Investigations on thiourea content in ternary Sn–Ag–Cu bath using electrochemical studies

We have developed a methane sulfonic acid (MSA) based ternary electrolytic bath for co-deposition of the eutectic Sn–Ag–Cu films. The bath contains thiourea (TU), which functioned as an effective chelating agent in controlling the bath stability as well as the elemental and microstructural properties of the deposited film. A study of the bath behaviour at TU concentrations in the range 0.06–0.2 M is undertaken with the help of elemental and microstructure analysis, cyclic voltammetry (CV) and impedance analysis. The deposited films have close to eutectic composition with slightly higher Cu content for all the TU concentrations. On the other hand, the microstructure is found to be increasingly refined with increasing TU content. The CV and impedance analysis confirm chelation of Ag and Cu with TU and absence of such chelation with Sn ions. It also indicates close deposition potentials for each metal ion. Impedance analysis specifically reveals presence of an adsorbed insulating film on cathode surface, contributed by MSA or water. It also reveals competitive deposition between the insulating film and metal ions.     

Effect of surfactant on the bath stability and electrodeposition of Sn-Ag-Cu films

A methanesulphonic acid based bath for the co-deposition of Sn-Ag-Cu films is developed. The bath contains thiourea as chelating agent, while iso-octyl phenoxy polyethoxy ethanol (OPPE) is added as a non-ionic surfactant. Studies show that OPPE plays a major role in improving the bath stability from few hours up to 1 week. However, there is no evidence of any strong chelation between any metal ion and OPPE. There is a slight modification in the reduction potentials of individual ions after addition of OPPE, which is attributed to some weak bonding through the lone-pair electrons of this molecule. Bath investigations confirm that thiourea forms chelates with electropositive Ag⁺ and Cu²⁺ ions and alters their deposition potentials. Consequently, the deposition of three elements takes place at a single potential of − 0.541 V. The proposed bath is capable of depositing Sn-Ag-Cu films having near eutectic composition that remains consistent even with increase in current density beyond 5 mA cm^− 2. This is attributed to the three metals reaching their limiting current density. The deposited films have compact microstructure with grain size in the range 6-8 μm and thickness in the range 20-100 μm. The studies show that OPPE brings about refinement in film microstructure.     

Lower bounds on the state complexity of linear tail-biting trellises

Lower bounds on the state complexity of linear tail-biting trellises are presented. One bound generalizes the total-span bound, while another bound can be regarded as a generalization of the cut-set bound. It is shown by examples that the new bounds may be tighter than any of the existing lower bounds.     

Solvent additives for tuning the photovoltaic properties of polymer-fullerene solar cells

We use solvent additives as a simple method to tune the photovoltaic performance of poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojuncton solar cells. 1,2-dichlorobenzene (oDCB) was used as the reference solvent; chlorobenzene (CB) and 1,2,3,4-tetrahydronaphthalene (THN) were used as additives to influence film formation. An increase in the short circuit current and the power conversion efficiency of solar cells with blends cast from mixed solvents was observed. Blends prepared with THN, the highest boiling point solvent, resulted in the best device performance, while blends prepared with the pure reference solvent resulted in the lowest photocurrent. In-plane investigations of the morphology using transmission electron microscopy (TEM) revealed improved phase segregation for blends prepared with mixed solvents, and increased crystallinity in the P3HT phase is demonstrated using atomic force microscopy (AFM) coupled with Kelvin probe force microscopy (KPFM). Optical modeling reveals that the increase in the photocurrent is not due to changes in the optical properties of the blends. Electrical characterization reveals that the electron mobilities decrease slightly in blends cast from mixed solvents, corresponding to a decrease in the fill factor and an increase in P3HT crystallinity observed at the surface of the blend. The increase in the photovoltaic performance is discussed in terms of increased charge separation at the donor-acceptor interface due to increased ordering in the P3HT phase induced by the solvent additives.     

Linear tail-biting trellises, the square-root bound, andapplications for Reed-Muller codes

Linear tail-biting trellises for block codes are considered. By introducing the notions of subtrellis, merging interval, and sub-tail-biting trellis, some structural properties of linear tail-biting trellises are proved. It is shown that a linear tail-biting trellis always has a certain simple structure, the parallel-merged-cosets structure. A necessary condition required from a linear code in order to have a linear tail-biting trellis representation that achieves the square root bound is presented. Finally, the above condition is used to show that for r⩾2 and m⩾4r-1 or r⩾4 and r+3⩽m⩽[(4r+5)/3] the Reed-Muller code RM(r, m) under any bit order cannot be represented by a linear tail-biting trellis whose state complexity is half of that of the minimal (conventional) trellis for the code under the standard bit order     

Isolation of Hederagenin and its Saponin from Alfalfa (Medicago Sativa)

A sapogenin isolated from the acid hydrolysates of roots or tops of alfalfa (Medicago sativa) has properties and constants identical to those of hederagenin. The corresponding saponin was isolated from a mixture of alfalfa saponins by successive chromatography on Al₂ O₃ and DEAE-Sephadex columns. Upon acid hydrolysis it yields glucose, arabinose and hederagenin, similarly to the saponin isolated from Hedera helix.     

Preparation,characterisation and some properties of saponins from lucerne tops and roots

Lucerne saponin extracts have been prepared from lucerne tops and roots by two different methods. The root extracts possess stronger haemolytic activity and to a certain extent are stronger foaming agents than those from the tops. Thin-layer chromatographic (t.l.c.) analyses showed that acid hydrolysates of the different preparations contain soyasapogenols A, B, C, D, E, medicagenic acid and an unidentified sapogenin-like spot. When submitted to t.l.c. and paper electrophoresis the first pair of extracts have been separated into six fractions each, and the other extracts into seven fractions each. The root extract and to a lesser extent that from the tops, depress growth of Tribolium castaneum larvae but the inhibitory effect can be reversed when cholesterol is incorporated in the diet. Germination of cotton seeds is inhibited in soils on which lucerne has been grown or on soils supplemented with lucerne meal from tops and roots.     

Bounds on the state complexity of codes from the Hermitian functionfield and its subfields

An upper bound on the minimal state complexity of codes from the Hermitian function field and some of its subfields is derived. Coordinate orderings under which the state complexity of the codes is not above the bound are specified. For the self-dual Hermitian code it is proved that the bound coincides with the minimal state complexity of the code. Finally, it is shown that Hermitian codes over fields of characteristic 2 admit a recursive twisted squaring construction