Oxidation kinetics of thin copper films and wetting behaviour of copper and Organic Solderability Preservatives (OSP) with lead-free solder

The oxide formation on thin copper films deposited on Si wafer was studied by XPS, SEM and Sequential Electrochemical Reduction Analysis SERA. The surfaces were oxidized in air with a reflow oven as used in electronic assembly at temperatures of 100 °C, 155 °C, 200 °C, 230 °C and 260 °C. The SERA analyses detected only the formation of Cu₂O but the XPS analysis done for the calibration of the SERA equipment proved also the presence of a CuO layer smaller than 2 nm above the Cu₂O oxide. The oxide growth follows a power-law dependence on time within this temperature range and an activation energy of 33.1 kJ/mol was obtained. The wettability of these surfaces was also determined by measuring the contact angle between solder and copper substrate after the soldering process. A correlation between oxide thickness and wetting angle was established. It was found that the wetting is acceptable only when the oxide thickness is smaller than 16 nm. An activation energy of 27 kJ/mol was acquired for the spreading of lead free solder on oxidized copper surfaces.From wetting tests on copper surfaces protected by Organic Solderability Preservatives (OSP), it was possible to calculate the activation energy for the thermal decomposition of these protective layers.     

Inverse subspace problems with applications

Given a square matrix A, the inverse subspace problem is concerned with determining a closest matrix to A with a prescribed invariant subspace. When A is Hermitian, the closest matrix may be required to be Hermitian. We measure distance in the Frobenius norm and discuss applications to Krylov subspace methods for the solution of large‐scale linear systems of equations and eigenvalue problems as well as to the construction of blurring matrices. Extensions that allow the matrix A to be rectangular and applications to Lanczos bidiagonalization, as well as to the recently proposed subspace‐restricted SVD method for the solution of linear discrete ill‐posed problems, also are considered.Copyright © 2013 John Wiley & Sons, Ltd.     

Central limit theorems for empirical product densities of stationary point processes

We prove the asymptotic normality of kernel estimators of second- and higher-order product densities (and of the pair correlation function) for spatially homogeneous (and isotropic) point processes observed on a sampling window \(W_n\) , which is assumed to expand unboundedly in all directions as \(n \rightarrow \infty \,\) . We first study the asymptotic behavior of the covariances of the empirical product densities under minimal moment and weak dependence assumptions. The proof of the main results is based on the Brillinger-mixing property of the underlying point process and certain smoothness conditions on the higher-order reduced cumulant measures. Finally, the obtained limit theorems enable us to construct \(\chi ^2\) -goodness-of-fit tests for hypothetical product densities.     

Crystal Structure of Bis -(2,2′-bipyridine-N,N′)-(dicyanamide-N)-copper(II) Tricyanomethanide. Electronic and Structural Parameters Describing the Shape of Coordination Polyhedra in Five-Coordinated Copper(II) Compounds

 The structure of the new compound [Cu(bpy)₂N(CN)₂]C(CN)₃ (6) is compared with thestructures of six copper(II) coordination compounds with phenanthroline or bipyridine ligands and N-donor pseudohalide anions: [Cu(phen)₂NCS]C(CN)₃ (1), [Cu(bpy)₂NCS]C(CN)₃ (2), [Cu(phen)₂NCS]ONC(CN)₂ (3), [Cu(phen)₂N(CN)₂]C(CN)₃ (4), [Cu(bpy)₂C(CN)₃]C(CN)₃ (5), and [Cu(bpy)₂NCO]C(CN)₃ (7). The Cu(II) atoms in all above compounds are five-coordinated with an N-donor atom of the pseudohalide anion located in the equatorial plane of a deformed trigonal bipyramid. The shape of the coordination polyhedra and the degree of trigonal bipyramidal distortion towards a tetragonal pyramid are discussed and described using one electronic and several structural criteria which are discussed and compared.     

Zur Bestimmung des specifischen Gewichtes von D?mpfen und permanenten Gasen

Ohne Zusammenfassung     

Functional Equations Connected With The Collatz Problem

In this paper, some aspects of the famous 3n + 1 problem, due to L. Coilatz, are studied. Introducing generating functions for the iterated mappings, we derive certain linear recursion formulae and investigate their properties. For the still unproved conjecture of L. Collatz we state two equivalent analytic versions, concerning the rational character of some generating functions, and the set of solutions of a linear functional equation, respectively.     

Asymptotische LÖsungen Der Translationsgleichung

For the solutions of the translation equation special asymptotic developments are considered. It is shown that the coefficients of such developments can be determined by linear recursion formulas or by Lie-series. Examples illustrate these results.     

Ionic Liquid for in situ Vis/NIR and Raman Spectroelectrochemistry: Doping of Carbon Nanostructures

1-butyl-3-methylimidazolium tetrafluoroborate (an ionic liquid) is an advantageous electrolyte for the study of charge-transfer reactions at single-walled carbon nanotubes (SWCNTs) and fullerene peapods (C₆₀@SWCNT). Compared to traditional electrolyte solutions, this medium offers a broader window of electrochemical potentials to be applied, and favorable optical properties for in situ Vis/NIR and Raman spectroelectrochemistry of nano-carbon species. The electrochemistry of both nanotubes and peapods is dominated by their capacitive double-layer charging. Vis/NIR spectroelectrochemistry confirms the charging-induced bleaching of transitions between Van Hove singularities. At high positive potentials, new optical transitions were activated in partly filled valence band. The bleaching of optical transitions is mirrored by the quenching of resonance Raman scattering in the region of tube-related modes. The Raman frequency of the tangential displacement mode of SWCNT shifts to blue upon both anodic and cathodic charging in the ionic liquid. The Raman modes of intratubular C₆₀ exhibit a considerable intensity increase upon anodic doping of peapods.