Capping and Decapping Series of Boranes

Whereas many of the capped series of carbonyl clusters of transition metals are known, those of corresponding borane series are unknown. These include the monocapped, bicapped, tricapped, tetracapped and so on. This paper attempts to correlate selected capped series of the carbonyl series with the hypothetical corresponding ones of boranes using 14n and 4n rules. Some selected examples of capped and decapped borane series have been generated and tabulated. The borane clusters are found to follow a precise numerical algorithm. A comparison of selected examples of carbonyl cluster of lower series such as closo, nido and arachno with the corresponding borane clusters has been made. The popularly cited Rudolph system of deducing shapes of clusters is also discussed in terms of decapping series. The use of fragments and their corresponding fragment series enormously simplifies the categorization of molecular formulas into series from which their shapes can be predicted with or without the use of the cluster number (k value). The fragment series vindicates the vital Hoffmann’s isolobal concept very well.

Review of Ni-Cu Based Front Side Metallization for c-Si Solar Cells

Given the high percentage of metal cost in cell processing and concerns due to increasing Ag prices, alternative metallization schemes are being considered. Ni-Cu based front side metallization offers potential advantages of finer grid lines, lower series resistance, and reduced costs. A brief overview of various front side patterning techniques is presented. Subsequently, working principle of various plating techniques is discussed. For electroless plated Ni seed layer, fill factor values nearing 80% and efficiencies close to 17.5% have been demonstrated, while for Light Induced Plating deposited layers, an efficiency of 19.2% has been reported. Various methods for qualifying adhesion and long term stability of metal stack are discussed. Adhesion strengths in the range of 1–2.7 N/mm have been obtained for Ni-Cu contacts tabbed with conventional soldering process. Given the significance of metallization properties, different methods for characterization are outlined. The problem of background plating for Ni-Cu based metallization along with the various methods for characterization is summarized. An economic evaluation of front side metallization indicates process cost saving of more than 50% with Ni-Cu-Sn based layers. Recent successful commercialization and demonstration of Ni-Cu based metallization on industrial scale indicate a potential major role of Ni-Cu based contacts in near future.

INTEGRATION OF N- AND P-CONTACTS TO GaN-BASED LIGHT EMITTING DIODES

Low-resistance Ohmic contacts are essential for the fabrication of electrical devices. While low contact resistance has been achieved to p -type layers or n -type layers separately, contacts are likely to degrade when both types need to be integrated into a single fabrication process, in particular when prior mesa etching is required. We present a solution to the problem, resulting in low-resistance Ohmic contacts on n -type GaN layers without post-deposition thermal anneal, while maintaining the quality of typical p -type contacts. We implement an integrated process for both, n - and p -contacts, involving an oxygen pretreatment to fabricate light emitting diodes with lower series resistance in the contacts and lower voltage drop at high current when compared to separately optimized contacts.

A new species of Phasmahyla Cruz, 1990 (Anura: Hylidae) from the Atlantic Rain Forest of the States of Minas Gerais and Bahia, Brazil

A new species of the genus Phasmahyla is described from Atlantic Rain Forest fragments at the Fazenda Duas Barras, Municipality of Santa Maria do Salto, northeastern State of Minas Gerais, at the Reserva Particular do Patrimônio Natural (RPPN) Serra do Teimoso, Municipality of Jussari, and at the Fazenda Santa Cruz, Municipality of Arataca, southern State of Bahia, Brazil. The new species is recognized by its medium size for the genus (SVL 33.3 to 38.0 mm in males, 42.8 to 48.6 mm in females); purple drops on flanks and concealed surfaces of forearm, thigh, and digits; male with moderate nuptial pad of minuscule horny asperities on finger I; tympanum distinct only on ventral half; supratympanic fold weakly developed and visible only behind the tympanum; loreal region slightly obtuse; larval oral disc with distinct upper and second lower series of horny teeth; and second lower series of horny teeth slightly shorter than the upper one.

The Effect of ZnO:Al Sputtering Condition on a-Si:H / Si Wafer Heterojunction Solar Cells

A-Si:H/Si wafer heterojunction solar cells with different ZnO:Al sputtering conditions were fabricated and the effects of sputtering conditions on device performance were evaluated. Various sputter condition(substrate temperature RT~200’C, working pressure 0.5mTorr~15mTorr, thickness 60~100nm) were tested and optimized as 130’C, 0.5mTorr, 80nm by measuring reflectance and sheet resistance of ZnO:Al layer on corning glass. However, when optimal ZnO:Al condition was applied to solar cells, series resistance was high which led to device efficiency ~10%. Dark I-V curves of with and w/o ZnO layer showed large difference, which means there is a kind of barrier to current flow between ZnO:Al and a-Si:H layer. Modified condition with double layer scheme was applied and lower series resistance and device efficiency above 12% could be reached. The improvement may be due to either suppression of Si oxide formation or less defect formation by impinging atoms.

Influence of Annealing on Crystallinity and Conductivity of p-type Nanocrystalline Si films

Nanocrystalline p-type Si:H layers are important for photovoltaic and MOSFET devices. A high conductivity in these layers leads to better voltages in PV devices and to lower series resistance in both PV and MOSFET devices. The lower resistance results in higher channel mobility in MOSFET devices and higher fill factors in PV devices. In this work, we discuss the improvement in conductivity and crystallinity of p-type nanocrystalline Si:H layers by the use of post-deposition annealing. The p layers were deposited at ~ 180C from mixtures of silane, hydrogen, helium and diborane using ECR plasma deposition techniques. It was found that addition of He to H at first improved both the conductivity and crystallinity, but too much He led to an amorphous phase and lower conductivity. The as-grown films were measured for their crystallinity using both Raman spectroscopy and x-ray diffraction. The conductivity and activation energies were also measured. The films were then successively annealed at temperatures of 250, 300, 350 and 400C. The crystallinity and grain size were found to increase as the annealing temperature increased. The greatest relative increase was during the initial annealing stages. The conductivity of the films increased significantly as a consequence of the annealing. Conductivities as large as 20 S/cm were obtained in very thin films (~50-150 nm). The corresponding activation energies were in the range of 0.03 eV. When these annealed layers were used for MOSFET and PV devices, there was an appreciable increase in performance characteristics.

Powder Zeeman NQR Study on 123Sb in Sb(C6H5)3

Powder Zeeman NQR spectra of 123Sb in Sb(C6H5)3 were studied by means of a computer simulation and an experiment. The 123Sb nucleus has spin 7/2. There are two non-equivalent 123Sb atoms in the crystal of Sb(C6H5)3, so that there are two series of three transition lines (higher series: ν1h, ν2h, ν3h; lower series: ν11, ν21, v31). The powder Zeeman spectra for ν1h, based on the transition between the levels mI = ±1/2 and ±3/2, were observed at 77 K under the two conditions that i) the oscillation coil and the static magnetic coil were set coaxially and parallel, and ii) they were set perpendicular to each other. The powder line shapes for ν1h, which is the lowest line of the higher series due to 123Sb nuclei, were in good agreement with those from a computer simulation under the conditions i) and ii), showing that the asymmetry parameter of the field gradient is very small (η = 0). The line shape from i) exhibits two shoulders (saddle type), as it appeared for nuclear spin 5/2 and η = 0. The quadrupole coupling constant for 1h, calculated from the resonance frequency 47.820 MHz and the observed η, is 669.480 MHz at 77 K.