Near-field photocurrent nanoscopy on bare and encapsulated graphene

Abstract

Optoelectronic devices utilizing graphene have demonstrated unique capabilities and performances beyond state-of-the-art technologies. However, requirements in terms of device quality and uniformity are demanding. A major roadblock towards high-performance devices are nanoscale variations of the graphene device properties, impacting their macroscopic behaviour. Here we present and apply non-invasive optoelectronic nanoscopy to measure the optical and electronic properties of graphene devices locally. This is achieved by combining scanning near-field infrared nanoscopy with electrical read-out, allowing infrared photocurrent mapping at length scales of tens of nanometres. Using this technique, we study the impact of edges and grain boundaries on the spatial carrier density profiles and local thermoelectric properties. Moreover, we show that the technique can readily be applied to encapsulated graphene devices. We observe charge build-up near the edges and demonstrate a solution to this issue.

Giant intrinsic photoresponse in pristine graphene

“…In addition, it persists from T = 4 to 300 K, even after many thermal annealing cycles. This universality and robustness strongly suggest that the new PC arises from the intrinsic graphene properties rather than extrinsic factors, such as impurities or contamination 24,25 .…”

Tipping solutions: emerging 3D nano-fabrication/ -imaging technologies

“…The absorption technique is better suited for the characterization of organic absorbing surfaces while scattering delivers high-fidelity imaging from metallic reflective surfaces and nanoparticles. Interpretation of data from the near-field requires further knowledge of probe-surface interaction, phase information of the reflected/transmitted light from sub-wavelength structures to reveal complex peculiarities of light-matter interactions at the nanoscale [118][119][120][121][122][123]. Recently, electron tunneling control by a single-cycle terahertz pulse illuminated onto a tip of scanning tunneling electron microscope (STEM) needle was demonstrated at 10 V/nm fields [124].…”

Probing Polaritons in 2D Materials

“…Figure a shows a representative schematic of photocurrent nanoscopy detection of the photocurrent from grain boundaries in graphene. The working principle is a locally concentrated optical field is generated by a mid‐infrared laser at the metal tip, which triggers a position‐dependent photocurrent in graphene, and the photocurrent is subsequently measured in situ via the contacted electrodes . The near‐field contribution to the total photocurrent can be isolated by oscillating the tip vertically, which is similar to the deduction of background signal for s‐SNOM …”