Aperture device and analyzer arrangement

A method for forming a high pressure between an aperture to a lens system and a sample surface of a particle emitting sample, the lens system comprising a first end at which the aperture is arranged, and a second end at a distance from the first end, wherein the lens system is arranged to form a particle beam of charged particles, emitted from the sample surface, which enter at the first end and to transport the charged particles to the second end,

• wherein the method comprises the steps of
• providing an aperture device, which is attachable to the lens system and comprises an end surface, an aperture arranged in the end surface, a length axis, which extends through the centre of said at least one aperture and is essentially perpendicular to the end surface,
• wherein the method is characterized in that it comprises the steps of
• providing at least one gas outlet at a transverse distance perpendicular from the length axis, being arranged to direct gas into a volume between the at least one aperture and the sample surface,
• attaching the aperture device to the lens system with the end surface facing the sample surface, to allow at least a part of said particles to enter the lens system,
• arranging the sample, the aperture device, and the first end of the lens system, in a chamber and pumping vacuum in the chamber, and
• providing a flow of gas from the at least one gas outlet,
• wherein the aperture device within a distance of less than 10 times the transverse distance, perpendicular from the length axis comprises gas flow constriction surface, to constrain the flow of gas from the volume between the at least one aperture and the sample surface and the gas flow constriction surface encircles the at least one gas outlet and the at least one aperture.