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J. Bubendorff

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Kemal Keseroglu

Cincinnati Children's Hospital Medical Center

PROF. OM PRAKASH SINHA

Amity University

Emi Normalina Omar

Universiti Teknologi Mara

Universitat Politecnica de Catalunya

National Council for Scientific Research

University of California, Los Angeles

University of Trento

Stephen Challacombe

Kings College London

Nilton Morimoto

University of Sao Paulo

University of Bern

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Papers by J. Bubendorff

Micrometer level structural and chemical evaluation of electrodeposited calcium phosphate coatings on TA6V substrate by STEM-EDXS

Journal of Materials Science Materials in Medicine

Hydroxyapatite (HA) coatings on titanium alloy substrates Ti6Al4V have been prepared in our labor... more Hydroxyapatite (HA) coatings on titanium alloy substrates Ti6Al4V have been prepared in our laboratory by electrodeposition and hydrothermal synthesis. In this paper, the morphology, crystal size, porosity and Ca/P atomic ratio are investigated using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), Raman microspectroscopy and X-ray energy dispersive spectroscopy (EDXS). The results obtained show that after being hydrothermally treated and calcined at high temperature, the electrodeposited brushite coating is converted into a stoichiometric hydroxyapatite having a crystal size which changes considerably from the surface to the substrate alloy. In addition, variation of the surface coating porosity as a function of the electrolyte temperature has also been carried out.

Origin of the magnetic anisotropy in ferromagnetic layers deposited at oblique incidence

Europhysics Letters (EPL), 2006

Ferromagnetic films evaporated at oblique incidence show invariably an uniaxial in-plane magnetic... more Ferromagnetic films evaporated at oblique incidence show invariably an uniaxial in-plane magnetic anisotropy component with easy axis perpendicular to the incidence plane. Scanning Tunneling Microscopy (STM) images reveal that oblique deposition results in rough films with highly anisotropic correlation functions of the surface profile. We show that simple shape anisotropy calculations using high-quality STM roughness data as input reproduce the

Thermally oxidized Inconel 600 and 690 nickel-based alloys characterizations by combination of global photoelectrochemistry and local near-field microscopy techniques (STM, STS, AFM, SKPFM)

Applied Surface Science, 2018

Thermally oxidized nickel-based alloys are studied by scanning tunnelling microscopy (STM), scann... more Thermally oxidized nickel-based alloys are studied by scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), atomic force microscopy (AFM), scanning kelvin probe force microscopy (SKPFM) and photoelectro-chemical techniques as a function of oxidation time at a fixed temperature of 623 K. By photoelectrochemistry measurements we identify the formation of three oxides NiO, Fe 2 O 3 , Cr 2 O 3 and determine the corresponding gap values. We use these values as parameter for imaging the surface at high bias voltage by STM allowing the spatial localization and identification of both NiO, Fe 2 O 3 oxide phases using STS measurements. Associated to Kelvin probe measurements we show also that STS allow to distinguished NiO from Cr 2 O 3 and confirm that the Cr 2 O 3 is not visible at the surface and localized at the oxide/steel interface.

Highly n -doped graphene generated through intercalated terbium atoms

Physical Review B, 2018

We obtained highly n-type doped graphene by intercalating terbium atoms between graphene and SiC(... more We obtained highly n-type doped graphene by intercalating terbium atoms between graphene and SiC(0001) through appropriate annealing in ultrahigh vacuum. After terbium intercalation angle-resolved-photoelectron spectroscopy (ARPES) showed a drastic change in the band structure around the K points of the Brillouin zone: the well-known conical dispersion band of a graphene monolayer was superposed by a second conical dispersion band of a graphene monolayer with an electron density reaching 10 15 cm −2. In addition, we demonstrate that atom intercalation proceeds either below the buffer layer or between the buffer layer and the monolayer graphene. The intercalation of terbium below a pure buffer layer led to the formation of a highly n-doped graphene monolayer decoupled from the SiC substrate, as evidenced by ARPES and x-ray photoelectron spectroscopy measurements. The band structure of this highly n-doped monolayer graphene showed a kink (a deviation from the linear dispersion of the Dirac cone), which has been associated with an electron-phonon coupling constant one order of magnitude larger than those usually obtained for graphene with intercalated alkali metals.

Investigation on Mn doping of Ge nanowires for spintronics

physica status solidi (c), 2014

ABSTRACT Various approaches are described to synthesize Mn-doped Ge NWs using UHV-CVD growth via ... more ABSTRACT Various approaches are described to synthesize Mn-doped Ge NWs using UHV-CVD growth via the VLS mechanism. We explored in-situ doping using an organo-metallic precursor (TCMn) and tested different catalyst seeds such as Au, Au-Mn or Ge-Mn. All in-situ attempts failed to incorporate Mn atoms into the NW. Moreover we observed that the use of TCMn and/or Au-Mn catalysts have a crippling effect on the growth kinetics. Finally, ex-situ doping with ion implantation is right now considered as a doping alternative. We report on preliminary results aiming at testing the radiation resistance of Ge NWs embedded in a removable silica matrix. (© 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Anion promoted Ni-underpotential deposition on Au(111)

Surface Science, 1997

In situ scanning tunneling microscopy (STM) and cyclic voltammetry show that a Ni monolayer can b... more In situ scanning tunneling microscopy (STM) and cyclic voltammetry show that a Ni monolayer can be deposited from a sulfamate solution on Au(111) at positive potentials with respect to the Nernst potential of the Ni/Ni 2 * couple. This process is specific to H2NSO3-anions since it could not be observed in the presence of sulfates. High resolution STM images suggest that the Ni layer builds up on the surface due to a complexation of Ni 2+ by the sulfamate adlayer on the gold surface.

Resolution in scanning near-field cathodoluminescence microscopy

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2000

ABSTRACT The lateral resolution in scanning near-field cathodoluminescence microscopy, in the cas... more ABSTRACT The lateral resolution in scanning near-field cathodoluminescence microscopy, in the case of bulk materials, is theoretically and experimentally studied. Although the theoretical resolution of near-field optical collection systems is determined by the probe size and thus should not be dependent on the energy dissipation volume in the material, it is theoretically shown that the contribution of the far-field signal caused by the radiative centers situated far from the probe can alter the resolution by adding a background noise to the near-field signal. In order to see the role of the energy dissipation volume, the electron beam accelerating voltage is varied and its influence on lateral resolution is studied in the case of a material that does not present a large energy transfer range, a fluorite doped with 0.3% europium. Cathodoluminescence images of this one confirm that the resolution is improved by working at low accelerating voltage to limit the energy dissipation volume, hence the contribution of the far-field radiative centers. On the other hand, for materials having a large energy transfer range (several micrometers) and therefore for which the far-field contribution can be strongly disturbing, the question concerning the efficiency of the near-field collection systems arises. Our experimental results on indented MgO crystal, which presents a large energy transfer range, demonstrates that near-field collection, despite the large contribution of the radiative centers situated far from the tip, gives still a better resolution than far-field collection. © 2000 American Vacuum Society.

Perpendicular Magnetization In Ultrathin Electrodeposited Cobalt Films

7th Joint MMM-Intermag Conference. Abstracts (Cat. No.98CH36275)

Electrodeposited ultrathin cobalt films on Au͑111͒ covered with a protective copper film can show... more Electrodeposited ultrathin cobalt films on Au͑111͒ covered with a protective copper film can show perpendicular magnetization exactly like their ultrahigh-vacuum-grown counterparts. At high deposition rates of cobalt, out-of-plane magnetization is stabilized in the thickness range from 2 to 8 atomic layers while low deposition rates favor in-plane magnetization at any thickness. The cobalt films possess hcp structure with the c axis perpendicular to the Au͑111͒ plane. The technique is versatile and leads to quality standards comparable to those obtained by molecular-beam epitaxy, but at a much lower cost. ͓S0163-1829͑97͒51236-7͔

Cathodoluminescence Properties of Zno Thin Films

Cathodoluminescence, 2012

Strain state in bcc Fe films grown on Si(111)

Surface Science, 2006

The strain state of Fe films grown on Si(1 1 1) has been investigated by X-ray diffraction (XRD) ... more The strain state of Fe films grown on Si(1 1 1) has been investigated by X-ray diffraction (XRD) in the thickness range between 11 and 304 monolayers. Fe grows tetragonally distorted with the orientation relationship Fe(1 1 1) h1 2 1i // Si(1 1 1) h 1 2 1i. At low coverage, the films grow pseudomorphic. Above 15 monolayers the films are characterized by the coexistence of a pseudomorphic phase with another one which relaxes with the Fe thickness. This relaxation proceeds rapidly in the earlier stages then slowly with the film thickness. The XRD characterization allows one to obtain quantitative information on the in-plane and out-of-plane strains.

Transition in the growth kinetics of vacancy islands on NbSe2

Surface Science, 1996

The evolution of etch pits of NbSe2 in air has been followed by AFM and STM. By minimizing the ti... more The evolution of etch pits of NbSe2 in air has been followed by AFM and STM. By minimizing the tip-surface interaction, the intrinsic evolution of monolayer deep depressions has been followed thoroughly. The time variation tβ of the lateral dimension of the triangular, monolayer deep depressions undergoes a transition from an exponent of β= 0.4±0.1 to β= 1±0.1 several tens of minutes after sample cleavage. The depression formation process is adequately described by the Burton-Cabrera-Frank theory (BCF) for the diffusion of ...

Nanostructuring of Fe films by oblique incidence deposition on a FeSi2 template onto Si(111): Growth, morphology, structure and faceting

Surface Science, 2009

The growth of thin Fe films deposited at oblique incidence on an iron silicide template onto Si(1... more The growth of thin Fe films deposited at oblique incidence on an iron silicide template onto Si(1 1 1) single crystal has been investigated as a function of Fe thickness (0 < t Fe 6 180 monolayers (MLs)) and incidence angle (0 6 h 6 80°). The growth mode is determined in situ by means of scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). Stripes oriented perpendicularly to the incident atomic flux are formed for h P 30°. Self-correlation functions are used to extract characteristic lengths from STM images. The correlation lengths in the direction of the incident flux (n x) and perpendicular to the atomic flux (n y) grow with different powers versus time (n x / t r and n y / t q , with r = 0.34 ± 0.03 and q = 0.67 ± 0.03) following the exact solution of the (1 + 1) dimensional Kardar-Parisi-Zhang (KPZ) equation. The root mean square roughness follows also a scaling law for t Fe < 120 ML leading to a growth exponent b = 0.73 ± 0.02. Shadowing and steering effects are discussed on the basis of our STM data.

Localized cathodoluminescence investigation on single Ga2O3 nanoribbon/nanowire

Solid State Communications, 2002

The cathodoluminescence (CL) upon electron excitation of the Ga 2 O 3 nanoribbons and nanowires w... more The cathodoluminescence (CL) upon electron excitation of the Ga 2 O 3 nanoribbons and nanowires was characterized using a hybrid setup based on combination of a scanning probe microscope (SPM) and a field emission scanning electron microscope (FE-SEM). An optical fiber was mounted in the system in such a way that it can be controlled to approach closely a selected nanostructure of interest so as to collect the local CL signal directly arising from it. The thicker nanoribbons (thickness. 170 nm) show an emission peak around 410 nm, while the thinner ribbons/nanowires, smaller than 40 nm in thickness/diameter, have a shifted emission around 490 nm. The observed shift in the CL peaks is attributed to the difference of the oxygen vacancies in the nanostructures. Our results demonstrate that the localized CL spectroscopy is a powerful means of selective addressing the optical properties of the semiconductor nanostructures.

Growth and magnetic anisotropy of Fe films deposited on Si(111) using an ultrathin iron silicide template

Physical Review B, 2005

The growth and magnetic properties of thin Fe films deposited at room temperature on ultrathin ir... more The growth and magnetic properties of thin Fe films deposited at room temperature on ultrathin iron silicide seed layer epitaxially grown on Si͑111͒ single crystal were investigated as a function of Fe thickness ͑0 Ͻ t Fe Ͻ 300 monolayers͒. The growth mode and structure have been determined in situ by means of scanning tunneling microscopy, low energy electron diffraction, and x-ray photoelectron diffraction. The magnetic properties were characterized ex situ by conventional polar and longitudinal magneto-optical Kerr effect, transverse biased initial inverse susceptibility and torque ͑TBIIST͒ measurements, and superconducting quantum interference device magnetometry. Fe growth is of Volmer-Weber type ͑island growth͒ and the epitaxial film adopts the bcc ␣-Fe structure. Onset of long-range ferromagnetic order occurs at 4.7 monolayers ͑ML͒, in the vicinity of the percolation threshold of the Fe islands. The Curie temperature increases continuously with Fe coverage, varying from 135 K for 4.7 ML to 260 K for 7.3 ML. Two different spin reorientation transitions have been observed versus Fe coverage. First, the magnetic easy axis rotates from normal to the film plane, for coverage below 6 ML, to in plane, for thickness above 7 ML. Then, in-plane magnetized films present tiny ͑anisotropy fields less than 4 Oe͒ uniaxial and sixfold magnetic anisotropies. From sixfold anisotropy the small higher order cubic anisotropy constant K 2 was measured precisely by TBIIST. It decreases monotonously with increasing coverage and changes its sign at approximately 20 ML, which in turn results in a switching of the sixfold anisotropy easy axis from ͗1-10͘ to ͗1-21͘ directions. It appears that TIBIIST magnetometry is a powerful method for a quantitative determination of the various contributions to in-plane magnetic anisotropies in ultrathin films.

Real time atomic force microscopy imaging during nanogap formation by electromigration

Nanotechnology, 2012

We present real time atomic force microscopy imaging during nanogap fabrication by feedback contr... more We present real time atomic force microscopy imaging during nanogap fabrication by feedback controlled electromigration of a gold nanowire. The correlated measurements of electrical resistance and atomic force microscopy reveal that the major structural changes appear at the early stage of the process. Moreover, despite important morphological changes, the resistance of the nanowire shows a weak increase of just a few ohms. The detailed analysis of the atomic force microscopy images clearly shows that the electromigration process is strongly influenced by the initial microstructure of the nanowire.

Anisotropic charge transport in large single crystals of π-conjugated organic molecules

Nanoscale, 2014

The electronic properties of organic semiconductors depend strongly on the nature of the molecule... more The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of π-π stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the π-π stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.

Effects of the substrate temperature on the growth and properties of hydrogenated nanostructured silicon thin films

Journal of Physics D: Applied Physics, 2001

Nanostructured silicon thin films were deposited by a pulsed plasma enhanced chemical vapour depo... more Nanostructured silicon thin films were deposited by a pulsed plasma enhanced chemical vapour deposition process using an argon-silane mixture. For each deposition temperature (TS), the plasma modulation was chosen in such a way that the discharge was switched off just before the onset of powder formation. The optical and electrical properties of the films were investigated as a function of TS and compared to those of films deposited under the same plasma conditions but with a continuous wave (CW) plasma. While the CW films show a gradual improvement in their properties with increasing TS, a drastic change appears in the optical and electrical properties of hydrogenated nanostructured silicon (ns-Si:H) films for TS>50 °C. In particular, for a deposition temperature of 150 °C a more compact material with a small surface roughness and a high conductivity was obtained. This improvement is correlated to the discharge conditions and particularly to the small size of the clusters embedded in the deposited film.

In-plane uniaxial magnetic anisotropy of thin Fe layers on Si(111) induced upon grazing deposition of a Si capping layer

Journal of Magnetism and Magnetic Materials, 2005

We demonstrate that an in-plane uniaxial magnetic anisotropy can be induced in Fe films grown on ... more We demonstrate that an in-plane uniaxial magnetic anisotropy can be induced in Fe films grown on Si(111) by means of an appropriate Si capping layer. It is shown that grazing-incidence Si deposition reduces the three-fold symmetry of the body-centered-cubic (BCC) Fe(111) surface to two-fold, thus generating a surface-type uniaxial in-plane magnetic anisotropy contribution. The relevant magnetic easy axis direction depends

Correlation between topographic and magnetic properties of electrochemically prepared nickel films

Journal of Magnetism and Magnetic Materials, 1997

ABSTRACT The correlation between the structural and the magnetic properties are investigated on e... more ABSTRACT The correlation between the structural and the magnetic properties are investigated on electrodeposited Ni films on (111) textured gold buffer layers on mica and glass substrates. The topological characteristics of the film surface are analyzed by atomic force microscopy (AFM) and the corresponding magnetic behavior is studied by ferromagnetic resonance (FMR). The FMR linewidth is found to depend strongly on the thickness of the Ni film samples and on the topography of the underlying gold film. Confrontation with AFM results indicate a loss in the lateral coherence length for the thinner Ni films.

Accurate measurement of the in-plane magnetic anisotropy energy function in ultrathin films by magneto-optics

Journal of Magnetism and Magnetic Materials, 2006

We present a sensitive and precise determination of an arbitrary thin film magnetic anisotropy en... more We present a sensitive and precise determination of an arbitrary thin film magnetic anisotropy energy Ea (or Ea/MS if the saturation magnetization MS is not known) versus in-plane polar angle θ by means of initial inverse susceptibility and torque measurements under constant transverse bias field HB. In this method coined TBIISTtwo magnetic fields HL and HB are applied in the

Micrometer level structural and chemical evaluation of electrodeposited calcium phosphate coatings on TA6V substrate by STEM-EDXS

Journal of Materials Science Materials in Medicine

Hydroxyapatite (HA) coatings on titanium alloy substrates Ti6Al4V have been prepared in our labor... more Hydroxyapatite (HA) coatings on titanium alloy substrates Ti6Al4V have been prepared in our laboratory by electrodeposition and hydrothermal synthesis. In this paper, the morphology, crystal size, porosity and Ca/P atomic ratio are investigated using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), Raman microspectroscopy and X-ray energy dispersive spectroscopy (EDXS). The results obtained show that after being hydrothermally treated and calcined at high temperature, the electrodeposited brushite coating is converted into a stoichiometric hydroxyapatite having a crystal size which changes considerably from the surface to the substrate alloy. In addition, variation of the surface coating porosity as a function of the electrolyte temperature has also been carried out.

Origin of the magnetic anisotropy in ferromagnetic layers deposited at oblique incidence

Europhysics Letters (EPL), 2006

Ferromagnetic films evaporated at oblique incidence show invariably an uniaxial in-plane magnetic... more Ferromagnetic films evaporated at oblique incidence show invariably an uniaxial in-plane magnetic anisotropy component with easy axis perpendicular to the incidence plane. Scanning Tunneling Microscopy (STM) images reveal that oblique deposition results in rough films with highly anisotropic correlation functions of the surface profile. We show that simple shape anisotropy calculations using high-quality STM roughness data as input reproduce the

Thermally oxidized Inconel 600 and 690 nickel-based alloys characterizations by combination of global photoelectrochemistry and local near-field microscopy techniques (STM, STS, AFM, SKPFM)

Applied Surface Science, 2018

Thermally oxidized nickel-based alloys are studied by scanning tunnelling microscopy (STM), scann... more Thermally oxidized nickel-based alloys are studied by scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), atomic force microscopy (AFM), scanning kelvin probe force microscopy (SKPFM) and photoelectro-chemical techniques as a function of oxidation time at a fixed temperature of 623 K. By photoelectrochemistry measurements we identify the formation of three oxides NiO, Fe 2 O 3 , Cr 2 O 3 and determine the corresponding gap values. We use these values as parameter for imaging the surface at high bias voltage by STM allowing the spatial localization and identification of both NiO, Fe 2 O 3 oxide phases using STS measurements. Associated to Kelvin probe measurements we show also that STS allow to distinguished NiO from Cr 2 O 3 and confirm that the Cr 2 O 3 is not visible at the surface and localized at the oxide/steel interface.

Highly n -doped graphene generated through intercalated terbium atoms

Physical Review B, 2018

We obtained highly n-type doped graphene by intercalating terbium atoms between graphene and SiC(... more We obtained highly n-type doped graphene by intercalating terbium atoms between graphene and SiC(0001) through appropriate annealing in ultrahigh vacuum. After terbium intercalation angle-resolved-photoelectron spectroscopy (ARPES) showed a drastic change in the band structure around the K points of the Brillouin zone: the well-known conical dispersion band of a graphene monolayer was superposed by a second conical dispersion band of a graphene monolayer with an electron density reaching 10 15 cm −2. In addition, we demonstrate that atom intercalation proceeds either below the buffer layer or between the buffer layer and the monolayer graphene. The intercalation of terbium below a pure buffer layer led to the formation of a highly n-doped graphene monolayer decoupled from the SiC substrate, as evidenced by ARPES and x-ray photoelectron spectroscopy measurements. The band structure of this highly n-doped monolayer graphene showed a kink (a deviation from the linear dispersion of the Dirac cone), which has been associated with an electron-phonon coupling constant one order of magnitude larger than those usually obtained for graphene with intercalated alkali metals.

Investigation on Mn doping of Ge nanowires for spintronics

physica status solidi (c), 2014

ABSTRACT Various approaches are described to synthesize Mn-doped Ge NWs using UHV-CVD growth via ... more ABSTRACT Various approaches are described to synthesize Mn-doped Ge NWs using UHV-CVD growth via the VLS mechanism. We explored in-situ doping using an organo-metallic precursor (TCMn) and tested different catalyst seeds such as Au, Au-Mn or Ge-Mn. All in-situ attempts failed to incorporate Mn atoms into the NW. Moreover we observed that the use of TCMn and/or Au-Mn catalysts have a crippling effect on the growth kinetics. Finally, ex-situ doping with ion implantation is right now considered as a doping alternative. We report on preliminary results aiming at testing the radiation resistance of Ge NWs embedded in a removable silica matrix. (© 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Anion promoted Ni-underpotential deposition on Au(111)

Surface Science, 1997

In situ scanning tunneling microscopy (STM) and cyclic voltammetry show that a Ni monolayer can b... more In situ scanning tunneling microscopy (STM) and cyclic voltammetry show that a Ni monolayer can be deposited from a sulfamate solution on Au(111) at positive potentials with respect to the Nernst potential of the Ni/Ni 2 * couple. This process is specific to H2NSO3-anions since it could not be observed in the presence of sulfates. High resolution STM images suggest that the Ni layer builds up on the surface due to a complexation of Ni 2+ by the sulfamate adlayer on the gold surface.

Resolution in scanning near-field cathodoluminescence microscopy

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2000

ABSTRACT The lateral resolution in scanning near-field cathodoluminescence microscopy, in the cas... more ABSTRACT The lateral resolution in scanning near-field cathodoluminescence microscopy, in the case of bulk materials, is theoretically and experimentally studied. Although the theoretical resolution of near-field optical collection systems is determined by the probe size and thus should not be dependent on the energy dissipation volume in the material, it is theoretically shown that the contribution of the far-field signal caused by the radiative centers situated far from the probe can alter the resolution by adding a background noise to the near-field signal. In order to see the role of the energy dissipation volume, the electron beam accelerating voltage is varied and its influence on lateral resolution is studied in the case of a material that does not present a large energy transfer range, a fluorite doped with 0.3% europium. Cathodoluminescence images of this one confirm that the resolution is improved by working at low accelerating voltage to limit the energy dissipation volume, hence the contribution of the far-field radiative centers. On the other hand, for materials having a large energy transfer range (several micrometers) and therefore for which the far-field contribution can be strongly disturbing, the question concerning the efficiency of the near-field collection systems arises. Our experimental results on indented MgO crystal, which presents a large energy transfer range, demonstrates that near-field collection, despite the large contribution of the radiative centers situated far from the tip, gives still a better resolution than far-field collection. © 2000 American Vacuum Society.

Perpendicular Magnetization In Ultrathin Electrodeposited Cobalt Films

7th Joint MMM-Intermag Conference. Abstracts (Cat. No.98CH36275)

Electrodeposited ultrathin cobalt films on Au͑111͒ covered with a protective copper film can show... more Electrodeposited ultrathin cobalt films on Au͑111͒ covered with a protective copper film can show perpendicular magnetization exactly like their ultrahigh-vacuum-grown counterparts. At high deposition rates of cobalt, out-of-plane magnetization is stabilized in the thickness range from 2 to 8 atomic layers while low deposition rates favor in-plane magnetization at any thickness. The cobalt films possess hcp structure with the c axis perpendicular to the Au͑111͒ plane. The technique is versatile and leads to quality standards comparable to those obtained by molecular-beam epitaxy, but at a much lower cost. ͓S0163-1829͑97͒51236-7͔

Cathodoluminescence Properties of Zno Thin Films

Cathodoluminescence, 2012

Strain state in bcc Fe films grown on Si(111)

Surface Science, 2006

The strain state of Fe films grown on Si(1 1 1) has been investigated by X-ray diffraction (XRD) ... more The strain state of Fe films grown on Si(1 1 1) has been investigated by X-ray diffraction (XRD) in the thickness range between 11 and 304 monolayers. Fe grows tetragonally distorted with the orientation relationship Fe(1 1 1) h1 2 1i // Si(1 1 1) h 1 2 1i. At low coverage, the films grow pseudomorphic. Above 15 monolayers the films are characterized by the coexistence of a pseudomorphic phase with another one which relaxes with the Fe thickness. This relaxation proceeds rapidly in the earlier stages then slowly with the film thickness. The XRD characterization allows one to obtain quantitative information on the in-plane and out-of-plane strains.

Transition in the growth kinetics of vacancy islands on NbSe2

Surface Science, 1996

The evolution of etch pits of NbSe2 in air has been followed by AFM and STM. By minimizing the ti... more The evolution of etch pits of NbSe2 in air has been followed by AFM and STM. By minimizing the tip-surface interaction, the intrinsic evolution of monolayer deep depressions has been followed thoroughly. The time variation tβ of the lateral dimension of the triangular, monolayer deep depressions undergoes a transition from an exponent of β= 0.4±0.1 to β= 1±0.1 several tens of minutes after sample cleavage. The depression formation process is adequately described by the Burton-Cabrera-Frank theory (BCF) for the diffusion of ...

Nanostructuring of Fe films by oblique incidence deposition on a FeSi2 template onto Si(111): Growth, morphology, structure and faceting

Surface Science, 2009

The growth of thin Fe films deposited at oblique incidence on an iron silicide template onto Si(1... more The growth of thin Fe films deposited at oblique incidence on an iron silicide template onto Si(1 1 1) single crystal has been investigated as a function of Fe thickness (0 < t Fe 6 180 monolayers (MLs)) and incidence angle (0 6 h 6 80°). The growth mode is determined in situ by means of scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). Stripes oriented perpendicularly to the incident atomic flux are formed for h P 30°. Self-correlation functions are used to extract characteristic lengths from STM images. The correlation lengths in the direction of the incident flux (n x) and perpendicular to the atomic flux (n y) grow with different powers versus time (n x / t r and n y / t q , with r = 0.34 ± 0.03 and q = 0.67 ± 0.03) following the exact solution of the (1 + 1) dimensional Kardar-Parisi-Zhang (KPZ) equation. The root mean square roughness follows also a scaling law for t Fe < 120 ML leading to a growth exponent b = 0.73 ± 0.02. Shadowing and steering effects are discussed on the basis of our STM data.

Localized cathodoluminescence investigation on single Ga2O3 nanoribbon/nanowire

Solid State Communications, 2002

The cathodoluminescence (CL) upon electron excitation of the Ga 2 O 3 nanoribbons and nanowires w... more The cathodoluminescence (CL) upon electron excitation of the Ga 2 O 3 nanoribbons and nanowires was characterized using a hybrid setup based on combination of a scanning probe microscope (SPM) and a field emission scanning electron microscope (FE-SEM). An optical fiber was mounted in the system in such a way that it can be controlled to approach closely a selected nanostructure of interest so as to collect the local CL signal directly arising from it. The thicker nanoribbons (thickness. 170 nm) show an emission peak around 410 nm, while the thinner ribbons/nanowires, smaller than 40 nm in thickness/diameter, have a shifted emission around 490 nm. The observed shift in the CL peaks is attributed to the difference of the oxygen vacancies in the nanostructures. Our results demonstrate that the localized CL spectroscopy is a powerful means of selective addressing the optical properties of the semiconductor nanostructures.

Growth and magnetic anisotropy of Fe films deposited on Si(111) using an ultrathin iron silicide template

Physical Review B, 2005

The growth and magnetic properties of thin Fe films deposited at room temperature on ultrathin ir... more The growth and magnetic properties of thin Fe films deposited at room temperature on ultrathin iron silicide seed layer epitaxially grown on Si͑111͒ single crystal were investigated as a function of Fe thickness ͑0 Ͻ t Fe Ͻ 300 monolayers͒. The growth mode and structure have been determined in situ by means of scanning tunneling microscopy, low energy electron diffraction, and x-ray photoelectron diffraction. The magnetic properties were characterized ex situ by conventional polar and longitudinal magneto-optical Kerr effect, transverse biased initial inverse susceptibility and torque ͑TBIIST͒ measurements, and superconducting quantum interference device magnetometry. Fe growth is of Volmer-Weber type ͑island growth͒ and the epitaxial film adopts the bcc ␣-Fe structure. Onset of long-range ferromagnetic order occurs at 4.7 monolayers ͑ML͒, in the vicinity of the percolation threshold of the Fe islands. The Curie temperature increases continuously with Fe coverage, varying from 135 K for 4.7 ML to 260 K for 7.3 ML. Two different spin reorientation transitions have been observed versus Fe coverage. First, the magnetic easy axis rotates from normal to the film plane, for coverage below 6 ML, to in plane, for thickness above 7 ML. Then, in-plane magnetized films present tiny ͑anisotropy fields less than 4 Oe͒ uniaxial and sixfold magnetic anisotropies. From sixfold anisotropy the small higher order cubic anisotropy constant K 2 was measured precisely by TBIIST. It decreases monotonously with increasing coverage and changes its sign at approximately 20 ML, which in turn results in a switching of the sixfold anisotropy easy axis from ͗1-10͘ to ͗1-21͘ directions. It appears that TIBIIST magnetometry is a powerful method for a quantitative determination of the various contributions to in-plane magnetic anisotropies in ultrathin films.

Real time atomic force microscopy imaging during nanogap formation by electromigration

Nanotechnology, 2012

We present real time atomic force microscopy imaging during nanogap fabrication by feedback contr... more We present real time atomic force microscopy imaging during nanogap fabrication by feedback controlled electromigration of a gold nanowire. The correlated measurements of electrical resistance and atomic force microscopy reveal that the major structural changes appear at the early stage of the process. Moreover, despite important morphological changes, the resistance of the nanowire shows a weak increase of just a few ohms. The detailed analysis of the atomic force microscopy images clearly shows that the electromigration process is strongly influenced by the initial microstructure of the nanowire.

Anisotropic charge transport in large single crystals of π-conjugated organic molecules

Nanoscale, 2014

The electronic properties of organic semiconductors depend strongly on the nature of the molecule... more The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of π-π stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the π-π stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.

Effects of the substrate temperature on the growth and properties of hydrogenated nanostructured silicon thin films

Journal of Physics D: Applied Physics, 2001

Nanostructured silicon thin films were deposited by a pulsed plasma enhanced chemical vapour depo... more Nanostructured silicon thin films were deposited by a pulsed plasma enhanced chemical vapour deposition process using an argon-silane mixture. For each deposition temperature (TS), the plasma modulation was chosen in such a way that the discharge was switched off just before the onset of powder formation. The optical and electrical properties of the films were investigated as a function of TS and compared to those of films deposited under the same plasma conditions but with a continuous wave (CW) plasma. While the CW films show a gradual improvement in their properties with increasing TS, a drastic change appears in the optical and electrical properties of hydrogenated nanostructured silicon (ns-Si:H) films for TS>50 °C. In particular, for a deposition temperature of 150 °C a more compact material with a small surface roughness and a high conductivity was obtained. This improvement is correlated to the discharge conditions and particularly to the small size of the clusters embedded in the deposited film.

In-plane uniaxial magnetic anisotropy of thin Fe layers on Si(111) induced upon grazing deposition of a Si capping layer

Journal of Magnetism and Magnetic Materials, 2005

We demonstrate that an in-plane uniaxial magnetic anisotropy can be induced in Fe films grown on ... more We demonstrate that an in-plane uniaxial magnetic anisotropy can be induced in Fe films grown on Si(111) by means of an appropriate Si capping layer. It is shown that grazing-incidence Si deposition reduces the three-fold symmetry of the body-centered-cubic (BCC) Fe(111) surface to two-fold, thus generating a surface-type uniaxial in-plane magnetic anisotropy contribution. The relevant magnetic easy axis direction depends

Correlation between topographic and magnetic properties of electrochemically prepared nickel films

Journal of Magnetism and Magnetic Materials, 1997

ABSTRACT The correlation between the structural and the magnetic properties are investigated on e... more ABSTRACT The correlation between the structural and the magnetic properties are investigated on electrodeposited Ni films on (111) textured gold buffer layers on mica and glass substrates. The topological characteristics of the film surface are analyzed by atomic force microscopy (AFM) and the corresponding magnetic behavior is studied by ferromagnetic resonance (FMR). The FMR linewidth is found to depend strongly on the thickness of the Ni film samples and on the topography of the underlying gold film. Confrontation with AFM results indicate a loss in the lateral coherence length for the thinner Ni films.

Accurate measurement of the in-plane magnetic anisotropy energy function in ultrathin films by magneto-optics

Journal of Magnetism and Magnetic Materials, 2006

We present a sensitive and precise determination of an arbitrary thin film magnetic anisotropy en... more We present a sensitive and precise determination of an arbitrary thin film magnetic anisotropy energy Ea (or Ea/MS if the saturation magnetization MS is not known) versus in-plane polar angle θ by means of initial inverse susceptibility and torque measurements under constant transverse bias field HB. In this method coined TBIISTtwo magnetic fields HL and HB are applied in the