First nucleation steps during deposition of SiO2 thin films by plasma enhanced chemical vapour deposition

The initial nucleation stages during deposition of SiO₂ by remote plasma enhanced chemical vapour deposition (PECVD) have been monitored by XPS inelastic peak shape analysis. Experiments have been carried out on two substrates, a flat ZrO₂ thin film and a silicon wafer with a native silicon oxide layer on its surface. For the two substrates it is found that PECVD SiO₂ grows in the form of islands. When the SiO₂ particles reach heights close to 10 nm they coalesce and cover completely the substrate surface. The particle formation mechanism has been confirmed by TEM observation of the particles grown on silicon substrates. The kinetic Monte Carlo simulation of the nucleation and growth of the SiO₂ particles has shown that formation of islands is favoured under PECVD conditions because the plasma species may reach the substrate surface according to off-perpendicular directions. The average energy of these species is the main parameter used to describe their angular distribution function, while the reactivity of the surface is another key parameter used in the simulations.     

Microstructural features and domain formation in (Ba,Sr)2TiSi2O8 fresnoites

The formation and co-existence of crystallographically modulated and non-modulated regions in (Ba,Sr)₂TiSi₂O₈ fresnoites is reviewed, particularly the dependence on local composition. It is shown that perturbations of the average fresnoite structure, determined from appreciable single crystals, are in some cases better described as nanometric domain intergrowths where departures from ideal stoichiometry are characteristics of incommensuration, while modulation is absent from volumes that are less perturbed chemically. Evidence for this differentiation is obtained from selected area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images. The domains are readily distinguished by their unique contrast in bright field electron micrographs. Fourier reconstructions of HRTEM images collected from areas with darker contrast show that modulation can change within relatively small volumes. Nearby areas with lighter contrast were found by SAED to be free of structural disorder and incommensurate reflections.     

Multilayers of Ge nanocrystals embedded in Al2O3 matrix: Structural and electrical studies

In this paper, Ge/Al₂O₃ multilayer systems were grown by pulsed laser ablation. The grown samples were annealed at 900 °C to promote the formation of Ge nanocrystals. Rutherford backscattering spectroscopy and transmission electron microscopy confirmed the presence of a multilayer system. Grazing incidence small angles X-ray scattering technique demonstrates the formation of Ge nanoclusters formed between alumina layers. Room temperature I-V measurements showed weak carrier trapping in the system. This was explained by the leakage caused by Ge diffusion through the multilayer.     

Relation of structure to performance characteristics of monolithic and perfusive stationary phases

Commercially available polymer-based monolithic and perfusive stationary phases were evaluated for their applicability in chromatography of biologics. Information on bed geometry, including that from electron microscopy (EM), was used to interpret and predict accessible volumes, binding capacities, and pressure drops. For preparative purification of biologics up to at least 7 nm in diameter, monoliths and perfusive resins are inferior to conventional stationary phases due to their low binding capacities (20–30 g/L for BSA). For larger biologics, up to several hundred nanometers in diameter, calculations from EM images predict a potential increase in binding capacity to nearly 100 g/L. The accessible volume for adenovirus calculated from the EM images matched the experimental value. While the pores of perfusive resins are essentially inaccessible to adenovirus under binding conditions, under non-adsorbing conditions the accessible intrabead porosity is almost as large as the interbead porosity. Modeling of breakthrough curves showed that the experimentally observed slow approach to full saturation can be explained by the distribution of pore sizes.     

TEM_(00)模转换成TEM_(10)模的二元光学元件衍射效果一维数值模拟

在用二元光学原理将氦氖高斯基模光束转换成 TEM10 模的一维设计基础上 ,模拟计算了距离的变化对衍射效果的影响。计算结果显示 :在距离偏离设计值± 1 .5 mm时 ,模拟光强值与预期光强值的相对平均误差小于 1 .8% ,与设计结果基本相同     

Structural Analysis of Electroplated Amorphous-Nanocrystalline Ni-W

 Ductile nickel-tungsten (Ni-W) alloys containing about 20–21 at.%W were electroplated onto copper substrates. The development of the amorphous/nanocrystalline microstructure towards a complete crystallization by isochronal heat treatments in vacuum was monitored by different methods. For medium annealing temperatures a solid-solution of W in the fcc-Ni lattice was achieved resulting in an increased hardness. For temperatures of 600 °C and upward recrystallization started and thermodynamically stable intermetallic compounds like Ni₄W and NiW were formed. A third phase, containing more than 80 at.%W was also detected but could not be identified so far. Only by combination of different methods and especially by use of analytical TEM structural analysis and phase identification in these amorphous-nanocrystalline Ni-W alloys were successful.     

Advanced FIB sample preparation techniques for high resolution TEM investigations of HEMT structures

In this paper advanced sample preparation techniques based on focused ion beam (FIB) optimized for TEM investigation of high electron mobility transistor (HEMT) structures are presented. It is shown that the usage of an innovative in-situ lift-out method combined with X2 window and backside milling techniques as well as live thickness control and end point detection can significantly improve the quality of electron transparent samples required for high resolution TEM investigations. This advanced preparation flow is evaluated and demonstrated at GaN HEMT structures for atomic resolution TEM investigation.     

Classification Performance of a Low Pressure Differential Mobility Analyzer for Nanometer-sized Particles

Size distribution measurements and classification tests by a low pressure differential mobility analyzer (LPDMA) for nanometer-sized silver particles and cesium iodide particles under low pressure conditions (123–300 Torr) were performed using a transmission electron microscope (TEM) and the tandem DMA technique. When the ratio of the sheath gas flow rate and the aerosol gas flow rate was set at 5 : 1, the targeted sizes calculated from the classification voltage applied to the LPDMA at 160 Torr are found to be in good correlation with the count mean Feret diameter obtained from the TEM observation of the particles collected after a classification ranging from 6 to 25 nm, although the targeted sizes set by the LPDMA were approximately 15% greater than the count mean Feret diameter measured by the TEM after classification. The geometric standard deviations of DMA-classified particles measured by TEM and those obtained from the tandem DMA method ranged from 1.08 to 1.17 and from 1.05 to 1.13, respectively. They were slightly greater than the ideal geometric standard deviations (1.05) of the particles classified with the LPDMA, which was calculated by neglecting the broadening effects due to Brownian diffusion. We experimentally demonstrated the validity of our LPDMA system for size measurements and classification of the nanometer-sized particles under low pressure conditions.     

The effects of thermal annealing on the microstructural,optical and electrical properties of beta silicon carbide films implanted with boron or nitrogen

The effects of annealing of B or N dual implanted regions in 15-20 Μm thick monocrystalline Β-SiC films has been investigated using cross-sectional TEM, SIMS, Raman spectroscopy, C-V and sheet resistance measurements. Implantation resulted in buried amorphous regions (in the B films) or highly disordered regions (in the N films) and residually strained regions. Annealing for 300 s at selected temperatures between 1173 and 2073 K caused structural reordering, precipitation (in the B samples) and dopant diffusion, as the temperature was progressively increased. Only slight changes were noted in the sheet resistance of either type of sample as a result of annealing to 1973 K. However, the values of this parameter decreased markedly atT > 1973 K in both implanted and as-grown samples. Thus, this phenomenon was most probably caused by the formation of additionaln-type defects in the bulk of the materials. Presented at the 1985 Electronic Materials Conference, Boulder, CO, June, 1985.     

TEM电子束诱导硅表面氧化的分析

洁净硅表面在电子束的作用下产生诱导氧化现象,在AES分析中已得到证实。本文利用TEM 200CX型电镜研究了洁净硅表面在电子束作用下的结果,实验表明,在TEM中同样存在着电子束诱导硅表面氧化的现象,氧化生成了SiO_2微晶,其氧主要来自硅晶体内氧的局部富集和电镜中残余气体在硅表面的吸附。