Probe size study of apatite irradiation in stem

Abstract

Abstract. The effect of electron beam irradiation of stoichiometric hydroxyapatite (Ca10(PO4)6(OH)2, HAP) is investigated using electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) mode equipped with a LaB6 gun. Initial irradiation at 160 A cm −2 dose rate shows no modification of the low loss spectra. No difference of mass loss for Ca, O and P is observed for two different probe diameters: 4 nm (dose rate = 160 A cm −2 ) and 24 nm (dose rate = 70 A cm −2 ). Furthermore no formation of CaO is observed for both experimental conditions. It is proposed that the low values of both electron dose rates and doses (from 350 to 2400 C cm −2 ) avoid mass loss. At the higher dose rate obtained with a field emission gun (FEG), transformations are observed for the lowloss signal as well as for the Ca, P and O signals. These results might be very useful for the future studies of apatite particles at the nanoscale.

Aberration-Corrected Transmission Electron Microscopic Study of the Central Dark Line Defect in Human Tooth Enamel Crystals

“…Thus, the expulsion of OH − is most probable when enamel interacts with the electron beam. Therefore, electron beam damage is an important parameter to take into account for obtaining information data on the CDL structure (Brès et al, 2014). In fact, the attempt was made to get some information from the CDL site by electron energy loss spectroscopy and X-ray energy dispersive spectroscopy (EDS), but the damage registered in the HTE crystals was substantial (Reyes-Gasga & Brès, 2015).…”

High Resolution STEM Images of the Human Tooth Enamel Crystals

“…Figure 2a shows the graphic representation of the dissolution of the human tooth enamel by acid attack, and Figure 2b shows its HRTEM image as they began to dissolve after treated with orthophosphoric acid for simulating acid attacks: the acid attack always started at the center of the crystals. Taking as a basis the hexagonal unit cell of HAP, during caries, the human tooth enamel crystals were destroyed systematically: first, a central lesion elongated along the [11][12][13][14][15][16][17][18][19][20] direction appeared on the basal (0001) planes; and secondly, the lesion developed anisotropically along the [0001] direction across the crystals [7].…”

“…Dental caries and periodontal diseases are the most common bacterial infections in humans [12]. As observed in Figure 2, at the nanoscale, during carious processes or other acidic attack, human tooth enamel crystals were destroyed systematically: first a central lesion elongated along the [11][12][13][14][15][16][17][18][19][20] direction appeared on the (0001) basal planes of the crystals; secondly, this lesion developed anisotropically along the [0001] direction across the crystals; and third, the crystals were break open [7]. No full explanation for the anisotropic crystal dissolution has yet been put forward.…”

“…Nevertheless, several common-sense observations have been made (Figure 2): (1) there was a structural feature on the center of the crystal basal faces different from the adjoining surface; (2) after dissolution, the lesion was hexagonal in shape and did not split the crystal along the [11][12][13][14][15][16][17][18][19][20] direction; (3) the dissolution process propagated anisotropically along the [0001] direction, which indicated that the structural feature was 3D.…”

“…Several approaches are followed to conduct the ongoing research on that subject such as the analysis of etch pits at the HAP surface [13,14] and surface energy calculations [15]. Defects in tooth enamel crystals aligned along the [11][12][13][14][15][16][17][18][19][20] direction have been analyzed by HRTEM. Brès et al [6] identified some types of disorders that may act as dissolution sites.…”