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We report the growth and low-temperature photoluminescent characteristics of well-aligned Ni-doped ZnO nanoneedles and V-doped ZnO nanostructured thin film grown by a modified pulsed laser deposition technique. Low-temperature photoluminescence spectra of the as-grown films show the presence of free excitonic as well as bound excitonic transitions, whose relative intensity changes with increasing temperature. Ni-doped ZnO films show a characteristic fine structure in the visible range (2.6-2.9 meV) attributed to either exciton-polariton longitudinal-transverse splitting or the splitting caused by electron-hole exchange interaction. The excitonic and visible region emission can be clearly seen as can the phonon replicas produced from longitudinal optical phonons. Different possible attributions of the various peaks in the emission band at low temperature have been discussed. The as-grown nanostructures of Ni- and V-doped ZnO thin films also clearly show the effect of doping on the microstructure of ZnO. [ABSTRACT FROM AUTHOR]

Nanostructured SnO(x) films were obtained by molecular beam epitaxy (MBE). The morphology, structure, and optical properties of obtained films annealed in the temperature range of 200 °C–1000 °C were studied. The reflection high-energy electron diffraction during the film deposition by the MBE method and the x-ray phase analysis showed that the initial films are in the polycrystalline phase. A single orthorhombic SnO _2 phase was obtained for the first time after annealing the SnO(x) film in the air at a temperature of about 500 °C. The sharp change in the optical constants near the temperature of 500 °C was established using ellipsometry. The pronounced absorption edge appears in the short-wave region at temperatures above 500 °C and it disappears at lower temperatures. The film thickness changed non-monotonically during the annealing in the air. At first, it grows from 45 nm to 65 nm (active oxidation to 500 °C), and then (above 600 °C) it begins to decrease. The annealing at temperatures of 500 °C–1000 °C leads to the film compaction, since the film thickness decreases to 50 nm, but the refractive index increases by 10%–15%. Optical constants track the progress of film phase and morphological changes.

We report a large chiro-optical response from a nanostructured film of aperiodic dielectric helices decorated with ellipsoidal metal nanoparticles. The influence of the inherent fabrication variation on the chiro-optical response of the wafer-scalable nanostructured film is investigated using a computational model which closely mimics the material system. From the computational approach, we found that the chiro-optical signal is strongly dependent on the ellipticities of the metal nanoparticles and the developed computational model can account for all the variations caused by the fabrication process. We report the experimentally realized dissymmetry factor ∼1.6, which is the largest reported for wafer scalable chiro-plasmonic samples till now. The calculations incorporate strong multipolar contributions of the plasmonic interactions to the chiro-optical response from the tightly confined ellipsoidal nanoparticles, improving upon the previous studies carried in the coupled dipole approximation regime. Our analyzes confirm the large chiro-optical response in these films developed by a scalable and simple fabrication technique, indicating their applicability pertaining to manipulation of optical polarization, enantiomer selective identification and enhanced sensing and detection of chiral molecules. [ABSTRACT FROM AUTHOR]

Motivated by the technological relevance of tungsten oxide nanostructures as valuable materials for energy saving technology, electrochemical and electrochromic characteristics of greener processed nanostructured W18O49-based electrodes are discussed in this work. For the purpose, microwave-assisted water-dispersible W18O49 nanorods have been synthesized and processed into nanostructured electrodes. An airbrushing technique has been adopted as a cost-effective large-area scalable methodology to deposit the W18O49 nanorods onto conductive glass. This approach preserves the morphological and crystallographic habit of native nanorods and allows highly homogeneous transparent coating where good electronic coupling between nanowires is ensured by a mild thermal treatment (250 °C, 30 min). Morphological and structural characteristics of active material were investigated from the synthesis to the nanocrystal deposition process by transmission and scanning electron microscopy, x-ray diffraction, atomic force microscopy and Raman spectroscopy. The as-obtained nanostructured film exhibited good reversible electrochemical features through several intercalation–deintercalation cycles. The electrochromic properties were evaluated on the basis of spectro-electrochemical measurements and showed significant optical contrast in the near-infrared region and high coloration efficiency at 550 nm. [ABSTRACT FROM AUTHOR]

In light of the nanostructured surface model, where half-spherical nanoparticles grow out symmetrically from a plane metallic film, the mathematical model for the partial electrical potential around nanospheres is developed when a uniform external electric field is applied. On the basis of these models, the three-dimensional spatial distribution of the partial electrical potential is obtained and given in the form of a curved surface using a numerical computation method. Our results show that the electrical potential distribution around the nanospheres exhibits an obvious geometrical symmetry. These results could serve as a reference for investigating many abnormal phenomena such as abnormal infrared effects, which are found when CO molecules are adsorbed on the surface of nanostructured transition metals. [ABSTRACT FROM AUTHOR]

The aim of this study was to reproduce the physico-mechanical antibacterial effect of the nanocolumnar cicada wing surface for metallic biomaterials by fabrication of titanium (Ti) nanocolumnar surfaces using glancing angle sputter deposition (GLAD). Nanocolumnar Ti thin films were fabricated by GLAD on silicon substrates. S. aureus as well as E. coli were incubated with nanostructured or reference dense Ti thin film test samples for one or three hours at 37 �C. Bacterial adherence, morphology, and viability were analyzed by fluorescence staining and scanning electron microscopy and compared to human mesenchymal stem cells (hMSCs).Bacterial adherence was not significantly different after short (1 h) incubation on the dense or the nanostructured Ti surface. In contrast to S. aureus the viability of E. coli was significantly decreased after 3 h on the nanostructured film compared to the dense film and was accompanied by an irregular morphology and a cell wall deformation. Cell adherence, spreading and viability of hMSCs were not altered on the nanostructured surface. The results show that the selective antibacterial effect of the cicada wing could be transferred to a nanostructured metallic biomaterial by mimicking the natural nanocolumnar topography. [ABSTRACT FROM AUTHOR]

Nanostructured films are deposited by a new technique that matches supersonic cluster beam deposition with flame spray pyrolysis production of nanoparticles (FlameBeam). These films are structured with micrometric lateral resolution, applying a lift-off method by pre-structuring a photoresist-PMMA bilayer with a suitable ‘mushroom-like’ cross-section, depositing a nanostructured silver film on top and lifting off the bilayer in an aqueous solution. Optical inspection revealed that line-shaped microstructures, having a minimal width of up to 3 µm, can be successfully obtained. The nanostructured films have survived the aqueous treatment, as demonstrated by electron microscopy imaging and electrical characterization through 4-point measurement method (Van-der-Pauw). The latter has been possible through sputtered gold pads that were realized on the substrate prior to the deposition of the photoresist and of the nanostructured film. These results disclose novel possibilities in the fine patterning of FlameBeam-deposited films and their integration into microelectromechanical systems devices in general. [ABSTRACT FROM AUTHOR]

β -Ga2O3 has been widely investigated for its stability and thermochemical properties. However, the preparation of β -Ga2O3 thin films requires complex growth techniques and high growth temperatures, and this has hindered the application of β -Ga2O3 thin films. In this study, β -Ga2O3 thin films with good crystalline quality were prepared using a green method, and an ultraviolet (UV) detector based on β -Ga2O3 with a photocurrent of 2.54 × 10–6 A and a dark current of 1.19 × 10–8 A has been developed. Two-dimensional materials have become premium materials for applications in optoelectronic devices due to their high conductivity. Here, we use the suitable energy band structure between Nb2C and Ga2O3 to create a high carrier migration barrier, which reduces the dark current of the device by an order of magnitude. In addition, the device exhibits solar-blind detection, high responsiveness (28 A W−1) and good stability. Thus, the Nb2C/ β -Ga2O3 heterojunction is expected to be one of the promising devices in the field of UV photoelectric detection. [ABSTRACT FROM AUTHOR]

Sol–gel derived, as-deposited amorphous tungsten oxide (WO3) films become nanocrystalline with a pseudocubic triclinic structure upon annealing at 600 °C. The annealed films are constituted of nanorods along with interconnected nanoparticles and pores. While the high transmission modulation and colouration efficiency in the visible region and the fast bleaching kinetics as shown by the nanostructured film were typical of amorphous WO3, the absorption coefficient spread in the 300–2000 nm wavelength range, the reflectance modulation and the colouration efficiency peak in the NIR region were reminiscent of crystalline WO3. The larger magnitude of the indirect band gap shift to blue than the direct gap shift for the same level of lithium intercalation (18 mC cm−2) and the irreversibility of the direct gap shift upon bleaching are characteristic of the nanocrystalline structure of the film. The moderate decline in the anodic peak current maximum, the diffusion coefficient for lithium and the optical modulation at 632.8 nm upon repetitive switching between the coloured and bleached states ratified that nanostructured films sustain 1000 cycles without much deterioration. [ABSTRACT FROM AUTHOR]

The electrophoretic deposition (EPD) of semiconductor ceramic nanoplatelets functionalized by self-assembled polyelectrolyte multilayers has been investigated. The influence of particle surface modification in the packing of the nanostructured film on a nickel cathode has been determined for different electrical conditions. A polymer multilayer shell has been fashioned onto β-Ni(OH)2 nanoplatelets surfaces by alternating the adsorption of Polyethylenimine (PEI) and Polyacrylic Acid (PAA). Two different core-shell systems with 1, 3 and 5 layers were considered using either linear or branched PEI as polycation to alternate with the anionic polyelectrolyte (PAA). The Layer by Layer, (LbL) build-up of polyanions and polycations was characterized both in terms of particle zeta potential measurements and in situ measurements of polyelectrolyte adsorption onto a flat substrate by optical fixed-angle reflectometry. The amount of polyelectrolyte required to build up each layer was determined from zeta potential measurements. Both data allowed the design of the in situ formation of the core-shell nanostructures as well as the shaping of the particulated coatings following the one-pot procedure, avoiding intermediate steps of drying or washing. The movement of the core-shell particles, their aggregation state and the coating growth during electrophoretic deposition were studied in situ using a laminar flow cell coupled to an optical microscope. The particle flux was calculated from the surface coverage of the cathode and compared to the values estimated by the EPD electrokinetic model, demonstrating the strong impact of the steric interactions between the core-shell particles in both the deposition rate of nanoplatelets and the coating morphology. [ABSTRACT FROM AUTHOR]

Networks of nanoscale objects are the subject of increasing interest as resistive switching systems for the fabrication of neuromorphic computing architectures. Nanostructured films of bare gold clusters produced in gas phase with thickness well beyond the electrical percolation threshold, show a non-ohmic electrical behavior and resistive switching, resulting in groups of current spikes with irregular temporal organization. Here we report the systematic characterization of the temporal correlations between single spikes and spiking rate power spectrum of nanostructured Au two-terminal devices consisting of a cluster-assembled film deposited between two planar electrodes. By varying the nanostructured film thickness we fabricated two different classes of devices with high and low initial resistance respectively. We show that the switching dynamics can be described by a power law distribution in low resistance devices whereas a bi-exponential behavior is observed in the high resistance ones. The measured resistance of cluster-assembled films shows a scaling behavior in the range of analyzed frequencies. Our results suggest the possibility of using cluster-assembled Au films as components for neuromorphic systems where a certain degree of stochasticity is required. [ABSTRACT FROM AUTHOR]

Here, the ability of using p-type tin oxide (SnOx) thin films as a thermal sensor has been investigated. Firstly, the thermoelectric performance was optimized by controlling the thickness of the SnOx film from 60 up to 160 nm. A high Seebeck coefficient of +263 μV K−1 and electrical conductivity of 4.1 × 102 (S m−1) were achieved in a 60 nm thick SnOx film, due to a compact nanostructured film and the absence of the Sn metallic phase, which was observed for the thicker SnOx film leading to a typical thermoelectric transport properties of a n-type Sn film. Moreover, x-ray photoelectron spectroscopy revealed the co-existence of SnO (79.7%) and SnO2 (20.3%) phases in the 60 nm thick SnOx film, while the optical measurements revealed an indirect gap of 1.8 eV and a direct gap of 2.7 eV, respectively. The 60 nm-SnOx thin film have been tested as a thermoelectric touch sensor, achieving a Vsignal/Vnoise ≈ 20, with a rise time <1 s. Therefore, this work provides an efficient way for developing highly efficient thermal sensors with potential use in display technologies. [ABSTRACT FROM AUTHOR]

Highly porous Germanium surfaces with uniformly distributed columnar nanovoid structures are fabricated over a large area (wafer scale) by large fluence Sn+ irradiation through a thin silicon nitride layer. The latter represents a one-step highly reproducible approach with no material loss to strongly increase photon harvesting into a semiconductor active layer by exploiting the moth-eye antireflection effect. The ion implantation through the nitride cap layer allows fabricating porous nanostructures with high aspect ratio, which can be tailored by varying ion fluence. By comparing the reflectivity of nanoporous Ge films with a flat reference we demonstrate a strong and omnidirectional reduction in the optical reflectivity by a factor of 96% in the selected spectral regions around 960 nm and by a factor of 67.1% averaged over the broad spectral range from 350 to 1800 nm. Such highly anti-reflective nanostructured Ge films prepared over large-areas with a self-organized maskless approach have the potential to impact real world applications aiming at energy harvesting. [ABSTRACT FROM AUTHOR]

Based on the nanostructured surface model, where conical nanoparticle arrays grow out symmetrically from a plane metal substrate, a theoretical model of the local electric potential near nanocones is built when a uniform external electric field is applied. In terms of this model, the electric potential distribution near the nanocone arrays is obtained and given by a curved surface using a numerical computation method. The computational results show that the electric potential distribution near the nanocone arrays exhibit an obvious geometrical symmetry. These results could serve as a basis for explaining many abnormal phenomena, such as the abnormal infrared effects (AIREs) which are found on nanostructured metal surfaces, as well as a reference for investigating the applications of nanomaterials, such as nanoelectrodes and nanosensors. [ABSTRACT FROM AUTHOR]

In this paper, hierarchically nanostructured magnetite films were in situ constructed on pure iron substrates by a Convenient solution process. The resulting magnetite film was characterized by scanning electron microscopy, X-ray diffraction, as well as transmission electron microscopy. The electrocatalytic performance of the nanostructured film was also tested, which showed both high sensitivity and selectivity for the detection of L-ascorbic acid (AA) in the presence of dopamine (DA). In addition, repeated measurements in consecutive months disclosed Constant catalytic responses at optimum potential, indicating both the stability and selectivity of the hierarchically nanostructured magnetite electrode for determining AA from DA without any interference. [ABSTRACT FROM AUTHOR]

Two methods for the synthesis of nanostructured silicon carbide films are discussed and compared, thermal plasma chemical vapour deposition (TPCVD) and hypersonic plasma particle deposition (HPPD). Both methods produce ?-SiC films with high growth rates on the order of 10?µm?min?1. In TPCVD the generation of nanoscale grain sizes is caused by the fact that the film growth rate is much higher than the rate of surface diffusion. In HPPD a nanostructured film is grown by direct nanoparticle impact. In general, the films grown by TPCVD are denser and harder than in HPPD. X-ray diffraction spectra show that ?-SiC is essentially the only crystalline phase in the TPCVD films, whereas in HPPD a silicon crystalline phase is also present, even for films that are overall carbon-rich. Evidence is presented to support the hypothesis that HPPD films actually grow by a combination of nanoparticle impact and CVD. If this parallel process can be controlled, it could potentially lead to the design and high-rate synthesis of new nanostructured materials. [ABSTRACT FROM AUTHOR]

By altering some synthesis variables, the morphology and structural properties of anodic TiO2 nanotube arrays (TiO2NTs) can be tailored to a specific application. This study aims to investigate the effect of electrolyte-containing ions from human plasma and annealing temperature on structural, morphological, and mechanical parameters of TiO2NTs films, targeting its potential biomedical applications. Bio-inspired TiO2NTs were grown from Ticp and its Ti6Al4V alloy by potentiostatic anodization in the recently developed SBF-based electrolyte, maintained at 10 °C and 40 °C. The thermal investigation was performed by TGA/DSC and used to define the phase transition temperatures used for annealing (450 °C and 650 °C). Morphological and structural parameters were evaluated by FE-SEM, XRD, contact angle measurements, and nanoindentation. Results show that self-organized as-formed TiO2NTs were grown under all synthesis conditions with different wettability profiles for each substrate group. At 450 °C annealing temperature, the beginning of nanostructures collapse starts, becoming evident at 650 °C. The nanoindentation characterization reveals that both electrolyte and thermal annealing exhibited low effects on the hardness and Young’s modulus. The tailoring of specific properties by different synthesis conditions could allow the individualization of treatments and better performance in vivo. [ABSTRACT FROM AUTHOR]

Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar bandgap (e.g.) and flat band potential (Efb) values of 1.93 ± 0.04 eV and 0.48 ± 0.06 eV respectively. Eonset of 0.48 ± 0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm−2 at 0 V vs reversible hydrogen electrode (RHE) of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for bare Cu2O photocathodes. [ABSTRACT FROM AUTHOR]

This paper reports the accomplishment of a noticeable enhancement in the photodegradation and antibacterial activity of α-Fe2O3 by a heterostructure formation between α-Fe2O3 and ZnO flakes. The heterostructure yields 97% photodegradation of methylene blue pollutant in water within 180 min, which is a fourfold increase compared to that observed with a pure α-Fe2O3 nanostructure. Further characterisations indicate that the improved results are attributable to the reduction in optical band gap, the increased electrical conductivity, the improved spatial separation of carriers and the enhanced amount of available hydroxyl radicals for the reaction. The stability and reusability of the photocatalysts are confirmed for four consecutive cycles of operations. The phase identification and structural studies are done using x-ray diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy in conjunction with surface morphology from field emission scanning electron microscopy. The enhancement of room temperature electrical conductivity by five times and band gap reduction from 1.98 eV to 1.75 eV for the heterostructures, when compared with α-Fe2O3 nanostructures, are obtained from voltage–current measurements and optical reflectance spectra. [ABSTRACT FROM AUTHOR]

In this Technical Note, we demonstrate a rectification method to enable the use of zinc oxide (ZnO) films in conductometric ultraviolet (UV) sensors. The phenomenon of persistent conductivity has long impeded the employment of ZnO films as conductometric UV sensors and eventually yields photo-induced current saturation in the film. To address this problem, we propose measuring the change in current in a transient response compromising of an OFF period of 60 s followed by an ON period of 20 s. In addition, we have investigated the effects of temperature and relative humidity, and dyanamic response of the sensor for different UV intensities. The experimental result shows that this measurement technique allows the ZnO film to act as a conductometric sensor even after prolonged exposures. [ABSTRACT FROM AUTHOR]

The growth of MoS2 films by sulfurization of Mo foils at atmospheric pressure is reported. The growth procedure provides, in a controlled way, mono- and few-layer thick MoS2 films with substrate-scale uniformity across square-centimeter area on commercial foils without any pre- or post-treatment. The prepared few-layer MoS2 films are investigated as counter electrodes for dye-sensitized solar cells (DSSCs) by assessing their ability to catalyse the reduction of I3– to I– in triiodide redox shuttles. The dependence of the MoS2 catalytic activity on the number of monolayers is explored down to the bilayer thickness, showing performance similar to that of, and stability against corrosion better than, Pt-based nanostructured film. The DSSC with the MoS2–Mo counter electrode yields a photovoltaic energy conversion efficiency of 8.4%, very close to that of the Pt–FTO-based DSSC, i.e. 8.7%. The current results disclose a facile, cost-effective and green method for the fabrication of mechanically robust and chemically stable, few-layer MoS2 on flexible Mo substrates and further demonstrate that efficient counter electrodes for DSSCs can be prepared at thicknesses down to the 1–2 nm scale. [ABSTRACT FROM AUTHOR]

Nanostructured thin films are widely investigated for application in multifunctional devices thanks to their peculiar optoelectronic properties. In this work anatase TiO2 nanoparticles (average diameter 10 nm) synthesised by a green aqueous sol-gel route are exploited to fabricate optically active electrodes for pseudocapacitive-electrochromic devices. In our approach, highly transparent and homogeneous thin films having a good electronic coupling between nanoparticles are prepared. These electrodes present a spongy-like nanostructure in which the dimension of native nanoparticles is preserved, resulting in a huge surface area. Cyclic voltammetry studies reveal that there are significant contributions to the total stored charge from both intercalation capacitance and pseudocapacitance, with a remarkable 50% of the total charge deriving from this second effect. Fast and reversible colouration occurs, with an optical modulation of ∼60% in the range of 315–1660 nm, and a colouration efficiency of 25.1 cm2 C−1 at 550 nm. This combination of pseudocapacitance and electrochromism makes the sol-gel derived titania thin films promising candidates for multifunctional 'smart windows'. [ABSTRACT FROM AUTHOR]

A simple technique is reported to create 31 and 45 μm thick, graded-index Si films in the form of nanospirals on a Si substrate using a dynamic, oblique angle deposition technique. We show that the success in producing such a thick, nanostructured film without delamination from the Si substrate is primarily due to the nano-porous nature of the film which effectively eliminates the stress generated during growth. Effective refractive indices of 1.9 and 2.1 were extracted from the terahertz time-domain reflectivity data, which correspond to 57% and 51% porosity for the 31 and 45 μm thick films, respectively. The gradient of porosity through the film was modeled to describe quantitatively the terahertz reflectance data in the 0.2–2.0 THz regime. [ABSTRACT FROM AUTHOR]

We report on the synthesis and UV–vis photodetection application of p-type MoO2 nanostructures (NSs) on Si substrate. β-MoO2 NSs have been synthesized from previously grown α-MoO3 structures/n-type Si via a hydrogenation process at 450 °C. After hydrogenation, the α-MoO3 structures were completely converted into β-MoO2 NSs without the presence of sub-oxidized phases of molybdenum oxide. The as-grown NSs exhibited very good p-type electrical conductivity of ≈2.02 × 103 S–cm−1 with hole mobility of ≈7.8 ± 1.3 cm2–V−1–Sec−1. To explore optoelectronic properties of p-type β-MoO2 NSs, we have fabricated a p-MoO2/n-Si heterojunction photodetector device with Au as the top and Al as the bottom contacts. The device exhibits peak photoresponsivity of ≈0.155 A W−1 with maximum detectivity ≈1.28 × 1011 cm–Hz1/2–W−1 and 44% external quantum efficiency around ≈436 nm, following the highest photoresponse (Iph/Id ≈ 6.4 × 102) and good response speed (rise time ∼29 ms and decay time ∼38 ms) at −1.5 V. Importantly, this device also shows good self-powered high-speed (rise time ∼47 ms and decay time ∼70 ms) photodetection performance with peak responsivity and detectivity of ≈45 mA W−1 and ≈4.05 × 1010 cm–Hz1/2–W−1, respectively. This broadband UV-visible light detection feature can be attributed to the coordinated effects of MoO2 band-edge absorption, interfacial defects and self absorption in Si. The photodetection behavior of the device has been understood by proposed energy-band diagrams with the help of an experimentally derived work function, band gap and valence band maximum position of MoO2 NSs. [ABSTRACT FROM AUTHOR]