Quantitative Automated Object Wave Restoration In High Resolution Electron Microscopy

Quantitative Automated Object Wave Restoration in High-resolution Electron Microscopy

Advances in Imaging and Electron Physics

The invention of the electron microscope more than 70 years ago made it possible to visualize a new world, far smaller than anything that could be seen with the traditional microscope. The biologist could study viruses and the components of cells, the materials scientist could study the structure of metals and alloys and many other substances, and especially their defects. But even the electron microscope had limits, and truly atomic structure was still too small to be observed directly. The so-called "limit of resolution" of the microscope was well understood, but attempts to use the necessary correctors were unsuccessful until the late 1990s. Such correctors now equip many microscopes in Europe, the USA and Japan and the results are extremely impressive. Moreover, microscopists feel that they are only at the beginning of a new era of subatomic microscopic imaging. In the present volume, we have brought together the principal contributors, instrument designers and microscopists to discuss this topic in depth. First book on the subject of correctors Well known contributors from academia and microscope manufacturers Provides an ideal starting point for preparing funding proposals

Quantitative Automated Object Wave Restoration in High-Resolution Electron Microscopy

The main problem addressed by this dissertation is the accurate and automated determination of electron microscope imaging conditions. This enables the restoration of the object wave, which confers direct structural information about the specimen, from sets of differently aberrated images. An important member in the imaging chain is the image recording device, in many cases now a charge-coupled device (CCD) camera. Previous characterisations of these cameras often relied on the unjustified assumption that the Modulation Transfer Function (MTF) also correctly describes the spatial frequency dependent attenuation of the electron shot noise. A new theory is therefore presented that distinguishes between signal and noise transfer. This facilitates the evaluation of both properties using a detailed Monte-Carlo simulation model for the electron and photon scattering in the scintillator of the camera. Furthermore, methods for the accurate experimental determination of the signal and noise transfer functions are presented. In agreement with the Monte-Carlo simulations, experimental results for commercially available CCD cameras show that the signal transfer is significantly poorer than the noise transfer. The centrepiece of this dissertation is the development of new methods for determining the relative aberrations in a set of images and the absolute symmetric aberrations in the restored wave. Both are based on the analysis of the phase information in the Fourier domain and give each Fourier component a weight independent of its strength. This makes the method suitable even for largely crystalline samples with little amorphous contamination, where conventional methods, such as automated diffractogram fitting, usually fail. The method is then extended to also cover the antisymmetric aberrations, using combined beam tilt and focal series. The applicability of the new method is demonstrated with object wave restorations from tilt and focal series of complex inorganic block oxi.