Nanorod Films Research Articles

Solid-State Dewetting of Gold Aggregates/Islands on TiO2 Nanorod Structures Grown by Oblique Angle Deposition.

A composite film made of a stable gold nanoparticle (NP) array with well-controlled separation and size atop a TiO2 nanorod film was fabricated via the oblique angle deposition (OAD) technique. The fabrication of the NP array is based on controlled, Rayleigh-instability-induced, solid-state dewetting of as-deposited gold aggregates on the TiO2 nanorods. It was found that the initial spacing between as-deposited gold aggregates along the vapor flux direction should be greater than the TiO2 interrod spacing created by 80° OAD to control dewetting and produce NP arrays. A numerical investigation of the process was conducted using a phase-field modeling approach. Simulation results showed that coalescence between neighboring gold aggregates is likely to have caused the uncontrolled dewetting in the 80° deposition, and this could be circumvented if the initial spacing between gold aggregates is larger than a critical value smin. We also found that TiO2 nanorod tips affect dewetting dynamics differently than planar TiO2. The topology of the tips can induce contact line pinning and an increase in the contact angle along the vapor flux direction to the supported gold aggregates. These two effects are beneficial for the fabrication of monodisperse NPs based on Rayleigh-instability-governed self-assembly of materials, as they help to circumvent the undesired coalescence and facilitate the instability growth on the supported material. The findings uncover the application potential of OAD as a new method to fabricate structured films as template substrates to mediate dewetting. The reported composite films would have uses in optical coatings and photocatalytic systems, taking advantage of their ability to combine plasmonic nanostructures within a nanostructured dielectric film.

A novel bilayer photoanode made of carbon nanotubes incorporated TiO2 nanorods and Mg2 + doped TiO2 nanorods for flexible dye-sensitized solar cells

TiO2 nanorods (NRs), Mg2+ doped TiO2 (Mg2+/TiO2) NRs, and carbon nanotubes incorporated TiO2 (CNTs/TiO2) NRs are fabricated from the corresponding electrospun nanofibers (NFs) by ultrasonic treatment, respectively. Then these NRs are made into various photoanodic films through electrospray deposition and hot-compression for flexible dye-sensitized solar cells (FDSSCs). The conversion efficiency of FDSSCs is improved with the CNTs incorporation or the Mg2+ ions doping of TiO2. To further improve the properties of FDSSCs, various bilayer photoanodic films made of the smaller diameter NRs as under-layer and the larger diameter NRs as over-layer are prepared. Finally, a highest conversion efficiency of 3.9% is obtained using the bilayer NRs film composed of the smaller diameter CNTs/TiO2 NRs and the larger diameter Mg2+/TiO2 NRs. This efficiency is much higher than that of the single-layer NRs film based FDSSCs. This may be attributed to the increased light harvesting resulting from the scattering layer of the larger diameter NRs and the faster electron transport due to the two-level energy steps of the bilayer NRs film.

Effective pseudocapacitive charge storage/release by hybrids of poly(3,4-ethylenedioxypyrrole) with Fe3O4 nanostructures or Co3O4 nanorods

The synergy between two redox materials, the high electrical conductivity and the chemically robust durable structure of poly(3,4-ethylenedioxypyrrole) (PEDOP) combined with the high theoretical capacities, cost-effectiveness and abundance of M3O4 (M: Fe or Co) type oxides is exploited. Hybrid films of PEDOP@Co3O4 nanorods (NRs) and PEDOP@Fe3O4 nanostructures (NSs) are fabricated over flexible carbon (C)-fabric substrates for the very first time. A symmetric supercapacitor cell based on the PEDOP@Fe3O4 NSs hybrid outperforms the remaining cells based on pristine oxides, polymer and even PEDOP@Co3O4 NRs. The PEDOP@Fe3O4 NSs hybrid based cell delivers a high specific capacitance of 673 F g−1 at 1 A g−1 with 83% retention after 5000 cycles. Additionally, it exhibits a wide voltage window of 1 V and an extraordinarily high energy density of 93 Wh kg−1 at a power density of 0.5 kW kg−1. Conducting atomic force microscopy studies reveal that the nanoscale (high) current flowing domains are uniform and almost seamless across the film of PEDOP@Fe3O4 NSs. In contrast, the insulating or low current flowing domains predominate the surfaces of PEDOP and PEDOP@Co3O4 NRs. The nano-level electrical conductivity for the PEDOP@Fe3O4 NSs film is also seven-fold times higher than that of PEDOP and PEDOP@Co3O4 NRs films. The reasons for enhanced electrochemical responses of the hybrids compared to the pristine oxides are explained. The porous morphology, enhanced electrical conduction, and lower ion-diffusion resistance offered by the PEDOP@Fe3O4 NSs film enables improved charge transfer and transport, thus manifesting in a good rate response, high energy density, and acceptable endurance parameters. A real time application of an illumination of green light emitting diode with three such cells also highlights the practical viability of this hybrid.

Improved electrochromic performance of WO3 films with size controlled nanorods

Electrochromic WO3 films with size controlled nanorods were successfully fabricated by a wet chemistry method. The structure and electrochromic properties of tungsten oxide nanorods and films were studied by High resolution transmission electron microscope, Scanning electron microscope, X-ray photoelectron spectroscopy, X-ray diffraction, and electrochemical methods. The average length and diameter of the monodispersed tungsten oxide nanorods increase from 38 × 3.2 nm to 89 × 4.5 nm with help from surfactants. The results show that the electrochromic response time of WO3 nanorod films are strongly dependent on the size of the nanorods. By simply changing the size of the nanorods, the response time of the nanorod films can be regulated nearly by about five times. The electrochemical impedance spectroscopy study showed that such trend can be attributed to the size effect of WO3 nanorods upon the dynamics of H ions diffusion. At the same time, all the nanorod films showed good electrochemical stability as there were no significant performance declines after 1000 cycles. The electrochromic modulations of transmittance at 633 nm were around 22%–49%. The above stated results demonstrate that, by controlling the size of WO3 nanorods, the electrochromic properties can be easily adjusted, especially the response time, indicating potential values for different response time required at different occasions.

Insight into carrier transportation and hydrogen production activity of two novel morphological CdS films

One-dimensional CdS nanorods film and conifer like CdS planar film electrode were prepared using hydrothermal method and ultrasonic spray pyrolysis method. The SEM image and fluorescence spectrum revealed that different carrier transportation dynamics of two samples, which explained why CdS nanorods film showed better photoelectrochemical (PEC) property and hydrogen production activity. Compare the H2 evolution results and PEC results of films, the linear relation of H2 gas volume practically measured and computed referring to photocurrent value was discussed and confirmed. However, CdS nanorods film experienced severe photocorrosion compare with CdS planar film, because photogenerated holes were not consumed by electrolyte efficiently. The stability of samples can be improved by adding sodium sulfite in the electrolyte.

Sandwiched ZnO@Au@CdS nanorod arrays with enhanced visible-light-driven photocatalytical performance

The development of high-performance photocatalysts is central to efforts focused on taking advantage of solar energy to overcome environmental and energy crises. Integrating different functional materials artfully into nanostructures can deliver more efficient photocatalytic activity. Here, sandwiched ZnO@Au@CdS nanorod films were synthesized via successive ZnO nanorod electrodeposition, Au sputtering and CdS electrodeposition. The as-synthesized composites were characterized by UV–vis spectrophotometer, x-ray diffractometer, scanning and transmission electron microscopy. Their photocatalytic activity was assessed by degrading Rhodamine B solution under visible light irradiation. ZnO@Au@CdS exhibited better photocatalytic performance than ZnO@CdS throughout the visible light region, and the corresponding enhancement factor of Au nanoparticles was measured as a function of CdS loading amount, and it could reach 190% with CdS deposition for 1 min. The normalized rate constant could reach 0.387 h−1 for ZnO@Au@CdS-1min, which was equivalent to or better than results in reference photocatalysts. The enhancement mechanism of Au nanoparticles was estimated by comparing the monochromatic photocatalytic action spectra with the absorption spectrum of ZnO@Au@CdS, and it was mainly determined by incident photon energy. With selective excitation of Au nanoparticles by incident photons, the excited hot electrons in Au NPs are transferred to the conduction band of ZnO to boost photocatalytic reaction. With selective excitation of CdS, the enhanced interband absorption of CdS and relay station effect of Au nanoparticles should be responsible for the enhanced photocatalytic performance. Our work not only opens the door to the design of efficient supported photocatalysts, but also helps to understand the enhancement mechanism of LSPR effect on the photoelectric conversion of semiconductors.

Quantum Dot Modified One-Dimensional C60 Nanorod in Situ Preparation and Photoinduced Charge Transfer

CdSe/CdS/ZnS quantum dot (QD) modified C60 nanorods were performed by the liquid–liquid interfacial precipitation method. Transmission electron microscopy and scanning electron microscopy were used to characterize the hybrid C60 structure and found that the CdSe/CdS/ZnS QDs were attached on the surface of C60 nanorods. UV–vis absorption spectroscopy, surface photovoltage spectroscopy (SPS), and steady-state and transient spectra photoluminescence (PL) were used to investigate the nanorods’ optoelectronic properties. The CdSe/CdS/ZnS QD PL quench, decreasing lifetime, and enhanced SPS response were observed for the hybrid QDs/C60 nanorod films. The charge transport property of a single C60 nanorod modified by CdSe/CdS/ZnS QDs was also investigated for photocurrent occurrence. It is considered that the photoinduced charge transfers from CdSe/CdS/ZnS QDs to C60 nanorods by tunneling through the oleylamine ligand. The hybrid QDs/C60 nanorod will be a good system for adjusting the interaction and the ability of charge transportation between the QDs and C60 by ligand exchange. The in situ preparation method for the hybrid QD/C60 nanorod films has high yield at room temperature.

Highly Aligned Plasmonic Gold Nanorods in a DNA Matrix

AbstractSince the Lycurgus Cup was made in the 4th century, metal nanoparticles have attracted much interest due to the characteristics of the plasmonic and metamaterials that show beautiful colors. Despite these fascinating properties, the practical use is limited because it is difficult to control the orientation of the plasmonic nanoparticles. Here, highly aligned plasmonic gold nanorods are obtained using self‐assembled DNA material. Simple mechanical shearing results in long‐range DNA–gold nanorod arrays which show parallel, perpendicular, and zigzag configurations due to the competition between the shear force and DNA elasticity. The resulting surface plasmonic resonance properties of the aligned DNA–gold nanorods film show highly polarization‐dependent behavior in a large area, which is critical for optical and photonic applications. This simple way to form anisotropic plasmonic films can be used for plasmonic nanoparticles in potential applications such as displays and sensors.

Comparative Study of Photoresponse from Vertically Grown ZnO Nanorod and Nanoflake Films.

Zinc oxide (ZnO) based ultraviolet (UV) photodetectors have been fabricated and their photoresponse is studied in Schottky diode configuration. A cost-effective single-step electrochemical deposition method is adopted for the growth of ZnO film with nanorod (NR) and nanoflake morphology. A comparative study of the photodetection parameters based on surface trap states, crystallinity, and strain is done for two different morphology films. Significant photocurrent enhancement is observed for the nanorods under UV light, with appreciable photoresponse in the blue region. A template-assisted growth of ZnO NR film is proposed for better photoresponse and sensitivity of the device, useful for various optoelectronic applications.

Facile preparation of Cu3BiS3 nanorods film through a solution dip-coating process

A novel Cu3BiS3 nanorods film was prepared by a facile dip-coating method and its compositional, structural and optoelectronic properties were systematically characterized. A possible reaction mechanism of Cu3BiS3 was also discussed briefly. Optical absorption investigation revealed that Cu3BiS3 nanorods film has a direct band gap of 1.46 eV. Photoelectrochemistry of hydrazine free unannealed film displays a strong p-type photoresponse, as high as ∼1.0 × 10−4 A/cm−2 at an applied potential of −0.5 V versus Ag/AgCl under the visible light irradiation. The photocurrent response measurement on the Cu3BiS3 nanorods film sheds light on the potential application as a low-cost, high-reproducibility and high-yield nanorods preparing approach towards efficient Cu3BiS3 photoelectricity and photovoltaic materials.

Functionalization of MgZnO nanorod films and characterization by FTIR microscopic imaging.

Metal organic chemical vapor deposition grown films consisting of MgxZn1-xO (4%<x<5%) nanorod arrays (MgZnOnano) were functionalized with 11-azidoundecanoic acid (1). The MgZnOnano was used instead of pure ZnO to take advantage of the etching resistance of the MgZnOnano during the binding and subsequent sensing device fabrication processes of sensor devices, while the low Mg composition level ensures that selected ZnO properties useful for sensors development, such as piezoelectricity, are retained. Compound 1 was bound to the MgZnOnano surface through the carboxylic acid group, leaving the azido group available for click chemistry and as a convenient infrared spectroscopy (IR) probe. The progress of the functionalization with 1 was characterized by FTIR microscopic imaging as a function of binding time, solvents employed, and MgZnOnano morphology. Binding of 1 was most stable in solutions of 3-methoxypropionitrile (MPN), a non-protic polar solvent. This occurred first in μm-scale islands, then expanded to form a rather uniform layer after 22h. Binding in alcohols resulted in less homogenous coverage, but the 1/MgZnOnano films prepared from MPN were stable upon treatment with alcohols at room temperature. The binding behavior was significantly dependent on the surface morphology of MgZnOnano. Graphical abstract The functionalization of MgZnO nanorod films with a click-ready linker and its dependence on bidning conditions and morphology has been studied by FTIR microscopic imaging using the azido group as the IR tag.

Branched open-ended TiO2 nanotubes for improved efficiency of flexible dye-sensitized solar cells

The anatase branched open-ended titanium dioxide (TiO2) nanotubes (NTs) are prepared using a combined method of electrospinning, hydrothermal processing and calcination. The branched open-ended TiO2 NT (BOTNT) is composed a trunk of a large sized NT, from which out growth many branches consisting of single-crystalline TiO2 nanosheets (NSs) and small NTs. The morphology and microstructure of the BOTNTs can be controlled by varying with the hydrothermal treatment time. When it is used in flexible dye-sensitized solar cells (FDSSCs) as multifunctional layer covering on the carbon nanotubes (CNTs) incorporated TiO2 (CNTs/TiO2) nanorods (NRs) layer, a high conversion efficiency of 4.70% is obtained. This efficiency is much higher than that of the cell assembled by the single-layer CNTs/TiO2 NRs film. This is attributed to the great increase in light harvesting efficiency, resulting from excellent light-scattering ability and high specific surface area for dye loading of the BOTNTs. Furthermore, the excellent electron transport ability of the BOTNTs due to their high level of interconnectivity, improves the performance of FDSSCs.

Synergistic Effect of Si Doping and Heat Treatments Enhances the Photoelectrochemical Water Oxidation Performance of TiO2 Nanorod Arrays

TiO2 is a very promising photocatalytic material due to its merits including low cost, nontoxicity, high chemical stability, and photocorrosion resistance. However, it is also known that TiO2 is a wide bandgap material, and it is still challenging to achieve high photocatalytic performance driven by solar light. In this paper, silicon‐doped TiO2 nanorod arrays are vertically grown on fluorine‐doped tin oxide substrates and then are heat treated both in air and in vacuum. It is found that the silicon doping together with the heat treatment brings synergic effect to TiO2 nanorod films by increasing the crystallinity, producing abundant oxygen vacancies, enhancing the hydrophilicity as well as improving the electronic properties. When used as photoanodes in photoelectrochemical water splitting, under the condition of AM 1.5G simulated solar irradiation and without using any cocatalysts, these nanorod films show photocurrent density as high as 0.83 mA cm−2 at a potential of 1.23 V versus reversible hydrogen electrode, which is much higher than that of the TiO2 nanorod films without doping or heat treating. The silicon‐doped TiO2 nanorod array films described in this paper are envisioned to provide valuable platforms for supporting catalysts and cocatalysts for efficient solar‐light‐assisted water oxidation and other solar‐light‐driven photocatalytic applications.

Strontium Titanate Based Artificial Leaf Loaded with Reduction and Oxidation Cocatalysts for Selective CO2 Reduction Using Water as an Electron Donor.

Thin film of SrTiO3 nanorods loaded with reduction and oxidation cocatalysts drove the selective reduction of carbon dioxide (CO2) into carbon monoxide (CO), as well as caused the production of equivalent oxygen molecules through water oxidation under UV irradiation. The described film functioned as a free-standing plate without any bias potential application, similar to a natural leaf. The film was facilely fabricated by a simple hydrothermal and annealing treatment of a titanium substrate to produce the SrTiO3 nanorod film (STO film) followed by two steps of loading the reduction and oxidation cocatalysts onto the surface of the STO. As a reduction cocatalyst, a CuxO nanocluster was chosen to achieve selective reduction of CO2 into CO, whereas a cobalt- and phosphate-based cocatalyst (CoPi) facilitated oxidation on the STO surface to promote oxygen generation. For the photocatalysis test, a wireless film was simply set into an aqueous solution bubbled with CO2 in a reactor, and CO production was observed in the headspace of the reactor under UV irradiation. Compared to the bare STO film, the dual cocatalyst-loaded STO film exhibited 2.5 times higher CO generation. H2 production was very limited in our system, and the amount of molecules generated by the reduction reaction was almost twice that of the generated oxygen molecules, proving that water molecules acted as electron donors. Our artificial leaf consists of abundant and nontoxic natural elements and represents the first achievement of stoichiometric CO2 reduction using water as an electron donor by a free-standing natural leaflike plate form.

A Designed ZnO@ZIF-8 Core-Shell Nanorod Film as a Gas Sensor with Excellent Selectivity for H2 over CO.

The development of H2 gas sensors is important for H2 production as a fuel. In this work, a ZnO@ZIF-8 core-shell nanorod film is designed and synthesized as a gas sensor through a facile solution deposition process. This film shows an excellent selective response for H2 over CO. By fine-tuning the reaction conditions, a ZnO@ZIF-8 core-shell structure with a thin, fine-grain, porous ZIF-8 shell is obtained. Owing to the facile H2 penetration through the ZIF-8 thin shell (≈110 nm) and the increased oxygen vacancies for the complex film, the ZnO@ZIF-8 nanorod film shows a higher H2 sensitivity than a raw ZnO nanorod film. More importantly, the ZnO@ZIF-8 nanorod film shows no response for CO at 200 °C. Because of the fine-grain confinement of the porous ZIF-8 shell (<140 nm), the molecular sieving effect is strengthened, which allows the effective separation of H2 over CO. This work provides a promising strategy for the design of high-performance H2 sensors.

Surface enhanced plasmon effects by gold nanospheres and nanorods in Langmuir-Blodgett films

Hydrophobic gold nanospheres and nanorods were synthesized by a reduction method and a seed-mediated growth method, respectively, and by the surface-modification with 1-dodecanethiol. Langmuir-Blodgett (LB) films of gold nanoparticles were prepared at different surface pressures and two-dimensional ordering of nanoparticles was evaluated. A plasmon band of nanospheres slightly red-shifted from 525nm in water to 543nm in chloroform but it was 634nm at LB film. Plasmon bands at 750 and 515nm of nanorods in water drastically changed to a band at 550nm in chloroform but it appeared at 621 and 1000nm. Moreover, Langmuir monolayer of eiocosanoic acid was transferred on LB films of nanospheres on CaF2 window and transmission surface enhanced infrared absorption spectra (SEIRAS) were measured. A CO stretching vibration band at 1702cm−1 was strongly enhanced compared to other vibration bands due to the selection rule of SEIRAS. That is, the dipole moment of CO stretching mode should be on the same direction as the surface enhanced electric field, which is perpendicular to the gold surface. From the comparison of SEIRAS for poly(amido amine) dendrimer on LB films of nanospheres and nanorods, it is apparent that the enhancement effect of nanorod LB film is higher than that of nanosphere LB film, although the surface coverage and the number density of nanorods in LB film are lower than those of nanosphere LB film, suggesting the effect of hot spots.

Novel nanocellulose/conducting polymer composite nanorod films with improved electrochromic performances

Novel nanocellulose (NC)/conducting polymer (CP) composite nanorod films have been successfully prepared by in situ polymerization. The nanocomposite films showed remarkable enhancement of film forming properties and electrochromic behaviors. The electrochromic properties were improved significantly because of the porous spaces among the NC/CP nanorods, which facilitated the diffusion of electrolyte ions. And the nanocomposite structure also offered larger surface areas for redox reactions. The excellent electrochromic performances of the NC/CP composite nanorod films make them be the promising candidates in electrochromic materials.

Novel CdSe nanorods/porous anodic alumina nanocomposite-based ethanol sensor: sensitivity enhancement by visible light illumination

In this present work, l-cysteine capped CdSe nanoparticles synthesized by a chemical route process were successfully embedded into porous anodic alumina (PAA) template via chemical bath deposition method. CdSe nanorods (NRs) were grown vertically on the PAA template via thermal annealing process at 350 °C under nitrogen. The morphological, structural, and optical properties of the prepared PAA and CdSe/PAA films were investigated in detail. The scanning electron microscopy exhibited the formation of CdSe NRs array with a pyramidal ends onto all sides of PAA matrix. Energy dispersive X-ray analysis confirmed that the prepared CdSe NRs/PAA are made of cadmium, selenium, and alumina materials. X-ray diffraction study revealed that the CdSe layer exhibit a hexagonal structure and the average crystallite size at about 9 nm. PL measurements showed green and bleu emissions peaks located at 2.05 eV and 2.7 that originate from the luminescent CdSe NRs and the oxygen defficiency centers formed in the PAA, respectively. CdSe NRs film on the PAA template was fabricated and employed as gas sensor for the detection of ethanol under visible-light illumination for 25–300 ppm at the optimum working temperature of 200 °C. Light illumination strongly enhance the sensor sensitivity. This effect has been discussed in term of light-matter interaction on the CdSe NRs surface. More hole are probably created which increase the conductance of the sensor and significantly improved the gas response

A facile preparation route of Bi2S3 nanorod films for photocatalytic H2 production from H2S

Photocatalytic splitting of H2S into H2 is beneficial for environmental remediation and clean energy production. However, the conventional photocatalyst in powder form is difficult to recover. In this work, Bi2S3 nanorod films are fabricated via the conversion of Bi films by annealing and hydrothermal treatment. The hydrothermal reaction time has a significant influence on the performance of photocatalytic splitting H2S to H2 over these samples. The optimized hydrothermal treatment time is 24h. Photocurrent and electrochemical impedance spectroscopy confirm that the Bi2S3 nanorod film obtained under this condition has an effective separation of electron-hole pairs, leading to enhanced photocatalytic activity.

Modulating the morphology of ZnO nanotower arrays by replenishing of the reaction precursors and their photodegradation properties

Different layered ZnO nanotower arrays can be successfully grown on ZnO nanorod films by in situ replenishing of the reaction precursors. The volume and timing of replenishment of the reaction precursors plays an important role in controlling the morphology of ZnO nanostructures. Two-layered ZnO nanotower arrays can provide a higher surface-to-volume ratio and more exposed polar surface, resulting in higher photocatalytic activity under 10W UV light irradiation.