The structural, optical and electrical properties of sputtered cuprous oxide thin films have been optimized through post-deposition thermal treatments. Moreover we have studied the effects of nitrogen doping introduced by ion implantation followed by the optimized oxidant thermal annealing. Three concentrations have been used, 0.6N%, 1.2N%, and 2.5N%. Along with the preservation of the Cu2O phase, a slight optical band gap narrowing and a significant conductivity enhancement has been observed with respect to the undoped samples. These results can be justified by the absence of further oxygen vacancies promoted by dopant introduction and by the substitution of O atoms by N ones. This lattice configuration has been guaranteed by the post implantation annealing in oxidant atmosphere. The used doping technique represents an original out-of-equilibrium approach toward the formation of low-resistivity contacts on Cu2O films for photovoltaic applications.

Electrochromic devices suitable for architectural applications must exhibit acceptable levels in specific performance indicators to carry out useful energy saving functions. These parameters indicate the global response of the window to the solar radiation and completely determine the energetic performance of the glazing. In this paper we present performance data of a home-made all solid state prototype which meets most of the basic requirements. The device is characterized by a visible transmittance modulation between around 68 and 14% (in the full bleaching and colouring states respectively) and demonstrates repeatable behavior after 12h cyclization.

To accomplish specific energetic and environmental tasks in buildings large area electrochromic windows must exhibit acceptable levels in specific performance indicators. These parameters concern a number of electrical, thermal and optical properties which depend on the structural composition and configuration of the electrochromic device. In this paper a comprehensive and systematic analysis of the optimal performance requirements of electrochromic windows from the perspective of building energy efficiency and indoor comfort has been carried out. A comparison with the performance of a home-made fully solid-state electrochromic device tested in laboratory controlled conditions and of large-area electrochromic glazing currently available in the market is also made. The study points out the actual potential of the electrochromic technology for smart window applications and identifies some desirable performance improvements for optimizing building integration.

ZnO nanorods (NRs) grown by chemical bath deposition (CBD) are among the most promising semiconducting nanostructures currently investigated for a variety of applications. Still, contrasting experimental results appear in the literature on the microscopic mechanisms leading to high aspect ratio and vertically aligned ZnO NRs. Here, we report on CBD of ZnO NRs using Zn nitrate salt and hexamethylenetetramine (HMTA), evidencing a double role of HMTA in the NRs growth mechanism. Beyond the well-established pH buffering activity, HMTA is shown to introduce a strong steric hindrance effect, biasing growth along the c-axis and ensuring the vertical arrangement. This twofold function of HMTA should be taken into account for avoiding detrimental phenomena such as merging or suppression of NRs, which occur at low HMTA concentration.

SiGeO films have been produced by a sol–gel derived approach and by magnetron sputtering deposition. Post-thermal annealing of SiGeO films in forming gas or nitrogen atmosphere between 600 and 900 °C ensured the phase separation of the SiGeO films and synthesis and growth of Ge nanoclusters (NCs) embedded in SiO2. Rutherford backscattering spectrometry analysis evidenced a similar Ge concentration (~12 %), but a different Ge out-diffusion after annealing between the two types of techniques with the formation of a pure SiO2 surface layer (~30 nm thick) in sol–gel samples. The thermal evolution of Ge NCs has been followed by transmission electron microscopy and Raman analysis. In both samples, Ge NCs form with similar size increase (from ~3 up to ~7 nm) and with a concomitant amorphous to crystalline transition in the 600–800 °C temperature range. Despite a similar Ge concentration, a significant lower NCs density is observed in sol–gel samples attributed to an incomplete precipitation of Ge, which probably remains still dispersed in the matrix. The optical absorption of Ge NCs has been measured by spectrophotometry analyses. Ge NCs produced by the sol–gel method evidence an optical band gap of around 2 eV, larger than that of NCs produced by sputtering (~1.5 eV). These data are presented and discussed also considering the promising implications of a low-cost sol–gel based technique towards the fabrication of light harvesting devices based on Ge nanostructures.

This work shows the application of metal ion-implantation to realize an efficient second-generation TiO2 photocatalyst. High fluence Fe+ ions were implanted into thin TiO2 films and subsequently annealed up to 550 °C. The ion-implantation process modified the TiO2 pure film, locally lowering its band-gap energy from 3.2 eV to 1.6–1.9 eV, making the material sensitive to visible light. The measured optical band-gap of 1.6–1.9 eV was associated with the presence of effective energy levels in the energy band structure of the titanium dioxide, due to implantation-induced defects. An accurate structural characterization was performed by Rutherford backscattering spectrometry, transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and UV/VIS spectroscopy. The synthesized materials revealed a remarkable photocatalytic efficiency in the degradation of organic compounds in water under visible light irradiation, without the help of any thermal treatments. The photocatalytic activity has been correlated with the amount of defects induced by the ion-implantation process, clarifying the operative physical mechanism. These results can be fruitfully applied for environmental applications of TiO2.

In this work, the morphological and structural evolution of gold nanodots deposited on Si substrates has been monitored for 2.4 × 10 3 h. Gold nanodots on Si are of great scientific interest because they can be used in numerous ways, for example as subwavelength antennas in plasmonics, as electrical contacts in nanometric devices, or as catalysts for the formation of quasi-1dimensional nanostructures. Their characteristics have been studied in a very large number of papers in literature, and among the several aspects, it is known that continuous Au films peculiarly interact with Si by interdiffusion even at room temperature. It would be expected that also small nanostructures could undergo to an interdiffusion and consequent modifications of their structure and shape after aging. Despite the cruciality of this topic, no literature papers have been found showing a detailed morphological and structural characterization of aged Au nanodots. Au nanoparticles have been deposited by sputtering on Si and stored in air at temperature between 20 and 23 °C and humidity of about 45 %, simulating the standard storage conditions of most of the fabrication labs. The morphological and structural characterizations have been performed by bright field transmission electron microscopy (TEM). A specific procedure has been used in order to avoid any modification of the material during the specimen preparation for the TEM analysis. A digital processing of the TEM images has allowed to get a large statistical analysis on the particles size distribution. Two different types of nanoparticles are found after the deposition: pure gold crystalline nanodots on the Si surface and gold amorphous nanoclusters interdiffused into the Si subsurface regions. While the nanodots preserve both morphology and structure all over the time, the amorphous agglomerates show an evolution during aging in morphology, structure, and chemical phase.

Multilayers of Ge quantum dots (QDs, 3 nm in diameter) embedded in SiO2, separated by SiO2 barrier layer (3, 9, or 20 nm thick), have been synthesized by sputter deposition and characterized by transmission electron microscopy and light absorption spectroscopy. Quantum confinement affects the optical bandgap energy (1.9 eV for QDs, 0.8 eV for bulk Ge); moreover, the absorption probability greatly depends on the QD-QD distance. A strong electronic coupling among Ge QDs is evidenced, with a significant increase of the light absorption efficiency when the QD-QD distance is reduced. These data unveil promising aspects for light harvesting with nanostructures.

Thin film Si:O alloys have been grown by plasma enhanced chemical vapor deposition, as intrinsic or highly doped (1 to 5 at. % of B or P dopant) layers. UV-visible/near-infrared spectroscopy revealed a great dependence of the absorption coefficient and of the optical gap (E-g) on the dopant type and concentration, as E-g decreases from 2.1 to 1.9 eV, for the intrinsic or highly p-doped sample, respectively. Thermal annealing up to 400 degrees C induces a huge H out-diffusion which causes a dramatic absorption increase and a reduction of E-g, down to less than 1.8 eV. A prototypal solar cell has been fabricated using a 400 nm thick, p-i-n structure made of Si:O alloy embedded within flat transparent conductive oxides. Preliminary electrical analyses show a photovoltaic (PV) effect with an open circuit voltage of 0.75 V and a spectral conversion efficiency blue-shifted in comparison to a-Si:H based cell, as expected since the higher E-g in Si:O alloy. These data are presented and discussed, suggesting Si:O alloy as promising material for PV device fabrication. (C) 2013 AIP Publishing LLC.

An innovative method for Si nanostructures (NS) fabrication is proposed, through nanosecond laser irradiation (λ = 532 nm) of thin Si film (120 nm) on quartz. Varying the laser energy fluences (425–1130 mJ/cm2) distinct morphologies of Si NS appear, going from interconnected structures to isolated clusters. Film breaking occurs through a laser-induced dewetting process. Raman scattering is enhanced in all the obtained Si NS, with the largest enhancement in interconnected Si structures, pointing out an increased trapping of light due to multiple scattering. The reported method is fast, scalable and cheap, and can be applied for light management in photovoltaics.

Fabrication processes of Au nanostructures on indium-tin-oxide (ITO) surface by simple, versatile, and low-cost bottom-up methodologies are investigated in this work. A first methodology exploits the patterning effects induced by nanosecond laser irradiations on thin Au films deposited on ITO surface. We show that after the laser irradiations, the Au film break-up into nanoclusters whose mean size and surface density are tunable by the laser fluence. A second methodology exploits, instead, the patterning effects of standard furnace thermal processes on the Au film deposited on the ITO. We observe, in this case, a peculiar shape evolution from pre-formed nanoclusters during the Au deposition stage on the ITO, to holed nanostructures (i.e. nanorings), during the furnace annealing processes. The nanorings depth, height, width, and surface density are shown to be tunable by annealing temperature and time.

In this paper, we study the metal-catalyzed synthesis of Si nanowires (Si-NWs) in a plasma based chemical vapor deposition system. In these deposition systems due to the high efficiency of precursor molecule dissociation, both uncatalyzed and catalyzed growth mechanisms can take place. The first one gives rise to the formation of the quasi one-dimensional (1D) Si-NWs, while the second one to a continuous two-dimensional (2D) Si layer over the substrate or on the nucleated Si-NWs. The Si-NWs formation is then the result of the competition between these two processes. The control parameters ruling these two contributions are here explored. Samples with different weights of 1D and 2D growth are deposited and characterized by using a plasma based chemical vapor deposition apparatus operating at T < 400 °C. It is found that the main control parameter of these processes is the plasma power through the distribution of the precursor dissociation products. By properly tuning the power, Si-NWs with 1 × 1010 cm−2 of density, up to 1 μm long and without uncatalyzed growth are obtained. The optical functionality of the samples, grown with different 1D/2D contributions, is investigated and it is demonstrated that the uncatalyzed layer produces a total reflectance as high as ∼40%, similar to that found in a planar Si wafer, while the highly dense Si-NWs, without the uncatalyzed deposition, produce a total reflectance of ∼15%.

Ge nanoclusters (NCs), synthesized by ion implantation and annealing up to 900 °C, result small (∼2 nm) and amorphous in Si3N4, crystalline and much larger in SiO2. The NCs ripening and crystallization kinetics in Si3N4 is retarded by larger interfacial energy and lower diffusivity of Ge in comparison to SiO2. Ge NCs absorb light more efficiently when embedded in Si3N4 than in SiO2. A significant effect of the barrier height on absorption was evidenced, in agreement with effective mass theory predictions. The smaller bandgap of Ge NCs embedded in Si3N4 and their closeness is promising features for light harvesting applications.

The effect of nanosecond laser irradiations on 5 nm thick sputter-deposited Au and Ag films on Indium-TinOxide surface is investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). After 500, 750, and 1000 mJ/cm 2 fluence irradiations, the breakup of the Au and Ag films into nanoscale islands is observed as a consequence of fast melting and solidification processes. The mean nanoparticles size and surface density are quantified, as a function of the laser fluence, by the AFM and SEM analyses. In particular, the comparison between the Au and Ag islands reveals the formation of larger islands in the case of Ag for each fixed fluence. The mechanism of the nanoscale islands formation is discussed, both for Au and Ag, in terms of the starting film thickness fluctuations (influencing the local threshold for melting), dewetting phenomenon and the Rayleigh criterion.

We analyze the results of an extensive characterization study involving electrical and optical measurements carried out on hydrogenated amorphous silicon (α-Si:H) thin film materials fabricated under a wide range of deposition conditions. By adjusting the synthesis parameters, we evidenced how conductivity, activation energy, electrical transport and optical absorption of an α-Si:H layer can be modified and optimized. We analyzed the activation energy and the pre-exponential factor of the dark conductivity by varying the dopant-to-silane gas flow ratio. Optical measurements allowed to extract the absorption spectra and the optical bandgap. Additionally, we report on the temperature dependence of the activation energy to satisfy the Meyer–Neldel rule. Finally, the influence of the individual films parameters upon the final performances of a single junction pin α-Si:H have been studied. The measurements show how a more than doubled enhancement in energy conversion efficiency can be obtained in an α-Si:H solar cell with a proper selection of synthesis conditions.

Al-doped ZnO (AZO)/Ag/AZO multilayer coatings (50–70nm thick) were grown at room temperature on glass substrates with different silver layer thickness, from 3 to 19nm, by using radio frequency magnetron sputtering. Thermal stability of the compositional, optical and electrical properties of the AZO/Ag/AZO structures were investigated up to 400°C and as a function of Ag film thickness. An AZO film as thin as 20nm is an excellent barrier to Ag diffusion. The inclusion of 9.5nm thin silver layer within the transparent conductive oxide (TCO) material leads to a maximum enhancement of the electro-optical characteristics. The excellent measured properties of low resistance, high transmittance in the visible spectral range and thermal stability allow these ultra-thin AZO/Ag/AZO structures to compete with the 1μm thick TCO layer currently used in thin film solar cells.

This work reports on the formation of Au nanoclusters and on their evolution in nanoring structures on indium-tin-oxide surface by sputtering deposition and annealing processes. The quantification of the characteristics of the nanorings (surface density, depth, height, and width) is performed by atomic force microscopy. The possibility to control these characteristics by tuning annealing temperature and time is demonstrated establishing relations which allow to set the process parameters to obtain nanostructures of desired morphological properties for various technological applications.

Thermally treated silicon rich oxides (SRO) used as starting material for the fabrication of silicon nanodots represent the basis of tunable bandgap nanostructured materials for optoelectronic and photonic applications. The optical modelization of such materials is of great interest, as it allows the simulation of reflectance and transmittance (R&T) spectra, which is a powerful non destructive tool in the determination of phase modifications (clustering, precipitation of new phases, crystallization) upon thermal treatments. In this paper, we study the optical properties of a variety of as-deposited and furnace annealed SRO materials. The different phases are treated by means of the effective medium approximation. Upon annealing at low temperature, R&T spectra show the precipitation of amorphous silicon nanoparticles, while the crystallization occurring at temperatures higher than 1000 degrees C is also clearly identified, in agreement with structural results. The existing literature on the optical properties of the silicon nanocrystals is reviewed, with attention on the specificity of the compositional and structural characteristics of the involved material.