Ion Sputtered Research Articles

Highly Localized Optical Field Enhancement at Neon Ion Sputtered Tungsten Nanotips.

We present laser-driven rescattering of electrons at a nanometric protrusion (nanotip), which is fabricated with an in situ neon ion sputtering technique applied to a tungsten needle tip. Electron energy spectra obtained before and after the sputtering show rescattering features, such as a plateau and high-energy cutoff. Extracting the optical near-field enhancement in both cases, we observe a strong increase of more than 2-fold for the nanotip. Accompanying finite-difference time-domain (FDTD) simulations show a good match with the experimentally extracted near-field strengths. Additionally, high electric field localization for the nanotip is found. The combination of transmission electron microscope imaging of such nanotips and the determination of the near-field enhancement by electron rescattering represent a full characterization of the electric near-field of these intriguing electron emitters. Ultimately, nanotips as small as single nanometers can be produced, which is of utmost interest for electron diffraction experiments and low-emittance electron sources.

Surface pre-treatments of Ti-Nb-Zr-Ta beta titanium alloy: The effect of chemical, electrochemical and ion sputter etching on morphology, residual stress, corrosion stability and the MG-63 cell response

Pre-treatment methods for titanium alloys are of great importance, both as regards the treatment of the surfaces of the implant and as regards the pre-deposition phase of the coating processes and the surface modifications. We have investigated the impact of chemical, electrochemical and ion sputter etching on the surface properties, the corrosion stability and the MG-63 cell response of Ti-35Nb-7Zr-5Ta alloy. In the initial state, the samples have a mechanically polished surface. The pre-treatments that were applied led to significant morphological changes in microscale and also in nanoscale. The wettability of the pre-treated surfaces varied from hydrophilicity to hydrophobicity. Changes in contact angle were controlled by surface chemistry rather than changes in morphology and roughness. Native oxides and suboxides of alloying elements with a predominant amount of Nb2O5 were found to provide high corrosion stability of Ti-35Nb-7Zr-5Ta alloy after mechanical polishing, after chemical etching and after electrochemical etching. Significantly reduced corrosion resistance in a physiological saline solution was observed for the ion sputtered surface. A decreasing trend in the cell spreading area correlated with increasing surface roughness and decreasing polarization resistance. There is discussion of the causes of the changes in surface properties and cell behaviour.

Influence of Ca doping on X‐ray photoelectron core‐level spectra of magnetoelectric bulk BiFeO3

The X‐ray photoelectron spectrum (XPS) core‐level spectra of pristine and doped bulk BiFeO3, namely Bi0.9BaxCayFeO3 with x + y = 0 and 0.1 were recorded on the Ar+‐ion sputtered sample surface at room temperature. Afterward, the obtained XPS spectra of Bi 4f, Fe 2p, O 1 s, Ba 3d and Ca 2p levels were inspected using the symmetric Gaussian‐Lorentzian product function, to study the influence of the spin‐orbit coupling and/or electrostatic interactions on these spectra. Our findings show all elements have a single valence state (except Bi) with the allowed spin‐orbit splitting energy (Δ) for their valence of Bi3+, Fe3+, O2−, Ba2+, and Ca2+. Here, the fraction of Bi atoms was converted into Bi‐metal Bio, due to the Ar+‐ion sputtering process. Interestingly, the Fe3+ 2p3/2 spectra of these samples were fitted well with four Gupta–Sen multiplets, due to the combined electrostatic and spin‐orbit interactions. Particularly, the chemical pressure induced by Ca doping considerably influences the Fe3+ 2p3/2 spectra of BiFeO3, due to the change in the FeO6 octahedra tilting and the change in the position of Fe cations upon Ca doping. So, the edge of the valence band of the Ca‐doped BiFeO3 materials shifted toward the Fermi level by about ~0.7 ± 0.1 eV when compared to BiFeO3.

Soft X-ray photoelectron spectroscopy study on the P segregation process and its effect on the electronic structure of Fe2P(0001)

The change in the amount of P atoms in the surface region of Fe2P(0001) as a function of annealing temperature and its effect on the surface electronic structure have been studied by Auger electron spectroscopy (AES) and soft X-ray photoelectron spectroscopy (PES). The AES study showed that the amount of surface P atoms was reduced by Ar+ ion sputtering (2 kV, 10 min). When the surface was subsequently annealed, the amount of surface P atoms was further reduced with increasing annealing temperatures up to 400 °C, while it was increased by annealing at temperatures higher than 400 °C. It was deduced from the analyzes of P 2p core-level PES spectra that two processes proceeded when the Ar+ ion sputtered Fe2P(0001) was subsequently annealed; one is the desorption of P atoms weakly bonded to the surface and the other is the segregation of P atoms from the bulk toward the surface. The AES results can be explained by the fact that the former and latter processes were dominant when the sputtered surface was annealed at <400 °C and at >400 °C, respectively. The valence band PES study showed that the 3d states of surface Fe atoms were not effectively stabilized by bonding with surrounding P atoms even when the segregation of P atoms toward the surface proceeded, unlike the situation of Ni2P(0001).

Defect-induced bandgap narrowing in low-k dielectrics

In this work, core-level X-ray photoelectron spectroscopy was utilized to determine the surface bandgap for various porous and non-porous low-k a-SiCOH dielectrics before and after ion sputtering. By examining the onset of inelastic energy loss in O 1s core-level spectra, the gap narrowing was universally found in Ar+ ion sputtered low-k dielectrics. The reduction of the bandgap ranges from 1.3 to 2.2 eV depending on the film composition. We show that the bandgap narrowing in these low-k dielectrics is caused by development of the valence-band tail as evidenced by the presence of additional electronic states above the valence-band maximum. Electron-spin-resonance measurements were made on a-SiCOH films to gain atomic insight into the nature of the sputtering-induced defects and reveal formation of carbon-related defects as the most probable origin of the gap states.

Kinetic Monte Carlo simulations of self organized nanostructures on Ta surface fabricated by low energy ion sputtering

Surfaces bombarded with low energy ion beams often display development of self assembled patterns and quasi-periodic structures. Kinetic Monte Carlo simulations have been performed to describe ion sputtered Tantalum surfaces. A weak nonlinearity in the relaxation process has been introduced and the results show that the positive Schwoebel barrier, produced by the nonlinear Hamiltonian, is necessary in describing ion bombarded Tantalum surfaces. Furthermore, their scaling exponents suggest presence of a class other than KPZ.

Tailoring the magnetic anisotropy, magnetization reversal, and anisotropic magnetoresistance of Ni films by ion sputtering

We studied surface morphology induced changes of magnetic anisotropy, magnetization reversal, and symmetry of the anisotropic magnetoresistance (AMR) in ion sputtered Ni films grown on MgO (001). Grazing-incidence ion sputtering generally develops anisotropic surface roughness of the Ni films, i.e., nanometer wide ripples parallel to the ion beam direction, giving rise to uniaxial magnetic anisotropy with the easy axis along the ion beam direction. The formed ripples act as domain wall nucleation and pinning sites during magnetization reversal, while two-jump domain wall motion dominates in the as-grown Ni films. More importantly, the azimuthal angular dependence of the AMR indicates a superposition of twofold symmetry and fourfold symmetry. By relying on grazing-incidence ion sputtering along specific crystallographic directions, we are able to tailor the relative weight of twofold and fourfold symmetry of AMR. We demonstrate that in contrast to the bulk case, the symmetry of the AMR becomes also sensitive to the surface morphology in thin films, which is in particular relevant for the design of magnetotransport based sensors.

Growth of palladium nanoparticles on nanostructured highly ordered pyrolytic graphite

We report on the growth of palladium nanoparticles on the basal plane of as-cleaved highly oriented pyrolytic graphite (HOPG) samples, and on CO2 ion sputtered nanostructured HOPG surfaces. The morphology of Pd nanostructures grown at room temperature is investigated by scanning tunneling microscopy (STM). The STM observations indicate that the morphology of the Pd films is strongly dependent on the HOPG surface. Stabilized Pd particles only form on the sputtered surface, while ramified Pd particles decorate the clean HOPG terraces. The prestructuring of HOPG surface leads to a selective location of particles at the rim of the nanopits generated by the CO2 ion sputtering and annealing of the surface. The correlation between size, form, density, spatial distribution of the Pd nanoparticles and the quantity of metal added on surface is discussed. We also describe trench channeling of graphite or graphene basal planes by means of Pd nanoparticles in an ambient environment. Copyright (c) 2014 John Wiley & Sons, Ltd.

Evolution of Surface morphology on Ion Sputtered of Some III-V (001) Semiconductors

Surface patterning of some III-V (001) compounds, under ion irradiation, has been&#x0D; investigated by means of Atomic Force Microscopy. The III-V(001) surfaces were exposed by&#x0D; Ar+ beam with varying incident angles (from 0° to 80° off-normal) with energy 2.0 keV and&#x0D; fluence 8.8 x1016 ion/cm2 at room temperature. Depending on the ion incident angle and target&#x0D; materials, different kinds of nanostructures have been observed on the surfaces, such as&#x0D; nanocavities, nanodots and well-ordered ripples at the oblique incidence angle of irradiation.&#x0D; The orientation of the ripples has been found to be incident angle dependent and it elongates&#x0D; along the projection of the ion beam on the irradiated surface. The RMS roughness and&#x0D; wavelength of the developed nanostructures are dependent on the angle and type of material.&#x0D; The results have been discussed in terms of ballistic processes of sputtering and Bradley Harper&#x0D; theory for surface modifications.

Ion beam sputtering of multicomponent targets: Surface composition change and cluster emission

Preferential sputtering effect, which occurs during irradiation of a multicomponent target by medium energy ions, was under our investigation. A new term characterizing the preferential sputtering, called “surface sputtering yield” and defined as average number of components i sputtered from a top surface layer per one primary ion, was suggested. A direct proportionality between the dimer emission and surface concentration of the component, forming the dimer, was concluded; this let us estimate the preferential sputtering of any target from the composition of the flux of secondary particles, analyzed directly during the ion sputtering process, and define the composition of the ion sputtered surface.

Erratum: Multiple Bifurcation Types and the Linear Dynamics of Ion Sputtered Surfaces [Phys. Rev. Lett.101, 246102 (2008)

Received 28 June 2011DOI:https://doi.org/10.1103/PhysRevLett.107.049902© 2011 American Physical Society

2D Angular distributions of ion sputtered germanium atoms under grazing incidence

Ion sputtering of germanium was studied within this work. Argon and nitrogen ions with energies of 20 keV were used for the sputtering experiments. Grazing ion incidence angles in the range of 60–85° were examined experimentally and by Monte-Carlo simulations. The range of ion incidence angles was chosen in order to observe a contribution of primary knock-on atoms to the total angular distribution. Experiments were performed using the collector technique. The collectors, 300 mm silicon wafers, were covered with a sub-monolayer concentration of germanium and were examined afterwards with spatial resolution using total X-ray reflection fluorescence (TXRF). Initially, simulation results significantly deviated from experiments. Therefore, the model of ion penetration into a target was modified, resulting in a better agreement between simulation and measurement.

Multiple Bifurcation Types and the Linear Dynamics of Ion Sputtered Surfaces

We study the patterns formed on ion sputtered Si surfaces as a function of ion energy and incidence angle, and identify a region in parameter space where the flat surface is stable. The boundaries between the stable and pattern-forming regions represent mathematical bifurcations. Our data set exhibits at least two different bifurcation types. We discuss the constraints imposed by these observations on the correct model of long wavelength dynamics of ion sputtered surfaces.

Crack Length Measurement with an Ion Sputtered Film

Crack length measurement and crack initiation detection in a fatigue process are extremely important techniques in the researches for the investigation of crack growth characteristics and the fatigue strength evaluation of machine elements. The purpose of this research is to show a simple and high precision method to measure the length of a crack as well as a micro crack using an extremely thin ion sputtered film. A grid pattern ion sputtered film was proposed to measure the crack length for a bending test specimen. Based on the comparisons between the measurement results and that by a microscope, it was clarified that the grid pattern ion sputtered film has a very high measurement precision. This method should be invaluable and practicable for the crack length measurement of insulating materials such as ceramics. Meanwhile, a rectangle ion sputtered film was used on a metal bending specimen, the possibility to apply the film in the crack length measurement of a metal machine element was confirmed by the change of the electric resistance of the film with crack growth.

Morphology of ion sputtered Cu(0 0 1) surface: Transition from unidirectional roughening to bidirectional roughening

We have previously shown that under off normal ion sputtering, ripples parallel to the beam with a periodicity of hundreds of nanometers can be formed on a Cu(001) surface. This ripple formation behavior can be well explained by the Bradley and Harper (BH) instability mechanism. However, by lowering the temperature at a constant flux, we find that the resultant morphology transitions from a unidirectional modulation to a bidirectional modulation. The lower temperature morphology is attributed to the presence of diffusion barrier across step edges. The time evolution of this morphology is also studied and the bidirectional modulation morphology is observed to change back to ripple morphology as the ion fluence increases.

Evaluation of Crack Growth Characteristics in Float Glass and Thermally Tempered Glass Based on the Crack Length Measurement Using Au Ion Sputtered Film

Thermal tempered glass is made by rapidly cooling after heating float glass to near the softening point. Compressive residual stresses at the surface layer of thermally tempered glass strengthen the material, and tensile residual stresses are also generated at the same time in the interior of the material to balance with the surface compressive residual stresses. It is considered that the fatigue crack growth characteristics of thermally tempered glass are remarkably different from that of float glass, due to the existence of those residual stresses. In this study, Au film made by ion sputtering method and an optical microscope are used to measure the crack length of the thermally tempered glass and float glass, and these fatigue crack growth characteristics are investigated. As a result, it is confirmed that the crack length measurement with an Au film has high accuracy of measurement. Furthermore, it is found that the higher stress intensity factor is needed to cause the crack growth in thermally tempered glas than in flat glass.

113 金属薄膜を用いたき裂長さ測定(OS1-4 き裂の評価・計測技術,OS1 機能性材料の損傷とその力学的背景)

113 金属薄膜を用いたき裂長さ測定(OS1-4 き裂の評価・計測技術,OS1 機能性材料の損傷とその力学的背景)

Calculation of the surface binding energy for ion sputtered particles

In this paper, we consider a simple model, based on the electronegativity concept, which makes it possible to calculate the surface binding energy of any particles, sputtered from a solid surface by ion bombardment. The model contains empirical equations for calculation of “ionic” and “covalent” parts of the binding energy happened between a surface atom and its close neighbors. The model is strongly desirable in the case of the ion sputtering of any strong electronegative (C, N, O, F, Cl, etc.) or electropositive elements (alkali metals, rare earth elements) from semiconductor surfaces, when the strong ionic binding between these elements and the surface atoms can be estimated.

Effect of Ar + ion sputtering on the electronic transport of MgB 2 surface

Scanning tunneling microscopy and spectroscopy (STM/STS) experiments on a high-density sintered MgB 2 surface were performed at 4.2 K, using a low-temperature STM. For a 20-min Ar + ion sputtered MgB 2 surface, a double-gap structure with gap values of Δ L=9.5 meV and Δ S=4.0 meV was clearly observed in the local tunneling spectra, exhibiting the BCS-shaped characteristic with a metallic background. But for a 2-h Ar + ion sputtered surface, the observed current–voltage characteristics of the MgB 2 surface show metallic electronic transport behavior. In an attempt to clarify the effect of Ar + ion sputtering on the electronic transport, the MgB 2 surface was characterized by Auger electron spectroscopy (AES). The compositional changes of the MgB 2 surface were investigated in real time during the course of Ar + ion sputtering. The detailed compositional analysis of the MgB 2 surface may help to elucidate the various electronic transport behavior observed in surface-sensitive STS measurements.

Enhancement of magnetoresistance in spin valves with ion sputtered Si substrates

The pattern of dots with height about 1.2 nm is formed on Si substrates by ion sputtering. Top, bottom spin valves, and bottom spin valves with a nano-oxide layer are fabricated on both non-ion sputtered and ion sputtered Si substrates. Magnetoresistance ratio increase around 10% has been achieved in the spin valves on the ion sputtered substrates.