Nanorod Films Research Articles

Enhanced Ultraviolet Photodetector Based on Mg-Doped ZnO Nanorods Films

Magnesium-doped zinc oxide (ZnO: Mg) nanorods and nanotubes films were prepared by hydrothermal method deposited on glass substrates. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL), and optical absorption spectroscopy (UV) were performed to characterize the prepared films. X-ray diffraction analysis showed a decrease in the lattice parameters of Mg doped ZnO NRs. The Photoluminescence of the undoped and Mg-doped ZnO NRs displayed a near band edge. At 10 V bias, the metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector performance of the Mg-doped ZnO prepared for various Mg concentrations of 0.0, 0.02, and 0.06 was investigated under radiation of 40μW/cm2 at the wavelengths of 365 and 385 nm UV light. The responsivity, detectivity and quantum efficiency of Mg-doped based on MSM detector were 0.118A/W, 1.0579*1012 and 40.05157 under UV of wavelength 365nm respectively.

Ag2S/ZnO Nanorods Composite Photoelectrode Prepared by Hydrothermal Method: Influence of Growth Temperature

Silver sulfide (Ag2S) attached to ZnO nanorods film has been successfully prepared by a two-step hydrothermal process. The prepared photoelectrodes were characterized by Field Emission Scanning Eletron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), X-ray diffractometry (XRD), UV-vis spectrophotometry (UV–vis) and photoelectrochemical measurements (PEC). The results revealed that Ag2S deposited onto the surface of ZnO nanorods was under the influence of growth temperature. The absorption in the visible region and efficient transfer of photoelectron between Ag2S/ZnO/ITO photoelectrode and the redox species in the electrolyte were significantly enhanced under the illumination intensity of 100 mW cm−2. The band gap values of the five different growth temperatures ranging from 50 °C to 90 °C were found to decrease from 2.93 eV to 1.57 eV. Besides, the photoelectrochemical measurements verified that Ag2S/ZnO nanocomposite grown at 60 °C exhibited the highest photocurrent density of 3.97 mA/cm2 at 1.0 V. The findings suggested that Ag2S/ZnO nanocomposite is an efficient alternative for photoelectrode applications.

Study of Annealing Influence on Basic Properties of Indium Tin Oxide Nanorod Films Deposited Using Glancing Angle Ion-Assisted Electron Beam Evaporation.

Indium tin oxide (ITO) nanorod films were deposited onto glass slides and Si wafers using ionassisted electron beam evaporation with a glancing angle deposition technique. The annealing influence on the basic properties of the as-deposited ITO nanorod films was studied in the range of 100-500 °C for two hours in air. The crystallinity of the ITO nanorod films was enhanced with the increasing annealing temperature, and the average transmission of the as-deposited ITO nanorod films in the visible range was 90%. This value did not change significantly after the annealing process. The optical bandgap of the as-deposited ITO nanorod films was 3.94 eV and increased slightly after annealing. The sheet resistance of the as-deposited ITO nanorod films was 12.9 Ω/ and increased to 57.8 Ω/ at an annealing temperature of 500 °C. The as-deposited ITO nanorod films showed nanorod structures with average diameters of 79 nm, which changed slightly with the annealing temperature. The root mean square roughness of the as-deposited ITO nanorod films was 7.9 nm and changed slightly with annealing. The as-deposited ITO nanorod films had an average contact angle of 110.9°, which decreased to 64.2° at an annealing temperature of 500 °C. The experimental results showed that varying the annealing temperature influenced the structural, electrical and wettability properties of the ITO nanorod films while the optical properties and surface morphology were almost unaffected.

Synthesis and Characterization of c-Axis Oriented Zinc Oxide Thin Film and Its Use for the Subsequent Hydrothermal Growth of Zinc Oxide Nanorods

ABSTRACTOriented ZnO seed layers were deposited by three different techniques, namely, simple drop casting (DC), sol-gel derived dip coating (DPC) and spin coating of ball-milled ZnO powder solution(BMD) for the subsequent growth of vertically aligned ZnO nanorods along the substrate normal. X-ray diffraction (XRD) analyses revealed that ZnO(DC) seed layer exhibit the highest preferential c-axis texturing among the ZnO seed layers synthesized by different techniques. The Scanning Electron Microscopy (SEM) analysis evident that the morphology of ZnO seed layer surface is compact and coherently carpets the underlying substrate. ZnO nanorods(NRs) were then grown by hydrothermal method atop the ZnO seeded and non-seeded substrates grown by different techniques to elucidate the best ZnO seed layer promoting well-aligned ZnO Nanorods. The presence of c-axis oriented ZnO(DC) seeding layers was found to significantly affect the surface morphology and crystallographic orientation of the resultant ZnO NRs films. The optical band gap of ZnO(DC) seed and ZnO NRs were estimated to be 3.30 eV and in the range of 3.18 – 3.25 eV respectively by using UV-VIS-NIR diffuse reflection spectroscopy. The room temperature photoluminescence analyses revealed that nanostructured ZnO films exhibit a sharp near-band-edge luminescence peak at ∼380 nm consistent with the estimated optical band gap and the ZnO nanorod arrays are notably free from defect-related green-yellow emission peaks.

Morphological and structural control of pulse electrodeposited ZnO thin films and its influence on the photoelectrocatalytic degradation of methyl orange

ZnO thin films were obtained by pulsed electrodeposition (PE). A potential of − 1.1 V is applied during the time-On (ton) period, while open-circuit potential is applied during the time-off (toff) period. The effect of the toff duration on the properties of ZnO films and their photoelectrocatalytic activity was studied in detail. Decreasing toff from 7 s to 1 s tailors the structural, morphological and optical properties of ZnO films and improves their photoelectrocatalytic activity. XRD analysis confirms a wurzite hexagonal structure along the (002) direction for all samples. The SEM images show an amelioration of ZnO morphology from nanosheets to nanorods films. The photocurrent response indicates a high value of 480 µA/cm2 for ZnO film deposited at toff = 1 s. All the electrodeposited films were tested for the photoelectrocatalytic degradation of methyl orange (MO). The ZnO film deposited at low toff (1 s) reveals a faster degradation of MO, reaching 67% after 360 min UV-irradiation. This is attributed to the nano-rod morphology that provides greater surface area and to the lower energy band-gap of the sample.

Highly sensitive ultraviolet sensor based on ZnO nanorod film deposited on ST-cut quartz surface acoustic wave devices

A highly sensitive surface acoustic wave (SAW) ultraviolet (UV) detector operated at room temperature was developed using a sensing layer of zinc oxide (ZnO) nanorods (NRs) grown on ST-cut quartz using a hydrothermal method. Under illumination of the UV light with a wavelength of 365 nm and an intensity of 6 μW cm−2, the resonant frequency of the SAW UV sensor based on ZnO NRs/ZnO nanofilm structure was decreased by ~200 Hz, mainly due to electroacoustic effect. The estimated enhancement in the sensitivity based on the experimental results is ~3.5 folds compared to a device with only a thin nanolayer ZnO film. Meanwhile, density of ZnO NRs over the ZnO seed layer was also investigated and an optimum design was proposed.

Defect-Assisted Broad-Band Photosensitivity with High Responsivity in Au/Self-Seeded TiO2 NR/Au-Based Back-to-Back Schottky Junctions.

TiO2 nanorods (NRs) have generated much interest for both fundamental understanding of defect formation and technological applications in energy harvesting, optoelectronics, and catalysis. Herein, we have grown TiO2 NR films on glass substrates using a self-seeded approach and annealed them in H2 ambient to modify their surface defects. It has been shown that broad-band photosensing properties of Au/self-seeded TiO2 NR/Au-based two back-to-back Schottky junctions (SJs) for a broad wavelength of light are much superior as compared to those of the pristine and the control samples. Photoresponsivity values for the H2-annealed sample are 0.42, 0.71, 0.07, and 0.08 A/W for detecting, respectively, 350, 400, 470, and 570 nm lights. Very low dark current and high photocurrent lead to a gain value as high as 1.85 × 104 for 400 nm light. Unprecedentedly modified NR-based SJs show excellent photoresponsivity for detecting as low as 25, 36, 48, and 28 μW/cm2 power densities of 350, 400, 470, and 570 nm lights, respectively. It is found that Ti3+ defects play a key role in an efficient photoelectron transfer from TiO2 to Au. Our work, for the first time, highlights the simplicity and reveals the rationale behind the excellent properties of Au/self-seeded TiO2 NR film/Au back-to-back SJs.

Multifunctional monoclinic VO2 nanorod thin films for enhanced energy applications: Photoelectrochemical water splitting and supercapacitor

Monoclinic VO2 nanorod thin films were deposited on indium‑tin-oxide-coated glass substrates using radio-frequency reactive magnetron sputtering at a substrate temperature of 300°C and various O2 flow rates. The thin films were characterized via standard analysis techniques. The VO2 thin films exhibited a highly crystalline monoclinic phase with an indirect band gap of ~1.73eV. At optimized O2 flow rate (4sccm), the thin films was observed nanorod structures, exhibited a remarkable photocurrent of ~0.08mAcm−2 during photoelectrochemical water splitting in the visible region. Electrochemical performance tests of the nanorod films revealed a specific capacitance of ~486mFcm−2 at a scan rate of 10mVs−1. In addition, amperometric I–t curves showed that VO2 thin film electrodes were highly stable during the photo-oxidation process. The nanorod films also exhibited a good specific capacitance of ~120mFcm−2 after 5000cycles at a scan rate of 100mVs−1. The photocurrents during photoelectrochemical water splitting and the specific capacitance of VO2 thin films deposited at O2 flow rates of 2 and 6sccm were 0.06 and 0.07mAcm−2 and 398 and 37mFcm−2, respectively. The films deposited under Ar at 8sccm and O2 at 4sccm showed the highest photoelectrochemical water splitting performance and specific capacitance, owing mainly to their nanorod-like morphology.

Highly sensitive nitric oxide gas sensor based on ZnO-nanorods vertical resistor operated at room temperature

We successfully demonstrated a simple and low-cost nitric oxide (NO) gas sensor to deliver parts-per-billion (ppb) regime detection at room temperature operation. A vertical-channel ZnO nanorods resistor is fabricated by putting silver nanowire electrode onto the hydrothermal ZnO nanorods film. With suitable process condition, the nanorods film exhibits a uniform morphology to enable the formation of gas-permeable nanowire top electrode while also the nanorods provide good surface-to-volume ratio to deliver strong reaction with NO gas. A detection limit to 10 ppb NO is observed while the sensing dynamic range from 10 ppb to 100 ppb is obtained. The sensor is reversible and the real-time sensing response is within 30 s. The results benefit the NO breath detection for patients with chronic inflammatory airway disease, such as asthma.

Influence of silver electrochemically deposited onto zinc oxide seed nanoparticles on the photoelectrochemical performance of zinc oxide nanorod films

The present article examines the synthesis and characterization of zinc oxide nanorods grown on zinc oxide and silver nanoparticle seeds. Zinc oxide seeds were electrodeposited on a support of fluorine-doped tin oxide glass and heat-treated at 380°C. Silver nanoparticles were then deposited on this substrate, which was heat-treated at 160°C. Their presence was confirmed using ultraviolet–visible spectroscopy, by observing an absorption peak around 400 nm, corresponding to surface plasmon resonance. Growth of zinc oxide nanorods was achieved in a chemical bath at 90°C. The obtained films were analyzed by cyclic voltammetry, X-ray diffraction, and scanning electron microscopy. They consisted of zinc oxide with a Wurtzite-type crystal structure, arranged as nanorods of 50 nm. X-ray photoelectron spectroscopy exhibits peaks attributed to silver (0) and to the formation of silver oxide on the silver nanoparticle surface. In addition, two types of oxygen (O 1 s) were observed: oxygen from the crystalline network (O–2) and chemisorbed oxygen (–OH), for the seed and the nanorod films, respectively. The nanorods grown on zinc oxide seeds with silver deposits had a round shape and greater photoactivity than those grown without silver. This difference is attributed to the additional reflection that silver provides to the light reaching the film, thereby increasing the photogeneration from the charge carriers.

Band gap engineered zinc oxide nanostructures via a sol-gel synthesis of solvent driven shape-controlled crystal growth.

A reliable sol–gel approach, which combines the formation of ZnO nanocrystals and a solvent driven, shape-controlled, crystal-growth process to form well-organized ZnO nanostructures at low temperature is presented. The sol of ZnO nanocrystals showed shape-controlled crystal growth with respect to the solvent type, resulting in either nanorods, nanoparticles, or nanoslates. The solvothermal process, along with the solvent polarity facilitate the shape-controlled crystal growth process, augmenting the concept of a selective adhesion of solvents onto crystal facets and controlling the final shape of the nanostructures. The XRD traces and XPS spectra support the concept of selective adhesion of solvents onto crystal facets that leads to yield different ZnO morphologies. The shift in optical absorption maxima from 332 nm in initial precursor solution, to 347 nm for ZnO nanocrystals sol, and finally to 375 nm for ZnO nanorods, evidenced the gradual growth and ripening of nanocrystals to dimensional nanostructures. The engineered optical band gaps of ZnO nanostructures are found to be ranged from 3.10 eV to 3.37 eV with respect to the ZnO nanostructures formed in different solvent systems. The theoretical band gaps computed from the experimental XRD spectral traces lie within the range of the optical band gaps obtained from UV-visible spectra of ZnO nanostructures. The spin-casted thin film of ZnO nanorods prepared in DMF exhibits the electrical conductivity of 1.14 × 10−3 S cm−1, which is nearly one order of magnitude higher than the electrical conductivity of ZnO nanoparticles formed in hydroquinone and ZnO sols. The possibility of engineering the band gap and electrical properties of ZnO at nanoscale utilizing an aqueous-based wet chemical synthesis process presented here is simple, versatile, and environmentally friendly, and thus may applicable for making other types of band-gap engineered metal oxide nanostructures with shape-controlled morphologies and optoelectrical properties.

Influence of the aqueous solution composition on the morphology of Zn1−xMgxO films deposited by spray pyrolysis

Compact films and nanorod films of Zn1−xMgxO with specific Mg contents were deposited by spray pyrolysis of varyingly composed aqueous solutions

All-Solid-State Electrochromic Device Based on Nanocellulose/PANI/PEDOT Ternary Hybrid System for High Optical Contrast and Excellent Cycling Stability

In this work, we present a novel all-solid-state electrochromic device based on a nanocellulose(NC)/polyaniline(PANI)/poly(3,4-ethylenedioxythiophene)(PEDOT) hybrid film system. This ternary hybrid system was composed of the rod-like NC/PANI/PEDOT nanocomposites with a core/shell structure using NC as matrix material and PANI and PEDOT as coating electrochromic functional components, which was prepared via in situ chemical oxidative polymerization. The resultant ternary NC/PANI/PEDOT core/shell nanorod film shows significant optical contrast (61% at 665 nm), short response time (1.2 s for coloring, 1.3 s for bleaching), high coloration efficiency (214.5 cm2/C) and good cycling stability (sustaining 85.6% of its initial contrast after subjecting 5000 s). Moreover, the all-solid-state electrochromic device (ECD-NPE) is successfully fabricated by assembling NC/PANI/PEDOT and PEDOT: poly(styrenesulfonate)(PSS) films as the anode and cathode, respectively. Large contrast ratio, fast switching speed, high coloration efficiency and excellent cycling stability (optical contrast decay of only 4.7% after cycling 5000 s) are achieved by the assembled ECD-NPE. The fascinating electrochromic device exhibits promising features for a wide range of applications in buildings, airplanes, automobiles, etc.

Preparation and Characterization of Te/Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)/Cu7Te4 Ternary Composite Films for Flexible Thermoelectric Power Generator.

In this work, Te/poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/Cu7Te4 ternary thermoelectric (TE) nanocomposite films were successfully fabricated by physical mixing and then drop casting. An optimum power factor of 65.3 μW/mK2 was acquired from a composite film containing 95 wt % PEDOT:PSS-coated Te (PC/Te) nanorods at 300 K, which was about 5 times as large as that of the PC/Cu7Te4 nanorod film and about 3 times as large as that of the PC/Te nanorod film. The power factor reached 112.3 μW/mK2 when the temperature was 380 K. Scanning transmission electron microscopy (STEM) and high-resolution STEM were used to observe the detailed internal microstructure of the composite film, revealing that the Te nanorods were single crystalline and the Cu7Te4 rods polycrystalline. The composite film was in fact a three-dimensional network interconnected with the PC/Te and PC/Cu7Te4 nanorods. The enhancement of the TE properties was ascribed to the synergetic effect of the two kinds of nanorods and the double-carrier filtering effect at the two heterointerfaces of Te/PEDOT:PSS and Cu7Te4/PEDOT:PSS. An eight single-leg flexible TE device consisting of the optimized composite film was fabricated, which produced a voltage of 31.2 mV and a maximum output power of 94.7 nW at a temperature gradient of 39 K.

Optical properties of ZnO nanorod films prepared by CBD method

ZnO nanorods were grown on ITO substrate by CBD method. The XRD and SEM show that nanorods with hexagonal column structure were uniformly distributed. Then the optical properties of NRs were investigated. The transmittance spectrum shows a sharp absorption edge in the UV region. The reflection spectrum has a certain oscillation frequency, so the thickness of film can be obtained by the principle of light interference. The PL spectrum shows a UV emission peak at about 380 nm and a broad green emission centered at around 550 nm. By readily adjusting the preparation parameters, the green emission was very weak.

Designed growth of WO3/PEDOT core/shell hybrid nanorod arrays with modulated electrochromic properties

Designed growth of tungsten oxide (WO3)/poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell hybrid nanorod arrays has been obtained by combining solvothermal and in situ electropolymerization techniques. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and Raman characterization results indicate that the hybrid nanorods are composed of single crystalline WO3 nanocores wrapped by thin amorphous PEDOT nanoshells. The hybrid nanorods exhibit promising electrochromic performance of much shorter response time (3.8 s for coloring and 3.6 s for bleaching) than the bare WO3 nanorods (12.4 s for coloring and 7.6 s for bleaching), while the optical contrast of the hybrid nanorods increases from 26% of PEDOT to 72% in 633 nm. And the coloring efficiency and stability of the core/shell hybrid nanorods are also enhanced compared to the individual components. Dynamic analysis suggests a synergistic effect between the WO3 nanocore and the PEDOT nanoshell. In addition, color depth and optical contrast of the hybrid nanorods can be modulated by adjusting the applied voltage and the deposition of the PEDOT nanoshell. The hybrid nanorod films obtained by the cost-effective wet chemical methods may find promising applications in energy-saving windows, smart displays as well as other energy efficient technologies.

Enhanced cellular osteogenic differentiation on Zn-containing bioglass incorporated TiO2 nanorod films.

Surface nanotopography and bioactive ions have been considered to play critical roles on the interactions of biomaterials with cells. In this study, a TiO2 nanorod film incorporated with Zn-containing bioactive glass (TiO2/Zn-BG) was prepared on tantalum substrate, trying to evaluate the synergistic effects of nanotopograpgy and bioactive ions to promote cellular osteogenic differentiation activity. The expression of osteogenic-related genes, ALP as well as the ECM mineralization on TiO2/Zn-BG film were significantly upregulated compared to that of the film without TiO2 nanorod nanostructure (Zn-BG) or without Zn (TiO2/BG). Moreover, a much low Zn2+ release level on TiO2/Zn-BG film was beneficial to promote the osteogenesis, which could be ascribed to that a semi-closed space established by TiO2 nanorods with adhered cells provided an appropriate micro-environment that facilitated Zn2+ adsorption.

“Carbon‐Glue” Enabled Highly Stable and High‐Rate Fe3O4 Nanorod Anode for Flexible Quasi‐Solid‐State Nickel–Copper//Iron Alkaline Battery

AbstractThe practical application of iron oxide anode in rechargeable alkaline batteries is greatly hampered by the poor electrochemical stability and low rate capability. In addition, flexible solid‐state iron anode‐based rechargeable batteries with distinctive counter electrode coupling are quite lacking. Herein, an interesting “carbon glue” penetration strategy toward Fe3O4 nanorod film anode is proposed. This design not only immobilizes the nanorods and maintains strong adhesion with the current collector but also ensures continuous electrically conductive pathway, resulting in dramatically increased stability (≈99% capacity retention after 1000 cycles) and excellent rate performance (1.2 min charging with ≈70.6% initial capacity kept). By pairing with a new‐type Ni0.49Cu0.51O nanowire array cathode, a unique 1.2 V flexible rechargeable nickel–copper//iron alkaline battery is further assembled, which stores energy based on redox electrochemistry of transition metal ions. It delivers high volumetric energy and power densities (7.21 mWh cm−3; 299.30 mW cm−3), and demonstrates outstanding stability up to 5000 cycles. In particular, with the utilization of quasi‐solid‐state electrolyte, the device still maintains good performance upon substantially bending and twisting. This work presents a new concept to design high stability iron anode‐based alkaline batteries and further pushes forward the development of emerging flexible energy storage systems.

Ultrahigh supercapacitance in cobalt oxide nanorod film grown by oblique angle deposition technique

Nanorod films of cobalt oxide (Co3O4) have been grown by a unique oblique angle deposition (OAD) technique in an e-beam evaporator for supercapacitor electrode applications. This technique offers a non-chemical route to achieve large aspect ratio nanorods. The fabricated electrodes at OAD 80° exhibited a specific capacitance of 2875 F/g. The electrochemically active surface area was 1397 cm−2, estimated from the non-Faradaic capacitive current region. Peak energy and power densities obtained for Co3O4 nanorods were 57.7 Wh/Kg and 9.5 kW/kg, respectively. The Co3O4 nanorod electrode showed a good endurance of 2000 charge-discharge cycles with 62% retention. The OAD approach for fabricating supercapacitor nanostructured electrodes can be exploited for the fabrication of a broad range of metal oxide materials.

Enhanced luminescence and prolonged lifetime of Eu-PMMA films based on Au@SiO2 plasmonic hetero-nanorods

In this work, the nanorod films were prepared by aggregating Au@SiO2 core-shell hetero-nanorods on surface of silica. The distribution of nanorod film is dependent upon the concentration of nanorods. The nanorod films prepared are used to be an excellent metal enhanced luminescence substrates. The high performance polymer luminescence using the plasmonic effect of nanorods are demonstrated. The photoluminescence intensity of the Eu(dbm)3phen doped films with Au@SiO2 nanorod films is increased by more than 200 times due to the great coupling between photons and a localized surface plasmonic resonances (LSPR), the best enhancement increases up to 263 folds. And the lifetime is prolonged. The lifetime ranged from 546 μs to 625 μs. In addition, the quantum yield is increased from 0.98% to 21.6%. We attribute the results to the change of the density of electron states. The strong luminescent and prolonged luminescence lifetime may have promising applications in many fields.