A Generalizable Single-Chip Calibration Method for Highly Quantitative SERS via Inkjet Dispense.

We present a calibration method for quantitative surface-enhanced Raman scattering (SERS) on a single-chip based on inkjet dispense (ID-SERS). We exploit the ability of inkjet to precisely pattern microdroplets at high resolution to encode multiple standard curves on the surface of a single 1 mm2 SERS substrate. We demonstrate quantitative SERS measurements with a relative standard error (RSE) below 3% for aqueous solutions of 1,2-bis(4-pyridyl)ethylene (BPE), the lowest reported to date. Most importantly, the RSE scales with patterning density and sensor size, showing the potential for even higher measurement accuracy. This calibration technique can be generalized to other plasmonic substrates and offers several additional advantages including speed (subsecond drop-and-dry), low sample volumes (<1 nL), and automation. Finally, we investigate factors impacting the limit of detection of this approach and demonstrate a 30-fold enhancement of sensitivity via layered inkjet dispense. We believe that ID-SERS paves the way for the development of reproducible plasmonic sensing for real-world quantitative applications.

Terahertz and mid-infrared plasmons in three-dimensional nanoporous graphene.

Two-dimensional (2D) graphene emerged as an outstanding material for plasmonic and photonic applications due to its charge-density tunability, high electron mobility, optical transparency and mechanical flexibility. Recently, novel fabrication processes have realised a three-dimensional (3D) nanoporous configuration of high-quality monolayer graphene which provides a third dimension to this material. In this work, we investigate the optical behaviour of nanoporous graphene by means of terahertz and infrared spectroscopy. We reveal the presence of intrinsic 2D Dirac plasmons in 3D nanoporous graphene disclosing strong plasmonic absorptions tunable from terahertz to mid-infrared via controllable doping level and porosity. In the far-field the spectral width of these absorptions is large enough to cover most of the mid-Infrared fingerprint region with a single plasmon excitation. The enhanced surface area of nanoporous structures combined with their broad band plasmon absorption could pave the way for novel and competitive nanoporous-graphene based plasmonic-sensors.

Topologically protected Dirac plasmons and their evolution across the quantum phase transition in a (Bi(1-x)In(x))2Se3 topological insulator.

A 3D Topological Insulator (TI) is an intrinsically stratified electronic material characterized by an insulating bulk and Dirac free electrons at the interface with vacuum or another dielectric. In this paper, we investigate, through terahertz (THz) spectroscopy, the plasmon excitation of Dirac electrons on thin films of (Bi1-xInx)2Se3 TI patterned in the form of a micro-ribbon array, across a Quantum Phase Transition (QPT) from the topological to a trivial insulating phase. The latter is achieved by In doping onto the Bi-site and is characterized by massive electrons at the surface. While the plasmon frequency is nearly independent of In content, the plasmon width undergoes a sudden broadening across the QPT, perfectly mirroring the single particle (free electron) behavior as measured on the same films. This strongly suggests that the topological protection from backscattering characterizing Dirac electrons in the topological phase extends also to their plasmon excitations.