Sample Mounting and Preparation Considerations Surface Analysis Facility (SAF)

 

Sample Size.

In general, if you have the luxury of cutting or preparing your sample prior to analysis, a sample size of 1 cm by 1 cm by 1 to 2 mm thick is ideal. Thinner or thicker samples can also be accommodated, although samples much thicker than about 1 cm are difficult to mount and insert into the instruments. A circular sample disk of 1 cm diameter is also ideal, with the same 1 to 2 mm thickness as for a square sample. Samples do not need to be square or circular. Smaller sample sizes can also be accommodated, as long as it is possible to physically hold and manipulate the sample with forceps.

Conducting versus Non-conducting.

It used to be the case that non-conducting samples could not be analyzed routinely by XPS or TOF-SIMS. Now any sample can be analyzed, and non-conducting samples are possible to analyze because both instruments use a low-energy electron beam to "bathe" the sample and thereby establish a uniform and hopefully steady charge state at the surface. The electrons act to replenish photoelectrons that leave the sample in XPS and ions and ion-induced secondary electrons that leave the sample in TOF-SIMS. It would help if you knew ahead of time whether your sample was insulating or conducting. Non-conducting samples will be mounted beneath a grounded metallic mask with a small-diameter aperture exposing the sample area to be analyzed. This will help ground the sample and expose only a small area of the sample to the ionizing radiation.

Sample Cleanliness.

Remember that your fingerprints on the sample will cause both a serious contamination effect in your analysis as well as sample outgassing problems in the vacuum chamber. Please always handle samples with clean latex or other gloves and avoid touching the face of the sample to be analyzed, even with gloves. Prior to arriving in the SAF, make sure that your samples have been cleaned appropriately and are carried to the SAF in a clean, closed container. If the sample surface is reactive and prone to contamination, it may be necessary for you to load your samples in a glove box or vacuum chamber and transport them to the SAF in a specially designed "vacuum suitcase". This allows the samples to be transferred directly into the vacuum chamber, never being exposed to the ambient atmosphere. Remember, whether your reactive sample is exposed to the atmosphere for a minute or a year, both situations represent more than a billion collisions per site, and so a minute is just as bad as a year, since it is all over in a nanosecond anyway!

Sample Outgassing.

Some types of samples will tend to give off gases in the vacuum chamber, preventing the system from attaining its ultimate low pressure, and possibly never even allowing it to pump down to a sufficiently low pressure to begin the analysis. If you anticipate that your sample may require special handling with respect to this problem, please let us know ahead of time. We may be able to place it into the sample introduction chamber and allow it to pump down overnight prior to a morning analysis.

Being Present for the Analysis.

We strongly encourage you to be present for the analysis. Your chances to learn the maximum amount of information about your sample, with the least amount of wasted time, are greatest when you are present. So save time and money, and learn more while you are at it!

A. If your sample is a solid such as a wafer or other flat, rigid material

B. If your sample is a powder

C. If your sample is a liquid containing dissolved solids that are the object of the analysis

D. If your sample is a liquid and the liquid is the object of the analysis