Electron‐Irradiated Polymer Brushes for Hollow Carbon Nanosphere Arrays

A thermally stable 2D array of spheres and their morphology control become important for the fabrication of novel nanostructures. Here, a simple method is presented for fabrication of large‐area and well‐ordered arrays of carbonized polystyrene (PS) hollow spheres with a controlled (close‐packed or non‐close‐packed hexagonal) morphology, prepared by combining the self‐assembly of PS‐grafted silica nanoparticles, etching, electron irradiation, and subsequent thermal annealing. Fine control in the 2D or 3D nanostructure of carbon materials can open up new opportunities for high‐performance nanoscale applications that require an efficient fabrication method for preparation of the porous carbon array.

     

Hindered rotation and phase transition in sodium gallohydride according to the NMR data

Polycrystalline sodium gallohydrides with different hydrogen isotope compositions, NaGaH₄, NaGaH_2.56D_1.44, and NaGaD₄, were studied over the temperature range 100–375 K by the ²H, ²³Na, and ^69,71Ga NMR methods in magnetic fields of 1.4, 1.88, and 7.04 T. The data on spin-lattice deuteron relaxation T ₁(²H) were used to determine the activation energy (～35 kJ/mol) of anion rotational motions and quadrupole coupling constant (QCC) χ _Q ⁰ (²H) = 90 kHz for the rigid lattice. To within measurement errors, the activation energy and ²H QCC were independent of the isotope composition. The low-temperature ²H NMR line was a doublet with ²H QCC χ(²H) = 70 kHz. The difference between χ ₀ and χ(T) was interpreted in terms of the librational averaging of the electric field gradient (EFG) according to the Bayer equation. The frequency of librations at 113 K was estimated (31 cm^?1). The shape of the ^69,71Ga NMR line was indicative of second-order quadrupole interaction with a nonzero asymmetry parameter η of the EFG tensor. Temperature variations in the QCC and η parameter at gallium were considered using the distorted tetrahedron model. The η value changed from 0.65 to zero (axial EFG tensor symmetry characteristic of tetragonal lattices) over the temperature range 140–295 K and again increased to 0.3 at 300–365 K, which was evidence of a change in the orientation of the distorted tetrahedral anion in the lattice. Changes in the asymmetry parameter were in agreement with the phase transition in sodium gallohydride recorded as a heat capacity jump.     

Source velocity at relativistic beams of <Superscript>4</Superscript>He

The source velocities (β = ν/c) extracted from rapidity plots of the fragment invariant probability distribution in terms of the longitudinal versus transversal velocity components has been studied for ⁴He + Au collisions at 4 and 14.6 GeV. It was found transition from broad range source velocities distribution in case of ⁴He(4 GeV) + Au to fixed source velocity in case of ⁴He(14.6 GeV) + Au.