential to be used in the next-generation optoelectronic and photonic devices. Herein, we have systemically investigated the temperature-dependent Raman spectroscopy to elucidate the phonon shift and thermal properties of the semiconducting TMD nanosheets grafted by a conjugated polymer (PG-MoS 2 and PG-MoSe 2) forming heterojunctions. Our results reveal that softening of Raman modes of PG-TMDs as temperature increases from 77 to 300 K is due to the negative temperature coefficient (TC) and anharmonicity. The TCs of E 1 2g and A 1g modes of PG-MoS 2 nanosheets and A 1g mode of PG-MoSe 2 were found to be −0.015, −0.010, and −0.010 cm −1 K −1 , respectively. The origin of negative TCs is explained on the basis of a double resonance process, which is more active in singleand few-layer MoS 2 and MoSe 2. Interestingly, the temperature-dependent behavior of the phonon modes of PG-MoS 2 and PG-MoSe 2 is similar to that of pristine nanosheets. Grafting by conjugated polymer does not affect the electron−phonon (e−p) interaction in the semiconducting (2H-phase) TMDs, hinting the application potential of such materials in field-effect electronic devices.

ACS Energy Letters, 2017

Heterostructures of zero/two-dimensional (0D/2D) materials, especially quantum dots (QDs)/nanoshe... more Heterostructures of zero/two-dimensional (0D/2D) materials, especially quantum dots (QDs)/nanosheets (NSs) have attracted several attentions for extracting photogenerated electrons/holes. Herein, we report the dissociation of exciton at the heterojunction of CdSe (cadmium selenide) QD and MoS 2 (molybdenum disulfide) nanosheet utilizing steady-state and time-resolved spectroscopic techniques. Quasi type II semiconductor like band energy alignment of the 0D/2D heterojunction facilitates exciton breaking via hole transfer from QD to MoS 2. Furthermore, we demonstrate the extraction of two holes from doubly excited QDs (created via high power exciation) following the dissociation of biexciton at the 0D/2D interface. This work is expected to provide a new concept of exploiting multiple exciton generation in quantum dot sensitized solar cells by harvesting multiple carriers.

The Journal of Physical Chemistry C, 2017

Organic-inorganic heterostructures are emerging materials for developing high performance, soluti... more Organic-inorganic heterostructures are emerging materials for developing high performance, solution processable organic electronic and optoelectronic devices. In particular, the heterostructures of semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDs) are interesting due to quantum confinement effect, extended solar light absorption and tunable optoelectronic properties. Here, we report a facile and fully solution processable method called semiconductive Polymer assisted chemical exfoliation (SPACE) of synthesizing polymer-MoS 2 nanoheterostructures. Synthesized polymer grafted MoS 2 (PG-MoS 2) nanoheterostructures consist of few layers of MoS 2 and are chemically quite stable. The phase integrity of MoS 2 in PG-MoS 2 is confirmed by various microscopic and spectroscopic techniques. Efficient

RSC Adv., 2016

We elucidate the carrier transport mechanism in a novel polyoxometalate–polymer (POM–MAPDST) hybr... more We elucidate the carrier transport mechanism in a novel polyoxometalate–polymer (POM–MAPDST) hybrid containing molybdenum transition metal.

Journal of Physics D: Applied Physics, 2015

Temperature dependent electrical conduction in as prepared and annealed graphene oxide (GO) thin ... more Temperature dependent electrical conduction in as prepared and annealed graphene oxide (GO) thin films was investigated. The electrical measurements on a sandwich structure of GO reveal space charge limited conduction in the presence of an exponential trap distribution within the temperature range of 83–288 K. However, for the annealed GO, at all temperatures and low bias voltage, charge transport is governed by a bulk limited process with a bias dependent crossover from Ohmic to trap free space charge limited conduction. At the high bias voltage and low temperature, the conduction becomes space charge limited with exponential distribution of traps. Moreover, we estimated trap densities in both pristine and annealed GO.

arXiv (Cornell University), May 27, 2024

MRS bulletin, Jun 25, 2024

IEEE Open Journal of Nanotechnology

We present the observations of Aharonov-Bohm (AB) oscillations in chemical vapor deposition (CVD)... more We present the observations of Aharonov-Bohm (AB) oscillations in chemical vapor deposition (CVD)-grown graphene rings via magnetotransport measurements at 4 K under out-of-plane external magnetic fields up to +/-2.1 T. Incorporating a baseline subtraction of the original conductance data allowed us to observe two-terminal conductance oscillations with a spacing of ΔBAB of 3.66 to 32.9 mT from the ring with an inner radius of 200 nm and arm-width of 400 nm, and spacing of ΔBAB from 2.1 mT to 8.2 mT from the ring with an inner radius of 400 nm and an arm-width of 400 nm. The fast-Fourier transform (FFT) data showed AB oscillation periods, with the interval of the h/e fundamental mode given by 30/T to 273/T for the ring with the inner radius of 200 nm and arm-width of 400 nm, and 122/T to 488/T for the ring with the inner radius of 400 nm. The broad spreading of FFT peaks is due to the aspect ratio of the inner radius r1 and the width w of the ring, r/w ∼ 1. Systematic numerical simulations were performed to elucidate the relation between the AB oscillation frequency and the geometry of the ring. This work shows AB oscillations in CVD-grown graphene rings at an elevated temperature (4 K).

Advanced Optical Materials, May 1, 2022

Optics Letters

Tin (II) monosulfide (SnS) has attracted considerable attention in emerging photonics and optoele... more Tin (II) monosulfide (SnS) has attracted considerable attention in emerging photonics and optoelectronics because of high carrier mobility, large absorption coefficient, anisotropic linear and nonlinear optical properties, and long-time stability. In this Letter, we report third-order nonlinear absorption and refraction of SnS quantum dots (QDs). Under excitation with 800-nm femtosecond pulses, QDs exhibit saturable absorption (saturation intensity ∼ 47.69 GW/cm2) and positive refractive nonlinearity (nonlinear refraction coefficient ∼ 1.24 × 10-15 cm2/W). Nonetheless, we investigate charge carrier dynamics using femtosecond transient absorption spectroscopy and propose the presence of midgap defect states which not only dictate carrier dynamics but also give rise to nonlinear optical properties in SnS QDs.

Advanced Science

Recent advances in atomically thin two dimensional (2D) anisotropic group IVA‐VI metal monochalco... more Recent advances in atomically thin two dimensional (2D) anisotropic group IVA‐VI metal monochalcogenides (MMCs) and their fascinating intrinsic properties and potential applications are hampered due to an ongoing challenge of monolayer isolation. Among the most promising MMCs, tin (II) sulfide (SnS) is an earth‐abundant layered material with tunable bandgap and anisotropic physical properties, which render it extraordinary for electronics and optoelectronics. To date, however, the successful isolation of atomically thin SnS single layers at large quantities has been challenging due to the presence of strong interlayer interactions, attributed to the lone‐pair electrons of sulfur. Here, a novel liquid phase exfoliation approach is reported, which enables the overcome of such strong interlayer binding energy. Specifically, it demonstrates that the synergistic action of external thermal energy with the ultrasound energy‐induced hydrodynamic force in solution gives rise to the systemati...

Advanced Optical Materials

Two‐dimensional (2D) tin(II) sulfide (SnS) crystals belong to a class of orthorhombic semiconduct... more Two‐dimensional (2D) tin(II) sulfide (SnS) crystals belong to a class of orthorhombic semiconducting materials with remarkable properties, such as in‐plane anisotropic optical and electronic response, and multiferroic nature. The 2D SnS crystals exhibit anisotropic response along the in‐plane armchair (AC) and zigzag (ZZ) crystallographic directions, offering an additional degree of freedom in manipulating their behavior. Here, advantage of the lack of inversion symmetry of the 2D SnS crystal, that produces second harmonic generation (SHG), is taken to perform polarization‐resolved SHG (P‐SHG) nonlinear imaging of the in‐plane anisotropy. The P‐SHG experimental data are fitted with a nonlinear optics model, allowing to calculate the AC/ZZ orientation from every point of the 2D crystal and to map with high resolution the AC/ZZ direction of several 2D SnS flakes belonging in the same field of view. It is found that the P‐SHG intensity polar patterns are associated with the crystallogr...

arXiv (Cornell University), Jun 20, 2021

Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive build... more Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive building block for electronic devices due to its highly anisotropic response. Two-dimensional (2D) SnS has shown to exhibit in-plane anisotropy in optical and electrical properties. However, the limitations in growing ultrasmall structures of SnS hinder the experimental exploration of anisotropic behavior in low dimension. Here, we present an elegant approach of synthesizing highly crystalline nanometer-sized SnS sheets. Ultrasmall SnS exhibits two distinct valleys along armchair and zigzag directions due to in-plane structural anisotropy like bulk SnS. We show that in such SnS nanosheet dots, the band gaps corresponding to two valleys are increased due to quantum confinement effect. We particularly observe that SnS quantum dots (QDs) show excitation energy dependent photoluminescence (PL), which originates from the two nondegenerate valleys. Our work may open up an avenue to show the potential of SnS QDs for new functionalities in electronics and optoelectronics.

Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive build... more Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as an attractive building block for electronic devices due to its highly anisotropic response. Two-dimensional (2D) SnS has shown to exhibit in-plane anisotropy in optical and electrical properties. However, the limitations in growing ultrasmall structures of SnS hinder the experimental exploration of anisotropic behavior in low dimension. Here, we present an elegant approach of synthesizing highly crystalline nanometer-sized SnS sheets. Ultrasmall SnS exhibits two distinct valleys along armchair and zig-zag directions due to in-plane structural anisotropy like bulk SnS. We show that in such SnS nanosheet dots, the band gaps corresponding to two valleys are increased due to quantum confinement effect. We particularly observe that SnS quantum dots (QDs) show excitation energy dependent photoluminescence (PL), which originates from the two nondegenerate valleys. Our work may open up an avenue to show the potent...

arXiv: Optics, 2018

Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven ... more Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven to be a phosphorene analogue. However, difficulty in isolating very thin layer of SnS pose challenges in practical utilization. Here, we prepare ultrathin SnS via liquid phase exfoliation. With transmission electron microscopy, we identify the buckled structure of 2D SnS. We employ temperature dependent Raman spectroscopy to elucidate electron-phonon interactions, which reveals a linear phonon shifts. The active Raman modes of ultrathin SnS exhibit higher sensitivity to temperature than other 2D materials. Moreover, we demonstrate strong light-matter interaction in ultrathin SnS using Z-scan and ultrafast spectroscopy. Rich exciton-exciton and coherent exciton-photon interactions arising from many-particle excited effects in ultrathin SnS eventually enhances the nonlinear optical properties. Our findings highlight the prospects for the synthesis of ultrathin anisotropic SnS towards the b...

Scientific Reports, 2020

Tailoring the photoluminescence (PL) properties in two-dimensional (2D) molybdenum disulfide (MoS... more Tailoring the photoluminescence (PL) properties in two-dimensional (2D) molybdenum disulfide (MoS2) crystals using external factors is critical for its use in valleytronic, nanophotonic and optoelectronic applications. Although significant effort has been devoted towards enhancing or manipulating the excitonic emission in MoS2 monolayers, the excitonic emission in few-layers MoS2 has been largely unexplored. Here, we put forward a novel nano-heterojunction system, prepared with a non-lithographic process, to enhance and control such emission. It is based on the incorporation of few-layers MoS2 into a plasmonic silver metaphosphate glass (AgPO3) matrix. It is shown that, apart from the enhancement of the emission of both A- and B-excitons, the B-excitonic emission dominates the PL intensity. In particular, we observe an almost six-fold enhancement of the B-exciton emission, compared to control MoS2 samples. This enhanced PL at room temperature is attributed to an enhanced exciton–pla...

Advanced Science, 2020

The family of emerging low‐symmetry and structural in‐plane anisotropic two‐dimensional (2D) mate... more The family of emerging low‐symmetry and structural in‐plane anisotropic two‐dimensional (2D) materials has been expanding rapidly in recent years. As an important emerging anisotropic 2D material, the black phosphorene analog group IVA–VI metal monochalcogenides (MMCs) have been surged recently due to their distinctive crystalline symmetries, exotic in‐plane anisotropic electronic and optical response, earth abundance, and environmentally friendly characteristics. In this article, the recent research advancements in the field of anisotropic 2D MMCs are reviewed. At first, the unique wavy crystal structures together with the optical and electronic properties of such materials are discussed. The Review continues with the various methods adopted for the synthesis of layered MMCs including micromechanical and liquid phase exfoliation as well as physical vapor deposition. The last part of the article focuses on the application of the structural anisotropic response of 2D MMCs in field ef...

npj 2D Materials and Applications, 2020

Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven ... more Two-dimensional (2D) tin(II) monosulfide (SnS) with strong structural anisotropy has been proven to be a phosphorene analog. However, difficulty in isolating a very thin layer of SnS poses challenges in practical utilization. Here, we prepare ultrathin SnS via liquid-phase exfoliation. With transmission electron microscopy, we identify the buckled structure of 2D SnS. We employ temperature dependent Raman spectroscopy to elucidate electron–phonon interactions, which reveals a linear phonon shifts. The active Raman modes of ultrathin SnS exhibit higher sensitivity to temperature than other 2D materials. Moreover, we demonstrate strong light-matter interaction in ultrathin SnS using Z-scan and ultrafast spectroscopy. Rich exciton–exciton and coherent exciton–photon interactions arising from many-particle excited effects in ultrathin SnS eventually enhances the nonlinear optical properties. Our findings highlight the prospects for the synthesis of ultrathin anisotropic SnS towards the ...

Organic Electronics, 2018

Photon harvesting by the active layers of bulk heterojunction (BHJ) polymer solar cells (PSCs) gr... more Photon harvesting by the active layers of bulk heterojunction (BHJ) polymer solar cells (PSCs) greatly influences the power conversion efficiency (PCE) of the devices. Inclusion of novel metal nanostructures in photoactive layers is one of the effective ways to enhance light trapping without increasing the device thickness. Here, we demonstrate a dramatic enhancement (up to 43%) of the power conversion efficiency (PCE) by exploiting gold nanostructures (AuNSs)-embedded graphene oxide (GO) as the hole transporting layer (HTL) in BHJ PSCs. The enhancement of the device performance could be attributed to the increase in both short circuit current density (J sc) and fill factor (FF). The increased FF is most likely the result of the enhanced charge collection through modified HTL and anode contact. Furthermore, the optical properties of the photovoltaic devices suggest that AuNSs cause light trapping via plasmonic effects resulting enhanced J sc .

ACS Omega, 2017

The heterojunctions of organic/two-dimensional transition metal dichalcogenides (TMDs) have the p... more The heterojunctions of organic/two-dimensional transition metal dichalcogenides (TMDs) have the potential to be used in the next-generation optoelectronic and photonic devices. Herein, we have systemically investigated the temperature-dependent Raman spectroscopy to elucidate the phonon shift and thermal properties of the semiconducting TMD nanosheets grafted by a conjugated polymer (PG-MoS 2 and PG-MoSe 2) forming heterojunctions. Our results reveal that softening of Raman modes of PG-TMDs as temperature increases from 77 to 300 K is due to the negative temperature coefficient (TC) and anharmonicity. The TCs of E 1 2g and A 1g modes of PG-MoS 2 nanosheets and A 1g mode of PG-MoSe 2 were found to be −0.015, −0.010, and −0.010 cm −1 K −1 , respectively. The origin of negative TCs is explained on the basis of a double resonance process, which is more active in singleand few-layer MoS 2 and MoSe 2. Interestingly, the temperature-dependent behavior of the phonon modes of PG-MoS 2 and PG-MoSe 2 is similar to that of pristine nanosheets. Grafting by conjugated polymer does not affect the electron−phonon (e−p) interaction in the semiconducting (2H-phase) TMDs, hinting the application potential of such materials in field-effect electronic devices.

ACS Energy Letters, 2017

Heterostructures of zero/two-dimensional (0D/2D) materials, especially quantum dots (QDs)/nanoshe... more Heterostructures of zero/two-dimensional (0D/2D) materials, especially quantum dots (QDs)/nanosheets (NSs) have attracted several attentions for extracting photogenerated electrons/holes. Herein, we report the dissociation of exciton at the heterojunction of CdSe (cadmium selenide) QD and MoS 2 (molybdenum disulfide) nanosheet utilizing steady-state and time-resolved spectroscopic techniques. Quasi type II semiconductor like band energy alignment of the 0D/2D heterojunction facilitates exciton breaking via hole transfer from QD to MoS 2. Furthermore, we demonstrate the extraction of two holes from doubly excited QDs (created via high power exciation) following the dissociation of biexciton at the 0D/2D interface. This work is expected to provide a new concept of exploiting multiple exciton generation in quantum dot sensitized solar cells by harvesting multiple carriers.

The Journal of Physical Chemistry C, 2017

Organic-inorganic heterostructures are emerging materials for developing high performance, soluti... more Organic-inorganic heterostructures are emerging materials for developing high performance, solution processable organic electronic and optoelectronic devices. In particular, the heterostructures of semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDs) are interesting due to quantum confinement effect, extended solar light absorption and tunable optoelectronic properties. Here, we report a facile and fully solution processable method called semiconductive Polymer assisted chemical exfoliation (SPACE) of synthesizing polymer-MoS 2 nanoheterostructures. Synthesized polymer grafted MoS 2 (PG-MoS 2) nanoheterostructures consist of few layers of MoS 2 and are chemically quite stable. The phase integrity of MoS 2 in PG-MoS 2 is confirmed by various microscopic and spectroscopic techniques. Efficient

RSC Adv., 2016

We elucidate the carrier transport mechanism in a novel polyoxometalate–polymer (POM–MAPDST) hybr... more We elucidate the carrier transport mechanism in a novel polyoxometalate–polymer (POM–MAPDST) hybrid containing molybdenum transition metal.

Journal of Physics D: Applied Physics, 2015

Temperature dependent electrical conduction in as prepared and annealed graphene oxide (GO) thin ... more Temperature dependent electrical conduction in as prepared and annealed graphene oxide (GO) thin films was investigated. The electrical measurements on a sandwich structure of GO reveal space charge limited conduction in the presence of an exponential trap distribution within the temperature range of 83–288 K. However, for the annealed GO, at all temperatures and low bias voltage, charge transport is governed by a bulk limited process with a bias dependent crossover from Ohmic to trap free space charge limited conduction. At the high bias voltage and low temperature, the conduction becomes space charge limited with exponential distribution of traps. Moreover, we estimated trap densities in both pristine and annealed GO.