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March 2016

EP4: Emerging Silicon Science and Technology

Daniel Chung, University of New South Wales

Photoluminescence Imaging for Quality Control in Silicon Solar Cell Manufacturing

Written by Tine Naerland

Solar cells made of multi-crystalline silicon (mc-Si) has recently proved to have more to offer in terms of efficiency consecutively lowering the cost of solar power. As the cell design becomes better and better, the quality of the mc-Si becomes more and more critical putting pressure on impurity control in the making of silicon for solar cells. In this talk by Daniel Chung of the University of New South Wales, a solar cell in-line tool based on photoluminescence (PL) imaging is shown to be capable of fast and reliable quantification of a wide range of electronic material and device parameters. The information is obtained on bricks without any specific sample preparation, which is particularly relevant, since the measurable information about bulk material quality is largely lost during wafer slicing.

SM6: Transient and Biologically-Inspired Electronics

Mary Donahue, École Nationale Supérieure des Mines de Saint-Étienne

Implantable organic bioelectroinics

Written by Mary Nora Dickson

Brain functions can be monitored and detected using electrical signals. Implantable electrode arrays have been successfully used as therapies for Parkinson’s disease and even blindness and deafness. However, these devices are rigid and can have difficulties integrating into the tissue, inducing scarring.  Researcher Mary Donahue presented on her work on novel flexible implantable electronics with George Malliaras at École Nationale Supérieure des Mines de Saint-Étienne in France.

They utilize thin (4 μm) parylene substrates and PDOT:PSS electrodes. Because of the thin and flexible nature of the substrate, the device is much less invasive than silicon-based devices, and leads to less scarring. The PDOT:PSS was found to be very effective in interfacing with the neurons. The researchers used this architecture to build a device that could locally stimulate the neurons.

Recent work focuses on seizure detection and treatment. Donahue’s team built a device for real-time monitoring of lactate concentration, a predictor of seizure. The group is also designing organic electrodes as ion pumps to locally deliver anti-seizure drugs. This could one day prevent epilepsy patients from having to take high doses of medication or facing the alternative of surgical removal of portions of the brain.

SM4: Engineering Biointerfaces with Nanomaterials

Ichiro Yamashita, Osaka University

Fabrication of device key nanostructures by protein supramolecules

Written by Mary Nora Dickson

Nature has developed exquisitely precise processes for the assembly of biomolecules into three-dimensional nanoarchitectures. Researcher Ichiro Yamashita of Osaka University has developed ways to combine natural bottom-up assemblies with traditional top-down fabrication for the manufacture of nanoscale functional materials, in a process he calls the “Bio-Nano-Process.”

For example, Yamashita utilized apoferritin protein-cages, found in nearly all cells, as a vessel for controlled cadmium sulfide infiltration and crystal growth. In this way, he was able to fabricate monodisperse 5 nm CdS nanocrystals. He utilized these nanocrystals for thermoelectric generation (the production of electric power from heat) by binding them to carbon nanotubes to form an electrically conductive but thermal nonconductive material. Another instance is Yamashita’s protein-templated growth of carbon nanotube forests for gas-sensing applications. There are myriad exciting applications for the Bio-Nano-Process, including solar energy generators, medical diagnostics, and sensors.

SM4: Engineering Biointerfaces with Nanomaterials

Neelkanth M. Bardhan, Massachusetts Institute of Technology

Enhanced graphene oxide nanosubstrates for rapid, highly efficient cell capture

Written by Mary Nora Dickson                                                                     

Graphene is a promising material for inexpensive and precise nanosensors. One scalable, low-cost way to manufacture usable graphene substrates is to exfoliate graphene by chemically oxidizing it to graphene oxide. However, the oxygen content cannot be easily controlled with this method. But now, Neelkanth M. Bardhan, working with Angela Belcher at the Massachusetts Institute of Technology, has developed a simple, scalable way to reduce graphene oxide—by thermal annealing—which yields much better surface properties.

The group annealed the films at 80°C for between one and nine days. This process actually concentrates the oxygen groups into islands on the surface. Then the researchers functionalize the surface with a nanobody that is selective for the capture of a particular type of cell. This surface is selective enough to capture target cells from whole blood. The surfaces perform about 200% better than graphene oxide surfaces not subjected to the annealing treatment. A major implication is that these cell capture devices are easy and cheap enough to build in the developing world.

MD9: Magnetic Materials—From Fundamentals to Applications

Axel Hoffman, Argonne National Laboratory

Manipulating room-temperature magnetic skyrmions

Written by Michael Lee

Magnetic skyrmions, a spin state with a net topological charge, were first discovered in 2009 by researchers studying the intricate MnSi magnetic phase diagram. The new form of charge was immediately promising as an alternative for electron motion in information technologies, but only emerged in magnetic materials with broken inversion symmetry. This is a phenomenon that occurs at the heterointerfaces of multilayer films, thus opening the door for designing materials capable of forming skyrmions. Axel Hoffman and collaborators have demonstrated not only the ability to generate skyrmions at room temperature by using a combination of applied field and electric current to push magnetic stripe domains through a geometric constriction, but fine control over their motion within wires. Already the finer details of motion induced by spin-Hall and edge effects have been elucidated, suggesting the rapid development of functional devices based on magnetic skyrmions.

SM4: Engineering Biointerfaces with Nanomaterials

Mary Nora Dickson, University of California, Irvine

A scalable biomimetic antibacterial polymer surface

Written by Devesh Mistry

Biofilms form on surfaces when bacteria grow and emit a slime. This slime makes it difficult to mechanically remove the bacteria and difficult to kill the bacteria using antibacterials. Nano-silver is one technology currently applied to surfaces which kills bacteria; however, as Mary Nora Dickson of the University of California, Irvine, highlighted, bacteria can develop a resistance to the nano-silver.

The wings of cicada and dragonflies are known to be antibacterial. This is achieved by a nanostructure of sharp pillars which cause bacterial cells to rupture. By nano imprinting a poly(methyl methacrylate) substrate with an array of features typically 20-200 nm in size, Dickson has been able to replicate such structures but on an industrial scale. Tests show that a range of different bacterial cells cannot survive on this surface as they appear to conform to the structure leading to an increase in internal pressure followed by cell rupture. SEM images show how the cells of e. coli appear deflated and have adopted the nanostructure.

One application Dickson is currently pursuing is using the structure on medical devices, specifically on artificial corneas. In this application, the structures have the additional benefit of antireflective properties due to a modification of the surface refractive index.

EP12: Materials Frontiers in Semiconductor Advanced Packaging

Beng S. Ong, Hong Kong Baptist University

Progress in polymer semiconductor materials and processes for printed transistors

Written by Tine Naerland

Beng S. Ong from Hong Kong Baptist University presented the very significant advances that have been made in polymer semiconductor materials for printed transistors. Polymer transistors can potentially revolutionize the application span of user-electronics as organic transistors are flexible, wearable and cost effective in addition to being capable of being integrated in textiles and withstanding difficult weather conditions. This quantum leap in polymer transistor performance has been propelled by both creative semiconductor design and process innovation but there still remain significant technical challenges to be resolved for translating printed polymer transistors from laboratory to marketplace.

Gecko Feet

The Gecko's feet stick to surfaces through simple van der waals forces.  The physics is simple, but the execution is quite difficult; the gecko accomplishes this feat using hair-like structures on their feet that split into small and flexible branches that are only 200nm thick.  John Main, of the defense sciences office at DARPA, points out  our current technology cannot easily replicate these structures; however, we can still use our technology to replicate the result.  This has been done, in the case of gecko feet, by micromachining a vast array of shapes into materials to maximize surface area contact and van der waals forces.  I mention this because it made me think of the vast array of miraculous technologies that nature achieves every day; how plants can convert sunlight to chemical energy and consume carbon dioxide in tandem, how starfish regenerate limbs, or how an octopus changes color to blend in with its environment; the list goes on.  We need not necessarily reproduce the structure that these lifeforms use, but we can still replicate the results in our own way.  

Thermal Photovoltaic Cells

Eli Yablonovitch blew me away today by pitching the thermal photovoltaic engine as a potential high-efficiency method for converting heat to electricity, a technology that could be used in cars, power-plants, spacecraft, and a variety of other applications.  The talk was entitled "Is there anything it cannot do: Can Opto-Electronics Provide the Motive Power for Future Vehicles?" (EE3.8.01/NT1.8.01).  The concept behind a thermophotovoltaic is that a photovoltaic can be used to convert the emitted photons from a sufficiently hot blackbody emitter to electricity.  There are many questions, but that is exactly the point; this concept has been pitched to us as a potential heat-to-electricity converter that could operate at high efficiency (perhaps 50%) and that can be used in a form factor smaller than a textbook.  Future science and efforts will reveal if this technology can be developed the way we hope.  Dr. Yablonovitch is renowned as a forward-thinking physicist and engineer, and it is exciting to think that this technology could have potential revolutionary impact in the future.


Symposium EP3: Crosslinkable materials for increased thermomechanical reliability of perovskite solar cells

Dr. Brian Watson, Stanford University

Following up from the interesting presentation about the "weakest" thermomechanical properties of perovskite solar cells on Monday, Dr. Brian Watson from Stanford University gave the talk about the crosslinkable materials to improve this property of perovskite solar cells. He also gave a great chart showing that as the the efficiency of perovskite solar cells go up, their fracture energies actually go down to less than 0.1 J/m2. In fact the electron and hole transport layers are even weaker than the perovskite layer in the real device. By using crosslinkable materials for electron and hole transport layers in perovskite solar cell, the fracture energy is improved and the efficiency of the device is also improved.