Element-specific structural analysis of Si/B<sub>4</sub>C using resonant X-ray reflectivity

Nayak, M.; Pradhan, P. C.; Lodha, G. S.

doi:10.1107/s1600576715005877

Cited by 3 publications

(2 citation statements)

References 65 publications

(49 reference statements)

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“…To obtain chemical profiles, 𝑐 𝑖 (𝑧), for all of the atomic species, 𝑖, composing the sample and to further refine the on-resonance atomic scattering factors of Sm 2+ and Sm 3+ we use resonant x-ray reflectometry, 35,36 which is an element and bulk sensitive technique, that previously proved to be useful in determining chemical composition, valence and magnetization profiles, orbital ordering, [91][92][93][94][95] and very recently was used to extract information about the electronic properties of oxide heterostructures. 65 The method relies on the fact that for a flat layered sample, the intensity of the specularly reflected x-ray beam 𝑅(𝑞 𝑧 , 𝐸) can be relatively easily obtained from the position-and energy-dependent complex refractive index, 𝑛(𝑧, 𝐸), which in turn is given by the sum of the contributions of all the atoms composing the material: 91,96…”

Section: Chemical and Valence Profiling Using X-ray Reflectometrymentioning

confidence: 99%

Chemical and valence reconstruction at the surface ofSmB6revealed by means of resonant soft x-ray reflectometry

et al. 2018

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Samarium hexaboride (SmB6), a Kondo insulator with mixed valence, has recently attracted much attention as a possible host for correlated topological surface states. Here, we use a combination of x-ray absorption and reflectometry techniques, backed up with a theoretical model for the resonant 4,5 absorption edge of Sm and photoemission data, to establish laterally averaged chemical and valence depth profiles at the surface of SmB6. We show that upon cleaving, the highly polar (001) surface of SmB6 undergoes substantial chemical and valence reconstruction, resulting in boron termination and a Sm 3+ dominated sub-surface region. Whereas at room temperature, the reconstruction occurs on a time scale of less than two hours, it takes about 24 hours below 50 K. The boron termination is eventually established, irrespective of the initial termination. Our findings reconcile earlier depth resolved photoemission and scanning tunneling spectroscopy studies performed at different temperatures and are important for better control of polarity and, as a consequence, surface states in this system.

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Section: Chemical and Valence Profiling Using X-ray Reflectometrymentioning

confidence: 99%

Chemical and valence reconstruction at the surface ofSmB6revealed by means of resonant soft x-ray reflectometry

et al. 2018

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“…It has come to the authors' attention that the paper published by Nayak et al (2015) contains the following errors: (i) an error in the calculated electron density contrast (i.e. fraction of electron density difference, Á/) between the Si and B 4 C layers and (ii) a numerical error during conversion of the measured angular reflectivity to q z = 4 sin /.…”

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Element-specific structural analysis of Si/B₄C using resonant X-ray reflectivity. Corrigendum

2016

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[786][787][788][789][790][791][792][793][794][795][796] are corrected.It has come to the authors' attention that the paper published by Nayak et al. (2015) contains the following errors: (i) an error in the calculated electron density contrast (i.e. fraction of electron density difference, Á / ) between the Si and B 4 C layers and (ii) a numerical error during conversion of the measured angular reflectivity to q z = 4 sin / . Regarding (i), Á / across the Si/B 4 C interface is 0.5%, not 0.05%. This Á / is still one order of magnitude lower than what can be measured using hard X-ray reflectivity (XRR). Regarding (ii), the reported q z range in Figs. 3-10 of the original article exceeds the actual measured angle. The original data files were modified by mistake and are not retrievable. To show that the proposed methodology and the conclusion drawn are not affected by the error in q z , fresh measurements on freshly prepared similar samples were performed.Three different samples were fabricated on Si wafers using electron beam evaporation with varying spatial position of the B 4 C layer (40 Å ) in the Si film (300 Å ). The B 4 C layer is at the top, middle and bottom of the Si film in samples S1, S2 and S3, respectively. A tungsten layer with thickness 10 Å is located between the substrate and the thin film. In the B 4 C layer, elementary boron is incorporated through co-deposition. The XRR profiles of the three samples, measured using a Cu K source, are nearly identical in nature [similar to Fig , for S1, S2 and S3, respectively. Thus, our original conclusion that XRR is not sensitive to the low-contrast Si/B 4 C interface (Á / =0.5%) still stands.The microstructural sensitivity of the resonant soft X-ray reflectivity (R-SoXR) to the low-contrast Si/B 4 C interface is demonstrated near the B K edge of B 4 C (Fig. 1a). R-SoXR measurements were done in s-polarization geometry using the Optics Beamline on the BESSY synchrotron (Sokolov et al., 2014). The enhanced scattering strength strongly modulates the R-SoXR owing to reflection from the Si/B 4 C interface (similar to Fig. 3 in the original paper). This provides experimental evidence for the sensitivity of resonant reflectivity to the spatial variation of position of a low-contrast interface structure.To obtain spectroscopic information on S1, R-SoXR measurements are performed across the B K edge of In S1 of the original paper the elementary boron was oxidized, but in the fresh sample S1 elementary boron is not oxidized. Similarly, in S2 and S3, we observed that only elementary boron is present in the B 4 C layer (similar to Fig. 5 of the original paper).The atomic percent of resonating element and the distribution were quantified near the B K edge of elementary boron for S1, S2 and S3. The fitting procedure of R-SoXR is similar to that described in the original paper. In S1, the optimized values for the thicknesses (roughnesses) of the Si and B 4 C layers are 294 Å (5 Å ) and 42 Å (13 Å ), respectively. A carbon-contaminated layer at the top of the B 4 C layer i...

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Interface structure in nanoscale multilayers near continuous-to-discontinuous regime

Pradhan

Majhi

Nayak

et al. 2016

Journal of Applied Physics

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Interfacial atomic diffusion, reaction, and formation of microstructure in nanoscale level are investigated in W/B4C multilayer (ML) system as functions of thickness in ultrathin limit. Hard x-ray reflectivity (XRR) and x-ray diffuse scattering in conjunction with x-ray absorption near edge spectroscopy (XANES) in soft x-ray and hard x-ray regimes and depth profiling x-ray photoelectron spectroscopy (XPS) have been used to precisely evaluate detailed interfacial structure by systematically varying the individual layer thickness from continuous-to-discontinuous regime. It is observed that the interfacial morphology undergoes an unexpected significant modification as the layer thickness varies from continuous-to-discontinuous regime. The interfacial atomic diffusion increases, the physical density of W layer decreases and that of B4C layer increases, and further more interestingly the in-plane correlation length decreases substantially as the layer thickness varies from continuous-to-discontinuous regime. This is corroborated using combined XRR and x-ray diffused scattering analysis. XANES and XPS results show formation of more and more tungsten compounds at the interfaces as the layer thickness decreases below the percolation threshold due to increase in the contact area between the elements. The formation of compound enhances to minimize certain degree of disorder at the interfaces in the discontinuous region that enables to maintain the periodic structure in ML. The degree of interfacial atomic diffusion, interlayer interaction, and microstructure is correlated as a function of layer thickness during early stage of film growth.

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Element-specific structural analysis of Si/B₄C using resonant X-ray reflectivity

Cited by 3 publications

References 65 publications

Chemical and valence reconstruction at the surface ofSmB6revealed by means of resonant soft x-ray reflectometry

Chemical and valence reconstruction at the surface ofSmB6revealed by means of resonant soft x-ray reflectometry

Element-specific structural analysis of Si/B₄C using resonant X-ray reflectivity. Corrigendum

Interface structure in nanoscale multilayers near continuous-to-discontinuous regime

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Element-specific structural analysis of Si/B4C using resonant X-ray reflectivity

Cited by 3 publications

References 65 publications

Chemical and valence reconstruction at the surface ofSmB6revealed by means of resonant soft x-ray reflectometry

Chemical and valence reconstruction at the surface ofSmB6revealed by means of resonant soft x-ray reflectometry

Element-specific structural analysis of Si/B4C using resonant X-ray reflectivity. Corrigendum

Interface structure in nanoscale multilayers near continuous-to-discontinuous regime

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Element-specific structural analysis of Si/B₄C using resonant X-ray reflectivity

Element-specific structural analysis of Si/B₄C using resonant X-ray reflectivity. Corrigendum