We report on scanning tunneling microscopy and spectroscopy of grain boundaries in highly oriented pyrolytic graphite. Grain boundaries showed a periodic structure and an enhanced charge density compared to the bare graphite surface. Two possible periodic structures have been observed along grain boundaries. A geometrical model producing periodically distributed point defects on the basal plane of graphite has been proposed to explain the structure of grain boundaries. Scanning tunneling spectroscopy on grain boundaries revealed two strong localized states at $-0.3$ and 0.4 V which extended up to a 4 nm distance from grain boundaries.

We show ferromagnetic properties of hydrogen-functionalized epitaxial graphene on SiC. Ferromagnetism in such a material is not directly evident as it is inherently composed of only nonmagnetic constituents. Our results nevertheless show strong ferromagnetism with a saturation of $0.9{\mu }_{\mathrm{B}}/\mathrm{\text{hexagon}}$ projected area, which cannot be explained by simple magnetic impurities. The ferromagnetism is unique to hydrogenated epitaxial graphene on SiC, where interactions with the interfacial buffer layer play a crucial role. We argue that the origin of the observed ferromagnetism is governed by electron correlation effects of the narrow Si dangling bond states in the buffer layer exchange coupled to localized states in the hydrogenated graphene layer. This forms a quasi-three-dimensional ferromagnet with a Curie temperature higher than 300 K.

We have developed an efficient and accurate formalism which allows the simulation at the ab initio level of inelastic electron tunneling spectroscopy data under a scanning tunneling microscope setup. It exploits fully the tunneling regime by carrying out the structural optimization and vibrational mode calculations for surface and tip independently. The most relevant interactions in the inelastic current are identified as the inelastic tunneling terms, which are taken into account up to lowest order, while all other inelastic contributions are neglected. As long as the system is under tunneling regime conditions and there is no physisorbed molecule on the surface or tip apex, this lowest order in inelastic tunneling (LOIT) approach reduces drastically the computational cost compared to related approaches while maintaining a good accuracy. Adopting the wide-band limit for both tip and surface further reduces calculation times significantly, and is shown to give similar results to when the full energy dependence of the Green's functions is taken into account. The LOIT is applied to the Cu(111)+CO system probed by a clean and a CO contaminated tip to find good agreement with previous works. Different parameters involved in the calculations such as basis sets, $k$ sampling, tip-sample distance, or temperature, among others, are discussed in detail.

We show the growth of high-quality epitaxial graphene on 6$H$-SiC with Raman signatures comparable to exfoliated flakes. We ascribe the remaining low-quality transport properties to the strong electron-phonon coupling to two low-energy phonon modes at 70 and 16 meV. The coupling of these modes is enhanced by the defects present in the SiC substrate and buffer layer. Measurements of the mobility versus carrier concentration show a square-root dependence, corroborating the importance of surface phonon scattering in the limited mobility of graphene on SiC.

Local electronic structures of nanometer-sized patches of epitaxial graphene and its interface layer with SiC(0001) have been studied by atomically resolved scanning tunneling microscopy and spectroscopy. Localized states belonging to the interface layer of a graphene/SiC system show to have essential influence on the electronic structure of graphene. Giant enhancement of inelastic tunneling, reaching 50% of the total tunneling current, has been observed at the localized states on a nanometer-sized graphene monolayer surrounded by defects.

Epitaxial transition-metal oxide perovskite catalysts form a highly active catalyst class for the oxygen evolution reaction (OER). Understanding the origin of chemical dissolution and surface transformations during the OER is important to rationally design effective catalyst. These changes arise from complex interactions involving dynamic restructuring and electronic/structural adaptations. Although initial instability is common, surfaces can reach equilibrium through chemical transformations. High entropy perovskite oxides (HEPOs), which incorporate multiple 3d metal cations in near-equimolar ratios, have emerged as promising catalysts due to their enhanced OER activity compared to single-cation variants, attributed to their high configurational entropy and compositional flexibility. To advance HEPO catalyst applications, understanding the mechanisms governing their surface (in)stability is important. In this work, we examine surface degradation in epitaxial La(Cr,Mn,Fe,Co,Ni)O_3-δ thin films before and after OER using complementary scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM reveals tip-induced degradation of as-grown films under positive bias, attributed to oxygen anion removal and charge trapping-induced lattice degradation, demonstrating its utility as a probe for surface stability dynamics. Post-OER XPS analysis shows irreversible surface transformations from the initial epitaxial phase, characterized by 3d-metal leaching and formation of La and d-metal (oxy)hydroxides. Our findings indicate that oxygen vacancies and lattice strain trigger structural breakdown in these multi-cation perovskite surfaces during the OER, leading to surface restructuring and diminished catalytic performance compared to the as-grown epitaxial HEPO phase. This work identifies oxygen leaching as the likely primary driver of surface transformation during the OER. We show that STM offers an important tool to probe the transformation even before operando conditions, which can find use in similar material studies.