Copyright © (2001) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics
: Enhancement c of the electrical field at the end of a tip relative to the incident field in a focused radiation beam is calculated by a Finite Difference Time Domain (FDTD) method. First, the reliability of the FTDT method is established by calculating the electric field on simple structures like thin cylinders, spheres and ellipsoids, and comparing the results with analytical solutions. The calculations on these test structures also reveal that phase retardation effects substantially modify c when the size of the structure is larger than approximately k/4, k being the radiation wavelength. For plasmon resonance in particular, phase retardation severely reduces the resonance and the expected field enhancement for a gold tip. The small value of c = 4 calculated by FDTD is about an order of magnitude smaller than the value found in recent published work. Resonance effects can be recovered for special tips, which have a discontinuity or a different material composition at the end of the tip. Some tuning of the discontinuity dimension is needed to maximize the resonance. Under optimal conditions for plasmon resonance, an enhancement in electric field of about 50 is
calculated at the end of a small gold protrusion mounted on a wider silicon or glass tip.
By: Yves C. Martin, Hendrick F, Hamann, H, Kumar Wickramasinghe
Published in: Journal of Applied Physics, volume 89, (no 10), pages 5774-8 in 2001
LIMITED DISTRIBUTION NOTICE:
This Research Report is available. This report has been submitted for publication outside of IBM and will probably be copyrighted if accepted for publication. It has been issued as a Research Report for early dissemination of its contents. In view of the transfer of copyright to the outside publisher, its distribution outside of IBM prior to publication should be limited to peer communications and specific requests. After outside publication, requests should be filled only by reprints or legally obtained copies of the article (e.g., payment of royalties). I have read and understand this notice and am a member of the scientific community outside or inside of IBM seeking a single copy only.
Questions about this service can be mailed to reports@us.ibm.com .