Plasmonic coupling in closed-packed ordered gallium nanoparticles

Abstract

plasmonic gallium (Ga) nanoparticles (nps) are well known to exhibit good performance in numerous applications such as surface enhanced fluorescence and Raman spectroscopy or biosensing. However, to reach the optimal optical performance, the strength of the localized surface plasmon resonances (LSPRs) must be enhanced particularly by suitable narrowing the NP size distribution among other factors. With this purpose, our last work demonstrated the production of hexagonal ordered arrays of Ga NPs by using templates of aluminium (Al) shallow pit arrays, whose LSPRs were observed in the VIS region. The quantitative analysis of the optical properties by spectroscopic ellipsometry confirmed an outstanding improvement of the LSPR intensity and full width at half maximum (FWHM) due to the imposed ordering. Here, by engineering the template dimensions, and therefore by tuning Ga NPs size, we expand the LSPRs of the Ga NPs to cover a wider range of the electromagnetic spectrum from the UV to the IR regions. More interestingly, the factors that cause this optical performance improvement are studied with the universal plasmon ruler equation, supported with discrete dipole approximation simulations. the results allow us to conclude that the plasmonic coupling between nps originated in the ordered systems is the main cause for the optimized optical response. The interaction between metallic nanoparticles (NPs) and the electromagnetic radiation has constituted the driving force for the studies of the light-matter interaction during the last decades 1-3. Due to their free electrons, the metallic NPs are capable to concentrate and amplify the electric near-field in the vicinities of their surfaces. The electron oscillations (plasmons) resonate with light at a certain frequency that is commonly known as the localized surface plasmon resonance (LSPR). This frequency strongly depends on the NP size, shape, contact angle, environment and, especially, on the metal type 4. For instance, in the most studied elements, silver (Ag) and gold (Au), their LSPRs are quite restricted to the visible (VIS) region 5 due to their low losses and interband transitions in the ultraviolet (UV) region. Thus, during the last years, there has been an effort in the scientific community to search for alternative metals 6-8. Among others, liquid gallium (Ga) has emerged as an ideal plasmonic candidate 9,10 since its LSPRs can be tuned from the UV to the infrared (IR) due to the lack of strong interband transitions in this wide region 11 in contrast to other candidates such as Al 12 , Cu 13 or Ni 14. This spectral tunability can be achieved by means of different methods: changing the NP size 15 , contact angle or substrate 16,17 , varying the gallium oxide shell thickness 18 , by hybridization with other plasmonic NPs 19 or by alloying 9,20. In addition to this, the Ga NPs can be grown in a facile, fast and up-scalable method such as Joule-effect thermal evaporation 21,22. This synthesis technique produces self-assembled hemispherical NPs formed by a liquid G...

Nanohelix‐Induced Optical Activity of Liquid Metal Nanoparticles

“…It agrees well with the previous results that a red shift of LSPR results from enlarging NPs. [1,37] The Ga NPs appear to have some deformation from a sphere, which can be quantitatively evaluated through calculating the circularity given by…”

“…The attached Ga NPs generally increase in their sizes with an increase of T Ga (Figure 2c-I,II,III; Figures S4, S6, and S8, Supporting Information), leading to red shift of LSPR (which will be discussed in Figure 3b) and the resonant CD peak. [1,34,37] For the helical templates with a P of ≈60 nm, with an increase of T Ga from 3 to 20 nm the Ga NPs become bigger (with an increase of d from 13 ± 2 nm to 30 ± 17 nm, Figure 2c-I) and the number of the Ga NPs on a SiO 2 NH appears to decrease (insets in Figure 2b-I), probably ascribed to an aggregation of the growing liquid Ga NPs resulting from an increase of T Ga . Note that the number of the Ga NPs attaching to an NH could not be quantitatively characterized, because the Ga NPs were immobilized on the 3D helical surfaces that could not be characterized using the 2D-projection mode of TEM.…”

MOCVD growth of gallium and indium microparticles for SERS applications

“…In addition to SERS in Au and Ag nanoparticles there has been an effort to search for alternative metals [8][9][10][11][12], in particular Al [13][14][15][16], Cu [17], Ni [18] or In [19][20][21]. In addition to these metals gallium (Ga) has emerged as an interesting plasmonic candidate [22][23][24][25][26]. Gallium nanoparticles can be interesting since their localized surface plasmon resonances can be tuned from UV to infrared due to the lack of any strong inter-band transitions in this range.…”

“…Ga nanoparticles can be grown by Joule-effect thermal evaporation [23,27] or by the MOCVD method [22]. Both growth methods produce hemispherical nanoparticles in the form of a liquid Ga core and an outer part composed of gallium oxide which maintains the stability of the structure [28].…”

Modification of the Mechanical Properties of Core‐Shell Liquid Gallium Nanoparticles by Thermal Oxidation at Low Temperature

“…Among the wide range of LMNPs and their alloys, [4] gallium (Ga) based LMNPs have stood out over other materials, [19,20] mainly because of their metallic properties since their local ized surface plasmon resonances (collective oscillations of elec trons) can be tuned from the ultraviolet to the infrared range of the electromagnetic spectrum. [21] Ga NPs can be grown by a simple, fast, and costeffective manner by thermal evaporation at low substrate temperature, which makes them compatible with many conductive and insulating substrates. [22][23][24] During deposition on flat surfaces, liquid Ga forms truncated, quasi hemispherical NPs due to the surface tension induced relaxa tion.…”