Dr Marco Sacchi

Royal Society University Research Fellow
Fellow of The Higher Education Academy
+44 (0)1483 686834
03 AZ 02


Areas of specialism

Surface Science; Materials Modelling; Computational Chemistry; Science Policy; Density Functional Theory

University roles and responsibilities

  • Chair of the Early Career Researchers' Forum of the University Doctoral College
  • Early Career Researcher Representative on the University Research & Innovation Committee
  • Energy and Materials Theme's Coordinator in the School of Chemistry and Chemical Engineering


    Research interests

    Research projects

    My publications


    Tamtögl, A.; Sacchi, M.; Avidor, N.; Calvo-Almazán, I.; Townsend, P. S. M.; Bremholm, M.; Hofmann, P.; Ellis, J.; Allison, W., Nanoscopic diffusion of water on a topological insulator. Nature Communications 2020, 11 (1), 278.



    Sacchi M, Wales DJ, Jenkins SJ (2011) Mode-Specific Chemisorption of CH4 on Pt{110}-(1 x 2) Explored by First-Principles Molecular Dynamics,Journal of Physical Chemistry C115(44)pp. 21832-21842 American Chemical Society
    The chemisorption of CH4 on Pt{110}-(1 2) has been studied by vibrational analysis of the reaction pathway defined by the potential energy surface and, in time reversal, by first-principles molecular dynamics simulations of CH4 associative desorption, with the electronic structure treated explicitly using density functional theory. We find that the symmetric stretch vibration ½1 is strongly coupled to the reaction coordinate; our results therefore provide a firm theoretical basis for recently reported state-resolved reactivity measurements, which show that excitation of the ½1 normal mode is the most efficient way to enhance the reaction probability.
    Bisson R, Sacchi M, Beck RD (2010) Mode-specific reactivity of CH4 on Pt(110)-(1 x 2) : The concerted role of stretch and bend excitation,Physical Review B82 The American Physical Society
    The state-resolved reaction probability of CH4 on Pt(110)?(1×2) was measured as a function of CH4 translational energy for four vibrational eigenstates comprising different amounts of C-H stretch and bend excitation. Mode-specific reactivity is observed both between states from different polyads and between isoenergetic states belonging to the same polyad of CH4. For the stretch/bend combination states, the vibrational efficacy of reaction activation is observed to be higher than for either pure C-H stretching or pure bending states, demonstrating a concerted role of stretch and bend excitation in C-H bond scission. This concerted role, reflected by the nonadditivity of the vibrational efficacies, is consistent with transition state structures found by ab initio calculations and indicates that current dynamical models of CH4 chemisorption neglect an important degree of freedom by including only C-H stretching motion.
    Madden DC, Temprano I, Sacchi M, Blanco-Rey M, Jenkins SJ, Driver SM (2014) Self-Organized Overlayers Formed by Alanine on Cu{311} Surfaces,Journal of Physical Chemistry C118(32)pp. 18589-18603 American Chemical Society
    Chirality can manifest itself in diverse ways when a molecule adsorbs on a metal surface. A clear understanding of the interplay between molecular chirality, ?footprint chirality?, and chirality in the long-range self-organization is crucial if metal surfaces are to be exploited for enantioselective heterogeneous catalysis or enantio-discriminating sensors. We have investigated the self-organization of l-alanine adsorbed as alaninate on Cu{311}, using reflection?absorption infrared spectroscopy in conjunction with first-principles calculations to determine bonding configurations, and low-energy electron diffraction and scanning tunnelling microscopy to elucidate structural features. Three ordered structures are seen. One has a symmetric lattice and 3-point adsorbate bonding (the ?symmetric lattice? or SL phase); the others, occurring at higher coverage, have chiral lattices and also involve 2-point bonding (the ?chiral lattice? or CL phase). Possible models for these structures are discussed, together with the roles of footprint chirality and of long-range chirality in the self-organization. These results set the forms of chirality seen in alaninate overlayers on Cu{110} and {100} surfaces into a wider context. The common underlying principles should help in establishing a general framework for understanding the behavior of chiral adsorbates on low-symmetry metal surfaces.
    Sacchi M (2012) Mode-specificity and transition state-specific energy redistribution in the chemisorption of CH4 on Ni{100},Physical Chemistry Chemical Physics14pp. 15879-15887 Royal Society of Chemistry
    We have investigated methane (CH4) dissociative chemisorption on the Ni{100} surface by first-principles molecular dynamics (MD) simulations. Our results show that this reaction is mode-specific, with the ½1 state being the most strongly coupled to efficient energy flow into the reaction coordinate when the molecule reaches the transition state. By performing MD simulations for two different transition state (TS) structures we provide evidence of TS structure-specific energy redistribution in methane chemisorption. Our results are compared with recently reported state-resolved measurement of methane adsorption probability on nickel surfaces, and we find that a strong correlation exists between the highest vibrational efficacy measured on Ni{100} for the ½1 state and the calculated highest fractional vibrational energy content in this mode.
    Madden DC, Temprano I, Sacchi M, Jenkins SJ (2015) Spontaneous Local Symmetry Breaking: A Conformational Study of Glycine on Cu{311},Journal of Physical Chemistry C119(23)pp. 13041-13049 American Chemical Society
    Understanding the interplay between intrinsic molecular chirality and chirality of the bonding footprint is crucial in exploiting enantioselectivity at surfaces. As such, achiral glycine and chiral alanine are the most obvious candidates if one is to study this interplay on different surfaces. Here, we have investigated the adsorption of glycine on Cu{311} using reflection?absorption infrared spectroscopy, low-energy electron diffraction, temperature-programmed desorption, and first-principles density-functional theory. This combination of techniques has allowed us to accurately identify the molecular conformations present under different conditions and discuss the overlayer structure in the context of the possible bonding footprints. We have observed coverage-dependent local symmetry breaking, with three-point bonded glycinate moieties forming an achiral arrangement at low coverages, and chirality developing with the presence of two-point bonded moieties at high coverages. Comparison with previous work on the self-assembly of simple amino acids on Cu{311} and the structurally similar Cu{110} surface has allowed us to rationalize the different conditions necessary for the formation of ordered chiral overlayers.
    Sacchi M, Galbraith MCE, Jenkins SJ (2012) The interaction of iron pyrite with oxygen, nitrogen and nitrogen oxides: a first-principles study,Physical Chemistry Chemical Physics14pp. 3627-3633 Royal Society of Chemistry
    Sulphide materials, in particular MoS2, have recently received great attention from the surface science community due to their extraordinary catalytic properties. Interestingly, the chemical activity of iron pyrite (FeS2) (the most common sulphide mineral on Earth), and in particular its potential for catalytic applications, has not been investigated so thoroughly. In this study, we use density functional theory (DFT) to investigate the surface interactions of fundamental atmospheric components such as oxygen and nitrogen, and we have explored the adsorption and dissociation of nitrogen monoxide (NO) and nitrogen dioxide (NO2) on the FeS2(100) surface. Our results show that both those environmentally important NOx species chemisorb on the surface Fe sites, while the S sites are basically unreactive for all the molecular species considered in this study and even prevent NO2 adsorption onto one of the non-equivalent Fe?Fe bridge sites of the (1 × 1)?FeS2(100) surface. From the calculated high barrier for NO and NO2 direct dissociation on this surface, we can deduce that both nitrogen oxides species are adsorbed molecularly on pyrite surfaces.
    Lechner BAJ, Hedgeland H, Ellis J, Allison W, Sacchi M, Jenkins SJ, Hinch BJ (2013) Quantum Influences in the Diffusive Motion of Pyrrole on Cu(111),Angewandte Chemie International Edition52(19)pp. 5085-5088
    Classical diffusion?quantum barrier: On Cu(111), pyrrole diffuses in channels, hopping between adjacent bridge sites over a barrier above hollow sites. The motion of the center of mass can be described classically; however, the activation barrier arises from the quantum character of internal vibrational modes that are largely unexcited during the motion. The unique helium spin?echo experiment is indicated by the green sphere and arrows.
    Sacchi M, Brewer AY, Parker JE, Truscott CL, Jenkins SJ, Clarke SM (2014) Supramolecular self-assembled network formation containing N-Br halogen bonds in physisorbed overlayers,Physical Chemistry Chemical Physics16pp. 19608-19617 Royal Society of Chemistry
    The formation of a halogen bonded self-assembled co-crystal physisorbed monolayer containing NïBr interactions is reported for the first time. The co-crystal monolayer is identified experimentally by synchrotron X-ray diffraction and the structure determined. Density functional theory (DFT) calculations are also employed to assess the magnitudes of the different interactions in the layer. Significantly, compared to other halogen bonds in physisorbed monolayers we have reported recently, the NïBr bond here is found to be non-linear. It is proposed that the increasing importance of the lateral hydrogen bond interactions, relative to the halogen bond strength, leads to the bending of the halogen bonds.
    Bisson R, Sacchi M, Beck RD (2010) State-resolved reactivity of CH4 on Pt(110)-(1 x 2): The role of surface orientation and impact site,Journal of Chemical Physics132(9) American Institute of Physics
    The reactivity of methane (CH 4 ) on Pt(110)-(1×2) Pt(110)-(1×2) has been studied by quantum state-resolved surface reactivity measurements. Ground state reaction probabilities, S 0 (v=0)ES 0 (laser-off) S0(v=0)ES0(laser-off) , as well as state-resolved reaction probabilities S 0 (2½ 3 ) S0(2½3) , for CH 4 CH4 excited to the first overtone of the antisymmetric C?H stretch (2½ 3 ) (2½3) have been measured at incident translational energies in the range of 4?64 kJ/mol. We observe S 0 (2½ 3 ) S0(2½3) to be up to three orders of magnitude higher than S 0 (v=0) S0(v=0) , demonstrating significant vibrational activation of CH 4 CH4 dissociation on Pt(110)-(1×2) Pt(110)-(1×2) by 2½ 3 2½3 excitation. Furthermore, we explored the azimuthal and polar incident angle dependence of S 0 (2½ 3 ) S0(2½3) and S 0 (v=0) S0(v=0) for a fixed incident translational energy E t =32?kJ/mol Et=32?kJ/mol . For incidence perpendicular to the missing row direction on Pt(110)-(1×2) Pt(110)-(1×2) and polar angles ¸>40° ¸>40° , shadowing effects prevent the incident CH 4 CH4 molecules from impinging into the trough sites. Comparison of this polar angle dependence with reactivity data for incidence parallel to the missing rows yields state-resolved site specific reactivity information consistent with a Pt(110)-(1×2) Pt(110)-(1×2) reactivity that is dominated by top layer Pt atoms located at the ridge sites. A comparison of S 0 (v=0) S0(v=0) measured on Pt(110)-(1×2) Pt(110)-(1×2) and Pt(111) yields a lower average barrier for Pt(110)-(1×2) Pt(110)-(1×2) by 13.7±2.0?kJ/mol 13.7±2.0?kJ/mol .
    Brewer AY, Sacchi M, Parker JE, Truscott CL, Jenkins SJ, Clarke SM (2013) The crystalline structure of the phenazine overlayer physisorbed on a graphite surface,Molecular Physics: an international journal in the field of chemical physics111(24)pp. 3823-3830 Taylor & Francis
    The monolayer crystal structure of phenazine adsorbed on graphite is determined by a combination of synchrotron X-ray diffraction and DFT calculations. The molecules adopt a rectangular unit cell with lattice parameters a = 13.55 Å and b = 10.55 Å, which contains 2 molecules. The plane group of the unit cell is p2gg, and each molecule is essentially flat to the plane of the surface, with only a small amount of out-of-plane tilt. Density functional theory (DFT) calculations find a minimum energy structure with a unit cell which agrees within 7.5% with that deduced by diffraction. DFT including dispersion force corrections (DFT+D) calculations help to identify the nature of the intermolecular bonding. The overlayer interactions are principally van der Waals, with a smaller contribution from weak C-H···N hydrogen bonds. This behaviour is compared with that of 4,42-bipyridyl.
    Sacchi M, Wales DJ, Jenkins SJ (2012) Bond-selective energy redistribution in the chemisorption of CH3D and CD3H on Pt{1 1 0}-(1 × 2): A first-principles molecular dynamics study,Computational and Theoretical Chemistry990pp. 144-151 Elsevier
    We have investigated the chemisorption of CH3D and CD3H on Pt{1 1 0}-(1 × 2) by performing first-principles molecular dynamics simulations of the recombinative desorption of CH3D (from adsorbed methyl and deuterium) and of CD3H (from adsorbed trideuteromethyl and hydrogen). Vibrational analysis of the symmetry adapted internal coordinates of the desorbing molecules shows that excitation of the single C?D (C?H) bond in the parent molecule is strongly correlated with energy excess in the reaction coordinate. The results of the molecular dynamics simulations are consistent with observed mode- and bond-specific reactivity measurements for chemisorption of methane and its isotopomers on platinum and nickel surfaces.
    Lechner BAJ, Sacchi M, Jardine AP, Hedgeland H, Allison W, Ellis J, Jenkins SJ, Dastoor PC, Hinch BJ (2013) Jumping, Rotating, and Flapping: The Atomic-Scale Motion of Thiophene on Cu(111),The Journal of Physical Chemistry Letters4(11)pp. 1953-1958 American Chemical Society
    Self-assembled monolayers of sulfur-containing heterocycles and linear oligomers containing thiophene groups have been widely employed in organic electronic applications. Here, we investigate the dynamics of isolated thiophene molecules on Cu(111) by combining helium spin-echo (HeSE) spectroscopy with density functional theory calculations. We show that the thiophene/Cu(111) system displays a rich array of aperiodic dynamical phenomena that include jump diffusion between adjacent atop sites over a 59?62 meV barrier and activated rotation around a sulfur?copper anchor, two processes that have been observed previously for related systems. In addition, we present experimental evidence for a new, weakly activated process, the flapping of the molecular ring. Repulsive inter-adsorbate interactions and an exceptionally high friction coefficient of 5 ± 2 ps?1 are also observed. These experiments demonstrate the versatility of the HeSE technique, and the quantitative information extracted in a detailed analysis provides an ideal benchmark for state-of-the-art theoretical techniques including nonlocal adsorbate?substrate interactions.
    Hedgeland H, Lechner BAJ, Tuddenham FE, Jardine AP, Allison W, Ellis J, Sacchi M, Jenkins SJ, Hinch BJ (2011) Weak Intermolecular Interactions in an Ionically Bound Molecular Adsorbate: Cyclopentadienyl/Cu(111),Physical Review Letters106(18) American Physical Society
    The dissociative adsorption of cyclopentadiene (C5H6) on Cu(111) yields a cyclopentadienyl (Cp) species with strongly anionic characteristics. The Cp potential energy surface and frictional coupling to the substrate are determined from measurements of dynamics of the molecule together with density functional calculations. The molecule is shown to occupy degenerate threefold adsorption sites and molecular motion is characterized by a low diffusional energy barrier of 40±3 meV with strong frictional dissipation. Repulsive dipole-dipole interactions are not detected despite charge transfer from substrate to adsorbate.
    Sacchi M, Jenkins SJ, Hedgeland H, Jardine AP, Hinch BJ (2011) Electronic Structure and Bonding of an Ionic Molecular Adsorbate: c-C5H5 on Cu{111},Journal of Physical Chemistry C115(32)pp. 16134-16141 American Chemical Society
    Self-assembled monolayers containing conjugated À systems find application in organic electronics to functionalize and modify the electronic properties of metals and metal oxides. Isolated cyclopentadienyl is an aromatic molecular anion similar in size to benzene that, unlike benzene, adsorbs quite strongly even on coinage metal surfaces. In this study, the electronic structure, bonding, and minimum energy configuration of cyclopentadienyl (c-C5H5 or Cp) adsorbed on Cu{111} are calculated via first-principles density functional theory (DFT). The Cu{111} surface has been modeled within a (2?3 × 2?3)R30° cell, and the adsorbed Cp has been found to reside preferentially on the hollow sites, with a binding energy of 1.73 eV. Electronic population analysis reveals a net charge transfer of <1.1 electrons from the metal to the Cp, indicating that the adsorption is dominated by ionic bonding. The surface diffusion barrier between two adjacent hollow sites was calculated to be 55 meV, in good agreement with previously reported measurements by helium spin echo (HeSE) spectroscopy. It was found that lateral interactions do not significantly influence the binding energy and mobility of the adsorbate. The physical?chemical properties of this strongly bound but weakly mutually interacting molecular adsorbate suggest that Cp could become a model system for ionically adsorbed molecular adsorbates.
    Sacchi M, Jenkins SJ (2014) Co-adsorption of water and glycine on Cu{110},Physical Chemistry Chemical Physics16pp. 6101-6107 Royal Society of Chemistry
    Amino acids are some of the simplest biological molecules, yet they nevertheless manifest the ability to construct an incredibly complex variety of structures in which a delicate balance of intermolecular chemical forces drives the dynamics of self-recognition and assembly. Understanding the mechanism by which chiral structures are naturally synthesized is also extremely relevant to pharmaceutical and biochemical industries, in which enantioselectivity and enantiospecificity are vital factors in producing biologically compatible drugs. In this context, the adsorption of simple, naturally occurring amino acids on single crystal surfaces has become the playground for studying chiral self-assembly at the atomic scale and investigating pathways to enantioselective catalytic synthesis using a bottom-up approach. In particular, in the last two decades, several groups have dedicated a concerted effort to understand the formation of chiral self-assembled supramolecular networks of alanine, glycine and proline on Cu{110}, Cu{100}1 and Cu{111} surfaces. In the past, with few exceptions,1 the vast majority of the atomistic studies on supramolecular assembly of amino acids on metal surfaces have been conducted under UHV conditions. It is therefore one of the main challenges ahead of the surface-science community to attempt to bridge the gap between experiments conducted under ?dry? vacuum conditions (in which the amino acids adsorb in the absence of a solvent and a co-adsorbate) and the more biologically and pharmaceutically relevant ?wet? studies. In fact, when water is present in the system, a competition exists between the formation of hydrogen bonds between an amino acid with another and between an amino acid and the water shell immediately surrounding it. The interaction between amino acids and water is also particularly relevant to corrosion protection, since amino acids have recently become a natural and ecologically compatible alternative to traditional amine-based corrosion inhibitors. In this work we study the co-adsorption of water with glycine, the simplest naturally occurring amino acid, using first-principles density functional theory. Although in the past some authors have tried to account for the solvation of amino acids in the gas-phase, few studies have treated the solvation and interaction between adsorbed glycine and water molecules quantum mechanically.
    Zhang T, Sacchi M, King DA, Driver SM (2012) Coverage-Dependent Structural Evolution in the Interaction of NO2 with Au{111},Journal of Physical Chemistry C116(9)pp. 5637-5645 American Chemical Society
    We have used low-temperature STM, together with DFT calculations incorporating the effects of dispersion forces, to study from a structural point of view the interaction of NO2 with Au{111} surfaces. NO2 adsorbs molecularly on Au{111} at 80 K, initially as small, disordered clusters at the elbows of the type-x reconstruction lines of the clean-surface herringbone reconstruction, and then as larger, ordered islands on the fcc regions. Within the islands, the NO2 molecules define a (?3 × 2)rect. superlattice, for which we evaluate structural models. By around 0.25 ML coverage, the herringbone reconstruction has been lifted, accompanied by the formation of Au nanoclusters, and the islands have coalesced. At this stage, essentially the whole surface is covered with an overlayer consisting predominantly of domains of the (?3 × 2)rect. structure, but also containing less well-ordered regions. With further exposure, the degree of disorder in the overlayer increases; saturation occurs close to 0.43 ML.
    Guo SY, Jenkins SJ, Ji W, Ning Z, Polanyi C, Sacchi M, Wang C-G (2015) Repulsion-Induced Surface-Migration, by Ballistics and Bounce,The Journal of Physical Chemistry Letters6(20)pp. 4093-4098 2015 American Chemical Society
    The motion of adsorbate molecules across surfaces is fundamental to self-assembly, material growth, and heterogeneous catalysis. Recent Scanning Tunneling Microscopy studies have demonstrated the electron-induced long-range surface-migration of ethylene, benzene, and related molecules, moving tens of Angstroms across Si(100). We present a model of the previously unexplained long-range recoil of chemisorbed ethylene across the surface of silicon. The molecular dynamics reveal two key elements for directed long-range migration: first ?ballistic? motion that causes the molecule to leave the ab initio slab of the surface traveling 3?8 Å above it out of range of its roughness, and thereafter skipping-stone ?bounces? that transport it further to the observed long distances. Using a previously tested Impulsive Two-State model, we predict comparable long-range recoil of atomic chlorine following electron-induced dissociation of chlorophenyl chemisorbed at Cu(110).
    Sacchi M, Brewer AY, Jenkins SJ, Parker JE, Fria i? T, Clarke SM (2013) Combined Diffraction and Density Functional Theory Calculations of Halogen-Bonded Cocrystal Monolayers, Langmuir: the ACS journal of surfaces and colloids29(48)pp. 14903-14911
    This work describes the combined use of synchrotron X-ray diffraction and density functional theory (DFT) calculations to understand the cocrystal formation or phase separation in 2D monolayers capable of halogen bonding. The solid monolayer structure of 1,4-diiodobenzene (DIB) has been determined by X-ray synchrotron diffraction. The mixing behavior of DIB with 4,42-bipyridyl (BPY) has also been studied and interestingly is found to phase-separate rather than form a cocrystal, as observed in the bulk. DFT calculations are used to establish the underlying origin of this interesting behavior. The DFT calculations are demonstrated to agree well with the recently proposed monolayer structure for the cocrystal of BPY and 1,4-diiodotetrafluorobenzene (DITFB) (the perfluorinated analogue of DIB), where halogen bonding has also been identified by diffraction. Here we have calculated an estimate of the halogen bond strength by DFT calculations for the DITFB/BPY cocrystal monolayer, which is found to be <20 kJ/mol. Computationally, we find that the nonfluorinated DIB and BPY are not expected to form a halogen-bonded cocrystal in a 2D layer; for this pair of species, phase separation of the components is calculated to be lower energy, in good agreement with the diffraction results.
    Calvo-Almazán I, Sacchi M, Tamtögl A, Bahn E, Koza M, Miret-Artés S, Fouquet P (2016) Ballistic Diffusion in Poly-aromatic Hydrocarbons on Graphite,Journal of Physical Chemistry Letters7pp. 5285-5290 American Chemical Society
    This work presents an experimental picture of molecular ballistic diffusion on a surface, a process which is difficult to pinpoint since it generally occurs at very short length scales. By combining neutron-time-of-flight data, with molecular dynamics simulations and density functional theory calculations, we provide a complete description of the ballistic translations and rotations of a poly-aromatic hydrocarbon (PAH) adsorbed on the basal plane of graphite. Pyrene, C16H10, adsorbed on graphite is a unique system where at relative surface coverages of about 10-20 %, its mean free path matches the experimentally accessible time/space scale of neutron time-of-flight spectroscopy (IN6 at the Institut Laue-Langevin). The comparison between the diffusive behavior of large and small PAHs such as pyrene and benzene adsorbed on graphite, brings a strong experimental indication that the interaction between molecules is the dominating mechanism in the surface diffusion of poly-aromatic hydrocarbons adsorbed on graphite.
    García Rey N, Sacchi M, Jenkins S, Arnolds H (2017) Dipole Moment Reversal in a Polar Organic Monolayer Probed by Sum and Difference Frequency Spectroscopy,The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces121(12)pp. 6692-6700 American Chemical Society
    We investigate the adsorption of pyridine on Cu(110) in ultra-high vacuum with a combination of work function measurements and femtosecond infrared-visible sum and difference frequency generation (SFG/DFG). A monolayer of pyridine substantially reduces the work function by 2.9 eV due to the large pyridine dipole. We perform density functional theory (DFT) calculations that provide us with a dipole moment change upon adsorption in very good agreement with the experimental results. The pyridine dipole strongly enhances the sum frequency response of the surface electrons, but surprisingly reduces the surface difference frequency signal. We propose a model based on the static electric field-induced nonlinear optical response generated by the collective electric field of the adsorbate layer. The pyridine dipole switches direction from the ground to the excited electronic state, as charge moves from nitrogen to the ring. SFG can then be enhanced by the electric field of adsorbed pyridine in its ground electronic state, while the 2.33 eV incident photon in DFG excites electrons into the pyridine LUMO, which reverses the electric field in the adsorbate layer and reduces the nonlinear optical response. The model is verified by 2.33 eV pump ? SFG probe spectroscopy, where the pump pulse is found to reduce the surface electron response on a subpicosecond timescale. This demonstrates the potential to manipulate the work function in organic electronic devices by photon-induced dipole moment reversal.
    We use helium spin-echo spectroscopy (HeSE) to investigate the dynamics of the diffusion of benzene adsorbed on Cu(111). The results of these measurements show that benzene moves on the surface through an activated jump-diffusion process between adsorption sites on a Bravais lattice. Density Functional Theory (DFT) calculations with van der Waals (vdW) corrections help us understand that the molecule diffuses by jumps through non-degenerate hollow sites. The results of the calculations shed light on the nature of the binding interaction between this prototypical aromatic molecule and the metallic surface. The highly accurate HeSE experimental data provide a quantitatively stringent benchmark for the vdW correction schemes applied to the DFT calculations and we compare the performances of several dispersion interactions schemes.
    Sacchi M, Wales D, Jenkins S (2017) Energy Landscapes and Dynamics of Glycine on Cu(110),Physical Chemistry Chemical Physics19(25)pp. 16600-16605 Royal Society of Chemistry
    Amino acids adsorbed over single crystal metal surfaces have emerged as prototypical systems for exploring the properties that govern the development of long-range chirality in self-assembled monolayers (SAM) and supramolecular 2D networks. In this study, we characterise the self-assembly mechanism for glycine on the Cu(110) surface. This process occurs on a time scale that is too fast for most atomically resolved microscopic techniques, so the mechanism we propose here provides new insight for an important unexplored surface phenomenon.
    Tamtogl A, Sacchi Marco, Calvo-Almazan I, Zbiri M, Koza MM, Ernst WE, Fouquet P (2017) Ultrafast Molecular Transport on Carbon Surfaces: The Diffusion of Ammonia on Graphite,CARBON126pp. 23-30 Elsevier
    We present a combined experimental and theoretical study of the self-diffusion of ammonia on exfoliated graphite. Using neutron time-of- flight spectroscopy we are able to resolve the ultrafast diffusion process of adsorbed ammonia, NH3, on graphite. Together with van der Waals corrected density functional theory calculations we show that the diffusion of NH3 follows a hopping motion on a weakly corrugated potential energy surface with an activation energy of about 4 meV which is particularly low for this type of diffusive motion. The hopping motion includes further a significant number of long jumps and the diffusion constant of ammonia adsorbed on graphite is determined with D = 3.9.10-8 m2/s at 94K.
    Hedgeland H, Sacchi M, Singh P, McIntosh A, Jardine A, Alexandrowicz G, Ward D, Jenkins S, Allison W, Ellis J (2016) Mass Transport in Surface Diffusion of van der Waals Bonded Systems - Boosted by Rotations?,Journal of Physical Chemistry Letters7(23)pp. 4819-4824 American Chemical Society
    Mass-transport at a surface is a key factor in heterogeneous catalysis. The rate is determined by excitation across a translational barrier and depends on the energy landscape and the coupling to the thermal bath of the surface. Here we use helium spin-echo spectroscopy (HeSE) to track the microscopic motion of benzene adsorbed on Cu(001) at low coverage (¸ < 0.07 ML). Specifically, our combined experimental and computational data determine both the absolute rate and mechanism of the molecular motion. The observed rate is significantly higher by a factor of 3.0±0.1 than is possible in a conventional, point-particle model and can only be understood by including additional molecular (rotational) coordinates. We argue that the effect can be described as an entropic contribution that enhances the population of molecules in the transition state. The process is generally relevant to molecular systems and illustrates the importance of the pre-exponential factor alongside the activation barrier in studies of surface kinetics.
    Nicklin Richard Edward John, Shavorskiy Andrey, Aksoy Akgul Funda, Liu Zhi, Bennett Roger Alexander, Sacchi Marco, Held Georg (2018) "Pop-On and Pop-Off" Surface Chemistry of Alanine on Ni{111} Under Elevated Hydrogen Pressures,The Journal of Physical Chemistry C122(14)pp. 7720-7730 American Chemical Society
    The co-adsorption of hydrogen with a simple chiral modifier, alanine, on Ni{111} was studied using Density Functional Theory in combination with ambient-pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy at temperatures of 300~K and above, which are representative of chiral hydrogenation reactions. Depending on the hydrogen pressure, the surface enables protons to "pop on and off" the modifier molecules, thus significantly altering the adsorption geometry and chemical nature of alanine from anionic tridentate in ultra-high vacuum to predominantly zwitterionic bidentate at hydrogen pressures above 0.1 Torr. This hydrogen-stabilised modifier geometry allows alternative mechanisms for proton transfer and the creation of enatioselective reaction environments.
    Amabilino David, Bâldea Ioan, Batteas James, Besenius Pol, Beton Peter, Buck Manfred, Chi Lifeng, Costantini Giovanni, Davies Philip, De Feyter Steven, Diaz Fernandez Yuri, Dwivedi Deepak, Ernst Karl-Heinz, Flood Amar, Hirsch Brandon, Humblot Vincent, Jones Robert, Kühnle Angelika, Lackinger Markus, Lin Nian, Linderoth Trolle R., Pradier Claire-Marie, Rahman Talat, Raval Rasmita, Robinson Neil, Sacchi Marco, Schwaminger Sebastian, Tait Steven L., Woodruff Phil, Zuilhof Han (2017) Supramolecular effects in self-assembled monolayers: general discussion,Faraday Discussions204pp. 123-158 Royal Society of Chemistry
    Amabilino David, Bâldea Ioan, Besenius Pol, Beton Peter, Blunt Matthew, Buck Manfred, Champness Neil R., Chi Lifeng, Clarke Stuart, Costantini Giovanni, De Feyter Steven, Diaz Fernandez Yuri, Dwivedi Deepak, Ernst Karl-Heinz, Flood Amar, Hirsch Brandon, Jones Robert, Kühnle Angelika, Lackinger Markus, Linderoth Trolle R., Martsinovich Natalia, Mount Andrew, Nalbach Martin, Pradier Claire-Marie, Rahman Talat, Raval Rasmita, Robinson Neil, Sacchi Marco, Schwaminger Sebastian, Tait Steven L., Woodruff Phil, Zuilhof Han (2017) Supramolecular systems at liquid?solid interfaces: general discussion,Faraday Discussions204pp. 271-295 Royal Society of Chemistry
    Tamtögl Anton, Sacchi Marco, Avidor Nadav, Calvo-Almazán Irene, Townsend Peter S. M., Bremholm Martin, Hofmann Philip, Ellis John, Allison William (2020) Nanoscale measurement of water diffusion on a topological insulator: The origin of correlated motion and friction,Nature Communications11278 (2020) Nature Research
    The microscopic motion of water is a central question, but gaining experimental information about the interfacial dynamics of water for instance in catalysis, biophysics and nanotribology is extremely challenging due to its ultrafast dynamics, and the complex interplay of intermolecular and molecule-surface interactions. Here we present the first experimental and computational study of the nanoscale-nanosecond motion of water at the surface of a topological insulator (TI, Bi2Te3). In addition to the technological relevance and scientific interest on the interfacial behaviour of water, understanding the interaction of TI surfaces with molecules is a key to design and manufacturing for future applications. However the surface chemistry of these materials has hitherto been hardly addressed and exploratory work on the motion of molecules on TI surfaces has been so far solely based on computational studies. By analysing the scattering lineshape from helium spinecho spectroscopy and comparing the results with van der Waals-corrected density functional theory calculations we are able to obtain a general insight into the diffusion and mobility of water on a topological insulator surface. Instead of the expected Brownian motion, we find strong evidence of a complex diffusion mechanism which follows an activated hopping motion on a corrugated potential energy surface and shows signatures of correlated motion with unusual repulsive interactions between the individual water molecules. From the experimental lineshape broadening we determine the diffusion coefficient, the diffusion energy and the pre-exponential factor.
    Tamtogl Anton, Sacchi Marco, Avidor Nadav, Calvo-Almazan Irene, Townsend Peter, Bremholm Martin, Hofmann Philip, Ellis John, Allison William (2020) Nanoscopic diffusion of water on a topological insulator.,Nature Communications11278 Nature Research
    The microscopic motion of water is a central question, but gaining experimental information about the interfacial dynamics of water in fields such as catalysis, biophysics and nanotribology is challenging due to its ultrafast motion, and the complex interplay of inter-molecular and molecule-surface interactions. Here we present an experimental and computational study of the nanoscale-nanosecond motion of water at the surface of a topological insulator (TI), Bi2Te3. Understanding the chemistry and motion of molecules on TI surfaces, while considered a key to design and manufacturing for future applications, has hitherto been hardly addressed experimentally. By combining helium spin-echo spectroscopy and density functional theory calculations, we are able to obtain a general insight into the diffusion of water on Bi2Te3. Instead of Brownian motion, we find an activated jump diffusion mechanism. Signatures of correlated motion suggest unusual repulsive interactions between the water molecules. From the lineshape broadening we determine the diffusion coefficient, the diffusion energy and the pre-exponential factor.