We substitute individual Pt atoms into monolayer MoS2 and study the resulting atomic structures with single-sideband ptychography (SSB) supported by ab initio simulations. We demonstrate that while high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) imaging provides excellent Z-contrast, distinguishing some defect types such as single and double sulfur vacancies remains challenging due to their low relative contrast difference. However, SSB with its nearly linear Z-contrast and high phase sensitivity enables reliable identification of these defect configurations, as well as various Pt dopant structures at significantly lower electron doses. Our findings uncover the precise atomic placement and highlight the potential of SSB for detailed structural analysis of dopant-modified 2D materials while minimizing beam-induced damage, offering new pathways for understanding and engineering atomic-scale features in 2D systems.

Fabricating dispersed single atoms and size-controlled metal nanoclusters remains a difficult challenge due to sintering. Here, we demonstrate that atoms and clusters can be immobilized using atomically clean defect-engineered graphene as the matrix. The graphene is first cleaned of surface contamination with laser heating, after which low-energy Ar irradiation is used to create spatially well-separated vacancies into it. Metal atoms are then evaporated either via thermal or ebeam evaporation onto graphene, where they diffuse until being trapped into a vacancy. The density of embedded structures can be controlled through irradiation dose, and the size of the structures through evaporation time. The resulting structures are confirmed through atomic-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. We demonstrate here incorporation of Al, Ti, Fe, Ag and Au single atoms or nanoclusters, but the method should work equally well for other elements.

Defect-engineered and even amorphous two-dimensional (2D) materials have recently gained interest due to properties that differ from their pristine counterparts. Since these properties are highly sensitive to the exact atomic structure, it is crucial to be able to characterize them at atomic resolution over large areas. This is only possible when the imaging process is automated to reduce the time spent on manual imaging, which at the same time reduces the observer bias in selecting the imaged areas. Since the necessary datasets include at least hundreds if not thousands of images, the analysis process similarly needs to be automated. Here, we introduce disorder into graphene and monolayer hexagonal boron nitride (hBN) using low-energy argon ion irradiation, and characterize the resulting disordered structures using automated scanning transmission electron microscopy annular dark field imaging combined with convolutional neural network-based analysis techniques. We show that disorder manifests in these materials in a markedly different way, where graphene accommodates vacancy-type defects by transforming hexagonal carbon rings into other polygonal shapes, whereas in hBN the disorder is observed simply as vacant lattice sites with very little rearrangement of the remaining atoms. Correspondingly, in the case of graphene, the highest introduced disorder leads to an amorphous membrane, whereas in hBN, the highly defective lattice contains a large number of vacancies and small pores with no indication of amorphisation. Overall, our study demonstrates that combining automated imaging and image analysis is a powerful way to characterize the structure of disordered and amorphous 2D materials, while also illustrating some of the remaining shortcomings with this methodology.

The van der Waals atomic solids of noble gases on metals at cryogenic temperatures were the first experimental examples of two-dimensional systems. Recently, such structures have also been created on surfaces under encapsulation by graphene, allowing studies at elevated temperatures through scanning tunnelling microscopy. However, for this technique, the encapsulation layer often obscures the arrangement of the noble gas atoms. Here we create Kr and Xe clusters in between two suspended graphene layers, and uncover their atomic structure through transmission electron microscopy. We show that small crystals (N < 9) arrange on the basis of the simple non-directional van der Waals interaction. Larger crystals show some deviations, possibly enabled by deformations in the encapsulating graphene lattice. We further discuss the dynamics of the clusters within the graphene sandwich, and show that although all the Xe clusters with up to N ≈ 100 remain solid, Kr clusters with already N ≈ 16 turn occasionally fluid under our experimental conditions (under a pressure of ~0.3 GPa). This study opens a way for the so-far unexplored frontier of encapsulated two-dimensional van der Waals solids with exciting possibilities for fundamental condensed-matter physics research and possible applications in quantum information technology.

Monolayer hexagonal boron nitride (hBN) has recently become the focus of intense research as a material to host quantum emitters. Although it is well known that such emission is associated with point defects, so far no conclusive correlation between the spectra and specific defects has been demonstrated. Here, we prepare atomically clean suspended hBN samples and subject them to low-energy ion irradiation. The samples are characterized before and after irradiation via automated scanning transmission electron microscopy imaging to assess the defect concentrations and distributions. We find an intrinsic defect concentration of ca. 0.03/nm2 (with ca. 55% boron and 8% nitrogen single vacancies, 20% double vacancies and 16% more complex vacancy structures). To be able to differentiate between these and irradiation-induced defects, we create a significantly higher (but still moderate) concentration of defects with the ions (0.30/nm2), and now find ca. 55% boron and 12% nitrogen single vacancies, 14% double vacancies, and 18% more complex vacancy structures. The results demonstrate that already the simplest irradiation provides selectivity for the defect types, and open the way for future experiments to explore changing the selectivity by modifying the irradiation parameters.

As a one-atom thick, mechanically strong, and chemically stable material with unique electronic properties, graphene can serve as the basis for a large number of applications. One way to tailor its properties is the controlled introduction of covalently bound heteroatoms into the lattice. In this study, we demonstrate efficient implantation of individual gold atoms into graphene up to a concentration of 1.7 × 1011 atoms cm−2 via a two-step low-energy ion implantation technique that overcomes the limitation posed by momentum conservation on the mass of the implanted species. Atomic resolution scanning transmission electron microscopy imaging and electron energy-loss spectroscopy reveal gold atoms occupying double vacancy sites in the graphene lattice. The covalently bound gold atoms can sustain intense electron irradiation at 60 kV during the microscopy experiments. At best, only limited indication of plasmonic enhancement is observed. The method demonstrated here can be used to introduce a controlled concentration of gold atoms into graphene, and should also work for other heavier elements with similar electronic structure.

Substituting heteroatoms into graphene can tune its properties for applications ranging from catalysis to spintronics. The further recent discovery that covalent impurities in graphene can be manipulated at atomic precision using a focused electron beam may open avenues towards sub-nanometer device architectures. However, the preparation of clean samples with a high density of dopants is still very challenging. Here, we report vacancy-mediated substitution of aluminium into laser-cleaned graphene, and without removal from our ultra-high vacuum apparatus, study their dynamics under 60 keV electron irradiation using aberration-corrected scanning transmission electron microscopy and spectroscopy. Three- and four-coordinated Al sites are identified, showing excellent agreement with ab initio predictions including binding energies and electron energy-loss spectrum simulations. We show that the direct exchange of carbon and aluminium atoms predicted earlier occurs under electron irradiation, although unexpectedly it is less probable than the same process for silicon. We also observe a previously unknown nitrogen-aluminium exchange that occurs at Al─N double-dopant sites at graphene divacancies created by our plasma treatment.

Lauft das Physikstudium im deutschsprachigen Raum im Grosen und Ganzen uberall auf die gleiche Art ab oder sind die Strukturen von Standort zu Standort verschieden? Wie lasst sich die Ahnlichkeit von Studiengangsstrukturen feststellen? Zur Beantwortung dieser Fragen lassen sich von der Zusammenkunft der deutschsprachigen Physikfachschaften (ZaPF) und der jungen Deutschen Physikalisch Gesellschaft (jDPG) schon langer organisierten und durchgefuhrten Umfragen nutzen. Sie bieten unter anderem Informationen zur inhaltlichen Schwerpunktsetzungen der Studiengange. Aus den Debatten des Studienreformforums ist nun die Notwendigkeit erwachsen, mehr noch die Struktur des Studiengange in den Blick zu nehmen; zeitgleich ist ein Vorschlag fur deren Darstellung entstanden. Im letzten Jahr ist angesichts dessen ein offentlich zugangliches Online-Tool entstanden, das es erlaubt, diese Darstellung halbautomatisiert aus den Informationen der Modulhandbucher zu erstellen. Die so erzeugten Darstellungen sollen nicht nur der Beforschung der Studiengange dienen, sondern gleichzeitig fur die Arbeit in den Fachbereichen nutzbar sein. Mittelfristig sollen die Datenerfassung der Umfragen und dieses Tools zusammenwachsen. Dieser Beitrag beschreibt das Tool und die Ideen dahinter und regt hoffentlich zur Nutzung an.

Die Umstellung des Lehrbetriebs an den Hochschulen auf Online-Lehre hat nicht nur technische, sondern vor allem auch didaktische Herausforderungen mit sich gebracht, die vielfaltig – und zum Teil sehr unterschiedlich – beantwortet wurden. An einer systematischen hochschulubergreifenden Auswertung fehlt es bislang aber noch. Im hir dokumentierten Workshop wurde der aktuelle Stand exemplarisch vorgestellt und diskutiert, wie es gelingen kann, dass die wertvollen Erfahrungen dieser Zeit nicht mit der Ruckkehr zur Prasenzlehre verloren gehen.

Das Studienreform-Forum befasst sich einerseits mit der Systematisierung von Studienreformen und Studienreform-Vorhaben, andererseits mit Grundsatzfragen der Studienreform. Beides zusammen bildet die Grundlage zur Weiterentwicklung von Studiengangen. Im Jahr 2020 hat das Studienreform-Forum erneut zur Einsendung von Beitragen zu diesen Fragen aufgerufen. Angesichts der Pandemie wurde dieser Aufruf verlangert und parallel eine Initiative zur Dokumentation und Auswertung der Lehre unter Pandemiebedingungen gestartet, deren Ergebnisse mittelfristig mit den ubrigen Beitragen in Bezug gesetzt werden sollen. Dieser Artikel dokumentiert die auf den Call for Papers eingesandten Beitrage.