ABSTRACT
We investigate the effect of H adsorption on the magnetic properties of individual Co atoms on Pt(111) with scanning tunneling microscopy. For pristine Co atoms, we detect no inelastic features in the tunnel spectra. Conversely, CoH and CoH2 show a number of low-energy vibrational features in their differential conductance identified by isotope substitution. Only the fcc-adsorbed species present conductance steps of magnetic origin, with a field splitting identifying their effective spin as Seff=2 for CoH and 3/2 for CoH2. The exposure to H2 and desorption through tunnel electrons allow the reversible control of the spin in half-integer steps. Because of the presence of the surface, the hydrogen-induced spin increase is opposite to the spin sequence of CoHn molecules in the gas phase.
ABSTRACT
We present a new method to engineer the charge carrier mobility and its directional asymmetry in epitaxial graphene by using metal cluster superlattices self-assembled onto the moiré pattern formed by graphene on Ir(111). Angle-resolved photoemission spectroscopy reveals threefold symmetry in the band structure associated with strong renormalization of the electron group velocity close to the Dirac point giving rise to highly anisotropic Dirac cones. We further find that the cluster superlattice also affects the spectral-weight distribution of the carbon bands as well as the electronic gaps between graphene states.
ABSTRACT
We present the first surface spin-wave (SW) dispersion measurements up to the surface Brillouin zone boundary of a two monolayer Fe film on W(110) by using spin-polarized electron energy loss spectroscopy. Pronounced features of SW peaks are observed in the spectra at room temperature. We found that the SW energies in the Fe film are strongly reduced compared to spin waves in bulk Fe and to theoretical predictions. Our results suggest that this reduction is caused by the reduction of exchange interaction within the 2 ML Fe on W(110) as compared to bulk Fe.
Subject(s)
Iron , Iron/chemistryABSTRACT
ssNMR (solid-state NMR) spectroscopy provides increasing possibilities to study the structural and dynamic aspects of biological membranes. Here, we review recent ssNMR experiments that are based on MAS (magic angle spinning) and that provide insight into the structure and dynamics of membrane systems at the atomic level. Such methods can be used to study membrane architecture, domain formation or molecular complexation in a way that is highly complementary to other biophysical methods such as imaging or calorimetry.
Subject(s)
Lipid Bilayers , Magnetic Resonance Spectroscopy/methods , Peptides/chemistryABSTRACT
The realm of high energy, large wave vector spin waves in ultrathin films and at surfaces is unexplored because a suitable method was not available up to now. We present experimental data for an 8 ML thick Co film deposited on Cu(001) which show that spin-polarized electron energy loss spectroscopy can be used to measure spin-wave dispersion curves of ultrathin ferromagnetic films up to the surface Brillouin zone boundary.
ABSTRACT
Quantitative rearrangement of pivalaldehyde to methyl isopropyl ketone is observed in acids such as trifluoromethanesulfonic acid, anhydrous HF, and trifluoroethyl alcohol-BF3 but not in trifluoroacetic acid. Studies in a mixture of trifluoroacetic acid and trifluoromethanesulfonic acid show that acids with H(o) < or = -11 are able to carry out complete isomerization. These results and density functional theory calculations at the B3LYP/6-31G level suggest that protonated pivalaldehyde undergoes further protosolvation at higher acidities to a reactive superelectrophilic species resulting in rearrangement. A mechanism for the pivalaldehyde rearrangement to methyl isopropyl ketone in strong protic acids involving a reactive protosolvated superelectrophilic intermediate is suggested. Aspects of the related mechanism of the reaction with isobutane with CO in HF/BF3 medium leading to methyl isopropyl ketone are also discussed.
