Electron Scanning Tunneling Microscopy Research Articles

Molecular Imaging of Alkanol Monolayers on Graphite

The structure and dynamics of monomolecular adsorbed layers of long-chain 1-alkanols can be made visible by electron scanning tunneling microscopy. The packing in single domains and the pattern at the domain boundaries (shown here for 1-octadecanol) confirm the crucial role of the hydroxy groups in the packing of molecules; the common structures at the domain boundaries suggest that all potential hydrogen bonds are indeed formed. The reorganization of regions containing many defects and the incorporation into the domain structure of impurities are also observed.

Raman scattering and scanning electron tunnelling studies of metal liquid‐like films produced from silver and gold sols

AbstractSurface‐enhanced Raman scattering (SERS) excited at several visible wavelengths and recorded using a cooled charged‐coupled device detector is reported from the mobile, interfacial, liquid‐like metal films (MELLFs) formed when solutions of metal complexes or pyridine in chlorocarbon solvents are mixed with aqueous sols of silver or gold. MELLF formation has not previously been reported for gold sols or for pyridine as stabilizer. Comparison of the spectra for the MELLFs formed from individual metal complexes and from 50:50 mixtures show that the spectral patterns observed for the latter are distinctive and are not generally equivalent to the sum of the spectra associated with the individual complexes, in contrast to the situation observed for sols where the individual spectra do appear to be additive. Raman scattering from both gold and silver MELLFs is readily observed at excitation wavelengths in the red, around 750 nm, but at 514 nm only that from silver films is detectable. These findings are considered in terms of particle size and absorption band intensities. A preliminary study of the film surface topography and particle size was carried out by scanning tunnelling electron microscopy (STM) of Ag MELLFs deposited on gold‐coated mica substrates. Computer‐processed images of the STM data show the presence on the film surface of finger‐like bars, 200–400 nm long with approximately square cross‐section, 40–60 nm side, together with other smaller cuboid features. The implications of these findings in relation to SERS are briefly considered.

Sample–tip coupling efficiencies of the photon-scanning tunneling microscope

The photon-scanning tunneling microscope is the photon analog to the electron-scanning tunneling microscope. It uses the evanescent field due to the total internal reflection of a light beam in a prism, modulated by a sample attached to the prism. The exponential decay of the evanescent field is characterized by the penetration depth dp and depends on the angle of incidence θ, the wavelength, and the polarization of the incident beam. The 1/e decay lengths range from 150 to 265 nm as deduced from the expression of the electric-field intensity in the rarer medium for θ = π/2. If we place another optically transparent medium near the surface, frustrated total reflection occurs. It is shown theoretically and experimentally that, if we choose an appropriate angle of incidence θ(θ ≠ π/2) and change the index of refraction of one of the media, the decay length of the electric field can be extremely small, so that images with an improved resolution can be produced.

The photon scanning tunneling microscope

The tunneling of photons from an evanescent wave to a sharpened optical fiber probe tip provides the basis for an analogous instrument to the electron scanning tunneling microscope. The transmission and reflection coefficients for s-polarized photons are exactly the same as those for electrons. Imaging at subwavelength resolution is made possible by the exponential character of the tunneling. We have constructed several photon scanning tunneling microscopes (PSTMs) and successfully imaged the topography of a number of samples placed on microscope slides. Each slide is coupled to a prism with an index matching gel and light is internally reflected within the sample. The reflection is frustrated as tunneling sets in when the probe tip is brought close to the surface. The electronics and software used are similar to those used in our electron STMs. Lateral resolution of λ/12 has been obtained and high-resolution spectroscopy has also been accomplished simultaneously. Images of several types of samples, including biological samples will be presented.

Composition and texture of thin films grown under 1 bar of fluorine at the surface of GaAs

The composition and texture of thin films obtained by the fluorination of GaAs(100) plates under 1 bar of fluorine are investigated by several complementary analysis techniques (Rutherford backscattering spectrometry, IR absorption and scanning tunnelling electron microscopy). They greatly depend on the fluorination temperature T f and time t f. For T f ≤ 300 °C, a significant oxygen content and a fluorine deficiency due to water absorption are observed after the layers have been exposed to air. However, for T f ≤ 400 °C, the composition of coating thin films is GaF 3 and does not change after the samples have been aged in moist air for several weeks. In this last instance, up to t f = 1 h which corresponds to 100nm thick fluoride layers, their thickness seems to be homogeneous, but for t f > 1 h, it is demonstrated that the fluorine diffusion, and consequently the thickness of the films, becomes inhomogeneous.

A scanning tunnelling and transmission electron microscopy comparison of the surface structure of evaporated and ion-assisted gold films

The surface topography of evaporated and ion-assisted deposited gold films on silica has been studied by scanning tunnelling and transmission electron microscopy. Both techniques demonstrate that the bulk microstructures of the ion-assisted films have lower average dimensions than that of the evaporated films. The STM is used to compare the surface roughness of the evaporated and ion-assisted films. We discuss some of the difficulties in identifying grain sizes and grain boundaries from STM and TEM images of thin films.

A Scanning Tunneling Microscopial (STM) Study of (NH4)2[Mo3S13] · H2O and its Thermal Decomposition Product MoS2

AbstractThe LDOS of films of (NH4)2[Mos3S13] · H2O on carbon supports have been studied with positive and negative bias voltage in the scanning tunneling electron microscope. The obtained pictures can be assigned to LUMO and HOMO states formed by the cluster anions, respectively. An important result is that the Mo3 planes are always found perpendicular to the support. This orientation is essentially retained when the film of the cluster compound is thermally decomposed to MoS2.

Photon scanning tunneling microscopy

An optical tunneling microscope is presented that operates in exactly the same way as the electron scanning tunneling microscope (ESTM). It takes advantage of evanescent fields generated by the total internal reflection (TIR) of light at the interface between materials of different optical densities. The photon scanning tunneling microscope (PSTM) employs an optically conducting probe tip to map spatial variations in the evanescent and scattered field intensity distributions adjacent to a sample surface, which forms or is placed on the TIR surface. These variations are due to the local topography, morphology, and optical activity of the surface and form the basis of imaging. Evanescent field theory is discussed and the evanescent field intensity as a function of surface-probe separation is calculated using several probe tip models. After a description of PSTM construction and operation, evanescent field intensity measurements are shown to agree with the model calculations. PSTM images of various sample surfaces demonstrate subwavelength resolution exceeding that of conventional optical microscopy, especially in the vertical dimension. Limitations and interpretation of PSTM images are discussed as well as the PSTMs applicability to other forms of surface analysis.

Surface investigations with a combined scanning electron–scanning tunneling microscope

AbstractWe have combined a scanning tunneling microscope (STM) with a scanning electron microscope (SEM) for surface investigations of atomically flat surfaces, ultrathin adsorbate films, and material surfaces. The mechanical stability of the hybrid instrument allows high‐resolution SEM of samples mounted on the STM stage and atomic resolution with the STM. Experimental results of combined SEM/STM investigations on textured material surfaces, submicron structures, and atomically flat conducting surfaces are presented. An example is given for surface machining with the STM under SEM control.

Scanning tunneling and transmission electron microscopy on identical areas of biological specimens

A methodology for tip and specimen-support manufacturing is described which allows for scanning tunneling microscopy (STM) and transmission electron microscopy (TEM) on identical areas of biological specimens, at comparable resolution. Topographs and dI/ds-maps were used to investigate tip-specimen interaction on native air-dried phage T4 polyheads where individual capsomeres and structural alterations upon repetitive scans have been observed at a tunnel current of 0.5 pA.

New form of scanning optical microscopy.

The exponential decay of the evanescent field due to the total internal reflection (TIR) of a light beam in a prism is used to advantage in a new form of scanning optical microscope, the photon scanning tunneling microscope (PSTM). The PSTM is the photon analogue of the electron scanning tunneling microscope. The sample is placed on or forms the TIR surface and spatially modulates the evanescent field. Changes in intensity are monitored by a probe tip scanned over the surface, and the data are processed to generate an image of the sample. Subwavelength resolution in three dimensions is obtained because of the exponential nature of the evanescent field intensity. Images produced by a prototype instrument using 633-nm light and a 1-\ensuremath{\mu}m probe tip are shown to have a lateral resolution of about 200 nm.

The Third International Conference on Scanning Tunnelling Electron Microscopy. Oxford, July 1988. Proceedings.

Journal of MicroscopyVolume 152, Issue 1 p. 1-1 The Third International Conference on Scanning Tunnelling Electron Microscopy W. M. Stobbs, W. M. StobbsSearch for more papers by this author W. M. Stobbs, W. M. StobbsSearch for more papers by this author First published: October 1988 https://doi.org/10.1111/j.1365-2818.1988.tb01355.xCitations: 5AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume152, Issue1October 1988Pages 1-1 RelatedInformation

Nonlocal response of a small coated sphere.

A theory for the response of a small spherical particle with a coating is developed using the semiclassical infinite-barrier model. Both the core and the outer layer are described by a nonlocal dielectric function. The theory is applied to an ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$-coated Al sphere and to an Sn-coated ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ sphere, and we find the coating to dominate the high-multipole response of the particle in either case. The optical-absorption and scanning tunneling electron microscopy spectra of the above systems are discussed.

Phenomenological model for the growth of small metallic clusters on a substrate

A two-component phenomenological model of small metallic cluster growth on a substrate is presented and solved. The results are compared with those of recent experimental scanning tunneling electron microscope (STEM) studies. It is shown that this model can quantitatively explain all the features found in the experimental study, including in particular the presence of an unshifting peak at small radius in the cluster size distribution function.

Scanning tunneling and scanning electron microscopy investigations of nonuniform surfaces

We have used scanning tunneling microscopy as well as scanning electron microscopy in order to study nonuniform surfaces of new materials like icosahedral alloys and high- T c superconductors. For such systems the interpretation of topographical images recorded with a scanning tunneling microscope is substantially eased by initial investigations with a scanning electron microscope. The experimental results obtained from a micrometer down to a subnanometer scale may shed light on the structure and formation process of icosahedral alloys and high- T c superconductors.

Scanning tunneling and scanning electron microscopy on high-Tc superconductors

We used scanning tunneling microscopy (STM) and scanning electron microscopy (SEM) at room temperature to investigate the surface morphology of high-Tc superconductors of the composition EuBa2Cu3O7−x from the micrometer down to the nanometer scale. STM images of uncoated surfaces show large topographical features, which can be compared to structures also visible in SEM, as well as smaller structural details exceeding the resolution of the SEM on this sample.

Scanning tunneling and scanning transmission electron microscopy of biological membranes

Scanning tunneling and scanning transmission electron microscopy of biological membranes

Scanning tunneling and scanning transmission electron microscopy of biological membranes

The feasibility of imaging porin membrane, which is a reconstituted biological membrane consisting of phospholipid and protein, was studied by scanning tunneling microscopy (STM). Due to detailed knowledge of its composition from biochemical and its three-dimensional (3D) structure from electron microscopical analysis, porin vesicles seem to be a suitable model specimen for exploring the application of STM in biology. Unstained vesicles adsorbed onto a thin amorphous carbon film supported by a finder grid were localized using a scanning transmission electron microscope (STEM) at low irradiation doses ( < 100 e − nm 2 ). Suitable areas of the sample were then positioned in the STM by a light optical telescope. STM images taken under ambient pressure from empty amorphous carbon films exhibited corrugations in the range of ⩽ 1 nm, whereas steps having a height of 5 nm were reproducibly observed on grids with porin vesicles. Since this value is in good agreement with that obtained from air-dried metal shadowed vesicles, we interpret these steps as the edges of porin membranes.

Determination of surface topography of biological specimens at high resolution by scanning tunnelling microscopy.

Although techniques are available for the determination of the three-dimensional structure of biological specimens, for example scanning electron microscopy, they all have some serious drawback, such as low resolution, the requirement for crystals or for the sample to be analysed in a high vacuum. In an attempt to develop a technique for high-resolution three-dimensional structure analysis of non-crystalline biological material, we have tested the applicability of scanning tunnelling microscopy (STM), a method that has been used successfully in the analysis of metal and semiconductor surface structures. We report here that scanning tunnelling electron microscopy can be used to determine the surface topography of biological specimens at atmospheric pressure and room temperature, giving a vertical resolution of the order of 1 A. Our results show that quantum mechanical tunnelling of electrons through biological material is possible provided that the specimen is deposited on a conducting surface.

The Third International Conference on Scanning Tunnelling Electron Microscopy

The Third International Conference on Scanning Tunnelling Electron Microscopy