Ar Ion Sputtering Research Articles

A system for real-time in situ photoelectron spectroscopy

A system is presented which combines photoelectron spectroscopy with complementary characterization techniques in order to provide in situ analysis of surfaces processes. The real-time capability of photoelectron spectroscopy has been enabled by an electron counting array detector that allows core and valence level spectra to be recorded in 1–10 s using a laboratory X-ray source and as low as 25 ms when coupled to synchrotron radiation source.The efficient detection system is combined with a versatile heater stage, temperature and vacuum monitoring, and controllable evaporation sources in order to monitor chemical, structural and electronic changes in situ. The heated stage allows a range of programmed heating and cooling regimes to be applied to samples. Evaporation sources are provided for medium-temperature materials such as small organic molecules and high-temperature metals such as aluminium. The system has a linked vacuum vessel for plasma etching and Ar ion sputtering for surface preparation.

Heating modification of an austenitic steel with high‐nitrogen content

AbstractThe micro‐structural changes of an austenitic steel with high‐nitrogen content have been investigated after heat treatments at 850 °C. Micro‐chemical composition of heat‐induced structures was analyzed using XPS, multipoint AES and photoemission spectro‐microscopy. Before the XPS, AES and photoemission spectro‐microscopy analyses, the samples were cleaned in situ by Ar ion sputtering. The results show that the discontinuous precipitation of Cr2 N from the nitrogen supersaturated γs phase is accompanied by a net flux of nitrogen toward the transformed zones, thus confirming that the principal force behind boundary migration is the nitrogen concentration gradient between the γ and γs phases. When γ and γs reach the same nitrogen concentration, the precipitation stops even if the transformation of the matrix has not yet been completed. Copyright © 2010 John Wiley & Sons, Ltd.

Magnetic Properties Optimization for Amorphous Soft Underlayers

Magneto-optical Kerr effect (MOKE) microscopy and vibrating sample magnetometer (VSM) were used to investigate the magnetic properties of CoFeTaZr and CoTaZr soft magnetic underlayers (SULs). When comparing the CoTaZr with the CoFeTaZr amorphous thin films, the CoFeTaZr films yielded superior magnetic properties. Pre-sputtering substrate Ar-ion milling and sputtering processing pressure were varied to control the magnetic properties of the amorphous films. Furthermore, it was discovered that the magnetic properties of the amorphous thin film strongly depended on the thickness of the SULs, seed layers and capping layers. The experimental results indicated that above a certain thickness, the media noise could be substantially reduced and the magnetic properties of the CoFeTaZr SULs would be optimized. It was also shown that CoFeTaZr SULs with a Ta capping layer and Ru seedlayer had lower coercivity.

Surface treatments toward obtaining clean GaN(0 0 0 1) from commercial hydride vapor phase epitaxy and metal-organic chemical vapor deposition substrates in ultrahigh vacuum

We studied processes of cleaning GaN(0 0 0 1) surfaces on four different types of wafers: two types were hydride vapor phase epitaxy (HVPE) free-standing substrates and two types were metal-organic chemical vapor deposition (MOCVD) films grown on these HVPE substrates and prepared by annealing and/or Ar ion sputtering in ultra high vacuum. We observed the surfaces through treatments using in situ low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy, and also using ex situ temperature programmed desorption, X-ray photoelectron spectroscopy, X-ray diffraction, and secondary ion mass spectrometry. For HVPE samples, we obtained relatively clean surfaces under optimized three-step annealing conditions (200 ° C for 12 h + 400 ° C for 1 h + 500 ° C for 5 min) without sputtering, after which the surface contamination of oxide and carbide was reduced to ∼ 20 % of that before annealing. Clear GaN(0 0 0 1) 1 × 1 patterns were obtained by LEED and RHEED. STM images showed flat terraces of ∼ 10 nm size and steps of ∼ 0.5 nm height. Upon annealing the HVPE-GaN samples at a much higher temperature ( > 550 ° C), three-dimensional (3D) islands with facets were formed and the surface stoichiometry was broken down with the desorption of nitrogen in the form of ammonia, since the samples include hydrogen as an impurity. Ar + sputtering was effective for removing surface contamination, however, postannealing could not recover the surface roughness but promoted the formation of 3D islands on the surface. For MOCVD/HVPE homoepitaxial samples, the surfaces are terminated by hydrogen and the as-introduced samples showed a clear 1 × 1 structure. Upon annealing at 500–600 ° C, the surface hydrogen was removed and a 3 × 3 reconstruction structure partially appeared, although a 1 × 1 structure was dominant. We summarize the structure differences among the samples under the same treatment and clarify the effect of crystal quality, such as dislocations, the concentration of hydrogen impurities, and the residual reactant molecules in GaN films, on the surface structure.

Chemical composition of superconducting SmFeAsO doped with fluorine

AbstractBulk samples of SmFeAsO with and without F doping were prepared by thermal synthesis of the powders. Some samples of obtained oxy‐pnictides were further pressed and sintered at 1300 °C.The crystalline structure of the samples was investigated by X‐ray powder diffraction. The samples were also characterized by resistivity measurements and SEM‐Energy Dispersive Spectroscopy (EDS) analysis. The chemical composition (atomic concentration and chemical states of constituent elements) of the samples' surface was analyzed by means of XPS before and after the sample cleaning by Ar ion sputtering. For the analysis of the bulk composition, the samples were scraped by using superfine diamond file and immediately transferred into XPS apparatus. In this way, the in‐depth distribution of fluorine and the contribution of surface oxides were revealed. Copyright © 2010 John Wiley & Sons, Ltd.

XPS study of gold‐based metallic glass

AbstractNew multinary amorphous materials, based on gold, that can be produced in bulk form due to their high glass‐forming tendency, were discovered recently. However little is known about their corrosion properties.In the present study, the characterization of Au49Cu26.9Ag5.5Pd2.3Si16.3 amorphous ribbons produced by melt spinning is reported. Their corrosion properties were tested by incubating the samples in artificial sweat and by monitoring the changes in surface structure by SEM and XRD. Before incubation, the surface of the samples was amorphous and flat, characterized only by microfeatures due to the liquid contact with the wheel during quenching. After treatment with artificial sweat, the formation of nanosized crystallites of Au on the sample surface was observed.The surface chemical composition of both sides of the ribbon samples was investigated by XPS. Atomic concentration and chemical states of constituent elements before and after the incubation in artificial sweat were determined. The depth profiling of both sides of the samples was carried out by using Ar ion sputtering combined with cyclic XPS measurements. The segregation of Si on one side of the samples and the changes of chemical composition, caused by the treatment in artificial sweat, were revealed. Copyright © 2010 John Wiley & Sons, Ltd.

Anelastic Phenomena at the Fibre-Matrix Interface of the Ti6Al4V-SiC<sub>f</sub> Composite

The composite, consisting of Ti6Al4V matrix reinforced by unidirectional SiC fibres (SCS-6), has been investigated by mechanical spectroscopy at temperatures up to 1,173 K. For comparison, the same experiments have been performed on the corresponding monolithic alloy. The internal friction (IF) spectrum of the composite exhibits a new relaxation peak superimposed to an exponentially increasing background. This peak, which is not present in the monolithic alloy, has an activation energy H = 186 kJ mol-1 and a relaxation time 0 = 2.3 x 10-15 s. The phenomenon has been attributed to a reorientation of interstitial-substitutional pairs in the  phase of Ti6Al4V matrix around the fibres. This explanation is supported by the results of micro-chemical characterization carried out by X-ray photoelectron spectroscopy (XPS) combined with Ar ion sputtering.

Surface Analysis of 1-Hydroxybenzotriazole and Benzotriazole Adsorbed on Cu by X-Ray Photoelectron Spectroscopy

The surface chemistry of two corrosion inhibitors, 1-hydroxybenzotriazole (BTAOH) and benzotriazole (BTAH), adsorbed on copper from 3% NaCl aqueous solution, was investigated by X-ray photoelectron spectroscopy (XPS). Surface and subsurface chemical structure, composition, and layer thickness were obtained from angle-resolved XPS measurements, from detailed analysis of the background in the XPS spectra by the Tougaard method, and from XPS depth profiling performed by Ar-ion sputtering. The main concern was the shape of the X-ray induced Auger Cu spectrum that offers the possibility to investigate the Cu(I) environment. The Auger Cu spectrum obtained after treatment in the BTAH-containing solution was decomposed into three components originating from the Cu(I)BTA complex layer, the underlayer, and the Cu substrate. This procedure indicates the formation of the Cu(I)BTA surface complex on the underlayer after BTAH treatment. The BTAH molecules [either in the Cu(I)BTA complex or uncomplexed] are directed toward the Cu surface through their triazole N atoms. In contrast to the BTAH treatment, the Cu-BTAOH layer formed on the Cu surface after treatment in the BTAOH solution is less ordered and is much thinner than the Cu-BTAH structure.

Precise XPS depth profile of soda-lime-silica glass using C60 ion beam

Abstract Ar ion sputtering is one of the most accepted techniques for depth profiling in practical X-ray photoelectron spectroscopy (XPS) analysis, while this technique is known to be inadequate for quantitative analysis of glass including mobile ions such as soda-lime-silica glass. For the precise depth profiling on XPS depth analysis, three methods, (i) coating of conductive thin film on glass surface, (ii) sample cooling at the temperature of −130 °C and (iii) buckminsterfullerene (C 60 ) ion sputtering, were investigated to suppress the migration of mobile ions in glass. In our best knowledge, it is the first time to succeed the precise XPS depth analysis of soda-lime-silica glass (70.4SiO 2 , 0.9Al 2 O 3 , 7.3MgO, 7.8CaO, 13.6Na 2 O in mol%) without compositional change by using C 60 ion sputtering. The precise analysis revealed that the ion implantation during Ar ion sputtering principally resulted in the compositional change due to the migration of mobile ions.

Sequential vortex hopping in an array of artificial pinning centers

We use low-temperature magnetic force microscopy (MFM) to study the hopping motion of vortices in an array of artificial pinning centers (APCs). The array consists of nanoscale holes etched in a niobium thin film by Ar-ion sputtering through an anodic aluminum-oxide template. Variable-temperature magnetometry shows a transition temperature of 7.1 K and an enhancement of the magnetization up to the third matching field at 5 K. Using MFM with attractive and repulsive tip-vortex interaction, we measure the vortex-pinning strength and investigate the motion of individual vortices in the APC array. The depinning force for individual vortices at low field ranged from 0.7 to 1.2 pN. The motion of individual vortices was found to be reproducible and consistent with movement between adjacent holes in the film. The movements are repeatable but the sequence of hops depends on the scan direction. This asymmetry in the motion indicates nonuniform local pinning, a consequence of array disorder and hole-size variation.

The study on the work function of CdZnTe with different surface states by synchrotron radiation photoemission spectroscopy

The work functions of CdZnTe single crystal with different surface states were measured using synchrotron radiation photoemission spectroscopy. The work function of CdZnTe after mechanical and chemical polishing is higher than that of clean and ordered surface. The damage layer deduced by Ar ion sputtering increases the work function. The Te adatoms of the CdZnTe (111)B (2×2) reconstruction form the interface dipole and increase the work function. The effects of H2O adsorption and Au evaporation on the work function of CdZnTe were investigated. The relationships among work function, surface dipole, valence band bending, ionization energy, and electron affinity of CdZnTe with different surface states were discussed.

Fabrication of nitrogen-doped TiO 2 layer on titanium substrate

In this paper, macropores TiO 2 layer was fabricated on titanium substrates based on plasma based ion implantation (PBII). In order to increase the photodegradation efficiency of fabricated TiO 2 layer, two approaches are used: (1) preparation of macropores on TiO 2 layer to increase the total photodegradation area and (2) nitrogen doping (N-doping) to increase light absorption efficiency. The fabrication process of the N-doped macropores TiO 2 layer comprises four steps: firstly, helium plasma based ion implantation (He-PBII) is employed to generate He bubbles in substrate; secondly, oxygen plasma based ion implantation (O-PBII) and a followed annealing in air are executed to obtain rutile and anatase mixture TiO 2 phases; thirdly, He bubbles are exposed to the surface via an Ar ion sputter process; lastly, the samples are doped by nitrogen PBII (N-PBII). The photodegradation of Rhodamine B solution under Xe lamp indicates that the TiO 2 layer with surface macropores and N-doping has higher light photocatalysis efficiency.

Localized Distributions of Quasi-Two-Dimensional Electronic States near Defects Artificially Created at Graphite Surfaces in Magnetic Fields

We measured the local density of states of a quasi two-dimensional electron system (2DES) near defects, artificially created by Ar-ion sputtering, on surfaces of highly oriented pyrolytic graphite (HOPG) with scanning tunneling spectroscopy (STS) in high magnetic fields. At valley energies of the Landau level spectrum, we found two typical localized distributions of the 2DES depending on the defects. These are new types of distributions which are not observed in the previous STS work at the HOPG surface near a point defect [Y. Niimi, Phys. Rev. Lett. 97, 236804 (2006).10.1103/PhysRevLett.97.236804]. With increasing energy, we observed gradual transformation from the localized distributions to the extended ones as expected for the integer quantum Hall state. We show that the defect potential depth is responsible for the two localized distributions from comparison with theoretical calculations.

Fabrication of a Well-Ordered Nanohole Array Stable at Room Temperature

We report on the fabrication of a new type of nanotemplate surface consisting of a hexagonally well-ordered array of one monolayer deep holes with a tunable size of about 4 nm (2) and a fixed spacing of 7 nm. The nanohole array fabrication is based on the strain-relief trigonal network formed in the 2 monolayer Ag on Pt(111) system. Removing about 0.1 ML of the Ag top layer of this surface structure, for example, by He- or Ar-ion sputtering, leads to the formation of nanoholes at specific domains of the trigonal network, which are stable at room temperature.

Carbon−Carbon Bond Formation on Model Titanium Oxide Surfaces: Identification of Surface Reaction Intermediates by High-Resolution Electron Energy Loss Spectroscopy

The interaction of CH2O with perfect and defective TiO2(110) surfaces (produced by overannealing and Ar ion sputtering methods) was studied by thermal desorption spectroscopy, high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations. Exposing the perfect TiO2(110) surface to CH2O at 100 K leads to the formation of physisorbed CH2O and to polymerization of CH2O, yielding paraformaldehyde. The latter is bound to the 5-fold coordinated surface Ti atoms and is found to decompose and release CH2O at about 270 K. On the defective TiO2(110) surface, CH2O adsorbs more strongly on oxygen vacancy sites, ultimately forming a diolate (−OCH2CH2O−) species, as demonstrated by HREELS. The assignment of the vibrational frequencies was aided by theoretical calculations on the DFT-B3LYP level. Upon heating to higher temperatures, this species undergoes deoxygenation, resulting in ethylene formation.

Morphological evolution of InP nano-dots and surface modifications after keV irradiation

Evolution and coarsening behaviour of self-assembled nano-dots fabricated on an InP surface by 3 keV Ar ion sputtering have been studied in conjunction with the structural modifications at the surface. The dots have been produced in off-normal geometry but in the absence of rotation. For small sputtering durations, the dots coarsen and agglomerate, up to a critical time tc, while the surface roughens and experiences a tensile stress. A relaxation in this stress is observed after the surface becomes amorphized at tc, beyond which an inverse coarsening, fragmentation of dots and a smoothened surface are observed.

Chemical composition of magnesium boride films obtained by CVD

AbstractThe films of magnesium boride were grown on Si(100) substrate by chemical vapor deposition, starting from the synthesis of the single‐source precursor Mg(BH4)2. The deposition time was varied to study its influence on the film composition. The chemical composition of produced samples was investigated by the XPS technique. The depth profiling of MgBx films was carried out by using Ar ion sputtering combined with cyclic XPS measurements. The contributions of different chemical species (boride and oxides) in the depth profiles were separated by peak‐fitting analysis of photoelectron B 1s and Auger Mg KLL spectra. In order to determine the correct parameters of peak fitting, the reference samples of MgB2 and MgO were studied as well. The produced samples were composed of MgBx film covered by an overlayer of magnesium and boron oxides, whose thickness was increasing with deposition time. The surface of the films was enriched with magnesium, while the volume was characterized by the B : Mg ratio exceeding 2. XPS results confirmed that the bulk decomposition of Mg(BH4)2 precursor was successful; therefore, some other phenomenon, such as Mg segregation, was responsible for the formation of MgBx films with x > 2. In addition, a prolonged deposition time resulted in a thicker surface overlayer of Mg and B oxides, but it did not change the stoichiometry of the boride film. Copyright © 2008 John Wiley & Sons, Ltd.

Studies of InP nano dots formation after keV Ar+ irradiation

Temporal evolution of nano dots fabricated, in off-normal geometry but in the absence of rotation, on InP(111) surfaces by 3keV Ar ion sputtering is reported here. After 10min of sputtering, self-assembled nano dots with mean diameter of 24±4nm display square short range weak ordering. Fully developed square celled arrays of dots with mean diameter of 90±26nm, are seen beyond the non-linear coarsening regime at the critical time of 40min. Inverse coarsening of dots in conjunction with surface smoothening, never seen in earlier studies of dot evolution, is observed beyond the critical time.

Plasmon-suppressed vertically-standing nanometal structures

The authors report plasmon-suppressed vertically-standing nanometal-stripe-array structures fabricated by Ar ion sputtering after electron-beam lithography and Ag deposition. When the width of the Ag stripe is comparable to the skin depth of a metal (~ 20 nm), the particle plasmon resonance is strongly suppressed for electric fields oscillating perpendicular to the length of the stripe. This suppression of the particle plasmon excitation is attributed to the limited movement of free electrons localized near the bottom of Ag stripe. This plasmon-suppressed vertically-standing nanometal structures could be used for broad band polarizers.

STM/STS measurements of quasi two-dimensional electronic states near artificially created defects in magnetic fields

We observed the local density of states (LDOS) of a quasi two-dimensional electron system near defects, artificially created by Ar-ion sputtering, on a surface of highly oriented pyrolytic graphite in magnetic fields with ultra-low temperature scanning tunneling spectroscopy. In differential tunnel conductance images taken at the valley energies in between the adjacent Landau levels, two typical localized distributions of the LDOS were observed depending on the defects. We reveal that the defect potential depth is responsible for the two types of the spatial distributions of LDOS.