With the aim of improving imaging using table-top extreme ultraviolet sources, we demonstrate coherent diffraction imaging (CDI) with relative bandwidth of 20%. The coherence properties of the illumination probe are identified using the same imaging setup. The presented methods allows for the use of fewer monochromating optics, obtaining higher flux at the sample and thus reach higher resolution or shorter exposure time. This is important in the case of ptychography when a large number of diffraction patterns need to be collected. Our microscopy setup was tested on a reconstruction of an extended sample to show the quality of the reconstruction. We show that high harmonic generation based EUV tabletop microscope can provide reconstruction of samples with a large field of view and high resolution without additional prior knowledge about the sample or illumination.
With progress in nanofabrication, new strategies have become available that allow precise control of nanoscale optical fields using metallic nanostructures. Here we review recent progress in the control of optical resonances in metal nanostructures for applications in sensing and spectroscopy. We discuss the use of new techniques, such as helium-ion beam milling, which allow precise sculpting of nanometer-scale gaps; new materials such as metal oxides, which have a response somewhere inbetween that of conventional dielectrics and noble metals; and new designs such as L-shaped gap antennas which allow controlling the polarization state of light through near-field interactions between closely spaced antennas.
Hiroshi Mizuta, Zakaria Moktadir, Stuart Boden, Nima Kalhor, Shuojin Hang, Marek Schmidt, Nguyen Tien Cuong, Dam Hieu Chi, Nobuo Otsuka, Manoharan Muruganathan, Yoshishige Tsuchiya, Harold Chong, Harvey Rutt, Darren Bagnall
In this paper we first present a new fabrication process of downscaled graphene nanodevices based on direct milling of
graphene using an atomic-size helium ion beam. We address the issue of contamination caused by the electron-beam
lithography process to pattern the contact metals prior to the ultrafine milling process in the helium ion microscope
(HIM). We then present our recent experimental study of the effects of the helium ion exposure on the carrier transport
properties. By varying the time of helium ion bombardment onto a bilayer graphene nanoribbon transistor, the change in
the transfer characteristics is investigated along with underlying carrier scattering mechanisms. Finally we study the
effects of various single defects introduced into extremely-scaled armchair graphene nanoribbons on the carrier transport
properties using ab initio simulation.
The eyes and wings of some species of moth are covered in arrays of subwavelength pillars that have been tuned
over millions of years of evolution to reflect as little sunlight as possible. We are investigating ways of exploiting
this to reduce reflection from the surfaces of silicon solar cells. Here, we report on the experimental realization
of biomimetic antireflective moth-eye arrays in silicon using a technique based on nanoimprint lithography and
dry etching. Areas of 1cm x 1cm have been patterned and analysis of reflectance measurements predicts a loss
in the performance of a solar cell of only 6.5% compared to an ideal antireflective coating. This compares well
with an optimized single layer Si3N4 antireflective coating, for which an 8% loss is predicted.
The challenge when applying photonics to photovoltaics is the need to provide broadband, multiple-angle solutions to
problems and both plasmonics and biomimetics offer broadband approaches to reducing reflection and enhancing lighttrapping.
Over millions of years nature has optimised nanostructures to create black, transparent, white and mirrored
surfaces, the antireflective "moth-eye" structures are perhaps the best known of these biophotonic materials. In this paper
we use simulated and experimental studies to illustrate how careful optimisation of nanoscale features is required to
ensure the optimum match between reflectivity, spectral bandwidth and device quantum efficiencies. In the case of lighttrapping
by plasmonic scattering there is more room for design and specific spectral regions can be targeted by precise
control of the size, shape and density of particular metal nanoparticles. We describe how the best opportunity for
plasmonics within inorganic solar cells appears to be enhanced light-trapping of near-band edge photons.
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