4 research outputs found
Mapping Photoemission and Hot-Electron Emission from Plasmonic Nanoantennas
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
High-Yield, Ultrafast, Surface Plasmon-Enhanced, Au Nanorod Optical Field Electron Emitter Arrays
Here we demonstrate the design, fabrication, and characterization of ultrafast, surface-plasmon enhanced Au nanorod optical field emitter arrays. We present a quantitative study of electron emission from Au nanorod arrays fabricated by high-resolution electron-beam lithography and excited by 35 fs pulses of 800 nm light. We present accurate models for both the optical field enhancement of Au nanorods within high-density arrays, and electron emission from those nanorods. We have also studied the effects of surface plasmon damping induced by metallic interface layers at the substrate/nanorod interface on near-field enhancement and electron emission. We have identified the peak optical field at which the electron emission mechanism transitions from a 3-photon absorption mechanism to strong-field tunneling emission. Moreover, we have investigated the effects of nanorod array density on nanorod charge yield, including measurement of space-charge effects. The Au nanorod photocathodes presented in this work display 100–1000 times higher conversion efficiency relative to previously reported UV triggered emission from planar Au photocathodes. Consequently, the Au nanorod arrays triggered by ultrafast pulses of 800 nm light in this work may outperform equivalent UV-triggered Au photocathodes, while also offering nanostructuring of the electron pulse produced from such a cathode, which is of interest for X-ray free-electron laser (XFEL) development where nanostructured electron pulses may facilitate more efficient and brighter XFEL radiation
Nanostructured Ultrafast Silicon-Tip Optical Field-Emitter Arrays
Femtosecond ultrabright electron
sources with spatially structured
emission are an enabling technology for free-electron lasers, compact
coherent X-ray sources, electron diffractive imaging, and attosecond
science. In this work, we report the design, modeling, fabrication,
and experimental characterization of a novel ultrafast optical field
emission cathode comprised of a large (>100 000 tips), dense
(4.6 million tips·cm<sup>–2</sup>), and highly uniform
(<1 nm tip radius deviation) array of nanosharp high-aspect-ratio
silicon columns. Such field emitters offer an attractive alternative
to UV photocathodes while providing a direct means of structuring
the emitted electron beam. Detailed measurements and simulations show
pC electron bunches can be generated in the multiphoton and tunneling
regime within a single optical cycle, enabling significant advances
in electron diffractive imaging and coherent X-ray sources on a subfemtosecond
time scale, not possible before. At high charge emission yields, a
slow rollover in charge is explained as a combination of the onset
of tunneling emission and the formation of a virtual cathode
Supplement 1: Terahertz-driven, all-optical electron gun
Supplementary Information Originally published in Optica on 20 November 2016 (optica-3-11-1209