Band gap engineering from Vis to NIR range in CdPbS nanoparticles synthesized by one-step low-temperature decomposition of xanthate compound.

In the present study, a generic method for the modification of optical band gap of CdS nanostructures material over a wide spectral range due to Pb doping and formation of Cd(1-x)Pb(x)S nanoparticles and its size confinement is reported. The composite investigated in this study was grown by thermal decomposition of metal xanthates and lead concentration was varied to obtain different lead doping. This is a direct decomposition one pot synthesis route that avoids use of toxic phosphine and injection of chemicals during the reaction. The prepared nanoparticles were characterized by XRD, SEM, EDX, and HRTEM. The optical absorption properties of the Cd(1-x)Pb(x)S nanostructures were investigated by UV-visible spectroscopy. Cd(1-x)Pb(x)S nanoparticles showed tuning of the band gap from 2.7 eV to 0.7 eV.

Evaluating Pb-based and Pb-free Halide Perovskites for Solar-Cell Applications: A Simulation Study.

Metal halide Pb-based and Pb-free perovskite crystal structures are an essential class of optoelectronic materials due to their significant optoelectronic properties, optical absorption and tuneable emission spectrum properties. However, the most efficient optoelectronic devices were based on the Pb as a monovalent cation, but its toxicity is a significant hurdle for commercial device applications. Thus, replacing the toxic Pb with Pb-free alternatives (such as tin (Sn)) for diverse photovoltaic and optoelectronic applications is essential. Moreover, replacing the volatile methylammonium (MA) with cesium (Cs) leads to the development of an efficient perovskite absorber layer with improved optical & thermal stability and stabilized photoconversion efficiency. This paper discusses the correlation between the experimental and theoretical work for the Pb-based and Pb-free perovskites synthesised using the hot-injection method at different temperatures. Here, simulation is also carried out using the help of SCAPS-1D software to study the effect of various parameters of CsSnI3 and CsPbI3 layers on solar cell performance. This experimental and theoretical comparative study of the Hot-injection method synthesised CsPbI3 and CsSnI3 perovskites is rarely investigated for optoelectronic applications.

Synaptic plasticity and learning behaviour in multilevel memristive devices.

This research explores a novel two-terminal heterostructure of the Pt/Cu2Se/Sb2Se3/FTO memristor, which exhibited essential biological synaptic functions. These synaptic functions play a critical role in emulating biological neural systems and overcoming the limitations of traditional computing architectures. By repeating a fixed pulse train, in this study, we realized a few crucial neural functions toward weight modulation, such as nonlinear conductance changes and potentiation/depression characteristics, which aid the transition of short-term memory to long-term memory. However, we also employed multilevel switching, which provides easily accessible multilevel (4-states, 2-bit) states, for high-density data storage capability along with endurance (102 pulse cycles for each state) in our proposed device. In terms of synaptic plasticity, the device performed well by controlling the pulse voltage and pulse width during excitatory post-synaptic current (EPSC) measurements. The spike-time-dependent plasticity (STDP) highlights their outstanding functional properties, indicating that the device can be used in artificial biological synapse applications. The artificial neural network with Pt/Cu2Se/Sb2Se3/FTO achieved a significant accuracy of 73% in the simulated Modified National Institute of Standards and Technology database (MNIST) pattern. The conduction mechanism of resistive switching and the artificial synaptic phenomena could be attributed to the transfer of Se2- ions and selenium vacancies. The neuromorphic characteristics of the Pt/Cu2Se/Sb2Se3/FTO devices demonstrate their potential as futuristic synaptic devices.

Performance evaluation of ZnSnN2 solar cells with Si back surface field using SCAPS-1D: A theoretical study.

The earth-abundant semiconductor zinc tin nitride (ZnSnN2) has garnered significant attention as a prospective material in photovoltaic and lighting applications, primarily due to its tunable narrow bandgap and high absorption coefficient. This study focuses on a numerical investigation of ZnSnN2 solar cell structures using the SCAPS 1-D software. The objective is to analyze the influence of various physical and geometrical parameters on solar cell performance. These parameters include the thicknesses of the ZnO window layer, CdS buffer layer, ZnSnN2 absorber layer, and Si back surface field layer (BSF), as well as operating temperature, series and shunt resistances (RS and Rsh), absorber layer defect density, interface defects, and the generation-recombination profile of the n-ZnO:Al/n-CdS/p-ZnSnN2/p-Si/Mo structure. We have evaluated the capabilities of this novel material absorber by investigating its performance across a range of thicknesses. We have started with ultrathin absorber thicknesses and gradually increased them to thicker levels to determine the optimal thickness for achieving high efficiency. Under optimal conditions, a thin solar cell with a thickness (wp) of 1 µm achieved an efficiency (η) of 23.9%. In a practical solar cell operating at room temperature, optimal parameters were observed with a thicker absorber layer (wp = 8 µm) and a BSF width of 0.3 µm. The cell exhibited resistances of Rsh = 106 Ω cm2 and Rs = 1 Ω cm2, along with a low defect density (Nt = 1010 cm-3) in the ZnSnN2 semiconductor. These factors combined to yield an impressive efficiency of 29.5%. Numerous studies on emerging ternary nitride semiconductors (Zn-IV-N2) have highlighted ZnSnN2 as a promising material for thin-film photovoltaics. This compound is appealing due to its abundance, non-toxicity, and cost-effectiveness. Unlike conventional solar cells that depend on rare, toxic, and costly elements, these components are still essential for today's solar cell technology.

Experimental analysis of methylammonium and Formamidinium-based halide perovskite properties for optoelectronic applications.

Nowadays, the toxicity of lead in metal-halide perovskites is the most precarious obstruction in the commercialization of perovskite-based optoelectronic devices. However, Pb-free metal halide perovskites as environment-friendly materials because of their exceptional properties, such as band-gap tunability, narrow emission spectra, low toxicity and easy solution-processability, are potential candidates for optoelectronic applications. Recently, literature reported the poor structural stability and low-emission intensity of Bi-based perovskite NCs. Still, this paper focuses on the fabrication of Formamidinium (FA)-based Bi mixed halide and Methylammonium(MA)-based Bi-pure halide perovskites using Ligand-Assisted Reprecipitation Technique (LARP) technique. XRD diffraction patterns of FA-based perovskites were slightly broad, signifying the nanocrystalline form and limited size of perovskite nanocrystals. While the XRD diffraction patterns of MA3Bi2X9 (X = Cl/Br/I) perovskites were narrow, signifying the amorphous nature and larger size of perovskite nanocrystals. The peak positions were varied in MA-based bismuth halide perovskites with respect to the halide variation from Br to Cl to I ions. The optical study shows the variation in band gap and average lifetime with respect to halide variation leading to enhanced optical properties for device applications. The band-gap of FA3Bi2BrxCl1-x & FA3Bi2IxCl1-x perovskites was calculated to be around 3.7 & 3.8 eV, respectively, while in MA-halide perovskites the band-gap was calculated to be 2.8 eV, 3.1 eV & 3.4 eV with respect to halide variation from I to Cl to Br in perovskite samples using Tauc's plot respectively. Moreover, simulation is carried out using the SCAPS-1D software to study the various parameters in MA & FA-based Bi-pure or mixed halide perovskites. Here, we discussed the variation in efficiency with respect to the thickness variation from 100 to 500 nm for MA3Bi2I9 halide perovskites. These MA3Bi2I9 halide perovskites show minimum efficiency of 4.65 % at 100 nm thickness, while the perovskite sample exhibits maximum efficiency of 10.32 % at 500 nm thickness. Thus, the results stated that the thickness of absorber layers directly affects the device characteristics for optoelectronic applications.

Highly luminescent-paramagnetic nanophosphor probes for in vitro high-contrast imaging of human breast cancer cells.

Highly luminescent-paramagnetic nanophosphors have a seminal role in biotechnology and biomedical research due to their potential applications in biolabeling, bioimaging, and drug delivery. Herein, the synthesis of high-quality, ultrafine, europium-doped yttrium oxide nanophosphors (Y(1.9)O(3):Eu(0.1)(3+)) using a modified sol-gel technique is reported and in vitro fluorescence imaging studies are demonstrated in human breast cancer cells. These highly luminescent nanophosphors with an average particle size of ≈6 nm provide high-contrast optical imaging and decreased light scattering. In vitro cellular uptake is shown by fluorescence microscopy, which visualizes the characteristic intense hypersensitive red emission of Eu(3+) peaking at 610 nm ((5)D(0)-(7)F(2)) upon 246 nm UV light excitation. No apparent cytotoxicity is observed. Subsequently, time-resolved emission spectroscopy and SQUID magnetometry measurements demonstrate a photoluminescence decay time in milliseconds and paramagnetic behavior, which assure applications of the nanophosphors in biomedical studies.

Faster response of NO2 sensing in graphene-WO3 nanocomposites.

Graphene-based nanocomposites have proven to be very promising materials for gas sensing applications. In this paper, we present a general approach for the preparation of graphene-WO(3) nanocomposites. Graphene-WO(3) nanocomposite thin-layer sensors were prepared by drop coating the dispersed solution onto the alumina substrate. These nanocomposites were used for the detection of NO(2) for the first time. TEM micrographs revealed that WO(3) nanoparticles were well distributed on graphene nanosheets. Three different compositions (0.2, 0.5 and 0.1 wt%) of graphene with WO(3) were used for the gas sensing measurements. It was observed that the sensor response to NO(2) increased nearly three times in the case of graphene-WO(3) nanocomposite layer as compared to a pure WO(3) layer at room temperature. The best response of the graphene-WO(3) nanocomposite was obtained at 250 °C.

Sb2Se3 as an HTL for Mo/Sb2Se3/Cs2TiF6/TiO2 solar structure: performance evaluation with SCAPS-1D.

Perovskite-based solar cells (PSCs) have recently gained much attention due to their distinctive optical and electrical properties. Cesium titanium fluoride (Cs2TiF6) is an example of lead-free perovskite absorber material with a bandgap of 1.9 eV, making it suitable for a solar device. However, the high cost of the hole transport material (HTM) and other considerations prevent their commercial production. Antimony selenide (Sb2Se3) is well suited for HTM as it is low-cost material with a tunable bandgap. The work presents the TiO2/Cs2TiF6/Sb2Se3-based solar cell performance using SCAPS-1D simulation software. The effect of all the active layer thicknesses, defect density, hole-electron mobility, and temperature on the device is also simulated. I-V, C-V, and QE curves and energy band diagrams show the photovoltaic device's excellent performance. The outputs are competent enough with an efficiency of 22.10 % when Sb2Se3 is used as a hole transport layer (HTL) in the device architecture. The results suggest that the lead-free solar cell is a promising future option for the solar cell community regarding environmental friendliness and high efficiency.

SnTe as a BSF enhances the performance of Sb2Se3 based solar cell: A numerical approach.

This theoretical investigation's primary goal is to investigate how the Sb2Se3 solar cell's performance may be improved. Here, SnTe, as an innovative back surface field (BSF) layer, has been added between the rear contact (Mo) and absorber layer (Sb2Se3). Above the absorber layer, the structure comprises a thin CdS buffer layer. For each layer of the Al/CdS/Sb2Se3/SnTe/Mo structure, the physical characteristics such as the active layer's thicknesses, carrier concentration, defect density, and rear electrode's work function are determined. The suggested cell outperformed the solar cell without the SnTe layer, which had an efficiency of 20.33%, with enhanced efficiency and open-circuit voltage (Voc) of 28.25% and 0.86 V, respectively, at 300 K. The above solar cell used 0.15 µm SnTe layer, 0.05 µm CdS, and 2.0 µm Sb2Se3 layer. The features of the antimony selenide (Sb2Se3) based solar structure is examined using the SCAPS-1D software, which simulates solar cells in one dimension. Investigations have also been done into how working temperatures influence the I-V parameters of the structure.

A study on structural, optical, and electrical characteristics of perovskite CsPbBr3 QD/2D-TiSe2 nanosheet based nanocomposites for optoelectronic applications.

Lead halide perovskite (CsPbBr3) quantum dots (QDs) and two-dimensional (2D) layered transition metal dichalcogenides have a significant application in solution-processed optoelectronic devices. Here, we report the oleylamine-assisted exfoliation of TiSe2 nanosheets (NSs) in dichlorobenzene with high concentration and stable dispersion. The functionalized TiSe2 NSs were used to synthesize the solution-processed perovskite CsPbBr3 QD/TiSe2 NS-based nanocomposite. The perovskite QDs and TiSe2 NSs were characterized by different techniques. The strong photoluminescence (PL) quenching and decreased lifetime decay of the nanocomposite indicates efficient charge transfer from photo-excited CsPbBr3 to TiSe2 NSs. The calculated charge-transfer rate constant (KET) from photo-excited CsPbBr3 to TiSe2 NSs increased from 1.50 × 108 to 2.79 × 108 s-1 in different concentrations of TiSe2 NSs (5 to 20 µg mL-1), respectively. Furthermore, the photo-currents of CsPbBr3 QD/TiSe2 NS nanocomposite devices were dramatically enhanced ∼2 times compared to pristine CsPbBr3 QD based devices, which supports the charge transfer and charge separation in nanocomposite devices.

Photovoltaic response of a topotaxially formed CdS-Cu(x)S single nanorod heterojunction.

In the present study, a combination of a hydrothermal route and a topotaxial conversion reaction has been used to grow a cadmium sulfide-copper sulfide (CdS-Cu(x)S) single nanorod heterojunction. The J-V characteristics of the CdS nanorods show Shockley behaviour consistent with the energy band diagram of the platinum conducting atomic force microscope (CAFM) probe-CdS nanorod combination. The photovoltaic response measured on the CdS-Cu(x)S nanorods using a CAFM probe shows the formation of a heterojunction with an open circuit voltage of 320 mV, a short circuit current density of 5.5 mA cm⁻² and a crossover of dark and light J-V curves related to the photoconductivity of the interfacial CdS layer. The lengthwise heterojunction fabricated in the present study has many potential advantages in comparison to other single nanorod junctions.

Fast response and recovery of hydrogen sensing in Pd-Pt nanoparticle-graphene composite layers.

This study reports the fast response and recovery of hydrogen sensing in nanoparticle-graphene composite layers fabricated using chemical methods and comprising of isolated Pd alloy nanoparticles dispersed onto graphene layers. For 2% hydrogen at 40 °C and 1 atm pressure, a response time of <2 s and a recovery time of 18 s are observed. The fast response and recovery observed during sensing are due to hydrogen-induced changes in the work function of the Pd alloy and modification in the distribution of defect states in the graphene band gap due to gas adsorption. The results of hydrogen sensing in the new class of Pd-Pt nanoparticle-graphene composite material are important for understanding the effect of gas adsorption on electronic conduction in graphene layers and for developing a new type of gas sensor based on changes in the electronic properties of the interface.

Resistive switching in copper oxide nanorods: a bottom up approach applicable for enhanced scalability.

Reversible, stable and reproducible resistive switching in a parallel network of Cu2O nanorods, observed in the present study, highlights the advantages of using nanorods in comparison to normally used thin films. Unipolar and symmetric current-voltage characteristics of the metal/insulator/metal structure consisting of Hg top contact/Copper oxide (Cu2O) nanorods/Ag bottom contact in a sandwich configuration shows electroforming at about 11 V, reproducible reset and set points at 0.53 +/- 0.03 and 4.2 +/- 0.02 V and a high OFF/ON resistance ratio > 10(3). Slope of current-voltage characteristics and current contrast in CAFM mapping indicate that filamentary conduction mechanism is responsible for resistive switching. This study sets the foundation for fabricating a nanorods based resistive random access memory device and thus a manifold increase in the device scalability.

A study on chemical exfoliation and structural and optical properties of two-dimensional layered titanium diselenide.

Titanium diselenide (TiSe2) is the least studied member of the transition metal dichalcogenide family due to a lack of available synthesis methodology, controlled bandgap engineering, and rapid characterization of layers. In this paper, we report the chemical exfoliation of TiSe2 platelets synthesized by the chemical vapor transport route in ortho-dichlorobenzene (o-DCB) functionalized with oleylamine (OLA), for the first time to the best of our knowledge. It is found that the addition of OLA supports the formation of a stable dispersion of a large area of the TiSe2 sheets due to surface capping with the OLA molecules indicating the importance of the ligand in dispersion behavior. The X-ray diffraction pattern confirms the hexagonal structure of the TiSe2 platelets with the space group P3[combining macron]m1 while Raman spectroscopy reveals that two modes of vibration i.e. A1g and E2g exist with layered structures having dimensions in micrometers as confirmed by scanning electron microscopy. Fourier transform infrared spectroscopy confirms the successful functionalization of chemically exfoliated TiSe2 nanosheets. Field-emission scanning electron microscopy reveals that exfoliated TiSe2 has a thickness of 15-55 nm whereas high-resolution transmission electron microscopy indicates thicker sheets for ligand-free exfoliated TiSe2 which are crystalline. Atomic force microscopy confirms the formation of nanosheets. UV-Visible, photoluminescence, and time-resolved PL spectroscopy showed an enhanced effect and better average lifetime of excitation for the exfoliated sheets with OLA than those without OLA. The C-V studies reveal that with increasing scan rate, the corresponding current also increases. The present study offers the possibility of their utilization in optoelectronics, advanced low-power electronics, voltage-controlled oscillators, ultra-fast electronics, and electrochemical devices.

Self-catalytic synthesis, structure and properties of ultra-fine luminescent ZnO nanostructures for field emission applications.

A facile method to produce high-quality ZnO nanostructures; either tetrapod (TP), nanotetraneedle (NTN) or multipod (MP) with a high degree of homogeneity for advanced field emission (FE) applications is presented. Among these nanostructures, NTN has been successfully employed to demonstrate enhanced current densities (2.6 mA cm(-2)), turn-on field (1.5 V microm(-1)) and field-enhancement factors (6930) over conventional multiwalled carbon nanotubes (MWCNTs), TP, MP and ZnO-spheroids. A comparative study of FE from various ZnO nanostructures, morphologies and site densities has lead to the conclusion that diameter of the tip is one of the vital parameters in enhancing the overall FE properties.

Synthesis and characterization of ultra-fine Y2O3:Eu3+ nanophosphors for luminescent security ink applications.

We report a simple method for the synthesis of ultra-fine Eu(3+)-doped yttria (Y(2)O(3)) nanophosphors with an average diameter of approximately 5 nm for development of a transparent colloid that could be used as a luminescent security ink. This has been achieved by suitably substituting Eu(3+) ions at the favorable C(2) symmetry sites of Y(3+) ions and quantum mechanically confining the growth of the nanophosphor using a novel acid-catalyzed sol-gel technique. This is one of the few reports that depict the development of a transparent aqueous-stable Y(2)O(3):Eu(3+) colloidal solution for strategic applications related to security codes. High resolution transmission electron microscopy images showed excellent lattice fringes that in turn support the presence of better crystal quality and enhanced photoluminescence (PL) emission from the Y(1.9)O(3)Eu(0.1)(3+) nanophosphor system. Time resolved emission spectroscopy measurement indicated a PL decay time in the range of a few milliseconds, suitable for making luminescent security ink and other advanced applications in optoelectronic devices and bio-labeling.

Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes.

We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes using thermal pyrolysis method and the effect of shape anisotropy on the static and dynamic magnetic properties were studied. Shape anisotropy of approximately 10% was introduced in nanocubes by making nanodiscs using a linear chain amine surfactant during synthesis process. It has been observed that, ferromagnetism persisted above room temperature and a sharp drop in magnetic moment at low temperatures in zero-field cooled magnetization may be associated with the spin disorder due to the effective anisotropy present in the system. Dynamic magnetic properties were studied using RF transverse susceptibility measurements at different temperatures and the singularities due to anisotropy fields were probed at low temperatures. Symmetrically located broad peaks are observed in the frozen state at the effective anisotropy fields and the peak structure is strongly affected by shape anisotropy and temperature. Irrespective of size the shape anisotropy gave rise to higher coercive fields and larger transverse susceptibility ratio at all temperatures. The role of shape anisotropy and the size of the particles on the observed magnetic behaviour were discussed.

Tuning the Thermoelectric Material's Parameter: A Comprehensive Review.

Thermoelectric is a device that converts heat into electricity. As thermodynamically it is not possible to make device which is 100 percent efficient, some amount of energy is wasted in the form of heat. Thermoelectric materials can play a major role in harnessing such waste energy. Although thermoelectric is a useful device still its efficiency is not good enough for commercialization. Therefore, lots of research have been carried out in finding out the best possible material, device geometry etc. There are thousands of papers describing various optimization processes. The present work reviews the basics of thermoelectric device parameters which determine the performance of the device and how to control these parameters for better thermoelectric efficiency. The efforts made to optimize parameters like power factor, thermal conductivity etc. have been summarized. Experimental results have been described with examples. Highest reported ZT values of various materials have been presented in this review.

Localized Surface Plasmon Resonance Studies on Pd/C Nano-Composite System: Effect of Metal Concentration and Annealing Temperature.

The effects of metal concentration and annealing temperature on the localized surface plasmon resonance (LSPR) properties of the Pd nanoparticles (NP) dispersed in carbon were investigated. The Pd/C nano-composite thin films with 7 to 39 atomic % concentration of metal content were deposited using the atom beam co-sputtering techniques and subjected to annealing at temperature varying from 300 °C to 600 °C. The UV-vis spectroscopy studies on as-prepared films displayed a Mie scattering profile, but not well-defined LSPR bands were observed for all the values of Pd concentration. This is attributed to the smaller size (3-4 nm) of Pd NPs and rough Pd/C interface, as confirmed from TEM studies. When samples were annealed at a temperature of 300 °C, three broad LSPR absorption bands in the visible region, along with a sharp peak at 210 nm, were observed and the effect of Pd concentration variation was insignificant on their position. The multiple LSPR bands were observed due to agglomeration NPs, which is consistent with earlier reports and is also observed in the TEM images. When annealing temperature was subsequently increased to 500 °C, a blue shift in the LSPR peak position with an increase in the Pd concentration was observed, which phenomena is attributed to the formation of bigger NPs with the formation of sharp NPs-interface at high temperature upon annealing. A monotonic increase in the magnitude and decrease in the FWHM with an increase in concentration suggested change in the dielectric function of sample due to the growth of NPs. This is further confirmed from XRD studies, where strain relaxation and grain growth were observed. The intensity of the SPR peak decreased with an increase in the annealing temperature. The LSPR peak disappeared on annealing at a temperature of 600 °C, suggesting the formation of continuous polycrystalline thin films of Pd. In summary, NPs size, metalmatrix interface, and concentration of metal play key roles in the tailoring the LSPR properties of the Pd.

Tunable synthesis of indium oxide octahedra, nanowires and tubular nanoarrow structures under oxidizing and reducing ambients.

We report the effect of oxidizing and reducing ambients on the growth of indium oxide (IO) nanostructures in the vapor phase evaporation method. Our results show that the oxidizing reagent, water, results in the growth of IO nanowires and preserves the In/O stoichiometry throughout the length of the nanowires. The reducing reagent, ethanol, makes the growth environment indium rich, resulting in the growth of indium-filled IO tubular nanoarrow structures. The growth of solid IO nanowires is attributed to a vapor-liquid-solid mechanism, whereas for indium-filled tubular nanoarrow structures a modified bottom-vapor-solid growth mechanism is proposed. The tunable synthesis of IO nanostructures in different morphologies with correction of their stoichiometry may have potential applications in future nanodevices.