Mapping Photoemission and Hot-Electron Emission from Plasmonic Nanoantennas

Abstract

Understanding plasmon-mediated electron emission and energy transfer on the nanometer length scale is critical to controlling light-matter interactions at nanoscale dimensions. In a high-resolution lithographic material, electron emission and energy transfer lead to chemical transformations. In this work, we employ such chemical transformations in two different high-resolution electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and hydrogen silsesquioxane (HSQ), to map local electron emission and energy transfer with nanometer resolution from plasmonic nanoantennas excited by femtosecond laser pulses. We observe exposure of the electron-beam resists (both PMMA and HSQ) in regions on the surface of nanoantennas where the local field is significantly enhanced. Exposure in these regions is consistent with previously reported optical-field-controlled electron emission from plasmonic hotspots as well as earlier work on low-electron-energy scanning probe lithography. For HSQ, in addition to exposure in hotspots, we observe resist exposure at the centers of rod-shaped nanoantennas in addition to exposure in plasmonic hotspots. Optical field enhancement is minimized at the center of nanorods suggesting that exposure in these regions involves a different mechanism to that in plasmonic hotspots. Our simulations suggest that exposure at the center of nanorods results from the emission of hot electrons produced via plasmon decay in the nanorods. Overall, the results presented in this work provide a means to map both optical-field-controlled electron emission and hot-electron transfer from nanoparticles via chemical transformations produced locally in lithographic materials.

Ultrafast Field‐Emission Electron Sources Based on Nanomaterials

“…Metal nanostructures, such as nanotips, nanowires, nanospheres, nanorods, nanotriangles, nanostars, and composite bow‐tie and nanorod antennae,[36,45b,53,62] are of particular interest for OFE experiments due to their relatively simple electronic structures and strong plasmonic near‐field enhancement. Many novel electron dynamics phenomena have been discovered during the investigation of OFE from metallic tips in this way.…”

Role of electron tunneling in the nonlinear response of plasmonic nanogaps

“…Moreover, since the incident pulse needed to observe nonlinear effects is intense, a frequency match with the plasmon resonance in the absorption cross section would result in strong electron emission. Precisely, this efficient conversion of the optical energy into electron-hole pairs via an intermediate plasmon excitation has made plasmonics a very attractive tool for solar energy harvesting or for photochemical applications [123][124][125][126][127][128][129] . However, in the present case, hot electron emission would result in a spread of the electron density over the entire computational grid, leading to the loss of precision.…”

Two-color multiphoton emission for comprehensive reveal of ultrafast plasmonic field distribution

“…Nowadays, several experimental approaches have been utilized to visualize the nearfield, including scanning near-field optical microscopy [8,9], electron energy loss microscopy [10], cathodoluminescence microscopy [11], nonlinear luminescence or fluorescent microscopy [12,13], nonlinear photopolymerization [14] and so on [15,16]. Since the amount of electron emission at the position of the excited plasmons is significantly increased due to strong near-field enhancement, the plasmon-mediated photoelectrons from the nanostructures has been used to image the plasmonic near-field distribution [17][18][19]. Photoemission electron microscopy (PEEM), an instrument that use light as an excitation source to image the near-field of a nanostructure by means of the photoelectrons, has the advantage of high spatial resolution, fast, non-invasive and temporally resolved accessibility, and it has become a powerful tool in advancing near-field characterization of plasmonics [18,[20][21][22][23].…”