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In this paper, we report on the in situ synthesis of graphene layers by means of chemical vapor deposition (CVD), directly on nickel micro-electromechanical systems (MEMS) surfaces. We have developed MEMS structures of which the temperature can be increased locally by Joule heating while in a methane environment. For our MEMS structures, the thermal time constant is 28 μs. As a result, we have control over the carbon precipitation time, thereby governing how many graphene layers are formed. Bi-layer to multi-layer graphene was observed using micro-Raman spectroscopy, but not single-layer graphene, as it gives no Raman signal when coupled on a nickel surface. The corresponding precipitation control theory is also presented in this paper, in which we relate the out-diffusion of carbon atoms from the grains of the nickel structure to the resulting number of graphene layers. Our method provides regulated carbon segregation from nickel and allows a prescribed number of graphene layers to form by tuning the precipitation time. In this way, we enable the direct in situ synthesis of graphene locally on the top and sidewalls of nickel MEMS structures, so that e.g. such graphene-coated MEMS surfaces can contribute towards a promising solution against friction and wear for MEMS devices with sliding components.

Single-crystal copper films on sapphire have recently been reported upon in relation to graphene growth on these films. In the present paper the kinetics of the formation of single crystal copper films is investigated. We demonstrate the importance of heating the sapphire substrate in 1000 hPa oxygen, followed by a fast cooling prior to depositing the copper film. The importance of this treatment is tentatively explained by the dissolution of oxygen in sapphire and subsequent out-diffusion during recrystallization of the copper film to form a copper-oxide interface layer. Also, the importance of avoiding oxygen incorporation in the sputter deposited film is demonstrated.

In this paper, we report on the influence of capillary condensation on the sliding friction of sidewall surfaces in polycrystalline silicon micro-electromechanical systems (MEMS). We developed a polycrystalline silicon MEMS tribometer, which is a microscale test device with two components subject to sliding contact. One of the components can be heated in situ by Joule heating to set the temperature of the contact and thereby control the capillary kinetics at the MEMS sidewalls. We used an optical displacement measurement technique to record the stick–slip motion of the slider with sub-nanometer resolution, and we assessed the friction force with nanonewton resolution. All friction measurements were performed under controlled ambient conditions while sweeping the contact temperature from room temperature to 300 °C, and from 300 °C to room temperature. We were able to distinguish the two ways in which energy is dissipated during sliding: the ‘semi-statically’ dissipated energy attributed to asperity deformation and contact yield, and the dynamically dissipated energy ascribed to the release of the tension in the slider during slip events. We observed an increase in the dynamically dissipated energy at 80 °C while sweeping down in temperature. This increase is caused by higher adhesion due to capillary condensation between the conformal surfaces. Our study highlights how energy is dissipated during the sliding contact of MEMS sidewalls, and it is helpful in overcoming friction in multi-asperity systems.

We report a nanoinfrared (IR) imaging study of the localized plasmon resonance modes of graphene nanoribbons (GNRs) using a scattering-type scanning near-field optical microscope (s-SNOM). By comparing the imaging data of GNRs that are aligned parallel and perpendicular to the in-plane component of the excitation laser field, we observed symmetric and asymmetric plasmonic interference fringes, respectively. Theoretical analysis indicates that the asymmetric fringes are formed due to the interplay between the localized surface plasmon resonance (SPR) mode excited by the GNRs and the propagative surface plasmon polariton (SPP) mode launched by the s-SNOM tip. With rigorous simulations, we reproduce the observed fringe patterns and address quantitatively the role of the s-SNOM tip on both the SPR and SPP modes. Furthermore, we have seen real-space signatures of both the dipole and higher-order SPR modes by varying the ribbon width.

The wear of pipelines, used in slurry transport, results in high costs for maintenance and replacement. The wear mechanism involves abrasion, corrosion, impact, and the interaction among them. In this work, we study the effect of impact on the wear mechanism and wear rate. Results show that when the effect of impact is small, the wear mechanism is dominated by electrochemically induced surface modification, which leads to a lower wear rate in a corrosive environment than in a non-corrosive environment. By contrast, when the effect of impact is large, the wear mechanism is drastically altered. In that regime plastic deformation is important. The influence of corrosion in the high impact regime can be neglected. Our findings show the importance of including impact effect in the distinction of wear of slurry pipes.

The aluminium alloy 7075-T6 is widely used in engineering. In some applications, like slurry transport, corrosion and abrasion occur simultaneously, resulting in early material failure. In the present work, we investigated the combined effect of corrosion and wear on the aluminium alloy 7075-T6. We performed two series of wear experiments to vary the conditions and severity of corrosion environment: chemically by using ethanol, deionized water and seawater, and electrochemically by applying various potentials using a potentiostat in seawater. Results show that, in seawater, the wear rate was higher than in deionized and ethanol; and in the potentiostat experiments, at the anodic potentials, the wear rates were higher than at the open circuit potential and the cathodic potentials. Seawater is the most corrosive one among the three liquids and the corrosion products can be easily removed. When applying anodic potentials, corrosion is accelerated, and the higher wear rate confirms that higher corrosion rate leads to higher wear rate due to the formation and removal of corrosion products during tribocorrosion.

We report on nano-infrared (IR) imaging studies of confined plasmon modes inside patterned graphene nanoribbons (GNRs) fabricated with high-quality chemical-vapor-deposited (CVD) graphene on Al2O3 substrates. The confined geometry of these ribbons leads to distinct mode patterns and strong field enhancement, both of which evolve systematically with the ribbon width. In addition, spectroscopic nano-imaging in mid-infrared 850-1450 cm-1 allowed us to evaluate the effect of the substrate phonons on the plasmon damping. Furthermore, we observed edge plasmons: peculiar one-dimensional modes propagating strictly along the edges of our patterned graphene nanostructures., Comment: 10 pages, 8 figures

We present results of molecular dynamics simulations of graphene on Cu surfaces. Interactions were modelled with the charge-optimized many-body potential, which gives a reasonable though not flawless description of the graphene–Cu system. The interaction between Cu and complete graphene sheets is characterized by an ‘averaged out’ interaction at a large bonding distance. Many bonding characteristics are indifferent to the details of how the Cu surface atoms are arranged, including the surface orientation and even if the surface is solid or molten. Graphene edges have a strong interaction with the Cu substrates. Systems were modelled at various temperatures, ranging from 0 K to the Cu melting temperature. At high temperature we find that the presence of graphene slightly stabilizes the Cu surface and retards surface melting. After cooling down to room temperature, the Cu substrate is 1.7% smaller than the graphene due to difference thermal expansion coefficients. This leads to the formation of wrinkles in graphene. Single wrinkles experience only small migration barriers and are quite mobile. When multiple wrinkles intersect, they form immobile knots that hinder further movement of the connected wrinkles. The elastic energy of the wrinkles and knots due to bending of the graphene is determined.

In this work, we have incorporated heaters in a MEMS device, which allow the in situ local heating of its contacting surfaces. This design offers a promising solution for MEMS devices with contacting components by preventing capillary-induced adhesion. The force of adhesion was assessed by optically measuring in-plane snap-off displacements. We were able to decrease adhesion from 500 nN to 200 nN with just one heated surface of which the temperature was set above 300 °C. The temperature should not be set too high: we observed increased adhesion due to a direct bonding process once the temperature was increased above 750 °C. Remarkably, adhesion increased by heating from room temperature to 75 °C, which is attributed to more water being transferred to the contact area due to faster kinetics. We observed the same effect in the cases where both surfaces were heated, although at slightly different temperatures. We demonstrated that heating only one surface to between 300 °C and 750 °C is sufficient to significantly lower adhesion, due to the removal of capillary menisci. The required heater is typically most easily implemented in a stationary part of the device.

When spatial objects are coated by plasma vapor deposition (PVD) or reactive PVD the objects perform a planetary motion in front of one or more targets. Sputtering from the target is achieved by an intense ion bombardment from a plasma in front of the target. This plasma is concentrated in front of the target by a magnet assembly behind the target. Usually a bias voltage is applied to the substrate in order to obtain an ion bombardment during the deposition. The function of this ion bombardment is to supply energy to the growing film in order to arrive at dense films under compressive stress. In the present article it is shown that for high quality coatings on spatial objects it is mandatory to guarantee not only a bias voltage, but also a bias current during all times of the deposition. For the coating of spatial objects this is realized by using a second plasma source to fill all of the deposition chamber with plasma.

In the absence of thermal stress, tensile stress in hard metal films is caused by grain boundary shrinkage and compressive stress is caused by ion peening. It is shown that the two contributions are additive. Moreover tensile stress generated at the grain boundaries does not relax by ion bombardment. In polycrystalline hard metal films the grain structure evolves during growth, leading to wider grains higher up in the film. The tensile component of the stress in the film is generated at the grain boundaries and therefore depends on film thickness. The effect of ion bombardment is independent of grain size, therefore compressive stress does not depend on film thickness. As a result in polycrystalline films deposited under a bias voltage a stress gradient exists from tensile at the interface to compressive at the top of the film.

Thin films on substrates are usually in a stressed state. An important, but trivial, contribution to that stress stems from the difference in thermal expansion coefficient of substrate and film. Much more interesting are the intrinsic stresses, resulting from the growth and/or microstructure of the film. Intrinsic compressive stress was explained by d’Heurle in 1970. Intrinsic tensile stress for recrystallizing metal films was treated succesfully by Doljack and Hoffman in 1972. In the present letter we explain the occurrence of tensile stress in nonrecrystallizing metal films. The explanation is based on modern grain growth models and accurate stress measurements. The key ingredient to the explanation is the proof of the existence of a stress gradient in nonrecrystallizing metal films.

We have investigated the effective contributions from surface and grain-boundary scattering to the overall resistivity in the quantum-transport regime in ultrathin ${\mathrm{CoSi}}_{2}$ metal films ranging from 2 to 300 nm in thickness. Grain boundaries were introduced by growing the films on Si(100) substrates. We find a clear crossover between two types of behavior as the film thickness is decreased. Down to 10 nm size effects on the resistivity are weak and the data are best approximated by grain-boundary scattering using the experimentally determined dependence of grain size on thickness. Below 10 nm the data approaches a power law \ensuremath{\rho}\ensuremath{\propto}${\mathit{d}}^{\mathrm{\ensuremath{-}}2.0}$ as surface scattering due to quantum size effects starts to dominate.

In this paper a thermodynamic and kinetic study of the new deposition process of tungsten on Silicon (100) from tungsten hexafluoride (WF6) and germane (GeH4) is presented. Thermodynamic calculations as well as experiments show, that the reaction occurring during deposition is : [MATH] The growth rate as a function of process parameters is obtained for selective depositions in the temperature range from 600 to 800 K, and a total pressure range from 150 to 1000 mTorr. Experiments show that the germane reduction of tungsten hexafluoride is 0.9 order in WF6, - 0.2 order in GeH4 and zero order in H2. The activation energy is 34 kJ/mol. These kinetic data of the GeH4/WF6 process differ markedly from the kinetics of the recently much studied SiH4/WF6 process. A fascinating observation is that the deposition rate does not change when SiH4 is added to the GeH4/WF6 mixture, while, on the contrary, a small amount of GeH4 reduces the growth rate from a SiH4/WF6 mixture considerably. The kinetic differences between the at first sight similar GeH4/WF6 and SiH4/WF6 process are used to get a better insight in both processes.