Spectral Measurement of Photon Emission from Individual Gold Nanoparticles Using Scanning Tunneling Microscopy

Abstract

The light emission spectra of individual Au nanoparticles induced by a scanning tunneling microscope (STM) have been investigated. Two-dimensional ensembles of tunnel-coupled Au particles were prepared by thermal evaporation onto a native oxide silicon wafer in ultrahigh vacuum (10-9 mbar). Our STM measurements show a single peak at photon energy 1.6 eV in the tunneling mode and two peaks at 2.2 eV (connected with the Mie plasmon) and 1.45 eV (a new peak which was not discussed in literature before) in the field emission mode.

Atomic-Scale Imaging and Spectroscopy of Electroluminescence at Molecular Interfaces

“…165,170,171 STM-induced luminescence of metallic nanoparticles was first investigated by Umeno et al, 172 and research has mostly focused on Ag, Au, and Cu nanoparticles. Usually, the particles are deposited on semiconductor substrates, such as Si, 53,168,169,173 TiO 2 , 164,166,167 ITO, 171 or ZnO, 174 or on ultrathin insulating films, such as Al 2 O 3 on NiAl(110) 108,166 or MgO on Mo(001). 170,175 Additionally, different monolayers of colloidal nanoparticles, capped with alkanethiols and carboxylic acids and deposited from solution either directly on metal surfaces 176−178 or on top of a self-assembled monolayer, 179 have been investigated.…”

“…At smaller voltages and distances, the strong electromagnetic coupling between tip and particle typically results in tip-induced gap plasmons. 53 Because of the much weaker coupling to the STM tip, the emission peaks of Mie plasmons generally occur at higher energy than those related to tip-induced gap plasmons. Their energy is determined by the particle size, the electromagnetic coupling to the tip and sample, as well as by the dielectric functions of the particle, the substrate, and the tip.…”

“…Their highly localized excitation in STM provides the possibility to study the influence of the shape, particle size, − and coupling to the substrate , on the plasmon modes of individual particles, to chemically identify individual and only a few nanometers small nanoparticles in binary mixtures, , and even to map the plasmon excitation on a subparticle scale. ,, STM-induced luminescence of metallic nanoparticles was first investigated by Umeno et al, and research has mostly focused on Ag, Au, and Cu nanoparticles. Usually, the particles are deposited on semiconductor substrates, such as Si, ,,, TiO 2 , ,, ITO, or ZnO, or on ultrathin insulating films, such as Al 2 O 3 on NiAl(110) , or MgO on Mo(001). , Additionally, different monolayers of colloidal nanoparticles, capped with alkanethiols and carboxylic acids and deposited from solution either directly on metal surfaces − or on top of a self-assembled monolayer, have been investigated.…”

“…In the tunneling regime, voltages and currents can be kept low enough to avoid disruption of weak intermolecular bonds and damage to the molecules. The transition to the larger distance field-emission regime has been explored in a few publications, ,, and the transition from the tunnel regime to the contact regime has been addressed in a series of studies. ,, …”

Emission Properties of Metal Nanoparticles

“…A scanning tunneling microscope surrounded by a parabolic mirror has been used benefiting from the large acceptance angle for the photon collection. These measurements have been carried out on a gold nanoparticle film on a native oxide-covered silicon wafer (n-type silicon, r $ 0.01 Ocm) [51]. Figures 24 and 25a show the light emission spectrum of a gold particle with size a = 5 nm at voltages on the tungsten tip (gap Handbook of Nanoparticles DOI 10.1007/978-3-319-13188-7_25-1 # Springer International Publishing Switzerland 2015 voltage) of U tip = 3 and 10 V (current from the point is equal to i tip = 1 and 10 nA), respectively.…”