bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymers on graphite and gold: molecular images and substrate defects
Authors: Rabe J. P. , Sano M. , Batchelder D. , Kalatchev A. A. 
Published: August 2011

SUMMARYSub‐monomolecular layers of a derivatized Phthalocyaninato‐poly‐siloxane (PCPS) and a Polydiacetylene (PDA) have been prepared on highly orientated pyrolytic graphite and gold by Langmuir‐Blodgett and Langmuir‐Schäfer techniques. Raman scattering and grazing‐incidence‐reflection infrared spectroscopy were used to characterize packing and molecular orientations within these films. It was found that PCPS forms similarly well ordered monolayers on both graphite and gold while PDA does not. Scanning tunnelling microscopy (STM) was performed in air using both the constant height and constant current mode. On highly orientated pyrolytic graphite substrates various defect structures based on a √3X√3 R 30° superstructure were found near localized defects and small graphite steps. They were carefully distinguished from molecular images of densely packed hydrocarbon chains. Defect rich graphite was characterized with both STM and Raman spectroscopy. Similarly, disordered and graphite‐like regions were found on carbon fibres. The sensitivity of STM to surface defects in graphitic material turned out to be large compared to that of the Raman spectroscopic method. STM images of PCPS monolayers on graphite and gold exhibited parallel polymer rods, 2 nm apart from each other.
New developments in fast image processing and data acquisition for STM
Authors: Béjar M. A. , Gómez‐Rodríguez J. M. , Gómez‐Herrero J. , Baró A. 
Published: August 2011

SUMMARYWe have developed new easy‐to‐use but powerful software in order to obtain the best scan rates in data acquisition and image processing for a PC‐AT microcomputer.The programs have been completely written in the C‐language, which made it possible to combine low‐level characteristics (quick access to memory, interrupt control, etc.) without losing the advantages of a high‐level language.The data acquisition software was intended to be sufficiently flexible to acquire either topographical or spectroscopic data with no configuration changes. In topographical (z=f(x,y)) and spectroscopic (I=f(V, z)) measurements, we can obtain up to 15,000 samples/s rates, with 12‐bit resolution in a ±10V range. Spectroscopic measurements are done by acquiring I(V) with the feedback off at several z values (up to 256) until I reaches a preset value; afterwards, z is reset automatically to the initial voltage to avoid tip‐sample contact.The image processing was designed to get the best performances in time and quality with a simple system such as a PC‐AT equipped with an IBM Professional Graphics Display (640times480 pixels and 256 simultaneous colours).It was structured in three parts: plane subtraction, image display (3‐D shaded surfaces, 3‐D surfaces with colour scales or 2‐D contour maps), and filtering (smoothing filters or FFT convolution‐deconvolution techniques).
Preparation of STM tips for in‐situ characterization of electrode surfaces
Authors: Heben Michael J. , Dovek Moris M. , Lewis Nathan S. , Penner Reginald M. , Quate Calvin F. 
Published: August 2011

SUMMARYThe total current between the tip and the sample in a scanning tunnelling microscopy study of a solid/liquid interface can be dominated by Faradaic charge transfer currents. In such a situation, feedback control of the tunnelling gap, and imaging, is precluded. In this contribution we describe the preparation of glass and polymer coated STM tips that possess < 100 Å2 of exposed metal. These tips effectively discriminate against Faradaic current and enable STM imaging in the presence of reversible electroactive solution species at appreciable tip/sample biases.
Battery‐operated STM
Authors: Valdés J. , Kohanoff J.J. , Lobbe E.E. , Bancalari R. López , Porfiri M.E. , Cantú R. García 
Published: August 2011

SUMMARYA scanning tunnelling microscope operating with ±12 V is described. A scanning range higher than 1 μm is achieved in the three orthogonal scanning directions for that low voltage. This translator arrangement, based on the use of piezoelectric discs mounted on metallic circular plates acting like flat springs, may provide a better performance than the tube scanners or rectangular bimorphs since it allows a greater volume to be run by the tip for a given voltage.
An STM for biological applications: Bioscope
Authors: Michel B. , Travaglini G. 
Published: August 2011

SUMMARYWe present an STM with an improved coarse positioning system and a large scan area which is especially suitable for biological applications. Three stepper motors are used to move an X‐Y‐Z table. Movements of motor axes are geared down to drive micrometer spindles so that steps of 250 nm can be performed. The stepper motors can be uncoupled from the STM for scanning operation. A piezo tube is used to scan areas of up to 10times10μm with low voltage operation. Probes can be scanned in air or in electrochemical cells. High stability against thermal drift and vibrations is achieved by a rigid and symmetrical design.
Mono‐ and multiatomic steps with constant periodicity as observed by STM in vicinal Au(111) surfaces
Authors: Ocal C. , de Parga A.L. Vazquez , Alvarez J. , Ferrer S. 
Published: August 2011

SUMMARYScanning tunnelling microscopy images of a vicinal Au(111) surface obtained in UHV are presented. Arrays of mono‐ and multiatomic steps along the [011] direction are seen with a peculiarly constant periodicity. The steps, exposing (100) facets, have a height ranging from one to seven atoms while the terrace width of eight atoms remains constant.
A real space investigation of the dimer defect structure of Si(001)‐(2times8)
Authors: Niehus H. , Köhler U. K. , Copel M. , Demuth J. E. 
Published: August 2011

SUMMARYThe atomic arrangement of the Si(001)‐(2 times 8) surface has been directly imaged in real space by scanning tunnelling microscopy. The superstructure is impurity induced and stablilized by as little as 1% Ni. Clean Si(001) surfaces do not form the (2times8) phase. The two‐dimensional Fourier transforms of the STM topographs correspond well to the (2times8) LEED pattern, but the real space images are in fact considerably more complex than previously concluded on the basis of recent diffraction technique measurements. The STM images clearly demonstrate that the (2times8) surface consists of a complex missing dimer structure, namely one and multiple dimer vacancies. Such a dimer defect appears related to the Ni impurity and intimately related to the ordering of the dimer defects probably by third layer dimerization to produce quasi‐ordered ‘channels’.
Imaging of hydrogen‐induced Si(111) surface with the scanning tunnelling microscope
Authors: Tokumoto Hiroshi , Miki Kazushi , Murakami Hiroshi , Morita Naotake , Bando Hiroshi , Sakai Akira , Wakiyama Shigeru , Ono Masatoshi , Kajimura Koji 
Published: August 2011

SUMMARYWe have directly observed the hydrogen‐induced changes of the Si(111)7times7 surface using a scanning tunnelling microscope (STM). The 7times7 reconstructed atomic structure was formed on a clean surface of Si(111). But when the clean surface was dosed with typically 1–2 L [1 L (Langmuir) = 1·33 times 10−4 Pa. sec] hydrogen, the 7 times 7 image was gradually smeared out and then a 1 times 1 unreconstructed pattern appeared. After dosing with 5–10 L hydrogen, the STM image exhibited a new long‐periodic structure together with the 1times1 structure underneath. These experimental results may be ascribed to the chemisorption of hydrogen atoms on clean Si surfaces.
Scanning tunnelling microscopy of B/Si(111) √3×√3 R(30°)
Authors: Dumas Ph. , Thibaudau F. , Salvan F. 
Published: August 2011

SUMMARYThe √3 superstructure induced by boron outdiffusion at the surface of highly p doped Si(111) samples is studied by means of Auger, LEED and STM. Simultaneous double imaging at different voltages allows us to probe both filled and empty electronic states. A modification of the T4 structural model of (Al, In, Ga)/Si(111) √3 is proposed for the B/Si(111) √3 superstructure.
Scanning tunnelling microscopy of charge density waves in 1T‐TaS2
Authors: Thomson R.E. , Walter U. , Ganz E. , Rauch P. , Zettl A. , Clarke J. 
Published: August 2011

SUMMARYUsing a variable temperature scanning tunnelling microscope we have observed both the lattice and the triple charge density wave (CDW) in 1T‐TaS2. We obtained images of the nearly‐commensurate (NC) phase between 350 and 200 K and the triclinic (T) phase between 220 and 280 K. We analysed the images to determine the local angle of rotation of the CDW relative to the lattice to determine if commensurate domains exist in this material. In the NC phase we do not see the hexagonal discommensurate domains proposed by Nakanishi el al. (1977), but observe a structure which is uniformly incommensurate. The orientation of the CDW relative to the lattice is observed to be locally incommensurate and to vary continuously with temperature as reported by Scruby et al. (1975). However, in the T phase we observe long narrow commensurate domains very similar to those described by Nakanishi and Shiba (1984) for this phase.
Scanning probe microscopy of biological samples and other surfaces
Authors: MARTI O. , Elings V. , Haugan M. , Bracker C. E. , Schneir J. , Drake B. , Gould S. A. C. , Gurley J. , Hellemans L. , Shaw K. , Weisenhorn A. L. , Zasadzinski J. , Hansma P. K. 
Published: August 2011

SUMMARYScanning probe microscopes derived from the scanning tunnelling microscope (STM) offer new ways to examine surfaces of biological samples and technologically important materials. The surfaces of conductive and semiconductive samples can readily be imaged with the STM. Unfortunately, most surfaces are not conductive. Three alternative approaches were used in our laboratory to image such surfaces.1. Crystals of an amino acid were imaged with the atomic force microscope (AFM) to molecular resolution with a force of order 10−8 N. However, it appears that for most biological systems to be imaged, the atomic force microscope should be able to operate at forces at least one and perhaps several orders of magnitude smaller. The substitution of optical detection of the cantilever bending for the measurement by electron tunnelling improved the reliability of the instrument considerably.2. Conductive replicas of non‐conductive surfaces enabled the imaging of biological surfaces with an STM with a lateral resolution comparable to that of the transmission electron microscope. Unlike the transmission electron microscope, the STM also measures the heights of the features.3. The scanning ion conductance microscope scans a micropipette with an opening diameter of 0·04‐0·1 μm at constant ionic conductance over a surface covered with a conducting solution (e.g., the surface of plant leaves in saline solution).
In‐situ STM studies of electrochemical underpotential deposition of Pb on Au(111)
Authors: Green M. P. , Richter M. , Xing X. , Scherson D. , Hanson K. J. , Ross P. N. , Carr R. , Lindau I. 
Published: August 2011

SUMMARYA modified scanning tunnelling microscope (STM) has been used to observe in‐situ deposition and stripping of an electrochemical film. With STM tip and sample immersed in an acid electrolyte, single atomic steps on Au(111) have been imaged during the deposition and stripping of a monolayer‐thick, underpotential deposit (UPD) of Pb. Integration of the electrochemical current passed during the film deposition and evidence from the STM images themselves confirm monolayer coverage. Our images show enhanced film growth at step edges and defect sites. Observations of single plating and stripping cycles indicate that the Au substrate returns unaltered. Except for atomic resolution images of Au(111), which we have not yet achieved in an electrolyte, all types of Au surface features seen in air are reproduced under the electrolytic solution. The modifications made to our STM in order to perform in‐situ electrochemical experiments are described.
Spatially resolved low‐temperature spectroscopy on niobium bulk samples
Authors: Berthe R. , Hartmann U. , Heiden C. 
Published: August 2011

SUMMARYUsing a low‐temperature STM, simultaneous measurements of the surface topography and of spatial variations in the current‐voltage characteristics have been performed on poly‐crystalline niobium bulk samples. A special electronic set‐up was developed which allows the tip bias to be swept at a constant tip position. From the resulting I(V) curves the actual magnitude of the superconducting energy gap is derived. The comparison of the surface morphology and gap distribution permits the detection of possible correlations between local variations in the superconductivity and in the topography. Upon the application of an external magnetic field, local variations of the gap are observed which have no topographic counterparts. This latter observation might indicate the existence of isolated vortices.
Fine structure in field emission resonances at surfaces
Authors: Coombs J. H. , Gimzewski J. K. 
Published: August 2011

SUMMARYWe have measured field‐emission resonances (FER) to much higher quantum states than previously observed enabling fine structure in the resonance amplitudes to be investigated. We show that this electron wave interference effect carries additional information in the resonance amplitudes and energies and is sensitive to lateral tip position in a scanning tunnelling microscope experiment. We propose a new method of data analysis that can distinguish between some of the possible origins of the fine structure.
High‐resolution force microscopy of in‐plane magnetization
Authors: Abraham David W. , Williams C. C. , Wickramasinghe H. K. 
Published: August 2011

SUMMARYWe have shown for the first time, in previous studies, that the force microscope fitted with a magnetic tip could be used to image magnetic domains in TbFe thin films. In this report we show that the information provided by the magnetic force microscope can also include a measurement of the component of magnetization in the sample which is parallel to the surface. Measurements were taken with a magnetized tip tilted at 45° with respect to the surface normal. In a first experiment, we imaged 1 μm diameter domains thermomagnetically written in a TbFe thin film. In a second measurement, we imaged a series of alternating domains in a thin film Co‐alloy disc which was decorated with small magnetized particles, allowing unambiguous identification of the domain boundaries. In both cases we interpret the asymmetric portion of the images to the in‐plane component of the sample magnetization.
Quasi‐crystals and their crystalline homologues in the Al60Mn11Ni4 ternary alloy
Authors: Van Tendeloo G. , Van Landuyt J. , Amelinckx S. , Ranganathan S. 
Published: August 2011

SUMMARYThe transition quasi‐crystalline→crystalline is found to be very sluggish in the ternary alloy Al60Mn11Ni4. This makes it possible to study in detail the relationship between the decagonal phase, obtained after furnace cooling, and two different crystalline phases, which result after long annealing at 400°C.Use is made of electron diffraction, high resolution electron microscopy and optical diffraction.The crystalline phases still exhibit features which are closely related to those of the decagonal phase. This can be concluded from a comparison of the electron diffraction patterns of the quasi‐crystalline phase along a number of zones, with those of the crystalline phases along corresponding zones.The crystalline phases contain different types of defects which are analysed in detail using high resolution images and diffuse scattering in the electron diffraction patterns.The close relationship between the electron diffraction patterns of the crystalline and quasi‐crystalline phases is explained in terms of general optical principles.Some characteristic features of a model of the quasi‐crystalline phase are tentatively proposed.
A model for logarithmic image processing
Authors: Jourlin Michel , Pinoli Jean‐Charles 
Published: August 2011

SUMMARYUp to now, image processing and image analysis techniques have borrowed their basic tools from functional analysis: Fourier filtering, differential and integral calculus, and so on. These tools, however, only realize their efficiency when they are put into a well‐defined algebraic frame, most of the time of a vectorial nature. Unfortunately, the class of functions modelling ‘images’, commonly referred to as ‘grey tone functions’ does not necessarily present this very type of structure. We present here an operation for the ‘addition’ of two images, with a physical justification in the context of transmitted light. Such an addition permits the construction of the family of ‘positive homothetics' of the grey tone function at hand. The vectorial context sought is well defined: The class of images associated with the class of their grey tone functions naturally becomes the positive cone of an ordered real vector space.Furthermore, the proposed model holds for logarithmic imaging and is compatible with what is known about the human visual process. This model has been called ‘LIP’ (logarithmic image processing model).
Three‐dimensional imaging in confocal imaging systems with finite sized detectors
Authors: Wilson T. , Carlini A. R. 
Published: August 2011

SUMMARYWe consider the effect of the finite size of the detector on both the lateral and axial resolution of the confocal system. The use of a finite sized detector means that the imaging is no longer truly coherent. We find that the lateral resolution is considerably more sensitive to the detector size than is the axial response. The question of the rejection of flare light is also considered. Experimental results are shown and we find that acceptable extended‐focus, auto‐focus and height images may be obtained from non truly‐confocal systems. We also find that lens apodization has a far greater effect on the axial resolution than the lateral resolution.
Soft X‐ray contact imaging of nucleolar chromatin using synchrotron radiation: a comparative scanning and transmission electron microscope study
Authors: Hill K. S. , Myring W. J. , Clarke D. T. , Veltkamp C. J. 
Published: August 2011

SUMMARYContact images (CI) of dehydrated, nucleolar chromatin from amphibian oocytes have been produced by soft X‐rays from a synchrotron radiation source. These CI have been compared with the morphology of the original chromatin as seen in scanning and transmission electron microscopes. The quality and informational content of the CI depend very much on certain preparative procedures. The following factors have a marked effect on image quality and need to be carefully controlled: the total X‐ray dose, the time and nature of development and the distance of the specimen from the photoresist. The preparation of the chromatin itself, providing that it is critically point dried, is less important. By following a regime of high X‐ray dose, sufficient for penetration of the rather thick chromatin rings, and gentle development so that fine detail is not dissolved from the resist surface, it has been possible to obtain images which closely resemble the original chromatin, although the detailed resolution of the CI is not as clear. The smallest biological structures clearly resolved in the CI are ribonucleoprotein granules, which vary in size from 200 to 800 nm. However, by further refinement of preparative conditions it should be possible to improve on the informational content of these images.
Stereological analysis of three‐dimensional structure organization of surfaces in multiphase specimens: statistical methods and model‐inferences
Authors: Kroustrup J. P. , Gundersen H. J. G. , Væth M. 
Published: August 2011

SUMMARYIn a multiphase material the structural components or phases are everywhere in contact with each other. The relative area of surface contact between various phases is an important aspect of the short‐range ordering or organization of the structure. The stereological quantitation of such specific interfaces is a simple and well‐known technique. The proper statistical definition of realistic models for the frequency of contact and the quantitative estimation of phase‐specific affinities is studied. The meaningful interpretation of sets of estimated affinities poses a major problem of statistical inference which is dealt with in detail and illustrated by a worked‐out biological example.
A comparison of soft X‐ray contact microscopy with light and electron microscopy for the study of algal cell ultrastructure
Authors: Stead A. D. , Ford T. W. , Myring W. J. , Clarke D. T. 
Published: August 2011

SUMMARYImages of filamentous and unicellular algae have been obtained by soft X‐ray (wavelength 2.05‐4.4 nm) contact microscopy (SXCM), using synchrotron radiation, and the images obtained compared to those obtained by scanning and transmission electron microscopy. After chemical development to leave areas corresponding to high X‐ray absorbance by the specimen the photoresists were examined by SEM. In two algae (Anabaena and Trebouxia) cytoplasmic detail, including photosynthetic lamellae, chloroplasts, nuclei and mitochondria, were identified. In a third alga (Cyanidium) the SXCM image revealed little internal detail due to the uniformly high X‐ray absorption by the cells. The successful imaging of whole cells by SXCM is discussed in relation to conventional TEM and the future possibilities for SXCM are outlined.
Energy‐dispersive X‐ray microanalysis of air‐dried microdroplets containing a macromolecular solute
Authors: Bostrom T. E. , Gyory A. Z. , Benson D. C. , Horgan E. , Nockolds C. E. , Beck F. X. , Cockayne D. J. H. 
Published: August 2011

SUMMARYIn the preparation of microdroplets of biological fluids for X‐ray microanalysis, we have found that incorporation of a macromolecular solute, dextran, to a final concentration of 1.5‐2.5% retards crystal formation and produces sufficiently uniform deposits on thin films to allow droplets to be analysed without prior freeze‐drying. Analyses have been carried out at 20 kV in a scanning electron microscope, using energy‐dispersive spectrometry. Absorption of Na X‐rays by the added solute can be significant but its effect is minimized by preparing droplets as thin as possible, and by using standards of similar composition. The minimum detectable concentrations are increased because of the extra background contribution, and for a single determination are about 6 mM for Na and 2 mM for Cl and K. These concentrations can be further reduced by measuring replicates.The reproducibility of analysis is significantly improved (to less than 5% for Na and K) over the use of calibration curves by calculating the element concentrations from a known element in the sample, chlorine. Under our analytical conditions loss of Cl did not occur. This method requires that the Cl is measured separately by microcoulometry, but eliminates the need for a range of standard droplets on the grid, and determination of the unknowns is then independent of droplet volume, beam current, counting time and magnification.We have compared, with biological samples, the results from using Cl as an internal standard with those obtained using an added standard element, cobalt. The reproducibility using Cl was approximately two‐times better than that obtained with Co, probably because of unavoidable volumetric errors when the Co is pipetted separately.