Relevant Growth Mechanism Research Articles

Step flow growth of β-Ga2O3 films on off-axis 4H-SiC substrates by LPCVD

In this work, β-Ga2O3 films were prepared on 4H-SiC (0001) substrates with 4° off-axis by low-pressure chemical vapor deposition (LPCVD). The crystalline structures, chemical compositions, optical properties, and surface/interface of the as-prepared films and heterostructures were all comprehensively investigated. X-ray diffraction and room temperature Raman spectrometry demonstrated β-Ga2O3 films are pure phase with highly preferential growth orientation along the (-201) plane. The Ga/O ratio estimated by X-ray photoelectron spectroscopy was 0.7, indicating the existence of Ga-O bonding. In addition, β-Ga2O3 films showed high transmittance at wavelengths over 300 nm, corresponding to an optical bandgap of about 4.88 eV. Remarkably, the growth of β-Ga2O3 films on 4H-SiC substrates with 4° off-axis followed the step-flow growth mode, reported for the first time. The relevant growth mechanism was discussed. These results demonstrated the feasible formation of heteroepitaxial growth of β-Ga2O3 films with high crystal quality and superior electrical properties on 4H-SiC substrates with off-axis angle by LPCVD, promising for applications in Ga2O3 based high power and optoelectronic devices.

TBIO-08. The molecular basis for rational targeting of FGFR-driven growth and invasiveness in pediatric brain tumors

Abstract The oncogenic activation of receptor tyrosine kinases (RTK) promotes growth, survival and dissemination in pediatric tumors including glioma, ependymoma and medulloblastoma (MB). Direct targeting of either the RTK or of downstream kinases can effectively block tumor promoting pathway functions. However, emergence of resistance is common. We hypothesized that alternative interference strategies that target protein-protein interactions (PPIs) instead of enzymatic activities could overcome the emergence of resistance. We characterized the molecular interactions downstream of the FGFR that regulate relevant growth and invasion-promoting mechanisms in MB cells, to identify potentially druggable PPIs. We found that the FRS2 protein is an essential up-stream effector of FGFR signaling towards invasiveness. Using a proteomics approach, we furthermore identified the Striatin 3 protein as a novel oncogenic effector of the FGFR pathway downstream of FRS2, as it integrates antagonistic growth and invasion signals downstream of FGFR. Mechanistically, Striatin 3 interacts with the Ser/Thr kinase MAP4K4, couples it to the protein phosphatase 2A, and thereby inactivates growth repressing activities of MAP4K4. In parallel, Striatin 3 enables MAP4K4-mediated phosphorylation of PKC-theta and VASP, which combined are necessary to promote tissue invasion. To selectively repress pro-invasive FGFR functions, we identified and functionally validated small molecule ligands of FRS2, that prevent FRS2 activation and downstream signaling. We demonstrate efficacy of these compounds in inhibiting invasion and growth promoting activities in vitro and in vivo, and identified potential off-target activities of the ligand using a proteome-wide interaction analysis. We propose inhibition of FRS2 by a small molecular PTB domain ligand as a strategy to repress FGF signaling in FGFR-driven tumors. The development of this ligand, and the de novo design of functional analogs thereof bear promise for further pre-clinical evaluation of these structures as anti-growth promoting and anti-metastatic therapeutics applicable to FGFR-driven tumors.

Achieving Good Protection on Ultra-High Molecular Weight Polythene by In Situ Growth of Amorphous Carbon Film

Ultra-high molecular weight polythene (UHMWPE), with outstanding characteristics, is widely applied in modern industry, while it is also severely limited by its inherent shortcomings, which include low hardness, poor wear resistance, and easy wear. Implementation of feasible protection on ultra-high molecular weight polythene to overcome its shortcomings would be of significance. In the present study, amorphous carbon (a-C) film was fabricated on ultra-high molecular weight polythene (UHMWPE) to provide good protection, and the relevant growth mechanism of a-C film was revealed by controlling carbon plasma currents. The results showed the in situ transition layer, in the form of chemical bonds, was formed between the UHMWPE substrate and the a-C film with the introduction of carbon plasma, which provided strong adhesion, and then the a-C film continued epitaxial growth on the in situ transition layer with the treatment of carbon plasma. This in situ growth of a-C film, including the in situ transition layer and the epitaxial growth layer, significantly improved the wetting properties, mechanical properties, and tribological properties of UHMWPE. In particular, good protection by in situ growth a-C film on UHMWPE was achieved during sliding wear.

Preparation of elongated mullite self-reinforced porous ceramics

Elongated mullite was synthesized using mullite powder as a raw material and AlF3·3H2O as an additive, and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The effects of AlF3·3H2O content and reaction temperature on the formation of elongated mullite were investigated, and the relevant growth mechanism was discussed based on the experimental results and density functional theory (DFT) calculations. When the optimal amount of AlF3·3H2O (4 wt% in the present work) was used, the length and diameter of elongated mullite increased with increasing the reaction temperature, and elongated mullite of 22.3 µm in average length and 4.6 µm in average diameter was formed after 5 h at 1873 K. Based on the results, elongated mullite self-reinforced porous ceramics were prepared by a combined foam-gelcasting and solid-reaction method, and their mechanical properties were examined. Elongated mullite in-situ formed in the porous samples evidently enhanced their mechanical strength. The flexural strength of the elongated mullite self-reinforced porous sample with 67.0% porosity (prepared using 6 wt% AlF3·3H2O) was as high as 13.9 MPa, which was about 26.4% higher than that of a porous sample (11.0 MPa) prepared without AlF3·3H2O.

Structure and ferromagnetism properties of leaf‐like ZnO nanostructures

Leaf-like macroscopic ZnO nanostructures have been synthesised via a conventional thermal evaporation method at 950°C, using a mixture of graphite, zinc oxide and CuO powders as a source material. The effect of CuO in a relevant growth mechanism was discussed. Its crystal structure properties were determined using X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. Photoluminescence spectra of the sample exhibit emission peaks centred at about 382, 525, 542 and 767 nm, respectively. The room temperature ferromagnetism was observed using a physical property measurement system.

Efficient photodegradation of dye pollutants using a novel plasmonic AgCl microrods array and photo-optimized surface-enhanced Raman scattering

A novel arrayed AgCl micro-rods have in situ grown on an Ag foil successfully for the first time. The preparation process is consisted of two facile steps: (1) immersed oxidation and (2) directional ions exchange. The structure of the as-synthesized arrayed substrate has been characterized comprehensively, and the relevant growth mechanism is proposed. This highly aligned AgCl arrays show a remarkable visible-light-driven photocatalytic activity towards degrading 10−5mol/L rhodamine 6G (R6G) aqueous solution. The ultra-stable catalytic performance of the plasmonic arrays was revealed by the recycled tests in the neutral and acidic conditions. Moreover, a facile SERS substrate based on the AgCl arrays was obtained with the optimal enhancement factor (EF) of ∼3.25×107, by directly putting the substrate under a Xe lamp in 7.5min. Amazingly, the photo-optimized surface-enhanced Raman scattering (SERS) substrate still shows a stable activity for photodegrading R6G. The photocatalytic and SERS mechanism are proposed in this study.

Property of Zinc Oxide (Zno) Nanostructures Potential for Biomedical System and Its Common Growth Mechanism

Zinc Oxide (ZnO) nanomaterials have received broad attention thanks to their distinguished performance in electronics, optics and photonics. Due to the novel applications in optoelectronics, sensors, transducers and biomedical sciences, ZnO materials have become a leading edge in nanotechnology. Therefore, the properties of ZnO nanostructures potential for applying in biotechnology are marked along with the relevant common growth mechanism aim to provide the vital information about the growing field related to nano-ZnO in the biomedical system with environmental friendly nature and biocompatibility

硼-硫酸-草酸电解液降压阳极氧化疏孔膜层制备及表征

使用铝合金在硼．硫酸．草酸电解液中阳极氧化制备有序多孔层。初步探讨了恒流和降压阳极氧化过程膜层生长机理，采用扫描电镜（SEM）观察膜层微观形貌，结合电化学阻抗和动电位极化曲线研究不同阳极化工艺制备膜层试样在3．5％NaCl溶液中的耐蚀行为。结果表明，采用三段变压方式制备的阳极氧化膜表面孔密度降低，孔壁增厚，孔径为10～13am。疏孔膜层的电化学行为表明孔壁及膜层厚度增大能提高试样电荷传递电阻和耐蚀性能。

Quantitative Relationship between Support Porosity and the Stability of Pore-Confined Metal Nanoparticles Studied on CuZnO/SiO2 Methanol Synthesis Catalysts

Metal nanoparticle growth represents a major deactivation mechanism of supported catalysts and other functional nanomaterials, particularly those based on low melting-point metals. Here we investigate the impact of the support porous structure on the stability of CuZnO/SiO2 model methanol synthesis catalysts. A series of silica materials with ordered cagelike (SBA-16 mesostructure) and disordered (SiO2-gel) porosities and varying pore sizes were employed as catalyst supports. Nitric oxide moderated nitrate decomposition enabled the synthesis of catalytically active Cu nanoparticles (3-5 nm) exclusively inside the silica pores with short interparticle spacings. Under relevant reactive conditions, confinement of the Cu particles in cagelike silica pores notably enhances catalyst stability by limiting Cu particle growth as compared to catalysts deposited in SiO2-gel host materials with also 3D and highly interconnected though unconstrained porosity. For both pore morphologies, we find a direct relationship between catalyst stability and support porosity, provided the narrowest characteristic pore dimension is employed as a porosity descriptor. For cagelike porosities this corresponds to the size of the entrances to the nanocages. Our results point to nanoparticle diffusion and coalescence as a relevant growth mechanism under reactive conditions and underscore the significance of the narrowest pore constrictions to mitigate growth and improve catalyst stability. This finding contributes to the establishment of general and quantitative structure-stability relationships which are essential for the design of catalysts and related functional nanostructures with long lifetimes under operation conditions.

Electric field influenced ZnO growth on nanoscale etched Si surface by continuous spray pyrolysis

This work reports ZnO growth by electric field influenced continuous spray pyrolysis reactor over seed layer assisted nanoscale etched Si surface. The comparative studies of ZnO growth in the presence and absence electric field on anisotropically etched Si surface are supported by XRD, SEM, EDX, FTIR and reflectance measurements. XRD measurements confirm preferable (002) oriented ZnO growth by certain amount of etching which is reduced with further anisotropic etching. The chlorine incorporation in ZnO thin film measured by EDX and FTIR may be attributed to the seed layer effect. This present investigation show that anisotropic etch pits surface energy profile has played an important role in deciding ZnO nanorods alignment and coalescence amongst ZnO species during self assembly at nucleation sites. It is observed that additional electric field force in spray droplets is enhancing population density, homogeneous growth and surface coverage of Si surface by ZnO nanorods for particular amount of etched Si surface and improved light coupling is confirmed by reflectance measurement. The relevant growth mechanisms for ZnO nanostructure layers comprising nanorods are also discussed.

Catalyst-Free InGaP Nanoneedles Grown on Si Substrate by Metalorganic Chemical Vapor Deposition

Catalyst-free InGaP nanoneedles were grown on Si substrate via metalorganic chemical vapor deposition. From scanning electron microscope (SEM) images, various nanoneedles were observed and the relevant growth mechanism was discussed.

Growth of zinc blende GaAs/AlGaAs heterostructure nanowires on Si substrate by using AlGaAs buffer layers

Vertical GaAs/AlGaAs heterostructure nanowires (NWs) with pure zinc blende structure were grown on Si (111) substrates by using AlGaAs/GaAs buffer layers. Axial and radial heterostructure NWs with different facets can be realized by tuning the growth temperature, so quantum wells with a triangular cross section enclosed by two {112} and one {110} facets can be obtained. Intensity of the room temperature photoluminescence can be greatly enhanced by passivating the surface states of GaAs NWs via growth of higher band-gap AlGaAs shells. The relevant growth mechanism is discussed.

Investigation about Synthesis of Carbon Nanotubes with Various Structures Governed by Temperature and Relevant Growth Mechanism

Multi-walled carbon nanotubes (CNTs)/Al in-situ composite powders over Al as catalyst carrier had been synthesized successfully using transition metal Ni by chemical vapor deposition. CNTs were mainly characterized by transmission electron microscopy. It was found that reaction temperature had great influences on the structures of carbon products obtained. Detailed discussions according to the structures of CNTs at different reaction temperatures were given. A deduced model for explaining the growth mechanism of CNTs governed by temperature was developed.

Growth of AlN hexagonal oriented complex nanostructures induced by nucleus arrangement

Growth of AlN hexagonal oriented complex nanostructures were induced by nucleus arrangement under certain conditions in a simple one step halide chemical vapor deposition (HCVD) system. The as-prepared AlN nanostructures obtained at different positions from the Al source involve nanomaze, hexagonal nested arrays, hexagonal nanorod arrays with a small pit on the top of each rod and nanoparticle films, respectively. A relevant growth mechanism was suggested and interpreted in detail with a focus on the “nucleus arrangement” combined with preferential growth. Observations of nucleus arrangement events certify the rationality of this mechanism. We found that the variable ratio of AlCl3/NH3 offers the power to mediate the arrangement of nucleus and crystal growth. There are some differences between the nucleus arrangement mechanism that we put forward here in the HCVD system and the oriented attachment that occurs in solution, because the former possesses a shorter mean free path of the nucleus.

Realizing Zinc Blende GaAs/AlGaAs Axial and Radial Heterostructure Nanowires by Tuning the Growth Temperature

Vertical zinc blende GaAs/AIGaAs heterostructure nanowires were grown at different temperatures by met-alorganic chemical vapor deposition via Au-assisted vapor-liquid-solid mechanism. It was found that radial growth can be enhanced by increasing the growth temperature. The growth of radial heterostructure can be realized at temperature higher than 500°C, while the growth temperature of axial heterostructure is lower than 440°C. The room temperature photoluminescence properties of the nanowires were investigated and the relevant growth mechanism was discussed.

Microstructural characteristics and texture of hot strip low carbon steel produced by flexible thin slab rolling with warm rolling technology

The mechanical properties and development of microstructure and texture of a low carbon steel produced by Flexible Thin Slab Rolling (FTSR) with warm rolling technology were investigated using scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction and X-ray diffraction etc. The microstructural features in the hot strip are mainly large polygonal ferrite grains with very few or hardly any pearlite colonies. The values of yield strength and tensile strength are in the range of 215–240 MPa and 305–335 MPa, respectively, and the elongation is in the range of 33–41%. The ferrite softening can be attributed to ferrite recrystallization. Even though the dominant bulk texture is the typical recrystallization texture, which can be grouped into the ND fibre ({111}<110–112>) having a <111> axis parallel to the normal direction, a weak {110}<112> transformation texture was also observed in the final microstructure by electron back-scattered diffraction. By analysis, the large grain size is explained in terms of ferrite recrystallization and relevant growth mechanisms, and the ferrite recrystallization can be considered to play a major role in determining the grain size in the microstructure of the low carbon steel produced by FTSR with warm rolling technology.

Modelling titania formation at typical industrial process conditions: effect of surface shielding and surface energy on relevant growth mechanisms

This work investigates the effects of reduced accessible surface area of aggregate particles and of surface energy on relevant particle formation and growth mechanisms during titania formation from the vapour phase at industrial process conditions. Growth due to surface reaction and due to condensation is related to the fraction of the surface area that is exposed to the collision with single molecules. Surface shielding is found to hamper surface reaction and condensation once fractal aggregates start to form. It leads to significantly retarded precursor consumption and produces aggregate particles, which consist of more, but smaller primary particles. Surface energy data are varied within a range as proposed by available literature data. Moderate and high surface energy values result in a thermodynamic barrier to the formation of new particles and are shown to reduce the formation of seed particles by several orders of magnitude. This leads to the formation of aggregate particles which consist of a rather small number of primary particles and mainly grow by surface reaction. The primary contribution of condensation to growth of individual primary particles is shown to be very little. However, condensation should not be neglected as it has a strong impact on particle formation rates and hence on product characteristics such as the number of primary particles and primary particle size.

Coal-derived carbon nanotubes by thermal plasma jet

A coal/arc-jet technique by directly and successively injecting coal fine particles into the arc plasma jet instead of arcing graphite or coal-based electrodes for producing carbon nanotubes (CNTs) from coal was developed. The derived carbon products by this technique were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray energy dispersive spectrum (EDS), X-ray diffraction (XRD) and Raman spectrum. The experimental results clearly indicated that the certain metal catalyst favored the growth of CNTs in the process, and the relevant growth mechanism was discussed in terms of the characterizations.

Effects of loading frequency on fatigue crack growth mechanisms in α/β Ti microstructure with large colony size

This paper deals with crack tip/microstructure interactions at 520 °C in lamellar Ti–6Al–2Sn–4Zr–2Mo–0.1Si (Ti6242) alloy under different fatigue loading frequencies. A series of heat treatments were performed in order to produce large colony microstructures that vary in their lamellar and colony size. Fatigue crack growth (FCG) experiments were conducted on these microstructures at loading frequencies of 10 and 0.05 Hz. The lower frequency was explored with and without imposing a 5 min hold-time at the peak stress level during each loading cycle. Results show that the crack growth behavior is sensitive to the loading frequency. For the same microstructure, the crack growth rate is found to be lower at 10 than at 0.05 Hz. The addition of a hold-time, however, did not alter the FCG rate indicating that creep strain during one loading cycle does not contribute significantly in the crack growth process. It is also shown that variations in lamella and colony size have no effects on the FCG rate except for the early stage of crack propagation. Scanning Electron Microscope examinations are performed on the fracture surface in order to identify the relevant crack growth mechanisms with respect to the loading frequency and the microstructure details. Quasi-cleavage of the α/β colonies along strong planar shear bands is shown to be a major mode of failure under all test condition. At a loading frequency of 10 Hz, the crack path proceeds arbitrary along planes either perpendicular or parallel to the long axis of α lamellae, while at 0.05 Hz, parallel-to-lamellae crack paths become favored. Corresponding differences of crack growth behavior are examined in terms of slip emission at the crack tip and interactions with the microstructure details.

Explanation for the Supersaturation-Dependent Morphology of Monoclinic Paracetamol

The growth morphology of monoclinic paracetamol as a function of the supersaturation is determined using Monte Carlo simulations based on the crystal structure. The results are compared with experimental results reported recently on both the morphology and the relevant growth mechanisms. The change of an elongated to a more bulky habit with increasing supersaturation is reproduced well by the simulations. The method used opens ways to predict the crystal morphology for real crystal structures in dependence of supersaturation once information on the relevant growth mechanism for the various faces is known.