Interplay of electronic structure and atomic ordering on surfaces: Momentum-resolved measurements of Cs atoms adsorbed on a Ag(111) substrate

Surface-state mediated interactions between adsorbates on surfaces can be exploited for the fabrication of self-organized nanostructures such as two-dimensional superlattices of adatoms. Using angle-resolved photoemission we provide experimental evidence that these interactions can be drastically modified by adsorbate-induced alterations in the surface potential barrier. This, in turn, will cause significant changes in the ordering of the adsorbates. For the studied case example of Cs adatoms on Ag(111) our momentum-resolved measurements reveal the surface state Fermi wave vector to be increased by as much as $\sim$100% for coverages around 0.03 ML. Our results unravel the origin for the hitherto puzzling and unexpectedly small lattice constant in the adatom superlattice observed for this system.Comment: 5 pages, 4 figure

Barrier and finite size effects on the extension of topological surface-states into magnetic insulators

The interplay between magnetic and topological order can give rise to phenomena such as the quantum anomalous Hall effect. The extension of topological surface states into magnetic insulators (MIs) has been proposed as an alternative to using intrinsically magnetic topological insulators (TIs). Here, we theoretically study how this extension of surface states into a magnetic insulator are influenced both by the interface barrier potential separating a topological insulator and a magnetic insulator and by finite size effects in such structures. We find that the the gap in the surface states depends non-monotonically on the barrier strength. A small, but finite, barrier potential turns out to be advantageous as it permits the surface states to penetrate even further into the MI. Moreover, we find that due to finite size effects in thin samples, increasing the spin-splitting in the MI can actually decrease the gap of the surface states, in contrast to the usual expectation that the gap opens as the spin-splitting increases.Comment: 5 pages, 5 figure

Direct Observation of Interband Spin-Orbit Coupling in a Two-Dimensional Electron System

We report the direct observation of interband spin-orbit (SO) coupling in a two-dimensional (2D) surface electron system, in addition to the anticipated Rashba spin splitting. Using angle-resolved photoemission experiments and first-principles calculations on Bi/Ag/Au heterostructures we show that the effect strongly modifies the dispersion as well as the orbital and spin character of the 2D electronic states, thus giving rise to considerable deviations from the Rashba model. The strength of the interband SO coupling is tuned by the thickness of the thin film structures

Влияние состава газовой среды на параметры упрочнения стали при азотировании в тлеющем разряде

В работе были исследованы процессы азотирования стальных деталей машиностроения в плазме тлеющего разряда при замене традиционного аммиака на смесь газов, состоящую из азота, аргона и метана. Проведено сравнение параметров азотированных слоев в зависимости от состава рабочей среды и длительности обработки. Оценены технологические параметры и возможности применения метода в реальном производстве.In the work, the processes of nitriding of steel parts of machine building in a glow discharge plasma were investigated when traditional ammonia was replaced by a mixture of gases consist of nitrogen, argon and methane. The parameters of the nitrided layers are compared depending on the composition of the working environment and the processing time. The technological parameters and possibilities of application of the method in real production are estimated

Formation of the BiAg2 surface alloy on lattice-mismatched interfaces

We report on the growth of a monolayer-thick BiAg2 surface alloy on thin Ag films grown on Pt(111) and Cu(111). Using low energy electron diffraction (LEED), angle resolved photoemission spectroscopy (ARPES), and scanning tunneling microscopy (STM) we show that the surface structure of the 13 ML Bi/x-ML Ag/Pt(111) system (x≥2) is strongly affected by the annealing temperature required to form the alloy. As judged from the characteristic (3×3)R30 LEED pattern, the BiAg2 alloy is partially formed at room temperature. A gentle, gradual increase in the annealing temperatures successively results in the formation of a pure BiAg2 phase, a combination of that phase with a (2×2) superstructure, and finally the pure (2×2) phase, which persists at higher annealing temperatures. These results complement recent work reporting the (2×2) as a predominant phase, and attributing the absence of BiAg2 alloy to the strained Ag/Pt interface. Likewise, we show that the growth of the BiAg2 alloy on similarly lattice-mismatched 1 and 2 ML Ag-Cu(111) interfaces also requires a low annealing temperature, whilst higher temperatures result in BiAg2 clustering and the formation of a BiCu2 alloy. The demonstration that the BiAg2 alloy can be formed on thin Ag films on different substrates presenting a strained interface has the prospect of serving as bases for technologically relevant systems, such as Rashba alloys interfaced with magnetic and semiconductor substrates.This work was supported by the Spanish Gouvernment (Grant No. MAT2013-46593-C6-4-P), the Basque Gouvernment (Grant No. IT621-13), and the Spanish Research Council (Grant No. CSIC-201560I022). Z.M.A. would like to acknowledge funding from DAAD and DIPC. P.L. would also like to acknowledge funding from the Deutsche Forschungsgemeinschaft via Project No.RE 1469/8-1.Peer Reviewe

Termination-dependent surface properties in the giant-Rashba semiconductors BiTeX (X=Cl, Br, I)

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).The noncentrosymmetric semiconductors BiTeX(X=Cl,Br,I) show large Rashba-type spin-orbit splittings in their electronic structure making them candidate materials for spin-based electronics. However, BiTeI(0001) single-crystal surfaces usually consist of stacking-fault-induced domains of Te and I terminations implying a spatially inhomogeneous electronic structure. Here we combine scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), and density functional theory calculations to systematically investigate the structural and electronic properties of BiTeX(0001) surfaces. For X=Cl, Br we observe macroscopic single-terminated surfaces. We discuss chemical characteristics among the three materials in terms of bonding character, surface electronic structure, and surface morphology.This work was financially supported by the Deutsche Forschungsgemeinschaft through FOR1162 and partly by the Ministry of Education and Science of Russian Federation (Grant No. 2.8575.2013), the Russian Foundation for Basic Research (Grants No. 15-02-01797 and No. 15-02-02717), and Saint Petersburg State University (Project No. 11.50.202.2015).Peer Reviewe