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We use molecular dynamics simulation to study the formation of glasses during severe plastic deformation of crystalline Cu|Zr nano-layers in a simple shear geometry. The early stage of plasticity is governed by dislocation plasticity. Dislocation-interface interaction induces interface roughening and slow atomic-level intermixing around interfaces. A solid-state crystal-to-amorphous transition starts near the interfaces. At high strain, the interfaces are refined to merge, leading to the formation of an intermixed glassy zone that eventually spans our simulation cell. Dislocation emission is then suppressed and strain is fully accommodated by this glassy phase. We characterize the crystal-to-amorphous transition using local structural measures, such as the pair distribution function and Voronoi analysis. The onset of glass formation occurs at a critical shear strain that increases with layer thickness. Our simulations indicate that the parameter controlling this onset is the theoretical affine interface distance, i.e. the amorphization occurs at a critical value of around 3-4 nm that increases slightly with the increase of layer thickness. Our work provides insights on mechanically driven glass formation in multicomponent systems, as e.g. realized in ball-mills or high-pressure torsion experiments.

Numerous rock engineering applications require a reliable estimation of fracture permeabilities to predict fluid flow and transport processes. Since measurements of fracture properties at great depth are extremely elaborate, representative fracture geometries typically are obtained from outcrops or core drillings. Thus, physically valid numerical approaches are required to compute the actual fracture geometries under in situ stress conditions. Hence, the objective of this study is the validation of a fast Fourier transform (FFT)-based numerical approach for a circular granodiorite fracture considering stress-dependent normal closure. The numerical approach employs both purely elastic and elastic-plastic contact deformation models, which are based on high-resolution fracture scans and representative mechanical properties, which were measured in laboratory experiments. The numerical approaches are validated by comparing the simulated results with uniaxial laboratory tests. The normal stresses applied in the axial direction of the cylindrical specimen vary between 0.25 and 10 MPa. The simulations indicate the best performance for the elastic-plastic model, which fits well with experimentally derived normal closure data (root-mean-squared error = 9 µm). The validity of the elastic-plastic model is emphasized by a more realistic reproduction of aperture distributions, local stresses and contact areas along the fracture. Although there are differences in simulated closure for the elastic and elastic-plastic models, only slight differences in the resulting aperture distributions are observed. In contrast to alternative interpenetration models or analytical models such as the Barton-Bandis models and the ""exponential repulsion model"", the numerical simulations reproduce heterogeneous local closure as well as low-contact areas (

Ni50Ti50 nm-sized amorphous particles are prepared using inert-gas condensation followed by in situ compaction. Elemental segregation of Ni and Ti is observed in the consolidated nanostructured material. Amorphous, nearly pure Nickel (96%) nanophases form within the amorphous Ni50Ti50 alloy. Combining atom probe tomography and scanning transmission electron microscopy with computer modelling, we explore the formation process of such amorphous nanophase structure. It is shown that the Ni rich amorphous phase in the consolidated nanostructured material is responsible for the ferromagnetic behavior of the sample whereas the rapidly quenched amorphous and crystalline samples with the same chemical composition (Ni50Ti50) were found to be paramagnetic. Due to the high cooling rate obtained using the inert gas condensation technique, an exceptional control over the crystallization processes is possible, promoting the formation of various amorphous phases, which are not obtained by standard rapid quenching techniques. Our findings demonstrate the potential of amorphous metallic nanostructures as advanced technological materials, and useful magnetic compounds.

Surface roughness affects the functional properties of surfaces, including adhesion, friction, hydrophobicity, biological response, and electrical and thermal transport properties. However, experimental investigations to quantify these links are often inconclusive because surfaces are fractal-like, and the values of measured roughness parameters depend on measurement size. Here, we demonstrate the characterization of topography of an ultrananocrystalline diamond (UNCD) surface at the angstrom scale using transmission electron microscopy (TEM), as well as its combination with conventional techniques to achieve a comprehensive surface description spanning 8 orders of magnitude in size. We performed more than 100 individual measurements of the nanodiamond film using both TEM and conventional techniques (stylus profilometry and atomic force microscopy). While individual measurements of root-mean-square (RMS) height, RMS slope, and RMS curvature vary by orders of magnitude, we combine the various techniques using the power spectral density and use this to compute scale-independent parameters. This analysis reveals that ""smooth"" UNCD surfaces have an RMS slope greater than 1, even larger than the slope of the Austrian Alps when measured on the scale of a human step. This approach of comprehensive multiscale roughness characterization, measured with angstrom-scale detail, will enable the systematic evaluation and optimization of other technologically relevant surfaces, as well as systematic testing of the many analytical and numerical models for the behavior of rough surfaces.

We present an embedded atom method (EAM) potential for the binary Cu-Au system. The unary phases are described by two well-tested unary EAM potentials for Cu and Au. We fitted the interaction between Cu and Au to experimental properties of the binary intermetallic phases Cu3Au, CuAu and CuAu3. Particular attention has been paid to reproducing stacking fault energies in order to obtain a potential suitable for studying deformation in this binary system. The resulting energies, lattice constant, elastic properties and melting points are in good agreement with available experimental data. We use nested sampling to show that our potential reproduces the phase boundaries between intermetallic phases and the disordered face-centered cubic solid solution. We benchmark our potential against four popular Cu-Au EAM parameterizations and density-functional theory calculations.

We carry out molecular statics simulations of the indentation of bare and graphene-covered Pt (111) surfaces with smooth and rough indenters of radius 1.5 to 10 nm. Our simulations show that the plastic yield of bare surfaces strongly depends on atomic-scale indenter roughness such as terraces or amorphous disorder. Covering surfaces with graphene regularizes this response to the results obtained for ideally smooth indenters. Our results suggest that graphene monolayers and other 2D materials mitigate the effect of roughness, which could be exploited to improve the fidelity of experiments that probe the mechanical properties of interfaces.

Multi-scale surface topography is critical to surface function, yet the very smallest scales of topography are not accessible with conventional measurement techniques. Here we demonstrate two separate approaches for measuring small-scale topography in a transmission electron microscope (TEM). The first technique harnesses 'conventional' methods for preparation of a TEM cross-section, and presents how these methods may be modified to ensure the preservation of the original surface. The second technique involves the deposition of the material of interest on a pre-fabricated substrate. Both techniques enable the observation and quantification of surface topography with Ångström-scale resolution. Then, using electron energy loss spectroscopy (EELS) to quantify the sample thickness, we demonstrate that there is no systematic effect of thickness on the statistical measurements of roughness. This result was verified using mathematical simulations of artificial surfaces with varying thickness. The proposed explanation is that increasing the side-view thickness of a randomly rough surface may change which specific features are sampled, but does not significantly alter the character (e.g. root-mean-square (RMS) values and power spectral density (PSD)) of the measured topography. Taken together, this work establishes a new approach to topography characterization, which fills in a critical gap in conventional approaches: i.e. the measurement of smallest-scale topography.

We used molecular dynamics calculations to study the influence of interdiffusion on the bicrystal interface of Cu$|$Au nanolaminates. Starting from an ideal bicrystal of 50 nm thickness with a $\{111\}$ semi-coherent interface, we created a diffusive interface region and annealed the system at 1000 K. We report the resulting interfacial crystallographic defects as a function of interface width. Our results show an increase of dislocation spacing as the interface becomes more diffuse. The most diffuse interfaces of $\sim$ 10 nm width studied here form stacking fault tetrahedra.

The atomic simulation environment (ASE) is a software package written in the Python programming language with the aim of setting up, steering, and analyzing atomistic simulations. In ASE, tasks are fully scripted in Python. The powerful syntax of Python combined with the NumPy array library make it possible to perform very complex simulation tasks. For example, a sequence of calculations may be performed with the use of a simple 'for-loop' construction. Calculations of energy, forces, stresses and other quantities are performed through interfaces to many external electronic structure codes or force fields using a uniform interface. On top of this calculator interface, ASE provides modules for performing many standard simulation tasks such as structure optimization, molecular dynamics, handling of constraints and performing nudged elastic band calculations.

Contact of a spherical tip with a flat elastic substrate is simulated with a Green's-function method that includes atomic structure at the interface while capturing elastic deformation in a semi-infinite substrate. The tip and substrate have identical crystal structures with nearest-neighbor spacing d and are aligned in registry. Purely repulsive interactions between surface atoms lead to a local shear strength that is the local pressure times a constant local friction coefficient a. The total friction between tip and substrate is calculated as a function of contact radius a and sphere radius R, with a up to 103d and R up to 4×104d. Three regimes are identified depending on the ratio of a to the core width of edge dislocations in the center of the contact. This ratio is proportional to aa2/Rd. In small contacts, all atoms move coherently and the total friction coefficient m=a. When the contact radius exceeds the core width, a dislocation nucleates at the edge of the contact and rapidly advances to the center where it annihilates. The friction coefficient falls as m∼a(aa2/Rd)-2/3. An array of dislocations forms in very large contacts and the friction is determined by the Peierls stress for dislocation motion. The Peierls stress rises with pressure, and m rises with increasing load.

Absolute binding energies of core electrons in molecules and bulk materials can be efficiently calculated by spin paired density-function theory employing a D-Kohn-Sham (DKS) scheme corrected by offsets that are highly transferable. These offsets depend on core level and atomic species and can be determined by comparing DKS energies to experimental molecular x-ray photoelectron spectra. We demonstrate the correct prediction of absolute and relative binding energies on a wide range of molecules, metals, and insulators.

Geometrically imposed force cancellations lead to ultralow friction between rigid incommensurate crystalline asperities. Elastic deformations may avert this cancellation but are difficult to treat analytically in finite and three-dimensional systems. We use atomic-scale simulations to show that elasticity affects the friction only after the contact radius a exceeds a characteristic length set by the core width of interfacial dislocations bcore. As a increases past bcore, the frictional stress for both incommensurate and commensurate surfaces decreases to a constant value. This plateau corresponds to a Peierls stress that drops exponentially with increasing bcore but remains finite.

Wear in self-mated tetrahedral amorphous carbon (ta-C) films is studied by molecular dynamics and nearedge X-ray absorption fine structure spectroscopy. Both theory and experiment demonstrate the formation of a soft amorphous carbon (a-C) layer with increased sp2 content, which grows faster than an a-C tribolayer found on selfmated diamond sliding under similar conditions. The faster sp3 --> sp2 transition in ta-C is explained by easy breaking of prestressed bonds in a finite, nanoscale ta-C region, whereas diamond amorphization occurs at an atomically sharp interface. A detailed analysis of the underlying rehybridization mechanism reveals that the sp3 --> sp2 transition is triggered by plasticity in the adjacent a-C. Rehybridization therefore occurs in a region that has not yet experienced plastic yield. The resulting soft a-C tribolayer is interpreted as a precursor to the experimentally observed wear.

At the molecular scale, there are strong attractive interactions between surfaces, yet few macroscopic surfaces are sticky. Extensive simulations of contact by adhesive surfaces with roughness on nanometer to micrometer scales are used to determine how roughness reduces the area where atoms contact and thus weakens adhesion. The material properties, adhesive strength, and roughness parameters are varied by orders of magnitude. In all cases, the area of atomic contact is initially proportional to the load. The prefactor rises linearly with adhesive strength for weak attractions. Above a threshold adhesive strength, the prefactor changes sign, the surfaces become sticky, and a finite force is required to separate them. A parameter-free analytic theory is presented that describes changes in these numerical results over up to five orders of magnitude in load. It relates the threshold adhesive strength to roughness and material properties, explaining why most macroscopic surfaces do not stick. The numerical results are qualitatively and quantitatively inconsistent with classical theories based on the Greenwood-Williamson approach that neglect the range of adhesion and do not include asperity interactions.

We study nanoindentation and scratching of graphene-covered Pt(111) surfaces in computer simulations and experiments. We find elastic response at low load, plastic deformation of Pt below the graphene at intermediate load, and eventual rupture of the graphene at high load. Friction remains low in the first two regimes, but jumps to values also found for bare Pt(111) surfaces upon graphene rupture. While graphene substantially enhances the load carrying capacity of the Pt substrate, the substrates intrinsic hardness and friction are recovered upon graphene rupture.

We present the main design concepts of the object-oriented particle dynamics code SYMPLER. With this freely available software, simulations can be performed ranging from microscopic classical molecular dynamics up to the Lagrangian particle-based discretisation of macroscopic continuum mechanics equations. We show how the runtime definition of arbitrary degrees of freedom and of arbitrary equations of motion allows for modular and symbolic computation with high flexibility. Arbitrary symbolic expressions for inter-particle forces can be defined as well as fluxes of arbitrarily many additional scalar, vectorial or tensorial degrees of freedom. The integration in a high performance grid computing environment makes huge geographically distributed computational resources accessible to the software by an easy-to-use interface.

Tetrahedral amorphous carbon coatings have the potential to significantly reduce friction and wear between sliding components. Here, we provide atomistic insights into the evolution of the sliding interface between naked and hydrogen-passivated ta-C sliding partners under dry and lubricated conditions. Using reactive classical atomistic simulations we show that sliding induces a sp3 to sp2 rehybridization and that the shear resistance is reduced by hydrogen-passivation and hexadecane-lubricationdespite our finding that nanoscale hexadecane layers are not always able to separate and protect ta-C counter surfaces during sliding. As asperities deform, carbon atoms within the hexadecane lubricant bind to the ta-C sliding partners resulting in degradation of the hexadecane molecules and in increased material intermixing at the sliding interface. Hydrogen atoms from the passivation layer and from the hexadecane chains continue to be mixed within a sp2 rich sliding interface eventually generating a tribo-l

Five new lithium chalcogenidotetrelates, so-called "LiChT" phases, with the elemental combination Li/Sn/Se, Li-4[SnSe4] (1), (1)(infinity){Li-2[SnSe3]} (2), and the respective solvates Li-4[SnSe4]center dot 13H(2)O (3), Li-4[Sn2SeO center dot 14H(2)O (4), and Li-4[SnSe4]center dot 16MeOH (5) were generated in single-crystalline form. We present and discuss syntheses, crystal structures, spectroscopic and thermal behavior, as well as Li+ ion conducting properties of the phases that represent uncommon Li+ ion conducting materials with a maximum conductivity found for 1 (sigma(20 degrees C) = 2 X 10(-5) S.cm(-1), sigma(100 degrees C) = 9 X 10(-4) S.cm(-1)). The latter was elucidated via impedance spectroscopy and further studied by electronic structure calculations, revealing vacancy migration as the dominant Li+ transport mechanism. Thus, studies on a selenido-LISICON family were found to be a very interesting starting point for an extension of the LISICON-related solid state lithium ion conductors (SSLIC).

We present a linear-scaling method based on self-consistent charge non-orthogonal tight-binding. Linear scaling is achieved using a many-body expansion, which is adjusted dynamically to the instantaneous molecular configuration of a liquid. The method is capable of simulating liquids over large length and time scales, and also handles reactions correctly. Benchmarking on typical carbonate electrolytes used in Li-ion batteries displays excellent agreement with results from full tight-binding calculations. The decomposition slightly breaks the Hellmann-Feynman theorem, which is demonstrated by application to water. However, an additional correction also enables dynamical simulation in this case.

Tetrahedral amorphous carbon (ta-C) coatings have attracted high scientific attention in recent years due to their outstanding low friction coefficients in lubricated environments and their superior resistance to abrasive as well as adhesive wear. Consequently, they are highly suitable as protective coatings in automotive components such as combustion engines to reduce wear and friction. Nevertheless, ta-C abrade under extreme conditions and an atomistic understanding of the wear processes in ta-C is crucial for optimizing its wear resistance. The present study employs atomic-scale simulations to investigate the basic principles of wear between hydrogen- free tetrahedral-amorphous carbon (ta-C) films, which are modeled state-of-the-art by an improved version of the well-known Brenner bond-order potential. During tribological contact, these mainly sp3 hybridized films tend to form an amorphous carbon (a-C) tribomaterial mainly consisting of carbon atoms in sp2 configuration. Furthermore, the observed tribolayer grows faster than the a-C between diamond surfaces under similar conditions, which can be explained by easy breaking of weak bonds in a finite ta-C region triggered by plasticity in the adjacent a-C while the diamond/a-C transition occurs at an atomically sharp interface. The difference in the a-C tribofilm formation between ta-C and diamond is in agreement with near-edge x-ray absorption fine structure spectroscopy (NEXAFS) studies published recently.

Nanocoatings have the potential to improve the surface properties of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed automotive engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. The present study employs atomic-scale simulations to investigate the basic principles of wear and friction between hydrogen-free tetrahedral-amorphous carbon (ta-C) films. The ta-C films are modeled state-of-the-art by an improved version of the well-known Brenner bond-order potential, which had been successfully applied to elucidate the wear processes during diamond polishing. We start our work by the preparation of the ta-C film structure, which is then characterized with respect to local and global film properties in comparison to experiments. After validating our ta-C nanocoatings with the help of experimental data, we perform computational sliding experiments to investigate mechanisms of friction and wear between interacting ta-C surfaces. During tribological contact, these diamond-like films (mainly sp3 hybridized) tend to form a soft-amorphous or graphite-like tribomaterial mainly consisting of carbon atoms in sp2 configuration. The sp3 to sp2 transition originates from atom-by-atom extraction events occurring at the sp3/sp2 interface. We discuss the underlying mechanisms by focusing on associated triboreactions and tribological properties such as shear forces.

Modeling interfacial phenomena often requires both a detailed atomistic description of surface interactions and accurate calculations of long-range deformations in the substrate. The latter can be efficiently obtained using an elastic Green's function if substrate deformations are small. We present a general formulation for rapidly computing the Green's function for a planar surface given the interatomic interactions, and then coupling the Green's function to explicit atoms. The approach is fast, avoids ghost forces, and is not limited to nearest-neighbor interactions. The full system comprising explicit interfacial atoms and an elastic substrate is described by a single Hamiltonian and interactions in the substrate are treated exactly up to harmonic order. This concurrent multiscale coupling provides simple, seamless elastic boundary conditions for atomistic simulations where near-surface deformations occur, such as nanoindentation, contact, friction, or fracture. Applications to surface relaxation and contact are used to test and illustrate the approach.

Nanocoatings have the potential to improve the surface properties of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed automotive engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. The present study employs atomic-scale simulations to investigate the basic principles of wear and friction between hydrogen-free tetrahedral-amorphous carbon (ta-C) films. The ta-C films are modeled state-of-the-art by an improved version of the well-known Brenner bond-order potential [1,2], which had been successfully applied to elucidate the wear processes during diamond polishing[3]. Our work starts with the preparation of ta-C film structures with different atomic densities, which are then characterized with respect to local and global film properties in comparison to experimental data. With these prepared nanocoatings, we perform computational sliding experiments to investigate mechanisms of friction and wear between interacting ta-C surfaces. Dry and lubricated sliding is considered. Especially for dry sliding and during tribological contact, these diamond-like films (mainly sp3 hybridized) tend to form a soft-amorphous or graphite-like tribomaterial mainly consisting of carbon atoms in sp2 configuration. We discuss underlying mechanisms of the dynamic triboreactions and investigate tribological properties such as shear forces at the sliding interface.

Linear sp-hybridized carbon chains have recently been proposed as one-dimensional nanostructures for electronic applications and as intermediate products in many nanoscale processes. However, their synthesis and observation are affected by their degradation upon oxygen exposure. Carbon chains consisting of alternating single and triple bonds (polyynic) are reported to be more stable than those consisting of double bonds (cumulenic), but the details of the degradation mechanism are still unknown. We use density functional theory to show that adsorption of O(2) on carbon chains anchored to carbon substrates can cause their cleavage through the collective scission of O-O and C-C bonds, yielding separate CO-terminated chains. Further O(2) attack progressively shortens them, causing CO(2) formation. While the shortening process has general validity, the cleavage step of the reaction is exothermic for cumulenic chains only. Perturbations of the ideal structure, such as bending of the chains or modifications to the structure of their termination, affect the oxidation mechanism and can make the cleavage reaction exothermic for polyynic chains as well. These results contribute to the interpretation of the available experimental results and reveal atomic-scale details of the oxidation process,. thus allowing predictions on the chemistry of nanostructured carbon surfaces and suggesting possible new directions for the study of the chemical stability of carbynoid structures.

Diamond is the hardest material on Earth. Nevertheless, polishing diamond is possible with a process that has remained unaltered for centuries and is still used for jewellery and coatings: the diamond is pressed against a rotating disc with embedded diamond grit. When polishing polycrystalline diamond, surface topographies become non-uniform because wear rates depend on crystal orientations. This anisotropy is not fully understood and impedes diamonds widespread use in applications that require planar polycrystalline films, ranging from cutting tools to confinement fusion. Here, we use molecular dynamics to show that polished diamond undergoes an sp 3 -sp 2 order-disorder transition resulting in an amorphous adlayer with a growth rate that strongly depends on surface orientation and sliding direction, in excellent correlation with experimental wear rates. This anisotropy originates in mechanically steered dissociation of individual crystal bonds. Similarly to other plan arization processes, the diamond surface is chemically activated by mechanical means. Final removal of the amorphous interlayer proceeds either mechanically or through etching by ambient oxygen.

The atomic-scale processes taking place during the sliding of diamond and diamond-like carbon surfaces are investigated using classical molecular dynamics simulations. During the initial sliding stage, diamond surfaces undergo an amorphization process, while an sp3 to sp2 conversion takes place in tetrahedral amorphous carbon (ta-C) and amorphous hydrocarbon (a-C:H) surface layers. Upon separation of the sliding samples, the interface fails. A rather smooth failure occurs for a-C:H, where the hydrogen atoms present in the bulk passivate the chemically active carbon dangling bonds. Conversely, sp-hybridized carbon chains are observed to form on diamond and ta-C surfaces. These carbynoid structures are known to undergo a fast degradation process when in contact with oxygen. Using quantum-accurate density functional theory simulations, we present a possible mechanism for the oxygen-induced degradation of the carbon chains, leading to oxidative wear of the sp phase on diamo nd and ta-C surfaces upon exposure to air. Oxygen molecules chemisorb on C-C bonds of the chains, triggering the cleavage of the chains through concerted O-O and C-C bond-breaking reactions. A similar reaction caused by adsorption of water molecules on the carbon chains is ruled out on energetic grounds. Further O2 adsorption causes the progressive shortening of the resulting, O-terminated, chain fragments through the same O-O and C-C bond breaking mechanism accompanied by the formation of CO2 molecules.

We present the application of the smoothed particle hydrodynamics (SPH) discretization scheme to Phillips' model for shear-induced particle migration in concentrated suspensions. This model provides an evolution equation for the scalar mean volume fraction of idealized spherical solid particles of equal diameter which is discretized by the SPH formalism. In order to obtain a discrete evolution equation with exact conservation properties we treat in fact the occupied volume of the solid particles as the degree of freedom for the fluid particles. We present simulation results in two-and three-dimensional channel flow. The two-dimensional results serve as a verification by a comparison to analytic solutions. The three-dimensional results are used for a comparison with experimental measurements obtained from computer tomography of injection moulded ceramic microparts. We observe the best agreement of measurements with snapshots of the transient simulation for a ratio D-c/D-eta = 0.1 of the two model parameters.

The lubrication mechanisms in ultrathin solid gold films confined between two rough nickel surfaces have been investigated employing classical molecular dynamics with a second moment tight-binding potential. Three types of nickel surfaces are considered: Ni(111), Ni(001) single- and an Ni(001) - (111) bicrystal. In all three systems, gold layers that have been quenched from the melt organise in (111) layers parallel to the nickel interfaces. The relative sliding of the two single crystal nickel tribopartners requires a shear stress of around 170 MPa - a value that is almost one order of magnitude lower than the ideal plastic shear stress of single crystal bulk gold. This reduced stress can be explained by a misfit dislocation mechanism in a single plane close to the Ni/Au interface. In the case of the Ni(001) - (111) bicrystal, the nickel grain boundaries induce grain boundaries in the quenched gold film which vanish during sliding. During subsequent sliding the nickel grain boundaries act as nucleation centres for dislocation loops leading to an increased shear stress of 490 MPa. The same is observed for an embedded hydrocarbon impurity. Also here dislocation loops are emitted on (111) planes that are tilted with respect to the sliding plane.

While carbon nanotubes have technological potential as actuators, the underlying actuation mechanisms remain poorly understood. We calculate charge-induced stresses and strains for electrochemical actuation of carbon nanotubes with different chiralities and defects, using densityfunctional theory and various tight-binding models. For a given deformation mode the concept of bonding and anti-bonding orbitals can be redefined depending on the sign of a differential band structure stress. We use this novel theoretical framework to analyse orbital contributions to the actuation. These show charge asymmetric behavior which is due to next-nearest-neighbor hopping, while Coulombic contributions account for approximately charge-symmetric isotropic deformations. In the typical case of a (10, 10) tube strains around 0.1% with 1 nN force along the tube axis are obtained. Defects and functional groups have negligible influence on the actuation. In multi-wall tubes we find charge inversion on the inner tubes due to Friedel-type oscillations which could lead to a slight magnification of charge-induced strains. Finally, we consider photo actuation of nanotubes and predict that transitions between van-Hove singularities can be expected to expand the tubes.

Amorphous hydrocarbon (a-C: H) films have enormous potential as low friction, wear resistant coatings. Here. we present a plasma assisted chemical vapour deposition process for a-C: H that exhibits growth rates of 100 nm min(-1) and higher. The tribological performance of the resulting a C : H films has been studied experimentally by reciprocating sliding of all a-C: H-coated Si3N4 ball oil all a-C: H-coated 100Cr6 steel substrate and by subsequent micro Raman spectroscopy of the wear track. Running-in of the coatings is observed and characterised by it rapid decrease ill the friction coefficient accompained by a significant increase ill sp(2) hybridisation ill the wear track. Ill order to gain a deeper understanding of the underlying running-in mechanisms the sliding of two a-C: H films under a load of 5 GPa has been studied by classical molecular dynamics employing a range-corrected Brenner bond-order potential. The simulations reproduce the experimental trends and explain the running-in by a combination of smoothing and chemical passivation of both tribosurfaces. Consequently, both mechanisms should be controlled in order to produce tribological coatings for applications with optimum energy-efficiency.