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We investigate the oxidation mechanism of the layered model system GeAs.

Cerium oxide nanoparticles (CeO2-NPs; or nanoceria) have been largely studied for biomedical applications due to their peculiar auto-regenerative antioxidant activity. This review focuses on ophthalmic applications of nanoceria. Many in vivo data indicate that nanoceria protect the retina from neurodegeneration. In particular, they have been tested in animal models of age-related macular degeneration and retinitis pigmentosa and their neuroprotective properties have been shown to persist for a long time, without any collateral effects. In vitro cytotoxicity studies have shown that CeO2-NPs could be safe for lens cells and could represent a new therapy for cataract treatment, but further studies are needed. To date, different pharmaceutical formulations based on nanoceria have been created looking at future clinical ophthalmic applications, such as water-soluble nanoceria, glycol chitosan-coated ceria nanoparticles (GCCNPs), and alginate-gelatin hydrogel loaded GCCNPs. GCCNPs were also effective in preventing choroidal neovascularization in vivo. Based on the nanosize of nanoceria, corneal permeation could be achieved to allow topical treatment of nanoceria. PEGylation and encapsulation in liposomes represent the main strategies to support corneal permeation, without altering nanoceria chemical-physical properties. Based on their great antioxidant properties, safety, and nanosize, nanoceria represent a new potential therapeutic for the treatment of several eye disorders.

Oxidation mechanism and kinetics of the layered model system GeAs.

We propose a simple method to fabricate a photodetector based on the carbon nanotube/silicon nitride/silicon (CNT/Si3N4/Si) heterojunction. The device is obtained by depositing a freestanding single-wall carbon nanotube (SWCNT) film on a silicon substrate using a dry transfer technique. The SWCNT/Si3N4/Si heterojunction is formed without the thermal stress of chemical vapor deposition used for the growth of CNTs in other approaches. The CNT film works as a transparent charge collecting electrode and guarantees a uniform photocurrent across the sensitive area of the device. The obtained photodetector shows a great photocurrent that increases linearly with the incident light intensity and grows with the increasing wavelength in the visible range. The external quantum efficiency is independent of the light intensity and increases with the wavelength, reaching 65% at 640 nm.

Clean water is vital for healthy ecosystems, for human life and, in a broader sense, it is directly linked to our socio-economic development. Nevertheless, climate change, pollution and increasing world population will likely make clean water scarcer in the near future. Consequently, it becomes imperative to develop novel materials and more efficient ways of treating waste and contaminated water. Carbon nanotube (CNT) sponges, for example, are excellent in removing oleophilic contaminants; however, due to their super-hydrophobic nature, they are not as efficient when it comes to absorbing water-soluble substances. Here, by means of a scalable method consisting of simply treating CNT sponges at mild temperatures in air, we attach oxygen-containing functional groups to the CNT surface. The functionalized sponge becomes hydrophilic while preserving its micro- and macro-structure and can therefore be used to successfully remove toxic contaminants, such as pesticides, that are dissolved in water. This discovery expands the current range of applications of CNT sponges to those fields in which a hydrophilic character of the sponge is more suitable.

In recent years, nanostructured materials have been deeply investigated for field emission applications. The exploitation of different geometries and morphologies is a key ingredient for the realization of proficient field emitter devices. In this work, we highlight the features of two differently shaped nanostructured materials such as molybdenum disulphide and gallium oxide. We show that Mo S 2 nanoflowers and β-Ga2O3 nanopillars can achieve different field emission performance in terms of maximum current density, turn-on field and field enhancement factor.

We report a detailed investigation of the field emission properties of transition metal dichalcogenides, namely MoS 2 and WSe 2 , taking advantage of an experimental setup realized inside a scanning electron microscope equipped with nano-manipulated probe-tips, used for positioning a tip-shaped anode at a nanometric distance from the emitting surface. For n-type WSe 2 monolayer on Si/SiO 2 substrate, we show that electrons can be extracted also from the flat part of the flake with a current intensity up to few nanoamperes. More interestingly, we demonstrate that the field emission current can be modulated by the back-gate voltage that controls the n-type doping of the WSe 2 monolayer. Similarly, we demonstrate that monolayer MoS 2 flakes are suitable for gate-controlled field emission devices, opening the way to the development of new field emission transistors based on ultrathin materials.

We report a systematic electrical characterization of Mos 2 and PdSe 2 based FETs, with Ti/Au and Pd/Au contacts respectively, to investigate the effect of electron beam irradiation on the transistor channel current, threshold voltage, and contact resistance. We use a 10 keV electron beam inside a scanning electron microscope to irradiate the channel and/or the contact regions of the transistors and perform in-situ electrical measurements profiting of high precision metallic nanoprobes working as the source and the drain contacts. For Mos 2 based devices, we investigate the effect of electron irradiation either on the contact region or on the channel regions. Irradiation of the contact region causes an improvement of the transistor conduction by lowering the contact resistance, which we explain in terms of Schottky barrier reduction at the metal/Moxa interfaces. The irradiation with fluence below 100 e−/nm2 on Mos 2 channel region increases the device conductance and shifts the threshold voltage towards more negative voltages. For PdS2 based devices, electron beam irradiation with larger fluence up to 4200 e−/nm2 is detrimental to the conduction properties of the device, causing modification of the conduction from n-type to p-type, likely due to the accumulation of negative charges at the Si/SiO 2 interface. Moreover, charge carrier mobility is reduced by the formation of defects both in the PdSe2 nanosheets and at the Si/Si02 interface.

A piezoelectrically driven metallic nanoprobe is installed inside a scanning electron microscope to perform local characterization of the field emission properties of InSb nanopillars. The tip-shaped anode can be precisely positioned at sub-micron distances from the emitters to collect electrons from areas as small as 1μm2 under the application of an external bias up to 100 V. Current-voltage characteristics are measured for cathode-anode separation down to 500 nm and are analyzed in the framework of the Fowler-Nordheim theory. We give estimation of performance parameters such as the field enhancement factor and the turn-on field and their dependence on the cathode-anode separation distance. We demonstrate the time stability of the emitted current for several minutes. Finally, we perform a finite element electrostatic simulation to calculate the electric field in proximity of the nanopillars and we evaluate the effective emitting area as well as the screening effect due to presence of other pillars in close vicinity. We show that InSb nanopillars are very stable emitters that allow current density as high as 104 A/cm2 and excellent time stability, crucial characteristics to envisage device exploitation.

The blood retinal barrier (BRB) is a fundamental eye component, whose function is to select the flow of molecules from the blood to the retina and vice-versa, and its integrity allows the maintenance of a finely regulated microenvironment. The outer BRB, composed by the choriocapillaris, the Bruch’s membrane, and the retinal pigment epithelium, undergoes structural and functional changes in age-related macular degeneration (AMD), the leading cause of blindness worldwide. BRB alterations lead to retinal dysfunction and neurodegeneration. Several risk factors have been associated with AMD onset in the past decades and oxidative stress is widely recognized as a key factor, even if the exact AMD pathophysiology has not been exactly elucidated yet. The present review describes the BRB physiology, the BRB changes occurring in AMD, the role of oxidative stress in AMD with a focus on the outer BRB structures. Moreover, we propose the use of cerium oxide nanoparticles as a new powerful anti-oxidant agent to combat AMD, based on the relevant existing data which demonstrated their beneficial effects in protecting the outer BRB in animal models of AMD.

In this work devices based on a MWCNTs-Si heterojunction were realized growing MWCNTs, by chemical vapor deposition, on an n-type Si substrate with the top and bottom surfaces covered by 140 nm thick Si3N4 layers. Two metal contacts, realized on the top and back of the Si surface, were used to perform I-V measurements of the vertical heterostructure. The photocurrent behavior, obtained by light illumination, was studied as a function of the thickness of the MWCNTs layer. A planar quantum efficiency map of the device was obtained by I-V measure when the active area of the device was rastered by a 1 mm diameter light spot. The thickness reduction of the MWCNTs was realized by adhesive tape. We found that the photocurrent intensity increased when the density of the MWCNTs layer was decreased. To check the substrate coverage by the MWCNTs, scanning electron microscope images were taken.

The IV–V groups binary compound germanium arsenide (GeAs) is a semiconductor that can be easily exfoliated in very thin nanosheets and is characterized by a band gap ranging from 0.6 eV (bulk form) up to 2.1 eV (monolayer). We investigate the field emission characteristics of exfoliated multilayer GeAs nanosheets by means of a tip-anode setup, where a nanomanipulated W-tip is positioned in front of the GeAs emitting layer at nanometric distance, all controlled inside a scanning electron microscope. We demonstrate that GeAs multilayers are suitable to develop electron sources, with turn-on field of the order of 102 Vµm-1, and field enhancement factor of about 70.

We fabricate AlGaN nanowires by molecular beam epitaxy and we investigate their field emission properties by means of an experimental setup using nano-manipulated tungsten tips as electrodes, inside a scanning electron microscope. The tip-shaped anode gives access to local properties and allows collecting electrons emitted from areas as small as 1$\mu m^2$. The field emission characteristics are analyzed in the framework of Fowler-Nordheim theory and we find a field enhancement factor as high as $\beta$ = 556 and a minimum turn-on field $E_{turn-on}$ = 17 V/$\mu$m for a cathode-anode separation distance d = 500 nm. We show that for increasing separation distance, $E_{turn-on}$ increases up to about 35 V/$\mu$m and $\beta$ decreases to 100 at d = 1600 nm. We also demonstrate the time stability of the field emission current from AlGaN nanowires for several minutes. Finally, we explain the observation of modified slope of the Fowler-Nordheim plots at low fields in terms of non-homogeneous field enhancement factors due to the presence of protruding emitters., Comment: 13 pages, 5 figures

This study reports the electrical transport and the field emission properties of individual multi-walled tungsten disulphide (WS

International audience; Allyl alcohol (AA) was obtained by the deoxydehydration (DODH) of glycerol performed in the presence of a number of Re compounds (oxides, phosphine and halide derivatives) in alcoholic solvent or in neat conditions. Independently of starting Re species, the resulting catalytic process featured a delay time, necessary to start the formation of both AA and an Re-alkoxide precipitate. However, no delay time was detected by operating DODH using a preformed precipitate obtained by either Re source. As a consequence, and based on IR spectral analysis, it was hypothesized that the Re precipitate is the actual catalyst of DODH. The mechanism of DODH catalysis operated by methyltrioxorhenium (MTO) was studied by experimental and theoretical approaches. The results suggest that MTO releases methane with the formation of an ReVII alkoxide that subsequently aggregates by yielding the precipitate. The ReVII centre precipitate surface then undergoes reduction by forming ReV catalytic spots. The calculated kinetics also indicate that the detected latency can be ascribed to the presence of two high barriers, i.e. methane release and ReVII → ReV reduction, whereas the downstream processes, i.e. glycation and AA release, are not rate determining.

InSb nanowire arrays with different geometrical parameters, diameter and pitch, are fabricated by top-down etching process on Si(100) substrates. Field emission properties of InSb nanowires are investigated by using a nano-manipulated tungsten probe-tip as anode inside the vacuum chamber of a scanning electron microscope. Stable field emission current is reported, with a maximum intensity extracted from a single nanowire of about 1$\mu A$, corresponding to a current density as high as 10$^4$ A/cm$^2$. Stability and robustness of nanowire is probed by monitoring field emission current for about three hours. By tuning the cathode-anode separation distance in the range 500nm - 1300nm, the field enhancement factor and the turn-on field exhibit a non-monotonic dependence, with a maximum enhancement $\beta \simeq $ 78 and a minimum turn-on field $E_{ON} \simeq$ 0.033 V/nm for a separation d =900nm. The reduction of spatial separation between nanowires and the increase of diameter cause the reduction of the field emission performance, with reduced field enhancement ($\beta, Comment: 20 pages, 6 figures

Background Therapeutic options against Multi Drug Resistant (MDR) pathogens are limited and the overall strategy would be the development of adjuvants able to enhance the activity of therapeutically available antibiotics. Non-specific outer membrane permeabilizer, like metal-oxide nanoparticles, can be used to increase the activity of antibiotics in drug-resistant pathogens. The study aims to investigate the effect of cerium oxide nanoparticles (CeO2 NPs) on bacterial outer membrane permeability and their application in increasing the antibacterial activity of antibiotics against MDR pathogens. Methods The ability of CeO2 NPs to permeabilize Gram-negative bacterial outer membrane was investigated by calcein-loaded liposomes. The extent of the damage was evaluated using lipid vesicles loaded with FITC-dextran probes. The effect on bacterial outer membrane was evaluated by measuring the coefficient of permeability at increasing concentrations of CeO2 NPs. The interaction between CeO2 NPs and beta-lactams was evaluated by chequerboard assay against a Klebsiella pneumoniae clinical isolate expressing high levels of resistance against those antibiotics. Results Calcein leakage increases as NPs concentrations increase while no leakage was observed in FITC-dextran loaded liposomes. In Escherichia coli the outer membrane permeability coefficient increases in presence of CeO2 NPs. The antibacterial activity of beta-lactam antibiotics against K. pneumoniae was enhanced when combined with NPs. Conclusions CeO2 NPs increases the effectiveness of antimicrobials which activity is compromised by drug resistance mechanisms. The synergistic effect is the result of the interaction of NPs with the bacterial outer membrane. The low toxicity of CeO2 NPs makes them attractive as antibiotic adjuvants against MDR pathogens.

Novel two-dimensional films and three-dimensional (3D) scaffolds based on chitosan (CHI), apatite (Ap), and graphene oxide (GO) were developed by an in situ synthesis in which self-assembly process was conducted to direct partial reduction of GO by CHI in acidic medium. Physical-chemical characterization was carried out by optical microscopy, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. In vitro biological studies using murine fibroblast (MC3T3) and human neuroblastoma (SH-SY5Y) cell lines were also performed. Cell growth and adherence on composites was also checked using SEM. Live and death staining by confocal microscope and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium of the samples were investigated. The results confirmed the incorporation of both Ap and GO sheets, into CHI polymeric matrix. Furthermore, it was confirmed a physical integration between inorganic Ap and organic CHI and strong chemical interaction between CHI and GO in the obtained composites. SH-SY5Y cell line showed preferential adherence on CHI/GO films surface while MC3T3 cell line displayed a good compatibility for all 3D scaffolds. This study confirms the biocompatibility of materials based on CHI, Ap, and GO for future tissues applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1585-1594, 2018.

We demonstrate room-temperature ferromagnetism in germanium counter-doped with manganese and arsenic at concentrations up to approximately 2.1 × 10 20 at/cm 3 : these values are one order of magnitude lower than those at which ferromagnetic behavior has previously been observed. Synthesis proceeded by ion implantation at 513 K followed by annealing in argon at 673 K. High resolution TEM, STEM, and EDX show single-phase diamond cubic material lacking Mn or As precipitates. These findings are consistent with the prediction of Chen et al. that counter-doping with approximately equal concentrations of a single-electron donor permits Mn, a two-electron acceptor, to be incorporated at high enough concentrations to yield a diluted magnetic semiconductor with a Curie temperature above room temperature.

We produce 120 um thick buckypapers from aligned carbon nanotubes. Transport characteristics evidence ohmic behavior in a wide temperature range, non linearity appearing in the current-voltage curves only close to 4.2 K. The temperature dependence of the conductance shows that transport is mostly due to thermal fluctuation induced tunneling, although to explain the whole temperature range from 4.2 K to 430 K a further linear contribution is necessary. The field emission properties are measured by means of a nanocontrolled metallic tip acting as collector electrode to access local information about buckypaper properties from areas as small as 1 um2. Emitted current up to 10-5A and turn-on field of about 140V/um are recorded. Long operation, stability and robustness of emitters have been probed by field emission intensity monitoring for more than 12 hours at pressure of 10-6 mbar. Finally, no tuning of the emitted current was observed for in plane applied currents in the buckypaper., 18 pages, 5 figures

Multiwall carbon nanotubes (MWCNTs) consist of multiple layers of graphite sheets arranged in concentric cylinders, from two to many tens. These systems are closely related to graphite layers but in some features, MWCNTs behave quite differently from graphite. In particular, their ability to generate a photocurrent in a wide wavelength range has been demonstrated either without or with the application of a draining voltage. In addition, the photocurrent signal has been found to reproduce the optical absorbance of MWCNTs, showing a maximum in the near UV region. In this paper main characteristics of a novel large area photodetector featuring low noise, high linearity and efficiency are reported. This detector has been obtained by coupling the optoelectronic characteristics of MWCNTs with the well-known properties of silicon. MWCNTs are growth on n-doped silicon layer by chemical vapour deposition creating a p–n heterojunction with high sensitivity to the radiation from UV to IR. An additional MIS junction is obtained with a metallic conductive layer deposited on the back of silicon substrate. Moreover, first results on the signals generated by pulsed laser are also reported.

We report a facile approach based on piezoelectric-driven nanotips inside a scanning electron microscope to contact and electrically characterize ultrathin MoS2 (molybdenum disulfide) flakes on a SiO2/Si (silicon dioxide/silicon) substrate. We apply such a method to analyze the electric transport and field emission properties of chemical vapor deposition-synthesized monolayer MoS2, used as the channel of back-gate field effect transistors. We study the effects of the gate-voltage range and sweeping time on the channel current and on its hysteretic behavior. We observe that the conduction of the MoS2 channel is affected by trap states. Moreover, we report a gate-controlled field emission current from the edge part of the MoS2 flake, evidencing a field enhancement factor of approximately 200 and a turn-on field of approximately &nbsp, 40 &nbsp, V / &mu, m at a cathode&ndash, anode separation distance of 900 &nbsp, nm .

Anisotropic two-dimensional materials possess intrinsic angle-dependent physical properties that originate from their low crystal symmetry. Yet, how these properties are affected by external impurities or structural defects in the material is still wholly unclear. Here, we address this question by investigating the electrical transport in the anisotropic layered model system germanium arsenide. First, we show that the ratio of conductivities along the armchair and zigzag crystallographic directions exhibits an intriguing dependence with respect to both temperature and carrier density. Then, by using a conceptually simple model, we demonstrate that this unexpected behavior is directly related to the presence of impurity-induced localized states in the band gap that introduce isotropic hopping conduction. The presence of this conduction mechanism in addition to the intrinsic band conduction significantly influences the anisotropic electrical properties of the material, especially at room temperature, i.e., at application-relevant conditions.

Metal contacts play a fundamental role in nanoscale devices. In this work, Schottky metal contacts in monolayer molybdenum disulfide (MoS2) field-effect transistors are investigated under electron beam irradiation. It is shown that the exposure of Ti/Au source/drain electrodes to an electron beam reduces the contact resistance and improves the transistor performance. The electron beam conditioning of contacts is permanent, while the irradiation of the channel can produce transient effects. It is demonstrated that irradiation lowers the Schottky barrier at the contacts because of thermally induced atom diffusion and interfacial reactions. The simulation of electron paths in the device reveals that most of the beam energy is absorbed in the metal contacts. The study demonstrates that electron beam irradiation can be effectively used for contact improvement through local annealing.

This study reports the electrical transport and the field emission properties of individual multi-walled tungsten disulphide (WS2 ) nanotubes (NTs) under electron beam irradiation and mechanical stress. Electron beam irradiation is used to reduce the nanotube-electrode contact resistance by one-order of magnitude. The field emission capability of single WS2 NTs is investigated, and a field emission current density as high as 600 kA cm-2 is attained with a turn-on field of ≈100 V μm-1 and field-enhancement factor ≈50. Moreover, the electrical behavior of individual WS2 NTs is studied under the application of longitudinal tensile stress. An exponential increase of the nanotube resistivity with tensile strain is demonstrated up to a recorded elongation of 12%, thereby making WS2 NTs suitable for piezoresistive strain sensor applications.

We investigate the field emission properties of AlGaN nanowires, grown on GaN nanowire templates on Si(111) substrate by means of radio-frequency plasma-assisted molecular beam epitaxy technique. The field emission measurement setup was realized inside the vacuum chamber of a scanning electron microscope equipped with piezo-driven metallic probe tips working as electrodes. Current-voltage characteristics were measured by precisely positioning a tip anode above the emitting AlGaN surface, with cathode-anode separation distance varied in the range 200–1500 nm. Experimental data are discussed according to the Fowler-Nordheim theory to confirm the field emission nature of the measured current and to estimate key figures of merit, such as field enhancement factor and turn-on field. We show that field emission curves become stable after electrical conditioning, that is after the burnout of individual protruding emitters. We demonstrate field enhancement factor as high as 250 for cathode-anode separation distance of 200 nm, and that it decreases for increasing distances. Similarly, minimum turn-on field of 19 V/µm is reported for a separation distance of 800 nm. Finally, we discuss the effect of a Schottky diode in a back-to-back configuration with the field emission device, that limits the exponential growth field emitted current.

We study the electrical transport in back-gate field-effect transistors with ultrathin palladium diselenide (PdSe2) channel. The devices are normally-on and exhibit dominant n-type conduction at low pressure. The electron conduction, combined with the sharp edge and the workfunction decreasing with the number of layers, opens the way to applications of PdSe2 nanosheets in vacuum electronics. In this work, we demonstrate field emission from few-layer PdSe2 nanosheets with current up to the uA and turn-on field below 100 V/um, thus extending the plethora of applications of this recently isolated pentagonal layered material., Comment: 12 pages, 4 figures