Basic Science

Single-Molecule Raman Imaging Reaches Record Sub-nm Resolution

A research team led by Prof. Dong Zhenchao and Prof. Hou Jianguo at the University of Science and Technology of China has achieved for the first time in the world single-molecule Raman spectroscopic mapping with sub-nanometer resolution, driving the spatial resolution with chemical recognition down to unprecedented 0.5 nm. This work was published in Nature on June 6 (Nature 2013, 498, 82). The Ph.D. students, Zhang Rui and Zhang Yao, are the co-first-authors of this paper. Visualizing individual molecules with chemical recognition is a long standing target for scientific community around the world, particularly in catalysis, bio-science, and molecular nanotechnology. By developing a combined system of low-temperature ultra high-vacuum scanning tunneling microscopy with ultra-sensitive optical detection, the team has achieved Raman spectroscopic imaging of a single porphyrin molecule with a record spatial resolution of about 0.5 nm, resolving even the inner structure and its configuration on the surface. The results of this work, says Dong Zhenchao, will open the doors to the chemical identification of molecules by optical spectroscopy that goes intramolecular and subnanometer. This ability is particularly valuable for exploring microscopic mechanisms of surface catalytic reactions, constituent elements of molecular nanodevices, and bio-molecular imaging such as DNA sequencing. The findings also open up new channels for probing nonlinear optics and photochemistry at the single-molecule scale.

Crucial Evidence of Mass Transfer in Binary Systems

Recently, Prof. Qian Shengbang’s group from Yunnan Observatories, CAS found a special close binary named V753 Monocerotis undergoing the mass transfer process, which provides the crucial evidence of mass transfer in binary systems. The results were published in The Astrophysical Journal Supplement Series (2013, ApJS 207, 22; Impact Factor =16.2). V753 Monocerotis has been monitored from 2006 with the 1.0-meter and 60-centimeter telescopes at Yunnan Observatories by Qian Shengbang’s group. Eighteen times of minimum light were derived based on those observations. Complete multi-color CCD light curves were obtained in 2011 January by using the 60-cm telescope. According to the light curve analysis, V753 Mon is a semi-detached binary where the hotter, slightly less massive component is filling the critical Roche lobe. The masses of the two components are close to each other (M1=1.597M⊙ and M2=1.674M⊙, M⊙ is the solar mass). The increase of the orbital period, the mass ratio very close to unity, and the semi-detached configuration with a less-massive lobe-filling component all suggest that V753 Mon is on a key evolutionary stage just after the evolutionary state with the shortest period during mass transfer. So far, V753 Mon is the only system found in this important evolutionary stage, which will shed light on the formation of massive contact binaries and the evolution of binary stars. The cyclic oscillation in the O-C diagram indicates that V753 Mon may be a triple system containing an unseen third body with the lowest mass of 0.16 M⊙.

New Evidence Supports Magnetic Field Reconnection as Drive of Solar Flares

On July 14, Dr. Su Yang and an international team (from University of Graz, CAS Purple Mountain Observatory, NASA-GSFC, Catholic University of America) published their work online in Nature Physics. Using the data from two NASA satellites, Solar Dynamics Observatory (SDO) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), they showed the most complete picture yet obtained of magnetic reconnection in a solar flare. Su searched the huge SDO-RHESSI database and found direct images of reconnection process in this C-class flare occurred on August 17, 2011. Although the magnetic field lines are invisible, they force the charged particles in plasma to move only along the field lines. The corona loops seen from telescopes outline the structures of magnetic field. By looking through a series of EUV images, Su and his team found two groups of loops approaching an X-shaped structure in between. They reconnected there and disappeared from low-temperature passbands. Newly formed hot loops (at temperature of 10 MK) flowed out from the reconnection region. The RHESSI X-ray data provided additional support for the reconnection process. The EUV and X-ray data also revealed some new features of magnetic reconnection.