Cleaned with Methanol (MeOH)

“Like Dissolves Like“

Cleaning with Methanol Warnings

Methanol (MeOH) can cause blindness if you breathe a lot of it everyday, or if you drink a few milliliters of it. It is a useful solvent, but it is flammable.
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 Methanol, will normally remove most of polar organics as long as the polarities are similar.
Methanol does not dissolve non-polar organics (such as plasma residues, or various photoresists).
Sometimes Methanol is partially absorbed by organics, making the surface pliable. Some polymers dissolve in Methanol, but many do not. This causes outgassing time in the load-lock.
In contrast, non-polar solvents such as hexane or xylene are normally effective to remove non-polar organics such as wax or grease.
Non-polar solvents (hexane, toluene) are not effective to remove organic alcohols, esters, ketones or acids.
To remove organic alcohols, esters, ketones or acids, you need a semi-polar solvent such as IPA, chloroform, or methylene chloride.
MeOH is almost as polar as Water. EtOH is less polar because it has an extra carbon. IPA starts to act like an non-polar organic but 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.

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 Methanol Notes

Methanol is very polar and behaves a lot like water. Ethanol is less polar.
Methanol is highly volatile and flammable solvent. Keep away from hotplates.
Methanol is a very highly polar organic solvent that dissolves a few polar organic contaminants and some inorganics.
Methanol normally contains some water unless it is freshly distilled and kept dry using some drying agent.
To avoid adding a new type of a viscous polar contaminant to the surface of your sample, you should freshly distill your Methanol and all other solvents.
Silicone oil which is a very common contaminant might be trapped in your bottle of Methanol, which is one important reason to freshly distill the Methanol.

Cleaning with Methanol Method

Methanol, due to polarity, has a modest ability to dissolve some inorganic materials so you need to test a spare sample before using it on the main sample.
After determining that Methanol will not harm your sample surface, then we must choose a method for the cleaning.
The surface can simply be spraying Methanol from a clean squirt bottle on both the back and front sides of the sample using as much as 50 ml of distilled Methanol.
The Methanol 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 aluminum foil covering the top with 100 mL of Methanol. 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 Methanol, 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. This includes water of hydration.
Water of hydration can take 30 minutes or several hours to finish ougassing from inorganic powders or other porous materials (sieves).
Solvents pulled into the roughing pump are eventually expelled from the pump exhaust which should be vented to outside or some trap.

Cleaning with other 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.