Dimethylamine is an important indicator to check the degradation and control the quality of seafood. In this work, we present a novel, simple, fast and inexpensive method to detect dimethylamine in the range of 5-50 ppm that might be potentially useful to control the seafood quality in the future. The developed gas sensor is based on niobium-doped titanium dioxide nanotubes. The tubular structures were successfully synthesized using anodic oxidation method. The sensing properties of the obtained materials were studied towards dimethylamine gas for the first time. Dimethylamine behaves like an electron donor and induces an increase in conductivity of the n-type titanium dioxide. The presence of niobium in the titanium dioxide structure plays a crucial role to improve the functional properties of the material. Niobium acts as a donor promoting the process of gas adsorption on the structure. The response of Nb doped-material towards 10 ppm of dimethylamine is higher more than an order of magnitude compared to the pristine titanium dioxide nanotubes, leading to an essential improvement in their gas sensing performance. The obtained results enable the development of a dimethylamine gas sensor device based on titanium dioxide for the real-time monitoring and freshness detection of seafood products.

Low-dimensional chemical sensors based on metal oxides have received great attention for the applications in security and medical diagnoses. [...]

The precise detection of flammable and explosive gases and vapors remains an important issue because of the increasing demand for renewable energy sources and safety requirements in industrial processes. Metal oxides (TiO2, SnO2, ZnO, etc.) are very attractive materials for the manufacturing of chemical gas sensors. However, their gas selectivity issues and further improvement in the sensing response remain a significant challenge. The incorporation of metal oxides with two-dimensional (2D) graphene oxide (GO) is considered to be a promising approach to obtaining hybrid structures with improved gas-sensing performance. Herein, we report the development of GO and niobium-doped titanium dioxide nanotube (NT) hybrid structures with a tunable selectivity and sensing response against hydrogen gas, achieved by properly controlling the degree of reduction and concentration of GO. The effects of these parameters are systematically studied in terms of the response amplitude and selectivity. It was found that, compared to undoped titanium dioxide nanotubes, the hybrid material with an optimal concentration of reduced-GO and the introduction of niobium shows an increase in hydrogen response of about an order of magnitude and a simultaneous reduction of the response to possible interfering compounds such as carbon monoxide and acetone, thus providing enhanced selectivity. This research may provide an efficient way to enhance the chemical sensing performance of metal oxide nanomaterials.

We have obtained and studied the sensing properties of porous titania-based nanostructures. The materials have been prepared using cost-effective techniques. The morphological and structural analyses of the prepared materials have been performed. The sensing properties of the samples have been studied towards carbon monoxide. The obtained results demonstrate that the prepared structures are promising for the potential applications in the area of chemical sensors for the environmental monitoring.

We have synthesized pure, mixed and multicomponent structures by coupling different cost-effective techniques.Prepared TiO2-based hierarchically assembled nanostructures have been thoroughly characterized by scanning electron microscope, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy.The sensing properties of materials have been studied towards explosive and toxic gaseous compounds.Investigations have shown the material crystalline structure, the variation of mixture concentration in the material and the modification of carbon-based layers have crucial effect on the response and the selectivity of materials.The obtained results demonstrate that the prepared multicomponent structures can be applied in the area of chemical sensors for the environmental monitoring and medical diagnoses.

Graphene oxide (GO) and reduced graphene oxide (RGO) have unique properties that can revolutionize the performances of functional devices. Graphene-based materials can be coupled with metal oxide nanomaterials for gas-sensing applications. In this work, we report the synthesis and gas-sensing properties of a composite material based on RGO-loaded TiO2 nanotubes. To properly tune the reduction of GO to RGO, we adopted a gas-phase process that can be applied in situ on each gas sensor device, allowing one to track the process effects through sensor conductance. We systematically investigated the gas-response dependence from the RGO loading and its reduction, showing the occurrence of an optimal RGO concentration arising from the interplay of these two parameters. Hence, these two factors should be considered in parallel to functionalize the metal oxide materials with GO for the fabrication of chemical sensor devices.

The specific surface area and effective thermal conductivity of ultrathin graphite foams (UGFs) grown by chemical vapor deposition (CVD) have been limited by the large pore sizes of reticulated nickel foam templates. Here we show that nickel templates formed by sintering of low-cost nickel powder can reduce pore size and increase specific surface area. Accordingly, the effective density of a free-stranding graphite foam grown on the high-surface area templates can be increased by an order of magnitude relative to one grown on a reticulated nickel foam template. This increase is accomplished without increasing the thickness of the CVD graphite or decreasing the structural quality of the graphite. Based on experiments with nickel powder with and without the reticulated nickel template present, we found that both the particle size and sintering temperature influenced template morphology. Because of a 68-times increase in the volumetric specific surface area of a graphite foam synthesized on a sacrificial sintered powder template compared to a UGF grown on a reticulated template, we have been able to increase the relative graphite density and effective thermal conductivity from 0.87 +/- 0.09% to 8.4 +/- 0.3% and from 2.1 +/- 0.3 Wm(-1)K(-1) to 16.3 +/- 1.1 Wm(-1)K(-1), respectively. (C) 2018 Published by Elsevier Ltd.

Plasmonic metasurfaces have been employed for moulding the flow of transmitted and reflected light, thereby enabling numerous applications that benefit from their ultra-thin sub-wavelength format. Their appeal is further enhanced by the incorporation of active electro-optic elements, paving the way for dynamic control of light's properties. In this paper, we realize a dynamic polarization state generator using a graphene-integrated anisotropic metasurface (GIAM) that converts the linear polarization of the incident light into an elliptical one. This is accomplished by using an anisotropic metasurface with two principal polarization axes, one of which possesses a Fano-type resonance. A gate-controlled single-layer graphene integrated with the metasurface was employed as an electro-optic element controlling the phase and intensity of light polarized along the resonant axis of the GIAM. When the incident light is polarized at an angle to the resonant axis of the metasurface, the ellipticity of the reflected light can be dynamically controlled by the application of a gate voltage. Thus accomplished dynamic polarization control is experimentally demonstrated and characterized by measuring the Stokes polarization parameters. Large changes of the ellipticity and the tilt angle of the polarization ellipse are observed. Our measurements show that the tilt angle can be changed from positive values through zero to negative values while keeping the ellipticity constant, potentially paving the way to rapid ellipsometry and other characterization techniques requiring fast polarization shifting. This article is part of the themed issue ‘New horizons for nanophotonics’.

We have developed innovative and efficient strategy for the preparation and improvement of sensing performance of well-ordered titania nanotubes. We have synthesized different materials based on titania nanotubes using cost-effective techniques. The morphological and structural analyses of the prepared materials have been carried out. The sensing properties of the structures have been studied towards NO2. Investigations have shown the functionalization process has crucial effect on sensing properties of titania nanotubes. The obtained results demonstrate that the prepared structures are promising for the potential applications in the area of chemical sensors for the environmental monitoring.

The measured frequencies and intensities of different first- and second-order Raman peaks of suspended graphene are used to show that optical phonons and different acoustic phonon polarizations are driven out of local equilibrium inside a submicron laser spot. The experimental results are correlated with a first-principles-based multiple temperature model to suggest a considerably lower equivalent local temperature of the flexural phonons than those of other phonon polarizations. The finding reveals weak coupling between the flexural modes with hot electrons and optical phonons. Since the ultrahigh intrinsic thermal conductivity of graphene has been largely attributed to contributions from the flexural phonons, the observed local nonequilibrium phenomena have important implications for understanding energy dissipation processes in graphene-based electronic and optoelectronic devices, as well as in Raman measurements of thermal transport in graphene and other two-dimensional materials.

The crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe2, the top layer of selenium atoms is substituted by sulfur atoms, while the bottom selenium layer remains intact. The structure of this material is systematically investigated by Raman, photoluminescence, transmission electron microscopy, and X-ray photoelectron spectroscopy and confirmed by time-of-flight secondary ion mass spectrometry. Density functional theory (DFT) calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction activity is discovered for the Janus monolayer, and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.

Transparent conductive films (TCFs) are widely used in solar cells, transistors, displays, sensors, and energy storage systems. New devices are setting additional criteria for TCFs: in addition to good optical transmittance and electrical conductivity, good chemical and thermal stability, compatibility with other device components, ease of integration in flexible electronics, and obviously low-cost are desirable. Since indium tin oxide (ITO) films cannot fulfill all these requirements, other options are sought. There are several promising alternatives involving networks of single component (e.g., carbon nanotubes (CNTs), Ag or Cu nanowires (NWs)) or multi-component (e.g., CNT/Ag NW, graphene/Cu NW, etc.) TCFs. Specifically, multi-component hybrid nanostructured films, in which the overall film performance can be improved due to synergy between individual components, are of a great importance in development of new TCFs. In this chapter, we present an overview of progress made in fabrication of hybrid nanostructured TCFs based on the assembly of one dimensional (1D) metal nanowires and two dimensional (2D) graphene films. Optoelectrical properties of such films can be comparable to/or better than ITO films. The concept of nanostructured hybrid films is expected to open up possibilities for developing next generation TCFs with multiple functionalities.

Herein, we report the preparation of a hybrid material by combination of modified graphene and ZnO. The morphological and compositional analyses of the obtained material have been performed by means of scanning electron microscopy and energy dispersive X-ray analysis. The functional properties of the prepared structures have been investigated for their application in gas sensor devices. The gas sensing performance of the hybrid material show that the structure can be used for fabrication of chemical sensors, as well as in electronic nose technology.

Coupling of graphene-based materials with metal oxide nanostructures is an effective way to obtain composites with improved gas sensing properties.

A hybrid nanostructure based on reduced graphene oxide and ZnO has been obtained for the detection of volatile organic compounds. The sensing properties of the hybrid structure have been studied for different concentrations of ethanol and acetone. The response of the hybrid material is significantly higher compared to pristine ZnO nanostructures. The obtained results have shown that the nanohybrid is a promising structure for the monitoring of environmental pollutants and for the application of breath tests in assessment of exposure to volatile organic compounds.

Strong interaction of graphene with light accounts for one of its most remarkable properties: the ability to absorb 2.3% of the incident light's energy within a single atomic layer. Free carrier injection via field-effect gating can dramatically vary the optical properties of graphene, thereby enabling fast graphene-based modulators of the light intensity. However, the very thinness of graphene makes it difficult to modulate the other fundamental property of the light wave: its optical phase. Here we demonstrate that considerable phase control can be achieved by integrating a single-layer graphene (SLG) with a resonant plasmonic metasurface that contains nanoscale gaps. By concentrating the light intensity inside of the nanogaps, the metasurface dramatically increases the coupling of light to the SLG and enables control of the phase of the reflected mid-infrared light by as much as 55° via field-effect gating. We experimentally demonstrate graphene-based phase modulators that maintain the amplitude of the reflected light essentially constant over most of the phase tuning range. Rapid nonmechanical phase modulation enables a new experimental technique, graphene-based laser interferometry, which we use to demonstrate motion detection with nanoscale precision. We also demonstrate that by the judicious choice of a strongly anisotropic metasurface the graphene-controlled phase shift of light can be rendered polarization-dependent. Using the experimentally measured phases for the two orthogonal polarizations, we demonstrate that the polarization state of the reflected light can be by modulated by carrier injection into the SLG. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.

Here we report an electrochemical method to simultaneously reduce and delaminate graphene oxide (G-O) thin films deposited on metal (Al and Au) substrates. During the electrochemical reaction, interface charge transfer between the G-O thin film and the electrode surface was found to be important in eliminating oxygen-containing groups, yielding highly reduced graphene oxide (rG-O). In the meantime, hydrogen bubbles were electrochemically generated at the rG-O film/electrode interface, propagating the film delamination. Unlike other metal-based G-O reduction methods, the metal used here was either not etched at all (for Au) or etched a small amount (for Al), thus making it possible to reuse the substrate and lower production costs. The delaminated rG-O film exhibits a thickness-dependent degree of reduction: greater reduction is achieved in thinner films. The thin rG-O films having an optical transmittance of 90% (λ = 550 nm) had a sheet resistance of 6390 ± 447 Ω/□ (ohms per square). rG-O-based stretchable transparent conducting films were also demonstrated.

A mild and environmental-friendly method is developed for fabricating a 3D interconnected graphene electrode with large-scale continuity. Such material has interlayer pores between reduced graphene oxide nanosheets and in-plane pores. Hence, a specific surface area up to 835 m(2) g(-1) and a high powder conductivity up to 400 S m(-1) are achieved. For electrochemical applications, the interlayer pores can serve as "ion-buffering reservoirs" while in-plane ones act as "channels" for shortening the mass cross-plane diffusion length, reducing the ion response time, and prevent the interlayer restacking. As binder-free supercapacitor electrode, it delivers a specific capacitance up to 169 F g(-1) with surface-normalized capacitance close to 21 μF cm(-2) (intrinsic capacitance) and power density up to 7.5 kW kg(-1), in 6 m KOH aqueous electrolyte. In the case of lithium-ion battery anode, it shows remarkable advantages in terms of the initiate reversible Coulombic efficiency (61.3%), high specific capacity (932 mAh g(-1) at 100 mA g(-1)), and robust long-term retention (93.5% after 600 cycles at 2000 mAh g(-1)).

We experimentally demonstrate amplitude and phase modulation in graphene-integrated Fano-resonant plasmonic metasurfaces. Order of magnitude modulation depth is achieved in mid-IR. Strong coupling between trapped graphene and metallic plasmons is predicted in high-mobility graphene.

Continuous ultrathin graphite foams (UGFs) have been actively researched recently to obtain composite materials with increased thermal conductivities. However, the large pore size of these graphitic foams has resulted in large thermal resistance values for heat conduction from inside the pore to the high thermal conductivity graphitic struts. Here, we demonstrate that the effective thermal conductivity of these UGF composites can be increased further by growing long CNT networks directly from the graphite struts of UGFs into the pore space. When erythritol, a phase change material for thermal energy storage, is used to fill the pores of UGF-CNT hybrids, the thermal conductivity of the UGF-CNT/erythritol composite was found to increase by as much as a factor of 1.8 compared to that of a UGF/erythritol composite, whereas breaking the UGF-CNT bonding in the hybrid composite resulted in a drop in the effective room-temperature thermal conductivity from about 4.1 ± 0.3 W m(-1) K(-1) to about 2.9 ± 0.2 W m(-1) K(-1) for the same UGF and CNT loadings of about 1.8 and 0.8 wt %, respectively. Moreover, we discovered that the hybrid structure strongly suppresses subcooling of erythritol due to the heterogeneous nucleation of erythritol at interfaces with the graphitic structures.