Zhang Research Group

Molecular Machine

The significance of miniaturizing machines found in the macroscopic world and developing functional nanomachines is evident by the 2016 Chemistry Nobel Prize. We collaborate with chemists in artificial molecular machines design and synthesis. In contrast of investigating the ensemble behavior of molecular machines in solution phase, SPM is utilized to operate individual molecular machines in the solid platform at single molecule level, and motions of nanomachines are systematically controlled. Nanomachines under investigation include but not limited to single molecule motor, unidirectional propellers, rotors network, and molecular transport devices on surfaces.

Nature Communications, 2019, 10, 3742

Mechanical Laws at Nanoscale

Historically, it is believed that macroscopic mechanical laws do not generally apply in nanoscale contacts. In our research group, by combining qPlus atomic force microscope (Q+AFM) and scanning tunnelling microscope (STM), we quantify forces involved in molecular motions at piconewton level and investigate mechanical rules governing molecules in motion on surfaces. Our research reveals there is a continuum at macroscale and nanoscale regarding laws of motion to some extent, but also indicates vast distinctions. We work on understanding fundamental laws of motion at nanoscale more comprehensively. Such precise measurement at single molecule level cannot be achieved without combining AFM with STM. AFM of high Q-factor plays the role of sensing the subtle tip-molecule/materials interactions, and the STM technique allows precise manipulation of molecule at angstrom scale.

Material Science

Various 2D materials and molecular systems are also fabricated in-situ and characterized by local spectroscopy of STM/Q+AFM, in seek of novel electrical, magnetic, and mechanical properties. The capability of local chemistry alteration allows a direct engineer on materials property at atomic scale. In addition, by combining the synchrotron radiation with traditional STM, we study magnetization and charge transfer phenomena of materials, molecular complexes, and buried interfaces. Magnetic contrast provided by synchrotron x-rays and high spatial resolution of STM offers localized x-ray circular dichroism (STM-XMCD).

Physical Chemistry

We construct supramolecules with diameters on the order of 20 nm via intra- and inter-molecular coordination-driven self-assembly. Characterization at sub-molecular resolution by STM and scanning tunneling spectroscopy enables the unambiguous atomic-scale determination of individual isomers. Statistics of isomers distribution are used to evaluate kinetic and thermodynamic control involved in self-assembly process.

Exploring the structure–property relationship of polymers remains challenging due to the variability and low atomic resolution of the amorphous single polymer chain. We develop a mark-up strategy to direct visualize single polymer chain and enhance the characterization of polymers at the single-molecule level.