Atomic Beam Laser-cooled Ion Source : towards sub-nm ion beam milling

This work discusses the predicted performance of the Atomic Beam Laser-cooled Ion Source (ABLIS) and the progress in its experimental realization. The ABLIS is a new source for focused ions beams (FIBs), which are tools that are used on a large scale in the semiconductor industry, to image and modify structures on the smallest possible length scale. On the contrary to other FIB sources such as the Liquid Metal Ion Source (LMIS), the ABLIS is based on the fact that the ions are created from atoms with a very small spread in velocity instead of a very small spread in position. The biggest application of an ABLIS-based FIB will be so called milling in which material is physically etched at the nanometer length scale.In the ABLIS setup a beam of atomic rubidium is created from a Knudsen cell. This beam is laser-cooled and -compressed after which it is photo-ionized by means of a very intense laser. The ions will be accelerated immediately to their demanded energy (mostly 30 keV) and finally focused to an as small as possible spot by a set of electrostatic lenses. Since the ionization will take place over a certain region, the energy spread of the ion beam, and therefore also the amount of chromatic aberration of the lens system, will be proportional to the electric field.The bottleneck of the setup will be disorder induced heating, which was investigated in this work. It is the effect that ions, which were created at random initial positions, will heat up due to relaxation of the potential energy associated with these random initial positions. Investigations in this work show that this effect can be counteracted by increasing the electric field at the position they are ionized. A relation was found between the electric field needed to suppress disorder induced heating and the beam current. This relation was used to calculate the amount of chromatic aberration of the lens system as a function of the current. Using this information, an analytical calculation was performed of the possible spot size of the ABLIS setup, including all individual contributions to the spot size, i.e., the brightness, spherical aberration and chromatic aberration. The result showed that a spot size of 0.2 nm is possible at a current of 1 pA, compared to the 5 nm spot size which is possible with the LMIS. The calculation was verified with particle tracking simulations, which were in good agreement.In order to perform laser cooling and compression, a laser is needed which is stable and can be precisely detuned from the cooling transition in rubidium. Furthermore a repump beam is needed which is tuned to a different transition in rubidium. The laser system which matches these requirements was finalized in the work discussed here. A double pass acousto-optic modulator (AOM) configuration was built to detune the laser frequency. Furthermore, an electro-optic modulator (EOM) was added to the setup, to create the repump beam.An experimental setup was built in which the efficiency of laser cooling can be tested with laser induced fluorescence. Simulations of this setup were performed, which showed the setup should be capable of measuring the effect of laser cooling on the atom beam. Furthermore, a simulation of the atoms in the collimating tube of the Knudsen cell is set up. Its results are in good agreement with earlier performed measurements and a theoretical model. This work discusses the predicted performance of the Atomic Beam Laser-cooled Ion Source (ABLIS) and the progress in its experimental realization. The ABLIS is a new source for focused ions beams (FIBs), which are tools that are used on a large scale in the semiconductor industry, to image and modify structures on the smallest possible length scale. On the contrary to other FIB sources such as the Liquid Metal Ion Source (LMIS), the ABLIS is based on the fact that the ions are created from atoms with a very small spread in velocity instead of a very small spread in position. The biggest application of an ABLIS-based FIB will be so called milling in which material is physically etched at the nanometer length scale.In the ABLIS setup a beam of atomic rubidium is created from a Knudsen cell. This beam is laser-cooled and -compressed after which it is photo-ionized by means of a very intense laser. The ions will be accelerated immediately to their demanded energy (mostly 30 keV) and finally focused to an as small as possible spot by a set of electrostatic lenses. Since the ionization will take place over a certain region, the energy spread of the ion beam, and therefore also the amount of chromatic aberration of the lens system, will be proportional to the electric field.The bottleneck of the setup will be disorder induced heating, which was investigated in this work. It is the effect that ions, which were created at random initial positions, will heat up due to relaxation of the potential energy associated with these random initial positions. Investigations in this work show that this effect can be counteracted by increasing the electric field at the position they are ionized. A relation was found between the electric field needed to suppress disorder induced heating and the beam current. This relation was used to calculate the amount of chromatic aberration of the lens system as a function of the current. Using this information, an analytical calculation was performed of the possible spot size of the ABLIS setup, including all individual contributions to the spot size, i.e., the brightness, spherical aberration and chromatic aberration. The result showed that a spot size of 0.2 nm is possible at a current of 1 pA, compared to the 5 nm spot size which is possible with the LMIS. The calculation was verified with particle tracking simulations, which were in good agreement.In order to perform laser cooling and compression, a laser is needed which is stable and can be precisely detuned from the cooling transition in rubidium. Furthermore a repump beam is needed which is tuned to a different transition in rubidium. The laser system which matches these requirements was finalized in the work discussed here. A double pass acousto-optic modulator (AOM) configuration was built to detune the laser frequency. Furthermore, an electro-optic modulator (EOM) was added to the setup, to create the repump beam.An experimental setup was built in which the efficiency of laser cooling can be tested with laser induced fluorescence. Simulations of this setup were performed, which showed the setup should be capable of measuring the effect of laser cooling on the atom beam. Furthermore, a simulation of the atoms in the collimating tube of the Knudsen cell is set up. Its results are in good agreement with earlier performed measurements and a theoretical model