Experimental investigation on the structural,dielectric, ferroelectric and piezoelectric properties of La doped ZnO nanoparticles and their application in dye-sensitized solar cells

Pure and lanthanum (La) doped ZnO nanorods were synthesized via co-precipitation method. The structure and morphology of as grown ZnO and La-ZnO nanoparticles were studied using transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) methods. The values of remnant polarization and coercive field were found to be 0.027 μC/cm² and 1.33 kV/cm, respectively, for as grown La-ZnO nanostructures. High Curie temperature (276 °C) for doped ZnO was observed in dielectric study. Piezoelectric coefficient at room temperature was found to be 101.30 pm/V. I-V characteristics were studied for both pure and doped ZnO nanoparticles. Photo-anodes of dye-sensitized solar cells (DSSCs) were made using ZnO and La-ZnO nanorods. The conversion efficiency and short circuit current density of La-ZnO nanorods based DSSC were 0.36% and 1.31 mA/cm², respectively, which were found to be largely enhanced when compared with that of pure ZnO based DSSC (0.20% and 0.94 mA/cm²).     

CVD合成的掺杂BNx-石墨烯纳米复合材料:结构和发光性能

用B₄C为硼源,利用CVD系统在N₂-H₂等离子体中合成了掺杂BN_x纳米棒,接着在掺杂BN_x纳米棒表面用CH₄生长了石墨烯纳米片,制备出掺杂BN_x-石墨烯三维纳米复合材料。一系列表征结果说明合成的纳米复合材料由C和O共掺杂的BN_x纳米棒和石墨烯纳米片组成,其形成与碳氢基团的转换和掺杂BN_x纳米棒的形变在石墨烯纳米片中产生的应力有关。室温发光性能表明石墨烯纳米片对掺杂BN_x纳米棒的紫外光和绿光有明显的猝灭作用,起源于掺杂BN_x-石墨烯界面上的电荷转移和电子散射。     

Room temperature ferromagnetism in Fe doped CuO nanorods

One dimensional CuO and Fe doped CuO nanorods have been synthesized by template free solution phase hydrothermal methods. The typical diameter and the length of the Cu_1−xFe_xO nanorods (x=0, 0.02, 0.05, 0.10) are 20-25 and 300-400 nm. Pure CuO nanorods show weak ferromagnetism and the introduction of Fe within CuO lattice improves significantly the ferromagnetic property with the Curie temperature far above room temperature. The shape anisotropy is the key point to understand ferromagnetism in Fe doped CuO nanorods.     

Dopant size dependent variable range hopping conduction in polyaniline nanorods

The present work investigates the electrical transport and dielectric relaxation of polyaniline (PAni) nanorods doped with organic camphorsulfonic acid (CSA) and inorganic hydrochloric acid (HCl) synthesized by interfacial polymerization technique. High resolution transmission electron micrographs (HRTEM) depict that initially spherical nuclei directionally grow into nanorods and CSA doped PAni produces more uniform and aligned structures. The electrical transport studies reveal that the CSA doped nanorods follow 1D Mott variable-range hopping (VRH), whereas the HCl doped nanorods exhibit 2D VRH conduction mechanism. The value of interchain charge transfer integral is found to be higher for smaller size HCl doped PAni than that for larger size CSA doped PAni. The resistivity measurements exhibit semiconducting behavior for both organic and inorganic dopants and the resistivity of the CSA doped nanorods is found to be smaller than that of the HCl doped nanorods. The dielectric relaxation studies suggest Debye type relaxation with a single relaxation peak for both the dopants and the relaxation time of the carriers of the CSA doped PAni nanorods is smaller than that of the HCl doped nanorods.     

Observation of memory behaviour in cadmium sulphide nanorods doped ferroelectric liquid crystal mixture

In this study, cadmium sulphide (CdS) nanorods doped ferroelectric liquid crystal (FLC) sample cells have been prepared and studied. A memory effect has been observed in CdS nanorods (≤0.3?wt%) doped FLC mixture and confirmed by textures, dielectric and optical studies. The addition of nanorods increases the memory behaviour and efficiency. The occurrence of memory behaviour has been explained due to charge transfer from liquid crystal molecules to CdS nanorods and exists there for 5–15?min in 0.1–0.3?wt% CdS nanorods doped samples. An improvement in polarization, switching time, threshold voltage and rise time parameters has also been noticed in CdS nanorods doped FLC samples.     

In掺杂的ZnO纳米棒的共振Raman光谱研究

本文报道In掺杂ZnO纳米棒的成功制备和对其结构以及光荧光性能的详尽研究。在室温条件下ZnO的共振拉曼谱线容易受到很强的荧光干扰, 甚至导致共振拉曼谱线完全被湮没。微量In掺杂入ZnO纳米棒中, 调控紫外发光峰由378 nm(纯ZnO)红移至397 nm; 另外, 在制备过程中引入过量的氧, 在样品中产生大量缺陷, 降低了ZnO的紫外近带边发光峰强度。这两方面导致在室温下可清楚的观察到In掺杂ZnO纳米棒的6阶LO拉曼峰。     

Intrinsic defects, impurities and doping in ZnO nanorods grown at low temperature

We report on the defect properties of single-crystalline ZnO nanorods grown from solutions at temperatures below 90 °C. The nanorods can easily be doped by providing impurity precursors during growth. In the as-grown state the nanorods exhibit considerable lattice strain and distortions which compromise their electrical and optical properties. Upon annealing at moderate temperatures of <400 °C the lattice strain is converted into dislocation-type defects, and the dopant impurities become optically active. In the annealed state the near-bandgap photoluminescence quantum efficiency is improved more than 5 times and reaches ～16 % at room temperature. Thus with moderate annealing, interesting device applications become feasible for nanorods grown at T<90 ^°C.     

Synthesis and properties of boron doped ZnO nanorods on silicon substrate by low-temperature hydrothermal reaction

Boron doped ZnO nanorods were fabricated by hydrothermal technique on silicon substrate covered with a ZnO seed layer. It is found that the concentration of boric acid in the reaction solution plays a key role in varying the morphology and properties of the products. The growth rate along the [0 0 0 1] orientation (average size in diameter) of the doped ZnO nanorods decreased (increased) with the increase of boric acid concentration. Based on the results of XRD, EDX and XPS, it is demonstrated that the boron dopants tend to occupy the octahedral interstice sites. The photoluminescence of the ZnO nanorods related to boron doping are investigated.     

Fabrication and characterization of ZnO and ZnMgO nanostructures grown using a ZnO/ZnMgO compound as the source material

ZnO and ZnMgO nanostructures were synthesized on Si (1 0 0) substrates with the assistance of a gold catalyst, using a thermal evaporation method with a ZnO/ZnMgO compound as the source material. The substrates were placed in different temperature zones. ZnO nanostructures with different morphologies and different compounds were obtained at different substrate temperatures. Nanostructures with nanorods and nanosheets morphologies formed in the low and high temperature zones, respectively. The nanorods grown in the low temperature zone had two phases, hexagonal and cubic. Energy dispersive X-ray (EDX) results showed that the nanorods with a cubic shape contained more Mg in comparison to the nanowires with a hexagonal shape. We found that the substrate temperature and the gold catalyst were two key factors for the doping of Mg and the formation of nanostructures with different morphologies. Room temperature photoluminescence spectroscopy showed a blue-shift for the nanostructures with the nanorods morphology. This shift could be attributed to Mg effects that were detected in the nanorods.     

Self-assembly of doped semiconductor nanocrystals leading to the formation of highly luminescent nanorods

Meso-scale self-assembly of doped semiconductor nanocrystals leading to the formation of monocrystalline nanorods showing enhanced photo- and electro-luminescence properties are reported. Polycrystalline ZnS: Cu⁺-Al³⁺ nanoparticles of zinc-blended (cubic) structure with an average size of ∼4 nm were aggregated in aqueous solution and grown into nanorods of length ∼400 nm and aspect ratio ∼12. Transmission electron microscope (TEM) images indicate crystal growth mechanisms involving particle-to-particle oriented-attachment assisted by sulphur-sulphur catenation leading to covalent-linkage. The nanorods exhibit self-assembly dependant luminescence properties such as quenching of the lattice defect-related emissions accompanied by enhancement of dopant-related emission, efficient low-voltage electroluminescence (EL) and super-linear voltage-brightness EL characteristics. This study demonstrates the technological importance of aggregation based self-assembly in doped semiconductor nanosystems.     

Spontaneous organisation of ZnS nanoparticles into monocrystalline nanorods with highly enhanced dopant-related emission

A natural self-assembly process of semiconductor nanoparticles leading to the formation of doped, monocrystalline nanorods with highly enhanced dopant-related luminescence properties is reported. ∼4 nm sized, polycrystalline ZnS nanoparticles of zinc-blende (cubic) structure, doped with Cu⁺-Al³⁺ or Mn²⁺ have been aggregated in the aqueous solution and grown into nanorods of length ∼400 nm and aspect ratio ∼12. Transmission electron microscopic (TEM) images indicate crystal growth mechanisms involving both Ostwald-ripening and particle-to-particle oriented-attachment. Sulphur-sulphur catenation is proposed for the covalent-linkage between the attached particles. The nanorods exhibit self-assembly mediated quenching of the lattice defect-related emission accompanied by multifold enhancement in the dopant-related emission. This study demonstrates that the collective behavior of an ensemble of bare nanoparticles, under natural conditions, can lead to the formation of functionalized (doped) nanorods with enhanced luminescence properties.     

Effect of KOH molarity and annealing temperature on ZnO nanostructure properties

In this work, ZnO nanorods (NRs) were fabricated using a low cost chemical bath deposition (CBD) method. The effect of the potassium hydroxide concentration on the fabricated ZnO nanostructures was studied in depth. The optical, structure, and surface morphology properties of the fabricated ZnO nanostructures were investigated using Uv-vis spectroscopy, XRD, and SEM. The results indicate that the formation of hexagonally structured ZnO nanorods with different lengths and diameters was dependent on the KOH concentration. The sample prepared with 2 M of KOH was the best one for optoelectronic applications, since it has the smallest diameters. This sample was annealed at different temperatures (473 K–1073 K). Positron Annihilation Lifetime Spectroscopy was used to determine the defects in the ZnO nanorods. The results show that the positron mean lifetime (τ_m) decreased as the annealing temperature increased, which means that the overall defects in the ZnO nanorods decreased with increasing temperature. Consequently, higher performance semiconductor devices based on ZnO nanorods could be fabricated after high annealing of the ZnO nanorods.     

Preparation and Characterization of Mn Doped ZnO Nanorods

Physics of the Solid State - Mn doped ZnO nanorods were prepared by chemical precipitation method. The micro-structural and structural properties of the nanorods were calculated from the X-ray...     

Iron doped vanadium sulfide anemone like nanorod structure for electrochemical water oxidation

Bare and Fe doped vanadium sulfide nanorods was synthesized by employing sol-gel method. The obtained (011) plane revealed and confirmed the orthorhombic phase of vanadium sulfide (VS). Fe doped vanadium sulfide anemone like nanorods structure were demonstrated by morphological evolution employing SEM studies. FTIR studies confirmed the vibrational frequencies of the prepared samples and identify the functional groups. Raman technique is also used to observe the vibrational modes of molecules and PL revealed the prepared samples optical-electronic nature. Additionally, electrochemical studies such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoampherometry (CA) was recorded for determination of specific capacitance, current density and stability. High doped vanadium sulfide has elevated 1372 F/g specific capacitance at 385 mA/g current density attained from CV and LSV curves at 10 mV/s and it has proven the excellent OER activity.     

Au/TiO2 nanorod‐based Schottky‐type UV photodetectors

TiO₂ nanorods (NRs) were synthesized on fluorine‐doped tin oxide (FTO) pre‐coated glass substrates using hydrothermal growth technique. Scanning electron microscopy studies have revealed the formation of vertically‐aligned TiO₂ NRs with length of ～2 µm and diameter of 110–128 nm, homogenously distributed over the substrate surface. 130 nm thick Au contacts using thermal evaporation were deposited on the n‐type TiO₂ NRs at room temperature for the fabrication of NR‐based Schottky‐type UV photodetectors. The fabricated Schottky devices functioned as highly sensitive UV photodetectors with a peak responsivity of 134.8 A/W (λ = 350 nm) measured under 3 V reverse bias. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth, properties and dye-sensitized solar cells–applications of ZnO nanorods grown by low-temperature solution process

Hexagonal-shaped small ZnO nanorods were grown in a large-quantity via simple aqueous solution process by using zinc nitrate as a source of zinc ions at low temperature under stirring. The as-grown hexagonal-shaped ZnO nanorods were characterized in detail in terms of their structural, optical and photovoltaic properties. The detailed structural investigations by HRTEM, SAED and FFT revealed that the as-synthesized ZnO nanorods are well-crystalline, possessing a perfect hexagonal ideal growth habits of wurtzite zinc oxide and grown along the [0001] direction in preference. The optical properties, composition and quality of the as-synthesized nanorods were examined by using UV-visible and FTIR spectroscopy. Moreover, films of as-grown nanorods were used as photoanode materials to fabricate the dye sensitized solar cells (DSSCs). An overall light to electricity conversion efficiency of 0.70% with a fill factor of 47.2%, short-circuit current of 1.8 mA/cm² and open-circuit voltage of 0.76 V were achieved for the solar cell based on hexagonal-shaped small ZnO nanorods.     

Investigation of Cu Doping,Morphology and Annealing Effects on Structural and Optical Properties of ZnO:Dy Nanostructures

Dysprosium (Dy) doped ZnO nanosheets and nanorods were synthesized by hydrothermal method. Effects of Cu doping, morphology and annealing in Oxygen ambient on structural and optical properties of ZnO nanostructures were investigated using X–ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectra (DRS) and photoluminescence (PL) spectroscopy. This study recommends that both of intrinsic and extrinsic defects facilitate energy transfer (ET) from the ZnO host to Dy³⁺ ions and consequently have an effective role on producing intense Dy emissions at indirect excitation. The results also revealed that annealing process improved the crystal structure of ZnO nanorods due to decrease of surface; however decreased ET and Dy emissions because of diminishing in oxygen vacancy. In addition, as a result of increasing of surface area in nanorods compared to nanosheets, the oxygen vacancies and ET were enhanced. Moreover the results exhibited that electrical and optical properties of ZnO:Dy can be tuned by various amount of Dy concentrations and also Cu doping.     

温和的苯热溶剂条件下GaP纳米棒的形成机理研究

采用金属Na，白磷和GaCl₃为原料，在温和的苯热溶剂条件下制备了直径为20—40nm，长度为200—500nm的GaP纳米棒和直径为20—40nm的球形颗粒.利用X射线衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)研究了反应条件对产物结晶性和形貌的影响.实验结果表明，当反应温度低于250℃时，产物基本上为GaP纳米棒，并随着反应温度升高，产物逐渐转化为球形纳米颗粒；当反应温度超过280℃时，产物完全为规则的球形.同时，GaP纳米棒的生长遵循SLS生长机理. 关键词： 纳米GaP 苯热 SLS生长机理     

Surface morphology of GaN nanorods grown by catalyst-free hydride vapor phase epitaxy

GaN nanorods were grown on c-plane sapphire substrates by using catalyst-free hydride vapor phase epitaxy (HVPE). The effects of substrate temperature, Ga boat temperature, and Ga pretreatment on the surface morphology of GaN nanorods were investigated. From the dependence of a radial and axial growth rate on the substrate temperature, the kinetically limited process was found to be a rate determining step in the growth of GaN nanorods in HVPE. In addition, the activation energy of the growth along the both axial and radial directions were estimated. The dependence of a Ga boat temperature and the Ga pretreatment effect revealed that the density of nanorods were dependent on the flux of Ga species on the substrate.     

Growth of ZnO nanorods by aqueous solution method with electrodeposited ZnO seed layers

ZnO nanorod arrays on ZnO-coated seed layers were fabricated by aqueous solution method using zinc nitrate and hexamethylenetetramine at low temperature. The seed layers were coated on ITO substrates by electrochemical deposition technique, and their textures were dominated by controlling the deposition parameters, such as deposition potential and electrolyte concentration. The effects of the electrodeposited seed layers and the growing parameters on the structures and properties of ZnO nanorod arrays were primarily discussed. The orientation and morphology of both the seed layer and successive nanorods were analyzed by using X-ray diffraction (XRD), SEM and TEM. The results show that the seed layer deposited at −700 mV has evenly distributed crystallites and (0 0 2) preferred orientation; the density of resultant nanorods is high and ZnO nanorods stand completely perpendicular onto substrates. Meanwhile, the size of nanorods quite also depends on the growth solution, and the higher concentration of growth solution primary leads to a large diameter of the ZnO nanorods.