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Cadmium (Cd)-free photodiodes based on n-type Zinc Selenide/p-type Zinc Telluride (n-ZnSe/p-ZnTe) heterojunctions were prepared by Radio Frequency-Magnetron Sputtering (RF-MS) technique, and their detailed optical and electrical characterization was performed. Onto an optical glass substrate, 100 nm gold (Au) thin film was deposited by Thermal Vacuum Evaporation (TVE) representing the back-contact, followed by the successive RF-MS deposition of ZnTe, ZnSe, Zinc Oxide (ZnO) and Indium Tin Oxide (ITO) thin films, finally resulting in the Au/ZnTe/ZnSe/ZnO/ITO sub-micrometric “substrate”-type configuration. Next, the optical characterization by Ultraviolet-Visible (UV-VIS) spectroscopy was performed on the component thin films, and their optical band gap values were determined. The electrical measurements in the dark and under illumination at different light intensities were subsequently performed. The Current–Voltage (I–V) characteristics in the dark are nonlinear with a relatively high asymmetry, following the modified Shockley–Read equation. From their analysis, the series resistance, shunt resistance, the ideality factor and saturation current were determined with high accuracy. It is worth noting that the action spectrum of the structure is shifted to short wavelengths. A sensibility test for the 420–500 nm range was performed while changing the intensity of the incident light from 100 mW/cm2 down to 10 mW/cm2 and measuring the photocurrent. The obtained results provided sufficient information to consider the present sub-micrometric photodiodes based on n-ZnSe/p-ZnTe heterojunctions to be more suitable for the UV domain, demonstrating their potential for integration within UV photodetectors relying on environmentally-friendly materials.

Environmental pollution with cadmium (Cd) is a major concern worldwide, with prolonged exposure to this toxic heavy metal causing serious health problems, such as kidney damage, cancer, or cardiovascular diseases, only to mention a few. Herein, a gold-coated reflection-type fiber optic–-surface plasmon resonance (Au-coated FO-SPR) sensor is manufactured and functionalized with (i) bovine serum albumin (BSA), (ii) chitosan, and (iii) polyaniline (PANI), respectively, for the sensitive detection of cadmium ions (Cd2+) in water. Then, the three sensor functionalization strategies are evaluated and compared one at a time. Out of these strategies, the BSA-functionalized FO-SPR sensor is found to be highly sensitive, exhibiting a limit of detection (LOD) for Cd2+ detection at nM level. Moreover, the presence of Cd2+ on the FO-SPR sensor surface was confirmed by the X-ray photoelectron spectroscopy (XPS) technique and also quantified consecutively for all the above-mentioned functionalization strategies. Hence, the BSA-functionalized FO-SPR sensor is sensitive, provides a rapid detection time, and is cheap and portable, with potential applicability for monitoring trace-level amounts of Cd within environmental or potable water.

In the present study, the synthesis of titanium nitride (TiN) by carbothermal reduction nitridation (CRN) reaction using nanocomposites made of mesoporous TiO2/acrylonitrile with different content of inorganic phase were explored. The choice of hybrid nanocomposite as precursor for the synthesis of TiN was made due to the possibility of having an intimate interface between the organic and inorganic phases in the mixture that can favours CRN reaction. Subsequently, the hybrid composites have been subjected to four-step thermal treatments at 290 °C, 550 °C, 1000 °C and 1400 °C under nitrogen atmosphere. The XRD results after thermal treatment at 1000 °C under nitrogen flow show the coexistence of two crystalline phases of TiO2, i.e. anatase and rutile, as well as TiN phase, together with the detection of amorphous carbon that proved the initiation of CRN reaction. Furthermore, the observations based on XRD patterns of samples thermally treated at 1400 °C in nitrogen atmosphere were in agreement with SEM analysis, that shows the formation of TiN by CRN reaction via hybrid nanocomposites mesoporous TiO2/acrylonitrile.

Zinc telluride thin films with different thicknesses were grown onto glass substrates by the rf magnetron sputtering technique, using time as a variable growth parameter. All other deposition process parameters were kept constant. The deposited thin films with thickness from 75 to 460 nm were characterized using X-ray diffraction, electron microscopy, atomic force microscopy, ellipsometry, and UV-Vis spectroscopy, to evaluate their structures, surface morphology, topology, and optical properties. It was found out that the deposition time increase leads to a larger growth rate. This determines significant changes on the ZnTe thin film structures and their surface morphology. Characteristic surface metrology parameter values varied, and the surface texture evolved with the thickness increase. Optical bandgap energy values slightly decreased as the thickness increased, while the mean grains radius remained almost constant at ~9 nm, and the surface to volume ratio of the films decreased by two orders of magnitude. This study is the first (to our knowledge) that thoroughly considered the correlation of film thickness with ZnTe structuring and surface morphology characteristic parameters. It adds value to the existing knowledge regarding ZnTe thin film fabrication, for various applications in electronic and optoelectronic devices, including photovoltaics.

Zinc selenide (ZnSe) thin films were deposited by RF magnetron sputtering in specific conditions, onto optical glass substrates, at different RF plasma power. The prepared ZnSe layers were afterwards subjected to a series of structural, morphological, optical and electrical characterizations. The obtained results pointed out the optimal sputtering conditions to obtain ZnSe films of excellent quality, especially in terms of better optical properties, lower superficial roughness, reduced micro-strain and a band gap value closer to the one reported for the ZnSe bulk semiconducting material. Electrical characterization were afterwards carried out by measuring the current–voltage (I-V) characteristics at room temperature, of prepared “sandwich”-like Au/ZnSe/Au structures. The analysis of I-V characteristics have shown that at low injection levels there is an Ohmic conduction, followed at high injection levels, after a well-defined transition voltage, by a Space Charge Limited Current (SCLC) in the presence of an exponential trap distribution in the band gap of the ZnSe thin films. The results obtained from all the characterization techniques presented, demonstrated thus the potential of ZnSe thin films sputtered under optimized RF plasma conditions, to be used as alternative environmentally-friendly Cd-free window layers within photovoltaic cells manufacturing.

Polycrystalline ZnX (X = S, Se) and CdTe thin films were prepared by rf magnetron sputtering and by thermal vacuum evaporation (CdTe films), respectively. The structural properties were studied by X-ray diffraction (XRD), which revealed that ZnX films are polycrystalline with a marked (111) texture. After irradiation with protons crystallite sizes decreased while mechanical strains increased. Thicknesses of ZnX films and surface roughness have been measured by X-ray reflectometry (XRR) with thickness values between 58 nm and up to 163 nm and with surface roughness between 1.7 nm and 2.4 nm. Morphological investigations were made by scanning electron microscopy (SEM), drops - free surfaces with compact and uniform aspect being deposited. Absorption and transmission measurements were carried out for all samples deposited on optical glass substrates. Experimentally determined bandgap energies were between 2.31–2.75 eV for ZnSe layers, respectively, 3.10–3.65 eV for ZnS films. Optical transmissions in VIS-NIR regions are higher than 60% for both ZnSe and ZnS films. Glass/ITO/ZnS/ZnSe/CdTe/Cu:Au structures in superstrate configuration were produced by depositing CdTe absorber layers by thermal vacuum evaporation (TVE). Action spectra of the external quantum energy (EQE) and the current-voltage (I-V) characteristics in AM 1.5 conditions (the density power of the incident light is equal with 100 mW/cm2) corresponding for double-heterojunction ZnS/ZnSe/CdTe photovoltaic structures were investigated before and after irradiations with high energy protons (3 MeV).

In this work, we report results on the fabrication and characterization of a surface plasmon resonance (SPR) pH sensor using platinum (Pt) and polyaniline (PANI) layers successively coated over an unclad core of an optical fiber (FO). The plasmonic thin Pt layer was deposited using a magnetron sputtering technique, while the pH-sensitive PANI layer was synthesized using an electroless polymerization method. Moreover, the formation of PANI film was confirmed by X-ray photoelectron spectroscopy (XPS) technique and its surface morphology was investigated using scanning electron microscopy (SEM). It was found that the PANI/Pt-coated FO-SPR pH sensor exhibits a fast and linear response in either acid or alkali solutions (pH operational range: 1 to 14). The proposed FO-SPR sensor could be used for biomedical applications, environmental monitoring or any remote, real-time on-site measurements.

Polymer electrolyte membrane fuel cells require cheap and active electrocatalysts to drive the oxygen reduction reaction. Nitrogen-doped carbons have been extensively studied regarding their oxygen reduction reaction. The work at hand looks beyond the nitrogen chemistry and brings to light the role of oxygen. Nitrogen-doped nanocarbons were obtained by a radio-frequency plasma route at 0, 100, 250, and 350 W. The lateral size of the graphitic domain, determined from Raman spectroscopy, showed that the nitrogen plasma treatment decreased the crystallite size. Synchrotron radiation photoelectron spectroscopy showed a similar nitrogen chemistry, albeit the nitrogen concentration increased with the plasma power. Lateral crystallite size and several nitrogen moieties were plotted against the onset potential determined from oxygen reduction reaction curves. There was no correlation between the electrochemical activity and the sample structure, as determine from Raman and synchrotron radiation photoelectron spectroscopy. Near-edge X-ray absorption fine structure (NEXAFS) was performed to unravel the carbon and nitrogen local structure. A difference analysis of the NEXAFS spectra showed that the oxygen surrounding the pyridinic nitrogen was critical in achieving high onset potentials. The work shows that there were more factors at play, other than carbon organization and nitrogen chemistry.

The paper reports for the first time an innovative polyaniline (PANI)/platinum (Pt)-coated fiber optic – surface plasmon resonance (FO-SPR) sensor used for highly-sensitive 4-nitrophenol (4-NP) pollutant detection. The Pt thin film was coated over an unclad core of an optical fiber (FO) using a DC magnetron sputtering technique, while the 4-NP responsive PANI layer was synthetized using a cost-effective electroless polymerization method. The presence of the electrolessly-grown PANI on the Pt-coated FO was observed by field-emission scanning electron microscopy (FE-SEM) and subsequently evidenced by energy dispersive X-ray analysis (EDX). These FO-SPR sensors with a demonstrated sensitivity of 1515 nm/RIU were then employed for 4-NP sensing, exhibiting am excellent limit of detection (LOD) in the low picomolar range (0.17 pM). The proposed sensor’s configuration has many other advantages, such as low-cost production, small size, immunity to electromagnetic interferences, remote sensing capability, and moreover, can be operated as a “stand-alone device”, making it thus well-suited for applications such as “on-site” screening of extremely low-level trace pollutants.

Tin‐based nanowire electrodes present desirable properties as lithium‐ion battery anodes, because they undergo volume changes without pulverization. However, they suffer from limited mass loading and propensity for surface parasitic reactions. Herein, we evaluate the electrochemical performances of interconnected nickel‐tin nanowire network electrodes (NiSn 3DNWN) with nanowire diameters of 40 nm, 105 nm, and 230 nm, respectively, that attain mass loadings of up to 3 mg cm‐2. To mitigate the surface parasitic reactions, the effects of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives are investigated as a function of nanowire diameter and additive concentration. The results show that FEC and VC of all compositions improve the capacity retentions and coulombic efficiencies of the NiSn 3DNWN electrodes. In 10 vol% FEC, the electrodes demonstrate a similar capacity of ∽ 550 mAh g‐1, but the capacity retentions after 100 cycles are 73.68%, 53.79%, 51.70% for the 40 nm, 105 nm, and 230 nm NiSn 3DNWN, respectively. However, the 105 nm‐diameter nanowire electrode has the highest average coulombic efficiency of 96.55%. Electrochemical impedance spectroscopy and post‐cycling investigations reveal that FEC has the most profound effect on the interphasial resistances, which is reflected in the rate performances of the tested electrodes. This article is protected by copyright. All rights reserved.

In the present study, the synthesis of titanium nitride (TiN) by carbothermal reduction nitridation (CRN) reaction using nanocomposites made of mesoporous TiO2/acrylonitrile with different content of inorganic phase were explored. The choice of hybrid nanocomposite as precursor for the synthesis of TiN was made due to the possibility of having an intimate interface between the organic and inorganic phases in the mixture that can favours CRN reaction. Subsequently, the hybrid composites have been subjected to four-step thermal treatments at 290 °C, 550 °C, 1000 °C and 1400 °C under nitrogen atmosphere. The XRD results after thermal treatment at 1000 °C under nitrogen flow show the coexistence of two crystalline phases of TiO2, i.e. anatase and rutile, as well as TiN phase, together with the detection of amorphous carbon that proved the initiation of CRN reaction. Furthermore, the observations based on XRD patterns of samples thermally treated at 1400 °C in nitrogen atmosphere were in agreement with SEM analysis, that shows the formation of TiN by CRN reaction via hybrid nanocomposites mesoporous TiO2/acrylonitrile.

The difficulty to generate and control large strain gradients in materials hinders the investigation and application of flexoelectricity and flexomagnetism. This work demonstrates that thermal expansion can be used to induce very large non-uniform strains at the nanoscale, resulting in giant strain gradients at moderate temperatures. This is demonstrated in a nanopatterned multiferroic hybrid layer consisting of a regular array of ferromagnetic metallic nanocylinders embedded in a ferroelectric polymer matrix. The thermally-induced strain gradients can fully depolarize the ferroelectric component, and modify the magnetization of the ferromagnetic component via flexoelectric and flexomagnetic effects, respectively. Finiteelement analysis provides a quantitative view on thermal expansion-induced strains and strain gradients supporting the experimental findings. This work shows that nanoscale thermal strain engineering provides an additional degree of freedom to control electrical polarization and magnetization, which paves the way for the design and operation of novel functional devices and nanostructures.

There is a proliferation of autonomous microscale devices, which are increasingly in need of power sources of commensurate form factors. The trade-off between the areal energy and power capabilities of miniature energy storage devices restrict their abilities to meet the requirements of these microscale devices. However, three-dimensional (3D) micro- and nanoarchitectures have the potential to meet the energy requirements of autonomous microscale devices, while retaining the power capabilities of thin-film systems. In this paper, we present a novel full-cell architecture and fabrication strategy for 3D microscale energy storage devices based on template-assisted electrodeposition of three-dimensionally interconnected metallic nanowire network, and its subsequent laser-patterning to form interdigitated nanostructured electrodes. The patterned nanowire networks are functionalized with the polyaniline active electrode material via an electroless deposition procedure. We show that a footprint areal capacitance/energy enhancement of more than 5 times is achieved by just 10 μm-high nanowire networks, in addition to enhanced power capabilities.

We developed a versatile template-based fabrication method for growing large arrays of three-dimensionally interconnected polypyrrole nanotubes (or nanowires) with easily tunable geometrical dimensions and spatial arrangement. Such a macroscopic network made up of conducting polymer elongated nanostructures provides an extremely large active surface with increased electrical connectivity, as well as an enhanced structural integrity of the flexible network. The three-dimensional array of polypyrrole nanofibers exhibited an excellent sensitivity towards gaseous ammonia, providing reliable and accurate detection at gas concentrations as low as 1 ppm. The novel preparation approach offers a cost-effective alternative for large-scale production of easily integrable chemiresistive sensors for different applications.

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures&rsquo, electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.

The active layer of the bulk heterojunction organic photovoltaic cells is typically based on a polymeric blend containing a donor polymer and a fullerene-based polymer electron acceptor. However, in the last decade non-fullerene polymer-based solar cells have seen a rapid progress, due to their extraordinary chemical, thermal and photo stability, and because of their ability to decrease the voltage loss. The conventional Organic Photovoltaic Cells (OPVs), structures based on either P3HT:PCBM bulk heterojunction (BHJ) polymeric blend or P3HT/PCBM bilayer heterojunction, have limited efficiency and stability, in principal due to the fullerene derivatives used as acceptor component. PCBM for example, as many other fullerene derivatives, exhibits some deficiencies, such as: limited chemical and energetic tunability, small range of absorption spectra, morphological instability and relatively high production costs. That is why in the last years, novel non-fullerene materials started to be used in order to overcome the above limits associated with the fullerene acceptors. In this paper two different non-fullerene acceptor materials have been tested as potential candidates for the efficient OPVs based on P3HT donor polymer as main absorber: a new conjugated polymer containing chelating ligands like 1,10-Phenanthroline (Phen), and a small-molecule acceptor like 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphine (TPyP). For both cell configurations a decrease of the voltage loss was obtained, and it was also observed that the thickness of the P3HT donor layer has an important contribution to the output power ( P max ) and fill factor ( FF ) of the OPV structures ( FF and P max increased almost two times by decreasing the thickness of the P3HT donor layer).

We reported an efficient way of preparing large and dense ferromagnetic arrays of vertically-aligned Ni nanotubes (NTs). The synthesis method allowed then for a direct, effective and controllable thermal conversion of the as-prepared Ni NTs into heterostructured Ni/NiO NTs, without compromising the nanostructures' verticality to the substrate and their initial tubular integrity. Next, we demonstrated the ability to tune the dipolar interaction field (DIF) in this array of one-dimensional (1D) Ni/NiO heterostructures, just by slightly changing the thickness of the antiferromagnetic NiO layer. Furthermore, the proposed fabrication method assures full compatibility with the standard Si processing, providing thus a direct pathway towards large-scale integrability and manufacturing of a new generation of magnetic devices relying on dense arrays of vertical 1D magnetic nanostructures.

In this work, we evaluated the piezoelectric properties of the ZnO nanorods (NRs), subsequently grown by a template-free electrochemical deposition (ECD) approach. The one-step preparation method yielded in a relatively short-time synthesis large arrays of high aspect-ratio ZnO NRs, vertically aligned to the substrate and exhibiting a well-defined hexagonal symmetry coupled with an excellent crystallinity. Piezoresponse force microscopy (PFM) was employed to extract the effective piezoelectric coefficient ( d 33 ) of the ZnO [0 0 0 1]-oriented NRs. A mean effective d 33 coefficient of 11.8 pm/V was measured over several individual NRs. The results have shown an increased piezoelectric response of the ZnO NRs, with ∼18% in respect to the ZnO bulk material, and with a factor ranging from 28% to 167% compared to similar ZnO nanostructures prepared by other counterpart techniques. Both morphology and crystalline quality of the obtained ZnO NRs, as well as the piezoelectric investigations, ranked the ECD as a promising low-cost pathway for possibly producing high quality nanostructured ZnO-based piezoelectric devices with enhanced performance.

We review the present state of the art on organic photovoltaic cells based on both small molecule and polymeric absorbers. In the case of small molecules, different configurations with one, two and three active layers have been synthesized and characterized. In the case of structures based on single layer polymeric absorbers, bilayer and blend configurations have also been investigated. The properties of each category of solar cells, based on small molecules and polymers, are discussed. Transport mechanisms and stability studies have been carried out on the organic materials and the photovoltaic structures fabricated from them. Generally, efficiency increases for cell structures composed of multi-layered small molecules or a blend of donor/acceptor polymers, and the efficiency of polymeric photovoltaic cells is always larger than that of small-molecule structures. Unfortunately, the stability of the former is poorer than that of the latter category. Factors influencing device stability are discussed and technological methods used to improve stability are also presented.

A new strategy to elaborate (1-3) type multiferroic nanocomposites with controlled dimensions and vertical alignment is presented. The process involves a supported nanoporous alumina layer as a template for growth of free-standing and vertically aligned CoFe

tIn this work, large and dense arrays of zinc oxide (ZnO) nanorods (NRs) were fabricated by an improvedtemplate-free electrodeposition (ECD) route on top of home-made Al-doped ZnO (AZO) thin filmsdeposited on glass. The AZO layer, acting as transparent conducting oxide, was found to display enhancedelectrical and morphological properties compared to other commercially available substrates, facilitat-ing the subsequent electrochemical growth of the ZnO nanostructures. In addition, its intrinsic columnarnature strengthened the vertical orientation of the obtained ZnO NRs. The one-step low-temperatureelectrochemical method did not require any additional seeding layer, being suitable for applications inwhich the process simplicity and substrate’s thermal toughness are essential requirements. The ECDprotocol was optimized as a function of the process temperature and duration, demonstrating the pos-sibility to yield reasonable aspect-ratio ZnO NRs in a relatively short time synthesis. Further structuralstudies confirmed the excellent orientation along c-axis of the ZnO Wurtzite phase and have shown apolycrystalline nature of the NRs, with a well-defined hexagonal symmetry of the crystallites.

A nanopatterned hybrid layer is designed, wherein the electric polarization can be flipped at room temperature by a magnetic field aided by an electrical field. This is achieved by embedding ferromagnetic nanopillars in a continuous organic ferroelectric layer, and amplifying the magnetostriction-generated stress gradients by scaling down the supracrystalline cell of the material.

A template method was used to obtain cadmium sulfide (CdS) nanowires. Polymer ion tracks foils (30 μm tick) were used as templates, after etching with solutions containing NaOH and methanol. CdS nanowires were electrochemically grown in the resulting pores. The nanowires were contacted by sputtering a gold layer on top of the membrane, and the electrical properties were recorded in the temperature range 40–300 K. An activated electrical resistance was observed, with activation energy of 0.27 eV at temperatures larger than 180 K. I–V characteristics show a symmetric, non-linear shape, in the voltage range used in this experiment.

The effects of irradiation with high-energy protons (3 MeV, up to a fluency of 1013 protons/cm2), on structural, electrical and optical properties of polycrystalline CdS and CdTe thin films have been investigated. XRD investigation has revealed that the films contain wurtzite-type CdS, (001) preferentially oriented in the growth direction, and cubic phase CdTe, respectively. The defects induced by ionizing radiations have been studied by thermally stimulated currents spectroscopy (TSC). Parameters of identified defect levels were determined and their possible origin is discussed.