A neutral matter-wave microscope (NEMI): Design and setup
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Matter wave microscopes such as electron microscopes or helium ion microscopes are vital tools in numerous fields of sciences. This thesis presents the design of a new matter wave microscope using neutral helium atoms as imaging probe. In contrast to the already well established helium atom scattering techniques where information about the surface is obtained through diffraction and spectroscopy analysis, Nemi (short for NEutral helium MIcroscopy) uses a focused beam of neutral ground-state helium atoms to image the surface of a sample. The main advantages which set this technique aside from already existing scanning probe techniques is that the helium probe has a much lower energy (less than 100 meV) for a de Broglie wavelength of less than 0.1 nm and that the helium atoms are uncharged and chemically inert. This means that the Nemi technique is in principle equally suitable for insulators, semiconductors, metals and organic samples provided they are vacuum compatible. The new Nemi technique is also particularly suited for the investigation of fragile samples. The focusing of the neutral helium beam is realized with a so called Fresnel zone plate. As a part of this thesis it is shown, for the first time, that sub-micron focusing with this type of diffraction grating is possible. A complete design concept for the microscope including a detailed evaluation of the expected helium flow rates in the probe beam as well as of the background gas between the vacuum chambers is presented. The functionality and technical design for the different components are discussed. First test results characterizing the probe beam of the assembled beam column are presented.