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17 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Probing the dye–semiconductor interface in dye-sensitized NiO solar cells Nathan T. Z. Potts , Tamara Sloboda , Maria Wächtler , Ruri Agung Wahyuono , Valeria D’annibale , Benjamin Dietzek , Ute B. Cappel , Elizabeth A. Gibson The Journal Of Chemical Physics 153 DOI: 10.1063/5.0023000 Diamond Proposal Number(s): [18517, 22807] Show Abstract ▼ Abstract: The development of p-type dye-sensitized solar cells (p-DSSCs) offers an opportunity to assemble tandem photoelectrochemical solar cells with higher efficiencies than TiO2-based photoanodes, pioneered by O’Regan and Grätzel [Nature 353, 737–740 (1991)]. This paper describes an investigation into the behavior at the interfaces in p-DSSCs, using a series of BODIPY dyes, BOD1-3. The three dyes have different structural and electronic properties, which lead to different performances in p-DSSCs. We have applied photoelectron spectroscopy and transient absorption spectroscopy to rationalize these differences. The results show that the electronic orbitals of the dyes are appropriately aligned with the valence band of the NiO semiconductor to promote light-induced charge transfer, but charge-recombination is too fast for efficient dye regeneration by the electrolyte. We attribute this fast recombination, which limits the efficiency of the solar cells, to the electronic structure of the dye and the presence of Ni3+ recombination sites at the NiO surface.	Nov 2020
I07-Surface & interface diffraction	Structure of two-dimensional Fe3O4 Lindsay R. Merte , Pär A. T. Olsson , Mikhail Shipilin , Johan Gustafson , Florian Bertram , Chu Zhang , Henrik Grönbeck , Edvin Lundgren The Journal Of Chemical Physics 152 DOI: 10.1063/1.5142558 Diamond Proposal Number(s): [10342] Show Abstract ▼ Abstract: We have investigated the structure of an ultrathin iron oxide phase grown on Ag(100) using surface x-ray diffraction in combination with Hubbard-corrected density functional theory (DFT+U) calculations. The film exhibits a novel structure composed of one close-packed layer of octahedrally coordinated Fe2+ sandwiched between two close-packed layers of tetrahedrally coordinated Fe3+ and an overall stoichiometry of Fe3O4. As the structure is distinct from bulk iron oxide phases and the coupling with the silver substrate is weak, we propose that the phase should be classified as a metastable two-dimensional oxide. The chemical and physical properties are potentially interesting, thanks to the predicted charge ordering between atomic layers, and analogy with bulk ferrite spinels suggests the possibility of synthesis of a whole class of two-dimensional ternary oxides with varying electronic, optical, and chemical properties.	Mar 2020
I09-Surface and Interface Structural Analysis	Probing structural changes upon carbon monoxide coordination to single metal adatoms P. T. P. Ryan , M. Meier , Z. Jakub , J. Balajka , J. Hulva , D. J. Payne , T.-l. Lee , C. Franchini , F. Allegretti , G. S. Parkinson , D. A. Duncan The Journal Of Chemical Physics 152 DOI: 10.1063/1.5137904 Diamond Proposal Number(s): [13817] Open Access Show Abstract ▼ Abstract: In this work, the adsorption height of Ag adatoms on the Fe3O4(001) surface after exposure to CO was determined using normal incidence x-ray standing waves. The Ag adatoms bound to CO ( Ag CO 1 Ag1CO ) are found to be pulled out of the surface to an adsorption height of 1.15 Å ± 0.08 Å, compared to the previously measured height of 0.96 Å ± 0.03 Å for bare Ag adatoms and clusters. Utilizing DFT+vdW+U calculations with the substrate unit cell dimension fixed to the experimental value, the predicted adsorption height for Ag CO 1 Ag1CO was 1.16 Å, in remarkably good agreement with the experimental results.	Feb 2020
I15-Extreme Conditions	Experimental and simulation study of the high-pressure behavior of squalane and poly-α-olefins Iain J. Prentice , Xiaojiao Liu , Oleg A. Nerushev , Sashi Balakrishnan , Colin Pulham , Philip J. Camp The Journal Of Chemical Physics 152 DOI: 10.1063/1.5139723 Diamond Proposal Number(s): [193351] Show Abstract ▼ Abstract: The equation of state, dynamical properties, and molecular-scale structure of squalane and mixtures of poly-α-olefins at room temperature are studied with a combination of state-of-the-art, high-pressure experiments and molecular-dynamics simulations. Diamond-anvil cell experiments indicate that both materials are non-hydrostatic media at pressures above ∼1 GPa. The equation of state does not exhibit any sign of a first-order phase transition. High-pressure x-ray diffraction experiments on squalane show that there are no Bragg peaks, and hence, the apparent solidification occurs without crystallization. These observations are complemented by a survey of the equation of state and dynamical properties using simulations. The results show that molecular diffusion is essentially arrested above about 1 GPa, which supports the hypothesis that the samples are kinetically trapped in metastable amorphous-solid states. The shear viscosity becomes extremely large at very high pressures, and the coefficient governing its increase from ambient pressure is in good agreement with the available literature data. Finally, simulated radial distribution functions are used to explore the evolution of the molecular-scale structure with increasing pressure. Subtle changes in the short-range real-space correlations are related to a collapse of the molecular conformations with increasing pressure, while the evolution of the static structure factor shows excellent correlation with the available x-ray diffraction data. These results are of indirect relevance to oil-based lubricants, as the pressures involved are comparable to those found in engines, and hence, the ability of lubricating thin films to act as load-bearing media can be linked to the solidification phenomena studied in this work.	Feb 2020
I06-Nanoscience	Photoemission core level binding energies from multiple sized nanoparticles on the same support: TiO 2 (110)/Au Andrew Mellor , Axel Wilson , Chi L. Pang , Chi M. Yim , Francesco Maccherozzi , Sarnjeet S. Dhesi , Christopher A. Muryn , Hicham Idriss , Geoff Thornton The Journal Of Chemical Physics 152 DOI: 10.1063/1.5135760 Diamond Proposal Number(s): [13723] Show Abstract ▼ Abstract: A novel method of measuring the core level binding energies of multiple sized nanoparticles on the same substrate is demonstrated using the early stage of Au nanoparticle growth on reduced r-TiO2(110). This method employed in situ scanning tunneling microscopy (STM) and microfocused X-ray photoemission spectroscopy. An STM tip-shadowing method was used to synthesize patterned areas of Au nanoparticles on the substrate with different coverages and sizes. Patterns were identified and imaged using a UV photoelectron emission microscope. The Au 4f core level binding energies of the nanoparticles were investigated as a function of Au nanoparticle coverage and size. A combination of initial and final state effects modifies the binding energies of the Au 4f core levels as the nanoparticle size changes. When single Au atoms and Au3 clusters are present, the Au 4f7/2 binding energy, 84.42 eV, is similar to that observed at a high coverage (1.8 monolayer equivalent), resulting from a cancellation of initial and final state effects. As the coverage is increased, there is a decrease in binding energy, which then increases at a higher coverage to 84.39 eV. These results are consistent with a Volmer-Weber nucleation-growth model of Au nanoparticles at oxygen vacancies, resulting in electron transfer to the nanoparticles.	Jan 2020
I09-Surface and Interface Structural Analysis	Type-II heterostructures of α -V 2 O 5 nanowires interfaced with cadmium chalcogenide quantum dots: Programmable energetic offsets, ultrafast charge transfer, and photocatalytic hydrogen evolution Saurabh Chauhan , Aaron Sheng , Junsang Cho , Sara Abdel Razek , Nuwanthi Suwandaratne , Matthew Y. Sfeir , Louis F. J. Piper , Sarbajit Banerjee , David F. Watson The Journal Of Chemical Physics 151 DOI: 10.1063/1.5128148 Diamond Proposal Number(s): [22148] Show Abstract ▼ Abstract: We synthesized a new class of heterostructures by depositing CdS, CdSe, or CdTe quantum dots (QDs) onto α-V2O5 nanowires (NWs) via either successive ionic layer adsorption and reaction (SILAR) or linker-assisted assembly (LAA). SILAR yielded the highest loadings of QDs per NW, whereas LAA enabled better control over the size and properties of QDs. Soft and hard x-ray photoelectron spectroscopy in conjunction with density functional theory calculations revealed that all α-V2O5/QD heterostructures exhibited Type-II band offset energetics, with a staggered gap where the conduction- and valence-band edges of α-V2O5 NWs lie at lower energies (relative to the vacuum level) than their QD counterparts. Transient absorption spectroscopy measurements revealed that the Type-II energetic offsets promoted the ultrafast (10−12–10−11 s) separation of photogenerated electrons and holes across the NW/QD interface to yield long-lived (10−6 s) charge-separated states. Charge-transfer dynamics and charge-recombination time scales varied subtly with the composition of heterostructures and the nature of the NW/QD interface, with both charge separation and recombination occurring more rapidly within SILAR-derived heterostructures. LAA-derived α-V2O5/CdSe heterostructures promoted the photocatalytic reduction of aqueous protons to H2 with a 20-fold or greater enhancement relative to isolated colloidal CdSe QDs or dispersed α-V2O5 NWs. The separation of photoexcited electrons and holes across the NW/QD interface could thus be exploited in redox photocatalysis. In light of their programmable compositions and properties and their Type-II energetics that drive ultrafast charge separation, the α-V2O5/QD heterostructures are a promising new class of photocatalyst architectures ripe for continued exploration.	Dec 2019
E02-JEM ARM 300CF	Decoration of plasmonic Mg nanoparticles by partial galvanic replacement Jérémie Asselin , Christina Boukouvala , Yuchen Wu , Elizabeth R. Hopper , Sean M. Collins , John S. Biggins , Emilie Ringe The Journal Of Chemical Physics 151 DOI: 10.1063/1.5131703 Diamond Proposal Number(s): [21980] Show Abstract ▼ Abstract: Plasmonic structures have attracted much interest in science and engineering disciplines, exploring a myriad of potential applications owing to their strong light-matter interactions. Recently, the plasmonic concentration of energy in subwavelength volumes has been used to initiate chemical reactions, for instance by combining plasmonic materials with catalytic metals. In this work, we demonstrate that plasmonic nanoparticles of earth-abundant Mg can undergo galvanic replacement in a nonaqueous solvent to produce decorated structures. This method yields bimetallic architectures where partially oxidized 200–300 nm Mg nanoplates and nanorods support many smaller Au, Ag, Pd, or Fe nanoparticles, with potential for a stepwise process introducing multiple decoration compositions on a single Mg particle. We investigated this mechanism by electron-beam imaging and local composition mapping with energy-dispersive X-ray spectroscopy as well as, at the ensemble level, by inductively coupled plasma mass spectrometry. High-resolution scanning transmission electron microscopy further supported the bimetallic nature of the particles and provided details of the interface geometry, which includes a Mg oxide separation layer between Mg and the other metal. Depending on the composition of the metallic decorations, strong plasmonic optical signals characteristic of plasmon resonances were observed in the bulk with ultraviolet-visible spectrometry and at the single particle level with darkfield scattering. These novel bimetallic and multimetallic designs open up an exciting array of applications where one or multiple plasmonic structures could interact in the near-field of earth-abundant Mg and couple with catalytic nanoparticles for applications in sensing and plasmon-assisted catalysis.	Dec 2019
	Interaction of hydrogen with actinide dioxide (111) surfaces James T. Pegg , Ashley E. Shields , Mark T. Storr , David O. Scanlon , Nora H. De Leeuw The Journal Of Chemical Physics 150 DOI: 10.1063/1.5087577 Show Abstract ▼ Abstract: The interaction of atomic and molecular hydrogen with actinide dioxide (AnO2, An = U, Np, Pu) (111) surfaces has been investigated by DFT+U, where noncollinear 3k antiferromagnetic behaviour and spin-orbit interactions are considered. The adsorption of atomic hydrogen forms a hydroxide group, coupled to the reduction of an actinide ion. The energy of atomic hydrogen adsorption on the UO2 (0.82 eV), NpO2 (−0.10 eV), and PuO2 (−1.25 eV) surfaces has been calculated. The dissociation of molecular hydrogen is not observed, shown to be due to kinetic rather than thermodynamic factors. As a barrier to the formation of a second hydroxyl group, an unusual charge distribution has been shown. This could be a limitation of a (1·1) unit cell method or an artefact of the systems. The recombination of hydrogen ions on the AnO2 (111) surfaces is favoured over hydroxide formation.	Apr 2019
I07-Surface & interface diffraction	Molecular structure of the substrate-induced thin-film phase of tetracene Linus Pithan , Dmitrii Nabok , Caterina Cocchi , Paul Beyer , Giuliano Duva , Joseph Simbrunner , Jonathan Rawle , Chris Nicklin , Peter Schäfer , Claudia Draxl , Frank Schreiber , Stefan Kowarik The Journal Of Chemical Physics 149 DOI: 10.1063/1.5043379 Diamond Proposal Number(s): [12895] Show Abstract ▼ Abstract: We present a combined experimental and theoretical study to solve the unit-cell and molecular arrangement of the tetracene thin film (TF) phase. TF phases, also known as substrate induced phases (SIPs), are polymorphs that exist at interfaces and decisively impact the functionality of organic thin films, e.g., in a transistor channel, but also change the optical spectra due to the different molecular packing. As SIPs only exist in textured ultrathin films, their structure determination remains challenging compared to bulk materials. Here, we use grazing incidence X-ray diffraction and atomistic simulations to extract the TF unit-cell parameters of tetracene together with the atomic positions within the unit-cell.	Oct 2018
I22-Small angle scattering & Diffraction	Not just fractal surfaces, but surface fractal aggregates: Derivation of the expression for the structure factor and its applications Rogier Besselink , Tomasz Stawski , Alexander E. S. Van Driessche , Liane G Benning The Journal Of Chemical Physics 145 DOI: 10.1063/1.4960953 Diamond Proposal Number(s): [9904] Open Access Show Abstract ▼ Abstract: Densely packed surface fractal aggregates form in systems with high local volume fractions of particles with very short diffusion lengths, which effectively means that particles have little space to move. However, there are no prior mathematical models, which would describe scattering from such surface fractal aggregates and which would allow the subdivision between inter- and intraparticle interferences of such aggregates. Here, we show that by including a form factor function of the primary particles building the aggregate, a finite size of the surface fractal interfacial sub-surfaces can be derived from a structure factor term. This formalism allows us to define both a finite specific surface area for fractal aggregates and the fraction of particle interfacial sub-surfaces at the perimeter of an aggregate. The derived surface fractal model is validated by comparing it with an ab initio approach that involves the generation of a “brick-in-a-wall” von Koch type contour fractals. Moreover, we show that this approach explains observed scattering intensities from in situ experiments that followed gypsum (CaSO4 ⋅ 2H2O) precipitation from highly supersaturated solutions. Our model of densely packed “brick-in-a-wall” surface fractal aggregates may well be the key precursor step in the formation of several types of mosaic- and meso-crystals.	Dec 2016

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