M. Sabieh Anwar

NMR Imaging of Catalytic Hydrogenation in Microreactors with the Use of para-Hydrogen

Catalysis is vital to industrial chemistry, and the optimization of catalytic reactors attracts considerable resources. It has proven challenging to correlate the active regions in heterogeneous catalyst beds with morphology and to monitor multistep reactions within the bed. We demonstrate techniques, using magnetic resonance imaging and para-hydrogen (p-H2) polarization, that allow direct visualization of gas-phase flow and the density of active catalyst in a packed-bed microreactor, as well as control over the dynamics of the polarized state in space and time to facilitate the study of subsequent reactions. These procedures are suitable for characterizing reactors and reactions in microfluidic devices where low sensitivity of conventional magnetic resonance would otherwise be the limiting factor.

Picomolar sensitivity MRI and photoacoustic imaging of cobalt nanoparticles

Multimodality imaging based on complementary detection principles has broad clinical applications and promises to improve the accuracy of medical diagnosis. This means that a tracer particle advantageously incorporates multiple functionalities into a single delivery vehicle. In the present work, we explore a unique combination of MRI and photoacoustic tomography (PAT) to detect picomolar concentrations of nanoparticles. The nanoconstruct consists of ferromagnetic (Co) particles coated with gold (Au) for biocompatibility and a unique shape that enables optical absorption over a broad range of frequencies. The end result is a dual-modality probe useful for the detection of trace amounts of nanoparticles in biological tissues, in which MRI provides volume detection, whereas PAT performs edge detection.

Room Temperature Magnetic Behavior of Sol-Gel Synthesized Mn Doped ZnO

Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto-combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of Mn doped ZnO dilute magnetic semiconductor. X-ray diffraction measurements indicate that Mn doped ZnO retain wurtzite type hexagonal crystal structure like ZnO. Compositional and morphological studies were carried out by energy dispersive X-ray analysis and scanning electron microscopy, respectively. Temperature dependent resistivity of the sample exhibited the semiconducting behavior of the DMS material. Room temperature magnetic properties determined by vibrating sample magnetometer, revealed the presence of ferromagnetic and diamagnetic contributions in Mn doped ZnO.

Structural and Magnetic Studies of Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O

Single-phase Zn0.95Co0.05O and Zn0.90Co0.05Al0.05O samples were prepared by a novel combustion method. X-ray diffraction studies exhibit the pure phase wurtzite structure of doped ZnO. Energy dispersive x-ray analysis confirms the incorporation of dopants into the host material. Scanning electron microscopy shows the ordered morphology in both of the samples. Temperature-dependent resistivity analysis describes the expected semiconducting behavior that is similar to the parent ZnO materials. Room-temperature magnetic measurements reveal the absence of ferromagnetism in Co-doped ZnO, while the Co and Al co-doped sample displays apparent room-temperature ferromagnetic behavior. The decrease of resistivity and presence of ferromagnetic behavior in Al-doped ZnCoO system corroborate the significant role of free carriers.

ENHANCEMENT OF ENERGY PRODUCT WITH INSERTION OF Ti BETWEEN EXCHANGE COUPLED Sm–Co AND Fe LAYERS

Bilayers of Sm–Co/Fe have been fabricated on 70 nm Cr buffered Si(100) substrate at an elevated temperature of 650°C by the help of DC and RF magnetron sputtering. Very thin layers (0–0.7 nm) of Ti were introduced at the interface of the Sm–Co and Fe phases. The samples were analyzed by X-ray diffraction (XRD) and alternating gradient magnetometer (AGM). All the samples showed strong exchange coupling and single phase behavior. The rise and fall in magnetization and energy product were observed with increasing Ti interlayer thickness. Energy product (BH)max value was found increased by 44% for 0.2 nm Ti interlayer as compared to the sample without Ti layer at interface.

Optimization of magnetodielectric coupling in Mn substituted BiFeO 3 for potential memory devices

Coexistence of spontaneous magnetization and polarization is a key phenomenon in multiferroic materials whereas coupling among these order parameters is anticipated to play a vital role in modern day engineering devices and information technology. In this context, Mn substituted BiFeO3 was synthesized using sol–gel accompanying auto-combustion method. X-ray diffraction of the calcined BiFe1−xMnxO3 samples exhibited a crystalline nature and phase purity of the samples. Among the samples, BiFe0.8Mn0.2O3 depicted more stable rhombohedral structure as compared to BiFeO3, whereas mixed phases of orthorhombic and monoclinic were observed in BiFe1−xMnxO3 at 0.4 ≤ x ≤ 1.0. Surface morphology, as seen using a field emission electron microscope, revealed decreasing granular size which interpreted modified magnetic attributes examined by vibrating sample magnetometer for specific Mn contents. Elemental wt% were confirmed by energy dispersive X-ray spectroscopy. To extract the optimized results from Mn substituted BiFeO3, magnetodielectric coupling was examined as well under 6 kOe applied magnetic field which declared BiFe0.8Mn0.2O3 as the most optimized composition. Hence, this research work has opened the way for the material scientists and engineers to pursue more efficient multiferroics. It is an effective way to rectify various issues relevant to device applications like quick switching, magnetically controlled supercapacitors and designing fast and higher density data storage devices that is magnetoelectric random-access memories.

Investigating properties of white noise in the undergraduate laboratory

This paper describes a simple noise circuit for the undergraduate physics laboratory. Students use this circuit to study the properties of electrical noise on a personal computer. This is made possible by using a data acquisition system that allows the experimenters to obtain large amounts of data on the computer, suitable for subsequent mathematical computations. Various properties such as mean, noise power, noise power density and the probability distribution of noise voltages are also explored.

Effect of Temperature on Structural and Magnetic Properties of Laser Ablated Iron Oxide Deposited on Si(100)

We fabricate Fe3O4 thin films on Si(100) substrates at different temperatures using pulsed laser deposition, and study the effect of annealing and deposition temperature on the structural and magnetic properties of Fe3O4 thin films. Subsequently, the films are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM). The XRD results of these films confirm the presence of the Fe3O4 phase and show room-temperature ferromagnetism, as observed with VSM. We demonstrate the optimized deposition and annealing conditions for an enhanced magnetization of 854 emu/cm3 that is very high when compared to the bulk sample.

IMPEDANCE SPECTROSCOPY (IS), XRD AND SEM OF OXIDE-ADDED Si3N4

Impedance spectroscopy (IS) is a non-destructive technique used for obtaining valuable information about bulk conductivities, dielectric constants, phase composition and grain boundaries of important ceramic materials, amongst many others. We obtained Nyquist plots for four different hot-pressed Si3N4 samples in two different frequency regimes: 1 Hz to 30 MHz and 1 kHz to 100 kHz. The information obtained was compared against results from scanning electron microscopy (SEM) and X-ray diffraction (XRD). The limitations of the frequency response techniques are also discussed.