Scientists from the Institute of Physics of the Czech Academy of Sciences (CAS) together with colleagues from Osaka University in Japan presented in the journal Nature Communications [1] a new method that significantly advances the current possibility for atomic force microscopes to image chemical structures of individual molecules. Recent developments in scanning microscopy enable us to resolve the chemical structure of individual molecules deposited on surfaces. The sub-molecular resolution of individual molecules opens up entirely new possibilities in the study of physical and chemical properties of molecular nanostructures. However, it was possible to carry out these measurements only at very low temperatures close to absolute zero with specially modified microscope tips.
The modification consists in targeted location of just a single molecule (e.g. carbon
monoxide) or a noble gas atom on the apex of the metal tip. The main obstacle to achieving
sub-molecular contrast is the relatively weak signal-to-noise ratio detected during measurements.
The presence of flexible particles on the apex of the tip results in a significant amplification of
the signal, which allows us to achieve high-resolution images. However, such tips are stable only
at very low temperatures, close to absolute zero. This condition has dramatically limited the use
of this method in terms relevant to important chemical and biological processes, for which e.g.
room temperature is essential.
A team of scientists from the Institute of Physics of the CAS and the University of Osaka
introduced in the July issue of the journal Nature Communications a new method that allows you to
achieve sub-molecular resolution even at room temperature with standard tips. Collaboration between
two teams led to the optimization of key scanning parameters supported by theoretical calculations.
The optimum measurement parameters enabled a significant enhancement of the detection signal even
without requirement of the special tip modification. This achievement pushes significantly the
limits of the molecular resolution by means of the scanning probe microscopes. The possibility of
imaging individual molecules on surfaces at ambient temperature represents essential prerequisite
for the study of catalytic reactions on solid surfaces.
This work builds on previous research of scientists from Nanosurf laboratory of the Institute
of Physics, which contributed significantly to the understanding of the mechanism leading to
sub-molecular resolution of single molecules using scanning probe microscopes. Scientists from the
Institute of Physics have formulated a new theoretical model that provides deeper understanding of
experimental measurements with aid of computer simulations (see [2] and [3]). The importance of the
theoretical model reflects considerable number of citations which the papers received in less than
one year after its publication (> 30). In addition, the purchase of low-temperature microscope
in 2013 allowed the scientists from the Institute of Physics of the CAS to achieve experimental
sub-molecular resolution. This achievement ranks the group among the few places in the world where
it is possible perform such experiments. The possibility of combining theoretical simulations and
experimental cutting-edge technology gives very good preconditions for further research of physical
and chemical properties of molecular nanostructures in the Institute of Physics of the Czech
Academy of Sciences.
Fig.1 A) Experimental image with the sub-molecular resolution of PTCDA molecule on the silicon
surface using an atomic force microscope at room temperature, B) calculated electron density
distribution above a PTCDA molecule, which contributes to the formation of high-resolution AFM
images, and C, D) optimized atomic structure of PTCDA molecule after deposition on the silicon
surface obtained by quantum mechanical computer simulations (see [1]).
References:
[1] K. Iwata et al., "
Chemical structure imaging of a single molecule by atomic force microscopy at room
temperature
”
Nature Communications6, 7766 (2015)
doi:10.1038/ncomms8766
[2] P. Hapala et al., „
Origin of high-resolution IETS-STM images of organic molecules with functionalized tips”
Phys. Rev. Lett. 113, 226101 (2014).
[3] P. Hapala et al., “
Mechanism of high-resolution STM/AFM imaging with functionalized tips”
Phys. Rev. B 90, 085421 (2014).
Contact:
Pavel Jelínek
Phone.: +420 220 318 430
Mobile: +420 734 353 740
E-mail:
pavel.jelinek@fzu.cz
WWW: nanosurf.fzu.cz
Address: Cukrovarnická 10, Praha 7, 162 00
6 Aug 2015
