Electron affinity diamond

A theoretical analysis based on ab-initio molecular dynamics has been reported [10], The study employed a plane wave basis, and soft core, norm conserving pseudopotentials were used to describe the ions. The supercells consisted of 10 - 12 layers of AIN with 4-16 atoms in each layer. For most calculations, a 12 A vacuum region separated the surfaces. One side of each slab was terminated by hydrogen atoms to reduce charge transfer caused by the finite width of the slab. The electron affinities of different surface configurations of AIN are listed in TABLE 1, where prior results for the diamond (111) surface are also listed. 

It is empirically known that as grown diamond films do not exhibit a charge-up under SEM observation, while it is not so for single erystal diamonds. This is most likely because of the effect of surface conduction by H-termination. It is also known that H-terminated undoped and B-doped diamonds exhibit negative electron affinity (NEA), where the vacuum level is energetically lower than the conduction band. It is thus expected that onee electrons are excited to the conduction band of diamond, they are spontaneously emitted to the vacuum presumably across a small barrier at the surface. 

Due to the wide bandgap, the conduction band of diamond approximates the vacuum level. Consequently, electrons excited into the conduction band may leave the diamond s surface as there is no significant potential difference between conduction band and vacuum level. In hydrogenated diamond films, the conduction band is even observed to exceed the vacuum level, resulting in a negative electron affinity of the respective film. This causes the emission of excited electrons from the film to occur all the easier. 

Apart from transistors, several other solid state devices have been discussed [78], like junctions, photon and electron beam switches and various kinds of sensors. One property of diamond which has stimulated considerable interest in the recent years is the negative electron affinity (NEA) of suitably prepared surfaces [78,80]. The electron affinity, of a material is defined as the difference between the energy of a free electron in vacuum and the bottom of the conduction band Fyac - E. In Fig. 8 the electronic bands of p-doped clean and H-terminated (111) diamond surfaces near the surface are depicted, based on the results of UV-photoemission measurements. For the H-terminated surface, the electron affinity becomes negative once an electron is injected into the conduction band from a suitable contact or by UV excitation, it will easily leave the crystal and be emitted into vacuum. This effect, which is also observed on monohydride terminated (100) surfaces, is not unique to diamond but was also observed in a few other semieonductors with high band gaps [80]. Apart from a scientific interest, the NEA of diamond makes it an attractive eandidate for the replacement of thermionic emitters as electron beam sourees and as a miniature electron emitter for field emission displays. 

S., Kudo, Y, Saito, 1., Koe,)., Kudo, M., Yamada, T., Takakuwa, Y, and Okano, K. (2009) Electron emission from conduction band of diamond with negative electron affinity. Phys. Rev. B, 80(16), 165321. 

In brief, saturation of surface dangling bonds by donor-like monovalent hydrogen atoms results in a dense surface dipole layer (C -H ), which results in an electrostatic potential step perpendicular to the surface. This negative electron affinity increases all energy levels of diamond by a defined amount (see Figure 5.9a). The valence band maximum (VBM) is now raised sufficiently with respect to the vacuum level to place it just above the chemical potential... 

Van Der Weide 1, Zhang Z, Baumann PK et al (1994) Negative-electron-affinity effects on the diamond (100) surface. Phys Rev B50 5803-5806... 

Cui IB, Ristein 1, Ley L (1998) Electron affinity of the bare tmd hydrogen covered single crystal diamond. Phys Rev Lett 81 429 32... 

As mentioned above (see Sect. 2.3.4, Table 2.16), the experimental values of the band gaps ( g) in most substances increase as the grain sizes decrease. Diamond is an exception, its g decreasing together with the grain sizes. Here, an important role is played by the curvature of the surface layer, which results in the negative electron affinity of nano-diamond particles [30, 31]. 

Edmonds MT, Pakes Cl, Mammadov S et al (2011) Surface band bending and electron affinity as a function of hole accumulation density in surface conducting diamond. Appl Phys Lett 98 102101... 

Accurate calculations for excitations with DMC are possible for systems as large as free-base porphyrin and models of the green fluorescent protein chromophore. Drummond et al. investigated the electron emission from diamondoids with DMC. Using DFT orbitals in DMC, they calculated the excitation energy for the HOMO-LUMO transition (optical gap), the electron affinity, and the ionization potential for carbon clusters with diamond structure up to CgvHvs. ... 

W.E. Pickett, Negative electron-affinity and low work function surface cesium on oxygenated diamond(lOO). Phys. Rev. Lett. 73(12), 1664-1667 (1994)... 

Tuning the Electron Affinity of Diamond from N ativeto Positive Electron Affinity... 

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