Table of contents

An advantageous micromechanical technique to deposit large area graphene nanoplatelet (GNP) thin films on a low-density polyethylene substrate is proposed. This method is based on the application of shear-stress and friction forces to a graphite platelets/ethanol paste on the surface of a polymeric substrate; it allows us to obtain a continuous film of superimposed nanoplatelets mainly made of 13–30 graphene layers. X-ray diffraction (XRD), atomic force and transmission electron microscopy (TEM) measurements support the occurrence of a partial exfoliation of the graphite platelets due to shear-stress and friction forces applied during film formation. Scanning electron microscopy (SEM) observations point out that the surface of the polymer is uniformly coated by the overlap of GNPs, and TEM analysis reveals the tendency of the nanoplatelets to align parallel to the interface plane. It has been found that the deposited samples, under white light illumination, exhibit a negative photoconductivity and a linear photoresponse as a function of the applied voltage and the optical power density in the −120 ÷ 120 mV and 20.9 ÷ 286.2 mW cm⁻² ranges, respectively.

To protect brittle layers in organic photovoltaic devices, the mechanical neutral plane strategy can be adopted through placing the brittle functional materials close to the neutral plane where stress and strain are zero during bending. However, previous research has been significantly limited in the location and number of materials to protect through using a single neutral plane. In this study, multiple neutral planes are generated using low elastic modulus adhesives and are controlled through quantitative analyses in order to protect the multiple brittle materials at various locations. Moreover, the protection of multiple brittle layers at various locations under both concave and convex bending directions is demonstrated. Multilayer structures that have soft adhesives are further analyzed using the finite element method analysis in order to propose guidelines for structural design when employing multiple neutral planes.

In this work, we propose a new method for the large-scale production of flexible, periodic alumina arrays with well-ordered pores. We show the incorporation of pre-patterning based on polystyrene (PS) nanosphere lithography into an aluminium anodization process. We prepared ordered monolayers of PS spheres with average diameters of (510 ± 10) nm and (430 ± 10) nm on a large area (1.5 × 1.5 cm²) of the Si substrate. Next, we deposited a 5 μm aluminium layer on arrays of PS nanospheres using the sputtering technique. After the deposition, we covered the aluminium film with a polymer Scotch adhesive tape, and separated it from the silicon substrate by ultrasonic-assisted lift-off. Finally, we performed the anodization of the aluminium. We compared the pore and cell sizes, and the pore distance for the templates obtained by this technique, with reference to the templates prepared by a two-step anodization process. Using this new approach, we obtained highly ordered hexagonal 2D lattices over a large area of up to 2 cm² with sparse defects, amounting to not more than four defects per 1000 μm² on average. Here, we show that the use of indentation techniques is not necessary and can be replaced by a fast, cheap and easy pre-patterning step based on nanosphere lithography.

Plasmonic or exciton/plasmon (plexcitonic) systems are presently described based on electromagnetic models, ignoring the need for an improved microscopic understanding. This is based on the fact that a full quantum mechanical approach on a micrometer scale still represents a considerable challenge. In this paper we report on the experimental observation of plexcitons in 2D gold nanorod array systems coupled to dye molecules and we provide a description of the experimental data using a quantum model. We show that treating the collective behavior in the array as being represented by a single quasiparticle is a suitable approximation that offers the opportunity to avoid the complicated calculation of long-distance interactions between the individual nanoparticles of the plexcitonic, periodic system. This enables us to model the optical response of plasmons in nanostructured arrays in contact with quantum emitters and to derive microscopic informations. Our work provides a potential tool for the design of plexcitonic devices, which rely on periodic metallic nanostructures.

In this work we present an extensive investigation of nanoscale physical phenomena related to oxygen-deficient centers (ODCs) in silica and Ge-doped silica by means of first-principles calculations, including nudged-elastic band, electron paramagnetic resonance parameters calculations, and many-body perturbation theory (GW and Bethe–Salpeter equation) techniques. We show that by neutralizing positively charged oxygen monovacancies we can obtain model structures of twofold Si and Ge defects of which the calculated absorption spectra and singlet-to-triplet transitions are in excellent agreement with the experimental optical absorption and photo-luminescence data. In particular we provide an exhaustive analysis of the main exciton peaks related to the presence of twofold defects including long-range correlation effects. By calculating the reaction pathways and energy barriers necessary for the interconversion, we advance a double precursory origin of the ${E}_{\alpha }^{\prime }$ and Ge(2) centers as due to the ionization of neutral oxygen monovacancies (Si–Si and Ge–Si dimers) and as due to the ionization of twofold Si and Ge defects. Furthermore two distinct structural conversion mechanisms are found to occur between the neutral oxygen monovacancy and the twofold Si (and Ge) atom configurations. Such conversion mechanisms allow to explain the radiation induced generation of the ODC(II) centers, their photobleaching, and also their generation during the drawing of optical fibers.

Multi-walled carbon nanotubes (CNTs) are subjected to electron-beam-induced etching (EBIE) in oxygen. The EBIE process is observed in situ by environmental transmission electron microscopy. The partial pressure of oxygen (10 and 100 Pa), energy of the primary electrons (80 and 200 keV), and environment of the CNTs (suspended or supported on a silicon nitride membrane) are investigated as factors affecting the etching rate. The EBIE rate of CNTs was markedly promoted by the effects of secondary electrons that were emitted from a silicon nitride membrane under irradiation by primary electrons. Membrane supported CNTs can be cut by EBIE with a spatial accuracy better than 3 nm, and a nanogap of 2 nm can be successfully achieved between the ends of two suspended CNTs.

Pulse electrochemical nanopatterning, a non-contact scanning probe lithography process using ultrashort voltage pulses, is based primarily on an electrochemical machining process using localized electrochemical oxidation between a sharp tool tip and the sample surface. In this study, nanoscale oxide patterns were formed on silicon Si (100) wafer surfaces via electrochemical surface nanopatterning, by supplying external pulsed currents through non-contact atomic force microscopy. Nanoscale oxide width and height were controlled by modulating the applied pulse duration. Additionally, protruding nanoscale oxides were removed completely by simple chemical etching, showing a depressed pattern on the sample substrate surface. Nanoscale two-dimensional oxides, prepared by a localized electrochemical reaction, can be defined easily by controlling physical and electrical variables, before proceeding further to a layer-by-layer nanofabrication process.

Organic–inorganic hybrid electronic devices (HEDs) offer opportunities for functionalities that are not easily obtainable with either organic or inorganic materials individually. In the strive for down-scaling the channel length in planar geometry HEDs, the best results were achieved with electron beam lithography or nanoimprint lithography. Their application on the wafer level is, however, cost intensive and time consuming. Here, we propose trench isolated electrode (TIE) technology as a fast, cost effective, wafer-level approach for the fabrication of planar HEDs with electrode gaps in the range of 100 nm. We demonstrate that the formation of the organic channel can be realized by deposition from solution as well as by the thermal evaporation of organic molecules. To underline one key feature of planar HED-TIEs, namely full accessibility of the active area of the devices by external stimuli such as light, 6,13-bis (triisopropylsilylethynyl) (TIPS)-pentacene/Au HED-TIEs are successfully tested for possible application as hybrid photodetectors in the visible spectral range.

Nanoselective area growth (NSAG) by metal organic vapor phase epitaxy of high-quality InGaN nanopyramids on GaN-coated ZnO/c-sapphire is reported. Nanopyramids grown on epitaxial low-temperature GaN-on-ZnO are uniform and appear to be single crystalline, as well as free of dislocations and V-pits. They are also indium-rich (with homogeneous 22% indium incorporation) and relatively thick (100 nm). These properties make them comparable to nanostructures grown on GaN and AlN/Si templates, in terms of crystallinity, quality, morphology, chemical composition and thickness. Moreover, the ability to selectively etch away the ZnO allows for the potential lift-off and transfer of the InGaN/GaN nanopyramids onto alternative substrates, e.g. cheaper and/or flexible. This technology offers an attractive alternative to NSAG on AlN/Si as a platform for the fabrication of high quality, thick and indium-rich InGaN monocrystals suitable for cheap, flexible and tunable light-emitting diodes.

Composites of micro- and mesoporous SiC flakes (SiCF) and ferroferric oxide (Fe₃O₄), SiCF/Fe₃O₄, were prepared via the chemical deposition of Fe₃O₄ on SiCF by the chemical reduction of an Fe precursor. The SiCF/Fe₃O₄ electrodes were fabricated at different Fe₃O₄ feeding ratios to determine the optimal Fe₃O₄ content that can maintain a high total surface area of SiCF/Fe₃O₄ composites as well as cause a vigorous redox reaction, thereby maximizing the synergistic effect between the electric double-layer capacitive effects of SiCF and the pseudo-capacitive effects of Fe₃O₄. The SiCF/Fe₃O₄ electrode fabricated with a Fe₃O₄/SiCF feeding ratio of 1.5:1 (SiCF/Fe₃O₄(1.5)) exhibited the highest charge storage capacity, showing a specific capacitance of 423.2 F g⁻¹ at a scan rate of 5 mV s⁻¹ with a rate performance of 81.8% from 5 to 500 mV s⁻¹ in an aqueous 1 M KOH electrolyte. The outstanding capacitive performance of the SiCF/Fe₃O₄(1.5) electrode could be attributed to the harmonious synergistic effect between the electric double-layer capacitive contribution of the SiCF and the pseudocapacitive contribution of the Fe₃O₄ nanoparticles introduced on the SiCF surface. These encouraging results demonstrate that the SiCF/Fe₃O₄(1.5) electrode is a promising high-performance electrode material for use in supercapacitors.

Hydrogen gas is produced photocatalytically using 470 nm light, PVP-coated carbon quantum dots (CQDs) as the photosensitizer, and nickel nanoparticles (NiNPs) as the catalyst. The effect of the amount of polyvinylpyrrolidone (PVP) on the ability of the CQD/NiNP composites to catalyze proton reduction was studied. A maximum of 330 mmols H₂/g CQD is produced using 68 μg ml⁻¹ of CQDs and 6 μg ml⁻¹ of NiNPs, with activity persisting for 4 h when 20 wt%-PVP-coated CQDs were used. The H₂ production quantum yield under these conditions is 6%. It was found that composites having higher weight percent PVP had decreased rates of H₂ production, but increased duration. Increasing the weight percent of PVP coating also increases the fluorescence quantum yield of CQDs. Fluorescence quenching titrations reveal that H₂ production could occur by either a reductive or oxidative quenching mechanism. The nanomaterials, prepared using simple methods, are used as the photosensitizer and catalyst in the proton reduction system that operates using visible light.

Nano-sized Mo-doped titania (Mo_0.1Ti_0.9O₂) and Nb-doped titania (Nb_0.25Ti_0.75O₂) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer–Emmett–Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO₂ negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5–3.0 V, the Mo_0.1Ti_0.9O₂/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg⁻¹ at a power of 180 W kg⁻¹ with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb_0.25Ti_0.75O₂/AC hybrid supercapacitor maintained its energy density of 45 Wh kg⁻¹ at 180 W kg⁻¹ better, showing 36 Wh g⁻¹ at 3200 W kg⁻¹, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0–3.0 V led to an increase in power density, with the Mo_0.1Ti_0.9O₂/AC hybrid supercapacitor giving energy densities of 12 Wh kg⁻¹ and 2.5 Wh kg⁻¹ at power densities of 6700 W kg⁻¹ and 14 000 W kg⁻¹, respectively.

Fluorescent carbon dots, zero-dimensional nanomaterials with surface ligands, have been studied extensively over the past few years in biolabelling or fluorescence-based live cell assays. In the past, synthetic organic dyes have been used as cell tracking materials, but they have severe limitations; fluorescent carbon dots may pave the way to biolabelling and cell imaging. In this work, green fluorescent carbon dots have been synthesized from a green source, gram, without any sort of covalent or ionic modifications. These gram-derived carbon dots are unique with respect to synthetic commercial cell-tracking dyes as they are non-toxic, cell internalization occurs quickly, and they have excellent bioconjugation with bacterial cells. Our aim is to establish these carbon dots in a biolabelling assay with its other physicochemical features like the tunable luminescence property, high degree of water solubility and low toxicity, towards various environments (wide range of pH, high ionic strength). Our study introduces a new perspective on the commercialization of carbon dots as a potential alternative to synthetic organic dyes for fluorescence-based cell-labelling assays.

Caffeine is the most popular psychoactive drug consumed in the world for improving alertness and enhancing wakefulness. However, caffeine consumption beyond limits can result in lot of physiological complications in human beings. In this work, we report a novel detection scheme for caffeine integrating nanohybrid membranes of reduced graphene oxide (rGO) in chitosan modified silica sol gel (rGO: chitosan: silica sol gel) with fiber optic surface plasmon resonance. The chemically synthesized nanohybrid membrane forming the sensing route has been dip coated over silver coated unclad central portion of an optical fiber. The sensor works on the mechanism of modification of dielectric function of sensing layer on exposure to analyte solution which is manifested in terms of red shift in resonance wavelength. The concentration of rGO in polymer network of chitosan and silica sol gel and dipping time of the silver coated probe in the solution of nanohybrid membrane have been optimized to extricate the supreme performance of the sensor. The optimized sensing probe possesses a reasonably good sensitivity and follows an exponentially declining trend within the entire investigating range of caffeine concentration. The sensor boasts of an unparalleled limit of detection value of 1.994 nM and works well in concentration range of 0–500 nM with a response time of 16 s. The impeccable sensor methodology adopted in this work combining fiber optic SPR with nanotechnology furnishes a novel perspective for caffeine determination in commercial foodstuffs and biological fluids.

This paper investigates the comproportionation reaction of Mn^II with ${{{\rm{MnO}}}_{4}}^{-}$ as a route for manganese oxide nanoparticle synthesis in the protein ferritin. We report that ${{{\rm{MnO}}}_{4}}^{-}$ serves as the electron acceptor and reacts with Mn^II in the presence of apoferritin to form manganese oxide cores inside the protein shell. Manganese loading into ferritin was studied under acidic, neutral, and basic conditions and the ratios of Mn^II and permanganate were varied at each pH. The manganese-containing ferritin samples were characterized by transmission electron microscopy, UV/Vis absorption, and by measuring the band gap energies for each sample. Manganese cores were deposited inside ferritin under both the acidic and basic conditions. All resulting manganese ferritin samples were found to be indirect band gap materials with band gap energies ranging from 1.01 to 1.34 eV. An increased UV/Vis absorption around 370 nm was observed for samples formed under acidic conditions, suggestive of MnO₂ formation inside ferritin.

Many effective anti-cancer drugs have limited use in hepatocellular carcinoma (HCC) therapy due to the drug resistance mechanisms in liver cells. In recent years, tumor-targeted drug delivery and the inhibition of drug-resistance-related mechanisms has become an integrated strategy for effectively combating chemo-resistant cancer. Herein, lactobionic acid-conjugated d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS-LA conjugate) has been developed as a potential asialoglycoprotein receptor (ASGPR)-targeted nanocarrier and an efficient inhibitor of P-glycoprotein (P-gp) to enhance etoposide (ETO) efficacy against HCC. The main properties of ETO-loaded TPGS-LA nanoparticles (NPs) were tested through in vitro and in vivo studies after being prepared using the nanoprecipitation method and characterized by dynamic light scattering (DLS). According to the results, smaller (∼141.43 nm), positively charged ETO-loaded TPGS-LA NPs were more suitable for providing efficient delivery to hepatoma cells by avoiding the clearance mechanisms. It was found that ETO-loaded TPGS-LA NPs were noticeably able to enhance the cytotoxicity of ETO in HepG2 cells. Besides this, markedly higher internalization by the ASGPR-overexpressed HepG2 cells and efficient accumulation at the tumor site in vivo were revealed in the TPGS-LA NP group. More importantly, animal studies confirmed that ETO-loaded TPGS-LA NPs achieved the highest therapeutic efficacy against HCC. Interestingly, ETO-loaded TPGS-LA NPs also exhibited a great inhibitory effect on P-gp compared to the ETO-loaded TPGS NPs. These results suggest that TPGS-LA NPs could be used as a potential ETO delivery system against HCC.

Thermal reduction of erbium nitrate and S-doped reduced graphene oxide (rGO) mixture resulted in the formation of small (∼3–18 nm sized) Er₂O₃–Er₂SO₂ nanoparticles with a high degree of surface coverage on the reduced GO support. The morphology, structure, and the chemical composition of the synthesized nanoparticles have been studied by scanning and transmission electron microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, and by optical spectroscopies. The rGO-supported Er₂O₃–Er₂SO₂ nanoparticles (Er₂O₃–Er₂SO₂/rGO) demonstrate sufficiently strong light emission (luminescence and upconversion) in the visible and near-infrared range via intra-4f Er³⁺ optical transitions. The reported synthetic approach demonstrates a novel method for synthesizing Er-containing nanoparticles for sensor applications.

This study uses the formation of a mixed metal oxide inside ferritin to tune the band gap energy of the ferritin mineral. The mixed metal oxide is composed of both Co and Mn, and is formed by reacting aqueous Co²⁺ with ${{{\rm{MnO}}}_{4}}^{-}$ in the presence of apoferritin. Altering the ratio between the two reactants allowed for controlled tuning of the band gap energies. All minerals formed were indirect band gap materials, with indirect band gap energies ranging from 0.52 to 1.30 eV. The direct transitions were also measured, with energy values ranging from 2.71 to 3.11 eV. Tuning the band gap energies of these samples changes the wavelengths absorbed by each mineral, increasing ferritin's potential in solar-energy harvesting. Additionally, the success of using ${{{\rm{MnO}}}_{4}}^{-}$ in ferritin mineral formation opens the possibility for new mixed metal oxide cores inside ferritin.

Monolayer and/or atomically thin transition metal dichalcogenides cover a wide range of two-dimensional (2D) materials, whose fascinating semiconducting and optical properties have made them promising candidate materials for optoelectronic devices. Controllable growth of these materials is critical for their device applications. By using MoCl₅ and H₂S as precursors, monolayer and ultrathin molybdenum disulfide (MoS₂) films with controlled lamellar structure have been directly built layer by layer on SiO₂ substrates without being followed by high-temperature annealing. Furthermore, the thickness of MoS₂ films can be precisely regulated by applying different atomic layer deposition (ALD) cycles. Once an ALD cycle is applied, one molecular layer of MoS₂ material will be 'added' on the substrate or original existing MoS₂ films. At the initial stage (one to three ALD cycles), the density of MoS₂ materials increases with an increase in ALD cycles, while a large area of continuous MoS₂ film on the substrate can be obtained when four or more ALD cycles are applied. In this way, excellent triangular crystals of MoS₂ with controlled atomic size in thickness and a highly oriented hexagonal crystal structures can be obtained by applying definite ALD cycles.

Understanding the mechanical behaviors of van der Waals heterogeneous 2D materials is important for their actual applications. Our extensive first-principles calculations and continuum mechanical modeling on the wrinkling of MoSe₂/WSe₂ heterobilayers caused by compression reveal that the bending stiffness of MoSe₂/WSe₂ wrinkles strongly depend on the wrinkle structures, which first increase and then decrease with increasing the compressive strain. The bending stiffness of MoSe₂/WSe₂ wrinkles could be effectively mediated and tuned by adjusting the wrinkle geometry and size. The underlying mechanisms are elucidated by the differences in electronic structures and bonding states at the top, middle and bottom parts of the wrinkles, and the relevance of the changes of bond lengths to flexural deformation. Our results suggest a feasible way to develop flexible devices and nanoelectromechanical systems by utilizing the correlation and coupling between the mechanical and electronic properties in MoSe₂/WSe₂ wrinkles.

In a fast developing field, it has been found that van der Waals heterostructures can overcome the weakness of single two-dimensional layered materials and extend their electronic and optoelectronic applications. Through first-principles methods, the studied MoS₂/stanene heterostructure preserves high-speed carrier characteristics and opens the direct band gap. Simultaneously, the band alignment shows that the electrons transfer from stanene to MoS₂, which forms an internal electric field. As an effective strategy, the out-of-plane strain remarkably changes the band gaps of the heterostructure and enhances its carrier concentration. In addition, the combined effects of the internal and external electric fields can further open the band gaps and induce a direct-to-indirect gap transition in the heterostructure. More interestingly, when the external electric field is equal to the reverse internal one, the heterostructure regains a Dirac cone. Our results show that the MoS₂/stanene heterostructure has potential applications in high-speed optoelectronic devices.

Molybdenum disulfide (MoS₂) film fabricated by a liquid exfoliation method has significant potential for various applications, because of its advantages of mass production and low-temperature processes. In this study, residue-free MoS₂ thin films were formed during the liquid exfoliation process and their electrical properties were characterized with an interdigitated electrode. Then, the MoS₂ film thickness could be controlled by centrifuge condition in the range of 20 ∼ 40 nm, and its carrier concentration and mobility were measured at about 7.36 × 10¹⁶ cm⁻³ and 4.67 cm² V⁻¹ s⁻¹, respectively. Detailed analysis on the films was done by atomic force microscopy, Raman spectroscopy, and high-resolution transmission electron microscopy measurements for verifying the film quality. For application of the photovoltaic device, a Au/MoS₂/silicon/In junction structure was fabricated, which then showed power conversion efficiency of 1.01% under illumination of 100 mW cm⁻².