Surfaces of silicon, germanium, graphite (carbon) and germanium-silicide are active in EPR measurements. 
Mainly group 14 (formerly group IV) elements show EPR signals from a surface after crushing. Crystals of elements from groups 13 to 15 prefer to have the (110) plane exposed as a surface. On this surface, an atom of group 13 has 3/4 dangling bond, and an atom of group 15 has 5/4 dangling bond. Because of dehybridization of surface orbitals (caused by the decreased number of nearest neighbor atoms around the surface atom), a group 13 atom will have a largely unfilled dangling orbital since it has valence 3 and makes three bonds, while a group 15 atom will have a fully occupied dangling orbital at the surface. In that case, there is hardly any unpaired electron density, which results in a weak EPR signal for such materials. 
Clean cleaved surfaces of such materials form paired electron localized states on alternate sites resulting in a very weak to no EPR signal. Not well-cleaved surfaces and microcracks obtained from crushing, cleaving, abrading, neutron or high-energy ion irradiation or heating and rapid cooling in vacuum give a measurable EPR signal (a characteristic signal in Si at g = 2,0055). The presence of oxygen and hydrogen gas affects the EPR signal from microcracks by affecting the single electron spin centers. The gas molecules can get trapped and, when staying close to a spin center, affect the EPR signal. When a microcrack is sufficiently small, the wave functions of the dangling bond states extend beyond the surface and can overlap with wave functions from the opposite surface. This can create shear forces in the crystal surface, causing atom layers to realign while creating dangling bonds in the process.
Due to the reactivity of dangling bonds, the semiconductor native oxide will form due to adsorption of gas molecules, the only remaining dangling bonds are located at oxygen vacancies. Dangling bonds form an sp-hybridized bond with the adsorbed molecule, which have a metallic character. They are often the only defect sites present on atomic semiconductors, which provide such "soft centers" for molecules to adsorb to. When no gas adsorption is possible (for example for clean surfaces in vacuum), the surface energy can be reduced by reorganizing bonding electrons, creating lattice strain in the process. In case of the (001) surface plane of silicon, a single dangling bond on each atom will be formed, while pairing the other electron with a neighboring atom. 
Removal of dangling bond surface states on the silicon (001) surface from the band gap can be achieved by treatment of the surface with a monolayer of selenium (alternatively, sulfur was proposed). Selenium can attach to the silicon (001) surface and can bind to surface dangling bonds, bridging between silicon atoms. This releases the strain in the silicon surface and terminates the dangling bonds, covering them from the outside environment. 
When exposed, dangling bonds can act as surface states in electronic processes.