Atomic, electronic and transport properties of In-Au 2D compound on Si(1 0 0).

Two-dimensional (In, Au)/Si(1 0 0)c(2 [Formula: see text] 2) compound was synthesized and its atomic arrangement, electron band structure and low-temperature transport properties were characterized using scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and four-point-probe resistivity measurements assisted with first-principles density-functional-theory calculations. The present results are compared to those obtained earlier for the parent (Tl, Au)/Si(1 0 0)c(2 [Formula: see text] 2) system.

Electronic properties of the two-dimensional (Tl, Rb)/Si(1 1 1)[Formula: see text] 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)[Formula: see text] 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)[Formula: see text] compound has been fully characterized experimentally and theoretically and compared with those of the hypothetical (Tl, H)/Si(1 1 1)[Formula: see text] 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)[Formula: see text] 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)[Formula: see text] system where Tl atoms reside in the T1 (on-top) sites and it shows up as a QSH material.

From C60 "trilliumons" to "trilliumenes:" Self-assembly of 2D fullerene nanostructures on metal-covered silicon and germanium.

We discovered a set of C60 nanostructures that appear to be constructed using a universal building block made of four C60 molecules on Si(111) or Ge(111) surfaces covered by an atomic layer of Tl, Pb, or their compound. The building block is a four-C60 cluster having a shape reminiscent of the three-petal flower "white trillium." Therefore, we call it "trilliumon" and the various 2D ordered nanostructures derived from it "trilliumenes." Self-assembly of the trilliumenes is a result of an intricate interplay among the adsorbed C60 molecules, metal atoms, and semiconductor substrates. Remarkably, all metal layers triggering formation of trilliumenes on the Si(111) surface have recently been reported to be the thinnest 2D superconductors. In this respect, the trilliumenes show promise to be 2D nanostructured superconductors whose properties are awaiting their exploration.

(Tl, Au)/Si(1 1 1)[Formula: see text] 2D compound: an ordered array of identical Au clusters embedded in Tl matrix.

Formation of the highly-ordered [Formula: see text]-periodicity 2D compound has been detected in the (Tl, Au)/Si(1 1 1) system as a result of Au deposition onto the Tl/Si(1 1 1) surface, its composition, structure and electronic properties have been characterized using scanning tunneling microscopy, angle-resolved photoelectron spectroscopy 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 [Formula: see text] 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(1 1 1)[Formula: see text] 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.

2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure.

Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), [Formula: see text]-(Tl, Pb) and [Formula: see text]-(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)[Formula: see text] system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound contains six Tl atoms and seven Pb atoms per [Formula: see text] unit cell (i.e. ∼0.67 ML Tl and ∼0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] and (Tl, Pb)/Ge(1 1 1)[Formula: see text] compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)[Formula: see text], these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

Two-Dimensional Superconductor with a Giant Rashba Effect: One-Atom-Layer Tl-Pb Compound on Si(111).

A one-atom-layer compound made of one monolayer of Tl and one-third monolayer of Pb on a Si(111) surface having √3×√3 periodicity was found to exhibit a giant Rashba-type spin splitting of metallic surface-state bands together with two-dimensional superconducting transport properties. Temperature-dependent angle-resolved photoelectron spectroscopy revealed an enhanced electron-phonon coupling for one of the spin-split bands. In situ micro-four-point-probe conductivity measurements with and without magnetic field demonstrated that the (Tl, Pb)/Si(111) system transformed into the superconducting state at 2.25 K, followed by the Berezinskii-Kosterlitz-Thouless mechanism. The 2D Tl-Pb compound on Si(111) is believed to be the prototypical object for prospective studies of intriguing properties of the superconducting 2D system with lifted spin degeneracy, bearing in mind that its composition, atomic and electron band structures, and spin texture are already well established.

Incommensurate superstructure in heavily doped fullerene layer on Bi/Si(111) surface.

Cs adsorption onto the C60-covered Si(111)-ß-√3×√3-Bi reconstruction has been studied by means of scanning tunneling microscopy and photoelectron spectroscopy. Unexpected increase in apparent size of every second C60 molecule has been detected, hereupon the close packed molecular array almost doubles its periodicity. The change affects only the fullerenes that are in direct contact with the metal-induced reconstruction and takes no place already in the second layer. Photoelectron studies have revealed that this incommensurate "2 × 2" superstructure of a heavily doped C60 monolayer remains in an insulating state regardless of doping level.

Effect of Na adsorption on the structural and electronic properties of Si(111)√3 × âˆš3-Au surface.

Adsorption of ∼0.1 ML of Na onto the Si(111)√3 × âˆš3-Au surface held at 300 °C has been found to induce pronounced changes in its structural and electronic properties. Domain wall networks, characteristic of the pristine surface, are removed completely, leading to the formation of a highly ordered homogeneous surface. The original atomic arrangement of the Si(111)√3 × âˆš3-Au is preserved and Na atoms occupy T4 adsorption sites at the centers of surface Si trimers. Upon Na adsorption, a pronounced metallic S1 surface-state band develops. It is characterized by a large spin splitting (momentum splitting at the Fermi level Δk∥ = 0.027 Å(-1) and consequent energy splitting ΔEF = 110 meV), large electron filling (on the order of 0.5 electrons per √3 × âˆš3 unit cell) and small effective electron mass of (0.028 ± 0.006)me. The natural consequence of the latter properties is a high surface conductivity of the Si(111)√3 × âˆš3-(Au, Na) surface.

Structural transformations in Pb/Si(111) phases induced by C60 adsorption.

Structural transformations at the Pb/Si(111) surface occurring upon C60 adsorption onto Pb/Si(111)1 × 1 phase at room temperature and Pb/Si(111)[Formula: see text] at low temperatures between 30 and 210 K, have been studied using scanning tunneling microscopy and low-energy electron diffraction observations. Typically, C60 fullerenes agglomerate into random molecular islands nucleated at the surface defects. C60 island formation is accompanied by expelling Pb atoms to the surrounding surface area where more dense Pb/Si(111) phases form. Productivity of C60-induced expelling of Pb atoms is controlled by surface defects and is suppressed dramatically when regular ('crystalline') C60 islands self-assemble at the defect-free Pb/Si(111) surface. When Pb atoms are ejected by the random C60 islands, extended structural transformations involving reordering of numerous Pb atoms are fully completed at the surface within the shortest possible time (a few dozen seconds) to reapproach and image the surface after C60 deposition. Estimations show that the observed transformations cannot be controlled by random walk diffusion of Pb adatoms, which implies a highly correlated motion of the Pb atom displacements within the layer.

Large spin splitting of metallic surface-state bands at adsorbate-modified gold/silicon surfaces.

Finding appropriate systems with a large spin splitting of metallic surface-state band which can be fabricated on silicon using routine technique is an essential step in combining Rashba-effect based spintronics with silicon technology. We have found that originally poor structural and electronic properties of the Au/Si(111) √3 x √3 surface can be substantially improved by adsorbing small amounts of suitable species (e.g., Tl, In, Na, Cs). The resultant surfaces exhibit a highly-ordered atomic structure and spin-split metallic surface-state band with a momentum splitting of up to 0.052 Å(-1) and an energy splitting of up to 190 meV at the Fermi level. The family of adsorbate-modified Au/Si(111) √3 x √3 surfaces, on the one hand, is thought to be a fascinating playground for exploring spin-splitting effects in the metal monolayers on a semiconductor and, on the other hand, expands greatly the list of material systems prospective for spintronics applications.

Stepwise self-assembly of C60 mediated by atomic scale moiré magnifiers.

Self-assembly of atoms or molecules on a crystal surface is considered one of the most promising methods to create molecular devices. Here we report a stepwise self-assembly of C60 molecules into islands with unusual shapes and preferred sizes on a gold-indium-covered Si(111) surface. Specifically, 19-mer islands prefer a non-compact boomerang shape, whereas hexagonal 37-mer islands exhibit extraordinarily enhanced stability and abundance. The stepwise self-assembly is mediated by the moiré interference between an island with its underlying lattice, which essentially maps out the adsorption-energy landscape of a C60 on different positions of the surface with a lateral magnification factor and dictates the probability for the subsequent attachment of C60 to an island's periphery. Our discovery suggests a new method for exploiting the moiré interference to dynamically assist the self-assembly of particles and provides an unexplored tactic of engineering atomic scale moiré magnifiers to facilitate the growth of monodispersed mesoscopic structures.

[Development of thermotolerance in Drosophila melanogaster line l(1) ts403 with a defect in heat shock protein synthesis]. / Formirovanie termotolerantnosti u linii Drosophila melanogaster l(1) ts403 s narushennym sintezom belkov teplovogo shoka.

To elucidate the role of heat shock proteins (HSP) in the formation of resistance to extreme factors and in the development of organismic and cell response to these factors, thermotolerance in a Drosophila melanogaster line with defective HSP synthesis was studied with regard to several criteria: (1) survival of adult-females; (2) damage to egg chambers in ovarioles; (3) dynamics of oviposition; (4) frequency of loss and nondisjunction of sex chromosomes in meiosis of females exposed to a heat shock (HS). According to all these criteria, the l(l)ts403 females were more sensitive to a HS 37 degrees C, the exposure at 37 degrees C for 1 h (HS37) than the females of the wild-type line Canton S. Only the data on the first three aforementioned parameters were indicative of thermotolerance development. In files exposed to HS35 followed by HS37, a decrease in nondisjunction and loss of sex chromosomes in the 3- and 4-day ovipositions was observed as compared to the flies exposed to HS37 only. This can be explained by the differences in oviposition dynamics and, consequently, in the realization rate of the oogenesis stages in these two experimental variants. The pleiotropic effect of the l(l)ts403 mutation that led to a disturbance in HSP gene expression at the posttranscriptional level and to an increase in the frequency of sex chromosome nondisjunction in the meiosis of females exposed to HS37 suggests that these processes were connected. As no thermotolerance was revealed by studying the sex chromosome nondisjunction, but thermotolerance was found by estimating the other parameters, we suggest that the product of the gene studied is involved in a signal system operating at a stage that precedes the HS-induced changes in the translation and division apparatuses of a cell.

[Cerebrospinal fluid studies in acute lymphoblastic leukemia and lymphosarcomas in children]. / Likvorologicheskie issledovaniia pri ostrom limfoblastnom leikoze i limfosarkomakh u detei.

The author presents data of cerebrospinal fluid (CSF) examinations in children with acute lymphoblastic leukemia and lymphosarcomas. CSF syndromes are described which permit a conclusion on increased permeability of the hematoencephalic barrier in this patient population. CSF changes polymorphism, cyclic pattern are demonstrated, as is a functional specificity of the hematoencephalic barrier in acute lymphoblastic leukemia and lymphosarcomas consisting in a trend to CSF normalization. The author claims that CSF remissions may occur which do not coincide with findings of clinical and morphologic examinations of the CNS in children with hemoblastoses.

[Results of neuroleukemia prevention in children with acute lymphoblastic leukemia]. / Rezul'taty profilaktiki neiroleikoza u detei s ostrym limfoblastnym leikozom.

The follow-up of 318 children with acute lymphoblastic leukemia given program therapy that included different treatments including chemo- and radioprevention of neuroleukemia demonstrated the high efficacy of the measures carried out, which reduced the incidence of neuroleukemia to 5.6%. No gross changes on the part of the neuropsychic status were revealed in the course of the follow-up of children who received the combined prophylaxis of neuroleukemia. The derangement of the CNS was recorded in 17 patients and ran its course in the form of leukemic meningitis and meningoencephalitis.

[Bioelectric activity of the brain of children with long-term remission of acute lymphoblastic leukemia receiving chemoradiation prevention of neuroleukemia]. / Bioélektricheskaia aktivnost' golovnogo mozga u detei s dlitel'noi remissiei ostrogo limfoblastnogo leikoza, poluchivshikh khimioluchevuiu profilaktiku neiroleikoza.

Investigation of the bioelectrical activity of the brain (EEG, echoEG) in 60 patients aged 8 to 20 years with a long relapse-free course of acute lymphoblastic leukemia (6-10 years) made it possible to distinguish 3 groups of patients in accordance with the changes seen on the EEG. A reverse relationship was noted between the characteristics of the leukemic process during disease diagnosis and neurophysiological disorders after intensive therapy including chemoradiation prophylaxis of neuroleukemia. It is recommended that the dose of radiation of the brain of children with acute lymphoblastic leukemia may be reduced, if there are no risk factors of the development of disease relapses.

[Biochemical polymorphic systems and psychological characteristics in residents of the Soviet North-East]. / Biokhimicheskie polimorfnye sistemy i psikhologicheskie osobennosti u zhitelei severo-vostoka SSSR.

15 biochemical polymorphic systems (AcP, PGM, GPT, GLO-1, EsD, PGP, Pp, AK, Gc, Hp, Tf, BO, MN, Le, P) were comparatively studied which possess psychodiagnostic features investigated by means of all-round personality study and 16-factors Kettle personality inventory in 340 healthy residents of Magadan. With the aid of computer cluster analysis, psychodiagnostic features were revealed which authentically differentiate clusters consisting of 5 combined polymorphic systems, three of them being different. Frequency of particular loci participation in differentiation of persons for psychodiagnostic tests is well-coordinated with a degree of their participation in genotype differentiation in those who left and remained in the region. Interrelations between psychological personality features and individual heterozygosis for 12 loci with codominant inheritance are determined. Authentic differences between low- and highly-heterozygous individuals are revealed using the same psychodiagnostic parameters as those in the cluster analysis.

[Effect on the fertility of female Drosophila of sterol metabolism in an ecological-genetic yeast-Drosophila system]. / Vliianie na plodovitost' samok drozofily metabolizma sterinov v ékologo-geneticheskoi sisteme drozhzhi--drozofila.

The consequences of sterol deficiency in feeding of adult Drosophila females have been studied. Feeding of Drosophila on nys 1 mutant strain yeast leads to significant increase of non-developed eggs in Drosophila females. The effect of sterol deficiency on oogenesis in virgin and fertilized females has been estimated using different regimens of feeding. Possible mechanisms of arising of fertility defects are discussed.

[Differential cell mutability during oogenesis and exposure to ethyleneimine and ethylmethane sulfonate in different Drosophila melanogaster lines]. / Differentsial'naia mutabil'nost' kletok v khode oogeneza pri deistvii étilenimina i étilmetansul'fonata u raznykh linii Drosophila melanogaster.

The rate of recessive sex-linked lethal mutations (RLM) was estimated by brood pattern method at different stages of oogenesis, initially, in the wild-type R-86 strain of Drosophila melanogaster after treatment with EI and EMS. The former which is known to induce dominant lethals in mature oocytes of the 14th stage with a high frequency was equally effective in inducing RLM in oocytes of different age and in oogonia. EMS which does not induce dominant lethals when used as vapour was shown to increase RLM frequency in mature fraction of oocytes (the 14A stage only). Similar type of different mutability was found in mutagen-sensitive strain mus-201G1 and in the control 3-4 strain having the same genetical background as mus mutation. Female germ cells of mus-201G1 strain appeared to have a higher mutability in the case of EI, though no differences in mutability between these strains after EMS treatment were registered. The data are discussed in view of the specificity of primer damages occurring as a result of comparable mutagens action and participation of different repair systems in elimination of these damages.