Tunable Nanoscale Metal‒Molecule‒Semiconductor Junctions via Light‐Controlled Molecular Orientation

Molecular electronics offers significant potential for the development of miniaturized and tunable electronic devices, with silicon (Si) remaining a cornerstone of modern semiconductor technology. This study presents a method for constructing tunable molecular circuits on Si electrodes using UV‐controlled hydrosilylation reaction, enabling precise control over molecular orientation and bonding. When hydrogen‐terminated Si surfaces are exposed to UV light in a solution of 9‐decyne‐1‐ol, hydroxyl (OH) groups form covalent Si─O─C bonds, while in the absence of UV light, alkyne groups instead react to form Si─C bonds. This tunability allows precise positioning of oxygen atoms near the Si surface, thereby enhancing charge transfer in metal–molecule–semiconductor junctions and at electrified semiconductor–electrolyte interfaces. Conducting atomic force microscopy (C‐AFM) measurements reveal that Pt─Si junctions exhibit Schottky diode characteristics, whereas Pt–molecule–Si junctions display Ohmic behaviour. Junctions formed via Si─O bonds demonstrate significantly lower resistance and at least a two‐fold higher electron transfer rate constant (ket) compared to those formed with Si─C bonds, indicating superior charge transfer when oxygen atoms are positioned near the Si electrode. These findings suggest that incorporating oxygen‐containing molecules reduces the space‐charge region, thereby facilitating current flow at the Si–metal and Si–electrolyte electrified interfaces.