Building confidence in 2D materials and unlocking new applications
Graphene research, within the quantum area at NPL, focuses on structural and functional engineering, physics and metrology of graphene, other 2D materials and their heterostructures.
We deploy the arsenal of quantum metrology, scanning probe microscopy and non‑contact microwave methods to support the development and application of graphene and 2D material based devices.
Graphene has the potential to surpass conventional materials in many important applications, such as super-capacitors, ultrafast analogue transistors and touchscreen displays. Metrology is called upon to underpin these developments.
Nucleation of chemical vapour deposited graphene and molybdenum disulfide revealed by confocal laser scanning microscopy.
- Robust measurement for characterisation of materials
- Non-destructive testing and evaluation methods for quality assurance
- Physical measurement methods utilising material and sensor innovation to accelerate process development and improve quality control
Reliable methods to determine the quality and physical properties of graphene and 2D materials are vital to their widespread inclusion in practical devices with novel functions. We use a wide suite of tools to characterise these materials in terms of their properties.
Structural properties – With our Atomic Force Microscopy (AFM), Scanning Tunnelling Microscopy (STM) and confocal Raman spectroscopy facilities, we can measure a variety of the structural properties of 2D materials, such as material thickness, coverage, defect state and strain.
Electric and electronic properties – We can probe properties such as surface potential, carrier density distribution, band structure, sheet resistance and electrical transport with techniques including Kelvin Probe Force Microscopy (KPFM), van der Pauw and Hall measurements, FET measurements (including Dirac point and conductivity vs. gate voltage), microwave resonator techniques and our conventional four probe and state of the art ultra high vacuum (UHV) four-probe STM system.
Optical properties – Our suite of optical techniques, including Raman and photoluminescence spectroscopy, as well as Scanning Near Field Optical Microscopy (SNOM), can measure the optical properties of 2D materials from the visible to the infrared.
Thermal properties – We measure the nanoscale thermal conductivities of a range of samples using Scanning Thermal Microscopy (SThM), in both ambient conditions and vacuum, and Nanoscale Thermal Analysis (nanoTA).
Chemical properties – With Raman and photoluminescence, we can distinguish and characterise many different 2D materials, using a mixture of spectroscopic analysis and spatial mapping of sample composition. Additionally, we can identify and pinpoint various chemical species, such as functionalised groups on graphene, with nanoscale spatial resolution using AFM-infrared spectroscopy (AFM-IR).
Graphene nanoribbons imaged with a variety of techniques, revealing different features.
NPL’s table-top quantum Hall instrument.
The quantum Hall effect is used to define the metrological standard for electrical resistance in terms of the ratio of fundamental constants of nature, Planck’s constant (h) and the square of the elementary charge (e). Graphene supports the quantum Hall effect in much more relaxed conditions, higher temperature and lower magnetic field, than conventional semiconductors. Our push-button quantum Hall resistance standards with graphene at their heart will be used in industry to create more accurate electronic components.
Find out more about NPL's Table-top quantum Hall (TTQH) instrument
The large surface area of graphene means it is very sensitive to molecules that contact its surface, which makes it ideal for use in sensors. With our in-house-designed environmental chamber, we perform a variety of electrical transport measurements on sensors in a controlled atmosphere, with variable gas content , temperature and humidity . We can also run AFM based experiments in a controlled environment, to investigate how atmospheric changes affect the structural and electronic properties of 2D materials. We investigate and develop graphene-based sensors, including gas sensors to detect harmful pollutants such as NO2 , CO and CO2.
We also develop novel biosensors which could detect hepatitis biomarkers, allergens and other disease-carrying pathogens.
Some highlights of our research include:
Read more about the graphene-based NO2 detectors from the Graphene Flagship: