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Title: Nanometre structures for electron optics
Author: Ito, Y.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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Manipulation of the phase of an electron wave has been demonstrated by three dimensional nanometer scale solid state diffraction gratings. The diffraction gratings with varying hole depths (three dimensional nanostructures) were created by controlling the dwell time of an electron probe. The gratings were directly made by using the computer controlled electron probe (diameter < 0.5nm) of a dedicated scanning transmission electron microscope (STEM) with a 100keV field emission gun. These structures were made in a thin film of amorphous (a-) AIF3 evaporated on a thin a-C or a-Si3N4 film. The electron optical properties of these devices were investigated in a conventional transmission electron microscope. Other instrumentation and technique developments included an improved electron energy loss (EEL) spectrometer and an energy filtered selected area electron diffraction mode in STEM. The most significant result is that a "wedge" depth profiled grating exhibited an asymmetrical diffraction pattern (a violation of Friedel's law), demonstrating conclusively that the grating acted as a strong phase object. Two practical electron optical devices were demonstrated, i.e. "biprism" profiled gratings and pixelated Fresnel phase (PFP) lenses. The "biprisms" exhibited overlap of two waves passing through each side of the biprism and possible electron interference fringes by the biprism action. Both convex and concave PFP lenses have been demonstrated for the first time. The designs showed that they are robust to the random phase error and the absorption effect was small. A simulation successfully explained the experimental observations. This simulation incorporated the proximity effect as an additional concave phase retardation of up to approximately 0.2π in the convex lenses and a variable hole diameter. The FWHM of the peak at the designed focal point for the large PFP lens was approximately 8nm, which matched well with the simulation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available