|
This step involves milling away the bonds on the top two corners of the membrane that were left by the frame cuts. Once these two
attachments are gone, the membrane is free from the bulk substrate. The TEM specimen often behaves in interesting ways at this
point. Shown in the images on this page is the TEM specimen tilting up and rising out of the trenches. This is a very typical
phenomena, which happens with specimens from all kinds of different materials. It is generally held that the membrane itself, due to all
the polishing with the positively charged ion beam, gains an electrostatic charge under the influence of the FIB. This charge is believed
to be the cause of the membrane rising out of the trench and is also responsible for the membrane sticking to the needle. Another
point of interest that is visible in the images on this page is that the membrane is actually still slightly attached to the substrate on
its left hand side. This small attachment could not be cut by the FIB without imaging the face of the specimen, which would do
damage to the membrane. This small strand of material does not pose a problem during the "lift-out" portion of the
specimen preparation technique.
The actual "lift-out" procedure involves the use of a glass needle and a micromanipulator, which is capable of moving the extremely narrow
tip of the glass needle through exceptionally fine motions with a great deal of control. With the use of these items
and a quality optical microscope, these FIB-machined electron transparent membranes can go through the final step before they are
ready to be imaged in the TEM. The TEM specimens are attracted to the glass needle and adhere to it when they come into contact
with it. The needle can then be moved over to a TEM grid, typically made from copper mesh with a thin film of support material coating
it, and the specimen can be transferred to the supporting film. This grid can be put into a TEM and the specimen imaged in much the
same way that any other TEM specimen would be.
|
