Scanning Microscopy


Theoretical approaches to coherent excitation of two plasmons in a metal do not well agree with one another and with experimental results from electron energy loss spectrometry (EELS). We measured EELS spectra of polycrystalline aluminum films for various specimen thickness. By means of a new deconvolution method for multiple scattering, we obtained values between 0.6% and 3.3% for the probability F2 of the coherent double plasmon event, relative to the single plamon event.

A review of earlier experimental as well as theoretical investigations is given. Our results together with a discussion of possible sources of error confirm our earlier findings that F2 is much smaller than previously thought, and is thickness dependent. We found the available predictions of the effect unsatisfactory; a full theoretical treatment of the problem is still missing.

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