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Monolayer MoSe2 flakes with varying shapes, including sharp triangle, truncated triangle, hexagon, and rough edge circle are synthesized using APCVD method. The lattice and quasiparticle dynamics are examined under different growth conditions.

The spectroscopic properties of APCVD-grown monolayer, bilayer, and ribbon structures of WSe2 flakes are investigated in detail. The synthesis pathway of the ribbon structures is interpreted on the basis of droplet motion.

To get insight into the thermal management of twisted bilayer graphene based devices, the interpretation of temperature variation on twisting properties becomes crucial. In this aspect, we report the temperature dependent Raman scattering of twisted bilayer graphene (tBLG) on the Si substrate having SiO2 thickness 300 nm. The tBLG samples have been directly grown on the copper foil substrate using a home-built low pressure chemical vapor deposition (LPCVD) setup. The temperature dependent Raman scattering has been studied on two samples of tBLG named as tB1 and tB2. The twisting nature of bilayer graphene film has been analyzed using R, G, and 2D peak characteristics in Raman spectra. The Raman mapping with respect to different peak parameters of G and 2D peak (intensity, width, and position), intensity ratio (I2D/IG) has been employed to probe the uniformity of tBLG film. In tB1, the R peak has been found at 1395.82 cm−1 and not observed in sample tB2 at room temperature. The temperature dependence of G and 2D peak frequency in Raman spectra has been investigated in the temperature range from 80 to 450 K. In tB1 and tB2, the temperature coefficient of G peak has been found to be - (0.97 ± 0.34) × 10−2 cm−1/K, and - (1.08 ± 0.15) × 10−2 cm−1/K, respectively. Further, the extracted value of temperature coefficient of 2D peak in tB1, and tB2 are - (2.92 ± 0.80) × 10−2 cm−1/K, and - (3.01 ± 0.29) × 10−2 cm−1/K respectively. Additionally, the twist angle has been estimated as ∼23°-27° for T ≤ 300 K and 3°-8° for T > 300 K in tB1. In tB2, it has been found to be ∼13°-16° for the temperature range of 80–200 K and 5°-9° for 250–450 K. These findings shed light on the twisting behavior of bilayer graphene film and its anharmonic properties.

Monolayer MoS2 has received special consideration owing to its intriguing properties and its potential to revolutionize modern technologies. Atmospheric pressure chemical vapor deposition (APCVD) is the traditional method to grow uniform and high-quality MoS2 flakes in a controlled manner. Little is known, however, about their synthesis mechanism and shape evolution. Herein, we report the synthesis of monolayer MoS2 flakes at atmospheric pressure using a home-built CVD setup. A wide range of shapes are grown from triangular shapes to many point stars, via in-between shapes such as four and six-point stars, using the weight ratio variation of MoO3 and S precursors at different growth temperatures. Further, the properties of the as-grown MoS2 flakes are probed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Raman spectroscopy, photoluminescence (PL), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), confirming that they are regular and good in quality. Moreover, the synthesis pathway and different shape formations are explained on the basis of the fluid model and the growing rate of Mo, S zigzag edges. Thus, this work provides a better insight into the synthesis mechanism of monolayer MoS2 and represents a significant step towards realizing potential future applications.

Polymer nanocomposites with vital reinforcements of conductive fillers have evinced as next-generation high-performance materials with multi-functional applications. Herein, we report the facile synthesis of thermally stable, highly electrically conducting polyaniline multi-walled carbon nanotubes (PANI/MWCNT) nanocomposites doped in two different protonic acids, i.e. hydrochloric acid (HCl) and sulphuric acid (H2SO4). The doping acids significantly affect the electric and dielectric properties of conducting polymer nanocomposites. The paper probes in the synergistic effects of MWCNTs and the effect of doping acid on the thermal stability, conductivity and dielectric properties of the nanocomposites based on PANI nanofibres. The structural, morphological, optical, thermal and electrical properties were evaluated through X-ray diffraction, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, thermogravimetric analysis and two-point probe technique. Ascribed to the high interfacial interaction between PANI and MWCNT, and considering the effect of doping acids, nanocomposites with high thermal stability, enhanced conductivity and high dielectric constant that can store large electrical charges have been synthesized by surfactant-assisted, in situ oxidative polymerization of aniline, in the presence of potassium persulfate as oxidant. The micellar structure of surfactant assists the dispersion of MWCNTs as well as the formation of PANI/MWCNT tubular structures. The effect of surfactant below and above critical micelle concentration was also studied. This complete study would affirm such a nanocomposite which procures excellent electrical and dielectric properties for microelectronic applications.

In the field of optoelectronics, all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) have gained significant interest on account of their superb processability and ultra-high stability among all the counterparts. In this study, we conducted an in-depth analysis of CsPbBr3 PNCs using joint transient optical spectroscopies (time-resolved photoluminescence and ultrafast transient absorption) in a very comprehensive manner. In order to understand the in-depth analysis of excited-state kinetics, the transient absorption spectroscopy has been performed. The structure of interest of CsPbBr3 PNCs was subjected to the rates of the radiation energy of 0.10 mW (κr/κnr = ∼0.62) and 0.30 mW (κr/κnr = ∼0.64). With the rate of radiation energy 0.30 mW, it was observed that there was a significant increase in hot carrier relaxation together with high radiative recombination, resulting in a decrease in charge trappings. Herein, we demonstrate that the tuning of the rate of radiation energies helps to understand the charge-carrier kinetics of CsPbBr3 PNCs, which would thus improve the manufacturing of efficient photovoltaic devices.

Heteroatom doping in graphene is now a practiced way to alter its electronic and chemical properties to design a highly-efficient gas sensor for practical applications. In this series, here we propose boron-doped few-layer graphene for enhanced ammonia gas sensing, which could be a potential candidate for designing a sensing device. A facile approach has been used for synthesizing boron-doped few-layer graphene (BFLGr) by using a low-pressure chemical vapor deposition (LPCVD) method. Further, Raman spectroscopy has been performed to confirm the formation of graphene and XPS and FESEM characterization were carried out to validate the boron doping in the graphene lattice. To fabricate the gas sensing device, an Si/SiO2 substrate with gold patterned electrodes was used. More remarkably, the BFLGr-based sensor exhibits an extremely quick response for ammonia gas sensing with fast recovery at ambient conditions. Hence, the obtained results for the BFLGr-based gas sensor provide a new platform to design next-generation lightweight and fast gas sensing devices.

A facile base-catalyzed hydrothermal method is used to synthesize a bifunctional luminomagnetic Er3+/Yb3+ doped Gd2O3 nanorods material. The as-synthesized nanorods material is investigated for structural/microstructural, upconversion, and magnetic properties. The intense emission bands at 520 nm, 540 nm, and 654 nm are observed upon excitation with a 980 nm solid state laser. The effect of Yb3+, Er3+ doping concentrations and incident laser power on the upconversion emission properties are also investigated, and the mechanism for the upconversion process is proposed. We further investigated the magnetic properties by room temperature M-H and M-T measurements in the temperature range of 2-300 K by standard ZFC-FC protocols. Cytotoxicity analysis of these bifunctional luminomagnetic nanorods in established cell lines did not show considerable cytotoxicity.

Redox active electrolyte supercapacitors differ significantly from the conventional electrolytes based storage devices but face a long term stability issue which requires a different approach while designing the systems. Here, we show the change in layered double hydroxides (LDHs) systems with rare earth elements (lanthanum) can drastically influence the stability of two dimensional LDH systems in redox electrolyte. We find that the choice of rare earth element (lanthanum) having magnetic properties and higher thermal and chemical stability has a profound effect on the stability of La-Co LDHs electrode in redox electrolyte. The fabricated hybrid device with rare earth based positive electrode and carbon as negative electrode having redox electrolyte leads to long stable high volumetric/gravimetric capacity at high discharge rate, demonstrates the importance of considering the rare earth elements while designing the LDH systems for redox active supercapacitor development.

The accurate and precise quantification of the number of layers of MoS2 nanosheets is highly desirable to accomplish the advanced optoelectronic device applications, which is a real challenge in cutting edge science. In recent years, multitudinous efforts have been put forward, but no certain protocol is available to validate the number of layers. In this aspect, we present various spectroscopic probes such as optical, Raman, and photoluminescence (PL) to quantify the number of layers in mechanically exfoliated MoS2 nanosheets. The contrast analysis of optical and scanning electron microscope (SEM) images has been performed to identify the number of layers. The Raman spectra indicate that E12g are shifted toward low-frequency and A1g peak in high-frequency direction during the transition from monolayer to bulk MoS2. The intensity, line width, and peak frequency of both Raman modes have shown the notable difference with the thickness variation. Moreover, the PL spectra show two prominent peaks at 679 and 6...

Methylammonium lead bromide (CH3NH3PbBr3) colloidal quantum dots (QDs) exhibit strong green photoluminescence (PL) with high photoluminescence quantum yield (PLQY) making it valuable for various optoelectronic applications. Under the influence of polar gaseous molecules, hybrid halide perovskites show changes in its structural and electrical properties. We, for the first time, have investigated the influence of NH3 gas molecules on the optical properties of CH3NH3PbBr3 colloidal QDs. The investigations carried out under a controlled environment reveal that even the presence of 37 ppm of ammonia (NH3) gas molecules causes a significant reduction in the PL intensity of CH3NH3PbBr3 colloidal QDs. The reduction rate of PL intensity can be tuned with the concentration of NH3 gas molecules. We propose that the decrease in PL intensity is because of the formation of a non-luminescent NH4PbBr3 phase under the presence of NH3 gas molecules. Further, the non-luminescent NH4PbBr3 retransformed into luminescent CH3NH3PbBr3 on the introduction of methylamine (CH3NH2) gas molecules. This reversible alternation in PL properties enables us to demonstrate its application for (NH3) gas sensing. The advantage of using CH3NH3PbBr3 colloidal QDs for luminescence-based sensing is that its green emission is visible with the naked eye even under daylight, which is easy to detect.

Strontium tellurite, lead tellurite and bismuth niobium tellurite glasses containing 1 to 2 mol% of Eu3+ and Er3+ were prepared by melt-quenching and found to contain anti-glass inclusions (droplet phase) of size of several micrometers. Anti-glasses are disordered crystals that have long-range order of the cations such as Sr2+, Pb2+, Bi3+, Nb5+ and Te4+ but have a disordered arrangement of the anions (O2−), therefore these materials exhibit sharp peaks in the X-ray diffraction patterns due to the long range cationic order but the Raman spectra show broad bands due to the vibrational disorder. The glass matrix and anti-glass inclusions in the samples were characterized by synchrotron micro-X-ray Fluorescence (XRF), Raman and photoluminescence mapping studies. The XRF line analysis confirmed that the anti-glass and glass matrix phases have equal concentration of metal ions. The samples containing Eu3+ show intense red photoluminescence at an excitation wavelength of 375 nm, while Er3+ doped samples exhibit strong green emission by the up-conversion of infrared photons (980 nm). The spatially resolved XRF, Raman and photoluminescence spectroscopy found that the inclusions and the glass matrix have the same metal ion concentration, short-range order, Te O speciation and the light emission properties.

The exfoliation of two dimensional (2D) transition metal dichalcogenides (TMDs) into mono- or few-layers without compromising their semiconductor properties has momentous interest for both point of view; fundamental studies and further implementation in practical applications. Herein, we reported a novel and inexpensive approach for high yield nanosheets from bulk MoS2 to few layers of strong luminescent MoS2 nanosheets using Triton X-100 as a surfactant with tailoring the bulk band gap 1.2 eV to 1.79 eV of few layers of nanosheets after chemical exfoliation process, which can be easily scaled-up in large quantity. The microstructural results reveal that the exfoliated nanosheets have thickness in the range of few layers and lateral dimension in the range of few hundred nanometers. Our findings may offer a new innovative one setup chemical exfoliation process to design a few layer of MoS2 nanosheets without suppressing luminescent properties, which is highly desirable for the next generation optoelectronic devices.

The excitonic behavior in two-dimensional (2D) heterostructures of transition metal dichalcogenide atomic layers has attracted much attention. Here, we report, for the first time, the ultrafast beh...

A novel strategy has been devised to develop a single excitable dual emissive luminescent pigment for the formulation of unclonable security ink. The new advanced security features of the ink have been demonstrated successfully and make it highly suitable for the printing of valuable products, such as currency, passports, pharmaceuticals, and so forth for protection against duplicity. The formulation of the single excitable dual emissive luminescent pigment is based on the unexplored combinatory concept of the fluorescence@phosphorescence phenomenon, which provides a new feature in the composite. It emits intense red color (611 nm) upon illumination with a 254 nm UV lamp excitation source and long persisting green color (532 nm) when the excitation source is switched off. To study the feasibility of the single excitable dual emissive luminescent security ink for commercial applications, the patterns printed using this ink were not only subjected to rigorous atmospheric conditions such as hot, cold and humid conditions for six months, but also examined after treatment with various bleaching agents (ethyl alcohol, ethyl acetate, xylene, acetone, soap solution and laundry detergent) to ensure their chemical stability. The security features printed using the single excitable dual emissive luminescent security ink were found to be very stable against all of these stringent conditions. Hence, the exceptional results obtained using the single excitable dual emissive luminescent security ink offer a new pathway to prevent counterfeiting by generating advanced security features.

Ultrafast transient absorption (TA) spectroscopy has been carried out to study the charge carrier dynamics of CdSe core and CdSe/V2O5 core/shell quantum dots (QDs). A significant redshift accompanied by broadening in the first excitonic peak was observed in the UV-Vis absorption spectra of the core/shell QDs as the shell thickness increases. This interesting observation is related to a quasi-type-II alignment characterized by the spatial separation of an electron into the core/shell and a hole into the core. The observed optical excitonic spectra have further been used to study the energetics of CdSe and charge separated states with the concept of Marcus theory and confirmed that electron transfer takes place in the Marcus inverted region (). Moreover, the growth kinetics of the CdSe core and CdSe/V2O5 core/shell QDs, studied with TA spectroscopy, exhibits slow electron cooling in core/shell QDs because of the de-coupling of the electronic wave functions with their hole counterpart. These exciting properties reveal a new paradigm shift from CdSe QDs to CdSe/V2O5 core/shell QDs for highly suitable applications in photovoltaics (PV) and optoelectronic devices.

The ever-growing bridge between stretchable electronic devices and wearable healthcare applications constitutes a significant challenge for discovery of novel materials for ultrasensitive wide-range healthcare monitoring. Herein, we propose a simplistic, amenable, cost-effective method for synthesis of a vertically aligned carbon nanotube (VACNT)/poly(dimethylsiloxane) (PDMS) thin-film composite structure for robust stretchable sensors with a full range of human motion and multimode mechanical stimuli detection functionalities. Notably, the sensor features the best reported response of carbon nanotube (CNT)-based sensors with extensive multiscale healthcare monitoring of subtle and vigorous ambulations ranging from 0.004 up to 30% strain deformations, coupled with an exceptionally high gauge factor of 6436.8 (at 30% strain), super-fast response time of 12 ms, recovery time of 19 ms, ultrasensitive loading sensing, and an excellent reproducibility over 10 000 cycles. The sensor evinces distinctive electromechanical performances and reliability in real time for motions like wrist pulsing, frowning, gulping, balloon inflation, finger bending, wrist bending, bending, twisting, gentle tapping, and rolling. Therefore, the VACNT/PDMS thin-film sensor reveals the ability to be a propitious candidate for e-skin and advanced wearable electronics.

After discovering the steppingstone of two-dimensional (2D) materials, i.e. graphene, researchers are keen to explore the world of 2D materials beyond graphene for new frontiers and challenges. Due to bandgap limitation, graphene does not fit for the logic and optoelectronic applications which need well defined on/off ratio. Recently, single-layer (SL) and few-layer (FL) transition metal dichalcogenides have emerged as a new family of layered materials with great interest, not only for the fundamental point of view, but also due to its potential application in ultrathin modern devices. As the transition metal dichalcogenides (TMDs) have a direct bandgap in their single layer, which falls under the visible region of the electromagnetic spectrum and has better physical and chemical properties, making them a suitable candidate for logic and optoelectronic applications. This review includes the recent extensive development on the synthesis and transfer strategies of MX2 (M = Mo, W and X = S, Se) 2D nanostructures of semiconducting TMDs. Further, this review covers the electronic and optoelectronic applications of these nanostructures along with progress in Van der Waal structures. The advantage and unambiguity of these materials are also discussed.

In the field of optoelectronics, all-inorganic CsPbBr

An attempt has been made to understand the thermodynamic mechanism study of the low-pressure chemical vapor deposition (LPCVD) process during single-layer graphene (SLG) growth as it is the most debatable part of the CVD process. The intensive studies are being carried out worldwide to enhance the quality of LPCVD-grown graphene up to the level of mechanically exfoliated SLG. The mechanism and processes have been discussed earlier by several research groups during the variation in different parameters. However, the optimization and mechanism involvement due to individual partial pressure-based effects has not been elaborately discussed so far. Hence, we have addressed this issue in detail including thermodynamics of the growth process and tried to establish the effect of the partial pressures of individual gases during the growth of SLG. Also, optical microscopy, Raman spectroscopy, and atomic force microscopy (AFM) have been performed to determine the quality of SLG. Furthermore, nucleation density has also been estimated to understand a plausible mechanism of graphene growth based on partial pressure. Moreover, the field-effect transistor (FET) device has been fabricated to determine the electrical properties of SLG, and the estimated mobility has been found as ∼2595 cm2 V–1 s–1 at n = −2 × 1012 cm–2. Hence, the obtained results trigger that the partial pressure is an important parameter for the growth of SLG and having various potential applications in high-performance graphene FET (GFET) devices.

In the present scenario, conducting and lightweight flexible polymer nanocomposites rival metallic and inorganic semiconducting materials as highly sensitive piezoresistive force sensors. Herein, we explore the feasibility of vertically aligned carbon nanotube (VACNT) nanocomposites impregnated in different polymer matrixes, envisioned as highly efficient piezoresistors in sensor applications. Polymer nanocomposites are selectively designed and fabricated using three different polymer matrixes, i.e., polydimethylsiloxane (PDMS), polyurethane (PU), and epoxy resins with ideal reinforcement of VACNTs to enhance the thermal stability, conductivity, compressibility, piezoresistivity, and sensitivity of these nanocomposites. To predict the best piezoresistive force sensor, we evaluated the structural, optical, thermal, electrical, mechanical, and piezoresistive properties of the nanocomposites using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), I-V measurements, compressive stress-strain measurements, hysteresis, sensitivity, and force studies. The results demonstrate that the PDMS/VACNT nanocomposite is capable of sustaining large force with almost complete recovery and enhanced sensitivity, thereby fulfilling the desirable need for a highly efficient conductive and flexible force sensor as compared to PU/VACNT and epoxy/VACNT nanocomposites.

Recently, the demand of the material manipulation with specific design is highly required for several strategic and societal applications such as in defence, nuclear, security, space, waste management, renewable energy generation and storage. To address these challenges, it is important to design the materials synergetically fit according to their demand in different applications. The impact of such materials is directly related to our daily life from health, wealth, energy and environment. In this direction, CSIR-NPL is designing new materials to indigenize the several new technologies such as luminescent security ink to curb against counterfeiting of passport, Indian currency note and protect secrete documents, carbon materials for fuel cell and battery applications, carbon composite fuel tubes for nuclear reactor applications, carbon fibre polymer composite to replace steel Ilizarov fixator for biomedical applications, lightweight carbon nanotubes polymer composites as EMI shielding materials etc. Moreover, in spite of this, CSIR-NPL is also developing the different technologies to manage the reuse of plastic, electronic, PV module and agriculture waste to ensure safeguard of environment and fully recycling of material for the societal applications. Hence, the central aim of CSIR-NPL is to design and develop the materials with metrological grade to convert into all laboratory research invention to innovation, which will directly help all industrial sectors to promote their quality products with world class infrastructure.

Commercial impacts of technology on any nation’s economy depends upon reliable measurements and tests that are accepted internationally, which helps in its continuous growth of gross domestic product (GDP). Materials play crucial role as building blocks in designing any new technology. Materials are the stepping stone for any technology but accurate and precise measurements with traceable calibration of equipment/devices provides the quality products for its commercial applications. For the wider acceptability of measurements of any materials and their properties demands an international collaboration associated with products which directly impact trade, innovation and hence competitiveness. On this aspect, Versailles Project on Advanced Materials and Standard (VAMAS) established in 1982. Now VAMAS has seventeen member countries particularly NMI of countries and India joined this group in 2008. The VAMAS activities conducted through Technical Work Areas (TWAs) covers most of the materials metrology. In this direction, CSIR-NPL has taken a major initiative on various types of materials development and their metrology for suitable applications which covers the aspects of synergetic materials designing as building blocks for technology development and to provide a quality infrastructure to support the major programmes of VAMAS. Moreover, CSIR-NPL is developing the national facility of quality infrastructure for materials and device testing for primary standard for solar cell including validation of solar cell performance, testing facility for body armour raw material testing. Apart from this, CSIR-NPL further focused on the development of newer materials including the emerging nanomaterials such as carbon nanotubes, electrospun nanofibres, graphene, graphene-based aerogel, organic metal complexes, quantum dots, plasmonics and metamaterials which are described in this chapter.

Herein, a novel strategy to design of unclonable triluminescent pigment derived security ink is formulated to protect valuable merchandise, bank notes, pharmaceuticals, confidential documents etc. against counterfeiting, by embedding luminescent security codes/images. This triluminescent security ink is designed with combinatory chemistry that involves the strategically admixing of the triluminescent functional composite pigments in commercially available polyvinyl chloride gold medium. The triluminescent functional composite pigment is composed of NaYF4: Yb3+, Er3+(Sodium Yttrium Fluoride doped with Ytterbium and Erbium ions), NaYF4: Eu3+ (Sodium Yttrium Fluoride doped with Europium ion) and ZnO (Zinc Oxide) materials which have multifunctional features as it looks white in ambient light and shows strong green (NaYF4: Yb3+, Er3+), red (NaYF4: Eu3+) and green (ZnO) colors at three different excitations of 980 nm, 254 nm and 379 nm wavelengths, respectively. The structural/microstructural and photoluminescence properties of triluminescent functional composite are confirmed by XRD (X-ray diffraction), SEM (Scanning electron microscope), TEM (Transmission electron microscope) and photoluminescence spectroscopic techniques, respectively. The quality and spatially distributed PL intensity of printed images/code from triluminescent ink was investigated by photoluminescence confocal mapping microscopy technique. Hence, the obtained results suggest that the security code/images printed by using ink formulated from triluminescent functional composite pigment provides one step ahead novel security features which could be easy to detect but extremely difficult to replicate.

The development of high volumetric or areal capacitance energy storage devices is critical for the future electronic devices. Hence, the hunting for next-generation electrode materials and their design is of current interest. The recent work in the two-dimensional metal hydroxide nanomaterials demonstrates its ability as a promising candidate for supercapacitor due to its unique structure and additional redox sites. This study reports a design of freestanding high-mass-loaded copper-cobalt hydroxide interconnected nanosheets for high-volumetric/areal-performance electrode. The unique combination of hydroxide electrode with high mass loading (26 mg/cm2) exhibits high areal and volumetric capacitance of 20.86 F/cm2 (1032 F/cm3) at a current density of 10 mA/cm2. This attributes to the direct growth of hydroxides on porous foam and conductivity of copper, which benefits the electron transport. The asymmetric supercapacitor device exhibits a high energy density of 21.9 mWh/cm3, with superior capacitance retention of 96.55% over 3500 cycles.