Extreme tunability in aluminum doped zinc oxide plasmonic materials for near-infrared applications.

Plasmonic materials (PMs), featuring large static or dynamic tunability, have significant impact on the optical properties due to their potential for applications in transformation optics, telecommunications, energy, and biomedical areas. Among PMs, the carrier concentration and mobility are two tunable parameters, which control the plasma frequency of a metal. Here, we report on large static and dynamic tunability in wavelengths up to 640 nm in Al-doped ZnO based transparent conducting degenerate semiconductors by controlling both thickness and applied voltages. This extreme tunability is ascribed to an increase in carrier concentration with increasing thickness as well as voltage-induced thermal effects that eventually diminish the carrier concentration and mobility due to complex chemical transformations in the multilayer growth process. These observations could pave the way for optical manipulation of this class of materials for potential transformative applications.

Self-assembled hierarchical nanostructures composed of novel chalcopyrite nanosheets for photovoltaic properties.

Self-assembled nanostructures of CulnGaSe2 (CIGS) comprising of nanosheets with sheet thickness of 20 nm have been developed via one-step electrochemically alloying technique. These self-assembled nanoplates exhibit highly intersecting behavior and transform from CuSe to CIGS as the reduction potential was varied. The morphological analysis indicated that the process resulted in a progression of crystallites to a series of heavy dense intersecting nanoplates. Further analyses revealed that the nanostructures keep their integrity on heat treatment. The structure confirms the inclusion of Indium and Gallium at higher reduction potentials and its transition from pseudoamorphous to polycrystalline structure. A strong correlation between reduction potential, and the composition was established. The spectroscopic and optical spectra clearly prove that the direct band gap for the as-grown and annealed thin films, and appropriate for solar cell applications. These self-assembled dense interweaved nanoplates structure have not been observed previously in CIGS semiconductor system and have potential implications forenergy applications.

Effects of surface potential on growth of ZnO nanorod arrays investigated by electric force microscopy.

The electric and Kelvin force probe microscopy were used to investigate the surface potentials on the ZnO seed layer, which shows a remarkable dependence on the annealing temperature. The optimum temperature for the growth of nanorod arrays normal to the surface was found to be at 600 degrees C, which is in the range of right surface potentials and energy measured between 500 degrees C and 700 degrees C. We demonstrated from both electric and Kelvin force probe microscopy studies that surface potential controls the growth of ZnO nanorods, illustrating the fact that this is a promising technique to visualize the control of ZnO nanorod arrays by studying their surface potentials. This study will provide important understanding of growth of other nanostructures.

Synthesis and magnetic characterizations of La(1-x)Sr(x)MnO3 nanoparticles for biomedical applications.

The La(1-x)Sr(x)MnO3 (LSMO) nanoparticles have been synthesized by citric gel process followed by ball milling method. These nanoparticles demonstrated high crystalline quality. Nanoparticle size was further decreased by ball milling technique as observed by the field-emission scanning electron microscopic studies. The ball milled and silica coated LSMO nanoparticles show magnetic transition at about 370 K with a superparamagnetic properties. The ferromagnetic resonance (FMR) spectra analysis of LSMO nanoparticles shows large FMR linewidth due to the surface strain of the nanoparticles. Both magnetization and FMR studies demonstrate that the LSMO nanoparticles are highly anisotropic. The toxicity of the nanoparticles was studied for safe biomedical applications. Measurement of intracellular reactive oxygen species (ROS) and MTT assay results show that LSMO nanoparticles are relatively nontoxic and the toxicity is further reduced by SiO2 coating. These results are very important for applications in the field of biotechnology.

Elongation of surface plasmon polariton propagation length without gain.

We have demonstrated that an addition of highly concentrated rhodamine 6G chloride dye to the PMMA film adjacent to a silver film can cause 30% elongation of the propagation length of surface Plasmon polaritons (SPPs). The possibility to elongate the SPP propagation length without optical gain opens a new technological dimension to low-loss nanoplasmonic and metamaterials.

Compensation of loss in propagating surface plasmon polariton by gain in adjacent dielectric medium.

We report the suppression of loss of surface plasmon polariton propagating at the interface between silver film and optically pumped polymer with dye. The large magnitude of the effect enables a variety of applications of 'active' nanoplasmonics. The experimental study is accompanied by the analytical description of the phenomenon. In particular, we resolve the controversy regarding the direction of the wavevector of a wave with a strong evanescent component in an active medium.

Enhancement of surface plasmons in an Ag aggregate by optical gain in a dielectric medium.

We have observed the compensation of loss in a metal by a gain in a dielectric medium in the mixture of an Ag aggregate and a Rhodamine 6G dye. The demonstrated sixfold enhancement of the Rayleigh scattering is the evidence of the enhancement of the surface-plasmon resonance. The reported experimental observation facilitates many applications of nanoplasmonics.

Optimization of the transport mean free path and the absorption length in random lasers with non-resonant feedback.

We have studied numerically the optimal range of the transport mean free path lt and the absorption length (at the pumping wavelength) la, which minimize the threshold and maximize the slope efficiency of a random laser with non-resonant feedback. The results of the calculations are in a good agreement with the experimental results obtained in the GaAs/Al2O3 random laser.

Respiratory sounds classification using cepstral analysis and Gaussian mixture models.

The Cepstral analysis is proposed with Gaussian Mixture Models (GMM) method to classify respiratory sounds in two categories: normal and wheezing. The sound signal is divided in overlapped segments, which are characterized by a reduced dimension feature vectors using Mel-Frequency Cepstral Coefficients (MFCC) or subband based Cepstral parameters (SBC). The proposed schema is compared with other classifiers: Vector Quantization (VQ) and Multi-Layer Perceptron (MLP) neural networks. A post processing is proposed to improve the classification results.

Diode-laser noise conversion in an optically dense atomic sample.

We report on oscillating complex noise spectra obtained when a diode-laser beam passes through a resonant dense Doppler-broadened cesium-vapor cell. Atomic coherence converts the laser phase noise into amplitude noise in the transmitted beam. We have found that the level of amplitude noise is orders of magnitude above the intrinsic laser noise. As a function of laser detuning, this noise extends over several inhomogeneous widths, depending on the spectral frequency. Numerical calculations based on a simple theory remarkably mimic the details of the experimental noise spectra.

DSP implementation of wavelet transform for real time ECG wave forms detection and heart rate analysis.

An algorithm based on wavelet transform (WTs) suitable for real time implementation has been developed in order to detect ECG characteristics. In particular, QRS complexes, P and T waves may be distinguished from noise, baseline drift or artefacts. This algorithm is implemented in a DSP (SPROC-1400) with a 50 MHz frequency clock. The performance of this algorithm is discussed, its accuracy is evaluated and a comparison is made with a similar algorithm implemented in C language. For the standard MIT/BIH arrhythmia database, this algorithm correctly detects 99.7% of the QRS complexes.