National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

Practical guides for x-ray photoelectron spectroscopy: First steps in planning, conducting, and reporting XPS measurements

Abstract: Over the past three decades, the widespread utility and applicability of X-ray photoelectron spectroscopy (XPS) in research and applications has made it the most popular and widely used method of surface analysis. Associated with this increased use has been an increase in the number of new or inexperienced users which has led to erroneous uses and misapplications of the method. This article is the first in a series of guides assembled by a committee of experienced XPS practitioners that are intended to assist inexperienced users by providing information about good practices in the use of XPS. This first guide outlines steps appropriate for determining whether XPS is capable of obtaining the desired information, identifies issues relevant to planning, conducting and reporting an XPS measurement, and identifies sources of practical information for conducting XPS measurements. Many of the topics and questions addressed in this article also apply to other surface-analysis techniques.

On the stability of viscous flow between parallel planes in the presence of a co-planar magnetic field

Abstract: Linearized equations are derived which govern the stability of a viscous, electrically conducting fluid in motion between two parallel planes in the presence of a co-planar magnetic field. With one suitable approximation, which restricts the valid range of Reynolds number of the theory, the problem of stability is reduced to the solution of a fourth-order ordinary differential. equation. The disturbances considered are neither amplified nor damped, but are neutral. Curves of wave number against Reynolds number for neutral stability are calculated for a range of values of a certain parameter, q, which represents the magnetic effects. For given physical and geometrical properties, the critical Reynolds number above which the flow is unstable rises with the strength of the magnetic field. These results are completely wi-thin the range of the approximation mentioned. In addition, an energy relation is derived which illustrates the balance between. energy transferred from the basic flow to the disturbances, and that dissipated by viscosity and by the magnetic field perturbations.

The effect of air and vacuum environments on fatigue crack growth rates in Ti-6Al-4V

Abstract: Fatigue crack propagation studies in vacua of 1.33 mN m-2, on Ti-6 A1-4V, at growth rates of 10-7 to 10-4 mm/cycle have shown that a threshold for growth exists at ‡K values of 6.3 to 7.6 MN m-3/2. The value of the threshold level is microstructure dependent, but growth above this value was structure insensitive according to both growth rates and fracture surface observations. Some slow (≈ 10-8 mm/cycle) crack extension was observed below the threshold values but prolonged cycling reduced the growth rate to a vanishingly small level. Fracture surface observations indicated that growth in this region was microstructure sensitive. Comparison with previously performed air work on the same material showed that while structure insensitive growth rates in vacuum were slower than those in air by a factor of 3 to 4, the low ‡K value structure sensitive rates were slower than the air ones by at least three orders of magnitude. A hypothesis is proposed to explain this in terms of a propagation mechanism for the structure sensitive mode of fatigue crack growth.

Calibration of the scales of areal surface topography-measuring instruments: part 1. Measurement noise and residual flatness

Abstract: In this paper, we present methods for determining the measurement noise and residual flatness of areal surface topography-measuring instruments. The methods are compliant with draft international specification standards on areal surface texture. We first introduce the international standards framework and then present current methods based on averaging and subtraction to isolate the measurement noise and residual flatness from the sample surface topography. These methods are relatively difficult to apply and time consuming in practice. An alternative method is presented based on thresholding and filtering techniques. This method is simple to apply in practice. Traceability and measurement uncertainty are discussed.