GeVn complexes for silicon-based room-temperature single-atom nanoelectronics

We characterize germanium-vacancy GeVn complexes in silicon using first-principles Density Functional Theory calculations with screening-dependent hybrid functionals. We report on the local geometry and electronic excited states of these defects, including charge transition levels corresponding to the addition of one or more electrons to the defect. Our main theoretical result concerns the GeV complex, which we show to give rise to two excited states deep in the gap, at -0.51 and -0.35 eV from the conduction band, consistently with the available spectroscopic data. The adopted theoretical scheme, suitable to compute a reliable estimate of the wavefunction decay, leads us to predict that such states are associated to an electron localization over a length of about 0.45 nm. By combining the electronic properties of the bare silicon vacancy, carrying deep states in the band gap, with the spatial controllability arising from single Ge ion implantation techniques, the GeVn complex emerges as a suitable ingredient for silicon-based room-temperature single-atom devices

Mitochondrial and Y-chromosome diversity of the Tharus (Nepal): a reservoir of genetic variation

Background Central Asia and the Indian subcontinent represent an area considered as a source and a reservoir for human genetic diversity, with many markers taking root here, most of which are the ancestral state of eastern and western haplogroups, while others are local. Between these two regions, Terai (Nepal) is a pivotal passageway allowing, in different times, multiple population interactions, although because of its highly malarial environment, it was scarcely inhabited until a few decades ago, when malaria was eradicated. One of the oldest and the largest indigenous people of Terai is represented by the malaria resistant Tharus, whose gene pool could still retain traces of ancient complex interactions. Until now, however, investigations on their genetic structure have been scarce mainly identifying East Asian signatures. Results High-resolution analyses of mitochondrial-DNA (including 34 complete sequences) and Y-chromosome (67 SNPs and 12 STRs) variations carried out in 173 Tharus (two groups from Central and one from Eastern Terai), and 104 Indians (Hindus from Terai and New Delhi and tribals from Andhra Pradesh) allowed the identification of three principal components: East Asian, West Eurasian and Indian, the last including both local and inter-regional sub-components, at least for the Y chromosome. Conclusion Although remarkable quantitative and qualitative differences appear among the various population groups and also between sexes within the same group, many mitochondrial-DNA and Y-chromosome lineages are shared or derived from ancient Indian haplogroups, thus revealing a deep shared ancestry between Tharus and Indians. Interestingly, the local Y-chromosome Indian component observed in the Andhra-Pradesh tribals is present in all Tharu groups, whereas the inter-regional component strongly prevails in the two Hindu samples and other Nepalese populations. The complete sequencing of mtDNAs from unresolved haplogroups also provided informative markers that greatly improved the mtDNA phylogeny and allowed the identification of ancient relationships between Tharus and Malaysia, the Andaman Islands and Japan as well as between India and North and East Africa. Overall, this study gives a paradigmatic example of the importance of genetic isolates in revealing variants not easily detectable in the general population

Fingerprints of sp1 Hybridized C in the near-edge X-ray absorption spectra of surface-grown materials

Carbon structures comprising sp1 chains (e.g., polyynes or cumulenes) can be synthesized by exploiting on-surface chemistry and molecular self-assembly of organic precursors, opening to the use of the full experimental and theoretical surface-science toolbox for their characterization. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) can be used to determine molecular adsorption angles and is here also suggested as a probe to discriminate sp1/sp2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp1/sp2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp2 systems. We then consider a mixed polymer alternating sp1 C4 units with sp2 biphenyl groups, recently synthesized on Au(111), as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the the presence of linear C chains. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp1 hybridization in surface-grown C structures

Effects of the introduction of a chromium oxide monolayer at the C60/Fe(001) interface

The introduction of a two-dimensional oxide layer at the interface between an organic semiconductor and a ferromagnetic metal (spinterface) can help in tailoring the formation of spin-polarized hybridized interface states. Here, we consider the case of a Cr4O5 monolayer at the C-60/Fe(001) interface, which is already known to feature the occurrence of spin-polarized states in the fullerene molecules. In this work, we employ scanning tunneling microscopy/spectroscopy and photoemission spectroscopy to show that the C-60/Cr4O5/Fe(001) spinterface is characterized by the formation of a well-ordered fullerene monolayer and of strongly hybridized interface states. These experimental results are discussed in terms of state-of-the-art ab lingo calculations of the structural, electronic, and magnetic properties at the interface

Surface states characterization in the strongly interacting graphene/Ni(111) system

By combining nonlinear photoemission experiments and density functional theory calculations, we study the modification of Ni(111) surface states induced by the presence of graphene. The main result is that graphene is able to displace the Ni(111) surface states from the valence band close to the Fermi level uncovering the d-band of Ni. The shift of the surface states away from the Fermi level modifies their k-dispersion and the effective mass. The unoccupied image state of graphene/Ni(111) has been also characterized. The ab initio calculations give a theoretical insight into the electronic properties of graphene/Ni(111) in the two stable top-fcc and top-bridge phases showing that the interface properties are poorly dependent on the stacking. The screening properties to an externally applied electric field are also discussed

The Mitogenome Relationships and Phylogeography of Barn Swallows (Hirundo rustica)

The barn swallow (Hirundo rustica) poses a number of fascinating scientific questions, including the taxonomic status of postulated subspecies. Here, we obtained and assessed the sequence variation of 411 complete mitogenomes, mainly from the European H. r. rustica, but other subspecies as well. In almost every case, we observed subspecies-specific haplogroups, which we employed together with estimated radiation times to postulate a model for the geographical and temporal worldwide spread of the species. The female barn swallow carrying the Hirundo rustica ancestral mitogenome left Africa (or its vicinity) around 280 thousand years ago (kya), and her descendants expanded first into Eurasia and then, at least 51 kya, into the Americas, from where a relatively recent (<20 kya) back migration to Asia took place. The exception to the haplogroup subspecies specificity is represented by the sedentary Levantine H. r. transitiva that extensively shares haplogroup A with the migratory European H. r. rustica and, to a lesser extent, haplogroup B with the Egyptian H. r. savignii. Our data indicate that rustica and transitiva most likely derive from a sedentary Levantine population source that split at the end of the Younger Dryas (YD) (11.7 kya). Since then, however, transitiva received genetic inputs from and admixed with both the closely related rustica and the adjacent savignii. Demographic analyses confirm this species' strong link with climate fluctuations and human activities making it an excellent indicator for monitoring and assessing the impact of current global changes on wildlife

Growth and electronic structure of 2D hexagonal nanosheets on a corrugated rectangular substrate

Graphene and h-BN are grown by chemical vapor deposition in ultra high vacuum conditions on the Pt(110) surface. Scanning tunneling microscopy measurements and low-energy electron diffraction data indicate that graphene forms a variety of differently oriented incommensurate domains although with a strong preference to align its [1120] direction with the [001] direction of Pt. Meanwhile, h-BN exhibits a c(8 7 10) commensurate superstructure, which presents a high level of defectivity that implies local variation of the periodicity (i.e. mixed c(8 7 10) and c(8 7 12) patches) and the introduction of local defects. The combination of advanced photoemission spectroscopy data (angle-resolved photoemission spectroscopy from the valence band) and ab initio calculations indicates that both 2D materials interact weakly with the substrate: graphene exhibits neutral doping and is morphologically flat, even if it nucleates on the relatively highly corrugated rectangular (110) surface. In the case of h-BN, the interaction is slightly stronger and is characterized by a small electron transfer from surface Pt atoms to nitrogen atoms. The (110) termination of Pt is therefore a quite interesting surface for the growth of 2D materials because given its low symmetry, it may favor the growth of selectively oriented domains but does not affect their pristine electronic properties

Magnetic properties of coordination clusters with Mn4 and Co4 antiferromagnetic cores

We present a joint experimental and theoretical characterization of the magnetic properties of coordination clusters with an antiferromagnetic core of four magnetic ions. Two different compounds are analyzed, with Co and Mn ions in the core. While both molecules are antiferromagnetic, they display different sensitivities to external magnetic field, according to the different atomic magnetic moments and strength of the intra-molecular magnetic couplings. In particular, the dependence of the magnetization versus field of the two molecules switches with temperature: at low temperature the magnetization is smaller in Mn4 than in Co4, while the opposite happens at high temperature. Through a detailed analysis of the electronic and magnetic properties of the two compounds we identify a stronger magnetic interaction between the magnetic ions in Mn4 with respect to Co4. Moreover Co4 displays not negligible spin–orbit related effects that could affect the spin lifetime in future antiferromagnetic spintronic applications. We highlight the necessity to account for these spin–orbit effects together with electronic correlation effects for a reliable description of these compounds