A Calibration-Free Optical Emission Spectroscopic Method to Determine the Composition of a Spark Discharge Plasma Used for AuAg Binary Nanoparticle Synthesis.

Spark discharge generators (SDGs) employ controlled gaseous environments to induce spark ablation of non-insulating electrodes, resulting in the formation of various nanostructures in the gas phase. The method offers technological advantages such as continuous particle production, scalable yield, and minimal waste. Additionally, the versatility of the process enables the generation of alloy nanoparticles from various material combinations, including immiscible ones. In order to fully exploit its potential, understanding the atomic mixing process during electrode ablation, particularly in the case of dissimilar electrodes, is crucial. Temporally and spatially resolved optical emission spectroscopy (OES) has been previously demonstrated as an effective characterization tool for spark plasmas in SDGs. However, to gain a deeper insight into the vapor mixing process, it is essential to quantitatively determine the plasma composition in both space and time. This paper introduces a calibration-free OES-based method tailored for spark plasmas utilized in binary nanoparticle generation. The method introduces the so-called multi-element combinatory Boltzmann plots, which use intensity ratios of emission atomic lines from different materials, allowing for the direct estimation of total number concentration ratios. The approach is tested using synthetic spectra and validated with experimental spark spectra obtained near an alloyed gold-silver (AuAg) electrode with a known composition. The study demonstrates the capabilities and robustness of the proposed method, with a focus on the AuAg system due to its significance in plasmonic research and frequent synthesis using spark ablation.

Continuous spark plasma synthesis of Au/Co binary nanoparticles with tunable properties.

We present here a scalable and environmentally friendly gas phase technique employing atmospheric pressure electrical spark discharge plasmas for the production of Au/Co binaries, an effective catalyst system for the decomposition of hydrogen-rich compounds, such as ammonium borane. We demonstrate that Au/Co alloy nanoparticles can be produced via the spark plasma-based technique. The possibility of varying the morphology and phase structure via real time heat treatment of the generated aerosol to form Au/Co/CoO particles with continuous control over a wide particle compositional range (from 24 to 64 at.% [Co]/([Co] + [Au]) content) is also demonstrated. Since our spark-based approach is proven to be capable of providing reasonable particle yields, these results may contribute to the transition of lab-scale, nanocatalyst-based hydrogen storage systems to real world applications.

One-step fabrication of fiber optic SERS sensors via spark ablation.

Spark ablation, a versatile, gas-phase physical nanoparticle synthesis method was employed to fabricate fiber-optic surface enhanced Raman scattering (SERS) sensors in a simple single-step process. We demonstrate that spark-generated silver nanoparticles can be simply deposited onto a fiber tip by means of a modified low-pressure inertial impactor, thus providing significant surface enhancement for fiber-based Raman measurements. The surface morphology of the produced sensors was characterized along with the estimation of the enhancement factor and the inter- and intra-experimental variation of the measured Raman spectrum as well as the investigation of the concentration dependence of the SERS signal. The electric field enhancement over the deposited silver nanostructure was simulated in order to facilitate the better understanding of the performance of the fabricated SERS sensors. A potential application in the continuous monitoring of a target molecule was demonstrated on a simple model system.

Full range tuning of the composition of Au/Ag binary nanoparticles by spark discharge generation.

Gold/silver bimetallic nanoparticles still attract extensive interest due to their favorable properties e.g. in plasmonics or catalysis. We present here a facile and robust way for the production of clean Au/Ag binary nanoparticles (BNPs) with a total control over the composition via the spark discharge nanoparticle generation technique. With the application of pure Ag and Au electrodes, a tuning range of 55 to 90% Au content was achieved, but this can be further extended to the full 0 to 100% range by using a couple of alloyed electrodes. An added benefit of the approach is that either the concentration or the mean particle size can be kept constant at every composition by adjusting the generator parameters. Based on the systematic experimental data collected, a semi-empirical model for the prediction of the Au/Ag BNP composition was also developed. This model was used to calculate the theoretically achievable Au/Ag composition at a given spark parameter set in the parameter range most commonly used in the literature.