The energetics and thermodynamic properties of two-dimensional binary graphene-like alloys made from graphene, silicene, or germanene are investigated by combining first-principles total energy ...calculations, and a statistical approach to account for disorder and composition effects. For the electronic properties the calculations are performed within the GGA1/2 approach for an approximate quasiparticle bands. We derive lattice constants, first-neighbor distances, and buckling parameters as a function of composition x. The system Si sub(1-x) Ge sub(x) is the only stable random alloy at usual growth temperatures. For Ge sub(1-x) C sub(x), we observe strong distortions of the lattice making the random configurations less favorable and leading to a pronounced tendency for phase separation. The situation for Si sub(1-x) C sub(x) alloys is completely different. An ordered structure with composition x = 0.5 is stable up to T approximately 1000 K, while intermediate compositions are mainly realized by silicongraphene and graphene or silicene. The ordering and decomposition effects have a strong influence on the average fundamental energy gap versus composition. Whereas large gaps appear for Si sub(1-x) C sub(x) systems they almost vanish for Ge sub(1-x) Si sub(x) and Ge sub(1-x) C sub(x). Moreover, the dependence of the energy gap on growth temperature is also obtained. The results can be very useful for chemical vapor deposition growth of these materials.
Recent genome-wide association studies have suggested novel risk loci associated with periodontitis, which is initiated by dysbiosis in subgingival plaque and leads to destruction of teeth-supporting ...structures. One such genetic locus was the tumor necrosis factor receptor–associated factor 3 interacting protein 2 (TRAF3IP2), a gene encoding the gate-keeping interleukin (IL)–17 receptor adaptor. In this study, we first determined that carriers of the lead exonic variant rs13190932 within the TRAF3IP2 locus combined with a high plaque microbial burden was associated with more severe periodontitis than noncarriers. We then demonstrated that TRAF3IP2 is essential in the IL-17–mediated CCL2 and IL-8 chemokine production in primary gingival epithelial cells. Further analysis suggested that rs13190932 may serve a surrogate variant for a genuine loss-of-function variant rs33980500 within the same gene. Traf3ip2 null mice (Traf3ip2–/–) were more susceptible than wild-type (WT) mice to the Porphyromonas gingivalis–induced periodontal alveolar bone loss. Such bone loss was associated with a delayed P. gingivalis clearance and an attenuated neutrophil recruitment in the gingiva of Traf3ip2–/– mice. Transcriptomic data showed decreased expression of antimicrobial genes, including Lcn2, S100a8, and Defb1, in the Traf3ip2–/– mouse gingiva in comparison to WT mice prior to or upon P. gingivalis oral challenge. Further 16S ribosomal RNA sequencing analysis identified a distinct microbial community in the Traf3ip2–/– mouse oral plaque, which was featured by a reduced microbial diversity and an overabundance of Streptococcus genus bacteria. More P. gingivalis was observed in the Traf3ip2–/– mouse gingiva than WT control animals in a ligature-promoted P. gingivalis invasion model. In agreement, neutrophil depletion resulted in more local gingival tissue invasion by P. gingivalis. Thus, we identified a homeostatic IL-17-TRAF3IP2-neutrophil axis underpinning host defense against a keystone periodontal pathogen.
We discuss the consequences of the quantum uncertainty on the spectrum of the electron emitted by the beta-processes of a tritium atom bound to a graphene sheet. We analyze quantitatively the issue ...recently raised by Cheipesh, Cheianov, and Boyarsky Phys. Rev. D 104, 116004 (2021), and discuss the relevant timescales and the degrees of freedom that can contribute to the intrinsic spread in the electron energy. We perform careful calculations of the potential between tritium and graphene with different coverages and geometries. With this at hand, we propose possible avenues to mitigate the effect of the quantum uncertainty.
This commentary integrates and expands on the preceding articles in this issue that document and celebrate a century of women’s achievements in the International Association for Dental Research ...(IADR). The increasing participation and leadership of women in dental and craniofacial research and within the IADR were viewed from the perspective of a changing culture of science. The steps that have been taken by the IADR to develop greater inclusiveness are acknowledged, and some of the challenges that remain are discussed in terms of obstacles that are most often social or cultural in origin. Comparisons are made across countries, and the social determinants that lead to differences in women’s participation are described. Recommendations are made for developing strategies to change elements of our institutional cultures that have provided advantages to some groups of researchers more than to others. The unconscious biases and a lack of commitment to diversity, equity, and inclusion that limit the participation of members of some groups limit the progress and achievements of science in general.
We investigate the chemically tunable properties of understoichiometric graphene oxide as a function of the growth temperature and the amount of hydroxyl and epoxy groups adsorbed on graphene. The ...structural disorder is modeled within a statistical approach based on a cluster expansion. A set of 308 cluster symmetry classes is investigated with ab initio calculations based on density functional theory. A complete scenario of energetics and phase stability is developed, yielding insight into the structure and electronic properties of graphene oxide. Our results show that the tendency to agglomeration of oxygen-containing groups is independent of their relative proportion and indicate the favorable formation of a unique oxygen-rich phase with both groups. Structural and electronic properties are predicted for the whole range of chemical compositions. The optical properties of oxygen-rich phases are also discussed in detail for different growth conditions.
We provide approximate quasiparticle-corrected band gap energies for quaternary cubic and hexagonal Al
x
Ga
y
In1–x–y
N semiconductor alloys, employing a cluster expansion method to account for the ...inherent statistical disorder of the system. Calculated values are compared with photoluminescence measurements and discussed within the currently accepted model of emission in these materials by carrier localization. It is shown that bowing parameters are larger in the cubic phase, while the range of band gap variation is bigger in the hexagonal one. Experimentally determined transition energies are mostly consistent with band-to-band excitations.
Two-dimensional materials are ideal platforms to explore new physical phenomena and reveal unique optical properties. Excitonic and quasiparticle effects are strongly enhanced by the reduced ...screening. The response to a perturbing electromagnetic field is dominated by in-plane light polarization. The quantum confinement of the atomic sheets in normal direction also allows out-of-plane pair excitations, which are ruled by selection rules and local-field effects. We apply the GW approximation and the Bethe-Salpeter equation to investigate optical transitions for light polarization both parallel and normal to the atomic planes. Prototypical systems range from semimetals to large-gap insulators such as graphene, graphene oxide, boron nitride, and molybdenum disulfide. For the considered materials, the out-of-plane absorption edge and the first van Hove singularities are blueshifted in dependence of the effective sheet thickness, while the intensity of the optical conductivity is reduced by orders of magnitude.
The (BN)1−x(C2)x alloys are promising materials for band-gap engineering in two-dimensional electronics. In this work, we provide a complete scenario of statistical possibilities for the distribution ...of atoms and its influence on electronic and optical properties. Using first-principles calculations combined with the generalized quasichemical approximation to account for disorder effects, we study the properties of these two-dimensional alloys as a function of their average composition. Our results show that atomic arrangements with C-C and B-N bonds are energetically favored over the ones with B-B and N-N bonds, explaining the known tendency to phase separation, verified by a T−x phase diagram. We calculate the energy gap as a function of the composition considering both composition fluctuation and phase separation effects. Experimental data are discussed in this context. Finally, we obtain absorption spectra reproducing a two-peak pattern for intermediate carbon concentrations found experimentally and identified with phase-segregated instead of homogeneous alloys.
First-principles calculations and statistical methods were combined to study electronic, magnetic, thermodynamic and structural properties of zincblende (III,Mn)V and (III,Cr)V magnetic semiconductor ...alloys, including both nitride and arsenide alloys. From phase diagrams it was observed that nitride alloys are much less stable than arsenide ones, although the former ones have more localized d-states at the Fermi level. It was observed that all alloys present an anisotropic behavior, with the strongest magnetic interaction in the 〈110〉 direction. The relationship between the structural properties of these alloys and their electronic and magnetic characteristics (i.e., their half-metallicity) was investigated.
At the same time that two-dimensional (2D) systems open possibilities for new physics and applications, they present a higher challenge for electronic structure calculations, especially concerning ...excitations. The achievement of a fast and accurate practical model that incorporates approximate quasiparticle corrections can further open an avenue for more reliable band structure calculations of complex systems such as interactions of 2D materials with substrates or molecules, as well as the formation of van der Waals heterostructures. In this work, we demonstrate that the performance of the fast and parameter-free DFT-1/2 method is comparable with state-of-the-art GW and superior to the HSE06 hybrid functional in the majority set of the 34 different 2D materials studied. Moreover, based on the knowledge of the method and chemical information of the material, we can predict the small number of cases in which the method is not so effective and also provide the best recipe for an optimized DFT-1/2 method based on the electronegativity difference of the bonding atoms.
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