Nanomechanical Behavior Research Articles

Elastic to elastic–plastic transition of Al2O3/TiC ceramics studied by nanoindentation

In this work load–penetration curves obtained by nanoindentation were analyzed, using a spherical tip approximation and applying the stress/strain concept by Tabor. Nanoindentation experiments were done on sapphire, pure TiC, and a mixed ceramic with in situ formed TiCxlayer, using a sharp cube-corner indenter at very low loads and penetration depths. With the implemented method it is possible to display the elastic to elastic–plastic transition of each investigated phase, and much more information can be extracted than by conventional analysis. Regarding the mixed ceramic, it was found that the present TiC phases exhibit slightly lower hardness than the alumina phase, but they can sustain much higher stresses during the transition from the elastic to the elastic–plastic regime. This is considered to be beneficial for the application as cutting material. No correlation was found between the nanomechanical behavior of the model materials sapphire and TiC and the corresponding phases of the mixed ceramic.

Nanomechanical behaviour of plasma sprayed PZT coatings

Nanomechanical properties of the plasma sprayed lead zirconate titanate (PZT) coating have been investigated using nanoindentation technique. PZT coating processed at higher plasma power of 32 kW exhibited lower elastic modulus E of 98 GPa compared with the modulus (113 GPa) of the coating processed at plasma power of 20 kW. The variation in the elastic modulus is attributed to the fine porosity of the PZT coating, which is formed during plasma spraying. Porosity increases by evaporation of PbO phase during plasma spraying. Overall effective elastic modulus of both coatings is computed using micromechanics models and compared with the experimentally obtained values. Hashin–Shtrikman and rule of mixtures models predict values that closely match with nanoindentation values.

Nanomechanical and surface behavior of polydimethylsiloxane-filled nanoporous anodic alumina

In this article, the mechanical and wetting behavior of anodic aluminum oxide (AAO) and nanoporous-filled AAO were investigated using nanoindentation and contact angle measurements. The results showed that the nanoporous AAO was hydrophobic with a contact angle of 105°. The polymer filling affected the surface property and reduced the contact angle to 84°. The effects of the nanoporous filling on the Young’s modulus and the hardness are investigated and discussed. A three-dimensional finite element model was also successfully developed to understand the nanoindentation-induced mechanism. A maximum von Mises stress of 1058 MPa occurred beneath the indenter.

Deformation partitioning provides insight into elastic, plastic, and viscous contributions to bone material behavior

The relative contributions of elastic, plastic, and viscous material behavior are poorly described by the separate extraction and analysis of the plane strain modulus, E ′ , the contact hardness, H c (a hybrid parameter encompassing both elastic and plastic behavior), and various viscoelastic material constants. A multiple element mechanical model enables the partitioning of a single indentation response into its fundamental elastic, plastic, and viscous deformation components. The objective of this study was to apply deformation partitioning to explore the role of hydration, tissue type, and degree of mineralization in bone and calcified cartilage. Wet, ethanol-dehydrated, and PMMA-embedded equine cortical bone samples and PMMA-embedded human femoral head tissues were analyzed for contributions of elastic, plastic and viscous deformation to the overall nanoindentation response at each site. While the alteration of hydration state had little effect on any measure of deformation, unembedded tissues demonstrated significantly greater measures of resistance to plastic deformation than PMMA-embedded tissues. The PMMA appeared to mechanically stabilize the tissues and prevent extensive permanent deformation within the bone material. Increasing mineral volume fraction correlated with positive changes in E ′ , H c , and resistance to plastic deformation, H ; however, the partitioned deformation components were generally unaffected by mineralization. The contribution of viscous deformation was minimal and may only play a significant role in poorly mineralized tissues. Deformation partitioning enables a detailed interpretation of the elastic, plastic, and viscous contributions to the nanomechanical behavior of mineralized tissues that is not possible when examining modulus and contact hardness alone. Varying experimental or biological factors, such as hydration or mineralization level, enables the understanding of potential mechanisms for specific mechanical behavior patterns that would otherwise be hidden within a more complex set of material property parameters.

Effect Of Beta-sheet-breaker Peptides On The Assembly, Morphology And Mechanical Stability Of Oriented aß25-35 Amyloid Fibrils

Amyloid fibrils are self-associating filamentous structures that play an important role in neurodegenerative and protein misfolding diseases. It has been shown that certain peptides, called beta-sheet-breaker (BSB) peptides, may interfere with amyloid fibril assembly. Although BSB peptides are prospective therapeutic agents in amyloidosis, there is ambiguity about the mechanisms and generality of their action.In the present work we analyzed the effect of LPFFD, Soto's BSB peptide, on the growth kinetics, morphological and mechanical properties of amyloid s25-35 (As25-35) fibrils assembled in an oriented array on mica surface. As25-35 is thought to represent the biologically active, toxic fragment of the full-length beta peptide. Growth kinetics and morphological features were analyzed by using in situ AFM in the presence of various concentrations of LPFFD. The mechanical stability of the fibrils was explored with force spectroscopy methods. We found that the addition of LPFFD did not alter the assembly kinetics of As25-35 fibrils. Already formed fibrils did not disassemble in the presence of high concentrations of LPFFD. The nanomechanical behavior of As25-35 fibrils is characterized by the appearance of force plateaus which correspond to the force-driven unzipping of protofilaments. We observed that the plateau force did not change in the presence of LPFFD. The lack of significant effects of LPFFD on As25-35 fibril assembly and stability may suggest that the beta-sheet-breaking effect of the peptide is not general. Alternatively, the As25-35 fibrils formed on mica are in a configuration which is inaccessible to the LPFFD peptide.

Nanomechanical behaviour and thermal degradation of nanoclays and supernanoclays enhanced marine gelcoat system

Novel nanoclay reinforced unsaturated polyester gelcoats for marine vessels are evaluated in terms of their thermal and mechanical performance. In this study, mechanical and thermal tests have been employed to characterise different gelcoat systems with various loading levels of nanoclays with and without X-treatment. Differences in mechanical properties were determined by using nano-indentation testing which shown an increase in hardness compared to the control system. Thermal degradation characteristics were determined using a thermogravimetric analyser (TGA). An increase in thermal stability was observed for all nanocomposites compared to the control system. Additionally, differential scanning calorimetry (DSC) showed that the effect of inclusion of nanoclays is to hinder the structure of unsaturated polyester gelcoats and hence increase glass transition temperatures. Furthermore, X-treated supernanoclay is shown to be significantly more effective than untreated nanoclay. Enhancement of mechanical property and thermal degradation could be attributed to the grafting of hydroxyl groups (?OH) in the nanoclays with polymer chains.

Study on nanomechanical and high temperature tribological behaviour of Ti2AlNb based alloys by plasma surface alloying

Plasma chromising and carburisation following plasma chromising (duplex treatment) were carried out on the Ti2AlNb based (O phase) alloys by the double glow plasma process. The dynamic ultramicro hardness and elastic modulus of the alloyed layers were investigated by the nano-indentation technique. Dry sliding friction tests on the samples against silicon nitride (Si3N4) balls were completed at high temperature by a ball-on-disc tribometer. The results indicated that the duplex-treated layer was mainly composed of Cr23C6 and Cr2Nb, while the chromised layer was consisted of Al8Cr5 and Cr2Nb phases. The ultramicro hardness of the duplex-treated layer was higher than that of the chromised layer, whereas the elastic modulus of the duplex-treated layer was lower than that of the chromised layer. The wear rates of the duplex-treated layer and the chromised layer were ∼6˙6 and 2˙5 times respectively, lower than that of substrate. The duplex-treated layer exhibited excellent high temperature wear resistance.

Nanomechanical behavior of single crystalline SiC nanotubes revealed by molecular dynamics simulations

Molecular dynamics simulations with Tersoff potentials were used to study the response of single crystalline SiC nanotubes under tensile, compressive, torsional, combined tension-torsional, and combined compression-torsional strains. The simulation results reveal that the nanotubes deform through bond-stretching and breaking and exhibit brittle properties under uniaxial tensile strain, except for the thinnest nanotube at high temperatures, which fails in a ductile manner. Under uniaxial compressive strain, the SiC nanotubes buckle with two modes, i.e., shell buckling and column buckling, depending on the length of the nanotubes. Under torsional strain, the nanotubes buckle either collapse in the middle region into a dumbbell-like structure for thinner wall thicknesses or fail by bond breakage for the largest wall thickness. Both the tensile failure stress and buckling stress decrease under combined tension-torsional and combined compression-torsional strain, and they decrease with increasing torsional rate under combined loading.

In situ Characterization of Nanomechanical Behavior of Free-standing Nanostructures

The present paper reports the development of an in situ nanotensilometer that enables highly reliable mechanical tensile testing on individual micro-/nano-scale structures. The device features independent measurement of force and displacement histories in the specimen with nanoNewton force and sub-nanometer displacement resolutions, respectively. Moreover, the device is well suited for in situ testing of free-standing micro/nano-structures within a high resolution scanning electron microscope (SEM), which permits continuous high-resolution imaging of the specimen during straining. The device is comprised of two main parts: (a) a three-plate capacitive transducer that doubles up both as an actuator and a force sensor, and (b) a commercially available nanomanipulator that facilitates transportation and positioning of nanoscale structures with sub-nanometer precision. In order to conduct the mechanical tests the ends of the specimen are attached to the probe tips of the device using ion-beam induced deposition. The general capabilities and features of the nanotensilometer are illustrated by presenting results of nanomechanical tensile tests on electrospun polyaniline microfibers.

Comparison of Nanomechanical Behavior of the Amorphous and Crystalline Phases of ALD HfO2

HfO2 films were deposited using atomic layer deposition (ALD) at temperatures ranging from 100oC to 250oC. We report detailed nanoindentation measurements on the pure amorphous, mixed-phase and polycrystalline phase of HfO2. We use nanoindentation techniques for determining the important mechanical properties such as hardness and effective modulus. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and atomic force microscopy (AFM) to determine the structural properties of the various phases of these ALD HfO2 films. We measured the effective modulus to be 370 GPa for amorphous low temperature ALD HfO2 and 240 GPa after crystallization with rapid thermal annealing (RTA). Similarly, the hardness measurements revealed a value of 18 GPa for amorphous HfO2 and a lower value of 15 GPa following the transition temperature from amorphous to polycrystalline HfO2.

Comparison of Nanomechanical Behavior of the Amorphous and Crystalline Phases of ALD HfO2

not Available.

AFM testing of the nanomechanical behaviour of MEMS micromembranes

Abstract The nanomechanical behaviour of micromembranes for high temperature applications of a microelectro mechanical system pressure sensor has been studied by use of atomic force microscopy. A method was elaborated and used for measure nanometre deformation of the membrane under application of high loads. This method was also useful for identifying failures of a membrane, e. g., undesired position against the substrate of the structure. The tests were performed for a series of membranes. The characteristics of the mechanical behaviour were plotted for different geometrical features of the membranes to identify the influence of geometry and dimension. The method was found to be very effective for the process characterisation of the fabricated MEMS micromembranes devoted, e. g., to high temperature pressure sensors.

Studies of diamond-like carbon (DLC) films deposited on stainless steel substrate with Si/SiC intermediate layers

In this work, diamond-like carbon (DLC) films were deposited on stainless steel substrates with Si/SiC intermediate layers by combining plasma enhanced sputtering physical vapour deposition (PEUMS-PVD) and microwave electron cyclotron resonance plasma enhanced chemical vapour deposition (MW-ECRPECVD) techniques. The influence of substrate negative self-bias voltage and Si target power on the structure and nano-mechanical behaviour of the DLC films were investigated by Raman spectroscopy, nano-indentation, and the film structural morphology by atomic force microscopy (AFM). With the increase of deposition bias voltage, the G band shifted to higher wave-number and the integrated intensity ratio ID/IG increased. We considered these as evidences for the development of graphitization in the films. As the substrate negative self-bias voltage increased, particle bombardment function was enhanced and the sp3-bond carbon density reducing, resulted in the peak values of hardness (H) and elastic modulus (E). Silicon addition promoted the formation of sp3− bonding and reduced the hardness. The incorporated Si atoms substituted sp2− bond carbon atoms in ring structures, which promoted the formation of sp3-bond. The structural transition from C—C to C–Si bonds resulted in relaxation of the residual stress which led to the decrease of internal stress and hardness. The results of AFM indicated that the films was dense and homogeneous, the roughness of the films was decreased due to the increase of substrate negative self-bias voltage and the Si target power.

Atomistic simulations of the mechanical properties of silicon carbide nanowires

Molecular-dynamics methods using the Tersoff bond-order potential are performed to study the nanomechanical behavior of [111]-oriented $\ensuremath{\beta}\text{-SiC}$ nanowires under tension, compression, torsion, combined tension-torsion, and combined compression-torsion. Under axial tensile strain, the bonds of the nanowires are just stretched before the failure of nanowires by bond breakage. The failure behavior is found to depend on size and temperatures. Under axial compressive strain, the collapse of the SiC nanowires by yielding or column buckling mode depends on the length and diameters of the nanowires, and the latter is consistent with the analysis of equivalent continuum structures using Euler buckling theory. The nanowires collapse through a phase transformation---from crystal to amorphous structure---in several atomic layers under torsion strain. Under combined loading the failure and buckling modes are not affected by the torsion with a small torsion rate, but the critical stress decreases by increasing the torsion rate. Torsion buckling occurs before the failure and buckling with a big torsion rate. Plastic deformation appears in the buckling zone by further increasing the combined loading.

Estimation of contact area of nanoparticles in chains using continuum elastic contact mechanics

The key challenge to understand the nanomechanical behavior of nanoparticle chain aggregates (NCA) is strongly dependent on accurate determination of the contact area between individual particles. Experimental determination of the contacting radius is extremely difficult and often not reliable. We present calculations based on elastic contact mechanics models, that predict the contact radii of nanoparticles. The model considers important parameters, such as the particle size, the elastic property of the materials and the effect of humidity that intervenes between the contacts. Calculations carried out for four selected materials show that there is a large difference between the radii of contacts formed in vacuum and in ambient conditions. In vacuum, the surface energy of the material is higher compared to that in ambient condition and the contact formation is dominated by the strong interactions between the surfaces. In ambient condition, the contact is dominated by the Laplace pressure due to the condensed water meniscus between the contacts. Calculations presented in this article show that the contact radius between nanoparticles depends on materials properties and the environment.

Influence of thickness on nanomechanical behavior of Black Diamond™ low dielectric thin films for interconnect and packaging applications

In the present study, we have investigated the thickness dependence of mechanical properties of the Black Diamond™ (SiOC:H, BD, Low-k) films, which are of great interest in current Cu/low-k Back End of the Line (BEOL) interconnect/packaging technologies. For this investigation the BD thin films of six different thicknesses 100, 300, 500, 700, 1,000 and 1,200 nm were deposited on the 8″ Si wafer by using plasma enhanced chemical vapor deposition (PECVD) technique. Nanoindentation and nanoscratch tests of the BD films were performed by using the Nano Indenter® XP (MTS Corp. USA). In nanoindentation testing of the BD films, significant differences in the elastic modulus of the BD films were observed. In nanoscratch testing, it is found that the critical load (Lc) and scratch width increases as the thickness of the film increases. Cross-sectional analysis of residual nanoindentation impressions was carried out using atomic force microscopy (AFM) to study the deformation behavior. The nanoindentation and nanoscratch responses of the BD thin films of six different thicknesses are different and they are expected mainly due to the molecular reorganization in thin/ultra thin films.

An energy model for nanomechanical deflection of cantilever-DNA chip

Nanomechanical behavior of cantilever-DNA chip in label-free biodetection is investigated by the energy method. First, using an equation of state for DNA liquid crystals and an alternative two-variable model for laminated cantilever beams, a relationship between chip energy and some factors, such as nanogeometrical, physical, chemical characteristics of DNA molecules, microscopical geometric dimension, macroscopical mechanical properties of chip, etc., is formulated in consideration of electrostatic energy, hydration energy and configurational fluctuations of DNA layer as well as mechanical energy of chip. Second, theoretical predictions of nanomechanical deflection of DNA chip by the minimum principle of energy are compared with experimental data in Wu's experiments. Third, the influence of stochastic interchain distances and stochastic elastic modulus on chip deflection is investigated. The validity of the simplified two-layer-beam model is also studied. Numerical results show that chip deflection enhances with the increase in length of DNA chains, and the interchain distances should be carefully controlled no less than 4 nm during the process of probe molecules self-assembly.

Imaging Biomolecular Interactions by Fast Three-Dimensional Tracking of Laser-Confined Carrier Particles

The quantitative study of the near-equilibrium structural behavior of individual biomolecules requires high-resolution experimental approaches with longtime stability. We present a new technique to explore the dynamics of weak intramolecular interactions. It is based on the analysis of the 3D Brownian fluctuations of a laser-confined glass bead that is tethered to a flat surface by the biomolecule of interest. A continuous autofocusing mechanism allows us to maintain or adjust the height of the optical trap with nanometer accuracy over long periods of time. The resulting remarkably stable trapping potential adds a well-defined femto-to-piconewton force bias to the energy landscape of molecular configurations. A combination of optical interferometry and advanced pattern-tracking algorithms provides the 3D bead positions with nanometer spatial and >120 Hz temporal resolution. The analysis of accumulated 3D positions has allowed us not only to identify small single biomolecules but also to characterize their nanomechanical behavior, for example, the force-extension relations of short oligonucleotides and the unfolding/refolding transitions of small protein tethers.

The Contribution of Crystallinity to Tissue-level Properties in Modern and Fossilized Bone

ABSTRACTA range of mineral content values and organization of the collagen and mineral phases are possible contributors to the significant variance demonstrated within the nanomechanical behavior of mineralized tissues. A combined approach using nanoindentation, to assess nanomechanical behavior, and X-ray diffraction, for analysis of crystallinity and composition, were used to investigate a range of modern and fossilized bone samples. This work provides new insight into the functional role of organization and composition of the mineral phase within heterogeneous, mineralized materials of biological origin. While the predominant influence on nanomechanical behavior is made by mineral volume fraction, the crystallinity was shown to play a significant role in the nanomechanical behavior of modern and fossilized bone samples. The interplay between material structure and function will ultimately help to elucidate the relative contributions of various factors to nanomechanical behavior and lead to improved development of biomimetic materials.

Muscle dystrophy single point mutation in the 2B segment of lamin A does not affect the mechanical properties at the dimer level

Lamin intermediate filaments at the inner nuclear membrane play a key role in mechanosensation and gene regulation processes, and further guarantee the mechanical stability of the cell's nucleus. The rod-like dimers are the elementary building blocks within the dense lamina meshwork, mainly consisting of four α-helical coiled-coil segments as fundamental building blocks. Several mutations in the 2B segment of the rod domain of lamin A have been linked to the disease muscle dystrophy. In these diseases, the cell nuclei have been shown to feature abnormalities in the shape and its mechanical properties, leading to torn nuclear envelopes or bleb formation. However, up to now the origin of these mechanical changes remains unknown, in particular whether or not the mutations in the rod domain influence the mechanical properties of individual dimers, or if the changes are due to effects at larger hierarchical scales. Here we report a series of large-scale molecular dynamics studies of lamin A dimer segments, systematically comparing the mechanical behavior of the wild-type protein structure and a missense mutated protein structure with the point mutation p.Glu358Lys. Our results show that the nanomechanical tensile behavior of the dimer segment does not vary under presence of this mutation, suggesting that this single point mutation in muscle dystrophy does not affect the mechanical properties of lamin at the dimer level, but probably influences higher hierarchical scales.