Nanoimprint Lithography Facilitated Plasmonic-Photonic Coupling for Enhanced Photoconductivity and Photocatalysis

Imprint lithography has emerged as a reliable, reproducible, and rapid method for patterning colloidal nanostructures. As a promising alternative to top-down lithographic approaches, the fabrication of nanodevices has thus become effective and straightforward. In this study, a fusion of interference lithography (IL) and nanosphere imprint lithography on various target substrates ranging from carbon film on transmission electron microscope grid to inorganic and dopable polymer semiconductor is reported. 1D plasmonic photonic crystals are printed with 75% yield on the centimeter scale using colloidal ink and an IL-produced polydimethylsiloxane stamp. Atomically smooth facet, single-crystalline, and monodisperse colloidal building blocks of gold (Au) nanoparticles are used to print 1D plasmonic grating on top of a titanium dioxide (TiO₂) slab waveguide, producing waveguide-plasmon polariton modes with superior 10 nm spectral line-width. Plasmon-induced hot electrons are confirmed via two-terminal current measurements with increased photoresponsivity under guiding conditions. The fabricated hybrid structure with Au/TiO₂ heterojunction enhances photocatalytic processes like degradation of methyl orange (MO) dye molecules using the generated hot electrons. This simple colloidal printing technique demonstrated on silicon, glass, Au film, and naphthalenediimide polymer thus marks an important milestone for large-scale implementation in optoelectronic devices.     

Information Capacity of Nonlinear Wavelength Division Multiplexing Fiber Optic Transmission Line

We report the first determination of the impact of optical nonlinearities on the information capacity of a fiber optic transmission channel. By modeling interchannel interference in a nonlinear wavelength division multiplexing transmission system as multiplicative Gaussian noise, we show that the information capacity is reduced below the Shannon capacity of the linear communications channel. For systems of practical interest, this imposes a fundamental limitation on the spectral efficiency of optical data transmission.     

Space-time adaptive processing using circular arrays

A direct data-domain (D³) least-squares space-time adaptive-processing (STAP) approach is presented for adaptively enhancing radar signals in a non-homogeneous environment of jammers, clutter, and thermal noise, utilizing a circular antenna array. The non-homogeneous environment may consist of non-stationary clutter. The D ³ approach is applied directly to the data collected by a circular antenna array (utilizing space), and in time (Doppler) diversity. Conventional STAP generally utilizes statistical methodologies, based on estimating a covariance matrix of the interference, using the data from various range cells of the circular array and assuming that it is a uniform linear array. However, for highly transient and inhomogeneous environments, the conventional statistical methodology may be difficult to apply. Moreover, the error in forming the covariance matrix by assuming that the data collected by the circular array is assumed to be a uniform linear array is highly problem dependent. Hence the D³ method is presented, as it analyzes the data in space and time over each range cell separately. However, it treats the antenna array as circular, i.e., it deals with the antenna structure in its proper form. Limited examples are presented to illustrate the application of this approach     

Time-domain measurements with the Hewlett-Packard network analyzerHP 8510 using the matrix pencil method

The generalized pencil of function (GPOF) method, also known as the matrix pencil method, is used to improve the resolution of HP 8510B network analyzer data in the time domain. This method provides for much higher resolution than the Fourier techniques. A comparison of the two methods is given for the example of the Beatty standard. The examples show that a parametric technique such as the GPOF can provide accurate and reliable results with a high degree of resolution even when the fast Fourier transform (FFT)-based technique fails     

HfAlOx high-k gate dielectric on SiGe: Interfacial reaction, energy-band alignment, and charge trapping properties

Ultra thin HfAlO_x high-k gate dielectric has been deposited directly on Si_1−xGe_x by RF sputter deposition. The interfacial chemical structure and energy-band discontinuities were studied by using X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (TOF-SIMS) and electrical measurements. It is found that the sputtered deposited HfAlO_x gate dielectric on SiGe exhibits excellent electrical properties with low interface state density, hysteresis voltage, and frequency dispersion. The effective valence and conduction band offsets between HfAlO_x (E_g = 6.2 eV) and Si_1−xGe_x (E_g = 1.04 eV) were found to be 3.11 eV and 2.05 eV, respectively. In addition, the charge trapping properties of HfAlO_x/SiGe gate stacks were characterized by constant voltage stressing (CVS).     

Using the matrix pencil method to estimate the parameters of a sumof complex exponentials

The approximation of a function by a sum of complex exponentials is a problem that is at least two centuries old. Fundamentally, all techniques discussed in this article proceed from using the same sequence of data samples and vary only, but importantly, in how those samples are used in achieving the parameter estimation. All of these techniques, in other words, seek the same quantitative parameters to represent the sampled data, but use different routes to get there. The techniques for estimating the parameters are either linear or nonlinear. The linear techniques are emphasized in this presentation. In particular, the matrix pencil method is described, which is more robust to noise in the sampled data. The matrix pencil approach has a lower variance of the estimates of the parameters of interest than a polynomial-type method (Prony's method belongs to this category), and is also computationally more efficient. A bandpass version of the matrix pencil can be implemented in hardware, utilizing an AT&T DSP32C chip operating in real time. A copy of the computer program implementing the matrix pencil technique is given in the appendix     

Design of a Variable Depth Axially Corrugated Horn Antenna at X-Band for Low Cross-Polarization Applications

Wireless Personal Communications - This paper presents a study of a class of iris localization algorithms in the presence of blurring. The effect of blurring is a serious problem in most image...     

On the implementation of a real-time information security architecture in frequency domain

This paper presents the real-time implementation of a watermarking-based information security architecture in frequency domain. The scheme emphasises on the human visual system (HVS)-supported watermarking approach using wavelet-lifting technique. In addition to HVS, image registration algorithm is also introduced in order to increase the resiliency as well as the security of the estimated recovered watermark image. The algorithmic steps with optimisation considerations about the real-time implementation on TMS320CDSK6416/6713 fixed/floating point digital signal processor are also projected.     

A simple unsupervised MRF model based image segmentation approach

A simple technique has been suggested to obtain optimal segmentation based on tonal and textural characteristics of an image using the Markov random field (MRF) model. The technique takes an initially over segmented image as well as the original image as its inputs and defines an MRF over the region adjacency graph (RAG) of the initially segmented regions. A tonal-region based segmentation technique due to Kartikeyan and Sarkar (1989) has been used for initial segmentation. The energy function has been defined over the first order cliques of the MRF. The essence of this approach is primarily based on quantitative values of the second order statistics, on region characteristics and consequently deciding upon the action of merging neighboring regions using the F-statistic. The effectiveness of our approach is demonstrated with wide variety of real life examples viz., indoor, outdoor and satellite and a comparison of its output with that of a previous work in the literature has been provided.     

An L-shaped array for estimating 2-D directions of wave arrival

A simple structured 2-D array, the L-shaped array, is presented. The L-shaped array consists of two uniform linear arrays (ULA) connected orthogonally at one end of each ULA. It is shown that the Cramer-Rao bounds (CRB) of the estimated wave directions based on the L-shaped array are about 37% smaller than those for the cross array. The CRB indicates the accuracy potential because it is the (reachable) lower bound on the variance of any unbiased estimate. An efficient maximum likelihood algorithm is developed utilizing the ULA structure inherent in the L-shaped array