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15 Jul 2002

Volume 81, Issue 3, pp. 391-566

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Optical performance of nanocrystalline transparent ceria films

P. Patsalas, S. Logothetidis, and C. Metaxa

Appl. Phys. Lett. 81, 466 (2002); http://dx.doi.org/10.1063/1.1494458 (3 pages) | Cited 39 times

Online Publication Date: 2 July 2002

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Ceria is a transparent oxide suitable for various optical and optoelectronic devices. In this work, we tailor independently the refractive index n and fundamental gap Eg of nanocrystalline Ceria films by varying the substrate temperature or using Ar+ ion beams during growth with electron beam evaporation. Spectroscopic ellipsometry and x-ray reflectivity are employed to study n and Eg and to identify the physical parameters that affect them. We correlate n (varies from 1.65 to 2.15 in the studied films) with the film density through a universal, square law. The film composition strongly affects Eg, which varies from 2.8 to ∼2.0 eV. The optical absorption below 3 eV and the Eg shift are attributed to O-defect states and not to modifications in interband transitions. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.66.Nk Insulators
77.55.-g Dielectric thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.Nq Composition and phase identification
71.55.Ht Other nonmetals

Structural characterization of nonpolar (11math0) a-plane GaN thin films grown on (1math02) r-plane sapphire

M. D. Craven, S. H. Lim, F. Wu, J. S. Speck, and S. P. DenBaars

Appl. Phys. Lett. 81, 469 (2002); http://dx.doi.org/10.1063/1.1493220 (3 pages) | Cited 222 times

Online Publication Date: 2 July 2002

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In this letter we describe the structural characteristics of nonpolar (11math0) a-plane GaN thin films grown on (1math02) r-plane sapphire substrates via metalorganic chemical vapor deposition. Planar growth surfaces have been achieved and the potential for device-quality layers realized by depositing a low temperature nucleation layer prior to high temperature epitaxial growth. The in-plane orientation of the GaN with respect to the r-plane sapphire substrate was confirmed to be [0001]GaN‖[math101]sapphire and [math100]GaN‖[11math0]sapphire. This relationship is explicitly defined since the polarity of the a-GaN films was determined using convergent beam electron diffraction. Threading dislocations and stacking faults, observed in plan-view and cross-sectional transmission electron microscope images, dominated the a-GaN microstructure with densities of 2.6×1010 cm−2 and 3.8×105 cm−1, respectively. Submicron pits and crystallographic terraces were observed on the optically specular a-GaN surface with atomic force microscopy. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
61.72.Nn Stacking faults and other planar or extended defects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Lk Linear defects: dislocations, disclinations
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition

M.-H. Cho, Y. S. Roh, C. N. Whang, K. Jeong, S. W. Nahm, D.-H. Ko, J. H. Lee, N. I. Lee, and K. Fujihara

Appl. Phys. Lett. 81, 472 (2002); http://dx.doi.org/10.1063/1.1487923 (3 pages) | Cited 163 times

Online Publication Date: 2 July 2002

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The thermal stability and structural characteristics for gate stack structure of HfO2 dielectrics deposited by atomic-layer deposition (ALD) were investigated. The structural characteristics and chemical state of the HfO2 films in relation to the film thickness and postannealing temperature were examined by x-ray diffraction and x-ray photoelectron spectroscopy. An interfacial layer of hafnium silicate with an amorphous structure was grown on the oxidized Si substrate at an initial growth stage. The structural characteristics of the HfO2 films are closely affected by the interfacial layer and are depended on the thickness of the films. The 45 Å thick HfO2 film with an amorphous structure was changed into a polycrystalline structure after rapid temperature annealing of 750 °C for 5 min, while thicker films were grown into a polycrystalline structure of monoclinic or tetragonal crystal structure. The silicate layer grown at the interfacial region is not stable even at 700 °C under ultrahigh vacuum condition and changes into the silicide layers. © 2002 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.49.Uv X-ray standing waves
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.-i Photoemission and photoelectron spectra

Synchrotron x-ray scattering study on the evolution of surface morphology of the InN/Al2O3(0001) system

Ik Jae Lee, Jin Woo Kim, Tae-Bong Hur, Yoon-Hwae Hwang, and Hyung-Kook Kim

Appl. Phys. Lett. 81, 475 (2002); http://dx.doi.org/10.1063/1.1489082 (3 pages) | Cited 9 times

Online Publication Date: 2 July 2002

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Dynamic scaling behavior was studied for InN films grown on sapphire(0001) substrates using high-resolution synchrotron x-ray reflectivity and atomic force microscopy measurements. In the early stage of growth, highly strained planar InN films were grown. As the film thickness approaches an effective critical thickness, the growth gradually crosses over to the island growth. Concurrently, the relaxation of the lattice strain begins and the growth front becomes rougher. The roughness increases mostly during the intermediate crossover regime where the strain is relieved. In this regime, the dynamic scaling exponent, β, is estimated as 1.754±0.071. The evolution of the surface roughness in the final-stage growth can be described by the dynamic scaling exponent of 0.236±0.022. © 2002 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)
78.70.Ck X-ray scattering
81.05.Ea III-V semiconductors
68.49.Uv X-ray standing waves
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Characterizing an implanted Si/Si p–n junction with lower doping level by combined electron holography and focused-ion-beam milling

Zhouguang Wang, Takeharu Kato, Noriyoshi Shibata, Tsukasa Hirayama, Naoko Kato, Katsuhiro Sasaki, and Hiroyasu Saka

Appl. Phys. Lett. 81, 478 (2002); http://dx.doi.org/10.1063/1.1491606 (3 pages) | Cited 9 times

Online Publication Date: 2 July 2002

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A Si/Si p–n junction with very low doping level was made via a standard device fabrication process by implanting As ions at 25 keV into a p-type Si substrate with a boron concentration of 1015 cm−3, followed by heat annealing at 1035 °C for 33 s. To characterize this junction, a pair of 45° wedge-shape cross sections was prepared simultaneously by focused-ion-beam milling and examined using off-axis electron holography. The reconstructed phase images clearly show the phase shift induced by the electrostatic potential drop across the p–n junction, indicating that the junction has been mapped successfully. Quantitative measurements from the phase images give the potential values of 12.21±0.40 and 11.50±0.27 V, respectively, for the n- and p-type sides of the junction, 0.71±0.05 V for the potential drop across the junction and 50.10±3.88 nm for the total electric dead layer thickness. This work demonstrates that electron holography is a powerful technique for characterizing low dopant level p–n junctions in practical devices. © 2002 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Cw Elemental semiconductors
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
61.05.jp Electron holography

Zn-induced features at the GaAs(110) surface and its importance in the growth of ZnSe on GaAs(110)

R. Miotto and A. C. Ferraz

Appl. Phys. Lett. 81, 481 (2002); http://dx.doi.org/10.1063/1.1494456 (3 pages)

Online Publication Date: 2 July 2002

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A possible model for the ZnSe growth on GaAs(110) is proposed based on a first-principles pseudopotential method. Our calculations suggest that ZnSe growth on GaAs(110) could be understood in a two-step process: (i) Zn atoms will be adsorbed over Ga and As sites of the GaAs(110) surface, and (ii) the Zn atom over the Ga site will be replaced by a Se atom, followed by layer-by-layer ZnSe growth. We have also investigated Zn-induced features at the GaAs(110) surface, during the initial Zn interaction with the surface. Zn was found to adsorb preferentially at Ga substitutional sites at the subsurface layer and over Ga and As surface atoms. Theoretical STM images show the presence of bright features related to the Zn at Ga substitutional sites in the subsurface layers in agreement with recent experimental works. © 2002 American Institute of Physics.
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68.55.A- Nucleation and growth
68.43.Mn Adsorption kinetics
68.43.Fg Adsorbate structure (binding sites, geometry)
68.35.Md Surface thermodynamics, surface energies
71.15.Nc Total energy and cohesive energy calculations
71.15.-m Methods of electronic structure calculations
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Midinfrared pump–probe reflection spectroscopy of the coupled phonon–plasmon mode in GaN

Masaya Nagai, Kazuhiro Ohkawa, and Makoto Kuwata-Gonokami

Appl. Phys. Lett. 81, 484 (2002); http://dx.doi.org/10.1063/1.1494460 (3 pages) | Cited 4 times

Online Publication Date: 2 July 2002

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Strong photoinduced reflectivity change in the midinfrared region in GaN is observed by femtosecond pump–probe measurements. By comparing the results of simultaneous emission and reflectivity measurements, we show that midinfrared reflectivity spectra are governed by coupled phonon-plasmon modes and spatial inhomogeneity of carrier density. Even when the plasma frequency lies in the far infrared region at low carrier density of 1018 cm−3, the strong plasmon–phonon coupling drives the position of upper phonon–plasmon mode to midinfrared region, allowing us to investigate dynamics of photogenerated free carriers in GaN-based materials by midinfrared reflectivity measurements. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
63.20.kk Phonon interactions with other quasiparticles
78.30.Fs III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.-e Optical properties of bulk materials and thin films

Coalescence and electron activation energy in CdTe/ZnTe nanostructures

T. W. Kim, D. C. Choo, D. U. Lee, H. S. Lee, M. S. Jang, and H. L. Park

Appl. Phys. Lett. 81, 487 (2002); http://dx.doi.org/10.1063/1.1490634 (3 pages) | Cited 16 times

Online Publication Date: 2 July 2002

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Atomic force microscopy (AFM) and photoluminescence (PL) measurements were carried out to investigate the coalescence and electron activation energy in CdTe/ZnTe nanostructures. The results of the AFM images show that uniform CdTe quantum dots (QDs) are formed and that the transformation from CdTe QDs to CdTe quantum wires is caused by the coalescence. The excitonic peaks corresponding to the transition from the ground electronic subband to the ground heavy-hole band in the CdTe/ZnTe QDs shifted to higher energy in comparison with those of the CdTe/ZnTe quantum wires. The activation energy of the electrons confined in the CdTe QDs, as obtained from the temperature-dependent PL spectra, was higher than those in CdTe quantum wells and quantum wires. The present results can help to improve the understanding of coalescence and electron activation energy in CdTe/ZnTe nanostructures. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
73.63.Kv Quantum dots
73.21.La Quantum dots
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
68.37.Ps Atomic force microscopy (AFM)
71.35.-y Excitons and related phenomena
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Quantitative analysis of the polarization fields and absorption changes in InGaN/GaN quantum wells with electroabsorption spectroscopy

F. Renner, P. Kiesel, G. H. Döhler, M. Kneissl, C. G. Van de Walle, and N. M. Johnson

Appl. Phys. Lett. 81, 490 (2002); http://dx.doi.org/10.1063/1.1493229 (3 pages) | Cited 35 times

Online Publication Date: 2 July 2002

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Electroabsorption measurements are reported for wurtzite InGaN/GaN quantum wells. The electroabsorption technique allows exact quantitative analysis of absorption and absorption changes in InGaN quantum wells and barrier layers, with recorded field-induced absorption changes as large as 7000 cm−1 below and almost 20000 cm−1 above the band edge. The technique thus allows precise determination of the strong internal fields that originate from strain-induced polarization and differences in spontaneous polarization. The fields measured on functioning diodes vary between 1.1 and 1.4 MV/cm for indium concentrations in InGaN quantum wells ranging from 7% to 9%. © 2002 American Institute of Physics.
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68.65.Fg Quantum wells
78.20.Jq Electro-optical effects

Electron mobility measurement using exciplex-type organic light-emitting diodes

Y. Kawabe and J. Abe

Appl. Phys. Lett. 81, 493 (2002); http://dx.doi.org/10.1063/1.1494105 (3 pages) | Cited 14 times

Online Publication Date: 2 July 2002

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A method to measure the electron mobility in organics is demonstrated. Bilayer organic light-emitting diodes composed of donor-type and acceptor-type materials often show exciplex emission. We employed a triphenyldiamine derivative and an oxadiazole derivative (PBD) as hole and electron transporters, respectively, and confirmed that the emission is from exciplex. From the transient response of the device after application of pulsed voltage, the electron mobility of neat PBD film was evaluated to be 2.0×10−5 cm2/V s under the electric field of 1 MV/cm. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.50.Dn Low-field transport and mobility; piezoresistance
71.70.-d Level splitting and interactions

Formation of pnp bipolar structure by thermal donors in nitrogen-containing p-type Czochralski silicon wafers

Xiangyang Ma, Xuegong Yu, Ruixin Fan, and Deren Yang

Appl. Phys. Lett. 81, 496 (2002); http://dx.doi.org/10.1063/1.1494466 (3 pages) | Cited 19 times

Online Publication Date: 2 July 2002

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The carrier concentration profile in boron-doped p-type nitrogen-containing Czochralski silicon wafer subjected to a one-step high-temperature (1150 °C) annealing followed by a prolonged 450 °C annealing has been investigated by spreading resistance profile. It is found that the carrier concentration profile is characteristic of a pnp bipolar structure, while, that in the control wafer of p-type conventional Czochralki silicon subjected to the identical thermal treatment is just characteristic of a p-n junction. Moreover, it is suggested that only one-step annealing at high temperatures is an efficient method for intrinsic gettering of a nitrogen-containing Czochralski silicon wafer due to the outdiffusion of oxygen and nitrogen in the near-surface region and the nitrogen-enhanced oxygen precipitation in the bulk region. © 2002 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.Tx Gettering
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.Yx Interaction between different crystal defects; gettering effect
81.30.Mh Solid-phase precipitation
61.72.uf Ge and Si
66.30.J- Diffusion of impurities

Growth and characterization of CaF2/Ge/CaF2/Si(111) quantum dots for resonant tunneling diodes operating at room temperature

A. I. Yakimov, A. S. Derjabin, L. V. Sokolov, O. P. Pchelyakov, A. V. Dvurechenskii, M. M. Moiseeva, and N. S. Sokolov

Appl. Phys. Lett. 81, 499 (2002); http://dx.doi.org/10.1063/1.1494465 (3 pages) | Cited 9 times

Online Publication Date: 2 July 2002

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Resonant tunneling diodes were implemented on Ge quantum dots fabricated using Stranski–Krastanov growth mode on CaF2 matrix, lattice matched to Si(111) substrates. The negative differential conductance and conductance oscillations due to hole resonant tunneling through the zero-dimensional states of Ge quantum dots are clearly observed at room temperature. From the period of conductance oscillations, the energy separations between the states of the quantum dots with different sizes are estimated to be 40–50 meV (i.e., >kT = 26 meV at T = 300 K). © 2002 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.07.Ta Quantum dots
85.35.Gv Single electron devices
73.21.La Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
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Accurate oxygen-content determination method for decreased sample amounts of superconductive and other functional oxides

Yukiko Yasukawa, Hisao Yamauchi, and Maarit Karppinen

Appl. Phys. Lett. 81, 502 (2002); http://dx.doi.org/10.1063/1.1490146 (3 pages) | Cited 3 times

Online Publication Date: 2 July 2002

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In a conventional wet-chemical redox analysis applied to the determination of oxygen contents of nonstoichiometric functional oxides such as superconductive copper oxides, the sample amount required for a single experiment is typically 50–100 mg. Here we demonstrate that an improved coulometric titration method works to precisely analyze oxygen contents of decreased amounts of various complex oxides containing, e.g., copper, cobalt, or iron at mixed valence values. The improved titration method is found to yield the oxygen content of the YBa2Cu3O7−δ reference sample with high reproducibility, i.e., ∣Δδ∣<0.01, for samples with a mass of only ∼ 10 mg. © 2002 American Institute of Physics.
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82.80.-d Chemical analysis and related physical methods of analysis
74.72.-h Cuprate superconductors

Probing microwave properties of high-Tc films via small dc magnetic fields

Peter Lahl and Roger Wördenweber

Appl. Phys. Lett. 81, 505 (2002); http://dx.doi.org/10.1063/1.1487902 (3 pages) | Cited 11 times

Online Publication Date: 2 July 2002

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It is demonstrated that the combination of vortex matter and rf measurements yields new insight into the microwave properties of superconducting thin-film devices, both in small magnetic fields and zero field. The comparison of field-cooled and different types of field-sweep experiments on coplanar high-Tc thin-film resonators shows that the microwave properties strongly depend on magnetization and vortex distribution in the superconducting film as well. Thus, using vortices as a kind of local probe for the microwave properties leads to a consistent explanation of the microwave power handling in nonzero and zero magnetic fields. In a model that is derived from the experiments, the nonlinear microwave behavior is explained by the limitation of the total current density in the device considering contributions of the rf field and the screening of the magnetic field and vortices to the current. The limiting current value seems to be related to the dc critical current of the superconductor. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.N- Response to electromagnetic fields
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines

State switching in Bi-doped La0.67Ca0.33MnO3 and the effects of current

J. R. Sun, J. Gao, and L. Kang

Appl. Phys. Lett. 81, 508 (2002); http://dx.doi.org/10.1063/1.1494109 (3 pages) | Cited 4 times

Online Publication Date: 2 July 2002

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Electronic transport and magnetic properties of La0.477Bi0.193Ca0.33MnO3 have been experimentally studied. Different resistive behaviors are observed in the cooling and warming processes. The system first stays at a high resistive state, and switches to a state of lower resistivity when it is cooled below a critical temperature. However, keeping the sample at a temperature below ∼60 K, a relaxation to the high resistive state takes place. This process is current dependent, and the application of a large current slows down the relaxation greatly. There is a strong competition between the two resistive states, which causes a switch of the system between states. © 2002 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
72.20.Fr Low-field transport and mobility; piezoresistance

Above-room-temperature ferromagnetism in GaSb/Mn digital alloys

X. Chen, M. Na, M. Cheon, S. Wang, H. Luo, B. D. McCombe, X. Liu, Y. Sasaki, T. Wojtowicz, J. K. Furdyna, S. J. Potashnik, and P. Schiffer

Appl. Phys. Lett. 81, 511 (2002); http://dx.doi.org/10.1063/1.1481184 (3 pages) | Cited 65 times

Online Publication Date: 2 July 2002

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Digital alloys of GaSb/Mn have been fabricated by molecular-beam epitaxy. Transmission electron micrographs showed good crystal quality with individual Mn-containing layers well resolved, no evidence of three-dimensional MnSb precipitates was seen in as-grown samples. All samples studied exhibited ferromagnetism with temperature-dependent hysteresis loops in the magnetization accompanied by metallic p-type conductivity with a strong anomalous Hall effect (AHE) up to 400 K (limited by the experimental setup). The anomalous Hall effect shows hysteresis loops at low temperatures and above room temperature very similar to those seen in the magnetization. The strong AHE with hysteresis indicates that the holes interact with the Mn spins above room temperature. All samples are metallic, which is important for spintronics applications. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.25.Dc Spin polarized transport in semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
68.37.Lp Transmission electron microscopy (TEM)
72.15.Gd Galvanomagnetic and other magnetotransport effects
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance
73.61.Ey III-V semiconductors

Tunneling magnetoresistance of Co clusters in MgF2

B. Hackenbroich, H. Zare-Kolsaraki, and H. Micklitz

Appl. Phys. Lett. 81, 514 (2002); http://dx.doi.org/10.1063/1.1494467 (3 pages) | Cited 11 times

Online Publication Date: 2 July 2002

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Samples of Co clusters embedded in a MgF2 matrix have been prepared by the codeposition of well-defined Co clusters (mean diameter L ≃ 4.5 nm) and MgF2 molecules onto a cold substrate. This system shows a temperature-dependent tunneling magnetoresistance (TMR) which has a value of 34.7(2)% at 2.5 K, the largest TMR value reported for a granular Co system. This large TMR value either is due to an antiferromagnetic coupling of those Co clusters between which the tunneling occurs or is caused by an enhanced spin-polarization of the tunneling electrons. The latter may be caused by a cluster–surface/matrix interaction leading to dominated d-electron tunneling due to Co(3d)–F(2p) hybridization. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
75.47.De Giant magnetoresistance

Miscut-angle dependence of perpendicular magnetic anisotropy in thin epitaxial CoPt3 films grown on vicinal MgO

B. B. Maranville, A. L. Shapiro, F. Hellman, D. M. Schaadt, and E. T. Yu

Appl. Phys. Lett. 81, 517 (2002); http://dx.doi.org/10.1063/1.1491610 (3 pages) | Cited 10 times

Online Publication Date: 2 July 2002

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The effect of vicinal substrates on the growth-induced perpendicular magnetic anisotropy of epitaxial CoPt3 films has been studied. A small (2°, 4°, or 10°) miscut angle of the vicinal substrate causes the crystallographic axes of the sample to be tilted along the miscut direction. The magnitude of the perpendicular anisotropy is unaffected by the presence of substrate steps produced by the miscut angle, while an additional, in-plane anisotropy develops with a larger miscut angle. Effects of the steps are seen in magnetic force microscopic images of domain wall pinning. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
81.05.Bx Metals, semimetals, and alloys
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Rt Magnetic force microscopy (MFM)
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Cobalt–oxide underlayers for cobalt–ferrite pinned spin valves

S. Maat, M. J. Carey, Eric E. Fullerton, T. X. Le, P. M. Rice, and B. A. Gurney

Appl. Phys. Lett. 81, 520 (2002); http://dx.doi.org/10.1063/1.1494461 (3 pages) | Cited 14 times

Online Publication Date: 2 July 2002

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We report on the advantages of employing insulating Co–oxide underlayers for spin valves utilizing Co–ferrite as a pinning layer. These underlayers provide for improved crystalline growth of Co-ferrite pinning layers, which can be reduced to as little as 3 nm in thickness while maintaining high coercivity and thermal stability. This allows a typical antiferromagnetically pinned spin valve to fit into a 50 nm gap, which is anticipated for recording densities >100 Gbit/in2. Magnetoresistance values ∼7%, excellent stability, and free layer properties are observed and pinned which is comparable to present PtMn based sensors of similar thickness. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Gg Ferrimagnetics
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
68.60.Dv Thermal stability; thermal effects
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Electrical conductivity and thermopower of Cu–SiO2 nanogranular films

W. Chen, J. J. Lin, X. X. Zhang, H. K. Shin, J. S. Dyck, and C. Uher

Appl. Phys. Lett. 81, 523 (2002); http://dx.doi.org/10.1063/1.1493668 (3 pages) | Cited 4 times

Online Publication Date: 2 July 2002

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We have measured the thermopower S and electrical conductivity σ in a series of Cux(SiO2)1−x nanogranular films between 2 and 300 K with Cu volume fraction x varying from 0.43 up to 1.0. At low temperatures, disorder-enhanced electron–electron interaction effects dictate the behavior of σ. A crossover of the temperature dependence from σ∝math to σ∝T1/3 is observed as x is lowered and the metal–insulator transition is approached. S is small, shows linear temperature dependence, and is rather insensitive to the change of x. Effects of annealing are also discussed. © 2002 American Institute of Physics.
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73.61.-r Electrical properties of specific thin films
73.50.Lw Thermoelectric effects
72.60.+g Mixed conductivity and conductivity transitions
61.72.Cc Kinetics of defect formation and annealing
72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Carbon nanofibers synthesized by decomposition of alcohol at atmospheric pressure

N. Jiang, R. Koie, T. Inaoka, Y. Shintani, K. Nishimura, and A. Hiraki

Appl. Phys. Lett. 81, 526 (2002); http://dx.doi.org/10.1063/1.1494102 (3 pages) | Cited 13 times

Online Publication Date: 2 July 2002

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In the present study, we fabricated the carbon nanofibers (CNFs) by decomposition of methyl alcohol at atmospheric pressure. The CNFs were grown on Ni/Si substrates using simplified hot-filament chemical vapor deposition equipment. The deposits mainly consist of the semicrystalline CNFs, in which a few of carbon nanotubes are included. On the 30-nm-thick Ni/Si substrates, the mean length of the CNFs is 2–3 μm, and their average diameter is less than 100 nm. The as-deposited CNFs were evaluated by both scanning and transmission electron microscopes. The field-electron-emission properties of CNFs were characterized as well. © 2002 American Institute of Physics.
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81.16.Be Chemical synthesis methods
81.07.De Nanotubes
81.05.U- Carbon/carbon-based materials
61.46.-w Structure of nanoscale materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
79.70.+q Field emission, ionization, evaporation, and desorption

Two-dimensional array of self-assembled AlInAs quantum wires

S. Francoeur, A. G. Norman, A. Mascarenhas, E. D. Jones, J. L. Reno, S. R. Lee, and D. M. Follstaedt

Appl. Phys. Lett. 81, 529 (2002); http://dx.doi.org/10.1063/1.1493222 (3 pages) | Cited 4 times

Online Publication Date: 2 July 2002

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We present the optical and structural characterization of a two-dimensional array of self-organized AlInAs quantum wires. The structure was created by epitaxially stacking along the [001] direction thin self-assembled, [100]-oriented, superlattices separated by homogeneous layers of Al0.48In0.52As. Vertical and lateral self-alignment results in a highly regular array of wires oriented along the [010] direction. The wire cross-sectional dimensions are about 10×14.4 nm2 and their density is 1.9×1011 cm−2. The energy and the nature of the electronic transitions are significantly affected by confinement in two dimensions: (1) a blueshift of about 100 meV is observed and (2) the two lowest energy transitions are both polarized along the [010] direction. For comparison, the two lowest energy transitions of a lateral superlattice with similar characteristics have a heavy- (polarization along [010]) and a light-hole character (polarization along [100]). Large polarization ratios are measured for both transitions. © 2002 American Institute of Physics.
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68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires

Single-electron transistor as a radio-frequency mixer

R. Knobel, C. S. Yung, and A. N. Cleland

Appl. Phys. Lett. 81, 532 (2002); http://dx.doi.org/10.1063/1.1493221 (3 pages) | Cited 25 times

Online Publication Date: 2 July 2002

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We demonstrate the use of the single-electron transistor as a radio-frequency mixer, based on the nonlinear dependence of current on gate charge. This mixer can be used for high-frequency, ultrasensitive charge measurements over a broad and tunable range of frequencies. We demonstrate operation of the mixer, using a lithographically defined thin-film aluminum transistor, in both the superconducting and normal states of aluminum, over frequencies from 10 to 300 MHz. We have operated the device both as a homodyne detector and as a phase-sensitive heterodyne mixer. We demonstrate a charge sensitivity of <4×10−3 e/math, limited by room-temperature electronics. An optimized mixer has a theoretical charge sensitivity of ≲1.5×10−5 e/math. © 2002 American Institute of Physics.
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85.35.Gv Single electron devices
85.25.Cp Josephson devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology
73.61.At Metal and metallic alloys
74.78.-w Superconducting films and low-dimensional structures
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
07.68.+m Photography, photographic instruments; xerography
06.30.-k Measurements common to several branches of physics and astronomy

Optical properties of Mn-doped CdS nanocrystals fabricated by sequential ion implantation

Yoshihiko Kanemitsu, Hiroki Matsubara, and C. W. White

Appl. Phys. Lett. 81, 535 (2002); http://dx.doi.org/10.1063/1.1494468 (3 pages) | Cited 32 times

Online Publication Date: 2 July 2002

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We have studied luminescence spectrum and dynamics of Mn-doped CdS nanocrystals fabricated by sequential Cd+, S+, and Mn+ ion implantation into Al2O3 matrices. The photoluminescence (PL) due to the Mn2+ intra-3d transition is clearly observed near 570 nm in Mn-doped CdS nanocrystals. The PL excitation spectrum of the Mn2+ luminescence in Mn-doped CdS nanocrystals is similar to the optical absorption spectrum and PL excitation spectrum of undoped CdS nanocrystals. Our spectroscopic data show that ion-beam synthesis is one of the methods of the fabrication of doped semiconductor nanocrystals. The luminescence mechanism of Mn-doped CdS nanocrystals will be discussed. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects

Resonant tunneling of Si nanocrystals embedded in Al2O3 matrix synthesized by vacuum electron-beam co-evaporation

Q. Wan, T. H. Wang, M. Zhu, and C. L. Lin

Appl. Phys. Lett. 81, 538 (2002); http://dx.doi.org/10.1063/1.1491298 (3 pages) | Cited 15 times

Online Publication Date: 2 July 2002

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High vacuum electron-beam co-evaporation, followed by N2 annealing at 500 °C is used for preparing of silicon nanocrystals (Si NCs) embedded in Al2O3 dielectric matrix. X-ray diffraction and transmission electron microscopy are used to investigate the structures of Si+Al2O3 films and estimate the mean diameter of the Si NCs. The electrical properties of the diode containing Si NCs embedded in Al2O3 are studied at room temperature and resonant tunneling effect with large voltage gap is observed. A circuit model based on resonant tunneling is proposed to simulate the measured I–V curve. © 2002 American Institute of Physics.
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73.63.Kv Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
73.23.-b Electronic transport in mesoscopic systems
73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Cc Kinetics of defect formation and annealing
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