S. Basu

Effect of size, shape and oxide content of metal particles on the formation of segregated networks in pvc composites

Abstract A theoretical model has been suggested to account for the formation of segregated networks in polymer/metal particulate composites; the proposed model takes into account the shape and size of the metal particles. The predicted values of critical metal loading for the formation of segregated networks were found to agree closely with the present experimental values. The results have also been compared with the published data. The onset of the segregated network was found to be independent of oxide coating of the metal particles and depends only on the geometry of the particles.

PVC-Cu composites with chemically deposited ultrafine copper particles

PVC-Cu composites with chemically deposited ultrafine (0.1 to 0.3 μm diameter) copper particles were prepared by hot-pressing copper-coated PVC powder (−106, +150 μm) at 120° C. Metallic copper in fine-particle form was deposited on the PVC particles by reducing an ammoniacal cupric acetate solution with hydrazine at 85° C. The electrical resistivity (d.c.) and transverse rupture strength of these composites were measured. Measurement of electrical resistivity indicated that in these composites copper particle network formation was initiated at a copper content of about 0.2 vol%; with further increase of copper content the resistivity dropped sharply from about 1014 (for pure PVC) to about 105 MN m−2 Ωcm at a copper content of about 0.5 vol%. Increase of copper loading beyond 0.5 vol% did not decrease resistivity significantly whereas the rupture strength increased continuously from 120 MN m−2 (for pure PVC) to a value of about 300 MN m−2 with 4 vol% copper loading. This high value of resistivity even after copper particle chain formation and the continuous increase of rupture strength, is thought to be due to formation of a thin layer of polymer film between the copper particles introducing a “quasi-random” character to the otherwise segregated network of copper particles.

Grain size dependence of mobility in polycrystalline n‐indium phosphide

Polycrystalline n‐indium phosphide (InP) with grain sizes varying from 15 to 2000 μm has been prepared by iodine chemical reaction and synthesis solute diffusion (SSD) techniques. The variation of electron mobility and hence electron mean free path with grain size has been determined from conductivity and Hall effect studies, taking into account the effect of compensation as discussed by Jensen. The results show that electron mobility at 300 K increases from 29 to 691 cm2/V s with grain sizes increasing from 15 to 2000 μm. While for a single crystal the electron mobility varied with temperature between 160–300 K as T−2.25, for polycrystalline InP the variation was T−2.44 (2000 μm in grain size) and T−2.97 (200 μm in grain size) showing the effect of grain boundary scattering. The impurity activation energies have also been determined and were found to increase with a decrease of grain size.

Effect of particle size on the mechanical properties of poly(vinylchloride)-copper particulate composite

The effect of particle size ratios on tensile strength, tensile modulus, impact strength, Vickers hardness and transverse rupture strength of particulate PVC-Cu composite has been studied. The strength values reach a maximum at a particular metal loading where the formation of a segregated network is believed to occur. This critical metal loading shifts towards lower values with increasing polymer-to-metal size ratios. The mean free path calculated from the proposed model is found to be same in all metal loadings, corresponding to strength maxima irrespective of the particle size ratios. A correlation between strength properties and the mean free path has been suggested.

Improved Schottky barrier on n-InP by surface modification

Abstract Modification of the surface of InP by ruthenium treatment increases the Schottky barrier height of Ag/n-InP junctions from 0.58 to 0.75 eV. The ideality factor n is found to decrease from 2.06 to 1.20, J0 from 4.8 × 10−6 to 1.47 × 10−7 A/cm2 and A ∗∗ from 22.2 to 8.6 A cm−2 K−2.

Scanning electron microscopy studies of abraded rubber surfaces

The surfaces of polybutadiene rubber (BR) and styrene-butadiene rubber (SBR) subjected to different degrees of abrasion have been studied by scanning electron microscopy (SEM). In the case of SBR it has been shown that abrasion begins with marks in the direction of rotation which are followed by fine ribbing and then by the formation of coarse, angular and prominent ridges. Prolonged abrasion produces folding and cavities on the surface. This change in abrasion mechanism has been explained as a result of heat build-up and high crack growth rate in SBR which occur beyond a certain stage. These help in softening the matrix and removing the surface. On the other hand, fractured surfaces of BR show that ridges begin to form at about 250 revolutions and there is no characteristic difference between the abraded surfaces at lower or higher degrees of abrasion.

Absorption and photoluminescence spectra of the diluted magnetic semiconductor Ga1−xFexSb

Bulk growth of the III–V diluted magnetic semiconductor, Ga1−xFexSb is reported for different iron concentrations. Room-temperature optical absorption coefficient measurements were performed. The dependence of the band gap Eg on the Fe concentration was studied. The band gap decreased with increasing x, and the variation was observed to follow a nonlinear trend. Photoluminescence (PL) measurements at 18 K were also carried out. The PL spectra showed a clear peak shift due to incorporation of Fe in the lattice, thus agreeing with the optical absorption results.

Improved junction properties of Au-n-GaSb Schottky diodes after chemical modification of GaSb surfaces

Abstract Polycrystalline n-GaSb grown by the vertical Bridgman method was chemically treated with Ru 3+ ions. Electrical characterisation showed improvement in the electron mobility from 1162 to 1442 cm 2 /V s, while the carrier concentration remained almost constant (1 × 10 17 cm 3 ). Schottky diodes were fabricated by thermal deposition of gold and characterised by I-V and C-V studies. An increase in the Schottky barrier height from 0.54 to 0.64 eV and a decrease in the ideality factor from 3.2 to 1.69 were repeatedly obtained. The featureless surface after Ru 3+ modification was verified by SEM and the presence of Ru 3+ on GaSb surfaces was confirmed by ESCA.

Effect of annealing on the electrical resistivity of conductive polyvinylchloride‐copper composites

Polyvinylchloride‐copper composites at different volume percent of copper are annealed at 50 °C for 10 days. The effect of temperature on the electrical resistivity of the resulting composites is studied between 0 and 40 °C using a four‐electrode device. Three clearly distinguished behaviors of the composites are observed after prolonged annealing. They exhibit (a) a positive temperature coefficient of resistance, (b) higher discrepancy in resistivity values for all metal loadings, and (c) an Ohmic current‐voltage relationship. We try to explain the positive temperature coefficient of resistance through the reduction of the contact pressure between the metal particles with increase in temperature.

Characterization of n-InP surfaces before and after surface modification

Abstract Modification of n-InP photoelectrode surfaces by matte etching followed by RuCl 3 treatment has been shown to enhance the performance and stability of PEC solar cells. The unmodified and modified surfaces have been examined by SIMS, Auger and Raman spectroscopy. These experiments indicate the formation of a thin oxide layer due to modification which results in reduced sub-band gap response and increased Schottky barrier height.