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ABSTRACT: 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 variety of e-beam
shapes, including point and elliptical line focus, as well as a comparison of LaB6 and field-emission guns (FEGs), to achieve versatile sculpting of nanodot arrays, nanobridges and nanotips. We operate our
patterning on free-standing nickel (Ni) thin film laterally connected to a silicon (Si) substrate as well as to free-standing
Ni nanotips, where we achieve a novel three-dimensional (3D) nano-sculpting methodology.
Applied Physics A 04/2012; 102(1):205-211. · 1.63 Impact Factor
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ABSTRACT: A new electron tomography methodology is presented which allows the reconstruction of external particle shape from lattice
resolved high-resolution electron microscopy images. The technique is based on the shape-from-silhouette binary backprojection
algorithm after filtering of the lattice contrast. The simultaneous availability of particle shape and crystallographic lattice
plane orientations allows the correlation of faceting with crystallographic orientations. The method is demonstrated using
a multiply twinned decahedral gold nanoparticle. Eligibility limits in terms of degree of convexity are derived.
KeywordsGold nanoparticles-Tomography-Twin boundaries-3D reconstruction-Instrumentation-Metrology
Journal of Nanoparticle Research 04/2012; 12(3):1045-1053. · 3.29 Impact Factor
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ABSTRACT: In this paper, we present a recently upgraded 7-degree-of-freedom nanomanipulation system inside a TEM with focus on applications in electron tomography of nanostructures. Previously it has been emphasised that the traditional way of mounting of nanoparticles on flat carbon films might not be the best way to achieve very high tilt angle series free of missing wedge for tomography. Mounting of particles ex-situ at the end of nanotips allows for higher tilt but poses challenges in the success rate of getting the object attached to the very tip. Our mixed translation & rotation nanomanipulator based on 3 coarse positioners in x, y, z by piezoelectric slip-stick actuation and 3 fine directions by a piezo-tube, as well as a rotational piezodrive, allows not only to rotate a cylindrical object by up to a full circle, but now also features a second specimen mount for a "fixed sample", which could host a reservoir of nanoparticles on carbon film, or nanoparticles inside nanopores. The translation system can then be used to pick up particles on demand and rotate them with the piezoelectric actuator. In particular, we describe how nanoparticles dispersed and transferred onto a normal TEM grid are picked up by a W tip for subsequent large tilt rotation.
Journal of Physics Conference Series 01/2012; 1(371):012051.
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ABSTRACT: Electron tomography is a valuable 3D characterization technique, so far limited to a nanometer scale resolution. This paper intends to explore the extension of the technique to the atomic scale. Computer simulations of three HREM technologies are performed on a CeO2 crystal and the effects of the voltage, focus spread and aberration correction are assessed. Experimental challenges related to the technique are discussed and illustrated on HREM images of a CeO2 nanoparticle acquired with the JEM 2200FS aberration-corrected TEM. Finally, geometric tomography is proposed as a complementary shape reconstruction technique when only few zone-axis tilt images are used for the lattice-resolved reconstruction.
Journal of Physics Conference Series 08/2010; 241(1):012071.
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ABSTRACT: Metallic multilayers have been used in cross-sectional TEM specimen geometry to explore nanostructuring routes using ion and electron beams (top-down) as well as self-organised nanopatterning (bottom-up). Intermetallic alloy formation during heat treatment is studied for binary and ternary layer compositions. A choice of pillars (0D), 1D and 2D layer geometries are used to explore dimensionality effects.
Journal of Physics Conference Series 08/2010; 241(1):012030.
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ABSTRACT: 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 point versus line focus and field-emission versus LaB6 guns. As an extension of this 2-D patterning of nanostructures, a 3-D nanofabrication technique has been introduced using a high tilt tomographic holder. An electrochemically etched nickel tip of initially 18 nm in radius is sculpted down to sub-5 nm diameter. In some cases, mostly in 3-D nanofabrication, a protrusion during hole drilling was observed and confirmed by EELS as pure nickel.
Journal of Physics Conference Series 08/2010; 241(1):012075.
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ABSTRACT: 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 hybrid tomogram. As the main application, composite nanoobjects are presented for which a low-resolution 3D chemical mapping mode for the object interior can be combined with a high-resolution surface sensitive mode to precisely define the object exterior shape.
Journal of Physics Conference Series 08/2010; 241(1):012008.
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ABSTRACT: Piezoelectric nanoactuators, which can provide extremely stable and reproducible positioning, are rapidly becoming the dominant means for position control in transmission electron microscopy (TEM). This technology links the accurate manipulation of samples at the nanometer regime with TEM's imaging resolution and therefore offers a better way to advance the understanding of the properties of nano-scale systems. A family of piezo-drives inserted into TEM goniometers have been developed for different applications, such as nano-contacting, electrical measurement, mechanical and tribological test by indentation, as well as electron tomography which reveals the objects' physical and chemical structures in three dimensions (3D).
Microscopy and Microanalysis 01/2010; 2(16):1784. · 3.01 Impact Factor
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B.D. Medford,
B.L. Rogers,
D. Laird,
N. Berdunov,
A.J. Lockwood,
T. Gnanavel,
W. Guan,
J. Wang, G. Möbus,
B.J. Inkson,
P.H. Beton
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ABSTRACT: 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 highly compact and co-linear and may be easily incorporated in an off-axis configuration, leaving a central cylindrical region with an approximate diameter of 3mm which is available to accommodate screened electrical wiring and optical fibres. We show that the tripod can be used to manoeuvre two metallic tips towards each other in-situ in a TEM in nanometre-scale lateral steps.
Journal of Physics Conference Series 01/2010; 1(241):012057.
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ABSTRACT: Metallic multilayers of Cu/Al/Ti composition were studied by transmission electron microscopy (TEM) and plasmon energy-loss mapping as prototypes of nanoscale reactive multilayer systems with exothermic alloy formation in oxygen-free conditions. The selection and arrangement of alloy phases by the system during ex situ and in situ heating experiments were found to depend not only on temperature but strongly on the initial volume ratios of metals, and to a lesser degree on the dimensionality of the reactive sample. Here, a two-dimensional sample was represented by ex situ heating of the full multilayer structure, a one-dimensional sample refers to in situ heating of thin cross-sectional TEM specimens, while a zero-dimensional sample (or metallic dot-array) was obtained after cutting thin pillars using focused ion beams. Lamellar self-organized alternation between Heusler phase and Cu 9 Al 4 was found.
Journal of Materials Research 01/2010; 25(6):1196-1203. · 1.43 Impact Factor
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ABSTRACT: Nanoscale energy dissipation and failure mechanics of silica nano- and micro-particle-filled polymer composite have been evaluated
using advanced electron microscopy, scanning probe microscopy and nanoindentation techniques. Objective of this study is to
understand the role of nano-microstructure and strength of particle–matrix interface and effects of geometrical gradient (spatial
variation of surface height) and mechanical gradient (spatial variation of effective modulus) on energy dissipation process
and subsequent failure mechanisms. In order to understand the role of geometrical gradient and mechanical gradient during
the energy dissipation process, we carried out amplitude modulation simulation of soft–hard–soft surfaces with zero initial
height and with 10nm initial height of the hard material. Nanoindentation results show hardness and reduced modulus of the
nanocomposite are homogeneous; however, the hardness and reduced modulus of the microcomposite were found to be heterogeneous.
In the microcomposite, the sharp edges of particles increase friction, and heterogeneous mechanical properties result in high-energy
dissipation. Large particles with weak interfacial bonding were easily removed, it resulting in defects on the sliding surface
that acted as failure “hot-spots”. These characteristics result in relatively high friction and wear of the microcomposite.
The nanocomposite showed better tribo-mechanical performance compared with that of the micro-particle-filled composite.
Tribology Letters 03/2009; 34(1):11-19. · 1.58 Impact Factor
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ABSTRACT: We examine chemical mapping of reaction phases in a Cu-Al multilayer system using low-loss electron energy loss spectroscopy spectrum imaging and image spectroscopy techniques. The sensitivity of the plasmon peak position and shape to various crystal structures and phases is exploited using postprocessing of spectra into second derivative plasmon maps and line scans. Analytical transmission electron microscopy is complemented by studies of the orientation relationship of the multilayer system using high-resolution electron microscopy of interfaces and selected area diffraction. The techniques have been applied to the Cu-Al multilayer sample and sharply bound epitaxial phases are found, before and after heat treatment.
Microscopy and Microanalysis 03/2009; 15(1):54-61. · 3.01 Impact Factor
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ABSTRACT: Electron tomography allows the 3D quantitative characterization of nanostructures, provided a monotonic relationship is fulfilled between the projected signal and the atomic number and thickness of the specimen. This requirement is not satisfied if the micrographs are affected by (i) diffraction contrast, (ii) detector saturation or (iii) contrast inversion due to absorption (high-angle scattering) at high thickness. Artefacts related to the non-monotonic tomography acquisition are examined using computer simulations and experimental tilt series of tungsten tips and CeO(2) nanoparticles. Conditions are derived under which in spite of the non-linear artefacts the information is sufficient for reconstructing the 3D morphology of convex objects by geometric tomography.
Journal of Microscopy 11/2008; 232(1):186-95. · 1.63 Impact Factor
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ABSTRACT: Piezoelectric nanoactuation, which is rapidly becoming established as state-of-the-art positioning control in transmission electron microscopy (TEM), is extended here to include a rotational degree of freedom. A piezoelectric goniometer with both translational and rotary drive action has been designed with high level of miniaturization to fit into a standard TEM specimen holder shaft without compromising any of the performance of the default TEM goniometer and without any modifications to the TEM. Enhanced functionality of such a goniometer-in-goniometer is outlined and experimental results for electron tomography of nanostructures over a full tilt range of views, without any missing angles, are demonstrated. Microsc. Res. Tech., 2008. © 2008 Wiley-Liss, Inc.
Microscopy Research and Technique 10/2008; 71(11):773 - 777. · 1.79 Impact Factor
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[show abstract]
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ABSTRACT: Piezoelectric nanoactuation, which is rapidly becoming established as state-of-the-art positioning control in transmission electron microscopy (TEM), is extended here to include a rotational degree of freedom. A piezoelectric goniometer with both translational and rotary drive action has been designed with high level of miniaturization to fit into a standard TEM specimen holder shaft without compromising any of the performance of the default TEM goniometer and without any modifications to the TEM. Enhanced functionality of such a goniometer-in-goniometer is outlined and experimental results for electron tomography of nanostructures over a full tilt range of views, without any missing angles, are demonstrated.
Microscopy Research and Technique 10/2008; 71(11):773-7. · 1.79 Impact Factor
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ABSTRACT: The three-dimensional (3D) morphology of two related classes of CeO2 nanostructures is reconstructed using electron tomography with three image acquisition modes for comparison. The samples include free standing nanoparticles of 40nm diameter with octahedral morphology and nanoscale precipitates of 100–200 nm diameter embedded in glass with dendritic morphology, both of fluorite-type CeO2. Tomograms were successfully constructed from (i) bright field (BF) TEM, (ii) a novel single-window energy-filtered TEM (EFTEM), and (iii) annular dark field STEM (ADF) modes. Advantages and disadvantages of the imaging modes are summarized.
Journal of Physics Conference Series 09/2008; 126(1):012016.
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ABSTRACT: 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 and the tip end can be modified. HREM and EELS characterisation is used to determine oxide layer thickness. For Ni the oxide layer is found to be extremely thin, while for W various thicknesses can be achieved. The particular amorphous WO3 layer is imaged by plasmon resonance mapping in EELS, which turns out to be a sensitive and discriminative technique exploiting the much larger plasmon peak width of the oxide compared to the pure metal.
Journal of Physics Conference Series 09/2008; 126(1):012071.
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ABSTRACT: In this work we have investigated the influence of nanoscale and microscale structure on the tribo-mechanical performance and failure mechanisms of two biocompatible dental polymer composites, with different reinforcing particulates, using advanced microscopy techniques. Nano- and micro structural analysis reveals the shape, size and distribution of the particles in the composites. In the microparticle filled polymer composite (microcomposite), the particles are of irregular shape with sharp edges with non-uniform distribution in the matrix. However, in the nanoparticle filled composites (nanocomposite), filler particles are spherical in shape with uniform distribution in the matrix. From nanoindentation measurements, hardness and reduced modulus of the microcomposite were found to be heterogeneous. However, the hardness and reduced modulus of the nanocomposite were found to be homogeneous. The nanocomposite shows better tribo-mechanical performance compared to that of the microcomposite.
Journal of Physics Conference Series 09/2008; 126(1):012057.
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Microscopy and Microanalysis 07/2008; 14:460 - 461. · 3.01 Impact Factor
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ABSTRACT: Over the last decade, electron tomography has developed into a powerful and widely applicable tool for three-dimensional (3D) characterisation problems in materials science [1-3]. However, the limited tilt range available from the commercial goniometers in modern TEMs of materials science laboratories remains a major problem to avoid missing wedge artefacts. Often the narrowest of available pole piece gaps is preferred in materials science for maximising lattice resolution which allows only size reduced specimens to be rotated to high angles [4].
EMC2008, Aachen, Germany; 01/2008
