Search

The purpose of this article is to examine the server activation policy (SAP) in a multi-server queuing-inventory system (MQIS). The queue has a total of c number of multi-threshold stages as well as c-homogeneous servers. The activation of each server begins one by one if there is an adequate queue length and inventory in the system; otherwise, they remain idle. The server deactivation process continues until the queue length exceeds the manageable level (predetermined stages) or there is insufficient stock. In addition, when we assume the length of the two successive threshold levels is one, the server activation policy model becomes a regular multi-server model. The Neuts matrix geometric approach is used to discuss the stability condition, stationary probability vector. The Laplace–Stieltjes transform (LST) is used to analyse the waiting time distributions of the queue and orbital customers. Additionally, significant system performance metrics and sensitivity analysis are used to investigate the effects of various parameters and cost values. In the comparative result between the server activation model (SAM) and without the server activation model (WSAM) on the expected total cost, we obtain the minimised cost in the SAM. Moreover, the results are obtained by assuming that the length of the intervals between the two successive threshold levels is to be taken into account as the non-uniform length. The expected inventory level, reorder rate, and waiting time of a customer in the waiting hall and orbit were explored numerically by the parameter analysis. [ABSTRACT FROM AUTHOR]

The use of a Markovian inventory system is a critical part of inventory management. The purpose of this study is to examine the demand for two commodities in a Markovian inventory system, one of which is designated as a major item (Commodity-I) and the other as a complimentary item (Commodity-II). Demand arrives according to a Poisson process, and service time is exponential at a queue-dependent rate. We investigate a strategy of (s , Q) type control for commodity-I with a random lead time but instantaneous replenishment for commodity-II. If the waiting hall reaches its maximum capacity of N, any arriving primary client may enter an infinite capacity orbit with a specified ratio. For orbiting consumers, the classical retrial policy is used. In a steady-state setting, the joint probability distributions for commodities and the number of demands in the queue and the orbit, are derived. From this, we derive a waiting time analysis and a variety of system performance metrics in the steady-state. Additionally, the physical properties of various performance measures are evaluated using various numerical assumptions associated with diverse stochastic behaviours. [ABSTRACT FROM AUTHOR]

This paper deals with an integrated and interconnected stochastic queuing-inventory system with a fresh item, a returned item, and a refurbished item. This system provides a multi-type service facility to an arriving multi-class customer through a dedicated channel. It sells fresh and refurbished items, buys used items from customers, refurbishes the used items for resale, and provides a repair service for defective items. The assumption of purchasing a used item from the customer and allowing them to buy a fresh item is a new idea in stochastic queuing-inventory modeling. To do so, this system has four parallel queues to receive four classes of customers and five dedicated servers to provide a multi-type service facility. Customers are classified according to the type of service they require. Each class of arrival follows an independent Poisson process. The service time of each dedicated server is assumed to be exponentially distributed and independent. This system assumes an instantaneous ordering policy for the replenishment of a fresh item. In the long run of this considered system, the joint probability distribution of the seven-dimensional stochastic process, significant system performance measures, and the optimum total cost are to be derived using the Neuts matrix geometric technique. The main objective of the system was to increase the occurrence of all kinds of customers by providing a multi-type service facility in one place. Buying a used item is unavoidable in an emerging society because it helps form a green society. Furthermore, the numerical result shows that the assumption of a system that allows a customer to sell their used item and purchase a new item will increase the number of customers approaching the system. [ABSTRACT FROM AUTHOR]

We report the determination of free-electron concentration and mobility of free-standing GaN nanowires (NWs) by line shape analysis of the coupled longitudinal optical phonon-plasmon Raman modes (L+). The E2high phonon mode at 566.9 cm-1 with a sharp linewidth of 2.8 cm-1 indicates strain free NWs with high crystalline perfection. The lattice temperature of the NWs was varied between 313 and 472 K by varying the excitation laser beam power. For unintentionally doped samples at room temperature, an average electron concentration and mobility of strain free NWs were found to be ∼2×1017 cm-3 and 460 cm2/V s, respectively. We have shown that the electron concentration does not change significantly over a temperature range between 313 and 472 K. The electron mobility decreases at high temperatures, in agreement with literature data for compact layers. For Si-doped NWs, the L+ phonon peak is strongly upshifted indicating a higher free-carrier concentration of about 1×1018 cm-3. Asymmetric broadening observed at the lower frequency side of the L+ phonon peak might be ascribed to the enhancement in surface optical modes due to the high surface-to-volume ratio of NWs. [ABSTRACT FROM AUTHOR]

The role of AlxGa1-xN buffers in the control of residual strain in GaN epitaxial layers grown on 6H-SiC (0001) substrates by molecular-beam epitaxy was investigated. The initial GaN layer on the AlxGa1-xN (x=0%–10%) buffer nucleates in two-dimensional form, which promotes a step-flow growth mode in subsequently grown GaN layers. As the Al content in the AlxGa1-xN (x∼20%) buffer was increased, GaN began to nucleate as incoherent polygonal islands, coalescing as the thickness increased to 15 nm. The overall residual strain induced in GaN is tensile ([variant_greek_epsilon]xx) for GaN grown directly on SiC and compressive (-[variant_greek_epsilon]xx) for GaN grown using an AlGaN buffer. The stiffness coefficient (-2C13/C33) of GaN on the AlxGa1-xN (x∼10%) buffer was estimated to be -0.53 assuming that the defect-induced hydrostatic stress of unstrained GaN (c0/a0) was constant. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) GaN nucleation on a gallium (Ga) induced 3×3-SiC (0001) surface was achieved by molecular-beam epitaxy. The Ga adsorbate on SiC (0001) revealed well-ordered [square_root_of_3]×[square_root_of_3]-R30° and 3×3 surface reconstructions with respect to Ga adatom coverage. The 3×3 surface was found to be highly reactive toward 2D GaN nuclei. This enhances the surface mobility of impinging adatoms during GaN growth, which promotes a step-flow growth mode. On the [square_root_of_3]×[square_root_of_3]-R30° surface, polygonal Stranski–Krastanov islands formed during the initial stages, coalescing as thickness increased. The GaN growth kinetics was found to depend on the Ga atomistic process of the reconstructed SiC (0001) surfaces. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We discuss the growth and transport properties of two-dimensional electron gas confined at the AlN/GaN heterointerface grown by plasma-assisted molecular-beam epitaxy. The sheet carrier density was found to be highly dependent on the barrier thickness of AlN grown on a doped or undoped GaN layer. The carrier sheet density monotonously increased from 0.8×10[sup 12] to 1.1×10[sup 13] cm[sup -2] as the AlN barrier thickness on a semi-insulating GaN layer increased from 15 to 25 Å due to spontaneous and piezoelectric polarization. An AlN barrier of 35 Å in thickness grown on n-GaN gave the highest sheet carrier density, which was 4.3×10[sup 13] cm[sup -2]. In thin AlN barrier layers, the sheet carrier density was low due to surface depletion. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the fabrication of one dimensional Silicon nanowires (Si NWs) using p-Si (100) substrate through facile two step metal assisted chemical etching (MACE) approach. The evolution of structural and optical properties of Si NWs by etching Si substrate was studied as a function of hydrogen peroxide (H 2 O 2 ), a strong oxidation agent. The length of the NWs increased linearly with the H 2 O 2 concentrations and reached maximum of 51 μm for etching of 60 min. The merits of metal free Si NWs as photocathode in the photoelectrochemical (PEC) neutral water splitting under the visible light was investigated. The performance of the photocathode highly depends on the morphology of Si nanostructure. A high density and well separated Si NWs fabricated by 0.6 M of H 2 O 2 results in maximum photocurrent density of 6 mA cm −2 with applied bias photocurrent conversion (ABPE) efficiency of 1.1% under visible light illumination. [ABSTRACT FROM AUTHOR]

A continuous review (s,S) inventory system at a service facility with finite homogeneous sources of demands and retrial is analysed. The lifetime of each item is assumed to be exponential. Before items are delivered to the customers, some basic service on the item must be performed. It is known as a regular or main service. The service may get interrupted according to a Poisson process and it restarts after an exponentially distributed time. If the server is idle at the time of arrival of a customer and the inventory level is positive, then the service begins immediately. After the completion of regular service, a customer may either abandon the system forever or demand for a second service from the same server, which is multi-optional. If any arriving customer finds that the server is busy or inventory level is zero, he/she either enters into the orbit with probability p or balks (does not enter) with probability 1-p. The stationary distribution of the number of customers in the system, server status and the inventory level is obtained by the matrix method. The Laplace-Stieltjes transform of the waiting time of the tagged customer is derived. Various system performance measures are derived and the total expected cost rate is computed under a suitable cost structure. A numerical illustration is given. [ABSTRACT FROM AUTHOR]

We report the combined effect of plasmonic far-field and improved hole injection towards enhancing the performance of OLEDs by the incorporation of gold and silver (Au and Ag) nanoparticles at the interface of anode/hole transport layer (HTL). The metal nanoparticles incorporated devices facilitate improved hole injection into HTL owing to the shift in vacuum level of anode resulting in three fold enhancement of current density in OLEDs. Hole only devices made with Au and Ag nanoparticles at anodes offer meliorated hole injection than the reference anode due to the reduced injection barrier. X-ray photoelectron spectroscopy analysis further corroborates the alteration of work function of metal nanoparticles infused ITO by exhibiting an abrupt shift in In 3d and Sn 3d photoelectron energy levels. In addition, time resolved photoluminescence spectra reveal that the interaction of far-field plasmons with the device emission accelerates the luminescence of OLEDs further. [ABSTRACT FROM AUTHOR]

We report selective area growth of large area homogeneous Bernal stacked bilayer epitaxial graphene (BLEG) on 4H-SiC (0001) substrate by electron-beam irradiation. Sublimation of Si occurs by energetic electron irradiations on SiC surface via breaking of Si-C bonds in the localized region, which allows the selective growth of graphene. Raman measurements ensure the formation of homogeneous BLEG with weak compressive strain of -0.08%. The carrier mobility of large area BLEG is ~5100 cm² V-1 s-1 with a sheet carrier density of 2.2 x 1013 cm-2. Current-voltage measurements reveal that BLEG on 4H-SiC forms a Schottky junction with an operation at mA level. Our study reveals that the barrier height at the Schottky junction is low (~0.58 eV) due to the Fermi-level pinning above the Dirac point. [ABSTRACT FROM AUTHOR]

We investigate the role of growth temperature on the optimization of lattice-matched In0.17Al0.83N/GaN heterostructure and its structural evolutions along with electrical transport studies. The indium content gradually reduces with the increase of growth temperature and approaches lattice-matched with GaN having very smooth and high structural quality at 450ºC. The InAlN layers grown at high growth temperature (480ºC) retain very low Indium content of ∽ 4 % in which cracks are mushroomed due to tensile strain while above lattice matched (>17%) layers maintain crack-free compressive strain nature. The near lattice-matched heterostructure demonstrate a strong carrier confinement with very high two-dimensional sheet carrier density of ∽2.9 × 1013 cm-2 with the sheet resistance of ∽450 Ω/ at room temperature as due to the manifestation of spontaneous polarization charge differences between InAlN and GaN layers. [ABSTRACT FROM AUTHOR]

The morphological evolution of ZnO nanostructures grown under various argon sputtering pressures and substrate temperatures has been systematically investigated. A surface phase diagram depicting compact two-dimensional thin films to various types of one-dimensional structures as a function of pressure and temperature is constructed. Structural studies of ZnO nanostructures reveal the preferential orientation along the -axis of a hexagonal wurtzite crystal structure with a highly crystalline nature. However, the c as-grown ZnO nanostructures slightly experience compressive strain, which increases with the argon sputtering pressure. Exciton recombination and point defects have been extensively analyzed by temperature-dependent photoluminescence spectroscopy. The observation of donor-bound exciton emission and its replicas reveals the high optical quality of the nanostructures. Nevertheless, the observed visible emission indicates the presence of point defects which significantly depend on the deposition pressure. The characteristic visible emission bands at 2.28 and 2.02 eV provide strong evidence for the existence of oxygen vacancies and interstitial sites in ZnO nanostructures irrespective of growth temperature and pressure. [ABSTRACT FROM AUTHOR]

We report an intrinsic ferromagnetism in vertical aligned GaN nanowires (NW) fabricated by molecular beam epitaxy without any external catalyst. The magnetization saturates at ~0.75 × emu/gm with the applied field of 3000 Oe for the NWs grown under the low-Gallium flux of 2.4 × 10-8 mbar. Despite a drop in saturation magnetization, narrow hysteresis loop remains intact regardless of Gallium flux. Magnetization in vertical standing GaN NWs is consistent with the spectral analysis of low-temperature photoluminescence pertaining to Ga-vacancies associated structural defects at the nanoscale. [ABSTRACT FROM AUTHOR]

We report the fabrication of quasi-aligned GaN nanowires (NWs) on Si(111) substrate by chemical vapor deposition using Ni as a catalyst. The structural and composition analysis of Ni-catalyst on the apex of the GaN NWs were investigated using high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. The catalyst contains only Ni-Ga alloy with the composition of ~66:33 having NiGa phase. GaN NWs exhibit wurtzite structure without any amorphous sheath layer or cubic inclusions, where the catalyst contains the mixture of both the crystalline and amorphous phases. During growth, the nitrogen radicals are expected to migrate on the surface of the catalytic droplet to incorporate into the growing lattice via the solid-liquid interface due to poor solubility of N in Ni, which forbids the alloying of nitrogen with Ni. Temperature-dependent photoluminescence reveals that the intensity of donor-bound exciton (DX) peak consistently increases with a blue shift as the temperature decreases. The DX peak is centered at 3.467 eV for 10 K. Interestingly, yellow band, the characteristic nature of defects-induced luminescence, is absent in Ni-catalytic-assisted growth of GaN NWs. [ABSTRACT FROM AUTHOR]

Abstract: Undoped vertically aligned ZnO nanowires have been grown on silicon (111) substrates by the rf magnetron sputtering technique without metal catalyst. The diameter, length and density distributions of the nanowires have been analyzed with respect to the different growth durations. The tapering of the nanowires is observed for the growth duration of 120min owing to the insufficient adatoms on the growth front. In the X-ray diffraction pattern, the dominant (002) peak with narrow full width at half maximum (FWHM) of ZnO nanowires indicates the c-axis orientation and high crystalline nature with hexagonal wurtzite crystal structure. The narrow FWHM of E 2 low and E 2 high phonon modes (1.4 and 9.1cm−1) provide an additional evidence for the high crystalline and optical properties of the nanowires. The low temperature photoluminescence spectra are dominated by the green emission at∼2.28eV induced by the electron transitions between shallow donor and acceptor energy levels. [Copyright &y& Elsevier]

Abstract: Hetero junction organic light emitting device consists of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)/tris-(8-hydroxyquinoline)aluminum (Alq3)/LiF/Al were fabricated on indium tin oxide coated corning glass substrate under various Alq3 deposition rates. We demonstrate the significance of deposition rate on the morphology of Alq3 layers and subsequently generation of photons in TPD/Alq3 hetero junction. The pin holes formed on the surface of Alq3 at low deposition rates are responsible for exciton quenching. The device fabricated with the deposition rate of 3.0Å/s exhibits the maximum luminescence and maximum current efficiency of 1.02×104 cd/m2 and ∼5cd/A, respectively, at 15V owing to the efficient recombination of excitons in Alq3 emissive layer. [Copyright &y& Elsevier]

Abstract: We report the growth and electron transport studies of two-dimensional electron gases confined at the lattice-matched In0.17Al0.83N/GaN heterostructure on GaN templates by plasma-assisted molecular beam epitaxy. The two-dimensional sheet carrier density, 2.68×1013 cm−2, at room temperature is the manifestation of spontaneous polarization charge differences between the InAlN and the GaN layers. The heterostructure shows the Hall mobilities of 1080 and 3330cm2/Vs at 300 and 20K, respectively. The variable temperature Hall measurements in the range of 20–300K reveal that the mobility and sheet carrier density have been nearly independent of temperature below about 150K, a typical behavior of 2DEG structures. The achievement of high mobility can be attributed to the improvement of InAlN epitaxial growth conditions and reduced alloy disorder scattering of carriers. [Copyright &y& Elsevier]

We carry out the surface potential (SP) measurements of Si-doped InN nanorods (NRs) grown by plasma-assisted molecular beam epitaxy. Photoluminescence and photoemission spectroscopic studies reveal that the Si-doped InN nanorods possess surface electron accumulation. To estimate the SP value of the InN nanorods, a contact potential difference is measured using Kelvin probe force microscopy (KPFM). In order to avoid the influence of the surface adsorbed species, KPFM measurements were carried out at a high vacuum condition of ∼7.5 × 10−7 mbar. The SP value of the Si-doped InN nanorods is found to depend on the size of nanorods. The size-dependent SP value of the Si-doped InN nanorods is attributed to the variation in the downward surface band bending caused by the change in the sheet carrier density of surface electron accumulation. The change in surface band bending is the result of the variation in the free-electron distribution with a size of the NRs. [ABSTRACT FROM AUTHOR]

We report the structural and surface morphologies of GaN layer directly grown on 6H-SiC (0 0 0 1) substrates by plasma-assisted molecular beam epitaxy. The structural properties of the GaN layers grown under Ga-rich conditions have been strongly influenced by the surface oxide-desorption through Ga-metal deposition and flash-off at high temperature. The resulting AFM surface morphology exhibits atomic steps with <5 A˚ rms surface roughness. The control of Ga-adatom migration governs the surface morphology of the grown layers, the atomic step features are realized with sufficient surface migration of Ga for the available N-radicals. The excellent structural quality of these layers is manifested by the narrow full-width at half-maximum of X-ray rocking curve (<124 arcsec) measured along the ω (0 0 0 2) diffraction. [Copyright &y& Elsevier]

An intrinsic property of vertically aligned InN nanowire (NW) ensembles have been investigated by analysis of coupled longitudinal optical (LO) phonon mode using μ-Raman scattering. Spectra were recorded in backscattering geometries in parallel and perpendicular to the axis of the NWs. The width of surface accumulation layer is estimated from the LO phonon peak intensity ratios. The carrier concentration is extracted to be 6.7×1016 cm-3. The pronounced peak at 627.2 cm-1 is related to the interaction of phonons with surface electrons. The surface charge density, Nsc is calculated to be ∼2.55×1013 cm-2 which provides surface accumulation field strength of 5.5 Mv/cm. [ABSTRACT FROM AUTHOR]

Low-dislocation-density GaN layers have been grown on 6H–SiC(0001) substrates by molecular-beam epitaxy using high-density (∼4×1011 cm-2) self-assembled Stranski–Krastanov GaN nanoislands buffer. The density of dislocations determined from hot-wet chemical etching and atomic force microscopy show that the insertion of coherent nanoislands as a buffer reduces the defect migration from the interface to the GaN epitaxial layers. The dislocation density is dramatically dropped to ∼107 cm-2 in GaN layers grown on coherent nanoislands as compared to ∼109 cm-2 in the typical GaN layers grown on the AIN buffer. [ABSTRACT FROM AUTHOR]

We report the fabrication of self-assembled coherent GaN nanoislands on Ga-adsorbed [Square_Root]3×[Square_Root]3 R30° 6H–SiC(0001) surfaces via Stranski–Krastanov (SK) growth mode by molecular-beam epitaxy at 760 °C. The initial GaN deposition reveals a stable two-dimensional growth (2D) mode under Ga-rich growth conditions (Ga/N>1), as evidenced by the variation of in-plane misfit strain (Δa/a0). We show that above ∼2.2 monolayer (ML) surface coverage, the 2D layer spontaneously transformed into SK islands by the accommodation of elastic strain in the epitaxial lattice misfit under a vacuum. The SK islands density is found to be ∼4×1011 cm-2 and the mean height and diameter is 2±0.5 nm and 20±5 nm for 3.2 ML surface coverage, respectively. [ABSTRACT FROM AUTHOR]

In this work, a single server implements a two-commodity inventory queueing system. We assume that both commodities have a finite capacity. Customers arrive by a Markovian Arrival Process, there is a need for a single item, and either or both types of commodities are required, and this requirement is modeled using certain probabilities. The lead times are exponentially distributed, and the service times have a PH distribution. We use matrix analytical techniques to investigate the queueing inventory system and adopt an (s, S)-type replenishment policy that is dependent on the type of commodity. In the steady state, the joint and individual probability distribution of the Esystem, inventory level, and server status is obtained. A few significant performance measures are attained. Our mathematical concept is then illustrated with a few numerical examples. [ABSTRACT FROM AUTHOR]

In recent times, we have encountered new situations that have imposed restrictions on our ability to visit public places. These changes have affected various aspects of our lives, including limited access to supermarkets, vegetable shops, and other essential establishments. As a response to these circumstances, we have developed a continuous review retrial queueing–inventory system featuring a single server and controlled customer arrivals. In our system, customers arriving to procure a single item follow a Markovian Arrival Process, while the service time for each customer is modeled by an exponential distribution. Inventories are replenished according to the (s , Q) reordering policy with exponentially distributed lead times. The system controls arrival in the waiting space with setup time. The customers who arrive at a not allowed situation decide to enter an orbit of infinite size with predefined probability. Orbiting customers make retrials to claim a place in the waiting space, and their inter-retrial times are exponentially distributed. The server may experience essential interruption (emergency situation) which arrives according to Poisson process. Then, the server goes for an emergency vacation of a random time which is exponentially distributed. In the steady-state case, the joint probability of the number of customers in orbit and the inventory level has been found, and the Matrix Geometric Method has been used to find the steady-state probability vector. In numerical calculations, the convexity of the system and the impact of F-policy and emergency vacation in the system are discussed. [ABSTRACT FROM AUTHOR]

Abstract We report the fabrication of hybrid Si nanowires @ g-C 3 N 4 nanosheets based photocathode using metal assisted chemical etching and facile liquid exfoliated process. The g-C 3 N 4 nanosheets on Si nanowires form hybrid heterojunction photocathode, which exhibits an enhanced photon induced water reduction activity enabling higher photocurrent density of 22 mA cm−2 with applied bias photocurrent conversion efficiency of 4.3% under visible light irradiation. The onset potential of cathodic photocurrent is positively shifted from 41 to 420 mV vs. RHE with the short circuit current density, J sc of 0.50 mA cm−2 owing to superior charge transport in hybrid photocathode as compared to pristine Si nanowires for hydrogen evolving reaction at pH∼7. The electrochemical impedance spectroscopy measurement elucidates the interface layer of g-C 3 N 4 nanosheets form hybrid heterojunction with Si nanowires that result significant increment in solar water reduction activity owing to low charge transferred resistance with high life time of excited electrons in conduction band. This strategy may open to design a new low cost stable hybrid heterostructure photocathode for solar induced water reduction. Graphical abstract Image 1 Highlights • Si NWs@g-C 3 N 4 NSs photocathode is fabricated using facile technique. • Hybrid photocathode shows the enhanced PEC water reduction performance. • A maximum photocurrent density of 22 mA cm−2 is achieved. • Exhibits low charge transfer resistance with high life time of excited electrons. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Graphene oxide (GO) resistive memory performances have improved by hydrogen plasma. • Increased on/off ratio demonstrated in GO resistive memory by H-plasma. • H-plasma establish thin interfacial layer at GO/Al for enhanced electron transport. • Oxygen reduction in GO corroborated with Raman, XPS and Impedance spectroscopy studies. Abstract We report the improved performance of graphene oxide (GO) based resistive random-access memory devices (ReRAM) through mild hydrogen plasma treatment. The threshold voltage of the ReRAM device is successfully reduced from 2.6 to 1.8 V together with an enhanced ON/OFF ratio of 103 with the help of hydrogen plasma treated GO (HGO). Significantly, the rise of a weak 2D band in Raman spectrum of HGO reveals the mild reduction of GO by H 2 plasma. The concurrent removal of oxygen moieties on basal plane and on edges of graphitic network in GO by the virtue of H 2 plasma is argued to contribute enhanced performance in ReRAM devices. The significant diminution of oxygen moieties on GO lattice in HGO infused device reduces the insulating barrier formed at Al/GO interface which reinforced the electron transport. The effective selection of plasma treatment is found to be one of the proficient routes to enhance the storage capabilities of GO based resistive memory devices. [ABSTRACT FROM AUTHOR]

Ytterbium doped langbeinite K 2 Ti 1.887 Yb 0.113 (PO 4 ) 3 (KTYP) single crystals were grown using high temperature molten salt flux growth method. Inclusion-free KTYP crystals with sizes up to 3×3×3 mm 3 were attained using K 6 P 4 O 13 molten flux. The complete melting point of solute and solvent is above at 1223 K. Langbeinite phase KTYP crystals are growing in higher concentration of Yb 2 O 3 in flux solution. KTYP emits a strong cooperative blue emission centered at 488 nm owing to Yb-Yb pairs under 980 nm laser excitation. To the best of our knowledge, phosphate based langbeinite crystal found exhibit cooperative upconversion emission at ~488 nm. [ABSTRACT FROM AUTHOR]

We report a stable bulk photovoltaic effect in [KNbO 3 ] 0.9 -[BaCo 1/2 Nb 1/2 O 3–δ ] 0.1 (KBCNO-91) solid solution as a result of the light-induced electric field in the orthorhombic phase of KBCNO. Introducing Ba2+ and Co3+ ions in the host lattice of perovskite solid solution, the bandgap can be tuned from 3.2 to 1.59 eV. A photovoltaic cell consists of a 43 nm thin KBCNO-91 perovskite oxide semiconductor sandwiched between the metal electrodes evoke open-circuit voltage (V OC) of >1.9 V, above the bandgap with short-circuit current of ∼1 nA at no external bias (0 V). The fabrication of a two-dimensional ferroelectric solid solution semiconductor with a narrow bandgap of ∼1.59 eV enables the conversion of visible photons into electrical energy in a compact electrode configuration. The device retains its stability for over one year and is expected to be a potential candidate for the next generation of photovoltaic cells. [Display omitted] • Ferroelectric [KNbO 3 ] (1-x) -[BaCo 1/2 Nb 1/2 O 3-δ ] x solid-solution film used to fabricate the solar cell. • The photovoltage is exceeding the bandgap of the [KNbO 3 ] (1-x) -[BaCo 1/2 Nb 1/2 O 3-δ ] x. • The ferroelectric [KNbO 3 ] (1-x) -[BaCo 1/2 Nb 1/2 O 3-δ ] x thin film device shows stable photocurrent of 1 × 10−9A. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) initial nucleation kinetics by the influence of SiC(0 0 0 1)Si surface structure has been investigated. The Ga induced √3×√3 R30° and 3×3 surface reconstructions are found to be more efficacious for GaN growth. During the initial stage of GaN/4H-SiC(0 0 0 1)Si growth by molecular-beam epitaxy, coherent polygon islands grow wide (∼40 nm) along the lateral directions. These coherent islands develop 2D growth through early coalescence as evidenced by the in situ reflection high-energy electron diffraction observation. The control of Ga-adatom migration and the adsorption of 1/3 and 1 monolayer (ML) of Ga-adatom govern the surface morphology of the GaN layers. The bulk surfaces of (1×1) and (2×1) introduces incoherent nuclei, resulting in a delay of GaN coalescence, exhibits rough growth front and poor surface morphology. [Copyright &y& Elsevier]

In the present work, the effect of transition metals (Ni, Fe, Co) doping on 2-dimensional (2D) molybdenum disulfide (MoS 2) nanosheets for electrocatalytic hydrogen evolution reaction (HER) was explored. A simple and cost-effective hydrothermal method was adopted to synthesis transition metals doped MoS 2 nanosheets. The morphological and spectroscopic studies evidence the formation of high-quality MoS 2 nanosheets with the randomly doped metal ions. Notably, the Ni–MoS 2 displayed superior HER performance with an overpotential of −0.302 V vs. reversible hydrogen electrode (RHE) (to attain the current density of 10 mA cm−2) as compared to the other transition metals doped MoS 2 (Co–MoS 2 , Fe–MoS 2). From the Nyquist plot, superior charge transport from the electrocatalyst to the electrolyte in Ni–MoS 2 was realized and confirmed that Ni doping provides the necessary catalytic active sites for rapid hydrogen production. The stable performance was confirmed with the cyclic test and chronoamperometry measurement and envisaged that hydrothermally synthesized Ni–MoS 2 is a highly desirable cost-effective approach for electrocatalytic hydrogen generation. [Display omitted] • This work explores the effect of transition metal doping on MoS 2 nanosheets for HER. • Ni–MoS 2 displayed superior HER performance with an over-potential of −0.302 V vs. RHE. • Ni doping provides the necessary catalytic active sites for rapid hydrogen production. • Chronoamperometry measurement shows a stable performance of Ni–MoS 2 nanosheets. [ABSTRACT FROM AUTHOR]

We report the electron transport properties of epitaxial graphene (EG) grown on 4H-SiC (0001) by low energy electron-beam irradiation. As-grown EG (AEG) on SiC interface exhibits rectifying current-voltage characteristics with a low Schottky barrier (SB) of 0.55 ± 0.05 eV and high reverse current leakage. The SB of AEG/SiC junction is extremely impeded by the Fermi level pinning (FLP) above the Dirac point due to charged states at the interface. Nevertheless, a gentle hydrogen intercalation at 900 °C enables the alleviation of both FLP and carrier scattering owing to the saturation of dangling bonds as evidenced by the enhancement of SB (0.75 6 0.05 eV) and high electron mobility well excess of 6000 cm² V-1 s-1. [ABSTRACT FROM AUTHOR]

We report the observation of Raman silent modes of B 1 low (276 cm −1 ) and B 1 high (582 cm −1 ) in vertically aligned ZnO nanorods due to the breakdown of translational symmetry. The structural studies reveal the high crystalline nature of the ZnO nanorods on the lattice mismatched silicon substrates. The dominant donor bound exciton emission and the phonon replicas signify the good quality of the nanorods which substantiate that the anomalous Raman modes could not be attributed to the intrinsic point defects. Further, our results show that the observed silent modes of wurtzite-ZnO become Raman active due to the breakdown of the wave-vector selection rule by loss of translational symmetry induced by nanorods geometry. [ABSTRACT FROM AUTHOR]

This paper explores the random environment with two classes of suppliers and impulse customers. The system's greatest inventory size is S, and it has an infinitely large orbit. In this case, there are two categories of suppliers: temporary suppliers and regular suppliers. Whenever the inventory approaches r, we place on order Q 1 (= S − r ) unit items to a temporary supplier. Similarly, when the inventory level drops to s (< Q 1 < r ), we place an order for Q 2 (= S − s > s + 1 ) units of items to our regular supplier. Two types of suppliers' lead times are considered to be exponentially distributed. Here, the customers who arrive from different states of the random environment (RE) are followed by the Markovian arrival process. If there is no inventory in the system when the customer arrives, they are automatically assigned to an orbit. The model was examined in steady state by using the matrix-analytic approach. Finally, the numerical examples for our structural model are discussed. [ABSTRACT FROM AUTHOR]

In this paper, we consider a continuous review perishable inventory system with a service facility having two heterogeneous servers, server 1 and server 2 , and the demands originate from a finite population of N sources. In such systems, the customers demand is satisfied only after some service is completed by any one of the two servers. Compared to most inventory models in which inventory is depleted at the demand rate, here it is depleted at the rate that the service is completed. It is assumed that server 1 is perfectly reliable and server 2 is subject to interruptions. The interrupted server is repaired at an exponential rate. The primary customer who finds either both servers are busy or there is no item (excluding those in service) in the stock, enters into an orbit with probability p and is lost forever with probability 1- p. A retrial customer in the orbit, finding the stock level (excluding those in service) is zero or both servers are busy, returns to the orbit with probability q and is lost forever with probability 1- q. The interval between two successive repeated attempts is exponentially distributed. The items of inventory have exponential life times. As and when the on-hand inventory level drops to a prefixed level s(⩾ 2), an order for Q(= S - s > s) units is placed. The ordered items are received after a random time which is distributed as exponential. The joint probability distribution of the number of customers in the orbit and the inventory level is obtained in the steady state case. The measures of system performance in the steady state are derived and the total expected cost rate is also calculated. The results are illustrated numerically. [ABSTRACT FROM AUTHOR]

The catalytic reactivity and photoactivity of WO 3 and BiVO 4 oxide semiconductors have general obstacles as electrodes in emergent photo-electrochemical (PEC) hydrogen evolution applications. The present work comprises the integration of photocatalyst with wide visible photon absorption material which is vital for hydrogen evolution in photo-electrocatalytic water splitting. Herein, the 1D WO 3 NWs have been integrated with stable water oxidation photocatalysts of BiVO 4 and Bi 2 S 3 as a photoanode (Bi 2 S 3 /BiVO 4 /WO 3) for photoelectrochemical hydrogen evolution reactions. The morphological variations in the Bi 2 S 3 /BiVO 4 /WO 3 heterostructure manifest catalytic activity and rapid charge transfer characteristics owing to band alignment and a wide range of visible photon absorption. The optimized Bi 2 S 3 /BiVO 4 /WO 3 multidimensional photoanode accomplishes a superior photocurrent density of 1.52 mA/cm2, a seven-fold higher than pristine WO 3 photoanode counterpart (0.2 mA/cm2) at 1 V vs. RHE. A prodigious lowest onset potential of −0.01 V vs. RHE) has been achieved which enables very high solar to hydrogen conversion. The photoelectrode with entangled morphology such as nanosheets, nanocrystals and nanorods expanded their surface to volume ratio having enhanced catalytic performance. The hybrid photoanodes have demonstrated the lowest charge transfer resistance of 360 Ohm/cm2 with a 7-fold rise in hydrogen evolution performance. The resultant triadic Bi 2 S 3 /BiVO 4 /WO 3 heterostructure appeared to be an emerging stable photo-electro catalyst for hydrogen evolution applications. [Display omitted] • A multidimensional Bi 2 S 3 /BiVO 4 /WO 3 is prepared by hydrothermal and SILAR method. • The hetero-structure upholds photo-excitation and enhances carriers' kinetics. • The open triadic structure improves the hydrogen evolution. • A type II band alignment in Bi 2 S 3 /BiVO 4 /WO 3 hetero-structure is proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The ex-situ surface functionalization in ZnO:Fe nanostructures by Tri-n-butylamine. [•] Enhancement of ferromagnetism in ZnO:Fe by amine capping. [•] The amine capping treatment induced zinc vacancies. [ABSTRACT FROM AUTHOR]

Highlights: [•] ZnO nanostructures have been grown by rf magnetron sputter deposition. [•] A morphologically superior and coalescence free ZnO nanowires have been realized. [•] Argon pressure significantly alters the morphology of ZnO nanostructures. [•] ZnO nanostructures exhibit hexagonal wurtzite crystal structure. [•] A dominant D0X emission indicates the high optical quality of the nanostructures. [Copyright &y& Elsevier]

Molybdenum doped zinc oxide thin films were deposited on the Corning glass substrates pre-heated to 400°C by spray pyrolysis technique. The effect of molybdenum doping concentration (0–2 at.%) on the structural and optical properties of zinc oxide thin films was studied. X-ray diffraction analysis confirmed that the molybdenum doped ZnO films belong to the hexagonal crystal structure of ZnO. Atomic force microscopic studies revealed the effect of molybdenum doping on the surface morphology of these films. The 1 at.% Mo doped ZnO exhibited highest average transmittance of ∼87% in the visible region (400–800 nm). Optical bandgap energy of the ZnO and Mo doped ZnO films lies in the range of 3.28–3.33 eV. Annealing of the high resistive ZnO and Mo doped ZnO films at 400°C in vacuum for 60 min improved their resistivity. The minimum resistivity of 4.7 × 10−2 Ω cm and the maximum carrier concentration of 1.27 × 1019 cm−3 were achieved for 1 at.% Mo doped ZnO films. [ABSTRACT FROM PUBLISHER]

Niobium-doped tin oxide thin films were deposited on glass substrates by the chemical spray pyrolysis method at a substrate temperature of 400 °C. Effects of Nb doping on the structural, electrical and optical properties have been investigated as a function of niobium concentration (0-2 at.%) in the spray solution. X-ray diffraction patterns showed that the films are polycrystalline in nature and the preferred growth direction of the undoped film shifts to (200) for Nb-doped films. Atomic force microscopy study shows that the surface morphology of these films vary when doping concentration varies. The negative sign of Hall coefficient confirmed the n-type conductivity. Resistivity of ~4.3 × 10Ω cm, carrier concentration of ~5 × 10cm, mobility of ~25 cmVs and an average optical transmittance of ~70% in the visible region (500-800 nm) were obtained for the film doped with 0.5 at.% niobium. [ABSTRACT FROM AUTHOR]

Abstract: Zirconium doped zinc oxide thin films with enhanced optical transparency were prepared on Corning 1737 glass substrates at the substrate temperature of 400°C by spray pyrolysis method for various doping concentrations of zirconium (IV) chloride in the spray solution. The X-ray diffraction studies reveal that the films exhibit hexagonal crystal structure with polycrystalline grains oriented along (002) direction. The crystalline quality of the films is found to be deteriorating with the increase of doping concentration and acquires amorphous state for higher concentration of 8at.% in precursor solution. The average transmittance for 5at.% (solution) zirconium doped ZnO film is significantly increased to ∼92% in the visible region of 500–800nm. The room temperature photoluminescence (PL) spectra of films show a band edge between 3.41 and 3.2eV and strong blue emission at 2.8eV irrespective of doping concentration and however intensity increases consistently with doping levels. The vacuum annealing at 400°C reduced the resistivity of the films significantly due to the coalescence of grains and the lowest resistivity of 2×10−3 Ωcm is observed for 3at.% (solution) Zr doped ZnO films which envisages that it is a good candidate for stable TCO material. [Copyright &y& Elsevier]

Abstract: Biosynthesis of nanoparticles is under exploration is due to wide biomedical applications and research interest in nanotechnology. Bioreduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) for the synthesis of silver and gold nanoparticles respectively with the plant extract, Mentha piperita (Lamiaceae). The plant extract is mixed with AgNO3 and HAuCl2, incubated and studied synthesis of nanoparticles using UV–Vis spectroscopy. The nanoparticles were characterized by FTIR, SEM equipped with EDS. The silver nanoparticles synthesized were generally found to be spherical in shape with 90nm, whereas the synthesized gold nanoparticles were found to be 150nm. The results showed that the leaf extract of menthol is very good bioreductant for the synthesis of silver and gold nanoparticles and synthesized nanoparticles active against clinically isolated human pathogens, Staphylococcus aureus and Escherichia coli. [Copyright &y& Elsevier]

Abstract: Bites due to Russell''s Viper (Daboia russelii) are common in Sri Lanka. Commonest haematological manifestation is consumptive coagulopathy and bleeding. Commonest neurological manifestations are ptosis, ophthalmoplegia and rarely respiratory failure which are due to presynaptic inhibition of neuromuscular transmission. There are no authenticated reports of acute ischemic strokes following bites by D. russelii. We report the first authenticated case series of ischemic strokes following bites by D. russelii in Sri Lanka. Methods: This was a prospective observational study of all atypical neurological manifestations following bites by D. russelii admitted to a hospital in Sri Lanka. We documented clinical features of all atypical neurological manifestations of D. russelii bites and recorded the findings of brain imaging. Results: During a period of 18 months, at one centre, 9 patients out of an estimated 500 victims of D. russelii bites were found to have Computerized Tomographic evidence of single or multiple ischemic (non-haemorrhagic) strokes of medium to large vessel territories of the brain. These patients had either low Glasgow coma scale or hemiparesis within minutes to 4 days following bites. One patient died and another had gross neurological deficit, while others had mild or no neurological deficit at three months. Discussion: This report confirms that ischemic strokes can occur following envenoming by D. russelii. Involvement of multiple medium to large vessel territories and absence of watershed infarctions points to prothrombotic properties of the venom as the putative mechanism. [Copyright &y& Elsevier]

We report on the enhanced photoelectrochemical water splitting of hybrid ZnS/ZnO core-shell nanorod arrays functionalized with Bi 2 S 3 nanosheets as photoanode. The ZnO nanorod arrays were prepared by a facile hydrothermal approach and sulphurized to form ZnS shell. Subsequently porous Bi 2 S 3 nanosheets were arbitrarily decorated on the nanorod arrays by ionic adsorption and reaction method. Substantial enhancement in photocurrents with twofold increment is observed for hybrid photoanode compared to pristine counterparts. The structural and morphological properties of nano hybrid Bi 2 S 3 /ZnS/ZnO samples were analyzed by field emission scanning electron microscopy and X-ray diffraction. The higher wavelength shift in the absorption edge of Bi 2 S 3/ ZnS/ZnO photocatalyst was observed in diffuse reflectance UV–Visible spectra. The low temperature photoluminescence and impedance spectra of Bi 2 S 3 /ZnS/ZnO photoanode confirm that Bi 2 S 3 functionalization reduces the recombination of electron–hole pair and facilitates barrier free charge transfer. The Bi 2 S 3 /ZnS/ZnO photoanode device exhibits photocurrent density of 220 μA/cm2 at 0.2 V vs. Ag/AgCl under the electrolyte solution at pH ~10.8. The resultant hybrid photoanode withhold good stability and maintain the facile charge carrier generation and separation. Bi 2 S 3 topological nanosheets are responsible for the absorption of complete visible photons while ZnS/Bi 2 S 3 inter-junction provides the robust electron-hole pair separation at their interface due to infiltration pathway. The photoactive hybridization of Bi 2 S 3 /ZnS/ZnO provokes the enhanced donor charge density for efficient hydrogen evolution reaction. Image 1 • 2D Bi 2 S 3 anchored 1D ZnS/ZnO core-shell photoanode fabricated. • 2D Bi 2 S 3 staging enhances the photo-electrochemical properties. • Bi 2 S 3 /ZnS/ZnO shows stable photocurrent density of 220 μA/cm-2. • Bi 2 S 3 /ZnS/ZnO enhances the photo-electrocatalytic water oxidation. [ABSTRACT FROM AUTHOR]

Manifold morphologies of GaN nanowires (NWs) were fabricated using halide chemical vapour deposition (HCVD) on an n-Si (111) substrate and demonstrated to be a promising photoelectrode for photo-electrochemical (PEC) water splitting applications. We report a substantial enhancement in the photocurrent for vertically-grown GaN NWs on a buffer layer as compared to other counterparts such as GaN whiskers, tapered nanostructures and thin films. GaN NWs grown on Si have advantages due to the absorption of photons in a wide spectral range from ultraviolet to infrared and thus are directly involved in PEC reactions. A GaN NW photoanode was demonstrated with a saturation photocurrent density of 0.55 mA cm−2 under 1 sun of illumination, which is much greater than its counterparts. The role of the buffer layer and the carrier density on the PEC performance of vertically-grown GaN NW photoanodes is further elucidated. Photo-electrochemical impedance spectroscopy and Mott-Schottky characterizations were employed to further explain the PEC performance of GaN NW embedded photoanodes. Here, photoanodes based on diverse GaN nanostructures were examined for a better PEC evaluation in order to support the conclusion. The results may pave the way for the fabrication of efficient photoelectrodes and GaN as a protective layer against corrosion for improved photo-stability in an NaOH electrolyte for enhancing the efficiency of water splitting. [ABSTRACT FROM AUTHOR]

We report, the fabrication of molybdenum disulphide (MoS 2) wrapped silicon nanowires (Si NWs) for visible light driven water splitting applications. The morphological and elemental studies ensure the vertical alignment of Si NWs wrapped with 2D layered MoS 2. The photoelectrocatalytic (PEC) results evidence the significant enhancement in performance of MoS 2 /Si NWs based hybrid photocathode with ~300 mV (under reversible hydrogen electrode (RHE)) anodic shift in onset potential as that of pristine Si NWs (+0.194 V vs. RHE), and the current density of −26.5 mA/cm2 was achieved at the applied bias of 0 V vs. RHE. Further, the electrochemical impedance studies ensure the interface resistance-free charge transfer between Si NWs and electrolyte via 2D MoS 2 layer which provokes rapid hydrogen production. The wrapping of Si NWs with MoS 2 protects the superlative photocathode from harsh acid electrolyte environment. The overgrown MoS 2 triangular particles with active sulphur edge sites are found to eventually augment the solar hydrogen evolution rate. Further, the PEC performance of our MoS 2 /Si NWs is also comparable with stable Pt/Si NWs photoelectrode. It is note-worthy that, MoS 2 /Si NWs hybrid heterostructure would be a potential candidate in future large scale, low cost and day-to-day solar water splitting applications. Image 1 • MoS 2 /Si NWs hybrid heterostructure overcomes the limitation of standalone Si NWs. • It shows excellent PEC performance with the onset potential of +0.194V vs. RHE. • The heterostructure is expected to be the potential electrode for PEC applications. • Our MoS 2 /Si NWs device exhibits an excellent stability over 20,000 seconds. [ABSTRACT FROM AUTHOR]

Abstract The growth of one-dimensional (1D) zinc oxide (ZnO) nano/micro rod arrays (N/MRAs) thin films by using a facile, reproducible and cost effective method could be triggering nano/micro morphological structure based devices in the semiconductor technology. Therefore, in this work, the chemical bath deposition (CBD) and hydrothermal (HTM) methods have been used for growing 1D ZnO N/MRAs thin films on ZnO seeded glass substrates. Subsequently, we have studied their fundamental physicochemical properties for determining and distinguishing the growth characteristic of deposition methods. The formation of hexagonal wurtzite crystal structure in the CBD and HTM grown 1D ZnO N/MRAs films has been confirmed by XRD and μ-Raman studies. The intensity of the preferentially oriented diffraction peaks and electron microscopic images depict that the crystallinity, number density and aspect ratio of the 1D ZnO N/MRAs are strongly dependent on level of degree of supersaturation and its changes under deposition method is highlighted here. Further, the size, shape and single crystalline nature of the N/MRAs are strongly confirmed by TEM images and SAED patterns respectively. The photons absorption in the UV region ratify the wide bandgap characteristic of ZnO. Eventually, the presence of localized electron trapping and/or relaxing states in ZnO nuclei layer and in 1D ZnO N/MRAs films are determined from photoluminescence spectra. Graphical abstract Image 1 Highlights • ZnO nano/micro rod arrays thin films were grown by chemical bath deposition and hydrothermal on spray deposited ZnO seeded substrates. • The number density, aspect ratio of the NRs and MRs are strongly depends on the synthetic methods with respect to changing level of degree of supersaturation. • The optical band gap value is found to be 3.18 and 3.15 eV for CBD and hydrothermal grown film respectively. [ABSTRACT FROM AUTHOR]

Abstract Drug delivery using synthetic mesoporous nanomaterials, including porous silicon, has been extensively used to ameliorate the constraints currently experienced with conventional chemotherapy. Owing to the amazing potential, the silica based nanomaterials have been used widely. Nevertheless, synthetic nanomaterial involves high cost, lack of scalability, and the use of toxic substances limits its utilization. These issues can be overcome by the use of nature generated nanoscale materials, such as diatoms would serve as a boon for pharmaceutical industries. In this study we investigate the use of a mesoporous, biodegradable nanomaterial obtained from the natural silica found in the diatom species Amphora subtropica (AMPS) for drug delivery applications. AMPS cultures cleaned and chemically treated to obtain Amphora frustules (exoskeleton) (AF), followed by surface functionalization with chitosan (Chi). Results of our experiments demonstrate high drug loading, strong luminescence, biodegradable and biocompatible nature of the doxorubicin tethered diatom. Further, toxicity studies employing immortalized lung cancer cell line (A549) indicates sustained drug delivery and less toxic compared to the free doxorubicin (DOX), suggesting AF could be an excellent substitute for synthetic nanomaterials used in drug delivery applications. Graphical abstract Unlabelled Image Highlights • Purification of Amphora subtropica to obtain Amphora frustules (AF) and surface of AF functionalized by chitosan (Chi@AF) • Tethering doxorubicin (DOX) to determine the efficacy of high encapsulation into the porous of Chi@AF (Chi@AF-DOX) • The AF, Chi@AF and Chi@AF-DOX were characterized by TEM, FESEM, Zeta potentials, FTIR, etc., • Haemocompatibility on RBC and cytotoxicity effect against A549 cell line of AF complexes were analyzed [ABSTRACT FROM AUTHOR]