Laser-induced heat and momentum transfer in nanostructure processing

Abstract

The ability to engineer materials with precise atomic structure represents one of the major challenges in chemistry and materials science. Steps toward this goal have led to applications in medicine, chemistry, physics, and engineering. Among the many possible synthetic parameters, light with wavelengths close to nanomaterial's size plays an increasingly important role due to its ability to resonantly target nanomaterials and to create highly non-equilibrium environments to explore new chemistry. Here, we leveraged Mie theory, chemistry, and photothermal effects to drive phase transformations in carbon and to assemble nanomaterial heterostructures. In the first part of this work, we developed a bottom-up method to synthesize doped nanodiamond with defects defined by small molecules. To demonstrate this process, we synthesized carbon aerogels doped with small molecules and drove a phase transformation at high pressures with photothermal heating. Photoluminescence revealed that the small molecules doped into the carbon aerogel persisted as active color centers in the nanodiamond product. These results open the door for designer defects that are precisely controlled by the stereochemistry of the molecular dopant, rather than thermodynamics. In addition, microscopy studies of the doped nanodiamond also revealed the incorporation of noble gas pressure media, which were previously thought to act only as spectators, challenging the existing view of the high pressure community. By leveraging the rapid timescale of photothermal heating, we also synthesized a new form of carbon with a rhombohedral unit cell, belonging to the Pban space group. We have tentatively named the phase Pban-carbon. In the second part of this work, we used light in the form of an optical trap, to manipulate, align, and assemble nanomaterial building blocks into complex heterostructures. To expand the range of accessible nanomaterials, we conducted these experiments in organic solvents for the first time. The fivefold decrease in thermal conductivity in organic solvents compared to water led to a nonlinear increase in temperature. We measured these temperatures optically with ratiometric quantum dots and used them to solder germanium nanorods together with bismuth nanocrystals.