Resistive switching memory characteristics of Ge/GeOx nanowires and evidence of oxygen ion migration

The resistive switching memory of Ge nanowires (NWs) in an IrO_x/Al₂O₃/Ge NWs/SiO₂/p-Si structure is investigated. Ge NWs with an average diameter of approximately 100 nm are grown by the vapor–liquid-solid technique. The core-shell structure of the Ge/GeO_x NWs is confirmed by both scanning electron microscopy and high-resolution transmission electron microscopy. Defects in the Ge/GeO_x NWs are observed by X-ray photoelectron spectroscopy. Broad photoluminescence spectra from 10 to 300 K are observed because of defects in the Ge/GeO_x NWs, which are also useful for nanoscale resistive switching memory. The resistive switching mechanism in an IrO_x/GeO_x/W structure involves migration of oxygen ions under external bias, which is also confirmed by real-time observation of the surface of the device. The porous IrO_x top electrode readily allows the evolved O₂ gas to escape from the device. The annealed device has a low operating voltage (<4 V), low RESET current (approximately 22 μA), large resistance ratio (>10³), long pulse read endurance of >10⁵ cycles, and good data retention of >10⁴ s. Its performance is better than that of the as-deposited device because the GeO_x film in the annealed device contains more oxygen vacancies. Under SET operation, Ge/GeO_x nanofilaments (or NWs) form in the GeO_x film. The diameter of the conducting nanofilament is approximately 40 nm, which is calculated using a new method.     

Optimized species growth in epoxy polymerization with real-coded NSGA-II

Satisfaction of twin objectives of maximization of M_n along with minimization of PDI do not necessarily guarantee the maximization of concentration of desired species in a semibatch epoxy polymerization process. As the final product consists of a number of polymer species, a need is felt to perform an advanced optimization study to come up with such process conditions for which the selective growth of a particular polymer species is maximized in minimum possible processing time and the population of other species should be at their lowest values. These above-mentioned conflicting objectives frame the platform for a multi-objective optimization problem, which is solved here using a real-coded non-dominated sorting genetic algorithm or NSGA II and Pareto optimal solutions are obtained. The decision variables are discrete addition rates of various ingredients, e.g. the amount of addition of bisphenol-A (a monomer), sodium hydroxide and epichlorohydrin at different time steps. All species balance equations, bounds on M_n, PDI and addition amounts are treated as constraints. Results are very promising in terms of optimized operations for selective enhancement of desired polymer species for the epoxy polymerization process. Total additions are kept very close to available experimental conditions to minimize probable extrapolation errors. It has been observed that preferential oligomer production is extremely difficult for epoxy polymerization. Lower chain polymers are the only choice for a good quality, stable polymer product.     

Architectural View of Flexible Aliphatic –OH Group Coordinated Hemi-Directed Pb(II)-Salen Coordination Polymer: Synthesis,Crystal Structure,Spectroscopic Insights,Supramolecular Topographies,and DFT Perspective

Journal of Inorganic and Organometallic Polymers and Materials - We serendipitously designed one novel 1D hetero-binuclear Zn(II)-Pb(II) coordination polymer, namely...     

Laser surface alloying of aluminium with WC + Co + NiCr for improved wear resistance

In the present study, laser surface alloying of aluminium with WC + Co + NiCr (in the ratio of 70:15:15) has been conducted using a 5 kW continuous wave (CW) Nd:YAG laser (at a beam diameter of 0.003 m), with the output power ranging from 3 to 3.5 kW and scan speed from 0.012 m/s to 0.04 m/s by simultaneous feeding of precursor powder (at a flow rate of 1 × 10^− 5 kg/s) and using He shroud at a gas flow rate of 3 × 10^− 6 m³/s. The effect of laser power and scan speed on the characteristics (microstructures, phases and composition) and properties (wear and corrosion resistance) of the surface alloyed layer have been investigated in details. Laser surface alloying leads to development of fine grained aluminium with the dispersion of WC, W₂C, Al₄C₃, Al₉Co₂, Al₃Ni, Cr₂₃C₆, and Co₆W₆C. The microhardness of the alloyed zone is significantly improved to a maximum value of 650 VHN as compared to 22 VHN of the as-received aluminium substrate. The mechanism of microhardness enhancement has been established. The fretting wear behavior of the alloyed zone was evaluated against WC by Ball-on-disc wear testing unit and the mechanism of wear was established.     

Effect of Dopants and Sintering Method on the Properties of Ceria-Based Electrolytes for IT-SOFCs Applications

Doped and co-doped ceria ceramics are used as electrolyte materials in solid oxide fuel cells. In this work, ceria-based oxides, Ce_0.90Gd_0.06Y_0.02M_0.02O_2?δ (M?=?Ca, Fe, La, and Sr) were prepared by conventional as well as microwave processing from the precursors prepared by the mixed oxide method. The consolidated calcined powders in pellet form were sintered in microwave energy at 1400°C for 20 min and in an electric furnace of IR radiation at 1400°C for 6 h. The x-ray diffraction analysis confirmed that all the compositions were crystallized into a cubic fluorite structure. Surface morphology of the sintered products was studied using scanning electron microscopy and the microhardness was investigated using the Vickers hardness test. The comparative results analysis shows that the microwave-sintered samples have uniform grain growth, higher density and higher microhardness than the corresponding conventionally sintered products. The microwave-sintered sample of composition Ce_0.90Gd_0.06Y_0.02Sr_0.02O_2?δ was found to have the highest microhardness among the four compositions due to its high density and smallest grain size.     

Structural correlation to magnetodielectricity and coercivity at room temperature in multiferroic Bi0.7Ba0.3−xPbxFeO3

We report an interesting structural correlation to the static dielectric constant (?₀), magnetodielectric (MD) response and coercivity at room temperature for Bi_0.7Ba_0.3?xPb_xFeO₃ at x = 0, 0.05, 0.10 and 0.15, above which a structurally single-phase material could not be achieved. The Pb doping leads to a ～2.4 times increase in ?₀. The Fe–O–Fe bond angle increases and approaches 180° with the Pb doping, which is associated with a considerable decrease in coercivity. Interestingly, the MD response is correlated with the average Bi–Fe bond length. This structural correlation is crucial for understanding the origin of moderately high MD response and improving the effects of this for technological applications.     

Weld Metal Microstructure Prediction in Submerged Arc Weld Metal of C‐Mn Steel

The prediction model has been developed for steel weld metal microstructural constituents as a function of flux ingredients such as CaO, MgO, CaF₂ and Al₂O₃ in submerged arc welding carried out at fixed welding parameters. The results of quantitative measurements of micro‐structural constituents on eighteen weld metal samples were utilised for developing the prediction equations of microstructural constituents applying statistical design of experiment for mixtures. Among the flux ingredients, CaO appears to be most important as an individual as well as interaction with other ingredients viz. CaF₂ and Al₂O₃ in influencing the amount of microstructural constituents in weld metal. The prediction equations have been checked for adequacy by performing tests on welding using randomly designed flux and found satisfactory. The iso‐response curves were developed for selected microstructural constituents to show their output levels at different percentage of flux ingredients.     

Application of response surface method for predicting electroless nickel plating

Electroless nickel plating process has been studied considering pure copper (99.99%) as a substrate material. Deposition per unit area has been considered as a response variable and individual as well as combined effects of process parameters on deposited mass have been studied. Regression analysis and Student’s t test have been used to identify the significant influencing process parameters. It has been observed that reducing agent (NaBH₄), source of metal (NiCl₂ · 6H₂O) and temperature significantly affect the deposition. The interactions among various process parameters have also been observed to be significant. Mathematical modeling has been carried out by a second-order response surface model with central composite design (CCD) to take into account the effect of curvature in the predicted response. Equations for response surfaces have been determined for various deposition times using MATLAB software package. Most of the response surfaces show that deposition thickness increases with increased values of process parameters within the adopted range but with different rates. The test for reliability for predicting response surface equations shows that these equations give an excellent fitting to the observed values.     

In vivo high resolution MRI of the calcaneus: differences in trabecular structure in osteoporosis patients

The purpose of this study was to use high resolution (HR) magnetic resonance (MR) images of the calcaneus to investigate the trabecular structure of patients with and without osteoporotic hip fractures and to compare these techniques with bone mineral density (BMD) in differentiating fracture and nonfracture patients. Axial and sagittal HR MR images of the calcaneus were obtained in 50 female (23 postmenopausal patients with osteoporotic hip fractures and 27 postmenopausal controls). A three-dimensional gradient-echo sequence was used with a slice thickness of 500 micron and in plane resolution of 195 x 195 micron. Texture analysis was performed using morphological features, analogous to standard histomorphometry and fractal dimension. Additionally, BMd measurements of the hip (dual-energy X-ray absorptiometry) were obtained in all patients. Significant differences between both patient groups were obtained using morphological parameters and fractal dimension as well as hip BMD (p < 0.05). Odds ratios for the texture parameters apparent (app.) bone volume/total volume and app. trabecular separation were higher than for hip BMD. Receiver operator characteristic values of texture measures and hip BMD were comparable. In conclusion, trabecular structure measures derived from HR MR images of the calcaneus can differentiate between postmenopausal women with and without osteoporotic hip fractures.     

Normalized cuts in 3-D for spinal MRI segmentation

Segmentation of medical images has become an indispensable process to perform quantitative analysis of images of human organs and their functions. Normalized Cuts (NCut) is a spectral graph theoretic method that readily admits combinations of different features for image segmentation. The computational demand imposed by NCut has been successfully alleviated with the Nystr?m approximation method for applications different than medical imaging. In this paper we discuss the application of NCut with the Nystr?m approximation method to segment vertebral bodies from sagittal T1-weighted magnetic resonance images of the spine. The magnetic resonance images were preprocessed by the anisotropic diffusion algorithm, and three-dimensional local histograms of brightness was chosen as the segmentation feature. Results of the segmentation as well as limitations and challenges in this area are presented.