Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies (V$_o$) were identified in ZnO nanorods (NRs) grown by low cost chemical bath deposition. A transient behaviour in the photoluminescence (PL) intensity of the two V$_o$ states was found to be sensitive to the ambient environment and to NR post-growth treatment. The largest transient was found in samples dried on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV exposure exhibited a transient behaviour in full agreement with the PL transient indicating a clear role of atmospheric O$_2$ on the surface defect states. A model for surface defect transient behaviour due to band bending with respect to the Fermi level is proposed. The results have implications for a variety of sensing and photovoltaic applications of ZnO NRs

A multi-stakeholder analysis of the economic efficiency of industrial energy efficiency policies: Empirical evidence from ten years of the Italian White Certificate Scheme

© 2019 There is growing interest worldwide in more effective policies to promote industrial energy efficiency and mitigate climate change. The White Certificates Scheme is a market-based mechanism aimed at stimulating the adoption of Energy Efficiency Measures. The Italian White Certificates scheme - one of the most long-standing and articulated - is a successful example of industrial energy efficiency policies, considered an interesting and remarkable case by other countries, especially due to its robustness in terms of the volume of certificates traded. Despite the considerable interest in White Certificates, an in-depth analysis of the economic efficiency of the mechanism from the perspective of different stakeholders is still lacking. To address this gap, this study develops a cost-benefit evaluation framework and a multi-stakeholder economic efficiency analysis of the Italian White Certificates scheme focusing on the Italian State, utilities, players in the energy efficiency value chain, and energy users. Our findings (also corroborated with sensitivity analyses) show that the White Certificates Scheme has led to several positive impacts for almost all stakeholders involved, with the exception of energy utilities that have suffered a major economic loss mainly due to a reduction of energy sold to end users. Such loss is likely to promote a deep change in the role of utilities in the energy market in terms of the services they offer and their business models. Our findings, in addition to providing useful directions for future research, offer interesting insights and implications for policymakers who may take inspiration from the pros and cons of the Italian White Certificates scheme when promoting energy efficiency through incentive mechanisms

Temperature dependence and quenching processes of the intra-4f luminescence of Er in crystalline Si

8 págs.; 7 figs.The luminescence quenching of Er in crystalline Si at temperatures between 77 and 300 K is investigated. Samples were prepared by solid-phase epitaxy of Er-implanted amorphous Si layers with or without O codoping. After epitaxial regrowth at 620°C, thermal annealing at 900°C for 30 sec was performed in order to eliminate residual defects in the regrown layer and electrically and optically activate the Er ions. Measurements of photoluminescence intensity and time decay were performed as a function of temperature and pump power. By increasing the temperature from 77 K to room temperature the luminescence intensity decreases by ~ three orders of magnitude in the Er-doped sample without O codoping, but only by a factor of 30 in the O-doped sample. In this sample room-temperature photo-luminescence and electroluminescence have been observed. Time-decay curves show a fast initial decay (~100 ¿sec) followed by a slow decay (~1 msec), with the relative intensity of these two components depending on temperature, pump power, and O codoping. The decay curves can be fitted by a sum of two exponential functions revealing the existence, in both samples, of two different classes of optically active Er sites. The concentration of excitable sites belonging to the slow-decaying class is similar for the samples with or without O codoping and rapidly decreases when temperature is increased. At temperatures above 150 K the Er luminescence is dominated by the fast-decaying centers the concentration of which is greatly increased by the presence of O. It is found that in the absence of oxygen room-temperature luminescence is hampered by the limited amount of excitable Er ions. In contrast, in O-doped samples the nonradiative decay of excited Er is the main quenching mechanism. The main factors determining the temperature quenching of Er luminescence and the crucial role of oxygen are discussed. © 1994 The American Physical Society.This work has been partially supported by GNSM-CNR. Work at the FOM Institute is part of the research program of the foundation for Fundamental Research on Matter (FOM), and was made possible by financial support from the Dutch organization for the Advancement of Research (NWO}, the Foundation for Technical Research (STW}, and the IC Technology Program (IOP Electro-optics) of the Ministry of Economic Affairs.Peer Reviewe

Optical and electrical doping of silicon with holmium

2 MeV holmium ions were implanted into Czochralski grown Si at a fluence of 5.5*10^14 Ho/cm^2. Some samples were co-implanted with oxygen to a concentration of (7±1)*10^19 cm^(-3). After recrystallization, strong Ho segregation to the surface is observed, which is fully suppressed by co-doping with O. After recrystallization, photoluminescence peaks are observed at 1.197, 1.96 and 2.06 lm, characteristic for the 5-I-6 --> 5-I-8 and 5-I-7 --> 5-I-8 transitions of Ho^(3+). The Ho^(3+) luminescence lifetime at 1.197 lm is 14 ms at 12 K. The luminescence intensity shows temperature quenching with an activation energy of 11 meV, both with and without O co-doping. The observed PL quenching cannot be explained by free carrier Auger quenching, but instead must be due to energy backtransfer or electron hole pair dissociation. Spreading resistance measurements indicate that Ho exhibits donor behavior, and that in the presence of O the free carrier concentration is enhanced by more than two orders of magnitude. In the O co-doped sample 20% of the Ho^(3+) was electrically active at room temperature

Electrical conduction of silicon oxide containing silicon quantum dots

Current-voltage measurements have been made at room temperature on a Si-rich silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000$^\circ$C. The thickness of oxide between Si quantum dots embedded in the film increases with the increase of annealing temperature. This leads to the decrease of current density as the annealing temperature is increased. Assuming the Fowler-Nordheim tunneling mechanism in large electric fields, we obtain an effective barrier height $\phi_{eff}$ of $\sim$ 0.7 $\pm$ 0.1 eV for an electron tunnelling through an oxide layer between Si quantum dots. The Frenkel-Poole effect can also be used to adequately explain the electrical conduction of the film under the influence of large electric fields. We suggest that at room temperature Si quantum dots can be regarded as traps that capture and emit electrons by means of tunneling.Comment: 14 pages, 5 figures, submitted to J. Phys. Conden. Mat

Alcamo Project: un laboratorio integrato per l’analisi e lo studio del settore officinale romano di Contrada Foggia ad Alcamo Marina (TP)

During the archaeological research activities carried out in the past three years near Alcamo Matina (TP) an officinal area of the Roman period was brought to light. The find was accidental and consisted of a series of kilns used for the cooking of ceramic material which dates back to the centuries I-V A.D. The architectonic and structural solutions adopted for the realization of the ceramic complex are very interesting, a series of kilns on various levels with a system of terracing of the ground, orientation of the axis and of the opening of the praefurnium towards the non dominant winds, alternation of containment and strengthening wall structures and structural fillings made of clay. Some studies under way help better understand the officinal complex, they focus on the analysis of the ceramic material found there and on the reconstruction of the territory on the basis of methods of satellite bearing (GPS) and on the basis of cartographic results of models on the GIS platform

The environmental impact of electric vehicles: A comparative LCA-based evaluation framework and its application to the Italian context

In the last years a progressive shift from the traditional internal combustion engine vehicles (ICEV) toward electric vehicles (EV) has been observed, which has as primary objective that of favouring a sustainable mobility. Indeed, one of the most important topics tightly linked with this alternative refers to the greenhouse gas (GHG) emissions produced along the entire vehicle's life cycle. The aim of the present work is to develop an emission-model that is able to calculate the CO2 emissions produced along the entire vehicle's life cycle, so to estimate EV CO2 emission values and compare them with those of ICEV. The emission model, developed leveraging on a thorough literature review on the topic, is then applied to the Italian context, to enable a comparison of the emission results for EVs and ICEVs taking into account the peculiarities of such country. It emerges that overall CO2 emissions associated to EVs are lower than the ones associated to ICEVs. A significant portion of emissions arising from the manufacturing of the battery pack still represents the main gap to be filled with respect to ICEVs. Evaluating both vehicle typologies and based on different assumption in terms of the geographical locations in which the stages of the vehicle life cycle take place, it emerges that EVs show a consistent CO2 emission reduction ranging between-11% to-50% compared to ICEVs over the entire vehicle's life cycle. The most relevant contribution for such performance is due to the cleaner energy mixes on which some countries can rely on compared to others. Given that the most impactful phase-in terms of CO2 emissions-is represented by the vehicle use, it has been performed a sensitivity analysis on the energy mix used for vehicle's charging. Results show that coupling of Renewable Energy Sources (RES) and EVs can be a key factor for achieving very low emission values