Two collagen-mimetic peptides, CP(+) and CP(-), are reported in which the sequences comprise a multiblock architecture having positively charged N-terminal (Pro-Arg-Gly)3 and negatively charged C-terminal (Glu-Hyp-Gly)3 triad extensions, respectively. CP(+) rapidly self-associates into positively charged nanosheets based on a monolayer structure. In contrast, CP(-) self-assembles to form negatively charged monolayer nanosheets at a much slower rate, which can be accelerated in the presence of calcium(II) ion. A 2:1 mixture of unassociated CP(-) peptide with preformed CP(+) nanosheets generates structurally defined triple-layer nanosheets in which two CP(-) monolayers have formed on the identical surfaces of the CP(+) nanosheet template. Experimental data from electrostatic force microscopy (EFM) image analysis, zeta potential measurements, and charged nanoparticle binding assays support a negative surface charge state for the triple-layer nanosheets, which is the reverse of the positive surface charge state observed for the CP(+) monolayer nanosheets. The electrostatic complementarity between the CP(+) and CP(-) triple helical cohesive ends at the layer interfaces promotes a (CP(-)/CP(+)/CP(-)) compositional gradient along the z-direction of the nanosheet. This structurally informed approach represents an attractive strategy for the fabrication of two-dimensional nanostructures with compositional control.

topological materials, such as the quintessential topological insulators in the Bi 2 X 3 family (X = o, S, Se, te), are extremely promising for beyond Moore's Law computing applications where alternative state variables and energy efficiency are prized. It is essential to understand how the topological nature of these materials changes with growth conditions and, more specifically, chalcogen content. In this study, we investigate the evolution of the magnetoresistance of Bi 2 te x Se 3−x for varying chalcogen ratios and constant growth conditions as a function of both temperature and angle of applied field. The contribution of 2D and 3D weak antilocalization are investigated by utilizing the Tkachov-Hankiewicz model and Hakami-Larkin-Nagaoka models of magnetoconductance.In topological insulators (TIs), a finite band gap in the bulk is accompanied by metallic surface states with linear dispersion, resulting from band inversion 1,2 . These surface states have a variety of potential applications owing to their robustness resulting from topological protection, potentially high mobilities, and spin-momentum locking, making them ideal candidates for spin-transport 3-8 . In particular, devices for applications in advanced computing and logic beyond Moore's law have been envisioned 9-13 . Bi 2 Se 3 and Bi 2 Te 3 are prototypical TIs that have been widely studied in order to understand this vibrant class of materials [14][15][16][17][18][19] . This is because they are relatively simple to grow as thin films 20-22 , and both possess a single Dirac point at accessible doping levels 23 . Despite the great amount of research into their topological nature, little work has been done to understand how changing concentrations with either Se or Te affect the overall topological properties. Insight into the nature of the conducting surface states as well as their robustness to chemical substitution is vital to effectively utilizing these materials. Further rationale for investigating Bi 2 Te x Se 3−x alloys is that they offer robust Dirac dispersion for surface conduction combined with a path toward reduced bulk conductivity compared to their parent compounds at either x = 0 or 3 24 . Specifically, the Bi 2 Te 2 Se alloy represents a special line compound whose bulk conductivity is sufficiently low that surface and bulk transport may be distinguished 25 . The interest, therefore, is to obtain high quality epitaxial thin films that facilitate transport mediated by topological surface states distinct from bulk electronic states. Moreover, in order to use these materials in the proposed applications, the material properties must be optimized.In this work, we perform magnetoresistance (MR) measurements on four Bi-based topological material films: Bi 2 Se 3 , Bi 2 Te 3 , and two films with a mixture of Se and Te under constant growth conditions. We observe the 2D weak anti-localization (WAL) indicative of topological materials and we explore anisotropic magnetoresistance effects. We find a strong angle-independent WAL contribution in Bi...

We report growth and characterization of epitaxial α-Sn thin films grown on CdTe(111)B. Noninvasive techniques verify the film's pseduomorphic growth before fabrication of magnetotransport devices, overcoming ex-situ obstacles on uncapped films for measurement in the Hall bar geometry. We identify a transition to metallic behavior at low temperature with large magnetoresistance, high mobility, and quantum oscillations tentatively suggesting an n-type Dirac semimetallic channel. A parallel p-type dopant channel with high carrier density is seen to dominate at thinner film thicknesses. Careful preparation of the CdTe surface before growth is considered crucial to attain a low dopant density and accessible topological states on an insulating substrate. arXiv:1903.06723v2 [cond-mat.str-el]

Bi2Se3, widely studied as a topological insulator, has great potential for applications in low-power electronics and quantum computing. Intrinsic doping, however, presents a persistent challenge, leading to predominantly bulk conduction. In this work, we use substitutional Sn dopants to control the Fermi level in Bi2Se3 films. Scanning tunneling microscopy (STM) shows a shift in the local density of states toward the Dirac point as more Sn is incorporated. Density functional theory calculations elucidate the STM results, showing that Sn adds metallic states near the Fermi level that are localized to the defect sites while leaving the Dirac cone undisturbed. Electronic transport measurements demonstrate that the Sn defects increase the separation between bulk and surface states, though bulk conduction remains a dominant component.

No abstract