Self-assembled quasi-1D and 2D nanostructures of fullerenes on silicon

The work was supported by Russian Foundation for Basic Researches (Grant No. 17-02-00577)

Single layer nickel disilicide on surface and as embedded layer

Single monolayers of various materials (e.g. graphene, silicene, bismuthene, plumbene, etc) have recently become fascinating and promising objects in modern condensed-matter physics and nanotechnology. However, growing a monolayer of non-layered material is still challenging. In the present report, it will be shown that single monolayer NiSi2 can be fabricated at Si(111) surface stabilized by either Tl, Pb or In monolayers. Nickel atoms were found to intercalate the stabilizing metal layers upon deposition and to reside in the interstitial sites inside the first silicon bilayer of bulk-like-terminated Si(111)1×1 surface. The interstitial positions almost coincide with the bulk NiSi2 atomic positions thus forming NiSi2 single layer. Atomic and electronic structure of formed systems is described in detail by means of a set of experimental techniques, including low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoemission spectroscopy and also first-principles density-functional-theory calculations. Quality of formed single monolayer NiSi2 was additionally confirmed by in situ four-probe transport measurements that show that single monolayer NiSi2 preserves a metallic-type conductivity down to 2.0 K. Moreover it was found that delta-type structure with atomic sheet of NiSi2 silicide embedded into a crystalline Si matrix can be fabricated using room-temperature overgrowth of a Si film onto the Tl stabilized NiSi2 surface layer. Confinement of the NiSi2 layer to a single atomic plane has been directly confirmed by high-resolution transmission electron microscopy

Synthesis of two-dimensional TlxBi1-x compounds and Archimedean encoding of their atomic structure

Crystalline atomic layers on solid surfaces are composed of a single building block, unit cell, that is copied and stacked together to form the entire two-dimensional crystal structure. However, it appears that this is not an unique possibility. We report here on synthesis and characterization of the one-atomic-layer-thick TlxBi1−x compounds which display quite a different arrangement. It represents a quasi-periodic tiling structures that are built by a set of tiling elements as building blocks. Though the layer is lacking strict periodicity, it shows up as an ideally-packed tiling of basic elements without any skips or halting. The two-dimensional TlxBi1−x compounds were formed by depositing Bi onto the Tl-covered Si(111) surface where Bi atoms substitute appropriate amount of Tl atoms. Atomic structure of each tiling element as well as arrangement of TlxBi1−x compounds were established in a detail. Electronic properties and spin texture of the selected compounds having periodic structures were characterized. The shown example demonstrates possibility for the formation of the exotic low-dimensional materials via unusual growth mechanisms

STM investigation of 2D alloys and compounds on Si(111) and Ge(111) surfaces

The work was supported by the Russian Science Foundation (Grant 14-12-00479)

Two-dimensional in-Sb compound on silicon as a quantum spin hall insulator

Two-dimensional (2D) topological insulator is a promising quantum phase for achieving dissipationless transport due to the robustness of the gapless edge states resided in the insulating gap providing realization of the quantum spin Hall effect. Searching for two-dimensional realistic materials that are able to provide the quantum spin Hall effect and possessing the feasibility of their experimental preparation is a growing field. Here we report on the twodimensional (In, Sb)2 3 ×2 3 compound synthesized on Si(111) substrate and its comprehensive experimental and theoretical investigations based on an atomic-scale characterization by using scanning tunneling microscopy and angle-resolved photoelectron spectroscopy as well as ab initio density functional theory calculations identifying the synthesized 2D compound as a suitable system for realization of the quantum spin Hall effect without additional functionalization like chemical adsorption, applying strain, or gating

(Tl, Au)/Si(1 1 1)√7×√7 2D compound: an ordered array of identical Au clusters embedded in Tl matrix

Formation of the highly-ordered √7×√7-periodicity 2D compound has been detected in the (Tl, Au)/Si(111) system as a result of Au deposition onto the Tl/Si(111) surface and its composition, structure and electronic properties have been characterized using scanning tunneling microscopy and angle-resolved photoelectron spectroscopy observations and density-functional-theory calculations. On the basis of these data, the structural model of the Tl-Au compound has been proposed, which adopts 12 Tl atoms and 10 Au atoms (in total, 22 atoms) per √7×√7 unit cell, i.e. ∼1.71 ML of Tl and ∼1.43 ML of Au (in total, ∼3.14 ML). Qualitatively, the model can be visualized as consisting of truncated-pyramid-like Au clusters with a Tl atom on top, while the other Tl atoms form a double layer around the Au clusters. The (Tl, Au)/Si(111)√7×√7 compound has been found to exhibit pronounced metallic properties at least down to temperatures as low as ∼25 K, which makes it a promising object for studying electrical transport phenomena in the 2D metallic systems

Electronic properties of the two-dimensional (Tl, Rb)/Si(1 1 1)√3x√3 compound having a honeycomb-like structure

Heavy metal layers having a honeycomb structure on the Si(1 1 1) surface were theoretically predicted to show prospects for possessing properties of the quantum spin Hall (QSH) insulators. The (Tl, Rb)/Si(1 1 1) atomic-layer compound synthesized in the present work is the first real system of such type, where atoms of heavy metal Tl are arranged into the honeycomb structure stabilized by Rb atoms occupying the centers of the honeycomb units. Electronic properties of the (Tl, Rb)/Si(1 1 1) compound has been fully characterized experimentally and theoretically and compared with those of the hypothetical (Tl, H)/Si(1 1 1) prototype system. It is concluded that the QSH-insulator properties of the Tl-honeycomb layers on Si(1 1 1) surface are dictated by the stable adsorption sites occupied by Tl atoms which, in turn, are controlled by the atom species centering the Tl honeycombs. As a result, the real (Tl, Rb)/Si(1 1 1) compound where Tl atoms occupy the T4 sites does not possess QSH-insulator properties in contrast to the hypothetical (Tl, H)/Si(1 1 1) system where Tl atoms reside in the T1 (on-top) sites and it shows up as a QSH material