| 1. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Jaramillo-Fernandez, Juliana, et al.
(författare)
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Thermal conductivity of epitaxially grown InP : experiment and simulation
- 2017
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Ingår i: CrystEngComm. - : ROYAL SOC CHEMISTRY. - 1466-8033. ; 19:14, s. 1879-1887
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Tidskriftsartikel (refereegranskat)abstract
- The integration of III-V optoelectronic devices on silicon is confronted with the challenge of heat dissipation for reliable and stable operation. A thorough understanding and characterization of thermal transport is paramount for improved designs of, for example, viable III-V light sources on silicon. In this work, the thermal conductivity of heteroepitaxial laterally overgrown InP layers on silicon is experimentally investigated using microRaman thermometry. By examining InP mesa-like structures grown from trenches defined by a SiO2 mask, we found that the thermal conductivity decreases by about one third, compared to the bulk thermal conductivity of InP, with decreasing width from 400 to 250 nm. The high thermal conductivity of InP grown from 400 nm trenches was attributed to the lower defect density as the InP micro crystal becomes thicker. In this case, the thermal transport is dominated by phonon-phonon interactions as in a low defect-density monocrystalline bulk material, whereas for thinner InP layers grown from narrower trenches, the heat transfer is dominated by phonon scattering at the extended defects and InP/SiO2 interface. In addition to the nominally undoped sample, sulfur-doped (1 x 10(18) cm(-3)) InP grown on Si was also studied. For the narrower doped InP microcrystals, the thermal conductivity decreased by a factor of two compared to the bulk value. Sources of errors in the thermal conductivity measurements are discussed. The experimental temperature rise was successfully simulated by the heat diffusion equation using the FEM.
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| 3. |
- Jaramillo-Fernandez, Juliana, et al.
(författare)
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Thermal conductivity of polycrystalline aluminum nitride films : Effects of the microstructure, interfacial thermal resistance and local oxidation
- 2015
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Ingår i: THERMINIC 2015 - 21st International Workshop on Thermal Investigations of ICs and Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467397056
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Konferensbidrag (refereegranskat)abstract
- The thermal conductivity of polycrystalline aluminum nitride (AlN) films with inhomogeneous structures is experimentally and theoretically investigated. The influence of the grain morphology and size evolution along the cross plane direction of the films is studied by thickness-dependent 3m measurements on AlN monolayers. For AlN/AlN multilayer samples, the impact of oxygen-related defects localized at the interface between two AlN layers, is also analyzed. When the total thickness of these multilayers is downsized from 1107 nm to 270 nm, their measured effective thermal conductivity reduces by 47%, which is smaller than the corresponding reduction of 58% for monolayers. In multilayers, this decrease is due to the additive contributions of the thermal resistances arising from the AlN and AlN/AlN interfaces. The experimental data are interpreted through an analytical model developed for nanocrystalline films with inhomogeneous structures. It is shown that the size effects on the phonon mean free paths and the intrinsic thermal resistance resulting from the inhomogeneous microstructure predominate as the film thickness increases, whilst the contribution of the interface thermal resistance strengthens when the thickness is scaled down.
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| 4. |
- Jaramillo-Fernandez, Juliana, et al.
(författare)
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Tuning of heat transport across thin films of polycrystalline AlN via multiscale structural defects
- 2015
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Ingår i: ECS Transactions. - : Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; , s. 53-64
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Konferensbidrag (refereegranskat)abstract
- The effective thermal conductivity of nanocrystalline films of AlN with inhomogeneous microstructure is investigated experimentally and theoretically. This is done by measuring the thermal conductivity of the samples with the 3-omega method and characterizing their microstructure by means of electron microscopy. The relative effect of the microstructure and the interface thermal resistance on the thermal conductivity is quantified through an analytical model. Thermal measurements showed that when the thickness of an AlN film is reduced from 1460 to 270 nm, its effective thermal conductivity decreases from 8.21 to 3.12 WYm-1?K-1, which is two orders of magnitude smaller than its bulk counterpart value. It is shown that both the size effects of the phonon mean free paths and the intrinsic thermal resistance resulting from the inhomogeneous microstructure predominate for thicker films, while the contribution of the interface thermal resistance strengthens as the film thickness is scaled down. The obtained results demonstrate that the structural inhomogeneity in polycrystalline AlN films can be efficiently used to tune their cross- plane thermal conductivity. In addition, thermal conductivity measurements of epitaxially grown InP layers on silicon using Raman spectroscopy are reported.
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| 5. |
- Sotomayor-Torres, Clivia M., 1955-, et al.
(författare)
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Raman thermometry analysis: Modelling assumptions revisited
- 2017
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Ingår i: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 130, s. 1175-1181
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Tidskriftsartikel (refereegranskat)abstract
- In Raman thermometry, several assumptions are made to model the heat conduction and to extract the thermal conductivity of the samples from the measured data. In this work, the heat conduction in bulk and mesa-like samples was investigated by numerical simulation and measured by the temperature-induced Raman shift method, to study the range of applicability of these assumptions. The effects of light penetration depth and finite sample size on the accuracy of the thermal conductivity determination were investigated by comparing the results of the finite element method with the usual analytical approximation for bulk samples. We found that the assumptions used in the analytical model can be applied to extract the thermal conductivity in solids if the following conditions are fulfilled: the ratio of light penetration depth to laser spot radius is smaller than 0.5, the ratio of spot radius to sample thickness is smaller than 0.1, and the ratio of spot radius to sample half width is smaller than 0.01.
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| 6. |
- Visser, Dennis, et al.
(författare)
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Ion bombardment induced formation of self-organized wafer-scale GaInP nanopillar assemblies
- 2020
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Ingår i: Journal of Vacuum Science and Technology B. - : AVS Science and Technology Society. - 2166-2746 .- 2166-2754. ; 38:1
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Tidskriftsartikel (refereegranskat)abstract
- Ion sputtering assisted formation of nanopillars is demonstrated as a wafer-scale, lithography-free fabrication method to obtain high optical quality gallium indium phosphide (GaInP) nanopillars. Compared to binary materials, little has been reported on the formation of self-organized ternary nanostructures. Epitaxial (100) Ga0.51In0.49P layers lattice matched to GaAs were sputtered by nitrogen (N2) ions with relatively low ion beam energies (∼400 eV) to reduce ion bombardment induced damage. The influence of process parameters such as temperature, sputter duration, ion beam energy, and ion beam incidence angle on the pillar formation is investigated. The fabricated GaInP nanopillars have average diameters of ∼75-100 nm, height of ∼220 nm, and average density of ∼2-4 × 108 pillars/cm2. The authors show that the ion beam incidence angle plays an important role in pillar formation and can be used to tune the pillar shape, diameter, and spatial density. Specifically, tapered to near cylindrical pillar profiles together with a reduction in their average diameters are obtained by varying the ion beam incidence angle from 0° to 20°. A tentative model for the GaInP nanopillar formation is proposed based on transmission electron microscopy and chemical mapping analysis. μ-Photoluminescence and μ-Raman measurements indicate a high optical quality of the c-GaInP nanopillars.
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