Edge state on hydrogen-terminated graphite edges investigated by scanning tunneling microscopy

The edge states that emerge at hydrogen-terminated zigzag edges embedded in dominant armchair edges of graphite are carefully investigated by ultrahigh-vacuum scanning tunneling microscopy (STM) measurements. The edge states at the zigzag edges have different spatial distributions dependent on the $\alpha$- or $\beta$-site edge carbon atoms. In the case that the defects consist of a short zigzag (or a short Klein) edge, the edge state is present also near the defects. The amplitude of the edge state distributing around the defects in an armchair edge often has a prominent hump in a direction determined by detailed local atomic structure of the edge. The tight binding calculation based on the atomic arrangements observed by STM reproduces the observed spatial distributions of the local density of states.Comment: 9 pages, 11 figures, accepted for Physical Review

ILP Recommender System: Explainable and More

In this paper, we explore the use of ILP thoroughly in generating explainable, negative, group and context-aware recommendation. ILP provides recommendation rules in if-then logical format that allows us to form a clear and concise explanation to accompany the suggested items. It can indirectly derive negative rules which tell us not to recommend certain products to users. It also emphasizes the use of universal representations which enables us to suggest the items to a group of users who share the same interest. Additionally, ILP requires no re-training if new contexts (e.g., location, time and mood) are added to the system to generate context-aware recommendations (CARS), only predicates and settings are simply specified. In this paper, we also propose the explainability evaluation in terms of transparency by comparing the items/features appearing in the explanation with the features presented in the user's review. The negative, group and dynamic recommendations can be evaluated using the standard measurement

Adaptive Uncertainty-Guided Model Selection for Data-Driven PDE Discovery

We propose a new parameter-adaptive uncertainty-penalized Bayesian information criterion (UBIC) to prioritize the parsimonious partial differential equation (PDE) that sufficiently governs noisy spatial-temporal observed data with few reliable terms. Since the naive use of the BIC for model selection has been known to yield an undesirable overfitted PDE, the UBIC penalizes the found PDE not only by its complexity but also the quantified uncertainty, derived from the model supports' coefficient of variation in a probabilistic view. We also introduce physics-informed neural network learning as a simulation-based approach to further validate the selected PDE flexibly against the other discovered PDE. Numerical results affirm the successful application of the UBIC in identifying the true governing PDE. Additionally, we reveal an interesting effect of denoising the observed data on improving the trade-off between the BIC score and model complexity. Code is available at https://github.com/Pongpisit-Thanasutives/UBIC.Comment: 17 pages, 15 figure

Observation of zigzag and armchair edges of graphite using scanning tunneling microscopy and spectroscopy

The presence of structure-dependent edge states of graphite is revealed by both ambient- and ultra-highvacuum- (UHV) scanning tunneling microscopy (STM) / scanning tunneling spectroscopy (STS) observations. On a hydrogenated zigzag (armchair) edge, bright spots are (are not) observed together with (SQRT(3) by SQRT(3))R30 superlattice near the Fermi level (V_S = −30 mV for a peak of the local density of states (LDOS)) under UHV, demonstrating that a zigzag edge is responsible for the edge states, although there is no appreciable difference between as-prepared zigzag and armchair edges in air. Even in hydrogenated armchair edge, however, bright spots are observed at defect points, at which partial zigzag edges are created in the armchair edge.Comment: 4 pages, 4 figures, contents for experimental/theoretical reseachers, accepted as an issue of Physical Review B (PRB

STM observation of the quantum interference effect in finite-sized graphite

Superperiodic patterns were observed by STM on two kinds of finite-sized graphene sheets. One is nanographene sheets inclined from a highly oriented pyrolitic graphite (HOPG) substrate and the other is several-layer-thick graphene sheets with dislocation-network structures against a HOPG substrate. As for the former, the in-plane periodicity increased gradually in the direction of inclination, and it is easily changed by attachment of a nanographite flake on the nanographene sheets. The oscillation pattern can be explained by the interference of electron waves confined in the inclined nanographene sheets. As for the latter, patterns and their corrugation amplitudes depended on the bias voltage and on the terrace height from the HOPG substrate. The interference effect by the perturbed and unperturbed waves in the overlayer is responsible for the patterns whose local density of states varies in space.Comment: 11 pages; 2 figures; accepted for publication in J. Phys. Chem. Solids; ISIC1