Symposium Organizers
Manfred Ruehle Max-Planck-Institute for Metals Research
Larry Allard Oak Ridge National Laboratory
Joanne Etheridge Monash University
David Seidman Northwestern University
NN1: Overviews and Techniques
Session Chairs
Monday PM, November 30, 2009
Room 204 (Hynes)
9:30 AM - **NN1.1
Correlating Atomic and Nanoscale 3D Structure and Chemistry by Aberration Corrected STEM, Electron Tomography and Atom Probe Tomography.
Matthew Weyland 1 2 , Xiang-Yuan Xiong 1 2 , Jasmine Shih 2 3 , Barry Muddle 3
1 Monash Centre for Electron Microscopy, Monash University, Clayton, Victoria, Australia, 2 Materials Engineering, Monash University, Clayton, Victoria, Australia, 3 ARC Centre of Excellence of Design in Light Metals, Monash University, Clayton, Victoria, Australia
Show AbstractThe nanoscale characterisation of engineering materials is being driven by advances in thee techniques; Aberration corrected (Scanning) Transmission Electron Microscopy (S)TEM, Electron Tomography (ET) and Atom Probe Tomography (APT). One of the principal challenges is the correlation of results from all three sources. However, this should be looked on as an opportunity; the weakness of one technique can be compensated directly by the strength of another. For example APT has a fundamentally high resolution but the data suffers from unavoidable geometric distortions. Conversely ET is of lower resolution but should be geometrically correct. A combination of these techniques would seem a logical step. Such a combined approach to nanoscale analysis will be presented by demonstrated by its application to one materials system; the 2xxx series Al-Cu-Li alloys. The strength to weight ratio of these alloys, combined with their weldability, has seen their use in high end aerospace applications. Their properties are derived from a dispersion of nanoscale secondary phases. Understanding the nucleation, growth and thermal evolution of which is critical for understanding both how properties arise and how they can be controlled. In particular the role of minor alloying elements in thermal ageing, such as Mg, Zn, Ag and Si needs to be understood. How these play a role in solute clustering and the precipitation of a population of small (<10 nm) intermediary precipitates are challenging to study using conventional (S)TEM and inconclusive using APT in isolation. Aberration corrected STEM was carried out on a double corrected Titan3 80-300 system, installed in a building and room optimised for the instrument; exceeding the manufactures environmental specifications for acoustic, vibration and magnetic fields by at least ten times. This allows for long time period imaging and spectral acquisitions with minimal distortions. This system also has single and dual axis ET capability in TEM and STEM. Atom probe tomography was carried out on an Oxford nanoScience 3DAP. While not as rapid as a newer local electrode AP or laser pulsed system the collection efficiency of this system is unmatched, leading high quality sampling statistics and mass resolution. Results will be demonstrated from both experimental techniques from different specimens from the same alloy. In addition initial results on combined analysis of the same needle geometry specimen will be presented
10:00 AM - **NN1.2
High-Precision Atomic Resolution Measurements by Aberration-Corrected Transmission Electron Microscopy.
Knut Urban 1
1 Solid State Research, Research Center Juelich, Juelich Germany
Show AbstractIn the new generation of aberration-corrected transmission electron microscopes genuine atomic resolution can be achieved. This resolution is defined by the condition that any change in the position or occupancy of an atomic site shows up in the image as an individual signal localised at the corresponding position. It has been demonstrated that individual lateral atomic shifts can be measured at picometer precision. The basis for atomic resolution is in general a series of images from which the electron-exit plane wave function (EPWF) is reconstructed. For this the aberration function of the objective lens has to be known. The EPWF does in general not show the specimen structure. It contains effects of the illumination conditions and it depends on sample thickness. To conclude from the EPWF to the structure requires an iterative solution of the Dirac-Schrödinger equation for a suitable atomic model. Only after this model is suitably precise (picometer precision) one can make the wanted measurements. There are cases where due to dynamic effects, e.g. electron radiation damage, a complete image series cannot be recorded. Experience shows that for favourable cases, provided the NCSI technique (see below) is used, the structure of the sample can nevertheless be reconstructed in a forward calculation (from a structure model to the image intensity distribution) even for the extreme case where only a single image is available. This is feasible if some of the interferometric information provided by the image series can be obtained by exploiting the different effective extinction conditions appertaining to atom columns occupied by different types of atoms. An example are perovskites, e.g. BaTiO3, where along high symmetry orientations differently occupied atomic columns occur. For crystalline specimens the technique exploiting the full potential of aberration correction is negative spherical aberration imaging (NCSI). In this technique the Zernike-type phase shift of the scattered waves to convert phase into amplitude information is achieved by employing an aberration function tilting the phase in mathematically negative direction (negative phase contrast). This can only be done in aberration-corrected instruments by adjusting the spherical aberration for a small negative residual value of the spherical aberration parameter and combining this with an overfocus. In order to arrive at an understanding of the contrast enhancement under NCSI conditions two assumptions of the classical contrast theory have to be abandoned. These are the weak-phase and the weak-amplitude object approximation. The extraordinary contrast under NCSI conditions is due to additive contributions of both amplitude and phase contrast. This is demonstrated by recent investigations on the LaAlO3/SrTiO3 interface, ferroelectric domain walls in PZT and dislocations in epitactic oxide heterostructures. In these physically relevant atomic shifts could be measured at the atomic level.
10:30 AM - **NN1.3
On the Many Advances in Laser Pulsing of Atom Probe Tomographs.
Thomas Kelly 1
1 , Imago Scientific Instruments Corporation, Madison, Wisconsin, United States
Show AbstractA resurgence of interest in laser pulsing of atom probe tomography occurred in the early part of this decade with the development of commercial instrumentation that needed to address the widest possible spectrum of materials. Since then, commercial instruments that are designed for ease of use and high performance have become widely adopted. There have been several key advances in this time including the advent of stable, high-optical-quality lasers (M2≈1, where M2 is a measure of the laser beam quality for focusing) with ultra-short pulses (electron thermalization times < 10 ps), and atom probe tomographs that take advantage of these features. These laser properties have made it possible to engineer systems with a small laser focus spot (< 10 micron diameter) that deliver high data collection rates (>106 atoms/second), large fields of view (> 200 nm diameter) and very high mass resolution (<1/1000 FWHM, 1/475 FW0.1M at full field of view for a mass-to-charge-state ratio of 27 Da) with high analytical sensitivity (<10 atomic parts per million). Engineering these lasers to achieve top performance, while maintaining ease of use has required development of automated laser alignment and laser focusing, vibration isolation of the specimen cooling system, and implementation of sub-50 ps timing electronics. Imago has remained focused on developing a practical instrument that delivers this high performance on all specimen material classes. This talk will present some of the most important developments in the field of laser pulsing of APT. Applications that benefit from these developments will be emphasized. These include dopant mapping of microelectronic devices, microstructural characterization of minerals and bulk dielectrics, and multilayer quantum well devices.
11:30 AM - NN1.4
Quantitative Scanning Transmission Electron Microscopy.
James LeBeau 1 , Scott Findlay 2 , Xiqu Wang 3 , Allan Jacobson 3 , Leslie Allen 4 , Susanne Stemmer 1
1 Materials Department, University of California, Santa Barbara, California, United States, 2 Institute of Engineering Innovation, The University of Tokyo, Tokyo, 113-8656, Japan, 3 Department of Chemistry, University of Houston, Houston, Texas, United States, 4 School of Physics, University of Melbourne, Melbourne, Victoria, Australia
Show AbstractThe accurate determination of TEM sample thickness is a necessity for quantitative comparisons between experimental and simulated images. This is of particular interest for the investigation of interface structures where a variety of interpretations can be possible if the specimen thickness is not known. Many of the commonly used techniques are either not suitable over a wide thickness range, or are influenced by parameters that are difficult to determine independently, such as surface layers in low-loss EELS. In other cases, thickness measurement techniques require changing the electron optical or imaging conditions. Here we present a new technique, position averaged CBED (PACBED), which, in conjunction with simulations, can be used to measure local sample thicknesses between 1 and 100 nm without changing from atomic resolution STEM imaging conditions. In the second part of this presentation, we will discuss the combination of accurate thickness determination with STEM images placed on an absolute intensity scale and will show that direct comparisons between simulation and experiment become possible. Using this approach, we have recently shown that high-angle annular dark-field (HAADF) STEM images of a SrTiO3 single crystal are in near perfect agreement with theory. To further investigate the possibility of an atomic number dependent contrast mismatch, we also present a study of single crystalline PbWO4, which contains two cations with large atomic numbers (ZPb = 82 and ZW = 74). By utilizing the PACBED method to determine experimental thicknesses, we show that near perfect agreement between simulations and experiments is achieved for PbWO4. We will emphasize the importance of incorporating accurate Debye-Waller factors. The variation of the image background intensity will be explored to highlight the importance of image simulations to fully appreciate the subtleties of electron scattering by crystals containing heavy elements.
11:45 AM - NN1.5
Imaging the Real Space Intensity Distribution of a Sub-Ångström Electron Probe after Scattering by a Crystal.
Sorin Lazar 1 2 , Gianluigi Botton 2 , Joanne Etheridge 3
1 , FEI Electron Optics, 5600 KA Eindhoven Netherlands, 2 Canadian Centre for Electron Microscopy, Dept of Materials Science and Engineering, Brockhouse Institute for Materials Research, McMaster University, Hamilton, L8S 4M1, Ontario, Canada, 3 Monash Centre for Electron Microscopy and Dept of Materials Engineering, Monash University, 3800, Victoria, Australia
Show AbstractThe development of aberration correctors has enabled the generation of electron probes smaller than one Ångström in diameter, enabling data to be obtained from atomic-scale volumes of a specimen. Theoretical calculations predict that sub-Ångström electron probes will rapidly disperse onto atomic columns adjacent to the initial probe position, so that imaging, diffraction and electron energy loss signals do not necessarily derive from atoms located immediately beneath the probe1-3. If this data is to be readily interpretable on the atomic scale, in 3 dimensions, it is critical that we understand from which atoms within the specimen the electron probe is scattered and use this understanding to develop methods that facilitate the easy extraction of local 3D atomic and electronic structure.To this end, we have measured, for the first time, the intensity distribution in real space of the scattered probe across a given optical plane within the specimen. A double-aberration corrected Titan3 80-300 FEG-TEM was aligned meticulously so that a plane within the specimen was imaged precisely onto the detector plane. The probe corrector is essential for forming the Ångström-scale probe and the image corrector is essential for the faithful transfer of the scattered probe onto the detector plane, with minimal disturbance by aberrations. It is emphasised that immense care was taken to align the two correctors to focus on to the same object plane. (This is similar but not identical to the confocal arrangement used to image the unscattered probe in a double-aberration corrected TEM4 and more recently to obtain depth resolution in STEM images of core/shell Au/Pt nanoparticles5.) The electron probe was scanned systematically across the specimen and the resulting scattered intensity distribution recorded at 0.2-0.5Å intervals during the scan. The experiments were conducted in an ultrastable environment, enabling the probe position on the specimen to be correlated reliably with the corresponding measurement of the scattered intensity distribution. By imposing a digital aperture on the data set, depth resolution can be obtained.Our first data sets were taken at 300kV under various probe forming and energy filtered conditions, with the probe located at multiple points on and between atom columns with different local 3D site symmetries in known atomic structures. An analysis of these results and their implications for extracting information from specific atomic-sites within a specimen will be discussed at this meeting.[1] C Dwyer, J Etheridge, Ultramic 96 343 (2003)[2] S Findlay, L Allen, M Oxley, C Rossouw Ultramic 96 65 (2003)[3] P Voyles, Grazul, D Muller Ultramic 96 251 (2003)[4] P Nellist, G Behan, A Kirkland, C Hetherington App Phys Lett 89 124105 (2006)[5] N Zaluzec, M Weyland, J Etheridge Micro.& Microanal. in press (2009)
12:00 PM - NN1.6
Theoretical Analysis and Applications of Annular Bright Field Scanning Transmission Electron Microscopy Imaging.
Scott Findlay 1 , Naoya Shibata 1 2 , Hidetaka Sawada 3 , Eiji Okunishi 3 , Yukihito Kondo 3 , Takahisa Yamamoto 1 4 , Yuichi Ikuhara 1 4 5
1 , The University of Tokyo, Tokyo Japan, 2 , PRESTO, Japan Science and Technology Agency, Saitama Japan, 3 , JEOL Ltd., Tokyo Japan, 4 , Japan Fine Ceramic Center, Nagoya Japan, 5 , Tohoku University, Sendai Japan
Show AbstractAnnular dark field imaging (ADF) scanning transmission electron microscopy (STEM) has become a highly popular atomic resolution imaging technique. That high angle ADF images are directly interpretable over a wide range of sample thicknesses and that the signal strength scales strongly (approximately quadratically) with atomic number are particularly attractive features of the method. However, because of the strong scaling with atomic number, columns consisting of light elements are generally not visible in images when columns consisting of heavy elements are also present. It has recently been shown that placing an annular detector within the bright field or direct scattering cone leads to an imaging mode wherein the locations of both light and heavy element columns can be imaged simultaneously. Referred to as annular bright field (ABF) imaging, by direct analogy to ADF imaging, ABF images have the appearance of absorption images: columns are indicated by dark contrast. The ABF imaging mode is also robust over a wide range of specimen thicknesses. There is a need for a simple model to establish the dynamics of ABF imaging and to aid the further development of this technique. The phase object approximation, the basis of conceptually similar investigations in the early days of STEM imaging, breaks down very quickly in the high resolution STEM imaging regime. Instead, we show that a simple s-state channeling model suffices to describe the primary scattering mechanism behind the formation of the ABF images. The interference between the s-state and the remainder of the wavefunction serves to deplete the electron scattering to the outer area of the bright field disk. For heavier columns, absorption due to thermal scattering also plays a significant role. Using this model we explore the imaging dynamics of ABF, the dependence on defocus, and consider optimum probe-forming and collection aperture sizes. Example experimental results are also presented.[S.D.F. is supported as a Japan Society for the Promotion of Science (JSPS) fellow. N.S. acknowledges support from Industrial Technology Research Grant program in 2007 from New Energy and Industrial Technology Development Organization (NEDO) of Japan.]
12:15 PM - NN1.7
Atomic Size Mismatch Strain Induced Reversed ADF-STEM Image Contrast Between Semiconductor Hetero-epitaxial Layers and Substrates.
Xiaohua Wu 1 , Jean-Marc Baribeau 1 , James Gupta 1
1 Institute for Microstructural Sciences, National Research Council Canada, Ottawa, Ontario, Canada
Show AbstractThe intensity of annular dark field scanning transmission electron microscopy (ADF-STEM) image is known to depend on the average atomic number, Z, in a simple Zn power-law relationship, where for most microscope geometries, n is in the range of 1.6 to 1.9. In this presentation, we report observations of reversed ADF-STEM image contrast between semiconductor heteroepitaxial layers and substrates. The molecular beam epitaxy grown dilute nitride GaNxAs1-x (x = 0.029 and 0.045) layers on GaAs and dilute carbide Si1-yCy (y ≤ 0.015) layers on Si were studied by ADF-STEM. Both GaNAs/GaAs and SiC/Si systems show a unique contrast characteristic in ADF-STEM images: the lower average atomic number heteroepitaxial strained layers GaNAs and SiC are brighter than the higher average atomic number Si and GaAs substrates for ADF detector semiangle up to 90 mrad. This reversed contrast is due to the localized strain resulting from the difference in atomic size between the substitutional atoms (N, C) and host atoms (GaAs, Si). The application of the reversed ADF-STEM contrast will be discussed in relation to the determination of very small amount of substitutional atom compositions in dilute systems, which is a very difficult task for analytical TEM techniques such as energy dispersive x-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS).
12:30 PM - NN1.8
Crystallographic Analysis of a Precipitate Phase in Ni30Pt20Ti50 Shape Memory Alloys.
Libor Kovarik 1 , Fan Yang 1 , Anita Garg 2 , Ronald Noebe 2 , David Diercks 3 , Michael Kaufman 4 , Michael Mills 1
1 , The Ohio State University, Columbus, Ohio, United States, 2 , NASA Glenn Research Center, Cleveland, Ohio, United States, 3 , University of North Texas, Denton, Texas, United States, 4 , Colorado School of Mines, Golden, Colorado, United States
Show AbstractShape memory alloys based on the NiPtTi system represent a promising material for high temperature applications up to 300°C due to their excellent work output and transformation strains. The precipitation of intermetallic phases in the NiPtTi alloys plays a key role for achieving the desirable shape memory properties. The previously unknown precipitate phase in a Ni30Pt20Ti50 alloy, which forms homogenously in the B2 austenite matrix by a nucleation and growth mechanism, and increases the martensitic transformation temperature of the base alloy, has been analyzed using electron diffraction, high-resolution STEM HAADF imaging and 3-D atom probe tomography. The analysis was performed on an FEI Tecnai TF20 operated at 200kV and an FEI Titan 80-300 with Cs-correction on the electron probe, and operated at 300kV. The 3-D atom probe tomography was performed on a LEAPTM 3000 built by Imago Scientific Instruments, Inc. The experimental observations show that the precipitates have non-periodic character along one of the primary crystallographic directions. It will be shown that the non-periodic character of the structure can be explained in terms of random stacking of three variants of a monoclinic crystal that coherently share (001). The monoclinic crystal structure is closely related to the high temperature cubic B2 phase; the departure of the structure from the B2 phase is attributed to: 1) ordering of Pt atoms on the Ni sublattice and 2) relaxation of the atoms (shuffle displacements) from the B2 sites. The shuffle displacements and the overall structural refinement were obtained from ab initio calculations. The combined use of electron diffraction analysis, high-resolution imaging, compositional analysis by the atom probe and ab initio calculations enable the full crystallographic description of this non-periodic precipitate phase to be determined.
12:45 PM - NN1.9
Combined TEM and APT Characterization of Nano-structured Ferritic Alloys.
James Bentley 1 , M. Miller 1 , D. Hoelzer 1
1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractWithin the last decade mechanically alloyed (MA) nanostructured ferritic alloys (NFA) with outstanding mechanical properties have been developed. A combination of sub-micrometer grains and high concentrations (>1023 m-3) of small (<5 nm diameter) Ti-Y-O nanoclusters (NC) that exhibit remarkable thermal stability is believed to be chiefly responsible for the attractive tensile, fracture and creep properties. An important potential application of NFA is for fission and proposed fusion reactors because of their mechanical properties and potential to be highly radiation-resistant through enhanced recombination of point defects and trapping of transmutation-produced He at NC. Since the discovery of NC in 12YWT (Fe-12wt.%Cr-3%W-0.4%Ti-0.3%Y2O3), atom probe tomography (APT) has continued to provide detailed information on the composition of both the NC and the matrix (e.g. solute levels) in NFA such as 14YWT, MA957 and Japanese 9Cr ODS steel. Sophisticated treatment of the APT data is required to yield reliable NC compositions. Transmission electron microscopy (TEM) was expected to complement APT by providing broader scale characterization of the often heterogeneously distributed NC. However, early efforts revealed that conventional TEM (including bright- and dark-field diffraction contrast, phase contrast, and high-resolution imaging) and high-angle annular dark-field (HAADF) scanning TEM (STEM) imaging were unreliable for imaging NC. Greater success was achieved with energy-filtered TEM (EFTEM) methods, especially Fe-M jump-ratio images that reliably reveal NC as small as 2 nm diameter for sufficiently thin specimens (<50 nm). Such images are insensitive to thin surface oxide films or modest surface contamination. Other EFTEM methods such as thickness and elemental (O, Ti-L, Cr-L and Fe-L) mapping have also been usefully applied. The ways in which characterization by combined APT and EFTEM continue to provide an improved understanding of the nature and behavior of NC in NFA will be described. Illustrative examples will be drawn from extensive results of structure-processing correlations that guide alloy development and structure-property correlations that help understand the response to tensile- and creep-testing or the effects of irradiation with ions or neutrons. Research supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, by the Office of Fusion Energy Sciences, by the Office of Nuclear Energy, Science and Technology through I-NERI 2001-007-F and the Advanced Fuel Cycle Initiative, and at the ORNL SHaRE User Facility by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
NN2: Instrumentation
Session Chairs
Monday PM, November 30, 2009
Room 204 (Hynes)
2:30 PM - **NN2.1
A Review of the TEAM Project at its Transition from the Development Phase to a Research Facility.
Ulrich Dahmen 1
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe major driving force for the TEAM (Transmission Electron Aberration-corrected Microscope) project was the idea of providing a sample space for electron scattering experiments in a tunable electron optical environment. The project was initiated as a five-year collaborative effort to redesign the electron microscope around aberration correcting optics. The resulting improvements in spatial, spectral and temporal resolution, the increased space around the sample, the enhanced signal to noise, and the possibility of unusual electron-optical settings serve to enable new types of experiments. At the transition of TEAM from a construction project to a research instrument in a user center, this talk will review the scientific motivation and progress of the project and describe the current status of the TEAM microscope as a user facility. The capabilities of the instrument will be illustrated in the context of its recent application to research in nanoscale materials science, ranging from interfaces in metals and alloys to the defect structures in graphene, oxides and semiconductors. This talk will conclude by outlining future scientific opportunities for aberration-corrected microscopy and challenges for further developments in instrumentation and technique.
3:00 PM - **NN2.2
Hitachi HD2700, a Dedicated High Spatial Resolution STEM for Materials Research.
Yimei Zhu 1 , Hiromi Inada 2 1 , Lijun Wu 1 , Dong Su 1 , Joe Wall 1
1 , Brookhaven National Laboratory, Upton , New York, United States, 2 , Hitachi High Technologies Corp.,, Ibaraki Japan
Show AbstractThe first Hitachi aberration corrected scanning transmission electron microscope (HD2700C STEM) was successfully installed and tested at Brookhaven’s Center for Functional Nanomaterials. The instrument has a cold-field-emission electron source with high brightness and small energy spread [1]. The excellent electro-optical design and aberration correction make the instrument ideal for atomically resolved STEM imaging and energy-loss spectroscopy using transmitted electrons as well as for atomically resolved SEM using secondary and backscattered electrons to retrieve structural, chemical and bonding information of materials. We have been working on single atom imaging and spectroscopy to push the resolution limit of the instrument. The ability to image surface and bulk structure simultaneously at atomic resolution can revolutionize the field of microscopy and imaging. Although aberration correction improves spatial resolution of the instrument, it does not make image interpretation easier due to the large convergent angles used to gain beam current. To understand the image contrast, we developed our own computer codes based on the multislice method with frozen phonon approximation to calculate annular-dark-field (ADF) images and compare them with experiment [2]. Our study demonstrates that the ADF image contrast (or Z-contrast) does not follow the simple I~Z2 or I~Z1.8 power rule as many expect. Although ADF images indeed show Z-dependence contrast, the power law is only valid under very high collection angles for very thin specimen. The ADF image intensity also strongly depends on dynamic and static lattice displacement of the sample. To correctly interpret the ADF images, the effect of atomic thermal vibration (Debye-Waller factor) of the atoms must be taken into account. Various case studies will be presented [3].[1] Y. Zhu, and J. Wall, chapter in: Aberration-corrected electron microscopy, ed. Hawkes P W, (Elsevier/Academic Press). pp. 481 (2008)[2] H. Inada, L. Wu, J. Wall, D. Su, and Y. Zhu, Journal of Electron Microscopy, 58, 111 (2009).[3] Work supported by the U.S. DOE, Office of Basic Energy Science, under Contracts No. DE-AC02-98CH10886.
3:30 PM - **NN2.3
State-of-the-Art Atom Probe Tomography.
Michael Miller 1 , Kaye Russell 1
1 MSTD, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe performance of the three-dimensional atom probe (3DAP) has made remarkable improvements over the last five years. The use of local counter electrodes positioned 10-50 μm from the apex of the specimen has enabled higher pulse repletion rates for voltage pulsing and consequently, markedly reduced the data acquisition times. Crossed delay line, single atom sensitive detectors may be positioned closer to the specimen to provide a wider field-of-view of the specimen and hence larger volumes of the needle-shaped specimen are sampled. Datasets in the billion atom range are now possible. This detector combined with the associated high speed digital timing system allows the identity of multiple ions striking the detector on an evaporation pulse to be correctly assigned to their atomic coordinates. The incorporation of a curved energy-compensating reflection lens into the time-of-flight mass spectrometer has significantly improved the mass resolution for voltage pulsed instruments so that the individual mass peaks of all elements can be fully resolved to the noise floor. The higher mass resolution enables simple background noise subtraction methods to be used and thus improves the quality of the compositional determinations. The re-introduction of laser pulsing together with focused ion beam (FIB) based specimen preparation techniques have extended the range of materials that may be characterized by atom probe tomography (APT). In addition, major advances have been made in the statistical analysis of the atom probe data. The performance and limitations of a state-of-the-art dual voltage- and laser-pulsed local electrode atom probe (LEAP®) will be described.Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
4:30 PM - NN2.4
Benefits of Cc-Corrected Imaging for High-Resolution and Energy-Filtered TEM.
Bernd Kabius 1 , Peter Hartel 2 , Maximilian Haider 2 , Heiko Mueller 2 , Stephan Uhlemann 2 , Ulrich Loebau 2 , Joachim Zach 2 , Goetz Hofhaus 1 , Irene Wacker 4 , Rasmus Schroeder 3
1 Material Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 , CEOS GmbH, Heidelberg Germany, 4 , Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen Germany, 3 CellNetworks, Heidelberg University, INF 267, Heidelberg Germany
Show AbstractChromatic aberration has been limiting spatial resolution for transmission electron microscopy (TEM) experiments where the energy spread of the beam and the coefficient of chromatic aberration of the objective lens (Cc) determine the optical properties of the instrument. This is the case for a wide scope of TEM applications such as in-situ experiments, energy filtered TEM, Lorentz TEM and tomography. A first prototype of an electron optical system correcting spherical as well as chromatic aberration has been designed [1] and fabricated within the TEAM project. Test experiments of the corrector have shown that Cc can be fully corrected for acceleration voltages between 80 and 300 kV. Cc can be adjusted with an accuracy of ±5 μm. The information limit at 80 kV is enhanced by Cc-correction from 1.8 Å to 1.0 Å. Cc-correction has a strong impact on energy-filtered TEM (EFTEM) which requires large energy windows to collect a sufficient number of electrons. Elemental maps at interfaces of oxide thin film samples have been derived from Cc-corrected energy-filtered images. As a result, the apparent width of the interface can be decreased significantly by Cc-correction [2]. Imaging of thick samples is important for in-situ applications, for thick biological sections and for tomographic experiments. Spatial resolution is degraded for these applications by inelastic scattering, which increases the energy width of the transmitted electrons. However, with the availability of chromatic and spherical aberration correction the focal length of the imaging system does not change significantly for electrons within a wide range of lost energy and thus a larger fraction of the electron beam contributes to image contrast in a productive manner. First experiments will be presented which demonstrate the benefit of Cc-correction for imaging of thick samples. The impact of Cc-correction for Lorentz microscopy and other scientific areas will be discussed.References[1] M. Haider, M. Müller, S. Uhlemann, J. Zach, U. Löbau and R Höschen, Ultramicroscopy, 108 (2008) 167.[2] B. Kabius, P. Hartel, M. Haider, H. Müller, S. Uhlemann, U. Loebau, J. Zach and H. Rose, Journal of Electron Microscopy, 58 (2009) 147.The submitted work has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357 as part of the TEAM project, a multilaboratory collaborative effort and under contract W-13-109-ENG-38.
4:45 PM - NN2.5
Using Imaging Cs-Correctors to Optimize Image Contrast: What are The Best Settings for, e.g., Graphene at 80kV and Why?
Edgar Voelkl 1 , Young-Chung Wang 1 , Bin Jiang 1 , Lianfeng Fu 1 , Jan Ringnalda 1 , Feng Shen 1 , Dong Tang 2
1 , FEI Company, Hillsboro, Oregon, United States, 2 , FEI Company, Einhoven Netherlands
Show AbstractOnce upon a time, before imaging correctors were available, certain techniques were used for optimizing image contrast and point resolution. The standard way to go about this was to consider the sample as “thin” to justify the argument that modifications to the electron wave traveling through the sample were occurring mostly to its phase and not its amplitude. In this context, the use of higher acceleration voltages was advantageous because the basic assumption of a thin sample was more justifiable while, at the same time, point resolution was improved (despite the spherical aberration coefficient Cs remaining rather fixed). Under these circumstances, spherical aberration and defocus were rather welcome with their means of making phase information visible. The imaging condition delivering the best phase image is known as Scherzer focus [Reimer], where the first pass-band of the phase-contrast-transfer-function (PCTF) provides the largest range of spatial frequencies to be transferred from the phase into the image intensity. For LaB6 systems this was ideal as information-limit and point-resolution basically coincide. For microscopes with a field emitter however, large amounts of extra information beyond the point resolution appears and complicates image interpretation.With today’s image correctors, Cs ~0μm, and thus Scherzer focus (~sqrt{Cs λ} ~0nm, with λ as wavelength) is close to the so-called Gauss focus [Reimer]. When plotting the PCTF for such a case it becomes obvious that very little phase information is transferred into the final image. What is recorded instead is mainly the amplitude modulation that was so nicely argued away in the pre-image-corrector age. This of course is fine for some samples, but certainly not for all.As an example, by dropping the acceleration voltage to 80kV it is possible, with today’s correctors, to fully resolve the Graphene lattice. As an added bonus, beam damage (knock-on damage) is significantly reduced and images can be acquired before the sample is destroyed. But although the decrease in acceleration voltage increases the amplitude contrast in general, a monolayer of Graphene turns out to be mainly a phase object, whereas a 20-30 nm thick semiconductor device is better imaged in focus as an amplitude object.Thus, it appears there are at least two corrector settings to consider and the choice has to be made according to the sample: for optimum amplitude contrast conditions: Cs = 0 and for optimum phase contrast conditions Cs < 0 [Jia].Even with a fully automated image corrector, life seems to have become just a little more complicated, as now there is a choice to make between imaging conditions that depend on the sample. This will be discussed in detail by comparing different imaging conditions for single layer Graphene versus a 20-30 nm thick semiconductor device.[Reimer] L Reimer, Transmission Electron Microscopy, 4th edition, Springer 1997[Jia] C. L. Jia et al., Science, Vol 299 (2003)
5:00 PM - NN2.6
Development of Multi-functional Analytical Environmental TEM and its Application.
Toshie Yaguchi 1 , Akira Watabe 1 , Yasuhira Nagakubo 1 , Takafumi Yotsuji 1 , Kazutoshi Kaji 1 , Takeo Kamino 1
1 , Hitachi High-Technologies Corporation, Hitachinaka-shi Japan
Show AbstractIn the field of nano-materials such as catalysts, demands on a transmission electron microscope (TEM) as characterization tool is rapidly increasing. In materials characterization using TEM, the features described as follows are strongly required from industries: one is the three dimensional characterizations. The others are the analysis of mechanism of materials formation or structural changes of materials in various environments. In response to the requirements, we improved the performance of H-9500 300kV analytical TEM. For 3D structural analysis of a specific site of materials, FIB-TEM compatible specimen rotation holder[1], [2] with new morse-taper-needle stub and improved rotation mechanism has been developed. For high temperature high resolution in-situ observation of standard sized TEM specimen, a double tilt specimen heating holder with and without thermocouple has been developed. The maximum heating temperature of the heating element is around 1800 degrees Celsius and a 0.2mm thick metal foil with the maximum diameter of 3.4mm can be heated to around 1300 degrees Celsius. For high temperature high resolution in-situ observation of nano-materials in gaseous atmosphere, a conventional pumping system has been replaced by newly developed differential pumping system with 3-sets of turbo molecular pump with the pumping speed of 260l/s and a direct-heating type specimen heating holder with a gas injection nozzle and a miniature metal evaporator has been developed [3], [4]. The specimen holder realized the possibility of synthesis, characterization and property measurement of the in-situ synthesized nano-materials in various environments in a TEM specimen chamber uninterrupted. Elemental analysis of the synthesized materials using EDX system can be carried out even at high temperatures up to around 700 degrees Celsius. Additionally, side entry environmental cell with a built-in specimen heater has been developed. The gas pressure inside the environmental cell can be varied in the range between vacuum of around 10-5Pa and atmospheric pressure. According to the kind of gas introduced to the cell and heating temperature, use of various kind of separating membrane with various thicknesses is considered. All of these newly developed specimen holders are possible to use with high resolution objective lens pole-piece with the lens gap of 4mm.TEM images and electron diffraction patterns of Si particle were observed at various pressures. References[1] T.Yaguchi et al., Proc. Microsc. Microanal. 9 (Suppl .2) (2003) 118-119.[2] T.Yaguchi et al.,Proc. Microsc. Microanal. 10 (Suppl .2) (2004) 1164-1165.[3] T.Kamino, et al.,Journal of Electron Microscopy 54(6) (2005) 497-503.[4] T.Kamino, et al.,Journal of Electron Microscopy 55(5) (2006) 245-252.
5:15 PM - NN2.7
Correlative STEM at the Atomic Scale: The Ultimate Materials Analysis Tool.
David Bell 1 4 , Stephan Irsen 2 , Richard Schillinger 3 , Stefan Meyer 3
1 School of Enginnering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 4 Center for Nanoscale Systems, Harvard University, Cambridge, Massachusetts, United States, 2 , Forschungszentrum Caesar, Bonn Germany, 3 Carl Zeiss NTS GmbH, Carl Zeiss SMT, Oberkochen Germany
Show AbstractAnalytical electron microscope development shows that the trend in electron gun design has been towards brighter emission with less energy spread. Aberration correction on a thermal FEG system has many well-known and demonstrated advantages over non-corrected electron microscopes both for TEM and STEM applications. The combination of a probe Cs correction with an electron source monochromator yields a further step along the path to an ideal microscope. The further benefits of workable monochromator integration are for applications that especially depend on energy resolution such as spectroscopy and advanced contrast mechanisms such as “atomic scale” energy filtered imaging. The addition of a probe corrector allows the illumination aperture size to be increased and provides significant increases in the beam current for the same probe size. There has been much work in the improvements of STEM technology for the applications of atomic resolution HAADF, column stability being of critical importance. Other features such as new improvements of collection optics of the spectrometer entrance aperture and minimizing the elastic scattering artifacts, further improve the ability to perform atomic-column EELS imaging.Probe aberration-correction, monochromator, in-column energy filter and advanced x-ray detection sensitivity combined on one analytical platform provide a foundation for correlative microscopy using simultaneous signal collection as an approach towards the realization of simultaneous atomic-column HAADF, EELS and XEDS analysis.
5:30 PM - NN2.8
On the Relation between Probe Size and Image Resolution in the Helium Ion Microscope.
Larry Scipioni 1
1 , Carl Zeiss SMT, Inc., Peabody, Massachusetts, United States
Show AbstractWe discuss the actual image resolution obtained on practical samples with the helium ion microscope (HIM). The probe shape of a charged particle optical system is determined by the properties of the beam source and the effect of the optics on that beam as it is brought to its final focus. Characterization of the probe involves simplifications that consider the beam to be an analytical shape (e.g. Gaussian) for which a single number can represent the beam distribution at the sample surface. Measurement of the probe is then carried out on a sample with edges that offer abrupt transitions in secondary electron signal. The most common metric is the distance scanned across a physical edge to get a rise of signal from 25% to 75% of the maximum, that is when the beam is parked on the material. Scanning in such a way over the edge of a suspended asbestos (crocidolite) fiber is used in HIM, and a probe size of 0.25 nm has been measured under optimized conditions.It is understood in scanning electron microscopy, however, that the resolution for small features on real samples is often much worse than the probe size specification stated for the instrument. This is due partially to beam-sample interactions that occur beneath the surface and subsequently contribute to the collected signal. Thus the resolution is degraded by non-local information. Furthermore, time-varying excitations penetrating the microscope system itself can broaden the beam by wobbling its landing position. All of these effects are integrated together to produce an apparent beam width that represents the practical information-gathering capability of the tool. In this paper we look at probe size definition and measurement in HIM. We extend the measurements to several real samples and also make comparison to SEM data, with the final aim to gain greater quantitative information on how the increased surface sensitivity observed in HIM imaging will translate into final spatial resolution.
5:45 PM - NN2.9
Laser-assisted Atom Probe Analysis of Bulk Ceramics.
Tadakatsu Ohkubo 1 , Yimeng Chen 2 , Masaya Kodzuka 2 , Koji Morita 1 , Kazuhiro Hono 1 2
1 , National Institute for Materials Science, Tsukuba Japan, 2 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba Japan
Show Abstract Recent successful implementation of pulse lasers to assist field evaporation have expanded the application areas of the atom probe technique to a wide variety of materials including semiconductors. However, little work has been carried out on the analysis of insulating materials. A few exceptions are the successful analysis of thin oxide films. To the authors' knowledge, there is no report on successful atom probe analyses of bulk insulating ceramics. The main objective of this work was to demonstrate that insulating bulk ceramics can be quantitatively analyzed by the 3DAP assisted with ultraviolent (UV) laser pulses [1]. As a demonstration sample, we have selected nanocomposite ceramics made of 3 mol% Y2O3 stabilized tetragonal ZrO2 with 30mol% MgAl2O4 spinel. These materials were developed to achieve high-strain-rate superplasticity [2]. The average grain size of the t-ZrO2 and MgAl2O4 were approximately 70 ~ 80 nm, respectively. The electrical resistivity of the sample was estimated at least 109 Ωcm. For 3DAP analysis, a Yb:KGW femtosecond laser with a third harmonic generator (λ=343nm, 1.4μJ/pulse, pulse duration of 400 fs) operating at the pulse frequency of 2kHz was adopted to a locally built 3DAP instrument with CAMECA's fast delay line detector. The laser was incidented at 90o to the long axis of the specimen, being focused to a spot size of approximately 150 μm and the polarization was parallel to the tip axis. The atom probe analysis was conducted at 64K with evaporation rates of 0.01~0.02 ion/pulse, and 4×106 ions were collected. The DC voltage applied on the tip was increase from 2.3 to 6.7 kV during the analysis. Even from such high resistivity material, we were able to observe field ion microscopy (FIM) images using Ne as an image gas. All the peaks of atom probe mass spectrum were attributed to the ions of all the constituent elements. Part of Al, Zr, and Y were detected as oxide molecular ions, and only Mg was detected as single atom ions without oxide molecular ions. The 3D reconstructed atom maps of Al+Mg, Y, Zr and O shows the presence of nanocrystalline Mg and Al rich grains (MgAl2O4) consistent with the microstructural feature observed by SEM and TEM. The atom probe tomography has also shown that Al and Y atoms were segregated along ZrO2/ZrO2 grain boundaries. This work has demonstrated that field ion microscopy as well as atom probe analysis are possible even with insulating bulk ceramics material. We will also show 3DAP data obtained from Al2O3, MgO, (Ce,Dy)O2, ZnO sintered bulk ceramics. This work opens up new application areas of the atom probe tomography. This work was supported by CREST, JST and the WPI Initiative on Materials Nanoarchitronics, MEXT, Japan.[1] Y. M. Chen, T. Ohkubo, M. Kodzuka, K. Morita, K. Hono, Scripta Mater. in press.[2] K. Morita, K. Hiraga and B. -N. Kim, Acta Mater. 55, 4517 (2007).
NN3: Poster Session
Session Chairs
Manfred Ruehle
Winfried Sigle
Tuesday AM, December 01, 2009
Exhibit Hall D (Hynes)
9:00 PM - NN3.1
The Advantages and Limitations of FIB-Based Specimen Preparation for Atom Probe Tomography.
Kaye Russell 1 , Michael Miller 1
1 MSTD, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractOver the last few years, the focused ion beam (FIB) milling technique has become widely adopted for fabricating atom probe needle-shaped specimens partly because of the wide range of new materials that may be characterized with the laser-assisted local electrode atom probe and also because of the need for extracting specimens from site-specific locations. For example, several techniques have been developed for making specimens from a variety of different starting geometries of materials including powders, ribbons, thin sheet, and even pre-thinned and characterized transmission electron microscopy (TEM) disks. Lift-out techniques enable atom probe specimens to be made from site-specific regions, such as specific phases, grain boundaries, interfaces, embedded or implanted regions, such as produced by ion irradiation, etc. Lift-out techniques also enable small volumes of material to be used, which significantly reduces the mass and hence the activity of radioactive materials.Traditionally, electropolishing has been the dominant technique for the