| 1. |
- Bordag, Michael, et al.
(författare)
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Parallel nano-assembly directed by short-range field forces
- 2006
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Ingår i: Proceedings of the 1st IEEE International Conference on Nano/Micro Engineered and Molecular Systems. - Piscataway, United States : IEEE Press. - 9781424401390 ; , s. 620-622
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Konferensbidrag (refereegranskat)abstract
- We present the ECs Sixth Framework Programme PARNASS project, which stands for 'Parallel nano assembling directed by short-range field forces' and represents a radical innovative approach to fabricating large volumes of hybrid nano electronic devices. The project combines in a synergy the 'top-down' and 'bottom-up' methods addressing one of the challenging physical and engineering problems of the very high accuracy over a large area. An array of specially designed nano-scale force field sources has to be a key part of this innovative approach to large-scale nano manufacturing. © 2006 IEEE.
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| 2. |
- Conache, Gabriela, 1977-, et al.
(författare)
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Nanowire friction with an applied bias
- 2009
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Konferensbidrag (refereegranskat)abstract
- Recently, we have shown how the friction acting on nanowires pushed across a surface by an AFM tip can be determined by measuring the radius of curvature of the bent wire aŸer manipulation. This technique allows us to study the friction properties of an extended mesoscale contact. Our main focus has been to determine whether such contacts behave like macroscopic objects, in which dišerences between the 'true' and 'apparent' contact areas play a key role and friction varies linearly with the applied normal force, or whether they are more like atomic-scale point contacts, wheremore fundamental processes dominate and friction oŸen is independent of the normal force. In this work we show how the friction between InAs nanowires and an insulating silicon nitride layer on a conductive silicon substrate varies when a DC voltage is applied to the AFM tip during manipulation. e tip charges the capacitor formed by the wire and the grounded silicon back contact, giving rise to attractive Coulomb forces and thus increasing the contact pressure between the wire and the silicon nitride. In this way we can vary the normal force on the sliding surfaces using a single wire, with a constant structure and contact geometry. Using nanowires of about 40-50 nm diameter and a few microns in length we have applied tip voltages in the range +12 to -12 V. Simplemodeling indicates that these voltages su›ce to give similar levels of band-lling and depletion to when the same wires are used in working wrap-gate or back-gate devices. A monotonic increase of the sliding friction with the voltage applied on the tip was observed. is implies that the friction increases with the normal force and that this mesoscopic system behaves more like a macroscopic contact, despite the nanometer size of the contact in the direction of motion.
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| 4. |
- Höglund, Linda, 1974-, et al.
(författare)
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Origin of photocurrent in lateral quantum dots-in-a-well infrared photodetectors
- 2006
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Ingår i: Applied Physics Letters. - New York : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 88:21
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Tidskriftsartikel (refereegranskat)abstract
- Interband and intersubband transitions of lateral InAs/In0.15Ga0.85As dots-in-a-well quantum dot infrared photodetectors were studied in order to determine the origin of the photocurrent. The main intersubband transition contributing to the photocurrent (PC) was associated with the quantum dot ground state to the quantum well excited state transition. By a comparison between intersubband PC measurements and the energy level scheme of the structure, as deduced from Fourier transform photoluminescence (FTPL) and FTPL excitation spectroscopies, the main transition contributing to the PC was identified.
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| 5. |
- Höglund, Linda, 1974-, et al.
(författare)
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Quantum dots-in-a-well infrared photodetectors for long wavelength infrared detection
- 2006
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Ingår i: Proceedings of SPIE. - Bellingham, Wash. : SPIE - International Society for Optical Engineering. - 9780819464996 ; 6401, s. 1-640109
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Konferensbidrag (refereegranskat)abstract
- We report on a quantum dots-in-a-well infrared photodetector (DWELL QDIP) grown by metal organic vapor phase epitaxy. The DWELL QDIP consisted of ten stacked InAs/In0.5Ga0.85As/GaAs QD layers embedded between n-doped contact layers. The density of the QDs was about 9 × 10 10 cm-2 per QD layer. The energy level structure of the DWELL was revealed by optical measurements of interband transitions, and from a comparison with this energy level scheme the origin of the photocurrent peaks could be identified. The main intersubband transition contributing to the photocurrent was associated with the quantum dot ground state to the quantum well excited state transition. The performance of the DWELL QDIPs was evaluated regarding responsivity and dark current for temperatures between 15 K and 77 K. The photocurrent spectrum was dominated by a LWIR peak, with a peak wavelength at 8.4 μm and a full width at half maximum (FWHM) of 1.1 μm. At an operating temperature of 65 K, the peak responsivity was 30 mA/W at an applied bias of 4 V and the dark current was 1.2×10-5 A/cm2. Wavelength tuning from 8.4 μm to 9.5 μm was demonstrated, by reversing the bias of the detector.
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| 6. |
- Höglund, Linda, et al.
(författare)
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Tuning of the detection wavelength in quantum dots-in-a-well infrared photodetectors
- 2008
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Ingår i: Proceedings of SPIE, 6940, Infrared Technology and Applications XXXIV, 694002. - : SPIE. - 9780819471314
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Konferensbidrag (refereegranskat)abstract
- In this study, bias mediated tuning of the detection wavelength within the infrared wavelength region is demonstrated for quantum dots-in-a-well (DWELL) infrared photodetectors. In DWELL structures, intersubband transitions in the conduction band occur from a discrete state in the quantum dot to a subband inthe quantum well. Compared to "conventional" quantum dot infrared photodetectors, where the transitions take place between different discrete bands in thequantum dots, new possibilities to tune the detection wavelength window are opened up, partly by varying the quantum dot energy levels and partly by adjusting the width and composition of the quantum well. In the DWELL structure used, an asymmetric positioning of the InAs quantum dot layer in a 8 nm wide In0.15Ga0.85As/GaAs QW has been applied which enables tuning of the peak detection wavelength within the long wavelength infrared (LWIR; 8 - 14 gm) region. When the applied bias was reversed, a wavelength shift from 8.5 to 9.5 mu m was observed for the peak position in the spectral response. For another DWELL structure, with a well width of 2 nm, the tuning range of the detector could be shifted from the medium wavelength infrared (MWIR; 3-5 mu m) region to the LWIR region. With small changes in the applied bias, the peak detection wavelength could be shifted from 5.1 to 8 mu m. These tuning properties ofDWELL structures could be essential for applications such as modulators and two-colour infrared detection. © (2008) COPYRIGHT SPIE--The International Society for Optical Engineering.
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| 7. |
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| 8. |
- Liu, Ruisheng, 1972-, et al.
(författare)
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Ferromagnetic single-electron transistors fabricated by atomic force microscopy
- 2006
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Konferensbidrag (refereegranskat)abstract
- We report on the fabrication and magneto-transport measurements of Ni/Au/Ni ferromagnetic single-electron transistors (F-SETs), fabricated by atomic force microscopy. By positioning a single Au disc (30 nm in diameter) into the gap between the Ni drain and source electrodes (of width 220 nm and 80 nm, respectively) step-by-step with Angstrom precision, and using plasma-processed NiOx as tunneling barriers, we can successfully fabricate F-SETs of high quality and substantial stability. The characteristic time interval of the device between two successive tunneling events is 10ps. The absence of any clear features in the transport related to the applied external magnetic field indicates that no spin-accumulation is maintained in the central Au disc. This interesting result indicates that the spin-relaxation time inside the central island should be shorter than 10ps. Based on these findings, we will discuss possible mechanisms of spin-relaxation in metal nano-structures triggered by spin-orbit interaction.
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| 9. |
- Nilsson, Pernilla, 1969-, et al.
(författare)
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En jämförande studie av olika elevgruppers förståelse av accelerationsbegreppet
- 2005
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Konferensbidrag (refereegranskat)abstract
- SyfteBegreppet acceleration har visat sig vara ett svårt begrepp att förstå, även i högre kurser i fysik. Kopplingen mellan acceleration och kraft är ofta oklar. Studenterna har svårt att förstå hur krafter verkar, eller vilka krafter som finns. De blandar t.ex. ofta in tröghets-krafter. I detta konferensbidrag diskuterar vi resultaten från en jämförande studie av hur 11-åringar, lärarstudenter F-5 och teknisk fysikstudenter (civilingenjörsstudenter) diskuterar och resonerar runt begreppet acceleration. Empirin bygger på fria gruppdiskussioner och intervjuer beträffande accelerationsbegreppet vid experiment i klassrummet och på nöjesparken Liseberg. I denna studie söker vi svar på frågor som: hur påverkas resonemanget och språket av förkunskaper och tidigare erfarenheter av fysik? Vilken inverkan har den lärandekontext de befinner sig i? Hur använder de olika elevgrupperna vardagsspråk kontra vetenskapligt språk då de beskriver begreppet acceleration? Vi är också intresserade av att se hur de tre elevgrupperna relaterar begreppet acceleration till begreppet kraft och om det finns det ett mönster beträffande missuppfattningar av accelerationsbegreppet och kraftbegreppet.Bakgrund och teoretisk utgångspunktGunstone & Watts (i Driver mfl, 1985) har sammanställt några av barns grundläggande idéer och tankar om relationen mellan kraft och rörelse. I dessa studier framkommer det att vanliga missuppfattningar är att det inte kan finnas någon kraft utan rörelse och att kraft har att göra med levande varelser.Studien bygger på ett perspektiv på lärande där kunskap fördjupas i diskurser och där språket är ett viktigt redskap för att utveckla och kommunicera kunskap (Vygotsky, 1934/1986; Dyste, 2003). I sina diskussioner visar barnen och studenterna på ett resonemang där flera fysikaliska termer och begrepp utvecklas, förklaras, exemplifieras och kopplas till ett vardagssammanhang.Forskning visar att elever ofta känner sig osäkra inför den naturvetenskapliga diskursen (Schoultz, 2000). De har svårigheter att använda naturvetenskapliga termer och begrepp i samtal och texter. Alltför ofta använder de endast termen för ett fenomen som en korrekt förklaring. För att förstå naturvetenskapen räcker det inte att endast ytligt känna till dessa termer och begrepp utan man måste ha en djupare förståelse av dessa, såväl som en förståelse av hur de är sammanlänkade till en enhetlig begreppsbild.I det objektiva naturvetenskapliga språket använder man ett begreppssystem som inte refererar till mänskliga upplevelser. Genom att koppla in de mäskliga upplevelserna av olika fenomen kan begreppen få en ny dimension som kan underlätta förståelsen och inlärningsprocessen.Empiriskt materialSamtliga elevgrupper i denna studie har diskuterat begreppet acceleration både med hjälp av olika klassrumsexperiment, och i samband med olika åkattraktioner på Liseberg. Därför består det empiriska materialet av video och kassettbandinspelningar av gruppdiskussioner vid klassrumsexperiment, men även av diskussioner och spontana intervjuer och videofilmer från Liseberg.
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