Original: He always used new observation techniques like low-energy electron diffraction ( LEED ) at the beginning of his career , later ultraviolet photoelectron spectroscopy ( UPS ) and scanning tunneling microscope ( STM ) yielding ground breaking results .
Simplified: One was called low-energy electron diffraction ( LEED ) used at the beginning of his career and later he worked on ultraviolet photoelectron spectroscopy ( UPS ) and scanning tunneling microscope ( STM ) .