Reflection Microspectroscopy Research Articles

Optical and Structural Phenomena at Multipulse Interference Femtosecond Laser Fabrication of Metasurfaces on a Thin Film of Amorphous Silicon

The formation of hexagonal microarrays of nanoholes (metasurfaces) in a 50-nm hydrogenated amorphous silicon film by means of three-beam interference of femtosecond laser pulses of the visible range (wavelength 515 nm) is studied experimentally with various exposures of the film. Characterization of arrays by scanning electron and optical microscopy, as well as optical transmission and reflection microspectroscopy, shows that an increase in the number of fixed energy laser pulses leads to a gradual evaporative formation of nanoholes in the film and, overall, the metasurface. Raman microspectroscopy reveals a simultaneous growth of the volume content of the crystal phase.

Optically Evolved Assembly Formation in Laser Trapping of Polystyrene Nanoparticles at Solution Surface.

Assembling dynamics of polystyrene nanoparticles by optical trapping is studied with utilizing transmission/reflection microscopy and reflection microspectroscopy. A single nanoparticle assembly with periodic structure is formed upon the focused laser irradiation at solution surface layer and continuously grows up to a steady state within few minutes. By controlling nanoparticle and salt concentrations in the colloidal solution, the assembling behavior is obviously changed. In the high concentration of nanoparticles, the assembly formation exhibits fast growth, gives large saturation size, and leads to dense packing structure. In the presence of salt, one assembly with the elongated aggregates was generated from the focal spot and 1064 nm trapping light was scattered outwardly with directions, while a small circular assembly and symmetrical expansion of the 1064 nm light were found without salt. The present nanoparticle assembling in optical trapping is driven through multiple scattering in gathered nanoparticles and directional scattering along the elongated aggregates derived from optical association of nanoparticles, which dynamic phenomenon is called optically evolved assembling. Repetitive trapping and release processes of nanoparticles between the assembly and the surrounding solution always proceed, and the steady state at the circular assembly formed by laser trapping is determined under optical and chemical equilibrium.

Magnesium degradation influenced by buffering salts in concentrations typical of in vitro and in vivo models

Magnesium and its alloys have considerable potential for orthopedic applications. During the degradation process the interface between material and tissue is continuously changing. Moreover, too fast or uncontrolled degradation is detrimental for the outcome in vivo. Therefore in vitro setups utilizing physiological conditions are promising for the material/degradation analysis prior to animal experiments. The aim of this study is to elucidate the influence of inorganic salts contributing to the blood buffering capacity on degradation. Extruded pure magnesium samples were immersed under cell culture conditions for 3 and 10days. Hank's balanced salt solution without calcium and magnesium (HBSS) plus 10% of fetal bovine serum (FBS) was used as the basic immersion medium. Additionally, different inorganic salts were added with respect to concentration in Dulbecco's modified Eagle's medium (DMEM, in vitro model) and human plasma (in vivo model) to form 12 different immersion media. Influences on the surrounding environment were observed by measuring pH and osmolality. The degradation interface was analyzed by electron-induced X-ray emission (EIXE) spectroscopy, including chemical-element mappings and electron microprobe analysis, as well as Fourier transform infrared reflection micro-spectroscopy (FTIR).

Raman and IR reflection micro‐spectroscopic study of Er:YAG laser treated permanent and deciduous human teeth

Permanent and deciduous human teeth treated by a dental Er‐doped yttrium‐aluminium‐garnet pulse laser (λ = 2940 nm) as well as by classical drilling tools under conditions typical of the clinical practice were studied by ultraviolet Raman and Fourier transform infrared (FTIR) reflection microspectroscopy. Enamel was analyzed by both spectroscopic methods, whereas dentine was studied only by FTIR reflection because of the high level of photoluminescence continuum background even when a wavelength of 325 nm was used in inelastic light scattering experiments. The applied energy and pulse frequency of the dental laser varied between 200 and 500 mJ and between 10 and 30 Hz, respectively. The most important result is that after the laser treatment, the hydroxyapatite structure in both permanent and deciduous enamel is preserved: the apatite Ca‐P‐O framework remains intact, and the content of channel OH‐ groups is not changed within experimental uncertainties. The calcium‐phosphate framework of dentine also exhibits negligible laser‐induced changes. The only alterations in enamel induced by laser as well as by mechanical drilling are reduction of the amount of CO32‐ in apatite and changes in the protein conformation. The laser impact on the organic material and carbonate groups is strongest for laser power of 8 W; for powers of 4 or 5 W, the combination of higher pulse energy and lower pulse frequency has less impact than the combination of lower energy and higher frequency. No differences between deciduous and permanent teeth in their resistivity to laser irradiation with λ = 2940 nm were detected. Copyright © 2013 John Wiley & Sons, Ltd.

Chemical surface alteration of biodegradable magnesium exposed to corrosion media

The understanding of corrosion processes of metal implants in the human body is a key problem in modern biomaterial science. Because of the complicated and adjustable in vivo environment, in vitro experiments require the analysis of various physiological corrosion media to elucidate the underlying mechanism of “biological” metal surface modification. In this paper magnesium samples were incubated under cell culture conditions (i.e. including CO 2) in electrolyte solutions and cell growth media, with and without proteins. Chemical mapping by high-resolution electron-induced X-ray emission spectroscopy and infrared reflection microspectroscopy revealed a complex structure of the formed corrosion layer. The presence of CO 2 in concentrations close to that in blood is significant for the chemistry of the oxidised layer. The presence of proteins leads to a less dense but thicker passivation layer which is still ion and water permeable, as osmolality and weight measurements indicate.

On the Use of Overtone and Combination Bands for the Analysis of the CaSO4—H2O System by Mid-Infrared Reflection Spectroscopy

With the aim of characterizing ground preparations of paintings by infrared reflection spectroscopy, the CaSO(4)-H(2)O system (gypsum/bassanite/anhydrite) has been re-investigated, evaluating and assigning the SO(4)(2-) and OH overtone and combination bands, respectively, in the ranges 1900-2700 cm(-1) and 5000-6000 cm(-1) resulting from reflection and high concentration transmission spectra. The second-order modes have been proven to be highly specific, reliable, and less affected by overlap with bands of organic binders and can hence be exploited for the identification of the sulfate hydration phase using infrared (IR) reflection spectroscopy. Subsequently, the characterization and identification of hydration phases in unknown sulfate-based ground preparations on authentic artworks have been carried out noninvasively by fiber-optic reflection IR spectroscopy and on cross-sections by infrared reflection micro-spectroscopy. The spectroscopic data collected both on standards and artworks have been cross-validated by X-ray diffraction.

Micro-spectroscopic characterization of organic and hydrous components in weathered Antarctic micrometeorites

Eight unmelted Antarctic micrometeorite (AMMs) recovered from Kuwagata Nunatak were studied on Al-foils by infrared (IR), Raman, and visible reflection micro-spectroscopy in combination with electron microscopy. Major element abundances of the AMMs studied were found to be similar to solar abundance, although all have the common characteristic of Mg-depletion. Absorption bands around 500 nm were detected for some of the AMMs by the visible micro-spectroscopic method, and these AMMs can be assigned to Fe-hydroxidelike materials. These results suggest that the studied AMMs experienced weathering in Antarctica. Four grains showed the presence of IR H2O and CH bands similar to those of type 2 carbonaceous chondrites, while these were found to be absent in two grains, as in type 3 carbonaceous chondrites. D (disordered: 1360 cm-1) and G (graphite: 1600 cm-1) Raman band features of graphitic carbonaceous materials in these AMMs were not similar to those for type 3 but were rather close to those for type 2 and 1 carbonaceous chondrites, although some data showed a degree of deviation. The genetic classification of individual AMM grains can thus be studied by these methods, although the weathering effects and the atmospheric entry heating on organics and hydrous components need to be evaluated. These multiple micro-spectroscopic reflectance methods are useful for the characterization of precious small samples.

A Study of Electric Field Standing Waves on Reflection Microspectroscopy of Polystyrene Particles

We have been investigating the mid-infrared (MIR) reflection spectrum of microparticles on mirrored substrates. Gold-coated porous alumina filters were used as a substrate to layer the particles and provide consistent reflection spectra. Polystyrene spheres with measured diameters of 0.42 microm were studied using Fourier transform infrared (FT-IR) reflection microspectroscopy, and spectra are shown for coverages in the range 0.5-6 monolayers (ML). Results show that absorption has a nonlinear, stairstep-like dependence on particle coverage and a wavelength dependence that can be explained by electric field standing waves (EFSW) caused by the mirrored substrate. The same effect is found to cause progressive weakening of the observed spectra as a function of increasing wavelength in sub-monolayer coverage measurements. Scattering effects in the spectra are consistent with surface scattering at the antinodes of the EFSW. These observations provide explanations for differences seen between optical properties of particles calculated using the specular-reflection method versus those calculated using traditional aerosol methods. A simple multilayer method for estimating particle absorption coefficients is demonstrated that compares well with values reported using ellipsometry for bulk polystyrene. Another simple method based on submonolayer coverage spectra provides spectra suitable for classification analysis but is only semi-quantitative at determining absorption coefficients.

Photo-electrochemical etching of macro-pores in silicon with grooves as etch seeds

Role of linear nucleation centres (surface grooves) in formation of macro-pores has been studied for n-type Si. It has been found that linear nucleation centres, contrary to the case of point nucleation pits, initiate formation of semi-regular pore pattern: along the grooves the pores are arranged randomly as a result of self organization process, across the grooves they follow the prescribed period a. The average distance between the pores along a groove line depends on a, and decreases as a increases. At the optimal value of etching current density and seed period a, the distinct pores can merge, thus forming a periodic structure of one-dimensional photonic crystal. Optical properties of grooved structures with merged pores have been investigated by means of Fourier infrared reflection micro-spectroscopy in the spectral range from 1.45 μm to 16.5 μm. Reflectance spectra reveal presence of photonic band gaps which positions in the middle IR range are in a good agreement with calculations by transfer matrix method. The fabrication approach developed is promising for application in silicon-based photonics.

Anisotropy Studied by Polarization-Modulated Fourier Transform Infrared Reflection Difference Microspectroscopy

We investigated anisotropic optical behavior in solid-state materials using Fourier transform infrared reflection microspectroscopy in combination with polarization modulation. For a Ca1.8Sr0.2RuO4 crystal with an isotropic optical surface, we found the reflection difference to be very close to zero, independent of the azimuthal angle of the sample. A Ca1.4Sr0.6RuO4 crystal with an anisotropic optical surface, however, exhibited a large anisotropic optical response with a strong angular dependence following a sinusoidal behavior. Furthermore, we examined the spatial distribution of the reflection difference in Bi0.17Ca0.83MnO3+delta using infrared synchrotron radiation and could clearly distinguish microscopic anisotropic domains having different optical axes. These results demonstrate that our experimental scheme can be used as a powerful tool to spectrally and spatially resolve anisotropy of solid-state materials in the mid-infrared region.

Microscopic exciton properties of fibril-shaped molecular J-aggregates prepared in ultra-thin polymer films

Results on microscopic fluorescence imaging and spectroscopy of fibril-shaped J-aggregates of pseudoisocyanine dyes prepared in thin film matrices of polyvinyl sulfate (PVS) are reported compared with simultaneous observation of the reflection micro-spectroscopy. While the shape of the local reflectance spectra show huge broadening and sometimes dip structures at higher local reflectance levels, we have found that local fluorescence spectra are rather simple and narrow single peak appears at 572 nm or bit longer which is almost coincide with that of ordinary J-band. The result is not inconsistent with the exciton–polariton onset scheme, based on which initial reflectance properties are interpreted. Anomalous local polarization dependences are also observed in fluorescent transition dipoles as in the local reflectance observation, indicating the anomaly is inherent to the fibril formation.

Local reflection micro-spectroscopy of excitons in fibril-shaped molecular J-aggregates prepared in PVA thin films

Results on microscopic reflection imaging and spectroscopy of fibril-shaped J-aggregates of pseudoisocyanyne dyes prepared in thin film matrices of polyvinyle alcohol (PVA) are reported. We have found that formation of fibril-shaped structures with sub-micron widths is also possible in PVA. Despite the aggregation mechanism should be different from those in polyvinyl sulfate, reflection images and local spectroscopy show that the exciton–polariton characters are basically similar in the two matrices. Anomalous polarization dependence is also observed in PVA and seems rather strengthened.

Mapping the orientation of exciton transition dipoles along individual nanostructures of molecular J-aggregates

Modulation of the polarization state of incident light in reflection microspectroscopy is used to study locally the orientations of exciton transition dipole moments of fiberlike nanostructures of J-aggregates of pseudoisocyanine dyes. The lowest exciton state assumes a wide range of directions with respect to the long axis of the fibers, from parallel to perpendicular. This behavior is correlated with the onset of polariton-like character of the local reflectance spectra. The results imply that a new structural model has to be conceived to explain the observed phenomena.

Attenuated Total Internal Reflection Microspectroscopy of Isolated Particles: An Alternative Approach to Current Methods

An alternative approach to conduct attenuated total internal reflection infrared microspectroscopy is described with the use of cartridge-based hemispherical internal reflection elements. The study demonstrates that the devices can be employed on any infrared microscope having reflectance capabilities. A comparison shows that the method provides the same signal-to-noise ratio in comparison to transmission studies for equal sample sizes. In addition, a 4× decrease in the sampled areas inherent with the method was verified for samples 60 μm in diameter and larger. Examples are presented that demonstrate the method's capability of studying small isolated samples without the use of a contaminating mounting media. Examples are also presented that demonstrate the potential to study samples without the effects of diffraction.

Characterization and Application of a Grazing Angle Objective for Quantitative Infrared Reflection Microspectroscopy

A grazing angle objective on an infrared microspectrometer is studied for quantitative spectroscopy by considering the angular dependence of the incident intensity within the objective's angular aperture. The assumption that there is no angular dependence is tested by comparing the experimental reflectance of Si and KBr surfaces with the reflectance calculated by integrating the Fresnel reflection coefficient over the angular aperture under this assumption. Good agreement was found, indicating that the specular reflectance of surfaces can straightforwardly be quantitatively integrated over the angular aperture without considering nonuniform incident intensity. This quantitative approach is applied to the thickness determination of dipcoated Krytox on gold. The infrared optical constants of both materials are known, allowing the integration to be carried out. The thickness obtained is in fair agreement with the value determined by ellipsometry in the visible. Therefore, this paper illustrates a method for more quantitative use of a grazing angle objective for infrared reflectance microspectroscopy.

Anisotropy of interchain interaction in polymeric (SN) x crystals

The technique of polarized reflection microspectroscopy was used to study anisotropy of polymeric sulfur nitride (SN) x in plasma edge region. The spectra taken from different faces of single crystals indicate the presence of strong anisotropy of interchain interaction due to orientation of the π-electron orbitals and suggest two-dimensional metallic behavior of the π-electron system in (SN) x .