Channelling and Related Effects in Electron Microscopy: The Current Status

The channelling or Borrmann effect in electron diffraction has been developed into a versatile, high spatial resolution, crystallographic technique with demonstrated applicability in solving a variety of materials problems. In general, either the characteristic x-ray emissions or the electron energy-loss intensities are monitored as a function of the orientation of the incident beam. The technique, as formulated in the planar geometry has found wide applications in specific site occupancy and valence measurements, determination of small atomic displacements and crystal polarity studies. For site occupancy studies, the appropriate orientations in most cases can be determined by inspection and the analysis carried out according to a simple classification of the crystal structure discussed in this paper. Concentration levels as low as 0.1 wt% can be easily detected. The reciprocity principle may be used to advantage in all these studies, if electron energy-loss spectra are monitored, as both the channelling of the incoming beam and the blocking of the outgoing beam are included in the formulation and analysis. The formulation in the axial geometry is an useful alternative, particularly for monatomic crystals. Localization effects are important if, either the experiment is performed in the axial geometry or if low atomic number elements (z\u3c11) are detected. In general, the sensitivity to L-shells is lower compared to K-shell excitations. Other experimental parameters to be considered include temperature of the sample, the acceleration voltage and parallelism of the incident beam. Any detrimental effects of channelling on conventional microanalysis can be minimized either by tilting the crystal to an orientation where no lower order diffraction vectors are excited or by using a convergent probe such that a large range of incident beam orientations are averaged in the analysis

Exchange anisotropy, engineered coercivity and spintronics in atomically engineered L1{sub 0} heterostructures

We identified and investigated some of the scientific and technically most challenging issues in thin film magnetism focusing on epitaxially grown layers of specific L1{sub 0} ordered, intermetallic, heterostructures with well-controlled crystallography and interface structures. Specifically, we addressed antiferromagnetic/ferromagnetic heterostructures, exhibiting exchange bias (EB) in both in-plane (MnPd/Fe) and perpendicular (IrMn/(Co/Pt){sub n}) geometries, and ferromagnetic/ferrimagnetic (Co/Y{sub 3}Fe{sub 5}O{sub 12}) bilayers with strong interlayer exchange coupling and exhibiting spin reorientation transitions. In the former case, the work included experimental and theoretical studies to gain more fundamental insight into the origin and magnitude of EB, as well as to address important aspects of EB such as the asymmetry in the magnetic reversal mechanism, the role of interfacial structure, including compensated or uncompensated spins, AF domains, competing anisotropies and the angular dependence of the magnetization reversal process. Exchange bias is central to many magnetic technologies and driven by the fast development of nanotechnology, there is much interest in understanding the phenomenon of exchange bias on the nanoscale. By patterning, as the FM domain size reaches a lateral scale comparable to the AF domain size (~100nm), each nano-element can be treated as a separate and isolated exchange bias system that behaves independently. Therefore, the non-averaged, intrinsic, exchange bias, in all its complexity, can be studied. Such size and dimensionality effects, particularly in structures with lateral dimension of the order of their domain sizes, were studied by developing and implementing a novel Nano-imprint as well as convention optical lithography/patterning. However, one limitation of the NIL method is that after imprinting the material-deposition or -evaporation has to be done at around room temperature in order to keep the resists structure undisturbed. As a result, the method is unsuitable for epitaxial growth, since the latter often involves growth at elevated temperatures higher than the glass transition temperature of the resist. Therefore, a mask transfer NIL process was developed to grow epitaxial nanostructure arrays at elevated temperatures where organic resists are rendered unstable. In the case of the metal/oxide heterostructures, the domain structure of the metal is carefully modulated by that of the underlying oxide, opening the possibility of carrying out novel experiments to study spin-dependent domain-wall scattering and quantify domain wall resistance in mesoscopic geometries. Utilizing state-of-the-art characterization methods, using synchrotron radiation and electron holography, we addressed the critical role of all aspects of the microstructure, at relevant length scales, in determining these specific magnetic properties. Two significant highlights of this project were the use of photoemission electron microscopy (PEEM) work to elucidate their asymmetric magnetization reversal mechanism and the use of element-specific X-ray magnetic reflectivity and x-ray resonant scattering to probe buried interfaces, both of importance in understanding the fundamental physics of exchange bias. In the latter case, a complex magnetic interfacial configuration in Fe/MnPd, consisting of a 2-monolayer-thick induced ferromagnetic region, and pinned uncompensated Mn moments that reach far deeper (~13 Å), both in the antiferromagnet, were found. Such epitaxial EB samples also show in-plane reorientation transitions, determined by the competition between the interface exchange coupling and the intrinsic uniaxial energies, and is driven by the temperature, as well as the thickness of MnPd and Fe layers. Complementing these results, work on multilayers show that perpendicular EB arise from a complex interplay between unidirectional anisotropy at the terminating FM/AFM interface, the perpendicular anisotropy of the FM/nonmagnet(NM) multilayer stack and the overall magnetostatic energy of the structure. Collaborative work with Prof. R. Stamps (UWA) in modeling and analysis of slow-dynamics, using an inductive ferromagnetic resonance technique, were also carried out. Further details of our research is presented below broadly in five thematic areas. Overall, this research allowed us to obtain a deeper understanding of the range of related magnetic phenomena and establish pathways for potential technological applications of these thin film and patterned heterostructures

Polygon Shaped 3G Mobile Band Antennas for High Tech Military Uniforms

Smart Textiles integrated with communicating components have been used in military for many applications. Wearable antenna can be attached or embedded into smart textiles which could be used for communication between combat soldiers in the battlefield. This paper presents the design of three different polygon shaped patch antenna operating on 3G Mobile Band frequency 2100 MHz embedded on three different dielectric constant materials for Military applications. The proposed polygon shaped patch antenna introduces horizontal slit in its patch to improve the antenna performance. The effect of slit length and slit width on the antenna performance is analyzed. &nbsp

Towards Picogram Detection of Superparamagnetic Iron-Oxide Particles Using a Gradiometric Receive Coil

Superparamagnetic iron-oxide nanoparticles can be used in a variety of medical applications like vascular or targeted imaging. Magnetic particle imaging (MPI) is a promising tomographic imaging technique that allows visualizing the 3D nanoparticle distribution concentration in a non-invasive manner. The two main strengths of MPI are high temporal resolution and high sensitivity. While the first has been proven in the assessment of dynamic processes like cardiac imaging, it is unknown how far the detection limit of MPI can be lowered. Within this work, we will present a highly sensitive gradiometric receive-coil unit combined with a noise-matching network tailored for the measurement of mice. The setup is capable of detecting 5 ng of iron in vitro at 2.14 sec acquisition time. In terms of iron concentration we are able to detect 156 {\mu}g/L marking the lowest value that has been reported for an MPI scanner so far. In vivo MPI mouse images of a 512 ng bolus at 21.5 ms acquisition time allow for capturing the flow of an intravenously injected tracer through the heart of a mouse. Since it has been rather difficult to compare detection limits across MPI publications we propose guidelines improving the comparability of future MPI studies.Comment: 15 Pages, 7 Figures, V2: Changed the initials of Author Kannan M Krishnan, added two citations, corrected typo

Wound Healing Ethnomedicinal Plants Popular among the Malayali Tribes in Vattal Hills, Dharmapuri, TN, India

Healing of chronic lower extremity wounds is a global problem, especially in developing countries where traditional medicine is often used by the people in remote places. India has a rich tradition of plant based knowledge pertinent to healthcare. A survey of ethnomedicinal plant species used by Malayali’s to heal cut/ wounds in Vattal Hills of Dharmapuri was made. A large number of plants/ extracts/ decoctions/ pastes are used by tribals to heal wounds, cuts and burns. In the present study, an attempt has been made to document ethnobotanical knowledge base and methods employed by Malayali’s for treatment of cut/ wounds. A large number of ethnomedicinal plants used by the Malayali’s have not been validated for wound healing potential. The present investigation resulted in the identification of 82 medicinal plant species distributed across 39 families that are used by Malayali’s to heal cut/ wounds. This study is an attempt to gather the information on the existing ethnobotanical knowledge base and document the traditional claims toward the development of safe of effective herbal drugs for cut/ wounds. Results of the study is organized in table form depicting the botanical name, family, vernacular name and habit with a brief note on plant parts used and method of administration

Development of Deep Learning based Intelligent Approach for Credit Card Fraud Detection

Credit card fraud (CCF) has long been a major concern of institutions of financial groups and business partners, and it is also a global interest to researchers due to its growing popularity. In order to predict and detect the CCF, machine learning (ML) has proven to be one of the most promising techniques. But, class inequality is one of the main and recurring challenges when dealing with CCF tasks that hinder model performance. To overcome this challenges, a Deep Learning (DL) techniques are used by the researchers. In this research work, an efficient CCF detection (CCFD) system is developed by proposing a hybrid model called Convolutional Neural Network with Recurrent Neural Network (CNN-RNN). In this model, CNN acts as feature extraction for extracting the valuable information of CCF data and long-term dependency features are studied by RNN model. An imbalance problem is solved by Synthetic Minority Over Sampling Technique (SMOTE) technique. An experiment is conducted on European Dataset to validate the performance of CNN-RNN model with existing CNN and RNN model in terms of major parameters. The results proved that CNN-RNN model achieved 95.83% of precision, where CNN achieved 93.63% of precision and RNN achieved 88.50% of precision

Antiferromagnetic correlations in Fe-Cu granular alloys: the role of the surface structure

Fe precipitates in a Cufcc matrix, prepared using the Bridgeman method and with an average composition of Cu97Fe3, displayed the coexistence of ferromagnetism ~FM!, spin glass-like ~SGL! behavior and antiferromagnetic ~AFM! correlations. The two former contributions may be attributed, respectively, to the segregation of FM, a-Febcc precipitates and to the few Fe spins distributed in the matrix. The annealing procedures increased the FM contribution and, as particle growth and phase segregation took place, the SGL behavior progressively disappeared. Results from high resolution transmission electron microscopy ~HRTEM!, x-ray photoelectron spectroscopy ~XPS!, and electron energy-loss spectroscopy ~EELS! suggest that the AFM correlations are due to the a-Fe particles that show a surface layer of a few nanometers in thickness, of either FeO and/or g-Fefcc . XPS and EELS measurements confirm the presence of FeO; however, the latter is only tentatively suggested by the HRTEM analysis of the particle/matrix interfaces