Nanomaterials and Nanotechnology

Multi-step chemical vapor deposition (CVD) is a synthesis method which is capable of producing a uniform, large area, and high-quality thin films. In this work, we report the effect of post-annealing on the structural and optical properties of few-layers (FL) MoS₂ thin films synthesized by multi-step CVD. Based on atomic force microscopic image, the thickness of the MoS₂ thin film is ∼3 nm, which is equivalent to five layers. After annealing at 900°C for 17 min, intensity of the A_1g and E   2 g 1 Raman modes increased by ∼3 times while the full-width-at-half-maximum (FWHM)* reduced from ∼10 cm⁻¹ to ∼7.5 cm⁻¹ for A_1g and from ∼13.6 cm⁻¹ to ∼7.5 cm⁻¹ for E   2 g 1 . Both of the as-grown and annealed samples showed X-ray (002) diffraction peak at 14.2° but the intensity was more prominent for the annealed sample. It was found that the annealed sample showed clear and distinct absorbance peaks at 666, 615, 448, 401, and 278 nm which correspond to the A, B, C, D, and E excitons, respectively. The results indicate that annealing significantly improved the optical and structural quality of the MoS₂ film. Field-effect transistor based on annealed MoS₂ thin film was fabricated and showed electron mobility of 0.21 cm²V⁻¹s⁻¹, on/off ratio of 1.3 × 10² and a threshold voltage of 0.72 V. Our work highlights the importance of high-temperature annealing in multi-step CVD to obtain a uniform and high-quality FL MoS₂ thin films.

This paper aims to explore structural, optical and wettability aspects of zinc oxide (ZnO) nano thin films prepared by radio frequency (RF) magnetron sputtering. The deposition time is varied from 10 to 50 minutes and sputtering pressure from 0.5 to 8.0 Pa. The increase of deposition time from 10 to 50 minutes leads to formation of a single (002) peak for ZnO films; (100), (101) and (110) peaks are not observed under these conditions. The intensity for (100), (002), (101) and (110) peaks decreases with a sputtering pressure value of 3.5 Pa and above. The optical transmission and band gaps are measured by a UV-Vis-NIR spectrophotometer. The wettability and contact-angle hysteresis (CAH) for deposited ZnO nano thin films are investigated for water, ethylene glycol, sunflower oil and formamide using a contact-angle goniometer.

To improve the photocatalytic property of titanium dioxide, titanous sulfate as the titanium source, cobalt nitrate hexahydrate as the cobalt source, undoped and Co²⁺-doped titania nanotubes were prepared via coprecipitation method combined with hydrothermal synthesis. Based on the degradation rate of methylene blue, the effects of the codoped rate on photocatalytic activities of the sample were researched. The result showed that doping cobalt could improve the photocatalytic performance of the titanium dioxide nanotubes under the ultraviolet light. The composition and structure of the samples were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, and selected area electron diffraction. Conclusions indicated that the low-concentration Co²⁺ has no influence on the crystal structure of titanium dioxide and no new crystals were formed in the whole process.

Heterogeneous photocatalysis using TiO₂ is a non-selective technique used for the degradation of organic molecules. Controlling the morphology of TiO₂ has recently been considered one of the important approaches for controlling the selectivity of TiO₂ In this work, TiO₂ nanotubes and nanosheets were synthesized from spherical TiO₂ nanoparticles using the hydrothermal method. The starting and prepared samples were characterized by XRD, TEM and FESEM. The selectivity of the three morphologies towards the photocatalytic degradation of three food dyes (colours yellow sunset, red allura and red carmoisine) was tested. Importantly, changes in morphology led to each dye being adsorbed preferentially by one of the three morphologies and decomposing more rapidly, where the optimum rate of degradation for sunset yellow, red allura and red carmoisine was achieved by TiO₂ nanosheets, spherical TiO₂ and TiO₂ nanotubes, respectively.

Nanocomposites based on few-layers graphene oxide (FGO) decorated with porphyrin nanorods (PN) were synthesized and the interfacial interaction between these two components was investigated by using scanning electron microscopy (SEM), photoluminescence spectroscopy, resonant Raman scattering and Fourier transform infrared (FT-IR) techniques. SEM showed good exfoliation of FGO and its successful interaction with the PN. The photoluminescence results showed an important interaction between FGO and PN resulting in a quenching of the photoluminescence of the PN-FGO composite. Resonant Raman with PN aggregates and FT-IR results revealed a π-π intermolecular interaction confirming the energy/charge transfer. Moreover, the investigation of X-ray diffraction confirmed the intercalation of PN in FGO and their disaggregation. The findings presented here are an important contribution to achieving the functionalization of graphene derivative surfaces with PN for various optoelectronic applications and particularly photovoltaic cells.

This study reports the performances of a single structured light-emitting diode (LED) devices based on polymer material poly(9,9-di-n-hexylfluorenyl-2,7-diyl) (PHF) mixed with various concentrations of perovskite oxide strontium titanate (SrTiO₃) particles deposited as a composite PHF: SrTiO₃ emitting layer. The performances of the single structured organic LED indium tin oxide (ITO)/PHF/aluminum (Al) device and the composite LED ITO/PHF: SrTiO₃/Al devices were compared in terms of turn-on voltage and luminance intensity. By incorporating perovskite SrTiO₃ particles into PHF emitting layer, the turn-on voltage of the device is significantly reduced from 11.25 V to 1.80 V and the luminance intensity increased from 57.7 cd/m² to 609 cd/m². The improvement of turn-on voltage and the electroluminescence spectrum of the composite devices were found to be dependent on the weight ratios of SrTiO₃ content in the PHF emitting layer.

In this study, novel titanium dioxide (TiO₂) and zinc oxide (ZnO) hybrid photocatalysts in the form of nanofibres were fabricated by a facile method using electrospinning followed by a calcination process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to investigate the morphology and structure of the heterogeneous nanofibres. The photocatalytic performances were evaluated via the photodegradation of Rhodamine B (RhB) under irradiation with UV light. Due to the low recombination rate of photo-induced charge carriers, the high utilization efficiency of UV light and the large contact area with the target molecules, the ZnO/TiO₂ hybrid nanofibres exhibited high catalytic activity towards the Rhodamine B, and the amount of Zn(OAc)₂ in the precursor of these nanofibres played an important role in determining the photo decomposition performance.

Mass printing processes are the key technology to produce mass products to the point of one-disposable. Carbon nanotube (CNT) based structures were prepared by flexographic printing using multi-walled carbon nanotube (MWCNT) dispersions in water. The carbon nanotubes were applied to a textile substrate made of polyester and polyamide microfilaments and to both-side coated paper to produce electrically conductive layers that can be used, for example, as heating elements. Carbon nanotube layers with sheet resistivity ranging from 0.12 to 3.00 kΩ/sq were obtained. The ratio of radiation power P_S (determined according to the Stefan-Boltzmann law) of the printed layers to the electrical power spent, represents the efficiency of the system. The samples on textile substrate with a surface temperature of 169°C have an efficiency of 25%, the paper samples with a surface temperature of 93 °C have an efficiency of about 15 %.

In this work, carbon nanotube (CNT) based interconnections and switches will be reviewed, discussing the possibility to use nanotubes as potential building blocks for signal routing in microwave networks. In particular, theoretical design of coplanar waveguide (CPW), micro-strip single-pole-single-throw (SPST) and single-pole-double-throw (SPDT) devices has been performed to predict the electrical performances of CNT-based RF switching configurations. Actually, by using the semiconductor-conductor transition obtained by properly biasing the CNTs, an isolation better than 30 dB can be obtained between the ON and OFF states of the switch for very wide bandwidth applications. This happens owing to the shape deformation and consequent change in the band-gap due to the external pressure caused by the electric field. State-of-art for other switching techniques based on CNTs and their use for RF nano-interconnections is also discussed, together with current issues in measurement techniques.

To maximize the utilization of its single-atom thin nature, a facile scheme to fabricate graphene multilayer films via a layer-by-layer self-assembled process was presented. The structure of multilayer films was constructed by covalently bonding graphene oxide (GO) using p-phenylenediamine (PPD) as a covalent cross-linking agent. The assembly process was confirmed to be repeatable and the structure was stable. With the π-π conjugated structure and a large number of spaces in the framework, the graphene multilayer films exhibited excellent electrochemical performance. The uniform ultrathin electrode exhibited a capacitance of 41.71 μF/cm² at a discharge current of 0.1 μA/cm², and displayed excellent stability of 88.9 % after 1000 charge-discharge cycles.

An analytical expression of diffraction line profiles of spherical hollow nanocrystals (NCs) is derived. The particular features of the profile lines, enhanced peak tail intensity, are analyzed and discussed as a function of the NC size parameters (outer and inner radius, shell thickness). The explicit formula for the integral breadth, the Fourier particle size, and the Scherrer constants are also obtained and discussed in detail. The diffraction line profiles of hollow CdS NCs of zincblende and wurtzite crystallographic structure are calculated and compared with Debye scattering profiles. The diffraction profiles of both approaches exhibit an enhanced peak tail intensity that can be considered as a fingerprint of the hollow NC structure.

In this work, we improved the photocurrent of self-powered ultraviolet photodetector via doping manganese in CsPbCl₃ perovskite nanocrystals light harvester. The doped manganese in nanocrystals has the following three features to assist electron transfer from CsPbCl₃ nanocrystals to titanium dioxide: (i) the fast exciton-to-manganese energy transfer process benefits for competing electrons with perovskite exciton recombination, (ii) the charge carrier lifetime is very long for manganese d-states due to its spin and orbital forbidden transition, and (iii) the electrons can effectively transfer to the titanium dioxide layer from ⁴T₁ of manganese d-states due to the smaller energy barrier. Based on the above, the self-powered photocurrent density of photodetectors has nearly twice enhancement from 0.08 mA·cm⁻² to 0.14 mA·cm⁻² and a high responsivity up to 7.3 mA·W⁻¹ was achieved at 340 nm.

In this work, we report a graphene-alkaline lignin-poly(3,4-ethylenedioxythiophene) polystyrene sulfonate composite as a transparent conductive electrode for indium tin oxide-free optoelectronic devices. The composite was prepared by dispersing exfoliated graphene-alkaline lignin into aqueous poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. The effect of graphene concentration on the electrical and optical properties of graphene-alkaline lignin-poly(3,4- ethylenedioxythiophene) polystyrene sulfonate was studied. The graphene-alkaline lignin-poly(3,4- ethylenedioxythiophene) polystyrene sulfonate thin films exhibit excellent electrical conductivity and high transparency properties. The electrical conductivity is further increased by 1.9 ± 0.01 × 10³ times when graphene content was augmented in the composites; however, the optical transparency was reduced due to the high optical absorbance of graphene. In this condition, the conductivity and optical transparency are as high as (4.19 ± 0.01) × 10³ S/cm and 94.2%, respectively. This achievement is attributed to the organization of higher ordered network between conductive exfoliated graphene and poly(3,4-ethylenedioxythiophene) chains that induced a better conducting channel for charge transportation. The poly(3,4-ethylenedioxythiophene) chains act as a bridge connecting the graphene flakes, which, in turn, facilitate the movement of hole charges between them.

The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocrystals (NC) embedded in an amorphous SiO₂ matrix has been studied. The investigation was conducted by means of laser Raman Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The irradiation of Ge-NC samples by a high dose of fast neutrons lead to a partial destruction of the nanocrystals. Full reconstruction of crystallinity was achieved after annealing the radiation damage at 800⁰C, which resulted in full restoration of the RS spectrum. HR-TEM images show, however, that the spatial distributions of Ge-NC changed as a result of irradiation and annealing. A sharp decrease in NC distribution towards the SiO₂ surface has been observed. This was accompanied by XPS detection of Ge oxides and elemental Ge within both the surface and subsurface region.

What makes three dimensional semiconductor quantum nanostructures so attractive is the possibility to tune their electronic properties by careful design of their size and composition. These parameters set the confinement potential of electrons and holes, thus determining the electronic and optical properties of the nanostructure. An often overlooked parameter, which has an even more relevant effect on the electronic properties of the nanostructure, is shape. Gaining a strong control over the electronic properties via shape tuning is the key to access subtle electronic design possibilities. The Pulsed Dropled Epitaxy is an innovative growth method for the fabrication of quantum nanostructures with highly designable shapes and complex morphologies. With Pulsed Dropled Epitaxy it is possible to combine different nanostructures, namely quantum dots, quantum rings and quantum disks, with tunable sizes and densities, into a single multi-function nanostructure, thus allowing an unprecedented control over electronic properties.

Electrospinning is a promising technique for enabling the manipulation of the structural properties of nano‐ or microfibrous mats by altering electrospinning parameters. In this paper, it is aimed to examine the morphological variations of electrospun mats fabricated by combinations of different collector types and feeding units. In horizontal electrospinning setup, PVA polymer solutions are transformed to polymer jets by the help of needle‐based feedings with single‐ and multinozzles. Electrospun fibers are deposited on four different collector types with identical collector‐nozzle distance, feeding rate, applied voltage, and environmental conditions. It is concluded that the coarsest nanofibers are fabricated by multineedle/disc collector combination and the disc collector causes flat nanofiber handling with multineedle feeding but not with single needle feeding. On plate collector, thicker electrospun mats are obtained whichever feeding type is used. Average pore sizes on mats are found higher in multineedle feeding, especially with deposition between rods of birdcage collector. Changing the feeding type from multineedle to single needle causes to manufacture of electrospun mats with a narrower surface area and an increase is observed in packing density, basis weight and % porosity but a decrease in pore size and mat thickness with this manipulation. Nanosized but flattened electrospun fibers are handled by multineedle/disc collector and two distinct compositions are incorporated by deposition of nanofibers on birdcage collector.

Unpleasant breathing can occur due to bad odors from wearing a medical mask. Electrospinning has been used to incorporate Eucalyptus extract into polyvinyl alcohol (PVA) to overcome the problem of medical masks and as an alternative, as part of an antiflu breathing face mask. This research aims to extend the shelf life of the pleasant odor by encapsulating Eucalyptus essential oil (EO) in nanofibers by coaxial electrospinning. Initially, nanofibers were produced using a blend structure of Eucalyptus aqueous extract (EA) and PVA, along with a core–shell structure of EO and PVA by electrospinning. The morphology of the nanofibers was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), showing average diameters of 270 ± 47 nm for the blend nanofibers and 343 ± 126 nm for the core–shell nanofibers. TEM confirmed a core–shell structure presumably caused by the nonmiscibility of EO and PVA, as well as the high viscosity of the PVA solution. The loading capacity (LC) and encapsulation efficiency (EE) were calculated for the core–shell nanofibers to be 16.43 ± 3.29 and 55.20 ± 2.31, respectively. The presence of EO in the nanofibers was shown through FT‐IR spectroscopy. At the same time, variations in peak intensity allowed tracing the displacement of EO and the aging of the nanofibers. A released study showed that after 7 hours of release in a conditioning room with 30°C and 70% humidity, the percentages of remaining Eucalyptol in the nanofibers were 68.36% and 83.63% for the blend and the core–shell structure, respectively. The size of the pores in these nanofibers on a layer ranged from 50 nm to 200 nm.

A ultaviolet–visible light responded photocatalytic nanocomposite, silver/silver bromide/titanium dioxide, supported on graphene oxide (GO; silver/silver bromide/titanium dioxide/GO) was fabricated via a layer intercalation method using n-butylamine, cetyltrimethyl ammonium bromide, titanium dioxide and silver/silver bromide-intercalated GO successively. The resultant silver/silver bromide/titanium dioxide/GO exhibited much stronger visible light absorption and enhanced photocatalytic efficiency than titanium dioxide/GO and titanium dioxide. Furthermore, the degradation efficiency of silver/silver bromide/titanium dioxide/GO was improved when irradiated under light without the ultaviolet cut filter. The apparent degradation rate constants, k, for silver/silver bromide/titanium dioxide/GO, titanium dioxide/GO and titanium dioxide are 0.5192, 0.2273 and 0.0627 h⁻¹. A possible photocatalytic degradation mechanism for degradation of 4-chlorophenol by silver/silver bromide/titanium dioxide/GO under irradiation with/without the ultaviolet cut filter was proposed. The factors including the visible light response from silver bromide, surface plasmon ‘hot’ electron effect from silver nanoparticles and efficient electron transfer among silver, silver bromide, titanium dioxide and GO are contributed to enhance the photocatalytic activity under visible light irradiation, while the additional factor of ultaviolet light response from titanium dioxide plays an important role under light irradiation without the ultaviolet cut filter. The resultant silver/silver bromide/titanium dioxide/GO possessed a good photochemical stability and reusability.

Microring resonators (MRRs) are the important devices for the development of silicon‐based optoelectronic integrated chips. Their composition of optical modules, such as optical modulators, switches, and optical logic gates, have greatly contributed to the development of the silicon‐based optoelectronics. However, due to the large radius of MRRs and the weak optical interaction of the silicon material itself, how to further improve integration and reduce power consumption is a great challenge. Combining graphene, which has many unique properties, with silicon‐based MRRs provides a good solution. Therefore, based on the interaction principle of graphene and light and the transmission principle of all‐pass silicon‐based MRRs, this article proposes for the first time a one‐bit optical numerical comparator based on MRRs, whose structure consists of four silicon‐based MRRs with a radius of 1.8 μm covering a single layer of graphene. The logic function of the one‐bit optical numerical comparator is realized by adjusting the different chemical potentials of the graphene. Simulation results shows that, with a TE mode light source at 1555.21 nm, the proposed optical numerical comparator obtains a minimum extinction ratio of 19.7 dB and a contrast ratio of 19.7 dB. Compared with the previously reported optical numerical comparators based on silicon‐based MRRs or ring resonators, the proposed optical numerical comparator has many advantages, such as high extinction ratio, high contrast ratio, compact structure, and high stability. It is beneficial to the development of silicon‐based photonic integrated devices.