VEPFIT applied to depth profiling problems

Veen, A. van; Schüt, H.; Clément, M.; Nijs, Jo; Kruseman, A.C.; Ijpma, M. R.

doi:10.1016/0169-4332(94)00334-3

Cited by 299 publications

(169 citation statements)

References 12 publications

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“…With a monoenergetic positron beam, the parameter ͑S͒ of positron annihilation can be measured as a function of the incident positron energy ͑E, keV͒, where S is defined as S = N s / N T , and N T and N s are the numbers of annihilation events occurring in the range of 503.8 keVՅ E ␥ Յ 518.2 keV or 510.24 keVՅ E ␥ Յ 511.76 keV, respectively. [8][9][10][11][12] Compared with the S of vacancy-free material, the S of a material may increase when open volume and/or density of vacancy-type defects increase. [8][9][10][11][12] In this article, we have found that the partial pressure of oxygen ͑P O 2 ͒ during cooling after growth, strain-state, and substrate material are very important in manipulating the density, diffusion, and distribution of V O s.…”

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confidence: 99%

“…The S was analyzed by the VEPFIT method S͑E͒ = S s F s ͑E͒ + ͚ S i F i ͑E͒ and F s ͑E͒ + ͚ F i ͑E͒ = 1, where F s ͑E͒ is the fraction of positrons annihilated at the surface and F i ͑E͒ is that in the ith layer, S s and S i are the S parameters corresponding, respectively, to the annihilation of positrons on the surface and that in the ith layer. [9][10][11][12] Three layers were chosen for all samples except two layers for 0.1-BFO/SRO/STO, and one fixed boundary at 300 nm was used during simulation. BFO surfaces were studied using atomic force microscopy ͑AFM͒ and ferroelectric domains of the BFO films were studied using piezoelectric force microscopy ͑PFM͒.…”

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confidence: 99%

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The dependence of oxygen vacancy distributions in BiFeO3 films on oxygen pressure and substrate

Yuan¹,

Martin²,

Ramesh³

et al. 2009

Applied Physics Letters

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The epitaxial ͑001͒-oriented 250 nm BiFeO 3 /50 nm SrRuO 3 films were deposited on DyScO 3 and SrTiO 3 substrates, respectively. Following the growth, the cooling in lower oxygen pressure results in the creation of oxygen vacancies at the surface of the BiFeO 3 film and the epitaxial strain drives these vacancies to diffuse from the film surface to the film interface. The SrTiO 3 substrate strongly absorbs oxygen vacancies from the BiFeO 3 film while the DyScO 3 substrate does not. Therefore, the depth distribution of oxygen vacancies depends on the oxygen pressure during cooling, the epitaxial strain, and the substrate absorbing oxygen vacancies.

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confidence: 99%

mentioning

confidence: 99%

The dependence of oxygen vacancy distributions in BiFeO3 films on oxygen pressure and substrate

Yuan¹,

Martin²,

Ramesh³

et al. 2009

Applied Physics Letters

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“…The S(E) curves for (A) the reference bulk Gd samples, (B) the Gd films loaded to various hydrogen concentrations. The solid lines show the fit of the curves by VEPFIT [8].…”

Section: Resultsmentioning

confidence: 99%

“…1A that S parameters measured at higher energies for the sample B reasonably converge the bulk value, too. From fitting of the S(E) curves by VEPFIT [8] (solid lines in Fig. 1A) we obtained the bulk positron diffusion length L +,Gd = (270 AE 30) and (280 AE 20) nm for the samples A and B, respectively.…”

Section: Resultsmentioning

confidence: 99%

Defect studies of hydrogen-loaded nanocrystalline Gd films

Čı́žek

Procházka

Vlach

et al. 2008

Applied Surface Science

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“…Eventually at high energies E > 22 keV some positrons penetrate into the Si substrate which leads to a further increase of S. The solid lines in Fig. 5a represent a fit performed using VEPFIT software package [11] assuming three layers (i.e. Pd cap, Nb layer and Si substrate).…”

Section: Resultsmentioning

confidence: 99%

Defect studies of hydrogen-loaded thin Nb films

Čı́žek

Procházka

Bräuer

et al. 2006

Applied Surface Science

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Hydrogen interaction with defects in thin niobium (Nb) films was investigated using slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thin Nb films on Si substrates were prepared using cathode beam sputtering at room temperature. Initially, the microstructure of the virgin (hydrogen-free) films was characterized. Subsequently, the films were step-by-step electrochemically charged with hydrogen and the evolution of the microstructure with increasing hydrogen concentration was monitored. Hydrogen loading leads to a significant lattice expansion which was measured by XRD. Contrary to free-standing bulk metals, thin films are highly anisotropic. The in-plane expansion is prevented because the films are clamped on the elastically hard substrate. On the other hand, the out-of-plane expansion is substantially higher than in the bulk samples. Moreover, an enhanced hydrogen solubility in the a-phase was found in nanocrystalline Nb films. It was found that most of positrons in the films are trapped at open-volume defects at grain boundaries (GBs). These defects represent trapping sites also for hydrogen atoms. Hydrogen trapping at vacancy-like defects like GBs leads to a local increase of the electron density and is reflected by a pronounced decrease of the S parameter in the hydrogen-loaded samples. In addition, it was found that new defects are introduced at higher concentrations of hydrogen due to the formation of NbH (b-phase) particles. #

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VEPFIT applied to depth profiling problems

Cited by 299 publications

References 12 publications

The dependence of oxygen vacancy distributions in BiFeO3 films on oxygen pressure and substrate

The dependence of oxygen vacancy distributions in BiFeO3 films on oxygen pressure and substrate

Defect studies of hydrogen-loaded nanocrystalline Gd films

Defect studies of hydrogen-loaded thin Nb films

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