Osmium Plasma Coaters
The ultimate coating device for coating SEM samples, especially for FESEM!
Select from these presently available models:
SPI Supplies is the exclusive distributor for the complete line of OPC
Osmium Plasma Coaters originally manufactured by Nippon Laser and
Electronics Laboratory, and then Laser Techno, but as a result of a
corporate restructuring, the manufacturing unit is now being done by Filgen,
Inc., an important and respected scientific instrument manufacturer in Japan.
This is a new and innovative concept for the deposition of fine structureless and
featureless thin film coatings on surfaces for applications in electron
microscopy, especially for those who are using a FESEM. We are honored to
have been selected first by Nippon Laser, and then by Laser Techno, and more recently
by Filgen to be the exclusive worldwide distributor (outside of Japan) for
this exciting new family of instruments. Most of the worldwide network of
agents and distributors of SPI Supplies have service departments set up to
service electron microscopes and vacuum evaporator and sputter coaters, and
servicing an OPC osmium plasma coater is actually easy in comparison to that
of the typical electron microscope.
What is Osmium Plasma Coating?
While "gold coating" in a
conventional sputter coater used in SEM laboratories is quite acceptable for users with
conventional SEM's, it seems clear that for those fortunate enough to be owners of a
new (actually any) FESEM, which of course has far higher resolving abilities than non-field emission SEMs,
in order to actually achieve the resolution of their instrument on nonconductive samples, they
have to do something about the grain size of the gold. After all, it is not possible to achieve
resolution finer than the size of the grain of the gold metallization. And that is the
main driving force for the popularity of coating systems offering the promise of a smaller grain size.
For example, in North America, leading researchers found a number of years
ago that a chromium coating exhibited substantially smaller grain size than
what would have been possible for sputtered gold. Ion beam sputtering (IBS)
offered another route to a smaller grain size. Unfortunately, even with
these reduced grain sizes, the grain is still resolved in a typical FESEM
and in the case of chromium, the metallization oxidizes so fast, it is a
challenge to get the sample into the SEM before it starts to oxidize and
become nonconductive. And of course, for a chromium coated sample, there is
no such thing as a "second look".
The advantage of a thinner coating thickness:
With conventional sputtering processes, the thickness must reach some
thickness before there is conductivity. Depending on whether one is using
gold or any of the other mentioned methods, the coating thickness still
tends to be minimum ~ 20 nm or higher. And with a thickness of that level,
there are numerous important features that are just being covered up. But
with the OPC osmium coaters, one achieves conductivity at a thickness of
slightly under 1 nm. One ends up being able to "see" all kinds of features
that would otherwise be getting covered up by a sputtered coating.
See our video ease use and over view of operating.
Shortcomings of chromium coating:
Chromium, as a coating, suffers from two major drawbacks for the FESEM application, and while not
normally found in the literature of those who manufacture such coating devices we would like to list them below:
- Virtually no shelf life for a chromium coated sample chromium since chromium metal starts to oxidize almost
immediately to a very nonconductive oxide. While one might contemplate storage of important
specimens in dry oxygen free environments, the fact is that chromium metal, in this form,
seems to want to oxidize no matter what is done to it. So the rule of thumb for chromium
coated samples pretty much is to "coat and look" almost as one operation. And there is no
such thing as going back to take a "second look" since that would require a second coating
resulting in a much thicker overall coating, and running the real risk of
covering up important structure that would otherwise be seen.
- The grain size of chromium is certainly greater than zero simply meaning that while the
grain size of sputtered chromium is far smaller than that of gold in a conventional gold coater,
the fact is that there still is a measurable grain size. Of course the degree to which this
grain size is a problem for any particular user would depend on what kind of resolution they are
trying to achieve.
- The minimum thickness of an electrically conductive sputtered
chromium coated surface is greater than 10 nm and some report even larger
numbers. This compares with the minimum electrically conductive coating of osmium
when deposited in the OPC coaters of slightly less than 1 nm.
As if this was not enough reason to seriously consider the osmium plasma coating alternative,
we do encounter at trade shows, on a regular basis, FESEM users who turn out to be using
conventional gold sputter coating systems. But upon further questioning, they are using the
gold for low magnification work that without the gold coating, lacks the kind of contrast one
has come to expect in an SEM image. So if you are one of those FESEM users who finds their
work does not require the ultra-high resolution that is normally associated with of a FESEM, then the osmium
coater might not be for you.
But if you are one who does push the limits of resolution of your FESEM, and are working on
nonconductive samples, or even low atomic number conductive samples, and are disappointed
with the lack of meaningful contrast (which happens more often than not), then you would definitely
be a good candidate for an osmium plasma coater.
There are also certain specific applications, not even necessarily at high magnification, such
as immunogold tagging of cells and
BSE imaging, or the examination of certain difficult
to coat (with gold) samples, such as polytetrafluoroethylene (e.g. PTFE)
or surfaces with thin lubricants (e.g. storage media, hypodermic syringe needles, catheters), then osmium
plasma coating often times does what gold can not do, namely, one can coat with osmium with out the
artifacts normally associated with gold deposited layers
There are also reports that the virtually zero heat contribution due to the operation of the
plasma makes possible the coating of otherwise unstable explosive particles that absolutely
could not be coated any other way.
So if you are experiencing any of the above mentioned problems, or are just unhappy with your
ability to get artifact-free coatings on the samples you are studying, even if with a
conventional SEM and at low magnifications, then one of the OPC systems is almost certainly
going to be worthy of your serious consideration.
Standard osmium tetroxide ampoules, specially sized to fit into the detachable reservoir on
the front of the unit. From a 0.1g ampoule, the number of actual runs one could get would
depend on the thickness being applied, but typically, one could expect to realize 10-15 runs. Note:
Some of the earlier units manufactured by Nippon Laser and now, Laser Techno were produced to take a
slightly non-standard size osmium ampoule. All units sold by SPI Supplies have been
manufactured specifically to accept normal sizes with respect to the starting ampoules.
But isn't osmium tetroxide dangerous?
Well of course it is! But then again, so is gasoline and we don't give a second thought about
getting into an automobile. The innovative design of all the OPC models permits one to install
a normal glass ampoule of osmium tetroxide, into a special holding device which is then tightly
capped. The analogy with the gasoline in an auto fuel tank is almost exact. When the system is
ready to operate, the vapors sublime into the now evacuated and therefore sealed chamber, the
molecule dissociates in the field of the DC glow discharge into its constituent elements, and
osmium is reduced to the metal which literally plates out as a completely amorphous film on the
sample to be coated. Unless there is a really good vacuum in the chamber,
they system absolutely can not be operated.
We would recommend that the system be vented to the outside or else operated inside a fume hood.
However, this might be over kill since many of these systems operate in Japanese laboratories
using only a regular oil mist filter. Our own belief is that any osmium in the tetroxide form
surely would be reduced (to the relatively harmless dioxide) instantly when in contact with the
hot pump oil. But until more is known about the safety issue, we recommend the system be used
only as indicated above.
One further comment: An OPC-40 and more recently, OPC-60A system has operated out in the open
during the running of the Lehigh University "Short Course" on SEM for the past three years. It has received the most
stringent scrutiny of some of the best known users of FESEMs in the world and no one has
expressed concerns about the operation of the system that way. The latest OPC-80T systems have the same identical safety features and interlocks and our
comments for the earlier units would also apply. The OPC-80T coats osmium in the automatic mode but
does other depositions including carbon in a manual mode of operation.
Examples of the superiority of osmium coatings:
Since a "picture is worth 10,000 words", we would prefer to have our
prospective customers see for themselves some
examples of the superior
results that can be obtained relative to sputter approaches. And for those who would
like to see results on a more controlled basis, we can present carefully obtained experimental results
comparing different popular coating methods on clean glass microscope slides.
Publications citing osmium plasma coating
We are starting a list of publications that include results using osmium
plasma coating. If you encounter publications not on this list,
please let us know
so that we can add them to our list.
Is this system "accepted"?
We will admit that we ourselves went into shock when first hearing about a coater
that "coated with osmium tetroxide". But we have become believers. Some of the technical
staff of SPI had extensive demonstrations of the first model, the OPC-40 (predecessor to the
OPC-60 and OPC-80's) at the ICEM in Cancun in August 1998. We were impressed with the fast turnaround time
between samples (relative to chromium coaters that require long pump down times with a turbo
pump). The OPC units use an ordinary rotary vane (e.g. "mechanical") pump. We were further
impressed when the marketing manager of a major FESEM manufacturer said to me that when they
do demos to prospective customers, they prefer to use the osmium coater because, well, they
do a "better demonstration" and have a better shot at making a sale.
Now that might not be sufficiently convincing, however in Japan, where the technology was
developed, more than 100 units of the OPC series have been sold both to FESEM and conventional
SEM users. Indeed, in Japan, there is an overwhelming preference for osmium coating instead
of chromium coating. And at the recently held APEM meeting in Kanazawa, several customers
in Japan expressed the thought "we can't understand why so many users in
North America are still using chromium."
Plasma coating with carbon
The concept of plasma coating when the starting material is a subliming solid is novel and
innovative. The Nippon Laser and Electronics and Laser Techno researchers have found that naphthalene, that also sublimes, just like
osmium, can be introduced into the chamber, and decomposed, again, much the same way as osmium
tetroxide, with the result being an ultrathin carbon coating that is completely amorphous,
and therefore also, structureless and featureless. Where as arc evaporated carbon (e.g. in
vacuum evaporator) is obviously "black", an evaporated film of carbon that has been done in
the OPC system is actually, visually transparent! Yes, we know that this flies against
conventional wisdom, but if the surface being coated is smooth, the deposited film is
transparent. We believe that this unique coating capability for carbon has a number of obvious
and also not-so-obvious advantages over vacuum evaporation deposited coatings. In addition to
the potential to make the world's finest carbon support films for TEM, such coatings are also
completely free of both nanotube and other nanoparticle artifacts that almost always are a
bi-product of arc evaporation in a vacuum evaporator. Unfortunately, with the
standard rotary vane mechanical pump, the carbon coater accessory does not
produce carbon films that seem to be "clean" enough for use as
TEM support films.
But when the carbon is applied to a sample destined for EDS
analysis, the deposited carbon film does exhibit a smaller grain size small
than we have seen with vacuum evaporation. For certain samples, such as
catalysts, nano particles or other nano-features, this kind of property is
To do carbon coating, one needs the Model OPC-80T Osmium Plasma Coater.
Whereas the OPC-60N is an all-automatic coater designed for the automatic
coating only of osmium, the OPC-80T can be operated in the
automatic mode for both osmium and carbon deposition. It can not be
operated in the manual mode. All coating is automatic and the only variable
is the coating time, and therefore the thickness. In the earlier units, there was a manual
mode but the newest models don't have that option.
If this all sounds very complicated, think of it this way: If you
want only an osmium coater and don't care about carbon, consider the OPC-60A
or even the OPC-40 which is still available. But if you want to do carbon
as well, then you really do need the OPC-80T.
How does the price of the OPC-80T compare with that of chromium coater?
Well it is a bit more expensive, but not all that much more expensive. The system does not
need a turbo pump and longer term, the operational and maintenance costs are far lower.
And don't forget that you are getting a superior carbon coater as part of the "package". From
our perspective, many who are purchasing a chromium coater, because of their relatively high cost,
more often than not, since other elements can be deposited in a typical Magnetron head chromium coater,
the costs can be split between the FESEM lab and other groups doing thin film coatings research.
However, a very big trade-off is given up for the SEM lab application and those
who have made this kind of compromise, in the end, never are able to realize
the full capabilities of their FESEM.
But in the case of the OPC-60A, there is only this one application, that is, the SEM laboratory
application and we don't see any comparable opportunity for the sharing of the funding for the
purchase. However, with the new carbon coating capability of the OPC-80T, one can use the
same unit both for coating SEM samples as well as samples to be
analyzed by EDS. We want to stress that in our opinion,
the carbon coating capability is not able to produce films suitable for support films for TEM
Substantiation of the claims being made:
We have provided some typical
examples of the high resolution benefits possible with the OPC family of osmium coaters.
Some will be recognized as extremely high magnification and resolution SEM micrographs whereas
some others offer direct comparisons between osmium plasma coating in one of the OPC systems
vs. conventional sputtering, ion beam sputtering or even chromium coating. We believe some of
these examples and comparisons are quite remarkable because it demonstrates that a conductive
layer is formed at far thinner thickness in comparison to sputtered films, not only of gold but
Model identification terminology:
The "60" in OPC-60A means that the chamber is 60 mm in diameter; the "80" means that the chamber
is 80 mm in diameter. OPC systems for osmium have been delivered as research instruments with
chambers as large as 180 mm. However, for all of the OPC units, the coating thickness has the
kind of uniformity one generally wants in the inner half of the radius. In other words, for the
OPC-80T, the area of uniform coating is confined to a circular area with diameter of ~ 40 mm.
The unique technology embodied in the OPC family of osmium plasma Coater is covered by
United States Patent #5855682: Plasma thin-film forming apparatus which issued on January 5, 1999. It is also covered under a patent
recently issued January 27, 1997 in the European Community (EC), #78952.
Selection of backing pump:
The OPC line of osmium coaters is using a standard hydrocarbon filled mechanical pump.
We recommend the two stage mechanical pump capable of 60 l/min for the OPC-60A and 200 l/min
for the OPC-80T. We suggest a Leybold pump for both systems. Some have asked about using a
scroll pump for this system. While it certainly can be done, the manufacturer generally
recommends that an oil filled pump by used since essentially the oil in these pumps acts as a
gutter for any osmium tetroxide that may have gotten past the reaction chamber.
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