We show results of in situ TEM (Transmission electron microscope) quantitative investigations on the compression behaviors of amorphous micropillars fabricated by focused ion beam from Cu47Ti33Zr11Ni6Sn2Si1 metallic glass (MG) ribbon. Pillars with well defined gauge sections and tip diameter ranging from 100 nm to 640 nm are studied. Quantitative compression tests were performed by a recently developed Picoindenter TEM holder, with the evolution of individual shear bands monitored in real time in TEM. It is found that the deformation of the MG pillars at the present size domain is still dominated by discrete shear banding as demonstrated by intermittent events in the load-displacement curves. However, the frequency, amplitude and distribution of these shear banding events are clearly size dependent at submicrometer scale, leading to an apparently transition in deformation mode from highly localized inhomogeneous deformation to less localized and more distributed deformation with decreasing pillars diameter. Deformation of a 105 nm diameter pillar having rounded tips is characterized with fully homogeneous bulge at the initial stage of deformation, indicating prompting effect of multi-axial stress state on transition to fully homogeneous deformation.

Measuring elastic properties of cells has gained importance in the study of malignant transformations. The stiffness of a cell, which is technically referred to as the modulus of elasticity or Young's Modulus, E, is the measure of the amount of cell deformation caused by an applied known force. In vitro studies have shown that cancer cells have much lower elastic stiffness than normal cells. These stiffness measurements and their differences can be used to study the behavioral mechanics of how cancer cells grow, profligate, and die in a patient. Another important use of this difference in elasticity is in cancer detection.

In this study, we explore the viability of measuring the elastic modulus of cancer cells by using a method that only requires the use of a low magnification microscope and a digital camera. In particular we are interested in applying the previously reported relationship between the wrinkling of thin films and the elastic properties of freely floating polystyrene (PS) films. Our work extends the scope of previous thin film studies by evaluating wrinkle formation in floating polystyrene films coated with biological cells. Our results show that the wrinkle formation is modified, both in morphology and in size, by the presence of a cellular monolayer on top of the PS film.

The early stages of plasticity in KBr single crystals have been studied by means of nanometer-scale indentation in complementary experiments using both a nanoindenter and an atomic force microscope. Nanoindentation experiments precisely correlate indentation depth and forces, while force microscopy provides high-resolution force measurements and images of the surface revealing dislocation activity. The two methods provide very similar results for the onset of plasticity in KBr. Upon loading we observe yield of the surface in atomic layer units which we attribute to the nucleation of single dislocations. Unloading is accompanied by plastic recovery as evident from a non-linear force distance unloading curve and delayed discrete plasticity events.

There is an increasing amount of experimental evidence that the plastic behavior of crystals changes at micro- and nano-scales in a way that is not necessarily captured by state-of-the-art plasticity models. In this paper, length scale effects in the plasticity of crystals are analyzed by means of direct numerical simulations that resolve the scale of the carriers of plasticity, i.e., the dislocations. A computationally efficient, atomistically informed dislocation dynamics framework which has the capability of reaching high dislocation densities and large strains at moderately low strain rates in finite volumes is recalled. Using this theoretical framework, a new type of size effect in the hardening of crystals subject to nominally uniform compression is discovered. In light of such findings, behavior transitions in the space of meaningful structural parameters, from forest-hardening dominated regime to an exhaustion hardening dominated regime are discussed. Various scalings of the flow stress with crystal size emerge in the simulations, which are compared with recent experimental data on micro- and nano-pillars.

Atomic force acoustic microscopy (AFAM) is a non-destructive method able to determine the indentation modulus of a sample with high lateral and depth resolution. We used the AFAM technique to measure the indentation modulus of film-substrate systems Msam and then to extract the value of the indentation modulus of the film Mf. The investigated samples were films of silicon oxide thermally grown on silicon single crystal substrates by use of dry and wet oxidation methods. The thickness of the samples ranged from 7 nm to 28 nm as measured by ellipsometry. Our results clearly show that the values of Msam obtained for the film-substrate systems depended on the applied static load and the film thickness. The observed dependency was used to evaluate the indentation modulus of the film. The values obtained for Mf ranged from 77 GPa to 95 GPa and were in good agreement with values reported in the literature.

Compressive strained Silicon from a Silicon on Insulator (SOI) substrate is obtained by replacing the buried oxide layer by a strained silicon nitride layer. The silicon overlayer and the buried dielectric are etched down to the substrate to form narrow wires (down to 300 nm wide). The Si overlayer is then expected to acquire compressive strain thanks to the relaxation of the SiN layer. The goal is to obtain a high uniaxial stress perpendicular to the wires. The structures and the strain are modeled using finite element simulations. The strain elements are used to calculate Raman spectra. Theoretical results are compared to experimental profiles deduced from resonant (UV) micro Raman experiments.

Ion-implantation has been used to introduce oxygen concentration-depth profiles into nominally oxygen-free amorphous silicon (a-Si). The effect of O concentrations in excess of 1018 cm−3 on the formation of high pressure crystalline phases (Si-III and Si-XII) during indentation unloading has been studied. By examination of unloading curves and post-indent Raman micro-spectroscopy O is found to inhibit the so-called pop-out event during unloading and, therefore, the formation of the crystalline phases. Furthermore, at high O concentrations (> 1021 cm−3) the formation of these phases is reduced significantly such that under indentation conditions used here the probability of forming the phases is reduced to almost zero. We suggest that the bonding of O with Si reduces the formation of Si-III/XII during unloading through a similar mechanism to that of oxygen-retarded solid phase crystallization of a-Si.

Compression tests with varying loading rates were performed on [001] and [235] oriented small-scale bcc Mo and Nb pillars to determine the contribution of thermally activated screw dislocation motion during deformation. Calculated activation volumes were shown to be in the range of 2 - 9 b3 and by further examination were found to decrease with pillar diameter. This suggests that the kink-pair nucleation of screw dislocations is enhanced by surface effects in the micron and submicron range.

Small-scale natural fibers are among the biological materials being studied by researchers seeking innovative methods to create new high performance materials. For example, spider dragline silk fibers are being studied because of their unique combination of high strength-to-weight ratio and high extensibility, which leads to a tough and lightweight fiber. Biomimetic fibers based on spider silk have been a focus of research for the past decade. However, there are still many unanswered questions about the mechanisms by which silk achieves its unique mechanical properties, as well as challenges in mechanical testing of biomimetic silk fibers (which is often hindered by both small diameters and limited material availability). A method to characterize local mechanical behavior in small diameter fibers was developed to both improve understanding of structure-property relationships in natural fibers and provide a method for comparing mechanical behavior in natural and biomimetic fibers. The deformation mapping technique described in this paper, which utilizes a piezoelectric micromanipulator with pulled glass tips, an inverted microscope with attached camera, and an image processing MATLAB program, is also applicable to the characterization of other micro- and nanoscale fibers where local deformation mechanisms may be of interest (e.g., for mechanical characterization of electrospun fibers).

Tensile deformation of individual electrospun polyvinyl alcohol (PVA) nanofibres was performed using a novel combination atomic force microscope (AFM)- scanning electron microscope (SEM) technique. The AFM was used to provide manipulation and mechanical testing of individual PVA nanofibers while the SEM was used to observe the deformation process. Resultant stress-strain curves show how the elastic modulus shows comparable, or even slightly increased, values to isotropic films. In addition, the electrospun fibers were tested to failure to measure their tensile strength.

The glass transition of individual electrospun PVA fibers was found using an AFM fiber bending technique within a heated chamber. A considerably loss in the measured elastic modulus was observed with temperature when the glass transition temperature was reached. The glass transition temperature was observed to decrease as the electrospun PVA fiber diameter decreased, indicating diameter dependent enhanced polymer chain mobility.

Molecular Dynamics (MD) simulations of nanoindentation on graphene membranes were performed. The 2-d Young's modulus of the graphene monolayer was determined as 243 ± 18 N/m and the breaking strength as 41 ± 3 N/m. These values agree reasonably well with recent experimental results [1]. In addition, the simulations allowed us to examine the atomic-scale dynamics of membrane breaking during the nanoindentation, involving formation of an increasing number of lattice defects until membrane is completely broken. The onset of defect appearance allowed us to determine the true elastic limit of graphene and the corresponding yield strength 29 ± 1 N/m which was not accessible experimentally. The defects consist of vacancies and Stone-Wales type defects. Long stable linear chains of sp bonded carbon atoms (carbynes) were observed under the indenter at the advanced stages of indentation. The dynamics of fracture propagation is governed by the shear stresses developed in the sample.

This paper focuses on the measurement of material properties of micro and nano-electromechanical systems. Two different methods are discussed: electrical or optical measurements of the resonance frequency, and measurements of the Raman frequency shift. The main focus of this paper is on challenges and pitfalls related to the use of these techniques for the study of MEMS and NEMS.

Recently, size effects in the initiation of plasticity have been clearly observed and reported in different geometries; e.g., bending (Ehrler et al. Phil. Mag. 2008), twisting (Ehrler et al., MRS, Spring Meeting 2009) and indentation (Zhu et al. J. Mech. Phys. Sol. 56, 1170, 2008). Strain gradient plasticity theory is the principal approach for explaining size effects during plastic deformation in these geometries. However, it fails to account for any size effect at the initial yield. Geometrical critical thickness theory was proposed to explain the yield size effect in bending and torsion (Dunstan and Bushby, Proc. Roy. Soc. A460, 2781, 2004). The theory shows that the initial yield strength is scaled with the inverse square root of the characteristic length scale without requiring any free fitting parameters. Here, we extend the theory to describe the yield size effect in indentation. The theory agrees fairly well with experimental observations in micro-torsion (Ehrler et al., MRS, Spring Meeting 2009) and nanoindentation (Zhu et al., J. Mech. Phys. Solid, 2008).

The materials properties of mica have surprising similarities to those of living systems. The mica hypothesis is that life could have originated between mica sheets, which provide stable compartments, mechanical energy for bond formation, and the isolation needed for Darwinian evolution. Mechanical energy is produced by the movement of mica sheets, in response to forces such as ocean currents or temperature changes. The energy of a carbon-carbon bond at room temperature is comparable to a mechanical force of 6 nanoNewtons (nN) moving a distance of 100 picometers. Mica's movements may have facilitated mechanochemistry, resulting in the synthesis of prebiotic organic molecules. Furthermore, mica's movements may have facilitated the earliest cell divisions, at a later stage of life's origins. Mica's movements, pressing on lipid vesicles containing proto-cellular macromolecules, might have facilitated the blebbing off of ‘daughter’ protocells. This blebbing-off process has been observed recently in wall-less L-form bacteria and is proposed to be a remnant of the earliest cell divisions (Leaver, et al. Nature457, 849 (2009).

The strength of submicron FCC structure metal columns, σ, fabricated by FIB machining or electrodeposition, shows a strong correlation with specimen diameter, d, with σ/μ = A(d/b)−0.63, where A is a constant, μ is the single crystal shear modulus resolved onto the slip system and b is the Burgers' vector. The strength of BCC structure metals does not show such a well defined correlation with size across different metals but the data occupies the same region of parameter space as with the FCC metals. Nanoporous gold specimens show a similar size-correlated behaviour but with an exponent of −0.5. This may indicate different mechanisms operating in each case.

Micro-scale Focused Ion Beam (FIB) machined cantilevers were manufactured in single crystal copper, polycrystalline copper and a copper-bismuth alloy. These were imaged and tested in bending using a nanoindenter. Cantilevers machined inside a single grain of polycrystalline copper were tested to determine their (anisotropic) Young's modulus: results were in good agreement with values calculated from literature values for single crystal elastic constants. The size dependence of yield behavior in the Cu microcantilevers was also investigated. As the thickness of the specimen was reduced from 23μm to 1.7μm the yield stress increased from 300MPa to 900MPa. Microcantilevers in Cu-0.02%Bi were manufactured containing a single grain boundary of known character, with a FIB-machined sharp notch on the grain boundary. The cantilevers were loaded to fracture allowing the fracture toughness of grain boundaries of different misorientations to be determined.