| 1. |
- Baier, Robert, et al.
(författare)
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Electronic properties of grain boundaries in Cu(In,Ga)Se-2 thin films with various Ga-contents
- 2012
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248. ; 103, s. 86-92
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Tidskriftsartikel (refereegranskat)abstract
- We present a study on the electronic properties of grain boundaries (GBs) in polycrystalline Cu(In,Ga)Se-2 (CIGSe) thin films by means of Kelvin probe force microscopy. As grown as well as KCN-treated films were investigated comparatively. No influence of the chemical treatment on the electronic properties of GBs was found. GBs generally exhibited large variations in their electronic properties. By means of a novel method of data analysis both potential barriers for holes and electrons were found at GBs, in a range from -118 mV to +114 mV, as well as GBs without potential barrier. No dependence of the electronic GB-properties on the Ga-content was detected. Consequently, we conclude that there is no correlation between the electronic properties of GBs and the obtained maximum efficiencies of CIGSe thin film solar cells as a function of the Ga-content. (C) 2012 Elsevier B.V. All rights reserved.
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| 2. |
- Hertzberg, Joachim, et al.
(författare)
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The RACE Project : Robustness by Autonomous Competence Enhancement
- 2014
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Ingår i: Künstliche Intelligenz. - : Springer Berlin/Heidelberg. - 0933-1875 .- 1610-1987. ; 28:4, s. 297-304
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on the aims, the approach, and the results of the European project RACE. The project aim was to enhance the behavior of an autonomous robot by having the robot learn from conceptualized experiences of previous performance, based on initial models of the domain and its own actions in it. This paper introduces the general system architecture; it then sketches some results in detail regarding hybrid reasoning and planning used in RACE, and instances of learning from the experiences of real robot task execution. Enhancement of robot competence is operationalized in terms of performance quality and description length of the robot instructions, and such enhancement is shown to result from the RACE system.
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| 3. |
- Lehmann, Jascha, et al.
(författare)
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Reliable wet-chemical cleaning of natively oxidized high-efficiency Cu(In,Ga)Se-2 thin-film solar cell absorbers
- 2014
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 116:23
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Tidskriftsartikel (refereegranskat)abstract
- Currently, Cu-containing chalcopyrite-based solar cells provide the highest conversion efficiencies among all thin-film photovoltaic (PV) technologies. They have reached efficiency values above 20%, the same performance level as multi-crystalline silicon-wafer technology that dominates the commercial PV market. Chalcopyrite thin-film heterostructures consist of a layer stack with a variety of interfaces between different materials. It is the chalcopyrite/buffer region (forming the p-n junction), which is of crucial importance and therefore frequently investigated using surface and interface science tools, such as photoelectron spectroscopy and scanning probe microscopy. To ensure comparability and validity of the results, a general preparation guide for "realistic" surfaces of polycrystalline chalcopyrite thin films is highly desirable. We present results on wet-chemical cleaning procedures of polycrystalline Cu(In1-xGax)Se-2 thin films with an average x = [Ga]/([In] + [Ga]) = 0.29, which were exposed to ambient conditions for different times. The hence natively oxidized sample surfaces were etched in KCN- or NH3-based aqueous solutions. By x-ray photoelectron spectroscopy, we find that the KCN treatment results in a chemical surface structure which is - apart from a slight change in surface composition - identical to a pristine as-received sample surface. Additionally, we discover a different oxidation behavior of In and Ga, in agreement with thermodynamic reference data, and we find indications for the segregation and removal of copper selenide surface phases from the polycrystalline material. (C) 2014 AIP Publishing LLC.
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| 4. |
- Aghaeipour, Mahtab, et al.
(författare)
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Optical response of wurtzite and zinc blende GaP nanowire arrays
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:23, s. 30177-30187
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Tidskriftsartikel (refereegranskat)abstract
- We compare the optical response of wurtzite and zinc blende GaP nanowire arrays for varying geometry of the nanowires. We measure reflectance spectra of the arrays and extract from these measurements the absorption in the nanowires. To support our experimental findings and to allow for more detailed investigations of the optical response of the nanowire arrays than possible in experiments, we perform electromagnetic modeling. This modeling highlights the validity of the extraction of the absorptance from reflectance spectra, as well as limitations of the extraction due to anti-reflection properties of the nanowires. In our combined experimental and theoretical study, we find for both zinc blende and wurtzite nanowires an absorption resonance that can be tuned into the ultraviolet by decreasing the diameter of the nanowires. This peak stops blue-shifting with decreasing nanowire diameter at a wavelength of approximately 330 nm for zinc blende GaP. In contrast, for the wurtzite GaP nanowires, the resonance continues blue-shifting at 310 nm for the smallest diameters we succeeded in fabricating. We interpret this as a difference in refractive index between wurtzite and zinc blende GaP in this wavelength region. These results open up for optical applications through resonant absorption in the visible and ultraviolet wavelength regions with both zinc blende and wurtzite GaP nanowire arrays. Notably, zinc blende and wurtzite GaP support resonant absorption deeper into the ultraviolet region than previously found for zinc blende and wurtzite InP and InAs. (C) 2015 Optical Society of America
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| 5. |
- Aghaeipour, Mahtab, et al.
(författare)
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Tunable absorption resonances in the ultraviolet for InP nanowire arrays
- 2014
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Ingår i: Optics Express. - 1094-4087. ; 22:23, s. 29204-29212
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to tune the photon absorptance spectrum is an attracting way of tailoring the response of devices like photodetectors and solar cells. Here, we measure the reflectance spectra of InP substrates patterned with arrays of vertically standing InP nanowires. Using the reflectance spectra, we calculate and analyze the corresponding absorptance spectra of the nanowires. We show that we can tune absorption resonances for the nanowire arrays into the ultraviolet by decreasing the diameter of the nanowires. When we compare our measurements with electromagnetic modeling, we generally find good agreement. Interestingly, the remaining differences between modeled and measured spectra are attributed to a crystal-phase dependence in the refractive index of InP. Specifically, we find indication of significant differences in the refractive index between the modeled zinc-blende InP nanowires and the measured wurtzite InP nanowires in the ultraviolet. We believe that such crystal-phase dependent differences in the refractive index affect the possibility to excite optical resonances in the large wavelength range of 345 < lambda < 390 nm. To support this claim, we investigated how resonances in nanostructures can be shifted in wavelength by geometrical tuning. We find that dispersion in the refractive index can dominate over geometrical tuning and stop the possibility for such shifting. Our results open the door for using crystal-phase engineering to optimize the absorption in InP nanowire-based solar cells and photodetectors. (C) 2014 Optical Society of America
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| 6. |
- Anttu, Nicklas, et al.
(författare)
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Crystal Phase-Dependent Nanophotonic Resonances in InAs Nanowire Arrays
- 2014
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:10, s. 5650-5655
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructures have many material, electronic, and optical properties that are not found in bulk systems and that are relevant for technological applications. For example, nanowires realized from III-V semiconductors can be grown into wurtzite crystal structure. This crystal structure does not naturally exist in bulk where these materials form the zinc-blende counterpart. Being able to concomitantly grow these nanowires in the zinc-blende and/or wurtzite crystal structure prlovides an important degree of control for the design and optimization of optoelectronic applications based on these semiconductor nanostructures. However, the refractive indices of this new crystallographic phase have so far not been elucidated. This shortcoming makes it impossible to predict and utilize he full potential of these new nanostructured materials for optoelectronics applications a careful design and optimization of optical resonances by tuning the nanostrucuted geometry is needed to achieve optimal performance. Here, we report and analyze striking differeences in the optical response of nanophotonic resonances in wurtzite and zinc-blend InAs nanowire arrays. Specifically, through reflectance measurements we find that the resonance can be tuned down to lambda approximate to 380 nm in wurtzite nanowires by decreasing the nanowire diameter. In stark contrast, a similar tuning to below approximate to 500 nm is not possible in the zinc-blende nanowires. Furthermore, we find that the wurtzite nanowires can absorb twice as strongly as the zinc-blende nanowires. We attribute these strikingly large differences in resonant behavior to large differences between the refractive indices of the two crystallographic phases realized in these nanostructures. We anticipate our finding to be relevant for other III-B materials as well as for all material systems that manifest polytypism. Taken together, our results demonstrate crystal phase engineering as a potentially new design dimension for optoelectronics applications.
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| 7. |
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| 8. |
- Bacic, Luka, et al.
(författare)
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Structure and dynamics of the chromatin remodeler ALC1 bound to a PARylated nucleosome
- 2021
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Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- The chromatin remodeler ALC1 is recruited to and activated by DNA damage-induced poly(ADP-ribose) (PAR) chains deposited by PARP1/PARP2/HPF1 upon detection of DNA lesions. ALC1 has emerged as a candidate drug target for cancer therapy as its loss confers synthetic lethality in homologous recombination-deficient cells. However, structure-based drug design and molecular analysis of ALC1 have been hindered by the requirement for PARylation and the highly heterogeneous nature of this post-translational modification. Here, we reconstituted an ALC1 and PARylated nucleosome complex modified in vitro using PARP2 and HPF1. This complex was amenable to cryo-EM structure determination without cross-linking, which enabled visualization of several intermediate states of ALC1 from the recognition of the PARylated nucleosome to the tight binding and activation of the remodeler. Functional biochemical assays with PARylated nucleosomes highlight the importance of nucleosomal epitopes for productive remodeling and suggest that ALC1 preferentially slides nucleosomes away from DNA breaks.
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| 9. |
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| 10. |
- Barker, David, et al.
(författare)
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Experimental Verification of the Work Fluctuation-Dissipation Relation for Information-to-Work Conversion
- 2022
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Ingår i: Physical Review Letters. - 0031-9007. ; 128:4
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Tidskriftsartikel (refereegranskat)abstract
- We study experimentally work fluctuations in a Szilard engine that extracts work from information encoded as the occupancy of an electron level in a semiconductor quantum dot. We show that as the average work extracted per bit of information increases toward the Landauer limit Formula Presented, the work fluctuations decrease in accordance with the work fluctuation-dissipation relation. We compare the results to a protocol without measurement and feedback and show that when no information is used, the work output and fluctuations vanish simultaneously, contrasting the information-to-energy conversion case where increasing amount of work is produced with decreasing fluctuations. Our study highlights the importance of fluctuations in the design of information-to-work conversion processes.
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| 11. |
- Berg, Alexander, et al.
(författare)
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Growth and characterization of wurtzite GaP nanowires with control over axial and radial growth by use of HCl in-situ etching
- 2014
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 386, s. 47-51
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis of non-tapered wurtzite (WZ) GaP nanowires by use of in-situ etching and the structural and optical characterization thereof. HCl was evaluated as an in-situ etchant in order to impede the onset of radial growth since the WZ crystal phase in GaP nanowires preferentially grows at relatively high growth temperatures around 600 degrees C, at which strong radial growth typically occurs. Transmission electron microscopy measurements confirmed non-tapered WZ GaP nanowires after growth. Photoluminescence characterization revealed defect related red emission, possibly related to transitions within the bandgap. Raman measurements show that the phonon energies in WZ GaP are very close in energy to the phonon energies in zinc blende GaP. (C) 2013 Elsevier B.V. All rights reserved.
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| 12. |
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| 13. |
- Calabrese, Claudia, et al.
(författare)
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Genomic basis for RNA alterations in cancer
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 578:7793, s. 129-136
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Tidskriftsartikel (refereegranskat)abstract
- Transcript alterations often result from somatic changes in cancer genomes1. Various forms of RNA alterations have been described in cancer, including overexpression2, altered splicing3 and gene fusions4; however, it is difficult to attribute these to underlying genomic changes owing to heterogeneity among patients and tumour types, and the relatively small cohorts of patients for whom samples have been analysed by both transcriptome and whole-genome sequencing. Here we present, to our knowledge, the most comprehensive catalogue of cancer-associated gene alterations to date, obtained by characterizing tumour transcriptomes from 1,188 donors of the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA)5. Using matched whole-genome sequencing data, we associated several categories of RNA alterations with germline and somatic DNA alterations, and identified probable genetic mechanisms. Somatic copy-number alterations were the major drivers of variations in total gene and allele-specific expression. We identified 649 associations of somatic single-nucleotide variants with gene expression in cis, of which 68.4% involved associations with flanking non-coding regions of the gene. We found 1,900 splicing alterations associated with somatic mutations, including the formation of exons within introns in proximity to Alu elements. In addition, 82% of gene fusions were associated with structural variants, including 75 of a new class, termed 'bridged' fusions, in which a third genomic location bridges two genes. We observed transcriptomic alteration signatures that differ between cancer types and have associations with variations in DNA mutational signatures. This compendium of RNA alterations in the genomic context provides a rich resource for identifying genes and mechanisms that are functionally implicated in cancer.
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| 14. |
- Chen, I. Ju, et al.
(författare)
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Conduction Band Offset and Polarization Effects in InAs Nanowire Polytype Junctions
- 2017
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 17:2, s. 902-908
-
Tidskriftsartikel (refereegranskat)abstract
- Although zinc-blende (ZB) and wurtzite (WZ) structures differ only in the atomic stacking sequence, mixing of crystal phases can strongly affect the electronic properties, a problem particularly common to bottom up-grown nanostructures. A lack of understanding of the nature of electronic transport at crystal phase junctions thus severely limits our ability to develop functional nanowire devices. In this work we investigated electron transport in InAs nanowires with designed mixing of crystal structures, ZB/WZ/ZB, by temperature-dependent electrical measurements. The WZ inclusion gives rise to an energy barrier in the conduction band. Interpreting the experimental result in terms of thermionic emission and using a drift-diffusion model, we extracted values for the WZ/ZB band offset, 135 ± 10 meV, and interface sheet polarization charge density on the order of 10-3 C/m2. The extracted polarization charge density is 1-2 orders of magnitude smaller than previous experimental results, but in good agreement with first principle calculation of spontaneous polarization in WZ InAs. When the WZ length is reduced below 20 nm, an effective barrier lowering is observed, indicating the increasing importance of tunneling transport. Finally, we found that band-bending at ZB/WZ junctions can lead to bound electron states within an enclosed WZ segment of sufficient length, evidenced by our observation of Coulomb blockade at low temperature. These findings provide critical input for modeling and designing the electronic properties of novel functional devices, such as nanowire transistors, where crystal polytypes are commonly found.
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| 15. |
- Davtyan, Arman, et al.
(författare)
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Characterization of individual stacking faults in a wurtzite GaAs nanowire by nanobeam X-ray diffraction
- 2017
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 24:5, s. 981-990
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Tidskriftsartikel (refereegranskat)abstract
- Coherent X-ray diffraction was used to measure the type, quantity and the relative distances between stacking faults along the growth direction of two individual wurtzite GaAs nanowires grown by metalorganic vapour epitaxy. The presented approach is based on the general property of the Patterson function, which is the autocorrelation of the electron density as well as the Fourier transformation of the diffracted intensity distribution of an object. Partial Patterson functions were extracted from the diffracted intensity measured along the direction in the vicinity of the wurtzite Bragg peak. The maxima of the Patterson function encode both the distances between the fault planes and the type of the fault planes with the sensitivity of a single atomic bilayer. The positions of the fault planes are deduced from the positions and shapes of the maxima of the Patterson function and they are in excellent agreement with the positions found with transmission electron microscopy of the same nanowire.The application of the synchrotron-radiation-based coherent nanobeam X-ray diffraction method to study the type, quantity and the exact distances in between stacking faults in single GaAs nanowires is demonstrated.
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| 16. |
- Debbarma, Rousan, et al.
(författare)
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Effects of Parity and Symmetry on the Aharonov-Bohm Phase of a Quantum Ring
- 2021
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992.
-
Tidskriftsartikel (refereegranskat)abstract
- We experimentally investigate the properties of one-dimensional quantum rings that form near the surface of nanowire quantum dots. In agreement with theoretical predictions, we observe the appearance of forbidden gaps in the evolution of states in a magnetic field as the symmetry of a quantum ring is reduced. For a twofold symmetry, our experiments confirm that orbital states are grouped pairwise. Here, a π-phase shift can be introduced in the Aharonov-Bohm relation by controlling the relative orbital parity using an electric field. Studying rings with higher symmetry, we note exceptionally large orbital contributions to the effective g-factor (up to 300), which are many times higher than those previously reported. These findings show that the properties of a phase-coherent system can be significantly altered by the nanostructure symmetry and its interplay with wave function parity.
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| 17. |
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| 18. |
- Debbarma, Rousan, et al.
(författare)
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Josephson Junction π-0 Transition Induced by Orbital Hybridization in a Double Quantum Dot
- 2023
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Ingår i: Physical Review Letters. - 0031-9007. ; 131:25
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we manipulate the phase shift of a Josephson junction using a parallel double quantum dot (QD). By employing a superconducting quantum interference device, we determine how orbital hybridization and detuning affect the current-phase relation in the Coulomb blockade regime. For weak hybridization between the QDs, we find π junction characteristics if at least one QD has an unpaired electron. Notably the critical current is higher when both QDs have an odd electron occupation. By increasing the inter-QD hybridization the critical current is reduced, until eventually a π-0 transition occurs. A similar transition appears when detuning the QD levels at finite hybridization. Based on a zero-bandwidth model, we argue that both cases of phase-shift transitions can be understood considering an increased weight of states with a double occupancy in the ground state and with the Cooper pair transport dominated by local Andreev reflection.
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| 19. |
- Dick Thelander, Kimberly, et al.
(författare)
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Parameter space mapping of InAs nanowire crystal structure
- 2011
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Ingår i: Journal of Vacuum Science and Technology B. - : American Vacuum Society. - 1520-8567. ; 29:4
-
Tidskriftsartikel (refereegranskat)abstract
- Crystal structure and defects have been shown to have a strong impact on III-V nanowire properties. Recently, it was demonstrated that the issue of random stacking and polytypism in semiconductor nanowires can often be controlled using accessible growth parameters (such as temperature, diameter, and V/III ratio). In addition, it has been shown that crystal phase can be tuned selectively between cubic zinc blende and hexagonal wurtzite within individual nanowires of III-V materials such as InAs. In order for such results to be generally applied to different growth setups, it is necessary to fully explore and understand the trends governing crystal phase dependencies on all accessible growth parameters, including how they relate to each other. In this study, the authors have systematically investigated the influence of temperature, diameter, V/III ratio, and total mass flow on the crystal structure of InAs nanowires grown by metal-organic vapor phase epitaxy over a broad parameter range. The authors observed that each of these accessible parameters can affect the resulting crystal structure, and that the trends for each parameter are affected by the magnitude of the others. The authors also noted that most of the parameter dependencies are nonlinear and, in fact, exhibit threshold values at which structure changes discontinuously. By optimizing each of the growth parameters, it is shown that pure ZB or pure WZ phase can be achieved for several different sets of growth conditions. The roles of nucleation kinetics, thermodynamics, and precursor chemistry are also discussed to compare the results to current nanowire growth models. The results in this work should facilitate comparison of data and transfer of knowledge between different growth systems and techniques, which, in turn, should lead to greater understanding of polytypism in nanowires and greater control and freedom in nanowire crystal phase engineering. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3593457]
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| 20. |
- Dorsch, Sven, et al.
(författare)
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Gate control, g factors, and spin-orbit energy of p -type GaSb nanowire quantum dot devices
- 2021
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Ingår i: Physical Review B. - 2469-9950. ; 103:24
-
Tidskriftsartikel (refereegranskat)abstract
- Proposals for quantum information applications are frequently based on the coherent manipulation of spins confined to quantum dots. For these applications, p-type III-V material systems promise a reduction of the hyperfine interaction while maintaining large g factors and strong spin-orbit interaction. In this Letter, we study bottom-gated device architectures to realize single and serial multiquantum dot systems in Schottky-contacted p-type GaSb nanowires. We find that the effect of potentials applied to gate electrodes on the nanowire is highly localized to the immediate vicinity of the gate electrode only, which prevents the formation of double quantum dots with commonly used device architectures. We further study the transport properties of a single quantum dot induced by bottom gating and find large gate-voltage dependent variations of the g∗ factors up to 8.1±0.2 as well as spin-orbit energies between 110 and 230 μeV.
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| 21. |
- Ek, M., et al.
(författare)
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Electron channelling : challenges and opportunities for compositional analysis of nanowires by TEM
- 2020
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 31:36
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Tidskriftsartikel (refereegranskat)abstract
- Energy dispersive x-ray spectroscopy in a transmission electron microscope is often the first method employed to characterize the composition of nanowires. Ideally, it should be accurate and sensitive down to fractions of an atomic percent, and quantification results are often reported as such. However, one can often get substantial errors in accuracy even though the precision is high: for nanowires it is common for the quantified V/III atomic ratios to differ noticeably from 1. Here we analyse the origin of this systematic error in accuracy for quantification of the composition of III-V nanowires. By varying the electron illumination direction, we find electron channelling to be the primary cause, being responsible for errors in quantified V/III atomic ratio of 50%. Knowing the source of the systematic errors is required for applying appropriate corrections. Lastly, we show how channelling effects can provide information on the crystallographic position of dopants.
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| 22. |
- Escobar Steinvall, Simon, et al.
(författare)
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Visualizing the Mechanism Switching in High-Temperature Au-Catalyzed InAs Nanowire Growth
- 2023
-
Ingår i: Crystal Growth and Design. - 1528-7483. ; 23:9, s. 6228-6232
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Tidskriftsartikel (refereegranskat)abstract
- We use environmental transmission electron microscopy to observe in situ the switch from an axial vapor-liquid-solid (VLS) growth mechanism in Au-catalyzed InAs nanowires toward a radial vapor-solid (VS) one, dominated by layers nucleating at the triple-phase line. At elevated temperatures, in addition to high V/III ratios, the affinity for In in the Au catalyst will be greater than that of In in InAs, which in turn reduces the driving force and probability for nucleation at the liquid-solid interface. Consequently, with increased temperature, the catalyst particle stops acting as a sink for incoming material and the decomposition of precursors away from the catalyst increases, making radial vapor-solid growth the dominating growth mechanism. It is further observed that the growth proceeds through multistep propagation rather than a layer-by-layer propagation under these conditions.
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| 23. |
- Gawel, Erik, et al.
(författare)
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Political Economy of Safe-guarding Security of Supply with High Shares of Renewables : Review of Existing Research and Lessons from Germany
- 2017
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Rapport (refereegranskat)abstract
- The increasing shares of wind power and solar PV in the European electricity markets have raised concerns about security of supply being jeopardized. The objective of this report is to synthesize the economic research on the nature and extent of intermittency problems in electricity markets, and not least discuss how to deal with these in the electricity market design. Particular attention is devoted to German experiences, and on identifying key lessons for Swedish market design.Specifically, we first discuss how security of supply can be defined, and why real-world so-called energy-only markets, i.e., markets without any pricing of capacityper se, may not provide an efficient level of security of supply. The latter includes a broad set of various market and policy failures. Furthermore, the report identifies and evaluates different regulatory options for addressing security of supply issues in the electricity system. These include three categories of options: measures to strengthen the energy-only market (e.g., removing price caps, strengthening the balancing market, etc.); the introduction of various forms of capacity mechanisms (i.e., focused, comprehensive, and decentralized capacity markets and strategic reserves); and various energy policy reforms (e.g., flexible renewable energy feed-in, improving demand-side management, adjusting network regulation, etc.).Unlike many previous economic studies, we also analyze the drivers of the policy debate on security of supply in Germany, and not least the extent to which the knowledge gained through previous research has penetrated this debate. This political economy perspective permits better understanding of the rationale behind the actual outcomes of the policy processes, i.e., in Germany’s case a strengthening of the energy-only market and the installation of a strategic reserve.A number of generic lessons from the German policy debate are highlighted: (a) all actors in the electricity supply system can in various ways contribute to security of supply; (b) underinvestment in security of supply most often have multiple causes, and should preferably be addressed through a portfolio of context-specific measures rather than through the use of single capacity mechanisms; (c) the energy transition taking place in, e.g., Germany, does not fundamentally question security of supply; (d) the measures implemented to safeguard security of supply should include an international perspective as well as consider the risks of potential institutional lock-in; and (e) the policy decision-making process needs to build on credible long-term commitments and transparent consultations with stakeholders.In terms of lessons for the Swedish market design, our conclusions are in line with earlier studies arguing for a wait, see and evaluate strategy. We contend, though, that policy should abstain from making early, future commitments regarding the introduction of quantitative measures and more extended capacity mechanisms. Quantitative measures of security of supply are far from straightforward to define, monitor and evaluate; there is a risk that such measures become too constraining and leads to an exaggerated focus on security-of-supply. A portfolio of measures that strengthen the existing Swedish market design (e.g., removing price caps, reduced trading intervals etc.) should help address the causes of security of supply concerns in a more targeted and cost-effective manner.
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| 24. |
- Gawel, Erik, et al.
(författare)
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Security of supply as a political bargaining issue : Why Germany opted against capacity markets
- 2022
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Ingår i: Energy Research & Social Science. - : Elsevier. - 2214-6296 .- 2214-6326. ; 86
-
Tidskriftsartikel (refereegranskat)abstract
- The large-scale deployment of intermittent renewable energy sources for electricity generation has raised concerns regarding the future security of supply. Previous research has studied efficient reforms of electricity markets to address these concerns. In contrast, our paper aims to explain actual policy choices made to provide security of supply. For this purpose, we develop a Public Choice framework, which looks at three interacting decision variables: the timing of regulatory intervention, the decision-making process and the market design. We apply this framework to study the policy debates and decisions related to Germany’s 2016 electricity market reform. The analysis builds on the rich empirical material made available through a consultation process preceding the German parliamentary decision. The electricity market reform eventually combined measures to strengthen the energy-only market and the implementation of only limited new capacity payments through a strategic reserve. This was despite the fact that conventional electricity producers strongly lobbied for a fully-fledged capacity market by which they would have benefited from new broad-band capacity payments. Our analysis suggests that the eventual market design decision was strongly affected by the timing of regulatory intervention (existing oversupply of generation capacity) and the decision-making process (an open consultation process revealing broad opposition against capacity markets).
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| 25. |
- Geijselaers, Irene, et al.
(författare)
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Atomically sharp, crystal phase defined GaAs quantum dots
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 119:26
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Crystal phase defined heterostructures, or polytype heterostructures, are atomically sharp with no intermixing, which makes them ideal contenders for a wide number of applications. Although polytype quantum dots have shown promising results as single photon sources, a high degree of control on the dimensions and number of polytype quantum dots is necessary before any application can be developed.In this work we show results from optical characterization of highly controlled wz-zb GaAs quantum dots with sharp photoluminescence signal and a strong indication of 0D density of states. One band effective mass calculations show good agreement with the measured data. Radially confined nanowires with a single wz-zb GaAs interface also show sharp photoluminescence signal and a 0D density of states. This indicates the existence of quantum dot like states in the triangular wells formed at the wz-zb GaAs interface. These results show the potential of polytype quantum dots for physics and optics applications.
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