Ph.D. / Applied Physics / This work was undertaken to determine the feasibility of using a field ionization (FI) source to produce fine focus ion beams. Operating parameters for a FI source have been measured and a source sensitivity of ~ 5 x 10[superscript-5] A sr[superscript -1] torr[superscript -1] was found for both H[subscript 2] and Ar at 77 K. The source is gas phase, differentially pumped with typical operating pressures of 1 - 30 x 10[superscript -3] torr at 77 K, resulting in a maximum source brightness ≈ 10[superscript 8] A cm[superscript -2] sr[superscript -1] and angular intensity of ≈ 10[superscript -6] A sr[superscript -1] with beam energies of 10 - 20 keV. Angular distributions were measured and found to be uniform near θ = 0°, with the beam confined to ±20°. A scanning ion microscope (SIM) was built to further evaluate the source. The SIM has been operated with currents on the specimen of 10[superscript -11] – 10[superscript -10 amperes in the secondary electron mode with contrast provided primarily by the sec (θ) dependence of the secondary electron yield, where θ is the angle between the beam and the specimen normal. Secondary electrons are detected and amplified with a channeltron multiplier and images generated as with a conventional SEM. All electrostatic optics are used in a doublet arrangement, and with this configuration current is independent of working distance which is 3 - 4 cm. A current of 5 x 10[superscript -11] A was focused into a spot of ≈ 6500 Å with H[subscript 2] gas, the resolution being limited by chromatic aberration caused by the ≈ 4 eV energy spread of the two component (H[superscript +] H[superscript +, subscript 2]) beam. Signal to noise ratio measurements on the source made at the specimen position show that the bulk of the noise power spectrum falls below f = 30 Hz.
| Identifer | oai:union.ndltd.org:OREGON/oai:content.ohsu.edu:etd/34 |
| Date | 12 1900 |
| Creators | Orloff, Jonathan Harris |
| Publisher | Oregon Health & Science University |
| Source Sets | Oregon Health and Science Univ. Library |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | Needs Adobe Acrobat Reader to view., pdf, 39289.445 KB |
| Rights | http://www.ohsu.edu/library/etd_rights.shtml |
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