Showing papers by "Vittorio Scardaci published in 2021"

Raman Spectroscopy Investigation of Graphene Oxide Reduction by Laser Scribing

Abstract: Laser scribing has been proposed as a fast and easy tool to reduce graphene oxide (GO) for a wide range of applications. Here, we investigate laser reduction of GO under a range of processing and material parameters, such as laser scan speed, number of laser passes, and material coverage. We use Raman spectroscopy for the characterization of the obtained materials. We demonstrate that laser scan speed is the most influential parameter, as a slower scan speed yields poor GO reduction. The number of laser passes is influential where the material coverage is higher, producing a significant improvement of GO reduction on a second pass. Material coverage is the least influential parameter, as it affects GO reduction only under restricted conditions.

Nonlinear Optical Properties of Ag Nanoplates Plasmon Resonance and Applications in Ultrafast Photonics

Abstract: Metal nanomaterials have attracted increasing attention due to their outstanding nonlinear optical and photonic properties, making them as potential saturable absorber (SA) candidates for realizing ultrafast photonic devices. In this article, we demonstrate the generation of mode-locked dual-wavelength pulse trains in an Ag nanoplates (AgNPTs)-based Yb-doped all-fiber laser for the first time to the best of our knowledge. The AgNPTs are synthesized by seed-mediated growth and then integrated into a fiber ferrule by optical deposition, which serve as SA in the ring laser cavity. The plasmonic properties of such nanoplates are measured by absorption spectrophotometry and their nonlinear optical properties are characterized by Z-scan. The measured nonlinear saturable absorption of the AgNPTs-based SA is 6.4%. In our laser, the dual-wavelength synchronous mode-locking is achieved at the center wavelengths of 1031.92 and 1033.24 nm with 3-dB spectral bandwidth of 0.52 and 0.46 nm, respectively, where 293-ps pulse trains with a repetition rate of 11.43 MHz are obtained at the pump power of 350 mW. The results demonstrate that the solution-processed AgNPTs are promising SA candidates for achieving stable and low-cost pulsed laser sources which could be used for spectroscopy and ultrafast photonics.

Surface Plasmon Resonance Dependent Third-Order Optical Nonlinearities of Silver Nanoplates

Abstract: A systematic study of the surface plasmon resonance (SPR)-dependent nonlinear optical response of Ag nanoplates is presented and discussed. The Ag nanoplates were synthesized using the well-known seed-mediated growth method. By performing the z-scan method with a nanosecond laser (532 nm, 5 ns), the optical nonlinearities of the Ag nanoplates, prepared tuning the SPR contribution in the 400–1000 nm range, were determined. The results showed a SPR-related competition between the saturable absorption and reverse saturable absorption mechanisms, while the nonlinear refraction changed from self-defocusing to self-focusing. Furthermore, the scattering effects contribute to determine the nature of the optical limiting response. The observed SPR-tunable third order optical nonlinearities make Ag nanoplates a suitable candidate to be used in different fields, i.e., laser pulse generation, optical limiting, or bio-imaging applications.

Laser Synthesized Graphene and Its Applications

Abstract: Since graphene was discovered, a great deal of research effort has been devoted to finding more and more effective synthetic routes, stimulated by its astounding properties and manifold promising applications. Over the past decade, laser synthesis has been proposed as a viable synthesis method to reduce graphene oxide to graphene as well as to obtain graphene from other carbonaceous sources such as polymers or other natural materials. This review first proposes to discuss the various conditions under which graphene is obtained from the reduction of graphene oxide or is induced from other materials using laser sources. After that, a wide range of applications proposed for the obtained materials are discussed. Finally, conclusions are drawn and the author’s perspectives are given.

Anisotropic Silver Nanomaterials by Photochemical Reactions: Synthesis and Applications.

Abstract: Silver-based nanoparticles have attracted a broad interest due to their outstanding optical and chemical properties and have been studied for applications in many fields. While different synthetic routes have been explored, photochemical synthesis has attracted a special interest for its limited use of chemicals and ease of control over the shape and size of the nanoparticles. This paper reviews the main factors affecting the synthesis of anisotropic silver nanoparticles, such as irradiation wavelength, pH, etc., and the role of specific key molecules, such as citrate. The paper is structured into different sections depending on how the synthesis is initiated; thus, after the introduction, the photochemical conversion reaction starting from nanoparticles, or seeds, obtained chemically, is covered, followed by reactions from nanoparticles obtained by laser ablation by seedless reactions. After that, the applications proposed for anisotropic nanoparticles obtained by the methods discussed in the previous sections are briefly covered and, finally, the conclusions and the author’s perspectives are given.

Copper Nanowires for Transparent Electrodes: Properties, Challenges and Applications

Abstract: Transparent electrodes are essential elements of devices bearing a screen or display, as well as solar cells, LEDs etc. To overcome the drawbacks presented by indium tin oxide, nanomaterials have been proposed for a long time as alternatives. Metal nanowires are particularly interesting for their high intrinsic electrical conductivity. Copper nanowires have attracted wide interest due to the low cost and high abundancy of the starting material. However, they are easily oxidized thus suitable strategies must be devised to prevent it. This review discusses the fundamental properties and challenges of copper nanowires, focusing on the efforts made to make them longer and thinner then the strategies to prevent oxidation and to join them in the network are presented. After that, mechanical properties are summarized and applications are presented, before conclusions and perspectives are finally given.

Fast One-Step Synthesis of Anisotropic Silver Nanoparticles

Abstract: The shape control of metal nanoparticles, along with the size, is critical for most of their applications as they control their optical properties. Anisotropic metal nanoparticles show superior performance in a number of applications compared to spherical ones. Shape control is usually achieved by a two-step process, where the first involves the formation of spherical nanoparticles and the second is about the actual shape transformation. In this paper, we report on a fast and facile synthesis of silver nanoplates in a single step, involving laser ablation of a silver target in a liquid medium while this is exposed to light irradiation and hydrogen peroxide flow. We obtained anisotropic particles with a mixture of shapes, of 70–80 nm in size and 10–20 nm in thickness, which showed a plasmon sensitivity greater than 200 nm/RIU.