| 11. |
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| 12. |
- Sjökvist, Robin, et al.
(författare)
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Compositional Correlation between the Nanoparticle and the Growing Au-Assisted InxGa1-xAs Nanowire
- 2021
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:31, s. 7590-7595
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Tidskriftsartikel (refereegranskat)abstract
- The nanowire geometry is favorable for the growth of ternary semiconductor materials, because the composition and properties can be tuned freely without substrate lattice matching. To achieve precise control of the composition in ternary semiconductor nanowires, a deeper understanding of the growth is required. One unknown aspect of seeded nanowire growth is how the composition of the catalyst nanoparticle affects the resulting composition of the growing nanowire. We report the first in situ measurements of the nanoparticle and InxGa1-xAs nanowire compositional relationship using an environmental transmission electron microscopy setup. The compositions were measured and correlated during growth, via X-ray energy dispersive spectroscopy. Contrary to predictions from thermodynamic models, the experimental results do not show a miscibility gap. Therefore, we construct a kinetic model that better predicts the compositional trends by suppressing the miscibility gap. The findings imply that compositional control of InxGa1-xAs nanowires is possible across the entire compositional range.
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| 13. |
- Thelander, Claes, et al.
(författare)
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Electrical properties of InAs-based nanowires
- 2004
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Ingår i: AIP Conference Proceedings. - 0094-243X .- 1551-7616. ; 723, s. 449-452
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Konferensbidrag (refereegranskat)abstract
- Semiconductor nanowires are grown using chemical beam epitaxy and metal organic vapor phase epitaxy from size-selected gold nanoparticles acting as catalysts. By changing materials during the growth it is possible to form heterostructures both along the length of the nanowires but also in a core-shell fashion. In particular, incorporation of pairs of InP tunnel barriers in InAs nanowires has been used to fabricate single-electron transistors and resonant tunneling diodes
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| 14. |
- Thelander, Claes, et al.
(författare)
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One dimensional heterostructures and resonant tunneling in III-V nanowires
- 2003
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Ingår i: 2003 International Symposium on Compound Semiconductors (Cat. No.03TH8675). - 0780378202 ; , s. 151-152
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Konferensbidrag (refereegranskat)abstract
- We use a bottom-up approach to grow epitaxially nucleated semiconductor nanowires from gold particles. Heterostructure barriers of InP are introduced inside InAs nanowires to form resonant tunneling diodes and single-electron transistors
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| 15. |
- Thelander, Claes, et al.
(författare)
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Single-electron transistors in heterostructure nanowires.
- 2003
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:10, s. 2052-2054
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor-based single-electron transistors have been fabricated using heterostructure nanowire growth, by introducing a double barrier of InP into InAs nanowires. From electrical measurements, we observe a charging energy of 4 meV for the approximately 55 nm diameter and 100 nm long InAs islands between the InP barriers. The Coulomb blockade can be periodically lifted as a function of gate voltage for all devices, which is a typical signature of single-island transistors. Homogeneous InAs nanowires show no such effect for the corresponding voltage ranges. ©2003 American Institute of Physics.
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| 16. |
- Tornberg, Marcus, et al.
(författare)
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Enabling In Situ Studies of Metal-Organic Chemical Vapor Deposition in a Transmission Electron Microscope
- 2022
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Ingår i: Microscopy and Microanalysis. - 1431-9276. ; 28:5, s. 1484-1492
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Tidskriftsartikel (refereegranskat)abstract
- The world of environmental microscopy provides the possibility to study and analyze transformations and reactions during realistic conditions to understand the processes better. We report on the design and development of a metal-organic chemical vapor deposition (MOCVD) system integrated with an environmental transmission electron microscope intended for real-time investigations of crystal growth. We demonstrate methods for achieving a wide range of precisely controlled concentrations of precursor gas at the sample, as well as for calibrating the sample partial pressure using the pressure measured elsewhere in the microscope column. The influences of elevated temperature and reactive gas within the pole-piece gap are evaluated with respect to imaging and spectroscopy. We show that X-ray energy-dispersive spectroscopy can be strongly affected by temperatures beyond 500C, while the spatial resolution is largely unaffected by heat and microscope pressure for the relevant conditions. Finally, the influence of the electron beam on the investigated processes is discussed. With this work, we aim to provide crucial input in the development of advanced in situ electron microscopy systems for studies of complex reactions in real time under realistic conditions, for instance as used during formation of semiconductor crystals.
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| 17. |
- Tornberg, Marcus, et al.
(författare)
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Kinetics of Au-Ga Droplet Mediated Decomposition of GaAs Nanowires
- 2019
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; , s. 3498-3504
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Tidskriftsartikel (refereegranskat)abstract
- Particle-assisted III-V semiconductor nanowire growth and applications thereof have been studied extensively. However, the stability of nanowires in contact with the particle and the particle chemical composition as a function of temperature remain largely unknown. In this work, we use in situ transmission electron microscopy to investigate the interface between a Au-Ga particle and the top facet of an ?1 1 1 ?-oriented GaAs nanowire grown via the vapor-liquid-solid process. We observed a thermally activated bilayer-by-bilayer removal of the GaAs facet in contact with the liquid particle during annealing between 300 and 420 °C in vacuum. Interestingly, the GaAs-removal rates initially depend on the thermal history of the sample and are time-invariant at later times. In situ X-ray energy dispersive spectroscopy was also used to determine that the Ga content in the particle at any given temperature remains constant over extended periods of time and increases with increasing temperature from 300 to 400 °C. We attribute the observed phenomena to droplet-assisted decomposition of GaAs at a rate that is controlled by the amount of Ga in the droplet. We suggest that the observed transients in removal rates are a direct consequence of time-dependent changes in the Ga content. Our results provide new insights into the role of droplet composition on the thermal stability of GaAs nanowires and complement the existing knowledge on the factors influencing nanowire growth. Moreover, understanding the nanowire stability and decomposition is important for improving processing protocols for the successful fabrication and sustained operation of nanowire-based devices.
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| 18. |
- Wallenberg, Marcus, et al.
(författare)
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A Research Platform for Embodied Visual Object Recognition
- 2010
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Ingår i: Proceedings of SSBA 2010 Symposium on Image Analysis. ; , s. 137-140
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present in this paper a research platform for development and evaluation of embodied visual object recognition strategies. The platform uses a stereoscopic peripheral-foveal camera system and a fast pan-tilt unit to perform saliency-based visual search. This is combined with a classification framework based on the bag-of-features paradigm with the aim of targeting, classifying and recognising objects. Interaction with the system is done via typed commands and speech synthesis. We also report the current classification performance of the system.
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| 19. |
- Wallenberg, Marcus, 1984-
(författare)
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A Simple Single-Camera Gaze Tracker using Infrared Illumination
- 2009
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Ingår i: Proceedings of SSBA 2009 Symposium on Image Analysis. ; , s. 53-56
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A single-camera gaze tracker has been created,based on previous implementations by Shih and Liu[5] and Hennessey et al. [3]. The method used is basedon controlled infrared illumination. The implementedsystem has been evaluated on both synthetic and realimage data and found to be capable of estimatinggaze point with an accuracy of approximately 1° visualangle.
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| 20. |
- Wallenberg, Marcus, 1984-, et al.
(författare)
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Attentional Masking for Pre-trained Deep Networks
- 2017
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Ingår i: Proceedings of IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS17). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538626825 ; , s. 6149-6154
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Konferensbidrag (refereegranskat)abstract
- The ability to direct visual attention is a fundamental skill for seeing robots. Attention comes in two flavours: the gaze direction (overt attention) and attention to a specific part of the current field of view (covert attention), of which the latter is the focus of the present study. Specifically, we study the effects of attentional masking within pre-trained deep neural networks for the purpose of handling ambiguous scenes containing multiple objects. We investigate several variants of attentional masking on partially pre-trained deep neural networks and evaluate the effects on classification performance and sensitivity to attention mask errors in multi-object scenes. We find that a combined scheme consisting of multi-level masking and blending provides the best trade-off between classification accuracy and insensitivity to masking errors. This proposed approach is denoted multilayer continuous-valued convolutional feature masking (MC-CFM). For reasonably accurate masks it can suppress the influence of distracting objects and reach comparable classification performance to unmasked recognition in cases without distractors.
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