Papers by Nicola Ferralis
Graphite has long been a prototypical substrate for physical adsorption. In light of recent exper... more Graphite has long been a prototypical substrate for physical adsorption. In light of recent experiments that indicate that Xe and other rare gases generally occupy low-coordination sites on metals, dynamical low-energy electron diffraction (LEED) was used to determine the adsorption geometry for Xe on graphite. Natural single crystals of graphite were used in these studies, and the clean graphite (0001)
The adsorption of Xe on decagonal Al-Ni-Co was studied using low-energy electron diffraction (LEE... more The adsorption of Xe on decagonal Al-Ni-Co was studied using low-energy electron diffraction (LEED) and low-temperature scanning tunneling microscopy (STM). The LEED pattern of the clean Al-Ni-Co surface has tenfold symmetry, and the distances between the diffraction peaks are related by powers of the golden mean. The observation of the LEED patterns while performing adsorption isobars in the temperature range 60-80 K indicates that no superlattice is formed upon adsorption of the first Xe layer. This suggests that either the first layer is disordered or that its structure conforms to the substrate quasicrystal structure. Upon adsorption of the second layer of Xe, a 30-fold pattern appears which is indicative of five rotational domains of a hexagonal structure that has a characteristic Xe-Xe spacing. The STM images of the Xe layer at 6 K indicate that the Xe monolayer grows out from the step edges, similar to observations of Xe growth on periodic metal surfaces.
Both the clean Pb(111) structure and the (3x3)R30^o structure formed by potassium adsorbed on Pb(... more Both the clean Pb(111) structure and the (3x3)R30^o structure formed by potassium adsorbed on Pb(111) have been investigated by dynamical low-energy electron diffraction (LEED). The relaxation of the topmost lead layers of the clean Pb(111) surface is the main deviation from the bulk geometry, in agreement to the results of a similar study [Y.S. Li, F. Jona, P.M. Marcus, Phys. Rev. B 43 (1991) 6337]. Upon adsorption of K at room temperature, a (3x3)R30^o structure is formed with K atoms occupying substitution sites. This result is rather unexpected considering that intermixing is unusual for large alkalis (larger than Li) adsorbed on close-packed substrates. The current calculation finds a K-Pb bond length of 3.62±0.3å, with no significant change to the Pb interlayer spacings [F.M. Pan, M. Caragiu, N. Ferralis, R.D. Diehl, Surf. Sci. 600 (2006) 537].
Journal of the Electrochemical Society, 2014
Mechanical degradation of lithium-ion battery (LIB) electrodes has been correlated with capacity ... more Mechanical degradation of lithium-ion battery (LIB) electrodes has been correlated with capacity fade and impedance growth over repeated charging and discharging. Knowledge of how the mechanical properties of materials used in LIBs are affected by electrochemical lithiation and delithiation could provide insight into design choices that mitigate mechanical damage and extend device lifetime. Here, we measured Young's modulus E, hardness H, and fracture toughness K Ic via instrumented nanoindentation of the prototypical intercalation cathode, Li X CoO 2 , after varying durations of electrochemical charging. After a single charge cycle, E and H decreased by up to 60%, while K Ic decreased by up to 70%. Microstructural characterization using optical microscopy, Raman spectroscopy, X-ray diffraction, and further nanoindentation showed that this degradation in K Ic was attributable to Li depletion at the material surface and was also correlated with extensive microfracture at grain boundaries. These results indicate that K Ic reduction and irreversible microstructural damage occur during the first cycle of lithium deintercalation from polycrystalline aggregates of Li X CoO 2 , potentially facilitating further crack growth over repeated cycling. Such marked reduction in K Ic over a single charge cycle also yields important implications for the design of electrochemical shock-resistant cathode materials.
Surface Science, 2004
Dynamical low-energy electron diffraction (LEED) was used to study the structures of graphite (0 ... more Dynamical low-energy electron diffraction (LEED) was used to study the structures of graphite (0 0 0 1) and graphite (0 0 0 1)-ð p 3 Â p 3ÞR30°-Xe. Natural single crystals of graphite were used in these studies, and their surface structure was found to be the same as the bulk structure. The adsorbed Xe was found to occupy the hollow sites of the honeycomb substrate at a distance of 3.59 ± 0.04 A A above the graphite plane.
The growth and ordering of Ne, Ar, Kr, and Xe films on a decagonal surface of Al73Ni10Co13 quasic... more The growth and ordering of Ne, Ar, Kr, and Xe films on a decagonal surface of Al73Ni10Co13 quasicrystal are studied with Grand Canonical Monte Carlo using Lennard-Jones interactions. We observe interesting phenomena that can only be attributed to the quasicrystallinity and/or corrugation of the substrate, including structural evolution of the overlayer films from commensurate pentagonal to incommensurate triangular, substrate-induced alignment
The ordering of Xe films on an Al73Ni10Co17 quasicrystals surface is studied using Grand Canonica... more The ordering of Xe films on an Al73Ni10Co17 quasicrystals surface is studied using Grand Canonical Monte Carlo simulations with Lennard-Jones interatomic potentials and an empirical adsorption potential. Isotherms and layer density profiles show interesting phenomena. The study confirms the experimental layer-by-layer growth in the explored temperature (T) range (70-280K). By increasing the pressure at low temperatures (70-110K) the first layer,
Journal of Physical Chemistry C, 2007
ABSTRACT The effects of thermal treatment in ultrahigh vacuum (UHV) of gold films galvanically di... more ABSTRACT The effects of thermal treatment in ultrahigh vacuum (UHV) of gold films galvanically displaced on the Si(111) surface are studied with low-energy electron diffraction, Auger electron spectroscopy, atomic force microscopy, Kelvin probe force microscopy, and X-ray photoelectron spectroscopy. Annealing the galvanically displaced gold on Si substrates to 1100 K produces films with similar structure, composition, and morphology to annealed gold films evaporated on Si in UHV. The surface morphology is consistent with the Stranski−Krastanov growth mode. Compared to the unannealed film, an interfacial gold silicide layer forms upon annealing, although with limited improvement in adhesion. We report the formation of submicrometer Au/Si islands with narrow size dispersion, separated by deep trenches and with local order and shape dictated by the symmetry of the substrate. A mechanism for the formation of these islands is proposed.
Surface Science, 2008
The surface Debye temperature of the 10-fold surface of the decagonal d-Al–Ni–Co quasicrystal was... more The surface Debye temperature of the 10-fold surface of the decagonal d-Al–Ni–Co quasicrystal was determined by measuring the decay of low-energy electron diffraction intensities with temperature. The surface Debye temperatures obtained from the logarithmic dependence of the Debye-Waller attenuation were 416±40K for an incident beam energy of 42eV, and 485±50K for an incident beam energy of 67eV. The values measured at the lowest energy are lower than measurements of the bulk value, by approximately 25%. The variation with beam energy is attributed to the penetration depth of the electrons, with the Debye temperature rapidly approaching the bulk value for a penetration of just a few layers. Although this is similar to the typical behavior observed in periodic crystals, it differs from the behavior observed in earlier studies of icosahedral quasicrystals.
Surface Science, 2006
Intermixed structures for alkalis (larger than Li) on close-packed substrates have previously bee... more Intermixed structures for alkalis (larger than Li) on close-packed substrates have previously been observed only on Al(1 1 1). This study shows that K forms an ordered intermixed structure on Pb(1 1 1). The structures of clean Pb(1 1 1) and Pb
Physical Review Letters, 2009
The spreading of a bilayer gold film propagating outward from gold clusters, which are pinned to ... more The spreading of a bilayer gold film propagating outward from gold clusters, which are pinned to clean Si(111), is imaged in real time by low energy electron microscopy. By monitoring the evolution of the boundary of the gold film at fixed temperature, a linear dependence of the spreading radius on time is found. The measured spreading velocities in the temperature range of 800 < T < 930 K varied from below 100 pm/s to 50 nm/s. We show that the spreading rate is limited by the reaction to form Au silicide, and the spreading velocity is likely regulated by the reconstruction of the gold silicide that occurs at the interface.
Physical Review Letters, 2008
The early stages of epitaxial graphene layer growth on the Si-terminated 6H-SiC(0001) are investi... more The early stages of epitaxial graphene layer growth on the Si-terminated 6H-SiC(0001) are investigated by Auger electron spectroscopy (AES) and depolarized Raman spectroscopy. The selection of the depolarized component of the scattered light results in a significant increase in the C-C bond signal over the second order SiC Raman signal, which allows to resolve submonolayer growth, including individual, localized C=C dimers in a diamond-like carbon matrix for AES C/Si ratio of ∼3, and a strained graphene layer with delocalized electrons and Dirac single-band dispersion for AES C/Si ratio >6. The linear strain, measured at room temperature, is found to be compressive, which can be attributed to the large difference between the coefficients of thermal expansion of graphene and SiC. The magnitude of the compressive strain can be varied by adjusting the growth time at fixed annealing temperature.
Physical Review Letters, 2005
We report results of the first computer simulation studies of a physically adsorbed gas on a quas... more We report results of the first computer simulation studies of a physically adsorbed gas on a quasicrystalline surface, Xe on decagonal Al-Ni-Co. The grand canonical Monte Carlo method is employed, using a semi-empirical gas-surface interaction, based on conventional combining rules, and the usual Lennard-Jones Xe-Xe interaction. The resulting adsorption isotherms and calculated structures are consistent with the results of LEED experimental data. The evolution of the bulk film begins in the second layer, while the low coverage behavior is epitaxial. This transition from 5-fold to 6-fold ordering is temperature dependent, occurring earlier (at lower coverage) for the higher temperatures.
Physical Review B, 2005
... J. Ledieu,* JT Hoeft, DE Reid, and JA Smerdon Surface Science Research Centre and Department ... more ... J. Ledieu,* JT Hoeft, DE Reid, and JA Smerdon Surface Science Research Centre and Department of Physics, The University of Liverpool, Liverpool L69 3BX, United Kingdom ... Theygrow in five orientations, re-flecting the symmetry of the underlying substrate. ...
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Papers by Nicola Ferralis