Изучены эффекты зарядки диэлектрических мишеней при облучении электронами средних энергий в сканирующем электронном микроскопе. Установлены существенные различия кинетики зарядки для исходных образцов и образцов, предварительно облученных электронами и ионами. Эти различия объясняются радиационно-стимулированным дефектообразованием в образцах Al2O3 (сапфир) и SiO2, имеющим, однако, различную природу. Показана роль модификации структуры поверхности и изменения электрофизических характеристик поверхности, в частности эффекта растекания зарядов. Обнаружены критические значения дозы облучения как ионами Ar+, так и электронами, при которых начинается активное дефектообразование в диэлектрических мишенях, а также критические значения внутренних полей зарядов, вносящих существенный вклад во временные характеристики зарядки Al2O3 и SiO2. Работа выполнена при финансовой поддержке РФФИ (грант N 15-02-07819а). DOI: 10.21883/FTT.2017.08.44749.460
The charging kinetics of Al_2O_3 (sapphire) and SiO_2 (α-quartz) dielectrics irradiated by inert gas ions (Ar^+), metal ions (Ga^+), and protons (H^+) has been studied. It has been found that charging kinetics depends considerably on the type of irradiating ion. Also, it has been established that preirradiation of a dielectric target by an ionizing corpuscular radiation (protons, ions) substantially changes the charge characteristics of the dielectric surface. These differences depend on irradiating ion energy, which governs the depth of an accumulated negative charge layer versus the depth of ion preimplantation.
Photoluminescence (PL) of sapphire single crystals as received and preirradiated by low energy Ar+ ions and electrons has been studied to reveal a relationship between sapphire charging under electron beam irradiation and radiation-induced defect formation. The photoluminescence spectra were obtained using a confocal microscope wavelength of 445 nm as well as by a nonconfocal method with excitation at a wavelength of 355 nm. The lines observed in PL spectra for all samples are associated with both intrinsic and impurity defects. It has been established that preliminary ion irradiation leads to disordering of the near-surface region of the sample resulting in a significant increase in the photoluminescence intensity. Preliminary electron irradiation can lead to a change in the charge state of defects that initially exist in the crystal.
To establish the effect of subthreshold defect formation on the charge accumulation in quartz glasses, a comprehensive study of the process of their electrization by electron beams was carried out. Earlier it was shown that the process of radiative electrization of quartz glasses consists of two stages. The short-term stage of charging can be explained by the accumulation of charge on the initial trap centers, and the long-term component can be caused by the generation of deep trap centers capable of capturing electrons. In the studied quartz samples, the trapping centers can be three-coordinated silicon atoms (E'-centers). The presence of two stages of the charging process is confirmed by two different methods for determining the surface potential. Despite the increase in the surface potential during irradiation and the resulting decrease in the energy of the incident electrons, an increase in the intensity of the cathodoluminescent signal is observed. Such an increase in intensity can be caused by an increase in the number of luminescent defects in quartz, a two-coordinated silicon atom or a non-bridging oxygen atom, as well as by charge accumulation at competing nonradiative trap centers.
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