Dopant compensation in HfO2 and other high K oxides

The theory of doping limits in semiconductors and insulators is applied to the case of wide gap oxides, crystalline, or amorphous, and used to explain that impurities do not in general give rise to gap states or a doping response. Instead, the system tends to form defect complexes or undergo symmetry-lowering reconstructions to expel gap states out of the band gap. The model is applied to impurities, such as trivalent metals, carbon, N, P, and B, in HfO2, the main gate dielectric used in field effect transistors. © 2014 AIP Publishing LLC.

High performance transistors based on the controlled growth of triisopropylsilylethynyl-pentacene crystals via non-isotropic solvent evaporation

Triisopropylsilylethynyl-pentacene (TIPS-PEN) has proven to be one of the most promising small molecules in the field of molecular electronics, due to its unique features in terms of stability, performance and ease of processing. Among a wide variety of well-established techniques for the deposition of TIPS-PEN, blade-metered methods have recently gained great interest towards the formation of uniform crystalline films over a large area. Following this rationale, we herein designed a versatile approach based on blade-coating, which overcomes the problem of anisotropic crystal formation by manipulating the solvent evaporation behaviour, in a way that brings about a preferential degree of crystal orientation. The applicability of this method was evaluated by fabricating field-effect transistors on glass as well as on silicon dioxide/silicon (SiO2/Si) substrates. Interestingly, in an attempt to improve the rheological and wetting behaviour of the liquid films on the SiO2/Si substrates, we introduced a polymeric interlayer of polystyrene (PS) or polymethylmethacrylate (PMMA) which concurrently acts as passivation and crystallization assisting layer. In this case, the synergistic effects of the highly-ordered crystalline structure and the oxide surface modification were thoroughly investigated. The overall performance of the fabricated devices revealed excellent electrical characteristics, with high saturation mobilities up to 0.72 cm2 V-1 s-1 (on glass with polymeric dielectric), on/off current ratio >104 and low threshold voltage values (<-5 V). This journal is © the Partner Organisations 2014.

Effect of microbial activities on the mobility of copper in stabilised contaminated soil

Stabilisation, using a wide range of binders including wastes, is most effective for heavy metal soil contamination. Bioremediation techniques, including bioaugmentation to enhance soil microbial population, are most effective for organic contaminants in the soil. For mixed contaminant scenarios a combination of these two techniques is currently being investigated. An essential issue in this combined remediation system is the effect of microbial processes on the leachability of the heavy metals. This paper considers the use of zeolite and compost as binder additives combined with bioaugmentation treatments and their effect on copper leachability in a model contaminated soil. Different leaching test conditions are considered including both NRA and TCLP batch leaching tests as well as flow-through column tests. Two flow rates are applied in the flow-through tests and the two leaching tests are compared. Recommendations are given as to the effectiveness of this combined remediation technique in the immobilisation of copper. © 2005 Taylor & Francis Group.

The dynamic effect of a piled-foundation building on an incident vibration field from an underground railway tunnel

This paper presents a three-dimensional comprehensive model for the calculation of vibration in a building based on pile-foundation due to moving trains in a nearby underground tunnel. The model calculates the Power Spectral Density (PSD) of the building's responses due to trains moving on floating-slab tracks with random roughness. The tunnel and its surrounding soil are modelled as a cylindrical shell embedded in half-space using the well-known PiP model. The building and its piles are modelled as a 2D frame using the dynamic stiffness matrix. Coupling between the foundation and the ground is performed using the theory of joining subsystems in the frequency domain. The latter requires calculations of transfer functions of a half-space model. A convenient choice based on the thin-layer method is selected in this work for the calculations of responses in a half-space due to circular strip loadings. The coupling considers the influence of the building's dynamics on the incident wave field from the tunnel, but ignores any reflections of building's waves from the tunnel. The derivation made in the paper shows that the incident vibration field at the building's foundation gets modified by a term reflecting the coupling and the dynamics of the building and its foundation. The comparisons presented in the paper show that the dynamics of the building and its foundation significantly change the incident vibration field from the tunnel and they can lead to loss of accuracy of predictions if not considered in the calculation.