G. A. D. Briggs

Gas permeation in silicon-oxide/polymer (SiOx/PET) barrier films: role of the oxide lattice, nano-defects and macro-defects

We propose a model for permeation in oxide coated gas barrier films. The model accounts for diffusion through the amorphous oxide lattice, nano-defects within the lattice, and macro-defects. The presence of nano-defects indicate the oxide layer is more similar to a nano-porous solid (such as zeolite) than silica glass with respect to permeation properties. This explains why the permeability of oxide coated polymers is much greater, and the activation energy of permeation much lower, than values expected for polymers coated with glass. We have used the model to interpret permeability and activation energies measured for the inert gases (He, Ne and Ar) in evaporated SiOx films of varying thickness (13-70 nm) coated on a polymer substrate. Atomic force and scanning electron microscopy were used to study the structure of the oxide layer. Although no defects could be detected by microscopy, the permeation data indicate that macro-defects (>1 nm), nano-defects (0.3-0.4 nm) and the lattice interstices (<0.3 nm) all contribute to the total permeation

High-Cooperativity Coupling of Electron-Spin Ensembles to Superconducting Cavities

Electron spins in solids are promising candidates for quantum memories for superconducting qubits because they can have long coherence times, large collective couplings, and many qubits could be encoded into spin waves of a single ensemble. We demonstrate the coupling of electron-spin ensembles to a superconducting transmission-line cavity at strengths greatly exceeding the cavity decay rates and comparable to the spin linewidths. We also perform broadband spectroscopy of ruby (Al₂O₃:Cr(3+)) at millikelvin temperatures and low powers, using an on-chip feedline. In addition, we observe hyperfine structure in diamond P1 centers.

The Effect of Tangential Force on the Contact of Elastic Solids in Adhesion

This paper describes a study of adhesion between elastic solids and in particular the effect of a tangential force upon the size of the contact area. In the first part of the paper, the relation between the stress intensity factor of the normally loaded contact and the overall energy balance approach is discussed. In the second and main part of the paper, an analysis is given for the influence of a tangential force on the adhesive contact. The equation derived to describe its effect on the contact size has been verified by experiments carried out on rubber hemispheres pressed against a glass flat. The experimental results show qualitatively a clear reduction in contact area when a tangential force acts and quantitatively a reasonable agreement with theory within the limits of experimental error.

Heterodyne force microscopy of PMMA/rubber nanocomposites: nanomapping of viscoelastic response at ultrasonic frequencies

We present measurements of the nanoscale elastic and viscoelastic properties of samples of poly(methylmetacrylate) (PMMA)/rubber nanocomposites. For these studies we have used a new technique based on atomic force microscopy (AFM) with ultrasonic excitation, heterodyne force microscopy (HFM), which provides a means of testing the viscoelastic response of polymeric materials locally (in tip-probed regions) at MHz frequencies. Phase-HFM contrast distinguishes local differences in the dynamic response of PMMA/rubber composites. Comparison of HFM with other AFM-based techniques (ultrasonic force microscopy, friction force microscopy and force modulation microscopy), while imaging the same surface region, emphasizes the unique capabilities of HFM for these kinds of studies, and reveals key nanostructural characteristics of the composites. Some of the toughening particles appear to be broken down, with areas of PMMA detached from the surrounding matrix.

Characterization of transparent aluminium oxide and indium tin oxide layers on polymer substrates

Abstract The structural, mechanical and gas barrier properties of aluminium oxide and indium tin oxide coatings deposited by DC reactive sputtering on poly(ethylene terephthalate) has been investigated. The oxygen and water vapour transmission rates of the films were measured as a function of temperature in order to assess the effectiveness of the oxides as gas barriers. Both types of composites exhibited good resistance to water vapour transmission. However, the indium tin oxide coating was significantly more effective as a gas barrier than the conventional aluminium oxide. The microstructural integrity of the oxide coatings was examined using scanning electron microscopy and atomic force microscopy. It was found that the sputtered layers featured a relatively low density of defects. The aluminium oxide films featured larger and many more defects than the indium tin oxide composites. This difference, along with a preliminary observation of a difference in the chemical interaction of water vapour with indium tin oxide (ITO) and aluminium oxide (AlOx), is believed to offer an explanation to the observed gas barrier properties. In addition to displaying good gas barrier characteristics, the ITO films were found to have better resistance to mechanical damage than either aluminium oxide and silicon oxide films.

Quantum computing with an electron spin ensemble.

We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized radiation field. The transformation between different spin waves is achieved by applying gradient magnetic fields across the sample, while a Cooper pair box, resonant with the cavity field, may be used to carry out one- and two-qubit gate operations.

Characterisation of aluminium oxynitride gas barrier films

In the last decade, metal oxide layers deposited on polymer substrates have been utilised as gas barrier films in food packaging as an alternative to the traditional aluminium foil. The resistance of these composite films to gas transmission is controlled predominantly by nano-scale defects created during the fabrication of the oxide layer. The size and density of these defects are believed to be strongly dependent on the intrinsic properties of the metal oxide layer. Changing the chemical composition of these coatings is one possible method to enhance the gas barrier properties of the films. In this work, aluminium oxynitride films, fabricated by reactive magnetron sputtering on Poly (ethylene terephthalate) substrates, have been investigated using a range of analytical techniques including: scanning proton microprobe; atomic force microscopy; scanning electron microscopy; transmission electron microscopy; uni-axial tensile testing; and gas permeation measurements to characterise the gas barrier properties of the film. The structural observations have been correlated with the measurements of the oxygen and water vapour permeation of the composite. Oxygen transmission rates as low as 1 cm3/m2 day·atm and water vapour transmission rates below 0.2 g/m2 day have been measured, and these competitive values can be explained by the relatively low density of defects in the barrier layers.

A microstructural study of transparent metal oxide gas barrier films

The relationship between the microstructure and the water vapour transmission rates of aluminium oxide and aluminium coatings deposited by magnetron sputtering on polyethylene terephthalate have been investigated. The gas barrier properties of the films have been measured as a function of temperature and a range of techniques used to characterize the coatings including atomic force microscopy, which also provided information on the early growth mechanism. It was found that the Al/PET film showed a better water vapour barrier than the AlOx/PET although the activation energy for water vapour permeation was the same for both. We propose that the interaction of water with the barrier coating plays a significant part in determining the observed gas barrier performance.

An STM study of the chemisorption of C2H4 on Si(001)(2 × 1)

The chemisorption of ethylene (C 2 H 4 ) on Si(001)(2×1) at 300 K has been studied by scanning tunneling microscopy (STM) and spectroscopy (STS). Exposure of the surface to C 2 H 4 does not cause large scale rearrangement of the original Si surface atoms. The adsorption of individual molecules and changes in the local structure can, however, be observed. At low coverage, the C 2 H 4 molecules prefer to adsorb on alternate dimer sites creating either a local (2×2) or c(2× 4) structure. The individual domains are relatively small (<50 A) and the change in reconstruction cannot be detected by any diffraction technique

Magnetic Field Sensing Beyond the Standard Quantum Limit Using 10-Spin NOON States

Quantum-Enhanced Measurement The single electron spin in a molecule, atom, or quantum dot precesses in a magnetic field and so can be used as a magnetic field sensor. As the number of spins in a sensor increases, so too does the sensitivity. Quantum mechanical entanglement of the spin ensemble should then allow the sensitivity to increase much more than would be expected from a simple increase in the number of individual spins in the ensemble. Using the highly symmetric molecule, trimethyl phosphite, a molecule containing a central P atom surrounded by nine hydrogen atoms, Jones et al. (p. 1166, published online 23 April) quantum mechanically entangled the 10 spins (or qubits) to generate a nearly 10-fold enhancement in the magnetic field sensitivity. The results pave the way for the further development of quantum sensors. Quantum mechanical entanglement of nuclei in a single molecule results in an enhancement of the magnetic field sensitivity. Quantum entangled states can be very delicate and easily perturbed by their external environment. This sensitivity can be harnessed in measurement technology to create a quantum sensor with a capability of outperforming conventional devices at a fundamental level. We compared the magnetic field sensitivity of a classical (unentangled) system with that of a 10-qubit entangled state, realized by nuclei in a highly symmetric molecule. We observed a 9.4-fold quantum enhancement in the sensitivity to an applied field for the entangled system and show that this spin-based approach can scale favorably as compared with approaches in which qubit loss is prevalent. This result demonstrates a method for practical quantum field sensing technology.