Ag colloids and arrays for plasmonic non-radiative energy transfer from quantum dots to a quantum well

Non-radiative energy transfer (NRET) can be an efficient process of benefit to many applications including photovoltaics, sensors, light emitting diodes and photodetectors. Combining the remarkable optical properties of quantum dots (QDs) with the electrical properties of quantum wells (QWs) allows for the formation of hybrid devices which can utilize NRET as a means of transferring absorbed optical energy from the QDs to the QW. Here we report on plasmon-enhanced NRET from semiconductor nanocrystal QDs to a QW. Ag nanoparticles in the form of colloids and ordered arrays are used to demonstrate plasmon-mediated NRET from QDs to QWs with varying top barrier thicknesses. Plasmon-mediated energy transfer. (ET) efficiencies of up to similar to 25% are observed with the Ag colloids. The distance dependence of the plasmon-mediated ET is found to follow the same d-4 dependence as the direct QD to QW ET. There is also evidence for an increase in the characteristic distance of the interaction, thus indicating that it follows a Frster-like model with the Ag nanoparticle-QD acting as an enhanced donor dipole. Ordered Ag nanoparticle arrays display plasmon-mediated ET efficiencies up to similar to 21%. To explore the tunability of the array system, two arrays with different geometries are presented. It is demonstrated that changing the geometry of the array allows a transition from overall quenching of the acceptor QW emission to enhancement, as well as control of the competition between the QD donor quenching and ET rates

Near-field relaxation of a quantum emitter to 2D semiconductors: surface dissipation and exciton polaritons

The total spontaneous emission rate of a quantum emitter in the presence of an infinite MoS2 monolayer is enhanced by several orders of magnitude, compared to its free-space value, due to the excitation of surface exciton polariton modes and lossy modes. The spectral and distance dependence of the spontaneous emission rate are analyzed and the lossy surface wave, surface exciton polariton mode and radiative contributions are identified. The transverse magnetic and transverse electric exciton polariton modes can be excited for different emission frequencies of the quantum emitter, and their contributions to the total spontaneous emission rate are different. To calculate these different decay rates we use the non-Hermitian description of light-matter interactions, employing a Green\u27s tensor formalism. The distance dependence follows different trends depending on the emission energy of the quantum emitter. For the case of the lossy surface waves, the distance dependence follows a z?n,n=2,3,4, trend. When transverse magnetic exciton polariton modes are excited, they dominate and characterize the distance dependence of the spontaneous emission rate of a quantum emitter in the presence of the MoS2 layers. The interaction between a quantum emitter and a MoS2 superlattice is investigated, and we observe a splitting of the modes supported by the superlattice. Moreover, a blueshift of the peak values of the spontaneous emission rate of a quantum emitter is observed as the number of layers is increased. The field distribution profiles, created by a quantum emitter, are used to explain this behavior

Nanoplasmonic Sensing at the Carbon-Bio Interface: Study of Protein Adsorption at Graphitic and Hydrogenated Carbon Surfaces

Various forms of carbon are known to perform well as biomaterials in a variety of applications and an improved understanding of their interactions with biomolecules, cells, and tissues is of interest for improving and tailoring their performance. Nanoplasmonic sensing (NPS) has emerged as a powerful technique for studying the thermodynamics and kinetics of interfacial reactions. In this work, the in situ adsorption of two proteins, bovine serum albumin and fibrinogen, were studied at carbon surfaces with differing chemical and optical properties using nanoplasmonic sensors. The carbon material was deposited as a thin film onto NPS surfaces consisting of 100 nm Au nanodisks with a localized plasmon absorption peak in the visible region. Carbon films were fully characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and spectroscopic ellipsometry. Two types of material were investigated: amorphous carbon (a-C), with high graphitic content and high optical absorptivity, and hydrogenated amorphous carbon (a-C:H), with low graphitic content and high optical transparency. The optical response of the Au/carbon NPS elements was modeled using the finite difference time domain (FDTD) method, yielding simulated analytical sensitivities that compare well with those observed experimentally at the two carbon surfaces. Protein adsorption was investigated on a-C and a-C:H, and the protein layer thicknesses were obtained from FDTD simulations of the expected response, yielding values in the 1.8–3.3 nm range. A comparison of the results at a-C and a-C:H indicates that in both cases fibrinogen layers are thicker than those formed by albumin by up to 80%