Recently discovered intrinsic antiferromagnetic topological insulator $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ Dirac cone. Here, using micro($\mu$)-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the Néel temperature at about 10–16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Furthermore, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ DP gap size.

We present a detailed study of 3,4,9,10-perylene- and 1,4,5,8-naphthalene-tetracarboxylic acid dianhydride monolayers adsorbed on Ag(111) film. The study is based on density functional theory with the use of a periodic slab model. The slab is chosen to contain an organic molecular monolayer on a silver thin film of different thicknesses (6, 9, and 12 layers) with the (111) orientation. We show that in both cases there is a similarity in formation of an unoccupied interface state from a surface state of the bare Ag(111) film due to the adsorbate-substrate interaction. The energy difference between the initial surface state and the resulting interface state varies with the film thickness, the adsorption distance, and the molecule size and geometry, whereas the effective mass of the state remains practically unchanged. Also, we demonstrate that the interface-state charge distribution preserves its localization in the interface region at different wave vectors k and in the vicinity of the molecular plane resembles lowest unoccupied orbitals of free molecules.

The change in the electronic structure of silver thin films of different thicknesses with the Ag( 111) orientation due to the interaction with an adsorbed monolayer of ordered organic molecules of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) has been investigated in terms of density functional theory. It has been shown that one of the two surface states of the pure films transforms into an unocc upied interface state due to the interaction so that all the main features of the initial state are retained. The relation of the resulting state to the unoccupied state experimentally observed in the PTCDA/Ag( 111 ) system by scanning tunneling and two-photon photoemi ssion spectroscopy has been discussed.

Electron attachment to the 4-bromobiphenyl molecule and the decay channels of its molecular anion were investigated by means of Dissociative Electron Attachment (DEA) spectroscopy with two different spectrometers. The first apparatus is equipped with a static magnet mass analyzer (Ufa group) and the second one with a quadrupole mass filter (Prague group). The dominant DEA channel at low electron energy leads to formation of Br⁻ negative fragments. Long-lived (τ_a = 40 µs at the temperature of 80 °C) molecular negative ions were detected only in the Ufa experiment. We explored the involved potential energy surfaces and found that the molecular anion has two distinct structures with the C–Br distances of 1.92 Å and 2.8 Å. The statistical model based on the Arrhenius approximation fully explains the experimental observations and sheds light on the earlier anion dissociation kinetic studies in solution.

We present a theoretical study of lifetimes of interface states (IS) on metal-organic interfaces PTCDA/Ag(111), NTCDA/Ag(111), PFP/Ag(111), and PTCDA/Ag(100), describing and explaining the recent experimental data. By means of unfolding the band structure of one of the interfaces under study onto the Ag(111) Brillouin zone we demonstrate that the Brillouin zone folding upon organic monolayer deposition plays a minor role in the phase space for electron decay, and hence weakly affects the resulting lifetimes. The presence of the unoccupied molecular states below the IS gives a small contribution to the IS decay rate, which is mostly determined by the change of the phase space of bulk states upon the energy shift of the IS. The calculated lifetimes follow the experimentally observed trends. In particular, we explain the trend of the unusual increase of the IS lifetimes with rising temperature.

The structural and vibrational properties of metal–organic interfaces have been examined by means of infrared (IR) absorption spectroscopy and density functional theory (DFT) with an approach accounting for long-range dispersive interactions. We focus on a comparative study of the PTCDA monolayer and bilayer on Ag(1 1 1). The equilibrium geometry at the molecule-metal interface and the IR spectrum of the chemisorbed monolayer of PTCDA on Ag(1 1 1) are well described by the computations. In the bilayer structure, the presence of a physisorbed adlayer on top of PTCDA/Ag(1 1 1) presents a challenge for DFT. As previously described for other systems, the polarization of the substrate is not captured correctly and results in too low energies of frontier molecular orbitals. This results in an apparent contribution from the vibrations of second-layer PTCDA to the IR spectrum due to interfacial dynamical charge transfer processes. After removing these peaks with artificially strong intensity, calculated and experimental data show good agreement and the IR spectrum can be described as the sum of the spectra of the PTCDA/Ag(1 1 1) contact layer and a physisorbed PTCDA monolayer on top.