Creation of <i>E</i>′ defects in vitreous SiO2 by energetic electrons produced by x irradiation

Kerwin, David B.; Galeener, F. L.

doi:10.1063/1.105811

Cited by 9 publications

(4 citation statements)

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“…The luminescence is due to radiative recombination of electrons and holes excited by the primary x-ray photons and, more efficiently, by secondary electrons. 45 In contrast to photoluminescence, this results in a dynamic spectrum of luminescence from several centers, rather than only those excited by a specific absorption band. Metastable defects which might not be observed in post-irradiation experiments may contribute to XRL.…”

Section: Resultsmentioning

confidence: 99%

X-ray induced luminescence of high-purity, amorphous silicon dioxide

Miller

Leisure

Austin

1999

Journal of Applied Physics

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A comprehensive study of x-ray stimulated luminescence has been carried out on four types of high-purity, amorphous silica (a-SiO2). Both high OH and low OH as well as oxygen-excess and oxygen-deficient materials were studied. The room-temperature, visible x-radio luminescence (XRL) was measured continuously as a function of x-ray dose from zero to 400 Mrad volume average dose. In addition to the XRL measurements, electron paramagnetic resonance (EPR) was used to determine the concentrations of the two key radiation-induced defects, the E′ center and the nonbridging oxygen hole center (NBOHC). The XRL spectra were deconvolved into four Gaussian components with centers at 1.9, 2.2, 2.6, and 2.75 eV. The same centers and widths could be used to describe the spectra in all four types of a-SiO2, only the intensities varied. The 2.6 and 2.75 eV lines are strongly dose dependent, rising from near zero intensity at zero dose in all four materials. These two lines are strongly correlated with each other; they have essentially the same dependence on dose and sample type. This correlation suggests that these two lines are due to the same radiation-induced defect, or to closely related defects. The dose dependence and sample-to-sample variation of these two lines bear some similarities to the E′ concentrations. In contrast to the 2.6 and 2.75 eV lines, the 1.9 eV line has a high intensity at the lowest doses measurable. A simple phenomenological model is proposed to describe the 1.9 eV XRL line. This model involves two populations of defects; one population is present at zero dose and is assumed to be dose independent, while the second population is dose dependent. Evidence is presented that the dose-dependent defect is the NBOHC. The XRL due to the dose-independent population may be associated with a transient response to the x rays, or to a metastable defect; this population may not be observable in post-irradiation experiments such as EPR and conventional photoluminescence. Similar to the 1.9 eV line, the 2.2 eV line also has relatively high intensity at the lowest measurable x-ray dose. The behavior of this line is in general agreement with the self-trapped exciton model.

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Section: Resultsmentioning

confidence: 99%

X-ray induced luminescence of high-purity, amorphous silicon dioxide

Miller

Leisure

Austin

1999

Journal of Applied Physics

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“…This phenomenon is explained by the electron irradiation, which has two consequences. First it causes oxide degradation that is damage in the bulk of the oxide [16,17] and at its interfaces, which make possible the passage of carriers through the oxide layer according to some mechanisms such as the Poole-Frenkel process [18] or tunneling effect via created traps [19]. Second, during the acquisition of the e-beam-induced current, holes are trapped in the Ge-NCs and at the surface states.…”

Section: Resultsmentioning

confidence: 99%

Conductive AFM microscopy study of the carrier transport and storage in Ge nanocrystals grown by dewetting

Gacem¹,

Hdiy²,

Troyon³

et al. 2010

Nanotechnology

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A combined conductive atomic force microscope (C-AFM)/scanning electron microscope (SEM) has been used to study the electric transport and retention mechanisms through Ge nanocrystals (NCs). The NCs were formed by a two-step dewetting/nucleation process on a silicon oxide layer grown on n-doped 001 silicon substrate. Without preliminary e-beam irradiation, electric images are obtained only with bias voltages larger than 8 V. This is due to the barrier height introduced by the presence of the native oxide on NCs and of the oxide layer on which the NCs are grown. After acquisition of an e-beam-induced current image, electric images (e-beam off) can be easily obtained at low bias voltages because of the trap creation in the oxide layer. We show that the critical threshold voltage to detect a current through the NCs decreases with NCs size. The band diagram of the contact in the presence of a p-doped diamond coated tip shows that the conduction mechanism is dominated by holes. At last we show a good memory effect with charge/discharge in the NCs resulting in a long retention time.

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“…In previous work it has been shown [9] that the creation of point defects in xirradiated SiC>2 occurs primarily through the damage caused by electrons (photo-and Auger) which are initially ejected by the absorption of an x ray. In the present work we have shown that the efficiencies of defect creation and activation increase with photon energy and vary approximately as the first and second powers of the x-ray ejected electron energies, respectively.…”

Section: Amount Of Energy Imparted In Our Experimentsmentioning

confidence: 99%

“…Kerwin and Galeener [9] have shown that essentially all of the E' defect creation in x-irradiated r-Si02 occurs due to damage by energetic photo-and Auger electrons which are initially produced when an x-ray photon is absorbed by either an O or Si atom. They have also concluded that an increase in defect production efficiency with increasing photon energy would be expected in bulk r-Si02.…”

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Energy dependence ofE’ spin production in x-irradiated vitreousSiO2

Kerwin

Galeener

1992

Phys. Rev. Lett.

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We have irradiated fused silica with monochromatic x rays from a synchrotron radiation source, and have shown for the first time that the efficiency of producing E' spins increases nonlinearly with photon energy for silica containing a large concentration of preexisting defects, and almost linearly for silica containing very few preexisting defects. It is concluded that £" defects are created or activated with efficiencies proportional to approximately the first or second powers, respectively, of the initial energy of the energetic electrons produced by x-ray absorption. PACS numbers: 6l.80.Cb, 61.42.+h, 76.30.Mi There are three distinct point defects which have been observed at room temperature by electron paramagnetic resonance (EPR) in irradiated high purity silica: the £" center, the nonbridging oxygen hole center (NBOHC), and the peroxyl radical oxygen hole center (PROHC). The nature of these dominant broken bond defects in vitreous (r-) SiC>2 has been reviewed by Griscom [1], The E' center was first studied by Weeks [2], and has been assigned by Feigl, Fowler, and Yip [3] to an electron trapped on a three-bonded Si atom which is part of an asymmetrically relaxed oxygen vacancy. The NBOHC has been assigned by Stapelbroek et al. [4] to a hole trapped on the unbonded p 2 orbital of a nonbridging oxygen, while the PROHC has been attributed by Friebele et al, [5] to a hole trapped on the unbonded p 2 orbital of the singly bonded oxygen atom in a dangling peroxyl radical. The growth of the E' signal with x irradiation in fused silica depends strongly on the concentration of hydroxyl groups, as well as the annealing history of the sample. Figure 1 displays data from Galeener and co-workers [6,7], showing the total number of E' spins (TV) produced as a function of dose (D) for identically annealed fused silica samples that had been irradiated with x rays from a 40-kV Cu-target x-ray tube. The N induced in Suprasil-1 [8] (a "wet" silica which contains a high concentration of hydroxyl groups, [OH] -1200 ppm) is linear with D over the entire dose regime investigated, while the "dry" Suprasil-Wl ([OH]-4 ppm) exhibits a nonlinear behavior. Galeener and co-workers [6,7] have shown that the new spins appearing in the high dose linear regions of Fig. 1 in both Suprasil-1 and Suprasil-Wl are due to the creation of new E' defect centers, while the nonlinear growth at lower doses in Suprasil-Wl is due to the activation of preexisting defects. Creation by x irradiation involves the breaking of one or more bonds at a previously completely bonded site, while activation merely involves the transfer of an electron or hole to or from a previously existing broken bond [7]. Quantitative analysis of the data in Fig. 1 shows that at doses below about 3 Mrad (SiOa) both curves are again linear, and that at least 80% of the E' spins observed in Suprasil-1 have been created, while in the Suprasil-Wl at least 80% have been activated from preexisting defects [7]. Thus creation dominates in wet Suprasil-1 and activation dominates in dry Supr...

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Creation of E′ defects in vitreous SiO2 by energetic electrons produced by x irradiation

Abstract: From experiments using synchrotron radiation, we present evidence that the spin-active defects created in v-SiO2 by x irradiation are predominantly the result of energetic electron damage, rather than the relaxation of the photoionized atoms.

Cited by 9 publications

References 10 publications

X-ray induced luminescence of high-purity, amorphous silicon dioxide

X-ray induced luminescence of high-purity, amorphous silicon dioxide

Conductive AFM microscopy study of the carrier transport and storage in Ge nanocrystals grown by dewetting

Energy dependence ofE’ spin production in x-irradiated vitreousSiO2

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