| 1. |
- Barthelmi, K., et al.
(författare)
-
Atomistic defects as single-photon emitters in atomically thin MoS2
- 2020
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 117:7
-
Tidskriftsartikel (refereegranskat)abstract
- Precisely positioned and scalable single-photon emitters (SPEs) are highly desirable for applications in quantum technology. This Perspective discusses single-photon-emitting atomistic defects in monolayers of MoS2 that can be generated by focused He-ion irradiation with few nanometers positioning accuracy. We present the optical properties of the emitters and the possibilities to implement them into photonic and optoelectronic devices. We showcase the advantages of the presented emitters with respect to atomistic positioning, scalability, long (microsecond) lifetime, and a homogeneous emission energy within ensembles of the emitters. Moreover, we demonstrate that the emitters are stable in energy on a timescale exceeding several weeks and that temperature cycling narrows the ensembles' emission energy distribution.
|
|
| 2. |
- Pettersson, H., et al.
(författare)
-
Excitons in self-assembled quantum ring-like structures
- 2000
-
Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - Amsterdam : Elsevier. - 1386-9477 .- 1873-1759. ; 6:1-4, s. 510-513
-
Tidskriftsartikel (refereegranskat)abstract
- A remarkable morphological change of self-assembled InAs quantum dots takes place during growth if a pause is introduced after overgrowing the dots with a few nm of GaAs. Atomic force microscopy indicates that the shape of the dots changes lens-like to ring-like. We report here the results of capacitance and interband transmission experiments on such ring-like structures embedded in a GaAs matrix. In particular, we compare the electronic properties of conventional dots with those of the rings. Significant changes are found which qualitatively support a quantum ring model. (C) 2000 Elsevier Science B.V. All rights reserved.
|
|
| 3. |
- Guseva, S., et al.
(författare)
-
Variable Physical Drivers of Near-Surface Turbulence in a Regulated River
- 2021
-
Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 57:11
-
Tidskriftsartikel (refereegranskat)abstract
- Inland waters, such as lakes, reservoirs and rivers, are important sources of climate forcing trace gases. A key parameter that regulates the gas exchange between water and the atmosphere is the gas transfer velocity, which itself is controlled by near-surface turbulence in the water. While in lakes and reservoirs, near-surface turbulence is mainly driven by atmospheric forcing, in shallow rivers and streams it is generated by bottom friction of gravity-forced flow. Large rivers represent a transition between these two cases. Near-surface turbulence has rarely been measured in rivers and the drivers of turbulence have not been quantified. We analyzed continuous measurements of flow velocity and quantified turbulence as the rate of dissipation of turbulent kinetic energy over the ice-free season in a large regulated river in Northern Finland. Measured dissipation rates agreed with predictions from bulk parameters, including mean flow velocity, wind speed, surface heat flux, and with a one-dimensional numerical turbulence model. Values ranged from to . Atmospheric forcing or gravity was the dominant driver of near-surface turbulence for similar fraction of the time. Large variability in near-surface dissipation rate occurred at diel time scales, when the flow velocity was strongly affected by downstream dam operation. By combining scaling relations for boundary-layer turbulence at the river bed and at the air-water interface, we derived a simple model for estimating the relative contributions of wind speed and bottom friction of river flow as a function of depth.Plain Language SummaryInland water bodies such as lakes, reservoirs and rivers are an important source of climate forcing trace gases to the atmosphere. Gas exchange between water and the atmosphere is regulated by the gas transfer velocity and the concentration difference between the water surface and the atmosphere. The gas transfer velocity depends on near-surface turbulence, but robust formulations have not been developed for river systems. Their surface area is sufficiently large for meteorological forcing to cause turbulence, as in lakes and reservoirs, but turbulence generated from bed and internal friction of gravity-driven flows is also expected to contribute. Here we quantify near-surface turbulence using data from continuous air and water side measurements conducted over the ice-free season in a large subarctic regulated river in Finland. We find that turbulence, quantified as the dissipation rate of turbulent kinetic energy, is well described using equations for predicting turbulence from meteorological data for sufficiently high wind speeds whereas the contribution from bottom shear dominated at higher flow velocities. A one-dimensional river model successfully captured these processes. We provide a fundamental model for estimating the relative contributions of atmospheric forcing and bottom friction as a function of depth.
|
|
| 4. |
- Lorke, A., et al.
(författare)
-
Technical note: drifting versus anchored flux chambers for measuring greenhouse gas emissions from running waters
- 2015
-
Ingår i: Biogeosciences. - : COPERNICUS GESELLSCHAFT MBH. - 1726-4170 .- 1726-4189. ; 12:23, s. 7013-7024
-
Tidskriftsartikel (refereegranskat)abstract
- Stream networks have recently been discovered to be major but poorly constrained natural greenhouse gas (GHG) sources. A fundamental problem is that several measurement approaches have been used without cross-comparisons. Flux chambers represent a potentially powerful methodological approach if robust and reliable ways to use chambers on running water can be defined. Here we compare the use of anchored and freely drifting chambers on various streams with different flow velocities. The study clearly shows that (1) anchored chambers enhance turbulence under the chambers and thus elevate fluxes, (2) drifting chambers have a very small impact on the water turbulence under the chamber and thus generate more reliable fluxes, (3) the bias of the anchored chambers greatly depends on chamber design and sampling conditions, and (4) there is a promising method to reduce the bias from anchored chambers by using a flexible plastic foil collar to seal the chambers to the water surface, rather than having rigid chamber walls penetrating into the water. Altogether, these results provide novel guidance on how to apply flux chambers in running water, which will have important consequences for measurements to constrain the global GHG balances.
|
|
| 5. |
- Miranda, A., et al.
(författare)
-
Electronic properties of freestanding Ti3C2Tx MXene monolayers
- 2016
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 108:3, s. 033102-1-033102-4
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the electrical characterization of single MXene Ti(3)C(2)Tx flakes ( where T is a surface termination) and demonstrate the metallic nature of their conductivities. We also show that the carrier density can be modulated by an external gate voltage. The density of free carriers is estimated to be 8 +/- 3 X 10(21) cm(-3) while their mobility is estimated to be 0.7 +/- 0.2 cm(2)/Vs. Electrical measurements, in the presence of a magnetic field, show a small, but clearly discernable, quadratic increase in conductance at 2.5 K. (C) 2016 AIP Publishing LLC.
|
|
