Electron Microscopy Specimen Preparation Laboratory
The equipment in this laboratory is used in the final stages of preparation of
specimens for electron microscopy. Currently we are only supporting preparation of
TEM specimens. The metallography equipment will take care of most of the SEM
specimen preparation but if sputter/coaters are needed they can usually be found in the
facility which offers the SEM services.
Note: TEM specimen preparation is generally difficult and time consuming so you'll want to do everything you can to improve your chances of success. What this means for the average TEM specimen preparation project is a bit of study, a bit of planning, and a modest investment in tools and supplies. Tweezers, specimen carriers and the like are things you will need both here and where ever you take your specimens so you definitely have to purchase your own. Some specialized tools, such as the dimpler tools (wheels), require such a level of care and maintenance that you won't want to share them with everyone else. We recommend that you purchase your own dimpler tools and supplies. Some of the other consumable supplies, such as mounting wax and silicon carbide abrasive, are provided but you'll need to purchase your own diamond slurries and alumina polishing compounds.
Gatan Ultrasonic Disk Cutter
The second step in preparing a specimen for transmission electron microscopy is
the cutting of 3 mm discs from 0.2 to 0.5 mm thick foils. (The first step is making the
foil.) The model 601 Ultrasonic Disc Cutter is used to cut these discs which are later
thinned and polished using dimplers, ion mills and electro-chemical polishers. It employs
a lead zirconate/titanate piezoelectric crystal to vibrate a tubular tool, pressed against
the foil, at frequency of approximately 26 kHz. A water-based hard grit slurry applied to
the tip of the tool combined with the high-frequency vibration erodes away a circular
impression, leaving a 3 mm diameter disc. Both cutting power and load can be adjusted to
maximize tool life and minimize cutting time. In addition to cutting discs from thin foils
this cutter can make cuts as deep as 5 mm, reducing the time spent in the wafering stage
of specimen preparation (making the original thin foil).
Silicon carbide grit, mounting wax and cutting tools are provided.
Gatan Precision Dimpler Grinder
The model 656 Precision Dimple Grinder is used to grind an accurately sized
depression into the surface of your disc. Its main applications are (1) pre-thinning TEM
specimen discs prior to ion milling or electro-chemical polishing and (2) exposing
near-surface concentration gradients for Auger or SIMS depth profile analysis. This
grinder is basically a precision counter-balanced (50 gm accuracy (check this spec))
grinding wheel rotating about a horizontal axis and resting on a specimen platform which
is rotating about a vertical axis. During grinding the wheel is gently lowered onto the
specimen and a sensitive (microns) dial indicator shows the specimen thickness. Grinding
is halted when a preset thickness (down to 5 to 10 microns) is reached. This dimple
grinder is complete with a selection of grinding wheels, specimen platforms and mounting
wax.
Suggestion: You should purchase, use and maintain your own grinding wheels and specimen platforms. This is the only realistic way to achieve the quality and productivity you expect. Also, you are welcome to use any abrasive slurries that are on hand but once again, you should purchase and maintain your own supplies.
VCR Model D500i Dimpler
The model D500i dimpler is a precision electro-mechanical lapping instrument
which has simple analog and digital controls that make this very effective and easy-to-use
dimpler. It continuously monitors and controls dimpling parameters and accurately
terminates at a preset specimen thickness. This automation of the dimpling process makes
it possible to produce very thin specimens (down to 5µm) repeatedly and reliably. In
fact, practically all operations are done via the control panel, minimizing operator
intervention. In addition, dimpling requires very little investment in the way of
supplies.
Supplies: Users are required to supply their own diamond slurry, tools and mounting wax. The tools, at a cost of $55 each, represent an investment but since proper care of these tools is so important and since people's standards for such care varies so much the only way we can guarantee that you have good tools to work with is to ask you to bring your own. Of course, you are welcome to use any tools and slurries that people have left behind.
Struers Tenupol-3 Jet Polisher/Thinner
The Tenupol-3 is capable of thinning TEM specimens to the thickness required
for electron transparency in just a few minutes. It works by applying a voltage and
shooting a jet of an electrolyte at one or both sides of the specimen. The combined
action of the voltage and the jet removes material is such a way that large areas of the
specimen are thinned without introducing any mechanical damage. The variables in
this process are the voltage and current, temperature (-20°C to 150°C) of the
electrolyte and thinning time or the process can be stopped automatically when a hole is
made in the specimen. This system is ideal for metals, particularly single-phase
metals, but it has been used to thin intermetallic materials and ceramics.
Warning: The chemicals used in this polisher are nearly always aggressive corrosives, often unstable, and may spontaneously ignite on contact with organic materials or even when stored properly overnight. You will be required to show how you plan to use, store and dispose of these chemicals before you use this polisher.
Permission: Do not use this equipment until you have discussed your needs with the laboratory's manager. You will be asked to write an SOP for your particular polishing procedure.
VCR Group Maxmill XLA Ion Mill
The MAXMILL XLA/2000 has been designed to execute all of the current techniques
for thinning TEM specimens by ion milling. Available techniques include variable omega
specimen rotation, specimen rocking, high-flux beam currents and glancing ion beam. This
instrument uses three high-flux ion/atom sources which provide both dedicated one-side or
two-sided ion milling using inert or reactive gases. All operations except controlling the
guns’ valves are computer controlled, making the XLA/2000 a flexible and easy to use
instrument for routine and special TEM specimen ion milling.
Important Note: This is a complicated and sophisticated instrument which must be kept in top condition. You will need to study the ion milling process and think hard about how best to use it to thin your specimen. You will also need a specimen which has been thinned to under 10 microns or else your milling times could be quite long. It is important that you minimize milling time because the guns must be cleaned every 200 hours or so (an expensive and time consuming process) plus long milling times will probably end up damaging your specimen.
Division of Materials Science
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Updated on June 25, 2001
Department of Chemical Engineering and Materials Science
University of California, Davis
Davis, CA 95616
USA
Phone: 530/752-0400
Web: www.chms.ucdavis.edu