Characterization of TiO 2 atomic crystals for nanocomposite materials oriented to optoelectronics

Atomic cluster (TiO 2 ) 3 is studied by means of state of the art techniques for structural, electronic and optical properties. We combine molecular dynamics, density functional theory, time dependent density functional theory and many body techniques, to provide a deep and comprehensive characterization of the system. Atomic clusters can be considered the starting seeds for the synthesis of larger nanostructures of technological interest. Also, given the complexity of the material itself, a clear theoretical description of its basic properties provides interesting results both from the solid state physics and chemistry point of view

Imaging Photoelectron Transmission through Self-Assembled Monolayers: The Work-Function of Alkanethiols Coated Gold

In this paper, we present a new approach for studying the electronic properties of self-assembled monolayers and their interaction with a conductive substrate, the low-energy photoelectron imaging spectroscopy (LEPIS). LEPIS relies on imaging of photoelectrons ejected from a conductive substrate and subsequently transmitted through organic monolayers. Using this method, we measure the relative work-function of alkanethiols of different length on gold substrate, and we are able to follow the changes occurring when the surface coverage is varied. We also computed the work-function of model alkanethiols using a plane-wave density functional theory approach, in order to demonstrate the correlation between changes in the work-function with the monolayer organization and density

A Shearless microfluidic device detects a role in mechanosensitivity for awcon neuron in Caenorhabditis elegans

AWC olfactory neurons are fundamental for chemotaxis toward volatile attractants in Caenorhabditis elegans. Here, it is shown that AWC(ON) responds not only to chemicals but also to mechanical stimuli caused by fluid flow changes in a microfluidic device. The dynamics of calcium events are correlated with the stimulus amplitude. It is further shown that the mechanosensitivity of AWC(ON) neurons has an intrinsic nature rather than a synaptic origin, and the calcium transient response is mediated by TAX-4 cGMP-gated cation channel, suggesting the involvement of one or more "odorant" receptors in AWC(ON) mechano-transduction. In many cases, the responses show plateau properties resembling bistable calcium dynamics where neurons can switch from one stable state to the other. To investigate the unprecedentedly observed mechanosensitivity of AWC(ON) neurons, a novel microfluidic device is designed to minimize the fluid shear flow in the arena hosting the nematodes. Animals in this device show reduced neuronal activation of AWC(ON) neurons. The results observed indicate that the tangential component of the mechanical stress is the main contributor to the mechanosensitivity of AWC(ON). Furthermore, the microfluidic platform, integrating shearless perfusion and calcium imaging, provides a novel and more controlled solution for in vivo analysis both in micro-organisms and cultured cells

Anomalous anisotropic exciton temperature dependence in rutile TiO2{\mathrm{TiO}}_{2}

Elucidating the details of electron-phonon coupling in semiconductors and insulators is a topic of pivotal interest, as it governs the transport mechanisms and is responsible for various phenomena such as spectral-weight transfers to phonon sidebands and self-trapping. Here, we investigate the influence of the electron-phonon interaction on the excitonic peaks of rutile TiO2, revealing a strong anisotropic polarization dependence with increasing temperature, namely, an anomalous blue shift for light polarized along the a axis and a conventional red shift for light polarized along the c axis. By employing many-body perturbation theory, we identify two terms in the electron-phonon interaction Hamiltonian that contribute to the anomalous blue shift of the a-axis exciton. Our approach paves the way to a complete ab initio treatment of the electron-phonon interaction and of its influence on the optical spectra of polar materials

An ab initio study of the magnetic-metallic CoPt(3)-Au interfaces.

Peer reviewe

Self-Energy and Excitonic Effects in the Electronic and Optical Properties of TiO2 Crystalline Phases

We present a unified ab-initio study of electronic and optical properties of TiO2 rutile and anatase phases, with a combination of Density Functional Theory and Many Body Perturbation Theory techniques. The consistent treatment of exchange-correlation, with the inclusion of many body one-particle and two-particles effects in self-energy and electron-hole interaction, produces a high quality description of electronic and optical properties, giving, for some quantities, the first available estimation for this compound. In particular, we give a quantitative, direct evaluation of the electronic and direct optical gaps, clarifying their role with respect to previous values obtained by various experimental techniques. We obtain a description for both electronic gap and optical spectra that is consistent with experiments, analysing the role of different contributions to the experimental optical gap and relating them to the level of theory used in our calculations. We also show the spatial nature of excitons in the two crystalline phases, highlighting the localization character of different optical transitions. This paper aims at understanding and firmly establishing electro-optical bulk properties, so far not yet clarified, of this material of fundamental and technological interest for green energy applications.Comment: 33 pages, 7 figure

A statistical mechanics investigation of unfolded protein response across organisms

Living systems rely on coordinated molecular interactions, especially those related to gene expression and protein activity. The Unfolded Protein Response is a crucial mechanism in eukaryotic cells, activated when unfolded proteins exceed a critical threshold. It maintains cell homeostasis by enhancing protein folding, initiating quality control, and activating degradation pathways when damage is irreversible. This response functions as a dynamic signaling network, with proteins as nodes and their interactions as edges. We analyze these protein-protein networks across different organisms to understand their intricate intra-cellular interactions and behaviors. In this work, analyzing twelve organisms, we assess how fundamental measures in network theory can individuate seed proteins and specific pathways across organisms. We employ network robustness to evaluate and compare the strength of the investigated protein-protein interaction networks, and the structural controllability of complex networks to find and compare the sets of driver nodes necessary to control the overall networks. We find that network measures are related to phylogenetics, and advanced network methods can identify main pathways of significance in the complete Unfolded Protein Response mechanism

Zinc Porphyrin‐Driven Assembly of Gold Nanofingers

Nanofingers of gold covered by porphyrins are prepared by a combination of atomic manipulation and surface self-organization. A submonolayer of zinc(II) 5,10,15,20-tetrakis(4-tert-butylphenyl)-porphyrin (ZnTBPP) axially ligated to a self-assembled monolayer of 4-aminothiophenol (4-ATP) on Au(111) is prepared and studied using a combination of ultrahigh vacuum techniques. Under the electric field produced by the STM tip, the relatively weakly bound Au surface atoms along the discommensuration lines become mobile due to the strong bond to 4-ATP, while the tendency of the porphyrins towards self-assembly result in a collective motion of gold clusters. The clusters diffuse onto the surface following well-defined pathways along the [112] direction and then reach the step edges where they assembled, thus forming nanofingers. First-principles density functional theory calculations demonstrate the reduction of the binding energies between the surface gold clusters and the substrate induced by adsorption of thiols. Scanning tunneling microscopy images show assemblies across three adjacent discommensuration lines of the Au(111)-(22 x square root 3) reconstruction, which collectively diffuse along these lines to form islands nucleated at step edges

Structure, electronic, and optical properties of TiO 2 atomic clusters: An ab initio study

Atomic clusters of TiO 2 are modeled by means of state-of-the-art techniques to characterize their structural, electronic and optical properties. We combine ab initio molecular dynamics, static density functional theory, time-dependent density functional theory, and many body techniques, to provide a deep and comprehensive characterization of these systems. TiO 2 clusters can be considered as the starting seeds for the synthesis of larger nanostructures, which are of technological interest in photocatalysis and photovoltaics. In this work, we prove that clusters with anatase symmetry are energetically stable and can be considered as the starting seeds to growth much larger and complex nanostructures. The electronic gap of these inorganic molecules is investigated, and shown to be larger than the optical gap by almost 4 eV. Therefore, strong excitonic effects appear in these systems, much more than in the corresponding bulk phase. Moreover, the use of various levels of theory demonstrates that charge transfer effects play an important role under photon absorption, and therefore the use of adiabatic functionals in time dependent density functional theory has to be carefully evaluated. © 2011 American Institute of Physics.We acknowledge financial support from Spanish MEC (FIS2011-65702-C02-01), ACI-Promociona (ACI2009- 1036), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT-319-07), the European Research Council Advanced Grant DYNamo (ERC-2010-AdG -Proposal No. 267374) and the European Research Council Starting Grant DEDOM (Grant Agreement No. 207441). We acknowledge support by the Barcelona Supercomputing Center, “Red Espanola de Supercomputacion,” SGIker ARINA (UPV/EHU), Transna tional Access Programme HPC-Europe++, CNS-Ipicyt, Mexico and CINECA. L.C. acknowledges funding from UPV/EHU through the “Ayudas de Especialización para Investigadores Doctores” program. A.H.R. has been supported by CONACyT Mexico under projects J-152153-F, and TAMU-CONACyT.Peer Reviewe

Prediction and modelling of RNA structure and interactions

BMC Bioinformatics is calling for submissions to our Collection on “Prediction and modelling of RNA structure and interactions”. This Collection welcomes submissions on novel algorithms, computational methods and tools on the topics of classification, analysis, comparison and evolution of RNA molecules , approaches to RNA structure (inverse) prediction —both at the level of secondary and tertiary structure— and study of RNA interactions with other biological or synthetic molecules. Focus on particular classes of RNAs, such as ribosomal RNA, long non-coding RNAs and viral genomes, is welcome