The femtosecond field-emission camera, a device for continuous observation of the motion of individual adsorbed atoms and molecules

A new instrument, the femtosecond field-emission camera (FFEC), has been developed to continuously record the motion of single adsorbed atoms or molecules, with an ultimate achievable time resolution of 10
⁻¹⁴
s. In the FFEC, the motion of an adsorbed species modulates a strong 10
⁻⁵
-A field-emission current from a sharp tip. The emitted electrons are focused into a beam, which is swept electrostatically across a detector screen. The tip substrate can be imaged atomically by field ion microscopy. In this paper, the construction and operating principles of the FFEC are described in some detail, and previously published experiments are reviewed. On a <111> W tip, single Cs atoms are observed to jump between sites instantaneously within the 2-ps instrumental resolution. Individual copper phthalocyanine molecules are observed vibrating with respect to the substrate with a period of ≃10 ps. The time resolution of the FFEC is limited principally by the time-of-flight spread of the electrons between the tip and the deflecting field.