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Instruments / Technical Area	Publication Details	Published	Actions
I09-Surface and Interface Structural Analysis	Atomic-scale structure of chemically distinct surface oxygens in redox reactions Anusheela Das , Haesun Park , Yanna Chen , Devika Choudhury , Tien-Lin Lee , Jeffrey W. Elam , Peter Zapol , Michael J. Bedzyk Journal Of The American Chemical Society DOI: 10.1021/jacs.1c07926 Diamond Proposal Number(s): [15748] Show Abstract ▼ Abstract: During redox reactions, oxide-supported catalytic systems undergo structural and chemical changes. Improving subsequent catalytic properties requires an understanding of the atomic-scale structure with chemical state specificity under reaction conditions. For the case of 1/2 monolayer vanadia on α-TiO2(110), we use X-ray standing wave (XSW) excited X-ray photoelectron spectroscopy to follow the redox induced atomic positional and chemical state changes of this interface. While the resulting XSW 3D composite atomic maps include the Ti and O substrate atoms and V surface atoms, our focus in this report is on the previously unseen surface oxygen species with comparison to density functional theory predictions.	Oct 2021
I07-Surface & interface diffraction	Dye nanoaggregate structures in MK-2, N3, and N749 dye…TiO2 interfaces that represent dye-sensitized solar cell working electrodes Ke Deng , Jacqueline M. Cole , Jonathan L. Rawle , Christopher Nicklin , Hao Chen , Angel Yanguas-Gil , Jeffrey W. Elam , Gavin B. G. Stenning Acs Applied Energy Materials DOI: 10.1021/acsaem.9b02002 Diamond Proposal Number(s): [15487] Show Abstract ▼ Abstract: The working electrode of a dye-sensitized solar cell (DSSC) consists of dye molecules adsorbed onto nanoparticles of a semiconductor such as TiO2. A reliable prediction of the DSSC photovoltaic performance of a given dye requires in-depth knowledge about the precise structure of the dye···TiO2 interface. X-ray reflectometry (XRR) and grazing-incidence small angle X-ray scattering (GISAXS) are herein employed to determine the dye···TiO2 interfacial structure and associated dye aggregation behavior of three high-performance DSSC dyes: an organic metal-free dye, MK-2, and the two archetypal ruthenium-based organometallic dyes, N3, and N749 (Black Dye). Results show that all three dyes form nanoaggregates in dye···TiO2 interfaces. We determine the dye nanoaggregate separations, sizes, distribution densities and the extent of short-range order within each dye self-assembly in the longitudinal and lateral directions. Dye···TiO2 composites fabricated using dye solutions of varying concentrations are analyzed. We find that nanoaggregates of the three dyes are separated by several hundred nanometers (158-203 nm) in dye···TiO2 interfaces that have been fabricated using concentrated dye solutions (0.5 mM or 1.0 mM). MK-2 and N749 dyes also display smaller inter-particle separations. Dye nanoparticle diameters are of the order of 156-198 nm, sizes that are comparable to the largest inter-particle separations. Thus, no extraneous dye particles can be fitted into gaps between particles, so the dye self-assembly is saturated. Self-assemblies of all three dyes exhibit both lateral and longitudinal short-range order; N3 displays a particularly short coherence length along the TiO2 surface, with extensive structured disorder along the longitudinal direction. The operation of DSSC working electrodes would therefore seem to be dependent on a dye self-assembly that may exhibit several levels of structural granularity and dye aggregation effects.	Dec 2019

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I09-Surface and Interface Structural Analysis

Atomic-scale structure of chemically distinct surface oxygens in redox reactions

Anusheela Das , Haesun Park , Yanna Chen , Devika Choudhury , Tien-Lin Lee , Jeffrey W. Elam , Peter Zapol , Michael J. Bedzyk

Journal Of The American Chemical Society

DOI: 10.1021/jacs.1c07926

Diamond Proposal Number(s): [15748]

Show Abstract ▼

Oct 2021

I07-Surface & interface diffraction

Dye nanoaggregate structures in MK-2, N3, and N749 dye…TiO2 interfaces that represent dye-sensitized solar cell working electrodes

Ke Deng , Jacqueline M. Cole , Jonathan L. Rawle , Christopher Nicklin , Hao Chen , Angel Yanguas-Gil , Jeffrey W. Elam , Gavin B. G. Stenning

Acs Applied Energy Materials

DOI: 10.1021/acsaem.9b02002

Diamond Proposal Number(s): [15487]

Show Abstract ▼

Abstract: The working electrode of a dye-sensitized solar cell (DSSC) consists of dye molecules adsorbed onto nanoparticles of a semiconductor such as TiO2. A reliable prediction of the DSSC photovoltaic performance of a given dye requires in-depth knowledge about the precise structure of the dye···TiO2 interface. X-ray reflectometry (XRR) and grazing-incidence small angle X-ray scattering (GISAXS) are herein employed to determine the dye···TiO2 interfacial structure and associated dye aggregation behavior of three high-performance DSSC dyes: an organic metal-free dye, MK-2, and the two archetypal ruthenium-based organometallic dyes, N3, and N749 (Black Dye). Results show that all three dyes form nanoaggregates in dye···TiO2 interfaces. We determine the dye nanoaggregate separations, sizes, distribution densities and the extent of short-range order within each dye self-assembly in the longitudinal and lateral directions. Dye···TiO2 composites fabricated using dye solutions of varying concentrations are analyzed. We find that nanoaggregates of the three dyes are separated by several hundred nanometers (158-203 nm) in dye···TiO2 interfaces that have been fabricated using concentrated dye solutions (0.5 mM or 1.0 mM). MK-2 and N749 dyes also display smaller inter-particle separations. Dye nanoparticle diameters are of the order of 156-198 nm, sizes that are comparable to the largest inter-particle separations. Thus, no extraneous dye particles can be fitted into gaps between particles, so the dye self-assembly is saturated. Self-assemblies of all three dyes exhibit both lateral and longitudinal short-range order; N3 displays a particularly short coherence length along the TiO2 surface, with extensive structured disorder along the longitudinal direction. The operation of DSSC working electrodes would therefore seem to be dependent on a dye self-assembly that may exhibit several levels of structural granularity and dye aggregation effects.

Dec 2019

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