Cold atomic beam ion source for focused ion beam applications

Abstract

Development and characterization of an iodine field emission ion source for focused ion beam applicationsHigh brightness inductively coupled plasma source for high current focused ion beam applications Performance of multicusp plasma ion source for focused ion beam applicationsWe report measurements and modeling of an ion source that is based on ionization of a laser-cooled atomic beam. We show a high brightness and a low energy spread, suitable for use in next-generation, high-resolution focused ion beam systems. Our measurements of total ion current as a function of ionization conditions support an analytical model that also predicts the cross-sectional current density and spatial distribution of ions created in the source. The model predicts a peak brightness of 2 Â 10 7 A m À2 sr À1 eV À1 and an energy spread less than 0.34 eV. The model is also combined with Monte-Carlo simulations of the inter-ion Coulomb forces to show that the source can be operated at several picoamperes with a brightness above 1 Â 10 7 A m À2 sr À1 eV À1 . We estimate that when combined with a conventional ion focusing column, an ion source with these properties could focus a 1 pA beam into a spot smaller than 1 nm. A total current greater than 5 nA was measured in a lowerbrightness configuration of the ion source, demonstrating the possibility of a high current mode of operation.

Detailed observation of space–charge dynamics using ultracold ion bunches

“…The initial charge distributions were determined from the measured laser spatial profiles by calculation of the atomic excitation. For two-step ionization at a high 480-nm pulse energy, the probability of ionization is proportional to the probability of being in the intermediate 5P state before the 480-nm laser pulse 18,24,33 , but the usual expectations of saturation for a two-level transition 34 are not applicable since we must include loss via field ionization. Indeed, experimentally, we can infer the number of ions produced from the space-charge-induced bunch expansion ( Fig.…”

“…Pioneering work with cold atom sources has shown evidence of space-charge effects 21,22 , and the role of Coulomb interactions in cold ion beams has been studied in detail for continuous-mode low charge density operation [23][24][25] . In this paper we investigate space-charge effects in arbitrarily shaped nanosecond duration cold ion bunches produced by near-threshold photoionization of laser-cooled atoms.…”

Performance predictions of a focused ion beam from a laser cooled and compressed atomic beam

“…The advantage of using a Knudsen cell is that it can produce a very high flux of atoms (>10 13 s À1 at 400 K when using rubidium) as compared to a so called 2D þ MOT. 17 In the next stage, this beam is laser cooled and compressed in the two transverse directions. Simulations of this magneto-optical compressor (MOC) showed that this increases the flux density / of the beam to 4 Â 10 19 m À2 s À1 , while the transverse temperature T ?…”

Ion microscopy based on laser-cooled cesium atoms

“…This means that ion or electron sources based on cold atom ionization would be able to create at low acceleration energy very small focal spots with relatively strong currents. Focused ion beams have been generated starting from both a magneto-optical trap (MOT) [10,11] and a slow and cold atomic beam [12]. Their properties as nanoprobes have been demonstrated first with chromium [13] and then with lithium [14] ions, the latter reaching a 27 nm resolution at 2 keV energy and 1 pA current.…”