Since the vibration energy of a molecule depends to a large extent on the environment of the molecule, it is necessary to measure the vibration energy of an individual molecule to obtain a deep understanding of the interaction of a molecule and a surface, taking into account the environment.

For example, a single molecule in isolation on a single crystal surface as shown in Figure 1A is an ideal target of this type of research.

The vibration energy of a single molecule can be investigated, with a scanning tunneling microscope (STM)*2), by placing the metal probe of STM right above the molecule and by precisely measuring the current by changing the voltage applied between the probe of STM and the surface.

As shown in Figure 2A, the current (I) and the voltage (V) show an approximately linear relationship, the second derivative of which (V derivative of dI/dV) shows a peak and trough pair as shown in Figure 2B.

Thus, using this method, the vibration energy of a single molecule can be determined.

It was previously reported, however, that when a metal probe was placed very close to a molecule in order to measure the current, the probe tip itself exerted a force on the molecule, affecting its vibration energy.

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