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1.
Chemically modified silk fibroin (SF) with an enzyme, Proteinase K, has been incorporated into hydroxyapatite (HAp)-based nanocomposite attempting to strengthen the interfacial bonding between the mineral phase and the organic matrix. Particular emphasis is laid on the microstructure and microhardness of the composite along with the crystallographic properties of HAp. The whisker-like HAp crystallites of nanometer size show the preferential self-assembly and anisotropic crystal growth along c-axis. There appears porous microstructure with 70% of open porosity and pore size distribution of 10–115 um in the composite. Attributed to the enzyme modification, the crosslinkage between HAp clusters and SF matrix is improved to form an enhanced three-dimensional network extending throughout the composites and an increase of 35% in microhardness of the composite is achieved as well. 相似文献
2.
Microstructure and Chemical States of Hydroxyapatite/silk Fibroin Nanocomposites Synthesized via A Wet-mechanochemical Route 总被引:3,自引:0,他引:3
Hydroxyapaptite (HAp)/silk fibroin (SF) nanocomposites were prepared via a wet-mechanochemical route at room temperature. The results reveal that the inorganic phase in the composites is carbonate-substituted HAp containing 2.9–3.1 wt% of carbonate ions. The primary HAp crystals are rod-like in shape with a typical size of 20–30nm in length and 8–10nm in width, and lattice parameters a = 9.423, c = 6.888. The self-assembled HAp crystals along their c-axes aggregate into bundles, which are connected with SF fibrils. Consequently, a three-dimensional porous network is formed in the composite, which is beneficial to inducing new bone formation in practical implantation. 相似文献
3.
W. Que Y. Zhou Y.L. Lam K. Pita Y.C. Chan C.H. Kam 《Applied Physics A: Materials Science & Processing》2001,73(2):209-213
Luminescence properties from erbium (III) oxide nanocrystals dispersed in titania/organically modified silane composite thin
films were studied. Erbium oxide nanocrystals were prepared by an inverse microemulsion technique. A strong room-temperature
photoluminescence was observed at 1.531 μm, with the full width at half maximum (FWHM) of 22 nm due to intra-atomic transitions
between 4
I
13/2 and 4
I
15/2 levels in the erbium (III) ion. The shape, peak position, and FWHM of the photoluminescence signals from the composite thin
films were quite comparable to those prepared by other methods. The photoluminescence peak of the composite thin films showed
a maximum intensity at the heat-treatment temperature of 300 °C. A room-temperature green up-conversion emission at 543 nm
(4
S
3/2?4
I
15/2) was observed for the composite thin films with different heat-treatment temperatures upon excitation at 993 nm. The up-conversion
emission mechanism was explained by means of an energy-level diagram and the lifetime of the visible up-conversion emission
was measured.
Received: 10 July 2000 / Accepted: 11 July 2000 / Published online: 5 October 2000 相似文献
4.
D.L. Wainstein A.I. Kovalev Cs. Ducso T. Jaszi P. Basa Zs.J. Horvath T. Lohner P. Petrik 《Physica E: Low-dimensional Systems and Nanostructures》2007,38(1-2):156
Si nanocrystals were formed in the non-stoichiometric Si-enriched SiNx low-pressure chemical vapor deposited (LPCVD) coatings on Si wafers treated by various modes. The coating structure as a function of technological conditions was investigated by ellipsometry and X-ray photoelectron spectroscopy (XPS) depth profiling. It was found that nanocomposites on base of SiNx films enriched by Si have a complex multilayered structure varying in dependence of deposition and annealing parameters. Analysis of the XPS spectra and Si 2s peaks shows the existence and quantity of four chemical structures corresponding to the Si–O, Si–N states, nanocrystalline and amorphous Si. The XPS results show evolution of the chemical structure of silicon nitride and formation of Si nanocrystals. It was found:
- • The LPCVD technology of nanocrystals formation allows to get enough high concentration of Si nanocrystals on different depths from the sample surface.
- • The volume fraction of nanocrystalline and amorphous Si is changed with depth; this relation depends from SiNx composition and annealing parameters.
- • XPS detects these two phase compositions of Si nanoparticles in SiNx and SiO2 layers. The ellipsometry, HR-TEM, and XPS results are in good agreement.
Keywords: Nano crystals; Si 相似文献
5.
A simple method, chemical precipitation at low temperature from Ca(NO3)2·4H2O and (NH4)2HPO4 to tailor single phase, highly crystalline nanocrystal hydroxyapatite (HAp) powders was introduced in this paper. HAp powders
with controlled morphologies (spherical and rod-like) and different grain sizes have been obtained by varying the reaction
temperature, reaction mode, and heat treatment accordingly. X-ray diffraction (XRD) results combined with the Fourier transform-infrared
spectroscopy (FT-IR) indicates that the single phase, nanocrystal HAp powder could be obtained in one-step without further
heat treatment. At 40 °C with a quick mixing mode, ultra-fine complete spherical HAp particles with diameter range size of
20–50 nm could be obtained. 相似文献
6.
High-affinity integration of hydroxyapatite nanoparticles with chemically modified silk fibroin 总被引:3,自引:0,他引:3
Hydroxyapatite (HA)-based nanocomposites were prepared by a co-precipitation method with silk fibroin (SF) serving as organic
matrix. Silk fibroin was chemically modified with an alkali solution or an enzyme attempting to improve the interface between
the mineral and the organic matrix. The influences of the alkali and enzyme pretreatments on microstructure and physicochemical
properties of HA–SF composite were examined and compared. The results reveal that both the two kinds of pretreatments facilitate
the formation of highly ordered three-dimensional porous network throughout the composites, increase the microhardness of
the composite, and promote the preferential growth of HA crystallites along c-axis. Among all the as-prepared samples, the composite containing the enzyme pretreated SF shows desirable hierarchical microstructure
with higher degree of organization and more uniform pore size distribution. Due to the enzyme pretreatment, HA crystallites
undergo obvious changes in morphology from rod-like to␣whisker-like and in crystal growth towards more apparent epitaxy along
c-axis. The alkali pretreatment induces the stronger chemical interactions between HA and SF and thus to strengthen the inorganic–organic
interfacial adhesion. The newly developed HA–SF composites are expected to be attractive biomedical materials for bone repair
and remodeling. 相似文献
7.
Guo-Long Tan Min Wang Kai Wang Lin Zhang Xue-Feng Yu 《Journal of nanoparticle research》2011,13(11):5799-5807
Cd1−x
Mn
x
Te (x = 0, 0.1, 0.2) nanocrystals have been synthesized by mechanical alloying (MA) Cd, Mn, and Se elemental powders. XRD patterns
and HRTEM images confirmed the formation of cubic Cd1−x
Mn
x
Te nanocrystals. All the diffraction peaks from elemental Cd, Mn, and Te powders disappeared completely in those XRD patterns
of as-milled Cd1−x
Mn
x
Te nanocrystals for more than 20 h. When the MA process was carried out for 40 h, typical zinc blende structure diffraction
mode was exhibited in the XRD pattern. Subsequently, capping the surface of as-milled Cd1−x
Mn
x
Te nanocrystals with long chain trioctylphosphine/trioctylphosphine oxide/nitric acid (TOP/TOPO/NA) molecules has achieved
colorful dispersion solution, which shows similar optical properties to those CdTe nanocrystals prepared by wet chemical process.
The grain size is within the range of 2–8 nm for the capped Cd1−x
Mn
x
Te nanocrystals being ball milled for 40 h. The PL excitation peak red shifts to longer wavelength side with increasing Mn
concentration. Pure CdTe nanocrystals show ferromagnetism behavior at room temperature, the saturation magnetization value
and magnetic hysteresis loop increase with the content of substituting Mn ions within the Cd1−x
Mn
x
Te nanocrystals. 相似文献
8.
Masanari TomozawaSachiko Hiromoto 《Applied Surface Science》2011,257(19):8253-8257
Hydroxyapatite (HAp) coatings were uniformly formed on pure Mg by a hydrothermal treatment using a C10H12N2O8Na2Ca (Ca-EDTA) solution. The growth mechanism of the HAp coating was investigated with XRD, SEM and TEM. At the initial stage, dome-shape HAp precipitates were formed on the Mg. Subsequently, the precipitates grew and the coating became a dual-layer consisting of an inner dense HAp layer and outer course layer consisting of rod-like HAp crystals. The protectiveness of the coatings with different treatment times was investigated by a polarization test in a 3.5 wt.% NaCl solution. The corrosion current density decreased with the growth of the HAp coating. 相似文献
9.
Structural, microstructural, X-ray photoemission spectra (XPS) and magnetic properties of transition metal ion [5 mol% of Co (SC5) and Fe (SF5)]-doped SnO2 nanoparticles have been studied. The SC5 and SF5 nanoparticles were synthesized by a chemical route using polyvinyl alcohol as surfactant. The doped SnO2 crystallites were found to exhibit a tetragonal rutile structure and the average grains size was measured by the Scherer relation of X-ray diffraction. Transmission electron micrographs showed that the average grain size of SC5 is smaller than SF5. SC5 nanoparticles showed strong ferromagnetic behaviour but SF5 exhibited an F-centre exchange (FCE) mechanism. Temperature-dependent magnetization showed the values of phase transition temperature. XPS confirmed the presence of Sn–O–Co and Sn–O–Fe bonds in these SC5 and SF5 nanoparticles. The oxidation states of Sn, Co and Fe were found to be +4, +2 and +2, respectively, while the core level XPS peaks of Sn 3d, O 1s, Co 2p and Fe 2p were analyzed. 相似文献
10.
D. Mourad G. Czycholl 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(4):497-507
Zero-dimensional nanocrystals, as obtained by chemical synthesis, offer a broad range of applications, as their spectrum and
thus their excitation gap can be tailored by variation of their size. Additionally, nanocrystals of the type A
x
B1-
x
C can be realized by alloying of two pure compound semiconductor materials AC and BC, which allows for a continuous tuning
of their absorption and emission spectrum with the concentration x. We use the single-particle energies and wave functions calculated
from a multiband sp
3 empirical tight-binding model in combination with the configuration
interaction scheme to calculate the optical properties of
Cd
x
Zn1-
x
Se nanocrystals with a spherical shape. In contrast to common mean-field approaches like the virtual crystal approximation
(VCA), we treat the disorder on a microscopic level by taking into account a finite number of realizations for each size and
concentration.
We then compare the results for the optical properties with recent experimental data and calculate the optical bowing coefficient
for further sizes. 相似文献
11.
W.-C. Liu A.-D. Li J. Tan D. Wu H. Ye N.-B. Ming 《Applied Physics A: Materials Science & Processing》2005,81(3):543-547
Pb(Zr0.52Ti0.48)O3 (PZT) nanocrystals and transparent polycarbonate (PC) composite thin films with useful properties for ferroelectric, piezoelectric and electro-optic devices were prepared by a spin-coating technique. Ultra-fine PZT (∼40–50 nm) nanocrystals with pure perovskite tetragonal phase were synthesized by a hydrothermal method. The structure and morphology of the composite thin films were studied by means of X-ray diffraction and scanning electron microscopy. To obtain the optimum electro-optic properties of poled composite films, the poling condition under an external electric field was optimized through the dielectric properties of PZT and PC polymer and effective field intensity theory. The electro-optic coefficient of the poled PZT/PC composite film is estimated to be 30.5 pm/V. The transparency spectra were measured and the optical band gaps of the unpoled, poled at 145 °C and poled at 165 °C composite thin films are estimated to be 4.26 eV, 4.21 eV and 4.18 eV, respectively. The measured dielectric constants of PZT/PC are in good agreement with the calculated values for the composite with a very small PZT volume fraction, based on the Onsager effective-field theory. This offers a reliable and indirect way to predict the dielectric constant of nanocrystals. PACS 81.40.Tv; 78.66.Sq; 78.66.Vs 相似文献
12.
We report on the chemical linkage of fullerenes to lead selenide (PbSe) nanocrystals by exchanging oleic acid ligands on PbSe nanocrystals with C60-bound dithiocarbamate ligands. To improve the solubility of C60-PbSe nanocrystals, a small-molecular-weight dithiocarbamate was used as a co-ligand in the ligand exchange reaction. The as-synthesized C60-PbSe nanoconjugates were characterized by 1H NMR, UV–vis and transmission electron microscopy (TEM). Photoelectrochemistry (PEC) of the C60-PbSe nanoconjugate revealed a reversed polarity of the photocurrent compared to those of C60 and PbSe nanoparticles separately, suggesting that C60 may serve as p-dopants to PbSe nanocrystals through the surface transfer doping process. 相似文献
13.
M. Gafurov T. Biktagirov B. Yavkin G. Mamin Y. Filippov E. Klimashina V. Putlayev S. Orlinskii 《JETP Letters》2014,99(4):196-203
Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20–50 nm and 1 μm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (byproducts) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO 3 2? paramagnetic centers detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from 1H and 31P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO 3 2? radicals preferably occupy PO 4 3? site in the HAp structure. 相似文献
14.
15.
N. Srinivasa Rao A.P. Pathak N. Sathish G. Devaraju V. Saikiran P.K. Kulriya D.C. Agarwal G. Sai Saravanan D.K. Avasthi 《Solid State Communications》2010,150(43-44):2122-2126
Ge nanocrystals embedded in an SiO2 matrix were prepared by the atom beam co-sputtering (ABS) method from a composite target of Ge and SiO2. The as-deposited films were rapid thermally annealed at the temperatures 700 and 800 °C in nitrogen ambience. The structure of the films was evaluated by using X-ray diffraction (XRD) and Raman spectroscopy. XRD results reveal that as-deposited films are amorphous in nature whereas annealed samples show crystalline nature. Raman scattering spectra showed a peak of Ge–Ge vibrational mode shifted downwards to 297 cm?1, presumably caused by quantum confinement of phonons in the Ge nanocrystals. Rutherford backscattering spectrometry has been used to measure the thickness and Ge composition of the composite films. Size variation of Ge nanocrystals with annealing temperature has been discussed. The advantages of ABS over other methods are highlighted. 相似文献
16.
Xiao-hua Jia Hao-Jie Song Chun-ying Min Xue-Qiang Zhang 《Applied Physics A: Materials Science & Processing》2012,109(2):261-265
A composite of graphene (GE) supported by rod-like Fe3O4 nanocrystals has been fabricated by a simple one-step chemical route. X-ray diffraction and transmission electron microscopy results show that the Fe3O4 nanorods with diameters in the range of 15?C20 nm and lengths of 150?C200 nm were firmly assembled on the GE nanosheet surface. Magnetic property investigation indicated that the Fe3O4/GE composites exhibit a ferromagnetic behavior and possess a saturation magnetization of 50.11?emu?g?1. Moreover, Fe3O4/GE composites showed a very high adsorption capacity of Congo red. 相似文献
17.
Sintering-free nanocrystals of calcined hydroxyapatite (HAp) having a rod-like morphology were fabricated by calcination at
800°C for 1 h with an anti-sintering agent surrounding original HAp particles and the agent was subsequently removed after
calcination. The original HAp particles having a rod-like morphology with a size ranging from 30 to 80 nm (short axis) and
300 to 500 nm (long axis) were prepared by wet chemical process, and poly(acrylic acid, calcium salt) (PAA-Ca) was used as
the anti-sintering agent. In the case of calcination without additives, the mean size of HAp crystals dispersed in an ethanol
medium increased by about 4 times and the specific surface area of the crystals exhibited a 25% decrease compared to those
of the original HAp particles because of calcination-induced sintering among the crystals. On the other hand, the HAp crystals
calcined with the anti-sintering agent, PAA-Ca, could be dispersed in an ethanol medium at the same size as the original particles,
and they preserved the specific surface area after calcination. These results indicate that PAA-Ca and/or its thermally decomposed
product, CaO, surrounded the HAp particles and protected them against calcination-induced sintering during calcination. The
HAp crystals calcined with PAA-Ca showed high crystallinity, and no other calcium phosphate phases could be detected after
washing with water. 相似文献
18.
Yong Cao Qingze Jiao Hongbo Liu Xinliang Tang Yun Zhao 《Physica E: Low-dimensional Systems and Nanostructures》2009,41(10):1824-1827
A magnetic composite of nitrogen-doped carbon nanotubes (CNx) decorated with nickel nanoparticles was synthesized by a chemical precipitation and deoxidization method. The decorated CNx were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The XRD pattern showed that CNx, nickel nanoparticles and little nickel oxides coexisted in the composite, TEM observation indicated that nickel nanoparticles were highly dispersed on the outer walls of CNx, Magnetic measurements by VSM demonstrated that the saturated magnetization and remanence of CNx were improved, while the coercivity was lowered after decorating with nickel nanoparticles. 相似文献
19.
Fei Gao Martin A. Green Eun-Chel Cho Ivan Perez-Wurfl 《Applied Surface Science》2008,254(22):7527-7530
Multilayered Ge nanocrystals embedded in SiOxGeNy films have been fabricated on Si substrate by a (Ge + SiO2)/SiOxGeNy superlattice approach, using a rf magnetron sputtering technique with a Ge + SiO2 composite target and subsequent thermal annealing in N2 ambient at 750 °C for 30 min. X-ray diffraction (XRD) measurement indicated the formation of Ge nanocrystals with an average size estimated to be 5.4 nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode downward shifted to 299.4 cm−1, which was caused by quantum confinement of phonons in the Ge nanocrystals. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge + SiO2) layers. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the ‘Z’ growth direction. 相似文献
20.
J.Y. Fan X.L. Wu H.X. Li H.W. Liu G.S. Huang G.G. Siu P.K. Chu 《Applied Physics A: Materials Science & Processing》2006,82(3):485-487
A procedure for preparing 3C-SiC/SiO2 composite nanocrystals embedded in Si matrix that emit blue light is reported. Through electrochemical etching of polycrystalline
3C-SiC wafers followed by ultrasonic treatment in water bath, we fabricated luminescent colloidal 3C-SiC nanocrystals. Porous
Si samples that have been naturally oxidized in air for 12 h were immersed in agitated aqueous suspension of 3C-SiC nanocrystals
for 10 min and then dried in air, followed by annealing in argon atmosphere to form core-shell structured 3C-SiC/SiO2 nanocrystals embedded in Si matrix. Our result shows that the luminescence of 3C-SiC/SiO2 composite nanocrystals is very stable over time or under high temperature. As robust and stable Si-based solid blue-emitters,
they have important implications for engineering photonic components in optoelectronics and photonics.
PACS 78.67.Bf; 78.55.Hx; 78.66.Sq 相似文献