Microscale wear behavior and crosslinking of PEG-like coatings for total hip replacements

The predominant cause of late-state failure of total hip replacements is wear-mediated osteolysis caused by wear particles that originate from the ultrahigh molecular weight polyethylene (UHMWPE) acetabular cup surface. One strategy for reducing wear particle formation from UHMWPE is to modify the surface with a hydrophilic coating to increase lubrication from synovial fluid. This study focuses on the wear behavior of hydrophilic coatings similar to poly(ethylene glycol) (PEG). The coatings were produced by plasma-polymerizing tetraglyme on UHMWPE in a chamber heated to 40°C or 50°C. Both temperatures yielded coatings with PEG-like chemistry and increased hydrophilicity relative to uncoated UHMWPE; however, the 40°C coatings were significantly more resistant to damage induced by atomic force microscopy nanoscratching. The 40°C coatings exhibited only one damage mode (delamination) and often showed no signs of damage after repeated scratching. In contrast, the 50°C coatings exhibited three damage modes (roughening, thinning, and delamination), and always showed visible signs of damage after no more than two scratches. The greater wear resistance of the 40°C coatings could not be explained by coating chemistry or hydrophilicity, but it corresponded to an approximately 26–32% greater degree of crosslinking relative to the 50°C surfaces, suggesting that crosslinking should be a significant design consideration for hydrophilic coatings used for total hip replacements and other wear-dependent applications

Predicting Scattering Scanning Near-field Optical Microscopy of Mass-produced Plasmonic Devices

Scattering scanning near-field optical microscopy enables optical imaging and characterization of plasmonic devices with nanometer-scale resolution well below the diffraction limit. This technique enables developers to probe and understand the waveguide-coupled plasmonic antenna in as-fabricated heat-assisted magnetic recording heads. In order validate and predict results and to extract information from experimental measurements that is physically comparable to simulations, a model was developed to translate the simulated electric field into expected near-field measurements using physical parameters specific to scattering scanning near-field optical microscopy physics. The methods used in this paper prove that scattering scanning near-field optical microscopy can be used to determine critical sub-diffraction-limited dimensions of optical field confinement, which is a crucial metrology requirement for the future of nano-optics, semiconductor photonic devices, and biological sensing where the near-field character of light is fundamental to device operation.Comment: article: 18 pages, 5 figures; SI: 15 pages, 12 figure

Reconfigurable ferromagnetic liquid droplets.

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs

Probe Tips Functionalized with Colloidal Nanocrystal Tetrapods for High-Resolution Atomic Force Microscopy Imaging

The performance and resolution of atomic force microscopy (AFM) imaging depends mainly on the quality and shape of the probe tip, since the obtained AFM image is a convolution of the tip profile and the sample structure. Therefore, tip radii that are smaller and aspect ratios that are higher than the sample features are desirable in order to obtain good images. Progress in the ability to design, fabricate, and assemble nanostructures in the size range of a few nanometers has raised the demand for probe tips with a corresponding resolution. Standard commercially available tips made of Si or SiN have a pyramidal shape with a tip radius of the order of 10 nm or larger and therefore do not image nanostructures with features in the few nanometer range adequately. One solution to this problem is the commercially available super-sharp Si probes with tip radius of 2 nm, which, however, obtain their high resolution at a price: the sharp tip can break easily during an experiment. These limitations have stimulated many efforts to enhance the resolution of AFMby functionalizing the probe tips with high-aspect-ratio nanostructures. Carbon nanotubes have demonstrated excellent properties in this respect. Different approaches for the attachment of the carbon nanotubes to the AFM cantilever have been developed, and a spatial resolution of only a few nanometers has been demonstrated. However, the attachment of carbon nanotubes to theAFM tip is still a time consuming and very difficult task, and often results in non-reproducible nanotube configuration and placement. The optimal attachment geometry, with the tip perpendicular to the sample under investigation, is particularly hard to realize. Also, the inherent thermal vibration of long nanotubes can cause difficulties when they are used for AFM imaging. Recent approaches to overcome these difficulties comprise the growth of multiwalled carbon nanotubes and the electron beam induced deposition of carbon nanocones on tipless cantilevers. For a recent review on AFM probes see elsewhere. Shape-controlled semiconductor nanocrystals are another very interesting family of nanostructures that can enhance the spatial resolution of AFM. Tetrapod-shaped nanocrystals are especially appealing for functionalizing AFM tips. Their ability to align on a surface with three supporting base arms, and the fourth arm pointing straight up, resembles an optimal geometry for the sensing of topography with the fourth, vertical arm. Recent advances in colloidal chemical synthesis have led to tetrapod samples with arm lengths of the order of several hundred nanometers and a diameter at the arm extremity well below 10 nm. Moreover, the optoelectronic properties of shape-controlled nanocrystals can extend the functionality of AFM beyond the probing of topography. Banin and coworkers, for example, showed that AFM probes functionalized with spherical core/shell nanocrystals can be used for near field optical imaging. Here, we report the positioning of single CdTe tetrapods on flattenedAFM tips and demonstrate the feasibility of these tips, via the vertical tetrapod arm, for high resolution AFM imaging. Withour tippreparationweachieve anoptimal probingangle of 908, due to the use of contactmode scanning for the preparation of the tip flat. This inherently leads to a tip geometrywith the flat parallel to thesampleplane,which, combinedwiththecapability of tetrapods to self-align with three arms contacting the surface and the fourth pointing vertically upward, results in a geometry where the vertical arm probes the topography at a 908 angle to the sample surface. The high aspect ratio shape of the tetrapod arms, with diameters ranging from 5 to 10nm and lengths ranging from 100 to 300 nm, provides excellent properties for high-resolution topography scanning. In particular, we find that the tetrapod-functionalized tips work very well for imaging surfaces that are covered with nanocrystal samples. Furthermore, our tip fabrication technique could open the way for the fabrication of high aspect ratio optically and electronically sensitive probe tips due to the semiconductor properties of the tetrapods. Large aspect ratio colloidal nanocrystal CdTe tetrapods with arm lengths ranging from 100 to 300 nm and diameters around 10 nm were fabricated by chemical synthesis as reported elsewhere and dissolved in toluene (see Supporting Information Fig. S2 for a TEM image of these very large tetrapods). The rapid growth of the tetrapod arms led to a pointed shape (i.e., to a decreasing arm diameter toward the arm extremity), which is advantageous for our purpose of high spatial resolution imaging (see Fig. 1b). Figure 1(b and c) show transmission electron microscopy (TEM) images of tetrapods deposited by drop casting onto a carbon coated TEM grid. The images show that the tetrapods self-align, with three arms contacting the substrate and the fourth arm pointing straight upward, appearing as a dark circular spot in the image. A sketch of the tetrapod-functionalized AFM probe is shown in Figure 1a. [!] Dr. R. Krahne, C. Nobile, A. Fiore, R. Mastria, Prof. R. Cingolani, Dr. L. Manna National Nanotechnology Laboratory of CNR-INFM Distretto Tecnologico ISUFI Via per Arnesano, Lecce 73100 (Italy) E-mail: [email protected]

Ferromagnetic resonators synthesized by metal-organic decomposition epitaxy

Metal-organic decomposition epitaxy is an economical wet-chemical approach suitable to synthesize high-quality low-spin-damping films for resonator and oscillator applications. This work reports the temperature dependence of ferromagnetic resonances and associated structural and magnetic quantities of yttrium iron garnet nanofilms that coincide with single-crystal values. Despite imperfections originating from wet-chemical deposition and spin coating, the quality factor for out-of-plane and in-plane resonances approaches 600 and 1000, respectively, at room temperature and 40 GHz. These values increase with temperature and are 100 times larger than those offered by commercial devices based on complementary metal-oxide semiconductor voltage-controlled oscillators at comparable production costs

Reactivity of Ozone with Solid Potassium Iodide Investigated by Atomic Force Microscopy

The reaction of ozone with the (100) plane of solid potassium iodide (KI) was investigated using atomic force microscopy (AFM). The reaction forming potassium iodate (KIO{sub 3}) initiates at step edges prior to reacting on the flat terraces. Small domains of KIO{sub 3}, initially 3.8 {angstrom} in height are formed on the top of step edges. Following reaction at the step edge, domains of KIO{sub 3} are formed across the terraces. With prolonged exposure to ozone, KIO{sub 3} domains nucleate further growth until the surface is evenly covered with KIO{sub 3} particles that are 4-6 nm in height, at which point the surface is passivated and the reaction terminates

Guiding kinetic trajectories between jammed and unjammed states in 2D colloidal nanocrystal-polymer assemblies with zwitterionic ligands

Mesostructured matter composed of colloidal nanocrystals in solidified architectures abounds with broadly tunable catalytic, magnetic, optoelectronic, and energy storing properties. Less common are liquid-like assemblies of colloidal nanocrystals in a condensed phase, which may have different energy transduction behaviors owing to their dynamic character. Limiting investigations into dynamic colloidal nanocrystal architectures is the lack of schemes to control or redirect the tendency of the system to solidify. We show how to solidify and subsequently reconfigure colloidal nanocrystal assemblies dimensionally confined to a liquid-liquid interface. Our success in this regard hinged on the development of competitive chemistries anchoring or releasing the nanocrystals to or from the interface. With these chemistries, it was possible to control the kinetic trajectory between quasi–two-dimensional jammed (solid-like) and unjammed (liquid-like) states. In future schemes, it may be possible to leverage this control to direct the formation or destruction of explicit physical pathways for energy carriers to migrate in the system in response to an external field

Effects of Impurity Content on the Sintering Characteristics of Plasma-Sprayed Zirconia

Yttria-stabilized zirconia powders, containing different levels of SiO2 and Al2O3, have been plasma sprayed onto metallic substrates. The coatings were detached from their substrates and a dilatometer was used to monitor the dimensional changes they exhibited during prolonged heat treatments. It was found that specimens containing higher levels of silica and alumina exhibited higher rates of linear contraction, in both in-plane and through-thickness directions. The in-plane stiffness and the through-thickness thermal conductivity were also measured after different heat treatments and these were found to increase at a greater rate for specimens with higher impurity (silica and alumina) levels. Changes in the pore architecture during heat treatments were studied using Mercury Intrusion Porosimetry (MIP). Fine scale porosity (<_50 nm) was found to be sharply reduced even by relatively short heat treatments. This is correlated with improvements in inter-splat bonding and partial healing of intra-splat microcracks, which are responsible for the observed changes in stiffness and conductivity, as well as the dimensional changes