1,940 research outputs found
Hydrogen adsorption and diffusion around Si(001)/Si(110) corners in nanostructures
While the diffusion of hydrogen on silicon surfaces has been relatively well
characterised both experimentally and theoretically, the diffusion around
corners between surfaces, as will be found on nanowires and nanostructures, has
not been studied. Motivated by nanostructure fabrication by Patterned Atomic
Layer Epitaxy (PALE), we present a density functional theory (DFT) study of the
diffusion of hydrogen around the edge formed by the orthogonal (001) and (110)
surfaces in silicon. We find that the barrier from (001) to (110) is
approximately 0.3 eV lower than from (110) to (001), and that it is comparable
to diffusion between rows on the clean surface, with no significant effect on
the hydrogen patterns at the growth temperatures used.Comment: 11 pages, 4 figure
Measurement Uncertainty of Liquid Chromatographic Analyses Visualized by Ishikawa Diagrams
Ishikawa, or cause-and-effect diagrams, help to visualize the parameters that influence a chromatographic analysis. Therefore, they facilitate the set up of the uncertainty budget of the analysis, which can then be expressed in mathematical form. If the uncertainty is calculated as the Gaussian sum of all uncertainty parameters, it is necessary to quantitate them all, a task that is usually not practical. The other possible approach is to use the intermediate precision as a base for the uncertainty calculation. In this case, it is at least necessary to consider the uncertainty of the purity of the reference material in addition to the precision data. The Ishikawa diagram is then very simple, and so is the uncertainty calculation. This advantage is given by the loss of information about the parameters that influence the measurement uncertaint
Error Tracking Down: A Peculiar Playground?
Errors in an analytical method are often not recognized as such or are underrated. Therefore, it is useful to compile and publish them. Error tracking down can even be an exciting field of research. Two different errors which can occur in chromatography are presented: The area of poorly
resolved peaks cannot be integrated accurately by the usual integrators or data systems due to geometrical reasons. Second, injected air can give rise to a retained peak in HPLC. Air injection can happen during a malfunction of the autosampler but the extra peak is unwanted because it can
overlap with the analyte peaks
The h Index – Help or Hype?
Three years ago a bibliometric index for the qualification of a person's scientific output was proposed by Hirsch, the so-called h index. This is an integer number which combines the number of papers of an author and the number of citations they gathered. Thus the h index is an indicator
for both the productivity and the impact of a scientist. This paper presents the properties of the h index and the great attention it attracted within a short time. Numerous other indices, claimed to be better than the original, were proposed in the meantime. These developments are discussed
critically
High-fidelity simulation increases obstetric self-assurance and skills in undergraduate medical students
Objective: Teaching intrapartum care is one of the most challenging tasks in undergraduate medical education. High-fidelity obstetric simulators might support students' learning experience. The specific educational impact of these simulators compared with traditional methods of model-based obstetric teaching has not yet been determined. Study design: We randomly assigned 46 undergraduate medical students to be taught using either a high-fidelity simulator or a scale wood-and-leather phantom. Their self-assessments were evaluated using a validated questionnaire. We assessed obstetric skills and asked students to solve obstetric paper cases. Main outcome measures: Assessment of fidelity-specific teaching impact on procedural knowledge, motivation, and interest in obstetrics as well as obstetric skills using high- and low-fidelity training models. Results: High-fidelity simulation specifically improved students' feeling that they understood both the physiology of parturition and the obstetric procedures. Students in the simulation group also felt better prepared for obstetric house jobs and performed better in obstetric skills evaluations. However, the two groups made equivalent obstetric decisions. Conclusion: This study provides first data on the impact of high-fidelity simulation in an undergraduate setting
Exact location of dopants below the Si(001):H surface from scanning tunnelling microscopy and density functional theory
Control of dopants in silicon remains the most important approach to
tailoring the properties of electronic materials for integrated circuits, with
Group V impurities the most important n-type dopants. At the same time, silicon
is finding new applications in coherent quantum devices, thanks to the
magnetically quiet environment it provides for the impurity orbitals. The
ionization energies and the shape of the dopant orbitals depend on the surfaces
and interfaces with which they interact. The location of the dopant and local
environment effects will therefore determine the functionality of both future
quantum information processors and next-generation semiconductor devices. Here
we match observed dopant wavefunctions from low-temperature scanning tunnelling
microscopy (STM) to images simulated from first-principles density functional
theory (DFT) calculations. By this combination of experiment and theory we
precisely determine the substitutional sites of neutral As dopants between 5
and 15A below the Si(001):H surface. In the process we gain a full
understanding of the interaction of the donor-electron state with the surface,
and hence of the transition between the bulk dopant (with its delocalised
hydrogenic orbital) and the previously studied dopants in the surface layer.Comment: 12 pages; accepted for publication in Phys. Rev.
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