Single-step fabrication of hybrid germanium-gold/silver nanoentities by femtosecond laser ablation and applications in SERS-based sensing

Abstract

We present a simple, fast, and single-step approach for fabricating hybrid semiconductor-metal nanoentities through liquid-assisted ultrafast (~50 fs, 1 kHz, 800 nm) laser ablation. Femtosecond (fs) ablation of Germanium (Ge) substrate was executed in (i) distilled water (DW) (ii) silver nitrate (AgNO3 - 3, 5, 10 mM) (iii) Chloroauric acid (HAuCl4 - 3, 5, 10 mM), yielding the formation of pure Ge, hybrid Ge-silver (Ag), Ge-gold (Au) nanostructures (NSs) and nanoparticles (NPs). The morphological features and corresponding elemental compositions of Ge, Ge-Ag, and Ge-Au NSs/NPs have been conscientiously studied using different characterization techniques. Most importantly, the deposition of Ag/Au NPs on the Ge substrate and their size variation were thoroughly investigated by changing the precursor concentration. By increasing the precursor concentration (from 3 mM to 10 mM), the deposited Au NPs and Ag NPs’ size on the Ge nanostructured surface was increased from ~46 nm to ~100 nm and from ~43 nm to ~70 nm, respectively. Subsequently, the as-fabricated hybrid (Ge-Au/Ge-Ag) NSs were effectively utilized to detect diverse hazardous molecules (e.g., picric acid and Thiram) via the technique of surface-enhanced Raman scattering (SERS). Our findings revealed that the hybrid SERS substrates achieved at 5 mM precursor concentration of Ag (denoted as Ge-5Ag) and Au (denoted as Ge-5Au) had demonstrated superior sensitivity with the enhancement factors (EFs) of ~2.5×104, 1.38×104 (for PA), and ~9.7×105 and 9.2×104 (for Thiram), respectively. Interestingly, the Ge-5Ag substrate has exhibited ~10.5 times higher SERS signals than the Ge-5Au substrate.

Wide-Spectrum Antireflective Properties of Germanium by Femtosecond Laser Raster-Type In Situ Repetitive Direct Writing Technique

“…This paper mainly regulates the period uniformity of Ge surface structure by adjusting laser irradiation parameters, processing methods, and cleaning methods [25,26]. We also investigated the mechanism of microstructure formation, optical properties (spectral broadband antireflection) and wettability [27][28][29][30]. We believe that a periodic dense microholes structure on Ge surface is the key to improving the anti-reflection performance.…”

Surface-Enhanced Raman Scattering Studies of Au-Ag Bimetallic Nanoparticles with a Tunable Surface Plasmon Resonance Wavelength Synthesized by Picosecond Laser Irradiation

“…But all these methods have different issues in the fabrication process; either we end up with hazardous chemical byproducts or high-cost synthesis procedures. There are reports available on the synthesis of bimetallic NPs via the femtosecond laser ablation of bulk bimetallic targets of respective metal alloys in liquids, which result in the formation of bimetallic NPs and are used for SERS-based sensing and explosive detection [31][32][33][34][35]. Here, we report a simple, single-step, and cost-effective laser irradiation method for synthesizing alloy NPs by directly irradiating the metallic salt solution obtained from the precursors.…”