A method of modifying a sample surface layer in the vacuum chamber of a particle-optical apparatus, the method performed in vacuum, the method comprising: Providing the microscopic sample attached to a manipulator, Providing a first liquid at a first (controlled) temperature, Dipping the sample in the first liquid, thereby causing a sample surface modification, Removing the sample from the first liquid, Providing a second liquid at a second (controlled) temperature, Dipping the sample in the second liquid, and Removing the sample from the second liquid. This enables the wet processing of a sample in-situ, thereby enhancing speed and/or avoiding subsequent alteration/contamination of the sample, such as oxidation, etc. The method is particularly useful for etching a lamella after machining the lamella with a (gallium) FIB to remove the surface layer where gallium implantation occurred, or where the crystal lattice is disturbed.