Low vacuum SEM

Method Specification

Low vacuum (LV) or variable pressure (VP) scanning electron microscopes are a group of special SEMs used mainly for uncoated nonconductive and soft materials. The SEM chamber’s vacuum can be varied by the introduction of gas molecules such as H2O or N2 at levels of 20-2000 Pa (the exact values depend on the instrument). The gas interacts with the electron beam and forms cations that neutralize the excess electrons that accumulate on the sample’s surface, thus preventing charging effects. SEM imaging under low vacuum conditions requires special detectors that are designed to collect the emitted signal under the varying vacuum and gas levels. The image resolution can vary with the gas characteristics (chemistry and pressure) as well as with the accelerating voltage. LV and VP SEMs are very useful for imaging of organic and inorganic materials that are not conductive and cannot be coated as well as for outgassing samples. LV and VP SEMs techniques are applicable both for material science and life science samples.

SEM in situ reactions - in some special cases the environment in the SEM chamber can be changed to other gases for the purpose of in situ synthesis, for instance N2:H2 95:5 can be used as carrier gas or CO2 and air can be also introduced into the chamber for some in situ reactions. Other gases might be checked for use upon request with Thermo Fisher Scientific.

Staff Contacts

Instrumentation

Gemini SEM 500 (Zeiss)
Quattro S- environmental SEM (Thermo Fisher Scientific)