Maximized Hole Trapping in a Polystyrene Transistor Dielectric from a Highly Branched Iminobis(aminoarene) Side Chain.

We synthesized highly branched and electron-donating side chain subunits and attached them to polystyrene (PS) used as a dielectric layer in a pentacene field-effect transistor. The influence of these groups on dielectric function, charge retention, and threshold voltage shifts (Δ) depending on their positions in dielectric multilayers was determined. We compared the observations made on an -perphenylated iminobisaniline side chain with those from the same side chains modified with ZnO nanoparticles and with an adduct formed from tetracyanoethylene (TCNE).

Template-Stripped Ultra-Smooth Aluminum Films (0.2 nm RMS) for the Surface Forces Apparatus.

We present a method for the fabrication of ultra-smooth (0.2 nm RMS), aluminum substrates through template stripping (TS). The method relies on the use of mica as a template in combination with thermal evaporation of Al at high (>10 nm/s) rates under vacuum (≤1 × 10 Torr).

Looking at education through the microscope.

Advanced research microscopes in universities can be used to enhance the education of STEM students, as demonstrated by initiatives at Johns Hopkins University that give students the opportunity to get hands-on experience with sophisticated microscopes.

Effect of Roughness and Elasticity on Interactions between Charged Colloidal Spheres.

The effects of realistic roughness and elasticity on the interactions between charged silica spheres are studied as a function of surface potential, screening length, interfacial energy, and roughness. The repulsive force that must be overcome to bring charged spheres into contact is relatively insensitive to elasticity unless spheres are hundreds of times softer than silica. is also insensitive to roughness and interfacial energy.

The disastrous copper. Comparing extraction and chelation treatments to face the threat of copper-containing inks on cellulose.

Iron gall inks are known to be detrimental to the permanence of historic documents. Among the transition metals present, copper is the greatest threat and an open challenge due to the lack of Cu-specific treatments. In this study, we address the inhibition of copper by comparing extraction (a newly proposed glucose-based treatment) vs.

Human astrocytes develop physiological morphology and remain quiescent in a novel 3D matrix.

Astrocytes are the most abundant glial cells in the brain and are responsible for diverse functions, from modulating synapse function to regulating the blood-brain barrier. In vivo, these cells exhibit a star-shaped morphology with multiple radial processes that contact synapses and completely surround brain capillaries. In response to trauma or CNS disease, astrocytes become activated, a state associated with profound changes in gene expression, including upregulation of intermediate filament proteins, such as glial fibrillary acidic protein (GFAP).

Dynamics of a disturbed sessile drop measured by atomic force microscopy (AFM).

A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r ∼ 20-30 μm) is brought into contact with a small sessile water drop resting on a polytetrafluoroethylene (PTFE) surface. When the microsphere touches the liquid surface, the meniscus rises onto it because of capillary forces.

Stick slip contact mechanics between dissimilar materials: effect of charging and large friction.

Measurements of the contact radius as a function of applied force between a mica surface and a silica surface (mica/silica) in air are reported. The load/unload results show that the contact radius generally increases with applied force. Because of the presence of charging due to contact electrification, both a short-range van der Waals adhesion force and longer-range electrostatic adhesive interaction contribute to the measured force.

3D force and displacement sensor for SFA and AFM measurements.

A new device has been designed, and a prototype built and tested, that can simultaneously measure the displacements and/or the components of a force in three orthogonal directions. The "3D sensor" consists of four or eight strain gauges attached to the four arms of a single cross-shaped force-measuring cantilever spring. Finite element modeling (FEM) was performed to optimize the design configuration to give desired sensitivity of force, displacement, stiffness, and resonant frequency in each direction (x, y, and z) which were tested on a "mesoscale" device and found to agree with the predicted values to within 4-10%.

Adhesion and friction force coupling of gecko setal arrays: implications for structured adhesive surfaces.

The extraordinary climbing ability of geckos is partially attributed to the fine structure of their toe pads, which contain arrays consisting of thousands of micrometer-sized stalks (setae) that are in turn terminated by millions of fingerlike pads (spatulae) having nanoscale dimensions. Using a surface forces apparatus (SFA), we have investigated the dynamic sliding characteristics of setal arrays subjected to various loading, unloading, and shearing conditions at different angles. Setal arrays were glued onto silica substrates and, once installed into the SFA, brought toward a polymeric substrate surface and then sheared.

Transient filamentous network structure of a colloidal suspension excited by stepwise electric fields.

Jamming and force networks observed in electrorheological (ER) fluids bear many similarities to those observed in various granular and colloidal systems. We have measured the time evolution (transient stresses) of filamentous networks of colloidal particles in suspensions subjected to continuous tensile strain concomitant with the switching on and off of electric fields. The density of particle chains was found to increase exponentially with the applied tensile strain via a rapid formation of single chains followed by a slower coarsening (aggregation) of the chains.