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The wonderful world of scanning electrochemical microscopy: Uncovering the secrets of the liquid-solid interface?
Scanning electrochemical microscopy (SECM) is an innovative technique used within the broad category of scanning probe microscopy (SPM) that can measure the local electrochemical behavior of liquid-solid, liquid-gas, and liquid-liquid interfaces. . This technology was first proposed and symbolized by Allen J. Bard, an electrochemist at the University of Texas in 1989. As the theoretical basis matures, SECM has been widely used in chemistry, biology and materials science. By measuring the current at a precise position at the ultramicroelectrode (UME) tip, spatially resolved electrochemical signals can be obtained. The interpretation of these signals is based on the concept of diffusion-limited currents, which in turn yields a picture of interfacial reactivity and chemical kinetics.
SECM technology can explore interfacial phenomena and has found significant applications in materials science, such as microstructuring and surface patterning.
History
The emergence of ultramicroelectrodes (UMEs) was an important turning point in the development of sensitive electroanalytical techniques such as SECM. In 1986, Engstrom conducted the first SECM-like experiment and observed the reaction pattern and short-lived intermediates. Alan J. Bader's experiments also pointed out that the current measured at large distances was not consistent with electron tunneling, but was caused by Faradaic current. This prompted further research into electrochemical microscopy. Budd proposed the theoretical basis of SECM in 1989 and introduced a variety of feedback modes.
How it works
The basic principle of SECM is to modulate the potential in a solution containing a redox couple via a UME tip. For example, in a system transportingFe2+/Fe3+, when a sufficiently negative potential is applied, Fe3+ will be reduced to Fe2+ at the UME tip, resulting in diffusion Limit current. This technology has two main modes of operation: feedback mode and collection-generation mode.
Feedback Mode
In the feedback mode, when the UME tip is close to the conductive substrate, the reduced products generated at the tip will be oxidized on the conductive surface, resulting in an increase in the tip current, forming a positive feedback. If the target is an insulating surface, the current will be reduced due to the inability to regenerate oxides, forming a negative feedback loop.
Collect-Generate Mode
In the collection-generation mode, the UME tip is held at a sufficient potential for chemical reaction, while the substrate is at an appropriate potential to collect or react with the products generated by the tip. This pattern provides insight into the dynamics of the electron transfer process in the system.
Applications
SECM has been used to probe the surface reactivity of solid-state materials, study the dissolution kinetics of ionic crystals in aqueous environments, screen electrocatalytic materials, analyze the activity of enzymes, and investigate the dynamic transport of synthetic/natural membranes.
SECM's microfabrication and planar design capabilities have enabled breakthroughs in the application of surface reactions, especially in the processes of metal deposition and surface patterning.
Future Outlook
With the advancement of technology, the application scope of SECM continues to expand and its sensitivity continues to improve. Smaller probes and higher spatial resolution mean scientists can observe phenomena that were previously out of reach. Behind these technologies, we can't help but wonder: In the process of exploring the microscopic world, can SECM help us solve deeper scientific mysteries?
