Electroplating-based engineering of plasmonic nanorod metamaterials for biosensing applications

Abstract

Sensing lower molecular weight in a diluted solution using a label-free biosensor is challenging and requires a miniaturized plasmonic structure, e.g., a vertical Au nanorod (AuNR) array based metamaterials. The sensitivity of a sensor mainly depends on transducer properties and hence for instance, the AuNR array geometry requires optimization. Physical vapour deposition methods (e.g., sputtering and e-beam evaporation) require a vacuum environment to deposit Au, which is costly, time-consuming, and thickness-limited. On the other hand, chemical deposition, i.e., electroplating deposit higher thickness in less time and at lower cost, becomes an alternative method for Au deposition. In this work, we present a detailed optimization for electroplating based fabrication of these metamaterials. We find that slightly acidic (6.0 < pH < 7.0) gold sulfite solution supports immersion deposition, which should be minimized to avoid uncontrolled Au deposition. Immersion deposition leads to plate-like (for smaller radius AuNR) or capped-like, i.e., mushroom (for higher radius AuNR) structure formation. The electroplating time and DC supply are the tuning parameters that decide the geometry of the vertically aligned AuNR array in area-dependent electroplating deposition. This work will have implications for developing plasmonic metamaterial based sensors.

Novel Nano-Electroplating-Based Plasmonic Platform for Giant Emission Enhancement in Monolayer Semiconductors

“…The cleaned quartz substrate was sputtered with a 5 nm-thick adhesive Ti-layer at a 2.1 nm/min rate, followed by a 20 nm Au film deposited at a 17 nm/min rate, resulting in a transparent and conductive quartz substrate. This conducting seed layer is essential for the nanoelectroplating process …”

“…This conducting seed layer is essential for the nanoelectroplating process. 28 The AuND array pattern is created on the sample using EBL. The AuND array has a diameter of 300 nm and periodicity 400 nm from center to center.…”

“…The DC power supply was operated in constant current mode at 0.001 A DC for 45 s. The sample was promptly removed and submerged in DI water to prevent immersion deposition. 28 The nanoelectroplating method for Au deposition depends on the exposed seed-layer area of the sample to the electrolyte (A), the DC current (I), and the deposition time (t). The thickness (T) of the electroplated Au layer can be formulated as given in eq 1.…”

“…In our previous work, we optimized the fabrication of a cylindrical flat-top AuND array using EBL followed by electroplating using a single-layer resist process. 28 In this study, we introduce a novel nanoelectroplating-based platform of AuND array to enhance the optical properties of monolayer MoS 2 . The results of our investigation demonstrate that the hybrid structure of AuND-MoS 2 exhibits 150-fold PL enhancement compared to the Au thin film without any normalization.…”

“…To the best of our knowledge, there is no work reported on nanoelectroplating-based plasmonic nanostructures for the engineering of the emission properties of TMDC to date. In our previous work, we optimized the fabrication of a cylindrical flat-top AuND array using EBL followed by electroplating using a single-layer resist process …”