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Crystallography
 
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Electron Microscopy

HRTEM_Icon
Using electron microscopy to complement powder diffraction


Dan Xie, Fabian Gramm, Lynne B. McCusker and Christian Baerlocher

The main emphasis of this project is to explore the possibility of using eletron microscopy data to complement powder diffraction data to solve complex crystal structures.

Electrons interact much more strongly with atoms than do X-rays, so a single-crystal electron diffraction pattern can be obtained from a very tiny crystallite (ca 20 nm). Unfortunately, this strong interaction generally results in intensities that are difficult or impossible to interpret unless the crystallite is extremely thin and the crystallite is quite likely to be destroyed in the beam.

An alternative way of combining powder diffraction and electron microscopy is to exploit the fact that high-resolution transmission electron microscopy (HRTEM) images contain phase information for the reflections contributing to it. This key information is lost in a diffraction experiment.

Framework structure of TNU-9 with a structure envelope showing the channel system
Framework structure of TNU-9 with a structure envelope showing the channel system
Even though only a fraction of the reflections contribute to any one HRTEM image, and not all of the phases can be derived reliably, this limited phase information has proven to be extremely useful in structure determination. The phases can be used to generate a structure envelope, or they can be combined with intensities extracted from a powder diffraction pattern in the program Focus. The latter allowed the structure of the zeolite TNU-9 (left), with 24 Si-atoms in the asymmetric unit (the most complex zeolite structure known), to be solved.

A similar combination of HRTEM and powder diffraction was also used to solve the structure of the similarly complex zeolite IM-5. In that case, charge flipping was used instead of Focus.

Supported by the Swiss National Science Foundation.

References:

F. Gramm, Ch. Baerlocher, L.B. McCusker, S.J. Warrender, P.A. Wright, B. Han, S.B. Hong, Z. Liu, T. Ohsuna and O. Terasaki, "Complex zeolite structure solved by combining powder diffraction and electron microscopy", Nature (2006), 444, 79-81

Ch. Baerlocher, F. Gramm, L. Massüger, L.B. McCusker, Z. He, S. Hovmöller and X. Zou, "Structure of the polycrystalline zeolite catalyst IM-5 solved by enhanced charge flipping", Science (2007), 315, 1113-1116

Ch. Baerlocher, D. Xie, L.B. McCusker, S.-J. Hwang, I.Y. Chan, K. Ong, A.W. Burton and S.I. Zones, "Ordered silicon vacancies in the framework structure of the zeolite catalyst SSZ-74" Nature Mater. (2008), 7, 631-635

D. Xie, Ch. Baerlocher and L.B. McCusker, "Combining precession electron diffraction dta with X-ray powder diffraction data to facilitate structure solution", J. Appl. Crystallogr. (2008) 41, 1115-1121

L.B. McCusker and Ch. Baerlocher, "Using electron microscopy to complement X-ray powder diffraction data to solve complex crystal structures" (2009), Chem. Commun. 1439-1451

L.B. McCusker and Ch. Baerlocher, "Electron crystallography as a complement to X-ray powder diffraction techniques" (2013) Z. Kristallogr. 228, 1-10

 

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