AlGaAs heterojunction lasers

The characterization of 8300 A lasers was broadened, especially in the area of beam quality. Modulation rates up to 2 Gbit/sec at output powers of 20 mW were observed, waveform fidelity was fully adequate for low BER data transmission, and wavefront measurements showed that phase aberrations were less than lamda/50. Also, individually addressable arrays of up to ten contiguous diode lasers were fabricated and tested. Each laser operates at powers up to 30 mW CW in single spatial mode. Shifting the operating wavelength of the basic CSP laser from 8300 A to 8650 A was accomplished by the addition of Si to the active region. Output power has reached 100 mW single mode, with excellent far field wave front properties. Operating life is currently approx. 1000 hrs at 35 mW CW. In addition, laser reliability, for operation at both 8300 A and 8650 A, has profited significantly from several developments in the processing procedures

Development of novel nano-structured materials for Enhanced Raman Spectroscopies: an insight in SERS and TERS applications

Owing to their ultrahigh selectivity and sensitivity, the plasmon-enhanced Raman spectroscopies (PERS) methods have emerged as diverse and exciting cutting-edge techniques for the investigation of biosystems at nanometric scales in air or water environments. By exploiting the plasmonic properties of noble metal nanoparticles, the PERS methods enable to remove the main obstacle of the Raman spectroscopy represented by the small Raman cross- section. Among them, the Surface Enhanced Raman Spectroscopy (SERS) is certainly the most important in terms of the number of applications in many fields of science (physics, chemistry, and biomedicine). One of the interesting features of the SERS is that the huge amplification of inelastic Raman photons can reach up to 12 orders of magnitude allowing even the detection at single-molecule level. In addition, the strong distance dependence of the plasmonic near-field effect (∼ 10-20 nm) makes effective the SERS only for molecules in proximity to metal-nanostructured surfaces and, thus, suitable not only for the bio-analysis of membranes but also for the surface characterization in science materials. Anyway, beyond the high sensitivity, the limitation of the SERS is represented by the diffracted-limited spatial resolution. A significant improvement is given by the modern tip-enhanced Raman spectroscopy (TERS) technique. By combining the high resolution of scanning-probe microscope (SPM) technology and the sensitivity of SERS, TERS is capable to correlate topographical and chemical information of a sample at nanoscale level. In fact, the Raman signal coming from the probed molecules is strongly enhanced via SERS effect when they are in proximity of the apex of a metalized or metallic SPM tips. Moreover, the scattering efficiency of TERS signal is greatly increased when the metal surface of the probe is nano-structured. The spatial resolution of TERS signals is mainly ruled by the tip-radius, which is typically of few tens of nanometers, therefore allowing to reach a lateral resolution in the range of 10-50 nm, far beyond the diffraction limit. Anyway, the development of reliable and effective plasmonic devices for SERS and TERS applications represents the major obstacle towards a wider diffusion of TERS/SERS as powerful analytical tools in material science and life science. In the case of TERS, the main technological challenge is based on the fabrication of metal nano-structures on the tip. Compared to SERS substrates that are produced on large-area surfaces, the sub-micron dimensions of the tip apex make the nano-structuring task more tricky. In this frame, the current thesis work aims to present a novel and versatile method for the preparation of appropriate AFM-TERS tips and SERS substrates. The innovative approach is based on the application of a radio-frequency discharge produced by an inductively coupled plasma (ICP) on commercial Ag-covered AFM probes. The plasma treatment produces an intriguing metallic porous nanotexture resembling a coral-like structure. The so-produced probes have been characterized by showing an amplification up to six orders of magnitude and a spatial resolution down to 10 nm, which render these devices particularly attractive for nanometer chemical characterization. In addition, this method has been successfully implemented for the fabrication of broad-band SERS-active platforms. This protocol has shown to be effective to produce substrates that can amplify the Raman signal up to seven orders of magnitude. Finally, another method for the fabrication of SERS substrates, based on the self-assembly of block copolymer (BCP) loaded with Ag-NPs, is proposed. The sensitivity of the so-prepared substrates has been tested by revealing the over-expression of target proteins in membranes of cancer cells

Análisis de serie de datos de gravedad de larga duración en Europa : consecuencias para el estudio de señales de pequeña amplitud y baja frecuencia incluyendo los efectos de resonancia del núcleo terrestre

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Matemáticas, Sección Departamental de Astronomía y Geodesía, leída el 24-04-2015El registro de las variaciones temporales de la gravedad tiene una larga tradición en Europa. En Estrasburgo el primer gravímetro adquirido con el propósito de observar dichas variaciones fue instalado en 1954. Desde entonces 8 modelos diferentes de gravímetros gravímetros de muelle, superconductores SG y gravímetros absolutos han estado registrando en períodos consecutivos. Durante estas seis décadas, los sensores, los sistemas de adquisición y las técnicas de análisis han mejorado drásticamente. Utilizando todas las series del observatorio J9 de Estrasburgo para verificar estas mejoras, se concluye que la precisión ha sido incrementada más de 10 veces con respecto a los primeros modelos de gravímetros de muelle utilizados. Posteriormente se utilizan varias de las series de datos de gravedad de mayor longitud registradas en Europa con diferentes modelos de gravímetros de muelle en BFO Alemania, 1980,2012, Walferdange Luxemburgo, 1980,1995 y Potsdam Alemania, 1974,1998, y varias estaciones de SGs con al menos 9 años de registro pertenecientes todas ellas a la red mundial GGP, Bad Homburg, Bruselas, Medicina, Membach, Moxa, Viena, Wettzell y J9, para poder comparar la sensibilidad de los diferentes tipos de instrumentos a través de la evolución temporal de los factores gravimétricos amplitud y desfase de las principales ondas de mareas diurnas y semidiurnas O1, P1, K1, M2, S2 y K2 y de la relación entre las amplitudes M2 O1 esta relación al ser independiente de la calibración instrumental es un muy buen indicador de la estabilidad del instrumento. Aparecen diversas variaciones temporales en los factores de amplitud de todas las series, siendo muy similares para casi todas las series de SGs, con una estabilidad entre el 0,03 y el 0,3 por ciento. Los posibles orígenes de estas variaciones son estudiados, para ello se analizan las correlaciones con efectos geofísicos, con el ruido instrumental y ambiental, etc. Y se lleva a cabo un estudio detallado de la estabilidad del factor de calibración del SG instalado en J9, a través de los numerosos experimentos de calibración realizados mediante el registro en paralelo de un gravímetro absoluto.Teniendo en cuenta todos estos resultados, se profundiza en los principales beneficios obtenidos al utilizar registros muy largos de SGs a la hora de realizar un análisis de mareas o un análisis espectral. Utilizando la serie de 27 años de los SGs instalados en J9, que es la serie más larga a nivel mundial, su longitud nos permite separar las contribuciones correspondientes a ondas con frecuencias muy cercanas, detectar señales muy débiles especialmente ondas derivadas del potencial de marea de grado 3 y detectar efectos con frecuencia muy bajas.En la última parte, después de revisar la historia de las primeras observaciones de la resonancia de la FCN utilizando datos de gravedad, se estiman los valores de sus parámetros Q y TFCN utilizando todas las series de J9 y del resto de las estaciones de SGs. Los valores obtenidos son muy cercanos a los valores estimados tanto mediante cálculos teóricos como a partir de observaciones de VLBI. También se estudia otro modo de rotación, el denominado FICN cuyos efectos no han sido nunca observados en los datos de gravedad, y del que los cálculos teóricos predicen un efecto muy pequeño de resonancia en las mareas terrestres. Para intentar observar alguna consecuencia derivada del FICN se desarrolla una metodología que nos permite ir limitando el rango de frecuencias de estudio, a través del análisis de mareas detallado en la banda de frecuencia diurna, separando ondas de amplitudes tan pequeñas que nunca antes habían sido observadas y que pudieran estar lo suficientemente próximas a la frecuencia asociada a la FCIN como para verse afectadas en términos de amplitud. Un posible efecto de resonancia aparece próximo a 1,00198 cpd 0,99924 CpsD, que correspondería a un período de alrededor de 1.300 días sid.Unidad Deptal. de Astronomía y GeodesiaFac. de Ciencias MatemáticasTRUEunpu

Theoretical Investigation of Static and Dynamic Properties of Zeolite ZSM-5 Based Amorphous Material

Results of molecular dynamics simulations on structural, vibrational and relaxational properties of zeolite ZSM-5 based amorphous solids are presented. The effects of extent of amorphization, measured by an energetic criterion, on properties like distribution of coordination numbers, internal surface area, ring statistics and effective pore size are studied. Ring statistics indicates that upon amorphization not only rings with larger size break down to give rings with smaller size, but that for intermediate degree of amorphization also larger rings are generated. The vibrational density of states was determined for different extents of amorphization. The vibrational modes are analyzed by projecting them on those of the SiO4 and Si-O-Si subunits and individual frequency-dependent contributions of stretching, bending and rotation are discussed. Analysis of low-frequency spectrum show that for higher crystallinity the intensity of the boson peak decreases upon amorphization, whereas the opposite behavior is observed for forms with lower crystallinity. These effects are explained in the framework of Maxwell counting of floppy modes. The modes associated with the boson peak for these materials are found to be mainly optic in nature. Relaxations were studied for temperatures below the critical temperature. At low temperatures the relaxations comprise mainly one-dimensional chains of atoms. The dimensionality of the relaxing centers increases with the temperature due to side branching. The possibility of having reversible jumps decreases with increasing temperature due to a strong drop in the potential energy during aging. There exist very prominent peaks in the van Hove correlation functions as a manifestation of the hopping processes. The dynamics of the oxygen atoms is found to be more heterogeneous than those of the silicon atoms. Ab initio many-body calculations on the strain energy ofW-silica, taken as a model system for edge-sharing tetrahedral SiO2-systems with respect to corner-sharing ones as in a-quartz was performed. Correlation contributions are found to play an important role to determine the stability of edge-sharing units. Our calculation reveal that edge-sharing SiO4 tetrahedra in (partially) amorphous silicate systems are possible at a modest energetic expense

Atomistic investigation of conjugated polymers for thermoelectric applications: from morphology to transport properties

Two centuries after its first discovery, thermoelectricity, i.e. the phenomenon of direct conversion of thermal power into electrical power, has only recently reached the possibility of implementation in a vast number of practical applications. This breakthrough was undoubtedly determined by the advent and diffusion of numerical atomistic simulation techniques, allowing a quick survey of large classes of materials as possible candidates for the realization of active parts for thermoelectric generators. To this aim, two classes of materials have been essentially identified, (I) inorganic thermoelectrics, based on metal alloys, and (II) organic conductive polymers. The latter ones are well suited for implementation in a large-scale economy because of their superior mechanical properties, such as flexibility and low specific weight, as well as simpler synthesis process, as spin coating, and the possibility of tuning the electrical conductivity through chemical doping. Among the most common conducting polymers, polyethylenedi-oxythiophene (PEDOT), the subject of this Thesis work, has clearly emerged as one of the most promising thermoelectric material. Despite its wide use, however, an unanimous and well-established understanding of the link existing between the synthesis process and the corresponding final thermoelectric properties is still missing and it is thus an active field of scientific investigation. The present Thesis represents a part of this research stream, specifically aiming to shed a light on the role and effect of the combinations of most commonly used polymerizing reagents for PEDOT in determining the micromorphology and the resulting thermal and electrical transport properties. In this respect, the description and development of a new computational algorithm, based on a multiscale approach, is presented, combining a purely quantum description based on the Density Functional Theory (DFT) with Classical Molecular Dynamics (MD). The comparison of the results obtained by numerical simulation with the experimental data currently available demonstrates the effective possibility of including the chemical description of the synthesis process in the context of an MD simulation, and allows to demonstrate and quantify the impact of the combination of reagents used on (i) micromorphological properties, such as chain length distribution and crystallinity, (ii) thermal transport properties, in particular thermal conductivity, and (iii) carrier transport properties, mainly hole mobility and conductivity, estimated by Marcus' theory of electron transport

Quantum Chemical Investigation of Electronic and Structural Properties of Crystalline Bismuth and Lanthanide Triborates

The origins of the optical effects and the chemical stability of BiB3O6 are studied by gradient-corrected hybrid B3PW density functional theory within the Gaussian-orbital-based CO-LCAO scheme. Including spin-orbit coupling, B3PW yields an estimate of the indirect band gap of 4.29~4.99 eV which is closer to the experimental value of 4.3 eV than the HF, LDA or GGA results. The crystal orbital overlap population is carried out to give a detailed first-principles analysis of chemical bonding. It is found that the Bi 6s couples with the O 2p in the primary interaction, which eventually forms both bonding and antibonding orbitals below the Fermi level. The Bi 6p is further involved in the secondary interaction with the filled Bi 6s-O 2p antibonding orbitals. The stereochemical activity of the Bi lone-pairs mainly originates from the primary interaction for the occupied Bi 6s-O 2p antibonding orbitals. It is found that the Bi 6p orbitals are not critically responsible for the non-spherical shape of the Bi lone-pairs. The densities of optical absorptions for the total BiB3O6 crystal, [BiO4]5- and [BO3]3- and [BO4]5- subunits are individually calculated by convoluting the total occupied density of states and the virtual densities of states of the corresponding unit. It is found that the [BiO4]5- units are mainly responsible for the optics of BiB3O6 in the long wavelength region. The reason is that the Bi-O covalent bonds lead to large spatial orbital overlappings and thus favor the electronic transfer from the occupied O 2p to the empty Bi 6p orbitals. The relativistic and correlation effects lead to fundamental differences of the band structure, chemical bonds and optical effects for BiB3O6 compared with non-relativistic and uncorrelated calculations. The harmonic frequencies of BiB3O6 are calculated by applying the numerical-difference technique. The complete 13 A and 14 B vibrational modes are assigned, graphically visualized and classified according to the Bi-O and B-O motions. Comparisons with previous experimental reports are discussed in detail. Crystal orbital adapted Gaussian (4s4p3d), (5s5p4d) and (6s6p5d) valence primitive basis sets are derived, in line with relativistic energy-consistent 4f-in-core lanthanide pseudopotentials of the Stuttgart-Köln variety, for calculating periodic bulk materials containing trivalent lanthanide ions, particularly in this thesis for the investigation of the relative stability of C2 and I2 phases of LnB3O6. Different segmented contraction schemes are calibrated on A-type Pm2O3 studying the basis set size effects. Further applications to the geometry optimization of other A-type Ln2O3 (Ln=La-Nd) show a satisfactory agreement with experimental data using the lanthanide valence basis sets (6s6p5d)/[4s4p4d]. The cohesive energies of A-Ln2O3 within both conventional Kohn-Sham DFT and the a posteriori-HF correlation DFT schemes are evaluated by using the corresponding augmented sets (8s7p6d)/[6s5p5d] with additional diffuse functions for the atomic energies of free lanthanide atoms. The I2 phases of LaB3O6 and GdB3O6 crystals are more stable than C2 phases according to both of the calculated energetic data and first-principles bond analysis. This is in agreement with the experimental results. A new method is developed to calculate the optical properties for large systems based on available wavefunction correlation approaches in the framework of the incremental scheme. The convergence behaviors of first- and second-order polarizabilities with respect to the domain distances and incremental expansion orders are examined and discussed for the model system Ga4As4H18