Studying Complex Surface Dynamical Systems Using Helium-3 Spin-Echo Spectroscopy
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Note in our experiment it is difficult to obtain an absolute experimental ratio of the phonon cross-section in graphene and nickel. The fact that the static electron density corrugation is significantly different will certainly affect the phonon intensities. However, there are also important changes in the relative intensities of the two main phonon modes. The inset in Figure 7 shows that the scattering cross section of the longitudinal resonance seems to be enhanced on the graphene covered surface when related to the intensity of the Rayleigh mode.
Summary and Conclusion. The epitaxial graphene layer exhibits an electron density corrugation with a peak to peak height of 0. Measurements of the surface phonon modes in the low energy region show the same modes as on the pristine Ni surface. Two of the three acoustic phonon modes of graphene are not accessible in our setup. The observation of the Ni surface modes can be explained in terms of a relatively strong binding to the substrate and the lighter mass of the graphite atoms compared to the substrate.
In addition, the ability of HAS to detect subsurface phonon modes due to the electron—phonon coupling can also enhance the scattered intensity from these substrate modes, even though the Ni substrate is covered by the graphene monolayer. In general, the intensity of the Rayleigh mode is smaller on the graphene coated surface compared to the Ni surface. The authors declare no competing financial interest. Graphene-nickel interfaces: a review Nanoscale , 6 , — DOI: Royal Society of Chemistry. Graphene on nickel is a prototypical example of an interface between graphene and a strongly interacting metal, as well as a special case of a lattice matched system.
The chem. This interaction causes a smaller sepn. Furthermore, the phys. Substrate induced geometric and electronic changes alter the phonon dispersion. As a consequence, monolayer graphene on nickel does not exhibit a Raman spectrum. In addn. The fundamental growth mechanisms of graphene by chem. Different growth modes depending on the sample temp. Finally, we give a brief summary for the synthesis of more complex graphene and graphitic structures using nickel as catalyst and point out some potential applications for graphene-nickel interfaces.
Graphene on metallic substrates: suppression of the Kohn anomalies in the phonon dispersion Nano Lett. American Chemical Society. This EPC, which has strong impact, for example, on Raman scattering and electron transport, can be strongly modified due to interaction with a metallic substrate. The out-of-plane modes also are strongly affected by the binding to the substrate. For other metallic substrates, where the distance between the graphene sheet and the substrate is larger, hybridization is much less pronounced and the Kohn anomaly is only weakly perturbed.
From exptl. Phonon dispersion of quasi-freestanding graphene on Pt J. Matter , 24 , DOI: Institute of Physics Publishing. EELS was used to probe phonon dispersion in quasi-freestanding graphene epitaxially grown on Pt Loss spectra clearly show different dispersing features related to both acoustic and optical phonons. The present results were compared with graphene systems which strongly interact with the substrate, i. This could be taken as an indication of the negligible interaction between the graphene sheet and the underlying Pt substrate.
The softening of out-of-plane modes obsd. Probing interlayer interactions between graphene and metal substrates by supersonic rare-gas atom scattering Phys. B: Condens. Matter Mater. Shichibe, H. American Physical Society. We demonstrate that highly surface-sensitive supersonic rare-gas He, Ar, and Xe atom scattering, in both the quantum and classical regimes, can probe and quantify the interlayer interactions between graphene monolayers and metal substrates in terms of the Debye temp.
As models of the strongly and weakly interacting graphene, we investigated two systems, graphene on Ru and Pt , resp. The exptl. Furthermore, asym. It is found that the "valley" region of the moire pattern has high effective mass reflecting stronger bonding to the substrate, contributing to the high reflectivity of the He beam reported for this system.
On the other hand, the effective mass of the "hill" region is found to be similar to that of HOPG, indicating that this region is well decoupled from the substrate.
Studying complex surface dynamical systems using helium-3 spin-echo spectroscopy
These results demonstrate a unique capability of atom scattering to probe and evaluate the mol. Maccariello, D. Elsevier Ltd. The structure and the acoustic phonon branches of graphene on Ru 0 0 0 1 have been exptl. In-plane interactions are unaffected by the interaction with the substrate. The energy of 16 meV for the vertical rigid vibration of graphene against the Ru 0 0 0 1 surface layer indicates an interlayer effective force const. The Rayleigh mode obsd. This is accounted for by the strong bonding to the substrate, which also explains the previously reported high reflectivity to He atoms of this system.
Finally, we report the observation of an addnl. Atomic beam diffraction from solid surfaces Rep. A review with many refs. This review concs. The theor. The main subjects covered are: structural detns. Diffraction results obtained with Ne, Ar, H2 and D2 are also summarized. Helium-3 spin-echo: principles and application to dynamics at surfaces Prog. In this review we give a detailed description of the recently developed helium-3 spin-echo technique and its application to several classes of surface dynamic measurements.
We review existing surface dynamical probes briefly and illustrate the need for new exptl. We then describe the helium-3 spin-echo method, which is one such tool, together with the approaches used to describe such measurements and the instrumentation developed to realize its application. The main application of helium-3 spin-echo is the study of surface dynamics, hence we review the approaches which have been established to interpret dynamical data and the signatures for various forms of motion, before going on to summarise the exptl.
We also describe Fourier transform atom spectroscopy, a new method for measuring elastic and resonant scattering that is facilitated by the availability of spin-echo instruments. Finally, we look towards future scientific challenges for the technique. Helium spin-echo spectroscopy: studying surface dynamics with ultra-high-energy resolution J. Matter , 19 , DOI: A review. Spin-echo measurements offer a major step forward in the technique of helium atom surface scattering. We describe the measurements within a double Fourier transform formalism, which by using appropriately selected 'tilted projections' for measurement allows elastic, inelastic and quasielastic measurements to be treated on an equal footing.
We illustrate the wide scope of application for helium spin-echo with measurements from each of these areas. Patera, Laerte L. The key atomistic mechanisms of graphene formation on Ni for technol. Upon cooling, addnl. The dominant graphene growth mechanism also critically depends on the near-surface carbon concn. The detailed XPS fingerprinting of these processes allows a direct link to high pressure XPS measurements of a wide range of growth conditions, including polycryst.
Ni catalysts and recipes commonly used in industrial reactors for graphene and carbon nanotube CVD. Atomic structure of monolayer graphite formed on Ni Surf. The at. Three different at. The final best-fit structure characterized by the min. Pendry's reliability factor of 0. The spacing between the flat overlayer and the topmost Ni layer is 2. Graphene on metal surfaces Surf. Elsevier B. The article reviews work on graphene monolayers adsorbed on metal surfaces.
Graphene layers on metals were prepd. The films are often not rotationally aligned to the metal surface. However, for a no. In most cases the well-ordered overlayers display moire structures with large periodicities, resulting from the lattice mismatch between graphene and the underlying metal. These structures are connected with a buckling of the graphene layer indicating local variations of the binding to the metal.
For the metal-graphene spacings values between approx. Reasons for these strong variations are not yet clear, but there are indications that the systems fall into 2 classes that differ qual. These variations are also reflected by the electronic structure. In other systems, the electronic structure of free-standing graphene is almost intact. The perfectness of the epitaxial moire phases offers promising applications, e. Atomic scale identification of coexisting graphene structures on Ni J.
Bianchini, Federico; Patera, Laerte L. Through a combined scanning tunneling microscopy STUM and d. By comparison of expts. STM images and characterizing the transitions between adjacent domains. Such transitions, described in detail through atomistic models, occur not only via sharp domain boundaries, with extended defects, but predominantly via smooth in-plane distortions of the carbon network, without disruption of the hexagonal rings, which are expected not to significantly affect electron transport.
American Institute of Physics. The interaction between graphene and Ni surface has been investigated systematically by d. PBE calcn. The accurate potential energy surfaces suggest that top-fcc, bridge-top, and top-hcp are possible stable structures of graphene on Ni surface, which are also found to have very close energies, in agreement with coexistence of different phases found exptl. Different from PBE, the optBvdW functional predicts that top-fcc is the most stable configuration, following by bridge-top and then top-hcp, which is consistent with the surface distribution given by a statistical anal.
The Dirac points are destroyed in chemisorbed phases of all stable structures. Further anal. The detailed binding mechanisms have been analyzed using differential charge d. Parreiras, D. XPS data indicate that graphene interacts strongly with the topmost Ni layer. Diffraction data show that graphene is deposited commensurably with the underlying Ni surface atoms. Twelve different graphene prepns. Considering the relative position between the carbon and Ni atoms, five exptl. The anal. Our first-principles calcns. Helium reflectivity and Debye temperature of graphene grown epitaxially on Ru Phys.
Politano, A. The high reflectivity for H2 mols. The Debye temp. A value of K was obtained, which is much higher than the K reported for graphite under similar conditions, and close to the value of K calcd. Helium-surface interaction potential of Sb from scattering experiments and close-coupling calculations Phys. Mayrhofer-Reinhartshuber, M. Helium atom scattering HAS was used to study the antimony Sb surface beyond the hard-wall model. HAS angular distributions and drift spectra show a no.
As their best representation, a potential with a depth of 4. Furthermore, the charge d. The kinematic focusing effects that occurred were in good agreement with surface phonon dispersion curves from already published d. Study of gas-graphite potential by means of helium atom diffraction Phys. Scattering of thermal He atoms from a low-temp.
The measured diffraction pattern shows that the repulsive part of the periodic gas-surface potential is rather well represented by the first Fourier component. The hard wall peak-to-peak spatial modulation is 0. Bound-state resonances allow to det. A comparison with available adsorption data is presented. Elastic and inelastic scattering components in the angular intensity distribution of He scattered from graphite Surf. The angular intensity distribution of thermal energy He beam scattered from highly oriented pyrolytic graphite HOPG surface has been measured by means of supersonic mol.
To sep. From the extd. On the basis of the HCM anal.
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Electronic and geometric corrugation of periodically rippled, self-nanostructured graphene epitaxially grown on Ru New J. Helium atom scattering from graphene grown on Rh J. C , , — DOI: Graphene growth on transition-metal surfaces leads to an ordered superlattice that appears as a series of hills and valleys in scanning tunneling microscopy. On Rh , the graphene forms an incommensurate epitaxial overlayer; the crystallog. Thus, the C atoms sit over different positions of the Rh lattice and their height above the Rh surface varies, but the different binding sites also affect the local electronic structure.
Scanning tunneling microscopy is affected by both of these factors. He scattering is more a measure of the geometrical corrugation, the variation of the height of the graphene sheet relative to the Rh surface. We compare the results of He diffraction measurements with those of previous scanning tunneling microscopy measurements to assess the relative geometric and electronic corrugations. Multiscale magnetic study of Ni and graphene on Ni Phys. Dzemiantsova, L. We have investigated the magnetism of the bare and graphene-covered surface of a Ni single crystal employing three different magnetic imaging techniques and ab initio calcns.
With low-temp. Spin contrast is also achieved on the graphene-covered surface, which means that the electron d. In accordance with our ab initio calcns.
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The latter also leads to an inversion of spin polarization with respect to the pristine surface. Room temp. Applying in-plane-fields, domain walls start to move at about 13 mT and a single domain state is achieved at mT. Via SEM with polarization anal. Atomic diffraction study of the interaction of helium atoms with the surface of an organic single crystal: The cleavage planes of guanidinium methanesulfonate J.
The cleavage planes of guanidinium methanesulfonate.
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The guanidinium methanesulfonate is a layered self-assembled org. However, since a more detailed knowledge of the He-surface interaction was lacking, in this paper we complete the investigation by studying the attractive part of the interaction potential between He and the surface terminated by Me groups projecting outward from the H-bonded sulfonate and guanidinium sheets. Four bound state levels were detd. The thermal attenuation of elastic scattering of helium from copper single crystal surfaces Surf.
The dependence of diffraction peak intensities on temp. The quant. A generalized Debye-Waller formalism is, at least as a 1st approxn. For the rougher surfaces the agreement remains good up to a threshold temp. This may be due to some kind of thermal roughening of the surface. Google Scholar There is no corresponding record for this reference. Different aspects of the Debye-Waller factor in various atom-surface scattering theories Surf.
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We discuss differences in the formal appearance, structure and phys. These differences are illustrated on the example of two most commonly used formalisms for description of inelastic atom scattering by multiple excitation of surface phonons. In the first of these approaches, one starts from the expression for transition rates for the projectile atom which is coupled to the phonon field to all orders in lattice displacements. In first-order Born approxn. By using a diagrammatic expansion to represent such correlation function we demonstrate that in this description the DWF occurs as a consequence of atom scattering by zero point motion of the lattice and is therefore expressed through dynamical variables which are not constrained to the energy shell.
In the second approach one starts from the expression for the scattering spectrum of the projectile and linear atom-phonon field coupling, which is then treated in a non-perturbative fashion to all orders in the coupling const. Here the dominant quantum contribution to the DWF arises from the projectile scattering through real uncorrelated multiphonon emission processes, which reduce the scattered beam intensity in the elastic channel.
Using analogous diagrammatic expansion we show that the corresponding DWF is expressed in terms of the on-the-energy-shell quantities, which then leads to a normalization of the total scattering spectrum so as to comply with the optical theorem. Only in the limit of fast collision and trajectory approxn.
We conclude by arguing that full correspondence between the expressions for the DWF in two discussed treatments could be achieved only by going beyond the presently employed approxns. Debye-Waller factor in He-Cu collisions revisited: the role of the interaction potentials Surf. Following the recently accumulated information on the vibrational properties of the Cu surface acquired through single- and multiphonon He atom scattering expts.
Attention was focused on the role which the various He-surface model potentials with their characteristic interaction parameters range of the interaction, momentum and energy transfer cut-offs etc. By combining the He-Cu potential, whose repulsive and attractive components are both allowed to vibrate, with the substrate phonon d. In contrast, by taking the phonon momentum transfer cut-off Qc as an adjustable parameter, as was frequently exploited in the literature, all the considered potentials can produce agreement with expts.
The magnitudes of such best fit Qc values are compared with those available in the literature and their phys. Communication: Semiclassical perturbation theory for the quantum diffractive scattering of atoms on thermal surfaces J. Inspired by the semiclassical perturbation theory of , the authors derive explicit expressions for the angular distribution of particles scattered from thermal surfaces. At very low surface temp. The angular distribution is a sum of diffraction peaks and a broad background reflecting the spectral d.
The theory is applied to measured angular distributions of Ne, Ar, and Kr scattered from a Cu surface. Quantum theory of atom-surface scattering: Debye-Waller factor Surf. Four models are discussed. In Model 1 a fast atom impinges on a surface whose atoms all vibrate deviating from their equil. In Model 2 again the impinging atom is fast, but the atoms in the surface vibrate incoherently rather than coherently. Both Models 1 and 2 yield the conventional Debye-Waller result in the infinite crystal atom mass limit for Model 2 Einstein oscillators have also to be assumed , and it is shown how corrections to this result can be built.
In Model 3 a slow atom impinges on a hard crystal surface, interacting with the rapidly varying potential of the vibrating solid. The Debye-Waller exponent can be written in terms of a time integral of the product of 2 correlations: the force correlation and the displacement correlation. The result is a dramatic increase of diffraction of relatively heavy atoms with respect to the conventional theory.
Finally, in Model 4 the impinging atom is again slow but the crystal is soft rather than hard. This case is more difficult to treat but a preliminary anal.
The scattering of helium atoms from surfaces J. C: Solid State Phys. A careful consideration of the Debye-Waller factor for atom-surface scattering explains the failure to observe diffracted scattering of He from most metal surfaces. Becker, James S. The surface structure and vibrational dynamics of CH3-Si and CD3-Si surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited a lattice const. The excellent quality of the obsd. The vibrational dynamics were investigated by measurement of the Debye-Waller attenuation of the elastic diffraction peaks as the surface temp.
The effective surface Debye temps. These relatively large Debye temps. The parallel mean-square displacements were 7. The obsd. These expts. Surface Debye temperature and vibrational dynamics of antimony from helium atom scattering measurements Surf. The surface Debye temp. The Debye-Waller attenuation of the elastic diffraction peaks was measured at surface temps. A surface Debye temp. The attractive well depth for the He-Sb interaction is detd. The perpendicular mean-square displacement for the surface at room temp.
Atomic vibrations at the graphite surface studied by He atom scattering Surf. He atom scattering was used to study inelastic bound state resonances and the Debye-Waller factor for the basal plane of graphite. The angular location of the resonant structures allows a dispersion curve to be obtained for the phonons involved in the inelastic process; this dispersion curve is very near that pertaining to TA.
The attenuation of the specular peak in the surface temp. The temp. This anomalous behavior is due to the layered structure and strong anisotropy of the crystal and can be explained in terms of the known low-frequency phonon spectrum of graphite. The interaction potential for the elastic and inelastic scattering of low-energy He atoms from the Cu and the Ag crystal surface is derived from the sum of semi ab initio pair potentials modified by a damping function which takes into account the smoothing effect of the conduction electrons at large parallel momentum transfer.
By adjusting only 2 free parameters of the potential model a very good fit is obtained to published exptl. Without any further adjustment of the potential new exptl. Theory of surface phonons at metal surfaces: recent advances J.
Matter , 22 , DOI: Benedek, G.