Experiments on the depolarization near-field scanning optical microscope

Adelmann, Christoph; Hetzler, J.; Scheiber, G.; Schimmel, Th.; Wegener, Martin; Weber, Heiko B.; Löhneysen, H. v.

doi:10.1063/1.122997

Cited by 33 publications

(20 citation statements)

References 8 publications

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“…The difference of behavior between the two propagating modes has been observed experimentally 11 and studied theoretically in pure dielectric structures in analogous configurations. 12 A parametric study as a function of the diameter of the probe apex demonstrates that the confinement depends highly on the volume of the protrusion.…”

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confidence: 91%

Propagation of the electromagnetic field in fully coated near-field optical probes

Vaccaro

Aeschimann

Staufer

et al. 2003

Applied Physics Letters

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Fully metal-coated near-field optical probes, based on a cantilever design, have been studied theoretically and experimentally. Numerical simulations prove that these structures allow nonzero modal emission of the electromagnetic field through a 60-nm-thick metallic layer, that is opaque when deposited on flat substrates. The far-field intensity patterns recorded experimentally correspond to the ones calculated for the fundamental and first excited LP modes. Moreover, this study demonstrates that a high confinement of the electromagnetic energy can be reached in the near-field, when illuminated with radially polarized light. Finally, it was verified that the confinement of the field depends on the volume of the probe apex.Nearly 20 years of intensive research in near-field optical microscopy have produced satisfying results in imaging and subwavelength resolution. 1

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confidence: 91%

Propagation of the electromagnetic field in fully coated near-field optical probes

Vaccaro

Aeschimann

Staufer

et al. 2003

Applied Physics Letters

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“…The 150 fs optical pulses at exc ϭ700 nm wavelength ͑⇔ប exc ϭ1.77 eV photon energy͒ with an average power of P exc ϭ100 nW are sent into the single-mode optical fiber. We use the constant height mode 8 with a typical tipsample separation of 100 nm, i.e., the feedback loop is switched off. The excited PL of the sample is collected by the fiber tip and sent into a 0.5 m grating spectrometer connected to the streak camera.…”

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confidence: 99%

“…The sample is cooled by a variable-temperature He-flow cryostat with symmetric heat exchanger, while the fiber tip is held at room temperature. [5][6][7] The scanning near-field optical microscope ͑SNOM͒ uses uncoated fiber tips, which are fabricated using a two-step selective etching process, 8 leading to an apex radius around 20 nm. The 150 fs optical pulses at exc ϭ700 nm wavelength ͑⇔ប exc ϭ1.77 eV photon energy͒ with an average power of P exc ϭ100 nW are sent into the single-mode optical fiber.…”

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confidence: 99%

Combining a scanning near-field optical microscope with a picosecond streak camera: Statistical analysis of exciton kinetics in GaAs single-quantum wells

Neuberth

Walter

Freymann

et al. 2002

Applied Physics Letters

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Combining a low-temperature scanning near-field optical microscope with a picosecond streak camera allows us to measure the complete wavelength-time behavior at one spot on the sample within about 13 min at excitation powers of 100 nW. We use this instrument to measure the variation of relaxation times in disordered single-GaAs quantum wells with sample position. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1477274͔Soon after the invention of scanning probe microscopy, many researchers got excited about combining scanning probe techniques with the established methods of femto-or picosecond optical spectroscopy-a combination, which would open the door to a whole new family of experiments. Several pioneering experiments were performed indeed, [1][2][3][4] however, much of the enthusiasm was largely damped over the years because of enormous technical difficulties which inhibited a routine application of these techniques. Here, we combine a low-temperature scanning near-field optical microscope ͑using uncoated optical fiber tips, allowing for large throughput͒ with a picosecond streak camera. While this combination has only modest spatial ͓200-300 nm resolution at 800 nm photoluminescence ͑PL͒ wavelength, see Fig. 1͔ and temporal ͑2-10 ps͒ resolution, it does allow for routine operation. Compared to, e.g., using solid immersion lenses, our setup allows for more flexibility: Large field of view, coarse sample positioning up to 5 mm and ability to also work at around 400 nm wavelength. 5,6 Figure 1 depicts the instrument. The sample is cooled by a variable-temperature He-flow cryostat with symmetric heat exchanger, while the fiber tip is held at room temperature. 5-7The scanning near-field optical microscope ͑SNOM͒ uses uncoated fiber tips, which are fabricated using a two-step selective etching process, 8 leading to an apex radius around 20 nm. The 150 fs optical pulses at exc ϭ700 nm wavelength ͑⇔ប exc ϭ1.77 eV photon energy͒ with an average power of P exc ϭ100 nW are sent into the single-mode optical fiber. We use the constant height mode 8 with a typical tipsample separation of 100 nm, i.e., the feedback loop is switched off. The excited PL of the sample is collected by the fiber tip and sent into a 0.5 m grating spectrometer connected to the streak camera. Without temporal resolution ͑i.e., without the streak camera͒, we typically detect several hundreds of counts per second in one wavelength channel ͑corresponding to 0.012 nm width͒ in the PL peaks under these conditions. As this number of counts is spreadout over time, i.e., over several hundreds of channels, one obviously needs photon-counting capability and significant integration ͑exposure͒ times when introducing the streak camera. The time resolution is 2 ps without spectrometer and 10 ps for the actual experiments ͑e.g., Fig. 2͒.The two samples investigated in this letter are highquality single-GaAs quantum wells ͑SQW͒. One is a 3.5 nm thin, 180 s growth-interrupted GaAs SQW with superlattice barriers ͓4 monolayers ͑ML͒ of AlAs, no interruption, 8...

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“…10 Clearly, in the latter cases only artifacts can be recorded. Furthermore, depolarization SNOM with an uncoated tip at 30 nm 'constant height' over a grooved metal surface (50 nm thick) on glass gave edge-contrast but not materials contrast, 11 although that experiment did not benefit from a sudden increase in reflectivity.…”

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confidence: 98%

Artifacts in scanning near-field optical microscopy (SNOM) due to deficient tips

Kaupp

Herrmann

Haak

1999

J. Phys. Org. Chem.

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Apertureless scanning near-field optical microscopy (SNOM) in the reflection-back-to-the-fiber configuration is possible on rough surfaces of practical importance and reaches 15 nm lateral resolution. The feedback for constant distance mode is provided by shear-force atomic force microscopy. Any artifacts in the atomic force microscopy will translate into artificial optical responses. Very sharp tapered tips (radius ca. 15 nm, apex angle`10°) are required. Only these give the strongly enhanced reflectance in shear-force distance, do not break as easily as do more blunt tips, and can follow the topography in order to provide chemical SNOM contrast without topographic errors. In the absence of significant reflectance enhancement, if blunt or abrased or broken tips are used, not SNOM but artificial 'optical contrast' is recorded. Metal-coated tips are unsuitable: they become hot, give poor resolution and are the source of numerous additional artifacts that are summarized for comparison. The SNOM artifacts are subdivided into:* topographic errors-if chemical uniform topography does give some optical response; * lack of spatial correlation-if the optical signal does not reproduce the site of the emitter or of the chemical contrast; * tip imaging-very large features and more or less negative differentials therefrom; * contrast inversion-false sign of optical contrast; * split optical contrast-signal is split into two unequal parts with the same (false) sign of the contrast; * artificial stripes-instead of chemical/emissive contrast artificial stripes, that are not always 'interference fringes' or 'edge-contrast'.The artifacts can be easily recognized in published images from different techniques and modes of SNOM. Their analysis would be facilitated if full x/y/z data were published instead of two-dimensional images. We therefore disclose interactively analyzable VRML data in the EPOC version.

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Experiments on the depolarization near-field scanning optical microscope

Cited by 33 publications

References 8 publications

Propagation of the electromagnetic field in fully coated near-field optical probes

Propagation of the electromagnetic field in fully coated near-field optical probes

Combining a scanning near-field optical microscope with a picosecond streak camera: Statistical analysis of exciton kinetics in GaAs single-quantum wells

Artifacts in scanning near-field optical microscopy (SNOM) due to deficient tips

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