Novel surfactant-free multi-branched gold stars characterized by inverse photocurrent

Multi-branched gold stars were spontaneously formed on a semiconductor (Ge) substrate in high yield via a surfactant-free galvanic displacement method at room temperature using a DMF-water (9/1) mixed solvent. The average length of the branches was estimated to be 561 nm, and the size and shape of the multi-branched gold stars can be controlled by varying the reaction time of the Ge wafer and gold precursor. A high volume ratio of DMF was found to be crucial for the formation of these multi-branched gold stars. Interestingly, the photocurrent of the prepared gold stars decreased by 10% upon irradiation with a 532 nm visible laser. The photocurrent was switched on and off >10 times without significant degradation, indicating high reproducibility and reliability of the inverse photoresponse of the gold stars under visible light.