KEYWORDS: Near field scanning optical microscopy, Liquids, Bacteria, Near field optics, Luminescence, Polymer optical fibers, Optical fibers, Near field
Some preliminary results and experimental details of Near-field Scanning Optical Microscopy (NSOM) operation in liquids have been reported by us earlier. Here we present the first use of custom made polystyrene/poly (methyl methacrylate) (PMMA) optical fibers to assemble new NSOM probe/sensor for operation in liquids. Assembled NSOM probe has quite large quality factor Q ranging 2000-6000 in air, and 300-900 when immersed 0.2-0.3 mm deep into the water. Such montage demonstrates high mechanical durability permitting to scan different samples during many hours or even days, and overall low cost in comparison with NSOM probes based on glass optical fibers. A specially prepared optical fiber with 125 μm diameter (from Paradigm Optics Company, USA) (polystyrene core diameter is 0.85 μm, ncore=1.59 and PMMA cladding, ncore=1.49) was chemically etched using a 9:1 mixture of dichloromethane and ethyl acetate. As result of the etching, a smooth and sharp tip is formed with a typical radius of the curvature equal to 50 - 170 nm. For completeness, earlier unpublished images of living Picocyanobacteria bacteria obtained using glass fiber- made NSOM probes are also presented.
Nowadays, sharpened glass fiber – made probes attached to a quartz tuning fork (TF) and exploiting the shear force – based feedback are by far the most popular in the field of SNOM. These probes are expensive, very fragile and their fabrication is difficult, hard to control and in many cases a hazardous process. Here we are presenting the first SNOM probes made from plastic optical fibers with a small, submicron size, core diameter. The sharp tips were prepared by chemical etching of the fibers in dichloromethane - ethyl acetate solution, and the probes were prepared by proper gluing of sharpened fibers onto the TF. These probes demonstrate excellent performance in both topographical and optical channels after intense use.
KEYWORDS: Near field scanning optical microscopy, Carbon, Near field optics, Optical fibers, Sensors, Glasses, Electron beams, Molecules, Scanning electron microscopy, Optical microscopes
We report the growth of ultrasharp carbon whiskers onto apertured near-field optical glass fiber probes. The ultrasharp
carbon whiskers are produced by the electron-assisted dissociation of residual oil vapors present in the vacuum chamber
during the electron beam exposition of the tip. This cost effective manufacturing procedure is reproducible, fast and
allows controlling the shape of the carbon whisker. The radius of curvature of the whisker apex is approximately 10 nm
while its small total length is around 100 nm thus fulfilling the requirements of aperture Scanning Near-Field Optical
Microscope (SNOM) probes, i.e. to keep the distance between the sample and the optical aperture during the scanning at
subwavelength scale. Furthermore, due to the intrinsic properties of the amorphous carbon whisker, the probes are
durable.
The carbon whisker optical fiber probes are mounted on tuning-forks using the earlier discussed double-resonant
principle. This process ensures a high quality factor of the sensor in the range 2000-5500, which enables to cope with the
large stiffness of the tuning-fork actuator and obtain a characteristic noise-limited sensitivity smaller than 10pN
necessary to image soft biological samples without destroying them. To illustrate the sensor's performances,
transmission near-field optical images of SNOM calibration grating as well as high-resolution state-of-the-art
topographic images of single DNA molecules are presented. Prospects of further improvements of the fabrication method
enabling to achieve the lighting rod enhancement of the optical near-field (nano-antenna effect) are briefly discussed.
KEYWORDS: Liquids, Near field scanning optical microscopy, Electronics, Sensors, Optical microscopes, Microscopes, Scanners, Signal processing, Glasses, Near field optics
The operation of the scanning near-field optical microscope based on the double-resonant montage of a fiber probe
onto the tuning fork (working frequency of the latter, that is 32 kHz, coincides with the second resonance frequency of
the bending oscillations of the free standing part of a fiber beam) in liquid is reported. It is shown that due to the
peculiarities of the probe montage (initially large, around 3,000 - 5,500 quality factor of the dithering and long
projection of the fiber beam beyond the tuning fork body) and microscope electronics, this SNOM is very fit to work
in liquids. Quality factor of the sensor drops down to the values around 300 - 600 when the probe tip is submerged on
the depth of 0.2 - 0.3 mm, thus remaining large enough to enable high quality imaging with rather small acting force
value laying in the subnanoNewton region. We also discuss the joint liquid recipient construction which connects the
liquid cell containing a sample with the large water reservoir via a flexible tube. This reservoir is placed onto separate
Z-stage and hence the water level in the cell can be regulated independently from the sample position which facilitates
the SNOM operation a lot.
KEYWORDS: Laser induced fluorescence, X-rays, Luminescence, Near field scanning optical microscopy, Lithium, Spatial resolution, Crystals, Nanostructures, Microscopy, Near field optics
The continuously shrinking of the photonic structures has stimulated the research and development of low-dimensionality photoluminescent patterns based on visible-emitting color centers (CCs) in thin films. In particular, Lithium Fluoride (LiF) treated with ionizing radiation by using versatile lithographic techniques, represents a very promising candidate for the realization of innovative photonic devices. Permanent tluorescent patterns based on CCs have been realized in LiF films by direct writing with a X ray microprobe -of the ESCA Microscopy beamline at ELETTRA synchrotron in different configuration. Luminescent nanostructures, written by scanning the LW specimen with respect to the X-ray beam, have been investigated by near-field optical microscope and a sub-wavelength spatial resolution is demonstrated.
It is shown that the high-resolution laser photoelectron microscope with subwavelength-spatial resolution can be used for an absolute values of the two-photon external photoelectric effect measurements with high (a few nm-scale) localization. The spatial distribution of light intensity in the near field is studied by observing the photoelectron projection images of a subwavelength nanoaperture. The imaging electrons are obtained as a result of two-photon external photoelectric effect induced in the aperture formed at the end of an optical fiber by femtosecond pulses of the second-harmonic radiation (410 nm) of a Ti:sapphire laser. The light-field distribution in the aperture is not distorted by any near-by object, which allows the first nonperturbing measurement of such a distribution.
Laser photoelectron projection microscope with the magnification of 105 and spatial resolution of up to 30 nm has been developed. Photoelectron images produced due to the laser photoselective ionization of light absorbing centers on LiF:F2 needle tip surface when irradiated by cw argon ion laser have been investigated and single color centers on its surface have been observed for the first time. In some experiments spectral dependence of photoelectron image on laser radiation wavelength has been observed. The results of the experiments can be regarded as a first realization of such a surface studying method which makes it possible to study the surfaces at a high spatial resolution and at the same time to identify some specific small structures in surfaces, i.e., has a high 'chemical selectivity.'
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