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1.
  • Thiagarajan, Kannan, 1981-, et al. (författare)
  • High-field electron transport in semiconducting zigzag carbon nanotubes
  • 2012
  • Ingår i: Nanotechnology. - Bristol, England. - 0957-4484 .- 1361-6528. ; 23:26, s. 265703-265709
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron transport in semiconducting zigzag carbon nanotubes is studied by solving the Boltzmann transport equation using the single-particle Monte Carlo technique. The electronic band structure is based on a standard nearest-neighbour tight-binding parameterisation, and the phonon spectrum is calculated using a fourth nearest-neighbour force constant model. The electron-phonon scattering probabilities are calculated within a tight-binding formalism. The steady-state drift velocities for the semiconducting zigzag nanotubes (8,0), (10,0), (11,0), (13,0), and (25,0) are computed as functions of electric field strength and temperature, and the results are analysed here. The results show the presence of negative differential resistance at high electric fields for some of the nanotubes. The drift velocity and the low field mobility reach a maximum value of and, respectively, for a (25,0) nanotube.
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2.
  • Chalangar, Ebrahim, et al. (författare)
  • Influence of morphology on electrical and optical properties of graphene/Al-doped ZnO-nanorod composites
  • 2018
  • Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 29:41
  • Tidskriftsartikel (refereegranskat)abstract
    • The development of future 3D-printed electronics relies on the access to highly conductive inexpensive materials that are printable at low temperatures (<100 C). The implementation of available materials for these applications are, however, still limited by issues related to cost and printing quality. Here, we report on the simple hydrothermal growth of novel nanocomposites that are well suited for conductive printing applications. The nanocomposites comprise highly Al-doped ZnO nanorods grown on graphene nanoplatelets (GNPs). The ZnO nanorods play the two major roles of (i) preventing GNPs from agglomerating and (ii) promoting electrical conduction paths between the graphene platelets. The effect of two different ZnO-nanorod morphologies with varying Al-doping concentration on the nanocomposite conductivity and the graphene dispersity are investigated. Time-dependent absorption, photoluminescence and photoconductivity measurements show that growth in high pH solutions promotes a better graphene dispersity, higher doping levels and enhanced bonding between the graphene and the ZnO nanorods. Growth in low pH solutions yields samples characterized by a higher conductivity and a reduced number of surface defects. These samples also exhibit a large persistent photoconductivity attributed to an effective charge separation and transfer from the nanorods to the graphene platelets. Our findings can be used to tailor the conductivity of novel printable composites, or for fabrication of large volumes of inexpensive porous conjugated graphene-semiconductor composites.
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3.
  • Devi, Chandni, et al. (författare)
  • Electrical transport properties of InAs nanowires synthesized by a solvothermal method
  • 2020
  • Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:23
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanowires are widely considered to be key elements in future disruptive electronics and photonics. This paper presents the first detailed study of transport mechanisms in single-crystalline InAs nanowires synthesized by a cheap solvothermal wet chemical method. From detailed analyses of temperature-dependent current-voltage characteristics, it was observed that contacted nanowires operate in a linear transport regime at biases below a critical cross-over voltage. For larger biases, the transport changes to space-charge-limited conduction assisted by traps. The characteristic parameters such as free electron concentration, trap concentration and energy distribution, and electron mobility were all calculated. It was demonstrated that the nanowires have key electrical properties comparable to those of InAs nanowires grown by molecular beam epitaxy. Our results might pave the way for cheap disruptive low-dimensional electronics such as resistive switching devices.
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4.
  • Hussain, Laiq, et al. (författare)
  • Defect-induced infrared electroluminescence from radial GaInP/AlGaInP quantum well nanowire array light- emitting diodes
  • 2017
  • Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:48
  • Tidskriftsartikel (refereegranskat)abstract
    • Radial GaInP/AlGaInP nanowire array light-emitting diodes (LEDs) are promising candidates for novel high-efficiency solid state lighting due to their potentially large strain-free active emission volumes compared to planar LEDs. Moreover, by proper tuning of the diameter of the nanowires, the fraction of emitted light extracted can be significantly enhanced compared to that of planar LEDs. Reports so far on radial growth of nanowire LED structures, however, still point to significant challenges related to obtaining defect-free radial heterostructures. In this work, we present evidence of optically active growth-induced defects in a fairly broad energy range in vertically processed radial GaInP/AlGaInP quantum well nanowire array LEDs using a variety of complementary experimental techniques. In particular, we demonstrate strong infrared electroluminescence in a spectral range centred around 1 eV (1.2 μm) in addition to the expected red light emission from the quantum well. Spatially resolved cathodoluminescence studies reveal a patchy red light emission with clear spectral features along the NWs, most likely induced by variations in QW thickness, composition and barriers. Dark areas are attributed to infrared emission generated by competing defect-assisted radiative transitions, or to trapping mechanisms involving non-radiative recombination processes. Possible origins of the defects are discussed.
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5.
  • Jafari Jam, R., et al. (författare)
  • Embedded sacrificial AlAs segments in GaAs nanowires for substrate reuse
  • 2020
  • Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:20
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the use of a sacrificial AlAs segment to enable substrate reuse for nanowire synthesis. A silicon nitride template was deposited on a p-type GaAs substrate. Then a pattern was transferred to the substrate by nanoimprint lithography and reactive ion etching. Thermal evaporation was used to define Au seed particles. Metalorganic vapour phase epitaxy was used to grow AlAs-GaAs NWs in the vapour-liquid-solid growth mode. The yield of synthesised nanowires, compared to the number expected from the patterned template, was more than 80%. After growth, the nanowires were embedded in a polymer and mechanically removed from the parent substrate. The parent substrate was then immersed in an HCl:H2O (1:1) mixture to dissolve the remaining stub of the sacrificial AlAs segment. The pattern fidelity was preserved after peeling off the nanowires and cleaning, and the semiconductor surface was flat and ready for reuse. Au seed particles were then deposited on the substrate by use of pulse electrodeposition, which was selective to the openings in the growth template, and then nanowires were regrown. The yield of regrowth was less optimal compared to the first growth but the pattern was preserved. Our results show a promising approach to reduce the final cost of III-V nanowire based solar cells.
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6.
  • Jain, Vishal, et al. (författare)
  • Bias-dependent spectral tuning in InP nanowire-based photodetectors
  • 2017
  • Ingår i: Nanotechnology. - Bristol : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanowire array ensembles contacted in a vertical geometry are extensively studied and considered strong candidates for next generations of industrial scale optoelectronics. Key challenges in this development deal with optimization of the doping profile of the nanowires and the interface between nanowires and transparent top contact. Here we report on photodetection characteristics associated with doping profile variations in InP nanowire array photodetectors. Bias-dependent tuning of the spectral shape of the responsivity is observed which is attributed to a Schottky-like contact at the nanowire-ITO interface. Angular dependent responsivity measurements, compared with simulated absorption spectra, support this conclusion. Furthermore, electrical simulations unravel the role of possible self-gating effects in the nanowires induced by the ITO/SiO x wrap-gate geometry. Finally, we discuss possible reasons for the observed low saturation current at large forward biases.
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7.
  • Bruhn, Benjamin, et al. (författare)
  • Controlled fabrication of individual silicon quantum rods yielding high intensity, polarized light emission
  • 2009
  • Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 20:50, s. 1-5
  • Tidskriftsartikel (refereegranskat)abstract
    • Elongated silicon quantum dots (also referred to as rods) were fabricated using a lithographic process which reliably yields sufficient numbers of emitters. These quantum rods are perfectly aligned and the vast majority are spatially separated well enough to enable single-dot spectroscopy. Not only do they exhibit extraordinarily high linear polarization with respect to both absorption and emission, but the silicon rods also appear to luminesce much more brightly than their spherical counterparts. Significantly increased quantum efficiency and almost unity degree of linear polarization render these quantum rods perfect candidates for numerous applications.
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8.
  • Sychugov, Ilya, et al. (författare)
  • Manifold Enhancement of Electron Beam Induced Deposition Rate at Grazing Incidence
  • 2010
  • Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 21:2, s. 025303-
  • Tidskriftsartikel (refereegranskat)abstract
    • It is shown how a significant drawback of the electron beam induced deposition technique, namely its low deposition rate, can be circumvented. By tilting a sample, a larger part of the primary electron beam energy becomes dissipated closer to the interface. This in turn increases the emission of secondary electrons, largely responsible for the deposition of the adsorbed molecule components on the surface. An order of magnitude increase in the deposition rate is reported in the fabrication of metal nanowires from organic precursor gas.
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9.
  • Sychugov, Ilya, et al. (författare)
  • Optical and Electrical Characterization at the Nanoscale by a Transparent Tip of a Scanning Tunneling Microscope
  • 2009
  • Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 20:14, s. 145706-
  • Tidskriftsartikel (refereegranskat)abstract
    • A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.
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10.
  • Sychugov, Ilya, et al. (författare)
  • Sub-10 nm crystalline silicon nanostructures by electron beam induced deposition lithography
  • 2010
  • Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 21:28, s. 285307-
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel top-down approach for the controllable fabrication of semiconductor nanostructures exhibiting quantum effects is described. By decomposing metal-rich precursor gas molecules with an electron beam, a sub-10 nm metal pattern can be formed and subsequently transferred to a semiconductor substrate. In such a way monocrystalline silicon nanodots and nanowires are produced as revealed by transmission electron microscopy. It is also shown how through controlled thermal or chemical oxidation the nanostructure surface can be passivated. By providing direct access to the sub-10 nm size range this method possesses promising potential for application in the quantum dot and nanoelectronics fields.
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