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

Exploiting the P L2,3 absorption edge for optics: spectroscopic and structural characterization of cubic boron phosphide thin films

The transmission of cubic boron phosphide (c-BP) thin films, prepared by chemical vapor deposition (CVD), was evaluated near the phosphorous L2,3 and boron K absorption edge. The c-BP films were analyzed with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES), to study their structural and chemical properties. The TEM analysis reveals that c-BP initially grows in islands. The merging of the P L2,3, P K and B K absorption edges culminates in a sharp absorption feature starting at 130 eV, showing that c-BP can be used in applications that require a relatively transparent material in the energy range just below that absorption feature. Due to experimental constraints the samples were grown at a temperature significantly below the temperature for optimal crystal growth. XANES analysis showed that, as a result of the reduced crystal quality, the intensities of the absorption transitions are reduced compared to those in high quality crystalline reference samples. Optimizing the quality of the BP films will increase the contrast in transmission across the absorption edge

Epitaxy of Boron Phosphide on Aluminum Nitride(0001)/Sapphire Substrate

The boron phosphide (BP) semiconductor has many remarkable features, including high thermal neutron capture cross section of the ¹⁰B isotope, making it attractive for neutron detection applications. Effective and efficient neutron detection require BP to also have high crystal quality with optimum electrical properties. Here, we present the heteroepitaxial growth of high quality BP films on a superior aluminum nitride(0001)/sapphire substrate by chemical vapor deposition. The effect of process variables on crystalline and morphological properties of BP was examined in detail. BP deposited at high temperatures and high reactant flow rate ratios produced films with increased grain size and improved crystalline orientation. Narrower full width at half-maximum values of BP Raman peaks (6.1 cm^–1) and ω rocking curves (352 arcsec) compared to values in the literature confirm the high crystalline quality of produced films. The films were <i>n</i>-type with the highest electron mobility of 37.8 cm²/V·s and lowest carrier concentration of 3.15 × 10¹⁸ cm^–3. Rotational twinning in BP due to degenerate epitaxy caused by 3-fold BP(111) on 6-fold AlN(0001) was confirmed by synchrotron white beam X-ray topography. This preliminary study showed that AlN is an excellent substrate for growing high quality BP epitaxial films with promising potential for further enhancement of BP properties

Maternal serum soluble CD30 is increased in normal pregnancy, but decreased in preeclampsia and small for gestational age pregnancies

OBJECTIVE: Women with preeclampsia and those who deliver small for gestational age (SGA) neonates are characterized by intravascular inflammation (T helper 1 (Th1)-biased immune response). There is controversy about the T helper 2 (Th2) response in preeclampsia and SGA. CD30, a member of the tumor necrosis factor receptor superfamily, is preferentially expressed in vitro and in vivo by activated T cells producing Th2-type cytokines. Its soluble form (sCD30) has been proposed to be an index of Th2 immune response. The objective of this study was to determine whether maternal serum concentration of sCD30 changes with normal pregnancy, as well as in mothers with preeclampsia and those who deliver SGA neonates. METHODS: This cross-sectional study included patients in the following groups: (1) non-pregnant women (N=49); (2) patients with a normal pregnancy (N=89); (3) patients with preeclampsia (N=100); and (4) patients who delivered an SGA neonates (N=78). Maternal serum concentration of sCD30 was measured by a specific and sensitive enzyme-linked immunoassay. Non-parametric tests with post-hoc analysis were used for comparisons. A p value <0.05 was considered statistically significant. RESULTS: (1) The median sCD30 serum concentration of pregnant women was significantly higher than that of non-pregnant women (median: 29.7 U/mL, range: 12.2-313.2 vs. median: 23.2 U/mL, range: 14.6-195.1, respectively; p=0.01); (2) Patients with preeclampsia had a significantly lower median serum concentration of sCD30 than normal pregnant women (median: 24.7 U/mL, range: 7.6-71.2 vs. median: 29.7 U/mL, range: 12.2-313.2, respectively; p<0.05); (3) Mothers with SGA neonates had a lower median concentration of sCD30 than normal pregnant women (median: 23.4 U/mL, range: 7.1-105.3 vs. median: 29.7 U/mL, range: 12.2-313.2, respectively; p<0.05); and (4) There was no significant correlation (r=-0.059, p=0.5) between maternal serum sCD30 concentration and gestational age (19-38 weeks) in normal pregnant women. CONCLUSIONS: (1) Patients with preeclampsia and those who deliver a SGA neonate had a significantly lower serum concentration of sCD30 than normal pregnant women; (2) This finding is consistent with the view that preeclampsia and SGA are associated with a polarized Th1 immune response and, perhaps, a reduced Th2 response