| 1. |
- Askari, Sadegh, et al.
(författare)
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Plasma-based processes for planar and 3D surface patterning of functional nanoparticles
- 2019
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Ingår i: Journal of nanoparticle research. - : SPRINGER. - 1388-0764 .- 1572-896X. ; 21:11
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Tidskriftsartikel (refereegranskat)abstract
- We present a gas-phase process for surface patterning and 3D self-assembly of nanoparticles (NPs) of functional materials such as metals, oxides, and nitrides. The method relies on electrostatic assembly of free-flying NPs with unipolar charge produced in plasma sources. We demonstrate the capability of the process in self-assembly of NPs, with the size in the range 10-60 nm, into arrays of free-standing 3D microstructures with complex morphologies. Considering that the plasma nanoparticle sources are compatible with synthesis of a large library of material NPs, the process introduces a novel approach for 3D printing of various functional NPs, high-precision device integration of NPs on sub-micrometer scales, and large-area parallel surface patterning of NPs.
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| 2. |
- Chalangar, Ebrahim, 1984-, et al.
(författare)
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Influence of morphology on electrical and optical properties of graphene/Al-doped ZnO-nanorod composites
- 2018
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Ingår i: Nanotechnology. - Bristol : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 29:41
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Tidskriftsartikel (refereegranskat)abstract
- The development of future 3D-printed electronics relies on the access to highly conductive inexpensive materials that are printable at low temperatures (<100 C). The implementation of available materials for these applications are, however, still limited by issues related to cost and printing quality. Here, we report on the simple hydrothermal growth of novel nanocomposites that are well suited for conductive printing applications. The nanocomposites comprise highly Al-doped ZnO nanorods grown on graphene nanoplatelets (GNPs). The ZnO nanorods play the two major roles of (i) preventing GNPs from agglomerating and (ii) promoting electrical conduction paths between the graphene platelets. The effect of two different ZnO-nanorod morphologies with varying Al-doping concentration on the nanocomposite conductivity and the graphenedispersity are investigated. Time-dependent absorption, photoluminescence and photoconductivity measurements show that growth in high pH solutions promotes a better graphene dispersity, higher doping levels and enhanced bonding between the graphene and the ZnO nanorods. Growth in low pH solutions yields samples characterized by a higher conductivity and a reduced number of surface defects. These samples also exhibit a large persistent photoconductivity attributed to an effective charge separation and transfer from the nanorods to the graphene platelets. Our findings can be used to tailor the conductivity of novel printable composites, or for fabrication of large volumes of inexpensive porous conjugated graphene-semiconductor composites. © 2018 IOP Publishing Ltd.
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| 3. |
- Jemsson, Tomas, et al.
(författare)
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Linearly polarized single photon antibunching from a site-controlled InGaN quantum dot
- 2014
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 105:8, s. 081901-1-081901-4
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Tidskriftsartikel (refereegranskat)abstract
- We report on the observation of linearly polarized single photon antibunching in the excitonic emission from a site-controlled InGaN quantum dot. The measured second order coherence function exhibits a significant dip at zero time difference, corresponding to g(m)(2) (0) = 0: 90 under continuous laser excitation. This relatively high value of g(m)(2) (0) is well understood by a model as the combination of short exciton life time (320 ps), limited experimental timing resolution and the presence of an uncorrelated broadband background emission from the sample. Our result provides the first rigorous evidence of InGaN quantum dot formation on hexagonal GaN pyramids, and it highlights a great potential in these dots as fast polarized single photon emitters if the background emission can be eliminated.
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| 4. |
- Jemsson, Tomas, et al.
(författare)
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Polarized single photon emission and photon bunching from an InGaN quantum dot on a GaN micropyramid
- 2015
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Ingår i: Nanotechnology. - : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 26:6, s. 065702-
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Tidskriftsartikel (refereegranskat)abstract
- We report on excitonic single photon emission and biexcitonic photon bunching from an InGaN quantum dot formed on the apex of a hexagonal GaN micropyramid. An approach to suppress uncorrelated emission from the pyramid base is proposed, a metal lm is demonstrated to eectively screen background emission and thereby signicantly enhance the signal-to-background ratio of the quantum dot emission. As a result, the second order coherence function at zero time delay g(2)(0) is signicantly reduced (to g(2)(0) = 0.24, raw value) for the excitonic autocorrelation at a temperature of 12 K under continuous wave excitation, and a dominating single photon emission is demonstrated to survive up to 50 K. The deterioration of the g(2)(0)-value at elevated temperatures is well understood as the combined eect of reduced signal-to-background ratio and limited time resolution of the setup. This result underlines the great potential of site controlled pyramidal dots as sources of fast polarized single photons.
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| 5. |
- Machhadani, Houssaine, et al.
(författare)
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Improvement of the critical temperature of NbTiN films on III-nitride substrates
- 2019
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Ingår i: Superconductors Science and Technology. - : IOP PUBLISHING LTD. - 0953-2048 .- 1361-6668. ; 32:3
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study the impact of using III-nitride semiconductors (GaN, AlN) as substrates for ultrathin (11 nm) superconducting films of NbTiN deposited by reactive magnetron sputtering. The resulting NbTiN layers are (111)-oriented, fully relaxed, and they keep an epitaxial relation with the substrate. The higher critical superconducting temperature (T-c = 11.8 K) was obtained on AIN-on-sapphire, which was the substrate with smaller lattice mismatch with NbTiN. We attribute this improvement to a reduction of the NbTiN roughness, which appears associated with the relaxation of the lattice misfit with the substrate. On AlN-on-sapphire, superconducting nanowire single photon detectors were fabricated and tested, obtaining external quantum efficiencies that are in excellent agreement with theoretical calculations.
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| 6. |
- Machhadani, Houssaine, et al.
(författare)
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Systematic study of near-infrared intersubband absorption of polar and semipolar GaN/AlN quantum well
- 2013
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:14
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Tidskriftsartikel (refereegranskat)abstract
- We report on the observation of intersubband absorption in GaN/AlN quantum well superlattices grown on (112)-oriented GaN. The absorption is tuned in the 1.5–4.5 μm wavelength range by adjusting the well thickness. The semipolar samples are compared with polar samples with identical well thickness grown during the same run. The intersubband absorption of semipolar samples shows a significant red shift with respect to the polar ones due to the reduction of the internal electric field in the quantum wells. The experimental results are compared with simulations and confirm the reduction of the polarization discontinuity along the growth axis in the semipolar case. The absorption spectral shape depends on the sample growth direction: for polar quantum wells the intersubband spectrum is a sum of Lorentzian resonances, whereas a Gaussian shape is observed in the semipolar case. This dissimilarity is explained by different carrier localization in these two cases.
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| 7. |
- Mukhtarova, Anna, et al.
(författare)
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Polarization-insensitive fiber-coupled superconducting-nanowire single photon detector using a high-index dielectric capping layer
- 2018
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Ingår i: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 26:13, s. 17697-17704
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Tidskriftsartikel (refereegranskat)abstract
- Superconducting-nanowire single photon detectors (SNSPDs) are able to reach near-unity detection efficiency in the infrared spectral range. However, due to the intrinsic asymmetry of nanowires, SNSPDs are usually very sensitive to the polarization of the incident radiation, their responsivity being maximum for light polarized parallel to the nanowire length (transverse-electric (TE) polarization). Here, we report on the reduction of the polarization sensitivity obtained by capping NbN-based SNSPDs with a high-index SiNx dielectric layer, which reduces the permittivity mismatch between the NbN wire and the surrounding area. Experimentally, a polarization sensitivity below 0.1 is obtained both at 1.31 and 1.55 mu m, in excellent agreement with simulations.
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