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.

Peptide self-assembly for nanomaterials: the old new kid on the block

Abstract: Peptide self-assembly is an increasingly attractive tool for nanomaterials. Perfected in biology peptide self-assembling systems have impacted on nearly any conceivable nanomaterial type. However, with all the information available to us commercialisation of peptide materials remains in its infancy. In an attempt to better understand the reasons behind this shortcoming we categorise peptide self-assembled materials in relation to their non-peptide counterparts. A particular emphasis is placed on the versatility of peptide self-assembly in terms of modularity, responsiveness and functional diversity, which enables direct comparisons with more traditional material chemistries.

Improved Electromagnetic Interference Shielding Properties of MWCNT–PMMA Composites Using Layered Structures

Abstract: Electromagnetic interference (EMI) shielding effectiveness (SE) of multi-walled carbon nanotubes–polymethyl methacrylate (MWCNT–PMMA) composites prepared by two different techniques was measured. EMI SE up to 40 dB in the frequency range 8.2–12.4 GHz (X-band) was achieved by stacking seven layers of 0.3-mm thick MWCNT–PMMA composite films compared with 30 dB achieved by stacking two layers of 1.1-mm thick MWCNT–PMMA bulk composite. The characteristic EMI SE graphs of the composites and the mechanism of shielding have been discussed. SE in this frequency range is found to be dominated by absorption. The mechanical properties (tensile, flexural strength and modulus) of the composites were found to be comparable or better than the pure polymer. The studies therefore show that the composite can be used as structurally strong EMI shielding material.

The Quadrupole Moment of the Carbon Dioxide Molecule

Abstract: A direct measurement of the magnitude and sign of the quadrupole moment of the carbon dioxide molecule has been made by determining the birefringence induced in gaseous CO2 by an inhomogeneous electric field. The method of measurement and the experimental details are described. The observable is the product of the molecular quadrupole moment Θ and the difference between parallel and perpendicular components of the optical polarizability tensor, Θ(α‖ − α⊥). For CO2, this quantity was found to have the value −(9·1 ± 0·5) x 10−50 e.s.u. a, — xi − x⊥ can be determined by other methods, but unfortunately the present uncertainty in this quantity is greater than that of the product Θ(α1 − α⊥). The most satisfactory value of α1 − α⊥ is taken to be 2·2 × 10−24 cm3, giving for the molecular quadrupole moment of CO2 −4·1 × 10−26 e.s.u., the sign indicating that the oxygen atoms are negative with respect to the carbon atom. The role of the ‘quadrupole polarizability’ of the molecule in complicating the interpretation of the experimental results is discussed, and experiments on argon and sulphur hexafluoride used to provide an estimate of its effect in the case of CO2.

Kinetics of surface segregation

Abstract: The kinetics of surface segregation, are analysed and illustrated by Auger electron spectroscopy observations of tin segregation to the free surface of iron. The analysis extends the diffusion approach of McLean (1957) by incorporating the effects of surface evaporation and by relaxing the constraint of a linear relation between the solute concentration at the surface and that in the adjacent bulk layer. Parameters are evaluated for the iron-tin system and the importance of the predictions is demonstrated by Auger electron measurement. It is found that marked deviations from McLean's analysis can occur at surfaces and that incorporation of the modifications presented here can lead to improvements in the accuracy of both the measurement of surface segregation levels and the deduction of solute diffusivity data, from the kinetic observations, by factors as high as 2 and 30, respectively. The method is applicable to solute diffusivities in the temperature range down to 450°C in iron.

Mechanism of Gold-Assisted Exfoliation of Centimeter-Sized Transition-Metal Dichalcogenide Monolayers

Abstract: Exfoliation of large-area monolayers is important for fundamental research and technological implementation of transition-metal dichalcogenides. Various techniques have been explored to increase the exfoliation yield, but little is known about the underlying mechanism at the atomic level. Here, we demonstrate gold-assisted mechanical exfoliation of monolayer molybdenum disulfide, up to a centimeter scale. Detailed spectroscopic, microscopic, and first-principles density functional theory analyses reveal that strong van der Waals (vdW) interaction between Au and the topmost MoS2 layer facilitates the exfoliation of monolayers. However, the large-area exfoliation promoted by such strong vdW interaction is only achievable on freshly prepared clean and smooth Au surfaces, while rough surfaces and surfaces exposed to air for more than 15 min result in negligible exfoliation yields. This technique is successfully extended to MoSe2, WS2, WSe2, MoTe2, WTe2, and GaSe. In addition, electrochemical characterization reveals intriguing interactions between monolayer MoS2 and Au. A subnanometer-thick MoS2 monolayer strongly passivates the chemical properties of the underlying Au, and the Au significantly modulates the electronic band structure of the MoS2, turning it from semiconducting to metallic. This could find applications in many areas, including electrochemistry, photovoltaics, and photocatalysis.