Synthesis of Au50Ag50 Alloy Nanoparticles From Metal Ions and Colloidal Nanoparticles Through Photochemical Reduction Methods Using Femtosecond Laser

Nanoparticles synthesized through photochemical reduction using femtosecond involve reducing agent that reduces metal ions into nanoparticles. We synthesized Au50Ag50 from metal ions and colloidal nanoparticles in four different conditions: (i) gold metal ions and silver metal ion, (ii) colloidal gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), (iii) gold metal ions and colloidal silver nanoparticles (AgNPs), and (iv) colloidal gold nanoparticles (AuNPs) and silver metal ions. Gold and metal ions were obtained from dilution of gold and silver metal salts. While gold and silver nanoparticles were obtained from gold and metal ions added into a quartz cuvette and irradiated by femtosecond laser in 10 minutes irradiation time. In the synthesis, every condition respectively mixed in 3 ml solution into a 10x10x45 mm quartz cuvette and irradiated by femtosecond laser in 5-, 10- and 15- minutes irradiation time. The result showed that Au50Ag50 alloy nanoparticles were successfully synthesized in four different conditions, and the LSPR (Localized Surface Plasmon Resonance) in 15 minutes irradiation time was observed at 454.51, 458.74, 459.60, and 457.29 nm in the condition (i), (ii), (iii), and (iv), respectively

Gold (Au), Silver (Ag) and Bimetallic Au/Ag Core-Shell Nanoparticles: Synthesis and Applications in 4-Nitrophenol Reduction Reactions

Au, Ag, and Au/Ag core-shell nanoparticles (NPs) were synthesized in aqueous solution by chemical reduction. UV-Vis absorption spectra confirmed a single surface plasmon resonance (SPR) peak for Au and Ag NPs, at 520 nm and 419 nm, respectively. Au/Ag core-shell NPs' UV-Vis spectra showed two distinct peaks at 385 and 480 nm, confirming a core-shell structure different from its alloy counterpart. Transmission electron microscopy (TEM) shows a relatively uniform spherical shape for both Au and core-shell Au/Ag NPs, while Ag NPs have a variety of forms such as a prism, rod, and spherical. The average size of the synthesized nanoparticles was quite similar, between 18 and 25 nm. The 4-nitrophenol reduction reaction model was used to study the catalytic ability of nanoparticles where Au/Ag core-shell NPs showed higher catalytic activity than the other monometallic NPs used in this study

Femtosecond Laser Lift‐Off with Sub‐Band Gap Excitation for Production of Free‐Standing GaN LED Chips

Laser lift‐off (LLO) is commonly applied to separate functional thin films from the underlying substrate, in particular light‐emitting diodes (LEDs) on a gallium nitride (GaN) basis from sapphire. By transferring the LED layer stack to foreign carriers with tailored characteristics, for example, highly reflective surfaces, the performance of optoelectronic devices can be drastically improved. Conventionally, LLO is conducted with UV laser pulses in the nanosecond regime. When directed to the sapphire side of the wafer, absorption of the pulses in the first GaN layers at the sapphire/GaN interface leads to detachment. In this work, a novel approach towards LLO based on femtosecond pulses at 520 nm wavelength is demonstrated for the first time. Despite relying on two‐photon absorption with sub‐bandgap excitation, the ultrashort pulse widths may reduce structural damage in comparison to conventional LLO. Based on a detailed study of the laser impact as a function of process parameters, a two‐step process scheme is developed to create freestanding InGaN/GaN LED chips with up to 1.2 mm edge length and ≈5 μm thickness. The detached chips are assessed by scanning electron microscopy and cathodoluminescence, revealing similar emission properties before and after LLO

Effect of Yield Silver Nanoparticles in Enhancing Raman Signal of SERS Substrate Fabricated on Whatman Filter Paper

On Whatman Filter Paper, Surface Enhanced Raman Scattering (SERS) Substrate was created from colloidal silver nanoparticles by drop casting in varied volume colloidal nanoparticles of 3 ml and 6 ml. Using Raman Spectroscopy, SERS substrates were investigated for their ability to enhance 500 ppm of Deltamethrin pesticides Raman Signal. The number of colloidal nanoparticles is related to the volume of colloidal nanoparticles, indicating that high yields nanoparticle synthesis. The results demonstrate that fabricating SERS substrates in 6 ml increased Raman signal more than fabricating nanoparticles in 3 ml

Femtosecond Laser-Induced Formation of Gold-Rich Nanoalloys from the Aqueous Mixture of Gold-Silver Ions

The synthesis of gold-silver (AuAg) nanoalloys of various compositions has been performed by direct irradiation of highly intense femtosecond laser pulse in the presence of polyvinylpyrrolidone (PVP). The mixture of Au and Ag ions of low concentration was simply introduced into a glass vial and subjected to femtosecond laser pulses for several minutes. The AuAg nanoalloys of 2-3 nm with reasonably narrow size distribution were formed, and the position of the surface plasmon resonance (SPR) increased monotonically with an increase in the gold molar fraction in the ion solutions. The high resolution transmission electron microscope (HRTEM) images exhibited the absence of core-shell structures, and the energy dispersive X-ray spectroscopy (EDX) analysis confirmed that the particles were Au-rich alloys even for the samples with large fraction of Ag+ ions fed in the solution mixture. The formation mechanism of the alloy nanoparticles in the high intensity optical field was also discussed

Liquid Surface-Enhanced Raman Spectroscopy (SERS) Sensor-Based Au-Ag Colloidal Nanoparticles for Easy and Rapid Detection of Deltamethrin Pesticide in Brewed Tea

Deltamethrin pesticides can cause inflammation, nephrotoxicity and hepatotoxicity as well as affect the activity of antioxidant enzymes in tissues. As a result of this concern, there is a rising focus on the development of fast and reliable pesticide residue testing to minimise potential risks to humans. The goal of this study is to use Au-Ag colloid nanoparticles as liquid surface-enhanced Raman spectroscopy (SERS) to improve the Raman signal in the detection of deltamethrin pesticide in a brewed tea. The liquid SERS system is fascinating to study due to its ease of use and its unlikeliness to cause several phenomena, such as photo-bleaching, combustion, sublimation and even photo-catalysis, which can interfere with the Raman signal, as shown in the SERS substrate. Our liquid SERS system is simpler than previous liquid SERS systems that have been reported. We performed the detection of pesticide analyte directly on brewed tea, without diluting it with ethanol or centrifuging it. Femtosecond laser-induced photo-reduction was employed to synthesise the liquid SERS of Au, Au-Ag, and Ag colloidal nanoparticles. The SERS was utilised to detect deltamethrin pesticide in brewed tea. The result showed that liquid SERS-based Ag NPs significantly enhance the Raman signal of pesticides compared with liquid SERS-based Au NPs and Au-Ag Nanoalloys. The maximum residue limits (MRLs) in tea in Indonesia are set at 10 ppm. Therefore, this method was also utilised to detect and improve, to 0.01 ppm, the deltamethrin pesticide Limit of Detection (LOD)

Liquid Surface-Enhanced Raman Spectroscopy (SERS) Sensor-Based Au-Ag Colloidal Nanoparticles for Easy and Rapid Detection of Deltamethrin Pesticide in Brewed Tea

Deltamethrin pesticides can cause inflammation, nephrotoxicity and hepatotoxicity as well as affect the activity of antioxidant enzymes in tissues. As a result of this concern, there is a rising focus on the development of fast and reliable pesticide residue testing to minimise potential risks to humans. The goal of this study is to use Au-Ag colloid nanoparticles as liquid surface-enhanced Raman spectroscopy (SERS) to improve the Raman signal in the detection of deltamethrin pesticide in a brewed tea. The liquid SERS system is fascinating to study due to its ease of use and its unlikeliness to cause several phenomena, such as photo-bleaching, combustion, sublimation and even photo-catalysis, which can interfere with the Raman signal, as shown in the SERS substrate. Our liquid SERS system is simpler than previous liquid SERS systems that have been reported. We performed the detection of pesticide analyte directly on brewed tea, without diluting it with ethanol or centrifuging it. Femtosecond laser-induced photo-reduction was employed to synthesise the liquid SERS of Au, Au-Ag, and Ag colloidal nanoparticles. The SERS was utilised to detect deltamethrin pesticide in brewed tea. The result showed that liquid SERS-based Ag NPs significantly enhance the Raman signal of pesticides compared with liquid SERS-based Au NPs and Au-Ag Nanoalloys. The maximum residue limits (MRLs) in tea in Indonesia are set at 10 ppm. Therefore, this method was also utilised to detect and improve, to 0.01 ppm, the deltamethrin pesticide Limit of Detection (LOD)

The Study of the Optical Properties of C60 Fullerene in Different Organic Solvents

C60 fullerene exhibits unique optical properties that have high potential for wide photo-optical applications. To analyze the optical properties of C60, its excitation and emission properties were studied using UV-Vis absorption and photoluminescence (PL) spectroscopy, which were performed in various, non-polar organic solvents such as toluene, xylene, and trichloroethylene (TCE). The C60 solutions in toluene, xylene, and TCE displayed similar excitation bands at 625, 591, 570, 535, and 404 nm corresponding to Ag → T1u and Ag → T1g transitions. However, these bands differed from the solid C60 observed by UV-Vis diffuse reflectance spectroscopy. The two emission band energies of C 60 solution in toluene and xylene were nearly the same (1.78 and 1.69 eV), whereas the C60 solution in TCE was shifted to 1.72 and 1.65 eV. Because the polarity of TCE is higher than that of toluene and xylene, the PL spectrum of the C 60 solution in TCE was red-shifted. The PL spectroscopy had a better capability than UV-Vis absorbance spectroscopy to distinguish the different interactions between C60 and the organic solvents due to their different solvent polarities

Surface-enhanced Raman Scattering (SERS) Substrate of Colloidal Ag Nanoparticles Prepared by Laser Ablation for Ascorbic Acid Detection

Ag nanoparticles were synthesized by laser ablation using an Ag plate in distilled water. This method was performed using a laser with a wavelength of 532 nm and energy of 30 mJ for 60 min. Ag nanoparticles successfully formed, confirmed by the selected area electron diffraction (SAED) which revealed four principal crystal planes of (111), (200), (220) and (311). The size distribution of Ag nanoparticles ranged from 5 to 40 nm, as estimated from electron imaging observed by transmission electron microscope (TEM). Ascorbic acid was used as the analyte to test the characteristics of surface-enhanced Raman scattering (SERS) of colloidal Ag nanoparticles. The concentration of ascorbic acid (1.0, 0.5 and 0.25 wt%) and incubation time (0 and 6 h) were varied to determine the limit of detection and the effect of incubation time. The Raman scattering spectroscopy results showed that the colloidal Ag nanoparticle substrate improved the signals for detection of ascorbic acid