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The Surface Science Lab is equipped with a scanning tunneling microscope (STM), scanning probe microscope (SPM), a Nano Indenter XP system, and a Localized Electrochemical Impedance Spectroscopy (LEIS).
SPM is the third generation of this type of high resolution microscopes, following STM and AFM. The samples for STM study must have, at least, modest conductance in order to sustain the tunneling current. Thus the technique could not be applied to insulating surfaces. To break the limitation, atomic force microscope (AFM) was invented in 1986. AFM measures the force between atoms at the tip and atoms at the sample's surface as the tip scans across the surface, thus the high resolution can be achieved even at the insulating surfaces. SPM, combining the function of STM and AFM and plus more, can be operated in multiple modes, e.g. current mode, contact force mode, lateral force mode, tapping mode, phase mode, frequency modulation mode, etc. We can use this device to analyze the morphology of the surface down to the atomic level. We can also gain information about the mechanical properties of the surface using different procedures, tips, and data collection techniques.
For the details of our SPM, please visit Digital Instruments website, " Nanoscope IIIa Scanning Probe Microscope."
Nano-indenter XP performs both indentation test and scratch test with a single head. In the indentation test, it can indent the surface of sample to a pre-selected load or a pre-selected depth (home-programmed) at various rates, thus measuring the hardness and elastic modulus under different conditions. In the scratch test, it can scratch the surface of samples at constant load, increasing load, or incremental load, while recording the penetrating depth and lateral force encountered by the scraping tip, thus measuring the mar resistance quantitatively and determining the critical forces for different scratching modes.
For the details of the Nano Indenter XP, please visit MTS Systems Corporation website, " Nano Indenter XP."
Due to the electrochemical nature of the corrosion process, the electrochemical impedance measurement has become a useful method in the study of corrosion. However, the conventional Electrochemical Impedance Spectrometer (EIS) measures the impedance over an area of about several square centimeters or larger. The actual corrosion of the metals covered by coatings initiates from defects, such as micro holes and voids at a much smaller size. The newly developed Localized Electrochemical Impedance Spectroscope (LEIS) measures the impedance at different frequencies while the probe scans across the sample, with a resolution of about 50mm, thus obtaining an impedance distribution map of the surface. It will help us identify the vulnerable spot where the corrosion initiates and monitor the corrosion development form the spots, thus better understanding the corrosion mechanism and suppressing it to protect the metals.
For the details of our LEIS, please visit Princeton Applied Research website, " LEIS270."