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 fabrication of the needle-shaped atom probe specimens. However, many materials do not electropolish uniformly due to the presence of different phases. More importantly, electropolishing can often produce a blade-shaped end-form, which results in different magnifications in the atom probe data along the major and minor axes of the blade. This asymmetry can be rectified by the use of a FIB-based annular milling technique. One of the disadvantages with FIB-based technique is the undesirable gallium implantation in the near surface regions of the specimen. Gallium implantation can alter the microstructure and, due to the comparably large size of gallium atoms, can impose significant stress in the surface layer of the atom probe specimen, which can cause premature failure during analysis. Implanted gallium levels up to 30% have been measured with the atom probe. Therefore, examination and positioning operations are performed with the electron beam to minimize exposure, and protective caps are used where possible. Low accelerating voltages, 2-5 keV, are used during the final stages of milling to reduce the extent of the gallium implanted layer. As atom probe tomography (APT) measures the local gallium content of the analyzed volume, the gallium-enriched surface regions must be excluded from subsequent data analysis. 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.
9:00 PM - NN3.10
Strain Relaxation in Planar InAs Epitaxial Layers Studied by High-Resolution Transmission Electron Microscopy.
Krishnamurthy Mahalingam 1 , Kurt Eyink 1 , Marlon Twyman 1 , Jodi Shoaf 1 , Larry Grazulis 1
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractThe growth of epitaxial InAs thin films on (100)-GaAs surface is of significant interest for a variety of optoelectronic device applications. In particular, the formation InAs self-assembled quantum dots (SAQDs) during growth under Arsenic-stabilized conditions is an active field of research. The main driving force for SAQD formation is the reduction strain energy (due to a lattice mismatch of about 7%), which leads to a transition from planar to 3D-island growth mode when the surface coverage exceeds ≈1.65 monolayers (ML) (5Å). Comparatively less studied is the strikingly different growth mode exhibited when InAs is grown under In-stabilized conditions wherein, the InAs layer is observed to maintain a planar morphology from growth onset to well beyond the 1.65 ML limit (i.e. thicknesses around 60 Å) [1,2]. A particularly interesting feature in this growth mode is that strain relaxation occurs predominantly via formation of Lomer dislocations, with the extent of relaxation depending on growth conditions employed. The inherently low threading dislocation density combined with the possibility to control the degree of strain relaxation makes planar InAs thin films interesting materials for a variety applications, such as "tunable substrates" with lattice constants ranging from 5.65 Å(GaAs) - 6.06 Å(InAs).In this work, we have performed a systematic study of the influence of growth conditions on the structure of planar InAs thin films. Specifically, we conducted several growth experiments wherein the substrate temperature was varied from 623K – 693K, under As flux conditions such that the In-rich (4x2) reconstruction was maintained. The samples so grown were investigated by plan-view and cross-sectional high-resolution transmission electron microscopy (TEM). The plan-view TEM examination of all films examined revealed a well developed periodic array of Lomer dislocations. Depending on growth temperature, the average dislocation spacing determined from these images was in the range 65Å – 88Å. In addition, the local strain relaxation in the InAs layer above and in-between dislocations in was determined from cross-sectional HRTEM lattice images. A systematic dependence between the dislocation spacing, degree of strain relaxation and film thickness was also observed. Further details on the correlations between observed results and growth conditions employed will be presented. References1. A.Trampert et al. Appl. Phys. Lett. 66, 2265 (1995).2. W.J.Schaffer et al. J. Vac. Sci. Tech B1, 688 (1983).
9:00 PM - NN3.11
Transmission Electron Microscopy Observation on Hydrothermally-treated Aluminum Film in Ultrapure Water.
Yusuke Hosoki 1 , Junichi Shimanuki 2 , Zhiyoug Qiu 1 , Takashi Ishiguro 1
1 Materials Science and Technology, Tokyo Univercity of Science, Noda Chiba Japan, 2 , NISSAN ARC, Co. Ltd., Yokosuka Kanagawa Japan
Show Abstract In our previous study, it was confirmed that rf sputtered metallic aluminum (Al) film on glass substrate was transformed into boehmite (AlOOH) film by boiling in ultrapure water. Its optical transmittance exceeded the glass substrate itself. Such a coating decreased the reflectance of the glass substrate, which was a useful characteristic of the anti-reflective coating. As for a possible optical explanation for this, it was confirmed that the coated film did in fact produce a refractive index between the air and the glass. However, the structural reason for this has not been clear. Also the mechanism of this hydrothermal reaction has not been clear. Therefore transmission electron microscopy observation on the hydrothermally treated Al specimen has been performed. The rf sputtered Al films were deposited on both substrates of elastic carbon (e-C) film and Corning #1737 glass substrates for plane view observation and cross-sectional observation. The hydrothermal treatment was induced at 368 K, in stirred ultrapure water (resistivity 18.2 MΩ cm) for the specimen with glass substrate and/or in a water steam bath for the specimen with an e-C substrate. In order to evaluate middle stage of the reaction, hydrothermal treatment was interrupted and then observed by transmission electron microscope (TEM). Specimen for the cross-sectional observation was prepared by using focused ion-beam (FIB) milling (FEI, Nova200 Nano Labo). TEMs of TECNAIG2F20 (FEI Co.) and JEM-2000FX (JEOL Ltd.) were used. Transformed boehmite film shows a porous structure including boehmite nanofibers. This is one of the reasons for the low density of the film and the smaller refractive index than the one for bulk boehmite. At the middle stage of the reaction, three distinguished layers were observed, namely, an upper porous layer of boehmite, a lower unreacted metallic Al layer, and a middle transient layer, which was relatively-oxygen-abundant substance. This fact suggests that the hydrothermal reaction of Al film is not as simple as 2Al+4H2O→2AlOOH+3H2, but more complex process. The detailed results will be described in the meeting.
9:00 PM - NN3.12
Aberration-Corrected HRTEM Analysis of Transition Structure in Phase Boundary of ZrO2 Ultra-Thin Film.
Takanori Kiguchi 1 2 , Toyohiko Konno 1 2 , Naoki Wakiya 3 , Kazuo Shinozaki 4
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 Center for Integrated NanoTechnology Support, Tohoku University, Sendai, Miyagi, Japan, 3 Department of Materials Science and Chemical Engineering, Shizuoka University, Hamamatsu, Shizuoka, Japan, 4 Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, Meguro, Tokyo, Japan
Show AbstractZrO2 has a monoclinic phase with a large spontaneous strain under room temperature, which leads to a complicated domain structure with a large roughness at surface and interfaces [1]. This fact means that the monoclinic phase ZrO2 itself cannot be used to gate dielectrics and buffer layers. IIt is known that ZrO2 experiences the phase transition from cubic to tetragonal, and to monoclinic phases. It is also reported that ZrO2 nano-particles have tetragonal phase [2]. This result suggests that the thinning of the ZrO2 film should make tetragonal phase stable, which would lead to analyze the tetragonal to monoclinic martensitic phase transformation of un-doped ZrO2 free from phase separation and point defects that often arise from the dopant cations and oxygen vacancy. The objectives of this study are, hence, to (1) apply an aberration-corrected HRTEM to atomic-resolution imaging including oxygen atoms of ZrO2 ultra-thin film, and (2) elucidate the atomic displacements around tetragonal-monoclinic phase boundary.Un-doped ZrO2 films were deposited on a p-Si(001) wafer with thin SiO2 layers by Pulsed-Laser Deposition (PLD) technique [1]. The nanostructure of the films were investigated using the aberration-corrected transmission electron microscope (TITAN80-300, 300kV,Cs<1um, FEI). The local two-dimensional Wiener filtering was applied to the images (HREM Research Inc.). The multislice image simulation was conducted by Mac TempasX (Total Resolution LLC).Plan-view images of ZrO2 layer show that approximately 10nm precipitates exist in the matrix. Diffractograms from the plan-view image indicate that the matrix is tetragonal or cubic phase and that the precipitate is monoclinic one. The monoclinic phase has the coherent interface between tetragonal matrixes without misfit dislocation. The image clearly shows the O atoms as light gray spots as well as Zr atoms as dark gray spots, which are confirmed by the multislice image simulation. The atomic resolution image around a tetragonal - monoclinic phase boundary and the profile of the projected Zr-Zr and O-O distance across the phase boundary as a function of atomic columns show that the transition layer of about 1.8nm, which corresponding to about 3.5 unit cells of ZrO2, exists along the phase boundary. The projected Zr-Zr and O-O distances shows a gradual change from the tetragonal to the monoclinic phase in the transition layer. This result indicates that the transition layer would relax the large strain, about +4% in volume strain due to the phase transition.The cross-sectional TEM observation shows that the tetragonal phase has the tetragonality of 1.026, which is larger than the reported data [3]. Then, the film is strained in the in-plane direction, which would control the nucleation of the monoclinic phase.[1] T.Kiguchi et al. Mater. Sci. Eng. B 148, 30 (2008) [2] M.W.Pitcher et al. J. Am. Ceram. Soc. 88, 160 (2005) [3] D.G. Lamas et al. Scripta Materialia 55, 553 (2006)
9:00 PM - NN3.13
On Texture and Grain Size Evolution in Electrodeposition.
Patrick Cantwell 1 2 , Matthew Schneider 1 2 , Eric Stach 1 2
1 Materials Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractCompetitive grain growth and crystallite orientation in Ni electrodeposits has been studied using the transmission electron microscope. A unique sample geometry enables plan view imaging of the Ni film as a function of distance from the substrate within a single specimen. By correlating hollow-cone dark-field images at a range of film thicknesses, the orientation distribution of crystallites at each film thickness can be determined and compared to the grain size distribution at that thickness. The goal of the study is to develop a better understanding of thin film growth by closely examining the relationship between competitive grain growth and texture development at discrete levels within a single thin film.
9:00 PM - NN3.14
Informatics for Quantitative Analysis of Atom Probe Tomography Images.
Krishna Rajan 1
1 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractThis presentation will outline the use of data dimensionality reduction techniques in quantifying atom probe images. The application of such methods in enhancing the detection of clustering and spatial associations of atoms in the presence of noisy data is discussed. The value of applying both linear (eg. principal component analysis) and non-linear data dimensionality reduction techniques (eg. IsoMap algorithms) are presented. The use of these methods to the study multicomponent clustering and spatial distribution maps is explored.
9:00 PM - NN3.2
Raman Imaging – New Tool for Materials Characterization.
Sergey Mamedov 1 , Eunah Lee 1 , Fran Adar 1 , Andrew Whitley 1
1 , Horiba Jobin Yvon Inc., Edison, New Jersey, United States
Show AbstractCarbon-carbon composites are used in aerospace materials as well as some automotive, high-end sports and helmet applications. Their advantages include stiffness, strength, and light weight, all properties which are superior to those of steel or other metals, and they can be used at high temperatures. However, even though they are less brittle than conventional ceramics, they do lack impact resistance. Because of the costs involved in manufacturing these materials, and the importance of their applications, especially in aerospace, any technique that can characterize them is of interest. Images of a composite created on a Raman microscope has been used to characterize a carbon-carbon composite. It is shown the information is encoded in both details of the spectral features and polarization behavior. This information can be useful in engineering these materials. Polarized Raman maps were collected on the Aramis using confocal optics, the 633nm laser and the 300g/mm grating. At each point in the map there is a spectrum that includes the G mode, the D mode (when present) and the overtone and combination bands between 2400 and 3300 cm-1 . Using multivariate techniques to extract information from the hyperspectral cube, it was possible to create Raman images where the fibers and the matrix carbon are differentiated, even though the spectral differences are quite subtle. Correlations between the polarized Raman images and standard polarized light microscopy enables determination of the orientation of the graphite planes in the matrix which can effect the physical properties of the composite.
9:00 PM - NN3.3
Difference Raman for Enhancing Image Resolution By Accurate Tip Positioning of An Atomic Force Probe That Enhances or Shadows The Raman Signal.
Rimma Dekhter 1 , Hesham Taha 1 , Avraham Israel 1 , David Lewis 1 , Aaron Lewis 2
1 , Nanonics Imaging Ltd., Jerusalem, 0, Israel, 2 , Hebrew University of Jerusalem, Jerusalem, 0, Israel
Show AbstractTip enhanced Raman scattering (TERS) has been shown as a potential technique for overcoming limitations of conventional micro Raman spatial resolution and for other apertureless near-field optical measurements based on plasmonic interactions. In this talk we will compare the resolutions obtainable by such plasmonic enhancement techniques as compared to a method we have developed based on the ultra-sensitive nature of difference Raman. In this latter technique an AFM probe with an exposed tip geometry that is optimized to block a nanometric region of a sample will be used in conjunction with difference Raman to obtain significant improvements in Raman image resolution over conventional far-field scattering. For this new imaging protocol one has to have not only exposed tip geometries but also an AFM system that can modulate and scan the probe independently of the sample scanning required for Raman imaging systems. The tip scanning is required for optimizing the position of the probe tip for maximizing the shadow effect on the sample in the near-field. The independent tip movement is required for bringing the probe in and out of the near-field of the sample so that a difference Raman can be recorded at each pixel and an image formed as the sample is scanned point by point. All of the above in terms of the Shadow protocol are predicated by having an AFM system that has a completely free optical axis from above and is completely independent from the lens of the micro-Raman. Results will be shown on structured thin films of strained silicon on silicon to show the relative fidelity of these imaging modalities. The results indicate that Shadow Near Field Scanning Optical Microscopy (sNSOM) is a powerful technique that can be applied for significant improvements in Raman imaging spatial resolution.
9:00 PM - NN3.4
Real Time, Digital Reciprocal Space X-ray Topographic Characterization of Substrate and Epitaxial Structures of Electronic and Related II-VI, III-V Type Materials.
Ravi Ananth 1
1 Metallyrgy & Materials Engineering, Deeco Metals, Irvington, New Jersey, United States
Show AbstractReal time X-ray reciprocal space topographic techniques have been successfully employed to quantitatively characterize micro-structural morphology of II-VI, III-V and other materials. These specimen included materials such as: HgCdTe, CdTe, HgMnTe, HgMnCdTe, GaAs, InGaAs/InP, AlGaAs/GaAs, Quartz, LiF, KCl etc. Substrates, Epitaxial structures, with and without active devices such as: FET’s, HEMT’s, Transverse Oscillator & PV Device were examined. This method being non-destructive, non-contact and non-intrusive is highly amenable to on-line process control for predicting devise performance, improving yield, saving processing and related costs/time, reducing waste, conserving resources and protecting our environment. The elegance of the results from this simple yet precise technique is a tribute to those like Curie, Bragg, Laue, Ewald et al, who explored this frontier and contributed enormously. The advent of image processing software /hardware and current state of computing power in PC’s have propelled this simple yet pricise technique forward tremendously. The timing is ideal for the consideration of this well established precise X-ray method for on-line production based process and quality control applications. The quantitative nature of the real time streaming data allows for robotics based production applications as well. The microstructural morphology and details revealed using this method have been calibrated using the K alpha 1 & K alpha 2 pairs of reflections for each pixel volume of real space. Several system induced distortions were successfully deconvoluted digitally from the raw data/image. Examples of some of these distortions are: 1) horizontal/vertical divergence of incident beam (size, shape, intensity profile) & 2) image distorsion due to geometry and X-ray optics. Fully analyzed images are obtainable at present in a matter of seconds from real time streaming data at 60 frames per second. Substrates and epitaxial structures both simple and complicated were analyzed such as: 3” GaAs Wafer with FET’s, CdTe PV devise, quartz transverse mode oscillator and Epitaxial layers grown by various methods ( LPE, MBE, VPE). It was possible to resolve signal from various depths and layers by altering the (hkl) reflection used for probing the reciprocal space.
9:00 PM - NN3.5
An Introduction to Backcatter Spectroscopy with the Helium Ion Microscope.
Sybren Sijbrandij 1 , Chuong Huynh 1 , John Notte 1 , Larry Scipioni 1
1 ALIS Business Unit, Carl Zeiss SMT Inc., Peabody, Massachusetts, United States
Show AbstractThe Helium ion microscope (HIM) provides unique capabilities relative to the traditional scanning electron microscope (SEM) and gallium based focused ion beam (FIB) instruments. By virtue of the HIM’s extremely bright gaseous field ion source, the ORION™ helium ion microscope is capable of producing a probe size smaller than 0.3 nm. And due to the nature of the interaction of the helium beam and the sample, it is capable of providing unique image data: When the secondary electron signal generated at the sample surface is used, the HIM produces images showing strong topographical contrast and crisp surface-specific detail. When the backscattered helium signal returned from the sample is used, the HIM produces strong materials contrast, and is capable of imaging nano-scale compositional inhomogeneities in the sample.In addition, the backscattered helium signal may be used to obtain quantitative information, via ion energy spectroscopy. To that end, a solid-state ion energy spectrometer has been added to the HIM, enabling the collection of backscatter ion energy spectra from selected areas of the sample surface. The technique is similar to other ion scattering spectrometry techniques, such as Low Energy Ion Spectroscopy (LEIS), Medium Energy Ion Spectroscopy (MEIS) and High Energy Ion Spectroscopy (HEIS) (a.k.a. Rutherford Backscatter Spectroscopy (RBS)), except that it is now coupled to an extremely powerful ion microscope, allowing for much improved spatial resolution, and more flexibility in the selection of the analysis area. The helium ion microscope’s imaging and spectrometry techniques will be reviewed and a number of initial application studies will be presented, including the compositional analysis of small particles, and the structural analysis of thin films.
9:00 PM - NN3.6
Imaging and Analysis of Biologically Induced Fe Phosphate Precipitates in Porous Silica.
James McKinley 1 , Tetyana Peretyazhko 1 , John Zachara 1 , Satyanarayana Kuchibhatla 1 , Donald Baer 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractThe reductive biotransformation of 6-line ferrihydrite located within porous silica (intragrain ferrihydrite) by Shewanella oneidensis MR-1 was investigated. The effect of buffer type (PIPES and NaHCO3) and phosphate (P) on the extent of reduction and formation of Fe(II) secondary phases was investigated under anoxic conditions. Electron microscopy, micro X-ray diffraction, He microscopy, and Atom Probe Tomography were applied to investigate the morphology and structure of the biogenic precipitates and to study the distribution of microorganisms on the surface of porous silica after bioreduction. In the intragrain ferrihydrite suspensions, 200-300 µmol L-1 dissolved Fe(III) was released during the initial stages of incubation. Reductive mineralization was not observed in the intragrain ferrihydrite incubations without P (and in that case, all biogenic Fe(II) concentrated in the aqueous phase). Distinctive surface precipitates of Fe(II) phosphates with spherical morphology were observed on porous silica when P was present. The rosettes were covered by microorganisms and fragments of extracellular materials suggesting that Fe(II) phosphate formation was influenced by microbial activity.For imaging, the rosette-bearing silica was washed and air-dried. The resultant powder was examined either as freestanding particles deposited on SEM planchettes, or as epoxy-imbedded particulates. For imbedding, a small amount of powder was mixed with low-viscosity epoxy, and the suspension was placed in a partial vacuum for degassing. The cured composite was sectioned by grinding, and then polished using a JEOL Ar-plasma Cross Section Polishing Tool. The flat surface was inspected using a JEOL 7001 SEM to locate and image cross sections of iron phosphate minerals interpenetrating the porous silica structure. SEM images were used as location maps for imaging using a Carl Zeiss Orion Plus He microsocope and an Imago LEAP HR atom probe.The polished samples were first cleaned, gently, using an Ar plasma system to remove the conductive carbon coat necessary for SEM imaging. He microscopy provided images of the Fe phosphate crystal habit, which were superior to SEM in detail. Relatively large radiating Fe phosphate crystals projected from the sample surface. In the internal silica space, smaller, radiating and branching crystals were observed. Overall, the phosphate needles penetrated in approximately straight radial lines across silica pore boundaries. In detail, the needles exploited joins between pores to maintain linear growth, but were observed to bend or turn corners when a straight pathway was unavailable. For atom probe imaging, the rosette surfaces were milled using an FEI dual-probe FIB system. The resultant sample needles were imaged by laser sputtering, and the Fe phosphate crystals were shown to have an heterogeneous compositional structure on an atom scale. Interpretation of the atom probe images and data is ongoing.
9:00 PM - NN3.7
Visualization of Actives Delivery to Stratum Corneum using Confocal Raman Microscopy.
Laurence Senak 1
1 Materials Science, ISP, Wayne, New Jersey, United States
Show AbstractThe delivery of salicylic acid to the stratum corneum layer of porcine skin can be monitored in terms of a map in the plane of the x and depth direction using confocal Raman micro-spectroscopy.A series of polymeric formulations containing salicylic acid have been evaluated for delivery on a spatial basis into the stratum corneum. Spectral monitoring is accomplished by monitoring the ratio of the salicylic acid C-O stretch at 1033 cm-1 to the SC phenylalanine band at 1003 cm-1.The resolution of these experiments is to the single micron level. Delivery in performance between these formulations are visualized and rationalized.
9:00 PM - NN3.8
Electron Holographic and HREM Characterization of Au/SrTiO3 Nano-hetero Catalysts.
Satoshi Ichikawa 1 , Seiji Takeda 2 , Tomoki Akita 3 , Koji Tanaka 3 , Masanori Kohyama 3
1 Institute for NanoScience Design, Osaka University, Toyonaka, Osaka, Japan, 2 Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan, 3 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan
Show AbstractGold shows a remarkable catalytic activity, when the gold nano particles are highly dispersed on certain metal oxides. The catalytic properties of gold show the size dependence and the support dependence. In the previous study, we found that the mean inner potential of Au nano particles supported on TiO2 depends on the size of Au particles and also the stoichiometry at the interfaces. The stoichiometry at the nano-hetero interface affects the electronic structure of Au particles and should have a close relation with the mechanism of the catalytic activities in particular. It is important for the material design of gold catalysts to control not only the size distribution and but also the stoichiometry at the interfaces between gold and support material.We made Au/SrTiO3 nano-hetero catalysts by the vacuum evaporation method (VE) in order to create new nano-hetero interfaces and characterized in nano-scale by high resolution electron microscopy (HREM) and electron holography. Au particles with the size over 2nm were deposited on SrTiO3 (001) and (011) planes with no orientation relationship in spite of the small mismatch of lattice constant. On the other hand, in the case of Au particle with the size 1nm, the orientation relationship as (002)[110]//SrTiO3(011)[100] was observed. The mean inner potential of the Au nano particles on SrTiO3 also exhibit the size dependence. When the size of Au particle is smaller than 4nm, the mean inner potential of Au increased gradually as the size decreases. When the size is smaller than 3nm, the mean inner potential of the Au is over 35V. This tendency is similar to that of Au/TiO2 catalysts prepared by the deposition precipitation method (DP) which is considered to have oxygen rich interfaces between Au and TiO2. Au nano particles on SrTiO3 should be deposited on oxygen rich planes of SrTiO3 surfaces.
9:00 PM - NN3.9
Multi-scale Characterization of Nd-Fe-B Permanent Magnets.
Tadakatsu Ohkubo 1 , Wanfeng Li 1 , Hossein Sepehri-Amin 1 , Kazuhiro Hono 1
1 Magnetic Materials Center, National Institute for Materials Science, Tsukuba Japan
Show AbstractNd-Fe-B based sintered magnets are the highest performance permanent magnets of today; however, due to new applications for hybrid cars and electric vehicles, the demand for higher performance magnets that can be used at elevated temperature has increased. The coercivity that we can achieve from Nd-Fe-B sintered magnets is around 10 kOe, which is less than 15% of the anisotropy field of the Nd2Fe14B hard magnetic phase. To increase the coercivity in the current magnets for automotive applications, Dy is substituted for Nd in the Nd2Fe14B lattice to intrinsic magnetocrstalline anisotropy; however, this causes a substantial decrease in the remanence and energy product (BH)max. In this regard, much effort is currently being made in Japan to develop a high coercive sintered magnets without Dy. To obtain the guideline for the process and alloy design for higher coercivity magnets, we have revisited the microstructures of the commercial Nd-Fe-B magnets at an atomic scale. The difficulty of the microstructural study of the sintered magnets is its multi-scalability with the grain size of typically 5 μm and the grain boundary phase of less than a few nm in width. To obtain quantitative information of the grain boundary chemistry of sintered magnets, we have employed high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HREM) and atom probe tomography (APT) in a complementary manner to characterize multi-scale microstructure/chemistry of Nd-Fe-B based sintered magnets and hydrogenation-decomposition-desorption -recombination (HDDR) processed powder magnets. Continuous thin layers of a Nd-rich amorphous phase were found along the grain boundaries of optimally annealed sintered magnets, whose chemical composition was determined to be Fe41Nd33Cu32, suggesting that the Nd2Fe14B grains are completely enveloped by a Cu and Nd enriched layer. Although the Nd-rich layer was also observed in the optimally processed Nd12.5Fe73Co8B6.5 HDDR powder, it was found to be crystalline with much less Nd-enrichment. Based on the information on the nanostructure feature of Nd-Fe-B magnets, we propose what we should do for developing higher coercivity Nd-Fe-B based magnets.
Symposium Organizers
Manfred Ruehle Max-Planck-Institute for Metals Research
Larry Allard Oak Ridge National Laboratory
Joanne Etheridge Monash University
David Seidman Northwestern University
NN4: Quantitative Imaging and Spectroscopy
Session Chairs
Tuesday AM, December 01, 2009
Room 204 (Hynes)
9:30 AM - **NN4.1
Quantitative Imaging and Spectroscopy of Light Atoms by Aberration-corrected STEM.
Stephen Pennycook 1 2 , Matthew Chisholm 1 , Maria Varela 1 , Juan-Carlos Idrobo 1 2 , Mark Oxley 1 2 , Valeria Nicolosi 3 , Matthew Murfitt 4 , Zoltan Szilagyi 4 , Niklas Dellby 4 , Ondrej Krivanek 4
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States, 3 Department of Materials, University of Oxford, Oxford United Kingdom, 4 , Nion Co., Kirkland, Washington, United States
Show AbstractA Nion UltraSTEM100, operating at 60 kV, resolves the six-membered rings in graphene and BN using a medium angle annular dark field (MAADF) detector. The MAADF detector gives an image which is largely incoherent so that intensity is directly related to atomic mass. Therefore, the number of layers can be determined simply from the average MAADF intensity. Furthermore, the relative mass differences between light atoms result in significant differences in their image intensities. B atoms can be distinguished from N atoms directly from their image intensity. The possibility of identifying adatom sites and species based on image intensities, image simulations and electron energy loss spectroscopy will be explored. Although 60 kV is below the damage threshold for the ideal BN and graphene structures, defects within the layers, adatoms on the layers and atoms at step edges are less well bonded and remain quite mobile. Examples will also be presented of the imaging of distorted O positions in complex oxides and N columns in Si3N4. Research sponsored by the Division of Materials Science and Engineering, US Department of Energy.
10:00 AM - **NN4.2
Quantitative Imaging of Nanostructures in 2D and 3D.
Gustaaf Van Tendeloo 1 , Sara Bals 1 , Sandra Van Aert 1 , Jo Verbeeck 1
1 , University of Antwerp, Antwerp Belgium
Show AbstractWith recent developments of lens corrected microscopes and monochromators, picometer type information becomes available. Together with the existence of powerfull software for image and data treatment, this opens new routes for studying nanomaterials. However in order to obtain quantitative data on atomic positions and composition these data should be treated very carefully. We will apply this to the study of ceramic interfaces such as e.g. LaAlO3-SrTiO3 and illustrate the importance of a statistical data treatment [1]. In this way the terminating layer of each compound can be determined and eventual diffusion can be detected. For EFTEM imaging on an atomic scale care should be taken to work under the correct conditions, as delocalization still may play an important role [2]. Also this will be illustrated for imaging perovskite based structures. When restoring nanostructures in 3D through electron tomography, the main bottleneck is the missing wedge and a correct data treatment. As to the latter aspect, discrete tomography has been shown to be extremely useful for the composition analysis of filled nanotubes or the unraveling of complex zeotile structures [3,4]. [1] S. Van Aert, A.J. den Dekker, A. van den Bos, D. Van Dyck, Advances in Imaging and Electron Physics (Academic Press) 130 (2004) 1-164.[2] J. Verbeeck, P. Schattschneider, A. Rosenauer, Ultramicroscopy, 109 (2009) 350 [3] S. Bals, K.J. Batenburg, J. Verbeeck, J. Sijbers and G. Van Tendeloo, Nano Letters,7 (2007) 3669.[4] S. Bals, K. J. Batenburg, D. Liang, G. Van Tendeloo, A. Aerts, J. A. Martens, C. E. A. Kirschhock, submitted to Advanced Materials.
10:30 AM - NN4.3
Probing the Chemistry and Bonding in Materials at the Atomic Scale.
Sorin Lazar 1 2 , Martin Couillard 2 , Lina Gunawan 2 , Yang Shao 2 , Gianluigi Botton 2
1 , FEI Electron Optics, 5600 KA Eindhoven Netherlands, 2 Canadian Centre for Electron Microscopy, Materials Science and Engineering, BIMR, McMaster University, Hamilton, Ontario, Canada
Show AbstractThe developments of aberration corrected microscopes equipped with electron energy loss spectrometers make it possible to probe the chemical environment of atoms in a solid with a spatial resolution that now approaches the Angstrom level as demonstrated recently in the literature. The requirements for such experiments are very stringent in terms of stability of the instrumentation, sensitivity of detectors and ultimately, electron beam damage of the samples. In addition, theoretical calculations have shown that detailed interpretation of maps requires calculations considering the inelastic process and the electron beam propagation. In this presentation we will demonstrate examples of applications of elemental mapping at the atomic level in perovskite-based compounds. These materials exhibit fascinating electronic properties that can be tuned by suitable changes in composition of the structure. However, elemental mapping, as demonstrated in perfect crystals, presents limitations in the study of practical systems where designed changes in composition are small. We will focus this presentation on the application of this technique and on the practical limits. Prospects of mapping of the changes in near-edge structures, with atomic resolution, at defects and interfaces will be discussed.
10:45 AM - NN4.4
Structure and Chemistry of Intergranular Films at Metal-Ceramic Interfaces.
Mor Baram 1 , Wayne Kaplan 1
1 Materials Engineering, Technion - Israel Institute of Technology, Haifa Israel
Show AbstractAs microstructural length-scales are reduced, metal-ceramic interfaces have a crucial role in determining the mechanical and functional properties of metal-ceramic composites. The existence of thin ~1nm partially ordered films (based on anorthite glass) at metal-ceramic interfaces was experimentally proven in previous studies, and the finite nanometer length-scale thickness was explained using accepted DLVO theory. The current study aims to answer fundamental questions regarding the atomistic structure and chemistry of intergranular films at metal-ceramic interfaces which may help in understanding their influence on the properties of composites.Within an on-going research program we have developed a novel experimental approach to form equilibrated Au particles in contact with sapphire, in the vicinity of small droplets of anorthite glass (CaO-2SiO2-Al2O3). Controlled dewetting experiments of Au on (0001) sapphire with and without the presence of anorthite glass were conducted. For samples equilibrated in the presence of anorthite, polished sapphire surfaces were partially coated via spreading of anorthite particles. These samples (and anorthite free samples) were then sputter-coated with thin (~60nm) Au films , and dewetted at 1100°C. As a result, a thin amorphous film was observed at Au-sapphire interfaces under two different conditions; gold particles which “sunk” from the surface of anorthite drops leading to the formation of a thin interfacial film after the particle reached the interface, and a thin film at Au-sapphire interfaces for Au particles in the vicinity of the bulk anorthite drops. In addition, adjacent to the glass drops, a ~1nm thick surficial film was also detected on the (0001) surface of sapphire substrates partially wetted by anorthite glass.The ~1nm thick films located at Au-Al2O3 interfaces were studied using monochromated and aberration corrected transmission electron microscopy (TEM) from site-specific cross-section specimens prepared using a modified technique in a dual-beam focused ion beam system. First, it was proven that quantitative HRTEM analysis can be done on TEM specimens prepared using the modified technique. Then, using this experimental approach, the thickness and the degree of order in the films (which lead to a reduced metal-ceramic interface energy) were characterized by quantitative HRTEM analysis. Additionally, the composition of the films was determined from both energy filtered TEM and energy dispersive spectroscopy (EDS).
11:30 AM - NN4.5
Quantitative High Resolution Electron Microscopy Investigation of the SrTiO3 Σ3(112) Grain Boundary.
Karleen Dudeck 1 , Nicole Benedek 2 , Mike Finnis 2 , David Cockayne 1
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 Department of Materials, Imperial College London, London United Kingdom
Show AbstractGrain boundaries play a critical role in determining the electronic and structural properties of polycrystalline SrTiO3. In order to develop a robust understanding of these properties, a knowledge of the grain boundary atomic structure is desirable. Reliable modelling of low-angle, high symmetry grain boundaries is possible and, when used in conjunction with experimental characterisation, can be used to verify structural properties of the boundary. Of the several possible experimental techniques for determining GB structure, high resolution electron microscopy (HREM) is the most direct [1].In this work aberration corrected HREM, focal series reconstruction and image simulation have been combined to quantitatively determine three-dimensional information about the structure, at the atomic level, of the symmetric tilt SrTiO3 Σ3(112) boundary. Analysis of the boundary using a combination of techniques provides robust characterisation and ensures validity of each technique. In addition to using a variety of experimental techniques, the boundary has been studied in two perpendicular crystallographic orientations – viewed down the [-110] tilt axis as well as in the [111] orientation. This provides additional information for comparison.The reconstructed exit wave function phases from both orientations have been quantitatively analysed. By comparing the experimental data to density functional theory (DFT) models from the literature [2], it has been possible to differentiate between the two energetically indistinguishable model structures. Motivated by the DFT results, we have been able to determine three-dimensional information about the atomic structure at the boundary. Comparison between key features of the experimental and energetically relaxed structures has yielded good agreement only in the case when atomic shifts within a given column are considered. References[1] W. M. Rainforth, Advances in Imaging and Electron Physics 132 (2004) 167-246.[2] N. A. Benedek, A. L. S. Chua, C. Elsasser, A. P. Sutton, M. W. Finnis, Physical Review B 78 (2008) 064110.
11:45 AM - NN4.6
An Atomistic Reconstruction of the Nanostructure of Pyrolitic Carbons Guided by HRTEM Data.
Jean-Marc Leyssale 1 , Patrick Weisbecker 1 , Raphael Vitti 2 , Jean-Pierre Da Costa 2 , Christian Germain 2 , Gerard Vignoles 3
1 Laboratoire des Composites ThermoStructuraux - UMR 5801, CNRS, Pessac France, 2 Laboratoire IMS - UMR 5218, Université de Bordeaux, Bordeaux France, 3 Laboratoire des Composites ThermoStructuraux - UMR 5801, Université de Bordeaux, Bordeaux France
Show AbstractAtomistic reconstruction methods are nowadays well-established tools for linking experimental characterization data to the atomic scale structure of matter. However, most of them are based on the reproduction of orientation-averaged structural features like pair distribution functions (PDF), making them less successful for dense graphene-based carbons, displaying a neatly anisotropic nanotexture. For instance, two PDF-based computer reconstructions of the same material show a drastically different nanotexture: one, quite isotropic, is an amorphous carbon with a dominating sp2 character [1] while the other one is a strongly anisotropic stack of faulted graphene sheets [2]. Recent developments in image analysis techniques allow a finer and finer description of the nanotexture to be drawn from High Resolution Transmission Electron Microscopy (HRTEM) lattice fringe images [3]. We propose a new reconstruction strategy based on HRTEM images. This method consists in: (i) quantitative structural and statistical analysis of experimental images; (ii) synthesis of 3D “HRTEM-like” images under an orthotropy condition; and (iii) molecular dynamics annealing simulations using the synthetic 3D images as a complementary potential energy to the REBO interatomic potential [4]. Starting from a liquid, the simulation slowly brings the system to adopt a “carbon-like” bonding while ensuring that the atoms sit preferentially in the dark areas of the 3D image. Preliminary results for a Rough Laminar pyrocarbon will highlight the promising nature of this new modeling approach. References:[1] M. Acharya, M. S. Strano, J. P. Mathews, S. J. L. Billinge, V. Petkov, S. Subramoney, H. C. Foley, Phil. Mag. B 79 (1999) 1499.[2] M. A. Smith, H. C. Foley, R. F. Lobo, Carbon 42 (2004) 2041.[3] C. Germain, R. Blanc, M. Donias, O. Lavialle, J.-P. Da Costa, P. Baylou, Image Analysis and Stereology 24 (2005) 1.[4] D. W. Brenner, O. A. Shenderova, J. A. Harrison, S. J. Stuart, B. Ni, S. B. Sinnott, J. Phys. Condens. Matter 14 (2002) 783.
12:00 PM - NN4.7
Atomic Resolution Imaging of Oxygen Positions in Perovskites.
Maria Varela 1 , Mark Oxley 2 1 , Jaume Gazquez 1 , Weidong Luo 2 1 , Matthew Chisholm 1 , Sokrates Pantelides 2 1 , Stephen Pennycook 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Vanderbilt University, Nashville, Tennessee, United States
Show AbstractDirect imaging of light atoms, such as O, in the electron microscope has only been achieved through the successful correction of spherical aberration. Electron probe sizes have been reduced below the 1 Ångström barrier in the aberration-corrected scanning transmission electron microscope (STEM). At the same time, improved post-specimen optics allow highly efficient electron energy loss spectroscopy (EELS), enabling the imaging of near edge spectral features with atomic resolution. Here, we apply atomic resolution EELS spectrum imaging combined with density functional theory and dynamical simulations to the imaging of O atoms in complex oxides with perovskite structure. These materials often exhibit exciting new physics: from high Tc superconductivity to colossal magnetoresistance, ferroelectricity, etc. In many case, these properties, many of which are not sufficiently understood, depend directly on the bonding between transition metals and the O atoms in octahedral configuration around them. Hence, being able to directly image and quantify their positions is a necessary ingredient to understand their physical properties. Possible artifacts in the images, due e.g. to specimen preparation, are examined. Other interesting effects such as those of non-locality or dechanneling giving rise to volcano-like contrast will also be discussed, together with the possibility of distinguishing inequivalent O species in Jahn-Teller distorted perovskites such as LaMnO3. All of these effects must be taken into account when trying to interpret atomic resolution EELS images obtained with aberration corrected electron probes. Research sponsored by the Division of Materials Science and Engineering US Department of Energy.
12:30 PM - NN4.9
High Resolution Bright-Field Tomography of Closed-Cage Structures – Closing the Gap to Atomic Resolution.
Maya Bar Sadan 1 , Lothar Houben 1 , Knut Urban 1
1 Institute of Solid State Research, Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Research Centre Juelich GmbH, Juelich Germany
Show AbstractCharacterization of nanostructures to atomic dimensions becomes more important, as devices based on a single particle are being produced. The knowledge of the three-dimensional structure and composition on the atomic scale, which is so far hidden, holds the information about the unique physical properties of nanomaterials compared with their bulk ancestors. Tomographic reconstruction from series of tilted objects is a widely used application in transmission electron microscopy (TEM), in particular in the biological sciences. In the field of physical sciences, the tomographic resolution attained so far has not surpassed the barrier of 1 nm3. The basis for our approach to high-resolution bright-field tomography is the use of simulations in order to validate a range of defocuses without contrast reversals, so to an answer the 'projection requirement' in tomography. By that, the intensity in the image can be associated with a true structural property of the sample. Thereafter, the tilt series can be acquired and the images processed. An example for that is given, by presenting a reconstruction of WS2 inorganic nanotubes where all the molecular layers (spaced by 0.62 nm) are resolved along the tube axis and inner filling can be identified.Taking the approach a step forward, the road to atomic-scale tomography can be realized as well, using the delocalisation-reduced phase contrast in an aberration-corrected TEM in combination with low voltage operation. The benefit of using negative spherical aberration imaging (NCSI) is a close representation of the projected potential for such weakly scattering objects in the image and high sensitivity for light elements. The point resolution of about 2 Å at 80 kV in the NCSI mode outperforms the point resolution of conventional microscopes at much higher acceleration voltages while the rate for knock-on radiation damage is significantly reduced so that radiation-damage sensitive materials can be investigated. First experimental data and a simulation study on the 3D reconstruction of inorganic MoS2 nanooctahedra are shown to give evidence for this procedure. First, tomographic reconstruction using weighted backprojection of simulated images for a model structure established from a quantum mechanical approach was performed. The tomogram reconstitutes key features of the physical properties within the atomic structure. Experimental tilt-series of MoS2 nanooctahedra were acquired in a FEI Titan 80-300. The tomogram was reconstructed from a set of 22 experimental images with an angular step of 3°. The resolution of 2.8 Å obtained for the projected Mo distances in the xy-plane agrees with a predicted resolution better than 3 Å. The nested shells with their separation of 6.15 Å are reproduced in all of the slices. The overall resolution in the experimental tomogram achieved so far is about 0.3×0.6×0.6 nm3 = 0.11 nm3, an improvement of nearly one order of magnitude compared to state of the art electron tomography.
12:45 PM - NN4.10
A Combined Approach to the Determination of As Depth Profiling in Si Ultra Shallow Junctions.
Andrea Parisini 1 , Vittorio Morandi 1 , Jaap van den Berg 2 , Michael Reading 2 , Damiano Giubertoni 3
1 , CNR-IMM Sezione di Bologna, Bologna Italy, 2 Institute for Materials Research, University of Salford, Salford United Kingdom, 3 , Fondazione Bruno Kessler-irst, Povo-Trento Italy
Show AbstractThe determination of the dopant depth distribution in ultra shallow junctions, USJ, in Si challenges the state-of-the-art of ion and electron beam characterization techniques. USJ are located at a depth of a few nanometers from the sample surface that consequently assumes a critical role in determining the dopant distribution during solid phase epitaxy, SPE, and post-implantation annealing. Dopant migration to the Si/SiO2 interface, limiting the amount of activated dopant up to half the implantation dose, has already been reported [1]. The need to reach a better understanding and a control of these phenomena is witnessed by recent publications discussing the relative importance of the two main mechanisms thought to be responsible for this effects, i.e. transient enhanced diffusion, TED, and an SPE-based segregation phenomenon.The analyses of these samples with electron and ion beam analytical techniques mainly requires a careful signal discrimination. In fact, owing to the presence of the sample surface, the SiO2/Si and eventually an a-Si/c-Si interface, the broadening due to ion beam mixing effects as well as the effects of displaced atoms onto the dopant and matrix atom signals have to be carefully identified and avoided during the data acquisition. In this work, we report an attempt to overcome the above described difficulties through a combined investigation by medium energy ion scattering, MEIS, secondary ion mass spectrometry, SIMS, and tilted sample annular dark field scanning transmission electron microscopy, TSADF-STEM, of as-implanted and annealed Si samples implanted with As at energies and doses ranging from 0.5 to 5 keV and from 5x1014 to 2x1015 As/cm2, respectively. Albeit renouncing to atomic resolution, the combined use of these quantitative techniques lead to a reliable determination of ultra shallow dopant profiles with high spatial resolution, i.e. on a sub-nanometer scale. Moreover, the investigation of the annealed samples shows that As accumulates on the Si side of the SiO2/Si interface with a negligible loss of dopant into the oxide [2]. Modeling of the effect [3] indicates that segregation occurring during SPE is the dominant cause of this dopant pileup [2]. Finally, the importance of the sample tilt procedure used in TSADF-STEM as well as the ability of this technique to obtain reliable dopant profiles in the very first nanometers from the sample surface will be discussed in connection with the use of ADF-STEM in electron tomography experiments and for purpose of comparison with atom probe tomography results, respectively.[1] R. Kasnavi et al., J. Appl. Phys. 87, 2255 (2000)[2] A. Parisini et al., Appl. Phys. Lett., 92, 261907 (2008).[3] K. Suzuki et al., IEEE Trans. Electron Devices 54, 262 2007.
NN5: Atomic Scale Chemical Imaging
Session Chairs
Tuesday PM, December 01, 2009
Room 204 (Hynes)
2:30 PM - **NN5.1
Atomic-Scale Chemical Imaging of Composition and Bonding by Aberration-Corrected Microscopy.
David Muller 1
1 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractAtomic-resolution electron microscopy and spectroscopy is now capable of unraveling bonding details at buried interfaces and clusters, providing both physical and electronic structure information. In some cases the sensitivity and resolution extends to imaging single dopant atoms or vacancies, allowing us to study identify the clusters responsible for electrical deactivation in integrated circuits. In fact, the smallest feature in a modern transistor, the gate dielectric, is already little more than an interfacial layer just over 1 nm thick, and the fundamental physical limits to device scaling are set by the measured electronic structure. A new generation of electron microscopes are now capable of recording full 2D spectroscopic images at atomic resolution in under a minute [1]. Changes in composition and electronic structure at buried interfaces and localized defects can be obtained from statistically meaningful samples. As examples, the effects of spatially inhomogeneous chemical intermixing at a 1-2 unit cell level on transport properties and magnetism in manganite/titanate multilayers, and in fuel-cell catalysts particles will be used to explore the potential and current limitations of the electron energy loss spectroscopy at the atomic scale. This work was supported by the NSF, ONR and the SRC.
[1] D. A. Muller, L. F. Kourkoutis, M. Murfitt, J. H. Song, H. Y. Hwang, J. Silcox, N. Dellby, O. L. Krivanek, Science 319, 1073 (2008).
3:00 PM - **NN5.2
Tomographic Atom Probe and Nanosciences.
Didier Blavette 1 2 , Oana Cojocaru-Miredin 1 , Emmanuel Cadel 1 , Bernard Deconihout 1
1 Physics, University, St Etienne du Rouvray France, 2 , Institut Universitaire de France, Paris France
Show AbstractAtom probe tomography (APT) is an extension in 3D of the atom-probe field ion microscope (APFIM) designed in the late sixties by E.W. Müller [1]. The two first prototypes were designed successively at the Universities of Oxford and Rouen [2][3]. APT makes it possible to give the spatial distribution of chemical species in the small volume analyzed (50x50x100 nm3). The 3D reconstruction of Cottrell atmospheres (tiny clouds of impurity atoms around dislocations in crystals) at the atomic-scale is one of the most salient result provided by APT [4]. 3DAP was up to recently restricted to good conductors. To overcome this limitation, we designed a new generation of 3DAP in which the material is field evaporated by ultrafast laser pulses (350 fs). This new instrument, namely the Laser assisted Wide-Angle Tomographic Atom Probe (LAWATAP - CAMECA) opens the technique to semi-conductors and oxides, that are key materials in micro-electronics [5]. A comparable instrument was designed by IMAGO and impressive results on microelectronics issues were obtained [6]. With the impressive progresses made in the miniaturisation of integrated circuits, microelectronics occupies a particular place in Nanoscience. The size of last generation nano-transistors is a hundred nanometers. The SIMS occupies a central position in microelectronics notably for dopant profiling in semiconductors. However, for nanotransistors SIMS faces to its ultimate limits. 3DAP has the advantage to have both a higher resolution and imaging capabilities so that clustering can be exhibited and characterized [7]. LaWaTAP appears to be a very powerful approach in Nanoscience in particular for the investigation of semiconductors, including nanowires [8] as well as for the study of magnetic multilayers including tunnel junctions (e.g. MgO/Fe/MgO). Unique capabilities of atom probe tomography in nanoscience will be highlighted on the basis of some selected illustrations.[1]E.W. Müller, J. Panitz, and S.B. Mc Lane, 1968, Rev. Sci. Instrum. 39, 83[2]A. Cerezo, I. J. Godfrey and G. D. W Smith, 1988, Rev. Sci. Instr. 59 (6), 862[3]D. Blavette, A. Bostel, J.M. Sarrau, B. Deconihout and A. Menand, 1993, Nature 363, 432[4]D. Blavette, E. Cadel, A. Fraczkiewicz, A. Menand, 1999, Science 17, 2317[5]B. Gault, F. Vurpillot, A. Vella, M. Gilbert, A. Menand, D. Blavette, B., 2006, Rev. Sci. Instr. 77, 043705[6]T. F. Kelly and M. K. Miller, 2007, Rev. Sci. Instrum. 78, 031101[7]D. Blavette, T. Al Kassab, E. Cadel, A. Mackel, M. Gilbert, O. Cojocaru, B. Deconihout, 2008, Intern. Journ. of. Mater. Res. 99 (5), 454[8]D.E. Perea, J.E. Allen, S.J. May, B.W. Wessels, D.N. Seidman, L.J. Lauthon, 2006, Nano lett. 6 (2) 181-185
3:30 PM - NN5.3
Monolayer-resolved STEM/EEL Spectroscopy for the Atomic-scale Analysis of Interfaces and 1-Dimensional Nanostructures.
Lothar Houben 1 , Markus Heidelmann 1 , Maya Bar Sadan 1 , Juri Barthel 2
1 Institute of Solid State Research, Research Centre Juelich, Juelich Germany, 2 Central Facility for Electron Microscopy, RWTH Aachen, Aachen Germany
Show AbstractA simple yet powerful technique for monolayer resolved electron energy loss (EEL) spectrometry at interfaces or 1-dimensional nanostructures in the scanning transmission electron microscope (STEM) was recently proposed in ref. [1]. The technique, named StripeSTEM, is based on an isochronous collection of a series of EEL spectra while a high-angle annular dark-field (HAADF) image is taken. The sequence of EEL spectra is taken with a minimum of spectrometer dead time during such an experiment. This enables, contrary to current approaches, the precise synchronisation of measurement location and EEL data after data collection, using the HAADF image as a simple record of the beam position during the measurement. The result of post-processing is a quantitative accuracy with a high tolerance against specimen and beam drift during the experiment. Another benefit for the practical application is the distribution of the electron dose along one spatial direction, enabling for a high signal-to-noise ratio at low dose per nm^2. Doses can be a kept as low as of 0.1 nC/nm^2 even in an aberration-corrected microscope, which is of considerable benefit for interfaces or 1-dimensional nanostructures that are sensitive to radiation damage, e.g. oxide heterointerfaces or nanotubes.This contribution evaluates limitations for the spatial resolution of the technique and gives application examples in materials science. A reference sample consisting of a monolayer basal plane of In2O3 in a ZnO matrix was used to validate atomic-scale spatial resolution of the EELS data taken in a probe-side corrected FEI Titan 80-300 at 300kV. Multislice calculations for the elastic electron beam dispersion in the sample and the convolution with and effective inelastic scattering cross sections were used to assess the residual delocalisation of the inelastic signal. Taking the remaining spatial delocalization due to the brightness limit of the Schottky field emitter used in the experiment into account, we can demonstrate that the StripeSTEM technique provides EEL signals with a spatial resolution close to the physical limit of the localization of inelastic scattering events. Exemplary analyses of single inorganic nanotubes and interfaces of oxides of different polarity with StripeSTEM will be presented. StripeSTEM reveals the chemical composition of composite nanotubes and yields a fingerprint of their bandgap [2]. Around interfaces between a polar and a non-polar layered oxides an intermixing in the cation lattice can be mapped in quantity, an important factor in the detailled charge balance in addition to oxygen deficiencies, valency changes and free charge carrier accumulation.[1] M. Heidelmann, L. Houben, J. Barthel and K. Urban, Proc. 14th EMC 2008; 1: 383, DOI: 10.1007/978-3-540-85156-1_12.[2] M. Bar Sadan, M. Heidelmann, L. Houben, R. Tenne, Applied Physics A 96 (2009) 343.
3:45 PM - NN5.4
Mechanical Alloying and Amorphization in Cu-Nb-Ag in Situ Composite Wires Studied by TEM and Atom Probe Tomography.
S. Ohsaki 2 , Dierk Raabe 1 , Kazuhiro Hono 2
2 , National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 Japan, 1 , Max-Planck-Institut fuer Eisenforschung, Duesseldorf Germany
Show AbstractWe study deformation-driven alloying in a Cu-5at.% Ag-3at.% Nb in situ composite wire by transmission electron microscopy and atom probe tomography. In addition to alloying at interfaces, amorphization of nanosized Cu areas is observed after heavy wire drawing (true strain: n=10.5) at some of the Cu-Nb interfaces. We discuss the mechancial alloying phenomenon in terms of slip and shear banding mechanisms where lattice dislocations penetrate the interfaces between abutting phases. We interpret local amorphization in terms of the thermodynamic destabilization of a Cu-Nb crystalline phase between 35 and 80 at.% Nb due to enforced mixing. Deformation-driven mechanical alloying and amorphization are hence, associated phenomena.
4:30 PM - **NN5.5
X-ray Analysis in Aberration-corrected Scanning Transmission Electron Microscopes for Atomic-column X-ray Imaging.
Masashi Watanabe 1
1 Dept. of Mater. Sci. & Eng., Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractThe recently developed aberration correctors have brought significant improvements in materials characterizations. Using aberration-corrected scanning transmission electron microscopes (STEMs), the incident probe dimensions can be refined and image resolution has already reached sub-Ångstrom levels in high-angle annular dark-field (HAADF)-STEM imaging. In addition, materials characterization at the atomic level can routinely be performed by electron energy-loss spectrometry (EELS) in the aberration-corrected STEMs. The aberration correction of the incident beam is also very useful for X-ray energy dispersive spectrometry (XEDS) because the spatial resolution can be improved to ~0.4 nm by the refined incident probes. Furthermore, the probe current can be increased in the same probe size by the aberration correction, which is one of the most crucial improvements for X-ray analysis in STEMs since both the X-ray generation and detection are very poor due to a reduced volume for analysis and to a limited capability of X-ray signal collection in a current XEDS detector. Therefore, analytical sensitivities (i.e. detectability limits) of X-ray analysis can also be improved by the aberration correction. To achieve such higher currents in the limited probe size, it is essential to optimize the probe formation conditions. With the improved spatial resolution and analytical sensitivity in aberration-corrected STEMs, it is feasible to apply atomic-column XEDS imaging, similar to atomic-column EELS imaging that has been performed. In order to achieve such atomic-column XEDS imaging, however, it is essential to employ advanced statistical approaches (e.g. multivariate statistical analysis) for offset of poor signal levels due to the limited X-ray generation and collection even in aberration-corrected STEMs. The feasibility of atomic-column XEDS imaging will be explored with required instrumental optimizations and essential tools, and then a preliminary result of an atomic-column X-ray image will be shown.
5:00 PM - NN5.6
Atomic-scale Distributions of Transition Metal Elements in Three-dimensions in Alloyed Nickel Monosilicide Thin Films Using Atom-probe Tomography.
Praneet Adusumilli 1 , Conal Murray 2 , Lincoln Lauhon 1 , David Seidman 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 , IBM T. J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractNickel monosilicide has been the material of choice for source/drain contacts to complementary-metal-oxide-semiconductor (CMOS) transistors in recent technology generations. Alloying with nominal amounts of transition metals such as Pt or Pd has been employed to overcome the integration challenges faced during processing. These include agglomeration of this low resistivity NiSi phase; and phase transformation to the higher resistivity NiSi2 phase during fabrication. Local-electrode atom-probe (LEAP) tomography is used in this study to map three-dimensional (3D) distributions of Pt or Pd in Ni monosilicide thin films to obtain insights into the role played by these transition metal elements in phase stabilization. Solid-solutions of Ni0.95M0.05 (M = Pd or Pt) thin films on Si (100) substrates are subjected to rapid thermal annealing to form the monosilicide phase. The focused-ion-beam microscope based lift-out technique is employed to prepare LEAP tomography samples. Pt and Pd are found to segregate at the silicide/silicon heterophase interface in both cases. A measured decrease of the interfacial Gibbs free energy due to the segregation at the silicide/silicon interface might be responsible for the stabilization of the monosilicide phase at elevated temperatures. Quantitative evidence for short-circuit diffusion of Pt via grain boundaries in the NiSi phase is observed in 3D direct space, providing valuable insights into the kinetics of the reactive diffusion process. The high spatial resolution possible coupled with the unique 3D nature of the measurements yields both very accurate and precise measurements of both the lattice and grain boundary diffusivities of Pt. The silicide/Si interface is also reconstructed in 3D on an atomic scale and its root-mean-square chemical roughness determined. This research is supported by the Semiconductor Research Corporation/Global Research Collaboration. The specimens employed were obtained from IBM T. J. Watson Research Center.
5:15 PM - NN5.7
Atom Probe Tomography Study of Rhenium Clustering in Nickel Superalloys.
Alessandro Mottura 1 , Michael Miller 2 , Mike Finnis 1 , Roger Reed 3
1 Department of Materials, Imperial College London, London United Kingdom, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham, United Kingdom
Show AbstractNickel superalloys are used in jet engine applications due to their superior performance at high temperature. The microsctructure and composition of these alloys is optimised to maximise their creep properties. Rhenium, amongst other elements, is especially important due to its positive effect on creep properties. Rhenium clustering has been suggested as the main reason behind the rhenium-effect: small rhenium clusters could hinder dislocation motion, thereby slowing down creep deformation mechanisms. This thesis is supported by discontinuities observed in the ladder diagram for rhenium obtained with one-dimensional atom probes. However, results obtained with Extended X-ray Absorpion Fine Structure and ab initio modelling, via the Density Functional Theory, suggest that rhenium clusters may not be present. Since this original atom probe study, the instrumentation and statistical tools used to collect and analyse atom probe tomography data have undergone major improvements, particularly with respect to the volume of material sampled, so that statistical analysis of rhenium clustering in nickel superalloys can now be performed. In this work, a friends-of-friends algorithm based on the maximum-separation method was used to detect the presence of clusters. The algorithm was extensively tested on simulated datasets to evaluate its ability to detect dispersed nano-sized and sub-nano-sized clusters. The algorithm was also applied to detect rhenium clustering in a Ni-10wt.%Re binary alloy as well as in the γ matrix phase of CMSX-4, a typical commercial nickel superalloy. Each dataset was compared to a random reference in order to detect and highlight any clustering above the levels expected for a random distribution of solute atoms. No clustering, above solute random distribution levels, was observed in Ni-Re and CMSX-4. However, ladder diagrams - reconstructed by analysing thin columnar regions cut from multi-million atom three-dimensional datasets - show small discontinuities, similar to those also observed in ladder diagrams obtained from the randomised datasets. This work strongly supports the idea that interactions between dislocations and nano-sized rhenium clusters cannot explain the mechanism underlying the rhenium-effect. The extraordinary strengthening effect of rhenium can be explained with normal solid solution hardening mechanisms, especially considering that rhenium is the slowest diffusing solute element in nickel superalloys.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.
5:30 PM - NN5.8
Atomic Scale Segregation of Carbon in Auto-Tempered Martensitic Steels Studied by Atom Probe Tomography.
Frederic Danoix 1 3 , Alain Guillet 2 , Harald Leitner 3
1 Groupe de Physique des Matériaux, CNRS Université de Rouen, Saint Etienne du Rouvray France, 3 Christian Doppler Laboratory for Early Stages of Precipitation, Department Physical Metallurgy and Materials Testing - Montanuniversität Leoben , Leoben Austria, 2 Département Mécanique, INSA de Rouen, Saint Etienne du Rouvray France
Show AbstractAmong the analytical advantages of atom probe tomography, its ability to detect quantitatively light elements such as carbon and nitrogen, makes it an indispensable instrument for the study of phase separation when these light elements are involved. In addition, due to its near atomic scale resolution, APT gives access to the distribution of carbon and nitrogen at the nanometer scale, even in the early stages of phase separation, when concentration fluctuations, and their associated disturbances are not developed enough to be detected by transmission electron microscopy. In the case of steels, APT offers the possibility of investigating the first stages of carbon segregation and precipitation at the nanometer scale. In martensitic steels, the distribution of carbon in the as received conditions is known to be dependent on the quenching conditions. In particular, if the martensitic transformation start temperature (Ms) is well above room temperature, a phenomenon known as auto-tempering will occur. During auto-tempering, carbon atoms have the possibility to diffuse in the supersaturated and highly distorted martensite. Carbon atoms have several potential sites for clustering, including dislocation lines and lath boundaries. In addition, intermediate carbide (in particular ε carbides) formation may also occur. In this study, we have investigated the distribution of carbon at the atomic scale in the case of as-quenched commercial C35 and C67 steels. Segregation is found to occur at different location, according to the cooling conditions. Some heat treatments at relatively low temperatures (i.e. lower than 300°C) have also been conducted in order to study the evolution of the carbon segregation during the early stages of low temperature tempering.
5:45 PM - NN5.9
Study of High k material HfO2 by Using Laser Assisted Atom Probe Tomography.
Baishakhi Mazumder 1 , Meenal Deo 2 , Vishal Thakare 2 , Angela Vella 1 , Francois Vurpillot 1 , Satish Ogale 2 , Bernard Deconihout 1
1 Groupe de Physique des Matériaux (GPM), University of Rouen, Saint Eteinne du Rouvray France, 2 Physical Chemistry Division, National Chemical Laboratory, Pune India
Show AbstractWith the scaling down of device feature sizes towards nanometer regime in all three dimensions use of traditional gate dielectrics is encountering severe limitations and therefore high k dielectrics which are structurally and electronically (interface states) compatible with silicon are being intensely researched. Hafnia (HfO2) is perhaps the most promising new gate dielectric material due to its relatively high dielectric constant, large band gap 5.5–5.8 eV, and good thermal and chemical stabilities. It is therefore of interest to examine the atomistic details of the chemical and electrical aspects of ultrathin films of HfO2 and their interfaces with silicon by various techniques to generate a better understanding for their use in MOS devices. Atom probe tomography is a powerful nano analysing instrument that provides 3D maps of the chemical distribution in small volumes of materials with sub nanometre spatial resolution. Due to the basic principle of the technique (field evaporation), the field of applications for this instrument have thus far been restricted to metals. The recent implementation of ultra fast laser assisted field evaporation first develpoed by our group has now been able to widen the scope of the technique considerably, making it applicable to nanoscale analyses of semiconductors, oxides and ceramic materials, which are key materials for micro electronics. Importantly, the analysis of the data intrinsically involves information about surface electrical barriers. In this paper we apply the laser assisted atom probe tomography technique to analyse pulsed laser deposited thin HfO2 films on silicon. The films were grown at a pulsed laser energy density of 2 J/cm2, rep rate of 5 Hz and substrate temperature of 7000C. A preheating step at higher temperature of 8500C was used to strip off the natural surface oxide on silicon. The films were characterized by analytical tools such as X ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. They were then subjected to the FIB tip processing and analysed by laser assisted field evaporation. The 3D tomography image shows that the interface between Si and HfO2 is fairly abrupt for the PLD conditions employed. The ions/radicals emanating from the surface upon laser assisted field evaporation include O and HfO complexes. This input is used to understand the nature of laser evaporation under excitation. By changing the thickness of the oxide the field evaporation is studied to get a better explanation of the underlying physical phenomena.
Symposium Organizers
Manfred Ruehle Max-Planck-Institute for Metals Research
Larry Allard Oak Ridge National Laboratory
Joanne Etheridge Monash University
David Seidman Northwestern University
NN6: EELS for all Energy Losses
Session Chairs
Wednesday AM, December 02, 2009
Room 204 (Hynes)
9:30 AM - **NN6.1
Electron Energy Loss Spectroscopy (EELS) for Plasmonic Mapping of Metallic Nanoparticles and Nanophotonic Devices.
Christian Colliex 1 , Mathieu Kociak 1 , Odile Stephan 1 , Stefano Mazzucco 1 , Guillaume Boudarham 1 , Jaysen Nelayah 1
1 Physique des Solides, CNRS Université Paris Sud 11, Orsay France
Show AbstractLocalized plasmon resonances constitute an important feature in the optical answer over the visible domain, for noble metal (Ag, Au) nanoparticles. As such, they have been the target of many experimental photon beams spectroscopic and theoretical modelling studies. Recent technical developments in electron energy loss spectroscopy and filtering modes have made the relevant near IR/visible/UV spectral range (1 to 3eV) accessible to the EELS approach. Rastering a sub-nm STEM probe over the surface of individual nanoparticles of different shapes and sizes provides the topographical and structural images simultaneously with the spectral maps, offering then a perfect correlation between the localization, the energy and the intensity of the different excited modes. This will be demonstrated for various sets of specimens prepared by photo-induced aggregation or by lithographic techniques. For the EELS experiments in the electron microscope, the nanoparticles are deposited on a very thin layer (mica, Si3N4 foil) with a band gap greater than the explored optical range. Specially adapted software for handling large numbers of spectra in the spectrum-image mode, for improving the energy resolution and the signal-to-noise ratio (multi-acquisition, realignment and summing of spectra, deconvolution, fitting with model curves), makes now possible to discriminate and map the spatial origin of peaks separated by about 0.3eV and to determine their position with a 0.1eV accuracy. It is sufficient to discriminate the major modes (tip, edge and centre for a triangle, polar and azimuthal for a decahedra, corner, edge and face in a cube, electrostatic and magnetic in a split resonator) and their symmetry in individual particles. It can also in certain cases reveal the interaction between adjacent particles or with the substrate. On model specimens, Maxwell equations are numerically solved using different methods (Boundary Element Method or Discrete Dipole Approximation) to calculate the near-field electromagnetic fields and the associated optical or EELS response, providing thus a solid background to interpret the results. Criteria are being investigated in order to distinguish the global response of an individual object from its local one determined by the change of shape or environment. This novel approach can significantly contribute to our understanding and mastering of sub-wavelength optics on nanosized objects.
10:00 AM - **NN6.2
Surface Plasmon Resonance Effects in Ag Nanoholes Studied by Energy-Filtering TEM.
Wilfried Sigle 1 , Jaysen Nelayah 1 , Christoph Koch 1 , Burcu Ogut 1 , Peter van Aken 1 , Lin Gu 1
1 , Max Planck Institute for Metals Research, Stuttgart Germany
Show AbstractThe visualization of localized plasmon resonances on the nanometer scale in combination with spectral information over the entire visible range is of prime importance in the field of biosensors, surface-enhanced Raman spectroscopy (SERS), apertureless scanning near-field optical microscopy (SNOM), and for the design of metamaterials. But also the understanding of the abnormal transmission of light through sub-wavelength holes may gain by this technique. With the advent of monochromators and highly dispersive energy filters, energy-filtering TEM has now become available for the study of the optical response of materials well into the infrared range. This technique was applied to the detection of band gaps [1] as well as to the study of surface plasmons on metal particles, like Ag nanoprisms [2–4] or Au nanorods [5]. It offers a spatial resolution in the nanometer range which is well below the resolution of present light-optical techniques.Here, the dielectric response of holes in a Ag film is studied by energy-filtering TEM [6]. Holes with 180 nm diameter were drilled into a 100 nm thick Ag film using a focused ion beam. The arrangement of the holes was chosen such that well separated holes, holes that are closely spaced, and interpenetrating holes were present. Taking advantage of the monochromated electron beam (FWHM below 0.1 eV) and the MANDOLINE energy filter of the Zeiss SESAM microscope, energy-filtered images were recorded in the energy range between 0.4 and 4 eV using energy steps of 0.2 eV. Depending on energy loss, we find a number of resonant features that can be ascribed either to resonances of single holes or to the coupled resonance of several holes. Using discrete-dipole calculations, we find that the single-hole resonances have dipolar and quadrupolar nature. The coupling effects between adjacent holes lead to very strong field enhancements which occur primarily in the infrared range. These results demonstrate the power of the EFTEM technique for the mapping of surface plasmon resonances of complex structures. [7] References[1] L. Gu et al., Phys. Rev. B 75 (2007) 195214.[2] J. Nelayah et al., Proc. 14th European Microscopy Congress, Aachen, S. Richter, A. Schwedt (Eds), Springer, Berlin (2008) 243.[3]C.T. Koch et al., Proc. 14th European Microscopy Congress, Aachen, M. Luysberg, K. Tillmann, T. Weirich (Eds.), Springer, Berlin (2008) 447.[4]J. Nelayah et al., to be published in Optics Letters (2009). [5]B. Schaffer et al., Phys. Rev. B 79 (2009) 041401.[6] W. Sigle et al., Optics Letters (2009) in print.[7]The authors acknowledge financial support from the European Union under the Framework 6 program under the contract for an Integrated Infrastructure Initiative. Reference 026019 ESTEEM.
10:30 AM - NN6.3
Measurement of Signal Delocalization in Atomic Scale Electron Energy Loss Spectroscopy.
Amish Shah 1 2 , Quentin Ramasse 3 , Xiaofang Zhai 2 4 , Jian-Guo Wen 2 , Steven May 5 , Anand Bhattacharya 5 6 , James Eckstein 2 4 , Jian-Min Zuo 1 2
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Fredrick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 National Center for Electron Microscopy, Lawrence-Berkeley National Laboratory, Berkeley, California, United States, 4 Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 5 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 6 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe imaging resolution of the scanning transmission electron microscope (STEM) has improved to 1 Å, or sub-Å, with the addition of probe forming aberration correctors. The resolution is sufficient to resolve columns of atoms in crystals at favorable orientations. For the study of interfaces, composition and electronic structure mapping using electron energy loss spectroscopy (EELS) requires signal localization on the same scale of the atomic structure. Delocalization can occur by the nature of inelastic scattering or due to a number of experimental factors including a small EELS acceptance angle, multiple scattering and probe spreading in thick samples. Understanding delocalization is essential for quantitative interfacial analysis. Here we report an experimental measurement of delocalization using a digital superlattice of 2xLaMnO3/2xSrTiO3 synthesized by atomic layer by layer molecular beam epitaxy. The small period of the superlattice provides the modulation of the EELS signals for a number of core loss edges that allows us to measure the response function of integrated EELS signals to the aberration corrected electron probe. We show experimentally measured full width at half maximum (FWHM) of the integrated intensities and compare the experimental values with the empirical model of Egerton (R. F. Egerton, Micron 34 2003) for different electron loss energies. We show that for heavy atomic columns of La, strong elastic scattering causes significant delocalization and deviation from the prediction of the Egerton’s model. We also show that the response function of some atomic columns can have significant long tails of a Lorentzian distribution. We expect that results presented here will further stimulate the discussion of the spatial resolution of EELS mapping.
10:45 AM - NN6.4
An Atom-Probe Tomographic and First-Principles Study of the Interplay between Tungsten and Tantalum Atoms in Ni-based Superalloys.
Yaron Amouyal 1 , Zugang Mao 1 , Christopher Booth-Morrison 1 , David Seidman 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractNi-based superalloys derive their properties for high-temperature applications from their microstructure comprising large volume fractions (>70%) of Ni3Al-type γ’(L12)-precipitates dispersed in a Ni-based γ(fcc)-matrix. The partitioning of refractory elements to the γ- and γ’-phases determines the lattice parameter mismatch at the coherent γ/γ’ interface, which affects their mechanical properties at high temperatures. We investigate the partitioning behavior of W in several model and concentrated multi-component (>10 elements) Ni-based alloys using three-dimensional (3D) atom-probe tomography (APT) and first-principles calculations. The alloys investigated are generally comprised of highly-curved γ/γ’ interfaces, with complex topologies, separating large γ’-precipitates and small regions of the γ-matrix, as narrow as 4 nm. Moreover, the elements that we are interested in quantifying have typical concentrations of 0.5-1 at.% or less. These conditions require both high spatial resolution (<0.5 nm) in parallel with high mass-resolution and detectability (<500 at. ppm), which are obtained utilizing 3D APT. Furthermore, the analysis of the 3D results obtained from APT enables to study topologically complex interfaces, projecting the elemental concentrations across these interfaces onto 2D plots, utilizing proximity histograms or “proxigrams” for short. Proxigrams acquired from 3D APT observations of ternary Ni-Al-W and quaternary Ni-Al-Cr-W alloys indicate that W partitions preferentially to the γ’-phase. Its partitioning behavior is, however, reversed in favor of the γ-phase in many concentrated multi-component Ni-based alloys. Tantalum having a strong preference for the γ’-phase, as demonstrated by 3D APT, is assumed to have a major effect on the partitioning behavior of W. Indeed, first-principles calculations of the substitutional formation energies of W and Ta predict that Ta has a larger driving force for partitioning to the γ’-phase than does W. Thus suggesting that Ta displaces W from the Al-sublattice sites of the γ’-precipitates into the γ-matrix in multi-component alloys, which is consistent with our 3D APT results. This research is supported by an AFOSR MEANS II grant, and partially by the NSF and a Marie Curie International Outgoing Fellowship.
11:30 AM - NN6.5
Characterisation of Samarium Doped Ceria Multilayer Thin Films for Fuel Cell Applications.
James Perkins 1 , Stuart Cook 1 , Srinivasan Rajagopalan 5 , Sarah Fearn 1 , Richard J Morris 4 , Chris Rouleau 2 , Geoff West 3 , Hans Christen 2 , Hamish Fraser 5 , Stephen Skinner 1 , John Kilner 1 , David McComb 1
1 Materials, Imperial College London, London United Kingdom, 5 Materials Science and Engineering, Ohio State University, Columbus, Ohio, United States, 4 , University of Warwick, Coventry United Kingdom, 2 Center for Nanophase Materials Sciences, ORNL, Oak Ridge, Tennessee, United States, 3 , Loughborough University, Loughborough United Kingdom
Show AbstractCeria based electrolytes for use in the field of solid oxide fuel cells (SOFC) have excited great interest in recent years, particularly for SOFCs operating in the lower and intermediate temperature range (600-800°C), as they have higher ionic conductivities than the commonly used yttria stabilised zirconia (YSZ). [1-3] Whilst doping with di- or trivalent cations is the conventional approach to increase the oxygen vacancy concentration and enhance oxygen ionic conductivity [4], more recently massively increased conductivities have also been reported for highly oriented epitaxial structures of several electrolyte materials such as epitaxial YSZ [1], Sm doped CeO2 [4], and ZrO2:Y2O3/SrTiO3 heterostructures. [5]In this contribution the results of an extensive study of CeO2/10mol%Sm2O3-doped multilayers will be discussed. The multilayer structures were grown using pulsed laser deposition and have been characterised by an array of advanced analytical methods including RHEED, XRD, SIMS and analytical STEM. Quantitative analysis of the oxygen concentration and ratio of Ce(III)/Ce(IV) by STEM-EELS on samples before and after annealing has surprisingly revealed that both oxidation states of cerium can be stabilised on either side of structurally sharp and chemically abrupt interfaces. This observation could provide new insights into the origin of enhanced ionic conductivity in some oxide multilayers. References1.Kosacki, I., Rouleau, C. M., Becher, P. F., Bentley, J. & Lowndes, D. H. Solid State Ionics 176, 1319-1326 (2005).2.Steele, B. C. H. Solid State Ionics 129, 95-110 (2000).3.Zhongliang Zhan, T.-L. W. H. T. a. Z.-Y. L. AC J. Electrochem. Soc. 148, A427-A432 (2001).4.Suzuki, T., Kosacki, I. & Anderson, H. U. Solid State Ionics 151, 111-121 (2002).5.Garcia-Barriocanal, J. et al. Science 321, 676-680 (2008)*Research at the CNMS is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy
11:45 AM - NN6.6
EELS Study of Optical Properties of Noble-metal Nanostructures and Their Assemblies.
Shaul Aloni 1
1 Molecular foundry, LBNL, Berkeley, California, United States
Show AbstractNoble-metal nanostructures and their assemblies provide a unique capability of confining and manipulating light at nanoscale dimensions. Due their small size, the correlation of the size, shape and composition with optical properties of individual nanocrystals is not straightforward. We used high resolution EELS spectral imaging in combination with high resolution STEM imaging in an aberration corrected, monochromated electron microscope to define the optical properties of plasmonic nanostructures. We will show that low-loss EELS measurements not only provide information about the plasmon-polariton modes of individual nanostructures, they also allow study of interaction between the modes of individual nano-particles. This method is particularly useful in evaluation of the properties of functional plasmonic nanostructures. This work supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-O5CH11231
12:00 PM - NN6.7
A New Method for the Imaging of Surface Plasmons Using Phase Shifts in the Transmission Electron Microscope.
Vicki Keast 1 , Michael Gladys 1 , Tim Petersen 2 , Gerald Kothleitner 3 , Christian Dwyer 4
1 School of Mathematical and Physical Sciences, The University of Newcastle, Newcastle, New South Wales, Australia, 2 Electron Microscope Unit, The University of Sydney, Sydney, New South Wales, Australia, 3 Institute for Electron Microscopy, Graz University of Technology, Graz Austria, 4 Monash Centre for Electron Microscopy, Monash University, Melbourne, Victoria, Australia
Show AbstractSurface plasmons have been of substantial research interest for a number of years. There is a considerable need to be able to correlate the local geometric structure of the metal nanostructure with the surface plasmon energy. Even though nearly all of the applications of surface plasmons rely on the interaction of surface plasmons with light, the finite wavelength limits our ability to acquire spatially resolved information. However, a surface plasmon can also be excited by an electron beam, which offers an alternative route for characterization.Electron energy-loss spectroscopy (EELS) has been shown to be a very useful method for mapping surface plasmons at the nanoscale. However it suffers the disadvantage that it requires the use of advanced instrumentation with very high energy resolution. This paper will present an alternative approach based on the measurements of phase that could potentially be used on any transmission electron microscope (TEM). Phase information in the TEM can be accessed by either electron holography, or by a defocus series in conjunction with phase retrieval algorithms. We have recently modified the phase retrieval approach based on the transport of intensity equation (TIE) to enable robust acquisition of fully quantitative phase maps. We have observed that large phase deviations occur in and outside metal nanoparticles. The phase deviations are only observed for gold particles and not non-metallic polystyrene particles. Further experiments, where the images have been acquired with the plasmon excitations filtered out have confirmed that these effects are due to plasmon excitation. Phase measurements may offer an alternative method for imaging surface plasmons at the nanoscale, available to any researcher with access to a conventional TEM.This paper will describe the experimental technique and evidence that the observed effects are due to plasmon excitation. The theoretical basis behind the approach will be described, which offers some interesting insights into inelastic scattering theory and quantum-classical interactions.
12:15 PM - NN6.8
Nd Distribution in Nd-doped Polycrystalline YAG.
Xin Li 1 , Juan Idrobo 2 , Steve Pennycook 2 , Adam Stevenson 1 , Gary Messing 1 , Beth Dickey 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Technology Division, Oak Ridge Nantional Lab, Oak Ridge, Tennessee, United States
Show Abstract1 at% Nd-doped polycrystalline YAG (Y3Al5O12) is one of the best materials for solid-state laser gain media, and recently there has been significant progress in developing polycrystalline transparent YAG for solid-state lasers [1]. Nd3+ ions are the active centers for the laser production, which substitute Y3+ ions in the YAG lattice. One of the most important factors that can influence the efficiency of laser production is the Nd distribution, i.e. whether it is homogenously distributed or clustered in the lattice and whether there is segregation at the grain boundaries and triple junctions in the polycrystalline materials. We address these questions through a combination of atomic-resolution high angle annular dark field (HAADF) STEM imaging and quantitative energy-dispersive x-ray spectroscopy (EDXS). The atomic resolution HAADF STEM images are taken on the FEI Titan S aberration-corrected TEM-STEM at Oak Ridge National Laboratory, which can resolve the Y and Al atomic columns in the [111] zone axis projection where the closest Y columns are spaced 1.2 Å apart. The Y columns projected as triangular rings with 3-fold symmetry are brighter than those projected as hexagonal rings with 6-fold symmetry due to electron channeling effects, which agrees well with multislice simulations of the HAADF images. It is also observed that among the same type of Y columns (i.e. triangular or hexagonal) there exist brightness variations, and through statistical analysis of the HAADF data we attribute the increased column intensities to the presence of Nd. STEM-EDXS analysis of 10 different grain boundaries and their adjacent grain interiors shows that the Nd concentrations in the grain boundary regions are around 0.2 at% higher than the bulk, corresponding to a Gibbsian interfacial excess of 0.789+/-0.494 cat/nm2. Atomic resolution Z-contrast images from the grain boundary regions combined with local EDXS analysis shows that the Nd is not segregated to the grain boundary cores, rather it resides in the adjacent atomic layers, most likely due to elastic strain energy interactions with the grain boundaries. [1] A. Ikesue, Y. L. Aung, T. Taira, T. Kamimura, K. Yoshica and G. L. Messing, “Progress in Ceramic Lasers,” Ann. Rev. Mater. Res., 36, 397-429 (2006).
12:30 PM - NN6.9
Atomic Level Analysis of Amino Acids by the Scanning Atom Probe.
Osamu Nishikawa 1 , Masahiro Taniguchi 1 , Atsushi Ikai 2
1 , Kanazawa Institute of Technology, Nonoichi Japan, 2 , Tokyo Insitute of Technology, Yokohama Japan
Show AbstractAtom probe (AP) is known to be a unique instrument that makes possible to mass analyze a specimen at atomic level. However, its application is mostly limited to metals and semiconductors because the AP analysis proceeds by field evaporating surface atoms applying the high field, 20-40 V/nm, on the specimen surface. In order to generate such a high field the analyzed area is an apex of a sharp tip. Metals and semiconductors can be formed in such a sharp tip easily. However, the formation of a sharp organic and bio molecule tip is not easy. Thus, we introduced a funnel shaped micro extraction electrode that scans over a specimen surface and confines the high field in a narrow space between the micro open hole at the apex of the electrode and a micro protrusion on a specimen surface. Thus, this type of the AP is named as scanning atom probe (SAP). Then, organic and bio molecules can be deposited on the micro protrusion on the specimen surface. The AP analysis of metals indicates that the field evaporation of metal atoms proceeds one atom by one atom implying that the binding between metal atoms are uniform and non-directional. On the other hand most atoms of non-metallic specimens are field evaporated as clustering atoms. For example, doubly charged thiophene monomers are detected when polythiophene is analyzed. This indicates that one sulfur and four carbon atoms are strongly bound. Similarly, the mass spectra of highly pure single walled carbon nano tubes (SWCNT) exhibit sharp mass peaks of C2+ and C+ indicating that carbon atoms are bound by non-directional strong bonds. This implies that the unique feature of the AP is not only in the identification of individual ion but also in the investigation of binding states of the atoms forming the materials. For the present analysis amino acids are deposited on a small ball of the SWCNT fibers in order to avoid the catalytic reaction of metals. The SWCNT ball is dipped in a solution of sample molecules. The glycine solution is made by dissolving 1 gram of glycine in 15 ml pure water. Cystine, leucine and methionine solutions are made by dissolving 50 mg of the molecules in 1 ml of 0.1 N HCl. Discrimination of the carbon ions of the SWCNT from the fragment ions of the molecules is relatively easy because nearly all of the SWCNT carbon ions are detected as C2+ and C+. Glycine is the smallest amino acid formed by a carboxy group, an amino group and a CH2 group. Thus, it is assumed that the analysis will provide a guideline for the analysis of larger molecule. However, the identification of fragments ions is not easy because many different fragments have the same mass such as CH3 and NH. This indicates that mass analyzer for the bio-molecules requires a mass spectrometer with the mass resolution m/Δm higher than 10,000. The characteristic mass spectra of the amino acids and the structure of a new SAP with a position sensitive ion detector with a spiral delay line will be presented.
12:45 PM - NN6.10
Imaging Buried Organic-Inorganic Interfaces in Biominerals.
Lyle Gordon 1 , Derk Joester 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractBiological organisms have a remarkable ability to control the structure and properties of inorganic minerals across a wide range of length scales from single nanometers to the macro-scale. In many cases, an organic matrix comprised of a variety of macromolecules interacting with the forming mineral is responsible for this control. For example, in the tooth of the chiton, the polysaccharide chitin, along with a number of proteins, has been shown to control and template the deposition of iron oxide minerals and their maturation to magnetite under very mild conditions. Furthermore, the same macromolecules are incorporated into the biomineral composite during growth. Incorporation can occur at different levels of hierarchy, e.g. intra- or inter-crystalline, and thus contribute to the outstanding fracture toughness and wear resistance of the material. An in-depth understanding of nucleation, growth, and the advanced material properties critically depends on the ability to characterize the interactions across the organic-inorganic interface. Atom-probe tomography is uniquely capable of providing structural insight at the atomic scale by directly probing the location and chemical identity of the atoms within a small sample of material, usually a metal or semi-conductor.We report here the application of atom-probe tomography (APT) to the tooth cusp of the chiton, Chaetopleura apiculata, to study the structure of the intra- and inter-crystalline organic compounds and buried organic-inorganic interfaces. The chiton tooth cusp is composed primarily of magnetite (Fe3O4) and its organic matrix contains fibrillar chitin as a key structural element. We used focused ion beam (FIB) lift-out and tip-sharpening techniques to prepare samples suitable for the atom-probe. We demonstrate here that the atom probe enables the identification and localization of small atomic and molecular fragments (C, N, CH, NH, ca. 500 ppm) within the magnetite mineral matrix. These fragments are characteristic of the organic macromolecules which template the magnetite mineralization. We furthermore present evidence from 3D reconstructions of tooth sample volumes (approx. 106 ions) that suggest a fibrillar, organic structure within the iron oxide. We interpret these fibrillar structures to be the self-assembled chitin fibrils observed in demineralized chiton teeth.
NN7: Structure and Microstructure
Session Chairs
Wednesday PM, December 02, 2009
Room 204 (Hynes)
2:30 PM - **NN7.1
Evolution of Alloy Microstructures at the Atomic Scale.
Emanuelle Marquis 1
1 Department of Materials, Oxford University, Oxford United Kingdom
Show AbstractThe ability to experimentally probe the chemical structure of materials at the atomic scale is key to ultimately control material properties. Atom-probe tomography is a unique technique that allows the chemical investigation of small volume of materials with near atomic resolution, allowing the quantitative study of atomic scale phenomena. I will present examples illustrating how atom-probe tomography can be used to characterize the structure of selected alloys and contribute to our understanding of the atomistic and nanoscale processes that underpin the kinetics evolution and equilibrium of solute distributions in metallic systems. Particular focus will be placed on energy materials. In the context of fusion and fission energy, controlling material properties during irradiation requires detailed understanding of the role of the defect sinks, i.e. nanoscale particles, grain boundaries, dislocations, etc. which in turn implies a detailed knowledge about the internal structure, chemistry, or interfacial structure of these microstructural features. The role of atom-probe tomography and electron microscopy for 3-D atomic scale characterization of steels and tungsten alloys will be discussed.
3:00 PM - **NN7.2
Ultra-high-vacuum Cs Corrected Scanning Transmission Electron Microscopy (STEM) and the Measurement of Small Lattice Displacement by STEM.
Kazuo Furuya 1
1 , National Institute for Materials Science (NIMS), Tsukuba, Ibaraki Japan
Show AbstractAberration correction of the probe forming lens used for STEM has been recently established at several laboratories, and exciting results are being produced. An aberration corrector provides a smaller probe size which enables atomic column-by-column analysis. However, a corrector that is compatible with a UHV environment has not been developed yet. We report here that UHV-STEM can be successfully modified for third-order spherical aberra tion (Cs) corrector. Some results with this contamination free UHV-STEM will be shown. Furthermore, even with sub-angstrom level electron beam, the lattice displacement embedded in the complex system of materials is difficult to measure. In this presentation, some of example on Al-Xe system will be demonstrated and the need for future development will be discussed.
3:30 PM - NN7.3
Influence of Analysis Parameters on the Microstructural Characterization of Nanoscale Precipitates.
Ai Serizawa 1 , Michael Miller 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe definition of the position of the interface between a precipitate and the matrix is important not only for investigating the size and morphology of precipitates but also for estimating the solute concentrations and the extent and amplitude of solute gradients on both sides of the interface. The accuracy of the position of the interface is particularly important for nanoscale (i.e., < 5 nm diameter) precipitates, as a large proportion of the solute atoms lie in the surface layer. In order to establish reliable and consistent estimates of these microstructural parameters, a series of simulated microstructures containing nanometer-scale precipitates was created. These data were then analyzed with the proximity histogram and the maximum separation method to determine the influence of the analysis parameters.An atom probe simulator was used to construct datasets containing nominally spherical (i.e., atomically faceted) 2-nm-radius precipitates with a number density of 1 x 1024 m-3 in which the solute concentrations of the precipitates and the matrix were systematically varied. The concentrations of cubic volume elements were determined for different voxel sizes and smoothing/delocalization parameters. Iso-concentration surfaces defining the interface were then constructed at the midpoint of the solute concentrations of the precipitate and matrix. The sharpness of the interface or the interface width was estimated from the distance between the 10 and 90% points of the solute concentrations in the precipitates and the matrix in the proximity histogram as a function of these parameters.For the simulated 2-nm-radius spherical precipitates, the optimized voxel size and delocalization were found to be 0.5-0.6 nm and 1.0-1.5 nm, respectively. Under optimum parameters, the voxelization process only slightly degrades the interface width determined from the proximity histogram to ~0.15 ± 0.04 nm. Generally, the interface width tended to increase slightly with increasing voxel size and degree of delocalization. However, when these parameters were too small, the solute concentration in the surface layers of the precipitates was overestimated. This overestimate arises because the solute concentration in precipitates was overestimated as a result of excluding the solvent atoms on the surface of the precipitates. 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.
3:45 PM - NN7.4
Hierarchical Nanostructures and Nanoscale Texture Measurements of Ultra-high Strength Aluminium Alloys.
Peter Liddicoat 1 , S. Ringer 1
1 Australian Key Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, New South Wales, Australia
Show AbstractMaterials with crystallographic features on the order of nanometres present extremely challenging conditions for electron microscopy and microanalysis. Images from the thinnest foils in TEM contain convolutions in contrast and spectroscopic information as most of the grains under study are significantly smaller than the foil thickness. High-resolution scanning electron microscopy can usually be used to image nanocrystalline grain structure, but quantitative information on grain orientation using electron backscattered diffraction is difficult below ~100 nm. To address these challenges in nanoscale microscopy and crystallography, we have developed new techniques in APT to quantitatively assess solute nanostructures and measure crystal orientation relationships. We have applied these techniques to ultra-fine grained aluminium alloys that exhibit record breaking mechanical properties. The origins of properties in these materials are not well understood largely due to the previously discussed observational limits. Our novel approach reveals the presence of hierarchical nanostructures not detected by TEM that we expect will make significant contributions to the understanding of structure-property relationships.
4:30 PM - NN7.5
Interface Atomic Structure of SiC/Ti3SiC2 by STEM and First Principles.
Wang Zhongchang 1 , Saito Mitsuhiro 1 , Tsukimoto Susumu 1 , Ikuhara Yuichi 1 2
1 , WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 Japan, 2 , Institute of Engineering Innovation, University of Tokyo, Tokyo 113-8656 Japan
Show AbstractObtaining an atomistic understanding of the impact of buried interface structures on electric properties is a long-standing goal in semiconductor material science. Generally, to achieve this objective, developing fundamental knowledge on how interfacial atoms bond at atomic-scale resolution is prerequisite before further studies on properties can be conducted. Recently, the scanning transmission electron microcopy (STEM) that bears the highest resolution makes the atomic-scale characterization of interface structures a reality, thereby opening up an avenue for relating structure to property on atomistic level[1,2]. However, because of the abrupt discontinuity and change at interface, understanding the observed image is not always straightforward but highly possible with additional first-principles (FP) calculations. Thus, combined STEM-FP studies are an important advance for addressing interface-related problems. Here, we have combined the STEM imaging with the first-principles modeling to determine atomic-scale structure of the 4H-SiC/Ti3SiC2 interface and its impact on electron transport, aimed at clarifying origin of the Ohmic contact to p-type SiC. Understanding of the role of 4H-SiC/Ti3SiC2 interface on the mechanism whereby the Schottky barrier becomes Ohmic is fundamental for device design and performance control of SiC electronics, a new substitute of Si as next-generation electronic device[3]. We have obtained direct atomic-resolution image that illustrates how the epitaxially grown Ti3SiC2 atomically bonds to the SiC substrates and inferred, from first-principles modeling based on the image, that a C layer emerges at interface. The presence of atomic layer of carbon atoms has been found to strengthen adhesion, lessen Schottky barrier, and enhance quantum transport property. This is a key factor to understand the origin of the Ohmic nature, which is attributed to a large interface dipole shift associated with considerable charge transfer. [1]M. Haider, H. Rose, S. Uhlemann, B. Kabius, and K. Urban, Nature (London) 392, 768 (1998).[2]P. D. Nellist et al., Science 305, 1741 (2004).[3]Z. Wang, S. Tsukimoto, M. Saito, and Y. Ikuhara, Phys. Rev. B 79, 045318 (2009).
4:45 PM - NN7.6
Properties of Multiferroic Interfaces from Atomic Displacements by STEM.
Hye Jung Chang 1 , A. Borisevich 1 , S. Kalinin 2 , O. Ovchinnikov 2 , R. Ramesh 3 , M. Huijben 4 , S. Pennycook 1
1 Materials Science Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Physics, University of California, Berkeley, California, United States, 4 Science & Technology, University of Twente, Enschede Netherlands
Show AbstractAberration-corrected microscopy is uniquely suited for imaging sub-Ångstrom structural distortions such as polarization-related displacements, making it a powerful tool for studies of ferroelectric materials [1]. Aberration-corrected Z-contrast scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) make it possible to analyze the composition and the electronic structure simultaneously with the atomic structure. In this work, we use a direct imaging approach to quantify the mechanical strain and polarization-induced displacements across the domain walls and interfaces between the ferroelectric and the electrode material. The structural data are also correlated with EELS.Epitaxial BiFeO3 (BFO) films were grown using molecular-beam epitaxy on single-crystal SrTiO3. (STO) substrates. A thin layer of epitaxial (La,Sr)MnO3 (LSMO) was used as both an electrical contact and heteroepitaxial growth buffer. STEM images and EEL spectra were collected using a VG Microscopes HB603U operated at 300 kV, equipped with Nion® aberration correctors and Gatan Enfina® spectrometer. Atomic positions were determined from the Z-contrast STEM images and refined using 2D Gaussian fits. Bi atom positions can be used to quantify local strain, while analysis of Bi and Fe positions gives local ferroelectric polarization. Additionally, when positions of O atoms are determined from simultaneous BF STEM, local octahedral rotations can also be mapped. Bi position analysis at the BFO-LSMO interfaces for both thick (50 nm) and ultrathin (3.2 nm) BFO films shows that the first 4 atomic layers of BFO exhibit expansive strain perpendicular to the interface. Ferroelectric polarization at the interface shows different behavior depending on film thickness and/or polarization direction. In an ultrathin 3.2 nm film, polarization is approximately constant inside the film and drops off quickly at the interface. Interestingly, the first 6 layers of LSMO also show small off-center displacements of Mn, indicating induced polarization in the half-metal electrode. In the 50 nm film, on the contrary, polarization falls off gradually at the interface, and no induced displacements are observed in LSMO. Implications for materials properties and correlation with both core-loss and low-loss EELS at the interfaces will be discussed. New possibilities for structural mapping from atomic column shapes via function fits and principal component analysis will also be introduced. Research supported by ORNL’s SHaRE Use Facility (AYB) and Center for Nanophase Materials Sciences (SVK, SJ), sponsored by the Scientific User Facilities Division; by the Division of Materials Science and Engineering (SJP), all Office of Basic Energy Sciences, U.S. Department of Energy, and by the ORNL LDRD program via a postdoctoral appointment administered jointly by ORNL and ORISE (HJC).[1] C. L. Jia et al., Nature Materials 6, 64 (2007).
5:00 PM - NN7.7
EELS/STEM Investigation of Electronic Structure in Conducting LaAlO3/SrTiO3 and LaGaO3/SrTiO3 Epitaxial Heterojunctions.
Claudia Cantoni 1 , Jaume Gazquez 1 , Maria Varela 1 , Paolo Perna 2 5 , Davide Maccariello 2 , Umberto Scotti di Uccio 2 , Fabio Miletto Granozio 2 , Daniele Marre` 3 , I. Pallecchi 3 , M. Codda 3 , Stefano Gariglio 4 , Andrea Caviglia 4 , Nicolas Reyren 4 , Jean Marc Triscone 4
1 Materials Science & Technology Division , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 CNR-INFM Coherentia and Dipartimento di Scienze Fisiche , Federico II University , Naples Italy, 5 IMDEA Nanociencia Campus, Universidad Autónoma de Madrid, Madrid Spain, 3 LAMIA CNR-INFM and Dipartimento di Scienze Fisiche, University of Genoa, Genoa Italy, 4 Condensed Matter Physics Department, DPMC, University of Geneva, Geneva Switzerland
Show AbstractRecently, there have been many efforts to understand the mechanism responsible for the formation of a 2-dimensional electron gas at the interface of the two band gap insulators SrTiO3 (STO) and LaAlO3 (LAO). Several explanations have been proposed for the transport properties observed in this system. Some arguments advocate an electronic reconstruction in response to the polar discontinuity arising from the different ionic charge of the (001) atomic planes in LAO and STO. Other approaches indicate oxygen vacancies and cation interdiffusion as the cause of the onset of interface conductivity. Moreover, the ground state of such a system is still being debated, as some studies describe the interface as magnetic and other studies describe it as superconducting. Atomically-resolved electron energy loss spectroscopy (EELS) in an aberration corrected STEM is an optimal tool for probing the atomic and electronic structure of such buried interfaces. In this study, we report on atomic-scale measurements of composition and electronic fine structure performed on the LAO/STO system as well as on a novel LaGaO3/STO interface that shows a superconducting transition at ~ 190 mK. The investigation of heterojunctions structurally similar to the LAO/STO, but grown using oxides with different chemical and physical properties, is a viable route to improve our understanding of the physics underlying such a peculiar phenomenon.Research sponsored by the US Department of Energy, Office of Electricity Delivery and Energy Reliability.
5:15 PM - NN7.8
Crystallite Size Analysis by Two-Dimensional XRD.
Bob He 1
1 , Bruker AXS, Madison, Wisconsin, United States
Show AbstractThe properties of polycrystalline materials are determined by the properties of each crystallite and the boundaries between crystallites. The size of the crystallites in a polycrystalline material has significant effects on many of its properties, such as thermal, mechanical, electrical, magnetic and chemical properties. For instance, the mechanical strength of polycrystalline metals and alloys are strongly dependent on the crystallite (grain) size. The deformation of metals is caused by the motion of dislocations and other defects under loading stress. Different crystallographic orientations and the boundaries between adjacent crystallites serve as barriers to the motion of dislocation and other crystal defects. A metal with finer crystallites, therefore, has more boundaries to impede dislocation motion. The grain size can be measured by two-dimensional diffraction with the conventional method based on the measurement of diffraction peak broadening or diffraction profile analysis. Although line broadening appears when the particle size is smaller than 100 nm, in practice, the Scherrer equation can adequately determine the average size of crystallites smaller than 30 nm when the broadening is significant enough to be resolved from instrumental broadening.This presentation introduces a new grain size measurement method based on the gamma-profile analysis on two-dimensional diffraction patterns. The availability of an area detector makes it possible to measure the spotty diffraction rings due to large grain size or poor sampling statistics. The gamma-profile analysis extended the measurement range from a few to 100 nanometers with the conventional method to a few millimeters depending on the x-ray incident beam size, divergence, sample shape and size, instrument geometry and detector resolution. The gamma-profile analysis is based on the sampling statistics. Sampling statistics believed to be “poor” for other applications are actually preferred for crystallite size determination. The sampling statistics are determined by both the sample structure and instrumentation. For a given instrument window, the number of grains contributing to a selected diffraction ring is determined by the effective diffraction volume, grain size and the multiplicity of the diffracting crystal planes. A two-dimensional diffraction system can be calibrated by a sample with known crystal size, crystal structure and x-ray absorption coefficient. The grain size of an unknown sample can then be determined by quantitative analysis of the spotty diffraction ring. The mathematic modeling for gamma-profile analysis and experimental examples are also given in this presentation.
5:30 PM - NN7.9
Quantitative Chemical Mapping of Engineered Interfaces in Quaternary III-V Semiconductor Heterostructures using Exit-Wave Retrieval High-Resolution Transmission Electron Microscopy.
Krishnamurthy Mahalingam 1 , Heather Haugan 1 , Gail Brown 1 , Kurt Eyink 1
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractHeterostructures derived from quaternary III-V semiconductor systems (such as those based on the InAs-GaSb and InAs-AlSb systems) are promising materials for a variety of next generation optoelectronic devices, such as mid-infrared lasers and tunable long-wavelength detectors. Interfaces are known to play a unique role in especially in these materials due to the distinctly different types of interfacial bonds obtainable depending on growth conditions (for instance the interfaces in InAs-GaSb heterostructures can be “InSb-like” or “GaAs-like”). Considerable attention is now focused on tailoring interface stoichiometry to optimize properties. A key requirement in this endeavor is the ability to accurately quantify the composition of interfaces (typically < 1 nm in width). Although several techniques based on high-resolution transmission electron microscopy (HRTEM) have been developed since the early 1990’s [1-3], these are applicable only to ternary systems (such as those based on the AlAs-GaAs and InAs-GaAs systems).We have recently developed a new approach for atomic scale compositional analysis of quaternary III-V semiconductor interfaces with mixing in both cation and anion sublattices [4]. Our approach utilizes the principles of phase retrieval HRTEM based on the focal series reconstruction technique, used in combination with multivariate statistical analysis for quantitative image analysis. In this study we use this approach to investigate the role of interface engineering in optimizing properties of InAs/GaSb superlattices. We present results from several structures, including those in which the alternating InAs and GaSb layers are grown with no interface control, and the others in which each interface is tailored to be “InSb-like,” wherein a controlled deposition of 0.8 ML (0.26 nm) of InSb precedes the growth of each InAs/GaSb layer. In addition, we have also studied the effects of growth interruption, wherein switching between the different layers was preceded by a soak under As2/Sb2 flux for a fixed period of time. Our studies show that untailored interfaces exhibit significant compositional grading in both the group-III and group-V sublattices. In the case of tailored interfaces, significant improvement in compositional abruptness is achieved at the InAs-on-GaSb interface. This effect is however observed to be less dramatic at the GaSb-on-InAs interface. Further studies on the correlations between the photoresponse spectra and the measured composition profiles and also strain profiles across each interface will be presented. The validity of our approach is demonstrated based on an image simulation study performed on model structures with abrupt and graded interfaces.References[1] A.Ourmazd et al., Ultramicroscopy 34 (1990) 237.[2] S.Thoma and H. Cerva, Ultramicroscopy 38 (1991) 265.[3] K.Tillmann, Ultramicroscopy 93 (2000) 1239.[4] K.Mahalingam et al., J. Microscopy 230 (2008), 372
5:45 PM - NN7.10
Polycrystalline Oxide Formation during Oxidation of (001) CuxNi1-x Binary Alloys Studied by In situ UHV-TEM.
Zhuoqun Li 1 , Katherine Rodgers 1 , Judith Yang 1
1 Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show Abstract Due to the lack of experimental capabilities previously, the nano-scale structural changes during the oxidation of metals were not considered in nearly all classical oxidation theories. Therefore, studies of the initial nano-scale stages of oxidation will broaden our understanding on how these early stages lead to the final oxides morphologies and properties. The initial nano-scale stages of oxidation, including oxides nucleation, growth and coalescence, of CuxNi1-x alloys have been investigated by in situ ultra-high vacuum transmission electron microscope (UHV-TEM) as an extension of our previous research on Cu and Cu-Au systems. The two components, Cu and Ni, are 100% solid soluble down to ~ 300°C but Cu2O and NiO show limited miscibility. Systematic in situ (UHV-TEM) and ex situ (XRD, TEM and AFM) studies of the surface dynamics of the initial oxidation behavior of Cu-Ni alloys have been done intensively. Dynamic responses to alloy components, temperature and environmental partial pressure of oxygen (pO2) are considered. In contrast to Cu (001) and Cu-Au (001) oxidation, remarkable differences exist in Cu-Ni (001) oxidation: 1) a second rapid nucleation of compact and dense oxide islands occurred and 2) polycrystalline oxides formed, where only cube-on-cube epitaxial Cu2O islands nucleated on Cu (001) and CuAu (001) for all temperatures and pressure studied. The first oxidation stage, which is characterized by a rapid nucleation followed by growth of oxides, supports an oxygen surface diffusion model; while the second rapid nucleation stage is due to the formation of NiO nano-particles. Further detailed structural studies of the oxides, interfaces, and the effect of small amounts of Ni additions to the surface changes of Cu-Ni (001) that result in irregular-shaped polycrystalline oxide formation is necessary to clarity the underlying mechanisms of the early and transient stages of selective oxidation.
Symposium Organizers
Manfred Ruehle Max-Planck-Institute for Metals Research
Larry Allard Oak Ridge National Laboratory
Joanne Etheridge Monash University
David Seidman Northwestern University
NN8: Segregation and Tomography
Session Chairs
Thursday AM, December 03, 2009
Room 204 (Hynes)
9:30 AM - **NN8.1
Cs Corrected STEM Characterization of Atomic Structures and Segregation Atoms of Ceramic Interfaces.
Yuichi Ikuhara 1 2 3 , Scott Findaly 1 , Naoya Shibata 1 , Teruyasu Mizoguchi 1 , Takahisa Yamamoto 1 2
1 Institute of Engineering Innovation, The University of Tokyo, Tokyo Japan, 2 Nanostructures Research Laboratory, Japan Fine Ceramic Center, Nagoya Japan, 3 WPI Advanced Institute for Materials Research, Tohoku University, Sendai Japan
Show AbstractInterfaces in ceramics play an important role on the various properties. It has been known that the addition of small amount of dopants strongly improve the mechanical and functional properties in polycrystalline ceramics. STEM (scanning transmission electron microscopy) is very powerful technique to experimentally determine the atomic site of the dopants segregated at grain boundaries. Annular dark field (ADF) STEM has become a highly popular atomic resolution imaging technique. As the image intensity in the high angle ADF (HAADF) is approximately proportional to the square of the atomic number, HAADF image is especially well suited for characterizing the role of heavy impurities in grain boundaries composed of much lighter ions. On the other hand, we found that even light elements can be directly observed at an atomic scale by annular bright field (ABF) images. In this case, the locations of both light and heavy element columns can be imaged as dark contrast. Similar to HAADF image, the ABF imaging mode is confirmed to be robust over a wide range of specimen thicknesses. In this presentation, the results obtained by Cs-corrected HAADF and ABF STEM techniques are demonstrated for well-defined grain boundaries in Al2O3, ZnO, SrTiO3 and TiO2 bicrystals with and without dopants. In addition, several examples are also demonstrated to characterize the interface atomic structures of SrTiO3 superlattice and Au/TiO2 catalytic system.References[1] S.D. Findlay, N. Shibata, H. Sawada, E. Okunishi, Y. Kondo, T. Yamamoto, Y. Ikuhara, MRS 2009, session NN, this abstract book (2009) [2] J.P. Buban, K. Matsunaga, J. Chen, N. Shibata, W.Y. Ching, T. Yamamoto and Y. Ikuhara, Science, 311(2006) 212 [2] N. Shibata, S. D. Findlay, S. Azuma, T. Mizoguchi, T. Yamamoto and Y. Ikuhara, Nature Mater. on line publication: 21 JUNE (2009)[3]Y. Sato, J. P. Buban, T. Mizoguchi, N. Shibata, M. Yodogawa, T. Yamamoto, and Y. Ikuhara, Phys. Rev. Lett., 97(2006) 106802.[4] N. Shibata, A.Goto, S.-Y. Choi, T. Mizoguchi, T. Yamamoto and Y. Ikuhara: Science,322(2008) 570.[5] H. Ohta, S.W. Kim, Y. Mune, T. Mizoguchi, K. Nomura, S. Ohta, T. Nomura, Y. Nakanishi, Y. Ikuhara, M. Hirano, H. Hosono and K. Koumoto: Nature Mater., 6(2007) 129.[6]S.-Y. Chung, S.-Y. Choi, T. Yamamoto, Y. Ikuhara: Phys. Rev. Lett.,100(2008) 125502
10:00 AM - **NN8.2
Investigations of the Chemistry of Interfaces with Nanometer Resolution.
Krystyna Stiller 1 , Mattias Thuvander 1 , Marie Sonestedt 1 , Jonathan Weidow 1
1 , Applied Physics, Göteborg Sweden
Show AbstractThe importance of interfaces for the properties of materials is very well recognised. Mechanical, chemical, thermal, electrical and magnetic properties all depend on the character and morphology of these boundaries. However, our understanding of all these properties was hampered in the past by the difficulty to describe real interfaces in sufficient detail. Recent development of the methods of high resolution opens new possibilities in studies and thereby the understanding of interfaces. High resolution TEM has evolved into a versatile tool for detailed investigations at sub-nm level. This covers the chemical analyses across boundaries, the application of elemental mapping via electron filtering techniques and combinations of such mapping with e.g. X-ray microanalysis, etc. However, true three-dimensional characterisation at this scale is not within the grasp of any of the techniques mentioned above. Atom-probe tomography (APT) on the other hand, is unbeatable in this respect: it is the only method that can routinely analyse and position individual atoms in a material with a spatial resolution of 0.1-0.5 nm. Recent development of the technique allows the use of a short laser pulse (a picosecond pulse time) to initiate field evaporation instead of an electric pulse making the analysis of materials with a low electrical conductivity possible. In addition, less mechanical stress is induced in the specimen needle, making the often occurring specimen failure by mechanical fracture less frequent. This is of special importance for analysis of specimens containing phase or grain boundaries that are often weak links in the structure. Furthermore the invention of focused ion beam milling techniques has created possibilities for routine preparation of APT specimens containing the desired interfaces close to the specimen tip. At the Department of Applied Physics at Chalmers University of Technology different electron microscopy techniques and APT are used to study material chemistry, structure and their development down to the atomic level. Investigations incorporate analyses of interfaces in steels, nickel base alloys, hard or oxidation resistant coatings and thin films. Some examples from these works will be presented with the focus on chemistry and its development in lath and grain boundaries in maraging steels, studies of interfaces in Ti2AlC (so called MAX-phase) coatings and investigations of grain and phase boundary segregation in WC/Co based materials. It will be demonstrated that in the maraging steels small amounts of segregating species such as Mo and Si could be detected and quantified by APT. Furthermore, an uneven distribution of segregating species at grain boundaries especially in Ti2AlC and WC/Co systems will be discussed.
10:30 AM - NN8.3
Investigation of Organic Multilayers using Aberration-corrected HRTEM.
Soumaya Mauthoor 1 , Salahud Din 1 , David McComb 1 , Sandrine E. Heutz 1
1 Department of Materials and London Centre for Nanotechnology, Imperial College London, London United Kingdom
Show AbstractMultilayer organic films are widely used in a number of functional devices such as heterojunction solar cells and have great potential in areas such as organic spintronics. The crystallinity and texture of the layers, their epitaxial relationship, and the interfaces can all have a major influence on the ultimate performance of a device based on such multilayer structures. In this contribution we will discuss the preparation of high quality cross-sections of organic multilayers. The samples prepared were characterised using a range of analytical methods and we will show that aberration-corrected high resolution transmission electron microscopy (HRTEM) has the potential to probe the crystal structure of the layers and their interfaces.Initial investigations were conducted using bulk copper phthalocyanine (CuPc) crystals. CuPc is an organometallic molecular crystal used in pigments and gas sensors, as well as organic solar cells. CuPc is relatively resistant to electron beam-induced radiation damage and has often been used as a standard for plan view molecular imaging by HRTEM[1, 2]. In this work cross-sections of CuPc were prepared by embedding bulk crystals in epoxy resin then sectioning using an ultramicrotome. The samples were examined using an aberration-corrected FEI Titan 80/300 TEM. The images and selected-area diffraction patterns obtained demonstrate that the physical damage caused by the ultramicrotome, while significant, does not destroy the crystallinity of the sample.The same sample preparation technique was therefore used to prepare cross-sections of organic multilayer films made up from CuPc, metal-free phthalocyanine (H2Pc) and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) which were deposited on polymer substrates by organic molecular beam deposition (OMBD). Bilayers of PTCDA/CuPc and mixed films of CuPc in H2Pc exhibit novel electronic and magnetic properties that are critically dependent on the molecular packing. So far, structural studies based on highly textured XRD patterns have been ambiguous, limiting the interpretation and optimisation of physical properties. In this work aberration corrected HRTEM and selected-area diffraction images of the cross-sections allow us to conclusively determine the packing of the molecules in each case and to probe the structure of the organic-organic interfaces. These results offer new insights into the device properties of complex molecular structures and demonstrate that HRTEM is a crucial tool for the development of organic electronics. [1] J. J. W. Menter, Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences 236, 119 (1956).[2] Y. Murata, J. R. Fryer, and T. Baird, Nature 263, 401 (1976).
10:45 AM - NN8.4
Trapping of Au Atoms at Twin Defects in Si Nanowires Characterized Using Advanced Electron Microscopy Techniques.
Eric Hemesath 1 , Sujing Xie 1 , Jinsong Wu 1 , Vinayak Dravid 1 , Lincoln Lauhon 1
1 Materials Science & Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractThe vapor-liquid-solid (VLS) growth mechanism has been broadly exploited in recent years to synthesize single component and heterostructured nanowires in a wide range of semiconductors. In general, the VLS growth technique yields single crystal material. In Si however, (111) planar defects are occasionally observed to form in nanowires that grow in <112> directions. These planar defects may extend along the entire length of the nanowire, and superlattices of (111) stacking faults can form polytypes.[1] Furthermore, using high-angle annular dark-field (HAADF) imaging in an aberration-corrected scanning transmission electron microscope (STEM), we have shown that isolated (111) twin planes can trap Au impurity atoms in a periodic arrangement.[2] This suggests the presence of a low-energy site that promotes the decoration of Au impurities on the defect interface. Interestingly, Au atoms are not trapped by the twin superlattices, whereas a significant fraction of singly twinned nanowires exhibit multiple lines of trapped Au atoms. We hypothesize that the linear arrays of Au atoms result from step edges in the defect plane. We have exploited the atomic resolution provided by a Cs-corrected STEM microscope in efforts to determine the precise atomic location of gold atoms on the defect interface. The (111) twin is a Σ3 grain boundary and therefore has coincident sites every three atomic planes along the interface. By imaging twinned nanowires on low index zone axes, we can identify the point-defect configuration of these Au impurities. These findings will assist in developing a more comprehensive understanding of impurity incorporation in nanowires grown with a metal nanocatalyst. To resolve the radial location of the Au atoms within the nanowire diameter, ongoing electron tomography experiments are being performed in an uncorrected JEOL 2100F operated in STEM mode. A tilt series of HAADF images are used to reconstruct the three dimensional structure of a twinned nanowire. This tomographic reconstruction will allow us to determine the radial position of the Au impurity atoms and provide further insights into the growth mechanism of nanowires with axial twin defects.1.Lopez, F.J., Hemesath, E.R. & Lauhon, L.J. Ordered Stacking Fault Arrays in Silicon Nanowires. Nano Letters ASAP 2.Allen, J.E. et al. High-resolution detection of Au catalyst atoms in Si nanowires. Nat Nano 3, 168-173(2008).
11:30 AM - **NN8.5
Atomistic Structure of Confined Solid-Liquid Interfaces.
Wayne Kaplan 1
1 Department of Materials Engineering, Technion - Israel Institute of Technology, Haifa Israel
Show AbstractAs microstructural length-scales are reduced, the role of interfaces in determining the properties of materials becomes more dominant. The importance of the correlation between interface structure and chemistry with interface (and bulk) properties is evident in a range of material systems, and is a topic of intense experimental and theoretical work for solid-solid interfaces. While detailed thermodynamic analysis of solid-liquid interfaces is routinely conducted, and now includes ex-situ microstructural investigations, knowledge of the local structure at solid-liquid interfaces is still incomplete. To be more specific, the correlation between the structure of the solid, and the structure in the liquid near the interface, has not been fully addressed. In this presentation, examples of in-situ high resolution transmission electron microscopy (HRTEM) of liquids in contact with crystals will be presented. Layers of atoms parallel to the interface with the crystal and ordering within the layers will be demonstrated. The impact of contrast delocalization on reaching conclusions regarding ordering in the liquid will be discussed, and the limits of hardware-based correction methods (aberration correction) and software-based correction methods will be compared. Constructive and destructive ordering due to confinement of the liquid within small geometrically defined cavities in the solid will be demonstrated. The results will be extended to segregation within the ordered layers at interfaces, and possible approaches for excess measurements at solid-liquid interfaces will be explored.
12:00 PM - NN8.6
Interfacial Segregation of Tungsten in Ni-Based Superalloys: An Atom-Probe Tomographic, Transmission Electron Microscopy, and First-Principles Study.
Yaron Amouyal 1 , Zugang Mao 1 , David Seidman 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractNi-based superalloys are utilized for turbine blades in aeronautical jet engines and land-based power generators owing to their excellent high temperature strength and creep resistance. These properties are associated with their unique microstructure comprising Ni3Al-γ’(L12)-precipitates dispersed in a Ni-based γ(fcc)-matrix. The segregation of refractory elements at the γ/γ’ interfaces correlate with the interfacial free energy of the latter, thus affecting the alloys’ mechanical properties at high temperatures. We investigate the interfacial segregation of W in multi-component Ni-based alloys using three-dimensional (3D) atom-probe tomography (APT), transmission electron microscopy (TEM), and first-principles calculations. TEM observations reveal that all of the detected flat γ/γ’ interfaces possess the same {100} crystallographic orientation. Taking the advantages of both high mass-resolution and detectability for low concentration elements (<500 at. ppm) along with high spatial resolution (<0.5 nm), 3D APT analyses of the same multi-component alloys enable us to distinguish between different geometries of interfaces and to detect interfacial excess values as small as 1 at/nm2. 3D APT analyses reveal two classes of γ/γ’ interfaces: flat, {100}-type and curved, non-{100} interfaces. It is found that the {100}-type interfaces exhibit a Gibbsian interfacial excess of tungsten, ΓW = 1.2±0.2 at/nm2, corresponding to a 5 mJ/m2 decrease in their interfacial free energy. Additionally, first-principles calculations for a Ni-Al-W alloy, with a {100} γ/γ’ interface, yield a concomitant decrease in the interfacial energy, when a W atom is placed as close as 1 to 3 atomic planes from the interface. Conversely, no measurable segregation of W is detected in 3D APT analyses of the curved, non-{100} γ/γ’ interfaces. Similar calculations for representative {110} and {111} γ/γ’ interfaces predict an increase of 1 and 9 mJ/m2 in their energies, respectively. This demonstrates how interfacial segregation of W can play a significant role in the microstructural evolution of the γ’-precipitates. This research is supported by an AFOSR MEANS II grant, and partially by the NSF and a Marie Curie International Outgoing Fellowship.
12:15 PM - NN8.7
Aberration-corrected Electron Microscopy of the Nanostructural Evolution During Emission from CsI Coated Carbon Fiber Cathodes.
Lawrence Drummy 1 , Richard Vaia 1 , Don Shiffler 2
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 Directed Energy Directorate, Air Force Research Laboratory, Kirtland AFB, New Mexico, United States
Show AbstractCarbon-based nano and microfiber cathodes exhibit very low voltages for the onset of electron emission, and thus provide exciting opportunities for applications ranging from high power microwave sources to field emission displays. CsI coatings have been shown to enhance the emission properties of carbon fibers, although little is known about the microstructure of the fibers themselves in their as-received state, after coating with CsI, or after being subjected to high voltage cycling. Understanding this microstructural evolution is critical to ascertaining the long-term failure processes limiting emission lifetimes. Recent advances in sample preparation techniques for transmission electron microscopy (TEM), such as focused ion beam (FIB) lift-out techniques, have allowed for thin sectioning of materials with varying geometries, such as 1-10 µm diameter fibers. Longitudinal cross sections of the CsI coated fibers produced by FIB lift-out reveal a nanostructured graphitic core surrounded by an amorphous layer with submicron sized islands of crystalline CsI on the outer surface. Aberration-corrected HREM of the fiber core achieved 0.10 nm resolution, with the graphite (200) clearly visible in FFTs of the 2-4 nm highly ordered graphitic domains. As the cathodes fibers are cycled at high voltage, HREM demonstrates that the graphitic ordering of the core increases with the number of cycles, however the structure and thickness of the amorphous layer remains unchanged. These results are consistent with micro-Raman measurements of the fiber D/G band ratios. After significantly prolonged high voltage cycling, a uniform 50 nm film at the fiber tip was evident in High Angle Annular Dark Field STEM. Low-dose electron diffraction techniques confirmed the amorphous nature of this film, and STEM with elemental mapping via EDS indicate this layer is composed of CsO. The oxidative evolution of tip composition and morphology due to oxygen impurities in the chamber, along with increased graphitization of the fiber core, must contribute to changes in emission behavior with cycling.
12:30 PM - NN8.8
Advanced Transmission Electron Microscopy Study of Cadmium Sulfide-Copper Sulfide Heterostructured Nanorods.
Haimei Zheng 1 2 3 , Bryce Sadtler 3 , Paul Alivisatos 2 3 , Christian Kisielowski 1 2
1 National Center for Electron Microscopy, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Chemistry, University of California, Berkeley, California, United States
Show AbstractWe apply lattice imaging and exit wave reconstruction as well as other TEM techniques such as energy filtered TEM and low temperature low dose electron diffraction to study CdS-Cu2S heterostructured nanorods prepared by a solution-based cation exchange process. The atomic structure and interfaces in CdS-Cu2S heterostructures are investigated. A previously reported phase transition of Cu2S from a low chalcocite to a high chalcocite structure under electron beam irradiation is directly observed and crystal structures are identified. Using a low acceleration voltage of 80 kV in the TEAM0.5 microscope we maintain excellent atomic resolution and are able to image this phase transition in real time. We have also characterized the electron beam irradiation effects include atom removal from surfaces and beam-induced ion diffusion. The diffusion of the highly mobile copper ions proceeds within the undisturbed sulfur sublattice and stimulates Cu-Cd atom exchange at CdS/Cu2S interfaces that is directly related to a low activation energy for the cation exchange process.
12:45 PM - NN8.9
A Simple Specimen Preparation Method for Investigating Nanoparticle-substrate Interactions.
Maria Messing 1 2 , Michael F. Wolff 3 , Kornelius Nielsch 3 , L. Reine Wallenberg 2 , Knut Deppert 1
1 Solid State Physics, Lund University, Lund Sweden, 2 Polymer and Materials Chemistry, Lund University, Lund Sweden, 3 Applied Physics, University of Hamburg, Hamburg Germany
Show AbstractDetailed investigations of nanoparticles are of utmost importance in order to understand their properties and how these relate to their morphology and chemical composition. Nanoparticles positioned on and interacting with a substrate exhibit special difficulties since advanced electron microscopy investigations require thin specimen and thus sophisticated and expensive preparation methods. We present here a simple and efficient preparation method that allows for advanced TEM investigations of nanoparticles positioned on a substrate as well as nanoparticle-substrate interactions.The method proposed here employs controlled deposition of nanoparticles onto free-standing nanowires and the subsequent TEM investigation of the nanowires with the particles attached in the microscope. The nanowires, having a diameter of several tens of nanometers serve here as the substrate for the nanoparticles. Since it is possible to create quite a number of different nanowires, e.g. of different metals and semiconductors, this allows for advanced microscopy studies of a number of particles on various substrates. Additionally, tuning the growth parameters of the nanowires may allow for the tailored generation of distinguished side facets and thus makes the study of interactions of the particles with different substrate surfaces possible.We demonstrate the method for the investigation of the formation of MnAs nanoparticles on GaAs nanowires. The nanowires were grown on a substrate by Metal Organic Vapor Phase Epitaxy (MOVPE) under standard growth conditions. Following growth, aerosol generated Mn particles with a monodisperse particle diameter were deposited onto the nanowires. In order to convert the Mn particles into MnAs particles the particle containing nanowires were subsequently heat-treated in a hydrogen atmosphere with an arsine background pressure. By applying the close proximity specimen preparation method, i.e. gently touching the nanowire containing substrate with a TEM grid, the particle containing nanowires were broken off onto the grid. HRTEM and STEM XEDS confirmed the conversion of the Mn nanoparticles into MnAs nanoparticles.Our work clearly demonstrates that by replacing a standard substrate with a nanowire of the substrate material of interest, time-consuming and complicated specimen preparation can be avoided when investigating nanoparticle-substrate interactions.
NN9: Nanomaterials and Catalysis
Session Chairs
Thursday PM, December 03, 2009
Room 204 (Hynes)
2:30 PM - **NN9.1
High Resolution 3-D Characterization of Nanomaterials using Electron and Atom Probe Tomography.
Ilke Arslan 1
1 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States
Show AbstractNanotechnology has become a key component in the field of materials science. Rather than analyzing and determining the properties of bulk single or poly-crystals where the third dimension is assumed to be uniform, we must now analyze materials that have a finite size and shape in three dimensions, and not necessarily uniform in any of the directions. This new demand on materials characterization has led to the development of electron tomography for inorganic materials using Z-contrast imaging in the scanning transmission electron microscope (STEM) and atom-probe tomography (APT). Each of these techniques on their own provides valuable information on the morphology and chemistry of materials in 3-D. However, each technique has its limitations in the form of artifacts. For example, one such artifact for electron tomograms is the ‘missing wedge’ due to limited tilt range, while one artifact in atom-probe tomograms is non-uniformity in evaporation. The combination of the two techniques allows for a more reliable reconstruction for both techniques, while also providing a quantification of each technique’s artifacts. The benefits, limitations, and combination of the techniques will be discussed through examples of different nanomaterials.
3:00 PM - **NN9.2
Advances in Atom Probe Tomography for Semiconductor Materials.
Ludovic Renaud 1 , Isabelle Martin 1 , Rabah Benbalagh 1 , Beatrice Salle 1 , Michel Schuhmacher 1
1 , CAMECA Compagny, Gennevilliers Cedex France
Show AbstractThe three dimensional Atom Probe (3D-AP or APT: Atom Probe Tomography) technique can be considered as the only technique which offers capabilities for both 3D imaging and chemical composition measurements capabilities at the atomic scale. Since its early developments, 3D Atom Probe has provided major contributions in materials science. Indeed, from the sample prepared in a form of a sharp tip, a 3D reconstruction of a small volume with quantitative elemental composition at nearly the atomic scale can be reached. The atoms of the sharp tip are evaporated by field effect (near 100% ionization) and projected to a position sensitive detector (detection efficiency near 50%). The nature of the atoms is determined by Time Of Flight mass spectrometry.Until the last few years, the field of investigation of the technique was limited to conductive materials. Furthermore, due to sample preparation method used, it was very difficult to obtain the analysis of a specific area of interest in a bulk material. These limitations have been largely overcome and the field of investigation of this technique has been greatly extended. The major breakthrough has been the introduction of the Laser pulsing mode in addition to the traditional High Voltage pulsing atom evaporation mode. Fast high voltage pulses cannot be efficiently propagated along a tip of non-conductive materials, inhibiting the field evaporation process of single atoms. Thus, the laser evaporation technique is well suited for the analysis of semi-conductor materials. The use of femtosecond laser pulses to create the atom field evaporation allows analysis of semiconductor samples. Moreover, with the help of Focused Ion Beam (FIB) techniques, it is now possible to extract and prepare a sample ready for 3D-AP analysis from a site-specific location of a bulk sample or from a piece of a wafer. In this presentation, we will review some of the recent applications of Atom Probe Tomography in the semiconductor field (such as localized dopant profiling, III-V layer homogeneity, modern thin insulating layers,…) which have become possible along with instrumentation developments. The potentials and limits of the 3D-AP technique for nano-scale materials analysis will be also discussed.
3:30 PM - NN9.3
HAADF-STEM Observation of Structure Change of Au Nano-particle on CeO2.
Tomoki Akita 1 , Shingo Tanaka 1 , Koji Tanaka 1 , Masanori Kohyama 1 , Masatake Haruta 2
1 , National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan, 2 , Tokyo Metropolitan University, Hachioji, Tokyo, Japan
Show AbstractThe catalytic properties of Au nano-particles are widely investigated for various reactions, and it is reported that the catalytic activity of Au is sensitive to the size of particles, the kind of metal oxide support and the interface structure between Au particles and metal oxide supports. A lot of researches have been done for the mechanism of gold catalysis and many experimental reports indicate that the perimeter of Au particles on metal oxide surfaces plays a key role. The understanding of detailed structures of the perimeter and interface of Au/metal-oxide systems is crucial to elucidate the essential mechanism of the catalytic activity. The structure of Au-CeO2 interface was observed by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) for Au-CeO2 model structure. The Au-CeO2 model structure was prepared by vacuum deposition of Au on poly-crystalline CeO2 substrate. The observations were carried out by JEOL JEM-3000F transmission electron microscope equipped with STEM system at an accelerating voltage of 300kV. The structure of Au-CeO2 interface was observed clearly by profile-view HAADF-STEM images. The structure change of Au nano-particles deposited on CeO2(111) surfaces also has been observed sequentially by HAADF-STEM. The layer-by-layer shrinkage of Au nano-particles caused by the electron beam was observed with sufficient resolution of Ce and Au atomic columns and two atomic-layer Au was observed. We have found the presence of displaced Au atomic columns at the perimeter during the electron beam irradiation, which seem to be involved in the Au diffusion process associated with surface oxygen vacancies cause by oxidation and reduction. The present structure changes of the perimeter configurations should be of great importance to understand the mechanisms of the environment-dependent structural changes and the catalytic properties of Au/CeO2 catalysts.
3:45 PM - NN9.4
3D Atom Probe Analysis of Au-Nanoclusters in Single Crystal Oxide Substrates.
Satyanarayana Kuchibhatla 1 , V. Shutthanandan 1 , Chongmin Wang 1 , Theva Thevuthasan 1 , Peter Clifton 2 , Ty Prosa 2 , D. Reinhard 2
1 , EMSL, PNNL, Richland, Washington, United States, 2 , Imago Scientific Instruments, Madison, Wisconsin, United States
Show AbstractThe influence of embedded nanoclusters on the optical, magnetic and electrical properties of bulk and surface oxides has been an active area of investigation. In this study, Au-rich nanoclusters have been embedded into TiO2, SrTiO3, and MgO substrates and the effect of high temperature annealing on the properties of the matrix and the secondary phase (Au) studied in detail. Electron microscopy analysis has shown that the embedded metal particles are often associated with various defects, which further contribute to property enhancement. Here, we report the first Local Electrode Atom Probe (LEAP®) analysis of bulk MgO implanted with 2MeVAu ions using the accelerator facility at EMSL. Following a 10hr anneal at 1000oC, these samples were analyzed using a combination of atom probe tomography and HAADF STEM imaging. High resolution electron microscopy clearly resolves the Au-rich nanoclusters and allows observation of the pronounced vacancy clustering associated with these features. These Au-rich nanoclusters were also observed in the atom probe data and their average size (~ 5 nm diameter) was in good agreement with those seen using HREM. The APT technique, however, due to the high three-dimensional spatial resolution, is also able to detect the presence of finer-scale Au clusters and can also directly measure the residual Au composition within the MgO matrix. These advantages will be discussed and a comparison of the atom probe and electron microscopy data will be presented highlighting the importance of correlative microscopy. In addition, the capability of the atom probe to detect the presence of the vacancy clusters will also be reviewed. Establishment of new atom probe tomography and related high resolution chemical imaging facilities at EMSL will also be outlined.
4:30 PM - NN9.5
Observing the Photocatalytic Active Sites in Niobate Photocatalytic Nanosheets by Cs-corrected STEM.
Miaofang Chi 1 , Erwin Sabio 2 , Frank Osterloh 2 , Nigel Browning 2
1 , Oak Ridge National Laboratory, Knoxville, Tennessee, United States, 2 , University of California, Davis, Davis, California, United States
Show AbstractThe efficient conversion of solar energy into chemical fuels has great economic and environmental significance. Photovoltaic and electrochemical solar cells that convert solar energy into electricity can reach up to 55–77% efficiency. Layered niobates, as a type of photocatalyst to generate H2 through water splitting, have attracted particular interest because of their good quantum efficiency. For example, the quantum efficiency for K4Nb6O17 can reach 20%. However, the relatively short recombination time (~1ns) of this type of material currently limits their H2 generation efficiency. Understanding the active sites in this type of material is crucial to material design in term of increasing the combination time and therefore improving the overall photoactivity of niobates. We have fabricated TBA[Ca2Nb3O10] nanosheets by exfoliating the parent solid with tetrabutylammonium (TBA) hydroxide. Metal and metal oxide were photo-deposited to observe the active sites. This is because the positions of metal and metal oxides should represent those of oxidation and reduction sites respectively. We have used aberration (Cs) corrected Scanning Transmission Electron Microscopy (STEM) to study the distributions of deposited particles, which includes Ag, Pt, MnO2, IrO2. Nanosheets deposited by these metal and metal oxides with different sizes(about 2, 5, and 10nm) were investigated in order to excluding possible errors from particle sizes. Our results show that larger particles (>5nm) tend to be randomly distributed on the nanosheets in both cases of metal or metal oxides. Smaller particles (1nm-5nm) distribute locally on the surface or the edge of the nanosheets. Individual metal or metal atoms or molecular clusters have also observed on both surface and edge. However, their locations on the surface of the nanosheets have atomic column preferences. For example, Ir atoms are associated with Ca-site on the surface, while Pt is more likely sitting on Nb atomic columns. Theoretical calculations of the surface/edge structure of the nanosheets will also be presented with experimental results in detail to reveal the active sites.
4:45 PM - NN9.6
Metal-oxide Interfaces at the Nanoscale.
Guangwen Zhou 1
1 Department of Mechanical Engineering and Multidisciplinary Program in Materials Science and Engineering, Binghamton University, Binghamton, New York, United States
Show AbstractThe metal-oxide interface is a crucial zone not only in the fundamental understanding of oxidation mechanism of metals but also for many technologically important processes including corrosion, catalysis, and thin film growth. Generally, the lattice parameter of an oxide is significantly larger than that of the metal from which it is formed. This large lattice misfit makes the formation of coherent metal-oxide interface energetically unfavorable although many oxides are nonetheless observed to grow crystallographically-aligned with the metal substrates. A classical model describing the occurrence of epitaxy in such a large-misfit system is the coincidence site lattice (CSL) interface that requires a minimum lattice misfit and is therefore energetically feasible for the heteroepitaxial growth. In this work we show that this minimum CSL misfit criterion is insufficient to predict the structure of nanoscale metal-oxide interfaces. Our results, obtained by high-resolution transmission electron microscopy (HRTEM) and electron moiré fringes, demonstrate that the interface configuration between Cu2O nanoislands and Cu(111) substrates adopts a 5 × 6 CSL that is accommodated by an increased lattice misfit strain compared with the minimum coincidence misfit of the 6 × 7 lattice registry. Calculation of the equilibrium strain in epitaxial oxide nanoislands reveals a previously unnoticed correlation between the interface structure and surface stress effects at the nanoscale. The insights obtained from this study are expected to have broader implications in understanding and controlling the interfacial atomic structures in heteroepitaxial growth of nanostructures.
5:00 PM - NN9.7
Aberration-Corrected Scanning Transmission Electron Microscopy of Cation Site Location and Occupancy in M1 Selective Oxidation Catalysts.
Douglas Blom 1 , William Pyrz 2 , Tom Vogt 1 , Douglas Buttrey 2 , Masahiro Sadakane 3 , Wataru Ueda 4 , Vadim Guliants 5
1 NanoCenter, University of South Carolina, Columbia, South Carolina, United States, 2 Center for Catalytic Science and Technology, University of Delaware, Newark, Delaware, United States, 3 Chemistry and Chemical Engineering, Hiroshima University, Hiroshima Japan, 4 Catalysis Research Center, Hokkaido University, Sapporo Japan, 5 Chemical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractSelective oxidation catalysts are extensively used to produce either intermediate chemicals or final products incorporated into consumer goods. Acrylic acid and acrylonitrile are two products in high demand worldwide that are currently produced using propene feeds over multi-component bismuth molybdate catalysts [1-2]. A multiphase MoVNbTeO catalyst (M1/M2) is one of the most promising candidates to allow for the substitution of propane for propene and corresponding cost savings [3]. The M1 phase is a complex metal oxide framework structure with an orthorhombic unit cell typically containing 3 cation species spread over 11 sites in the framework and two types of channels into which additional specie(s) can intercalate. Most of the cation sites exhibit partial substitution as measured from simultaneous Rietveld refinement of neutron and X-ray diffraction datasets [4]. Acrylonitrile yields for M1-type catalysts vary widely depending on the details of the synthesis method and extent of chemical substitution [1, 2, 5]. Aberration-corrected high-angle annular dark field (HAADF) STEM imaging has been used to study a number of M1 phases produced by various methods and research groups. Detailed analyses of both the cation site locations and chemical compositions have been performed. Measurements of the framework cation site locations from the HAADF images indicate that the orthorhombic unit cell structure is consistent regardless of chemical substitution for well-crystallized specimens [6]. This result suggests that the wide variation of catalytic performance of these specimens is not a result of variations in the metal-to-metal distances in the crystal, although structural defects may still play a role in the performance variability. As a first approximation, the signal in a HAADF STEM image exhibits a Z2 dependence (Z being atomic number). Substitution of V for Mo in the framework cation sites has been found via detailed diffraction studies [4]. Estimates of the distribution between V and Mo at several of the cation sites have been formed from analysis of the HAADF images. In agreement with the model structure from [4], the V content in the various cation sites is not uniformly distributed. Trends in composition of the various cation sites with both overall V content and Nb or Ta concentration will be presented. Multi-slice image simulations [8] have been performed for some of the compositions studied here and are in good agreement with the simple incoherent image contrast assumption.References [1] R. K. Grasselli et al. Top Catal 38 (2006) 7.[2] P. Korovchenko et al. Top Catal 50 (2008) 43.[3] R. K. Grasselli. Top Catal 21 (2002) 79.[4] P. DeSanto et al. Z Krist 219 (2004) 152.[5] N. Watanabe and W. Ueda. Ind and Eng Chem Research 45 (2006) 607.[6] W. D. Pyrz et al. Cat Today 142 (2009) 320.[7] N. Yamazoe and L. Kihlborg. Acta Crystallogr Sect B 31 (1975) 1666.[8] Earl J. Kirkland. Advanced Computing in Electron Microscopy (1998).
5:15 PM - NN9.8
Size Effects on the Melting Temperature of Silver Nanoparticles: In-situ TEM Observations.
Michael Asoro 1 , John Damiano 2 , Paulo Ferreira 1
1 Materials Science and Engineering, University of Texas at Austin, Austin, Texas, United States, 2 , Protochips Inc., Raleigh, North Carolina, United States
Show AbstractThe melting temperature (Tm) of a material is crucial for many applications. In bulk systems, the surface-to-volume ratio is small and the curvature of the surface is negligible. Thus, surface effects on Tm can be disregarded. However, for the case of nanoparticles, for which the surface-to-volume ratio is large and the surface curvature is high, Tm is size dependent.In this work, in-situ heating experiments on silver nanoparticles, ranging from 5nm to 25nm, were performed in a JEOL 2010F transmission electron microscope (TEM) to determine the effect of size on Tm. The in-situ heating experiments were conducted with a novel AduroTM heating stage designed by Protochips, which exhibits no drift even at high temperatures. Starting from room temperature, the samples were heated in-situ in the TEM in increments of 25°C until all the nanoparticles melted and vaporized.A sequence of TEM images showing the melting and vaporization of silver nanoparticles were taken at various temperatures. As expected, Tm decreases with decreasing particle size. However, significant differences between Tm predicted from thermodynamics and the experimentally measured Tm were found. This seems to be due to scale effects on the solid-liquid interfacial energy.
5:30 PM - NN9.9
Electron Microscopy Characterization of Novel Surface Layer in Polycrystalline Y 2O3 Formed at High Pressure and Temperature Conditions.
Jafar Al-Sharab 1 , Stuart Deutsch 1 , Stephen Tse 2 , Bernard Kear 1
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 Mechanical & Aerospace Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractA reversible transformation process has been utilized recently for grain size refinement of Y2O3. This is a two step reaction where 300 μm cubic polycrystalline Y2O3 material is transformed into monoclinic Y2O3 with <100 nm grains under high temperature and pressure (1000°C and 8GPa) for short period of time (<15 minutes). The sample is then transformed back to its cubic phase at 1 GPa/1000 GPa while maintaining the grain size <100 nm.It has been observed that increasing the holding during the first reaction step for periods greater than 4 hours led to surface modification by growing columnar grains with lower stiffness and hardness than sample interior. Moreover, chemical analysis by EDS shows that these grains are oxygen deficient compared to sample interior. Moreover, electron diffraction confirms that the columnar grains have cubic symmetry while sample interior exhibits monoclinic phase. A detailed electron microscopy which includes high resolution TEM analysis, growth orientation and defect analysis were applied to understand the nature of this new surface effect.
5:45 PM - NN9.10
The Origin of the Anomalous Interatomic Distances in Suspended Gold Atomic Chains Revisited.
Pedro Autreto 1 , Maureen Lagos 1 2 , Fernando Sato 3 , Varlei Rodrigues 1 , Daniel Ugarte 1 , Douglas Galvao 1
1 Applied Physics, State University of Campinas, Campinas, São Paulo, Brazil, 2 , Brazilian Synchrotron Light Laboratory, Campinas, São Paulo, Brazil, 3 Physics, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil
Show AbstractThe study of metallic nanowires (NWs) has been object of intense experimental and theoretical investigations due to new physical phenomena (such as conductance quantization, unusual structures, etc.) and potential applications in nanoelectronics [1-2]. In spite of the large amount of works carried out to these systems some aspects remain unclear, as for example, the origin of the anomalous large interatomic gold distances experimentally observed in suspended linear atomic chains (LACs) obtained from NW stretching [1]. The observation of these long interatomic distances (between 3.6 and 5.0 Angstroms) have been attributed to the existence of impurities (atoms or molecules) [3] inserted between gold atoms, which are not perceptible in electron microscopy imaging due to their lower atomic number. The precise origin and identification of these contaminants has been object of debate in the literature, H and C atoms believed to be the most probable contaminants. In this work we report new experimental (real-time atomic-resolution transmission electron microscopic (dynamical HRTEM)) and theoretical (ab initio density functional total energy methods) data for this LAC problem. By performing the experiments and ab initio quantum molecular dynamics simulations at different temperatures (150K and 300K), we have been able to obtain detailed information on the atomic species that could originate these anomalous distances. The comparison of the results at these different temperatures have provided strong evidences supporting that C atoms, originated from hydrocarbon decomposition, is the most plausible impurity to explain the large distances in Au LACs. [1] N. Agrait, A. L. Yeyati, and J. M. van Ruitenbeek, Physics Reports 377, 81 (2003).[2] M. J. Lagos, F. Sato, J. Bettini, V. Rodrigues, D. S. Galvao and D. Ugarte, Nature Nanotechnology. 4, 149 (2009).[3] S. B. Legoas, D. S. Galvao, V. Rodrigues, and D. Ugarte, Phys. Rev.Lett. 88, 076105 (2002).[4] S. B. Legoas, V. Rodrigues, D. Ugarte, and D. S. Galvao, , Phys. Rev.Lett. 88, 216103 (2004), and references therein cited.