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Although single-atom catalysts (SACs) have been largely explored in lithium-sulfur (Li-S) batteries, the commonly reported nonpolar transition metal-N

A raindrop solar cell can work either on rainy days to collect mechanical energy of the raindrops or on sunny days to harvest solar energy, which achieves high energy conversion efficiency in various energy environments. However, the low efficiency of raindrop energy harvesting is a dominating barrier to the raindrop solar cells in practical applications. In this work, a MoO

A PbSe colloidal quantum dot (QD) is typically a solution-processed semiconductor for near-infrared (NIR) optoelectronic applications. However, the wide application of PbSe QDs has been restricted due to their instability, which requires tedious synthesis and complicated treatments before being applied in devices. Here, we demonstrate efficient NIR photodetectors based on the room-temperature, direct synthesis of semiconducting PbSe QD inks. The in-situ passivation and the avoidance of ligand exchange endow PbSe QD photodetectors with high efficiency and low cost. By further constructing the PbSe QDs/ZnO heterostructure, the photodetectors exhibit the NIR responsivity up to 970 mA/W and a detectivity of 1.86 × 1011 Jones at 808 nm. The obtained performance is comparable to that of the state-of-the-art PbSe QD photodetectors using a complex ligand exchange strategy. Our work may pave a new way for fabricating efficient and low-cost colloidal QD photodetectors.

Solid-state electrolytes (SSEs) have attracted considerable attention as an alternative for liquid electrolytes to improve safety and durability. Sodium Super Ionic CONductor (NASICON)-type SSEs, typically Na3Zr2Si2PO12, have shown great promise because of their high ionic conductivity and low thermal expansivity. Doping La into the NASICON structure can further elevate the ionic conductivity by an order of magnitude to several mS/cm. However, the underlying mechanism of ionic transportation enhancement has not yet been fully disclosed. Herein, we fabricate a series of Na3+xLaxZr2-xSi2PO12 (0 ≤ x ≤ 0.5) SSEs. The electronic and local structures of constituent elements are studied via synchrotron-based X-ray absorption spectroscopy, and the ionic dynamics and Na-ion conduction mechanism are investigated by solid-state nuclear magnetic resonance spectroscopy. The results prove that La3+ ions exist in the form of phosphate impurities such as Na3La(PO4)2 instead of occupying the Zr4+ site. As a result, the increased Si/P ratio in the NASICON phase, accompanied by an increase in the sodium ion occupancy, makes a major contribution to the enhancement of ionic conductivity. The spin-lattice relaxation time study confirms the accelerated Na+ motions in the altered NASICON phase. Modifications on the Si/P composition can be a promising strategy to enhance the ionic conductivity of NASICON.

Efficient and low-cost electrocatalysts for oxygen evolution reaction (OER), particularly in neutral conditions, are of significant importance for renewable energy technologies such as CO2 reduction and seawater splitting electrolysis. High-valent transition-metal sites have been considered as OER active sites; however, the rational design and construction of these sites remain a big challenge. Here, we report a trimetallic NiFeCu oxyhydroxide electrocatalyst, in which high-valent Ni sites are promoted and stabilized by the atomically embedded Cu, as evidenced by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Through compositional optimization, Ni6Fe1Cu1 catalysts achieved an overpotential of 385 mV at 10 mA cm(-2), a Tafel slope of 164 mV dec(-1), and a stability of 100 h at pH = 7.2. Density function theory calculations demonstrated that the Cu-doping facilitates the formation of high-valent Ni and thus promotes OER electrocatalysis through modulating the d-band center of Ni and reducing the adsorption energy of oxygenated intermediates on the surface of the catalyst. This work paves a promising avenue for the construction of desired high-valent metal OER catalysts by embedding redox inactive metals.

Although there has been rapid advancement in wearable electronics, challenges still remain in developing wearable and sustainable power sources with simple fabrication and low cost. In this work, we demonstrate a flexible coaxial fiber by fabricating a one-dimensional triboelectric nanogenerator (TENG) outside and a supercapacitor (SC) inside, which can not only harvest mechanical energy but also store energy in the all-in-one fiber. In such a coaxial fiber, carbon fiber bundles are utilized as the electrode material for the TENG as well as the active and electrode material for the SC. Meanwhile, silicone rubber serves as the separator between the SC and TENG, as the triboelectric material for the TENG, and as the encapsulation material for the whole fiber as well. Moreover, both SC and TENG exhibit good performance and stability, which ensures their long-term use in daily life. Because of the flexibility and durability of the carbon fiber and silicone rubber, the proposed coaxial fibers show great flexibility, which could be further knitted as cloth for sustainably powering wearable electronic devices. This work presents a promising platform for wearable electronics as well as smart textiles.

Two-dimensional (2D) nonlayered nanomaterials have attracted extensive attention for electronic and optoelectronic applications recently because of their distinct properties. In this work, we first employed a facile one-step method to synthesize 2D nonlayered cadmium sulfide selenide (CdS xSe1- x, x = 0.33) nanosheets with a highly crystalline structure and then we introduced a generic spin-coating approach to fabricate hybrid nanomaterials composed of PbS quantum dots (QDs) and 2D CdS xSe1- x nanosheets and demonstrated their potential for high-performance broadband photodetectors. Compared with pure 2D CdS xSe1- x nanosheet photodetectors, the photoelectric performance of the PbS/CdS xSe1- x hybrid nanostructure is enhanced by 3 orders of magnitude under near-infrared (NIR) light illumination and maintains its performance in the visible (Vis) range. The photodetector exhibits a broadband response range from Vis to NIR with an ultrahigh light-to-dark current ratio (3.45 × 106), a high spectral responsivity (1.45 × 103 A/W), and high detectivity (1.05 × 1015 Jones). The proposed QDs/2D nonlayered hybrid nanostructure-based photodetector paves a promising way for next-generation high-performance broadband optoelectronic devices.

High-energy and high-power-density lithium-ion batteries are promising energy storage systems for future portable electronics and electric vehicles. Here, three-dimensional (3D) patterned electrodes are created through the paste-extrusion-based 3D printing technique realizing a trade-off between high energy density and power density. The 3D electrodes possess several distinct merits over traditional flat thick electrodes, such as higher surface area, shorter ion transport path, and improved mechanical strength. Benefiting from these advantages, the 3D-printed thick electrodes present the higher specific capacity and improved cycling stability compared with those of the conventional thick electrodes. Upon comparison to the previous studies on 3D-printed electrodes, this study investigates the influence and optimization of 3D-printed LiFePO4 (LFP) electrodes with three different geometric shapes to achieve a high rate performance and long-term cycling stability. Accordingly, a series of 3D electrodes with d...

Loading metal guests within metal–organic frameworks (MOFs) via secondary functional groups is a promising route for introducing or enhancing MOF performance in various applications. In this work, 14 metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Zn2+, Co2+, Mn2+, Ag+, Cd2+, La3+, In3+, and Pb2+) have been successfully introduced within the MIL-121 MOF using a cost-efficient route involving free carboxylic groups on the linker. The local and long-range structure of the metal-loaded MOFs is characterized using multinuclear solid-state NMR and X-ray diffraction methods. Li/Mg/Ca-loaded MIL-121 and Ag nanoparticle-loaded MIL-121 exhibit enhanced H2 and CO2 adsorption; Ag nanoparticle-loaded MIL-121 also demonstrates remarkable catalytic activity in the reduction of 4-nitrophenol.

Hematite is one of the most promising photoanodes for photoelectrochemical (PEC) solar water splitting. However, due to the low conduction band position for water reduction, an external bias is necessarily required with the consumption of extra power. In this work, a titanium modified hematite (Ti-Fe2O3) photoanode-based self-powered PEC water splitting system in tandem with a rotatory disc-shaped triboelectric nanogenerator (RD-TENG) has been developed. It is a fantastic strategy to effectively drive the hematite-based PEC water splitting by using the environmental mechanical energy through a TENG. When the rotation speed is 65 rpm (water flowing rate ∼0.61 m/s), the peak current reaches to 0.12 mA under illumination contrast to that in the dark with almost zero. As for 80 rpm, the peak currents are 0.17 and 0.33 mA in the dark or under illumination, respectively, indicating the simultaneous occurrence of electrolysis and PEC water splitting. When higher than 120 rpm, the peak current in the dark is near...

Solar cells, as promising devices for converting light into electricity, have a dramatically reduced performance on rainy days. Here, an energy harvesting structure that integrates a solar cell and a triboelectric nanogenerator (TENG) device is built to realize power generation from both sunlight and raindrops. A heterojunction silicon (Si) solar cell is integrated with a TENG by a mutual electrode of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film. Regarding the solar cell, imprinted PEDOT:PSS is used to reduce light reflection, which leads to an enhanced short-circuit current density. A single-electrode-mode water-drop TENG on the solar cell is built by combining imprinted polydimethylsiloxane (PDMS) as a triboelectric material combined with a PEDOT:PSS layer as an electrode. The increasing contact area between the imprinted PDMS and water drops greatly improves the output of the TENG with a peak short-circuit current of ∼33.0 nA and a peak open-circuit voltage of ∼2.14 V, respectively. The hybrid energy harvesting system integrated electrode configuration can combine the advantages of high current level of a solar cell and high voltage of a TENG device, promising an efficient approach to collect energy from the environment in different weather conditions.

The structure-dependent optical properties of ZnO nanostructures have attracted considerable attention due to their fascinating optoelectronic properties and great structural diversity. Novel ZnO nanocomb and ZnO nanoflag have been successfully synthesized by chemical vapor deposition (CVD) method using Au nanoparticles (NPs) as the catalyst at the deposition temperatures of 900 and 950 °C, respectively. X-ray diffraction and high-resolution transmission electron microscopy results show that the ZnO nanocomb handle and its teeth grow in [0111] and [0001] orientations, respectively, while the ZnO nanoflag sheet and its pole grow along [0001] and [2110] orientations, respectively. Au NPs as well as deposition temperature played an important role in the growth of the nanocomb handle and nanoflag pole. Synchrotron-based scanning transmission X-ray microscopy (STXM) reveals the thickness distribution and the crystallinity of ZnO nanocomb and ZnO nanoflag. For the near-surface emission, photoluminescence and...

Hematite is recognized as a promising photocatalyst for solar water oxidation. However, its practical performance at a low bias is still very low due to large onset potential. Here we report a combination of F-treatment and Rh-treatment on Fe2TiO5/Fe2O3 to lower the onset potential with a large value of 230 mV. The final onset potential is 0.63 V versus RHE comparable to the lowest value ever reported for hematite. The F- and Rh-cotreated photoanode yields a high photocurrent of 1.47 mA/cm2 at 1.0 V versus RHE, which is more than 3 times that of the pristine sample. X-ray photoelectron spectroscopy reveals the existence of surface Ti–F bonds after F-treatment. Moreover, the surface groups can be further modified after immersion in the working NaOH solution, which can form an interfacial hydrogen-bond network to accelerate the hole transfer. The surface Fe atoms are also partly reduced to accelerate the hole transport. Rh-treatment can further lower the onset potential with a good stability. The enhanced p...

The molecular orientation and ordering of films produced by a vapor-phase deposition technique known as molecular layer deposition (MLD) is investigated. Specifically, the influence of incorporating an inorganic component into MLD films is determined. Film growth properties and surface saturating conditions of a purely organic polyurea film and a mixed inorganic–organic polyurea film are investigated by in situ quartz crystal microbalance. Polarization-dependent X-ray absorption spectroscopy was employed to determine the orientation and ordering of these films. Both films demonstrate preferential orientation parallel to the substrate surface. However, the degree of ordering between the films is found to be starkly different. In-depth analysis revealed that the hybrid inorganic–organic films display a high degree of ordering compared to purely organic polyurea films. This study sheds light on the ability of MLD to finely tune oligomer packing density, growth rate, molecular orientation, and film ordering.

Atomic layer deposition was employed to deposit maghemite (γ-Fe2O3) nanoparticles on carbon nanotubes (CNTs) to prepare the γ-Fe2O3@CNTs composites, which exhibit a superior lithium storage performance as the anode of lithium ion batteries (LIBs). The high reversible capacity of 859.7 mA h/g was observed after 400 cycles at a current density of 500 mA/g. Even at the high current density of 10000 mA/g, the specific cyclic capacity of 464.4 mA h/g can still be obtained. Furthermore, electron energy loss spectroscopy results reveal that the Fe chemical state plays a critical role in the evolution of the capacity of γ-Fe2O3@CNTs composite anodes during the cycling process. The incomplete conversion of the chemical state in γ-Fe2O3 reduces the capacity, while the recovery of the chemical state of γ-Fe2O3 during the cycling process may cause the increase in capacity. This work provides insight into understanding the detailed working mechanism of transition metal oxides in LIBs, which helps in the design of elec...

Uniform one-dimensional Pt nanowires prepared by etching FePt nanowires precursor exhibit high conversion yield and selectivity in aromatic azo compounds reaction compared to the other Pt-based catalysts, such as Pt nanorods and Pt nanoparticles. The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were employed to investigate the electronic structure and short-range local environment of the three Pt nanostructures, revealing that the high density of unsaturated coordinated atoms in the short-range local structure of Pt nanowires contribute to the superior catalytic performance of the nanowires. Furthermore, the quasi in situ XANES was carried out to monitor the electronic structural evolution of the Pt nanowires during the different stages in the whole reaction process, which further clarify the Pt–OH involved catalytic reaction mechanism. This work delineates the correlation between catalytic performance and structural sensitivity of Pt-based catalysts in...

Large-area monolayer fluorinated graphene (FG) is synthesized by a controllable SF6 plasma treatment. The functional groups of FG are elucidated by various spectroscopies, including Raman spectroscopy, X-ray photoemission spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Raman results suggest that the defects are introduced into the monolayer graphene during the fluorination process. The fluorine content can be varied by the plasma treatment and can reach the maximum (∼24.6 atom % F) under 20 s of plasma treatment as examined by XPS measurement. The angle-dependent NEXAFS results reveal that the fluorine atoms interact with the graphene matrix to form covalent C-F bonds, which are perpendicular to the basal plane of FG. FG is applied as a gas-sensing material and owns much better performance for ammonia detection compared to pristine graphene. On the basis of our density functional theory simulation results, the fast response/recovery behavior and high sensitivity of the FG gas sensor are attributed to enhanced physical absorption due to the C-F covalent bonds on the surface of FG.

Graphene oxide (GO) has attracted considerable attention due to its interesting structure and properties. The photoluminescence (PL) of GO is much stronger than that of graphene owing to the opening of an energy band gap. However, the origin of the PL bands in the ultraviolet and visible ranges remains controversial. In this paper, we report the dependence of the PL spectrum of GO on the pH value and concentration of GO aqueous solutions. It was discovered that PL in the visible range becomes prominent when the pH value is low and/or the GO concentration is high. As revealed by the time-resolved photoluminescence, the lifetime of the PL in the visible range is longer than that in the UV range. These results evidence the formation of excimers and prove that the PL band at the long wavelength is caused by the GO excimers.

A series of crystalline mixed cocrystal microtubes comprising organic charge-transfer (CT) complexes has been prepared. The emission colors of the mixed cocrystal microtubes can be tailored from green to orange at low dopant concentrations (0 < x ⩽ 5%), while their hexagonal cross sections can transform into square ones gradually at higher concentrations (0.15 < x < 1). In addition, we can further extend the solvent-processed synthetic route to other CT pairs based on structural compatibility consideration.

High-quality and wafer-scale graphene on insulating gate dielectrics is a prerequisite for graphene electronic applications. For such applications, graphene is typically synthesized and then transferred to a desirable substrate for subsequent device processing. Direct production of graphene on substrates without transfer is highly desirable for simplified device processing. However, graphene synthesis directly on substrates suitable for device applications, though highly demanded, remains unattainable and challenging. Here, we report a simple, transfer-free method capable of synthesizing graphene directly on dielectric substrates at temperatures as low as 600 °C using polycyclic aromatic hydrocarbons as the carbon source. Significantly, N-doping and patterning of graphene can be readily and concurrently achieved by this growth method. Remarkably, the graphene films directly grown on glass attained a small sheet resistance of 550 Ω/sq and a high transmittance of 91.2%. Organic light-emitting diodes (OLEDs) fabricated on N-doped graphene on glass achieved a current density of 4.0 mA/cm(2) at 8 V compared to 2.6 mA/cm(2) for OLEDs similarly fabricated on indium tin oxide (ITO)-coated glass, demonstrating that the graphene thus prepared may have potential to serve as a transparent electrode to replace ITO.

Well-ordered Cu-doped and undoped SnO2 porous thin films with large specific surface areas have been fabricated on a desired substrate using a self-assembled soft template combined with simple physical cosputtering deposition. The Cu-doped SnO2 porous film gas sensor shows a significant enhancement in its sensing performance, including a high sensitivity, selectivity, and a fast response and recovery time. The sensitivity of the Cu-doped SnO2 porous sensor is 1 order of magnitude higher than that of the undoped SnO2 sensor, with average response and recovery times to 100 ppm of H2S of ∼ 10.1 and ∼ 42.4 s, respectively, at the optimal operating temperature of 180 °C. The well-defined porous sensors fabricated by the method also exhibit high reproducibility because of the accurately controlled fabrication process. The facile process can be easily extended to the fabrication of other semiconductor oxide gas sensors with easy doping and multilayer porous nanostructure for practical sensing applications.

Although some achievements of constructing chiral metal-organic frameworks (MOFs) with diverse achiral ligands have been made, there is still a lack of full understanding of the origin and formation mechanism of chirality, as well as the reasonable principles for the design and construction of chiral frameworks. The concept of prochirality in organic molecules and complex systems inspires us to explore the synthetic strategy of chiral MOFs based on achiral sources. Here, an achiral compound [Cu(en)][(VO3)2] (1) was isolated in the CuCl2/NH4VO3/en system, while further chiral frameworks [Cu(en)(Im)2][(VO3)2] (2a and 2b) were obtained by the reaction between compound 1 and another achiral ligand Im (ethanediamine = en and imidazole = Im). In the present system, compound 1 has the characteristic of a quasi-plane structure unit. Further reaction of compound 1 and the achiral ligand (Im) induced the formation of chiral Λ/Δ Cu centers, and then a pair of chiral frameworks containing one-dimensional (1D) helical chains was formed. The chiral symmetry breaking phenomenon of compounds 2a and 2b can also be expected and explained based on this kind of prochirality synthetic strategy.

A one-pot universal approach with simple metal sputtering onto room temperature ionic liquids has been developed to prepare bimetal-nanoparticle (NP)-graphene hybrids, and the process is environmentally friendly and completely free of additives and byproducts. The graphene-supported bimetallic NPs have an Ag-based core and an Au/Pd-rich shell, demonstrated by the scanning transmission electron microscopy. The X-ray absorption near-edge spectroscopy using synchrotron radiation reveals the occurrence of charge redistribution at both the Ag@Au and Ag@Pd core-shell interfaces. The as-prepared Ag@Au and Ag@Pd bimetal-NP-graphene hybrids are highly catalytically active for reduction of 4-nitrophenol, whose catalytic activity is superior to the corresponding monometallic hybrids. The catalytic superiority is ascribed to the electronic structure modification and morphological irregularity of the graphene-supported bimetallic NPs.

The electronic structure of graphdiyne exposed to air is investigated utilizing X-ray absorption spectroscopy and scanning transmission X-ray microscopy. It is found that carbon–carbon triple bonds at defect sites in graphdiyne have been changed to double bonds after 3 months in air. The experimental results reveal the existence of oxygen and nitrogen functional groups and indicate that the oxidation takes place throughout the aged graphdiyne while the nitrogen contamination is mainly on its surface. Buckling of the aged graphdiyne is observed, resulting from bond length change due to the opening of triple bonds. It is also shown that annealing at a high temperature such as 800 °C may remove most of the functional groups in the aged graphdiyne.

The electronic structure of individual carbon nanotubes (CNTs) with different diameters has been investigated by scanning transmission X-ray microscopy (STXM). Various factors that may alter the STXM spectral features in CNT bundles have been discussed. Tube diameter has been found to be proportional to the spectral intensity, whereas it has negligible effect on the spectral shape. Disordered structure in CNTs introduced in the synthesis process was observed, which significantly affected the X-ray absorption spectrum by a reduction of the π* excitation. Moreover, tube–tube interaction in CNT bundles was detected, which can enhance the π* excitation. Insights into the nature of CNT bundles with various electronic structures may provide a new vision to understand the performance of CNT-based devices.

Silver nanoparticles (AgNPs) have been reductively fabricated on the hydrogen-terminated surface of germanium nanowires (GeNWs), which exhibited moderate reactivity toward the direct reduction of Ag (I) ion to metal nanoparticles in aqueous solution at room temperature. The electronic properties of the AgNPs/GeNWs system have been studied by X-ray photoelectron spectroscopy. The Ag nanoparticle-embedded germanium nanowires have been used as a unique surface-enhanced Raman scattering substrate, which could achieve the single molecule detection. The observed enhancement factor of the fabricated AgNPs/GeNWs substrate was estimated to be 107.

High-quality single-crystalline germanium oxide nanowires (GeONWs) have been synthesized by a thermal evaporation method under a vapor–liquid–solid mechanism. The morphology and nanostructure of the as-synthesized GeONWs were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) of the GeONWs showed the presence of substoichiometric oxygen. The electronic structure and local structure of GeONWs were also investigated by X-ray absorption fine structure (XAFS), which showed disorder and degradation of long-range order in the nanowires due to the nanosize in one-dimension and oxygen vacancies in the nanowires. Synchrotron-radiation-based X-ray-excited optical luminescence (XEOL) from GeONWs exhibits strong green light at 2.3 eV (540 nm), which corresponds to the photoluminescence (PL) spectrum of the individual GeONWs excited by laser. The strong emission i...

The surface stability of silicon nanowires (SiNWs) is crucial to their applications in nanodevices, such as transistors, sensors, photovoltaic cells, Li-ion batteries, etc. In this study, X-ray pho...

It was found that hydrocarbon nanotubes (HCNTs) and nano-onions (HCNOs) (hereafter collectively referred to as HCNT(O)s) can be converted to carbon nanotubes (CNTs) and nano-onions (CNOs) (hereafter collectively referred to as CNT(O)s) upon prolonged sonication via hybrid CNT⊂HCNT and CNO⊂HCNO nanostructures as intermediates, respectively. These intermediate hybrid carbon nanostructures may thus be considered as snapshots in the transformation process. The morphologies and the characteristic properties of these carbon nanostructures are reported. The formation of HCNT(O)s, and their subsequent transformation from HCNT(O)s to the hybrid CNT(O)⊂HCNT(O) nanostructures, and ultimately to the conventional CNT(O)s, have been elucidated by recording the HRTEM images of the products as a function of sonication time and in different solvents. On the basis of these experimental results, detailed formation mechanism and transformation pathways of these carbon nanomaterials, as well as their interrelationships, are p...

C(60) is a symbol of nanoscience. Its impact is far beyond the initial interest in this nanometer molecule itself. This paper reviews the current status of the nonlinear optical and ultrafast dynamics investigations of C(60). The review starts with the nonlinear optical response, in particular the dispersion spectra of harmonic generation and two-photon absorption. Both the experimental and theoretical challenges are highlighted. The main focus is on femtosecond and picosecond degenerate and nondegenerate four-wave mixing and pump-probe techniques as a tool to investigate ultrafast electron and nuclear dynamics, charge transfer and photoexcitation in C(60). Theoretical investigations are essential to understand these processes. Theory predicts a longer relaxation time for charge transfer than photoexcitation and reveals the underlying reasons for the normal mode excitations and changes in the electron density of states, which is directly linked to the time-resolved photoemission spectra. Theory also resolves a long-time puzzle about the dependence of normal mode excitations on the laser pulse duration and predicts that time-resolved pump-probe spectroscopy is able to probe electron correlation effects. Finally, high-harmonic generation in C(60) is reviewed. The review concludes with prospectives and possible applications.

We report the synthesis and characterization of 1D Si-CdSe heteronanostructures with different morphologies such as coaxial, biaxial, sandwiched, pattern wrapping, coiling, structures etc., via a one-step metal catalyzed thermal evaporation method. Both Si and CdSe exhibit single crystalline characteristics in the heterostructures, as revealed by scanning transmission electron microscopy. The Si nanowires formed directly from the Si substrate via the solid-liquid-solid process acts as the absorption site for CdSe deposition as well as the template for the formation of 1D Si-CdSe heterostructures. Time-resolved X-ray excited optical luminescence from the 1D Si-CdSe heteronanostructures reveals two main emission features at 530 and 637 nm with slow and fast decay lifetime, respectively. The 530 and 637 nm emission is associated with the Si and CdSe component of the heterostructures, respectively.

High-quality nanowires of germanium telluride (GeTe), a one-dimensional chalcogenide phase-change nanostructure, were synthesized via thermal evaporation method under vapor−liquid−solid mechanism. The physical morphology, chemical composition, and crystal structure of the as-synthesized GeTe nanowires were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and X-ray photoemission spectroscopy. Through real-time TEM imaging of nanowire sample heated in an incrementally controllable heating system, the melting point of a single crystalline GeTe nanowire (∼40−80 nm diameter) is found to be significantly lower than that of its bulk counterpart (46% reduction, from 725 to 390 °C). The significant reduction in melting point makes one-dimensional phase-change chalcogenide nanowire a potential material for application in low-power high-density resistive switching nonvolatile data storage in which the thermal energy for mat...

A simple sonochemical solution method using silicon nanowires (SiNWs) as templates has been developed to synthesize a wide variety of carbon nanostructures under ambient conditions (room temperature and atmosphere pressure). In addition to the conventional carbon nanotubes (CNTs) and nano-onions (CNOs), with interlayer spacings of 3.4 A, a new class of hydrocarbon nanostructures, characterized as hydrocarbon nanotubes (HCNTs) and nano-onions (HCNOs), which exhibit variable interlayer spacings greater than 3.4 A, has been discovered. A wide variety of morphologies of these hydrocarbon nanostructures were observed, including, but not limited to, tubes (both solid and hollow tubes); onions (both solid and hollow onions); tubular networks; open, closed, or connected loops or other networks; and twisted tubes or loops. Strong evidence for the templating effect of the SiNWs, including the molding and the demolding (extrusion) processes, were provided by direct transmission electron microscopic observations. The...

A systematic study of the etching behavior of one-dimensional (1-D) Si nanowires (SiNWs) in various HF and NH4F etching solutions is reported. The concentration and pH dependences of the etching time (which is inverse to the "stability") of the SiNWs in these solutions were investigated. A V-shaped bimodal etching curve was observed for HF solutions with concentrations of 0.5-40%. Specifically, SiNWs exhibit high stability in both low (0.5%) and high (40%) concentrations of HF solution, with the lowest stability (i.e., fastest etching rate) occurring at 2% (1 M) HF solution. With NH4F, the time needed to totally etch away the SiNWs sample decreases with increasing concentration (from 1-40%). The opposite is true when the pH of the NH4F solution was maintained at 14. These surprising results were rationalized in terms of "passivation" of the SiNW surfaces by HF or related molecules via hydrogen bonding for Si-H-terminated surfaces in HF solutions (with low pH values) and by NH4(+) ions via ionic bonding for Si-O(-)-terminated surfaces in NH4F solutions (with high pH values), respectively. Furthermore, it was found that SiNWs are stable only in relatively narrow pH ranges in these solutions. When SiNWs are etched with HF, the stability range is pH = 1-2 where the surface moieties are Si-H(x) species (x = 1-3). When SiNWs are etched with NH4F, the stability range is pH = 12-14 where the surface moieties are mainly Si-(O-)x species (x = 1-3). These rationales were confirmed by attenuated total reflection Fourier transform infrared spectroscopy measurements, which showed that, while etching SiNWs with HF gave rise to Si-H(x) surface species, no Si-H(x) species were observed when SiNWs were etched with NH4F. The latter finding is at odds with the corresponding results reported for the two-dimensional (2-D) Si wafers where etching with either HF or NH4F produces Si-H(x) species on the surface. This difference suggests either that the etching mechanisms for NH4F versus HF are different for SiNWs or, more likely, that the Si-H(x) surface species produced in NH4F solutions are so unstable that they are hydrolyzed readily at pH > 4. The similarities and differences of the etching behaviors and the resulting surface speciations between the 1-D SiNWs and the 2-D Si wafers suggest that the nanoscale structures as well as the low dimensionality of SiNWs may have contributed to the rapid hydrolysis of the surface Si-H(x) species in NH4F solutions, especially at high pH values.

Palladium and rhodium nanoparticles have been reductively fabricated on the hydrogen-passivated surfaces of silicon nanowires (SiNWs), which exhibited moderate reactivity toward the reduction of Pd...

It was demonstrated that zeolite can be used as a pseudo-template to grow very fine and uniform silicon nanostructures via disproportionation reaction of SiO by thermal evaporation. Three distinct types of composite nanowires and nanotubes of silicon and silica were grown on the surfaces of zeolite Y pellets. The first type is formed by an ultrafine crystalline silicon nanowire sheathed by an amorphous silica tube (a silicon nanowire inside a silica nanotube). The second type is formed by a crystalline silicon nanotube filled with amorphous silica (a silicon nanotube outside a silica nanowire). The third type is a biaxial silicon-silica nanowire structure with side-by-side growth of crystalline silicon and amorphous silica. These silicon nanostructures exhibit unusually intense photoluminescence (in comparison to ordinary silicon nanowires).

Well-aligned multiwalled carbon nanotubes (CNTs) were grown by microwave plasma-enhanced chemical vapor deposition using N 2 and NH 3 as the carrier gases and CH 4 as the carbon source. Iron films with 1-5 nm thickness onsilicon substrates acted as catalysts. Scanning electron microscopy revealed that the CNTs grew via the base growth mechanism at a rate ∼100 nm/s. Transmission electron microscopy showed that multiwalled CNTs had a "bamboo" structure, and the smallest CNTs of ∼6 nm in diameter were acquired on 1 nm Fe film. These "smallest" CNTs were comprised of amorphous structure, due to the formation of sp 3 C-H bonds as proven by Fourier transform infrared spectroscopy and electron energy loss spectroscopy, suggesting hydrogen incorporation during growth of CNTs. Without N 2 gas, no CNTs could be grown, while curly CNTs with poor alignment were grown with no NH 3 . In both cases, high-purity CNTs with no CN x impurities were obtained. Field electron emission revealed that the lowest turn-on and threshold fields were obtained from the CNTs grown on the 1 nm thick iron films on silicon substrate, i.e., 3.5 V/μm and 4.5 V/μm, respectively. Under an applied field of 7.5 V/μm, emission current density of 0.63 A/cm 2 can be obtained.

One-dimensional silicon-carbon nanotubes and nanowires of various shapes and structures were synthesized via the reaction of silicon (produced by disproportionation reaction of SiO) with multiwalled carbon nanotubes (as templates) at different temperatures. A new type of multiwalled silicon carbide nanotube (SiCNT), with 3.5-4.5 A interlayer spacings, was observed in addition to the previously known beta-SiC (cubic zinc blende structure) nanowires and the biaxial SiC-SiO(x) nanowires. The SiCNT was identified by high-resolution transmission microscopy (HRTEM), elemental mapping, and electron energy loss spectroscopy (EELS). The multiwalled SiCNT was found to transform to a beta-SiC crystalline structure by electron beam annealing under TEM.

The reductive growth of metal clusters on silicon nanowires (SiNWs) is reported. The HF-etched SiNWs were found to reduce ligated Au-Ag clusters of single size, shape, composition, and structure. In the process, the surfaces of the SiNWs were reoxidized. The reductive cluster growth on the SiNW surface was followed by high-resolution transmission electron microscopy (HRTEM). The reduced metal clusters grew to different sizes in the nanometer regime (1-7 nm in diameter) on the SiNW surfaces. At sizes greater than approximately 7 nm, they tend to separate from the SiNW surfaces. Further growth and/or agglomeration of these colloidal particles to sizes greater than roughly 25 nm in diameter eventually causes the particles to precipitate from solution. Two interesting phenomena, the "sinking cluster" and the "cluster fusion" processes, were observed under TEM.

An easy and convenient method, using the well-established microtome technique, has been developed to precision cut nanowires into nanodots of well-defined sizes and shapes. The technique allows the determination of the growth direction, the shape of the cross section, the internal atomic structure (including twinning or other stacking faults, if any) of single nanowires. In our experiments, both the coaxial structure of vertical cross section of normal silicon nanowires (SiNWs) and horizontal cross section of necklace-like SiNWs were obtained and examined under TEM.

A new type of well-structured, hydrocarbon nanomaterial including nanotubes and onions, with interlayer spacing ranging from 3.4 to 5.8 A, was discovered by reacting SiNWs with common organic solvents in a laboratory sonicator under ambient conditions (room temperature and atmospheric pressure).