Development of laser-fired contacts for amorphous silicon layers obtained by Hot-Wire CVD

In this work we study aluminium laser-fired contacts for intrinsic amorphous silicon layers deposited by Hot-Wire CVD. This structure could be used as an alternative low temperature back contact for rear passivated heterojunction solar cells. An infrared Nd:YAG laser (1064 nm) has been used to locally fire the aluminium through the thin amorphous silicon layers. Under optimized laser firing parameters, very low specific contact resistances (ρc ∼ 10 mΩ cm2) have been obtained on 2.8 Ω cm p-type c-Si wafers. This investigation focuses on maintaining the passivation quality of the interface without an excessive increase in the series resistance of the device.

Structural characterization of laser-treated Cr3C2-NiCr coatings

The interconnected porosity of the Cr3C2-NiCr coatings obtained by high-velocity oxy fuel spraying is detrimental in corrosion and wear resistance applications. Laser treatments allow sealing of their surfaces through melting and resolidification of a thin superficial layer. A Nd:YAG laser beam was used to irradiate Cr3C2-NiCr coatings either in the continuous wave mode or at different repetition rates in the pulsed one. Results indicated that high peak and low mean laser irradiances are not good, since samples presented deep grooves and an extensive crack network. At low peak and higher mean laser irradiances the surface was molten, and only a few shallow cracks were observed. The interconnected porosity was completely eliminated in a layer up to 80 m thick, formed by large Cr7C3 grains imbedded in a NiCr matrix.

Characterization of hydroxyapatite laser ablation plumes by fast intensified CCD-imaging

ArF excimer laser pulses (193 nm, 20 ns, 150 mJ) have been focused on a hydroxyapatite (HA) target in similar conditions to those normally used for thin film deposition. Fast intensified CCD images of HA laser ablation plumes have been taken in vacuum and under different water vapor pressures ranging from 0.01 mbar to 1 mbar. Images of HA ablation in vacuum have shown a plume freely expanding at a constant velocity of 2.3 106 cm/s. HA ablation under a water vapor pressure of 0.01 mbar has revealed an expansion behavior very similar to that of ablation in vacuum. Images taken under a water vapor pressure of 0.1 mbar have shown the formation of a shock structure in the plume. Finally, HA ablation under a water vapor pressure of 1 mbar has revealed the development of some irregularities in the shape of the plume.

Spectroscopic ellipsometry study of the In1-x Gax Asy P1-y / InP Heterojunctions grown by metalorganic chemical-vapor deposition

The dielectric functions of InP, In0.53Ga0.47As, and In0.75Ga0.25As0.5P0.5 epitaxial layers have been measured using a polarization modulation spectroscopic ellipsometer in the 1.5 to 5.3 eV region. The oxide removal procedure has been carefully checked by comparing spectroscopic ellipsometry and x ray photoelectron spectroscopy measurements. These reference data have been used to investigate the structural nature of metalorganic chemical vapor deposition grown In0.53Ga0.47As/InP and In0.75Ga0.25As0.5P0.5/InP heterojunctions, currently used for photodiodes and laser diodes. The sharpness of the interfaces has been systematically compared for the two types of heterojunctions: In1 xGaxAsy/InP and InP/In1 xGaxAsyP1 y. The sharpest interface is obtained for InP growth on In0.75Ga0.25As0.5P0.5 where the interface region is estimated to be (10±10) Å thick. The importance of performing in situ SE measurements is emphasized.

Thermal increment due to ErCr: YSGG and CO2 laser irradiation of different implant surfaces. A pilot study

Objective: An evaluation and comparison is made of the thermal increment at different implant surfaces during irradiation with CO2 and ErCr:YSGG lasers. Study design: Five threaded and impacted implants with four types of surfaces were inserted in an adult pig rib: two implants with a hydroxyapatite surface (HA)(impacted and threaded, respectively), a machined titanium surface implant (TI mach), a titanium plasma spray surface implant (TPS), and a sandblasted, acid-etched surface implant (SBAE). A 0.5-mm diameter bone defect was made in the implant apical zone, and a type-K thermocouple (Termopar)® was placed in contact with the implant. The implants were irradiated in the coronal zone of each implant with a CO2 (4 W continuous mode) and an ErCr:YSGG laser (1.5 W, pulsed mode) first without and then with refrigeration. The temperature variations at the implant apical surface were recorded. Results: An apical temperature increase was recorded in all cases during CO2 and ErCr:YSGG laser irradiation without refrigeration. However, when the ErCr:YSGG was used with a water spray, a decrease in temperature was observed in all implants. The acid-etched and sandblasted surfaces were those most affected by the thermal changes. Conclusions: The ErCr:YSGG laser with a water spray applied to the sealing cap or coronal zone of the implants does not generate thermal increments in the apical surface capable of adversely affecting osseointegration and the integrity of the peri-implant bone tissue

Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

The singular properties of hydrogenated amorphous carbon (a-C:H) thin filmsdeposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, make it suitable as protective coating with low surface energy for self-assembly applications. In this paper, we designed fluorine-containing a-C:H (a-C:H:F) nanostructured surfaces and we characterized them for self-assembly applications. Sub-micron patterns were generated on silicon through laser lithography while contact angle measurements, nanotribometer, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface. a-C:H:F properties on lithographied surfaces such as hydrophobicity and friction were improved with the proper relative quantity of CH4 and CHF3 during deposition, resulting in ultrahydrophobic samples and low friction coefficients. Furthermore, these properties were enhanced along the direction of the lithographypatterns (in-plane anisotropy). Finally, self-assembly properties were tested with silicananoparticles, which were successfully assembled in linear arrays following the generated patterns. Among the main applications, these surfaces could be suitable as particle filter selector and cell colony substrate.

Empleo de óptica adaptativa y fluorescencia en un oftalmoscopio laser de barrido para el registro de células

Estudio elaborado a partir de una estancia en la Universidad de Rochester, Estados Unidos, de octubre del 2006 a enero del 2007. La estancia realizada en la Universidad de Rochester estuvo orientada al aprendizaje en profundidad del oftalmoscopio láser de barrido. El oftalmoscopio láser de barrido emplea una técnica confocal con la finalidad de visualizar diferentes estructuras retinianas en seres vivos. El instrumento diseñado y desarrollado en el Centro de Ciencias de la Visión incorpora un sistema de óptica adaptativa y fluorescencia. La óptica adaptativa aplicada en este oftalmoscopio tiene como objetivo corregir las aberraciones existentes en el ojo y así permitir observar detalles de la retina que de otra forma se verían emborronados. De esta forma se consigue alcanzar valores de resolución muy cercanos a los impuestos por difracción. Por otro lado el uso de fluorescencia tiene por objetivo el permitir la visualización de células y estructuras que, de no ser teñidas, son transparentes a la luz y visible. Esta técnica se ha estado utilizando principalmente en primates y ratas, aunque actualmente también se están llevando a cabo medidas de células de epitelio pigmentario en seres humanos ya que el pigmento contenido en estas células permite la aplicación de la fluorescencia sin necesidad de utilizar tinción.

Terrestrial laser scanning for landslides deformation monitoring

Within last few years a new type of instruments called Terrestrial Laser Scanners (TLS) entered to the commercial market. These devices brought a possibility to obtain completely new type of spatial, three dimensional data describing the object of interest. TLS instruments are generating a type of data that needs a special treatment. Appearance of this technique made possible to monitor deformations of very large objects, like investigated here landslides, with new quality level. This change is visible especially with relation to the size and number of the details that can be observed with this new method. Taking into account this context presented here work is oriented on recognition and characterization of raw data received from the TLS instruments as well as processing phases, tools and techniques to do them. Main objective are definition and recognition of the problems related with usage of the TLS data, characterization of the quality single point generated by TLS, description and investigation of the TLS processing approach for landslides deformation measurements allowing to obtain 3D deformation characteristic and finally validation of the obtained results. The above objectives are based on the bibliography studies and research work followed by several experiments that will prove the conclusions.

Technological innovation in creative clusters. The case of laser in conservation of artworks in Florence

The field of laser application to the restoration and cleaning of cultural assets is amongst the most thriving developments of recent times. Ablative laser technological systems are able to clean and protect inestimable works of art subject to atmospheric agents and degradation over time. This new technology, which has been developing for the last forty year, is now available to restorers and has received a significant success all over Europe. An important contribution in the process of laser innovation has been carried out in Florence by local actors belonging to a creative cluster. The objects of the analysis are the genesis of this innovation in this local Florentine context, and the relationships among the main actors who have contributed in it. The study investigates how culture can play a part in the generation of ideas and innovations, and which are the creative environments that can favour it. In this context, the issue of laser technologies for the restoration of cultural heritage has been analysed as a case study in the various paths taken by the Creative Capacity of the Culture (CCC).

Sistemes lidar (radar laser) d'ona contínua i baixa potència per a la detecció i mesura de concentració de gasos amb resolució espacial

The present project has performed the study and development of a new technique for the detection of gases with range resolution. This technique called FMCW-lidar is a technique that evolves from the FMCW-radar technique to be applied to lidar systems. Moreover, it takes advantage of the appearance of spectral absorption lines because of the interaction between light and gases to tune the light wavelength of a laser emitter with one of this spectral lines and then detects the backscattered light and analyzes it in order to obtain gas concentration measurements. The first part of the project consisted in the analysis of the WMS technique which is a technique for the in-situ measurement of gases. A complete theoretical analysis has been performed and some experiments have been carried out in order to test the technique and to validate its application to an FMCW-modulated system for the detection of gases. The second part of the project consisted in the analysis of the lidar FMCW technique for solid target detection and its extension to continuous media. The classical form of this technique has been analyzed for a distributed medium and a filtering effect has been found which prevents the accurate acquisition of the medium response. A modification of the technique has been proposed and a validation via simulations and some experiments has been carried on. After performing these tests, a novel system is proposed to be developed and tested in order to perform the indicated gas detection with range resolution.

Obtenció de capes primes d'alúmina mitjançant "Atomic Layer Deposition"

En aquest projecte s'ha estudiat la posada a punt d’un equip comercial ALD per a l’obtenció de capes primes d'alúmina a escala nanomètrica utilitzant vapor d’aigua i TMA com a precursors. Per tal de comprovar a bondat de les receptes experimentals aportades pel fabricant així com comprovar alguns aspectes de la teoria ALD s’han realitzat una sèrie de mostres variant els diferents paràmetres experimentals, principalment la temperatura de deposició, el nombre de cicles, la durada del cicle i el tipus de substrat. Per a la determinació dels gruixos nanomètrics de les capes i per tant dels ritmes de creixement s’ha utilitzat la el·lipsometria, una de les poques tècniques no destructives capaç de mesurar amb gran precisió gruixos de capes o interfases de pocs àngstroms o nanòmetres. En una primera etapa s'han utilitzat els valors experimentals donats pel fabricant del sistema ALD per determinar el ritme de creixement en funció de la temperatura de dipòsit i del numero de cicles, en ambdós casos sobre diversos substrats. S'ha demostrat que el ritme de creixement augmenta lleugerament en augmentar la temperatura de dipòsit, tot i que amb una variació petita, de l'ordre del 12% en variar 70ºC la temperatura de deposició. Així mateix s'ha demostrat la linealitat del gruix amb el número de cicles, tot i que no s’observa una proporcionalitat exacta. En una segona etapa s'han optimitzat els paràmetres experimentals, bàsicament els temps de purga entre pols i pols per tal de reduir considerablement les durades dels experiments realitzats a relativament baixes temperatures. En aquest cas s’ha comprovat que es mantenien els ritmes de creixement amb una diferencia del 3,6%, 4,8% i 5,5% en optimitzar el cicles en 6,65h, 8,31h, o 8,33h, respectivament. A més, per una d'aquestes condicions s’ha demostrat que es mantenia l’alta conformitat de les capes d’alúmina. A més, s'ha realitzat un estudi de l'homogeneïtat del gruix de les capes en tota la zona de dipòsit del reactor ALD. S’ha demostrat que la variació en gruix de les capes dipositades a 120ºC és com a màxim del 6,2% en una superfície de 110 cm2. Confirmant l’excepcional control de gruixos de la tècnica ALD.

Involvement of Dab1 in APP processing and [beta]-amyloid deposition in sporadic Creutzfeldt-Jakob patients.

Alzheimer"s disease and prion pathologies (e.g., Creutzfeldt-Jakob disease) display profound neural lesions associated with aberrant protein processing and extracellular amyloid deposits. For APP processing, emerging data suggest that the adaptor protein Dab1 plays a relevant role in regulating its intracellular trafficking and secretase-mediated proteolysis. Although some data have been presented, a putative relationship between human prion diseases and Dab1/APP interactions is lacking. Therefore, we have studied the putative relation between Dab1, APP processing and Aβ deposition, targets in sCJD cases. Our biochemical results categorized two groups of sCJD cases, which also correlated with PrPsc types 1 and 2 respectively. One group, with PrPsc type 1 showed increased Dab1 phosphorylation, and lower βCTF production with an absence of Aβ deposition. The second sCJD group, which carried PrPsc type 2, showed lower levels of Dab1 phosphorylation and βCTF production, similar to control cases. Relevant Aβ deposition in the second sCJD group was measured. Thus, a direct correlation between Dab1 phosphorylation, Aβ deposition and PrPsc type in human sCJD is presented for the first time.