Granular Crystallites Research Articles

Spatial Distribution of the Amorphous Region Constrained by Polymer Crystallites

Many studies have supported the existence of the amorphous region with reduced mobility induced by crystallization in semicrystalline polymers. However, the spatial distribution of the amorphous region with reduced mobility (rigid amorphous region) has not been fully clarified. Therefore, we applied contrast variation small-angle X-ray scattering (CV-SAXS) to the swollen ethylene-octene copolymer with granular crystallites to clarify the spatial distribution of the rigid amorphous region. The analysis with CV-SAXS revealed that the rigid amorphous region existed around the crystallites and bridged among the crystallites. Furthermore, the weight fraction of the rigid amorphous region estimated by CV-SAXS was in good agreement with that obtained by pulsed proton nuclear magnetic resonance measurements.

Formation characteristics of nickel-based diamond abrasive segment by selective laser melting

Selective Laser Melting (SLM) technique provides an alternative to fabricating a metal bond grinding wheel with a high porosity ratio and controllably complex geometries. In this paper, SLM is applied to making nickel-based diamond abrasive segments based on single-tracks SLM tests. The characteristics of the SLMed wheel segments are investigated through analyses on morphology, porosity, cracks, and diamond grains. Balling phenomenon of the Ni-Cr alloys, which leads to the rough surface and porosities, is observed through the surface and cross-sectional observations. The porosity ratio of the as-built abrasive segment ranges from 22.6% to 27.3%. Two types of diamond spatters, entrainment-driven and vapor-driven diamond spatters, are formed in the SLM process based on the observation by a high-speed video camera. Diamond spatters are considered the main cause of the balling phenomenon. Based on microstructure and hardness measurements, the eutectic structure and granular crystallites result in high hardness and increase the cracking susceptibility of the Ni-Cr alloys. This paper reveals the formation characteristics of the SLMed nickel-based wheel segments and the mechanism of porosity formation in the SLM process.

Tunable conductivity in mesoporous germanium

Germanium-based nanostructures have attracted increasing attention due to favourable electrical and optical properties, which are tunable on the nanoscale. High densities of germanium nanocrystals are synthesized via electrochemical etching, making porous germanium an appealing nanostructured material for a variety of applications. In this work, we have demonstrated highly tunable electrical conductivity in mesoporous germanium layers by conducting a systematic study varying crystallite size using thermal annealing, with experimental conductivities ranging from 0.6 to 33 (×10−3) Ω−1 cm−1. The conductivity of as-prepared mesoporous germanium with 70% porosity and crystallite size between 4 and 10 nm is shown to be ∼0.9 × 10−3 Ω−1 cm−1, 5 orders of magnitude smaller than that of bulk p-type germanium. Thermal annealing for 10 min at 400 °C further reduced the conductivity; however, annealing at 450 °C caused a morphological transformation from columnar crystallites to interconnecting granular crystallites and an increase in conductivity by two orders of magnitude relative to as-prepared mesoporous germanium caused by reduced influence of surface states. We developed an electrostatic model relating the carrier concentration and mobility of p-type mesoporous germanium to the nanoscale morphology. Correlation within an order of magnitude was found between modelled and experimental conductivities, limited by variation in sample uniformity and uncertainty in void size and fraction after annealing. Furthermore, theoretical results suggest that mesoporous germanium conductivity could be tuned over four orders of magnitude, leading to optimized hybrid devices.

Analysis of Oxides Formed on the Surface of the Alloy 690 in Hydrogenated Supercritical Water

The oxides formed on the surface of the alloy 690 in hydrogenated supercritical water at 400 °C for 1000 h were investigated using scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. The oxides on the surface of the alloy 690 exhibited multi-layer structure: an outer layer consisted of granular crystallites (NiO and NiFe2O4) and a compact inner layer (spinel and Cr2O3). Chemical analysis indicated that the outer layer was enriched in nickel but depleted in chromium, whereas the inner layer was enriched in chromium and iron but depleted in nickel. The inner layer was also characterized as layered structure by Fe-rich spinel on top of continuous Cr2O3 layer. Besides, Cr2O3 nodules were readily observed at the oxides/alloy interface.

Magnetic, dielectric, and ferroelectric properties in Bi3+-substituted Li0.35Zn0.3Fe2.35-xBixO4 (x = 0.1) nanocrystallites

Bi3+-substituted Li0.35Zn0.3BixFe2.35-xO4 (x = 0.1) nanocrystallites of ∼32 nm synthesized via a citrate-gel combustion and then annealed at 400 °C for 2 h in air shows a saturation magnetization Ms = 11.25 emu/g (with a high coercivity Hc = 273 Oe) at 5 K. Frequency (f) dependence of dielectric properties describes a mechanism of polarization. Granular crystallites offers a high polarization Ps = 1.956 μC/cm2 at 9 kV/cm applied field.

Deposition of cadmium sulfide and zinc sulfide thin films by aerosol-assisted chemical vapors from molecular precursors

New complexes with the general formula [M(S2CNnBu2)2] [where M = CdII (1) and ZnII (2)] were synthesized and used as single source precursors to deposit thin films of cadmium sulfide and zinc sulfide by the aerosol-assisted chemical vapor deposition technique. The single crystal X-ray structures of 1 and 2 are also reported. Thermogravimetric analysis of 1 and 2 showed that both precursors decompose cleanly in a single step to produce their respective metal sulfides. The deposition of thin films was carried out on soda glass substrates in the 350--450 °C temperature range under inert conditions. The as-deposited thin films were characterized by powdered X-ray diffraction and field emission scanning electron microscopy. Thin films of CdS deposited at low temperature (350 °C) consist of densely packed granular crystallites with an average size of ca. 150 nm, while at higher temperatures (400 and 450 °C) particles with varying sizes and mixed morphologies are observed. The ZnS thin films deposited at 400 °C showed rod-like structures, whereas dense globular-like structures were obtained at 450 °C. Energy dispersive X-ray analysis was performed to study the chemical composition of the thin films.

The Synthesis and Characterization of Novel Cadmium Sulphide Nanocrystallites and their Thin Films

Diethyl dithiocarbamate [Cd (S2CN Et2)2] complex is used to deposit the cadmium sulphide thin film at much lower temperature by Aerosol Assisted Chemical Vapour deposition (AACVD) and same precursor is used to synthesize the nanocrystals in Oleylamine at elevated temperature. Thermogravimetric analysis shows that precursor [Cd (S2CN Et2)2] decomposes in the single stage, losing 62% of total weight. Deposition of thin films at 300 °C and 400 °C showed the growth of CdS clusters which were made of granular crystallites. These results are confirmed by SEM analysis. Thermolysis of the precursor in oleylamine at 240 °C gave the nanoparticles most of them are monodispersed spherical shape, few having mono and dipod structures. TEM images confirm the structures. XRD results show the thin films and nanoparticles have hexagonal phase of CdS.

Modification of optical and electrical properties of zinc oxide-coated porous silicon nanostructures induced by swift heavy ion

Morphological and optical characteristics of radio frequency-sputtered zinc aluminum oxide over porous silicon (PS) substrates were studied before and after irradiating composite films with 130 MeV of nickel ions at different fluences varying from 1 × 1012 to 3 × 1013 ions/cm2. The effect of irradiation on the composite structure was investigated by scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), and cathodoluminescence spectroscopy. Current–voltage characteristics of ZnO-PS heterojunctions were also measured. As compared to the granular crystallites of zinc oxide layer, Al-doped zinc oxide (ZnO) layer showed a flaky structure. The PL spectrum of the pristine composite structure consists of the emission from the ZnO layer as well as the near-infrared emission from the PS substrate. Due to an increase in the number of deep-level defects, possibly oxygen vacancies after swift ion irradiation, PS-Al-doped ZnO nanocomposites formed with high-porosity PS are shown to demonstrate a broadening in the PL emission band, leading to the white light emission. The broadening effect is found to increase with an increase in the ion fluence and porosity. XRD study revealed the relative resistance of the film against the irradiation, i.e., the irradiation of the structure failed to completely amorphize the structure, suggesting its possible application in optoelectronics and sensing applications under harsh radiation conditions.

Thio- and Dithio-Biuret Precursors for Zinc Sulfide, Cadmium Sulfide, and Zinc Cadmium Sulfide Thin Films

Zinc and cadmium complexes of 1,1,5,5-tetraalkyl-2-4-dithiobiurets [M(N(SCNR2)2)2] [M = Zn, R = methy (1), ethyl (2) and M = Cd, R = methyl (4), ethyl (5)] and 1,1,5,5-tetraalkyl-2-thiobiurets [M(SON(CNR2)2)2] [M = Zn, R = isopropyl (3) and M = Cd, R = isopropyl (6)] have been synthesized. The single crystal X-ray structures of complexes (2), (3), (4), and (5) were determined. Thermogravimetric analysis confirmed that all six complexes decomposed in a single step to their corresponding metal sulfides. The complexes were used as single source precursors for the deposition of zinc sulfide (ZnS), cadmium sulfide (CdS), and zinc cadmium sulfide (ZnxCd1−xS) thin films by aerosol assisted chemical vapor deposition (AACVD). The zinc complexes (1) and (3) deposited cubic ZnS films with small rods and granular crystallites at 300 and 350 °C, whereas at 400 and 450 °C hexagonal ZnS with granular crystallites were dominant. Complex (2) gave granular hexagonal ZnS films at all deposition temperatures. Cadmium complex...

Thermal properties and influence of orientation on crystalline morphologies in stereoblock polypropylene and related elastomers

AbstractAtomic force microscopy (AFM), small angle X‐ray scattering (SAXS), temperature modulated differential scanning calorimetry (TMDSC), variable heating rate DSC, an independent rapid heating rate method for melting points, and cyclic mechanical testing were used to study semicrystalline thermoplastic elastomeric polypropylenes (ELPPs) and related semicrystalline polyolefins including ethylene copolymers. Low crystallinity (ca., 9 and 15%) ELPP samples were studied by AFM in the nonoriented and melt‐oriented states. AFM images taken as a function of time after quenching of a melt‐drawn and highly nucleated film resolved details of secondary crystallization involving lateral growth on the ordered row‐nucleated structures. For nonoriented films, isothermal melt crystallization at high temperatures (110 °C) led to similar features for the two ELPPs. The dominant crystalline morphology studied by AFM consisted of small (several nm in width) granular crystallites organized into immature but large spherulites spanning tens of microns. A striking cross‐hatch morphology was detected in regions of the surface in 110 °C crystallized samples, which is contrasted with melt‐drawn films where row nucleated structures dominated the morphology in the film under no external stress. AFM was also used to monitor the morphological changes that occurred as the films were stretched at 25 °C. Break‐down of lamellae was observed, resulting in oriented narrow fibrils. Cyclic stress‐strain curves showed the expected result where lower crystallinity ELPPs had higher recoverable levels of set after both 100 and 500% elongation. TMDSC was used to resolve the broad melting and recrystallization regions in these low to medium crystallinity ELPP systems, and to contrast the results with ethylene copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Selective Deposition of Cobalt Sulfide Nanostructured Thin Films from Single-Source Precursors

The cobalt(III) complexes of 1,1,5,5-tetramethyl- and 1,1,5,5-tetraethyl-2,4-dithiobiuret and the cobalt(II) complex of 1,1,5,5-tetra-iso-propyl-2-thiobiuret have been synthesized. The single-crystal X-ray structure of the thiocyanide (1) and cobalt tetrachlorate (2) salts of the parent cyclized ligand, together with complexes [Co{N(SCNMe2)2}3] (3), [Co{N(SCNEt2)2}3] (4) and [Co{N(SOCNiPr2)2}2] (5) have been determined. The thermal decomposition of 3, 4, and 5 was studied. The complexes were used as single source precursors for the deposition of cobalt sulfide thin films by aerosol assisted chemical vapor deposition (AACVD). The X-ray diffraction (XRD) of the deposited films showed hexagonal Co1−xS from complexes (3) and (4) whereas complex (5) gave a mixture of cubic and hexagonal Co4S3. The morphology of films was characterized by scanning electron microscope (SEM) and showed rod like crystallites from 3, granular crystallites from 4 and stalagmitic structures from 5. Transmission electron microscopy (TEM) of the samples obtained from thin films from 3 and 4 show that the films are composed of hexagonal nanoplates with nanocubes from 5. Magnetic measurements showed the para or ferro-magnetic behavior from crystallites. The mechanism for decomposition of precursors to the cobalt sulfide was studied by pyrolysis gas chromatography (Py-GC-MS).

Microstructure and element composition of shell plates of Liolophura japonica

The microstructure characteristics of shell plates of chiton Liolophura japonica Lischke were analyzed using environmental scanning electron microscopy (ESEM). The results show that the internal structure of the shell plate of chiton Liolophura japonica is composed of seven calcium layers which were crossed lamellar crystallites, homogeneous structure, granular crystallites, and trabecular type crystallites. The element compositions of shell plates were analyzed using X-ray photoelectron spectroscopy (XPS). The results determined by XPS show that the surface chemical states of various layers are different. There are 13 elements (Na, O, N, C, S, P, Ca, Cl, Si, Al, K, Fe, Mg) on the shell plate of chiton L. japonica. Among the 13 elements, 11 are on the outside pigment layer except K and S. Among seven layers of shell plate, there is the largest quantity of elements on the outside pigment layer, and the least quantity of elements is on layer C (Articulamentum auctorum). There are 7 elements on the layer C (Articulamentum auctorum). Besides calcium carbonate, there are some inorganic compounds on the shell plate, such as NaCl, MgO, Al2O3, silicate, sulfate and phosphate. There are some organic chemical components, such as carbohydrate, organic sulfide, and organic nitride on the shell plates.

High‐Pressure Synthesis of Tantalum Nitride Having Orthorhombic U2S3 Structure

AbstractAmong binary compounds, there is a high potential for discovery of novel members (polymorphic phases or compounds) of the nitrides of transition metals group due to a pronounced dependence of the oxidation state of the metals (M) on pressure. The power of high pressure–high temperature (HP‐HT) route for synthesis of binary nitrides has already been demonstrated by the discovery of cubic nitrides of the group 4 and 14 elements, of crystalline polymorphs of P3N5, and by reports on formation of four noble metal nitrides. It is anticipated that such HP products exhibit, in addition to enhanced elastic and mechanical behavior, other functional properties making them interesting for industrial applications. Here, HP–HT synthesis research is extended to nitrides of group 5 elements, resulting in the discovery of a novel hard tantalum nitride, exhibiting U2S3 structure: η‐Ta2N3 (Pbnm, a = 8.1911(17) Å, b = 8.1830(17) Å, c = 2.9823(3) Å). The stoichiometry is supported by two independent means, verifying that η‐Ta2N3 is the first thermodynamically stable transition metal nitride with a N:M ratio exceeding 4:3. Due to its high hardness and peculiar texture (needle‐like and granular crystallites), η‐Ta2N3 may find practical applications as a hard fracture resistant material.

The underpotential deposition of Bi 2Te 3− ySe y thin films by an electrochemical co-deposition method

Bi 2Te 3− y Se y thin films were grown on Au(1 1 1) substrates using an electrochemical co-deposition method at 25 °C. The appropriate co-deposition potentials based on the underpotential deposition (upd) potentials of Bi, Te and Se have been determined by the cyclic voltammetric studies. The films were grown from an electrolyte of 2.5 mM Bi(NO 3) 3, 2 mM TeO 2, and 0.3 mM SeO 2 in 0.1 M HNO 3 at a potential of −0.02 V vs. Ag|AgCl (3 M NaCl). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to characterize the thin films. XRD and EDS results revealed that the films are single phase with approximate composition of Bi 2Te 2.7Se 0.3. SEM studies showed that the films are homogeneous and have micronsized granular crystallites.

Synthesis and Morphological Control of Nickel Hydroxide for Lithium−Nickel Composite Oxide Cathode Materials by an Eddy Circulating Precipitation Method

Spherical nickel hydroxide with high density was synthesized via an eddy-circulating precipitation method, in which a Ni(NO3)2 solution was reacted with a NaOH solution at 65−70 °C, and NH4NO3−NH3·H2O was used as a buffer reagent. The resulting nickel hydroxide particles, with a tap density of 2.20 g/cm3 and the average particle size of 30.6 μm, are aggregated by the granular crystallites. The morphology of the crystallite can be controlled by changing the anions. The LiNi0.8Co0.2O2 that has been prepared using this nickel hydroxide shows excellent electrochemical performance, which delivers an initial discharge capacity of 190.90 mAh/g at a current rate of 25 mA/g between 3.0 V and 4.35 V and exhibits good cycle stability.

Crystal Structure and Dielectric Properties of Radio Frequency Magnetron Sputtered Nanocrystalline SrTiO3 Thin Films

Nanocrystalline SrTiO3 thin films have been successfully deposited by radio frequency (RF) magnetron sputtering. The perovskite phase was obtained for the SrTiO3 thin films deposited on Pt/Ti/SiO2/Si substrates at 500°C. The SrTiO3 thin films deposited at 500°C were composed of granular crystallites with a size of approximately 35 nm and a thickness of 150 nm. The crystallite size increases with increasing film thickness. The dielectric constant of SrTiO3 thin films decreases with decreasing film thickness by changing the temperature, frequency and bias voltage.

Characterization and leakage current density of radio frequency magnetron sputtered nanocrstalline SrTiO 3 thin films

The nanocrystalline SrTiO 3 thin films have been successfully deposited by a radio frequency magnetron sputtering. The perovskite phase was obtained for the SrTiO 3 deposited on Pt/Ti/SiO 2/Si substrates at 500°C. The peak intensity of XRD increases with increasing thickness of the SrTiO 3 films. The morphology of the SrTiO 3 thin films deposited at 500°C is composed of granular crystallites with a size of about 45.0 nm for a thickness of 450.0 nm. The films thickness of 150.0 and 450.0 nm had the leakage current density (mid 10 −6–10 −9 A/cm 2)–voltage (5 V) characteristic which is suitable for a dielectric films of dynamic random access memory capacitor.

Nanostructure Evolution of Homogeneous Poly(ethylene‐co‐1‐octene) as a Function of Strain

AbstractPolyolefin elastomers with varying 1‐octene content and different thermal history are studied by wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) during drawing and after relaxation. The multidimensional chord distribution function (CDF) reveals the nanostructure made from crystallites in the amorphous matrix. Both lamellae and granular crystals are found. Lamellae do not form stacks. The SAXS peak is observed because each lamella is covered by an amorphous layer of well‐defined thickness. Arrangement, rotation, fine chain slip and failure of the domains are directly observed as a function of elongation. During straining and relaxation a well oriented macrolattice with colloidal dimensions but short‐ranging order is formed. Two processes are generating microfibrils, namely (1) arrangement of granular crystallites, and (2) irreversible disruption of lamellae (coarse slip) followed by arrangement of their fragments. The second process stabilizes the colloidal lattice permanently. The higher the comonomer content, the later the irreversible process starts. Quenching from the melt shifts the onset to lower deformation. Deformation of microfibrils is not homogeneous. Instead, there is a limiting long period that cannot be exceeded without disruption. It is related to the position of the maximum in the SAXS pattern (which is almost constant).Long periods in the CDF z(r12, r3) of an ethylene‐octene block copolymer after relaxation from drawing.magnified imageLong periods in the CDF z(r12, r3) of an ethylene‐octene block copolymer after relaxation from drawing.

Dielectric Properties of Nanocrystalline Barium Titanate Thin Films Deposited by RF Magnetron Sputtering

The nanocrystalline thin films of BaTiO3 have been deposited on the Pt/Ti/SiO2/Si substrates by RF magnetron sputtering at 500°C. The film deposited at 500°C has a thickness of 450.0 nm and is composed of granular crystallites of about 45.0 nm size. The crystallite size decreases with decreasing film thickness. The dielectric constant of the nanocrystalline BaTiO3 thin films increases with increasing film thickness. For the film thicknesses of 150.0 and 450.0 nm, the leakage current density is below 1.0×10-9 A/cm2 for the applied voltage of less than 5 V.

Crystal structure and ferroelectricity of nanocrystalline barium titanate thin films

The nanocrystalline thin films of barium titanate (BaTiO 3) have been deposited on the Pt/Ti/SiO 2/Si substrates by RF magnetron sputtering at 500°C. The XRD result shows only single perovskite structure phase of BaTiO 3 and the intensity of reflection decreases with decreasing film thickness. The film deposited at 500°C has a thickness of 45.0 nm and is composed of granular crystallites of about 30.0 nm in size. The crystallite size decreases with decreasing film thickness. The structure changes from tetragonal to pseudocubic. The remnant polarization ( P r) and coercive field ( E c) of the 450.0 nm thick BaTiO 3 films are 5 μC/cm 2 and 1.5 kV/cm, respectively, exhibiting ferroelectricity, being one-eighth and 10 times of the bulk values, respectively.