He always used new observation techniques like low-energy electron diffraction -LRB- LEED -RRB- at the beginning of his career , later ultraviolet photoelectron spectroscopy -LRB- UPS -RRB- and scanning tunneling microscope -LRB- STM -RRB- yielding ground breaking results .

One was called low-energy electron diffraction -LRB- LEED -RRB- used at the beginning of his career and later he worked on ultraviolet photoelectron spectroscopy -LRB- UPS -RRB- and scanning tunneling microscope -LRB- STM -RRB- .
