Chemical Imaging With a Scanning Probe Microscope

Scanning Probe Microscopy (SPM) is a superb tool for topographical analysis of samples. However, traditional varieties of SPM such as Atomic Force, Scanning Tunneling and Near-field Scanning Optical Microscopy have limited chemical contrast capability. Recently, several advanced techniques have been reported which provide chemical information in addition to topographical data. All these methods derive advantage from combinations of scanning probe methodologies and some other, chemically sensitive technique. Examples of such approaches are: Near-field Scanning Raman Imaging, Near-field Scanning Infrared Microscopy and mass spectrometric analysis with laser ablation through fiber probes. In this contribution we report the development of a new method in this family of chemically sensitive scanning probe techniques: Laser Induced Breakdown Spectroscopy with Shear Force Microscopy, LIBS-SFM. Traditional LIBS experiments involve focusing a pulsed laser beam onto the sample and observing optical emission from the plasma formed in the ablation area. The emissions are mostly in the UV/visible range, and the signal is due to electronic transitions in excited atoms and ions in the plasma plume. The spectra are analyzed to identify chemical elements. The spatial resolution of LIBS is limited by the wavelength and beam quality of the laser used for ablation. The experiments may be conducted in vacuum, controlled atmosphere, or ambient air.