One-Dimensional Plasmonic Excitations in Gold-Induced Superstructures on Si(553): Impact of Gold Coverage and Silicon Step Edge Polarization

Abstract

Free charge carriers confined to atomic chains such as the gold-induced superstructures on the stepped Si(553) surface enable experimental insight into one-dimensional physics. Embedding into the higher dimensional substrate allows for additional couplings between the free charge carriers and their surroundings, which might modify the one-dimensional characteristics. The gold atom superstructures on Si(553) consist of a parallel arrangement of metallic chains from Au and Si atoms on the terraces and of parallel Si step edges with some of the Si atoms having dangling bonds with one unpaired electron. The metallic chains give rise to localized plasmonic excitations. We have studied these plasmonic resonances with infrared spectroscopy that enables the detection of resonance shifts as small as 1 meV or even less. The plasmonic behavior of the conductive chains of the high- and the low-coverage gold superstructures on Si(553) is investigated at various temperatures and additionally after filling electrons into certain electronic states by placing gold adatoms onto the high-coverage structure. When cooling to 20 K, the strong plasmonic signals of the undoped superstructures become even stronger but shift to lower frequencies, which is attributed to the temperature dependent change of the orientational polarization of the Si dangling bonds. Regarding their plasmonic resonance shifts, the conductive atom chains work just like refractive index sensors.

Plasmon Standing Waves by Oxidation of Si(553)–Au

“…Strong absorption is only seen for polarization parallel to the wires (in the [110] direction), which reflects the anisotropic metallicity of self-assembled Au wires. The observed absorption feature is associated with the low-energy plasmonic excitation in metal-induced atomic chains, as studied previously [7][8][9]17 for different surfaces. The weak absorption signal around 950 cm −1 appears upon oxygen adsorption.…”

“…The initial value of about 31 nm effective length without oxygen is in good agreement with the result obtained in ref. 7 Oxidation, which happens mainly on the HC Si chain, 32 still has a significant influence also on plasmon scattering by defects, which strongly increases so that the effective wire length for plasmons decreases correspondingly, as shown in this figure . A very similar trend is seen when taking the inverse halfwidths (FWHM) of the ×2 streaks along the [1 10] direction in LEED (see Fig. 6a)) from measurements similar to those in Fig.…”

“…One was equipped with an IR spectrometer and RHEED. 7 The other chamber was equipped with a high-resolution spot profile analysis low energy diffraction (SPA-LEED) system and an electron energy loss spectrometer that combines both high momentum resolution with high energy resolution (EELS-LEED). 26 The EELS-LEED yields 0.01 A −1 momentum and 12 meV energy resolution.…”

“…24 Because of finite wire lengths, the plasmon resonance becomes optically detectable due to the dipolar character of excitations. 7,25 It is thus a very valuable tool for complementing our HREELS study that is also important to discriminate between finite size effects of wire lengths and possible adsorbate induced band gap opening.…”

Plasmon Localization by H-Induced Band Switching

“…The substrate–wire interaction is an additional parameter that can be used to modify plasma frequencies, e.g., by the use of distinct adsorbates and terraced substrates of different step densities. Several experimental and theoretical studies have been dedicated to these topics. − Concentrating on Au submonolayers, and starting from Si(111), , high-index Si­( hhk ) surfaces provide tunable terrace size and local structural motifs, which allow controlling the wire geometry and the interwire coupling. ,,,− However, the nanowires are also susceptible to defects and impurities on the atomic scale. Embedding involves contact and interaction with the environment, which can be used, in turn, to tune the wire properties.…”