Surface sensitive techniques potential problems

Potential Problems. Most, but not all, of the surface sensitive techniques require measurements to be made in a vacuum, frequently near room temperature. Because these conditions are usually different from the corrosion conditions, the possibility that the desired information will be lost in the transfer from the corrosion chamber to surface analysis chamber is a major concern. There is also a possiblity that the measurement itself will alter the composition or chemistry of interest. Various aspects of those problems may apply to any method for which analysis occurs under conditions different from those in which the sample is generated, but they are of particular concern for surface methods that examine the very outer layers of the material. 

The three most commonly applied external reflectance techniques can be considered in terms of the means employed to overcome the sensitivity problem. Both electrically modulated infrared spectroscopy (EMIRS) and in situ FTIR use potential modulation while polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) takes advantage of the surface selection rule to enhance surface sensitivity. 

Surface pressure distribution measurement is of fundamental importance in the experimental study of aerodynamic problems in the fields of avionics, car, rocket, aerospace, and aircraft design [1]. The conventional methods based on pressure taps or transducers have a number of limitations. The most serious problem is that their very nature limits them to providing information only at discrete points on the surface of a substrate. A new approach to surface pressure distribution measurement, the use of pressure-sensitive paint (PSP), has recently developed that offers the potential of revolutionizing the nature of such measurements in the field of aerodynamics. This method employs the oxygen sensitivity of fluorescent materials in the form of a paint, in conjunction with image processing techniques, to map the pressure field over... 

---