Nanoscale Imaging & Spectroscopy

Graphene transistor device

IRa-SCOPE can measure high-quality confocal Raman maps of a functional Graphene transistor. Recorded Raman spectra obtained with 532 nm illumination depict the well-known 2D, G or D bands characteristic for CVD-grown Graphene on an SiO substrate. Spectroscopic Raman imaging is enabled by a dedicated 100x high-NA short-distance objective providing excellent lateral resolution of <300 nm with maximum collection efficiency. Analyzing the ratio of Raman band highlights the spatial distribution of graphene thickness and structural defects (folds, wrinkles).

Atomic Force Microscopy (AFM) height imaging verifies Graphene wrinkles, multilayer structures and individual atomic layers defects with nanometer spatial resolution (height scale: 0 – 4 nm).

Simultaneously to AFM height IRa-SCOPE measures nano-FTIR reflectivity and imaging at an infrared frequency of 940 cm^-1 delivers high-resolution mid-IR maps of the Graphene conductivity, clearly visualizing with much higher resolution not only multilayer structures and defects observed in the Raman map, but also grain boundaries not captured by Raman or AFM (see orange arrows). 

Micron-Sized MOF Crystallites

Drop casting Metal Organic Framework (MOF F@ZIF-L) particles filled with fluorophore on Si surface result in isolated crystallites easily identifiable by the IRa-SCOPE integrated inspection optics. 

Hyperspectral Raman mapping of individual particles reveals MOF specific Raman bands (e.g. 2920 cm^-1) that depict a homogeneous crystalline structure. Interestingly, analysis of characteristic spectroscopic signatures (e.g. 1420 cm^-1 and 1570 cm^-1) indicate higher fluorophore concentration at crystallite edges.

IRa-SCOPE tapping AFM-IR⁺ spectroscopy of the very same crystallite shows the characteristic signature of MOF, in excellent agreement with its FTIR references. However, imaging at 1258 cm^-1 with 10 nm spatial resolution reveals that the sample is covered by small lamellae about 9 nm in height, which show spectroscopic signature of PVAc-PVA copolymer – an otherwise unrecognized contaminant. Control nano-IR spectra taken at the substrate between lamellae show no signatures as expected, confirming the results and the spatial resolution.

Heterogeneous Polymer Blend

A ca. 50-70 nm thin PS-LDPE polymer film on Si substrate shows clear phase separation of materials. Integrated 20x optical inspection objective of IRa-SCOPE allows for easy finding of regions of interest. AFM phase images verify clear phase separation as well as the different mechanical properties of two polymers.

Confocal Raman imaging with 532 nm excitation reveals characteristic spectral signatures of the PS and LDPE polymers enabling their chemical identification as well as visualizing their spatial distribution at a resolution of ca. 300 nm. 

Changing the instrument mode of operation to highly sensitive nano-FTIR allows for rapid imaging of exactly the same sample region at specific vibrational modes. For example, imaging at 700 cm^-1 absorption line of Polystyrene with sub-10 nm spatial resolution reveals a sharp material interfaces and even smaller LDPE islands that are not visible in the Raman map. Further, measuring sample nano-FTIR absorption spectra enables nanoscale chemical identification, and in combination with Raman spectra, significantly improves chemical identification accuracy.