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.

Measurement of sputtering yields and damage in C60 SIMS depth profiling of model organic materials

Abstract: Sputter-depth profiles of model organic thin films on silicon using C 60 primary ions have been employed to measure sputtering yields and depth resolution parameters. We demonstrate that some materials (polylactide, Irganox 1010) have a constant and high sputtering yield, which varies linearly with the primary ion energy, whereas another material (Alq 3 ) has lower, fluence-dependent sputtering yields. Analysis of multi-layered organic thin films reveals that the depth resolution is a function of both primary ion energy and depth, and the sputtering yield depends on the history of sputtering. We also show that ∼30% of repeat units are damaged in the steady-state regime during polylactide sputtering.

The measurement of viscosity of alloys—a review of methods, data and models

Abstract: Values of the viscosities of liquid metals are important in the prediction of fluid flow in many metallurgical manufacturing processes This paper describes a number of methods used to measure the viscosity of liquid metals, including capillary, oscillating vessel, rotational bob or crucible, oscillating plate, draining vessel, levitation using the damping of surface oscillations and acoustic methods A number of models used to estimate viscosity for elements, the temperature dependence of viscosity, and viscosity of multicomponent systems are also given, including the Andrade equation, Arrhenius equation, Hildebrand's free volume theory, Chhabra models, Moelwyn-Hughes model and thermodynamic models The scatter of data available in the literature are highlighted by comparing two reviews of data for elements

Room-temperature solid-state maser

Abstract: Using an organic molecular crystal as gain medium allows a maser to be operated in pulsed mode in air, at room temperature and in the terrestrial magnetic field, so avoiding many of the obstacles that have previously hindered the application of masers The maser is the microwave-frequency precursor of the now ubiquitous laser — or 'optical maser', as it was once known But it has had little technological impact compared with the laser, in large part because of inconvenience: masers typically require vacuum and/or low-temperature operating conditions Overcoming these obstacles would pave the way for significant maser-based innovations, including drastically more sensitive measurements across a range of scientific disciplines, from molecular biology to radio astronomy And, if the history of the laser is any indication, applications not yet dreamt of Mark Oxborrow, Jonathan Breeze and Neil Alford have now developed a solid-state room-temperature maser, based on an organic molecular crystal, that should enhance the potential of the maser as a tool for science and technology The invention of the laser has resulted in many innovations, and the device has become ubiquitous However, the maser, which amplifies microwave radiation rather than visible light, has not had as large an impact, despite being instrumental in the laser’s birth1,2 The maser’s relative obscurity has mainly been due to the inconvenience of the operating conditions needed for its various realizations: atomic3 and free-electron4 masers require vacuum chambers and pumping; and solid-state masers5, although they excel as low-noise amplifiers6 and are occasionally incorporated in ultrastable oscillators7,8, typically require cryogenic refrigeration Most realizations of masers also require strong magnets, magnetic shielding or both Overcoming these various obstacles would pave the way for improvements such as more-sensitive chemical assays, more-precise determinations of biomolecular structure and function, and more-accurate medical diagnostics (including tomography) based on enhanced magnetic resonance spectrometers9 incorporating maser amplifiers and oscillators Here we report the experimental demonstration of a solid-state maser operating at room temperature in pulsed mode It works on a laboratory bench, in air, in the terrestrial magnetic field and amplifies at around 145 gigahertz In contrast to the cryogenic ruby maser6, in our maser the gain medium is an organic mixed molecular crystal, p-terphenyl doped with pentacene, the latter being photo-excited by yellow light The maser’s pumping mechanism exploits spin-selective molecular intersystem crossing10 into pentacene’s triplet ground state11,12 When configured as an oscillator, the solid-state maser’s measured output power of around −10 decibel milliwatts is approximately 100 million times greater than that of an atomic hydrogen maser3, which oscillates at a similar frequency (about 142 gigahertz) By exploiting the high levels of spin polarization readily generated by intersystem crossing in photo-excited pentacene and other aromatic molecules, this new type of maser seems to be capable of amplifying with a residual noise temperature far below room temperature

Thickness-Dependent Hydrophobicity of Epitaxial Graphene

Abstract: This article addresses the much debated question whether the degree of hydrophobicity of single-layer graphene (1LG) is different from that of double-layer graphene (2LG). Knowledge of the water affinity of graphene and its spatial variations is critically important as it can affect the graphene properties as well as the performance of graphene devices exposed to humidity. By employing chemical force microscopy with a probe rendered hydrophobic by functionalization with octadecyltrichlorosilane (OTS), the adhesion force between the probe and epitaxial graphene on SiC has been measured in deionized water. Owing to the hydrophobic attraction, a larger adhesion force was measured on 2LG Bernal-stacked domains of graphene surfaces, thus showing that 2LG is more hydrophobic than 1LG. Identification of 1LG and 2LG domains was achieved through Kelvin probe force microscopy and Raman spectral mapping. Approximate values of the adhesion force per OTS molecule have been calculated through contact area analysis. Fur...