报告时间:1月2日(周一)14:30
报告地点:科技创新大楼C501室
报告人:蔡伟照
Aromatic
hydrocarbons under pressure
Abstract: Pressure
being analogous to temperature, is an appropriate approach to modify bond distances
of materials and explore their exceptional physical properties. In this talk, I
will present our recent results on two aromatic hydrocarbons under compression.
First, I will show pressure-induced polymerization of benzene and its
isotopologue C6D6. We found both isotopologues demonstrate negligible effect in
the first-order phase transition and onset of chemical reaction. Raman spectra
of polymeric products recovered from different pressures show a pronounced
kinetic isotope effect: C6D6 polymerization reaction proceeds considerably
slower than C6H6, leading to substantially lower fractions of sp 3 bonding in
C6D6-polymers recovered from comparable pressures.
Then I will
show another herringbone-type hydrocarbon benz[a]anthracene (BaA). The ambient-pressure
phase of BaA was found to be stable up to ~15.0 GPa. And an exceptional
piezochromic color change was observed simultaneously. DFT calculations suggest
that the formation of crystalline polymeric phase can take place between 30-117
GPa. Optical absorption measurements reveal that the band gap of BaA decreases
at high pressure, from 2.4 eV at 0.5 GPa to 1.0 eV at 50.6 GPa. The DFT
calculations further suggest that the band gap of BaA in molecular phase could
reduce to ~0.1 eV at 117 GPa. Photoconductivity measurements show a continuous
increase of photocurrent in the molecular phase region, which is most likely
originated from the increase of carrier mobility under pressure.