Atomic layer deposition: an overview.

The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. We show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters to be approximately 2 nanometers. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials.

https://science.sciencemag.org/content/sci/328/5982/1135.full.pdf

Self-Assembled Plasmonic Nanoparticle Clusters

Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

We have designed and realized a three-dimensional invisibility-cloaking structure operating at optical wavelengths based on transformation optics. Our blueprint uses a woodpile photonic crystal with a tailored polymer filling fraction to hide a bump in a gold reflector. We fabricated structures and controls by direct laser writing and characterized them by simultaneous high-numerical-aperture, far-field optical microscopy and spectroscopy. A cloaking operation with a large bandwidth of unpolarized light from 1.4 to 2.7 micrometers in wavelength is demonstrated for viewing angles up to 60 degrees.

http://science.sciencemag.org/content/sci/328/5976/337.full.pdf

Three-Dimensional Invisibility Cloak at Optical Wavelengths

Atomic layer deposition (ALD) has recently become the method of choice for the semiconductor industry to conformally process extremely thin insulating layers (high-k oxides) onto large-area silicon substrates. ALD is also a key technology for the surface modification of complex nanostructured materials. After briefly introducing ALD, this Review will focus on the various aspects of nanomaterials and their processing by ALD, including nanopores, nanowires and -tubes, nanopatterning and nanolaminates as well as low-temperature ALD for organic nanostructures and biomaterials. Finally, selected examples will be given of device applications, illustrating recent innovative approaches of how ALD can be used in nanotechnology.

https://www-old.mpi-halle.mpg.de/mpi/publi/pdf/7999_07.pdf

Synthesis and Surface Engineering of Complex Nanostructures by Atomic Layer Deposition

A new invisibility cloak was recently proposed for hiding objects in front of a highly reflecting mirror. This cloak requires only modest values of optical constants with minimal anisotropy and thus can be implemented by using non-resonant dielectric materials, making it an ideal system for optical frequency operation. We implemented the cloak using an array of silicon nanorods fabricated by electron-beam lithography. We then directly visualized the cloaking effect by monitoring the light propagation inside the device using the near-field optical microscopy.

http://ecee.colorado.edu/~wpark/papers/2009%20Lee.pdf

Direct visualization of optical frequency invisibility cloak based on silicon nanorod array.

A new bottom-up approach for fabricating the optical metamaterial is reported. An array of metal nanoparticle clusters can provide both electric and magnetic activity in the optical frequency region through the excitation of the collective plasmon resonance. A two-dimensional square array of gold nanoparticle clusters (nanoclusters) was fabricated by using the template-directed colloidal self-assembly. The optical measurements showed strong extinction peaks in the near-infrared region owing to the electric resonance supported by the nanoclusters. The peak positions were in excellent agreement with the numerical simulations. The metal nanocluster metamaterial represents a promising new architecture for an optical metamaterial that can be fabricated by a scalable bottom-up fabrication technique.

http://ecee.colorado.edu/~wpark/papers/2009%20Lee-1.pdf

Metal nanocluster metamaterial fabricated by the colloidal self-assembly.

Aluminum oxide (Al2O3) atomic layer deposition (ALD) on synthetic opal was explored as a model system to understand the growth of ALD films on photonic crystals. Al2O3 ALD was used to coat the sili...

Modification of opal photonic crystals using Al2O3 atomic layer deposition

We experimentally observe magnetic resonance in the visible frequency region from self-assembled silver nanocluster metamaterials. Extensive numerical modeling studies were conducted to find the optimal nanocluster dimensions. Self-assembly of silver nanoparticles coated with nanoscale silica coating was then performed on polymer templates fabricated by laser interference lithography. The nanoclusters supported magnetic resonance in the visible region, and the extracted effective permeability exhibited Lorentz-like resonance. The experimentally observed lowest value for the real part of permeability was 0.06. The nanocluster metamaterial represents a practical metamaterial architecture that is compatible with the scalable bottom-up manufacturing process.

http://ecee.colorado.edu/~wpark/papers/2010%20Tamma-1.pdf

Visible frequency magnetic activity in silver nanocluster metamaterial

Three-dimensional metallic photonic crystal is fabricated by self-assembly of gold nanoshells. In order to fabricate highly ordered crystal structure, fabrication parameters such as silica coating thickness, the zeta potential and the concentration of gold nanoshells are carefully controlled and optimized. Highly ordered gold nanoshell opal is fabricated and its structural and optical properties are presented.

Jin Hyoung Lee

Papers

Direct visualization of optical frequency invisibility cloak based on silicon nanorod array.

Metal nanocluster metamaterial fabricated by the colloidal self-assembly.

Modification of opal photonic crystals using Al2O3 atomic layer deposition

Visible frequency magnetic activity in silver nanocluster metamaterial

Three-dimensional metallic photonic crystal based on self-assembled gold nanoshells