An Investigation Into Beam Damage of Mesoporous Materials

In 1992, researchers at Mobil Research and Development created a new class of porous silicates, most notably mesoporous MCM-41.^2-3 This material features a hexagonal arrangement of linear pores and surface areas in excess of 1000 m² g^-1. MCM-41 exhibits narrow pore size distributions in the nanometer range. The walls of MCM-41 are essentially amorphous silica, but its porous nature makes it about 3 kJ mol^-1 less stable than the collapsed form. Particles of MCM-41 are beam sensitive and it appears that they cannot withstand the large current densities required to obtain reliable analytical data at the nanometer scale in the transmission electron microscope (TEM). For example, low beam currents were used to preserve the pore structure but resulted in energy-filtered TEM elemental maps of oxygen K and Ti L_2,3 edge intensities that were too noisy to reveal structure at 5 nm resolution.