Institute for Technical Physics and Materials Science

Cora I., Fogarassy Z., Fornari R., Bosi M., Rečnik A., Pécz B.

The temperature-driven phase transformation of metastable κ-Ga2O3 layers deposited on sapphire was studied by high resolution TEM. Annealing experiments up to 1000 °C were performed either in situ in vacuum within the TEM or ex situ in ambient air. This allowed for the detection of the atomistic mechanisms at the basis of κ to β phase transition. In the case of in situ TEM observations we could even record in real time the atomic rearrangement. We provide in this paper the relevant crystallographic relations between original κ and new β lattice. Surprisingly, the ex situ experiments demonstrated the additional formation of a γ-Ga2O3 intermediate phase at 820 °C. The remarkably different behavior between in situ and ex situ annealing experiments is explained in terms of ambient (ambient air or high vacuum) and heating rate. An extensive investigation of γ-Ga2O3, also a metastable phase, showed that it has a cubic defect spinel structure ( F d 3 ¯ m ) with disordered vacancies. Repeated observations of the metastable γ-Ga2O3 after two months show that the vacancies tend to order, and that the vacancies are fully ordered after one year.

Németh P., McColl K., Smith R.L., Murri M., Garvie L.A., Alvaro M., Pécz B., Jones A.P., Corà F., Salzmann C.G., McMillan P.F.

The search for new nanostructural topologies composed of elemental carbon is driven by technological opportunities as well as the need to understand the structure and evolution of carbon materials formed by planetary shock impact events and in laboratory syntheses. We describe two new families of diamond-graphene (diaphite) phases constructed from layered and bonded sp3 and sp2 nanostructural units and provide a framework for classifying the members of this new class of materials. The nanocomposite structures are identified within both natural impact diamonds and laboratory-shocked samples and possess diffraction features that have previously been assigned to lonsdaleite and postgraphite phases. The diaphite nanocomposites represent a new class of high-performance carbon materials that are predicted to combine the superhard qualities of diamond with high fracture toughness and ductility enabled by the graphitic units and the atomically defined interfaces between the sp3- and sp2-bonded nanodomains.

Sztilkovics M., Gerecsei T., Peter B., Saftics A., Kurunczi S., Szekacs I., Szabo B., Horvath R.

Single-cell adhesion force plays a crucial role in biological sciences, however its in-depth investigation is hindered by the extremely low throughput and the lack of temporal resolution of present techniques. While atomic force microcopy (AFM) based methods are capable of directly measuring the detachment force values between individual cells and a substrate, their throughput is limited to few cells per day, and cannot provide the kinetic evaluation of the adhesion force over the timescale of several hours. In this study a high spatial and temporal resolution resonant waveguide grating based label-free optical biosensor was combined with robotic fluidic force microscopy to monitor the adhesion of living cancer cells. In contrast to traditional fluidic force microscopy methods with a manipulation range in the order of 300–400 micrometers, the robotic device employed here can address single cells over mm-cm scale areas. This feature significantly increased measurement throughput, and opened the way to combine the technology with the employed microplate-based, large area biosensor. After calibrating the biosensor signals with the direct force measuring technology on 30 individual cells, the kinetic evaluation of the adhesion force and energy of large cell populations was performed for the first time. We concluded that the distribution of the single-cell adhesion force and energy can be fitted by log-normal functions as cells are spreading on the surface and revealed the dynamic changes in these distributions. The present methodology opens the way for the quantitative assessment of the kinetics of single-cell adhesion force and energy with an unprecedented throughput and time resolution, in a completely non-invasive manner.

Wang S., Chen X., Szolnoki A.

Prosocial incentive can promote cooperation, but providing incentive is costly. Institutions in human society may prefer to use an incentive strategy which is able to promote cooperation at a reasonable cost. However, thus far few works have explored the optimal institutional incentives which minimize related cost for the benefit of public cooperation. In this work, in combination with optimal control theory we thus formulate two optimal control problems to explore the optimal incentive strategies for institutional reward and punishment respectively. By using the approach of Hamilton-Jacobi-Bellman equation for well-mixed populations, we theoretically obtain the optimal positive and negative incentive strategies with the minimal cumulative cost respectively. Additionally, we provide numerical examples to verify that the obtained optimal incentives allow the dynamical system to reach the desired destination at the lowest cumulative cost in comparison with other given incentive strategies. Furthermore, we find that the optimal punishing strategy is a cheaper way for obtaining an expected cooperation level when it is compared with the optimal rewarding strategy.

Sun W., Liu L., Chen X., Szolnoki A., Vasconcelos V.V.

Summary Finding appropriate incentives to enforce collaborative efforts for governing the commons in risky situations is a long-lasting challenge. Previous works have demonstrated that both punishing free-riders and rewarding cooperators could be potential tools to reach this goal. Despite weak theoretical foundations, policy makers frequently impose a punishment-reward combination. Here, we consider the emergence of positive and negative incentives and analyze their simultaneous impact on sustaining risky commons. Importantly, we consider institutions with fixed and flexible incentives. We find that a local sanctioning scheme with pure reward is the optimal incentive strategy. It can drive the entire population toward a highly cooperative state in a broad range of parameters, independently of the type of institutions. We show that our finding is also valid for flexible incentives in the global sanctioning scheme, although the local arrangement works more effectively.

Pécz B., Nicotra G., Giannazzo F., Yakimova R., Koos A., Kakanakova‐Georgieva A.

The properties of 2D InN are predicted to substantially differ from the bulk crystal. The predicted appealing properties relate to strong in- and out-of-plane excitons, high electron mobility, efficient strain engineering of their electronic and optical properties, and strong application potential in gas sensing. Until now, the realization of 2D InN remained elusive. In this work, the formation of 2D InN and measurements of its bandgap are reported. Bilayer InN is formed between graphene and SiC by an intercalation process in metal–organic chemical vapor deposition (MOCVD). The thickness uniformity of the intercalated structure is investigated by conductive atomic force microscopy (C-AFM) and the structural properties by atomic resolution transmission electron microscopy (TEM). The coverage of the SiC surface is very high, above 90%, and a major part of the intercalated structure is represented by two sub-layers of indium (In) bonded to nitrogen (N). Scanning tunneling spectroscopy (STS) measurements give a bandgap value of 2 ± 0.1 eV for the 2D InN. The stabilization of 2D InN with a pragmatic wide bandgap and high lateral uniformity of intercalation is demonstrated.

Kakanakova-Georgieva A., Gueorguiev G.K., Sangiovanni D.G., Suwannaharn N., Ivanov I.G., Cora I., Pécz B., Nicotra G., Giannazzo F.

The possibility for kinetic stabilization of prospective 2D AlN was explored by rationalizing MOCVD processes of AlN on epitaxial graphene.

Kakanakova-Georgieva A., Giannazzo F., Nicotra G., Cora I., Gueorguiev G.K., Persson P.O., Pécz B.

• Formation of 2D InO by confinement at graphene/SiC interface in MOCVD processes. • 2D InO manifests itself in a different hexagonal structure than 2D InN. • Distinct structure underpinned by In atoms in “atop” positions imaged by STEM. • Wide bandgap value of 4.1 eV estimated by conductive atomic force microscopy. Realization of semiconductor materials at the two-dimensional (2D) limit can elicit exceptional and diversified performance exercising transformative influence on modern technology. We report experimental evidence for the formation of conceptually new 2D indium oxide (InO) and its material characteristics. The formation of 2D InO was harvested through targeted intercalation of indium (In) atoms and deposition kinetics at graphene/SiC interface using a robust metal organic chemical vapor deposition (MOCVD) process. A distinct structural configuration of two sub-layers of In atoms in “atop” positions was imaged by scanning transmission electron microscopy (STEM). The bonding of oxygen atoms to indium atoms was indicated using electron energy loss spectroscopy (EELS). A wide bandgap energy measuring a value of 4.1 eV was estimated by conductive atomic force microscopy measurements (C-AFM) for the 2D InO.

Kakanakova-Georgieva A., Ivanov I.G., Suwannaharn N., Hsu C., Cora I., Pécz B., Giannazzo F., Sangiovanni D.G., Gueorguiev G.K.

Appearance of luminescent centers with narrow spectral emission at room temperature in nanometer thin AlN is reported.

Szolnoki A., de Oliveira B.F., Bazeia D.

Lotka's seminal work (Lotka A. J., Proc. Natl. Acad. Sci. U.S.A., 6 (1920) 410) "on certain rhythmic relations" is already one hundred years old, but the research activity about pattern formations due to cyclical dominance is more vibrant than ever. It is because non-transitive interactions have a paramount role on maintaining biodiversity and adequate human intervention into ecological systems requires a deeper understanding of the related dynamical processes. In this Perspective we overview different aspects of biodiversity, with focus on how it can be maintained based on mathematical modeling of the last years. We also briefly discuss the potential links to evolutionary game models of social systems, and finally, give an overview about potential prospects for future research.