Gordon, M. J. and Giapis, K. P. (2005) Low-energy ion beamline scattering apparatus for surface science investigations. Review of Scientific Instruments, 76 (8). Art. No. 083302. ISSN 0034-6748. http://resolver.caltech.edu/CaltechAUTHORS:GORrsi05
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We report on the design, construction, and performance of a high current (monolayers/s), mass-filtered ion beamline system for surface scattering studies using inert and reactive species at collision energies below 1500 eV. The system combines a high-density inductively coupled plasma ion source, high-voltage floating beam transport line with magnet mass-filter and neutral stripping, decelerator, and broad based detection capabilities (ions and neutrals in both mass and energy) for products leaving the target surface. The entire system was designed from the ground up to be a robust platform to study ion-surface interactions from a more global perspective, i.e., high fluxes (>100 µA/cm2) of a single ion species at low, tunable energy (50–1400±5 eV full width half maximum) can be delivered to a grounded target under ultrahigh vacuum conditions. The high current at low energy problem is solved using an accel-decel transport scheme where ions are created at the desired collision energy in the plasma source, extracted and accelerated to high transport energy (20 keV to fight space charge repulsion), and then decelerated back down to their original creation potential right before impacting the grounded target. Scattered species and those originating from the surface are directly analyzed in energy and mass using a triply pumped, hybrid detector composed of an electron impact ionizer, hemispherical electrostatic sector, and rf/dc quadrupole in series. With such a system, the collision kinematics, charge exchange, and chemistry occurring on the target surface can be separated by fully analyzing the scattered product flux. Key design aspects of the plasma source, beamline, and detection system are emphasized here to highlight how to work around physical limitations associated with high beam flux at low energy, pumping requirements, beam focusing, and scattered product analysis. Operational details of the beamline are discussed from the perspective of available beam current, mass resolution, projectile energy spread, and energy tunability. As well, performance of the overall system is demonstrated through three proof-of-concept examples: (1) elastic binary collisions at low energy, (2) core-level charge exchange reactions involving 20Ne+ with Mg/Al/Si/P targets, and (3) reactive scattering of CF<sub>2</sub><sup>+</sup>/CF<sub>3</sub><sup>+</sup> off Si. These studies clearly demonstrate why low, tunable incident energy, as well as mass and energy filtering of products leaving the target surface is advantageous and often essential for studies of inelastic energy losses, hard-collision charge exchange, and chemical reactions that occur during ion-surface scattering.
|Additional Information:||©2005 American Institute of Physics (Received 9 May 2005; accepted 14 June 2005; published online 28 July 2005) The authors would like to express their gratitude to Mike Roy in the Caltech Chemistry Machine Shop for his design assistance and tireless hours of fabrication which made the beamline system a reality. This research work was funded in part by the NSF (Grant No. CTS-0317397) and Applied Materials. Additionally, M. Gordon would like to thank the Intel Foundation and Applied Materials for personal scholarship support.|
|Subject Keywords:||mass spectrometer accessories; surface scattering; plasma sources; plasma transport processes; plasma-wall interactions; ion-surface impact|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Archive Administrator|
|Deposited On:||17 Jul 2006|
|Last Modified:||26 Dec 2012 08:56|
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