Surface Science Session

Surface Science Session

Surface Science Session

Chair: Baran Eren (WIS)

 

10:20-10:40

Leo Gross (IBM Zurich)
Keynote Speaker

Title:
Molecular reactions, charge transitions and excited states investigated by AFM

Abstract:
Atomic force microscopy (AFM) with functionalized tips achieves atomic and bond-resolved resolution providing insights into the structure, aromaticity, charge states and bond-order relations of individual molecules [1]. Importantly for on-surface synthesis, the products and intermediates of chemical reactions can be identified and characterized. Recently, we generated by atom manipulation the elusive carbon allotrope cyclo[18]carbon and resolved its debated structure [2].
On insulating substrates, we can control the charge states of molecules. With ultra-high-resolution imaging we resolve how the charge state of molecules affects their structure [3]. By alternatively attaching and detaching single charges from a molecule on an insulator, we probe transitions between different charge states including neutral excited states and quantify the reorganization energy [4] and singlet and triplet excitation energies [5]. Accessing excited states this way, triplet lifetimes and their quenching by molecular oxygen have been measured recently by J. Peng et al. [6].

 

References
[1] L. Gross et al. Angew. Chem Int. Ed. 57, 3888 (2018)
[2] K. Kaiser et al. Science 365, 1299 (2019)
[3] S. Fatayer et al. Nat. Nano. 13, 376 (2018)
[4] S. Fatayer et al. Science 365, 142 (2019)
[5] S. Fatayer et al. Phys. Rev. Lett. 126, 176801 (2021)
[6] J. Peng et al. Science 373, 452 (2021)

 

10:40-11:00

Martin Castell (Oxford)
Keynote Speaker

Title:
Multiple frame averaging of scanning tunneling microscope images

Abstract:
The resolution of the STM has barely improved since its inception. Only small advances have been achieved through low noise electronics, enhanced vibration damping, and low temperature operation. These incremental gains stand in stark contrast to the advances made with the atomic force microscope (AFM), and it is now possible to take non-contact AFM (nc-AFM) images with intramolecular resolution. The advantage however, that the STM still has over nc-AFM is that the scan speed is typically around two orders of magnitude faster. In effect this means that for the time taken to acquire one nc-AFM image it is possible to acquire around a hundred STM images. This has not been viewed as a particularly significant advantage because operator practice is such that only the best one of these hundred images will be used and the others discarded. However, if all the hundred images are averaged then we would expect a ten-fold improvement in the signal to noise ratio (SNR) as the random noise diminishes with the square root of the number of averaged images. This improved SNR leads to a commensurate increase in the resolving power of the STM. The reason that this kind of multiple frame averaging (MFA) is not performed routinely is that unique and locally varying distortions in each of the images prevent them from being aligned in perfect registry with each other. However, software packages now exist to circumvent these issues [1].  In this presentation I will show how a step change in the resolving power of the STM can be achieved through automated distortion correction and MFA [2]. I will demonstrate the broad utility of this approach with examples from a variety of surfaces. I will show a 6-fold enhancement of the SNR of the Si(111)-(7 × 7) reconstruction, and will demonstrate that images with sub-picometre height precision can be routinely obtained as demonstrated for a monolayer of Ti2O3 on Au(111). I will show automated classification of the two chiral variants of the (4 × 4) reconstructed SrTiO3(111) surface. I will also show how dynamic effects in STM movies can easily be identified using this technique. Our new approach to STM imaging allows a wealth of structural and electronic information from surfaces to be extracted that was previously buried in noise.  

[1]   L. Jones, H. Yang, T.J. Pennycook, M.S.J. Marshall, S.V. Aert, N.D. Browning, M.R. Castell and   

       P.D. Nellist, Advanced Structural and Chemical Imaging, 1, 8 (2015).  
[2]   L. Jones, S. Wang, X. Hu, S.U. Rahman and M.R. Castell, Advanced Structural and Chemical 

       Imaging, 4, 7 (2018).

 

11:00-11:15

Nurit Avraham (WIS)
Invited Speaker

Title:
Visualization of Topological Boundary Modes Manifesting Topological Nodal-Point Superconductivity

Abstract:
Topological superconductors are an essential component for topologically protected quantum computation and information processing. Although signatures of topological superconductivity have been reported in heterostructures, material realizations of intrinsic topological superconductors are rather rare. In my talk I will present scanning tunneling spectroscopy measurements of the transition metal dichalcogenide 4Hb-TaS2, that interleaves superconducting 1H-TaS2 layers with strongly correlated 1T-TaS2 layers, showing spectroscopic evidence for the existence of topological surface superconductivity [1]. These include edge modes running both along 1H layer terminations and under 1T layer terminations, where they separate between superconducting regions of distinct topological nature. We also observe signatures of zero-bias states in vortex cores. All boundary modes exhibit crystallographic anisotropy, which together with a finite in-gap density of states throughout the 1H layers allude to the presence of a topological nodal-point superconducting state. Our theoretical model attributes this phenomenology to an inter-orbital pairing channel that necessitates the combination of surface mirror symmetry breaking and strong interactions.

[1] A. Nayak et. al. Nature physics, November (2021)

 

11:15-11:30

Oded Millo (HUJI)
Invited Speaker

Title:
Magnetic-like states and triplet superconductivity induced in a conventional superconductor upon chiral molecules adsorption

Abstract:
Motivated by our previous scanning tunnelling spectroscopy (STS) works that provide evidence for the emergence of triplet superconductivity at superconductor-ferromagnet interfaces, which will be briefly reviewed, we demonstrate that similar phenomena can be induced on a surface of a conventional superconductor upon chemisorbing non-magnetic chiral molecules. By applying scanning tunneling spectroscopy, we show that the singlet-pairing s-wave order parameter of Nb, NbN and NbSe2 is significantly altered upon the adsorption of chiral polyalanine alpha-helix molecules on the surface. The tunneling spectra exhibit zero-bias conductance peaks embedded inside gaps or gap-like features, suggesting the emergence of a triplet-pairing component, corroborated by fits to theoretical spectra. Conductance spectra measured on devices comprising exfoliated NbSe2 flakes over which these chiral molecules were adsorbed, exhibit, in some cases, in-gap states nearly symmetrically positioned around zero bias. These states shift apart with magnetic field, akin to magnetic-impurity induced Shiba states, as corroborated by theoretical simulations. Other samples show evidence for a collective phenomenon of hybridized Shiba-like states giving rise to unconventional, possibly triplet superconductivity, manifested in the conductance spectra by the appearance of a zero bias conductance peak that diminishes, but does not split, with magnetic field. The transition between these two scenarios appears to be governed by the density of adsorbed molecules. Recent muon spin rotation data indicate the appearance of unconventional Meissner screening and a broken time-reversal state upon the adsorption of these chiral molecules on Nb films, providing further evidence for chiral-induced triplet superconductivity.

 

11:30-11:40

Sidney Cohen (WIS)
Contributed Speaker

Title:
In-situ measurement of the influence of ice-binding proteins on ice growth by atomic force microscopy in aqueous solutions

Abstract:
Besides enabling organisms to thrive in cold environments, ice-binding proteins (IBPs) hold great promise in tissue preservation and food processing. These proteins lower the freezing point by binding to ice surfaces thus inhibiting crystal growth. Despite their importance, the microscopic action of these proteins is largely unknown due to until-now unresolved difficulties of achieving high-resolution, in-situ imaging. We present here a novel system design which enables dynamic atomic force microscopy (AFM) imaging of the ice-IBP system. Two different types of protein systems were studied, one exhibiting moderate ice-growth inhibition, and the other hyperactive inhibition. These proteins bind to different faces of the growing ice crystals, leading to characteristic structures which can be rationalized by the selective inhibition. AFM images reveal such structures at the tens of nm scale for the first time, and will be discussed in relation to previous, lower resolution optical images. Besides revealing the nascent crystal growth, the AFM was used to create mappings of local adhesion which gave insights on the location of protein binding.
In order to achieve these results, several challenges had to be overcome including moderating and controlling heating from the AFM head and detection laser, preventing cantilever freezing, and isolating and monitoring the boundary between liquid and solid as observed at the growing ice front. Using the new set-up enabled control of growth in both slow and fast regimes, and even demonstrated the feasibility of measuring less-controlled ice growth in absence of the IBPs. Small pits were observed near the apex of growing tapered structures, which can be understood in light of the attachment of the IBP to specific planes. Although there exist several studies on crystals growing in thin films, this is the first demonstrated imaging of a growing bulk crystal immersed in its own melt with AFM.

 

11:40-11:50

Elad Gross (HUJI)
Contributed Speaker

Title:
What makes a catalyst active? Insights from IR nanospectroscopy measurements on single nanoparticles

Abstract:
The development of optimized catalysts that can address the grand energy challenges of the 21st century requires in depth understanding of the basic elements that direct the reactivity and selectivity of catalytic nanoparticles. In this talk I will demonstrate that structure-reactivity correlations within single catalytic nanoparticles can be identified by conducting Infrared nanospectroscopy measurements, while using N-heterocyclic carbene molecules as probes for surface-induced reactivity. Using this approach, we probed the influence of different surface sites on the catalytic reactivity of Au and Pt particles and the ways by which site-dependent reactivity varies in response to reaction conditions. In addition, by conducting single particle measurements we uncovered the influence of communication between highly-reactive and less-reactive surface sites on the nanoscale and globular reactivity pattern. These findings demonstrated the crucial impact of nanoscale properties on the catalytic reactivity to provide guidelines for the design of optimized catalysts.

 

11:50-12:10

Roundtable Discussion


Moderator: Sidney Cohen (WIS)
Panel members:
Michael Stern (BIU), Andrea Morello (Univ. New S. Wales, Australia)

Atomic-scale manufacturing, surface science and quantum circuits

Atomically-precise techniques, including but not limited to scanning probes, are now able to construct memories and devices of nm or even single-atom size.  At the same time, great strides have been made in quantum computing and the potential for harnessing these tools to push computing into the quantum age is enormous. We will discuss current trends and efforts, and analyze the feasibility of some of the pioneering approaches.

 

12:10-12:20

 
 

Our Sponsors

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IVS-IPSTA 2021 - 39th Annual Conference
November 17, 2021 | ONLINE

Conference Organizing Team


Gilbert Daniel Nessim (IVS President, BIU) | Ilya Grinberg (BIU) | Haim Barak (BIU)

Tatyana Bendikov (WIS) | Elad Koren (Technion) | Muhammad Bashouti (BGU) 
Noa Lachman-Senesh (TAU) | Igal Kronhaus (Technion)
Sharon Waichman (NRCN, Rotem Industries)