Electron Diffraction Diagrams Research Articles

Epitaxial growth and magnetic properties of Mn5(SixGe1-x)3 thin films

Structural and magnetic properties of Mn5(SixGe1-x)3 thin films were investigated. Ferromagnetic Mn5Ge3 and anti-ferromagnetic Mn5Si3 thin films have been synthesized and characterized as these compounds exhibit interesting features for the development of spintronics. Here, Mn5(SixGe1-x)3 thin films were grown on Ge(111) substrates by co-deposition using molecular beam epitaxy. Crystalline thin films can be produced with controlled Si concentrations ranging from 0 to 1. The thin films were relaxed by dislocations at the interface with the substrate. A lattice parameter variation was observed as the Si content increased, which is comparable to previous works done in bulk. Reflection high-energy electron diffraction diagrams and X-ray diffraction profiles showed that lattice parameters a and c are shrinking and that the surface roughness and crystallinity degrade as the Si amount increases. Magnetometric measurements revealed a ferromagnetic behavior for all Si concentrations. The measured average ferromagnetic moment per manganese atom decreased from 2.33 to 0.05 μB/Mn atom. No ferro to anti-ferromagnetic transition was observed contrary to the bulk Mn5(SixGe1-x)3 compound.

Growth Mechanism of Periodic-Structured MoS2 by Transmission Electron Microscopy.

Molybdenum disulfide (MoS2) was grown on a laser-processed periodic-hole sapphire substrate through chemical vapor deposition. The main purpose was to investigate the mechanism of MoS2 growth in substrate with a periodic structure. By controlling the amount and position of the precursor, adjusting the growth temperature and time, and setting the flow rate of argon gas, MoS2 grew in the region of the periodic holes. A series of various growth layer analyses of MoS2 were then confirmed by Raman spectroscopy, photoluminescence spectroscopy, and atomic force microscopy. Finally, the growth mechanism was studied by transmission electron microscopy (TEM). The experimental results show that in the appropriate environment, MoS2 can be successfully grown on substrate with periodic holes, and the number of growth layers can be determined through measurements. By observing the growth mechanism, composition analysis, and selected area electron diffraction diagram by TEM, we comprehensively understand the growth phenomenon. The results of this research can serve as a reference for the large-scale periodic growth of MoS2. The production of periodic structures by laser drilling is advantageous, as it is relatively simpler than other methods.

Effect of the Lithium Salt Concentration on Deposition and Dissolution of Lithium in a Bis(fluorosulfonyl)Amide-Based Ionic Liquid Electrolyte

Lithium metal is considered to be an ideal anode material for high-power lithium secondary batteries because of the high theoretical specific capacity of 3860 mAh g-1 and the negative redox potential. However, dendritic, needle-like or whisker-like growth of Li deposits may cause the internal short circuit and thermal runaway of the battery. The detachment of lithium from the current collector also leads to the capacity loss. The formation of homogeneous and stable solid electrolyte interphase (SEI) on the anode is considered to suppress the concentration of the current and dendritic growth of Li deposits.The addition of LiFSA (FSA- = bis(fluorosulfonyl)amide) to organic electrolytes has been reported to improve the reversibility of the Li anode probably due to the formation of FSA--derived SEI. Moreover, the reversibility of the Li anode was known to be improved in ionic liquids containing a high concentration of LiFSA[1, 2]. However, the formation mechanism and the chemical composition of the SEI in the electrolytes composed of FSA- are still unclear. In the present study, the charge-discharge behavior of the Li anode and the characterization of the SEI were investigated in FSA--based ionic liquids containing different concentrations of LiFSA.BMPFSA (BMP = 1-butyl-1-methylpyrrolidinium) and LiFSA were mixed at the molar ratios of 1 : 0.3 (1.1 M) and 1 : 1 (2.9 M). The charge-discharge measurement was conducted using a coin-type cell at 0.1 mA cm-2. Cu was used as a working electrode and Li was used as a counter electrode. Celgard 3501 was used as a separator. SEI was prepared on a Cu electrode by keeping the potential at 0 V prior to the measurement. The morphology of Li deposits on the Cu electrode was observed by scanning electron microscopy (SEM) after the charge-discharge measurement. The electrochemical impedance spectroscopy (EIS) was carried out at the open circuit potential before and during the SEI formation. The SEI formed on Cu by immersing a Cu substrate in the electrolytes in contact with Li metal was characterized using X-ray photoelectron spectroscopy (XPS) and transmittance electron microscopy (TEM) without exposure to air.The coulombic efficiency for deposition and dissolution of Li on a Cu electrode was ca. 97 % after cycling in both 1.1 and 2.9 M LiFSA/BMPFSA. Although needle-like Li deposits were observed in the 1st cycle, nodule-like deposits were obtained after 100 cycling regardless of the compositions. A semicircle corresponding to the SEI appeared after keeping the potential of a Cu electrode at 0 V for 6 hours in the Nyquist plots. The diameter of the semicircle in 1.1 M LiFSA/BMPFSA was larger than that in 2.9 M LiFSA/BMPFSA probably because the Li+ conductivity of the SEI reflected the concentration of Li+ in the electrolyte. XPS spectra of the SEI formed on the Cu substrate indicated the existence BMP+, FSA-, and/or their decomposition products. The SEI with a thickness of 20 nm was observed by TEM regardless of the composition. Furthermore, the spots corresponding to LiF and Li2S were found in the electron diffraction diagrams of the SEI.Reference[1] G. M. A. Girard, M. Hilder, N. Dupre, D. Guyomard, D. Nucciarone, K. Whitbread, S. Zavorine, M. Moser, M. Forsyth, D. R. MacFarlane, and P. C. Howlett, ACS Appl. Mater. Interfaces, 10, 6719 (2018).[2] T. Iwahashi, Y. Miwa, W. Zhou, Y. Sakai, M. Yamagata, M. Ishikawa, D. Kim, and Y. Ouchi, Electrochem. Commun.,72, 54 (2016).

Characterization of Solid Electrolyte Interphase Formed in Li[N(CF3SO2)2]-Sulfolane-Based Electrolytes

A highly concentrated electrolyte composed of sulfolane (SL) and lithium bis(trifluoromethylsulfonyl)amide (LiTFSA) attracts attention as an electrolyte for the lithium-sulfur battery because of the low solubility of lithium polysulfides. 1,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) is often added to the electrolyte in order to decrease the viscosity[1]. It is important to improve the cyclability of the Li anode to develop the Li-S battery having a high energy density. The deposition and dissolution of Li have been known to be affected by the formation and growth of a solid electrolyte interphase on the anode surface. In the present study, formation of the SEI on Cu and Li electrodes in LiTFSA-SL-based electrolytes was investigated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM).The mixtures of LiTFSA, SL and HFE at various ratios were used as the electrolytes. The SEI was formed on a Cu substrate by holding its potential at 0 V vs. Li|Li(I) in the electrolytes. The impedance measurements were conducted at the open circuit potential using a coin-type or three-electrode cell using a Li foil as a reference and counter electrode. The samples for TEM and XPS analysis were prepared by immersing a Cu foil or grid in the electrolytes in contact with Li. After washing the sample with monoglyme, TEM observation and XPS measurement were conducted without exposure to air. The SEI was formed on Li deposited galvanostatically on a Cu grid placed in a coin-type cell.Formation of the SEI was not confirmed on a Cu electrode after keeping the potential at 0 V for 24 hours in LiTFSA-SL (1 : 2) by EIS, suggesting sluggish formation and/or poor adhesion of the reduced products. On the other hand, a semicircle attributable to the SEI appeared in LiTFSA-SL-HFE (1 : 2 : 2), indicated the decomposition of HFE played an important role in the SEI formation.The XPS spectra of a Cu electrode after the SEI formation at 0 V in LiTFSA-SL-HFE indicated the existence of TFSA– and/or its decomposition products in the SEI. On the other hand, LiF was found to be absent in the SEI, suggesting LiF was not formed by the cathodic decomposition of the electrolyte on a Cu electrode.The SEI with a thickness of 10-100 nm was observed by TEM on a Cu grid after the SEI formation in LiTFSA-SL-HFE. The shrinkage of the film was observed during the observation, suggesting that the SEI was composed of organic materials. No spot was observed in the electron diffraction diagrams of the SEI. On the other hand, the ring asignable to Li2O was observed in the electron diffraction diagram of the SEI formed on Li deposits. Thus, the composition of the SEI formed on Li was considered different from that on Cu.AcknowledgmentThis study was supported by Advanced Low Carbon Technology Research and Development of Program (ALCA) of the Japan Science and Technology Agency (JST).Reference[1] A. Nakanishi et al., J. Phys. Chem. C, 123, 14229 (2019).

Evaluation of the Surface Film Formed on Cu in Li[N(CF3SO2)2]-Tetraglyme Solvate Ionic Liquids

Rechargeable lithium-sulfur batteries have been investigated as a next generation battery due to low cost and abundant resources. Li-S batteries using conventional organic electrolytes have been realized by addition of some additives forming some protecting films on the Li anode in order to avoid self-discharge due to dissolution of lithium polysulfides in the electrolytes. On the other hand, it has been known that the solubility of lithium polysulfides is very low in the ionic liquids composed of [N(CF3SO2)2]– (bis(trifluoromethylsulfonyl)amide, TFSA–) because of its weak coordinating ability. The equimolar mixture of LiTFSA and tetraglyme (G4) has been known to give a liquid composed of [Li(G4)]+ and TFSA– at room-temperature. This liquid is called a solvate ionic liquid (SIL). LiTFSA-G4 SILs have such favorable properties as high lithium ion concentration and low solubility of lithium polysulfides. Therefore, the LiTFSA-G4 SILs have been studied as the promising electrolytes for rechargeable Li-S batteries. In order to realize Li-S batteries using the LiTFSA-G4 SILs, it is necessary to evaluate the performance of the Li anode in the SILs. We have already reported that the coulombic efficiency of deposition and dissolution of lithium on a Cu substrate was improved by the formation of the surface film (solid-electrolyte interphase) on the Cu substrate at the potential of Li(I)/Li[1]. In the present study, the surface film formed in LiTFSA-G4 SILs with and without a diluent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (HFE), has been characterized using electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) without exposing the samples to air. LiTFSA-G4 SILs were prepared by mixing LiTFSA and G4 at the specified molar ratios (50.0 : 50.0 and 54.5 : 45.5). EIS was conducted using an air-tight three electrode cell. A Cu disk electrode (3 mm in diameter) was used as the working electrode. Li foil was used as the counter and reference electrode. The surface film was prepared on the Cu electrode by keeping the potential at 0 V vs. Li/Li(I). The EIS spectra were taken at 0 V vs. Li/Li(I) with an amplitude of 5 mV in the frequency range from 1 Hz to 20 kHz. TEM grids made of Cu and Cu foils in contact with Li foil were immersed in the SILs with different compositions for three days. The samples were washed with monoglyme (G1) and dried under dry Ar atmosphere. The samples were installed into TEM equipped with EDX using a transfer holder. XPS spectra were obtained by focused Al Kα radiation with Ar+ and Ar gas cluster ion beam (GCiB) etching guns. The impedance spectra assignable to the surface films formed on the Cu electrodes at 0 V vs. Li/Li(I) were observed in the SILs with and without addition of HFE. The resistance of the surface film in 54.5-45.5 mol% LiTFSA-G4 SIL was larger than that in 50.0-50.0 mol% one, suggesting the ionic conductivity of the surface film reflect the concentration of Li(I) in the electrolyte. The resistance of the surface film increased with addition of HFE probably due to a decrease in the concentration of Li(I). The formation of the surface films with the thickness of 20-100 nm was confirmed by TEM. The shrinkage of the films was observed during TEM observation, indicating the decomposition of organic substances and/or elevation of temperature occurred by electron irradiation. Although no spot was observed in the electron diffraction diagram at the beginning of the observation, the spots assignable to LiF and Li2S appeared after the shrinkage of the film by electron irradiation, indicating LiF was not formed electrochemically at 0 V vs. Li/Li(I) in the SILs. In addition, no peak assignable to LiF was not observed in the XPS spectra of the surface films with Ar GCiB etching gun. Therefore, the surface films formed in the SIL were considered to composed of the organic substances derived from reductive decomposition of G4 and the ions existing in the SIL.Reference[1] Y. Katayama, N. Tachikawa, and N. Serizawa, 235th ECS meeting, A02-0265, Dallas, (2019).

Study of Sodium Adsorption on Pb/Si(111) Surfaces

The new reconstructions formed by sodium adsorption on Pb-terminated Si (111) surface were obtained: 2x2+2sqrt3x2sqrt3, 4x1, 3x3 and others. These surface structures have been observed by low-energy electron diffraction (LEED) and phase diagram for 2D binary (Na,Pb)/Si (111) system has been obtained. The (Na,Pb)/Si (111) system is considered as a two-dimensional alloy layer with highly ordered structure. Influence of two-dimensional alloys on surface conductivity of Si (111) substrate has been studied in situ by four-point-probe method.

Typical Zirconium Alloys Microstructures in Nuclear Components

Abstract The different microstructures typically found in nuclear components made of zirconium alloys are discussed in this paper. These include material in a variety of thermo-mechanical conditions, e. g., cold rolled, stress relieved, recrystallized, welded, biphasic, together with minority second phases belonging to the original material or incorporated due to in-service conditions. The anisotropic crystalline structure of zirconium is exploited in microscopical observations by means of polarizer filters that enhance the contrast between different grains, and greatly aid the identification in most microstructures. Most microstructural variations across a wide range of length-scales, such as those produced by welding processes, can be effectively resolved by traditional optical microscopy (OM). However, some finer microstructures like those found in CANDU1 (CANada Deuterium Uranium) reactor pressure tube material, or some minority second phase particles like the Zr(Fe, Cr)2 precipitates in Zircaloy-4 cannot be completely resolved by this technique. Thus, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are required in such cases. For SEM observations we show the valuable issue of the scale in specific microstructural studies, which allows quantifying microstructural parameters using image analysis. For TEM observations, we have greatly benefited from the electron diffraction diagrams, which have allowed us to investigate the crystalline structure of irradiated second phase particles, which would remain unnoticed to both, OM or SEM observations.

Morphology and Structure of the β Phase Crystals of Monodisperse Polyfluorenes

Lenticular crystals of the β phase of monodisperse poly(9,9-dioctylfluorene)s (PFOs) have been prepared from o-dichlorobenzene (ODCB) solution. The diffraction analysis combined with X-ray and electron diffraction diagrams indicates that PFOs can crystallize in the orthorhombic system which have the lattice parameters of a = 1.32 nm, b = 2.10 nm, and c = 3.36 nm. In these single crystals, the backbone chains are packed parallel to the long axis of crystals. Furthermore, a variation of the annealing temperature from 90 to 130 °C demonstrates that there exists morphology and structure evolution, which has been systematically investigated by optical microscopy and electron microscopy.

The continuing debate over the structure of cellulose: historical perspective and outlook

The crystalline structure of native cellulose, with its unique microfibrillar morphology resulting from a complex biogenesis mechanism, has not only been the most studied subject in polymer science, but is still generating great interest along with lively debates and controversies. This issue of Cellulose features such a debate in the form of two articles dealing with the conformational analysis of the glucosidic bond in the cellulose chains. This debate is but the latest incident in a long string of events, which represent the foundation of our current understanding of this important material. This makes this an opportune moment to reflect on some of the major milestones in the history of cellulose structure evaluation, which also often involved debates and controversies. It was in 1913, i.e. close to one century ago, that Nishikawa and Ono showed the first diffraction patterns of two cellulose-based plant materials, namely bamboo and hemp, taking advantage of the discovery of the interference phenomena of X-rays reported 1 year earlier by Laue, Friedrich and Knipping. Following this early report, diffraction diagrams of a large number of cellulose materials were duly recorded and subjected to analysis, as it was felt that the knowledge of the crystalline structure of cellulose was of great importance for the development and improvement of cellulose-based products. While recording diffraction patterns of these specimens, it was soon realized that even the X-ray data sets of the most crystalline samples remained limited and it was therefore hard to deduce from them alone the required structural details. It is only when the diffraction data could be complemented by the occurrence of new techniques that substantial advances toward the structural description of cellulose could be made. The sequential emergence of such techniques explains the succession of steps leading to the present understanding. In the progress toward the molecular description of the crystal structure of cellulose from X-ray diffraction data, a first landmark was the incorporation of the stereochemistry of the glucosyl moieties in the molecular models built by, among others, Meyer and Mark (1928), later revised by Meyer and Misch (1937), who presented a model where the crystal of cellulose consisted of two antiparallel chains. This last model, which remained the established standard for at least two decades, was confronted with a series of conflicting data, resulting from new techniques. In 1958, the recording of electron diffraction diagrams of frozen Valonia cell wall fragments allowed Honjo and Watanabe to obtain diffraction data sets far better H. Chanzy—affiliated with the Universite Joseph Fourier and member of the Institut de Chimie Moleculaire de Grenoble.

Molecular and Crystal Structure of 7-Fold V-Amylose Complexed with 2-Propanol

Single crystals of amylose V2-propanol, i.e., amylose cocrystallized with water and 2-propanol, were prepared from synthetic linear amylose. When observed under frozen hydrated conditions, these crystals yielded base-plane electron diffraction diagrams containing more than 100 independent diffraction spots, whose intensities were used to solve the crystal structure of this complex. The molecular and crystal structure of amylose V2-propanol clearly indicated that the amylose molecules were organized in 7-fold left-handed helices, with 2-propanol and water molecules located as guests both within and between the helices. The V2-propanol unit cell contains four helices, distributed in two antiparallel pairs of parallel helices organized along the P212121 symmetry. The helices are organized along alternating motifs of four helices in a close-packed hexagonal arrangement together with four others in a nearly square organization surrounding a central column of water and 2-propanol. Whereas the location of the amylose helices is well established in the unit cell, the coordinates of the guest molecules could not be defined with certainty, most likely due to a positional disorder. A tentative model of the guest molecule distribution is presented, which consists of two 2-propanol and two water molecules within the helical cavity together with four water molecules and two 2-propanol molecules between the helices. The mobility of the guest and its description as a continuum, rather than at fixed crystallographic positions, explain why so many structures isomorphous to V2-propanol can be obtained with different guest molecules, while yielding similar electron diffraction diagrams.

Noncrystalline micromachining of amorphous alloys using femtosecond laser pulses

Femtosecond laser micromachining of a Zr-based amorphous alloy in air, including measuring the ablation threshold, micro-drilling and trenching, was investigated. The threshold of ablating this amorphous alloy was determined by experiment. Laser-induced ablation and associated damage were examined by means of optical microscope, scanning electron microscopy, transmission electron microscopy and electron diffraction diagram. The results show that conventional processing method induced defects in the vicinity of machined area, such as crystallization, molten trace and spatter, were absent in femtosecond laser ablation area with selected parameters. This indicates that femtosecond laser ablation is a promising method for micromachining amorphous alloys without crystallization.

Structural Aspects in Semicrystalline Samples of the Mannan II Family

A series of samples having the mannan II character were prepared by either (i) desincrusting stems of Acetabularia crenulata, or (ii) acetylating these stems, followed by dissolution and recrystallization under deacetylation conditions, or (iii) recrystallizing at low temperature the alkali soluble fraction of ivory nut mannan. The samples were characterized by transmission electron microscopy, X-ray and electron diffraction analysis together with (13)C CP/MAS NMR spectroscopy. Whereas the A. crenulata stems consisted of a mixture of mannan I and mannan II, the recrystallized samples were all of the hydrated mannan II family and occurred in a ribbonlike morphology where the mannan chains were organized with their molecular axis perpendicular to the ribbon long axis. The recrystallized ivory nut mannan samples presented X-ray and electron diffraction diagrams, together with (13)C solid-state NMR spectra recorded at 95% RH, different from those of recrystallized A. crenulata recorded under the same RH conditions. They corresponded therefore to a new allomorph of the mannan II family. Despite this difference, when the recrystallized samples were in an aqueous environment, they revealed an additional well-defined perhydrated phase, which showed the same (13)C solid-state NMR spectrum for both samples. As this phase, which gave 6-band NMR spectra with narrow line-width and low T1, had no counterpart in X-ray diffraction, it was attributed to specific amorphous segments of mannan chains, gaining some mobility when swollen in water. When the samples were totally dried, their NMR spectra lost their resolution, thus indicating the role played by water for the structural organization of the crystalline and amorphous components of mannan II.

X‐Ray and Electron Diffraction Study of Poly(p‐dioxanone)

AbstractSummary: Solution‐grown lamellar crystals of poly(p‐dioxanone) (PPDX) have been crystallized isothermally from butane‐1,4‐diol at 100 °C. The crystal structure of PPDX has been determined by interpretation of X‐ray fiber diagrams of PPDX fibers and electron diffraction diagrams of lozenge‐shaped chain‐folder lamellar crystals. The unit cell of PPDX is orthorhombic with space group P212121 and parameters: a = 0.970 nm, b = 0.742 nm, and c (chain axis) = 0.682 nm. There are two chains per unit cell, which exist in an antiparallel arrangement.Transmission electron micrograph of PPDX chain‐folded lamellar crystals obtained by isothermal crystallization and its electron diffraction diagram.imageTransmission electron micrograph of PPDX chain‐folded lamellar crystals obtained by isothermal crystallization and its electron diffraction diagram.

Crystal Structure and Morphology of Poly(11-undecalactone) Solution-Grown Single Crystals

Solution-grown lamellar single crystals of poly(11-undecalactone) (PUDL) have been prepared in 1-hexanol. The lozenge and hexagonal-shaped single crystals were grown simultaneously, and these crystals gave well-resolved electron diffraction diagrams from which the orthogonal reciprocal lattice with the parameters a* = 1.346 nm-1, b* = 2.004 nm-1, and γ* = 90° could be determined. The growth faces of both crystals were considered as mainly {110}, and the average chain-folding direction was parallel to these growth planes, suggesting that the hexagonal crystal has pseudohexagonal symmetry but actual orthogonal packing of the PUDL molecules. The diffraction analysis combined with X-ray and electron diffraction diagrams indicated that PUDL crystallized in the orthorhombic system which had the lattice parameters of a = 0.743 ± 0.001 nm, b = 0.499 ± 0.001 nm, and c(chain axis) = 1.519 ± 0.003 nm. There are two chains per unit cell, which existed in an antiparallel arrangement. The fiber repeat distance is appropriate for an all-trans backbone conformation for the straight stems. Molecular packing of this structure has been studied in detail, taking into account both diffraction data and energy calculations. The setting angles, with respect to a axis, were 59° for the corner and center chains according to intensity measurements and structure factor calculations. A final model was obtained to yield R = 0.173 with X-ray diffraction data and R = 0.152 with electron diffraction data. A brief comparison is also made with related polymer structures.

Crystal structure, thermal behavior and enzymatic degradation of poly(tetramethylene adipate) solution-grown chain-folded lamellar crystals.

Solution-grown chain-folded lamellar single crystals of poly(tetramethylene adipate) (PTMA) were prepared from a dilute solution of 2-methyl-1-propanol by isothermal crystallization. PTMA crystals were hexagonal-shaped and polyethylene decoration of the crystals resulted in a "six cross-sector" surface morphology and showed that the average direction of chain folding is parallel to the crystal growth planes of [110] and [010]. Chain-folded lamellar crystals gave well-resolved electron diffraction diagrams corresponding to all the equatorial reflections of the X-ray fiber diagram obtained from stretched PTMA melt-quenched film (beta structure). The unit cell parameters of the beta structure of PTMA were determined as a = 0.503 nm, b = 0.732 nm and c (fiber axis) = 1.442 nm with an orthorhombic crystal system. The fiber repeat distance is appropriate for an all-trans backbone conformation for the straight stems. The setting angle, with respect to the a axis, is +/-46 degrees for the corner and center chains. Thermal behavior of lamellar crystals has been investigated by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM). The lamellar thickness at the edges of the crystal increased after thermal treatment with taking the molecular chains into recrystallization parts; the holes then opened up at the thickening front of the crystal. The morphological changes of lamellar crystals after enzymatic degradation by Lipase type XIII from Pseudomonas sp. and water-soluble products were characterized by TEM, AFM, gel permeation chromatography, high performance liquid chromatography and fast atom bombardment mass spectrometry. The degradation progressed mainly from the edges of the lamellar crystals without decreasing the molecular weights and the lamellar thicknesses. The central portion of single crystals was often degraded by enzymatic attacks. This result combined with thermal behavior indicates that the loosely chain-packing region exists inside the single crystal, and that molecular chains in this region have higher mobility against thermal and enzymatic treatments.

Surface structures of MnAs grown onGaAs(111)Bsubstrates

Atomically flat MnAs epilayers grown on $\mathrm{GaAs}(111)B$ substrates by molecular-beam epitaxy present surface structures depending on the sample temperature and on the surface stoichiometry: the known $(2\ifmmode\times\else\texttimes\fi{}2)$ reconstruction and two new phases, i.e., a $(3\ifmmode\times\else\texttimes\fi{}1)$ reconstruction and a mixed phase of $(2\ifmmode\times\else\texttimes\fi{}2)$ and $(3\ifmmode\times\else\texttimes\fi{}1).$ By monitoring the reflection high-energy electron-diffraction diagram evolution as a function of the annealing temperature, it was possible to ascribe the $(3\ifmmode\times\else\texttimes\fi{}1)$ as being the As richest phase and the $(2\ifmmode\times\else\texttimes\fi{}2)$ as the As poorest phase. Two structural models for the observed reconstructions [i.e., $(3\ifmmode\times\else\texttimes\fi{}1)$ and $(2\ifmmode\times\else\texttimes\fi{}2)]$ are proposed.

Morphology and enzymatic degradation of poly(ϵ‐caprolactone) single crystals: does a polymer single crystal consist of micro‐crystals?

AbstractSolution‐grown lamellar single crystals of poly(ϵ‐caprolactone) (PCL) were prepared from a dilute solution of n‐hexanol by the isothermal crystallization condition or the self‐seeding method. Hexagonal‐shaped lamellar crystals with and without spiral growth were obtained, and the crystals produced well‐resolved electron diffraction diagrams. The chain‐packing structure and morphological complexity in lamellar crystals were investigated by bright‐field and dark‐field diffraction contrast methods of transmission electron microscopy. Based on both diffraction contrast images, it was revealed that both tightly and loosely chain‐packing regions exist in one lamellar crystal. Thus, it was emphasized that PCL solution‐grown lamellar single crystals consist of micro‐crystals with nano‐order size for the crystalline core region. Lipase type XIII from Pseudomonas sp was used for the enzymatic degradation of the PCL lamellar crystals. Enzymatic degradation progressed perpendicularly from the crystal lateral sides, without decrease of the molecular weight and lamellar thickness, yielding notched‐shaped morphologies to the crystals. These results further indicate that PCL lamellar crystals consist of nano‐order micro‐crystals, and that enzyme hydrolyzes the loosely chain‐packing regions between the tightly chain‐packing regions (micro‐crystal regions).© 2002 Society of Chemical Industry

Nanostructure and thermoelectric properties of ReSi 2+/-x thin films.

Anomalies in the nanostructure evolution of ReSi(2+/-x) thin films have proved to be of large interest in connection with their thermoelectric properties. By means of electron microscopic methods the correlation between structural properties and transport behaviour has been studied. The short-range order of the amorphous state was characterised by reduced density functions calculated from diffuse electron diffraction diagram and is found to correlate with the temperature dependence of the electrical resistance. The crystallisation process observed in situ in the transmission electron microscope starts with the formation of relatively large ReSi(1.75) grains (up to 100 nm). In later stages, only smaller grains are growing. This leads to a decrease in the mean grain size and to the increase of the nanocrystalline volume fraction during the heat treatment. This behaviour allows the investigation of the thermopower as function of the nanocrystalline volume fraction. Thus, at a nanocrystalline content of about 35% the thermopower exhibits a maximum in accordance with calculations.

Morphology and Crystal Structure of Solution-Grown Single Crystals of Poly[(R)-3-hydroxyvalerate

Solution-grown lamellar single crystals of bacterial poly[(R)-3-hydroxyvalerate] (P([R]-3HV)) have been prepared in a mixture of chloroform and methanol. P([R]-3HV) crystals were square-shaped and gave well-resolved electron diffraction diagrams from which the reciprocal lattice parameters a* = 1.052 nm-1, b* = 0.990 nm-1, and γ* = 90° could be determined. Systematic absences were confirmed at every odd reflection along the orthogonal axes a* and b* by a series of tilted electron diffraction diagrams. Thus, the electron diffraction pattern is consistent with a p2gg symmetry. The diffraction analysis combined with X-ray and electron diffraction diagrams indicated that P([R]-3HV) crystallized in the P212121 orthorhombic space group which had the lattice parameters of a = 0.950 nm, b = 1.010 nm, and c(fiber axis) = 0.556 nm with the 2-fold screw symmetry along the molecular axis. The growth planes of P([R]-3HV) single crystals are {110}, and the average direction of chain folding determined by polyethylene d...

Cellulose-II single crystals from dilute copper-(II) ethylenediamine solution

This paper presents a new method for the preparation of cellulose-II single crystals by slow diffusion of hydrogen chloride into dilute copper-(II) ethylenediamine solution. The electron diffraction diagrams of the obtained crystals distinctly show the single crystal characteristic of the analyzed crystals. The magnitude of observable diffraction maxima is reported for the first time. The evaluation of the diffraction maxima determined by densitometric methods conforms well with the results published in literature.