Contrast mechanism for resolving organic molecules with tunnelling microscopy

Spong, J. K.; Mizes, H. A.; LaComb, Lloyd; Dovek, M.; Frommer, Jane; Foster, John S.

doi:10.1038/338137a0

Cited by 221 publications

(97 citation statements)

References 12 publications

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“…For the STM image of a molecule it is therefore expected from this theory that the tunneling current distribution corresponds to maxima of the electron densities of the molecule. Alternatively it has been proposed by Spong et al that a modulation of the local work function of the substrate by insulating polarizable molecular adsorbates can explain the observed molecular images [23]. This mechanism would also require high electron densities at the maxima of the tunneling current.…”

Section: Discussionmentioning

confidence: 94%

Video-STM, LEED and X-ray diffraction investigations of PTCDA on graphite

Ludwig

Gompf

Glatz

et al. 1992

Z. Physik B - Condensed Matter

158

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Thin films of the organic molecule perylene-3,4,9,10-tetracarboxylic-dianhydride ("PTCDA") on graphite(0001) have been investigated from the mono-to the multilayer regime with low energy electron diffraction (LEED), X-ray-diffraction in Bragg-Brentano geometry, and high resolution scanning tunneling microscopy (STM). These different methods proved epitaxial growth in a coincident superstructure and yielded congruent results concerning details of the crystallographic structure of the epilayer. In addition it was possible to resolve submolecular structures in high resolution STM images; a comparison of the 10 resolved maxima of the tunneling current with the molecular structure leads us to question the conventional model description of tunneling.

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Section: Discussionmentioning

confidence: 94%

Video-STM, LEED and X-ray diffraction investigations of PTCDA on graphite

Ludwig

Gompf

Glatz

et al. 1992

Z. Physik B - Condensed Matter

158

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“…Therefore ordered organic monolayers on weak interacting substrates are ideal systems to study the image contrast in STM images of organic adsorbates. Several models have been proposed to explain the observed STM image contrast of molecules, but the underlying mechanisms are still under discussion [6][7][8]. The systematic study presented in this work allows us to discriminate between these different models and to develop a new approach based on the influence of a molecular pseudopotential.…”

Section: Introductionmentioning

confidence: 99%

STM investigations of PTCDA and PTCDI on graphite and MoS2. A systematic study of epitaxy and STM image contrast

Ludwig

Gompf

Petersen

et al. 1994

Z. Physik B - Condensed Matter

197

147

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Abstract.Monolayers of the organic molecules perylene-3,4,9,10-tetra-carboxylic-dianhydride (PTCDA) and -diimide (PTCDI) on graphite and MoS 2 have been imaged with scanning tunneling microscopy. The epitaxial growth of the two molecules is determined by the intermolecular interaction but nearly independent of the substrate. On both substrates the STM image contrast in the submolecularly resolved images is dominated by the aromatic perylene system whereas the polar oxygen and nitrogen groups are invisible. The correlation of the observed inner structure of the molecules to their molecular structure allows us to compare our results with theoretical considerations.

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“…Since specimens can be scanned under ambient conditions with low energies, these microscopes offer a (potentially) powerful means of examining functioning molecules with usual AFM operating conditions (12). Currently, the resolution of atomic structure is only routinely achieved with hard crystalline surfaces (1, 7) and organic adsorbates such as smectic liquid crystal monolayers (28,33). Subnanometer resolution of cellular surfaces has been difficult to achieve because of masking of atomic structure through the use of heavy metal contrasting agents and problems associated with the stabilization of the specimen during STM and AFM imaging (3,14,25,37,39).…”

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confidence: 99%

Transmission electron microscopy, scanning tunneling microscopy, and atomic force microscopy of the cell envelope layers of the archaeobacterium Methanospirillum hungatei GP1

et al. 1993

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Methanospirllum hungatei GP1 possesses paracrystalline cell envelope components including end plugs and a sheath formed from stacked hoops. Both negative-stain transmission electron microscopy (TEM) and scanning tunneling microscopy (STM) distinguished the 2.8-nm repeat on the outer surface of the sheath, while negative-stain TEM alone demonstrated this repeat around the outer circumference of individual hoops. Thin sections revealed a wave-like outer sheath surface, while STM showed the presence of deep grooves that precisely defined the hoop-to-hoop boundaries at the waveform nodes. Atomic force microscopy of sheath tubes containing entrapped end plugs emphasized the end plug structure, suggesting that the sheath was malleable enough to collapse over the end plugs and deform to mimic the shape of the underlying structure. High-resolution atomic force microscopy has revised the former idea of end plug structure so that we believe each plug consists of at least four discs, each of which is -3.5 nm thick. Pt shadow TEM and STM both demonstrated the 14-nm hexagonal, particulate surface of an end plug, and STM showed the constituent particles to be lobed structures with numerous smaller projections, presumably corresponding to the molecular folding of the particle.All current techniques for ultrahigh resolution of biomolecular structure have inherent drawbacks. For example, not only does transmission electron microscopy (TEM) usually require heavy metal contrasting agents, it also produces high energy loads and high vacuums on the specimen. Only in exceptional cases, such as the purple membrane of Halobacterium spp. (18), have molecular folding data been obtained. The inception of scanning tunneling microscopy (STM) (7) and atomic force microscopy (AFM) (6) has certainly made the atomic resolution of hard, inanimate surfaces feasible, and there is a good possibility that this same resolution can be approached in biology. STM and AFM are currently being used on a number of biostructures and their constituent biopolymers, but they are still relatively new techniques in structural biology, and submolecular resolution must be interpreted with caution since biomaterials are loosely bonded and easily deformable. Specimens must be chosen with care, and close attention must be paid to the possibility of induced artifacts. It is best to take a multitechnique approach which combines high-resolution methodologies based on different principles; uniformity of high-resolution detail from each ensures accuracy of interpretation. Using this rationale, we have combined TEM, STM, and AFM to study paracrystalline surfaces possessed by the archaeobacterium Methanospirillum hungatei.STM and AFM rely on the raster scanning of a fine-tip probe over a surface, with piezoelectric ceramics to control movement to within subnanometer distances, which forms a topographical three-dimensional image of the specimen. In STM, the vertical tip displacement during scanning is depen-* Corresponding author. dent on the tunneling current between the pen...

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Contrast mechanism for resolving organic molecules with tunnelling microscopy

Cited by 221 publications

References 12 publications

Video-STM, LEED and X-ray diffraction investigations of PTCDA on graphite

Video-STM, LEED and X-ray diffraction investigations of PTCDA on graphite

STM investigations of PTCDA and PTCDI on graphite and MoS2. A systematic study of epitaxy and STM image contrast

Transmission electron microscopy, scanning tunneling microscopy, and atomic force microscopy of the cell envelope layers of the archaeobacterium Methanospirillum hungatei GP1

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