Reflection Scanning Near-field Optical Microscopy Research Articles

Tapping mode atomic force microscope combined with reflection scanning near-field optical microscope (AF/RSNOM)

A new kind of scanning probe microscope is introduced in this paper, which is a combination of atomic force microscope and reflection scanning near field optical microscopy (AF/RSNOM) with equi-amplitude tapping mode. The principle and recent experiment result of AF/RSNOM are reported. Besides convenient operation, the bi-functional probe tip of AF/RSNOM brings an even illumination for every sampling position. Experiment result and analysis show that the signal to noise ratio (SNR) of AF/RSNOM optical image is much better than that of other RSNOM without tapping working mode.

Reflection scanning near-field optical microscopy in ultrahigh vacuum

A reflection scanning near-field optical microscope with polarization-sensitive light detection for operation in ultrahigh vacuum is presented. All necessary stages to reach the final goal of subwavelength resolution in magneto-optics are considered step by step, validating our approach and demonstrating the usefulness of the final instrument. A number of problems are attacked and discussed, but some are only treated to an extent necessary to bring the instrument to operation. Sub-λ resolution of a nonmagnetic polarization signal is demonstrated.

SNOM imaging of very fine pits formed by EB lithography for ultrahigh density optical recording

The possibility to optically image the very fine pit structure formed by electron beam (EB) writing has been researched using scanning near-field optical microscopy (SNOM). Fine test pit samples were formed in an electron resist (ZEP520) with a minimum pit size of 30 nm×160 nm. From experimental results using the pits, a conventional reflection SNOM could not image fine pit structures with a size of less than 100 nm. The technique was improved by coating the metal film on the optical probe and adopting an optical depolarization technique in the SNOM optics efficiently to detect near-field light reflected from the sample surface. We demonstrated that very fine pits with a minimum size of 30 nm were imaged and discussed that reflection type depolarization SNOM has a potential to achieve an ultrahigh density optical reading with 1.2 Tb/in. 2, which is limited by EB fabrication of the pits.

Energy transfer from fluorescent thin films to metals in near-field optical microscopy: Comparison between time-resolved and intensity measurements

The fluorescence intensity, fluorescence decay time, and shear-force images of a thin film have been simultaneously investigated by reflection scanning near-field optical microscopy using an uncoated fiber tip. The sample is made of a europium chelate embedded in a 32-nm thick polymer layer that coats a periodic structure of gold and chromium. It is contended that the three images carry different and somewhat complementary information; the shear force supplying the sample profile while the intensity mainly depends on the local sample’s reflectance. Moreover, the decay time exhibits the local-energy-transfer process that takes place between the metallic substrate and the dye layer.

Polarization-resolved imaging with a reflection near-field optical microscope

Using a rigorous microscopic point-dipole description of probe–sample interactions, we study imaging with a reflection scanning near-field optical microscope. Optical content, topographical artifacts, sensitivity window—i.e., the scale on which near-field optical images represent mainly optical contrast—and symmetry properties are considered for optical images obtained in constant-distance mode for different polarization configurations. We demonstrate that images obtained in cross-polarized detection mode are free of background and topographical artifacts and that the cross-circular polarization configuration is preferable to the cross-linear one, since it ensures more isotropic (in the surface plane) near-field imaging of surface features. The numerical results are supported with experimental near-field images obtained by using a reflection microscope with an uncoated fiber tip.

Pseudo modulation transfer function in reflection scanning near-field optical microscopy

In near-field optical microscopy, the resolution is strongly related to the experimental conditions of illumination and to the distance between the tip and the sample. Therefore, an intrinsic modulation transfer function is generally meaningless in near-field microscopes. In this paper, we show that experimental microscopes can be characterized by a linear transfer, according to a few experimental conditions, we consequently establish the existence of a pseudo modulation transfer function (PMTF). We calculate it, in the R-SNOM (reflection scanning near-field optical microscope) case. The PMTF is an efficient tool for determining the SNOM capabilities, if the tip to sample distance is large enough, without resorting to well-known test samples. This characterization could provide information on the resolving power of the microscope, working on a wide scanning zone, to choose an interesting sample area.

Direct characterization of ultraviolet-light-induced refractive index structures by scanning near-field optical microscopy

We have applied a reflection scanning near-field optical microscope to directly probe ultraviolet (UV)-light-induced refractive index structures in planar glass samples. This technique permits direct comparison between topography and refractive index changes (10/sup -5/-10/sup -3/) with submicrometer lateral resolution. The proposed method yields detailed information about the topography and index profiles of UV-written waveguides.

Compact stand-alone near-field optical microscope combined with force detection

We present a compact stand-alone near-field optical microscope combined with force detection in which manufactured atomic force microscope (AFM) microcantilevers are used for both optical and force detection. Because of the stand-alone design, the combination allows a great variety of operation modes, including the scanning tunneling optical microscope (STOM), and possibly the reflection scanning near-field optical microscope modes. The first images obtained in the AFM and the STOM mode are presented. A polarization study is carried out to confirm the optical nature of the detected signal and to discuss possible artifacts.

Reflection scanning near-field optical microscopy (R-SNOM) in constant height mode with a dielectric probe Image interpretation and resolution for high topographic variations

The understanding of the correlation between the near-field images that are recorded by scanning near-field optical microscopy (SNOM) and the local optical properties of the sample surface (topography, index, etc.) is a condition for the development of such microscopes. The aim of this paper is to show that the “constant height imaging” (CHI) mode provides useful near-field characterizations, even in case of high-relief samples. Actually, the CHI near-field signal is free from perturbations brought by usual feedback regulation systems. Furthermore, we show a comparison between experimental and theoretical data to explain near-field image formation. Finally, we develop a specific method based on the Fourier spectral analysis to characterize the experimental SNOM setup working in CHI mode.

Sub-wavelength imaging by depolarization in a reflection near-field optical microscope using an uncoated fiber probe

We present a reflection scanning near-field optical microscope utilizing counter-directional light propagation in an uncoated fiber probe, cross-polarized detection and shear-force feedback. Topographical and near-field optical imaging with a scanning speed of up to 10 μm/s and a lateral resolution better than 40 nm are demonstrated with a latex projection test sample. Determination of the optical resolution as well as correlation between topographical and near-field optical images are discussed.

Image resolution in reflection scanning near-field optical microscopy using shear-force feedback: characterization with a spline and Fourier spectrum

Scanning near-field optical microscopes (SNOM's) actually lead to nanometric lateral resolution. A combination with shear-force feedback is sometimes used to keep the SNOM tip at a constant force from the sample. However, resolutions in shear-force and optical data are different. An estimation of both resolutions is important for characterizing the capabilities of such systems. The basic principle of the measurement is to compare a spline-fitted logarithm of the power spectra calculated with the optical image with that of the shear force image in which resolution is determined a priori. Quantitative results are given in the case of periodic or untested sample and simulated data. Moreover the accuracy and the stability of the method are discussed.

Reflection scanning near-field optical microscopy with uncoated fiber tips: How good is the resolution really?

We have investigated the optical resolution of a scanning near-field optical microscope in reflection collection mode using an uncoated fiber tip. We demonstrate that the apparent resolution in the optical signal (better than 70 nm) is a topography-induced effect. We believe that the purely optical resolution is only of the order of λ/2 and diffraction limited.

Simple reflection Scanning Near-field Optical Microscope using the back reflected light inside the laser cavity as detection mode

A new simple and compact technique of optical detection in reflection SNOM is proposed and developed. It consists of detecting the perturbation induced in a laser cavity by the reflected light coming from the sample. Two cases have been studied: the first one involves a classical HeNe laser and the second one exploits the properties of a pigtailed laser diode. Whereas the HeNe laser is too unstable to provide exploitable images, highly compact pigtail diodes could be an interesting alternative to usual beam-splitter techniques.

A design of reflection scanning near-field optical microscope and its application to AlGaAs/GaAs heterostructures

A scanning near-field microscope design using the reflected light intensity as the feedback mechanism is described. Multiple fibers with high numerical apertures provide a high collection efficiency in a reflection geometry. The performance with regard to its response to large spatial variations has been tested by using a Si-grating sample and with regard to variations of local indices of refraction by using GaAs/AlGaAs heterostructure samples. In addition, spatially resolved spectroscopy on GaAs/AlGaAs heterostructures has been obtained.

Scanning near-field optical microscope with a laser diode and nanometer-sized bit recording

We demonstrate 80 nm diameter bit recording for the first time using a phase change recording film and a reflection scanning near-field optical microscope with a 785 nm wavelength laser diode. The sample structure was a 20 nm thick ZnS-SiO 2 protection layer/30 nm thick Ge 2Sb 2Te 5 recording film/150 nm thick ZnSSiO 2 protection layer/polycarbonate substrate. Writing was performed with pulsed laser light of 8.4 mW for 5 ms and 0.5 ms, and 8.0 mW for 5 ms. Written bits were observed in reflection by illuminating a small light of 0.2 mW. In this form of recording, a formation of phase change domains of about 50 nm in diameter is expected if the surface deformation is suppressed. Our results indicate the possibility to achieve an ultra-high recording density of more than 100 Gb in −2.

Correlation between optical and topographical images from an external reflection near-field microscope with shear force feedback

An external reflection scanning near-field optical microscope with shear force regulation of the tip-surface distance is described. Near-field optical and shear force topographical images are compared for various samples. It is shown that the most important correlative relationships between these images can be deduced from symmetry considerations. The possibility of extracting additional information from the optical images is demonstrated on images of human blood cells.

Reflection-scanning near-field optical microscopy and spectroscopy of opaque samples

Opaque samples are imaged by Scanning Nearfield Optical Microscopy (SNOM) in reflection mode: A quartz glass fiber tip is used both to illuminate the sample and to collect light locally reflected from or emitted by the surface. The collected light is coupled out by a 2×2 fiber coupler and fed into a grating spectrometer for spectral analysis at each sampled point. The tip-sample distance is controlled by a shear-force feedback system. The simultaneous measurement of topography and optical signals allows an assessment of imaging artifacts, notably topography-induced intensity changes. It is demonstrated that an optical reflectance contrast not induced by topographic interference can be found on suitable samples. Local spectral analysis is shown in images of a photoluminescent layer.