Surface plasmons (SPs) of metals enable the tight focusing and strong absorption of light to realize an efficient utilization of photons at nanoscale. In particular, the SP-generated hot carriers have emerged as a promising way to efficiently drive photochemical and photoelectric processes under moderate conditions. In situ measuring of the transport process and spatial distribution of hot carriers in real space is crucial to efficiently capture the hot carriers. Here, we use electrochemical tip-enhanced Raman spectroscopy (EC-TERS) to in situ monitor an SP-driven decarboxylation and resolve the spatial distribution of hot carriers with a nanometer spatial resolution. The transport distance of about 20 nm for the reactive hot carriers is obtained from the TERS imaging result. The hot carriers with a higher energy have a shorter transport distance. These conclusions can be guides for the design and arrangement of reactants and devices to efficiently make use of plasmonic hot carriers.

Tip-enhanced Raman spectroscopy (TERS), known as nanospectroscopy, has received increasing interest as it can provide nanometer spatial resolution and chemical fingerprint information of samples simultaneously. Since Ag tips are well accepted to show a higher TERS enhancement than that of gold tips, there is an urgent quest for Ag TERS tips with a high enhancement, long lifetime, and high reproducibility, especially for atomic force microscopy (AFM)-based TERS. Herein, we developed an electrodeposition method to fabricate Ag-coated AFM TERS tips in a highly controllable and reproducible way. We investigated the influence of the electrodeposition potential and time on the morphology and radius of the tip. The radii of Ag-coated AFM tips can be rationally controlled at a few to hundreds nanometers, which allows us to systematically study the dependence of the TERS enhancement on the tip radius. The Ag-coated AFM tips show the highest TERS enhancement under 632.8 nm laser excitation and a broad localized surface plasmon resonance (LSPR) response when coupled to a Au substrate. The tips exhibit a lifetime of 13 days, which is particularly important for applications that need a long measuring time.

In the spectral range from ultraviolet to near infrared, graphene lacks the capability to support plasmon polaritons, and has low optical absorptivity for applications due to its extremely small thickness. Many photonic structures based on sophisticated nanofabrication or metal plasmonics have been adopted to conquer this limitation, but they suffer from high expenses or metal parasitic losses. Here, a single-channel coherent perfect absorber simply based on two unpatterned dielectric layers is proposed to reach ~100% light absorption in monolayer and few-layer graphene. The schemes for narrowband and broadband perfect absorption in graphene are systematically demonstrated, and their potential applications on fibre-integrated narrowband perfect absorbers, high-performance optical sensors, electric-optic modulators and broadband perfect absorbers are also investigated. Our research provides a simple and costeffective method to completely trap the light from ultraviolet to near infrared in a subnanometre scale for a lot of high-performance photonic and optoelectronic devices based on graphene and potentially other 2D materials.

Plasmonic structures with sophisticated nanofabrication have revolutionized the ability to trap light on the nanoscale and enable high-sensitivity refractive index sensing. Previous theoretical research has indicated that the sensitivity and figure of merit around the wavelength of 1 μm for a plasmonic sensing system can be up to 13000 nm/RIU and 138, respectively. In order to improve the sensing performance, we propose a graphene-based nonplasmonic sensor with the sensitivity over 440000 nm/RIU at the wavelength of 1 μm, which is 33 times more than the theoretical result of plasmonic sensors. Our graphene sensor is a nanofabrication-free design with perfect light confinement within a monolayer of graphene. Meanwhile, its figure of merit is up to the scale of thousands, which is also much higher than plasmonic sensors. Our scheme uses a simple dielectric structure with a monolayer of graphene and shows a great potential for low-cost sensing with high performance.