A Strategic Approach to Design Multi-Functional RGB Luminescent Security Pigment Based Golden Ink with Myriad Security Features to Curb Counterfeiting of Passport.

Authentication and verification of the most important government issued identity proof, i.e. passport has become more complex and challenging in the last few decades due to various innovations in ways of counterfeiting by fraudsters. Here, the aim is to provide more secured ink without altering its golden appearance in visible light. In this panorama, a novel advanced multi-functional luminescent security pigment (MLSP) based golden ink (MLSI) is developed that provides an optical authentication and information encryption features to protect the legitimacy of the passport. The advanced MLSP is derived from the ratiometric combination of different luminescent materials to form a single pigment which emits red (620 nm), green (523 nm) and blue (474 nm), when irradiated via 254, 365 and 980 nm NIR wavelengths, respectively. It also includes magnetic nanoparticles to generate magnetic character recognition feature. The MLSI has been fabricated to examine its printing feasibility and stability over different substrates using the conventional screen-printing technique against harsh chemicals and under different atmospheric conditions. Hence, these advantageous multi-level security features with golden appearance in visible light is a new breakthrough toward curbing the counterfeiting of passport as well as bank cheques, government documents, pharmaceuticals, military equipment, and many more.

New insights into APCVD grown monolayer MoS2 using time-domain terahertz spectroscopy.

In modern era, wireless communications at ultrafast speed are need of the hour and search for its solution through cutting edge sciences is a new perspective. To address this issue, the data rates in order of terabits per second (TBPS) could be a key step for the realization of emerging sixth generation (6G) networks utilizing terahertz (THz) frequency regime. In this context, new class of transition metal dichalcogenides (TMDs) have been introduced as potential candidates for future generation wireless THz technology. Herein, a strategy has been adopted to synthesize high-quality monolayer of molybdenum di-sulfide (MoS2) using indigenously developed atmospheric pressure chemical vapor deposition (APCVD) set-up. Further, the time-domain transmission and sheet conductivity were studied as well as a plausible mechanism of terahertz response for monolayer MoS2 has been proposed and compared with bulk MoS2. Hence, the obtained results set a stepping stone to employ the monolayer MoS2 as potential quantum materials benefitting the next generation terahertz communication devices.

Synthesis and Characterization of Highly Crystalline Bi-Functional Mn-Doped Zn2SiO4 Nanostructures by Low-Cost Sol-Gel Process.

Herein, we demonstrate a process for the synthesis of a highly crystalline bi-functional manganese (Mn)-doped zinc silicate (Zn2SiO4) nanostructures using a low-cost sol-gel route followed by solid state reaction method. Structural and morphological characterizations of Mn-doped Zn2SiO4 with variable doping concentration of 0.03, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 wt% were investigated by using X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) techniques. HR-TEM-assisted elemental mapping of the as-grown sample was conducted to confirm the presence of Mn in Zn2SiO4. Photoluminescence (PL) spectra indicated that the Mn-doped Zn2SiO4 nanostructures exhibited strong green emission at 521 nm under 259 nm excitation wavelengths. It was observed that PL intensity increased with the increase of Mn-doping concentration in Zn2SiO4 nanostructures, with no change in emission peak position. Furthermore, magnetism in doped Zn2SiO4 nanostructures was probed by static DC magnetization measurement. The observed photoluminescence and magnetic properties in Mn-doped Zn2SiO4 nanostructures are discussed in terms of structural defect/lattice strain caused by Mn doping and the Jahn-Teller effect. These bi-functional properties of as-synthesized Zn2SiO4 nanostructures provide a new platform for their potential applications towards magneto-optical and spintronic and devices areas.

Role of processing parameters in CVD grown crystalline monolayer MoSe2.

The quality of as-synthesized monolayers plays a significant role in atomically thin semiconducting transition metal dichalcogenides (TMDCs) to determine the electronic and optical properties. For designing optoelectronic devices, exploring the effect of processing parameters on optical properties is a prerequisite. In this view, we present the influence of processing parameters on the lattice and quasiparticle dynamics of monolayer MoSe2. The lab-built chemical vapour deposition (CVD) setup is used to synthesize monolayer MoSe2 flakes with varying shapes, including sharp triangle (ST), truncated triangle (TT), hexagon, and rough edge circle (REC). In particular, the features of as-synthesized monolayer MoSe2 flakes are examined using Raman and photoluminescence (PL) spectroscopy. Raman spectra reveal that the frequency difference between the A1g and E1 2g peaks is >45 cm-1 in all the monolayer samples. PL spectroscopy also shows that the synthesized MoSe2 flakes are monolayer in nature with a direct band gap in the range of 1.50-1.58 eV. Furthermore, the variation in the direct band gap is analyzed using the spectral weight of quasiparticles in PL emission, where the intensity ratio {I(A0)/I(A-)} and trion binding energy are found to be ∼1.1-5.0 and ∼23.1-47.5 meV in different monolayer MoSe2 samples. Hence, these observations manifest that the processing parameters make a substantial contribution in tuning the vibrational and excitonic properties.

Designing of two dimensional lanthanum cobalt hydroxide engineered high performance supercapacitor for longer stability under redox active electrolyte.

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.

Ultrasensitive Boron-Nitrogen-Codoped CVD Graphene-Derived NO2 Gas Sensor.

Recent trends in 2D materials like graphene are focused on heteroatom doping in a hexagonal honeycomb lattice to tailor the desired properties for various lightweight atomic thin-layer derived portable devices, particularly in the field of gas sensors. To design such gas sensors, it is important to either discover new materials with enhanced properties or tailor the properties of existing materials via doping. Herein, we exploit the concept of codoping of heteroatoms in graphene for more improvements in gas sensing properties and demonstrate a boron- and nitrogen-codoped bilayer graphene-derived gas sensor for enhanced nitrogen dioxide (NO2) gas sensing applications, which may possibly be another alternative for an efficient sensing device. A well-known method of low-pressure chemical vapor deposition (LPCVD) is employed for synthesizing the boron- and nitrogen-codoped bilayer graphene (BNGr). To validate the successful synthesis of BNGr, the Raman, XPS, and FESEM characterization techniques were performed. The Raman spectroscopy results validate the synthesis of graphene nanosheets, and moreover, the FESEM and XPS characterization confirms the codoping of nitrogen and boron in the graphene matrix. The gas sensing device was fabricated on a Si/SiO2 substrate with prepatterned gold electrodes. The proposed BNGr sensor unveils an ultrasensitive nature for NO2 at room temperature. A plausible NO2 gas sensing mechanism is explored via a comparative study of the experimental results through the density functional theory (DFT) calculations of the adsorbed gas molecules on doped heteroatom sites. Henceforth, the obtained results of NO2 sensing with the BNGr gas sensor offer new prospects for designing next-generation lightweight and ultrasensitive gas sensing devices.

Ultrasensitive Wearable Strain Sensors based on a VACNT/PDMS Thin Film for a Wide Range of Human Motion Monitoring.

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.

Correction to "Partial Pressure Assisted Growth of Single-Layer Graphene Grown by Low-Pressure Chemical Vapor Deposition: Implications for High-Performance Graphene FET Devices".

[This corrects the article DOI: 10.1021/acsomega.0c02132.].

Partial Pressure Assisted Growth of Single-Layer Graphene Grown by Low-Pressure Chemical Vapor Deposition: Implications for High-Performance Graphene FET Devices.

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.

A Comparative Study of Compressible and Conductive Vertically Aligned Carbon Nanotube Forest in Different Polymer Matrixes for High-Performance Piezoresistive Force Sensors.

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.

Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature.

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.

Influence of the rate of radiation energy on the charge-carrier kinetics application of all-inorganic CsPbBr3 perovskite nanocrystals.

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 (κ r/κ nr = ∼0.62) and 0.30 mW (κ r/κ nr = ∼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.

Correction: Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature.

[This corrects the article DOI: 10.1039/C9RA08707A.].

Wide spectral photoresponse of template assisted out of plane grown ZnO/NiO composite nanowire photodetector.

Zinc oxide (ZnO) one-dimensional nanostructures are extensively used in ultra-violet (UV) detection. To improve the optical sensing capability of ZnO, various nickel oxide (NiO) based p-n junctions have been employed. ZnO/NiO heterojunction based sensing has been limited to UV detection and not been extended to the visible region. In the present work, p-NiO/n-ZnO composite nanowire (NW) heterojunction based UV-visible photodetector is fabricated. A porous anodic aluminum oxide template based electrochemical deposition method is adopted for well separated and vertically aligned growth of composite NWs. The photoresponse is studied in an out of plane contact configuration. The fabricated photodetector shows fast response under UV-visible light with a rise and decay time of tens of ms. The wide spectral photoresponse is analyzed in terms of conduction from defect states of ZnO and interfacial defects during p-n junction formation. Light interaction with heterojunction along the length of the composite NW results in enhanced visible photoresponse of the detector and is further supported by simulation.

Continuous Growth of Highly Reproducible Single-Layer Graphene Deposition on Cu Foil by Indigenously Developed LPCVD Setup.

Continuous growth of high-quality single-layer graphene (SLG) is highly desirable in several electronic and optoelectronic applications. To fulfill such requirements, we proposed a low-cost, highly reproducible high-quality SLG synthesized by indigenously developed low-pressure chemical vapor deposition (LPCVD) setup. The quality of SLG is examined by Raman spectroscopy, where we have probed the I 2D/I G ratio for continuous 30 runs to assess the reproducibility and quality of single-layer using proposed indigenous LPCVD setup for device fabrication. The highest I 2D/I G ratio of SLG (5.82) was found with full width at half maximum values of 2D peak and G peak of ∼30.10 cm-1 and ∼20.86 cm-1, respectively. Further, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy have been performed to study the quality of SLG. Thickness measurement of graphene with graphene grain size is calculated from atomic force microscopy studies, and the average grain size is found to be 1-3 µm. Moreover, I-V characteristics have also been investigated by the two-probe method to ensure the quality of SLG. The lowest resistance of the SLG (∼387 Ω) was found at room temperature. Thus, this new indigenously developed low-cost setup provides a novel alternative method to produce highly reproducible metrology-grade continuous SLG on Cu substrate for next-generation quantum devices.

Studies of Ultrafast Transient Absorption Spectroscopy of Gold Nanorods in an Aqueous Solution.

Herein, ultrafast transient absorption spectroscopy is performed to probe the electron transfer studies between aqueous solution and gold nanorods (Au NRs). The seed-mediated growth method is used to synthesize crystalline cylindrical Au NRs having longitudinal plasmon resonance peak maximum at 825 nm. The as-synthesized Au NRs show average width and length of ∼10 ± 2 and ∼50 ± 2 nm, respectively, with an aspect ratio in the range of ∼5. The time-resolved decay profiles have been studied in a subpicosecond resolution range using pump wavelength at 410 nm excitation and probe wavelengths from visible to near-infrared region. The plasmon dynamics studies of Au NRs depend on the electron heating phenomena, coherent acoustic phonon vibration and electronic transient behavior, i.e., electron-phonon coupling, and homogenous dephasing processes. Thus, the obtained results highlighted that the ultrafast charge transfer dynamics studies in Au NRs could play an important role to elucidate their electronic, photothermal, and optical properties for molecular imaging, photothermal therapy, and optoelectronic and light-harvesting devices.

Probing reversible photoluminescence alteration in CH3NH3PbBr3 colloidal quantum dots for luminescence-based gas sensing application.

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.

A Facile Synthesis of Alkaline Electrolyte Based Graphene Sheets, Their Functionalization and Attachment of Some Drugs.

High-quality graphene is highly enviable material due to its seminal role amongst several areas in modern technology including its role as nanocarrier for site selective drug grafting and delivery applications. Here, we report a facile, cost-effective and single-step method to produce high-quality graphene through customised electrochemical exfoliation of graphite anode in alkaline electrolyte medium. The quality of graphene sheets (GS) were investigated by Raman, TEM/HRTEM, AFM, and FTIR techniques. The high quality as well as excellent Π-Π stacking nature of the honeycomb lattice of graphene was confirmed by measuring the quenching capability through photo-luminescence spectroscopy using organic dyes. A plausible mechanism for the graphite exfoliation has been given where evolution of high density of oxygen molecules exerts large force on the graphitic layers leads to exfoliation and consequent synthesis of graphene. Furthermore, to explore the application of the graphene sheets so synthesized, we carried out studies which may make them as suitable carriers for drug delivery. For this, graphene sheets were functionalized with L-cysteine and attached with the drugs Amphotericin-B (AmB) and Tamoxifen citrate (TMX). The conjugation of drugs with L-cysteine functionalized graphene has been confirmed through FTIR and Raman spectroscopic techniques. The drug loading efficiency of FGS for AmB and TMX was 75.00% and 94.31%, respectively. The present formulation of drugs (AmB and TMX) conjugated with graphene is suitable for the targeted drug delivery as it will enhance the efficacy and reduce cytotoxicity associated with drug.

Ultrafast charge carrier dynamics in CdSe/V2O5 core/shell quantum dots.

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.

Highly Efficient, Chemically Stable, and UV/Blue-Light-Excitable Biluminescent Security Ink to Combat Counterfeiting.

A strategy has been demonstrated to design a biluminescent security ink using Eu(TTA)3Phen (ETP) and fluorescein for protecting the currency and other essential documents, viz., passport, bank check, certificates, etc. against counterfeiting. The biluminescent security ink exhibits strong red and green emission under 367 and 445 nm excitations, respectively. As it is quite challenging to prepare a material that possesses two prominent (green and red) and distinguishable colors upon excitation with two separate light-emitting diode (LED) sources, emitting at different wavelengths, the biluminescent security ink would be hard to counterfeit as compared with the existing luminescent security ink that exhibits single color under UV light exposure. To check its feasibility for security application, the patterns printed out using the biluminescent security ink were kept under a hot and humid atmosphere for 150 days. Also, the ETP and fluorescein fluorophores were exposed to UV light for a prolonged time, which do not show any sign of deterioration in their luminescence intensities. Furthermore, to check their chemical stability, printed patterns were also exposed to chemicals that have potential to wipe out ink, viz., detergent, ethanol, acetone, and sodium hypochlorite (bleach) solution, and it was noticed that it is well stable against these chemicals. Because of the reasons mentioned above and easy availability of 367 and 445 nm LEDs at low cost, authors believe that the application of this biluminescent security ink can trigger the realization of the full potential of this advanced security feature in detecting fake currency.