| 1. |
- Moberg, Christina, et al.
(författare)
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De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 2. |
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| 3. |
- Faggiani, Rémi, et al.
(författare)
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Modal Analysis of the Ultrafast Dynamics of Optical Nanoresonators
- 2017
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 4:4, s. 897-904
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Tidskriftsartikel (refereegranskat)abstract
- We propose a semianalytical formalism based on a time-domain resonant-mode-expansion theory to analyze the ultrafast temporal dynamics of optical nanoresonators. We compare the theoretical predictions with numerical data obtained with the FDTD method, which is commonly used to analyze experiments in the field. The comparison reveals that the present formalism (i) provides deeper physical insight onto the temporal response and (ii) is much more computationally efficient. Since its numerical implementation is easy, the formalism, albeit approximate, can be advantageously used to both analyze and design ultrafast nano-optics experiments.
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| 4. |
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| 5. |
- Hjort, Martin, et al.
(författare)
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Electron microscopy imaging of proteins on gallium phosphide semiconductor nanowires
- 2016
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 8:7, s. 3936-3943
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Tidskriftsartikel (refereegranskat)abstract
- We have imaged GaP nanowires (NWs) incubated with human laminin, serum albumin (HSA), and blood plasma using both cryo-transmission electron microscopy and synchrotron based X-ray photoemission electron microscopy. This extensive imaging methodology simultaneously reveals structural, chemical and morphological details of individual nanowires and the adsorbed proteins. We found that the proteins bind to NWs, forming coronas with thicknesses close to the proteins' hydrodynamic diameters. We could directly image how laminin is extending from the NWs, maximizing the number of proteins bound to the NWs. NWs incubated with both laminin and HSA show protein coronas with a similar appearance to NWs incubated with laminin alone, indicating that the presence of HSA does not affect the laminin conformation on the NWs. In blood plasma, an intermediate sized corona around the NWs indicates a corona with a mixture of plasma proteins. The ability to directly visualize proteins on nanostructures in situ holds great promise for assessing the conformation and thickness of the protein corona, which is key to understanding and predicting the properties of engineered nanomaterials in a biological environment.
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| 6. |
- Kennedy, S. M., et al.
(författare)
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Characterizing the geometry of InAs nanowires using mirror electron microscopy
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:12
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Tidskriftsartikel (refereegranskat)abstract
- Mirror electron microscopy (MEM) imaging of InAs nanowires is a non-destructive electron microscopy technique where the electrons are reflected via an applied electric field before they reach the specimen surface. However strong caustic features are observed that can be non-intuitive and difficult to relate to nanowire geometry and composition. Utilizing caustic imaging theory we can understand and interpret MEM image contrast, relating caustic image features to the properties and parameters of the nanowire. This is applied to obtain quantitative information, including the nanowire width via a through-focus series of MEM images.
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| 7. |
- Lorek, Eleonora, et al.
(författare)
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Size and shape dependent few-cycle near-field dynamics of bowtie nanoantennas
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:24, s. 31460-31471
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Tidskriftsartikel (refereegranskat)abstract
- Metal nanostructures can transfer electromagnetic energy from femtosecond laser pulses to the near-field down to spatial scales well below the optical diffraction limit. By combining few-femtosecond laser pulses with photoemission electron microscopy, we study the dynamics of the induced few-cycle near-field in individual bowtie nanoantennas. We investigate how the dynamics depend on antenna size and exact bowtie shape resulting from fabrication. Different dynamics are, as expected, measured for antennas of different sizes. However, we also detect comparable dynamics differences between individual antennas of similar size. With Finite-difference time-domain simulations we show that these dynamics differences between similarly sized antennas can be due to small lateral shape variations generally induced during the fabrication.
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| 8. |
- Lönngren, Johanna, 1985-, et al.
(författare)
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Breaking Catch22 of Engineering Education for Sustainable Development : An Example of Parallell Learning of Teachers and Students
- 2012
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Konferensbidrag (refereegranskat)abstract
- Both research and practical experience show that teachers have trouble implementing Education for Sustainable Development (ESD) (Bursjöö 2011), especially in engineering education where a culture of value-neutrality and objectivity still seems to prevail (see for example Holmberg et al 2008). Consequently, the integration of ESD into engineerig curricula is often insufficient in respect to requirements set up by the Swedish Higher Education Act: graduates of engineering are expected to possess complex skills connected to ethics and sustainable development (Högskoleförordningen 1993).The purpose of this presentation is to provide a positive example of how these problems have been overcome in a specific engineering program at Lund University. We discuss the introduction of an innovative course by a group of students and faculty without substantive prior expertise or experience in Engineering Education for Sustainable Delopment (EESD). We (some of the course developers/course leaders) use collaborative action research methodology to discuss similarities and differences in teachers’ (ours) and students’ learning in the process of creating and subsequently improving this specific EESD-intervention. Our analysis is based on personal reflections and focus group discussions by the course developers/course leaders, as well as students’ course evaluations from three consecutive years, and EESD litterature.As an analytical lens, we use the concept of Communities of Practice(CoP). We identify two levels of CoPs: 1. The team of teachers (senior teachers in collaboration with highly motivated students) working with the course over the years, and 2. All actors involved in each years’ course cycle. This includes both a group of teachers and the enroled students. In relation to these CoPs, we also identify two (partly overlapping) cycles of action learningwhich relate, respectively, to the course development over the years, and our work with each specific course cycle. The purpose of this analysis and discussion is to uncover parallell learning of teachers and students as the course evolves.Another purpose is to facilitate the implementation of EESD. Therefore, we also reflect on the perceived prerequisite of teachers’ expertise for teaching sustainable development in engineering curricula. We discuss the specific conditions that allowed the creation and execution of our course with the aim to empower other teachers to venture on the undertaking of EESD in their courses by trusting the development of their own skills “by doing EESD”. Thus we hope to contribute to an icnreased integration of ESD into engineering programs in Sweden and abroad.
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| 9. |
- Mikkelä, Mikko-Heikki, et al.
(författare)
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Bismuth-oxide nanoparticles: study in a beam and as deposited
- 2024
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Ingår i: Physical chemistry chemical physics : PCCP. - 1463-9084. ; 26:13, s. 10369-10381
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Tidskriftsartikel (refereegranskat)abstract
- Bi2O3 is a promising material for solid-oxide fuel cells (SOFC) due to the high ionic conductivity of some phases. The largest value is reached for its δ-phase, but it is normally stable at temperatures too high for SOFC operation, while nanostructured oxide is believed to have more suitable stabilization temperature. However, to manufacture such a material with a controlled chemical composition is a challenging task. In this work, we investigated the fabrication of nanostructured Bi2O3 films formed by deposition of free Bi-oxide nanoparticles created in situ. The particle-production method was based on reactive sputtering and vapour aggregation. Depending on the fabrication conditions, the nanoparticles contained either a combination of Bi–metal and Bi-oxide, or only Bi-oxide. Prior to deposition, the free particles were probed in the beam – by synchrotron-based photoelectron spectroscopy (PES), which allowed assessing their composition “on the-fly”. The nanoparticle films obtained after deposition were studied by PES, scanning electron microscopy, transmission electron microscopy, and electron diffraction. The films' chemical composition, grain dimensions, and crystal structure were probed. Our analysis suggests that our method produced Bi-oxide films in more than one polymorph of Bi2O3.
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| 10. |
- Mårsell, Erik, et al.
(författare)
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Direct subwavelength imaging and control of near-field localization in individual silver nanocubes
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:20
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the control of near-field localization within individual silver nanocubes through photoemission electron microscopy combined with broadband, few-cycle laser pulses. We find that the near-field is concentrated at the corners of the cubes, and that it can be efficiently localized to different individual corners depending on the polarization of the incoming light. The experimental results are confirmed by finite-difference time-domain simulations, which also provide an intuitive picture of polarization dependent near-field localization in nanocubes. (C) 2015 AIP Publishing LLC.
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| 11. |
- Mårsell, Erik, et al.
(författare)
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Nanoscale imaging of local few-femtosecond near-field dynamics within a single plasmonic nanoantenna.
- 2015
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:10, s. 6601-6608
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Tidskriftsartikel (refereegranskat)abstract
- The local enhancement of few-cycle laser pulses by plasmonic nanostructures opens up for spatiotemporal control of optical interactions on a nanometer and few-femtosecond scale. However, spatially resolved characterization of few-cycle plasmon dynamics poses a major challenge due to the extreme length and time scales involved. In this letter, we experimentally demonstrate local variations in the dynamics during the few strongest cycles of plasmon-enhanced fields within individual rice-shaped silver nanoparticles. This was done using 5.5 fs laser pulses in an interferometric time-resolved photoemission electron microscopy setup. The experiments are supported by finite-difference time-domain simulations of similar silver structures. The observed differences in the field dynamics across a single particle do not reflect differences in plasmon resonance frequency or dephasing time. They instead arise from a combination of retardation effects and the coherent superposition between multiple plasmon modes of the particle, inherent to a few-cycle pulse excitation. The ability to detect and predict local variations in the few-femtosecond time evolution of multi-mode coherent plasmon excitations in rationally synthesized nanoparticles can be used in the tailoring of nanostructures for ultrafast and nonlinear plasmonics.
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| 12. |
- Mårsell, Erik
(författare)
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Photoemission Electron Microscopy for Ultrafast Nano-Optics - Femtoseconds to Attoseconds
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ultrafast nano-optics is a new and quickly evolving research field centred around the control, manipulation, and application of light on a nanometre and femtosecond scale. This can lead to improved electro-optical devices, more sensitive spectroscopy, and real-time control of chemical reactions. However, understanding the simultaneous nanometre and femtosecond evolution of nano-optical fields requires characterization methods with ultrahigh spatiotemporal resolution. A method that during the past 15 years has shown great promise for such studies is photoemission electron microscopy (PEEM) in combination with ultrashort laser pulses. Both PEEM, nanostructure fabrication methods, and a large variety of pulsed light sources are under rapid parallel development, leading also to quickly increasing possibilities of nanometre and femtosecond characterization. This thesis explores the combination of PEEM with various state-of-the-art lab-based sources of femtosecond and attosecond pulses with wavelengths spanning from 30 nm to 1.55 µm for studies of ultrafast nano-optics. It is based on experiments carried out with five different laser systems, studying light interaction with tailored metallic and semiconducting nanostructures. The work comprises construction of new experimental setups, PEEM measurements, development of data analysis tools, and complementary investigations using techniques such as scanning electron microscopy, X-ray photoelectron spectroscopy, and scanning tunnelling microscopy. Using few-cycle pulses from an ultra-broadband Ti:sapphire oscillator, localized surface plasmons in metallic nanostructures were studied with a temporal resolution down to a few femtoseconds. Metallic structures were also studied with PEEM using femtosecond pulses in the telecommunication wavelength regime. Other light sources employed include an optical parametric chirped pulse amplification system, with which anisotropy effects in semiconductor nanowires were studied. Finally, the thesis explores the use of extreme ultraviolet attosecond pulse trains produced by high-order harmonic generation (HHG) as light source for PEEM. Working with 1 kHz repetition rate, the spatial resolution was found to be limited by space charge effects to a few hundred nanometres. However, with a new HHG system working at 200 kHz repetition rate, the resolution was improved by a factor of 2—3, along with a reduction in acquisition time by an order of magnitude. Novel high-repetition rate attosecond light sources are therefore expected to play a key role in pushing the temporal resolution of PEEM into the attosecond regime.
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| 13. |
- Mårsell, Erik, et al.
(författare)
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Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths
- 2015
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 117:8
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Tidskriftsartikel (refereegranskat)abstract
- We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 mu m. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate. (C) 2015 AIP Publishing LLC.
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| 14. |
- Mårsell, Erik, et al.
(författare)
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Secondary electron imaging of nanostructures using Extreme Ultra-Violet attosecond pulse trains and Infra-Red femtosecond pulses
- 2013
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804. ; 525:1-2, s. 162-170
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Tidskriftsartikel (refereegranskat)abstract
- Surface electron dynamics unfold at time and length scales down to attoseconds and nanometres, making direct imaging with extreme spatiotemporal resolution highly desirable. However, this has turned out to be a major challenge even with the advent of reliable attosecond light sources. In this paper, photoelectrons from Ag nanowires and nanoparticles excited by extreme ultraviolet (XUV) attosecond pulse trains and infrared femtosecond pulses using a PhotoEmission Electron Microscope (PEEM) are imaged. In addition, the samples were investigated using Scanning Electron Microscopy (SEM) and synchrotron based X-ray photoelectron spectroscopy (XPS). To achieve contrast between the nanostructures and the substrate in the XUV images, three different substrate materials were investigated: Cr, ITO and Au. While plasmonic field enhancement can be observed on all three substrates, only on Au substrates do the Ag nanowires appear significantly brighter than the substrate in XUV-PEEM imaging. 3-photon photoemission imaging of plasmonic hot-spots was performed where the autocorrelation trace is observed in the interference signal between two femtosecond Infra-Red (IR) beams with sub-cycle precision. Finally, using Monte Carlo simulations, it is shown how the secondary electrons imaged in the XUV PEEM can potentially reveal information on the attosecond time scale from the near surface region of the nanostructures.
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| 15. |
- Mårsell, Erik, et al.
(författare)
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Spatial Control of Multiphoton Electron Excitations in InAs Nanowires by Varying Crystal Phase and Light Polarization
- 2018
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:2, s. 907-915
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the control of multiphoton electron excitations in InAs nanowires (NWs) by altering the crystal structure and the light polarization. Using few-cycle, near-infrared laser pulses from an optical parametric chirped-pulse amplification system, we induce multiphoton electron excitations in InAs nanowires with controlled wurtzite (WZ) and zincblende (ZB) segments. With a photoemission electron microscope, we show that we can selectively induce multiphoton electron emission from WZ or ZB segments of the same wire by varying the light polarization. Developing ab initio GW calculations of first to third order multiphoton excitations and using finite-difference time-domain simulations, we explain the experimental findings: While the electric-field enhancement due to the semiconductor/vacuum interface has a similar effect for all NW segments, the second and third order multiphoton transitions in the band structure of WZ InAs are highly anisotropic in contrast to ZB InAs. As the crystal phase of NWs can be precisely and reliably tailored, our findings open up for new semiconductor optoelectronics with controllable nanoscale emission of electrons through vacuum or dielectric barriers.
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| 16. |
- Nigge, P., et al.
(författare)
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Room temperature strain-induced Landau levels in graphene on a wafer-scale platform
- 2019
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 5:11
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Tidskriftsartikel (refereegranskat)abstract
- Graphene is a powerful playground for studying a plethora of quantum phenomena. One of the remarkable properties of graphene arises when it is strained in particular geometries and the electrons behave as if they were under the influence of a magnetic field. Previously, these strain-induced pseudomagnetic fields have been explored on the nano- and micrometer-scale using scanning probe and transport measurements. Heteroepitaxial strain, in contrast, is a wafer-scale engineering method. Here, we show that pseudomagnetic fields can be generated in graphene through wafer-scale epitaxial growth. Shallow triangular nanoprisms in the SiC substrate generate strain-induced uniform fields of 41 T, enabling the observation of strain-induced Landau levels at room temperature, as detected by angle-resolved photoemission spectroscopy, and confirmed by model calculations and scanning tunneling microscopy measurements. Our work demonstrates the feasibility of exploiting strain-induced quantum phases in two-dimensional Dirac materials on a wafer-scale platform, opening the field to new applications.
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| 17. |
- Wright, Charles, et al.
(författare)
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Tin Oxides : Insights into Chemical States from a Nanoparticle Study
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:35, s. 19414-19419
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Tidskriftsartikel (refereegranskat)abstract
- Tin oxides are semiconductor materials currently attracting close attention in electronics, photovoltaics, gas sensing, and catalysis. Depending on the tin oxidation state-Sn(IV), Sn(II), or intermediate-the corresponding oxide has either n- or p-type natural conductivity, ascribed to oxygen or metal deficiency in the lattice. Such crystalline imperfections severely complicate the task of establishing tin oxidation state, especially at nanoscale. In spite of the striking differences between SnO2 and SnO in their most fundamental properties, there have been enduring problems in identifying the oxide type. These problems were to a great extent caused by the controversy around the characteristic chemical shift, that is, the difference in electron binding energy of a certain core level in an oxide and its parent metal. Using in situ fabricated bare tin oxide nanoparticles, we have been able to resolve the controversy: Our photoelectron spectroscopic study on tin oxide nanoparticles shows that, in contrast to a common opinion of a close chemical shift for SnO2 and SnO, the shift value for tin(IV) oxide is, in fact, 3 times larger than that for tin(II) oxide. Moreover, our investigation of the nanoparticle valence electronic structure clarifies the question of why previously the identification of oxidation states encountered problems.
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| 18. |
- Zakharov, Alexei, et al.
(författare)
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Manipulating the Dynamics of Self-Propelled Gallium Droplets by Gold Nanoparticles and Nanoscale Surface Morphology
- 2015
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 9:5, s. 5422-5431
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Tidskriftsartikel (refereegranskat)abstract
- Using in situ surface-sensitive electron microscopy performed in real time, we show that the dynamics of micron-sized Ga droplets on Ga P(111) can be manipulated locally using Au nanoparticles. Detailed measurements of structure and dynamics of the surface from microns to atomic scale are done using both surface electron and scanning probe microscopies. Imaging is done simultaneously on areas with and without Au particles and on samples spanning an order of magnitude in particle coverages. Based on this, we establish the equations of motion that can generally describe the Ga droplet dynamics, taking into account three general features: the affinity of Ga droplets to cover steps and rough structures on the surface, the evaporation-driven transition of the surface nanoscale morphology from rough to flat, and the enhanced evaporation due to Ga droplets and Au nanoparticles. Separately, these features can induce either self-propelled random motion or directional motion, but in combination, the self-propelled motion acts to increase the directional motion even if the directional force is 100 times weaker than the random force. We then find that the Au particles initiate a faster native oxide desorption and speed up the rough to flat surface transition in their vicinity. This changes the balance of forces on the Ga droplets near the Au particles, effectively deflecting the droplets from these areas. The model is experimentally verified for the present materials system, but due to its very general assumptions, it could also be relevant for the many other materials systems that display self-propelled random motion.
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| 19. |
- Zhang, Chaofan, et al.
(författare)
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Alloying and oxidation of in situ produced core-shell Al@Yb nanoalloy particles-An "on-the-fly" study.
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:8
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Tidskriftsartikel (refereegranskat)abstract
- Core-shell-structured nanoalloy particles with an Al-dominated interior covered by few Yb monolayers have been fabricated using a vapor-aggregation method involving magnetron sputtering. The radially segregated structure of the Yb-Al nanoparticles has been disclosed by "on-the-fly" photoelectron spectroscopy monitoring of the nanoparticle beam in Yb 4f and Al 2p electron binding energy regions. Both, the binding energy values and the electron microscopy images taken on the deposited nanoparticles, allow estimating their dimensions to be in the 5-10 nm range. The photoelectron spectroscopy results suggest that in these nanoparticles no trivalent Yb - the typical case for the macroscopic Yb-Al alloy - is present. The oxidation of preformed Yb-Al nanoparticles was successfully attempted, leading to the appearance of divalent Yb surface oxide - in contrast to the bulk macroscopic Yb which is trivalent in the oxide. Our results suggest that at intermediate oxygen exposures "sandwich-like" nanoparticles of YbO/Yb/Al were synthesized. At higher O2 exposures, the oxygen seems to penetrate all the way to the Yb-Al interface. The results of the present study have to be considered when photonic applications of Yb-doped garnet nanoparticles are planned.
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