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6 Mar 2006

Volume 88, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 103107 (2006); http://dx.doi.org/10.1063/1.2182096 (3 pages)

A. B. Djurišić, Y. H. Leung, K. H. Tam, L. Ding, W. K. Ge, H. Y. Chen, and S. Gwo
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Optical properties of nanocrystalline diamond thin films

P. Achatz, J. A. Garrido, M. Stutzmann, O. A. Williams, D. M. Gruen, A. Kromka, and D. Steinmüller

Appl. Phys. Lett. 88, 101908 (2006); http://dx.doi.org/10.1063/1.2183366 (3 pages) | Cited 38 times

Online Publication Date: 8 March 2006

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The optical properties of nanocrystalline diamond films grown from a hydrogen-rich CH4/H2 gas phase by hot filament chemical vapor deposition, as well as from an argon-rich Ar/CH4 gas phase by microwave plasma enhanced chemical vapor deposition, are reported. The influence of nitrogen incorporation on the optical absorption is investigated. The diamond films are characterized by photothermal deflection spectroscopy and temperature dependent spectrally resolved photoconductivity. An onset of absorption at about 0.8 eV in undoped films is attributed to transitions from π to π states introduced into the band gap by the high amount of sp2 bonded carbon at the grain boundaries. Incorporation of nitrogen leads to a strong absorption in the whole energy spectrum, as a result of the increasing number of sp2 carbon atoms. The effect of surface states has been observed in the high energy region of the spectrum. Transitions to the conduction band tail and photothermal ionization processes account for the observed onset at 4.4 eV. Photocurrent quenching at about 3.3 eV is observed in the case of samples grown from a hydrogen-rich CH4/H2 gas phase.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
73.61.Cw Elemental semiconductors
61.72.Mm Grain and twin boundaries
73.20.At Surface states, band structure, electron density of states
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Straining of monocrystalline silicon thin films with the use of porous silicon as stress generating nanomaterial

O. Marty, T. Nychyporuk, J. de la Torre, V. Lysenko, G. Bremond, and D. Barbier

Appl. Phys. Lett. 88, 101909 (2006); http://dx.doi.org/10.1063/1.2179620 (3 pages) | Cited 12 times

Online Publication Date: 8 March 2006

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A simple and low cost technological approach for the straining of thin crystalline silicon (Si) films using porous silicon (PS) as stress generating nanomaterial is reported. Structural analysis of the PS/Si structures is performed by transmission electron microscopy. Raman scattering spectroscopy is used for the evaluation of stress and strain values in the strained thin Si films. Depending on the thickness of the strained Si films, the maximum strain values are found to be in a range from 1% to 1.4%. Various modifications of electronic properties of the strained Si films are observed by photoluminescence spectroscopy. For example, strain induced redshift of the Si energy band gap and splitting of the valence band are detected.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
73.61.Cw Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Passivation of an isoelectronic impurity by atomic hydrogen: The case of ZnTe:O

Marco Felici, Antonio Polimeni, Mario Capizzi, Y. Nabetani, T. Okuno, K. Aoki, T. Kato, T. Matsumoto, and T. Hirai

Appl. Phys. Lett. 88, 101910 (2006); http://dx.doi.org/10.1063/1.2183809 (3 pages) | Cited 9 times

Online Publication Date: 8 March 2006

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We investigated the optical properties of ZnTe:O/GaAs before and after atomic hydrogen irradiation. Oxygen incorporation gives rise to energy levels associated with single O atoms, O–O pairs, and O clusters, and to a blueshift of the energy gap of the material with respect to that of pure ZnTe/GaAs. All of these effects disappear progressively after irradiation with H, which also leads to an increase in the tensile strain of the epilayer. These observations provide experimental evidence of H-induced passivation of an isoelectronic impurity in II–VI alloys.
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61.72.uj III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
61.80.Lj Atom and molecule irradiation effects
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

Ab initio calculations for properties of MAX phases Ti2TlC, Zr2TlC, and Hf2TlC

J. A. Warner, S. K. R. Patil, S. V. Khare, and K. C. Masiulaniec

Appl. Phys. Lett. 88, 101911 (2006); http://dx.doi.org/10.1063/1.2182009 (3 pages) | Cited 7 times

Online Publication Date: 8 March 2006

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Using ab initio calculations we have computed the lattice constants, bulk moduli, and local and total density of states of the MAX phases, Ti2TlC, Zr2TlC, and Hf2TlC in the hexagonal P63/mmc space group. The results for lattice constants are within 2% of experimental results. The bulk moduli are predicted to be 125, 120, and 131 GPa, respectively. These are the lowest values of bulk moduli among all MAX phases studied to date. The electronic density of states shows that all three materials are conducting. These low values of their bulk moduli are attributed to weak metal M (M = Ti,Zr,Hf) bonding with the A element thallium.
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71.15.-m Methods of electronic structure calculations
61.66.Fn Inorganic compounds
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
71.20.Ps Other inorganic compounds
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Thermal stability of a HfO2/SiO2 interface

Nobuyuki Ikarashi, Koji Watanabe, Koji Masuzaki, and Takashi Nakagawa

Appl. Phys. Lett. 88, 101912 (2006); http://dx.doi.org/10.1063/1.2182023 (3 pages) | Cited 7 times

Online Publication Date: 8 March 2006

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Using high-angle annular-dark-field scanning transmission electron microscopy, we showed how annealing at 1000 °C changes the chemical composition distribution at a HfO2/SiO2 interface. The observed change in the distribution was analyzed in terms of Hf diffusion in SiO2; the diffusion coefficient was estimated to be 2.5×10−18 cm2/s. This diffusion coefficient indicates that the high-temperature annealing, such as that in the conventional dopant activation process used to fabricate semiconductor devices, barely changes the chemical composition distribution at the HfO2/SiO2 interface.
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81.40.Gh Other heat and thermomechanical treatments
66.30.-h Diffusion in solids
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
82.80.-d Chemical analysis and related physical methods of analysis

Raman study of N+-implanted ZnO

J. B. Wang, H. M. Zhong, Z. F. Li, and Wei Lu

Appl. Phys. Lett. 88, 101913 (2006); http://dx.doi.org/10.1063/1.2185261 (3 pages) | Cited 31 times

Online Publication Date: 9 March 2006

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Raman scattering has been used to study the influence of nitrogen, a potential acceptor in ZnO, on the lattice dynamics of ZnO. It is found that N+ implantation increased the lattice disorder and induced some vibration modes to be Raman active at 275, 504, and 644 cm−1, respectively. Based on theoretical and experimental study, the origin of the additional Raman peak at about 275 cm−1 is attributed to the vibration of Zn atoms, where part of its first nearest neighbor O atoms are replaced by N atoms in the crystal lattice.
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78.30.Fs III-V and II-VI semiconductors
63.20.Pw Localized modes
61.72.S- Impurities in crystals

Giant enhancement of luminescence induced by second-harmonic surface plasmon resonance

H. Y. Lin and Y. F. Chen

Appl. Phys. Lett. 88, 101914 (2006); http://dx.doi.org/10.1063/1.2183819 (3 pages) | Cited 5 times

Online Publication Date: 9 March 2006

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Strong ultraviolet luminescence having intensity comparable with device-quality GaN epifilms has been observed in Au nanoparticles. It is identified that the luminescence involves radiative recombination of electrons in band 6 (sp conduction band) with holes in band 4 (secondary top d band), near the L symmetry point. We show that the strong emission is a consequence of the second-harmonic surface plasmon resonance (SHSPR), which is an inherent nature of metallic nanoparticles with high density of surface plasmons. The newly discovered SHSPR is very different from the conventional second-harmonic generation (SHG). In the conventional SHG, it requires an intense incident laser to generate two-photon absorption and radiation. However, for the SHSPR discussed here, we only need a weak pumping source to trigger the second-harmonic absorption of very dense surface plasmons in Au nanoclusters. In addition to Au nanoparticles, we demonstrate that SHSPR provides a very efficient way to enhance the luminescence of a material incorporated with metal nanoparticles. As an example, incorporation of Au nanoparticles into SiO2 nanoparticles can enhance the luminescence intensity by two orders of magnitude. We thus point out that SHSPR can serve as one of the underlying mechanisms responsible for surface-enhanced nonlinear optical phenomena.
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78.66.Bz Metals and metallic alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
78.68.+m Optical properties of surfaces
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations

Laser-based measurement of elastic and mechanical properties of layered polycrystalline silicon structures with projection masks

A. Bennis, A. M. Lomonosov, Z. H. Shen, and P. Hess

Appl. Phys. Lett. 88, 101915 (2006); http://dx.doi.org/10.1063/1.2181187 (3 pages) | Cited 6 times

Online Publication Date: 9 March 2006

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The Young’s modulus, density, and thickness of a 20.3 μm polycrystalline silicon layer deposited on a silicon wafer covered with a ∼ 2.5-μm-thick silicon-oxide interface layer were measured using projection masks to generate surface acoustic waves (SAWs) with higher harmonics approaching 600 MHz. The propagating SAW train was detected with a laser probe-beam-deflection setup. The characteristic strongly nonlinear dispersion effect allowed the simultaneous extraction of several unknown film properties. The dispersion was described theoretically by the boundary element method model. A Young’s modulus of 152 GPa, a density of 2.25 g/cm3, and a film thickness of 20.3 μm were determined for the polycrystalline silicon film.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.35.Iv Acoustical properties

Thermally stable optical characteristics of sol-gel hybrid material films

Abderrafia Moujoud, Woo-Soo Kim, Byeong-Soo Bae, and Sang-Yung Shin

Appl. Phys. Lett. 88, 101916 (2006); http://dx.doi.org/10.1063/1.2186111 (3 pages) | Cited 1 time

Online Publication Date: 10 March 2006

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Thermo-optic (TO) coefficients for transverse-electric and transverse-magnetic polarized light (dnTE/dT and dnTM/dT, respectively) were measured for sol-gel-derived, new organic-inorganic hybrid materials. The absolute values of dnTE/dT are comparable to those of dnTM/dT, indicating low anisotropy (dnTE/dT-dnTM/dT) in the TO coefficients. The low anisotropy is evidenced by the very small polarization dependence of the refractive index (nTE−nTM). The high stability of these materials is consistent with a high glass transition temperature (Tg>150 °C), and evidenced by an absence of hysteresis in the refractive index and in film thickness during temperature cycling between 30 and 150 °C.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
42.70.-a Optical materials

In situ monitoring of internal strain and height of InAs nanoislands grown on GaAs(001)

Masamitu Takahasi, Toshiyuki Kaizu, and Jun’ichiro Mizuki

Appl. Phys. Lett. 88, 101917 (2006); http://dx.doi.org/10.1063/1.2186106 (3 pages) | Cited 9 times

Online Publication Date: 10 March 2006

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A monitoring technique for molecular beam epitaxial growth of InAs/GaAs(001) nanoislands is presented. With the help of synchrotron radiation, x-ray diffraction intensity mapping in reciprocal space has been measured during growth. The internal strain distribution and height of the Stranski-Krastanov islands were monitored at a temporal resolution of 9.6 s. The relaxation process of internal strain inside the Stranski-Krastanov islands displayed significant dependence on the growth temperature.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Alternating layers of vacancy-type and interstitial-type defects in Ge ion implanted silicon

R. Kögler, A. Peeva, A. Mücklich, F. Eichhorn, and W. Skorupa

Appl. Phys. Lett. 88, 101918 (2006); http://dx.doi.org/10.1063/1.2186068 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2006

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The defect structure of Ge-implanted and annealed silicon was investigated. A stacked structure of alternating layers of vacancy-type defects (cavities) and interstitial-type defects (dislocation loops) was detected. These defects form a substructure within the basic dual structure consisting of a near surface vacancy-dominated and a deeper interstitial-dominated region. The appearance of vacancy clusters in the interstitial-dominated region and of dislocation loops in the vacancy-dominated region indicates significant vacancy-vacancy and interstitial-interstitial clustering in addition to the vacancy-interstitial defect recombination. The observed defect structure is in contrast to the widely accepted +1 model which predicts the complete local recombination of ion-generated vacancies and interstitials. Limits of the +1 model are discussed.
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61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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Charge transport across pressure-laminated thin films of molecularly doped polymers

Richard A. Klenkler, Gu Xu, John F. Graham, and Zoran D. Popovic

Appl. Phys. Lett. 88, 102101 (2006); http://dx.doi.org/10.1063/1.2172142 (3 pages) | Cited 3 times

Online Publication Date: 6 March 2006

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Discrete interfaces between successive layers in an organic semiconducting device simplify any examination of interface barriers for charge transport. To form discrete interfaces between organic layers we propose lamination as an alternate approach to physical vapor deposition. Transient photocurrent measurements as a function of pressure, thickness, and electric field were performed on cells of 1,1-bis[(di-4-tolylamino)phenyl]-cyclohexane (TAPC), N,N-bis(3,4-dimethylphenyl)-4-aminobiphenyl (DMPAB), and N,N’-diphenyl-N,N’-bis(3-methylphenyl)-[1,1’-biphenyl]-4,4’-diamine (TPD). It was found that, in the range 0.8–3.0 MPa, a pressure-laminated interface between two identical materials causes no measurable perturbation to charge transport. This justifies the use of pressure lamination to study interfaces between nonidentical layers.
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85.30.-z Semiconductor devices
73.61.Ph Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
62.50.-p High-pressure effects in solids and liquids

Conductivity of single-stranded and double-stranded deoxyribose nucleic acid under ambient conditions: The dominance of water

T. Kleine-Ostmann, C. Jördens, K. Baaske, T. Weimann, M. Hrabe de Angelis, and M. Koch

Appl. Phys. Lett. 88, 102102 (2006); http://dx.doi.org/10.1063/1.2182027 (3 pages) | Cited 27 times

Online Publication Date: 6 March 2006

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We investigate the conductivity of single-stranded and double-stranded herring deoxyribose nucleic acid (DNA) in buffer solution spotted and dried on Au nanocontacts. We find an exponential increase of the conductivity with increasing humidity that is identical for single- and double-stranded DNA within the measurement accuracy. While the small conductivity of dry DNA is comparable to that of a large band-gap semiconductor, we attribute the increase at high humidity levels to water molecules accumulated at the phosphate backbone. For high humidities we observe s-shaped current-voltage characteristics that can be well explained by the dissociation of water attached to the DNA molecules.
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87.14.G- Nucleic acids
87.15.R- Reactions and kinetics

Metal–polymer composite with nanostructured filler particles and amplified physical properties

D. Bloor, A. Graham, E. J. Williams, P. J. Laughlin, and D. Lussey

Appl. Phys. Lett. 88, 102103 (2006); http://dx.doi.org/10.1063/1.2183359 (3 pages) | Cited 15 times

Online Publication Date: 7 March 2006

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The limits of conductivity of a novel elastomeric matrix–nanostructured nickel powder composite are reported. The conductivity falls by a factor of ≥ 2×1014 for compression and by a similar amount in extension. Uncompressed and highly compressed composite displays ohmic behavior but between these limits the current-voltage characteristics are highly nonlinear. The matrix intimately coats the filler so that even above the expected percolation threshold the composite has a very low conductivity. The conductivity of the composite is increased under all mechanical deformations. These and other unusual properties are amplified versions of smaller effects seen in composites containing less highly structured fillers.
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81.40.Rs Electrical and magnetic properties related to treatment conditions
72.80.Tm Composite materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Reactive metal contact at indium–tin–oxide/self-assembled monolayer interfaces

Jeong Ho Cho, Yeong Don Park, Do Hwan Kim, Woong-Kwon Kim, Ho Won Jang, Jong-Lam Lee, and Kilwon Cho

Appl. Phys. Lett. 88, 102104 (2006); http://dx.doi.org/10.1063/1.2183371 (3 pages) | Cited 6 times

Online Publication Date: 8 March 2006

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With the aim of improving the electrical and adhesion properties of the indium–tin–oxide (ITO) electrode/organic interface, we tested Cl- and CF3-terminated self-assembled monolayers (SAMs), which react with the indium atoms of the electrode, and compared the results to those obtained using a CH3-terminated SAM. The contact resistance of the interface between the Cl-terminated surface and the ITO electrode (1.5 kΩ) was found to be much lower than that of the interface between the ITO and the CF3-terminated surface (21.3 kΩ), which can be attributed to the higher dipole moment of the In–Cl complex compared to the In–F complex. In the ITO films deposited on the CH3-terminated surface, the contact resistance (138.0 kΩ) was much higher than those of the reactive metal contacts because the ITO thin film deposited on the CH3-terminated surface does not react with the SAM.
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73.40.Cg Contact resistance, contact potential

Random telegraph signal in nanoscale back-side charge trapping memories

H. Silva and S. Tiwari

Appl. Phys. Lett. 88, 102105 (2006); http://dx.doi.org/10.1063/1.2182070 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2006

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Random telegraph signal (RTS) was observed in the front and back channel source-drain current of nanoscale double-gated back-side charge trapping memories. The front gate dielectric is silicon oxide and the back gate dielectric is a stack of silicon oxide–silicon nitride–silicon oxide (ONO). The structure provides a tool for traps characterization at multiple interfaces and combinations of materials. Bias dependence of RTS due to a trap in the back ONO was measured to determine the position of the trap in the dielectric. The results show that the individual trap is located within the tunneling oxide, 1.3 nm away from the silicon interface. RTS due to traps responsible for the memory properties, located in the silicon nitride or its interface, was not observed.
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84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices

Temperature-dependent strain relaxation of the AlGaN barrier in AlGaN/GaN heterostructures with and without Si3N4 surface passivation

D. J. Chen, K. X. Zhang, Y. Q. Tao, X. S. Wu, J. Xu, R. Zhang, Y. D. Zheng, and B. Shen

Appl. Phys. Lett. 88, 102106 (2006); http://dx.doi.org/10.1063/1.2186369 (3 pages) | Cited 4 times

Online Publication Date: 9 March 2006

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The temperature dependence of strain relaxation in Al0.22Ga0.78N layers, with and without a Si3N4 surface passivation layer, was investigated at temperatures from room temperature to 813 K using high-resolution x-ray diffraction. A small strain relaxation occurs in the unpassivated Al0.22Ga0.78N layers at high temperature. After passivating, an additional in-plane tensile strain and an initial increase of the residual tensile strain with increasing temperature were observed in Al0.22Ga0.78N layers, and at higher temperatures the residual tensile strain only decreases slightly in the 100-nm-thick Al0.22Ga0.78N layer, but a pronounced strain relaxation occurs in the 50-nm-thick one. The degree of strain relaxation of the passivated 50-nm-thick Al0.22Ga0.78N layer increases by about 33%, which results in the two-dimensional electron gas concentration reduction of about 16% at the whole temperature range in our measurements.
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68.60.Bs Mechanical and acoustical properties
81.65.Rv Passivation
68.35.Gy Mechanical properties; surface strains

Band-edge electroluminescence from N+-implanted bulk ZnO

Hung-Ta Wang, B. S. Kang, Jau-Jiun Chen, T. Anderson, S. Jang, F. Ren, H. S. Kim, Y. J. Li, D. P. Norton, and S. J. Pearton

Appl. Phys. Lett. 88, 102107 (2006); http://dx.doi.org/10.1063/1.2186508 (3 pages) | Cited 20 times

Online Publication Date: 10 March 2006

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N+ ion implantation at moderate doses (1013–1014 cm−2) into nominally undoped (n ∼ 1017 cm−3) bulk single-crystal ZnO substrates followed by annealing in the range 600–950 °C was used to fabricate diodes that show visible luminescence at 300 K and band-edge electroluminescence at 120 K ( ∼ 390 nm) under forward bias conditions. The current-voltage behavior of the diodes are characteristic of metal-insulator-semiconductor devices and suggest the implantation creates a more resistive region in the n‐ZnO in which holes are created by impact ionization during biasing, similar to the case of electroluminescence in ZnO varistors. The series resistance is only 25 Ω due to the use of the conducting ZnO substrate.
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85.30.Kk Junction diodes
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.30.Tv Field effect devices
78.60.Fi Electroluminescence
61.72.Cc Kinetics of defect formation and annealing
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Pinning in c-axis oriented YBa2Cu3O7−δ films studied with angular dependent magnetoresistivity

M. Abdelhadi, K. H. Chow, J. Jung, E. K. Hollmann, and A. V. Tumarkin

Appl. Phys. Lett. 88, 102501 (2006); http://dx.doi.org/10.1063/1.2181652 (3 pages) | Cited 2 times

Online Publication Date: 6 March 2006

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We report measurements of the angular dependence of the magnetoresistivity in c-axis oriented YBa2Cu3O7−δ films near their superconducting transition temperature. The behavior of the samples falls into two categories. In some films, a local minimum in the resistivity is observed when the magnetic field is applied along the c axis, indicating that strong pinning of vortices is taking place. In other samples, no such minimum exists. The correlations between this behavior and the physical properties of the film are discussed, and possible candidates for the pinning centers presented.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Exchange bias-like phenomenon in SrRuO3

Li Pi, Shixiong Zhang, Shun Tan, and Yuheng Zhang

Appl. Phys. Lett. 88, 102502 (2006); http://dx.doi.org/10.1063/1.2182015 (3 pages) | Cited 14 times

Online Publication Date: 6 March 2006

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Exchange bias-like phenomenon is observed in the SrRuO3 polycrystalline. After the sample is cooled down to 4 K in a magnetic field, the magnetic hysteresis loop shifts in the opposite direction to the applied biasing field. The shift decreases as the sweeping range of the measuring field increases. This phenomenon may arise from the spin glass property of SrRuO3. Since SrRuO3 is widely used in spintronics devices, the observation of exchange bias-like shift in SrRuO3 itself suggests that the application of SrRuO3 should be more carefully considered.
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75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Lk Spin glasses and other random magnets

Temperature dependence of magnetocrystalline anisotropy constants in the single variant state of L10-type FePt bulk single crystal

K. Inoue, H. Shima, A. Fujita, K. Ishida, K. Oikawa, and K. Fukamichi

Appl. Phys. Lett. 88, 102503 (2006); http://dx.doi.org/10.1063/1.2177355 (3 pages) | Cited 17 times

Online Publication Date: 7 March 2006

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The temperature dependence of magnetocrystalline anisotropy constants and the saturation magnetization in a single variant state have been investigated for L10-type Fe60Pt40 bulk single crystal prepared under compressive stress. The uniaxial magnetocrystalline anisotropy constant Ku evaluated from the magnetization curve is 6.9×107 erg cm−3 at 5 K. The values of the second- and fourth-order magnetocrystalline anisotropy constants K1 and K2 at 5 K determined by the Sucksmith–Thompson method are 7.4 and 0.13×107 erg cm−3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio c/a due to the thermal expansion.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
65.40.De Thermal expansion; thermomechanical effects

Influence of bicrystal microstructural defects on high-transition-temperature direct-current superconducting quantum interference device

C. H. Wu, U. C. Sou, J. C. Chen, K. L. Chen, H. C. Yang, M. H. Hsu, T. S. Lai, J. T. Jeng, Y. S. Tsai, and H. E. Horng

Appl. Phys. Lett. 88, 102504 (2006); http://dx.doi.org/10.1063/1.2182066 (3 pages) | Cited 10 times

Online Publication Date: 8 March 2006

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Using atomic force microscopy and scanning electron microscopy (SEM), we investigate the correlations between the microstructural defects and the electrical characteristics of the bicrystal grain-boundary Josephson junctions and dc superconducting quantum inference devices (SQUIDs). The structural defects are shown to correlate qualitatively with the characteristics of grain-boundary Josephson junctions patterned on the YBa2Cu3O7−x film. SEM images show that these defects grown on the grain boundary were a few submicron depth of the groove. The low flux noise characteristics were observed when the groove depth was smaller than 18 nm in the junctions of the SQUID. The existence of these defects is expected to affect the supercurrent and the motion of the magnetic flux in the films, which dominate the excess noise in the SQUID with bicrystal junctions.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
61.72.Mm Grain and twin boundaries
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures

Tuning of magnetocaloric effect in a La0.69Ca0.31MnO3 single crystal by pressure

Young Sun, J. Kamarad, Z. Arnold, Zhi-qi Kou, and Zhao-hua Cheng

Appl. Phys. Lett. 88, 102505 (2006); http://dx.doi.org/10.1063/1.2183824 (3 pages) | Cited 11 times

Online Publication Date: 8 March 2006

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We report a study of the effect of hydrostatic pressure on the magnetocaloric effect in a La0.69Ca0.31MnO3 single crystal. The single crystal exhibits a much larger magnetic entropy change (ΔSm) than the corresponding polycrystalline samples, reaching 5.2 J/kg K and 8.5 J/kg K for a magnetic field variation of 1 T and 5 T, respectively. Under hydrostatic pressure, the peak position of ΔSm significantly moves to higher temperatures due to the shift of the magnetic phase transition, from 213.5 K under ambient pressure up to 236.5 K under a pressure of 1.1 GPa, while the maximum value of ΔSm remains nearly the same. These exceptional results demonstrate that the magnetocaloric effect in magnetic materials with strong spin-lattice coupling can be effectively tuned by pressure.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
65.40.G- Other thermodynamical quantities

Microscopic interfacial structures and magnetic properties of ultrathin Co/Si(111) films

J. S. Tsay, T. Y. Fu, M. H. Lin, C. S. Yang, and Y. D. Yao

Appl. Phys. Lett. 88, 102506 (2006); http://dx.doi.org/10.1063/1.2185259 (3 pages) | Cited 16 times

Online Publication Date: 9 March 2006

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The relation between magnetic properties and microscopic structure for a metal/semiconductor system is described. Cobalt films on a CoSi interface possess an in-plane easy axis of magnetization as the result of magnetocrystalline anisotropy of the Co/CoSi interface. On a Si(111)-7×7 surface, direct evidence for the formation of CoSi2 compounds at the interface was found by the appearance of doubled spot defects in scanning tunneling microscopic images. The interfacial effects cause the easy axis of magnetization of a Co/Si interface to be canted out of plane.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
68.35.Ct Interface structure and roughness

Nature of the transient BaF2-related phases in the “BaF2” processing of Ba2YCu3O7−x superconductors

W. Wong-Ng, I. Levin, L. P. Cook, and R. Feenstra

Appl. Phys. Lett. 88, 102507 (2006); http://dx.doi.org/10.1063/1.2184757 (3 pages) | Cited 6 times

Online Publication Date: 10 March 2006

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Transient BaF2-based oxyfluoride phases are thought to play a critical role in the formation of the c-textured Ba2YCu3O7−x layers of coated conductors. In situ high-temperature x-ray diffraction from the precursor films containing pure BaF2 as well as pseudobinary BaF2–Y, BaF2–Cu, and Y–Cu mixtures and heat treated in water vapor under reduced conditions revealed that the transient BaF2-based superstructures, similar to those observed during formation of Ba2Cu3O7−x, develop even from the pure BaF2 precursor. These superstructures results from the dissolution of oxygen in BaF2 leading to formation of the oxyfluoride phase, Ba(F2−2x◻x)Ox, with an ordered arrangement of O, F, and F vacancies.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
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