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The optical trapping of colloidal semiconductor nanomaterials would enable single-particle photophysics, sensing, and chemical measurements. Yet, the trapping of these materials has lagged behind other dielectric and metallic materials due to the prevalence of aqueous solvents in optical trapping experiments, which are not suitable for many semiconductors. Here, we trap particles in multiple solvents and study the impact of nonaqueous solvents on optical trapping dynamics. These experiments and calculations show that there exists an optimal refractive index of the media that maximizes trapping strength and for colloidal nanomaterials a universal relationship to enhance trap strength. We also find that viscosity has no impact on the trap strength and changes only the residence times of particles in unstable traps. Trap stiffness measurements also show that photothermal effects, which are enhanced in nonaqueous solvents, can lead to convection, which modifies trap stiffnesses. These results provide an understanding of how solvent selection impacts trapping dynamics and general design rules for experiments in nonaqueous solvents, opening the door for improved sensing, chemistry, and photophysics studies using colloidal micro- and nanomaterials.
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Optically oriented attachment of nanoscale metal-semiconductor heterostructures in organic solvents via photonic nanosoldering
Abstract As devices approach the single-nanoparticle scale, the rational assembly of nanomaterial heterojunctions remains a persistent challenge. While optical traps can manipulate objects in three dimensions, to date, nanoscale materials have been trapped primarily in aqueous solvents or vacuum. Here, we demonstrate the use of optical traps to manipulate, align, and assemble metal-seeded nanowire building blocks in a range of organic solvents. Anisotropic radiation pressure generates an optical torque that orients each nanowire, and subsequent trapping of aligned nanowires enables deterministic fabrication of arbitrarily long heterostructures of periodically repeating bismuth-nanocrystal/germanium-nanowire junctions. Heat transport calculations, back-focal-plane interferometry, and optical images reveal that the bismuth nanocrystal melts during trapping, facilitating tip-to-tail “nanosoldering” of the germanium nanowires. These bismuth-semiconductor interfaces may be useful for quantum computing or thermoelectric applications. In addition, the ability to trap nanostructures in oxygen- and water-free organic media broadly expands the library of materials available for optical manipulation and single-particle spectroscopy.
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- Award ID(s):
- 1719797
- PAR ID:
- 10153541
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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