Chiou 1 Transmission Electron Microscopy of Mineralogy_070806

Transmission Electron Microscopy of Mineralogy

Wen-An Chiou

Materials Characterization Center (MC2)

and

Department of Chemical Engineering and Materials Science

University of California, Irvine

Irvine, CA 92697-2575

USA

Pan-American Advanced Studies Institute on Transmission Electron Microscopy in Materials Science

July 11, 2006

Beginning with a cloud of dust and gas

from which the solar system formed some 5 billion years ago, to the birth of the Earth about 4.7 billions years ago. The earth is a very special place – and not just because we humans inhabit it..

To the planet we know today, with its hospitable atmosphere and rich resources, a planet still active inside – as evidenced by earthquakes, volcanoes, ocean basins that open and close, and continents that drift apart.

Geology – We explore not only the Earth as it exists today; we also seek answers how it was formed, what it was like when first born, to understand the Earth, both present and the past.

From the Small World to the Huge Earth and the Universe

PURPOSES

(1) To give a general overview/review of the application of TEM in the mineralogical and geological sciences research.

(2) To show examples of mineralogical and geological researches that have been utilizing TEM.

(3) To stimulate, hopefully, the direction of future mineralogical and geological research in the application of TEM.

The Rock Record• The only record we have of things that happened on Earth in the

geological past is the rock.• What is a rock? A rock is many things. It is a collection of the

particular chemical elements that make it up.• Physical and chemical characteristics of minerals in the rocks – most

tangible link with the history of the Earth. The logical beginning of the science of geology.

• Minerals are also important in practical way. Civilization history and technological culture are related to minerals and rocks.

• 1851, Henry Clifton Sorby, developed a technique of preparing rock thin section (25 um thick), and examined with an optical microscope.

• 1912, von Laue, diffraction of X-ray by crystal, and W. L. Bragg Law of crystal diffraction, from which the actual positions of atoms in a crystal can be determined.

• For many years, polarized LM and XRD have been the major techniques for study of minerals.

• In the past a few decades, many techniques used for investigating the structure and properties of materials have been utilized in mineralogical research.

• In the past two decades, growing awareness that the study of mineral behavior has important implications in related disciplines in earth sciences, even to the level where continental-scale tectonic phenomena are being considered in terms of processes taking place within individual mineral grains.

Brief History of Mineralogical/Geological Research Related to Microscopy

• Fleet and Ribbe (1961) - Probably the first significant application of TEM to an important rock-forming mineral (found submicroscopic microstructure of alternating lamellae of orthoclase which provide a detailed explanation of complex diffraction pattern)

• Early 1960s, other feldspars were studied by the Cambridge group, and also by Nissen and by McLaren group.

• McLaren and phakey (1965), first series of papers on variety of quartz (found dislocations in milky vein quartz and determined Brazil and Dauphine twin boundaries)

• However, little work was done at the time on these nonmetallic materials compared with the very great use that was made on TEM in metallurgy. The main reason was the difficulty of preparing thin enough samples

• Development of ion beam thinning technique has the similar impact like that Sorby’s until early 1970s, these serious limitations were largely overcome by ion beam thinning technique (originated by Paulus and Reverchon in 1961).

• Wenk (1976) edited the book “Electron Microscopy in Mineralogy”, TEM had changed the aspect of mineralogy.

• TEM-as an instrument for high resolution imaging, electron diffraction, and chemical analysis has produced a major impact in mineralogical/geological studies in a relative short time despite the late take off of TEM application in mineralogy (as compared with materials science and biological/medical sciences).

• Imaging Diffraction Analytical tech. Of TEM

• Optical M XRD Geochemical Method

• It is not exaggerate to say:The study of minerals has been among the most important contribution of HRTEM (because many minerals, unlike metals or other simple structures, have relative large unit cell and large scale defects that can be imaged successfully with TEM).

• The most important pieces of information required to characterize a mineral are:

– (1) Crystal structure

– (2) Chemical composition

• TEM is capable to obtain both structure and chemical information from a small area down to 1 nm (in diameter).

• No other technique can provide imaging (both texture/fabric and internal structure), crystallographic information (electron diffraction), and chemical composition simultaneously from a very small region (1 nm).

• TEM is a logical complement and extension of some of the more established mineralogical techniques and instruments.

Geomaterials vs. Man-made Materials• The goal of mineralogical research coincide with those for many

other materials research.• Minerals (geomaterials) Materials Science

– God’s Materials Man-made materials– Unknown Known composition – Complex Simpler– All crystallographic systems Most cubic, tetragonal,

hexagonal– Recorder of geological processes and events– Important tool for reconstructing the past

• TEM has had its great mineralogical impact in the study of localized structure and chemical perturbations in minerals.– E.g., Crystal defects, twinning, exsolution lamellae,

intergrowth– All contain much information regarding the history of a

mineral, thus of geological interest.

Relationship both within and between grains of a rock

• Grain boundary

• The geometry of fine-grained mineral intergrowth

• The interfaces

• Minerals inclusions and precipitates

• Compositional zoning

• Pure crystallography

• Structural and chemical disorder

• Nonstoichiometry

• Reaction mechanisms

• Polymorphic and polytypic transformations

Major Research Groups (I)

• Hard Rock:– Wenk, H.-R., (UC, Berkeley), 1976, ed., Electron Microscopy in

Mineralogy, Springer-Verlag, This book changed the aspect of mineralogy.

– Buseck, P. R., (ASU), 1988, co-ed., High-Resolution Transmission Electron Microscopy and Associated Techniques, Oxford U Press

– Banfield, J. F., (UC, Berkeley)– Veblen, D. R. (John Hopkins)– Mclaren A. C. (Australian National Univ.), 1991, Transmission

Electron Microscopy of Minerals and Rocks, Cambridge Univ. Press

– Ewing, R. (U of Michigan), emphasis on radiation damage on rocks

– American Mineralogists (Journal by the Mineralogical Society of America)

– Others

Major Research Groups (II)

• Soft Rock:• 1967, Zvyagin, Boris B., (translated by Simon Lyse), Electron-

Diffraction Analysis of Clay Mineral Structures, Plenum Press.• The geometry theory of electron diffraction and analysis of clay

mineral diffraction patterns. The determination of intensities in layer silicate diffraction patterns.Experimental electron diffraction studies of clays and related minerals.

• 1968, Beutelspacher, H. and H. W. Van Marel, Atlas of Electron Microscopy of Clay Minerals and their Admixtures, A Picture Atlas, Elsvier Publishing Co.

• A very comprehensive electron microscopy survey of morphology from a variety of clay and associated minerals.

• 1971, Gard, J. A. (ed.), The Electron-Optical Investigation of Clays, Mineralogical Society (Clay Minerals Group). A thorough study of the crystallography and morphology of a variety of clay and related minerals using transmission electron microscopy.

• 1990, Mackinnon, I. D. R. and F. A. Mumpton, Electron-Optical Methods in Clay Science, The Clay Minerals Society.

• Clay mineralogy studies:

– Veblen, D. R. group– Peacor, D. group (Univ. of Michigan) – University of Tokyo (Japan) group– European research groups– Clay and Clay Minerals, by the Clay Minerals Society.– Others

• 1986, Bennett, R. H. and M. H. Hulbert, Clay Microstructure, International Human Resources Development Corp.

• 1991, Bennett, R. H., W. R. Bryant and M. H. Hulbert, Microstructure of Fine-Grained Sediments, From Mud to Shale, Springer-Verlag.

• Clay fabric studies – geotechnical properties using TEM– Texas A&M group– Naval Research Laboratories– Civil Engineering groups

Application of TEM in Earth Sciences• (1) in mineralogical and geological sciences

– This presentation– (a) Conventional TEM – Minerals ID

- Defect and microstructure– (b) HRTEM – Determination of the atomic structure

Perfect and defected minerals/crystals

• (2) in clay science and civil engineering– Thursday (July 13th) presentation

• (3) in biominerals and biomineralization– Tuesday (July 18th) presentation

• (4) in-situ environmental TEM research– Friday (July 20th) presentation

Mineralogical Applications (1) - Conventional TEM

• Mineral Identification– Morphological

– Only on some very typical minerals such as some clay minerals

– Kaolinite: Hexagonal

– Attapulgite: Needle

(Both images from Beutelspacher, H. and H. W. Van Marel, 1968)

• Mineral identification– Electron diffraction:

Positive ID, assisted with chemical analysis (EDS)

(From Zvyagin, 1967)

Mineral IdentificationElectron diffraction: Shape factor and crystal morphology

(From Gard, 1971)

• Defect and Microstructure– 1950s Metallurgists studies the

dislocation in the plastic deformation of crystalline materials.

– 1960s, The mechanism of dislocation movement have established.

– At low temperature dislocations move “conservatively” on slip planes, requiring only small shearing stresses. Their density increases and due to increasing forces the strain energy of the deformed crystals augments.

– Example: High dislocation density in a low carbon steel (typical structure of materials deformed plastically at low temperature, “cold work”).

– On annealing (‘hard work”), dislocations leave the slip planes and climb into the positions which are closer to equilibrium such as networks.

– 1960s Structural geologists concerned with deformation of rocks (slow to respond to the new concept) (Turner and Weiss, 1963 Structural Analysis of Metamorphic Tectonites)

– 1965, McLaren and Phakey, dislocations in thin milky vein quartz.

– 1967, McLaren et al. first direct observation of dislocation and other defects in thin foils of deformed specimens.

Purpose of study dislocation microstructures in a wide range of naturally and experimentally deformed minerals and rocks are:

– (1) to determine the deformation mechanism;– (2) to interpret the microstructure observed in

naturally deformed specimens;– (3) to determine their deformation theory.

Deformation of “wet” synthetic quartz

• Dislocations in a deformed region where the original density of clusters was low. There are two sets of dislocations. It appears no clusters or strain-free bubbles in specimens deformed in low temperature. The observation suggests that the water (originally in the cluster) is now distributed in the dislocation cores, assuming that it has not diffused out of the crystal. The ragged fine structure of these dislocation images suggests the presence of many pinning points along the dislocations, which actually produce a drag on the dislocation glide.

Significant microstructural change of deformed crystals after annealing. Dislocations are smoothly curved, and many have interacted to form network; also much debris of small dislocation loops, and noticeable decrease in dislocation density – indicate that considerable recovery due to dislocation climb (has occurred during annealing). Annealed specimens show many bubbles (both isolated and linked by dislocations). It appears to confirm that specimens deformed in low temperatures the water originally in the cluster is distributed in the dislocation cores.

Small bubbles are more easily identified in out-of-focus phase contract images in which the dislocations are out of contrast.

Deformation of Carbonates(1) Microstructures in deformed calcite

The twin boundaries commonly contain closely spaced arrays of twinning dislocations, and the twinned lamellae usually contain numerous glide dislocation generated by the twinning. The untwined matrix may contain only a low density of preexisting dislocations.However, deformation twinning can generate glide dislocations in both the twin lamellae and the matrix, due to the need to relax the intense stress produced by he shape change at the surface near the tip of a moving twin lamella.

Deformation of Carbonates(1) Microstructures in deformed dolomite

The deformation characteristics of dolomite are markedly different from those of calcite. Not only are the twin laws different, but twinning in dolomite occurs only at temperature above 250oC.The lower dislocation density in twinned dolomite and at twin intersections is perhaps due to the greater ease of stress relaxation at the higher temperatures required for twinning.

Deformation of Olivine

- Olivine is the major mineral constituent of the upper mantle and presumably dominates the flow of the asthenosphere. Thus of great geophysical and geological interest.

- Olivine deformed atstrain rate of 10-4 and 10-5 sec-1, the dislocation configuration vary considerably with temperature.

• Determination of the Atomic Structure - In TEM, eD pattern is obtained in the back focal plane of the objective lens. This similar to the case of XRD, the Fourier transform of electrostatic potential differences in the specimen which corresponds to the electron density distribution. - But in contrast to XRD, the TEM can be used to obtain the inverse transform of diffraction pattern experimentally in the image plane without losing the phase information.- Two dimensional images of the electron density with resolution of better than 0.14 nm in which the contrast from single atoms can be recognized.

Mineralogical Application (2) - HRTEM

Z-projection of the electrostatic potential difference in tourmaline (left), a close correspondence to the crystal structure as determined by XRD (right)TEM shows intensity variation from unit cell to unit cell (due to short-range order), but cannot be seen with XRD.XRD provide a more precise determination of the average electron density in the unit cell of the lattice, while TEM resolves imperfections of the lattice as local site occupancies.

(From Wenk, 1976)

• Application of HREM• Graphite crystallization• Carbon occurs ubiquitous (organi

c debris in sedimentary rocks, subcrystalline in low-grade metamorphic rocks, and well-crystallized graphite in igneous and high-grade metamorphic rocks.

• C in sedimentary rock is of biological origin, and some such rocks are older than the oldest rocks that contain fossils. Thus, study of graphite precursors might provide insight into the earliest life forms on the Earth.

• E.g., Laboratory annealing experiments in an attempt to understand the development of graphite from noncrystalline organic precursors.

• Application of HREM• Cordierite (Mg2Al4Si5O18) tr

ansformation• Two polymorphs, with a transfor

mation temperature of about 1450oC.

• Above 1450oC the equilibrium form is hexagonal with space group p6/mcc (the same space group as beryl).

• Below 1450oC, it is orthorhomibic, Cccm.

• Transformation occurs as a result of Al-Si ordering among tetrahedral sites that are equivalent in the hexagonal polymorph, thereby producing the change in symmetry from hexagonal to orthorhombic.

• HRTEM in Mineral Nomenclature• International Mineral. Asso. Commission on New Minerals and Mineral Names• Requires the demonstration that structurally and chemically unique on the basis of XRD data a

nd chemical analyses, combined with determination of properties such as refractive indices, and density.

• The present international system generally functions well. However, HRTEM and other TEM methods do raise questions for the future.

• TEM can play an important role in description of new minerals.• The combination of TEM and XRD will be the best, i.e., complement each other.

Other Important Techniques Closely Related to HRTEM

• For each new detector that is fitted to an EM, a new sub-discipline of electron microscopy is created.

• These subdisciplines are usually closely related to exiting well established fields, e.g.,– Cathodoluminescence (CL) Photoluminescence (PL)– EDS X-ray fluorescence spectroscopy– EELS X-ray absorption studies– Electron loss near edge structure Near-edge-structure study– (ELNES) (XANES)

Near-edge X-ray absorption fine structure (NEXAFS)

– Extended electron-loss fine structure Extended X-ray absorption fine (EXELFS) structure (EXAFS)

• Both of these have much in common with photoelectron spectroscopy using either incident X-ray (XPS) or X-ray photoelectron spectroscopy.

(From Spence in Buseck, 1988)

• Unlike HRTEM (which records the positions of atoms), spectroscopy is concerned with the measurement of energies.

• Historically, the most important techniques are: – (1) those that derive from the discovery of the photoelectric

effect (such as XPS, UPS, ARPES, X-ray photoelectron spectroscopy, and some EXAFS and XANES);

– (2) those that derive from the original Frank-Hertz experiments (such as ELNES) and those based on optical-absorption measurement (such as EXAFS and XANES).

• The important distinction is between absorption and emission experiments.

• Spectroscopy provides important information in materials characterization

Summary• (1) This presentation provided a general review of the TEM applicatio

n in mineralogical (and geological) sciences.

• (2) It cannot be emphasized more that the importance of TEM in mineralogical research. Description of domains, lamellae, and dislocation provide geological information which cannot be obtained with standard mineralogical and geochemical methods.

• (3) The TEM has applied to a wide variety of mineralogical and geological problems ranging from a study of the crystal structure to the dimension of the universe.

• (4) The TEM has become a standard instrument in such diverse disciplines as crystallography, mineralogy, petrology, geophysics and geotectonics, linking together all the earth sciences in an even more general way the optical microscope.

• (5) Nevertheless, the progresses of TEM application in mineralogical research has been slow (as compare with other areas of research). More works are awaiting you to explore.

ReferencesMany photographs, statement presented in the talk were taken from

the following books, and papers cited in those books:

– Wenk, H.-R., ed., 1976, ed., Electron Microscopy in Mineralogy, Springer-Verlag.

– Buseck, P. R., 1988, co-eds., High-Resolution Transmission Electron Microscopy and Associated Techniques, Oxford U Press.

– Mclaren A. C., 1991, Transmission Electron Microscopy of Minerals and Rocks, Cambridge Univ. Press.

– Zvyagin, Boris B., (translated by Simon Lyse), 1967, Electron-Diffraction Analysis of Clay Mineral Structures, Plenum Press.

– Beutelspacher, H. and H. W. Van Marel, 1968, Atlas of Electron Microscopy of Clay Minerals and their Admixtures, A Picture Atlas, Elsvier Publishing Co.

– Gard, J. A. (ed.), 1971, The Electron-Optical Investigation of Clays, Mineralogical Society (Clay Minerals Group).

Thank You

Muchas Gracias