16 research outputs found
Fabrication of Large Area Periodic Nanostructures Using Nanosphere Photolithography
Large area periodic nanostructures exhibit unique optical and electronic properties and have found many applications, such as photonic band-gap materials, high dense data storage, and photonic devices. We have developed a maskless photolithography method—Nanosphere Photolithography (NSP)—to produce a large area of uniform nanopatterns in the photoresist utilizing the silica micro-spheres to focus UV light. Here, we will extend the idea to fabricate metallic nanostructures using the NSP method. We produced large areas of periodic uniform nanohole array perforated in different metallic films, such as gold and aluminum. The diameters of these nanoholes are much smaller than the wavelength of UV light used and they are very uniformly distributed. The method introduced here inherently has both the advantages of photolithography and self-assembled methods. Besides, it also generates very uniform repetitive nanopatterns because the focused beam waist is almost unchanged with different sphere sizes
A Novel Self-aligned and Maskless Process for Formation of Highly Uniform Arrays of Nanoholes and Nanopillars
Fabrication of a large area of periodic structures with deep sub-wavelength features is required in many applications such as solar cells, photonic crystals, and artificial kidneys. We present a low-cost and high-throughput process for realization of 2D arrays of deep sub-wavelength features using a self-assembled monolayer of hexagonally close packed (HCP) silica and polystyrene microspheres. This method utilizes the microspheres as super-lenses to fabricate nanohole and pillar arrays over large areas on conventional positive and negative photoresist, and with a high aspect ratio. The period and diameter of the holes and pillars formed with this technique can be controlled precisely and independently. We demonstrate that the method can produce HCP arrays of hole of sub-250 nm size using a conventional photolithography system with a broadband UV source centered at 400 nm. We also present our 3D FDTD modeling, which shows a good agreement with the experimental results
Giant Phonon-induced Conductance in Scanning Tunneling Spectroscopy of Gate-tunable Graphene
The honeycomb lattice of graphene is a unique two-dimensional (2D) system
where the quantum mechanics of electrons is equivalent to that of relativistic
Dirac fermions. Novel nanometer-scale behavior in this material, including
electronic scattering, spin-based phenomena, and collective excitations, is
predicted to be sensitive to charge carrier density. In order to probe local,
carrier-density dependent properties in graphene we have performed
atomically-resolved scanning tunneling spectroscopy measurements on
mechanically cleaved graphene flake devices equipped with tunable back-gate
electrodes. We observe an unexpected gap-like feature in the graphene tunneling
spectrum which remains pinned to the Fermi level (E_F) regardless of graphene
electron density. This gap is found to arise from a suppression of electronic
tunneling to graphene states near E_F and a simultaneous giant enhancement of
electronic tunneling at higher energies due to a phonon-mediated inelastic
channel. Phonons thus act as a "floodgate" that controls the flow of tunneling
electrons in graphene. This work reveals important new tunneling processes in
gate-tunable graphitic layers