Electronic states spectroscopy of Hydroxyapatite ceramics

Abstract

Photoluminescence, surface photovoltage spectroscopy and high-resolution characterization methods (Atomic Force Microscopy, Scanning Electron Microscopy, X-ray spectroscopy and DC conductivity) are applied to nanostructured Hydroxyapatite (HAp) bioceramics and allowed to study electron (hole) energy states spectra of the HAp and distinguish bulk and surface localized levels. The measured trap spectra show strong sensitivity to preliminary heat treatment of the ceramics. It is assumed that found deep electron (hole) charged states are responsible for high bioactivity of the HAp nanoceramics.

Компьютерные Исследования Наноструктур Гидроксиапатита, Их Особенности И Свойства

“…-the electron energy band structures of initial HAP clusters computed by PM3 methods correspond well to the data reported (both experimental and simulated) [10,21,22,26,41,42,47] (see more details in [30] and in Table 4) -the main values obtained for the energy gap are Eg ∼ 3.54 eV for fixed PC (C3 symmetry), Eg ∼ 4.56 eV for relaxed PC (C1 symmetry) as compared with known data Eg ∼ 4.43 eV for the last structure in [41,42], and Eg ∼ 5.41 eV for the smallest HAP (C1 symmetry) as compared with Eg ∼ 5.38 eV for fixed HAP bulk [42]; -the computed data show some variations of the energies of the electronic band structures (E HOMO and E LUMO) with the addition of hydrogen atoms and corresponding variations of Eg (4.02-5.56 eV, see Table 4), and have a tendency for a decrease of Eg at the finally filled hydrogen bonds -all these data are in good agreement with the experimentally measured Eg ∼ 4.0 eV for a surface charged HAP samples in [47]; -the change of the total dipole moment and polarization are varied with increase of added hydrogen, but average values slightly decrease as compared with the initial state (see Table 3, Table 4). These results are very urgent for practical applications, because recent studies of the influence of electrical charge on HAP specimens surface on the osteoblast behavior and bone tissue growth clearly show that the deposition on the HAP surface of a negative charge enhances attachment and proliferation of the osteoblasts and fabrication of the bone tissue [36][37][38][39][40].…”

“…These data are confirmed in reference [60], where it was observed that with heating of HAP samples (fabricated by the same PERCERAMICS [15] technology) the OH group is annealed and removed from the HAP surface, which leads to a rise in the energy level Ei ~ Ev+3.5 eV, which the authors of [47] connected with the rise of OH vacancies. As it can be seen, a similar value of energy for OH vacancies case was obtained in [35] (Table 6 and Fig.…”

“…For further analysis, here Eg0 and ϕ0 as the energy gap and work function for initial HAP were introduced, while for all the cases with defects, etc., the new changed values were Eg and ϕ. Supposing that electron affinity changes only slightly (χ ~ const < ~ 1 eV [47]), it is possible to compare the calculated data of all Eg changes under the influences of defects, etc., with changes of the electron work function, which were experimentally measured by PEE method. In this case, for all the changes it is possible to write that Δϕ = ϕ -ϕ0 = Eg -Eg0 = ΔEg.…”

“…Because HAP is preferably an insulator (or p-type semiconductor [47] with wide forbidden energy gap Eg > ~ 4 eV), it have as usual dielectric a rather large screening Debye length LD. Therefore, the dependence of the displacement of the energy bands looks linear for the considered HAP clusters.…”

“…Therefore, the dependence of the displacement of the energy bands looks linear for the considered HAP clusters. There is an experimentally established [47] surface level with the energy E5 = Ev + 3.3 eV, giving a major contribution to the photoelectric effect (see on Fig. 9, here the Ei energies are the bulk energy levels, χ is the electron affinity, ϕ is the electron work function).…”