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12 Apr 2004

Volume 84, Issue 15, pp. 2721-2955

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 2883 (2004); http://dx.doi.org/10.1063/1.1702137 (3 pages)

Pu Xian Gao and Zhong L. Wang
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Directed nanostructural evolution in Ti0.8Ce0.2N layers grown as a function of low-energy, high-flux ion irradiation

T.-Y. Lee, S. Kodambaka, J. G. Wen, R. D. Twesten, J. E. Greene, and I. Petrov

Appl. Phys. Lett. 84, 2796 (2004); http://dx.doi.org/10.1063/1.1699468 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2004

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We use a combination of alloying and low-energy ion irradiation during film growth to controllably manipulate the nanostructure of TiN-based layers. Ti0.8Ce0.2N films are grown on SiO2 at 350 °C using UHV reactive magnetron sputtering in N2. The N2+-to-metal ratio incident at the growing film is maintained constant at 15, while the ion energy EN2+ is varied from 14 to 45 eV. Films grown with EN2+ = 14 eV consist of equiaxed nanograins with an average size of 2.0 nm, while layers deposited with EN2+ = 45 eV exhibit a 2-nm-wide nanocolumnar structure. In both cases, the films are dense, atomically smooth, and have strong 002 texture with low stress. This is in dramatic contrast to TiN films deposited under the same conditions, which are underdense with extremely rough surfaces and consist of broad (≃ 30 nm) columns. We attribute the formation of controlled nanostructures to the interplay between ion-irradiation-induced effects and thermally driven Ce surface segregation, leading to continuous renucleation during film growth. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
61.82.Rx Nanocrystalline materials
61.80.Jh Ion radiation effects
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.35.Dv Composition, segregation; defects and impurities
68.55.A- Nucleation and growth

Compression of Ti3Si0.5Ge0.5C2 to 53 GPa

Bouchaib Manoun, H. P. Liermann, R. P. Gulve, S. K. Saxena, A. Ganguly, M. W. Barsoum, and C. S. Zha

Appl. Phys. Lett. 84, 2799 (2004); http://dx.doi.org/10.1063/1.1699477 (3 pages) | Cited 32 times

Online Publication Date: 7 April 2004

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Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti3Si0.5Ge0.5C2 sample. Up to a pressure of 53 GPa, no phase transformations were observed. As for the isostructural hexagonal Ti3SiC2, the compressibility along the c axis was greater than along a. The bulk modulus is 183±4 GPa with a pressure derivative of 3.4±0.2. This work shows that the replacement of Si by Ge in Ti3SiC2 results in a systematic decrease in the bulk moduli. © 2004 American Institute of Physics.
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62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.50.-p High-pressure effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
61.66.Fn Inorganic compounds

Effects of spacer thickness on quantum efficiency of the solar cells with embedded Ge islands in the intrinsic layer

Arnold Alguno, Noritaka Usami, Toru Ujihara, Kozo Fujiwara, Gen Sazaki, Kazuo Nakajima, Kentaro Sawano, and Yasuhiro Shiraki

Appl. Phys. Lett. 84, 2802 (2004); http://dx.doi.org/10.1063/1.1697632 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2004

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We report on the effects of spacer thickness on the external quantum efficiency (EQE) of the solar cells with Ge islands embedded into the intrinsic region of the Si-based p-i-n diode. The EQE response of the solar cells in the near-infrared region is dependent on the spacer thickness that separates the layers of self-assembled Ge islands. It was found that the EQE response has an optimum value when the spacer thickness can sustain a good vertical ordering of islands. On the other hand, random nucleation of islands due to a thicker spacer layer exhibits an inferior EQE response. Furthermore, a drastic decrease of the EQE response of the solar cells for a thinner spacer layer was observed. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.55.Ap Elemental semiconductors

Effects of electron concentration on the optical absorption edge of InN

J. Wu, W. Walukiewicz, S. X. Li, R. Armitage, J. C. Ho, E. R. Weber, E. E. Haller, Hai Lu, William J. Schaff, A. Barcz, and R. Jakiela

Appl. Phys. Lett. 84, 2805 (2004); http://dx.doi.org/10.1063/1.1704853 (3 pages) | Cited 87 times

Online Publication Date: 7 April 2004

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InN films with free electron concentrations ranging from mid-1017 to mid-1020 cm−3 have been studied using optical absorption, Hall effect, and secondary ion mass spectrometry. The optical absorption edge covers a wide energy range from the intrinsic band gap of InN of about 0.7 to about 1.7 eV which is close to the previously accepted band gap of InN. The electron concentration dependence of the optical absorption edge energy is fully accounted for by the Burstein–Moss shift. Results of secondary ion mass spectrometry measurements indicate that O and H impurities cannot fully account for the free electron concentration in the films. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.-a Thin film structure and morphology
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.61.Ga II-VI semiconductors

Optical transition in discrete levels of Si quantum dots

X. L. Wu and F. S. Xue

Appl. Phys. Lett. 84, 2808 (2004); http://dx.doi.org/10.1063/1.1704872 (3 pages) | Cited 16 times

Online Publication Date: 7 April 2004

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Photoluminescence (PL) measurements have been carried out on Si quantum dots (QDs) with sizes of 2–4 nm embedded in Si oxide films. Conspicuous multiple PL peaks separated in energy by up to 104 meV are observed and attributed to optical transitions in discrete energy levels of Si QDs. A band-mixing model of direct and indirect gaps in a nanometer environment consisting of nc-Si core and SiOx surface layer has been proposed for calculation of electronic states. Good agreement is achieved between the observed PL peaks and calculated results. This work provides a path for realizing Si QD laser. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Ap Elemental semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots

Fatigue failure mechanisms of single-walled carbon nanotube ropes embedded in epoxy

Y. Ren, Y. Q. Fu, K. Liao, F. Li, and H. M. Cheng

Appl. Phys. Lett. 84, 2811 (2004); http://dx.doi.org/10.1063/1.1703837 (3 pages) | Cited 15 times

Online Publication Date: 7 April 2004

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In this work, fatigue failure mechanisms of single-walled carbon nanotube (SWCNT) bundles embedded in epoxy matrix under repeated tensile load were studied. Observed damage and failure modes include: (1) splitting of SWCNT bundles, (2) kink formation and subsequent failure in SWCNTs, and (3) fracture of SWCNT bundles. Patterns of crack propagation under tension in SWCNTs were studied by molecular mechanics simulations, where defect-free SWCNTs and SWCNTs with two different modes of Stone–Wales defects were studied. It is demonstrated by the results of molecular mechanics simulation that the observed fracture surfaces of SWCNT can be reproduced reasonably well, suggesting possible fatigue failure mechanisms of SWCNT in the composite. © 2004 American Institute of Physics.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
61.46.-w Structure of nanoscale materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Strain relaxation and its effect in exciton resonance energies of epitaxial ZnO layers grown on 6H-SiC substrates

A. B. M. Almamun Ashrafi, Naguyen Thanh Binh, Bao-ping Zhang, and Yusaburo Segawa

Appl. Phys. Lett. 84, 2814 (2004); http://dx.doi.org/10.1063/1.1705722 (3 pages) | Cited 16 times

Online Publication Date: 7 April 2004

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Thickness-dependent strain relaxation and its role on exciton resonance energies of epitaxial ZnO layers grown on 6H-SiC substrates have been studied. The magnitudes of strain were determined experimentally by x-ray diffraction measurements. The strain ratios under biaxial stresses (Δc/c0)/(Δa/a0) of epitaxial ZnO layers grown on SiC and Al2O3 substrates were estimated to be 0.38 and 0.50, respectively. The strain-induced band shift δEA/δεzz for ZnO/SiC and ZnO/Al2O3 heterostructures was analyzed by photoluminescence with the values of 13.1 and 14.6 eV, respectively. These comparative strain-induced band shifts, as well as Poisson ratios, evidenced the role of lattice deformation kinetics induced by different lattice mismatches in the ZnO/SiC and ZnO/Al2O3 heterostructures. © 2004 American Institute of Physics.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
78.66.Hf II-VI semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.Gy Mechanical properties; surface strains
78.55.Et II-VI semiconductors
62.20.D- Elasticity

Narrow photoluminescence linewidth (<17 meV) from highly uniform self-assembled InAs/GaAs quantum dots grown by low-pressure metalorganic chemical vapor deposition

Tao Yang, Jun Tatebayashi, Shiro Tsukamoto, Masao Nishioka, and Yasuhiko Arakawa

Appl. Phys. Lett. 84, 2817 (2004); http://dx.doi.org/10.1063/1.1711163 (3 pages) | Cited 19 times

Online Publication Date: 7 April 2004

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We report highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3 μm, grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition. By optimizing the InAs growth rate and capping the QDs with GaAs using triethylgallium as a gallium source, we have achieved a narrow photoluminescence (PL) inhomogeneous linewidth of 16.5 meV (at 7 K) from QDs with a density of 1.7×1010 cm−2. Furthermore, we show by temperature-dependent PL measurements that the QDs exhibit almost no dependence of linewidth on temperature due to their high uniformity. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.16.Dn Self-assembly

Domain wall displacement induced by subnanosecond pulsed current

C. K. Lim, T. Devolder, C. Chappert, J. Grollier, V. Cros, A. Vaurès, A. Fert, and G. Faini

Appl. Phys. Lett. 84, 2820 (2004); http://dx.doi.org/10.1063/1.1711168 (3 pages) | Cited 51 times

Online Publication Date: 7 April 2004

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We show that a single current pulse as short as 0.4 ns can trigger domain wall (DW) displacement in spin-valve stripes of 0.3 μm width inserted into a coplanar waveguide. The experiments were carried out with varying current pulse amplitude, duration, polarity, and applied static magnetic field. In zero field, DW displacement occurs in the same direction as the conduction electron current. In finite applied field, the direction of DW displacement is that favored by the field orientation. In both cases, the DW displacement occurs only above a critical current density jc of the order of 106 A/cm2. The distance traveled by the DW along the stripe increases with the current pulse amplitude and applied field strength, but it does not depend on the pulse duration between 0.4 and 2 ns. © 2004 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
85.75.Bb Magnetic memory using giant magnetoresistance
75.47.De Giant magnetoresistance

Fluctuation microscopy studies of medium-range ordering in amorphous diamond-like carbon films

Xidong Chen, J. P. Sullivan, T. A. Friedmann, and J. Murray Gibson

Appl. Phys. Lett. 84, 2823 (2004); http://dx.doi.org/10.1063/1.1713048 (3 pages) | Cited 22 times

Online Publication Date: 7 April 2004

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In this letter, we report fluctuation microscopy studies of medium-range ordering in amorphous diamond-like carbon films and the effect of annealing on this ordering. Annealed and unannealed diamond-like carbon films have almost identical short-range order. Our fluctuation microscopy results, however, indicate the presence of medium range order or clustering in the films on a lateral length scale that exceeds 1 nm. Within the clustered regions, the dominant local ordering appears to be diamond-like, and graphite-like ordering is not observed. Thermal annealing up to 600 °C leads to an increase in diamond-like clustering with no onset of graphite-like clustering. However, after high temperature annealing up to 1000 °C, graphite-like clustering becomes apparent as a result of the conversion of diamond-like carbon to graphite-like carbon. The results on the as-deposited films and films annealed up to 600 °C suggest that a spontaneous medium range ordering process occurs in diamond-like carbon films during and subsequent to film growth, and this may play an important role in stress relaxation. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.37.-d Microscopy of surfaces, interfaces, and thin films
61.43.Er Other amorphous solids
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
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Magnetic imprinting of submicron ferromagnetic wires on a diluted magnetic semiconductor quantum well

H. Schömig, A. Forchel, S. Halm, G. Bacher, J. Puls, and F. Henneberger

Appl. Phys. Lett. 84, 2826 (2004); http://dx.doi.org/10.1063/1.1695199 (3 pages) | Cited 13 times

Online Publication Date: 7 April 2004

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Hybrid structures consisting of submicron ferromagnetic dysprosium wires on a diluted magnetic semiconductor quantum well have been prepared and investigated by micro-magnetoluminescence spectroscopy. A magnetic field dependent redshift of the semiconductor band gap just beneath the dysprosium wires with respect to a reference area clearly demonstrates the impact of the magnetic fringe field on the optical properties of the underlying semiconductor. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Cc Other ferromagnetic metals and alloys
78.67.De Quantum wells
68.65.Fg Quantum wells
78.20.Ls Magneto-optical effects
78.55.Et II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Hall mobility of narrow Si0.2Ge0.8–Si quantum wells on Si0.5Ge0.5 relaxed buffer substrates

S. Tsujino, C. V. Falub, E. Müller, M. Scheinert, L. Diehl, U. Gennser, T. Fromherz, A. Borak, H. Sigg, D. Grützmacher, Y. Campidelli, O. Kermarrec, and D. Bensahel

Appl. Phys. Lett. 84, 2829 (2004); http://dx.doi.org/10.1063/1.1695102 (3 pages) | Cited 17 times

Online Publication Date: 7 April 2004

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We studied in-plane transport of a two-dimensional hole gas in modulation-doped p-Si0.2Ge0.8 quantum wells (QWs) on Si0.5Ge0.5 relaxed buffer substrates with thicknesses L between 2.5 and 7 nm. We found that interface roughness scattering limits the low-temperature mobility μ of the samples with L between 2.5 and 4.5 nm. The interface roughness parameters were evaluated by fitting the experiment with the calculated μ limited by interface roughness scattering. We found that the obtained parameters were consistent with the values estimated from x-ray reflectivity and the transmission electron micrograph of the samples. When L is increased from 4.5 to 7 nm, μ increases only gradually and the highest μ of 0.44 m2/V s was observed for 7-nm-thick QWs. The scattering by defects, interface charge, and strain fluctuation are discussed as possible additional mobility-limiting mechanisms. © 2004 American Institute of Physics.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
68.35.Ct Interface structure and roughness
73.61.Cw Elemental semiconductors

Hopping transport in TiO2:Co: A signature of multiphase behavior

R. J. Kennedy, P. A. Stampe, Erhong Hu, Peng Xiong, Stephan von Molnár, and Yan Xin

Appl. Phys. Lett. 84, 2832 (2004); http://dx.doi.org/10.1063/1.1704857 (3 pages) | Cited 24 times

Online Publication Date: 7 April 2004

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TiO2:Co films have been grown in the rutile phase under varying oxygen growth pressures. Detailed microstructural analysis using transmission electron microscopy shows that reduced growth pressure increases the presence of cobalt clusters. The resistivity is found to follow a log(ρ) ∼ T−1/2 dependence over a wide temperature range. This behavior is characteristic of hopping transport in multiphase systems and implies the presence of cobalt clustering. Thus, transport measurements are shown to be sensitive to the appearance of metallic clusters in these systems and suggest a rapid method for determing the presence of clustering in these and other magnetically doped semiconductor systems. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
72.20.Ee Mobility edges; hopping transport
72.80.Jc Other crystalline inorganic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
81.15.Fg Pulsed laser ablation deposition
61.72.S- Impurities in crystals
73.61.Le Other inorganic semiconductors

Temperature-dependent characteristics of Pt Schottky contacts on n-type ZnO

K. Ip, Y. W. Heo, K. H. Baik, D. P. Norton, S. J. Pearton, S. Kim, J. R. LaRoche, and F. Ren

Appl. Phys. Lett. 84, 2835 (2004); http://dx.doi.org/10.1063/1.1705726 (3 pages) | Cited 37 times

Online Publication Date: 7 April 2004

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The Schottky barrier height of Pt contacts on n-type (n ∼ 1016 cm−3) thin film ZnO deposited by pulsed laser deposition was obtained from current–voltage measurements as a function of temperature. The resulting values ranged from 0.61±0.04 eV at 25 °C to 0.46±0.06 eV at 100 °C with saturation current densities of 1.5×10−4 A cm−2 (25 °C) to 6.0×10−2 A cm−2 (100 °C), respectively. The reverse current magnitude was larger than predicted by thermionic emission alone. The measured barrier height for Pt on ZnO is similar to the value reported for both Au and Ag rectifying contacts on this material. © 2004 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition

Influence of surface and grain-boundary scattering on the resistivity of copper in reduced dimensions

W. Wu, S. H. Brongersma, M. Van Hove, and K. Maex

Appl. Phys. Lett. 84, 2838 (2004); http://dx.doi.org/10.1063/1.1703844 (3 pages) | Cited 53 times

Online Publication Date: 7 April 2004

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We examine the influence of surface and grain-boundary scattering on the total electrical resistivity of copper as dimensions are reduced close to the bulk electron mean free path (39 nm). Through resistivity and grain size characterization on copper wires with sizes down to 95×130 nm2 in a temperature range of 4.2 to 293 K, it was found that the influence of surface scattering is less than previously speculated, while grain-boundary scattering is dominant. A reduction of the background scattering length due to small grains accounts for the observed behavior. The reflection coefficient varies as expected from impurity enrichment in the grain boundaries. © 2004 American Institute of Physics.
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73.63.Nm Quantum wires

Structure and electrical activity of rare-earth dopants in GaN

J.-S. Filhol, R. Jones, M. J. Shaw, and P. R. Briddon

Appl. Phys. Lett. 84, 2841 (2004); http://dx.doi.org/10.1063/1.1710710 (3 pages) | Cited 40 times

Online Publication Date: 7 April 2004

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Density functional theory is used to investigate Eu, Er, and Tm rare earth (RE) impurities in GaN, paying particular attention to their structure, energetics, and electronic properties. The most stable site is when the RE is located at a Ga substitutional site but none of the defects possess deep energy levels. RE–VN close pairs are stable at temperatures greater than 1000 °C for 1 at. % RE doping and possess shallow levels possibly exciting intra-f luminescence in the visible. RE–VGa and RE-interstitial defects possess deep levels which exclude them as sources for visible RE-related luminescence. © 2004 American Institute of Physics.
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61.72.Bb Theories and models of crystal defects
61.72.uj III-V and II-VI semiconductors

InAs/GaP/InGaP high-temperature power Schottky rectifier

A. Chen and J. M. Woodall

Appl. Phys. Lett. 84, 2844 (2004); http://dx.doi.org/10.1063/1.1711180 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2004

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An InAs/GaP/InGaP rectifier has been fabricated using a semiconductor-semiconductor “Schottky” junction to utilize the thermal stability of the semiconductor-semiconductor interface. The InAs/GaP/InGaP system demonstrates rectifying characteristics with an ideality factor of 2.3 and a current–voltage extracted barrier height of 0.96 eV. It exhibits low reverse bias leakage current and achieves breakdown electric field of 0.6 MV/cm. The InAs/GaP/InGaP system maintains the rectifying characteristics up to 600 °C. Further improvement of the thermal stability is expected to be achieved by reducing the diffusion of Si dopant atoms across the InAs/GaP interface at high temperature. © 2004 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices
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Magnetic phase diagram of two identical coupled nanomagnets

D. C. Worledge

Appl. Phys. Lett. 84, 2847 (2004); http://dx.doi.org/10.1063/1.1695632 (3 pages) | Cited 48 times

Online Publication Date: 7 April 2004

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The theoretical magnetic phase diagram of two identical nanomagnets is presented. The nanomagnets are assumed to be single domains in the shape of very flat ellipsoids, in order to approximate technologically relevant thin-film samples patterned into ellipses. The phase diagram is organized by type of easy axis hysteresis loop and takes into account, using exact closed analytic expressions, the effect of thickness, width, length, magnetization, and uniaxial intrinsic anisotropy of the two nanoparticles, and exchange coupling between the two particles. Two phase diagrams are presented for the two cases where the intrinsic anisotropy is parallel to either the long or short in-plane axis of the nanoparticles. Complete descriptions of all hysteresis loops and exact analytic formulas for all switching fields are given. © 2004 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Gw Magnetic anisotropy
75.40.Mg Numerical simulation studies

Fe- and Ni-doped TiO2 thin films grown on LaAlO3 and SrTiO3 substrates by laser ablation

Nguyen Hoa Hong, W. Prellier, Joe Sakai, and Awatef Hassini

Appl. Phys. Lett. 84, 2850 (2004); http://dx.doi.org/10.1063/1.1695103 (3 pages) | Cited 32 times

Online Publication Date: 7 April 2004

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Room temperature ferromagnetic Fe- and Ni-doped TiO2 thin films were grown by the laser ablation on both LaAlO3 and SrTiO3 substrates. Most of the films are pure anatase, and only the films of Ni content of 3.6% and 4.6% are rutile. Films on LaAlO3 substrates are more crystallized than films on SrTiO3 substrates resulting from the lattice mismatch. Our magnetic measurements also suggest that the ferromagnetism in Fe/Ni:TiO2 films is not due to Fe/Ni segregations but due to Fe/Ni:TiO2 matrices. © 2004 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
68.55.A- Nucleation and growth
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.S- Impurities in crystals
64.70.K- Solid-solid transitions
81.30.Mh Solid-phase precipitation
81.15.Fg Pulsed laser ablation deposition
75.50.Pp Magnetic semiconductors

Magnetic patterning of exchange-coupled multilayers

Vladislav E. Demidov, Dmitry I. Kholin, Sergej O. Demokritov, Burkard Hillebrands, Frederik Wegelin, and Jan Marien

Appl. Phys. Lett. 84, 2853 (2004); http://dx.doi.org/10.1063/1.1699475 (3 pages) | Cited 12 times

Online Publication Date: 7 April 2004

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The local modification of antiferromagnetic (AF) interlayer exchange coupling by focused ion-beam irradiation has been studied experimentally in the epitaxial Fe/Cr/Fe(001) trilayer systems. Square ferromagnetic (FM) areas of 200×200 μm2 were created in the initially AF trilayer by ion irradiation with a fluence of 1015 ions/cm2. It was found, that in the range of the external magnetic field of about ±200 Oe, the change of magnetic properties at the boundaries separating FM and AF areas occurs within distances of less than 200 nm. This fact allows the use of the technique for magnetic patterning of antiferromagnetically coupled trilayers on the submicrometer scale. © 2004 American Institute of Physics.
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75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.80.Jh Ion radiation effects
68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)

Observation of room-temperature magnetoelectric coupling in pulsed-laser-deposited Bi0.6Tb0.3La0.1FeO3 thin films

V. R. Palkar, K. Ganesh Kumara, and S. K. Malik

Appl. Phys. Lett. 84, 2856 (2004); http://dx.doi.org/10.1063/1.1695204 (3 pages) | Cited 38 times

Online Publication Date: 7 April 2004

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Magnetoelectrics, characterized by simultaneous ferroelectric and magnetic ordering, have potential applications in information storage, sensors, etc. However, there are very few materials exhibiting the coexistence of ferroelectric and ferromagnetic ordering at room temperature. Hence, in normal practice, desired magnetoelectric effect is achieved by growing heterostructures of ferroelectric and magnetic materials. Realization of heterostructures with desired properties is not only difficult but also involves complicated lengthy procedures. BiFeO3 is weakly ferroelectric and antiferromagnetic at and above room temperature. We have been successful in enhancing both the ferroelectric and the magnetic properties of BiFeO3 by partial substitution of Tb at Bi site. Thin films of Bi0.6Tb0.3La0.1FeO3, integrated on Si/SiO2/TiO2/Pt substrate by using pulsed laser deposition technique, show good ferroelectric and magnetic properties and also coupling between them. Single step growth of thin films with desired magnetoelectric properties is certainly a cost effective, reliable, and simple alternative to heterostructures. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
75.80.+q Magnetomechanical effects, magnetostriction
77.80.Dj Domain structure; hysteresis
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Superconducting properties of the 18 K phase in yttrium sesquicarbide system

T. Nakane, T. Mochiku, H. Kito, J. Itoh, M. Nagao, H. Kumakura, and Y. Takano

Appl. Phys. Lett. 84, 2859 (2004); http://dx.doi.org/10.1063/1.1702132 (3 pages) | Cited 12 times

Online Publication Date: 7 April 2004

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The metastable phase of an yttrium sesquicarbide compound, which was recently reported as having a superconductive phase with a Tc of 18 K (18 K phase), was prepared under high pressure from the nominal composition of Y2C3 and Y2C2.9B0.1 in order to investigate this phase. We have succeeded in reproduction, and in the transport measurement for this 18 K phase. It is considered that the reason for the higher Tc than the 11.5 K reported previously is not the small amount of B as the impurity element from the BN crucible. The Bc2 at 0 K estimated from the resistivity data for the 18 K phase seems to be over 30 T. It means that the Tc and the Bc2 of the 18 K phase are as high as those of the general A15-type intermetallic compounds. © 2004 American Institute of Physics.
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74.10.+v Occurrence, potential candidates
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities

Spiral exchange interaction in diluted magnetic semiconductor junction

Shih-Jye Sun, Song-Shien Cheng, and Hsiu-Hau Lin

Appl. Phys. Lett. 84, 2862 (2004); http://dx.doi.org/10.1063/1.1705725 (3 pages) | Cited 4 times

Online Publication Date: 7 April 2004

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We studied the exchange interactions mediated by polarized itinerant carriers in diluted magnetic semiconductor (DMS) junction. In contrast to the ordinary Ruderman–Kittel–Kasuya–Yosida oscillations, the induced moment possesses an interesting spiral motion, accompanied by angular oscillations. The spiral motion remains robust in the entire T<Tc regime while the oscillatory motion gets enhanced as T→Tc. To explore the phenomena, it is proposed that a ferromagnet/DMS/ferromagnet junction would bring out interesting spin-dependent transport properties and possible applications in spintronics. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.30.Et Exchange and superexchange interactions
72.25.Rb Spin relaxation and scattering
75.30.Cr Saturation moments and magnetic susceptibilities
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.25.Dc Spin polarized transport in semiconductors

In situ magnetoresistance of Ni nanocontacts

C.-S. Yang, C. Zhang, J. Redepenning, and B. Doudin

Appl. Phys. Lett. 84, 2865 (2004); http://dx.doi.org/10.1063/1.1705723 (3 pages) | Cited 18 times

Online Publication Date: 7 April 2004

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Magnetoresistance properties of Ni nanocontacts in the ballistic quantum regime are investigated in situ during closure and opening of electrochemically grown planar electrodes. The magnitude of conductance change when sweeping the magnetic field is of the order of the quantum conductance e2/h for conductance values spanning 1–100 quanta. The relative orientation of electric current and applied magnetic field changes the magnetoresistance sign, with symmetry properties reminiscent of bulk anisotropy magnetoresistance. Ex situ investigations of samples of higher conductance values, of the order of 1000 quanta, unambiguously show the analogy with bulk anisotropy magnetoresistance. © 2004 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.63.Rt Nanoscale contacts
75.30.Gw Magnetic anisotropy
82.45.Fk Electrodes
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Phosphorus ion implantation and POCl3 doping effects of n+-polycrystalline-silicon/high-k gate dielectric (HfO2 and Al2O3) films

Chihoon Lee, Jihoon Choi, Moonju Cho, Doo Seok Jeong, Cheol Seong Hwang, and Hyeong Joon Kim

Appl. Phys. Lett. 84, 2868 (2004); http://dx.doi.org/10.1063/1.1697646 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2004

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Phosphorus (P)-doped polycrystalline-silicon gate/HfO2 or HfO2–Al2O3/p-type Si (100) metal–oxide–semiconductor capacitors were fabricated using either a POCl3 diffusion or an ion implantation technique to investigate the relationship between P penetration and the electrical properties of the high-k gate dielectric stacks. The HfO2–Al2O3 bilayer showed higher P diffusion blocking properties as a result of the 4.1-nm-thick amorphous interface layer including Al2O3 (or Al-silicate). The P ion-implanted sample with the HfO2–Al2O3 bilayer sample had the smallest leakage current density of −8.8×10−10 A/cm2 at −1 V, which was due to the lower P penetration, and the higher trap depth of approximately 1.3±0.02 eV compared to 0.9±0.02 eV of the sample with only HfO2. However, the P doping by POCl3 diffusion was too excessive and only very leaky devices were produced. © 2004 American Institute of Physics.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
61.72.up Other materials
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