Improved Analytical Model for Thermal Softening in Aluminum Alloys Form Room Temperature to Solidus.

In advanced solid-state manufacturing processes such as friction stir welding, the metal's temperature ranges from room temperature to the solidus temperature. The material strength in the temperature range is generally required for investigating the mechanical behaviors. In this communication paper, an analytical model is proposed for describing the thermal softening of aluminum alloys for room temperature to solidus temperature, in which the concept of temperature-dependent transition between two thermal softening regimes is implemented. It is demonstrated that the proposed model compares favorably to the well-known Sellars-Tegart model and Johnson-Cook model. The constants of the proposed model for nine typical engineering commercial aluminum alloys are documented.

Structure Inheritance in Nanoparticle Ink Direct-Writing Processes and Crack-Free Nano-Copper Interconnects Printed by a Single-Run Approach.

When nanoparticle conductive ink is used for printing interconnects, cracks and pores are common defects that deteriorate the electrical conductivity of the printed circuits. Influences of the ink solvent, the solid fraction of the ink, the pre-printing treatment and the sintering parameters on the interconnect morphology and conductivity were investigated. It was found that the impacts of all these factors coupled with each other throughout the whole procedure, from the pre-printing to the post-printing processes, and led to a structure inheritance effect. An optimum process route was developed for producing crack-free interconnects by a single-run direct-writing approach using home-made nano-copper ink. A weak gel was promoted in the ink before printing in the presence of long-chain polymers and bridging molecules by mechanical agitation. The fully developed gel network prevented the phase separation during ink extrusion and crack formations during drying. With the reducing agents in the ink and slow evaporation of the ink solvent, compact packing and neck joining of copper nanoparticles were obtained after a two-step sintering process. The crack-free interconnects successfully produced have a surface roughness smaller than 1.5 µm and the square resistances as low as 0.01 Ω/□.

Plasmon-Induced Heterointerface Thinning for Schottky Barrier Modification of Core/Shell SiC/SiO2 Nanowires.

In this work, plasmon-induced heterointerface thinning for Schottky barrier modification of core/shell SiC/SiO2 nanowires is conducted by femtosecond (fs) laser irradiation. The incident energy of polarized fs laser (50 fs, 800 nm) is confined in the SiO2 shell of the nanowire due to strong plasmonic localization in the region of the electrode-nanowire junction. With intense nonlinear absorption in SiO2, the thickness of the SiO2 layer can be thinned in a controllable way. The tuning of the SiO2 barrier layer allows the promotion of electron transportation at the electrode-nanowire interface. The switching voltage of the rectifying junction made by the SiC/SiO2 nanowire can be significantly tuned from 15.7 to 1 V. When selectively thinning at source and drain electrodes and leaving the SiO2 barrier layer at the gate electrode intact, a metal/oxide/semiconductor (MOS) device is fabricated with low leakage current. This optically controlled interfacial engineering technology should be applicable for MOS components and other heterogeneous integration structures.

Improving the electrical contact at a Pt/TiO2 nanowire interface by selective application of focused femtosecond laser irradiation.

In this paper, we show that tightly focused femtosecond laser irradiation is effective in improving nanojoining of an oxide nanowire (NW) (TiO2) to a metal electrode (Pt), and how this process can be used to modify contact states. Enhanced chemical bondings are created due to localized plasmonically enhanced optical absorption at the Pt/TiO2 interface as confirmed by finite element simulations of the localized field distribution during irradiation. Nano Auger electron spectroscopy shows that the resulting heterojunction is depleted in oxygen, suggesting that a TiO2-x layer is formed between the Pt electrode and the TiO2 NW. The presence of this redox layer at the metal/oxide interface plays an important role in decreasing the Schottky barrier height and in facilitating chemical bonding. After laser irradiation at the cathode for 10 s at a fluence of 5.02 mJ cm-2, the Pt/TiO2 NW/Pt structure displays different electrical properties under forward and reverse bias voltage, respectively. The creation of this asymmetric electrical characteristic shows the way in which modification of the electronic interface by laser engineering can replace the electroforming process in resistive switching devices and how it can be used to control contact states in a metal/oxide interface.