Engineering plasmonic nanostructured surfaces by pulsed laser deposition

Abstract

The synthesis and the optical response of gold nanoparticles (NPs) and thin nanostructured films grown by pulsed laser deposition (PLD) are here studied. Different PLD process parameters-including background gas pressure and the number of laser shots as well as post-deposition annealing treatments-have been varied to control the growth of Au NPs and films, thus tuning the surface plasmon characteristics. The mechanisms of NPs and film growth have been explored performing a morphological characterization by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), and the correlation with the optical behavior is investigated. We show that the size distribution and the morphology of the as deposited Au NPs depend on growth mechanisms which are controlled by tuning the deposition process, while the optical behavior is strongly affected by the average size and surface density of NPs or by the length of percolated Au domains. Furthermore, nucleation in gas phase has been reported at high (1000 Pa Ar) background pressures, enabling independent control of NP size and coverage, contrary to surface driven NP growth by diffusion and aggregation on substrate.

Growth dynamics of pulsed laser deposited nanofoams

“…It is well understood that PLD carbon nanofoams are essentially void-rich, fractal-like structures made of carbon nanoparticles [30], with an average diameter ranging from a few nanometers up to tens of nanometers [7,18,19,21,31]. Production of nanoparticles by pulsed laser ablation has been observed both in nanosecond [32][33][34] and subpicosecond regimes [35][36][37]. Generally speaking, nanoparticles are formed in the first stages of laser ablation process either by a direct ejection from the target (typically in the case of subpicosecond laser pulses) or during the expansion of the ablated species in a background atmosphere.…”

Integrated Au/TiO2 Nanostructured Photoanodes for Photoelectrochemical Organics Degradation

“…It is clear that the large Au NPs at the bottom of the film (sample TiO 2 /Au) act as scattering centers and, while the Au/TiO 2 sample is not characterized by increased light diffusion, the combination of the two Au NP layers has a synergetic effect (sample Au/TiO 2 /Au with the highest haze). Small NPs on top or distributed inside the film are instead characterized by a plasmonic absorption feature centered at about 650-700 nm for the TiO 2 -Au sample (as reported in [23]), which is also characterized by a large absorption in the whole visible-near infrared (vis-NIR) range (transmittance <40% in the visible range and <60% in the NIR); Au NPs at the bottom of the film (~100 nm size) are, instead, characterized by plasmonic absorption centered at about 700-800 nm [22]. Synthesized samples are submitted to electrochemical characterization in order to investigate their behavior in dark and irradiated conditions.…”

“…An Edwards E306 thermal evaporator (Edwards) was employed to deposit a 10 nm Au film, followed by thermal de-wetting (air annealing at 500 • C with 4 • C/min ramp, 2 h dwell) to induce NP growth. The Au/TiO 2 sample (i.e., the configuration substrate/TiO 2 film/Au NPs) was obtained depositing a TiO 2 film by PLD (details above), followed by deposition of Au NPs by PLD, ablating an Au target in 1000 Pa Ar with a laser fluence of 2 J/cm 2 [22]. The Au/TiO 2 /Au sample was obtained by combining the Au/TiO 2 and the TiO 2 /Au synthesis procedures.…”

“…For a long time, our research group investigated nanostructured TiO 2 materials for photoelectrocatalytic applications [18][19][20][21], mostly facing the well-known major problems of TiO 2 which are the low quantum efficiency and the poor activation by visible light (i.e., solar light). More recently, some of us proposed the use of Pulsed Laser Deposition (PLD) for the synthesis of plasmonic Au NPs and their integration in hierarchical TiO 2 nanostructures [22], which have been preliminarily tested for the photodegradation of methyl orange under simulated natural sunlight [23]. Indeed, the use of hierarchical 3D nanostructures, with high roughness, can promote light absorption due the scattering effect over a large angular range.…”

Highly sensitive detection of estradiol by a SERS sensor based on TiO2 covered with gold nanoparticles

“…Three nominal thicknesses values of 3, 6 and 15 nm were chosen, in order to obtain NPs with different diameters (see Table 1). After deposition of Au, samples underwent an annealing treatment in a furnace at 500°C for 2 h, which leads to crystallization of TiO2 to the anatase phase (as demonstrated by Raman spectra, not shown) and caused a dewetting processes on the Au layer and the formation of NPs [33]. Evaporation-dewetting of Au on TiO2 layers with different porosity was aimed at exploiting the effect of the surface morphology on the formation of Au NPs with different size distribution and density.…”