Showing papers by "Vittorio Scardaci published in 2022"

Surface analysis insight note: Differentiation methods applicable to noisy data for determination of sp2‐ versus sp3‐hybridization of carbon allotropes and AES signal strengths

Abstract: The derivatives of the spectra are commonly used for quantification in Auger Electron Spectroscopy (AES) spectra, while the derivative of the KLL C Auger line has proven to be valuable in obtaining a measure of the relative proportions of sp2‐ and sp3‐hybridization using the D‐parameter in both AES and X‐ray Photoelectron Spectroscopy (XPS). Differentiation of X‐ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) spectra by numerical means is presented and illustrated for polymeric, such as PEEK and Nylon, as well as for graphitic materials including highly ordered pyrolytic graphite and graphene oxide. The most commonly available Savitzky–Golay method is explained mathematically and developed through the case of constructing a 5‐point quadratic polynomial convolution kernel suitable for differentiating spectra of adequate signal to noise. The concept of differentiation of spectra where signal to noise is less than adequate is also developed. Two alternative strategies to Savitzky–Golay differentiation are presented, which fit curves to data that allow derivatives to be obtained where Savitzky–Golay would otherwise fail. These alternative methods involve constructing a parametric curve that fits data over the entire energy interval of interest. Derivatives of spectra are then obtained by differentiating these parametric curves directly. A comparison of results for different materials for which specific sp2‐ vs sp3‐hybridized carbon proportions are of interest is used to emphasize the importance of characterizing methods used to differentiate spectra and understanding the characteristics of instrumentation used to measure spectra. The case for using Principal Component Analysis noise reduction with C KLL spectra is made for spectra collected from a heterogeneous graphene oxide sample.

Silver Nanoplate Composites as Nonlinear Saturable Absorbers for a Q-Switched Laser

Abstract: Metal nanomaterials have promising applications in ultrafast photonics due to their broadband operation, large third-order nonlinear susceptibility, and ultrafast recovery time. We realized a Q-switched pulsed erbium-doped fiber laser based on a silver nanoplate polyvinyl alcohol film as a saturable absorber. This film, with a modulation depth of 15.7%, was integrated into a fiber laser by means of a sandwich structure. We obtained Q-switched pulses in the 1.5-μm band, which plays an important role in telecommunications and atmospheric detection. Stable Q-switched pulses were obtained at the pump power of 135 mW, with a single pulse energy of 33.8 nJ, a pulse width of 2.3 μs, a repetition rate of 62.4 kHz, and a signal-to-noise ratio of about 45 dB. When increasing the pump power up to a maximum value of 246 mW, the maximum single pulse energy of 57.8 nJ was achieved. This study first demonstrates the potential of silver nanoplates as saturable absorbers in generating stable laser pulses with high energy.