87 research outputs found
Three-Dimensional Metal-Oxide Nanohelix Arrays Fabricated by Oblique Angle Deposition: Fabrication, Properties, and Applications
Three-dimensional (3D) nanostructured thin films have attracted great attention due to their novel physical, optical, and chemical properties, providing tremendous possibilities for future multifunctional systems and for exploring new physical phenomena. Among various techniques to fabricate 3D nanostructures, oblique angle deposition (OAD) is a very promising method for producing arrays of a variety of 3D nanostructures with excellent controllability, reproducibility, low cost, and compatibility with modern micro-electronic processes. This article presents a comprehensive overview of the principle of OAD, and unique structural and optical properties of OAD-fabricated thin films including excellent crystallinity, accurate tunability of refractive indices, and strong light scattering effect which can be utilized to remarkably enhance performances of various systems such as antireflection coatings, optical filters, photoelectrodes for solar-energy-harvesting cells, and sensing layers for various sensors.1114Ysciescopu
Design, fabrication and characterization of three-dimensional chiral photonic crystals
In this thesis, we have investigated an exciting subclass of photonic nanostructures: Chiral three-dimensional photonic crystals. We have fabricated several high-quality structures by using direct laser writing and have characterized them by transmission experiments and numerical calculations. This material class shows a high potential for applications because of intense response to circularly polarized light
Self-Assembled Chiral Photonic Crystals From Colloidal Helices Racemate
Chiral crystals consisting of micro-helices have many optical properties
while presently available fabrication processes limit their large-scale
applications in photonic devices. Here, by using a simplified simulation
method, we investigate a bottom-up self-assembly route to build up helical
crystals from the smectic monolayer of colloidal helices racemate. With
increasing the density, the system undergoes an entropy-driven
co-crystallization by forming crystals of various symmetries with different
helical shapes. In particular, we identify two crystals of helices arranged in
the binary honeycomb and square lattices, which are essentially composed by two
sets of opposite-handed chiral crystal. Photonic calculations show that these
chiral structures can have large complete photonic bandgaps. In addition, in
the self-assembled chiral square crystal, we also find dual polarization
bandgaps that selectively forbid the propagation of circularly polarized lights
of a specific handedness along the helical axis direction. The self-assembly
process in our proposed system is robust, suggesting possibilities of using
chiral colloids to assemble photonic metamaterials.Comment: Accepted in ACS Nan
Understanding Nickel Thin Film crystallization using X-Ray Diffractometry
Normal, helical and zigzag deposited Ni films were produced by letting a vapour stream of source material impinge on Corning 1737 glass substrates at oblique incidence while rotating the substrate during deposition. Films produced by glancing angle deposition (GLAD) technique while rotating the substrate. The microstructures of these Ni films were studied using X-ray diffractometry technique. The X-ray diffraction (XRD) patterns depicted 100% and 42% relative intensity (RI) peaks identified for normal and helical deposited Ni films but none for the zigzag deposited Ni film. Higher degree of crystallinity of Ni was demonstrated by the helical thin film sample having 200 nm thickness (sample Ni40) compared to the normal thin film which had only the 100% RI peak defined. Should anapplication therefore require Ni thin films of high crystallinity, it would be the film prepared with helical microstructure of 200 nm thickness that will be employed
Cavity quantum electrodynamics with three-dimensional photonic bandgap crystals
This paper gives an overview of recent work on three-dimensional (3D)
photonic crystals with a "full and complete" 3D photonic band gap. We review
five main aspects: 1) spontaneous emission inhibition, 2) spatial localization
of light within a tiny nanoscale volume (aka "a nanobox for light"), 3) the
introduction of a gain medium leading to thresholdless lasers, 4) breaking of
the weak-coupling approximation of cavity QED, both in the frequency and in the
time-domain, 5) decoherence, in particular the shielding of vacuum fluctuations
by a 3D photonic bandgap. In addition, we list and evaluate all known photonic
crystal structures with a demonstrated 3D band gap.Comment: 21 pages, 6 figures, 2 tables, Chapter 8 in "Light Localisation and
Lasing: Random and Pseudorandom Photonic Structures", Eds. M. Ghulinyan and
L. Pavesi (Cambridge University Press, Cambridge, 2015, ISBN
978-1-107-03877-6
Simultaneous fabrication of line defects-embedded periodic lattice by topographically assisted holographic lithography
We have demonstrated simultaneous fabrication of designed defects within a periodic structure. For rapid fabrication of periodic structures incorporating nanoscale line-defects at large area, topographically assisted holographic lithography (TAHL) technique, combining the strength of hologram lithography and phase-shift interference, was proposed. Hot-embossing method generated the photoresist patterns with vertical side walls which enabled phase-shift mask effect at the edge of patterns. Embossing temperature and relief height were crucial parameters for the successful TAHL process. Periodic holes with a diameter of 600 nm at a 1 μm-pitch incorporating 250 nm wide line-defects were obtained simultaneously
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Large-area metallic photonic lattices for military applications.
In this project we developed photonic crystal modeling capability and fabrication technology that is scaleable to large area. An intelligent optimization code was developed to find the optimal structure for the desired spectral response. In terms of fabrication, an exhaustive survey of fabrication techniques that would meet the large area requirement was reduced to Deep X-ray Lithography (DXRL) and nano-imprint. Using DXRL, we fabricated a gold logpile photonic crystal in the <100> plane. For the nano-imprint technique, we fabricated a cubic array of gold squares. These two examples also represent two classes of metallic photonic crystal topologies, the connected network and cermet arrangement
Blending of nanoscale and microscale in uniform large-area sculptured thin-film architectures
The combination of large thickness ( m), large--area uniformity (75
mm diameter), high growth rate (up to 0.4 m/min) in assemblies of
complex--shaped nanowires on lithographically defined patterns has been
achieved for the first time. The nanoscale and the microscale have thus been
blended together in sculptured thin films with transverse architectures.
SiO () nanowires were grown by electron--beam evaporation onto
silicon substrates both with and without photoresist lines (1--D arrays) and
checkerboard (2--D arrays) patterns. Atomic self--shadowing due to
oblique--angle deposition enables the nanowires to grow continuously, to change
direction abruptly, and to maintain constant cross--sectional diameter. The
selective growth of nanowire assemblies on the top surfaces of both 1--D and
2--D arrays can be understood and predicted using simple geometrical shadowing
equations.Comment: 17 pages, 9 figure
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