Interfacial and surface energetics of CoSi2

The energetics of the CoSi2‐Si interface and the CoSi2 surface have been investigated by analyzing the equilibrium shapes of isolated silicide precipitates. CoSi2 precipitates grown by heating 2 Å of Co on a clean, reconstructed Si{100} surface formed with a number of orientations that remained stable upon annealing to high temperatures. Precipitates buried by a Si capping layer were shown to form along {111} and {100} interfaces. A ratio of the CoSi2‐Si interfacial free energies has been measured from the shapes of a large number of buried precipitates indicating that γ{100}/γ{111}=1.43±0.07. It is suggested that the shape of CoSi2 equilibrated within vacuum consists of {111}, {100}, and {110} facets.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70558/2/JAPIAU-76-9-5190-1.pd

Surface roughening during low temperature Si(100) epitaxy

Reflection high energy electron diffraction (RHEED) was used to investigate surface roughening during low temperature Si(100) homoepitaxy. The use of RHEED allowed in situ real-time collection of structural information from the growth surface. RHEED patterns were analyzed using a simple kinematic diffraction model which related average surface roughness and average in-plane coherence lengths to the lengths and widths of individual RHEED diffraction features, respectively. These RHEED analyses were quantified by calibrating against cross-section transmission electron microscopy (TEM) analyses of surface roughening. Both the RHEED and TEM analyses revealed similar scaling of surface roughness with deposited thickness, with RHEED analyses resulting in roughness values a factor of ∼2 times lower than those obtained from TEM analyses. RHEED was then used to analyze surface roughening during Si(100) homoepitaxial growth in a range of temperatures, 200–275 °C. Initially, surface roughness increased linearly with deposited thickness at a roughening rate that decreased with increasing growth temperature. At each growth temperature, near the crystalline/amorphous Si phase transition, the rate of surface roughening decreased. This decrease coincided with the formation of facets and twins along Si{111} planes. Surface roughness eventually saturated at a value which followed an Arrhenius relation with temperature Eact ∼ 0.31±0.1Eact∼0.31±0.1 eV. This activation energy agrees well with the activation energy for the crystalline/amorphous Si phase transition, Eact ∼ 0.35Eact∼0.35 eV, and suggests that limited thickness epitaxy is characterized by this saturation roughness. Once the saturation roughness was reached, no significant changes in surface roughness were detected. In addition, the decay of average in-plane coherence lengths was also temperature dependent. Values of average coherence lengths, at the crystalline/amorphous Si phase transition, also increased with growth temperature. All of these data are consistent with a model that links surface roughening to the formation of critically sized Si{100} facets and the eventual breakdown in crystalline growth. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70948/2/JAPIAU-82-3-1157-1.pd

Effect of hydrogen on surface roughening during Si homoepitaxial growth

Hydrogen is shown to have a strong influence on the evolution of surface morphology during low temperature (310 °C) Si(100) homoepitaxy. Molecular beam epitaxy growth in the presence of deuterium shows a surface roughness within the epitaxial film that increases rapidly until the Si film exhibits a crystalline to amorphous transition. The rate at which the surface roughens depends critically on the partial pressure of deuterium. Although the kinetics of growth are sensitive to small pressures (4×10−8 Torr) of D, it appears that the breakdown of epitaxy does not result from a ‘‘critical’’ D concentration at the surface. This work suggests that the crystalline to amorphous transition, instead, results from increased roughening during epitaxy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71213/2/APPLAB-63-26-3571-1.pd

Mortality differences and inequalities within and between 'protected characteristics' groups, in a Scottish Cohort 1991-2009

Background: Little is known about the interaction between socio-economic status and 'protected characteristics' in Scotland. This study aimed to examine whether differences in mortality were moderated by interactions with social class or deprivation. The practical value was to pinpoint population groups for priority action on health inequality reduction and health improvement rather than a sole focus on the most deprived socioeconomic groups. Methods: We used data from the Scottish Longitudinal Study which captures a 5.3 % sample of Scotland and links the censuses of 1991, 2001 and 2011. Hazard ratios for mortality were estimated for those protected characteristics with sufficient deaths using Cox proportional hazards models and through the calculation of European age-standardised mortality rates. Inequality was measured by calculating the Relative Index of Inequality (RII). Results: The Asian population had a polarised distribution across deprivation deciles and was more likely to be in social class I and II. Those reporting disablement were more likely to live in deprived areas, as were those raised Roman Catholic, whilst those raised as Church of Scotland or as 'other Christian' were less likely to. Those aged 35-54 years were the least likely to live in deprived areas and were most likely to be in social class I and II. Males had higher mortality than females, and disabled people had higher mortality than non-disabled people, across all deprivation deciles and social classes. Asian males and females had generally lower mortality hazards than majority ethnic ('White') males and females although the estimates for Asian males and females were imprecise in some social classes and deprivation deciles. Males and females who reported their raised religion as Roman Catholic or reported 'No religion' had generally higher mortality than other groups, although the estimates for 'Other religion' and 'Other Christian' were less precise. Using both the area deprivation and social class distributions for the whole population, relative mortality inequalities were usually greater amongst those who did not report being disabled, Asians and females aged 35-44 years, males by age, and people aged <75 years. The RIIs for the raised religious groups were generally similar or too imprecise to comment on differences. Conclusions: Mortality in Scotland is higher in the majority population, disabled people, males, those reporting being raised as Roman Catholics or with 'no religion' and lower in Asians, females and other religious groups. Relative inequalities in mortality were lower in disabled than nondisabled people, the majority population, females, and greatest in young adults. From the perspective of intersectionality theory, our results clearly demonstrate the importance of representing multiple identities in research on health inequalities.Publisher PDFPeer reviewe

Effect of H on Si molecular‐beam epitaxy

In Si crystal growth by molecular‐beam epitaxy (MBE) at low temperatures there is known to be an epitaxial thickness: an initially crystalline regime before the deposited film becomes amorphous. The predominant impurity in MBE is hydrogen, but the role of background H in low‐temperature MBE has not previously been assessed. Here the effect of deliberate dosing of the Si surface with atomic H during low‐T growth is studied. The epitaxial thickness is shown to be sensitive to very small additional H fluxes (≊10−9 Torr, i.e., an increase in H only marginally above ambient). With further increases in dose rate, the epitaxial thickness decreases as hepi=h0−k(ln PH). Using secondary‐ion‐mass spectrometry data on the segregated H at the interface, we argue that breakdown in epitaxy is not caused directly by the surface concentration of adsorbed impurities. It is deduced that very small concentrations of H may influence the Si surface diffusion rate. The possible effect of background H adsorption on previous experiments on Si steps and surface diffusion is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69704/2/JAPIAU-74-11-6615-1.pd

Marine Monitoring Program: Annual Report for inshore pesticide monitoring 2018–19

[Extract] This component of the Marine Monitoring Program provides an understanding of nearshore pesticide profiles and the exposure risk to marine organisms, as a part of water quality condition on the Great Barrier Reef. Data are collected from eleven fixed monitoring sites located in four Natural Resource Management regions — the Wet Tropics (five sites: Low Isles, High Island, Normanby Island, Dunk Island and Lucinda), Burdekin (one site: Barratta Creek), Mackay-Whitsundays (four sites: Repulse Bay, Flat Top Island, Sandy Creek and Sarina Inlet) and Fitzroy (one site: North Keppel Island). The suite of pesticides monitored includes photosystem II (PSII) inhibiting herbicides (such as diuron, atrazine (and its metabolites), ametryn, hexazinone, tebuthiuron), which all affect photosynthesis, and are commonly detected due to their high usage in adjacent catchments, and their high solubility. Other pesticides monitored include those that have non-photosynthetic effects (such as imidacloprid and metolachlor) and knockdown herbicides (such as 2,4-D)

Wetting layer thickness and early evolution of epitaxially strained thin films

We propose a physical model which explains the existence of finite thickness wetting layers in epitaxially strained films. The finite wetting layer is shown to be stable due to the variation of the non-linear elastic free energy with film thickness. We show that anisotropic surface tension gives rise to a metastable enlarged wetting layer. The perturbation amplitude needed to destabilize this wetting layer decreases with increasing lattice mismatch. We observe the development of faceted islands in unstable films.Comment: 4 pages, 3 eps figure

Theory of Adsorption and Surfactant Effect of Sb on Ag (111)

We present first-principles studies of the adsorption of Sb and Ag on clean and Sb-covered Ag (111). For Sb, the {\it substitutional} adsorption site is found to be greatly favored with respect to on-surface fcc sites and to subsurface sites, so that a segregating surface alloy layer is formed. Adsorbed silver adatoms are more strongly bound on clean Ag(111) than on Sb-covered Ag. We propose that the experimentally reported surfactant effect of Sb is due to Sb adsorbates reducing the Ag adatom mobility. This gives rise to a high density of Ag islands which coalesce into regular layers.Comment: RevTeX 3.0, 11 pages, 0 figures] 13 July 199

Thermally activated reorientation of di-interstitial defects in silicon

We propose a di-interstitial model for the P6 center commonly observed in ion implanted silicon. The di-interstitial structure and transition paths between different defect orientations can explain the thermally activated transition of the P6 center from low-temperature C1h to room-temperature D2d symmetry. The activation energy for the defect reorientation determined by ab initio calculations is 0.5 eV in agreement with the experiment. Our di-interstitial model establishes a link between point defects and extended defects, di-interstitials providing the nuclei for the growth.Comment: 12 pages, REVTeX, Four figures, submitted to Phys. Rev. Let