Optical content and resolution of near-field optical images: Influence of the operating mode

Carminati, Rémi; Madrazo, A.; Nieto‐Vesperinas, M.; Greffet, Jean‐Jacques

doi:10.1063/1.366270

Cited by 57 publications

(22 citation statements)

References 28 publications

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“…The optical signal has to be attributed to material contrast, which is expected here, because at the wavelength of 685 nm GaAs exhibits a refractive index of n = 3.79 and a penetration depth of L = 370 nm, whereas for GaP n = 3.26 and the absorption is negligible. High scattering of the analyzed III-V semiconductors provides ennhancement of the purely optical contribution in our working configuration [21], justifying the high contrast obtained.…”

Section: Transmission Measurements On Gaas/ Gap(111) (B Polarity)mentioning

confidence: 72%

“…In the following, we report on a qualitative analysis of possible topographical artifacts in our case, bearing in mind that the issue has recently been put in a quantitative basis by Bozhevolnyi [19] and Carminati et al [21]. In emission-mode aperture NSOM, light-level variations as a function of gapwidth z occur because of interference between the far-field emitted from the tip and the multiply reflected light between the sample and the tip that reaches the detector.…”

Section: Discussion Of Artifactsmentioning

confidence: 95%

“…Let us suppose that the tip is placed in the middle of a flat island of GaP, present over the above mentioned GaPsurface. The em fields emerging from the tip would be modified in such a way that they depend on the geometry of the island within a range of a few aperture diameters [23], especially for samples characterized by high optical scattering [21]. In the limiting case of an island much wider than the aperture, though, there would be no chance of distinguishing the two situations from the optical signal level.…”

Section: Discussion Of Artifactsmentioning

confidence: 99%

See 2 more Smart Citations

Assessment of NSOM resolution on III-V semiconductor thin films

Labardi¹,

Gucciardi²,

Allegrini³

et al. 1998

Applied Physics A: Materials Science & Processing

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Emission-mode aperture near-field scanning optical microscopy (NSOM) is applied to semiconductor thin films for resolution assessment and artifact investigation purposes. We have used GaAs thin films deposited on GaP (111) substrates with A and B polarities by metal organic vapour phase epitaxy (MOVPE). Optical discrimination of GaAs islands on GaP(111) has been accomplished with a lateral resolution better than 20 nm (λ/35) in the transmission mode. These samples have proven valuable for inspection of contrast mechanisms, based on discrimination of materials having different refractive index and absorption coefficients, as well as investigation of topography and shadowing artifacts in optical near-field imaging.Since its invention in 1984 [1] the near-field scanning optical microscope (NSOM) has become a widely adopted tool for optical investigation in the submicron range, well beyond the diffraction limit. Nowadays, near-field microscopy is applied to a variety of issues: nanospectroscopy [2], nanowriting [3], the study of biological samples [4], polymers [5], and magnetic samples [6], among others. Different working configurations have been demonstrated [7], but the most commonly used is the emission-mode aperture NSOM, as also witnessed by commercially available instruments. In the emission mode the near-field is generated by means of a tapered, metalcoated optical fiber with an aperture on the free edge in the range from 20 to 200 nm in diameter, coupled to a light source (usually a laser beam). The light scattered by the sample is collected afterwards in the far field, by means of a microscope objective, and detected by a photomultiplier (PMT). The tip is held at a constant distance from the sample by shear-force detection and stabilization [8] in order to maintain the sensor in the near-field region and to avoid damaging it. Lateral resolution of the aperture NSOM appears to be limited by the effective size of the aperture, which is determined by the penetration depth of the metal defining the aperture itself, which is ≈ 15 nm in the visible range. With the invention of the apertureless NSOM [9] the resolution limit has been pushed further by another order of magnitude. A resolution of few nm has been demonstrated; atomic resolution is theoretically predicted. In this configuration the subwavelength illuminating source is reduced to extreme limits, with a few dipoles located at the apex of a very sharp AFM or STM tip. When these dipoles are irradiated by an external light source they act as scattering centers and generate the near field that is used to probe the sample surface. Thus the mechanisms responsible here for enhanced resolution are of "particle imaging particle" kind [9,10]. This excellent resolution is reached at the expenses of a more complex and critical experimental setup, as witnessed by the fact that at present, to our knowledge, only a few apertureless NSOM prototypes are operating. In this article we illustrate aperture NSOM measurements, on semiconductor thin films, that we have used for...

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Section: Transmission Measurements On Gaas/ Gap(111) (B Polarity)mentioning

confidence: 72%

Section: Discussion Of Artifactsmentioning

confidence: 95%

Section: Discussion Of Artifactsmentioning

confidence: 99%

See 1 more Smart Citation

Assessment of NSOM resolution on III-V semiconductor thin films

Labardi¹,

Gucciardi²,

Allegrini³

et al. 1998

Applied Physics A: Materials Science & Processing

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show abstract

“…The NSOM-optical images taken in constant-amplitude mode are known to contain z-motion artifacts in the form of crosstalk between topographic and optical images. 21,22 This is evident as a strong phase-shift correlation between features in topographic and NSOM-optical images in Figs. 2͑a͒ and 2͑b͒.…”

Section: Resultsmentioning

confidence: 75%

Near-field scanning optical microscopy of ZnO nanopatterns fabricated by micromolding in capillaries

Donthu

Pan

Shekhawat

et al. 2005

Journal of Applied Physics

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“…We model the experimental situation with an analytical dipole model which gives insight into the main factors influencing the optical contrast. [9][10][11] We consider here only the elastic contribution in the recorded image. The simplicity of the model gives the opportunity to use the same model in real time while scanning the surface.…”

mentioning

confidence: 99%

Optical space and time coherence near surfaces

2002

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We have examined the local optical fields within a few wavelengths off the surface ͑middle-field region, krϽ1 -50) by scanning an optical probe in collection mode in the overlap region of the incident and scattered optical waves. We have applied an analytical dipole model and have used optical space and time coherence to describe the recorded image of submicron-sized particles on a substrate. We find that the relative intensity of the lateral and vertical standing waves gives information about the local polarizability of the particle and the support surface as well as information about the polarization of the incident beam, its wavelength, the distance of the image plane, and the tilt of the image plane with respect to the surface.There is considerable technological and fundamental interest to control light waves on surfaces at subwavelength scale for their application in ultimate optical active and passive components or for optical information transport. Optical investigation at high lateral resolution requires the knowledge of the local optical field.When adopting the scattering approach, the local optical field in the neighborhood of a surface depends on the pathlength difference and amplitude of the contributing paths, that is, on the space and time coherence of the incident, reflected, and scattered fields. 1 Since the reflected or scattered field depends on the morphology, recording of the local optical field can be used to obtain information about the lateral surface morphology. The time averaged superposition or interference of the incident wave with the scattered wave leads in general to the formation of lateral and vertical standing waves. These standing waves resemble optical modes in cavities. It is expected that the fundamental optical processes on structured surfaces are modified 2 leading to the inhibition or enhancement of spontaneous emission, directed emission, and spectral narrowing in analogy with what has been observed for cavities. 3 In near-field optics, a high lateral resolution is obtained by the detection or illumination with a subwavelength-sized probe in the proximity of the surface (Ͻ/50) taking advantage of the enlarged evanescent optical field or divergence of the electromagnetic field in the neighborhood of its source. While the incident field induces a charge in the surface region, the evanescent field is related to the quasielectrostatic field of the induced charge. This quasielectrostatic field component, longitudinal and nonpropagative, 4 is concentrated along the dipole axis for a particle or falls off exponentially for a uniform surface. The evanescent field of the probe, however, influences the induced charge in the surface region when operated in the proximity of the surface. As a result the presence of the tip influences the recorded local optical field. 5,6 Earlier studies 7 have noted that near-field optical images recorded in illumination mode are not necessarily directly correlated to the topography and it was pointed out that the probe-surface distance strongly influe...

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Optical content and resolution of near-field optical images: Influence of the operating mode

Cited by 57 publications

References 28 publications

Assessment of NSOM resolution on III-V semiconductor thin films

Assessment of NSOM resolution on III-V semiconductor thin films

Near-field scanning optical microscopy of ZnO nanopatterns fabricated by micromolding in capillaries

Optical space and time coherence near surfaces

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