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.

Gold-black coatings for freestanding pyroelectric detectors

Abstract: We describe the process of depositing gold-black on thin, freestanding pyroelectric detector substrates and compare this with previous work documented in the literature. We have evaluated gold-black coatings on thin, freestanding pyroelectric detector substrates by means of scanning electron microscope, Fourier transform infrared spectrophotometer reflectance, and spectral responsivity measurements. Spectrophotometric measurements indicate that reflectance at normal incidence varies by less than 1% at wavelengths shorter than 2.5 µm and by less than 10% at 10 µm. These results are correlated with the spectral responsivity of the detector and demonstrate that radiation not reflected by the gold-black is absorbed by the detector element. We have evaluated gold-black coatings as a function of position at two wavelengths and found variations of less than 1% at 1.25 µm and less than 5% at 10.3 µm, which demonstrates that spatial uniformity can be coating dependent. Gold-black coatings exposed to a 193 nm wavelength excimer laser were evaluated by visual inspection for damage and determined to have a damage threshold of approximately 38 mJ cm−2.

Multi-walled carbon nanotubes/sol–gel-derived silica/chitosan nanobiocomposite for total cholesterol sensor

Abstract: Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) have been immobilized via glutaraldehyde as a cross-linker onto sol–gel-derived silica (SiO2)/chitosan (CHIT)/multi-walled carbon nanotubes (MWCNT)-based nanobiocomposite film deposited onto indium-tin-oxide (ITO) glass for estimation of esterified cholesterol. The ChEt–ChOx/MWCNT/SiO2–CHIT/ITO bioelectrode characterized using Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and electrochemical techniques and shows response time of 10 s, linearity as 10–500 mg/dL for esterified cholesterol (cholesterol oleate), sensitivity as 3.8 μA/mM and shelf-life of about 10 weeks under refrigerated conditions. The value of Michaelis–Menten constant (Km) estimated as 0.052 mM using Lineweaver–Burke plot indicates high affinity of ChEt and ChOx to cholesterol oleate. Attempts have been made to utilize this electrode for estimation of total cholesterol in blood serum samples.

Influence of Surface Modified MWCNTs on the Mechanical, Electrical and Thermal Properties of Polyimide Nanocomposites

Abstract: Polyamic acid, the precursor of polyimide, was used for the preparation of polyimide/multiwalled carbon nanotubes (MWCNTs) nanocomposite films by solvent casting technique. In order to enhance the chemical compatibility between polyimide matrix and MWCNTs, the latter was surface modified by incorporating acidic and amide groups by chemical treatment with nitric acid and octadecylamine (C18H39N), respectively. While the amide-MWCNT/polyimide composite shows higher mechanical properties at low loadings (<3 wt%), the acid-MWCNT/polyimide composites perform better at higher loadings (5 wt%). The tensile strength (TS) and the Young’s modulus (YM) values of the acid-MWCNT/polyimide composites at 5 wt% MWCNT loadings was 151 and 3360 MPa, respectively, an improvement of 54% in TS and 35% in YM over the neat polyimide film (TS = 98 MPa; YM = 2492 MPa). These MWCNT-reinforced composites show remarkable improvement in terms of thermal stability as compared to that for pure polyimide film. The electrical conductivity of 5 wt% acid modified MWCNTs/polyimide nanocomposites improved to 0.94 S cm−1(6.67 × 10−18 S cm−1for pure polyimide) the maximum achieved so far for MWCNT-polyimide composites.

Observation of an Electric Octupole Transition in a Single Ion

Abstract: The $^{2}S_{1/2}\ensuremath{-}^{2}F_{7/2}$ electric octupole $(E3)$ transition in ${}^{172}{\mathrm{Yb}}^{+}$ has been detected by observing quantum jumps in a single laser cooled ion, stored in an electrodynamic trap. The transition frequency is 642 116 785.3(0.7) MHz $(1\ensuremath{\sigma})$. Consideration of the transition rate and laser parameters implies a $^{2}F_{7/2}$ level lifetime of 3700 days. This is the first time an atomic $E3$ transition has been driven. This transition has applications as an optical frequency reference.