Ghulam Nabi

Synthesis of CuS flowers exhibiting versatile photo-catalyst response

Hierarchically structured covellite copper sulfide (CuS) microflowers composed of nanosheets have been successfully fabricated via a one-pot sonochemical process, using copper sulfate and thiourea aqueous solution as precursors in the presence of citric acid, without any prefabricated template. Large-scaled architectures are homogeneous and quite separately displaced and assembled by pure hexagonal single-crystalline CuS nanosheets, having thickness within 20 nm. The as obtained hierarchical CuS structures possess rather high surface area and unique double pore size distributions measured from N2 adsorption isotherms. Moreover, a possible growth mechanism for the CuS hierarchical architectures is proposed on the basis of temporal evolution controlled experiments. Most importantly, these hierarchically structured CuS catalysts showed highly efficient and versatile photo-catalytic activities as well as excellent recyclability in degrading highly concentrated dye aqueous solutions of methylene blue (MB), rhodamine B (RhB) and their mixed solution (MB + RhB) with the help of hydrogen peroxide (H2O2) under natural light irradiation, suggesting a promising application in wastewater purification.

Electrical and optical properties of single zigzag SnO2 nanobelts

We report here on investigations of electrical and optical properties of single zigzag SnO2 nanobelts. Large scale zigzag nanobelts were obtained on a silicon substrate by a Chemical Vapor Deposition (CVD) approach. The average value of carrier concentrations (Nd) and electron mobility (μ) were calculated to be 1.39 × 1018 cm−3 and 70.76 cm2 V−1 s−1, respectively. Room temperature PL exhibits a broad emission peak centred at 600 nm. Three Raman active modes at 474.8, 633.8, 775.8 cm−1 were observed. Electron paramagnetic resonance measurements suggest the presence of many singly ionized states.

Nanostructured-based WO 3 photocatalysts: recent development, activity enhancement, perspectives and applications for wastewater treatment

The growth of highly ordered architectures of semiconductor metallic oxide photocatalyst has acknowledged great consideration due to natural growth along with exceptional morphology properties and potential application ways to resolve the problem of freshwater shortages in this world. Tungsten trioxide (WO3) is a well-known semiconductor photocatalyst due to its better response in solar spectrum, fine metal interactions, mechanical strength, high efficiency, harmlessness and cost-effectiveness. This review focuses on a precise and overall description of the recent literature relating pure and doped/composite WO3 catalyst, photocatalytic enhancement mechanism. Moreover, it will also elaborate the experimental conditions used photocatalyst synthesis processes, optimization of the parameters affecting the degradation efficiency of various dyes. Furthermore, strategies for improving photocatalytic activity of WO3 like metal doping, semiconductor coupling, metal sulfides and metal nitrides coupling are systematically summarized and highlighted. After this, future perspectives about advancement and applications are reviewed. It is expected that this review article could offer strategies for designing novel WO3-based photocatalysts which can have promising prospects of multifunctional applications to meet the imperative demands of highly efficient solar energy conversion.

Synthesis, photoluminescence and field emission properties of well aligned/well patterned conical shape GaN nanorods

Vertically well aligned, well patterned and high density conical shaped GaN nanorods have been synthesized on a Si substrate by pre-treating the GaN powder with aqueous NH3via a facile chemical vapor deposition method without any catalyst. The nanorods obtained have been characterized by XRD, EDX, TEM, HRTEM and SAED. The observed diameter of the nanorods is 80–100 nm whereas their sharp tip angle measured is 55°. The calculated number of sharp nanorod tips in 1 mm2 is approximately 1.56 × 108, indicating high growth density of nanorods which is crucial for field emission properties. The GaN nanorods have exhibited impressive field emission properties and high stability with a lower turn-on field of 3.35 V μm−1 (0.01 mA cm−2) at room temperature which is sufficient for electron emission devices, field emission displays and vacuum nano-electronic devices. Moreover, uniform, well-aligned, well-patterned and high-density growth of GaN nanorods also make them promising candidates for nano-device design and integration in the future. The room-temperature PL emission with a strong peak at 370 nm (3.35 eV) indicates that GaN nanorods have potential application in light-emitting nano-devices. A vapor–solid growth mechanism for GaN nanorods has also been discussed briefly.

First-principle electronic, elastic, and optical study of cubic gallium nitride.

The ab initio pseudopotential (PP) method within the generalized gradient approximation (GGA) has been used to investigate the electronic, elastic constants, and optical properties of zinc-blende GaN. An underestimated band gap along with higher DOS and squeezed energy bands around the fermi level is obtained. The d-band effect is briefly discussed for electronic band structure calculations. With the help of elastic constants, acoustic wave speeds are calculated in [100], [110], and [111] planes. The dielectric constant, refractive index, and its pressure coefficient are well illustrated. The effect of hydrostatic pressure is explicated for all these properties. The results of the present study are evaluated with the existing experimental and first-principle calculations.

The shift of the optical absorption band edge of ZnO/ZnS core/shell nanotube arrays beyond quantum effects

Unlike conventional investigations that focus on the manipulation of optical absorption band edge for a single componential material through quantum confinement effects, in this paper, we study the optical absorption properties of well-ordered ZnO/ZnS core/shell nanotube arrays. Our data point out that the profile of the absorbance spectrum of ZnO/ZnS nanotube arrays is determined by the two components and geometrical parameters of the nanostructure arrays. We find that both of the ZnO and ZnS show a decrease in the optical band gap with the increase in ZnS thickness and the diameter of the nanotube arrays, which is interestingly out of explanation from the material aspect. The subsequent finite-difference-time-domain simulations support such observations and illustrate that the geometrical and periodical parameters could also impact the optical absorption of the core/shell nanostructure arrays, even without concerning the quantum effects.

Highly-Ordered 3D Vertical Resistive Switching Memory Arrays with Ultralow Power Consumption and Ultrahigh Density

Resistive switching random access memories (RRAM) have attracted great scientific and industrial attention for next generation data storage because of their advantages of nonvolatile properties, high density, low power consumption, fast writing/erasing speed, good endurance, and simple and small operation system. Here, by using a template-assisted technique, we demonstrate a three-dimensional highly ordered vertical RRAM device array with density as high as that of the nanopores of the template (10(8)-10(9) cm(-2)), which can also be fabricated in large area. The high crystallinity of the materials, the large contact area and the intimate semiconductor/electrode interface (3 nm interfacial layer) make the ultralow voltage operation (millivolt magnitude) and ultralow power consumption (picowatt) possible. Our procedure for fabrication of the nanodevice arrays in large area can be used for producing many other different materials and such three-dimensional electronic device arrays with the capability to adjust the device densities can be extended to other applications of the next generation nanodevice technology.

Structural, elastic constant, and vibrational properties of wurtzite gallium nitride: a first-principles approach.

Perdew-Wang proposed generalized gradient approximation (GGA) is used in conjunction with ultrasoft pseudopotential to investigate the structural, elastic constant, and vibrational properties of wurtzite GaN. The equilibrium lattice parameters, axial ratio, internal parameter, bulk modulus, and its pressure derivative are calculated. The effect of pressure on equilibrium lattice parameters, axial ratio, internal parameter (u), relative volume, and bond lengths parallel and perpendicular to the c-axis are discussed. At 52 GPa, the relative volume change is observed to be 17.8%, with an abrupt change in bond length. The calculated elastic constants are used to calculate the shear wave speeds in the [100] and [001] planes. The finite displacement method is employed to calculate phonon frequencies and the phonon density of states. The first- and second-order pressure derivative and volume dependent Gruneisen parameter (γ(j)) of zone-center phonon frequencies are discussed. These phonon calculations calculated at theoretical lattice constants agree well with existing literature.

Large tunable luminescence by Mn(II) aggregates in Mn-doped ZnS nanobelts

Tunable emission from the visible to infrared region in II–VI semiconductor nanostructures makes them ideal candidates for the development of optoelectronic devices. In this study, Zn1−xMnxS (x = 0.01–0.15%) nanobelts (NBs) were prepared via the chemical vapor deposition (CVD) method. The as-grown NBs were investigated by XRD and electron paramagnetic resonance (EPR). A significant lower angle shift was observed in the XRD spectra, which indicated the incorporation of Mn ions. A hyperfine interaction constant A of 68.6 G obtained from the EPR spectra confirmed that Mn2+ ions were successfully incorporated into the ZnS matrix. For higher Mn concentrations, the broadening of the EPR profile was attributed to the aggregation of Mn2+ ions. Moreover, successful Mn-ion doping in individual ZnS NBs was itentified by SEM–EDS and Raman scattering analysis. Raman spectroscopy studies revealed a red-shift at the LO phonons, confirming the presence of Mn ions in ZnS NBs. Room-temperature photoluminescence (PL) showed that the Mn concentration plays an important role in tuning the emission from 452 nm to 877.6 nm (blue to near-infrared:NIR); whereby, up to 15% Mn, PL showed emissions are centered at 447, 535, 580.7, 651.1, and 877.6 nm. Herein, the first two peaks were assigned to anti-ferromagnetic coupling of 4 Mn ions, and the interaction of 2 Mn ions with stack faults in ZnS NBs. The next peak was from the typical d–d transition (4T1(4G) → 6A1(6S)) of Mn2+, and the last two peaks were assigned to the aggregate made up of 2 Mn ions and (MnS)5 cluster-related emission with ferromagnetic coupling. NIR emission was also detected from the 10% Mn-doped CdS NBs. To the best of our knowledge, herein, NIR emission was observed for the first time in ZnS nanostructures. These kinds of nanomaterials may have potential applications in photovoltaics, telecommunications, and remote sensing.

Efficient biosensing through 1D silver nanostructured devices using plasmonic effect

The current work explores the excitation of surface plasmon polaritons (SPPs) on a one dimensional (1D) silver nano-grating device, simulated on glass substrate, which can sense a very small change in the refractive index of an analyte adjacent to it. The most recent modeling technique finite element analysis is applied in this work by using a COMSOL RF module. The models of 1D grating devices of different slit widths with fixed periodicity and film thickness are simulated. The data is collected and then used to study higher refractive index unit per nanometer (RIU/nm) as well as the effect of the widths of the slits on the RIU. A number of investigations are done by the simulated data, like a dip in the transmission spectra of p-polarized light. This dip is due to SPP resonance with the variation of slit width. Furthermore, the most fascinating part of the research is the COMSOL modeling that provides an opportunity to look into factors affecting higher RIU/nm, while visualizing the cross-sectional view of the grating device and strong electric field enhancement at the surface of the metallic device. When the slit width is almost equal to half of the periodicity of the grating device, SPP resonance increases and it is at maximum for the slit width equal to two-thirds of the periodicity, because the coupling efficiency is at maximum.