We investigated the effect of stacking fault free energy (SFE), on the magnitude of the indentation size effect (ISE) of several pure FCC metals using nanoindentation. The metals chosen were 99.999% Aluminum, 99.95% Nickel, 99.95% Silver, and 70/30 Copper Zinc (α-brass). Aluminum has a high SFE of about 200 mJ/ m2, whereas α -brass has a low SFE of less than 10 mJ/ m2. Nickel and Silver have intermediate SFE of about 128 mJ/ m2 and 22 mJ/m2 respectively. The SFE is an important interfacial characteristic and plays a significant role in the deformation of FCC metals due to its influence on dislocation movement and morphology. The SFE is a measure of the distance between partial dislocations and has a direct impact on the ability of dislocations to cross slip during plastic deformation. The lower the SFE the larger the separation between partial dislocations and thus cross slip and dynamic recovery are inhibited. The SFE impacts pure metals differently from alloys. It was discovered that the characteristic ISE behavior for the pure metals was different when compared to the α-brass which is an alloy. Several additional alloys were chosen for comparison including 7075 Aluminum and 70/30 Nickel Copper.

Nanomechanical resonators made from silicon nitride with residual stress is actuated using dielectric field gradient force. Doubly clamped nanomechanical resonators are made from SiNx-SiO2-Si tri-layer substrate and DC electric field induces a temporary dipole moment while a small AC electric field drives beam resonator by dielectric force. Realized nanomechanical resonators show resonant motion of high resonant frequency (up to ~31 Mhz) and mechanical quality factor up to over 48,000 at room temperature and moderate vacuum condition. From the FEA (Finite Element Analysis) of resonant motion, doubly clamped resonator shows torsional motion and in-plane motion which can be assigned to additional multiple modes in resonant response measurement

The influence of surface segregation on the elastic properties of Pt-M (M = Ni, Co, or Fe) nanowires (NWs) are examined by comparing the predicted Young’s moduli of the segregated and non-segregated nanowires using density functional theory (DFT) calculations and the computed stress-strain curves under tensile loading using molecular dynamics (MD) simulation method. The moduli of the segregated NWs were found to be higher than that of the non-segregated ones. It is believed that the surface segregation increases the number of Pt-M bonds across the outermost and second surface layers, and thus enhances the Young’s modulus of the segregated Pt-M nanowires. MD results confirm our DFT results and it is found that onset of plastic deformation could be altered by the surface segregation process, as well.

In this paper we examine the mechanical properties of individual lamellae from bone material using novel atomic force microscopy (AFM)-scanning electron microscopy (SEM) techniques. Individual lamellar beams were selected from bone using focussed ion beam (FIB) microscopy and mechanically deformed with the AFM while observing failure modes using SEM. Both the elastic and fracture behavior of the bone lamellae were determined using these techniques.

Using molecular dynamics simulations, we have investigated the effect of embedding nanoclusters of radius 3-7 Å on the dynamical and mechanical properties of 1,4-cispolybutadiene melts. To see the effect of polymer-nanocluster interaction strength on the bulk modulus, the van der Waals interactions (vdW) between the polymer chain and nanocluster have been varied from weak to very stong while keeping polymer-polymer and nanoclusternanocluster interactions constant. The modulus depends on the interaction strength, but not on nanocluster size. Residence time of chains on the surface of the nanocluster (τr) has an increasing trend that reaches to a plateau as the vdW strength is increased. τr also doubles from 100 ps to 200 ps as the nanocluster size is increased from 3 to 7 Å. Our findings give clues on how the properties of polymeric materials may be controlled by nanoparticles of different chemistry and size.

Nanotribology, the study of friction, wear and lubrication at the nanoscale is an important area of research; however in practice due to the size scale, requires specifically designed tools to characterize nanoscale contacts. We have developed a TEM triboprobe incorporating an advanced nano-positioner with 3D programmable motion inside a transmission electron microscope (TEM) which allows us to selectively apply multiple reciprocating wear cycles to a nanoscale surface, and observe in real-time dynamical changes and the evolution of wear around a sliding nano-contact.

Nanoscale cyclic rubbing of an automotive aluminum-silicon alloy processed by focused ion beam (FIB) reveals dynamical surface fragmentation and the generation of nanoscale debris particles. The nanoparticles undergo complex motion as they interact with the sliding nano-contact. Over hundreds of reciprocating cycles, frictional heating leads to a phase separation of the Ga+ ions implanted by FIB forming liquid Ga nano-droplets and liquid bridges. The addition of nanoscale debris particles and liquid droplets dramatically changes the wear dynamics and transforms a 2-body sliding contact into a complex 4-body solid–liquid system exhibiting time-dependent, non-equilibrium kinetic behavior.

TEM nanotribology opens up new possibilities for the real-time quantification of cyclic friction, wear and dynamic solid–liquid nano-mechanics, which will have widespread applications in many areas of nano-science and nanotechnology.

Hydrogen blister rates in Si (100), Si (111) and Ge (100) substrates are compared as a function of annealing temperature and time, for a range of implant energies and fluences. For each material, the rate of blister formation was found to exhibit Arrhenius behavior and to be characterised by a single activation energy over the temperature range examined. The extracted activation energies were 2.28±0.03 eV, 2.17±0.06 eV and 1.4±0.03 eV for (100) Si; (111) Si and (100) Ge, respectively. These results are compared with reported measurements and discussed in relation to proposed models of hydrogen blistering.

We investigated pure FCC metals including Aluminum, Nickel, Silver, and 70/30 Copper Zinc (alpha-brass) alloy for the indentation size effect (ISE) and the bilinear behavior using a single Berkovich indenter tip in a single test machine. The results were consistent with those reported by Elmustafa and Stone, 2003 of the ISE and the bilinear behavior using two separate indenter tips (Berkovich and Vickers) from two separate machines. This behavior is mechanistic in nature and is observed regardless of the type of the self similar indenter tip employed. Furthermore, the research presented in this paper would seem to also validate the conclusions that Elmustafa et al (2004) articulate that the Strain Gradient Plasticity collapses at small scales and that the bilinear behavior of these FCC metals is attributed to the presence of long range shear stresses induced by geometrically necessary dislocations. Also, we observed what has been defined as a “tapping” issue for materials with high E/H ratios when using the CSM. The CSM protocol results in erroneous hardness results at very shallow depths for high E/H ratio soft metals due to the so called “tapping” of the stylus as articulated by Pharr et al. (2009). This method should only be used as a secondary technique to the load control protocol when examining the ISE effect.

Nanomechanical and structural properties of pulsed laser deposited niobium nitride thin films were investigated using X-ray diffraction, atomic force microscopy, and nanoindentation. NbN film reveals cubic δ-NbN structure with the corresponding diffraction peaks from the (111), (200), and (220) planes. The NbN thin films depict highly granular structure, with a wide range of grain sizes that range from 15-40 nm with an average surface roughness of 6 nm. The average modulus of the film is 420±60 GPa, whereas for the substrate the average modulus is 180 GPa, which is considered higher than the average modulus for Si reported in the literature due to pile-up. The hardness of the film increases from an average of 12 GPa for deep indents (Si substrate) measured using XP CSM and load control (LC) modes to an average of 25 GPa measured using the DCM II head in CSM and LC modules. The average hardness of the Si substrate is 12 GPa.

Fe12%Cr was irradiated with 2MeV and 0.5MeV Fe+ ions at 320°C, to create a layer with a mean level of displacement damage of 6.18dpa to a depth of ∼800nm. Spherical indentation, with a nominal tip radius of 10μm, was used to investigate the mechanical properties of the damage layer. Indents produced with loads of 2mN, 3mN, 5mN and 10mN were cross-sectioned and fabricated into TEM foils using an in situ lift-out technique in a dual beam FIB-SEM microscope. The extent of the plastic zone beneath the indent was observed in the TEM for each indentation. The indentation results were analysed so as to give an indentation stress-strain curve, in which strain softening was found to occur beyond the yield point. At loads up to 3mN the plastic zone remained entirely within the damage layer, implying strain-softening of the damaged material. At higher indentation loads the plastic zone was observed to extend into the softer un-irradiated substrate, giving rise to a further fall in flow stress with increasing strain.

Escherichia coli, like other gram-negative bacteria, is protected from the surrounding harsh environment by a cell wall consisting of the peptidoglycan and outer membrane. Whereas the cytoplasmic membrane is the selective barrier, the cell wall provides mechanical strength for the cell. As bacteria navigate various environments, osmotic pressure can change dramatically due to changes in local solute concentration. The peptidoglycan together with the cellular proteins mitigates the osmotic stress that would otherwise cause lysis. The mechanical properties of E. coli cells and its individual layers have been largely indeterminable until the recent development of probe-based measurement tools. Since their invention, scientists have reported significant data measuring elasticity, modulus, and stiffness using atomic force microscopy (AFM). Fundamentally, in order to determine these mechanical properties through probe-based techniques, the contact area and load should be well defined. The load can be precisely calculated through the AFM cantilever spring constant. However, the silicon tip contact area can only be estimated, potentially leading to compounding uncertainties. Therefore, we developed a methodology to determine nanomechanical properties of E. coli using a nanoindenter.

Localized heating of metals and alloys using a focused laser beam in ambient atmosphere produces dielectric oxide layers that have characteristic optical appearances including different colors. Nanoindentation probed the deformation and fracture of laser-fabricated oxides on 304L stainless steel. Conductive nanoindentation measured electrical contact resistance (ECR) of the same colored oxides indicating a correlation between laser exposure, conductance during loading, current-voltage (I-V) behavior at constant load, and indentation response. Microscopy and X-ray diffraction examined the microstructure and chemical composition of the oxides. Combining techniques provides a unique approach for correlating mechanical behavior and the resulting performance of the films in conditions that cause wear.

The formation and strength of dislocations in the hexagonal closed-packed material are studied through dislocation junctions and the critical stress required to completely break them. Dislocation dynamics calculations of junctions are compared to an analytical line tension approximation in order to verify the simulations. Results show agreements between the models. Also the critical shear stress necessary to break a short and a long dislocation junction is computed numerically. Unzipping envelopes are mapped out for these junctions to describe their stability regions as functions of resolved shear stresses on the glide planes. The example of two non-coplanar binary dislocation junctions with slip systems [2 -1 -1 0] (0 1 -1 0) and [-1 2 -1 0] (0 0 0 1) corresponding to a prismatic and basal slip respectively is chosen to verify and validate our implementation.

Torsion experiments on 50μm diameter Cu wires are reported, using the load/unload method and a gauge length of 1m to obtain torsional strain sensitivity better than unity microstrain. The experiments are able to resolve reversible and irreversible deformation at such very low strains. Plastic deformation, dislocation creep and the Bauschinger effect are easily observed at room temperature and at about 300°C, both in the low-strain regime where it is unlikely that dislocation sources are activated, and at higher plastic strain.

The analysis of the structures and microstructures of nanostructured thin layers can be performed using laboratory grazing incidence diffraction, provided accurate corrections are performed to handle the instrumental broadening effects related to the experiment geometry for an impinging beam close to the critical angle. Implementing these corrections in Rietveld refinement software allows the accurate extraction of quantitative relevant information about the structure (strain and atomic positions) and the microstructure (crystallite size and microstrain), selectively probing the material on a depth of few nanometers.

Teflon amorphous fluoropolymer (TAF) multi-walled carbon nanotube (MWCNT) suspensions have the potential for creating conductive coatings on insulating films for numerous applications. However, there are few studies on polymer MWCNT suspension properties and even fewer that use Teflon. To define mechanical and electrical property relationships, bilayer films of TAF-MWCNT were created with differing concentrations of MWCNTs. Nanoindentation revealed that addition of 8 wt% MWCNTs to TAF increased the elastic modulus by about 25% and hardness by about 15%. Conducting indentation showed 8 wt% MWCNT films exhibit uniform stable conductance once indentation depth exceeds several hundred nanometers. Films with lower concentrations of CNTs were insulating. The two techniques provide a unique description of structure property relationships in this suspension film system.

The surface of polymer nanofibers plays a significant role in many applications thus measurement of their surface properties is essential but challenging due to their relatively small size. This study details AFM wetting tests for individual electrospun Poly (Vinyl Alcohol) nanofibers in order to measure their polar and dispersive surface free energy components. Individual electrospun PVA nanofibers have been immersed and removed from three different low vapor pressure liquids using AFM. The polymer nanofiber-liquid interactions can be monitored by AFM and accurate measurements of contact angle between liquids and the nanofiber surface can be made. These wetting data were used to produce Owens-Wendt plot giving the dispersive and polar components of the nanofiber surface. Results are compared with bulk polymer films to conclude how the surface properties of electrospun polymer nanofibers are different from bulk polymer material.

Polyacetal is a resin which has excellent property. However, polyacetal has a poor adherence property using adhesive material. Therefore, for the improvement of the adhesive strength, simultaneous surface treatments of polyacetal by irradiation of vacuum ultra-violet (VUV) light and deposition of nanometer-sized particles using laser ablation with C, Si and Ti targets were carried out. The surface treatments were carried out with different wavelengths, energies, processing times and substrate locations from normal direction of targets. The targets were irradiated with a pulsed laser from Nd-YAG laser. After surface treatments, tensile test pieces of polyacetal were bonded by epoxide-based adhesive. And, longitudinal shear strengths were measured. As a result, after surface treatment of polyacetal using C target, the highest shear bond strength which is approximately 8 times larger than that of untreated polyacetal sample was measured (5.6 MPa). It was found that increasing functional groups and increasing surface roughness are affecting improvement of the adhesive strength. The improvement of the adhesive strength is also caused by the new-creation of the dangling-bonds on the polymer surface by VUV irradiation and preservation of each dangling-bonds from re-bonding each other by a separation effect of deposited nanometer-sized particles. This method can be expected for new applications of polymers.

A nanoscale dynamic mechanical analysis (nano-DMA) measurement method has been successfully developed for use in evaluating nanoscale dynamic viscoelastic properties in small-scale polymer materials over a range of non-ambient temperatures from -120 oC to 500 oC. Measurements have been obtained with a nanoindentation measurement system, in which two key techniques are applied. One is a thermal protection system for control and prevention of thermal drift and noise. The other is an environmental control system for preventing corrosion at high temperatures and dew condensation at low temperatures. Measurement reliability was examined by using a combination of a thermal-mechanically stable fused silica and a homogeneous sample of isotropic polyethylene terephthalate (PET). Constant hardness and modulus values of the fused silica from -120 oC to 500 oC indicated that the measurements were not affected by thermal load drift and noise even at elevated temperatures. The PET sample exhibited no significant difference in temperature dispersions of storage elastic modulus, loss elastic modulus and loss tangent between the nanoindentation measurement data and bulk data measured with a conventional DMA method. A practical application involving surface-deteriorated polyethylene (PE) tubes was used to demonstrate the validity and usefulness of this nano-DMA method. Infrared spectroscopic imaging revealed that the surface layer of the PE tubes was oxidized to form a carbonylated (O=C<) layer. The storage elastic modulus and glass-transition temperature of the surface layer were much higher than the corresponding values of the interior. These data indicate a plausible reason for why the PE tube surface deteriorates to form brittle cracks.