Ordered networks of ZnO-nanowire hierarchical urchin-like structures for improved dye-sensitized solar cells

Quasi-1D ZnO nanowires (NWs) ordered as patterned 3D hollow hierarchical urchin-like structures have been prepared on transparent conducting substrates by electrodeposition. The ZnO NWs have been grown on self-assembled ordered polystyrene microspheres with electrical charge densities ranging from 5 to 30 C cm(-2) and organized arrays of mono and multi-urchin layers have been built. These layers have been sensitized by the highly absorbing D149 indoline organic dye. The optical characterizations and dye titrations have shown a significant increase in the light scattering and absorption as well as dye loading for the organized structures compared to randomly vertically aligned ZnO NWs grown under the same conditions. The dye-sensitized solar cells (DSSC) prepared using the sensitized layers have been characterized by current-voltage (J-V) measurements, IPCE and by electrochemical impedance spectroscopy. We show that the best performances are obtained for the 3D urchin monolayer structures. The conversion efficiency is increased by up to 4 times compared to their counterparts made of randomly dispersed vertical ZnO NWs. Impedance spectroscopy results show a very fast charge transfer in the ZnO NWs and urchin monolayers and that the electron lifetime is in the 4-14 ms range.     

Scanning tunneling microscopy of lead selenide monocrystals and epitaxial layers on barium fluoride

Summary The topography and atomic arrangement on the (100) surface of n- and p-PbSe monocrystals have been studied in air by scanning tunneling microscopy (STM). It was shown that the chemically polished surface is more rough than the freshly cleaved one. The regular patterns of the atomic scale STM images correspond well to the crystallographic positions of atoms on (100) plane. Several types of surface defects were observed. The peculiarities of the registrations of atomic scale STM images of PbSe monocrystals are discussed. STM was also applied to structure analysis of molecular beam epitaxial layers of PbSe on BaF₂ substrate. The topography of epitaxial layers and their atomic structure have been visualized. It appeared that with certain substrate temperatures (100) and (111) oriented grains of PbSe are formed.     

Aspect ratio dependent air stability of PbSe nanorods and photovoltaic applications

Development of unique strategies to overcome Shockley–Queisser (SQ) limit in solar cells has gained a great deal of interest. Multiple exciton generation (MEG) process has been considered as one of the best approaches to the SQ limitation. In this respect, PbSe quantum dots (QDs) and nanorods (NRs) have been regarded as promising solar energy harvesting materials owing to their noticeable MEG yields. Although air stability has been regarded as one of the main disadvantage of PbSe QDs, no study has pointed out to the air sensitivity of PbSe NRs yet. Here, we reveal the effect of aspect ratio on air sensitivity and optical properties of PbSe NRs and discover that NRs with higher aspect ratios are more air stable, attributed to the reduced density of NR ends with air sensitive {100} facets. Furthermore, a band offset was created by utilization of tetrabutylammonium iodide and 1,2-ethanedithiol ligands in cell designs. We found that solar cells based on pristine PbSe NRs are limited by low open circuit voltages due to leakage current pathways. On the other hand, modified cells comprising light absorbing layers prepared by blending NRs and QDs and hole transporting QD layer exhibit a 10-fold improvement in solar cell efficiency.     

Solvothermal Synthesis and Characterization of PbSe Nanostructures with the Aid of Schiff-base Ligand

In this work, Pb(II)N,N-bis(salicylidene)-ethylenediamine; [Pb(salen)]; was applied as lead precursor to synthesis PbSe nanostructures. Besides [Pb(salen)], SeCl₄ and reducing agents like N₂H₄·H₂O have been employed for the production of PbSe nanostructures via a solvothermal route at 180 °C for 3 h in propylene glycol. The effect of preparation factors such as temperature, reaction time, and surfactant on the morphology of PbSe nanostructures was investigated. The experimental results indicated that PbSe synthesized at 150 and 210 °C was composed of agglomerated particles. On the other hand, the use of KBH₄ as reducing agent led to produce PbSe with higher particle size and agglomeration. The as-prepared PbSe nanostructures were characterized by XRD, SEM, TEM, EDS, and FT-IR.     

超声电化学制备PbSe纳米枝晶

近年来，纳米晶态半导体粒子因其具有大的表面体积比、高的活性、特殊的电学性质和独特的光学性质引起了科学界的广泛关注犤１，２犦。基于半导体纳米粒子的量子尺寸效应和表面效应，半导体纳米粒子在发光材料犤３犦、非线性光学材料犤４犦、光敏传感器材料犤５犦、光催化材料犤６犦等方面具有广阔的应用前景。如何实现对半导体纳米粒子的尺寸大小、粒度分布以及形状和表面修饰的控制，寻找更简便的合成方法以及改善制备环境等是半导体纳米粒子研究的关键。超声电化学是结合了电化学和超声辐照而建立起来的一种新方法，它显示了两者的优点犤…     

Solvothermal synthesis of monodisperse PbSe nanocrystals

Size-controllable monodisperse PbSe and PbSe/PbS nanocrystals (NCs) have been successfully synthesized with a solvothermal method. Octadecylamine (ODA) molecules were found effective in organizing the nanocrystals to form an ordered monolayer. It is expected that these narrow-band-gap semiconductor NCs with tunable size would have potential applications in near- and mid-IR telecommunication laser sources, electroluminescence, and solar cell materials.     

Silica nanowires: Growth,integration, and sensing applications

This review (with 129 refs.) gives an overview on how the integration of silica nanowires (NWs) into micro-scale devices has resulted, in recent years, in simple yet robust nano-instrumentation with improved performance in targeted application areas such as sensing. This has been achieved by the use of appropriate techniques such as di-electrophoresis and direct vapor-liquid-growth phenomena, to restrict the growth of NWs to site-specific locations. This also has eliminated the need for post-growth processing and enables nanostructures to be placed on pre-patterned substrates. Various kinds of NWs have been investigated to determine how their physical and chemical properties can be tuned for integration into sensing structures. NWs integrated onto interdigitated micro-electrodes have been applied to the determination of gases and biomarkers. The technique of directly growing NWs eliminates the need for their physical transfer and thus preserves their structure and performance, and further reduces the costs of fabrication. The biocompatibility of NWs also has been studied with respect to possible biological applications. This review addresses the challenges in growth and integration of NWs to understand related mechanism on biological contact or gas exposure and sensing performance for personalized health and environmental monitoring. Figure

Silica nanowires decorated micro-electrodes for sensing application     

Germanium telluride nanowires and nanohelices with memory-switching behavior

We report the synthesis of single-crystalline GeTe nanowires (NWs) and nanohelices (NHs) using a vapor transport method assisted by metal catalysts. The NWs have typical diameters of 65 +/- 20 nm and lengths reaching up to 50 mum, while NHs have an average helix diameter of 135 +/- 30 nm, with widely varying pitches. Electron microscopy and diffraction measurements show that these NWs and NHs are single crystalline and exhibit a rhombohedral structure. The devices incorporating individual GeTe NWs exhibit nonvolatile resistance changes associated with voltage-driven crystalline-amorphous transitions, suggesting that these NWs can be the basis of an electrically driven nonvolatile memory.     

Selected-control solution-phase route to multiple-dendritic and cuboidal structures of PbSe

Well-crystalline PbSe multiple-dendritic hierarchical structures have been prepared through a facile hydrothermal process in an alkaline glycerol/water solution system using SeO₂ as selenium source and hydrous hydrazine as reducing agent at 160 °C for 12 h. The obtained products were characterized by X-ray powder diffraction, field emission scanning electron microscopy and transmission electron microscopy, which showed that the obtained products were face-centered cubic PbSe multiple-dendritic superstructures with length of each dendrite ranging from 1.0 to 1.5 μm. Additionally, cuboidal PbSe microcrystals with different concave faces can be obtained through a similar process except for using Se powders instead of SeO₂ as selenium source and without hydrous hydrazine. The edge lengths of these cuboidal microcrystals range from 1.0 to 2.5 μm observed by field emission scanning electron microscopy. The influencing factors for the formation of the two kinds of PbSe microstructures were discussed and the possible growth mechanisms were proposed from the point of crystallographic and kinetic views. The studies on the corresponding photoluminescence (PL) properties of the two kinds of PbSe structures are also carried out.     

Characteristics of Ga and Ag-doped ZnO-based nanowires for an ethanol gas sensor prepared by hot-walled pulsed laser deposition

Pure ZnO and Ga (3 % w/w) and Ag (3 % w/w)-doped ZnO nanowires (NWs) have been grown by use of the hot-walled pulse laser deposition technique. The doping characteristics of Ga and Ag in ZnO NWs were analyzed by use of photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) and the results were compared with those for pure ZnO NWs. We also fabricated gas sensors by use of pure ZnO and Ga and Ag-doped ZnO NWs. Among the NW sensors, the Ag-doped NW sensor was most sensitive. We synthesized the NWs on sapphire substrates under different conditions, for example temperature, time, gas flow, and distance between target and substrate. The diameter and length of NWs were <100 nm and several microns, respectively. To analyze the effect of Ag doping on ZnO NWs, we investigated the near band edge emission by use of low-temperature PL and XPS. Significant changes in resistance and sensitivity were observed. When the sensors were used at 300 °C for detection of 1 ppm ethanol vapor, the sensitivity of the pure ZnO and the Ga and Ag-doped ZnO NW gas sensors was 97, 48, and 203 %, respectively.     

The first synthesis of Pb(1-x)Mn(x)Se nanocrystals

In this work, Mn-doped PbSe nanocrystals (NCs) have been, for the first time, prepared through a high-temperature organic solution approach. To ensure that all the Mn2+ ions are indeed incorporated into the NCs and not only physically presented at the surface, Mn-Se prebonded precursor was selected, and a ligand-exchange process was also conducted before and after the synthesis, respectively. Various analyses including EDS, ICP, XRD, SQUID, and EPR confirm that the Mn2+ ions have been successfully doped into PbSe NCs.     

Electrochemical Formation of Amorphous Selenium Films Doped by Lead Selenide Nanoparticles

The formation of amorphous Se films doped by PbSe nanoparticles during the cathodic co-deposition of Se and Pb is studied. Doping Se with PbSe makes the charge transfer more efficient both in the film bulk and at the heterojunction with electrolyte, thus making it possible to deposit Se(PbSe) films a few micrometers thick. Co-deposition of Se and Pb results from electrodeposition of adsorbed Pb atoms on surface atoms of Se at potentials more positive than the equilibrium potential of the Pb reduction (underpotential deposition). For the Se(PbSe) electrodes, spectral sensitization of photocurrent is observed up to 900 nm. As opposed to Se, which is characterized by absorption at < 600 nm, the edge of optical absorption of Se(PbSe) is displaced towards the long-wave region of the spectrum. The underpotential deposition on the Se(PbSe) surface is possible in dark, permitting their additional modification by PbSe monolayers.     

Composited hybrid electrocatalysts of Pt-based nanoparticles and nanowires for low temperature polymer electrolyte fuel cells

A new and highly improved electrocatalytic system of a composited hybrid electrode with Pt-based nanoparticles (NPs) and nanowires (NWs) is reported for low temperature polymer electrolyte fuel cells. Pt-based NWs have been realized as an option that can provide facile charge transport with a high activity for oxidation of fuels, for overcoming the disadvantages of Pt-based NPs as the state-of-the-art electrocatalysts. Moreover, a network-like electrode structure using the anisotropic morphology of Pt-based NWs can also supply efficient mass transport and mitigate uneconomical use of Pt by reducing embedded catalyst particles. Herein, we demonstrate that an advanced and very efficient hybrid structure of electrode, composited with highly-dispersed Pt-based NPs and NWs, shows significantly improved performances both in the CH₃OH-fueled and H₂-fueled fuel cells via synergistic effects by integrating advantages of two different morphologies.     

Solution-based growth and structural characterization of homo- and heterobranched semiconductor nanowires

Colloidal homobranched ZnSe nanowires (NWs) and heterobranched CdSe-ZnSe NWs are successfully synthesized by combining a sequential seeding strategy with the solution-liquid-solid (SLS) growth process. We have developed an efficient approach to deposit secondary bismuth nanoparticles onto the NW backbone to induce the subsequent SLS branch growth. The density, length, and diameter of branches are rationally controlled by varying reaction conditions. Structural characterization reveals that crystalline branches grow epitaxially from the backbone in both homo- and heterobranched NWs. Two different branching structures are observed in the CdSe-ZnSe heterobranched NWs, owing to the phase admixture, i.e., cubic and hexagonal crystal structures, coexisting in the CdSe NW backbones. These branched NWs with well-designed architectures are expected to have potential as three-dimensional building blocks in the fabrication of nanoscale electronics and photonics.     

PbSe quantum dots: Preparation in a high boiling point solvent and characterization

A novel approach to preparing PbSe quantum dots in a high-boiling-point solvent (paraffin liquid) was studied. PbSe quantum dots obtained were transferred from the organic phase to aqueous phase. The PbSe samples were characterized by transmission electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis, which demonstrated that high-quality PbSe quantum dots with regular shape and uniform size were prepared. The mechanism of PbSe quantum dot formation was briefly discussed. The text was submitted by the authors in English.     

Silica nanowires: Growth,integration, and sensing applications

This review (with 129 refs.) gives an overview on how the integration of silica nanowires (NWs) into micro-scale devices has resulted, in recent years, in simple yet robust nano-instrumentation with improved performance in targeted application areas such as sensing. This has been achieved by the use of appropriate techniques such as di-electrophoresis and direct vapor-liquid-growth phenomena, to restrict the growth of NWs to site-specific locations. This also has eliminated the need for post-growth processing and enables nanostructures to be placed on pre-patterned substrates. Various kinds of NWs have been investigated to determine how their physical and chemical properties can be tuned for integration into sensing structures. NWs integrated onto interdigitated micro-electrodes have been applied to the determination of gases and biomarkers. The technique of directly growing NWs eliminates the need for their physical transfer and thus preserves their structure and performance, and further reduces the costs of fabrication. The biocompatibility of NWs also has been studied with respect to possible biological applications. This review addresses the challenges in growth and integration of NWs to understand related mechanism on biological contact or gas exposure and sensing performance for personalized health and environmental monitoring.

Silica nanowires decorated micro-electrodes for sensing application

     

Facile Synthesis Of Composition‐Controllable PtPdAuTe Nanowires As Superior Electrocatalysts For Direct Methanol Fuel Cells

Multicomponent Pt‐based nanowires (NWs) have attracted widespread attention as eletrocatalysts toward direct alcohol fuel cells because of their unique one‐dimensional structure and high reaction dynamics. Quaternary PtPdAuTe NWs are designed via a facile template method, and NWs with a different composition are obtained by adjusting the feed ratio of metal precursors. The direct displacement reaction of metal precursors with Te NWs and the partial oxidation of Te lead to the formation of quaternary NWs. The rough surface and abundant reactive sites deriving from the rearrangement of metal atoms on the Te NWs surface endow the PtPdAuTe NWs with a superior electrocatalytic property and durability for methanol oxidation. The Pt₂₀Pd₂₀Au₁₀Te₅₀ NWs display the largest mass activity and best stability among all catalysts. The preparation of PtPdAuTe NWs could provide a viable strategy for the preparation of other multicomponent NWs.     

Electrodeposition of micro- and nanocrystalline lead selenide from alkaline selenosulfate solutions

Cathodic electrodeposition of PbSe is carried out in aqueous alkaline selenosulfate (SeSO ₃ ^2? ) bath of lead complex ions at various conditions of electrolysis. Micro- and nanocrystalline PbSe thin films were grown onto glassy carbon (GC) substrates by potentiostatic and cyclic voltammetric (CV) methods respectively. Structure and surface morphology of thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray diffraction indicates that the PbSe films have cubic structure without any impurities. The SEM micrograph showed the films cover GC substrate completely and consisted of irregular shaped grains.     

Preparation of Pt@Fe2O3 nanowires and their catalysis of selective oxidation of olefins and alcohols

Iron oxide coated platinum nanowires (Pt@Fe(2)O(3)NWs) with a diameter of 2.8 nm have been prepared by the oxygen oxidation of FePt NWs in oleylamine. These "cable"-like NWs were characterised by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption fine structure analysis. These Pt@Fe(2)O(3) NWs were used as "non-support" heterogeneous catalysts in oxidation of olefins and alcohols. The results revealed that it is an active and highly selective catalyst. Styrene derivatives were tested with molecular oxygen as the sole oxidant, with benzaldehyde successfully obtained from styrene in an absolute yield of 31%, whereas the use of tert-butyl hydroperoxide as the sole oxidant in the oxidation of alcohols led to yields of more than 80% of the corresponding ketone or aldehyde. This unsupported catalyst was found to be more active (TOF=96.5 h(-1)) than other reported Fe(2)O(3) nanoparticle catalysts and could be recycled multiple times without any notable decrease in activity. Our findings will extend the use of such nanomaterial catalysts to new catalytic systems.     

Utilizing the lability of lead selenide to produce heterostructured nanocrystals with bright, stable infrared emission

Infrared-emitting nanocrystal quantum dots (NQDs) have enormous potential as an enabling technology for applications ranging from tunable infrared lasers to biological labels. Notably, lead chalcogenide NQDs, especially PbSe NQDs, provide efficient emission over a large spectral range in the infrared, but their application has been limited by instability in emission quantum yield and peak position on exposure to ambient conditions. Conventional methods for improving NQD stability by applying a shell of a more stable, wider band gap semiconductor material are frustrated by the tendency of lead chalcogenide NQDs toward Ostwald ripening at even moderate reaction temperatures. Here, we describe a partial cation-exchange method in which we take advantage of this lability to controllably synthesize PbSe/CdSe core/shell NQDs. Critically, these NQDs are stable against fading and spectral shifting. Further, these NQDs can undergo additional shell growth to produce PbSe/CdSe/ZnS core/shell/shell NQDs that represent initial steps toward bright, biocompatible near-infrared optical labels.