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Silver nanowire (Ag NW) networks are one of the most promising candidates for the replacement of indium tin oxide (ITO) thin films in many different applications. Recently, Ag-NW-based transparent heaters (THs) showed excellent heating performance. In order to overcome the instability issues of Ag NW networks, researchers have offered different hybrid structures. However, these approaches not only require extra processing, but also decrease the optical performance of Ag NW networks. So, it is important to investigate and determine the thermal performance limits of bare-Ag-NW-network-based THs. Herein, we report on the effect of NW density, contact geometry, applied bias, flexing and incremental bias application on the TH performance of Ag NW networks. Ag-NW-network-based THs with a sheet resistance and percentage transmittance of 4.3 Omega sq(-1) and 83.3%, respectively, and a NW density of 1.6 NW mu m(-2) reached a maximum temperature of 275 degrees C under incremental bias application (5 V maximum). With this performance, our results provide a different perspective on bare-Ag-NW-network-based transparent heaters.

We investigate the electronic transport properties of atomic carbon chain-graphene junctions by using the density-functional theory combining with the non-equilibrium Green's functions. The results show that the transport properties are sensitively dependent on the contact geometry of carbon chain. From the calculated I-V curve we find negative differential resistance (NDR) in the two types of junctions. The NDR can be considered as a result of molecular orbitals moving related to the bias window.

This paper reports that the organic field-effect transistors with hybrid contact geometry were fabricated, in which the top electrodes and the bottom electrodes were combined in parallel resistances within one transistor. With the facility of the novel structure, the difference of contact resistance between the top contact geometry and the bottom contact geometry was studied. The hybrid contact devices showed similar characteristics with the top contact configuration devices, which provide helpful evidence on the lower contact resistance of the top contact configuration device. The origin of the different contact resistance between the top contact device and the bottom contact device was discussed.

The equilibrium electron transport of 1,4-diaminobenzene sandwiched between two Au electrodes is simulated by using a first principles analysis. The results show that equilibrium conductance increases with the molecule- electrode distance decreasing, and a platform occurs at the distance varying from 1.4 A to 1.9 A, implying the insensitiveness of 1,4-diaminobenzene equilibrium conductance to molecule-electrode distance. This is helpful to understand the improved reliability and reproducibility of conductance measurements using amines.

The effect of the geometry of the smaller sliding partner on plasma (triboplasma) generation has been investigated as a function of the tip radius of a diamond pin, which slides against a single crystal sapphire disk under atmospheric dry air pressure. It was found that the diameter and the total intensity of the circular triboplasma increase parabolically with an increase in the tip radius of the pin under constant normal force and sliding velocity. The plasma is most intense at the crossing point of the plasma ring and the frictional track in the plasma circle. The gap distance at the crossing point is independent of the tip radius. The ring diameter increases with an increase in the tip radius, keeping the gap distance constant and obeying Paschen's law of gas discharge.

In the context of contact geometry, we investigate one aspect of the symmetry of thermodynamics. If with a thermodynamic system with n degrees of freedom we associate a (2n + 1)-dimensional thermodynamic phase space then we show that the structure group of its tangent bundle can be reduced to the group U(n) × 1.

Self-heating induced by vias and metal/Si contacts in VLSI circuits is undoubtedly one of the most important reliability issues for microelectronic integrated circuits. In this study the thermal characteristics of Ni/poly-Si contacts subject to an electrical current stressing were investigated. The self-heating induced contact temperature rises were measured for the Ni/poly-Si contacts having different contact resistivity, poly-Si sheet resistance and contact geometry. A current crowding phenomenon inside the contact window was analysed numerically based on a two-dimensional computation model. The temperature rise at the Ni/poly-Si contacts was found to increase proportionally with the heating power density of the contact. The extent of current crowding inside the contact window shows a strong dependence on Rs/ρc ratio and contact size. The effect of contact misalignment on the thermal properties of the contact is also discussed.

We discuss the use of mechanically controllable break-junctions (MCBs) as electrodes for contacting individual objects such as clusters or molecules. A big advantage of MCB electrodes is the possibility of varying the contact geometry and, accordingly, the contact resistances and the quantum coherent transport properties between the object under study and the electrodes. We compare the suitability of single-atom contacts of different elements as electrode material. Finally, we present preliminary results on electronic transport through individual (or a few) fullerene molecules contacted by gold MCB electrodes. The typical resistances are in the order of the quantum of conductance. The circuits sustain voltages of the order of 1 V and are mechanically more stable than single-atom contacts between the gold electrodes alone.

In this paper, the frictional behaviours of single and multi-balls slid against micro-grooved silicon surfaces were investigated by using a micro-tribotester built inside a scanning electron microscope. Various micro-grooves were fabricated on the silicon surface to investigate the frictional behaviour with respect to the contact geometry between the surface asperities. Particularly, fast Fourier transform (FFT) analyses of the friction signals were performed with the motivation to assess the contact conditions. The primary objective of this paper was to understand better the asperity interaction condition at the sliding interface by analysing the frictional force signal using FFT. The experimental and numerical simulation results showed that the relative geometric ratio and the distribution of contact asperities on the surfaces could be predicted by the power and frequency spectra of the FFT analysis of the friction signal. Also, the frictional behaviour for multi-asperities was found to be the result of superposition of the frictional interaction of each asperity contact. It is expected that these observations will be utilized for the design of micro-structured surface with optimum geometry for better tribological performance.

The paper presents a combined solution for multi-body dynamics of a modified cycloidal cam to flat follower with transient lubricated finite line contact conjunction. The solution to the dynamics of the valve train system is undertaken in the Euler frame of reference, which includes valve surge due to the non-linear behaviour of the spring. The elastohydrodynamic transient contact conjunction is analysed in each integration step time by simultaneous solution of the Reynolds' equation in space-time co-ordinates with the instantaneous elastic film shape equation, taking into account the generalized contact elasticity for finite line contact geometry. This approach, not hitherto reported in the literature, yields high generated pressures and thin films at contact extremities that govern wear and fatigue spalling performance of such contacts. Results show that the usual approaches in both quasi-static analyses and transient line contact solutions yield results that are not in line with actual prevailing conditions.

The uniformity of emission from deep ultraviolet light emitting diodes (UV LEDs) is investigated. The AlGaN-based heterostructures of the UV LEDs emitting around 235 nm were grown by metalorganic vapor phase epitaxy on epitaxially laterally overgrown AlN/sapphire substrates. The impact of different device designs on the spatial distribution of the electroluminescence for a series of UV LEDs is studied. Due to the relatively high resistivities of n-AlGaN and p-AlGaN layers, ranging from 10 to 0.1 Ω cm as well as specific contact resistances approaching 1 Ω cm2, the emission patterns revealed heavy current crowding at the mesa edges causing a drop of power in the center of the emitting area and an asymmetry towards the side of the bonding pad of the n-contact. Simple analytical models considering the transfer and the current spreading length could only qualitatively explain the observed emission pattern. Using a 3D electro-thermal simulation of the current spreading in the LEDs the experimentally observed emission pattern could also be quantitatively reproduced. Based on these findings the 3D electro-thermal simulation was employed to optimize the contact geometry of the deep UV LEDs in order to achieve a more uniform power distribution.

Existing solutions for the contact problem involving viscoelastic materials often require numerical differentiation and integration, as well as resolution of transcendental equations, which can raise convergence issues. The algorithm advanced in this paper can tackle the contact behaviour of the viscoelastic materials without any convergence problems, for arbitrary contact geometry, arbitrary loading programs and complex constitutive models of linear viscoelasticity. An updated algorithm for the elastic frictionless contact, coupled with a semi-analytical method for the computation of viscoelastic displacement, is employed to solve the viscoelastic contact problem at a series of small time increments. The number of equations in the linear system resulting from the geometrical condition of deformation is set by the number of cells in the contact area, which is a priori unknown. A trial-and-error approach is implemented, resulting in a series of linear systems which are solved on evolving contact areas, until static equilibrium equations and complementarity conditions are fully satisfied for every cell in the computational domain. At any iteration, cells with negative pressure are excluded from the contact area, while cells with negative gap (i.e. cells where the contacting bodies are predicted to overlap) are reincluded. The solution is found when pressure is stabilized in relation to the imposed normal load. This robust algorithm is expected to solve a large variety of contact problems involving viscoelastic materials.

This study develops a method of solving an inverse problem of a nonlinear ordinary differential equation with incomplete initial conditions. The investigation was originally motivated by the studies in biomedical research on white blood cell-endothelia cell (WBC) adhesion and its related contact geometry. The WBC-EC interaction depends strongly on WBC deformability and the expression of EBC-EC adhesion molecules. A biomechanical model developed to explain this biological interaction has led us to this mathematical problem. Two algorithms for solving the equations have been developed.

The paper describes various analytical procedures that account for the influence of the geometry of a rigid indenter upon the measured contact compliance of a smooth perfectly elastic half space. The analytical solutions provide a means of interrelating the reaction force, P, and the displacement, h, characteristics in terms of the contact geometry and the reduced elastic modulus E*. The general form is P=gE*hn, where g and n are functions only of the indenter geometry. This relationship is incorporated into a curve-fitting procedure and used to evaluate the influence of the indenter geometry upon the computed modulus of a poly(isobutylene) rubber. The method described provides a viable means of incorporating the imperfections, associated with the geometry of an indenter, into the interpretation of contact compliance data.

Height and wavelength parameters of surface roughness are varied to show that three types of surface contact can exist in relation to tribology. These are (i) predominantly plastic asperity contact with gaps in the contact interface, (ii) the same contact geometry but with predominantly elastic asperity contact and (iii) almost total surface contact under an elastic state of stress (this state approaches the theoretical smooth surface conditions). These contact states are confirmed by rough surface contact techniques of a ball-on-flat geometry. Results from simple boundary-lubricated sliding tests are also presented to show that the frictional and tribological behaviour differs significantly for each of these contact states. The fundamental implications for tribology are discussed in relation to this work.

Prediction of mechanical contact performance based on elastic models is not accurate in case of viscoelastic materials; however, a closed-form description of the viscoelastic contact has yet to be found. This paper aims to advance a semi-analytical method for computation of displacement induced in viscoelastic materials by arbitrary surface tractions, as a prerequisite to a semi-analytical solution for the viscoelastic contact problem. The newly advanced model is expected to provide greater generality, allowing for arbitrary contact geometry and / or arbitrary loading history. While time-independent equations in the purely elastic model can be treated numerically by imposing a spatial discretization only, a viscoelastic constitutive law requires supplementary temporal discretization capable of simulating the memory effect specific to viscoelastic materials. By deriving new influence coefficients, computation of displacement induced in a viscoelastic material by a known but otherwise arbitrary history of surface tractions can be achieved via superposition authorized by the Boltzmann superposition theory applicable in the frame of linear viscoelasticity.

In this paper, we have investigated the dependence of the parameters of partial rear metal contact (PRC) solar cells on two commonly used geometrical configurations, viz. grid contact and square contact. It is demonstrated that while the geometry of rear metallic contact having the same fractional coverage changes the base spreading resistance significantly, rear surface passivation and back reflectance depend only on the fractional coverage of the real metal contact and are independent of the geometry of the contact. The performed analysis indicates that the base spreading resistance is much higher for square contact cells compared to that of grid contact cells having the same fractional coverage. While open-circuit voltage and short-circuit current are found to be essentially independent of the contact geometry, the fill factor is significantly affected by the geometry, indicating that the design of high-efficiency cells with partial rear grid contact is less critical in comparison to that of square contact cells for optimized performance. Results indicate that for a 180 μm cell, an efficiency enhancement of 14% is possible for

An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state of the device reached up to 7.5 meV, probably due to the hard wall confinement by using shallow electron gas and sharp point contact geometry. The two-dimensional non-equilibrium shot noise contour map shows noise suppression characteristics in a wide range of bias voltage. Fano factor analysis indicates spin-polarized transport through a short quantum point contact.

Standard statistical mechanics of conservative systems relies on the symplectic geometry of the phase space. This is exploited to derive Hamilton's equations, Liouville's theorem and to find the canonical invariant measure. In this work we analyze the statistical mechanics of a class of nonconservative systems stemming from contact geometry. In particular, we find out the generalized Hamilton's equations, Liouville's theorem and the microcanonical and canonical measures invariant under the contact flow. Remarkably, the latter measure has a power law density distribution with respect to the standard contact volume form. Finally, we argue on the several possible applications of our results., Comment: 8 pages, Theorem 1 added, it matches the published version

We propose a strategy to obtain a hyperelastic constitutive law for film-like systems from molecular dynamics (MD) simulations. The aim is to furnish a computationally efficient continuum model with this description of the material. In particular, two different methods are suggested, both of which consist of virtual experiments that are performed on the material to sample systematically the stress–strain relation. The latter is then fitted to a suitable functional form. We use a polymeric self-assembled monolayer, which spans a height of only a few nanometers, as a test case. Having determined the response function, we then apply it within a finite-element simulation of a continuum mechanical nanoindentation problem. Several contact quantities such as normal reaction forces and the contact geometry are extracted from these calculations and are compared to those from an analogous, fully atomistic nanoindentation simulation. We find that the considered benchmark quantities as obtained from the continuum surrogate model reproduce well the corresponding values of the MD simulation.

Contact geometry and electronic transport properties of a silicon atom sandwiched between Au electrodes in three different anchoring configurations are investigated by using the density functional theory combined with the non-equilibrium Green function method. We simulate the nanoscale junction breaking process and calculate the corresponding cohesion energy, obtain the equilibrium conductance and the projected density of states of junctions in an optimal postion. We also calculate the conductance and the current of junctions at the equilibrium position under small bias voltage. It is found that all junctions have large conductance and show a linear I—V relationship, but the current and conductance of a hollow-hollow configuration is always the biggest under the voltage range of −1.2 V~1.2V. The calculated results proved that the coupling morphology of a silicon atom connected with electrodes has an important effect on the electronic transport properties of the nanoscale junction.

In Seebeck coefficient metrology, the present diversity in apparatus design, acquisition methodology and contact geometry has resulted in conflicting materials data that complicate the interlaboratory confirmation of reported high efficiency thermoelectric materials. To elucidate the influence of these factors in the measurement of the Seebeck coefficient at high temperature and to identify optimal metrology protocols, we measure the Seebeck coefficient as a function of contact geometry under both steady-state and transient thermal conditions of the differential method, using a custom developed apparatus capable of in situ comparative measurement. The thermal gradient formation and data acquisition methodology, under ideal conditions, have little effect on the measured Seebeck coefficient value. However, the off-axis 4-probe contact geometry, as compared to the 2-probe, results in a greater local temperature measurement error that increases with temperature. For surface temperature measurement, the dominant thermal errors arise from a parasitic heat flux that is dependent on the temperature difference between the sample and the external thermal environment, and on the various thermal resistances. Due to higher macroconstriction and contact resistance in the 4-probe arrangement, the measurement of surface temperature for this contact geometry exhibits greater error, thereby overestimating the Seebeck coefficient.

GaN light-emitting diodes (LEDs) based on circular mesa structure are fabricated and their electrical and optical characterizations are performed. The uniform current flow in the circular LED (C-LED) was conducted in the radial direction, from the n-type GaN island electrode at the center to the p-type GaN ring electrode around the perimeter. The symmetric electrode structuring substantially improved the electrical and optical performances. The operating voltage for C-LED at a reference current (100 mA) was 20.9% lower than that of a conventionally structured LED (CV-LED). Also, C-LED showed 19.4% higher optical output power than CV-LED.

Force and conductance were simultaneously measured during the formation of Cu-C60 and C60-C60 contacts using a combined cryogenic scanning tunneling and atomic force microscope. The contact geometry was controlled with submolecular resolution. The maximal attractive forces measured for the two types of junctions were found to differ significantly. We show that the previously reported values of the contact conductance correspond to the junction being under maximal tensile stress.

Applying molecular-level technique to the construction of molecular spin valves is a challenging issue in organic spintronics, in which the magnetoresistive performance is highly sensitive to the device's local contact geometry. Here, we propose a molecular spin-valve design of large-area molecular junction to reduce the geometrical impact. Room-temperature tunneling magnetoresistance and well-defined parallel/antiparallel states are achieved in the spin valve with a molecular spacer. The results hold promise for the development of future molecular-level nonvolatile electronic devices.

Fretting fatigue is a consequence of small oscillatory movement between two contacting parts. This type of damage may give rise to significant reduction in fatigue life of the components. Many parameters such as contact geometry, contact load, friction, material strength and hardness can influence the resistance of materials against fretting damage. Experimental study of fretting fatigue parameters such as crack length measurement at the initial stages of crack growth is either very difficult or not very accurate. Numerical simulations provide a suitable tool for parametric study of fretting fatigue behavior of materials and in particular crack growth measurement. In this work, the effect of pad geometry on crack propagation is investigated by numerical simulation. The simulations are carried out using the finite element codes ANSYS and FRANC2D/L and are validated by the results of some fretting fatigue tests. It is shown that the simulations can predict the crack growth and the number of cycles from the principals of fracture mechanics.

Differential analysis of current-voltage characteristics, obtained on the surface of epitaxial films of ferroelectric lead zirconate titanate (Pb(Zr(0.2)Ti(0.8))O(3)) using scanning probe microscopy, was combined with spatially resolved mapping of variations in local conductance to differentiate between candidate mechanisms of local electronic transport and the origin of disorder. Within the assumed approximations, electron transport was inferred to be determined by two mechanisms depending on the magnitude of applied bias, with the low-bias range dominated by the trap-assisted Fowler-Nordheim tunneling through the interface and the high-bias range limited by the hopping conduction through the bulk. Phenomenological analysis of the I-V curves has further revealed that the transition between the low- and high-bias regimes is manifested both in the strength of variations within the I-V curves sampled across the surface, as well as the spatial distribution of conductance. Spatial variations were concluded to originate primarily from the heterogeneity of the interfacial electronic barrier height with an additional small contribution from random changes in the tip-contact geometry.

We present a statistical model of contact angles and force correlations in granular media with and without friction. The model is motivated by recent measurements of the contact angles and is based on force balance, geometric, and static friction constraints. It reveals preferential alignment of the two largest forces on a grain, which give rise to chain-like force correlations. The dependence of the inter-force angle distributions on coordination number, minimum angle between contacts, space dimension, and stress anisotropy is investigated. The numerical results show qualitative agreement with earlier experiments and simulations, suggesting the importance of the contact geometry in understanding the spatial arrangement of forces in packing.

The friction and adhesion developed between nominally clean monofilaments of polyethylene-terephthalate in a crossed-cylinder configuration. The adhesion is determined by the free surface energy of the fibres and by the contact geometry. A single region of contact is assumed, this provides a means of estimating the effective geometry of the fibres in the contact zone. From the deduced contact geometry, the area of contact as a function of normal load may be calculated using classical elasticity equations. The friction as a function of normal load may be deduced assuming that it arises primarily from shear of polymer at the interface. The calculated values are in good agreement with friction measurements carried out over a wide range of positive and negative loads. However, the friction experiments at negative loads are best considered as a special case of adhesive failure.

The current distribution at the contact to the two-dimensional electron gas has been measured using a specially designed sample geometry. Possible influence of the contacts on magnetotransport measurements has been studied with emphasis on the current distribution in the quantum Hall regime. Finally, we propose a way of optimizing the contact geometry for accurate measurement of the quantized Hall resistance.

It is shown that the compliance of an orthogonal grain-grain contact is so insensitive to the grain geometry in the contact region that this geometry is not at present an important parameter in theories of the speed of propagation of elastic waves in granular media, such as occur in the Earth and in the Moon.

Studies the effect of various surface treatments upon the nanometre-scale thermodynamic and plastic properties of titanium interfaces. A mechanical microprobe technique gives curves of electrical contact resistance versus applied load. The curve shape depends upon the state of the original titanium surfaces. A characteristically stable contact area approximately=10-14 m2, can often be achieved through a combination of surface forces and a high enough load, despite the initial microroughness of the surface. With the help of field emission measurements of contact geometry, surface cleanliness and extent of plastic deformation, values of gamma (Dupre adhesion energy) and H (nanometre-scale hardness of the softer of the two samples) are derived. Ion implantation can reduce the value of gamma by a factor of three, and low values may be associated with the improved wear resistance that such treatment can give.

Friction measurements are reported for the sliding of rubber over individual glass lenses, wavy-surface glass and abrasive paper. Two different apparatuses were employed to obtain friction data. All the experiments were made with the same vulcanised rubber compound moulded with smooth test surfaces to facilitate contact area observations. The measurements covered large ranges of sliding speed (0.001 to 10 mm s-1), ambient temperature (-60 to +90 degrees C), normal load (0.01-57 N) and contact geometry (R=1-18 mm). Some results are given as a function of the sliding velocity by use of the WLF transform. It was found that, particularly for smooth surfaces, the friction varied only slightly with rate (WLF parameter). For the test arrangements employed the viscoelastic response of the rubber compound appeared to be of less importance than the geometry of contact, except when operating conditions were near to the glassy region of the rubber. A simple plot of friction coefficient as a function of the Hertz contact area brought together all the diverse measurements. In the course of experimentation the influence of the method of surface cleaning upon friction was investigated. New insight was also obtained concerning the nature and magnitude of the static friction of rubber.

CONTENTS Introduction Chapter I. Symplectic geometry § 1. Symplectic manifolds § 2. Submanifolds of a symplectic space § 3. Lagrangian manifolds, bundles, maps, and singularities Chapter II. Applications of the theory of Lagrangian singularities § 4. Oscillatory integral § 5. Integral points § 6. Metamorphoses of caustics Chapter III. Contact geometry § 7. Wave fronts § 8. Singularities of fronts § 9. Metamorphoses of fronts Chapter IV. The convolution of invariants and its generalizations § 10. Vector fields tangent to a front § 11. The linearized convolution of invariants § 12. Period maps and intersection forms Chapter V. Lagrangian and Legendrian topology § 13. Lagrangian and Legendrian cobordisms § 14. Lagrangian and Legendrian characteristic classes Chapter VI. Projections § 15. Singularities of projections of surfaces to a plane § 16. Singularities of projections of complete intersections § 17. The geometry of bifurcation diagrams References