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GaAs/AlGaAs heterostructure nanowires studied by cathodoluminescence

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Nano Research 2014年第4期7卷 473-490页

作者： Jessica Bolinsson Martin Ek Johanna Tragardh Kilian Mergenthaler Daniel Jacobsson Mats-Erik Pistol Lars Samuelson Anders Gustafsson solid state physics and the nanometer structure consortium Lund University Box 118 SE-221 00 Lund Sweden Polymer and Materials Chemistry Lund University Box 124 SE-221 00 Lund Sweden

In this report we explore the structural and optical properties of GaAs/A1GaAs heterostructure nanowires grown by metalorganic vapour phase epitaxy using gold seed-particles. The optical studies were done by low-temperature cathodo- luminescence （CL） in a scanning electron microscope （SEM）. We perform a systematic investigation of how the nanowire growth-temperature affects the total photon emission, and variations in the emission energy and intensity along the length of the nanowires. The morphology and crystal structures of the nanowires were investigated using SEM and transmission electron microscopy （TEM）. In order to correlate specific photon emission characteristics with variations in the nanowire crystal structure directly, TEM and spatially resolved CL measurements were performed on the same individual nanowires. We found that the main emission energy was located at around 1.48 eV, and that the emission intensity was greatly enhanced when increasing the GaAs nanowire core growth temperature. The data strongly suggests that this emission energy is related to rotational twins in the GaAs nanowire core. Our measurements also show that radial overgrowth by GaAs on the GaAs nanowire core can have a deteriorating effect on the optical quality of the nanowires. Finally, we conclude that an in situ pre-growth annealing step at a sufficiently high temperature significantly improves the optical quality of the nanowires.

关键词： GaAs/AlGaAs core shellnanowires metalorganic vapourphase epitaxy (MOVPE) cathodoluminescence twin defects transmission electronmicroscopy

Valence Band Splitting in Wurtzite InP Nanowires Observed by Photoluminescence and Photoluminescence Excitation Spectroscopy

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Nano Research 2011年第2期4卷 159-163页

作者： Gerben L. Tuin Magnus T. Borgstrom Johanna Tragardh Martin Ek L. Reine Wallenberg Lars Samuelson Mats-Erik Pistol solid state physics/nanometer structure consortium Box 118 Lund University S-221 00 Lund Sweden Polymer ＆ Materials Chemistry/nCHREM Lund University S-22100 Lurid Sweden

We have investigated individual bulk-like wires of wurtzite InP using photoluminescence, photoluminescence excitation spectroscopy and transmission electron microscopy. Using two different methods we find that the top of the valence band is split, as expected theoretically. This splitting of the valence band is peculiar to wurtzite InP and does not occur in zinc blende InP. We find the energy difference between the two bands to be 40 meV.

关键词： wurtzite InP photoluminescence excitation spectroscopy valence band structure

Large-energy-shift photon upconversion in degenerately doped InP nanowires by direct excitation into the electron gas

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Nano Research 2013年第10期6卷 752-757页

作者： Kilian Mergenthaler Azhar Iqbal Jesper Wallentin Sebastian Lehmann Magnus T. Borgstrom Lars Samuelson Arkady Yartsev Mats-Erik Pistol solid state physics/the nanometer structure consortium Lund University P. O. Box 118 SE-22100 Lund Sweden Division of Chemical physics Lund University P O. Box 118 SE-22100 Lund Sweden

Realizing photon upconversion in nanostructures is important for many next- generation applications such as biological labelling, infrared detectors and solar cells. In particular nanowires are attractive for optoelectronics because they can easily be electrically contacted. Here we demonstrate photon upconversion with a large energy shift in highly n-doped InP nanowires. Crucially, the mechanism responsible for the upconversion in our system does not rely on multi-photon absorption via intermediate states, thus eliminating the need for high photon fluxes to achieve upconversion. The demonstrated upconversion paves the way for utilizing nanowires--with their inherent flexibility such as electrical contactability and the ability to position individual nanowires--for photon upconversion devices also at low photon fluxes, possibly down to the single photon level in optimised structures.

关键词： nanowires photon upconversion photoluminescence indium phosphide

Absorption of light in InP nanowire arrays

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Nano Research 2014年第6期7卷 816-823页

作者： Nicklas Anttu Alireza Abrand Damir Asoli Magnus Heurlin Ingvar Aberg Lars Samuelson Magnus Borgstrom Division of solid state physics and the nanometer structure consortium at Lund University (nmC@LU) Lund University Box 118 Lund 22100 Sweden Sol Voltaics AB Ideon Science Park Scheelevagen 17 Lund 22370 Sweden

An understanding of the absorption of light is essential for efficient photovoltaic and photodetection applications with III-V nanowire arrays. Here, we correlate experiments with modeling and verify experimentally the predicted absorption of light in InP nanowire arrays for varying nanowire diameter and length. We find that 2,000 nm long nanowires in a pitch of 400 nm can absorb 94% of the incident light with energy above the band gap and, as a consequence, light which in a simple ray-optics description would be travelling between the nanowires can be efficiently absorbed by the nanowires. Our measurements demonstrate that the absorption for long nanowires is limited by insertion reflection losses when light is coupled from the air top-region into the array. These reflection losses can be reduced by introducing a smaller diameter to the nanowire-part closest to the air top-region. For nanowire arrays with such a nanowire morphology modulation, we find that the absorptance increases monotonously with increasing diameter of the rest of the nanowire.

关键词： indium phosphide semiconductor nanowire absorption of light

Absorption through a coupled optical resonance in a horizontal InP nanowire array

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Photonics Research 2015年第4期3卷 125-128页

作者： Ali Hosseinnia Nicklas Anttu Division of solid state physics and The nanometer structure consortium(nmC LU) Lund University

We study through electromagnetic modeling the absorption of light of a given wavelength in an array of horizontal In P nanowires of diameter less than 100 nm. Such absorption is performed most efficiently by using polarized light and by exciting a coupled optical resonance in a sparse array. In that case, we excite a resonance in the individual nanowires and couple the resonances in neighboring nanowires through a lattice resonance of the periodic *** such a resonance, an array with nanowires of 80 nm in diameter can absorb more than eight times more strongly than a tight-packed array, despite containing a seven times smaller amount of the absorbing InP material.

关键词： Absorption through a coupled optical resonance in a horizontal InP nanowire array InP

Electromechanical Behavior of Interdigitated SiO2 Cantilever Arrays

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Chinese physics Letters 2010年第2期27卷 307-310页

作者：管志强罗刚 MONTELIUS Lars 徐红星 Nanoscale physics and Devices Laboratory Institute of Physics Chinese Academy of Sciences Beijing 100190 Division of solid state physics/the nanometer structure consortium Lund University Lund S-221 00 Sweden

Bending and first flexural mode vibration behavior of electrostatic actuated nanometer-sized interdigitated cantilever arrays are characterized under vacuum conditions. The pull-in＇＇ effect in dc driving and the hard spring effect＇＇ in ac driving are observed. A mass sensitivity of 20 fg is expected for our devices due to the ultra-small mass of the arm and relative high Q factor. The mass-spring lump model combined with Green＇s function method is used to fit the dc driving behaviors including the pull-in voltage. For the ac driving case, the polynomial expansion of the capacitive force is used in the model. The successfully fittings of the pull-in voltage and the hard spring effect prove that our simulation method could be used for guiding the geometrical design of cantilever-based sensors.

关键词： Electronics and devices Instrumentation and measurement Condensed matter: structural mechanical & thermal Nanoscale science and low-D systems

A facile synthesis of branched silver nanowire structures and its applications in surface-enhanced Raman scattering

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Frontiers in Biology 2012年第5期7卷 521-526页

作者： Feng-Zi Cong Hong Wei Xiao-Rui Tian Hong-Xing Xu Beijing National Laboratory for Condensed Matter physics and Institute of physics Chinese Academy of Sciences Box 603-146 Beijing 100190 China Division of solid state physics/the nanometer structure consortium Lund University Box 118 S-22100 Lund Sweden

We report a facile method of preparing novel branched silver nanowire structures such as Y-shaped, K-shaped and other multi-branched nanowires. These branched nanostructures are synthesized by reducing silver nitrate （AgNO3） in polyethylene glycol （PEG） with polyvinglpyrrolidone （PVP） as capping agent. Statistical data indicate that for the ＂y＂ typed branched nanowire, the branches grow out from the side of the trunk nanowire in a preferential orientation with an angle of 55° between the branch and the trunk. Transmission electron microscopy （TEM） studies indicate that the defects on silver nanowires could support the growth of branched nanowires. Conditions such as the molar ratio of PVP/AgNO3, the reaction temperature, and the degree of polymerization of reducing agent and PVP play important roles in determining the yield of the silver branches. Due to the rough surface, these branched nanostructures can be used as efficient substrates for surface-enhanced Raman scattering applications.

关键词： branched silver nanowire surface-enhanced Raman scattering (SERS)

Optical and electrical properties and phonon drag effect in low temperature TEP measurements of AgSbSe_2 thin films

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Journal of Semiconductors 2014年第5期35卷 1-6页

作者： T Namitha Asokan K S Urmila Rajani Jacob Rachel Reena Philip G S Okram V Ganesan B Pradeep solid state physics Laboratory Department of Physics Cochin University of Science and Technology Thin Film Research Lab Department of Physics Union Christian College UGC-DAE consortium for Scientific Research

Polycrystalline thin films of silver antimony selenide have been deposited using a reactive evaporation technique onto an ultrasonically cleaned glass substrate at a vacuum of 10-5 torr. The preparative parameters, like substrate temperature and incident fluxes, have been properly controlled in order to get stoichiometric, good quality and reproducible thin film samples. The samples are characterized by XRD, SEM, AFM and a UV-vis-NIR spectrophotometer. The prepared sample is found to be polycrystalline in nature. From the XRD pattern, the average particle size and lattice constant are calculated. The dislocation density, strain and number of crystallites per unit area are evaluated using the average particle size. The dependence of the electrical conductivity on the temperature has also been studied and the prepared AgSbSe2 samples are semiconducting in nature. The AgSbSe2 thin films exhibited an indirect allowed optical transition with a band gap of 0.64 eV. The compound exhibits promising thermoelectric properties, a large Seebeck coefficient of 30 mV/K at 48 K due to strong phonon electron interaction. It shows a strong temperature dependence on thermoelectric properties, including the inversion of a dominant carrier type from p to n over a low temperature range 9-300 K, which is explained on the basis of a phonon drag effect.

关键词： silver antimony selenide reactive evaporation thermoelectric power phonon drag effect

Synthesis of monodispersed nanometer-sized YAG powders by a modified coprecipitation method

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Journal of Rare Earths 2008年第5期26卷 674-677页

作者：潘林秦晓英李地张建 Key Laboratory of Materials physics Institute of Solid State Physics Chinese Academy of Sciences

nanometer-sized yttrium aluminum garnet （YAG） powders were synthesized by using the coprecipitation method with ammo- nium hydrogen carbonate as a precipitant. The results indicated that an extremely loose YAG precursor was obtained when iodine was intro- duced in the coprecipitation process on the condition that the initial concentrations of Y^3＋ and Al^3＋ in the solution were set at 0.018 and 0.03 mol/L, respectively, and pH=8. Consequently, the resulting YAG powders after calcination at 1173 K for 2 h were composed of monodispersed particles with an average grain size of 30 nm and better sinterability. The present results indicated that the modified coprecipitation method, with iodine as an additive, was superior to the conventional coprecipitation method, to synthesize ultrafine YAG powders.

关键词： nanostructured materials precipitation yttrium aluminum garnet agglomeration iodine rare earths