The central key issues we want to address during this CECAM workshop are detailed below.
Phase sensitive experiments and electrochemistry. Within the past recent years, the development of phase sensitive SFG experiments, in particular developed by the group of Prof Y.R. Shen at UC Berkeley, have allowed to unveil molecular orientations at interfaces in a direct way. For example in case of mineral surfaces they have permitted to address microscopic details at surfaces, including the types of functional groups present, their protonation state and bond orientations, and the nature of near-surface water organization and orientation.1 The SFG is facing new challenges when extending the environment which can be probed with this interface sensitive technique, i.e. beyond simple water at the interface. In particular one of the very recent progress includes the extension of SFG to electrochemical interfaces. By exploiting surface plasmon resonant enhancement at electrochemical interfaces, Prof Y.R. Shen and coworkers have
demonstrated the feasibility of using SFG spectroscopy to measure in situ real-time vibrational spectra during electrochemical reactions. The success of this approach is significant as it could bring more insight and better understanding of such reactions, directly at the molecular level.2
From the theoretical point of view characterization of electrochemical interfaces is also a fast developing and evolving field with many open questions. Amongst some of them we would like to mention electrodes descriptions. The unified treatment of oxidation/reduction and (de)protonation reactions is crucial to that end and faces large theoretical challenges. Incorporation of the electric double layer in the models is one of these related challenges.3 Theoreticians with large experience in the analysis and understanding of solid/liquid interfaces at electrochemical interfaces will provide a picture of what are the current theoretical achievements and understandings, and what are the steps we still need to cover in order to have a direct comparison of theory and experiments. Amongst our invited speakers, Prof A. Gross (University of Ulm) has been recently addressing metal/electrolyte interfaces with ab initio simulations,4 Prof M. Sprik (University of Cambridge) addresses metal oxides/water interfaces5 as
well as Dr K. Leung (Sandia Lab, New Mexico, USA).6 Prof E. Spohr investigates metal deposition7 and ab initio molecular dynamics simulations of proton transport in polymer electrolytes,8 while Dr M-L. Doublet9 is coming from the surface science community where electrochemistry is also a major topic.
Solid/liquid interfaces in environmental science and inhomogeneous catalysis.
Another important theme of our workshop will include discussions on environmental solid/liquid interfaces. Interestingly some of the challenges that modelling has to face in that domain are closely related to those in electrochemistry, namely the modelling of ions in the aqueous solution and the accompanying description of the electric double layer.10 Also incorporating surface reactivity is a common theme to both electrochem-
istry and geoscience communities. Major advances on the experimental point of view include for example running flow SFG experiments which have been recently achieved in the spectroscopy group at the Max Planck Institute in Mainz, Germany. Prof M. Bonn and Dr E. Backus will be invited to present their most recent works in this area.11
Prof V.H. Grassian from Ohio University, USA, has been one of the major contributors in the field of environmental solid-liquid interfaces,12, 13 and will be one of our key speakers. Also invited in the field of solid-liquid environmental science are Prof H. Allen from Ohio University,14 Prof M.L. Machesky15 from University of Illinois, and Prof R. B. Gerber16, 17 from the Jerusalem Hebrew University, Israel. Inhomogeneous catalysis at solid-liquid interfaces is another domain where modelling can be extremely useful for getting a real understanding of the mechanisms at play, and provide more
rational design for catalysts to be used more efficiently. Researchers at the Institut Francais du Petrole (IFP) of Lyon in France are pioneers in that domain,18 and Dr P. Raybaud will be invited as a key speaker presenting the new advances and challenges opened.
Nano- and microparticles have optical, structural, and chemical properties that differ from both their building blocks and the bulk materials themselves, due to the high surface-to-volume ratio. To understand the properties of nano- and microparticles, it is of fundamental importance to characterize the particle surfaces and their interactions with the surrounding medium. Recent developments of nonlinear light scattering techniques have resulted in a deeper insight of the underlying light-matter interactions.19
They have shed new light on the molecular mechanisms of surface kinetics in solution, properties of interfacial water in contact with hydrophilic and hydrophobic particles and droplets, molecular orientation distribution of molecules at particle surfaces in solution,20 interfacial structure of surfactants at droplet interfaces, acid-base chemistry on particles in solution, and vesicle structure and transport properties. S. Roke from EPFL Lausanne has been the major developer of such topic in the experimental area,
and will be one of one key speakers. Nano and microparticles have also attracted much of attention in connection with their possibility to interact with living matter. Indeed understanding of how proteins interact with solid surfaces and nanoparticles is vital to ensure the continued development of biomaterials such as implants and biosensors. In this section two experimentalists, Prof. D.K. Hore from university of Victoria, Canada,
and Prof. GL Richmond from University of Oregon, USA, will address the biomolecular structure at solid-liquid interfaces as revealed by nonlinear optical spectroscopy,21.22
From the theoretical point of view we will have the contributions from Prof. R. Netz from Freie Universitaet Berlin who is a leader in the computational investigation of biopolymers at the water/solid interface and of microhydrodynamics at interfaces.23 and Prof. A. Foster from AAlto University, Finland who is leading a computational group on surfaces and interfaces at the nanoscale.24
Multidimensional SFG spectroscopy. Finally another key topic of our workshop will be the recently developed25, 26 femtosecond SFG-2D-IR spectroscopy. This technique combines the interface selectivity with time resolution and permits to address energy transfer dynamics. Such experiments provide knowledge not only on the interfacial structural organisation but also on the dynamics at the interface. A key question is
how the bulk energy transfer compares to the surface one and how the energy transfer mechanism changes when going from bulk to surface. Water is a striking example, due to its very rapid resonant energy relaxation dynamics which it exhibits both in bulk and at the surface.27 A rather striking point is why/how interfaces with similar static SFG response can have a different relaxation dynamics.27 Moreover ions can have a strong role on shaping water dynamical properties depending on their surface propen-
sity.28 The group of Prof M. Bonn at the Max Planck Institute in Mainz, Germany, is the leader in this field and will be presenting his most recent developments and results. The group of Prof E. Borguet at Temple University USA, has also recently been developing several key multidimensional SFG experiments, including time-dependent ones, and will also be a key speaker at the workshop.29