The rapidly increasing information density required of modern magnetic data storage devices raises the question of the fundamental limits in bit size and writing speed. At present, the magnetization reversal of a bit can occur as quickly as 200 ps (ref. 1). A fundamental limit has been explored by using intense magnetic-field pulses of 2 ps duration leading to a non-deterministic magnetization reversal. For this process, dissipation of spin angular momentum to other degrees of freedom on an ultrafast timescale is crucial. An even faster regime down to 100 fs or below might be reached by non-thermal control of magnetization with femtosecond laser radiation. Here, we show that an efficient novel channel for angular momentum dissipation to the lattice can be opened by femtosecond laser excitation of a ferromagnet. For the first time, the quenching of spin angular momentum and its transfer to the lattice with a time constant of 120+/-70 fs is determined unambiguously with X-ray magnetic circular dichroism. We report the first femtosecond time-resolved X-ray absorption spectroscopy data over an entire absorption edge, which are consistent with an unexpected increase in valence-electron localization during the first 120+/-50 fs, possibly providing the driving force behind femtosecond spin-lattice relaxation.

The authors report on photoelectron emission spectroscopy measurements of the oxygen 1s orbital of liquid water, using a liquid microjet in ultrahigh vacuum. By suitably changing the soft x-ray photon energy, within 600–1200 eV, the electron probing depth can be considerably altered as to either predominantly access the surface or predominantly bulk water molecules. The absolute probing depth in liquid water was inferred from the evolution of the O1s signal and from comparison with aqueous salt solution. The presence of two distinctive components in the core-level photoelectron spectrum, with significantly different binding energies, is revealed. The dominant contribution, at a vertical binding energy of 538.1 eV, was found in bulk and surface sensitive spectra. A weaker component at 536.6 eV binding energy appears to be present only in bulk water. Hartree-Fock calculations of O1s binding energies in different geometric arrangements of the water network are presented to rationalize the experimental distribution of O1s electron binding energies

Relative interaction strengths between cations (X = Li (+), Na (+), K (+), NH 4 (+)) and anionic carboxylate groups of acetate and glycine in aqueous solution are determined. These model systems mimic ion pairing of biologically relevant cations with negatively charged groups at protein surfaces. With oxygen 1s X-ray absorption spectroscopy, we can distinguish between spectral contributions from H 2O and carboxylate, which allows us to probe the electronic structure changes of the atomic site of the carboxylate group being closest to the countercation. From the intensity variations of the COO (-) aq O 1s X-ray absorption peak, which quantitatively correlate with the change in the local partial density of states from the carboxylic site, interactions are found to decrease in the sequence Na (+) > Li (+) > K (+) > NH 4 (+). This ordering, as well as the observed bidental nature of the -COO (-) aq and X (+) aq interaction, is supported by combined ab initio and molecular dynamics calculations.

Doped conjugated polymers can exhibit exceptionally high conductivity (>10 3 S cm -1 ). [1][2][3] Here, doping refers to the formation of charge-transfer complexes (CTCs) or salts by combining appropriate pairs of donors and acceptors. Similar phenomena can be found in crystalline CTCs comprising small molecules. [4][5][6][7] For several decades, the nature of charge transfer (CT) and the dimensionality of charge transport in conducting polymers and small molecule crystals have been at the focus of research. For instance, the degree of CT influences conductivity and determines whether metallic or insulating character prevails, [8,9] and the strength of interchain interactions determines whether primarily 1D or 3D electronic properties prevail. [10,11] In addition, disorder-on both a molecular and mesoscopic scale-has a tremendous impact on these properties. [12,13] In fact, true metallic behavior of a doped conjugated polymer was demonstrated only recently by significantly improving the structural quality of thin films. [14] Apart from the interest in fundamental phenomena occurring in such systems, recent progress in the field of organic electronics has intensified efforts toward improving the understanding of conducting polymers, as they are a key element for the successful realization of printed all-organic (opto-) electronic devices. [15][16][17] At present, formulations of poly(ethylenedioxythiophene)/poly(styrenesulfonate) dominate applications; [17][18][19][20] however, it should be interesting to develop alternative routes to conducting polymers that are not based on an aqueous dispersion and thus allow for new processing options and functionality. [21,22] The most widely studied class of semiconducting polymers that can be rendered conducting upon doping (with inorganic acceptors) is based on polythiophene, [3,23] which has donor character; tetrafluorotetracyanoquinodimethane (F4TCNQ) is one of the strongest known molecular electron acceptors and has been used for doping molecular organic semiconductors. [8,9,[24][25][26] However, combinations of polythiophenes and strong molecular acceptorshave not yet been investigated.Here we show that mixtures of the prototypical soluble polythiophene variant poly(3-hexylthiophene) (P3HT) and F4TCNQ form CTCs with high conductivity in thin films (ca. 1 S cm -1 ). Because of the flexibility of the polymer chains and the variety of possible interchain interactions, a large number of different local conformations in P3HT/F4TCNQ CTCs can be expected, leading to large variations in the electronic structure and transport properties within a macroscopic sample. We investigated the local conformation and electronic structure of P3HT/F4TCNQ CTCs in thin films by combining X-ray absorption near edge structure (XANES) measurements with theoretical modeling using density functional theory (DFT). Most notably, we found that only one specific CTC conformation predominated, in which F4TCNQ was strongly bent out of its neutral planar form because of pronounced electron donation from...