Many challenging problems in the modern science and technology are related to preparation, properties, and utilization of novel functional materials. The polymer chemistry and the chemical microelectronics programs represent parts of the multidisciplinary effort in this field. The many-pronged approach includes: synthesis and molecular characterization of well-defined block and graft copolymers; preparation of new engineering thermoplastics and liquid crystalline materials; synthesis, modification and processing of polymers in super-critical carbon dioxide; chemical design of hybrid polymers for catalysis and photoredox activity, polymers for microelectronics applications including 193 nm and 157 nm photoresists and low-k dielectrics, and defined microstructures.
Chemical microelectronics is focused on preparation of organic and inorganic electronic materials; microscopic patterning of thin films using novel techniques, plasma, ion beam, laser beam, etc.; kinetics of etching and film formation; characterization of mechanical, electronic, and optical properties; spatially resolved chemical analysis of surfaces, interfaces, and thin films and microstructures. A broad variety of expertise includes visualization and probing of submicrometer surface structures by scanning probe microscopy, characterization of polymer dynamics by NMR techniques and light scattering, measurement of molecular conductivity, and analytical as well as computational and numerical methods in polymers.
Semiconductor nanowires, NWs, often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indices of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small volumes of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely determine the economic viability of NW-based solar cells. Published in Nano Letters, researchers in the Cahoon Group, demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielectric shells
Scattering and absorption measurements on Si NWs coated with shells of SiNx or SiOx exhibit a broadband enhancement of light absorption by ≈50–200% and light scattering by ≈200–1000%. The increased light–matter interaction leads to a ≈80% increase in short-circuit current density in Si photovoltaic devices under 1 sun illumination. Optical simulations reproduce the experimental results and indicate the dielectric–shell effect to be a general phenomenon for groups IV, II–VI, and III–V semiconductor NWs in both lateral and vertical orientations, providing a simple route to approximately double the efficiency of NW-based solar cells.
Additive manufacturing processes such as 3D printing use time-consuming, stepwise layer-by-layer approaches to object fabrication. As published in Science, and becoming that issue's cover story, researchers in the DeSimone Group demonstrate the continuous generation of monolithic polymeric parts up to tens of centimeters in size with feature resolution below 100 micrometers.
Continuous liquid interface production is achieved with an oxygen-permeable window below the ultraviolet image projection plane, which creates a "dead zone," or persistent liquid interface, where photopolymerization is inhibited between the window and the polymerizing part. By delineating critical control parameters the researchers show that complex solid parts can be drawn out of the resin at rates of hundreds of millimeters per hour. These print speeds allow parts to be produced in minutes instead of hours, and have become "game changing" properties of this technology.
Nanocapillarity-Mediated Magnetic Assembly of Nanoparticles into Ultraflexible Filaments and Reconfigurable Networks. Bhuvnesh Bharti, Anne-Laure Fameau, Michael Rubinstein & Orlin D. Velev. Nature Materials (2015) doi:10.1038/nmat4364, published online 03 August 2015.
Elastin-like Polypeptide Diblock Copolymers Self-Assemble into Weak Micelles. Wafa Hassouneh, Ekaterina B. Zhulina, Ashutosh Chilkoti, and Michael Rubinstein. Macromolecules, 2015, 48 (12), pp 4183–4195.
Hopping Diffusion of Nanoparticles in Polymer Matrices. Li-Heng Cai Sergey Panyukov, and Michael Rubinstein. Macromolecules, 2015, 48 (3), pp 847–862.
Doubling Absorption in Nanowire Solar Cells with Dielectric Shell Optical Antennas. Kim, Sun-Kyung; Zhang, Xing; Hill, David J.; Song, Kyung-Deok; Park, Jin-Sung; Park, Hong-Gyu; Cahoon, James F.. NANO LETTERS, 15 (1):753-758; 10.1021/nl504462e JAN 2015.
Continuous Liquid Interface Production of 3D Objects. John R. Tumbleston, David Shirvanyants, Nikita Ermoshkin, Rima Janusziewicz, Ashley R. Johnson, David Kelly, Kai Chen, Robert Pinschmidt, Jason P. Rolland, Alexander Ermoshkin, Edward T. Samulski, Joseph M. DeSimone. Science 20 March 2015, Vol. 347 no. 6228 pp. 1349-1352.
The Role of Temperature in Forming Sol–Gel Biocomposites Containing Polydopamine. Jason Christopher Dyke, Huamin Hu, Dong Joon Lee, Ching-Chang Ko, and Wei You. J. Mater. Chem. B, 2014,2, 7704-7711.
Lubrication by Polyelectrolyte Brushes. Ekaterina B. Zhulina and Michael Rubinstein. Macromolecules, 2014, 47 (16), pp 5825–5838.
Shapeshifting: Reversible Shape Memory in Semicrystalline Elastomers. Jing Zhou, Sara A. Turner, Sarah M. Brosnan, Qiaoxi Li, Jan-Michael Y. Carrillo, Dmytro Nykypanchuk, Oleg Gang, Valerie S. Ashby, Andrey V. Dobrynin, and Sergei S. Sheiko. Nature Methods 11, 959–965 (2014).
Waveguide Scattering Microscopy for Dark-Field Imaging and Spectroscopy of Photonic Nanostructures. David J. Hill , Christopher W. Pinion , Joseph D. Christesen , and James F. Cahoon. ACS Photonics, 2014, 1 (8), pp 725–731.
Switchable Micropatterned Surface Topographies Mediated by Reversible Shape Memory. Sara A. Turner, Jing Zhou, Sergei S. Sheiko, and Valerie Sheares Ashby. ACS Appl. Mater. Interfaces, 2014, 6 (11), pp 8017–8021.