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SUMMARY:Some ideas how to improve quantification of chemical signals in tr
 ansmission electron microscopy studies of very thin layers - Thomas Walthe
 r\, Department of Electronic and Electrical Engineering\, University of Sh
 effield
DTSTART:20061031T150000Z
DTEND:20061031T160000Z
UID:TALK5815@talks.cam.ac.uk
CONTACT:Edmund Ward
DESCRIPTION:Thin layer structures can be produced by many different techni
 ques and are important for a variety of different applications. Transmissi
 on electron microscopy (TEM) is a unique method to investigate such layers
  locally and to obtain information on crystallographic structure\, defects
 \, thickness\, interface roughness\, compositional grading and chemistry w
 ith spatial resolution on the (sub) nm scale\, usually rather direct witho
 ut the need of extensive modelling. This talk will give an overview of nov
 el experimental methods to determine the chemistry of very thin layers usi
 ng a number of different TEM methods:\na) Spectroscopic transverse image p
 rofiling in energy-filtered TEM with a Gatan Imaging Filter allows to meas
 ure shifts of the energy- loss near edge structure (ELNES) across interfac
 es with a precision much better than both the energy-resolution or the typ
 ical long-term energy stability of the system\,\nb) Linear least-squares f
 itting of series of spectra acquired with different electron beam sizes ca
 n be applied to either energy- dispersive X-ray (EDX) or electron  energy-
 loss spectra (EELS) and\, by making use of a rather simple geometrical app
 roach\, yields segregation levels of elements to a precision  an order of 
 magnitude better than standard analytical approaches\,\nc) Energy-filtered
  annular dark-field imaging is shown to allow accurate interpretation of t
 he image contrast in terms of pure Rutherford scattering if the image cont
 rast is plotted as a function of the camera length and then extrapolated t
 o zero (i.e. infinite scattering angle)\,\nd) Monochromatic aberration cor
 rected scanning TEM (MacSTEM) will allow us in the future to form well-def
 ined small electron probes intense enough for a local chemical analysis of
  single atomic columns in crystals. \n
LOCATION:T001 [Tower Seminar Room]\, Materials Science and Metallurgy\, De
 partment of
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