AFM for the imaging of large and steep submicroscopic features, artifacts and scraping with asymmetric cantilever tips

Herrmann

Haak

1999

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.

Section: Artifacts By Surface Modi®cation In Afmmentioning

confidence: 99%

Section: Artifacts In Afm Topographies On Rough Surfacesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Herrmann

Haak

1999

“…Therefore, we undertook an atomic force microscopic (AFM) study of the solid-solid * Author to whom correspondence should be addressed. (2) and - [4,5]decane (3) and interpret the experimental results in the light of the crystallographic data for neat 2 and 3. 7 We chose the systems 1-2 and 1-3 for the first mechanistic AFh4 investigation of a solid-solid clathration.…”

Section: Introductionmentioning

confidence: 97%

Mechanism of solid-solid resolution of pantolactone

Schmeyers

Toda

et al. 1996

The enantioselective solid-solid clathration of (S)-pantolactone ( I ) into (R,R)-trans-2,3-bis(diphenylhydroxymethyl)-l,4-dioxaspiro[4~4]nonane (2) and -[4.5]decane (3) was studied preparatively and mechanistically using atomic force microscopy (AFM) measurements and crystal packing data. Shortdistance solid-to-solid sublimation mechanisms occur in both cases with initial formation of epitaxial floes along the b-axis in 2 and random craters in 3. The bulk control in the phase rebuilding stage is understood from the particular crystal packings. Bulk control was largely lost in the phase transformation stage when passivation of the surfaces occurred in both cases. The host lattices of 2 and 3 exhibit closed molecular double layers with all hydroxyl groups inside and lacking access for intercalation of I. The reaction has to start at isolated surface defects. Once started, new doors for further entrance of guest molecules (S)-I are opened in the double layer. For practical use, both the crystallographic difficulties and the passivation have to be overcome. A slurry technique involving addition of stoichiometric amounts of water to the solids provided useful conditions for the preparative resolution of (R/S)-I or further racemates exhibiting passivation, whereas heating alone speeded up the resolution of 2-methylpiperwine with 2.

Chemical contrast in scanning near-field optical microscopy

Herrmann

1997

Repeatable and stable scanning near-field optical microscopy (SNOM) images are obtained under shear-force control if uncoated, i.e. cold and sharp, tapered fiber tips are used. True chemical contrast is seen for the first time on organic crystals due to the different near-field reflectivities of different chemical species on partly oxidized anthracene. The topography spans a Z-range of 500 nm. The surface roughness is tolerable and the sites of reaction can be related to crystal structure data. A submicroscopic local resolution of 18 nm has been obtained for chemical contrast, discriminating different chemical species even with poorly reflecting organics on rough crystal surfaces. Thus, reflectionback-to-the-fiber SNOM will find wide applications for both transparent and opaque samples. All drawbacks with blunt and hot metal-coated tips at a < 10 nm distance from the surface in previous SNOM setups are overcome. ©