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A review of crystallographic textures in chemical
vapor-deposited diamond films
Tao LIU, Dierk RAABE, Wei-Min MAO,
Front. Mater. Sci.. 2010, 4 (1): 1-16.
https://doi.org/10.1007/s11706-010-0011-6
Diamond is one of the most important functional materials for film applications due to its extreme physical and mechanical properties, many of which depend on the crystallographic texture. The influence of various deposition parameters matters to the texture formation and evolution during chemical vapor deposition (CVD) of diamond films. In this overview, the texture evolutions are presented in terms of both simulations and experimental observations. The crystallographic textures in diamond are simulated based on the van der Drift growth selection mechanism. The film morphology and textures associated with the growth parameters α (proportional to the ratio of the growth rate along the〈100〉direction to that along the 〈111〉direction) are presented and determined by applying the fastest growth directions. Thick films with variations in substrate temperature, methane concentration, film thickness, and nitrogen addition were analyzed using high-resolution electron back-scattering diffraction (HR-EBSD) as well as X-ray diffraction (XRD), and the fraction variations of fiber textures with these deposition parameters were explained. In conjunction with the focused ion beam (FIB) technique for specimen preparation, the grain orientations in the beginning nucleation zones were studied using HR-EBSD (50nm step size) in another two sets of thin films deposited with variations in methane concentration and substrate material. The microstructures, textures, and grain boundary character were characterized. Based on the combination of an FIB unit for serial sectioning and HR-EBSD, diamond growth dynamics was observed using a 3D EBSD technique, with which individual diamond grains were investigated in 3D. Microscopic defects were observed in the vicinity of the high-angle grain boundaries by using the transmission electron microscopy (TEM) technique, and the advances of TEM orientation microscopy make it possible to identify the grain orientations in nano-crystalline diamond.
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Diameters of single-walled CNTs (SWCNTs) and
related nanochemistry and nanobiology
Jie MA, Jian-Nong WANG, Chung-Jung TSAI, Buyong MA, Ruth NUSSINOV,
Front. Mater. Sci.. 2010, 4 (1): 17-28.
https://doi.org/10.1007/s11706-010-0001-8
We reviewed and examined recent progresses related to the nanochemistry and nanobiology of signal-walled carbon nanotubes (SWCNTs), focusing on the diameters of SWCNTs and how the diameters affect the interactions of SWCNT with protein and DNA, which underlay more complex biological responses. The diameters of SWCNTs are closely related to the electronic structure and surface chemistry of SWCNTs, and subsequently affect the interaction of SWCNTs with membrane, protein, and DNA. The surfaces of SWCNT with smaller diameters are more polar, and these with large diameters are more hydrophobic. The preference of SWCNT to interact with Trp/Phe/Met residues indicates it is possible that SWCNT may interfere with normal protein-protein interactions. SWCNT-DNA interactions often change DNA conformation. Besides the promising future of using SWCNTs as delivering nanomaterial, thermal therapy, and other biological applications, we should thoroughly examine the possible effects of carbon nanotube on interrupting normal protein-protein interaction network and other genetic effects at the cellular level.
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Electrospun nanofibers: Work for medicine?
Susan LIAO, Casey K. CHAN, S. RAMAKRISHNA,
Front. Mater. Sci.. 2010, 4 (1): 29-33.
https://doi.org/10.1007/s11706-010-0009-0
Attempts have been made to fabricate nanofibrous scaffolds to mimic the chemical composition and structural properties of the extracellular matrix (ECM) for tissue/organ replacement. Nanofiber scaffolds with various patterns have been successfully produced from synthetic and natural polymers through a relatively simple technique of electrospinning. The resulting patterns can mimic some of the diverse tissue-specific orientation and three-dimensional (3D) fibrous structures. Studies on cell-nanofiber interactions, including studies on stem cells, have revealed the importance of nanotopography on cell adhesion, proliferation and differentiation. Furthermore, clinical application of electrospun nanofibers including wound healing, tissue regeneration, drug delivery and stem cell therapy are highly feasible due to the ease and flexibility of fabrication of making nanofiber with this cost-effective method using electrospinning. In this review, we have highlighted the current state of the art and provided future perspectives on electrospun nanofiber in medical applications.
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The potential of Zr-based bulk metallic glasses
as biomaterials
Qi CHEN, Lin LIU, Sheng-Min ZHANG,
Front. Mater. Sci.. 2010, 4 (1): 34-44.
https://doi.org/10.1007/s11706-010-0004-5
Zr-based bulk metallic glasses (BMGs) are a new type of metallic materials with disordered atomic structure that exhibit high strength and high elastic strain, relatively low Young’s modulus, and excellent corrosion resistance and biocompatibility. The combination of these unique properties makes the Zr-based BMGs very promising for biomaterials applications. In this review article, the authors give an overview of the recent progress in the study of biocompatibility of Zr-based BMGs, especially the relevant work that has been done in the metallic glasses group in Huazhong University of Science and Technology (HUST), including the development of Ni-free Zr-based BMGs, the mechanical and wear properties, the bio-corrosion resistance, the in vitro and in vivo biocompatibility and the bioactive surface modification of these newly developed BMGs.
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Fabrication of mesoporous silica/carbon black
nanospheres and load-sensitive conducting rubber nanocomposites
En-Rong LI, Qian-Jun ZHANG, Wei WANG, Qing-Wen ZHU, Long BA,
Front. Mater. Sci.. 2010, 4 (1): 52-56.
https://doi.org/10.1007/s11706-010-0015-2
Mesoporous silica nanospheres (MSNs) with regular pores have been fabricated using cetyltrimethylammonium bromide (CTAB) as surfactant in high pH solution. The average size of the MCM-41 silica nanospheres was reduced from 95 to 48€nm, while the concentration of CTAB increases from 7.7 to 11.5mmol/L. Carbon black was deposited on MSNs using hexane as the carbon source. By mixing such materials with silicone rubber, the composites become conducting when equivalent carbon volume fraction is higher than a certain region, which is less sensitive to the morphology of the deposited carbon. The improved piezoresistance repeatability has been found on the composite sample of MSNs/carbon plus extra high conducting carbon black. The load and strain sensitive range up to 0.35MPa and 0.10, respectively, with less resistance fluctuation during multiple press loading cycles.
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Thermal degradation behavior and kinetic analysis
of poly(L-lactide) in nitrogen and air atmosphere
Ming-Tao RUN, Xin LI, Chen-Guang YAO,
Front. Mater. Sci.. 2010, 4 (1): 78-83.
https://doi.org/10.1007/s11706-010-0008-1
The non-isothermal and isothermal degradation behaviors and kinetics of poly(L-lactide) (PLLA) were studied by using thermogravimetry analysis (TGA) in nitrogen and air atmosphere, respectively. At lower heating rate ((5–10)°C/min), PLLA starts to decompose in air at lower temperature than those in nitrogen atmosphere; however, at higher heating rate ((20–40)°C/min), the starting decomposition temperature in air are similar to those in nitrogen atmosphere, not only showing that PLLA has better thermal stability in nitrogen than in air atmosphere, but also suggesting that the faster heating rate will decrease the decomposition of PLLA in thermal processing. Whether in air or in nitrogen atmosphere, the decomposition of PLLA has only one-stage degradation with a first-order decomposed reaction, suggesting that the molecular chains of PLLA have the similar decomposed kinetics. The average apparent activation energy of non-isothermal thermal degradation (Ēnon) calculated by Ozawa theory are 231.7kJ·mol−1 in air and 181.6kJ·mol−1 in nitrogen; while the average apparent activation energy of isothermal degradation (Ēiso) calculated by Flynn method are 144.0kJ·mol−1 in air and 129.2kJ·mol−1 in nitrogen, also suggesting that PLLA is easier to decompose in air than in nitrogen. Moreover, the decomposed products of PLLA are also investigated by using thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS). In air atmosphere the volatilization products are more complex than those in nitrogen because the oxidation reaction occurring produces some oxides groups.
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Effect of AAc-GA content on swelling behaviors
of temperature-sensitive PNIPAAm-based hydrogels
You-Yu DONG, Li CHEN, Hao-Jie LI, Xiao-Ling HE, Fan-Yong YAN,
Front. Mater. Sci.. 2010, 4 (1): 84-89.
https://doi.org/10.1007/s11706-010-0002-7
A series of temperature-sensitive poly(NIPAAm-co-AAc-GA) hydrogels were synthesized by the copolymerization of glycyrrhetinic acid with vinyl monomer (AAc-GA) and N-isopropylacrylamide (NIPAAm) in N, N-dimethylformamide (DMF). Since GA has the specific binding capacity to asialoglycoprotein receptors on the membrane of hepatocyte, the hydrogel with GA could be expected as good candidate for hepatic cell culture. The results showed that macroporous and channel network structure was formed in the hydrogel matrix. With increasing the AAc-GA content, the swelling ratios of hydrogels and lower critical solution temperature (LCST) increased because of the hydrophilic group of AAc-GA and the macroporous structure. In addition, the prepared hydrogels could respond quickly to temperature and exhibited good reversible temperature-responsive characteristics.
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A novel blue emitting phosphor NaBa 0.98 Eu 0.02 PO 4 and the improvement of its luminescence properties
Juan GU, Bo YUE, Guang-Fu YIN, Xiao-Ming LIAO, Zhong-Bing HUANG, Ya-Dong YAO, Yun-Qing KANG,
Front. Mater. Sci.. 2010, 4 (1): 90-94.
https://doi.org/10.1007/s11706-010-0003-6
€€€€€€A €€€€€€novel€€€ €€€blue-emitting €€€€€€phosphor NaBa0.98Eu0.02PO4 was synthesized by conventional solid state reaction, and it exhibits efficient blue emission under near-ultraviolet (n-UV) excitation. The emission spectrum shows a single band centered at about 440 nm, which corresponds to the 4f65d1-4f7 transition of Eu2+. The excitation spectrum is a broad band in the wavelength range between 200 and 450nm, which can match the emission of white light emitting diodes (LEDs) by the method of n-UV conversion. The Ca2+, Sr2+ and Mg2+ were co-doped into NaBa0.98Eu0.02PO4 respectively. Special attention was paid to the sample co-doped with Ca2+ that could possess a higher luminous efficacy than the analogs co-doped with Sr2+ and Mg2+. With the co-doping of Ca2+, the enhanced intensity of the excitation and emission band appears. The optimum co-doping concentration of Ca2+ is 7 mol.%. The emission intensity of NaBa0.91Ca0.07Eu0.02PO4 phosphoris about 1.68 times than that of NaBa0.98Eu0.02PO4 phosphor. The as-prepared phosphors are the potential blue phosphors for application in white LEDs.
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Amine-terminated TEG-derived PAMAM dendrimer
as template for preparation of gold nanoparticles in water
Jiang-Yu WU, Yan LI, Yong MAO, Jia XU, Xu ZHOU,
Front. Mater. Sci.. 2010, 4 (1): 95-99.
https://doi.org/10.1007/s11706-010-0006-3
Nano-sized monodisperse gold particles (AuNPs) have received significant attention in the past decade, due to their unique physical properties and good chemical stability, which can lead to a wide variety of potential applications. In this work, TEG-derived PAMAM dendrimers with amine-terminating groups were synthesized and characterized by 1H NMR and FT-IR. These dendrimers were investigated as the templates for preparation of gold nanoparticles through the reduction of HAuCl4 by NaBH4 in water. Stable gold nanoparticles with diameters around 10 nm were obtained in the presence of G2.0 – G5.0 dendrimers and characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The particle size of the produced AuNPs decreased with increasing dendrimer generations. A dendrimer of higher generation has a rigid structure with many end groups on the surface and may play a powerful role in the growth of the AuNPs, as well as having a solid stabilization effect on the AuNPs.
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Effects of high magnetic field on thermodynamic
properties of pure Fe and Cu
Na-Qiong ZHU, Lin LI, Yan-Lin HE, Guang-Jie SHAO, Mei-Bo TANG, Jing-Tai ZHAO,
Front. Mater. Sci.. 2010, 4 (1): 100-102.
https://doi.org/10.1007/s11706-010-0007-2
By the use of PPMS (Physics Property Measurement System), specific heat values of pure Cu at 2–300 K were determined under the magnetic field of 0, 3, 6 and 9 T, respectively. Magnetization curves of pure Fe under the magnetic field of 0–9 T were obtained at different temperature ranging from 5 to 300 K. Analyses of the experimental results indicate that below 300 K, magnetic fields have no effects on the specific heat values of diamagnetic Cu and very little effects on those of ferromagnetic Fe.
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