bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoluminescence and Photoacoüstic Spectroscopy of Si Single-and Multi-Step Ingot- and Wafer-Annealed GaAs Crystals
Authors: Ka O. , Oda O. , Shigetomi S. , Ikari T. , Makita Y. , Yamada A.
Published: September 2012

SI GaAs crystals submitted to single- or multi-step, ingot-or wafer-annealing are investigated using photoluminescence (PL) and photoacoustic spectroscopy (PA). The near-band-edge PL transitions are well resolved, with a neutral acceptor-bound exciton recombination displayed as a split doublet. The improvement induced by wafer-annealing is illustrated by the absence of additional defect-related transitions found after ingot-annealing. For the room temperature PA measurements, the intensity of a peak occuring at 1.39 eV is shown to lead to an estimation of the arsenic micro-defect density as evaluated by AB etching. The 1.39 eV PA band is also asserted to be the non-radiative recombination path of a 1.482 eV band found in the low-temperature PL spectra.
Detailed Photoluminescence Studies of Heat-Treated InP
Authors: Pressel Klaus , Hiller C. , Bohnert G. , Prinz F. , Dörnen A.
Published: September 2012

We present highly resolved photoluminescence studies on heat-treated nominally undoped InP, which was either unprotected or protected by SiO2 or Si3N4 caps during the annealing procedures. Annealing of InP above 350°C leads to six different sharp emissions in the wavelength range between 8790 and 8900 Å, which are not observed at 4 K in Zn-doped or Fe-doped samples. Based on temperature-dependent photoluminescence studies, time-resolved measurements and preliminary magnetic field studies we ascribe these emissions to isoelectronic bound exciton transitions. It is also shown that the two emissions at 8883 Å (11254 cm-1) (E) and 8889 Å (11246 cm-1) (F) belong to one center. We observe that the lines not only depend on the heat treatment but also on some unintentionally incorporated or residual impurities of a low concentration level. Possible candidates are discussed.
Polysilicon/Silicon Interfaces: Effect of Processing Parameters on Physical and Electrical Properties
Authors: Srikrishna K. , Moinpour M. , Landau B.
Published: September 2012

An arsenic doped polysilicon emitter structure is widely used as an important technology for high speed BiPolar and BiCMOS VLSI devices. The electrical behavior of such emitters is dictated to a large degree by the structure of the polysilicon/silicon interface and the extent of any interfacial oxide. In particular the contact resistance of n+ and p+ diffused regions of the polysilicon is sensitive to the interfacial structure. The microstructure of the polysilicon, in addition to the interface, dictates the junction depth and electrical properties and is determined by the deposition conditions and subsequent doping and annealing processes. The interface itself is defined largely by the cleaning procedure and the initial stages of the deposition process. In this paper we report the effects of process variables, such as deposition temperature, doping and annealing times and temperatures and pre-cleans on the microstructure and electrical properties of poly-emitters.
Carrier Profile Variation of a Channel Conductive Layer Through Phospho-Silicate-Glass Cap Annealing of N+ Si-Implanted GaAs Crystals
Authors: Saito Yasuyuki
Published: September 2012

This paper reports the variation of carrier concentration depth profile in Si-implanted channel conductive layers of liquid- encapsulated-Czochralski- technique (LEC) grown GaAs crystals, the Vth scattering amplitude variation and the averaged Vth variation before and after phospho-silicate-glass (PSG) cap annealing of high-dose-Si-ion implanted crystal layers. Furthermore, the PSG-cap-annealing Vth variation difference between the As-rich LEC crystal and the near-stoichiometric LEC crystal is presented. These results, and carrier depth profile of Si-implanted active layers in LEC GaAs crystals through model of implanted Si atom move (like diffusion) and Si atom capture of a crystal lattice and siteing on lattice are discussed.
Rapid Thermal Annealing of Neutron Transmutation Toped Czochralski Silicon
Authors: Berezina G. M. , Kdrshunov F. P. , Sobolev N. A. , Voevodova A. V. , Stuk A. A.
Published: September 2012

The influence of the rapid thermal annealing (RTA) in comparison with that of the standard furnace annealing (FA) on the electrical parameters and photoluminescence (PL) of Czochralski silicon (Cz Si) subjected to neutron irradiation at various temperatures has been studied. The role of the irradiation temperature on the annealing behaviour of electrical parameters in Cz Si has been established. The possibility of getting neutron transmutation doped (NTD) Cz Si having the calculated resistivity by means of the RTA is shown.
Use of Selective Area Defect Creation for Isolation of III-V Multilayer Structures
Authors: Pearton S. J. , Ren F. , Fullowan T. R. , Katz A. , Hobson W. S. , Abernathy C. R. , Lothian J. R. , D'asaro L. A. , Elliman R. G. , Ridgway M. C. , Jagadish C. , Williams J. S.
Published: September 2012

Deep level acceptor and donor centers are created in III-V materials by energetic ion bombardments. The controlled introduction of these centers by selective area implantation can be used to provide electrical and optical isolation of neighbouring devices. We will contrast the implant isolation characteristics of GaAs and AlGaAs with materials such as InP and InGaAs, and also with the ternary compounds InGaP and AllnP, for which there has previously been little information. In all of these materials the as implanted resistivity is controlled by hopping conduction processes, with p « e×p (T 0.25). Post-implant annealing can be used to achieve resistivities of > 108 Ωcm in initially highly doped material provided the implant doses are correctly chosen. These defect engineered regions may be made many microns deep by using overlapping multiple-energy keV implants or a single MeV implant. In the latter case a nearly flat damage profile can be achieved over depths typical of HBT, SEED or long-wavelength laser epitaxial thicknesses. Examples of these devices which rely on controlled introduction of deep level defects for their operation will be given.
Comparison of Mesa- Etched and Ion- Implanted GexSi1-x Heterojunction Bipolar Transistors
Authors: Greve D. W. , Racanelli M.
Published: September 2012

We report a comparison of the characteristics of germanium- silicon base heterojunction bipolar transistors fabricated using mesa- etched and ion- implanted processes. The base currents of both device structures are dominated by peripheral currents associated with the plasma- SiO2 covered junction edge. After an implant damage anneal at 800 or 900 C, the ion- implanted process exhibited the lowest base currents. There was no evidence of strained layer relaxation even for the 900 C anneal.
Device Degradation on a Full-Frame CCD Image Sensor with a Transparent Gate Electrode
Authors: Hseih Biay-Cheng , Kosman S. , Lo Y.C. , Jayakar K. , Mehra M. , Roselle P. , Chang W. C.
Published: September 2012

The electrical and optical properties of Indium-Tin-Oxide (ITO) films, deposited by radio frequency (r.f.) magnetron sputtering, were studied. ITO films, when deposited using optimum sputtering conditions, were reproducibly prepared with resistivity as low as 1.5 × 10−4 Ω-cm and optical transmissivity higher than 80% over the wavelength range of interest. Device stability when ITO is used as a replacement for polysilicon as a gate electrode in silicon charge-coupled device (CCD) image sensors was also studied. After an anneal process at 950 °C in N2 the device degraded. The degradation can be attributed to the generation of oxide charge and interface states in the ITO/SiO2/Si system.
Room Temperature Local Tailoring of Electronic Properties of Hg1-xCdxTe by Application of an External Electric Field
Authors: Gartsman Konstantin , Chernyak Leonid , Marc Gilet Jean , Triboulet Robert , Cahen David
Published: September 2012

Electronic properties of originally homogeneous samples of (Hg, Cd)Te, CuInSe2 and (CuAg)InSe2 have been modified on a local scale, in a stable manner, at room temperature, by reverse biasing of small area Schottky contacts on them. This is shown, after the bias voltage is lifted, by I-V measurements and by Electron Beam Induced Current scans. The creation of a clear diode-like, and, in the case of (CuAg)InSe2, transistor-like structure, in the vicinity of the Schottky contact, on a scale of about hundred um, could be explained by electromigration of electrically active ions and by the simultaneous generation of point and line defects. The latter type of defects is revealed for (Hg,Cd)Te by chemical etch, after application of the field.
Improvement of Gate Oxide Integrity Characteristics in CZ-Grown Si Crystals by H2 annealing
Authors: Adachi N. , Nishikawa H. , Komatsu Y. , Hourai H. , Sano M. , Shigematsu T.
Published: September 2012

The mechanism of improvement in gate oxide integrity (GOI) characteristics by H2 annealing in CZ-grown Silicon wafers was investigated. Grown-in defects that are considered to degrade GOI and which can be detected correlatively as 0.1 μm level size pits appearing after SC-1 cleaning, decrease drastically by H2 annealing, while other inert gases, i.e., N2 and Ar, do not exhibit such effect. Besides, H2 annealing shrinks or extinguishes oxygen precipitates significantly, while other gases do not. On the other hand, oxygen outdiffusion is exactly the same among H2, N2 and Ar annealing. From these results, it was concluded that the dominant mechanism for GOI characteristics improvement by H2 annealing is due to decomposition of the grown-in defects having Si-O bonding by the reduction reaction between Si-O bonding and hydrogen, and not due to a mere thermal decomposition enhanced by oxygen outdiffusion.
Control of Ordering-Disordering Defect Parameters for the Realization of Efficient Opto-Electronic Devices
Authors: André J. P. , Bellon P.
Published: September 2012

Epitaxial growth of III/V compounds with tight band gap engineering is essential for the realization of efficient optoelectronic devices. Using MOVPE, high quality materials have been grown with anomalous low band gap energy. The order/disorder phenomena and their relation to the band gap energy in the GalnP/AlGalnP system are reported. The effect of the growth parameters on the ordered phase and the band gap Eg will be presented by using TEM and PL characterizations. The growth models will be discussed. The importance of the ordering phenomena will be illustrated by short wavelength laser application, the emission wavelength being as low as 650 ran at 300 K. And a possible future laser structure will be proposed.
Role of Impurities in Reducing Grown-in Dislocations in Compound Semiconductor Crystals
Authors: Sumino Koji
Published: September 2012

lmpurity effects on the mobility of dislocations and dislocation generation from generation centers in III - V compound semiconductor crystals are first reviewed on the basis of experimental observations of dynamic behavior of individual dislocations. Dislocation multiplication process is then discussed to account for experimental stress-strain characteristics of these materials obtained in mechanical tests. Using all of such knowledge on dislocation processes in the compound semiconductor crystals, an argument is developed to show how impurities play the role in reducing grown-in dislocations in crystals of these materials. It is shown that immobilization of dislocations caused by impurity gettering plays the decisive role and results in even the growth of dislocation-free crystals.
Disordering and Characterization Studies of 69GaAs/71GaAs Isotope Superlattice Structures: The Effect of Outdiffusion of the Substrate Dopant Si
Authors: Tan T. Y. , You H. M. , Yu S. , Gitesele U. M. , Jäger W. , Zypman F. , Tsu R. , Lee S. -T.
Published: September 2012

Undoped 69GaAs/71GaAs isotope superlattice structures grown by MBE on n-type GaAs substrates, doped by Si to ∼3×1018 cm−3, have been used to study Ga self-diffusion in GaAs by disordering reactions. In the temperature range of 850–960°C, the SIMS measured Ga self-diffusivity values showed an activation enthalpy of 4 eV, and are larger than previously compiled Ga self-diffusivity and Al-Ga interdiffusivity values obtained under thermal equilibrium and intrinsic conditions, which are characterized by a 6 eV activation enthalpy. SIMS, CV, and TEM characterizations showed that the as-grown superlattice layers were intrinsic which became p-type with hole concentrations up to ∼2×1017 cm−3 after annealing, because the layers contain carbon. Dislocations of a density of ∼106-107 cm−2 were also present. However, the factor responsible for the presently observed larger Ga self-diffusivity values appears to be Si outdiffusion from the substrate, which was determined using CV measurements. Outdiffusion of Si decreases the n value in the substrate which causes the release of excess Ga vacancies into the superlattice layers where the supersaturated Ga vacancies enhance Ga self-diffusion.
Hydrogen Passivation of Defects in InGaAs/AlxGal-xAs Quantum Wells
Authors: Lord S. M. , Roos G. , Pezeshki B. , Harris J. S. , Johnson N. M.
Published: September 2012

The effect of the diffusion of monatomic hydrogen into InGaAs/AlGaAs quantum wells has been investigated using photoluminescence (PL) and Secondary Ion Mass Spectroscopy (SIMS). The structures were grown by molecular beam epitaxy and hydrogenated with a remote plasma. For In0.2Ga0.8AlxGA1-xAs quantum wells, hydrogenation significant increases the integrated PL intensity from bound excitons at 77 K. The enhancement of the PL is ascribed to removal of nonradiative recombination centers by hydrogen passivation of defects either at the heterojunction interface or within the epilayers. This PL enhancement (and defect passivation) increases as the Al concentration in the AlGaAs layers increases from 0 to 33 at%. A 50% increase of PL intensity is observed for InGaAs/GaAs. For 33 at%, the increase is a factor of 9. We also diffused deuterium into these InGaAs/AlGaAs quantum wells. The enhancement of the PL by deuteration was similar to that by hydrogenation. The isotopie substitution permits the determination of the depth distribution of deuterium in the multilayered structure by SIMS. SIMS results support the conclusion that more defects are passivated in the higher Al concentration samples.
Mechanisms of Transition-Element-Gettering in Silicon
Authors: Gilles Dieter
Published: September 2012

The unique properties of 3d-transition elements in silicon are reviewed that are essential for an understanding of gettering phenomena. Transition-element-gettering techniques are divided into two groups, depending on whether or not the dominant gettering mechanism operates during annealing or cooling down of silicon wafers. Experiments that identify the gettering mechanism are presented for oxygen precipitation-induced gettering (internal gettering) as well as phosphorus-diffusion gettering. It is concluded that only the latter technique operatesduringhigh-temperature treatment.
Defect Control in Cz Silicon
Authors: Kirscht F. G. , Kim S. B. , Yeh J. J. , Wildes P. D.
Published: September 2012

Generic and interaction aspects of oxygen precipitation, related defect formation and denudation in Cz-Si wafers are presented. Bulk defect profiles and homogenization control are shown to be achievable by proper design of post-growth annealing.

Gettering-related phenomena are discussed including stacking fault-rich bulk defect structures and peculiarities in different epitaxy systems.
Gettering and Gettering Stability of Metals at Oxide Particles in Silicon
Authors: Falster R. , Laczik Z. , Booker G. R. , Bhatti A. R. , Török P.
Published: September 2012

Several aspects of metal gettering at internal oxide particle sites in Cz Si have been studied by ‘haze tests’, scanning infra-red microscopy (SIRM) and transmission electron microscopy (TEM). Haze tests indicated that complete gettering of Cu, Ni, Co and Pd can occur even when the amount of oxygen precipitated is below the detectable limit. TEM showed that the gettering of Cu, Pd and Ni proceeds by one of three different self-perpetuating mechanisms involving oxide particles and associated dislocations, the particular mechanism depending on the oxide particle size and the metal type. Haze tests and SIRM showed that for Cu and Ni there were minimum oxide particle number densities for effective gettering, and also maximum oxide particle number densities above which the additional oxide particles played no role in the gettering. These number densities depended on the metal type and specimen cooling rate. For all of these gettering behaviours, mechanisms are suggested to explain the results. The SIRM was also used to investigate for Cu and Ni the thermal stability of the gettering sites and the precipitated metals. The results showed that during repeated heat treatments the gettering occurs by a dynamic process.
Use of Porous Silicon to Minimize Oxidation Induced Stacking Fault Defects in Silicon
Authors: Shieh S.-Y. , W. Evans J.
Published: September 2012

Present methods for minimizing stacking fault defects, generated during oxidation of silicon, include damaging the back of the wafer or depositing poly-silicon on the back. In either case a highly defective structure is created and mis is capable of gettering either self-interstitials or impurities which promote nucleation of stacking fault defects.

A novel method of minimizing these defects is to form a patch of porous silicon on the back of the wafer by electrochemical etching. Annealing under inert gas prior to oxidation may then result in the necessary gettering. Experiments were carried out in which wafers were subjected to this treatment. Subsequent to oxidation, the wafers were etched to remove oxide and reveal defects. The regions of the wafer adjacent to the porous silicon patch were defect-free, whereas remote regions had defects. Deep level transient spectroscopy has been used to examine the gettering capability of porous silicon, and the paper discusses the mechanism by which the porous silicon getters.
Phosphorus Gettering by Rapid Thermal Processing
Authors: Hartiti Ecuchaib , Slaoui Abdelilah , Muller Jean-Claude , Siffert Paul
Published: September 2012

We have investigated the rapid thermal diffusion of phosphorus into p-type silicon from a spin-on coated film as a function of the process temperature and time duration. The electron diffusion length LD measurements performed by the Surface PhotoVoltage (SPV) method present evidence for a get-tering phenomena since the LD values of the diffused samples are significantly improved. This result is important for the future of RTP in the area of silicon devices where carrier transport is controlled by the bulk lifetime.
The Effects of Iron Contamination on Thin Oxide Breakdown -Experimental and Modeling
Authors: Henley Worth B. , Jastrzebski Lubek , Haddad Nadim F.
Published: September 2012

The effect of iron contamination in silicon on the properties of thermally grown thin oxides is studied through electrical modelling and experimental MOSDOT testing. Iron concentration is measured using a surface photovoltage / diffusion length technique. Failure mechanisms related to iron contamination are proposed. Contamination limits for various gate oxide thicknesses are defined. Experimental results show that reduction of oxide thickness from 20nm to lOnm requires a reduction in iron conntamination by 100 times.
Oscillatory Indirect Coupling Between Perpendicularly Magnetized Co Monolayers Through Cu (111)
Authors: Gradmann Ulrich , Elmers Hans-Joachim , Kohlhepp Juergen
Published: September 2012

Co-Monolayers, prepared by MBE on Cu (111) -surfaces at room temperature and covered by Cu, are ferromagnetic with a Curie-temperature of about 430 K. They are magnetized perpendicularly because of a strong perpendicular magnetic surface anisotropy of the Cu/Co (111) -interface. They provide a remarkably good representation of the 2-dimensional Ising Model. The indirect coupling between these perpendicularly magnetized ferromagnetic monolayers was investigated using samples of type Cu (111) /lCo/DçuCu/lCo/Cu, containing Co/Cu/Co-trilayers composed of Co-Monolayers and a spacer consisting of DCu atomic layers of Cu (111). Torsion oscillation magnetometry of these samples showed clearly a coupling between the monolayers with an oscillatory dependence on DCu. The amplitude of the oscillation is strongly reduced if the coupled Co-films consist of 5 ML instead of 1 M.L. The present controversy on the presence or absence of antiferromagnetic and oscillatory indirect coupling in the Co/Cu (111) -system is discussed in the light of these experiments. The discussion shows that the oscillatory coupling is an intrinsic property of ideal (111)-structures, and can be understood by the RKKY-type theory of indirect coupling between ferromagnetic Monolayers. The usual application of this theory to the coupling between thicker films is justified. However, in the fcc (111) -system there is apparently a specific barrier against complete coalescence, resulting in a tendency to retain holes and channels in the Cu-spacer. This tendency is stronger in flat single-crystal samples than in sputtered films with high densities of atomic steps. Apparently, this results in competing ferromagnetic hole coupling which may more or less completely obscure the intrinsic oscillatory coupling, preferentially in samples grown on extremely flat single crystal surfaces.
Perpendicular Magnetoresistance of Microstructured Pillars in Fe/Cr Magnetic Multilayers
Authors: Gijs M.A.M. , Lenczowski S.K.J. , Giesbers J.B.
Published: September 2012

We have fabricated pillar-like microstructures of high vacuum sputtered Fe/Cr Magnetic Multilayers and measured the giant magnetoresistance effect in the configuration where the measuring current is perpendicular to the film plane from 4.2 K to 300 K. At 4.2 K we find a magnetoresistance of 108 % for multilayers with a Fe thickness of 3 nm and a Cr thickness of 1 nm. The pronounced temperature dependence of the perpendicular magnetoresistance is studied for samples with different Cr thicknesses and tentatively explained by electron-Magnon scattering. The low-temperature data are compared with existing low-temperáture models.
Studies of Exchange Coupling in Fe (001) Whisker/Cr/Fe Structures using BLS and Rheed Techniques.
Authors: Heinrich B. , From M. , Cochran J.F. , Liao L. X. , Celiński Z. , Schneider C.M. , Myrtle K.
Published: September 2012

The conditions for an almost perfect growth of smooth Cr (001) films on an iron whisker substrate have been investigated by means of reflection high energy electron diffraction (RHEED). The exchange interaction between 20 Monolayer thick Fe (001) films separated from a bulk whisker Fe (001) substrate by a variable number of Cr (001) Monolayers (ML) has been investigated by means of Brillouin light scattering experiments (BLS). These experiments show unambiguously that the exchange coupling strength between the iron film and the iron whisker can be described by a short wavelength oscillatory term superposed on a slowly varying antiferromagnetic background. The BLS data enabled one to separate the bilinear and the biquadratic contributions to the antiferromagnetic exchange coupling terms. Both the bilinear and the biquadratic coupling strengths exhibited a short period oscillatory dependence on the Cr interlayer thickness (∼2 Monolayers). Maxima in the bilinear antiferromagnetic coupling strength occur for an odd number of Cr Monolayers. This observation is not in agreement with first principles calculations. The first phase inversion has been found to occur between 4 and 5 ML of Cr.
Direct Evidence of Biquadratic Coupling in multilayers by Neutron Scattering Experiments.
Authors: Andrieu Stéphane , Hennion Martine , Piecuch Michel
Published: September 2012

We present small angle neutron scattering experiments on (001) Fe/Ir superlattices. A short period oscillated coupling is observed. However, antiferro and ferromagnetic peaks are simultaneously measured on neutron diagram, which cannot be simply explained. A biquadratic coupling model is proposed to account for this behaviour.
Effect of Hybridization on Exchange Coupling in Magnetic Multilayers
Authors: Mathon J. , Villeret M.A. , Mander J.M. , Edwards D.M. , Muniz R.B.
Published: September 2012

An earlier theory of the exchange coupling between two ferromagnets separated by a nonmagnetic transition metal spacer was based on size quantization of the electron energies in the spacer. It is now generalized to include the effect of hybridization between the conduction and d bands both in the ferromagnet and in the spacer. The new theory thus unifies the approach based on coupling via d electrons, valid for transition metal spacers, with RKKY-type theories for noble and simple metals which rely on coupling via conduction electrons. The theory is applied to calculate the period and strength of the long-period oscillatory coupling in (001) CO/Cu trilayer.
Giant Magnetoresistance and Soft Magnetic Properties of NiFeCo/Cu Multilayers
Authors: Tsunashima S. , Jimbo M. , Kanda T. , Goto S. , Uchiyama S.
Published: September 2012

Giant Magnetoresistance (GMR) and soft magnetic properties together with their structural characteristics were investigated for Ni66Fe16Co18/Cu Multilayers. The Multilayers were prepared by the conventional rf sputtering method on glass or Si substrates using various buffer layers including Fe, NiFeCo, NiFe and CoZr. Although Most of the multilayers exhibited (111) preferred orientation, Fe buffered multilayers showed a considerable (200) X-ray diffraction peak at Cu thicknesses around 1 nm and 2.2 nm which corresponded to the peak positions of GMR. By using fee or amorphous underlayers the (200) diffraction intensity decreased while antiferromagnetic coupling strength was much reduced. Cross-sectional transmission electron micrograph revealed that the (100) oriented multilayer was grown on the (100) oriented Fe underlayer. By controlling the crystal orientation and the layer structure, significantly large magnetoresistance ratio of more than 10 % can be achieved in a field as low as 30 Oe.
Combined Spin Valve and Anisotropic Magnetoresistance in NiFe/Cu/NiFe Layered Thin Films
Authors: Rijks Th.G.S.M. , Coehoorn R. , De Jonge W.J.M.
Published: September 2012

We present a theoretical study of the combined effect of spin valve and anisotropie magnetoresistance in NiFe/Cu/NiFe layered thin films, using an extended form of the semiclassical Camley and Barnás Model for electron transport. The anisotropie magnetoresistance is treated by introducing spin-dependent anisotropie mean free paths in the NiFe layers. From calculations of both magnetoresistance effects as a function of NiFe and Cu thickness, we discuss the validity of a description of the combined effect in terms of a simple summation of spin valve and anisotropie Magnetoresistance.
Annealed Cu/Co/Cu/NïFe/Femn Spin Valves: Nanostructure and Magnetism
Authors: Meny C. , Jay J.P. , Panissod P. , Humbert P. , Speriosu V.S. , Lefakis H. , Nozieres J.P. , Gurney B.A.
Published: September 2012

Magnetic, Magnetotransport and structural properties of Cu/Co/Cu/NiFe/Femn spin-valve structures were studied before and after sequential annealing in the temperature range 240–360°C. Since no extended interdiffusion is observed, the overall deterioration of the magnetic and magnetoresistive properties of the spin valve is believed to originate from morphological and structural changes. In particular, annealing was found to decrease the magnetoresistive properties of Co as a result of structural changes within the Co layer and at the CO/Cu interface. These changes are accompanied by modifications of the magnetic properties. For annealing temperatures above 240°C, strong grain growth within the Co layer and increasing amount of fee Co explain the increased magnetic hardness of this layer.
Oscillations in Exchange Coupling in Co/Cu Multilayers Grown by MBE
Authors: Greig D. , Hall M.J. , Howson M.A. , Hickey B.J. , Walker M.J. , Xu J.
Published: September 2012

We have observed oscillations with non-Magnetic spacer layer thickness in the saturation fields and characteristic exchange fields of CO/Cu Multilayers grown by MBE. The Specimens consisted of a set of samples in which the thickness of copper layers took a series of values between 5Å and 20Å, while the cobalt layer thickness was set at 15Å throughout. The Multilayers were grown epitaxially on GaAs (110) with Ge, Co (110) and Au in the buffer region, resulting in CO/Cu bilayers in the (111) orientation. Although oscillations were observed in these magnetic measurements, no oscillations were observed in the magnetoresistance itself. These observations are somewhat at odds with similar measurements made on samples prepared by sputtering. We conclude with a discussion involving exchange coupling, in-plane anisotropy and defects in the magnetic structure in an attempt to account for these conflicting results.
Magnetic Anisotropy in Epitaxial Ni/Cu (100) Thin Films
Authors: Bochi G. , Ballentine C. A. , Inglefield H. E. , Bogomolov S. S. , Thompson C. V. , Ohandley R. C.
Published: September 2012

Epitaxial Ni/Cu (001) films grown on Si (001) by Molecular Beam Epitaxy were studied in-situ using the Surface Magneto-optic Kerr Effect (SMOKE) and ex-situ with a Vibrating Sample Magnetometer (VSM). Perpendicular Magnetization is observed for Ni thicknesses 15 Å ≤ h ≤ 60 Å and fully in-plane magnetization for h ≥ 70 Å when the films are characterized in-situ. The reversal in magnetic anisotropy observed in-situ at 60 Å shifts to 125 Å when the films are exposed to air. 100 Å Ni films deposited on Cu1−x-Nix alloy substrates also show a reversal in magnetic anisotropy as x is changed. These results suggest that changes in magnetic anisotropy correlate with misfit strain accommodation.
Vanadium as Overlayer on Ag(001)
Authors: Nait-Laziz H. , Demangeat C. , Mokrani A.
Published: September 2012

The electronic and magnetic structure of small vanadium clusters adsorbed on Ag (001) is studied as a function of the exchange integral J of the Hubbard Hamiltonian and cluster size with bcc structure. For each topological arrangement, the transition from nonmagnetic to magnetic order is characterized. As in the case of films (1 or 2 layers thick) epitaxially grown on Ag (001), antiferromagnetic coupling between V atoms is usually obtained. However, because the symmetry is lower in the present case, various magnetic configurations are displayed.
Strong Influence of Tb Concentration on Domain Structure and Kerr Effect of TbxFe1−x Thin Films
Authors: Florescu V. , Rau C. , Zheng N. J.
Published: September 2012

Amorphous TbFe films with perpendicular magnetic anisotropy are attracting wide attention as promising candidates for erasable high - density Magneto - optical recording and thermomagnetic printing. TbxFe1−x thin films with 0 ≤ × ≤ 0.37 are deposited on glass substrates using r.f. sputtering. The Magnetic remanent domain structures are studied at room temperature using the longitudinal and polar Kerr effect. Samples with 0 ≤ × ≤ 0.23 exhibit magnetic in-plane anisotropy, while samples with 0.26 ≤ × ≤ 0.37 possess uniaxial anisotropy with easy axis perpendicular to the film plane. The remanent domain structures depend strongly on Tb content. High remanence and high coercivity are found for samples with 0.27 ≤ × ≤ 0.34 which is confirmed by additional vibrating sample Magnetometer (VSM) Measurements.
Magnetic Properties and Crystal Structure of High Moment FeTaN Thin Films
Authors: Qiu G. , Haftek E. , Cates J. C. , Alexander C. , Barnard J. A.
Published: September 2012

High Moment single layer FeTaN films with excellent soft magnetic properties have been grown by high rate reactive dc magnetron sputtering. The best combination of properties (easy and hard axis coercivities < 1 Oe, saturation Magnetization > 1650 emu/cc, anisotropy field of 5 Oe, and initial permeability of 4800) are found in films containing ∼3.2 a/O Ta and ∼7.5 a/o N after 400°C annealing in a 200 Oe dc field for two hours. These properties are associated with a single phase, random, nanocrystalline structure consisting of a-Fe crystallites (grain size of ∼ 100Å) whose lattice is expanded by both Ta and N.
High-Field Giant Magnetoresistance in Co-Cu Superlattices
Authors: Barlett Darryl , Tsui Frank , Lauhon Lincoln , Mandrekar Tushar , Uher Ohrad , Clarke Roy
Published: September 2012

We present evidence for a new type of giant magnetoresistance in (111) cobalt-copper superlattices with atomically smooth interfaces. We propose that the lowered dimensionality of the structure leads to an enhancement of the scattering of conduction electrons from paramagnetic interfaces obeying a Langevin-like saturation at very high fields, well beyond the switching field of the Co layers. The findings help to explain similarities in magnetotransport behavior with recently reported granular systems as well as differences with antiferromagnetically coupled Multilayers.
Development of Crystallographic Texture in RF Sputter Deposited CoCrTa/Cr Thin Films
Authors: Feng Y. C. , Laughlin D. E. , Lambeth D. N.
Published: September 2012

It is well known that Cr sputtered on glass or NiP/Al substrates has either the (002) or (110) crystallographic texture (depending on the substrate temperature) and that the Co-alloy layers which are deposited on the Cr underlayers have either the (1120) or (1011) textures respectively. However, the dependence of the crystallographic textures on other sputtering parameters is not clear. We report here on the study of the dependence of crystallographic textures of CoCrTa/Cr films on substrate bias. It is found that both Cr (110) and Cr (002) textures can form at elevated temperature, depending on the substrate bias. The development of the crystallographic texture is discussed with a Model. It is also found that the epitaxy of CoCrTa layer depends on the sputtering conditions of both the Cr and the CoCrTa layers. The extrinsic magnetic properties (such as He, S and S*) of thin films with various textures are also presented. By controlling the sputtering procedure, the effects of crystallographic textures on magnetic properties were separated from the effects of film Morphology.
The Influence of Quantizing Magnetic Field on The Magnetic Susceptibilities in Ultra Thin Films of Dilute Magnetic Materials
Authors: Ghatak Kamakhya P , Biswas S. N.
Published: September 2012

In this paper we have studied the dia and paramagnetic susceptibilities of the holes in ultrathin films of dilute magnetic materials in the presence of a quantizing magnetic field and compared the same with that of the bulk specimens under magnetic quantization for the purpose of relative comparison. It is found, taking Hg1−xMnxTe and Cd1−xMnxSe as examples, that both the susceptibilities increase with decreasing film thickness and increasing surface concentration in oscillatory Manners. The numerical values of the susceptibilities in ultrathin films of dilute magnetic materials are greater than that of the bulk and the theoretical analysis is in agreement with the experimental data as reported elsewhere.
Giant Magnetoresistance in Single Layer and Multilayer Phase Separating Alloy Films
Authors: Hossain S. , Waknis A. , Seale D. , Tan M. , Parker M.R. , Barnard J.A.
Published: September 2012

The phenomenon of giant magnetoresistance (GMR), previously measured only in multilayer films comprising ferromagnetic layers separated by nonmagnetic spacers, has recently been observed in single layer ‘granular’ alloy thin films prepared by cosputtering a ferromagnet and a nonmagnet which tend to phase separate (cluster) under equilibrium conditions. We have systematically studied the magnetoresistance of two new phase separating GMR systems (Ni66Fe16Co18-Ag and Co9oFelo-Ag) both of which exhibit large room temperature GMR (>11% and >14%, respectively). We have also attempted to influence the details of the field dependence of the magnetoresistance in the previously studied Co-Ag system by employing novel processing methods including interrupted sputtering and layering of the Co-Ag alloy with Cu spacers.
A Microstructural Study of Iron Carbides Formed by Plasma-Enhanced Chemical Vapor Deposition (50–800 nm Thick)
Authors: Siriwardane H. , James W.J. , Pringle O.A. , Newkirk J.W.
Published: September 2012

Thin Mirror-like iron carbide films were prepared by introducing iron pentacarbonyl [Fe(CO)5] and hydrogen [H2] into a glow discharge. The deposition temperatures were varied from 200–500°C. The iron to carbon ratios of the resulting films were controlled by adjusting the gas flow ratios. The Microstructure and phase transformations occurring in these films were studied before and after annealing at 400°C for four hrs. Characterization techniques used included x-ray diffraction, electron diffraction, Auger spectroscopy and atomic force Microscopy.

X-ray diffraction data of plasma-deposited films on glass substrates maintained at 400°C showed the presence of only Fe3C. However, the x-ray diffraction data of films on carbon coated glass, and transmission electron microscopy selected area diffraction patterns of films on carbon coated copper grids indicated the presence of a second phase, the closely related Metastable Fe7C3, as well as small amounts of Fe3O4. Atomic force microscopy of crystallites on the surface of films deposited at 400°C and annealed at 400°C for four hours revealed a periodic structure of oblate spheroids. The Measured spacings and angle, when compared to projected models of high reticular density planes, suggested the surface to have a structure corresponding to that of bulk FesC or Fe3C or Fe7C3. However the data were not of sufficient quality to unambiguously determine such.
Dynamical Scattering of Polarized Neutrons by Thin Magnetic Films
Authors: Nunez V. , Majkrzak C.F. , Berk N.F.
Published: September 2012

Using Larmor precession as a clock, Buttiker1 identified theoretical times for the scattering of particles from an opaque slab coincident with a magnetic field. The subsequent model generated interesting predictions for the influence of opaque regions on the magnetic polarization of the transmitted and reflected beams. Previous attempts to verify these predictions were unable to do so unambiguously2. Here, Biittiker's formulae are extended to more general geometries. An experiment has been devised to test the theory by measuring neutron beam polarization in both reflection from and transmission through magnetic films below the critical angle for external reflection.
Structural Characterization of Thin Co/Cu Superlattices
Authors: Smith David J. , Modak A.R. , Parkin S.S.P.
Published: September 2012

High-resolution electron microscopy has been used to characterize the microstructure of thin CO/Cu Metallic Multilayers grown on Si (100) substrates by dc magnetron sputtering. The nature of the buffer layer between the silicon wafer and the multilayer had a significant effect on the structural integrity of the Multilayer. An increase in grain size was observed as a function of Cu layer thickness, with grain sizes typically being at least 3–4 times the bilayer period. A high degree of structural ordering was observed in superlattices comprised of thicker Cu layers with large grains often spanning the complete multilayer stack. Complementary Magnetic Measurements enabled the microstructure to be related to the oscillatory exchange coupling and large magnetoresistance exhibited by these thin magnetic films.
Modification of Magnetic Coupling in Antiferromagnetically Coupled Bilayers Due to the Existence of Ferromagnetic Pin Holes.
Authors: Bobo J.F. , Fischer H. , Piecuch M.
Published: September 2012

We have calculated numerical simulations and analytical solutions of the influence of a pin hole on the magnetization curves of multilayer systems. The Magnetization curves we obtained can be described by a biquadratic coupling model and are close to the experimental curves.
Spin Configurations and the Dynamic Response of Antiferromagnetically Coupled Systems
Authors: Nörtemann F.C. , Stamps R.L. , Camley R.E.
Published: September 2012

We present a calculation of spin waves in coupled multilayered structures which is based on exact evaluation of both exchange and dipolar fields. The ground state spin configuration in antiferromagnetically coupled multilayers can differ significantly from the uniformly canted ground state usually assumed. This non-uniform ground state is found to radically alter the character of the spin wave modes and sometimes lead to a strong localization of the wave to the outermost magnetic films of the Multilayer.
Magnetization Loops in Fe/Ag/Fe/Ni (001) Structures
Authors: Heinrich B. , Celiński Z. , Konno H. , Arrott A. S. , Rührig M. , Hubert A.
Published: September 2012

The lattice reconstructed bec Ni (001) in Fe/Ni (001) ultrathin layers allows one to engineer films in which the in-plane 4-fold anisotropies and coercive fields can be varied and adjusted according to specific requirements. Magnetization reversals have been studied in layered structures of Fe/Ag/Fe/Ni (001). For Ag (001) interlayers thicker than 13 ML Magnetization reversal can proceed in two steps. In these samples the minor loops switch the magnetization of the Fe (001) layer from the parallel to the antiparallel configurations with respect to the magnetic moment of the Fe/Ni film. Such Minor loops exhibit a rectangular behavior with switching fields of 15–25 Oe. The lattice transformed Fe/Ni layers could be useful in spin-valve structures.
Magneto Optical Kerr Spectroscopy as a Probe of Chemical Ordering in CoPt
Authors: Harp G. R. , Weiler D. , Rabedeau T. A. , Farrow R. F. C. , Marks R. F.
Published: September 2012

We demonstrate that the photon energy dependence of the polar Kerr effect can be used as a sensitive probe of chemical ordering effects in binary intermetallic alloys. We demonstrate this effect in the Co50Pt50 alloy, which is known to have a Ll0 phase (critical temperature ∼825°C). Kerr spectra of the ordered and disordered phases of the Co50Pt50 alloy composition differ drastically from each other and the ordered phase shows an unprecedented, new peak at 2.2eV photon energy. The intensity of this new peak correlates with the degree of chemical ordering and the magnetic anisotropy in these films.
Magneto-Optical Spectra of Copt3: Experiments and First Principles Calculations
Authors: Welter D. , Sticht J. , Harp G.R. , Farrow R.F.C. , Marks R.F. , Brandie H.
Published: September 2012

The Magneto-optical Kerr effect of CoPt3 ordered compounds and alloys is investigated experimentally and analyzed theoretically using first principles band structure calculations.

The calculations confirm the experimental results and allow for the first time a detailed, bandstructure based interpretation of the electronic transitions leading to the well known strong uv peak at around 4eV. This feature can be unambiguously attributed to Magneto-optical transitions within the Pt p and d bands.
Roughness and Magnetic Properties of Pt/CO Multilayered Films
Authors: Sumi S. , Kusumoto Y. , Teragaki Y. , Torazawa K. , Tsunashima S. , Uchiyama S.
Published: September 2012

Magnetic properties and roughness of sputter-deposited Pt/CO films strongly depend on preparation conditions such as rf input power, underlayers and their etching. Large coercivity was obtained by using suitable underlayers such as ZnO and adjusting input power higher for Co and lower for Pt. The coercivity in Pt/CO films seems to depend on the roughness of the surface and/or the layer interface as well as the perpendicular anisotropy.
Influence of Superlattice Potentials on Transport in magnetic multilayers
Authors: Zhang Shufeng , Levy Peter M.
Published: September 2012

We discuss the effect of the superlattice potential on the magnetotransport properties of magnetic multilayers for current parallel and perpendicular to the plane of the layers. While quantum well states affect the Magnetotransport, they are not the primary origin of the giant Magnetoresistance observed in these materials for currents in the plane of the layers. In general, it is necessary to include both spin-dependent scattering and the effects of superlattice potentials in order to explain the magnetoresistance of multilayered structures.
Magnetism and Magnetic Interactions at Transition Metal Surfaces and Interfaces
Authors: Wu Ruqian , Wang Dingsheng , Freeman A.J.
Published: September 2012

In the exciting field of low dimensional magnetic systems including surfaces, interfaces and thin-films, local spin density (LSD) functional ab initio electronic structure calculations have played a key role by not only providing a clearer understanding of the experimental observations but also predicting new systems with desired properties. Our extensive calculated results demonstrate that: (i) Magnetic clean surfaces or interfaces with inert substrates undergo strong magnetic moment enhancements; (ii) the strong interaction with nonmagnetic transition metals diminishes (completely in some cases) the ferromagnetism and usually stabilizes the antiferromag-netic configuration. By including spin-orbit coupling as a perturbation, (i) reliable results for the Magneto-crystalline anisotropy of ultra-thin films can be obtained using the state-tracking procedure, although the anisotropy energy is a few tenths of a MeV; (ii) spectra of the Magneto-optical Kerr effects and magnetic circular dichroism in the soft x-ray region can be determined.
Mechanism for the magnetoresistance of Pure Bulk Ferromagnets and Composite Thin Film Structures
Authors: Stearns Mary Beth
Published: September 2012

A unified explanation is given of the long-standing question of the origin of the low-field magnetoresistance, MR, behavior in pure ferromagnetics and the large magnetoresistance effects seen in magnetic layered and granular structures. It is shown that the main contributions to these effects are due to the scattering that occurs at the magnetic boundaries between non-aligned magnetic regions. This scattering occurs because the predominant conduction electrons in 3d ferromagnetics are the highly polarized itinerant d electrons. As a result of this polarization the Majority-band d electrons are strongly reflected at an antiparallel magnetic boundary due to a lack of available states for occupancy. The traversing electrons are further scattered as they cross the boundary due to a discontinuity in the potential caused by the interchange of their kinetic and exchange energies at the boundary. Expressions for the magnetoresistance due to these scattering mechanisms are derived and shown to describe very well the wide variety of magnetoresistance values and other features found in the literature for both pure Fe and nano-structures of Fe or Co with non-Magnetic Materials. The MR Magnitude is seen to vary inversely with the domain size. Thus the domain size and sample purity are seen to be the main factors that determine the magnitude of the MR effect in pure ferromagnets. The large MR values seen in layered and granular magnetic structures arise from the small effective domain size attainable in these structures. This is achieved by introducing a non-Magnetic Material into these structures which allows the effective domain size to be decreased from the micron range of the pure ferromagnetic elements into the nanometer range.
Probing the Surface-Vacuum Interface with Spin-Sensitive Metastable Atom Deexcitation, Electron Capture and Electron Emission Spectroscopies
Authors: Walters G. K. , Rau C.
Published: September 2012

Spin-Polarized Metastable Atom Deexcitation (SPMDS) and Electron Capture (ECS) Spectroscopies probe the exponential tails of electronic wavefunctions extending from the surface into the vacuum, and are consequently extremely sensitive to the surface-vacuum interface. The use of SPMDS to probe the near-surface vacuum magnetization of Ni (l 10) and Fe (l 10) and the dramatic changes that result upon exposure to ambient gases is discussed, as is the use of ECS and Spin-Polarized Electron EMission Spectroscopy (SPEES) to determine the ferromagnetic and critical behavior of surfaces and ultra-thin epitaxial systems.