Animesh Layek

Luminescent S-doped carbon dots: an emergent architecture for multimodal applications

A facile route has been developed to synthesise and isolate sulphur doped fluorescent carbon dots for the first time. Such carbogenic quantum dots exhibit a wide band gap of 4.43 eV with a high open circuit voltage (VOC) of 617 mV along with a fill factor (FF) as high as 37%, using phenyl-C60-butyric acid methyl ester (PCBM) as the electron transporting layer. Besides the wide band gap, which is useful in the fabrication of solar cells, sulphur modified carbon dots also exhibit a high fluorescence quantum yield of 11.8% without any additional surface passivation, producing a unique fluorescent probe for further applications. In addition, the particles have a strong tendency to interact with the surface of gold nanoparticles and produce a thin fluorescent layer over their surfaces. Moreover, as they are completely biocompatible in nature, the highly fluorescent S-doped carbon dots have a strong potential for use in bioimaging applications. Interestingly, owing to the presence of oxygen and sulphur functionality, the highly negatively charged particles can easily bind with positively charged DNA-PEI complexes, simply by mixing them, and after interaction with DNA, bright blue fluorescence has been observed under an excitation wavelength of 405 nm .

Cd(II) based metal–organic framework behaving as a Schottky barrier diode

A metal-organic framework (MOF) of cadmium(ii) is reported here which is the first example of an experimentally achieved MOF based electronic device, and in the present case it is a Schottky diode.

Investigation of charge transport properties in less defective nanostructured ZnO based Schottky diode

In this report the synthesis of novel zinc oxide (ZnO) with a lower defect density and its effect on the Al/ZnO Schottky junction has been demonstrated. The defect density was estimated by positron annihilation lifetime measurement which ensures the materials superiority (i.e. free from point defects or any type of vacancies) over the earlier reported results. The thin film device of synthesized ZnO was fabricated on an ITO coated glass substrate. As the front contact was made by aluminium, the characteristic I–V produced rectifying Schottky behavior. The underlying charge transport mechanism through a metal–semiconductor (i.e. Al/ZnO) junction was analyzed on the basis of thermoionic emission theory to find out the quality of the fabricated device. In this regard we have studied the charge transport mechanism by measuring the density of states (DOS) at the Fermi level, mobility-lifetime product and diffusion length.

One step hydrothermal synthesis of a rGO–TiO2 nanocomposite and its application on a Schottky diode: improvement in device performance and transport properties

The presence of a Schottky barrier (SB) at a metal–semiconductor (MS) interface is of paramount importance to numerous application fields. In this report, we demonstrate the performance comparison of Schottky diodes fabricated with TiO2 and rGO–TiO2 nanocomposites, in contact with aluminium. From forward I–V characteristics, important diode parameters i.e. rectification ratio, ideality factor, series resistance and barrier height were obtained. A photoresponse comparison of the diodes has also been performed. It was found that the rGO–TiO2 based junction showed improved performance. The rectification ratio increased by ∼94% and the barrier height was lowered by ∼10%, under dark conditions. For better realization of the junction, here we provide insight into the carrier transport properties with the help of space charge limited current (SCLC) theory. After introducing graphene, the carrier mobility and carrier concentration increased by 64% and 21% respectively, while the diffusion length is found to be improved by 13.4%. These results illustrate that rGO incorporation has led to a much improved carrier transport and electron hole separation. Due to greater light absorption, the improvement in diode parameters and transport properties were even better when the device was subjected to irradiation.

Novel CuFeS2 pellet behaves like a portable signal transporting network: studies of immittance

A novel synthesis of CuFeS2 nanoparticles has been demonstrated here. This is the first time we have thoroughly investigated the frequency dependent dielectric behavior of iron-chalcopyrite (CuFeS2) pellets (with σd.c. = 47.27 × 10−9 S cm−1). The room temperature a.c. conductivity of the material has also been investigated in the frequency range 200 Hz–2 MHz. Frequency dependent impedance analysis of the material indicates the charging and discharging behavior of the capacitor. Throughout this report we have analyzed the frequency dependent complex impedance, electric modulus and the loss tangent of the CuFeS2 pallet as series and parallel combinations of capacitors and resistors.

Synthesis and incorporation of high quality FeS2 nanoparticles within poly(3-hexylthiophene):Phenyl-C60-butyric acid methyl ester to increase the photosensitivity of composite material

In this study, high quality environment friendly FeS2 nanoparticle was synthesized in hydrothermal route with capping reagent. Band gap energy of FeS2 has been modified and applied in polymer:inorganic nanocomposite. Pyrite structure of FeS2 nanoparticle has been confirmed by different structural characterization techniques. Thermal stability has been studied by thermogravimetric analysis technique. Finally, FeS2 has been introduced within a poly(3-hexylthiophene):Phenyl-C60-butyric acid methyl ester (P3HT:PCBM) matrix at different weight ratios to increase the photosensitivity of the nanocomposite. The composite film of P3HT:PCBM:FeS2 with weight ratio 2:1:0.2 shows highest photosensitivity. Increased photosensitivity has been explained from photoluminescence data.

Multifunctional mixed ligand metal organic frameworks: X-ray structure, adsorption, luminescence and electrical conductivity with theoretical correlation

Two new mixed ligand metal–organic frameworks of Zn(II) with disodium 5-hydroxyisophthalate and 4,4′-azobispyridine (azbpy) ligands, {[Zn(azbpy)(HO-1,3-bdc)(H2O)]·(azbpy)}n (1) and {[Zn(azbpy)0.5(HO-1,3-bdc)(C2H5OH)]·(H2O)}n (2) have been synthesized by changing the reaction medium (methanol to ethanol) and structurally characterized by elemental analysis, IR, PXRD, TG and single crystal X-ray diffraction. Compound 1 exhibits a 2D sheet network structure with free azbpy ligands in its void space, and is stabilized by π–π and C–H⋯π interactions, whereas 2 has a 2D layered architecture with lattice water molecules in its void space. Compound 2 has a flexible structure and shows gated adsorption (gas and solvent) behavior, while framework 1 is nonporous. These two MOFs exhibit remarkable electrical conductivity values at room temperature and their comparison is discussed carefully. Theoretical calculations suggest that both the compounds are p-type semiconductors and correlate the structure–property relationship. Schottky barrier diode electronic devices have been fabricated by using these two semiconductor materials with aluminium (Al) and indium tin oxide (ITO) in sandwich configuration, ITO/MOF-1 or 2/Al, and both the devices exhibit sound rectification behavior. The photoluminescent properties of both the compounds in the solid state are also investigated in detail.

Application Possibility of Mn 0.04 Cu 0.05 Zn 0.91 O in Electronic and Magnetic Devices

In this literature, we have investigated the magnetic properties and Schottky device-based charge transport properties of hydrothermally derived Mn0.04Cu0.05Zn0.91O nanorod. The doping of 3-D transitional metals, Mn and Cu, within ZnO makes it potentially applicable in spin-based electronics, whereas its temperature-dependent conductivity (of the order of 10−3 in C.G.S.) makes it suitable for semiconductor-based devices. The observation of intrinsic ferromagnetism of the synthesized composite and its variation of magnetization with magnetic field and temperature exhibited the suitability of spin-based electronic application. To check the applicability in optoelectronic devices, metal–semiconductor (Al/Mn0.04Cu0.05Zn0.91O) junction was fabricated and analyzed. The current–voltage characteristic represented the rectifying behavior of the junction with on/off current ratio 4.3 at ±1 V in dark and potential barrier height 0.61 eV. The significant change in rectification due to the influence of incident radiation makes this material suitable for photosensing electronic device application.

Temperature dependent growth of cadmium(II) oxide nanocrystals: studies on morphology based optical, electrical and dielectric properties

Nanocrystalline cadmium(II) oxide were obtained by calcining a hydrated cadmium-organic hybrid precursor, (C10H2O8)Cd2·xH2O, obtained by a chemical reduction method using cadmium acetate dihydrate, 1,2,4,5-benzenetetracarboxylic acid, and triethylamine. Calcined CdO at different temperature possess different morphology, revealed by field emission scanning electron microscope analysis. In this article, the photosensitivity, dielectric behavior, frequency dependant loss-tangent and complex impedance spectra of the morphology driven CdO nanoparticles were studied aptly.

Synthesis of Mn0.04Cu0.05Zn0.91O nanorod and its application in optoelectronic switching device

The optical absorption of ZnO nanorod had been reduced by introducing Mn as doping element. In this present study the optical absorption of ZnO nanorod has been improved by simultaneous doping of the element Mn and Cu. The hydrothermal reaction was adopted for the synthesis. The electrical conductivity and the optical band gap of the Mn0.04Cu0.05Zn0.91O were measured as 1.16 × 10−3Scm−1 and 3.07eV respectively, assigned the semiconductor behavior. The light induced rectification in time dependent current response characteristic of Al/ Mn0.04Cu0.05Zn0.91O/ITO was investigated to check the performance of the composite in opto-electronic switching device.