Nanotechnologists assemble intricate nanodevices, such as computer chips, molecule by molecule using ‘bottom-up’ techniques that mirror nature. One approach shuttles molecules along surfaces into new and functional arrangements using electrons from a scanning tunneling microscope (STM) tip.
However, because energy transfer between the atomic-scale tip and the surface chemical involves many complex interactions, laborious efforts are currently needed to understand even the simplest reactions.
Results from a new theoretical and experimental study, however, may soon allow non-specialists to easily construct molecular devices. Kenta Motobayashi and Yousoo Kim from the RIKEN Advanced Science Institute in Wako and their colleagues from RIKEN and Japanese universities have developed a mathematical formula that describes how STM-induced molecular vibrations couple with dynamic movements on surfaces—enabling precise calculation of the energy and number of electrons needed to initiate single molecule motions1.
When scientists use an STM to perform a straightforward molecular movement—for example, making carbon monoxide (CO) compounds ‘hop’ on palladium surfaces—they see that the fraction of successful movements depends heavily on the applied voltage. For CO, this is because hopping from one surface site to another requires a tunneling electron to initiate a specific stretching vibration. In the voltage range corresponding to this vibrational energy, CO hopping can increase exponentially, giving rise to so-called ‘action spectra’: curves of movement yields versus voltage with shapes characteristic to particular surface reactions.
Motobayashi, Kim and colleagues sought to uncover the microscopic mechanisms behind STM-stimulated diffusion by proposing a formula that relates movement yields to the energy transfer efficiency needed to excite reaction-triggering vibrations, while also accounting for thermal interactions. Fitting the CO action spectra to this formula revealed the exact magnitudes of critical reaction properties, like vibrational energies and rate constants, because the spectral curves were highly sensitive to small modification of the fit parameters.
Furthermore, the team’s new equation proved versatile enough to analyze the more complex motions of butene (C4H8) molecules on palladium, a process that involves multiple excitations. Analyzing the butene action spectra with the formula showed the presence of three distinct vibrations and enabled calculation of the reaction order—a fundamental chemical property that identifies the number of tunneling electrons needed to initiate surface movement.
According to Motobayashi, the surprising abilities of this simple method should expand bottom-up nanotechnology practices. “STM-based action spectroscopy, which can precisely identify chemical species thanks to our spectral fittings, promises to contribute greatly to the technique of composing molecular devices,” he states.
The corresponding author for this highlight is based at the Surface and Interface Science laboratory, RIKEN Advanced Science Institute
1. Motobayashi, K., Kim, Y., Ueba, H. & Kawai, M. Insight into action spectroscopy for single molecule motion and reactions through inelastic electron tunneling. Physical Review Letters 105, 076101 (2010).
Fingerprint' technique spots frog populations at risk from pollution
27.03.2017 | Lancaster University
Parallel computation provides deeper insight into brain function
27.03.2017 | Okinawa Institute of Science and Technology (OIST) Graduate University
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
27.03.2017 | Life Sciences
27.03.2017 | Life Sciences
27.03.2017 | Earth Sciences