We report the fabrication and performance evaluation of hybrid surface-enhanced Raman scattering (SERS) substrates involving laser ablation and chemical routes for the trace-level detection of various analyte molecules. Initially, picosecond laser ablation experiments under ambient conditions were performed on pure silver (Ag) and gold (Au) substrates to achieve distinct nanosized features on the surface. The properties of the generated surface features on laser-processed portions of Ag/Au targets were systematically analyzed using UV–visible reflection and field emission scanning electron microscopy studies. Later, hybrid-SERS substrates were achieved by grafting the chemically synthesized Au nanostars on the plain and laser-processed plasmonic targets. Subsequently, we employed these as SERS platforms for the detection of a pesticide (thiram), a molecule used in explosive compositions [ammonium nitrate (AN)], and a dye molecule [Nile blue (NB)]. A comparative SERS study between the Au nanostar-decorated bare glass, silicon, Ag, Au, and laser-processed Ag and Au targets has been established. Our studies and the obtained data have unambiguously determined that laser-processed Ag structures have demonstrated reasonably good enhancements in the Raman signal intensities for distinct analytes among other substrates. Importantly, the fabricated hybrid SERS substrate of “Au nanostar-decorated laser-processed Ag” exhibited up to eight times enhancement in the SERS intensity compared to laser-processed Ag (without nanostars), as well as up to three times enhancement than the Au nanostar-loaded plain Ag substrates. Additionally, the achieved detection limits from the Au nanostar-decorated laser-processed Ag SERS substrate were ∼50 pM, ∼5 nM, and ∼5 μM for NB, thiram, and AN, respectively. The estimated enhancement factors accomplished from the Au nanostar-decorated laser-processed Ag substrate were ∼10 6 , ∼10 6 , and ∼10 4 for NB, thiram, and AN, respectively.
The prototypical plum-free, one-phase multiferric ferrite BiFeO 3 (BFO) is solid, parallel, with a high ferroelectric Curie temperature and Neel temperature and antiferromagnetic and ferroelectric propagation. This work aims to synthesize pure-phase BFO in the quickest possible way. We followed the microwave-assisted solvothermal (MWAST) method to achieve pure-phase BFO in the shortest duration of 3 min. The experiment involves simple optimizations with KOH concentration and microwave power levels. The surface morphology along with magnetic properties of BFO synthesized via the MWAST method are altered with varying KOH concentrations and microwave (MW) power levels. Our X-ray diffraction findings reveal that the pure-phase BFO is formed at 800 W MW power, and the structural characterizations like transmission electron microscopy, field emission scanning electron microscopy with energy-dispersive X-ray analysis have displayed the formation of uniformly distributed spherical microflowers of pure-phase BFO exhibiting a single-crystalline nature. Besides, the magnetic measurements affirmed a reliable weak ferromagnetic behavior (magnetization ∼1.25 emu/g) in BFO synthesized at 800 W MW power. In addition, good dielectric behavior with low dielectric loss was accompanied by frequency-dependent dielectric studies indicating an excellent frequency response of the material, and also the room-temperature ferroelectric properties were studied using a ferroelectric analyzer. The polarization of pure-phase BFO increases with the applied electric field and exhibits unsaturated polarization–electric field loops due to leakage current. Moreover, the Fourier transform infrared spectrum of the synthesized material has indicated the pure-phase BFO, and the Raman data have elucidated the vibrational modes of BFO. Further, the analysis of X-ray photoelectron spectroscopy data has confirmed the presence of fewer Fe 2+ ions and oxygen vacancies in the pure-phase BFO. Therefore, the collective characterizations and detailed analysis of BFO material have revealed the uniqueness of the MWAST method in producing the pure-phase BFO in 3 min with improved magnetic and dielectric properties, and hence the BFO synthesized via the MWAST method can be a potential candidate for multiferroic applications.
We have produced femtosecond Bessel beam ablated bimetallic nanoparticles, exhibiting prominent ultrafast optical switching. Subsequently, the plasmonic nanoparticles were engaged in trace-level sensing of real-time explosives through the surface enhanced Raman scattering technique (SERS).
In this study, we have generated a femtosecond (fs), non-diffracting Bessel beam (800 nm, 1 kHz, 50 fs) of zeroth order through an axicon (IR range, 100, AR coated). We have performed laser ablation of a bimetallic alloy (50% gold, 50 % silver) in the air engaging the generated fs Bessel beam. The high-intensity Bessel beam-matter interaction resulted in the fabrication of exotic bimetallic nanostructures. Extensive field emission scanning electron microscope and atomic force microscopy characterizations were undertaken to study the nanoscale topographical formations. The fs Bessel beam-induced ablation on the alloy target, involving the beam profile imprint on a single surface spot, followed by overlapping two ablation zones, has been meticulously explored. The central lobe ablated area, along with concentric rings-ablated exotic patterns, were thoroughly investigated in the topographical characterization. In the case of the complete raster scan ablation, ladder-like periodic surface structures (with sub ~20 nm growths on the ladder steps) were observed. Energy-dispersive X-ray mapping was performed to confirm the elemental distribution in the nanostructured areas. Subsequently, these plasmonic nanostructures were utilized as surface-enhanced Raman scattering (SERS) platforms to detect traces of real-time explosives, ammonium nitrate (AN), and Tetryl (TL). The SERS spectra of AN depicted a signature Raman peak at 1043 cm -1 , whereas TL exhibited a signature peak near 1353 cm -1 . The lowest possible detected traces were 10 µM and 5 µM, for AN and TL, respectively.
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