Near-field Optical Microscope Probe Research Articles

Propagation constant-based diameter measurement technique for a submicrometer-scale optical fiber.

Diameter is a critical parameter for determining the physical properties of a submicrometer optical fiber and requires an accurate measurement. In this study, we proposed, to our knowledge, a novel diameter measurement technique derived from the waveguide theory, utilizing the pitch of a standing-wave near-field light generated by two counter-propagating lights within the submicrometer optical fiber. In a submicrometer optical fiber, the propagating light extends into the surrounding air as near-field light, existing within a range approximately equivalent to one wavelength from the surface of the fiber. By generating the standing-wave near-field light with the incident lights from both ends of the fiber, the pitch of the standing-wave near-field light can be measured by scanning along the fiber's central axis with a scanning near-field optical microscopy probe. The fiber diameter is subsequently acquired by solving the optical fiber eigenvalue equation. Based on the feasibility verification experiment, a high-precision measurement of approximately 0.50 µm was realized for the diameter of the optical fiber.

An Apertureless Scanning Near-Field Optical Microscope Probe with a Lateral Resolution of 10 – 15 nm Observed with a Semiconductor Structure

An Apertureless Scanning Near-Field Optical Microscope Probe with a Lateral Resolution of 10 – 15 nm Observed with a Semiconductor Structure

Mechanism of near-field optical nanopatterning on noble metal nano-films by a nanosecond laser irradiating a cantilevered scanning near-field optical microscopy probe.

To overcome the diffraction limit, a laser irradiating cantilevered scanning near-field optical microscopy (SNOM) probe has been used in near-field optical nanopatterning. In this paper, the mechanism of nanopatterning on noble metal nano-films by this technique is investigated by the finite element method. It is proposed that the main mechanism of this phenomenon is the melt and reshaping of the nano-film under the SNOM tip. The melt is caused by the surface plasmon polariton-assisted enhancement and restriction within the SNOM tip aperture. The impacts of the gap g between the tip and substrate and the polarization of the laser are further analyzed.

Fabrication of nanostructure on Au nano-film by nanosecond laser coupled with cantilevered scanning near-field optical microscopy probe

Diffraction limit has been the constraint of the nanostructure fabrication. Because the scanning near-field optical microscopy (SNOM) can work in the evanescent near-field region, its application in nano-processing has received extensive attention from researchers globally. In this paper, we combined nanosecond laser with cantilevered SNOM probe. Utilizing the high precision of the confinement and enhancement effect of probe tip and the high instantaneous energy of the laser, we realized nanostructure fabrication and in situ detection on Au nano-film. Feature sizes down to 47 nm full width at half maximum were fabricated. We investigated the laser propagation through the SNOM tip aperture and the light field intensity distribution on the surface of substrate theoretically. The calculation results demonstrate that the laser is highly restricted within the SNOM aperture and enhanced on the exit plane at the rim of aperture. After the transmission, the light field intensity distribution on the surface of the Au nano-film was enhanced due to the localized surface plasmon resonance. The thermal distribution on the surface of Au nano-film indicates that the peak of the temperature distribution appeared at the surface right underneath the center of the aperture. It is proved that the simulation results are consistent with the experimental results.

Cloaked near-field probe for non-invasive near-field optical microscopy

Near-field scanning optical microscopy is a powerful technique for imaging below the diffraction limit, which has been extensively used in biomedical imaging and nanophotonics. However, when the electromagnetic fields under measurement are strongly confined, they can be heavily perturbed by the presence of the near-field probe itself. Here, taking inspiration from scattering-cancellation invisibility cloaks, Huygens–Kerker scatterers, and cloaked sensors, we design and fabricate a cloaked near-field probe. We show that, by suitably nanostructuring the probe, its electric and magnetic polarizabilities can be controlled and balanced. As a result, probe-induced perturbations can be largely suppressed, effectively cloaking the near-field probe without preventing its ability to measure. We experimentally demonstrate the cloaking effect by comparing the interaction of conventional and nanostructured probes with a representative nanophotonic structure, namely, a 1D photonic-crystal cavity. Our results show that, by engineering the structure of the probe, one can systematically control its back action on the resonant fields of the sample and decrease the perturbation by > --> 70 % with most of our modified probes, and by up to 1 order of magnitude for the best probe, at probe-sample distances of 100 nm. Our work paves the way for non-invasive near-field optical microscopy of classical and quantum nanosystems.

Measurement properties of electric field intensity distribution of whispering gallery mode with near-field optical probe

The distribution of the external electric field intensity of the whispering gallery mode (WGM) can be measured using a scanning near-field optical microscopy (SNOM) probe. As probing the resonator influences the optical resonance state, the measurement properties of the SNOM probe are worth studying. In this study, the measurement mechanism of WGMs using a glass SNOM probe was analyzed numerically. A probe with a nanometric-diameter is generally preferable. The results showed that the high-contrast measurement was possible; however, the signal was weak. Using a tip with a diameter equal to half the resonant wavelength, the signal strength was maximized with the same high contrast level as the nanoprobe. Interestingly, the measurement mechanism was different depending on tip size. With the nanoprobe, the interaction with the WGMs varied depending on the sensing locations; therefore, the resonant states were modulated during the measurements, which may have induced unexpected mode hopes. The resonance state was steady during measurements using a probe tip with a diameter of half the resonance wavelength. Although the mechanisms were different, the measured electric field intensity distributions were the same for both tip diameters.

Design and characterization of a new microscopy probe using COMSOL and ANSYS

This paper presents the design, simulation, and analysis of different 3D-shapes of scanning near-field optical microscopy probes, allowing the acquisition of both topographic and optical images. The study is conducted using COMSOL and ANSYS simulation tools to study the probe sensitivity and deflection. The simulation calculations of deflection and von Mises stress are denoted, analyzed, and compared based on the change in the probe shapes for the same applied force. The results obtained from the two finite element tools were similar, converged to the same ideal design, and showed the impact of the probe structure on the probe performance.

Simulation of Optical Nano-Manipulation with Metallic Single and Dual Probe Irradiated by Polarized Near-Field Laser

Nano-manipulation technology, as a kind of “bottom-up” tool, has exhibited an excellent capacity in the field of measurement and fabrication on the nanoscale. Although variety manipulation methods based on probes and microscopes were proposed and widely used due to locating and imaging with high resolution, the development of non-contacted schemes for these methods is still indispensable to operate small objects without damage. However, optical manipulation, especially near-field trapping, is a perfect candidate for establishing brilliant manipulation systems. This paper reports about simulations on the electric and force fields at the tips of metallic probes irradiated by polarized laser outputted coming from a scanning near-field optical microscope probe. Distributions of electric and force field at the tip of a probe have proven that the polarized laser can induce nanoscale evanescent fields with high intensity, which arouse effective force to move nanoparticles. Moreover, schemes with dual probes are also presented and discussed in this paper. Simulation results indicate that different combinations of metallic probes and polarized lasers will provide diverse near-field and corresponding optical force. With the suitable direction of probes and polarization direction, the dual probe exhibits higher trapping force and wider effective wavelength range than a single probe. So, these results give more novel and promising selections for realizing optical manipulation in experiments, so that distinguished multi-functional manipulation systems can be developed.

Far-Infrared Near-Field Optical Imaging and Kelvin Probe Force Microscopy of Laser-Crystallized and -Amorphized Phase Change Material Ge3Sb2Te6.

Chalcogenide phase change materials reversibly switch between non-volatile states with vastly different optical properties, enabling novel active nanophotonic devices. However, a fundamental understanding of their laser-switching behavior is lacking and the resulting local optical properties are unclear at the nanoscale. Here, we combine infrared scattering-type scanning near-field optical microscopy (SNOM) and Kelvin probe force microscopy (KPFM) to investigate four states of laser-switched Ge3Sb2Te6 (as-deposited amorphous, crystallized, reamorphized, and recrystallized) with nanometer lateral resolution. We find SNOM to be especially sensitive to differences between crystalline and amorphous states, while KPFM has higher sensitivity to changes introduced by melt-quenching. Using illumination from a free-electron laser, we use the higher sensitivity to free charge carriers of far-infrared (THz) SNOM compared to mid-infrared SNOM and find evidence that the local conductivity of crystalline states depends on the switching process. This insight into the local switching of optical properties is essential for developing active nanophotonic devices.

Quantification of electron accumulation at grain boundaries in perovskite polycrystalline films by correlative infrared-spectroscopic nanoimaging and Kelvin probe force microscopy

Organic–inorganic halide perovskites are emerging materials for photovoltaic applications with certified power conversion efficiencies (PCEs) over 25%. Generally, the microstructures of the perovskite materials are critical to the performances of PCEs. However, the role of the nanometer-sized grain boundaries (GBs) that universally existing in polycrystalline perovskite films could be benign or detrimental to solar cell performance, still remains controversial. Thus, nanometer-resolved quantification of charge carrier distribution to elucidate the role of GBs is highly desirable. Here, we employ correlative infrared-spectroscopic nanoimaging by the scattering-type scanning near-field optical microscopy with 20 nm spatial resolution and Kelvin probe force microscopy to quantify the density of electrons accumulated at the GBs in perovskite polycrystalline thin films. It is found that the electron accumulations are enhanced at the GBs and the electron density is increased from 6 × 1019 cm−3 in the dark to 8 × 1019 cm−3 under 10 min illumination with 532 nm light. Our results reveal that the electron accumulations are enhanced at the GBs especially under light illumination, featuring downward band bending toward the GBs, which would assist in electron-hole separation and thus be benign to the solar cell performance.Correlative infrared-spectroscopic nanoimaging by the scattering-type scanning near-field optical microscopy and Kelvin probe force microscopy quantitatively reveal the accumulated electrons at GBs in perovskite polycrystalline thin films.

Fluorescence spectra of colloidal self-assembled CdSe nano-wire on substrate of porous Al2O3/Au nanoparticles**Project supported by the National Natural Science Foundation of China (Grant Nos. 61741505 and 61865002), the Guizhou Provincial Science and Technology Support Plan, China (Grant No QKHZ [2017]2887), the Guiding Local Science and Technology Development Plan of the Central Government of China (Grant No. QKZYD [2017]4004), the Guizhou

We present a self-assembly method to prepare array nano-wires of colloidal CdSe quantum dots on a substrate of porous Al2O3 film modified by gold nanoparticles. The photoluminescence (PL) spectra of nanowires are in situ measured by using a scanning near-field optical microscopy (SNOM) probe tip with 100-nm aperture on the scanning near-field optical microscope. The results show that the binding sites from the edge of porous Al2O3 nanopores are combined with the carboxyl of CdSe quantum dots’ surface to form an array of CdSe nanowires in the process of losing background solvent because of the gold nanoparticles filling the nano-holes of porous Al2O3 film. Compared with the area of non-self-assembled nano-wire, the fluorescence on the Al2O3/Au/CdSe interface is significantly enhanced in the self-assembly nano-wire regions due to the electron transfer conductor effect of the gold nanoparticles’ surface. In addition, its full width at half maximum (FWHM) is also obviously widened. The method of enhancing fluorescence and energy transfer can widely be applied to photodetector, photocatalysis, optical display, optical sensing, and biomedical imaging, and so on.

Dual-color plasmonic probes for improvement of scanning near-field optical microscopy

Design and modeling of a class of scanning near-field optical microscope (SNOM) probe for improving performance are reported. The basic idea is to generate more than one hot spot with well-known spatial distribution. This not only enables one to calibrate out many sorts of errors in conventional SNOM but also results in the increase in the speed of imaging. We utilize plasmonic nanocolor sorter structures to design aperture probes that create two spatially distinct hot spots. The method of moment analysis technique is employed to tune the probe for operation at standard Ar-ion laser wavelengths (457.9 and 514.5 nm).

Investigation of photoconductivity of individual InAs/GaAs(001) quantum dots by Scanning Near-field Optical Microscopy

The spatial distribution of the photocurrent in the input window plane of a GaAs-based p–i–n photodiode with embedded self-assembled InAs quantum dots (QDs) has been studied with the photoexcitation through a Scanning Near-field Optical Microscope (SNOM) probe at the emission wavelength greater than the intrinsic absorption edge of the host material (GaAs). The inhomogeneities related to the interband absorption in the individual InAs/GaAs(001) QDs have been observed in the photocurrent SNOM images. Thus, the possibility of imaging the individual InAs/GaAs(001) QDs in the photocurrent SNOM images with the lateral spatial resolution ∼ 100 nm (of the same order of magnitude as the SNOM probe aperture size) has been demonstrated.

A simple model of the scanning near-field optical microscopy probe tip for electric field enhancement

A simple model of the scanning near-field optical microscopy probe tip for electric field enhancement

Simple modeling of the ratio of fields at a tip and at contacting surface

AbstractThe proposed concept of Raman probe for nearfield optical microscopy raises the question about the similarity of fields acting on specimens deposited at the tip apex and contacting surface. The signal generated at these two close but different points is defined by local fields, so it is the ratio of the fields at these points, that is the quantity of interest here. This work is concerned with the application of a simple dipole model for the analysis of the ratio of fields at the tip apex and at contacting surface as a function of their separation.

Study of light emission and collection in a transparent dielectric cantilever-based near-field optical probe.

We report the design of a new type of scanning near-field optical microscopy probes combining the advantages of both tapered optical fibres type and cantilever type commercial scanning near-field optical microscopy probes. The material is an organomineral synthesized by the sol-gel method. This material matches mechanical and optical performances for such a scanning near-field optical microscopy probe fabrication. Numerical calculations were carried out using finite element method in order to study the optical transmission of the probe in emission and collection modes. The influence of the probe geometry on the intensity distribution in the vicinity of the aperture and in the extremity of the cantilever is studied in details.

Using ferrule-top opto-mechanical probes as a new tool in VCSEL reliability experiments.

Today, vertical cavity surface emitting lasers (VCSELs) are used in many high-end applications, for which the laser lifetime is a critical parameter. Changes in the spatial distribution of the various emission modes of the VCSEL can be used as an early sign of device degradation, enhancing the speed and detail of failure mode analysis. We have developed a ferrule-top combined atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) probe that can be used to analyze the transverse mode pattern of the 850 nm radiation at a <200 nm spatial resolution. During accelerated lifetime testing, the newly developed method shows that small local changes in the optical output can already be detected before any sign of device degradation is observed with conventional methods.

Tuning Localized Surface Plasmon Resonance in Scanning Near-Field Optical Microscopy Probes.

A reproducible route for tuning localized surface plasmon resonance in scattering type near-field optical microscopy probes is presented. The method is based on the production of a focused-ion-beam milled single groove near the apex of electrochemically etched gold tips. Electron energy-loss spectroscopy and scanning transmission electron microscopy are employed to obtain highly spatially and spectroscopically resolved maps of the milled probes, revealing localized surface plasmon resonance at visible and near-infrared wavelengths. By changing the distance L between the groove and the probe apex, the localized surface plasmon resonance energy can be fine-tuned at a desired absorption channel. Tip-enhanced Raman spectroscopy is applied as a test platform, and the results prove the reliability of the method to produce efficient scattering type near-field optical microscopy probes.

Fabrication and mechanical properties of an organo-mineral cantilever-based probe for near-field optical microscopy

We present the design, batch fabrication sequences and mechanical characterization of an optical near-field probe. The probe structure is made of a hybrid organo-mineral material synthesized using a sol–gel process. The cantilever-type probe was designed for Scanning Near-field Optical Microscopy (SNOM) in collection mode and its design was optimized by simulations. The mechanical properties of the probes were measured and topographical images of a standard surface obtained with the fabricated probes are presented.

Dielectric probe for scattering-type terahertz scanning near-field optical microscopy

Dielectric material was used as the probe material for a scattering-type terahertz scanning near-field optical microscope (THz S-SNOM). It was found that the dielectric probe exhibits a strong near-field scattering signal with an amplitude comparable to that of the metallic probe. The behavior of the electric near-field around the tip was calculated using the finite-difference time-domain method, showing the field enhancement comparable to that of the metallic probe. The dielectric probe also exhibited a faster temporal response compared to the response of the metallic probe. Introduction of a non-metallic probe would enlarge the application field of the THz S-SNOM technique.