bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective Si/SiGe Heterostructures for Advanced CMOS and BiCMOS Technologies
Authors: Regolini J. L.
Published: April 2011

New device architectures for advanced Integrated Circuits (IC) have been studied within the frame of our GRESSI Program through the technological development of the well known but less implemented low temperature selective epitaxial Si and SiGe films. High performance IC manufacturing requirements, such as large diameter wafer uniformity, reproducibility, throughput and reliability can be met by commercial integrated processing, single wafer cluster tools.

Using an industrially available CVD single wafer reactor, special care has been taken to integrate these films into advanced CMOS and BiCMOS processes with a minimum of drawbacks. Indeed, the Si and SiGe growth rate dependence on filling ratio as well as full selectivity are major issues. The loading effect as a function of temperature, gas mixture, Ge and dopant incorporation has been studied and optimized for these applications.

Finally, device results are compared between conventional and developed architectures showing real improvements with minimum process modifications.
Critical Technologies for Poly-Si TFT in High Resolution AM-LCD
Authors: Wu I-Wei
Published: April 2011

Polycrystalline silicon (p-Si) TFT offers higher aperture ratio with integrated driver circuits compared to the conventional a-Si TFT in AM-LCD application. The advantages of the p-Si TFT as the pixel switching element will be more pronounced for AM-LCDs with large number of scan lines and/or high pixel density. This paper reviews challenges and issues associated with the technology of p-Si TFT, particularly in active silicon layer deposition, solid phase and laser crystallization, hydrogenation, leakage current, performance of different device architectures and reliability. Critical issues affecting the p-Si TFT AMLCD pixel design are analyzed, including: lithographic resolution and overlay accuracy, pixel density and aspect ratio, display format, storage to LC capacitance ratio, and gate dielectric thickness. Predictions on the regimes of dominance for different flat-panel technologies by advantages in performance and-or cost with respect to panel size and pixel density will be presented.
A Novel Multi-Channel Poly-Si TFT Improving Hydrogen Passivation
Authors: Park C. M. , Jeon J.-H. , Yoo J.-S. , Han M.-K.
Published: April 2011

ABSTARCT:

We have fabricated a new multi-channel polycrystalline silicon thin film transistor (ploy-Si TFT), of which structure may be more effectively hydrogenated than conventional multi-channel poly-Si TFT. The new multi-channel TFT has stripe-cuts in gate electrode so that more hydrogen radicals penetrate into the gate oxide and passivate the active poly-Si layer. After 90 min. hydrogenation of the new device, the electrical characteristics such as threshold voltage and field effect mobility are improved more than those of conventional device.

The new multi-channel poly-Si TFT, which receives more hydrogen radicals thorough gate oxide than the conventional multi-channel TFT, can be hydrogenated effectively in long channel devices. Besides the improvement of the device characteristics, our experimental results show that the dominant hydrogenation path is the diffusion though the gate oxide.
The Performance of Polycrystalline Silicon Thin film Transistors and CMOS Driving Circuits with Various Active Films
Authors: Yoo Juhn-Suk , Kim Cheon-Hong , Park Ki-Chan , Han Min-Koo
Published: April 2011

The performance of poly-Si TFTs and CMOS circuits with various active films prepared by different deposition processes and annealing methods, such as SPC(Solid Phase Crystallization) and ELA(Excimer Laser Annealing), have been investigated. We have examined the effects of DC characteristics of poly-Si TFT, such as mobility, threshold voltage and ON- OFF- current level, on the dynamic performance of the CMOS circuits.

We have fabricated poly-Si TFT devices and CMOS circuits with various process conditions, such as active layer preparation source gases, annealing method, film thickness and source/drain impurity doping. The TFTs with ELA active films exhibit much higher field effect mobility and ON/OFF current ratio than those with SPC active film due to low intragranular trap state density. The TFTs with active film deposited using Si2H6 have higher mobility and sub-threshold slope than those with active film deposited using SiH4 because of the large poly-Si grain size and less grain boundary defects. We have observed that the device ON-current, mobility and VTH are the dominant characteristics to control the operation speed of CMOS circuits. We have also found that the effects of active film thickness and source/drain doping process on the performance of CMOS ring oscillator may not be neglected and that it should be optimized for AMLCD applications.
Field Emission from Tetrahedrally Bonded Amorphous Carbon
Authors: Milne W. I. , Robertson J. , Satyanarayanan B. S. , Hart A.
Published: April 2011

A series of tetrahedrally bonded carbon (ta-C) films have been produced using a Filtered Cathodic Vacuum Arc System. The threshold field and current densities achievable have been investigated as a function of sp3/sp2 bonding ratio and nitrogen content. Typical undoped ta-C films have a threshold field of 15–20V/μm and optimally nitrogen doped films exhibit threshold fields as low as ∼ 5 V/μm. Current densities of typically 10-4 A/cm2 at an applied field of 20V/micron were also obtained.
Rare Earth Doped Porous Silicon Prepared by Electro-Chemical Method
Authors: Zheng W. H. , Gong M. L. , Lian D. L. , Wong W. K. , Cheah K. W.
Published: April 2011

We have carried out an investigation of the electro-chemical doping (ECD) of porous silicon (PS) with rare earth elements, especially Er was chosen for the main doping element in our work. Under certain conditions, after doping a blue shift was shown in the visible range photoluminescence (PL), and enhancement of PL intensity was observed. We address this that the impurity states in forbidden gap increase the optical probability of trapping carriers and the optical transition probability. Moreover, in the Infrared (IR) range, luminescence is observed around 1.54μm at room temperature and is assigned to the optical transitions from intra-4f energy levels of Er3+. X-ray Photo-electronic Spectroscopy (XPS) showed that at least 3 atomic percen of the rare earth element has been incorporated into porous silicon layer. In conclusion, by choosing suitable electrolyte, we successfully doped rare earth elements into porous silicon by electro-chemical method.
Electrical and Optical Properties of Low Dielectric Constant Planarization Polymer for High-Aperture-Ratio a-Si:H TFT-LCDs
Authors: Lan Je-Hsiung , Chou Tsung-Kuan , Chiang Chun-Sung , Kanicki Jerzy
Published: April 2011

We have evaluated the electrical and the optical properties of a planarization polymer (benzocyclobutene; BCB) having a dielectric constant of 2.65 for the application to high aperture-ratio a-Si:H TFT-LCDs. An average optical transmittance of 96 % was found for the BCB film having a thickness of 3 μm in the visible-light region (400–700 nm) of the absorption spectrum. Experimental results showed that the back-channel etched a-Si:H TFT electrical performance was not significantly affected by the BCB passivation. In addition, the three-dimensional analysis of the coupling capacitances between ITO pixel electrode and metal bus lines have indicated that the low dielectric constant of planarization polymer is necessary for the application of this material to the high-aperture-ratio a-Si:H TFT-LCDs. Finally, we have established that for a given tolerance margin, a certain value of polymer thickness is needed to suppress the feed-through voltage and the vertical cross-talk between pixel electrode and metal bus lines.
Annealing Characteristics of Electron Beam Evaporated Magnesium Oxide Thin Film
Authors: Kang Y. C. , Baik J. B. , Lee B. H. , Choi J. H. , Kim J. M. , Park K. Y.
Published: April 2011

The effect of the annealing characteristics of MgO thin film, which is used as a protecting layer and known to play an important role to life time and lower the firing voltage in AC plasma displays, was investigated experimentally. MgO films were deposited on glass substrates by an electron beam evaporation method and annealed at different temperatures with varying heat treatment time. The characteristics of the crystallization and surface morphology of MgO films were changed by various annealing conditions, confirmed with X-ray diffraction method and scanning and transmission electron microscopes (SEM & TEM). With increasing annealing time and higher temperature, the intensity of the X-ray diffraction peak and the crystalline grain size of MgO increases. With the change of crystallinity and the decrease in grain boundary area, it is considered that the characteristics of firing voltage and life time of the plasma display panel can be improved with appropriate annealing process.
Preparation of The Double-Sided YBa2Cu3O7-δ Thin Film by Hot-Wall Type Mocvd
Authors: Ito Y. , Iwata M. , Yoshida Y. , Takai Y. , Hirabayashi I.
Published: April 2011

A hot-wall type metal organic chemical vapor deposition (MOCVD) apparatus has been developed for the deposition of the YBa2Cu3O7-δ (YBCO) films using liquid metal organic sources on arbitrary shaped substrates. By improving the reactor shape and gas flow of the source materials, we succeeded in fabricating the double-sided YBCO films for electronic and microwave devices and the YBCO-coated conductor on oxide fiber for power applications. Tc(zero)'s of the YBCO film on both sides of the LaAlO3 (100) substrate were 90K and 86K, respectively. The films on the facet of the single crystalline SrTiO3 fiber showed the single phase c-axis orientation with biaxially alignment in the a / b plane.
The (001) Surface of Fe3O4 Grown Epitaxially on MgO and Characterized by Scanning Tunneling Microscopy.
Authors: Gaines J. M. , Kohlhepp J. T. , van Eemeren J.T.W.M. , Elfrink R.J.G. , Roozeboom F. , de Jonge W.J.M.
Published: April 2011

Spinel Fe3O4 contains two sites for iron: tetrahedrally coordinated sites containing Fe3+ ions and octahedrally coordinated sites containing a mixture of Fe2+ and Fe3+ ions. Scanning tunneling microscopy performed on the (001) surface of Fe3O4, grown epitaxially on MgO, shows localized charge density at the tetrahedral sites. The images show that the p(1×1) surface reconstruction (also observed during molecular beam epitaxy of Fe3O4) is produced by a displacement of the two tetrahedrally coordinated Fe ions on the unit cell surface from their bulk positions toward each other. The octahedral Fe ions are imaged as extended rows of charge density, with no resolution of atom-size features along the rows. This slight corrugation of electron charge density along the octahedral sites is consistent with the original conjectures explaining the high electrical conductivity in bulk Fe3O4: electrons move by hopping between the Fe3+ and Fe2+ atoms along the octahedral rows of Fe ions.
Vacancy Related Defects in La0.5Sr0.5CoO3-δ Thin Films
Authors: Keeble D. J. , Madhukar S. , Nielsen B. , Krishnan A. , Asoka-Kumar P. , Aggarwal S. , Ramesh R. , Poindexter E. H.
Published: April 2011

Laser ablated La0.5Sr0.5CoO3-δ thin films have been studied by Doppler-broademng-detected positron annihilation using a variable-energy positron beam. The oxygen partial pressure during cooling from the growth temperature was altered through the range 760 torr to 10−5 torr to change the oxygen non-stoichiometry of the films.

The measured Doppler broadened lineshape parameter S was found to increase with increasing oxygen nonstoichiometry. For films cooled with an oxygen partial pressure of ≤ 10−4 Torr positron trapping to monovacancy type defects is infered. It is proposed that Sr ion oxygen vacancy complexes are likely trapping sites.

For the film cooled in 10−5 torr oxygen the magnitude of the increase in S, with respect to that measured from the film cooled in 760 Torr oxygen, showed positron trapping to vacancy cluster defects is occuring.
Pulsed Laser Deposition of (Sr1-xCa)RuO3and Sr(Ru1-xTix)O3Thin Films by Sequential Multilayer Process
Authors: Mffiville L. , Antognazza L. , Char K. , Geballe T. H.
Published: April 2011

We report on the growth and properties of (Sr1-xCax)Ru03and Sr(Ru1-xTix)O3thin films obtained by pulsed laser deposition. A sequential deposition of sub-monolayers from SrTiO3and CaRuO3end members has been successfully used to substitute Ca- and Ti- in the SrRuO3perovskite structure. Magnetization measurements as well as transport properties exhibit very different behavior for each type of substitution. In the case of Ca- substituted samples, the resistivity remains metallic and is consistent with the expected behavior for intermediate compositions. A progressive reduction of the Curie temperature with higher doping is reported. In the case of Ti- substituted samples, we observe a stronger reduction of the Curie temperature and remanent magnetization with increasing Ti substitution. Resistivity as a function of temperature shows a crossover from metallic to semiconducting behavior with variable range hopping process for a high level of Ti doping and points out the clear differences between the two substitutions sites. In both cases, the observed reduction of the magnetization with increasing doping concentration can be well described by assuming a random distribution of substituted sites in the perovskite structure.
Oxide Quantum Structures for Future Electro-Photonics
Authors: Kawasaki M. , Ohtomo A. , Tsuchiya R. , Nishino J. , Koinuma H.
Published: April 2011

We show our recent development on the epitaxial growth of oxide thin films by laser molecular beam epitaxy directed towards a possible new field of electro-photonics based on metal-oxide quantum structures. Examples of quantum structures include superlattices and tunnel junctions (2-dimensional), superconducting quantum wire arrays (1-dimensional), and quantum dots for photonic application (O-dimensional). For fabricating such structures, it is vitally important to prepare the substrate surface and to understand the growth dynamics. Such electro-phptonic functions as Josephson effect in high Tc tunnel junctions and excitonic UV-laser operation at room temperature in self-organized hexagonal nanocrystal ZnO films are presented.
Characteristics of Y2O3 films on Si(100) by ionized cluster beam deposition
Authors: Cho M. H. , Whangbo S. W. , Whang C. N. , Choi S. C. , Kang S. B. , Lee S. I. , Lee M. Y.
Published: April 2011

In this study, the Y2O3 films on p-type Si(100) have been fabricated by UHV reactive ionized cluster beam deposition(r-ICB) systems. The crystallinity of the films was investigated by glancing X-ray diffraction(GXRD) and in-situ reflection of high energy electron diffraction(RHEED) analyses. The results show that the preferentially oriented crystallinity of the films was increased with acceleration voltages as well as substrate temperatures. Especially, at the substrate temperature of 700 °C and the acceleration voltage of 5kV, the Y2O3 films grow epitaxially in direction of Y2O3(110)//Si(100). The characteristics of Al/Y2O3/Si MIS structure were obtained by C-V, and I-V measurements. The breakdown field strength of the epitaxially grown films increases up to 2MV/cm without any interface silicon oxide layer, and the dielectric constant is found to be ε=15.6. these results demonstrated that the yttrium oxide films have potential application to the gate insulator of the future VLSI/ULSI devices.
Role of Ag in the Epitaxial Growth of Oxide Thin Films
Authors: Lee Clinton B. , Kumar D. , Singh Rajiv K. , Mathis Derrick , Moxey Donovan
Published: April 2011

In this paper, we have reported our investigations related to the growth of high temperature superconducting YBa2Cu3O7-δ (YBCO) and colossal magnetoresistive La0.7MnxO3-δ (LMO) thin films in presence of silver. The films were grown using pulsed laser deposition (PLD) techniques and characterized using x-ray diffraction, scanning electron microscopy, Squid magnetometer. The focus of our work is on the realization of significant improvement in microstructural and physical properties of these films by the addition of a common material (silver) to the films during their in-situ formation. Optical emission studies of plumes emanating from Ag target have been carried out to find the role of Ag acting as additional source of oxygen-supply to oxide lattices during film-growth.
Heteroepitaxial Growth Of ZnO Films BY PLD
Authors: Vispute R. D. , Talyansky V. , Trajanovic Z. , Choopun S. , Downes M. , Sharma R. P. , Venkatesan T. , Wood M. C. , Lareau R. T. , Jones K. A. , Li Y. X. , Salamanca-Riba L.
Published: April 2011

Here we present our recent work on the fabrication of high crystalline and optical quality ZnO films on sapphire (001) by pulsed laser deposition. The influence of deposition parameters such as the substrate temperature, oxygen pressure, laser fluence, and pulse repetition rate on the crystalline quality of ZnO layers has been studied. The Ω-rocking curve FWHM of the (002) peak for the films grown at 750°, oxygen pressure 10−5 Torr was 0.17°. The XRD-Ф scans studies revealed that the films were epitaxial with a 30° rotation of the unit cell with respect to the sapphire to achieve a low energy configuration for epitaxial growth. The high degree of crystallinity was confirmed by ion channeling technique providing a minimum Rutherford backscattering yield of 2–3% in the near surface region (-2000Å). The atomic force microscopy revealed smooth hexagonal faceting of the films. The optical absorption edge measured by UV-Visible spectroscopy was sharp at 383 nm. Excellent crystalline properties of these epi-ZnO/sapphire heterostractures are thus promising for III-V nitride heteroepitaxy.
In-Situ Caiciss Study Of Dynamic Process Of Oxygen Desorption On TiO2-Terminated SrTiO3(001) Surface
Authors: Nishihara T. , Ishiyama O. , Hayashi S. , Shinohara M. , Yoshimoto M. , Ohnishi T. , Koinuma H.
Published: April 2011

The topmost atoms of TiO2 - terminated SrTiO3(001) annealed at temperatures between room temperature and 800°C in ultra high vacuum (UHV), have been studied by means of in-situ coaxial impact collision ion scattering spectroscopy (CAICISS). Both time-of-flight spectra at the incident angle of 45.0°C along [ 100] azimuth and of 35.3°C along [110] azimuth revealed Ti and weak O peaks and no Sr peak at 150°C, which means that the topmost layer at 150°C is terminated by TiCh-plane, completely. On the other hand, as increasing the substrate temperature, Sr peak began to appear above 400°C. This Sr peak intensity from both directions was drastically increased with elevating the substrate temperature. This indicates that the topmost O and Ti atoms desorb from the surface at the higher substrate temperature. The ratio Sr/Ti corresponds to the amount of the topmost oxygen or titanium vacancies due to the desorption. It was found that 40 % of the topmost oxygen atoms and 32% of the topmost titanium atoms desorb from TiO2-terminated SrTiO3(001) surface at 800°C. The activation energies for oxygen and titanium desorption were 0.28eV and 0.40eV, respectively.
Growth of ZnO Thin Films on Sapphire Substrates by ECR-Assisted MBE
Authors: Kang Hee-Bog , Nakamura Kiyoshi , Ishikawa Kazuo
Published: April 2011

Epitaxial ZnO films were grown on c-plane sapphire substrate at low temperature using the electron cyclotron resonance-assisted molecular beam epitaxy(ECR-assisted MBE) technique. In this method, Zn vapor provided by a Knudsen cell reacts with oxygen activated in an ECR source on the surface of sapphire substrate. The crystal structure, surface morphology and epitaxial relationship of the films were investigated. It was confirmed that the ECR-assisted MBE technique was capable of growing a high quality epitaxial ZnO films on c-plane sapphire substrates at low temperatures in comparison with CVD and RF sputtering. The FWHM of an x-ray rocking curve of the (0002) peak for a 0.33μ-thick ZnO film was as narrow as 0.58°. The epitaxial relationship between ZnO film and c-plane sapphire substrate was determined to be (0001)ZnO//(0001)Al2O3 with in-plane alignment of [1100]ZnO//[2110]Al2O3, which is equivalent to the 30° rotation of ZnO relative to sapphire in the c-plane.
Improved Dielectric Response in Strontium Titanate Thin Films Grown by Pulsed Laser Ablation
Authors: Dalberth M. J. , Stauber R. E. , Price J. C. , Rogers C. T. , Galt David
Published: April 2011

We have grown epitaxial strontium titanate films on lanthanum aluminate substrates at a range of oxygen pressures and substrate temperatures. The complex dielectric function was measured versus frequency (10 kHz to 1 MHz) and temperature (room temperature to 4.2 K) on coplanar capacitors patterned on the films. Preliminary data from 1.5 to 2.5 GHz is also presented. The dielectric constant εr was as high as 4600 at 65 K, a factor of two greater than previously reported for strontium titanate thin films and a factor of 1.8 greater than the bulk value at the same temperature. Tuning the capacitor by applying a dc bias of ±15 V across the 3 μm coplanar gap at 4.2 K yielded a ratio of maximum to minimum dielectric constant of 2.8. At 101 K this ratio was 2.2. A bulk capacitor does not show tuning over such a large temperature range.
Mechanism of Oxygenation of YBaCuO Thin Films During in Situ Growth by Cathodic Sputtering: Thermodynamic and Kinetic Aspects
Authors: Siejka J. , Garcia-Lopez J. , Lemaître Y. , Mercandalli L. M.
Published: April 2011

The recent experimental results obtained for c-axis oriented YBaCuO thin films deposited at the optimized conditions for the microwave applications are presented and discussed. The emphasis is on the study of the relationship between oxygen profiles, crystallographic structure and electrical and physical properties of the films formed in situ at the same and optimized conditions of sample deposition and further submitted to the different conditions of sample cooling. The studies of the oxygen depth concentration profiles and of the oxygen contents are carried out using the recently developed Nuclear Reaction Analysis (NRA). These results are correlated, on one hand, with the measurements of the atomic composition and structure by RBS, XRD and TEM and, on the other hand, by the measurements of the electrical and physical properties Tc, Jc and microwave surface resistance Rs. All results are consistent with the idea that the fully oxygenated films are formed during in situ growth at T∼ 700°C. For T< 300°C, the oxygen interface transfer coefficient is very small and the oxygen content is practically preserved. However a large room temperature oxidation (corrosion like) takes place in the presence of water vapor. The fundamental and applied consequences of these findings for the mechanism of thin films growth and for the properties of the films in the presence of cathodic plasma or laser plume are analysed.
Epitaxial YBa2Cu3O7-δ/Sr2RuO4 Heterostructures
Authors: Schlom D. G. , Merritt B. A. , Madhavan S. , Liu Ying , Hawley M. E. , Brown G. W. , Dabkowski A. , Dabkowska H. A. , Uecker R. , Reiche P.
Published: April 2011

The anisotropie oxide superconductors YBa2Cu3O7-Dgr; and Sr2RuO4 have been epitaxially combined in various ways (c-axis on c-axis, c-axis on a-axis, and a-axis on a-axis) though the use of appropriate substrates. Phase-pure a-axis oriented or c-axis oriented epitaxial Sr2RuO4 films were grown by pulsed laser deposition. YBa2Cu3O7-δ films were then grown on both orientations of Sr2RuO4 films and the resulting epitaxy was characterized.
Microstructural Defects in SrTiO3 Bicrystals and Their Influence on YBa2Cu3O7 Film Growth and Junction Performance
Authors: Hsu J. W. P. , McDaniel E. B. , Rao R. A. , Eom C. B.
Published: April 2011

We use a near-field scanning optical microscope (NSOM) to investigate microstructural defects at the fusion boundaries of SrTiO3 bicrystal substrates. The optical transmission across the fusion boundary shows circular dark spots with diameters varying from 0.1 to 1 μm that are distributed non-uniformly along the boundary. After detailed characterization of the substrates, a thin YBa2Cu3O7 (YBCO) film (∼ 40 nm) was deposited on a 24° bicrystal. Combining NSOM and scanning force microscopy, we show that these substrate defects can cause the grain boundary of a YBCO thin film grown on the bicrystal to wander up to 0.8 micron in the film. Strain fields associated with these substrate defects are attributed to their influence on YBCO growth. The relation between these structural defects and the electrical characteristics of YBCO grain boundary junctions are also discussed.
Magnetic easy axis switching in ultrathin Co/Cu(110) films
Authors: Hope S. , Gu E. , Tselepi M. , Bland J.A.C.
Published: April 2011

We have studied the magnetic properties of the Co/Cu(110) system at 300K, using the magneto-optic Kerr effect. After a given deposition of Co in the thickness range 5ML<dCo<40ML, the M-H loop is observed to evolve continuously in time until the magnetic easy axis has switched 90° from the [001] to [1–10] direction. We attribute this behaviour to the reversal in sign of the effective in-plane uniaxial anisotropy constant, due to the adsorption of submonolayer quantities of a residual gas from the UHV environment. STM images reveal the growth of elongated Co island structures preferentially oriented along the [001] direction providing ‘step like’ edge sites for gas adsorption. We find the easy axis can be switched back to the [001] direction by depositing a submonolayer Cu overlayer, and that for relatively thick Co films (>15ML) the Cu overlayer can cause the magnetisation to take up intermediate angles. We analyse this behaviour using a simple model of the effective anisotropy energies.
Structural and Magnetotransport Properties of NiMnSb/Cu and NiMnSb/Ag Multilayers
Authors: Caballero J.A. , Petroff F. , Cabbibo A. , Park Y.D. , Childress J.R.
Published: April 2011

We report on the integration of the predicted half-metallic (100% spin-polarized) ferromagnetic Heusler alloy NiMnSb into NiMnSb/Cu and NiMnSb/Ag multilayer structures, and on their magnetic, microstructural and magnetotransport properties. The NiMnSb layer thickness was fixed at 30Å and those of Cu and Ag were varied from 5 to 60Å. The multilayers were characterized using x-ray diffraction (XRD), four-wire resistivity measurements, atomic force microscopy, SQUID magnetometry and magnetotransport measurements. Moderate substrate temperatures (250°C) are shown to be sufficient to produce stochiometric Clb-structured NiMnSb. XRD data confirm that the NiMnSb ultra-thin layers retain their crystalline quality and texture. SQUID measurements shows that the bulk saturation magnetization (∼740 emu/cm3) is maintained and that it is strongly sensitive to interlayer diffusion and roughness. AFM studies show that the surface roughness, which can be as low as 4Å, depends on the choice of spacer layer, layer thickness and substrate temperature. The relationship between the measured magnetoresistance, NiMnSb crystalline quality, magnetic properties and interfacial roughness are discussed.
Perpendicular Magnetic Anisotropy in Nanostructured Pseudomorphic Fe(110) Films on W(110)
Authors: Elmers H.J. , Weber N. , Wagner K. , Hauschild J. , Gradmann U.
Published: April 2011

Pseudomorphic Fe(110) films, deposited on W(110) at room temperature, with a mean thickness of 1.5 monolayers. are composed of double layer islands with a diameter of the order of 10 nm on a monolayer sea. The double layer islands are ferromagnetic (superparamagnetic) below 500 K, the monolayer sea becomes ferromagnetic below 222 K. Magnetic anisotropy is uniaxial in both components. The easy axis is perpendicular to the film plane in the double layer islands and within the film plane (along [110]) in the monolayer sea. The perpendicular anisotropy in the double layer islands apparently is caused by the pseudomorphic strain. The lateral scale for the anisotropy switching roughly coincides with the exchange lengths in both media. The strength of the exchange interaction between double layer islands rapidly increases when the monolayer sea becomes ferromagnetic.
Magnetization Reversal by Rotation in Magnetic Thin Films Deposited on Step Bunched Si(111) Substrates
Authors: Sussiau M. , Encinas A. , Nguyen Van Dau F. , Vaurès A. , Schuhl A. , Galtier P.
Published: April 2011

Magnetic and magnetoresistive properties of magnetic thin films deposited on periodically structured substrates have been studied. By using a thermodynamical heat treatment, we activate the step bunching phenomenon on vicinal Si(111) substrates misoriented towards [112] which results in a laterally modulated surface with a period around 0.1 μm. Epitaxial magnetic thin films deposited on these substrates exhibit an in-plane uniaxial anisotropy and a specific magnetoresistive behavior which characterizes the magnetization reversal process. In this contribution, we demonstrate that these properties can also be observed in non-epitaxial structures grown either by molecular beam epitaxy or by sputtering. In particular, magnetotransport measurements show that by varying parameters such as the nature of the magnetic metal, the layer thickness or the strength of the induced anisotropy, we can modulate the interplay between the anisotropy and the exchange stiffness, and, consequently, observe gradual magnetization reversal behaviors between a Stoner-Wohlfarth uniform mode and a non-uniform mode.
Structural and Magnetic Properties of XMnSb/PtMnSb Clb Heusler Alloy Superlattices (X=Ni,Cu)
Authors: Bobo J.F. , Bessho K. , Mancoff F.B. , Johnson P.R. , Kautzky M.C. , White R.L. , Clemens B.M.
Published: April 2011

We have grown superlattices based on the Clb Heusler alloys PtMnSb, CuMnSb and NiMnSb between 200–500°C on A12O3 (0001). X-ray diffraction (XRD) indicates (111) oriented ordered structures for growth at 300°C. Higher deposition temperature leads to interdiffusion, loss of the multilayer structure and appearance of extra phases. Growth at 200°C slightly reduces the intermixing but also reduces the quality of the crystal structure. For PtMnSb/CuMnSb, we found an enhancement of the saturation magnetization compared to equivalent PtMnSb single layer films and a CuMnSb spacer thickness dependence of the squareness of the M(H) 100ps suggestive of interlayer coupling. Short periodicity NiMnSb/PtMnSb superlattices show an in-plane magnetic easy axis, but correction for shape anisotropy indicates a tendency for perpendicular anisotropy.
Magnetic Domain Structure and Spin Reorientation Transition in the System Co/Au/W(110)
Authors: Duden T. , Bauer E.
Published: April 2011

Ultrathin epitaxial Co layers grown on Au(111) show strong perpendicular magnetic aniso-tropy resulting in out-of-plane magnetization in thin films. With increasing Co thickness the increasing contribution of the shape anisotropy leads to a reorientation transition of the magnetization which has already been subject of many other studies. In the dynamic in-situ experiments reported here bulk Au(111) is replaced by epitaxially grown Au(111)/W(110). The high time resolution (0.05 ML Co deposition per acquisition cycle) allows to extract several mechanisms which occur during the spin reorientation transition.
Macroscopic Magnetic Measurements on Microscopic Quantities of Materials
Authors: Foner Simon
Published: April 2011

The principles of several of the most popular macroscopic magnetic measurement techniques are discussed for the vibrating sample magnetometer, SQUID magnetometer, ac susceptometer, ac force magnetometer, and torque magnetometers. These types of instruments are available commercially as stand-alone computer-controlled systems, Selected examples of recent measurements on thin films, small particles, and clusters of magnetic ions are presented.
Growth and Magnetic Anisotropy of Polycrystalline (110) (NiFe/Ni/NiFe)/Cu Multilayer on 4 ° TILT-CUT Si(111)
Authors: Song Yong-Jin , Lee Byung-Il , Joo Seung-Ki
Published: April 2011

[Cu(20Å)/NiFe(7Å)/Ni(6Å)/NiFe(7Å)]10Cu(50Å) multilayers were deposited on 4 ° tilt-cut Si(lll) using 3-gun rf magnetron sputtering system. An in-plane uniaxial magnetic anisotropy was found and the uniaxial magnetic anisotropy constant was about 3×104 erg/cm3. The multilayers on non tilt-cut Si(lll) with Cu underlayer did not show any anisotropy. The crystal structure of the multilayer on 4 ° tilt-cut Si(111) was studied using TEM work and the magnetic anisotropy is originated from the growth of (110) preferred orientation of the multilayer. When other material such as Ni or NiFe was used as an underlayer for the multilayer, the magnetic anisotropy disappeared and the crystal structure was (111). The multilayer without underlayer did not show any magnetic anisotropy either. It is thought that Cu underlayer was grown with (110) orientation on 4 ° tilt-cut Si(111) through the ledges in Si wafer and worked as a template for the growth of the multilayer.
Magnetic Thin Films of Cobalt Nanocrystals Encapsulated in Graphite-Like Carbon
Authors: Hayashi T. , Hirono S. , Tomita M. , Umemura S. , Delaunay J.-J.
Published: April 2011

Granular thin films consisting of cobalt nanocrystals encapsulated in graphite-like carbon were fabricated by co-deposition of cobalt and carbon with subsequent annealing. The gram size and the crystal structure of the Co-C films depended on the substrate temperature, the carbon concentration, and the annealing temperature. The film deposited with 36 at.% carbon at 200°C consisted of crystalline carbide and hep cobalt, which transformed into hep cobalt and graphite-like carbon by annealing at ≥300 °C. The as-deposited film with a carbon of 46 at.% had an amorphous-like phase and grain sizes of ≤10 nm. By annealing at ≥300°, the amorphous-like phase transformed into cobalt grains with a random stacking structure encapsulated in graphite-like carbon, and the initial size of the grains was unchanged. The saturation magnetization and the in-plane coercivity of these films were also reported.
Magnetic Dichroism in Resonant Photoemission and Photoabsorption from Gd Metal
Authors: Starke K. , Van Der Laan G. , Hu Z. , Arenholz E. , Navas E. , Bauer A , Mühlig A. , Langeheine C. S- , Weschke E. , Goodkoep J. , Brookes N. , Kaindl G.
Published: April 2011

We report on the study of MCD in resonant PE, using Gd metal as an example. When the photon energy is changed across the Gd 4d → 4ƒ excitation region, the PE-MCD spectrum varies substantially. Based on atomic-multiplet theory, we present a consistent picture of MCD in resonant 4d → 4ƒ PE and x-ray absorption at the 4d-edge, where all spectral changes can be explained by the angular-momentum of the intermediate absorption state. The present analysis shows: when tuning to a specific line of the 4d x-ray absorption spectrum with a total angular momentum J', only the associate multiplet component is found to resonate. At the ‘giant resonance’, the shape of the MCD-PE signal closely resembles the off-resonance case; this finding is explained within atomic-multiplet theory allowing a straightforward use of MCD in 4d-resonant PE (i) for element-specific analysis of multicomponent magnetic systems with high surface sensitivity and (ii) for surface-domain imaging by PE microscopy.
Anisotropic Local Structure of Co-Pd Alloy and Pd/Co Multilayer Films Having Perpendicular Magnetic Anisotropy
Authors: Kim Sang-Koog , Chernov V.A. , Kortright J. B. , Koo Yang-Mo
Published: April 2011

Anisotropie short-range structure in Co-Pd alloy and Pd/Co multilayer films is determined using polarized Co K-edge extended x-ray absorption fine structure. A local modulation of Co fraction exists along the growth direction in the alloy films. Pd underlayer and Pd spacers alternated with the alloy layer influence an effective strain anisotropy. Pd/Co multilayers have an alloy-like region near nominal interfaces by diffuse interface. Pd spacers in the multilayer play a role in coherency strain rather than on broken symmetry of Co atoms. Local structural anisotropy of both strain and chemical environment contribute to the perpendicular magnetic anisotropy observed in these films.
Interaction of Magnetic Impurities with Surfaces
Authors: Szunyogh L. , Györffy B.L.
Published: April 2011

The interaction of a magnetic (Fe) impurity with the surface of a non-magnetic (Au) semi-infinite host is investigated in terms of fully relativistic spin-polarized first principles calculations. It is shown that the surface induces a magnetic anisotropy on the impurity which is considerably larger than in the bulk. It is also found that the anisotropy constant K(d) is an oscillating function of the distance d between the impurity and the surface with an amplitude which falls as 1/d2 and a period which is determined by the shape of the Fermi Surface of the bulk Au host. However, the question still remains open whether the magnitude of the anisotropy energy is sufficiently large to explain the thickness dependence of the Kondo amplitude B in thin films of dilute FecAu1-c alloys.
Magnetic and Transport Properties of Ga1-xMnxAs, a New III-V Diluted Magnetic Semiconductor
Authors: Van Esch A. , Van Bocksta L. , De Boeck J. , Verbanck G. , Van Steenbergen A. , Bogaerts R. , Herlach F. , Borghs G.
Published: April 2011

Ga1-xMnxAs is a new III-V diluted magnetic semiconductor that can be grown by MBE with Mn concentrations up to x ∼ 0.09. Below a critical temperature Tc, determined by the Mn concentration (about 50 K for x = 0.05) the material becomes ferromagnetic. This is attributed to the magnetic long-range order of Mn-hole complexes, the latter being the result of the strong antiferromagnetic interaction between the holes and Mn 3d spins. Transport and magnetic properties of the Ga1-xMnxAs system are strongly correlated. Above Tc, all samples show transport behaviour characteristic for materials near the metal insulator transition. Below Tc, resistivity decreases as the magnetic ordering sets in. When the magnetisation has reached its saturation value (below ∼ 20 K), variable range hopping is the main transport mechanism. Also, a negative magnetoresistance is observed below Tc.
Influence of the Sputtering Parameters on the Properties of A12O3 and Ain Insulators in Spin Tunneling Junctions
Authors: Plaskett T.S. , Freitas P.P. , Sun J.J. , Sousa R.C , da Silva F. F. , Galvão T.T.P. , Pinho N.M. , Cardoso S. , da Silva M.F. , Soares J.
Published: April 2011

The role of the sputtering parameters on the properties of thin A12O3 and A1N insulator layers for spin dependent tunneling junctions was studied. A12O3 insulators were prepared by rf sputtering from an A12O3 target in an Ar or Ar-O2 atmosphere and also by plasma oxidation in an O2 atmosphere of a thin Al layer. The thin Al layer was deposited by rf sputtering at room temperature. A1N was prepared by reactive sputtering from an Al target in a Ar-N2 atmosphere. The index of refraction n measured by ellipsometry, was used to optimize the sputtering parameters, and chemical etch rates were used for information on pin-hole density. The aimed values were n=1.75 for A12O3 (corundum structure) and n=2.2 for A1N. For reactively sputtered A12O3, under optimized deposition conditions, n reaches 1.65 for films 300 Å thick. A12O3 thin layers fabricated by plasma oxidation of a thin Al film were also prepared but the oxide layer was too thin for ellipsometry characterization. A1N insulating films show a constant n value of 1.92 from 400 Å down to 60 Å thick films. Rutherford backscattering analysis show that the ratio of Ar to N2 must be less than 1 to avoid O2 incorporation in the film. Junctions of the type glass/buffer/FM/insulator/FM, where FM is either Co or NiFe, were made by contact metal masks with a junction area of 0.25 mm.2 The A12O3 deposited by sputtering from an A12O3 target under conditions expected to give n>1.5 had a magnetoresistance at room temperature MR(RT) of 2.5% with a junction resistance Rj of 2.2 m Ω and by fitting the I-V curve to existing tunneling theory gave an effective barrier thicknesst of 20 Å and a barrier heightΦ of 2.2 eV. These occurred in only one sample (9 junctions) and were not reproducible. The A12O3 insulators prepared by plasma oxidation of a thin Al layer gave a MR(RT)= 4%, tj = 22 Å, Rj=250 k,Ω and Φ =1.4 eV. The A1N insulator with n =1.9 gave a MR(RT)= 1.6 %, t = 20 A, Rj = 4.8 kΦ and barrier height 1.2 eV. In the last two cases junctions with MR at room temperature can be produced with reasonable reproducibility, Al2O3 samples showed a 15–20% increase in MR as the temperature was lowered to 17 K, while AIN junctions show an increase of a factor of 2 in MR at 77 K.
Effect of Ru Impurities on Magnetoresistance in Co/Ru/Co(Ru) Sandwiches
Authors: Dinia A. , Rahmouni K. , Persat N. , Stoeffler D. , Ounadjela K. , van den Berg H.A.M.
Published: April 2011

Magnetoresistance (MR) measurements have been performed on two series of Co(3.2 nm)/Ru(x=0.5 to 3 nm)/Co(3.2 nm) and Co(3.2 nm)/Ru(x)/Co.92Ru.08 (3.2 nm) sandwiches prepared by ultra high vacuum evaporation onto mica substrates. At 300 K, all samples of the first series present giant magnetoresistance (GMR) whereas the samples of the second series, and with the same Ru spacer thickness, show an inverse GMR. This inverse GMR is induced by alloying the second Co layer with 8 at% Ru and can be attributed to the change of the scattering coefficients ratio (α) between the two magnetic layers. Indeed, for the first Co layer the scattering coefficient ratio a1 = p↓/↑> 1. However, for the second magnetic layer, alloying Co and Ru may induce an increase of the density of states at the Fermi level for majority spin electrons and as a consequence 0C2 = p↓/↑< 1
Magnetic Properties of Thin Eu Films on Gd(0001) Studied by Magnetic Circular Dichroism in Photoemission
Authors: Arenholz E. , Starke K. , Kaindl G.
Published: April 2011

The magnetic order of ultra-thin Eu films on Gd(0001) was studied in an element-specific and layer-resolved way using magnetic circular dichroism (MCD) in 4ƒphotoemission (PE). It was found that Eu films up to 2 monolayers (ML) exhibit a high net magnetization parallel to that of the Gd substrate. For Eu coverages exceeding 2 ML, the ferromagnetic alignment of the Eu moments breaks down, except for the Eu interface layer. A comparison of the temperature dependences of the Eu-4/ and Gd-4/ MCD-PE signals for 1-ML-Eu/Gd(0001) with the results of a layer-resolved mean-field calculation results in values for the exchange-coupling constants within the Eu monolayer as well as between Eu and the Gd substrate.
Formation and Properties of Nanosize Ferromagnetic MnAs Particles in Low Temperature GaAs by Manganese Implantation
Authors: Wellmann P.J. , Garcia J.M. , Feng J.-L. , Petroff P.M.
Published: April 2011

The synthesis of ferromagnetic particles of the size of several nm (10… 100nm) imbedded in semiconductors is of particular interest for device applications such as magnetic sensors, switches or memories based on integrated semiconductor devices. We have investigated the formation as well as the structural and magnetic properties of MnAs nanomagnets (size ≈ 20nm) in low temperature grown GaAs (LT-GaAs). The MnAs nanomagnets which show ferromagnetism at room temperature have been synthesized using ion implantation with Mn and subsequent rapid thermal annealing (RTA). To characterize these nanomagnets, we present SQUID measurements (superconducting quantum interference device), TEM analysis (transmission electron microscopy) and EDX analysis (electron beam induced x-ray fluorescence).
Effects of Impurities And Alloying Elements on Iron Grain Boundary Cohesion
Authors: Ellis D.E. , Chen X. , Olson G.B.
Published: April 2011

In metallic materials, where grain boundaries(GB) are of crucial importance, impurities and alloying elements play an important role in determining their physical and mechanical properties because the behavior of a grain boundary may change drastically with the presence of impurities and alloying elements. For example, in iron and its alloys, including industrially important steels, the intergranular embrittlement is usually associated with segregation of impurities, like P and S, toward the GBs. On the other hand, alloying elements, like Mo and Pd, are helpful for intergranular cohesion in iron, due to either direct cohesion effect or effect upon embrittling potency of other impurities. Understanding the mechanisms of impurity-promoted embrittlement and the consequent cohesion(decohesion) effects is becoming more and more important and remains as a challenge for materials scientists. There have been intensive investigations on these mechanisms for a long time and with the progress in computing techniques in recent years, calculations on more realistic representations of impurity-doped grain boundaries have become possible[1–4].
Tight Binding KKR - Application to CoCu(001): Electronic Structure and Transport
Authors: Zahn P. , Mertig I. , Zeller R. , Dederichs P.H.
Published: April 2011

Starting from a tight binding formulation of the KKR (Korringa-Kohn-Rostocker) Green function method we developed a self consistent band structure code. By using a reference system containing repulsive muffin tin potentials we obtain structure constants which decay exponentially with distance. In the case of multilayered systems the numerical effort scales linearly with the number of monolayers in a unit cell. We report about calculations of CoCu(001) systems. With our method we are able to consider the electronic structure, the interlayer exchange coupling, and the transport properties (conductivity, giant magnetoresistance = GMR) on an equal footing.
Effect of Cap-Layers on Interlayer Exchange Coupling
Authors: Kudrnovský J. , Drchal V. , Bruno P. , Coehoorn R. , De Vries J.J. , Wildberger K. , Dederichs P.H. , Weinberger P.
Published: April 2011

The effect of non-magnetic cap-layers on the amplitudes and the phases of the oscillations of interlayer exchange coupling (IEC) is studied theoretically on ab initio level. We employ a spin-polarized surface Green function technique within the tight-binding linear muffin-tin orbital method and the Lloyd formulation of the IEC. Application is made to Co/Cu/Co(001) trilayers with Cu-cap layers interfacing vacuum through the dipole barrier.
Study of perpendicular induced magnetic moments in the Ag of Ag/Fe multilayers
Authors: Phale T. , Dekoster J. , De Moor P. , Schuurmans P. , Severijns N. , Trhlik M. , Van Geert A. , Vanneste L. , Vereecke B. , Brewer W.D.
Published: April 2011

We investigated the induced magnetic behaviour of the Ag of Fe/Ag multilayers with low temperature nuclear orientation. The experiments show induced magnetic moments in all samples. Furthermore, multilayers with 2ML and 4ML of Ag, these moments do not lie in the plane of the multilayer at low external magnetic fields.