Perfect Surface Morphology Research Articles

A New Self-Healing Hydrogel Containing hucMSC-Derived Exosomes Promotes Bone Regeneration.

BackgroundFractures are a medical disease with a high incidence, and about 5–10% of patients need bone transplantation to fill the defect. In this study, we aimed to synthesize a new type of coralline hydroxyapatite (CHA)/silk fibroin (SF)/glycol chitosan (GCS)/difunctionalized polyethylene glycol (DF-PEG) self-healing hydrogel and to evaluate the therapeutic effects of this novel self-healing hydrogel as a human umbilical cord mesenchymal stem cells (hucMSC)-derived exosome carrier on bone defects in SD rat.MethodsHucMSCs were isolated from fetal umbilical cord tissue and characterized by surface antigen analysis and pluripotent differentiation in vitro. The cell supernatant after ultracentrifugation was collected to isolate exosomes, which were characterized by transmission electron microscopy and western blot analysis. In vitro cell induction experiments were performed to observe the effects of hucMSC-derived exosomes on the biological behavior of mouse osteoblast progenitor cells (mOPCs) and human umbilical vein endothelial cells (HUVECs). The CHA/SF/GCS/DF-PEG hydrogels were prepared using DF-PEG as the gel factor and then structural and physical properties were characterized. HucMSCs-derived exosomes were added to the hydrogel and their effects were evaluated in SD rats with induced femoral condyle defect. These effects were analyzed by X-ray and micro-CT imaging and H&E, Masson and immunohistochemistry staining.ResultsHucMSC-derived exosomes can promote osteogenic differentiation of mOPCs and promote the proliferation and migration of HUVECs. The CHA/SF/GCS/DF-PEG hydrogel has a high self-healing capacity, perfect surface morphology and the precipitated CHA crystals have a small size and low crystallinity similar to natural bone minerals. The MTT results showed that the hydrogel was non-toxic and have a good biocompatibility. The in vivo studies have shown that the hydrogel containing exosomes could effectively promote healing of rat bone defect. The histological analysis revealed more new bone tissue and morphogenetic protein 2 (BMP-2) in the hydrogel-exosome group. In addition, the hydrogel-exosome group had the highest microvessel density.ConclusionA self-healing CHA/SF/GCS/DF-PEG hydrogel was successfully prepared. The hydrogel has excellent comprehensive properties and is expected to become a new type of bone graft material. This hydrogel has the effect of promoting bone repair, which is more significant after the addition of hucMSC-derived exosomes.

On a Possibility to Fabricate YBCO Bridges with the Perfect Surface, Critical Temperature over 88 K and Critical Current Density up to 5 × 106 A/cm2

When manufacturing YBCO structures using traditional methods, a certain compromise is usually reached, namely: films with the relevant morphology, but with low electrophysical parameters are used. In this paper, it is shown that YBCO bridges 4 μm in width with the perfect surface morphology, i.e., without defects, with the critical current density Jc ≥ 3 × 106 A/cm2 at temperature 77 K and critical temperature Tc ≥ 88 K can be obtained using the master mask method. The perfect morphology of the bridge surface, values of the critical current density and critical temperature are retained even after the repeated (additional) deposition of the YBCO layer onto the structure with the master mask. The results obtained from the experiments with fifteen samples suggest that, unlike electrophysical characteristics, the fixation of the standard (basic) parameters of the growth process is not sufficient to obtain the perfect morphology of the YBCO film surface.

О возможности изготовления мостиков YBCO с совершенной поверхностью, критической температурой более 88 K и плотностью критического тока до 5·10-=SUP=-6-=/SUP=- A/cm-=SUP=-2-=/SUP=-

In the fabrication of YBCO structures by traditional methods, as a rule, some compromise is reached, namely, films with acceptable morphology are used, but with reduced electrophysical parameters. In this paper, it is shown that YBCO bridges up to 4 microns wide with perfect surface morphology, i.e. free from defects, with a critical current density Jc ≥ 3106 A/cm2 at a temperature T = 77 K and a critical temperature Tс ≥ 88 K. can be obtained using the preliminary topology mask method. Moreover, the perfect morphology of the bridge surface, the values of the critical current density and the critical temperature are preserved even after repeated (additional) deposition of the YBCO layer on the structure with the preliminary topology mask. Based on the results obtained in a series of fifteen samples, it is concluded that, in contrast to the electrophysical characteristics, it is not enough to fix the standard (basic) parameters of the growth process for the stable implementation of the perfect surface morphology of YBCO films.

Formation and Reduction of Large Growth Pits on 100 mm 4° 4H-SiC

The large growth pits (LGPs) dependence of substrate quality, growth rate, and C/Si ratio have been discussed in the 4H-SiC epitaxial growth on 100 mm N-type 4H-SiC Si-face substrates misoriented by 4° toward [11-20] with a warm-wall planetary reactor. The formation and reduction of LGPs have been investigated by adjusting the growth process parameters. With the optimized process, the perfect surface morphology with lower LGPs density has been obtained on the high quality substrate.

Preparation for Bragg grating of 808 nm distributed feedback laser diode**Project supported by the National Natural Science Foundation of China (No. 11474036), and the National Key Lab of High Power Semiconductor Lasers Foundations (No. 9140C310103120C3101).

The second-order Bragg grating structure of an 808 nm distributed feedback semiconductor laser diode was designed and optimized. The grating with a period of 240 nm was fabricated on GaAs substrate by holographic photolithography and wet etching. Images of optical microscopy, scanning electron microscopy and atomic force microscopy show that the grating has a period of 240 nm, duty cycle of 0.25, depth of 80 nm, with perfect surface morphology, good fringe continuity and uniformity.

Structural and magnetic properties of NiZn–ferrite thin films prepared by radio frequency magnetron sputtering

Polycrystalline NiZn–ferrite thin films were deposited on Si(100) substrate by rf magnetron sputtering, using targets with a nominal composition of Ni0.5Zn0.5Fe2O4. The effects of substrate condition, sputtering pressure, and postannealing on the structure and magnetic properties of thin films have been investigated. Our results show that the preferred orientation of the NiZn spinel film changed from (311) to (400) with increasing the Ar pressure from 0.8 to 1.6 Pa, meanwhile, the grain size also increased. Atomic force microscopy analysis indicates that perfect surface morphology of the film can be obtained at a relatively lower sputtering pressure of 1.0 Pa. The relative percentage of residual oxygen increases significantly on a condition of lower sputtering pressure, and plays an important role in film structure due to the strong molecular adsorption tendency of oxygen on the film surface during the deposition process. A thin film with a typical thickness of 1 μm, a saturation magnetization of 150 emu/cm3, and a coercivity of 8.8 kA/m has been obtained after annealing at 800 °C, which has the potential application in magnetic integrated circuits.

E-BEAM PUMPED VCSEL ON MOVPE-GROWN HEXAGONAL CdSSe/CdS MQW STRUCTURE

The first electron-beam pumped VCSEL was fabricated on CdSSe / CdS MQW structure grown by metalorganic vapor phase epitaxy on CdS substrate misoriented by 12–16° from (0001) towards (1010). Substrate misorientation results in more perfect surface morphology and intense cathodoluminesence. Lasing in the 535–590 nm spectral range was achieved at room temperature with different VCSELs. The laser power maximum of one VCSEL was as high as 2 W at RT, with electron energy 50 keV and current 1.7 mA. The threshold current was lower than that for the bulk CdSSe laser although the heterostructure used in the VCSEL has the type-II band alignment.

Epitaxial ZnO films grown by RF-assisted low-temperature CVD method

A low-temperature modification of the Chemical vapor deposition (CVD) growth with the RF-discharge plasma generated in CVD reactor during the growth process has been reported. This method allows us to significantly increase the effective pressure of atomic oxygen during the deposition, and to shift the stoichiometry of the growing film to oxygen excess. With RF activation we could lower the substrate temperature by more than 200°C, down to 420°C. The obtained zinc oxide/ α-sapphire films feature high crystallinity, perfect surface morphology and good electrical and optical properties at the expense of both the decrease in the width of the transition layer and amount of the uncontrolled impurities.

Ga0.72Al0.28As/Ga0.99Be0.01As heterojunction bipolar transistor grown by molecular beam epitaxy

We report the first heterojunction bipolar transistor (HBT) with base doping level as high as 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The device is grown by molecular beam epitaxy (MBE) with growth conditions adjusted to keep perfect surface morphology and to avoid dopant diffusion even at ultra-high doping levels. Maximum dc current gain of 10 is observed, for a base thickness of 40 nm. This is a new step in the optimization of HBT's structures for high-speed logic and microwave applications.

Investigation of surface roughness of molecular beam epitaxy Ga1−xAlxAs layers and its consequences on GaAs/Ga1−xAlxAs heterostructures

We report a detailed investigation of the surface morphology of Ga1−xAlxAs layers grown by molecular beam epitaxy (MBE) as a function of the layer parameters and the growth conditions. Under some conditions Ga1−xAlxAs layers exhibit a surface roughness characterized by a degradation of the in situ electron diffraction pattern and a very broad photoluminescence peak. The amplitude of the roughness, as observed by optical microscopy and measured by alphastep profiler, increases with the layer thickness, the growth rate r, and goes through a maximum for a substrate temperature TS≂650 °C, a flux ratio R=JV/JIII≂6 and an Al composition x≂0.5. However, smooth layers can be obtained using growth conditions like high TS (≥700 °C), low flux ratio (R≤2.5), or low growth rate (&amp;lt;0.5 μm/h). No surface roughness was observed for GaAs and AlAs layers. Moreover, a high concentration of foreign atoms at the surface of the growing layer (Sn dopant for example) yields to a quite perfect surface morphology. This paper also contains data on the consequences of Ga1−xAlxAs surface morphology on the crystalline and optical quality as characterized by x-ray diffraction and 300 K photoluminescence, of single and multiquantum well structures grown on a Ga0.7Al0.3As buffer layer. This quality which decreases with increasing thickness of the Ga0.7Al0.3As buffer layer can be restored using optimized growth conditions or a tin doping flux. Some explanations of the mechanism responsible for the surface morphology of ternary layers are discussed.

Ultra-high doping levels of GaAs with beryllium by molecular beam epitaxy

P-type doping levels up to 2×1020 at cm−3 in GaAs are presented using molecular beam epitaxy and beryllium as acceptor impurity. The epilayers present a perfect surface morphology and Be is not found to diffuse into the substrate, which permits the incorporation of such films into multilayer structures for device applications.

Photoluminescence of strained-layer superlattices

The strained-layer superlattices (SLS's) of In x Ga 1− x AsGaAs and the single hetero-structure of In x Ga 1− x As on GaAs were grown by MBE method. The samples obtained have a perfect surface morphology. The alloy composition of In x Ga 1− x As layer and the growth rate were determined with high accuracy by in situ observation of the intensity oscillation of RHEED pattern. Photoluminescence peak energies of SLS's are in agreement with the calculated value by the Kronig-Penny analysis.