10-04 :: April 2010
News in Brief
will tend to enclose the graphene sheet to which they are attached.
The tails don‘t merely act as a cage, however. They also serve as a handle for the organic solvent so that the entire structure can be dissolved. Li and his colleagues were able to dissolve 30 mg of the species per 30 mL of solvent.
“In this paper, we found a new way to make gra-
phene soluble,” Li said. “This is just as important as the relatively large size of the graphene itself.”
To test the effectiveness of their graphene light ac- ceptor, the scientists constructed rudimentary solar cells using titanium dioxide as an electron acceptor. The scientists were able to achieve a 200-microam-
pere-per-square-cm current density and an open- circuit voltage of 0.48 volts. The graphene sheets absorbed a significant amount of light in the visible to near-infrared range (200 to 900nm or so) with peak absorption occurring at 591nm.
The scientists are in the process of redesigning the graphene sheets with sticky ends that bind to titani- um dioxide, which will improve the efficiency of the solar cells.
Xin Yan, Xiao Cui, Binsong Li and Liang-shi Li: Large, Solu- tion-Processable Graphene Quantum Dots as Light Absor- bers for Photovoltaics, In: Nano Letters AOP, April 8, 2010, DOI:10.1021/nl101060h: http://dx.doi.org/10.1021/nl101060h
New Theory //
New Principle In Material Science
rown University scientist Huajian Gao and researchers from the University of Alabama and
China report a new mechanism that governs the peak strength of nanostructured metals. By perfor-
ming 3-D atomic simulations of divided grains of na- nostructured metals, Gao and his team observed that dislocations organize themselves in highly ordered, necklace-like patterns throughout the material. The nucleation of this dislocation pattern is what deter- mines the peak strength of materials, the researchers report. The finding could open the door to producing stronger, more ductile metals, said Gao, professor of
engineering at Brown. “This is a new theory governing strength in materials science,” he added. “Its signifi- cance is that it reveals a new mechanism of material strength that is unique for nanostructured materials.”
Divide a grain of metal using a specialized technique, and the pieces may reveal boundaries within the grain that scientists refer to as twin boundaries. These are generally flat, crystal surfaces that mirror the crystal orientations across them. The Chinese authors created nanotwinned boundaries in copper and were analyzing the space between the boundaries when