If the leaf can do it, can we do it even better?
Photosynthesis is the process by which light energy is converted to chemical energy. It is one of the most important biological processes as it provides energy, food, and oxygen for all organisms living on earth. Artificial photosynthesis is a novel strategy with the aim to improve the underlying mechanism for producing sustainable fuels. The question is: Can we beat nature at her own game?
Plants and many species of bacteria are photosynthetic. The light energy is trapped by the chlorophyll molecules which are arranged as regular arrays within membranes. When a chlorophyll molecule absorbs light, it is electronically excited. It may either realize a photochemical energy transfer or return to its ground state through relaxation mechanisms. A high efficiency of photosynthesis requires a minimization of the relaxation mechanisms.
In this paper, we introduced neutron spectroscopy to measure the light-induced relaxation effects on a photosynthetic membrane system. We detected the existence of photo-excited lattice modes which tells us where, and how much, energy is lost in the initial steps of photosynthesis. In addition, we found evidence for „freezing“ of lattice modes under light irradiation which results in an optimum orientation of the chlorophylls. These exploratory results are essential towards the engineering of new photosynthetic materials to improve the efficiency of the photosynthetic process beyond the limits given by nature.
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LH12180
Cloudy skies above a metal surface
According to quantum mechanics electrons that carry electrical currents in metals do not appear as particles with a well defined position, but rather as fuzzy moving objects, i.e. electron clouds. While it has been known for a long time that electron clouds can escape from the metal surface and move freely above it, we demonstrate in our paper that the clouds can get trapped above a small nanometer size metal island.
The electrons escaping from the surface still interact with the surface because they create positively charged holes that attract the negatively charged electrons. This way a series of “image-potential” states with quantized separation emerges that can be occupied by the electrons. The occupied states are detected with the atomically sharp needle of a tunneling microscope that probes the shape of electron clouds by measuring the electrical current flowing between the needle and the clouds. Our results reveal the triangular symmetry of the clouds that are trapped by the edges of a triangular cobalt island on a flat gold surface. The fuzzy edges of the clouds reflect the “uncertainty” that is imposed by quantum mechanics, implying that the clouds can leak out from the triangular confinement.
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LL11820
Atomic-scale Distribution of Water Molecules at Mica/Water Interface Visualized by Three-dimensional Scanning Force MicroscopyWe have developed a method referred to as three-dimensional scanning force microscopy (3D-SFM), which enables to visualize water distribution at solid/water interface with atomic-scale resolution in less than 1 min. Interfacial phenomena at solid/water interface play important roles in the industrial technologies as well as in the biological processes. However, the lack of a method able to visualize 3D distribution of water molecules has impeded progresses in molecular-scale understanding of such interfacial phenomena. 3D-SFM sheds light on this issue. As the first application of 3D-SFM, we investigated mica/water interface. This interface has been intensively studied due to the importance in ecological and geological sciences as well as in engineering and physics. The atomically-resolved 3D-SFM image visualizes 3D distributions of adsorbed water molecules as well as a hydration layer. In addition, the image also reveals the detailed atomic-scale structure of a cleaved mica surface next to an aqueous environment, indicating the existence of surface relaxation. So far, such real-space information has been discussed based on indirect spectroscopic data obtained by beam technologies. The direct real-space 3D images obtained by 3D-SFM should provide important information that has not been accessible by conventional technologies.
