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Based on a low temperature scanning tunneling microscopy study, we present a direct visualization of a cycloaddition reaction performed for some specific fluorinated maleimide molecules deposited on graphene. These studies showed that the cycloaddition reactions can be carried out on the basal plane of graphene, even when there are no pre-existing defects. In the course of covalently grafting the molecules to graphene, the sp2 conjugation of carbon atoms was broken and local sp3 bonds were created. The grafted molecules perturbed the graphene lattice, generating a standing-wave pattern with an anisotropy which was attributed to a (1,2) cycloaddition, as revealed by T-matrix approximation calculations. DFT calculations showed that while both (1,4) and (1,2) cycloaddition were possible on free standing graphene, only the (1,2) cycloaddition could be obtained for graphene on SiC(0001). Globally averaging spectroscopic techniques, XPS and ARPES, were used to determine the modification in the elemental composition of the samples induced by the reaction, indicating an opening of an electronic gap in graphene., Comment: 20 pages, 6 figures

Deep Inelastic Neutron Scattering provides a means of directly and accurately measuring the momentum distribution of protons in water, which is determined primarily by the protons ground state wavefunction. We find that in water confined on scales of 20A, this wave function responds to the details of the confinement, corresponds to a strongly anharmonic local potential, shows evidence in some cases of coherent delocalization in double wells, and involves changes in zero point kinetic energy of the protons from -40 to +120 meV difference from that of bulk water at room temperature. This behavior appears to be a generic feature of nanoscale confinement. It is exhibited here in 16A inner diameter carbon nanotubes, two different hydrated proton exchange membranes(PEMs), Nafion 1120 and Dow 858, and has been seen earlier in xerogel and 14A diameter carbon nanotubes. The proton conductivity in the PEM samples correlates with the degree of coherent delocalization of the proton., Comment: 5 pages, 3 figures

Water is often viewed as a collection of monomers interacting electrostatically with each other. We compare the water proton momentum distributions from recent neutron scattering data with those calculated from two electronic structure based models. We find that below 500 K the electrostatic models are not able to even qualitatively account for the sizable vibrational zero-point contribution to the enthalpy of vaporization. This discrepancy is evidence that the change in the proton well upon solvation cannot be entirely explained by electrostatic effects alone.

The zero point kinetic energy of protons in water is large on the scale of chemical interaction energies(29 Kj/mol in bulk room temperature water). Its value depends upon the structure of the hydrogen bond network, and can change as the network is confined or as water interacts with surfaces. These changes have been observed to be large on a chemical scale for water confined in carbon nanotubes and in the pores of xerogel, and may play a fundamental, and neglected, role in biological processes involving confined water. We measure the average momentum distribution of the protons in salmon Na-DNA using Deep Inelastic Neutron Scattering, for a weakly hydrated (6w/bp) and a dehydrated fiber sample. This permits the determination of the change in total kinetic energy of the system per water molecule removed from the DNA and placed in the bulk liquid. This energy is equal, within errors, to the measured enthalpy for the same process, demonstrating that changes in the zero point motion of the protons, arising from changes in structure as water molecules are incorporated in the DNA, are a significant factor in the energetics of the transition from the A to B phase with hydration, in this case, providing the entire binding energy of the water molecules to the DNA. The shape of the momentum distribution in the dehydrated phase is consistent with coherent delocalization of some of the protons in a double well potential, with a separation of the wells of .2 Angstroms., Comment: 5 pages 1 figure

The paper in the title [1] reports measurements of neutron scattering from hydrogen in the 1-100 eV range of energy transfers, using the direct geometry MARI spectrometer at ISIS. Stock et al claim that their measurements have better or comparable energy resolution to those on the inverse geometry VESUVIO spectrometer at ISIS. Most importantly the main conclusions of ref [1] are not valid unless this claim is true: in particular the conclusion that anomalous neutron cross sections measured on VESUVIO [2] are "the result of experimental issues using indirect geometry spectrometers". We present here overwhelming evidence that the energy resolution of the measurements in ref [1] is much coarser than on VESUVIO. It follows that the conclusions of Stock et al are unfounded. In reality the measurements of reference [1] serve mainly to demonstrate that at eV neutron energies, direct geometry chopper spectrometers have greatly inferior energy resolution to inverse geometry spectrometers based on resonance foil methods., Comment: 20 pages

The momentum distribution in KD2PO4(DKDP) has been measured using neutron Compton scattering above and below the weakly first order paraelectric-ferroelectric phase transition(T=229K). There is very litte difference between the two distributions, and no sign of the coherence over two locations for the proton observed in the paraelectric phase, as in KH2PO4(KDP). We conclude that the tunnel splitting must be much less than 20mev. The width of the distribution indicates that the effective potential for DKDP is significantly softer than that for KDP. As electronic structure calculations indicate that the stiffness of the potential increases with the size of the coherent region locally undergoing soft mode fluctuations, we conclude that there is a mass dependent quantum coherence length in both systems., Comment: 6 pages 5 figures

Born-Oppenheimer (BO) potential in any material. The proton potential surfaces in the hydrogen bonded superprotonic conductor Rb3H(SO4)2 are extracted from the momentum distribution measured using Deep Inelastic Neutron Scattering(DINS). The potential has a single minimum along the bond direction, which accounts for the absence of the antiferroelectric transition seen in the deuterated material, and a saddle point off the bond direction for tunneling into the next well with a barrier height of 350 meV. The measured potential is in qualitative agreement with phenomenological double Morse potentials that have been used to describe hydrogen bonds in other systems.

The momentum distribution of the protons in ice Ih, ice VI, high density amorphous ice and water in carbon nanotubes at low temperatures has been measured using deep inelastic neutron scattering. We find that the momentum distribution for the water in the nanotubes is qualitatively unlike that in any other phase of water or ice. The kinetic energy of the protons is 35mev less than that in ice Ih at the same temperature, and the high momentum tail of the distribution, characteristic of the molecular covalent bond and the stretch mode of the proton in the hydrogen bonds, is not present. We observe a phase transition between 230K and 268K in the nanotube data. The high momentum tail is present in the higher temperature measurement, which resembles that of ice Ih at the same temperature. Molecular dynamics simulations show the phase transition to be associated with the reordering of the hydrogen bonds of the 2-D ice layer, coating the interior of the nanotube at low temperatures, into a 3-D structure at 268K. We conclude that the protons in the hydrogen bonds in the 2-D ice layer are coherently delocalized, and that the 2-D ice layer is a qualitatively new phase of ice., Comment: 10 pages 4 figures

Neutron Compton Scattering measurements in a variety of materials have shown a relative deficit in the total signal from hydrogen compared to deuterium and heavier ions. We show here that a breakdown in the Born-Oppenheimer approximation in the final states of the scattering process leads to such a deficit, and may be responsible for the effect.

Neutron Compton Scattering measurements presented here of the momentum distribution of hydrogen in water at temperatures slightly below freezing to the supercritical phase show a dramatic change in the distribution as the hydrogen bond network becomes more disordered. Within a single particle interpretation, the proton moves from an essentially harmonic well in ice to a slightly anharmonic well in room temperature water, to a deeply anharmonic potential in the supercritical phase that is best described by a double well potential with a separation of the wells along the bond axis of about .3 Angstroms. Confining the supercritical water in the interstices of a C60 powder enhances this anharmonicity. The changes in the distribution are consistent with gas phase formation at the hydrophobic boundaries., Comment: 6 pages, 3 figures, 2 tables

In 1993 Tang proposed [1] that vortex avalanches should produce a self organized critical state in superconductors, but conclusive evidence for this has heretofore been lacking. In the present paper, we report extensive micro-Hall probe data from the vortex dynamics in superconducting niobium, where a broad distribution of avalanche sizes scaling as a power-law for more than two decades is found. The measurements are combined with magneto-optical imaging, and show that over a widely varying magnetic landscape the scaling behaviour does not change, hence establishing that the dynamics of superconducting vortices is a SOC phenomenon., Comment: 3 pages + 4 figures, a reference added, citation typos fixed

Neutron Compton Scattering measurements presented here of the momentum distribution of hydrogen in $KH_2PO_4$ (KDP) just above and well below the ferroelectric transition temperature show clearly that the proton is coherent over both sites in the in the high temperature phase, a result that invalidates the commonly accepted order-disorder picture of the transition. The Born-Oppenheimer potential for the hydrogen, extracted directly from data for the first time, is consistent with neutron diffraction data, and the vibrational spectrum is in substantial agreement with infrared absorption measurements. The measurements are sensitive enough to detect the effect of surrounding ligands on the hydrogen bond, and can be used to study the systematic effect of the variation of these ligands in other hydrogen bonded systems., Comment: 5 pages, 3 figures

We show that deep inelastic neutron scattering from hydrogen(or other light nuclei) can be used to measure a spectrum of anharmonic contributions to the target atom momentum distribution with high and known accuracy . The method is applied here to determine the momentum distribution of the hydrogen in the hydrogen bonded system KHC2O4(potassium binoxalate), where 13 anharmonic coefficients are obtained at the 2-sigma to 3-sigma level. The momentum distribution is obtained to an accuracy of better than few percent at all significant values of momentum.