Scientific advancement is highly inspired and imitative of natural phenomenon’s, which exhibits extremely developed and well-organized nanostructures to cope with challenges under different environmental circumstances, such as moth eyes protuberances for efficient antireflective (AR) performance. Innovative researches have been performed in the past to exterminate the undesirable reflectance in common optical components and optoelectronic industrial applications by biomimetic and replicating moth eye nanostructures creating gradient effect using metal oxides, composites, or polymers in multilayer AR coatings. However, in few multilayer AR designs, the properties mismatch at interfaces, high cost, low mechanical durability, wetting issues, or thermal stability bounds their practical applicability. Herein, we develop an approach for fabricating efficient, high-performance Teflon (polytetrafluoroethylene [PTFE]) AR nanostructures for glass-based supporting materials. Nanotailoring, the morphology and structure of PTFE, have been efficaciously carried out for fabricating high-performance AR coatings according to predicted optical simulation. The total reflectance from polymer AR coating lessens to <0.05% in a visible wavelength range which according to our best knowledge seems to be the superior AR performance by a polymer coating ever reported. Furthermore, the fabricated polymer AR coatings are omnidirectional, mechanically durable, and thermally stable up to 200 °C. Moreover, we modify and tune the refractive index of PTFE from 1.34 to 1.156 by inducing porosity and changing deposition angle.Keywords: broadband antireflectance; hydrophobic surface; mechanical resilience; polymer optical coating; water contact angle;

•[111] oriented γ-Mo2N thin film was prepared by reactive dc magnetron sputtering.•The formation of (111) texture gives excellent electrochemical property.•The optimum deposition temperature is much lower than that of the chemical route.•The Mo2N film is a promising candidate of anode materials for micro-supercapacitors.The γ-Mo2N thin films were deposited using reactive dc magnetron sputtering, and tested as an electrode material in an aqueous solution of Li2SO4 with a working potential window of 0.05V∼-0.85 V versus SCE. The morphology, structure and electrochemical properties were systematically studied for the films of different deposition conditions. It was found that the electrochemical property of the γ-Mo2N film depends not only on the deposition temperature but also on the nitrogen concentration in Ar-N2 gas mixture. The sample deposited for 1 h at 400 °C with nitrogen concentration x = 0.35 shows a dense microstructure and strong (111) texture. It exhibits the best electrochemical property, with a high volumetric capacitance of 722 F cm−3 at 5 mV s−1, moderate rate capability with a relaxation time constant of 220 ms, and excellent cycling stability of 100% capacitance retention after 2000 cycles. The (111)-oriented γ-Mo2N film is suggested to be a promising candidate of anode materials for micro-electrochemical-capacitors.[111] oriented γ-Mo2N thin film was prepared by reactive dc magnetron sputtering. It exhibits excellent electrochemical property due to the formation of (111) texture and is suggested to be a promising candidate of anode materials for micro-supercapacitors.Download high-res image (284KB)Download full-size image

The importance of tuning refractive index in a multilayer antireflection coating (ARC) system can not be denied. In practical applications, regulation of refractive index is complex due to limited choice and availability of appropriate materials for the trilayer AR coating assembly. To overcome this issue, we used a single inorganic material, HfO2, for the construction of a trilayer AR light harvesting moth eye, resembling hierarchical nanostructure coatings, for exploring new generation photovoltaics and optoelectronic devices. In the trilayer AR HfO2 (TAR-H) assembly, using a glancing angle deposition technique (GLAD), the dense bottom layer was steadily changed into a spongy middle layer that further changed to a highly porous top layer micmiking a moth eye, reducing the refractive index of the coating from 1.87 to 1.30. The broadband omnidirectional properties of the TAR-H coating, with superior thermal stability and improved scratch resistance, in the visible wavelength range were experimentally demonstrated. The TAR-H coating on FTO and sapphire substrates achieved reflectance of up to <1% in the visible wavelength range.

Subwavelength closely spaced metallic nanorod arrays form attractive plasmonic structures. Describing their optical dispersion with an analytical model has been challenging to date, yet the collective resonances in the lattice can be finely tuned by changes in geometrical parameters and dielectric media, as reported by various publications. In this paper, we determine the plasmon dispersion relation in subwavelength closely spaced Au nanorod arrays for both hexagonal and square lattices. By 3D plasmon mapping using the finite element method (FEM), the orders of cavity modes in the lattice can be confirmed directly. Both the numerical and experimental results agree well with an analytical model for plasmon dispersion in planar metal–insulator–metal (MIM) waveguides of equivalent widths. This analytical model enables us to successfully predict the resonance wavelengths as well as the orders of cavity modes in the lattice. We attribute the physical origin of the equivalent width to a geometric effect, which can be qualitatively understood considering the Coulomb interactions between neighbouring nanorods. The work here is of significant benefit to both the optimized design of active plasmonic devices and the fundamental understanding of nano-optics.

Aligned silver nanorods wrapped with Al2O3 layers about 0.85, 1.54 nm thickness were utilized to study the SERS response and adsorption behavior of uranyl ion. Relatively broad and asymmetric SERS bands were observed due to the contribution of several hydrolyzed uranyl complexes and multiple coordination between uranyl complexes and SERS substrates. The mechanism of sorption on SERS substrates is discussed. The effect of the pH value of sample solutions was also studied. Results show that the Al2O3 layers enhance the stability of silver nanorod. It is found that the Al2O3 layer is consumed in acidic or basic solutions, while the SERS performance of silver nanord is maintained. Uranyl ion can be quantified by this method in concentration down to 10−9 M.

Antireflective (AR) coating with both high antireflectance and omnidirectional characteristic is desired for many advanced optical device applications and photovoltaic thin-film solar cells. The application of double-layer antireflective (DLAR) coating to reduce reflectance is largely constrained at wide wavelength range due to refractive index variation within individual layer and between the air–substrate interfaces. In this article, high performance gradient refractive index double-layer AR coatings with periodically patterned hierarchical porous hafnia nanorods that mimic moth compound eyes are fabricated on a dense hafnia matrix layer using glancing angle deposition technique. The refractive indices for the top and bottom layers of the DLAR hafnia coatings are 1.36 and 1.87. The fabricated films possess high transparency showing zero reflectance at calculated wavelength of 550 nm but also give <1% reflectance over broad range of visible spectrum at different angles of light incidence displaying its omnidirectional characteristic. The shifting and tuning of reflectance to nearly <1% in visible, infrared, and ultraviolet regions was achieved for wide range of substrate materials by tailoring refractive index through porosity and film thickness of the two layers. Moreover, the DLAR hafnia thin films show high thermal stability at high temperatures up to 300 °C.

TiO2 nanorod arrays (NRAs) with 540 nm length and an amorphous porous structure, were fabricated by oblique angle deposition method. The as-prepared amorphous TiO2 NRAs transform gradually into anatase phase after annealing with a temperature higher than 350 °C, whereas the specific surface area decreases due to the better crystallinity. The intensity of hydroxyl groups increases with enhancing annealing temperature, then decreases above 450 °C. The photocatalytic and photo-conversion properties benefit from the high crystallinity of TiO2 NRAs and high density of hydroxyl groups on the surface. It shows that TiO2 NRAs annealed at 450 °C exhibit the highest photoconversion efficiency and maximum degradation rate of MO, which can be ascribed to the excellent crystallization and the optimum density of hydroxyl groups on the surface of TiO2. The TiO2 NRAs with enhanced crystallinity and fine structures are very promising for photocatalyst materials for environmental protection.

•An aqueous polymer quenchant was adopted to evaluate the thermal shock resistance.•Thermal shock behavior could be adjusted through varying the polymer concentration.•The critical maximum instantaneous thermal shock cooling rate was a constant value.•Heat transfer coefficient gradient was an important factor of thermal shock failure.•Polymer quenching is a promising method for studying the thermal shock resistance.An aqueous polymer quenching technique combing with a thermocouple real-time temperature acquisition technique were adopted to evaluate the thermal shock resistance of a hot-pressed ZrB2–SiC–graphite composite. The thermal shock behavior of the composite at different testing temperatures could be controlled and adjusted through varying the polymer concentration in the aqueous quenching solution. Experimental data showed that the critical maximum instantaneous thermal shock cooling rate at different testing temperatures was a constant value of 500 °C s−1(ν(max)c), and surface microcracks were assigned to the thermal shock failure. Heat transfer coefficient (h) gradient in samples, surface generated under two different quenching media, i.e. water and aqueous silicone oil solution, resulted in different tendency of decrease in strength. Thermal shock failure was presumed to be related to not only the body temperature gradient but also the surface h gradient in samples to produce thermal stress damage. The results indicate a promising method for studying the thermal shock resistance of ceramic materials.Download high-res image (537KB)Download full-size image

•Glancing angle deposition technique is used to fabricate various columnar nanostructures in a single step to tune physiochemical properties.•Enhanced surface area induces porosity, with dispersion of active sites at different length scales of pores.•The increase interface between nanostructures and organic dye is promising factor to enhance photocatalytic degradation.•Morphologies having high surface to volume ratio increases the number of catalytic reaction sites to facilitate organic molecules adsorption favorable for reaction kinetics.Hierarchical nanostructures have drawn significant attention and incredible performance in photodriven chemical conversion area due to its unique physicochemical properties. Herein, we study the morphological influence of TiO2 nanostructures on photocatalytic degradation of different organic dyes methyl blue, methyl violet and methyl orange present in industrial wastewater. Nanorod, nanohelics and nanozigzag TiO2 nanofilms were fabricated by using galancing angle deposition technique (GLAD). TiO2 nanofilms were characterized by scanning electron microscope (SEM), X-ray powder diffraction (XRD), and raman analysis. BET surface area analysis were carried out by using nitrogen adsorption desorption curves. The results show that TiO2 morphology had great influence on photocatalytic degradation of organic dyes due to difference in specific surface area and pore volume of nanostructures. The photocatalytic degradation experiments were carried out for three hours under UV–vis light irradiation. Catalysis recycling and organic dyes concentration influence were also studied. In case of high concentration of organic dyes, negligible degradation rate is observed. TiO2 nanozigzag films show better degradation performance than nanohelics and nanorod due to presence of large surface area for reaction, higher porosity with dispersion of active sites at different length scales of pores and presence of oxygen vacancies.Download high-res image (228KB)Download full-size image

Ag nanorods coated with an ultrathin HfO2 shell (Ag NRs@HfO2) were prepared for the synthesis of a versatile, robust, and easily recyclable surface-enhanced Raman scattering (SERS) substrate. This substrate maximizes the high melting point of the HfO2 shell and thus ensures the excellent plasmonic efficiency of Ag NRs. Therefore, it possesses extraordinary thermal stability and SERS activity, which could act as a reusable and cost-effective SERS detector. After SERS detection, the regeneration of Ag NRs@HfO2 was achieved by annealing the substrate within several seconds. This procedure led to the thermal release of adsorbed molecules and resulted in a refreshed substrate for subsequent measurements. The composite substrate maintained its SERS efficiency well during multiple “detection–heating” cycles, hence demonstrating the stability and recyclability of Ag NRs@HfO2. Furthermore, in addition to revealing the feasibility of SERS sensing in liquids, Ag NRs@HfO2 also provided continuous real-time monitoring of vapor-phase samples at ultralow concentrations. This work provides a robust and renewable SERS sensor with advantages of high sensitivity, stability, cost effectiveness, and easy operation, which can be implemented for both aqueous and gaseous analyte detection and is thus an intriguing candidate for practical applications in environmental, industrial, and homeland security sensing fields.Keywords: aqueous and vapor-phase molecule sensing; core−shell structure; recyclability; SERS; thermal stability

Vertically aligned α-Fe2O3 nanopillar arrays (NPAs) were fabricated by thermally oxidizing Fe NPAs on Si, quartz and F-doped SnO2 (FTO) substrates prepared by glancing angle e-beam deposition (GLAD). The photocatalytic activity of these NPAs was evaluated by measuring the photodegradation of crystal violet (CV) and methyl orange (MO) in the presence of H2O2 under visible light irradiation. Moreover, the photoelectrochemical (PEC) performance was also studied. Typically the sample oxidized at 400 °C exhibits both the highest degradation efficiency and photocurrent density compared with those oxidized at other temperatures (e.g. 300 °C, 350 °C, 450 °C, 500 °C). This phenomenon might be attributed to a trade-off between two opposite effects. On the one hand, with the increase of the oxidation temperature, the improvement of NPAs' crystallinity will enhance the photocatalytic performance accordingly. On the other hand, increasing oxidation temperature may cause the reduction of oxygen vacancies on the NPAs' surface, which are regarded as the photoreaction active sites. This will thus degrade the photocatalytic performance.

Successful employment of surface-enhanced Raman scattering (SERS) as a powerful means for trace analyte detection depends greatly on the nanostructures of noble metals as substrates, which to date are not able to satisfy the many prerequisites for quantitative SERS analysis, e.g., excellent SERS sensitivity, long-term SERS stability in air, chemical inertness, corrosion resistivity, superior reproducibility, good chemisorption of target molecules, and so forth. We report here that Ag nanorods coated with a subnanometer-thick, pinhole-containing Al2O3 shell (Ag NRs@Al2O3) could serve as such a substrate that meets most of the above requirements. Because of the coverage of ultrathin Al2O3 shell, the Ag NRs@Al2O3 substrate exhibited superior SERS sensitivity and was able to work for a long time in very corrosive and harsh environments. Meanwhile, with the Al2O3 pinholes contained, this specially designed core–shell nanostructure was capable of quantifying a variety of molecules at trace levels, i.e., those that can be adsorbed chemically on the surface of either Ag or Al2O3 or both. This study provides a simple approach to prepare highly sensitive, corrosion resistive, and chemically inert SERS substrates for practical, quantitative SERS analysis with wide detection fields.

Interconnecting different carbon building blocks, such as 1-dimensional (1D) carbon nanotubes (CNTs) and 2-dimensional (2D) graphene sheets, is an effective way to build hybrid carbon architectures with fascinating new properties. Here we report the synthesis of a binder-free reduced graphene oxide/carbon nanotube (rGO/CNT) hybrid film and its capacitive behaviour in both positive and negative potential window with 1 M Na2SO4 aqueous electrolyte. It is found that intercalating small amount of CNTs into rGO sheets result in excellent specific capacitance of 272 F g−1 at a scan rate of 5 mV s−1 in negative potential window of −0.8 to 0 V. In contrast, moderate specific capacitance of 132 F g−1 at the same scan rate is obtained in positive potential window of 0 to 0.8 V. The reason of the enhanced capacitance in negative potential window is discussed. We propose that the remarkable improvement of capacitance in negative potential window is mainly due to the strong cation adsorption at the oxidized surface of rGO sheets. The addition of CNTs can significantly improve the rate capability and cyclic stability of the electrode compared to that of pure rGO electrode. As-synthesized rGO/CNT hybrid film shows great potential in neutral aqueous electrolyte based asymmetric supercapacitors as high performance negative electrode, and other applications such as flexible batteries, seawater desalination, and biomedical applications.

In the field of plasmonics, the nanogap effect is often related to one aspect like the near-field enhancement at a single excitation wavelength or the far-field resonance shift. In this study, taking full advantage of finite element method (FEM) calculations, we present a comprehensive and quantitative analysis of the nanogap effect on the plasmonic behaviors of metallic nanoparticle dimers. Firstly, near-field spectroscopy is proposed in order to extract the near-field resonance wavelengths. Focusing on the bonding dipole mode, it is found that the near-field enhancement factors exhibit a weak power-law dependence on the gap size, while the near-field resonance shift decays nearly exponentially as the gap size increases, with a lower decay length than that for the far-field resonance shift. The spectral deviation between these two shifts is suggested to be taken into account for spectroscopy applications of plasmonic devices, although it may be negligible for dimer structures with rather small gaps.

The reversible transition between hydrophilicity and hydrophobicity of Ti NRAs induced by alternating X-ray irradiation and ethanol immersion has been revealed. The wettability modification is attributed to the chemisorption of alkyl groups on TNRA surfaces from airborne molecules.

In this paper, a ZnO/Zn2SiO4/SiO2/Si multilayer structure is fabricated on silicon substrate. The highly c-axis oriented ZnO layer was prepared by pulsed electron deposition system. XRD and HRTEM results show that the initial ZnO/Si bilayer structure transferred to ZnO/Zn2SiO4/SiO2/Si multilayer structure after heat treatment due to interfacial reaction. Enhancements of ultraviolet and visible light emissions were observed due to the improved ZnO crystallinity and the formation of Zn2SiO4 nanoparticles embedded in the amorphous interfacial layer. This study facilitates the understanding of optical behaviors of ZnO, also suggests a potential method to fabricate ZnO/Zn2SiO4/SiO2/Si multilayer structure for luminescence and phosphorescence.

Undoped ZrO2 thin films are prepared on 〈100〉 Si substrates by reactive DC magnetron sputtering using a Zr target. By controlling the oxygen partial pressure during the deposition process, we can successfully control the phase structure of the as-deposited film, which can be tetragonal, monoclinic or a mixture of them. A magnetic property measurement reveals that phase-dependent d0 ferromagnetism exists in ZrO2 thin films. Specifically, only tetragonal ZrO2 thin films can be room-temperature ferromagnetic. Photoluminescence measurements, X-ray photoelectron spectroscopy analyses and post thermal annealing experiments suggest the d0 ferromagnetism in undoped tetragonal ZrO2 films is mainly driven by oxygen vacancies.

In the past several decades, dilute magnetic semiconductors, particularly the dilute magnetic oxides have evolved into an important branch of materials science due to their potential application in spintronic devices combining of properties of semiconductors and ferromagnets. In spite of a major effort devoted to the mechanism of ferromagnetism with a high Curie temperature in these materials, it still remains the most controversial research topic, especially given the unexpected d0 ferromagnetism in a series of undoped wide-band-gap oxides films or nanostructures. Recently, an abundance of research has shown the critical role of various defects in the origin and control of spontaneous magnetic ordering, but contradicting views from intertwined theoretical calculations and experiments require more in-depth systematic research. In our previous work, considerable efforts have been focused on two major oxides, i.e. ZnO and ZrO2. This review will present a summary of current experimental status of this defect-driven ferromagnetism in dilute magnetic oxides (DMOs).

200 keV Xenon irradiation experiments were performed on magnetron sputtered Zr–Ti films under different doses up to 9 * 1015 ions/cm2. XRD, FE-SEM, AFM, HRTEM, nano-indentation and white light interferometer characterizations were applied to study the structural and mechanical properties modification introduced by the bombardment. Upon Xenon irradiation, structure of film matrix kept stable while the crystallinity of the top surface degraded significantly. Meanwhile, properties of irradiated films such as hardness, modulus and sheet resistance evolved with the same tendency, i.e. increased firstly and decrease with further increasing the irradiation dose. By selective area irradiation, competition between the surface sputtering and swelling was revealed, by which surface defects evolution was highlighted. The micro-defects evolution during Xenon irradiation was believed to be responsible for the macro-properties’ modification.

•TiO2 nanorod arrays/CdS quantum dots/ALD-TiO2 nanostructures were fabricated as photocatalyst.•Enhanced photoelectrochemical properties are observed and the degradation rate of methyl orange under visible light is enhanced by ca.156%.•Additionally, the stability of the TiO2 nanorod arrays/CdS quantum dots is increased by the ALD-TiO2 coating.TiO2 nanorod arrays/CdS quantum dots/ALD-TiO2 nanostructures were fabricated as photocatalyst and its related properties were investigated comprehensively. Enhanced photoelectrochmical properties are observed and the degradation rate of methyl orange under visible light is enhanced by ca.156% compared to the nanorod arrays/CdS quantum dots, which is due to the enhancement of the separation of electrons-holes induced by the introduction of the ultrathin TiO2 top layer. Moreover, the stability of the TiO2 nanorod arrays/CdS quantum dots is increased by the ALD-TiO2 coating. These results suggest that the design of TiO2 nanorod arrays/CdS quantum dots/ALD-TiO2 nanostructures gives a promising strategy to improve the photoelectrochemical and photocatalytic properties in solar energy conversion, along with reduced photo-corrosion in the semiconductor-semiconductor heterojunction.

•Conductive MoO2+x film composed by crystallized MoO2 grains and amorphous MoOx is prepared.•Such film shows high volumetric capacitance and stable property.•Good stability, high energy and power density are obtained from the asymmetric micro- capacitor of MoO2+x(-)//2 M Li2SO4//MnO2 (+).•MoO2 grains are crucial in achieving superior property for the MoO2+x film electrode.Conductive MoO2+x film deposited at 150 °C by magnetron sputtering is investigated as negative electrode material for micro-scale electrochemical capacitors. It is found that the film 860 nm thick exhibits high volumetric capacitance (385 F cm−3), good rate capability (47% capacitance retained at 500 mV s−1 relative to that at 20 mV s−1) and excellent cycling stability (100% retained after 5000 cycles). An asymmetric micro-device of MoO2+x(-)//2 M Li2SO4//MnO2(+) is obtained, showing a high energy density of 2.8 μWh cm−2 at a real power density of 0.35 mW cm−2, and good stability with no capacitance loss for 10000 cycles. It is revealed that the amorphous MoOx species with oxidation state of +5 to +6 provides pseudocapacitance through reversible insertion/extraction of H+ and Li+. More importantly, extra capacitance is contributed by catalytic decomposition of hydrated water on MoO2 grain surfaces, and the presence of large amounts of MoO2 grains ensures fast electronic transfer and structural stability. Thus the superior capacitive property of the MoO2+x film can be attributed to its multivalent and multi-phase structure with integrated functions.

•Ti nanorod arrays were grown by oblique angle deposition method.•Ti@MoOx core–shell nanorod arrays were prepared by electrodeposition.•Ti@MoOx nanorod arrays exhibit superior electrochemical properties.•Rate capability is remarkably improved after post-annealing in H2/Ar.Ti@MoOx core–shell nanorod arrays with diameters within 100 nm were fabricated by electrodepositing MoOx on a Ti nanorod array prepared by oblique angle deposition. A high areal capacitance of 27 mF cm− 2 and satisfactory cycling stability were obtained. After post-annealing, MoO2 grains were introduced to enhance the rate capability, suggesting a potential pseudocapacitive micro-electrode.

Helical silver nanorod arrays with different arm numbers are designed by oblique angle deposition and their surface-enhanced Raman scattering properties are characterized. Assuming that the hot spots are located at the bends between the arms, and considering the optical absorbance of different layers, the SERS behavior can be predicted qualitatively.

Aligned Ag nanorods were prepared by glancing angle deposition on micro-patterns of silicon fabricated by electron beam lithography, forming hexagonal lattices. Excited by a 633 nm He–Ne laser, Raman scattering of Rhodamine 6G molecules on the hexagonal lattices has been investigated. The enhancement of the Raman signals by the hexagonal lattices was found to be dependent on the separation distance of the micro-patterns, i.e. it reached the maximum when the patterns are separated by ∼200 nm or closely packed, suggesting a coupling effect at the micro-nano scales. This study also provides an idea to further enhance the Raman scattering.Graphical AbstractPatterning Ag nanorods to further enhance SERS sensitivity.Highlights▶ Hexagonal patterns of aligned Ag nanorods were prepared. ▶ The patterned nanorods exhibited enhancement in the SERS sensitivity. ▶ The enhancement was dependent on the pattern separation distance.

Carbon nanotubes (CNTs) have been synthesized from Ar-CH4 mixtures using rf-plasma enhanced chemical vapor deposition (rf-PECVD) at 500°C. Reduction gases such as H2 and NH3 were found unnecessary for carbon nanotube formation compared to thermal CVD. The relationship between the growth of CNTs and the plasma condition in PECVD has been investigated by in situ self bias measurement. Plasma conditions were controlled by changing the interelectrode distance, rf power and the applied substrate negative bias. By increasing the interelectrode distance and rf power, the spatial density of CNTs was on a rise as a result of the increase in ions density and self bias. As the applied substrate negative bias increased, the spatial density of CNTs decreased possibly due to the positive ions over bombarding effect.

Isomers and homologues of organic pollutants are hard to distinguish-especially in trace amounts-due to the similarities in their physical and chemical properties. We report here that by identifying the Raman characteristics of isomers of monochlorobiphenyls, these compounds can be recognized, even at trace levels, by using the surface-enhance Raman scattering method with silver nanorods as a substrate. When dissolved in acetone, 2-, 3-, and 4-chlorobiphenyls were detected at a concentration of 10−8 mol/L, at which their characteristic Raman peaks were visible. This study may provide a fast, simple, and sensitive method for the detection and recognition of organic pollutants such as polychlorinated biphenyls.

Slanted Fe nanorods prepared by glancing angle deposition on silicon substrates exhibited easy magnetization along their growth axis. By using a thin gold film on a silicon substrate as a buffer layer, slanted Fe nanorods can be realigned towards the substrate surface normal by a strong magnetic field. After realignment, the Fe nanorods retained the easy magnetization axis along their growth axis. The effects of the realignment by the strong magnetic field on the properties of the slanted Fe nanorods were also investigated. This study provides a possible way to fabricate magnetic nanostructures for perpendicular recording applications.

Films consisting of vertically aligned VO2 nanorods were prepared on planar silicon substrate by thermally heating a sheet of vanadium in a rough vacuum. These nanorods were found to be of a body-centered-cubic (BCC) structure with a lattice constant of 0.94 nm, which was not observed before for VO2. Due to their sharp tip of the nanometer scale, the BCC VO2 nanorods exhibited excellent field emission properties, which make them possible candidate materials for applications in field emission devices.

Positive or negative silicon patterns (nanometers high or deep) were created on silicon substrates directly by xenon ion implantation, by compromising defects generated in silicon and surface sputtering. A diagram was constructed to show how to produce positive or negative silicon patterns, by controlling the energy and dose of xenon ions. Interestingly, carbon nanotubes showed different growth behaviors on the substrates with positive or negative patterns. Since the ion-implantation technique is well established and has been widely applied in semiconductor industries, this study might provide a simple method to fabricate nanometer-scale patterns.

Vanadium dioxide (VO2) is a well-known semiconductor material with a band gap of 0.7 eV, and is seldom used as a photocatalyst. We report here a new crystal structure for nanostructured VO2, with body-centered-cubic (bcc) structure and a large optical band gap of ∼2.7 eV, which surprisingly shows excellent photocatalytic activity in hydrogen production. The bcc VO2 phase exhibited a high quantum efficiency of ∼38.7% when synthesized as nanorods. Using films of the aligned VO2 nanorods, the hydrogen production rate can be tuned by varying the incident angle of UV light on the films and reaches a high rate of 800 mmol/m2/h from a mixture of water and ethanol under UV light, at a power density of ∼27 mW/cm2, allowing possible commercial application of this material as photoassisted hydrogen generators.Keywords: hydrogen generator; nanorod; photocatalysis; vanadium oxide

Niobium oxide amorphous films were deposited on silicon substrates at a temperature range of 300–400 °C by heating a pure niobium foil in a rough vacuum. The films were amorphous in structure and with morphology of vertically aligned nano-columns. This feature resulted in interesting photoluminescence (PL) property in the visible light range. The intensity of the photoluminescence spectrum of the as-deposited amorphous film is small. However, the PL intensity of the same sample after annealing below 500 °C increases greatly and consists of two peaks centered at ~ 630 nm (1.97 eV) and ~ 715 nm (1.74 eV). The mechanism for the PL behavior of the amorphous niobium oxide films was also investigated and discussed.

Arrays of MoO2 nanorods were fabricated on silicon substrates within a typical growth time of ∼1 min by direct heating of a molybdenum spiral coil in a low vacuum. The nanorods grown with Au particles as catalyst have similar diameters but with sharper tips than that grown without catalyst, and exhibit a lower switch-on voltage for field emission. The orientation of the nanorods with sharper tips can be considerably improved by increasing the coil temperatures, thus leading to increased field emission currents. For example, the turn-on voltage of the nanorods decreases from ∼18 to ∼4 V/μm when the coil temperature goes up from ∼800 to ∼1000 °C. The present study provides a way to fabricate metal oxides nanorods on flat substrates as well as to modify their field emission performance.

Carbon nanotube self-assembly into honeycomb-networks via controlling the ratio of the catalyst over hydrocarbon in the vapor phase using a tunable chemical vapor deposition process.

Films consisting of vertically aligned VO2 nanorods were grown on silicon substrates by thermally oxidizing a sheet of pure vanadium in a rough vacuum. These VO2 nanorods, when heated in air at ≥400 °C, were oxidized further into V2O5 in which oxygen defects were introduced. The oxygen-deficient V2O5 films exhibited intense photoluminescence at room temperature in the visible light range and interestingly, are sensitive to oxygen and hydrogen in the environment, suggesting the possibility of applying oxygen-deficient materials in sensing oxygen. This study provides an alternative idea to synthesize oxygen sensing materials.Graphical abstractOxygen deficient V2O5 nanorods are sensitive in sensing oxygen.Download full-size imageHighlights► V2O5 nanorods were formed by thermally oxidizing VO2 nanorods in air. Oxygen vacancies were generated in the V2O5 nanorods. ► The oxygen deficient V2O5 nanorods are sensitive to oxygen and hydrogen.

CdS nanoparticles (NPs) decorated α-Fe2O3 nanopillar arrays (NPAs) were fabricated through several steps. Fe NPAs were firstly fabricated by glancing angle deposition technique and oxidized in air to gain α-Fe2O3 NPAs. Then these NPAs were decorated by CdS NPs through successive ion layer adsorption and reaction (SILAR). Here we have tested photodegredation of methylene blue (MB) and photoelectrochemical properties under visible light. Especially, when SILAR cycle number reaches to 10, it shows the highest degradation efficiency (94% in 75 min on MB) which improves 72% comparing with pure one and the highest photocurrent density (2.0 mA cm−2 at 0.4 V vs Ag/AgCl electrode). α-Fe2O3/CdS hetero-junctions could greatly enhance photocatalytic performance, which can help to accomplish sufficient usage of solar energy and be exploited on pollution abatement in future.Figure optionsDownload full-size imageDownload high-quality image (81 K)Download as PowerPoint slide

Subwavelength closely spaced metallic nanorod arrays form attractive plasmonic structures. Describing their optical dispersion with an analytical model has been challenging to date, yet the collective resonances in the lattice can be finely tuned by changes in geometrical parameters and dielectric media, as reported by various publications. In this paper, we determine the plasmon dispersion relation in subwavelength closely spaced Au nanorod arrays for both hexagonal and square lattices. By 3D plasmon mapping using the finite element method (FEM), the orders of cavity modes in the lattice can be confirmed directly. Both the numerical and experimental results agree well with an analytical model for plasmon dispersion in planar metal–insulator–metal (MIM) waveguides of equivalent widths. This analytical model enables us to successfully predict the resonance wavelengths as well as the orders of cavity modes in the lattice. We attribute the physical origin of the equivalent width to a geometric effect, which can be qualitatively understood considering the Coulomb interactions between neighbouring nanorods. The work here is of significant benefit to both the optimized design of active plasmonic devices and the fundamental understanding of nano-optics.

Helical silver nanorod arrays with different arm numbers are designed by oblique angle deposition and their surface-enhanced Raman scattering properties are characterized. Assuming that the hot spots are located at the bends between the arms, and considering the optical absorbance of different layers, the SERS behavior can be predicted qualitatively.

In the field of plasmonics, the nanogap effect is often related to one aspect like the near-field enhancement at a single excitation wavelength or the far-field resonance shift. In this study, taking full advantage of finite element method (FEM) calculations, we present a comprehensive and quantitative analysis of the nanogap effect on the plasmonic behaviors of metallic nanoparticle dimers. Firstly, near-field spectroscopy is proposed in order to extract the near-field resonance wavelengths. Focusing on the bonding dipole mode, it is found that the near-field enhancement factors exhibit a weak power-law dependence on the gap size, while the near-field resonance shift decays nearly exponentially as the gap size increases, with a lower decay length than that for the far-field resonance shift. The spectral deviation between these two shifts is suggested to be taken into account for spectroscopy applications of plasmonic devices, although it may be negligible for dimer structures with rather small gaps.