Ken-ichi Katayama

Crystal structure of stereocomplex of poly(L-lactide) and poly(D-lactide)

Abstract An equimolar mixture of poly(L-lactide) and poly(D-lactide) was crystallized into a stereocomplex whose crystal system is triclinic (P1) with cell dimensions: a = 0.916 nm, b = 0.916 nra, c (chain axis) = 0.870 nm, α = 109.2°, β - 109.2°, and γ = 109.8°. In the unit cell, a poly(L-lactide) segment and a poly (D-lactide) segment are contained as a pair and packed laterally in parallel fashion. The L- and D-poly(lactides) in the complex take a 31 helical conformation, which is a little extended from a 103 helix in the homopolymer crystal with the α-form. Homopolymers are also able to take the 31 helical conformation and form the β-form crystal. The 31 helix in the homopolymer crystal is less stable than the 103 one, and hence the β-form is easily transformed to the α-form by annealing.

Direct imaging of molecular chains in a poly(p-xylylene) single crystal

Abstract Individual chains comprising a β-form poly( p -xylylene) (PPX) single crystal were resolved with a high resolution electron microscope (JEM-500). In a polymer crystal the important limiting factor for resolution is radiation damage. The total end point dose of a PPX crystal is about 0.5 coulomb cm −2 for 500 kV electron irradiation which is more than 20 times greater than that for a polyethylene crystal. The high resolution image obtained was processed by optical filtering to reduce noise due to the granularity of film. The processed image, which corresponds to the ab -plane projection of polymer chains, shows clearly the mutual arrangement of each molecule in the crystal. This high resolution image is sufficient to provide a starting point for determining the unknown crystal structure of the β-modification of PPX.

Structural analysis of β-form poly(p-xylyene) starting from a high-resolution image

Abstract The crystal structure of β-form poly( p -xylylene) is analysed starting from a high-resolution image of a single crystal of this polymer. The high-resolution image corresponding to the projection of molecules onto the ab -plane along the chain axis shows clearly the mutual position of each molecule in a unit cell. The molecules are aligned wavily in the direction along the a -axis and the rough positions of their centres in a unit cell can be determined from the image. The refinement of the structure is carried out by the usual least-squares method using the intensities of electron and X-ray diffractions. The space group of the β-form is trigonal, P3, and the lattice dimensions are a =2.052 nm, c =0.655 nm and γ =120°. The unit cell contains 16 molecules and one of them is considered to occupy statistically one of three equivalent orientations so as to satisfy the P3 symmetry.

Effect of Ultraviolet Light Irradiation on Noncontact Laser Microwave Lifetime Measurement

An ultraviolet (UV) irradiation effect on minority-carrier recombination lifetime measured by a noncontact laser/microwave (LM) method is investigated for silicon wafers with native oxide. After UV irradiation, the surface recombination velocity greatly decreased resulting in the increase in the effective recombination lifetime (τeff). The effect disappears rapidly with time after the irradiation, and τeff recovers to the initial value after several minutes at room temperature. Since the UV irradiation process is noncontact and nondestructive, the irradiation is proposed to minimize the surface effect of sample, in turn, to obtain the bulk lifetime (τb) with a noncontact LM lifetime measurement method.

Thickening process of polyethylene single crystals at an early stage of annealing

By the use of a position sensitive proportional counter, changes in small and wide angle X-ray scattering during annealing of polyethylene single crystal mats were measured from the start in successive spans of very short measuring time. At high temperatures, the long period relating to stacking of lamellae rapidly increased at an early stage, passed through a plateau, and thereafter again increased gradually. With a decrease in annealing temperature, the amount of its first rapid increase was reduced and the plateau changed into an ascending slope. At much lower annealing temperatures, the long period increased following the logt law after an induction time. The integral breadth of a peak corresponding to the long period first increased rapidly, simultaneously with the rapid increase in the long period, and thereafter decreased. Wide angle X-ray measurement showed that the integrated intensity of 110 reflection first decreased and then increased during annealing at high temperatures. This fall and rise process was more marked, when the annealing temperature is higher and the initial thickness of lamellae is smaller. From these observations, it was inferred that in the thickening process, stacking order of lamellae at first decreased because of rapid reorganization due to partial melting or melt-recrystallization and subsequently increased through increasing evenness of lamellar thickness.

High resolution electron microscopy of (SN)x

Pristine and iodinated (SN)x were studied by high resolution electron microscopy. High resolution electron micrographs showing lattice fringes up to 0.22 nm were obtained. In these electron micrographs, the texture of (SN)x crystals was elucidated to be fibrillar or mosaic; the lattice fringes were observed in domains extended along the molecular axis (b-axis) and very narrow in the perpendicular direction. Each crystallite varied from place to place in size but maintained the b-axis orientation.The high resolution image of iodinated (SN)x did not show directly the location of iodine atoms and their presence was deduced only from the optical transform of the image. The optical transform showed that iodine atoms were not intercalated uniformly, but localized at the skin region on (SN)x fibers, where the crystal lattice was highly distorted. Then the iodination of (SN)x is supposed to result in the destruction of the crystal lattice by invasion of iodine atoms or to take place preferentially at a distorted crystal region.

High-resolution electron microscopy of solution-grown crystals of poly (p-phenylene sulphide)

Crystals of poly (p-phenylene sulphide) were obtained from anα-chloronaphthalene solution. The chain axis (the crystalc-axis) was usually normal to the support-film. For these crystals, high-resolution electron microscopic images were taken as the projection of the molecular chains on theab plane along the chain axis. Occasionally it was observed that crystals took different orientations on the support-film for undefined reasons. From such orientations, the high-resolution image of a crystal rotated by 28.7° around thea-axis from the usual orientation, was also obtained.

Iodine Atoms Structured in (SN)x

Electron diffraction pattern of iodinated (SN)x shows that iodine atoms are structured as a chain along the molecular axis of (SN)x. High resolution electron micrograph and its optical transform show that the crystalline lattice is severely distorted by iodination, but the (02) plane is comparatively stable for iodine invasion. Iodine atoms are considered to be settled on the (02) plane, where iodine atoms are structured as iodine chains and the two iodine chains tend to pair.

Thickening process of polyethylene single crystals at an early stage of annealing. II: Computer simulation of lamellar thickening

The thickening process of polyethylene single crystals was simulated with computer by the Monte Carlo method. According to the experimental results in the previous report, the time dependence of the long period changed greatly with annealing temperature; at lower temperatures the long period increased gradually, while at high temperatures the long period rapidly increased at a very early stage of annealing and then increased gradually after passing through a plateau. Through computer simulation, it was shown that such a great change in the time dependence of the long period with annealing temperature can be explained by combining two mechanisms: (A) sliding diffusion of molecular segments along the chain axis and (B) local melt-recrystallization (namely, local melting followed by recystallization).

Investigation on Defects in Czochralski Silicon with High-Sensitive Laser/Microwave Photoconductance Technique

High sensitivity of a noncontact laser/microwave photoconductance (LM-PC) technique for defects in heat-treated Czochralski (CZ) silicon crystals was confirmed in comparison with other diagnostic techniques such as Fourier transform infrared spectroscopy (FT-IR) and deep-level transient spectroscopy (DLTS). The energy levels of recombination centers (ET) in samples subjected to a three-step intrinsic gettering (IG) thermal process were obtained with LM-PC although no significant oxygen reduction in the samples was observed with FT-IR. The defect density detection limits of LM-PC and DLTS for samples after the three-step IG process are estimated to be ≤1×107 cm-3 and ~1×1010 cm-3, respectively. Moreover, the dependence of effective minority-carrier recombination lifetime on defect density was found to be influenced greatly by carbon concentration through the enhancement effect on oxygen precipitation.