Publications

Another installment in the annals of the bullying of the Shockley surface state, this time the trick isn’t exotic adatoms or massive molecular weight, just a 120° tilt of hexaazatriphenylene (HAT) ligands that converts an achiral lattice into a pair of enantiomeric 2-D metal–organic frameworks. The result: chirality-imposed scattering potentials that lift degeneracies and open ΔE ≈ 80 meV gaps in the Ag(111) two-dimensional electron gas while leaving the global periodicity intact. ...

Jules has put in the hard yards implementing nanonisTCP as a python module, and leveraged that to create scanbot, a tool for automating the tasks of preparing a good imaging & spectroscopy probe, as well as a suite of functions for performing nuanced, drift-corrected measurements over very long timescales. See the below example of systematically grid scanning 100x100nm images to concatenate a comprehensive view of the surface. Right is the upper left red corner, where self-assembled molecular islands are visible. ...

Ben & Bernard’s work on the two-dimensional kagome metal-organic framework is out this week (26 April 2024) in Nature Comms. It was fantastic to see interesting electronic properties emerge at relatively big energy scales for this sort of work, when we were finally able to get the 2d kagome MOF composed of Cu adatoms & DCA molecules, to self-assemble on insulating hexagonal boron nitride (hBN) supported by a Cu111 metallic substrate. We teamed up with Ben Powell’s group at UQ for the many-body expertise required to understand the tunnel junction and substrate work function dependent modulations of the electronic gap in the language of Mott physics. ...

While pursuing metal-organic frameworks, we stumbled on something unexpected but experimentally robust back in June of 2019. DCA molecules and Au adatoms on Ag111 form DCA-Au-DCA units, and the cyano groups aren’t involved as you’d intuitively expect. It took some heroic effort and creative thinking from Adam & the team in Prague to “just run this one through the computer real quick”, but nonetheless we’re pleased to have this explanation of the selective C-H scisson necessary to justify the observed end products. ...

We had the opportunity to use the new toroidal analyzer at the Australian synchrotron to do ARPES of self-assembled monolayers of MgPc on Ag100. Careful simultaneous fitting of different high-symmetry EDC measurements, in concert with the structural understanding gleaned from ncAFM & LEED characterization, allowed us to tease out a feature with bandwidth 20 meV, which was surprising to us given that we did the ARPES at room temperature. ...

9-azidophenanthrene produces a rich manifold of products when deposited on Ag(111). The images we took for this study inspired this work to develop a lightweight script to count the molecules we observed, and categorize them. Our personal journey of computer vision rediscovery led us to Zernike moments, a rotationally invariant basis set that solves the problem of identifying the same molecules with relative rotations, in an image. We put some effort into making this module user-friendly, the example scripts offer a reasonable template to apply to any old SXM file you might want to histogram. ...

Dhaneesh Kumar has extensively studied the on-surface properties of the DCA molecule for his PhD. After getting a good handle on just the DCA on Ag111, we started sprinkling some Cu atoms into the mix. We observed the same honeycomb kagome structure that forms on Cu111– as seen in an ncAFM force volume shown in the right image. It has also been synthesized on graphene. The key difference we observed on Ag111 was the Kondo effect, an STS peak at Fermi we tracked up to 150 K! The consistent spatial distribution of this feature across the MOF was another key observation. ...

We stumbled on a very curious observation in the summer of 2018 with DABQDI molecules provided by Olivier Siri‘s team. ncAFM image of 26 molecule chain. Unfiltered data. Repeated manipulations with STM tip are capable of dragging a DABQDI chain around the Au111 surface. While evaluating its experimental suitability for 1d coordination with metals, which has already proven to be fruitful, we noticed the molecules forming chain-like structures even before we introduced metal adatoms. The low temperature SPM results are sublime: unusual mechanical stability, distinctive intermolecular bonding, and near-Fermi electronic states lighting up at the ends of the chains. ...

nc-AFM atomic registration of single MgPc molecule on Ag100 (surface atoms top and bottom stripes) Marina Castelli studied the phthalocyanine containing magnesium (MgPc) via 5K scanned probe microscopies extensively during her PhD. ‘Routine’ STM characterisation showed that the molecules were interacting with one another on the Ag100 surface. ncAFM showed identical contrast for all molecules, pointing to an electronic origin to the observed changes in appearance. Our key observation was to track the shape of the occupied LUMO for different pairwise distances, an electronic feature that otherwise remained isoenergetic. ...

Iolanda DiBernardo reviewed the development of Na3Bi as a topological electronic material. The physics of Dirac semimetals (“3d graphene”) is introduced, and the results from the last half decade are tied together in one narrative, in particular our work at Monash demonstrating that Na3Bi grows directly on insulators, and that indeed an electric field will open a topological gap, two key ingredients to achieving a working “topological transistor”. “Progress in Epitaxial Thin‐Film Na3Bi as a Topological Electronic Material”, Advanced Materials, 2021. 10.1002/adma.202005897 ...