In this work we present unique signatures manifested by the local electronic properties of the topological surface state in BiTe nanostructures as the spatial limit is approached. We concentrate on the pure nanoscale limit (nanoplatelets) with spatial electronic resolution down to 1 nm. The highlights include strong dependencies on nanoplatelet size: (1) observation of a phase separation of Dirac electrons whose length scale decreases as the spatial limit is approached, and (2) the evolution from heavily n-type to lightly n-type surface doping as nanoplatelet thickness increases. Our results show a new approach to tune the Dirac point together with reduction of electronic disorder in topological insulator (TI) nanostructured systems. We expect our work will provide a new route for application of these nanostructured Dirac systems in electronic devices.

The goal of this work is to study transformations that occur upon heating BiSe to temperatures up to 623 K. X-ray diffraction (XRD) and scanning tunneling microscopy (STM) and spectroscopy (STS) techniques were used in our investigation. XRD was measured following the 00L and 01L truncation rods. These measurements revealed that upon heating there is a coexistence of a major BiSe phase and other ones that present structures of quintuple-layers intercalated with Bismuth bilayers. STM measurements of the surface of this material showed the presence of large hexagonal BiSe domains embedded in a BiSe matrix. STS experiments were employed to map the local electronic density of states and characterize the modifications imposed by the presence of the additional phases. Finally, density functional theory (DFT) calculations were performed to support these findings.

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We report on the successful synthesis of a crystal of the strong topological insulator Bi 4 Te 3 and the study of its surface electronic response. A combination of theoretical and experimental techniques allowed for a systematic study of the composition and electronic properties of the sample. These techniques include density functional theory (DFT), scanning tunneling microscopy and spectroscopy (STM-STS). DFT predicts that distinct surface topological states exist for the two surface terminations of Bi 4 Te 3 , i.e. Bi 2 and Bi 2 Te 3 . These terminations are also clearly distinguished in STS measurements, which allow choosing the main conducting channel through a combination of topography and electronic response. We find that the density of states are similar to those of their parent crystals Bi 2 and Bi 2 Te 3 , albeit shifted in energy.

RESUMOA caminhabilidade pode ser entendida como um aspecto qualitativo do lugar que permite ao pedestre acessar os diferentes pontos da cidade. Desse modo, avaliar a qualidade dos percursos diários dos citadinos se mostra imprescindível para compreender o quão convidativo é o deslocamento pedonal. O objetivo deste trabalho é apresentar os resultados dos níveis de caminhabilidade de trajetos cotidianos realizados na cidade de Goiás (GO), localizada no centro-oeste brasileiro. A revisão bibliográica fundamentou a sistematização dos parâmetros de qualidade do espaço. Em um primeiro momento, certiicou-se o enquadramento dos percursos a uma distância ideal para os deslocamentos a pé. Em seguida, os critérios de análise da qualidade espacial foram deinidos, constituídos de cenários com possibilidade de ocorrência no meio urbano, valorados a uma escala de zero a cinco. Os percursos analisados foram divididos em trechos aos quais foram veriicados os critérios analíticos. Os resultados mostram que a cidade possui condições desfavoráveis à caminhabilidade, com equipamentos de uso cotidiano localizados a distâncias pouco convidativas ao deslocamento a pé e infraestrutura pedonal subdimensionada, apresentando ainda pouca proteção às intempéries, oferta insuiciente de mobiliários de apoio e obstáculos nas calçadas, desestimulando o deslocamento a pé nessa cidade de pequeno porte. ABSTRACTWalkability can be understood as a qualitative aspect of space, which allows pedestrians to access diferent points of the city. Thus, evaluating the quality of the city's daily journeys is essential for understanding how inviting displacement on foot is. The aim of this work is to present the results of walkability levels in daily paths held in Goiás city, located in Brazilian center--west region. The bibliographical review gave us basis for the systematization of space quality parameters. First, we veriied the framing of those chosen trails into an ideal distance for displacement on foot. Then, we deined the analytical criteria for spatial quality, which were constituted by sceneries with possibility of occurrence into urban space, rated on a scale of zero to ive. The analyzed trails were divided in parts, on which were veriied the analytical criteria. The results show us that the city has unfavorable conditions for walkability, with daily use equipments located at distances that uninvite walk displacements. Also, the pedestrian infrastructure is undersized, ofers little protection for weather conditions, insuicient urban furniture of support and obstacles on the sidewalks. This context discourages displacement on foot in this small town.