A Cs Corrected HRTEM: Initial Applications in Materials Science

electron optics instrumentation A CS Corrected HRTEM: Volume 37E Number 1 July 20, 2002 Initial Applications in Materials Science Contents A Cs Corrected HRTEM: Initial Applications in Materials Science..........2 Quantitative Environmental Cell - Transmission Electron Microscopy: Studies of Microbial Cr(VI) and Fe(III) Reduction................................................6 Simulations of Kikuchi Patterns and John L. Hutchison†, John M. Titchmarsh†, David J. H. Cockayne†, Comparison with † † † Experimental Patterns...........................14 Guenter Möbus , Crispin J. D. Hetherington , Ron C. Doole , Experimental Atomically Resolved Fumio Hosokawa††, Peter Hartel††† and Max Haider††† HAADF-STEM Imaging -A Parametric Study .............................22 †Department of Materials, Oxford University Observation of Waterborne Protozoan †† Oocysts Using Electron Optics Division, JEOL Ltd. ††† a Low-Vacuum SEM............................26 CEOS GmbH A Possible Efficient Assay: Low-Vacuum SEM Freeze Drying and Its Application for Assaying Bacillus thuringiensis Formulations Quality............................29 Observations of Algae and Their Floc in A new aberration-corrected TEM/STEM is being designed for applications in Water Using Low-Vacuum SEM and materials science. Here we describe preliminary tests of the objective lens CS EDS.......................................................34 corrector, and present images showing some of the advantages in applications Development of Nano-Analysis Electron of CS corrected HREM in the study of advanced materials. Microscope JEM-2500SE ....................40 Development of JSM-7400F; New Secondary Electron Detection Systems Permit Observation of Introduction and energy-filtered imaging, EDS and hologra- Non-Conductive Materials ...................44 phy. A wide objective lens pole-piece gap is Applications of Image Processing Since the invention of the electron micro- possible because of the CS correction and Technology in Electron Probe scope over 60 years ago the effects of aberra- allows a large range of specimen tilt while Microanalyzer.......................................48 tions in round electromagnetic lenses have retaining HREM imaging capability. In order Technology of Measuring Contact Holes imposed fundamental limits on their perform- to minimise interference and to maximise ther- Using Electric Charge in a Specimen ..54 ance. In the case of HREM, spherical aberra- mal stability, the microscope column, power Organic EL Display Production Systems supplies and operating consoles will all be -ELVESS Series-..................................59 tion was shown by Scherzer [1] to limit inter- In-Situ Observation of Freeze Fractured pretable resolution, although special tech- installed in separate, adjacent rooms within a Red Blood Cell with High-Vacuum niques have been devised to get around this, purpose-built laboratory, now under construc- Low-Temperature Atomic Force such as “aberration-free focus” for particular tion. Components of the new instrument are Microscope ...........................................62 crystal structures [2]. Small-probe techniques, being independently developed and tested Peak Deconvolution of Analysis in and in particular STEM, are similarly limited prior to final assembly. Auger Electron Spectroscopy..............66 by spherical aberration in the probe-forming JEOL's Challenge to Nanotechnology ....70 lenses. The need for a small, well-defined Assessment and Preliminary Progress in Development of High-Density probe with a high current remains a pressing Applications of CS Corrected Reactive Ion Plating .............................74 need here. The recent successful development Applications of High-Power Built-in of aberration correctors for electromagnetic Objective Lens Plasma Gun...........................................78 lenses [3, 4] will radically change this situa- The objective lens CS corrector [5] has now Introduction of New Products.................81 tion, as they offers dramatic improvements for been developed and tested on a separate JEM- direct interpretation of image contrast as well 2010F instrument and we illustrate here some as for microanalysis with improved spatial res- of the initial results. Tests have confirmed the Cover micrograph olution and sensitivity in materials science stability of the corrector over lengthy periods. Experimental Kikuchi pattern (left) and simu- applications. This corrector is based on the design concept lated Kikuchi pattern (right) of MgO [100]. of Rose [6], and consist of a series of two (See pages 14 to 21) A New Aberration-Corrected hexapole and two transfer lenses doublets Microscope (round lenses) located between the objective Courtesy of Professor Emeritus Michiyoshi and first intermediate lenses in the microscope Tanaka, Institute of Multidisciplinary Research In order to exploit these benefits a new column. This is shown in Fig. 1. The col- for Advanced Materials, Tohoku University. TEM with aberration correction of both con- umn height is increased by some 24 cm. The denser and objective lenses is now being successful operation of the corrector depends developed for installation at Oxford University. upon accurate measurement of the main aber- This instrument is based on the JEM-2010FEF rations present, and this is done by acquiring instrument with a Schottky field emission images of an amorphous film and measuring source and aims to provide an HREM informa- relative changes in two-fold astigmatism and tion limit and HAADF resolution close to 0.1 defocus with changes in incident beam tilt. nm. Analytical features will include EELS This in turn is achieved by calculating Fourier transforms of the images, and displaying these †Parks Road, Oxford, OX1 3PH, UK as a tableau showing the variations as a func- Serving Advanced Technology †E-mail: john. [email protected] tion of beam tilt and azimuthal orientation. ( 2) JEOL News Vol. 37E No.1 2 (2002) very close to zero. A more detailed comparison of this image with those obtained using other techniques will be presented elsewhere [10]. It has been noted that while direct interpretation of aberration-corrected images prom- ises to be more accurate in many applications, image simulation will still be required [11]. Suppression of phase contrast A new area in which aberration correction will provide further significant benefits is the characterization of nanometer-sized particles. Important parameters are microstructure, shape and size, all of which are difficult to determine accurately by conventional HREM imaging. First, in conventional HREM imaging, i.e. at Scherzer focus, the presence of a prominent Fresnel fringe around the edge of a small particle will make precise size measurement difficult. Second, delocalised contrast (see above) gives rise to “ghost images”, particularly in a FEG instrument. Third, free-standing nanoparticles must be supported, usually on amorphous substrates for plan-view imaging. The immediate advantages of CS-corrected imaging are clearly illustrated in Fig. 5. This shows an image of a small (~ 4 nm) CdSe quantum dot on an amorphous carbon support film. In an uncorrected image of such a small particle recorded at Scherzer defocus, the presence of strong Fresnel fringes and “ghost” images would obscure the fine scale structural features, which are further upset by strong phase contrast arising from the carbon film. The image recorded in the aberration-corrected state provides the following immediate advantages: the image is recorded at very close to Gaussian focus so that there is no Fresnel fringe around the edges of the particle; there are no ghost images present and the phase contrast from the amorphous support film has been almost completely suppressed. Under these conditions the amplitude contrast contribution is optimised, and the contribution from Fig. 1. Column of JEM-2010F microscope with CS corrector installed. the more strongly scattering Cd and Se is enhanced. The size, shape and internal struc- ture of the crystallite, only 2 nm in size, are thus revealed with much improved clarity [12]. This method was first described by Zemlin and (0.8 eV) and objective lens chromatic aberra- co-workers as a way of determining coma-free tion coefficient of 1.2 mm for the URP pole- Atomic resolution imaging of alignment conditions for HREM [7]. Figure 2 piece operating at 200 keV. complex oxide structures shows a tableau of diffractograms from a spec- Although high resolution images of com- imen of amorphous Ge imaged in an uncor- Applications of CS Corrected plex oxide structures have been widely studied rected state: here the electron beam has been for many years the resolution of contrast at aligned approximately to the voltage axis, and HREM in Materials Science oxygen sub-lattice sites remains a serious chal- two-fold astigmatism has been corrected. The Localised contrast at boundaries lenge. High-voltage HREM has been used inner four off-axis diffractograms represent a [13], and more recently image restoration tech- beam tilt of 9 mrad, the outer twelve a tilt of One of the major limitations in the current niques have been successfully developed to 18 mrad. The strong effects of axial coma, 3- generation of field-emission-gun HREM achieve this [14]. It is now clear that the fold astigmatism and spherical aberration are instruments is the delocalisation of contrast at enhanced high resolution capability afforded all evident; the tableau is evidently non-centro- boundaries and interfaces

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