Monodisperse Colloidal Gallium Nanoparticles: Synthesis, Low Temperature Crystallization, Surface Plasmon Resonance and Li-Ion Storage

Abstract

We report a facile colloidal synthesis of gallium (Ga) nanoparticles with the mean size tunable in the range of 12–46 nm and with excellent size distribution as small as 7–8%. When stored under ambient conditions, Ga nanoparticles remain stable for months due to the formation of native and passivating Ga-oxide layer (2–3 nm). The mechanism of Ga nanoparticles formation is elucidated using nuclear magnetic resonance spectroscopy and with molecular dynamics simulations. Size-dependent crystallization and melting of Ga nanoparticles in the temperature range of 98–298 K are studied with X-ray powder diffraction, specific heat measurements, transmission electron microscopy, and X-ray absorption spectroscopy. The results point to delta (δ)-Ga polymorph as a single low-temperature phase, while phase transition is characterized by the large hysteresis and by the large undercooling of crystallization and melting points down to 140–145 and 240–250 K, respectively. We have observed size-tunable plasmon resonance in the ultraviolet and visible spectral regions. We also report stable operation of Ga nanoparticles as anode material for Li-ion batteries with storage capacities of 600 mAh g–1, 50% higher than those achieved for bulk Ga under identical testing conditions.

Gallium Plasmonics: Deep Subwavelength Spectroscopic Imaging of Single and Interacting Gallium Nanoparticles

“…NP growth took 263 s at 300 K resulting in Ga NPs in a liquid state. 10,16 During deposition the Ga film self-assembled into nanoparticles through a process of adsorption, surface diffusion, and coalescence through Ostwald ripening. 31,63 Real-time monitoring of this process was performed by in situ spectroscopic ellipsometry (SE) from λ 0 = 200À820 nm at a 20°g razing angle of incidence, permitting the termination of growth when the desired optical properties were attained ( Figure 1E).…”

“…These methods include self-assembly during molecular beam epitaxy (MBE), 6,7 optically regulated self-assembly, 8 thermal evaporation, 9 and colloidal synthesis. 10 When exposed to atmosphere following synthesis, Ga NPs form a thin, self-terminating native oxide shell that protects the pure metallic core. This Ga 2 O 3 oxide layer, 11 which is 0.5À3 nm thick, 10À12 provides both structural and chemical stability, allowing the optical response of Ga NPs to remain stable B under atmospheric conditions over many months or years.…”

“…This Ga 2 O 3 oxide layer, 11 which is 0.5À3 nm thick, 10À12 provides both structural and chemical stability, allowing the optical response of Ga NPs to remain stable B under atmospheric conditions over many months or years. 7,10 This stability exceeds other UV-compatible plasmonic materials including silver, which lacks a passivating native oxide, and aluminum. 13,14 Already, novel applications have been demonstrated that rely on the unique optical and material properties of Ga NPs: UV spectroscopy substrates for simultaneous fluorescence and surface-enhanced Raman spectroscopy (SERS), 15 highly compact solidÀliquid phase change memory elements, 16À21 phase transition nonlinear substrates, 22 and graphene/plasmon nanocomposites.…”

“…7 Within such arrays, standard optical microscopy techniques, such as darkfield spectroscopy, cannot resolve single particles as the interparticle separation lies substantially below the far-field diffraction limit. Recent progress in synthesis has allowed the preparation of colloidal particles with size distributions of 7À8%, 10 although inhomogeneous broadening will still affect the resulting ensemble spectra.…”

Plasmonics in the Ultraviolet with Aluminum, Gallium, Magnesium and Rhodium

“…Moreover, the new range of bottom-up fabrications techniques that allow the production of Ga NPs, make this material very appealing for practical purposes. These fabrication methods include molecular beam epitaxy (MBE) [24,56], optically regulated self-assembly [57], thermal evaporation [58], and colloidal synthesis [59]. In addition, unlike either Al or Mg, its very low tendency to oxidation (1-2 nm oxide shell thickness), minimally affects its optical properties, keeping them stable over months or even years [23,24].…”