Search results for " bonding"

Electronic Transitions in Tetrathiafulvalene and Its Radical Cation:  A Theoretical Contribution

2001

The low-lying electronic states of tetrathiafulvalene (TTF) and its radical cation (TTF+) have been studied using the multistate extension of a multiconfigurational second-order perturbation method (MS−CASPT2). The minimum-energy equilibrium geometries optimized at the CASSCF level have a boatlike conformation for the neutral molecule, with no significant barrier toward planarity. A more aromatic planar structure is, however, found for the ionic system. For TTF, the calculations of the vertical excitation energies comprise valence singlet and triplet states as well as the lowest members of the Rydberg series converging to the first ionization limit. Valence doublet states have been consider…

Design and setup of a Linear Friction Welding fixture

2011

300°C SiC Blocking Diodes for Solar Array Strings

2009

Silicon Carbide 300V-5A Ni and W Schottky diodes with high temperature operation capability (up to 300°C) have been fabricated. This paper reports on the stability tests (ESA space mission to Mercury, BepiColombo requirements) performed on these diodes. A DC current stress of 5A has been applied to these diodes at 270°C for 800 hours. These reliability tests revealed both, degradation at the Schottky interface (forward voltage drift) and at the diode top surface due to Aluminum diffusion (bond pull strength degradation). The use of W as Schottky metal allows eliminating the forward voltage drift producing stable metal–semiconductor interface properties. Nevertheless, SEM observations of the…

Improving the Quality Management of the Thermosonic Welding Process of Gold Wires in Automotive Industry

2018

Abstract This scientific paper conducts a study meant to improve the quality management of the thermosonic welding process of gold wires in the automotive industry. Within the large amount of electronic products manufactured worldwide, the gold wire bonding is the preferred technology for creating the needed interconnections in the microelectronic industry. In this paper, the quality management improving starts with an experimental research in the automotive industry, based on the gold wire thermosonic bonding, in terms of: conformal structuring, robustness and integrity of the electrical contacts. The experimental research is based on the processing parameters and on the independent variab…

Comparative evaluation of the effect of the substrate thickness and inherent process defects on the static and fatigue performance of FSW and adhesiv…

2021

Abstract This work aims at evaluating the mechanical performance of joints in an AA6016 alloy, manufactured by means of two alternative processes: friction stir welding and adhesive bonding. Given its wide use in industrial fields such as automotive and aeronautics, an overlap configuration of joints was selected for the study, and a specific method based on the overlap length evaluation has been developed to allow comparisons among the cases. Two substrate thicknesses are considered in order to vary the overall joint stiffness, and the effect of such geometrical parameter on the mechanical behavior of the joined system is experimentally investigated. The experimental findings highlight tha…

Investigations on the linear friction welding process through numerical simulations and experiments

2012

Abstract Linear Friction Welding (LFW) is a solid-state joining process applied to non-axisymmetric components. LFW involves joining of materials through the relative motion of two components undergoing an axial force. In such process the heat source is given by the frictional forces work decaying into heat determining a local softening of the material and eventually bonding conditions. In the paper the authors present a designed and assembled laboratory fixture for LFW operations and the results of an experimental and numerical campaign aimed to weld steel parts. The dedicated fixture permitted to highlight the effect of the most important process parameters. Process conditions allowing ef…

Impedance analysis of perovskite solar cells: a case study

2019

Metal halide perovskites are mixed electronic-ionic semiconductors with an extraordinary rich optoelectronic behavior and the capability to function very efficiently as active layers in solar cells, with a record efficiency surpassing 23% nowadays. In this work, we carry out an impedance spectroscopy analysis of two perovskite solar cells with quite distinct optical and electrical characteristics, i.e. MAPbI3 and CsPbBr3-based devices. The main aim of the analysis is to establish how, regardless the inherent complexity of the impedance spectrum due to ionic effects, information like ideality factors, recombination losses and the collection efficiency can be qualitative and quantitatively as…

Interaction of Charged Amino-Acid Side Chains with Ions: An Optimization Strategy for Classical Force Fields

2014

Many well-established classical biomolecular force fields, fitted on the solvation properties of single ions, do not necessarily describe all the details of ion pairing accurately, especially for complex polyatomic ions. Depending on the target application, it might not be sufficient to reproduce the thermodynamics of ion pairing, but it may also be necessary to correctly capture structural details, such as the coordination mode. In this work, we analyzed how classical force fields can be optimized to yield a realistic description of these different aspects of ion pairing. Given the prominent role of the interactions of negatively charged amino-acid side chains and divalent cations in many …

Electroplated Indium Bumps as Thermal and Electrical Connections of NTD-Ge Sensors for the Fabrication of Microcalorimeter Arrays

2012

We are developing a method to build arrays of Ge-based microcalorimeters for soft X-rays detection using micro-photolithographic techniques. A key element of the process is the electrical and thermal connection between the germanium sensors and the interconnection electrical tracks, that lay on a substrate acting as mechanical support and thermal sink. The geometry of the sensors, that have a square base truncated pyramid shape, makes feasible a connection through indium soldering. We describe a technique, based on microlithography and electroplating, adopted to grow indium bumps of a few tens of square microns of area and several microns high on top of the contact pads patterned on the sub…

Cyclic tetraureas with variable flexibility--synthesis, crystal structures and properties.

2008

Macrocyclic molecules containing several amide or urea functions may serve as anion receptors. We describe the synthesis of 32-membered macrocycles, in which four rigid xanthene units (X) and/or diphenyl ether units (D) as flexible analogues are linked via urea groups. All six possible combinations of these units (XXXX, XXXD, XXDD, XDXD, XDDD and DDDD) were synthesized and two examples were characterised by single-crystal X-ray analyses (DDDD and two structures for XXXD). Both macrocycles showed distinct differences in their overall conformation and consequently in their hydrogen-bonding pattern. Hydrogen-bonded solvent molecules are found for both compounds and intramolecular hydrogen bond…