| 1. |
- Hjort, Martin, et al.
(författare)
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Doping profile of InP nanowires directly imaged by photoemission electron microscopy
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:23
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Tidskriftsartikel (refereegranskat)abstract
- InP nanowires (NWs) with differently doped segments were studied with nanoscale resolution using synchrotron based photoemission electron microscopy. We clearly resolved axially stacked n-type and undoped segments of the NWs without the need of additional processing or contacting. The lengths and relative doping levels of different NW segments as well as space charge regions were determined indicating memory effects of sulfur during growth. The surface chemistry of the nanowires was monitored simultaneously, showing that in the present case, the doping contrast was independent of the presence or absence of a native oxide. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662933]
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| 2. |
- Hjort, Martin, et al.
(författare)
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Surface Chemistry, Structure, and Electronic Properties from Microns to the Atomic Scale of Axially Doped Semiconductor Nanowires.
- 2012
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851.
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Tidskriftsartikel (refereegranskat)abstract
- Using both synchrotron-based photoemission electron microscopy/spectroscopy and scanning tunneling microscopy/spectroscopy, we obtain a complete picture of the surface composition, morphology, and electronic structure of InP nanowires. Characterization is done at all relevant length scales from micrometer to nanometer. We investigate nanowire surfaces with native oxide and molecular adsorbates resulting from exposure to ambient air. Atomic hydrogen exposure at elevated temperatures which leads to the removal of surface oxides while leaving the crystalline part of the wire intact was also studied. We show how surface chemical composition will seriously influence nanowire electronic properties. However, opposite to, for example, Ge nanowires, water or sulfur molecules adsorbed on the exterior oxidized surfaces are of less relevance. Instead, it is the final few atomic layers of the oxide which plays the most significant role by strongly negatively doping the surface. The InP nanowires in air are rather insensitive to their chemical surroundings in contrast to what is often assumed for nanowires. Our measurements allow us to draw a complete energy diagram depicting both band gap and differences in electron affinity across an axial nanowire p-n junction. Our findings thus give a robust set of quantitative values relating surface chemical composition to specific electronic properties highly relevant for simulating the performance of nanoscale devices.
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| 3. |
- Adolfsson, Karl, et al.
(författare)
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Fluorescent Nanowire Heterostructures as a Versatile Tool for Biology Applications
- 2013
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:10, s. 4728-4732
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires are increasingly used in biology, as sensors, as injection devices, and us model systems for toxicity studies. Currently, in situ visualization of nanowires in biological media is done using organic dyes, which a;:e prone to photobleaching, or using microscopy methods which either yield poor resolution or require a sophisticated setup. Here we show that inherently fluorescent nanowire axial heterostructnies c:an be used to localize and identify nanowires in cells and tissue; By synthesizing GaP GaInP nanowire heterostructures, with nonfluorescent GaP segments and fluorescent GaInP segments, we created a barcode labeling system enabling the distinction of the nanowire morphological and chemical properties using fluorescence microscopy. The GaInP photoluminescence stability, combined with the fact that the nanowires can be coated with different materials while retaining their fluorescence, make these nanowires promising tools for biological and nanotoxicological studies.
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| 4. |
- Ahlford, Marianne, et al.
(författare)
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Uppsala Underdogs - A Robot Soccer Project
- 2006
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Rapport (populärvet., debatt m.m.)abstract
- In this paper, we describe the four-legged soccer team Uppsala Underdogs developed by a group of 4th year computer science students at Uppsala University during the fall of 2004. The project is based on the experience from two similar previous projects. This year the emphasis of the project has been on distribution of data and on support for evaluation and reconfiguration of strategies. To support data distribution, a middleware has been developed, which implements a replication algorithm and provides a clean interface for the other software modules (or behaviors). To enable easy reconfiguration of strategies, an automata-based graphical description language has been developed, which can be compiled into code that uses the database and the lower level modules, such as tactics and positioning, to make decisions and control the robot. In addition, a graphical simulator has been developed in which the strategies can be evaluated.
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| 5. |
- Anttu, Nicklas, et al.
(författare)
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Beyond ray optics absorption of light in CsPbBr3perovskite nanowire arrays studied experimentally and with wave optics modelling
- 2023
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Ingår i: Nanotechnology. - 0957-4484. ; 35:9
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Tidskriftsartikel (refereegranskat)abstract
- We study experimentally and with wave optics modelling the absorption of light in CsPbBr3perovskite nanowire arrays fabricated into periodic pores of an anodized aluminum oxide matrix, for nanowire diameters from 30 to 360 nm. First, we find that all the light that couples into the array can be absorbed by the nanowires at sufficient nanowire length. This behavior is in strong contrast to the expectation from a ray-optics description of light where, for normally incident light, only the rays that hit the cross-section of the nanowires can be absorbed. In that case, the absorption in the sample would be limited to the area fill factor of nanowires in the hexagonal array, which ranges from 13% to 58% for the samples that we study. Second, we find that the absorption saturates already at a nanowire length of 1000-2000 nm, making these perovskite nanowires promising for absorption-based applications such as solar cells and photodetectors. The absorption shows a strong diameter dependence, but for all diameters the transmission is less than 24% already at a nanowire length of 500 nm. For some diameters, the absorption exceeds that of a calculated thin film with 100% coverage. Our analysis indicates that the strong absorption in these nanowires originates from light-trapping induced by the out-of-plane disorder due to random axial position of each nanowire within its pore in the matrix.
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| 6. |
- Björling, Alexander, et al.
(författare)
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Three-Dimensional Coherent Bragg Imaging of Rotating Nanoparticles
- 2020
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 125:24
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Tidskriftsartikel (refereegranskat)abstract
- Bragg coherent diffraction imaging is a powerful strain imaging tool, often limited by beam-induced sample instability for small particles and high power densities. Here, we devise and validate an adapted diffraction volume assembly algorithm, capable of recovering three-dimensional datasets from particles undergoing uncontrolled and unknown rotations. We apply the method to gold nanoparticles which rotate under the influence of a focused coherent x-ray beam, retrieving their three-dimensional shapes and strain fields. The results show that the sample instability problem can be overcome, enabling the use of fourth generation synchrotron sources for Bragg coherent diffraction imaging to their full potential.
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| 7. |
- Borgström, Magnus, et al.
(författare)
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Dynamics of extremely anisotropic etching of InP nanowires by HCl
- 2011
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 502:4-6, s. 222-224
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Tidskriftsartikel (refereegranskat)abstract
- We report on the dynamics of in situ etching of nanowires using an etching agent which allows for parameter optimization for nanowire synthesis without concerns of tapering issues. Upon etching of InP nanowires using HCl it is found that HCl mainly reacts with the precursor TMI, its decomposition species, and physisorbed In. The reaction with solid InP is less rapid and diffusion limited. We find a gas-phase etch process which is metal assisted and has a high aspect ratio of 1:100. (C) 2011 Elsevier B.V. All rights reserved.
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| 8. |
- Borgström, Magnus, et al.
(författare)
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Fabrication and characterization of AlP-GaP core-shell nanowires
- 2011
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 324:1, s. 290-295
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Tidskriftsartikel (refereegranskat)abstract
- We report on the particle assisted synthesis of core-shell AlP-GaP nanowires by use of metal-organic vapor phase epitaxy. The core-shell approach is chosen such as to stabilize the AlP which is highly sensitive to water. The nanowires were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. These nanowires have an indirect band-gap and form a type II staggered heterojunction. By designed capping of the AlP cores by GaP, we find the nanowires to be stable for more than a year. (C) 2011 Elsevier B.V. All rights reserved.
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| 9. |
- Borgström, Magnus, et al.
(författare)
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In Situ Etching for Total Control Over Axial and Radial Nanowire Growth
- 2010
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 3:4, s. 264-270
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Tidskriftsartikel (refereegranskat)abstract
- We report a method using in situ etching to decouple the axial from the radial nanowire growth pathway, independent of other growth parameters. Thereby a wide range of growth parameters can be explored to improve the nanowire properties without concern of tapering or excess structural defects formed during radial growth. We demonstrate the method using etching by HCl during InP nanowire growth. The improved crystal quality of etched nanowires is indicated by strongly enhanced photoluminescence as compared to reference nanowires obtained without etching.
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| 10. |
- Borgström, Magnus, et al.
(författare)
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Nanowires With Promise for Photovoltaics
- 2011
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X. ; 17:4, s. 1050-1061
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Tidskriftsartikel (refereegranskat)abstract
- Solar energy harvesting for electricity production is regarded as a fully credible future energy source: plentiful and without serious environmental concerns. The breakthrough for solar energy technology implementation has, however, been hampered by two issues: the conversion efficiency of light into electricity and the solar panel production cost. The use of III-V nanowires (NWs) in photovoltaics allows to respond to both these demands. They offer efficient light absorption and significant cost reduction. These low-dimensional structures can be grown epitaxially in dense NW arrays directly on silicon wafers, which are abundant and cheaper than the germanium substrates used for triple-junction solar cells today. For planar structures, lattice matching poses a strong restriction on growth. III-V NWs offer to create highly efficient multijunction devices, since multiple materials can be combined to match the solar spectrum without the need of tightly controlled lattice matching. At the same time, less material is required for NW-based solar cells than for planar-based architecture. This approach has potential to reach more than 50% in efficiency. Here, we describe our work on NW tandem solar cells, aiming toward two junctions absorbing different parts of the solar spectrum, connected in series via a tunnel diode.
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