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Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...

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Related Experiment Video

Updated: Mar 7, 2026

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

Published on: December 4, 2017

Surface single-molecule dynamics controlled by entropy at low temperatures.

J C Gehrig¹, M Penedo¹, M Parschau¹

¹Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland.

Nature Communications

|February 10, 2017

Summary

This summary is machine-generated.

Investigating single molecule transitions on surfaces reveals that tip-molecule interactions significantly alter energy barriers and attempt rates. This study demonstrates enthalpy-entropy compensation, crucial for understanding molecular dynamics at low temperatures.

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Area of Science:

Surface Science
Physical Chemistry
Nanotechnology

Background:

Molecular and atomic transitions on surfaces are typically modeled using Arrhenius kinetics.
Significant variations in pre-exponential factors and energy barriers are observed even for identical systems.

Purpose of the Study:

To investigate the influence of scanning tunneling microscopy (STM) tip position on single-molecule transition dynamics.
To explore the phenomenon of enthalpy-entropy compensation in molecular transitions.

Main Methods:

Utilized low-temperature scanning tunneling microscopy (STM) to probe individual dibutyl sulfide molecules on Au(111).
Precisely controlled the relative position of the STM tip apex and the molecule.

Main Results:

STM tip positioning, even by a fraction of molecular size, significantly alters transition energy barriers and pre-exponential factors.
Observed a strong correlation between changes in barrier and attempt rate, indicating single-molecular enthalpy-entropy compensation.
Demonstrated the ability to tune transition rates by selecting specific STM tip operating points.

Conclusions:

Enthalpy-entropy compensation is a critical factor in single-molecule transition rates, even at low temperatures.
The STM tip's influence on molecular configurations must be considered in surface dynamics studies.
Precise control over tip-molecule interactions offers a method to manipulate molecular transition rates.