Properties Of Nanoscale Materials Research Articles

Contribution of Collagen, Mineral and Water Phases to the Nanomechanical Properties of Bone

ABSTRACTCortical bone is an anisotropic material, and its mechanical properties are determined by its composition as well as its microstructure. Mechanical properties of bone are a consequence of the proportions of, and the interactions between, mineral, collagen and water. Mid-shaft palmar cortical tissue from the equine third metacarpal bone is relatively dense and uniform with low porosity. The mainly primary osteons are aligned to within a few degrees of the long axis of the bone. Beams of compact cortical bone were prepared to examine effects of dehydration and embedding and to study contribution of collagen and mineral to nano-scale material properties. Five beams were tested: untreated (hydrated); 100% ethanol (dehydrated); or embedded in poly-methylmethacrylate (PMMA) for one normal, one decalcified, and one deproteinated bone sample. Elastic modulus was obtained by nanoindentation using spherical indenters, with the loading direction transverse [1] and longitudinal to the bone axis. By selectively removing water, mineral and organic components from the composite, insights into the ultrastructure of the tissue can be gained from the corresponding changes in the experimentally determined elastic moduli.

Macromolecules at surfaces: Research challenges and opportunities from tribology to biology

AbstractA comprehensive review of ongoing and recommended research directions concerning the structure, dynamics, and interfacial activity of synthetic and naturally occurring macromolecules at the solid–liquid interface is presented. Many new developments stem from the ability to target new size regimes of 1–100 nm. These rapid developments are reviewed critically with respect to chemical synthesis, processing, structural characterization, dynamic processes, and theoretical and computational analysis. The common problems shared by flat and particulate surfaces are emphasized. A broad spectrum of material properties are discussed, from the control of interfacial friction between surfaces in moving contact, to the mechanical strength and durability of the interfaces in hybrid materials, to optical and electronic properties. Future research opportunities are identified that involve (1) the emergence of nanoscale material properties, (2) polymer‐assisted nanostructures, and (3) the crossroads between interfacial science and biological and bioinspired applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2755–2793, 2003

Vibrational properties of nanoscale materials: From nanoparticles to nanocrystalline materials

The vibrational density of states (VDOS) of nanoclusters and nanocrystalline materials are derived from molecular-dynamics simulations using empirical tight-binding potentials. The results show that the VDOS inside nanoclusters can be understood as that of the corresponding bulk system compressed by the capillary pressure. At the surface of the nanoparticles the VDOS exhibits a strong enhancement at low energies and shows structures similar to that found near flat crystalline surfaces. For the nanocrystalline materials an increased VDOS is found at high and low phonon energies, in agreement with experimental findings. The individual VDOS contributions from the grain centers, grain boundaries, and internal surfaces show that, in the nanocrystalline materials, the VDOS enhancements are mainly caused by the grain-boundary contributions and that surface atoms play only a minor role. Although capillary pressures are also present inside the grains of nanocrystalline materials, their effect on the VDOS is different than in the cluster case which is probably due to the inter-grain coupling of the modes via the grain-boundaries.

Square representative volume elements for evaluating the effective material properties of carbon nanotube-based composites

Carbon nanotubes (CNTs) demonstrate unusually high stiffness, strength and resilience, and may become an ideal reinforcing material for new nanocomposites. However, much work has to be done before the potentials of CNT-based composites can be fully realized. Evaluating the effective material properties of such nanoscale materials is one of many difficult tasks. Simulations using molecular dynamics and continuum mechanics models can play significant roles in this development. Currently, the continuum approach seems to be the only feasible approach for such large scale analysis. In this paper, effective mechanical properties of CNT-based composites are evaluated using a square representative volume element (RVE) based on the continuum mechanics and with the finite element method (FEM). Formulas to extract the effective material constants from solutions for the square RVEs under two load cases are derived based on the elasticity theory. Numerical results using the FEM show that the load carrying capacities of the CNTs in a matrix are significant. For example, with the addition of CNTs in a matrix at a volume fraction of 3.6%, the stiffness of the composite can increase as much 33% in the axial direction with long CNTs. These simulation results are consistent with the experimental results reported in the literature and the earlier results using cylindrical RVEs.

Photoluminescence properties of silica-based mesoporous materials similar to those of nanoscale silicon

Photoluminescence (PL) from composites of 7- and 15-nm sized silica nanoparticles (SNs) and mesoporous silicas (MSs) induced by 266- (4.66-) and 532-nm (2.33-eV) laser light has been studied at room temperature. The multiband PL from MSs in the range of 1.0-2.1 eV is evidenced to originate from isolated bulk and surface non-bridging oxygens (NBOs) and from NBOs combined with variously placed 1-nm sized pore wall oxygen vacancies (OVs). The nature and diversity of NBO light-emitters are confirmed by ab initio calculations. The PL from SNs exhibits only a short wavelength part of the bands (1.5-2.1 eV) originated from isolated bulk and surface NBOs. This fact indicates that the highly OV-bearing structures occur only in extremely thin (∼ 1 nm) silica layers. The similarity of spectroscopic properties of silica-based nanoscale materials to those of surface-oxidized silicon nanocrystals and porous silicon, containing silica-passivating layers of the same width, is discussed.

Quantitative nanoscale metrology study of Cu/SiO2 interconnect technology using transmission x-ray microscopy

This letter describes quantitative nondestructive measurements of multilayer submicron Cu/SiO2 interconnect structures such as Cu lines, vias, and W lines with lateral dimensions down to 300 nm and electromigration defect structures using scanning transmission x-ray microscopy employing a 0.2 μm x-ray beam. Typical measurement accuracies are ⩽60 nm for widths and lengths and ⩽10% in height. The high-resolution and nondestructive nature of this technique provide a very powerful probe of physical properties of nanoscale and submicron materials and structures.

Measurements of stiff-material compliance on the nanoscale using ultrasonic force microscopy

Ultrasonic force microscopy (UFM) was introduced to probe nanoscale mechanical properties of stiff materials. This was achieved by vibrating the sample far above the first resonance of the probing atomic force microscope cantilever where the cantilever becomes dynamically rigid. By operating UFM at different set force values, it is possible to directly measure the absolute values of the tip-surface contact stiffness. From this an evaluation of surface elastic properties can be carried out assuming a suitable solid-solid contact model. In this paper we present curves of stiffness as a function of the normal load in the range of 0–300 nN. The dependence of stiffness on the relative humidity has also been investigated. Materials with different elastic constants (such as sapphire lithium fluoride, and silicon) have been successfully differentiated. Continuum mechanics models cannot however explain the dependence of stiffness on the normal force and on the relative humidity. In this high-frequency regime, it is likely that viscous forces might play an important role modifying the tip-surface interaction. Plastic deformation might also occur due to the high strain rates applied when ultrasonically vibrating the sample. Another possible cause of these discrepancies might be the presence of water in between the two bodies in contact organizing in a solidlike way and partially sustaining the load.

Synthesizing submicrometer and nanoscale particles via self-assembled molecular membranes

The unique properties of submicrometer and nanoscale materials have stimulated a great deal of research into the synthesis of such structures. One avenue being explored is the use of organic precursors. This article describes some recent work in the use of self-assembled molecular membranes as templates for submicrometer and nanoscale structures.