Electrically Excited Plasmonic Ultraviolet Light Sources

The emission of photons from metal-insulator-metal (MIM) nanojunctions through inelastic tunneling of electrically driven electrons is a well-acknowledged approach to develop miniaturized light sources and ultradense photonic instruments. Generally, the existing research in the optimization of electromigrated tunneling junctions is principally centered on the generation of visible and near-infrared lights. This study reports on the near-ultraviolet (NUV, λ ≈ 355 nm) light emission from enhanced tunneling of electrons using aluminum nanoelectrodes. Compared to conventional noble metals, the high electron density and low screening of aluminum enable supporting of pronounced local fields at high energies (i.e, ultraviolet (UV)). As the color of light can be straightforwardly determined by the properties of tunneling structures, the exquisite features of aluminum have empowered the fashioning of tunneling devices that are able to effectively sustain plasmons at short wavelengths and emit UV light with high photon yield. This demonstration is a breakthrough in the generation of high-energy beams using electrically excited aluminum tunneling platforms, which promisingly accelerates the implementation of electrically tunable and ultradense UV light sources.

Auger Suppression of Incandescence in Individual Suspended Carbon Nanotube pn-Junctions

There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral characteristics that provide important information. Here we report suppression of incandescence via Auger recombination in suspended carbon nanotube pn-junctions generated from dual-gate CNT field-effect transistor (FET) devices. By applying equal and opposite voltages to the gate electrodes (i.e., V_g1 = -V_g2), we create a pn-junction within the CNT. Under these gating conditions, we observe a sharp peak in the incandescence intensity around zero applied gate voltage, where the intrinsic region has the largest spatial extent. Here, the emission occurs under high electrical power densities of around 0.1 MW/cm² (or 6 μW) and arises from thermal emission at elevated temperatures above 800 K (i.e., incandescence). It is somewhat surprising that this thermal emission intensity is so sensitive to the gating conditions, and we observe a 1000-fold suppression of light emission between V_g1 = 0 and 15 V, over a range in which the electrical power dissipated in the nanotube is roughly constant. This behavior is understood on the basis of Auger recombination, which suppresses light emission by the excitation of free carriers. Based on the calculated carrier density and band profiles, the length of the intrinsic region drops by a factor of 7-25× over the range from |V_g| = 0 to 15 V. We, therefore, conclude that the light emission intensity is significantly dependent on the free carrier density profile and the size of the intrinsic region in these CNT devices.

Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111)

Monolayers of transition metal dichalcogenides are interesting materials for optoelectronic devices due to their direct electronic band gaps in the visible spectral range. Here, we grow single layers of MoS2 on Au(111) and find that nanometer-sized patches exhibit an electronic structure similar to their freestanding analogue. We ascribe the electronic decoupling from the Au substrate to the incorporation of vacancy islands underneath the intact MoS2 layer. Excitation of the patches by electrons from the tip of a scanning tunneling microscope leads to luminescence of the MoS2 junction and reflects the one-electron band structure of the quasi-freestanding layer.

On the Surface Mapping using Individual Cluster Impacts

This paper describes the advantages of using single impacts of large cluster projectiles (e.g. C(60) and Au(400)) for surface mapping and characterization. The analysis of co-emitted time-resolved photon spectra, electron distributions and characteristic secondary ions shows that they can be used as surface fingerprints for target composition, morphology and structure. Photon, electron and secondary ion emission increases with the projectile cluster size and energy. The observed, high abundant secondary ion emission makes cluster projectiles good candidates for surface mapping of atomic and fragment ions (e.g., yield >1 per nominal mass) and molecular ions (e.g., few tens of percent in the 500 < m/z < 1500 range).

Analysis of Fluorescent Proteins with a Nanoparticle Probe

This letter presents the first application of high energy, single nanoparticle probes (e.g., 520 keV Au(400) 2nm NP) in the characterization of surfaces containing fluorescent proteins (e.g., GFP variants) by their co-emitted photon, electron and secondary ion signals. NP induced protein luminescence increases with the NP incident energy, is originated by the NP impact and is transferred to the protein fluorophor via electronic energy transfer. Multi-electron emission is observed per single NP impacts and their distributions are specific to the target morphology and composition. Fragment ions of protein sub-units consisting of 2-7 amino acid peptides are observed under individual NP impacts that can be correlated to the random protein orientation relative to the impact site (e.g., outer layer or "skin" of the protein).

Photon emission from massive projectile impacts on solids

First evidence of photon emission from individual impacts of massive gold projectiles on solids for a number of projectile-target combinations is reported. Photon emission from individual impacts of massive Au(n) (+q) (1 ≤ n ≤ 400; q = 1-4) projectiles with impact energies in the range of 28-136 keV occurs in less than 10 ns after the projectile impact. Experimental observations show an increase in the photon yield from individual impacts with the projectile size and velocity. Concurrently with the photon emission, electron emission from the impact area has been observed below the kinetic emission threshold and under unlikely conditions for potential electron emission. We interpret the puzzling electron emission and correlated luminescence observation as evidence of the electronic excitation resulting from the high-energy density deposited by massive cluster projectiles during the impact.

Photon, Electron and Secondary Ion Emission from Single C(60) keV Impacts

This paper presents the first observation of coincidental emission of photons, electrons and secondary ions from individual C(60) keV impacts. An increase in photon, electron and secondary ion yields is observed as a function of C(60) projectile energy. The effect of target structure/composition on photon and electron emissions at the nanometer level is shown for a CsI target. The time-resolved photon emission may be characterized by a fast component emission in the UV-Vis range with a short decay time, while the electron and secondary ion emission follow a Poisson distribution.