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Research in Chemistry Division

Postdoctoral Publication Prize Awarded to Felicia Taw and Richard Schaller

Two Chemistry Division postdocs have been awarded the Postdoctoral Publication Prize in Experimental Sciences. This biennial prize is sponsored by Damon Giovanielli (former P Division Leader, now retired) and the Laboratory, and is awarded for the best article in experimental sciences in the past two years. The winning papers are selected by a panel of technical staff members, and the research presented always represents a seminal contribution to the field. Taw and Schaller were the only winners during this cycle.

According to Giovanielli, the prize is awarded to the best of the best at Los Alamos. He says of the winners, “We want you to know we’re watching you—and not just when you mess up. People like you are the future of the Lab.” Giovanielli made surprise visits to both researchers at their labs during the week of June 6th, 2005 to let them know about the award.

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Director’s Postdoctoral Fellow Felicia Taw was recognized for her paper “Early Transition Metal Perfluoroalkyl Complexes,” published in The Journal of the American Chemical Society in November 2003 [Taw, F. L.; Scott, B. L.; Kiplinger, J. L.; J. Am. Chem. Soc.; (Communication); 2003; 125(48); 14712-14713].  Taw is a Director’s Funded Postdoctoral Fellow who came to Los Alamos to work in November 2002. She currently works in Chemistry’s Actinide, Catalysis, and Separations Chemistry group.

The publication concerns the synthesis and characterization the first examples of early transition metal (groups 3, 4, and 5) perfluoroalkyl complexes. Specifically, Taw discovered that Ti-F fluoride bonds are reactive and that Cp2TiF2 readily reacts with Me3SiCF3 in the presence of CsF (as a catalyst) to give Cp2Ti(CF3)(F) (Cp = cyclopentadienyl, C5H5-).  Similarly, Cp2Ti(CF3)(F) reacts with Me3SiOTf to afford Cp2Ti(CF3)(OTf).  These remarkable complexes possess a Ti-CF3 linkage, the very existence of which was thought to be impossible for over 40 years.

Taw’s work is relevant to the mission of Los Alamos National Laboratory for a number of reasons.  First, these novel complexes can act as catalysts for the polymerization of fluorinated olefins, allowing for the preparation of previously inaccessible fluorinated materials. Fluorinated polymers are employed as binders for high explosives due to their high density and inertness.  Many of the fluorinated polymers currently used by the DOE complex are no longer being manufactured by industry.  Felicia’s discovery opens the door to address this critical need for the first time and it is anticipated that new fluorinated materials developed will possess properties that will be of interest to several sectors within the DOE and the DoD. 

Taw’s nomination was supported by letters of recommendation from five recognized experts in transition metal chemistry. These industry experts confirm that her work is already being considered a seminal contribution to transition metal coordination and organometallic chemistry in general. Professor Russell P. Hughes of Dartmouth College states, “This is a result that will be a textbook citation for many years to come, and, perhaps more importantly, one that has already caused a dramatic reshaping of thought and strategy by chemists in the fluorocarbon field.”  Professor William D. Jones of Rochester University and the Associate Editor for JACS echoes these sentiments and asserts, “I have never seen a development in early transition metal chemistry that matches the utility of this method.”  He also says Felicia’s manuscript “represents a crowning achievement in experimental chemistry.”

According to her mentor, Jackie Kiplinger, “Felicia was not only the intellectual driver of this research and dominant experimental contributor to this landmark study, but she also wrote the manuscript entirely on her own, requiring virtually no editing on my part!”

 

Reines Distinguished Postdoctoral Fellow Richard Schaller was recognized for his paper entitled “High Efficiency Carrier Multiplication in PbSe Nanocrystals: Implications for Solar Energy Conversion,” [R. D. Schaller and V. I. Klimov, Physical Review Letters, 2004, 92, 186601]. Schaller is currently a Reines Distinguished Postdoctoral Fellow in the Chemistry Division’s Physical Chemistry and Applied Spectroscopy group.


Damon Giovanielli (left) informed Richard Schaller (right) of the prize in person.

This Physical Review publication provides experimental proof of a physical phenomenon that can potentially double the electrical output of solar cells. The principle of operation of solar cells (absorption of a single photon by a semiconductor produces a single exciton) has remained unchanged for nearly 50 years despite the enormous and well-funded efforts directed at the problem. The situation has changed dramatically after the recent breakthrough publication by Schaller and Klimov, which demonstrated that nanosized semiconductor particles, known also as quantum dots, can produce multiple excitons in response to a single absorbed photon. Because of this carrier-multiplication effect, nanocrystals made of lead and selenide (PbSe nanocrystals) react to absorbed photons at the green-blue end of the spectrum by producing twice the electrons compared to conventional bulk semiconductors. This increase in the number of electrons can lead to greater electrical current output from solar cells. At a recent DOE workshop on Grand Challenges in Energy (Crystal City, March 2004), it was recognized that while solar photovoltaics are an important clean energy source, practical large-scale applications of solar cells will require new concepts for solar energy conversion such as this one.

This ground-breaking work has enormous implications for alternative energy research and could potentially take solar cell efficiency a “quantum” leap forward. Professor Arthur Nozik, who holds joint appointments at the University of Colorado, Boulder and the National Renewable Energy Lab called this publication an "important scientific advance" in an article in Science News and noted that his research group had been searching for this effect for six years. However, it was innovative thinking about experimental methods for detecting the process that allowed the LANL scientists to discover the effect first.

Victor Klimov, Schaller’s research adviser, says, “This award is a very well deserved recognition. Rich truly loves science. He is enthusiastic, full of ideas, and has this magic touch, which makes any experiment work. I am very proud of Rich and wish him continued success in his research endeavors.” As a result of this work, Schaller was invited to give a presentation at the March 2005 American Physical Society meeting.

The quantum-dot team of which Schaller is a member is currently filing a patent on the research, as the potential value of this discovery could be very significant. Furthermore, this work has resulted in the funding of an LDRD ER grant for which Schaller is the PI, an unusual honor for a postdoctoral researcher. The subject is also the topic of a joint DARPA proposal among the LANL team, Honeywell International, and Professor Michael Graetzel’s at Polytechnique Federale de Lausanne.

The studies of carrier multiplication recognized by this award are a part of the strong Chemistry Division program in quantum dots that focuses on both fundamental and technological aspects of nanoscale semiconductors. This program has led to a number of important innovations over the past several years including the development of fundamental principles of nanocrystal lasing, demonstration of a new approach for activating nanocrystals via noncontact energy transfer, and, most recently, the development of multicolor light emitting diodes.  Additional information of Los Alamos quantum dot research is available at http://quantumdot.lanl.gov/

6/05


 
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