Nanoindentation and nanomachining characteristics of gold and platinum thin films

Molecular dynamics (MD) simulation and an experimental method were carried out to study the effects of applied load, hold time, and temperature on nanoscratching and nanoindentation of gold and platinum thin films. The simulated results showed that the wear depth of gold decreased as the scratching velocity was increased and the temperature was decreased. The results also indicated that when the simulated nanoindentation of gold film hold time was increased, the plastic indentation depth and the plastic energy both increased. In addition, the experimental results showed that the groove depth for gold films was larger than that of platinum films under the same machining load. The wear depth and the surface roughness of platinum films were larger than those of gold films under the same lateral machining feed. Furthermore, the simulated plastic energy of gold films was compared during nanoindentation test.     

Nanomechanical characterization of multilayered thin film structures for digital micromirror devices

The digital micromirror device (DMD), used for digital projection displays, comprises a surface-micromachined array of up to 2.07 million aluminum micromirrors (14 μm square and 15 μm pitch), which switch forward and backward thousands of times per second using electrostatic attraction. The nanomechanical properties of the thin-film structures used are important to the performance of the DMD. In this paper, the nanomechanical characterization of the single and multilayered thin film structures, which are of interest in DMDs, is carried out. The hardness, Young's modulus and scratch resistance of TiN/Si, SiO₂/Si, Al alloy/Si, TiN/Al alloy/Si and SiO₂/TiN/Al alloy/Si thin-film structures were measured using nanoindentation and nanoscratch techniques, respectively. The residual (internal) stresses developed during the thin film growth were estimated by measuring the radius of curvature of the sample before and after deposition. To better understand the nanomechanical properties of these thin film materials, the surface and interface analysis of the samples were conducted using X-ray photoelectron spectroscopy. The nanomechanical properties of these materials are analyzed and the impact of these properties on micromirror performance is discussed.     

Nanoscratch behavior of carbon nanotube reinforced aluminum coatings

Nanoscratch experiments have been carried out on plasma sprayed aluminum alloy coatings reinforced with 0, 5 and 10 wt.% carbon nanotubes (CNTs). Scratches have been performed at loads of 1000, 2000 and 3000 μN load using Berkovich indenter. The contact and true wear volumes of the scratches have been calculated. The nano-scale wear resistance is shown to increase by 4 times by addition of 10 wt.% CNTs. Improvement in the wear resistance is discussed with respect to strengthening effect and increased elastic recovery by addition of CNTs. Direct evidence of increased recovery and small decrease in the coefficient of friction with CNT content is provided using the true and instantaneous depth plots and the corresponding scanning probe microscope and scanning electron microscope images of the scratches. Friction coefficient was found to be load independent and was found to vary slightly with the CNT content.     

Atomic-scale anisotropy of nanoscratch behavior of single crystal iron

In this paper a parallel molecular dynamics (MD) model has been developed to investigate the nanoscratch process of single crystal iron. The simulations were performed for two cases with different crystallographic orientations and scratch directions. In Case I the scratch plane is (1 0 0) and the scratch direction is [0 0 1]. In Case II the scratch plane and the scratch direction are (1,−1,2) and [1 1 1], respectively. To validate the MD simulation the nanoscratch testing was conducted using the TriboIndenter. The simulation results reveal that the vertical force and the lateral force tend to increase with the scratch displacement for both cases. Case I has smaller forces than Case II. However, the coefficient of friction for both cases is similar, which is in good agreement with the experimental value. The crystallographic orientation also affects the scratch hardness. The scratch hardness of Case I is smaller than that of Case II.     

Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates

In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN) epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM) to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ) and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.     

QUANTITATIVE EVALUATION OF ADHESION STRENGTH OF INK DEPOSITED ON PLASTIC FILMS WITH A NANO INDENTER AND A SCANNING PROBE MICROSCOPE

As our lifestyles change, the convenience food industry booms. Many convenience food products use flexible, boilable, and microwavable plastic packaging. Almost every package is printed with ink, promoting what is inside the package, listing ingredients and nutrition data, giving preparation instructions, etc. The adhesion of ink on plastic films merits increasing attention to ensure quality packaging. However, this property has not been systematically studied and lacks a scientific method to measure the adhesion strength quantitatively. We are developing a technique of using a Nano-Indenter and a Scanning Probe Microscope to evaluate the adhesion strength of ink deposited on plastic films. It shows promise, and the measurement will be helpful in better understanding the adhesion mechanism, thus giving direction as to how to improve the adhesion.     

Nanoindentation and nanoscratch measurements on silicone thin films synthesized by pulsed laser ablation deposition (PLAD)

Nanoindentation and nanoscratch studies were conducted on silicone thin films synthesized by pulsed laser ablation deposition (PLAD). The nanoindentation studies showed that the modulus of the silicone films varied as a function of the energy density of deposition. The modulus values measured for PLAD silicone films were in the range of 1–6 GPa compared to 5–10 MPa reported for a typical silicone elastomer. Nanoscratch measurements also showed that PLAD silicone films exhibited much greater scratch resistance compared to silicone elastomer. These studies demonstrated that, even for low energy density depositions, the PLAD process can produced films which were are stronger and more abrasion resistant than conventional cross-linked silicone elastomers. Received: 27 June 2001 / Accepted: 27 June 2001     

Nanoindentation and nanoscratch tests of YAG single crystals: An investigation into mechanical properties,surface formation characteristic,and theoretical model of edge-breaking size

Nanoindentation and nanoscratch tests of YAG single crystals were systematically performed. The mechanical properties including elastic recovery rate, elastic modulus, nano hardness and fracture toughness of YAG single crystals were obtained by the nanoindentation tests. The surface morphologies of the scratched grooves were analysed using scanning electron microscopy. The formation characteristics of YAG single crystals induced by varied-depth nanoscratch indicated that there was distinct brittle-to-ductile transition phenomenon during the scratching process. Surface radial cracks occurred prior to the edge-breaking phenomenon, and transverse cracks extending to the surface of the work material dominated the brittle removal of YAG single crystals. A theoretical model of the edge-breaking size during the nanoscratch process was developed by considering the stress intensity factor, elastic recovery rate, and residual force. This model indicated that the edge-breaking size increased as the normal force, average elastic recovery rate and elastic modulus increased, but decreased as the nanoindenter tip radius, fracture toughness and nano hardness increased. When the average elastic recovery rate was within 17.5%–20% (the maximum elastic recovery rate was within 35%–40%), the values predicted by the theoretical model agreed well with the experimental values, and the average error was less than 5%. The model could provide theoretical guidance for analysing the surface generation characteristics of brittle solid materials during the abrasive processing at brittle removal regime.     

Surface Morphological and Nanomechanical Properties of PLD-Derived ZnO Thin Films

This study reports the surface roughness and nanomechanical characteristics of ZnO thin films deposited on the various substrates, obtained by means of atomic force microscopy (AFM), nanoindentation and nanoscratch techniques. ZnO thin films are deposited on (a- and c-axis) sapphires and (0001) 6H-SiC substrates by using the pulsed-laser depositions (PLD) system. Continuous stiffness measurements (CSM) technique is used in the nanoindentation tests to determine the hardness and Young’s modulus of ZnO thin films. The importance of the ratio (H/E _film) of elastic to plastic deformation during nanoindentation of ZnO thin films on their behaviors in contact-induced damage during fabrication of ZnO-based devices is considered. In addition, the friction coefficient of ZnO thin films is also presented here.     

Mechanical characterization of polymeric films using depth-sensing instrument: Correlation between viscoelastic-plastic properties and scratch resistance

The scratch behavior of polymer films deposited on PMMA substrate by three different coating techniques is investigated by scratch tests using a depth-sensing instrument. Using an improved measurement technique, we develop an advanced methodology based on a more appropriated model that includes an estimation of realistic stress and strain states during scratch tests. The scratch resistance is evaluated by comparing the average contact pressure for which the coating cracks, by taking into account the elastic–plastic behavior of the layer. The proposed model allows the determination of the true contact depth and the elastic recovery at the rear side of the elastic–plastic contact, and thus the true projected contact area between the moving tip and the polymeric surface. This determination depends first on a rheological factor estimated from standard load–displacement curves obtained by nanoindentation and then on the tip geometry. The viscoplacticity index and the activation volume of each type of coating are then determined by nanoscratch. The viscoplasticity index determined during an elastic–plastic contact and the activation volume related to the ductile–brittle transition are discussed as reliable criteria for determining which bilayer system (polymeric film on PMMA substrate) will truly exhibit better wear and scratch resistances in service.