Preparation of gold-tellurium hybrid nanomaterials for surface-enhanced Raman spectroscopy

We report a simple method for preparing three different SERS-active substrates. Concentrated hydrazine solution as the reducing agent and tellurium dioxide as the precursor were used to prepare Te nanowires (NWs). The as-prepared Te NWs have an average length of 547.7 +/- 111.6 nm and an average width of 15.1 +/- 2.7 nm. Through the reaction of Te NWs with sodium tetrachloroaurate in the presence of hexadecyltrimethylammonium bromide (CTAB) over reaction times of 10, 20, and 60 min, gold-tellurium nanodumbbells, gold-tellurium nanopeapods, and gold pearl-necklace nanomaterials (Au PNNs) were obtained, respectively. By controlling the reaction time, the distance between adjacent gold nanoparticles (Au NPs) in each Te nanowire was tunable, allowing us to investigate its effect on the SERS signals. Having shorter distances among Au NPs (greater electromagnetic fields), the Au PNNs provided a reproducible enhancement factor of 5.6 x 10(9).     

Vapor-liquid-solid and vapor-solid growth of phase-change Sb2Te3 nanowires and Sb2Te3/GeTe nanowire heterostructures

We report the synthesis and characterization of radial heterostructures composed of an antimony telluride (Sb2Te3) core and a germanium telluride (GeTe) shell, as well as an improved synthesis of Sb2Te3 nanowires. The synthesis of the heterostructures employs Au-catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) mechanisms. Energy-dispersive X-ray spectrometry indicates that Sb and Ge are localized in the Sb2Te3 and GeTe portions, respectively, confirming the alloy-free composition in the core/shell heterostructures. Transmission electron microscopy and diffraction studies show that Sb2Te3 and GeTe regions exhibit rhombohedral crystal structure. Both Sb2Te3 and GeTe grow along the [110] direction with an epitaxial interface between them. Electrical characterization of individual nanowires and nanowire heterostructures demonstrates that these nanostructures exhibit memory-switching behavior.     

One‐Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super‐ionic Phase Attributes

Cuprous selenide nanocrystals have hallmark attributes, especially tunable localized surface plasmon resonances (LSPRs) and super‐ionic behavior. These attributes of cuprous selenide are now integrated with a one‐dimensional morphology. Essentially, Cu₂Se nanowires (NWs) of micrometer‐scale lengths and about 10 nm diameter are prepared. The NWs exhibit a super‐ionic phase that is stable at temperatures lower than in the bulk, owing to compressive lattice strain along the radial dimension of the NWs. The NWs can be switched between oxidized and reduced forms, which have contrasting phase transition and LSPR characteristics. This work thus makes available switchable, one‐dimensional waveguides and ion‐conducting channels.     

Synthesis and characterization of Ge2Sb2Te5 nanowires with memory switching effect

Ge2Sb2Te5 nanowires (NWs) were synthesized by vaporizing GeTe, Sb, and Te precursors assisted by metal catalysts. Current-voltage measurement of the Ge2Sb2Te5 NW device displays fast and reversible switching between two distinct resistive states, which is due to the crystalline-amorphous phase transition nature of these materials     

A single-source precursor route to unusual PbSe nanostructures by a solution-liquid-solid method

PbSe nanowires (NWs) have been synthesized by using a single-source precursor route. Carefully controlling the conditions of individual reactions leads to PbSe NWs with well-defined diameters (8-25 nm) and lengths (100 nm-1 μm). The as-grown PbSe NWs are highly crystalline, defect free, and readily dispersible in organic solvents. The NWs have been characterized by X-ray diffraction and high-resolution transmission electron microscopy.     

Effects of ZnO nanowire length on surface-assisted laser desorption/ionization of small molecules

The effects of nanowire (NW) length on surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) of small molecules were investigated using ZnO NWs of 50 nm diameter with a broad range of lengths ranging from 25 to 1600 nm. Characterization of the ZnO NWs revealed that the length was the only parameter that varied in this study, while other properties of the NWs remained essentially the same as the bulk properties. Experiments on SALDI efficiency exhibited that the SALDI processes on NWs have a certain length window. In the present case of ZnO NWs, the SALDI efficiency was found to be enhanced on the nanowires of 250 nm length, corresponding to an aspect ratio of 5. The roles of NW length in the SALDI processes were discussed from the viewpoint of efficient energy-transfer media as well as physical obstacles screening laser irradiation and preventing the escape of nascent ions from NW surfaces. The existence of the length window may provide valuable insight for tailoring new nanostructures for efficient SALDI of small molecules.     

Simple method for synthesis of silicon nanowire: Pulsed laser deposition in furnace from p-Si wafer target

Si nanowires (NWs) were fabricated in a vacuum furnace using a Nd:YAG pulsed laser with the wavelength of 325 nm. Commercial p-type Si wafer is used for the target, and no catalytic materials are used. Scanning electron microscopy (SEM) images indicate that the diameters of Si NWs ranged from 10 to 150 nm. Si NWs have various sizes and shapes with a substrate position inside the furnace, and their morphologic construction is reproducible. The formation mechanism of the NWs is discussed.     

Experimental determination of the absorption cross-section and molar extinction coefficient of CdSe and CdTe nanowires

Absorption cross-sections and corresponding molar extinction coefficients of solution-based CdSe and CdTe nanowires (NWs) are determined. Chemically grown semiconductor NWs are made via a recently developed solution-liquid-solid (SLS) synthesis, employing low melting Au/Bi bimetallic nanoparticle "catalysts" to induce one-dimensional (1D) growth. Resulting wires are highly crystalline and have diameters between 5 and 12 nm as well as lengths exceeding 10 microm. Narrow diameters, below twice the corresponding bulk exciton Bohr radius of each material, place CdSe and CdTe NWs within their respective intermediate to weak confinement regimes. Supporting this are solution linear absorption spectra of NW ensembles showing blue shifts relative to the bulk band gap as well as structure at higher energies. In the case of CdSe, the wires exhibit band edge emission as well as strong absorption/emission polarization anisotropies at the ensemble and single-wire levels. Analogous photocurrent polarization anisotropies have been measured in recently developed CdSe NW photodetectors. To further support fundamental NW optical/electrical studies as well as to promote their use in device applications, experimental absorption cross-sections are determined using correlated transmission electron microscopy, UV/visible extinction spectroscopy, and inductively coupled plasma atomic emission spectroscopy. Measured CdSe NW cross-sections for 1 microm long wires (diameters, 6-42 nm) range from 6.93 x 10(-13) to 3.91 x 10(-11) cm2 at the band edge (692-715 nm, 1.73-1.79 eV) and between 3.38 x 10(-12) and 5.50 x 10(-11) cm2 at 488 nm (2.54 eV). Similar values are obtained for 1 microm long CdTe NWs (diameters, 7.5-11.5 nm) ranging from 4.32 x 10(-13) to 5.10 x 10(-12) cm2 at the band edge (689-752 nm, 1.65-1.80 eV) and between 1.80 x 10(-12) and 1.99 x 10(-11) cm2 at 2.54 eV. These numbers compare well with previous theoretical estimates of CdSe/CdTe NW cross-sections far to the blue of the band edge, having order of magnitude values of 1.0 x 10(-11) cm2 at 488 nm. In all cases, experimental NW absorption cross-sections are 4-5 orders of magnitude larger than those for corresponding colloidal CdSe and CdTe quantum dots. Even when volume differences are accounted for, band edge NW cross-sections are larger by up to a factor of 8. When considered along with their intrinsic polarization sensitivity, obtained NW cross-sections illustrate fundamental and potentially exploitable differences between 0D and 1D materials.     

Amplified ultraviolet detection of natural DNA based on Mo6S9-xIx nanowires

We demonstrate that Mo_6S_(9_x)I_x nanowires(MoSI NWs) can serve as an excellent signal-intensifying nanomaterial for highly sensitive and label-free detection of DNA by ultraviolet(UV) spectrophotometry.The DNA extinction at 260 nm was greatly enhanced after addition of MoSI NWs solute,and the extinction value was linear with DNA concentration in the range of 0.0289-11.68 μg/mL with the real determination limit of 28.9 ng/mL.The association of DNA with the nanowires was characterized by transmission electronmicroscopy and circular dichroic spectroscopy.The results illustrate that the UV response amplification of DNA in the presence of MoSI NWs is attributed to the greater DNA coverage on the MoSI NW surface and the conformational transformation of DNA due to interaction of DNA with MoSI NWs.MoSI NWs are a promising nano-structured material for developing ultrasensitive sensors for detection of DNA.     

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.     

Si衬底上生长的铁硅化合物结构和取向分析

采用分子束外延法分别在650-920℃的Si(110)和920℃的Si(111)衬底表面生长出铁的硅化物纳米结构,并主要分析了920℃高温下纳米结构的形貌、组成相及其与Si衬底的取向关系.扫描隧道显微镜(STM)研究表明,920℃高温下,Si(110)衬底上生长的铁硅化合物完全以纳米线的形式存在,且其尺寸远大于650℃低温下外延生长的纳米线尺寸;Si(111)衬底上生长出三维岛和薄膜两种形貌的铁硅化合物,其中三维岛具有金属特性且直径约300 nm、高约155 nm,薄膜厚度约2 nm.电子背散射衍射研究表明920℃高温下Si(110)衬底上生长的纳米线仅以β-FeSi2的形式存在,且β-FeSi2相与衬底之间存在唯一的取向关系:β-FeSi2(101)//Si(11 1);β-FeSi2[010]//Si[110];Si(111)衬底上生长的三维岛由六方晶系的Fe2Si相组成,Fe2Si属于164空间群,晶胞常数为a=0.405 nm,c=0.509 nm;与衬底之间的取向关系为Fe2Si(001)∥Si(111)和Fe2Si[1 20]//Si[112].     

Halogen Vacancies Enable Ligand‐Assisted Self‐Assembly of Perovskite Quantum Dots into Nanowires

Interest has been growing in defects of halide perovskites in view of their intimate connection with key material optoelectronic properties. In perovskite quantum dots (PQDs), the influence of defects is even more apparent than in their bulk counterparts. By combining experiment and theory, we report herein a halide‐vacancy‐driven, ligand‐directed self‐assembly process of CsPbBr₃ PQDs. With the assistance of oleic acid and didodecyldimethylammonium sulfide, surface‐Br‐vacancy‐rich CsPbBr₃ PQDs self‐assemble into nanowires (NWs) that are 20–60 nm in width and several millimeters in length. The NWs exhibit a sharp photoluminescence profile (≈18 nm full‐width at‐half‐maximum) that peaks at 525 nm. Our findings provide insight into the defect‐correlated dynamics of PQDs and defect‐assisted fabrication of perovskite materials and devices.     

Synthesis of silver nanodisks using polystyrene mesospheres as templates

We report the synthesis of Ag nanodisk using polystyrene mesospheres as templates. TEM measurements show that the average disk thickness is 9.0 +/- 1.0 nm and the diameter is 36 +/- 8 nm. The particles exhibit an intense electronic spectrum that differs markedly from that for spheres (purple vs yellow solutions). We present electromagnetic theory calculations which exhibit a qualitative match with the observed spectrum, enabling us to assign several of the plasmon resonance features.     

A universal strategy for fast,scalable, and aqueous synthesis of multicomponent palladium alloy ultrathin nanowires

Noble metal alloy nanowires(NWs)with ultrathin diameters(2–3 nm)and precisely controllable elemental compositions have attracted dramatically growing attention for(electro)catalysis.Despites numerous achievements in past two decades,noble metal alloy NWs are mostly synthesized with the traditional oil-phase methods that suffer from some undesirable drawbacks.Here,we report a general strategy for fast,scalable,and aqueous synthesis of multicomponent Pd-based alloy ultrathin NWs with an average diameter of 2.6 nm,ranging from bimetallic PdM(PdFe,PdCo,PdNi,PdCu,PdZn,PdRu,PdRh,PdAg,PdCd,PdIr,PdPt,PdAu)and binary PdS/PdP NWs,to trimetallic PdM1M2 NWs(PdAuCu,PdCoNi,PdCuZn,PdCuNi,PdAgCu,PdAuCu,PdRuAg,PdAuRu,and PdPtAu),and to tetrametallic PdM1M2M3 NWs(PdAuAgCu,PdCoCuNi,PdAuCuNi,PdPtAuCu,and PdIrPtAu).The key to the success of this aqueous synthesis is the utilization of N2H4 as the extremely strong reducing agent that directs the synchronous reduction and anisotropic nucleation growth of multicomponent Pd alloy NWs along nanoconfined columnar phase assembled with amphiphilic dioctadecyldimethylammonium chloride.As-resultant Pd-based alloy ultrathin NWs exhibit multiple structural and compositional synergies,which remarkably optimize the removal of poisoning ethoxy intermediates and thus improve electrocatalytic performance towards ethanol oxidation reaction(EOR).Among them,tetrametallic PdAuCuNi alloy ultrathin NWs hold a high EOR activity of 5.14 A mg-1 Pd and a low activation energy of 13.1 kJ mol^-1,both of which are much better than its counterpart catalysts alloyed with less elements.This work represents an important advance in precise aqueous synthesis of multicomponent noble metal alloy ultrathin NWs as the high-performance electrocatalysts for various targeted applications.     

From Precursor Powders to CsPbX3 Perovskite Nanowires: One‐Pot Synthesis,Growth Mechanism,and Oriented Self‐Assembly

The colloidal synthesis and assembly of semiconductor nanowires continues to attract a great deal of interest. Herein, we describe the single‐step ligand‐mediated synthesis of single‐crystalline CsPbBr₃ perovskite nanowires (NWs) directly from the precursor powders. Studies of the reaction process and the morphological evolution revealed that the initially formed CsPbBr₃ nanocubes are transformed into NWs through an oriented‐attachment mechanism. The optical properties of the NWs can be tuned across the entire visible range by varying the halide (Cl, Br, and I) composition through subsequent halide ion exchange. Single‐particle studies showed that these NWs exhibit strongly polarized emission with a polarization anisotropy of 0.36. More importantly, the NWs can self‐assemble in a quasi‐oriented fashion at an air/liquid interface. This process should also be easily applicable to perovskite nanocrystals of different morphologies for their integration into nanoscale optoelectronic devices.     

Si衬底上生长的铁硅化合物结构和取向分析

采用分子束外延法分别在650-920 ℃的Si（110）和920 ℃的Si（111）衬底表面生长出铁的硅化物纳米结构,并主要分析了920 ℃高温下纳米结构的形貌、组成相及其与Si 衬底的取向关系. 扫描隧道显微镜（STM）研究表明,920 ℃高温下,Si（110）衬底上生长的铁硅化合物完全以纳米线的形式存在,且其尺寸远大于650 ℃低温下外延生长的纳米线尺寸;Si（111）衬底上生长出三维岛和薄膜两种形貌的铁硅化合物,其中三维岛具有金属特性且直径约300 nm、高约155 nm,薄膜厚度约2 nm. 电子背散射衍射研究表明920 ℃高温下Si（110）衬底上生长的纳米线仅以β-FeSi₂的形式存在,且β-FeSi₂相与衬底之间存在唯一的取向关系：β-FeSi₂（101）//Si（111）;β-FeSi₂ [010]//Si[110];Si（111）衬底上生长的三维岛由六方晶系的Fe₂Si 相组成,Fe₂Si 属于164 空间群,晶胞常数为a=0.405 nm,c=0.509 nm;与衬底之间的取向关系为Fe₂Si（001）∥Si（111）和Fe₂Si[120]//Si[112].     

Gel electrophoresis of polystyrene particles in glutaraldehyde crosslinked polyvinyl alcohol

Polystyrene sulfate and carboxylate particles (19-189 nm radius) were subjected to electrophoresis in glutaraldehyde crosslinked polyvinyl alcohol of molecular weight 25.000 and 650.000 Da at various concentrations. The degree of crosslinking is severely limited by the mechanical properties of the gels that deteriorate beyond a glutaraldehyde concentration which decreases with increasing polyvinyl alcohol chain length. The effective fiber radius of the short-chain and long-chain polymer fiber was 45 +/- 25 and 131 +/- 47 nm, respectively. Thus, these media do not significantly exceed the apparent fiber thickness of agarose, are more difficult to prepare--but are well-defined synthetic products rather than natural ones, and have the advantage of carrying no net charge and can therefore be expected to exhibit no electroendosmosis.     

Photodissociation dynamics of fluorobenzene (C6H5F) at 157 and 193 nm: Branching ratios and distributions of kinetic energy

Following photodissociation of fluorobenzene (C6H5F) at 193 and 157 nm, we detected the products with fragmentation-translational spectroscopy by utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Between two primary dissociation channels observed upon irradiation at 193 (157) nm, the HF-elimination channel C6H5F --> HF + C6H4 dominates, with a branching ratio of 0.94+/-0.02 (0.61+/-0.05) and an average release of kinetic energy of 103 (108) kJ mol(-1); the H-elimination channel C6H5F --> H + C6H4F has a branching ratio of 0.06+/-0.02 (0.39+/-0.05) and an average release of kinetic energy of 18.6 (26.8) kJ mol(-1). Photofragments H, HF, C6H4, and C6H4F produced via the one-photon process have nearly isotropic angular distributions. Both the HF-elimination and the H-elimination channels likely proceed via the ground-state electronic surface following internal conversion of C6H5F; these channels exhibit small fractions of kinetic energy release from the available energy, indicating that the molecular fragments are highly internally excited. We also determined the ionization energy of C6H4F to be 8.6+/-0.2 eV.     

Luminescent properties of pure cubic phase Y2O3/Eu3+ nanotubes/nanowires prepared by a hydrothermal method

One-dimensional pure cubic Y(2)O(3)/Eu(3+) nanocrystals (NCs) were synthesized by a hydrothermal method at various temperatures. The NCs prepared at 130 degrees C yielded nanotubes (NTs) with wall thickness of 5-10 nm and outer diameter of 20-40 nm. The NCs prepared at 170 and 180 degrees C yielded nanowires (NWs) with diameters of approximately 100 and approximately 300 nm, respectively. Their luminescent properties, including electronic transition processes, local environments surrounding Eu(3+) ions, electron-phonon coupling, and UV light irradiation induced spectral changes have been systematically studied and compared. The results indicate that the Y(2)O(3)/Eu(3+) NTs and NWs have strong red (5)D(0)-(7)F(2) transitions. The fluorescence lifetime of (5)D(1)-(7)F(1) hardly changes in different samples, while that of (5)D(0)-(7)F(2) decreases a small amount in Y(2)O(3)/Eu(3+) NTs. The (5)D(0)-(7)F(2) lines originate from the emissions of Eu(3+) ions occupying one C(2) site, like that in the bulk powders. The phonon sideline with a frequency shift of 40-50 cm(-1) appears at the low-energy side of the (7)F(0)-(5)D(0) zero phonon line. The relative intensity of the sideline to zero phonon line increases by varying from NTs to NWs, and the spectral position of the phonon sideline shifts red. The UV light irradiation induced spectral change in the charge-transfer band was studied. The results indicate that the spectral change is dependent on sample size and is wavelength selective. A detailed model was proposed to explain the light-induced spectral change.     

Rapid Capillary-Assisted Solution Printing of Perovskite Nanowire Arrays Enables Scalable Production of Photodetectors

Despite recent progress in producing perovskite nanowires (NWs) for optoelectronics, it remains challenging to solution-print an array of NWs with precisely controlled position and orientation. Herein, we report a robust capillary-assisted solution printing (CASP) strategy to rapidly access aligned and highly crystalline perovskite NW arrays. The key to the CASP approach lies in the integration of capillary-directed assembly through periodic nanochannels and solution printing through the programmably moving substrate to rapidly guide the deposition of perovskite NWs. The growth kinetics of perovskite NWs was closely examined by in situ optical microscopy. Intriguingly, the as-printed perovskite NWs array exhibit excellent optical and optoelectronic properties and can be conveniently implemented for the scalable fabrication of photodetectors.