International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 3.5, p. 173

Section 3.5.1.4. Final thinning by chemical etching

N. J. Tighe,a J. R. Fryerb and H. M. Flowerc

a42 Lema Lane, Palm Coast, FL 32137-2417, USA,bDepartment of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, and cDepartment of Metallurgy, Imperial College, London SW7, England

3.5.1.4. Final thinning by chemical etching

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Chemical dissolution methods for preparing electron-transparent specimens were developed before ion thinning was perfected. These methods are not used extensively, but they have some advantages particularly where ion thinning may disturb the surface composition or structure of a particular material. It is advantageous to use chemical dissolution in some stages of specimen preparation, for example to relate etch pits to dislocations, to prepare a defect-free surface, and to remove the ion-damaged surface from thin disc specimens (Barber & Tighe, 1965[link]). The thinning conditions must be chosen carefully to avoid artefacts such as preferential dissolution at grain boundaries, precipitates, and dislocations, or surface precipitates produced by a supersaturated solution.

Suitable solvents and dissolution conditions must be found for each new material. Some of the chemical etchants used for thin-section preparation are listed in Table 3.5.1.1[link].

Table 3.5.1.1| top | pdf |
Chemical etchants used for preparing thin foils from single-crystal ceramic materials; symbols: I immersion method; SFJ separatory funnel jet; CJ convection jet; BJ boiling jet

MaterialEtchantReferences
Al2O3 85% H3PO4, 723–733 K I, BJ Tighe (1964[link])
BaTiO3 H2SO4 CJ Kirkpatrick & Amelinckx (1962[link])
CaCO3 C6H8O7 (dilute) I Braillon et al. (1974[link])
CoO 85% H3PO4 CJ Remaut et al. (1964[link])
LiNbO3 KOH, 623–673 K I Wicks & Lewis (1968[link])
MgO 85% H3PO4, 373 K I, SFJ Washburn et al. (1960[link])
MgAl2O4 85% H3PO4, 523–723 K I Lewis (1966[link])
MnO HCl + NO3   Barber & Evans (1970[link])
SiO2 NH4F·HF, 453–473 K I Tighe (unpublished)
HF, 373 K I
TiO2 NaOH, 823 K I Barber & Farabaugh (1965[link])
ZrSiO4 NH4F·HF + KF (1:1), 693–703 K I Tighe (unpublished)
Y3Al5O12 85% H3PO4, 573 K I Keast (1967[link])

Devices that squirt a jet of chemical solvent at the disc or slab specimen are used to obtain careful control over the final thinning to electron transparency (Kirkpatrick & Amelinckx, 1962[link]; Tighe, 1964[link]; Washburn, Groves, Kelly & Williamson, 1960[link]).

Predictable dissolution rates are obtained by varying the concentration and temperature of the etchant. Solutions can be found that will produce a smooth surface polish or an etch-pitted surface. For example, corundum is etched in boiling phosphoric acid at a temperature approximately 50 K lower than the temperature used for polishing. Surfaces with different crystallographic orientations have different dissolution rates. Useful sources of information about possible etchants are mineralogical and chemical handbooks that discuss production of etch figures and crystallographic facets (Dana & Ford, 1922[link]; Honess, 1927[link]).

References

Barber, D. J. & Evans, R. G. (1970). Dislocations, ordering and antiferromagnetic domains in MnO. Proc. EMSA, pp. 522–523. Baton Rouge: Claitor.
Barber, D. J. & Farabaugh, E. N. (1965). Dislocations and stacking faults in rutile crystals grown by flame fusion methods. J. Appl. Phys. 36, 2803–2806.
Barber, D. J. & Tighe, N. J. (1965). Electron microscopy and diffraction of synthetic corundum crystals. I. Pure aluminum oxide grown by the Verneuil process. Philos. Mag. 11, 495–512.
Braillon, P., Mughier, J. & Serughetti, J. (1974). Transmission electron microscope observations of dislocations in calcite single crystals. Cryst. Lattice Defects, 5, 73–78.
Dana, E. S. & Ford, W. E. (1922). A textbook on mineralogy. New York: John Wiley.
Honess, A. P. (1927). The nature, origin and interpretation of the etch figures on crystals. New York: John Wiley.
Keast, D. J. (1967). A chemical thinning technique for the simultaneous preparation of foils for transmission electron microscopy. Application to yttrium aluminum garnet (YAG). J. Sci. Instrum. 44, 862–863.
Kirkpatrick, H. B. & Amelinckx, S. (1962). Device for chemically thinning crystals for transmission electron microscopy. Rev. Sci. Instrum. 33, 488–489.
Lewis, M. H. (1966). Defects in spinel crystals grown by the Verneuil process. Philos. Mag. 14, 1003–1008.
Remaut, G., Lagasse, A. & Amelinckx, S. (1964). Electron microscope study of the domain structure in anti-ferromagnetic cobalteous oxide. Phys. Status Solidi, 5, 497–510.
Tighe, N. J. (1964). Jet thinning device for preparation of Al2O3 electron microscopy specimens. Rev. Sci. Instrum. 35, 520–521.
Washburn, J., Groves, G. W., Kelly, A. & Williamson, G. K. (1960). Electron microscope observations of deformed magnesium oxide. Philos. Mag. 5, 991–999.
Wicks, B. J. & Lewis, M. H. (1968). Direct observations of ferroelectric domains in lithium niobate. Phys. Status Solidi, 26, 571–576.








































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