Photothermal Heating of Nanowires

Abstract

A theoretical model is developed here in tandem with single-beam laser trapping experiments to elucidate the effects of the numerous thermal, optical, and geometric parameters that affect internal temperature distributions within finite nanowires (NWs) during laser irradiation. Analytical solutions to the heat-transfer equation are presented to predict internal temperature distributions within individual nanowires based on numerical calculations of the internal electromagnetic heat source. Single-beam laser-trapping experiments are performed to measure photothermal heating of silicon NWs. Silicon has not been considered to date for photothermal heating applications due to its indirect band gap and low absorption coefficient in the near-infrared tissue-transparency window. We also show here that ion implantation may be used to increase the optical absorption of silicon nanowires (SiNWs), leading to significant heating to temperatures greater than 42 °C in an aqueous environment at an irradiance of 3 MW/cm2. Experimental observations of photothermal heating agree well with theoretical predictions. Calculations for comparison with amorphous carbon NWs reveal significantly greater heating effects, as well as internal radial gradients not observed for SiNWs.

Laser refrigeration of hydrothermal nanocrystals in physiological media

“…The laser trap setup is outlined in Materials and Methods, and the CBM temperature analysis is described in SI Appendix, section A. Briefly, the single-beam laser trap was used to extract the surrounding local temperature profile of YLF particles through observations of forward-scattered laser radiation profiles that are processed to yield both the calibrated power spectral density and diffusion coefficient for individual YLF crystals (33). The laser refrigeration of 10% (mol%) Yb 3+ :YLF (i.e., 10% Yb 3+ ions, 90% Y 3+ ions) nanocrystals by more than 10°C in PBS and Dulbecco's modified Eagle medium (DMEM) was observed at a trapping wavelength of λ = 1,020 nm (Table 1).…”

“…Trapping data were acquired using a diode-pumped solid-state Table 1 were determined using methods outlined in ref. 33. Silica beads (SS04N/9857, Bangs Laboratories) were used for their monodisperse size distribution (1,010-nm diameter), and they have shown to minimally heat when trapped with a laser tweezer at NIR wavelengths (50).…”

Nanoscale materials for hyperthermal theranostics

“…[57]). The doping is achieved through either intrinsic defects (such as copper deficiencies in copper chalcogenides 58–60 and oxygen deficiencies in transition-metal oxides 61,62 ) or the addition of extrinsic impurities 63,64 . Moreover, while the NIR absorption of metallic NPs is largely due to their LSPR, NIR absorption in semiconductors is a combined consequence of their LSPR as well as band-to-band transition of the charge carrier.…”

“…Elemental silicon has been shown to be biocompatible in human subjects and will biodegrade into soluble silicic acid followed by urinary excretion with a half-life of less than 3 hours for 90% of the absorbed silicon 70 . For these reasons, many semiconducting nanoparticles have been examined as potential PTT agents, including copper chalcogenides 58,59,67,71–74 , cadmium chalcogenides 75 , transition-metal oxides 61,62,66,76–78 , bismuth selenide 79,80 , germanium 81 , and silicon 64,68,82–84 .…”

“…For instance, the magnitude of internal electric fields can be increased for constant incident irradiance by tuning the nanoparticle size to a morphology-dependent resonance (MDR) 89–91 . Additionally, the effective photothermal heating efficiency of an irradiated nanoparticle has been shown to be highly dependent on its defect concentration which can be altered using methods such as ion implantation 64 . The defects act as recombination centers for generated bound excitons as well as scattering sites for both charge carriers and phonons.…”