How strain controls electronic linewidth in single beta-phase polyfluorene nanowires

Low-temperature single-molecule fluorescence spectroscopy reveals pure, virtually defect-free chains of the one-dimensional crystalline beta-phase of polyfluorene. The likelihood of beta-phase formation is shown to correlate directly with the initial shape of the polymer chain, with extended chains preferentially forming this planarized phase. Planarized chains, characterized by a distinct spectroscopic signature can, however, exhibit substantial bending within the plane. This bending results in a strong increase in the elementary transition linewidth of the conjugated segment. The transition linewidth provides a lower limit to the electronic dephasing time of the excited state of >3 ps at 5 K. Remarkably, bending does not appear to disrupt the pi-electron conjugation so that the emission from a single bent beta-phase chromophore is not necessarily linearly polarized as is generally assumed.     

Mass and stiffness calibration of nanowires using thermally driven vibration

Cantilevered or suspended nanowires show promise for force or mass sensing applications due to their small mass, high force sensitivity and high frequency bandwidth. To use these as quantitative sensors, their bending stiffness or mass must be calibrated experimentally, often using thermally driven vibration. However, this can be difficult because nanowires are slightly asymmetric, which results in two spatially orthogonal bending eigenmodes with closely spaced frequencies. This asymmetry presents problems for traditional stiffness calibration methods, which equate the measured thermal vibration spectrum near a resonance to that of a single eigenmode. Moreover, the principal axes may be arbitrarily rotated with respect to the measurement direction. In this work, the authors propose a method for calibrating the bending stiffness and mass of such nanowires' eigenmodes using a single measurement taken at an arbitrary orientation with respect to the principal axes.     

Rapid mass production of ZnO nanowires by a modified carbothermal reduction method

ZnO nanowires are one of the most important nanomaterials for future optoelectronic nanodevices. However, the challenge of producing great quantities of ZnO nanowires has hindered the wide application and commercialization of ZnO nanowires. Here, we employ a modified carbothermal reduction method to synthesize great quantities of ZnO nanowires within 5 min. The synthesis was carried out in a quartz tube furnace at atmospheric pressure without using any catalysts. A nitrogen/air mixed gas was used as a reactive and carrier gas. About 0.85 g ZnO nanowires were obtained using 1 g ZnO and 1 g graphite powder as source materials. The prepared ZnO nanowires exhibited a hexagonal wurtzite crystal structure. The average length and diameter of the prepared ZnO nanowires were about 1.8 μm and 35 nm, respectively. Optical absorption and photoluminescence properties of the prepared ZnO nanowires have also been investigated.     

Wurtzite-zincblende superlattices in InAs nanowires using a supply interruption method

Crystal phase control in single III-V semiconductor nanowires has emerged recently as an important challenge and possible complement to conventional bandgap engineering in single material systems. Here we investigate a supply interruption method for precise crystal phase control in single nanowires. The nanowires are grown by metalorganic vapor phase epitaxy using gold particles as seeds and are analyzed by transmission electron microscopy. It is observed that wurtzite segments with controlled length and position can be inserted on demand into a pure InAs zincblende nanowire. The interface between wurtzite and zincblende segments can be made atomically sharp and the segments can be made only a few bilayers in thickness. The growth mechanisms, applicability and limitations of the technique are presented and discussed.     

Assessment of bioengineering ceramic coatings using the wetting method

The wettability of coatings, including ceramic ones, which show considerable promise for the use on bioengineering products, with physical solution (0.9% NaCl) have been studied. It has been found that the use of coatings of all types under study increases the wetting angles on the surface as compared with the initial metal materials (stainless steel of the 12X18H10T grade, titanium alloy of the BT6-grade, Co-Cr-Mo alloy), which serves as a prerequisite for an improvement in the biocompatibility of implants. The degree of the coating bioinertness increases in the following order: titanium nitride → diamond carbon films → aluminum nitride → titanium oxide (anodic oxide film) → nitride (oxidized) → oxide → titanium oxide (anodic-spark coating).     

Preparation of carbon nanotubes with iron nanowires inside using a simple microwave-based method

The importance of synthesizing carbon nanotubes with iron nanowires inside (Fe-MWNTs) via microwave radiation lies in the fact that it allows to improve aspects such as selective and uniform heating of the sample, reduction of the time of synthesis, avoiding complex experimental procedures and lowering the cost of production. In this paper we synthesize and characterize carbon nanotubes with iron nanowires inside using a mixture of graphite and iron acetate powders as starting materials and a 900 W domestic microwave oven used as power source. A mixture of the starting materials inside a vacuum sealed quartz ampoule was subjected to radiation for 7 min. As a result straight Fe nanowires are obtained with lengths between 5 and 15 microns, and a wide variety of partially Fe filled nanotubes with diameters in the 30–80 nm range. Samples were characterized with scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

Mass production of ZnO nanotetrapods by a flowing gas phase reaction method

We have developed a flowing gas phase reaction method for synthesizing ZnO nanotetrapods. The synthesis was carried out in a tube furnace under air pressure using air and nitrogen as reactive and carrying gases. The zinc precursor was provided by carbothermal reduction of ZnO powder. The source material transformation efficiency is higher than 90%. ZnO nanotetrapods were nucleated and grown in the gas phase via a vapor-solid mechanism. The reaction occurred at a temperature controlled to 1050-1200?°C and gas flow rate controlled to 0.7-2?L/min. The high flow rate suppressed the diffusion of growth precursors and productions towards the tube wall, and localized them into a gas phase pipe. The harvested ZnO nanotetrapods were carried by the flowing gas and collected outside of the furnace. The sizes of the nanotetrapods range from several hundred nanometers to more than 10?μm with leg diameters of 30-200?nm. The flowing gas phase reaction method provides a relatively uniformity environment for nanotetrapod growth and simplifies the product collection procedure compared with other techniques. This technique is simple and inexpensive, which is promising for realizing continuous mass production of ZnO nanotetrapods on a factory scale.     

One-step growth of curled GaN nanowires using chemical vapor deposition method

The studies of curled GaN nanowires grown on sapphire and silicon substrate using chemical vapor deposition method have been reported in this article. The mean diameters of the nanowires grown on sapphire and silicon were 108.1 nm and 98 nm respectively. A growth model was proposed to describe the growth of nanowires. X-ray diffraction pattern and Raman spectroscopy revealed that the nanowires were hexagonal wurtzite in structure. Gaussian fitting was done on photoluminescence spectra, which revealed two sub-bands that could be attributed to band emission and surface disorder caused by impurities. The absence of yellow luminescence signified undoped case and minimal shallow level defects.     

等离子体射流法制备高纯竹节状碳纳米管

以乙醇为碳源，二茂铁为催化剂，氮气为电弧工作气体，利用等离子体射流在常压下制备高纯度竹节状多壁碳纳米管。用TEM和HRTEM等技术对所得产品进行表征。发现在电弧电压140V～150V，电流220A～240A，将二茂铁和乙醇混合溶液（质量比为1：100）以50mL／min速度连续加入反应器，反应120S后，即可批量制备纯度在90％以上的竹节状碳纳米管；这些竹节状碳纳米管的管径尺寸均匀，为20nm左右，长度为数微米，其管壁呈典型的鱼骨状。产品中含有部分分叉结构，呈Y形竹节状碳纳米管。认为竹节状碳纳米管的形成涉及以下几个步骤：乙醇在等离子体射流中裂解产生大量碳活性物种，同时溶解在乙醇中的二茂铁生成催化剂颗粒：碳活性物种在催化剂颗粒上溶解、扩散并从催化剂颗粒上析出堆积成为碳纳米管管壁碳层，由于催化剂颗粒运动与碳层生长速度的差异，最终形成竹节状结构的碳纳米管。     

Synthesis of copper telluride nanowires using template-based electrodeposition method as chemical sensor

Copper telluride (CuTe) nanowires were synthesized electrochemically from aqueous acidic solution of copper (II) sulphate (CuSO₄·5H₂O) and tellurium oxide (TeO₂) on a copper substrate by template-assisted electrodeposition method. The electrodeposition was conducted at 30 °C and the length of nanowires was controlled by adjusting deposition time. Structural characteristics were examined using X-ray diffraction and scanning electron microscope which confirm the formation of CuTe nanowires. Investigation for chemical sensing was carried out using air and chloroform, acetone, ethanol, glycerol, distilled water as liquids having dielectric constants 1, 4·81, 8·93, 21, 24· 55, 42·5 and 80·1, respectively. The results unequivocally prove that copper telluride nanowires can be fabricated as chemical sensors with enhanced sensitivity and reliability.     

Large-scale synthesis of silver nanowires via a solvothermal method

Silver nanostructures have been synthesized through a simple solvothermal method by reducing silver nitrate (AgNO₃) with ethylene glycol (EG) and using poly(vinylpyrrolidone) (PVP) as an adsorption agent. Different concentrations of ferric chloride (FeCl₃) are added into the solution. It is found that AgCl colloids formed in the initial stage greatly influence the final morphologies of the products. When a low-concentration FeCl₃ solution is used, there is a mixture of silver nanoparticles and nanowires. However, when a high-concentration FeCl₃ solution (100 μM) is used, large amounts of AgCl colloids appear, resulting in decreasing free Ag⁺ during initial formation of silver seeds and slowly releasing of Ag⁺ to the solution in the subsequent reaction. This leads to the formation of silver nanowires. Furthermore, an increase in the concentration of FeCl₃ from 100 to 300 μM results in the synthesis of silver nanowires with larger sizes. In addition, Fe(III) is reduced to Fe(II) form which in turn reacts with and removes adsorbed atomic oxygen from the surface of silver seeds. In this case, uniform silver nanowires can be obtained.     

Measurement of wetting properties of individual boron nitride nanotubes with the wilhelmy method using a nanotube-based force sensor

The wetting properties of individual boron nitride nanotubes (BNNTs) were studied with the Wilhelmy method in ambient conditions. A nanotube-based force sensor having a force resolution of 0.1 nN, calibrated with the wetting force method, was used to study the interactions between BNNTs and liquids in situ. The static contact angles of the liquids on BNNTs were evaluated, and the surface tension of the BNNT along with its surface tension components was determined based on the Owens and Wendt method and the van Oss-Chaudhury-Good acid-base theory.     

Toward local growth of individual nanowires on three-dimensional microstructures by using a minimally invasive catalyst templating method

We present a novel minimally invasive postprocessing method for catalyst templating based on focused charged particle beam structuring, which enables a localized vapor-liquid-solid (VLS) growth of individual nanowires on prefabricated three-dimensional micro- and nanostructures. Gas-assisted focused electron beam induced deposition (FEBID) was used to deposit a SiO(x) surface layer of about 10 × 10 μm(2) on top of a silicon atomic force microscopy cantilever. Gallium focused ion beam (FIB) milling was used to make a hole through the SiO(x) layer into the underlying silicon. The hole was locally filled with a gold catalyst via FEBID using either Me(2)Au(tfac) or Me(2)Au(acac) as precursor. Subsequent chemical vapor deposition (CVD)-induced VLS growth using a mixture of SiH(4) and Ar resulted in individual high quality crystalline nanowires. The process, its yield, and the resulting angular distribution/crystal orientation of the silicon nanowires are discussed. The presented combined FIB/FEBID/CVD-VLS process is currently the only proven method that enables the growth of individual monocrystalline Si nanowires on prestructured substrates and devices.     

Fabrication and characteristics of polyfluorene based organic photodetectors using fullerene derivatives

The characteristics of organic photodetectors (OPDs) by solution process using one of the polyfluorene derivatives poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) and two fullerene derivatives [6-6]phenyl-C61-butyric acid methyl ester (PCBM) or N-Ts aziridinofullerene (TsAF) are investigated. F8T2:PCBM devices showed good rectifying characteristics in a dark state and photosensitive characteristics, and fast frequency responses. Weight ratio of 1:1 device showed larger photocurrent than 1:4 device and obtained over 50 MHz of cutoff frequency under reverse bias voltage of 10 V. This result suggests that F8T2:PCBM device can be applied to a photodetector for detecting several tens of megahertz optical signals under blue light irradiation. The polarity of J–V characteristics of F8T2:fullerene derivative device is strongly affected by charge injection and extraction between fullerene derivative and electrodes.     

Synthesis of aluminum borate nanowires via a novel flux method

Nanowires made of aluminum borate formed of Al₁₈B₄O₃₃ have been synthesized in high yield by improving the traditional chemical flux method for the growth of aluminum borate with the fibrous structure. In this study, aluminum powder was added into the aluminum oxide and boron oxide reactants as an additive in order to control the morphology of the final products. The chemical method reported here is utilized to decrease the diameters of traditional aluminum borate fiber into nanoscale and to increase their lengths. The optimum experimental parameters and possible growth mechanism for the compound nanowires have been presented.     

Synthesis of FePt nanorods and nanowires by a facile method

FePt nanorods and nanowires have been synthesized by the reduction of Pt(acac)(2) and the thermal decomposition of Fe(CO)(5) in the presence of solvents/surfactants by simply controlling the sequence of addition of surfactants. The as-synthesized FePt nanorods and nanowires have a face centered cubic structure with average diameter of 3?nm. Length of nanorods and nanowires can be adjusted in the range of 15-150?nm by varying reaction parameters. Nanocrystalline L1(0) FePt phase with coercivity up to 24?kOe was obtained after heat treatments.     

Complete composition tunability of InGaN nanowires using a combinatorial approach

The III nitrides have been intensely studied in recent years because of their huge potential for everything from high-efficiency solid-state lighting and photovoltaics to high-power and temperature electronics. In particular, the InGaN ternary alloy is of interest for solid-state lighting and photovoltaics because of the ability to tune the direct bandgap of this material from the near-ultraviolet to the near-infrared region. In an effort to synthesize InGaN nitride, researchers have tried many growth techniques. Nonetheless, there remains considerable difficulty in making high-quality InGaN films and/or freestanding nanowires with tunability across the entire range of compositions. Here we report for the first time the growth of single-crystalline In(x)Ga(1-x)N nanowires across the entire compositional range from x=0 to 1; the nanowires were synthesized by low-temperature halide chemical vapour deposition and were shown to have tunable emission from the near-ultraviolet to the near-infrared region. We propose that the exceptional composition tunability is due to the low process temperature and the ability of the nanowire morphology to accommodate strain-relaxed growth, which suppresses the tendency toward phase separation that plagues the thin-film community.