Scanning Optical Microscopy Measurements Research Articles

Vitamin E effects on the wear resistance of UHMWPE sheets against an EBM-produced Ti6Al4V pin

The present article shows preliminary findings on the impact of adding vitamin E to polyethylene. Specimens of ultra-high-molecular-weight polyethylene UHMWPE, both pure and modified with vitamin E, were produced and tested by a pin-on-disc apparatus. The specimens were analyzed using techniques such as differential scanning calorimetry, Shore-D tests, optical microscopy, and surface profile measurements. To replicate the actual wear conditions in prosthetic joints, a pin made of Ti6Al4V, produced using electron beam melting, was used. The wear test results demonstrated that lubrication with simulated synovial fluid reduces debris volume. Furthermore, the addition of vitamin E to the polymer further reduced debris production.

Vibrational Properties in Highly Strained Hexagonal Boron Nitride Bubbles.

Hexagonal boron nitride (hBN) is widely used as a protective layer for few-atom-thick crystals and heterostructures (HSs), and it hosts quantum emitters working up to room temperature. In both instances, strain is expected to play an important role, either as an unavoidable presence in the HS fabrication or as a tool to tune the quantum emitter electronic properties. Addressing the role of strain and exploiting its tuning potentiality require the development of efficient methods to control it and of reliable tools to quantify it. Here we present a technique based on hydrogen irradiation to induce the formation of wrinkles and bubbles in hBN, resulting in remarkably high strains of ∼2%. By combining infrared (IR) near-field scanning optical microscopy and micro-Raman measurements with numerical calculations, we characterize the response to strain for both IR-active and Raman-active modes, revealing the potential of the vibrational properties of hBN as highly sensitive strain probes.

Binding of lambda carrageenan to bovine serum albumin and non-equilibrium effects of complexation

Binding of lambda carrageenan (lCG) to bovine serum albumin (BSA) and the effect of the formation path, namely mixing (M) at specific pH versus titration (T) from a neutral mixture, on complexation have been studied using turbidimetry, phase analysis, dynamic light scattering, confocal laser scanning and bright-field optical microscopy, circular dichroism and fluorescence measurements. The sizes and shape of the complex particles formed under T-conditions differ significantly from those obtained under M-conditions, and at maximal complexation T-complexes contain significantly less lCG as compared to M-complexes. At a pH below pIBSA phase analysis reveals two domains of q corresponding to an approximately constant lCG/BSA weight ratio in the complex phase q* (domain I), and a decreasing q* (domain II). Binding stoichiometries at pH 4.2 and 4.7 are 1:77 and 1:119 mole lCG/mole BSA. The yield of BSA in the complex phase is higher than 98% at pH 4.2 and 4.7, and the complexes form and are stable in the presence of 1.0M–1.5M NaCl. The interaction did not lead to protein denaturation or significant changes in the tertiary and secondary structure and illustrates an enhancement of the hydrophobicity of the protein within the complex particles. At pH 5.2 (pH on the wrong side of PIBSA) up to 37.6% BSA was bound to lCG, and the weight ratio of lCG/BSA in the complex particles (q*) was weakly dependent on q in the complete q range studied. The molecular origin of the unusually strong interaction between lCG and BSA is discussed.

Microring Zone Structure for Near-Field Probes

Recent advances in Surface Plasmon Resonance (SPR) technologies have shown the possibility of transmission enhancement of localized modes propagating through sub-diffraction wide slits and apertures, resulting in the strong near-field focusing of metallic planar nanostructures. This work presents a new approach to the fabrication of high-resolution near-field optical probes using 3D lithography in combination with numerical finite difference time domain (FDTD) simulations. A narrow 500 nm depth of field focus area was observed both by numerical analysis and near field scanning optical microscopy (NSOM) measurements. Further research and optimization are planned in order to achieve subwavelength focal regions and increased signal intensities.

Near-field studies of anisotropic variations and temperature-induced structural changes in a supported single lipid bilayer.

Temperature-controlled polarization modulation near-field scanning optical microscopy measurements of a single supported L_{β^{'}} 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer are presented. The effective retardance (S=2π(n_{e}-n_{o})t/λ, where t is the thickness of the bilayer and λ is the wavelength of light used) and the direction of the projection of the acyl chains (θ) were measured simultaneously. We demonstrate how one is able to align the system over the sample and measure a relative retardance ΔS, a crucial step in performing temperature-controlled experiments. Maps of ΔS and θ, with a lateral resolution on the order of ∼100 nm are presented, highlighting variations deriving from changes in the average molecular orientation across a lipid membrane at room temperature. A discussion of how this information can be used to map the average three-dimensional orientation of the molecules is presented. From ΔS and the known thickness of the membrane t the birefringence (n_{e}-n_{o}) of the bilayer was determined. Temperature-controlled measurements yielded a change of ΔS∼(3.8±0.3) mrad at the main transition temperature (T_{m}∼41^{∘}C) of a single planar bilayer of DPPC, where the membrane transitioned between the gel L_{β^{'}} to liquid disorder L_{α} state. The result agrees well with previous values of (n_{e}-n_{o}) in the L_{β^{'}} phase and translates to an assumed average acyl chain orientation relative to the membrane normal (〈ϕ〉∼32^{∘}) when T<T_{m} and 0^{∘} when T>T_{m}. Evidence of super heating and cooling are presented. A discussion on how the observed behavior as T_{m} is approached, could relate to the existence of varying microconfigurations within the lipid bilyer are presented. This conversation includes ideas from a Landau-Ginzburg picture of first-order phase transitions in nematic-to-isotropic systems.

PH-Dependent Foam Formation Using Amphoteric Colloidal Polymer Particles.

Near-monodispersed micrometer-sized polystyrene (PS) particles carrying amidino and carboxyl groups on their surfaces were synthesized by soap-free emulsion polymerization using an amphoteric free radical initiator. The resulting amphoteric PS particles were characterized in terms of diameter, morphology, disperibility in aqueous media and surface charge using scanning electron microscopy (SEM), optical microscopy (OM), sedimentation rate and electrophoretic measurements. At pH 2.0, where the amidino groups are protonated (positively charged), and at pH 11.0, where the carboxyl groups are deprotonated (negatively charged), the PS particles were well dispersed in aqueous media via electrostatic repulsion. At pH 4.8, where the surface charges are neutral, the PS particles were weakly aggregated. Furthermore, it was confirmed that the PS particles can function as a pH-sensitive foam stabilizer: foamability and foam stability were higher at pH 2.0 and 4.8, where the PS particles can be adsorbed to the air–water interface, and lower at pH 11.0, where the PS particles tend to disperse in bulk aqueous medium. SEM and OM studies indicated that hexagonally close-packed arrays of PS particles were formed on the bubble surfaces and moiré patterns were observed on the dried foams. Moreover, the fragments of dried foams showed iridescent character under white light.

Effects of Ta Content on Thermodynamic Properties and Transformation Temperatures of Shape Memory NiTi Alloy

In the present work, Ni32-x-Ti-Ta18+x (x = 0, 2, 3, 4, 5, 6, 7, 8) shape memory alloys, produced by arc-melting method. Then, differential scanning calorimetry (DSC), optical microscopy (OM), x-ray diffraction (XRD), and Vickers micro-hardness measurements were carried out to investigate thermodynamic parameters, microstructure, crystal structure, and mechanical properties of the alloys, respectively. The DSC results showed that, as the amount of Ta increased, the phase transformation temperatures of the specimens significantly changed. In addition, increasing of Ta composition raised the mass density and electron participation of NiTi alloy, and thus, the vibrational term of entropy overcomes the electron participation; consequently, the total entropy declined in the alloys. It is found that OM images possess a dendritic microstructure, where by increasing the amount of Ta, the dendrites length increase while random orientations decrease. Moreover, XRD patterns exhibited the existence of each austenite phase (B2), martensite phase (B19ʹ), and β-Ta riched phase in all samples.

Probing magnetic and electric optical responses of silicon nanoparticles

We study experimentally both magnetic and electric optically induced resonances of silicon nanoparticles by combining polarization-resolved dark-field spectroscopy and near-field scanning optical microscopy measurements. We reveal that the scattering spectra exhibit strong sensitivity of electric dipole response to the probing beam polarization and attribute the characteristic asymmetry of measured near-field patterns to the excitation of a magnetic dipole mode. The proposed experimental approach can serve as a powerful tool for the study of photonic nanostructures possessing both electric and magnetic optical responses.

Au@polymer core-shell nanoparticles for simultaneously enhancing efficiency and ambient stability of organic optoelectronic devices.

In this paper, we report and discuss our successful synthesis of monodispersed, polystyrene-coated gold core-shell nanoparticles (Au@PS NPs) for use in highly efficient, air-stable, organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). These core-shell NPs retain the dual functions of (1) the plasmonic effect of the Au core and (2) the stability and solvent resistance of the cross-linked PS shell. The monodispersed Au@PS NPs were incorporated into a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film that was located between the ITO substrate and the emitting layer (or active layer) in the devices. The incorporation of the Au@PS NPs provided remarkable improvements in the performances of both OLEDs and OPVs, which benefitted from the plasmonic effect of the Au@PS NPs. The OLED device with the Au@PS NPs achieved an enhancement of the current efficiency that was 42% greater than that of the control device. In addition, the power conversion efficiency was increased from 7.6% to 8.4% in PTB7:PC71BM-based OPVs when the Au@PS NPs were embedded. Direct evidence of the plasmonic effect on optical enhancement of the device was provided by near-field scanning optical microscopy measurements. More importantly, the Au@PS NPs induced a remarkable and simultaneous improvement in the stabilities of the OLED and OPV devices by reducing the acidic and hygroscopic properties of the PEDOT:PSS layer.

In Situ Generation of Surface Plasmon Polaritons Using a Near-Infrared Laser Diode

We demonstrate a semiconductor laser-based approach which enables plasmonic active devices in the telecom wavelength range. We show that optimized laser structures based on tensile-strained InGaAlAs quantum wells-coupled to integrated metallic patternings-enable surface plasmon generation in an electrically driven compact device. Experimental evidence of surface plasmon generation is obtained with the slit-doublet experiment in the near-field, using near-field scanning optical microscopy measurements.

Plasmonic V-groove waveguides with Bragg grating filters via nanoimprint lithography

We demonstrate spectral filtering with state-of-the-art Bragg gratings in plasmonic V-groove waveguides fabricated by wafer scale processing based on nanoimprint lithography. Transmission spectra of the devices having 16 grating periods exhibit spectral rejection of the channel plasmon polaritons with 8.2 dB extinction ratio and -3 dB bandwidth of Δλ = 39.9 nm near telecommunications wavelengths. Near-field scanning optical microscopy measurements verify spectral reflection from the grating structures, and the oscillations of propagating modes along grating-less V-grooves correspond well with effective refractive index values calculated by finite element simulations in COMSOL. The results represent advancement towards the implementation of plasmonic V-grooves with greater functional complexity and mass-production compatibility.

Plasmonic properties of a nanoporous gold film investigated by far-field and near-field optical techniques

We report a study of the plasmonic properties of a 20-nm-thick nanoporous Au film by far-field and near-field optical techniques. The film is prepared sequentially by deposition of gold and copper, thermal annealing, and chemical etching, and has randomly distributed nanopores with sizes ranging between 20 and 350 nm. The absorbance of the nanoporous Au film is much higher than that of a plain Au film and can be attributed to the conversion of incident light into surface plasmon polaritons (SPPs). In addition, a broad peak appears at around 630 nm in the scattering spectrum and serves as evidence of hole plasmon resonance. From transmission mode near-field scanning optical microscopy measurements, two types of local field enhancement are observed. One has a small spatial extent of around 200 nm and the other has a large spatial extent of around 1 μm. The two types of enhancement correspond to strong and weak SPP localizations, respectively.

Thermodynamic analysis and characterization of Bi–Cu–Sn alloys as advanced lead-free solder materials for high temperature application

Due to the frequent use of Cu as a substrate material in electronics, it is important to understand the interactions between the solders and the substrates, based on the knowledge of the phase equilibria, thermodynamics and other characteristics of the Bi–Cu–Sn system. The results of thermodynamic analysis and characterization of Bi–Cu–Sn alloys as advanced lead-free solder materials for high temperature application are presented in this paper. The research includes analytical investigations done by thermodynamic predicting according to general solution model in temperature range 1,073–1,273 K and experimental investigations performed by differential thermal analysis, differential scanning calorimetry, optical microscopy, hardness and electroconductivity measurements for the sections with molar ratio Bi:Cu = 1:1, 1:3 and 3:1.

Nanoscale measurements of local junction breakdown in epitaxial film silicon solar cells

In this contribution, the authors report on near-field scanning optical microscopy measurements of the luminescence emitted from localized junction breakdown in epitaxial silicon solar cells. Our measurements suggest that the observed local reduction in breakdown voltage results from avalanche multiplication assisted by the reinforcing combination of (i) the local enhancement of the electrostatic field at the apex of inverted pyramid pits and (ii) the participation of defect states in the avalanche breakdown. Transmission electron microscopy reveals the microstructure of the defect responsible for the local junction breakdown.

Influence of plastic deformation on occurrence of discontinuous precipitation reaction in Ni-3 at% In alloy

This present study is an attempt to investigate the plastic deformation effect on development of discontinuous precipitation reaction in Ni-3 at% In alloy by applying three different pre-reduced samples by cold rolling ( ε=10%, 30% and 60%). Differential scanning calorimetry (DSC), X-ray diffraction, optical microscopy and microhardness measurements were used as techniques of characterization. We have found that the occurrence of this reaction depends mainly on the deformation ratio before heat treatments. The variation of heating rate using the DSC technique has allowed us to calculate two kinetics parameters of precipitation, which are the Avrami exponent and the activation energy of the process.

Development and characterization of ionic liquid doped solid polymer electrolyte membranes for better efficiency

Solid polymer electrolyte membranes based on poly(ethylene oxide) (PEO) polymer electrolyte incorporated with low viscosity ionic liquid (IL), 1-ethyl 3-methylimidazolium trifluoromethanesulfonate (EMImTFO −) have been prepared and used in dye-sensitized solar cell (DSSC) application. Ionic conductivity ( σ) measurement shows improvement in σ due to reduced crystallinity and free charge carriers provided by IL which was further affirmed by our differential scanning calorimetry (DSC) and optical microscopy (OM) measurements. Surface feature of films was characterized by scanning electron microscopy (SEM) measurement. The photovoltaic characteristics of the fabricated DSSC are compared with those without IL, in which the low viscosity IL doped solid polymer electrolyte system shows excellent improvement in efficiency.

Fabrication and characterization of multi-filament copper matrix–polyethylene fibres composite wire

In this work, the process of co-drawing followed by bundling and restacking was used to fabricate composite wires with a metallic copper matrix and High Density Polyethylene (HDPE) polymer fibres. After processing, copper matrix composite wires with 3770 polymer domains of approximately 20 μm in diameter were obtained. Differential Scanning Calorimetry analysis, optical microscopy and microhardness measurements were performed on the polymer and the copper components of the composites. The volume fraction and the degree of crystallinity of the polymer remain constant during the drawing. This procedure leads to a lamellar reorganization and fragmentation of the crystalline HDPE phase.

Effect of weakly interacting nanofiller on the morphology and viscoelastic response of polyolefins

AbstractEffect of silica nanofiller on the deformation response and morphology of low‐ and high‐density polyethylene (HDPE, LDPE) and isotactic polypropylene (PP) modified with fumed silica was investigated. The dynamic‐mechanical thermal spectroscopy, differential scanning calorimetry, optical microscopy, and density measurements were carried out to determine the temperature dependence of storage and loss moduli as well as nanocomposite morphology. It was demonstrated that the degree of matrix reinforcement is considerably affected by the extent of matrix crystallinity, especially, in the temperature range from (Tm–130°C) to Tm. Based on experimental evidence and literature review, it is proposed that this phenomenon may be attributed to the alpha‐mechanical relaxation process occurring above matrix Tg. As a result of adding silica into the melted matrix, mobility of chains in contact with silica particles became reduced. This caused substantial changes in morphology of these semicrystalline nanocomposites. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Near-field scanning optical microscopy studies of thin film surfaces and interfaces

In this article, the results of the modeling of topography related artifacts appearing in near-field scanning optical microscopy measurements are presented. The results obtained for near-field scanning optical microscope operation in reflection mode with off-axis far field detector position are compared with experimental results. It is shown that the chosen numerical method – Finite Difference in Time Domain method (FDTD) – can be used for efficient modeling of main topography related artifact. It is also seen that the far field detector position can have large influence on the resulting reflection mode optical images.

Epitaxial lateral overgrowth of a-plane GaN by metalorganic chemical vapor deposition

We report on epitaxial lateral overgrowth (ELO) of (112¯0) a-plane GaN by metalorganic chemical vapor deposition. Different growth rates of Ga- and N-polar wings together with wing tilt create a major obstacle for achieving a smooth, fully coalesced surface in ELO a-plane GaN. To address this issue a two-step growth method was employed to provide a large aspect ratio of height to width in the first growth step followed by enhanced lateral growth in the second by controlling the growth temperature. By this method, the average ratio of Ga- to N-polar wing growth rate has been reduced from 4–6 to 1.5–2, which consequently reduced the wing-tilt induced height difference between the two approaching wings at the coalescence front, thereby making their coalescence much easier. Transmission electron microscopy showed that the threading dislocation density in the wing regions was 1.0×108 cm−2, more than two orders of magnitude lower than that in the window regions (4.2×1010 cm−2). However, a relatively high density of basal stacking faults of 1.2×104 cm−1 was still present in the wing regions as compared to c -plane GaN, where they are rarely observed away from the substrate. Atomic force microscopy (AFM) measurements showed two orders of magnitude higher density of surface pits in the window than in the wing regions, which were considered to be terminated by dislocations (partial ones related to stacking faults and full ones) on the surface. The existence of basal stacking faults was also revealed by AFM measurements on the a-plane ELO sample after wet chemical etching in hot H3PO4∕H2SO4 (1:1). The extensions of Ga-polar wings near the meeting fronts were almost free of stacking faults. The improvement of crystalline quality in the overgrown layer by ELO was also verified by near field scanning optical microscopy and time-resolved photoluminescence measurements; the former showing strongly enhanced luminescence from the wing regions, and the latter indicating longer decay times (0.25 ns) compared to a standard a-plane GaN template (40 ps).