Crystalline Growth Mechanism Research Articles

Characterization and synthesis of cubic Zn2TiO4 crystalline films deposited on MgAl2O4 (100) substrates

Cubic Zinc titanate (Zn2TiO4) films were deposited on magnesium aluminate (MgAl2O4) (100) substrates by metalorganic chemical vapor deposition. The film annealed at 950°C in air exhibited the best crystalline quality with a dominant orientation along the Zn2TiO4 (400). The relationship between Zn2TiO4 films and MgAl2O4 (100) substrates was determined as Zn2TiO4 (400)‖MgAl2O4 (400) with Zn2TiO4 [001]‖MgAl2O4 [001] by the X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analysis. A diagram was proposed to illustrate the crystalline growth mechanism. The optical band gap of the film annealed at 950°C, which was evaluated by the reflectance spectrum, was 3.09 eV.

Stereocomplex Crystallization of Star-Shaped Four-Armed Stereo Diblock Poly(lactide) from the Melt: Effects of Incorporated Linear One-Armed Poly(l-lactide) or Poly(d-lactide).

Star-shaped four-armed stereo diblock poly(lactide) (4-LD) and linear one-armed PLLA or PDLA (1-L or 1-D) having a molecular weight similar to that of 4-LD [higher molecular weight 1-L(H) or 1-D(H)] and that of one block of 4-LD [lower molecular weight 1-L(L) or 1-D(L)] were synthesized, and the effects of incorporated 1-L or 1-D on the isothermal and nonisothermal crystallization of 4-LD blends from the melt were investigated. Solely stereocomplex crystallites were formed in unblended 4-LD and 4-LD blends incorporated with 1-L or 1-D during isothermal and nonisothermal crystallization. Incorporated 1-L or 1-D increased normalized stereocomplex crystallinity and accelerated cold nonisothermal crystallization and isothermal crystallization. The accelerating effect became higher with decreasing the molecular weight of 1-L or 1-D. The crystalline growth mechanism was not altered by the incorporation of 1-L and 1-D, whereas the crystalline growth geometry changed from line to sphere or circle, depending on the type of sample and Tc. The difference in crystallization half time and cold crystallization temperature between 4-LD/1-L(H) and 4-LD/1-D(H) blends or 4-LD/1-L(L) and 4-LD/1-D(L) blends was explained by the difference in radial growth rate and spherulite density, which was further discussed considering the non-interpenetrating and interpenetrating models.

Stereocomplex‐ and Homo‐Crystallization and Phase‐Transition Behavior of Relatively High‐Molecular‐Weight Linear One‐ and Two‐Armed and Star‐Shaped Four‐Armed Poly(l‐lactide)/Poly(d‐lactide) Blends

AbstractRelatively high‐molecular‐weight linear one‐ and two‐armed and star‐shaped four‐armed poly(l‐lactide) and poly(d‐lactide) are synthesized and the multiplicate effects of arm‐number (branching architecture, coinitiator moiety), crystallization temperature (Tc), and number‐average molecular weight (Mn) on stereocomplex (SC)‐ and homo‐crystallization and phase‐transition behavior are investigated. For nonisothermal and isothermal crystallization, in addition to SC crystallites, homo‐crystallites are formed in the blends with higher Mn values, irrespective of arm number. For isothermal crystallization, the transition Tc ranges below which in addition to SC crystallites, homo‐crystallites are formed depended on Mn per one arm‐determining melting temperature or thickness of homo‐crystallites. The transition Mn ranges above which in addition to SC crystallites, homo‐crystallites are formed are not affected by arm number. The high molecular weight disturbs the change of crystalline growth mechanism of one‐ and two‐armed blends, whereas the branching architecture inhibits the change of crystalline growth mechanism of four‐armed blends.

High efficiency CdTe solar cells with a through-thickness polycrystalline CdTe thin film

CdTe preferential growth with through-thickness grains has been achieved. A crystalline growth mechanism assisted by an oxide liquid phase is proposed.

Long terminal linear alkyl group as internal crystallization accelerating moiety of poly(l-lactide)

Poly(l-lactide) (PLLA) polymers having terminal n-alkyl groups with a wide variety of lengths (C0–C22) were synthesized by ring-opening polymerization of l-lactide in the presence of coinitiators of l-lactic acid (C0), 1-hexanol (C6), 1-dodecanol (C12), and 1-docosanol (C22) and their segmental mobility and non-isothermal and isothermal crystallization behavior were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). Glass transition and cold crystallization temperatures of melt-quenched samples during heating decreased with an increase in the length of terminal n-alkyl groups. The enhanced PLLA segmental mobility and hydrophobic interaction-based accelerated PLLA nucleation by the presence of terminal long n-alkyl groups should have caused the accelerated non-isothermal and isothermal crystallization of PLLA segments traced by cold crystallization temperature during heating and by radial growth rate of spherulites, respectively. The crystallization accelerating effect became higher with the length of terminal n-alkyl groups. The effects of the length of terminal n-alkyl group on the crystalline growth mechanism of PLLA at the lowest crystallizable temperature was insignificant, whereas the effects of the length of terminal n-alkyl group on the nucleation mechanism of PLLA chains were significant and insignificant for PLLA having Mn of 6–7 × 103 of 2 × 104 g mol−1, respectively. WAXD measurements revealed that the transition crystallization temperature at which crystalline modification changes from δ-form to α-form was affected by the length of terminal n-alkyl group for PLLA having Mn of 6–7 × 103 g mol−1, but was not altered by the length of terminal n-alkyl group for PLLA having Mn of 2 × 104 g mol−1.

Polymeric Nanocubes Spontaneously Formed from Poly(ε-caprolactone).

A facile and economical approach was successfully developed to prepare polymeric nanocubes from poly(ε-caprolactone) (PCL). Nanocubes which are rarely achieved with polymer were obtained simply by a proper thermal treatment on PCL thin film on a glass slide or silicon wafer. The results of scanning electron microscopy (SEM) and atomic force microscopy (AFM) observation showed that the nanocubes were as small as ∼70 nm with high yield (up to ∼130 000 nanocubes in 1 cm2 area). The combination of high-resolution transmission electron microscopy (HRTEM) and fast Fourier transform (FFT) demonstrated that these particles were single nanocrystals. We suggest that the formation of these nanocubes is based on a dewetting and crystallization mechanism. In addition, the size and yield of nanocubes could be controlled by the solution concentration and architecture of polymer as well as substrate. This work might not only facilitate gaining further basic knowledge about nucleation and crystalline growth mechanism of PCL but also provide a new way to fabricate nonspherical polymeric nanoparticles.

Large-scale synthesis and growth conditions dependence on the formation of CuGeO 3 nanowires

CuGeO 3 nanowires in bulk with the diameter of 20–100 nm and length of several dozens of micrometers have been synthesized via a facile hydrothermal process using GeO 2 and Cu(CH 3COO) 2·H 2O as the raw materials in the absence of any surfactants. The synthesized nanowires are single crystals with an orthorhombic phase based on the X-ray diffraction, scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy characterizations. The dependence of different growth conditions, such as reaction temperature, reaction time, compactness, GeO 2 concentration, copper source materials, surfactants and solvents on the formation, morphologies and sizes of CuGeO 3 nanostructures have been investigated. Proper selection and combination of the growth conditions are the key aspect to control the formation, morphology and size of the CuGeO 3 nanostructures. The nucleation and crystalline growth mechanism are proposed to explain the formation and growth of CuGeO 3 nanowires. The photoluminescence spectrum of the CuGeO 3 nanowires exhibits three fluorescence emission peaks centered at 421 nm, 488 nm and 529 nm as the excitation wavelength is 235 nm.

Large-scale synthesis and the roles of growth conditions on the formation of Zn 2GeO 4 nanorods

Large-scale Zn 2GeO 4 nanorods with a length of about 10 μm have been synthesized via a facile hydrothermal process in the absence of any surfactant. The synthesized nanorods are single crystals with a rhombohedral phase. The dependence on the growth conditions, such as reaction temperature, reaction time, compactness and GeO 2 concentration, of the formation, morphologies and sizes of the Zn 2GeO 4 nanostructures has been investigated. Proper selection and combination of the growth conditions are the key aspects to control the formation, morphologies and sizes of the Zn 2GeO 4 nanostructures. The nucleation and crystalline growth mechanism are proposed to explain the formation and growth of Zn 2GeO 4 nanorods. The photoluminescence spectrum of the Zn 2GeO 4 nanorods exhibits three fluorescence emission peaks centered at 421, 488 and 529 nm when the excitation wavelength is 235 nm.

Synthesis and characterizations of calcium germanate nanowires

Crystalline calcium germanate nanowires with a diameter of 50–200 nm and length of several dozens of micrometres have been synthesized by a simple and facile hydrothermal process. X-ray diffraction and high-resolution transmission electron microscopy results show that the crystalline calcium germanate nanowires are mainly composed of tetragonal Ca2GeO4, orthorhombic Ca2Ge7O16 and triclinic CaGe2O5 phases. The role of different growth conditions demonstrates that the hydrothemral temperature, reaction time, compactness, Ca source materials and surfactants play an essential role in the formation and size of the calcium germanate nanowires. The nucleation and crystalline growth mechanism are proposed to explain the formation and growth of the calcium germanate nanowires. The photoluminescence spectrum of the calcium germanate nanowires shows three fluorescence emission peaks centered at 421 nm, 488 nm and 529 nm, exhibiting a promising potential for optical applications.

急速加熱熱処理によるＦｅＰｔ薄膜のＬ１０規則化

L10 ordering of FePt sputtered thin films was studied by using rapid thermal annealing (RTA). The volume of an L10 particle (V) was evaluated from the grain size by Scherrer's method. The coercivity (Hc) increases linearly with increasing V reaches 11 kOe at Vc (=1200 nm3), and becomes constant above Vc. The (001) crystal growth normal to the film plane is enhanced at an annealing condition where V is about 1000 nm3, a little lower than Vc. The crystalline growth mechanism and the correlation between Hc and V are discussed.

High temperature internal friction of engineering ceramics

Poly(l-lactide) (PLLA) polymers having terminal n-alkyl groups with a wide variety of lengths (C0–C22) were synthesized by ring-opening polymerization of l-lactide in the presence of coinitiators of l-lactic acid (C0), 1-hexanol (C6), 1-dodecanol (C12), and 1-docosanol (C22) and their segmental mobility and non-isothermal and isothermal crystallization behavior were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). Glass transition and cold crystallization temperatures of melt-quenched samples during heating decreased with an increase in the length of terminal n-alkyl groups. The enhanced PLLA segmental mobility and hydrophobic interaction-based accelerated PLLA nucleation by the presence of terminal long n-alkyl groups should have caused the accelerated non-isothermal and isothermal crystallization of PLLA segments traced by cold crystallization temperature during heating and by radial growth rate of spherulites, respectively. The crystallization accelerating effect became higher with the length of terminal n-alkyl groups. The effects of the length of terminal n-alkyl group on the crystalline growth mechanism of PLLA at the lowest crystallizable temperature was insignificant, whereas the effects of the length of terminal n-alkyl group on the nucleation mechanism of PLLA chains were significant and insignificant for PLLA having Mn of 6–7 × 103 of 2 × 104 g mol−1, respectively. WAXD measurements revealed that the transition crystallization temperature at which crystalline modification changes from δ-form to α-form was affected by the length of terminal n-alkyl group for PLLA having Mn of 6–7 × 103 g mol−1, but was not altered by the length of terminal n-alkyl group for PLLA having Mn of 2 × 104 g mol−1.