Double Tip Research Articles

Evaluating local properties of magnetic tips utilizing an antiferromagnetic surface

We infer the most relevant local magnetic properties of different iron-coated tips by comparing atomic scale contrasts obtained by magnetic exchange force microscopy utilizing the well-known structural, chemical, and magnetic configurations of NiO(001). Tips with only a single magnetic atom at the apex reflect the genuine antiferromagnetic structure of the nickel atoms, while for magnetic double tips an apparent magnetic contrast on oxygen atoms is observed. Furthermore, we found that even large external flux densities are not sufficient to fully align all magnetic moments of the tip and that local reconfigurations at the apex strongly influence magnitude and direction of the magnetic moments of the foremost tip atom. Knowing what kind of processes take place at tip apices will help to understand and tailor magnetic-sensitive tips for scanning probe techniques.

Numerical simulation of tip clearance flow passive control in axial turbine

This paper focuses on the effects of five different passive turbine tip clearance flow control methods on the tip clearance flow physics, which consists of a partial suction side squealer tip, a double squealer tip, a pressure side tip shelf with inclined squealer tip on a double squealer tip, a tip platform extension edge in pressure side and in suction side respectively. A pressure-correction based, 3D Reynolds-averaged Navier-Stokes equations CFD code with Reynolds Stress Model was adopted. The variable specific heat was considered. The detailed tip clearance flow field with different squealer rims was described with the streamline and the velocity vector. Accordingly, the mechanisms of five passive controls were elucidated; the effects of the passive controls on turbine efficiency and tip clearance flow field were illuminated. The results showed that the secondary flow loss near the outer casing including the tip leakage losses and the passage vortex losses could be reduced in all the five passive control methods. The turbine efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine efficiency, and the efficiency increased by 0.215%.

Measurement of gas phase characteristics using a monofibre optical probe in a three-phase flow

The study of gas–liquid–solid systems structure requires reliable measurement tools. In this paper, preliminary results on the potential use of a monofibre optical probe to investigate such flow are presented. This probe, manufactured at LEGI, allows the simultaneous measurement of the gas phase residence time and gas phase velocity. This specificity makes this probe more interesting than classical single tip probes (which measure only the gas residence time) or double tip probes (which are more intrusive). Although extensively used in two-phase gas–liquid, this probe was never used in gas–liquid–solid systems. First, the probe signal response is studied for three-phase flow conditions in the presence of solids. Results show that for soft solids, the probe tips can be contaminated when the probe pierces the solid. The signal processing procedure was modified accordingly to take into account these events. Second, the probe results are validated by comparing global results (global void fraction, gas flowrate) deduced from profile measurements with measurements performed by independent means. Lastly, void fraction profiles and interfacial area are studied more in detail. Depending on the solid loading, these profiles exhibit different behaviours. These features are associated to characteristics of the flow such as the transition from an homogeneous regime to an heterogenous regime, and are consistent with global observation performed by independent means. This demonstrates the ability of the probe to connect local information to the global behaviour and structure of the flow.

Development of apertureless near‐field scanning optical microscope tips for tip‐enhanced Raman spectroscopy

In this study, we suggested two types of novel metallized tip for the apertureless near-field scanning optical microscope probe. The first is a silver nanorod immobilized tip and the other is a double metallized probe. We calculated the electric field enhancement factor and the electric field distribution of a single sphere, aggregated spheres, an ellipse and a nanorod by the finite-differential time-domain method to improve the silver nanosphere immobilized tip developed in our previous studies. The enhanced field of the nanorod is localized at the external surfaces. The simulation results of the nanorod revealed that the position of the maximum peak is shifted to a longer wavelength and that its electric field enhancement factor increases as the aspect ratio increases. Thus, we developed the silver nanorod immobilized tip, and the tip-enhanced Raman spectrum of rhodamine 6G molecule on the substrate could be measured by the tip though it could not be detected by the previous nanosphere immobilized tip. Further, the finite-differential time-domain calculation predicted that the double metallized tips considerably enhance the electric field and that its enhancement factor in the longer wavelength region (500-600 nm) does not decrease when the tip is rounded. The results show that the proposed metallized tips were useful for the apertureless near-field scanning optical microscope system.

Controlled damaging and repair of self-organized nanostructures by atom manipulation atroom temperature

The possibility of controlled local demolition and repair of the recently discoveredself-organized Pt nanowires on Ge(001) surfaces has been explored. These nanowires arecomposed of Pt dimers, which are found to be rather weakly bound to the underlyingsubstrate. Using this property, we demonstrate the possibility of carrying the constitutingdimers of the Pt nanowires from point to point with atomic precision at room temperature.Pt dimers can be picked-up in two configurations: (i) a horizontal configuration at the tipapex, resulting in double tip images and (ii) a configuration where the Pt dimer is attachedto the side of the tip apex, resulting in well-defined atomically resolved images.

Double Exchange Biased Magnetic Force Microscopy Tip and Comparison of Its Imaging Performance with Commercial Tips

A double exchange biased magnetic force microscopy tip, which is coated with an antiferromagnet (IrMn)/ferromagnet (CoFe)/antiferromagnet (IrMn) multilayer on one side of a bare tip, has been fabricated and studied. In this design, the CoFe layer can be very thin due to its high moment, which leads to high spatial resolution without sacrificing the signal intensity. The exchange coupling between IrMn and CoFe stabilizes the magnetization of the latter which enables this kind of tip to have a better sensitivity and thermal stability as compared to conventional single ferromagnet layer tips. The performance of the double exchange biased tips has been evaluated through imaging the magnetic patterns recorded on longitudinal magnetic recording media. Micromagnetic modeling has been conducted to understand the underlying mechanism of the tip performance improvement.

Electrode form design of large holes of die material in ultrasonic electrochemical finishing

This paper uses ultrasonic energy to assist the dregs discharge in electrochemical finishing for the improvement of surface finish of large holes beyond traditional drilling, boring, rough turning, or extruding for die material during the polishing process. Six types of feeding electrodes and another six types of inserted electrodes are connected with both continuous and pulsed direct current in the ultrasonic electrochemical finishing. For inserted electrodes, a slant discharge flute on the plate with small edge rounding radius provides more sufficient discharge space, which is advantageous for polishing. A single plate electrode performs better than the double plate. The electrode of the single plate with borer shape edge and slant discharge flute shows the best polishing effect. For feeding electrodes, a smaller end radius of the borer tip produces more space for dregs discharge and better polishing. An electrode of single-side borer tip performs better than the double tips. The electrode with single-side half borer tip performs the best polishing effect in the current investigation. The average effect of the ultrasonic energy is advantageous than the pulsed current while the machining time needs not to be prolonged by the off-time. The geometry of the electrode contributes the most to the improvement of surface finish. Using the adequate electrode geometry as well as the ultrasonic aid, an effective and low-cost electrochemical finishing of large holes is presented.

Fabrication of cantilevers and double AFM tips for the NanoProfiler

The constant downscaling of CMOS technology is accompanied by a constant downscaling of transistor junctions. In a few years, electrical junctions will reach a depth of ∼20 nm and the electrical characteristics of these junction conditions the working of a transistor. However, this downscaling has not been followed by a parallel downscaling of the characterization techniques. As a matter of fact, the spreading resistance probe (SRP) technique commonly used for carrier profiling is not suited anymore for ultra-shallow junction profiling, mainly because of the dimensions of the measurement tool. We have thus developed a new concept, the NanoProfiler, based on the downscaling of the SRP technique to atomic force microscopy (AFM) concept. This paper presents the first achievements towards the practical realization of such a novel promising technique: realization of double sharp tips with sub-micron spacing, and of cantilevers with integrated conducting channels to individually connect both tips to the outside world for data acquisition. We separately designed two fabrication processes for making double tips with sub-micron spacing and for making cantilevers with integrated conducting channels, thus proving the feasibility of the NanoProfiler concept.

Turbine Rotor with Various Tip Configurations Flow and Heat Transfer Prediction

A numerical study is performed to simulate the leakage flow and heat transfer on a flat tip, a double squealer tip, and a single suction-side squealer tip of a scaled up General Electric-E 3 blade. The simulations for a nonrotating blade at a pressure ratio of 1.2 are in reasonable agreement with the experimental data on the blade tip and suction side, but the heat transfer coefficients were overpredicted on the pressure side. Numerical simulations were then performed for nonrotating and rotating blades under high-temperature, high-pressure ratio, and high Mach number conditions to investigate the blade tip leakage flow and heat transfer characteristics under more realistic engine operating conditions

Successive reduction of the last instar larva of Loricifera, as evidenced by two new species of Pliciloricus from the Great Meteor Seamount (Atlantic Ocean)

Two new species of the genus Pliciloricus Higgins & Kristensen, 1986, are described from coarse sand at the plateau of the Great Meteor Seamount. Together with other species of the genus, Pliciloricus corvus sp. n. and Pliciloricus senicirrus sp. n., demonstrate that the last or seventh instar Higgins-larva can be more and more reduced. Additionally, in the life cycle of P. corvus sp. n. a simplified adult is discovered which has a simplified body with persisting neck region and a sack-like trunk. The adult of P. corvus sp. n. is characterized, e.g., by 15 broad cross-walls in the clavoscalids, midventral spinoscalids of the second row transformed into a new type of double-organ, a secondary double-organ in the third row of scalids, type B spinoscalids of the fourth row ending in a grappling hook, a crescent-shaped ornamentation of the lorica margin with rounded gaps and protrusions, and a pair of longitudinal cuticular protrusions on the end cone. Distinguishing features of the first to sixth instar Higgins-larvae of P. corvus sp. n. are, e.g., setae of moderate length and long end spines of toes with double bulges. The seventh instar Higgins-larva of P. corvus sp. n. is not fully developed, e.g., the abdominal region is indistinct; the scalids, toes, and all five pairs of setae are clearly shorter than in the preceding instars of Higgins-larvae. The adult of P. senicirrus sp. n. is characterized, e.g., by clavoscalids with many fine transversal striae, claw-like type B spinoscalids of the fourth row ventrally winged and with seven embedded needle-like teeth, edge of the lorica with 24 small protrusions, and 20 papillate flosculi at caudal end. The Higgins-larva of P. senicirrus sp. n. is characterized, e.g., by the wide and frill-like first section of the mouth cone, the second segment of spinoscalids with ventral serration and double tip, long anterosetae with strong spinules, and by the toes being nearly as long as the short lorica, to name a few. The most obvious feature is the extreme length of the three pairs of posterosetae. The posteroterminal setae are nearly as long as the whole body. The seventh instar Higgins-larva of P. senicirrus sp. n. is not reduced as in the case of P. corvus sp. n.

Surface-state conduction through π-bonded chains

The surface-state conduction of the (111)2\ifmmode\times\else\texttimes\fi{}1 surfaces of group-IV semiconductors is studied theoretically. The conductance between the surfaces and a single tip or double tips is calculated using the Landauer formalism. The calculated conductance shows strong site dependence and polarity asymmetry in the cases of the Si and Ge surfaces. But they do not appear in the case of the diamond surface. These differences in the conduction properties reflect the difference in the buckling of the topmost atoms of the \ensuremath{\pi}-bonded chain structures. The double-tip conductance shows directional anisotropy which is reduced by the buckling.

STM investigation of electron transport features in cytochrome c Langmuir–Blodgett films

Abstract The morphological and electron-transfer properties of cytochrome c monolayer Langmuir–Blodgett (LB) films deposited on a graphite electrode have been studied using scanning tunneling microscopy (STM) and tunneling spectroscopy techniques in a double tunnel junction configuration STM tip–cytochrome c monolayer–conducting substrate. Monolayer cytochrome c LB films were deposited successfully by horizontal lifting method via protein Langmuir monolayer formation using preliminary solubilization of the protein in water bubbles of reverse microemulsion of Aerosol OT in hexane. Electronic spectroscopy of a single cytochrome c molecule was carried out with sub-nanometer spatial resolution at the ambient conditions. The STM spectroscopic study, by recording tunneling current–bias voltage (I–V) curves, revealed nonsymmetric I–V curves with steps of variable widths and heights dependent on the STM tip position over the protein molecule. Complex-rich structure of the tunneling current–voltage spectra can be a result of the interplay between Coulomb charging effects and tunneling through discrete electronic levels of the cytochrome c molecule. It can also be determined by the tunnel junctions parameters, dependent on the state of cytochrome c molecules in the gap between the STM tip and the substrate, presence of absorbates and ‘electron paths’ effects in the protein molecule.

Calculation of ballistic conductance through Tamm surface states

Ballistic conduction through Tamm surface states is studied theoretically. We calculate the conductance in systems of scanning tunneling microscopy (STM) with double tips as well as a single tip. Conductance spectra of flat surfaces containing surface states are qualitatively proportional to the density of states at the first layer of surfaces if we calculate on boundary conditions that allow net current to flow parallel to surfaces. The potential difference between the first layer and inner layers enhances the conduction through Tamm states. When a STM tip is put on an island of a surface, the conductance varies as a function of the step height of the island. The variation is explained by the difference in the step-height dependence between surface-state and bulk-state conduction. The tunneling between the surface states of islands and substrates is the main path of the surface-state conduction at low step heights. The study of the conduction in islands demonstrates the importance of the conduction path in surfaces to electrodes. The ballistic conductance spectra between two tips in double-tip systems show one-dimensional features, which suggests high conductance when the Fermi energy is located near band edges of surface states.

STM study of morphology and electron transport features in cytochrome c and nanocluster molecule monolayers

The morphology and electron tunneling through single cytochrome c and nanocluster Pt 5(CO) 7[P(C 6H 5)] 4 molecules organized as monolayer Langmuir–Blodgett (LB) films on graphite substrate have been studied experimentally using scanning tunneling microscopy (STM) and spectroscopy techniques with sub-nanometer spatial resolution in a double barrier tunnel junction configuration STM tip–monomolecular film–conducting substrate at ambient conditions. STM images of the films revealed globular structures with characteristic diameters (∼3.5 nm for the protein molecule and ∼1.2 nm for the nanocluster). The spectroscopic study by recording the tunneling current–bias voltage ( I– V) curves revealed tunneling I– V characteristics with features as steps of different width and heights that are dependent on the STM tip position over the molecule in the monolayer, giving evidence for sequential discrete electron-tunneling effects with the combination of the single electron Coulomb-charging energy and the electronic energy level separation (molecular spectrum) in such immobilized metalloprotein and nanocluster structures that can be of interest for the development of bioelectronic and hybrid functional nanosystems.

Technology to Reduce the Aperture Size of Microfabricated Silicon Dioxide Aperture Tips

Batch fabrication of miniaturized apertures by thermal oxidation of structured silicon wafers at temperatures below the glass temperature of silicon dioxide has proven to be an adequate technological process. It exploits the retarded oxide growth due to the compressive mechanical stress distribution at concave structures in the silicon dioxide layer to obtain single and double aperture tips with 170-190 nm dimensions. Numerical simulations performed to investigate this phenomenon are in good agreement with experimental results. Furthermore, an improved technological process is presented to reduce the aperture size of silicon dioxide tips to 100 nm. It is explained in view of the theological behavior of silicon dioxide at elevated temperatures of 1100°C. A further reduction of the aperture dimension down to 50 nm is achieved by deposition of thin metal films. © 2001 The Electrochemical Society. All rights reserved.

18aWD-4 ダブルティップのSi(001)STM像への影響

18aWD-4 ダブルティップのSi(001)STM像への影響

Influence of tip geometry in light emission from the scanning tunnelling microscope

In the scanning tunnelling microscopy of metal surfaces, electrons tunnelling inelastically emit light via the decay of coupled plasmons of the tip and the sample. We present an experimental study of the influence of the tip shape in light emission for a double tip system which is specially suitable to isolate the influence of the tip shape from other features in fluorescence spectra. Model calculations for various tip shapes show qualitative agreement with the experimental features, emphasizing the importance of tip shape in light emission.

Statistical method to calculate local interfacial variables in two-phase bubbly flows using intrusive crossing probes

This paper presents a statistical method to calculate local interfacial variables in two-phase gas–liquid bubbly flows from data taken with double-sensor intrusive probes. Firstly, one derives the geometrical relationship existing between the apparent and actual bubble velocity for a single spherical bubble flowing in a multidimensional flow field. The apparent variables are obtained from the experimental data when one assumes that the bubble trajectory is aligned with the probe axis. A similar relationship exists for the intersected chord length and bubble diameter. Then, the analysis is extended to a swarm of bubbles. The ratio between the apparent to the actual bubble velocity and the intersected chord length to the bubble diameter appear now as probability density functions. The experimental data were taken for air–water bubbly flow regime in a vertical round pipe with a double tip electrical probe. Processing the phase density function generated by the bubble events, one determines distribution function of the bubble velocity and intersected chord length, termed the apparent distributions. The variables of interest, actual bubble velocity and diameter, come out of the solution of a linear system of equations relating the probability function of the measured and estimated bubble velocity and bubble size ratio. The probability density function of the actual bubble velocity and bubble diameter, plus the bubble frequency, add up to various interfacial properties calculated with this technique: the void fraction, the bubble velocity, the bubble size, the interfacial area density and the interface velocity fluctuation intensity. To validate the method, the paper compares local and area averaged quantities with previously published results, volumetric measurements and extensively used correlation.

Reproducible Large‐Area Microfabrication of Sub‐100 nm Apertures on Hollow Tips

We report on a silicon‐based microfabrication process to generate apertures with dimensions of less than 100 nm at the apex of hollow silicon dioxide tips. The fabrication process is self‐adjusting and leads to highly reproducible aperture dimensions. It relies substantially on the inhomogeneous thickness distribution and modified etch rate of a silicon dioxide layer thermally grown on structured (001) oriented silicon wafers at relatively low temperatures of about 900–950°C. Process parameters are presented to obtain single or double aperture tips. Once the apertures are fabricated, a further reduction of aperture size below 80 nm is achieved by thin film deposition of, e.g., metal layers or other materials. The possibility of fabricating apertures reliably and reproducibly on large areas, e.g., complete silicon wafers, is emphasized. © 2000 The Electrochemical Society. All rights reserved.

Effects of self-modifying multiple tips on STM surface pictures

During the study of a mechanically produced hole in a graphite of approximately 500 Å diameter, the STM image showed two holes separated by a distance of about 560 Å due to a double tip. In addition, a continuous change in the contrast of the images of the hole, resulting from a continuous change in the relative position of the tips in the z-direction, was observed. This means the tip is modifying during the scan. When the two tips were at equal distances from the sample, the depth of the holes appeared to reduce by half since the total tunnelling current comprises contributions from both tips. Methods for reducing the chance of formation of multiple tips by picking up particles from the etching solution are also discussed.