X-ray spectroscopy delivers strong impact across the physical and biological sciences by providing end users with highly detailed information about the electronic and geometric structure of matter. To decode this information in challenging cases, e.g., in operando catalysts, batteries, and temporally evolving systems , advanced theoretical calculations are necessary. The complexity and resource requirements often render these out of reach for end users, and therefore, the data are often not interpreted exhaustively, leaving a wealth of valuable information unexploited. In this talk, I will discuss our recently developed method based upon supervised machine learning of X-ray absorption spectra through the development of a deep neural network (DNN) . This DNN is able to estimate Fe K-edge X-ray absorption near-edge structure spectra in less than a second with no input beyond geometric information about the local environment of the absorption site. We predict peak positions with sub-eV accuracy and peak intensities with errors over an order of magnitude smaller than the spectral variations that the model is engineered to capture. I will also discuss its extension to other absorption edges, the properties of the network and also highlights areas on which future developments should focus.
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C. D. Rankine, M. M. M. Madkhali, and T. J. Penfold J. Phys. Chem. A 2020, 124, 21, 4263?4270
This presentation will take place at 6 pm Monday, Seattle (Los Angeles) time / 9 am Tuesday, Beijing time using Zoom. For the Zoom link and password, visit https://tinyurl.com/XAFStalks within 30 minutes of the beginning of the presentation.
The Linac Coherent Light Source (LCLS) upgrade to a high repetition source offers new avenues to pump/probe X-ray spectroscopies. Here I will briefly introduce the new capabilities of the LCLS focusing on the Tender X-ray Instrument (TXI). The TXI instrument is a dual-beam instrument, fed by both the soft X-ray and hard X-ray undulators of LCLS; a feature currently unique among XFEL instruments. The tender x-ray instrument will enable x-ray pump/x-ray probe techniques especially in the emerging field of nonlinear x-ray science, support tender X-ray spectroscopy measurements, and provide a coherent scattering/ forward diffraction instrument for sub-micron samples. It is designed to accommodate a variety of additional techniques, such as absorption and photoemission spectroscopy, as well as an array of samples from fixed targets to gases, aerosols, and liquid jet targets.
Extraterrestrial materials such as meteorites and interplanetary dust particles are often very complex and non-uniform, with diverse species within a small sample. In some cases, especially for the products of sample-return missions, the available samples are small and precious. X-ray micro- and nano-spectroscopy are ideal complements to other methods such as TEM and nano-SIMS. In this talk, I will review several examples from the literature showing how X-ray spectromicroscopy has been used to study extraterrestrial materials and infer their histories of formation and alteration. I will also review some experimental techniques, especially STXM.
Sandford, Scott A., et al. “Organics captured from comet 81P/Wild 2 by the Stardust spacecraft.” Science 314, no. 5806 (2006): 1720-1724.
Lo, Yuan Hung, et al. “Multimodal x-ray and electron microscopy of the Allende meteorite.” Science advances 5, no. 9 (2019): eaax3009.
Van Aken, P. A., and B. Liebscher. “Quantification of ferrous/ferric ratios in minerals: new evaluation schemes of Fe L 23 electron energy-loss near-edge spectra.” Physics and Chemistry of Minerals 29, no. 3 (2002): 188-200.
Hefei Light Source (HLS) is the first dedicated synchrotron radiation facility in China with electron ring energy of 0.8 Gev, which is located on the West Campus of the University of Science and Technology of China (USTC). With the completion of twice constructions and recent upgradation, HLS become a fully upgraded soft X-ray synchrotron radiation facility, now operating ten experimental stations (Infrared Spectroscopy and Microspectroscopy, Combustion and Flame, Mass Spectrometry, Soft X-ray Microscopy, Spectral Radiation Standard and Metrology, Atomic & Molecular Physics, Photoemission Spectroscopy, Catalysis and Surface Science, X-Ray Magnetic Circular Dichroism, Angle-resolved Photoemission Spectroscopy) . The well-designed beamlines and experimental stations at HLS, together with the Shanghai synchrotron Radiation Facility and the Beijing Synchrotron Radiation Facility, allow us to perform cutting edge scientific experiments. Here, I will briefly introduce the soft X-ray endstations at HLS, and present our recent studies based on X-ray absorption techniques. In particular, two progress will be discussed: (1) adopt the rational atom-binding strategy and develop the method of precise nano-confined synthesis, subsequently establish the structure-property relationships in several functional nanomaterials anchored with single atoms by combining synchrotron XAS and XPS [2-5]; (2) propose the controllable ion-intercalating and ion-exchanging strategies and develop the method of in-situ reconstructed synthesis, eventually clarify the working mechanism of cation-/anion-modulated functional nanomaterials by the means of operando XAS with synchrotron-on-line devices[6-9].
Achieving Efficient Alkaline Hydrogen Evolution Reaction over a Ni5P4 Catalyst Incorporating Single-Atomic Ru Sites, Advanced Materials, 2020, 32:1906972. https://doi.org/10.1002/adma.201906972
Electrochemical Conversion of CO2 to Syngas with Controllable CO/H2 Ratios over Co and Ni Single-Atom Catalysts, Angewandte Chemie International Edition, 2020, 59:3033-3037. https://doi.org/10.1002/anie.201912719
Stable Metallic 1T-WS2 Nanoribbons Intercalated with Ammonia Ions: The Correlation between Structure and Electrical/Optical Properties, Advanced Materials, 2015, 27:4837-4844. https://doi.org/10.1002/adma.201502134
Coherent X-ray scattering (diffraction) methods will be key to exploiting the high coherent flux of 4th generation synchrotron sources. Ptychography is a coherent diffraction technique that allows rapid, reliable inversion of arrays of diffraction images into real space images by using overlapping spatial areas to constrain the reconstruction . While ptychography is quite well developed in the hard X-ray regime and in electron and optical microscopy, the implementation of soft X-ray ptychography is in its infancy. Soft X-ray ptychography is a coherent diffraction imaging technique readily implemented in Scanning Transmission X-ray Microscopy (STXM) . 4D imaging by soft X-ray ptychography – chemically specific, quantitative 3D mapping of nanostructures can provide insight into the physical and chemical properties. By measuring spectro-ptycho-tomography – 2D ptychographic images at multiple photon energies and multiple tilt angles – 3D chemical distribution can be derived .
Shapiro D A, Yu Y S, Tyliszczak T, et al. Chemical composition mapping with nanometre resolution by soft X-ray microscopy. Nature Photonics, 2014, 8(10): 765-769.
Wu J, Zhu X, Shapiro D A, et al. Four-dimensional imaging of ZnO-coated alumina aerogels by scanning transmission X-ray microscopy and ptychographic tomography. The Journal of Physical Chemistry C, 2018, 122(44): 25374-25385. https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.8b07363
W. Jumpathong et al., Exploitation of missing linker in Zr-based metal-organic framework as the catalyst support for selective oxidation of benzyl alcohol, APL Mater. 7 (2020), 111109. https://doi.org/10.1063/1.5126077
The solar light-driven splitting of water for hydrogen fuel production is a promising alternative to fossil fuels due to their rapid depletion and concomitant environmental pollution. The design of light-driven devices composed of organic, inorganic or hybrid materials that can mimic natural photosynthetic processes is extremely desirable. An essential component of such systems is the light-harvesting chromophore, analogous to the photosynthetic pigments, which can absorb the energy of the incident photons. Consequently, the light energy is converted into an electronically excited state for the creation of a charge-separated state that helps to generate the required thermodynamic driving force for subsequent catalytic reactions.
Commonly used molecular photosensitizers traditionally contain precious and scarce 4d or 5d transition metals such as Platinum, Ruthenium, Rhenium or Iridium. However, over the past decades, a range of noble metal-free photosensitizers based on earth-abundant metals such as Copper, Chromium, and Zinc appeared, with the aim to bring these light-harvesting molecules into more practical applications. A systematic series novel homo- and heteroleptic Cu(I) photosensitizers based on tetradentate 1,10-phenanthroline ligands of the type X^N^N^X containing two additional donor moieties in the 2,9-position (X = SMe or OMe) were designed. Time-resolved X-ray absorption spectroscopy in the picosecond time scale, coupled with time-dependent density functional theory calculations, provided in-depth information on the excited state electron configurations. For the first time, a significant shortening of the Cu-X distance and a change in the coordination mode to a pentacoordinated geometry is shown in the excited states of the two homoleptic complexes. These findings are important with respect to a precise understanding of the excited state structures and a further stabilization of this type of photosensitizers. This talk will further demonstate the reaction pathways of several cobalt and nickel-based hydrogen evolving complexes, examined in unprecedented detail with picosecond time resolution when coupled with copper and ruthenium-based photosensitizers. Results shown will enable the rational design of molecular hydrogen-evolving photocatalysts that can perform beyond the current microsecond time scale, and suggest ways in which the ligand structures can be adjusted to facilitate protonation and catalytic efficiency.
The Australian XAFS community started from small beginnings and currently, XAFS is one of the most oversubscribed techniques at the Australian Synchrotron. The community has been fostered by access to facilities; initially the Australian National Beamline Facility (ANBF) at the Photon Factory, to more recently the XAS beamline at the Australian Synchrotron. The ANBF was a simple and versatile, non focussed bend magnet beamline, which was retired in ~ 2010. The XAS beamline is a Wiggler based, focussed beamline, with much greater flux and high photon energies, and has been operational since 2007. User demand has resulted in two new beamlines, currently under construction at the Australian Synchrotron – the Medium Energy X-Ray Absorption Spectroscopy Beamlines (MEX 1 and 2). These beamlines share a bend magnet, and are aimed to cover the Tender and medium energy range with differing beamsizes – from microns’s to mm’s. MEX will be equipped with 4 endstations in total, including a microprobe, a 5 crystal Rowland circle spectrometer and a custom low energy X-Ray spectrometer.
I this talk, I will briefly describe the past, present and the bright future of XAFS in the Australian context. I will briefly summarise the ANBF, the capabilities and performance of the XAS beamline and highlight the scientific opportunities and complementary nature of the new MEX beamlines.
Single atoms catalysts (SACs) have been heavily investigated in the recent years because of their good catalytic properties (especially activity and selectivity) for many chemical reactions . In addition to that, in SACs, the supported metals are used with extremely high efficiency compared to their nano counterparts. That is very important for noble metals, which are naturally scare yet widely used in industry for a vast number of important chemical reactions. Despite of the progress that has been made, there are fundamental questions remained unaddressed: what is the structure (electronic and atomic) that responsible for the improved catalytic properties? How does the structure respond to the reaction environment? Only by addressing these questions, are we able to improve synthesis processes to get desired catalysts.
The key to address the above-mentioned questions is the capability of characterizing the structure of single atoms catalysts. The challenge originates from: 1) for SACs, the weight loading of single atoms on the support is usually low, 2) the heterogeneity of the single atom sites owing to the surface heterogeneity of most solid supports, and 3) the complex structure of the single atoms system resulted from the strong correlation between the single atoms and the support. This work aimed to address those issues by developing synthesis methods for obtaining homogeneously distributed single atoms with high weight loadings and combining multiple experimental techniques (STEM, DRIFTS, XPS, RIXS, XAS) with calculation methods to study the electronic and atomic structure of single atoms with the presence of strong metal-support interactions. For demonstration, the specific system studied here is ceria supported Pt single atoms .
M. Kottwitz, Y. Li, R. M. Palomino, Z. Liu, Q. Wu, G. Wang, J. Huang, J. Timoshenko, S. D. Senanayake, M. Balasubramanian, D. Lu, R. G. Nuzzo, A. I. Frenkel, Local structure and electronic state of atomically dispersed Pt on nanosized CeO2 support, ACS Catalysis 9, 8738-8748 (2019). https://doi.org/10.1021/acscatal.9b02083
Ion reactions offer a huge playground for tuning the electronic and crystal properties of inorganic solids for energy applications. Our research focuses on resolving a longstanding question in materials electrochemistry regarding redox active solids: how does the mesoscale chemical distribution influence ion reactions at different length scales? Through manipulating the thermodynamics and kinetics of the ion intercalation chemistry, our goal is to develop experimental methodologies and establish novel design principles to enhance the electrochemical properties of ion-intercalating solids for batteries and electrocatalysis. Our studies are largely facilitated by synchrotron X-ray spectroscopic and imaging techniques that provide fundamental insights into intercalation chemistries. In this presentation, we will first highlight our recent progress in understanding and improving electrode materials for lithium and sodium batteries. We design novel synthetic approaches to overcome the surface challenges of oxide cathode materials for high energy density, high power density and long cycle life. Then, we will discuss how we make use of interfacial ion reactions to modulate the electronic properties of water splitting electrocatalysts. We will highlight that tailoring the phase segregation at the catalyst-electrolyte interface constitutes a large space for stabilizing catalytic activity.