Quantum Optics and Photonics

Contains reports on five research projects.Joint Services Electronics Program (Contract DAALO3-86-K-0002)National Science Foundation (Grant PHY 82-10369)U.S. Air Force - Office of Scientific Research (Contract F49620-82-C-0091)U.S. Air Force - Rome Air Development Cente

Self-assembly of Silver Nanoparticles and Multiwall Carbon Nanotubes on Decomposed GaAs Surfaces

Atomic Force Microscopy complemented by Photoluminescence and Reflection High Energy Electron Diffraction has been used to study self-assembly of silver nanoparticles and multiwall carbon nanotubes on thermally decomposed GaAs (100) surfaces. It has been shown that the decomposition leads to the formation of arsenic plate-like structures. Multiwall carbon nanotubes spin coated on the decomposed surfaces were mostly found to occupy the depressions between the plates and formed boundaries. While direct casting of silver nanoparticles is found to induce microdroplets. Annealing at 300°C was observed to contract the microdroplets into combined structures consisting of silver spots surrounded by silver rings. Moreover, casting of colloidal suspension consists of multiwall carbon nanotubes and silver nanoparticles is observed to cause the formation of 2D compact islands. Depending on the multiwall carbon nanotubes diameter, GaAs/multiwall carbon nanotubes/silver system exhibited photoluminescence with varying strength. Such assembly provides a possible bottom up facile way of roughness controlled fabrication of plasmonic systems on GaAs surfaces

Tunable defect states in 1D photonic bandgap nanostructures

The fabrication of one dimensional photonic bandgap nanostructures is described and the optical properties of these structures are examined. Using a deposition technique known as a glancing angle deposition (GLAD), porous films with a predefined nanoscale geometry are created. Specifically, in the present work we consider GLAD fabricated thin films characterized by periodically varying refractive index in one-dimension. We introduce a variety of planar defect layers into the structures and investigate the resulting changes observed in the photonic bandgap of the system. Theoretical simulation of transmittance spectra of GLAD fabricated films is performed with the finite-difference time-domain (FDTD) method and the results are compared with experimental measurements. Modifications of the transmittance spectra are investigated by changing the geometry of the defect layer and varying the void region effective index. It is shown that the spectral width and location of states within the bandgap is controlled by the geometry of defect and film microstructure. Active tunability of the defect states is obtained by considering infilling of the void regions of the structure with nematic liquid crystals and then analyzing the optical spectrum for various orientations of the liquid crystal director axis.NRC publication: Ye

The quantum regime in tunneling plasmonics

Trabajo presentado al Quantum Nano-Optics Workshop, celebrado en Barcelona (España) del 10 al 11 de Septiembre de 2012.Electron transfer due to quantum tunnelling between two metallic structures strongly modifies the plasmonic resonances of the system. For small particles, the resulting optical behaviour can be studied using Time-Dependent Density Functional Theory (TDDFT). The particles used in typical plasmonics applications, however, often have dimensions that are tens, hundreds of even thousands of nanometers long, and thus they are too large to be treated with state-of-the-art TDDFT. Here, we present a Quantum Corrected Model (QCM) that includes the effect of quantum tunnelling in the calculation of the plasmonic response of large structures at subnanometer separation distances. The model requires to define an effective material in the region where tunnelling is happening, with the properties of the material given by exact quantum calculations from a simplified system. A standard solver of Maxwell equations can then be used to obtain the response of the entire system. QCM is straightforward to implement for arbitrary geometries, which can exhibit narrow gaps or particles in contact. We first test the QCM results against small Na spheres that can be also simulated using TDDFT, and find very good agreement between both methods. Next, we consider the case of large Drude-like Au structures to illustrate the effect of tunnelling in realistic plasmonic systems formed by large nanometric structures. As expected from previous work in small particles, we observe a spectral redistribution of the modes for all the geometries and a collapse of the near-field enhancement at very short separation distances.. We also consider the experimental situation of two approaching gold tips, a system which we have recently tested to experimentally reveal quantum effects in plasmonic gaps at subnanometer separation distances. The modelled structures (longer than 1 micrometer), exceed by several orders of magnitude the sizes typically tackled with TDDFT. Notably, the measured and calculated far-field spectra are in good agreement, which further emphasizes the relevance of the proposed method to correctly address experimental situations. Moreover, our QCM simulations open the possibility to predict both the optimal near field enhancement and confinement expected a task that has still not been yet reported experimentally.Peer Reviewe

Thin Film Room: 102 C -Session TF+MI-WeM Magnetic Thin Films and Nanostructures 8:00am TF+MI-WeM1 Recent Advances and Challenges in Magnetic Recording Media 9:00am TF+MI-WeM4 Mössbauer Study of Disordering in Thin Sputtered FeCo-SiO 2 and FeCo Films

INVITED For perpendicular magnetic recording (PMR) beyond areal density of 700 Gb/in 2 , signal to noise ratio (SNR) and write-ability improvements are becoming extremely challenging to realize. The present exchanged coupled composite (ECC) recording medium has become quite complex and consists of multiple magnetic layers. To enable 1Tb/in 2 areal density, it is required to (i) improve grain isolation for SNR (ii) increase magnetic anisotropy for thermal stability and (iii) reduce all the dimensions, such as thicknesses of the magnetic layers and media grain size. Improvement in grain isolation with maintaining magnetic anisotropy poses challenges on material selection and process optimization and higher anisotropy materials limits the write-ability of the media. It was estimated that the media grain size <8nm can achieve higher SNR due to reduced jitter and transition noise. However, for last several years, the media grain size has hardly changed in optimized PMR media. The increased inter-granular exchange coupling in small grain size media degrades recording media noise characteristics. Also, thermal stability is compromised on media with small grain size. Here, we discuss recent developments and efforts on perpendicular recording media with small grain size and will present our major findings in terms of SNR, write-ability and thermal stability characteristics. We will also discuss advanced ECC media structure with multiple exchange break layers that offers advantages towards enabling reduced grain size. We also describe advanced characterization methods to quantify the effect of inter granular interactions and their relation with materials and sputtering processes. 8:40am TF+MI-WeM3 FePt Nanopillars for Advanced Media by Glancing Angle Deposition, H. Su, A. Montgomery, S. Gupta, The University of Alabama Granular L1 0 FePt films are leading candidates for next generation magnetic recording, for instance, heat assisted magnetic recording (HAMR). This is due to its high magnetocrystalline energy constant (~7.0 x 10 7 erg/cm 3 ), which can maintain thermal stability even with a reduced grain size of 3nm Acknowledgements This work was supported by National Science Foundation Grant ECCS-0901858, "GOALI: Nanopatterned Graded Media". The authors acknowledge the Central Analytical Facility (CAF) and Microfabrication Facility (uamicro)for their support and facilities. Thin metal films (h = 130 nm) were deposited via DC magnetron sputtering onto a PET substrate; the DC magnetron operating regime (time, pressure and discharge parameters) was identical during the composite synthesis. To sputter SiO 2 , a RF magnetron was applied; both magnetrons were sputtering simultaneously. To derive structure information, a Mossbauer spectroscopy, X-ray diffraction (GIXD) and electron microscopy data were gathered. Magnetic properties were studied using VSM and a coaxial line technique for a microwave permeability. Reference The results reported may be applied to design thin film microwave devices. Literature 1. S.S. Maklakov, S.A. Maklakov, I.A. Ryzhikov, K.N. Rozanov, A.V. Osipov Maklakov, S.A. Maklakov, I.A. Ryzhikov, V.A. Amelichev, K.V. Pokholok , A.N. Lagarko

Using spacer layers to control metal and semiconductor absorption in ultrathin solar cells with plasmonic substrates

We systematically explore the performance of ultrathin amorphous silicon solar cells integrated on plasmonic substrates of several different morphologies. Angle-resolved reflectance, external quantum efficiency measurements, and finite-difference time-domain simulations highlight the importance of the spacer layer in determining the mode profiles to which light can couple. Coupling mechanisms are found to strongly differ between periodic silver nanovoid arrays and randomly textured silver substrates. Tailoring the spacer thickness leads to 50% higher quantum efficiencies and short-circuit current densities by tuning the coupling between the near-field and trapped modes with enhanced optical path lengths. The balance of absorption for the plasmonic near field at the metal/semiconductor interface is analytically derived for a broad range of leading photovoltaic materials. This yields key design principles for plasmonic thin-film solar cells, predicting strong near-field enhancement only for CdTe, CuInGaSe2, and organic polymer devices