Surface single-molecule dynamics controlled by entropy at low temperatures

Abstract

Configuration transitions of individual molecules and atoms on surfaces are traditionally described using an Arrhenius equation with energy barrier and pre-exponential factor (attempt rate) parameters. Characteristic parameters can vary even for identical systems, and pre-exponential factors sometimes differ by orders of magnitude. Using low-temperature scanning tunnelling microscopy (STM) to measure an individual dibutyl sulfide molecule on Au(111), we show that the differences arise when the relative position of tip apex and molecule changes by a fraction of the molecule size. Altering the tip position on that scale modifies the transition's barrier and attempt rate in a highly correlated fashion, which results in a single-molecular enthalpy-entropy compensation. Conversely, appropriately positioning the STM tip allows selecting the operating point on the compensation line and modifying the transition rates. The results highlight the need to consider entropy in transition rates of single molecules, even at low temperatures.

Simple Accurate Verification of Enthalpy‐Entropy Compensation and Isoequilibrium Relationship

“…There is a longstanding debate in the literature regarding the physical basis of the so‐called enthalpy‐entropy compensation ( EEC ), which is observed in a wide range of fields in chemistry [1–8] , biology [9–15] and solid‐state physics [16–19] . EEC describes a linear relation between two thermodynamic parameters ‐ the enthalpy Δ H and entropy Δ S ‐ of a series of similar reactions.…”

Single Quality Factor for Enthalpy‐Entropy Compensation, Isoequilibrium and Isokinetic Relationships

“…There is a longstanding debate in the literature regarding the physical basis of the so-called enthalpy-entropy compensation (EEC), which is observed in a wide range of fields in chemistry; [1][2][3][4][5][6][7][8] biology [9][10][11][12][13][14][15] and solid-state physics: [16][17][18][19] EEC describes a linear relation between two thermodynamic parameters, the enthalpy~H and entropy~S, of a series of similar reactions. Examples include the denaturation of closely related proteins, reactions in slightly varying solvents, or reactions of hydrogen with metal alloys.…”

Enthalpy-entropy compensation of atomic diffusion originates from softening of low frequency phonons

“…We exhibit such an example with amorphous Ni 80 P 20 . In addition, the fundamental nature of the softening mechanism revealed here suggests that it extends beyond atomic diffusion and explains the ubiquity of enthalpy-entropy compensation relations for processes controlled by a single microscopic-free energy barrier, observed across disciplines, including materials science 9,24 , chemistry 25,26 , and biology 27 .…”