Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Journal Article Local Chemistry of Complex Nanostructures and Their Interfaces in Block Copolymer-Templated Nanocomposite Electrodes for Rechargeable Lithium Batteries Get access V J Leppert, V J Leppert Department of Chemical Engineering and Materials Science, University of California, One Shields Ave., Davis, California, 95616-5294 Search for other works by this author on: Oxford Academic Google Scholar EC Nelson, EC Nelson National Center for Electron Microscopy, MS 72-150, Berkeley, CA 94720 Search for other works by this author on: Oxford Academic Google Scholar S C Mui, S C Mui National Center for Electron Microscopy, MS 72-150, Berkeley, CA 94720 Search for other works by this author on: Oxford Academic Google Scholar E A Olivetti, E A Olivetti Department of Materials Science and Engineering, Massachusetts Institute of Technology, 13-5025, 77 Massachusetts Ave., Cambridge, MA 02139 Search for other works by this author on: Oxford Academic Google Scholar A M Mayes A M Mayes Department of Materials Science and Engineering, Massachusetts Institute of Technology, 13-5025, 77 Massachusetts Ave., Cambridge, MA 02139 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 9, Issue S02, 1 August 2003, Pages 388–389, https://doi.org/10.1017/S1431927603441949 Published: 19 July 2003

Journal Article Structure Analysis of CoPt Nanoparticles Get access Y H Huang, Y H Huang Department of Physics, University of Delaware; Newark, DE 19716 Search for other works by this author on: Oxford Academic Google Scholar Y Zhang, Y Zhang Department of Physics, University of Delaware; Newark, DE 19716 Search for other works by this author on: Oxford Academic Google Scholar C E Nelson, C E Nelson NCEM, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Search for other works by this author on: Oxford Academic Google Scholar G C Hadjipanayis, G C Hadjipanayis Department of Physics, University of Delaware; Newark, DE 19716 Search for other works by this author on: Oxford Academic Google Scholar D Weller D Weller Seagate Technology; Pittsburgh, PA 1520 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 8, Issue S02, 1 August 2002, Pages 1376–1377, https://doi.org/10.1017/S1431927602103503 Published: 01 August 2002

Journal Article Application of Energy-Filtered Imaging and HREM in the Study of Terbium Nanoparticles Get access Y Zhang, Y Zhang Department of Physics & Astronomy, University of Delaware, Newark, DE 19716, USA Search for other works by this author on: Oxford Academic Google Scholar C E Nelson, C E Nelson NCEM, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA Search for other works by this author on: Oxford Academic Google Scholar Z C Yan, Z C Yan Department of Physics & Astronomy, University of Delaware, Newark, DE 19716, USA Search for other works by this author on: Oxford Academic Google Scholar V Skumryev, V Skumryev Department of Physics & Astronomy, University of Delaware, Newark, DE 19716, USA Search for other works by this author on: Oxford Academic Google Scholar G C Hadjipanayis G C Hadjipanayis Department of Physics & Astronomy, University of Delaware, Newark, DE 19716, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 8, Issue S02, 1 August 2002, Pages 1360–1361, https://doi.org/10.1017/S1431927602103424 Published: 01 August 2002

Microcharacterization of defects is greatly facilitated with improvement in resolution. By improving temporal coherence (chromatic aberration) and compensating spatial incoherence, we have achieved the goal of the 1 Angstrom microscope (O AngstromM) project at the US Department of Energy's National Center for Electron Microscopy by extending the limits of high-resolution transmission electron microscopy to sub-angstrom levels. The O AngstromM combines focal-series image-processing software with a modified 300 keV electron microscope equipped with a highly coherent field emission electron gun. By operating at an 'alpha -null' value of underfocus in order to minimize the effects of spatial incoherence, and by reducing the O AngstromM's electron-gun extraction voltage to improve temporal coherence, we are able to transfer information below 0.8 Angstrom In a test specimen of silicon viewed in the [112] orientation in the O AngstromM we are able to 'see' atoms separated by only 0.78 Angstrom. Sub-angstrom resolution at this level offers the materials researcher an effective tool for the characterization of defects with unprecedented precision.

Sub-Ångstrom transmission electron microscopy has been achieved at the National Center for Electron Microscopy (NCEM) by a one-Ångstrom microscope (OÅM) project using software and enhanced hardware developed within a Brite-Euram project (Ultramicroscopy 64 (1996) 1). The NCEM OÅM provides materials scientists with transmission electron microscopy at a resolution better than 1Å by using extensive image reconstruction to exploit the significantly higher information limit of an FEG-TEM over its Scherzer resolution limit. Reconstruction methods chosen used off-axis holograms and focal series of underfocused images. Measured values of coherence parameters predict an information limit of 0.78Å. Images from a [110] diamond test specimen show that sub-Ångstrom resolution of 0.89Å has been achieved with the OÅM using focal series reconstruction.

In 1999 NCEM's One Ångstrom Microscope (OAM) became fully operational. The OAM is a Philips CM300 FEG/UT field emission microscope with holographic capabilities that is equipped with a Gatan Image Filter (GIF) and operates at 300 kV. It was designed to reach a resolution close to the “magic barrier” around one Ångstrom (100 pm) by combining mid voltage technology with advanced computer processing [1,2]. Ahardware correction of the three-fold astigmatism allows for aberration free imaging down to sub Ångstrom values [3]. In this contribution it will be shown that the instrument's performance exceeded expectations because sub Ångstrom resolution can be achieved by reconstructing electron exit waves from focal series [4].Figure la depicts a simulated [110] lattice image of a 90° partial dislocation in silicon. Tersoff potentials were used to calculate the exact atomic positions around dislocations with different core structures [5].

High resolution electron microscopes with field emission sources opened the possibility to investigate solids on a 100 pm range. Either electron holograpy can be applied or an information limit that may even extend into a region below 100 pm can be exploited to reach this goal [1]. However, lens aberrations such as the three-fold astigmatism often complicate an image interpretation in the 100 pm range or even make it impossible [2]. On the other hand, there is growing need to understand physical processes at a mono-atomic level in order to further develop artificially structured materials such as nano-crystals, ceramic coatings or semiconductors. Commonly, such materials contain light elements like C, N, or O with bond lengths that are shorter than a typical 180 pm point resolution of a high resolution, electron microscope. The carbon-carbon distance of 150 pm is the shortest bond length value in crystalline solids. Moreover, any projection of a diamond lattice along a low index zone axis for lattice imaging leads to a reduced C-C distance.

Nowadays, H igh R esolution E lectron M icroscopes are capable to resolve structures on a scale below 100 pm. They can be equipped for E lectron H olography in order to detect electric / magnetic fields and for chemical analyses ( E lectron E nergy L oss S pectroscopy & E nergy D ispersed X -ray's) that can be performed with a lateral resolution of 0.5 to 1 nm [1]. With the aid of computer sciences it became also possible to quantify local strain. We utilize Philips CM200 and CM300 field emission instruments with attached image filters, the JEOL Atomic Resolution Microscope and specialized software [2] to perform these tasks. On the other hand, a recent highlight in materials sciences is the development a GaN technology that is driven by a fast trial and error approach and aims to revolutionize lighting [3]. It was unavoidable that basic materials properties of the nano-structured thin films are barely understood because of the rapid progress [4].

GaN and the related AlN semiconducting materials have recently attracted considerable attention because of their versatile applications for optoelectronics. Large stresses are present in the GaN/AlN thin-film heterostructure and can exceed GPa's. They originate from a large lattice mismatch between the substrate(sapphire)/GaN (14%) and the AlN/GaN interface (-2.7%) in quantum well structures. The strain is expected to induce local piezoelectric fields in these polar materials. It is essential for a further development of GaN based thin films to fully understand the formation and the local strength of these fields. Previous studies show that there are unusual large fluctuations of the patterns in lattice images present across GaN/Al x Ga 1-x N and GaN/In y Ga 1-y N quantum wells. They are attributed to compositional fluctuations and have been studied by quantitative high resolution electron microscopy. Differences between the strain profiles and the electrostatic (scattering) potential profiles were observed.

The latest transmission electron microscopes with field emission guns and imaging filters now provide much of the microanalysis and imaging necessary in applications such as ULSI device development. The installation and operating environment of the instruments are critical to their successful operation. Information from two such installations is presented here, one in a purpose built facility and the other in an existing building. Ground vibration, acoustic noise, stray electromagnetic fields, air flow and temperature variation are considered, and the measures implemented to achieve desirable levels of each parameter are discussed. The physical layout of an installation is also shown.

The transmission electron microscope (TEM) is one of the most useful tools available to the materials scientist. Yet both the complexity and expense of the equipment, and the huge investment in time necessary to become proficient in specimen preparation and image acquisition and analysis, mean that it is difficult for most industrial institutions to maintain a state-of-the-art TEM facility. How can industry overcome this problem? One solution is to set up a collaboration with a university, an industrial partner, or a government research laboratory. Such collaborations can be extremely valuable to the company, which gains access to microscopes, specimen-preparation equipment and the expertise of professional microscopists, and to the research laboratory, which benefits from the industrial perspective and the private sector's proficiency in materials preparation and processing.Such collaborations exist, and they can produce excellent results. In this article, we present three case studies in which successful collaboration has occurred between industry and one of the Department of Energy's scientific user facilities, the National Center for Electron Microscopy (NCEM-see sidebar). Our aim is not only to describe results that we hope will be of scientific interest but also to encourage industrial researchers to consider collaborations with institutes such as NCEM.

Epitaxial thin films of the group III nitrides play an increasingly important role in the fabrication of high-efficiency light emitting diodes in the range between yellow and blue. Growth of such films on sapphire requires the use of low temperature buffer layers of AIN or GaN. Silicon carbide has a much closer lattice parameter match than sapphire to AIN, and promises to produce better AIN layers. Since the atomic arrangement at the interface between AIN and SiC determines the degree of perfection of the epitaxial layer, we have attempted to determine the structure of this interface by hign-resolution transmission electron microscopy. Devices were grown by MOCVD; AIN was deposited on the Si-face of α-6H SiC, followed by GaN. The specimen was cut for HRTEM observation in the SiC projection, mechanically thinned to 20μm and ion-milled to electron transparency. Observations were made using the NCEM JEOL ARM-1000 operated at 800keV. Images were obtained at a specimen thickness of 85A (determined by extrapolation to the first extinction distance of the wedge). The most-useful defocus was −1050Å at which the important spacings from both SiC and AIN are passed with the same phase (fig.1).