Gnanavel Thirunavukkarasu

University of Birmingham · School of Metallurgy and Materials

Composites of sodium-exchanged zeolite chabazite particles with attached superparamagnetic nanoparticles of Fe 3 O 4 and CoFe 2 O 4 ferrite spinels have been produced using a novel solvothermal route. These have been characterized by a combination of techniques, including powder x-ray diffraction, x-ray fluorescence spectroscopy, vibrating sample m...

γ2-Al8Mn5 intermetallic particles are generally present in commercial Mg-Al-Zn alloys. The present study is concerned with the effect of solutionizing on the morphology and phase stability of the γ2-Al8Mn5 particles in an as-cast AZ91 alloy. Analysis using energy dispersive spectroscopy (EDS) and electron back scattered diffraction (EBSD) in a scan...

The development of new electrode approaches from highly active electrocatalysts to replace the state-of-the-art Pt/C is most desirable for enhancing power performance and durability in proton exchange membrane fuel cells. However, the deployment of advanced, often shape-controlled Pt alloy electrocatalysts in actual electrodes has remained challeng...

The effect of a small lanthanum (La) addition on Mg–10 wt% Dy alloy has been studied using isothermal aging at 120 °C. A combination of scanning transmission electron microscope (STEM) imaging and high-angle annular dark field (HAADF) based electron tomography has been used to characterize the precipitates. βF′ and β′ precipitates were determined,...

The effect of a small lanthanum (La) addition on Mg–10 wt% Dy alloy has been studied using isothermal aging at 120 °C. A combination of scanning transmission electron microscope (STEM) imaging and high-angle annular dark field (HAADF) based electron tomography has been used to characterize the precipitates. 𝛽′𝐹 and 𝛽′ precipitates were determined,...

A clear understanding of catalytic activity enhancement mechanisms in fuel cell operation is necessary for a full degree translation of the latest generation of non-Pt/C fuel cell electrocatalysts into high performance electrodes in proton exchange membrane fuel cells (PEMFCs). In this work, PtNi nanowire (NW) array gas diffusion electrodes (GDEs)...

The excellent catalytic activities and stabilities of one-dimensional (1D) AgPt alloy nanostructure have been well reported toward oxygen reduction reaction (ORR). However, their real application in proton exchange membrane fuel cells (PEMFCs) is still highly challenging due to the large difficulties with their preparation and fabrication into prac...

Non-platinum group metal (non-PGM) oxygen reduction reaction (ORR) catalysts have been widely reported, but their application in proton exchange membrane fuel cells (PEMFCs) is challenging due to their poor performance in acidic environments. Here [BMIM][NTf2] ionic liquid (IL) modification of microporous ZnCoNC catalysts (derived from ZIF-ZnCo) is...

Structured electron beams carrying orbital angular momentum are currently of considerable interest, both from a fundamental point of view and for application in electron microscopy and spectroscopy. Until recently, most studies have focused on the azimuthal structure of electron vortex beams with well-defined orbital angular momentum. To unambiguou...

Structured electron beams carrying orbital angular momentum are currently of considerable interest, both from a fundamental point of view and for application in electron microscopy and spectroscopy. Until recently, most studies have focused on the azimuthal structure of electron vortex beams with well-defined orbital angular momentum. To unambiguou...

Structured electron beams carrying orbital angular momentum are currently of considerable interest, both from a fundamental point of view and for application in electron microscopy and spectroscopy. Until recently, most studies have focused on the azimuthal structure of electron vortex beams with well-defined orbital angular momentum. To unambiguou...

The recent prediction and subsequent creation of electron vortex beams in a number of laboratories occurred after almost 20 years had elapsed since the recognition of the physical significance and potential for applications of the orbital angular momentum carried by optical vortex beams. A rapid growth in interest in electron vortex beams followed,...

Wavefront engineering is an important quantum technology. Here, we demonstrate the design and production of a robust C-shaped and orbital angular momentum (OAM) carrying beam in which the doughnut shaped structure contains an adjustable gap. We find that the presence of the vortex line in the core of the beam is crucial for the robustness of the C-...

Electron vortex beams constitute the first class of matter vortex beams which are currently routinely produced in the laboratory. Here, we briefly review the progress of this nascent field and put forward a natural quantum basis set which we show is suitable for the description of electron vortex beams. The normal modes are truncated Bessel beams (...

A general orbital angular momentum (OAM) mode selection principle is put forward involving the rotationally symmetric superposition of chiral states. This principle is not only capable of explaining the operation of spiral zone plate holograms and suggesting that naturally occurring rotationally symmetric patterns could be inadvertent sources of vo...

The recent discovery of vortex electron beams [1–3] has generated many interests and the new understanding may lead to applications in material characterization [4]. The method of creating vortex electron beams using a forked aperture [2] is popular but has a drawback that electron vortex beams with different orders are produced side‐by‐side in the...

Recent methods of dark field TEM are being explored to extent the information and frequency of data capture in dynamic in-situ experiments on nanocatalyst systems under reaction conditions (1). The broad need is for a faster frame rate than can conveniently be achieved with HAADF STEM imaging, starting from the similarly expressed goals for tomogra...

Based on the vectorial Rayleigh diffraction integral, the analytical propagation expression of a nonparaxial vectorial vortex beam carrying orbital angular momentum (OAM), diffracted at a circular aperture, is presented. The effects of both f parameter and topological charge (m) on the nonparaxiality of apertured vectorial vortex beams are studied....

The development of metamaterials operating at visible light wavelengths requires metamaterials to be produced with nanoscale structure over large areas. Improvements in the efficiency of electron beam lithography (EBL) could play an important role in accelerating this development. In this paper we show the production of a shaped probe for use in EB...

We report the synthesis of cobalt nanoparticles of a range of sizes from raw cobalt fluoride powder using high intensity focused electron beams and their characterisation in-situ in a TEM. A variety of beam intensities with different focussing level in a JEOL JEM 3010 TEM at an acceleration voltage of 300 kV is used. Depending on the beam intensity...

of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

We report a versatile electron beam (e-beam) synthesis method for the local fabrication of ferromagnetic nanocrystals “on demand”. A localized irradiation in a transmission electron microscope (TEM) is used to convert a raw cobalt fluoride material into ferromagnetic metal by means of formation of a short-range ordered distribution of well-defined...

Various metal fluoride crystals were subjected to electron beam irradiation at 200 and 300 kV using transmission electron microscopy in order to study in-situ fabrication of 3D metal nanostructures. Lithium fluoride, cobalt fluoride and aluminum fluoride salt fragments were chemically reduced and transformed by the electron beam to the correspondin...

We report an in-situ transmission electron microscope method for the fabrication of three dimensional nickel nanobeads. Conversion of nickel fluoride into a three dimensional porous, partially fluorine depleted aggregate is shown as intermediate state, followed by transformation into metallic beads. The bead size ranges from 10-600 nm and can be co...

We report an electron beam (e-beam) fabrication method to produce sub-5 nm structures, e.g. nanohole-arrays, nanojunctions and nanotips inside a TEM. The method is demonstrated using ferromagnetic nickel cross-sectional TEM specimens as well as electrochemically etched nickel tips. Different e-beam shapes and electron guns are compared, including p...

Electron tomograms can be reconstructed from a variety of projection imaging techniques in TEM, some of which are sensitive to the surface or the bulk, to the structure or chemistry, or operate under different resolution regimes. We introduce a concept of combining two acquisition series using two different complementary modes to form a single hybr...

We present a design for a novel coarse positioning system based on a tilting platform which is positioned using linear slip/stick motors. The design differs from common arrangements of stacked x, y, and z motors, and also ball mounted slip/stick motors, by allowing easy access along the central axis of the microscope holder. The drive motors are hi...

We report about a novel combination of two etching techniques for generating nanostructures, which individually are well established: (i) metal tip etching in NaOH, as e.g. used for STM or atom probe tip making, and (ii) anodic oxidation of aluminium for the generation of self-organised ordered pores. The non-planar geometry in both these etching p...

Electron beam (e-beam) fabrication of nanostructures by transmission electron microscopy (TEM) is rapidly developing into a top-down nanofabrication method for the sub-5 nm fabrication of structures that cannot usually be realised using resist based lithographic techniques or by the focused ion beam patterning methods. We describe the usage of a va...

A variety of tomographic experiments and modes for electron tomography of nanostructures are introduced, derived from the general concepts of quantitative computed tomography, binarised geometric tomography, including shape-from-silhouette, and spectroscopic chemical mapping. Our emphasis is on working out concepts of combining at least two of thes...

We present the extension of electron tomography from a pure characterization technique into a three-dimensional nanofabrication technique using focused electron beams in the scanning transmission electron microscope. Two-dimensional surface patterning techniques are insufficient to achieve full three-dimensional nanosculpting, instead, multiple sam...

Etching techniques are used to fabricate nickel and tungsten tips suitable as probes for in-situ SEM and TEM experiments. The smallest tip radius achieved is 10nm for Ni and 1.5 nm for W. Depending on the electrolyte concentration and speed of tip movement during etching, the macroscopic morphology can be changed between conical and concave shapes...

of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Electron beam nanofabrication is a powerful technique to generate finest structures by atom ablation while concurrently observing the progress by TEM imaging [1–3].