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1999 | Buch

Impact of Electron and Scanning Probe Microscopy on Materials Research

herausgegeben von: David G. Rickerby, Giovanni Valdrè, Ugo Valdrè

Verlag: Springer Netherlands

Buchreihe : NATO ASI Series

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SUCHEN

Über dieses Buch

The Advanced Study Institute provided an opportunity for researchers in universities, industry and National and International Laboratories, from the disciplines ofmaterials science, physics, chemistry and engineering to meet together in an assessment of the impact of electron and scanning probe microscopy on advanced material research. Since these researchers have traditionally relied upon different approaches, due to their different scientific background, to advanced materials problem solving, presentations and discussion within the Institute sessions were initially devoted to developing a set ofmutually understood basic concepts, inherently related to different techniques ofcharacterization by microscopy and spectroscopy. Particular importance was placed on Electron Energy Loss Spectroscopy (EELS), Scanning Probe Microscopy (SPM), High Resolution Transmission and Scanning Electron Microscopy (HRTEM, HRSTEM) and Environmental Scanning Electron Microscopy (ESEM). It was recognized that the electronic structure derived directly from EELS analysis as well as from atomic positions in HRTEM or High Angle Annular Dark Field STEM can be used to understand the macroscopic behaviour of materials. The emphasis, however, was upon the analysis of the electronic band structure of grain boundaries, fundamental for the understanding of macroscopic quantities such as strength, cohesion, plasticity, etc.

Inhaltsverzeichnis

Frontmatter
The Impact of Electron Microscopy on Materials Research
Abstract
We live, work and play in a world of materials. Modern technology depends critically on the availability of advanced materials, in such areas as transportation, communications, data processing, and production systems, and more and more emphasis is being placed on the research and development of materials. In the world of sports, records fall as a result of the continual improvement in equipment, e.g., composites for field sports, skiing, etc. Industrial laboratories and even some production facilities, in addition to universities and leading research centers, have become heavy users of electron microscopes. There are well over 10, 000 instruments in use in the Western world. Materials research and development in metals, ceramics, and composites (including designing for better mechanical and physical properties, processing, forming, joining, catalysis, etc.) require analyses by scanning (SEM) and transmission electron microscopy (TEM) because of the small scale of relevant microstructures and composition. Because TEM instruments are central to all fields of structural characterization, electron microscopy is perhaps the most interdisciplinary field in today’s complex world. [2] Biologists, materials scientists, engineers, physicists, chemists, etc., all rub shoulders at national and international meetings.
Gareth Thomas
Microstructural Design and Tailoring of Advanced Materials
Abstract
In order to successfully achieve microstructural tailoring of materials for desired properties, it is necessary to understand processing-structure-property linkages in great detail. Boundaries and interfaces, where most of the “action” occurs, pose particularly difficult problems, but progress in high resolution characterization techniques, especially electron optical, are certainly proving to be enormously helpful. This chapter presents some applications to show how such methods have allowed quite successful microstructural tailoring to be accomplished for specified properties. Examples are drawn from our current research programs on low carbon steels, refractory ceramics based on Si3N4, and magnetic alloys.
Gareth Thomas
Nanostructured Materials
Abstract
The study of nanostructured materials is a very active and exciting area of research and development that has been in progress for the more than a decade. These fine-grained materials often exhibit unique and novel properties that are superior to those of their coarse-grained counterparts. The utilization of advanced techniques of electron microscopy has played and continues to play a pivotal role in the study and development of these materials and the realization of their full potential in many technological applications. This paper first reviews the basic characteristics and properties of nanostructured materials together with some examples of current and future applications. Various synthesis and processing methods are briefly described, pointing out the very important role that synthesis and processing have on the ensuing properties. The critical function of advanced electron optical techniques have in the progress of these materials is illustrated by three original examples. These examples refer to the use of detailed microstructural analysis to get a better understanding on the nature of grain boundaries and its effects on properties; the use of microstructural analysis to study and to understand the effects of grain size, chemical composition and microstructural constraints on the thermal stability and the mechanical behavior of nanocomposites for high temperature use; and, the properties of fullerene-reinforced nanocomposites are briefly reviewed. The paper concludes with a retrospective view on the importance: in clearly differentiating between intrinsic and extrinsic grain boundary facets and in accounting fully for the contamination products that may present, all of which profoundly affect the resulting properties.
Virgil Provenzano
Characterization of Heterophase Transformation Interfaces by High-Resolution Transmission Electron Microscope Techniques
Abstract
This paper describes the application of several high-resolution transmission electron microscope (HRTEM) techniques to determine the structure, composition and dynamics of heterophase transformation interfaces at the atomic level. Emphasis is placed on the use of: 1) HRTEM to determine the atomic structure of heterophase interfaces, 2) energy-filtering TEM (EFTEM) to determine the composition at heterophase interfaces, and 3) in situ HRTEM to determine the atomic mechanisms and dynamics of interface motion. The importance of image simulation in the analysis of experimental HRTEM images and many practical aspects concerning specimen and microscope conditions during imaging are discussed.
J. M. Howe
High Resolution Scanning Electron Microscopy Observations of Nano-Ceramics
Abstract
Ceramic materials are widely used for their excellent performance in applications where other types of material may fail. Possible applications are in situations where materials have to withstand high temperatures, corrosive environments and severe wear. However, metals instead of ceramics may possess mechanical properties that better meet the demands upon mechanical loading. In current research programs in the field of materials science and engineering, a substantial amount of effort is put in the development and design of combining the specific properties of metals and ceramics [1]. However, the presence of dissimilar materials will lead to differences in expansion and contraction upon heating or cooling of the material. Both effects may be a source of internal stresses in the material that may persist after the production process and may alter the mechanical performance of the final product in a negative sense.
J.Th.M. De Hosson, M. De Haas, D. H. J. Teeuw
Metal-Ceramic Interfaces Studied with High Resolution Transmission Electron Microscopy
Abstract
Tailoring materials with a desirable set of physical and chemical properties has always been a dream of materials scientists and engineers. It is accurate to say that important properties of materials in high-technology applications are strongly affected or controlled by the presence of solid interfaces. For example, a great deal of the electronic industry is based on the interesting electrical properties of semiconductor interfaces, with ceramic-semiconductor, metal-semiconductor and also metal-ceramic interfaces playing a crucial role. Interfaces are also important in the field of surface engineering. For techniques designed to enhance corrosion resistance of surfaces or to optimise their performance in catalytical or tribological applications, interfaces play a determining role. In the field of semiconductor technology as well as in the area of surface engineering, metal-oxide interfaces are frequently encountered. Despite their obvious technological importance, our basic understanding of interfaces, even relatively simple interfaces like grain-boundaries, is still rudimentary in relation to materials properties. The importance of interfaces is determined primarily by their inherent inhomogeneity, i.e. the fact that physical and chemical properties may change dramatically at or near the interface itself. It should be realised that physical properties, like elastic moduli, thermal expansion or electrical resistivity may differ near interfaces by orders of magnitude from those in bulk regions. As a result of these sharp gradients an isotropic bulk solid may change locally into a highly anisotropic medium. Consequently all processes that are controlled by interface phenomena, such as de-cohesion, segregation, cavitation and diffusion, occur in a very narrow region, of the order of a few lattice spacings, where the two materials join. Thus, the atomic structure of interfaces needs to be understood in order to establish the physical mechanisms of various boundary phenomena. Experimental techniques capable of revealing the structure with atomic resolution are necessary for their investigation. In this work the emphasis is on the understanding of interfaces between metals and oxides at the atomic structure level, using High Resolution (Transmission) Electron Microscopy (HRTEM) as the experimental method.
J.Th.M. De Hosson, H. B. Groen, B. J. Kooi, W. P. Velinga
Z-Contrast Scanning Transmission Electron Microscopy
Abstract
Historically, the development of the transmission electron microscope has followed the path of continually increasing the degree of coherence of the imaging process. This is despite the fact that coherent high resolution images suffer from the phase problem which means they cannot be directly inverted to give the object. Interpretation must necessarily rely on simulation of images of trial objects. Even with the prospect of spherical aberration correction, coherent images will still take many forms depending on objective lens defocus and specimen thickness, and the inversion problem will remain.
S. J. Pennycook, P. D. Nellist
Electron Energy Loss Spectrometry in the Electron Microscope
Part 1 - Introduction
Abstract
Modern electron microscopes permit the acquisition of the electron energy loss spectrum from a focused probe of sub-nanometre diameter. The spectrum is presented in a form which can be analysed quantitatively, thus it is strictly’ spectrometry’, not’ spectroscopy’, as usually said. Instrumentation is briefly described.
L. M. Brown
Electron Energy Loss Spectrometry in the Electron Microscope
Part 2 - Eels in the Context of Solid State Spectroscopies
Abstract
Intense efforts to understand the structure and properties of solids have taken place in several academic disciplines in parallel: physicists tending to concentrate on electronic structure defined in terms of the states available to electrons in an infinite, perfect solid; chemists tending to emphasize the bonding of atoms or ions by the overlap of electronic wavefunctions and by Coulombic forces between ions, regarding the solid as a particularly large molecule to which chemical methods can be applied; and the science of materials concerned more with the atomic structure of solids, both perfect and imperfect, a study which is the natural outcome of crystallography and the development of microscopies on the verge of atomic resolution. One satisfying aspect of electron energy loss spectrometry in the electron microscope is that it unites all three points of view in one instrument. It is by its nature interdisciplinary, at the triple point of physics, chemistry, and the science of materials. The techniques permit microanalysis, or more strictly correct, nanoanalysis, the determination of chemical composition point by point in the sample, as well as producing information on the electronic structure of the solid and its atomic structure via convergent beam diffraction (micro- or nano- diffraction) and imaging. In this chapter we concentrate on the relationship between EELS and other spectroscopies of solids (see also the Chapter by L.M.Trudeau).
L. M. Brown
Electron Energy Loss Spectrometry in the Electron Microscope
Part 3 - Interfaces and Localised Spectrometry
Abstract
The main point of spectrometry performed point-by-point using an electron probe of nanometre dimensions is to acquire chemical and electronic information about the defects and interfaces which control structural, electronic and optical properties of materials. According to some, our civilisation now depends upon electrical current sheets travelling along the interfaces between silicon and its oxide; others claim that it depends upon load transfer across the interfaces between weak, ductile metals bonded to strong but brittle fibres. Every polycrystalline material depends upon its grain boundaries, whether for strength or for optical transparency. Analytical electron microscopy, particularly EELS acquired using STEM, is the unique experimental method available to probe the interfacial density of states as well as the chemistry and the structure of such interfaces. Although it is a relatively new technique still improving, it has already solved a number of problems which could not otherwise be tackled. However, its main fundamental limitation is the damage caused to the material by the intense focused probe of electrons in the time required to extract the desired information.
L. M. Brown
Eels Near Edge Structures
Application to intermetallic alloys and other materials
Abstract
The beginning of EELS near edge structure work in a transmission electron microscope with particular aim at comparing results to electronic structure calculations can be traced to Egerton and Whelan [1]. Later, Grunes and Leapman [2] also applied the method to study transition metal oxides and attempted to compare the experimental results to band structure calculations. Then followed more systematic electronic structure work at much higher energy resolution (but on a dedicated spectrometer with no spatial resolution) by Fink [3]. Presently, with the development of commercially available efficient parallel spectrometers and energy filters which are attached to transmission electron microscopes the possibilities have increased as different scientist enter the field with different backgrounds to study new problems. The quality of the spectra has become comparable, in terms of energy resolution, to the current synchrotrons [4] but with the clear and incomparable advantage of very high spatial resolution which now reaches the sub-nanometer level in standard commercial instruments. The applications of EELS have thus impressively increased in the last 10 years and a significant portion of these are beyond the microanalysis applications and concentrate on the variations of fine structure to identify various compounds and to probe the local coordination. Reviews of this type of work including energy filtering for elemental mapping can be found in the references of reviews on the technique [5–9]. The second edition of the book by Egerton in 1996 [9] shows the dramatic increase in the number of application of the technique due to the availability of the instruments (parallel spectrometers and energy filters) integrated in analytical transmission electron microscopes and dedicated scanning transmission electron microscopes. In the chapters by L.M. Brown and J.M. Howe included in this book, many examples are described.
Gianluigi A. Botton
Surface Chemistry and Microstructure Analysis of Novel Technological Materials
Abstract
More and more, our understanding of surface structure and chemical composition is becoming fundamental in materials development. The purpose of this review is to present different surface analysis techniques that can help researchers to increase their understanding of the surface microstructure or nanostructure. Three analytical methods will be discussed: Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS) and Secondary Ions Mass Spectroscopy (SIMS). Some of the physical principles behind these techniques will be briefly described together with their advantages, the detection limits and also some possible related artifacts. The main objective of this paper is to show the importance of our understanding of the surface structure and chemistry in the development of technologically important materials. The different sections will present a number of materials development programs and hopefully will illustrate the significance of the information obtained using these surface analytical tools.
Michel L. Trudeau
Convergent Beam Electron Diffraction
Abstract
Convergent beam electron diffraction (CBED) is one of the most important techniques in electron microscopy and electron diffraction since it provides a wealth of information about the material being studied. The single most important feature of CBED is that it provides localised diffraction information about the specimen from regions which can be as small as only a single atom across. As will be explained later, CBED patterns are formed using an electron beam which is focused onto the specimen. The spatial resolution of the CBED patterns is therefore the minimum size of the focused electron beam on the specimen. In older microscopes this is about 10 nm, but in a field emission gun scanning transmission electron microscope (FEGSTEM) or a field emission gun transmission electron microscope (FEGTEM) the focused probe size is better then 1 nm. In the most recent instruments the focused probe size is approaching 1Å, hence CBED patterns can come from single atomic columns (beam spreading effects due to elastic and inelastic scattering must of course be taken into account when considering the spatial resolution). CBED is an extremely important and useful technique on both older and newer electron microscopes for the reasons outlined below.
Colin J. Humphreys
New Developments in Scanning Probe Microscopy
Abstract
Four topics will be treated in this article:
1)
One of the central questions of contact force microscopy is the determination of contact area. Imaging of well-defined structures is one way to estimate the size of the contact. Recently, continuum elasticity models were used to describe the nanometer-sized contact. The lateral contact stiffness method was found to be particularly interesting, because it is rather independent of the selected formalism.
 
2)
Progress has been made with non-contact force microscopy, where true atomic resolution has been achieved. It is found that the instrument has to be operated at similar tip-sample distances as in STM. On Si(111)7×7, the strongest attraction is found for the adatoms, which is in agreement with theoretical models. The contrast at step sites is found to be influenced by short-range chemical forces and long-range electrostatic or van der Waals forces. Spectroscopic methods were used to investigate the frequency shifts between the upper and lower terrace. Local variations of the contact potential are found to be below the detection limit, whereas variations of electrostatic forces due to changes in the interaction volume are found to be predominant.
 
3)
Some artifacts of scanning probe microscopy are briefly discussed. The tip artifact, where the sample topography is convoluted with the tip geometry is the most common artifact. The second artifact is related to laser beam interference between the sample surface and the rear side of the cantilever, which can cause interference patterns in laser beam deflection force microscopy images.
 
4)
The application of AFM-based technology to the construction of chemical and physical sensors is found to be extremely successful. Micro-machined cantilevers are the central part of these sensors. After the chemieal treatment of the cantilevers (active or functional probes), the conditions of the surface film are monitored with a sensitive deflection sensor. The reaction with environmental gases leads to changes of surface stress (stress mode) or mass changes, which are detected as a resonanee frequency shift (frequency mode). Using the bimetallic effect, small heat changes can be translated into cantilever deflections (calorimeter mode).
 
E. Meyer, M. Guggisberg, Ch. Loppacher, F. Battiston, T. Gyalog, M. Bammerlin, R. Bennewitz, J. Lü, T. Lehmann, A. Baratoff, H.-J. Güntherodt, R. Lüthi, Ch. Gerber, R. Berger, J. Gimzewski, L. Scandella
Low-Energy Scanning Electron Microscope for Nanolithography
Abstract
We present a new low-energy (~300 eV) scanning electron microscope with 30-nm resolution. The instrument operates with a flat integrated chip lens which performs electron extraction, e-beam focusing and deflection. An important feature is that the electron emitter is positioned 1-2 mm away from the extractor anode (consisting of an aperture of 1 μm diameter), so that their precise alignment is not necessary. The extension of the application of the instrument to a multicolumn array of electron beams for multipattern writing is quite feasible.
A. Zlatkin, N. García
Application of Low Voltage Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy
Abstract
The application of field emission sources in scanning electron microscopy has resulted in significant improvements in spatial resolution, especially at low, <5kV, accelerating voltages. Low voltage operation has the advantage of reducing the interaction volume within the specimen, thus increasing the surface specificity of the technique [1, 2]. By working at the second crossover energy it is possible to neutralize the surface charge build-up at the surface of non-conducting specimens [3]. Theoretical and experimental methods for determining the optimum accelerating voltage will be described. Due to the reduced interaction volume, the contrast mechanisms may differ from those in the higher voltage range, >15kV, more generally used for scanning electron microscopy. Differential charging may strongly influence the local secondary electron yield, giving rise to anomalous atomic number contrast [4, 5]. The use of Monte Carlo modelling for image simulation and estimation of the size of the interaction volume will be illustrated with practical examples related to semiconductor critical dimension measurement and multilayer thin film studies.
D. G. Rickerby
Environmental SEM and Related Applications
History of the Environmental SEM and Basic Design Concepts
Abstract
The first ESEM design was conceived in the mid 1970’s at the University of New South Wales in Australia by the researchers Gerry Danilatos and Vivian Robinson for the purpose of studying native wool fibers.
Thomas A. Hardt
Environmental SEM and Related Applications
Gas Interactions and Gaseous Amplification
Abstract
The key to the imaging technology in the ESEM is the ionization of gas molecules by the secondary electrons from the sample and the collection of this amplified signal. Secondary electrons that are generated by the interaction of the primary electron beam with the sample are the signal of choice for high resolution imaging. The primary beam strikes a sample generating both secondary and backscattered electrons. In the ESEM, the secondary electrons are specifically collected by a confined electrostatic field that is generated by gaseous secondary electron detector above the sample. Within this field, the secondary electrons strike gas molecules generating an additional electron; a process termed cascade amplification. The image formed by collection of these electrons is very similar to the image formed by the conventional Everhart-Thornley detector, even though the signal amplification process is different. Scattering of the primary beam electrons also results in the formation of amplified electrons, but contains no relevant image information.
Thomas A. Hardt
Environmental SEM and Related Applications
Applications
Abstract
A key to defining the extent of the applicability of the ESEM can be found in the ability to image samples in multiple environments; from different gas compositions to different environments of sample temperature and humidity. Within these environments, many different applications have been developed. The most common is the imaging of non-conductive and beam sensitive samples using a wider range of accelerating voltages and the imaging of wet and live specimens. Other applications include dynamic imaging of solid-solid or gas-solid reactions, tensile force kinetics, as well as micro-liquid injection.
Thomas A. Hardt
ESEM Image Contrast and Applications to Wet Organic Materials
Abstract
In the Environmental Scanning Electron Microscope (ESEM) there is a gas in the chamber above the sample. This is the crucial difference between it and conventional scanning electron microscopy (CSEM), which permits a wide range of samples to be investigated of a type inaccessible to CSEM. When the gas is water vapour, then damp/wet samples (or even essentially pure water) can be investigated without the need for careful prior specimen preparation to remove all the liquid. This obviously has the advantage that reduction in specimen preparation means a reduction in the liklihood of artefacts being introduced. However, the presence of the gas leads to a variety of new effects due to the interaction of the electrons with the gas molecules. Some of these effects are desirable and, as we will see below, can be usefully harnessed to provide novel sources of contrast. However, other consequences are less desirable, leading to both a reduction in spatial resolution and signal/noise ratio. Hence, in order to optimise use of the ESEM, it is important to have a clear understanding of the nature of the potential gas molecule/electron interactions, and their impact on image formation.
Athene M. Donald, Bradley L. Thiel
Advanced Electron and Scanning Probe Microscopy on Dental and Medical Materials Research
Abstract
Microscopic and spectroscopic characterization techniques have improved dramatically in the last decade and are currently being exploited in physics and materials science. These novel methodologies are now being extended to the development and testing of the “next generation” of dental and medical materials.
Giovanni Valdre’
Correlative Microscopy and Probing in Materials Science
Abstract
Each procedure of microscopic investigation, depending on its purpose, has advantages and drawbacks. The inherent limitations of each method may be circumvented or at least minimized if a correlative application of different microscopic techniques is performed.
Giovanni Valdre’
Backmatter
Metadaten
Titel
Impact of Electron and Scanning Probe Microscopy on Materials Research
herausgegeben von
David G. Rickerby
Giovanni Valdrè
Ugo Valdrè
Copyright-Jahr
1999
Verlag
Springer Netherlands
Electronic ISBN
978-94-011-4451-3
Print ISBN
978-0-7923-5940-1
DOI
https://doi.org/10.1007/978-94-011-4451-3