Thickness-Dependent Drude Plasma Frequency in Transdimensional Plasmonic TiN

Abstract

Plasmonic transdimensional materials (TDMs), which are atomically thin metals of precisely controlled thickness, are expected to exhibit large tailorability and dynamic tunability of their optical response as well as strong light confinement and nonlocal effects. Using spectroscopic ellipsometry, we characterize the complex permittivity of ultrathin films of passivated plasmonic titanium nitride with thicknesses ranging from 1 to 10 nm. By measuring passivated TiN, we experimentally distinguish between the contributions of an oxide layer and thickness to the optical properties. A decrease in the Drude plasma frequency and increase in the damping in thinner films is observed due to spatial confinement. We explain the experimental trends using a nonlocal Drude dielectric response theory based on the Keldysh−Rytova (KR) potential that predicts the thicknessdependent optical properties caused by electron confinement in plasmonic TDMs. Our experimental findings are consistent with the KR model and demonstrate quantum-confinement-induced optical properties in plasmonic transdimensional TiN.

Determination of thickness-dependent damping constant and plasma frequency for ultrathin Ag and Au films: nanoscale dielectric function

“…This latter parameter will be discussed in Section 3.1.1. Shah et al 47 consider an additive term of the form A / d to account for the surface roughness (0.2–0.3 nm) for thicknesses as small as 1 nm, where A is a constant. In our paper this situation is not considered since all film thicknesses analyzed were larger than 4 nm.…”

Controlling Single-Photon Emission with Ultrathin Transdimensional Plasmonic Films

“…[1][2][3] The term 'transdimensional' refers to the transitional range of thicknesses -a regime that is neither three (3D) nor two (2D) dimensional but rather something in between, turning into 2D as thickness tends to zero, challenging to study what the 3D-to-2D continuous transition has to offer to improve material functionalities. Currently available due to the rapid progress in nanofabrication techniques, [4][5][6][7][8][9][10][11] such materials offer high tailorability of their electronic and optical properties not only by altering their chemical and/or electronic composition (stoichiometry, doping) but also by merely varying their thickness (number of monolayers). [12][13][14][15] Materials like these are indispensable for studies of fundamental properties of the light-matter interaction as it evolves from a single 2D atomic layer to a larger number of layers approaching the 3D bulk material properties.…”

“…[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Plasmonic TD materials (ultrathin metallic films) offer controlled light confinement, large tailorability and dynamic tunability of their optical properties due to their thickness-dependent localized surface plasmon (SP) modes, [14][15][16][17][18][19][20][21] which are distinctly different from those of conventional thin films commonly described by either purely 2D or by 3D material properties with boundary conditions imposed on their top and bottom interfaces. [33][34][35][36][37][38][39][40][41] In such systems, the vertical quantum confinement enables a variety of new quantum phenomena, including the thickness-controlled plasma frequency red shift, 2,11 the SP mode degeneracy lifting, 14,18 a series of magneto-optical effects, 13 and even atomic transitions that are normally forbidden, 1,20,21 to mention a few.…”

“…Previously, we have implemented the confinement-induced nonlocal Drude response model based on the Keldysh-Rytova (KR) pairwise electron interaction potential 2 to study theoretically the electronic properties of ultrathin TD plasmonic films 13,14 and demonstrate their major manifestations experimentally. 11,42 The KR interaction potential takes into account the vertical electron confinement, 43,44 which makes it much stronger than the electron-electron Coulomb potential, 43 offering also the film thickness as a parameter to control the electronic properties of the TD plasmonic films. Here, we use the KR model to further explore the capabilities of the TD plasmonic films, focusing on the light-scattering properties of a quantum dipole emitter (DE) placed at a distance near the film surface; see the inset in Fig.…”

“…The presence itself of this split-off mode is a remarkable feature of the confinement-induced nonlocality captured by the KR model we use. 11,14 To see how the DE coupling to the plasma modes in Fig. 1 (a) affects its spontaneous emission intensity profile, we use the analytical approach previously developed by one of us for an analogous problem of the DE coupled to a resonance of the local density of photonic states (LDOS) close to the nanotube surface.…”