Conversion of silver nanoprisms into colloidal nanoparticles induced by femtosecond laser pulses

Abstract

Shape transformation of silver nanoprisms in aqueous solution was studied using femtosecond laser pulses. Irradiation of a pulsed Ti:Sapphire laser at 800 nm caused the shape change of the nanoprisms from triangle into sphere, forming a stable colloid of a narrow size distribution with the particle diameters having ∼10 nm. The effects of laser fluence on fragmentation and conversion were investigated using UV-vis absorption spectroscopy and transmission electron microscopy. The mechanism of laser-induced colloid formation is discussed.Absorption spectra of the silver nanoprisms after exposure to 800 nm femtosecond laser pulses for various time lengths. The important things of materials research in nanometer regime are not only the materials production but also the exploration of both chemical and physical properties of the nanomaterials for practical applications. The properties of these nanostructured materials show a strong dependence on size and shape [1]. There is currently an intense interest in the utilization of improved experimental equipments or techniques such as plasmon excitation [2], femtosecond laser pulses [3] and nanosphere lithography [4] to control the growth or to obtain the detailed knowledge of the ultrafast dynamics of the surface plasmons or other optical properties of metallic nanostructures, because these metallic nanoparticles with specific morphologies and structures exhibit unusual optical properties and have important applications in catalysis [5], biotechnology [6], optoelectronics [7], and other areas [8]. Once the nanoparticles are formed in the host materials, it is very difficult to change their size and shape with traditional technologies available. In the case of laser irradiation, however, the particles can be melted, reshaped or fragmented without significantly perturbing the environment in glasses or other matrix media. Since the heating is very selective, thus, the laser-induced shape change of metal nanostructures not only provide a simple means for "post-preparation" shape control but also pertain to the physically important issue of laser-nanostructure interactions and some complicated relaxation dynamics of the deposited laser energy [9]. Most of the early studies on the laser-induced change of metal nanoparticles were concentrated on the size reduction of noble metal particles, particularly gold and silver, as a breaking-down process to produce fine metal nanoparticles [10,11]. Among others, the recent laser-induced transformation studies of gold nanorods in colloidal solutions or metal-island films into spherical particles represent a particularly drastic shape change using ultrafast femtosecond or nanosecond laser pulses [12][13][14]. Therefore, to apply Conversion of silver nanoprisms into colloidal nanoparticles induced by femtosecond laser pulses

Laser‐induced shape transformation and electrophoretic analysis of triangular silver nanoplates

“…3). We consider that as triangular silver nanoplates have been reported to decompose into colloidal nanoparticles by laser pulses 22, laser irradiation truncates the vertices of the triangular silver nanoplates to form nearly regular‐hexagonal and spherical silver nanoplates gradually. Compared with triangular nanoplates, the dipole resonance peaks of nearly regular‐hexagonal and spherical silver nanoplates are decreased due to the lack of sharp corners 5.…”

“…Since the heating is very selective, the laser‐induced shape change of metal nanostructures provides simple means for post‐preparation shape control 11–17. Most of the early studies on the laser‐induced change of metal nanoparticles were concentrated on the size reduction of noble metal particles as a breaking‐down process to produce fine metal nanoparticles 18–22. We have recently reported that not only the mutual transposition of the core and the shell of a Au@Pt core/shell nanosphere but also the excavation of the silver core of a Ag@Pt nanoparticle can be obtained by exciting the surface plasmon resonances of platinum with picosecond laser pulses to form a new, reversed core/shell Pt@Au nanosphere 16 and a hollow platinum nanosphere 17, respectively.…”

“…The laser‐induced formation mechanism of noble metal nanostructures is not understood well yet although the laser‐induced size reduction and shape alteration of gold nanoparticles in water have been explained to occur through melting and vaporization 11, 14, 20, 21. The dependence of melting temperatures on metals has been exploited to fabricate or alter metal nanocomposites optically 9–17, 21, 22. Considered that the absorption coefficient of metallic particles depends on the particle size according to the Mie theory, it is feasible to excite nanoparticles size selectively using the wavelength tunability of the laser.…”

On Nanoparticle Formation by Laser Ablation in Liquids

“…9 In addition, laser pulses can be also used to fragment, reshape, and conjugate NPs. [10][11][12] Under carefully chosen experimental conditions, the stability of the obtained colloidal solutions can be very high, so that the NPs can be used for many applications in such fields as medicine, sensing, electronics, optics, and biophotonics. Colloidal gold NPs, for instance, are used for tumor-targeted drag delivery and cancer therapy.…”

Combining superior surface enhanced Raman scattering and photothermal conversion on one platform: a strategy of ill-defined gold nanoparticles

“…3e and f), the plasmon band becomes very broad, which may originate from the overlap of different dipole resonances. 23 It is worth noting that the characteristic plasmon for the ID-GNPs occurs as well, but it extends to the near infrared region (Fig. 3c and d).…”