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Patterning of nanowires in a controllable, tunable manner is important for the fabrication of functional nanodevices. MRSEC researchers have used standing surface acoustic waves (SSAW) to construct large-scale nanowire arrays with well-controlled patterning geometry and spacing within 5 seconds. By controlling the distribution of a SSAW field, metallic nanowires can be assembled into different patterns.
Following the discovery (ACS Nano 2012, 6, 6122) of bio-compatible, acoustically powered nanorod motors, MRSEC researchers have collaborated with scientists at ESPCI (Paris Tech) and NIST to study the interactions of the motors with live cells. Metallic rods that incorporate a thin nickel stripe can be deliiberately steered towards cells in vitro by using the weak external field of a Nd-Fe-B permanent magnet. Preliminary experiments involving live HeLa cells incubated with gold nanorods show them being taken up by the cells.
A Y-shaped microfluidic device generates a gradient in the concentration of “substrate,” the fuel for an enzyme. Both catalase and urease enzyme molecules move towards areas of higher substrate concentration, the first demonstration of chemotaxis by enzyme molecules. By using glucose oxidase and glucose to generate a hydrogen peroxide gradient, we also induce the migration of catalase towards glucose oxidase – a more complex sequence of chemical triggers.
Silver phosphate micromotors exhibit reversible transition between two collective behaviors: repulsive dispersion-like “exclusion” and attractive clustering-like “schooling” by the addition and removal of NH3. Hierarchical particle clustering is observed when other inert particles are also present. Upon the addition of NH3, large Ag3PO4 microparticles function as pumps, pushing away inert particles from their vicinity. We also find that the transition from dispersion to clustering can be halted with UV light.
Piezoelectric materials convert electrical to mechanical energy. They are typically lead-based solid-solutions that exhibit a morphotropic phase boundary, an intermediate compositional region separating two distinct phases, where a new bridging phase with enhanced properties arises. We show that even simple perovskite ferroelectrics such as BaTiO3 and KNbO3 exhibit analogous “thermotropic” phase boundaries in wide temperature regions around thermal phase transitions.
The Franklin Institute (a science museum in Philadelphia) and the MRSEC have been engaged in a longtime partnership which most recently resulted in a 5th museum show kit called Pocket Tech. At a training meeting in October 2013, this set of hands-on, interactive, visual demonstrations was awarded and distributed to representatives of 16 science museums nationwide from small, medium, and large institutions in a variety of geographical and socio-economic areas. During 2014, this kit is expected to be seen by more than 250,000 visitors.
The Penn State MRSEC has recognized that, in order to further increase the diversity of our own Center participation, we need to target institutional-level change by addressing pipeline issues of recruiting, support and retention. While continuing
the historically most effective diversity-focused efforts that have provided consistent Center representation of female and URM participants above departmental levels, three brand new diversity initiatives were fully implemented in the past year:
John V. Badding and co-workers demonstrate on p. 1461 the ability to fabricate silicon p-i-n junctions within high aspect ratio optical fibers, and which exhibit photovoltaic response. These structures are flexible, even when removed from their silica glass templates, despite their crystalline nature. Junctions of up to one meter length have been fabricated, but also a Si wire with a length of over 10 meters has been made. This Si wire can be wound onto a spool and even woven into a fabric.
A thin aluminum wire is contacted by 4 wider electrodes, as shown at left. The larger upper plot shows the resistance of this wire as a function of temperature at zero and non-zero magnetic field, following the standard practice of averaging over many repeated measurements. The paradoxical return of the resistive state at low temperature is a consequence of the antiproximity effect, where the superconductivity of the wire is suppressed when the electrodes become superconducting. The lower plots show the resistance of the wire obtained by a single measurement.
A crack in a high mineral-content material, like bone or a synthetic mineral/polymeric composite, generates ion gradients which can be utilized for active targeting and repair. Employing is technique, an active self-propelled particle-based detection, delivery, and repair strategy for cracks is designed by utilizing the damaged matrix itself as both the trigger and the fuel. Our approach augments current research methods focused on promoting bone healing by delivery of a therapeutic agent to the bone via passive diffusion.