Growth of ZnO Thin Films on Polar Oxide Surfaces By Atomic Layer Deposition

Polar heterointerfaces of MgO(111) and the II-VI semiconductor ZnO are of technological interest for transparent conducting electrode applications. Growth and structure of thin films on polar surfaces can be different than on non-polar surfaces due to the large surface energy of polar surfaces. We have grown ZnO on unreconstructed MgO(111)-(1x1)-OH terminated and reconstructed MgO(111)-(√3x√3)R30° polar oxide surfaces using atomic layer deposition. A homemade UHV-interfaced viscous-flow atomic layer deposition (ALD) reactor with in-situ quartz crystal monitor was used to grow ZnO thin films on the MgO(111) substrates. Surface morphology studies revealed that the surface roughness increases with ZnO film thickness and that reconstructed MgO(111) is a better substrate for production of smooth ZnO films. Thin-film structural analysis revealed that ZnO thin films are polycrystalline, having the wurtzite structure, with preferential growth along the c-axis. ZnO grown on MgO(111)-(√3x√3)R30° substrates show strong preferential growth along the polar (002) direction. In contrast, growth along the non-polar (100) and (101) directions is also observed when grown on MgO(111)-(1x1) substrates. These observations indicate the crystal orientation during ALD ZnO growth depends not only on temperature but also on the surface terminations and symmetry of the substrates. We also investigated the growth of ALD ZnO on polar 6H-SiC(0001) substrates and non-polar MgO(100), α-Al2O3(0001) and oxidized Si(100). Our study revealed that, for non-polar substrates, ALD ZnO grows along the non-polar (100) and (101) directions along with the polar (002) direction. Highly c-axis-oriented ALD ZnO thin film growth on 6H-SiC(0001) indicates that lattice matched substrates favor growth of high-quality ALD ZnO. Finally, we investigated ZnO thin film growth on unreconstructed MgO(111)-(1x1)-OH terminated and reconstructed MgO(111)-(√3x√3)R30° polar oxide surfaces using pulsed-laser deposition (PLD). Structural studies revealed that surface termination affects the PLD ZnO growth similar to the way it affected ALD ZnO growth

Parametrically controlling solitary wave dynamics in modified Kortweg-de Vries equation

We demonstrate the control of solitary wave dynamics of modified Kortweg-de Vries (MKdV) equation through the temporal variations of the distributed coefficients. This is explicated through exact cnoidal wave and localized soliton solutions of the MKdV equation with variable coefficients. The solitons can be accelerated and their propagation can be manipulated by suitable variations of the above parameters. In sharp contrast with nonlinear Schr\"{o}dinger equation, the soliton amplitude and widths are time independent.Comment: 4 pages, 5 eps figure

Palladium-based ferroelectrics and multiferroics : theory and experiment

Palladium normally does not easily substitute for Ti or Zr in perovskite oxides. Moreover, Pd is not normally magnetic (but becomes ferromagnetic under applied uniaxial stress or electric fields). Despite these two great obstacles, we have succeeded in fabricating lead zirconate titanate with 30% Pd substitution. For 20:80 Zr:Ti the ceramics are generally single-phase perovskite (>99%), but sometimes exhibit 1% PbPdO2, which is magnetic below T=90K. The resulting material is multiferroic (ferroelectric-ferromagnet) at room temperature. The processing is slightly unusual (>8 hrs in high-energy ball-milling in Zr balls), and the density functional theory provided shows that it occurs because of Pd+4 in the oversized Pb+2 site; if all Pd+4 were to go into the Ti+4 perovskite B-site, no magnetism would result.PostprintPeer reviewe

Evidence of strong magneto-dielectric coupling and enhanced electrical insulation at room temperature in Nd and Mn co-doped bismuth ferrite

The search for a room temperature single phase multiferroic material displaying strong magnetoelectric coupling and low leakage current for practical device applications has been underway and a long-standing challenge. In continuation to our investigations for achieving robust ME coupling and enhanced electrical insulation at room temperature, we report magnetic, electrical insulation, and magneto-dielectric properties of Nd and Mn co-doped BiFeO3 (Bi0.95Nd0.05)(Fe0.97Mn0.03)O-3 (BNFM) polycrystalline electro-ceramics. Magnetic studies have been carried out in two different temperature regions, i.e., 15-300K and 300-800K. The doping of Nd and Mn in the BiFeO3 (BFO) lattice slightly reduces the Neel temperature (T-N) with broad weak ferromagnetic (FM) to paramagnetic (PM) phase transition by increasing ferromagnetic domain fractions. A small amount of magnetic frustration is also found in the low temperature regions, below 300K at fields of 100 and 200Oe, and below 200K at higher field cooled and zero field cooled; this may be due weak long range ordering and small magnitude of magnetic moments. High temperature magnetic results imply the existence of a weak ferromagnetic phase with a FM to PM phase transition around 630K (+/- 5K) and significant suppression of the spin frustration and canting properties of BFO. The Nd and Mn co-doping also substantially improved the electrical insulating properties of BFO. The leakage current analysis suggests that the Simmons' mechanism is probably a dominant conduction mechanism in BNFM at room temperature. The observation of dielectric anomaly around the T-N and significant variation of dielectric parameters with different static magnetic field in BNFM implies the existence of strong magnetodielectric coupling. The enhanced magnetic and electrical insulation properties with strong magnetodielectric coupling at room temperature elucidate the possible potential candidates for multifunctional and spintronics device applications

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Not AvailableIn the present investigation, the photosynthetic potential of the wild and cultivated apples was examined. The indigenous Himalayan wild apple Malus baccata (Shillong) showed the highest photosynthetic pigments, viz., chlorophyll a (2.53 mg/g FW), chlorophyll b (0.78 mg/g FW) and total chlorophyll content (3.33 mg/g FW), which was at par with disease resistant apple genotype Liberty. The photosynthetic potential and disease resistance ability of the indigenous Himalayan wild apple M. baccata (Shillong) accessions make them fit for further exploration as commercial rootstock with dwarfing ability besides biotic and abiotic stress tolerance types.Not Availabl

Biosensors as Nano-Analytical Tools for COVID-19 Detection

Selective, sensitive and affordable techniques to detect disease and underlying health issues have been developed recently. Biosensors as nanoanalytical tools have taken a front seat in this context. Nanotechnology-enabled progress in the health sector has aided in disease and pandemic management at a very early stage efficiently. This report reflects the state-of-the-art of nanobiosensor-based virus detection technology in terms of their detection methods, targets, limits of detection, range, sensitivity, assay time, etc. The article effectively summarizes the challenges with traditional technologies and newly emerging biosensors, including the nanotechnology-based detection kit for COVID-19; optically enhanced technology; and electrochemical, smart and wearable enabled nanobiosensors. The less explored but crucial piezoelectric nanobiosensor and the reverse transcription-loop mediated isothermal amplification (RT-LAMP)-based biosensor are also discussed here. The article could be of significance to researchers and doctors dedicated to developing potent, versatile biosensors for the rapid identification of COVID-19. This kind of report is needed for selecting suitable treatments and to avert epidemics

Ultra-high sensitivity infra-red detection and temperature effects in a graphene-tellurium nanowire binary hybrid

The optoelectronic performance of hybrid devices from graphene and optically sensitive semiconductors exceeds conventional photodetectors due to a large in-built optical gain. Tellurium nanowire (TeNW), being a narrow direct band gap semiconductor similar to 0.65 eV), is as an excellent potential candidate for near infra-red NIR) detection. Here we demonstrate a new graphene-TeNW binary hybrid that exhibits a maximum photoresponsivity of similar to 10(6) A W-1 at 175 K in the NIR regime 920 nm-1720 nm), which exceeds the photoresponsivity of the most common NIR photodetectors. The resulting noise-equivalent power NEP) is as low as 2 x 10(-18) W Hz(-1/2), and the specific detectivity (D*) exceeds 5 x 10(13) cm Hz1/ 2 W-1 Jones). The temperature range of optimal operation, which extends up to approximate to 220 K and approximate to 260 K for 1720 nm and 920 nm excitation, respectively, is primarily limited by the electrical conductivity of the TeNW layer, and can further be improved by lowering of the defect density as well as inter-wire electronic coupling