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19 May 2003

Volume 82, Issue 20, pp. 3379-3570

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 3266 (2003); http://dx.doi.org/10.1063/1.1572970 (3 pages)

Michael Mück, Christian Welzel, and John Clarke
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Continuous formation and faceting of SiGe islands on Si(100)

P. Sutter, P. Zahl, and E. Sutter

Appl. Phys. Lett. 82, 3454 (2003); http://dx.doi.org/10.1063/1.1577386 (3 pages) | Cited 27 times

Online Publication Date: 12 May 2003

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The multiscale mechanisms leading to the formation of faceted quantum dot (QD) islands during Si1−xGex/Si(100) heteroepitaxy were studied by scanning tunneling microscopy. The entire evolution from an initial morphological instability of the strained alloy to final {105} faceted pyramidal QD islands is continuous. Shallow mounds, generated by the alloy instability, are bounded by alternating (100) terraces and single-layer steps. Growth of the mounds in height without lateral expansion drives a continuous increase in mound slope and step density up to a critical angle of about 6°. Kinetic constraints then force the nucleation of small {105} protofacets, which expand and ultimately coalesce to form the {105} facets bounding pyramidal QD islands. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.-a Thin film structure and morphology

Contributions from gallium vacancies and carbon-related defects to the “yellow luminescence” in GaN

R. Armitage, William Hong, Qing Yang, H. Feick, J. Gebauer, E. R. Weber, S. Hautakangas, and K. Saarinen

Appl. Phys. Lett. 82, 3457 (2003); http://dx.doi.org/10.1063/1.1578169 (3 pages) | Cited 45 times

Online Publication Date: 12 May 2003

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Carbon-doped GaN layers grown by molecular-beam epitaxy are studied with photoluminescence and positron annihilation spectroscopy. Semi-insulating layers doped with >1018 cm−3 carbon show a strong luminescence band centered at ∼2.2 eV (yellow luminescence). The absolute intensity of the 2.2 eV band is compared with the gallium vacancy concentration determined by positron annihilation spectroscopy. The results indicate that a high concentration of gallium vacancies is not necessary for yellow luminescence and that there is in fact a causal relationship between carbon and the 2.2 eV band. Markedly different deep-level ionization energies are found for the high-temperature quenching of the 2.2 eV photoluminescence in carbon-doped and reference samples. We propose that while the model of Neugebauer and Van de Walle [Appl. Phys. Lett. 69, 503 (1996)] applies for GaN of low carbon concentration, a different yellow luminescence mechanism is involved when the interstitial carbon concentration is comparable to or exceeds the gallium vacancy concentration. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters

Structural and optical properties of epitaxial BaTiO3 thin films grown on GdScO3(110)

J. Schubert, O. Trithaveesak, A. Petraru, C. L. Jia, R. Uecker, P. Reiche, and D. G. Schlom

Appl. Phys. Lett. 82, 3460 (2003); http://dx.doi.org/10.1063/1.1575935 (3 pages) | Cited 24 times

Online Publication Date: 12 May 2003

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We have prepared 1-μm-thick epitaxial BaTiO3 thin films on GdScO3(110) using pulsed laser deposition. The structural perfection of the films was revealed by a rocking curve width of Δω=0.13° for the 002 BaTiO3 reflection and a Rutherford backscattering spectrometry/channeling minimum yield, χmin, of 0.5% measured for the Ba signal behind the surface peak. High-resolution transmission electron microscopy revealed an epitaxial relationship between BaTiO3 and GdScO3 and a sharp interface between the substrate and the film. The refractive index of the BaTiO3 film was no = 2.329±0.002 and ne = 2.307±0.002 at a wavelength of 632.8 nm and no = 2.248±0.002 and ne = 2.228±0.002 at a wavelength of 1523 nm. The optical losses were less than 2 dB/cm at a wavelength of 632.8 nm. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Far-infrared-magneto-optic ellipsometry characterization of free-charge-carrier properties in highly disordered n-type Al0.19Ga0.33In0.48P

T. Hofmann, M. Schubert, C. M. Herzinger, and I. Pietzonka

Appl. Phys. Lett. 82, 3463 (2003); http://dx.doi.org/10.1063/1.1578162 (3 pages) | Cited 11 times

Online Publication Date: 12 May 2003

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For highly disordered n-type Al0.19Ga0.33In0.48P grown lattice matched to an undoped GaAs substrate, using far-infrared-magneto-optic generalized ellipsometry, the room-temperature free-charge-carrier parameters effective mass m∗ = 0.12(0.01) m0, concentration N = 6.7(0.2)×1017 cm−3, and mobility μ = 339(15) cm2/(V s) are determined by modeling the observed magneto-optic birefringence originating from the far-infrared free-charge-carrier excitations in the Al0.19Ga0.33In0.48P layer without additional electrical measurements. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Ls Magneto-optical effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.20.Fm Birefringence

Pulsed-laser-deposited ultraviolet-emitting SrS:Te thin films

J. M. Fitz-Gerald, J. Hoekstra, P. D. Rack, and J. D. Fowlkes

Appl. Phys. Lett. 82, 3466 (2003); http://dx.doi.org/10.1063/1.1571660 (3 pages) | Cited 3 times

Online Publication Date: 12 May 2003

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SrS has an indirect band gap of ∼4.32 eV, however, when it is doped with tellurium, ultraviolet emission occurs at 360 nm and 400 nm due to recombination from bound exciton states. In this letter, we discuss the ultraviolet emission of pulsed-laser-deposited thin films of SrS:Te grown at room temperature on Si. The deposited film thickness ranged from 0.1–1.5 μm, with optimized films grown at ∼0.5 μm. Te doping was incorporated by both ion implantation and conventional diffusion of deposited Te films. The characteristics of the ultraviolet emission will be discussed and correlated to the microstructural, chemical, and optical properties of the films. © 2003 American Institute of Physics.
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78.66.Li Other semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
68.55.-a Thin film structure and morphology
42.72.Bj Visible and ultraviolet sources
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Fluorine-enhanced boron diffusion in amorphous silicon

J. M. Jacques, L. S. Robertson, K. S. Jones, M. E. Law, Mike Rendon, and Joe Bennett

Appl. Phys. Lett. 82, 3469 (2003); http://dx.doi.org/10.1063/1.1576508 (3 pages) | Cited 28 times

Online Publication Date: 12 May 2003

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Silicon wafers were preamorphized with 70 keV Si+ at a dose of 1×1015 atoms/cm2, generating a deep amorphous layer of 1800 Å. Implants of 500 eV 11B+, with and without 6 keV F+, followed at doses of 1×1015 atoms/cm2 and 2×1015 atoms/cm2, respectively. After annealing at 550 °C, secondary ion mass spectroscopy determined that the diffusivity of boron in amorphous silicon is significantly enhanced in the presence of fluorine. Ellipsometry and cross-sectional transmission electron microscopy indicate the enhanced diffusion only occurs in the amorphous layer. Fluorine increases the boron diffusivity by approximately five orders of magnitude at 550 °C. It is proposed that the ability of fluorine to reduce the dangling bond concentration in amorphous silicon may reduce the formation energy for mobile boron, enhancing its diffusivity. © 2003 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.uf Ge and Si
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.37.Lp Transmission electron microscopy (TEM)

Atomic-layer doping in Si by alternately supplied NH3 and SiH4

Youngcheon Jeong, Masao Sakuraba, and Junichi Murota

Appl. Phys. Lett. 82, 3472 (2003); http://dx.doi.org/10.1063/1.1576910 (3 pages) | Cited 4 times

Online Publication Date: 12 May 2003

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Low-temperature Si growth on the atomic-layer order nitrided Si(100) surface with N amount of 1–6×1014 cm−2 formed by NH3 reaction at 400 °C were investigated using an ultraclean low-pressure chemical vapor deposition system. The epitaxial growth of Si film on the nitrided Si(100) with the initial N amount as high as about 3×1014 cm−2 is realized at 500 °C, although the film becomes amorphous in the case at the initial surface N amount of 6×1014 cm−2. By the analysis of the x-ray photoelectron spectroscopy, it is observed that the surface structure of the atomic-layer order nitrided Si(100) is changed into Si3N4 structure by the increase of the surface N amount. It is suggested that the crystallinity of Si film deposited on the atomic-layer order nitrided Si(100) is degraded by the existence of Si3N4 structure. Depth profile of N atomic-layer doped Si film clearly shows that most of the N atoms are confined within about 1-nm-thick region. © 2003 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
79.60.Dp Adsorbed layers and thin films
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Magnetic anisotropy and thermal stability study on FePt nanoparticle assembly

X. W. Wu, K. Y. Guslienko, R. W. Chantrell, and D. Weller

Appl. Phys. Lett. 82, 3475 (2003); http://dx.doi.org/10.1063/1.1576501 (3 pages) | Cited 16 times

Online Publication Date: 12 May 2003

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The temperature dependence of the first-order magnetic anisotropy constant has been investigated for off-stoichiometric chemically ordered L10, Fe45Pt55 nanoparticle samples. A representative sample shows an anisotropy energy density of Ku = 0.7×107 erg/cm3 and a thermal stability factor of KuV/kBT = 77 at room temperature. With decreasing temperature, from room temperature to 5 K, a 50% increase of Ku, accompanied by a 25% increase of the saturation magnetization MS is observed. The temperature dependence of Ku is explained on the basis of the spin-Hamiltonian approach with an Fe effective spin. The estimated median “magnetic” grain size, obtained from time-dependent measurements, decreases by about 15% with decreasing temperature from 298 to 100 K. This magnetic grain size reduction is attributed to the decrease of the superparamagnetic fraction in the FePt nanoparticle sample. © 2003 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.10.Dg Crystal-field theory and spin Hamiltonians

Magnetic behavior of nanoparticles in patterned thin films

J. Escrig, P. Landeros, J. C. Retamal, D. Altbir, and J. d’Albuquerque e Castro

Appl. Phys. Lett. 82, 3478 (2003); http://dx.doi.org/10.1063/1.1573333 (3 pages) | Cited 9 times

Online Publication Date: 12 May 2003

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The magnetic behavior of truncated conical nanoparticles in patterned thin films is investigated as a function of their size and shape. Using a scaling technique, phase diagrams giving the relative stability of characteristic internal magnetic structures of the particles are obtained. The role of the uniaxial anisotropy in determining the magnetic properties of such systems is discussed, and a simple method for establishing its strength is proposed. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
61.46.-w Structure of nanoscale materials
75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Thermal effect on the field-dependent refractive index of the magnetic fluid film

Y. F. Chen, S. Y. Yang, W. S. Tse, H. E. Horng, Chin-Yih Hong, and H. C. Yang

Appl. Phys. Lett. 82, 3481 (2003); http://dx.doi.org/10.1063/1.1576292 (3 pages) | Cited 13 times

Online Publication Date: 12 May 2003

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The field-dependent refractive index (nMF–H curve) of the magnetic fluid film (MFF) is measured at various temperatures to investigate the thermal effect on the refractive index. It was found, at a certain temperature, that the refractive index becomes higher under higher magnetic fields. This nMF–H curve is moved toward the region with lower nMF when the temperature is raised. Since the variation in the refractive index of the MF under external fields is due to the formation of the magnetic columns, the structural patterns are then examined to clarify the origin of the change in the nMF–H curve with the temperature. Under a given field strength, the particles of columns are dispersed into the liquid carrier at a higher temperature. This depresses the phase separation in the MFF under fields, and in turn, reduces the refractive index of the MFF. The observed results also reveal that the temperature exhibits a compensation effect on the refractive index of the MFF with respect to the magnetic field. © 2003 American Institute of Physics.
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78.66.Nk Insulators
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
75.50.Mm Magnetic liquids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.15.+e Liquid thin films
64.75.-g Phase equilibria

Hybridization reduction of the magnetization for N-doped FeCo superlattices

Miyoung Kim and A. J. Freeman

Appl. Phys. Lett. 82, 3484 (2003); http://dx.doi.org/10.1063/1.1576917 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2003

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In search of a soft magnetic material exhibiting high magnetization, we investigated the magnetic and structural properties of an (Fe3Co)4Nm superlattice (SL) with (m = 2) and without (m = 0) N doping via first principles full-potential linearized augmented plane wave calculations in order to examine the possible magnetic enhancement by (i) N addition (which has drawn considerable attention since the first report (in 1972) of a giant magnetic moment for quasistable α″-Fe16N2) and (ii) the lowered dimensionality of the SL. The structural optimization was fully accomplished by total energy and atomic force calculations within the generalized-gradient approximation. Despite the lattice expansion by 9% due to the N insertion, the magnetization of (Fe3Co)4N2 was found to be reduced from the value of the Fe3Co superlattice by the strong hybridization of N with Fe and Co. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Monolithic low-transition-temperature superconducting magnetometers for high resolution imaging magnetic fields of room temperature samples

F. Baudenbacher, L. E. Fong, J. R. Holzer, and M. Radparvar

Appl. Phys. Lett. 82, 3487 (2003); http://dx.doi.org/10.1063/1.1572968 (3 pages) | Cited 12 times

Online Publication Date: 12 May 2003

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We have developed a monolithic low-temperature superconducting quantum interference device (SQUID) magnetometer and incorporated the device in a scanning microscope for imaging magnetic fields of room temperature samples. The instrument has a ∼ 100 μm spatial resolution and a 1.4 pT/Hz1/2 field sensitivity above a few hertz. We discuss design constraints on and potential applications of the SQUID microscope. © 2003 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Laser ablation of Co:ZnO films deposited from Zn and Co metal targets on (0001) Al2O3 substrates

W. Prellier, A. Fouchet, B. Mercey, Ch. Simon, and B. Raveau

Appl. Phys. Lett. 82, 3490 (2003); http://dx.doi.org/10.1063/1.1578183 (3 pages) | Cited 82 times

Online Publication Date: 12 May 2003

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We report on the synthesis of high-quality Co-doped ZnO thin films using the pulsed laser deposition technique on (0001)-Al2O3 substrates performed in an oxidizing atmosphere, using Zn and Co metallic targets. We first optimized the growth of ZnO in order to obtain the less strained film. Highly crystallized Co:ZnO thin films are obtained by an alternative deposition from Zn and Co metal targets. This procedure allows an homogenous repartition of the Co in the ZnO wurzite structure which is confirmed by the linear dependence of the out-of-plane lattice parameter as a function of the Co dopant. In the case of 5% Co doped, the film exhibits ferromagnetism with a Curie temperature close to the room temperature. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
68.55.-a Thin film structure and morphology
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition
75.70.Ak Magnetic properties of monolayers and thin films
68.60.Bs Mechanical and acoustical properties
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Domain structure study of SrBi2Ta2O9 ferroelectric thin films by scanning capacitance microscopy

Ching-Chich Leu, Chih-Yuan Chen, Chao-Hsin Chien, Mao-Nan Chang, Fan-Yi Hsu, and Chen-Ti Hu

Appl. Phys. Lett. 82, 3493 (2003); http://dx.doi.org/10.1063/1.1576308 (3 pages) | Cited 22 times

Online Publication Date: 12 May 2003

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Scanning capacitance microscopy was used to image the polarization-induced microstructural patterns of sol-gel derivative SrBi2Ta2O9 (SBT) thin films. A sharp image contrast was induced between the nanosized domains owing to the various polarities, so that the domain structure in the SBT thin film was clearly revealed. As a result, the switched and unswitched regions could be unequivocally identified. This investigation also confirms that the reversal polarization process of a ferroelectric domain is much easier inside a large grain than in a small grain. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.80.Dj Domain structure; hysteresis

Ferroelectric behavior of orientation-controlled PbBi4Ti4O15 thin films

Wen Xu Xianyu, Wan In Lee, Taegyung Ko, and June Key Lee

Appl. Phys. Lett. 82, 3496 (2003); http://dx.doi.org/10.1063/1.1576307 (3 pages) | Cited 12 times

Online Publication Date: 12 May 2003

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Ferroelectric lead bismuth titanate (PbBi4Ti4O15) thin films, selectively controlled in c-axis and off-c-axis orientation, were fabricated on a Pt layer by a chemical solution deposition method. The off-c-axis oriented PbBi4Ti4O15 films demonstrated much higher remanent polarization (8.7 μC/cm2) than those of c-axis oriented films (3.7 μC/cm2). Regardless of grain orientation, PbBi4Ti4O15 films were not fatigued up to 1010 cycles under 9-V application. It is deduced that the role of Bi2O22+ layer in inducing fatigue-free property for this Bi-layered perovskite structure is the self-regulation of space charge. © 2003 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
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Dependence of the pyroelectric response on internal stresses in ferroelectric thin films

Z.-G. Ban and S. P. Alpay

Appl. Phys. Lett. 82, 3499 (2003); http://dx.doi.org/10.1063/1.1576503 (3 pages) | Cited 28 times

Online Publication Date: 12 May 2003

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The role of internal stresses on the pyroelectric properties of ferroelectric thin films is analyzed theoretically via a thermodynamic model. The pyroelectric coefficient as a function of the misfit strain is calculated for (001) Ba0.6Sr0.4TiO3 epitaxial thin films. It is shown that this property is highly dependent on the misfit strain. A very large pyroelectric response (0.65 μC/cm2 K) is theoretically predicted at a critical misfit strain (∼−0.05%) corresponding to the ferroelectric to paraelectric phase transformation. The analysis shows that internal tensile stresses are particularly not desirable with significant degradation close to an order of magnitude in the pyroelectric response. © 2003 American Institute of Physics.
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77.70.+a Pyroelectric and electrocaloric effects
77.55.-g Dielectric thin films
77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

High-dielectric-constant all-polymer percolative composites

Cheng Huang, Q. M. Zhang, and Ji Su

Appl. Phys. Lett. 82, 3502 (2003); http://dx.doi.org/10.1063/1.1575505 (3 pages) | Cited 74 times

Online Publication Date: 12 May 2003

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We report here an all-polymer high-dielectric (dielectric constant K>1000 at 1 kHz) percolative composite material, fabricated by a combination of conductive polyaniline particles (K>105) within a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer matrix (K>50). These high-K polymer hybrid materials also exhibit high electromechanical responses. For example, 1.5% strain, which is proportional to the square of the field applied, can be induced by a field of 9.5 MV/m, an eightfold reduction in field applied compared with that in a fluoroterpolymer matrix. © 2003 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)
81.05.Qk Reinforced polymers and polymer-based composites
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
72.80.Le Polymers; organic compounds (including organic semiconductors)
77.65.-j Piezoelectricity and electromechanical effects

Kelvin probe force microscopy study of SrBi2Ta2O9 and PbZr0.53Ti0.47O3 thin films for high-density nonvolatile storage devices

J. Y. Son, S. H. Bang, and J. H. Cho

Appl. Phys. Lett. 82, 3505 (2003); http://dx.doi.org/10.1063/1.1576916 (3 pages) | Cited 17 times

Online Publication Date: 12 May 2003

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Polycrystalline ferroelectric thin films of SrBi2Ta2O9 (SBT) and PbZr0.53Ti0.47O3 (PZT) were deposited on Pt/Ti/SiO2/Si substrate by pulsed laser deposition using an eclipse method and the surface potentials were observed by Kelvin probe force microscopy. The data suggest that the surface charge trap is a dominant effect over the ferroelectric polarization when a high electric field is applied on a cantilever during writing. This results from the increase of surface trapped charge and the saturation of ferroelectric remanent polarization. The data also indicate that the SBT thin films can easily trap surface charges than that of the PZT thin films. By properly biasing low voltage, the magnitude and the sign of surface potential are determined by the ferroelectric polarization than by the trapped surface charges. © 2003 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
85.50.Gk Non-volatile ferroelectric memories
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 and H2O

J. F. Conley, Y. Ono, R. Solanki, G. Stecker, and W. Zhuang

Appl. Phys. Lett. 82, 3508 (2003); http://dx.doi.org/10.1063/1.1575934 (3 pages) | Cited 23 times

Online Publication Date: 12 May 2003

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We report on the electrical properties of HfO2 deposited via atomic layer deposition using Hf(NO3)4 precursor for metal/oxide/semiconductor gate dielectric applications. Thin films, with less than 1% variation in accumulation capacitance over a 150 mm wafer, have been deposited directly on hydrogen-terminated Si wafers. The effective dielectric constant of thin (<10 nm) films was in the range of κeff = 10–12, the breakdown voltage was about 6–9 MV/cm, and the leakage current was between 3–6 orders of magnitude lower than that of SiO2. The relative benefit of lower leakage current of HfO2 over SiO2 decreased with decreasing effective thickness. Electron trapping was observed under constant voltage stressing. © 2003 American Institute of Physics.
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77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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Eu3+ ion as fluorescent probe for detecting the surface effect in nanocrystals

Chun-Hua Yan, Ling-Dong Sun, Chun-Sheng Liao, Ying-Xin Zhang, Yi-Qiang Lu, Shi-Hua Huang, and Shao-Zhe Lü

Appl. Phys. Lett. 82, 3511 (2003); http://dx.doi.org/10.1063/1.1575504 (3 pages) | Cited 46 times

Online Publication Date: 12 May 2003

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Nanocrystalline yttrium vanadate doped with trivalent europium ions, YVO4:Eu3+, was synthesized via the microemulsion mediated hydrothermal process. Laser selective excitation spectra were employed to probe the local environments of Eu3+ ions in YVO4 nanocrystals. The local environments of the dopant ions were diversified because of the surface effect in nanocrystals, which led to an increase in linewidth in excitation and emission spectra. Furthermore, the change of site symmetry from the interior to the surface of nanoparticles was clearly exhibited in the emission spectra of Eu3+ ions under different excitation wavelengths. The results show that the fluorescent behavior of doped Eu3+ ions may be a useful probe for detecting the surface effect in nanosize materials. © 2003 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.68.+m Optical properties of surfaces
78.55.Hx Other solid inorganic materials
61.46.-w Structure of nanoscale materials
61.72.S- Impurities in crystals
68.35.Dv Composition, segregation; defects and impurities

Direct fabrication of nanowires in an electron microscope

N. Silvis-Cividjian, C. W. Hagen, P. Kruit, M. A. J. v.d. Stam, and H. B. Groen

Appl. Phys. Lett. 82, 3514 (2003); http://dx.doi.org/10.1063/1.1575506 (3 pages) | Cited 55 times

Online Publication Date: 12 May 2003

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Electron-beam-induced deposition (EBID) is a potentially fast and resistless deposition technique which might overcome the fundamental resolution limits of conventional electron-beam lithography. We advance the understanding of the EBID process by simulating the structure growth. The merit of our model is that it explains the shapes of structures grown by EBID quantitatively. It also predicts the possibility to directly fabricate structures with lateral sizes smaller than 10 nm and points out the ideal conditions to achieve this goal. We verify these predictions by fabricating sub-10-nm lines and dots in a state-of-the-art scanning transmission electron microscope. © 2003 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials

Self-assembling of Ge on finite Si(001) areas comparable with the island size

L. Vescan, T. Stoica, B. Holländer, A. Nassiopoulou, A. Olzierski, I. Raptis, and E. Sutter

Appl. Phys. Lett. 82, 3517 (2003); http://dx.doi.org/10.1063/1.1576498 (3 pages) | Cited 24 times

Online Publication Date: 12 May 2003

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Voids in ultrathin oxide and electron-beam lithography-patterned windows were used to deposit Ge selectively. The number of islands is a function of the total amount of Ge deposited in a void or window. Our results show that islands smaller than the void/window size nucleate mainly near the periphery. This might be due to the tensile strain in the Si substrate near the oxide edge. The interruption of the wetting layer reduces the loss of excitons by lateral diffusion, resulting in considerable increase in optical emission from islands. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Effect of length and spacing of vertically aligned carbon nanotubes on field emission properties

S. H. Jo, Y. Tu, Z. P. Huang, D. L. Carnahan, D. Z. Wang, and Z. F. Ren

Appl. Phys. Lett. 82, 3520 (2003); http://dx.doi.org/10.1063/1.1576310 (3 pages) | Cited 106 times

Online Publication Date: 12 May 2003

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The length and the spacing of carbon nanotube (CNT) films are varied independently to investigate their effect on the field-emission characteristics of the vertically aligned CNT films grown by plasma-enhanced hot filament chemical vapor deposition using pulsed-current electrochemically deposited catalyst particles. It is shown that, in general, the macroscopic electric field Emac,1, defined as the electric field when the emission current density reaches 1 mA/cm2, can be reduced by increasing the length and the spacing of CNTs. However, for the very-high-density CNT films, the increase of length increases Emac,1 slightly, whereas for the very short CNT films, the increase of spacing does not effectively reduce Emac,1. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.45.Db Field emitters and arrays, cold electron emitters

Spatial ordering in InP/InGaP nanostructures

J. R. R. Bortoleto, H. R. Gutiérrez, M. A. Cotta, J. Bettini, L. P. Cardoso, and M. M. G. de Carvalho

Appl. Phys. Lett. 82, 3523 (2003); http://dx.doi.org/10.1063/1.1572553 (3 pages) | Cited 12 times

Online Publication Date: 12 May 2003

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We report the observation of a spatially-ordered bidimensional array of self-assembled InP quantum dots grown on slightly In-rich InGaP layers. The alignment of InP dots is observed along [100] and [010] directions. This effect is enhanced when 2° off vicinal substrates are used; it is also strongly dependent on growth temperature. Our results suggest that the density and size of CuPt-type atomically ordered regions as well as compositional modulation of InGaP layers play an important role on the spatial alignment of InP/InGaP quantum dots. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Dn Self-assembly

Diamond-like carbon nanocomposite films

Liang-Yih Chen and Franklin Chau-Nan Hong

Appl. Phys. Lett. 82, 3526 (2003); http://dx.doi.org/10.1063/1.1576909 (3 pages) | Cited 31 times

Online Publication Date: 12 May 2003

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Diamond-like carbon (DLC) nanocomposite films were deposited at room temperature by inductively coupled plasma chemical vapor deposition using hexamethyldisilane (HMDS), hexamethyldisilazane (HMDSN), and hexamethyldisiloxane (HMDSO) precursors. High-resolution transmission electron microscopy showed that all the films contained nanoparticles. The DLC nanocomposite films deposited by HMDS contained hollow spherical nanocrystallites, called nanoballs, of hexagonal silicon carbide. The nanocomposite films deposited by HMDSN contained crystalline Si3N4 nanoparticles. The nanocomposite films deposited by HMDSO contained amorphous SiOx nanoparticles. Although both types of films had similar hardness, the DLC nanocomposite films exhibited much lower compressive stresses than the DLC films deposited by methane, i.e., 1.5 vs 11 GPa, respectively. Through the enhancement of gas phase reactions, the inductively coupled plasma should be responsible for the formation of nanoparticles in the nanocomposite films. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Bs Mechanical and acoustical properties
52.77.Dq Plasma-based ion implantation and deposition
81.05.U- Carbon/carbon-based materials
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
81.07.Bc Nanocrystalline materials
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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