Surface Plasmonic Lens Driven Photoelectron Source for Multi-beam Applications

Surface plasmon polariton (SPP) assisted photoelectron source array is proposed for use in distributed multiple electron beam lithography applications. Individual source is composed of a metal/dielectric surface structure with concentric circular grooves of subwavelength width surrounding a sub-wavelength aperture. Such optical power concentrators, called "plasmonic lenses", collect light incident over a broad area by converting it to surface electromagnetic waves, specifically SPP's, through diffraction by the sub-wavelength grooves surrounding the aperture. Through constructive interference of the generated SPPs between neighboring grooves, controlled by the periodicity of the grooves, high optical power densities can be achieved at the center of the lens near the aperture. This facilitates high transmission of optical power through the aperture which results in more light being transmitted than is incident on the aperture itself. Such an approach results in a focal spot at the exit side of the aperture with highly enhanced optical power density compared to the incident light.;Optimization of the circular groove-aperture plasmonic lens is demonstrated through finite-difference-in-time-domain simulations that focus on the overall performance of the optical power density enhancement at the operating wavelength of 266 nm. The basic method for the fabrication of plasmonic lenses based on electron beam lithography and reactive ion etching techniques is demonstrated. Additionally, the fabricated structures are tested by the measurement of plasmonic lens facilitated photoemission current driven by a 266 nm laser. Experimental results of the performance of the fabricated structures, composed of Al and a-SiO2, is measured and analyzed. The plasmonic lens fabricated with the optimized design exhibit ∼15 enhancement of the incident optical power density.;The plasmonic lens arrays are designed to drive photoelectron emission from nanodots with diamters in the sub-100 nm range. These nanoscale emitters reduce the electron emission area, which allows reduced source size of the completed source. Experimental investigations of photoelectron emission from nano-dots of three different metals (Mg, Ag, and Au) all exhibit periodic enhancements of photoelectron emission with changes in diameter. Highest enhancement is experimentally measured to be 38X for 52.2 nm diameter Mg nano-dots. A basic theory of the photoelectron emission enhancement is proposed based on the excitation of quasi-bound electronic states possible for nanoscale metal emitters that contribute to the electron emission process.;Feasibility of the proposed source array is analyzed based on the experimentally measured values. The nano-dot photoelectron emission enhancement observed for the 39.4 nm diameter Au nano-dots and the plasmonic lens optical power density enhancement of the 190 nm pitch periodic concentric circular groove plasmonic lens are used to calculate the optical power required to generate 1 nA individual source current as 0.5 mW.