Atomic force microscopy (AFM) is an imaging technique whose framework is based on scanning force microscopy used for imaging various substances such as ceramics and nanomaterials. A study published in Applied Surface Sciences focuses on the preparation of lightweight composite structures for nanoindentation and nanochemical analysis using Gas Cluster Ion Beam (GCIB) etching.
AFM techniques for substance analysis
Enhanced AFM procedures for microstructural and nanochemical investigation develop a distinctive way to accurately probe the structure and functional composition of a wide variety of material interfaces with spatial and temporal resolution well below standard optical scattering thresholds.
A variety of subresonant and resonant microstructural and nanomechanical modeling techniques, among others, provide exceptional sensitivity and accuracy.
Some limitation exists when using AFM to spatially image surfaces. This occurs near the size of the probe radius (about less than 50 nm/pixel). At such fine resolution, interpretation of changes in mechanical characteristics becomes difficult due to the confounding effects of exterior topography, subsurface attributes, and adjacent facets.
As a result, the high-resolution AFM method is generally confined to sample prototypes that are either specifically designed for AFM research or have interfaces that can be produced efficiently using a very limited set of procedures.
Why is a surface preparation technique necessary?
The limitation of sample preparation greatly limits the use of high-precision AFM scanning for operationally responsible materials and the in situ study of bulk polymer composite materials.
Given these considerations, a sample preparation process that enables the ubiquitous fabrication of ultra-smooth, damage-free interfaces from functionally viable composites and elements, such as biomaterials, energy storage, and photovoltaic devices, is desperately needed. Hard and soft phases are used together in such applications, and variation in nanotechnology properties can inform macro-level function and efficiency.
Gas cluster ion beam (GCIB) method
One possibility is to use a gas-cluster ion beam for etching (GCIB). A GCIB produces clusters of 100 to 1000 Argon atoms, ionizes the atoms, and then propels them out of a targeted material. The massive clusters of the GCIB spread impact kinetic energy over a wide region, limiting sample degradation to a shallow surface region that is then removed during etching.
Comparison of Traditional Monatomic Ion Guns and GCIB
Unlike the GCIB, monatomic ion systems, which are more typically used as etching tools, propel individual Argon ions which seep deep into a material and produce severe surface defects that are not erased by further etching. .
As a result, GCIB can erode reactive polymeric substances while leaving a smooth finish, while single atom ions can permanently disrupt delicate polymers like PMMA due to ester bond cleavage.
GCIB guns are frequently used in combination with interface-sensitive chemical analysis methods such as X-ray Photoelectron Spectroscopy (XPS) or Supplemental Ion Mass Spectroscopy (SIMS), which analyze topologically essential chemical alterations when the substance is scratched.
A series of tests were used to illustrate the ability of GCIB to remove materials and generate defect-free and damage-free composite substrates.
The polymer overlay material was found to be flawless at the starting surface (0 s). Some early working materials were detected to have weak phase characteristics after about 15-30 seconds of GCIB etching. After 1 minute of etching, there was an obvious shift from the relatively featureless overburden layer to the composite material layer.
Prior to etching, the first XPS trace primarily picked up the C 1s signal from the PS overburden material, with a relatively tiny Si 2p signal reflecting the OCS in the composite layer. The etched and overloaded regions of the PMMA composites were used to acquire AFM-IR spectra.
AFM-IR data show peaks that correspond to both OCS and PMMA; however, the relative amplitudes differ in the dug and the overburden. AFM-IR data indicated peaks correlated to both OCS and PMMA; however, the relative amplitudes differ in sunken and overburdened areas.
As AFM-IR signal intensity is also affected by thermal properties, it is believed that the observed difference in comparative signal intensity is caused by AFM-IR being more sensitive to PMMA than to AFM-IR. ‘OCS due to the greater expansion coefficient of PMMA.
The considerable spectrum shift after removal of the 50 nm PMMA coating revealed that the AFM-IR sensitivity was biased towards near-surface species. With reference to OCS signal changes, the PMMA spectra revealed no significant difference from the carbonyl peak, supporting XPS findings that GCIB did not significantly affect the chemical substance of the residual PMMA substance. .
In summary, the current study revealed a new avenue for the nanoscale characterization of polymer composites using interfacial methods, which is crucial for understanding structure-property associations in complex material systems.
Collinson, DW et. al. 2022. Gas cluster etching for the universal preparation of polymer composites for nanochemical and mechanical analysis with AFM. Applied surface sciences. 599. 53954. Available at: https://doi.org/10.1016/j.apsusc.2022.153954