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1

Ultrafast scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

1995-09-01

2

Josephson scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose a set of scanning tunneling microscopy experiments in which the surface of superconductor is scanned by a superconducting tip. Potential capabilities of such experimental setup are discussed. Most important anticipated results of such an experiment include the position-resolved measurement of the superconducting order parameter and the possibility to determine the nature of the secondary component of the order parameter at the surface. The theoretical description ...

Smakov, Jurij; Martin, Ivar; Balatsky, Alexander V.

2000-01-01

3

Scanning Tunneling Microscopy  

Science.gov (United States)

Use a virtual scanning tunneling microscope (STM) to observe electron behavior in an atomic-scale world. Walk through the principles of this technology step-by-step. First learn how the STM works. Then try it yourself! Use a virtual STM to manipulate individual atoms by scanning for, picking up, and moving electrons. Finally, explore the advantages and disadvantages of the two modes of an STM: the constant-height mode and the constant-current mode.

The Concord Consortium

2011-12-11

4

Photon scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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.

Reddick, R.C.; Warmack, R.J.; Chilcott, D.W.; Sharp, S.L.; Ferrell, T.L. (Health and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, TN (USA) Department of Physics and Astronomy, University of Tennessee, Knoxville, TN (USA))

1990-12-01

5

Scanning Tunneling Spectroscopy of Graphene on Graphite  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report low temperature high magnetic field scanning tunneling microscopy and spectroscopy of graphene flakes on graphite that exhibit the structural and electronic properties of graphene decoupled from the substrate. Pronounced peaks in the tunneling spectra develop with field revealing a Landau level sequence that provides a direct way to identify graphene and to determine the degree of its coupling to the substrate. The Fermi velocity and quasiparticle lifetime, obtaine...

Li, Guohong; Luican, Adina; Andrei, Eva Y.

2008-01-01

6

Photon scanning tunneling microscopy  

International Nuclear Information System (INIS)

The PSTM is shown to be the photon analogue of the electron STM. In the PSTM, externally-supplied plane waves undergo total internal reflection at a dielectric interface. This creates an exponentially-decaying evanescent field adjacent to the interface. Photons can be made to tunnel to a nearby optically conducting fiber optic tip. The transmitted light signal is strongly dependence upon the tip to interface distance and can be regulated by feedback control to stabilize this distance. Perturbations caused by irregularities in the interface can therefore be imaged by scanning the tip laterally in the same way as STM. Subwavelength lateral and vertical resolution is demonstrated. Lateral resolution is governed by the decay of the evanescent field and the probe shape. Vertical resolution is governed by electrical and mechanical noise. Controllable parameters include the angle of incidence, wavelength, polarization, index of refraction, and probe shape. Direct imaging of standing waves caused by the interference of two coherent surface waves at the interface will also be shown

7

Scanning Tunneling Optical Resonance Microscopy  

Science.gov (United States)

Scanning tunneling optical resonance microscopy (STORM) is a method, now undergoing development, for measuring optoelectronic properties of materials and devices on the nanoscale by means of a combination of (1) traditional scanning tunneling microscopy (STM) with (2) tunable laser spectroscopy. In STORM, an STM tip probing a semiconductor is illuminated with modulated light at a wavelength in the visible-to-near-infrared range and the resulting photoenhancement of the tunneling current is measured as a function of the illuminating wavelength. The photoenhancement of tunneling current occurs when the laser photon energy is sufficient to excite charge carriers into the conduction band of the semiconductor. Figure 1 schematically depicts a proposed STORM apparatus. The light for illuminating the semiconductor specimen at the STM would be generated by a ring laser that would be tunable across the wavelength range of interest. The laser beam would be chopped by an achromatic liquid-crystal modulator. A polarization-maintaining optical fiber would couple the light to the tip/sample junction of a commercial STM. An STM can be operated in one of two modes: constant height or constant current. A STORM apparatus would be operated in the constant-current mode, in which the height of the tip relative to the specimen would be varied in order to keep the tunneling current constant. In this mode, a feedback control circuit adjusts the voltage applied to a piezoelectric actuator in the STM that adjusts the height of the STM tip to keep the tunneling current constant. The exponential relationship between the tunneling current and tip-to-sample distance makes it relatively easy to implement this mode of operation. The choice of method by which the photoenhanced portion of the tunneling current would be measured depends on choice of the frequency at which the input illumination would be modulated (chopped). If the frequency of modulation were low enough (typically < 10 Hz) that the feedback circuit could respond, then the voltage applied to the piezoelectric tip-height actuator could be measured by use of a lock-in amplifier locked to the modulation (chopping) signal. However, at a high modulation frequency (typically in the kilohertz range or higher), the feedback circuit would be unable to respond. In this case, the photoenhanced portion of the tunneling current could be measured directly. For this purpose, the tunneling current would be passed through a precise resistor and the voltage drop would be measured by use of the lock-in amplifier.

Bailey, Sheila; Wilt, Dave; Raffaelle, Ryne; Gennett, Tom; Tin, Padetha; Lau, Janice; Castro, Stephanie; Jenkins, Philip; Scheiman, Dave

2003-01-01

8

Scanning Tunneling Optical Resonance Microscopy  

Science.gov (United States)

Scanning tunneling optical resonance microscopy (STORM) is a method, now undergoing development, for measuring optoelectronic properties of materials and devices on the nanoscale by means of a combination of (1) traditional scanning tunneling microscopy (STM) with (2) tunable laser spectroscopy. In STORM, an STM tip probing a semiconductor is illuminated with modulated light at a wavelength in the visible-to-near-infrared range and the resulting photoenhancement of the tunneling current is measured as a function of the illuminating wavelength. The photoenhancement of tunneling current occurs when the laser photon energy is sufficient to excite charge carriers into the conduction band of the semiconductor. Figure 1 schematically depicts a proposed STORM apparatus. The light for illuminating the semiconductor specimen at the STM would be generated by a ring laser that would be tunable across the wavelength range of interest. The laser beam would be chopped by an achromatic liquid-crystal modulator. A polarization-maintaining optical fiber would couple the light to the tip/sample junction of a commercial STM. An STM can be operated in one of two modes: constant height or constant current. A STORM apparatus would be operated in the constant-current mode, in which the height of the tip relative to the specimen would be varied in order to keep the tunneling current constant. In this mode, a feedback control circuit adjusts the voltage applied to a piezoelectric actuator in the STM that adjusts the height of the STM tip to keep the tunneling current constant. The exponential relationship between the tunneling current and tip-to-sample distance makes it relatively easy to implement this mode of operation. The choice of method by which the photoenhanced portion of the tunneling current would be measured depends on choice of the frequency at which the input illumination would be modulated (chopped). If the frequency of modulation were low enough (typically tunneling current could be measured directly. For this purpose, the tunneling current would be passed through a precise resistor and the voltage drop would be measured by use of the lock-in amplifier.

Bailey, Sheila; Wilt, Dave; Raffaelle, Ryne; Gennett, Tom; Tin, Padetha; Lau, Janice; Castro, Stephanie; Jenkins, Philip; Scheiman, Dave

2003-01-01

9

Scanning Tunneling Optical Resonance Microscopy  

Science.gov (United States)

Scanning tunneling optical resonance microscopy (STORM) is a method, now undergoing development, for measuring optoelectronic properties of materials and devices on the nanoscale by means of a combination of (1) traditional scanning tunneling microscopy (STM) with (2) tunable laser spectroscopy. In STORM, an STM tip probing a semiconductor is illuminated with modulated light at a wavelength in the visible-to-near-infrared range and the resulting photoenhancement of the tunneling current is measured as a function of the illuminating wavelength. The photoenhancement of tunneling current occurs when the laser photon energy is sufficient to excite charge carriers into the conduction band of the semiconductor. Figure 1 schematically depicts a proposed STORM apparatus. The light for illuminating the semiconductor specimen at the STM would be generated by a ring laser that would be tunable across the wavelength range of interest. The laser beam would be chopped by an achromatic liquid-crystal modulator. A polarization-maintaining optical fiber would couple the light to the tip/sample junction of a commercial STM. An STM can be operated in one of two modes: constant height or constant current. A STORM apparatus would be operated in the constant-current mode, in which the height of the tip relative to the specimen would be varied in order to keep the tunneling current constant. In this mode, a feedback control circuit adjusts the voltage applied to a piezoelectric actuator in the STM that adjusts the height of the STM tip to keep the tunneling current constant. The exponential relationship between the tunneling current and tip-to-sample distance makes it relatively easy to implement this mode of operation. The choice of method by which the photoenhanced portion of the tunneling current would be measured depends on choice of the frequency at which the input illumination would be modulated (chopped). If the frequency of modulation were low enough (typically measured by use of a lock-in amplifier locked to the modulation (chopping) signal. However, at a high modulation frequency (typically in the kilohertz range or higher), the feedback circuit would be unable to respond. In this case, the photoenhanced portion of the tunneling current could be measured directly. For this purpose, the tunneling current would be passed through a precise resistor and the voltage drop would be measured by use of the lock-in amplifier.

Bailey, Sheila; Wilt, Dave; Raffaelle, Ryne; Gennett, Tom; Tin, Padetha; Lau, Janice; Castro, Stephanie; Jenkins, Philip; Scheiman, Dave

2003-01-01

10

Scanning Tunneling Microscopy and Spectroscopy.  

Science.gov (United States)

A scanning tunneling microscope (STM) operating at 4.2K has been used to study charge density waves (CDWs) in select group IV and V transition metal dichalcogenides. It is found that the STM image is directly related to the surface electronic structure, especially the electronic local density of states (LDOS). Besides topographic informations, the STM can also be used to obtain reliable spectroscopic data. It will be proved that by obtaining both topographic and spectroscopic information, we can identify the effects of the modifications of the surface local density of states at the Fermi level. The modifications studied here are the direct result of the CDW transitions. Also it is shown that the tunneling barrier height plays a very important role in the spectroscopic measurements. The group V 1T phase dichalcogenides have images dominated by large amplitude modulations at a CDW wavelength of sqrt{13}a_0. The energy gaps due to the CDW transition in both 1T-Ta compounds are measured to be Delta~ 150 meV at 4.2 K, compared with smaller values of Delta = 50 and 80 meV for 2H-TaS2, 2H-TaSe2 respectively. The latter two compounds show a different type of CDW modulations, 3a_0times3a _0, and the surface atomic modulation is comparable with CDW modulation. Another compound studied is 2H-NbSe2 which has a 3a_0times3a _0 CDW superlattice, and a CDW energy gap of Delta = 34 meV. All of the energy gaps mentioned above give values of 2Delta/kT _{c} larger than expected from the weak coupling theory. In 1T-TiSe2, a group IV dichalcogenide, STM images at 4.2K reveal a 2a_0times2a_0 superlattice superimposed on the atomic lattice. The associated CDW energy gap is 0.2 eV. Scanning tunneling spectroscopy (STS) studies on Fe single crystals offer the possibility to compare with the earlier spectroscopy work on Fe-FeO_ {x} solid junctions. This earlier work showed that Fe-Fe_{x} junctions had very low tunneling barrier heights. STS studies reveale a similar result. Theoretical computation using stationary state theory yielded relatively good fits, and correspondingly low values for the barrier heights as expected. Various anamalous effects in spectroscopy measurements will also be discussed, such as the Coulomb blockade effect and the surface state effect.

Wang, Chen

11

Ultraviolet light emission from Si in a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ultraviolet and visible radiation is observed from the contacts of a scanning tunneling microscope with Si(100) and (111) wafers. This luminescence relies on the presence of hot electrons in silicon, which are supplied, at positive bias on n- and p-type samples, through the injection from the tip, or, at negative bias on p-samples, by Zener tunneling. Measured spectra reveal a contribution of direct optical transitions in Si bulk. The necessary holes well below the valence b...

Schmidt, Patrick; Berndt, Richard; Vexler, Mikhail I.

2007-01-01

12

Scanning tunneling spectroscopy of Pb thin films  

Energy Technology Data Exchange (ETDEWEB)

The present thesis deals with the electronic structure, work function and single-atom contact conductance of Pb thin films, investigated with a low-temperature scanning tunneling microscope. The electronic structure of Pb(111) thin films on Ag(111) surfaces is investigated using scanning tunneling spectroscopy (STS). Quantum size effects, in particular, quantum well states (QWSs), play a crucial role in the electronic and physical properties of these films. Quantitative analysis of the spectra yields the QWS energies as a function of film thickness, the Pb bulk-band dispersion in {gamma}-L direction, scattering phase shifts at the Pb/Ag interface and vacuum barrier as well as the lifetime broadening at anti {gamma}. The work function {phi} is an important property of surfaces, which influences catalytic reactivity and charge injection at interfaces. It controls the availability of charge carriers in front of a surface. Modifying {phi} has been achieved by deposition of metals and molecules. For investigating {phi} at the atomic scale, scanning tunneling microscopy (STM) has become a widely used technique. STM measures an apparent barrier height {phi}{sub a}, which is commonly related to the sample work function {phi}{sub s} by: {phi}{sub a}=({phi}{sub s}+{phi}{sub t}- vertical stroke eV vertical stroke)/2, with {phi}{sub t} the work function of the tunneling tip, V the applied tunneling bias voltage, and -e the electron charge. Hence, the effect of the finite voltage in STM on {phi}{sub a} is assumed to be linear and the comparison of {phi}{sub a} measured at different surface sites is assumed to yield quantitative information about work function differences. Here, the dependence of {phi}{sub a} on the Pb film thickness and applied bias voltage V is investigated. {phi}{sub a} is found to vary significantly with V. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of {phi}{sub a}, which are related to the QWSs in the Pb films. It is shown how accurate quantitative information about work function differences can be obtained and how these differences depend on the QWSs in the Pb thin films. The electron transport properties and mechanical characteristics of atom-sized metallic contacts are of fundamental interest in view of future nanoscale device technologies. Proximity probes like STM, metal break junctions, and related techniques, together with computational methods for simulating tip-sample interactions, have made it possible to address this question. While the importance of atomic structure and bonding for transport through single-atom junctions has repeatedly been emphasized, investigations of the influence of subsurface bonding properties have been rare. Here, the contact formation of a STM tip approaching Pb(111) thin films supported on Ag(111) substrates is investigated. Contacts on monolayer films are found to differ from contacts made on thicker Pb films. This behavior is explained in terms of different vertical bonding-strengths due to a charge-transfer induced surface dipole. Furthermore, the single-atom contact conductance on Pb(111) films beyond the first monolayer is determined. It is shown that analyses based on hitherto widely used conventional conductance histograms may overestimate the single-atom contact conductance by as much as 20%. (orig.)

Becker, Michael

2010-12-13

13

Scanning tunneling microscope assembly, reactor, and system  

Energy Technology Data Exchange (ETDEWEB)

An embodiment of a scanning tunneling microscope (STM) reactor includes a pressure vessel, an STM assembly, and three spring coupling objects. The pressure vessel includes a sealable port, an interior, and an exterior. An embodiment of an STM system includes a vacuum chamber, an STM reactor, and three springs. The three springs couple the STM reactor to the vacuum chamber and are operable to suspend the scanning tunneling microscope reactor within the interior of the vacuum chamber during operation of the STM reactor. An embodiment of an STM assembly includes a coarse displacement arrangement, a piezoelectric fine displacement scanning tube coupled to the coarse displacement arrangement, and a receiver. The piezoelectric fine displacement scanning tube is coupled to the coarse displacement arrangement. The receiver is coupled to the piezoelectric scanning tube and is operable to receive a tip holder, and the tip holder is operable to receive a tip.

Tao, Feng; Salmeron, Miquel; Somorjai, Gabor A

2014-11-18

14

Tunnelling spectra of individual magnetic endofullerene molecules.  

Science.gov (United States)

The manipulation of single magnetic molecules may enable new strategies for high-density information storage and quantum-state control. However, progress in these areas depends on developing techniques for addressing individual molecules and controlling their spin. Here, we report success in making electrical contact to individual magnetic N@C(60) molecules and measuring spin excitations in their electron tunnelling spectra. We verify that the molecules remain magnetic by observing a transition as a function of magnetic field that changes the spin quantum number and also the existence of non-equilibrium tunnelling originating from low-energy excited states. From the tunnelling spectra, we identify the charge and spin states of the molecule. The measured spectra can be reproduced theoretically by accounting for the exchange interaction between the nitrogen spin and electron(s) on the C(60) cage. PMID:18931670

Grose, Jacob E; Tam, Eugenia S; Timm, Carsten; Scheloske, Michael; Ulgut, Burak; Parks, Joshua J; Abruña, Héctor D; Harneit, Wolfgang; Ralph, Daniel C

2008-11-01

15

Scanning tunneling microscopy studies on optical disc  

International Nuclear Information System (INIS)

The areas with and without data stampers are all observed carefully using scanning tunneling microscope (STM). Three-dimensional images of the disc surface clearly demonstrate the period, depth of the grooves and the shape of data stampers. Some phenomena of STM imaging are also discussed

16

Spectroscopy of Light Emission from a Scanning Tunneling Microscope in Air  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Light emission has been detected at the tip-sample junction of a Scanning Tunneling Microscope (S.T.M.) in air on noble metallic surfaces. A spectroscopic study of emitted photons for Au-Au and PtIr-Au tunneling junctions is presented. The general aspect of the spectra depends on the materials used in the junctions; a study of the spectra as a function of tunneling current and surface bias voltage reveals similar and reproducible characteristics.

Pe?chou, R.; Coratger, R.; Girardin, C.; Ajustron, F.; Beauvillain, J.

1996-01-01

17

Scanning tunnelling microscopy of ion etched silicon  

International Nuclear Information System (INIS)

Ion etched silicon surfaces have been studied using scanning tunnelling microscopy (STM). The sample is bombarded with 300 eV argon ions from a broad beam Kaufman type ion source. The microscope and the ion source are in the same vacuum chamber, so there is no atmospheric contamination of the etched sample. One effect of the ion bombardment is to roughen the surface, and a measure of this can be made. After appropriate annealing atomically flat regions are observed. STM is also used to make tunnelling spectroscopic measurements on etched surfaces, revealing information about the surface density of states. (author)

18

Scanning Tunneling Spectroscopy of Potassium on Graphene  

Science.gov (United States)

We investigate the effect of charged impurities on the electronic properties of large single crystal CVD grown graphene using scanning tunneling microscopy. Mono- and multilayer crystals were prepared by transferring graphene from copper onto exfoliated boron nitride flakes on 300 nm SiO2 substrates. The boron nitride provides an ultra flat surface for the graphene. Potassium atoms are controllably deposited on the graphene at low temperature by heating a nearby getter source. Scanning tunneling spectroscopy and transport measurements were performed in ultra high vacuum at 4.5 K. Transport measurements demonstrate the shifting of the Dirac point as the samples are doped, while STM measurements demonstrate the size, arrangement and local electronic influence of the potassium atoms.

Cormode, Daniel; Leroy, Brian; Yankowitz, Matthew

2012-02-01

19

Scanning Tunneling Microscopy of a Luttinger Liquid  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Explicit predictions for Scanning Tunneling Microscopy (STM) on interacting one-dimensional electron systems are made using the Luttinger liquid formalism. The STM current changes with distance from an impurity or boundary in a characteristic way, which reveals the spin-charge separation and the interaction strength in the system. The current exhibits Friedel-like oscillations, but also carries additional modulated behavior as a function of voltage and distance, which shows ...

Eggert, Sebastian

1999-01-01

20

Constant height scanning tunneling spectroscopy using an alternating voltage signal  

Science.gov (United States)

A method of performing scanning tunneling spectroscopy (STS) at a constant height while maintaining feedback control is described. By using sinusoidal voltage oscillations the ac tunneling current can be separated from the displacement current present in current-voltage (i-V) measurements. The method allows statistically well averaged spectra spanning both occupied and unoccupied states of the sample to be obtained from a continuous set of i-V curves. The unoccupied ?* state on graphite is observed using the technique described, and the utility of the technique is further demonstrated by the detection of several bulk states on NiTe2 and PdTe2, two transition metal dichalcogenides. A weighting towards k perpendicular states is seen in the STS spectra. These results show that the fast alternating current form of STS is suitable for probing low amplitude electron states on metal surfaces within 2 eV of the Fermi level.

Ryan, George W.; Tornallyay, J.

1999-05-01

 
 
 
 
21

A SCANNING TUNNELING MICROSCOPE FOR SURFACE MODIFICATION  

Digital Repository Infrastructure Vision for European Research (DRIVER)

With the recent success for the scanning tunneling microscope (STM) has come question of whether the instrument might be used for material modifications lithography. We embarked on the design of an STM with this application in mind. Its features include a wide x-y piezoelectric scan range of 10 or more microns, plus coarse mechanical motion in the x direction to a new region on the sample while in vacuum. Coarse motion in the z direction is accomplished with a micrometer drive, while fine mov...

Mccord, M.; Pease, R.

1986-01-01

22

Scanning Tunneling Optical Resonance Microscopy Developed  

Science.gov (United States)

The ability to determine the in situ optoelectronic properties of semiconductor materials has become especially important as the size of device architectures has decreased and the development of complex microsystems has increased. Scanning Tunneling Optical Resonance Microscopy, or STORM, can interrogate the optical bandgap as a function of its position within a semiconductor micro-structure. This technique uses a tunable solidstate titanium-sapphire laser whose output is "chopped" using a spatial light modulator and is coupled by a fiber-optic connector to a scanning tunneling microscope in order to illuminate the tip-sample junction. The photoenhanced portion of the tunneling current is spectroscopically measured using a lock-in technique. The capabilities of this technique were verified using semiconductor microstructure calibration standards that were grown by organometallic vapor-phase epitaxy. Bandgaps characterized by STORM measurements were found to be in good agreement with the bulk values determined by transmission spectroscopy and photoluminescence and with the theoretical values that were based on x-ray diffraction results.

Bailey, Sheila G.; Raffaelle, Ryne P.; Lau, Janis E.; Jenkins, Phillip P.; Castro, Stephanie L.; Tin, Padetha; Wilt, David M.; Pal, Anna Maria; Fahey, Stephen D.

2004-01-01

23

Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope  

Science.gov (United States)

The low-temperature scanning tunneling microscope (STM) system described by LeDuc et al. (1987) was used to observe the phonon density of states effects in a superconductor. Using techniques based on those employed in macroscopic tunneling spectroscopy, electron tunneling current-voltage (I-V) spectra were measured for NbN and Pb, and dI/dV vs V spectra were measured using standard analog derivative techniques. I-V measurements on NbN and Pb samples under typical STM conditions showed no evidence for multiparticle tunneling effects.

Leduc, H. G.; Kaiser, W. J.; Hunt, B. D.; Bell, L. D.; Jaklevic, R. C.

1989-01-01

24

A compact low temperature scanning tunneling microscope  

International Nuclear Information System (INIS)

We describe the design and fabrication of a compact Low Temperature Scanning Tunneling Microscope (LT-STM) together with a dipper cryostat for cooling the STM down to liquid helium temperatures. The STM, based on the piezo-tube walker as coarse approach mechanism, is suspended inside a cryostat vacuum can using three soft helical springs. The can is dipped into a liquid helium storage container for cooling the STM. Its compact size makes it less susceptible to mechanical vibrations and so the STM works with atomic resolution with a simple spring suspension. We demonstrate the performance of this STM for atomic resolution imaging and tunneling spectroscopy by observing the 3 x3 charge modulation and the energy gap in the Charge Density Wave (CDW) phase of 2H-NbSe2 at liquid helium temperatures.

25

Simulation of scanning tunneling spectroscopy of supported carbon nanotubes  

International Nuclear Information System (INIS)

The angle and energy dependent transmission of wave packets was calculated through a jellium potential model of a scanning tunneling microscope (STM) junction containing different arrangements of carbon nanotubes. The total tunnel current as a function of STM bias was calculated by statistical averaging over a distribution of wave packets in the allowed energy window. Three tunneling situations were studied: (i) a STM tunnel junction with no nanotube present, (ii) one single wall nanotube in the STM junction, and (iii) a nanotube 'raft'. The effects of point contacts at the STM tip/nanotube, at the nanotube/substrate, and at both interfaces were also investigated. The theory allowed us to identify components of pure geometrical origin responsible for the asymmetry in the scanning tunneling spectroscopy (STS) spectrum of the carbon nanotubes with respect to bias voltage polarity. The calculations show that for tip negative bias the angular dependence of the transmission is determined by the tip shape. The particular tip shape introduces an asymmetry on the negative side of the STS spectrum. For tip positive bias the angular dependence of the transmission depends strongly on the nature of the nanosystem in the STM gap. While the transmission of the STM tunnel junction with no nanotube present can be well represented by a one dimensional model, all other geometries cause a large normal-transverse momentum mixing of the wave packet. A diffraction-grating-like behavior is t. A diffraction-grating-like behavior is seen in the angular dependence of the transmission of the nanotube raft. Point contacts between the nanotube and the substrate cause an asymmetry in the positive side of the STS spectrum. Calculated STS spectra are compared to experimental ones

26

Scanning tunneling microscopy of titanium silicide nanoislands  

Energy Technology Data Exchange (ETDEWEB)

In this work, ultrathin titanium silicide layers were grown on Si(1 1 1) substrates, with the aim to stimulate spontaneous growth of nanostructures by self-assembly. Scanning tunneling microscopy was used as a primary tool for a close, in situ monitoring of the related surface processes. This method enabled a detailed observation of the formation and subsequent evolution of the silicide nanoislands as a function of deposition parameters and annealing treatments. Nanoisland shape and, possibly, phase transformations were analyzed in real time and space with atomic, or near atomic resolution. The results of these measurements are discussed, and plausible explanations offered.

Goldfarb, I.; Grossman, S.; Cohen-Taguri, G.; Levinshtein, M

2004-11-15

27

Scanning tunneling microscopy of titanium silicide nanoislands  

International Nuclear Information System (INIS)

In this work, ultrathin titanium silicide layers were grown on Si(1 1 1) substrates, with the aim to stimulate spontaneous growth of nanostructures by self-assembly. Scanning tunneling microscopy was used as a primary tool for a close, in situ monitoring of the related surface processes. This method enabled a detailed observation of the formation and subsequent evolution of the silicide nanoislands as a function of deposition parameters and annealing treatments. Nanoisland shape and, possibly, phase transformations were analyzed in real time and space with atomic, or near atomic resolution. The results of these measurements are discussed, and plausible explanations offered

28

Scanning tunneling spectroscopy of epitaxial graphene nanoisland on Ir(111)  

Science.gov (United States)

Scanning tunneling spectroscopy (STS) was used to measure local differential conductance (d I/d V) spectra on nanometer-size graphene islands on an Ir(111) surface. Energy resolved d I/d V maps clearly show a spatial modulation, which we ascribe to a modulated local density of states due to quantum confinement. STS near graphene edges indicates a position dependence of the d I/d V signals, which suggests a reduced density of states near the edges of graphene islands on Ir(111).

Phark, Soo-hyon; Borme, Jérôme; Vanegas, Augusto León; Corbetta, Marco; Sander, Dirk; Kirschner, Jürgen

2012-05-01

29

Scanning tunneling spectroscopy of epitaxial graphene nanoisland on Ir(111)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling spectroscopy (STS) was used to measure local differential conductance (dI/dV) spectra on nanometer-size graphene islands on an Ir(111) surface. Energy resolved dI/dV maps clearly show a spatial modulation, which we ascribe to a modulated local density of states due to quantum confinement. STS near graphene edges indicates a position dependence of the dI/dV signals, which suggests a reduced density of states near the edges of graphene islands on Ir(111).

Phark, Soo-hyon; Borme, Je?ro?me; Vanegas, Augusto Leo?n; Corbetta, Marco; Sander, Dirk; Kirschner, Ju?rgen

2012-01-01

30

A millikelvin scanning tunneling microscope with two independent scanning systems  

CERN Document Server

We describe the design, construction and operation of a scanning tunneling microscope (STM) with two tips that can independently acquire simultaneous scans of a sample. The STM is mounted on a dilution refrigerator and the setup includes vibration isolation, rf-filtered wiring, an ultra high vacuum (UHV) sample preparation chamber and sample transfer mechanism. We present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 $\\mu$eV. Atomic resolution topographic images of an Au(100) surface taken with the inner and outer tips were found to have root mean square roughness of 1.75 $\\pm$ 0.01 pm and 3.55 $\\pm$ 0.03 pm respectively.

Roychowdhury, A; Anderson, J R; Lobb, C J; Wellstood, F C; Dreyer, M

2013-01-01

31

Ultimate Vortex Confinement Studied by Scanning Tunneling Spectroscopy  

Science.gov (United States)

We report a detailed scanning tunneling microscopy study of a superconductor in a strong vortex confinement regime. This is achieved in a thin nanoisland of Pb having a size d about 3 times the coherence length, and a thickness h such that h?d??, where ? is the London penetration depth. In this geometry the magnetic field evolution of local tunneling spectra reveals only two superconducting configurations to exist: zero and single vorticity. The normal state is reached at ?0Hc=0.46T, about 6 times the critical field of bulk Pb, with no higher order vorticity observed. Basing on our STS data, we discuss the role of local supercurrents in both configurations.

Cren, Tristan; Fokin, Denis; Debontridder, François; Dubost, Vincent; Roditchev, Dimitri

2009-03-01

32

DIRECT TIP STRUCTURES DETERMINATION BY SCANNING TUNNELING MICROSCOPY  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An electrochemical etched scanning tunneling microscope tip is studied, using a long scan tunneling microscope and scanning electron microscopy, in order to characterize the neighborhood of the tip apex. Observed microstructure and protrusions are discussed in relation to chemical etching and mechanical resistance.

Garci?a Cantu?, R.; Huerta Garnica, M.

1989-01-01

33

Scanning tunneling microscopy studies of topological insulators.  

Science.gov (United States)

Scanning tunneling microscopy (STM), with surface sensitivity, is an ideal tool to probe the intriguing properties of the surface state of topological insulators (TIs) and topological crystalline insulators (TCIs). We summarize the recent progress on those topological phases revealed by STM studies. STM observations have directly confirmed the existence of the topological surface states and clearly revealed their novel properties. We also discuss STM work on magnetic doped TIs, topological superconductors and crystalline symmetry-protected surface states in TCIs. The studies have greatly promoted our understanding of the exotic properties of the new topological phases, as well as put forward new challenges. STM will continue to play an important role in this rapidly growing field from the point view of both fundamental physics and applications. PMID:25214502

Zhao, Kun; Lv, Yan-Feng; Ji, Shuai-Hua; Ma, Xucun; Chen, Xi; Xue, Qi-Kun

2014-10-01

34

Imaging of proteins by scanning tunnelling microscopy.  

Science.gov (United States)

Scanning tunnelling microscopy has been used to examine the structure of proteins deposited on a graphite surface. Three molecules have been studied; immunoglobulin G (IgG), Complement component 1q (C1q) and ATP-citrate lyase (ACL). The images show IgG as a tri-lobed molecule, consistent with the known 3D structure as determined by X-ray crystallography. The C1q images differ from the well known "tulip bunch" model derived by electron microscopy, but are consistent with the model if it is assumed that the six globular heads have aggregated. Molecules of ACL are visible as discrete units, with some hints of substructure. These results highlight the potential of STM in studying protein structures, but also illustrate the difficulties of interpreting micrographs of proteins whose structure is currently unknown. PMID:1413259

Wells, T N; Stedman, M; Leatherbarrow, R J

1992-07-01

35

Imaging graphite in air by scanning tunneling microscopy - Role of the tip  

Science.gov (United States)

Atomically resolved images of highly oriented pyrolytic graphite (HOPG) in air at point contact have been obtained. Direct contact between tip and sample or contact through a contamination layer provides a conduction mechanism in addition to the exponential tunneling mechanism responsible for scanning tunneling microscopy (STM) imaging. Current-voltage (I-V) spectra were obtained while scanning in the current imaging mode with the feedback circuit interrupted in order to study the graphite imaging mechanism. Multiple tunneling tips are probably responsible for images without the expected hexagonal or trigonal symmetry. The observations indicate that the use of HOPG for testing and calibration of STM instrumentation may be misleading.

Colton, R. J.; Baker, S. M.; Driscoll, R. J.; Youngquist, M. G.; Baldeschwieler, J. D.; Kaiser, W. J.

1988-01-01

36

Measuring voltage transients with an ultrafast scanning tunneling microscope  

DEFF Research Database (Denmark)

We use an ultrafast scanning tunneling microscope to resolve propagating voltage transients in space and time. We demonstrate that the previously observed dependence of the transient signal amplitude on the tunneling resistance was only caused by the electrical sampling circuit. With a modified circuit, where the tunneling tip is directly connected to the current amplifier of the scanning tunneling microscope, this dependence is eliminated. Ail results can be explained with coupling through the geometrical capacitance of the tip-electrode junction. By illuminating the current-gating photoconductive switch with a rigidly attached fiber, the probe is scanned without changing the probe characteristics. (C) 1997 American Institute of Physics.

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1997-01-01

37

Principles and Application of Heterodyne Scanning Tunnelling Spectroscopy  

Science.gov (United States)

Detection of the extremely weak signals in spectroscopy over an extremely wide frequency region is central to diverse sciences, including materials science, biology, astronomy and chemistry. Here we show a new type of atomic-scale spectroscopy, heterodyne scanning tunnelling spectroscopy (HSTS), which is based on the innovative application of the nonlinear heterodyne-mixing detection at the metal-insulator-metal (MIM) heterojunction of STM tip-vacuum-sample. The principle of HSTS is identical to that of the Atacama Large Millimeter Array (ALMA) space telescope in terms of using heterojunction for detecting extremely weak signals by converting from terahertz region to lower frequency regions. The MIM detector of ALMA, which is composed of niobium-titanium-nitride (NbTiN) tip-insulator-NbTiN, is very similar in shape and size to that of HSTS. We successfully detect a heterodyne beat signal f3 (= |f2 - f1|) and intermodulation distortion via tunnelling current by superimposing two different AC signals, f1 and f2, onto the DC tunnelling current at a highly oriented pyrolytic graphite (HOPG) surface. We then obtain spectra of the localized electronic states of HOPG by using f3. HSTS can be performed with a high resolution and over a wide energy range, including the terahertz range.

Matsuyama, Eiji; Kondo, Takahiro; Oigawa, Haruhiro; Guo, Donghui; Nemoto, Shojiro; Nakamura, Junji

2014-10-01

38

Infrared spectroscopy of molecular submonolayers on surfaces by infrared scanning tunneling microscopy: tetramantane on Au111.  

Science.gov (United States)

We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions. PMID:24093277

Pechenezhskiy, Ivan V; Hong, Xiaoping; Nguyen, Giang D; Dahl, Jeremy E P; Carlson, Robert M K; Wang, Feng; Crommie, Michael F

2013-09-20

39

Shifts and dips in inelastic-electron-tunneling spectra due to the tunnel-junction environment  

International Nuclear Information System (INIS)

In general, the tunnel-junction environment has proved to be surprisingly benign; tunneling spectra of molecules included within tunnel junctions are similar to infrared and Raman spectra of molecules not covered by a metal electrode. Peak shifts have been typically less than the linewidth of the peaks, and peaks intensities have been comparable to infrared and Raman intensities. Here we report a different situation for tunnel junctions containing molecules adsorbed on metal particles. Specifically, we find that different-top-metal electrodes give different tunneling spectra for CO on alumina-supported iron and rhodium particles. Though metals with similar atomic radii give similar spectra, metals with dissimilar atomic radii can give qualitatively different spectra. We also find anomalies concerning intensities. Specifically, for methyl isocyanide adsorbed on alumina-supported rhodium particles, the strongest peak in the infrared spectrum, the --NequivalentC stretching mode, appears as a dip in the tunneling spectrum

40

Scanning tunneling microscopy and inelastic electron tunneling spectroscopy studies of methyl isocyanide adsorbed on Pt(111)  

Energy Technology Data Exchange (ETDEWEB)

A low-temperature scanning tunneling microscope (STM) was used to investigate the adsorption state of a single methyl isocyanide (MeNC) molecule on the Pt(111) surface at 4.7 K. We found that MeNC was resolved as a round-shaped protrusion in the STM image. The STM image of paired MeNC is highly protruded in comparison with that of isolated MeNC due to the charge transfer from Pt to MeNC. Inelastic electron tunneling spectroscopy with the STM system (STM-IETS) was also employed in order to reveal the adsorption state of individual MeNC molecules on Pt(111). The STM-IETS spectrum of MeNC exhibits peaks at 8, 48 and 375 mV. Referring to the vibrational spectra reported previously, we assigned these peaks to the frustrated translation mode, PtC stretching mode and CH{sub 3} stretching mode, respectively. The absence of other vibrational modes could be due to a reduction of the elastic tunneling current.

Katano, Satoshi [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Kim, Yousoo; Hori, Masafumi; Kawai, Maki [Surface Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan (Japan); Trenary, Michael, E-mail: maki@riken.j, E-mail: skatano@riec.tohoku.ac.j [Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061 (United States)

2010-06-01

 
 
 
 
41

Solid-State Quantum Computer Based on Scanning Tunneling Microscopy  

CERN Document Server

We propose a solid-state nuclear spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field ($\\sim 10$T) and at low temperature $\\sim 1$K.

Berman, G P; Hawley, M E; Tsifrinovich, V I

2001-01-01

42

Scanning Tunneling Spectroscopy on the novel superconductor CaC6  

CERN Document Server

We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC$_6$. The tunneling conductance spectra, measured between 3 K and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with $\\Delta(0)$ = 1.6 $\\pm$ 0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows to deduce a coherence length in the ab plane $\\xi_{ab}\\simeq$ 33 nm.

Bergeal, N; Noat, Y; Sacks, W; Roditchev, D; Emery, N; Herold, C; Mareche, J F; Lagrange, P; Loupias, G

2006-01-01

43

AgBr microcrystals studied by scanning tunneling microscopy  

Science.gov (United States)

Silver bromide crystals deposited on graphite were investigated with scanning tunneling microscope under ambient conditions. Different shape and size microcrystals, including cubic and octahedral forms and tabular grains, were observed and examined. Surface lattice parameters have been determined from high resolution images. In addition, the AgBr crystals were examined by scanning electron microscope.

Gordon, W. S.; Szuba, S.

1997-06-01

44

Theoretical study of tunneling spectra of tetramantane on Au(111) surface  

Science.gov (United States)

Diamondoids are a class of carbon-based molecules in which the carbon atoms are structured in a diamond-like fashion with all dangling bonds saturated with hydrogen atoms. Recently, scanning tunneling microscopy experiments were carried out to study the tunneling spectra of tetramantane on Au (111) surface. The elastic tunneling images have a LUMO-like character in a broad energy range around the Fermi level, while the inelastic signal shows spatial localization. We use ab-initio density functional theory calculations to study the molecule-surface system and discuss the observed elastic and inelastic tunneling spectra. This work was supported by National Science Foundation Grant No. DMR04-39768, by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and by an NSF Graduate Research Fellowship. Computational resources have been provided by NERSC and NPACI.

Kioupakis, Emmanouil; Wang, Y.; Yamachika, R.; Lu, X.; Crommie, M. F.; Louie, Steven G.

2007-03-01

45

Transient measurements with an ultrafast scanning tunneling microscope  

DEFF Research Database (Denmark)

We use a photoconductively gated ultrafast scanning tunneling microscope to resolve laser-induced transients on transmission lines and photoconductors. The photoconductive switch on the tunneling probe is illuminated through a rigidly attached fiber. The use of the fiber enables us to scan across the transmission line while the change in delay time between pump beam (on the sample) and probe beam (on the probe) provides the temporal information. The investigated photoconductor sample is a low-temperature-grown GaAs layer placed on a sapphire substrate with a thin, semitransparent gold layer. In tunneling mode the probe is sensitive to laser-induced field changes in the semiconductor layer. Laser-induced transient signals of 2.2 ps widths are detected. As for the transmission lines, the signals can be explained by a capacitive coupling across the tunneling gap.

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

46

Scanning tunneling microscope as a probe for local conductivity  

Energy Technology Data Exchange (ETDEWEB)

A new technique useful to detect local changes on surface conductivity while tunneling is described. It is possible to obtain scanning tunneling microscopy topographic images simultaneously with well defined patterns of conductivity variations, working at air pressure, from a copper sample. The authors also show results obtained from austenitic steel samples. Current noise signals have been analyzed and have been correlated with trapping sites in SiO{sub 2}.

Cantu, R.G.; Garnica, M.A.H. (Departmento de Ingenieria Electrica, (Mexico))

47

Detection of electronic nematicity using scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electronic nematic phases have been proposed to occur in various correlated electron systems and were recently claimed to have been detected in scanning tunneling microscopy (STM) conductance maps of the pseudogap states of the cuprate high-temperature superconductor Bi2Sr2CaCu2O8+x (Bi-2212). We investigate the influence of anisotropic STM tip structures on such measurements and establish, with a model calculation, the presence of a tunneling interference effect within an S...

Neto, Eduardo H. Da Silva; Aynajian, Pegor; Baumbach, Ryan E.; Bauer, Eric D.; Mydosh, John; Ono, Shimpei; Yazdani, Ali

2013-01-01

48

Scanning tunneling microscopy and spectroscopy of C70 thin films  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling microscopy of C-70 films deposited on HOPG and gold substrates has been carried but to investigate the 2D packing, defects and disorder. Besides providing direct evidence for orientational disorder, high resolution; images showing the carbon skeleton as well as the molecular arrangement in a solid solution of C-70 and C-60 are presented. Tunneling conductance measurements Indicate a small gap in the C-70 film deposited on HOPG substrate.

Aiyer, Hemantkumar N.; Govindaraj, A.; Rao, Cnr

1994-01-01

49

Solid-state quantum computer based on scanning tunneling microscopy.  

Science.gov (United States)

We propose a solid-state nuclear-spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling-current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field (approximately 10 T) and at low temperature approximately 1 K. PMID:11531599

Berman, G P; Brown, G W; Hawley, M E; Tsifrinovich, V I

2001-08-27

50

Scanning Tunneling Microscopy in the superconductor LaSb2  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present very low temperature (0.15 K) scanning tunneling microscopy and spectroscopy experiments in the layered superconductor LaSb$_2$. We obtain topographic microscopy images with surfaces showing hexagonal and square atomic size patterns, and observe in the tunneling conductance a superconducting gap. We find well defined quasiparticle peaks located at a bias voltage comparable to the weak coupling s-wave BCS expected gap value (0.17 meV). The amount of states at the F...

Galvis, J. A.; Suderow, H.; Vieira, S.; Bud Ko, S. L.; Canfield, P. C.

2013-01-01

51

Scanning tunneling microspectroscopy of solids and surfaces  

International Nuclear Information System (INIS)

Major progress has been made this year in our work on single crystals of Bi2Sr2CaCu2O8+y (BSCCO) grown in our laboratory in a transverse temperature gradient. We have obtained large crystals of improving quality and tunneling data which are superior to any we have seen elsewhere. In our first publication on this, we have identified a pair breaking process which appears near Tc and apparently is related to the absence of the Hebel-Slichter peak in 1/T1 vs T in this material. In more recent work much improved data reveal features in the tunnel conductance dI/dV which appear to agree with the ''proximity effect-superlattice'' model of the tunneling conductance of BSCCO described by Tachiki and coworkers. We devote a major portion of this report to this and other research topics, on which work is continuing, and briefly describe advances in Instrumentation that have occurred this year

52

Observation of random telegraphic noise in scanning tunneling microscopy of nanoparticles on highly oriented pyrolytic graphite  

International Nuclear Information System (INIS)

Random telegraphic noise in scanning tunneling microscopy of dodecane thiol capped Au nanoparticles on highly oriented pyrolytic graphite surface has been investigated. The presence of nanoparticles gives rise to random switching of tunneling current between two discrete levels. The experimental power spectra of these current fluctuations show 1/f2 dependence. Analysis of the behavior of the power spectrum indicates that observed noise originates from Brownian motion of the trapped nanoparticle. Statistical analysis of the fluctuations shows exponential behaviour with time width ? ? 18 ms. The results suggest a method of producing an electrostatic trap analogus to laser tweezer

53

Scanning tunneling microscopy and spectroscopy studies of superconducting boron-doped diamond films  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond grown by using the microwave plasma-assisted chemical vapor deposition method. STM/STS measurements were performed by 3He-refrigerator based STM under ultra-high vacuum. The STM topography on the film surface shows a corrugation (with a typical size of ~1 ?m) and grain-like microstructures (~5–20 nm). The tunneling conductance spectra do not show ...

Terukazu Nishizaki, Yoshihiko Takano

2006-01-01

54

The effect of the top metal electrode on tunneling spectra  

International Nuclear Information System (INIS)

We report experiments on the effect of the top metal electrode on the vibrational spectra of molecules adsorbed on metal particles within tunnel junctions. We find differences in the tunneling spectrum of CO bonded to iron particles with different top metal electrodes. The hydrocarbon vibrations of methyl isocyanide bonded to rhodium particles are not shifted due to different top metal electrodes. However, we find anomalies concerning intensities. Specifically for methyl isocyanide the N identical C stretching mode appears as a dip in the tunneling spectrum. (orig.)

55

Scanning Tunneling Luminescence of Pentacene Nanocrystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Organic semiconductors are promising materials for future electronic and electroluminescence applications. A detailed understanding of organic layers and nano-sized crystals down to single molecules can address fundamental questions of contacting organic semiconductors at the nanometer limit and obtaining luminescence from them. In this thesis, electroluminescence spectra from pentacene, a policyclic hydrocarbon (acene), are discussed. The luminescenc...

Kabakchiev, Alexander

2010-01-01

56

Light emission from a scanning tunneling microscope: Fully retarded calculation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The light emission rate from a scanning tunneling microscope (STM) scanning a noble metal surface is calculated taking retardation effects into account. As in our previous, non-retarded theory [Johansson, Monreal, and Apell, Phys. Rev. B 42, 9210 (1990)], the STM tip is modeled by a sphere, and the dielectric properties of tip and sample are described by experimentally measured dielectric functions. The calculations are based on exact diffraction theory through the vector eq...

Johansson, Peter

1998-01-01

57

Ab initio modeling of STM elastic and inelastic tunneling spectra of tetramantane on Au(111) surface.  

Science.gov (United States)

The recent discovery of the higher diamondoids in crude oil has stimulated interest in their study and several potential technological applications of these molecules have already been proposed. In studying the electronic properties of molecular or nanoscale structures on surfaces, the scanning tunneling microscope is usually the probe of choice. Currently, scanning tunneling microscopy experiments of isolated tetramantane molecules on a (111) gold surface are being carried out. We have performed ab initio pseudopotential density functional theory calculations of the electronic properties of tetramantane and provide a comparison of the elastic and inelastic tunneling spectra between our simulation and the ongoing experiment. This work was supported by the NSF Grant Nos. DMR04-39768 and EEC-0425914 and U.S. DOE Contract No. DE-AC03-76SF00098.

Kioupakis, Emmanouil; Yamachika, R.; Wang, Y.; Lu, X. H.; Crommie, M. F.; Louie, Steven G.

2006-03-01

58

Light emission from Na/Cu(111) induced by a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Measurements of light emission from a scanning tunneling microscope probing a Na overlayer on the (111) surface of Cu are reported along with results of a model calculation that essentially agree with the experimental ones. The observed light emission spectra show two characteristic features depending on the bias voltage. When the bias voltage is smaller than the energy of the second quantum well state formed outside the Na overlayer the light emission is due to a plasmon-me...

Johansson, Peter; Hoffmann, Germar; Berndt, Richard

2002-01-01

59

A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy  

Science.gov (United States)

Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a ?/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 1020 cm-2 s-1 is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.

Jäck, Berthold; Eltschka, Matthias; Assig, Maximilian; Hardock, Andreas; Etzkorn, Markus; Ast, Christian R.; Kern, Klaus

2015-01-01

60

Tunneling spectra for quasi-one-dimensional organic superconductors  

CERN Document Server

The tunneling conductance spectra of a normal-metal/insulator/quasi-one-dimensional superconductor is calculated by using the Blonder-Tinkham-Klapwijk formulation. The pairing symmetry of the superconductor is assumed to be $p$, $d$, and $f$-wave. It is found that there is a well defined zero energy peak in electron tunneling along the direction parallel to the chains or normal to these when the transmitted quasiparticles feel different sign of the pair potential. The actual line shape of the spectra is sensitive to the nodes of the pair potential on the Fermi surface.

Stefanakis, N

2002-01-01

 
 
 
 
61

Nanoscale dynamics probed by laser-combined scanning tunneling microscopy  

International Nuclear Information System (INIS)

With the miniaturization of functional devices, the difference in the electronic properties, for example, due to the structural nonuniformity in each element of nanoscale blocks has an ever more crucial influence on macroscopic functions. Laser-combined scanning tunneling microscopy, a potential method that enables us to probe the photoinduced carrier dynamics on the nanoscale, is reviewed with the latest results

62

Nanoscale dynamics probed by laser-combined scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

With the miniaturization of functional devices, the difference in the electronic properties, for example, due to the structural nonuniformity in each element of nanoscale blocks has an ever more crucial influence on macroscopic functions. Laser-combined scanning tunneling microscopy, a potential method that enables us to probe the photoinduced carrier dynamics on the nanoscale, is reviewed with the latest results.

Shigekawa, Hidemi [Institute of Applied Physics, CREST-JST, 21st COE, University of Tsukuba, Tsukuba 305-8573 (Japan); Yoshida, Shoji; Takeuchi, Osamu; Aoyama, Masahiro; Terada, Yasuhiko; Kondo, Hiroyuki; Oigawa, Haruhiro [Institute of Applied Physics, CREST-JST, 21st COE, University of Tsukuba, Tsukuba 305-8573 (Japan)

2008-03-03

63

Quadrupolar Echo Spectra of the Tunneling CD 3Group  

Science.gov (United States)

Deuteron NMR spectra of both single crystal and powder samples of acetylsalicylic acid-CD 3were measured using the quadrupolar-echo technique. The experiments were done in the temperature range 17-100 K, with a special emphasis on the range 20- 30 K, in which the observable tunneling frequency decreases rapidly from its low-temperature value of 2.7 down to 1.2 MHz. In the tunneling regime, modulations of the line intensities and phases as a function of the echo time ? are observed in the single-crystal spectra. The modulation frequency is equal to the orientation-dependent displacement of the inner satellite pairs (? lines) from the Larmor frequency. These effects were confirmed in numerical simulations and fully explain the phase-modulation effects observed previously in quadrupolar-echo spectra of methyl-deuterated methanol and para-xylene guest molecules in some inclusion compounds. By measuring the temperature and orientation dependence of the quadrupolar lineshapes, it was found that the echo spectra are more sensitive to the value of the tunneling frequency than the spectra obtained from the free induction decay. It is pointed out that, because of the modulation effects, special care must be taken when structural parameters are to be extracted from quadrupolar-echo spectra, in particular from spectra of powder samples.

Olejniczak, Z.; Detken, A.; Manz, B.; Haeberlen, U.

64

Measurement of turbulence spectra using scanning pulsed wind lidars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Turbulent velocity spectra, as measured by a scanning pulsed wind lidar (WindCube), are analyzed. The relationship between ordinary velocity spectra and lidar derived spectra is mathematically very complex, and deployment of the three-dimensional spectral velocity tensor is necessary. The resulting scanning lidar spectra depend on beam angles, line-of-sight averaging, sampling rate, and the full three-dimensional structure of the turbulence being measured, in a convoluted way. The model captu...

Sathe, Ameya; Mann, Jakob

2012-01-01

65

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks correspondi...

Nazin, G. V.; Wu, S. W.; Ho, W.

2005-01-01

66

Mechanism of nanoparticle manipulation by scanning tunnelling microscopy  

International Nuclear Information System (INIS)

Scanning tunnelling microscopy (STM) imaging was performed on gold surfaces with a large coverage of monodispersed silver nanoparticles soft-landed on the surface from the gas phase. In both ambient and ultra-high vacuum conditions, STM scanning was found to displace the particles out of the scanning area, due to weak adhesion of the particles to the substrate surface. Calculations based on contact mechanics and electrostatics show that the particles can overcome the force of adhesion to the surface and jump onto the STM tip beyond the tunnelling distance. The observation provides the possibility for patterning or arranging nanoparticles on a surface, which is demonstrated, and offers the potential for a multiplexed approach to create very precise surface patterns and particle arrangements

67

Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces  

CERN Document Server

Insulating materials are widely used in electronic devices. Bulk insulators and insulating films pose unique challenges for high resolution study since most commonly used charged particle surface analysis techniques are incompatible with insulating surfaces and materials. A, method of performing scanning tunneling microscopy (STM) on insulating surfaces has been investigated. The method is referred to as electron-beam assisted scanning tunneling microscopy (e-BASTM). It is proposed that by coupling the STM and the scanning electron microscopy (SEM) as one integrated device, that insulating materials may be studied, obtaining both high spatial resolution, and topographic and electronic resolution. The premise of the technique is based on two physical consequences of the interaction of an energetic electron beam (PE) with a material. First, when an electron beam is incident upon a material, low level material electrons are excited into conduction band states. For insulators, with very high secondary electron yi...

Bullock, E T

2000-01-01

68

Crystal-edge scanning tunnelling spectroscopy on aluminium-doped magnesium diboride  

International Nuclear Information System (INIS)

We report on the first scanning tunnelling spectroscopy measurements on the edge of aluminium-doped magnesium diboride (Mg1-xAlxB2,x = 0.085) single crystals. To target their edge (?30 ?m thick) we have developed a low temperature STM facility featuring a home built compact STM head coupled to an inertially driven carriage. This allows linear submicronic positioning over millimetric distances. We demonstrate the capabilities of our system by showing reproducible tunnelling spectra obtained both parallel and perpendicular to the crystalline c axis. Tunnelling on the edge reveals the gap originating in the highly 2D ? band but in contrast with pure MgB2 does not show the signature of the ? gap

69

Spin-polarized quantum confinement in nanostructures: Scanning tunneling microscopy  

Science.gov (United States)

Experimental investigations of spin-polarized electron confinement in nanostructures by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are reviewed. To appreciate the experimental results on the electronic level, the physical basis of STM is elucidated with special emphasis on the correlation between differential conductance, as measured by STS, and the electron density of states, which is accessible in ab initio theory. Experimental procedures which allow one to extract the electron dispersion relation from energy-dependent and spatially resolved STM and STS studies of electron confinement are reviewed. The role of spin polarization in electron confinement is highlighted by both experimental and theoretical insights, which indicate variation of the spin polarization in sign and magnitude on the nanometer scale. This review provides compelling evidence for the necessity to include spatial-dependent spin-resolved electronic properties for an in-depth understanding and quantitative assessment of electron confinement in magnetic nanostructures and interaction between magnetic adatoms.

Oka, Hirofumi; Brovko, Oleg O.; Corbetta, Marco; Stepanyuk, Valeri S.; Sander, Dirk; Kirschner, Jürgen

2014-10-01

70

Plasma etching of superconducting Niobium tips for scanning tunneling microscopy  

International Nuclear Information System (INIS)

We have developed a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250??m diameter are dry etched in an SF6 plasma in a Reactive Ion Etcher. The gas pressure, etching time, and applied power are chosen to control the ratio of isotropic to anisotropic etch rates and produce the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100?nm, mechanically stable, and superconducting. They generate good STM images and spectroscopy on single crystal samples of Au(111), Au(100), and Nb(100), as well as a doped topological insulator Bi2Se3 at temperatures ranging from 30 mK to 9?K.

71

Ni nanocrystals on HOPG(0001): A scanning tunnelling microscope study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The growth mode of small Ni clusters evaporated in UHV on HOPG has been investigated by scanning tunnelling microscopy. The size, the size distribution, and the shape of the clusters have been evaluated for different evaporation conditions and annealing temperatures. The total coverage of the surface strongly depends on the evaporation rate and time, whereas the influence of these parameters is low on the cluster size. Subsequent stepwise annealing has been performed. This results in a reduct...

Marz, Michael; Sagisaka, Keisuke; Fujita, Daisuke

2013-01-01

72

The electroluminescence and scanning tunneling microscopy of single molecules  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The scanning tunneling microscopy (STM) of single molecules has become a prominent experimental method in the field of molecular electronics. It has been found that in STM experiments, when an electric current flows through a single molecule, the molecule may luminesce. This electroluminescence, in conjunction with traditional STM data, provides a potentially important additional degree of freedom for understanding nanoscale systems. This thesis describes exploratory theoretical work on the n...

Buker, John William

2009-01-01

73

Distinction of Nuclear Spin States with the Scanning Tunneling Microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We demonstrate rotational excitation spectroscopy with the scanning tunneling microscope for physisorbed hydrogen and its isotopes hydrogen-deuterid and deuterium. The observed excitation energies are very close to the gas phase values and show the expected scaling with moment of inertia. Since these energies are characteristic for the molecular nuclear spin states we are able to identify the para and ortho species of hydrogen and deuterium, respectively. We thereby demonstr...

Natterer, Fabian Donat; Patthey, Franc?ois; Brune, Harald

2013-01-01

74

Structure of YSi2 nanowires from scanning tunneling spectroscopy and ?rst-principles  

Energy Technology Data Exchange (ETDEWEB)

Exceptionally long and uniform YSi2 nanowires are formed via self-assembly of yttrium atoms on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a new class of YSi2 nanowires that violate the odd-multiple rule. The structure of the thinnest wire in this category is determined by comparing the normalized differential con- ductance spectra from scanning tunneling spectroscopy (STS) with the projected surface density of states (DOS) of various candidate models, obtained from ?rst-principles, by means of a R-factor analysis. The Pendry R-factor appears to be a useful indicator for selecting the best structure model from the tunneling spectra of individual nano objects.

Iancu, Violeta [University of Tennessee, Knoxville (UTK); Kent, Paul R [ORNL; Zeng, C. [University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL); Weitering, Hanno [University of Tennessee, Knoxville (UTK)

2009-01-01

75

Tip preparation for usage in an ultra-low temperature UHV scanning tunneling microscope  

Directory of Open Access Journals (Sweden)

Full Text Available This work deals with the preparation and characterization of tungsten tips for the use in UHV low-temperature scanning tunneling microscopy and spectroscopy (STM and STS, respectively. These specific environments require in situ facilities for tip conditioning, for further sharpening of the tips, as well as for reliable tip characterization. The implemented conditioning methods include direct resistive annealing, annealing by electron bombardment, and self-sputtering with noble gas ions. Moreover, results from in situ tip characterization by field emission and STM experiments were compared to ex situ scanning electron microscopy. Using the so-prepared tips, high resolution STM images and tunneling spectra were obtained in a temperature range from ambient down to 350 mK, partially with applied magnetic field, on a variety of materials.

S. Ernst, S. Wirth, M. Rams, V. Dolocan and F. Steglich

2007-01-01

76

A study of surfaces using a scanning tunneling microscope (STM  

Directory of Open Access Journals (Sweden)

Full Text Available Sweeping/scanning microscopes have become an experimental scientist’s hands and eyes in this century; they have become a powerful and necessary tool for nanoscale characterisation in education and research laboratories all around the world. This arti- cle presents the modifications made in the mechanical (isolation or designing an anti-vibration system and electrical (piezoelec- tric and scanning system characterisation implementation of a scanning tunnelling microscope (STM, thereby allowing nanosca- le surfaces to be visualised and modified. A methodology for visualising and characterising surfaces using the aforementioned instrument is described, bidimensional quantification of up to 1,300 nm2, with ~15 nm resolution being reached. This experi- mental methodology took critical parameters for tunnelling current stability into account, such as scanning speed and microscope tip geometry and dimensions. This microscope’s versatility allowed defects in highly oriented pyrolytic graphite (HOPG samples to be modified and visualised by applying a voltage between the tip and the sample. The concepts of topography scanning and lithography can be easily understood by using the instrument implemented here.

Alba Graciela Ávila Bernal

2010-05-01

77

Manifestation of the Verwey Transition in the Tunneling Spectra of Magnetite Nanocrystals  

CERN Document Server

Tunneling transport measurements performed on single particles and on arrays of Fe3O4 (magnetite) nanocrystals provide strong evidence for the existence of the Verwey metal-insulator transition at the nanoscale. The resistance measurements on nanocrystal arrays show an abrupt increase of the resistance around 100 K, consistent with the Verwey transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak structure around zero bias voltage. The tunneling spectra obtained on isolated particles using a Scanning Tunneling Microscope reveal an insulator-like gap structure in the density of states below the transition temperature that gradually disappeared with increasing temperature, transforming to a small peak structure at the Fermi energy. These data provide insight into the roles played by long- and short-range charge ordering in the Verwey transition.

Poddar, P; Markovich, G M; Sharoni, A; Katz, D; Wizansky, T; Millo, O; Poddar, Pankaj; Fried, Tcipi; Markovich, Gil; Sharoni, Amos; Katz, David; Wizansky, Tommer; Millo, Oded

2003-01-01

78

Tunneling Spectra of Skutterudite PrOs_4Sb_{12}  

CERN Document Server

The tunnel conductance in normal-metal / insulator / PrOs$_4$Sb$_{12}$ junctions is theoretically studied, where skutterudite PrOs$_4$Sb$_{12}$ is considered to be an unconventional superconductor. The conductance are calculated for several pair potentials which have been proposed in recent works. The results show that the conductance is sensitive to the relation between the direction of electric currents and the position of point nodes. We also show that the conductance spectra often deviate from the shape of the bulk density of states and that the sub gap spectra have peak structures in the case of the spin-triplet pair potentials. The results indicate that the tunnel conductance is a useful tool to obtain an information of the pairing symmetry.

Asano, Y; Matsuda, Y; Kashiwaya, S

2003-01-01

79

Optical and electrical characterization at the nanoscale with a transparent probe of a scanning tunnelling microscope  

International Nuclear Information System (INIS)

A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.

80

Optical and Electrical Characterization at the Nanoscale by a Transparent Tip of a Scanning Tunneling Microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.

Sychugov, Ilya; Omi, Hiroo; Murashita, Toru; Kobayashi, Yoshihiro

2009-01-01

 
 
 
 
81

Low-current Scanning Tunneling Microscope for Nanoscale Imaging  

Directory of Open Access Journals (Sweden)

Full Text Available Advances in the nanotechnology, which is still in its infancy, will depend on our ability todesign, build, replicate, and mass-produce usable nanoscale systems. At sub-nanometer lengthscales, scanning tunneling microscopy (STM and the related techniques, collectively calledscanning probe microscopies, replace the optical microscopy for real-space imaging andmanipulation of materials. STM operation is based on measurement of current due to tunnelingof electrons across a finite potential barrier between the probe and the sample. In conventionalSTM, tunneling current of tens of nA and probe-sample distance of a few Å are maintained.These conditions, while necessary for atomic-scale imaging under ultra high vacuum environment,are not suited to handle nanostructures. Quantum structures deposited on a flat substrate usuallypresent a non-metallic sample, and the roughness levels involved are much too high forconventional STM. STM operation with low tunneling current (few pA and larger tunneling gap(several nm is preferred to overcome these difficulties. This paper presents experimental workand theoretical considerations for developing an atmospheric low-current STM (LC-STM.Researchers from diverse fields can build their own LC-STM for routine imaging and spectroscopy.Several design details are included keeping this aspect in mind.

R.K. Kale

2006-10-01

82

SPATIAL REPARTITION OF CURRENT FLUCTUATIONS IN A SCANNING TUNNELING MICROSCOPE  

Directory of Open Access Journals (Sweden)

Full Text Available Scanning Tunneling Microscopy (STM is a technique where the surface topography of a conducting sample is probed by a scanning metallic tip. The tip-to-surface distance is controlled by monitoring the electronic tunneling current between the two metals. The aim of this work is to extend the temporal range of this instrument by characterising the time fluctuations of this current on different surfaces. The current noise power spectral density is dominated by a characteristic 1/f component, the physical origin of which is not yet clearly identified, despite a number of investigations. A new I-V preamplifier was developed in order to characterise these fluctuations of the tunnelling current and to obtain images of their spatial repartition. It is observed that their intensity is correlated with some topographical features. This information can be used to get insights on the physical phenomena involved that are not accessible by the usual STM set-up, which is limited to low frequencies.

Jerome Lagoute

2011-05-01

83

Size-Dependent Energy Levels of InSb Quantum Dots Measured by Scanning Tunneling Spectroscopy.  

Science.gov (United States)

The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other III-V materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with L-valley of InSb QDs rather than through states of the ?-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined III-V nanomaterials. PMID:25531244

Wang, Tuo; Vaxenburg, Roman; Liu, Wenyong; Rupich, Sara M; Lifshitz, Efrat; Efros, Alexander L; Talapin, Dmitri V; Sibener, S J

2015-01-27

84

Bases for time-resolved probing of transient carrier dynamics by optical pump-probe scanning tunneling microscopy.  

Science.gov (United States)

The tangled mechanism that produces optical pump-probe scanning tunneling microscopy spectra from semiconductors was analyzed by comparing model simulation data with experimental data. The nonlinearities reflected in the spectra, namely, the excitations generated by paired laser pulses with a delay time, the logarithmic relationship between carrier density and surface photovoltage (SPV), and the effect of the change in tunneling barrier height depending on SPV, were examined along with the delay-time-dependent integration process used in measurement. The optimum conditions required to realize reliable measurement, as well as the validity of the microscopy technique, were demonstrated for the first time. PMID:23929439

Yokota, Munenori; Yoshida, Shoji; Mera, Yutaka; Takeuchi, Osamu; Oigawa, Haruhiro; Shigekawa, Hidemi

2013-10-01

85

Versatile scanning tunneling microscopy with 120ps time resolution  

CERN Document Server

We describe a fully ultra-high vacuum compatible scanning tunneling microscope (STM) optimized for radio-frequency signals. It includes in-situ exchangeable tips adapted to high frequency cabling and a standard sample holder, which offer access to the whole range of samples typically investigated by STM. We demonstrate a time resolution of 120 ps using the nonlinear I(V)-characteristic of the surface of highly oriented pyrolithic graphite. We provide atomically resolved images in pulse mode related to a spatially varying nonlinearity of the local density of states of the sample, thus, demonstrating the possible spatial resolution of the instrument in pulse mode. Analysis of the noise reveals that changes in the tunneling junction of 50 pA are dynamically detectable at 120 ps time resolution.

Saunus, Christian; Pratzer, Marco; Morgenstern, Markus; 10.1063/1.4790180

2013-01-01

86

Apparent Barrier Height in Scanning Tunneling Microscopy Revisited  

DEFF Research Database (Denmark)

The apparent barrier height phi(ap), that is, the rate of change of the logarithm of the conductance with tip-sample separation in a scanning tunneling microscope (STM), has been measured for Ni, Pt, and Au single crystal surfaces. The results show that phi(ap) is constant until point contact is reached rather than decreasing at small tunneling gap distances, as previously reported. The findings for phi(ap) can be accounted for theoretically by including the relaxations of the tip-surface junction in an STM due to the strong adhesive forces at close proximity. These relaxation effects are shown also to be generally relevant under imaging conditions at metal surfaces.

Olesen, L.; Brandbyge, Mads

1996-01-01

87

Challenges in cross-sectional scanning tunneling microscopy on semiconductors  

International Nuclear Information System (INIS)

Cross sectional scanning tunneling microscopy (X-STM) has now become a well established method for the investigation of the structural and electronic properties of semiconductor nano-structures down to the scale of individual impurity atoms. Nevertheless, some aspects still remain challenging, for example in the sample preparation by cleavage as well as in the quantitative interpretation of the results. We present a brief overview of the techniques and geometries employed to cleave different semiconductors such as the lll-V materials, mainly GaAs, and the elementary semiconductors Si and Ge. Furthermore, we discuss the inevitable impact of the surface on the properties of the addressed impurities. This is mainly an issue when the surface reconstruction creates electronic surface states in the band gap. But also the unreconstructed GaAs(110) surface significantly modifies the symmetry of acceptor wave functions and the binding energy of donors and acceptors in the first few atomic layers. The impact of the tip will be addressed as a third quite important challenge, which is frequently neglected in the analysis of X-STM data. On surfaces with an unpinned Fermi level, the presence of the STM tip and the voltage applied to the tunneling contact significantly modifies the spectral positions of the observed electronic states and bands. Furthermore, different band bending situations open up qualitatively different tunneling paths to address individual electronic states in the sample. Detailed knowledge of the tunneling mechanism and of the tip properties, mainly apex radius and work function, is required in order to correctly extract the energetic levels from the tunneling spectroscopy data

88

Challenges in cross-sectional scanning tunneling microscopy on semiconductors  

Science.gov (United States)

Cross sectional scanning tunneling microscopy (X-STM) has now become a well established method for the investigation of the structural and electronic properties of semiconductor nano-structures down to the scale of individual impurity atoms. Nevertheless, some aspects still remain challenging, for example in the sample preparation by cleavage as well as in the quantitative interpretation of the results. We present a brief overview of the techniques and geometries employed to cleave different semiconductors such as the lll-V materials, mainly GaAs, and the elementary semiconductors Si and Ge. Furthermore, we discuss the inevitable impact of the surface on the properties of the addressed impurities. This is mainly an issue when the surface reconstruction creates electronic surface states in the band gap. But also the unreconstructed GaAs(110) surface significantly modifies the symmetry of acceptor wave functions and the binding energy of donors and acceptors in the first few atomic layers. The impact of the tip will be addressed as a third quite important challenge, which is frequently neglected in the analysis of X-STM data. On surfaces with an unpinned Fermi level, the presence of the STM tip and the voltage applied to the tunneling contact significantly modifies the spectral positions of the observed electronic states and bands. Furthermore, different band bending situations open up qualitatively different tunneling paths to address individual electronic states in the sample. Detailed knowledge of the tunneling mechanism and of the tip properties, mainly apex radius and work function, is required in order to correctly extract the energetic levels from the tunneling spectroscopy data.

Garleff, J. K.; Wijnheijmer, A. P.; Koenraad, P. M.

2011-06-01

89

Observation of diamond turned OFHC copper using Scanning Tunneling Microscopy  

Energy Technology Data Exchange (ETDEWEB)

Diamond turned OFHC copper samples have been observed within the past few months using the Scanning Tunneling Microscope. Initial results have shown evidence of artifacts which may be used to better understand the diamond turning process. The STM`s high resolution capability and three dimensional data representation allows observation and study of surface features unobtainable with conventional profilometry systems. Also, the STM offers a better quantitative means by which to analyze surface structures than the SEM. This paper discusses findings on several diamond turned OFHC copper samples having different cutting conditions. Each sample has been cross referenced using STM and SEM.

Grigg, D.A.; Russell, P.E.; Dow, T.A.

1988-12-01

90

Fabrication of metallic nanowires with a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A procedure to pattern thin metal films on a nanometer scale with a scanning tunneling microscope (STM) operating in air is reported. A 30 nm film of hydrogenated amorphous silicon (a?Si:H) is deposited on a 10 nm film of TaIr. Applying a negative voltage between the STM tip and the a?Si:H film causes the local oxidation of a?Si:H. The oxide which is formed is used as a mask to wet etch the not?oxidized a?Si:H and subsequently, the remaining pattern is transferred into the metal fil...

Kramer, N.; Birk, H.; Jorritsma, J.; Scho?nenberger, C.

1995-01-01

91

A scanning tunneling microscope study of polymer surface morphology  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The goal of this work was to determine the utility of the scanning tunneling microscope (STM) for the study of the surface morphology of polymer structures. This thesis will present details of the mechanical design of a new STM. It will also discuss the computer hardware and software required to make the STM function. A detailed study of polyethylene crystals will be presented. The results of this study will be related to the growth and defects of these crystals. A calculation of tip-sample c...

Piner, Richard Dean

1990-01-01

92

Photon scanning tunneling microscopy of tailor-made photonic structures  

Science.gov (United States)

Optical field distributions around individually fabricated subwavelength scatterers mapped with a photon scanning tunneling microscope are presented. The photonic structures are produced from ridge waveguides using focused-ion-beam milling. This flexible technique allows us to make single holes and slits of sizes down to 30 nm. A quantitative analysis of the observed optical pattern due to interference between incoming and reflected light yields insight about subwavelength scatterers in waveguides. We conclude that light scattering into high-loss modes of the waveguide occurs.

Peeters, C.; Flück, E.; Otter, A. M.; Balistreri, M. L. M.; Korterik, J. P.; Kuipers, L.; van Hulst, N. F.

2000-07-01

93

Measurement of shear strength for HOPG with scanning tunneling microscopy by thermal excitation method.  

Science.gov (United States)

An experimental observation of force interactions in scanning tunneling microscopy (STM) is presented. A technique for measuring force interactions between a conventional STM probe and a sample by spectra analysis of its thermal fluctuations from tunneling current in STM is developed theoretically and experimentally. Thermally excited fluctuation of the STM probe is exactly discerned in air and then force gradient is determined from its corresponding eigen-frequency with a formula similar to that for a small-amplitude atomic force microscopy (AFM). The observed force interactions are consistent with forces in dynamic AFM. Shear strength of 7 GPa for highly oriented pyrolytic graphite (HOPG) under compressive stress is obtained from the experiment and using the elastic theory. We believe that this technique is of scientific significance as it enables accurate measurement of short-range force interactions at atomic scale under true STM conditions. PMID:22446198

Ding, X D; Wang, Y Z; Xiong, X M; Du, X S; Zhang, J X

2012-04-01

94

Resonant-enhanced spectroscopy of molecular rotations with a scanning tunneling microscope.  

Science.gov (United States)

We use rotational excitation spectroscopy with a scanning tunneling microscope to investigate the rotational properties of molecular hydrogen and its isotopes physisorbed on the surfaces of graphene and hexagonal boron nitride (h-BN), grown on Ni(111), Ru(0001), and Rh(111). The rotational excitation energies are in good agreement with ?J = 2 transitions of freely spinning p-H2 and o-D2 molecules. The variations of the spectral line shapes for H2 among the different surfaces can be traced back to a molecular resonance-mediated tunneling mechanism. Our data for H2/h-BN/Rh(111) suggest a local intrinsic gating on this surface due to lateral static dipoles. Spectra on a mixed monolayer of H2, HD, and D2 display all three J = 0 ? 2 rotational transitions, irrespective of tip position, thus pointing to a multimolecule excitation, or molecular mobility in the physisorbed close-packed layer. PMID:24998795

Natterer, Fabian Donat; Patthey, François; Brune, Harald

2014-07-22

95

Scanning tunneling microscopy and spectroscopy study of charge inhomogeneities in bilayer graphene  

Science.gov (United States)

We report a room-temperature scanning tunneling microscopy and spectroscopy study of bilayer graphene prepared by mechanical exfoliation on a SiO 2/Si surface and electrically contacted with gold pads using a mechanical mask. The bulk conductivity shows contributions from regions of varying electron density, indicating significant charge inhomogeneity. Large-scale topographic images show ripple-like structures with a roughness of ˜1 nm, while the small-scale atomic resolution images show graphite-like triangular lattices. The local ( dI/dV-V) tunnel spectra have an asymmetric V-shape with the minima location showing significant spatial variation, indicating inhomogeneity in electron density of order 10 11 cm -2. The minimum in spectrum at a fixed location also shifts linearly with the gate voltage with a slope consistent with the field-induced carrier density.

Choudhary, Shyam K.; Gupta, Anjan K.

2011-03-01

96

Combined Scanning Force Microscopy and Scanning tunneling spectroscopy of an electronic nanocircuit at very low temperature.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have developed a combined microscope Atomic Force Microscope (AFM) / Scanning Tunneling Microscope (STM) at very low temperature. This microscope allows the study of the electronic Local Density Of States (LDOS) on current biased nanocircuits. We have developed a nanofabrication process to obtain superconducting wires of niobium (Nb) with 10×300 nm2 section.This process gives on Nb a subnanometric surface roughness. We describe also the method of tip's fabrication which are glued on...

Senzier, Julien

2007-01-01

97

Imaging of submicron index variations by scanning optical tunneling  

Energy Technology Data Exchange (ETDEWEB)

The scanning tunneling optical microscope (SNOM, STOM, PSTM, etc.) is the equivalent of the electron scanning tunneling microscope in the electromagnetic domain. Although it was born at the same time, its actual development is more recent. Here, some new results obtained with the version working in total reflection (STOM/PSTM) are reported. A grating of a periodicity of 417 nm and a thickness of 5 nm have been imaged both in TM and TE modes. It is first noted that the optical image is well resolved. Furthermore, the difference of behavior of the field versus the polarization of the incident light has been shown. More precisely, the TM mode seems to be highly sensitive to small index and topography variations due to surface contaminants. Such effects are generally not imaged by atomic force microscopy working in attractive mode, because they affect the surface topography slightly. The SNOM could be thus a very powerful tool for detecting pollutants over the surface of objects like glasses, lenses, gratings, etc., and in the biology domain. 13 refs., 4 figs.

Courjon, D.; Bainier, C.; Spajer, M. (Universite de Franche-Comte, Besancon (France))

98

The electroluminescence and scanning tunneling microscopy of single molecules  

Science.gov (United States)

The scanning tunneling microscopy (STM) of single molecules has become a prominent experimental method in the field of molecular electronics. It has been found that in STM experiments, when an electric current flows through a single molecule, the molecule may luminesce. This electroluminescence, in conjunction with traditional STM data, provides a potentially important additional degree of freedom for understanding nanoscale systems. This thesis describes exploratory theoretical work on the newly emerging phenomenon of molecular electroluminescence, and its relationship to the scanning tunneling microscopy of single molecules. A local electrode framework is progressively developed, in order to explain single-molecule electroluminescence data as well as simulating STM current-voltage characteristics and topographic maps for molecules on complex substrates. The molecule Zn(II)-etioporphyrin I is chosen for detailed analysis and comparison with experiment. Electron transport is studied using Landauer theory that relates electric current to the transmission probability for an electron to scatter through the molecule. The theoretical approach utilizes tight binding and extended Huckel approaches for the electrodes and molecule, a charge-conserving scheme to self-consistently model the influence of electric fields and electric currents on the molecular energy level structure, and Fermi's golden rule in calculating electroluminescence. A single coherent framework is ultimately achieved that explains for the first time both the electric current data and molecular electroluminescence in a molecular system and elucidates the physics underlying a rich and previously puzzling array of interlinked optical and transport phenomena.

Buker, John William

99

Influence of the quasiparticle lifetime effect on local tunneling spectra of high-T c superconductors  

International Nuclear Information System (INIS)

The local electronic states of optimally doped Bi2Sr2CaCu2O8-? and Ln-doped Bi2Sr2CuO6-? (Ln-Bi2201, Ln = La, Gd) were measured by low-temperature scanning tunneling spectroscopy. The spectra showed enhanced coherence peaks when the gap amplitude was relatively small, while the peaks in the spectra were gradually suppressed as the gap amplitude became larger. In the case of Ln-Bi2201, the spectra showed the enhancements of residual conductance reflecting the impurity scattering due to doped Ln ions. We demonstrate that these trends are systematically reproduced based on the conductance formula that takes account of the energy dependent damping factor corresponding to the quasiparticle lifetime. The consistency suggests that one of the main factors dominating the spectral line shapes is the energy dependence of the quasiparticle lifetime

100

Measurement of turbulence spectra using scanning pulsed wind lidars  

DEFF Research Database (Denmark)

Turbulent velocity spectra, as measured by a scanning pulsed wind lidar (WindCube), are analyzed. The relationship between ordinary velocity spectra and lidar derived spectra is mathematically very complex, and deployment of the three-dimensional spectral velocity tensor is necessary. The resulting scanning lidar spectra depend on beam angles, line-of-sight averaging, sampling rate, and the full three-dimensional structure of the turbulence being measured, in a convoluted way. The model captures the attenuation and redistribution of the spectral energy at high and low wave numbers very well. The model and measured spectra are in good agreement at two analyzed heights for the u and w components of the velocity field. An interference phenomenon is observed, both in the model and the measurements, when the diameter of the scanning circle divided by the mean wind speed is a multiple of the time between the beam measurements. For the v spectrum, the model and the measurements agree well at both heights, except at very low wave numbers, k1 <0.005 m?1. In this region, where the spectral tensor model has not been verified, the model overestimates the spectral energy measured by the lidar. The theoretical understanding of the shape of turbulent velocity spectra measured by scanning pulsed wind lidar is given a firm foundation.

Sathe, Ameya; Mann, Jakob

2012-01-01

 
 
 
 
101

Measurement of shear strength for HOPG with scanning tunneling microscopy by thermal excitation method  

Energy Technology Data Exchange (ETDEWEB)

An experimental observation of force interactions in scanning tunneling microscopy (STM) is presented. A technique for measuring force interactions between a conventional STM probe and a sample by spectra analysis of its thermal fluctuations from tunneling current in STM is developed theoretically and experimentally. Thermally excited fluctuation of the STM probe is exactly discerned in air and then force gradient is determined from its corresponding eigen-frequency with a formula similar to that for a small-amplitude atomic force microscopy (AFM). The observed force interactions are consistent with forces in dynamic AFM. Shear strength of 7 GPa for highly oriented pyrolytic graphite (HOPG) under compressive stress is obtained from the experiment and using the elastic theory. We believe that this technique is of scientific significance as it enables accurate measurement of short-range force interactions at atomic scale under true STM conditions. -- Research highlights: Black-Right-Pointing-Pointer An experimental observation of force interactions in conventional STM. Black-Right-Pointing-Pointer Thermally excited vibration mode in an STM tip used as a shear force sensor. Black-Right-Pointing-Pointer Spectra analysis of the thermal fluctuations of the probe from tunneling current. Black-Right-Pointing-Pointer Shear strength of 7 Gpa for HOPG is obtained under compressive stress. Black-Right-Pointing-Pointer Stimulating ideas for the measurement of short-range forces at atomic scale.

Ding, X.D.; Wang, Y.Z.; Xiong, X.M.; Du, X.S. [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics Science and Engineering, Sun Yat-sen University, Guangzhou 510275, People' s Republic of China (China); Zhang, J.X., E-mail: gzdxd@sina.com [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics Science and Engineering, Sun Yat-sen University, Guangzhou 510275, People' s Republic of China (China)

2012-04-15

102

Measurement of shear strength for HOPG with scanning tunneling microscopy by thermal excitation method  

International Nuclear Information System (INIS)

An experimental observation of force interactions in scanning tunneling microscopy (STM) is presented. A technique for measuring force interactions between a conventional STM probe and a sample by spectra analysis of its thermal fluctuations from tunneling current in STM is developed theoretically and experimentally. Thermally excited fluctuation of the STM probe is exactly discerned in air and then force gradient is determined from its corresponding eigen-frequency with a formula similar to that for a small-amplitude atomic force microscopy (AFM). The observed force interactions are consistent with forces in dynamic AFM. Shear strength of 7 GPa for highly oriented pyrolytic graphite (HOPG) under compressive stress is obtained from the experiment and using the elastic theory. We believe that this technique is of scientific significance as it enables accurate measurement of short-range force interactions at atomic scale under true STM conditions. -- Research highlights: ? An experimental observation of force interactions in conventional STM. ? Thermally excited vibration mode in an STM tip used as a shear force sensor. ? Spectra analysis of the thermal fluctuations of the probe from tunneling current. ? Shear strength of 7 Gpa for HOPG is obtained under compressive stress. ? Stimulating ideas for the measurement of short-range forces at atomic scale.

103

Scanning tunneling microscopy and spectroscopy studies of superconducting boron-doped diamond films  

Directory of Open Access Journals (Sweden)

Full Text Available We report on scanning tunneling microscopy/spectroscopy (STM/STS experiments on (1 1 1-oriented epitaxial films of heavily boron-doped diamond grown by using the microwave plasma-assisted chemical vapor deposition method. STM/STS measurements were performed by 3He-refrigerator based STM under ultra-high vacuum. The STM topography on the film surface shows a corrugation (with a typical size of ~1 ?m and grain-like microstructures (~5–20 nm. The tunneling conductance spectra do not show large spatial dependence and superconductivity is observed independent of the surface structures. The tunneling spectra are analyzed by the Dynes function and the superconducting energy gap is estimated to be ?=0.87 meV at T=0.47 K, corresponding to 2?/kBTc=3.7. The relatively large value of the broadening parameter ?=0.38 meV is discussed in terms of the inelastic electron scattering processes.

Terukazu Nishizaki, Yoshihiko Takano, Masanori Nagao, Tomohiro Takenouchi, Hiroshi Kawarada and Norio Kobayashi

2006-01-01

104

Fully low voltage and large area searching scanning tunneling microscope  

International Nuclear Information System (INIS)

We present a novel scanning tunneling microscope (STM), which allows the tip to travel a large distance (millimeters) on the sample and take images (to find microscopic targets) anywhere it reaches without losing atomic resolution. This broad range searching capability, together with the coarse approach and scan motion, is all done with only one single piezoelectric tube scanner as well as with only low voltages (<15 V). Simple structure, low interference and high precision are thus achieved. To this end, a pillar and a tube scanner are mounted in parallel on a base with one ball glued on the pillar top and two balls glued on the scanner top. These three balls form a narrow triangle, which supports a triangular slider piece. By inertial stepping, the scanner can move the slider toward the pillar (coarse approach) or rotate the slider about the pillar (travel along sample surface). Since all the stepping motions are driven by the scanner's lateral bending which is large per unit voltage, high voltages are unnecessary. The technology is also applicable to scanning force microscopes (SFM) such as atomic force microscopes (AFM), etc

105

Co nanoislands on Au(111) and Cu(111) surfaces studied by scanning tunneling microscopy and spectroscopy.  

Science.gov (United States)

Co nanoislands on the Au(111) and Cu(111) surfaces have been studied by scanning tunneling microscopy and spectroscopy. The experimental results showed that Co nanoislands prefer to aggregate at the step edge and dislocation sites on the reconstructed Au(111) surface and at the step edge on the Cu(111) surface, respectively. In addition, based on dZ/dV-V spectra, in both the Co/Au(111) and the Co/Cu(111) systems, Gundlach oscillation was observed. From the peak shift of dZ/dV-V spectra between Co nanoisland and substrate surface, we can quantitatively obtain that the constant energy separation is -0.13 +/- 0.01 eV for the Co/Au(111) system, and 0.41 +/- 0.02 eV for the Co/Cu(111) system, respectively. These values indicate the work function difference between Co nanoisland and these surfaces. PMID:21128475

Chang, H W; Wu, B F; Yao, Y D; Su, W B; Chang, C S

2010-07-01

106

High tunnel magnetoresistance in spin-polarized scanning tunneling microscopy of Co nanoparticles on Pt(111)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We employ variable-temperature spin-polarized scanning tunneling microscopy in constant current mode to read the magnetic state of monodomain cobalt nanoparticles on Pt(111). In order to avoid stray fields we use in situ prepared antiferromagnetically (Cr) coated W tips. The contrast in apparent height between nanoparticles with opposite magnetization is typically Delta z=0.20 +/- 0.05 A, but can reach up to 1.1 A, indicating 80% spin-polarization of the nanoparticles and 850% magnetoresistan...

Rusponi, S.; Weiss, N.; Cren, T.; Epple, M.; Brune, H.

2005-01-01

107

A high stability and repeatability electrochemical scanning tunneling microscope  

Science.gov (United States)

We present a home built electrochemical scanning tunneling microscope (ECSTM) with very high stability and repeatability. Its coarse approach is driven by a closely stacked piezo motor of GeckoDrive type with four rigid clamping points, which enhances the rigidity, compactness, and stability greatly. It can give high clarity atomic resolution images without sound and vibration isolations. Its drifting rates in XY and Z directions in solution are as low as 84 pm/min and 59 pm/min, respectively. In addition, repeatable coarse approaches in solution within 2 mm travel distance show a lateral deviation less than 50 nm. The gas environment can be well controlled to lower the evaporation rate of the cell, thus reducing the contamination and elongating the measurement time. Atomically resolved SO42- image on Au (111) work electrode is demonstrated to show the performance of the ECSTM.

Xia, Zhigang; Wang, Jihao; Hou, Yubin; Lu, Qingyou

2014-12-01

108

Scanning Tunneling Microscopy and Spectroscopy of Topological Insulators  

Science.gov (United States)

We performed cryogenic scanning tunneling microscopy and spectroscopy measurements of the surface and defect states in topological insulators Bi2Se3 and Bi2Te3. Our measurements demonstrate gapless surface states in both materials. While Bi2Te3 is naturally p-doped, we observed both p- and n-doped regions on the cleaved surface. These observations can be correlated with local cleaving within quintuple layers seen from topography measurements, suggesting a new route for surface doping of topological insulators. We also describe unique clover-shaped defects states appearing inside the bulk valence band. Our band structure calculations show that these states originate from a combination of bonding anisotropy and surface band bending, resulting in formation of subsurface resonances.

Urazhdin, Sergei; Tessmer, Stuart; Kyratsi, Theodora; Kanatzidis, Mercouri

2010-03-01

109

An electromagnetic microscopic positioning device for the scanning tunneling microscope  

Science.gov (United States)

We have developed a device that is capable of moving with steps as small as 70 Å in any direction over a flat surface. The device that we call the Maggot consists of two permanent magnets attached to the corners of a triangular plate that stands on a flat base with three fixed ball-bearing feet. The Maggot is propelled across the base by the magnetic fields from two coils that are powered by computer-controlled current pulses. Steering of the Maggot is made by vector addition of the pulses by the computer. A complete electromagnetic force theory is given in order to find the best magnet and solenoid geometries for maximum performance. The Maggot is UHV compatible, operates from 500 to 4.2 °K, and is most suitable for operation on a vibration-isolated base. Movement data is measured with both optical and scanning tunneling microscopy.

Corb, B. W.; Ringger, M.; Güntherodt, H.-J.

1985-12-01

110

Scanning Tunneling Spectroscopy of Graphene on Hexagonal Boron Nitride  

Science.gov (United States)

Recent work has found hexagonal boron nitride (hBN) to be a good substrate for graphene devices due to its ability to screen charged impurities in the underlying substrate and increase graphene mobility. We investigated graphene on hBN heterostructures using scanning tunneling microscopy and spectroscopy. Because hBN has the same bond structure as graphene with a slightly longer lattice constant, a rotationally dependent Moir'e pattern is formed in graphene on hBN heterostructures. The Moir'e pattern creates a weak periodic potential for the charge carriers in graphene. We performed an experimental and theoretical investigation of its effect on the local density of states. We observed a Moir'e wavelength dependent modification of the local density of states in good agreement with theory predictions.

Yankowitz, Matthew; Xue, Jiamin; Cormode, Daniel; Sanchez-Yamagishi, Javier; Jarillo-Herrero, Pablo; Watanabe, K.; Taniguchi, T.; Jacquod, Philippe; Leroy, Brian

2012-02-01

111

Scanning tunneling microscope with two-dimensional translator.  

Science.gov (United States)

Since the invention of the scanning tunneling microscope (STM), it has been a powerful tool for probing the electronic properties of materials. Typically STM designs capable of obtaining resolution on the atomic scale are limited to a small area which can be probed. We have built an STM capable of coarse motion in two dimensions, the z- and x-directions which are, respectively, parallel and perpendicular to the tip. This allows us to image samples with very high resolution at sites separated by macroscopic distances. This device is a single unit with a compact design making it very stable. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures. PMID:21280836

Nichols, J; Ng, K-W

2011-01-01

112

Atomic-scale imaging of DNA using scanning tunnelling microscopy  

Science.gov (United States)

THE scanning tunnelling microscope (STM) has been used to visualize DNA1 under water2, under oil3 and in air4-6. Images of single-stranded DNA have shown that submolecular resolution is possible7. Here we describe atomic-resolution imaging of duplex DNA. Topographic STM images of uncoated duplex DNA on a graphite substrate obtained in ultra-high vacuum are presented that show double-helical structure, base pairs, and atomic-scale substructure. Experimental STM profiles show excellent correlation with atomic contours of the van der Waals surface of A-form DNA derived from X-ray crystallography. A comparison of variations in the barrier to quantum mechanical tunnelling (barrier-height) with atomic-scale topography shows correlation over the phosphate-sugar backbone but anticorrelation over the base pairs. This relationship may be due to the different chemical characteristics of parts of the molecule. Further investigation of this phenomenon should lead to a better understanding of the physics of imaging adsorbates with the STM and may prove useful in sequencing DNA. The improved resolution compared with previously published STM images of DNA may be attributable to ultra-high vacuum, high data-pixel density, slow scan rate, a fortuitously clean and sharp tip and/or a relatively dilute and extremely clean sample solution. This work demonstrates the potential of the STM for characterization of large biomolecular structures, but additional development will be required to make such high resolution imaging of DNA and other large molecules routine.

Driscoll, Robert J.; Youngquist, Michael G.; Baldeschwieler, John D.

1990-07-01

113

Scanning tunneling spectroscopy of fullerenes, diamondoids, and organometallic molecular nanostructures  

Science.gov (United States)

Molecule-based carbon nanostructures display a great variety of geometries and electronic features, making them a promising basis for novel technological applications. Understanding their local electronic properties is of essential importance for future molecule-based device construction. This dissertation is aimed at understanding and manipulating the electronic properties of molecule-based carbon nanostructures. The dissertation is divided into three main parts. The first part describes the technical aspects of a home-built low-temperature ultra-high vacuum (UHV) scanning tunneling microscope (STM), which was the main instrument used in our studies. The second part discusses scanning tunneling spectroscopy (STS) studies for three different molecules that have great nanotechnological potential: C60 fullerenes, diamondoids, and organometallic magnetic molecules. Our studies of C60 behavior include observation of energy-resolved molecular orbitals, molecule-substrate interactions, and the Jahn-Teller effect. Our studies of new sp3 bonded diamondoid molecules are focused on the tetramantane molecule. We have characterized this molecule both with elastic and inelastic spectroscopy, and have performed single-molecule manipulation using the "sliding process" and voltage-pulses. The organometallic element focused on here is the titanocene chloride dimer. This molecule shares many characteristics of the fullerenes, such as conjugated carbon rings, but it has additional magnetic properties due to the incorporation of two spin-12 Ti atoms in an antiferromagnetic configuration. Ordered patterns for submonolayer coverages of this molecule on Au(111) were synthesized and will be discussed, including spectroscopic features. STS of the some disordered titanocene molecules shows sharp resonances near the Fermi energy that may be magnetic in origin. The third part of this thesis is focused on the development of new techniques for investigating local magnetic and spin properties. The construction of a spin-polarized STM, capable of characterizing fluctuations in spin density at the Angstrom scale, will be discussed. Our progress in construction of a STM electron spin resonance (ESR) instrument will also be addressed.

Lu, Xinghau

114

Node-like excitations in superconducting PbMo6S8 probed by scanning tunneling spectroscopy  

CERN Document Server

We present the first scanning tunneling spectroscopy study on the Chevrel phase PbMo6S8, an extreme type II superconductor with a coherence length only slightly larger than in high-Tc cuprates. Tunneling spectra measured on atomically flat terraces are spatially homogeneous and show well-defined coherence peaks. The low-energy spectral weight, the zero bias conductance and the temperature dependence of the gap are incompatible with a conventional isotropic s-wave interpretation, revealing the presence of low-energy excitations in the superconducting state. We show that our data are consistent with the presence of nodes in the superconducting gap.

Dubois, C; Santi, G; Berthod, C; Manuel, A A; Decroux, M; Fischer, O; Potel, M; Chevrel, R

2007-01-01

115

Scanning acoustic tunneling microscopy and spectroscopy: A probing tool for acoustic surface oscillations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A method is presented for the universal probing of surface acoustic waves (SAWs). For measuring high frequency SAWs by scanning tunneling microscopy (STM) a stroboscopic snapshot technique was employed, named scanning acoustic tunneling microscopy. The amplitude and the phase of a state of oscillation within a SAW field are a superposition of the surface topography and the oscillation trajectory. Measuring with atomic resolution the observed contrast can be understood by a spherical tunneling...

Hesjedal, T.; Chilla, E.; Frohlich, Hj

1997-01-01

116

Optical characterication of probes for photon scanning tunnelling microscopy  

DEFF Research Database (Denmark)

The photon scanning tunnelling microscope is a well-established member of the family of scanning near-field optical microscopes used for optical imaging at the sub-wavelength scale. The quality of the probes, typically pointed uncoated optical fibres, used is however difficult to evaluate in a direct manner and has most often been inferred from the apparent quality of recorded optical images. Complicated near-field optical imaging characteristics, together with the possibility of topographically induced artefacts, however, has increased demands for a more reliable probe characterization technique. Here we present experimental results obtained for optical characterization of two different probes by imaging of a well-specified near-field intensity distribution at various spatial frequencies. In particular, we observe that a sharply pointed dielectric probe can be highly suitable for imaging when using p-polarized light for the illumination. We conclude that the proposed scheme can be used directly for probe characterization and, subsequently, for determination of an optical transfer function, which could allow one to deduce from an experimentally obtained image of a weakly scattering sample the field distribution existing near the sample surface inthe absence of the probe.

Vohnsen, Brian; Bozhevolnyi, Sergey I.

1999-01-01

117

Piezoresistive cantilevers utilized for scanning tunneling and scanning force microscope in ultrahigh vacuum  

Science.gov (United States)

Piezoresistive cantilevers have been utilized in a novel ultrahigh vacuum scanning probe microscope which allows in situ scanning tunneling microscopy (STM), contact atomic force microscopy (AFM), and noncontact atomic force microscopy. The instrument uses interchangeable tungsten tips (for STM imaging) and piezoresistive cantilevers (for AFM or STM imaging) and is capable of atomic resolution in both STM and AFM modes of operation. In situ tip exchange under vacuum conditions is performed quickly and reliably using a high precision rotary/linear feedthrough and a tip/cantilever storage system. Piezoresistive force-sensing cantilevers provide a new detection scheme for AFM, using an all-electronic detector that requires no alignment or optical detection system. The microscope features a high-resolution, dual-axis, inertial-drive translation stage with an open access sample mount designed to optimize vibration isolation.

Giessibl, F. J.; Trafas, B. M.

1994-06-01

118

Substrate effects on the surface topography of evaporated gold films: a scanning tunnelling microscopy investigation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Direct observation of surface roughness on metal films is a longstanding problem in thin film characterization. In this work the high quality of scanning tunnelling microscopy (STM) was used for investigation of evaporated gold films. A scanning tunnelling microscope able to scan areas up to 0.8 × 0.8 micro m with high reproducibility is presented. The topography of 80 nm thick gold films grown under identical evaporation conditions was investigated as a function of the selected substrate ma...

Vancea, Johann; Reiss, Gu?nter; Schneider, F.; Bauer, K.; Hoffmann, Horst

1989-01-01

119

Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors  

International Nuclear Information System (INIS)

In the first three years since the discovery of Fe-based high Tc superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s± within a single family, FeTe1-xSex. Second, STM has imaged C4 ? C2 symmetry breaking in the electronic states of both parent and superconducting materials. As a local probe, STM is in a strong position to understand the interactions between these broken symmetry states and superconductivity. Finally, STM has been used to image the vortex state, giving insights into the technical problem of vortex pinning, and the fundamental problem of the competing states introduced when superconductivity is locally quenched by a magnetic field. Here we give a pedagogical introduction to STM and QPI imaging, discuss the specific challenges associated with extracting bulk properties from the study of surfaces, and report on progress made in understanding Fe-based superconductors using STM techniques.

120

Scanning tunneling microscope with long range lateral motion  

International Nuclear Information System (INIS)

We present our work on a recently built scanning tunneling microscope (STM), with coarse motion in two-dimensions. The tip of this STM can be translated a few millimeters in directions both parallel and perpendicular to the tip. This feature allows sampling of a larger area for experiments such as the study of how the electrical properties of charge density waves evolve between contacts, the proximity effect near a normal metal–superconducting interface, charge transport near the contact of a semiconductor interface, and for finding microscopically small samples like graphene. This STM is based on one of our previous one-dimensional designs. It utilizes orchestrated motion of six piezoelectric tubes in a slip–stick configuration in order to produce long range motion for the walker. This device is a single unit with a compact design making it very stable. It is stable enough to obtain atomic resolution on HOPG. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures. It was designed entirely from non-magnetic materials for potential work in a magnetic field.

 
 
 
 
121

Scanning tunneling microscope with long range lateral motion  

Science.gov (United States)

We present our work on a recently built scanning tunneling microscope (STM), with coarse motion in two-dimensions. The tip of this STM can be translated a few millimeters in directions both parallel and perpendicular to the tip. This feature allows sampling of a larger area for experiments such as the study of how the electrical properties of charge density waves evolve between contacts, the proximity effect near a normal metal-superconducting interface, charge transport near the contact of a semiconductor interface, and for finding microscopically small samples like graphene. This STM is based on one of our previous one-dimensional designs. It utilizes orchestrated motion of six piezoelectric tubes in a slip-stick configuration in order to produce long range motion for the walker. This device is a single unit with a compact design making it very stable. It is stable enough to obtain atomic resolution on HOPG. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures. It was designed entirely from non-magnetic materials for potential work in a magnetic field.

Nichols, J.; Ng, K.-W.

2012-06-01

122

Oxygen-free in situ scanning tunnelling microscopy  

DEFF Research Database (Denmark)

Scanning tunneling microscopy under full electrochemical potential control (in situ STM) has been used extensively as an efficient method to characterize microstructures at solid/liquid interfaces at the atomic and molecular levels. However, under ambient conditions oxygen may interfere in open in situ STM systems by diffusion through the solutions. Such interference can be serious for oxygen sensitive systems both for the target molecules themselves and for chemical linker molecules bound to the electrode surface for example, via Au-S bonding. This is strikingly illustrated in the present report. We present here oxygen-free in situ STM, in which the samples are contained in an argon atmosphere which removes oxygen in the system. Interference from oxygen is profoundly reduced in this setup and demonstrated by three examples. Two of these are in situ STM of the intermediate-size sulfur containing organic molecule cysteamine and the biomolecule homocysteine. The third example is the iron-sulfur protein ferredoxin (Pyrococcus furiosus). Monolayers of these molecules on Au(111) are imaged to molecular resolution and the images compared in the presence and absence of oxygen. In all the cases, the STM image quality of the monolayer structures has improved significantly in the absence of oxygen. Reasons for the drastic effects of dioxygen based on both chemical surface reactivity and electron scattering effects are discussed. These observations are important in general for STM of oxygen sensitive chemical and biological samples.

Zhang, Jingdong; Ulstrup, Jens

2007-01-01

123

Fabrication and characterization of scanning tunneling microscopy superconducting Nb tips having highly enhanced critical fields  

CERN Document Server

We report a simple method for the fabrication of Niobium superconducting (SC) tips for scanning tunnelling microscopy which allow atomic resolution. The tips, formed in-situ by the mechanical breaking of a niobium wire, reveal a clear SC gap of 1.5 meV and a critical temperature Tc=9.2+-0.3 K as deduced from Superconductor Insulator Normal metal (NIS) and Superconductor Insulator Superconductor (SIS) spectra. These match the values of bulk Nb samples. We systematically find an enhanced value of the critical magnetic field in which superconductivity in the tip is destroyed (around 1 T for some tips) up to five times larger than the critical field of bulk Nb (0.21 T). Such enhancement is attributed to a size effect at the tip apex

Kohen, A; Proslier, T; Lacaze, E; Aprili, M; Sacks, W; Roditchev, D

2004-01-01

124

Effects of plasmon energetics on light emission induced by scanning tunneling microscopy.  

Science.gov (United States)

A theoretical model of plasmon and molecular luminescence induced by scanning tunneling microscopy using a molecule-covered tip on clean metal surfaces is developed. The effects of coupling between molecular exciton and interface plasmon on the luminescence spectra are investigated for variable energy of plasmon modes by means of the nonequilibrium Green's function method. It is found that spectral features arising from interference between the processes of energy absorption by the molecule and interface plasmons appear near the energy of the excitonic mode. For the energy of plasmon above (below) the energy of excitonic mode, an additional peak structure appears in the energy range slightly below (above) the energy of the excitonic mode. Prominent peak and dip structures observed in recent luminescence experiments are interpreted by the developed theory whereby its utility in the fields of plasmonics and nanophotonics is demonstrated. PMID:24810264

Miwa, K; Sakaue, M; Gumhalter, B; Kasai, H

2014-06-01

125

Fabrication and characterization of scanning tunneling microscopy superconducting Nb tips having highly enhanced critical fields  

International Nuclear Information System (INIS)

We report a simple method for the fabrication of Niobium superconducting (SC) tips for scanning tunneling microscopy which allow atomic resolution. The tips, formed in situ by the mechanical breaking of a niobium wire, reveal a clear SC gap of 1.5 meV and a critical temperature Tc = 9.2 ± 0.3 K, as deduced from Superconductor Insulator Normal metal (SIN) and Superconductor Insulator Superconductor (SIS) spectra. These match the values of bulk Nb samples. We systematically find an enhanced value of the critical magnetic field in which superconductivity in the tip is destroyed (around 1 T for some tips) up to five times larger than the critical field of bulk Nb (0.21 T). Such enhancement is attributed to a size effect at the tip apex

126

A fast-scanning, low- and variable-temperature scanning tunneling microscope  

Science.gov (United States)

The design and performance of a fast-scanning, low- and variable-temperature, scanning tunneling microscope (STM) incorporated in an ultrahigh vacuum system is described. The sample temperature can be varied from 25 to 350 K by cooling the sample using a continuous flow He cryostat and counter heating by a W filament. The sample temperature can be changed tens of degrees on a time scale of minutes, and scanning is possible within minutes after a temperature change. By means of a software implemented active drift compensation the drift rate can be as low as 1 nm/day. The STM is rigid, very compact, and of low weight, and is attached firmly to the sample holder using a bayonet-type socket. Atomic resolution on clean metal surfaces can be achieved in the entire temperature range. The performance of the instrument is further demonstrated by images of adsorbed hexa-tert-butyl-decacyclene molecules on Cu(110), by STM movies, i.e., sequential STM images with a time resolution down to 1 s/image (100×100 Å2 with 256×256 pixels), of the mobility of these molecules, and finally by constant current images of standing waves in the electronic local density of states on Cu(110).

Petersen, L.; Schunack, M.; Schaefer, B.; Linderoth, T. R.; Rasmussen, P. B.; Sprunger, P. T.; Laegsgaard, E.; Stensgaard, I.; Besenbacher, F.

2001-02-01

127

Two-photon Induced Hot Electron Transfer to a Single Molecule in a Scanning Tunneling Microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photo-excited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by t...

Wu, Shiwei; Ho, Wilson

2010-01-01

128

Light amplification by stimulated emission from an optically pumped molecular junction in a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Here, we introduce and experimentally demonstrate optical amplification and stimulated emission from a single optically pumped molecular tunneling junction of a scanning tunneling microscope. The gap between a sharp gold tip and a flat gold substrate covered with a self-assembled monolayer of 5-chloro-2-mercaptobenzothiazole molecules forms an extremely small optical gain medium. When electrons tunnel from the molecules highest occupied molecular orbital to the tip, holes ar...

Braun, K.; Kern, A. M.; Wang, X.; Adler, H.; Peisert, H.; Chasse, T.; Zhang, D.; Meixner, A. J.

2013-01-01

129

The study of transition metal surfaces and thin films with inverse photoemission and scanning tunnelling microscopy  

CERN Document Server

clean Cr(001) and the thick films. This suggests that hybridisation between the substrate bands and the film bands and interface induced states are significant. The spectra taken from sub-monolayer coverages of Fe show marked intensity increase at the Fermi energy, this is a feature of LDOS calculations on Fe atoms at the Fe/Cr interface. Fe growth on surfaces of Cu(100) precovered with c(2x2)N has been studied with scanning tunnelling microscopy. The images show that the Fe does not grow on areas covered with nitrogen. Two different c(2x2)N templates have been used and the shape and size of the Fe islands is seen to be altered. The unoccupied electronic states at the surface of Cr(001) have been observed using k-resolved inverse photoemission. Normal incidence IPE spectra have been taken over a range of incident electron energies (14-24 eV). The spectra show only small variation with incident energy, this is attributed to densities of states effects due to the absence of symmetry allowed initial states at th...

Wilson, L K

1997-01-01

130

Scanning tunneling microscopy investigations of metal dichalcogenide materials  

Science.gov (United States)

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) were used to characterize the atomic level structure of electronic properties, reactivity, and wear of metal dichalcogenide materials that are or have potential as solid state lubricants. Single crystals of MoS2, Ni(x)Mo(1-x)S2, MoS(2-x)Se(x), and MoS(2-x)Te(x) were prepared to determine how chemical modifications affect the local structure and electronic properties of this lubricant. STM images of Ni-doped MoS2 show localized electronic states due to the Ni atoms, while images of Se- and Te-doped materials indicate that anion substitution is electronically delocalized. AFM studies of Te-doped MoS2 show, however, that the tellurium dopants form atomic scale structural protrusions that may reduce sliding friction. AFM was also used to characterize nanometer scale wear and oxidation on MoS2 and NbSe2 surfaces. In atmosphere at room-temperature AFM studies showed that NbSe2 wears approximately three times faster than MoS2. Furthermore, oxidation studies demonstrated that NbSe2 was significantly more reactive than MoS2 with molecular oxygen. These results indicate that the intrinsic stability of the MoS2 surface make it an effective lubricant, AFM was also used to elucidate the growth of MoO3 on the surface Of MoS2 during oxidation, and to study wear properties of these MoO3 crystallites. The AFM tip was used to define lines with 10 nm resolution in MoO3 and to manipulate distinct MoO3 structures on the MoS2 surface. In addition, metal-substitution in TaS2 was studied systematically using STM and theoretical methods.

Lieber, Charles M.

1993-10-01

131

Field emission characteristics of the scanning tunneling microscope for nanolithography  

Energy Technology Data Exchange (ETDEWEB)

We present a systematic study of the performance of scanning tunneling microscope (STM)-based, low energy electron beam lithography, using simulations of field emission from STM tips, emphasizing realistic conditions of tip geometry and operation. We calculate the potentials and electric field for a hemispherical model emitter in an axially symmetric system. Emission current density at the tip is calculated using the Fowler{endash}Nordheim equation, and current density at the sample is obtained by calculating trajectories of emitted electrons. We characterize the beam diameter at the sample as a function of emitter radius, tip{endash}sample bias, emission current, resist thickness, and tip work function. The beam diameter is primarily affected by the tip{endash}sample gap, increasing at larger gaps, characteristic of high bias and large tip curvature. For optimal tip radius the beam diameter increases linearly with bias from approximately 2 nm at 5 V to 25 nm at 50 V. Beam diameter is nearly independent of emission current over the range 0.05{endash}50 nA. Dielectric resist films cause an increase in beam diameter due to increased tip{endash}substrate gap. Beam diameter is very sensitive to tip work function, increasing dramatically for low work function tips. Tips comprised of asperities on flat surfaces produce significantly smaller beams compared to {open_quote}{open_quote}standard{close_quote}{close_quote} tips of the same emitter radius. However, for low bias ({lt}15 V) beam diameter becomes insensitive to tip geometry. We compare these simulations to selected experimental results to evaluate the limitations to performance and assess the feasibility of routine sub-10 nm structure fabrication using STM-based low energy electron beam lithography. {copyright} {ital 1996 American Vacuum Society}

Mayer, T.M.; Adams, D.P.; Marder, B.M. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1413 (United States)

1996-07-01

132

Spectroscopy of surface adsorbed molecules (scanning tunneling microscopy). Progress report, May 1, 1985-April 30, 1986  

International Nuclear Information System (INIS)

A review of the scanning tunneling microscopy program is given. This article contains a description of the design and fabrication of the microscope in addition to description of studies which use the microscope: studies of charge-density waves and studies of tunnel junctions doped with metals and semiconductors. 48 refs., 26 figs

133

Pseudogap formation and unusual quasiparticle tunneling in cuprate superconductors: Polaronic and multiple-gap effects on the tunneling spectra  

Energy Technology Data Exchange (ETDEWEB)

We propose new simple and generalized multiple-gap models of quasiparticle tunneling across the high-T{sub c} cuprate superconductor (HTSC)/insulator/normal metal (SIN) junction based on the two different mechanisms for tunneling at positive and negative bias voltages, and the gap inhomogeneity (i.e., multiple-gap) picture. The tunneling of electrons from the normal metal into the quasiparticle states in HTSC with the BCS-type density of states (DOSs) takes place at V>0, while the tunneling of Cooper pairs and large polarons from the HTSC with the BCS DOS and quasi-free state DOS (which appears only in the dissociation of polarons) into the normal metal occurs at V<0. We show that most of the unusual features of tunneling spectra such as nearly U- and V-shaped subgap features, peak-dip-hump structure (appearing systematically at V<0) and asymmetry of the conductance peaks and their temperature and doping dependences, and shoulder-like features inside the main conductance peaks arise naturally in our specific models of SIN tunneling. The experimental tunneling spectra of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+?} are adequately reproduced by using the specific multiple-gap models and taking into account the distribution of BCS and polaronic gap values.

Dzhumanov, S., E-mail: dzhumanov@inp.uz; Ganiev, O.K.; Djumanov, Sh.S.

2013-10-15

134

Observation of zigzag and armchair edges of graphite using scanning tunneling microscopy and spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The presence of structure-dependent edge states of graphite is revealed by both ambient- and ultra-highvacuum- (UHV) scanning tunneling microscopy (STM) / scanning tunneling spectroscopy (STS) observations. On a hydrogenated zigzag (armchair) edge, bright spots are (are not) observed together with (SQRT(3) by SQRT(3))R30 superlattice near the Fermi level (V_S = ?30 mV for a peak of the local density of states (LDOS)) under UHV, demonstrating that a zigzag edge is respo...

Kobayashi, Yousuke; Fukui, Ken-ichi; Enoki, Toshiaki; Kusakabe, Koichi; Kaburagi, Yutaka

2005-01-01

135

Scanning tunnelling microscopy on organic field-effect transistors based on intrinsic pentacene  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The full potential of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy for in-situ characterization of organic semiconductors has so far not been accessible. Here, we demonstrate that the underlying problem, the low intrinsic conductivity, can be overcome by working in a field-effect geometry. We present high resolution surface topographies obtained by STM on pentacene organic field-effect transistors (OFETs). By virtue of the OFET geometry, the hole accumulation laye...

Roelofs, W. S. Christian; Charrier, Dimitri S. H.; Dzwilewski, Andrzej; Janssen, Rene A. J.; Leeuw, Dago M.; Kemerink, Martijn

2014-01-01

136

Prediction of the bias voltage dependent magnetic contrast in spin-polarized scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work is concerned with the theoretical description of the contrast, i.e., the apparent height difference between two lateral surface positions on constant current spin-polarized scanning tunneling microscopy (SP-STM) images. We propose a method to predict the bias voltage dependent magnetic contrast from single point tunneling current or differential conductance measurements, without the need of scanning large areas of the surface. Depending on the number of single poin...

Palota?s, Krisztia?n

2012-01-01

137

Scanning Tunnelling Spectroscopic Studies of Dirac Fermions in Graphene and Topological Insulators  

Science.gov (United States)

We report novel properties derived from scanning tunnelling spectroscopic (STS) studies of Dirac fermions in graphene and the surface state (SS) of a strong topological insulator (STI), Bi2Se3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD), strain-induced scalar and gauge potentials are manifested by the charging effects and the tunnelling conductance peaks at quantized energies, respectively. Additionally, spontaneous time-reversal symmetry breaking is evidenced by the alternating anti-localization and localization spectra associated with the zero-mode of two sublattices while global time-reversal symmetry is preserved under the presence of pseudo-magnetic fields. For Bi2Se3 epitaxial films grown on Si(111) by molecular beam epitaxy (MBE), spatially localized unitary impurity resonances with sensitive dependence on the energy difference between the Fermi level and the Dirac point are observed for samples thicker than 6 quintuple layers (QL). These findings are characteristic of the SS of a STI and are direct manifestation of strong topological protection against impurities. For samples thinner than 6-QL, STS studies reveal the openup of an energy gap in the SS due to overlaps of wave functions between the surface and interface layers. Additionally, spin-preserving quasiparticle interference wave-vectors are observed, which are consistent with the Rashba-like spin-orbit splitting.

Yeh, N.-C.; Teague, M. L.; Wu, R. T.-P.; Chu, H.; Boyd, D. A.; Bockrath, M. W.; He, L.; Xiu, F.-X.; Wang, K.-L.

2012-03-01

138

The Density of States of hole-doped Manganites A Scanning Tunneling Microscopy\\/Spectroscopy study  

CERN Document Server

Variable temperature scanning tunneling microscopy/spectroscopy studies on single crystals and epitaxial thin films of hole-doped manganites, which show colossal magnetoresistance, have been done. We have investigated the variation of the density of states, at and near the Fermi energy ($E_f$), as a function of temperature. Simple calculations have been carried out, to find out the effect of temperature on the tunneling spectra and extract the variation of density of states with temperature, from the observed data. We also report here, atomic resolution images, on the single crystals and larger range images showing the growth patterns on thin films. Our investigation shows unambiguously that there is a rapid variation in density of states for temperatures near the Curie temperature ($T_c$). While for temperatures below $T_c$, a finite DOS is observed at $E_f$, for temperatures near $T_c$ a hard gap opens up in the density of states near $E_f$. For temperatures much higher than $T_c$, this gap most likely give...

Biswas, A K; Raychaudhuri, A K; Bhat, H L; Biswas, Amlan; Elizabeth, Suja

1999-01-01

139

Charge fluctuations and the tunneling spectra of non-magnetic metallic nanoparticles  

CERN Document Server

We present microscopic transport calculations of the tunneling spectra of non-magnetic metal nanoparticles. We show that charge fluctuations give rise to tunneling resonances of a new type. Positive and negative fluctuations have differing kinetics and thus account for previously unexplained spectral features that are found experimentally under only forward or only reverse applied bias. The observed clustering of tunneling resonances of Al nanoparticles arises naturally from our theory.

Narvaez, G A; Narvaez, Gustavo A.; Kirczenow, George

2002-01-01

140

The readout of the fullerene-based quantum computing by a scanning tunneling microscope  

CERN Document Server

We consider to detect the electron spin of a doped atom, i.e., a nitrogen or a phosphorus, caged in a fullerene by currently available technique of the scanning tunneling microscope (STM), which actually corresponds to the readout of a qubit in the fullerene-based quantum computing. Under the conditions of polarized STM current and Coulomb blockade, we investigate the tunneling matrix elements involving the exchange coupling between the tunneling polarized electrons and the encapsulated polarized electron, and calculate the variation of the tunneling current with respect to different orientations of the encapsulated electron spin. The experimental feasibility of our scheme is discussed under the consideration of some imperfect factors.

Feng, M; Hu, B

2006-01-01

 
 
 
 
141

Development of a Millikelvin dual-tip Josephson scanning tunneling microscope  

Science.gov (United States)

In this thesis, I first describe the design and construction of a dual-tip millikelvin STM system. The STM is mounted on a dilution refrigerator and the setup includes vibration isolation, rf-filtered wiring, an ultra high vacuum (UHV) sample preparation chamber and sample transfer mechanism. Next I describe a novel superconducting tip fabrication technique. My technique involves dry-etching sections of 250 mum diameter Nb wire with an SF6 plasma in a reactive ion etcher. I present data taken with these tips on various samples at temperatures ranging from 30 mK to 9 K. My results demonstrate that the tips are superconducting, achieve good spectroscopic energy resolution, are mechanically robust over long time periods, and are atomically sharp. I also show data characterizing the performance of our system. This data is in the form of atomic resolution images, spectroscopy, noise spectra and simultaneous scans taken with both tips of the STM. I used these to examine the tip-sample stability, cross talk between the two tips, and to extract the effective noise temperature (˜185 mK) of the sample by fitting the spectroscopy data to a voltage noise model. Finally, I present spectroscopy data taken with a Nb tip on a Nb(100) sample at 30 mK. The enhanced spectroscopic resolution at this temperature allowed me to resolve peaks in the fluctuation-dominated supercurrent at sub-gap voltages. My analysis indicates that these peaks are due to the incoherent tunneling of Cooper pairs at resonant frequencies of the STM's electromagnetic environment. By measuring the response of the STM junction to microwaves, I identified the charge carriers in this regime as Cooper pairs with charge 2e. The amplitude of the response current scales as the square of the Bessel functions, indicating that the pair tunneling originates from photon assisted tunneling in the incoherent regime, rather than the more conventionally observed Shapiro steps in the coherent regime.

Roychowdhury, Anita

142

Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy  

International Nuclear Information System (INIS)

We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy.

143

Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy.

Oberbeck, Lars [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); TOTAL Marketing Services, New Energies, La Défense 10, 92069 Paris La Défense Cedex (France); Reusch, Thilo C. G.; Hallam, Toby; Simmons, Michelle Y., E-mail: n.curson@ucl.ac.uk, E-mail: michelle.simmons@unsw.edu.au [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); Schofield, Steven R. [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); London Centre for Nanotechnology, UCL, London WC1H 0AH (United Kingdom); Department of Physics and Astronomy, UCL, London WC1E 6BT (United Kingdom); Curson, Neil J., E-mail: n.curson@ucl.ac.uk, E-mail: michelle.simmons@unsw.edu.au [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); London Centre for Nanotechnology, UCL, London WC1H 0AH (United Kingdom); Department of Electronic and Electrical Engineering, UCL, London WC1E 7JE (United Kingdom)

2014-06-23

144

To probe quantum criticality with scanning tunneling spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the role of quantum coherence in tunneling conductance, where quantum criticality turns out to suppress Fano resonance. Based on the nonequilibrium noncrossing approximation, we show that the linear tunneling conductance exhibits weak Fano line-shape with sharp cusp at zero energy in the multichannel Kondo effect, resulting from incoherence associated with quantum criticality of impurity dynamics. In particular, shift of the peak position in the Fano resonance...

Tran, Minh-tien; Kim, Ki-seok

2009-01-01

145

Note: Long-range scanning tunneling microscope for the study of nanostructures on insulating substrates  

International Nuclear Information System (INIS)

The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies

146

Long-range Scanning Tunneling Microscope for the study of nanostructures on insulating substrates  

CERN Document Server

The Scanning Tunneling Microscope is a powerful tool for studying the electronic properties at the atomic level, however it's relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting on conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies.

Molina-Mendoza, Aday; Rubio-Bollinger, Gabino; Agraït, Nicolás

2013-01-01

147

Note: Long-range scanning tunneling microscope for the study of nanostructures on insulating substrates  

Energy Technology Data Exchange (ETDEWEB)

The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies.

Molina-Mendoza, Aday J., E-mail: aday.molina@uam.es [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Rodrigo, José G.; Rubio-Bollinger, Gabino [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Island, Joshua; Burzuri, Enrique; Zant, Herre S. J. van der [Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Agraït, Nicolás [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, E-28049 Madrid (Spain)

2014-02-15

148

Scanning Tunneling Microscope Nanolithography on SrRuO3 Thin Film Surfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nanoscale lithography on SrRuO3 (SRO) thin film surfaces has been performed by scanning tunneling microscopy under ambient conditions. The depth of etched lines increases with increasing bias voltage but it does not change significantly by increasing the tunneling current. The dependence of line width on bias voltage from experimental data is in agreement with theoretical calculation based on field-induced evaporation. Moreover, a three-square nanostructure was successfully ...

Liu, Yun; Zhang, Jia

2009-01-01

149

Scanning Tunnelling Spectroscopic Studies of Dirac Fermions in Graphene and Topological Insulators  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report novel properties derived from scanning tunnelling spectroscopic (STS) studies of Dirac fermions in graphene and the surface state (SS) of a strong topological insulator (STI), Bi2Se3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD), strain-induced scalar and gauge potentials are manifested by the charging effects and the tunnelling conductance peaks at quantized energies, respectively. Additionally, spontaneous time-reversal symmetry breaking is evidenced by ...

-l, Wang K.; -x, Xiu F.; He L.; Bockrath M. W.; Boyd D. A.; Chu H.; -p, Wu R. T.; Teague M. L.; -c, Yeh N.

2012-01-01

150

Spin-polarized scanning tunneling microscopy at the solid/liquid interface  

Science.gov (United States)

We show strong indications for spin-polarized tunneling between a magnetic tip of a scanning tunneling microscope and a magnetic substrate at a solid/liquid interface under electrochemical conditions at room temperature. As a model system Co islands of several 100 nm in diameter were electrochemically grown on Au(111). They show a perpendicular easy axis of the magnetization for two and three atomic layers of Co.

Majer, C.; Schindler, W.

2015-01-01

151

Three-dimensional scanning force/tunneling spectroscopy at room temperature  

International Nuclear Information System (INIS)

We simultaneously measured the force and tunneling current in three-dimensional (3D) space on the Si(111)-(7 × 7) surface using scanning force/tunneling microscopy at room temperature. The observables, the frequency shift and the time-averaged tunneling current were converted to the physical quantities of interest, i.e. the interaction force and the instantaneous tunneling current. Using the same tip, the local density of states (LDOS) was mapped on the same surface area at constant height by measuring the time-averaged tunneling current as a function of the bias voltage at every lateral position. LDOS images at negative sample voltages indicate that the tip apex is covered with Si atoms, which is consistent with the Si-Si covalent bonding mechanism for AFM imaging. A measurement technique for 3D force/current mapping and LDOS imaging on the equivalent surface area using the same tip was thus demonstrated. (paper)

152

Vacuum tunneling spectroscopy of superconducting Bi2Sr2CaCuO2O8 using scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

The authors report STM spectroscopy measurements of in-situ cleaved Bi2Sr2CaCu2O8 single crystals at 4.8 Kelvin, where they achieved strong evidences for true vacuum tunneling. These careful experiments result in very reproducible spectroscopy s a function of position on the surface, and as a function of tip/sample spacing. The characteristic features of the tunneling spectra are a significant filling of the gap region, a large density of states at the gap edges and a weak dip about 70meV below the Fermi level. Such IV characteristics are not compatible with a single gap BCS-like s-wave theory. Furthermore, they report spatially resolved spectroscopy where they, observe regions with two distinct gap values. A double gap structure appears in the tunneling spectra acquired in the vicinity of the boundary between these regions. They believe the double gap structure they observe in this case does not reflect an intrinsic gap anisotropy, but seems rather related to crystalline inhomogeneities. This demonstrates the potential of the STM's spatial resolution to shed some light on the controversy among the tunneling spectroscopy of high temperature superconductors published so far

153

Dopant enhanced etching of TiSe2 by scanning tunneling microscopy.  

Science.gov (United States)

The surfaces of pure and Mn doped TiSe(2) were etched using a scanning tunneling microscope. Both types of samples were found to etch easily when scanning was performed in ambient conditions. This process was enhanced at step edges or other surface defects. In pure samples, material was removed in a layer-by-layer fashion with a strong dependence on the scanning direction of the tip. Doped samples etched far more rapidly, to the point that stable scanning conditions were difficult to establish. Doped samples also showed a greater number of pits and other defects on their surface. A relatively small percentage of dopants was necessary to strongly impact the surface topography and stability. These results show that impurities can play a dominant role when using scanning tunneling microscopy to create surface nanostructures. PMID:20550168

Kidd, Timothy E; Gamb, Brett I; Skirtachenko, Polina I; Strauss, Laura H

2010-07-01

154

The Scanning Tunneling Microscope -- What it is and how it works...  

Science.gov (United States)

This site comes from the Institut für Angewandte Physik at the University of Wien shows how the scanning tunneling microscope (STM) works. An animated drawing shows the parts of a microscope produce the image. The site provides a link to a gallery of scanning tunneling microscope images. Additional links to other galleries involving physics are provided. Some of these include: dislocations, surface reconstructions, crystallography of iron films, chemical contrast in scanning tunneling microscope, adsorption and adsorbates, segregation of impurity atoms, growth of lead on copper, growth of copper in lead and electron waves and orbitals. Overall, this is a nice collection of resources for those interested in more advanced aspects of physics.

2009-12-10

155

Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy  

DEFF Research Database (Denmark)

This thesis is concerned with fundamental research into electronic and magnetic interaction on the nanoscale. From small metallic and magnetic islands and layers to single atoms. The research revolves around magnetic interaction probed through the spectroscopic capabilities of the scanning tunneling microscope (STM). Especially at low temperatures the Kondo resonance is used to probe magnetic interaction with ferromagnetic islands and between two atoms. The latter showing a crossover between Kondo screened atoms and antiferromagnetically coupled atoms close to the quantum critical point. This is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at low coverage the silver preferably nucleates on top of the bilayer high cobalt islands compared to directly on the Cu(111) substrate. Furthermore, the silver forms a combination of a reconstruction and a Moire pattern which is investigated with low-energy electron diraction and spectroscopic STM mapping at 6. The heterostructure is found to have very interesting electronic properties. The d-related state from the now buried cobalt island is visible through the silver capping layer, but the silver Moire pattern modulates the spin-polarized cobalt d-related state in amplitude, energy position and width. This is related to the d-band model for catalytic reactions. The largest change is in the amplitude of the state, however the "reversed" structure of cobalt on Ag(111) show similar properties, but with a large shift in energy instead of amplitude. The Kondo eect is used to probe magnetic interaction between the aforementioned silver-capped cobalt islands (and additionally gold-capped cobalt islands) and single cobalt atoms positioned on the Moire pattern. A split Kondo resonance due to the exchange interaction between the island and the atom is observed. In a more technical section of the thesis, it is shown how a gold-coated STM tip will make the tip apex susceptible to a single cobalt atom. The tip is indented either directly in a Au(111) surface or gold akes are picked up from cobalt islands on Cu(111). A change in the local barrier height (work function) of the tip-sample junction indicates that the apex is gold-coated and a single cobalt atom can be pickup up. The cobalt atom attached to the tip displays a Kondo resonance formed between the atom and the tip similar to the resonance displayed when the atom is on the surface with a clean tip. Here, this is used to show how a two-impurity Kondo system consisting of two cobalt atoms, one on the tip and one on the Au(111) sample, is undergoing a continuous crossover from Kondo screened atoms to antiferromagnetically coupled atoms when the atoms are moved from non-interacting to strongly interacting. In the Kondo screened regime, the Kondo temperature is believed to be constant, but the Fano line ii shape changes continuously from a dip to a peak. In the antiferromagnetic regime, inelastic spin-ip excitations reveal a splitting with a continuous increase in energy levels when pushing the atoms further together. This is supported by numerical renormalization group calculations. The crossover between the two regimes is furthermore interesting because it occurs in an area of the phase diagram close to the elusive quantum critical point, where the phase transition line meets absolute zero temperature. This freely positionable Kondo system on the tip represents a novel way to probe magnetic interaction with the possibility to continuously change the position of the probing Kondo system. The experiment is believed to be one of many applications possible and the method opens up for a new eld within STM. We expect that our work has direct impact in other research areas, such as for heavy fermion materials, a class of materials whose properties are governed by the competition between Kondo screening an

Bork, Jakob

2010-01-01

156

Scanning tunneling microscopy of initial nitridation processes on oxidized Si(100) surface with radical nitrogen  

CERN Document Server

We have investigated the initial nitridation processes on oxidized Si(100) with radical nitrogen at a substrate temperature of 850degC using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). It is found that the thin oxide layer suppresses the changes of original Si step structures during nitridation, and this effect critically depends on the growth conditions of the oxide layer. Comparison of the nitride island morphology to the case of the clean surface suggests that the migration of the precursor during nitridation is suppressed by the oxygen in the layer. (author)

Takahashi, R; Ikeda, H; Sakashita, M; Sakai, A; Yasuda, Y; Nakatsuka, O; Zaima, S

2003-01-01

157

Thin films of metal oxides on metal single crystals: Structure and growth by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Detailed studies of the growth and structure of thin films of metal oxides grown on metal single crystal surfaces using Scanning Tunneling Microscopy (STM) are presented. The oxide overlayer systems studied are iron oxide and titanium oxide on the Pt(III) surface. The complexity of the metal oxides and large lattice mismatches often lead to surface structures with large unit cells. These are particularly suited to a local real space technique such as scanning tunneling microscopy. In particular, the symmetry that is directly observed with the STM elucidates the relationship of the oxide overlayers to the substrate as well as distinguishing, the structures of different oxides.

Galloway, H.C.

1995-12-01

158

Thin films of metal oxides on metal single crystals: Structure and growth by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Detailed studies of the growth and structure of thin films of metal oxides grown on metal single crystal surfaces using Scanning Tunneling Microscopy (STM) are presented. The oxide overlayer systems studied are iron oxide and titanium oxide on the Pt(III) surface. The complexity of the metal oxides and large lattice mismatches often lead to surface structures with large unit cells. These are particularly suited to a local real space technique such as scanning tunneling microscopy. In particular, the symmetry that is directly observed with the STM elucidates the relationship of the oxide overlayers to the substrate as well as distinguishing, the structures of different oxides

159

Tunneling Current Spectra of a Metal Core/Semiconductor Shell Quantum Dot Molecule  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The transport properties of a metal core/semiconductor shell quantum dot molecule (QDM) embedded in a matrix connected to metallic electrodes are theoretically studied in the framework of Keldysh Green function technique. The effects of the electron plasmon interactions (EPIs) on the tunneling current spectra of QDM are examined. The energy levels of the QDs, intradot and interdot Coulomb interactions, electron interdot hopping strengths, and tunneling rates of QDs are renor...

Kuo, David M. -t

2013-01-01

160

Sub-barrier Coulomb effects on the interference pattern in tunneling ionization photoelectron spectra  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use a quantum trajectory-based semi-classical method to account for Coulomb interaction between the photoelectron and the parent ion in the classically forbidden, sub-barrier region during strong-field tunneling ionization processes. We show that---besides the well-known modification of the tunneling ionization probability---there is also an influence on the interference pattern in the photoelectron spectra. In the long-wavelength limit, the shift of the intra-cycle inter...

Yan, Tian-min; Bauer, D.

2012-01-01

 
 
 
 
161

Three-dimensional laser scanning for geometry documentation and construction management of highway tunnels during excavation.  

Science.gov (United States)

Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels. It provides a detailed overview of the static laser scanning method, its principles of operation and applications for tunnel construction operations. Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction. Specific case studies are considered based on two construction sites in Greece. Particularly, the potential of the method is examined for checking the tunnel profile, producing volume computations and validating the smoothness/thickness of shotcrete layers at an excavation stage and during the completion of excavation support and primary lining. An additional example of the use of the method in the geometric documentation of the concrete lining formwork is examined and comparisons against dimensional tolerances are examined. Experimental comparisons and analyses of the laser scanning method against conventional surveying techniques are also considered. PMID:23112655

Gikas, Vassilis

2012-01-01

162

Understanding the electroluminescence emitted by single molecules in scanning tunneling microscopy experiments  

Science.gov (United States)

We explore theoretically the electroluminescence of single molecules. We adopt a local-electrode framework that is appropriate for scanning tunneling microscopy (STM) experiments where electroluminescence originates from individual molecules of moderate size on complex substrates: Couplings between the STM tip and molecule and between the molecule and multiple substrate sites are treated on the same footing as local electrodes contacting the molecule. Electron flow is modeled with the Lippmann-Schwinger Green’s function scattering technique. The evolution of the electronic energy levels of the molecule under bias is modeled assuming the total charge of the molecule to be invariant, consistent with Coulomb blockade considerations, but the electronic occupations of the molecular highest occupied molecular orbital and lowest unoccupied molecular orbital levels vary with changing bias. The photon-emission rate is calculated using Fermi’s golden rule. We apply this theoretical approach to the STM/Zn-etioporphyrin/ Al2O3/NiAl(110) system and simulate various configurations of coupling strength between the molecule and substrate. We compare our results to the experimental observations of Qiu [Science 299, 542 (2003)] for this system and find that our model provides a comprehensive explanation of a multitude of previously unexplained observations. These include the different types of current-voltage characteristics (CVCs) that are observed experimentally, the observed association of electroluminescence with some CVCs and not others, and key properties of the observed photon spectra. Theoretical predictions are presented for further single-molecule electroluminescence experiments.

Buker, John; Kirczenow, George

2008-09-01

163

Fabrication of tungsten tip for scanning tunneling microscope by the lever principle  

International Nuclear Information System (INIS)

A novel experimental setup was designed to fabricate tungsten tips for scanning tunneling microscope (STM), based on simple mechanical lever principle. The equipment can quickly separate the tip from electrolyte to avoid the further etching of the fine-shaped tungsten tip. The setup is advantageous for its simplicity over complex electronic control systems. The use result in scanning electron microscope demonstrates that the radius of the tip can reach 50 nm. The tip was applied to scan the surface of highly-oriented pyrolytic graphite, and the results were satisfactory. It is shown that the tip can be used for the scanning of atomically resolved images. (authors)

164

Tunneling spectra for ($d_{x^2-y^2}+is$)-wave superconductors versus tunneling spectra for ($d_{x^2-y^2}+id_{xy}$)-wave superconductors  

CERN Document Server

The tunneling conductance spectra of a normal metal / insulator / singlet superconductor is calculated from the reflection amplitudes using the Blonder-Tinkham-Klapwijk (BTK) formulation. The pairing symmetry of the superconductor is assumed to be $d_{x^2-y^2}+is$, or $d_{x^2-y^2}+id_{xy}$. It is found that in the ($d_{x^2-y^2}+is$)-wave case there is a well defined conductance peak in the conductance spectra, in the amplitude of the secondary s-wave component. In the ($d_{x^2-y^2}+id_{xy}$)-wave case the tunneling conductance has residual values within the gap, due to the formation of bound states. The bound state energies depend on the angle of the incident quasiparticles, and also on the boundary orientation. On the basis of this observation an electron focusing experiment is proposed to probe the ($d_{x^2-y^2}+id_{xy}$)-wave state.

Stefanakis, N

2001-01-01

165

New design of a variable-temperature ultrahigh vacuum scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the design of a variable-temperature ultrahigh vacuum (UHV) scanning tunneling microscope which can be operated between 20 and 400 K. The microscope is mounted directly onto the heat exchanger of a He continuous flow cryostat without vibration isolation inside the UHV chamber. The coarse approach is performed with an inertial slider driven by the same piezo tube that is also used for scanning. The performance of the instrument is demonstrated by two different kinds of measurements:...

Mugele, F.; Rettenberger, A.; Boneberg, J.; Leiderer, P.

1998-01-01

166

Methyl group rotational tunneling in vibrational spectra of crystals at low temperatures  

Science.gov (United States)

The effect of methyl group nuclear spin conversion on the Raman spectra is reported for two crystals: 2,6-dibromomesitylene and 4-methylpyridine (4MP). In both crystals the tunneling splitting is large and population changes of the tunneling sublevels upon cooling to 4.2 K are easily observable as changes of intensity and lineshape in the Raman spectra of the CH 3 torsional modes and of modes coupled to these. The spin conversion time at 4.2 K is 350±30 min for DBM and 170±20 min for 4MP. The intensity ratio of the lowest frequency Raman transitions of the two spin isomers is determined.

Plazanet, M.; Neumann, M. A.; Trommsdorff, H. P.

2000-04-01

167

First-principles theory of inelastic currents in a scanning tunneling microscope  

DEFF Research Database (Denmark)

A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent experimental data. [S0163-1829(98)09036-5].

Stokbro, Kurt; Hu, Ben Yu-Kuang

1998-01-01

168

Transient measurements with an ultrafast scanning tunneling microscope on semiconductor surfaces  

DEFF Research Database (Denmark)

We demonstrate: the use of an ultrafast scanning tunneling microscope on a semiconductor surface. Laser-induced transient signals with 1.8 ps rise time are detected, The investigated sample is a low-temperature grown GaAs layer plated on a sapphire substrate with a thin gold layer that serves as st bias contact, For comparison, the measurements are performed with the tip in contact to the sample as well as in tunneling above the surface, In contact and under bias, the transient signals are identified as a transient photocurrent, An additional signal is generated by a transient voltage induced by the nonuniform carrier density created by the absorption of the light (photo Dember effect). The transient depends in sign and in shape on the direction of optical excitation. This signal is the dominating transient in tunneling mode. The signals are explained by a capacitive coupling across the tunneling gap, (C) 1998 American Institute of Physics.

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

169

Light amplification by stimulated emission from an optically pumped molecular junction in a scanning tunneling microscope  

CERN Document Server

Here, we introduce and experimentally demonstrate optical amplification and stimulated emission from a single optically pumped molecular tunneling junction of a scanning tunneling microscope. The gap between a sharp gold tip and a flat gold substrate covered with a self-assembled monolayer of 5-chloro-2-mercaptobenzothiazole molecules forms an extremely small optical gain medium. When electrons tunnel from the molecules highest occupied molecular orbital to the tip, holes are left behind. These can be repopulated by hot electrons induced by the laser-driven plasmon oscillation on the metal surfaces enclosing the cavity. Solving the laser-rate equations for this system shows that the repopulation process can be efficiently stimulated by the gap modes near field, TERS scattering from neighboring molecules acting as an optical seed. Our results demonstrate how optical enhancement inside the plasmonic cavity can be further increased by a stronger localization via tunneling through molecules. We anticipate that st...

Braun, K; Wang, X; Adler, H; Peisert, H; Chasse, T; Zhang, D; Meixner, A J

2013-01-01

170

Electronic structure of single DNA molecules resolved by transverse scanning tunnelling spectroscopy  

Science.gov (United States)

Attempts to resolve the energy-level structure of single DNA molecules by scanning tunnelling spectroscopy span over the past two decades, owing to the unique ability of this technique to probe the local density of states of objects deposited on a surface. Nevertheless, success was hindered by extreme technical difficulties in stable deposition and reproducibility. Here, by using scanning tunnelling spectroscopy at cryogenic temperature, we disclose the energy spectrum of poly(G)-poly(C) DNA molecules deposited on gold. The tunnelling current-voltage (I-V) characteristics and their derivative (dI/dV-V) curves at 78K exhibit a clear gap and a peak structure around the gap. Limited fluctuations in the I-V curves are observed and statistically characterized. By means of ab initio density functional theory calculations, the character of the observed peaks is generally assigned to groups of orbitals originating from the different molecular components, namely the nucleobases, the backbone and the counterions.

Shapir, Errez; Cohen, Hezy; Calzolari, Arrigo; Cavazzoni, Carlo; Ryndyk, Dmitry A.; Cuniberti, Gianaurelio; Kotlyar, Alexander; di Felice, Rosa; Porath, Danny

2008-01-01

171

Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces  

Science.gov (United States)

In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively.

Münnich, Gerhard; Donarini, Andrea; Wenderoth, Martin; Repp, Jascha

2013-11-01

172

Scanning Tunneling Microscopy Studies of Topological Insulators Grown by Molecular Beam Epitaxy  

Directory of Open Access Journals (Sweden)

Full Text Available We summarize our recent scanning tunneling microscopy (STM study of topological insulator thin films grown by molecular beam epitaxy (MBE, which includes the observation of electron standing waves on topological insulator surface and the Landau quantization of topological surface states. The work has provided valuable information to the understanding of intriguing properties of topological insulators, as predicted by theory.

Xue Qikun

2012-03-01

173

Local investigation of magnetic structures in superconductors by a low-temperature scanning tunneling microscope  

International Nuclear Information System (INIS)

A low temperature scanning tunneling microscope device was constructed which allows a simultaneous spectroscopic and morphological measurement up to 4.2 K and 1T. Layers of niobium and NbSe2 were measured and flux lines were determined. (WL)

174

Surface x-ray scattering and scanning tunneling microscopy studies at the Au(111) electrode  

International Nuclear Information System (INIS)

This chapter reviews Surface X-ray Scattering and Scanning Tunneling Microscopy results carried out at the Au(111) surface under electrochemical conditions. Results are presented for the reconstructed surface, and for bromide and thallium monolayers. These examples are used to illustrate the complementary nature of the techniques

175

Partial sequencing of a single DNA molecule with a scanning tunnelling microscope  

Science.gov (United States)

The scanning tunnelling microscope is capable of the real-space imaging and spectroscopy of molecules on an atomic scale. Numerous attempts have been made to use the scanning tunnelling microscope to sequence single DNA molecules, but difficulties in preparing samples of long-chain DNA molecules on surfaces, and problems in reproducing results have limited these experiments. Here, we report single-molecule DNA sequencing with a scanning tunnelling microscope by using an oblique pulse-injection method to deposit the molecules onto a copper surface. First, we show that guanine bases have a distinct electronic state that allows them to be distinguished from the other nucleic acid bases. Then, by comparing data on M13mp18, a single-stranded phage DNA, with a known base sequence, the `electronic fingerprint' of guanine bases in the DNA molecule is identified. These results show that it is possible to sequence individual guanine bases in real long-chain DNA molecules with high-resolution scanning tunnelling microscope imaging and spectroscopy.

Tanaka, Hiroyuki; Kawai, Tomoji

2009-08-01

176

Streamlined Inexpensive Integration of a Growth Facility and Scanning Tunneling Microscope for in situ Characterization  

CERN Document Server

The integration of a scanning tunneling microscope chamber with a sample growth facility using non-custom, commercially available parts is described. The facility also features a newly-designed magnetic wobble stick to increase the reliability of sample transfer in a cost-effective manner.

Xu, P; Barber, S D; Cook, C T; Ackerman, M L; Thibado, P M

2015-01-01

177

Preparation of Chemically Etched Tips for Ambient Instructional Scanning Tunneling Microscopy  

Science.gov (United States)

A first-year laboratory experiment that utilizes concepts of electrochemical tip etching for scanning tunneling microscopy (STM) is described. This experiment can be used in conjunction with any STM experiment. Students electrochemically etch gold STM tips using a time-efficient method, which can then be used in an instructional grade STM that…

Zaccardi, Margot J.; Winkelmann, Kurt; Olson, Joel A.

2010-01-01

178

Local crystallography analysis for atomically resolved scanning tunneling microscopy images  

International Nuclear Information System (INIS)

Scanning probe microscopy has emerged as a powerful and flexible tool for atomically resolved imaging of surface structures. However, due to the amount of information extracted, in many cases the interpretation of such data is limited to being qualitative and semi-quantitative in nature. At the same time, much can be learned from local atom parameters, such as distances and angles, that can be analyzed and interpreted as variations of local chemical bonding, or order parameter fields. Here, we demonstrate an iterative algorithm for indexing and determining atomic positions that allows the analysis of inhomogeneous surfaces. This approach is further illustrated by local crystallographic analysis of several real surfaces, including highly ordered pyrolytic graphite and an Fe-based superconductor FeTe0.55Se0.45. This study provides a new pathway to extract and quantify local properties for scanning probe microscopy images. (paper)

179

Effects of intermolecular interaction on inelastic electron tunneling spectra  

Science.gov (United States)

We have examined the effects of intermolecular interactions on the inelastic electron tunneling spectroscopy (IETS) of model systems: a pair of benzenethiol or a pair of benzenedithiol sandwiched between gold electrodes. The dependence of the IETS on the mutual position of and distance between the paired molecules has been predicted and discussed in detailed. It is shown that, although in most cases, there are clear spectral fingerprints present which allow identification of the actual structures of the molecules inside the junction. Caution must be exercised since some characteristic lines can disappear at certain symmetries. The importance of theoretical simulation is emphasized.

Kula, Mathias; Luo, Yi

2008-02-01

180

Electronic structure and tunneling resonance spectra of nanoscopic aluminum islands  

CERN Document Server

The electronic structure of nanoscopic oxide-coated aluminum islands is investigated using a tight-binding model that incorporates the geometry, chemistry and disorder of the particle. The oxide coat is found to significantly increase the volume accessible to electrons at the Fermi level. The level statistics agree with random matrix theory predictions. States near the Fermi level show pronounced clustering regardless of disorder. It is suggested that the observed clusters of tunneling resonances may have a more complex origin than if they were solely due to many-body non-equilibrium effects.

Narvaez, G A; Narvaez, Gustavo A.; Kirczenow, George

2002-01-01

 
 
 
 
181

Scanning tunneling microscopy and spectroscopy of pn junctions formed by ion implantation  

International Nuclear Information System (INIS)

In this paper the results of an investigation into the use of scanning tunneling microscopy (STM) to delineate pn junctions are presented. Results of scanning tunneling spectroscopy measurements of left-angle 100 right-angle n- and p-type silicon are reported. Measurements were made in air on surfaces with a native oxide. Different I/V characteristics were observed for differently doped samples, indicating that the surfaces were unpinned. Images are presented of pn junctions formed by the implantation of phosphorus into boron doped Si wafers. The pn junction, or the boundary between implant and substrate regions, was observed in both constant current and constant height scans. The junction was imaged with 125 angstrom point-to-point resolution

182

Defects, Tunneling, and EPR Spectra of Single-Molecule Magnets  

CERN Document Server

We examine theoretically electron paramagnetic resonance (EPR) lineshapes as functions of resonance frequency, energy level, and temperature for single crystals of three different kinds of single-molecule nanomagnets (SMMs): Mn$_{12}$ acetate, Fe$_8$Br, and the $S=9/2$ Mn$_4$ compound. We use a density-matrix equation and consider distributions in the uniaxial (second-order) anisotropy parameter $D$ and the $g$ factor, caused by possible defects in the samples. Additionally, weak intermolecular exchange and electronic dipole interactions are included in a mean-field approximation. Our calculated linewidths are in good agreement with experiments. We find that the distribution in $D$ is common to the three examined single-molecule magnets. This could provide a basis for a proposed tunneling mechanism due to lattice defects or imperfections. We also find that weak intermolecular exchange and dipolar interactions are mainly responsible for the temperature dependence of the lineshapes for all three SMMs, and that ...

Park, K; Dalal, N S; Hill, S; Rikvold, P A; Bhaduri, S; Christou, G; Hendrickson, D N; Park, Kyungwha

2003-01-01

183

Direct probing of the stacking order and electronic spectrum of rhombohedral trilayer graphene with scanning tunneling microscopy  

Science.gov (United States)

Recently, rhombohedral trilayer graphene (r-TLG) has attracted much attention because of its low-energy flat bands, which are predicted to result in many strongly correlated phenomena. However, there has been a need for more experimental evidence for these flat bands in the r-TLG, since the supporting substrates usually have strong destructive effects on the low-energy band structure of graphene systems. Here, we demonstrate that it is possible to directly probe the stacking order and electronic spectrum of the r-TLG on a graphite surface with scanning tunneling microscopy around a monoatomic step edge of the top graphene layer. The tunneling spectra of the r-TLG exhibit four adjacent peaks, which are generated by the low-energy flat bands, flanking the charge neutrality point. Based on these spectra, the true energy gap and the energy gap at the K point of the r-TLG are determined as about 9 and 23 meV, respectively. The observed features are well reproduced by a low-energy effective Hamiltonian.

Xu, Rui; Yin, Long-Jing; Qiao, Jia-Bin; Bai, Ke-Ke; Nie, Jia-Cai; He, Lin

2015-01-01

184

Superconducting LiFeAs as seen by scanning tunneling microscopy/spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Among the entire class of iron-based superconductors the material LiFeAs is of particular interest since an absence of nesting between electron and hole pockets suggests an unconventional type of pairing in this material. Using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS) we investigate topographic properties of the surface as well as the temperature dependency of the superconducting gap. The good agreement of our results with model calculations for the tunnelling conductance allows us to draw conclusions about the low energy properties of the superconducting system. Furthermore, we compare our results with Transport- and NMR-measurements.

Pohle, Rico; Scheffler, Martha; Schlegel, Ronny; Haenke, Torben; Baumann, Danny; Bachmann, Anne; Bombor, Dirk; Sykora, Steffen; Harnagea, Luminita; Wurmehl, Sabine; Hess, Christian; Buechner, Bernd [Institut fuer Festkoerperforschung IFW Dresden (Germany)

2012-07-01

185

Note: optical optimization for ultrasensitive photon mapping with submolecular resolution by scanning tunneling microscope induced luminescence.  

Science.gov (United States)

We report the development of a custom scanning tunneling microscope equipped with photon collection and detection systems. The optical optimization includes the comprehensive design of aspherical lens for light collimation and condensing, the sophisticated piezo stages for in situ lens adjustment inside ultrahigh vacuum, and the fiber-free coupling of collected photons directly onto the ultrasensitive single-photon detectors. We also demonstrate submolecular photon mapping for the molecular islands of porphyrin on Ag(111) under small tunneling currents down to 10 pA and short exposure time down to 1.2 ms/pixel. A high quantum efficiency up to 10(-2) was also observed. PMID:23822393

Chen, L G; Zhang, C; Zhang, R; Zhang, X L; Dong, Z C

2013-06-01

186

Single atom extraction by scanning tunneling microscope tip-crash and nanoscale surface engineering  

CERN Document Server

We report a novel atom extraction mechanism from the native substrate by means of a scanning tunneling microscope tip-crash on a Ag(111) surface at 5 K. Individual atoms are scattered on the surface when a silver coated tip is dipped into the substrate at low tunneling biases. Quantitative analyses reveal that the mechanical energy supplied by the tip-crash dominates the atom extraction process. Application of this procedure is demonstrated by constructing quantum structures using the extracted atoms on an atom-by-atom basis.

Hla, S W; Iancu, V; Deshpande, Abhay A; Hla, Saw Wai; Braun, Kai-Felix; Iancu, Violeta; Deshpande, Aparna

2004-01-01

187

Scanning tunneling microscopy characterization of potential molecules for implementing molecular-quantum-dot cellular automata  

Science.gov (United States)

Quantum-dot cellular automata (QCA) which is a transistorless paradigm for fabricating computational hardware has gained considerable attention since cells, wires, and majority gates (made using metal dots connected by tunnel junctions) have all been experimentally demonstrated. To explore the additional advantages of the QCA paradigm, a molecular scale implementation is pursued. Two viable candidates (Si-phthalocyanine and ruthenium complexes) for the molecular QCA approach have been examined carefully using UHV-scanning tunneling microscopy and spectroscopy. These results as well as data obtained by ellipsometry, x-ray photoelectron spectroscopy, and cyclic voltammetry will be discussed in this talk.

Peiris, Frank; Snider, Gregory; Li, Zhiyong; Chellamma, Sudha; Varughese, Bindhu; Lieberman, Marya

2001-03-01

188

Field-Induced Deformation as a Mechanism for Scanning Tunneling Microscopy Based Nanofabrication  

DEFF Research Database (Denmark)

The voltage between tip and sample in a scanning tunneling microscope (STM) results in a large electric field localized near the tip apex. The mechanical stress due to this field can cause appreciable deformation of both tip and sample on the scale of the tunnel gap. We derive an approximate analytical expression for this deformation and confirm the validity of the result by comparison with a finite element analysis. We derive the condition for a field-induced jump to contact of tip and sample and show that this agrees well with experimental results for material transfer between tip and sample by voltage pulsing in ultrahigh vacuum.

Hansen, Ole; Ravnkilde, Jan Tue

1998-01-01

189

EDITORIAL: Three decades of scanning tunnelling microscopy that changed the course of surface science Three decades of scanning tunnelling microscopy that changed the course of surface science  

Science.gov (United States)

Three decades ago, with a tiny tip of platinum, the scientific world saw the real space imaging of single atoms with unprecedented spatial resolution. This signalled the birth of one of the most versatile surface probes, based on the physics of quantum mechanical tunnelling: the scanning tunnelling microscope (STM). Invented in 1981 by Gerd Binnig and Heinrich Rohrer of IBM, Zurich, it led to their award of the 1986 Nobel Prize. Atoms, once speculated to be abstract entities used by theoreticians for mere calculations, can be seen to exist for real with the nano-eye of an STM tip that also gives real-space images of molecules and adsorbed complexes on surfaces. From a very fundamental perspective, the STM changed the course of surface science and engineering. STM also emerged as a powerful tool to study various fundamental phenomena relevant to the properties of surfaces in technological applications such as tribology, medical implants, catalysis, sensors and biology—besides elucidating the importance of local bonding geometries and defects, non-periodic structures and the co-existence of nano-scale phases. Atom-level probing, once considered a dream, has seen the light with the evolution of STM. An important off-shoot of STM was the atomic force microscope (AFM) for surface mapping of insulating samples. Then followed the development of a flurry of techniques under the general name of scanning probe microscopy (SPM). These techniques (STM, AFM, MFM, PFM etc) designed for atomic-scale-resolution imaging and spectroscopy, have led to brand new developments in surface analysis. All of these novel methods enabled researchers in recent years to image and analyse complex surfaces on microscopic and nanoscopic scales. All of them utilize a small probe for sensing the surface. The invention of AFM by Gerd Binnig, Calvin Quate and Christopher Gerber opened up new opportunities for characterization of a variety of materials, and various industrial applications could be envisaged. AFM observations of thin-film surfaces give us a picture of surface topography and morphology and any visible defects. The growing importance of ultra-thin films for magnetic recording in hard disk drive systems requires an in-depth understanding of the fundamental mechanisms occurring during growth. This special issue of Journal of Physics D: Applied Physics covers all of the different aspects of SPM that illustrate the achievements of this methodology: nanoscale imaging and mapping (Chiang, and Douillard and Charra), piezoresponse force microscopy (Soergel) and STM engineering (Okuyama and Hamada, and Huang et al). Chiang takes the reader on a journey along the STM imaging of atoms and molecules on surfaces. Jesse and Kalinin explore the band excitations that occur during the corresponding processes. Jia et al propose STM and molecular beam epitaxy as a winning experimental combination at the interface of science and technology. Douillard and Charra describe the high-resolution mapping of plasmonic modes using photoemission and scanning tunnelling microscopy. Cricenti et al demonstrate the importance of SPM in material science and biology. Wiebe et al have probed atomic scale magnetism, revealed by spin polarized scanning tunnelling microscopy. In addition, Simon et al present Fourier transform scanning tunnelling spectroscopy and the possibility to obtain constant energy maps and band dispersion using local measurements. Lackinger and Heckl give a perspective of the use of STM to study covalent intermolecular coupling reactions on surfaces. Okuyama and Hamada investigated hydrogen bond imaging and engineering with STM. Soergel describes the study of substrate-dependent self-assembled CuPc molecules using piezo force microscope (PFM). We are very grateful to the authors and reviewers for the papers in this special issue of Journal of Physics D: Applied Physics. Their contributions have provided a comprehensive picture of the evolution, status and potential of scanning probe microscopy, conveying to the readers the full excitement of this forefront do

Ramachandra Rao, M. S.; Margaritondo, Giorgio

2011-11-01

190

Electronic structure and electron-phonon coupling in carbon diamondoids studied by scanning tunneling microscopy  

Science.gov (United States)

Diamondoids are hydrocarbon molecules with diamond-like cage structures. Their structural complexity and chemical bond tunability make them ideal building blocks for creating novel nanostructures. We have used cryogenic scanning tunneling spectroscopy to examine the electronic structure of individual diamondoid molecules on the Au(111) surface. We observed variations in the filled and empty state local density of states for individual 121-tetramer diamondoid molecule. Despite a large HOMO-LUMO gap (? > 5eV) around the Fermi energy, there exists a strong interaction between the tunneling electrons and the diamondoid C-H stretch mode, as revealed by inelastic tunneling spectroscopy (IETS). We further show that the strength of the electron-phonon coupling has a distinct spatial distribution with the dominant inelastic channel localized to a specific region of the diamondoid molecule.

Wang, Yayu; Lu, X. H.; Yamachika, R.; Wachowiak, A.; Kioupakis, E. S.; Louie, S. G.; Crommie, M. F.; Dahl, J. E.; Liu, S. G.; Carlson, R. M. K.

2006-03-01

191

A compact atomic force-scanning tunneling microscope for studying microelectronics and environmental aerosols  

International Nuclear Information System (INIS)

This dissertation describes the characteristics and the construction of a compact atomic force/scanning tunneling microscope (AFM/STM). The basics and the method of preparing a tunneling junction between a chemically etched tunneling tip and a micro-manufactured cantilever is outlined by analyzing the forces between tunneling tip and cantilever as well as between force-sensing tip and sample surfaces. To our best knowledge this instrument is the first one using a commercial cantilever with only one piezoelectric tube carrying the whole tunneling sensor. The feedback control system has been optimized after a careful analysis of the electronic loop characteristics. The mode of operation has been determined by analyzing the dynamic characteristics of the scan heads and by investigating the time characteristics of the data acquisition system. The vibration isolation system has been calibrated by analyzing the characteristics of the damping setup and the stiffness of the scan head. The calculated results agree well with the measured ones. Also, a software package for data acquisition and real time display as well as for image processing and three-dimensional visualization has been developed. With this home-made software package, the images can be processed by means of a convolution filter, a Wiener filter and other 2-D FFT filters, and can be displayed in different ways. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) and graphite surfaces have been oe (HOPG) and graphite surfaces have been obtained in AFM and STM mode. New theoretical explanations have been given for the observed anomalous STM and AFM images of graphite by calculating the asymmetric distribution of quantum conductance and tip-surface forces on a graphite surface. This not only resolved the theoretical puzzles of STM and AFM of graphite, but also revealed the relation between atomic force microscopy and scanning tunneling microscopy of graphite. Applications of STM and AFM to micro-electronic devices have been investigated by imaging ion-etched silicon surfaces and oxidized silicon surfaces. Tip artifacts and the vertical hysteresis of STM images of surfaces with deep grooves have been investigated and proved to be dependent not only on the shape of the tips but also on the noise of the detection system and the characteristics of the feedback circuit. Moreover, aerosol particles have been studied with this instrument. To our best knowledge, this is the first application of tunneling controlled AFM on environmental aerosol samples. (author)

192

Point contact tunnelling studies on ceramic YBCO with scanning tunnelling microscope tips  

International Nuclear Information System (INIS)

A detailed study of point contact tunneling into ceramic YBCO with electrochemically ectched tips of Pt, Nb and W is reported. The superconducting gap parameter (?) has been extracted from I-V and dI/dV-V curves using various procedures. The results indicate a gap value of about 20 meV. It is observed that the zero bias conductance is strongly dependent on the junction resistance. The normal state conductance varies linearly with bias voltage and the conductance curves are asymmetric with respect to polarity of the bias voltage. With contacts of very high junction resistance, it is observed that G(0)/G(100 mV) has a value as low as 1/6. This may be the lowest value reported so far. (author). 17 refs., 10 figs

193

Highly reproducible low temperature scanning tunneling microscopy and spectroscopy with in situ prepared tips.  

Science.gov (United States)

An in situ tip preparation procedure compatible with ultra-low temperature and high magnetic field scanning tunneling microscopes is presented. This procedure does not require additional preparation techniques such as thermal annealing or ion milling. It relies on the local electric-field-induced deposition of material from the tip onto the studied surface. Subsequently, repeated indentations are performed onto the sputtered cluster to mechanically anneal the tip apex and thus to ensure the stability of the tip. The efficiency of this method is confirmed by comparing the topography and spectroscopy data acquired with either unprepared or in situ prepared tips on epitaxial graphene grown on Ru (0001). We demonstrate that the use of in situ prepared tips increases the stability of the scanning tunneling images and the reproducibility of the spectroscopic measurements. PMID:22955323

Castellanos-Gomez, Andres; Rubio-Bollinger, Gabino; Garnica, Manuela; Barja, Sara; Vázquez de Parga, Amadeo L; Miranda, Rodolfo; Agraït, Nicolás

2012-11-01

194

Nanolithography on graphene by using scanning tunneling microscopy in a methanol environment.  

Science.gov (United States)

Since it was discovered in 2004, graphene has attracted enormous attention as an emerging material for future devices, but it has been found that conventional lithographic processes based on polymer resist degrade its intrinsic performance. Recently, our group studied a resist-free scanning tunneling microscopy-based lithography in various atmospheres by injecting volatile liquids into a chamber. In this study, multilayer graphene was scanned and etched by controlling bias voltage under methanol pressure. We focused on improving patterning results in terms of depth and line width, while the previous study was performed to find an optimum gas environment for patterning on a graphite surface. Specifically, we report patterning outputs depending on conditions of voltage, current, and pressure. The optimum conditions for methanol environment etching were a gas pressure in the range of 41-50 torr, a -4 V tip bias, and a 2 nA tunneling current. PMID:24016389

Kim, Chulsu; Park, Joonkyu; Seo, Yongho; Ahn, Jinho; Park, In-Sung

2013-12-01

195

Radio frequency scanning tunneling spectroscopy for single-molecule spin resonance.  

Science.gov (United States)

We probe nuclear and electron spins in a single molecule even beyond the electromagnetic dipole selection rules, at readily accessible magnetic fields (few mT) and temperatures (5 K) by resonant radio-frequency current from a scanning tunneling microscope. We achieve subnanometer spatial resolution combined with single-spin sensitivity, representing a 10 orders of magnitude improvement compared to existing magnetic resonance techniques. We demonstrate the successful resonant spectroscopy of the complete manifold of nuclear and electronic magnetic transitions of up to ?I(z)=±3 and ?J(z)=±12 of single quantum spins in a single molecule. Our method of resonant radio-frequency scanning tunneling spectroscopy offers, atom-by-atom, unprecedented analytical power and spin control with an impact on diverse fields of nanoscience and nanotechnology. PMID:25302884

Müllegger, Stefan; Tebi, Stefano; Das, Amal K; Schöfberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

2014-09-26

196

Radio Frequency Scanning Tunneling Spectroscopy for Single-Molecule Spin Resonance  

Science.gov (United States)

We probe nuclear and electron spins in a single molecule even beyond the electromagnetic dipole selection rules, at readily accessible magnetic fields (few mT) and temperatures (5 K) by resonant radio-frequency current from a scanning tunneling microscope. We achieve subnanometer spatial resolution combined with single-spin sensitivity, representing a 10 orders of magnitude improvement compared to existing magnetic resonance techniques. We demonstrate the successful resonant spectroscopy of the complete manifold of nuclear and electronic magnetic transitions of up to ?Iz=±3 and ?Jz=±12 of single quantum spins in a single molecule. Our method of resonant radio-frequency scanning tunneling spectroscopy offers, atom-by-atom, unprecedented analytical power and spin control with an impact on diverse fields of nanoscience and nanotechnology.

Müllegger, Stefan; Tebi, Stefano; Das, Amal K.; Schöfberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

2014-09-01

197

Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs  

DEFF Research Database (Denmark)

We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers of nanocrystals. STS measurements showed rectifying behaviour, with high currents at the opposite sample bias to that previously observed for CdSe nanocrystals adsorbed on Si substrates. We explain the rectifying behaviour by considering the interaction between the electronic states of the nanocrystals and the bands in the substrate which are bent under the influence of the strong electric field between the closely separated semiconductor substrate and STM tip. The polarity of the forward bias direction is determined by the alignment of the CdSe electronic states with the semiconductor bands. (C) 2003 Elsevier Science B.V. All rights reserved.

Walzer, K.; Marx, E.

2003-01-01

198

Highly reproducible low temperature scanning tunnelling microscopy and spectroscopy with in situ prepared tips  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An in situ tip preparation procedure compatible with ultra-low temperature and high magnetic field scanning tunneling microscopes is presented. This procedure does not require additional preparation techniques such as thermal annealing or ion milling. It relies on the local electric-field-induced deposition of material from the tip onto the studied surface. Subsequently, repeated indentations are performed onto the sputtered cluster to mechanically anneal the tip apex and th...

Castellanos-gomez, Andres; Rubio-bollinger, Gabino; Garnica, Manuela; Barja, Sara; Parga, Amadeo L. Va?zquez; Miranda, Rodolfo; Agrai?t, Nicola?s

2012-01-01

199

Structure of YSi2 nanowires from scanning tunneling spectroscopy and first principles  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Exceptionally long and uniform YSi2 nanowires are formed via self-assembly on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a class of nanowires that violates the “odd multiple” rule. The structure of the thinnest wire in this category is determined by comparing scanning tunneling spectroscopy measurements with the calculated surface density of states of candidate models by means of the Pendry...

Iancu, V.; Kent, P. R. C.; Zeng, C. G.; Weitering, H. H.

2009-01-01

200

Assessment of Scanning Tunneling Spectroscopy Modes Inspecting Electron Confinement in Surface-Confined Supramolecular Networks  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling spectroscopy (STS) enables the local, energy-resolved investigation of a samples surface density of states (DOS) by measuring the differential conductance (dI/dV) being approximately proportional to the DOS. It is popular to examine the electronic structure of elementary samples by acquiring dI/dV maps under constant current conditions. Here we demonstrate the intricacy of STS mapping of samples exhibiting a strong corrugation originating from electronic density and local w...

Krenner, Wolfgang; Ku?hne, Dirk; Klappenberger, Florian; Barth, Johannes V.

2013-01-01

 
 
 
 
201

Charge-density-wave origin of cuprate checkerboard visualized by scanning tunnelling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

One of the main challenges in understanding high-Tc superconductivity is to disentangle the rich variety of states of matter that may coexist, cooperate or compete with d-wave superconductivity. At centre stage is the pseudogap phase, which occupies a large portion of the cuprate phase diagram surrounding the superconducting dome1. Using scanning tunnelling microscopy, we find that a static, non-dispersive, 'checkerboard'-like electronic modulation exists in a broad regime of the cuprate phas...

Wise, W. D.; Boyer, Michael C.; Chatterjee, Kamalesh; Kondo, Takeshi; Takeuchi, T.; Ikuta, H.; Wang, Yayu; Hudson, Eric

2008-01-01

202

Tip preparation for usage in an ultra-low temperature UHV scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work deals with the preparation and characterization of tungsten tips for the use in UHV low-temperature scanning tunneling microscopy and spectroscopy (STM and STS, respectively). These specific environments require in situ facilities for tip conditioning, for further sharpening of the tips, as well as for reliable tip characterization. The implemented conditioning methods include direct resistive annealing, annealing by electron bombardment, and self-sputtering with noble gas ions. Mor...

S Ernst, S. Wirth

2007-01-01

203

Scanning tunnelling microscopy study of phosphorus dopants on the Si(001)2x1 surface  

International Nuclear Information System (INIS)

Full text: We report an atomic resolution scanning tunnelling microscopy study of phosphorus dopant surface segregation on the silicon (001)2x1 surface. An understanding of the surface segregation of dopants in Si is of fundamental interest and technological importance for the fabrication of a P in Si based quantum computer. Although there are a number of studies of surface segregation of boron in Si, a detailed study of P segregation has not yet been reported

204

A theoretical model for single-molecule incoherent scanning tunneling spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Single-molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Huckel theory (EHT)-based mean-field non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effect of the temperatu...

Raza, H.

2008-01-01

205

HIGH RESOLUTION ELECTRON BEAM INJECTION IN SEMICONDUCTORS USING A SCANNING TUNNELING MICROSCOPE  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The tip of a scanning tunneling microscope is used as a source of ultralow-energy electrons to excite luminescence in model AlGaAs/GaAs(001) heterostructures. This beam injection technique has the advantage of providing a nanometer-sized charge generation volume. We demonstrate the application of this technique to determine minority charge carrier transport parameters such as the thermalization length of hot electrons and the diffusion length of minority electrons.

Alvarado, S.; Renaud, Ph; Meier, H.

1991-01-01

206

Determination of relative binding affinities of labeling molecules with amino acids by using scanning tunneling microscopy.  

Science.gov (United States)

The binding behaviour of labeling molecule copper phthalocyanine tetrasulfonate sodium (PcCu(SO(3)Na)(4)) on the assemblies of representative polyamino acids has been studied by using scanning tunneling microscopy (STM). By directly visualizing the adsorption and distribution of the labeling species on the peptide assemblies in STM images, one could obtain relative binding affinities of the labeling molecule with different amino acid residues. PMID:21869951

Wang, Chenxuan; Mao, Xiaobo; Yang, Aihua; Niu, Lin; Wang, Shengnan; Li, Denghua; Guo, Yuanyuan; Wang, Yibing; Yang, Yanlian; Wang, Chen

2011-10-14

207

The tip-sample water bridge and light emission from scanning tunnelling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Light emission spectrum from a scanning tunnelling microscope (LESTM) is investigated as a function of relative humidity and shown to be a novel and sensitive means for probing the growth and properties of a water meniscus in the nm-scale. An empirical model of the light emission process is formulated and applied successfully to replicate the decay in light intensity and spectral changes observed with increasing relative humidity. The modelling indicates a progressive water ...

Boyle, Michael G.; Mitra, J.; Dawson, Paul

2009-01-01

208

Circularly polarized light emission in scanning tunneling microscopy of magnetic systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Light is produced when a scanning tunneling microscope is used to probe a metal surface. Recent experiments on cobalt utilizing a tungsten tip found that the light is circularly polarized; the sense of circular polarization depends on the direction of the sample magnetization, and the degree of polarization is of order 10 %. This raises the possibility of constructing a magnetic microscope with very good spatial resolution. We present a theory of this effect for iron and cob...

Apell, S. P.; Penn, D. R.; Johansson, P.

2000-01-01

209

Visible Light Emission from Atomic Scale Patterns Fabricated by the Scanning Tunneling Microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spectroscopically in the visible spectral range. The light emission is based on a novel mechanism involving optical transitions between a tip state and localized states on the sample surface. The wavelength of the photons can be changed by the bias voltage of the STM. The spatial reso...

Thirstrup, C.; Sakurai, M.; Stokbro, Kurt; Aono, M.

1999-01-01

210

Identification of DNA--cisplatin adducts in a blind trial of in situ scanning tunneling microscopy.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling microscopy (STM) reveals nanometer scale details of hydrated DNA but the interpretation of the images is controversial because of substrate artifacts and the lack of a theory for image contrast. We demonstrate that we have overcome these problems by identifying five DNA samples by their STM images alone in a blinded trial. The samples were single-stranded and double-stranded DNA with and without covalent modification by the anti-tumor drug cisplatin. The cisplatin adducts w...

Jeffrey, A. M.; Jing, T. W.; Derose, J. A.; Vaught, A.; Rekesh, D.; Lu, F. X.; Lindsay, S. M.

1993-01-01

211

Lateral electrical conductivity of mica-supported lipid bilayer membranes measured by scanning tunneling microscopy.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Lateral electric conductivity of mica-supported lipid monolayers and of the corresponding lipid bilayers has been studied by means of scanning tunneling microscopy (STM). The surface of freshly cleaved mica itself was found to be conductive when exposed to humid air. Lipid monolayers were transferred onto such a surface by means of the Langmuir-Blodgett technique, which makes the mica surface hydrophobic and suppresses the electric current along the surface in the experimentally accessible hu...

Heim, M.; Cevc, G.; Guckenberger, R.; Knapp, H. F.; Wiegra?be, W.

1995-01-01

212

Nuclear and electronic resonance spectroscopy of single molecules by radio-frequency scanning tunnelling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The ongoing miniaturization in nanoscience and -technology challenges the sensitivity and selectivity of experimental analysis methods to the ultimate level of single atoms and molecules. A promising new approach, addressed here, focuses on the combination of two well-established complementary techniques that have proven to be very successful in their own fields: (i) low-temperature scanning tunneling microscopy (STM), offering high spatial resolution for imaging and spectro...

Mu?llegger, Stefan; Tebi, Stefano; Das, Amal K.; Scho?fberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

2014-01-01

213

Pulse Plating on Gold Surfaces Studied by In Situ Scanning Tunneling Microscopy  

DEFF Research Database (Denmark)

Deposition of bulk copper on thin film gold surfaces is carried out by computer-aided pulse plating. It is demonstrated that the morphology of the copper deposit can be studied by in situ scanning tunnelling microscopy both in potentiostatic experiments and in galvanostatic experiments. Optimized procedures for obtaining smooth deposits by pulse plating are explained in terms of a levelling effect. Possible non-faradaic processes observed in measurements with high frequency pulse plating are discussed.

Andersen, Jens Enevold Thaulov; Bech-Nielsen, Gregers

1994-01-01

214

The electrochemistry and scanning tunnelling microscopy of the flavoprotein, putidaredoxin reductase from Pseudomonas putida  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Cyclic voltammetry studies of putidaredoxin reductase (PdR) were carried out on 1-hexanethiol- and 1-dodecanethiol-modified gold electrodes, and the effect of NAD+/NADH were investigated. Electron transfer rate constants were calculated for both electrode modifiers, and a catalytic reduction current was observed in the presence of NAD+ at dodecanethiol-modified gold surfaces. Complementary in situ scanning tunnelling microscopy images of the electrode surface at high resolution were obtained ...

Mcgee, W.; Djuricic, D.; Lorimer, K.; Wong, L-l; Hill, Hao

2002-01-01

215

Note: Fabrication and characterization of molybdenum tips for scanning tunneling microscopy and spectroscopy  

Science.gov (United States)

We present a method for the preparation of bulk molybdenum tips for Scanning Tunneling Microscopy and Spectroscopy and we assess their potential in performing high resolution imaging and local spectroscopy by measurements on different single crystal surfaces in UHV, namely, Au(111), Si(111)-7 × 7, and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g., cobalt.

Carrozzo, P.; Tumino, F.; Facibeni, A.; Passoni, M.; Casari, C. S.; Li Bassi, A.

2015-01-01

216

Three-Dimensional Laser Scanning for Geometry Documentation and Construction Management of Highway Tunnels during Excavation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the...

Vassilis Gikas

2012-01-01

217

Electronic and Geometrical Structure of Phthalocyanines on Surfaces : An Electron Spectroscopy and Scanning Tunneling Microscopy Study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Core- and Valence Photoelectron Spectroscopy (PES), X-ray- and Ultraviolet-Visible Absorption Spectroscopy (XAS and UV-Vis), Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) calculations are used to study the electronic and geometrical structure of a class of macro-cyclic molecules, Phthalocyanines (Pc), on surfaces. These molecules are widely studied due to their application in many different fields. Multilayer and monolayer coverages of Iron Phthalocyanine (FePc) and ...

A?hlund, John

2007-01-01

218

Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy Study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on top of which ferromagnetic SRO islands were grown epitaxially in-situ. When measured on the ferromagnetic islands, the density of states exhibits small gap-like features consistent with the expected short range penetration of the order parameter into the ferromagnet. However, anomalous split-gap structures are measured on the superconductor in the vicinity of ferromagnetic islands. This observation...

Asulin, Itay; Yuli, Ofer; Koren, Gad; Millo, Oded

2009-01-01

219

Scanning Tunneling Microscopy and Low-Energy Electron Diffraction Studies of Quantum Wires on Si(332)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this master thesis I have investigated one-dimensional nanostructures, so called quantum wires. The goal was to grow them in situ on a stepped silicon surface and thereafter do several kinds of measurements, like Scanning Tunneling Microscopy, Low-Energy Electron Diffraction and Photoemission. The surface that was used was a Si(332) surface and the metals used in the growth of the quantum wires were gold and silver. After the preparation and measurement of the stepped surface, evaporation ...

Gladh, Jo?rgen

2006-01-01

220

Measurements with an ultrafast scanning tunnelling microscope on photoexcited semiconductor layers  

DEFF Research Database (Denmark)

Summary form only given. We demonstrate the use of a ultrafast scanning tunnelling microscopes (USTM) for detecting laser-induced field transients on semiconductor layers. In principle, the instrument can detect transient field changes thus far observed as far-field THz radiation in the near-field regime and resolve small signal sources. For photoexcited low temperature (LT) GaAs we can explain the signal by a diffusion current driven by the laser-induced carrier density gradient

Keil, Ulrich Dieter Felix; Jensen, Jacob Riis

1998-01-01

 
 
 
 
221

Single pentagon in a hexagonal carbon lattice revealed by scanning tunneling microscopy  

International Nuclear Information System (INIS)

The electronic structure of a single pentagon in a hexagonal carbon lattice has been revealed on an atomic scale by scanning tunneling microscopy. The pentagon is located at the apex of the conical protuberance of the graphitic particle. The enhanced charge density localized at each carbon atom in the pentagon is identified, and the ringlike pattern of the (?3 x ?3)R30 degree superstructure of graphite is clearly observed around the pentagon. [copyright] 2001 American Institute of Physics

222

Single pentagon in a hexagonal carbon lattice revealed by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure of a single pentagon in a hexagonal carbon lattice has been revealed on an atomic scale by scanning tunneling microscopy. The pentagon is located at the apex of the conical protuberance of the graphitic particle. The enhanced charge density localized at each carbon atom in the pentagon is identified, and the ringlike pattern of the ({radical}3{times}{radical}3)R30{degree} superstructure of graphite is clearly observed around the pentagon. {copyright} 2001 American Institute of Physics.

An, B.; Fukuyama, S.; Yokogawa, K.; Yoshimura, M.; Egashira, M.; Korai, Y.; Mochida, I.

2001-06-04

223

Analyzing multiple encounter as a possible origin of electron spin resonance signals in scanning tunneling microscopy on Si(111) featuring C and O defects  

Science.gov (United States)

The Si(111)7 × 7 surface exposed to 0.1 L of O2 and the carbonized Si(111) surface are investigated by electron spin resonance scanning tunneling microscopy (ESR-STM) using frequency sweeps and magnetic field sweeps. Only after oxidizing the clean Si(111)7 × 7 or by using the carbonized Si(111), spatially averaged ESR-STM spectra exhibit several peaks and dips around the frequencies corresponding to g = 2. The energy difference between these features is close to the known hyperfine splitting of A ? 9 MHz for vacancies in SiC interacting with next-nearest neighbor 29Si. Such spectra with peaks and dips can be qualitatively reproduced by introducing a primary encounter of the lead electrons with the localized spin correlating the two spins which afterwards evolve in different local hyperfine fields, thus, developing a relative spin angle prior to tunneling.

Manassen, Y.; Averbukh, M.; Morgenstern, M.

2014-05-01

224

Fabrication of nano-devices in silicon using scanning tunneling microscopy  

International Nuclear Information System (INIS)

Full text: Recently our group has demonstrated, using a scanning tunneling microscope, the ability to place individual phosphorus atoms in silicon at precise locations. These dopants can then be encapsulated in epitaxial silicon with minimal diffusion and segregation. We have extended the scheme to fabricate and electrically characterize 2D and 1D nano-devices by the use of an elegant registration technique, involving an in-situ scanning electron microscope etched registration markers on the samples and optical lithography. Here we will discuss this fabrication strategy and present electrical transport measurements from a number of devices. Copyright (2005) Australian Institute of Physics

225

Atomic resolution scanning tunneling microscopy in a cryogen free dilution refrigerator at 15 mK  

Energy Technology Data Exchange (ETDEWEB)

Pulse tube refrigerators are becoming more common, because they are cost efficient and demand less handling than conventional (wet) refrigerators. However, a downside of a pulse tube system is the vibration level at the cold-head, which is in most designs several micrometers. We implemented vibration isolation techniques which significantly reduced vibration levels at the experiment. These optimizations were necessary for the vibration sensitive magnetic resonance force microscopy experiments at milli-kelvin temperatures for which the cryostat is intended. With these modifications we show atomic resolution scanning tunneling microscopy on graphite. This is promising for scanning probe microscopy applications at very low temperatures.

Haan, A. M. J. den, E-mail: arthur.denhaan@gmail.com; Wijts, G. H. C. J.; Galli, F.; Oosterkamp, T. H. [Department of Interface Physics, Leiden University, Niels Bohrweg 2, 2333CA Leiden (Netherlands); Usenko, O. [Leiden Cryogenics, Kenauweg 11, 2331BA Leiden (Netherlands); Baarle, G. J. C. van; Zalm, D. J. van der [Leiden Spin Imaging (LSI), J.H. Oortweg 21, 2333CH Leiden (Netherlands)

2014-03-15

226

Local Ionization Dynamics Traced by Photoassisted Scanning Tunneling Microscopy: A Theoretical Approach  

CERN Document Server

For tracing the spatiotemporal evolution of electronic systems, we suggest and analyze theoretically a setup that exploits the excellent spatial resolution based on scanning tunneling microscopy techniques combined with the temporal resolution of femtosecond pump-probe photoelectron spectroscopy. As an example, we consider the laser-induced, local vibrational dynamics of a surface-adsorbed molecule. The photoelectrons released by a laser pulse can be collected by the scanning tip and utilized to access the spatiotemporal dynamics. Our proof-of-principle calculations are based on the solution of the time-dependent Schrooedinger equation supported by the ab initio computation of the matrix elements determining the dynamics.

Schueler, M; Berakdar, J

2013-01-01

227

Atomic resolution scanning tunneling microscopy in a cryogen free dilution refrigerator at 15 mK  

International Nuclear Information System (INIS)

Pulse tube refrigerators are becoming more common, because they are cost efficient and demand less handling than conventional (wet) refrigerators. However, a downside of a pulse tube system is the vibration level at the cold-head, which is in most designs several micrometers. We implemented vibration isolation techniques which significantly reduced vibration levels at the experiment. These optimizations were necessary for the vibration sensitive magnetic resonance force microscopy experiments at milli-kelvin temperatures for which the cryostat is intended. With these modifications we show atomic resolution scanning tunneling microscopy on graphite. This is promising for scanning probe microscopy applications at very low temperatures

228

Atomic resolution scanning tunneling microscopy in a cryogen free dilution refrigerator at 15 mK  

Science.gov (United States)

Pulse tube refrigerators are becoming more common, because they are cost efficient and demand less handling than conventional (wet) refrigerators. However, a downside of a pulse tube system is the vibration level at the cold-head, which is in most designs several micrometers. We implemented vibration isolation techniques which significantly reduced vibration levels at the experiment. These optimizations were necessary for the vibration sensitive magnetic resonance force microscopy experiments at milli-kelvin temperatures for which the cryostat is intended. With these modifications we show atomic resolution scanning tunneling microscopy on graphite. This is promising for scanning probe microscopy applications at very low temperatures.

den Haan, A. M. J.; Wijts, G. H. C. J.; Galli, F.; Usenko, O.; van Baarle, G. J. C.; van der Zalm, D. J.; Oosterkamp, T. H.

2014-03-01

229

Characterization of thin film semiconductors by scanning probe microscopy and tunneling spectroscopy  

Science.gov (United States)

We have used scanning tunneling microscopy, atomic force microscopy, tunneling spectroscopy, resonance Raman spectroscopy and electrochemistry to study the electrosynthesis of II-VI compound semiconductors with special emphasis on ZnS, CdS, and HgS. This dissertation will focus mainly on the electrochemical and scanning probe (STM and AFM) applications to these compounds, in addition to novel materials such as CoSb. We hope to understand the structural, as well optical properties of these materials. Finally, we hope to develop a recipe for the electrosynthesis of high quality semiconductor films. In Chapter 2, we report an electrochemical, scanning probe microscopic and Raman spectroscopic investigation of thin US films grown by electrochemical atomic layer epitaxy (EC-ALE) aimed at understanding the role played by the order of deposition on film quality. In Chapter 3, we report a study of electrosynthesized CdS-HgS heterojunctions using scanning tunneling microscopy (STM), photoluminescence spectroscopy (PL), and electrochemistry. US thin films were grown by electrochemical atomic layer epitaxy onto Au(111) substrates and were terminated with a single HgS monolayer. In Chapter 4, the structure and chemical composition of electrosynthesized ZnS thin films on Au(111) substrates grown by alternating underpotential deposition and oxidative adsorption cycles of S and Zn from solution precursors was studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In Chapter 5, conditions for the growth of. stable mercury sulfide (HgS) monolayers on Au(111) surfaces using electrochemical atomic layer epitaxy have been investigated. HgS thin films were characterized by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Chapter 6: This chapter describes the use of resonance Raman spectroscopy to characterize thin films of the II-VI compound semiconductors electrosynthesized on metal surfaces. We describe how resonance Raman experiments can provide information about both the electronic band structure of a material as well as time dependent phenomena such as charge carrier trapping. In Chapter 7, the use of electrochemical atomic layer epitaxy for the electrosynthesis of high quality thin films of thermoelectric materials is studied. Specifically, the use of sequential underpotential deposition cycles of Sb and Co for the production of CoSb phases on Au substrates is investigated.

Gichuhi, Anthony

230

Multiple-scanning-probe tunneling microscope with nanoscale positional recognition function  

International Nuclear Information System (INIS)

Over the past decade, multiple-scanning-probe microscope systems with independently controlled probes have been developed for nanoscale electrical measurements. We developed a quadruple-scanning-probe tunneling microscope (QSPTM) that can determine and control the probe position through scanning-probe imaging. The difficulty of operating multiple probes with submicrometer precision drastically increases with the number of probes. To solve problems such as determining the relative positions of the probes and avoiding of contact between the probes, we adopted sample-scanning methods to obtain four images simultaneously and developed an original control system for QSPTM operation with a function of automatic positional recognition. These improvements make the QSPTM a more practical and useful instrument since four images can now be reliably produced, and consequently the positioning of the four probes becomes easier owing to the reduced chance of accidental contact between the probes.

231

Probing ultrafast spin dynamics with optical pump-probe scanning tunnelling microscopy.  

Science.gov (United States)

Studies of spin dynamics in low-dimensional systems are important from both fundamental and practical points of view. Spin-polarized scanning tunnelling microscopy allows localized spin dynamics to be characterized and plays important roles in nanoscale science and technology. However, nanoscale analysis of the ultrafast dynamics of itinerant magnetism, as well as its localized characteristics, should be pursued to advance further the investigation of quantum dynamics in functional structures of small systems. Here, we demonstrate the optical pump-probe scanning tunnelling microscopy technique, which enables the nanoscale probing of spin dynamics with the temporal resolution corresponding, in principle, to the optical pulse width. Spins are optically oriented using circularly polarized light, and their dynamics are probed by scanning tunnelling microscopy based on the optical pump-probe method. Spin relaxation in a single quantum well with a width of 6 nm was observed with a spatial resolution of ? 1 nm. In addition to spin relaxation dynamics, spin precession, which provides an estimation of the Landé g factor, was observed successfully. PMID:24974938

Yoshida, Shoji; Aizawa, Yuta; Wang, Zi-han; Oshima, Ryuji; Mera, Yutaka; Matsuyama, Eiji; Oigawa, Haruhiro; Takeuchi, Osamu; Shigekawa, Hidemi

2014-08-01

232

Scanning tunneling microscopy study of Fe, Co and Cr growth on Re(0001)  

Science.gov (United States)

Atomically flat terraces of the Re(0001) surface with a contaminant density below 0.5% have been obtained by oxygen annealing followed by a flash to higher temperature. This Re(0001) single crystal has been used as a substrate for the deposition of Fe, Co and Cr atoms. Scanning Tunneling Microscopy experiments characterize the growth mode for the submonolayer coverage regime. Co, Cr and Fe atoms self-assemble to form monolayer high islands. Despite a large lattice mismatch between film and substrate, Co and Fe grow pseudomorphically up to half a monolayer. Cr islands are pseudomorphic only for a size below 10 nm. Higher coverage leads to reconstructed islands with an element-dependent reconstruction pattern. Scanning Tunneling Spectroscopy measurements at 8 K reveal the electronic properties of Fe and Re. Differential conductance measurements on the Re(0001) show the presence of standing waves, possibly due to a rhenium surface state. Atomic resolution images of Fe attached to a Re step edge lead to the conclusion that the Fe atoms occupy hcp hollow sites. A Néel magnetic ordered state of the Fe hcp monolayer is revealed with Spin-Polarized Scanning Tunneling Microscopy and Magnetic Atom Manipulation Imaging.

Ouazi, S.; Pohlmann, T.; Kubetzka, A.; von Bergmann, K.; Wiesendanger, R.

2014-12-01

233

Probing ultrafast spin dynamics with optical pump-probe scanning tunnelling microscopy  

Science.gov (United States)

Studies of spin dynamics in low-dimensional systems are important from both fundamental and practical points of view. Spin-polarized scanning tunnelling microscopy allows localized spin dynamics to be characterized and plays important roles in nanoscale science and technology. However, nanoscale analysis of the ultrafast dynamics of itinerant magnetism, as well as its localized characteristics, should be pursued to advance further the investigation of quantum dynamics in functional structures of small systems. Here, we demonstrate the optical pump-probe scanning tunnelling microscopy technique, which enables the nanoscale probing of spin dynamics with the temporal resolution corresponding, in principle, to the optical pulse width. Spins are optically oriented using circularly polarized light, and their dynamics are probed by scanning tunnelling microscopy based on the optical pump-probe method. Spin relaxation in a single quantum well with a width of 6 nm was observed with a spatial resolution of ~1 nm. In addition to spin relaxation dynamics, spin precession, which provides an estimation of the Landé g factor, was observed successfully.

Yoshida, Shoji; Aizawa, Yuta; Wang, Zi-Han; Oshima, Ryuji; Mera, Yutaka; Matsuyama, Eiji; Oigawa, Haruhiro; Takeuchi, Osamu; Shigekawa, Hidemi

2014-08-01

234

Symmetry-Based Tunnelings in High-Resolution Rovibrational Spectra of Octahedral Molecules  

Science.gov (United States)

High-resolution spectra of spherical-top molecules are known to demonstrate rotational level clustering. This clustering is well described as a rotational phase-space effect Multiple equivalent phase-space regions allow tunneling and thus splitting of the rotational clusters. So far this has been done with an ad hoc tunneling Hamiltonian. Similar splittings have been shown for low dimensional systems, also with an ad hoc parameterization. While ad hoc tunneling parameterization is simple to understand, it becomes extremely difficult to apply for higher symmetries and for locally low-symmetry clustering when many tunneling paths are possible. Symmetry-based parameterization mitigates this complication. This presentation will discuss how symmetry-based tunneling is applied for octahedral molecules and demonstrate how local-C1, C2, C3 or C4 clusters may be evaluated perturbatively. Connections to non-rotational systems, such as large amplitude motion, will be discussed as well. W.G. Harter and C.W. Patterson, Phys Rev Lett 38, 224 (1977) W.G. Harter and C.W. Patterson, J Chem Phys 66, 4872 (1977) J.T. Hougen J Mol Spect 123, 197 (1987)

Mitchell, Justin; Harter, William

2010-06-01

235

Tunneling conductance spectra of a metal/ferromagnet junction within a two-band model  

Energy Technology Data Exchange (ETDEWEB)

We present a theory based on a scattering matrix approach to explain the tunneling spectroscopy of a metal/ferromagnet junction. The isotropic one-band free electron model was used to describe the energy dispersion relation of the electrons in a metal layer, while two-band approximation was used to examine the electronic dispersion relation within the ferromagnetic material. s-band and d-band coupling were considered using the two-band approximation. In this work, interfacial spin-flip scattering was neglected. The energy dispersion and tunneling conductance spectra were calculated to study the effect of the coupling strength between the two bands. With no coupling, the energy band will have the crossing point between the bands. In contrast, a gap is opened up at the crossing points. It was found that the size of the gap depends on the coupling strength. Some kinks occurred in the energy band corresponding to the crossing points. The rich features of conductance spectra occurring in the metallic regime have the effects more significant than those occurring in the tunneling regime. In both regimes the conductance spectrum becomes largest if the effective mass of free electrons in the majority of the bands in the ferromagnetic material is approximately in the same order as that of the free electrons in metals. - Highlights: Black-Right-Pointing-Pointer Tunneling conductance spectra of two-band ferromagnet/superconductor are calculated. Black-Right-Pointing-Pointer s-band and d-band of ferromagnet are mixed. Black-Right-Pointing-Pointer The conductance spectra consist of several kinks, depending on the coupling strength. Black-Right-Pointing-Pointer Two-band ferromagnet model is very essential.

Pasanai, K., E-mail: krisakronmsu@gmail.com [Department of Physics, Faculty of Science, Mahasarakham University, Khamriang Sub-District, Kantarawichai District, Maha Sarakham 44150 (Thailand); Pairor, P. [School of Physics, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000 (Thailand)

2013-02-15

236

Nonequilibrium effects in the tunneling conductance spectra of small metallic particles  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The tunneling spectra of small metallic grains shows an unusual structure of the differential conductance peaks. Namely, resonance peaks appear in clusters, or develop substructure as the the gate voltage is changed. These features are manifestations of a nonequilibrium behavior which appears when the applied source-drain voltage is sufficiently large. Electron-electron Coulomb interaction as well as an attractive pairing interaction play an important role in determining the...

Agam, Oded

1998-01-01

237

Resonance tunneling spectroscopy of heteropoly compounds  

International Nuclear Information System (INIS)

The electron tunneling spectra of phosphomolybdic and phosphomolybdovanadic acids have been measured using a scanning tunneling microscope. A new mechanism of negative differential resistance (NDR) formation in tunneling nanocontacts is established, which is general for all systems featuring the Wannier-Stark localization effect. A two-center inelastic resonance tunneling model is constructed, which allows the values of both electron and vibrational energy parameters to be determined from the measured spectra.

238

INTER-LAYER INTERACTION IN DOUBLE-WALLED CARBON NANOTUBES EVIDENCED BY SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY  

DEFF Research Database (Denmark)

Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes is provided by the experimental tunneling spectra and the contribution of the inner tube to the local density of states of the "composite" double-walled system is identified in agreement with previous theoretical calculations. An explicit correlation between the chirality of the two constituent tubes, the inter-wall interaction and the overall electronic structure for double-walled carbon nanotubes, is demonstrated by our experiments, showing that the effect the inner tube has on the overall electronic structure of double-walled nanotubes cannot be neglected, and is key to the opto-electronic properties of the system. We postulate that previous analysis of the opto-electronic properties on multiple-walled carbon nanotubes based purely on the outer layer chirality of the tube needs significant modification based on new understanding brought forth with our analysis.

Giusca, Cristina E; Tison, Yann

2008-01-01

239

Characterization of GaSb-based heterostructures by scanning electron microscope cathodoluminescence and scanning tunnelling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) rising a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to t...

Storgardsstorgards, J.; Me?ndez Marti?n, Bianchi; Piqueras Noriega, Javier; Storgards, M.; Dimroth, F.; Bett, A. W.

2004-01-01

240

Fabrication of nanoscale alumina on NiAl(1 0 0) with a scanning tunneling microscope  

International Nuclear Information System (INIS)

Highlights: ? Nanoscale alumina was fabricated on NiAl(1 0 0) surface with a STM tip. ? Varied powers (bias × current) give two distinct modes of oxidation. ? In the high-power mode alumina forms on the surface near the tip. ? In the low-power mode alumina grows along direction [0 0 1] or [0 1 0] of NiAl(1 0 0). ? The grown alumina strips have minimal width about 3 nm. - Abstract: Nanoscale alumina was fabricated on NiAl (1 0 0) surface using a scanning tunneling microscope in an ultrathin vacuum condition. With the tunneling current greater than 0.4 nA and the power (bias voltage × tunneling current) greater than 0.24 nW, Al and pre-adsorbed O atoms were activated to form alumina (with thickness 0.25–1.0 nm) on the surface directly vicinal to the tip; the width and thickness of the grown alumina strips are controllable by the current and bias. With an evidently smaller power and a smaller bias (?1.0 V), crystalline alumina were grown along direction [0 0 1] or [0 1 0] of NiAl(1 0 0) in the tip-scanned area of either O-chemisorbed or oxidized surfaces, independent of the direction of tip movement. The alumina strips grown through the latter mode have minimal width near 3 nm.

 
 
 
 
241

New directions in point-contact spectroscopy based on scanning tunneling microscopy techniques (Review Article)  

International Nuclear Information System (INIS)

Igor Yanson showed 38 years ago for the first time a point-contact measurement where he probed the energy resolved spectroscopy of the electronic scattering inside the metal. Since this first measurement, the pointcontact spectroscopy (PCS) technique improved enormously. The application of the scanning probe microscopy (SPM) techniques in the late 1980s allowed achieving contacts with a diameter of a single atom. With the introduction of the mechanically controlled break junction technique, even spectroscopy on freely suspended chains of atoms could be performed. In this paper, we briefly review the current developments of PCS and show recent experiments in advanced scanning PCS based on SPM techniques. We describe some results obtained with both needle-anvil type of point contacts and scanning tunneling microscopy (STM). We also show our first attempt to lift up with a STM a chain of single gold atoms from a Au(110) surface.

242

MgB2 Energy Gap Determination by Scanning Tunneling Spectroscopy  

CERN Document Server

We report scanning tunneling spectroscopy (STS) measurements of the gap properties of both ceramic MgB2 and c-axis oriented epitaxial MgB2 thin films. Both show a temperature dependent zero bias conductance peak and evidence for two superconducting gaps. We report tunneling spectroscopy of superconductor-insulator-superconductor (S-I-S) junctions formed in two ways in addition to normal metal-insulator-superconductor (N-I-S) junctions. We find a gap delta=2.3-2.8 meV, with spectral features and temperature dependence that are consistent between S-I-S junction types. In addition, we observe evidence of a second, larger gap, delta=7.2 meV, consistent with a proposed two-band model.

Heitmann, T W; Kim, D M; Choi, J H; Giencke, J; Eom, C B; Regan, K A; Rogado, N S; Hayward, M A; He, T; Slusky, J S; Khalifah, P; Haas, M; Cava, R J; Larbalestier, D C; Rzchowski, M S

2002-01-01

243

Scanning tunneling microscopy simulations of poly(3-dodecylthiophene) chains adsorbed on highly oriented pyrolytic graphite  

CERN Document Server

We report on a novel scheme to perform efficient simulations of Scanning Tunneling Microscopy (STM) of molecules weakly bonded to surfaces. Calculations are based on a tight binding (TB) technique including self-consistency for the molecule to predict STM imaging and spectroscopy. To palliate the lack of self-consistency in the tunneling current calculation, we performed first principles density-functional calculations to extract the geometrical and electronic properties of the system. In this way, we can include, in the TB scheme, the effects of structural relaxation upon adsorption on the electronic structure of the molecule. This approach is applied to the study of regioregular poly(3-dodecylthiophene) (P3DDT) polymer chains adsorbed on highly oriented pyrolytic graphite (HOPG). Results of spectroscopic calculations are discussed and compared with recently obtained experimental dat

Dubois, M; Latil, S; Rubio, A; Scifo, L

2006-01-01

244

Quantitative analysis of Scanning Tunneling Microscopy images for surface structure determination: Sulfur on Re(0001)  

Energy Technology Data Exchange (ETDEWEB)

Scanning Tunneling Microscopy (STM) images of adsorbed atoms and molecules on single crystal substrates provide important information on surface structure and order. In many cases images are interpreted qualitatively based on other information on the system. To obtain quantitative information, a theoretical analysis of the STM image is required. A new method of calculating STM images is presented that includes a full description of the STM tip and surface structure. This method is applied to experimental STM images of sulfur adsorbed on Re(0001). Effects of adsorption site, adsorbate geometry, tip composition and tunnel gap resistance on STM image contrast are analyzed. The chemical identity of tip apex atom and substrate subsurface structure are both shown to significantly affect STM image contrast.

Ogletree, D.F.; Dunphy, J.C.; Salmeron, M.B. [Lawrence Berkeley Lab., CA (United States); Sautet, P. [ENS, Lyon (France). Lab. de Chemie Theoretique]|[Centre National de la Recherche Scientifique (CNRS), 69 - Villeurbanne (France). Inst. de Recherches sur la Catalyse

1993-02-01

245

Contacting single molecules to metallic electrodes by scanning tunnelling microscope manipulation: model systems for molecular electronics  

International Nuclear Information System (INIS)

The electronic contact between a molecular wire and a metallic electrode will play an important role in future molecular electronics as its properties determine the conductivity of the molecule-metal system. Scanning tunnelling microscopy manipulation reveals various advantages for the investigation of electronic contacts at the atomic scale. In this review, several examples of molecular wire-electrode systems are presented, where single molecules are placed in contact in a controlled way. Changed chemical structures of the molecule and, on the other hand, different shapes and dimensions of electrodes lead to a variety of contact configurations. The contact can be characterized using the additional contribution to the tunnelling current, but also using the influence on the electronic states of the electrode and the molecule. The quality of the contact is discussed in terms of the vertical distance between the molecular wire and the metal atoms and of the chemical composition of the molecular end group

246

Observation of single dinuclear metal-complex molecules using scanning tunneling microscopy.  

Science.gov (United States)

We report a scanning tunneling microscopy (STM) investigation of a dinuclear organometallic molecule, trans-[Cl(dppe)2Ru(C[triple bond]C)6Ru(dppe)2Cl] (Ru2), absorbed on a Au(111) surface; this molecule is a potential candidate for use in molecular quantum-dot cellular automata (QCA) devices. Isolated Ru2 molecules were observed under ultra-high-vacuum conditions. Submolecular structure was clearly discernible in the STM images, with a bright feature corresponding to each of the two Ru-ligand complexes within the Ru2 molecule. Rotation and translation of the Ru2 molecules were observed to be induced by the STM tip under some tunneling conditions. PMID:17064149

Wei, Zhongqing; Guo, Song; Kandel, S Alex

2006-11-01

247

Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy  

Science.gov (United States)

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.

Kanazawa, Ken; Yoshida, Shoji; Shigekawa, Hidemi; Kuroda, Shinji

2015-02-01

248

Antenna-based ultrahigh vacuum microwave frequency scanning tunneling microscopy system.  

Science.gov (United States)

The instrumental synthesis of high resolution scanning tunneling microscopy (STM) with the ability to measure differential capacitance with atomic scale resolution is highly desirable for fundamental metrology and for the study of novel physical characteristics. Microwave frequency radiation directed at the tip-sample junction in an STM system allows for such high-resolution differential capacitance information. This ability is particularly critical in ultrahigh vacuum environments, where the additional parameter space afforded by including a capacitance measurement would prove powerful. Here we describe the modifications made to a commercial scanning tunneling microscope to allow for broad microwave frequency alternating current scanning tunneling microscopy (ACSTM) in ultrahigh vacuum conditions using a relatively simple loop antenna and microwave difference frequency detection. The advantages of our system are twofold. First, the use of a removable antenna on a commercial STM prevents interference with other UHV processes while providing a simple method to retrofit any commercial UHV-STM with UHV-ACSTM capability. Second, mounting the microwave antenna on a translator allows for specific tuning of the system to replicate experimental conditions between samples, which is particularly critical in sensitive systems like organic thin films or single molecules where small changes in incident power can affect the results. Our innovation therefore provides a valuable approach to give nearly any commercial STM, be it an ambient or UHV system, the capability to measure atomic-scale microwave studies such as differential capacitance or even single molecule microwave response, and it ensures that experimental ACSTM conditions can be held constant between different samples. PMID:21639510

Giridharagopal, Rajiv; Zhang, Jun; Kelly, Kevin F

2011-05-01

249

Structure of YSi(2) nanowires from scanning tunneling spectroscopy and first principles.  

Science.gov (United States)

Exceptionally long and uniform YSi(2) nanowires are formed via self-assembly on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a class of nanowires that violates the "odd multiple" rule. The structure of the thinnest wire in this category is determined by comparing scanning tunneling spectroscopy measurements with the calculated surface density of states of candidate models by means of the Pendry R-factor analysis. The relative stability of the odd and even wire systems is analyzed via first-principles calculations. PMID:19859579

Iancu, V; Kent, P R C; Zeng, C G; Weitering, H H

2009-09-21

250

Initiation of ion-beam-induced nanopatterns on Si (001) surface: a scanning tunneling microscopy study  

International Nuclear Information System (INIS)

Si (001) surface, modified using low energy (5 keV) Ar+ ion-beam, is studied by scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. The evolution of surface for ion bombardment in presence of temperature is observed through STM images and is characterized by height-height correlation function. It has been observed that the temperature and dose play important roles for the control of the surface evolution, especially; post-annealing helps to form nanoscale ripple-like structures at relatively low temperature. (author)

251

Graphene, Polycyclic Aromatic Hydrocarbons and Topological Insulators : A scanning tunneling microscopy study  

DEFF Research Database (Denmark)

I denne afhandling præsenterer jeg resultater for graphen, polyaromatiske kulbrinter (PAH’er) og topologiske isolatorer. Hovedparten af afhandlingen fokuserer på graphen, hvor vi har undersøgt følgende: Groning af høj-kvalitets graphene på forskellige metaloverflader; Introduktion af et båndgap i graphen via hydrogenering af graphen; Graphens coating egenskaber på en metaloverflade mod forskellige gasser. Kapitlet omhandlende PAH’er fokuserer på coronene på Cu(100) og hydrogenering af dette system. Jeg præsenterer scanning tunnel mikroskopi (STM) afbildninger af hydrogenerede coronene molekyler med submolekylær opløsning. Vores topologiske isolator forskning er udført med krystaller af Bi2Se3, for hvilke vi undersøgte stabiliteten af de topologiske beskyttede tilstande i forhold til inducerede defekter.

Nilsson, Louis

2013-01-01

252

Measuring many-body effects in carbon nanotubes with a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electron-electron interactions and excitons in carbon nanotubes are locally measured by combining Scanning tunneling spectroscopy and optical absorption in bundles of nanotubes. The largest gap deduced from measurements at the top of the bundle is found to be related to the intrinsic quasi-particle gap. From the difference with optical transitions, we deduced exciton binding energies of 0.4 eV for the gap and 0.7 eV for the second Van Hove singularity. This provides the firs...

Lin, Hong; Lagoute, Je?ro?me; Repain, Vincent; Chacon, Cyril; Girard, Yann; Lauret, Jean-se?bastien; Ducastelle, Franc?ois; Loiseau, Annick; Rousset, Sylvie

2009-01-01

253

Atomic-scale structure of dislocations revealed by scanning tunneling microscopy and molecular dynamics  

DEFF Research Database (Denmark)

The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations, the simulations can be used to determine dislocation structure and orientation in the near-surface region. In a similar way, the subsurface structure of other extended defects can be studied. The simulations show dislocations to reorient the partials in the surface region leading to an increased splitting width at the surface, in agreement with the STM observations. Implications for surface-induced cross slip are discussed.

Christiansen, Jesper; Morgenstern, K.

2002-01-01

254

Scanning tunneling microscopy at 70 mK in the dichalcogenide superconductor TaSe2  

Science.gov (United States)

We present scanning tunneling microscopy and spectroscopy measurements of the layered dichalcogenide 2H-TaSe2, performed in a dilution refrigerator cryostat equipped with a three axis superconducting magnet. In this compound superconductivity and charge density wave (CDW) ordering coexist below 200mK. We find CDW order corresponding to hexagonal (2H) symmetry, but we also find areas where CDW order corresponding to trigonal (1T) symmetry appears. We study the superconducting density of states as a function of position and magnetic field at 70mK and relate the results to the CDW patterns.

Galvis, Jose; Suderow, Hermann; Vieira, Sebastian

2012-02-01

255

Scanning tunneling microscopy of a stage-1 CuCl2 graphite intercalation compound  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a scanning-tunneling-microscope (STM) study of a stage-1 graphite intercalation compound (GIC) of approximate stoichiometry C6CuCl2. When the sample bias is positive with respect to the tip, we observe a hexagonal symmetry in which all the atoms of the graphite surface plane are imaged. This is in contrast to the threefold symmetry usually seen in atomic-resolution STM images of highly oriented pyrolytic graphite (HOPG), which we also observe on a reference sample of HOPG. The three...

Olk, C. H.; Heremans, J.; Dresselhaus, M. S.; Speck, J. S.; Nicholls, J. T.

1991-01-01

256

SCANNING TUNNELING MICROSCOPY STUDY OF ALKALI METAL ADSORPTION ON THE Si (001) 2x1 SURFACE  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Li and K adsorption on the Si(001)2x1 surface has been investigated by field ion-scanning tunneling microscopy (FI-STM). The STM images have shown that at the initial stage of adsorption Li (K) atoms (1) adsorb on top of one of the dimer forming Si surface atoms and stabilize asymmetric (buckled) dimerization and (2) form linear chains, perpendicular to the substrate 2x1 dimer rows. Our observations suggest that alkali metal adsorption on the Si(001)2x1 surface may be significantly different ...

Hasegawa, Y.; Hashizume, T.; Kamiya, I.; Ide, T.; Sumita, I.; Hyodo, S.; Sakurai, T.; Tochihara, H.; Kubota, M.; Murata, Y.

1989-01-01

257

Influence of dimer buckling on dimer diffusion: A scanning tunneling microscopy study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The diffusion of Ge dimers along the substrate dimer rows of Ge(001) has been investigated with scanning tunneling microscopy. The jump frequency of on-top Ge dimers along symmetric dimer rows at room temperature is found to be eight times higher than the diffusion along asymmetric dimer rows (0.36 s–1 versus 0.044 s–1). We ascribe this difference to limitations associated with the rocking motion that a dimer has to perform while diffusing along asymmetric dimer rows.

Huijben, Jeroen; Houselt, Arie; Zandvliet, Harold J. W.; Poelsema, Bene

2006-01-01

258

Contact to single atoms and molecules with the tip of a scanning tunnelling microscope  

International Nuclear Information System (INIS)

Experiments using the tip of a scanning tunnelling microscope to contact atoms and molecules adsorbed on surfaces are reviewed. Conductance quantization upon forming or breaking a contact between the tip and surfaces as well as between the tip and specifically chosen atoms and molecular orbitals is addressed. Imaging the contact area prior to and after contact measurements allows one to monitor the status of the contacted object as well as that of the contacting electrodes. Spectroscopy with the tip in contact with individual atoms or molecules reveals the reproducibility of and control over such experiments today. (topical review)

259

Electronic properties of (Zn,CoO systems probed by scanning tunnelling spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this paper is to gain insight into theelectronic properties of (Zn,CoO system - a widebandgap Diluted Magnetic Semiconductors (DMSshowing room temperature (RT ferromagnetism undern-type doping conditions. On the experimental side, ultrahigh-vacuum scanning tunnelling microscopy andspectroscopy (STM and STS at variable temperature (Tare used to probe the local electronic structure of thesystem. It is presented the map of the local density ofstates (LDOS of polar ZnO surfaces. Then, it is possibleto decorate (incorporate Co atoms onto (into thesemiconductor.

L. Moldovan

2008-05-01

260

STM in liquids : a scanning tunnelling microscopy exploration of the liquid-solid interface  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis reports of a series of atomic scale studies of the liquid-solid interface, carried out with a home-built liquid-cell Scanning Tunnelling Microscope (STM). The home-built liquid-cell STM is described in detail, and numerical simulations are performed to show that surfaces immersed in the liquid-cell STM can be equally clean and well-defined as surfaces in ultra-high vacuum. First a model system is studied: the gold-alkane interface (Au(111)-n-tetradecane). It is shown that alkanes ...

Hulsken, Bas

2008-01-01

 
 
 
 
261

Scanning Tunneling Microscopy and Molecular Dynamics Simulations of Dislocations Intersecting a Ag(111) Surface  

CERN Document Server

Using an interplay between molecular dynamics (MD) and scanning tunneling microscopy (STM) we have studied the intersection of dislocations with a Ag(111) surface, a model system for the more general situation of an extended crystal defect intersecting a metal surface. The broken translational symmetry at the surface permits the dissociation width of the dislocation to change significantly at the surface, which is clearly observed in both simulations and experiment. The near-surface structures obtained from the simulation are in good agreement with the STM data. Hereby a link is established between atomically resolved experimental surface structures and bulk structures inaccessible by STM.

Christiansen, J; Schiøtz, J; Jacobsen, K W; Braun, K F; Rieder, K H; Laegsgaard, E; Besenbacher, F

2002-01-01

262

Controlled low-temperature molecular manipulation of sexiphenyl molecules on Ag(111) using scanning tunneling microscopy  

CERN Document Server

A novel scanning tunneling microscope manipulation scheme for a controlled molecular transport of weakly adsorbed molecules is demonstrated. Single sexiphenyl molecules adsorbed on a Ag(111) surface at 6 K are shot towards single silver-atoms by excitation with the tip. To achieve atomically straight shooting paths, an electron resonator consisting of linear standing wave fronts is constructed. The sexiphenyl manipulation signals reveal a pi-ring flipping as the molecule moves from hcp to fcc site. Abinitio calculations show an incorporation of the Ag atom below the center of a pi-ring.

Hla, S W; Wassermann, B; Rieder, K H; Hla, Saw-Wai; Braun, Kai-Felix; Wassermann, Bernhard; Rieder, Karl-Heinz

2004-01-01

263

Real-time scanning tunneling microscopy studies of thin film deposition and ion erosion  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis I present my research on the physics of some important processes in the production of thin films. I studied physical vapour deposition (PVD) and thin film modification through ion bombardment using a newly developed, high-speed scanning tunneling microscope (STM). The instrument has the special property that it can be tilted and azimuthally rotated to allow atom or ion beams a direct line-of-sight access to the region of the surface that is being imaged by the STM tip. With the...

Fokkema, Vincent

2011-01-01

264

Scanning tunneling spectroscopy on graphene nanoislands, iron nanoislands and phase change materials  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis is concerned with scanning tunnelling spectroscopy (STS) of graphene nanoisland on Ir(111), Fe nanoisland on W(110) and phase change materials Ge1Sb2Te4. Low-temperature STS is used to map the local density of states of graphene dots supported on Ir(111). Because of a band gap in the projected Ir band structure around the graphene K-point, the electronic properties of the quantum dots are dominantly graphene-like. Comparison with tight binding calculations on the honeycomb lattice...

Subramaniam, Dinesh

2012-01-01

265

Resonant-Enhanced Spectroscopy of Molecular Rotations with a Scanning Tunneling Microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use rotational excitation spectroscopy with a scanning tunneling microscope to investigate the rotational properties of molecular hydrogen and its isotopes physisorbed on the surfaces of graphene and hexagonal boron nitride (h-BN), grown on Ni(111), Ru(0001), and Rh(111). The rotational excitation energies are in good agreement with Delta J = 2 transitions of freely spinning p-H-2 and o-D-2 molecules. The variations of the spectral line shapes for H-2 among the different surfaces can be tr...

Natterer, Fabian Donat; Patthey, Franc?ois; Brune, Harald

2014-01-01

266

A 30 mK, 13.5 T scanning tunneling microscope with two independent tips  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows \\textit{in situ} transfer from an ultra high vacuum (UHV) preparation chamber while the STM...

Roychowdhury, A.; Gubrud, M. A.; Dana, R.; Anderson, J. R.; Lobb, C. J.; Wellstood, F. C.; Dreyer, M.

2013-01-01

267

Photon scanning tunneling optical microscopy with a three-dimensional multiheight imaging mode  

Science.gov (United States)

A photon scanning tunneling microscope with a three-dimensional multiheight mode has been developed for the mapping of optical field distributions in integrated optical waveguide structures. The optical field is measured at different heights above the waveguide surface. The multiheight measurements also contain the optical information gathered with the commonly used constant gap measurements in addition to the topography of the waveguide surface. With the multiheight method, the decay length of the evanescent field is readily determined as function of the in-plane coordinate. Moreover, the evanescent light can be distinguished from scattered light.

Balistreri, M. L. M.; Korterik, J. P.; Kuipers, L.; van Hulst, N. F.

2000-12-01

268

Scanning tunneling microscopy studies of III-nitride thin film heteroepitaxial growth  

International Nuclear Information System (INIS)

The current status of studies and new trends in obtaining and exploring surface characteristics of III-nitride semiconductors are analyzed and reviewed. Using a unique setup combining a scanning tunneling microscope (STM) with an inline molecular-beam epitaxy (MBE) chamber, the surface atomic structures on both hexagonal and cubic GaN films grown by nitrogen-plasma-assisted MBE have been studied in situ over a broad range of temperatures and [N]/[Ga] ratios. Models of the observed surface phases are developed based on the comparative analysis of their atomic-resolution STM images and ab initio total energy calculations. (reviews of topical problems)

269

Scanning tunneling microscopy studies of III-nitride thin film heteroepitaxial growth  

Energy Technology Data Exchange (ETDEWEB)

The current status of studies and new trends in obtaining and exploring surface characteristics of III-nitride semiconductors are analyzed and reviewed. Using a unique setup combining a scanning tunneling microscope (STM) with an inline molecular-beam epitaxy (MBE) chamber, the surface atomic structures on both hexagonal and cubic GaN films grown by nitrogen-plasma-assisted MBE have been studied in situ over a broad range of temperatures and [N]/[Ga] ratios. Models of the observed surface phases are developed based on the comparative analysis of their atomic-resolution STM images and ab initio total energy calculations. (reviews of topical problems)

Bakhtizin, Raouf Z [Department of Physical Electronics, Bashkir State University, Ufa (Russian Federation); Xue, Qi-Zhen; Wu, Ke-Hui; Sakurai, Toshio [Institute for Materials Research, Tohoku University, Sendai (Japan); Xue, Qi-Kun [Institute of Physics, Chinese Academy of Sciences, Beijing (China)

2004-04-30

270

Scanning tunneling microscopy in TTF-TCNQ: Phase and amplitude modulated charge density waves  

DEFF Research Database (Denmark)

Charge density waves (CDWs) have been studied at the surface of a cleaved tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) single crystal using a low temperature scanning tunneling microscope (STM) under ultrahigh-vacuum conditions, between 300 and 33 K with molecular resolution. All CDW phase transitions of TTF-TCNQ have been identified. The measurement of the modulation wave vector along the a direction provides evidence of the existence of domains comprising single plane wave modulated structures in the temperature regime where the transverse wave vector of the CDW is temperature dependent, as hinted by the theory more than 20 years ago.

Wang, Z.Z.; Gorard, J.C.

2003-01-01

271

Growth mode of 2-mercaptobenzoxazole on Cu(1 0 0) studied by scanning tunneling microscopy  

Science.gov (United States)

The adsorption of 2-mercaptobenzoxazole (C 7H 5NOS) on Cu(1 0 0) at room temperature was studied by scanning tunneling microscopy. The deposition was performed in ultrahigh vacuum in the range of exposure 0.15-90 L by sublimation of the molecule. After the exposure of 0.8 L it is possible to locate ordered domains with well-defined parallel rows. After 38 L of deposition the surface appears completely covered by rounded protrusions randomly distributed. These results suggest a Stranski-Krastanov growth mode: initially an ordered monolayer forms and above this layer other molecules are adsorbed with a random distribution.

Contini, G.; Castro, V. Di; Angelaccio, A.; Motta, N.; Sgarlata, A.

2000-12-01

272

Direct observation of long chain alkane bilayer films on graphite by scanning tunneling microscopy  

Science.gov (United States)

The interface between a solution of hexatriacontane (n-C 36H 74) in decane and the basal plane of graphite has been studied by scanning tunneling microscopy at room temperature. For the first time, we show that a second layer which is rotated by 60° with respect to the first layer may grow at the interface. We demonstrate that the carbon skeleton of the molecule is parallel to the graphite surface. We propose a model for the arrangement of the molecular layers and an explanation for the origin of the second layer rotation.

Watel, G.; Thibaudau, F.; Cousty, J.

1993-01-01

273

Four-probe measurements with a three-probe scanning tunneling microscope  

International Nuclear Information System (INIS)

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe

274

Design criteria for scanning tunneling microscopes to reduce the response to external mechanical disturbances.  

Science.gov (United States)

We present a simple one-dimensional model to find design criteria for a scanning tunneling microscope (STM) minimizing the response of the tip-sample distance to external mechanical disturbances. The underlying concept-achieving a response that is in phase and same amplitude-goes beyond the conventional approach to construct the STM as stiff as possible. It introduces optimization conditions relating the resonance frequencies of the different components to the STM assembly, which can be implemented accordingly during the STM design process. In this way an improvement in the response to external disturbances of several orders of magnitude can be achieved. Calculations for three typical STM designs are presented along with the corresponding optimization criteria. For one of the designs an improvement in performance has been experimentally verified. The results can also be extended to other scanning probe techniques. PMID:19044422

Ast, Christian R; Assig, Maximilian; Ast, Alexandra; Kern, Klaus

2008-09-01

275

Variable-temperature independently driven four-tip scanning tunneling microscope.  

Science.gov (United States)

The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface. PMID:17552823

Hobara, Rei; Nagamura, Naoka; Hasegawa, Shuji; Matsuda, Iwao; Yamamoto, Yuko; Miyatake, Yutaka; Nagamura, Toshihiko

2007-05-01

276

Four-probe measurements with a three-probe scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe.

Salomons, Mark [National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta T6G 2M9 (Canada); Martins, Bruno V. C.; Zikovsky, Janik; Wolkow, Robert A., E-mail: rwolkow@ualberta.ca [National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta T6G 2M9 (Canada); Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada)

2014-04-15

277

What is the orientation of the tip in a scanning tunneling microscope?  

CERN Document Server

We introduce a statistical correlation analysis method to obtain information on the local geometry and orientation of the tip used in scanning tunneling microscopy (STM) experiments based on large scale simulations. The key quantity is the relative brightness correlation of constant-current topographs between experimental and simulated data. This correlation can be analyzed statistically for a large number of modeled tip orientations and geometries. Assuming a stable tip during the STM scans and based on the correlation distribution, it is possible to determine the tip orientations that are most likely present in an STM experiment, and exclude other orientations. This is especially important for substrates such as highly oriented pyrolytic graphite (HOPG) since its STM contrast is strongly tip dependent, which makes interpretation and comparison of STM images very challenging. We illustrate the applicability of our method considering the HOPG surface in combination with tungsten tip models of two different ap...

Mándi, Gábor; Palotás, Krisztián

2015-01-01

278

Four-probe measurements with a three-probe scanning tunneling microscope  

Science.gov (United States)

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe.

Salomons, Mark; Martins, Bruno V. C.; Zikovsky, Janik; Wolkow, Robert A.

2014-04-01

279

Calibration of tip and sample temperature of a scanning tunneling microscope using a superconductive sample  

International Nuclear Information System (INIS)

The temperature of the electrodes is a crucial parameter in virtually all tunneling experiments. The temperature not only controls the thermodynamic state of the electrodes but also causes thermal broadening, which limits the energy resolution. Unfortunately, the construction of many scanning tunneling microscopes inherits a weak thermal link between tip and sample in order to make one side movable. Such, the temperature of that electrode is badly defined. Here, the authors present a procedure to calibrate the tip temperature by very simple means. The authors use a superconducting sample (Nb) and a standard tip made from W. Due to the asymmetry in the density of states of the superconductor (SC)—normal metal (NM) tunneling junction, the SC temperature controls predominantly the density of states while the NM controls the thermal smearing. By numerically simulating the I-V curves and numerically optimizing the tip temperature and the SC gap width, the tip temperature can be accurately deduced if the sample temperature is known or measureable. In our case, the temperature dependence of the SC gap may serve as a temperature sensor, leading to an accurate NM temperature even if the SC temperature is unknown

280

Scanning tunneling microscopy and spectroscopy for cluster and small particle research  

International Nuclear Information System (INIS)

Scanning tunneling microscopy (STM) and spectroscopy (STS) are new methods to investigate atomic arrangements and electronic structures of clusters and small particles of atoms. In this paper we review recent developments in this field, in particular the work from our laboratory. We show studies of single adatoms, small clusters and larger particles of platinum and a trimer of aluminium imaged with atomic resolution on highly-oriented pyrolytic graphite. We find different isomeric structures for clusters of a specific size. Taking the substrate lattice as reference we determine bond lengths and angles for the clusters. We find that adsorbed Pt-particles have a strong influence on the substrate. Periodic charge density modulations on the graphite lattice surrounding the particles are observed. We also discuss recent STS experiments which showed Coulomb blockade in electron tunneling. A silicon-oxide-graphite tip-junction is used where a mesoscopic insulating area containing trap levels for temporary electron storage is responsible for the blockade of single electron transport. Such an ultra-small insulator capacitor shows large voltage steps in current-voltage characteristics and quantization of the tunneling current. (orig.)

 
 
 
 
281

A compact combined ultrahigh vacuum scanning tunnelling microscope (UHV STM) and near-field optical microscope  

International Nuclear Information System (INIS)

We have designed and constructed a hybrid scanning near-field optical microscope (SNOM)–scanning tunnelling microscope (STM) instrument which operates under ultrahigh vacuum (UHV) conditions. Indium tin oxide (ITO)-coated fibre-optic tips capable of high quality STM imaging and tunnelling spectroscopy are fabricated using a simple and reliable method which foregoes the electroless plating strategy previously employed by other groups. The fabrication process is reproducible, producing robust tips which may be exchanged under UHV conditions. We show that controlled contact with metal surfaces considerably enhances the STM imaging capabilities of fibre-optic tips. Light collection (from the cleaved back face of the ITO-coated fibre-optic tip) and optical alignment are facilitated by a simple two-lens arrangement where the in-vacuum collimation/collection lens may be adjusted using a slip-stick motor. A second in-air lens focuses the light (which emerges from the UHV system as a parallel beam) onto a cooled CCD spectrograph or photomultiplier tube. The application of the instrument to combined optical and electronic spectroscopy of Au and GaAs surfaces is discussed

282

Dielectric breakdown of ultrathin aluminum oxide films induced by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Dielectric breakdown of 7-Aa-thick Al2O3 (111) films grown on Ni3Al(111) under ultrahigh vacuum conditions is induced by increasing the bias voltage on the scanning tunneling microscopy tip under constant current feedback. Breakdown is marked by the precipitous retreat of the tip from the surface, and the formation of an elevated feature in the scanning tunneling microscopy image, typically greater than 5 nm high and ?100 nm in diameter. Constant height measurements performed at tip/sample distances of 1 nm or less yield no tip/substrate physical interaction, indicating that such features do not result from mass transport. Consistent with this, current/voltage measurements within the affected regions indicate linear behavior, in contrast to a band gap of 1.5 eV observed at unaffected regions of the oxide surface. A threshold electric field value of 11±1 MV cm-1 is required to induce breakdown, in good agreement with extrapolated values from capacitance measurements on thicker oxides. (c) 2000 American Institute of Physics

283

Optical spectroscopy and scanning tunneling microscopy studies of molecular adsorbates and anisotropic ultrathin films. Final report  

Energy Technology Data Exchange (ETDEWEB)

The bonding, chemistry and ordering of molecular adsorbates on well defined single crystal surfaces and in ultrathin films was to be studied in an effort to develop sufficient fundamental understanding to allow the controlled preparation of anisotropic ultrathin films of organic monolayers. In this research the authors combine the use of optical probes (Raman spectroscopy, laser induced thermal desorption with Fourier transform mass spectrometry detection) with scanning tunneling microscopy (STM) and conventional methods of UHV surface science (Auger electron spectroscopy, x-ray photoelectron spectroscopy, low energy electron diffraction, and thermal desorption spectroscopy). The conventional surface probes provide well tested methods for the preparation and characterization of single crystal substrates. The optical probes used in the experiments provide powerful methods for the molecular identification of adsorbates in monolayers and ultrathin films. Scanning tunneling microscopy provides one with the ability to determine the detailed molecular level ordering of the molecular adsorbates. The emphasis of this research is on more complex molecular absorbates some of which are monomer precursors to ultrathin polymer films. Enhanced methods of Raman spectroscopy have been developed for the study of monolayer adsorbates on surfaces in ultrahigh vacuum environments. This report gives an overview of recent research results, including the construction of UHV variable temperature STM, analysis of STM images, growth and chemistry of intermetallic single crystal ultrathin films, and electron beam induced chemistry of tetracyanoquinodimethane.

Hemminger, J.C.

1998-09-01

284

Anisotropic Superconducting Gap Revealed by Angle Resolved Specific Heat, Point Contact Tunneling and Scanning Tunneling Microscope in Iron Pnictide Superconductors  

Science.gov (United States)

Angle resolved specific heat was measured in FeSe0.55Te0.45 single crystals. A four-fold oscillation of C/T, with the minimum locating at the Fe-Fe bond direction, was observed when the sample was rotated at 9 T, which can be understood as due to the gap modulation on the electron pocket within the scheme of S± pairing. Accordingly, by measuring the point contact Andreev reflection spectrum on the BaFe2-xNixAs2 single crystals in wide doping regimes, we found a crossover from nodeless to nodal feature of the superconducting gap. In K-doped BaFe2As2 single crystals, we performed the low temperature STM measurements and observed a well ordered vortex lattice in local region. In addition, the statistics on over 3000 dI/dV spectra illustrate clear evidence of two gaps with magnitude of 7.6 meV and 3.3 meV, respectively. Detailed fitting to the tunneling spectrum shows an isotropic superconducting gap. Work collaborated with B. Zeng, C. Ren, L. Shan, Y. L. Wang, B. Shen, G. Mu, H. Q. Luo, T. Xiang, H. Yang, I. I. Mazin and P. C. Dai. References: [4pt] [1] B. Zeng, et al., arXiv:1007.3597, Nature Communications, 2010, in press.[0pt] [2] C. Ren, et al., to be published.[0pt] [3] L. Shan, et al., arXiv:1005.4038.

Wen, Hai-Hu

2011-03-01

285

High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat  

Science.gov (United States)

We report on the design and operation of a cryogenic ultra-high vacuum (UHV) scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Thermal drift analysis showed that under optimized conditions, the lateral stability of the STM scanner can be as low as 0.18 Å/h. Scanning Tunneling Spectroscopy measurements based on the lock-in technique were also carried out, and showed no detectable presence of noise from the closed-cycle cryostat. Using this cooling approach, temperatures as low as 16 K at the STM scanner have been achieved, with the complete cool-down of the system typically taking up to 12 h. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic scale.

Hackley, Jason D.; Kislitsyn, Dmitry A.; Beaman, Daniel K.; Ulrich, Stefan; Nazin, George V.

2014-10-01

286

High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat  

Energy Technology Data Exchange (ETDEWEB)

We report on the design and operation of a cryogenic ultra-high vacuum (UHV) scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Thermal drift analysis showed that under optimized conditions, the lateral stability of the STM scanner can be as low as 0.18 Å/h. Scanning Tunneling Spectroscopy measurements based on the lock-in technique were also carried out, and showed no detectable presence of noise from the closed-cycle cryostat. Using this cooling approach, temperatures as low as 16 K at the STM scanner have been achieved, with the complete cool-down of the system typically taking up to 12 h. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic scale.

Hackley, Jason D.; Kislitsyn, Dmitry A.; Beaman, Daniel K.; Nazin, George V., E-mail: gnazin@uoregon.edu [Department of Chemistry and Biochemistry, 1253 University of Oregon, Eugene, Oregon 97403 (United States); Ulrich, Stefan [RHK Technology, Inc., 1050 East Maple Road, Troy, Michigan 48083 (United States)

2014-10-15

287

Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields  

Science.gov (United States)

Scanning magnetic microscopy is a new methodology for mapping magnetic fields with high spatial resolution and field sensitivity. An important goal has been to develop high-performance instruments that do not require cryogenic technology due to its high cost, complexity, and limitation on sensor-to-sample distance. Here we report the development of a low-cost scanning magnetic microscope based on commercial room-temperature magnetic tunnel junction (MTJ) sensors that typically achieves spatial resolution better than 7?µm. By comparing different bias and detection schemes, optimal performance was obtained when biasing the MTJ sensor with a modulated current at 1.0 kHz in a Wheatstone bridge configuration while using a lock-in amplifier in conjunction with a low-noise custom-made preamplifier. A precision horizontal (x-y) scanning stage comprising two coupled nanopositioners controls the position of the sample and a linear actuator adjusts the sensor-to-sample distance. We obtained magnetic field sensitivities better than 150 nT/Hz1/2 between 0.1 and 10?Hz, which is a critical frequency range for scanning magnetic microscopy. This corresponds to a magnetic moment sensitivity of 10-14 A m2, a factor of 100 better than achievable with typical commercial superconducting moment magnetometers. It also represents an improvement in sensitivity by a factor between 10 and 30 compared to similar scanning MTJ microscopes based on conventional bias-detection schemes. To demonstrate the capabilities of the instrument, two polished thin sections of representative geological samples were scanned along with a synthetic sample containing magnetic microparticles. The instrument is usable for a diversity of applications that require mapping of samples at room temperature to preserve magnetic properties or viability, including paleomagnetism and rock magnetism, nondestructive evaluation of materials, and biological assays.

Lima, E. A.; Bruno, A. C.; Carvalho, H. R.; Weiss, B. P.

2014-10-01

288

Manifestation of dynamic Jahn-Teller distortions and surface interactions in scanning tunnelling microscopy images of fullerene anion C?60  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using scanning tunnelling microscopy (STM), it is possible to observe detailed structure of the molecular orbitals (MOs) of fullerene anions C?60. However, understanding the experimental observations is not straightforward because of the inherent presence of Jahn–Teller (JT) interactions, which (in general) split the MOs in one of a number of equivalent ways. Tunnelling between equivalent distortions means that any observed STM image will be a superposition of images arising from the indi...

Dunn, Janette L.; Lakin, Andrew J.; Hands, Ian D.

2012-01-01

289

An easy-to-implement filter for separating photo-excited signals from topography in scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

In order to achieve elemental and chemical sensitivity in scanning tunneling microscopy (STM), synchrotron x-rays have been applied to excite core-level electrons during tunneling. The x-ray photo-excitations result in tip currents that are superimposed onto conventional tunneling currents. While carrying important physical information, the varying x-ray induced currents can destabilize the feedback loop causing it to be unable to maintain a constant tunneling current, sometimes even causing the tip to retract fully or crash. In this paper, we report on an easy-to-implement filter circuit that can separate the x-ray induced currents from conventional tunneling currents, thereby allowing simultaneous measurements of topography and chemical contrasts. The filter and the schematic presented here can also be applied to other variants of light-assisted STM such as laser STM.

Wang Kangkang; Rosenmann, Daniel; Holt, Martin; Winarski, Robert; Hla, Saw-Wai [Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Rose, Volker [Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

2013-06-15

290

Scanning tunneling microscopy and spectroscopy of sodium-chloride overlayers on the stepped Cu(311) surface: Experimental and theoretical study  

CERN Document Server

The physical properties of ultrathin NaCl overlayers on the stepped Cu(311) surface have been characterized using scanning tunneling microscopy (STM) and spectroscopy, and density functional calculations. Simulations of STM images and differential conductance spectrum were based on the Tersoff-Hamann approximation for tunneling with corrections for the modified tunneling barrier at larger voltages and calculated Kohn-Sham states. Characteristic features observed in the STM images can be directly related to calculated electronic and geometric properties of the overlayers. The measured apparent barrier heights for the mono-, bi-, and trilayers of NaCl and the corresponding adsorption-induced changes in the work function, as obtained from the distance dependence of the tunneling current, are well reproduced by and understood from the calculated results. The measurements revealed a large reduction of the tunneling conductance in a wide voltage region, resembling a band gap. However, the simulated spectrum showed ...

Olsson, F E; Repp, J; Meyer, G

2005-01-01

291

In situ scanning tunnelling microscopy of redox molecules. Coherent electron transfer at large bias voltages  

DEFF Research Database (Denmark)

Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared with the molecular and solvent reorganisation Gibbs energy, E-r. However, a large V-bias is frequently needed for stable imaging. This applies particularly to in situ STM of redox metalloproteins, emerging as a new approach to imaging of biological processes directly in aqueous medium. We provide first an extension of previous theoretical work on in situ STM of redox molecules, to large bias voltages, \\eV(bias)\\ > E-r. Large bias voltages give tunnelling contrasts independent of the overpotential over a broad range, as both the oxidised and reduced redox levels are located within the 'energy tip' between the substrate and tip Fermi levels. STM here involves coherent two-step interfacial electron transfer between the redox level and the enclosing substrate and tip. We have also extended previous experimental in situ STM studies of the blue copper protein Pseudomonas aeruginosa azurin, adsorbed on Au(111), to cover a broad tunnelling current-overpotential range at a constant (large) bias voltage of +0.2 V. The current is found to be constant over a 0.25 V overpotential range, which covers roughly the range where the oxidised and reduced redox levels are located within the energy tip. STM contrast and apparent adsorbate coverage decrease outside this range. This could reflect in part redox processes of azurin, but also tip-induced disassembly of the azurin monolayer.

Zhang, Jingdong; Kuznetsov, A.M.

2003-01-01

292

Probe effect in scanning tunneling microscopy on Si(001) low-temperature phases  

International Nuclear Information System (INIS)

The probe effect, the effect of parameters in scanning tunneling microscopy (STM) measurement, on the Si(100) surface with two competing phases in delicate balance, was investigated systematically by reexamining its influence on the Si(100) dimer flip-flop motions at 5 and 80 K. On the basis of the results, the complex array of the phenomena of the Si(100) surface structures was comprehended. The phase transition between c(4x2) and p(2x2) structures below ?40 K was studied by STM, as well as by low-energy electron diffraction, and the appearance of the p(2x2) structure at a reduced probe effect was confirmed. In these investigations, a phase with long-range ordering of the c(4x2) and p(2x2) structures was observed

293

Assessment of scanning tunneling spectroscopy modes inspecting electron confinement in surface-confined supramolecular networks.  

Science.gov (United States)

Scanning tunneling spectroscopy (STS) enables the local, energy-resolved investigation of a samples surface density of states (DOS) by measuring the differential conductance (dI/dV) being approximately proportional to the DOS. It is popular to examine the electronic structure of elementary samples by acquiring dI/dV maps under constant current conditions. Here we demonstrate the intricacy of STS mapping of samples exhibiting a strong corrugation originating from electronic density and local work function changes. The confinement of the Ag(111) surface state by a porous organic network is studied with maps obtained under constant-current (CC) as well as open-feedback-loop (OFL) conditions. We show how the CC maps deviate markedly from the physically more meaningful OFL maps. By applying a renormalization procedure to the OFL data we can mimic the spurious effects of the CC mode and thereby rationalize the physical effects evoking the artefacts in the CC maps. PMID:23503526

Krenner, Wolfgang; Kühne, Dirk; Klappenberger, Florian; Barth, Johannes V

2013-01-01

294

Structure investigation of Cellobiohydrolase I from Trichoderma pseudokoningii S38 with a scanning tunneling microscope  

Science.gov (United States)

Cellobiohydrolase I (CBH I) was isolated from a cellulolytic fungal strain Trichoderma pseudokoningii S38, and its ultrastructure was investigated with a scanning tunneling microscope (STM). The STM images showed that the shape of intact CBH I was tadpole-like, consisting of a big head and a long tail. It could be deduced that the head domain was the core protein for the catalytic function, and the long tail was the cellulose binding domain for substrate binding. Thus, for this enzyme molecule, functional differentiation is reflected in the structure peculiarities. This is the first direct observation of the three-dimensional structure of intact CBH I from real space at nanometer scale. The functional mechanism is also discussed.

Zhang, Y. Z.; Liu, J.; Gao, P. J.; Ma, L. P.; Shi, D. X.; Pang, S. J.

295

Construction of a Versatile Ultra-Low Temperature Scanning Tunneling Microscope  

CERN Document Server

We constructed a dilution-refrigerator (DR) based ultra-low temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 20 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in a UHV environment to an STM head keeping low temperature and UHV conditions. After then, the system can be cooled back to the base temperature within 3 hours. Due to these capabilities, it has a variety of applications not only for cleavable materials but also for almost all conducting materials. The present ULT-STM has also an exceptionally high stability in the presence of magnetic field and even during field sweep. We describe details of its design, performance and applications for low temperature physics.

Kambara, H; Niimi, Y; Fukuyama, H

2007-01-01

296

Scanning tunneling microscopy study of the superconducting properties of three-atomic-layer Pb films  

Energy Technology Data Exchange (ETDEWEB)

Ultrathin Pb films with a thickness of three monolayers (ML) were prepared on ?-?(3)×?(3)Pb/Si(111) (Pb-SIC) substrate by molecular beam epitaxy. Despite significant defect scattering, low temperature scanning tunneling microscopy reveals a high superconducting transition temperature T{sub c} of 6.9?K, compared with the bulk T{sub c} (7.2?K). By applying external magnetic field, magnetic vortices were directly imaged, which demonstrates the robustness of superconductivity. By comparing to nearly free-standing Pb films on graphitized SiC (0001) substrate, we suggest that the higher T{sub c} of 3 ML Pb films on Pb-SIC originates from the combined effects of quantum confinement and substrate-enhanced electron-phonon coupling.

Wang, Yilin; Li, Zhi; Wang, Lili; He, Ke; Ma, Xucun, E-mail: xcma@iphy.ac.cn [State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Chen, Mu [State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Xue, Qi-Kun [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China)

2013-12-09

297

Identification of nitrogen dopants in single-walled carbon nanotubes by scanning tunneling microscopy.  

Science.gov (United States)

Using scanning tunnelling microscopy and spectroscopy, we investigated the atomic and electronic structure of nitrogen-doped single walled carbon nanotubes synthesized by chemical vapor deposition. The insertion of nitrogen in the carbon lattice induces several types of point defects involving different atomic configurations. Spectroscopic measurements on semiconducting nanotubes reveal that these local structures can induce either extended shallow levels or more localized deep levels. In a metallic tube, a single doping site associated with a donor state was observed in the gap at an energy close to that of the first van Hove singularity. Density functional theory calculations reveal that this feature corresponds to a substitutional nitrogen atom in the carbon network. PMID:23829349

Tison, Yann; Lin, Hong; Lagoute, Jérôme; Repain, Vincent; Chacon, Cyril; Girard, Yann; Rousset, Sylvie; Henrard, Luc; Zheng, Bing; Susi, Toma; Kauppinen, Esko I; Ducastelle, François; Loiseau, Annick

2013-08-27

298

In-gap states of In2O3 single crystals investigated by scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

The influence of intrinsic point defects on the electronic structure of n-type In2O3 single crystals grown by two methods, namely chemical vapor transport and from the melt, was examined by scanning tunneling spectroscopy. This method is a very surface sensitive technique for measuring the local density of states. So far not resolved states within the fundamental band gap have been observed. The gap states have been studied at different crystals and after several annealing treatments in an oxidizing atmosphere. The spectroscopic results will be compared to state of the art DFT-calculations revealing hints on the origin of the gap states of In2O3 to be due to oxygen vacancies as well as indium and oxygen interstitials. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

299

A density-functional theory study of tip electronic structures in scanning tunneling microscopy  

International Nuclear Information System (INIS)

In this work, we report a detailed analysis of the atomic and electronic structures of transition metal scanning tunneling microscopy tips: Rh, Pd, W, Ir, and Pt pyramidal models, and transition metal (TM) atom tips supported on the W surface, by means of ab initio density-functional theory methods. The d electrons of the apex atoms of the TM tips (Rh, Pd, W, Ir, and Pt tetrahedral structures) show different behaviors near the Fermi level and, especially for the W tip, dz2 states are shown to be predominant near the Fermi level. The electronic structures of larger pyramidal TM tip structures with a single apex atom are also reported. Their obtained density of states are thoroughly discussed in terms of the different d-electron occupations of the TM tips. (paper)

300

Ex situ elaborated proximity mesoscopic structures for ultrahigh vacuum scanning tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

We apply ultrahigh vacuum Scanning Tunneling Spectroscopy (STS) at ultra-low temperature to study proximity phenomena in metallic Cu in contact with superconducting Nb. In order to solve the problem of Cu-surface contamination, Cu(50?nm)/Nb(100?nm) structures are grown by respecting the inverted order of layers on SiO{sub 2}/Si substrate. Once transferred into vacuum, the samples are cleaved at the structure-substrate interface. As a result, a contamination-free Cu-surface is exposed in vacuum. It enables high-resolution STS of superconducting correlations induced by proximity from the underlying superconducting Nb layer. By applying magnetic field, we generate unusual proximity-induced superconducting vortices and map them with a high spatial and energy resolution. The suggested method opens a way to access local electronic properties of complex electronic mesoscopic devices by performing ex situ STS under ultrahigh vacuum.

Stolyarov, V. S. [UMR 7588, Institut des Nanosciences de Paris, UPMC Univ Paris 06, Sorbonne Universités, F-75005 Paris (France); CNRS, UMR 7588, Institut des Nanosciences de Paris, F-75005 Paris (France); Institute of Solid State Physics RAS, 142432 Chernogolovka (Russian Federation); Moscow Institute of Physics and Technology, 141700 Dolgoprudny (Russian Federation); Kazan Federal University, 420008 Kazan (Russian Federation); Moscow State University, 119991 Moscow (Russian Federation); Cren, T., E-mail: tristan.cren@upmc.fr; Debontridder, F.; Brun, C. [UMR 7588, Institut des Nanosciences de Paris, UPMC Univ Paris 06, Sorbonne Universités, F-75005 Paris (France); CNRS, UMR 7588, Institut des Nanosciences de Paris, F-75005 Paris (France); Veshchunov, I. S. [Université de Bordeaux, LP2N, 351 cours de la Libération, F-33405 Talence (France); Institute of Solid State Physics RAS, 142432 Chernogolovka (Russian Federation); Skryabina, O. V. [Institute of Solid State Physics RAS, 142432 Chernogolovka (Russian Federation); Rusanov, A. Yu. [LLC “Applied radiophysics” 142432 Chernogolovka (Russian Federation); Roditchev, D. [UMR 7588, Institut des Nanosciences de Paris, UPMC Univ Paris 06, Sorbonne Universités, F-75005 Paris (France); CNRS, UMR 7588, Institut des Nanosciences de Paris, F-75005 Paris (France); LPEM-UMR 8213, CNRS, ESPCI-ParisTech, UPMC, 10 rue Vauquelin, F-75005 Paris (France)

2014-04-28

 
 
 
 
301

Adsorption geometry of Cu(111)-Cs studied by scanning tunneling microscopy  

CERN Document Server

Using scanning tunneling microscopy at low temperatures we investigated the adsorbate system Cu(111)-Cs for various cesium coverages. At low coverages we observe a hexagonally ordered Cs adsorption layer with a mutual adsorbate distance of 1.1 nm. This distance is discussed in terms of a commensurate adsorption superstructure which is stabilized by long-range adsorbate interactions mediated by Cu(111) surface state electrons. Intermediate coverages are characterized by incommensurate superstructures which are rotated with respect to the substrate lattice. The rotation behavior at 9K follows a general trend which is consistent with models of epitaxial rotation. With increasing coverage the adsorption layers are found to rotate toward alignment with the substrate.

Von Hofe, T; Berndt, R; Hofe, Th. von

2006-01-01

302

Scanning tunneling microscopy of surface modifications induced by UNILAC heavy-ion irradiation  

International Nuclear Information System (INIS)

The processes and modifications induced by the passage of heavy ions through solids have for a long time been the subject of intensive research. Scanning tunneling microscopy (STM) provides a novel access to highly resolved imaging of ion tracks, complementing classical methods such as electron microscopy, X-ray and neutron scattering analysis. Our investigations concentrated on STM of surface modifications of highly oriented pyrolytic graphite (HOPG), and polycarbonate foil. All samples were irradiated at the GSI heavy-ion accelerator UNILAC with highly charged ions, having kinetic energies of several GeV. The impacts of 15 MeV/u Au24+ ions on HOPG created little hills (rather than craters). Within the damaged surface areas the graphite lattice is disturbed to an extent which no longer allows atomic resolution. Single submicron pores in a polymer foil, created by etching ion tracks, became accessible to STM by covering the surface with a thin gold layer. (orig.)

303

Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies  

CERN Document Server

We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently contains both gamma-Fe2O3 and alpha-Fe2O3. Changes to the electronic structure of these materials were studied under reducing conditions. We show that the surface band gap of the electronic excitation spectrum can differ from that of bulk material and is dominated by surface effects.

Preisinger, M; Rudolf, T; Horn, S; Strongin, D R

2005-01-01

304

Invited Article: Autonomous assembly of atomically perfect nanostructures using a scanning tunneling microscope  

Science.gov (United States)

A major goal of nanotechnology is to develop the capability to arrange matter at will by placing individual atoms at desired locations in a predetermined configuration to build a nanostructure with specific properties or function. The scanning tunneling microscope has demonstrated the ability to arrange the basic building blocks of matter, single atoms, in two-dimensional configurations. An array of various nanostructures has been assembled, which display the quantum mechanics of quantum confined geometries. The level of human interaction needed to physically locate the atom and bring it to the desired location limits this atom assembly technology. Here we report the use of autonomous atom assembly via path planning technology; this allows atomically perfect nanostructures to be assembled without the need for human intervention, resulting in precise constructions in shorter times. We demonstrate autonomous assembly by assembling various quantum confinement geometries using atoms and molecules and describe the benefits of this approach.

Celotta, Robert J.; Balakirsky, Stephen B.; Fein, Aaron P.; Hess, Frank M.; Rutter, Gregory M.; Stroscio, Joseph A.

2014-12-01

305

Iron-induced reconstructions on the Ge(001) surface: a scanning tunneling microscopy study  

Energy Technology Data Exchange (ETDEWEB)

Low-dimensional systems can be realized by self-organized arrays of adatoms on semiconductor surfaces. In the last years, significant advances have been made in the growth and spectroscopy of nanowire systems, especially on Ge(001). A fascinating and still open question is whether one can grow such structures with magnetic atoms, which might lead to spin-ordered chains. Here we study the growth of Fe atoms on Ge(001) by scanning tunneling microscopy (STM). Deposition of Fe at {proportional_to}400 C substrate temperature leads to formation of two different Fe-induced reconstructions: A (2 x 1) reconstruction exhibiting chain-like character, and a c(4 x 2) reconstruction that shows a two-dimensional architecture. The structural features for both phases as seen in STM, as well as their occurence in the phase diagram are discussed in detail.

Lochner, Michael [Physikalisches Institut, Universitaet Wuerzburg, 97074 Wuerzburg (Germany); Fachbereich Naturwissenschaften, Universitaet Kassel, 23132 Kassel (Germany); Blumenstein, Christian; Schaefer, Joerg; Claessen, Ralph [Physikalisches Institut, Universitaet Wuerzburg, 97074 Wuerzburg (Germany)

2010-07-01

306

In situ scanning tunneling microscope tip treatment device for spin polarization imaging  

Science.gov (United States)

A tip treatment device for use in an ultrahigh vacuum in situ scanning tunneling microscope (STM). The device provides spin polarization functionality to new or existing variable temperature STM systems. The tip treatment device readily converts a conventional STM to a spin-polarized tip, and thereby converts a standard STM system into a spin-polarized STM system. The tip treatment device also has functions of tip cleaning and tip flashing a STM tip to high temperature (>2000.degree. C.) in an extremely localized fashion. Tip coating functions can also be carried out, providing the tip sharp end with monolayers of coating materials including magnetic films. The device is also fully compatible with ultrahigh vacuum sample transfer setups.

Li, An-Ping [Oak Ridge, TN; Jianxing, Ma [Oak Ridge, TN; Shen, Jian [Knoxville, TN

2008-04-22

307

Visible Light Emission from Atomic Scale Patterns Fabricated by the Scanning Tunneling Microscope  

DEFF Research Database (Denmark)

Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spectroscopically in the visible spectral range. The light emission is based on a novel mechanism involving optical transitions between a tip state and localized states on the sample surface. The wavelength of the photons can be changed by the bias voltage of the STM. The spatial resolution of the photon maps is as good as that of STM topographic images and the photons are emitted from a quasipoint source with a spatial extension similar to the size of a dangling bond. [S0031-9007(98)08376-8].

Thirstrup, C.; Sakurai, M.

1999-01-01

308

Scanning tunneling microscopy studies of organic monolayers adsorbed on the rhodium(111) crystal surface  

Energy Technology Data Exchange (ETDEWEB)

Scanning Tunneling Microscopy studies were carried out on ordered overlayers on the (111) surface of rhodium. These adsorbates include carbon monoxide (CO), cyclohexane, cyclohexene, 1,4-cyclohexadiene, para-xylene, and meta-xylene. Coadsorbate systems included: CO with ethylidyne, CO with para- and meta-xylene, and para-xylene with meta-xylene. In the case of CO, the structure of the low coverage (2x2) overlayer has been observed. The symmetry of the unit cell in this layer suggests that the CO is adsorbed in the 3-fold hollow sites. There were also two higher coverage surface structures with ({radical}7x{radical}7) unit cells. One of these is composed of trimers of CO and has three CO molecules in each unit cell. The other structure has an additional CO molecule, making a total of four. This extra CO sits on a top site.

Cernota, Paul D.

1999-08-01

309

Scanning tunneling spectroscopy of lead sulfide quantum wells fabricated by atomic layer deposition  

Energy Technology Data Exchange (ETDEWEB)

We report the use of scanning tunneling spectroscopy (STS) to investigate one-dimensional quantum confinement effects in lead sulfide (PbS) thin films. Specifically, quantum confinement effects on the band gap of PbS quantum wells were explored by controlling the PbS film thickness and potential barrier height. PbS quantum well structures with a thickness range of 1-20 nm were fabricated by atomic layer deposition (ALD). Two barrier materials were selected based on barrier height: aluminum oxide as a high barrier material and zinc oxide as a low barrier material. Band gap measurements were carried out by STS, and an effective mass theory was developed to compare the experimental results. Our results show that the band gap of PbS thin films increased as the film thickness decreased, and the barrier height increased from 0.45 to 2.19 eV.

Lee, Wonyoung; Dasgupta, Neil P; Lee, Jung-Rok; Prinz, Fritz B [Department of Mechanical Engineering, Stanford University, CA 94305 (United States); Jung, Hee Joon; Sinclair, Robert, E-mail: leewy@stanford.edu [Department of Materials and Science Engineering, Stanford University, CA 94305 (United States)

2010-12-03

310

Scanning tunneling spectroscopy of lead sulfide quantum wells fabricated by atomic layer deposition  

Energy Technology Data Exchange (ETDEWEB)

We report the use of scanning tunneling spectroscopy (STS) to investigate one-dimensional quantum confinement effects in lead sulfide (PbS) thin films. Specifically, quantum confinement effects on the band gap of PbS quantum wells were explored by controlling the PbS film thickness and potential barrier height. PbS quantum well structures with a thickness range of 1–20 nm were fabricated by atomic layer deposition (ALD). Two barrier materials were selected based on barrier height: aluminum oxide as a high barrier material and zinc oxide as a low barrier material. Band gap measurements were carried out by STS, and an effective mass theory was developed to compare the experimental results. Our results show that the band gap of PbS thin films increased as the film thickness decreased, and the barrier height increased from 0.45 to 2.19 eV.

Lee, W. J.; Dasgupta, N. P.; Jung, H. J.; Lee, J. R.; Sinclair, R.; Prinz, F. B.

2010-01-01

311

Scanning tunneling spectroscopy of lead sulfide quantum wells fabricated by atomic layer deposition.  

Science.gov (United States)

We report the use of scanning tunneling spectroscopy (STS) to investigate one-dimensional quantum confinement effects in lead sulfide (PbS) thin films. Specifically, quantum confinement effects on the band gap of PbS quantum wells were explored by controlling the PbS film thickness and potential barrier height. PbS quantum well structures with a thickness range of 1-20 nm were fabricated by atomic layer deposition (ALD). Two barrier materials were selected based on barrier height: aluminum oxide as a high barrier material and zinc oxide as a low barrier material. Band gap measurements were carried out by STS, and an effective mass theory was developed to compare the experimental results. Our results show that the band gap of PbS thin films increased as the film thickness decreased, and the barrier height increased from 0.45 to 2.19 eV. PMID:21063050

Lee, Wonyoung; Dasgupta, Neil P; Jung, Hee Joon; Lee, Jung-Rok; Sinclair, Robert; Prinz, Fritz B

2010-12-01

312

Scanning Tunneling Spectroscopy of Self-assembled Nanoribbons of C60-Diamantane Hybrid Molecules  

Science.gov (United States)

As transistors approach the nanoscale, single molecules become viable alternatives for macroscopic devices. In terms of utilizing carbon, diamondoids -- single cages of the bulk diamond lattice -- have recently become available as the smallest units to explore these structures. We use low temperature scanning tunneling microscopy to perform electron mapping studies on self-assembled monolayers of novel hybrid molecules consisting of a single C60 fused with the double diamond cage called diamantane. Unlike standard C60 self-assembled monolayers, these hybrid molecules tend to form strips or nanoribbon assemblies as opposed to large-scale single sheets. We find spectroscopic differences between these hybrid molecules and the ``parent'' molecule C60, and utilize spatial mapping to find electronic differences in the edge states of these ribbons. We discuss these results in terms of rectification and the potential of these hybrid molecules for molecular electronics.

Randel, J. C.; Niestemski, F. C.; Melinte, S.; Manoharan, H. C.

2012-02-01

313

Cross-sectional scanning tunneling microscopy of semiconductor vertical-cavity surface-emitting laser structure  

International Nuclear Information System (INIS)

Scanning tunneling microscopy (STM) studies of a semiconductor vertical-cavity surface-emitting laser (VCSEL) device viewed in cross section on an atomic scale are reported. The strained layer In0.2Ga0.8As/GaAs multiple-quantum wells (MQWs) in the laser active region are imaged with atomic resolution. For the first time, the interface roughness of In0.2Ga0.8As/GaAs MQWs is revealed by imaging spectroscopically different individual indium and gallium atoms. It was found that STM images can directly map the interface electronic structure of Al0.67Ga0.33As/GaAs multiple layers in the Bragg reflectors of the VCSEL. The images reflect enhanced or reduced interface electron concentration in regions with a spatial extension of ?100 A. The bias effect is also discussed in the imaging of heterostructures

314

Analysis of scanning tunneling microscope topographs of graphite surfaces roughened by Ar+ ion bombardment  

International Nuclear Information System (INIS)

The scanning tunneling microscopy (STM) has been used to investigate graphite surfaces roughened by 5 keV Ar+ ion bombardment. The (0001) surfaces of several samples were etched with the same total ion dose but with different sputter rates for each surface. STM images taken after sputtering show that the roughness of the sputtered surfaces depended on the sputter rate and that the surface topography of each sample appeared self-similar over a large range of length scales. These experimental observations agree with predictions of the recently proposed Shadow Model. The two dimensional height-height correlation function is utilized as a means of quantitative analysis for STM topographs of sputtered surfaces

315

Theoretical analysis of a dual-probe scanning tunneling microscope setup on graphene  

DEFF Research Database (Denmark)

Experimental advances allow for the inclusion of multiple probes to measure the transport properties of a sample surface. We develop a theory of dual-probe scanning tunneling microscopy using a Green's function formalism, and apply it to graphene. Sampling the local conduction properties at finite length scales yields real space conductance maps which show anisotropy for pristine graphene systems and quantum interference effects in the presence of isolated impurities. Spectral signatures in the Fourier transforms of real space conductance maps include characteristics that can be related to different scattering processes. We compute the conductance maps of graphene systems with different edge geometries or height fluctuations to determine the effects of nonideal graphene samples on dual-probe measurements. © 2014 American Physical Society.

Settnes, Mikkel; Power, Stephen R.

2014-01-01

316

Dynamic covalent chemistry of bisimines at the solid/liquid interface monitored by scanning tunnelling microscopy  

Science.gov (United States)

Dynamic covalent chemistry relies on the formation of reversible covalent bonds under thermodynamic control to generate dynamic combinatorial libraries. It provides access to numerous types of complex functional architectures, and thereby targets several technologically relevant applications, such as in drug discovery, (bio)sensing and dynamic materials. In liquid media it was proved that by taking advantage of the reversible nature of the bond formation it is possible to combine the error-correction capacity of supramolecular chemistry with the robustness of covalent bonding to generate adaptive systems. Here we show that double imine formation between 4-(hexadecyloxy)benzaldehyde and different ?,?-diamines as well as reversible bistransimination reactions can be achieved at the solid/liquid interface, as monitored on the submolecular scale by in situ scanning tunnelling microscopy imaging. Our modular approach enables the structurally controlled reversible incorporation of various molecular components to form sophisticated covalent architectures, which opens up perspectives towards responsive multicomponent two-dimensional materials and devices.

Ciesielski, Artur; El Garah, Mohamed; Haar, Sébastien; Kova?í?ek, Petr; Lehn, Jean-Marie; Samorì, Paolo

2014-11-01

317

Scanning tunnelling microscopy study of atomic hydrogen adsorption on the Si(111) 7 x 7 surface  

International Nuclear Information System (INIS)

We studied initial atomic hydrogen adsorption onto Si(111) 7 x 7 adatoms by scanning tunnelling microscopy in an ultrahigh vacuum. Adatom reaction probabilities were measured as a function of atomic hydrogen exposure time for room-temperature and hightemperature surfaces. Hydrogen uptake was well represented by Langmuir adsorption at 361 and 414 K, while depression of uptake was seen at 481 K after one of six adatoms was terminated by hydrogen. Hydrogen adsorption had positive adsorption correlations between adjacent centre adatoms and corner adatoms across the 7 x 7 half unit. These correlations were enhanced at 481 K. In accordance with the positive reaction correlation between these adjacent adatoms, the average number of reacted adatoms in adjacent 7 x 7 half units was also enhanced as the number of reacted adatoms increased in the half unit

318

Ex situ elaborated proximity mesoscopic structures for ultrahigh vacuum scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

We apply ultrahigh vacuum Scanning Tunneling Spectroscopy (STS) at ultra-low temperature to study proximity phenomena in metallic Cu in contact with superconducting Nb. In order to solve the problem of Cu-surface contamination, Cu(50?nm)/Nb(100?nm) structures are grown by respecting the inverted order of layers on SiO2/Si substrate. Once transferred into vacuum, the samples are cleaved at the structure-substrate interface. As a result, a contamination-free Cu-surface is exposed in vacuum. It enables high-resolution STS of superconducting correlations induced by proximity from the underlying superconducting Nb layer. By applying magnetic field, we generate unusual proximity-induced superconducting vortices and map them with a high spatial and energy resolution. The suggested method opens a way to access local electronic properties of complex electronic mesoscopic devices by performing ex situ STS under ultrahigh vacuum

319

Epitaxial clusters studied by synchrotron x-ray diffraction and scanning tunneling microscopy  

DEFF Research Database (Denmark)

Nanoscale clusters are often formed during heteroepitaxial crystal growth. Misfit between the lattice parameter of the substrate and the adsorbate stimulates the formation of regular clusters with a characteristic size. The well-known "hut-clusters" formed during the growth of Ge on Si(001) are a good example of this type. Adsorbates can also produce another type of nanocluster; if the surface free energy of a particular crystallographic plane becomes lower than that of the geometrical surface of the substrate, then the entire surface will break up into regular arrays of small facets which look similar to the "hut clusters". We demonstrate that X-ray diffraction in combination with scanning tunneling microscopy can be used to determine the fundamental properties of such clusters. (C) 1998 Elsevier Science B.V. All rights reserved.

Nielsen, M.; Feidenhans'l, R.

1998-01-01

320

Memristor effect on bundles of vertically aligned carbon nanotubes tested by scanning tunnel microscopy  

Science.gov (United States)

We report on the results of experimental study of an array of vertically aligned carbon nanotubes (VA CNTs) by scanning tunnel microscopy (STM). It is shown that upon the application of an external electric field to the STM probe/VA CNT system, individual VA CNTs are combined into bundles whose diameter depends on the radius of the tip of the STM probe. The memristor effect in VA CNTs is detected. For the VA CNT array under investigation, the resistivity ratio in the low- and high-resistance states at a voltage of 180 mV is 28. The results can be used in the development of structures and technological processes for designing nanoelectronics devices based on VA CNT arrays, including elements of ultrahigh-access memory cells for vacuum microelectronics devices.

Ageev, O. A.; Blinov, Yu. F.; Il'in, O. I.; Kolomiitsev, A. S.; Konoplev, B. G.; Rubashkina, M. V.; Smirnov, V. A.; Fedotov, A. A.

2013-12-01

 
 
 
 
321

Design and Implementation of a 4K Cryocooler-Based Scanning Tunneling Microscope  

Science.gov (United States)

Low temperature, ultra-high vacuum scanning tunneling microscopes (STMs) have proved to be excellent tools for the study of electronic properties of complex materials. Unfortunately, with the continuing increase in liquid helium prices, already a dominant cost for operating these systems, their use is becoming exceedingly expensive. Here we describe the design and implementation of a STM cooled by a Cryomech PT407 Remote Motor Cryorefrigerator, allowing us to reach helium temperatures using a closed thermodynamic cycle with zero cryogen waste. Unfortunately, this refrigeration technique is not ultra-high vacuum (UHV) compatible and introduces vibrations. To tackle these problems, we separately house the cryocooler in a high-vacuum (HV) chamber. This provides both a UHV environment for the STM and mechanical isolation to minimize vibrations reaching the instrument. However, it makes for more challenging thermal connections. This last difficulty we solve by introducing a novel coaxial thermal feedthrough between the HV and UHV chambers.

Vishnubhotla, Ramya; Harrington, Neal; Dusch, Bill; Geng, Carrie; Bannerjee, Riju; Pabbi, Lavish; Hudson, Eric W.

2013-03-01

322

Scanning tunneling microscopy study of the superconducting properties of three-atomic-layer Pb films  

International Nuclear Information System (INIS)

Ultrathin Pb films with a thickness of three monolayers (ML) were prepared on ?-?(3)×?(3)Pb/Si(111) (Pb-SIC) substrate by molecular beam epitaxy. Despite significant defect scattering, low temperature scanning tunneling microscopy reveals a high superconducting transition temperature Tc of 6.9?K, compared with the bulk Tc (7.2?K). By applying external magnetic field, magnetic vortices were directly imaged, which demonstrates the robustness of superconductivity. By comparing to nearly free-standing Pb films on graphitized SiC (0001) substrate, we suggest that the higher Tc of 3 ML Pb films on Pb-SIC originates from the combined effects of quantum confinement and substrate-enhanced electron-phonon coupling

323

The Ni(111) surface electrons investigated with low-temperature scanning tunneling spectroscopy  

Science.gov (United States)

The electronic structure of the ferromagnetic Ni(111) surface has been attracting interest for a long time. Despite experimental and theoretical effort, reported values of binding energies, effective masses and number of the surface states and surface resonances differed substantially. Working with a local probe technique reveals relevant contributions from adsorbates and defects. Here we present an extensive scanning tunneling microscopy and spectroscopy investigation at low temperature, employing fourier transform methods for the analysis. The results show a parabolic surface state with an upward dispersion at --165 meV with a surprisingly low effective mass of 0.17 me and a downward dispersing surface resonance at --230 meV. From the decay of the standing wave pattern at step edges electron and hole lifetimes have been determined with values considerably smaller than found on noble metal surfaces. Details of the surface electronic structure have been revealed including an anti-resonance at the Fermi energy.

Braun, Kai-Felix; Flipse, C. F. J.; Rieder, K.-H.

2005-03-01

324

Scanning Tunneling Microscopy Reveals Single-Molecule Insights into the Self-Assembly of Amyloid Fibrils  

DEFF Research Database (Denmark)

Many severe diseases are associated with amyloid fibril deposits in the body caused by protein misfolding. Structural information on amyloid fibrils is accumulating rapidly, but little is known about the assembly of peptides into fibrils at the level of individual molecules. Here we investigate self-assembly of the fibril-forming tetrapeptides KFFE and KVVE on a gold surface under ultraclean vacuum conditions using scanning tunneling microscopy. Combined with restrained molecular dynamics modeling, we identify peptide arrangements with interesting similarities to fibril structures. By resolving individual peptide residues and revealing conformational heterogeneities and dynamics, we demonstrate how conformational correlations may be involved in cooperative fibril growth. Most interestingly, intermolecular interactions prevail over intramolecular interactions, and assembly of the phenyl-rich KFFE peptide appears not to be dominated by ?-? interactions. This study offers interesting perspectives for obtaining fundamental single-molecule insights into fibril formation using a surface science approach to study idealized model systems.

Kalashnyk, Nataliya; Nielsen, Jakob T

2012-01-01

325

Charge-density waves studied with the use of a scanning tunneling microscope  

Science.gov (United States)

Scanning tunneling microscope (STM) images of charge-density waves (CDW's) formed in the layered-structure dichalcogenide crystals TaS2 and TaSe2 have been obtained with a microscope operating in a bath of liquid nitrogen. In 1T-TaS2 and 1T-TaSe2 the images show a hexagonal network of mounds spaced at the CDW wavelength, ?CDW= ?13 a0 where a0 is the atom spacing. The microscope tip deflection in the constant-current mode is extremely large (~2 Å) which gives an image of the 1T-phase surface which is completely dominated by the CDW. In 2H-TaSe2 the CDW is much weaker and careful adjustment of the microscope parameters can give STM images which show superimposed modulations at the atomic wavelength and at the CDW wavelength, ?CDW=3a0. However, in general the STM scans of the 2H phases are dominated by patterns at the atomic wavelength. At 77 K the 4Hb-TaS2 crystals produce STM images with some areas showing atoms only and others showing CDW's only consistent with the existence of a CDW in the octahedral layers only. The STM results for all of the phases of TaS2 and TaSe2 are consistent with the expected variations in the CDW formation and electron transfer as determined by calculation and experiment. However, the unusually large deflection of the tunneling tip caused by the stronger CDW amplitudes in the 1T phases needs further analysis.

Slough, C. G.; McNairy, W. W.; Coleman, R. V.; Drake, B.; Hansma, P. K.

1986-07-01

326

Studies of superconductors by low temperature scanning tunneling microscopy and spectroscopy  

International Nuclear Information System (INIS)

Scanning tunneling microscope which operates at very low temperature (0.45 K) under high magnetic field (14.5 T) (LT·HM-STM/STS) has been developed to be applied for the scanning tunneling spectroscopy (STS) study of superconductivity. Its spatial resolution is in the atomic scale under the high field and STS can be performed with high energy resolution. It was found with this unique instrument that Cooper pairs in Bi2Sr2CaCu2OX had d-character component from the observation of local distribution of state density near the superconductive and normal boundary. Vortex-line lattices were observed on 2H-NbSe2, Bi2Sr2CaCu2OX, YNi2B2C and CeRu2 up to now with LT·HM-STM/STS. Bound state of Cooper pairs confined in the core of magnetic flux of 2H-NbSe2 was observed up close to Hc2 and the behavior how the superconductivity decays there was followed. Since very clean surface is needed to observe superconducting magnetic line lattices it is only seven materials for which the STS flux observation was successfully performed by now. A new method has been developed to cleave or crack samples at low temperatures in vacuum or in helium atmosphere. The method lead to the successful observation of the four materials described above. It was observed that the flux lattice of YNi2B2C changes from triangular lattice to square one when magnetic field is increased. The magnetic flux lattice of Bi2Sr2CaCu2OX was observed under 11.5 T, which is the highest magnetic field under which magnetic flux has been observed in the real space. (S. Funahashi)

327

Scanning Tunneling Microscopy and Spectroscopy: I. Semimetals and Semiconductors. I. Atom-Resolved Imaging of DNA.  

Science.gov (United States)

The topographic and electronic structure of semimetal and semiconductor surfaces were investigated using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), respectively. The long-range morphology and atomic -scale characteristics of cleaved materials, including highly oriented pyrolitic graphite (HOPG), boronated pyrolitic graphite (BPG), titanium disulfide, and gallium arsenide (GaAs), were revealed by STM performed in ultrahigh vacuum (UHV). Atom-resolved constant current topographs and current -imaging data, as well as barrier height information, are presented. Both point and line defects were observed on these surfaces. Visual evidence of coulombic screening caused by adsorption of charged species on n-GaAs(110) is provided. On BPG samples, containing up to 0.5% boron, boron substituent atoms appeared as protrusions approximately 3 A in diameter, with a density consistent with the known concentration. The BPG surface contained numerous line defects, including large-angle grain boundaries, and monolayer -deep etch pits. The effects of stress on the morphology of an annealed vicinal Si(111) wafer were explored. The height and orientation of step bunches, as well as terrace widths, on the (7 x 7) surface were determined. Line fault defects at step kinks were observed; theories for the origin and structure of these features based on stress relief are proposed. Current imaging tunneling spectroscopy (CITS) revealed differences between the adatom sites of the (7 x 7) surface. Atom-resolved barrier height images were also obtained. The measured barrier height was seen to depend strongly on the "cleanliness" of the STM tip. In addition, atom-resolved STM images of duplex DNA supported on a HOPG surface were obtained in UHV. These images revealed double-helical structure, major and minor groove alternation, base pairs, and atomic-scale substructure. The DNA dimensions derived from the STM data were in agreement with dimensions from x-ray crystallography for "random sequence" A-DNA. Cross-sectional profiles of the experimental STM data showed excellent correlation with the atomic contours of the van der Waals surface of A-DNA. Barrier height cross-sections showed general correlation with the atomic -scale topography over the phosphate-sugar backbone but distinct anticorrelation over the base pair region.

Driscoll, Robert James

1993-01-01

328

Investigation of cross-sectional area of the carpal canal by CT scanning as a factor causing carpal tunnel syndrome  

International Nuclear Information System (INIS)

The cross-sectional area of the carpal tunnel in patients with carpal tunnel syndrome (CTS) and healthy controls was measured using CT scanning to investigate the relationship between the cross-sectional area and the occurrence of this syndrome. The cross-sectional area in patients with idiopathic CTS was significantly narrowed at the levels of proximal part (Pm) where scaphoid and pisiform bones were visualized and of the distal part (D1, D2) where the trapezium and hook of hamate were visualized, as compared with the controls, suggesting that the median nerve within the carpal tunnel is easily compressed at the level D1. Narrowing of the cross-sectional area of the carpal tunnel can be estimated by measuring the transverse and antero-posterior diameters. (namekawa, k.)

329

Scanning tunneling microscopy combined with hard X-ray microbeam of high brilliance from synchrotron radiation source  

International Nuclear Information System (INIS)

In situ scanning microscopy (STM) with highly brilliant hard X-ray irradiation was enabled at SPring-8. To obtain a good signal-to-noise ratio for elemental analysis, an X-ray beam with a limited size of ?10?m was aligned to a specially designed STM stage in ultrahigh vacuum. Despite various types of noises and a large radiation load around the STM probe, STM images were successfully observed with atomic resolution. The use of a new system for elemental analysis was also attempted, which was based on the modulation of tunneling signals rather than emitted electrons. Among tunneling signals, tunneling current was found to be better than tip height as a signal to be recorded, because the former reduces markedly the error of measurement. On a Ge nanoisland on a clean Si(111) surface, the modulation of tunneling current was achieved by changing the incident photon energy across the Ge absorption edge. (author)

330

Joule Heating and Spin-Transfer Torque Investigated on the Atomic Scale Using a Spin-Polarized Scanning Tunneling Microscope  

Science.gov (United States)

The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments.

Krause, S.; Herzog, G.; Schlenhoff, A.; Sonntag, A.; Wiesendanger, R.

2011-10-01

331

Fabrication of nanometer flat areas onto YBa2Cu3O7-x thin film surfaces by scanning tunneling microscope  

International Nuclear Information System (INIS)

A scanning tunneling microscope was used to mechanically ''mill'' nanometer flat areas of up to 1600 ?m2 on high temperature superconducting (HTS) films of YBa2Cu3O7-x which were originally formed by laser ablation. Flatness to a standard deviation of 2 nm in height was found to be characteristic of milled areas. It was subsequently possible to mill trenches and ditches onto these flat areas. Scanning tunneling measurements of the exposed layered structure of the milled HTS surface are also reported. Surface modifications are also possible by the application of voltage pulse to the tunneling tip. The combination of electrical pulses and milling offer a possibility of mixed electromechanical patterning of the film

332

Chiral recognition in dimerization of adsorbed cysteine observed by scanning tunnelling microscopy.  

Science.gov (United States)

Stereochemistry plays a central role in controlling molecular recognition and interaction: the chemical and biological properties of molecules depend not only on the nature of their constituent atoms but also on how these atoms are positioned in space. Chiral specificity is consequently fundamental in chemical biology and pharmacology and has accordingly been widely studied. Advances in scanning probe microscopies now make it possible to probe chiral phenomena at surfaces at the molecular level. These methods have been used to determine the chirality of adsorbed molecules, and to provide direct evidence for chiral discrimination in molecular interactions and the spontaneous resolution of adsorbates into extended enantiomerically pure overlayers. Here we report scanning tunnelling microscopy studies of cysteine adsorbed to a (110) gold surface, which show that molecular pairs formed from a racemic mixture of this naturally occurring amino acid are exclusively homochiral, and that their binding to the gold surface is associated with local surface restructuring. Density-functional theory calculations indicate that the chiral specificity of the dimer formation process is driven by the optimization of three bonds on each cysteine molecule. These findings thus provide a clear molecular-level illustration of the well known three-point contact model for chiral recognition in a simple bimolecular system. PMID:11859364

Kühnle, Angelika; Linderoth, Trolle R; Hammer, Bjørk; Besenbacher, Flemming

2002-02-21

333

Scanning tunneling microscope design with a confocal small field permanent magnet  

International Nuclear Information System (INIS)

The field of ultra-sensitive measurements with scanning probes requires the design and construction of novel instruments. For example, the combination of radio frequency detection and scanning probe can be exploited to measure thermal properties and mechanical resonances at a very low scale. Very recent results by Komeda and Manassen (2008 Appl. Phys. Lett. 92 212506) on the detection of spin noise with the scanning tunneling microscopy (STM) have further expanded previous results reported by one of the authors of this manuscript (Messina et al 2007 J. Appl. Phys. 101 053916). In a previous publication, one of the authors used a new STM instrument (Messina et al J. Appl. Phys. 2007 101 053916 and Mannini et al 2007 Inorg. Chim. Acta 360 3837–42) to obtain the detection of electron spin noise (ESN) from individual paramagnetic adsorbates. The magnetic field homogeneity at the STM tip–sample region was limited. Furthermore, vacuum operation of the STM microscope was limited by the heat dissipation at the electromagnet and the radio frequency (RF) recovery electronics. We report here on a new STM head that incorporates a specially designed permanent magnet and in-built RF amplification system. The magnet provides both a better field homogeneity and freedom to operate the instrument in vacuum. The STM microscope is vacuum compatible, and vertical stability has been improved over the previous design (Messina et al 2007 J. Appl. Phys. 101 053916), despite the presence os. 101 053916), despite the presence of a heat dissipative RF amplifier in the close vicinity of the STM tip

334

New insights into nano-magnetism by spin-polarized scanning tunneling microscopy  

International Nuclear Information System (INIS)

Highlights: ? We measure the magnetization reversal of individual nm small Co island by spin-STM. ? We identify an inhomogeneous magnetic anisotropy within a single Co island. ? The magnetic anisotropy near the rim is negligible as compared to 0.148 meV/atom at the island center. ? A crossover of the magnetization reversal from an exchange-spring behavior to domain wall formation is suggested. ? The impact of the observed spatial variation of the spin-dependent electronic properties on reversal is discussed. -- Abstract: We study the magnetization reversal and the position dependence of the spin-dependent electronic properties of nm small bilayer Co islands on Cu(1 1 1) by spin-polarized scanning tunneling microscopy in magnetic fields at low temperatures of 8 K. The analysis of the energy barrier of magnetization reversal from measurements of the switching field suggests a crossover of the magnetization reversal mode with increasing island size around 7500 atoms from exchange-spring behavior to domain wall formation. The quantitative analysis of the island size dependence of the energy barrier indicates an inhomogeneous magnetic anisotropy of the island. The island rim is magnetically soft, whereas the center shows a pronounced effective anisotropy of 0.148 meV/atom. We speculate that this inhomogeneity of the magnetic anisotropy might be a consequence of the spatial dependence of the spin-dependent electronic properties. We measure a spin-polarization and a tunnel magneto resistance ratio of opposite sign at the rim as compared to the island center

335

Superconducting ?-ZrNClx probed by scanning-tunnelling and break-junction spectroscopy  

International Nuclear Information System (INIS)

Highlights: •STM/STS combined with break-junction tunnelling spectroscopy (BJTS) on ?-ZrNCl. •STM image on the ab plane shows triangular atomic lattice spots with a period of 0.36 nm. •The gap peaks are widely distributed (?p–p = 9–28 meV)over the area of 100 nm2. •Average gap ratio 2?/kBTc ? 10 is confirmed by both STS and BJTS. -- Abstract: Superconducting layered compound ?-ZrNClx (x = 0.7) with the critical temperature Tc = 13–14 K was investigated by means of scanning tunnelling microscopy/spectroscopy. The single-crystal domain facet of ?100 ?m2 in the c-axis-oriented polycrystal was used as a probing surface. The STM image at 4.9 K shows triangular atomic lattice spots with the period of ?0.36 nm, which agrees with the X-ray diffraction measurements. The STS measurements of the local conductance, dI/dV, exhibit broadened gap structures with a substantial distribution of the gap-edge values. Most frequently observed peak-to-peak value of ?20 mV is remarkably similar to the superconducting gap edge of the isostructural ?-HfNClx with Tc = 24 K. Temperature, T, dependence of the dI/dV shows that the gap structure disappears above Tc ? 13 K. Fitting of the dI/dV curve by the broadened BCS density of states leads to the superconducting gap of 2?(4.9 K) = 11–13 meV. This is in accordance with our former break-junction data confirming the intrinsic character of the previously obtained extremely large gap to Tc ratio 2?(0)/kBTc ? 10 (kB is the Boltzmann constant), thereby pointing to the unusual superconducting properties of this compound

336

Scanning Tunneling Microscopy on Freeze Fracture Replicas of Ripple Phase of Dimyristoyl Phosphatidylcholine.  

Science.gov (United States)

The development of a technique for imaging freeze fracture replicas with the scanning tunneling microscope (STM) is presented. It is shown that calibrated reproducible images of replicas can be made. The technique is used to measure the conformation of the P_{ beta'} or ripple phase of dimyristoyl phosphatidylcholine (DMPC) for the first time. Scanning tunneling microscopes and atomic force microscopes (AFM) are capable of providing atomic resolution images of crystalline samples. However, many biological or other soft samples cannot be imaged directly because they cannot withstand the forces present during STM or AFM imaging. Using freeze fracture replication a sample can be rapidly frozen to cryogenic temperatures, preserving the structure of the sample. A thin metal film can then be deposited on the surface to create a replica of the surface topography. The technique of freeze fracture replication, originally developed for electron microscopy, has been modified to optimize imaging with the STM. The roles of various forces present during STM imaging are discussed and it is shown that both in theory and in practice the Laplace pressure of a fluid meniscus formed by condensation from laboratory air is capable of deforming samples during imaging. By imaging Langmuir -Blodgett films with known feature heights it is shown that the meniscus and corresponding forces are eliminated by imaging under a dry nitrogen environment. The z (height) direction of the STM is calibrated to the known height of these features. The STM is used to image replicas of the P _{beta'}, phase of DMPC. DMPC belongs to a class of lipids which are the primary components of cell membranes. When mixed with water the lipids form bilayer structures spontaneously. Between 14 C and 23.5 C a fully hydrated DMPC bilayer becomes corrugated or rippled with a ripple wavelength of 12 nm, as opposed to its usual flat appearance. Measurements of the ripple conformation of fully hydrated samples at different temperatures are presented. We find that the amplitude of the ripples decreases with decreasing temperature while the wavelength of the ripple is independent of temperature.

Woodard, John Taylor, IV

337

Direct Probing of Transient Photocurrent Dynamics in p-WSe2 by Time-Resolved Scanning Tunneling Microscopy  

Science.gov (United States)

We have carried out time-resolved scanning tunneling microscopy on a layered semiconductor with an indirect bandgap, p-WSe2, and the dynamics of nonequilibrium photocurrent generated by ultrashort-pulse-laser excitation was analyzed. The photocurrent dynamics reflecting the flow of excited photocarriers at the surface, which is determined by the balance between the diffusion and tunneling rates, was successfully probed. Furthermore, the excess minority carriers transiently trapped at the surface for a few nanoseconds, which produce a transient surface photovoltage and cannot be detected by conventional methods, were directly observed and evaluated.

Yoshida, Shoji; Terada, Yasuhiko; Yokota, Munenori; Takeuchi, Osamu; Mera, Yutaka; Shigekawa, Hidemi

2013-01-01

338

Quantitative impedance characterization of sub-10 nm scale capacitors and tunnel junctions with an interferometric scanning microwave microscope.  

Science.gov (United States)

We present a method to characterize sub-10 nm capacitors and tunnel junctions by interferometric scanning microwave microscopy (iSMM) at 7.8 GHz. At such device scaling, the small water meniscus surrounding the iSMM tip should be reduced by proper tip tuning. Quantitative impedance characterization of attofarad range capacitors is achieved using an 'on-chip' calibration kit facing thousands of nanodevices. Nanoscale capacitors and tunnel barriers were detected through variations in the amplitude and phase of the reflected microwave signal, respectively. This study promises quantitative impedance characterization of a wide range of emerging functional nanoscale devices. PMID:25213481

Wang, Fei; Clément, Nicolas; Ducatteau, Damien; Troadec, David; Tanbakuchi, Hassan; Legrand, Bernard; Dambrine, Gilles; Théron, Didier

2014-10-10

339

Scanning tunneling microscopy/spectroscopy investigations of the interference effects caused by the circular pits on thermally oxidized graphite surface  

International Nuclear Information System (INIS)

The thermal oxidation of the graphite leads to the removal of monoatomic carbon layers from the surface and formation of circular pits on the exposed plane. Near the pit edges the scanning tunneling spectroscopy measurements show a series of very narrow flat regions on the I/V characteristics. The observed I/V flat regions appear only when the characteristic is recorded very close to the pit edges. The appearance of tunneling current steps can be explained by the oscillating character of the local density of states near the pit edges. A simple quantum mechanical model in 2D based on boundary condition for an electron wave function is proposed. (author)

340

Measurements of the superconducting gap of La-Sr-Cu-O with a scanning-tunneling microscope  

International Nuclear Information System (INIS)

We report the first tunneling measurements made on the new high-transition-temperature perovskite superconductors. These were obtained using an ultrahigh-vacuum low-temperature scanning-tunneling microscope. The superconducting gap of a La/sub 1.85/Sr/sub 0.15/CuO/sub 4-//sub y/ sample is 12 +- 3 mV, and the onset T/sub c/ is 40 K, from which 2?/k/sub B/T/sub c/ = 7 +- 2. The possibility that this surprisingly high ratio may be due to a mechanism other than superconductivity is discussed

 
 
 
 
341

Combining scanning tunneling microscopy and synchrotron radiation for high-resolution imaging and spectroscopy with chemical, electronic, and magnetic contrast  

Energy Technology Data Exchange (ETDEWEB)

The combination of high-brilliance synchrotron radiation with scanning tunneling microscopy opens the path to high-resolution imaging with chemical, electronic, and magnetic contrast. Here, the design and experimental results of an in-situ synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system are presented. The system is designed to allow monochromatic synchrotron radiation to enter the chamber, illuminating the sample with x-ray radiation, while an insulator-coated tip (metallic tip apex open for tunneling, electron collection) is scanned over the surface. A unique feature of the SXSTM is the STM mount assembly, designed with a two free-flex pivot, providing an angular degree of freedom for the alignment of the tip and sample with respect to the incoming x-ray beam. The system designed successfully demonstrates the ability to resolve atomic-scale corrugations. In addition, experiments with synchrotron x-ray radiation validate the SXSTM system as an accurate analysis technique for the study of local magnetic and chemical properties on sample surfaces. The SXSTM system's capabilities have the potential to broaden and deepen the general understanding of surface phenomena by adding elemental contrast to the high-resolution of STM. -- Highlights: Black-Right-Pointing-Pointer Synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system designed. Black-Right-Pointing-Pointer Unique STM mount design allows angular DOF for tip alignment with x-ray beam. Black-Right-Pointing-Pointer System demonstrates ability to resolve atomic corrugations on HOPG. Black-Right-Pointing-Pointer Studies show chemical sensitivity with STM tip from photocurrent and tunneling. Black-Right-Pointing-Pointer Results show system's ability to study local magnetic (XMCD) properties on Fe films.

Cummings, M.L. [Rice University, Mechanical Engineering and Materials Science Department, Houston, TX 77005 (United States); Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439 (United States); Chien, T.Y.; Preissner, C. [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States); Madhavan, V. [Boston College, Department of Physics, Chestnut Hill, MA 02467 (United States); Diesing, D. [University of Duisburg-Essen, Faculty for Chemistry, 45141 Essen (Germany); Bode, M. [Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439 (United States); Freeland, J.W. [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States); Rose, V., E-mail: vrose@anl.gov [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States)

2012-01-15

342

Scanning tunneling microscopy studies of surface structures of icosahedral aluminum-copper-iron quasicrystals  

Science.gov (United States)

We investigate the atomic structure of fivefold surface of icosahedral (i-) Al-Cu-Fe quasicrystal using scanning tunneling microscopy (STM) under ultra high vacuum (UHV). Annealing the sputtered surface at appropriate temperature produces a step-terrace structure on the surface. Our STM analysis indicates that the terraces are separated with primarily two stepheights in the ratio of t=5+1 /2 , a characteristic ratio in quasiperiodic structures. The measurements agree with the results from dynamical low energy electron diffraction (LEED) calculations. The spatial distribution of stepheights along the fivefold axis does not follow the quasiperiodic Fibonacci sequence. The existence of such stacking defects in the bulk structure is confirmed with the screw dislocations often observed in the STM scans. The first atomic resolution STM images on this type of material are obtained. The flat terraces are dominated with "ten-petal flower-like" motif, locally arranged with fivefold symmetry. Similar structural features can be identified in the atomically-dense planes generated from one of the available bulk structure models. Based on these results, we conclude that the fivefold i-AlCuFe surface corresponds to a two-dimensional cut of the bulk material. After examining the clean surface, we investigate the nucleation and growth of aluminium metallic thin films on the quasicrystalline i-Al-Cu-Fe fivefold surface. Upon deposition at room temperature, aluminium adatoms nucleate as pentagonal "starfish" with uniform size and in the same orientation. The same structure features are observed for different fluxes at low coverages. Based on the experimental results and the available bulk structure model, we identify the specific nucleation sites on the substrate and develop a model for the formation of the pentagonal starfish.

Cai, Tanhong

2001-07-01

343

Development, design and signal processing of a scanning tunneling microscope for measurement of rough surfaces  

International Nuclear Information System (INIS)

In this work the development and the construction of a scanning tunneling microscope (STM) are described, which is also able to measure relatively rough surfaces. Rough surfaces are considered to have an elevation of the gradient of 45o and more. Such measurements pose special requirements for the construction and especially for the signal processing and control of the STM. For the reconstruction of the sample surface by the raw data delivered by the STM the knowledge about the exact behavior of the STM is essential. For this reason the identification of the individual components is very important. Especially the mechanical behavior of the probe head which positions the sensor tip over the sample is a matter of particular interest. To calculate the exact position of the sensor tip a mechanical model is introduced. The unknown parameters of this model are determined using a laser vibrometer. Because of cost and space limitations the mechanical deflections of the piezoelectric actuators of the probe head aren't checked by range sensors. So an identification of the piezoelectric actuators is required. In particular, the hysteresis behavior of piezoelectric transducers represents a major challenge. Using the mathematical hysteresis model of Coleman and Hodgdon succeeds in solving this problem. To carry out an effective control, the behavior of the STM is modeled in a simulation. Using this model, the design of a fast controller is described. The controller imprntroller is described. The controller improves the dynamic behavior of the STM and allows short measurement periods. The work includes detailed descriptions of the mechanical setup and electronics of the STM in the form of working drawings, schematics and PCB layouts. In addition instructions for two different methods of tip preparation are given. The presented methods and solutions are not limited to the STM, but can be directly transferred to other varieties of scanning probe microscopes. (author)

344

Local low-energy electrical excitation of localized and propagating surface plasmons with a scanning tunneling microscope  

Science.gov (United States)

The highly confined nature of the fields from surface plasmons makes them excellent candidates for future nano-optical devices. Most often, optical excitation is used to excite surface plasmons. However, a local, low energy, electrical method for surface plasmon excitation would be preferable for device applications. The scanning tunneling microscope (STM) is an ideal, low energy, local source of electrons that can excite both localized (LSP) and propagating surface plasmons (SPP). Its local nature, along with the ability to precisely position the excitation source and the absence of any background light from the excitation are essential for our experiments. We have used this technique to locally excite surface plasmons on a variety of metal structures. In our setup, the STM is coupled to an inverted optical microscope and the resulting emitted light is collected through the glass substrate. In such a configuration, both the light emitted from localized plasmons as well as the leakage radiation from propagating surface plasmons may be recorded. Both real plane (spatial information) and Fourier plane (angular information) images may be obtained, as well as emission spectra. In this article we will present the results of STM-SPP excitation on thin Au films on glass and investigate the effect of Au film thickness on the SPP propagation length. These results demonstrate the unique features of STM-excited SPPs: the STM plasmon source may be considered equivalent to a series of oscillating vertical point dipoles, and the resulting plasmons consist of a 2D circular wave with a broadband spectrum. These properties are then exploited to study how SPPs scatter into photons from super and sub-wavelength sized holes. It is found that the larger the hole diameter, the more directional the scattering light. From a type of SPP-Young's experiment we determine that the orientation of the electric field is maintained when SPPs are scattered into photons at holes.

Boer-Duchemin, Elizabeth; Wang, Tao; Le Moal, Eric; Rogez, Benoît; Comtet, Geneviève; Dujardin, Gérald

2014-05-01

345

Superperiodic features observed on graphite under solution with scanning tunneling microscopy  

Science.gov (United States)

Graphite has become one of the most commonly used substrates in scanning tunneling microscopy (STM). It is easily cleaved to yield atomically flat areas (and atomic resolution of the basal plane). However, it suffers some disadvantages. Steps are much more reactive than the basal plane and are easily decorated with contamination. Even clean surfaces yield unusual images: one example is the well-known giant corrugations out of the plane on graphite surfaces [1-3]. This paper deals with yet another unusual effect, which is the observation of superperiodic (SP) features in the plane of the basal layer. Structures with periods of up to several hundred ångströms may be seen on "clean" surfaces. These features have been reported by Hashizume et al. [4] and Kuwabara et al. [5] in air while Lyding et al. [6] have reported similar air observations of graphite surfaces treated with a phosphotungstic acid solution. In this communication, we report these features as observed on a freshly cleaved graphite surface maintained under solution along with some details of the boundary between the "normal" and superperiodic graphite. Our characterization of graphite surfaces under solution with STM has revealed that a small percentage of the surface (˜ 1% or less) shows superperiodic features with observed periodicities in the plane ranging from approximately 45 to 440 Å with peak-to-peak amplitudes out of the plane extending from 2 to 5 Å. We see abrupt boundaries between the superperiodic and "normal" graphite with these boundaries showing high amplitude features.

Oden, P. I.; Thundat, T.; Nagahara, L. A.; Lindsay, S. M.; Adams, G. B.; Sankey, O. F.

1991-08-01

346

Scanning Tunneling Microscopy and Spectroscopy of Sr2RuO4  

Science.gov (United States)

We report scanning tunneling microscopy/spectroscopy (STM/STS) studies of the spin-triplet superconductor Sr2RuO4 at temperatures down to 30 mK and in magnetic fields up to 6 T. Clean sample surfaces were prepared by cleaving the single crystals along the ab plane at 100 K in an ultrahigh vacuum environment. In most cases of the 1.5-K phase samples (Tc ˜ 1.5 K), we observed a gap structure (? ˜ 5 meV) in the local density of states for cleaved surfaces which are likely the SrO planes. This gap is not related to the superconducting state and consistent with the data reported recently by C. Lupien et al. On the other hand, for the 3-K phase samples (Sr2RuO4-Ru eutectic system, Tc ˜ 3 K), thin line defects of about 1 nm width were observed. The topography of the defects depends strongly on the bias voltage applied between sample and tip, which suggests that the electronic state varies largely near the defects.

Kambara, H.; Niimi, Y.; Takizawa, K.; Yaguchi, H.; Maeno, Y.; Fukuyama, Hiroshi

2006-09-01

347

Au/ITO dual-layer-coated optical fiber probe for multifunctional scanning tunneling microscopy  

International Nuclear Information System (INIS)

We have fabricated an Au/ITO (indium-tin-oxide) dual-layer optical fiber probe with functions for high-quality scanning tunneling microscope (STM) imaging and near-field excitation and detection of STM-induced electroluminescence (STML). The inner ITO layer is kept ?150 nm in thickness to ensure the conductivity of the fiber probe. The outer Au layer is kept ?13 nm in thickness to obtain a better combination of high electron injection efficiency and optical transparency. High-quality STM images, and STML corresponding to maximum quantum efficiencies of 7 x 10-4 and 1 x 10-4 photons/electron are obtained on Au(111)/mica and p-GaAs(110) surfaces at room temperature (RT), respectively. The outer Au layer on the Au/ITO-coated fiber probe shows an effective role in improving the quality of STM imaging, the tip apex geometry and durability of the fiber probe, the stability and reproducibility of STML and enhancing the intensity of plasmon-mediated STML from the Au(111) surface but it shows no effect in enhancing the intensity of STML from the GaAs(110) surface.

348

Scanning tunneling microscope-quartz crystal microbalance study of temperature gradients at an asperity contact.  

Science.gov (United States)

Investigations of atomic-scale friction frequently involve setups where a tip and substrate are initially at different temperatures. The temperature of the sliding interface upon contact has thus become a topic of interest. A method for detecting initial tip-sample temperature differences at an asperity contact is described, which consists of a scanning tunneling microscope (STM) tip in contact with the surface electrode of a quartz crystal microbalance (QCM). The technique makes use of the fact that a QCM is extremely sensitive to abrupt changes in temperature. In order to demonstrate the technique's capabilities, QCM frequency shifts were recorded for varying initial tip-substrate temperature differences as an STM tip was brought into and out of contact. The results are interpreted within the context of a recent model for thermal heat conduction at an asperity contact, and it is concluded that the transient frequency response is attributable to small changes in temperature close to the region of contact rather than a change in the overall temperature of the QCM itself. For the assumed model parameters, the results moreover reveal substantial temperature discontinuities at the boundary between the tip and the sample, for example, on the order of 10-15 °C for initial temperature differences of 20 °C. PMID:23387679

Pan, L; Krim, J

2013-01-01

349

Quantifying many-body effects by high-resolution Fourier transform scanning tunneling spectroscopy.  

Science.gov (United States)

High-resolution Fourier transform scanning tunneling spectroscopy (FT-STS) is used to study many-body effects on the surface state of Ag(111). Our results reveal a kink in the otherwise parabolic band dispersion of the surface electrons and an increase in the quasiparticle lifetime near the Fermi energy Ef. The experimental data are accurately modeled with the T-matrix formalism for scattering from a single impurity, assuming that the surface electrons are dressed by the electron-electron and electron-phonon interactions. We confirm the latter as the interaction responsible for the deviations from bare dispersion. We further show how FT-STS can be used to simultaneously extract real and imaginary parts of the self-energy for both occupied and unoccupied states with a momentum and energy resolution competitive with angle-resolved photoemission spectroscopy. From our quantitative analysis of the data we extract a Debye energy of ??D=14±1??meV and an electron-phonon coupling strength of ?=0.13±0.02, consistent with previous results. This proof-of-principle measurement advances FT-STS as a method for probing many body effects, which give rise to a rich array of material properties. PMID:24483688

Grothe, S; Johnston, S; Chi, Shun; Dosanjh, P; Burke, S A; Pennec, Y

2013-12-13

350

Ultrafast Electron Emission and Molecular Dynamics in a Scanning Tunneling Microscope  

Science.gov (United States)

In pursuit of measurements at the limits of space and time relevant to chemistry, we have developed the cross-polarized double beat (CPDB) method. This method employs phase modulation in a Mach-Zehnder type interferometer to enable signal modulation without intensity modulation of the incident light. The method is applied to a scanning tunneling microscope (STM) tip, where the ultrafast induced electron emission properties are measured. The mechanism of electron emission is found to be the result of a nonlinear excitation of the surface plasmon, followed by a Fowler-Nordheim type field emission. This is determined through analysis of the dependence of the current on laser power, incident polarization, and delay time (in a pump-probe type measurement). We have also discovered latent time information in traditional STM measurements on Zinc(II) Etioporphyrin. The Jahn-Teller active electron of the anion couples the vibrational and electronic densities, allowing complete reconstruction of its vibrational superposition from the topography and electroluminescent spectrum. ZnEtio- also undergoes a spin flip transition which allows it to be used as a tunable molecular switch.

Perdue, Shawn Michael

351

Scanning tunneling microscope-quartz crystal microbalance study of temperature gradients at an asperity contact  

Science.gov (United States)

Investigations of atomic-scale friction frequently involve setups where a tip and substrate are initially at different temperatures. The temperature of the sliding interface upon contact has thus become a topic of interest. A method for detecting initial tip-sample temperature differences at an asperity contact is described, which consists of a scanning tunneling microscope (STM) tip in contact with the surface electrode of a quartz crystal microbalance (QCM). The technique makes use of the fact that a QCM is extremely sensitive to abrupt changes in temperature. In order to demonstrate the technique's capabilities, QCM frequency shifts were recorded for varying initial tip-substrate temperature differences as an STM tip was brought into and out of contact. The results are interpreted within the context of a recent model for thermal heat conduction at an asperity contact, and it is concluded that the transient frequency response is attributable to small changes in temperature close to the region of contact rather than a change in the overall temperature of the QCM itself. For the assumed model parameters, the results moreover reveal substantial temperature discontinuities at the boundary between the tip and the sample, for example, on the order of 10-15 °C for initial temperature differences of 20 °C.

Pan, L.; Krim, J.

2013-01-01

352

Scanning Tunneling Microscopy Evidence for the Dissociation of Carbon Monoxide on Ruthenium Steps  

DEFF Research Database (Denmark)

In heterogeneous catalysis, identifying the active site for key reaction steps is an important contribution for the optimization of industrial synthesis. The structure sensitivity of CO dissociation on a metal catalyst, which is the rate-limiting step for the methanation and the Fischer–Tropsch processes under certain conditions, has been debated for years. Here, scanning tunneling microscopy (STM) and density functional theory (DFT) are used to clarify the role of monatomic steps in the splitting of CO on a stepped Ru(0 1 54) crystal, which displays alternating steps with either 4-fold or 3-fold symmetry. After CO doses at elevated temperatures, the STM images reveal step decorations characteristic of atomic oxygen resulting from CO dissociation on every second step. The comparison of the STM images with the results of DFT calculations shows that the step decoration occurs on the steps displaying the 4-fold symmetry. We conclude that the active sites for CO dissociation on ruthenium are located on the 4-foldsymmetry monatomic steps.

Tison, Yann; Nielsen, Kenneth

2012-01-01

353

A New Scanning Tunneling Microscope Reactor Used for High Pressure and High Temperature Catalysis Studies  

Energy Technology Data Exchange (ETDEWEB)

We present the design and performance of a home-built high-pressure and high-temperature reactor equipped with a high-resolution scanning tunneling microscope (STM) for catalytic studies. In this design, the STM body, sample, and tip are placed in a small high pressure reactor ({approx}19 cm{sup 3}) located within an ultrahigh vacuum (UHV) chamber. A sealable port on the wall of the reactor separates the high pressure environment in the reactor from the vacuum environment of the STM chamber and permits sample transfer and tip change in UHV. A combination of a sample transfer arm, wobble stick, and sample load-lock system allows fast transfer of samples and tips between the preparation chamber, high pressure reactor, and ambient environment. This STM reactor can work as a batch or flowing reactor at a pressure range of 10{sup -13} to several bars and a temperature range of 300-700 K. Experiments performed on two samples both in vacuum and in high pressure conditions demonstrate the capability of in situ investigations of heterogeneous catalysis and surface chemistry at atomic resolution at a wide pressure range from UHV to a pressure higher than 1 atm.

Tao, Feng; Tang, David C.; Salmeron, Miquel; Somorjai, Gabor A.

2008-05-12

354

Scanning tunneling microscopy/spectroscopy of picene thin films formed on Ag(111)  

Science.gov (United States)

Using ultrahigh-vacuum low-temperature scanning tunneling microscopy and spectroscopy combined with first principles density functional theory calculations, we have investigated structural and electronic properties of pristine and potassium (K)-deposited picene thin films formed in situ on a Ag(111) substrate. At low coverages, the molecules are uniformly distributed with the long axis aligned along the [11bar 2] direction of the substrate. At higher coverages, ordered structures composed of monolayer molecules are observed, one of which is a monolayer with tilted and flat-lying molecules resembling a (1bar 10) plane of the bulk crystalline picene. Between the molecules and the substrate, the van der Waals interaction is dominant with negligible hybridization between their electronic states; a conclusion that contrasts with the chemisorption exhibited by pentacene molecules on the same substrate. We also observed a monolayer picene thin film in which all molecules were standing to form an intermolecular ? stacking. Two-dimensional delocalized electronic states are found on the K-deposited ? stacking structure.

Yoshida, Yasuo; Yang, Hung-Hsiang; Huang, Hsu-Sheng; Guan, Shu-You; Yanagisawa, Susumu; Yokosuka, Takuya; Lin, Minn-Tsong; Su, Wei-Bin; Chang, Chia-Seng; Hoffmann, Germar; Hasegawa, Yukio

2014-09-01

355

A 30 mK, 13.5 T scanning tunneling microscope with two independent tips  

International Nuclear Information System (INIS)

We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows in situ transfer from an ultra high vacuum preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of CuxBi2Se3. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 ?eV

356

Voltammetry and In Situ Scanning Tunneling Microscopy of Cytochrome c Nitrite Reductase on Au(111)-Electrodes  

DEFF Research Database (Denmark)

Escherichia coli cytochrome c nitrite reductase (NrfA) catalyzes the six-electron reduction of nitrite to perform an important role in the biogeochemical cycling of nitrogen. Here we describe NrfA adsorption on single-crystal Au(111) electrodes as an electrocatalytically active film in which the enzyme undergoes direct electron exchange with the electrode. The adsorbed NrfA has been imaged to molecular resolution by in situ scanning tunneling microscopy (in situ STM) under full electrochemical potential control and under conditions where the enzyme is electrocatalytically active. Details of the density and orientational distribution of NrfA molecules are disclosed. The submonolayer coverage resolved by in situ STM is readily reconciled with the failure to detect nonturnover signals in cyclic voltammetry of the NrfA films. The molecular structures show a range of lateral dimensions. These are suggestive of a distribution of orientations that could account for the otherwise anomalously low turnover number calculated for the total population of adsorbed NrfA molecules when compared with that determined for solutions of NrfA. Thus, comparison of the voltammetric signals and in situ STM images offers a direct approach to correlate electrocatalytic and molecular properties of the protein layer, a long-standing issue in protein film voltammetry.

Gwyer, James; Zhang, Jingdong

2006-01-01

357

Scanning tunneling microscopy assisted by synchrotron radiation light for high-resolution element specific imaging  

International Nuclear Information System (INIS)

Microscope having atomic resolution with chemical sensitivity is one of the ultimate microscopes for the material science. Scanning tunneling microscope (STM) assisted by the core-level excitation by synchrotron radiation (SR) may be a possible candidate of such an ultimate microscope. In this paper we will demonstrate that we can observe element specific images of surfaces in the spatial resolution of several tens of nanometer by measuring the photon induced current images taken with an STM tip detecting the secondary electrons produced by the electron-hole recombination after the core-level excitation. Importance of the chemical contrast-enhancement by dividing the SR-STM image taken at photon absorption edge top by that of at the edge bottom is demonstrated by the observation of transition metal micro patterns. Possibility of a nanometer scale chemical imaging such as C60 domain structure on Si(111) ?3 x ?3-Ag surface with an assistance of high-brilliant light sources is also suggested. (author)

358

Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy.  

Science.gov (United States)

Surfaces of thin oxide ?lms were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001) and line defects in aluminum oxide on NiAl(110), respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM) and the electronic structure by scanning tunneling spectroscopy (STS). On magnesium oxide, different color centers, i.e., F(0), F(+), F(2+) and divacancies, have different effects on the contact potential. These differences enabled classi?cation and unambiguous differentiation by KPFM. True atomic resolution shows the topography at line defects in aluminum oxide. At these domain boundaries, STS and KPFM verify F(2+)-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide ?lms beyond imaging the topography of the surface atoms. PMID:21977410

König, Thomas; Simon, Georg H; Heinke, Lars; Lichtenstein, Leonid; Heyde, Markus

2011-01-01

359

Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Surfaces of thin oxide ?lms were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001 and line defects in aluminum oxide on NiAl(110, respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM and the electronic structure by scanning tunneling spectroscopy (STS. On magnesium oxide, different color centers, i.e., F0, F+, F2+ and divacancies, have different effects on the contact potential. These differences enabled classi?cation and unambiguous differentiation by KPFM. True atomic resolution shows the topography at line defects in aluminum oxide. At these domain boundaries, STS and KPFM verify F2+-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide ?lms beyond imaging the topography of the surface atoms.

Thomas König

2011-01-01

360

TOPICAL REVIEW: Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Recent developments in the application of scanning tunneling microscopy (STM to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneous point-contact formation caused by field-enhanced diffusion to the apex of the tip. Transfer through the application of z-direction pulses is also introduced. Sub-nanometer displacement pulses along the z-direction form point contacts that can be used for reproducible nanodot deposition. Next, the discovery of the STM structural manipulation of surface phases is discussed. It has been demonstrated that superstructures on Si(001 surfaces can be reverse-manipulated by controlling the injected carriers. Finally, the fabrication of an atomic-scale one-dimensional quantum confinement system by single-atom deposition using a controlled point contact is presented. Because of its combined nanofabrication and nanocharacterization capabilities, STM is a powerful tool for exploring the nanotechnology and nanoscience fields.

Daisuke Fujita and Keisuke Sagisaka

2008-01-01

 
 
 
 
361

Nanometer-Scale Compositional Structure in III-V Semiconductor Heterostructures Characterized by Scanning Tunneling Microscopy  

Energy Technology Data Exchange (ETDEWEB)

Nanometer-scale compositional structure in InAsxP1.InNYAsxPl.x-Y/InP, grown by gas-source molecular-beam epitaxy and in InAsl-xPJkAsl$b#InAs heterostructures heterostructures grown by metal-organic chemical vapor deposition has been characterized using cross-sectional scanning tunneling microscopy. InAsxP1-x alloy layers are found to contain As-rich and P-rich clusters with boundaries formed preferentially within (T 11) and (111) crystal planes. Similar compositional structure is observed within InNYAsxP1-x-Y alloy layers. Imaging of InAsl-xp@Asl#bY superlattices reveals nanometer-scale clustering within both the hAsI-.p and InAsl$bY alloy layers, with preferential alignment of compositional features in the direction. Instances are observed of compositional structure correlated across a heterojunction interface, with regions whose composition corresponds to a smaller unstrained lattice, constant relative to the surrounding alloy material appearing to propagate across the interface.

Allerman, A.A.; Bi, W.G.; Biefeld, R.M.; Tu, C.W.; Yu, E.T.; Zuo, S.L.

1998-11-10

362

Scanning tunnelling microscopy and spectroscopy of ultra-flat graphene on hexagonal boron nitride.  

Science.gov (United States)

Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy-momentum dispersion relations which cross at the Dirac point. However, accessing the physics of the low-density region at the Dirac point has been difficult because of disorder that leaves the graphene with local microscopic electron and hole puddles. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance. Here we use scanning tunnelling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moiré patterns. However, contrary to predictions, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron-hole charge fluctuations are reduced by two orders of magnitude as compared with those on silicon oxide. This leads to charge fluctuations that are as small as in suspended graphene, opening up Dirac point physics to more diverse experiments. PMID:21317900

Xue, Jiamin; Sanchez-Yamagishi, Javier; Bulmash, Danny; Jacquod, Philippe; Deshpande, Aparna; Watanabe, K; Taniguchi, T; Jarillo-Herrero, Pablo; LeRoy, Brian J

2011-04-01

363

Scanning tunneling microscopy study of molecular growth structures of Gd@C82 on Cu(111)  

International Nuclear Information System (INIS)

The coverage and temperature-dependent nucleation behaviors of the Gd@C82 metallofullerenes on Cu(111) have been studied by low-temperature scanning tunneling microscopy (LT-STM) in detail. Upon molecular deposition at low temperature, Gd@C82 molecules preferentially decorate the steps and nucleate into single layer islands with increasing coverage. Further annealing treatment leads some of the Gd@C82 molecules to assemble into bright and dim patches, which are correlated to the adsorption induced substrate reconstruction. Upon sufficient thermal activation, Gd@C82 molecules sink into the Cu(111) surface one-copper-layer-deep, forming hexagonal close-packed molecular islands with intra-molecular details observed as striped patterns. By considering the commensurability between the Gd@C82 nearest-neighbor distance and the lattice of the underlying Cu(111), we clearly identified two kinds of in-plane molecular arrangements as (?19 × ?19)R23.4° and (?19 × ?19)R36.6° with respect to Cu(111). Within the assembled Gd@C82 molecular, island molecules with dim—bright contrast are spatially distributed, which may be modulated by the preexisted species on Cu(111). (rapid communication)

364

Bulk crystalline copper electrodeposition on polycrystalline gold surfaces observed by in-situ scanning tunneling microscopy  

DEFF Research Database (Denmark)

Bulk copper electrodeposition onto technical gold surfaces in electrolytes of 0.05 M H2SO4 and 1 mM CuSO4 was investigated by in-situ scanning tunnelling microscopy at fixed overpotentials. At potentials between -60 and -30 mV the growth of bulk copper proceeds in cycles of nucleation, agglomeration and crystallization. Crystalline copper is seen as involving an intermediate stage in the progress of growth. The final stage in the growth involves an equilibrium of copper electrochemically dissolving and precipitating. The drift velocity was measured for a gold surface subjected to flame annealing and subsequently installed in the cell compartment. It was found that the drift velocity decays with time in an exponential-like manner, and a 70 min waiting time before experiments with atomic resolution is recommended. Atomic resolution on Au(111) has been obtained, and an apparent surface reconstruction was observed. It is suggested that in reality no reconstruction took place, and that the observation was due to a distortion of the image caused by a constant drift velocity. A mathematical expression which relates the observed surface structure to the drift velocity is presented.

Andersen, Jens Enevold Thaulov; Bech-Nielsen, Gregers

1994-01-01

365

Adsorption stages of O on Ru(0001) studied by means of scanning tunnelling microscopy  

CERN Document Server

The adsorption of O on Ru(0001) at a temperature of 400 K is studied in detail by means of scanning tunnelling microscopy (STM). With increasing O coverage, an ordered p(2x2) structure develops, followed by a p(2x1) structure. While the p(2x2) structure grows via island formation, the p(2x1) structure is abruptly formed by a disorder - order phase transition. After completion of the p(2x2) structure at a coverage of 0.25 ML, the surface develops a rough structure where the (2x2) units remain visible but appear with different heights. As the origin of this phenomenon, we propose additional O-O interactions and/or subsurface O due to the increase in O coverage. At coverages between 0.3 monolayer (ML) and 0.35 ML, different preformations of the p(2x1) structure are observed. First, small fragments of p(2x1) rows develop, which are randomly distributed over the surface and rotated by 120 deg. with respect to each other. They grow in one dimension and induce a criss-cross arrangement of linear chains of O atoms. T...

Meinel, K; Ammer, C; Beckmann, A; Neddermeyer, H

1997-01-01

366

Electron--Vibron Interaction Effects on Scanning Tunneling Microscopy Current through Melamine Adsorbed on Cu(100)  

Science.gov (United States)

Electron transport through the melamine molecule was studied. Melamine molecules adsorbed on a Cu(100) surface were investigated by density functional theory (DFT) calculations with the dynamical matrix method. On the basis of calculation results, a model Hamiltonian for a system composed of scanning tunneling microscope (STM), a melamine molecule, and a Cu surface was proposed, taking into account electron--vibron (electron--molecular vibrations) interactions within the melamine molecule. Then, the electronic current was formulated by the nonequilibrium Green's function (NEGF) method. Results show that current is affected by the electron--vibron interactions defined in the melamine molecule through its controllable structural changes. The rectification and fluctuation of current are triggered by low-energy electron--vibron interactions. Furthermore, the electron--vibron interaction effect is found to be enhanced as temperature increases to where higher-energy vibrons begin to be excited at lower energies. However, current becomes uniform at higher temperatures, which shows an undesired sensitivity. The weakening of the electron--vibron interaction of the out-of-molecular-plane vibrational motion can transfer the melamine molecule in its tautomerization state into a current rectifier. The reduction or induction of the repulsion of lone pairs of consecutive N atoms causes the induction or reduction of the low-energy in-plane vibrational motion, which in turn causes the switching of the I--V characteristics between less stable melamine tautomers.

Sarhan, Abdulla; Sakaue, Mamoru; Nakanishi, Hiroshi; Kasai, Hideaki

2012-10-01

367

First-principles modelling of scanning tunneling microscopy using non-equilibrium Green's functions  

DEFF Research Database (Denmark)

The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff-Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a novel STM simulation scheme based on non-equilibrium Green's functions (NEGF) and Wannier functions which is both accurate and very efficient. The main novelty of the scheme compared to the Bardeen and Tersoff-Hamann approaches is that the coupling to the infinite (macroscopic) electrodes is taken into account. As an illustrating example we apply the NEGF-STM method to the Si(001)(2x1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods.

Lin, H.P.; Rauba, J.M.C.

2010-01-01

368

Scanning tunneling microscopy studies of thin foil x-ray mirrors  

DEFF Research Database (Denmark)

In this paper scanning tunneling microscopy (STM) measurements of x-ray mirrors are presented. The x-ray mirrors are 0.3 mm thick dip-lacquered aluminum foils coated with gold by evaporation, as well as state-of-the-art polished surfaces coated with gold, platinum, or iridium. The measurements reveal that the surfaces consist of islands with different topographic features. The microroughness is found to be in the range from 7 to 1 5 Å, and the characteristic length scale for this microroughness is estimated to be between 0.03 and 0.06 m. For the thin foil mirrors it is found that the microroughness depends on the thickness of the gold layer. The roughness is smallest (~7 to 9 Å) for gold layers between ~100 and ~250Å, and it becomes significantly greater (~10 to 15Å) for gold layers thicker than ~350 Å. With a few exceptions the STM measurements agree well with recent x-ray studies. The results can be used as a guide when selecting the best coating process in the production of x-ray mirrors.

Christensen, Finn Erland; Besenbacher, Flemming

1990-01-01

369

High-resolution scanning tunneling microscopy characterization of mixed monolayer protected gold nanoparticles.  

Science.gov (United States)

Gold nanoparticles protected by a binary mixture of thiolate molecules have a ligand shell that can spontaneously separate into nanoscale domains. Complex morphologies arise in such ligand shells, including striped, patchy, and Janus domains. Characterization of these morphologies remains a challenge. Scanning tunneling microscopy (STM) imaging has been one of the key approaches to determine these structures, yet the imaging of nanoparticles' surfaces faces difficulty stemming from steep surface curvature, complex molecular structures, and the possibility of imaging artifacts in the same size range. Images obtained to date have lacked molecular resolution, and only domains have been resolved. There is a clear need for images that resolve the molecular arrangement that leads to domain formation on the ligand shell of these particles. Herein we report an advance in the STM imaging of gold nanoparticles, revealing some of the molecules that constitute the domains in striped and Janus gold nanoparticles. We analyze the images to determine molecular arrangements on parts of the particles, highlight molecular "defects" present in the ligand shell, show persistence of the features across subsequent images, and observe the transition from quasi-molecular to domain resolution. The ability to resolve single molecules in the ligand shell of nanoparticles could lead to a more comprehensive understanding of the role of the ligand structure in determining the properties of mixed-monolayer-protected gold nanoparticles. PMID:24024977

Ong, Quy Khac; Reguera, Javier; Silva, Paulo Jacob; Moglianetti, Mauro; Harkness, Kellen; Longobardi, Maria; Mali, Kunal S; Renner, Christoph; De Feyter, Steven; Stellacci, Francesco

2013-10-22

370

Scanning tunneling microscopy/spectroscopy of picene thin films formed on Ag(111)  

International Nuclear Information System (INIS)

Using ultrahigh-vacuum low-temperature scanning tunneling microscopy and spectroscopy combined with first principles density functional theory calculations, we have investigated structural and electronic properties of pristine and potassium (K)-deposited picene thin films formed in situ on a Ag(111) substrate. At low coverages, the molecules are uniformly distributed with the long axis aligned along the [112¯] direction of the substrate. At higher coverages, ordered structures composed of monolayer molecules are observed, one of which is a monolayer with tilted and flat-lying molecules resembling a (11¯0) plane of the bulk crystalline picene. Between the molecules and the substrate, the van der Waals interaction is dominant with negligible hybridization between their electronic states; a conclusion that contrasts with the chemisorption exhibited by pentacene molecules on the same substrate. We also observed a monolayer picene thin film in which all molecules were standing to form an intermolecular ? stacking. Two-dimensional delocalized electronic states are found on the K-deposited ? stacking structure

371

A versatile variable-temperature scanning tunneling microscope for molecular growth.  

Science.gov (United States)

We describe and discuss the design of a variable-temperature scanning tunneling microscope (STM) system for the study of molecules at temperatures between 18 and 300 K in ultrahigh vacuum. The STM head is a refinement of a very rigid design developed and successfully operated in Hamburg. In the current version, the head is connected to a liquid helium flow cryostat, thereby reaching a base temperature of 18 K. To minimize the heat load on the STM head, a helium back flow cooled radiation shield is installed. The dimensions and the choice of materials are based on simulations of the heat dissipation. The STM is galvanically isolated from the vacuum chamber to minimize electronic noise and mechanically decoupled by means of springs and an eddy current damping stage. Additionally, the design of the STM head allows the deposition of several molecular materials onto the same cold sample surface. The operation of the STM in imaging mode is demonstrated for TPP/Cu(111) and FePCNaClCu(111). Spectroscopic capabilities of the system are shown for electronic states on NaClCu(111) and TPP/Cu(111). PMID:19044360

Kuck, Stefan; Wienhausen, Jan; Hoffmann, Germar; Wiesendanger, Roland

2008-08-01

372

Versatile bottom-up construction of diverse macromolecules on a surface observed by scanning tunneling microscopy.  

Science.gov (United States)

The heterocoupling of organic building blocks to give complex multicomponent macromolecules directly at a surface holds the key to creating advanced molecular devices. While "on-surface" synthesis with prefunctionalized molecules has recently led to specific one- and two- component products, a central challenge is to discover universal connection strategies that are applicable to a wide range of molecules. Here, we show that direct activation of C-H bonds intrinsic to ?-functional molecules is a highly generic route for connecting different building blocks on a copper surface. Scanning tunneling microscopy (STM) reveals that covalent ?-functional macromolecular heterostructures, displaying diverse compositions, structures and topologies, are created with ease from seven distinct building blocks (including porphyrins, pentacene and perylene). By exploiting differences in C-H bond reactivity in the deposition and heating protocols we also demonstrate controlled synthesis of specific products, such as block copolymers. Further, the symmetry and geometry of the molecules and the surface also play a critical role in determining the outcome of the covalent bond forming reactions. Our "pick-mix-and-link" strategy opens up the capability to generate libraries of multivariate macromolecules directly at a surface, which in conjunction with nanoscale probing techniques could accelerate the discovery of functional interfaces. PMID:25191836

Haq, Sam; Hanke, Felix; Sharp, John; Persson, Mats; Amabilino, David B; Raval, Rasmita

2014-09-23

373

Realizing a Four-Step Molecular Switch in Scanning Tunneling Microscope Manipulation of Single Chlorophyll-a Molecules  

CERN Document Server

Single chlorophyll-a molecules, a vital resource for the sustenance of life on Earth, have been investigated by using scanning-tunneling-microscope manipulation and spectroscopy on a gold substrate at 4.6 K. The chlorophyll-a binds on Au(111) via its porphyrin unit while the phytyl-chain is elevated from the surface by a support of four CH3 groups. By injecting tunneling electrons from the STM-tip, we are able to bend the phytyl-chain, which enable switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunnelling-electron energy-transfer process, which induces bond rotation within the phytyl-chain.

Iancu, V; Iancu, Violeta; Hla, Saw-Wai

2006-01-01

374

Strong tip-sample coupling in thermal radiation scanning tunneling microscopy  

CERN Document Server

We analyze how a probing particle modifies the infrared electromagnetic near field of a sample. The particle, described by electric and magnetic polarizabilities, represents the tip of an apertureless scanning optical near-field microscope (SNOM). We show that the interaction with the sample can be accounted for by ascribing to the particle dressed polarizabilities that combine the effects of image dipoles with retardation. When calculated from these polarizabilities, the SNOM signal depends only on the fields without the perturbing tip. If the studied surface is not illuminated by an external source but heated instead, the signal is closely related to the projected electromagnetic local density of states (EM-LDOS). Our calculations provide the link between the measured far-field spectra and the sample's optical properties.We also analyze the case where the probing particle is hotter than the sample and evaluate the impact of the dressed polarizabilities on near-field radiative heat transfer. We show that suc...

Joulain, Karl; Chapuis, Pierre-Olivier; De Wilde, Yannick; Babuty, Arthur; Henkel, Carsten

2014-01-01

375

Use of in situ scanning tunneling microscopy for the study of dye sensitization of semiconductor electrodes. Progress report, September 15, 1992--August 15, 1995  

Energy Technology Data Exchange (ETDEWEB)

In the three years of this contract, the authors have set up a state-of-the-art computer-controlled photoelectrochemical characterization laboratory with facilities to measure Mott-Schottky behavior, photocurrent spectra and photocurrent voltage curves on semiconductor electrodes. They have also set up a Bridgeman crystal growth furnace for preparing their own single crystals of SnS{sub 2} and other semiconductor materials for the photoelectrochemical studies. The first boules of SnS{sub 2} have recently been prepared. They have also modified a scanning tunneling microscope to perform photo-STM experiments to spatially resolve photocurrents on semiconductor surfaces. In addition, the acquisition of a Ti:sapphire laser system from the DOE-URI program will give us the power and flexibility in the light source to provide a better chance of single molecule detection. The results on sensitization will be summarized below.

Parkinson, B.

1995-12-31

376

In situ high-temperature scanning tunneling microscopy study of bilayer graphene growth on 6H-SiC(0001)  

International Nuclear Information System (INIS)

Using in situ high-temperature (1395 K), ultra-high vacuum, scanning tunneling microscopy (STM), we investigated the growth of bilayer graphene on 6H-SiC(0001). From the STM images, we measured areal coverages of SiC and graphene as a function of annealing time and found that graphene grows at the expense of SiC. Graphene domains were observed to grow, at comparable rates, at (I) graphene-free SiC step edges, (II) graphene–SiC interfaces, and (III) the existing graphene domain edges. Based upon our results, we suggest that the rate-limiting step controlling bilayer graphene growth is the desorption of Si from the substrate. - Highlights: ? Use of scanning tunneling microscopy at temperatures as high as 1395 K. ? Direct observation of graphene formation on SiC surfaces at the growth temperature. ? Identification of atomic-scale pathways for bilayer graphene growth.

377

A first principles scanning tunneling potentiometry study of an opaque graphene grain boundary in the ballistic transport regime.  

Science.gov (United States)

We report on a theoretical interpretation of scanning tunneling potentiometry (STP), formulated within the Keldysh non-equilibrium Green's function description of quantum transport. By treating the probe tip as an electron point source/sink, it is shown that this approach provides an intuitive bridge between existing theoretical interpretations of scanning tunneling microscopy and STP. We illustrate this through ballistic transport simulations of the potential drop across an opaque graphene grain boundary, where atomistic features are predicted that might be imaged through high resolution STP measurements. The relationship between the electrochemical potential profile measured and the electrostatic potential drop across such a nanoscale defect is also explored in this model system. PMID:25248965

Bevan, Kirk H

2014-10-17

378

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

379

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

Kumar, Mahesh; Roul, Basanta [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India); Central Research Laboratory, Bharat Electronics, Bangalore-560013 (India); Rajpalke, Mohana K.; Bhat, Thirumaleshwara N.; Krupanidhi, S. B. [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India); Kalghatgi, A. T. [Central Research Laboratory, Bharat Electronics, Bangalore-560013 (India)

2011-12-01

380

Design and properties of a cryogenic dip-stick scanning tunneling microscope with capacitive coarse approach control  

Science.gov (United States)

We present the design, setup, and operation of a new dip-stick scanning tunneling microscope. Its special design allows measurements in the temperature range from 4.7 K up to room temperature, where cryogenic vacuum conditions are maintained during the measurement. The system fits into every 4He vessel with a bore of 50 mm, e.g., a transport dewar or a magnet bath cryostat. The microscope is equipped with a cleaving mechanism for cleaving single crystals in the whole temperature range and under cryogenic vacuum conditions. For the tip approach, a capacitive automated coarse approach is implemented. We present test measurements on the charge density wave system 2H-NbSe2 and the superconductor LiFeAs which demonstrate scanning tunneling microscopy and spectroscopy data acquisition with high stability, high spatial resolution at variable temperatures and in high magnetic fields.

Schlegel, R.; Hänke, T.; Baumann, D.; Kaiser, M.; Nag, P. K.; Voigtländer, R.; Lindackers, D.; Büchner, B.; Hess, C.

2014-01-01

 
 
 
 
381

Superconducting ?-ZrNCl{sub x} probed by scanning-tunnelling and break-junction spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •STM/STS combined with break-junction tunnelling spectroscopy (BJTS) on ?-ZrNCl. •STM image on the ab plane shows triangular atomic lattice spots with a period of 0.36 nm. •The gap peaks are widely distributed (?{sub p–p} = 9–28 meV)over the area of 100 nm{sup 2}. •Average gap ratio 2?/k{sub B}T{sub c} ? 10 is confirmed by both STS and BJTS. -- Abstract: Superconducting layered compound ?-ZrNCl{sub x} (x = 0.7) with the critical temperature T{sub c} = 13–14 K was investigated by means of scanning tunnelling microscopy/spectroscopy. The single-crystal domain facet of ?100 ?m{sup 2} in the c-axis-oriented polycrystal was used as a probing surface. The STM image at 4.9 K shows triangular atomic lattice spots with the period of ?0.36 nm, which agrees with the X-ray diffraction measurements. The STS measurements of the local conductance, dI/dV, exhibit broadened gap structures with a substantial distribution of the gap-edge values. Most frequently observed peak-to-peak value of ?20 mV is remarkably similar to the superconducting gap edge of the isostructural ?-HfNCl{sub x} with T{sub c} = 24 K. Temperature, T, dependence of the dI/dV shows that the gap structure disappears above T{sub c} ? 13 K. Fitting of the dI/dV curve by the broadened BCS density of states leads to the superconducting gap of 2?(4.9 K) = 11–13 meV. This is in accordance with our former break-junction data confirming the intrinsic character of the previously obtained extremely large gap to T{sub c} ratio 2?(0)/k{sub B}T{sub c} ? 10 (k{sub B} is the Boltzmann constant), thereby pointing to the unusual superconducting properties of this compound.

Ekino, Toshikazu, E-mail: ekino@hiroshima-u.ac.jp [Hiroshima University, Graduate School of Integrated Arts and Sciences, Higashi-Hiroshima 739-8521 (Japan); Sugimoto, Akira [Hiroshima University, Graduate School of Integrated Arts and Sciences, Higashi-Hiroshima 739-8521 (Japan); Gabovich, Alexander M. [Institute of Physics, National Academy of Sciences of Ukraine, 46, Nauka Avenue, Kyiv 036680 (Ukraine); Zheng, Zhanfeng; Yamanaka, Shoji [Hiroshima University, Graduate School of Engineering, Higashi-Hiroshima 739-8527 (Japan)

2013-11-15

382

Towards automated discrimination of lipids versus peptides from full scan mass spectra.  

Science.gov (United States)

Although physicochemical fractionation techniques play a crucial role in the analysis of complex mixtures, they are not necessarily the best solution to separate specific molecular classes, such as lipids and peptides. Any physical fractionation step such as, for example, those based on liquid chromatography, will introduce its own variation and noise. In this paper we investigate to what extent the high sensitivity and resolution of contemporary mass spectrometers offers viable opportunities for computational separation of signals in full scan spectra. We introduce an automatic method that can discriminate peptide from lipid peaks in full scan mass spectra, based on their isotopic properties. We systematically evaluate which features maximally contribute to a peptide versus lipid classification. The selected features are subsequently used to build a random forest classifier that enables almost perfect separation between lipid and peptide signals without requiring ion fragmentation and classical tandem MS-based identification approaches. The classifier is trained on in silico data, but is also capable of discriminating signals in real world experiments. We evaluate the influence of typical data inaccuracies of common classes of mass spectrometry instruments on the optimal set of discriminant features. Finally, the method is successfully extended towards the classification of individual lipid classes from full scan mass spectral features, based on input data defined by the Lipid Maps Consortium. PMID:25414814

Dittwald, Piotr; Nghia, Vu Trung; Harris, Glenn A; Caprioli, Richard M; Van de Plas, Raf; Laukens, Kris; Gambin, Anna; Valkenborg, Dirk

2014-09-01

383

Atomic origin of the scanning tunneling microscopy images of charge-density-waves on 1T-TaSe2  

International Nuclear Information System (INIS)

We show atomically resolved scanning tunneling microscopy (STM) images of charge density waves (CDWs) at room temperature together with angle-resolved photoelectron band-mapping of 1T-TaSe2. By comparing the results of these two techniques, we demonstrate the atomic structure of the CDW-features observed by the STM and atomic origin of the reconstructed band-structure in this material

384

Electroluminescence of a Polythiophene Molecular Wire Suspended between a Metallic Surface and the Tip of a Scanning Tunneling Microscope  

Science.gov (United States)

The electroluminescence of a polythiophene wire suspended between a metallic surface and the tip of a scanning tunneling microscope is reported. Under positive sample voltage, the spectral and voltage dependencies of the emitted light are consistent with the fluorescence of the wire junction mediated by localized plasmons. This emission is strongly attenuated for the opposite polarity. Both emission mechanism and polarity dependence are similar to what occurs in organic light emitting diodes (OLED) but at the level of a single molecular wire.

Reecht, Gaël; Scheurer, Fabrice; Speisser, Virginie; Dappe, Yannick J.; Mathevet, Fabrice; Schull, Guillaume

2014-01-01

385

Proposed alteration of images of molecular orbitals obtained using a scanning tunnelling microscope as a probe of electron correlation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Scanning tunneling spectroscopy (STS) allows to image single molecules decoupled from the supporting substrate. The obtained images are routinely interpreted as the square moduli of molecular orbitals, dressed by the mean-field electron-electron interaction. Here we demonstrate that the effect of electron correlation beyond mean field qualitatively alters the uncorrelated STS images. Our evidence is based on the ab-initio many-body calculation of STS images of planar molecul...

Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

2012-01-01

386

From Soccer-Ball and Rugby-Ball to Giant Fullerene Molecules:. a Scanning Tunneling Microscopy and Spectroscopy Study  

Science.gov (United States)

Thin films of carbon fullerene molecules, Cn, prepared on metallic substrates are studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) under both ambient and ultrahigh vacuum conditions. The STM and AFM images provide real-space atomic-resolution views of these fascinating molecules and their monolayer growth on metal surfaces which reflect both the intermolecular interactions and interactions with the underlying substrates.

Chen, Ting; Sarid, Dror

387

Discretization of electronic states in large InAsPInP multilevel quantum dots probed by scanning tunneling spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The topography and the electronic structure of InAsP/InP quantum dots are probed by crosssectionnal scanning tunneling microscopy and spectroscopy. The study of the local density of states in such large quantumdots con?rms the discrete nature of theelectronic levels whose wavefunctions are measured by di?erential conductivity mapping. Due to their large dimensions, the energy separation between the discrete electronic levels is low, allowing for quantization both in the lateral and growth...

Fain, Bruno; Robert-philip, Isabelle; Beveratos, Alexios; David, Christophe; Wang, Zhao-zhong; Sagnes, Isabelle; Girard, Jean-christophe

2012-01-01

388

Structure and structural transition of chiral domains in oligo(p-phenylenevinylene) assembly investigated by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

OPV3-CHO molecules are employed to prepare assembly on highly oriented pyrolytic graphite, and the so-prepared assembly is investigated by scanning tunneling microscopy. In the assembly chiral domains are observed with various structures such as linear and windmill. The chiral structural formation, stability, transition, and possible unification are intensively studied. After thermal annealing, linear structure was the only structure. To achieve a unified assembly with a single structure, an ...

Chen, Qing; Chen, Ting; Wang, Dong; Liu, Hui-biao; Li, Yu-liang; Wan, Li-jun

2010-01-01

389

Scanning tunneling microscopy of Fe- and O-sublattices on Fe3O4(1 0 0)  

International Nuclear Information System (INIS)

We present scanning tunneling microscopy of an octahedral (B) plane terminated (?(2)x?(2))R450-reconstructed surface of a natural magnetite (1 0 0) crystal. Implementing a W-tip we achieve the same resolution on Fe rows as was reported in the past either with the use of antiferromagnetic tips or on magnetite (Fe3O4) films. We show images of Fe or O sublattices of Fe3O4 with atomic resolution

390

Geometrical indications of adsorbed hydrogen atoms on graphite producing starlike and ellipsoidal features in scanning tunneling microscopy images  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent scanning tunneling spectroscopy (STM) experiments display images with star and ellipsoidal like features resulting from unique geometrical arrangements of a few adsorbed hydrogen atoms on graphite. Based on first-principles STM simulations, we propose a new model with three hydrogen atoms adsorbed on the graphene sheet in the shape of an equilateral triangle with a hexagon ring surrounded inside. The model reproduces the experimentally observed starlike STM patterns. ...

Khazaei, Mohammad; Ranjbar, Ahmad; Bahramy, Mohammad Saeed; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki

2008-01-01

391

A high-stability scanning tunneling microscope achieved by an isolated tiny scanner with low voltage imaging capability  

International Nuclear Information System (INIS)

We present a novel homebuilt scanning tunneling microscope (STM) with high quality atomic resolution. It is equipped with a small but powerful GeckoDrive piezoelectric motor which drives a miniature and detachable scanning part to implement coarse approach. The scanning part is a tiny piezoelectric tube scanner (industry type: PZT-8, whose d31 coefficient is one of the lowest) housed in a slightly bigger polished sapphire tube, which is riding on and spring clamped against the knife edges of a tungsten slot. The STM so constructed shows low back-lashing and drifting and high repeatability and immunity to external vibrations. These are confirmed by its low imaging voltages, low distortions in the spiral scanned images, and high atomic resolution quality even when the STM is placed on the ground of the fifth floor without any external or internal vibration isolation devices

392

Spatial homogeneity and doping dependence of quasiparticle tunneling spectra in cuprate superconductors  

CERN Document Server

Scanning tunneling spectroscopy (STS) studies reveal long-range (~100 nm) spatial homogeneity in optimally and underdoped superconducting YBa_2Cu_3O_{7-\\delta} (YBCO) single crystals and thin films, and macroscopic spatial modulations in overdoped (Y_{0.7}Ca_{0.3})Ba_2Cu_3O_{7-\\delta} (Ca-YBCO) epitaxial films. In contrast, STS on an optimally doped YBa_2(Cu_{0.9934}Zn_{0.0026}Mg_{0.004})_3O_{6.9} single crystal exhibits strong spatial modulations and suppression of superconductivity over a microscopic scale near the Zn or Mg impurity sites, and the global pairing potential is also reduced relative to that of optimally doped YBCO, suggesting strong pair-breaking effects of the non-magnetic impurities. The spectral characteristics are consistent with d_{x^2-y^2} pairing symmetry for the optimally and underdoped YBCO, and with (d_{x^2-y^2}+s) for the overdoped Ca-YBCO. The doping-dependent pairing symmetry suggests interesting changes in the superconducting ground state, and is consistent with the presence of n...

Yeh, N C; Hammerl, G; Mannhart, J; Tajima, S; Yoshida, K; Schmehl, A; Schneider, C W; Schulz, R R

2001-01-01

393

Scanning tunneling microscopy of charge density wave structure in 1T- TaS{sub 2}  

Energy Technology Data Exchange (ETDEWEB)

I have used a scanning tunneling microscope (STM) to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS{sub 2}) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9{degrees} relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS{sub 2} exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both of these phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10{degrees} and 12.5{degrees} relative to the atomic lattice. Such a rotated CDW would create an interference pattern with the underlying atomic lattice regardless of the existence of a true domain superstructure. Previous work on 1T-TaS{sub 2} has not adequately accounted for the possibility of this moire pattern. However, around each fundamental CDW peak in the Fourier transform of the real space STM images, several satellite spots are visible, which conclusively prove the existence of domains in the NC phase.

Thomson, R.E.

1991-11-01

394

Scanning tunneling microscopy of charge density wave structure in 1T- TaS sub 2  

Energy Technology Data Exchange (ETDEWEB)

I have used a scanning tunneling microscope (STM) to image simultaneously the atomic lattice and the charge density wave (CDW) superstructure in tantalum disulfide (1T-TaS{sub 2}) over the temperature range of 370-77K. In the lowest temperature (commensurate) phase, present below 180K, the CDW is at an angle of 13.9{degrees} relative to the lattice and is uniformly commensurate. In the incommensurate phase, present above 353K, the CDW is aligned with the lattice. 1T-TaS{sub 2} exhibits two other phases; the triclinic (T) phase which is present between 223K and 283K upon warming the sample, and the nearly-commensurate (NC) phase which is present between 353K and 180K upon cooling the sample and between 283K and 353K upon warming the sample. In both of these phases, discommensurate models where the CDW is arranged in small commensurate domains have been proposed. In the NC phase the CDW is rotated between 10{degrees} and 12.5{degrees} relative to the atomic lattice. Such a rotated CDW would create an interference pattern with the underlying atomic lattice regardless of the existence of a true domain superstructure. Previous work on 1T-TaS{sub 2} has not adequately accounted for the possibility of this moire pattern. However, around each fundamental CDW peak in the Fourier transform of the real space STM images, several satellite spots are visible, which conclusively prove the existence of domains in the NC phase.

Thomson, R.E.

1991-11-01

395

Submonolayer growth of Pd on Cu(111) studied by scanning tunneling microscopy  

DEFF Research Database (Denmark)

The growth mode of sub-monolayer amounts of Pd on Cu(111) in the temperature range - 80-300 degrees C has been investigated by scanning tunneling microscopy (STM), Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES). Below approximate to 100 degrees C, the Pd induced phase nucleates at ascending steps in fingered brims and, on large terraces, in fingered islands. The lack of order suggests that the brims and islands are a disordered alloy formed by exchange between Pd and Cu from the layer underneath. For temperatures exceeding approximate to 160 degrees C, Cu is dug out from the surface in extended, monolayer deep pits, and concurrently, the brims and islands increase in height by one layer. High-resolution STM images of brims and islands in this phase are interpreted as evidence for Cu capping. For Pd evaporation at temperatures of 220-300 degrees C, the surface is characterized by the appearance of individual Pd atoms substituted into the first layer and the presence of subsurface Pd. A short-range order that excludes the population of nearest-neighbour, in-plane sites is revealed by pair-correlation analysis. The Pd atoms form bands in the upper terrace next to steps. These bands are surprisingly stable against further diffusion, possibly due to an attractive interaction with second- and third-nearest (in-plane) neighbours and with subsurface Pd. The lack of any ordering is explained, based on a calculation of the surface energy. Once the population of nearest-neighbour sites is excluded, there is practically no energy gain by ordering. (C) 1998 Elsevier Science B.V. All rights reserved.

Lægsgaard, E.; Ruban, Andrei

1998-01-01

396

Characterization and Properties of Oligothiophenes Using Scanning Tunneling Microscopy for Possible Use in Organic Electronics  

International Nuclear Information System (INIS)

A scanning tunneling microscopy study has been made on a group of alkyl-substituted oligothiophenes. The self-assembled monolayers of this type of semi-conducting oligomers on graphite were observed and characterized. To control the self-assembly, it is important to first understand the forces that drive the spontaneous ordering of molecules at interfaces. For the identification of the forces, several substituted oligothiophenes were examined: carboxylic acid groups, methyl ester carboxylic acid, and iodine atoms at one end and benzyl esters at the other end of the oligomers this is in addition to the non-functionalized oligothiophehens, Self-assembled monolayers of these molecules were then examined by STM. A detailed analysis of the driving forces and parameters controlling the formation of the self-assembled 2- D crystal monolayers was carried out by performing modeling of the experimental observations. The theoretical calculations gave us a conclusive insight into the intermolecular interactions, which lead to the observed conformation of molecules on the surface. An attempt to react two iodinated oligomers on the surface after the formation of the monolayer has been done; a topochemical reaction studies using UV/Vis light irradiation has been preceded. The targeted reaction was achieved. This can be considered as a great step towards the formation of nano-wires and other organic electronic devices. The applicability of the above method of force-driven self organisation in different patterns was examined as template for building donor-nano structures for electronic devices. It was necessary to examine the stability of the formed templates in air. The monolayers were left to dry and STM images were taken; C60 was then added to the monolayer, and the complexation of the C60 (as acceptor) with the formed monolayer template was examined.

397

A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability  

Science.gov (United States)

We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid 4He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of 4He, which can be reduced to ?400 mK when using 3He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6 fA/sqrt{Hz}. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition.

Zhang, L.; Miyamachi, T.; Tomani?, T.; Dehm, R.; Wulfhekel, W.

2011-10-01

398

Local secondary-electron emission spectra of graphite and gold surfaces obtained using the Scanning Probe Energy Loss Spectrometer (SPELS)  

International Nuclear Information System (INIS)

Secondary-electron emission (SEE) spectra have been obtained with the Scanning Probe Energy Loss Spectrometer at a tip-sample distance of only 50 nm. Such short working distances are required for the best theoretical spatial resolution (<10 nm). The SEE spectra of graphite, obtained as a function of tip bias voltage, are shown to correspond to unoccupied states in the electronic band structure. The SEE spectra of thin gold films demonstrate the capability of identifying (carbonaceous) surface contamination with this technique.

399

Studies on switching mechanisms in Pd-nanodot embedded Nb2O5 memristors using scanning tunneling microscopy  

International Nuclear Information System (INIS)

Current imaging tunneling spectrum obtained from scanning tunneling microscopy has been used to probe the formation and/or rupture of conductive filaments responsible for bipolar switching in Pd nano-dots embedded Nb2O5 memristors. Filamentary conduction mechanism has been confirmed by scanning tunneling microscopy study using a Pt–Ir tip that enabled performing electroforming and reset operations at the nanoscale. The back and forth transition between the fully oxidized and metallic sub-oxide states of niobium under applied bias, as observed from X-ray photoelectron spectroscopy, is believed to be the source of bipolar switching in Nb2O5 memristors. The incorporation of Pd nanodots in Nb2O5 matrix plays a critical role by acting as an oxygen ion reservoir and/or by polarizing a large volume of oxygen vacancies. The formation and/or rupture of the conducting filaments through trapping–detrapping phenomena are found to boost the memristive switching performance. - Highlights: ? STM technique has been applied to study the resistance switching. ? Use of Pd nanodots enhances the switching in Nb2O5 memristors. ? Origin of switching is found to be due to multiple oxide states of Nb.

400

Co on Pt(111) studied by spin-polarized scanning tunneling microscopy and spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

In this thesis the electronic properties of the bare Pt(111) surface, the structural, electronic, and magnetic properties of monolayer and double-layer high Co nanostructures as well as the spin-averaged electronic structure of single Co atoms on Pt(111) were studied by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The experiments on the bare Pt(111) surface and on single Co atoms have been performed in an STM facility operating at temperatures of down to 0.3 K and at magnetic fields of up to 14 T under ultra-high vacuum conditions. The facility has been taken into operation within the time period of this thesis and its specifications were tested by STS measurements. These characterization measurements show a very high stability of the tunneling junction and an energy resolution of about 100 {mu}eV, which is close to the thermal limit. The investigation of the electronic structure of the bare Pt(111) surface reveals the existence of an unoccupied surface state. By a comparison of the measured dispersion to first-principles electronic structure calculations the state is assigned to an sp-derived surface band at the lower boundary of the projected bulk band gap. The surface state exhibits a strong spin-orbit coupling induced spin splitting. The close vicinity to the bulk bands leads to a strong linear contribution to the dispersion and thus to a deviant appearance in the density of states in comparison to the surface states of the (111) surfaces of noble metals. A detailed study of Co monolayer and double-layer nanostructures on the Pt(111) surface shows that both kinds of nanostructures exhibit a highly inhomogeneous electronic structure which changes at the scale of only a few Aa due to a strong stacking dependence with respect to the Pt(111) substrate. With the help of first principles calculations the different spectroscopic appearance for Co atoms within the Co monolayer is assigned to a stacking dependent hybridization of Co states with the substrate states. Despite this electronic inhomogeneity, the magnetic domains and domain walls are clearly observed by spin-resolved STS. For both types of Co nanostructures the out-of-plane orientation of the magnetic moments is proven. Furthermore, new insights into the anisotropy of the Co nanostructures as well as a strong dependence of the coercivity on the local sample morphology for Co double-layer islands were found. The experiments performed on single Co atoms on the Pt(111) surface show that two groups of Co atoms are present on the surface. Each group can be characterized by a specific spectroscopic signature. An analysis of the spectroscopy and atom manipulation experiments proves that the spectroscopic differences are related to the two possible adsorption sites of the Co atoms on the Pt(111) substrate. (orig.)

Meier, F.K.

2006-07-01

 
 
 
 
401

Time-resolved detection of surface plasmon polaritons with a scanning tunneling microscope  

DEFF Research Database (Denmark)

We present the time-resolved detection of surface plasmon polaritons with an STM. The results indicate that the time resolved signal is due to rectification of coherently superimposed plasmon voltages. The comparison with differential reflectivity measurements shows that the tip itself influences the decay of the plasmon-field coherence. Generation of the measured signal at the tunneling junction offers the possibility to observe ultrafast effects with a spatial resolution determined by the tunneling junction

Keil, Ulrich Dieter Felix; Ha, T.

1998-01-01

402

Submolecular Electronic Mapping of Single Cysteine Molecules by in Situ Scanning Tunneling Imaging  

DEFF Research Database (Denmark)

We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2 x 2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrastsof the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate and tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(I 10) atomic rows and with the amine and carboxyl group toward the solution bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment, suggesting solvent plays a role during molecular assembly.

Zhang, Jingdong; Chi, Qijin

2009-01-01

403

Silicon surface chemistry in aqueous solutions studied with a novel scanning tunneling microscope  

Science.gov (United States)

I have constructed a novel electrochemical scanning tunneling microscope (STM) that operates in controlled atmospheres. The design is convenient both for in-situ STM observations of air-sensitive electrochemical systems and for ex-situ STM observations of air-sensitive surfaces. Using this STM as an ex-situ tool, I present a study of the surface chemistry of silicon in aqueous solutions. There are two motivations for this study. First, as the length scales of integrated circuit (IC) devices continue to decrease, it is becoming increasingly important to prepare extremely clean, atomically smooth silicon surfaces during the initial wet processing steps in order to optimize device performance. A better understanding of the chemistry of wet silicon processing is essential to minimize surface roughness and contamination. A second motivation is that hydrogen-terminated silicon is used as a substrate for forming organic self-assembled monolayers, first synthesized by Linford and Chidsey in our laboratory. I show by ex-situ STM that dissolved oxygen in aqueous 40% ammonium fluoride solution initiates the formation of etch pits in the terraces of the otherwise ideal H-Si(111) surface. I propose that oxygen molecules are reduced to superoxide anion radicals at the negative open-circuit potential of the silicon surface. A small fraction (less than 0.4%) of these superoxide anions abstract hydrogen atoms from the H-Si(111) terraces to form silicon radicals (dangling bonds), which are then susceptible to etching in neutral to basic aqueous solutions. I next present a more comprehensive study that explores the reactivity of H-Si(111) with dissolved Osb2 and added Hsb2Osb2 in both neutral and acidic fluoride solutions. Detailed roughening mechanisms are proposed involving initiation via hydrogen-atom abstraction from the H-Si(111) surface by reactive radical intermediates formed from the reduction of Osb2 and Hsb2Osb2 by the silicon surface. Two final studies are presented which explore the reactivity of H-Si(111) related to metal contamination and removal-a key issue for IC's. Photochlorination, an effective metal removal process, is shown here to modify H-Si(111)(1 x 1) to form an ordered Cl-Si(111)(1 x 1) surface. I also present the initial stages of copper deposition on H-Si(111) from aqueous solution.

Wade, Christopher Paul

404

A review and outlook for an anomaly of scanning tunnelling microscopy (STM): superlattices on graphite  

International Nuclear Information System (INIS)

Since its invention in 1981, scanning tunnelling microscopy (STM) is well-known for its supreme imaging resolution enabling one to observe atomic-scale structures, which has led to the flourishing of nanoscience. As successful as it is, there still remain phenomena which are observed using STM but are beyond our understanding. Graphite is one of the surfaces which have been most extensively studied using STM. However, there are a number of unusual properties of graphite surfaces. First reported in the 1980s, superlattices on graphite have since been observed many times and by many groups, but as yet our understanding of this phenomenon is quite limited. Most of the observed superlattice phenomena are widely believed to be the result of a Moire rotation pattern, arising from the misorientation between two graphite layers, as verified experimentally. A Moire pattern is a lattice with larger periodicity resulting from the overlap of two lattices with smaller periodicities. As graphite layers are composed of hexagonal lattices with a periodicity of 0.246 nm, as observed using STM, when there are misoriented graphite layers overlapping each other, a Moire pattern with larger periodicity, depending on the misorientation angle, will be produced and appear as a superperiodic hexagonal structure on top of the graphite atomic lattice of the topmost surface layer. It is important to study graphite superlattices because, firstly, knowledge of this phenomenon will enable us to proe of this phenomenon will enable us to properly interpret STM images; secondly, it helps us to understand the correlation between electronic structures and atomic-structure rearrangement of graphite which is of tremendous aid for engineering material properties; thirdly, and perhaps most importantly, the observation of the phenomenon exhibits the capability of STM to produce images indicating the nature of internal defects which are below the surface. Over recent years, experimental and modelling techniques have been developed to study this anomalous regime of STM; however, there is a lack of a systematic classification of this scattered information. This review article thus serves the purpose of organizing all these results so as to enable a more comprehensive understanding of this phenomenon. We review the discovery of graphite superlattices, the observation of the associated properties, and the research efforts on this subject. An effort is made to envision the future experimental and theoretical research possibilities to unveil the mystery of this anomaly of STM. Applications of graphite superlattices are also proposed. (topical review)

405

Investigating Atomic Scale Disordered Stripes in the Cuprate Superconductors with Scanning Tunneling Microscopy  

Science.gov (United States)

The high-Tc cuprate superconductors have been studied for 25 years in the search for the mechanism underlying their superconductivity. In the process, experiments learned that the correlated electrons in these materials organize themselves in a variety of patterns. One such pattern is a type of short-range charge modulations that exist both in and outside of the superconducting phase, which has been linked to the cuprate pseudogap phase. In optimal and slightly underdoped Bi2Sr 2CuO6+delta this charge order (labeled Q*) has wavelength ˜ 5a0. A second and, I argue, related order (Q**) has wavelength of ˜1.25a0. These modulations are highly disordered and for this reason their nature is not fully understood. In this thesis I use scanning tunneling microscopy (STM) to study the disorder of these charge modulations, as an avenue to understanding the nature of the charge order itself. Locally, the charge modulations have a preferred orientation, with a wavevector pointing along one crystal axis or the other. But globally, there is no preferred direction. Our most striking finding is that the local orientation is the same for the Q* and Q** orders, strong new evidence that these two types of charge modulations have the same physical cause. Next, we find that Q* and Q** are subject to two kinds of disorder. Disorder in the optimal local wavelength competes with defect pinning of crests and troughs to produce the disordered modulations that we see. To get our final result, I view the local orientation of the charge modulations as an Ising spin, and compare the resulting Ising maps to theoretical predictions for different classes of disorder. I find the disorder to be consistent with 3D Random Field disorder. New analytical tools were necessary to carry out these measurements. I describe a new algorithm to map the local wavevector of a modulation. Then I present a second new algorithm to correct an STM image for the effects of a slightly anisotropic tip, This thesis also describes the construction of a new spin-polarized STM that might (but hasn't yet) shed further light on electronic order in the cuprates.

Main, Elizabeth

406

Energy-Level Splitting of Ligand-Stabilized Au55 Clusters Observed by Low-Temperature Scanning Tunneling Spectroscopy  

Science.gov (United States)

Low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) were employed to analyze the electronic structure of Au55 clusters stabilized by [P(C6H5)3]12Cl6 ligands. At low temperature, the thermal motion of the clusters as well as the thermal drift of the STM are reduced, so that measurements can be performed reproducibly with highest spatial and spectroscopic resolution. At 7 K we imaged for the first time the actual arrangement of the C6H5 rings of the ligand molecules. Spectroscopic data acquired from well defined locations within a cluster reveal energy-level splitting which can be attributed to the Au55 core. The individual energy levels are deduced by using a Monte Carlo simulation of electronic transport through a double tunnel junction. Experimental results are compared with those obtained by density-functional tight-binding calculations.

Zhang, Huijing; Grzeschik, Holger; Sarkar, Pranab; Springborg, Michael; Hartmann, Uwe

2003-12-01

407

NaCl multi-layer islands grown on Au(111)-(22x?3) probed by scanning tunneling microscopy  

International Nuclear Information System (INIS)

The growth of multi-layer NaCl islands on Au(111)-(22x?3) surfaces was investigated using scanning tunneling microscopy (STM). We observed that the aspect of the NaCl islands drastically differs depending on the tunneling conditions. It is therefore possible to observe the layers forming an NaCl island or to image the gold reconstruction below the first NaCl layer. Atomically resolved STM images obtained on the first NaCl layer demonstrate that NaCl grows as an epitaxial crystalline film on Au(111)-(22x?3). STM images also suggest that some NaCl layers can be non-crystalline.

408

Graphene ripples as a realization of a two-dimensional Ising model: A scanning tunneling microscope study  

Science.gov (United States)

Ripples in pristine freestanding graphene naturally orient themselves in an array that is alternately curved-up and curved-down; maintaining an average height of zero. Using scanning tunneling microscopy (STM) to apply a local force, the graphene sheet will reversibly rise and fall in height until the height reaches 60%-70% of its maximum at which point a sudden, permanent jump occurs. We successfully model the ripples as a spin-half Ising magnetic system, where the height of the graphene plays the role of the spin. The permanent jump in height, controlled by the tunneling current, is found to be equivalent to an antiferromagnetic-to-ferromagnetic phase transition. The thermal load underneath the STM tip alters the local tension and is identified as the responsible mechanism for the phase transition. Four universal critical exponents are measured from our STM data, and the model provides insight into the statistical role of graphene's unusual negative thermal expansion coefficient.

Schoelz, J. K.; Xu, P.; Meunier, V.; Kumar, P.; Neek-Amal, M.; Thibado, P. M.; Peeters, F. M.

2015-01-01

409

Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001¯) surfaces  

Science.gov (United States)

An epitaxial silicon-oxide monolayer of chemical composition of Si2O3 (the Si2O3 layer) formed on hexagonal SiC(0001¯) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si2O3 layer are found to be missing SiOn (n = 1, 2, 3) molecules. The band gap of the Si2O3 layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO2, 8.9 eV. It is proposed that the Si2O3 layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

Tochihara, Hiroshi; Shirasawa, Tetsuroh; Suzuki, Takayuki; Miyamachi, Toshio; Kajiwara, Takashi; Yagyu, Kazuma; Yoshizawa, Shunsuke; Takahashi, Toshio; Tanaka, Satoru; Komori, Fumio

2014-02-01

410

Three-dimensional Wentzel-Kramers-Brillouin approach for the simulation of scanning tunneling microscopy and spectroscopy  

Science.gov (United States)

We review the recently developed three-dimensional (3D) atom-superposition approach for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) based on ab initio electronic structure data. In the method, contributions from individual electron tunneling transitions between the tip apex atom and each of the sample surface atoms are summed up assuming the one-dimensional (1D) Wentzel-Kramers-Brillouin (WKB) approximation in all these transitions. This 3D WKB tunneling model is extremely suitable to simulate spin-polarized STM and STS on surfaces exhibiting a complex noncollinear magnetic structure, i.e., without a global spin quantization axis, at very low computational cost. The tip electronic structure from first principles can also be incorporated into the model, that is often assumed to be constant in energy in the vast majority of the related literature, which could lead to a misinterpretation of experimental findings. Using this approach, we highlight some of the electron tunneling features on a prototype frustrated hexagonal antiferromagnetic Cr monolayer on Ag(111) surface. We obtain useful theoretical insights into the simulated quantities that is expected to help the correct evaluation of experimental results. By extending the method to incorporate a simple orbital dependent electron tunneling transmission, we reinvestigate the bias voltage- and tip-dependent contrast inversion effect on the W(110) surface. STM images calculated using this orbital dependent model agree reasonably well with Tersoff-Hamann and Bardeen results. The computational efficiency of the model is remarkable as the k-point samplings of the surface and tip Brillouin zones do not affect the computational time, in contrast to the Bardeen method. In a certain case we obtain a relative computational time gain of 8500 compared to the Bardeen calculation, without the loss of quality. We discuss the advantages and limitations of the 3D WKB method, and show further ways to improve and extend it.

Palotás, Krisztián; Mándi, Gábor; Hofer, Werner A.

2014-12-01

411

Giant fullerenes formed on C60 films irradiated with electrons field-emitted from scanning tunneling microscope tips  

International Nuclear Information System (INIS)

It has been found that spherical large clusters of carbon atoms are formed by irradiation of crystalline C60 films grown on Si(1 1 1)-(7 x 7) surfaces with electrons field-emitted from a scanning tunneling microscope probe tip. The size distribution of the clusters deduced from surface profile measurements suggests that the dominant clusters were not necessarily C60n (n = 2-4) expected from the simple fusion of C60 molecules. It was proposed that electronic excitations of C60 molecules caused the fragment and coalescence of the molecules to form the giant fullerenes as in the photo-induced similar effects

412

GaSb/GaAs quantum dot formation and demolition studied with cross-sectional scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a cross-sectional scanning tunneling microscopy study of GaSb/GaAs quantum dots grown by molecular beam epitaxy. Various nanostructures are observed as a function of the growth parameters. During growth, relaxation of the high local strain fields of the nanostructures plays an important role in their formation. Pyramidal dots with a high Sb content are often accompanied by threading dislocations above them. GaSb ring formation is favored by the use of a thin GaAs first cap layer an...

Smakman, E. P.; Garleff, J. K.; Young, R. J.; Hayne, M.; Rambabu, P.; Koenraad, P. M.

2012-01-01

413

Characterization of Si3N4/SiO2 optical channel waveguides by photon scanning tunneling microscopy  

Science.gov (United States)

Photon scanning tunneling microscopy (PSTM) is used to characterize Si3N4/Si02 optical channel waveguides being used for integrated optical-micromechanical sensors. PSTM utilizes an optical fiber tapered to a fine point which is piezoelectrically positioned to measure the decay of the evanescent field intensity associated with the waveguide propagating mode. Evanescent field decays are recorded for both ridge channel waveguides and planar waveguide regions. Values for the local effective refractive index are calculated from the data for both polarizations and compared to model calculations.

Wang, Yan; Chudgar, Mona H.; Jackson, Howard E.; Miller, Jeffrey S.; De Brabander, Gregory N.; Boyd, Joseph T.

1993-01-01

414

Scanning tunneling microscopy of the formation, transformation, and property of oligothiophene self-organizations on graphite and gold surfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two alkyl-substituted dual oligothiophenes, quarterthiophene (4T)-trimethylene (tm)-octithiophene (8T) and 4T-tm-4T, were used to fabricate molecular structures on highly oriented pyrolytic graphite and Au(111) surfaces. The resulted structures were investigated by scanning tunneling microscopy. The 4T-tm-8T and 4T-tm-4T molecules self-organize into long-range ordered structures with linear and/or quasi-hexagonal patterns on highly oriented pyrolytic graphite at ambient temperature. Thermal a...

Yang, Zhi-yong; Zhang, Hui-min; Yan, Cun-ji; Li, Shan-shan; Yan, Hui-juan; Song, Wei-guo; Wan, Li-jun

2007-01-01

415

A variable-temperature nanostencil compatible with a low-temperature scanning tunneling microscope/atomic force microscope  

International Nuclear Information System (INIS)

We describe a nanostencil lithography tool capable of operating at variable temperatures down to 30 K. The setup is compatible with a combined low-temperature scanning tunneling microscope/atomic force microscope located within the same ultra-high-vacuum apparatus. The lateral movement capability of the mask allows the patterning of complex structures. To demonstrate operational functionality of the tool and estimate temperature drift and blurring, we fabricated LiF and NaCl nanostructures on Cu(111) at 77 K

416

Proximity effect in gold-coated YBa(2)Cu(3)O(7-delta) films studied by scanning tunneling spectroscopy.  

Science.gov (United States)

Scanning tunneling spectroscopy on gold layers overcoating c-axis YBa(2)Cu(3)O(7-delta) (YBCO) films reveals proximity-induced gap structures. The gap size reduces exponentially with the distance from a-axis facets, indicating that the proximity effect is primarily due to the (100) YBCO facets. The penetration depth of superconductivity into the gold is approximately 30 nm, in good agreement with estimations for the dirty limit. The extrapolated gap at the interface is approximately 15 meV, similar to the value of an s-wave component of the order parameter measured at the YBCO surface in recent point-contact experiments. PMID:14754012

Sharoni, Amos; Asulin, Itay; Koren, Gad; Millo, Oded

2004-01-01

417

Imaging Josephson Vortices on the Surface Superconductor Si(111)-(sqrt[7]×sqrt[3])-In using a Scanning Tunneling Microscope.  

Science.gov (United States)

We have studied the superconducting Si(111)-(sqrt[7]×sqrt[3])-In surface using a ^{3}He-based low-temperature scanning tunneling microscope. Zero-bias conductance images taken over a large surface area reveal that vortices are trapped at atomic steps after magnetic fields are applied. The crossover behavior from Pearl to Josephson vortices is clearly identified from their elongated shapes along the steps and significant recovery of superconductivity within the cores. Our numerical calculations combined with experiments clarify that these characteristic features are determined by the relative strength of the interterrace Josephson coupling at the atomic step. PMID:25541798

Yoshizawa, Shunsuke; Kim, Howon; Kawakami, Takuto; Nagai, Yuki; Nakayama, Tomonobu; Hu, Xiao; Hasegawa, Yukio; Uchihashi, Takashi

2014-12-12

418

Interplay of single particle and Josephson Cooper pair tunnelings on the electronic spectra of bilayer cuprate superconductors  

International Nuclear Information System (INIS)

We have investigated the interplay of single particle and Josephson Cooper pair tunnelings on the electronic spectra of optimal and overdoped bilayer cuprate (Bi2Sr2CaCu2O8+x) superconductors using tight binding bilayer Hubbard Hamiltonian within BCS d-wave superconducting state. On the basis of the numerical computation of the spectral function at (?, 0) point of the Brillouin zone, a reduction in bilayer splitting energy is pointed out due to the existence of Josephson Cooper pair tunneling in the superconducting state. We have explained our theoretical analysis of the spectral function in the light of recent angle resolved photoemission spectroscopic (ARPES) measurements on optimal doped bilayer cuprates, where a reduction in the bilayer splitting energy is observed in the superconducting state as compared to normal state

419

Adsorbate structures and catalytic reactions studied in the torrpressure range by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

High-pressure, high-temperature scanning tunneling microscopy (HPHTSTM) was used to study adsorbate structures and reactions on single crystal model catalytic systems. Studies of the automobile catalytic converter reaction [CO + NO {yields} 1/2 N{sub 2} + CO{sub 2}] on Rh(111) and ethylene hydrogenation [C{sub 2}H{sub 4} + H{sub 2} {yields} C{sub 2}H{sub 6}] on Rh(111) and Pt(111) elucidated information on adsorbate structures in equilibrium with high-pressure gas and the relationship of atomic and molecular mobility to chemistry. STM studies of NO on Rh(111) showed that adsorbed NO forms two high-pressure structures, with the phase transformation from the (2 x 2) structure to the (3 x 3) structure occurring at 0.03 Torr. The (3 x 3) structure only exists when the surface is in equilibrium with the gas phase. The heat of adsorption of this new structure was determined by measuring the pressures and temperatures at which both (2 x 2) and (3 x 3) structures coexisted. The energy barrier between the two structures was calculated by observing the time necessary for the phase transformation to take place. High-pressure STM studies of the coadsorption of CO and NO on Rh(111) showed that CO and NO form a mixed (2 x 2) structure at low NO partial pressures. By comparing surface and gas compositions, the adsorption energy difference between topsite CO and NO was calculated. Occasionally there is exchange between top-site CO and NO, for which we have described a mechanism for. At high NO partial pressures, NO segregates into islands, where the phase transformation to the (3 x 3) structure occurs. The reaction of CO and NO on Rh(111) was monitored by mass spectrometry (MS) and HPHTSTM. From MS studies the apparent activation energy of the catalytic converter reaction was calculated and compared to theory. STM showed that under high-temperature reaction conditions, surface metal atoms become mobile. Ethylene hydrogenation and its poisoning by CO was also studied by STM on Rh(111) and Pt(111). Poisoning was found to coincide with decreased adsorbate mobility. Under ethylene hydrogenation conditions, no order is detected by STM at 300 K, as hydrogen and ethylidyne, the surface species formed by gas-phase ethylene, are too mobile. When CO is introduced, the reaction stops, and ordered structures appear on the surface. For Rh(111), the structure is predominantly a mixed c(4 x 2), though there are some areas of (2 x 2). For Pt(111), the structure is hexagonal and resembles the Moire pattern seen when Pt(111) is exposed to pure CO. From these studies it is concluded that CO poisons by stopping adsorbate mobility. This lack of adsorbate mobility prevents the adsorption of ethylene from the gas phase by hindering the creation of adsorption sites.

Hwang, Kevin Shao-Lin

2003-05-23

420

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between {theta} = 78.5 and {theta} = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For {theta} = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount of material as a function of the ion fluence. This method is also applicable under less grazing angles of incidence. The investigations show that the sputtering yield at step edges depends on the azimuthal orientation of the impinging ions with respect to the surface. This change is attributed to the orientation dependence of subsurface channeling. The step edge sputtering yield at small adatom clusters is measured. In this case, the topmost layer (which forms the step edge) has a small lateral extension in ion beam direction. The evaluation shows that the step edge yield is, compared to step edges with a long upper terrace, decreased by a factor of three. The physical reason can be traced back to subsurface channeling. The ions are able to pass underneath the cluster and exit the crystal without a large scattering event. Little energy is transfered to the crystal which results in a low sputtering yield. The influence of adsorbates on sputtering and surface damage in grazing incidence ion erosion is studied for the case of oxygen and carbon monoxide. A partial surface coverage with adsorbates causes an enhancement of the erosion rate (the amount of removed material per ion fluence) by a factor of up to 40 compared to the clean case. The study is performed for 5 keV Ar{sup +} ions for various grazing angles between 81 and 87 and temperatures ranging from 400 K to 550 K. Finally, coarsening of ion beam induced ripple patterns is analyzed. For surface temperatures of 450 K or below coarsening is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation of sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monoatomic steps illuminated by the ion beam. (orig.)

Redinger, Alex

2009-07-10

 
 
 
 
421

Surface damage through grazing incidence ions investigated by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between ? = 78.5 and ? = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For ? = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount of material as a function of the ion fluence. This method is also applicable under less grazing angles of incidence. The investigations show that the sputtering yield at step edges depends on the azimuthal orientation of the impinging ions with respect to the surface. This change is attributed to the orientation dependence of subsurface channeling. The step edge sputtering yield at small adatom clusters is measured. In this case, the topmost layer (which forms the step edge) has a small lateral extension in ion beam direction. The evaluation shows that the step edge yield is, compared to step edges with a long upper terrace, decreased by a factor of three. The physical reason can be traced back to subsurface channeling. The ions are able to pass underneath the cluster and exit the crystal without a large scattering event. Little energy is transfered to the crystal which results in a low sputtering yield. The influence of adsorbates on sputtering and surface damage in grazing incidence ion erosion is studied for the case of oxygen and carbon monoxide. A partial surface coverage with adsorbates causes an enhancement of the erosion rate (the amount of removed material per ion fluence) by a factor of up to 40 compared to the clean case. The study is performed for 5 keV Ar+ ions for various grazing angles between 81 and 87 and temperatures ranging from 400 K to 550 K. Finally, coarsening of ion beam induced ripple patterns is analyzed. For surface temperatures of 450 K or below coarsening is athermal and kinetic, unrelated to diffusion and surface free energy. Similar to the situation of sand dunes, coarsening takes place through annihilation reactions of mobile defects in the pattern. The defect velocity derived on the basis of a simple model agrees quantitatively with the velocity of monoatomic steps illuminated by the ion beam. (orig.)

422

First performance results of two novel spectroradiometers developed for fast scanning of solar spectra UV irradiance  

Science.gov (United States)

Two recently developed different types of fast spectroradiometers measuring solar UV irradiance have been compared in a field campaign: i) the UV spectroradiometer on filter model basis (UV-SPRAFIMO) and ii) the modified version of the spectroradiometer SPECTRO 320D by Instrument Systems. The all-weather UV-SPRAFIMO instrument combines a UV filter radiometer with 5 narrow-band (FBHM ~ 2.0 to 2.5 nm) filters centered within +/- 0.01 nm at 303.5, 309.0, 314.5, 327.0 and 387.0 nm, and an advanced neural network-based model. It allows up to 5 measurements per second to be taken that are averaged within time intervals between 5 and 30 s. The neural networks model that is embedded in the PC-based processing software converts the 5 measured irradiances into a full spectrum from 280 to 450 nm at small wavelength steps (>= 0.05 nm). These spectra can be convoluted with user-defined slit function and integrated to broad-band and action-spectra-weighted irradiance values. Users can access the data stored in the internal data logger by a serial RS232 interface or by a modem and display them on a PC-based Graphical User Interface. The spectroradiometer SPECTRO320D consists of a grating double monochromator with a cooled (-20°C) PMT receiver. The modified instrument version run by DWD uses a Schreder type cosine diffuser that directs the solar global irradiance via quartz fiber optics onto the spectroradiometer's entrance slit. The spectroradiometer used at the campaign was installed in a thermostatted (22 +/- 0.02)°C aluminum box. The modified instrument version performs a spectral scan over the whole UV region in two subsequent parts, with a lower speed in the UV-B than in the UV-A to account for the exponential changes of solar irradiance with increasing wavelengths in the UV-B and for the almost linear change in the UV-A region. In the configuration applied in the comparison, i.e. wavelength steps of 0.2 nm within the scan range from 290 nm to 450 nm, the resulting scan time of the SPECTRO 320D was 23 s. The two spectroradiometers, which both have been absolutely calibrated in the DWD lab using FEL 1000 W halogen lamps traceable to the German Physikalisch-Technische Bundesanstalt (PTB), were used in a field campaign at Izana (Tenerife Island) at a height of 2409 m to compare measured spectral and integral values of solar irradiance. Results of that comparison and the instruments" characteristics revealed under those special field conditions will be discussed.

Feister, Uwe; Kaifel, Anton K.; Grewe, Rolf-Dieter; Kaptur, Jasmine; Reutter, Oliver; Wohlfart, Michael; Gericke, Klaus

2003-11-01

423

Infrared spectra and tunneling dynamics of the N2-D2O and OC-D2O complexes in the v2 bend region of D2O  

Science.gov (United States)

The rovibrational spectra of the N2-D2O and OC-D2O complexes in the v2 bend region of D2O have been measured in a supersonic slit jet expansion using a rapid-scan tunable diode laser spectrometer. Both a-type and b-type transitions were observed for these two complexes. All transitions are doubled, due to the heavy water tunneling within the complexes. Assuming the tunneling splittings are the same in Ka = 0 and Ka = 1, the band origins, all three rotational and several distortion constants of