bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth Temperature Dependence of magnetoresistance in Co/Cu (111) Wedged Superlattices
Authors: Harp G. R. , Parkin S. S. P. , Farrow R. F. C. , Marks R. F. , Toney M. F. , Lam Q. H. , Rabedeau T. A. , Cebollada A. , Savoy R. J.
Published: September 2012

The Magnetoresistance of MBE deposited Co/Cu (111) superlattices as a function of Cu layer thickness is studied at various growth temperatures. Wedged superlattices are fabricated with uniform Co layers but with Cu layers whose thickness varies with position along the length of the substrate. Cu thickness is varied over the range 7–75Å. Only one Maximum M Magnetoresistance (MR) is observed for a Cu layer thickness ∼ 10Å for all growth temperatures studied (0°, 150°, 200°C). The optimal magnetoresistance values are achieved with 150°C growth temperature.
Giant Magnetoresistance and Structure of Phase-Segregated Epitaxial Metals
Authors: Marks R.F. , Farrow R.F.C. , Harp G.R. , Parkin S.S.P. , Rabedeau T.A. , Toney M.F. , Cebollada A. , Thangaraj N. , Krishnan Kannan M.
Published: September 2012

Giant Magnetoresistance, GMR, in thin metal films elicits attention due to its technological potential as well as its relevance to theory of exchange coupling. Epitaxial, phase-segregated ferromagnet/paramagnet Mixtures have been grown by UHV evaporation. Such films show spontaneous formation of ferromagnetic clusters, leading to large values of GMR (40% at room temperature) as grown. The growth of Co-Cu, Co-Ag, Fe-Ag and Permalloy-Ag films are described. Structural analysis by grazing-incidence small angle X-ray scattering (GISAXS) provides a measure of cluster size and characteristic spacing. Effects of growth temperature and subsequent annealing on GMR and film structure are described. Preliminary results of TEM examination of (001) Fe-Ag and Co-Ag granular films are presented for the first time.
Perpendicular Magnetoresistance in Cu/Co and Cu/(NiFe) Multilayers
Authors: Schroeder P. A. , Bass J. , Holody P. , Lee S.-F. , Loloee R. , Pratt W. P. , Yang Q.
Published: September 2012

The Magnetoresistance Measured perpendicular to the plane of the Multilayer, (CPP-MR) has been measured for the Cu/CO and Cu/ (Ni/Fe) systems. The predictions of a two spin-channel model are summarized, and the Cu/CO data are analysed in terms of this theory. The Cu/ (NiFe) data show a more complex behaviour.
New BCT Iron Phase in (100) Felr Superlattices
Authors: Andrieu S. , Hübsch J. , Piecuch M. , Hennet L. , FISCHER H.
Published: September 2012

In this paper, the synthesis of a new structure of iron in (100) Felr superlattices grown by Molecular Beam Epitaxy is reported. Two-dimensional growth up to 4 planes at 400K occurs, as shown by RHEED oscillations. Electron diffraction also gives evidence that the Fe lattice is pseudomorphic to the Ir one during the 2D-growth, and relaxes to the bcc lattice for thicker deposits. An X-Ray analysis shows that the Fe structure is a body centered tetragonal one with a c/a ratio close to 1.25. This phase is observed to be non-Magnetic at room temperature, as a weak ferromagnetic behaviour is observed at low temperatures, except at small Ir thicknesses. This is the evidence of the existence of a low spin phase which seems to undergo a second order phase transition with the atomic volume of iron.
Epitaxial Ferromagnetic MnGa and (MnNi) Ga Thin Films with Perpendicular Magnetization on GaAs
Authors: Tanaka M. , Harbison J.P. , Sands T.D. , Philips B.A. , De Boeck J. , Cheeks T.L. , Florez L.T. , Keramidas V.G.
Published: September 2012

We have successfully grown thermodynamically stable ferromagnetic MnxGa1-x (x=0.55∼0.60) thin films with thicknesses ranging from 3 nm to 60 nm on GaAs substrates by molecular beam epitaxy. The c-axis of the tetragonal structure of the MnGa film is shown to be aligned perpendicular to the substrate. Both Magnetization Measurements and extraordinary Hall effect measurements indicate perpendicular magnetization of the MnGa films, exhibiting squarelike hysteresis characteristics. Furthermore, we have investigated the effect of Ni additions as a substitution for mn in (Mn60-yNiy) Ga40 alloy thin films with y=0 – 30 at% Ni. With increasing Ni, the perpendicular component of the magnetization becomes smaller up to y=18 where the magnetization is in-plane. At y=30, the magnetization is again perpendicular.
Studies of Magneto-Optical Recording in Multi-Magnetic-Layer Disk by Analytic and Simulating Approaches
Authors: Kawazoe Yoshiyuki , Hu Xiao , Honma Shigeru
Published: September 2012

The effect of magnetic coupling in Multi-layer system is discussed by an analytic approach and computer simulation. The dependence of the enhancement of external field on the magnetic properties of the relevant materials is studied. Comparison between the theoretical estimate, simulation result and experimental observations are presented.
Anomalous Perpendicular Anisotropy in Ultra-Thin Co Films
Authors: Wiedmann Michael H. , Engel Brad N. , Van Leeuwen Robert A. , Mibu Ko , Shinjo Teruya , Falco Charles M.
Published: September 2012

We have used in situ polar Kerr effect measurements to study the magnetic coercivity and anisotropy of MBE-grown Pd (111) /Co/X and Au (111) /Co/X trilayers, where χ is the nonmagnetic noble or transition metal overlayer Ag, Cu or Pd. Polar hysteresis curves were Measured in situ for systematically varied Co and overlayer thicknesses 2 Å ≤ tco ≤ 20 Å and 0 Å ≤ tx ≤ 50 Å. We find the coercivity and total anisotropy display a strongly peaked perpendicular contribution at ∼1 atomic layer (2 Å) non-Magnetic Metal coverage. For Cu, where the effect is strongest, the total anisotropy energy rapidly decreases by a factor of 3 from its peak value after a total coverage of ∼2 atomic layers (4 A) of Cu.
Spin-Resolved Photoemission Study of n = 2 Core Levels of Iron
Authors: Klebanoff L.E. , Van Campen D.G. , Pouliot R.J.
Published: September 2012

The first spin-resolved x-ray photoelectron spectroscopy (SRXPS) study of the n = 2 core levels of ferromagnetic Fe are reported. The 2p3/2, 2p1/2and 2s core levels all display interesting spin-dependent structures and splittings. The spectral complexity predicted by a purely atomic picture is not observed in the data. The results indicate that theories incorporating the delocalization of the 3d valence band are more applicable to the description of core-level photoemission in iron.
Giant Magnetoresistance Calculated from First Principles
Authors: Butler W. H. , MacLaren James M. , Zhang X.-G.
Published: September 2012

The Layer Korringa Kohn Rostoker-Coherent Potential Approximation technique was used to calculate the low temperature Giant Magnetoresistance from first principles for Co|Cu and permalloy|Cu superlattices. Our calculations predict large giant Magnetoresis-tance ratios for Co|Cu and extremely large ratios for permalloy|Cu for current perpendicular to the layers. Mechanisms such as spin-orbit coupling which mix spin channels are expected to greatly reduce the GMR effect for permalloy|Cu.
Spin-Polarization in Ultrathin Rh Layers on Fe (001)
Authors: Chouairi A. , Dreysse H. , Nait-Laziz H. , Demangeat C.
Published: September 2012

The origin of the Rh polarization at the interface with Fe is discussed within a self-consistent mean-field parameterized tight-binding model. Since experimentally it is not yet known how Rh grows on Fe (001), in this paper we consider both fee and bec growth. When Rh grows in the fee structure, it expands its lattice parameter and a polarization is present up to 3 layers, whereas in the bec case only the Rh atoms at the interface are polarized. The results obtained are compared to recent spin- and angle-resolved photoelectron spectroscopy experiments. Good agreement with experiment is obtained in the case of a fee Rh configuration.
Magnetic Order of Fe and Co on Cu (001)
Authors: Haroun A. , Chouairi A. , Ouannasser S. , Jensen P.J. , Bennemann K.H. , Dreysse H.
Published: September 2012

We determine the initial growth mode of Co and Fe on Cu (001). In the monolayer range Co and Fe present a clear trend to form clusters on Cu (001). Supposing a perfect epitaxy and fee lattice, the magnetic moment distribution is determined by using a tight binding Hubbard-like Hamiltonian. The influence of the temperature is taken into account in order to compare the theoretical predictions with experimental results.
Magnetic Circular Dichroism in X-Ray Absorption and Core-Level Photoemission
Authors: Tobin J.G. , Waddill G.D. , Gouder T.H. , Colmenares C.A. , Pappas D.P.
Published: September 2012

Here is reported observation of magnetic circular dichroism in both x-ray absorption and core-level photoemission of ultra thin magnetic films using circularly polarized x-rays. Iron films (1–4 ML) grown on a Cu (001) substrate at 150 K and magnetized perpendicular to the surface show dramatic changes in the L2,3 absorption branching ratio for different x-ray polarizations. For linearly-polarized x-rays perpendicular to the magnetic axis of the sample the branching ratio was 0.75. For films ≥ 2 ML, this ratio varied from 0.64 to 0.85 for photon spin parallel and anti-parallel, respectively, to the magnetic axis. This effect was observed either by changing the x-ray helicity for a fixed magnetic axis, or by reversing the magnetic axis for a fixed x-ray helicity. Our observation can be analyzed within a simple one-electron picture, if the raw branching ratios are normalized so that the linear value becomes statistical. Furthermore, warming the films to -300 K eliminated this effect, indicating a loss of magnetization in the film over a temperature range of -30 K. Finally, reversing the relative orientation of the photon spin and the magnetic axis from parallel to anti-parallel allowed measurement with photoemission of the exchange splitting of the Fe 2p and 3p core levels which were found to be 03 eV and 0.2 eV, respectively. These results are consistent with earlier studies, but the use of off-plane circularly-polarized x-rays from a bending magnet monochromator offers -2 orders of magnitude greater intensity than typical spin-polarization measurements. Finally, we have performed preliminary x-ray absorption studies of UFe2, demonstrating the feasibilty of MCD Measurements in 5f as well as 3d Materials.
Evidence for Spin Polarization of Metallic Copper in CO/Cu and Fe/Cu Multilayers
Authors: Pizzini S. , Giorgetti C. , Fontaine A. , Dartyge E. , Krill G. , Bobo J.F. , Piecuch M.
Published: September 2012

Magnetic circular x-ray dichroism measurements on CO/Cu and Fe/Cu Multilayers at the K edge of copper show that the 4p -states of copper are significantly spin-polarized by the adjacent magnetic layers. In relation to the phase opposition of the copper thickness-dependent magnetoresistance of CO/Cu and Fe/Cu Multilayers it is of prime importance to notice that the polarization of the conduction electrons of copper follows specifically the polarization of the conduction electrons of the adjacent magnetic element.
Magnetic and Structural Analysis of Ultra-Thin Magnetic Films, Multilayers, and Superlattices by Mössbauer Spectroscopy
Authors: Freeland J. , Keavney D. , Storm D. , Calvin Walker J.
Published: September 2012

In the study of thin films and surfaces as well as the examination of superlattices, the careful characterization of these systems including their structural, Magnetic, transport, and other properties has been absolutely crucial to the advancement of the field. As Means of sample preparation have progressed, techniques for evaluating the flatness, continuity, crystallinity, etc. of thin films and surfaces have become ever more necessary to understand the resulting magnetic and electronic properties. Because iron is often a constituent of Magnetic thin films and because the isotope 57Fe shows a strong Mossbauer Effect over a wide temperature range the technique of Mossbauer Spectroscopy offers much to the study of surfaces, thin films, and superlattices.
Hyperfine Fields in Ultrathin Fe and FeAu Alloy Films on Au (111)
Authors: Brockmann M. , Pfau L. , Lugert G. , Bayreuther G.
Published: September 2012

Magnetic properties of ultrathin Fe and Fe60Au40, alloy films on Au (111) were studied by SQUID Magnetometry and conversion electron Mössbauer spectroscopy. In order to get information on the influence of interdiffusion, iron films with thin alloy zones at the interfaces to Au have been prepared by co-evaporation of iron and gold and compared with iron films with presumably sharp interfaces. It was found that the presence of an 0.5 ML (Mass coverage in Monolayer) alloy zone reduces the effective magnetic interface anisotropy field and affects the growth mode of a subsequently deposited iron film such that the film is more sensitive to annealing. Groundstate Magnetic Moments and hyperfine fields are significantly enhanced in Fe/Au(111) (tFe ≤ 4 ML) and Fe60Au40 films, compared to bulk Fe.
Modeling Giant Magnetoresistance and Relative Permeability in Granular Films
Authors: Parker M.R. , Barnard J.A. , Hossain S. , Seale D. , Tan M. , Waknis A.
Published: September 2012

A Model for the field dependence of giant Magnetoresistance (GMR) in ‘granular’ co-sputtered alloy thin films (based on a relatively simple spin-dependent scattering concept appropriate to superparamagnetic and weakly ferromagnetic films) is applied to new experimental data from the Co90Fe10-Ag system. The Model and the experimental data can be shown to compare very well with the help of a single adjustable parameter related to spin correlation of adjacent Co-Fe clusters. A careful fit of field-dependent MR data and theory leads to a fairly reliable determination of spin-cluster radius. An analysis of the relative permeability of granular GMR films derived from the generalized form of the Clausius-Mossoti relationship is also presented. For a non-Magnetic Matrix the effective relative permeability is shown to be materials independent. The permeability model is applied to Co-Au granular films.
Polarized Neutron Reflectivity Measurements of Collinear and Non-Collinear Magnetic Structures in Fe/Cr (100) Superlattices
Authors: Ankner J.F. , Schleyer A. , Zeidler Th. , Majkrzak C.F. , Zabel H. , Wolft J.A. , Grünbergt P.
Published: September 2012

We have used polarized neutron reflectivity to study the magnetic microstructure of two Fe/Cr (100) superlattices grown by molecular beam epitaxy. The first film, of nominal composition [0.9 nm Cr/5.5 nm Fe]5, and atomically sharp interfaces, exhibits classical collinear antiferromagnetic structure. The other film ([1.2 nm Cr/5.5 nm Fe]5), grown at a higher temperature, shows the field-dependent non-collinear features attributed to biquadratic coupling. We will describe these measurements and our preliminary structural analysis.
Neutron Scattering Study of Antiferromagnetic and Ferromagnetic Coupling in Ni/Ag Multilayers
Authors: Rodmacq B. , Burlet P. , Mangin Ph. , Hennion M.
Published: September 2012

Indirect Magnetic coupling in sputtered Ni/Ag Multilayers has been recently studied by magnetization and magnetoresistance techniques. These experiments indicate that coupling is anti ferromagnetic through 11 and 30 A of silver, and probably ferromagnetic through 20 Å. We present here direct evidence for such a magnetic coupling for all three thicknesses, as obtained from low angle neutron scattering experiments. Multilayers in which the Ag layer thickness is either 11 or 30 Å both exhibit a supplementary diffraction peak at a q value corresponding to twice the chemical period. Its evolution with both temperature and applied field confirms its purely magnetic origin. In order to study the coupling through 20 Å of silver, we prepared a multilayer in which the Ag layers are alternately 11 and 20 Å thick. In this case, we also observe a doubling of the chemical period. The coupling through 11 Å being anti ferromagnetic, this unambiguously shows that the coupling through 20 Å is ferromagnetic.
Magnetic and Magneto-Optic Properties of dc Magnetron Sputtered Co-Cr/Al Multilayers
Authors: Auner G.W. , Naik R. , Rao U.M. , Zhao Y. , Wang B.
Published: September 2012

Single layers of Co82?l8 with thickness in me ranee of 100–1500Å and multilayers of Co-Cr/Al with Co-Cr thickness in the range of 100–200A and Al at 7Å were prepared by dc magnetron sputtering. The films were deposited on to Si (111) and glass substrates at room temperature. A 100Å thick Al buffer layer was deposited to improve the c-axis orientation. X-ray diffraction (XRD) Measurements on the multilayers show a predominant Co-Cr (00.2) peak. Polar Magneto-optic measurements were performed to determine the Kerr rotation (θK) and figure of Merit. The results indicated an enhancement in the figure of merit at λ = 632.8 nm for the multilayered structures compared to single layer samples. All of the films show a 4πMs value around 6 kG and ferromagnetic resonance measurements indicate an enhancement in the perpendicular anisotropy field for the 150Å multilayered sample.
Giant Magnetoresistance in Sputter-Deposited Granular Ag-Co Thin Films
Authors: Lee W. Y. , Deline V. R. , Gorman G. , Kellock A. , Miller D. , Neiman D. , Savoy R. , Vazquez J. , Beyers R.
Published: September 2012

Giant Magnetoresistance (GMR) is reported in as-deposited Ag1−xCox (x = 0.26–0.53) films co-sputtered on Si from separate Ag and Co targets. GMR ratios (10 K Oe Maximum field) exceeding 0.50 and 0.19 at 5 and 295 K, respectively, are observed for the Ag067Co033 films deposited at ≃28 to 175 °C. The Maximum ratios of 0.55 and 0.24 occur at a substrate temperature of ≃125 °C for these films. The ratios decrease rapidly for the films deposited at temperatures > 175 °C and reduce to ≃0.15 and 0.04 at deposition temperatures >300 °C. This deposition temperature dependence of GMR ratios is interpreted in terms of the change in the spin-dependent interfacial electron scatterings due to the change in the size and number of ferromagnetic Co particles within the electron mean free path. The initial increase and the subsequent decrease in GMR ratios with increasing deposition temperature are attributed to the increase in the mean free path, and the Co and Ag particle size, respectively. Changes in mean free path are obtained from the resistivities of these films while changes in Ag and Co particles are deduced mainly from the X-ray diffraction patterns, transmission electron Micrographs, and the coercivities of these films.
Structural Characterization of Pt/Co Multilayers for Magnetooptic Recording Using X-Ray Diffraction
Authors: Bain James A. , Clemens Bruce M. , Brennan Sean
Published: September 2012

Structural features in magnetic multilayer films such as interfacial sharpness and in-plane stress are regarded as responsible for the perpendicular magnetic anisotropy observed in these films. The Multilayers often consist of alternating magnetic and non-Magnetic layers, and the degree of interfacial sharpness between the two is a critical component in producing perpendicular anisotropy. Additionally, in-plane stress affects the anisotropy through Magnetostriction. In this work, we measure both the composition modulation and the stress in multilayers of Pt/CO with x-ray diffraction. Quantitative information about the composition modulation is extracted by recursively fitting a model of multilayer diffraction to the high angle superlattice lines. The Model incorporates a composition modulation of variable amplitude, along with a statistical description of the layer thickness fluctuations.
Magnetic and Magneto-Optic Properties of PtFe (001) and PtCo (001) Thin Films
Authors: Lairson Bruce M. , Visokay Mark R. , Sinclair Robert , Clemens Bruce M.
Published: September 2012

We report on the magnetic and Magneto-optical properties of PtFe and PtCo intermetallic thin films when they have the CuAu(I) tetragonal structure and their crystallographic C axis is oriented out of the film plane. These films possess large perpendicular magnetic anisotropy energies. We observe changes in the Magneto-optic Kerr rotations of Pt-Fe and Pt-Co alloys associated with the formation of the uniaxial CuAu(I) crystal structure. In particular, we report the observation of up to 60% enhancement in the Magneto-optic Ken-rotation for ordered, epitaxial PtFe intermetallic alloy over that of the random face centered cubic alloy. This enhancement is wavelength dependent, with a peak in the visible light range at 2.0 eV.
Magnetic Properties and Crystallography of Selected Co/Pt Multilayers with Rare-Earth Additions
Authors: Bertero G.A. , White R.L. , Sinclair R.
Published: September 2012

We have sputter-deposited a series of Pt/CO Multilayers with differing amounts of rare-earth (RE) in an effort to improve the uniaxial perpendicular anisotropy in these structures. The present work investigates the influence on the magnetic properties of Tb and Ho incorporated both at the interfaces of Pt/CO Multilayers and into the Co layers. The uniaxial anisotropy improved significantly only for those multilayers that showed poor perpendicular anisotropy in the undoped state, in particular, those with large (∼30 Å) bilayer periods. High resolution transmission electron microscopy was used to study these multilayers in cross-section. The Multilayer structures present strong [111] texture with grain sizes ranging from 200 to 600 Å. It is found that the RE does not produce a significant change in the growth texture of the multilayers until a critical amount is introduced beyond which the multilayer structure amorphizes resulting in a compositionally modulated amorphous film.
The Microstructure and Giant Magnetoresistance of NiFeAg Thin Films
Authors: Parker Michael A. , Coffey K. R. , Hylton T. L. , Howard J. K.
Published: September 2012

Although Much has been published on giant Magnetoresistance (GMR) in co-deposited thin films [1–4], only little [5] has been published on the structure-property relationships limiting the effect. Here, we report the results of microstructural characterization of NiFeAg thin films that exhibit a GMR effect. The as-deposited films show a sizeable GMR effect. The Maximum GMR effect observed was 6.4% with -4k0e FWHM of the 6P/P peak. Upon annealing these films, the GMR at first increases, and then decreases. We present microstructural evidence from TEM and XRD, amongst other techniques, which shows that this is a consequence of the initial NiFeAg thin film agglomerating into NiFe grains in a predominantly Ag segregant Matrix. Upon extended annealing, excessive grain growth leads to a decrease in the GMR as predicted by the model of Berkowitz, et al. [1].
Structural Analysis of Pulsed Laser Deposited FeSi2 Films
Authors: Karpenko O.P. , Olk C.H. , Doll G.L. , Mansfield J.F. , Yalisove S.M.
Published: September 2012

This study focuses on the characterization of iron silicide grown, for the first time, by pulsed laser deposition on Si(111). Silicide growth was attempted both by deposition of pure Fe followed by annealing, and congruent deposition of Fe and Si from a stoichiometric FeSi2 target. The films formed by deposition of pure Fe and annealing did not grow epitaxially on Si(111) and contained a number of phases including β-FeSi2. Films grown by congruent deposition of Fe and Si did grow epitaxially on Si(111) and contained either pure β-FeSi2 or a mixture of both FeSi and β-FeSi2, depending on deposition conditions. The following epitaxial orientations were observed: β-FeSi2(001)//Si(111), β-FeSi2[010]//Si<110> with three variants, and FeSi(111)//Si(111), FeSi[110]//Sit[112^. Films of various thicknesses were analyzed with conventional transmission electron diffraction and microscopy.
Electronic Structure and Total-Energy of FeSi2 Pseudomorphic Phases
Authors: Miglio Leo , Malegori Giovanna
Published: September 2012

By fitting orthogonal tight binding parameters to the ab inlio bands of Calciumfluorite FeSi2 (γ-phase) and Cesiumcloride FeSi, we calculate the electronic structure (bands and density of states) and the total-energy of the semiconductive, orthorombic β-phase and the disordered, cubic one. The latter, the γ and the β nfigurations, have been recently observed at different annealing temperatures in thin films grown on Si (111) by Molecular Beam Epitaxy. The transferability of our method among different phases allows for a comparison of the cohesive energy curves which, in turn, supplies an interpretation of the relative stability and the growth kinetics.
Electrical and Optical Properties of FeSi2 Layers
Authors: Radermacher K. , Skeide O. , Carius R. , Klomfaß J. , Manti S.
Published: September 2012

We fabricated α-FeSi2 and α-FeSi2 layers by using two methods: Ion Beam Synthesis (IBS) and Molecular Beam Allotaxy (MBA). In the latter technique a trapezoidal-shaped Fe profile was embedded in the Si matrix by codeposition of Si and Fe at temperatures of about 650°C. A rapid thermal anneal of the IBS and MBA samples at 1150°C for 10 s is necessary to obtain continuous α-FeSi2 layers. The Fe vacancy concentration of the α-FeSi2 layers was varied by a further anneal at lower temperatures. Resistivity measurements indicate a decrease of the resistivity with decreasing Fe vacancy concentration. The α-FeSi2 was transformed to a continuous β-FeSi2 layer by an anneal at 800°C for several hours. To investigate the nature of the band gap we performed absorption measurements at room temperature and 77 K. The analysis of the room temperature data revealed a direct transition at 0.84 eV and an additional indirect transition at 0.78 eV. At 77 K the direct transition shifts to ≈ 0.875 eV and the indirect to ≈ 0.86 eV.
Electric and Magnetic Transport in Ion-Beam Synthesised α-FeSi2
Authors: Larsen K. Kyllesbech , Van Hove M. , Lauwers A. , Maex K. , Rossum M. Van
Published: September 2012

Measurements of the electrical resistivity and magnetoresistivity are reported for 100 nm buried α-FeSi2 in the temperature range 1.2 to 300 K, and in magnetic fields up to 5 Tesla.The metallic α-FeSi2 phase, formed by ion-beam synthesis and subsequent rapid-thermal annealing, is found to have a high residual resistivity of about 227 μΩ2 cm. Furthermore, a minimum in the electrical resistivity is found at 40 K. Combined with mnagnetore si stance measurements it is concluded that this minimum cannot be attributed to the Kondo effect, but is caused by weak localisation and spin-orbit interaction due to the very strong elastic scattering in the material. From the magnetoresistance measurements, at temperatures below 40 K, the relaxation times due to inelastic and spin-orbit scattering are deduced. The inelastic scattering rate is found to saturate below 4.2 K, and follow a T3 power law between 4.2 K to 40 K.
Characterization of β-FeSi2/Si Heterostructures grown by Gas-Source-MBE
Authors: Rösen B.N.E. , Freundt D. , Dieker Ch. , Gerthsen D. , Rizzi A. , Carius R. , Lüth H.
Published: September 2012

Heteroepitaxy of β-FeSi2 on (100) and (111) silicon surfaces has been achieved by gas source molecular beam epitaxy (GSMBE). Fe(CO)5 and SiH4 are used as sources for the silicide growth in the substrate temperature range 400 – 750°C. Depending on growth temperature different growth modes are observed. Concerning morphology two best temperatures were identified for the growth of β-FeSi2 on Si(111). Tg = 550°C - the epitaxial relationship with the substrate is β-FeSi2(100)||Si(111) as shown by High Resolution Transmission Electron Microscopy (HRTEM) and Low Energy Electron Diffraction (LEED); a thin γ-FeSi2 (metallic cubic phase) layer is seen to be stabilized at the interface acting as a buffer layer for the further growth of the orthorhombic semiconducting phase. Tg = 700°C - the same epitaxial relationship as in SPE grown layers is observed: β-FeSi2(101) or β-FeSi2(110)||Si(111) and no γ-FeSi2 is present at the substrate interface. In accord with the lower growth temperature, the silicide layers show slightly higher surface roughness. On Si(100) the epitaxial relationship with the substrate is β-FeSi2(100)||Si(100) in the whole temperature range. On both Si substrates domains with different azimuthal orientations are observed by LEED. In-situ electronic characterization is performed by photoelectron and electron energy loss spectroscopies. Electrical characterization at room temperature shows relatively high mobility values (up to 70cm2/Vs) but the complex temperature behaviour of the Hall constant suggests the presence of both carrier types in the β-FeSi2 grown layers. Measurements of the absorption coefficient at RT show an indirect minimum gap for β-FeSi2.
Titanium Silicides and their Technological Applications
Authors: Clevenger L.A. , Mann R.W.
Published: September 2012

Titanium silicides are used as source, gate and drain contacts and local interconnections in CMOS integrated circuits. In these applications, it is important that the titanium silicide phase have a low resistivity (< 20μΩ-cm) and not agglomerate during high temperature processing. The Ti/Si system has two silicide phases that are useful for electronic applications, high resistivity C49-TiSi2 (60-70 μΩ-cm) which forms at 600 - 700°C and low resistivity (15-20 μΩ-cm) C54-TiSi2 which forms from 700 to 850°C. This paper will review how the size of the thermal annealing process window for forming low resistivity C54-TiSi2 from high resistivity C49-TiSi2 without having the silicide agglomerate varies with annealing treatments, electronic dopants, and contact size. In addition, processing methods to improve the size of the process window will be discussed.
Formation of CoSi2 Wires by Maskless Implantation with the Focused Ion Beam
Authors: Teichert J. , Bischoff L. , Hesse E. , Panknin D. , Skorupa W.
Published: September 2012

The maskless ion implantation with the focused ion beam as a new method for ion beam synthesis of cobalt sulicide wires is presented. In order to perform the implantation a special achromatic mass separator was implemented into the ion column, liquid alloy ion sources for cobalt ions were developed and a substrate heating was built. Ion implantation was performed with 30 keV Co+ and 60 keV Co++ ions. The dose dependence for room temperature implantation and the influence of the substrate temperature were investigated.
Ion Beam Synthesis of Buried CoxNi1−xSi2 Layers in Silicon
Authors: Wu M.F. , De Wachter J. , Van Bavel A.-M. , Pattyn H. , Langouche G. , Vanhellemont J. , Bender H. , Temst K. , Wuyts B. , Bruynseraede Y.
Published: September 2012

Heteroepitaxial CoxNi1−xSi2 layers with good crystalline quality have been formed by ion beam synthesis. Rutherford Backscattering (RBS) - Channeling, Auger Electron Spectroscopy (AES), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) have been used to study the buried layers. For a sample with x=0.66, we found that this ternary silicide layer contains 11% type B and 89% type A orientation. The TEM investigation reveals that the type B component is mainly located at the interfaces with a thickness of a few monolayers. XRD studies show that the strain of the type B component is smaller than that of the type A component, and this is probably the reason for such a unique distribution of the type B component in the epilayer.
Ion Beam Synthesis of IrSi3 by 1-MeV Ir Ion Implantation into Si(111)
Authors: Sjoreen T. P. , Hinneberg H.- J.
Published: September 2012

The formation of a Si/IrSi3/Si heterostructurie by 1-MeV Ir ion implantation and subsequent annealing has been studied for different doses (0.1-2.25 × 1017 Ir/cm2), substrate temperatures (450°-600°C) and annealing temperatures (1000°-1200°C) using Rutherford backscattering spectrometry, ion channeling and cross-sectional transmission electron microscopy. The heterostructure formation is observed to depend strongly on the processing conditions. The best structure, nearly continuous and precipitate-free, is obtained by implanting 1.8-2.0× 1017 1r/cm2 at a substrate temperature of 550°C and annealing at 1100°C for 5 h. A stoichiometric IrSi3 layer can also be produced by furnace annealing at 1150°C for 1 h or by rapid-thermal-annealing at 1200°C for 3 min. Other substrate temperatures generally lead to a structure with a discontinuous IrSi3 layer frequently interrupted by large surface precipitates or islands. The origin of these islands, as well as the dependence of the heterostructure on processing parameters, is discussed.
Thickness Dependence of Electrical Transport in Buried CoSi2 Films Fabricated by Ion Beam Synthesis
Authors: Radermacher K. , Jebasinski R. , Manti S. , Monroe D. , White A.E. , Short K.T.
Published: September 2012

We have performed electrical transport measurements on thin epitaxial buried CoSi2 layers in (111) and (100)Si with thicknesses ranging from 11.5 to 110 nm. The resistivity as a function of temperature exhibits metallic behaviour. The increase of residual resistivity with decreasing thickness can be explained by quantum mechanical weak localization effects induced by the interface roughness. This is supported by magnetoresistance measurements which provide long phase coherence lengths of 1Փ, ≈ 0.75 μm in (111)Si and 1Փ, ≈ 2.3 μm in (100)Si at 4.2 K.
Study of PtSi/Si(100) Interfaces by Ballistic -Electronemission Microscopy
Authors: Turner Bruce R. , Schowalter L. J. , Lee E. Y. , Jimenez J. R.
Published: September 2012

The PtSi/Si interface is of technological interest for Schottky barrier infrared detectors. We are studying PtSi/Si heterostructures using ballistic -electron-emission microscopy (BEEM), an STM-based technique that uses the STM tip to inject hot electrons at a particular energy into the metal overlayer. The BEEM technique allows imaging of the Schottky barrier with good spatial resolution (of the order of tens of nanometers) and allows the measurement of the hot electron attenuation length in the metal overlayer. Our results indicate a Schottky barrier of 0.87 eV for PtSi/Si n-type, and an attenuation length of 4 nm for electrons with an energy of 1 eV above the metal Fermi level. The attenuation length we measure is a convolution of the electron elastic and inelastic mean free path lengths.

We have also used an ac BEEM technique to observe inelastic scattering events at the metalsemiconductor interface in PtSi/Si(100) n-type. There are several features visible in the spectrum, including one at 1040 meV which we attribute to optical phonon-assisted electron-hole pair creation near the metal- semiconductor interface in analogy to a feature we have observed at the same energy in the Au/Si(100) ac BEEM spectrum. Higher-energy features appear at 1230 meV and 1300 meV. Similar features appeared in the Au/Si(100) spectrum at 1120 meV and 1230 meV.

We also suggest that the traditional assumption of momentum conservation parallel to the Schottky barrier interface is unnecessary to obtain a quadratic turn on of the BEEM current above the threshold. If electrons are elastically scattered at the interface so that momentum is not conserved, the increase in the ratio of the density of states in the semiconductor to those in the metal will also give a quadratic turn on even when the band structure is much more complicated than a nearly free electron model. This model also explains why the simple square-root dependence of the photoresponse on wavelength above threshold observed in all metal/semiconductor Schottky barriers despite the complications in band structure.
CoSi2/Si(111) Interface Structure and its Influence on the Schottky Barrier
Authors: Sullivan J. P. , Graham W. R. , Schrey F. , Eaglesham D. J. , Kola R. , Tung R. T.
Published: September 2012

The interface structure and Schottky barrier height Of CoSi2/Si(111) interfaces may be controlled by manipulating the thin film growth conditions. Single crystal CoSi2 films on Si(111) were prepared by ultra-high vacuum processing, analyzed electrically by currentvoltage techniques, and characterized structurally by plan-view and cross-section high resolution transmission electron microscopy (HRTEM) and transm-ission electron diffraction (TED). Interfaces exhibiting n-type barrier heights ranging from 0.27 to 0.69 eV, and p-type barrier heights ranging from 0.43 eV to over 0.71 eV were prepared -by varying the processing conditions. HRTI3M and TED revealed the existence of a √3 × √3 interface reconstruction for the low barrier n-type/high barrier p-type samples. Possible models of the interface reconstruction are discussed.
Silicides for Infrared Applications
Authors: Pellegrini Paul W.
Published: September 2012

This paper discusses the attributes of metal silicides as they are applied to detection of infrared photons. These materials have a long history in the silicon community as interconnects and are easily integrated into manufacturing. The technology is currently only sensitive to 10 μm in the infrared. New results obtained from silicon germanium alloys are discussed that will help overcome these spectral limitations.
Electrical Properties of Copper Silicide/Silicon Interfaces
Authors: Svensson B.G.
Published: September 2012

The electrical properties of Cu/Si(100) and Cu3Si/Si(100) interfaces have been studied using both n- and p-type silicon samples. Current-voltage and capacitance-voltage measurements were performed in the temperature range 80-295 K in order to monitor Schottky barrier formation and electrical carrier concentration profiles. Deep-level transient spectroscopy was employed to observe Cu-related energy levels in the forbidden band gap of Si, and different ion beam analysis techniques were applied to study the interfacial reaction between Cu and Si. Emphasis is put on determination of Schottky barrier heights and their variation with temperature, dopant passivation by Cu atoms and interaction of Cu with irradiation-induced point defects in silicon.
Effects of Rapid Thermal Annealing on W/Si1−xGex Contacts
Authors: Aubry V. , Meyer F. , Laval R. , Clerc C. , Warren P. , Dutartre D.
Published: September 2012

Thermal reaction of W with Si1−xGex films epitaxially grown by Rapid Thermal Chemical Vapor Deposition was investigated in the temperature range 500°C - 1000°C. The samples were annealed either in a Rapid Thermal Annealing (RTA) system or in a conventional furnace, both in flowing nitrogen. The reaction products were investigated by Rutherford Backscattering Spectroscopy (RBS), Energy Dispersive Spectrometry (EDS) and X-ray diffraction (XRD). Sheet resistance measurements were also performed to follow the progress of the reaction. The reaction of W with Si0.67Ge0.33 is similar to that of W with silicon. W reacts with silicon to form tetragonal WSi2. The Ge-content in the silicide is lower than that of the asdeposited alloy. It is shown that an oxygen contamination occurs during conventional annealing and leads to the formation of non homogeneous Si1−x Gex unreacted alloy below the silicide film. Rapid thermal annealing prevents this parasitic effect and the unreacted film remains homogeneous although a slight decrease in the Ge-content is observed. These results are correlated with Schottky barrier height measurements on p-Si0.83Ge0.17 partially strained films. We observed an increase of the barrier height with increasing the temperature for annealing from 500°C to 1000°C. This trend may be explained either by strain relaxation or (and) Ge-content decrease in the unreacted alloy.
Self-Aligned Formation of C54 Titanium Germanosilicide Using Rapid Thermal Processing and Application to Raised, Ultrashallow Junctions
Authors: Ashburn Stanton P. , Grider Douglas T. , ÖztÜrk Mehmet C. , Harris Gari , Maher Dennis M.
Published: September 2012

In this paper we present results on solid state reactions between Ti and Si1−xGex alloys selectively deposited onto Si (100) substrates using rapid thermal annealing (RTA) for contact applications in novel device structures. Germanium concentrations of 0%, 30%, 50%, and 100% within the reacting Si1−xGex alloy are investigated. The Si1−xGex alloys (approximately 2500 ° thick) are deposited using rapid thermal chemical vapor deposition (RTCVD). Titanium is then deposited by evaporation. Sheet resistance measurements as a function of RTA temperature (10 second anneals) provide indications of various phases that occur during the reactions through the formation of constant sheet resistance plateaus. The RTA temperature required for the formation of a minimum resistivity phase is observed to increase for increasing Ge concentrations within the reacting Si1−xGex alloy. Using x-ray diffraction we have determined that for the reactions of Ti with Si the C49 TiSi2 metastable phase forms prior to the minimum resistivity C54 TiSi2 phase. For the reactions between Ti and Ge a minimum resistivity TiGe2 phase also with the C54 structure forms, however, this phase is preceeded not by a C49 TiGe2 structure, but by a Ti6Ge5 phase. The minimum resistivity phases for Ti reactions with 30% and 50% Ge Si1−xGex, alloy reactions also have a C54 structure with unit cell dimensions varying from that of TiSi2) to TiGe2 as the Ge concentration is increased. The grain structures for the reactions are investigated by cross-sectional transmission electron microscopy (XTEM). As the Ge concentration within the reacting alloy decreases the lateral grain size for the C54 structures increases. A self-aligned germanosilicide process is identified and used to fabricate raised, ultrashallow junctions with Ti(SiGe)2 (germanosilicide) contacts. Forward and reverse bias characterization of the junctions indicate that leakage current induced during silicidation can be eliminated using raised junctions with germanosilicide contacts.
Enhanced Relaxation of Strained GexSi1−x Layers Induced by Co/GexSi1−x Thermal Reaction
Authors: Ridgway M.C. , Rao M.R. , Baribeau J.-M.
Published: September 2012

Silicide formation on strained GexSilx layers by the thermally-induced metal/GexSi1−x reaction results in enhanced relaxation of the underlying strained layer. Silicide formation on an amorphous layer is a potential means of decreasing processing temperatures, increasing reacted-layer/GexSi1−x interface planarity and hence, decreasing strained layer relaxation. For the present report, the thermally-induced Co/Ge.17Si.83 reaction on crystalline and amorphous substrates at temperatures of 500-600°C has been compared. Though the rate of silicide formation increased with amorphous substrates, strained layer relaxation was not inhibited.
Direct Solid State Phase Transformation from Co to Epitaxial CoSi2 in Co / Thin Ti / (100) Si Structure and its Application for Shallow Junction Formation
Authors: Ogawa Shinichi , Fair James A. , Kouzaki Takashi , Sinclair Robert , Jones Erin C. , Cheung Nathan W. , Fraser David B.
Published: September 2012

Direct epitaxial CoSi2 formation from Co, which is contrary to the reported silicidation process : Co→Co2 Si→CoSi→CoSi2, has been found during anneal of Co / Ti / (100) Si system. 2 nm thick Ti and 15 nm thick Co films were sputter deposited, and then annealed for 30 min at temperatures between 375°C and 900°C. At room temperature, the 2 nrm Ti immediately forms an amorphous Ti-Si-Co layer between the Co and Si. Epitaxial CoSi2 begins to form at 400°C, while the amorphous layer continues to act as both a Co diffusion retardant and Si diffusion suppressant even at 900°C. This retarded diffusion of Co reduces the growth rate of the CoSi2 over the entire temperature range studied. Superiority of the epitaxial to polycrystalline silicide has been demonstrated. In self aligned structures, an epitaxial CoSi2 film is formed by a single-step anneal without any overgrowth onto adjacent field oxide areas utilizing the amorphous diffusion controlling layer. A p+/n junction of 40 nm depth with reduced leakage and low ideality factor has been obtained by impurity diffusion from epitaxial CoSi2.
Kinetics and Mechanism of the C49 to C54 Titanium Disilicide Polymorphic Transformation
Authors: Ma Z. , Ramanath G. , Allen L.H.
Published: September 2012

The kinetics and mechanism of the C49 to C54 TiSi2 polymorphic transformation have been investigated in a temperature range from 660 to 720°C using in situ sheet resistance measurement and transmission electron microscopy. The kinetics results were correlated with the microstructural changes during the phase transformation. The main structural characteristics demonstrating the mechanism of the transformation were established by examining the nucleation and growth of the C54-TiSi2 in the polycrystalline C49-TiSi2 thin films. It was found that the C54 nuclei predominantly formed at grain edges (three-grain junctions) of the C49 phase and grew very fast by moving its incoherent interphase boundaries. Preliminary results have not revealed rigorous orientation relationships between the two phases. It is suggested that the C49 to C54 structural transition is massive in nature.
Local Structural Studies of TiSi2 and ZrSi2 Thin Films on Si(111) Surfaces
Authors: Dao Y. , Edwards A.M. , Sayers D.E. , Nemanich R.J.
Published: September 2012

This study explores the local structures of TiSi2 and ZrSi2 films on Si. The strain effect on the surface morphologies and phase stability of the films is investigated. Titanium silicide and zirconium silicide films were fabricated on atomically clean Si(111) substrates in UHV using electron gun evaporation followed by in situ annealing. A quantitative X-ray absorption spectroscopy analysis was performed to study the formation of epitaxial TiSi2 and ZrSi2 films on the Si surfaces, as well as the phase transition of TiSi2 from the metastable C49 structure to the stable C54 structure. The surface morphologies and the surface roughness of the films were studied using atomic force microscopy (AFM). The strains of these films were determined by comparing the calculated bond lengths with the measured bond lengths using the extended X-ray absorption fine structure (EXAFS) technique. The final stable C54 structure of TiSi2 has less strain than the initially formed metastable C49 phase. While the surface and interface free energies and the bulk free energy are critical to the structural formations and phase changes of the films, the energy associated with the lattice strain is another important factor.
Interactions of Cu with PtSi and TiSi2 with and without Como Barrier Layers
Authors: Hong Stella Q. , Mayer J. W.
Published: September 2012

Interactions of Cu with PtSi and TiSi2 films grown on Si (100) substrates have been studied in the temperature range of 250-500°C with Rutherfold backscattering spectrometry, Auger electron spectrometry, and x-ray diffraction. Upon annealing Cu migrates across the intermediate PtSi or TiSi2 layers and reacts with Si substrates to form Cu silicides. Unlike what were reported in the literature, no indications of the reaction of Cu with PtSi or TiSi2 have been observed. Both PtSi and TiSi2 retain their original thicknesses and compositions during Cu penetration. The structural integrity of the metal suicides in contact with Cu films is attributed to low formation energies of Cu-silicides. A 50-nm thick amorphous CoMo barrier impedes Cu diffusion up to 550°C, but fails as a diffusion barrier at higher temperatures due to CoMo-Si reaction.
Thermal Stability Study on Cu/Tin/TiSi2/Si
Authors: Chang Tzong-Sheng , Wang Wen-Chun , Wang Lih-Ping , Hwang Jenn-Chang , Huang Fon-Shan
Published: September 2012

We have investigated TiN/TiSi2 films as diffusion barriers between copper and silicon. The TiN/TiSi2 films were formed by annealing Ti/Si via rapid thermal process at a temperature of 850'C for 30 seconds in N2 ambient. The contact resistance and leakage current of the Cu/TiN/TiSi 2/n+-p Si contact system were measured after sintering at 350-600°C for 30 minutes in an N2 ambient. We found an abrupt increase of contact resistance occurred at a sintering temperature of 600°C. From the leakage current of n+-p diode, we observed that the thermally stable temperature was about 475ycC. Meanwhile, XTEM photographs showed small Cu3Si crystallites with size of about 0.25 μm precipitated in the n+Si substrate at a sintering temperature 500°C. The formation of Cu3Si increases the occupied volume, generates the gap between TiSi2 and n+Si, and gradually increases the specific contact resistance. SIMS profiles also showed that a certain amount of Cu atoms diffused into the n+-p Si junction and that Si atoms existed in the Cu film. The Cu3Si formation across the n+-p junction can explain the abrupt increase in the leakage current measurement at 500°C. So the failure mechanisms for contact resistance and leakage current are different.