1,354,682 research outputs found
Germanium Quantum Dot Grätzel-Type Solar Cell
No full textSolar cells fabricated from sustainable quantum dot materials are currently not commercially available, but ongoing research provides a steady increase in efficiency and stability of laboratory devices. In this work, the first germanium quantum dot solar cell made with a gas aggregation nanoparticle source is presented. UV-vis spectroscopy reveals quantum confinement, and the spectral response of the germanium quantum dot Gratzel-type solar cell confirms the presence of large and small band gap optical absorption due to a mix of particle sizes. Some of the particles are small enough to have substantial quantum confinement while others are so large that they have bulk-like properties. The efficiency of the germanium quantum dot solar cells is very low but could reach 1% if the formation of germanium oxide layers is avoided in future experiments. This first quantum dot solar cell made with a gas aggregation nanoparticle source demonstrates, as a proof of concept, the technological potential for research and applications combining the fields of photovoltaics and gas aggregation nanoparticle sources
Shifting from a standard protocol of communication to an emergency protocol in the monitoring of large infrastructural systems
No full textRecent catastrophic failures of civil engineering infrastructures have drawn attention on the need to better manage these complex engineered systems to ensure their safe use by the society. Structural health monitoring (SHM) has emerged over the past decade as an active, interdisciplinary research field dealing with the development of sensing technologies and data processing methods aimed to perform condition assessment and damage detection of structural systems. Though many advances have been made over that period, measuring displacements from civil structures is often challenging and costly with the conventional structural health monitoring applications. To overcome the drawbacks due to the wired solutions and the use of expensive equipment, alternative methods were recently developed. This thesis comes with two main innovative aspects. The advancement of wireless sensors to reduce the cost of monitoring systems is at the core of the dissertation. After that, the author activity addresses the need to transmit the information also in emergency situation, by satellites, to the location where the collected data are supposed to be processed. The proposed system is validated, showing control mechanism and laboratory tests, in order to provide a reliable way that may be adopted in the real-time structural health monitoring and managed by remote control
Elongated Nanostructured Solar Cells with a Plasmonic Core
No full textIn this chapter the effects of the plasmonic response in an elongated nano-scale solar cell with a silver nanoneedle core are explored by measuring photocurrents. The silver nanoneedles formed the support of a conformally grown hydrogenated amorphous silicon (a-Si:H) n-i-p junction around it. A spherical morphology of the solar cell functions as a nano-lens, focusing incoming light directly on the plasmonic silver nanoneedle. We found that plasmonics, geometric optics, and Fresnel reflections affect the nanostructured solar cell performance, depending strongly on light incidence angle and polarization. Besides the plasmonic effects, nano-focusing, and orthogonalization of carrier and photon pathways are simultaneously present at illumination of this structure. In this chapter the photovoltaics characterization techniques and simulations are explained and discussed as well. This work provides valuable insight in solar cell processes in which novel concepts such as plasmonics, elongated nanostructures, and nanolenses are used
Very Long Plasmon Oscillation Lifetimes in the Gap Between Two Gold Particles
No full textA small gap between metal nanoparticles provides a strong local field enhancement when illuminated with light. This local field enhancement has proven to be very useful to enhance the response in Raman spectroscopy and may even contribute to increased efficiency in solar cells. Here, the nature of the field enhancement and the effect on the optical absorption spectrum has been identified by measuring the electro-magnetic fields within and outside the nanoparticle gap. Time resolved measurement of the electric field component showed that the plasmon resonance within the gap lives much longer than the excitation pulse duration. These results elucidate the optical properties of the plasmonic gap and provide ideas for future research
Improving optical absorption in a-Si thin films with TiO2 Mie scatterers
No full textTo increase the optical absorption in very thin a-Si films is relevant for more efficient and
inexpensive photovoltaics. In this work we deposited TiO2 particles with a gas aggregation source on top
of a-Si thin films and study the effect on optical absorption. When using thin films, anti-reflection and
enhanced-reflection occurs depending on the thickness, which was employed in this study. The experiments
were compared with finite difference time domain (FDTD) simulations which yielded good agreement. Both
increased and decreased optical absorption was measured, depending on the photon energy range. This
work demonstrates that by tailoring the various parameters, the TiO2 particles can contribute to increasing
the efficiency of an a-Si based solar cell
Deflection and Mass Filtering
No full textIn this chapter the mass filtering systems often used in combination with cluster sources and which were developed over the last decades are discussed and compared. Deflection of nanoparticles in magnetic and electric fields is a returning theme in mass filters. The mass of the nanoparticles determines the amount of deflection which translates in a spatial change which is used to select/filter the right mass. Mass filters such as the (Reflectron) Time‐of‐flight mass filter, Quadrupole Mass Filters, Aerodynamic lenses, Wien Filter and Cluster Ion trap are discussed. Today's main challenge for mass filters is sufficient yield, which is necessary for commercial applications of mass selected nanoparticles from cluster sources. A new development in the field of matter‐wave interferometry, in which mass selected nanoparticles are used, forms a bridge to possible future developments. This chapter is concluded with a short overview of applications for mass selected nanoparticles which are currently being studied and are promising
Quantifying the plasmonic orthogonalisation of light for Si, a-Si, and perovskite solar cells
No full textThe orthogonalisation of light is realized by placing a plasmonic nanostructure on a metal plate, which generates a plasmon resonance upon illumination. The plasmon resonance in the plasmonic nanostructure generates surface plasmon polaritons (SPPs) on the metal surface. These SPPs can transfer their energy to semiconductors on top, which could increase the efficiency of solar cells. In this work, such a system has been explored by finite difference time domain simulations for silver nanoparticles on a silver plate with Si, a-Si and perovskite thin layers on top. It was found that the SPPs generated by the silver nanoparticle can only transfer their energy to the semiconductor on top if the plasmon resonance energy matches with the semiconductor band gap. This constraint was lifted when a plasmonic nanoparticle was placed outside the illuminated area; it functioned as an antenna, converting the SPP energy back into light, increasing the optical absorption strongly. This information is important for the design of future nanostructured thin film solar cells which want to employ orthogonalisation to increase the solar energy conversion efficiency
Using nanoparticles as a bottom-up approach to increase solar cell efficiency
No full textNanostructures in solar cells are used both for the active layers and for light management techniques. Particularly thin-film solar cells will benefit strongly from such nanoscale approaches as the light absorption needs to be improved. Nanoparticles produced by wet chemical techniques, sometimes in the form of quantum dots, are currently used to fabricate thin-film solar cells for research purposes. Light management studies use nanostructures that are often created by lithographic methods but which are too expensive for an industrial realisation. In this review paper, the opportunities for using nanoparticles as a bottom-up approach for both the active layer and light management nanostructures is discussed. Since both the wet chemical method and lithographic techniques have considerable limitations, the use of gas aggregation cluster sources is proposed as a promising method to advance the use of bottom-up nanoparticles for solar cells. Plasmonics, Mie scattering, quantum dots and new materials are reviewed with respect to the nanoparticle potential. The increase of solar cell efficiency by using ultra-clean and crystalline nanoparticles which are produced with a vacuum-compatible technique at low temperatures should be very interesting for science and technology, ultimately leading to industrial products
Developing a Reciprocating Mechanism for the Emergency Implementation of a Mechanical Pulmonary Ventilator using an Integrated CAD-MBD Procedure
No full textFollowing the COVID-19 outbreak, the redesign of an emergency mechanical pulmonary ventilator that is cheap and easily portable became necessary in several contexts, such as emergency hotspots and environments with poor resources. To address this important issue, a general multibody approach is employed in this paper to develop a reciprocating mechanism suitable for retrofitting the existing manual mechanical ventilators through computer-aided engineering tools. By analyzing various basic articulated mechanisms typically found in engineering mechanics, a prototype is created and reproduced in a threedimensional environment using SOLIDWORKS's CAD software. Subsequently, a high-fidelity mechanical model is developed starting from the CAD geometry and employing the SIMSCAPE MULTIBODY software, an extension of the MATLAB family of programs that can effectively and efficiently perform kinematic and dynamic simulations of the mechanism of interest. As discussed in the paper, by carrying out numerous numerical experiments, the virtual simulations predict several fundamental medical parameters, such as the airflow introduced into patients, the respiratory rate, and the respiratory ratio
A study into the clinical effects of the rapid palatal expansion
No full textThis thesis contains different studies on the effects of the rapid palatal expansion.The purpose of this thesis is to investigate some of the effects of palatal expansion which are still unaddressed in literature.
The first part of the thesis, after a brief introduction to the transverse maxillary contraction and palatal expansion, will outline the results of clinical trials that relate to the non-orthodontic effects that palatal expansion may have on: cervical vertebrae, posture and upper airways.The second part will show the first results, from an orthodontical point of view, of a multicentric randomized clinical trial designed to analyze the possible different effects of palatal expander anchored on deciduous or permanent teeth
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