Quantum mechanical tunneling phenomena in metal–semiconductor junctions

The impact of the quantum mechanical tunneling effect on the operation of MESFET device structure has been investigated. Due to the presence of a Schottky barrier in a highly doped semiconductor, the depletion region is so narrow that electrons can tunnel through the barrier and contribute to the gate leakage current. This, in turn, facilitates current gain of the Schottky junction transistor (SJT) in the subthreshold region. In a simulation of a SJT we have used 2D Monte Carlo particle-based simulations. Quantum mechanical tunneling effects have been accounted for by using the Airy function transfer matrix approach, valid for piecewise linear potential barriers.     

Gas‐Separation Membranes Loaded with Porous Aromatic Frameworks that Improve with Age

Porosity loss, also known as physical aging, in glassy polymers hampers their long term use in gas separations. Unprecedented interactions of porous aromatic frameworks (PAFs) with these polymers offer the potential to control and exploit physical aging for drastically enhanced separation efficiency. PAF‐1 is used in the archetypal polymer of intrinsic microporosity (PIM), PIM‐1, to achieve three significant outcomes. 1) hydrogen permeability is drastically enhanced by 375 % to 5500 Barrer. 2) Physical aging is controlled causing the selectivity for H₂ over N₂ to increase from 4.5 to 13 over 400 days of aging. 3) The improvement with age of the membrane is exploited to recover up to 98 % of H₂ from gas mixtures with N₂. This process is critical for the use of ammonia as a H₂ storage medium. The tethering of polymer side chains within PAF‐1 pores is responsible for maintaining H₂ transport pathways, whilst the larger N₂ pathways gradually collapse.     

Eisen und Stahl

Ohne Zusammenfassung     

[1,1,2,2‐(CO)4‐1,2‐μ‐(CO)‐4,11‐(SMe2)2‐closo‐1,2‐Co2B10H8]

The title compound, 1,1,2,2‐tetra­carbonyl‐1,2‐μ‐carbonyl‐4,11‐di­methyl­sulfido‐closo‐1,2‐dicobaltadodecaborane, [Co₂(C₄H₂₀B₁₀S₂)(CO)₅], has a closo 12‐vertex {1,2‐Co₂B₁₀H₈} structure with SMe₂ ligands at the exo‐4‐ and 11‐positions. The cluster displays close structural similarities to the SEt₂ analogue.     

Single-electron quantum dots in silicon MOS structures

We present experimental results for two types of quantum dots, which are embedded within a silicon metal-oxide-semiconductor structure. Evidence is found for single-electron charging at low temperature, and for an asymmetric shape of the dot. First results of simulations of these dots are presented. Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000     

Evaluation of a knowledge‐based potential of mean force for scoring docked protein–ligand complexes

The Biomolecular Ligand Energy Evaluation Protocol (BLEEP) is a knowledge‐based potential derived from high‐resolution X‐ray structures of protein–ligand complexes. The performance of this potential in ranking the hypothetical structures resulting from a docking study has been evaluated using fifteen protein–ligand complexes from the Protein Data Bank. In the majority of complexes BLEEP was successful in identifying the native (experimental) binding mode or an alternative of low rms deviation (from the native) as the lowest in energy. Overall BLEEP is slightly better than the DOCK energy function in discriminating native‐like modes. Even when alternative binding modes rank lower than the native structure, a reasonable energy is assigned to the latter. Breaking down the BLEEP scores into the atom–atom contributions reveals that this type of potential is grossly dominated by longer range interactions (>5 Å), which makes it relatively insensitive to small local variations in the binding site. However, despite this limitation, the lack, at present, of accurate protein–ligand potentials means that BLEEP is a promising approach to improve the filtering of structures resulting from docking programs. Moreover, BLEEP should improve with the continuously increasing number of complexes available in the PDB. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 673–688, 2001     

An x-pes study of the semiconductor-metal transition in NbO2

Marked changes in the Nb4d band in the X-ray photo-electron spectrum accompany the semiconductor-metal transition in NbO₂. The Nb4d band progressively shifts towards the O2p band with increase in temperature.     

X-ray and UV photoelectron spectra of the metal sesquioxides

He(I,II) and MgKα valence region photoelectron spectra of polycrystalline Ti₂O₃, V₂O₃, Cr₂O₃, Mn₂O₃, Fe₂O₃ and Rh₂O₃ have been recorded. The method of sample preparation employed gave rise to UV-PE spectra which are significantly different from those previously reported. While clear changes are observed in the spectra accompanying the semiconductor-to-metal transition of V₂O₃ at 150 K, there is no apparent modification of the Ti₂O₃ spectra accompanying its second order transition at 500 K. The remaining first row transition metal sesquioxides exhibit spectra indicative of localised 3d electrons.