1/9/97

Is there a best way to clean the specimen holder on the TEM? How do most people

clean their holders?

Linda.Iadarola@quickmail.yale.edu

Linda Iadarola

Dear Linda,

We put our stage tips in a plasma cleaner for ~20 min. That seems

to get the petrified grease off, and the method can be used on all tips,

not just those constructed of a single piece of metal. It works on our

tilt-rotation tip (mostly aluminum), our double-tilt tip (mostly stainless

steel) and our aperture holders (phosphor bronze).

Yours,

Bill Tivol

tivol@wadsworth.org

Linda Iadarola requested information on cleaning TEM specimen holders. A

commonly used technique is to polish with a metal polish such as Wenol or

Pol then either wipe or rinse in methanol. Extreme care does need to be

taken to avoid trapping the polishing paste in the crevices of the holder.

Also, depending on the type of specimen holder, ultrasonic cleaning must

NOT be used since the potential exists to weaken or break epoxy bonds

(particularly in the case of cyro holders).

Another possibility is to plasma clean the holder. Most of the

contamination resident on holders is organic (hydrocarbon). An air or

oxygen/argon plasma is quite effective in reducing this contamination. The

plasma creates disassociated oxygen which chemically combines with the

carbonaceous material and reduces it to CO, CO2 and H2O. Depending on the

ion energies used, cleaning can occur without adversely effecting the

specimen holder.

Should you have any further questions, please do not hesitate to e-mail me

directly.

Best regards,

Paul E. Fischione

E.A. Fischione Instruments, Inc is the manufacturer of the Model 1400

Plasma Cleaner.

Paul.Fischione@internetmci.com

I normally use Q tip with a little bit of Wenol to clean the holder first.

Then use Kimwipes to rub over entire surfce. Sonicate the holder in the

acetone bath for 10 min and once again in the fresh acetone bath for

another 10 min. After that use air gun to dry it. That is all I do.

Ming H. Chen, PhD

Medicine/Dentistry Electron Microscopy Unit

University Of Alberta.

Edmonton, Alberta, Canada

Don't :)

No part of a specimen holder that goes into the vacuum of a TEM needs to

be, or should be touched by dirty fingers (or anything else). If you follow

appropriate handling procedures, in the majority of cases, holders do not

need cleaning.

They may often 'look dirty' but this is usually some sort of oxidation and

doesn't cause any problems in the TEM. Unless a particular specimen rod is,

without question, causing contamination problems when you do microanalysis

or microdiffraction, and the problems really are only apparent with that

specific rod, then 'if it ain't broke, don't fix it'.

Certainly, there should be no necessity for a regular cleaning routine and

in general, I have never cleaned holders for which I have had

responsibility. The only exceptions are the external O-ring seal on the

barrel and the jewel bearing on the tip.

Having said that, problems do occur. Simple holders (single tilt) can

usually be cleaned successfully by ultrasonic in a solvent, rinse in

distilled water and warm air blow dry. However, more complex holders may be

almost impossible to clean fully - it is difficult to fully penetrate all

the crevices and internal spaces effectively and solvent/ultrasonic may

weaken or damage expoxy joints and seals. Plasma discharge is pretty

effective, but again is unlikely to fully penetrate internal spaces -

although if you have serious contamination in an internal space then

whoever is responsible probably needs introducing to a few of life's

realities - try to find an old HT tank for them to clean!

Whatever the problem, don't use wehnol or similar abrasive metal polishes -

if it needs something that powerful to remove the dirt, then it wasn't a

problem to start with - but it may be after you have filled the crevices

with metal polish.

Minor contamination of holder tips by specimens can sometimes be a problem.

Usually, this can be cured by leaving the holder, without a specimen, in

the TEM contiuosly for a long period - say a weekend - and it will pump

clean.

The only exception to all the above is cryo-holders. They frequently get

horribly dirty. Often, however, it is only the tip region that is the

problem. If you don't have access to a suitable plasma system, then just

the tip can be suspended and ultrasoniced in a solvent - also, check with

the manufacturer regarding cleaning. You may find that you have to start by

removing the worst with wooden cocktail sticks. You will avoid the worst

problems if you can get users to remove specimens from the holders while

still frozen.

Regards,

Larry Stoter

Dr L. P. Stoter Technical Editor, MICROSCOPY & ANALYSIS

Technesis

17, Rocks Park Road email: LPS@teknesis.demon.co.uk

Uckfield, E. Sussex Phone: +44 (0)1825 766911

TN22 2AT Fax: +44 (0)1825 766911

United Kingdom

Can Be cups be cleaned in plasma systems without damage?

Kenneth JT Livi

Department of Earth and Planetary Sciences

34th and Charles Streets

The Johns Hopkins University

Baltimore, Maryland 21218

klivi@jhu.edu (e-mail)

Dear Ken,

Yes. I'd be careful where the pump exhaust is vented, however.

The presence of Be dust in the exhaust is a possibility (at least in

theory), and that is *very* toxic. The particles would likely be in the

submicron range, and therefore easily inhaled. I'd think it unlikely

that a Be cup with a smooth surface would be etched too readily. Does

anyone else on the list have other info?

Yours,

Bill Tivol

tivol@wadsworth.org

There are many reasons for NOT using grease-base polishes for cleaning

parts to be inserted into the interior of high vacuum sysstems (See Vacuum

Methods in Electron Microscopy, Portland Press, pp. 69-74). Basically,

this is the equivalent of taking a bath in a mud puddle. One principal

reason for cleaning is to remove hydrocarbon materials from the surfaces of

the parts, and so it makes no sense at all to use a greasey material to do

the job. In addition, as noted by others, the grease and abrasive materials

are likely to get embedded in cracks and crevice and then not be completely

removed, whereupon they will act as a very effective source of

contamination.

Very effective cleaning can usually be accomplished simply by

thoroughly scrubbing with one of the many modern detergent solutions

formulated for use in the electronics inductry (see above reference) or

with Tilex Soap Scum Remover (available in most supermarkets), rinsing with

running hot tap water, ultra sonic treatment in a warm detergent solution,

rinsing again with hot tap water, rinsing with reagent grade isopropyl

alcohol, and drying with a gas blaster. If you find you need an abrasive

in the initial stage to remove stubborn deposits (or if you feel you must

enhance the surface finish) try using a bit of Comet Cleaner (the kind

formulated for use on plastic tubs and showers, which wont seriously

scratch most metals) and then rinsing with hot water, before the initial

scrubbing step. This procedure involves no solvents other than water and

isopropyl alcohol (a common constituent of rubbing alcohol, and therefor

perfectly safe to use) and so no expensive or complicated safety procedures

are necessary, and it usually does the job quite nicely.

The Tilex Soap Sum Remover will even remove silicone oils from most

metal surfaces, and I have also used it to remove spots of various kinds

from clothing, grease spots from carpets and auto seat covers, and

semi-dried paint from my hands after painting. Needless to say, it works

great for its intended purpose of cleaning bathtubs, wash basins, shower

curtains and shower tiles. (No commercial interest, it is just very handy

stuff to know about)

W. C. Bigelow (bigelow@umich.edu)

Wilbur C. Bigelow, Prof. Emeritus

Materials Sci. & Engr., University of Michigan

Ann Arbor, MI 48109-2136 e-mail: bigelow@umich.edu;

Fx:313-763-4788; Ph:313-764-3321

This is a rather important process that should be done very carefully. I

devoted several pages to discussing methods for cleaning parts for vacuum

systems in my book 'Vacuum Methods in Electron Microscopy' p.69-74.

If you are using the standard top-entry type of holder, cleaning

should be straightforward - scrub it thoroughly with Tilex Soap Scum

Remover, rinse with hot running water, sonicate in a strong detergent

solution, rinse with hot tap water, rinse with reagent grade isopropyl

alcohol, dry with a gas blaster.

If you are using a side entry stage you can use essentially the same

procedure, but you must then be careful to avoid getting the solutions

inside the holder if it is one that has provisions for manipulating the

specimen. Often, enough cleaning can be done to get rid most contamination

problems by sonicating just the end of the holder in isopropyl alcohol,

then drying with a blaster. The latest method for these holders is Plasma

Discharge Cleaning, and Southbay Technologies markets a device that is

specially designed for this purpose.

W. C. Bigelow (bigelow@umich.edu)

Wilbur C. Bigelow, Prof. Emeritus

Materials Sci. & Engr., University of Michigan

Ann Arbor, MI 48109-2136 e-mail: bigelow@umich.edu;

Fx:313-763-4788; Ph:313-764-3321

I would like to further the discussion on plasma cleaning, the need to

clean specimen holders, and cleaning Be holder components. In the past I

have found it extremely beneficial to pre-clean the TEM specimen holder

from the vacuum o-ring to the tip. Although no one admits to touching the

specimen holder, it does occur. In fact, after a few minutes of plasma

cleaning, fingerprints become quite apparent on the specimen holder. I've

also seen o-ring grease wind up on the shoulder of the rod.

In addition, specimen holders are often times stored in less than ideal

conditions and surface contamination becomes inevitable. A recommended

solution is to store the specimen holder under vacuum (oil-free) when not

in use.

Another cause of specimen holder contamination is from adhesives which

adhere to the specimen holder's clamping mechanism. Plasma cleaning with

the clamping mechanism open is quite effective in removing this

contamination. With the plasma flow being multi-directional, even hard to

access areas of the specimen holder are cleaned.

The Be situation raises a much larger issue when discussing plasma. All

types of plasma are not equal. Depending on the plasma generation system,

high energy (>100 eV) ions can be created. At this level, ion impingement

results in the sputtering of the specimen, specimen holder, plasma chamber

walls, and electrodes, if they too are immersed in the plasma.

The critical need for applying plasma to TEM specimens is to produce a

plasma of sufficiently low energy so that it is below the threshold

required to break a molecular bond (approximately 35 volts). One

acceptable means of generating low energy ions is with a high frequency,

inductively coupled plasma, whereby the electrodes are located external to

the plasma chamber. As long as the ion energy is sufficiently low, plasma

cleaning can occur without the risk of sputtering Be.

We have conducted measurements on the ion energies in our plasma cleaner

and found them to be, under given conditions, in the 12-15 eV range, well

below the sputtering threshold. In this energy range, a chemical reduction

of the carbonaceous material occurs without altering the material's

structure.

I hope that this information is helpful. Do not hesitate to contact me

directly with any specific questions.

Kind regards,

Paul E. Fischione

E.A. Fischione is the manufacturer of the Model 1400 Plasma Cleaner and

Vacuum Storage Containers.

Paul.Fischione@internetmci.com

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