Institute of Solid State Physics


SS22WS22SS23WS23SS24WS24      Guidelines for Master Students

Optimizing the environmental scanning electron microscope for the investigation of wet samples
H. Fitzek
Institute for Electron Microscopy and Nanoanalysis, Graz University of Technology
12:00 - 12:20 Monday 28 September 2015 Hörsaal I, Alte Technik

In environmental scanning electron microscopy applications in the kPa regime are of increasing interest for the investigation of wet and biological samples, because neither sample preparation nor extensive cooling is necessary [1].
Unfortunately the applications are limited by poor image quality. The scattering of the primary electron beam strongly increases and the secondary electron (SE) amplification decreases with pressure and thus the image quality vanishes [2]. High acceleration voltages and beam currents are necessary to obtain acceptable image quality in the kPa regime using commercially available ESEM. Therefore, the advantages of high pressure environmental scanning electron microscopy are significantly reduce, as high acceleration voltages and beam currents lead to beam damage. However, modifications that greatly improve the capabilities of low vacuum SEM (LEO SUPRA 35VP FESEM; pressures up to 133 Pa) have been demonstrated [3].
We present modifications that maintain the advantages offered by pressures in the kPa regime by significantly improving image quality even at low acceleration voltages and small beam currents. Our modifications and experiments were done on FEI Quanta line ESEM (Q200, Q600) and both an experimental evaluation of the improvements and an example of an in situ wetting experiment will be presented. The improvements are achieved by reducing the scattering of the primary beam, through modifications to the pressure limiting system of the microscope, while making sure that ideal operation conditions are maintained for the secondary electron detector, which is done by introducing a new electrode setup for the SE-detector. Furthermore, our modifications make the simultaneous use of the backscatter electron detector and the SE-detector possible. It is worth noting that all modifications are done to exchangeable parts of the microscope and therefore can be immediately applied to any FEI Quanta line ESEM without imposing any restriction on the operation of the microscope or making the operation of the microscope more complicated.
To demonstrate the overall improvements figure 1 shows images of tin spheres on carbon, acquired using water vapor (1500 Pa) as imaging gas, an acceleration voltage of 5 keV, a beam current of 1 nA and a dwell time of 30 µs/pixel.