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971.
A transitory etching regime after SiO2 dissolution and before bulk Si(1 1 1) etching in neutral NH4F solutions was monitored by in situ Brewster-angle reflectometry (BAR). An observed intermediate increase of the BAR reflectance signal is attributed to a fast dissolution of a stressed/strained interlayer beneath the SiO2/Si(1 1 1) interface. Similar effects were observed on thin thermal oxides (18.2 nm), grown on float zone silicon, as well as on ultra-thin native oxides (1.2 nm) on Czochralsky silicon. Native oxide covered samples showed an increased surface roughness in the course of interlayer dissolution while the surface is progressively covered with compounds of fluorinated silicon. The etch rate, determined by atomic force microscopy (AFM) and compared to the etch rate of bulk silicon, is increased by a factor of four. In the limit of extended etching, the known low etch rates for silicon in 40% NH4F are observed. Structural and chemical properties of the interfacial layer were analyzed by synchrotron radiation photoelectron spectroscopy (SRPES) which confirmed the presence of Si3+/4+ valence states throughout the interlayer and by near open-circuit potential (N-OCP) dark current measurements. As a result, oxide etch rates in NH4F in the pH-range 7–8 as well as the silicon interlayer depth can be assessed by in situ BAR. 相似文献
972.
The physical properties of magnetic domain walls and electrical conductivity of permalloy thin films under external magnetic fields were studied. Using a magnetic force microscope (MFM), we observed the variation of domain configurations with the change of applied magnetic field for different film thicknesses of 245, 320, and 415 nm. A superconducting quantum interference device (SQUID) was exploited to measure the magnetization loop for the applied magnetic field either parallel or perpendicular to the normal direction of the surface. We also found that the resistivity increases significantly as the electrical current conduction changed from parallel to perpendicular to the domain walls. 相似文献
973.
Using high-resolution atomic force microscope we observed in ambient atmosphere the slow morphological transitions of the incipient adlayer of gold grown on (0 0 0 1) sapphire substrate by pulsed laser deposition. The equivalent average uniform thickness of the gold deposition was about 0.55 Å, which is about one-fourth of its monolayer. A dynamic simulation revealed that about 10% of the gold was implanted into the substrate up to the depth of about 3.3 nm and the top monolayer of the sapphire surface was almost completely depleted of oxygen atoms due to the preferential sputtering by the plume particles. The gold adlayer transformed into a labile phase which enhanced the surface roughness and had a preferred orientation of a wavy structure during 24 h of the deposition. The auto-correlation function of this wavy structure in labile metastable phase revealed two-fold symmetry and provided a preferential size of about 4 nm (peak to peak) with a mean separation of 8 nm. At the end of about 6 days this phase was found to completely transform into an apparently de-wetted phase of beads with average in-plane diameter of ∼20 nm and height of ∼7 nm having large size distribution. Each bead was seen to have coating of a concentric corona layer, which might be that of the condensed moisture or other gaseous species from atmosphere because subjecting these samples to vacuum removed this layer. These observations shed light on the dynamics of the pulsed laser deposited metastable gold adlayer in the incipient stage of its growth on sapphire and their wetting or de-wetting mechanisms in ambient atmosphere. 相似文献
974.
介绍了一种全新的基于飞秒激光局域场加强效应的纳米加工技术,通过使用了微焦级别脉宽为130 fs、波长800 nm的飞秒激光照射于原子力显微镜的探针针尖,利用其局域场加强效应在金薄膜表面加工出各种纳米图形。对加工参数对加工线宽的影响中,我们发现了随着加工能量的减小和加工速度的不断增大将导致加工线宽不断减小,最终达到了极限线宽(~10 nm)。这项技术可以广泛的应用与各种材料的加工中,尤其适合各种金属薄膜的加工,特别是结合了现有的自动化控制系统更是可以加工出任意复杂的二维纳米图形。 相似文献
975.
Manoj K. Singh Hyun M. Jang H. C. Gupta Ram S. Katiyar 《Journal of Raman spectroscopy : JRS》2008,39(7):842-848
The first‐ and second‐order Raman‐active phonons in the orthorhombic Pbnm NdFeO3 single crystals were studied by means of polarized Raman scattering and lattice dynamics computations (LDC). The zone‐center phonons of Ag symmetry were distinguished from the B1g eigenmodes by performing polarized Raman scattering experiments using two parallel polarization configurations, X′(ZZ)X′ and Z(X′X′)Z. With the help of LDC, we were able to assign most of the observed Raman‐active modes, including phonons of B2g and B3g symmetry. The LDC results indicated that among the 16 force constants employed, the one corresponding to the stretching vibration between the central Fe cation and the axial oxygen atom in a FeO6 octahedron unit had the largest value. This suggests that the B‐site Fe cation is more tightly bound to the axial O1 ion than the other two equatorial O2 ions. It was further shown that at higher wavenumbers, the displacement of oxygen atoms contributed dominantly to the zone‐center vibrations. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
976.
Live morphological analysis of taxol-induced cytoplasmic vacuolization [corrected] in human lung adenocarcinoma cells 总被引:1,自引:0,他引:1
Taxol (paclitaxel), one of the most active cancer chemotherapeutic agents, can cause programmed cell death (PCD) and cytoplasmic vacuolization. The objective of this study was to analyze the morphological characteristics induced by taxol. Human lung adenocarcinoma (ASTC-a-1) cells were exposed to various concentration of taxol. CCK-8 was used to assay the cell viability. Atomic force microscopy (AFM), plasmid transfection and confocal fluorescence microscopy were performed to image the cells morphological change induced by taxol. Fluorescence resonance energy transfer (FRET) was used to monitor the caspase-3 activation in living cells during taxol-induced cell death. Cells treated with taxol exhibited significant swelling and cytoplasmic vacuolization which may be due to endoplasmic reticulum (ER) vacuolization. Caspase-3 was not activated during taxol-induced cytoplasmic vacuolization and cell death. These findings suggest that taxol induces caspase-3-independent cytoplasmic vacuolization, cell swelling and cell death through ER vacuolization. 相似文献
977.
978.
979.
研究了负折射率材料对产生Casimir排斥效应的影响. 两材料板间的Casimir排斥力的发生取决于两板以及其间媒质的电磁特性,通过理论与数值结果的分析研究给出电磁特性所影响排斥力的产生趋势. 对于由Drude-Lorentz型色散关系描述等效介电常数和磁导率的负折射率材料,调节各特征频率参数可实现Casimir排斥效应.
关键词:
Casimir排斥力
负折射率材料
Drude-Lorentz型色散关系 相似文献
980.
以界面摩擦为研究对象,探讨了基于耦合振子模型(coupled-oscillator model)的滑动摩擦微观机理,分析了滑动过程中的能量耗散问题. 采用Maugis-Dugdal接触模型替代界面摩擦中的Lennard-Jones势能,并将该模型融入耦合振子模型之中,通过计算振子在一个周期内的能量增加值,推导出了界面摩擦力的理论计算公式. 理论分析表明,对于探针-试样接触系统,滑动摩擦力近似随着法向载荷的2/3次方增加,这与纳米摩擦学经典理论是相符的.理论计算结果与超高真空原子力显微镜镀铜探针在Cu(111)晶面扫描实验结果符合良好,表明本文提出的理论和方法可行.
关键词:
耦合振子模型
界面摩擦
摩擦力
法向载荷 相似文献