Naomi E. Chayen, John R. Helliwell, and Edward H. Snell
- Published in print:
- 2010
- Published Online:
- May 2010
- ISBN:
- 9780199213252
- eISBN:
- 9780191707575
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199213252.003.0018
- Subject:
- Physics, Crystallography: Physics
Crystallography is a powerful technique but also one that has limitations. There are a number of complementary techniques that significantly add to the information available crystallographically.
Crystallography is a powerful technique but also one that has limitations. There are a number of complementary techniques that significantly add to the information available crystallographically.
Kannan M. Krishnan
- Published in print:
- 2021
- Published Online:
- July 2021
- ISBN:
- 9780198830252
- eISBN:
- 9780191868665
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780198830252.003.0002
- Subject:
- Physics, Condensed Matter Physics / Materials
We review the structure of atoms to describe allowed intra-atomic electronic transitions following dipole selection rules. Inner shell ionization is followed by characteristic X-ray emission or ...
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We review the structure of atoms to describe allowed intra-atomic electronic transitions following dipole selection rules. Inner shell ionization is followed by characteristic X-ray emission or non-radiative de-excitation processes leading to Auger electrons that involve three atomic levels. Photon incidence also results in characteristic photoelectron emission, reflecting the energy distribution of the electrons in the solid. We present details of laboratory and synchrotron sources of X-rays, and discuss their detection by wavelength or energy-dispersive spectrometers, as well as microanalysis with X-ray (XRF), or electron (EPMA) incidence. Characteristic X-ray intensities are quantified in terms of composition using corrections for atomic number (Z), absorption (A), and fluorescence (F). Electron detectors use electrostatic or magnetic dispersing fields; two common designs are electrostatic hemispheric or mirror analyzers. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), used for surface analysis, require ultra-high vacuum. AES is a weak signal, best resolved in a derivative spectrum, shows sensitivity to the chemical state and the atomic environment, provides a spatially-resolved signal for composition mapping, and can be quantified for chemical analysis using sensitivity factors. Finally, we introduce the basics of XPS, a photon-in, electron-out technique, discussed further in §3.Less
We review the structure of atoms to describe allowed intra-atomic electronic transitions following dipole selection rules. Inner shell ionization is followed by characteristic X-ray emission or non-radiative de-excitation processes leading to Auger electrons that involve three atomic levels. Photon incidence also results in characteristic photoelectron emission, reflecting the energy distribution of the electrons in the solid. We present details of laboratory and synchrotron sources of X-rays, and discuss their detection by wavelength or energy-dispersive spectrometers, as well as microanalysis with X-ray (XRF), or electron (EPMA) incidence. Characteristic X-ray intensities are quantified in terms of composition using corrections for atomic number (Z), absorption (A), and fluorescence (F). Electron detectors use electrostatic or magnetic dispersing fields; two common designs are electrostatic hemispheric or mirror analyzers. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), used for surface analysis, require ultra-high vacuum. AES is a weak signal, best resolved in a derivative spectrum, shows sensitivity to the chemical state and the atomic environment, provides a spatially-resolved signal for composition mapping, and can be quantified for chemical analysis using sensitivity factors. Finally, we introduce the basics of XPS, a photon-in, electron-out technique, discussed further in §3.
Kannan M. Krishnan
- Published in print:
- 2021
- Published Online:
- July 2021
- ISBN:
- 9780198830252
- eISBN:
- 9780191868665
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780198830252.003.0003
- Subject:
- Physics, Condensed Matter Physics / Materials
The electronic structure of molecules includes electronic (2-10 eV, UV-Vis absorption), vibrational (10-2 - 2 eV, infrared spectroscopy & Raman scattering), and rotational (10–5 – 10–3 eV, microwave ...
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The electronic structure of molecules includes electronic (2-10 eV, UV-Vis absorption), vibrational (10-2 - 2 eV, infrared spectroscopy & Raman scattering), and rotational (10–5 – 10–3 eV, microwave spectroscopy) energy levels that are probed by appropriate spectroscopy methods. Light, incident on a molecule or molecular solid, is either absorbed (IR, single photon, non-zero derivative of dipole moment), or elastically (Rayleigh) or inelastically (Raman, two-photon, non-zero derivative of the polarizability) scattered. Fourier transform infrared (FTIR) spectroscopy finds much use in materials characterization, including in studying the curing of polymer composites now incorporated in aircraft structures. When atoms form solids their electronic structure, particularly the energy levels of the outer electrons involved in the bonding, are significantly altered. Both occupied and unoccupied levels in solids are probed. Photoemission spectroscopy (PES) with X-rays (XPS) or ultraviolet light (UPS) incidence, and inverse PES probe occupied and unoccupied energy levels of surfaces, respectively. X-ray absorption spectroscopy (XAS) complements XPS, and probes unoccupied energy levels of solids. X-ray absorption near-edge structure (XANES) provides information on the final density of unoccupied states, the transition probabilities, and many body effects. Extended X-ray absorption fine structure (EXAFS) provides element-specific nearest neighbor distances and their coordination number.Less
The electronic structure of molecules includes electronic (2-10 eV, UV-Vis absorption), vibrational (10-2 - 2 eV, infrared spectroscopy & Raman scattering), and rotational (10–5 – 10–3 eV, microwave spectroscopy) energy levels that are probed by appropriate spectroscopy methods. Light, incident on a molecule or molecular solid, is either absorbed (IR, single photon, non-zero derivative of dipole moment), or elastically (Rayleigh) or inelastically (Raman, two-photon, non-zero derivative of the polarizability) scattered. Fourier transform infrared (FTIR) spectroscopy finds much use in materials characterization, including in studying the curing of polymer composites now incorporated in aircraft structures. When atoms form solids their electronic structure, particularly the energy levels of the outer electrons involved in the bonding, are significantly altered. Both occupied and unoccupied levels in solids are probed. Photoemission spectroscopy (PES) with X-rays (XPS) or ultraviolet light (UPS) incidence, and inverse PES probe occupied and unoccupied energy levels of surfaces, respectively. X-ray absorption spectroscopy (XAS) complements XPS, and probes unoccupied energy levels of solids. X-ray absorption near-edge structure (XANES) provides information on the final density of unoccupied states, the transition probabilities, and many body effects. Extended X-ray absorption fine structure (EXAFS) provides element-specific nearest neighbor distances and their coordination number.
Helge Kragh
- Published in print:
- 2012
- Published Online:
- May 2012
- ISBN:
- 9780199654987
- eISBN:
- 9780191741692
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199654987.003.0004
- Subject:
- Physics, History of Physics, Atomic, Laser, and Optical Physics
With A. Sommerfeld’s extension of the Bohr theory in 1915–1916, it was turned into a powerful tool of atomic research and adopted and further developed by German physicists in particular. The new and ...
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With A. Sommerfeld’s extension of the Bohr theory in 1915–1916, it was turned into a powerful tool of atomic research and adopted and further developed by German physicists in particular. The new and more general Bohr–Sommerfeld theory described the atom in terms of two quantum numbers, while Bohr had originally used only one quantum number. With this extension the theory provided an explanation of the Stark effect, the ordinary Zeeman effect, and the fine structure of the hydrogen spectrum. Other developments based on X-ray spectroscopy were less successful, as were attempts to understand the structure of the helium atom. Yet, by 1920 nearly all physicists accepted the theory as the only viable framework for atomic and quantum research. But not all agreed: the chapter includes an account of conceptual and other objections against the theory raised by J. Stark in Germany and a few other physicists.Less
With A. Sommerfeld’s extension of the Bohr theory in 1915–1916, it was turned into a powerful tool of atomic research and adopted and further developed by German physicists in particular. The new and more general Bohr–Sommerfeld theory described the atom in terms of two quantum numbers, while Bohr had originally used only one quantum number. With this extension the theory provided an explanation of the Stark effect, the ordinary Zeeman effect, and the fine structure of the hydrogen spectrum. Other developments based on X-ray spectroscopy were less successful, as were attempts to understand the structure of the helium atom. Yet, by 1920 nearly all physicists accepted the theory as the only viable framework for atomic and quantum research. But not all agreed: the chapter includes an account of conceptual and other objections against the theory raised by J. Stark in Germany and a few other physicists.
André Authier
- Published in print:
- 2013
- Published Online:
- September 2013
- ISBN:
- 9780199659845
- eISBN:
- 9780191748219
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199659845.003.0010
- Subject:
- Physics, Crystallography: Physics
The early applications of X-ray crystallography in different fields of science in the period up to 1913 are described. Chemistry: the first crystal structure determinations shed a new light on the ...
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The early applications of X-ray crystallography in different fields of science in the period up to 1913 are described. Chemistry: the first crystal structure determinations shed a new light on the nature of chemical bonds in solids and led to Goldschmidt’s and Pauling’s rules; the benzene ring was shown to be planar. Metallurgy: the crystal structures of many elements and alloys were determined, and accurate phase diagrams established; preliminary studies were made of annealing and cold-working. Mineralogy: the crystal structures of many minerals were determined and, most importantly, the classification of silicates was established. Physics: the existence of zero-point energy, predicted by Planck, was confirmed; Planck’s constant, h, was determined with high accuracy; preliminary structural interpretation of the piezoelectricity of quartz was made. Biochemistry: the structure of natural fibres and, in particular, of keratin was analysed. X-ray spectroscopy expanded rapidly, experimentally with de Broglie, Wagner, and the Siegbahn school, and theoretically with Kossel and Sommerfeld.Less
The early applications of X-ray crystallography in different fields of science in the period up to 1913 are described. Chemistry: the first crystal structure determinations shed a new light on the nature of chemical bonds in solids and led to Goldschmidt’s and Pauling’s rules; the benzene ring was shown to be planar. Metallurgy: the crystal structures of many elements and alloys were determined, and accurate phase diagrams established; preliminary studies were made of annealing and cold-working. Mineralogy: the crystal structures of many minerals were determined and, most importantly, the classification of silicates was established. Physics: the existence of zero-point energy, predicted by Planck, was confirmed; Planck’s constant, h, was determined with high accuracy; preliminary structural interpretation of the piezoelectricity of quartz was made. Biochemistry: the structure of natural fibres and, in particular, of keratin was analysed. X-ray spectroscopy expanded rapidly, experimentally with de Broglie, Wagner, and the Siegbahn school, and theoretically with Kossel and Sommerfeld.
André Authier
- Published in print:
- 2013
- Published Online:
- September 2013
- ISBN:
- 9780199659845
- eISBN:
- 9780191748219
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199659845.001.0001
- Subject:
- Physics, Crystallography: Physics
2012 marked the centenary of one of the most significant discoveries of the early twentieth century: the discovery of X-ray diffraction in March 1912 by Laue, Friedrich, and Knipping, and of the ...
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2012 marked the centenary of one of the most significant discoveries of the early twentieth century: the discovery of X-ray diffraction in March 1912 by Laue, Friedrich, and Knipping, and of the birth of X-analysis with Bragg’s law in November 1912. The discovery of X-ray diffraction confirmed the wave nature of X-rays and the space-lattice hypothesis. The book stresses the unique role played by X-ray diffraction in the analysis of the structure of atoms and in the determination of the atomic structure of materials. It relates the discovery itself and the context in which it was made: the local context (Munich) and the scientific context (the discussions taking place at that time about the nature, wave or corpuscular, of X-rays, and about the concept of space lattice). The way the discovery spread round the world and the early investigations are described. The book explains how the basic theories of X-ray diffraction and the main methods of investigations were developed, and how the first crystal structures were determined, and recounts which were the first applications of X-ray crystallography in chemistry, mineralogy, material science, biology, physics, and X-ray spectroscopy. It also tells how the concept of space lattice matured between Ancient times and the end of the nineteenth century, and how our understanding of the nature of light has changed over time. The contributions of the main actors of the story, prior to the discovery, at the time of the discovery, and immediately afterwards, are described through their writings and are put into a contemporary context, accompanied by brief biographical details.Less
2012 marked the centenary of one of the most significant discoveries of the early twentieth century: the discovery of X-ray diffraction in March 1912 by Laue, Friedrich, and Knipping, and of the birth of X-analysis with Bragg’s law in November 1912. The discovery of X-ray diffraction confirmed the wave nature of X-rays and the space-lattice hypothesis. The book stresses the unique role played by X-ray diffraction in the analysis of the structure of atoms and in the determination of the atomic structure of materials. It relates the discovery itself and the context in which it was made: the local context (Munich) and the scientific context (the discussions taking place at that time about the nature, wave or corpuscular, of X-rays, and about the concept of space lattice). The way the discovery spread round the world and the early investigations are described. The book explains how the basic theories of X-ray diffraction and the main methods of investigations were developed, and how the first crystal structures were determined, and recounts which were the first applications of X-ray crystallography in chemistry, mineralogy, material science, biology, physics, and X-ray spectroscopy. It also tells how the concept of space lattice matured between Ancient times and the end of the nineteenth century, and how our understanding of the nature of light has changed over time. The contributions of the main actors of the story, prior to the discovery, at the time of the discovery, and immediately afterwards, are described through their writings and are put into a contemporary context, accompanied by brief biographical details.
