bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin Polarized Photoemission Studies of Quantum well States in Thin Films
Authors: Johnson P.D. , Brookes N.B. , Chang Y. , Garrison K.
Published: September 2012

Spin polarized photoemission is used to study the electronic structure of noble metals deposited on ferromagnetic substrates. Studies of Ag deposited on an Fe (001) substrate reveal a series of minority spin interface or quantum well states with binding energies dependent on the thickness of the silver. Similar behavior is observed for Cu films deposited on a fee Co (001) substrate. Tight-binding Modeling reproduces many of the observations and shows that hybridization of the sp-bands with the noble metal d-bands cannot be ignored.
Magnetic Spectro-Microscopy Using Magneto-Dichroic Effects in Photon-Induced Auger Electron Emission
Authors: Schneider C.M. , Meinel K. , Holldack K. , Oepen H.P. , Grunze M. , Kirschner J.
Published: September 2012

We have imaged the magnetic domain structure on the surface of Fe (100) single crystals using energy resolved photoemission microscopy with circularly polarized soft x-rays. The contrast between different domains arises due to Magneto-dichroic effects in the emitted Auger electrons. This new approach offers a surface sensitive way to combine chemical and magnetic information on a microscopic scale.
MCD Observed by Photoemission on the 2p Lines of Iron Films Under an External Applied Field.
Authors: Boeglin C. , Beaurepaire E. , Carrière B. , Hricovini K. , Krill G.
Published: September 2012

Circular Dichroic X-ray Photoemission Spectroscopy (CDXPS) experiments have been performed on the 2p core level spectra of polycrystalline Fe film which was magnetized by a low excitation field. The ability to perform the CDXPS experiments in a non remanent mode at a photon energy of 2100 eV opens new and interesting possibilities for the MCD technique in the study of surface and interface Magnetism. Our work on this polycrystalline iron gives some new insights into the understanding of the MCD Mechanism. First results show a similar angular variation for the measured asymmetry, as those observed on a Fe bcc (100) single crystal remanently magnetized in the [100] direction. Our results make clear that the parameters governing the behaviour of the asymmetry factor (A) are not completely described by the relative direction of the Magnetization (M) with the polarization vector of the incident beam (q) and the direction of detection of the photoelectrons (z). The specific outcoming of this work is to clearly show that this behaviour of A is not connected to the crystalline structure of the film for our geometries.
Strong Magnetic Circular Dichroism in 4F Photoemission
Authors: Starke Kai , Navas E. , Baumgarten L. , Kaindl G.
Published: September 2012

We report on strong magnetic circular dichroism (MCD) in 4f photoemission (PE) from Magnetized Gd(0001)/W(110) films. The shape of the 4f6–7FJ final-state PE Multiplet depends on the relative orientation between photon spin and sample magnetization and can be described within an atomic Model. The spectra rule out antiferromagnetic alignment of the (0001) surface layer and the bulk of Gd. This MCD in 4f-PE from rare-earth materials opens new perspectives in the analysis of surface and thin-film magnetism and as a sensor for circular polarization of soft x-rays.
Auger Electron and Photoelectron Diffraction in Magnetic Thin Films
Authors: Idzerda Y.U. , Ramaker D.E.
Published: September 2012

The role of the final-state character of the emitted electron in Auger electron diffraction (AED) and x-ray photoelectron diffraction (XPD) is examined with respect to magnetic materials. Single scattering cluster calculations with the inclusion of the spherical wave character and the final-state character of the emitted electron (both angular momentum quantum number and magnetic quantum number) show that selective emission from different M-levels, generated by a non-statistical distribution of initial M-levels or by an M-selective excitation process, results in distinctly different emission patterns.
Perpendicular Magnetic Anisotropy in Ultrathin Fe (110) Films on Cr (110)
Authors: Fritzscht Helmut , Gradmann Ulrich
Published: September 2012

In contrast to Fe(110) -films on W(110), which are magnetized always in the plane as a result of easy-plane magnetic surface anisotropies (MSA), Fe(110) -films on Cr(110) show perpendicular magnetization up to a thickness of roughly 3 Monolayers, as a result of a perpendicular MSA of the Fe(110)/Cr/(110) interface. Acoordingly, Fe(110) -films on W(110), covered with Cr(110), show asymmetric MSA, the easy-plane mSA of the W(110)/Fe(110) -interface opposing the perpendicular one of the Fe(110)/Cr(110) -interface. It turns out that MSA is asymmetric too in Fe(110) films on W(110) covered by Cu, Ag, Au or UHV.
Microstructural Dependence of the Perpendicular Magnetic Anisotropy in Co-Pt Alloys
Authors: Marinero E. E. , Farrow R. F. C. , Harp G. R. , Geiss R. H. , Bain J. A. , Clemens B.
Published: September 2012

To establish the structural origins of the perpendicular magnetic anisotropy in Co-Pt alloys, a variety of magnetic and structural characterization techniques have been utilized. We have determined that the development of out-of-plane magnetization in these alloys, strongly depends on growth temperature and in contrast to CO/Pt Multilayers, the highest anisotropics and coercivities are observed in polycrystalline alloys with negligible preferred crystallographic orientation. Lattice strain Measurements, surface roughness determination and crystal growth studies indicate that contributions from magnetostrictive and magnetostatic contributions to the perpendicular anisotropy in these alloys are not significant. H RTEM and synchrotron-based x-ray diffraction experiments, on the other hand, confirm the existence of ordered CoPt3 at elevated temperatures. We suggest that the strong temperature dependence of the perpendicular anisotropy is correlated to the onset of spontaneous chemical ordering during the growth which results in anisotropie pair ordering. A tentative model explaining this strong temperature dependence is described.
The Microstructure of Fe7C3 Formed at 300°C by Plasma Enhanced Chemical Vapor Deposition (PECVD)
Authors: Siriwardane H. , Fraundorf P. , Newkirk J.W. , Pringle O.A. , James W.J.
Published: September 2012

Thin iron carbide films were prepared by introducing iron penta carbonyl (FeCO5) and hydrogen (H2) into a glow discharge. The films are of potential interest in corrosion and wear resistant applications. X-ray diffraction data of films (≈ 7000 Å thick) deposited on glass at 300°C evidenced only Fe7C3. Thinner films were required for examination by analytical and high resolution transmission electron Microscopy. Therefore, two sets of films (“thin” < 200 Å and “thick” ≈ 800 Å) were plasma-deposited on carbon or holey carbon films supported on copper grids. The thin TEM specimens exhibited a fine texture and gave rise to ring diffraction patterns, whereas the thick TEM specimens evidenced two types of structure: (i) half-Micron sized grains separated from one another by 1–2 Microns on the support, although sometimes interconnected by single crystal platelets and (ii) 300 Å grapelike clumps of 100–200 Å crystals, each individually surrounded by a 50 Å non-crystalline coating. The latter structure may result from a post-formation oxidation process which expels carbon from the iron phase into grain boundaries.
UHV Preparation and In-Situ Surface Analysis of MNFE/Nife Exchange Structures: Interfacial Impurity Incorporation
Authors: Cohen Susan L. , Baker John M. , Russak Michael A. , Scilla Gerald J. , Hwang Cherngye , Rossnagel Stephen M.
Published: September 2012

MnFe/NiFe exchange structures have been prepared in an ultra-high vacuum sputtering/surface analysis system. Controlled introduction of residual gas impurities such as O2 and H2O at the MnFe/NiFe interface is studied by in-situ x-ray photoelectron spectroscopy (XPS) and the exchange structures are magnetically characterized. Due to the extreme reactivity of the NiFe surface towards O2, the exchange coupling is severely degraded by only small exposures of this molecule to the NiFe surface. In contrast, H2O does not oxidize the NiFe surface and therefore can be tolerated in greater quantities in the sputtering chamber without detrimental loss of exchange. This understanding of the basic surface chemistry of the MnFe and NiFe surfaces can lead to improved sputtering practices in actual manufacturing applications.
Application of High-Resolution Electron Microscopy to the Study of Magnetic Thin Films and Multilayers
Authors: Sinclair R. , Nolan T.P. , Bertero G.A. , Visokay M.R.
Published: September 2012

The performance of a wide range of modern magnetic thin-film materials for information storage is found to depend dramatically on grain nucleation and coherence at interfaces. Three such systems, Fe/Pt Multilayers, CO/Pt Multilayers, and CoCrTa/Cr bilayers are considered here. High-resolution electron Microscopy (HREM) shows that ordered CoPt and FePt L1o structures can be formed and oriented, using coherence with the substrate, with their magnetically easy c-axes perpendicular to the film plane. This orientation results in the perpendicular magnetization required for Magneto-optic recording Media. Different sputtering gases used in producing CO/Pt Multilayers result in varying degrees of interfacial intermixing, which is shown to strongly affect the perpendicular magnetic anisotropy energy. The required high in-plane coercivity of longitudinal recording media is also correlated with the observed interface coherence and the resulting oriented growth of CoCrTa with the magnetically hard <110> axis perpendicular to the film plane. Many features of the microstructure can be observed directly at the atomic level by HREM, and so the usefulness of this technique is emphasized in this paper.
Initial Growth and morphology of Ultrathin Magnetic Films Studied Using Scanning Tunneling Microscopy.
Authors: Chambliss David D. , Johnson K.E. , Kalki K. , Chiang S. , Wilson R.J.
Published: September 2012

The room-temperature growth of Fe on Cu(100) has been studied using the scanning tunneling Microscope (STM) to determine low-coverage growth mode and local structures related to the FCC-BCC structural transformation. Results for submonolayer deposition demonstrate an initial interchange of deposited Fe atoms with substrate Cu. This leads to a highly rough Fe-Cu interface and growth characteristics that for different experimental techniques can resemble 3-D island growth or layer-by-layer growth. For a thickness ∼14 Monolayers, the FCC-BCC transition is observed to occur via the formation of fairly large martensitic grains, rather than by a change in atomic aggregation. The implications of the instability of FCC-Fe, as evident in both low- and high-coverage data, are considered.
Scanning-Ion Microscopy with Polarization Analysis (Simpa)
Authors: Zheng N. J. , Rau C.
Published: September 2012

We have developed a novel, high-resolution magnetic imaging technique, scanning-ion microscopy with polarization analysis (SIMPA). In SIMPA, a highly-focused, scanning Ga+ ion beam is used to excite spin-polarized electrons at surfaces of ferromagnetic Materials. By Measuring the intensity and the spin polarization of the emitted electrons using a newly developed, compact mott polarimeter, topographic and magnetic images of magnetic structures are obtained. We report on first SIMPA studies on single-crystalline Fe samples.
Structure and Magnetic Properties of FE/ZR Multilayer Films
Authors: Konno Toyohiko J. , Nakayama Takenori , Clemens Bruce M. , Sinclair Robert
Published: September 2012

We investigated structural and magnetic properties of Fe/Zr Multilayer films using high-resolution transmission electron Microscopy, X-ray diffraction and vibrating sample Magnetometry. For films with wavelength (Λ) ≥ 80Å, the interface region between the Fe and Zr layers exhibits a 15–20Å thick amorphous structure. The Magnetization curves of these films showed a monotonous decrease in the saturation magnetizations with Λ, whose trend is well explained by a simple asymptotic model that assumes the interface amorphous layer to be non-ferromagnetic. Films with Λ≤40Å exhibit a compositionally-Modulated amorphous structure. The latter films are paramagnetic except for the one with Λ=40Å, which showed a superparamagnetic behavior.
Structural and Magnetoresistance Properties of Co/Cu Multilayers Doped with Fe
Authors: George J.M. , Barthelemy A. , Durand O. , Duvail J. L. , Fert A. , Galtffir P. , Heckmann O. , Pereira L.G. , Petroff F. , Valet T.
Published: September 2012

We have studied the influence of ultra-thin interfacial Fe layers on the structural and magnetoresistance properties of CO/Cu Multilayers. Our results show that the giant magnetoresistance arises from spin dependent scattering at the CO/Cu interfaces and in the bulk of Co, the interfacial contribution being predominant. We also demonstrate that the close-packed crystallographic structure of Co and Cu is very sensitive to the insertion of interfacial bec Fe layers: for small thicknesses, Co as well as Cu adopt a metastable bec structure.
Resistance and magnetoresistance of Gadolinium/Tungsten Multilayers
Authors: Heys A. , Donovan P. E. , Astrakharchik E. G. , George B.
Published: September 2012

The resistance and magnetoresistance of Gd/W Multilayers have been measured at temperatures between 300K and 4K and in fields of up to 7 Tesla. The temperature coefficent of resistance is strongly influenced by the thickness of the Gd layers, becoming negative at a Gd layer thickness of 0.8nm. The Magnetoresistance is dominated by the Gd below about 100K. Multilayers which show reduced saturation magnetisation at 4K also have an unusual form of magnetoresistance around 100K. We suggest that this may be due to antiferromagnetic alignment of the Gd and W Moments at low applied fields.
Transmission Electron Microscopy Studies of NiFe/Cu/Co/Cu on Si.
Authors: Gautier P. , Valet T. , Durand O. , Jacquet J.C. , Chevalier J.P.
Published: September 2012

(NiFe/Cu/Co/Cu) Multilayers grown on (100) Si by RF sputtering have been studied by transmission electron Microscopy. The samples are found to be polycristalline and are only weakly textured. The period of the multilayers is clearly visible by small angle electron diffraction and Fresnel imaging. The waviness of the layers appears to be related to the columnar structure of the samples. Experimental images with Fresnel contrast are compared with simulations in order to assess the thickness and roughness of each individual layer.
Neutron Scattering Measurements of the Staggered Magnetization of an Antiferromagnetic Epitaxial thin Film FeF2
Authors: Belanger D. P. , Lui M. , Erwin R. W.
Published: September 2012

Elastic neutron scattering measurements performed at the NIST reactor have been used to measure the staggered magnetization near the transition temperature in a thin antiferromagnetic epitaxial film of FeF2 of thickness 0.8μm and diameter 1cm grown on a diamagnetic (001) ZnF2substrate by MBE. The use of a thin film permits extinction-free Bragg intensities, something which has proven impossible in bulk crystals. The growth techniques yield sufficient crystal quality to observed resolution limited Magnetic Bragg scattering peaks and to approach the transition within a reduced temperature of |t| = 0.003. The structure quality of this sample has been characterized using X-ray double crystal diffraction with a measured rocking curve lin ewidth of less than 30 arc sec. The sample thickness, while small enough to eliminate extinction, is sufficiently large to assure three-dimensional Ising Model critical behavior. We indeed observe critical behavior consistent with theoretical predictions. The success of the thin film experiments demonstrates the possibilities of extinction-free Bragg scattering measurements in a variety of antiferromagnetic Materials, including multilayered systems.
A Comparative Study of Structural, Magnetic, and Transport Properties of Co-Re Superlattices Sputtered on Glass and Si Substrates
Authors: Leal J.L. , Barradas N.P. , Soares J.C. , da Silva M.F. , Rots M. , Freitas P.P.
Published: September 2012

Antiferromagnetically coupled (Co17A°Re5A°)×15 superlattices were deposited simultaneously onto glass and Si substrates, with an intervening Re buffer layer. Samples grown on glass show sharper interfaces than those grown on Si. This effect reflects on Magnetoresistance, Magnetization, Rutherford backscattering, and hyperfine field results. The influence of the Re buffer layer thickness and annealing temperature on these properties is discussed.
Interfacial Exchange Coupling and the magnetization of Iron Oxide/Nickel Oxide Superlattices
Authors: Berry S. D. , Lind D. M. , Lochner E. , Shaw K. A. , Hilton D. , Erwin R. W. , Borchers J. A.
Published: September 2012

The role of interfacial exchange coupling in the magnetic behavior of metal oxide materials has been investigated through the study of Fe3O4/NiO superlattices. We report results on a series of superlattices grown where one bilayer constituent was held to a fixed thickness while varying the other from single unit cell dimensions upward. High crystalline quality was confirmed by XRD, RHEED and neutron diffraction. Magnetization profiles show substantial deviations from bulklike iron oxide results, with an increase in domain rotation energies observed in the superlattices over that of bulk iron oxide (increasing with NiO layer thickness) indicating the strong nature of Fe3O4/NiO interfacial linkage. Neutron scattering at elevated temperatures shows that the NiO remains ordered above the 523 K bulk Néel temperature. This suggests that at least a portion of the NiO within a layer remains ordered well above the Néel temperature, with an increase in effective Néel transition temperature that approaches the Fe3O4 Curie temperature in the limit of very thin NiO layers. Although the exchange coupling dominates these effects, strain also plays an important role.
Interface and Volume Anisotropy of MBE-Grown Co/Pt (111), (110) and (001) and Sputtered CO/Pt Multilayers
Authors: Weiler D. , Farrow R.F.C. , Marks R.F. , Harp G.R. , Notarys H. , Gorman G.
Published: September 2012

A quantitative determination of interface (Ks) and volume anisotropy {?ψ) constants of MBE and sputtered CO/Pt Multilayers is reported. Torque and VSM Magnetometry were used to determine the total average anisotropy and the room temperature magnetization of four different series of films with varying Co thickness and nearly constant Pt thickness. All films were characterized with X-ray diffraction and X-ray fluorescence, allowing the determination of the “Magnetic” volume with good accuracy. Both Ks and Jeff are found to be orientation dependent. We find the following results for MBE films grown on Ag buffered GaAs substrates and highly < 111 > textured films, grown on etched SiNx buffers:

(111) Ks = 0.97mJ/m2, Kveff =-0.74MJ/m3 MBE

(111) Ks = 0.92mJ/m2, Kveff =-l.lIMJ/m3 sputtered

(110) Ks = 0.42mJ/m2, Kveff =-l.95MJ/m3 MBE

(001) Ks = 0.59mJ/m2, Kveff =-5.98MJ/m3 MBE

The [110]-oriented MBE films show in addition a large (intrinsic) in-plane anisotropy constant K‖0≃-3MJ/m3 which is found to be independent of the Co thickness. [100] is the easy and [110] the hard in-plane direction.
Valence Instability and Magnetic Polarization of Ce Atoms near the Interface of Ce/Fe Multilayers Studied by Magnetic Circular X-Ray Dichroism.
Authors: Klose F. , Pizzini S. , Giorgetti C. , Schulte O. , Baudelet F. , Dartyge E. , Krill G. , Felsch W. , Fontaine A.
Published: September 2012

An experimental study of conventional x-ray absorption and of magnetic circular x-ray dichroism has been performed on Ce/Fe Multilayers at the Ce L2,3 and the Fe-K edge, to characterize the impact of the interaction of Ce and Fe on the local electronic and magnetic structure of the interface. The spectra reveal that the interaction has two effects. First, on a depth scale of up to 15 A near the interface, the Ce atoms adopt the electronic structure of the oc-phase, with itinerant 4f states. Second, a large portion (=10 Å) of these cc-like Ce atoms is magnetically polarized and carries an ordered Magnetic 5d Moment. The Fe-3d and Ce-5d Moments are antiferromagnetically coupled. Interface Mixing on a length scale of the magnetic polarization can be excluded.
Orientational Dependence of Oscillatory Exchange Coupling
Authors: Johnson M.T. , Bloemen P.J.H. , Coehoorn R. , de Vries J.J. , McGee N.W.E. , Jungblut W. R. , Reinders A. , aan de Stegge J.
Published: September 2012

The role of the interlayer Fermi surface in driving oscillatory exchange coupling of ferromagnetic layers has been critically tested in a series of MBE-grown coherent epitaxial sandwiches prepared on single-crystal substrates. The wedge-shaped Cu (or Cu-based) interlayers have been modified in a number of different ways, achieving orientational, compositional and structural alteration of the Cu Fermi surface. Observed phenomena include multiperiodic coupling oscillations in both the ferromagnetically and antiferromagnetically coupled regions of (lOO) -oriented Co/Cu/Co samples, extended oscillatory periods across CuNi alloy interlayers, and extremely short-period oscillations in a bcc (100) Fe/Cu/Fe system. These phenomena are straightforwardly explained in terms of calculated Fermi surface variations.
Phonon Spectra Dependence on Growth and Sample Treatment in β-FeSi2
Authors: Guizzetti G. , Marabelli F. , Patrini M. , Mo Y. , Onda N. , Von KÄnel H.
Published: September 2012

Transmittance, reflectance and Raman measurements have been performed from 50 to 700 cm−1 on different thin films of β-FeSi2 epitaxially grown by MBE on Si substrates. Vibrational spectra show much more structures than the five phonons usually observed in this material; the dependence on the crystalline orientation, the thickness, the growth and the annealing temperature has been studied.
Fe-Silicides Formed with Molecular Beam Epitaxy and Studied with Conversion Electron Mössbauer Spectroscopy
Authors: Degroote S. , Langelaar M.H. , Kobayashi T. , Dekoster J. , Wachter J. De , Moons R. , Niesen L. , Langouche G.
Published: September 2012

Fe-sulicides were formed by annealing MBE-deposited thin 57Fe layers with thicknesses between 20 Å and 60 Å on (7x7) reconstructed Si(111) substrates. During the growth the substrate was held at room temperature. The silicide formation upon annealing in the temperature range of 200°C to 900°C was studied in-situ with RH-EED. Samples were studied with in-situ CEMS (Conversion Electron Mossbauer Spectroscopy) as well as with ex-situ CEMS after covering with Ag to prevent oxidation. RBS/Channeling was used to study the epitaxial quality and the structure of these layers.

Using the 57Fe nuclear probe, it is shown that silicide formation occurs at the interface already at room temperature. Metastable silicides with cubic structure are observed in the low temperature annealing range, and characterized by their Mossbauer parameters. At higher temperatures stable ε-FeSi and β-FeSi2 are formed.
New Resistive Materials Based on Iron Disilicide Alloys
Authors: Engalychev A.E. , Fedorov M.I. , Kaliazin A.E. , Alekseeva G.T. , Ioffe A.F.
Published: September 2012

The electrical conductivity of a number of the semiconducting alloys of iron disilicide with the iron group transition metals and some elements of Vb group have been investigated in detail. Wide temperature regions of linear temperature dependence of resistance were found. The temperature coefficient of resistance (TCR) in these regions is low enough. There is an opportunity of varying the resistivity of these alloys by means of modification of the alloy composition.
Effects of annealing and cobalt implantation on the optical properties of βFeSi2
Authors: Finney M S , Yang Z , Harry M A , Reeson K J , Homewood K P , Gwilliam R M , Sealy B J
Published: September 2012

In this paper optical absorption and photoluminescence (PL) techniques are used to study the optical properties of βFeSi2 layers fabricated by Ion Beam Synthesis (IBS). The way in which the band-gap varies when a small dose of Co is added before Fe implantation is also investigated. Our results indicate that the band-gap for βFeSi2 is direct with a value of 0.87eV. When a sufficiently high dose (1 ×10 16cm2) of Co is implanted prior to Fe we see the appearance of an additional band-gap after annealing at 1173K which we attribute to the formation of a ternary CoxFeySiz phase. We also show that by placing the sample in a hydrogen plasma it is possible to raise the temperature at which PL occurs in βFeSi2 to σ 200K.
Evolution of Defect and Impurity Profile During High Dose Co Implantation into Si at Elevated Temperatures
Authors: Schippel S. , Witzmann A.
Published: September 2012

<111> -Si was implanted with 250 keV Co ions at a target temperature of 350°C. The ion dose was varied between 1 × 1014 cm−2 and 2 × 1017 cm−2. The evolution of the defect and impurity profile was investigated by Rutherford Backscattering Spectrometry (RBS), channeling and transmission electron microscopy (TEM).

Up to a dose of 1 × 1015 Co cm−2 no defects can be detected. At higher Co doses, we find correlated defects in the center of the Co distribution and point defects in the region below. Moreover, damage accumulation at the surface is observed. The concentration of defects increases with increasing ion dose and reaches its level of saturation at a dose of 2 × 1016 cm−2.

The Co profiles of samples implanted at 350°C differ considerably from the Gaussian shape. The near surface and the back flank are parts of Gaussian distributions. However, the standard deviation of the near surface flank is always smaller than that of the back flank. Moreover, the distributions show tails into the substrate at depths > 320 nm. This proves that radiation damage acts as an effective center for the nucleation of CoSi2.

During annealing we find a redistribution of Co towards the defective regions for Co doses between 1 × 1016 cm−2 and 5 × 1016 cm−2.
Crystallographic Structure of Mesotaxial IrSi3 in Six
Authors: Hinneberg H.-J. , Sjoreen T. P. , Chisholm M. F.
Published: September 2012

A buried epitaxial IrSi3 layer has been produced in (111) oriented Si by high dose Ir+- implantation (1 MeV, 1.7× 1017 Ir+/cm2, 550°C) and subsequent annealing (5 h at 1100°C). Transmission electron microscopy and ion channeling show that the hexagonal IrSi3 prefers to form with its (2110) plane oriented parallel to Si(111). while its [0001] direction is parallel to either [112], [121], or [211]. Thus, the IrSi3 film is made up of three differently oriented crystals, each occupying about 1/3 of the silicide volume.

A dose of 3.5× 1016 1r+/cm2 leads to the formation of a band of large, isolated precipitates. They have the same epitaxial relationship to Si, but the Si(111) plane is no longer the only one to which the (2110) of IrSi3 is parallel. Instead precipitates are also observed oriented parallel to (111), (111), and (111) in Si in roughly equal numbers. Consequently, there are now 12 possible orientations of lrSi3 crystals. We assume that strain relief and interface area minimization are the main factors suppressing the additional orientations in the continuous lrSi3 films formed by the coalescence of precipitates at higher doses.
Metal Vapour Vacuum Arc Ion Source to Synthesize Refractory Metal Silicides
Authors: Liu B.X. , Zhu D.H. , Lu H.B. , Tao K.
Published: September 2012

Metal Vapour Vacuum Arc (MEVVA) Ion Source was employed, for the first time, to synthesize metal silicides. Refractory metal silicides NbSi2, TaSi2, WSi2 and MoSi2; were successfully formed by implanting respective metal ions into Si(111) wafers. It was found that the high current density metal ion implantation not only provided the metal components but also caused a simultaneous annealing for various metal-silicide phases to grow. When the imp ytation was conducted at 40 kV, the Nb ion current density was up to 76 μA/cm at a dose of 4×1011/cm2, and the Ta, W and Mo ion current densities were up to 65 μA/cm2 at a dose of 5×1017 ions/cm2, hexagonal NbSi2, TaSi2, MoSi2 and WSi2 were formed. Post annealing transformed the WSi2 and MoSi2 phases from hexagonal to tetragonal structure, featuring lower resistance than that of the as-implanted ones.
The Influence of Implantation-Induced Non-Stoichionetry on the Epitaxial Recrystallization of CoSi2
Authors: Ridgway M.C. , Vantomme A. , Bavel A.-M. Van , Langouche G.
Published: September 2012

Epitaxial CoSi2 layers on Si substrates have been amorphized with Co and/or Si ion implantation. The influence of nonstoichiometry on the rate of solid-phase epitaxial growth (SPEG) of amorphized CoSi2 has been investigated with time-resolved reflectivity, Rutherford backscattering spectrometry and Mossbauer spectrometry, the latter with radioactive 57Co probes. A decrease in SPEG rate was apparent with an increase in nonstoichiometry. For a given ion dose, the decrease was greater following Co implantation. The means by which non-stoichiometry is accommodated in a crystalline CoSi2 lattice - either through phase separation or defect formation - has been considered. SPEG rate retardation was also evident in samples implanted with both Si and Co ions with a Si:Co dose ratio of 2:1. Additional mechanisms may thus also contribute to the observed SPEG rate reduction.
Electron Microscopy Evidence of Interfacial Steps Controlling the Kinetics of NiSi2 Formation
Authors: Hesse D. , Werner P. , Heydenreich J. , Mattheis R.
Published: September 2012

The kinetics and phase formation sequence of thin-film solid-state reactions, including silicide forming reactions, have frequently been considered to be controlled by interfacial kinetic reaction barriers. These are purely phenomenological quantities which describe the finite rate of the interfacial reaction in terms of limited particle fluxes crossing the respective interfaces. No atomic mechanisms that might be responsible for the action of such barriers have so far been indicated, with the exception of Schmalzried's formulation. The latter says that the interfacial barrier is due to the limited relaxation time needed by the particles to rearrange into the proper sublattice after having crossed the interface. We present correlated kinetic and structural observations during the 2Ni + Si → NiSi2 reaction on the Si(111) surface and discuss them with the help of a model involving the formation and lateral propagation of interfacial steps of different height. The model allows us to explain the kinetic observations by reaction barriers formed as a result of the crystallographic boundary conditions of the reaction.
Characterization of Epitaxial CoSi2 Film Growth on Si(100) by Slow Positron Beam
Authors: Liu Ping , Lin Chenglu , Zhou Zuyao , Weng Huiming , Li Bingzong , Han Rongdian , Zou Shichang
Published: September 2012

A slow positron beam was used to investigate the solid state reaction of Co/Si and Co/Ti/Si. Variable-energy (0-20 keV) positrons were implanted into samples at different depths. The Doppler broadening of the annihilation -y-ray energy spectra, measured at a number of different incident positron energies were characterized a line-shape parameter “5”. It was found that the measured S parameters were sensitive to thin film reaction and crystalline characteristics. In particular, the S parameter of epitaxial CoSi2 formed by the ternary reaction was quit different from that of the polycrystalline CoSi2 formed by direct reaction of Co with Si.
Atomistic Aspects of Silicide Reactions Studied with STM
Authors: Bennett P. A. , Parikh S. A. , Lee M. Y. , Cahill David G. , Copel M. , Tromp R. M.
Published: September 2012

We discuss atomistic aspects of the silicide contact reaction inferred primarily from STM observations of the prototype system Co/Si(1 11). For room temperature deposition and low coverage (0.01M1) we find that metal atoms exist as near-surface interstitials within the 7×7 reconstruction. Bond breaking associated with silicide formation occurs only at higher coverages. Deposition at 320C results in flat-topped triangular islands of epitaxial CoSi2 with a metastable 7-fold (111) interface, stabilized by the lateral silicon-silicide interface along the island edges. Some islands are covered with a 2×2 array of silicon adatoms. Very high temperature annealing (1200C) results in an “impurity stabilized 1×1” surface which is in fact a lattice gas of ring-clusters that appear like tiny donuts or bagels in empty states STM images. These structures phase-separate from the clean 7×7 structure upon cooling below 850C.
Nondestructive Study of Metal-Silicon Interfaces Using Soft X-Ray Emission Spectroscopy
Authors: Watabe H. , Iwami M. , Hirai M. , Kusaka M. , Nakamura H. , Miyashita H.
Published: September 2012

Si L2,3 valence band soft x-ray emission spectrum (SXES) due to an e ectron excitation for silicides shows a clear modification from that for Si single crystal. Using this fact in combination with the incident angle variation(IAV) device, a non-destructive in-depth analysis of a Au(thin film)-Si(lll) contact is successfully carried out. Also, the SXES method has clarified the fact that a fair amount of the Si-s valence band density of state (yB-DOS) is included in the upper part of the yB-DOS for a Au-Si alloy, or Au-silicide, due to the Au-Si bond formation, which is a clear contrast to proposals given so far.
Interfacial Structures of Nickel Silicides in the SiaNi/Sic System
Authors: Tseng Bae-Heng , Hsieh Chia-Dar , Wu Show-Gin
Published: September 2012

A laterally uniform formation of NiSi2 at low temperature had been reported for the SiaNi/Sic system. In this work, the interfacial structure of NiSi2 is studied by the high-resolution electron microscopy. We observe an amorphous layer (5–10 nm in thickness) between Sic and NiSi2 in a Sia(300nm)/Ni(5Onm)/Sic sample after annealing at 450°C. The NiSi2 phase in this sample has a polycrystalline structure. We also find that a contaminated amorphous-Si film can not promote a reaction with Ni. A SIMS depth profile shows that this amorphous-Si layer is high in oxygen and carbon. In this case, the silicide formation is similar to the Ni/Sic system.
Electrical Transport Properties of Cu3Ge Thin Films
Authors: Aboelfotoh M. O.
Published: September 2012

We present results of electrical transport studies performed on thin films of ε1-Cu3Ge in the temperature range 4.2 – 300 K. It is found that ε1-Cu3Ge which has a long-range ordered monoclinic crystal structure, exhibits a remarkably low metallic resistivity of σ 6 μΩ cm at room temperature. The density of charge carriers, which are predominantly holes, is σ 8 × 1022/cm3 and is independent of temperature and film thickness. The Hall mobility at 4.2 K is σ 132 cm2/V s, considerably higher than in pure copper. The elastic mean free path is found to be σ 1200Å, which is surprisingly large for a metallic compound film. The results show that the residual resistivity is dominated by surface scattering rather than grain-boundary scattering. It is also found that by varying the Ge concentration from 0 to 40 at. % the resistivity exhibits anomalous behavior. This behavior is correlated with changes observed in the crystal structure of the thin-film alloys as the Ge concentration is increased. The resistivity remains close to that of the ε1-Cu3Ge phase over a range of Ge concentration which extends from 25 to 35 at. %
Schottky Barrier Heights of PT Silicides on SiGe
Authors: Jimenez J.R. , Xiao X. , Sturm J.C. , Pellegrini P.W. , Chi M.
Published: September 2012

Silicide/SiGe Schottky barriers are of importance for applications in infrared detectors and SiGe contacts, as well as for fundamental studies of metal-semiconductor interfaces. We have fabricated silicide/SiGe Schottky diodes by the reaction of evaporated Pt and Ir films on p-SiGe alloys with a thin Si capping layer. The onset of metal-SiGe reactions was controlled by the deposited metal thickness. The Schottky barrier heights were determined from internal photoemission. Pt-SiGe and Ir-SiGe reacted diodes have barrier heights that are higher than the corresponding silicide/p-Si diodes. PtSi/Si/SiGe diodes, on the other hand, have lower “barrier heights” that decrease with increasing Ge concentration. The smaller barrier heights in such silicide/Si/SiGe diodes are due to tunneling through the unconsumed Si layer. Equations are derived accounting for this tunneling contribution, and lead to an extracted “barrier height” that is the Si barrier height reduced by the Si/SiGe band offset. Highly bias-tunable barrier heights are obtained (e.g. 0.30 eV to 0.12 eV) by allowing the SiGe/Si band offset to extend higher in energy than the Schottky barrier, leading to a cut-off-wavelength-tunable silicide/SiGe/Si Schottky diode infrared detector.
Applications of CoSi2 to VLSI and ULSI
Authors: Murarka S. P.
Published: September 2012

Silicides have found application as high conductivity, high temperature, and corrosion resistance materials that form good electrical contacts to silicon and good low resistivity cladding on polysilicon films used as gate metal. Of various silicides investigated in past CoSi2 offers several advantages including lowest resistivity, self-aligned formation, low lattice mismatch with silicon, stability in presence of dopants and on SiO2, Si3N4, or Sioxynitrides, and reliability to process temperatures ≤900°C even when used in thicknesses as thin as 50-60 nm. Thus, CoSi2 has found an application in VLSI and ULSI. In this paper, the properties, formation and processing, reliability, and applicability of CoSi2 will be reviewed. It will be shown that CoSi2 is only silicide that offers properties and reliability for continued use in sub-0.25 pm VLSI and ULSI integrated circuits.
Titanium Germanosilicide: Phase Formation, Segregation, and Morphology
Authors: Aldrich D.B. , Chen Y.L. , Sayers D.E. , Nemanich R.J.
Published: September 2012

The high temperature solid phase reaction of Ti with SixGe1−x produces a low resistivity titanium germanosilicide which is isomorphic with the C54 phase of TiSi2 and TiGe2. The composition of the final C54 Ti(SiyGe1−y)2 film is dependent on the composition of the initial Si-Ge alloy and on the annealing conditions. The intermediate phases of the Ti-Si and Ti-Ge reactions are C49 TiSi2 and Ti6Ge5 respectively. The reaction path of Ti - SixGe1−x shifts from that of Ti-Si to that of Ti-Ge as the SixGe1−x alloy composition changes (×=1→0). Phase separations were observed at low temperatures for Ti reactions with Si-Ge alloys and the C54 formation temperature was observed to decrease as the Si-Ge alloy composition approached Si.5Ge.5. Surface and interface morphologies were examined using SEM and TEM. The formation of smooth, large grain, low resistivity films has been observed for the reaction of Ti with low Ge content alloys (x≥0.7). As germanium content is increased the formation of faceted islands is observed. Reactions with high Ge content alloys (x≤0.3) produce films with morphologies similar to those of the Ti-Ge reaction.
Nonalloyed Ohmic Contacts to N-Si Using a Strained Si0.5Ge0.5 Buffer Layer
Authors: Liou Hsing-Kuen , Yang Edward S. , Tu K. N.
Published: September 2012

Nonalloyed shallow ohmic contacts to n-Si have been fabricated by using an 80 Å thick strained Si0.5Ge0.5 buffer layer grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was employed to investigate the Si 2p and Ge 3d core level binding energies of the strained and the relaxed Si0.5Ge0.5 and to determine their relative Fermi level positions. It was found that the surfaces of strained Si0.5Ge0.5 exhibit pinning very close to the conduction band. Rutherford backscattering and Auger depth profiling were employed to determine the contact reactions using Ti, W or Pt as contact metals. In the case of Pt, a 500 Å W diffusion barrier can protect the ohmic behavior up to 550 °C for 30 min. The specific contact resistance of the Pt/W/Si0.5Ge0.5/n-Si contact extracted from the D-type cross-bridge Kelvin resistor was 3.5x10-5 Ω·cm2.
The Fabrication of Self-Aligned Ohmic Cobalt Contacts to Relaxed, N-Type Si0.7Ge0.3
Authors: Watson G. Patrick , Monroe Don , Cheng J-Y , Fitzgerald Eugene A. , Xie Ya-Hong , Vandover R. Bruce
Published: September 2012

Co(SiGe)x contacts have been formed on low defect density, relaxed Si0.7Ge0.3 layers by conventional self-aligned contact processing techniques. Test structures measuring the contact metal sheet resistance indicate that the resistivity is high for anneal temperatures from 450°C to 750°C. The lowest sheet resistivity was 100 Ω/□, about 10 times the resistivity of a comparable amount of CoSi2. Contact resistivities, measured by the transmission line method, were as low as 2 × 10−5 Ω cm2. There is a large discrepancy between contact resistivities measured by transmission line and 4 point Kelvin test structures that may be due to the fabricated contact sizes.
Raman Scattering Study of Interface Reactions of Co/SiGe
Authors: Ying Hong , Wang Zhihai , Aldrich D. B. , Sayers D. E. , Nemanich R. J.
Published: September 2012

Raman scattering measurements are used to characterize Co/Si, Co/Ge and CO/Si0.8Ge0.2 thin film reactions. For Co/Si samples, the phase transitions Co--CoSi--CoSi2 are identified by Raman spectroscopy. For Co/Ge samples, Raman features associated with Co5Ge 7 and CoGe2 phases were observed. For CO/Si0.8Ge0.2 samples, only CoSi was identified along with Ge enriched SiGe alloy peaks. No features associated with CoGe or Co(SiGe) were found.
Solid State Amorphization in Silicide—Forming Systems
Authors: Chen L.J. , Hsieh W.Y. , Lin J.H. , Lee T.L. , Chen J.F. , Liang J.M. , Wang M.H.
Published: September 2012

Solid phase amorphization has been found to occur in all refractory metal and a number of rare—earth and platinum group metal thin film on silicon systems. For Ti/Si, Zr/Si, Hf/Si, V/Si, Nb/Si and Ta/Si systems, the growth of amorphous interlayer (a—interlayer) was found to follow a linear law in the initial stage. Si atom was found to be the dominant diffusing species in the solid phase amorphization in Ti/Si, Zr/Si and Hf/Si systems. For the Y/Si system, the stability of amorphous interlayer depends critically on the composition of the amorphous films.

Auto–correlation function analysis was utilized to determine the structure of the amorphous interlayers. HRTEM in conjunction with the fast Fourier transform were applied to determine the first nucleated crystalline phase. Simultaneous presence of multiphases was observed to occur in a number of refractory metal/Si systems. Interesting electrical properties of amorphous interlayers were found for Ti/Si, Zr/Si and Hf/Si systems.
Silicides for Highly Integrated Memory and Logic Circuits
Authors: Winnerl Josef
Published: September 2012

State of the art DRAM and logic processes widely make use of silicides formed by refractory metals like Ta, Mo, W, Ti, Co, or others. The methods for silicide formation range from sputtering, reaction with predeposited metal, to selective CVD deposition.

The most common application of silicides in state of the art CMOS processes is to use them as a conducting layer that can withstand high temperature processes and that has a significantly lower sheet resistivity than doped mono or poly crystalline silicon. Besides their role as a temperature stable conductor silicides have further interesting properties when using them as a diffusion source for impurities to generate shallow junctions, or as an alternative gate material with a work function in the middle of the silicon band gap.

Based on the example of the self aligned silicidation with titanium silicide the limitations of the state of the art technology will be shown and requirements for future applications will be discussed.
CoSi and CoSi2 Phase Formation on Bulk and Soi Si Substrates
Authors: Hsia S. L. , Tan T. Y. , Smith P. L. , Mcguire G. E.
Published: September 2012

We have studied the CoSi and CoSi2 phase formation sequence in (001) bulk and SOI Si wafers, using Co/Ti bimetallic layers as source materials which are suitable for growing epitaxial CoSi2 films on (001) Si. In bulk Si, co-formation of polycrystalline CoSi and epitaxial CoSi2 phases at T>500°C have been observed. These phases form respectively at the metal and Si sides of the film. For very long times and/or at high temperatures, only epitaxial CoSi2 is observed, e.g., for samples annealed at 560°C for 30 min or at 900°C for 10 s. When using (001) SOI Si with inexhaustible Co supply, only polycrystalline CoSi has been formed for a 900°C 10 s annealing, which is in contrast to the bulk Si results. This phenomenon is understood on the basis of Gibbs free energy reduction in forming the two phases. In the CoSi2 formation temperature range, Gibbs free energy release in forming CoSi2 is only ∼10% more than that of forming CoSi. Consequently, after all Si atoms have been consumed, the formation of CoSi becomes energetically more favorable, since the free energy reduction due to formation of 2x mole of CoSi is much larger than that due to formation of lx mole of CoSi2, where x is the SOI Si mole number.
Silicidation Mechanism of Co/(Refractory-Metal) Bilayer and Epitaxial Growth of CoSi2 on Si(100) Substrate
Authors: Byun Jeong S. , Kim Woo S. , Choi Min S. , Cho Ho J. , Klm Hyeong J.
Published: September 2012

The structures of CoSi2 formed from the bilayer of Co/(refractory metal) have been investigated. For a layer reversal and epitaxial growth of CoSi2 on Si substrate, the silicidation temperature of interposed refractory metal should be higher than that of Co and the oxidation potential of the refractory should also be negatively higher than that of Si to remove the native oxide on Si substrate. The main role of the refractory metal layer in the epitaxial growth of CoSi2 is to limit the Co diffusion to Si substrate, controlling the Co-Si reaction rate. Thus Co atoms are able to locate their stable positions with the lowest energy in CoSi2 lattice.
Microstructure Analysis of Agglomerated Epitaxial Columns of Si/PtSi/Si(111) Double Heterostructure
Authors: Park Kyung-Ho , Kumagai Y. , Hasegawa F.
Published: September 2012

Micro structures and interface structures of epitaxially grown PtSi and over-capping Si films on Si(111) substrates prepared by MBE were studied by RHEED, HREM, SEM and XRD. An epitaxially grown Si layer on the PtSi layer, which was fabricated by coevaporation of Pt and Si with the stoichiometric ratio (Pt/Si=l/1), was obtained as a Si(111)/PtSi(010)/Si(111) double heterostructure at the substrate temperature of 400°C. On the other hand, it was found that the PtSi layer transformed into epitaxial columns and/or walls when a Si over-capping layer was grown on the PtSi layer at a substrate temperature of 600°C or higher. These columns and/or walls were surrounded by a Si matrix which showed epitaxial relations to the Si substrate with stacking faults.
Arsenic Diffusion and Segregation Behavior at the Interface of Epitaxial CoSi2 Film and Si Substrate
Authors: Hsia S. L. , Tan T. Y. , Smith P. L. , Mcguire G. E.
Published: September 2012

Arsenic diffusion and segregation properties at the interface of the epitaxial CoSi2 and Si substrate have been studied. Samples have been prepared using Co-Ti bimetallic source materials and two types of (001) Si substrates: n+ (doped by As to ∼2}1019 cm−3) and p. For the n+ Si cases, the lower limit of the CoSi2 film formation temperature is increased by ∼200°C to ∼700°C. SIMS results showed As segregation into Si. For epitaxial CoSi2 film formation at 900°C, the As concentration has increased by a factor of ∼2 within a distance of ∼30nm from the interface, while the incorporated As in the film is ∼30-50 times less than that in Si. For p-type Si substrate cases, the epitaxial CoSi2 film was first grown and followed by As+ implantation (into the film) and drive-in processes. It is observed that As was segregated to the CoSi2-Si interface and diffused into Si. This is in qualitative agreement with our results obtained from the n+ substrate experiments and the results of other authors involving the use of polycrystalline CoSi2 films. In the present cases, all implanted As were conserved at a drive in-temperature of 1000°C for up to 100 s. This is in contrast to the polycrystalline CoSi2 film results which involve a substantial As loss to the film free surfaces. The physical reasons of this difference have been discussed.