XPS/ESCA Sample Handling Guidelines

Asemblon Surface Analysis Lab: Sample Guidelines

The Importance of Maintaining a Clean Sample Surface

Since ESCA/XPS only analyzes the upper 5 to 10 nm of the surface, even low levels of surface contaminants can mask the surface chemistry of interest. Therefore, it is very important to handle and prepare your samples with great care. The following guidelines are given to maximize the chances of getting useful information from your samples.

Sample Preparation

Gloves: Use only polyethylene gloves. Other gloves may contain silicones that can contaminate the surface.
Keep Everything Clean: Make sure everything used to handle or store your samples is clean (tweezers, etc). It is recommended to have a dedicated set of clean tools for handling your samples. In particular take care to avoid grease, oils and silicone contaminants around your tools and work area. Keep your samples in a “clean” environment. A laminar flow hood or a clean laboratory environment is strongly suggested. A general cleaning protocol that often works is to clean the utensils that will handle samples with the following solvents (in this order): Hexanes, Methylene chloride, Methanol, Acetone.
Common Contaminants: Common surface contaminants and their sources include:

Hydrocarbons: Pump oil, greasy finger prints, dirty dessicators, dirty solvents.

Silicones: Non-approved gloves, glass-fitting-grease, dirty dessicators, hair, hand lotion.

Salts: Sodium, chlorine, potassium, can be introduced through improper rinsing or exposure to water that has not been properly purified.

In general avoid using or working around silicone materials if possible. Silicones, such as polydimethyl siloxane (PDMS), are low energy polymers that often contain low molecular weight components that can volatilize and deposit on surrounding surfaces. Since silicones are low energy materials they tend to adsorb onto almost anything and form a thin film on the surface. If there are any silicones near your samples, they will be on your surface and possibly be all that we will see from the analysis.

Use Good Planning and Experimental Design

Controls: It is important to include control samples with the sample(s) of interest. A control could include a sample of just the underlying substrate and/or a sample of the underlying substrate exposed to solvent used for the surface modification without the actual modifying agent. Duplicates: Please send duplicate samples, even if only one is to be analyzed. This will help to minimize delays in the case that samples are damaged during transport or, on a very rare occasion, damaged while loading for analysis. Please Include With All Samples

A Sample Summary: Include a list of the specific samples that are included and what is on them. The more details you provide with your samples, the better we will be able to interpret your data.

Structures: Though unknown samples can be analyzed by ESCA/XPS, it is very useful to know the structure of the desired surface bound species and knowledge of the underlying substrate. Without this information accurate analysis of the data can be difficult.

Sample Size: The Asemblon ESCA/XPS system can accommodate a wide variety of sample sizes and shapes though an 'ideal' sample size is 1 cm x 1 cm (Figure 1). Samples that are too large to fit in the instrument, or that are not able to be pumped down to operating pressures, will have to be cut down in size before analysis. You will be notified before any action is taken if this is necessary with your samples. Make sure you discuss the size and shape of your samples when you inquire about analysis. We have experience with a wide range of sample types and materials and know how to handle and prepare samples for analysis.

Figure 1: ESCA sample holder top view showing the mounting of 1cm x 1cm conductive samples. The sample holder is ~5cm in diameter and can potentially hold samples slightly larger than the holder size. Outgassing: ESCA/XPS is an ultra high vacuum technique. Typical vacuum pressures within the analytical chamber during analysis are around 5 x 10-9 Torr. Materials that are highly porous, "spongy", and that adsorb water or outgas can have trouble pumping down to suitable analysis pressures. In some cases sample outgassing makes it impossible to analyze a set of samples. However, in most cases these types of samples can be run by reducing the size of the samples and/or scheduling an extended pump down time. Please inform us if you know your sample may present a problem in an ultra high vacuum environment.

Sample Shipping

Packaging: Regardless of how you choose to ship your samples, it is recommended that you package them so that nothing touches the surface of your samples. Please note that some plastic bags contain polymer release materials that can contaminate your samples. In general, we recommend packaging samples in tissue culture polystyrene (TCPS) dishes, with lids, with the edges sealed with parafilm. To prevent the samples from rattling around during transport, use a small piece of double sided tape to secure the back of the samples to the bottom of the TCPS dish. It is very important to only stick a small corner of the sample to the tape. If the center of the samples is stuck to the tape or there is tape under the entire sample it can be nearly impossible to remove the samples without damaging them. Please try sticking down a “test” sample and be sure it can easily be removed before packaging other samples. We have shipped many samples without incident and have discovered that only taping a small part of the corner is required to secure most samples (see Figure 2). We recommend using 3M double sided tape for mounting samples. Do not use the double sided tape used for SEM analysis as this often contains silicones that can migrate onto the sample surface. If only 1 side of your samples is treated, make sure you mark the backside so it is easy to tell which side should be up during the analysis.

Figure 2: Only a small piece of tape at the sample corner should be sufficient to fix your samples in place for shipping. Know Your Contact Be sure that you are shipping your samples to the correct address and contact person. The shipping address will be given out once samples have been approved for analysis. Also, inform your contact when the samples are being shipped and when they are expected to arrive. Please only send the samples discussed and approved for analysis. If you have a change in samples or want to send additional samples, they must be approved before shipment to our labs.