Amina Zafar - Academia.edu (original) (raw)

Papers by Amina Zafar

Research paper thumbnail of Nickel foam supported hierarchical NiCo2S4@NiFe LDH heterostructures as highly efficient electrode for long cycling stability supercapacitor

Electrochimica Acta

Layered double hydroxides (LDHs) based heterostructures provide an opportunity for the developmen... more Layered double hydroxides (LDHs) based heterostructures provide an opportunity for the development of highperformance supercapacitors. Up till now, hierarchical NiCo 2 S 4 @NiFe LDH heterostructure is scarcely investigated for supercapacitor. In this work, the hierarchical NiCo 2 S 4 @NiFe LDH heterostructure nanosheet arrays on Ni-foam (NF) were synthesized by a facile hydrothermal method. As the supercapacitor electrode, it has been revealed that the incorporation of NiFe can significantly increase the capacitive performance of the heterostructure. At a current density of 1 Ag − 1 , a specific capacitance of NiCo 2 S 4 @NiFe LDH electrode was reached up to 827 Fg − 1 , outperforming that of pristine NiCo 2 S 4 and NiFe LDH. Moreover, the electrode keeps 90.2% of its preliminary capacitance after 12,000 cycles at 5 A g − 1. In addition, NiCo 2 S 4 @NiFe LDH electrode offer high energy density of 38.1 W h kg − 1 and power density of 1800 W kg − 1. According to DFT calculations, NiFe-LDH adsorption on NiCo 2 S 4 is strong and governed by large interfacial interactions with a charge transfer of 0.44 eV to NiCo 2 S 4 surface thus demonstrating the significantly improved electrochemical performance. Hence, such an outstanding electrochemical finding suggest that NiCo 2 S 4 @NiFe LDH heterostructures could be attractive electrode materials as practical supercapacitors for next generation energy storage devices.

Research paper thumbnail of Development of MoS2-ZnO heterostructures: an efficient bifunctional catalyst for the detection of glucose and degradation of toxic organic dyes

New Journal of Chemistry

The heterostructure catalyst MoS2-ZnO possesses binary properties and provides a novel platform f... more The heterostructure catalyst MoS2-ZnO possesses binary properties and provides a novel platform for the remediation of environmental as well as health issues.

Research paper thumbnail of A study on causes and community response regarding diabetes as a community disease of southern Punjab Pakistan

Journal of King Saud University - Science

Research paper thumbnail of An amphiphilic polyoxometalate–CNT nanohybrid as a highly efficient enzyme-free electrocatalyst for H2O2 sensing

New Journal of Chemistry

A highly active electrochemical amphiphilic POM–CNT nanohybrid using non-covalent interactions fo... more A highly active electrochemical amphiphilic POM–CNT nanohybrid using non-covalent interactions for highly efficient detection of H2O2 is reported. The synergy between POMs and CNTs results in 10 times higher current response than pristine POM.

Research paper thumbnail of Mesoporous NiCo2S4 nanoflakes as an efficient and durable electrocatalyst for non-enzymatic detection of cholesterol

Nanotechnology

The detection of cholesterol is very crucial in clinical diagnosis for rapid and accurate monitor... more The detection of cholesterol is very crucial in clinical diagnosis for rapid and accurate monitoring of multiple disease-biomarkers. There is a great need for construction of a highly reliable and stable electrocatalyst for the efficient detection of cholesterol. In this work, mesoporous NiCo2S4 nanoflakes of enhanced electrochemical properties are prepared through a facile hydrothermal approach. The developed nanoflakes modified nickel foam electrode exhibits outstanding electrocatalytic properties for the detection of cholesterol with high selectivity. The electrode displays excellent sensitivity of 8623.6 μA mM−1 cm−2, in the wide linear range from 0.01 to 0.25 mM with a low detection limit of 0.01 μM. In addition, NiCo2S4 structure reveals good thermal stability and reproducibility over a period of 8 weeks. Moreover, the nanoflakes show good response for detection of cholesterol in real samples. Our results demonstrate the potential use of NiCo2S4 as a catalyst for the developme...

Research paper thumbnail of MWCNT synergy for boosting the electrochemical kinetics of V2O5 cathode for lithium-ion batteries

New Journal of Chemistry, 2022

V2O5/MWCNT hybrid system has been developed and investigated as cathode in LIBs. The developed el... more V2O5/MWCNT hybrid system has been developed and investigated as cathode in LIBs. The developed electrode shows superior performance as compare to pristine V2O5 and V2O5/rGO hybrid structure due to the synergy between V2O5 and MWCNT.

Research paper thumbnail of Fluorescence manipulation from graphene and hydrogen-terminated graphene covered Au nanoparticles

AIP Advances, 2021

This paper presents the fluorescence manipulation of Rhodamine-6G (R6G) due to Au nanoparticles (... more This paper presents the fluorescence manipulation of Rhodamine-6G (R6G) due to Au nanoparticles (Au-NPs) covered by pristine graphene and hydrogen-terminated graphene. By taking florescence signals of R6G on a quartz substrate as the standard reference, we observe an ∼fourfold increase in fluorescence intensity of R6G on bare Au-NPs deposited on the quartz substrate. However, this enhancement reduces to ∼1.8-fold when Au-NPs are covered by H-terminated graphene. In the case of Au-NPs covered by pristine graphene, the fluorescence of R6G is significantly quenched by a factor of ∼7.6-fold. The resulting fluorescence level can be attributed to the local field enhancement from Au-NPs and the quenching effect of graphene in the Au–graphene hybrid nanostructure, which are confirmed by our controlled experimental and simulation results. Our work reveals that the surface modification of metal NPs by graphene materials would bring a great impact on fluorescence, providing a simple approach f...

Research paper thumbnail of Controlled layer growth of WS 2 grains by chemical vapor deposition

Bulletin of the American Physical Society, 2018

Research paper thumbnail of Oxygen vacancies boosted vanadium doped ZnO nanostructures-based voltage-switchable binary biosensor

Nanotechnology, 2021

The development of a reliable non-enzymatic multi-analyte biosensor is remained a great challenge... more The development of a reliable non-enzymatic multi-analyte biosensor is remained a great challenge for biomedical and industrial applications. In this prospective, rationally designed electrode materials having voltage switchable electrocatalytic properties are highly promising. Here, we report vanadium doped ZnO engineered nanostructures (Zn1−x V x O where 0 ≤ x ≤ 0.1) which exhibit voltage switchable electrocatalytic properties for accurate measurements of glucose and hydrogen peroxide. Microstructures and chemical analysis show that the oxygen vacancies in the material can be tuned by controlling the stoichiometric ratios which play key role for voltage dependent measurements of different analytes. The developed Zn1−x V x O nanostructures exhibit outstanding sensing ability for binary analytes with a high selectivity, low detection limit, thermal stability and long-term stability. The Zn0.9V0.1O/glassy carbon (GC) electrode shows 3-fold increase in reproducible sensitivity for both glucose (655.24 μA mM−1 cm−2) and H2O2 (13309.37 μA mM−1 cm−2) as compared to the pristine ZnO/GC electrode. Moreover, the electrode also shows good response for human blood serum and commercially available samples. The results demonstrate that defect engineering is a promising route for the development of cost-effective non-enzymatic multi-analyte sensors for practical applications.

Research paper thumbnail of Frequency stable dielectric constant with reduced dielectric loss of one-dimensional ZnO–ZnS heterostructures

Nanoscale, 2021

ZnO–ZnS heterostructure is developed which shows frequency stable dielectric response at ≥103 Hz ... more ZnO–ZnS heterostructure is developed which shows frequency stable dielectric response at ≥103 Hz due to coupling of the bare charges in the form of overlapping large polaron and Zn2+–VO dipoles present at ZnO–ZnS heterostructure interface.

Research paper thumbnail of The Thinnest Light Disk: Rewritable Data Storage and Encryption on WS 2 Monolayers (Adv. Funct. Mater. 36/2021)

Advanced Functional Materials, 2021

The thinnest light disk is demonstrated at the atomic level by developing an erasable method to d... more The thinnest light disk is demonstrated at the atomic level by developing an erasable method to directly write encrypted information onto WS2 monolayers. The write‐in is realized by precise control of photoluminescence emission by means of ozone functionalization and scanning focused laser beam. The visual decryption and reading‐out of information are enabled by fluorescence contrast. The high encryption level is ensured by the threshold power upon which the data deletion will be triggered. Owing to the high spatial resolution and power sensitivity, the storage capacity within <1 nm thickness can be up to ≈62.5 MB cm−2, and the writing speed can reach ≈6.25 MB s−1. Density functional theory calculations suggest that the disk formatting is realized by ozone molecule adsorption induced localized unoccupied states, while the read‐in relies on the passivation of defects via substitution of the sulfur vacancies with oxygen atoms. The results of this study promote data storage and encryption on the atomic scale.

Research paper thumbnail of High-Performance Graphene-Based Electrostatic Field Sensor

IEEE Electron Device Letters, 2017

Electrostatic sensing technology is widely utilized in both military and civilian applications, i... more Electrostatic sensing technology is widely utilized in both military and civilian applications, including electrostatic prevention in gas stations and various electronic devices. The high sensitivity of electrostatic sensor is capable to detect not only weak electrostatic charges, but also the weak disturbance of electrostatic field in distant. Here, we present a high-performance graphene-based electrostatic sensor. Combining the ultrahigh mobility of graphene and the long lifetime of carriers in lightly doped SiO 2 /Si substrate, our device achieves a fast response of ~2 s and detection limit of electrostatic potential as low as ~5 V, which is improved by an order of magnitude as compared to commercial product. The proposed device structure opens a promising pathway to high-sensitive electrostatic detection, and also greatly facilitates the development of novel sensors, e.g. portable and flexible electrostatic sensor. Correspondence and requests for materials should be addressed to Z. N.

Research paper thumbnail of Photoluminescence characterization of the grain boundary thermal stability in chemical vapor deposition grown WS2

Materials Research Express, 2017

Monolayer transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have been considered as pr... more Monolayer transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have been considered as promising candidate materials in nanophotonic applications. However, the structure stability of TMDs based optoelectronic devices is highly sensitive to the working environment. Here we present a successive photoluminescence study of the thermal stability characterization of grain boundary in chemical vapor deposition grown monolayer WS2. Results show that PL intensity enhancement in grain boundaries can be significantly weakened during the annealing process. Transformation temperature starts around 210 °C, substantially lower than the surrounding non-grain-boundary area. First-principle calculations results show that the PL quenching of grain boundaries is caused by the increased structural defects induced by annealing process, which makes the transition of electrons more difficult. Our results provide a route for characterizing the structure stability of two dimensional (2D) semiconductors, calling for extra attention to nanophotonic device working condition.

Research paper thumbnail of Reconstruction of 1,000 Projection Neurons Reveals New Cell Types and Organization of Long-Range Connectivity in the Mouse Brain

SSRN Electronic Journal, 2019

Neuronal cell types are the nodes of neural circuits that determine the flow of information withi... more Neuronal cell types are the nodes of neural circuits that determine the flow of information within the brain. Neuronal morphology, especially the shape of the axonal arbor, provides an essential descriptor of cell type and reveals how individual neurons route their output across the brain. Despite the importance of morphology, few projection neurons in the mouse brain have been reconstructed in their entirety. Here we present a robust and efficient platform for imaging and reconstructing complete neuronal morphologies, including axonal arbors that span substantial portions of the brain. We used this platform to reconstruct more than 1,000 projection neurons in the motor cortex, thalamus, subiculum, and hypothalamus. Together, the reconstructed neurons comprise more than 75 meters of axonal length and are available in a searchable online database. Axonal shapes revealed previously unknown subtypes of projection neurons and suggest organizational principles of long-range connectivity.

Research paper thumbnail of Sulfur‐Mastery: Precise Synthesis of 2D Transition Metal Dichalcogenides

Advanced Functional Materials, 2019

Chemical vapor deposition (CVD) has been developed as the most promising method for the growth of... more Chemical vapor deposition (CVD) has been developed as the most promising method for the growth of transition metal dichalcogenides (TMDs). In this work, the key factor determining the growth of TMDs is ascertained. A straightforward method is devised to directly achieve a holistic control of thickness, shape, and size of WS 2 flakes via a single parameter control, namely, the status of the S-precursor. The thickness-dependent growth of WS 2 flakes from mono-to quad-layers is achieved by precise control of the feeding rate of elemental S-precursor. Moreover, the explicit control over amount and exposure time of S-precursor determines the most optimum combination of these parameters to tune the shape of the crystals from triangular to hexagonal with appropriate size. Hence, the experimental findings provide a promising strategy to engineer the growth evolution of WS 2 atomic layers by fine tuning of the sulfur supply, paving a pathway to scalable electronic and photonic devices.

Research paper thumbnail of Thermally enhanced optical contrast of graphene oxide for thickness identification

Nanotechnology, 2019

We present a simple, but rapid and accurate approach to identify the layer number of graphene oxi... more We present a simple, but rapid and accurate approach to identify the layer number of graphene oxide (GO) by using its thermally enhanced optical contrast via vacuum heating. As expected, changes have been observed both in the thicknesses and chemical structures of the material upon the thermal treatment, which can be attributed to the reduction of the amount of intercalated water and oxygen content. This results in the increase of refractive index and absorption coefficient approaching the values for intrinsic graphene. Finally, we achieve an almost complete recovery of optical contrast of GO compared with the one of graphene. The method would be made suitable for the thickness identification of mass-produced GO since it can greatly facilitate sample evaluation and manipulation, and provide immediate feedback to improve synthesis and processing strategies.

Research paper thumbnail of Tuning interlayer coupling by laser irradiation and broadband photodetection in vertical MoTe2/WS2 vdW heterostructure

APL Materials, 2019

van der Waals (vdW) heterostructures constructed by stacking different two dimensional layered ma... more van der Waals (vdW) heterostructures constructed by stacking different two dimensional layered materials are extensively utilized in designing novel optoelectronic devices, such as photodetectors and light-emitting diodes. However, the performance of vertical heterostructures is impeded by challenges in effectively achieving interlayer coupling. Here, the systematic demonstration of vertical MoTe2/WS2 vdW heterostructures assembled by a mechanical transfer technique is reported, whereas the interlayer interaction is tuned from weak coupling to strong coupling by laser irradiation. Thereafter, the improved interlayer interaction of heterostructures is characterized by photoluminescence spectroscopy and further confirmed by electrical transport. Moreover, visible-infrared broadband photoresponse is achieved in the vertical stacking with the built-in field generated between MoTe2 and WS2. Thus, the outstanding findings of our experimental approach can facilitate novel two-dimensional d...

Research paper thumbnail of Producing air-stable InSe nanosheet through mild oxygen plasma treatment

Semiconductor Science and Technology, 2018

Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier ... more Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier mobility and broadband optical absorption, is considered as a promising candidate for electronic and optoelectronic devices. It has been a challenge to produce air-stable mono- or few-layer InSe nanosheets because they degrade rapidly in an ambient environment. Here, we demonstrate a facile mild oxygen plasma treatment route to fabricate air-stable few-layer InSe samples. Photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS) analysis indicate that the plasma treatment can introduce an oxidation process that forms a dense InSe1−xOx capping layer on the surface, and thus prevent the sample from degradation. Furthermore, the oxide layer would introduce a PL quenching of the pristine InSe, while a new and strong PL peak belonging to the emission from InSe1−xOx appears. This work offers a practical and efficient route to improve the performance of InSe based electrical and optoelectronic devices.

Research paper thumbnail of Nonvolatile Memory Based On Molecular Ferroelectric/Graphene Field Effect Transistor

ACS applied materials & interfaces, Jan 8, 2018

Ferroelectric thin films are extensively attractive as next-generation non-volatile memories. Rec... more Ferroelectric thin films are extensively attractive as next-generation non-volatile memories. Recently molecular ferroelectrics (MFe), as an emerging new class, have been a new research focus due to their desirable characteristics such as good solution processability, tunable chemical properties and bio-friendly compositions. However, traditional uniaxial MFe only possess one polar axis which greatly limits their application as it requires restricted orientational control in single crystal. To achieve macroscopic ferroelectricity and thus fully realize technological advantages of MFe, development of multi-axes is imperative to maximize effective polarization in specific crystallographic orientations. Herein, we present an early exploration on polycrystalline multiaxial MFe thin-film of [Hdabco]ReO4 with two-dimensional (2D) graphene hybrid nonvolatile memory device. The polarization switching of MFe is experimentally realized by the non-volatile modulation of two current states in gr...

Research paper thumbnail of Improving the electrical performance of MoS2 by mild oxygen plasma treatment

Journal of Physics D: Applied Physics, 2017

Two-dimensional (2D) molybdenum disulfide (MoS2) is considered as a promising candidate for elect... more Two-dimensional (2D) molybdenum disulfide (MoS2) is considered as a promising candidate for electronic and optoelectronic devices. However, structural defects in MoS2 are widely reported and can greatly degrade its electrical and optical properties. In this work, we investigate the structural defects in MoS2 by low temperature photoluminescence (PL) spectroscopy and study their effects on the electrical performance, i.e. carrier mobility. We also adopt the mild oxygen plasma treatment to repair the structural defects and found that the carrier mobility of monolayer MoS2 can be greatly improved. This work would therefore offer a practical route to improve the performance of 2D dichalcogenide-based electrical and optoelectronic devices.

Research paper thumbnail of Nickel foam supported hierarchical NiCo2S4@NiFe LDH heterostructures as highly efficient electrode for long cycling stability supercapacitor

Electrochimica Acta

Layered double hydroxides (LDHs) based heterostructures provide an opportunity for the developmen... more Layered double hydroxides (LDHs) based heterostructures provide an opportunity for the development of highperformance supercapacitors. Up till now, hierarchical NiCo 2 S 4 @NiFe LDH heterostructure is scarcely investigated for supercapacitor. In this work, the hierarchical NiCo 2 S 4 @NiFe LDH heterostructure nanosheet arrays on Ni-foam (NF) were synthesized by a facile hydrothermal method. As the supercapacitor electrode, it has been revealed that the incorporation of NiFe can significantly increase the capacitive performance of the heterostructure. At a current density of 1 Ag − 1 , a specific capacitance of NiCo 2 S 4 @NiFe LDH electrode was reached up to 827 Fg − 1 , outperforming that of pristine NiCo 2 S 4 and NiFe LDH. Moreover, the electrode keeps 90.2% of its preliminary capacitance after 12,000 cycles at 5 A g − 1. In addition, NiCo 2 S 4 @NiFe LDH electrode offer high energy density of 38.1 W h kg − 1 and power density of 1800 W kg − 1. According to DFT calculations, NiFe-LDH adsorption on NiCo 2 S 4 is strong and governed by large interfacial interactions with a charge transfer of 0.44 eV to NiCo 2 S 4 surface thus demonstrating the significantly improved electrochemical performance. Hence, such an outstanding electrochemical finding suggest that NiCo 2 S 4 @NiFe LDH heterostructures could be attractive electrode materials as practical supercapacitors for next generation energy storage devices.

Research paper thumbnail of Development of MoS2-ZnO heterostructures: an efficient bifunctional catalyst for the detection of glucose and degradation of toxic organic dyes

New Journal of Chemistry

The heterostructure catalyst MoS2-ZnO possesses binary properties and provides a novel platform f... more The heterostructure catalyst MoS2-ZnO possesses binary properties and provides a novel platform for the remediation of environmental as well as health issues.

Research paper thumbnail of A study on causes and community response regarding diabetes as a community disease of southern Punjab Pakistan

Journal of King Saud University - Science

Research paper thumbnail of An amphiphilic polyoxometalate–CNT nanohybrid as a highly efficient enzyme-free electrocatalyst for H2O2 sensing

New Journal of Chemistry

A highly active electrochemical amphiphilic POM–CNT nanohybrid using non-covalent interactions fo... more A highly active electrochemical amphiphilic POM–CNT nanohybrid using non-covalent interactions for highly efficient detection of H2O2 is reported. The synergy between POMs and CNTs results in 10 times higher current response than pristine POM.

Research paper thumbnail of Mesoporous NiCo2S4 nanoflakes as an efficient and durable electrocatalyst for non-enzymatic detection of cholesterol

Nanotechnology

The detection of cholesterol is very crucial in clinical diagnosis for rapid and accurate monitor... more The detection of cholesterol is very crucial in clinical diagnosis for rapid and accurate monitoring of multiple disease-biomarkers. There is a great need for construction of a highly reliable and stable electrocatalyst for the efficient detection of cholesterol. In this work, mesoporous NiCo2S4 nanoflakes of enhanced electrochemical properties are prepared through a facile hydrothermal approach. The developed nanoflakes modified nickel foam electrode exhibits outstanding electrocatalytic properties for the detection of cholesterol with high selectivity. The electrode displays excellent sensitivity of 8623.6 μA mM−1 cm−2, in the wide linear range from 0.01 to 0.25 mM with a low detection limit of 0.01 μM. In addition, NiCo2S4 structure reveals good thermal stability and reproducibility over a period of 8 weeks. Moreover, the nanoflakes show good response for detection of cholesterol in real samples. Our results demonstrate the potential use of NiCo2S4 as a catalyst for the developme...

Research paper thumbnail of MWCNT synergy for boosting the electrochemical kinetics of V2O5 cathode for lithium-ion batteries

New Journal of Chemistry, 2022

V2O5/MWCNT hybrid system has been developed and investigated as cathode in LIBs. The developed el... more V2O5/MWCNT hybrid system has been developed and investigated as cathode in LIBs. The developed electrode shows superior performance as compare to pristine V2O5 and V2O5/rGO hybrid structure due to the synergy between V2O5 and MWCNT.

Research paper thumbnail of Fluorescence manipulation from graphene and hydrogen-terminated graphene covered Au nanoparticles

AIP Advances, 2021

This paper presents the fluorescence manipulation of Rhodamine-6G (R6G) due to Au nanoparticles (... more This paper presents the fluorescence manipulation of Rhodamine-6G (R6G) due to Au nanoparticles (Au-NPs) covered by pristine graphene and hydrogen-terminated graphene. By taking florescence signals of R6G on a quartz substrate as the standard reference, we observe an ∼fourfold increase in fluorescence intensity of R6G on bare Au-NPs deposited on the quartz substrate. However, this enhancement reduces to ∼1.8-fold when Au-NPs are covered by H-terminated graphene. In the case of Au-NPs covered by pristine graphene, the fluorescence of R6G is significantly quenched by a factor of ∼7.6-fold. The resulting fluorescence level can be attributed to the local field enhancement from Au-NPs and the quenching effect of graphene in the Au–graphene hybrid nanostructure, which are confirmed by our controlled experimental and simulation results. Our work reveals that the surface modification of metal NPs by graphene materials would bring a great impact on fluorescence, providing a simple approach f...

Research paper thumbnail of Controlled layer growth of WS 2 grains by chemical vapor deposition

Bulletin of the American Physical Society, 2018

Research paper thumbnail of Oxygen vacancies boosted vanadium doped ZnO nanostructures-based voltage-switchable binary biosensor

Nanotechnology, 2021

The development of a reliable non-enzymatic multi-analyte biosensor is remained a great challenge... more The development of a reliable non-enzymatic multi-analyte biosensor is remained a great challenge for biomedical and industrial applications. In this prospective, rationally designed electrode materials having voltage switchable electrocatalytic properties are highly promising. Here, we report vanadium doped ZnO engineered nanostructures (Zn1−x V x O where 0 ≤ x ≤ 0.1) which exhibit voltage switchable electrocatalytic properties for accurate measurements of glucose and hydrogen peroxide. Microstructures and chemical analysis show that the oxygen vacancies in the material can be tuned by controlling the stoichiometric ratios which play key role for voltage dependent measurements of different analytes. The developed Zn1−x V x O nanostructures exhibit outstanding sensing ability for binary analytes with a high selectivity, low detection limit, thermal stability and long-term stability. The Zn0.9V0.1O/glassy carbon (GC) electrode shows 3-fold increase in reproducible sensitivity for both glucose (655.24 μA mM−1 cm−2) and H2O2 (13309.37 μA mM−1 cm−2) as compared to the pristine ZnO/GC electrode. Moreover, the electrode also shows good response for human blood serum and commercially available samples. The results demonstrate that defect engineering is a promising route for the development of cost-effective non-enzymatic multi-analyte sensors for practical applications.

Research paper thumbnail of Frequency stable dielectric constant with reduced dielectric loss of one-dimensional ZnO–ZnS heterostructures

Nanoscale, 2021

ZnO–ZnS heterostructure is developed which shows frequency stable dielectric response at ≥103 Hz ... more ZnO–ZnS heterostructure is developed which shows frequency stable dielectric response at ≥103 Hz due to coupling of the bare charges in the form of overlapping large polaron and Zn2+–VO dipoles present at ZnO–ZnS heterostructure interface.

Research paper thumbnail of The Thinnest Light Disk: Rewritable Data Storage and Encryption on WS 2 Monolayers (Adv. Funct. Mater. 36/2021)

Advanced Functional Materials, 2021

The thinnest light disk is demonstrated at the atomic level by developing an erasable method to d... more The thinnest light disk is demonstrated at the atomic level by developing an erasable method to directly write encrypted information onto WS2 monolayers. The write‐in is realized by precise control of photoluminescence emission by means of ozone functionalization and scanning focused laser beam. The visual decryption and reading‐out of information are enabled by fluorescence contrast. The high encryption level is ensured by the threshold power upon which the data deletion will be triggered. Owing to the high spatial resolution and power sensitivity, the storage capacity within <1 nm thickness can be up to ≈62.5 MB cm−2, and the writing speed can reach ≈6.25 MB s−1. Density functional theory calculations suggest that the disk formatting is realized by ozone molecule adsorption induced localized unoccupied states, while the read‐in relies on the passivation of defects via substitution of the sulfur vacancies with oxygen atoms. The results of this study promote data storage and encryption on the atomic scale.

Research paper thumbnail of High-Performance Graphene-Based Electrostatic Field Sensor

IEEE Electron Device Letters, 2017

Electrostatic sensing technology is widely utilized in both military and civilian applications, i... more Electrostatic sensing technology is widely utilized in both military and civilian applications, including electrostatic prevention in gas stations and various electronic devices. The high sensitivity of electrostatic sensor is capable to detect not only weak electrostatic charges, but also the weak disturbance of electrostatic field in distant. Here, we present a high-performance graphene-based electrostatic sensor. Combining the ultrahigh mobility of graphene and the long lifetime of carriers in lightly doped SiO 2 /Si substrate, our device achieves a fast response of ~2 s and detection limit of electrostatic potential as low as ~5 V, which is improved by an order of magnitude as compared to commercial product. The proposed device structure opens a promising pathway to high-sensitive electrostatic detection, and also greatly facilitates the development of novel sensors, e.g. portable and flexible electrostatic sensor. Correspondence and requests for materials should be addressed to Z. N.

Research paper thumbnail of Photoluminescence characterization of the grain boundary thermal stability in chemical vapor deposition grown WS2

Materials Research Express, 2017

Monolayer transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have been considered as pr... more Monolayer transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have been considered as promising candidate materials in nanophotonic applications. However, the structure stability of TMDs based optoelectronic devices is highly sensitive to the working environment. Here we present a successive photoluminescence study of the thermal stability characterization of grain boundary in chemical vapor deposition grown monolayer WS2. Results show that PL intensity enhancement in grain boundaries can be significantly weakened during the annealing process. Transformation temperature starts around 210 °C, substantially lower than the surrounding non-grain-boundary area. First-principle calculations results show that the PL quenching of grain boundaries is caused by the increased structural defects induced by annealing process, which makes the transition of electrons more difficult. Our results provide a route for characterizing the structure stability of two dimensional (2D) semiconductors, calling for extra attention to nanophotonic device working condition.

Research paper thumbnail of Reconstruction of 1,000 Projection Neurons Reveals New Cell Types and Organization of Long-Range Connectivity in the Mouse Brain

SSRN Electronic Journal, 2019

Neuronal cell types are the nodes of neural circuits that determine the flow of information withi... more Neuronal cell types are the nodes of neural circuits that determine the flow of information within the brain. Neuronal morphology, especially the shape of the axonal arbor, provides an essential descriptor of cell type and reveals how individual neurons route their output across the brain. Despite the importance of morphology, few projection neurons in the mouse brain have been reconstructed in their entirety. Here we present a robust and efficient platform for imaging and reconstructing complete neuronal morphologies, including axonal arbors that span substantial portions of the brain. We used this platform to reconstruct more than 1,000 projection neurons in the motor cortex, thalamus, subiculum, and hypothalamus. Together, the reconstructed neurons comprise more than 75 meters of axonal length and are available in a searchable online database. Axonal shapes revealed previously unknown subtypes of projection neurons and suggest organizational principles of long-range connectivity.

Research paper thumbnail of Sulfur‐Mastery: Precise Synthesis of 2D Transition Metal Dichalcogenides

Advanced Functional Materials, 2019

Chemical vapor deposition (CVD) has been developed as the most promising method for the growth of... more Chemical vapor deposition (CVD) has been developed as the most promising method for the growth of transition metal dichalcogenides (TMDs). In this work, the key factor determining the growth of TMDs is ascertained. A straightforward method is devised to directly achieve a holistic control of thickness, shape, and size of WS 2 flakes via a single parameter control, namely, the status of the S-precursor. The thickness-dependent growth of WS 2 flakes from mono-to quad-layers is achieved by precise control of the feeding rate of elemental S-precursor. Moreover, the explicit control over amount and exposure time of S-precursor determines the most optimum combination of these parameters to tune the shape of the crystals from triangular to hexagonal with appropriate size. Hence, the experimental findings provide a promising strategy to engineer the growth evolution of WS 2 atomic layers by fine tuning of the sulfur supply, paving a pathway to scalable electronic and photonic devices.

Research paper thumbnail of Thermally enhanced optical contrast of graphene oxide for thickness identification

Nanotechnology, 2019

We present a simple, but rapid and accurate approach to identify the layer number of graphene oxi... more We present a simple, but rapid and accurate approach to identify the layer number of graphene oxide (GO) by using its thermally enhanced optical contrast via vacuum heating. As expected, changes have been observed both in the thicknesses and chemical structures of the material upon the thermal treatment, which can be attributed to the reduction of the amount of intercalated water and oxygen content. This results in the increase of refractive index and absorption coefficient approaching the values for intrinsic graphene. Finally, we achieve an almost complete recovery of optical contrast of GO compared with the one of graphene. The method would be made suitable for the thickness identification of mass-produced GO since it can greatly facilitate sample evaluation and manipulation, and provide immediate feedback to improve synthesis and processing strategies.

Research paper thumbnail of Tuning interlayer coupling by laser irradiation and broadband photodetection in vertical MoTe2/WS2 vdW heterostructure

APL Materials, 2019

van der Waals (vdW) heterostructures constructed by stacking different two dimensional layered ma... more van der Waals (vdW) heterostructures constructed by stacking different two dimensional layered materials are extensively utilized in designing novel optoelectronic devices, such as photodetectors and light-emitting diodes. However, the performance of vertical heterostructures is impeded by challenges in effectively achieving interlayer coupling. Here, the systematic demonstration of vertical MoTe2/WS2 vdW heterostructures assembled by a mechanical transfer technique is reported, whereas the interlayer interaction is tuned from weak coupling to strong coupling by laser irradiation. Thereafter, the improved interlayer interaction of heterostructures is characterized by photoluminescence spectroscopy and further confirmed by electrical transport. Moreover, visible-infrared broadband photoresponse is achieved in the vertical stacking with the built-in field generated between MoTe2 and WS2. Thus, the outstanding findings of our experimental approach can facilitate novel two-dimensional d...

Research paper thumbnail of Producing air-stable InSe nanosheet through mild oxygen plasma treatment

Semiconductor Science and Technology, 2018

Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier ... more Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier mobility and broadband optical absorption, is considered as a promising candidate for electronic and optoelectronic devices. It has been a challenge to produce air-stable mono- or few-layer InSe nanosheets because they degrade rapidly in an ambient environment. Here, we demonstrate a facile mild oxygen plasma treatment route to fabricate air-stable few-layer InSe samples. Photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS) analysis indicate that the plasma treatment can introduce an oxidation process that forms a dense InSe1−xOx capping layer on the surface, and thus prevent the sample from degradation. Furthermore, the oxide layer would introduce a PL quenching of the pristine InSe, while a new and strong PL peak belonging to the emission from InSe1−xOx appears. This work offers a practical and efficient route to improve the performance of InSe based electrical and optoelectronic devices.

Research paper thumbnail of Nonvolatile Memory Based On Molecular Ferroelectric/Graphene Field Effect Transistor

ACS applied materials & interfaces, Jan 8, 2018

Ferroelectric thin films are extensively attractive as next-generation non-volatile memories. Rec... more Ferroelectric thin films are extensively attractive as next-generation non-volatile memories. Recently molecular ferroelectrics (MFe), as an emerging new class, have been a new research focus due to their desirable characteristics such as good solution processability, tunable chemical properties and bio-friendly compositions. However, traditional uniaxial MFe only possess one polar axis which greatly limits their application as it requires restricted orientational control in single crystal. To achieve macroscopic ferroelectricity and thus fully realize technological advantages of MFe, development of multi-axes is imperative to maximize effective polarization in specific crystallographic orientations. Herein, we present an early exploration on polycrystalline multiaxial MFe thin-film of [Hdabco]ReO4 with two-dimensional (2D) graphene hybrid nonvolatile memory device. The polarization switching of MFe is experimentally realized by the non-volatile modulation of two current states in gr...

Research paper thumbnail of Improving the electrical performance of MoS2 by mild oxygen plasma treatment

Journal of Physics D: Applied Physics, 2017

Two-dimensional (2D) molybdenum disulfide (MoS2) is considered as a promising candidate for elect... more Two-dimensional (2D) molybdenum disulfide (MoS2) is considered as a promising candidate for electronic and optoelectronic devices. However, structural defects in MoS2 are widely reported and can greatly degrade its electrical and optical properties. In this work, we investigate the structural defects in MoS2 by low temperature photoluminescence (PL) spectroscopy and study their effects on the electrical performance, i.e. carrier mobility. We also adopt the mild oxygen plasma treatment to repair the structural defects and found that the carrier mobility of monolayer MoS2 can be greatly improved. This work would therefore offer a practical route to improve the performance of 2D dichalcogenide-based electrical and optoelectronic devices.