p-n hetero-junction diode arrays of p-type single walled carbon nanotubes and aligned n-type SnO₂ nanowires

p-n hetero-junction diode arrays were fabricated using specific direct techniques for the transfer of p-type single walled carbon nanotubes (SWCNTs) and aligned n-type SnO? nanowires (NWs) onto a patterned substrate surface. Their electronic and optoelectronic properties were characterized. Perpendicular crossings of the p- and the n-channels with each other were confirmed by transfer characteristics with respect to the bottom gate. The resulting diode showed a good rectifying behavior with a rectification ratio of over 102 at ±5 V, where the equivalent circuit model of a serially connected diode and resistor was used for analysis of the electrical properties. Both the forward and the reverse currents were observed to increase with the application of a positive gate bias, indicating an n-type gate dependence. Under a forward bias, the dominant contribution of the SnO? NW channel to the total resistance of the equivalent model is attributed to the n-type gate dependence since the resistance of the n-channel increased with a negative gate bias, resulting in the decrease of the forward current. Under a reverse bias, positive gate increased the concentration of valence electrons in the SWCNTs, enhancing direct tunneling to the conduction band of the SnO? NWs. High sensitivity to UV irradiation under the reverse bias was also demonstrated with a photosensitivity over 102, suggesting potential applicability of the hetero-junction diodes in optoelectronic devices.     

Synthesis of aligned arrays of “Microropes” of silica nanowires by gas-jet electron beam plasma chemical vapor deposition method

For the first time, aligned arrays of bundles (“microropes”) of silica nanowires were synthesized from a monosilane-hydrogen mixture by gas-jet electron beam plasma chemical vapor deposition method. The synthesis was performed on single-crystal silicon substrates coated by micron-sized particles of stannic catalyst. A bundle (“microrope”) of silica nanowires each of which is about 15 nm in diameter grows from a catalyst particle. It seems that the synthesis proceeds by the vapor-liquid-solid mechanism, and several nanowires grow synchronously from the surface of one catalyst particle. The “microrope” growth rate was about 25 nm/s at a synthesis temperature of 400°C. A possible growth model was proposed to explain these results.     

Synthesis and field emission properties of topological insulator Bi₂Se₃ nanoflake arrays

High quality Bi(2)Se(3) nanoflake arrays with a large area and high-yield production have been fabricated by chemical vapor deposition. As the essential candidate for a topological insulator, the unique surface electronic states are considered to play a crucial role distinct from the bulk. Our experimental results show that environmental doping significantly affects the field emission properties of the synthesized Bi(2)Se(3) nanoflake arrays. X-ray photoelectron spectroscopy characterizations indicate that the rapid surface oxidation may prohibit the detection of the topological surface state and results in a low field emission current. This work provides another insight to investigate the surface state of topological insulator materials.     

Selective growth of vertically aligned double- and single-walled carbon nanotubes on a substrate at 590 °C

Vertically aligned double-?and single-walled carbon nanotubes (DWNTs and SWNTs) were synthesized on a substrate at 590?°C by hot-filament chemical vapor deposition. An optimized combination of iron and aluminum layers as the catalyst resulted in iron particles ranging from 1-5?nm floating in an aluminum matrix after annealing. Selective synthesis of DWNTs and SWNTs from such particles was achieved by adjusting the dilution ratio of acetylene that was used as the source gas. The yield of DWNTs among all CNTs was as high as 81%, while that of SWNTs was almost 100%. The diameter distribution of DWNTs was narrow, with a standard deviation of about 12%.     

Investigation of superconductivity in electrochemically fabricated AuSn nanowires

We have fabricated intermetallic AuSn nanowires by electrochemical deposition in porous polycarbonate membranes. By controlling the deposition parameters, nanowires of a single intermetallic phase, namely AuSn, can be fabricated. AuSn nanowires are found to be crystalline and fairly resistant to oxidation. Electrical transport measurements on arrays of nanowires showed a superconducting transition temperature, T(c)～1.5?K. In addition, four-probe measurements were made on individual freestanding nanowires with electrodes formed by a focused ion beam (FIB). Results from the two sets of measurements are found to be in close agreement.     

Buckling of Cu–Zr-based metallic glasses nanowires: molecular dynamics study of surface effects

The phenomenon of buckling in Cu₄₅Zr₄₅Al₁₀ metallic glass nanowires with different slenderness ratios was studied by means of molecular dynamics simulation. The values of critical stress versus slenderness ratio for two nanowire diameters were obtained. We analyzed the results within the framework of the modified Euler theory of buckling, obtaining values for the surface elastic modulus and the residual surface stress for the two different diameters. Our results show that the Cu₄₅Zr₄₅Al₁₀ metallic glass in nanometric size become stiffer and exhibits a lower Young’s modulus than that of a bulk sample.     

The growth of aligned carbon nanotubes on quartz substrate by spray pyrolysis of hexane

Vertically aligned multiwall carbon nanotubes were grown by spray pyrolysis of hexane as the carbon source in the presence of ferrocene as catalyst precursor on a quartz substrate. In recent work we used optimal experimental parameters for the feeding method, reactor conditions, reaction temperature and time, concentration of catalyst and flow rate of feed and gas. The process parameters were chosen so as to obtain multiwall carbon nanotubes and aligned multiwall carbon nanotubes. The tubes are around 15-80?nm in diameter. The morphology and structure of the samples were characterized by x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses.     

Sol–gel template synthesis and characterization of aligned anatase-TiO2 nanorod arrays with different diameter

Template-based growth has been demonstrated as an attractive method for the synthesis of oxide nanorod arrays. In this paper, TiO₂ nanorod arrays in anodic alumina membranes have successfully been synthesized by an improved sol–gel template method. TiO₂ nanorods were obtained to injection of prepared TiO₂-sol from the sol–gel process and then the samples were immediately immersed into boiling TiO₂-sol solutions. Aligned TiO₂ nanorod arrays were polycrystalline anatase-phase after annealing at 400 °C for 2 h with diameters about 160–250, 80–130 and 40–70. A lateral shrinkage approximately 15–20% was found in TiO₂ nanorods with respect to the template pore diameter. This size difference is likely due to the volume shrinkage caused by removing residual materials and densification during annealing.     

Efficient growth of aligned SnO2 nanorod arrays on hematite (α-Fe2O3) nanotube arrays for photoelectrochemical and photocatalytic applications

SnO₂ nanorod arrays were fabricated on hematiete nanotube arrays by an efficient hydrothermal method. The hematiete nanotube arrays were prepared by anodization of pure iron foil in an ethylene glycol solution. SnO₂ nanorod arrays grew from the bottom of hematite nanotubes and were firmly combined with the iron foil substrate. The morphology and microstructure of SnO₂ nanorod arrays are investigated by field-emission scanning electron microscopy, grazing incidence X-ray diffraction and UV–Vis absorbance spectra. The sample presented typical SnO₂ nanorod arrays (reacted for 2 h) generally of 400 nm in length and 50 nm in side width showed the best photocatalytic activity and photoelectrochemical response under the UV illumination. It should be attributed to the effective electron–hole separation and the excellent electron transfer pathway along the 1D SnO₂ nanorod arrays and hematiete nanotube arrays.     

Field emission and I–V characteristics of template synthesised nickel nanowires on semiconducting substrate

Ion track technology makes it possible to produce a low cost template for the synthesis of nanowires. In this article, spin-coated polycarbonate films have been irradiated by energetic 150?MeV Ni ion at a fluence of 8E7, followed by UV irradiation and chemical etching in aqueous NaOH (6N,?29°C). Ni nanowires were electrochemically synthesised in the pores created in the polycarbonate film. The nanostructures thus synthesised were morphologically analysed using scanning electron microscopy and further studied for their electrical and field emission properties.     

Characterization of the Response of CaWO4 on Recoiling Nuclei from Surface Alpha Decays

A potentially harmful background for experiments attempting direct dark matter detection like the CRESST (= Cryogenic Rare Event Search with Superconducting Thermometers) experiment is caused by recoiling nuclei from ²¹⁰Po alpha decays on surfaces close to the detector. In order to characterize this kind of background in CRESST, calibration measurements have been performed at the TU München. A for this purpose an optimized version of the CRESST detector has been developed consisting of a 38 g CaWO₄ crystal and a separate cryogenic light detector, both equipped with Ir/Au transition edge sensors (TESs). The simultaneous measurement of the phonon signal and the scintillation light from the CaWO₄ crystal allows to discriminate between electron and nuclear recoils using their different light outputs. The unexpected results of a first measurement with a ²¹⁰Po source can be understood with the help of a Monte Carlo simulation performed for a similar system.      

Facile loading of metal ions in the nanopores of polymer thin films and in situ generation of metal sulfide nanoparticle arrays

Two facile strategies for loading metal ions in the nanopores of polystyrene-b-polyisoprene (PS-b-PI) polymeric thin films have been developed. In the first approach, through the controlled epoxidation of the polyisoprene (PI) component of the template, the hydrophilicity of the interior wall of the nanopores was increased, and the penetration of metal salt solutions into the nanopores was dramatically enhanced. However, thin film damage was observed sometimes during the PI epoxidation. Using a 'fully wetted' method, large capillary forces were suppressed, and the metal ions were easily introduced into the nanopores. The validation of the methods was illustrated for the generation of large-area and high-density CdS and ZnS nanoparticle arrays in nanoporous PS-b-PI polymeric thin films, which were characterized using atomic force microscopy (AFM), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), electron diffraction (ED), and UV-vis spectroscopy.     

Plasmon tuning and local field enhancement maximization of the nanocrescent

We present a systematic numerical study of plasmon resonance of the nanocrescent. We show that by varying the nanocrescent geometry, the plasmon resonance peak can be tuned into the near-infrared and local field enhancement can be increased significantly, with maximum enhancement of the electric field amplitude of approximately 100 for realistic geometric parameters. Because of its wide tunability, high local field enhancement, and geometry which utilizes both sharp features and intra-particle coupling, the nanocrescent is a structure well suited for in vivo cellular imaging as well as in vitro diagnostic applications.     

Dynamic emission of dislocations from a crack tip — a computer simulation

The behavior of dynamic emission of dislocations from the tip of a stationary crack under mode II or mode III loading is examined. A critical stress intensity factor, K _D is assumed for dislocation emission. After emission, the dislocation moves with a velocity which varies with the effective shear stress to the third power. The effective shear stress is due to the applied stress , modified by the presence of the crack and all other dislocations minus the lattice friction stress, ^F. The effects of K _D, , and ^F on the rate of emission, the plastic zone strain rate, the plastic zone size, the dislocation distribution, and the dislocation-free zone are reported.

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Résumé On a examiné le comportement d'une émission dynamique de dislocations depuis l'extrémité d'une fissure stationnaire. On suppose que l'émission de dislocations est caractérisée par un facteur critique d'intensité de constrainte K _D. Après son émission, la dislocation se meut avec une vitesse qui varie avec le cube de la constrainte effective de cisaillement. Celle-ci résulte de la constrainte appliquée , modifiée par la présence de la fissure et de toutes les autres dislocations, et sous déduction de la contrainte de friction du réseau, ^F.On étudie les effects de K _D, et ^F sur la vitesse d'émission des dislocations, la vitesse de déformation plastique, la taille de la zone plastique, la distribution des dislocations, et sur la zone qui en est dépourvue.

     

Formation of dot arrays with a pitch of 20 nm × 20 nm for patterned media using 30 keV EB drawing on thin calixarene resist

We studied the possibility of achieving very fine-pitch dot arrays with a pitch of 20?nm × 20?nm using 30?keV electron beam (EB) drawing on negative calixarene resist. In order to form such patterns, we studied the dependence on resist thickness of the dot size and the packing. We propose EB drawing on an extremely thin film for very highly packed dot-array formation. Our experimental results demonstrate the possibility of forming highly packed dot-array patterns with a pitch of 20?nm × 20?nm and a resist thickness of about 13?nm, which corresponds to about 1.6?Tbits?in(-2).     

Magneto-Absorption Spectra from Selected Chirality of Single-Walled Carbon Nanotubes

Magneto-absorption spectra of SWNTs (Single-Walled Carbon Nanotubes) in the region of near infrared were measured under high magnetic fields up to 54 T. We succeeded to observe clear peak shifts and splittings for four different chiralities of SWNTs, (7,5), (7,6), (8,6), and (8,7). We employed PFO (poly(9,9-dioctylfluorenyl-2,7-diyl))-SWNTs. Absorption peaks are very sharp and we could observe well-defined peaks of each chirality with less mixture of the other peaks of different chirality. Energy positions of band-edge bright and dark excitons were determined distinctly in each chirality.     

A Big-Data-based platform of workers’ behavior: Observations from the field

Behavior-Based Safety (BBS) has been used in construction to observe, analyze and modify workers’ behavior. However, studies have identified that BBS has several limitations, which have hindered its effective implementation. To mitigate the negative impact of BBS, this paper uses a case study approach to develop a Big-Data-based platform to classify, collect and store data about workers’ unsafe behavior that is derived from a metro construction project. In developing the platform, three processes were undertaken: (1) a behavioral risk knowledge base was established; (2) images reflecting workers’ unsafe behavior were collected from intelligent video surveillance and mobile application; and (3) images with semantic information were stored via a Hadoop Distributed File System (HDFS). The platform was implemented during the construction of the metro-system and it is demonstrated that it can effectively analyze semantic information contained in images, automatically extract workers’ unsafe behavior and quickly retrieve on HDFS as well. The research presented in this paper can enable construction organizations with the ability to visualize unsafe acts in real-time and further identify patterns of behavior that can jeopardize safety outcomes.