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SUMMARY:Cryo-STEM: A new tool for SEM and Dualbeam instruments - Harald Do
 bberstein\, Cavendish Laboratory\, University of Cambridge
DTSTART:20061212T150000Z
DTEND:20061212T160000Z
UID:TALK6049@talks.cam.ac.uk
CONTACT:Edmund Ward
DESCRIPTION:Scanning transmission electron microscopy (STEM) has become a 
 standard option in SEM. The STEM detectors are based on doped semiconducto
 rs with low work-functions\, where the incident electrons generate multipl
 e electron-hole (E-H) pairs and the free charge carriers can be collected 
 and further processed. Currently\, all commercially available STEM detecto
 rs are built for EM observations at room temperature. However\, FEI Compan
 y recently introduced a so called 'Wet-STEM' detector for imaging of wet a
 nd hydrated specimens in environmental SEMs. The STEM design includes a Pe
 ltier stage\, where the specimen temperature can be lowered to around 0°C
 . In collaboration with FEI we went a step further and developed a cryo-ST
 EM holder which allows imaging and analyzing native specimens in both tran
 smission and conventional secondary electron modes from room to liquid nit
 rogen temperatures (~ -190°C). The new cryo-STEM design involves two part
 s. First\, the main cryo-holder in the SEM sample chamber has been modifie
 d to house a state-of-the-art second generation STEM detector. Second\, th
 e sledge has been redesigned to meet following four requirements: (1) The 
 TEM grid can be loaded into the sledge in a protected and cooled environme
 nt\, such as in a FEI Vitrobot (TM) or cryo-chamber of an ultramicrotome. 
 Further\, (2) the sample needs to be maintained at liquid nitrogen tempera
 ture during transport and transfer into the cryo-transfer chamber. Also\, 
 (3) the frozen sample has to be protected from moisture in air or liquid n
 itrogen\, to avoid ice formation on the sample surface and finally\, (4) t
 he sledge needs to be compatible with the stage in a commercial cryo-trans
 fer chamber. Another feature of the cryo-holder is that it can be used in 
 Dualbeam FIB/SEM instruments. Electron transparent cross-sections of froze
 n biological specimens can be produced by focused ion beam (FIB) milling a
 nd subsequently viewed in the same microscope using the cryo-STEM detector
 . In this presentation I will introduce the cryo-STEM/SEM design and show 
 first results of frozen tissue\, cell monolayers and polymers.
LOCATION:T001 [Tower Seminar Room]\, Materials Science and Metallurgy\, De
 partment of
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