Sample Handling, Transport & Storage
Good sample handling, storage, and transport methods are vital in surface science as the signals emanating from surface contamination can overwhelm the signals from the sample that originate from the top 5-15 nm of the surface.
Basics of Sample Handling, Accidental Contamination, Transport, and Storage
- Gloves (powder free high quality nitrile or polyethylene) and clean tweezers should be used and any glassware must be thoroughly cleaned before use. Tweezers should be cleaned regularly by sonication in isopropyl alcohol (IPA). Be careful not to use gloves that transfer silicone oil (PDMS) to your tools or sample stage.
- Samples can be stored or transported in clean petri dishes, new plastic dishes (e.g. polystyrene), or clean glass vials.
- Avoid ALL other plastic containers, including plastic sample bags. Many bags and inexpensive plastic boxes have low levels of silicone oil or organics that can contaminate your sample by simple physical contact when placed in long term storage containers.
- Remember: Silicone oil (PDMS) loves to creep across surfaces until the oil has spread a uniform coating.
- A good alternative to plastic or glass containers is new, clean aluminum foil or cellulose paper envelops. A few kitchen-grade foils can be useful, but some have oils.
- In situ sample cleaning by Ar+ etching after analyzing the original (as-received) surface can be used to decrease or remove thin oxide or organic layers but the process of cleaning may cause surface chemical damage. The new Argon cluster guns are slow but useful to remove surface contamination.
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If the sample has been immersed in electrolytes/salt solutions then wash in distilled water and let dry in air.
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Samples with high surface area, high vapor pressure or which have been immersed in liquids will require longer to pump down prior to insertion into the instrument. In general, this type of sample should be inserted into the load lock the previous evening to dry it.
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Samples which are sensitive to oxygen or water vapor should be mounted and loaded into the vacuum transfer vessel in the glove box.
- When you cut, cleave, or fracture a hard sample, then be sure the tool used is clean. Razor blades must be lightly sanded and then wiped with IPA or acetone.
Sample Handling
Handling with Gloves as a Source of Silicone Oil (accidental contamination)
Here is a table that I made 40 years ago, when I was a Demo-Sales Engineer in Tokyo selling XPS and AES instruments. I put on the glove and touched clean aluminum foil, and then analyzed the “no longer clean” aluminum foil by XPS.
Sources of Typical Surface Contaminants (other accidental contaminants)
An Example of Possible Contamination of the Sample Stage
This photo shows the analyst loading a sample stage into a Thermo K-Alpha load-lock. If this type of glove has been tested for Silicone Oil and powders before using this type of glove, then it is acceptable to handle the sample stage. There are only a few types of gloves that do not contain or transfer Silicone Oil to the sample stage. Three that I know of are: old style semiconductor woven Nylon gloves, very cheap crisp poly-ethylene gloves, or expensive nitro-cellulose gloves that are white.
Commercial Cleaning Aerosols can Contaminate – Depositing from the Lab Air !!!
Your sample surfaces, your tools, or your work-bench
These aerosols are used by your cleaning people to clean tables and floors. Some can spray significant silicone oil everywhere.
These data are from survey spectra of Aluminum foil sprayed with the aerosol, allowed to dry, and then analyzed. Al % was removed
Schematic of Natural Surface Contamination and Structure
Common Tools used for Sample Preparation, Handling, and Storage
