||In 1905 Albert Einstein received the Nobel Prize in Physics for his quantum mechanical interpretation of the photoelectric effect. Based on the results of Heinrich Hertz and Max Planck about the nature of light being an electromagnetic wave and about the general existence of discrete energy portions, nowadays named “quantum”, this has been a big step for basic science. At this time nobody knew, that this will evolve into the most important method for non-destructive surface chemical analysis. |
To reach this understanding the development of energy dispersive electron analyzers had been necessary. Thus it took several decades until Kai Siegbahn developed and experimentally realized the first experiment of this kind in the late 1960s, again resulting in a Nobel Prize in Physics. By excitation of electrons from solid samples using characteristic X-rays and detecting the number of photoelectrons in dependence of their kinetic energies it became possible to use the element-specific electron energies to derive the chemical composition of sample surfaces without destroying them. He named the method Electron Spectroscopy for Chemical Analysis, or in short ESCA.
The global success of X-ray Photoelectron Spectroscopy (XPS) is a result of the development of methods for reliable and precise quantification of ESCA data with an elemental detection limit of <1% in the uppermost surface layers. Already in the early 1970s Kai Siegbahn realized, that the Ultra-High Vacuum (UHV) environment necessary in conventional ESCA machines is limiting the applications of this method to solid sample surfaces. So he suggested applying ESCA to liquids, using a differential pumping setup for the analyzer and X-ray source. He was able to reach a maximum pressure of 10-2 mbar at that time.
Again it took almost three decades in experimental development to reach pressures of up to 1 mbar in synchrotron experiments. Near Ambient Pressure XPS (NAP-XPS) was born, yielding fundamental insight in the operation of catalysts and the analysis of liquids and liquid solid interfaces. State-of-the-art instrumentation for NAP-XPS allows for purely laboratory-based NAP-XPS systems as the use of synchrotron radiation is not mandatory anymore.
It is time for the next step in evolution. EnviroESCA.