Pulsed laser-induced dewetting and thermal dewetting of Ag thin films for the fabrication of Ag nanoparticles

Abstract

Two different dewetting methods, namely pulsed laser-induced dewetting (PLiD)—a liquid-state dewetting process and thermal dewetting (TD)—a solid-state dewetting process, have been systematically explored for Ag thin films (1.9–19.8 nm) on Si substrates for the fabrication of Ag nanoparticles (NPs) and the understanding of dewetting mechanisms. The effect of laser fluence and irradiation time in PLiD and temperature and duration in TD were investigated. A comparison of the produced Ag NP size distributions using the two methods of PLiD and TD has shown that both produce Ag NPs of similar size with better size uniformity for thinner films (<6 nm), whereas TD produced bigger Ag NPs for thicker films (≥8–10 nm) as compared to PLiD. As the film thickness increases, the Ag NP size distributions from both PLiD and TD show a deviation from the unimodal distributions, leading to a bimodal distribution. The PLiD process is governed by the mechanism of nucleation and growth of holes due to the formation of many nano-islands from the Volmer−Weber growth of thin films during the sputtering process. The investigation of thickness-dependent NP size in TD leads to the understanding of void initiation due to pore nucleation at the film-substrate interface. Furthermore, the linear dependence of NP size on thickness in TD provides direct evidence of fingering instability, which leads to the branched growth of voids.

Formation and Removal of Alloyed Bimetallic Au–Ag Nanoparticles from Silicon Substrates for Tunable Surface Plasmon Resonance

“…The morphology of both the undewetted Au­(2.6 nm)­Ag­(2.5 nm) (Figure a) and Ag­(2.3 nm)­Au­(2.3 nm) (Figure g) films shows bicontinuous structures, indicating Volmer–Weber growth in which thin film growth proceeds through the formation of nanoislands . Similar thin film morphologies have been reported for both Au and Ag films individually. At 80 °C (Figure b,h), both bilayer films show deepening of the grain boundaries and initiation of voids.…”

“…The thermal dewetting of single-layer Au and Ag along with Pt on SiO 2 /Si substrates has been studied in detail in our previous work. , It was found that void growth started right above the Hüttig temperature of the metal and complete dewetting into isolated NPs occurred at a temperature in between the Hüttig and Tammann temperatures, the temperatures at which the surface and bulk atoms in the metal become mobile, respectively. Considering the values of the Hüttig and Tammann temperatures for Ag (97 and 344 °C) and Au (128 and 396 °C), the effect of temperature on the dewetting of Au–Ag bilayer thin films was studied in the range of 80–450 °C at a fixed time of 30 min.…”

“…For example, the diameters of Au NPs from thermal dewetting of 1.7 and 2.8 nm thick Au film are 7 ± 1 and 18 ± 4 nm, respectively, 21 and that of the Ag NPs from 2.6 nm thick Ag film is 16 ± 4 nm. 34 This strongly indicates that it is the NPs. 31 The surface diffusivity of Ag is known to be ∼2 orders of magnitude greater than that of Au, 38 which explains why mixing Au with Ag leads to an improvement in Au dewetting but hinders the dewetting ability of Ag.…”

“…The bilayer metallic thin films were prepared by sequentially sputtering each metal layer. Thermal dewetting to make monometallic and bimetallic nanostructures was described previously. , In short, thermal dewetting of Au, Ag, and Au–Ag bilayer films was carried out under vacuum (∼2 × 10 –3 Torr) in a quartz tube at temperatures ranging from 80 to 450 °C for 30 min.…”

β-Ga2O3 Nanostructures: Chemical Vapor Deposition Growth Using Thermally Dewetted Au Nanoparticles as Catalyst and Characterization

“…Before sputtering, the phosphorous-doped n -type Si (100) wafers with a resistivity of 1–20 Ω cm (Wafer World Inc., West Palm Beach, FL, USA) were cleaned successively with acetone, ethanol, and methanol, and dried using high-purity N 2 gas (99.999%, Praxair). Details of thermal dewetting to make metal NPs were described previously [ 36 , 37 , 38 ]. Briefly, thermal dewetting of 2.9 nm thick Au films on Si substrates was carried out in vacuum (~2 × 10 −3 Torr) at 600 °C for 1 h.…”