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4 Apr 2005

Volume 86, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 142101 (2005); http://dx.doi.org/10.1063/1.1895476 (3 pages)

M. Hanke, T. Boeck, A.-K. Gerlitzke, F. Syrowatka, F. Heyroth, and R. Köhler
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Surface treatment for the atomic layer deposition of HfO2 on silicon

J-F. Damlencourt, O. Renault, F. Martin, M-N. Séméria, T Billon, and F. Bedu

Appl. Phys. Lett. 86, 141913 (2005); http://dx.doi.org/10.1063/1.1899237 (3 pages) | Cited 7 times

Online Publication Date: 1 April 2005

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The atomic layer deposition (ALD) of HfO2 on silicon with a Cl2 surface treatment is investigated by physicochemical and electrical techniques. The specificity of this treatment is to create, on a HF-dipped silicon surface, the nucleation sites necessary for the ALD growth. The growth rates obtained by spectroscopic ellipsometry and total x-ray fluorescence spectroscopy indicate that the nucleation sites (i.e., the –OH groups), which are necessary to perform some bidimensional ALD growth, are generated during this surface treatment. After deposition of thin HfO2 layers (from a few monolayers up to 8.7 nm), a very thin parasitic SiOx layer, underneath 1 monolayer of Hf silicate, is observed by x-ray photoelectron spectroscopy. Nevertheless, an equivalent oxide thickness of 1.1 nm is obtained with an as-deposited 3.7 nm thick HfO2 layer.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.65.Cf Surface cleaning, etching, patterning
68.55.A- Nucleation and growth
79.60.Dp Adsorbed layers and thin films
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.55.-a Thin film structure and morphology
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Size, shape, and ordering of SiGe/Si(001) islands grown by means of liquid phase epitaxy under far-nonequilibrium growth conditions

M. Hanke, T. Boeck, A.-K. Gerlitzke, F. Syrowatka, F. Heyroth, and R. Köhler

Appl. Phys. Lett. 86, 142101 (2005); http://dx.doi.org/10.1063/1.1895476 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2005

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Applying scanning electron microscopy, we have studied the evolution of shape and lateral positional correlation of Si1−xGex/Si(001) Stranski–Krastanov islands grown by means of liquid phase epitaxy (LPE). However, in contrast to conventional near-equilibrium LPE, a distinctly higher cooling rate of 10 K/min ensures extremly nonequilibrium growth conditions. The facet inclination of subsequent island stages decreases from nearly vertical sidewalls toward {111}- and {101}-type facets. Energy dispersive x-ray microanalysis yields a size-independent germanium content of 8.9% within islands between 760 and 1700 nm base width which is—by more than a factor of 2—smaller than islands of the same concentration grown in a near-equilibrium LPE process. Square-like formations of subsequently smaller islands around a large central island indicate only next to island interactions during the lateral self-assembling.
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81.05.Hd Other semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Controlled orientation of liquid-crystalline polythiophene semiconductors for high-performance organic thin-film transistors

Yiliang Wu, Ping Liu, Beng S. Ong, Tharan Srikumar, Ni Zhao, Gianluigi Botton, and Shiping Zhu

Appl. Phys. Lett. 86, 142102 (2005); http://dx.doi.org/10.1063/1.1894597 (3 pages) | Cited 54 times

Online Publication Date: 29 March 2005

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The silane self-assembled monolayer (SAM) modification of a SiO2 gate dielectric surface improved the molecular ordering of organic channel semiconductor in organic thin-film transistors (OTFTs), leading to a significant improvement in transistor performance. Mobility of up to 0.18 cm2/V s (current on∕off ratio of 107) was obtained for OTFTs with a liquid-crystalline polythiophene semiconductor built on an octyltrichlorosilane-modified SiO2 gate dielectric layer, a 450 times improvement over those built on a nonmodified dielectric layer. The mobility enhancement was attributed to the edge-on orientation of the polythiophene molecules induced by the silane SAM layer as deduced from the crystal domain structures in the atomic force microscopic images.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices
68.37.Ps Atomic force microscopy (AFM)
73.50.Dn Low-field transport and mobility; piezoresistance
77.55.-g Dielectric thin films

Physical mechanisms of negative-bias temperature instability

L. Tsetseris, X. J. Zhou, D. M. Fleetwood, R. D. Schrimpf, and S. T. Pantelides

Appl. Phys. Lett. 86, 142103 (2005); http://dx.doi.org/10.1063/1.1897075 (3 pages) | Cited 26 times

Online Publication Date: 28 March 2005

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We report first-principles calculations that elucidate the mechanisms that underlie key features of negative-bias temperature instability (NBTI). We show that the depassivation of Si–H bonds by protons released in the Si substrate is consistent with the observed increase in interface-trap density. The calculated activation energy of 0.36 eV is in excellent agreement with observations for long stress times. Adequate amounts of hydrogen, needed to initiate depassivation, are likely to exist in the substrate, trapped in complexes with dopants. The role of holes in the H release mechanism is identified. Finally, we explain how the above mechanisms can account for various experimental NBTI observations.
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85.30.De Semiconductor-device characterization, design, and modeling

Radiative and nonradiative recombination processes in InN films grown by metal organic chemical vapor deposition

R. Intartaglia, B. Maleyre, S. Ruffenach, O. Briot, T. Taliercio, and B. Gil

Appl. Phys. Lett. 86, 142104 (2005); http://dx.doi.org/10.1063/1.1897428 (3 pages) | Cited 21 times

Online Publication Date: 28 March 2005

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The 800 meV photoluminescence band in indium nitride is excited under pulsed excitation conditions and is investigated as a function of temperature and time. Our results are consistent with a composite photoluminescence feature composed of two overlapping bands separated by an ∼ 10 meV splitting, with populations described by a thermal equilibrium model. Efficient nonradiative recombination channels rule both the temperature dependence of the time-integrated photoluminescence spectra and the recombination dynamics. At 10 K, the radiative recombination time is of the order of 300 ns, while the nonradiative recombination time, which is ruled by activation energy of 8 meV, is about 100 ps.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.45.Wx Polymers and organic materials in electrochemistry
82.50.-m Photochemistry

Femtosecond spectroscopy of unipolar nanometer-scale high-field transport of holes in Al0.08Ga0.92As

S. Trumm, M. Betz, F. Sotier, A. Leitenstorfer, A. Schwanhäußer, M. Eckardt, S. Malzer, M. Hanson, D. Driscoll, A. C. Gossard, and G. H. Döhler

Appl. Phys. Lett. 86, 142105 (2005); http://dx.doi.org/10.1063/1.1898442 (3 pages) | Cited 1 time

Online Publication Date: 29 March 2005

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High-field transport in GaAs is investigated tracing ultrafast modifications of the Franz–Keldysh absorption spectrum of a AlxGa1−xAs heterostructure diode. A sophisticated sample design allows us to isolate the unipolar tranport properties of holes in combination with a nanometer scale definition of layers for both photoexcitation and detection of the propagating carrier distribution. Transient velocities and spatial broadening of the hole ensemble are directly measured for electric fields between 15 and 200 kV∕cm comparing room temperature operation to results for TL = 4 K. Even at low temperatures, the transient hole velocities are found not to exceed a value of 1.2×107 cm/s which is a result of ultrafast optical phonon emission with a scattering time below 25 fs.
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85.30.Kk Junction diodes
73.40.Ty Semiconductor-insulator-semiconductor structures
73.50.Fq High-field and nonlinear effects
78.20.Jq Electro-optical effects
78.47.-p Spectroscopy of solid state dynamics

Role of interface traps on breakdown process of a magnetic tunnel junction

Kwang-Seok Kim and B. K. Cho

Appl. Phys. Lett. 86, 142106 (2005); http://dx.doi.org/10.1063/1.1897846 (3 pages) | Cited 8 times

Online Publication Date: 30 March 2005

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Time dependent dielectric breakdown (TDDB) measurements were carried out for magnetic tunneling junctions (MTJs) with different electron trap densities at the interface between a bottom electrode and an insulating barrier. The TDDB shows a strong bias-polarity dependence, which becomes bigger with increasing trap density. In addition, the current creep before total dielectric breakdown consistently shows bias-polarity dependence. The polarity dependence of the breakdown in MTJs with an ultrathin tunneling barrier (15–20 Å) is believed to be caused by precursor effect of the traps at the bottom interface, which enhances the trap generation rate in a tunneling barrier, resulting in acceleration of the breakdown process.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.21.Ac Multilayers
75.47.Np Metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
77.22.Jp Dielectric breakdown and space-charge effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Diffusion and dissociation mechanisms of vacancy-oxygen complex in silicon

Masayuki Furuhashi and Kenji Taniguchi

Appl. Phys. Lett. 86, 142107 (2005); http://dx.doi.org/10.1063/1.1897433 (3 pages) | Cited 7 times

Online Publication Date: 30 March 2005

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We are examining diffusion mechanisms of the vacancy-oxygen complex (VO) in bulk Si using ab initio calculations based on a 64-atom supercell. We found two atomic mechanisms involved in the VO diffusion; one is caused by migration of an interstitial oxygen atom, another by migration of a vacancy. The energy barrier of the mechanism due to an oxygen migration is 2.02 eV, and that caused by a vacancy migration is 1.98 eV. These energy barriers are close to the experimental activation energy of 2.0 eV required for the dissociation and diffusion of VO. The derived activation energies of the two mechanisms suggest that these mechanisms plausibly occur simultaneously. In addition, we clarify that the dissociation energy of VO, 1.85 eV, is lower than the diffusion energy of VO.
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68.08.-p Liquid-solid interfaces
64.70.-p Specific phase transitions
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Examining the screening limit of field effect devices via the metal-insulator transition

X. Hong, A. Posadas, and C. H. Ahn

Appl. Phys. Lett. 86, 142501 (2005); http://dx.doi.org/10.1063/1.1897076 (3 pages) | Cited 30 times

Online Publication Date: 28 March 2005

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The electronic screening length, the distance over which an electric field is attenuated in a material, imposes a lower physical bound on the lateral size scaling of semiconductor field effect devices. Alternatives will be needed to achieve devices whose characteristic dimensions approach a nanometer. In this work, we demonstrate the atomic-scale nature of screening at high electron densities, using the polarization field of a ferroelectric oxide, Pb(Zr,Ti)O3, to electrostatically modulate the metallicity of ultrathin manganite La1−xSrxMnO3 (LSMO) films near the metal-insulator transition. Within the screening length, the transport characteristics of LSMO vary sharply at the scale of a single atomic layer.
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85.30.Tv Field effect devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
71.30.+h Metal-insulator transitions and other electronic transitions
73.61.Ng Insulators
72.20.Fr Low-field transport and mobility; piezoresistance
77.22.Ej Polarization and depolarization

Domain decoration in dipolar coupled ferromagnetic stacks with perpendicular anisotropy

S. Wiebel, J.-P. Jamet, N. Vernier, A. Mougin, J. Ferré, V. Baltz, B. Rodmacq, and B. Dieny

Appl. Phys. Lett. 86, 142502 (2005); http://dx.doi.org/10.1063/1.1897845 (3 pages) | Cited 22 times

Online Publication Date: 29 March 2005

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The dipolar stray field effects between two nonuniformly magnetized ferromagnetic Co/Pt stacks with perpendicular anisotropy are investigated by polar magneto-optical Kerr effect microscopy. Decoration of a reversed domain in the hard stack by a domain ring in the soft stack is evidenced and interpreted by magnetostatic calculations. Mirrored 360° domain walls are strongly stabilized by these interactions.
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75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.65.Ac Multilayers

Giant magnetoresistance in an epitaxial NiMnSb/Cu/CoFe multilayer

E. Girgis, P. Bach, C. Rüster, C. Gould, G. Schmidt, and L. W. Molenkamp

Appl. Phys. Lett. 86, 142503 (2005); http://dx.doi.org/10.1063/1.1897828 (3 pages) | Cited 3 times

Online Publication Date: 29 March 2005

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We have fabricated current-in-plane giant magnetoresistive (GMR) devices based on multilayers of epitaxial NiMnSb and sputtered Cu and CoFe. The devices show a magnetoresistance of up to 3.5% at room temperature. The amplitude of the current-in-plane GMR signal and the nature of the coupling between the two magnetic layers depend on the thickness of the Cu layer. For a 1.5 nm thick Cu layer, the device exhibits antiferromagnetic coupling, whereas a parallel alignment is observed for 2.2 or 3 nm thick Cu layers at low field.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions

Composite media (dynamic tilted media) for magnetic recording

Jian-Ping Wang, W. K. Shen, J. M. Bai, R. H. Victora, J. H. Judy, and W. L. Song

Appl. Phys. Lett. 86, 142504 (2005); http://dx.doi.org/10.1063/1.1896431 (3 pages) | Cited 54 times

Online Publication Date: 1 April 2005

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We designed and fabricated a composite magnetic recording medium with exchange decoupled magnetic grains that consist of two vertically exchange-coupled magnetic regions (one is magnetically soft and one is magnetically hard) as an approach to alleviate the writing field limitation of perpendicular magnetic recording heads. A nonmagnetic layer with different thickness was put between the hard and soft layer to tune the exchange coupling. With proper coupling, significant drop of the coercivity field was observed for this composite medium while still maintaining good thermal stability. Better recording performance was obtained for such medium compared to perpendicular and longitudinal medium. The results have proved the possibility of fabricating a writable recording medium having an ultrahigh magnetic anisotropy constant (Ku) value.
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75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ww Permanent magnets
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
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Density functional theory study of adsorption and dissociation of HfCl4 and H2O on Ge/Si(100)-(2×1): Initial stage of atomic layer deposition of HfO2 on SiGe surface

Wei Chen, Hong-Liang Lu, David Wei Zhang, Min Xu, Jie Ren, Jian-Yun Zhang, Ji-Tao Wang, and Li-Kang Wang

Appl. Phys. Lett. 86, 142901 (2005); http://dx.doi.org/10.1063/1.1899253 (3 pages) | Cited 2 times

Online Publication Date: 30 March 2005

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We have investigated adsorption and dissociation of water and HfCl4 on Ge/Si(100)-(2×1) surface with density functional theory. The Si–Ge heterodimer and Ge–Ge homodimer are employed to represent the Si1−xGex surface. The activation energy for adsorption of water on Ge–Ge homodimer is much higher than that on Si–Ge heterodimer. No net activation barrier exists during the adsorption of HfCl4 on both SiGe surface dimers. The differences in the potential energy surface between reactions on Si–Ge and Ge–Ge dimers are due to different bond strengths. It should also be noticed that the activation energy for HfCl4 is quite flat, thus HfCl4 adsorbs and dissociates on Ge/Si(100)-(2×1) easily.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.43.Mn Adsorption kinetics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Nr Association, addition, insertion, cluster formation
68.55.-a Thin film structure and morphology

Epitaxial nature and anisotropic dielectric properties of (Pb,Sr)TiO3 thin films on NdGaO3 substrates

Y. Lin, X. Chen, S. W. Liu, C. L. Chen, Jang-Sik Lee, Y. Li, Q. X. Jia, and A. Bhalla

Appl. Phys. Lett. 86, 142902 (2005); http://dx.doi.org/10.1063/1.1897078 (3 pages) | Cited 15 times

Online Publication Date: 30 March 2005

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Epitaxial behavior of (Pb,Sr)TiO3 thin films on (110) NdGaO3 substrates fabricated in different conditions have been investigated using high resolution x-ray diffraction and characterized with interdigital dielectric measurement. A slow cooling results in films with a-axis normal to the surface (a-axis growth), whereas a fast cooling leads to growth of c-axis oriented films. The dielectric properties of the films prepared under different cooling rates are closely related to the crystalline structure of the films.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Reducing azimuthal domains in epitaxial ferroelectric lanthanum-substituted bismuth titanate films using miscut yttria-stabilized zirconia substrates

Sung Kyun Lee, Dietrich Hesse, Ulrich Gösele, and Ho Nyung Lee

Appl. Phys. Lett. 86, 142903 (2005); http://dx.doi.org/10.1063/1.1897044 (3 pages) | Cited 2 times

Online Publication Date: 31 March 2005

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We report the effect of a definite miscut of yttria-stabilized zirconia (YSZ) (100) single-crystal substrates onto the number of azimuthal domain variants within epitaxial La-substituted Bi4Ti3O12 (BLT) ferroelectric thin films as well as within SrRuO3 electrode layers, both grown on these substrates. YSZ substrates with a miscut angle of 5° were studied, with two different directions of the miscut, viz., YSZ[001] and YSZ[011]. A reduction of the number of azimuthal domain variants by 50% was attained on substrates with a [011]-directed miscut. Due most probably to the reduced number of azimuthal domain boundaries, larger remanent polarization values were attained in BLT films when grown on miscut substrates.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
82.45.Mp Thin layers, films, monolayers, membranes

Strain relaxation of epitaxial SrTiO3 thin films on LaAlO3 by two-step growth technique

Tomoaki Yamada, Konstantin F. Astafiev, Vladimir O. Sherman, Alexander K. Tagantsev, Paul Muralt, and Nava Setter

Appl. Phys. Lett. 86, 142904 (2005); http://dx.doi.org/10.1063/1.1897047 (3 pages) | Cited 24 times

Online Publication Date: 31 March 2005

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Using pulsed-laser deposition, a two-step growth technique was applied to epitaxial SrTiO3 (STO) thin films on LaAlO3 substrates providing a way to obtain an effective strain relaxation in these films otherwise strained due to lattice mismatch between film and substrate. By changing the thickness of a first layer, deposited at a temperature as low as 100 °C before the deposition of the main layer at 750 °C, different strain relaxation states of the films could be systematically realized. With a 10-nm-thick first layer, an almost full strain relaxation at the deposition temperature of the main layer was achieved, suggesting a strong impact of this method on strain relaxation. The in-plane dielectric measurements displayed that the ferroelectric transition temperature increases with strain relaxation during the growth. This trend is correct and compatible with the theoretical prediction of the behavior of strained STO derived from Landau theory.
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81.16.Mk Laser-assisted deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Effect of dc bias on the Curie–Weiss exponent in 0.76Pb(Mg1/3Nb2/3)O3–0.24PbTiO3 ferroelectric single crystal

S. G. Lu, Z. K. Xu, Haydn Chen, X. Y. Zhao, H. S. Luo, J. Wang, H. L. W. Chan, and C. L. Choy

Appl. Phys. Lett. 86, 142905 (2005); http://dx.doi.org/10.1063/1.1897063 (3 pages) | Cited 4 times

Online Publication Date: 1 April 2005

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Permittivity versus temperature characteristics and Curie–Weiss exponent (CWE) γ in the universal Curie–Weiss law [ε−1 = εm−1[1+(T−Tc)γ/(2δ2)](1 ⩽ γ ⩽ 2)] as a function of dc bias field were obtained for ⟨001⟩, ⟨011⟩, and ⟨111⟩ oriented 0.76Pb(Mg1/3Nb2/3)O3–0.24PbTiO3 single crystals. Results indicated that γ is a function of dc bias field and three different oriented crystals show slight different γ values but the similar dc field dependence.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions

Preparing Pb(Zr,Ti)O3 films less than 100 nm thick by low-temperature metalorganic chemical vapor deposition

A. Nagai, H. Morioka, G. Asano, H. Funakubo, and A. Saiki

Appl. Phys. Lett. 86, 142906 (2005); http://dx.doi.org/10.1063/1.1899770 (3 pages) | Cited 4 times

Online Publication Date: 1 April 2005

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Polycrystalline Pb(Zr,Ti)O3 (PZT) films 70–80 nm thick on (111)Ir/TiO2/SiO2/Si substrates were prepared at 415 °C by metalorganic chemical vapor deposition (MOCVD). At 3 V, the remanent polarization (Pr) of the as-deposited films was approximately 22 μC/cm2. Inserting PbTiO3 seeds between the PZT films and Ir bottom electrodes improved the crystallinity of the films markedly but improved their ferroelectric properties only slightly. Low-temperature postannealing, on the other hand, even at 400 °C (i.e., below the deposition temperature), improved Pr values and hysteresis loop shapes without obviously improving the crystallinity of the films. The electrical properties were improved even more when the films were annealed at 500 °C. These results suggest that the low-temperature processing and sub-100-nm film thickness needed for making three-dimensionally structured ferroelectric capacitors can be obtained by using low-temperature MOCVD to deposit PZT films, and then annealing those films at a temperature no greater than 500 °C.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.40.Tv Optical and dielectric properties related to treatment conditions

Dynamic leakage current compensation in ferroelectric thin-film capacitor structures

René Meyer, Rainer Waser, Klaus Prume, Torsten Schmitz, and Stephan Tiedke

Appl. Phys. Lett. 86, 142907 (2005); http://dx.doi.org/10.1063/1.1897425 (3 pages) | Cited 11 times

Online Publication Date: 1 April 2005

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We report on a measurement procedure to separate ferroelectric switching current and dielectric displacement current from the leakage current in leaky ferroelectric thin-film capacitor structures. The ac current response is determined for two adjacent frequencies. Taking advantage of the different frequency dependencies of the ferroelectric switching current, dielectric displacement current and ohmic current, the hysteresis loop is calculated without performing a static leakage current measurement, which causes a high dc field stress to the sample. The applicability of the proposed measurement procedure is demonstrated on a Pt/Pb(Zr,Ti)O3/IrO2 ferroelectric capacitor revealing a high leakage current.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.55.-g Dielectric thin films
73.40.Ns Metal-nonmetal contacts
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
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Efficient charge collection in hybrid polymer/TiO2 solar cells using poly(ethylenedioxythiophene)/polystyrene sulphonate as hole collector

P. Ravirajan, D. D. C. Bradley, J. Nelson, S. A. Haque, J. R. Durrant, H. J. P. Smit, and J. M. Kroon

Appl. Phys. Lett. 86, 143101 (2005); http://dx.doi.org/10.1063/1.1890468 (3 pages) | Cited 41 times

Online Publication Date: 28 March 2005

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We report a study of the optimization of power conversion efficiency in hybrid solar cells based on nanostructured titanium dioxide and a poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) based conjugated polymer. Charge collection efficiency is enhanced by introducing a poly(ethylenedioxythiophene)/polystyrene sulphonate (PEDOT) layer (under the gold electrode) as the hole collector. Device performance is maximized for a device with a net active layer thickness of 100 nm. The optimized device has peak external quantum efficiencies ≈ 40% at the polymer’s maximum absorption wavelength and yield short circuit current density ≥ 2 mA cm−2 for air mass (AM) 1.5 conditions (100 mW cm−2, 1 sun). The AM 1.5 open circuit voltage for this device is 0.64 V and the fill factor is 0.43, resulting in an overall power conversion efficiency of 0.58%.
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84.60.Jt Photoelectric conversion

Fabrication of CdS/Si nanocable heterostructures by one-step thermal evaporation

X. L. Fu, Y. J. Ma, P. G. Li, L. M. Chen, W. H. Tang, X. Wang, and L. H. Li

Appl. Phys. Lett. 86, 143102 (2005); http://dx.doi.org/10.1063/1.1897043 (3 pages) | Cited 7 times

Online Publication Date: 28 March 2005

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Coaxial CdS/Si nanocable heterostructures with a length of hundreds of micrometers and an average diameter of 100 nm were fabricated via one-step thermal evaporation of CdS powder under experimentally controlled conditions. The CdS cores have a hexagonal crystal structure. The Si sheaths are amorphous and can be directly grown on the CdS surfaces from the silicon substrate via a vapor-liquid-solid mechanism without an extra Si source. The photoluminescence of the nanocables presents two emission bands, around 510 and 590 nm. This simple method may be applied to other Si-sheathed heterostructures, which can be used in nanodevices with various functions.
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61.46.-w Structure of nanoscale materials
71.55.Gs II-VI semiconductors
81.16.−c

Fabrication of atomic-scale gold junctions by electrochemical plating using a common medical liquid

A. Umeno and K. Hirakawa

Appl. Phys. Lett. 86, 143103 (2005); http://dx.doi.org/10.1063/1.1897444 (3 pages) | Cited 19 times

Online Publication Date: 28 March 2005

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Fabrication of nanometer-separated gold junctions has been performed using “iodine tincture,” a medical liquid known as a disinfectant, as an etching/deposition electrolyte. In the gold-dissolved iodine tincture, gold electrodes were grown or eroded slowly enough to form quantum point contacts in an atomic scale. The resistance evolution during the electrochemical deposition showed plateaus at integer multiples of the resistance quantum, (2e2/h)−1, at room temperature (e: the elementary charge, h: the Planck constant). Iodine tincture is a commercially available common material, which makes the fabrication process to be simple and cost effective. Moreover, in contrast to the conventional electrochemical approaches, this method is free from highly toxic cyanide compounds or extraordinarily strong acids.
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81.16.-c Methods of micro- and nanofabrication and processing
82.45.Qr Electrodeposition and electrodissolution
85.65.+h Molecular electronic devices

Nanomechanical hydrogen sensing

X. M. H. Huang, M. Manolidis, Seong Chan Jun, and J. Hone

Appl. Phys. Lett. 86, 143104 (2005); http://dx.doi.org/10.1063/1.1897445 (3 pages) | Cited 39 times

Online Publication Date: 28 March 2005

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A nanomechanical beam resonator is used as a sensitive, specific hydrogen sensor. The beam is fabricated from AuPd alloy and tested by magnetomotive transduction at room temperature. The fundamental resonance frequency decreases significantly and reversibly at hydrogen pressures above 10−5 Torr, whereas the frequency shifts observed for other gases are significantly smaller. The large frequency shift is likely due to the formation of interstitial hydrogen in the metal alloy lattice, which relieves the built-in tensile stress in the resonator beam. The uptake of hydrogen as measured by frequency shift is consistent with previous studies.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Surface-charge-induced asymmetric electrokinetic transport in confined silicon nanochannels

R. Qiao and N. R. Aluru

Appl. Phys. Lett. 86, 143105 (2005); http://dx.doi.org/10.1063/1.1897430 (3 pages) | Cited 14 times

Online Publication Date: 28 March 2005

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Molecular dynamics simulations of a NaF solution transport in a confined silicon nanochannel indicated that the water flux and the ionic conductivity through two oppositely charged silicon channels, that are otherwise similar, differ by a factor of more than three, and the co-ion fluxes are in the opposite direction. Such a behavior cannot be predicted by the classical electrokinetic transport theory, and is found to originate from the asymmetric dependence of the transport properties of water near the charged silicon surface.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.60.-i Flow phenomena in quasi-one-dimensional systems
66.10.-x Diffusion and ionic conduction in liquids

Selective etching of InGaAs∕GaAs(100) multilayers of quantum-dot chains

Zh. M. Wang, L. Zhang, K. Holmes, and G. J. Salamo

Appl. Phys. Lett. 86, 143106 (2005); http://dx.doi.org/10.1063/1.1898425 (3 pages) | Cited 8 times

Online Publication Date: 29 March 2005

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We report selective chemical etching as a promising procedure to study the buried quantum dots in multiple InGaAs∕GaAs layers. The dot layer-by-dot layer etching is demonstrated using a mixed solution of NH4OH:H2O2:H2O. Regular plan-view atomic force microscopy reveals that all of the exposed InGaAs layers have a chain-like lateral ordering despite the potential of significant In–Ga intermixing during capping. The vertical self-correlation of quantum dots in the chains is observed.
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.Hb Quantum dots (patterned in quantum wells)
68.65.Ac Multilayers
68.37.Ps Atomic force microscopy (AFM)
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