| 61. |
- Dick Thelander, Kimberly, et al.
(författare)
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Growth of GaP nanotree structures by sequential seeding of 1D nanowires
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 272:1-4, s. 131-137
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Tidskriftsartikel (refereegranskat)abstract
- Complex nanostructures are becoming increasingly important for the development of nanoscale devices and functional nanomaterials. Precise control of size and morphology of these structures is critical to their fabrication and exploitation. We have developed a method for stepwise growth of tree-like nanostructures via the vapour liquid-solid (VLS) growth mode, demonstrated for III-V semiconductor materials. This method uses the initial seeding of nanowires by catalytic aerosol nanoparticles to form the trunk, followed by sequential seeding of branching structures. Here we present a detailed study of the growth of these complex structures using Gap. Diameter of each level of nanowires is directly determined by seed particle diameters, and number of branches is determined by seed particle density. Growth rate is shown to increase with temperature to a maximum corresponding to the temperature of complete decomposition of the Group-III precursor material, and subsequently decrease due to competition with bulk growth. Growth rate also depends on flow of the Group-III precursor, but not on the Group-V precursor. Finally, there is a relationship between the number of branches and their growth rate, suggesting that material diffusion plays a role in nanowire branch growth. (C) 2004 Elsevier B.V. All rights reserved.
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| 62. |
- Dick Thelander, Kimberly, et al.
(författare)
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Self-assembled InAs nanowire networks
- 2005
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Ingår i: Book of extended abstracts: MRS Fall Meet, Boston, Ma, USA, 2005.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 63. |
- Dick Thelander, Kimberly, et al.
(författare)
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Synthesis of branched 'nanotrees' by controlled seeding of multiple branching events
- 2004
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Ingår i: Nature Materials. - : Springer Science and Business Media LLC. - 1476-4660 .- 1476-1122. ; 3:6, s. 380-384
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Tidskriftsartikel (refereegranskat)abstract
- The formation of nanostructures with controlled size and morphology has been the focus of intensive research in recent years(1-10). Such nanostructures are important in the development of nanoscale devices and in the exploitation of the properties of nanomaterials(9). Here we show how tree-like nanostructures ('nanotrees') can be formed in a highly controlled way. The process involves the self-assembled growth of semiconductor nanowires via the vapour-liquid-solid(11) growth mode. This bottom-up method uses initial seeding by catalytic nanoparticles(12) to form the trunk, followed by the sequential seeding of branching structures. Each level of branching is controlled in terms of branch length, diameter and number, as well as chemical composition. We show, by high-resolution transmission electron microscopy, that the branching mechanism gives continuous crystalline (monolithic) structures throughout the extended and complex tree-like structures. The controlled seeding method that we report here has potential as a generic means of forming complex branching structures, and may also offer opportunities for applications, such as the mimicking of photosynthesis in nanotrees.
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| 64. |
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| 65. |
- Dimitrova Mårtensson, Linda-Maria, et al.
(författare)
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Water use efficiency and shoot biomass production under water limitation is negatively correlated to the discrimination against 13C in the C3 grasses Dactylis glomerata, Festuca arundinacea and Phalaris arundinacea
- 2017
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Ingår i: Plant Physiology and Biochemistry. - : Elsevier BV. - 0981-9428 .- 1873-2690. ; 113, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- Climate change impacts rainfall patterns which may lead to drought stress in rain-fed agricultural systems. Crops with higher drought tolerance are required on marginal land with low precipitation or on soils with low water retention used for biomass production. It is essential to obtain plant breeding tools, which can identify genotypes with improved drought tolerance and water use efficiency (WOE). In C-3 plant species, the variation in discrimination against C-13(Delta,13C) during photosynthesis has been shown to be a potential indicator for WOE, where discrimination against C-13 and WUE were negatively correlated. The aim of this study was to determine the variation in the discrimination against C-13 between species and cultivars of three perennial C-3 grasses (Dactylis glomerate (cocksfoot), Festuca arundinacea (tall fescue) and Phalaris arundinacea (reed canary grass)) and test the relationships between discrimination against C-13, season-long water use WUEB, shoot and root biomass production in plants grown under well-watered and water-limited conditions. The grasses were grown in the greenhouse and exposed to two irrigation regimes, which corresponded to 25% and 60% water holding capacity, respectively. We found negative relationships between discrimination against C-13 and WUEB and between discrimination against C-13 and shoot biomass production, under both the well-watered and water-limited growth conditions (p < 0.001). Discrimination against C-13 decreased in response to water limitation (p < 0.001). We found interspecific differences in the discrimination against C-13, WUEB, and shoot biomass production, where the cocksfoot cultivars showed lowest and the reed canary grass cultivars highest values of discrimination against C-13. Cocksfoot cultivars also showed highest WUEB, shoot biomass production and potential tolerance to water limitation. We conclude that discrimination against C-13 appears to be a useful indicator, when selecting C-3 grass crops for biomass production under drought conditions. (C) 2017 Elsevier Masson SAS. All rights reserved.
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| 66. |
- Eckersten, Henrik, et al.
(författare)
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Nitrogen leaching and soil organic carbon sequestration of a Barley crop with improved N use efficiency : A regional case study
- 2017
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Ingår i: Acta Agriculturae Scandinavica - Section B. - : Taylor and Francis Ltd.. - 0906-4710 .- 1651-1913. ; 67:7, s. 615-627
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Tidskriftsartikel (refereegranskat)abstract
- The potential of modified spring barley crops with improved nitrogen (N) use efficiency to reduce nitrogen (N) leaching and to increase soil organic carbon (SOC) storage was assessed at the regional scale. This was done using simulation model applications designed for reporting according to the Helcom (Helsinki Commission) and Kyoto protocols. Using model simulations based on modified crops N dynamics and SOC were assessed for three agro-ecological regions (latitudes ranging 55°20′–60°40′ N) in Sweden over a 20-year period. The modified N use properties of spring barley were implemented in the SOILNDB model (simulating soil C, N, water and heat, and plant N dynamics) by changing the parameters for root N uptake efficiency and plant N demand within a range given by previous model applications to different crops. A doubling of the daily N uptake efficiency and increased N demand (by ca 30%) reduced N leaching by 24%–31%, increased plant N content by 9%–12%, depending on region. The effects of the modified crop on SOC was simulated with the ICBM model, resulting in an increased SOC content (0–25 cm depth) by 57–79 kg C ha−1 y−1. The results suggest that a modified crop might reduce N leaching from spring barley area, in a range similar to the targets of relevant environmental protection directives, a result which held more in the northern than southern regions. The simulated SOC increase on a hectare basis was highest for the central region and least for the most northern region. For the total agricultural area the share of spring barley area was small and more crops would need to be modified to reach the emission reduction targets.
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| 67. |
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| 68. |
- Eng, Mattias P, 1977, et al.
(författare)
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Triplet excitation energy transfer in porphyrin-based donor-bridge-acceptor systems with conjugated bridges of varying length: An experimental and DFT study
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110:13, s. 6483-6491
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Tidskriftsartikel (refereegranskat)abstract
- A series of donor-bridge-acceptor (D-B-A) systems with varying donor-acceptor distances have been studied with respect to their triplet energy transfer properties. The donor and acceptor moieties, zinc(II), and free-base porphyrin, respectively, were separated by 2-5 oligo-p-phenyleneethynylene units (OPE) giving rise to edge-to-edge separations ranging between 12.7 and 33.4 angstrom. The study was performed in 2-MTHF at 150 K and it was established that triplet excitation energy transfer occurs with high efficiency in all of the studied D-B-A systems. The distance dependence was exponential with an attenuation factor, beta, equal to 0.45 +/- 0.015 angstrom(-1). The experimental study was also supported by quantum mechanical DFT and TD-DFT calculations on a series of closely related model systems. A thorough analysis of the OPE-bridge conformational dynamics led to an equation that quantitatively models the distance dependence of the electronic coupling found in the experimental study.
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| 69. |
- Eng, Mattias P, 1977, et al.
(författare)
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Triplet photophysics of gold(III) porphyrins
- 2005
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:9, s. 1776-1784
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Tidskriftsartikel (refereegranskat)abstract
- Gold porphyrins are often used as electron-accepting chromophores in donor-acceptor complexes for the study of photoinduced electron transfer, and they can also be involved in triplet-triplet energy-transfer interactions with other chromophores. Since the lowest excited singlet state is very short-lived (240 fs), the triplet state is usually the starting point for the transfer reactions, and it is therefore crucial to understand its photophysics. The triplet state of various gold porphyrins has been reported to have a lifetime of around 1.5 ns at room temperature and to have a biexponential decay both in emission and in transient absorption with decay times of around 10 and 100,us at 80 K. In this paper, the triplet photophysics of two gold porphyrins (Au-III 5,15-bis(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-tetrame thylporphyrin and Au-III 5,10,15,20-tetra(3,5-di-tert-butylphenyl)porphyrin) are studied by steady-state and time-resolved absorption and emission spectroscopy over a wide temperature range (4-300 K). The study reveals the existence of a dark state with an approximate lifetime of 50 ns, which was not previously observed. This state acts as an intermediate between the short-lived singlet and the triplet state manifold. In addition, we present DFT calculations, in which the core electrons of the central metal were replaced by a pseudopotential to account for the relativistic effects, which suggest that the lowest excited singlet state is an optically forbidden ligand-to-metal charge-transfer (LMCT) state. This LMCT state is an obvious candidate for the experimentally observed dark state, and it is shown to dictate the photophysical properties of gold porphyrins by acting as a gate for triplet state formation versus direct return to the ground state.
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| 70. |
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