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Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Adsorption behavior of organic molecules: a study of benzotriazole on Cu(111) with spectroscopic and theoretical methods Chiara Gattinoni , Panayiotis Tsaousis , Chanan Euaruksakul , Rachel Price , David A. Duncan , Tod Pascal , David Prendergast , Georg Held , Angelos Michaelides Langmuir DOI: 10.1021/acs.langmuir.8b03528 Diamond Proposal Number(s): [12800] Show Abstract ▼ Abstract: The adsorption of organic molecules on solid substrates is important to applications in fields such as catalysis, photovoltaics, corrosion inhibition, adhesion, and sensors. The molecular level description of the surface-molecule interaction and of the adsorption structures in these complex systems is crucial to understand their properties and function. Here we present the investigation of one such system, benzotriazole (BTAH) on single crystal Cu(111) in vacuum conditions. BTAH is the most widely used corrosion inhibitor for copper and thus a molecule of great industrial relevance. We show that the co-application of a wide range of spectroscopic techniques with theoretical methods provides unique insight in the description of the atomistic details of the adsorbed structures. Specifically, spectroscopic photoemission, absorption and standing wave experiments combined with ab initio computational modeling allowed us to identify that benzotriazole forms overlayers of intact BTAH when deposited at low temperature and it dissociates into BTA and H at room temperature and above. The dissociated molecule then forms complex structures of mixed chains and dimers of BTA bound to copper adatoms. Our work also reveals that copper adatoms at low concentrations, such as the theoretically predicted superstructures cannot be be resolved by means of current X-ray photoelectron spectroscopy (XPS) as the modelled Cu 2p spectra are practically indistinguishable from those for a Cu surface without adatoms. Overall this study significantly deepens understanding of BTAH on Cu – a system studied for more than 50 years – and it highlights the benefits of combining spectroscopic and computational methods in order to obtain a complete picture of a complex adsorption system.	Jan 2019
Optics	Compensation of x-ray mirror distortion by cooling temperature control Matthew Hand , Hongchang Wang , Maria Harkiolaki , Federica Venturini , Rosa Arrigo , Pilar Ferrer Escorihuela , Simon Alcock , Ioana Nistea , Andy Marshall , Stewart Scott , Liz Duke , Georg Held , Kawal Sawhney Proceedings of the 13th International Conference on Synchrotron Radiation Instrumentation – SRI2018 DOI: 10.1063/1.5084675 Open Access Show Abstract ▼ Abstract: Synchrotron radiation is emitted from a bending magnet source in a wide ray fan which is collected by the first optical element in a beamline. In order to maximize angular acceptance, and hence flux, it is beneficial to increase the length of this mirror and optical design requirements may necessitate that the optical surface be over 1 m in length. Such mirrors also require cooling as they may be subject to high heat loads from the incident radiation. Two beamlines, B07 and B24, at Diamond Light Source, UK, use 1.4 m long toroidal mirrors which utilize a similar side-clamped cooling manifold design. While this scheme has been successful in providing effective cooling of the mirror, it has also been discovered that it introduces deformation of the radius of curvature which is sufficient to alter the focusing characteristics of the mirror. At both beamlines, the horizontal focus of the beam was found to differ by up to several meter from the design position at the exit slit which resulted in poor flux throughput, reduced energy resolution and other side effects. A pencil beam scan method has been used to diagnose this issue and infer the position of the focus and mirror shape. Through the use of a standalone chiller to alter the temperature of the water within the cooling loop, it has been possible to correct the distortion of the radius and restore the focus to its nominal position.	Jan 2019
B18-Core EXAFS E01-JEM ARM 200CF	Operando spectroscopy study of the carbon dioxide electro-reduction by iron species on nitrogen-doped carbon Chiara Genovese , Manfred E. Schuster , Emma K. Gibson , Diego Gianolio , Victor Posligua , Ricardo Grau-crespo , Giannantonio Cibin , Peter Wells , Debi Garai , Vladyslav Solokha , Sandra Krick Calderon , Juan J. Velasco-velez , Claudio Ampelli , Siglinda Perathoner , Georg Held , Gabriele Centi , Rosa Arrigo Nature Communications 9 DOI: 10.1038/s41467-018-03138-7 Diamond Proposal Number(s): [17031, 10306] Open Access Show Abstract ▼ Abstract: The carbon–carbon coupling via electrochemical reduction of carbon dioxide represents the biggest challenge for using this route as platform for chemicals synthesis. Here we show that nanostructured iron (III) oxyhydroxide on nitrogen-doped carbon enables high Faraday efficiency (97.4%) and selectivity to acetic acid (61%) at very-low potential (−0.5 V vs silver/silver chloride). Using a combination of electron microscopy, operando X-ray spectroscopy techniques and density functional theory simulations, we correlate the activity to acetic acid at this potential to the formation of nitrogen-coordinated iron (II) sites as single atoms or polyatomic species at the interface between iron oxyhydroxide and the nitrogen-doped carbon. The evolution of hydrogen is correlated to the formation of metallic iron and observed as dominant reaction path over iron oxyhydroxide on oxygen-doped carbon in the overall range of negative potential investigated, whereas over iron oxyhydroxide on nitrogen-doped carbon it becomes important only at more negative potentials.	Mar 2018
	Combined Experimental and Theoretical Study of Methyl Acetoacetate Adsorption on Ni{100} Panayiotis Tsaousis , Jorge Ontaneda , Luca Bignardi , Roger A. Bennett , Ricardo Grau-crespo , Georg Held The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.8b00204 Show Abstract ▼ Abstract: The enantioselective hydrogenation of methyl acetoacetate (MAA) over modified Ni-based catalysts is a key reaction in the understanding of enantioselective heterogeneous catalysis as it represents the only example of this class of reactions catalyzed by base metals. Yet, there is very little molecular-level information available about the adsorption complex formed by the reactants on Ni surfaces. Here, we report a combined experimental and theoretical study of the adsorption of MAA on the Ni{100} surface. X-ray photoelectron spectroscopy shows that MAA forms stable multilayers at low temperatures, which desorb between 200 and 220 K. At higher temperatures a single chemisorbed layer is formed, which decomposes between 300 and 350 K. Density functional theory modeling predicts an enolate species with bidentate coordination as the most stable chemisorbed species. Comparison of photoelectron spectroscopy and X-ray absorption data with simulations using this adsorption model show good qualitative and quantitative agreement. The molecular plane is tilted with respect to the surface plane by about 50°. This breaking of symmetry provides a mechanism for the enantioselective hydrogenation.	Mar 2018
	"Pop-On and Pop-Off" Surface Chemistry of Alanine on Ni{111} Under Elevated Hydrogen Pressures Richard E. J. Nicklin , Andrey Shavorskiy , Funda Aksoy Akgul , Zhi Liu , Roger A. Bennett , Marco Sacchi , Georg Held The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.8b00186 Show Abstract ▼ Abstract: 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.	Mar 2018
	Adsorption of Methyl Acetoacetate at Ni{111}: Experiment and Theory Jorge Ontaneda , Richard E. J. Nicklin , Alix Cornish , Alberto Roldan , Ricardo Grau-crespo , Georg Held The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.6b10023 Show Abstract ▼ Abstract: The hydrogenation of methyl acetoacetate (MAA) over modified Ni catalysts is one of the most important and best studied reactions in heterogeneous enantioselective catalysis. Yet, very little molecular-level information is available on the adsorption complex of the reactant. Here, we report on a combined experimental and theoretical study of MAA adsorption on Ni{111}. XPS shows that the chemisorbed layer is stable up to 250 K; above 250 K, decomposition sets in. In ultra-high-vacuum conditions, multilayers grow below 150 K. DFT modeling predicts a deprotonated enol species with bidentate coordination on the flat Ni{111} surface. The presence of adatoms on the surface leads to stronger MAA adsorption in comparison with the flat surface, whereby the stabilization energy is high enough for MAA to drive the formation of adatom defects at Ni{111}, assuming the adatoms come from steps. Comparison of experimental XPS and NEXAFS data with theoretical modeling, however, identifies the bidentate deprotonated enol on the flat Ni{111} surface as the dominant species at 250 K, indicating that the formation of adatom adsorption complexes is kinetically hindered at low temperatures.	Nov 2016
	The Partial Oxidation of Methane Over Pd/Al2O3 Catalyst Nanoparticles Studied In-Situ by Near Ambient-Pressure X-ray Photoelectron Spectroscopy Rachel Price , Tugce Eralp-erden , Ethan Crumlin , Sana Rani , Sonia Garcia , Richard Smith , Liam Deacon , Chanan Euaruksakul , Georg Held Topics In Catalysis 59, 516 - 525 DOI: 10.1007/s11244-015-0520-8 Open Access Show Abstract ▼ Abstract: Near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is used to study the chemical state of methane oxidation catalysts in-situ. Al2O3–supported Pd catalysts are prepared with different particle sizes ranging from 4 to 10 nm. These catalysts were exposed to conditions similar to those used in the partial oxidation of methane (POM) to syn-gas and simultaneously monitored by NAP-XPS and mass spectrometry. NAP-XPS data show changes in the oxidation state of the palladium as the temperature increases, from metallic Pd0 to PdO, and back to Pd0. Mass spectrometry shows an increase in CO production whilst the Pd is in the oxide phase, and the metal is reduced back under presence of newly formed H2. A particle size effect is observed, such that CH4 conversion starts at lower temperatures with larger sized particles from 6 to 10 nm. We find that all nanoparticles begin CH4 conversion at lower temperatures than polycrystalline Pd foil.	Mar 2016
	Stereochemistry and thermal stability of tartaric acid on the intrinsically chiral Cu{531} surface Silvia Baldanza , Jacopo Ardini , Angelo Giglia , Georg Held Surface Science 643, 108 - 116 DOI: 10.1016/j.susc.2015.08.021 Show Abstract ▼ Abstract: Intrinsically chiral metal surfaces provide enantiospecific reaction environments without the need of co-adsorbed modifiers. Amongst the intrinsically chiral copper surfaces, Cu{531} has the smallest unit cell and the highest density of chiral sites. XPS, NEXAFS and TPD were employed to investigate the adsorption and decomposition behaviour of the two chiral enantiomers of tartaric acid on this surface. The results obtained from XPS and NEXAFS show that at saturation coverage both enantiomers of tartaric acid adsorb in a μ4 configuration through the two carboxylic groups, which are rotated with respect to each other by 90° ± ≈ 15° within the surface plane. At intermediate coverage the R,R enantiomer adopts a similar configuration, but the S,S enantiomer is different and shows a high degree of dissociation. Growth of multilayers is observed at high exposures when the sample is kept at below 370 K. TPD experiments show that multilayers desorb between 390 K and 470 K and decomposition of the chemisorbed layer occurs between 470 K and 600 K. The desorption spectra support a two-step decomposition mechanism with a Odouble bond; length as m-dashCdouble bond; length as m-dashCdouble bond; length as m-dashO or HO–HCdouble bond; length as m-dashCH–OH intermediate that leads to production of CO2 and CO. Enantiomeric differences are observed in the desorption features related to the decomposition of the chemisorbed layer.	Jan 2016
	Surface Chemistry of Alanine on Ni{111} Richard E. J. Nicklin , Alix Cornish , Andrey Shavorskiy , Silvia Baldanza , Karina Schulte , Zhi Liu , Roger A. Bennett , Georg Held The Journal Of Physical Chemistry C 119 (47), 26566 - 26574 DOI: 10.1021/acs.jpcc.5b08814 Show Abstract ▼ Abstract: The adsorption of l-alanine on Ni{111} has been studied as a model of enantioselective heterogeneous catalysts. Synchrotron-based X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to determine the chemical state, bond coordination, and out-of-plane orientation of the molecule on the surface. Alanine adsorbs in anionic and zwitterionic forms between 250 and ≈320 K. NEXAFS spectra exhibit a strong angular dependence of the π* resonance associated with the carboxylate group, which is compatible with two distinct orientations with respect to the surface corresponding to the bidentate and tridentate binding modes. Desorption and decomposition begin together at ≈300 K, with decomposition occurring in a multistep process up to ≈450 K. Comparison with previous studies of amino acid adsorption on metal surfaces shows that this is among the lowest decomposition temperatures found so far and lower than typical temperatures used for hydrogenation reactions where modified Ni catalysts are used.	Nov 2015
I06-Nanoscience	The atomic structure of low-index surfaces of the intermetallic compound InPd G. Mcguirk , J. Ledieu , E. Gaudry , M. C. De Weerd , M. Hahne , P. Gille , D. C. A. Ivarsson , M. Armbrüster , J. Ardini , G. Held , F. Maccherozzi , A. Bayer , M. Lowe , K. Pussi , R. D. Diehl , V. Fournee The Journal Of Chemical Physics 143 (7) DOI: 10.1063/1.4928650 PMID: 26298146 Diamond Proposal Number(s): [8821] Show Abstract ▼ Abstract: The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and “global” measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature	Aug 2015

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