Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation

We present experimental results on the photoluminescence (PL) of gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL spectra in the UV spectral region correspond to the exciton recombination in the nanoclusters which are crystallized and cooled down to the temperature of the ambient gas in the ablation chamber. The time evolution of the spectra as well as their dependence on the ambient gas pressure are discussed.Comment: EMRS-2004, Strasbourg, France. Paper N-I.

Thermodynamic model of the compaction of powder materials by shock waves

For powder materials a model is proposed to predict the mean temperature behind the shock wave, the ratio between the increase of thermal energy and increase of total internal energy, as well as the mean final temperature after release of adiabatic pressure. Further, the change of pressure, specific volume, and the internal energy behind the shock wave are calculated together with the shock-wave velocity. All these variables are supposed to depend exclusively on flyer plate velocity, initial powder density, and initial powder temperature. The ratio between the increase of thermal energy and increase of total internal energy decreases rapidly upon decreasing initial powder density, resulting in a higher shock temperature and a lower shock pressure; therefore, a lower initial powder density results in a better bonding between the particles and fewer cracks after pressure release. Calculations are carried out for copper and agree fairly well with experiments.

Shock wave equation of state of powder material

A model is proposed to predict the following quantities for powder materials compacted by shock waves: the pressure, the specific volume, the internal energy behind the shock wave, and the shock-wave velocity Us. They are calculated as a function of flyerplate velocity up and initial powder specific volume V00. The model is tested on Cu, Al2024, and Fe. Calculated Us vs up curves agree well with experiments provided V00 is smaller than about two times the solid specific volume. The model can be used to predict shock-wave state points of powder or solid material with a lower or higher initial temperature than room temperature.

Laser penetration spike welding:A microlaser welding technique enabling novel product designs and constructions

A novel method for laser penetration microspot welding of sheet metal is presented. With this so called "laser spike-welding," large gap tolerances are allowed. Depending on the ratio of laser spot radius to top plate thickness, gaps of 100% of the top layer thickness and more can be bridged. With conventional keyhole penetration welding this is only 20%-40% at most. So, with spike welding the gap between the metal plates can be increased by a factor of 2.5-5. In this way a powerful and attractive welding technique for joining of thin metal plates is available. The laser spike weld method can handle larger production tolerances and will enable novel and cheap product designs and welding of dissimilar materials. (C) 2003 Laser Institute of America

On the role of dislocations in heavily strained YBa2Cu3O7-δ

Dense pellets of polycrystalline YBa2Cu3O7-δ have been made by shock compaction. While YBa2Cu3O7-δ is brittle at ambient conditions, the high pressure generated during the shock deformation is known to enhance its plasticity. Plastic deformation as well as fracture occurs when the shock wave passes through the initially loose powder, and multiple defects are expected to be generated. The paper reports on the interaction of dislocations with twin boundaries, and their role in the cleavage behaviour. The observations are performed on shock-loaded samples, compacted at E/M ratios ranging from 0.8 to 2.3. The microstructure of shock-compacted samples is compared to that of the initial, non-compacted powders. Apart from the well established <100>{100} glide system, the role of the novel [110](11¯0) and [010](100) glide systems is studied. All glide systems are found to interact with the ferroelastic domains of the material, each in a different way.