Nanoscale size effects give rise to near-field thermal considerations when heating nanoparticles under high laser power. We solve Maxwell’s equations in the frequency domain to analyze near-field thermal energy effects for three nanoparticle assemblies with different variances in particle sizes and show that heat dissipation generally decreases as the spread in nanoparticle sizes increases within the nanoparticle packing. For this study, log-normally distributed copper nanoparticle packings with a mean radius of 116 nm and three different standard deviations (12, 48, and 84 nm) were created by using a discrete element model in which a specified number of particles is generated. The nanoparticle packings in the simulation are created by randomly placing each nanoparticle into the packing domain with a random initial velocity and a position. The nanoparticles are then allowed to interact with each other under gravitational and weak van der Waals forces until they settle to form a stable packing configuration. A finite-difference frequency-domain analysis, which yields the electromagnetic field distribution, is then applied to the packing by solving Maxwell’s equations to obtain absorption, scattering, and extinction coefficients. This analysis is used to calculate the surface plasmon effects due to the electromagnetic coupling between the nanoparticles and the dielectric medium under the different distributions and show that different particle distributions can create different plasmonic effects in the packing domain, which results in nonlocal heat transport. Overall, this analysis helps to reveal how sintering quality can be enhanced by creating stronger laser–particle interactions for specific groups of nanoparticles.
Nanoscale size effects bring additional near-field thermal considerations when heating nanoparticles under
high laser power. Scanning electron micrographs of a typical copper nanoparticle powder bed reveal that the
nanoparticles are distributed log-normally with 116 nm mean radius and 48 nm standard deviation. In this paper, we
solve Maxwell’s equations in frequency domain to understand near-field thermal energy effects for different standard
deviations. Log-normally distributed copper nanoparticle packings which have 116 nm mean radius with 3 different
standard deviations (12, 48 and 84 nm) are created by using Discrete Element Model (DEM) in which certain number
of particles are generated, specifying a position and radius for each. The solid particles interacting with the
neighbouring particles are to be distributed randomly into the bed domain with an initial velocity and a boundary
condition, which creates the particle packing within a defined time range under gravitational and weak van der Waals
forces. Finite Difference Frequency Domain analysis, which yields the electromagnetic field distribution, is applied
by solving Maxwell's equations to obtain absorption, scattering and extinction coefficients. We show that different
particle distributions create different plasmonic effects in the bed domain which results in non-local heat transport.
We calculate the surface plasmon effect due to the electromagnetic coupling between the nanoparticles and the
dielectric medium under the different distributions. This analysis helps to reveal how sintering quality can be enhanced
by creating stronger laser-particle interactions for specific groups of nanoparticles.
Raman scattering is a powerful probe of local bonding, strain, temperature, and other properties of materials via their influence on vibrational modes or optical phonons. Tip-enhanced Raman spectroscopy (TERS), in which plasmonic modes are excited at the apex of a metal-coated scanning probe tip, enables Raman scattering signals to be detected from nanoscale volumes with precise positional control. We discuss the application of TERS to characterize a variety of semiconductor nanostructures. In studies of Ge-SiGe core-shell nanowires, we measure spatially resolved Raman spectra along the length of a tapered nanowire to demonstrate the ability to measure local strain distributions with nanoscale spatial resolution. In tip-induced resonant Raman spectroscopy of monolayer and bilayer MoS2, we observe large enhancements in Raman signal levels measured for MoS2 associated with excitation of plasmonic gap modes between an Au-coated probe tip and Au substrate surface onto which MoS2 has been transferred. Transitions in B exciton photoluminescence intensity between monolayer and bilayer regions of MoS2 are observed and discussed. Significant differences in nanoscale Raman spectra between monolayer and bilayer MoS2 are also observed. The origins of specific resonant Raman peaks, their dependence on MoS2 layer thickness, and spatial resolution associated with the transition in Raman spectra between monolayer and bilayer regions are described.
We report progress in developing optimized diffraction gratings for coupling solar radiation from the airmass 0 spectrum
into waveguide modes of ultrathin quantum dot solar cells (QDSCs). Electromagnetic simulations have been used to
optimize the grating geometry and to analyze the nature of diffraction within the device structure. These results suggest
that increases in photocurrent of over 100% at wavelengths of QD absorption, corresponding to over 10% improvement
in short-circuit current, can be achieved in optimal ultrathin devices by incorporating gratings in the rear contact.
A variety of approaches are examined for exploiting the optical properties of metal or dielectric nanoparticles, particularly those associated with surface plasmon polariton resonances, to improve the performance of semiconductor photodetectors and photovoltaic devices. Early and recent concepts for employing optical absorption and local electromagnetic field amplitude increases associated with surface plasmon polariton excitation to improve photocurrent generation in organic photovoltaic devices are briefly reviewed. The application of optical scattering properties of nanoparticles to improve transmission of optical power into, and consequently photocurrent response in, Si and a-Si:H photodiodes is then described, and effects related to scattered-wave phase shifts and interference effects between scattered and directly transmitted wave components in producing either enhancement or suppression of photocurrent response at different wavelengths are discussed. Coupling of photons incident normal to the surface of a semiconductor thin-film device into lateral, optically confined paths within waveguide structures formed by refractive index contrast either within the semiconductor structure, or between the semiconductor and surrounding dielectric material, is discussed in the context of early and recent studies of such coupling in silicon-on-insulator photodetectors, and recent work on engineering of photon propagation paths in III-V compound semiconductor quantum well solar cells.
We describe experimental and theoretical analysis of coupling of light scattered by metal or dielectric nanoparticles into
waveguide modes of InP/InGaAsP quantum-well solar cells. The integration of metal or dielectric nanoparticles above
the quantum-well solar cell device is shown to couple normally incident light into lateral optical propagation paths, with
optical confinement provided by the refractive index contrast between the quantum-well layers and surrounding material.
Photocurrent response spectra yield clear evidence of scattering of photons into the multiple-quantum-well waveguide
structure, and consequently increased photocurrent generation, at wavelengths between the band gaps of the barrier and
quantum-well layers. With minimal optimization, a short-circuit current density increase of 12.9% and 7.3% and power
conversion efficiency increases of 17% and 1% are observed for silica and Au nanoparticles, respectively. A theoretical
approach for calculating the optical coupling is described, and the resulting analysis suggests that extremely high
coupling efficiency can be attained in appropriately designed structures.