Avalanche-Induced Current Enhancement in Semiconducting Carbon Nanotubes

Semiconducting carbon nanotubes under high electric field stress (~10 V/um) display a striking, exponential current increase due to avalanche generation of free electrons and holes. Unlike in other materials, the avalanche process in such 1D quantum wires involves access to the third sub-band, is insensitive to temperature, but strongly dependent on diameter ~exp(-1/d^2). Comparison with a theoretical model yields a novel approach to obtain the inelastic optical phonon emission length, L_OP,ems ~ 15d nm. The combined results underscore the importance of multi-band transport in 1D molecular wires

A Comparison Between GaAs Mesfet and Si NMOS ESD Behaviour

Work is in hand at Loughborough University to investigate and compare the ESD sensitivity of GaAs D-MESFETs and unprotected enhancement mode NMOS structures

Failure mechanisms in MOS devices

Continuous and pulsed voltage stressmg of metal oxide semiconductor (MOS) transistors and capacitors has been mvestigated. The expenmental work followed a survey of failure mechanisms in semiconductor devices which Identified Electrical Overstress Damage (EOS)/Electrostatic Discharge (ESD) damage as the most frequent cause of failure, accounting for over 50% of all damage observed. The survey itself, covered all aspects of semiconductor reliability including reliability modelling and quality assurance. A qualitative model of oxide breakdown in MOS structures was developed as a result of the experimental work. Two different mechanisms have been proposed for continuous and pulsed voltage breakdown. Continuous voltage breakdown simulating EOS conditions, was temperature and voltage dependent. The long time-scales involved, lead to a model whereby breakdown IS the result of conduction of charge earners through the oxide, via electron traps and impunty Sites with energies m the forbidden gap. Pulsed voltage breakdown simulating ESD, was voltage dependent but not temperature dependent. The very short time-scales involved indicate that breakdown is the direct result of electron transport m the oxide conduction band. Electrons are inJected into the conduction band via quantum-mecharucal tunnelling from the cathode. Both mechanisms were found to be dependent on the surface charge concentratiOn of the Silicon and, therefore, polanty dependent. The models explain this effect by analysing the charge injection process under high electric fields

Genome editing in plants using the compact editor CasΦ

Clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins (CRISPR-Cas) systems have been developed as important tools for plant genome engineering. Here, we demonstrate that the hypercompact CasΦ nuclease is able to generate stably inherited gene edits in Arabidopsis, and that CasΦ guide RNAs can be expressed with either the Pol-III U6 promoter or a Pol-II promoter together with ribozyme mediated RNA processing. Using the Arabidopsis fwa epiallele, we show that CasΦ displays higher editing efficiency when the target locus is not DNA methylated, suggesting that CasΦ is sensitive to chromatin environment. Importantly, two CasΦ protein variants, vCasΦ and nCasΦ, both showed much higher editing efficiency relative to the wild-type CasΦ enzyme. Consistently, vCasΦ and nCasΦ yielded offspring plants with inherited edits at much higher rates compared to WTCasΦ. Extensive genomic analysis of gene edited plants showed no off-target editing, suggesting that CasΦ is highly specific. The hypercompact size, T-rich minimal protospacer adjacent motif (PAM), and wide range of working temperatures make CasΦ an excellent supplement to existing plant genome editing systems