Raman and cathodoluminescence spectroscopies of magnesium-substituted hydroxyapatite powders

2005 ◽  
Vol 20 (4) ◽  
pp. 1009-1016 ◽  
Author(s):  
S. Sprio ◽  
G. Pezzotti ◽  
G. Celotti ◽  
E. Landi ◽  
A. Tampieri
Keyword(s):  
Crystal Defects ◽  
Crystallographic Structure ◽  
Raman Analysis ◽  
Ca Ions ◽  
Synthetic Hydroxyapatite ◽  
Intensity Ratios ◽  
Amorphous Surface ◽  
Analytical Tools ◽  
New Evidence ◽  
Mg Doped

Stoichiometric and magnesium-substituted synthetic hydroxyapatite (HA) powders with different Mg contents were characterized by Raman and cathodoluminescence (CL) spectroscopies. The substitution of Ca ions by Mg is presently of great interest because it may improve activity in the first stage of the bone remodeling process. In this paper, we show new evidence that CL spectroscopy has the capability to detect the presence of crystal defects, related to the presence of magnesium substituting calcium in Mg-doped HA powders. The dependence of CL spectra of stoichiometric and magnesium-doped HA powders on their chemical composition was studied, and the results are compared with Raman analysis and data previously collected by other analytical tools. All the investigated powders showed five distinct CL bands; moreover, in magnesium-doped HA, an additional band at higher energy was found. The intensity ratios between selected CL bands showed some relationships with the powder crystallinity and the estimated amount of magnesium both in the HA lattice and in the amorphous surface layer; moreover the band observed only in magnesium-substituted powders could be directly related to the amount of magnesium entered into the HA lattice. Such results can contribute to improve the knowledge of the crystallographic structure of Mg-substituted hydroxyapatite.

scholarly journals Electrical and Magnetic Investigations of Magnesium-doped Epitaxial Gadolinium Nitride Thin Films

2021 ◽  
Author(s):  
◽  
Chang Min Lee
Keyword(s):  
Thin Films ◽  
Magnetic Measurements ◽  
Crystallographic Structure ◽  
X Ray Diffraction ◽  
Undoped Film ◽  
Mg Doping ◽  
Insulating Films ◽  
Gadolinium Nitride ◽  
Hall Effect Measurements ◽  
Mg Doped

<p>Mg-doped epitaxial GdN thin films with various Mg-doping levels were grown using molecular beam epitaxy, and their electric, magnetic and optoelectronic properties were investigated. Characterisation through X-ray diffraction technique showed that there is no systematic variation in the crystallographic structure of the films with increasing level of Mg-doping, for Mg concentrations up to ~5 x 10¹⁹ atoms/cm³. However, from Mg concentration ~2 x 10²⁰ atoms/cm³ a clear deterioration in the crystalline quality was seen. We observed an increase in the resistivity of the films from 0.002 Ωcm to 600 Ωcm at room temperature when increasing the Mg-doping level, resulting in semi-insulating films for Mg concentrations up to 5 x 10¹⁹ atoms/cm³. Hall effect measurements revealed that the n-type carrier concentration was reduced from 7 x 10²⁰ cm⁻³ for an undoped film to 5 x 10¹⁵ cm⁻³ for a heavily doped film, demonstrating electron compensation in GdN via Mg-doping. Magnetic measurements exhibited substantial contrasts in the films, with a Curie temperature of ~70 K for an undoped film reduced down to ~50 K for a heavily Mg-doped film. Finally, photoconductivity measurements showed that films with higher level of Mg-doping displaying a faster photoconductive response. The decay time of 13000 s for an undoped film was reduced to 170 s with a moderate level of Mg-doping, which raises the possibility of Mg impurities providing hole traps that act as recombination centres in n-type GdN films.</p>

scholarly journals Electrical and Magnetic Investigations of Magnesium-doped Epitaxial Gadolinium Nitride Thin Films

2021 ◽  
Author(s):  
◽  
Chang Min Lee
Keyword(s):  
Thin Films ◽  
Magnetic Measurements ◽  
Crystallographic Structure ◽  
X Ray Diffraction ◽  
Undoped Film ◽  
Mg Doping ◽  
Insulating Films ◽  
Gadolinium Nitride ◽  
Hall Effect Measurements ◽  
Mg Doped

<p>Mg-doped epitaxial GdN thin films with various Mg-doping levels were grown using molecular beam epitaxy, and their electric, magnetic and optoelectronic properties were investigated. Characterisation through X-ray diffraction technique showed that there is no systematic variation in the crystallographic structure of the films with increasing level of Mg-doping, for Mg concentrations up to ~5 x 10¹⁹ atoms/cm³. However, from Mg concentration ~2 x 10²⁰ atoms/cm³ a clear deterioration in the crystalline quality was seen. We observed an increase in the resistivity of the films from 0.002 Ωcm to 600 Ωcm at room temperature when increasing the Mg-doping level, resulting in semi-insulating films for Mg concentrations up to 5 x 10¹⁹ atoms/cm³. Hall effect measurements revealed that the n-type carrier concentration was reduced from 7 x 10²⁰ cm⁻³ for an undoped film to 5 x 10¹⁵ cm⁻³ for a heavily doped film, demonstrating electron compensation in GdN via Mg-doping. Magnetic measurements exhibited substantial contrasts in the films, with a Curie temperature of ~70 K for an undoped film reduced down to ~50 K for a heavily Mg-doped film. Finally, photoconductivity measurements showed that films with higher level of Mg-doping displaying a faster photoconductive response. The decay time of 13000 s for an undoped film was reduced to 170 s with a moderate level of Mg-doping, which raises the possibility of Mg impurities providing hole traps that act as recombination centres in n-type GdN films.</p>

scholarly journals 3D printing of crystallographic models and open access databases

2014 ◽  
Vol 70 (a1) ◽  
pp. C1278-C1278 ◽  
Author(s):  
Werner Kaminsky ◽  
Trevor Snyder ◽  
Peter Moeck
Keyword(s):  
Open Access ◽  
3D Printing ◽  
College Education ◽  
Structural Data ◽  
Data Bank ◽  
3D Models ◽  
Crystal Defects ◽  
Crystallographic Structure ◽  
Performance Improvements ◽  
Basic Infrastructure

Although introduced 30 years ago, cost and performance improvements have only recently made 3D printing affordable. The industry wide input file format for 3D printers incorporates explicit mesh - `STL' data. Molecules and crystal structures, when including symmetry, crystal morphologies, or crystal defects are encoded in the parametrical `CIF' syntax. Free software for converting directly CIF data to STL files has just been developed, available online [1]. First examples of printed 3D models from STL-files created with these programs include molecules of sucrose, herapathite [2a], caffeine, humulone [2b], an alpha-quartz crystal and its Japanese {112} twin or a brilliant cut diamond. Far more CIF encoded models are available, even open access. The Crystallography Open Database (COD) features over 245,000 entries and has recently developed into the world's premier open-access source for structures of small to medium unit cell-sized inorganic and molecular crystals [3a], complementing the well-established open-access Worldwide Protein Data Bank [3b]. The Cambridge Crystallographic Data Centre in the United Kingdom provides crystal structure data of small (organic) molecules free for bona fide research [3c]. Structural data on inorganic crystals, metals and alloys can be obtained free of charge from the Inorganic Material Database (AtomWork) [3d]. Related to the COD, the crystallographic open-access databases [3e] ("COD offspring") provide CIF data for interdisciplinary college education. With this basic infrastructure in place, any interested college educator may print out her or his favorite crystallographic structure model in 3D and use it in hands on class room demonstrations [3f].

Crystal Defects in Epitaxial Layer on Nitrogen-doped Czochralski-grown Silicon Substrate (I) –Investigation of the Crystallographic Structure–

2004 ◽  
Vol 43 (4A) ◽  
pp. 1241-1246 ◽  
Author(s):  
Katsuhiko Nakai ◽  
Koichi Kitahara ◽  
Yasumitsu Ohta ◽  
Atsushi Ikari ◽  
Masahiro Tanaka
Keyword(s):  
Epitaxial Layer ◽  
Silicon Substrate ◽  
Crystal Defects ◽  
Crystallographic Structure ◽  
Nitrogen Doped

scholarly journals Origin of the biphase nature and surface roughness of biogenic calcite secreted by the giant barnacle Austromegabalanus psittacus

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Antonio G. Checa ◽  
Elena Macías-Sánchez ◽  
Alejandro B. Rodríguez-Navarro ◽  
Antonio Sánchez-Navas ◽  
Nelson A. Lagos
Keyword(s):  
Surface Roughness ◽  
Complex Shape ◽  
Crystal Surface ◽  
Crystallization Front ◽  
Amorphous Structure ◽  
Crystallographic Structure ◽  
Amorphous Calcium Carbonate ◽  
Attachment Model ◽  
Biphase Structure ◽  
New Evidence

Abstract The calcite grains forming the wall plates of the giant barnacle Austramegabalanus psittacus have a distinctive surface roughness made of variously sized crystalline nanoprotrusions covered by extremely thin amorphous pellicles. This biphase (crystalline-amorphous) structure also penetrates through the crystal’s interiors, forming a web-like structure. Nanoprotrusions very frequently elongate following directions related to the crystallographic structure of calcite, in particular, the <− 441> directions, which are the strongest periodic bond chains (PBCs) in calcite. We propose that the formation of elongated nanoprotrusions happens during the crystallization of calcite from a precursor amorphous calcium carbonate (ACC). This is because biomolecules integrated within the ACC are expelled from such PBCs due to the force of crystallization, with the consequent formation of uninterrupted crystalline nanorods. Expelled biomolecules accumulate in adjacent regions, thereby stabilizing small pellicle-like volumes of ACC. With growth, such pellicles become occluded within the crystal. In summary, the surface roughness of the biomineral surface reflects the complex shape of the crystallization front, and the biphase structure provides evidence for crystallization from an amorphous precursor. The surface roughness is generally explained as resulting from the attachment of ACC particles to the crystal surface, which later crystallised in concordance with the crystal lattice. If this was the case, the nanoprotrusions do not reflect the size and shape of any precursor particle. Accordingly, the particle attachment model for biomineral formation should seek new evidence.

Controllable Luminescent Properties of Phosphors Sr2.97-XCaxMgSi2O8: Eu0.012+, Dy0.023+ by Adjusting Sr/Ca Ratio

2010 ◽  
Vol 663-665 ◽  
pp. 118-124
Author(s):  
Jun Fu Chu ◽  
Yi Hua Hu ◽  
Hai Wang Yin ◽  
Yi Wu Hao
Keyword(s):  
Size Variation ◽  
Emission Spectra ◽  
Luminescent Properties ◽  
Crystal Defects ◽  
Co Doping ◽  
Long Afterglow ◽  
Ion Doping ◽  
Ca Ions ◽  
Small Change ◽  
Reductive Atmosphere

Divalent europium and trivalent dysprosium co-doping in the compounds Sr2.97-xCaxMgSi2O8 (x=0, 0.5, 1.5, 2, 2.5, 2.97) produces phosphors of high luminescence yield. These phosphors were prepared at high temperature and weak reductive atmosphere. The ratio of Eu/Dy is 1/2. The phosphors were characterized for their crystal phases by x-ray powder diffraction. Slight shifts of the peaks in the structure, which indicate a small change of the interplanar crystal spacing, were observed for each different x’s. The interplanar spacing becomes narrow as increasing the value of x. These phosphors respond well to the ultraviolet excitation. The peak of the emission band occurs at progressively longer wavelength and widens as the ratio of alkaline earth Sr/Ca ions is decreased. The emission peaks of the phosphors indicated on the emission spectra range from 463nm to 490nm. It is probably due to the influence of 5d electron states of Eu2+ in the crystal field because of atomic size variation causing crystal defects. Dy3+ ion doping in the phosphor generates deep traps, which results in long afterglow phosphorescence. As the proportion of Ca in the composition increases, the attenuation time of the phosphors becomes short.

Systematic effects in observed parallaxes

1978 ◽  
Vol 48 ◽  
pp. 31-35
Author(s):  
R. B. Hanson
Keyword(s):  
Error Estimates ◽  
Zero Point ◽  
Absolute Zero ◽  
Apparent Magnitude ◽  
Coherent System ◽  
Preliminary Results ◽  
General Catalogue ◽  
Systematic Effects ◽  
New Evidence ◽  
Right Ascension

Several outstanding problems affecting the existing parallaxes should be resolved to form a coherent system for the new General Catalogue proposed by van Altena, as well as to improve luminosity calibrations and other parallax applications. Lutz has reviewed several of these problems, such as: (A) systematic differences between observatories, (B) external error estimates, (C) the absolute zero point, and (D) systematic observational effects (in right ascension, declination, apparent magnitude, etc.). Here we explore the use of cluster and spectroscopic parallaxes, and the distributions of observed parallaxes, to bring new evidence to bear on these classic problems. Several preliminary results have been obtained.

Ultrastructural Aspects of Golgi Complex Function in Parathyroid Cells of Winter Frogs

1973 ◽  
Vol 31 ◽  
pp. 680-681
Author(s):  
William J. Dougherty
Keyword(s):  
Golgi Complex ◽  
Secretory Granules ◽  
Complex Function ◽  
Secretory Activity ◽  
Secretory Proteins ◽  
Perivascular Spaces ◽  
Pituitary Cells ◽  
Electron Microscopic ◽  
Ca Ions ◽  
Regulation Of Secretion

The regulation of secretion in exocrine and endocrine cells has long been of interest. Electron microscopic and other studies have demonstrated that secretory proteins synthesized on ribosomes are transported by the rough ER to the Golgi complex where they are concentrated into secretory granules. During active secretion, secretory granules fuse with the cell membrane, liberating and discharging their contents into the perivascular spaces. When secretory activity is suppressed in anterior pituitary cells, undischarged secretory granules may be degraded by lysosomes. In the parathyroid gland, evidence indicates that the level of blood Ca ions regulates both the production and release of parathormone. Thus, when serum Ca is low, synthesis and release of parathormone are both stimulated; when serum Ca is elevated, these processes are inhibited.

The Imaging of Crystal Structures and Crystal Defects

1978 ◽  
Vol 36 (3) ◽  
pp. 207-217
Author(s):  
J.M. Cowley
Keyword(s):  
Electron Microscope ◽  
Crystal Structures ◽  
Phase Contrast ◽  
Crystal Defects ◽  
Atom Density ◽  
Lack Of Information ◽  
Spatial Frequencies

The problem of "understandinq" electron microscope imaqes becomes more acute as the resolution is improved. The naive interpretation of an imaqe as representinq the projection of an atom density becomes less and less appropriate. We are increasinqly forced to face the complexities of coherent imaqinq of what are essentially phase objects. Most electron microscopists are now aware that, for very thin weakly scatterinq objects such as thin unstained bioloqical specimens, hiqh resolution imaqes are best obtained near the optimum defocus, as prescribed by Scherzer, where the phase contrast imaqe qives a qood representation of the projected potential, apart from a lack of information on the lower spatial frequencies. But phase contrast imaqinq is never simple except in idealized limitinq cases.

Microstructural comparison of synthetic bioceramics with natural bioceramics

1991 ◽  
Vol 49 ◽  
pp. 38-39
Author(s):  
Shulin Wen ◽  
Jingwei Feng ◽  
A. Krajewski ◽  
A. Ravaglioli
Keyword(s):  
Recent Work ◽  
Human Body ◽  
Human Tissues ◽  
Main Constituent ◽  
Laboratory Furnace ◽  
Chinese Adult ◽  
Human Enamel ◽  
Biological Compatibility ◽  
Synthetic Hydroxyapatite ◽  
Synthetic Work

Hydroxyapatite bioceramics has attracted many material scientists as it is the main constituent of the bone and the teeth in human body. The synthesis of the bioceramics has been performed for years. Nowadays, the synthetic work is not only focused on the hydroapatite but also on the fluorapatite and chlorapatite bioceramics since later materials have also biological compatibility with human tissues; and they may also be very promising for clinic purpose. However, in comparison of the synthetic bioceramics with natural one on microstructure, a great differences were observed according to our previous results. We have investigated these differences further in this work since they are very important to appraise the synthetic bioceramics for their clinic application.The synthetic hydroxyapatite and chlorapatite were prepared according to A. Krajewski and A. Ravaglioli and their recent work. The briquettes from different hydroxyapatite or chlorapatite powders were fired in a laboratory furnace at the temperature of 900-1300°C. The samples of human enamel selected for the comparison with synthetic bioceramics were from Chinese adult teeth.

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