High Spectral Peak Research Articles

Plasmon Hybridization in Silver Nanoislands as Semishells Arrays Coupled to a Thin Metallic Film

We obtained experimentally strong plasmon interactions between localized surface plasmon with delocalized surface plasmon polaritons in a new nanosystem of silver semishells island film arrays arranged as a closed-packing structure coupled to an adjacent thin silver film. We show that plasmon interactions for such a nanosystem exhibits two pronounced resonances and interpret the coupling in terms of Fano resonances. The higher energy resonance is identified as a symmetric hybridization mode between localized plasmon resonances in the island semishell array and surface plasmon polaritons in the metal film and while the lower energy resonance is identified as a corresponding anti-symmetric hybridization mode. Increasing the size of the particle arrays enhances and red shifts the resonances. We show that adding a dielectric spacer between the semishell island array and the metal film results in a red shifting of the resonances and introduce an additional high energy spectral peak. The effect of the spacer layer is interpreted as a reduced hybridization and the generation of additional localized surface plasmon resonances.

Flat supercontinuum generation in cascaded fibers pumped by a continuous wave laser

We realize the flattening and extending of a CW-pumped supercontinuum with a high spectral intensity peak at the pump region. It is achieved by cascading a long zero-dispersion wavelength high-nonlinearity fiber with the output photonic crystal fiber, in order to improve the conversion efficiency of residual pump energy to long-wavelength continuum based on the effect of cascaded stimulated Raman scattering. Compared with the non-flattened continuum of 10.3 W with 3 dB bandwidth of 62 nm and 10 dB bandwidth of 360 nm, a flat continuum of 8 W with 3 dB spectral range of 340 nm and 10 dB spectral range of 420 nm is obtained. The spectral peak at the pump region decreases more than 5 dB, below the level of long-wavelength spectral intensity. Also, the long-wavelength edge has been extended by 60 nm.

High-power soliton-induced supercontinuum generation and tunable sub-10-fs VUV pulses from kagome-lattice HC-PCFs

We theoretically study a novel approach for soliton-induced high-power supercontinuum generation by using kagome lattice HC-PCFs filled with a noble gas. Anomalous dispersion and broad-band low loss of these fibers enable the generation of two-octave broad spectra by fs pulses, with high coherence and high spectral peak power densities up to five orders of magnitude larger than in standard PCFs. In addition, up to 20% of the output radiation energy forms a narrow UV/VUV band, which can be tuned by controlling the pressure in the range from 350 nm to 120 nm. In the temporal domain this corresponds to sub-10-fs UV/VUV pulses with pulse energy of few tens of microJ, caused by the formation of a high-order soliton emitting non-solitonic radiation.

High-power, high-coherence supercontinuum generation in dielectric-coated metallic hollow waveguides

In this paper we theoretically study a novel approach for soliton-induced supercontinuum generation based on the application of metallic dielectric-coated hollow waveguides. The low loss of such waveguides permits the use of smaller diameters with enhanced dispersion control and enables the generation of two-octave-broad spectra with unprecedentedly high spectral peak power densities up to five orders of magnitude larger than in standard PCFs with high coherence. The predicted high coherence of the supercontinuum is related to the coherent seed components formed by the abruptly rising plasma density. We also predict that high-power supercontinua in the vacuum ultraviolet can be generated in such waveguides.

Dynamic Electrowetting on Nanofilament Silicon for Matrix-Free Laser Desorption/Ionization Mass Spectrometry

Dynamic electrowetting on nanostructured silicon surfaces is demonstrated as an effective method for improving detection sensitivity in matrix-free laser desorption/ionization mass spectrometry. Without electrowetting, silicon surfaces comprising dense fields of oriented nanofilaments are shown to provide efficient ion generation and high spectral peak intensities for deposited peptides bound to the nanofilaments through hydrophobic interactions. By applying an electrical bias to the silicon substrate, the surface energy of the oxidized nanofilaments can be dynamically controlled by electrowetting, thereby allowing aqueous buffer to penetrate deep into the nanofilament matrix. The use of electrowetting is shown to result in enhanced interactions between deposited peptides and the nanofilament silicon surface, with improved signal-to-noise ratio for detected spectral peaks. An essential feature contributing to the observed performance enhancement is the open-cell nature of the nanofilament surfaces, which prevents air from becoming trapped within the pores and limiting solvent penetration during electrowetting. The combination of nanofilament silicon and dynamic electrowetting is shown to provide routine detection limits on the order of several attomoles for a panel of model peptides.

2 W/nm peak-power all-fiber supercontinuum source and its application to the characterization of periodically poled non-linear crystals

We demonstrate a uniform high spectral brightness and peak power density all-fiber supercontinuum source. The source consists of a nanosecond Ytterbium fiber laser and an optimal length PCF producing a continuum with a peak power density of 2W/nm and less than 5dB of spectral variation between 590 and 1500nm. The Watt level per nm peak power density enables the use of such sources for the characterization of non-linear materials. Application of the source is demonstrated with the characterization of several periodically poled crystals.

Study of Inhibition Characteristics of Slurry Additives in Copper CMP using Force Spectroscopy

Using a reference slurry, ammonium dodecyl sulfate (ADS), an anionic and environmentally friendly surfactant, was investigated as an alternative to BTA for its inhibition and lubrication characteristics. Results demonstrated that the inhibition efficiency of ADS was superior to that of BTA. Coefficient of friction (COF) was the lowest when the slurry contained ADS. This suggested that adsorbed ADS on the surface provided lubricating action thereby reducing the wear between the contacting surfaces. Temperature results were consistent with the COF and removal rate data. ADS showed the lowest temperature rise again confirming the softening effect of the adsorbed surfactant layer and less energy dissipation due to friction. Spectral analysis of shear force showed that increasing the pad-wafer sliding velocity at constant wafer pressure shifted the high frequency spectral peaks to lower frequencies while increasing the variance of the frictional force. Addition of ADS reduced the fluctuating component of the shear force and the extent of the pre-existing stick-slip phenomena caused by the kinematics of the process and collision event between pad asperities with the wafer. By contrast, in the case of BTA, there were no such observed benefits but instead undesirable effects were seen at some polishing conditions. This work underscored the importance of real-time force spectroscopy in elucidating the adsorption, lubrication and inhibition of additives in slurries in CMP.

Numerical simulations of ECE spectra under the L-2M experimental conditions

Results are presented from numerical simulations of electron-cyclotron emission spectra from the plasma of the L-2M stellarator under the conditions corresponding to experiments on electron-cyclotron resonance heating. The spectra are calculated in the model of a two-component electron plasma, each component (thermal and suprathermal) having a Maxwellian distribution. It is shown that, even when suprathermal electrons contribute insignificantly to the total plasma energy, they may considerably affect both the shape and intensity of the electron-cyclotron emission spectrum. The occurrence of a high spectral peak at the frequency corresponding to the resonance ω = 2ωce on the low-field side of the plasma column in regimes with a high specific heating power is explained.

Study of Inhibition Characteristics of Slurry Additives in Copper CMP Using Force Spectroscopy

Using a reference slurry, ammonium dodecyl sulfate (ADS), an anionic and environmentally friendly surfactant, was investigated as an alternative to BTA for its inhibition and lubrication characteristics. Results demonstrated that the inhibition efficiency of ADS was superior to that of BTA. Coefficient of friction (COF) was the lowest when the slurry contained ADS. This suggested that adsorbed ADS on the surface provided lubricating action thereby reducing the wear between the contacting surfaces. Temperature results were consistent with the COF and removal rate data. ADS showed the lowest temperature rise again confirming the softening effect of the adsorbed surfactant layer and less energy dissipation due to friction. Spectral analysis of shear force showed that increasing the pad-wafer sliding velocity at constant wafer pressure shifted the high frequency spectral peaks to lower frequencies while increasing the variance of the frictional force. Addition of ADS reduced the fluctuating component of the shear force and the extent of the pre-existing stick-slip phenomena caused by the kinematics of the process and collision event between pad asperities with the wafer. By contrast, in the case of BTA, there were no such observed benefits but instead undesirable effects were seen at some polishing conditions. This work underscored the importance of real-time force spectroscopy in elucidating the adsorption, lubrication and inhibition of additives in slurries in CMP.

Frequency Characteristics of Fluctuating Pressure on Rotor Blade in a Propeller Fan.

A wavelet transform is introduced to analyze frequency characteristics of the fluctuating pressure on rotor blade in a propeller fan. The fluctuating pressure on the rotor blade is obtained by using the results of a large eddy simulation. The frequencies having high spectral peaks of the fluctuating pressure are determined by taking the time average of the local absolute modulus of the wavelet. The dominant frequency of the real-time pressure selected at the high pressure fluctuation region corresponds well to that of the fluctuating rotor torque and the experimental result of fan noise. It is mainly generated due to the unsteady behavior of the vortical flow, such as the tip vortex and the leading edge separation vortex, in the propeller fan. A frequency in the separation bubble region on the suction surface is higher than that of the dominant frequency caused by the vortical flow.

Noncontact photothermal infrared radiometric deep-level transient spectroscopy of GaAs wafers

A novel infrared photothermal radiometric deep-level transient spectroscopy (PTR-DLTS) has been developed for semiconductor noncontact characterization and applied to GaAs wafer diagnostics. The technique is based on rate-window detection combined with wafer temperature ramping. Unlike other deep-level methodologies, PTR-DLTS should be easily implemented remotely for on-line or off-line impurity/electronic defect diagnostics and enjoys high spectral peak separation and spatial resolution limited only by the pump laser beam focus (≥1 μm). The impurity level in a Cr-compensated semi-insulating GaAs wafer has been detected at ∼375 K using the 514 nm line of an Ar+ laser. A Te-doped GaAs sample exhibited behavior consistent with photoinjected carrier lifetime enhancement due to surface state (trap) thermal filling at elevated temperatures.

Power spectra of inspiratory nerve activity with lung inflations in cats.

To investigate the effect of lung inflations on the high-frequency synchrony (70-122 Hz) observed in the inspiratory activity of respiratory motor nerves of decerebrate cats, I applied a step increase in lung inflation pressure at fixed delays into the inspiratory phase and computed power spectra of phrenic neurograms before and during inflation. In 25 decerebrate paralyzed cats the frequency of the high spectral peak was 92.3 +/- 11.1 Hz before and 105.3 +/- 12.1 Hz during the step in inflation pressure, shifting upward by 13.0 +/- 6.0 Hz. For 8 of the 25 cats, the recurrent laryngeal and phrenic neurograms were recorded simultaneously. The high spectral peak was present during inspiration in the recurrent laryngeal power spectra and coherent with the high peak in the phrenic power spectra. In response to lung inflation, the high peak disappeared from the power spectra of the recurrent laryngeal nerve as the inspiratory activity was inhibited; a shift upward in frequency was not detectable. Comparing inspiratory times (TI, based on the phrenic neurograms) for breaths with no lung inflations to those for breaths with lung inflations, I found that lung inflations early in inspiration caused a decrease in TI, lung inflations at intermediates times had no effect on TI, and lung inflations late in inspiration caused an increase in TI. Despite lung inflation decreasing, not affecting, or increasing inspiratory duration and amplitude of the phrenic neurogram, lung inflation always caused a shift upward in the high-frequency peak of the phrenic power density. The fact that lung inflation, a powerful respiratory stimulus, affected the frequency of the high peak in a consistent manner suggests that the high-frequency synchrony is an important and robust feature of the central respiratory pattern generator.

Do slow orbital periodicities appear in the record of Earth's magnetic reversals?

Time‐series spectral analysis has been performed on the dates of geomagnetic reversals of the last 20 Myr BP and earlier. Possible evidence is found from the presence of high spectral peaks for two very long periodicities, 0.4 Myr and 1.3 Myr, that may be associated with slow variations of the Earth's orbital eccentricity as predicted by Berger. However, statistical significance tests and a number of other arguments do not confirm the two detections.

Testing Correlated "BEG-Like" Data for Normality Using a Modified Kolmogorov-Sminov Statistic

The one-sample Kolmogorov-Smirnov goodness-of-fit test (KS) is designed for use with independent data and can be highly sensitive to correlated data. Standard critical values for KS cannot be used with data with known correlations. For data with EEG-like spectra (low frequency, high amplitude spectral peaks) an empirically derived correction for KS provides correct critical values and retains much of the power of the original KS. The. correction is based on a simple quadratic expression involving a parameter ? computed from zero-crossing measurements.

Electroencephalographic correlates of learning in subcortical and cortical structures

1. 1. Spectral analysis was applied to EEG records taken from amygdala, subthalamus, midbrain reticular formation and visual cortex simultaneously with records from hippocampus during a discrimination learning experiment in cats. High spectral peaks were located in all these structres at 1, 2 and 3 c/sec, indicating an increase in regularity of these slow wave rhythms in advanced stages of training. 2. 2. Spectral peaks in the theta range (particularly at 5 and 6 c/sec) appeared during approach period in the advanced training in all these structures, but were less pronounced and more variable than in hippocampus. 3. 3. Computations of coherences between pairings of EEG records from different structures revealed high degrees of linear interrelation. High and consistent coherences were found between homotopic points in the hippocampal formation of the two hemispheres. More variable coherences were seen between hippocampus and subthalamus, midbrain reticular formation and visual cortex. These relationships were most consistent in the theta range, in the approach epoch and in the advanced stage of learning. 4. 4. Our data indicate that during the period of consolidation of learning, the hippocampus plays a leading role in complex interacting neural circuits comprising hippocampus, subthalamus, midbrain reticular formation and cerebral cortex.