A facile method to prepare PbS nanorods

PbS nanorods with an average diameter of about 30 nm have been successfully prepared through a simple polyglycol-assisted route for the first time. The obtained PbS nanorods have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electronic diffraction (SAED). Experiments show that polyglycol plays an important role for the control of the morphology of PbS nanostructures. The preliminary result of the UV-vis absorption spectrum of the PbS nanorods is also presented.     

Electrical transport studies of individual IrO(2) nanorods and their nanorod contacts

We have studied the electrical transport properties of individual single-crystalline IrO(2) nanorods prepared by the metal-organic chemical vapour deposition method. With the help of the standard electron-beam lithographic technique, individual nanorods are contacted by Cr/Au submicron electrodes from above. Utilizing two-probe, three-probe and four-probe measurement configurations, not only the intrinsic electrical transport properties of the individual nanorods but also the electronic contact resistances, R(c)(T), have been determined from 300?K down to liquid-helium temperatures. Our measured resistivity behaviour of the nanorods is in close agreement with the current theoretical understanding of this rutile material. On the other hand, we found that the temperature behaviour of the electronic contact resistance obeys the law [Formula: see text] over an extremely wide temperature range, from approximately 100?K down to liquid-helium temperatures. This latter conduction process is ascribed to the hopping of electrons through nanoscale Cr granules and/or an amorphous coating incidentally formed at the interface between the submicron Cr/Au electrode and the nanorod.     

Synthesis and characterization of ultra small PbS nanorods in sucrose ester microemulsion

In the present study, we report for the first time the synthesis of ultra small PbS nanorods in a non-ionic sugar based water-in-oil (w/o) microemulsion system using food grade sucrose ester as surfactant. PbS was formed by mixing lead nitrate and thioacetamide in the water core of the microemulsion system. The as-prepared PbS nanorods were characterized by X-ray diffractometry (XRD), uv–visible absorption spectroscopy (UV–VIS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The diameter of the PbS nanorods were found to be extremely small, which is in the range of 2.64 nm to 2.91 nm depending on reaction aging time. Spherical PbS nanoparticles were formed after 12 h and PbS nanorods were formed after more than 1 day of reaction aging time.     

Conductance, surface traps, and passivation in doped silicon nanowires

We perform ab initio calculations within the Landauer formalism to study the influence of doping on the conductance of surface-passivated silicon nanowires. It is shown that impurities located in the core of the wire induce a strong resonant backscattering at the impurity bound state energies. Surface dangling bond defects have hardly any direct effect on conductance, but they strongly trap both p- and n-type impurities, as evidenced in the case of H-passivated wires and Si/SiO2 interfaces. Upon surface trapping, impurities become transparent to transport, as they are electrically inactive and do not induce any resonant backscattering.     

Enhanced visible-light-responsive photocatalytic property of CdS and PbS sensitized ZnO nanocomposite photocatalysts

CdS and PbS nanoparticles sensitized ZnO nanorods were synthesized by successive ionic layer adsorption and reaction method. The photocatalytic activity of different structures was evaluated by photocatalytic degeneration yield of methyl orange. Co-sensitization of CdS and PbS nanoparticles on ZnO nanorods showed enhanced photocatalytic activity due to its response at visible light area and the stepwise band gap constructed in ZnO/CdS/PbS nanostructures.     

Shape control of PbS nanocrystals using multiple surfactants

A novel technique is presented for preparing PbS nanorods with all spatial dimensions comparable to the excitonic Bohr radius of PbS. The shape of the PbS nanocrystals is entirely controlled by using a combination of three different surfactants with different end functional groups. Oleylamine, oleic acid and trioctylphosphine are used to tune the shape of the PbS nanocrystals from cubic, stars, to rods and then to branched nanowires. The PbS nanorods have rock-salt structure with growth along the [220] direction.     

Polymer assisted preferential growth of PbS and PbS:Mn nanorods: structural and optical properties

We report here the structural and optical properties of PbS and PbS:Mn nanorods (diameter 30–80 nm) grown in a polymer (polypyrrole) matrix. X-ray diffraction data of nanorods clearly reveals preferential growth of PbS nanorods with a strong lattice distortion from a bulk cubic to tetragonal one. The strain introduced lattice distortion is inherent to the growth process and strongly depends on polymer concentration. The polymer concentration is found to play an important role in controlling the structural properties. The effect of Mn²⁺ incorporation into PbS lattice shows no appreciable change in the structural properties. Optical absorption behaviors in such PbS and PbS:Mn nanorods are also reported. The absorption peak energy shows blue-shift with increase in Mn²⁺ concentration to some critical value beyond which red-shift is observed.     

Preparation and photoluminescence properties of reverse type-I ZnO/PbS core/shell nanorods

ZnO/PbS one-dimensional core/shell nanorods have been fabricated by a two-step growth method. Photoluminescence properties of these samples with different shell thickness are studied in detail. The result reveals that the photoluminescence intensity of the ZnO/PbS core/shell nanorods changes with the increase of thickness of PbS shell. When the shell is very thin, the increase in photoluminescence intensity is attributed to the modification of surface defect state. When the shell becomes thicker, the formation of a reverse type-I band alignment between the core and shell is ascribed to be the factor resulting in the decrease in intensity of the photoluminescence properties.     

A Novel Hydrothermal Synthesis of Single Crystalline PbS Nanorods and Their Characterization

1.IntroductionDuring the past decade,one-dimensional(1D)nanos-tructures,such as nanorods,nanowires,nanobelts andnanotubes,have attracted increasing attentions due totheir novel electrical,optical and magnetic properties,and their potential applications in nanoscale eletronics,photonics and functional materials[1~3].Great effortshave been made to prepare1D semiconductor nanostruc-tures such as Si nanowires[4],ZnO nanorods[5]and GaNnanowires[6].At the same time,chalcogenide nanostruc-tures su…     

Nonlinear optical properties of the PbS nanorods synthesized via surfactant-assisted hydrolysis

PbS nanorods were synthesized by surfactant-assisted homogenous hydrolysis. The products were characterized by UV–vis spectrophotometer, X-ray powder diffraction (XRD) and transmission electron microscope (TEM). PbS nanorods were measured by the Z-scan technique to investigate the third-order nonlinear optical (NLO) properties. The result of the NLO measurements shows that the PbS nanorods have the third-order nonlinear optical properties of both NLO absorption and NLO refraction with self-focusing effects. The nonlinear absorption coefficient and refractive index of the PbS nanorods are 2.16 × 10^− 9 m/W and 3.52 × 10^− 16 m²/W respectively.     

Synthesis of single-crystal PbS nanorods via a simple hydrothermal process using PEO-PPO-PEO triblock copolymer as a structure-directing agent

Single-crystal PbS nanorods were successfully synthesized through a simple hydrothermal route using PEO-PPO-PEO triblock copolymer (P123) as a structure-directing agent. The XRD pattern indicates that the crystal structure of the nanorods is face-centre-cubic rocksalt. A SEM image shows that the nanorods have a diameter of 40-70 nm and a length of 200-600 nm, and both tips exhibit taper-like structures. HRTEM and SAED images reveal the single-crystalline nature of the nanorods with the growth along the (111) direction. The experimental results indicated that the P123 concentration and reaction temperature played important roles in controlling the morphology of the PbS nanostructures. The optical property of PbS nanorods was investigated by UV-Vis absorption spectroscopy and the band structure was calculated by the B3LYP hybrid density functional theory.     

Large scale hydrothermal synthesis of PbS nanorods

PbS nanorods with a diameter of 20-50 nm have been synthesized successfully by surfactant-assisted hydrothermal route. The product was over 90% yield according to the amount of Pb(CH₃CHOO)₂ used. Experiments showed that the concentration of N-cetyl-N,N,N-trimethyl- ammonium bromide (CTAB) and thiourea (Tu), reaction time and sulfur sources played important roles in the formation of the PbS nanorods. A reasonable mechanism for the formation of the PbS nanorods is also discussed.     

Thermoelectric Transport Properties of a Quantum Wire,Coupled to a Quantum Dot: Finite Band Effects

We study the thermoelectric transport properties through a quantum wire, modeled on a tight-binding linear chain, with an embedded gate-defined quantum dot. We obtain the thermopower, thermal conductance and electrical conductance with a lateral Fano resonance, linked to a many-body renormalized quantum dot resonant level at the edge of the conduction band strongly hybridized with the van Hove singularity of the one-dimensional density of states of the lead; this resonance appears above the Kondo temperature and is due to a quantum interference thermally activated. We discuss the possibility of practical application of the system to a mesoscopic cooling process and thermopower generators, based on the thermoelectric figure of merit and thermal conductance values. Our results for the thermal transport properties are consistent with those obtained previously for electronic transport.     

Large intrinsic energy bandgaps in annealed nanotube-derived graphene nanoribbons

The usefulness of graphene for electronics has been limited because it does not have an energy bandgap. Although graphene nanoribbons have non-zero bandgaps, lithographic fabrication methods introduce defects that decouple the bandgap from electronic properties, compromising performance. Here we report direct measurements of a large intrinsic energy bandgap of approximately 50 meV in nanoribbons (width, approximately 100 nm) fabricated by high-temperature hydrogen-annealing of unzipped carbon nanotubes. The thermal energy required to promote a charge to the conduction band (the activation energy) is measured to be seven times greater than in lithographically defined nanoribbons, and is close to the width of the voltage range over which differential conductance is zero (the transport gap). This similarity suggests that the activation energy is in fact the intrinsic energy bandgap. High-resolution transmission electron and Raman microscopy, in combination with an absence of hopping conductance and stochastic charging effects, suggest a low defect density.     

Stress dependent band gap shift and valence band studies in ZnO nanorods

ZnO nanorods are grown on seedless and ZnO seeded glass substrates using chemical solution method and their structural, morphological, optical and valence band studies have been carried out. On seedless substrate horizontal nanorods are observed whereas for the seeded substrates vertically aligned hollow and solid nanorods grows. X-ray diffraction analysis revealed the presence of tensile stress in the vertical nanorods. Blue shift has been observed in the band gap of the vertical nanorods as compared to the horizontal nanorods which is attributed to the presence of tensile stress in the vertically aligned nanorods. Photoluminescence spectra revealed the dominance of Zinc vacancies (V(Zn)) related defects in the nanorods and oxygen defects are found to be higher in the vertically aligned nanorods as compared to the horizontal nanorods. The difference between the Fermi level and valence band maxima for horizontal, hollow vertical and solid vertical nanorods are found to be approximately 0.56 eV, approximately 0.70 eV and approximately 0.92 eV respectively indicating the possibility of p-type of conduction in the nanorods which has been attributed to presence of V(Zn) defects in the ZnO nanorods.     

Template-free hydrothermal synthesis of PbS nanorod by the oriented attachment mechanism

In this work, PbS nanocubes and nanorods were fabricated via a facile hydrothermal method without using any template and surfactant. The structure and morphology of as-prepared PbS nanocrystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). It was found that the anisotropic structure of PbS nanorods were composed of numerous assembled nanocubes, which had an uniform morphology with the mean diameters of about 100-200 nm and lengths of 0.5-7 μm. Furthermore, a possible growth mechanism was proposed to explain the formation of the nanorods on the basis of the time-dependent experimental results.     

扩散诱导的锌间隙相关施主缺陷对ZnO纳米棒结构及光电特性的影响

采用射频磁控溅射技术和水浴法在SiO2单晶衬底上生长了Zn纳米颗粒/ZnO纳米棒复合材料(Zn/ZnO)。后期热处理促使Zn/ZnO界面之间发生元素相互扩散,直接向ZnO纳米棒中引入额外锌杂质,从而获得了富锌的ZnO纳米棒材料。借助扫描电子显微镜、X射线衍射仪、霍尔测试仪、分光光度计和拉曼光谱仪研究了富锌ZnO纳米棒的形貌、结构以及光电特性。结果表明,所有ZnO纳米棒均呈整齐的六角纤锌矿结构,相比ZnO纳米棒,富锌纳米棒具有相对较差的结晶质量,较好的导电性,较低的透射率和较窄的禁带宽度。拉曼光谱研究表明,通过扩散法向ZnO纳米棒引入的锌间隙相关施主缺陷,是其拉曼光谱中出现异常的275 cm^-1振动模的来源,也是导致富锌ZnO纳米棒微结构以及光电特性显著变化的主要原因。     

Electrical transport properties of thin film of a-Se87Te13 nanorods

We have studied the electrical transport properties of thin film of a-S₈₇Te₁₃ nanorods. Initially, the glassy alloy of S₈₇Te₁₃ is prepared by melt-quenching technique. The amorphous nature of this alloy is verified by using X-ray diffraction technique. The nanorods of a-S₈₇Te₁₃ are synthesised on a glass substrate under an ambient gas (Ar) atmosphere using physical vapour condensation system. The morphology and microstructure of these nanorods are studied using scanning electron microscopy and transmission electron microscopy. The temperature dependence of dc conductivity for these nanorods is also studied over a temperature range of 500–100?K. On the basis of the temperature dependence of dc conductivity, the conduction mechanism in these nanorods is investigated. The results reveal that the thermally activated process is responsible for the transport of carriers in the temperature range 500–300?K. While the conduction takes place via variable range hopping (VRH) for temperature region 300–100?K. It is therefore, suggested that three-dimensional Mott's variable range hopping (3D VRH) is the conduction mechanism responsible for the transport of charge carriers in the temperature region 300–100?K. Various Mott's parameters such as density of states, degree of disorder, hopping distance and hopping energy are estimated on the basis of best fitting to our experimental data for Mott's 3D VRH model.     

PbS量子点能级结构的尺寸和配体依赖性及其对异质结电池性能的影响

通过电化学循环伏安测试和吸收光谱测试, 确定了有机配体(油酸)和原子配体(四正丁基碘化铵, TBAI)钝化的不同粒径(2.6~4.5 nm)PbS量子点的导带和价带能级, 并研究了量子点尺寸对PbS/TiO₂异质结电池(空气气氛中制备)性能的影响。结果表明：PbS量子点的能级结构受其粒径大小和表面配体特性的影响。当PbS量子点尺寸从2.6 nm增加至4.5 nm时, 油酸包覆PbS量子点的导带底从-3.67 eV减小到-4.0 eV, 价带顶从-5.19 eV增加到-4.97 eV; 而对于TBAI配体置换的PbS量子点, 其导带底和价带顶则分别从-4.15 eV和-5.61 eV变化至-4.51 eV和-5.46 eV。粒径为3.9 nm的PbS量子点所制备的电池性能最优, 其能量转化效率达到2.32%, 这可归因于其适宜的禁带宽度、结晶质量和良好的PbS/TiO₂界面能级匹配度。     

Colloidal-quantum-dot photovoltaics using atomic-ligand passivation

Colloidal-quantum-dot (CQD) optoelectronics offer a compelling combination of solution processing and spectral tunability through quantum size effects. So far, CQD solar cells have relied on the use of organic ligands to passivate the surface of the semiconductor nanoparticles. Although inorganic metal chalcogenide ligands have led to record electronic transport parameters in CQD films, no photovoltaic device has been reported based on such compounds. Here we establish an atomic ligand strategy that makes use of monovalent halide anions to enhance electronic transport and successfully passivate surface defects in PbS CQD films. Both time-resolved infrared spectroscopy and transient device characterization indicate that the scheme leads to a shallower trap state distribution than the best organic ligands. Solar cells fabricated following this strategy show up to 6% solar AM1.5G power-conversion efficiency. The CQD films are deposited at room temperature and under ambient atmosphere, rendering the process amenable to low-cost, roll-by-roll fabrication.