Cleaned with Xylene

“Like Dissolves Like“

Cleaning with Xylene Warnings

Xylene is a non-polar, organic solvent that has a benzene ring and 2 methyl groups. Benzene has only the benzene ring which is considered cancerous with long exposure.
By comparison to benzene, xylene is safe to use but not ingest. The body can degrade xylene and expell it from the body as an acid.
Because we never know what type of contamination is on a surface, sample cleaning with solvents, can be a trial and error experiment that involves using the XPS as the detector.
Cleaning a metal, ceramic, inorganic, or silicon wafer surface with an organic solvent, such as Xylene, will normally remove non-volatile polar organics and non-polar organics.
Xylene is not volatile at room temperature so it does not evaporate into the air, unless it is heated on a ceramic topped hotplate in a vacuum hood.
Xylene does can dissolve various greases and waxes that other organic hydrocarbon solvents can not. Warm xylene is very useful for this.
Sometimes Xylene is partially absorbed by organics, making the surface pliable. This causes outgassing time in the load-lock.
Xylene might be effective to remove some organic alcohols, esters, ketones or acids.
To remove organic alcohols, esters, ketones or acids, you usually need a semi-polar or polar solvent such as EtOH, CHCl3, methylene chloride or such..
Xylene acts a bit like an non-polar organic and is useful to dissolve sharpie ink from solid surfaces.
To learn more about which solvent is best you will have to explore and ask what is the most likely chemistry on the surface that you will analyze.
At the bottom of this page there are 4 tables showing the increase in polarity of organic solvents.

Book Series for Surface Cleaning Methods
“Developments in Surface Contamination an Cleaning”, Volumes 1-8, edited by K.L. Mittal and R. Kohli, Published by Elsevier In, 2008

This series of books contains extensive information about the nature of surface contamination and methods useful to clean surfaces. There are many ideas, lists of measuring equipment, and methods that apply to different material classes. Chapter 11 in Volume 1 is titled “Cleaning with Solvents (pages 479-577) has the information most relevant to cleaning surfaces before analysis by XPS.

Cleaned with Xylene Notes

Xylene is a non-volatile, but still flammable solvent.
Xylene often contains large organics unless it has been distilled and kept dry using some drying agent.

Cleaning with Xylene Method

Xylene, due to its non-polarity, can not dissolve inorganic materials.
After determining that Xylene will not harm your sample surface, then we must choose a method for the cleaning.
The surface can simply be spraying Xylene from a clean squirt bottle on both the back and front sides of the sample using as much as 50 ml of distilled Xylene.
The Xylene should be captured in a beaker and then discarded in a waste solvent can filled with only organic solvents to be sent to disposal.
In a different method, the sample can be immersed in a beaker or a flask with foil covering the top with 100 mL of Xylene. If possible use a magnetic stirrer to agitate the solvent for 1 hour.
Using clean tweezers, remove the sample and spray with a few mL of distilled Xylene, then cover sample with loose piece of aluminum foil on top of a clean cloth to dry.
Most volatile solvents, still trapped on the sample, will be pulled into the vacuum of the roughing pump attached to the XPS load-lock, but not all.
Solvents, such as xylene, are pulled into the roughing pump and are eventually expelled from the pump exhaust which should be vented to outside or some trap.

Cleaning with other Solvents

At the bottom of this page there are 4 tables showing the increase in polarity of organic solvents.
Other solvents can be used to clean the surface of your sample, and you should match the polarity of the solvent to the contaminants that you hope to remove.
It is often useful to start with a non-polar solvent and move to a semi-polar solvent followed by a highly polar solvent if you want to remove most of the organics.
It is possible that the organics you are trying to remove, are firmly chemically bonded to an oxygen or metal atom at the surface. These can not be removed with solvents.
Organic solvents can only remove non-volatile organics that are not chemically bonded to the sample, unless you first rinse with a mild acid or mild base solution.

Organic Solvent Polarity Index Tables

In Organic Chemisty Lab, chemists are taught that

“Like Dissolves Like“

This means that more polar solvents are useful to dissolve more polar contaminants, and
that less polar solvents are useful to dissolve less polar contaminants.
With this in mind, you can, to some degree, selectively remove different types of surface contaminants.