Materials Characterization - Center for Materials Research
Electron Microscopy
The Helios SEM has a Schottky FEG with resolutions down to 0.7 nm at 30 kV or 0.7 nm at 1.0 kV (good for imaging ceramic or non-conductive samples). For materials that are especially sensitive to an electron beam, e.g., most polymers, a bias can be applied to the stage to reduce electron landing energies, improving imaging on these surfaces. An immersion mode is included for higher resolution of nano particles and sub-micron structures on surfaces. The Helios contains five separate detectors for imaging with electrons and ions for enhanced contrast of materials during imaging.
The X-FEG system combines the benefits of high total current, long-term stability and long lifetime with the high brightness values of a cold FEG. All without the increased vacuum requirements or tip-flashing. The X-FEG delivers about five times the beam current of a standard Schottky FEG while keeping the convergence angle small. This provides improved signal-to-noise ratio in STEM and EDS/EELS and improves spatial coherence for holography and HRTEM applications.
Optical Microscopy
Surface Analysis
The surface area and pore size of a material can be estimated using a Quantachrome Nova 4200e analyzer. In practice, the sample is degassed in a glass cell and then small amounts of gas (typically N2) are admitted, in steps, into the evacuated sample chamber. During this step gas molecules stick to the surface of the solid and form a thin layer. The number of molecules required to cover the adsorbent surface with a monolayer of adsorbed molecules can be estimated, and the surface area calculated, using the BET (Brunauer, Emmett and Teller) method.
The addition of gas beyond the monolayer formation will cause the equilibrium adsorbate pressures to approach saturation and pores will completely fill with adsorbate, what will produce an adsorption isotherm. By measuring the volume of gas absorbed by the material across a range of preset pressures, the pore sizes could be computed from equilibrium gas pressures using diverse methods. Knowing the density of the adsorbate, the volume it occupies and hence the total pore volume of the sample can be estimated.