Sub-stoichiometric molybdenum oxide (MoOx) has attracted significant attention as hole-transport/selective layer in optoelectronic devices. However, its integration on Si is hindered by interfacial redox-reactions that can alter oxide stoichiometry and electronic properties.In this work, MoOx films, 5 nm thick, were deposited by non-reactive RF sputtering from a stoichiometric MoO3 ceramic target onto bare and thermally-oxidized Si substrates. Morphological analyses confirmed the formation of continuous and dense coatings, Kelvin probe mapping revealed spatially uniform WF of 5.06 eV. Angle-resolved XPS showed sub-stoichiometric composition (x=2.6) regardless of substrate, with no variations across the film thickness. These results were corroborated by HAADF-STEM, which revealed uniform Mo and O distributions, confirming the absence of interfacial oxide reactions. Compared to thermally evaporated counterparts, sputtered films exhibit superior compositional stability due to the higher kinetic energy of sputtered species involved in the film growth. Overall, non-reactive sputtering enables the growth of stable films suitable for optoelectronic and photovoltaic applications.

Low-cost and environmentally friendly electrochemical energy storage systems are crucial to address the increasing global energy demand. Nanomaterials can play a pivotal role in catalysing charge storage and/or exchange, still the underlying mechanism often remains poorly investigated, as for ZnO/ZnS nanostructures onto Ni foam. In this work, we investigate hydrothermally grown ZnO/ZnS nanostructures decorating Ni foam for energy storage application. Morphology, structure and composition are evaluated via electron microscopy-based methodologies. The electrochemical energy storage performance is evaluated by cyclic voltammetry (CV) measurements with the aim to highlight the energy storage mechanism. When nickel foam (NF) is used as substrate, the system shows a predominant pseudocapacitive behaviour. By contrast, a modest and capacitive performance is measured on graphene paper (GP). Mott-Schottky (M-S) and open circuit potential (OCP) measurements suggests a key role of hole reservoir in ZnS decoration which boosts NF performances.

Nanostructured gallium nitride (GaN) shows strong potential in enhancing ultraviolet (UV) photodetectors through improved sensitivity and in light-emitting diodes (LEDs) via better spatial resolution. It is also promising for quantum photonics, particularly as a scalable, room-temperature single-photon emitter vital for quantum communication and sensing. A cost-effective photo-electroless etching (PEE) technique was employed to fabricate various GaN nanostructures, including vertically aligned nanowires (NWs) with a mean length of 1.75 +/- 0.21 mu m and a diameter of 39.36 +/- 11.28 nm, as well as complex nano- and microporous layers. The study evaluated how different illumination conditions, power levels, and etching durations influenced the etching efficiency and surface morphology. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed the transition from porous layers to vertical NWs, which eventually detached from the substrate. Energy-dispersive X-ray spectroscopy (EDX) confirmed that the structures consist primarily of gallium and nitrogen, consistent with GaN composition, while photoluminescence (PL) and cathodoluminescence (CL) spectroscopies were employed to investigate their optical properties. The efficiency of UV photon emission relative to visible emission was quantified, revealing a strong dependence on the morphology. These results prove how PEE enhances photon extraction, positioning GaN as a versatile platform for future quantum technologies.

Stoichiometry of molybdenum oxide, MoOx, thin films was controlled by simply modulating the argon working pressure during the non-reactive sputtering deposition. Rutherford Backscattering Spectrometry revealed that the O/Mo ratio increased between 2.6 and 3.0 as the argon pressure increased. X-Ray Photoemission Spectroscopy (XPS) analyses pointed out that the sub-stoichiometry led to the formation of oxygen vacancies, closely related to the presence of Mo5+ reduced oxidation state, while in fully stoichiometric films only Mo6+ oxidation state appeared. The strong correlation between composition and optical properties was demonstrated through optical absorption measurements. Sub-stoichiometric films exhibited a narrower bandgap and significant infrared absorption at 1.55 eV, attributed to increased disorder and a higher number of defects, such as oxygen vacancies. Finally, by merging the XPS and optical absorption data, we demonstrated that the band structure of MoOx was effectively controlled by simply modulating the Argon deposition pressure. This tunability offers significant potential for tailoring the optical and electronic properties of MoOx for applications in energy storage, photovoltaic and photonic devices.

Hybrid nanostructures combining semiconductor materials and noble metal clusters of atoms (nanoparticles) are of high interest in the energy sector and catalysis, with the idea of tuning the physicochemical properties of the system toward the desired performance. The design of this type of complex system requires the appropriate selection of the material combination to optimize the desired properties. However, less attention has been devoted to the effect of cluster size. In this work, we investigate the size and density effects for mass-selected monometallic Au clusters decorating ZnO-based nanostars. The Au clusters were prepared with narrow control of their size, in terms of atoms per cluster, via cluster deposition in a vacuum and mass selection with a cluster beam source. We study the coupling of ZnO nanostars with deposited Au N (N = 55, 147, and 309) clusters. We exploit transmission electron microscopy and Rutherford backscattering spectrometry for the structural characterization and for the determination of Au cluster density, obtaining 3.43 × 1012, 4.55 × 1011, and 7.98 × 1010 clusters/cm2 for samples decorated with Au clusters containing 55, 147, and 309 atoms, respectively. Moreover, we highlight the formation of a Schottky junction by performing photoluminescence investigations. We find distinctive changes in the behavior of the visible and UV emission as a function of the cluster size and density on the ZnO-based nanostars, identifying an increase of the photoluminescence efficiency with the decrease of the cluster dimension. Our findings indicate the enormous potential that a proper selection of cluster size offers in the fabrication of nanocomposite materials with precise electronic properties.

The development of high-performance silicon heterojunction (SHJ) solar cells heavily relies on the precise engineering of layer architectures. In recent years, the introduction of passivating and carrier-selective contacts has driven major advancements in silicon-based solar cells, enabling significant efficiency improvements. However, optical losses, the reliance on capital-intensive deposition processes, and scalability to large-area substrates remain key challenges for widespread adoption. In this work, we propose an alternative approach to replace both the conventional p-doped and intrinsic amorphous hydrogenated silicon (a-Si:H) layers in SHJ solar cells with sputter-deposited MoOx ultra-thin films. This approach aims to enhance hole selectivity and suppress interfacial recombination, while the superior optical transparency of MoOx compared to p-doped a-Si:H allows for improved light absorption in the crystalline silicon (c-Si) absorber. Experimental results confirm promising device performance, validating the potential of this architecture. Furthermore, to overcome passivation limitations, we preliminarily explore an alternative wide-bandgap oxide layer, gallium oxide, paving the way for innovative SHJ designs in mainstream c-Si photovoltaic technology.

In this work we report on ultra-thin Zirconium doped In2O3 transparent conductive films grown at room temperature via RF-Magnetron co-sputtering. Samples from 15 nm to 90 nm thick, and low Zr atomic concentration (0.6-0.9 at.%), were annealed at T = 200 degrees C after the deposition. The phase-transition from amorphous to crystalline, confirmed by XRD measurements, leads to an improvement of both electrical and optical properties. The thinnest film (15 nm) shows electrical resistivity as low as 5 x 10-4 Omega cm, with carrier mobility of 20 cm2V- 1s- 1, and optical transmittance up to 80 % in visible and near-infrared range. IZrO electrode performances were tested through external quantum efficiency (EQE) measurements on a semi-finite Silicon Heterojunction bifacial solar cell. The EQE values for 90 nm thick film are comparable to that of standard ITO when IZrO films are implemented as front electrodes. These results suggest that ultra-thin IZrO films may be successfully used to reduce costs and the amount of Indium used in Indium-based transparent conductive oxide layers for solar cells.

Indium oxide (In2O3) is one of the most used materials for the synthesis of transparent electronics devices and currently tin-doped indium oxide (ITO) dominates the field of Transparent Conductive Oxides for most applications, from ICT to photovoltaics. In this work we present a study on the responses of indium oxide upon the formation, and stabilization, of point defects induced with different methods. After the deposition of In2O3 thin films via RF magnetron sputtering, treatments such as Ion Implantation (I.I.), Ultraviolet (UV) irradiation and Sun exposure were employed to generate oxygen vacancies as intrinsic dopants. Both I.I. and UV irradiations significantly improved the electrical conductivity of films, increasing the carrier density by up to 3 orders of magnitude. Moreover, after I.I. also the crystalline quality of the films was enhanced. To monitor the stability of oxygen vacancies upon exposure to ambient atmosphere, the ageing of samples was followed and recorded for a couple of weeks, reporting a fast and strong degradation of electrical properties. As a facile strategy to counteract the sheet resistance increase, samples were encapsulated in an ultra-thin (approximate to 10 nm) SiO2 layer deposited via sputtering. Irradiated and encapsulated films retained a much lower sheet resistance throughout the observation time, preserving the samples conductivity.

The realization of polymeric nanocomposites is a promising strategy for large-scale applications of photocatalytic nanomaterials, limiting their dispersion into the environment. In addition, in order to obtain very efficient materials, a valid solution can be the formation of heterojunctions that, reducing the electron-hole recombination phenomena, increases the performances of the photocatalysts. For this work, we have realized promising photocatalytic polymeric nanocomposites through the simple method of sonication and solution casting, using poly (methyl methacrylate) (PMMA) as supporting matrix, ZnO nanoparticles as photoactive material, and MoS2 nanoflakes as co-catalyst for the realization of the heterojunction. Materials with several quantities of MoS2 have been synthetized and characterized by scanning electron microscopy (SEM), contact angle measurements, X-ray diffraction analysis (XRD), UV–Vis spectroscopy, transmission electron microscopy (TEM), and photoluminescence (PL). The photocatalytic performances of the obtained materials were evaluated by the photodegradation under UV light irradiation of two different common pollutants: rhodamine B (RhB) and sodium dodecyl sulfate (SDS). The mechanism of the involved photocatalytic process was studied by the investigation of the main oxidants responsible of the photodegradation, using hole or radical scavengers. The antibacterial properties were investigated using Escherichia coli as a model organism. The eventual toxic effects of the prepared materials were studied on Artemia salina.

Lanthanide-doped yttrium oxide nanoparticles can display selective upconversion properties, rendering them invaluable in the field of nanomedicine for both sensing and diagnostics. Different syntheses of Er:Y2O3 and Nd:Y2O3 nanoparticles (NPs) were studied and optimized to obtain small particles of regular shape and good crystallinity. The morphological and compositional characterizations of the nanoparticles were obtained with different techniques and showed that both Er:Y2O3 and Nd:Y2O3 NPs were well dispersed, with dimensions of the order of a few tens of nanometers. The photoluminescence and cathodoluminescence measurements showed that both Er:Y2O3 and Nd:Y2O3 NPs had good emission as well as upconversion. The nanophosphors were functionalized by a pegylation procedure to suppress unwanted reactions of the NPs with other biological components, making the NP systems biocompatible and the NPs soluble in water and well dispersed. The pegylated core/shell nanoparticles showed the same morphological and optical characteristics as the core, promoting their strategic role as photoactive material for theragnostics and biosensing.

Gallium nitride (GaN) has superior physical properties suitable for the realization of power switching and highfrequency transistors with better performances than of conventional Si-based devices. In the presence of a bidimensional electron gas (2DEG) close to the interface of AlGaN/GaN heterojunctions, High Electron Mobility Transistors (HEMT) can be fabricated. Ion implantation is an affordable industrial process for the electrical isolation of 2DEG in adjacent AlGaN/GaN HEMTs devices. In this work, we studied the electrical isolation of the 2DEG produced by Ar ion implantation. 2DEG of heterostructure consisting of 18 nm Al0.2Ga0.8N were grown onto carbon doped n-type GaN. The 2DEG has been isolated by Ar ions implantation at 15, 22.5 and 60 keV and fluence of 7 x 1013 cm-2, respectively. The implanted samples were annealed at 600, 750 and 900 degrees C, respectively, and the thermal stability of the crystal damage and isolation were analyzed by photoluminescence spectroscopy (PL) and capacitance-voltage profiling (CV) through mercury probe analysis. We found that Ar ion implantation at the explored ion energies and fluence produces a significant reduction of the PL peak intensity assigned to radiative recombination at the band edge of GaN, confirming the crystal lattice damage induced by the implant. The PL spectral features are matched by a significant reduction of the 2 DEG carrier density of about six orders of magnitude with respect to the undamaged sample. The reduction of carrier density and, then, the isolation of the 2DEG was found stable at temperature up to 900 degrees C.

Here, we report the development of high-performance supercapacitor devices using manganese-doped zinc oxide nanowires (Mn-doped ZnO NWs) and copper-doped zinc oxide nanoparticles (Cu-doped ZnO NPs) as a positive electrode with MXene as a negative electrode. Both transition metal (TM)-based electrodes were used separately with MXene, and the performance was tested. When used in combination with MXene as a second electrode, TM-ZnO samples displayed a major increase in the supercapacitors’ performance. The highest-performance supercapacitor recorded values of 151 F/g specific capacitance along with 84 Wh/kg energy density and a power density of 75 kW/kg. Electron paramagnetic resonance and photoluminescence spectroscopy of Mn/Cu-doped ZnO reveals intrinsic and extrinsic defect signals, which were discussed and attributed to the enhancement of the capacitive performance. The presence of the aforementioned defects optimizes the intrinsic properties and boosts the reaction kinetics, thus providing increased electrochemical activity and superior supercapacitor device performance.

In this work, we report the growth of MoO3 nanowires (NWs) by thermal evaporation with the aim of evaluating their use as catalysts for oxygen evolution reaction (OER) in water splitting application. Growth was performed on two different kinds of substrates, Si(100) and Si(111), and at different growth temperatures between 200 and 400 degrees C. The effect of such experimental parameters on the morphological, structural, and compositional properties was investigated. The deposited materials were characterized by in situ reflection high-energy electron diffraction, scanning electron microscopy, transmission electron microscopy, Rutherford backscattering spectroscopy, and X-ray diffraction. For a growth temperature of 200 degrees C, a flat and amorphous oxide layer is obtained, while as the temperature is increased, one-dimensional (1D) growth prevails on 2D layer formation. In particular, at 400 degrees C, the deposited material consists of a high-density array of MoO3 crystalline NWs a few nm in diameter and up to about 0.5 mu m in length. Only in the case of Si(111) substrates have small three-dimensional structures formed and coexisted with NWs since the beginning of the growth process. Finally, the OER activity of MoO3 NWs was evaluated. The nanostructures were deposited on graphene paper, and their electrochemical activity was investigated and compared to other nonprecious metal-based catalysts for alkaline OER. Our MoO3-based electrodes showed overpotentials of 330 and 340 mV at 10 mA/cm(2) (eta(10)) depending on the average length of NWs and a quite high mass activity associated with a low catalyst loading, thus fitting the best performing electrocatalysts. Our results demonstrate that MoO3 NWs are suitable candidates for the development of anode electrodes for water splitting application.

Recent advancements in quantum key distribution (QKD) protocols opened the chance to exploit nonlaser sources for their implementation. A possible solution might consist in erbium-doped light emitting diodes (LEDs), which are able to produce photons in the third communication window, with a wavelength around 1550 nm. Here, we present silicon LEDs based on the electroluminescence of Er:O complexes in Si. Such sources are fabricated with a fully-compatible CMOS process on a 220 nm-thick silicon-on-insulator (SOI) wafer, the common standard in silicon photonics. The implantation depth is tuned to match the center of the silicon layer. The erbium and oxygen co-doping ratio is tuned to optimize the electroluminescence signal. We fabricate a batch of Er:O diodes with surface areas ranging from 1 µm × 1 µm to 50 µm × 50 µm emitting 1550 nm photons at room temperature. We demonstrate emission rates around 5 × 106 photons/s for a 1 µm × 1 µm device at room temperature using superconducting nanowire detectors cooled at 0.8 K. The demonstration of Er:O diodes integrated in the 220 nm SOI platform paves the way towards the creation of integrated silicon photon sources suitable for arbitrary-statistic-tolerant QKD protocols.

Energy storage devices based on earth-abundant materials are key steps towards portable and sustainable technologies used in daily life. Pseudocapacitive devices, combining high power and high energy density features, are widely required, and transition metal oxides represent promising building materials owing to their excellent stability, abundance, and ease of synthesis. Here, we report an original ZnO-based nanostructure, named nanostars (NSs), obtained at high yields by chemical bath deposition (CBD) and applied as pseudocapacitors. The ZnO NSs appeared as bundles of crystalline ZnO nanostrips (30 nm thin and up to 12 µm long) with a six-point star shape, self-assembled onto a plane. X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL) were used to confirm the crystal structure, shape, and defect-mediated radiation. The ZnO NSs, dispersed onto graphene paper, were tested for energy storage by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) analyses, showing a clear pseudocapacitor behavior. The energy storage mechanism was analyzed and related to oxygen vacancy defects at the surface. A proper evaluation of the charge stored on the ZnO NSs and the substrate allowed us to investigate the storage efficiency, measuring a maximum specific capacitance of 94 F g−1 due to ZnO nanostars alone, with a marked diffusion-limited behavior. The obtained results demonstrate the promising efficacy of ZnO-based NSs as sustainable materials for pseudocapacitors.

Quantum Key Distribution allows two users to exchange secret keys and it is based on the transmission of single photons or attenuated laser pulses. Recently, sources based on multiple single-photon emitters were demonstrated to be suitable for QKD. Here, we present a CMOS compatible multiple single-photon emitters source realized on a SOI wafer by a standard silicon diode doped with erbium ions. Particular emphasis is placed on the fabrication of such a device enhancing the erbium electroluminescence signal by adopting a proper oxygen co-doping. Finally, electroluminescence characterization at room temperature of the device is presented.

ZnO nanorods (NRs) play a crucial role in the manufacturing of electronic and optical devices and sensors. Using complementary techniques, we explore how their optical and conductive performances can be improved by Excimer Laser Annealing (ELA) at 75 and 100 mJ/cm(2). Our data show that ELA induces the melting and re-crystallization of the NRs surface, resulting into the reduction of the average crystallite size and lattice parameter of the system and suggesting a partial transition towards metallic Zn. The increase of Zn and the removal of oxygen defects at the surface are compatible with photoelectron spectroscopies (UPS and XPS) data and explain the enhancement of the UV/visible emission ratio observed in photoluminescence. The ELA also affects the in-plane electrical conductivity: the carriers mobility improves up to 4 times depending on the laser energy density. Our results demonstrate that ELA is effective in tuning the surface properties of ZnO NRs affecting the Zn concentration at the surface and removing some oxygen defects. The combination of these two effects results into the improvement of the optical and electrical responses of the systems.

According to their high electron density and ultrasmall size, gold nanoclusters (AuNCs) have unique luminescence and photoelectrochemical properties that make them very attractive for various biomedical fields. These applications require a clear understanding of their interaction with biological membranes. Here we demonstrate the ability of the AuNCs as markers for lipidic bilayer structures such as synthetic liposomes and biological extracellular vesicles (EVs). The AuNCs can selectively interact with liposomes or EVs through an attractive electrostatic interaction as demonstrated by zetametry and fluorescence microscopy. According to the ratio of nanoclusters to vesicles, the lipidic membranes can be fluorescently labeled without altering their thickness until charge reversion, the AuNCs being located at the level of the phosphate headgroups. In presence of an excess of AuNCs, the vesicles tend to adhere and aggregate. The strong adsorption of AuNCs results in the formation of a lamellar phase as demonstrated by cryo-transmission electron microscopy and small-angle X-ray scattering techniques.

A fractal array of room-temperature (RT) luminescent Si nanowires (NWs) is realized by thin-film metal-assisted chemical etching, a cost-effective, fast, and maskless Si technology compatible approach. This process permits obtaining Si NWs with interesting structural and optical features for a wide range of applications, from photonics to sensing. For what concern photonics, the possibility to fabricate artificial fractals based on Si NWs that integrate other interesting elements is reported. In particular, an artificial fractal based on the Er:Y2O3 decoration of Si NWs where the Er emission can be tuned as a function of the decoration angle is shown. In the sensor field, the use of Si NW luminescence can represent an interesting and innovative sensing mechanism for the realization of a novel class of sensing platform. In this work, a light-emitting Si NWs-based label-free sensor for both selective isolation and ultrasensitive quantification of small extracellular vesicles (sEVs) is reported opening the route toward liquid biopsy applications.

In this paper we show for the first time the possibility to direct grow and tune the size and optical properties of high quality InAs/GaAs quantum dots on transferable crystalline silicon nanomembranes. The transferable silicon nanomembranes have been grown via in-situ H2 prebake of porous silicon in Ultra High Vacuum Chemical vapour Deposition (UHV-CVD) reactor. Flat and continuous transferable crystalline nanomembranes with thicknesses below 30 nm have been obtained. The mechanical strain in the silicon nanomembranes has been tuned via sintering temperature between 900 and 1100 °C for the direct crystalline growth of transferable InAs/GaAs (QDs)/Si foils. The size and band gap energy of these InAs/GaAs quantum dots are tuned via strain engineering in silicon nanomembranes. Several advanced techniques such as Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD), Photoluminescence (PL) spectroscopy are used to investigate the structural and optical properties of transferable silicon nanomembranes and the grown InAs/GaAs QDs. High quality InAs/GaAs QDs with tuned sizes grown on flat and continuous transferable crystalline nanomembranes have been obtained. The obtained results have shown that this novel process allows the growth of well separated InAs/GaAs QDs with well defined shape, high density around 2 × 1010/cm2 and a well controlled size variation as function of the substrate strain between 2 and 10 nm. The high quality of the structural and optical properties of the InAs/GaAs QDs monolithically grown on a transferable Si nanomembranes and its compatibility with standard Si solar cells technologies offer a great opportunity for growing a cheap and high performance InAs/GaAs quantum dots/Si third generation solar cells and microelectronic devices.