Modelling electron tunnelling in the presence of adsorbed materials

University of Technology, Sydney. Institute for Nanoscale Technology.The transport characteristics of single-molecule Au(lll) junctions are investigated using density functional theory (DFT) together with the non-equilibrium Green’s functions formalism (NEGF). DFT optimisations of the adsorption of various molecules on a Au(lll) surface are used as starting points for the equilibrium junction geometries. Test calculations are performed to find a recommended set of parameters for the final DFT results. The interaction energies of several molecules with the Au(lll) surface obtained within the same level of theory are compared. Amine compounds bind preferentially in an adatom geometry and weakly in the out op site. A Z-matrix optimiser is implemented in the SIESTA code as a useful tool for future surface and molecular junction optimisations. Transport properties are calculated for molecular junctions in their equilibrium geometry. While the conductances are orders of magnitude larger than experimental data, the sizes are in line with expectation. The junction geometries are altered in various ways. Changing the binding site or altering the nature of the sulphur-gold interaction in a phenylenedimethanethiol junction, reduces the conductance by a factor of two. Orders of magnitude reduction of conductance is only observed when increasing the distance between a physisorbed molecule and the surface. Increasing this distance for a chemisorbed molecule, results in a surprising increase in conductance. This is attributed to an interplay between the coupling strength of the molecule with the surface and the location of the molecular energy levels relative to the Fermi level. When the chemical bond is broken, the system is spin-polarised and the conductances for electrons of opposite spin types are different by a factor of 250 - the junction acts as a spin-filter. When stretching a diethynylbenzene junction, the strong gold-carbon bond does not break, but rather extracts a gold atom from the surface. In this case the conductance decreases rapidly with stretching. A WKB tunnel barrier model is used as an alternate much faster method for calculating I(V) characteristics. With the surface work functions acting as barrier heights, the relative junction conductances are in good agreement with the DFT results. However, the direction of asymmetry in the I(V) characteristics predicted by the two levels of theory are opposite. More sophisticated barrier shapes may be needed to correctly predict the asymmetries. The tunnelling model is used in conjunction with the DFT results to quantify the effect a gap between an STM tip and monolayer may have on STS measurements

Cardinal\u27s The Words to Say it: The Words to Reproduce Mother

The Words to Say it, an autobiographical novel by Algerian-born Frenchwoman Marie Cardinal, earned praise for the accuracy with which it documents a classic psychoanalysis. Quickly sketched, the plot seems to suggest that the separation from an overpowering mother is effected by paternal language and phallic law—the normal, normative psychic itinerary of the human subject. In its reconsideration of the Oedipal, this essay explores Irigaray\u27s idea of the ambiguities of separation from mother and the possibility that the story of (feminine) subjectivity begins with the mother, begins with affiliation and affirmation even as it speaks of separateness. From this perspective, the protagonist\u27s cure comes about when she associates with her mother\u27s belated madness and sees it as a revolt against the phallic laws of their bourgeois class and against the colonial laws of their Algerian homeland. In the last stages of analysis, the protagonist remembers the language her mother taught her to evoke all the particularities of Algeria; this maternal tongue connects the protagonist both to mother and Motherland. The image of a nurturing Algeria calls for a re-analysis of the cultural drama of the unnamed Algerian war. If the book models an investigation of other psychic versions that challenge what otherwise might be too readily assumed as psychoanalytic law, the book also suggests re-articulating what otherwise might be too readily assumed as cultural law and order

The effect of reciprocal-space sampling and basis set quality on the calculated conductance of a molecular junction

We perform density functional theory and non-equilibrium Green's function calculations of the conductance of a gold wire and a 1,4-phenylenedimethanethiol (XYL) molecule adsorbed between Au(111) electrodes using the TranSIESTA software package. The effect of varying different computational parameters is investigated. We find that the conductance is more sensitive to the reciprocal-space sampling grid than the quality of the basis set employed. The conductance can vary up to a factor of five as a result of the choice of computational parameters. We report a set of computational parameters that yields a well-converged conductance value

Implementation of a Z-matrix approach within the SIESTA periodic boudnary conditions code and its application to surface adsorption

We implement a flexible Z-matrix approach in the density functional theory (DFT) periodic boundary conditions code, SIESTA. This allows a mixture of Z-matrix and Cartesian coordinates to be used for geometry specification and optimisation. In addition, geometry constraints in the form of fixed coordinates and fixed linear relationships between coordinates can be specified. A Z-matrix approach in condensed phase calculations can be advantageous, for example in studying molecular adsorption onto a surface, both in terms of flexibility and efficiency.We demonstrate our implementation for the case of thiol adsorption on the Au(111) surface

Effect of dipole moment on current-voltage characteristics of single molecules

We perform empirical calculations of the tunneling current through various small organic molecules sandwiched between gold electrodes by using the Wenzel-Kramers-Brillouin (WKB) approximation. The barrier to tunneling is taken to be the work function of gold and calculated from a first principles electronic structure code. The current-voltage characteristics of these molecules are compared in the context of existing first principles and experimental results. In this model the surface dipole moment, induced by the adsorbed molecule, can have a significant effect on the current and hence dipole moments may be an important property for prediction of the conductance characteristics of a molecule. © 2006 IEEE

Depression is associated with decreased severity and lower mortality in non-elderly hospitalized adults with influenza in the United States

Background: Depression is associated with risk for chronic disease, though its relationship with infectious diseases is less understood. Depression may modify the clinical outcomes of patients with infectious diseases such as influenza via its association with inflammation. The objective of this study was to evaluate the relationships between depression and clinical outcomes in non-elderly adults with influenza infection. Methods: This was a secondary analysis of the Nationwide Inpatient Sample database, years 2012-2016. Hospitalized adults aged 18-65 admitted during each influenza season were included. Depression status was documented via ICD-10 codes. The association between depression and clinical outcomes (e.g. disease severity, length of hospital stay, and inpatient all-cause mortality) were evaluated using multivariable regression modeling. Results: A total of 44,292 patients were included, 12% with depression. After adjustment for confounding, non-elderly influenza patients with depression had a 3.8% decreased risk of a severe disease (95% CI: 1.9% - 5.7%; P=0.028). Conclusions: This study suggests that in non-elderly hospitalized patients with influenza, depression is associated with a decreased severity of illness and acute mortality. Chronic inflammation in those with depression may enhance the ability of the immune response to limit influenza infection or reduce pathologic acute inflammation associated with influenza disease

Evaluation of half wave induction motor drive for use in passenger vehicles

Research performed at the University of Missouri-Columbia to devise and design a lower cost inverter induction motor drive for electrical propulsion of passenger vehicles is described. A two phase inverter motor system is recommended. The new design is predicted to provide comparable vehicle performance, improved reliability and a cost advantage for a high production vehicle, decreased total rating of the power semiconductor switches, and a somewhat simpler control hardware compared to the conventional three phase bridge inverter motor drive system. The major disadvantages of the two phase inverter motor drive are that it is larger and more expensive than a three phase machine, the design of snubbers for the power leakage inductances produce higher transient voltages, and the torque pulsations are relatively large because of the necessity to limit the inverter switching frequency to achieve high efficiency

A new class of self-assembled monolayers on gold using an alkynyl group as a linker

The geometry and energetics for adsorption of ethynylbenzene on Au(111) have been studied using Density Functional Theory. The alkynyl group, following removal of the terminal H atom, adsorbs covalently to the surface in the fcc hollow site with a bond energy of about 70 kcal.mol-1. Intermediate adsorption states are also possible via a hydrogen 1,2 shift to form a surface-bound vinylidene, or through the opening of the C-C triple bond without removing the hydrogen atom. © 2006 IEEE