Call ASAP or E-mail the Internal or External XPS Lab to Start Discussing Your Analysis Needs, Goals, and Materials
Before Discussing Sample Submission, Let’s Review Common Surface Contaminants
Nearly every material or sample in the world is contaminated by Adventitious Carbon compounds that are semi-volatile organic compounds composed of Carbon, Oxygen, and Hydrogen. It is the most common contaminant. The thickness of Adventitious Carbon ranges from 1-5 nm depending on dielectric nature of the surface. XPS does not detect Hydrogen.
Adventitious Carbon is one of many Air-borne Molecular Contaminants that include air-borne inorganic particulates and gases such as: sulfates, halides, ammoniates, acids, sulfides. Silicone oil is the second most common contaminant in the world. There are thousands of sources of silicone oil. Silicone oil (PDMS) and similar silicone greases very easily and very quickly spread across the surface of most materials. Silicone oil contamination very often causes many different problems to basic research and industrial manufacturing. Silicone oils that cause severe problems are often present as a minor contaminant appearing as a small XPS peak labelled as “Si (2p)” with a Binding Energy near 102.5 eV.
Describe ESSENTIAL Goal of Analyses ?
- Determine surface chemistry?
- Determine bulk chemistry?
- Find contamination on surface?
- Compare A to B sample?
- Start Quality Control program?
- Learn why material has color change?
- Determine if supplier gave wrong sample or material?
- Measure thickness of contamination?
- Perform Depth Profile?
- If depth profile, then how thick are the top layers?
- What elements are expected?
- Is any layer non-conductive?
- If fast turn time is needed, then get a PO today ASAP
- Be sure to give your name, company name, and email
Prior to XPS Analysis
Do NOT Analyze Area of Interest by SEM-EDX or Auger Prior to XPS Analysis
To measure the true surface chemistry from your material or product, the region of interest to be analyzed by XPS must NOT be exposed to any electron beam methods, such as SEM-EDX or Auger.
The area of interest for XPS analysis must not be analyzed by ToF-SIMS if the ToF-SIMS analysis time is more than 4-5 minutes. SEM-EDX, Auger, and ToF-SIMS provide nice images, but they degrade the true chemistry of the surface regions that you want to analyze by XPS.
Why?
SEM uses a 1-25 kV electron beam that causes low vacuum gases to break into reactive atoms or molecular fragments which contaminate or react with the surface which was just activated by the electron beam wherever the electron beam strikes the sample. This is why you see Squares or Circles on samples because this is where the beam irradiated and paused at the edges or center more than it irradiated the middle region. The electron beam can cause carbon contamination that is thick enough (several nm) to hide the true surface contamination.
Please note that SEM-EDX element information is mainly due to bulk chemistry. Only at very low KE will SEM-EDX give you near surface chemistry. XPS gives chemistry from top 1-12 nm, but normal EDX at 5-10 kV gives chemistry from 0.5 – 2 microns (2,000 nm) below the surface.
ToF-SIMS is even more surface sensitive than XPS. ToF-SIMS gives information from the top 1-3 nm. ToF-SIMS normally does not degrade the surface as long as the analysis time is less than 4-5 minutes.
Auger (AES) is also more surface sensitive than XPS. Auger gives information from the top 1-5 nm. Unfortunately, the electron beam in Auger will do more damage than the SEM-EDX due to the much higher current of Auger electron beam.
When discussing Goals and Needs we need to understand the nature of your problem, your goals, and can work with you to develop a plan of action for analysis. Be certain to identify the region that will be analyzed by using a 500 micron X-ray beam by using a carbide tip to scribe a circle around the feature or region of interest, or use a Sharpie marking pen. Label the sample package with the name of the sample.
NOTE: Please ask your Purchasing Department or Supervisor to issue a Purchase Order # as soon as possible. Some purchasing departments are very strict that PO# is required before shipping samples.
Guidelines
The XPS Lab needs to understand the expected surface chemistry and the final chemical or physical treatment applied to your sample.
- A photo of the sample with a ruler is very helpful.
- To avoid contaminating the surface of your sample, never touch area to be analyzed.
- Never touch with gloves.
- Never analyze area for XPS analysis to be analyzed by SEM-EDX or Auger because high kV electrons often cause contamination or degradation.
- Never place sample inside a plastic bag or a moulded plastic box due to presence of silicone oil or erucamide slip agents inside the bag or box.
- Use Polystyrene, PET, PETE, and PP boxes with sharp square corners. They are clean.
- It is best to wrap sample in either aluminum foil (UHV or kitchen grade) or a paper or manila envelop.
- Handle samples by their edges.
- Most cheap gloves are dirty. Some new nitrocellulose gloves are clean. You might want to test your gloves for transfers. Some gloves have powders inside the glove that spray out when you put the glove on.
Handling, Packaging, Size, Mounting, Labelling, Storage, and Treatment
Most gloves have silicone oil !!! Silicone oil very easily and very quickly spreads across most surfaces. Surface of sample must never be touched with any kind of glove. Label the sample package with the name of the sample. Please wrap sample inside Aluminum foil or place inside paper envelop. Do not place samples in plastic bags or moulded boxes (they often have silicone contamination). Most materials have low level surface adventitious carbon contamination that is due to production, handling, air-borne organics, or storage. Carbon contamination can also occur by physical transfer contact to some equipment or tool that has adventitious carbon on its surface.
Large samples will be cut, broken, or cleaved so that several samples fit on sample stage.
Largest diameter size: 75 mm (even so, the XPS lab may break or cut the sample down to 25 mm)
Tallest sample size: 25 mm (5 mm if instrument uses a magnetic lens)
Sample will be analyzed in the “as-received” condition, unless you request surface treatment (ion etch, solvent cleaning). Label the sample package with the name of the sample.
Be sure to label each sample with a name or number. Use sharpie or carbide scribe. If possible, please send photos of samples next to a ruler by email. XPS can also measure true bulk chemistry after the solid sample has been broken or cleaved. Powders will be pressed onto foil using clean spatula. Powders will be lightly ground to expose bulk chemistry.
Outgassing samples will be reduced to minimum size to minimize wait time in loadlock. Max wait time with no cost: 30 minutes. Samples will be trapped on the sample mount by a clip, double sided tape, or graphite paint. Samples will be returned to you. Graphite fibers must be cut to fit and taped down
What names do you want to use to identify samples and spectra?
Use Carbide Tip to Scribe a Circle around area to be analyzed by 500 micron X-ray beam.
Write the name or number of the sample on the outside of the foil or envelop.
Without a Purchase Order # Your Work May be Delayed
Your purchasing department might require you to obtain a Purchase Order # before analysis can be started. If you can not wait for PO#, then use a company credit card and send card details verbally.