Electron microscopy was first conducted in the 1930s with the advent of the
TEM and later the STEM. In 1969, the first commercial SEM was released,
with the possibility of retrofitting it to behave like a STEM following soon
afterwards. In 1979, Danilatos and Robinson advanced electron microscopy
by creating a new type of SEM which allowed a controlled quantity of gas
into the sample chamber, termed ESEM. The most recent evolution in this
line was the combination of ESEM and STEM in 2005, a procedure termed
Wet STEM.
The focus of this work is on investigating applications of this new technique,
along with the contrast mechanisms involved in forming an image. To
that end, a wide variety of samples will be imaged. Clay and paint suspensions
(colloids) are used to test Wet STEM’s capacity to image submerged
objects, as well as thin objects which are stacked together. Diblock copolymer
films are used to test Wet STEM’s ability to distinguish chemically similar
materials without staining, the physical effects of heavy metal staining and
to demonstrate the necessity of gas for the purpose of charge neutralisation.
Single cell biological samples are also investigated. Internal contrast in
mammalian cells is visible without recourse to staining, but chemical fixation
is required despite maintaining a high relative humidity. Bacteria are more
resilient and as such are easier to image than animal cells, requiring no prior
treatment. When exposed to low relative humidity, bacteria are found to
collapse. The collapse pattern is observed to differ between wild-type and
cytoskeletal-deficient bacteria of the same species and strain, so it is likely
that dehydration-induced collapse offers information about the position and
shape of the bacterial cytoskeleton.This work was funded by the EPSRC [grant number EP/P50385X/1] and by a CASE studentship from FEI Company
