Raman system used to study 2D materials at Boston University
Founded in 1839, Boston University has over 33,000 students. The Department of Electrical and Computer Engineering houses the Optical Characterization and Nanophotonics (OCN) laboratory. Here, research focuses on developing, and applying, advanced optical characterization techniques to the study of solid-state and biological phenomena, at the nanoscale. The group uses Renishaw Raman spectrometers to measure strain in 2D materials and the friction between 2D materials and their underlying substrates.
Anna Swan is an associate Professor in the Electrical and Computer Engineering Department, and one of the three directors running the multi-disciplinary lab at Boston University. The research group is currently focusing on 2D materials, such as graphene, boron nitride, molybdenum disulphide and phosphorene. They are interested in how strain, and designed strain fields, can be used to manipulate the electronic and optical properties in these materials. For example, a certain strain field configuration creates a magnetic pseudo field that can localize electrons and create Landau levels. For this work, they are looking at how they can control the boundary conditions and manipulate the extent of friction between the 2D material and substrate. They are using Raman spectroscopy to measure strain, the coupling between strain and Raman shifts, and the friction.
Commenting on her use of a Renishaw inVia confocal Raman microscope system, Dr Casiraghi says, "inVia is a user-friendly and sensitive Raman spectrometer which can be equipped with both mapping and multi-wavelength capabilities. Both are very useful in the study of graphene and other carbon nanostructures. Mapping allows us to collect the Raman signal from a particular area of the sample, while multi-wavelength Raman spectroscopy enables us to study if, and how, the Raman spectrum changes when the material is excited at different energies. This is very important for graphene and sp²-bonded carbon nanostructures because there are certain peaks that change in position when the excitation energy is changed. This behaviour is correlated to the properties of the material. We recently purchased a Renishaw inVia system for the new National Graphene Institute (NGI). The instrument is equipped with several laser lines, ranging from visible to near-UV (325 nm), and has a Raman mapping capability. It is very easy to change the wavelength. The UV capability is also very attractive, as the 325 nm line can be easily added to the visible lines, so it does not require buying two separate instruments. The instrument will be used for metrology studies and to set standards for graphene, in collaboration with the National Physical Laboratory (NPL)."
Continuing to describe her work, Dr Casiraghi said that the Casiraghi Group recently used the new Renishaw inVia to demonstrate the use of Raman spectroscopy as a non-destructive and rapid technique for probing the van der Waals forces between two atomically thin crystals (K-G Zhou et al, ACS Nano, 2014, 8 (10), pp 9914–9924). By performing Raman mapping on several types of heterostructures, they showed that information on the quality of the interface can be derived by looking at the changes in positions of the Raman peaks of the transition metal dichalcogenide crystal.
For further details of Renishaw's inVia confocal Raman microscope and other spectroscopy solutions, click here.
Contact: David Reece at Rennishaw