1 Nanoplasmonics: From Present into Future
13
1.2.4.1 Enhanced Mechanical Forces in Nanoplasmonic Systems
The resonantly enhanced local fields in the vicinity of plasmonic nanoparticles lead to
enhanced nanolocalized forces acting between the nanoparticles, see, e.g., Refs. [79–
85]. A perspective application of plasmonically-enhanced forces is optical manipulation (tweezing) of micro- and nanoparticles [86–92].
Another direction of research is opened up by the recently introduced theoretically
surface-plasmon-induced drag-effect rectification (SPIDER) [93], which is based on
transfer of the linear momentum from decaying surface-plasmon polaritons (SPPs)
to the conduction electrons of a metal nanowire. The SPIDER effect bears a promise
to generate very high terahertz fields in the vicinity of the metal nanowire.
1.2.4.2 Interaction Between Electrons and Surface Plasmons
The surface plasmonics, as it is called today, originated by a prediction of electron
energy losses for an electron beam in thin metal films below the energy of the bulk
plasmons [94]. This is how coherent electronic excitations called SPPs today were
predicted. Soon after this prediction, the SPP-related energy losses were experimentally confirmed [95, 96]. Presently, the electron energy loss spectroscopy (EELS) in
nanopalsmonics is a thriving field of research. We refer to a recent review [97] for
further detail.
A distinct and original direction of research is control of mechanical motion of
metal nanoparticles using electron beams [98]. It is based on the same principles
as optically-induced forces. The difference in this case is that the SP oscillations
in nanoparticles are excited locally, with an angstrom precision, by a beam of fast
electrons—see also Sect. 1.2.4.1 above.
There are other important phenomena in plasmonics based on electron-SP interaction called nonlocality [99]. One of them is dephasing of plasmons causing their
decay into electron-hole pairs, which is called Landau damping, contributing to
Im ε m . There is necessarily a related phenomenon of spatial dispersion contributing
to Re ε m . These become important for plasmonics when the size of the nanosystem
become too small, R l nl —see Eq. (1.9). The nonlocality and Landau damping
degrade plasmonic effects. The nonlocal effects lead to an increased decay rate of
dipolar emitters at metal surfaces [34] and limits resolution of plasmonic imaging,
making the so-called “perfect” lens [100] rather imperfect [35]. In aggregates, the
nonlocality of dielectric responses causes reduction of local fields and widening of
plasmonic resonances [101]. These broadening effects have initially been taken into
account purely phenomenologically by adding an additional contribution to the width
of plasmonic resonances ∼A/τ nl , where A = const [102]. Practically, if the size of
a nanoparticle is less then 3 nm, the non-local broadening of the SP resonances is
very significant; otherwise, it can be neglected in a reasonable approximation.
The above-mentioned publications [34, 35, 99, 101] on the nonlocality phenomena are based on a semi-phenomenological approach where the nonlocality is treated
via applying additional boundary conditions stemming from the electron scattering
13
1.2.4.1 Enhanced Mechanical Forces in Nanoplasmonic Systems
The resonantly enhanced local fields in the vicinity of plasmonic nanoparticles lead to
enhanced nanolocalized forces acting between the nanoparticles, see, e.g., Refs. [79–
85]. A perspective application of plasmonically-enhanced forces is optical manipulation (tweezing) of micro- and nanoparticles [86–92].
Another direction of research is opened up by the recently introduced theoretically
surface-plasmon-induced drag-effect rectification (SPIDER) [93], which is based on
transfer of the linear momentum from decaying surface-plasmon polaritons (SPPs)
to the conduction electrons of a metal nanowire. The SPIDER effect bears a promise
to generate very high terahertz fields in the vicinity of the metal nanowire.
1.2.4.2 Interaction Between Electrons and Surface Plasmons
The surface plasmonics, as it is called today, originated by a prediction of electron
energy losses for an electron beam in thin metal films below the energy of the bulk
plasmons [94]. This is how coherent electronic excitations called SPPs today were
predicted. Soon after this prediction, the SPP-related energy losses were experimentally confirmed [95, 96]. Presently, the electron energy loss spectroscopy (EELS) in
nanopalsmonics is a thriving field of research. We refer to a recent review [97] for
further detail.
A distinct and original direction of research is control of mechanical motion of
metal nanoparticles using electron beams [98]. It is based on the same principles
as optically-induced forces. The difference in this case is that the SP oscillations
in nanoparticles are excited locally, with an angstrom precision, by a beam of fast
electrons—see also Sect. 1.2.4.1 above.
There are other important phenomena in plasmonics based on electron-SP interaction called nonlocality [99]. One of them is dephasing of plasmons causing their
decay into electron-hole pairs, which is called Landau damping, contributing to
Im ε m . There is necessarily a related phenomenon of spatial dispersion contributing
to Re ε m . These become important for plasmonics when the size of the nanosystem
become too small, R l nl —see Eq. (1.9). The nonlocality and Landau damping
degrade plasmonic effects. The nonlocal effects lead to an increased decay rate of
dipolar emitters at metal surfaces [34] and limits resolution of plasmonic imaging,
making the so-called “perfect” lens [100] rather imperfect [35]. In aggregates, the
nonlocality of dielectric responses causes reduction of local fields and widening of
plasmonic resonances [101]. These broadening effects have initially been taken into
account purely phenomenologically by adding an additional contribution to the width
of plasmonic resonances ∼A/τ nl , where A = const [102]. Practically, if the size of
a nanoparticle is less then 3 nm, the non-local broadening of the SP resonances is
very significant; otherwise, it can be neglected in a reasonable approximation.
The above-mentioned publications [34, 35, 99, 101] on the nonlocality phenomena are based on a semi-phenomenological approach where the nonlocality is treated
via applying additional boundary conditions stemming from the electron scattering