Practical method for high-resolution imaging of polymers by low-voltage scanning electron microscopy

Synthesis and Characterisation of Acrylic Resin-Al Powder Composites Suitable for Additive Manufacturing

Stereolithography is an additive manufacturing technology commonly used to build either prototypes or final parts. Nevertheless, the manufacture of structural parts has been ruled out owing to the poor mechanical properties of conventional UV-curable resins. Moreover, the inventory of available commercial resins is still limited and they exhibit low thermal and electrical conductivity values. In this work, some composite materials were designed using Al microparticles dispersed within an SLA commercial resin matrix. These composites overcame the difficulties caused by the light scattering effect during the photopolymerisation process in the SLA technology. Dispersion of the filler was characterised by means of SEM/EDX and AFM. The composites exhibited improved thermal and mechanical behaviour in comparison with the pristine resin. The simplicity of the synthesis method used to prepare the composites provides a convenient starting point to explore new ways of designing composites for SLA with improved mechanical and functional properties.

Study of YAG : Ce and Polymer Composite Properties for Application in LED Devices

The cost of the rare-earth metal cerium means that preparation of YAG : Ce is expensive. To overcome this, the garnet could partially be replaced by cheaper alternatives, while retaining the original properties of YAG : Ce. Composites with different polymers such as polyethylene glycol diacrylate (M280) and dipentaerythrityl hexaacrylate (M600) were therefore studied. YAG : Ce and boron nitride were added into the polymer matrix in order to obtain composites with enhanced thermal conductivity, necessary for high-optical-density applications. The physical properties of the composites were measured by using XRD, DSC, SEM, and NMR, and the most important characteristics for LED materials such as emission, excitation, decay time and quantum efficiency were analyzed. An LED prototype was developed to test and demonstrate the composites for practical applications. That developed device exhibited optical properties very close to those comprising a commercial garnet prototype, which was also developed for comparison. The main advantage of the proposed technology is that by using 2 time less the amount of YAG : Ce, almost the same light output was obtained compared to commercial phosphors.

Imaging low-dimensional nanostructures by very low voltage scanning electron microscopy: ultra-shallow topography and depth-tunable material contrast

We demonstrate the implications of very low voltage operation (<1 kV) of a scanning electron microscope for imaging low-dimensional nanostructures where standard voltages (2-5 kV) involve a beam penetration depth comparable to the cross-section of the nanostructures. In this common situation, image sharpness, contrast quality and resolution are severely limited by emission of secondary electrons far from the primary beam incidence point. Oppositely, very low voltage operation allows reducing the beam-specimen interaction to an extremely narrow and shallow region around the incidence point, enabling high-resolution and ultra-shallow topographic contrast imaging by high-angle backscattered electrons detection on the one hand, and depth-tunable material contrast imaging by low-angle backscattered electrons detection on the other. We describe the performance of these imaging approaches on silicon nanowires obtained by the vapor-liquid-solid mechanism. Our experimental results, supported by Monte Carlo simulations of backscattered electrons emission from the nanowires, reveal the self-assembly of gold-silica core-shell nanostructures at the nanowire tips without any ad-hoc thermal oxidation step. This result demonstrates the capacity of very low voltage operation to provide optimum sharpness, contrast and resolution in low-dimensional nanostructures and to gather information about nanoscaled core-shell conformations otherwise impossible to obtain by standard scanning electron microscopy alone.

Synthesis of Functional Particles by Condensation and Polymerization of Monomer Droplets in Silicone Oils

We studied the synthesis of poly(4-vinylpyridine) and poly(2-hydroxyethyl methacrylate) polymer particles in silicone oil using a sequential vapor phase polymerization method in which monomer droplets were first condensed onto a layer of silicone oil and subsequently polymerized via a free radical mechanism. The viscosity of the silicone oil was systematically varied. At lower viscosities, a heterogeneous particle size distribution was produced where small particles were formed by engulfment of the monomer droplets at the liquid surface and large particles were formed by coalescence of the monomer droplets inside the liquid layer. Coalescence could be inhibited by increasing the viscosity of the silicone oil leading to a decreased average radius and a narrower size distribution of the polymer particles. The advantages of our method for the fabrication of polymer particles are that it does not require surfactants or organic solvents.

Phototocatalytic lithography of poly(propylene sulfide) block copolymers: toward high-throughput nanolithography for biomolecular arraying applications

Photocatalytic lithography (PCL) is an inexpensive, fast, and robust method of oxidizing surface chemical moieties to produce patterned substrates. This technique has utility in basic biological research as well as various biochip applications. We report on porphyrin-based PCL for patterning poly(propylene sulfide) block copolymer films on gold substrates on the micrometer and submicrometer scales. We confirm chemical patterning with imaging ToF-SIMS and low-voltage SEM. Biomolecular patterning on micrometer and submicrometer scales is demonstrated with proteins, protein-linked beads. and fluorescently labeled proteins.

The morphology of submicronsized core–shell latex particles: An electron microscopy study

The core-shell structure of a range of acrylic-acrylic latexes has been investigated by combining different specimen preparation methods with transmission electron microscopy (TEM), dark-field scanning transmission electron microscopy (DSTEM) and low-voltage scanning electron microscopy (LV-SEM), including the first reported use of LV-SEM to observe composite latex particles at ambient and subambient temperatures. Spin-coating of liquid latex dispersions directly onto TEM grids or SEM stubs is shown to be a relatively straightforward mean of avoiding film formation during specimen preparation. In conjunction with double staining techniques, it has been found to be particularly convenient for characterizing the fine structure of particles with diameters down to below 100 nm.