FePt L10 ordering and grain growth using millisecond pulse laser processing

The structural and magnetic properties of ∼12 nm thick FePt thin films grown on Si substrates annealed using a 1064 nm wavelength laser with a 10 ms pulse have been examined. The A1 to L1₀ ordering phase transformation was confirmed by electron and X-ray diffraction. An order parameter near 50% and a maximum coercivity of 12 kOe were obtained with laser energy densities of 25-32 J/cm². Grain growth, quantified by dark field transmission electron microscopy, occurred during chemical ordering at the laser pulse widths studied.     

Coherent transport of neutral atoms in spin-dependent optical lattice potentials

We demonstrate the controlled coherent transport and splitting of atomic wave packets in spin-dependent optical lattice potentials. Such experiments open intriguing possibilities for quantum state engineering of many body states. After first preparing localized atomic wave functions in an optical lattice through a Mott insulating phase, we place each atom in a superposition of two internal spin states. Then state selective optical potentials are used to split the wave function of a single atom and transport the corresponding wave packets in two opposite directions. Coherence between the wave packets of an atom delocalized over up to seven lattice sites is demonstrated.     

High-spin states in the 96Tc nucleus

High-spin states in the ⁹⁶Tc nucleus have been studied with the reactions ⁸²Se(¹⁹F,5nγ) at 68 MeV and Zn(³⁶S,αpxn) at 130 MeV. Two γ-ray cascades (irregular bandlike structures) have been observed up to an excitation energy of about 10 MeV and spin 21-22?. Received: 19 January 2001 / Accepted: 30 March 2001     

Free-carrier absorption modulation in silicon nanocrystal slot waveguides

Free-carrier absorption (FCA) has proven to be an important obstacle in the development of a silicon-based laser; however, FCA may serve as a potential advantage in active silicon-based switches or modulators. In this work, we present FCA modulation in slot waveguides with silicon nanocrystals (Si-ncs) embedded in SiO(2) as the low-index slot material. Slot waveguides were fabricated with and without Si-ncs, and the presence of Si-ncs was shown to increase the pump-induced FCA loss in the waveguides by a factor of 4.5. We modeled the Si-nc material using a four-level rate equation analysis to estimate the excited population of Si-ncs, allowing us to extract a value of 2.6 × 10(-17) cm(2) for the FCA cross section of the Si-nc material.     

Preparation of hydrogels via ultrasonic polymerization

Several acrylic hydrogels were prepared via ultrasonic polymerization of water soluble monomers and macromonomers. Ultrasound was used to create initiating radicals in viscous aqueous monomer solutions using the additives glycerol, sorbitol or glucose in an open system at 37 °C. The water soluble additives were essential for the hydrogel production, glycerol being the most effective. Hydrogels were prepared from the monomers 2-hydroxyethyl methacrylate, poly(ethylene glycol) dimethacrylate, dextran methacrylate, acrylic acid/ethylene glycol dimethacrylate and acrylamide/bis-acrylamide. For example a 5% w/w solution of dextran methacrylate formed a hydrogel in 6.5 min in a 70% w/w solution of glycerol in water at 37° C with 20 kHz ultrasound, 56 W cm^?2. The ultrasonic polymerization method described here has a wide range of applications such a biomaterial synthesis where initiators are not desired.     

Material Discrimination in Nanoparticle Hetero-Aggregates by Analysis of Scanning Transmission Electron Microscopy Images

Hetero-contacts are interfaces between different materials at the nanoscale leading to novel functional properties. In hetero-aggregates, primary particles of at least two different materials are mixed at primary particle or cluster level. Double flame spray pyrolysis (DFSP) is a versatile technique for the controlled synthesis of such materials. Characterization of hetero-aggregates by scanning transmission electron microscopy (STEM) requires acquisition and evaluation of many aggregate images in order to derive statistically significant results. Usually, STEM energy dispersive X-ray spectroscopy (EDXS) is used to acquire elemental maps providing the material distribution of the primary particles within hetero-aggregates. However, the acquisition of a single EDXS map takes up to several minutes. For this reason, determination of material types of primary particles from the intensity in high-angle annular dark field STEM images alone is desirable. These images can be acquired within a couple of seconds. In the present work, a method is suggested which allows for achieving this objective. It can be applied to distinguish materials with a significant difference in their atomic number and hence sufficient material contrast in the STEM images.     

Synthesis of Benzopyran Derivatives,XIV: New Procedure for the Preparation of 2,2-Dimethyl-2H-chromenes

2,2-Dimethyl-4-methoxychromans (1–12) have been converted into 2,2-dimethyl-2H-chromenes (13–24) in acidic media.