Методом фотоэлектронной спектроскопии с угловым разрешением проведено сравнительное исследование графена, полученного методом крекинга пропилена (С 3 Н 6) на поверхностях никеля с различной ориентацией: Ni(111) и Ni(100) Показано, что графен на Ni(111) является хорошо упорядоченным на большой площади поверхности, в то время как графен на поверхности Ni(100) имеет ярко выраженную доменную структуру. Установлено, что электронная структура обеих систем схожа, графен сильно связан с подложкой Ni. Показано, что интеркаляция монослоя Au для двух систем приводит к формированию электронной структуры, свойственной для квазисвободного графена. Работа выполнена в рамках НИР № 15.61.202.2015 и программы G-RISC. Исследования проводились на оборудовании Ресурсного центра " Физические методы исследования поверхности" Научного парка СПбГУ и на российско-немецком канале вывода синхронного излучения BESSY-II.

The electronic structure of magnetically-doped TI with stoichiometry Bi1.09Gd0.06Sb0.85Te3 in the region of the Dirac point has been studied in detail by angle-resolved photoelectron spectroscopy (ARPES) at various temperatures (above and below the Néel temperature, 1-35 K) and different polarizations of synchrotron radiation. It has shown that the energy gap in photoemission spectra opens at the Dirac point and remains open above the temperature of the long-range magnetic ordering, Tn. Measurements of magnetic properties by the superconducting magnetometry method (SQUID) have shown antiferromagnetic ordering with a transition temperature to the paramagnetic phase equal to 8.3 K. Study of the temperature dependence of the Dirac cone state intensity at the Г point by ARPES has confirmed the magnetic transition and has shown a possibility of its indication directly from photoemission spectra. A more detailed analysis of the splitting between the upper and lower Dirac cone states (i.e. the energy gap) at the Dirac point in the photoelectron spectra has shown the dependence of the measured gap on the synchrotron radiation polarization (about 28-30 meV for p-polarization and 22-25 meV for circularly polarized radiation of opposite chirality). The mechanism of opening the gap at a Dirac point above the Tn was proposed due to the “pairing” of the Dirac fermions with opposite momentum and spin orientation as a result of their interaction with the spin texture generated by photoemission in the region of the photoemission hole on a magnetic impurity atom (Gd). It was shown that the gap at the Dirac point, measured above Tn, is dynamic and is formed directly during photoemission process. At the same time, the origin of the gap remains magnetic (even when the long-range magnetic ordering is destroyed) and is associated with the properties of the magnetic topological insulator that determines a practically unchanged size of the gap above Tn. The dynamic origin of the generated gap is confirmed by the dependence of its magnitude on the polarization of synchrotron radiation.

Investigation of graphene on an ultrathin CoSi/CoSi2 cobalt silicide layer on a SiC(0001) substrate after the Au intercalation has been carried out. It was shown that deposition of Au and subsequent annealing of the system at a temperature of 500°C leads to the intercalation of Au atoms and the formation of gold silicide under graphene with a stoichiometry close to that of Au2Si. The study of the electronic structure of the system in the region of the K point of the surface Brillouin zone revealed the quasi-freestanding character of graphene with a linear spectrum of π states and a Dirac point near the Fermi level. The measurements using photoelectron microscopy showed the homogeneity of the work function along the surface of the sample on a micrometer scale.