In this contribution we present a theoretical investigation of the energy transfer efficiency between quantum systems placed in proximity of a monolayer of conducting graphene. We calculate the spontaneous emission rate of a quantum system and the energy transfer rate between a donor-acceptor pair, and thus the energy transfer efficiency, using a Green's tensor formalism. The direct interaction between the donor and acceptor dominates when they are close to each other, but is modified from its free-space behavior due to the presence of the graphene monolayer and its interaction with the donor and acceptor. We report on a very large influence of the graphene monolayer on the energy transfer efficiency due to both the Förster mechanism and the propagating graphene plasmon mode. In particular, the Förster radius R 0 is modified from its free-space value of 20 nm and can reach values of 120 nm when close to a graphene monolayer. As the donor-acceptor separation is increased, their direct interaction is overshadowed by the interaction via the surface plasmon mode. Due to the large propagation length of the surface plasmon mode on graphene, an energy transfer efficiency as high as 50% can still be achieved for distances as large as 300 nm. The interaction via the surface plasmon mode is tunable via the doping of the graphene monolayer and the surface plasmon channel can also be switched off this way.

The spontaneous emission and energy transfer rates of quantum systems in proximity to a dielectrically coated metallic cylinder are investigated using a Green's tensor formalism. The excitation of surface plasmon modes can significantly modify these rates. The spontaneous emission and energy transfer rates are investigated as a function of the material and dimensions of the core and coating, as well as the emission wavelength of the donor. For the material of the core we consider gold and silver, whose surface plasmon wavelengths lie in the visible part of the electromagnetic spectrum. The spontaneous emission rate is enhanced by several orders of magnitude when the emission wavelength is close to the surface plasmon wavelength. The energy transfer rate enhancement is found to be concentrated in hot spots around the circumference of the coated cylinder. Introducing the energy transfer efficiency as a parameter, we find that, when the donor emission and acceptor absorption spectra are resonant with the surface plasmon modes excited on the coated cylinder, the energy transfer efficiency can be significantly enhanced compared to the off-resonance situation. Tuning the surface plasmon wavelength to the emission wavelength of the donor via the geometrical and material parameters of the coated cylinder allows, therefore, control of the energy transfer efficiency.

The total spontaneous emission rate of a quantum emitter in the presence of an infinite MoS 2 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's tensor formalism. The distance dependence follows different trends depending on the emission energy of 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 MoS 2 layers. The interaction between a quantum emitter and a MoS 2 superlattice is investigated and we observe a splitting of the modes supported by the superlattice. Moreover, a blue shift 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.

In this paper, we present a theoretical investigation of the energy transfer efficiency between a pair of quantum emitters placed in proximity to a conducting graphene nanodisk. The energy transfer efficiency quantifies the contribution of the energy transfer process to the relaxation of the donor quantum system, as compared to the spontaneous emission rate of the donor in the absence of the acceptor. We use in our calculations the Green's tensor formalism in the electrostatic limit. This approximation works very well for the nanodisks considered here, for which the radius is much smaller than the emission wavelength of the donor. The approximate analytical solutions obtained are used to investigate the decay rate of a single quantum emitter and the energy transfer rate between quantum emitters in the vicinity of the graphene nanodisk. We find that these rates are enhanced several orders of magnitude compared with their free-space values. We determine the resonance frequencies of the spontaneous emission rate of a single quantum emitter to a graphene nanodisk, and the energy transfer rate between a pair of quantum emitters in proximity to a graphene nanodisk. We identify the surface modes which give the largest contributions to the energy transfer function. We connect the resonance frequency values and their surface plasmon wave numbers, which depend on the radius of the graphene nanodisk, with the dispersion relation of an infinite graphene monolayer at the same chemical potential. Analyzing the distance dependence of these rates, we are able to fit the full numerical results with a simple analytical expression which depends only on the geometrical characteristics of the graphene nanodisk, i.e., its radius. We show that the interaction distance depends on the transition dipole moment orientation and the different order resonance frequencies. The interaction distance between a pair of quantum emitters increases from a free-space value of 20 nm to reach values of 120 nm in the presence of a graphene nanodisk.

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%.