Optical Reflection Microscopy Research Articles

Recent horizontal stress directions in basement rocks of southern Sweden deduced from open microcracks

The strike direction of open intragranular microcracks in quartz and feldspar host grains was determined using optical transmission and reflection microscopy on eight oriented samples taken in two study areas in Precambrian basement rocks of southern and south-central Sweden.For an area of about 160 km2 (SW of Västervik) and two sample locations (W of Uppsala), the vast majority of open microcracks displays a strong preferred NW–SE strike direction. According to the common assumptions that natural cracks in crystalline rocks are predominantly extensional (mode I), and that open cracks belong to the latest microcrack generation, these strike directions should reflect the (sub-) recent main horizontal stress direction (σH) of the recent tectonic stress field.This conclusion is supported by corresponding directions known from in situ stress measurements and focal plane solutions in the vicinity of the study areas. It is remarkable that even in samples taken close (i.e. a few hundred metres) to recently active large scale faults the orientation of microcracks does not deviate from this common direction. This may point to slip on already softened faults, very local stress reorientations (e.g. m-scale) or that local stress relief was accomplished by other processes at micro-scale, e.g. mechanical twinning in favourably oriented feldspar crystals, or slip on grain boundaries.

Physical, chemical and thermal characterization of alumina–magnesia–carbon refractories

Alumina–magnesia–carbon refractories (AMC) are of great technological interest for their use as linings for iron and steelmaking ladles. In this paper, the methodology implemented for the physical, chemical and thermal characterization of AMC refractories is presented along with the obtained results. These results are essential for the study of the chemical and mechanical behavior of these materials, which the present work frames. AMC bricks comprise different amounts of alumina, sintered or electrofused magnesia, graphite and antioxidant additives bonded together with a phenolic resin. The variety of components, be they oxidic, metallic or polymeric in nature, and the complexity of the final microstructure and texture make characterizing these refractories a difficult task. In the present work, several complementary techniques were used in combination: X-ray fluorescence, plasma emission spectroscopy, gravimetry, X-ray diffraction, differential thermal and thermogrametric analyses, reflection optical microscopy and scanning electron microscopy, density and porosity measurements, dilatometric analysis and permanent linear change measurements. The results of these different techniques were analyzed separately and together in order to obtain a detailed description of each refractory in relation to its physical and chemical characteristics and thermal evolution. In addition, the characterization was completed by evaluating the mechanical properties at room temperature, such as the mechanical strength and Young׳s modulus.

Ridge waveguide fabrication by combining ion implantation and precise dicing on a LiNbO3 crystal

A ridge waveguide structure was prepared on a z-cut LiNbO3 crystal wafer by a combined process of ion implantation and precise dicing. The single-crystal LiNbO3 was implanted at room temperature using 3MeV oxygen ions at a fluence of 5×1014ions/cm2. After annealing to 200°C, ridge structures were formed on the wafer surface by precise diamond blade dicing. Two different ridge widths, 8 and 10μm, were chosen for comparison. The refractive index profile was reconstructed, and the near-field intensity distribution of the mode was recorded by a CCD camera using the end-face coupling method. FD-BPM was used to simulate the guided mode profile. Transmission and reflection optical microscopy were used to obtain micro-photograph images of the waveguide structure.

Crystallization-Driven Surface Segregation and Surface Structures in Poly(l-lactide)-block-Poly(ethylene glycol) Copolymer Thick Films

In this work, we used poly(L-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) copolymer thick films to investigate the effect of crystallization on surface segregation, surface crystal orientation, and morphology by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), reflection optical microscopy (ROM), and two-dimensional grazing incident wide-angle X-ray scattering (2D GIWAXS) methods. ATR-FTIR results indicated that the surface fraction of PLLA block increased from 0.48 to 0.79 when T(c,PLLA) increased from 70 to 110 °C. Polarized ATR-FTIR and 2D GIWAXS results indicated that PLLA crystal lamellae preferentially oriented parallel to the film surface with increasing T(c,PLLA). The surface crystallinity of PLLA was almost independent of T(c,PLLA), while the surface crystallinity of PEG decreased with increasing T(c,PLLA). On the basis of surface crystal orientation and crystallization kinetics, we suggested that the excess of PLLA component at the surface was mainly dominated by a coupling effect of crystallization behavior and surface segregation.

Colloidal crystallization of spindle-shaped hematite particles coated with polymer brush in deionized aqueous suspension

Colloidal crystallization of highly monodisperse spindle-shaped hematite particles coated with poly(poly(ethylene oxide) methyl ether methacrylate) brush (SHB) was studied by reflection spectroscopy and optical microscopy. SHB suspensions were deionized exhaustively with the mixtures of cation- and anion-exchange resins more than 6 months. The liquid thin film along the vertical cell wall above the horizontal air–liquid interface showed the strong color bands. Furthermore, the reflection spectra composed of many sharp peaks shifted continuously toward shorter wavelengths with time. These observations support the presence of thin film of SHB suspension, where the width is thickened downward by the gravity and the layered liquid further flow downward with time. The rigidities of SHB crystals in the bulk phase estimated from the optical microscopy in the sedimentation equilibrium were 0.007 to 0.7 Pa as SHB concentration increased from 0.006 to 0.35 wt.%. The fluctuation parameter, b-factors of the anisotropic crystals, was from 0.025 to 0.035 and decreased slightly as particle concentration increased. Rigidities and the fluctuation parameters of SHB suspensions support that the elastic properties of the anisotropic-shaped colloidal crystals are close to those of typical crystals of colloidal spheres. Compression of the SHB crystals by the gravity is also suggested in the sedimentation equilibrium state.

Non-invasive investigation on a VI century purple codex from Brescia, Italy

Purple codices are among the most relevant and prestigious book productions of Late Antique and Medieval age. They usually contained texts from Holy Writings written with golden or silver inks on parchment dyed in a purple hue. According to the tradition, the colour of parchment was obtained by the well renowned Tyrian purple dye. From the material point of view, however, very little is known about the compounds actually used in the manufacture of these manuscripts. Presently, the information available is limited to the ancient art treatises, with very few diagnostic evidences supporting them and, moreover, none confirming the presence of Tyrian purple. It is more than apparent, then, the need to have at disposal larger and more complete information at the concern, in order to verify what came to us from the literary tradition only. In this study, preliminary results are presented from non-invasive investigation on a VI century purple codex, the so-called CodexBrixianus, held in the Biblioteca Civica Queriniana at Brescia (Italy). Analyses were carried out with XRF spectrometry, UV–visible diffuse reflectance spectrophotometry, molecular spectrofluorimetry and optical microscopy. The results suggest the hypothesis that Tyrian purple had been used as a minor component mixed with other less precious dyes such as folium or orchil.

Optical visualization of ultrathin mica flakes on semitransparent gold substrates

We show that optical visualization of ultrathin mica flakes on metallic substrates is viable using semitransparent gold as substrates. This enables to easily localize mica flakes and rapidly estimate their thickness directly on gold substrates by conventional optical reflection microscopy. We experimentally demonstrate it by comparing optical images with atomic force microscopy images of mica flakes on semitransparent gold. Present results open the possibility for simple and rapid characterization of thin mica flakes as well as other thin sheets directly on metallic substrates.

Effects of surface wetting induced segregation on crystallization behaviors of melt-miscible poly(l-lactide)-block-poly(ethylene glycol) copolymer thin film

The effects of wetting induced surface segregation on the crystal nucleation, growth rate, morphology and crystal orientation of melt-miscible crystalline–crystalline diblock copolymer of poly(l-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) thin films (∼90 nm) were investigated in this work with reflection optical microscopy (ROM), atomic force microscopy (AFM), and two-dimensional grazing incident wide angle X-ray scattering (2D GIWAXS) methods. The XPS results demonstrated that the wetting induced surface enrichment of PLLA block on the free surface of PLLA-b-PEG thin films occurred when the thin films annealed at 160 °C (molten state). When the PLLA-b-PEG thin film annealed at 160 °C for 30 min, the fraction of PLLA block (fPLLA) on the free surface could reach to ∼90%. The ROM, AFM and 2D GIWAXS results indicated that the nucleation, crystal growth, morphology and crystal orientation of PLLA block in PLLA-b-PEG thin films were significantly influenced by prior wetting process. For the PLLA-b-PEG thin film with wetting time shorter than 15 min (∼52% < fPLLA <∼75%), the O-shaped flat-on nucleus preferentially formed on the free surface of thin films. However, for the thin film with wetting time longer than 15 min (fPLLA>∼ 75%), the S-shaped edge-on nucleus preferentially formed on the free surface at early stage of crystallization and then grew into tilted flat-on lamella. Furthermore, the overall spherulite growth rate of PLLA in PLLA-b-PEG thin films decreased with increase of wetting time. We found that the crystallization behavior of PLLA on the free surface in the PLLA-b-PEG thin films was strongly influenced by surface wetting induced changes of surface energy, composition and chain alignments. Our results demonstrated that the crystallization kinetics, morphology and crystal orientation of crystalline block copolymer thin films can be controlled by prior wetting process.

Enhancement of graphene visibility on transparent substrates by refractive index optimization

Optical reflection microscopy is one of the main imaging tools to visualize graphene microstructures. Here is reported a novel method that employs refractive index optimization in an optical reflection microscope, which greatly improves the visibility of graphene flakes. To this end, an immersion liquid with a refractive index that is close to that of the glass support is used in-between the microscope lens and the support improving the contrast and resolution of the sample image. Results show that the contrast of single and few layer graphene crystals and structures can be enhanced by a factor of 4 compared to values commonly achieved with transparent substrates using optical reflection microscopy lacking refractive index optimization.

Self-adhesive restoratives as pit and fissure sealants: A comparative laboratory study

ObjectivesTo evaluate the properties of self-adhesive restorative materials used as sealants in comparison with sealants with hydrophobic or hydrophilic monomers. MethodsThe self-adhesive materials tested were Fusio (FS) and Vertise-Flow (VF) and the sealants Embrace Wetbond (EM/hydrophilic) and Helioseal-F (HS/hydrophobic). The properties tested were: (a) degree of cure (%DC, n: 5, ATR-FTIR), (b) extent of oxygen inhibition (n: 5, transmission optical microscopy), (c) flow (n: 5, ASTM D-4242 method), (d) hardness (VH0.2kp/10s dry/1w in water), (e) adaptation, microleakage and fissure penetration (n: 10, 1% fuschin dye, reflection optical microscopy and ESEM). Statistical analysis was performed by one-way ANOVA plus Tukey test (a–d), Fisher's exact and Kruskal–Wallis plus Tukey tests (e) at a 95% confidence level. ResultsVF showed the highest %DC(76.1) followed by HS(68.7) and EM(61.3), FS(59.2). HS demonstrated the highest extent of oxygen inhibition (23μm vs. 13–10μm of the rest). EM and HS exhibited the greatest flow, followed by FS and VM. The VHN(0.2kp/10s) ranking before and after 1week water exposure was FS≥VF>EM≥HS. Water storage increased VF and reduced HS values. The lowest adaptation and microleakage scores were found in HS. FS and VF after alumina sandblasting showed the worst adaptation and leakage scores, that were improved after acid-etching. Improved fissure penetration was found in HS, EM and FS, VF after acid-etching. SignificanceAlthough the self-adhesive materials presented improved setting characteristics, their low flow affected fissure penetration capacity. When combined with enamel acid-etching, adaptation and microleakage scoring were substantially improved in comparison with enamel sandblasting. The sealant with the hydrophobic monomers demonstrated the best sealing characteristics.

Nonlinear regime of the excitation of a surface electromagnetic wave on the silicon surface by an intense femtosecond laser pulse

A surface electromagnetic wave has been excited on an atomically smooth silicon surface by an intense infrared femtosecond laser pulse as a result of its self-diffraction on a microscale short-lived optical inhomogeneity of the excitation region rather than on the roughness of its surface relief. This wave has been visualized in the form of the pattern of its interference with the same incident infrared ultrashort pulse, which corresponds to the instantaneous surface dielectric constant grating (reflection), as well as the resulting surface relief grating, using time-resolved far-field optical reflection microscopy.

Thermal melting and ablation of silicon by femtosecond laser radiation

The space-time dynamics of thermal melting, subsurface cavitation, spallative ablation, and fragmentation ablation of the silicon surface excited by single IR femtosecond laser pulses is studied by timeresolved optical reflection microscopy. This dynamics is revealed by monitoring picosecond and (sub)nanosecond oscillations of probe pulse reflection, which is modulated by picosecond acoustic reverberations in the dynamically growing surface melt subjected to ablation and having another acoustic impedance, and by optical interference between the probe pulse replicas reflected by the spalled layer surface and the layer retained on the target surface. The acoustic reverberation periods change during the growth and ablation of the surface melt film, which makes it possible to quantitatively estimate the contributions of these processes to the thermal dynamics of the material surface. The results on the thermal dynamics of laser excitation are supported by dynamic measurements of the ablation parameters using noncontact ultrasonic diagnostics, scanning electron microscopy, atomic force microscopy, and optical interference microscopy of the modified regions appearing on the silicon surface after ablation.

A micro-Raman spectroscopic investigation of He^+-irradiation damage in LiNbO_3

Imaging micro-Raman spectroscopy is used to investigate the materials physics of radiation damage in congruent LiNbO3 as a result of high-energy (~MeV) He+ irradiation. This study uses a scanning confocal microscope for high-resolution three-dimensional micro-Raman imaging along with reflection optical microscopy (OM), and scanning electron microscopy (SEM). The tight optical excitation beam in the Raman system allows spatial mapping of the Raman spectra both laterally and normal to the irradiation axis with ≤1 μm resolution. Point defects and compositional changes after irradiation and surface deformation including blistering and microstress are observed in the stopping region. We demonstrate that the probed area of the damaged region is effectively “expanded” by a beveled geometry, formed through off-angle polishing of a crystal facet; this technique enables higher-resolution probing of the ion-induced changes in the Raman spectra and imaging of dislocation line defects that are otherwise inaccessible by conventional probing (depth and edge scan). Two-dimensional (2D) Raman imaging is also used to determine the defect uniformity across an irradiated sample and to examine the damage on a sample with patterned implantation. The effects of different He+ doses and energies, together with post-irradiation treatments such as annealing, are also discussed.

Salt-induced pattern formation in evaporating droplets of lysozyme solutions

Solute self-organization during evaporation of colloidal sessile droplets has attracted the attention of researchers over the past few decades due to a variety of technological applications. Recently, pattern formation during evaporation of various biofluids has been studied due to potential applications in screening and diagnosis. The complex morphological patterns in the deposit are unique to various disorders and are influenced by various physical mechanisms occurring during evaporation. These complex patterns can be better understood by studying evaporation of model solutions of biological relevance. Here, we examine the general features of pattern formation during sessile droplet evaporation of aqueous lysozyme solutions with varying concentrations of NaCl. Lysozyme is a globular protein found in biological fluids such as tears and saliva. The morphological evolution of the droplet is studied by time-lapse video during evaporation via reflection optical microscopy. The final deposits exhibit an amorphous peripheral ring and interior regions containing crystallites and dendritic forms, dependent on NaCl concentration. Scanning electron microscopy (SEM) images demonstrate the multi-scale hierarchical nature of these structures.

Nonintrusive Optical Visualization of Surface Nanobubbles

Individual surface nanobubbles are visualized with nonintrusive optical interference-enhanced reflection microscopy, demonstrating that their formation is not a consequence of the hitherto used intrusive atomic force microscopy technique. We then use this new and fast technique to demonstrate that surface nanobubbles form in less than a few seconds after ethanol-water exchange, which is the standard procedure for their preparation, and examine how they react to temperature variations.

The structural, optical and morphological properties of CaF2 thin films by using Thermionic Vacuum Arc (TVA)

In this study, calcium fluoride (CaF2) thin films have been prepared by Thermionic Vacuum Arc (TVA) technique on glass substrates. In this technique CaF2 thin films are produced by condensing the plasma of anode material generated in the TVA setup under high vacuum conditions on glass substrates. Crystal structures as well as optical and surface properties of CaF2 antireflective (AR) coated thin films were investigated. X-ray diffraction (XRD) measurements showed that amorphous CaF2 thin films were formed. Optical and surface properties of CaF2 films have been studied based on optical transmittance, reflectance, refractive index and atomic force microscopy imaging (AFM). Our results also show that CaF2 coated samples exhibit lower reflectance (R). From our optical studies, we have observed that CaF2 thin films have high AR properties.

A comparative spectroscopic study of single and dual pulse laser produced UV tin plasmas

A comparative study of single-pulse (SP) and dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) using two Q-switched Nd:YAG lasers emitting at 532nm is presented. Both lasers were combined in the same direction (collinear beam scheme) to focus on planar Sn targets at ambient pressure. The effect of the delay times between the incident laser pulse and the ICCD gate, placement of the laser beam focal position with respect to the illuminated surface, incident laser irradiance, and ambient argon pressure on the signal intensity enhancement for the dual pulse scheme have been studied. Atomic and ionic emission lines of Sn were recorded in the 272–296nm UV spectral region. By using the DP-LIBS excitation technique, the intensity of Sn lines was enhanced by nearly seven times as compared to the single pulse signal that could help the analytical performance of the LIBS technique in terms of increasing sensitivity and reducing self-absorption effects for Sn targets. In the case of the DP-LIBS scheme, the intensities of the atomic Sn I at 283.9nm were recorded at different optimal angles of 45° and 90° and were compared. This comparison was done at different positions of the laser beam focus with respect to the illuminated surface (at 2.45mm in front of the surface, on the surface, at 1.7mm and 4.7mm behind the surface). Furthermore, in the DP-LIBS scheme, an intensity enhancement of the atomic Sn I line at 283.9nm occurs when the signal was recorded at an angle of 90° to the plasma expansion along the direction of the incident laser beam and the detector set at short delay times. The investigation proved that an optimized value of short delay times between the incident laser pulse and the ICCD gate is required. Variations in the electron temperature (Te) and electron number density (Ne) as a function of gate delay time and laser irradiance have been studied by using the emission lines of neutral tin. Special attention was paid to possible self-absorption of the different transitions. The micro-craters created by SP and DP laser ablation were compared using a reflection optical microscopy (ROM).

Preparação e caracterização de microesferas poliméricas magnéticas à base de estireno, divinilbenzeno e acetato de vinila

Microesferas poliméricas magnéticas à base de estireno (STY), divinilbenzeno (DVB), acetato de vinila (VAc) e ferro foram preparadas via polimerização em suspensão e semi-suspensão. Foram estudadas as influências da concentração de VAc adicionado na polimerização e da presença de ferro sobre as características das partículas poliméricas. Estas foram caracterizadas por espectroscopia vibracional na região do infravermelho por transformada de Fourier (FT-IR), análise termogravimétrica (TGA/DTGA), microscopia óptica por reflexão (MO), microscopia eletrônica de varredura (SEM) e magnetometria de amostra vibrante (VSM). Foram obtidas com sucesso microesferas poliméricas com propriedades magnéticas à base de estireno, divinilbenzeno e acetato de vinila. Estes materiais apresentaram bom controle morfológico esférico e partículas de ferro aglomeradas por toda a superfície da microesfera. O maior rendimento de microesferas magnéticas foi encontrado na faixa de 288 μm. Apresentaram também boas propriedades magnéticas (22,62 a 73,75 emu.g-1) com comportamento próximo de materiais superparamagnéticos e boa estabilidade térmica (444 °C).

Adsorption of PVA on Stainless Steel During the PVC Synthesis

The formation of scale on the inner part of reactors during suspension polymerization of Vinyl Chloride Monomer (VCM) has always been a technical and economical problem for PolyVinyl Chloride (PVC) producers. This process leads to the presence of a thick and large polymer build-up, which is stuck to the surface of the autoclaves. This phenomenon will affect among others the properties of the final product at the end of the polymerization and the reactor productivity. The aim of this study was to investigate the physical and chemical origins of this scale formation and to determine the factors responsible for this process. Stainless steel plates (to simulate the reactor's walls) were immersed in the polymerization reactor and analyzed as a function of the immersion time. Infrared Reflection Absorption Spectroscopy (IRRAS) and optical microscopy were used in this study to follow the crust formation during the polymerization process in order to propose a mechanism for the formation of scale.

High resolution imaging of few-layer graphene

In this work, we successfully demonstrate how imaging ellipsometry can be applied to obtain high-resolution thickness maps of few-layer graphene (FLG) samples, with the results being thoroughly validated in a comparative study using several complementary techniques: Optical reflection microscopy (ORM), atomic force microscopy (AFM), and scanning confocal Raman microscopy. The thickness map, revealing distinct terraces separated by steps corresponding to mono- and bilayers of graphene, is extracted from a pixel-to-pixel fitting of ellipsometric spectra using optical constants (n = 2.7 and k = 1.2) derived by fitting slab model calculations to averaged Ψ and Δ spectra collected in large homogenous sample areas. An analysis of reflection spectra and contrast images acquired by ORM confirm the results by quantifying the number of graphene layers and retrieving the FLG optical constants using a simple Fresnel-law-based slab model. The morphology results are further corroborated with AFM and Raman images, the latter unambiguously verifying that the thinnest part of the FLG consists of a graphene bilayer and providing additional information of electronic origin that might help identifying subtle FLG features, such as the presence of impurities, variations in stacking order, or rolling and folding at the FLG edges.