Surface and sub-surface thermal oxidation of thin ruthenium films

A mixed 2D (film) and 3D (nano-column) growth of ruthenium oxide has been experimentally observed for thermally oxidized polycrystalline ruthenium thin films. Furthermore, in situ x-ray reflectivity upon annealing allowed the detection of 2D film growth as two separate layers consisting of low density and high density oxides. Nano-columns grow at the surface of the low density oxide layer, with the growth rate being limited by diffusion of ruthenium through the formed oxide film. Simultaneously, with the growth of the columns, sub-surface high density oxide continues to grow limited by diffusion of oxygen or ruthenium through the oxide fil

Self-healing in B12P2 through Mediated Defect Recombination

Citation: Self-healing in B12P2 through Mediated Defect Recombination. S. P. Huber, E. Gullikson, C. D. Frye, J. H. Edgar, R. W. E. van de Kruijs, F. Bijkerk, and D. Prendergast. Chemistry of Materials 28 8415--8428 (2016) 10.1021/acs.chemmater.6b04075The icosahedral boride B12P2 has been reported to exhibit “self-healing” properties, after transmission electron microscopy recordings of sample surfaces, which were exposed to highly energetic particle beams, revealed little to no damage. In this work, employing calculations from first-principles within the density functional theory (DFT) framework, the structural characteristics of boron interstitial and vacancy defects in B12P2 are investigated. Using nudged elastic band simulations, the diffusion properties of interstitial and vacancy defects and their combination, in the form of Frenkel defect pairs, are studied. We find that boron icosahedra maintain their structural integrity even when in a degraded state in the presence of a vacancy or interstitial defect and that the diffusion activation energy for the recombination of an interstitial vacany pair can be as low as 3 meV, in line with the previously reported observation of “self-healing”

Mo/Si multilayer-coated amplitude division beam splitters for XUV radiation sources

Amplitude-division beam splitters for XUV radiation sources have been developed and extensively characterized. Mo/Si multilayer coatings were deposited on 50 nm-thick SiN membranes. By changing the multilayer structure (periodicity, number of bilayers, etc.) the intensity of the reflected and transmitted beams were optimized for selected incident radiation parameters (wavelength, incident angle). The developed optical elements were characterized by means of XUV reflectometry and transmission measurements, atomic force microscopy and optical interferometry. Special attention was paid to the spatial homogeneity of the optical response and reflected beam wavefront distortions. Here the results of the characterization are presented and improvements required for advanced applications at XUV free-electron lasers are identified. A flatness as low as 4 nm r.m.s. on 3 × 3 mm beam splitters and 22 nm r.m.s. on 10 × 10 mm beam splitters has been obtained. The high-spatial-frequency surface roughness was about 0.7-1 nm r.m.s. The middle-spatial-frequency roughness was in the range 0.2-0.8 nm r.m.s. The reflection and transmission of the beam splitters were found to be very homogeneous, with a deviation of less than 2% across the full optical element

Determining crystal phase purity in c-BP through X-ray absorption spectroscopy

Citation: Determining crystal phase purity in c-BP through X-ray absorption spectroscopy. S. P. Huber, V. V. Medvedev, E. Gullikson, B. Padavala, J. H. Edgar, R. W. E. van de Kruijs, F. Bijkerk, and D. Prendergast. Phys. Chem. Chem. Phys. 19 8174--8187 (2017) 10.1039/c6cp06967cWe employ X-ray absorption near-edge spectroscopy at the boron K-edge and the phosphorus L2,3-edge to study the structural properties of cubic boron phosphide (c-BP) samples. The X-ray absorption spectra are modeled from first-principles within the density functional theory framework using the excited electron core-hole (XCH) approach. A simple structural model of a perfect c-BP crystal accurately reproduces the P L2,3-edge, however it fails to describe the broad and gradual onset of the B K-edge. Simulations of the spectroscopic signatures in boron 1s excitations of intrinsic point defects and the hexagonal BP crystal phase show that these additions to the structural model cannot reproduce the broad pre-edge of the experimental spectrum. Calculated formation enthalpies show that, during the growth of c-BP, it is possible that amorphous boron phases can be grown in conjunction with the desired boron phosphide crystalline phase. In combination with experimental and theoretically obtained X-ray absorption spectra of an amorphous boron structure, which have a similar broad absorption onset in the B K-edge spectrum as the cubic boron phosphide samples, we provide evidence for the presence of amorphous boron clusters in the synthesized c-BP samples

Detection of defect populations in superhard semiconductor boron subphosphide B12P2 through X-ray absorption spectroscopy

Citation: Detection of defect populations in superhard semiconductor boron subphosphide B12P2 through X-ray absorption spectroscopy. S. P. Huber, E. Gullikson, J. Meyer-Ilse, C. D. Frye, J. H. Edgar, R. W. E. van de Kruijs, F. Bijkerk, and D. Prendergast J. Mater. Chem. A 5 5737--5749 (2017) 10.1039/c6ta10935gRecent theoretical work has shown for the first time how the experimentally observed property of “self-healing” of the superhard semiconductor boron subphosphide (B12P2) arises through a process of mediated defect recombination. Experimental verification of the proposed mechanism would require a method that can detect and distinguish between the various defect populations that can exist in B12P2. X-ray absorption near-edge spectroscopy (XANES) is such a method and in this work we present experimentally collected spectra of B12P2samples with varying crystalline qualities. By simulating the X-ray spectroscopic signatures of potential crystallographic point defects from first-principles within the density functional theory framework, the presence of defect populations can be determined through spectroscopic fingerprinting. Our results find an increasing propensity for the presence of phosphorus vacancy defects in samples deposited at lower temperatures but no evidence for comparable populations of boron vacancies in all the samples that have been studied. The absence of large amounts of boron vacancies is in line with the “self-healing” property of B12P2