Near-field Optical Microscope Probe Research Articles

1.5-Mbit/s direct readout of line-and-space patterns using a scanning near-field optical microscopy probe slider with air-bearing control

We have demonstrated 1.5-Mbit/s signal readout of a 0.25 μm line-and-space (L&S) pattern on a rotating disk by using a scanning near-field optical microscopy (SNOM) probe slider with air-bearing control. The light transmittance of the probe was greatly increased through direct irradiation of a focused light to a pyramidal probe tip. The bit rate of the signal was enhanced by two orders of magnitude compared to that of existing SNOM systems that use a tapered-fiber probe. The signal contrast, signal-to-noise ratio, and carrier-to-noise ratio for the 0.25 μm L&S pattern were 19%, 17 dB, and 37 dB, respectively. The estimated resolution limit of the probe corresponded to a L&S width of ∼130 nm.

Thermal-expansion effects in near-field optical microscopy fiber probes induced by laser light absorption

We present a study on thermal-expansion effects induced by laser light coupling into metal-coated probes for near-field scanning optical microscopy. An expansion of the probe edge of 170 nm per mW of coupled power has been observed as an effect of the temperature raise due to light absorption in the metal coating. The phenomenon has been studied in both time and frequency domains by modulating the coupled laser power, in order to measure the typical time constants related to heat exchange processes, that turned out to be of the order of a few milliseconds. An analytical model, taking into account both the heat conduction through the coating and the convection losses, provides scales for the system parameters and fits the experimental data remarkably well.

Fabrication of single-mode chalcogenide fiber probes for scanning near-field infrared optical microscopy

We fabricate scanning near-field optical microscope (IR-SNOM) probe tips made from singlemode chalcogenide fiber and test them using a standard SNOM setup and free-electron laser. SEM micrographs, showing tips with submicrometer physical dimensions, demonstrate the feasibility of the thermal micropipette puller process used to create the tips. Topographical data obtained using a shear-force near-field microscope exhibit spatial resolution in the range of 80 to 100 nm. Optical data in the IR (near 3.5 $\mu$m), using the probe tips in collection mode, indicate an optical spatial resolution of approximately $\lambda/15$.

Nano-slit probes for near-field optical microscopy fabricated by focused ion beams.

The near-field probes described in this paper are based on metallized non-contact atomic force microscope cantilevers made of silicon. For application in high-resolution near-field optical/infrared microscopy, we use aperture probes with the aperture being fabricated by focused ion beams. This technique allows us to create apertures of sub-wavelength dimensions with different geometries. In this paper we present the use of slit-shaped apertures which show a polarization-dependent transmission efficiency and a lateral resolution of < 100 nm at a wavelength of 1064 nm. As a test sample to characterize the near-field probes we investigated gold/palladium structures, deposited on an ultrathin chromium sublayer on a silicon wafer, in constant-height mode.

Towards better scanning near-field optical microscopy probes--progress and new developments.

Several approaches are described with the aim of producing near-field optical probes with improved properties. Focused ion beam milling allows the fabrication of small apertures in a controlled fashion, resulting in probes with excellent polarization properties and increased transmission. Microfabrication processes are described that allow the production of apertures of 30-50 nm, facilitating the mass-fabrication of apertured tip structures that can be used in a combined force/near-field optical microscope. Finally, possible future developments are outlined.

A novel fabrication method for fluorescence-based apertureless scanning near-field optical microscope probes.

We report a novel method for the fabrication of probes with localized sub-wavelength fluorescing media at their extremities. We present our first results and discuss future plans to extend this technique to the systematic fabrication of fluorescent probes for apertureless scanning near-field optical microscopy.

Singlemode chalcogenide fiber infrared SNOM probes

We have fabricated and tested infrared scanning near-field optical microscope (IR-SNOM) probe tips made from singlemode chalcogenide fiber. The process used to create the tips was similar to conventional micropipette-puller techniques, with some modifications to allow for the lower melting temperature and tensile strength of the chalcogenide fiber. SEM micrographs, showing tips with sub-micrometer physical dimensions, demonstrate the feasibility of this process. Topographical data obtained using a shear-force near-field microscope exhibits spatial resolution in the range 80–100 nm. Optical data in the infrared (near 3.5 μm), using the probe tips in collection mode, indicates an optical spatial resolution approximately λ/15.

Scanning near-field optical microscopy using piezoelectric cantilevers

Microfabricated cantilevers for atomic force microscopy (AFM), used as scanning near-field optical microscopy (SNOM) probes, have remarkable advantages because the fabrication process is well established. In addition, the SNOM probe can be combined with an atomic fore microscope, which is capable of detecting various surface properties. However, the optical method for measuring the deflection of the cantilever often disturbs the detection of weak evanescent light. We have developed a new SNOM probe using a microfabricated cantilever with a piezoelectric thin film as an integrated deflection sensor so that any optical measurements for the deflection are not required. The cantilever is made of Si with deposited layers of Pt/lead ziconate titanate (PZT)/Pt and an SiN hollow pyramidal tip at the en The light scattered by the tip can transmit the cantilever when the PZT cantilever is brought in close proximity to a sample surface. The tip-to-sample distance is regulated using the piezoelectric current while the cantilever is vibrated at its resonance frequency. Both topographic and optical images were obtained successfully by the new SNOW probe.

Micromachined SPM probes with sub-100 nm features at tip apex

We have developed a fabrication process that allows thin films to be patterned at the end of a sharp tip. Using this method, many different material contrasts can be achieved on the apex of a scanning probe microscope tip. For example, small apertures down to 30 nm have been patterned into an aluminium film covering quartz tips to form scanning near-field optical microscopy probes. Also, small well-defined metal electrodes can be fabricated on the tip apex, which can be used for electrochemical measurements. The tip structuring process is a batch fabrication method and is based on CMOS-compatible technologies, which means that it can be integrated easily into an existing microfabrication process. Furthermore, it allows the patterning of a wide range of tip heights, materials or geometries. Copyright © 1999 John Wiley & Sons Ltd.

Apparent superresolution in near-field optical imaging of periodic gratings

A superresolution phenomenon in images of diffraction gratings obtained with a near-field optical microscope probe positioned at distances of the order of 1>mu;m from the surface was recently reported [Appl. Opt. 33, 876 (1994)]. This experiment was interpreted in terms of evanescent waves observed in the far field. We show that the effect observed in that experiment is a very well known far-field optical phenomenon called the Talbot effect. The existence of self-imaging Talbot planes for gratings with periods of the order of a few micrometers appears promising for many practical applications.

The use of a near-field probe for the study of semiconductor heterostructures

We present a calculation to determine the intensity profile and polarization state within a semiconductor sample of the electric field emission from a scanning near-field optical microscope (SNOM) probe. The propagation of radiation from the apex of a metal-coated tapered optical fibre to the sample, and the subsequent propagation of the electric field through the sample are calculated by using the Bethe-Bouwkamp model, considering the problem to be that of diffraction of linearly polarized monochromatic light by a subwavelength circular hole in a perfectly conducting metallic screen. The sample chosen in our calculation, GaAs, allows us to demonstrate that subwavelength imaging is possible on buried heterostructures.

High definition aperture probes for near-field optical microscopy fabricated by focused ion beam milling

We have improved the optical characteristics of aluminum-coated fiber probes used in near-field scanning optical microscopy by milling with a focused ion beam. This treatment produces a flat-end face free of aluminum grains, containing a well-defined circularly-symmetric aperture with controllable diameter down to 20 nm. The polarization behavior of the tips is circularly symmetric with a polarization ratio exceeding 1:100. The improved imaging characteristics are demonstrated by measuring single molecule fluorescence. Count rates increase more than one order of magnitude over unmodified probes, and the molecule images map a spatial electric field distribution of the aperture in agreement with calculations.

Development of a fiber used for fabricating application oriented near-field optical probes

We propose and develop a new fiber for application oriented probes for near-field optical microscopy. Based on a geometric model of selective etching, we design the fiber having the germanosilicate-doped silica core, an inner pure silica cladding, and an outer fluorine doped silica cladding. The fiber is fabricated by vapor-phase axial deposition. By selective etching of the fiber in buffered hydrogen fluoride solutions, we fabricated three probes having high-resolution capability and/or high-transmission efficiency for applications to high-resolution imaging and local spectroscopy. The apex diameters of the probes were less than 10 nm.

(3) Developement of localized plasmon resonance probe for novel near-field optical microscopy

(3) Developement of localized plasmon resonance probe for novel near-field optical microscopy

人工膜と生体膜の接点を探る 最近の膜研究の方法 原子間力制御型近視野顕微鏡による生体イメージング

A scanning near-field optical/atomic-force microscope (SNOAM) system was applied to simultaneous topographic and fluorescence imaging of biological samples in air and liquid. The SNOAM uses a bent optical fiber simultaneously as a dynamic mode atomic-force microscopy (AFM) cantilever and a scanning near-field optical microscopy (NSOM) probe. Optical resolution of this system indicated about 50-100 nm in a fluorescence mode for fluorescent latex beads on a quartz glass plate. The SNO-AM system used 458 or 488 nm from Ar ion laser multiline of excitation of green fluorescent protein (GFP), since a native GFP has been known to give a maximum at 395 nm and a broad absorption spectrum until 500 nm. Topographic and fluoresence images of recombinant E. coli were obtained simultaneously with a high spatial resolution which was apparently better than that of a conventional confocal microscope. Nanoscopic GFP fluorescence spectrum was obtained by positioning the optical fiber probe above the bright area of the E. coli cells. Comparing topographic and fluorescence images, individual E. coli cells expressed different fluorescent intensity. Fluorescence obtained by SNOAM indicated GFP oxidation possibly occured near cell surface. SNOAM also provided us with simultaneous topographical and optical images of human chromosomes. Native chromosomes were spread out onto a coverslip using the surface-spreading whole-mount method. Topographic images clearly indicated duplicated structure on metaphase chromosome, while fluorescence images were a different shape probably because it depended on the combination of SYBRTM Green I and chromosome DNA. Atomic force images have some artefacts, however they can be corrected by comparison with the fluorescence image. Topography and fluorescence images of RBL-2H3 mast cells surface were determined with/without DNP-BSA stimulation by SNOAM system. Near-field fluorescence images were obtained from the granules stained with quinacrine. Fluorescence profiles and intensities were largely changed after allergen stimulation. Exocytotic events of granules were specially discussed based on SNOAM.

Simultaneous topographic and fluorescence imagings of recombinant bacterial cells containing a green fluorescent protein gene detected by a scanning near-field optical/atomic force microscope.

A scanning near-field optical/atomic force microscope (SNOAM) system was applied for simultaneous topographic and fluorescence imaging of biological samples in air and liquid. The SNOAM uses a bent optical fiber simultaneously as a dynamic mode atomic force microscopy cantilever and as a scanning near-field optical microscopy probe. Optical resolution of this system was about 50-100 nm in fluorescence mode for fluorescent latex beads on a quartz glass plate. Green fluorescent protein (GFP) is a convenient indicator of transformation and should allow cells to be separated by fluorescence-activated cell sorting. The gene coding to GFP was cloned in recombinant Escherichia coli. The SNOAM system used 458- or 488-nm irradiation from a multiline Ar ion laser for excitation of GFP, since a native GFP has been known to give a maximum at 395 nm and a broad absorption spectrum until 500 nm. Topographic and fluorescence images of recombinant E. coli were obtained simultaneously with a high spatial resolution which was apparently better than that of a conventional confocal microscope. A nanoscopic GFP fluorescence spectrum was obtained by positioning the optical fiber probe above the bright area of the E. coli cells. Comparing topographic and fluorescence images, it can be seen that individual E. coli cells expressed different fluorescence intensities. Fluorescence obtained by SNOAM indicated that GFP oxidation possibly occurred near the cell surface. A SNOAM system also indicated the possibility of precise imaging of native cells in liquid.

Mechanical resonance behavior of near-field optical microscope probes

The mechanical resonance behavior of near-field optical microscope probes is examined with a simple experiment on a flat pyrex sample. While our tapered-fiber probe is locked on the second resonance for servo control, the vibration characteristics around the first resonance are investigated. We find that the overwhelming cause of decreased vibration amplitude as the tip approaches the sample is an increase in damping presumably due to a fluidlike layer on the sample. A small additional effect is also observed that could be due to force derivatives.

Fabrication of multimode fiber tapers with a high reproducibility of the subwavelength extremity size: application to scanning near-field optical microscope probes

A new method for the fabrication of multimode fiber tapers is presented. The process is aimed at elaborating fiber tips with a subwavelength size extremity. After creating a Biconical Taper (BT) with a standard fusion splicer, the elongated part is immersed in an HF acid solution. The light transmitted through the BT is collected by a photodiode, and thus the chemical etching is monitored by analysing the transmitted power. After calibration, it gives rise to a high reproducibility of the tip extremity with a subwavelength size. It has been applied to the fabrication of UV-Scanning Near-Field Optical Microscope probes. Multimode fibers are only available for UV light.

Studying topography and sub-surface structure of 8CB liquid crystal films with shear-force microscopy

Scanning shear-force microscopy, which is usually employed to track scanning near-field optical microscopy probes across samples, was used to observe the sub-surface smectic layer structure through the thickness of a film of the alkyl cyanobiphenyl liquid crystal 8CB on a highly oriented pyrolytic graphite substrate from force-distance measurements. With the noncontact imaging shear-force microscopy supplies, it was possible to follow, in the topography, the movement of a monolayer of the 8CB molecules. This has enabled the diffusion of molecules in a precursor film of 8CB to be observed without significantly disrupting the free liquid surface.

A simple reproducible technique for producing sub-micrometre fibre-optic probes for near-field optical microscopy and chemical sensors

Near-field optical techniques enable the optical diffraction limit to be surpassed, thus allowing objects to be resolved with a spatial resolution of better than lambda /50. Many of these techniques involve the scanning of probes with sub-micrometre tips or apertures in close proximity (<20 nm) to the object surface in order to generate images of sub-wavelength resolution. We present a simple one-step method for producing optical probes with excellent reproducibility for applications in super-resolution microscopy and near-field chemical sensing. In addition, we demonstrate via experiment the light delivery and collection ability of probes manufactured using this technique.