The nanogranular nature of C-S-H

Despite its ubiquitous presence as binding phase in all cementitious materials, the mechanical behavior of calcium-silicate-hydrates (C-S-H) is still an enigma that has deceived many decoding attempts from experimental and theoretical sides. In this paper, we propose and validate a new technique and experimental protocol to rationally assess the nanomechanical behavior of C-S-H based on a statistical analysis of hundreds of nanoindentation tests. By means of this grid indentation technique we identify in situ two structurally distinct but compositionally similar C-S-H phases heretofore hypothesized to exist as low density (LD) C-S-H and high density (HD) C-S-H, or outer and inner products. The main finding of this paper is that both phases exhibit a unique nanogranular behavior which is driven by particle-to-particle contact forces rather than by mineral properties. We argue that this nanomechanical blueprint of material invariant behavior of C-S-H is a consequence of the hydration reactions during which precipitating C-S-H nanoparticles percolate generating contact surfaces. As hydration proceeds, these nanoparticles pack closer to center on-average around two characteristic limit packing densities, the random packing limit (η=64%) and the ordered face-centered cubic (fcc) or hexagonal close-packed (hcp) packing limit (η=74%), forming a characteristic LD C-S-H and HD C-S-H phase.     

原子力显微镜针尖诱导聚氧乙烯熔体结晶的研究

原子力显微镜(AFM)是研究高分子结晶行为的一种重要实验手段.在使用AFM原位观察高分子结晶时,为保证能真实地反映结晶过程,一个必须注意的问题是要避免AFM针尖的影响.与此同时,人们考察了在AFM扫描时针尖诱导高分子结晶成核的情况.若使用AFM接触模式(contactmode),扫描时容易造     

Polymer-silica nanocomposites prepared by sol-gel technique: Nanoindentation and tapping mode AFM studies

Polymer-silica nanocomposites based on poly(2-hydroxyethyl acrylate) (PHEA) have been prepared by the simultaneous polymerization of the organic and the silica phases in a sol-gel process with the silica precursor tetraethyl orthosilicate (TEOS). The structure of this system is investigated using atomic force microscopy (AFM) in the tapping mode and in nanoindentation experiments. The structure of the PHEA/silica hybrids strongly depends on the ratio of both components in the system. For silica weight fractions lower than 0.15, the system consists of aggregated silica particles dispersed in the organic matrix; above that concentration of silica the structure is co-continuous with that of the organic matrix, similarly to two interpenetrated networks.     

Ion implantation for semiconductor processing

The potential advantages of ion implantation have been exploited in virtually every kind of semiconductor device. Several commercially important devices owe their existence to this technique.

Ion implantation provides precise control over the amount of dopant, concentration profile and lateral dimensions in device fabrication. The high degree of uniformity and reproducibility have made it possible to produce sophisticated devices and integrated circuits with high yield and tight tolerances. This is a truly planar process. It is possible to achieve high doping concentrations with relatively lower processing temperatures thereby avoiding lifetime degradation. The process is carried out in an inherently clean environment. A wide range of dopants is available and one is not limited by the particular properties of the substrate. There is great flexibility in choice of masking materials and self-alignment of doped regions in MOS devices is facilitated.

The increasing impact of ion implantation on device technology is discussed with reference to some recent developments. Specific commercially manufactured devices are mentioned.

Ion implantation machines continue to undergo development aimed at higher throughputs and cleaner vacuum. There is the need for greater reliability of machines. Effort is also directed at the development of low cost machines for dedicated applications.

Design of implanted devices continues to be an empirical process in some respects. The ability to accurately predict profile shapes in samples implanted (perhaps through a screen oxide) and subject to complicated post-implantation process steps, would cut down development time and costs.     

Investigation of Viscoelastic Properties of Amorphous Selenium near Glass Transition Using Depth‐Sensing Indentation

Abstract

New procedures involving depth‐sensing indentation are used to measure the submicron scale elastic modulus, hardness, viscosity, and activation energy and volume for creep of amorphous selenium below glass transition. The accurate measurement of Young's modulus in a highly viscoelastic situation using depth‐sensing indentation remains a challenge, and a creep correction procedure is employed here to measure the modulus. The measured Young's modulus exhibits a strong decreasing trend from ～10 GPa to 4.4 GPa as temperature increases from ～302 K to 309 K, in reasonably good agreement with bulk behavior. Two new procedures are also proposed here to measure the viscosity. The measured shear viscosity decreases from ～1×10¹² Pa‐s to ～2×10¹⁰ Pa‐s when the temperature increases over the same range, and the variation with temperature is found to obey an Arrehnius rate equation. The activation energy for the viscous creep process is found to be ～463 kJ/mol. Both the viscosity and the activation energy are lower than the bulk values, and this is thought to be due to the much higher stress levels of over 200 MPa involved in the nanoindentation experiments here. The apparent activation volume exhibits a rising trend from 1.04×10^?31 to 2.35×10^?30 m³ over the same temperature range.     

Measurement of viscoelastic properties for polymers by nanoindentation

A new method has been proposed and verified to measure the viscoelastic properties of polymers by nanoindentation tests. With the mechanical response of load–displacement curves at different loading rates, the parameters of creep compliance and relaxation modulus are calculated through the viscoelastic contact model. Dynamic thermomechanical analysis (DMA) tests are conducted to compare the results by the proposed technique. The results show that the correlation coefficients between DMA tests and the new method are above 0.9 in the entire range, which verified the feasibility of the method. The loading curves fitted by the model are identical to the experimental curves within the discrete points and so it shows that this technique is more suitable for general linear viscoelastic materials. Numerical creep tests are carried out to examine the effectiveness of the proposed method by input the Prony series calculated by the three-element Maxwell model and the viscoelastic contact model. The good agreement shows that the proposed technique can be applied in practice.     

Probing mechanical properties of thin film and ceramic materials in micro- and nano-scale using indentation techniques

In this study, we report on the mechanical properties, failure and fracture modes in two cases of engineering materials; that is transparent silicon oxide thin films onto poly(ethylene terephthalate) (PET) membranes and glass-ceramic materials. The first system was studied by the quazi-static indentation technique at the nano-scale and the second by the static indentation technique at the micro-scale. Nanocomposite laminates of silicon oxide thin films onto PET were found to sustain higher scratch induced stresses and were effective as protective coating material for PET membranes. Glass-ceramic materials with separated crystallites of different morphologies sustained a mixed crack propagation pattern in brittle fracture mode.     

Nanoindentation and the indentation size effect: Kinetics of deformation and strain gradient plasticity

A study of the indentation size effect (ISE) in aluminum and alpha brass is presented. The study employs rate effects to examine the fundamental mechanisms responsible for the ISE. These rate effects are characterized in terms of the rate sensitivity of the hardness, , where H is the hardness and is an effective strain rate in the plastic volume beneath the indenter. can be measured using indentation creep, load relaxation, or rate change experiments. The activation volume V∗, calculated based on which can traditionally be used to compare rate sensitivity data from a hardness test to conventional uniaxial testing, is calculated. Using materials with different stacking fault energy and specimens with different levels of work hardening, we demonstrate how increasing the dislocation density affects V∗; these effects may be taken as a kinetic signature of dislocation strengthening mechanisms. We noticed both H and exhibit an ISE. The course of V∗ vs. H as a result of the ISE is consistent with the course of testing specimens with different level of work hardening. This result was observed in both materials. This suggests that a dislocation mechanism is responsible for the ISE. When the results are fitted to a strain gradient plasticity model, the data at deep indents (microhardness and large nanoindentation) exhibit a straight-line behavior closely identical to literature data. However, for shallow indents (nanoindentation data), the slope of the line severely changes, decreasing by a factor of 10, resulting in a “bilinear behavior”.     

SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties

In this work amorphous silicon oxynitride films with similar composition (ca. Si_0.40N_0.45O_0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N₂-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus.The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N₂ gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.     

Preparation and characterizations of amorphous nanostructured SiC thin films by low energy pulsed laser deposition

Amorphous silicon carbide (SiC) thin films were deposited on silicon substrates by pulsed laser ablation at room temperature. Thicknesses and surface morphology of the thin films were characterized using optical profilers, atomic force and field emission scanning electron microscopy. Nanohardnes, modulus and scratch resistance properties were determined using XP nanoindenter. The results show that crack free, smooth and nanostructured thin films can be deposited using low laser energy densities.