From Aluminum Foil to Two-Dimensional Nanocrystals Using Ultrasonic Exfoliation

Abstract

Al nanostructures have unique optical properties such as widely tunable surface plasmon resonances from deep UV to NIR that can be used for label-free fluorescence enhancement and surface-enhanced Raman scattering. Various Al nanostructures have been fabricated using sophisticated "top-down" lithographic and "bottom-up" colloidal methods. Here, we developed a simple and efficient method of synthesizing two-dimensional (2D) aluminum (Al) nanocrystals from commercially available Al foil using ultrasonic exfoliation under ambient environment. 2D Al nanocrystals with sizes from a few hundred nanometers to several micrometers and thickness in the tens of nanometers were isolated through centrifugation separation. The exfoliated 2D Al nanocrystals are covered with a passivated Al 2 O 3 nanolayer. The determined exfoliation mechanism is a combination of the preferred cleavage along the (111) surface planes and layer-by-layer Al 2 O 3 exfoliation from the surface of the 2D Al nanocrystals. We demonstrate that the 2D Al nanocrystals can be assembled at water/air interface and transferred to different substrates to form 2D Al nanocrystal films. These 2D Al nanocrystal films exhibit surface plasmon resonance in the visible spectral range and show enhanced Raman signals of adenine using a 532 nm excitation. These 2D Al nanocrystal films could be further developed for new optical and sensing applications.

Colloidal Synthesis of Crystalline Aluminum Nanoparticles for UV Plasmonics

“…14 However, the presence of byproducts in the solution was hindering the usefulness of the method. Note that very recently, a related approach was reported by Lu et al, 11 who demonstrated the creation of crystalline 2D nanocrystals (flakes) after ultrasonic exfoliation of commercial Al foils. The method remains limited to the synthesis of 2D nanoparticles and their size is not under control.…”

“…While the chemical synthesis of gold and silver nanoparticles is common knowledge, the synthesis of Al nanoparticles is not so easy, with only a handful of reports published so far. [8][9][10][11] The underlying reason is the fact that the method used for noble metals, the reduction of a metallic salt, cannot be directly translated to aluminum because the classical reducers cannot reduce aluminum salt. Hence, other approaches are required.…”

Emerging metallenes: synthesis strategies, biological effects and biomedical applications

“…37 Lu et al ultrasonically exfoliated small pieces of aluminum foil into 2D aluminum sheets of approximately 1 mm in ethylene glycol. 90 Yadav et al employed an easily scalable technique to synthesize 2D metal alloys from 3D quasicrystal precursors. 91 They extracted the corresponding 2D structures of decagonal quasicrystals (QCs) from the bulk Al 66 Co 17 Cu 17 alloy via high-strength exfoliation in a pressurized ultrasonic reactor.…”

Colloidal Synthesis of Crystalline Aluminum Nanoparticles for UV Plasmonics

“…However, the presence of byproducts in the solution was hindering the usefulness of the method. Note that very recently, a related approach was reported by Lu et al, who demonstrated the creation of crystalline 2D nanocrystals (flakes) after ultrasonic exfoliation of commercial Al foils. The method remains limited to the synthesis of 2D nanoparticles and their size is not under control.…”

“…Furthermore, chemical approaches generally yields crystalline and shape-controlled nanoparticles, giving better quality (i.e., higher quality factor) plasmonic resonances. While the chemical synthesis of gold and silver nanoparticles is common knowledge, the synthesis of Al nanoparticles is not so easy, with only a handful of reports published so far. − The underlying reason is the fact that the method used for noble metals, the reduction of a metallic salt, cannot be directly translated to aluminum because the classical reducers cannot reduce aluminum salt. Hence, other approaches are required.…”