bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coherent electron emission from point sources
Authors: Serena P. A. , Escapa L. , Sáenz J. J. , García N. , Rohrer H. 
Published: August 2011

SUMMARYWe study the electron emission and propagation in ultrasharp tips field‐emission experiments. The intensity‐voltage characteristics as well as the angular spreading of the electron beam is analysed. We show that non‐coherent emission cannot explain the very narrow experimental electron beams. The properties of coherent electron sources and the beam spatial coherence width are discussed. The quantum mechanical current distribution of field‐emitted electrons from tubes seems to explain the experimental beam widths.
The importance of current density ‘focusing’ in STM image resolution
Authors: Aers G. C. , Leavens C. R. 
Published: August 2011

SUMMARYIn a previous paper we incorporated Tersoff and Hamann's model of an STM tip into Lang's transfer Hamiltonian result for the tunnelling current density and applied the resulting simple expression to Tersoff's six‐plane‐wave model of a monolayer of graphite. In this paper the results for a more realistic model of a graphite surface and a more complete selection of tip positions are presented. They support the previous conclusions that the normal component of the current density takes on both positive and negative values in a complex flow pattern and that its lateral falloff away from the (projected) tip position is much slower than expected from the extraordinary lateral resolution (∼1 Å) evident in the best STM images of graphite. This shows that sharp ‘focusing’ of the current density directly under the tip is not a necessary condition for high lateral resolution.
A combined scanning tunnelling and field ion microscope
Authors: Michely Th. , Besocke K. H. , Teske M. 
Published: August 2011

SUMMARYThe construction of a combined scanning tunnelling and field ion microscope allowing the in situ preparation and analysis of the tunnelling tip is described. The apparatus is based on the Besocke type STM and includes a fast, automated sample approach, a sample transfer manipulator and a tip‐cooling mechanism for the FIM operation mode. The design is simple and needs a mechanical feedthrough only for sample transfer. A method has been developed to produce sharp tungsten tips with small clusters on the apex plane. Test‐run results of FIM and STM operation modes are discussed.
A small scanning tunnelling microscope with large scan range for biological studies
Authors: Emch R. , Descouts P. , Niedermann Ph. 
Published: August 2011

SUMMARYWe have developed a scanning tunnelling microscope specially designed for biological applications presenting some new features: the scanner tube is mounted parallel to the surface of the sample which enables a high resolution optical microscope to be brought close to the sample when working in air or liquids. The maximum scan range is 5×20 μm with a vertical range of 20 μm and the total size of the system does not exceed 10×40 mm. The piezo‐sensitivity of the scanner tube versus applied voltage was analysed by interferometry measurements and by using scanning tunnelling microscopes. We found a value for the piezoelectric constant d13 of −1·71 Å/V at low voltages (under a few volts) going up to −2 Å/V for higher voltages. Large‐scale images of a carbon grid showed a surprisingly good linearity of the scanner tube.
Topography of YBa2Cu3O7‐δ single crystals, spectroscopy of thin films and sintered YBa2Cu3O7‐δ: theory and STM observations
Authors: van de Leemput L. E. C. , van Bentum P. J. M. , Driessen F. A. J. M. , Gerritsen J. W. , van Kempen H. , Schreurs L. W. M. , Bennema P. 
Published: August 2011

SUMMARYWe report topographic scanning tunnelling microscopy measurements on the (001) and (100) surfaces of YBa2Cu3O7‐δ single crystals, together with a theoretical basis by which the surface structures can be understood. We show that it is possible to obtain reproducible topographic data on a clean (001) and (100) surface in air. The results show various structures at scales from 0·1 to 100 nm. Among the observed features on the (001) surface were growth steps which had heights that were multiples of the lattice constant in the [001] direction. This indicates that the bulk crystal structure extends to the surface, and that the surface is relatively stable, even in humid air. We also found small (013) facets on the (001) surface, in accordance with theoretical pradictions. Occasionally, we found evidence for a one‐dimensional corrugation on the surface. This is possibly a direct consequence of the orthorhombic distortion in the a‐b plane with ordered oxygen vacancies, which gives rise to chain‐like Cu‐O structures along the b‐axis.In addition, we measured the energy gap of sintered pellets and thin films of this superconductor, using a low‐temperature STM. We discuss some effects which may influence the measurements and present criteria to check for these effects. We found an energy gap of δ=14±2 eV, in good agreement with the BCS pradiction 2δ/kTc=3·5. This is not contradicted by the results we obtained by far infrared spectroscopy and Andreev reflection measurements.
A spectroscopic study of some high‐temperature superconductors using a low‐temperature STM
Authors: Gallagher M. C. , Adler J. G. 
Published: August 2011

SUMMARYWe used a scanning tunnelling microscope (STM) to measure both the tunnel current, I, and the dynamic conductance, dI/dV, at 4·2 K for a number of high‐transition temperature oxide superconductors. Large spatial variations in the tunnelling characteristics are observed. At low tunnel resistances, all samples show evidence of single electron tunnelling and incremental charging. Results on BiSrCaCu2Ox show the coexistence of charging with Josephson coupling between grains within the sample. Results on both the Bi sample and a single crystal of YBa2Cu3O6·5+x reveal possible energy gap (2A) values of 17 and 20 meV, respectively. A very sharp 5 meV gap, observed in ceramic samples of YBa2Cu3O6·5+x and Y0·5Al0·05Ba2Cu3O6·5+x, may indicate the presence of a lower temperature phase in these samples.
Characterization and local modification of atomically flat gold surfaces by STM
Authors: Emch R. , Nogami J. , Dovek M. M. , Lang C. A. , Quate C. F. 
Published: August 2011

SUMMARYIn order to characterize the surface of epitaxial gold on mica in air we have used a scanning tunnelling microscope (STM) to image and to modify this surface. It was possible to create controlled features by applying voltage pulses on the tip while scanning. The voltage threshold for writing (about 3 V, 100 ns pulses) was dependent of the tip condition. The lowest pulses were associated with sub‐50 Å feature size. We observed that at ambient temperature the written features disappeared in a time scale of half an hour for the smallest (<30 Å) to a few hours for the bigger features (∼500 Å). We have used the same surface as a substrate for organic imaging. We also present images of a polymer deposited on gold.
Scanning tunnelling microscopy on reconstructed Si(110)
Authors: Neddermeyer H. , Tosch St. 
Published: August 2011

SUMMARYWe have prepared clean surfaces of reconstructed Si(110), which showed a distinct 4×5 LEED pattern with particularly high intensity of the diffraction beams corresponding to a 2×1 periodicity of the surface. Images obtained by scanning tunnelling microscopy on the same surfaces are characterized by rows of reconstructed Si atoms along the direction. On high‐resolution images, atomic subunits in a 2×5 periodicity of ideal Si(110) have been identified. By using these subunits as building blocks for both the 4×5 and the 2×1 reconstruction, a previously reported phase transition between both reconstructions may be explained by a loss of order along the direction.
Supported metal model catalyst surfaces examined by scanning tunnelling microscopy
Authors: Komiyama Masaharu , Morita Seizo , Mikoshiba Nobuo 
Published: August 2011

SUMMARYTopographic and/or barrier‐height images of ultrafine Pt and Au metal particles supported on a vacuum‐deposited carbon film or titanium oxide thin films grown on titanium metal sheets were obtained. The topographic images of colloidal Au particles (5‐nm diameter) adsorbed on a titanium oxide thin film showed a structure elongated in the direction normal to the x scan, indicating their weak interaction with the support surface. The topographic images of Pt vacuum‐deposited on a carbon film showed c. 4‐nm diameter particles, larger than those observed in electron microscopy. The problems inherent to the STM observation of such dispersed metal systems are identified. In the case of Pt particles vacuum‐deposited on titanium oxide film, its barrier‐height image gave better indication of different phases on the surface than its topographic image. The significance of obtaining barrier‐height images along with topographic images for such sample systems is demonstrated.
Adsorbate deformation as a contrast mechanism in STM images of biopolymers in an aqueous environment: images of the unstained, hydrated DNA double helix
Authors: Lindsay S. M. , Thundat T. , Nagahara L. 
Published: August 2011

SUMMARYA stable residual aggregate remains on a submerged gold surface after electrophoretic deposition of DNA. We present scanning tunnelling microscope (STM) images of these aggregates which show many objects with the geometry of DNA, clearly displaying the 3·4 nm helix pitch. These images are quite distinctive, and cannot be generated when the deposition technique is used without DNA in the buffer solution. A characteristic of these images is that the tip is observed to dip down over the DNA molecule at the same time as the apparent barrier height drops by a factor of about four. The tip displacement is accounted for by a model in which contrast is dominated by local fluctuations in the deformability of the adsorbate layer, a quantity deduced from measurements of the apparent barrier heights in air, water, over small molecule adsorbates, and over DNA.
STM measurements on graphite using correlation averaging of the data
Authors: Soethout L. L. , Gerritsen J. W. , Groeneveld P. P. M. C. , Nelissen B. J. , van Kempen H. 
Published: August 2011

SUMMARYImages of the (0001) surface of highly oriented pyrolytic graphite observed using scanning tunnelling microscopy, in both constant distance and current imaging modes, show a strong asymmetry of the unit cell. This asymmetry depends on the tunnelling current and voltage. We have also found clear evidence that multiple‐tip tunnelling occurs. To improve the resolution of the imaged unit cells, a method of correlation averaging is introduced.
Comparative study of lithium fluoride and graphite by atomic force microscopy (AFM)
Authors: Meyer E. , Heinzelmann H. , Grütter P. , Jung Th. , Weisskopf Th. , Hidber H.‐R. , Lapka R. , Rudin H. , Güntherodt H.‐J. 
Published: August 2011

SUMMARYThe atomic force microscope (AFM) offers the possibility to image the topography of insulating as well as conductive surfaces. Highly oriented pyrolytic graphite (HOPG) was chosen as an example for a layered material and compared to single crystalline lithium fluoride (LiF). Both materials are easily prepared and inert at ambient pressure. Furthermore they are well characterized by Helium atom scattering experiments and other techniques.On HOPG atomic resolution has been achieved. Distortions can be observed which we interpret as a frictional effect. In addition we performed large area scans where we seldomly observed dislocations. For the first time we present measurements on LiF, showing steps of one unit cell height. On larger areas the surface of LiF showed terraces, separated by steps of variable heights, ranging from a few ångströms to 100 Å.We used a static method to get information about the distance dependence of the force between lever and sample. By slowly expanding and retracting the sample piezo and simultaneous measurement of the lever deflection, plots were recorded, showing the force as a function of sample position. The results were compared with theoretical calculations. We could determine the tip radius and found differences between LiF and HOPG being characteristic for the samples.
Contact resistance and saturation effects in the scanning tunnelling microscope: the resistance quantum unit
Authors: Martín‐Rodero A. , Ferrer J. , Flores F. 
Published: August 2011

SUMMARYWe present a theoretical analysis of the contact resistance in the Scanning Tunnelling Microscope. Under the assumption of a single contact atom on the tip's apex, we find that the resistance saturates at close contact, its value being h/2e2. Our analysis of the recent experimental results of Gimzewski & Möller (1987), shows that the mechanical instability pradicted by Pethica & Sutton (1988), appears for a distance 1·5 Å larger than the close contact distance between the tip and the sample.
A role of a tip geometry on STM images
Authors: Hashizume T. , Kamiya I. , Hasegawa Y. , Sano N. , Sakurai T. , Pickering H. W. 
Published: August 2011

SUMMARYScanning tunnelling microscopes operable in both ultrahigh vacuum (UHV) and aqueous conditions are described with emphasis on a tip geometry. An atomically resolved STM image was obtained for the Si(111)‐Mo√3 surface in UHV condition and changes of a diffraction grating surface in aqueous condition due to an electrochemical reaction were monitored.
In situ fabrication and regeneration of microtips for scanning tunnelling microscopy
Authors: Binh Vu Thien 
Published: August 2011

SUMMARYProgress in STM, in particular for the interpretation of the tunnel signals of corrugated surfaces, is related to the possibility of sharpening and regenerating in situ reproducible tips for use as the probe. We proposed two techniques for the production of tips with controlled geometry at the atomic level. These two techniques are based on the production of tips with equilibrium profiles obtained under heat treatments in vacuum and in the presence of an electric field. Based on the pseudo‐stationary profile principle, the microtips can be sharpened in situ and in a reproducible manner, either from initial cylindrical (111)‐W wire, or from breakdown tips; in both cases without the need for heavy control devices (like FIM for example).
Design and operation of a variable temperature scanning tunnelling microscope
Authors: Lyding J.W. , Skala S. , Hubacek J.S. , Brockenbrough R. , Gammie G. 
Published: August 2011

SUMMARYA new variable temperature STM has been developed which utilizes two concentric piezoelectric tubes; an inner scanning tube, and an outer thermal compensation tube which also provides for inertial translation of the sample into tunnelling range. With this design, continuously variable temperature operation is demonstrated for the first time in an STM. Also, by eliminating all mechanical components such as springs, levers and gears, which normally couple directly to the tunnelling gap in other designs, atomic resolution operation is demonstrated in which no vibration isolation is necessary. During operation, the inside of the scanning tube is maintained at ground potential while the feedback signal is electronically summed to the scanning voltages applied to the outer quadrants. In addition to shielding the sensitive tunnelling circuit, this mode of operation enables one to electronically balance out mechanical imperfections of the scanning tube. To date, this new STM has been operated over the 77–400 K temperature range with the observed thermal drift as low as 1 Å/h and 10 Å/K. Another useful feature of this new design is the ability to reposition a sample to within 200 Å of the same location after it has been translated macroscopic distances (several mm) out of tunnelling range.
Finite element analysis of PZT tube scanner motion for scanning tunnelling microscopy
Authors: Carr R. G. 
Published: August 2011

SUMMARYThis article is a presentation of the results of a finite element method analysis of piezoelectric tube scanners of the type presently in wide use in scanning tunnelling microscopes. The tube scanner moves a tunnelling tip by bending sideways when unsymmetrical voltages are applied to longitudinal stripes of metallization on its walls. It also can be extended and contracted in length by application of symmetrical voltages. One wishes to know the characteristics and magnitudes of the resulting three‐dimensional motion. We divided a model tube into radially polarized elements, and constructed a computer program to perform electromechanical stress calculations. The results show the dependence of motion upon applied voltage, tube material, and tube dimensions.
Increasing the scanning speed of scanning tunnelling microscopes
Authors: Robinson R. S. 
Published: August 2011

SUMMARYThe scanning speed and quality of images obtained with a scanning tunnelling microscope can be increased by replacing the tunnelling tip holder with an active, high resonance frequency piezoelectric positioner. The combination tip holder and positioner has a resonance frequency near 100 kHz, allowing fast closed‐loop feedback control of the STM. With appropriate electronic shielding, the active tip holder can also be used to modulate the tip to surface distance at high frequencies for work function mapping.The high speed positioner is complemented by a ‘tip‐saver’ circuit which senses imminent tip‐surface contact, preventing tip crashes. The circuit, when driving the fast positioner, has a response time of under 20 μs and is not subject to the oscillation problems normally associated with closed‐loop feedback systems operated at high gains and large signal bandwidths.
Scanning tunnelling microscopy and spectroscopy on Cu(111) and Au(111)
Authors: Brodde A. , Tosch St. , Neddermeyer H. 
Published: August 2011

SUMMARYWe have studied Cu(111) and Au(111) by means of scanning tunnelling microscopy and spectroscopy. The constant current topographies showed flat parts as well as regions with a high density of monoatomic steps (in particular on Au(111)). Local I/U characteristics have been determined at a fixed sample‐tip distance in the range of −10 V≤U≤10 V. They show a linear behaviour near the Fermi level and a nearly exponential dependency for larger values of U. Neither an influence of the sp‐like surface states or an onset due to d electron contributions of the sample could be observed.
Investigation of intrinsic crystalline Si(111) and amorphous silicon surfaces in air with STM
Authors: Okoniewski A. M. , Yelon A. 
Published: August 2011

SUMMARYCrystalline (111) and amorphous silicon surfaces have been studied by scanning tunnelling microscopy. An orientated, reproducible, corrugated structure has been observed on Si(111) surfaces. The voltage dependence of the corrugation amplitude may be attributable to surface states. The surfaces of amorphous silicon thin films show some reproducible structure in the range of a few tens of ångströms, observable only when the applied voltage between the tip and sample is between −1·3 and +0·4V.
Clean and metal‐contaminated Si(110) surfaces studied by RHEED, XPS and STM
Authors: van Loenen E. J. , Dijkkamp D. , Hoeven A. J. 
Published: August 2011

SUMMARYWe have studied the atomic structure of clean and metal‐contaminated Si(110) surfaces in real space with Scanning Tunnelling Microscopy (STM) and compared the results with Reflection High Energy Electron Diffraction (RHEED) data taken on samples from the same wafer.On clean Si(110) surfaces flatreconstructed regions coexist with (15 17 1), (15 173) and related facets. Thesurface consists of periodically‐alternating high and low terraces, with a height difference corresponding to the interlayer spacing (0·19 nm). This structure is found in two domains, with terrace edges aligned along the and directions respectively. Atomic scale zig‐zag chains can be recognized on the terraces.Contamination of the surface with Ni or Cu results in the formation of reconstructions with drastically different unit cells, all orientated along [001] and . The transition proceeds via a disordered 5×1‐like intermediate phase for Ni coverages around 0·007 ML.
Scanning tunnelling microscopy of oxidized graphite
Authors: Porte L. , Richard D. , Gallezot P. 
Published: August 2011

SUMMARYScanning tunnelling microscopy (STM) and transmission electron microscopy (TEM) have been used to investigate the surface of a pyrolitic graphite oxidized in liquid phase by NaClO. Two main features of the oxidized HOPG are revealed by STM. First, a large number of steps of different heights have developed on the graphite surface. These steps can be observed by TEM on another kind of graphite, HSAG 12, but this technique cannot give any information on their heights. Another kind of defect on the previously flat surface of HOPG consists in patches where the surface is rough and perturbed. These domains are very difficult to observe by TEM due to a poor contrast. Thus for the study of surface heterogeneities intentionally created on graphite, STM, providing information along three directions, appears to be complementary of TEM which gives only images of project area.
Investigation of Bloch wall fine structures by magnetic force microscopy
Authors: Göddenhenrich T. , Hartmann U. , Anders M. , Heiden C. 
Published: August 2011

SUMMARYUsing a magnetic force microscope (MFM), measurements have been performed on single crystal iron whiskers. These samples exhibit a comparatively simple magnetic domain structure and a high degree of crystallographic perfection. STM measurements yield an average surface corrugation of about 3 nm. These nearly ideal boundary conditions permit an investigation of the undistorted surface configuration of Bloch walls in a cubic bulk crystal. Interactions between the stray field configuration of the sample and a ferromagnetic microscope tip have been measured with a new MFM device which is based on direct compliance detection. Measurements have been performed in the constant‐current mode, as well as in the constant‐compliance, mode. Control observation by means of the Kerr magneto‐optic effect permit an interpretation of the obtained MFM data in terms of isolated 180° Bloch walls. The fine structure of these walls has been analysed and compared with results obtained from model calculations.
Real‐time scanning tunnelling microscopy of surfaces under active electrochemical control
Authors: Robinson R. S. 
Published: August 2011

SUMMARYA scanning tunnelling microscope has been designed which allows tunnelling microscopy to be performed in the presence of an externally applied electrochemical current. Separate, isolated electrodes were used for electrochemical control, and up to 1 mA was passed during real‐time, video‐rate, in situ STM observation of the surfaces, without interfering with the operation of the STM.The noise level of these STM images is only slightly higher than images taken with the electrochemical circuitry disconnected. Surfaces were observed during the formation of surface films in aqueous electrolytes.
Real space imaging of co‐adsorbed CO and benzene molecules on Rh(111)
Authors: Chiangs S. , Wilson R. J. , Mate C. M. , Ohtani H. 
Published: August 2011

SUMMARYScanning tunnelling microscope (STM) images of the c(2√3×4)rect layer of benzene and carbon monoxide co‐adsorbed on the Rh(111) surface are shown. For the first time, individual CO molecules have been resolved, as well as ring‐like benzene structures.