Application of the ESEM technique in wood research: Part I. Optimization of imaging parameters and working conditions

A study using the ESEM (Environmental Scanning Electron Microscopy) technique was performed on wood objects in order to assess the particular advantages, possibilities, and limitations of this microscopic tool. In contrast to conventional high vacuum SEM, in ESEM specimens can be investigated in a gaseous atmosphere, usually of water vapor. This enables the observation of non-conductive, polymeric, composite, and porous materials (such as wood) in their natural state, without drying, evacuating, or sputtering them with a layer of carbon or metal. Further advantages include observations in a wide range of temperatures (-15° to 1000°C), conduction of dynamic processes such as condensation, freezing, and thawing of the specimen during observation, or mechanical testing. The imaging quality of ESEM for natural samples, however, is inferior to that of conventional SEM, and the specimens are liable to beam damage. The process of acquiring an image in ESEM is more complex than in SEM, demanding the optimization of a number of interacting parameters. These include the physical conditions of the specimen, conditions of the chamber environment, and electronic parameters of the formation and optimization of the image. The work on the ESEM can be performed throug h several operational modes that offer various sets of environmental and imaging conditions. This article presents guidance for assessment of influential operating parameters and their selection for the optimization of the ESEM work with wood.