Maciej.bazarnik

Recent advances in scanning probe techniques rely on the chemical functionalization of the probe-tip termination by a single molecule. The success of this approach opens the prospect of introducing spin sensitivity through functionalization by a magnetic molecule. We used a nickelocene-terminated tip (Nc-tip), which offered the possibility of producing spin excitations on the tip apex of a scanning tunneling microscope (STM). When the Nc-tip was 100 picometers away from point contact with a surface-supported object, magnetic effects could be probed through changes in the spin excitation spectrum of nickelocene. We used this detection scheme to simultaneously determine the exchange field and the spin polarization of iron atoms and cobalt films on a copper surface with atomic-scale resolution.

Nature, Published online: 30 October 2019; doi:10.1038/s41586-019-1718-x

Nature, Published online: 30 October 2019; doi:10.1038/s41586-019-1695-0

Spooky chirality: Long‐range chirality recognition is presented between neighboring 3‐bromo‐naphthalen‐2‐ol (BNOL) stripes on an inert Au(111) surface across the herringbone reconstruction as investigated by STM and DFT calculations. The key to achieving such long‐range chirality recognition is the herringbone reconstruction‐induced local dipole accumulation at the edges of the BNOL stripes.

Abstract

Chiral molecular self‐assemblies were usually achieved using short‐range intermolecular interactions, such as hydrogen‐, metal–organic, and covalent bonding. However, unavoidable surface defects, such as step edges, surface reconstructions, or site dislocations may limit the applicability of short‐range chirality recognition. Long‐range chirality recognition on surfaces would be an appealing but challenging strategy for chiral reservation across surface defects at long distances. Now, long‐range chirality recognition is presented between neighboring 3‐bromo‐naphthalen‐2‐ol (BNOL) stripes on an inert Au(111) surface across the herringbone reconstruction as investigated by STM and DFT calculations. The key to achieving such recognition is the herringbone reconstruction‐induced local dipole accumulation at the edges of the BNOL stripes. The neighboring stripes are then forced to adopt the same chirality to create the opposite edged dipoles and neutralize the neighbored dipole moments.

Nature Materials, Published online: 23 September 2019; doi:10.1038/s41563-019-0483-4

Author(s): Martin Schmitt, Chong H. Park, Paula Weber, Andreas Jäger, Jeannette Kemmer, Matthias Vogt, and Matthias Bode

We present a survey of the structural and magnetic properties of submonolayer transition metal dioxides on the (001) surfaces of the heavy face-centered cubic noble metals Ir and Pt performed by spin-averaged scanning tunneling microscopy (STM) and spin-polarized (SP) STM. Our STM results confirm th...

[Phys. Rev. B 100, 054431] Published Thu Aug 22, 2019

The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity, and aromaticity, with implications for on-surface synthesis, catalysis, photoconversion, and applications in molecular electronics. On insulating, multilayer sodium chloride (NaCl) films, we controlled the charge state of organic molecules and resolved their structures in neutral, cationic, anionic, and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using carbon monoxide (CO)–functionalized tips. We detected changes in conformation, adsorption geometry, and bond-order relations for azobenzene, tetracyanoquinodimethane, and pentacene in multiple charge states. Moreover, for porphine, we investigate the charge state–dependent change of aromaticity and conjugation pathway in the macrocycle. This work opens the way to studying chemical-structural changes of individual molecules for a wide range of charge states.

The discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) crystals has generated widespread interest. Making further progress in this area requires quantitative knowledge of the magnetic properties of vdW magnets at the nanoscale. We used scanning single-spin magnetometry based on diamond nitrogen-vacancy centers to image the magnetization, localized defects, and magnetic domains of atomically thin crystals of the vdW magnet chromium(III) iodide (CrI₃). We determined the magnetization of CrI₃ monolayers to be 16 Bohr magnetons per square nanometer, with comparable values in samples with odd numbers of layers; however, the magnetization vanishes when the number of layers is even. We also found that structural modifications can induce switching between ferromagnetic and antiferromagnetic interlayer ordering. These results demonstrate the benefit of using single-spin scanning magnetometry to study the magnetism of 2D vdW magnets.

Nature, Published online: 22 May 2019; doi:10.1038/s41586-019-1226-z

Magnetic single atoms and molecules are receiving intensifying research focus because of their potential as the smallest possible memory, spintronic, and qubit elements. Scanning probe microscopes used to study these systems have benefited greatly from new techniques that use molecule-functionalized tips to enhance spatial and spectroscopic resolutions and enable new sensing capabilities. We demonstrate a microscopy technique that uses a magnetic molecule, Ni(cyclopentadienyl)₂, adsorbed at the apex of a scanning probe tip, to sense exchange interactions with another molecule adsorbed on a Ag(110) surface in a continuously tunable fashion in all three spatial directions. We further used the probe to image contours of exchange interaction strength, revealing angstrom-scale regions where the quantum states of two magnetic molecules strongly mix. Our results pave the way for new nanoscale imaging capabilities based on magnetic single-molecule sensors.

Author(s): Maciej Bazarnik, Mikel Abadia, Jens Brede, Michał Hermanowicz, Emil Sierda, Micha Elsebach, Torben Hänke, and Roland Wiesendanger

The magnetic structure of a monolayer-thick GdAu2 surface alloy on Au(111) has been investigated down to the atomic level by spin-polarized scanning tunneling microscopy. Spin-resolved tunneling spectroscopy combined with density-functional theory calculations reveal the local spin polarization of b...

[Phys. Rev. B 99, 174419] Published Tue May 21, 2019

Visualizing vibrational normal modes of a single molecule with atomically confined light

Visualizing vibrational normal modes of a single molecule with atomically confined light, Published online: 03 April 2019; doi:10.1038/s41586-019-1059-9

Author(s): A. Martín-Jiménez, J. M. Gallego, R. Miranda, and R. Otero

A periodic structure deposited on copper produces an electron density pattern that could affect the chemical and physical properties of the surface.

[Phys. Rev. Lett. 122, 176801] Published Tue Apr 30, 2019

Defects in conventional semiconductors substantially lower the photoluminescence (PL) quantum yield (QY), a key metric of optoelectronic performance that directly dictates the maximum device efficiency. Two-dimensional transition-metal dichalcogenides (TMDCs), such as monolayer MoS₂, often exhibit low PL QY for as-processed samples, which has typically been attributed to a large native defect density. We show that the PL QY of as-processed MoS₂ and WS₂ monolayers reaches near-unity when they are made intrinsic through electrostatic doping, without any chemical passivation. Surprisingly, neutral exciton recombination is entirely radiative even in the presence of a high native defect density. This finding enables TMDC monolayers for optoelectronic device applications as the stringent requirement of low defect density is eased.