Optical Reflection Microscopy Research Articles

Bi-composite sandwich moldings: processing, mechanical performance and bioactive behavior.

Two composite systems composed of high-density polyethylene (HDPE) filled with hydroxyapatite (HA) and carbon fiber (C fiber) were compounded in a co-rotating twin screw extruder and subsequently molded in a two component injection molding machine in order to produce test bars with a sandwich-like morphology. These moldings are based on a HDPE/HA composite outer layer and a HDPE/C fiber composite core. The mechanical performance of the obtained specimens was assessed by tensile and impact testing. The fracture surfaces were observed by scanning electron microscopy (SEM) and optical reflectance microscopy was used to characterize the morphology within the moldings. In order to study the bioactivity of the molded specimens, the samples were immersed for different periods of time up to 30 days in a simulated-body fluid (SBF) with an ion composition similar to human blood plasma. After each immersion period, the surfaces of the specimens were characterized by SEM. The chemical composition and the structure of the deposited films were studied by electron dispersive spectroscopy (EDS) and thin-film X-ray diffraction (TF-XRD). The evolution of the elemental concentrations in the SBF solution was determined by induced coupled plasma emission (ICP) spectroscopy. Bi-composite moldings featuring a sandwich-like morphology were successfully produced. These moldings present a high stiffness as a result of the C fiber reinforcement present in the molding core. Furthermore, as a result of the HA loading, the sandwich moldings exhibit a clear in vitro bioactive behavior under simulated physiological conditions, which indicates that an in vivo bone-bonding behavior can be expected for these materials.

Contrast enhancement of modulated optical reflectance microscopy of semiconductor devices

Photothermal microscopy based on combined optical and electrical excitation has been applied to insulating lines prepared by focused ion beam implentation on oxygen implanted mesas. The double excitation technique permits to image electrical properties of the implanted structures which are complementary to simple defect tracing when a single excitation is applied. In addition, the contrast of imaging of implanted structures can be increased considerably. Apart from combining modulated optical excitation with electrical direct current voltages, double modulation configurations can improve the contrast further, by detecting either on a higher harmonic of the single excitation frequency or on the sum or difference of two different excitation frequencies. The influence of different parameters characterizing the experimental configuration gives information on the physical processes of the signal generation, indicating that the observed contrast enhancement is mainly of thermal origin related to the photoinduced currents.

Reflection second-harmonic microscopy of individual semiconductor microstructures

Second-harmonic scanning optical microscopy in reflection is used to image at room temperature individual GaInP/GaAs microstructures formed on a GaAs (001) substrate. Second-harmonic images of individual microstructures are recorded along with first-harmonic images for four combinations of polarizations of the pump and second-harmonic radiation with different pump wavelengths in the range of 720–920 nm. We observe different second-harmonic images for different polarization configurations and their evolution when changing the pump wavelength. Comparing the dependencies of the second-harmonic signal from the bare sample surface with those related to the microstructures, we conclude that the second-harmonic radiation detected when illuminating the microstructures originates from the substrate at short wavelengths and directly from the microstructures at ∼900 nm of the pump wavelength. The appearance of the second-harmonic images for different polarization configurations is used to discuss the nonlinear properties of the investigated microstructures.

Castaing's Electron Microprobe and its Impact On Materials Science

Abstract A central theme of modern materials science has been the exploration of the relationship between the microstructure of a material and its macroscopic properties. Beginning in the late 19th century, the developing field of metallography permitted scientists to view the microstructure of metal alloys. Mechanical polishing followed by selective chemical etching produced differential relief on chemically distinct phases or at grain boundaries. With such specimens, reflection optical microscopy revealed structures with micrometer and even finer dimensions. The microstructural world that was found proved to be highly complex, and most alloys were observed to be chemically differentiated into two or more distinct phases.

Particle Aggregated Structure in Silica Particle Filled Epoxy Resin Composite System.

Optical microscopy in reflection and transparent modes with normal and cross-polarized lights contributes to understand the particle-aggregated structures and their peculiar characteristics in the viscosity of an epoxy resin composite system filled with silica particles. The apparent viscosity of a 17 μm-SiO2 particle filled system shows minimum values compared with those of 13 and 27 μm particle systems. Only SiO2 primary properties such as particle size distribution and specific surface area are not enough for the understanding of the characteristics. Optical microscopy reveals that the 17 μm particle system has the smallest particle-aggregated structure of SiO2 in epoxy resin. This appears to explain the rheological properties and confirmed the possibility of the optical characterization to identify the particle-aggregated structure of epoxy composite filled with silica particle.

Castaing’s Electron Microprobe and its Impact on Materials Science

Abstract A central theme of modern materials science has been the exploration of the relationship between the microstructure of a material and its macroscopic properties. Beginning in the late 19th century, the developing field of metallography permitted scientists to view the microstructure of metal alloys. Mechanical polishing followed by selective chemical etching produced differential relief on chemically distinct phases or at grain boundaries. With such specimens, reflection optical microscopy revealed structures with micrometer and even finer dimensions. The microstructural world that was found proved to be highly complex, and most alloys were observed to be chemically differentiated into two or more distinct phases. The answer to many materials science questions required knowledge of the specific composition of such fine scale phases. Castaing’s research was motivated by these considerations, as evidenced by the title of his first paper, “Application of electron probes to metallographic analysis”. The subsequent impact of Castaing’s electron probe microanalyzer (EPMA) has occurred across a broad range of the physical and biological sciences. Materials science has been one of the most active areas and chief beneficiaries, as well as a source of researchers who not only employed electron beam microanalysis to solve their problems but who also contributed innovations that advanced the microprobe field. For example, the abstracts of the First National Conference on Electron Probe Microanalysis contain numerous examples of advanced applications of the electron microprobe to materials science, including analysis of (1) refractory metal coatings (P. Lubllin and W. Sutkowski), (2) diffusion in the Ti-Nb system (D. Nagel and L. Birks), (3) Au-Al alloys (C. Nealey), (4) various steels (H. Nikkei), (5) Al-V-Mo-Ti alloys (R. Olsen), (6) corrosion of Ni-Co alloy (C. Spengler and R. Stickler), and (7) analysis of metal oxides and carbides (T. Ziebold). Integrated over 50 years, the impact of electron probe microanalysis on materials science has been so broad and varied, especially in its continued development and incorporation within scanning electron microscopy and analytical electron microscopy, that a suitably comprehensive review could consume the entire presentation time available for all topics to be covered in this conference! Instead, selected examples of critical applications will be presented to illustrate the impact in materials science.

Optical modelling vs. FTIR reflectance microscopy: characterization of laser treated ceramic fibres

Ceramic silicon carbide (SiC) based fibres treated by a laser induced chemical vapour deposition process (LCVD) have been investigated by MIR-FTIR reflectance microscopy. A significant change of the spectral behaviour has been detected after laser irradiation and after fibre coating. A strong SiC resonance appears and the damped interference waves in the short wavelength region vanish simultaneously. Spectra modelling has been used to interpret the measured near-normal specular reflectance spectra. The dielectric function of the fibre material is described by a Lorentzian oscillator model. Because of the cylindrical shape of the fibre with a diameter close to the wavelength of the used light the Maxwell based algorithm for spectra simulation of flat layered samples with smooth interfaces has been extended by a term of interface irregularities which modifies the phase of the reflected beam. Based on this model the measured spectra have been well described and the dielectric functions of the fibres have been derived. The interference-like waves result from retro-reflections inside the fibre. Spectral changes due to laser treatment of fibres have been attributed to re-crystallization of the originally amorphous SiC based material resulting in scattering on the crystallite interfaces.

Effects of Low-Energy End Groups on the Dewetting Dynamics of Poly(styrene) Films on Poly(methyl methacrylate) Substrates

The influence of surface-active fluorocarbon-terminated poly(styrene) (PS−F) additives on the dewetting dynamics of thin melt films of poly(styrene) (PS) deposited onto poly(methyl methacrylate) (PMMA) substrates is investigated by reflection optical microscopy. The dewetting velocity is found to be time invariant and decreases with increase in PS−F content. Dewetting is completely eliminated for the neat PS−F films. The surface tension reduction due to PS−F addition is characterized by analysis of water contact angles on the PS blends and by measurement of equilibrium contact angles for droplets of the dewetted blends on PMMA by atomic force microscopy. Increasing the PS−F content decreases the PS blend surface tension and reduces its equilibrium contact angle on PMMA. Lower molecular weight PS−F is more effective in reducing the dewetting velocity owing to its higher fluorocarbon content and subsequently larger reduction in surface tension. The dependence of dewetting velocity (V) on the PS blend viscos...

Image Enhancement in a Reflection Optical Microscope by Suppression of Diffusing Photons Using Polarizing Annular Objectives.

: In this report, we describe the implementation of an angle-gating mechanism into a reflection optical microscope for imaging through a turbid medium. A significant improvement in image resolution and contrast is obtained when a polarizing annular objective is used to image a reflective test bar through various turbid media. The experimental results confirm that the improvement is caused by the efficient suppression of diffused photons scattered from the turbid medium when a polarized annular objective is employed as an angular gate.

Examination of the two-dimensional pupil function in coherent scanning microscopes using spherical particles.

The determination of the modulus of the pupil function in reflection acoustic and optical microscopy with the help of spherical particles is demonstrated. The theoretical examination shows that this method can give good results if the pupil function drops smoothly towards the edge. For a pupil with a sharp edge this technique can give the accurate pupil function only by imaging large spheres. The dependence of the accuracy of the method on the size of the spherical particle is analyzed. Numerical and experimental results obtained for the confocal scanning optical microscope and the scanning acoustic microscope are examined.

A Reflection Near-Field Scanning Optical Microscope Technique for Subwavelength Resolution Imaging of Thin Organic Films

A dual mode near-field scanning optical microscopy (NSOM) technique, in which light is both emitted from and collected by a subwavelength aperture, is described and demonstrated. This dual mode configuration is capable of high contrast (via the refractive index) as well as high-resolution optical microscopy in reflection. The contrast in these images is shown to depend strongly on the interference of the light incident to and reflected from the sample surface. We show that with the dual mode configuration the topography induced contrast can be quantitatively separated from the true optical contrast resulting in a mapping of the refractive index of the sample. This separation has proven difficult, if not impossible, for other reflection NSOM geometries. To demonstrate the utility of this technique for thin organic films we present dual mode images of a nine-layer organic/inorganic self-assembled multilayer film on a silicon substrate.

The effect of the moulding conditions on the semicrystalline structure of polypropylene

The semicrystalline structure of isotactic polypropylene (iPP) moulded by oscillating melt-flow (rheomoulding) has been studied using low-frequency Raman scattering (coupled with optical interference reflection microscopy and wide-angle X-ray scattering). It was compared to the structure of typically moulded iPP. We observed that only the relatively narrow central zone of the bar has a spherulitic organization in the rheomoulded specimen, while the external layers on each side have a perfectly oriented crystalline structure. The crystal structure, the orientation, the size of the crystallites and the effect of annealing were determined.

Dual-optical-mode near-field scanning optical microscopy

The simultaneous operation of near-field scanning optical microscopy (NSOM) in reflection and transmission modes is demonstrated. In the transmission mode, a low-noise, large-area silicon photodetector was mounted between the piezoelectric transducer scanning stage and the sample. In the reflection mode, either a photomultiplier tube or two large-area silicon detectors was used for signal collection. The reflection-mode setup consisting of two silicon detectors provides a large numerical aperture of 0.9 as well as symmetrical detection of emitting photons. The dielectric thin films and the light-emitting polymers were used to demonstrate the capability of these two modes of NSOM. A comparison between these two different setups is also presented.

Imaging with reflection near-field optical microscope: contributions of middle and far fields

Within the framework of a microscopic formalism, we present a theoretical analysis of the imaging properties of scanning near-field optical microscopy in reflection. The detected optical signal is assumed to be proportional to the intensity of the self-consistent field at the site of the probe dipole. Influence of different components (near, middle and far fields) of the field propagator on the total field intensity is numerically studied for two arrangements of object dipoles and for various probe-surface distances. We demonstrate that for relatively large distances the middle-field components dominate in the total field and ensure the subwavelength resolution. Imaging properties of the reflection near-field microscopy observed experimentally are qualitatively explained with the help of our numerical simulations.

Near-field scanning optical microscopy in reflection: A study of far-field collection geometry effects

We have designed and demonstrated two simple and versatile reflection mode near-field scanning optical microscopes (NSOMs). In one scanner far-field collection is coaxial with the NSOM tip, and in the other scanner, the far-field collection is at a 45° angle to the NSOM tip. We quantitatively compare images obtained with the two scanners. While off-axis collection offers a significantly higher signal-to-noise ratio, it also introduces tip shadowing in samples with topographic features larger than approximately 40 nm. The additional contrast from the shadowing further complicates image interpretation and must be considered when performing NSOM in reflection with off-axis collection. In addition, we discuss some general issues that should be considered when designing a reflection NSOM.

Multi-detection and polarisation contrast in scanning near-field optical microscopy in reflection

We present a scanning near-field optical microscope operating in reflection suitable for simultaneous bright field and fluorescence imaging. A non-coated pulled optical fibre is used in true reflection mode, i.e. both as emitter and collector. Beam splitters, dichroic mirrors and polarisers are combined to discriminate the different wavelength and polarisation signals. The distance between fibre and sample is controlled by shear force feedback. Bright field and fluorescence images with polarisation contrast of dielectric samples have been obtained with 200 nm lateral resolution. We show the fluorescence polarisation dependence with the molecular orientation in application to Langmuir-Blodgett thin film domains.

Optically Active Polyethers. 2. Atomic Force Microscopy of Melt-Crystallized Poly(epichlorohydrin) Enantiomers and Their Equimolar Blend

The surface morphologies of melt-crystallized spherulites of the optically active R and S forms of poly(epichlorohydrin) and their equimolar blend have been investigated by atomic force microscopy (AFM). For the banded spherulites formed from the optically pure polyenantiomers, a regular pattern of alternating concentric ridges and valleys observed by AFM corresponds directly to the pattern of birefringent extinction bands observed under the polarized light microscope. Examination of the surface topography of these banded spherulites, either by reflectance optical microscopy or by AFM, reveals a spiral form with a sense or handedness that is dependent on the chirality of the constituent polyenantiomer. In contrast, a relatively featureless surface is observed for the spherulites formed upon crystallization of the equimolar blend. AFM images of the spherulitic surface indicate the presence of predominantly flat lamellae in the equimolar blend while those of the pure polyenantiomer appear to have an alternating flat to edge-on orientation, corresponding to the banding pattern. These observations are discussed in the context of the current theories of lamellar organization in banded spherulites.

Optical and atomic force microscopy studies of rhombohedral domains in C70crystals

Abstract On the {100} and {111} surfaces of C70 crystals the phase transition of the f.c.c. structure towards the trigonal structure has been studied in situ with the help of optical reflection microscopy. Extensive ex situ studies of domain patterns on both types of surface have been performed using both optical and atomic force microscopy. A detailed interpretation of the domain patterns is given. An additional phase transition was observed in situ at 303 K.

Structure analysis of plasma-nitrided pure iron

Pure iron, plasma nitrided in low pressure triode ion plating equipment, has been investigated by optical reflection microscopy, scanning transmission electron microscopy and glancing-angle X-ray diffraction, using conventional and synchrotron radiation. The total thickness of the compound layer does not obey the square-root time dependence, as a result of the continuous Ar + N ion bombardment during the nitriding process. The grain size is also reduced in the compound layer. In addition to the variation in thickness of the nitride layers with increasing process time, a change in the nitrogen concentration at the top of the compound zone also is observed. Increasing the nitriding time and/or the N 2 partial pressure in the nitriding apparatus results in a larger nitrogen concentration in the top layer of the ε phase. Also, a sin 2 ψ method analysis has been carried out to measure the residual macroscopic stresses in the different nitride layers of the compound zone.

Residual carbon from pulverized-coal-fired boilers. 2. Morphology and physicochemical properties

The morphology and bulk physicochemical properties of residual carbon in eight fly ash samples from commercial power plants were investigated. Enriched carbon samples extracted from the bulk fly ash were characterized by high-depth-of-field optical microscopy, reflected-light microscopy, scanning electron microscopy, elemental analysis (C, H, O), and CO 2 adsorption. The crystalline structure of the carbon was characterized by X-ray diffraction, optical reflectance, and high-resolution transmission electron microscopy fringe imaging. The results were compared with measurements on laboratory-generated chars in the early-to-intermediate stages of combustion. Compared with those chars, the residual carbon is of similar elemental composition, petrographic composition and surface area but higher crystallinity. The fuel-related mechanisms that can contribute to carbon carryover in boilers are discussed, including inertinite persistence, mineral matter encapsulation and char deactivation by pregraphitization, as well as the implications for utilization of residual carbon.