| 1. |
- Bryllert, Tomas, et al.
(författare)
-
Designed emitter states in resonant tunneling through quantum dots
- 2002
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:15, s. 2681-2683
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant tunneling through a single layer of self-assembled quantum dots (QDs) is compared to tunneling through two layers of vertically aligned (stacked) dots. The difference can be viewed as going from a two-dimensional emitter to a zero-dimensional emitter. The temperature dependence of current peaks originating in tunneling through individual QDs and individual stacks is used to clarify this point. In addition, we show that the statistical size distribution of self-assembled quantum dots causing the inhomogeneous broadening in luminescence experiments can be analyzed in a resonant tunneling experiment. (C) 2002 American Institute of Physics.
|
|
| 2. |
- Bryllert, Tomas, et al.
(författare)
-
Resonant tunneling through coupled self-assembled quantum dots and the influence of inhomogeneous broadening
- 2002
-
Ingår i: 7th International Conference on Nanometer-Scale Science and Technology and 21st European Conference on Surface Science.
-
Konferensbidrag (refereegranskat)abstract
- Resonant tunneling through a single layer of self-assembled quantum dots (QDs) as well as tunneling through two layers of vertically aligned (stacked) dots is investigated. The difference between single and double layers of QDs can be viewed as going from a two-dimensional emitter to a zero-dimensional emitter. By fabricating small-area devices we are able to probe single stacks of quantum dots, revealing details of the coupling between the stacked dots. Very sharp resonances, with peak-to-valley ratios of several hundred, have been measured in the current-voltage characteristics. We also show that the statistical size distribution of self-assembled quantum dots causing the inhomogeneous broadening in luminescence experiments can be analysed in a resonant tunneling experiment
|
|
| 3. |
- Gustafson, Boel, et al.
(författare)
-
Coupling between lateral modes in a vertical resonant tunneling structure
- 2002
-
Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - 1386-9477. ; 13:2-4, s. 950-953
-
Tidskriftsartikel (refereegranskat)abstract
- We present experimental results and theoretical calculations of the vertical electron transport through a laterally constricted resonant tunneling transistor. Current-voltage measurements at 4.2 K show numerous current peaks that exhibit a complex dependence on the applied gate voltage. A scattering-matrix approach combined with the Landauer formalism was used to perform quantum mechanical calculations of the electron transport through a quantum dot structure with laterally confined emitter and collector regions. The simulations qualitatively reproduce the measured data, suggesting a strong coupling between the lateral modes in the quantum dot and the collector
|
|
| 4. |
- Ohlsson, Lars, et al.
(författare)
-
Slot-Coupled Millimeter-Wave Dielectric Resonator Antenna for High-Efficiency Monolithic Integration
- 2013
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 61:4, s. 1599-1607
-
Tidskriftsartikel (refereegranskat)abstract
- A readily mass-producible, flip-chip assembled, and slot-coupled III-V compound semiconductor dielectric resonator antenna operating in the millimeter-wave spectrum has been fabricated and characterized. The antenna has a 6.1% relative bandwidth, deduced from its 10 dB return loss over 58.8-62.5 GHz, located around the resonance at 60.5 GHz. Gating in the delay-domain alleviated the analysis of the complex response from the measured structure. The radiation efficiency is better than -0.1 dB in simulations fed from the on-chip coupling-structure, but reduced by 3.7 dB insertion loss through the measurement assembly feed. Antenna gain measurements show distortion in relation to the simulated pattern, which has a maximum gain of 6 dBi, mainly caused by interference from the electrically large connector used in the assembly. Mode degeneration in the utilized quadratic-footprint resonator was not seen to influence the performance of the antenna. The antenna is intended for on-chip integration and the fabrication technology allows scaling of the operation frequency over the complete millimeter-wave spectrum.
|
|
| 5. |
- Wernersson, Lars-Erik, et al.
(författare)
-
Metalorganic vapor phase epitaxy-grown GaP/GaAs/GaP and GaAsP/GaAs/GaAsP n-type resonant tunnelling diodes
- 2002
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:10, s. 1841-1843
-
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.
|
|
| 6. |
- Wernersson, Lars-Erik, et al.
(författare)
-
Thin layers of GaInP, GaP and GaAsP in metalorganic vapour phase epitaxy-grown resonant tunnelling diodes
- 2002
-
Ingår i: Applied Surface Science. - 1873-5584. ; 190:1, s. 252-257
-
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.
|
|
| 7. |
- De Abreu Goes, Jesus, 1989, et al.
(författare)
-
Correlation between Vehicle- and Rapid- Aged Commercial Lean NOx Trap Catalysts
- 2017
-
Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 10:4, s. 1613-1626
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Even though substantial improvements have been made for the lean NOx trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation compared to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was vehicle-aged in the vehicle chassis dynamometer for 100000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions. Engine dynamometer studies were performed with a Volvo mid-sized diesel engine with the purpose of testing the NOx storage and reduction performance, as well as the THC and CO conversion activity of the catalysts under controlled conditions. The aged catalysts activity was shown to be significantly degraded, mainly at low working temperatures compared to the fresh LNT, and one reason for this could be limited NO oxidation. In addition, the oven-aged sample was found to be well correlated to the vehicle-aged catalyst. On top of that, several vehicle emission cycles were carried out in the vehicle chassis dynamometer with a 2.0 l Volvo XC90 diesel vehicle in order to study the catalysts performance under real driving conditions and monitor the gradual deterioration of the vehicle-aged catalyst during the vehicle aging testing.
|
|
| 8. |
- Stille, Håkan, et al.
(författare)
-
Application of new theories and technology for grouting of dams and foundations on rock
- 2012
-
Ingår i: Geotechnical and Geological Engineering. - : Springer Science and Business Media LLC. - 0960-3182 .- 1573-1529. ; 30:3, s. 603-624
-
Tidskriftsartikel (refereegranskat)abstract
- Permeation grouting is used to improve rock conditions under dams and foundations. During recent decades, there has been a substantial increase of understanding of the mechanism behind grout spread in fractured rock. It is the penetrability of the grout mix and the spread in the joints which will be the governing factors for the quality of the grout curtain. The flow properties and the pressure will give the required time to achieve the quality. The empirical based refusal and completion criteria of today can be replaced by a more engineering based grouting process. An active control method has been developed in order to govern the grout spread during the grouting operation based on the new theory of spreading of grout. The concept is called the "real time grouting control method". The concept and the latest finding of the mechanism of spreading of the grout in the fractures of the rock mass are presented in the paper. The application of the method on two dam projects is also presented.
|
|
| 9. |
- Johansson, S. C., et al.
(författare)
-
Surface modification of PM gearlever
- 2010
-
Ingår i: World Powder Metallurgy Congress and Exhibition, World PM 2010; Florence; Italy; 10 October 2010 through 14 October 2010. - : European Powder Metallurgy Association (EPMA). - 9781899072194 ; 3
-
Konferensbidrag (refereegranskat)abstract
- A novel manufacturing concept for a gearlever has been evaluated by manufacturing of test components of two materials. Iron-based powders were used, and pressing and sintering was followed by a few different variants of hardening and surface densification. The components have been evaluated by means of component function testing, component fatigue testing, microstructure characterization, hardness measurements and residual stress determination. The gearlever is found to perform well in the function testing and shows also good fatigue properties that well match the demands for the intended application. The porosity in the sintered material is inhomogeneous, and some compaction-induced defects were observed in the material, which thus seems not to give any significant negative impact on the sintered product performance. The results show a doubling in hardness after hardening. If the materials were shot-peened (or shot-blasted) after hardening the surface hardness increased down to a depth of approximately 0.2 mm compared to the hardened material. The case-hardening should be applied after shot-peening to obtain significant effect on surface hardness within the outermost 0.1 mm. In principle no surface densification was created if shoot-peening was performed after hardening.
|
|
| 10. |
|
|
