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Intrinsically ferromagnetic and semiconducting two-dimensional (2D) H-phase vanadium disulfide (VS2) holds tremendous promise for future electronics, optoelectronics, spintronics and valleytronics applications. However, its thermodynamic instability and the formation of intermediate stoichiometric polymorphs during its growth have stymied any progress towards synthesis of high quality 2D VS2 films. In this article, we circumvent these challenges and accomplish large area growth of monolayer VS2 films using atmospheric pressure chemical vapor deposition (APCVD) technique. By incorporating excess sulfur during the growth process which suppresses the formation of intermediate compounds, good quality large-area VS2 film can be synthesized. Furthermore, the electronic and optoelectronic properties of VS2 were explored by fabricating photosensitive memtransistor devices, which reveal an n-type carrier transport along with a high responsivity to red, green, and blue wavelengths of light. In addition the device exhibited multiple non-volatile conductance states through electrical programming. To the best of our knowledge, this is the first comprehensive report on memtransistors built from large area grown H-phase VS2 that integrate compute, sense, and storage functionalities in a single device.

Nowadays, cancer is increasingly becoming one of the foremost threats to human being life worldwide, and diagnosing this deadly disease is one of the major priorities of researchers. Described as a monolayer-thin-sheet of hexagonally patterned carbon atoms, ‘graphene’ is considered an innovative evergreen carbon material ideal for a wide array of sensing applications and nanotechnologies. Graphene-based materials (GBMs) have acquired a huge share of interest in the scope of biosensor fabrication for early and accurate cancer diagnosis. Herein, we have insights reviewed the various routes and technologies for synthesized graphene, and GBMs including 3D graphene (i.e. hydrogels, foams, sponges and porous) and 0D graphene (i.e. quantum dots). Moreover, we have introduced the different types of graphene/GBMs biosensors (i.e. electrochemical biosensors, optical biosensors, field-effect transistors biosensors, electrochemiluminescence biosensors and microfluidics biosensors) and their merits and applications for cancer pre-stage detection.

Large-area-based field-effect transistor (FET) gas sensor has the potential to provide a larger sensing area for a chemical analyte. So far, graphene FETs (GFETs) are mostly fabricated by expensive lithographic techniques with a minimum channel length. We have demonstrated a simple way to fabricate a very large channel length of 0.45 mm GFET using ion-conducting dielectric with thermally evaporate source/drain electrodes and has been demonstrated for an application of ambient atmosphere ammonia gas sensing. Ion-conducting Li5AlO4 gate dielectric has reduced operating voltage up to 2.0 V with good current saturation. The chemical vapor deposition (CVD) grown uniform monolayer of graphene has been used as an active channel layer of FET. The fabricated device has been tested for different concentrations of ammonia in ambient environment conditions at 25 °C temperature, which indicates that the Dirac point voltage of the device varies up to 0.8 V when the concentration of ammonia has been changed from 0 to 3 ppm. Moreover, this study also reveals that this GFET is capable of detecting ammonia up to the concentration level of 0.1 ppm.

Wastewater produced by the textile industry contains various dyes and organic compounds that directly or indirectly affect surface water or groundwater pollution. Visible-light-driven semiconductor photocatalysis is the leading pathway for the degradation of environmental pollutants. Herein we report the bottom-up hydrothermal growth of 2D tin disulfide nanostructures (SnS2 NSs) for the efficient photodegradation of organic pollutants such as Rhodamine B (Rh.B) and Methyl Violet (M.V) in an aqueous medium under visible light (λ > 400 nm) irradiation. The as-synthesized SnS2 NSs were characterized by various structural, morphological, and optical techniques such as XRD, RAMAN, TEM, UV–Vis, Brunauer–Emmett–Teller, etc. Furthermore, the low bandgap (∼1.6 eV), the high surface area (56 m2/g), and the anionic nature of SnS2 NSs attribute to it as an efficient photocatalyst for photocatalytic applications. The photocatalytic properties of SnS2 NSs showed good degradation efficiency of 94 and 99.6% for Rh. B and M.V, respectively, in 25 min. The kinetic rate constant of these dyes was estimated by using the Langmuir–Hinshelwood model. Here we also performed the recyclability test of the photocatalyst and discussed the plausible mechanism for the photocatalytic degradation of organic pollutants. The XPS spectra of SnS2 NSs were studied before and after the photodegradation of Rh.B and M.V, indicating the high stability of the photocatalyst. Moreover, in vitro cytotoxicity was also evaluated against human cervical cancer cell lines (HeLa cells) with different concentrations (0–1,000 μg/ml) of as-synthesized SnS2 NSs. This intended work provides a possible treatment for the degradation of organic pollutants under visible light to balance the aquatic ecosystems.

Atomically thin semiconducting 2D transition metal dichalcogenides have garnered remarkable attention from the scientific community due to their prodigious contributions in the field of next-generation electronic and optoelectronic devices. In this continuation, we report a facile synthesis protocol of monolayer WSe2 films via the atmospheric-pressure chemical vapor deposition (APCVD) technique using hydrothermally synthesized hexagonal-phase tungsten oxide ( h-WO3) nanorods. The as synthesized WSe2 crystal is a monolayer of ∼0.9 nm thickness as confirmed by atomic force microscopy. The confocal Raman and photoluminescence (PL) mapping suggests that the grown monolayer WSe2 triangles have lattice defects at edge sites, with a slight red-shift of ∼2 nm in PL, a blue-shift of ∼2 cm−1 in Raman peak and reduction in both the intensities. Confocal time-resolved PL mapping at edges reveals a fast-decay component of ∼582 ps and a slow-decay component of ∼2.18 ns that also signifies the presence of lattice defects, which serves as localized-states for photon-generated charge excitons. Furthermore, we have also investigated its electrical property by devising field-effect transistors (FETs). The fabricated WSe2 based FET shows intrinsic n-type behavior. WSe2 FET offers an electron mobility ( μ) of ∼13.2 cm2 V−1 s−1, current ON/OFF ratio of ∼107 with a subthreshold slope (SS) of ∼397 mV/decade, which is relatable to the other reported works on WSe2 based FETs. In addition, the device exhibits very high on-current of order of ∼150 μA/ μm. These results indicate that h-WO3 nanorod assisted APCVD synthesized WSe2 has prospective of being a competitor for next-generation optoelectronic, and valley-tronic devices.

This work reports the green to red color tunable upconversion emission in a newly synthesized Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor, prepared by solid-state reaction (SSR) method. The crystal phase formation has been confirmed by X-Ray diffraction analysis. The Fourier transform infrared (FTIR) spectrum show bands at different frequencies due to V-O and Ta-O, and found to play a vital role in relaxation (radiative and non-radiative) processes. The synthesized phosphor sample show intense upconversion (UC) emission in green (∼539 nm), red (∼659 nm) and in near infrared (NIR∼ 754 nm) regions on 980 nm laser excitation. These bands appear as a result of (5F4+5S2→5I8), (5F5→5I8) and (5F4+5S2→5I7) transitions of Ho3+ ion, respectively. The tunability in color from green to orange-red is observed on varying the pump power of NIR laser (980 nm excitation). The intrinsic optical bistability is observed in both, green & red upconversion bands with the increase and decrease in power of NIR source. The Ln I-Ln P plots suggest that green & red UC emissions are due to two photon absorption at low laser power. A decrease in the slope values at higher pump powers confirms the laser induced optical heating (LIOH) in the material. The pump power based color tunable emission and optical bistability can be utilized in security detection, optical memory, optical color coding, color switching and in various advanced applications.

In recent years, two-dimensional (2D) atomically thin crystals ranging from insulator to superconductor such as graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDs), etc. have attracted extensive attention due to their exceptional properties and many potential applications in various areas. In this chapter we focus on the experimental characterization of 2D materials and their heterostructures andcover brief introduction and detailed structural, optical, and chemical characterizations of some important 2D materials.

Dual-mode luminescence (downshifting-DS and upconversion-UC) properties of Pr3+/Yb3+ co-doped Y1−xGdxNbO4 (x = 0.0, 0.5, and 1.0) phosphors synthesized by solid state reaction technique have been explored with and without Gd3+ ion. The structural characterizations (XRD, SEM, and FTIR) confirm the pure phase of YNbO4 phosphor. Further, with the Gd3+ ion co-doping, the YNbO4 phosphors having a random shape and the large particle size are found to be transformed into nearly spherical shape particles with the reduced particle size. The optical band gaps (Eg) of Y1−xGdxNbO4 (x = 0.00, 0.25, 0.50, and 1.00) calculated from UV-Vis-NIR measurements are ∼3.69, 4.00, 4.38, and 4.44 eV, respectively. Moreover, YNbO4 phosphor is a promising blue emitting material, whereas Y1−x−y−zPryYbzGdxNbO4 phosphor gives intense green, blue, and red emissions via dual-mode optical processes. The broad blue emission arises due to (NbO4)3− group of the host with λex = 264 nm, whereas Pr3+ doped YNbO4 phosphor gives dominant red and...

In this paper, we present two stylized models of the financial system. We make the case that in order to realize the potential of a well-functioning complete financial market, financial system designers and financial service providers will need to think about ways to deliver financial propositions that are customized to individual households by responding to their unique circumstances. This will entail the presence of proximate, well-trained providers that intermediate between the customer and those large “product manufacturers†whose goal is financial well being and not merely product sales. These providers would need to use expertise in financial advice or wealth management to develop integrated financial propositions for clients. We also highlight some of the important debates that arise in making this stylized financial system a reality.