A rapid nano-indentation measurement technique is employed to produce surface maps of hardness. Each indentation cycle requires less than three seconds, including surface approach, contact detection, force application, withdrawal, and movement to the next indentation site. Traditional nano-indentation analyses are applied to the force-displacement measurements from each indentation, but information storage and presentation owe much to scanning-probe technology. Consequently, this nano-indentation technique produces three-dimensional images of mechanical properties which are stored and manipulated just like scanned images.

In the present work, we use this technique to map the hardness of a SAC 305 solder joint with gold plating. After extended isothermal aging, the solder joint comprises three constituents: a tin-rich matrix, a bulk intermetallic AuSn4, and an interfacial intermetallic (Cu, Ni, Au)6Sn5. The softest material is the tin-rich matrix, which has a hardness of 0.51±0.07 GPa. The hardness of the bulk intermetallic is 2.12±0.18 GPa. The interfacial intermetallic has extraordinary hardness— greater than 8 GPa. Under uniform plastic strain, the mismatch in hardness between the interfacial intermetallic and surrounding material may increase the local stress intensity factor which drives interfacial fracture.

A plethora of applications in pharmacy, cosmetics, food industry and other areas are directly linked to the research fields of particle technology and contact mechanics. Here, a typical particle ensemble features particle sizes ranging from the nanometer up to the micrometer regime. In this context we introduce a nanoindentation based approach capable of probing mechanical interaction of micron-sized particles. Basically, the concept of the colloid probe technique, which is well established in the AFM community, is transferred to a nanoindenter. In particular, this setup allows addressing limitations, which are typically associated with AFM based techniques, such as particle weight and accessible load regime. Additionally, we will show the versatility of this approach by presenting simple experimental paths capable of probing sliding, rolling and torsional friction. The potential of such setting is shown by studying rolling friction of silica microspheres featuring radii of about 2.5µm, 10µm, 25 and 50µm in contact with various substrates, respectively. Substrates utilized within the framework of this study are Si surfaces featuring various roughness as well as flat gold films (300nm film thickness). Key aspects of this work include the influence of surface roughness, adhesion force, humidity and the elastic/plastic transition on the rolling contact of the corresponding particles.

Adsorption of charged biomolecules onto atomically flat mica substrates is facilitated by the deposition of metal ions. Despite successfully acting as preferential anchoring sites, the presence of ions on the mica surface also changes its physicochemical characteristics something that is rarely quantified from a nanoscale point of view. In this study the nanoscale physicochemical properties of nickel-functionalized Muscovite mica are investigated by reconstructing the conservative force profile between an atomic force microscopy (AFM) tip and the surface. Various nickel ion concentrations (i.e. 1.0 mM to 20.0 mM) along with different incubation times (30 seconds and 5 minutes) are directly analyzed. Details in the spatial and temporal variations in surface properties due to the ion mediated adsorption of water are presented in details and in light of the binding efficiency of the metal ions. This insight benefits our understanding in the behavior of ion distribution that plays a crucial role in biomolecule imaging using AFM.

Atomic force microscopy (AFM) suffers from an important limitation: it does not provide quantitative information about the scanned sample. This is because too many unknowns come into play in AFM measurements. The shape of the tip is probably the most important. A technique able to characterize in situ the shape of the tip apex would represent an important step ahead to turn the AFM into a quantitative tool.

Standard methods can be destructive to the tip and are time consuming. Two main methods are currently used to characterize the tip radius in situ without affecting its shape. The first consists of characterizing the tip radius by monitoring the dynamics of the cantilever. The value of free amplitude, for which transitions from the attractive to repulsive force regimes are observed, strongly depends on the curvature of the tip. The second method to characterize the tip radius consists instead on fitting the capacitance curve of the tip-sample system with an analytical function.

In this work we compare the two methods to characterize in situ the tip radius and results are verified with SEM images. The value of the free amplitude is correlated with the value of R while the capacitance curve is derived with a method we proposed. Tips with different tip radii are used. The investigation is conducted with the aim of determining the most reliable technique for characterizing the tip radius for both sharp and blunt tips.

In electrostatic force microscopy (EFM), a conductive atomic force microscopy (AFM) tip is electrically biased against a grounded sample and electrostatic forces are investigated. This methodology has been broadly used in the scientific community to characterize dielectric properties of samples at the nanoscale. Two are the main operating conditions associated with this technique. The oscillation amplitude is usually kept to very small values to allow a linearized approach to the force reconstruction and the tip-sample distance is maintained elevated. However, this latter condition negatively affects the lateral resolution of the technique. Thus, electrostatic interaction should be probed in the vicinity of the sample. Theoretically, in this region the force can be linearized using oscillation amplitudes in the order of Å. This might cause the trapping of the tip on the surface (snap-in). Furthermore, at small distances, short-range forces (i.e. Van der Waals’) might reach values comparable to electrostatic forces.

Here we present a framework that combines EFM and dynamic amplitude modulation AFM to achieve decoupled reconstruction of forces. It permits reconstructing the real shape of the electrostatic force and the capacitance of the tip-sample system even in the vicinity of the surface. This is done using a technique proposed in literature by Sader and Katan to reconstruct the force without the linearization approximation. The steps needed to decouple short-range and electrostatic forces are explained in detail. This data can be employed to derive the electrical properties of thin films with enhanced lateral resolution with respect to the commonly used EFM techniques.

Bacteriophytochromes (BphPs) are red-light photoreceptors found in photosynthetic and nonphotosynthetic bacteria that have been recently engineered as infrared fluorescent tissue markers. Light-induced, global structural changes are proposed to originate within their covalently bound biliverdin chromophore and propagate through the protein. Classical BphPs undergo reversible photoconversion between spectrally distinct light absorbing states, red (Pr) and far-red (Pfr), respectively. RpBph3 (P3), from Rhodopseudomonas palustris, photoconverts between a Pr and a unique near-red (Pnr) light-absorbing state. Due to size and photosensitivity of BphPs, structures of the intact proteins have not been resolved by nuclear magnetic resonance and/or X-ray crystallography. Therefore, structural details about the light and dark-adapted structures of the intact BphPs are not well understood at the molecular level. We have utilized fluid cell atomic force microscopy (AFM) to investigate the domain structure of intact P3 in its light-adapted state (Pnr). By varying the concentration of the protein, deposition time, and the ionic strength of the buffer, the aggregation of P3 on a mica surface can be controlled and single dimers may be observed in a biologically relevant media. Domain resolution has been achieved for several orientations of the dimer on the surface. The structural dimensions of the dimer have been compared to a modeled BphP in its intact form generated using PyMOL software. AFM experiments are currently underway to analyze the dark-adapted state (Pr) of P3 in order to observe the anticipated structural changes. Ultimately, the goal is to use AFM and other surface analytical methods such as scanning tunneling microscopy and electron microscopy to gain new insight into the unique photochemistry of P3.

Understanding crystal orientation at the ferroelectric domain level, using a non destructive technique, is crucial for the design and characterization of nano-scale devices. In this study, piezoresponse force spectroscopy (PFS) is used to identify ferroelectric domain orientation. The impact of crystal orientation on the switching field of ferroelectric BaTiO3 is also investigated at the domain level. The preferential domain orientations for BaTiO3 thin films prepared by pulsed laser deposition (PLD) in this study are [001], [101] and [111]. They have been mapped onto PFS spectra to show three corresponding switching fields of 460, 330 and 120 kV/cm respectively. In addition, the electric field at which the enhanced piezoresponse occurs was found to vary, due to a phase change. The polarization reversal occurs via a 2-step process (rotation and switching) for [101] and [111] orientations. The piezoresponse enhancement is absent for the [001] (pure switching) domains. The results demonstrate that an electric field induced phase change causes the [101] and [111] domains to reverse polarization at a lower field than the [001] domain.

In this study a scanning near-field ellipsometric microscope (SNEM), a hybrid device of an atomic force microscope (AFM) and an ellipsometer, is used to obtain optical images of heterogeneous polymer thin films with a resolution below the diffraction limit of light. SNEM optical images of a microphase separated PS-b-P2VP block copolymer film collected with gold coated and bare silicon AFM probe tips were compared to obtain a deeper insight into the nature of the SNEM contrast mechanism. Furthermore, intensity vs. distance curves were recorded on a PS-b-PMMA block copolymer film simultaneously during the acquisition of force-displacement curves to study the far-field contribution of the optical signal to the optical image.