A Universal Description of Workfunction

At the surfaces of materials, the bulk symmetry of the charge density is broken and electron spill-out into the vacuum region creates a surface dipole. Such spill-out has been historically calculated by Lang and Kohn [Phys. Rev. B \textbf{3}, 1215 (1971)] using average electron density to sucessfully explain the workfunction in metals. However, despite its initial success, in the fifty years since it has not been extended beyond simple metals. Here we show that the degree of charge spill-out is largely controlled by the innate bulk workfunction $\phi_I$, which is the Fermi level position of $\it bulk$ relative to the ideal vacuum. By incorporating the contribution of $\phi_I$ to the surface dipole we show that Lang-Kohn's $\it jellium$ based approach can be broadly expanded to understand the workfunction over a wide range of metals, semiconductors, and insulators.Comment: 5 pages, 4 figure

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures.

The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs

Ultrafast Charge Transfer Enhancement in CdS-MoS2 via Linker Molecule

Hybrid systems, which take advantage of low material dimensionality, have great potential for designing nanoscale devices. Quantum dots (QDs) -- a 0D nanostructure -- can be combined with 2D monolayers to achieve success in photovoltaics and photocatalytic water splitting. In such colloidal systems, ligand molecules such as cysteine play an important role in device performance. The role of the ligand molecule in these QD heterostructures is poorly understood. In this study, time-dependent density functional theory (TD-DFT) is employed in order to explore how the ligand affect the charge transfer at the ultra-fast timescale. We study the charge transfer dynamics in CdS-MoS2 heterostructures both with and without an organic linker molecule. We find that the ligand molecule enhances the ultrafast charge transfer, and that electrons are preferentially transferred from CdS to MoS2 as band alignment would predict. The electronic dynamics and time-evolved projection character are sensitive to the ionic temperature and excitation density.Comment: 7 pages; 6 figure

Development of reverse-transcription PCR techniques to analyse the density and sex ratio of gametocytes in genetically diverse Plasmodium chabaudi infections

We have developed cross-genotype and genotype-specific quantitative reverse-transcription PCR (qRT-PCR) assays to detect and quantify the number of parasites, transmission stages (gametocytes) and male gametocytes in blood stage Plasmodium chabaudi infections. Our cross-genotype assays are reliable, repeatable and generate counts that correlate strongly (R(2)s > 90%) with counts expected from blood smears. Our genotype-specific assays can distinguish and quantify different stages of genetically distinct parasite clones (genotypes) in mixed infections and are as sensitive as our cross-genotype assays. Using these assays we show that gametocyte density and gametocyte sex ratios vary during infections for two genetically distinct parasite lines (genotypes) and present the first data to reveal how sex ratio is affected when each genotype experiences competition in mixed-genotype infections. Successful infection of mosquito vectors depends on both gametocyte density and their sex ratio and we discuss the implications of competition in genetically diverse infections for transmission success

Observation of Coulomb repulsion between Cu intercalants in CuxBi2Se3

Using scanning tunneling microscopy and ab initio simulations, we have identified several configurations for Cu dopants in CuxBi2Se3, with Cu intercalants being the most abundant. Through statistical analysis, we show strong short-range repulsive interactions between Cu intercalants. At intermediate range (\u3e5 nm), the pair distribution function shows oscillatory structure along the \u3c 10 (1) over bar \u3e directions, which appear to be influenced by different diffusion barriers along the \u3c 10 (1) over bar \u3e and \u3c 2 (1) over bar(1) over bar \u3e directions

Toward systems biology in brown algae to explore acclimation and adaptation to the shore environment.

International audienceBrown algae belong to a phylogenetic lineage distantly related to land plants and animals. They are almost exclusively found in the intertidal zone, a harsh and frequently changing environment where organisms are submitted to marine and terrestrial constraints. In relation with their unique evolutionary history and their habitat, they feature several peculiarities, including at the level of their primary and secondary metabolism. The establishment of Ectocarpus siliculosus as a model organism for brown algae has represented a framework in which several omics techniques have been developed, in particular, to study the response of these organisms to abiotic stresses. With the recent publication of medium to high throughput profiling data, it is now possible to envision integrating observations at the cellular scale to apply systems biology approaches. As a first step, we propose a protocol focusing on integrating heterogeneous knowledge gained on brown algal metabolism. The resulting abstraction of the system will then help understanding how brown algae cope with changes in abiotic parameters within their unique habitat, and to decipher some of the mechanisms underlying their (1) acclimation and (2) adaptation, respectively consequences of (1) the behavior or (2) the topology of the system resulting from the integrative approach