| 81. |
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| 82. |
- Svenningsson, Roger, et al.
(författare)
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Influence of the surface roughness on the fatigue properties in ausferritic ductile irons (ADI)
- 2014
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Ingår i: MATEC Web of Conferences. - : EDP Sciences. - 2261-236X.
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Konferensbidrag (refereegranskat)abstract
- Heat treatment of cast ductile iron (DI) to ausferritic ductile iron (ADI) is known to increase fatigue properties. However, the surface roughness of the cast material is also of significant importance. In this investigation, test rods with seven different surface qualities were cast from the same melt i.e. with same chemical composition. The surfaces of the test rods were varied by a number of parameters; grain size of the moulding sand, coated or non-coated mould surfaces, as-cast or machined and polished, shot peened or not. In addition, a reference material in conventional DI was cast and tested. All eight series were subjected to high-cycle fatigue bending tests. The results show that surface defects, such as micro porosity and minor inclusions drastically decrease the fatigue properties. For some ADI materials the stress amplitude limit was actually lower compared to the non-heat treated DI. The machined, polished and shot-peened material demonstrated the best fatigue properties, which is as expected.
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| 83. |
- Timm, Rainer, et al.
(författare)
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Current−Voltage Characterization of Individual As-Grown Nanowires Using a Scanning Tunneling Microscope
- 2013
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:11, s. 5182-5189
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing semiconductor nanowires for (opto)- electronics requires exact knowledge of their current−voltage properties. We report accurate on-top imaging and I−V characterization of individual as-grown nanowires, using a subnanometer resolution scanning tunneling microscope with no need for additional microscopy tools, thus allowing versatile application. We form Ohmic contacts to InP and InAs nanowires without any sample processing, followed by quantitative measurements of diameter dependent I−V properties with a very small spread in measured values compared to standard techniques.
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| 84. |
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| 85. |
- Troian, Andrea, et al.
(författare)
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Nanobeam X-ray Fluorescence Dopant Mapping Reveals Dynamics of in Situ Zn-Doping in Nanowires
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; , s. 6461-6468
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Tidskriftsartikel (refereegranskat)abstract
- The properties of semiconductors can be controlled using doping, making it essential for electronic and optoelectronic devices. However, with shrinking device sizes it becomes increasingly difficult to quantify doping with sufficient sensitivity and spatial resolution. Here, we demonstrate how X-ray fluorescence mapping with a nanofocused beam, nano-XRF, can quantify Zn doping within in situ doped III-V nanowires, by using large area detectors and high-efficiency focusing optics. The spatial resolution is defined by the focus size to 50 nm. The detection limit of 7 ppm (2.8 × 1017 cm-3), corresponding to about 150 Zn atoms in the probed volume, is bound by a background signal. In solar cell InP nanowires with a p-i-n doping profile, we use nano-XRF to observe an unintentional Zn doping of 5 × 1017 cm-3 in the middle segment. We investigated the dynamics of in situ Zn doping in a dedicated multisegment nanowire, revealing significantly sharper gradients after turning the Zn source off than after turning the source on. Nano-XRF could be used for quantitative mapping of a wide range of dopants in many types of nanostructures.
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| 86. |
- Wallentin, Jesper, et al.
(författare)
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Degenerate p-doping of InP nanowires for large area tunnel diodes
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:25
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated p-doping of InP nanowires using diethyl zinc. Two-terminal devices showed non-linear source-drain characteristics and p-type gate dependence. Electron beam induced current measurements were employed to determine minority carrier diffusion lengths. We used large-area tunnel diodes to demonstrate degenerate doping, showing peak current densities of up to 0.11 A/cm(2) and room temperature peak to valley current ratios of 5.3. These results demonstrate that high p- and n-doping, paired with sharp doping profiles, can be achieved in InP nanowires. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3669697]
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| 87. |
- Wernersson, Lars-Erik, et al.
(författare)
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Metalorganic vapor phase epitaxy-grown GaP/GaAs/GaP and GaAsP/GaAs/GaAsP n-type resonant tunnelling diodes
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:10, s. 1841-1843
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Tidskriftsartikel (refereegranskat)abstract
- We have studied GaP/GaAs/GaP and GaAsxP1-x/GaAs/GaAsxP1-x double-barrier resonant tunnelling diodes grown by metalorganic vapor phase epitaxy. We find that GaP tensile strained barriers in GaP/GaAs/GaP diodes may be grown with a barrier thickness below the critical thickness of about 12 monolayers. However, a corrugation of the strained barrier is observed by transmission electron microscopy. This variation may explain the low peak-to-valley ratio of the diodes (about 2). In contrast, GaAsxP1-x/GaAs/GaAsxP1-x resonant tunnelling diodes have been grown with a homogeneous thickness of the barriers, consequently showing a substantially improved electrical performance compared to the GaP diodes with peak-to-valley ratios >5.
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| 88. |
- Wernersson, Lars-Erik, et al.
(författare)
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Thin layers of GaInP, GaP and GaAsP in metalorganic vapour phase epitaxy-grown resonant tunnelling diodes
- 2002
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Ingår i: Applied Surface Science. - 1873-5584. ; 190:1, s. 252-257
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the epitaxial growth and electrical performance of Al-free, GaAs-based, resonant tunnelling diodes (RTDs) including thin barriers of GaInP, GO, or GaAsxP1-x. n-Type tunnelling diodes have been fabricated and the symmetry in the current-voltage (I-V) characteristics, as well as the peak-to-valley ratios, are found to be sensitive probes for the inter-face quality in the heterostructures. For GaInP RTDs, we show that the introduction of Gap intermediate layers is crucial for the realisation. of a useful tunnelling current. RTDs including thin barriers (less than about 10 monolayers (ML)) of Gap are realised, but the strong mismatch between the materials limit the useful thickness. Finally, RTDs with GaAslambdaP1-x alloys are fabricated showing the best peak-to-valley ratio of the diodes (about 5), as well as a symmetric I-V characteristics. The electrical data are further compared to studies by transmission electron microscopy (TEM) in the various material systems.
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| 89. |
- Winge, David, et al.
(författare)
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Artificial nanophotonic neuron with internal memory for biologically inspired and reservoir network computing
- 2023
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Ingår i: Neuromorphic Computing and Engineering. - 2634-4386. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- Neurons with internal memory have been proposed for biological and bio-inspired neural networks, adding important functionality. We introduce an internal time-limited charge-based memory into a III-V nanowire (NW) based optoelectronic neural node circuit designed for handling optical signals in a neural network. The new circuit can receive inhibiting and exciting light signals, store them, perform a non-linear evaluation, and emit a light signal. Using experimental values from the performance of individual III-V NWs we create a realistic computational model of the complete artificial neural node circuit. We then create a flexible neural network simulation that uses these circuits as neuronal nodes and light for communication between the nodes. This model can simulate combinations of nodes with different hardware derived memory properties and variable interconnects. Using the full model, we simulate the hardware implementation for two types of neural networks. First, we show that intentional variations in the memory decay time of the nodes can significantly improve the performance of a reservoir network. Second, we simulate the implementation in an anatomically constrained functioning model of the central complex network of the insect brain and find that it resolves an important functionality of the network even with significant variations in the node performance. Our work demonstrates the advantages of an internal memory in a concrete, nanophotonic neural node. The use of variable memory time constants in neural nodes is a general hardware derived feature and could be used in a broad range of implementations.
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| 90. |
- Winge, David O., et al.
(författare)
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Implementing an Insect Brain Computational Circuit Using III-V Nanowire Components in a Single Shared Waveguide Optical Network
- 2020
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 7:10, s. 2787-2798
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments in photonics include efficient nanoscale optoelectronic components and novel methods for subwavelength light manipulation. Here, we explore the potential offered by such devices as a substrate for neuromorphic computing. We propose an artificial neural network in which the weighted connectivity between nodes is achieved by emitting and receiving overlapping light signals inside a shared quasi 2D waveguide. This decreases the circuit footprint by at least an order of magnitude compared to existing optical solutions. The reception, evaluation, and emission of the optical signals are performed by neuron-like nodes constructed from known, highly efficient III-V nanowire optoelectronics. This minimizes power consumption of the network. To demonstrate the concept, we build a computational model based on an anatomically correct, functioning model of the central-complex navigation circuit of the insect brain. We simulate in detail the optical and electronic parts required to reproduce the connectivity of the central part of this network using previously experimentally derived parameters. The results are used as input in the full model, and we demonstrate that the functionality is preserved. Our approach points to a general method for drastically reducing the footprint and improving power efficiency of optoelectronic neural networks, leveraging the superior speed and energy efficiency of light as a carrier of information.
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