Optical Microscopy Probe Research Articles

Plasmon Polariton Imaging Characteristics of Near-Field Optical Fiber Probes

The influence of different near-field optical (near-field scanning optical microscopy) probes on the imaging of surface plasmon polaritons propagating on thin metal films is investigated. Metal-coated fiber probes exhibit a suppression of the measured plasmon signal close to the metal film surface and increased local scattering of the plasmon field. Purely dielectric fiber probes are shown to be largely free of these effects.

Welding of nickel-based alloy 617 using modified dip arc processes

The widespread application of nickel-based alloys as structural materials in chemical, nuclear and power generation industries is often limited due to weldability issues. Technological and metallurgical problems such as lack of fusion or hot cracking require specific welding guidelines as well as knowledge of the welding metallurgy to produce welds that fulfill high quality requirements. Due to the lower heat input modified dip arc welding is a potential alternative joining technique for hot crack sensitive nickel-based alloys. This paper contributes to the application of modified dip arc processes for butt welding of alloy 617 (2.4663). The influence of reduced heat input on microstructural and mechanical properties were investigated. Particular attention was given to the occurrence of hot cracking in the weld metal and base metal HAZ (heat-affected zone) using light optical microscopy, EDS analysis and electron probe microanalysis. The results indicate that the modified dip arc processes provide excellent weld quality and economic efficiency. However, microstructural observations showed that hot cracking in the form of microcracks could not be completely avoided. The modified dip arc welded joints exhibited good tensile strength and impact toughness. The mechanical properties are comparable to commonly GMA (gas metal arc) pulsed arc welding and are not influenced by the microcracks.

Resonant Antenna Probes for Tip-Enhanced Infrared Near-Field Microscopy

We report the development of infrared-resonant antenna probes for tip-enhanced optical microscopy. We employ focused-ion-beam machining to fabricate high-aspect ratio gold cones, which replace the standard tip of a commercial Si-based atomic force microscopy cantilever. Calculations show large field enhancements at the tip apex due to geometrical antenna resonances in the cones, which can be precisely tuned throughout a broad spectral range from visible to terahertz frequencies by adjusting the cone length. Spectroscopic analysis of these probes by electron energy loss spectroscopy, Fourier transform infrared spectroscopy, and Fourier transform infrared near-field spectroscopy corroborates their functionality as resonant antennas and verifies the broad tunability. By employing the novel probes in a scattering-type near-field microscope and imaging a single tobacco mosaic virus (TMV), we experimentally demonstrate high-performance mid-infrared nanoimaging of molecular absorption. Our probes offer excellent perspectives for optical nanoimaging and nanospectroscopy, pushing the detection and resolution limits in many applications, including nanoscale infrared mapping of organic, molecular, and biological materials, nanocomposites, or nanodevices.

Microstructural evolution in 10Ni3MnCuAl precipitation hardened steel after aging at 510°C

The precipitate hardened plastic mould steel 10Ni3MnCuAl after aging at 510°C is investigated by optical microscopy, X-ray diffractometry, TEM and three-dimensional atom probe. The results show that its microstructure is granular bainite with a certain amount of retained austenite after soluted and cooled in furnace, and its content decreases until close to 0. By TEM observation, the age hardening of the 10Ni3MnCuAl steel is mainly ascribed to the precipitation of a high density, ultrafine and fully coherent NiAl precipitation with the B2 structure at 510°C for 4 h, and a multicomponent precipitate can be found in steel for 100 h aging. The three-dimensional atom probe researches show that its age hardening derives from a spherical multicomponent precipitate containing Fe, Ni, Al, Mn and Cu, and the content of Fe decreases with aging time, while those of Ni, Al, Mn and Cu are opposite, and the ratio between Ni and Al is roughly 1, and the Cu precipitates are surrounded by Ni, Al and Mn clusters for 100 h aging. The hardness variation is related to the size and number density of the precipitates, and it follows the cutting mechanism during early aging while obeys Orowan mechanism during overaging.

A functional probe with bowtie aperture and bull's eye structure for nanolithograph

The bowtie aperture surrounded by concentric gratings (the bull's eye structure) integrated on the near-field scanning optical microscopy (NSOM) probe (aluminum coated fiber tip) for nanolithography has been investigated using the finite-difference time domain (FDTD) method. By modifying the parameters of the bowtie aperture and the concentric gratings, a maximal field enhancement factor of 391.69 has been achieved, which is 18 times larger than that obtained from the single bowtie aperture. Additionally, the light spot depends on the gap size of the bowtie aperture and can be confined to sub-wavelength. The superiority of the combination of the bowtie aperture and the bull's eye structure is confirmed, and the mechanism for the electric field enhancement in this derived structure is analyzed.

Discrimination of field components in optical probe microscopy

We demonstrate that the conventional optical signal in near-field scanning optical microscopy and the optical force induced topography contain complementary information about the complex three-dimensional field distribution. Crucially, the additional information about the field distribution can be retrieved without increasing the measurement complexity.

Fabrication of corrugated Ge-doped silica fibers

We present a method of fabricating Ge-doped SiO2 fibers with corrugations around their full circumference for a desired length in the longitudinal direction. The procedure comprises three steps: hydrogenation of Ge-doped SiO2 fibers to increase photosensitivity, recording of Bragg gratings with ultraviolet light to achieve modulation of refractive index, and chemical etching. Finite-length, radially corrugated fibers may be used as couplers. Corrugated tapered fibers are used as high energy throughput probes in scanning near-field optical microscopy.

A Novel Nanostructured Scanning Near Field Optical Microscopy Probe Based on an Adirectional Asymmetry

A Novel Nanostructured Scanning Near Field Optical Microscopy Probe Based on an Adirectional Asymmetry

Following Single mRNAs from Birth to Death in Living Cells

Live cell imaging has been instrumental in analyzing the dynamic properties of RNA. New technologies in optical microscopy and fluorescent probe development have been pushing the envelope of our analysis capabilities. We have been dedicated to developing and implementing these technologies to further the understanding of single mRNA dynamics in cells and organisms. We have utilized computational approaches to analyze real-time transcription activities of endogenous genes from yeast to human cells. We have employed a plethora of imaging methods, ranging from confocal and multiphoton microscopy, long-term cell imaging, high-speed real-time widefield microscopy, single molecule tracking, and we have developed super-registration microscopy and fluorescence fluctuation analysis. We have investigated key processes of RNA synthesis: initiation, elongation, termination, as well as nuclear pore export, cytoplasmic trafficking, localization and decay. Mathematical modeling allowed us to extract quantitative kinetic parameters that precisely describe these processes in living cells.Supported by NIH GMS Grants to RH Singer.

Near-Field Optical Tweezers Based on NSOM and AFM Probes

By applying the direct calculation of Maxwell stress tensor using finite difference time domain method, the feasibility of using a metal-coated fiber probe and using the combination of a near-field scanning optical microscopy (NSOM) probe and an atomic force microscopy (AFM) probe to create near-field optical tweezers is investigated. Numerical results indicate that these schemes are able to trap particles in the range of tens of nano-meters. In experiments 120 nm polystyrene particles are trapped in multi-circular shape with a minimum size of 400 nm, and the polystyrene cluster consisting of three polystyrene particles is obtained for the fabrication of stable polymer nano-structures.

Thermal cycle fatigue behaviors of a single crystal Ni3Al base alloy

The thermal cycle fatigue behaviors of a single crystal Ni3Al base alloy named as IC6SX have been investigated under the test condition of 1000←→15°C. The experimental results showed that the thermal fatigue resistance of the transversal specimens of the alloy was superior to that of the longitudinal specimens. The cracks of the specimens propagated along the interdendritic region more easily than the dendrite, and might pass through the dendrite due to the accumulation of the thermal strain. Optical Microscopy (OM) and Electron Probe X-ray Microanalysis (EPXM) were adopted to observe the crack growth and the microstructural evolution, and composition near the fatigue crack, respectively. The mechanism of the thermal fatigue damage of the alloy was discussed.

Efficient apertureless scanning probes using patterned plasmonic surfaces

We present a novel concept to design apertureless plasmonic probes for near-field scanning optical microscopy (NSOM) with enhanced optical power throughput and near-field enhancement. Specifically, we combine unidirectional surface plasmon polariton (SPP) generation along the tip lateral walls with nanofocusing of SPPs through adiabatic propagation towards an apertureless tip. Three key design parameters are considered: the nanoslit width, the pitch period of nanogrooves for unidirectional plasmonic excitation and the pyramidal geometry of the NSOM probe for SPP focusing. Optimal design parameters are obtained with 2D analysis and two realistic probe geometries with patterned plasmonic surfaces are proposed using the optimized designs. The electromagnetic properties of the designed probes are characterized in the near-field and compared to those of a conventional single-aperture probe with same pyramidal shape. The optimized probes feature FWHM around 150nm, comparable with conventional NSOM designs, but over 3 orders of magnitude larger field enhancement, without degrading its spatial resolution. Our ideas effectively combine the resolution of apertureless probes with throughput levels much larger than those available even in aperture-based devices.

Effects of RE on Iron-Phase Morphology in As-Cast Al-7Si-0.3Mg Alloy Containing 1.2%Fe

In this work, the effects of the addition amount of rear earth on iron phase morphology of Al-7Si-0.3Mg alloy with 1.2%Fe were studied by Optical microscopy (OM), X-ray diffraction (XRD) and electron probe (EPMA). The results showed that: (1) the defined amount of RE addition can significantly inhibit the needle-like iron phase in Al-Si alloy. RE can make the needle-like β-Fe thick thinning, and some even blow or bending. When the addition of RE is 0.36%～0.48%, the modification effect to needle-like β-Fe phase are best. In high iron Al-Si alloys modified by RE, a small amount of bone-like Fe-rich compounds caused by Re were found. (2) after adding excess of RE (RE%>0.48%), a deterioration phenomenon emerged with the formation of large amount of needle-like and plate-like (AlSiRE) intermetallic compounds.

ChemInform Abstract: Phase Equilibria of the Cu—Ni—Si System at 700 °C.

AbstractThe phase equilibria at the 700 °C isothermal section of the title system are determined by XRD, SEM, optical microscopy, X‐ray spectroscopy, and electron probe microanalysis.

Oxide-Ion Conductivity of Highly c-Axis-Oriented Apatite-Type Lanthanum Silicate Polycrystal Formed by Reactive Diffusion between La2SiO5 and La2Si2O7

We have successfully synthesized the highly c-axis-oriented polycrystals of apatite-type lanthanum silicate by the reactive diffusion technique. When the La2SiO5/La2Si2O7 diffusion couples were isothermally heated at 1773–1873 K for 5–100 h, the apatite polycrystals were readily produced in the form of a layer at the interfacial boundaries. The annealed couples were characterized using optical microscopy, micro-Raman spectroscopy, X-ray diffractometry, and electron probe microanalysis. The product layers were composed of the highly c-axis-oriented prismatic crystallites, with their elongation directions being almost parallel to the diffusion direction. The formation of the apatite layer was controlled by volume diffusion, the overall reaction of which is described by (10 + 6x)La2SiO5 + (4–3x)La2Si2O7 → 3La9.33+2x(SiO4)6O2+3x (0.01 ≤ x ≤ 0.13). The apatite layer formed at 1873 K was characterized by the steady decrease of the x-value along the diffusion direction from 0.13 at the La2SiO5/apatite interface ...

Microstructure, mechanical properties and texture evolution of AZ31 alloy containing trace levels of strontium

The effect of low levels of Sr (0.01, 0.03, 0.05 wt.%) on the microstructure, mechanical properties and texture of AZ31 magnesium alloy has been investigated. Thermodynamic modeling has been used to study the effect of Sr on phase precipitation at different temperatures. Cooling curve analysis reveals a decrease in solidification superheat with the addition of 0.03 wt.% Sr to AZ31. The as-cast microstructures of the alloys have been studied using optical microscopy (OM) and electron probe micro analysis (EPMA). Results show the refining effect of Sr on the grain size and on the β-Mg17Al12 precipitates through growth poisoning and inoculation, respectively. To investigate the mechanical properties of the alloys, as-cast samples were compression tested at elevated temperatures. Hot compression peak stress (σmax) and critical strain before recrystallization (εc) initially drop but then increase. σmax first decreases due to the depletion of Al from solid solution and then increases when the amount of the Al–Sr precipitates reach a significant amount. εc drops due to the acceleration of dynamic recrystallization kinetics as a result of grain refinement. It increases with increasing Sr when the concentration Sr in solid solution is increased leading to dislocation pinning and retardation of recrystallization. X-ray texture measurements on the hot compressed and extruded samples show a decrease in maximum intensity of the basal pole figures with increasing Sr as a result of reduced twining and the changes in Al and Sr concentrations in solid solution.

Particles nanomanipulation by the enhanced evanescent field through a near-field scanning optical microscopy probe

A near-field scanning optical microscopy (NSOM) probe and a polarized semiconductor laser (808 nm, cw) were applied to push the trapping resolution down to 120 nm on near-field optical manipulation. A multi-circular shape with a minimum size of 400 nm consisting of 120 nm polystyrene particles can be obtained. They are at a resolution of d ( d: NSOM probe tip diameter) and λ/7 ( λ: laser wavelength), respectively. It is proved that sample concentration and laser power can affect feature size of trapping patterns. In this paper, the effect of trapping forces acted on a nanoparticle along three axis directions on trapping positions is studied, and different trapping positions are generated: the aperture edge in polarization direction and center surface of the probe tip. The result indicates that the single mode NSOM fiber probe is able to trap nanoparticles in a circular shape with lower laser intensity than that required by conventional optical tweezers. The simulated trapping positions around the probe tip based on the conservation law of momentum are found to agree well with experimental results.

Fully Metal-Coated Scanning Near-Field Optical Microscopy Probes with Spiral Corrugations for Superfocusing under Arbitrarily Oriented Linearly Polarised Excitation

We study the effect of a spiral corrugation on the outer surface of a fully metal-coated scanning near-field optical microscopy (SNOM) probe using the finite element method. The introduction of a novel form of asymmetry, devoid of any preferential spatial direction and covering the whole angular range of the originally axisymmetric tip, allows attaining strong field localization for a linearly polarised mode with arbitrary orientation. Compared to previously proposed asymmetric structures which require linearly polarised excitation properly oriented with respect to the asymmetry, such a configuration enables significant simplification in mode injection. In fact, not only is the need for the delicate procedure to generate radially polarised beams overcome, but also the relative alignment between the linearly polarised beam and the tip modification is no longer critical.

The residence probability: single molecule fluorescence correlation spectroscopy and reversible geminate recombination

The residence probability of a freely diffusing particle within an open d-dimensional ball is calculated as a function of time, for an initial distribution that is either a spherical delta function or uniform within the sphere. The latter is equivalent to the autocorrelation function (ACF) of fluorescence correlation spectroscopy (FCS) when utilizing near-field scanning optical microscopy (NSOM) probes. Starting from the general equation for the Laplace transform of the residence probability, we solve it in Laplace space for any dimensionality, inverting it into the time domain in one- and three-dimensions. The short- and long-time asymptotic behaviors of the residence probability are derived and compared with the exact results. Approximations for the two-dimensional ACF are discussed, and a new approximation is derived for the NSOM-FCS ACF. Also of interest is an analytic expression for a three-dimensional ACF, which could be useful for two-photon FCS. Analogy with the binding probability for reversible geminate recombination suggests that more information could be extracted from the long-time tails in FCS experiments.

Nanoscale Fluorescence Correlation Spectroscopy on Intact Living Cell Membranes with NSOM Probes

Characterization of molecular dynamics on living cell membranes at the nanoscale is fundamental to unravel the mechanisms of membrane organization and compartmentalization. Here we demonstrate the feasibility of fluorescence correlation spectroscopy (FCS) based on the nanometric illumination of near-field scanning optical microscopy (NSOM) probes on intact living cells. NSOM-FCS applied to fluorescent lipid analogs allowed us to reveal details of the diffusion hidden by larger illumination areas. Moreover, the technique offers the unique advantages of evanescent axial illumination and straightforward implementation of multiple color excitation. As such, NSOM-FCS represents a powerful tool to study a variety of dynamic processes occurring at the nanometer scale on cell membranes.