Työfunktion

Työfunktion, or work function, is the minimum energy required to remove an electron from a solid to the vacuum level. It is a surface property that reflects the alignment between the material’s Fermi level and the vacuum energy level, as well as the influence of the surface dipole layer. The value is usually expressed in electronvolts (eV) and applies to the outermost atomic layer, not the bulk.

In metals, the work function depends on surface structure, cleanliness, and adsorbates. Different crystallographic orientations, oxide layers, and chemical species on the surface can raise or lower the value. In semiconductors, the concept becomes more complex and relates to electron affinity and band bending near the surface; the measured work function can vary with doping, surface states, and terminus.

Typical values range from about 4 to 5 eV for many metals (for example, gold around 5.1 eV, copper about 4.7 eV, silver about 4.3 eV). Graphitic materials and some semiconductors have similar ranges, but exact numbers depend on surface treatment and measurement conditions. Temperature has a relatively small effect on metals, while surface chemistry often dominates the observed value.

Applications and measurement methods are closely linked. The work function is central to electron emission devices, photocathodes, and photoemission spectroscopy. It can be measured with ultraviolet photoelectron spectroscopy (UPS) to determine the energy of emitted electrons, or inferred from photoelectric thresholds. Non-contact methods such as Kelvin probe techniques determine the contact potential difference between the surface and a reference probe, providing another route to assess work function variations across a surface.