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采用扫描电镜(SEM)和电子背散射衍射(EBSD)技术,观察和分析了GaAs和GaN晶片热压键合的界面热应力和晶片键合质量.利用EBSD测量了GaAs-GaN键合界面的菊池花样质量、晶格转动、晶格错配和位错密度等应力敏感参数.结果表明,晶片键合质量良好,键合界面中心区域的热应力小于边缘区域的热应力.GaN层和GaAs层中的应力影响范围,在中心区域分别约为100 nm和300 nm,在边缘区域分别约为100 nm和500nm.EBSD显示的应力分布图与模拟应力场相似.模拟和计算表明,最大剥离应力和剪切应力分布在键合界面的边缘.剥离应力是导致晶片解键合的主要原因. 相似文献
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Microbubbles promise to enhance the efficiency of ultrasound-mediated drug delivery and gene therapy by taking advantage of artificial cavitation nuclei.The purpose of this study is to examine the ultrasound-induced hemolysis in the application of drug delivery in the presence of microbubbles.To achieve this goal,human red blood cells mixed with microbubbles were exposed to 1-MHz pulsed ultrasound.The hemolysis level was measured by a flow cytometry,and the cavitation dose was detected by a passive cavitation detecting system.The results demonstrate that larger cavitation dose would be generated with the increase of acoustic pressure,which might give rise to the enhancement of hemolysis.Besides the experimental observations,the acoustic pressure dependence of the radial oscillation of microbubble was theoretically estimated.The comparison between the experimental and calculation results indicates that the hemolysis should be highly correlated to the acoustic cavitation. 相似文献
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Microstreaming velocity field and shear stress created by an oscillating encapsulated microbubble near a cell membrane 下载免费PDF全文
Sonoporation mediated by microbubbles is being extensively studied as a promising technology to facilitate gene/drug delivery to cells. However, the theoretical study regarding the mechanisms involved in sonoporation is still in its infancy. Microstreaming generated by pulsating microbubble near the cell membrane is regarded as one of the most important mechanisms in the sonoporation process. Here, based on an encapsulated microbubble dynamic model with considering nonlinear rheological effects of both shell elasticity and viscosity, the microstreaming velocity field and shear stress generated by an oscillating microbubble near the cell membrane are theoretically simulated. Some factors that might affect the behaviors of microstreaming are thoroughly investigated, including the distance between the bubble center and cell membrane (d), shell elasticity (χ), and shell viscosity (κ). The results show that (i) the presence of cell membrane can result in asymmetric microstreaming velocity field, while the constrained effect of the membrane wall decays with increasing the bubble-cell distance; (ii) the bubble resonance frequency increases with the increase in d and χ, and the decrease in κ, although it is more dominated by the variation of shell elasticity; and (iii) the maximal microstreaming shear stress on the cell membrane increases rapidly with reducing the d, χ, and κ. The results suggest that microbubbles with softer and less viscous shell materials might be preferred to achieve more efficient sonoporation outcomes, and it is better to have bubbles located in the immediate vicinity of the cell membrane. 相似文献
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Ultrasound-mediated transdermal drug delivery of fluorescent nanoparticles and hyaluronic acid into porcine skin in vitro 下载免费PDF全文
Transdermal drug delivery(TDD) can effectively bypass the first-pass effect. In this paper, ultrasound-facilitated TDD on fresh porcine skin was studied under various acoustic parameters, including frequency, amplitude, and exposure time. The delivery of yellow–green fluorescent nanoparticles and high molecular weight hyaluronic acid(HA) in the skin samples was observed by laser confocal microscopy and ultraviolet spectrometry, respectively. The results showed that,with the application of ultrasound exposures, the permeability of the skin to these markers(e.g., their penetration depth and concentration) could be raised above its passive diffusion permeability. Moreover, ultrasound-facilitated TDD was also tested with/without the presence of ultrasound contrast agents(UCAs). When the ultrasound was applied without UCAs,low ultrasound frequency will give a better drug delivery effect than high frequency, but the penetration depth was less likely to exceed 200 μm. However, with the help of the ultrasound-induced microbubble cavitation effect, both the penetration depth and concentration in the skin were significantly enhanced even more. The best ultrasound-facilitated TDD could be achieved with a drug penetration depth of over 600 μm, and the penetration concentrations of fluorescent nanoparticles and HA increased up to about 4–5 folds. In order to get better understanding of ultrasound-facilitated TDD, scanning electron microscopy was used to examine the surface morphology of skin samples, which showed that the skin structure changed greatly under the treatment of ultrasound and UCA. The present work suggests that, for TDD applications(e.g., nanoparticle drug carriers, transdermal patches and cosmetics), protocols and methods presented in this paper are potentially useful. 相似文献
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Strontium titanate(SrTiO3),which is a crucial perovskite oxide with a direct energy band gap of 3.2 eV,holds great promise for ultraviolet(UV)photodetection.However,the response performance of the conventional SrTiO3-based photodetectors is limited by the large relative dielectric constant of the material,which reduces the internal electric field for electron-hole pair separation to form a current collected by electrodes.Recently,graphene/semiconductor hybrid photodetectors by van-der-Waals heteroepitaxy method demonstrate ultrahigh sensitivity,which is benefit from the interface junction architecture and then prolonged lifetime of photoexcited carriers.Here,a graphene/SrTiO3 interface-based photodetector is demonstrated with an ultrahigh responsivity of 1.2×106 A/W at the wavelength of 325 nm and~2.4×104 A/W at 261 nm.The corresponding response time is in the order of~ms.Compared with graphene/GaN interface junctionbased hybrid photodetectors,~2 orders of magnitude improvement of the ultrahigh responsivity originates from a gain mechanism which correlates with the large work function difference induced long photo-carrier lifetime as well as the low background carrier density.The performance of high responsivity and fast response speed facilitates SrTiO3 material for further efforts seeking practical applications. 相似文献
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Electron transfer reactions take place readily between 2, 2, 6, 6-tetramethylpiperidine oxoammonium ions (1a, 1b) and phenothiazines (2a—2g), giving corresponding nitroxides (3a, 3b) and phenothiazine radical cations (4a—4g). The rate constants for the electron self-exchange reactions between 1 and 3, as well as between 2 and 4, are determined by EPR and ~1H NMR line-broadening effect in acetonitrile. By application of the Marcus theory, the kinetics of the cross-exchange reactions between 1 and 2 is studied. 相似文献