UC Santa Cruz

With the advent of aberration corrected electron microscopy, the need for ultra stable power supplies for controlling the currents in magnetic lenses becomes one of the limiting factors in attaining atomic resolution. When we talk about resolution and depth of the field it is always assumed that all the components of the microscope are perfect and will focus the light/electron from any point on the object to a similar unique point in the image, but this is not the case because of the lens aberrations and diffraction. Unlike light optics, where lenses are used to refract and bend light rays for image formation, in electron optics magnetic lenses are used to do the same thing. Magnetic force is used to change the direction of electrons in the same way that a lens changes the direction of light rays. Therefore one of the limiting factors of resolution in electron microscopy is variation of the current that creates the magnetic field. With the advancement in lowering aberrations in electron microscopic lenses the need for higher stability in the lens current supplies becomes paramount. In order to achieve resolution of 0.5 angstrom level or better we need current supplies that are stable up to 1 part in 10-8. In this work, the aim is to design a high stability current supply capable of producing 1 Amp of current within 0.01 parts per million (ppm) of stability for electron microscopy. In this thesis, an ultra stable current supply was designed and simulated. The stability of the current is 0.0086 ppm/OC, over 15 minutes which is within the range that is required for this design.