| 1. |
- Palma, Carlos-Andres, et al.
(författare)
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Photo-induced C-C reactions on insulators towards photolithography of graphene nanoarchitectures
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136, s. 4651-4658
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Tidskriftsartikel (refereegranskat)abstract
- On-surface chemistry for atomically precise sp2 macromolecules requires top-down lithographic methods on insulating surfaces in order to pattern the long-range complex architectures needed by the semiconductor industry. Here, we fabricate sp2-carbon nm-thin films on insulators and under ultra-high vacuum (UHV) conditions from photo-coupled brominated precursors. We reveal that covalent coupling is initiated by C-Br bond cleavage through photon energies exceeding 4.4 eV, as monitored by laser desorption ionization (LDI) mass spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) gives insight into the mechanisms of C-Br scission and C-C coupling processes. Further, unreacted material can be sublimed and the coupled sp2-carbon precursors can be graphitized by e-beam treatment at 500°C, demonstrating promising applications in photolithography of graphene nanoarchitectures. Our results present UV-induced reactions on insulators for the formation of all sp2-carbon architectures, thereby converging top-down lithography and bottom-up on-surface chemistry into technology.
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| 2. |
- Barth, Joachim, et al.
(författare)
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Investigation of the thermoelectric properties of LiAlSi and LiAlGe
- 2010
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 1543-186X .- 0361-5235. ; 39:9, s. 1856-1860
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Tidskriftsartikel (refereegranskat)abstract
- The compounds LiAlSi and LiAlGe were synthesized and their thermoelectric properties and temperature stability were investigated. The samples were synthesized by arc melting of the constituent elements. For the determination of the structure type and the lattice parameter, x-ray powder diffraction was used. Both compounds were of the C1 b structure type. The stability of the compounds was investigated by differential thermal analysis and thermal gravimetry. The Seebeck coefficient and the electrical resistivity were determined in the temperature range from 2 K to 650 K. All compounds showed p-type behavior. The thermal conductivity was measured from 2 K to 400 K. The evaluation of the thermal conductivity yielded values as low as 2.4 W m -1 K -1 at 400 K for LiAlGe. The low values are ascribed to high mass fluctuation scattering and a possible rattling effect of the Li atoms.
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| 3. |
- Ohrwall, G, et al.
(författare)
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Femtosecond interatomic Coulombic decay in free neon clusters: Large lifetime differences between surface and bulk
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93:17
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Tidskriftsartikel (refereegranskat)abstract
- A quantitative determination of 2s vacancy lifetimes in surface and bulk atoms of free Ne clusters has been made. While for free atoms the 2s inner-valence hole has a ps lifetime, it reduces to 6+/-1 fs for cluster bulk atoms. For surface atoms, the lifetime is on average longer than 30 fs. The lifetime estimate was obtained from fits of high-resolution photoelectron spectra of Ne clusters. The shortening of the lifetime is attributed to the coordination dependent interatomic Coulombic decay, which is extremely sensitive to internuclear distances.
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| 4. |
- Snezhkova, Olesia, et al.
(författare)
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Iron phthalocyanine on Cu(111): Coverage-dependent assembly and symmetry breaking, temperature-induced homocoupling, and modification of the adsorbate-surface interaction by annealing.
- 2016
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 144:9
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Tidskriftsartikel (refereegranskat)abstract
- We have examined the geometric and electronic structures of iron phthalocyanine assemblies on a Cu(111) surface at different sub- to mono-layer coverages and the changes induced by thermal annealing at temperatures between 250 and 320 °C by scanning tunneling microscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. The symmetry breaking observed in scanning tunneling microscopy images is found to be coverage dependent and to persist upon annealing. Further, we find that annealing to temperatures between 300 and 320 °C leads to both desorption of iron phthalocyanine molecules from the surface and their agglomeration. We see clear evidence of temperature-induced homocoupling reactions of the iron phthalocyanine molecules following dehydrogenation of their isoindole rings, similar to what has been observed for related tetrapyrroles on transition metal surfaces. Finally, spectroscopy indicates a modified substrate-adsorbate interaction upon annealing with a shortened bond distance. This finding could potentially explain a changed reactivity of Cu-supported iron phthalocyanine in comparison to that of the pristine compound.
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| 5. |
- Snezhkova, Olesia, et al.
(författare)
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Nature of the bias-dependent symmetry reduction of iron phthalocyanine on Cu(111)
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:7
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Tidskriftsartikel (refereegranskat)abstract
- Subtle changes in the geometric and electronic properties of supported molecules, with a potential impact on the functioning of molecular devices, can typically be imaged by scanning probe microscopy, but their exact origin and nature often remain unclear. Here we show explicitly that the symmetry reduction of iron phthalocyanine upon adsorption on Cu(111) can be observed not only in scanning tunneling microscopy, but also in core-level spectroscopy, and that it is related to nonisotropic charge transfer into the two principal molecular axes, but in combination with topographic influences.
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| 6. |
- Veers, Paul, et al.
(författare)
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Grand challenges in the science of wind energy
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 336:6464
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Tidskriftsartikel (refereegranskat)abstract
- Harvested by advanced technical systems honed over decades of research and development, wind energy has become a mainstream energy resource. However, continued innovation is needed to realize the potential of wind to serve the global demand for clean energy. Here, we outline three interdependent, cross-disciplinary grand challenges underpinning this research endeavor. The first is the need for a deeper understanding of the physics of atmospheric flow in the critical zone of plant operation. The second involves science and engineering of the largest dynamic, rotating machines in the world. The third encompasses optimization and control of fleets of wind plants working synergistically within the electricity grid. Addressing these challenges could enable wind power to provide as much as half of our global electricity needs and perhaps beyond.
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| 7. |
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