Static magnetic order in Na0.75_{0.75}CoO2_2 detected by muon spin rotation and relaxation

The nature of the magnetic transition of the Na-rich thermoelectric Na$_{0.75}$CoO$_2$ at 22K was studied by positive muon-spin-rotation and relaxation ($\mu^+$SR) spectroscopy, using a polycrystalline sample in the temperature range between 300 and 2.5 K. Zero field $\mu$SR measurements indicated the existence of a static internal magnetic field at temperatures below 22 K (= $T_{\rm m}$). The observed muon spin precession signal below $T_{\rm m}$ consisted of three components with different precession frequencies, corresponding to three inequivalent muon$^+$ sites in the Na$_{0.75}$CoO$_2$ lattice. The total volume fraction of the three components was estimated as $\sim$21% at 2.5 K; thus, this magnetic transition was not induced by impurities but is an intrinsic change in the magnetism of the sample, although the sample was magnetically inhomogeneous otherwise. On the other hand, a similar experiment on a Na$_{0.65}$CoO$_2$ sample exhibited no magnetic transition down to 2.5 K; which indicates that the average valence of the Co ions is responsible for inducing the magnetic transition at 22 K.Comment: 5 pages, 4 figures, Phys. Rev. B 68 (2003) in pres

In situ reflection imaging and microspectroscopic study on three-dimensional crystal growth of L-phenylalanine under laser trapping

We investigate growth behavior of an L-phenylalanine crystal formed by laser trapping with the use of reflection imaging and microspectroscopy. Optical reflection micrographs show colored images of the crystal due to constructive interference of incident white light. The color distribution on the crystal is dynamically changed under laser trapping, which is in addition to enlargement of the crystal plane area. The temporal change in the crystal thickness is examined by measuring reflection spectra of the crystal. We discuss the three-dimensional crystal growth under laser trapping by comprehensively considering the changes in crystal thickness and crystal plane area. (C) 2019 The Japan Society of Applied Physic

Bubble generation and molecular crystallization at solution surface by intense continuous-wave laser irradiation

We demonstrate bubble generation outside the focus induced by irradiating a focused 1064 nm continuous-wave laser beam into the surface of water and L-phenylalanine H2O solutions. In the former case of water, bubbles stay at positions distant from the focus during the irradiation, and their size and location are controllable by the laser power. In the latter solution, bubbles move outward toward the surrounding area, and subsequently crystallization takes place at the focus. We discuss these behaviors from the viewpoints of the temperature elevation accompanying the decrease in air solubility as well as the optical trapping of L-phenylalanine clusters giving a single crystal. (C) 2018 The Japan Society of Applied Physic

Femtosecond Laser Trapping Dynamics of Nanoparticles: A Single Transient Assembly Formation Leading to Their Directional Ejection

© XXXX American Chemical Society. We investigated femtosecond laser trapping dynamics of silica nanoparticles with different hydrophobic surface properties. We demonstrated that the hydrophobic surface on the silica nanoparticles facilitates mutual association of the nanoparticles in the optical trapping site. Such association of optically trapped nanoparticles is a prerequisite to induce their directional ejection away from the trapping site. The directional ejection of the optically trapped nanoparticles is most probably due to asymmetric three-dimensional ejecting forces generated by the electromagnetic interaction between transient assembly in the focal spot and the incident pulses. These findings provide important insights into the directional ejection of nanoparticles from the trapping site in the femtosecond laser trapping, and this physicochemical phenomenon is controlled by both the trapping laser and material properties.status: publishe

Millimeter-Scale Dense Liquid Droplet Formation and Crystallization in Glycine Solution Induced by Photon Pressure

A millimeter-scale dense liquid droplet of glycine is prepared by focusing a CW near-infrared laser beam at the glass/solution interface of a thin film of its supersaturated heavy water solution. The formation process is investigated by direct observation with CCD and by measuring temporal change of the surface height with a displacement meter. The droplet becomes much larger than a focal spot size, a few mm width and ∼150 μm height, and observable with the naked eye. Interestingly, the droplet remains for a few tens of seconds even after switching off the laser beam. Whereas the droplet is kept during laser irradiation, the crystallization is immediately attained by shifting the laser beam to the air/droplet surface. It is considered that the droplet is possibly the early stage of the multistep crystallization process and plays an important role in photon pressure-induced crystallization of glycine

Laser Trapping and Crystallization Dynamics of l‑Phenylalanine at Solution Surface

We present laser trapping behavior of l-phenylalanine (l-Phe) at a surface of its unsaturated aqueous solution by a focused continuous-wave (CW) near-infrared (NIR) laser beam. Upon the irradiation into the solution surface, laser trapping of the liquid-like clusters is induced concurrently with local laser heating, forming an anhydrous plate-like crystal at the focal spot. The following laser irradiation into a central part of the plate-like crystal leads to laser trapping at the crystal surface not only for l-Phe molecules/clusters but also for polystyrene (PS) particles. The particles are closely packed at crystal edges despite that the crystal surface is not illuminated by the laser directly. The molecules/clusters are also gathered and adsorbed to the crystal surface, leading to crystal growth. The trapping dynamics and mechanism are discussed in view of optical potential formed at the crystal surface by light propagation inside the crystal