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24 Sep 2001

Volume 79, Issue 13, pp. 1933-2115

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Temperature-dependent conduction of W-containing composite diamond films

M. L. Terranova, V. Sessa, S. Piccirillo, S. Orlanducci, D. Manno, G. Micocci, A. Serra, A. Tepore, and M. Rossi

Appl. Phys. Lett. 79, 2007 (2001); http://dx.doi.org/10.1063/1.1403335 (3 pages) | Cited 2 times

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We report on the synthesis and electrical characterizations of composite W-containing diamond films. These layers have been produced by a hybrid chemical-vapor-deposition/powder flowing technique that allows control of the dispersion of the foreign W phase inside a diamond matrix. The electrical behavior of such material in the 25–500 K temperature range is found characterized by a nonlinear response, typical of metal/insulator composite materials, with conductivity reaching the maximum value of 95 Ω−1 cm−1 at 148 K. Structural and morphological investigations performed by reflection high-energy electron diffraction, scanning electron microscopy, and dispersive x-ray spectrometry indicate that the presence of a percolating network of metallic grains did not perturb the quality of the diamond lattice. © 2001 American Institute of Physics.
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73.61.-r Electrical properties of specific thin films
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.55.-a Thin film structure and morphology

Real-time evolution of trapped charge in a SiO2 layer: An electrostatic force microscopy study

G. H. Buh, H. J. Chung, and Y. Kuk

Appl. Phys. Lett. 79, 2010 (2001); http://dx.doi.org/10.1063/1.1404404 (3 pages) | Cited 29 times

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Time-dependent motion of localized electrons and holes trapped in a SiO2 layer is visualized with electrostatic force microscopy. Both negative and positive charges of up to ∼ 1010 e/cm2 are trapped at a SiO2–Si interface in ∼ 500-nm-diam area with a voltage stress between the tip and the sample. There is a higher probability for trapped charges to spread out in the plane direction than to de-trap toward the Si substrate. The dynamics is explained with diffusion and drift of the charges induced by Coulombic interaction. © 2001 American Institute of Physics.
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73.61.Ng Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Ps Atomic force microscopy (AFM)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Cg Contact resistance, contact potential

Tunneling carrier escape from InAs self-assembled quantum dots

J. Ibáñez, R. Leon, D. T. Vu, S. Chaparro, S. R. Johnson, C. Navarro, and Y. H. Zhang

Appl. Phys. Lett. 79, 2013 (2001); http://dx.doi.org/10.1063/1.1402642 (3 pages) | Cited 9 times

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Deep-level transient spectroscopy measurements in InAs quantum dots (QDs) grown in both n-GaAs and p-GaAs show that tunneling is an important mechanism of carrier escape from the dots. The doping level in the barrier strongly affects the tunneling emission rates, enabling or preventing the detection of a transient capacitance signal from a given QD level. The relative intensity of this signal acquired with different rate windows allows the estimation of tunneling emission energies. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.63.Kv Quantum dots
71.55.Eq III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Solubility limit and precipitate formation in Al-doped 4H-SiC epitaxial material

M. K. Linnarsson, M. S. Janson, U. Zimmermann, B. G. Svensson, P. O. Å. Persson, L. Hultman, J. Wong-Leung, S. Karlsson, A. Schöner, H. Bleichner, and E. Olsson

Appl. Phys. Lett. 79, 2016 (2001); http://dx.doi.org/10.1063/1.1402160 (3 pages) | Cited 17 times

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Heavily Al-doped 4H–SiC structures have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in an Ar atmosphere in a rf-heated furnace between 1500 °C and 2000 °C for 0.5 to 3 h. Secondary ion mass spectrometry has been utilized to obtain Al concentration versus depth as well as lateral distributions (ion images). Transmission electron microscopy (TEM) has been employed to study the crystallinity and determine phase composition after heat treatment. A solubility limit of ∼ 2×1020 Al/cm3 (1900 °C) is extracted. Three-dimensional ion images show that the Al distribution does not remain homogeneous in layers heat treated at 1700 °C or above when the Al concentration exceeds 2×1020 cm−3. Al-containing precipitates are identified by energy-filtered TEM. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.S- Impurities in crystals
81.30.Mh Solid-phase precipitation
64.75.-g Phase equilibria

Ultraviolet and visible resonance-enhanced Raman scattering in epitaxial Al1−xInxN thin films

V. M. Naik, W. H. Weber, D. Uy, D. Haddad, R. Naik, Y. V. Danylyuk, M. J. Lukitsch, G. W. Auner, and L. Rimai

Appl. Phys. Lett. 79, 2019 (2001); http://dx.doi.org/10.1063/1.1404402 (3 pages) | Cited 16 times

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We report the observation of ultraviolet and visible near-resonance enhanced Raman scattering in epitaxial wurtzite Al1−xInxN (0001) (0 ⩽ x<0.7) thin films. The films (thickness ∼ 150 nm) were grown by plasma source molecular beam epitaxy on sapphire (0001) substrates. A substantial spectral enhancement is seen for Al-rich samples using 244 nm (5.01 eV) radiation due to the closeness of their band gap energy to the excitation energy. On the other hand, samples with x ∼ 0.6 (energy band gap ∼ 2.5 eV) show significant enhancement with 514.5 nm (2.41 eV) excitation. The A1(LO) and E2 zone center phonons have been observed for all the samples. The A1(LO) phonon frequency shows the expected decrease with increasing x. The E2 mode shows a two-mode behavior supporting the recent theoretical predictions. Due to increased resonance enhancement, strong second- and third-order spectra are seen in some films. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.20.Nr Semiconductor compounds

Metalorganic vapor-phase epitaxial growth and photoluminescent properties of Zn1−xMgxO(0 ⩽ x ⩽ 0.49) thin films

W. I. Park, Gyu-Chul Yi, and H. M. Jang

Appl. Phys. Lett. 79, 2022 (2001); http://dx.doi.org/10.1063/1.1405811 (3 pages) | Cited 163 times

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High-quality Zn1−xMgxO(0.00 ⩽ x ⩽ 0.49) thin films were epitaxially grown at 500–650 °C on Al2O3(00⋅1) substrates using metalorganic vapor-phase epitaxy. By increasing the Mg content in the films up to 49 at. %, the c-axis constant of the films decreased from 5.21 to 5.14 Å and no significant phase separation was observed as determined by x-ray diffraction measurements. Furthermore, the near-band-edge emission peak position showed blueshifts of 100, 440, and 685 meV at Mg content levels of 9, 29, and 49 at. %, respectively. Photoluminescent properties of the alloy films are also discussed. © 2001 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors

Transport spectroscopy of the ultrasmall silicon quantum dot in a single-electron transistor

Masumi Saitoh, Toshiki Saito, Takashi Inukai, and Toshiro Hiramoto

Appl. Phys. Lett. 79, 2025 (2001); http://dx.doi.org/10.1063/1.1405805 (3 pages) | Cited 25 times

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We investigate electron transport through the ultrasmall silicon quantum dot in a single-electron transistor. The device is fabricated in the form of a silicon point-contact channel metal–oxide–semiconductor field-effect transistor. The size of the formed dot is estimated to be as small as 5.3 nm. Negative differential conductance is clearly observed up to 25 K. It turns out that this is caused by discreteness of quantum levels in the silicon dot and variation of the tunneling rates to each level. The fine structure of conductance persists up to 77 K. Modeling of the electron transport through the silicon dot is carried out. Good agreement between experiment and calculation is obtained, which confirms the validity of our model. © 2001 American Institute of Physics.
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73.63.Kv Quantum dots
72.80.Cw Elemental semiconductors
85.35.Gv Single electron devices
85.30.Tv Field effect devices

Anisotropic electrical conductivity of delafossite-type CuAlO2 laminar crystal

M. S. Lee, T. Y. Kim, and D. Kim

Appl. Phys. Lett. 79, 2028 (2001); http://dx.doi.org/10.1063/1.1405809 (3 pages) | Cited 32 times

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Delafossite-type CuAlO2 laminar crystals (Rmathm) were prepared through melt by a cooling method from 1423 K. The layer-by-layer structure of the crystal was observed. Because of the structural anisotropy of the crystal, electrical conductivity along the ab plane (σab) was higher than that along the c axis (σc), σab≳25σc. The anisotropy unveiled that the main conduction path of the crystal is closed-packed Cu+ layers. The values of the activation energies which were estimated from the Arrhenius plot were ∼0.20 and ∼0.13 eV for σc and σab, respectively. The linearity in the log σ vs (1/T)1/4 plot and the positive thermoelectric power (>+300 μV/K) of the crystal suggested p-type variable-range hopping conduction. © 2001 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Ee Mobility edges; hopping transport
72.80.Ga Transition-metal compounds
72.80.Sk Insulators

Si/SiGe modulation-doped heterostructures grown on silicon-on-insulator substrates for high-mobility two-dimensional electron gases

L. Di Gaspare, K. Alfaramawi, F. Evangelisti, E. Palange, G. Barucca, and G. Majni

Appl. Phys. Lett. 79, 2031 (2001); http://dx.doi.org/10.1063/1.1400769 (3 pages) | Cited 7 times

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The growth of high-mobility modulation-doped Si/SiGe heterostructures on silicon-on-insulator substrates is demonstrated. The structural and electrical properties of the samples are reported to be comparable with those of similar samples grown on standard Si substrates. Electron mobilities as high as 2900 cm2/Vs at room temperature and 8.2×104 cm2/Vs at 4.2 K were obtained. © 2001 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
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Asymmetry diffraction magneto-optical phenomenon of NiFe grating

Y. T. Shen, Y. H. Wu, T. C. Chong, H. Xie, Z. B. Guo, K. B. Li, and J. J. Qiu

Appl. Phys. Lett. 79, 2034 (2001); http://dx.doi.org/10.1063/1.1404126 (3 pages) | Cited 3 times

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We report the asymmetry of longitudinal magneto-optical Kerr loops obtained from diffracted spots of a NiFe grating. The analysis of several series of diffracted Kerr hysteresis loops reveals that the unsaturated magnetic structure not only contributes to the shape change of Kerr loops, but also results in asymmetric feature of Kerr loops because of the nonzero value of second-order magnetic response. A suitable pattern dimension, which defines the form factor, is helpful to observe asymmetry Kerr loops. Our experiment indicates that out-of-incidence-plane diffraction may offer an alternative method to observe lateral edge domain movements in patterns. © 2001 American Institute of Physics.
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42.79.Dj Gratings
78.20.Ls Magneto-optical effects
42.30.Kq Fourier optics
75.60.Ch Domain walls and domain structure

Electron energy-loss spectroscopy study of a (LaMnO3)8(SrMnO3)4 heterostructure

J. Verbeeck, O. I. Lebedev, G. Van Tendeloo, J. Silcox, B. Mercey, M. Hervieu, and A. M. Haghiri-Gosnet

Appl. Phys. Lett. 79, 2037 (2001); http://dx.doi.org/10.1063/1.1403316 (3 pages) | Cited 9 times

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An epitaxially grown heterostructure consisting of alternating layers of LaMnO3 (8 unit cells) and SrMnO3 (4 unit cells) on a SrTiO3 substrate has been studied by a combination of electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM) on an atomic scale. Excitation edges of all elements are captured with subnanometer spatial accuracy, and parametrized to obtain chemical profiles. The fine-edge structure of O K and Mn L2,3 edges are interpreted as signatures of the local electronic structure and show a spatial modulation of the concentration of holes with O 2p character. The chemical concentration is found to be different for the bottom and top interface of a SrMnO3 layer. HRTEM complements the EELS results and confirms the asymmetry of the interfaces. © 2001 American Institute of Physics.
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68.65.Cd Superlattices
79.20.Uv Electron energy loss spectroscopy

Large magnetocaloric effect in manganites with charge order

P. Sande, L. E. Hueso, D. R. Miguéns, J. Rivas, F. Rivadulla, and M. A. López-Quintela

Appl. Phys. Lett. 79, 2040 (2001); http://dx.doi.org/10.1063/1.1403317 (3 pages) | Cited 35 times

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In this work, we report the magnetocaloric effect (∣ΔSM∣), around the charge/orbital ordering transition in the mixed valent manganite Nd0.5Sr0.5MnO3. The magnitude of ∣ΔSM∣ around this first-order transition is around three times larger than that obtained around the second-order transition (ferromagnetic-metallic-to-paramagnetic-insulator) in the same compound. Actually, the magnetocaloric response around the charge-order transition is comparable to pure Gd, the rare earth with the highest magnetocaloric effect. The possibility of an easy tuning of the charge-order transition temperatures in doped manganites opens a way of investigation materials usable in magnetic refrigerators. © 2001 American Institute of Physics.
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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.)
71.45.-d Collective effects

Effect of perimeters of induced shielding current loops on levitation force in melt grown single-domain YBa2Cu3O7−x bulk

W. M. Yang, L. Zhou, Y. Feng, P. X. Zhang, C. P. Zhang, Z. M. Yu, and X. D. Tang

Appl. Phys. Lett. 79, 2043 (2001); http://dx.doi.org/10.1063/1.1404999 (3 pages) | Cited 5 times

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Effects of perimeters of induced shielding current loops (ISCL) on a levitation force have been investigated for a single-domain YBa2Cu3O7−x sample. The sample was prepared by a top-seeded melt–growth process. The levitation force of the sample decreases monotonously with the increasing perimeters of ISCL while the depth of the cutting slot increases along its diameter from one side to another. The maximum levitation force of the sample without any cutting slot is about 1.68 times higher than that of the sample bisected. A simple physical model is afforded to interpret the experimental results. © 2001 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena

As-grown superconducting MgB2 thin films prepared by molecular beam epitaxy

Kenji Ueda and Michio Naito

Appl. Phys. Lett. 79, 2046 (2001); http://dx.doi.org/10.1063/1.1405421 (3 pages) | Cited 100 times

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Superconducting thin films of magnesium diboride (MgB2) were prepared on various substrates [SrTiO3 (001), sapphire R, sapphire C and Si (111)] by molecular beam epitaxy. The growth temperature was examined in the ambient to 650 °C. Only films formed at temperatures between 150 and 320 °C showed superconductivity. The best TConset of 36 K with a sharp transition width of ∼1 K was observed. The TC of the as-grown superconducting MgB2 thin films is close to the bulk value. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.72.-h Cuprate superconductors
74.10.+v Occurrence, potential candidates
68.55.A- Nucleation and growth

Millisecond electron–phonon relaxation in ultrathin disordered metal films at millikelvin temperatures

M. E. Gershenson, D. Gong, T. Sato, B. S. Karasik, and A. V. Sergeev

Appl. Phys. Lett. 79, 2049 (2001); http://dx.doi.org/10.1063/1.1407302 (3 pages) | Cited 29 times

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We have measured directly the thermal conductance between electrons and phonons in ultrathin Hf and Ti films at millikelvin temperatures. The experimental data indicate that electron–phonon coupling in these films is significantly suppressed by disorder. The electron cooling time τϵ follows the T−4 dependence with a record-long value τϵ = 25 ms at T = 0.04 K. The hot-electron detectors of far-infrared radiation, fabricated from such films, are expected to have a very high sensitivity. The noise-equivalent power of a detector with the area 1 μm2 and the noise limited by fluctuations of the temperature are expected to be (2–3)×10−20 W/math, which is two orders of magnitude smaller than that of the state-of-the-art bolometers. © 2001 American Institute of Physics.
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73.61.At Metal and metallic alloys
71.38.-k Polarons and electron-phonon interactions
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
68.55.-a Thin film structure and morphology
85.60.Gz Photodetectors (including infrared and CCD detectors)
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Impact of domain wall displacements on the dielectric permittivity of epitaxial Ba0.5Sr0.5TiO3 films

Yu. A. Boikov and T. Claeson

Appl. Phys. Lett. 79, 2052 (2001); http://dx.doi.org/10.1063/1.1405147 (3 pages) | Cited 6 times

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Contributions of ferroelectric domain wall oscillations to the loss factor, tan δ, and the real part of the dielectric permittivity, ε′, of 700 nm thick Ba0.5Sr0.5TiO3 layers were considered. The domain wall related relaxation in the ferroelectric layer exhibited thermally activated behavior with a hindering barrier φ ≈ 0.08 eV. The tan δ(T) of the layer peaked and there was a hump anomaly in ε′(T) at a temperature where the relaxation rate matched the frequency of measurement. © 2001 American Institute of Physics.
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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.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation

Direct effect of illumination on ferroelectric properties of lead zirconate titanate thin films

A. L. Kholkin, S. O. Iakovlev, and J. L. Baptista

Appl. Phys. Lett. 79, 2055 (2001); http://dx.doi.org/10.1063/1.1402639 (3 pages) | Cited 7 times

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Photosensitive ferroelectric materials exhibit various photoferroelectric phenomena due to the strong influence of nonequilibrium charge carriers on polarization and phase transition. These phenomena are essential for a number of applications including photodriven actuators and sensitive photodetectors. In this work, the effect of UV illumination on dielectric and piezoelectric properties is investigated in lead zirconate titanate (PZT) thin films, which are currently the most promising material for microactuator applications. The effective piezoelectric coefficient (d33) and dielectric permittivity (ϵ) of PZT films are simultaneously measured under a weak ac electric field during illumination with a band gap light (λ = 280–400 nm). It is shown that both d33 and ϵ decrease under UV illumination. The reduction of permittivity, however, is much smaller than that of d33 and demonstrates a much slower time relaxation. The d33 decrease is attributed to the reduction of average remanent polarization under the UV light. Thus a direct effect of the photoactive light on ferroelectric polarization is observed under essentially nondestructive (weak-field) conditions. The origin of the observed effect is discussed along with the possible implications for thin-film devices. © 2001 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
72.40.+w Photoconduction and photovoltaic effects
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)
77.65.Bn Piezoelectric and electrostrictive constants

Nanopolar reorientation in ferroelectric thin films

C. Hubert, J. Levy, T. V. Rivkin, C. Carlson, P. A. Parilla, J. D. Perkins, and D. S. Ginley

Appl. Phys. Lett. 79, 2058 (2001); http://dx.doi.org/10.1063/1.1406146 (3 pages) | Cited 12 times

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The influence of varying oxygen pressure P(O2) during the growth of Ba0.4Sr0.6TiO3 thin films is investigated using dielectric and local optical probes. A transition from in-plane to out-of-plane ferroelectricity is observed with increasing P(O2). Signatures of in-plane and out-of-plane ferroelectricity are identified using dielectric response and time-resolved confocal scanning optical microscopy (TRCSOM). At the crossover pressure between in-plane and out-of-plane polarization (Pc = 85 mTorr), TRCSOM measurements reveal a soft, highly dispersive out-of-plane polarization that reorients in plane under modest applied electric fields. At higher deposition pressures, the out-of-plane polarization is hardened and is less dispersive at microwave frequencies, and the dielectric tuning is suppressed. Nanopolar reorientation is believed to be responsible for the marked increase in dielectric tuning at P(O2) = Pc. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
77.55.-g Dielectric thin films

Significant dielectric enhancement in 0.3BiFeO3–0.7SrBi2Nb2O9

Haoshuang Gu, Junmin Xue, and John Wang

Appl. Phys. Lett. 79, 2061 (2001); http://dx.doi.org/10.1063/1.1405420 (3 pages) | Cited 15 times

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Significant dielectric enhancement is observed in 0.3BiFeO3–0.7SrBi2Nb2O9, when a single-phase layered perovskite structure was formed by sintering the mechanically activated oxide composition. The Curie point of xBiFeO3–(1−x)SrBi2Nb2O9 was shifted upward with an increase in the BiFeO3 content. 0.3BiFeO3–0.7SrBi2Nb2O9 exhibits a dielectric constant of 1.84×105 at the Curie point of 750 °C. The lattice dimensions of xBiFeO3–(1−x)SrBi2Nb2O9 decrease slightly with an increase in the content of BiFeO3 over the composition range of x=0–0.2, while 0.3 mol BiFeO3 in SrBi2Nb2O9 led to recovery in the lattice dimensions. The much enhanced dielectric properties observed in 0.3BiFeO3–0.7SrBi2Nb2O9 are therefore due to the enlarged rattling space for both Nb5+ and in particular for smaller Fe3+. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.66.Fn Inorganic compounds
77.22.Ch Permittivity (dielectric function)

Impurities in dielectrics and hydrogen barriers for SrBi2Ta2O9-based ferroelectric memories

B. Yang, S. H. Oh, C. H. Chung, K. H. Noh, Y. M. Kang, S. S. Lee, S. K. Hong, N. S. Kang, and J. H. Hong

Appl. Phys. Lett. 79, 2064 (2001); http://dx.doi.org/10.1063/1.1403664 (3 pages) | Cited 3 times

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We report results of systematic investigation of impurities in dielectrics and hydrogen barriers (Ti and Al2O3 films) during the integration process of SrBi2Ta2O9-based ferroelectric memories. The capacitors integrated with Ti hydrogen barriers are not electrically degraded regardless of the annealing conditions of the subdielectrics. On the contrary, electrical properties of the capacitors using Al2O3 hydrogen barriers significantly depend on the annealing temperatures for subdielectrics. It turned out that interaction of the dielectrics with plasma during sputtering of the Ti films caused fragmentation of the moisture in the dielectrics and absorption of the hydrogen in the Ti films, making annealing irrelevant. However, the alumina films blocked both hydrogen and moisture in the subdielectrics during the passivation process, resulting in dependence on the annealing temperatures. © 2001 American Institute of Physics.
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85.50.Gk Non-volatile ferroelectric memories
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
77.55.-g Dielectric thin films
61.72.Cc Kinetics of defect formation and annealing
81.15.Cd Deposition by sputtering
77.80.Dj Domain structure; hysteresis

Low leakage current and good ferroelectric properties of SrBi2(Ta0.7Nb0.3)2O9–Bi3TiTaO9 solid solution thin film

Masatoshi Mitsuya, Norimasa Nukaga, Takayuki Watanabe, Hiroshi Funakubo, Keisuke Saito, and Minoru Osada

Appl. Phys. Lett. 79, 2067 (2001); http://dx.doi.org/10.1063/1.1407858 (3 pages) | Cited 5 times

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(1−x)SrBi2(Ta0.7Nb0.3)2O9+xBi3TiTaO9 (x = 0–0.5) solid-solution (SBTN+BTT) films of low defect contents were directly crystallized on (111)Pt/Ti/SiO2/Si substrates at 650 °C by metalorganic chemical vapor deposition. The deposited films showed a strong (103) orientation. The remanent polarization (Pr) of the directly crystallized SBTN (x = 0) was very small. However, the Pr value increased to 7.1 μC/cm2 by adding 30% of BTT (x = 0.3) and was almost equal to that of Sr0.8Bi2.2(Ta0.7Nb0.3)2O9(S0.8B2.2TN), which is widely studied for nonvolatile memory applications. The leakage current density of the SBTN+BTT solid solution was on the order of 10−8 A/cm2 for fields up to 200 kV/cm due to its low defect contents character, while that of S0.8B2.2TN was above 10−6 A/cm2 due to the existence of defects in the Sr sites. The solid-solution film showed a fatigue-free character. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ej Polarization and depolarization
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Single-crystal aluminum nitride nanomechanical resonators

A. N. Cleland, M. Pophristic, and I. Ferguson

Appl. Phys. Lett. 79, 2070 (2001); http://dx.doi.org/10.1063/1.1396633 (3 pages) | Cited 63 times

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Aluminum nitride is a light, stiff, piezoelectrically active material that can be epitaxially grown on single-crystal Si. AlN is beginning to play a role in the integration of semiconducting electronic and surface acoustic wave devices, and may prove useful for the integration of other types of mechanical devices as well. We describe the growth and subsequent electron-beam patterning and etching of epitaxial AlN-on-silicon films into nanomechanical flexural resonators. We have measured resonators with fundamental mechanical resonance frequencies above 80 MHz, and quality factors in excess of 20 000. © 2001 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.65.Cf Surface cleaning, etching, patterning
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Removable template route to metallic nanowires and nanogaps

R. Šordan, M. Burghard, and K. Kern

Appl. Phys. Lett. 79, 2073 (2001); http://dx.doi.org/10.1063/1.1405813 (3 pages) | Cited 24 times

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A general method for the fabrication of nanowires with a thickness of ∼6 nm and width of 15–20 nm is presented. The approach is applicable to inorganic and organic materials and is demonstrated here for metallic systems. The wires are produced by ion-beam etching of a gold–palladium thin films covered by chemically modified vanadium–pentoxide nanowires as an etching mask. The two-probe room-temperature resistance of the wires is found to range between 7.8 and 18.1 kΩ. Nanogaps with a length on the order of 1 nm were created within the nanowires by breaking via electromigration. © 2001 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Lk Nanocontacts
73.63.Rt Nanoscale contacts
81.65.Cf Surface cleaning, etching, patterning

Electroluminescence from silicon nanocrystals in Si/CaF2 superlattices

V. Ioannou-Sougleridis, A. G. Nassiopoulou, T. Ouisse, F. Bassani, and F. Arnaud d’Avitaya

Appl. Phys. Lett. 79, 2076 (2001); http://dx.doi.org/10.1063/1.1405004 (3 pages) | Cited 4 times

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Electroluminescence (EL) from silicon nanocrystals in Si/CaF2 superlattices grown by molecular-beam epitaxy at room temperature was investigated and compared with that obtained from silicon nanocrystals in Si/SiO2 superlattices. EL spectra exhibited current-tunability, similar to that observed in silicon nanocrystals in SiO2, which was attributed to three main effects: (a) Auger quenching of photoluminescence, which occurs when more than one electron-hole pair is present in the same nanocrystal and which quenches luminescence from relatively larger nanocrystals, (b) size-dependent carrier injection, and (c) the effect of the applied field, when this one is significantly high. In the case of Si/CaF2 superlattices, this last factor did not apply, so the two other factors are mainly at the origin of the effect. © 2001 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.60.Fi Electroluminescence
73.21.Cd Superlattices
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Field emission from short and stubby vertically aligned carbon nanotubes

M. Chhowalla, C. Ducati, N. L. Rupesinghe, K. B. K. Teo, and G. A. J. Amaratunga

Appl. Phys. Lett. 79, 2079 (2001); http://dx.doi.org/10.1063/1.1406557 (3 pages) | Cited 74 times

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Electron emission from vertically aligned carbon nanotubes grown by plasma enhanced chemical vapor deposition has been measured using a parallel plate anode and a 1 μm tungsten probe. The field emission characteristics were measured as a function of the nanotube diameter, length, and areal density. It was found that less densely populated “short and stubby” nanotubes with diameters of 200 nm and heights of 0.7 μm showed the best emission characteristics with a threshold voltage of 2 V/μm and saturation emission current density of 10 mA/cm2. A triple junction between nanotube, substrate, and vacuum is proposed to explain our results.© 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
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