The 37th annual Nelson W. Taylor Lecture included talks by four noted Penn State faculty followed by a lecture from this year’s Taylor honoree, Tobin J. Marks of Northwestern University.  Marks, a chemist and materials scientist, is winner of the National Medal of Science.  This year’s talks were organized around the interactions of light with matter. A brief summary of each of the speakers’ remarks follows.

2009 Nelson W. Taylor Lecture in Materials

Tobin Marks, Vladimer N. Ipatieff Professor of Chemistry and Professor of Materials Science and Engineering, Northwestern University 

Akhlesh Lakhtakia is one of the modern developers of a technique called sculptured thin films, which he describes as assemblies of parallel curved nanowires.  By changing the angle of deposition, the optical quality of the light reflecting from the nanowire thin film can be controlled.

In the 1990s, Lakhtakia recalled, he was taken by the light transmitting qualities of a material called ulexite, which has a fibrous structure.  He asked his Penn State colleague, Russell Messier, if such fibrous structures could be made using polymer thin films, and was told that indeed they could be. Lakhtakia decided to try laying down the thin film at an oblique angle, and to figure out the mathematical basis to the properties that were emerging, including the dielectric, magnetic, and magnetoelectric properties.  He found that the chirality, or left- or right-handedness of the film, affects the light transmisssion.  If the handedness of the light and the film are the same, it can be very bright.  If they are opposite, the light is low.  He also showed it was possible to shift the color of the film after deposition by annealing the film.
 
Sculptured thin films have a large range of possible uses, including light filters, fluid concentration sensors, biosensors, electrical switching, lab-on-a-chip, bioreplication, and bioscaffolding, as a substrate for cell growth.  A recent, interesting use of sculptured thin films is in bioreplication, the exact reproduction of biological specimens, such as the multifaceted eyes of fruit flies, for possible light harvesting purposes.

What gives rise to the spectacular colors in nature, for instance the intense, iridescent blue of certain South American butterflies?  It’s not, as some might think, a kind of natural pigmentation.  Instead, micrometer and nanometer structures in the butterfly’s wings scatter certain wavelengths of light to form a continuous color from all angles as the butterfly moves.   Over millions of years, nature has evolved structural color, Theresa Mayer told the Taylor Lecture audience.

Nature inspired optical device design is one of the thrusts at Penn State’s Center for Nanoscale Science, a National Science Foundation-funded Materials Research Science and Engineering Center (MRSEC).  With colleague Doug Werner, a professor of electrical engineering, Mayer attempts to build nanoscale structures based on Werner’s nature-inspired genetic algorithms.

Through a process that mimics evolution, the fittest designs are retained and the rest discarded.  Over the course of many generations, the designs get closer to nature’s original design. Werner’s genetic algorithms include fabrication design rules that exclude structures that can’t possibly be built in the lab. With the design optimized, Werner turns it over to Mayer, who uses physical vapor deposition techniques to create 3D structures down to sub-50-nanometer size. Then, using etching tools, such as the focused ion beam, she etches the required features into the material.

Mayer and Werner would like to go beyond nature to make materials with controllable electromagnetic responses of any type.  Such manmade materials, called metamaterials, can be used to create near zero index materials (ZIM), for focusing light.  ZIM waves exit a material at right angles from the direction of entry.  So far, they have designed and manufactured a ZIM metamaterial for manipulating infrared light and they are now working on improving absorption loss and intrinsic impedance, using the design strategies mentioned above.

They are exploring building multilayer structures made of metals, dielectrics, and air using their feed-forward fabrication and design methods, which, she says, should allow them to access fundamentally new physical regimes for technologies.

Gopalan uses nonlinear optics to investigate materials’ structures and phases, from multiferroic oxides to biological materials such as bone cells.  Nonlinear optics is a powerful new technique for probing materials using optical signals. Gopalan compares using light as a probe to plucking the strings of a musical instrument.  In linear optics, a string is plucked lightly and a single pure tone emerges, which is a vibration equivalent to the entering light wave.  In nonlinear optics, the string, which is actually the cloud of electrons surrounding the nucleus of an atom, is plucked with more force.  When this happens, part of the electron cloud oscillates at a frequency equivalent to the light striking the cloud, while another part of the cloud vibrates at twice the frequency, a third part vibrates at three times, some at four times, etc.  It is the equivalent of a musical chord.  These vibrations, called the second, third, and fourth harmonics, have information about the local structure of a material.

Using symmetry arguments, it is possible to tell whether or not an atom is surrounded by exactly similar atoms, because the higher even-number harmonics only result if there is a break in the inversion symmetry, that is, if the atom is sitting in an environment where up is not the same as down or left is not the same as right.  When the symmetry of the atoms is exact, the even harmonics disappear.

Materials that have a polar nature, positive and negative poles, produce the higher harmonics because they are not symmetrical.  You can also watch polar materials go through a phase transformation as the temperature increases, because at a certain temperature the polar nature disappears and so do the even harmonics. 

Gopalan is working with biomaterials researchers to look at bone cells using nonlinear optics. Biological materials are filled with helical structures – DNA, RNA, proteins, and collagen for example.  Helixes are nonsymmetrical, so they can be investigated using harmonics, which makes nonlinear optics a powerful tool for imaging biological molecules, Gopalan concluded. 

TOBIN J. MARKS
Vladimir N. Ipatieff Professor of Chemistry and Professor of Materials Science and Engineering at
Northwestern University.

Interface Engineering of Tailored Interfaces for
Organic Opto-Electronics and Photovoltaics

11:05a.m.

Tobin J. Marks is the Vladimir N. Ipatieff Professor of Chemistry and Professor of Materials Science and Engineering at Northwestern University. He received his B.S. from the University of Maryland (1966) and Ph.D. from MIT (1971), and came to Northwestern immediately thereafter. Of his 75 named lectureships and awards, he has received American Chemical Society Awards in Polymeric Materials, 1983; Organometallic Chemistry, 1989; Inorganic Chemistry, 1994; the Chemistry of Materials, 2001; and for Distinguished Service in the Advancement of Inorganic Chemistry, 2008. He was awarded the 2000 F. Albert Cotton Medal, Texas A&M American Chemical Society Section; 2001 Willard Gibbs Medal, Chicago American Chemical Society Section; 2001 North American Catalysis Society Burwell Award; 2001 Linus Pauling Medal, Pacific Northwest American Chemical Society Sections; 2002 American Institute of Chemists Gold Medal; 2003 German Chemical Society Karl Ziegler Prize; 2003 Ohio State University Evans Medal; 2004 Royal Society of Chemistry Frankland Medal, 2005 Bailar Medal, Champaign-Urbana Section of the American Chemical Society, Fellow, American Academy of Arts and Sciences, 1993. He is a Member, U. S. National Academy of Sciences (1993); Member, German National Academy of Sciences (2005); Fellow, Royal Society of Chemistry (2005); Fellow Chemical Research Society of India (2008); Fellow, Materials Research Society (2009); 2009 Herman Pines Award, Chicago Catalysis Society; 2009 Nelson W. Taylor Award in Materials Research, Penn. State U.; 2009 von Hippel Medal, Materials Research Society; 2010 William H. Nichols Medal, ACS New York Section. In 2006, he was awarded the National Medal of Science, the highest scientific honor bestowed by the United States Government. Marks is on the editorial boards of 9 major journals; consultant or advisor for 6 major corporations and start-ups, and has published 935 research articles and holds 93 U.S. patents.