Thin layers of GaInP, GaP and GaAsP in metalorganic vapour phase epitaxy-grown resonant tunnelling diodes

We have studied the epitaxial growth and electrical performance of Al-free, GaAs-based, resonant tunnelling diodes (RTDs) including thin barriers of GaInP, GaP, or GaAs_xP_1−x. n-Type tunnelling diodes have been fabricated and the symmetry in the current–voltage (I–V) characteristics, as well as the peak-to-valley ratios, are found to be sensitive probes for the interface quality in the heterostructures. For GaInP RTDs, we show that the introduction of GaP intermediate layers is crucial for the realisation of a useful tunnelling current. RTDs including thin barriers (less than about 10 monolayers (ML)) of GaP are realised, but the strong mismatch between the materials limit the useful thickness. Finally, RTDs with GaAs_xP_1−x alloys are fabricated showing the best peak-to-valley ratio of the diodes (about 5), as well as a symmetric I–V characteristics. The electrical data are further compared to studies by transmission electron microscopy (TEM) in the various material systems.     

Langmuir-Blodgett films of polymethacrylates with side chains containing functionalized aromatic schiff's bases

Langmuir-Blodgett (LB) film formation has been investigated for polymers in which non-linear optical (NLO) moieties are attached to the side chain of a polymethacrylate (PMA) backbone. Polymer monolayers were successfully transferred onto hydrophilic glass substrates using a moving-wall type LB trough. The LB films were characterized by pressure-area isotherms, polarized ultraviolet visible spectra, ellipsometry, and second harmonic generation measurements. The characterization shows that NLO moieties in the side chain are inclined at a shallow angle to the plane of the substrate. The second-order nonlinear optical coefficient and molecular hyperpolarizability were also calculated. © 1993 John Wiley & Sons, Inc.     

Is copper(I) really soft? Probing the hardness of Cu(I) with pyridinecarboxaldehyde ligands

Cu(I) complexes of formula Cu(PPh₃)₂LClO₄ [L = 2 or 3 pyridine carboxaldehyde] are synthesised and characterised to explore the coordination of an aldehyde, a hard and neutral oxygen donor to a soft Cu(I) centre. The structural and spectroscopic results illustrate that only in 2-pyridinecarboxaldehyde, the ‘C=O’ group coordinates to soft Cu(I) centres due to a favourable chelate effect, while in 3-pyridinecarboxaldehyde, it remains uncoordinated. Upon chelation via N and O donors, 2-pyridinecarboxaldehyde resembles bipyridine or phenanthroline in terms of its bite angle and spectroscopic features. Such chelation can be easily challenged with coordinating anions like bromide, or more basic pyridines. A drastic change in the MLCT absorption signals the decomplexation of the ‘C=O’ group. The observed results point out that the Cu(I) centre can readily exchange the hard ‘O’ donor for softer ligands.     

First diphosphinoamine ligand bearing a polymerizable side chain: Complexation with copper(I)

A diphosphinoamine ligand with a polymerizable side chain, (PPh₂)₂N? CH₂? C₆H₄? CH?CH₂ (vbzpnp or 1 ), was synthesized. The ligand could be polymerized by anionic polymerization with n‐butyllithium as the initiator. Polyvbzpnp was soluble in tetrahydrofuran and chloroform but was insoluble in methanol and was characterized with NMR, IR, and gel permeation chromatography. The number‐average and weight‐average molecular weights were 40,050 and 55,690, respectively, and the polydispersity index was 1.39. [Cu(CH₃CN)₄]ClO₄ formed a bischelated complex with the monomer and produced [Cu( 1 )₂]ClO₄ ( 2 ), and CuCl formed a tetramer, Cu₄( 1 )₂Cl₄ ( 3 ). All the compounds ( 1 , 2 , and 3 ) were characterized with single‐crystal‐structure determination, NMR, and IR spectroscopy. The addition of [Cu(CH₃CN)₄]ClO₄ to polyvbzpnp resulted in an insoluble crosslinked polymer, which was characterized with solid‐state ³¹P {¹H} magic‐angle‐spinning NMR. The copolymerization of styrene and 1 produced a styrene–vbzpnp copolymer that was found to be soluble in common organic solvents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3411–3420, 2005     

Decay pathways and entry-state population in (α, xnγ) and (3He, xnγ) reactions on 150Nd

Exclusive neutron spectra and angular distributions have been measured by n-γ coincidence techniques for $\text{(α, x}\text{n}\text{γ)}\text{and}\text{(}{}^3\text{He}\text{, x}\text{n}\text{γ)}$ reactions on ¹⁵⁰Nd in the 25–44 MeV range. The results show that pre-equilibrium processes dominate low-energy light-ion induced reactions at certain beam energies. Analysis of the yrast γ-ray cascades in the residual nuclei shows that a well-defined minimum entry-state spin exists in final nuclei populated by pre-equilibrium processes. This in turn implies the existence of a minimum classical impact parameter for these reactions. These results are discussed in terms of phenomenological models of the reaction mechanisms.     

Anion-exchange chromatography of organic acids in magnesium acetate medium

Magnesium acetate solution is a useful eluant in the separations of dibasic organic acids by anion-exchange chromatography. The following acids were separated: oxalic, tartronic, malic, glucaric, galactaric, tartaric and maleic acids. The eluate was analyzed automatically using chromic acid oxidation.     

Surviving conduction symmetries in non-linear response

In linear response, the electric conductance of mesoscopic, two-terminal devices is symmetric with respect to the direction of an external magnetic field. The conductance symmetry, in general, breaks down in the non-linear regime of transport. Here we consider semiconductor quantum dots and show certain symmetries survive in the non-linear conductance with respect to the bias voltage and magnetic field that can be measured.     

生长过程中磷压对MOVPE GaP电致发光谱的影响

对在不同磷压下生长的MOVPE GaP二极管的电致发光(EL)谱进行了测量。参照对相应的肖特基势垒样品进行的结技术测量和对衬底进行的光致发光(PL)测量结果,对观测到的几个强度随生长时所用磷压明显变化的EL带的起因作了讨论。将其中相对强度随磷压增加的两个EL带分别试归因于与反位磷PGa的一次和二次离化态有关的辐甜复合;将相对强度随磷压减小而增大的一个EL带归因于与氧有关。