CRITICAL MATERIALS
Characterization of just one atom using synchrotron X-rays
Physics World reveals its top 10 Breakthroughs of the Year for 2023.
- In this paper published in Nature, a multi-institutional team of scientists set a new standard for X-rays on the microscopic level, characterizing a single atom for the first time. The co-authors included Tomas Rojas, Naveen Dandu and Anh Ngo of University of Illinois Chicago. Image adapted from our publication in Nature.
- When X-rays (blue color) illuminate onto an iron atom (red ball at the center of the molecule), core-level electrons are excited. X-ray excited electrons then tunnel to the detector tip (gray) via overlapping atomic/molecular orbitals, which provide elemental and chemical information of the iron atom.
A chiral molecular propeller designed for unidirectional rotations on a surface
- Synthetic molecular machines designed to operate on materials surfaces can convert energy into motion and they may be useful to incorporate into solid state devices.
- To understand the observed molecular propeller structure on Au(111) surface by experimentalist Saw et. al., we have performed density functional theory (DFT) calculations. Geometrically relaxed calculations reveal that the Cp ring of the stator is located 3.7 Å above the top surface layer of Au(111), and the binding of the stator to the Au(111) surface stabilizes the tilting of the phenyl-rings.
- The DFT calculation further reveals that rotation of the propeller blade alters the tilt angle of the phenyl rings. Here, when the propeller blade is approached towards the phenyl ring, its tilt angle becomes smaller.
- Our work is published in Nature Communications volume 10, Article number: 3742 (2019). Image is adapted from this citation.
Intra- and intermolecular self-assembly of a 20-nm-wide supramolecular hexagonal grid
- Figure represents DFT calculations. a, Projected Density of States (PDOS) of the Fe and Ru atoms in the hexagonal ring. b, The HOMO and c, the LUMO orbitals of the hexagonal ring. Insets show the HOMO and LUMO orbitals around Ru and Fe atoms. Figure adapted from Nat Chem. 2020 Jun;12(6):579. doi: 10.1038/s41557-020-0486-4.
- Theoretical Bandgap Differentiation: Fe(II): Calculated band gap = 2.4 eV and Ru(II): Calculated band gap = 2.8 eV
- These results are in excellent agreement with experimental STS measurements: Fe(II): Experimental HOMO–LUMO gap ≈ 2.4–2.5 eV and Ru(II): Experimental HOMO–LUMO gap ≈ 2.8–2.9 eV
- This gap difference allows unambiguous assignment of metal centers on STM-imaged grids.
- The theoretical PDOS confirmed distinct spectral fingerprints for Fe(II) and Ru(II).
- Fe(II) centers, with higher magnetic moments, were predicted to exhibit stronger Kondo resonances due to localized spin-electron interactions—consistent with STS features and DFT magnetic predictions.
Our publications related to Critical Materials Research
- Daniel J Trainer, Kyaw Zin Latt, Xinyue Cheng, Naveen Kumar Dandu, Larry A Curtiss, Sergio E Ulloa, Anh T. Ngo, Eric Masson, Saw Wai Hla Gating Single Molecules with Counterions. ACS nano 19 (16), 15272-15280 (2025).
- Daniel Trainer, Alex Taekyung Lee, Sanjoy Sarkar, Vijay Singh, Xinyue Cheng, Naveen K Dandu, Kyaw Zin Latt, Shaoze Wang, Tolulope Michael Ajayi, Sineth Premarathna, David Facemyer, Larry A Curtiss, Sergio E Ulloa, Anh T. Ngo , Eric Masson, Saw Wai Hla. 2D Ionic Liquid-Like State of Charged Rare-Earth Clusters on a Metal Surface. Advanced Science, 2308813 (2024).
- Tolulope M Ajayi, et, al. , Anh T. Ngo, Saw-Wai Hla. Characterization of just one atom using synchrotron X-rays. Nature 618, 69–73 (2023).
- Zhe Zhang, Yiming Li, Bo Song, Yuan Zhang, Xin Jiang, Ming Wang, Ryan Tumbleson, Changlin Liu, Pingshan Wang, Xin-Qi Hao, Tomas Rojas, Anh T. Ngo, Jonathan L Sessler, George R Newkome, Saw Wai Hla, Xiaopeng Li . “ Intra-and intermolecular self-assembly of a 20-nm-wide supramolecular hexagonal grid” Nature Chemistry 12, 468–474 (2020).
- Yuan Zhang, Jan Patrick Calupitan, Tomas Rojas, Ryan Tumbleson, Guillaume Erbland, Claire Kammerer, Tolulope Michael Ajayi, Shaoze Wang, Larry A Curtiss, Anh T. Ngo, Sergio E Ulloa, Gwénaël Rapenne, Saw Wai Hla. “ A chiral molecular propeller designed for unidirectional rotations on a surface” Nature Communications 10, 3742 (2019).
- Yang Li, Anh T. Ngo, Andrew DiLullo, Kyaw Zin Latt, Heath Kersell, Brandon Fisher, Peter Zapol, Sergio E Ulloa, Saw-Wai Hla. “ Anomalous Kondo resonance mediated by semiconducting graphene nanoribbons in a molecular heterostructure ” Nature Communications 8, 946 (2017).