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5 May 2003

Volume 82, Issue 18, pp. 2939-3130

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 2957 (2003); http://dx.doi.org/10.1063/1.1571977 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, Suguru Sangu, and Motoichi Ohtsu
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Dependence of morphology on miscut angle for Si(111) etched in NH4F

Joseph Fu, Hui Zhou, John Kramar, Richard Silver, and Satoshi Gonda

Appl. Phys. Lett. 82, 3014 (2003); http://dx.doi.org/10.1063/1.1569426 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2003

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Hydrogen-terminated silicon surfaces are important and commonly used in several nanotechnology applications. A significant obstacle to their widespread use has been the repeatable preparation of large, flat surfaces. Using scanning probe microscopy, we have examined the surfaces of several vicinal Si(111) samples, with miscut angles ranging from 1.1° to 0.01°, produced by etching in a NH4F aqueous solution. Although the miscut angle sets the nominal terrace width, we have found that with wet chemical etch processing, as the vicinal angle decreases, the terrace width increases only to a maximum of ∼200 nm, limited by the etching anisotropy. The result is that for miscut angles below a critical angle, the surface roughness actually increases. © 2003 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
68.37.Ps Atomic force microscopy (AFM)
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Influences of central metal ions on the electroluminescene and transport properties of tris-(8-hydroxyquinoline) metal chelates

B. J. Chen, X. W. Sun, and Y. K. Li

Appl. Phys. Lett. 82, 3017 (2003); http://dx.doi.org/10.1063/1.1572474 (3 pages) | Cited 10 times

Online Publication Date: 29 April 2003

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A series of tris-(8-hydroxyquinoline) metal chelates with central metal ions of Al3+, Ga3+, and In3+ was synthesized, characterized, and used in organic electroluminescent devices. The ionization potential and optical band gap of the three chelates were measured by ultraviolet photoelectron spectroscopy and ultraviolet-visible spectrum, respectively. Two types of devices, with configurations of indium tin oxide (ITO)/N,N′-diphenyl-N,N′-(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) (80 nm)/Mq3 (80 nm)/Mg:Ag (200 nm) and ITO/TPD (60 nm)/TPD:rubrene (3%) (20 nm)/Mq3 (80 nm)/Mg:Ag (200 nm) (M = Al, Ga, or In), were fabricated and characterized based on these metal chelates. In the first type of configuration, the metal chelates were used as both the emitter and the electron-transporting layer. In the second type of configuration, the metal chelates were believed to only act as electron-transporting layer. As the central ion changed, both the luminescence and the carrier transport properties of the metal chelates were changed. By comparing the performance of the two types of devices, we found that as the size of the metal ion increased, the luminance efficiency decreased and the electron mobility increased. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
72.80.Le Polymers; organic compounds (including organic semiconductors)

Effect of low-temperature annealing on (Ga,Mn)As trilayer structures

D. Chiba, K. Takamura, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 82, 3020 (2003); http://dx.doi.org/10.1063/1.1571666 (3 pages) | Cited 132 times

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The effect of low-temperature annealing on (Ga,Mn)As/GaAs/(Ga,Mn)As trilayer structures is studied. Low-temperature annealing significantly increases the ferromagnetic transition temperature TC of top (Ga,Mn)As layers, reaching as high as 160 K, whereas no apparent effect is observed on bottom (Ga,Mn)As layers. The annealing effect on Be-doped trilayers is also presented. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Cc Kinetics of defect formation and annealing

Absence of carrier recombination associated with the defect pool model in intrinsic amorphous silicon layers: Evidence from current–voltage characteristics on p–i–n and n–i–p solar cells

J. Deng, J. M. Pearce, R. J. Koval, V. Vlahos, R. W. Collins, and C. R. Wronski

Appl. Phys. Lett. 82, 3023 (2003); http://dx.doi.org/10.1063/1.1571985 (3 pages) | Cited 13 times

Online Publication Date: 29 April 2003

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Forward bias current–voltage characteristics (JD–V) were studied for both p–i–n (superstrate) and n–i–p (substrate) (a-SiC:H p)/(a-Si:H i) solar-cell structures having different p/i interface layers and different thickness i-layers. Contributions of the p/i interfaces to the JD–V characteristics were separated, and the dependence on the thickness of the i-layers was established. Equivalence was observed in a comparison of the characteristics of p–i–n and n–i–p cells. The various JD–V characteristics are found to be consistent with uniform densities of defects in the i-layers, and thus inconsistent with the spatially varying large densities of defects predicted for solar-cell structures by the defect pool model. © 2003 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.61.Cw Elemental semiconductors

Highly stable and textured hydrogenated ZnO thin films

Seung Yeop Myong and Koeng Su Lim

Appl. Phys. Lett. 82, 3026 (2003); http://dx.doi.org/10.1063/1.1571651 (3 pages) | Cited 37 times

Online Publication Date: 29 April 2003

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We investigated intentionally hydrogenated zinc oxide (ZnO:H) fabricated by combining photoassisted metalorganic chemical vapor deposition and mercury-sensitized hydrogen addition methods. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved surface roughness of the ZnO:H film due to an enhancement of (11math0) orientation. The high-quality ZnO:H film is promising as a back reflector material for thin-film solar cells. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Dv Thermal stability; thermal effects
84.60.Jt Photoelectric conversion
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Hydrogen density-of-states in polycrystalline silicon

N. H. Nickel and K. Brendel

Appl. Phys. Lett. 82, 3029 (2003); http://dx.doi.org/10.1063/1.1570924 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2003

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The influence of laser crystallization on hydrogen bonding in polycrystalline silicon is investigated employing hydrogen effusion measurements. Fully crystallized poly-Si samples contain a residual H concentration of up to 1.5×1022 cm−3. From the effusion spectra, the H density-of-states distribution is derived. Interestingly, hydrogen bonding is affected by the deposition temperature of the amorphous starting material. Below the H transport states, four peaks are observed in the H density of states at ≈ −2.15, −2.4, −2.7, and −3.25 eV. © 2003 American Institute of Physics.
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71.55.Cn Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing

Nanometer-scale switches using copper sulfide

T. Sakamoto, H. Sunamura, H. Kawaura, T. Hasegawa, T. Nakayama, and M. Aono

Appl. Phys. Lett. 82, 3032 (2003); http://dx.doi.org/10.1063/1.1572964 (3 pages) | Cited 168 times

Online Publication Date: 29 April 2003

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We describe a nanometer-scale switch that uses a copper sulfide film and demonstrate its performance. The switch consists of a copper sulfide film, which is a chalcogenide semiconductor, sandwiched between copper and metal electrodes. Applying a positive or negative voltage to the metal electrode can repeatedly switch its conductance in under 100 μs. Each state can persist without a power supply for months, demonstrating the feasibility of nonvolatile memory with its nanometer scale. While biasing voltages, copper ions can migrate in copper sulfide film and can play an important role in switching. © 2003 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
85.30.-z Semiconductor devices

Electric-field-induced heating and energy relaxation in GaN

T. A. Eckhause, Ö. Süzer, Ç. Kurdak, F. Yun, and H. Morkoç

Appl. Phys. Lett. 82, 3035 (2003); http://dx.doi.org/10.1063/1.1571982 (3 pages) | Cited 9 times

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Electric-field-induced heating is studied using noise measurements in n-type GaN grown on sapphire substrates. The measured electron temperature is found to be an order of magnitude higher than what is expected based on calculations of electron–phonon coupling via acoustic deformation potential scattering processes in GaN. The discrepancy may be explained by a large thermal boundary resistance between the GaN film and the sapphire substrate. © 2003 American Institute of Physics.
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72.70.+m Noise processes and phenomena
73.61.Ey III-V semiconductors
71.38.-k Polarons and electron-phonon interactions

Influence of in situ applied stress during thermal oxidation of (111)Si on Pb interface defects

A. Stesmans, D. Pierreux, R. J. Jaccodine, M.-T. Lin, and T. J. Delph

Appl. Phys. Lett. 82, 3038 (2003); http://dx.doi.org/10.1063/1.1555277 (3 pages) | Cited 17 times

Online Publication Date: 29 April 2003

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The results of a series of experiments are reported in which constant, controlled levels of in-plane stress were applied in situ to oxidizing (111) silicon substrates. Electron spin resonance measurements show that the properties of inherently incorporated electrically active Pb defects at the (111)Si/SiO2 interface are affected; among others, tensile stresses decrease the number of Pbs, while compressive stresses have the opposite effect. The results are in agreement with the generally accepted relationship between Pb-defect generation and interfacial mismatch (stress). © 2003 American Institute of Physics.
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81.65.Mq Oxidation
68.35.Ct Interface structure and roughness
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
76.30.Mi Color centers and other defects

Enhanced p-type conduction in GaN and AlGaN by Mg-δ-doping

M. L. Nakarmi, K. H. Kim, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 82, 3041 (2003); http://dx.doi.org/10.1063/1.1559444 (3 pages) | Cited 21 times

Online Publication Date: 29 April 2003

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Mg-δ-doping in GaN and AlGaN epilayers has been investigated by metalorganic chemical vapor deposition. It was demonstrated through electrical, optical, and structural studies that Mg-δ-doping improves not only p-type conduction, but also the overall quality of p-type GaN and AlGaN epilayers. A twofold (fivefold) enhancement in lateral (vertical) p-type conduction have been achieved for GaN and AlGaN epilayers. It is argued that the observed dislocation density reduction (of about one order of magnitude) is due to the growth interruption in the Mg-δ-doping duration that partially terminates the dislocation propagation in the growth direction. Furthermore, Mg-δ-doping also reduces Mg impurity self-compensation and enhances hole concentrations in Mg-δ-doped GaN or AlGaN. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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Isothermal tuning of exchange bias using pulsed fields

J. Nogués, J. Sort, S. Suriñach, J. S. Muñoz, M. D. Baró, J. F. Bobo, U. Lüders, E. Haanappel, M. R. Fitzsimmons, A. Hoffmann, and J. W. Cai

Appl. Phys. Lett. 82, 3044 (2003); http://dx.doi.org/10.1063/1.1565711 (3 pages) | Cited 21 times

Online Publication Date: 29 April 2003

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Exchange bias, HE, and coercivity, HC, of antiferromagnetic (AFM)/ferromagnetic bilayers can be adjusted, after deposition, at temperatures below the Néel temperature of the AFM by subjecting the samples to large pulsed fields (in excess of HPulse = 550 kOe). The efficiency of the process depends on the AFM system and the direction of the applied field with respect of the unidirectional anisotropy direction. Textured (111) Fe19Ni81/Fe50Mn50 bilayers show an HE reduction and a HC increase when the pulse field is applied antiparallel to the unidirectional anisotropy, while they only exhibit a reduction in HC when the pulse is applied parallel to their unidirectional anisotropy. On the other hand, textured (111) NiO/Co bilayers exhibit a change of the angular dependence of HE when the pulse is applied away from the unidirectional anisotropy. The effects could be caused by field induced changes in the domain structure of the AFM or transitions in the AFM (spin–flop or AFM–paramagnetic). © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Synthesis, characterization, and modeling of high quality ferromagnetic Cr-doped AlN thin films

Stephen Y. Wu, H. X. Liu, Lin Gu, R. K. Singh, L. Budd, M. van Schilfgaarde, M. R. McCartney, David J. Smith, and N. Newman

Appl. Phys. Lett. 82, 3047 (2003); http://dx.doi.org/10.1063/1.1570521 (3 pages) | Cited 83 times

Online Publication Date: 29 April 2003

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We report a theoretical and experimental investigation of Cr-doped AlN. Density functional calculations predict that the isolated Cr t2 defect level in AlN is 1/3 full, falls approximately at midgap, and broadens into an impurity band for concentrations over 5%. Substitutional Al1−xCrxN random alloys with 0.05 ⩽ x ⩽ 0.15 are predicted to have Curie temperatures over 600 K. Experimentally, we have characterized and optimized the molecular beam epitaxy thin film growth process, and observed room temperature ferromagnetism with a coercive field, Hc, of 120 Oe. The measured magnetic susceptibility indicates that over 33% of the Cr is magnetically active at room temperature and 40% at low temperature. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.55.Eq III-V semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Small-angle neutron scattering measurements of magnetic cluster sizes in magnetic recording disks

Michael F. Toney, Kurt A. Rubin, Sung-Min Choi, and Charles J. Glinka

Appl. Phys. Lett. 82, 3050 (2003); http://dx.doi.org/10.1063/1.1571652 (3 pages) | Cited 9 times

Online Publication Date: 29 April 2003

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We describe small-angle neutron scattering measurements of the magnetic cluster size distributions for several longitudinal magnetic recording media. We find that the average magnetic cluster size is slightly larger than the average physical grain size, that there is a broad distribution of cluster sizes, and that the cluster size is inversely correlated to the media signal-to-noise ratio. These results show that intergranular magnetic coupling in these media is small and they provide empirical data for the cluster-size distribution that can be incorporated into models of magnetic recording. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Et Exchange and superexchange interactions

Giant-magnetoimpedance-based sensitive element as a model for biosensors

G. V. Kurlyandskaya, M. L. Sánchez, B. Hernando, V. M. Prida, P. Gorria, and M. Tejedor

Appl. Phys. Lett. 82, 3053 (2003); http://dx.doi.org/10.1063/1.1571957 (3 pages) | Cited 41 times

Online Publication Date: 29 April 2003

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We study the magnetoimpedance effect, using a Co67Fe4Mo1.5Si16.5B11 amorphous, ribbon-based sensitive element, in the presence of a commercial Ferrofluid® liquid thin layer covering the ribbon surface. The magnetoimpedance response is clearly dependent on the presence of the magnetic ferroliquid, the value of the applied magnetic field, and the parameters of the driving current. The magnetoimpedance-based prototype is proposed as a biosensor with high sensitivity to the fringe field produced by magnetic nanoparticles. A special advantage of this sensor is its high stability to chemical aggressive media; hence, it can be used for in situ measurements during fabrication of biomaterials with a high level of affinity and specificity with nanoparticles employed as bimolecular labels. © 2003 American Institute of Physics.
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87.80.-y Biophysical techniques (research methods)

Nanostructure and magnetic properties of BN-encapsulated Fe(B) and Fe2N nanoparticles prepared by dual ion-beam sputtering

D. Babonneau, M. Jaouen, M.-F. Denanot, P. Guérin, and F. Petroff

Appl. Phys. Lett. 82, 3056 (2003); http://dx.doi.org/10.1063/1.1571230 (3 pages) | Cited 9 times

Online Publication Date: 29 April 2003

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BN–Fe nanocomposite films have been produced by dual ion-beam sputtering codeposition. The effect of using a reactive nitrogen assistance beam during the elaboration process has been studied by transmission electron microscopy, selected area electron diffraction, grazing incidence small-angle x-ray scattering, and magnetic measurements. Experimental results show that without assistance, we produce nearly spherical Fe(B) nanoparticles (2–3 nm in diameter) exhibiting a superparamagnetic behavior. When growing under assistance, we obtain vertically elongated nanoparticles of paramagnetic ζ-Fe2N encapsulated in disordered hexagonal BN. This study demonstrates the possibility of producing encapsulated nanoparticles with high shape anisotropy by activating the surface diffusion of the incoming deposited species. © 2003 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Cd Deposition by sputtering
75.30.Gw Magnetic anisotropy
68.35.Fx Diffusion; interface formation

A stabilizer for superconducting quantum interference device gradiometers for operation in lightly shielded environments

Koichi Yokosawa, Akihiko Kandori, Tsuyoshi Miyashita, Daisuke Suzuki, Keiji Tsukada, and Akira Tsukamoto

Appl. Phys. Lett. 82, 3059 (2003); http://dx.doi.org/10.1063/1.1571956 (3 pages) | Cited 1 time

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A stabilizer for superconducting quantum interference device (SQUID) magnetometers operating in lightly shielded environments is proposed. When the stabilizer is applied in an electrical gradiometer, which operates by obtaining differences between the outputs of the two SQUID magnetometers, the intrinsic noise of the stabilizer can be neglected. The operation of an electrical gradiometer where the SQUID magnetometers are of the high-critical-temperature (high-Tc) type is shown to be substantially more stable in a lightly magnetically shielding cylinder with the addition of the stabilizer function. Very clear magnetocardiograms were obtained by a gradiometer of this type. © 2003 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
87.80.-y Biophysical techniques (research methods)
74.72.-h Cuprate superconductors

Element-specific magnetic properties of the epitaxial NiFe/Cr/NiFe trilayers

I. F. Lee, M. Y. Shen, Y. Y. Lay, J. C. Jan, J. W. Chiou, H. M. Tsai, W. F. Pong, M.-H. Tsai, H. H. Hsieh, H.-J. Lin, J. F. Lee, C. A. Ku, and J. C. A. Huang

Appl. Phys. Lett. 82, 3062 (2003); http://dx.doi.org/10.1063/1.1563743 (3 pages) | Cited 1 time

Online Publication Date: 29 April 2003

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Ni and Fe L3,2-edge magnetic circular dichroism (MCD) and Cr K-edge x-ray absorption near-edge structure measurements have been performed for the Py/Cr(tCr)/Py (Py = Ni80Fe20) trilayers with tCr = 5, 10, 15, 20, and 25 Å. The MCD asymmetry ratios in the Ni and Fe L3-edges spectra are found strongly affected by the thickness of the Cr layer. The moments of the Fe and Ni 3d states are found, respectively, to decrease and increase suddenly when tCr increases beyond 20 Å. The measured magneto-optical Kerr effect hysteresis loops show a ferromagnetic-to-antiferromagnetic phase transition at about the same Cr-layer thickness. The transition of the magnetic property is found to correlate with the structural transition of the Cr spacer layer from a pseudomorphic fcc-like structure to a bcc structure. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.66.Bz Metals and metallic alloys
68.65.Ac Multilayers
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Anisotropy, damping, and coherence of magnetization dynamics in a 10 μm square Ni81Fe19 element

A. Barman, V. V. Kruglyak, R. J. Hicken, A. Kundrotaite, and M. Rahman

Appl. Phys. Lett. 82, 3065 (2003); http://dx.doi.org/10.1063/1.1572969 (3 pages) | Cited 34 times

Online Publication Date: 29 April 2003

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We have studied magnetization precession in a square Ni81Fe19 element, of 10 μm width, by time-resolved scanning Kerr effect microscopy. From the frequency of precession, we deduce a fourfold in-plane anisotropy of about 30 Oe at the center of the square. Larger damping of the precession was observed at the center of the element when the static field was applied parallel to a diagonal rather than to an edge of the square. Dynamic images show that the apparent increase in damping is associated with nonuniformity of the dynamic magnetization that is associated with the sample shape. © 2003 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Gw Magnetic anisotropy
78.20.Ls Magneto-optical effects
75.50.Ss Magnetic recording materials
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Rubbing-induced polar ordering in nylon-11

Seok-Cheol Hong, Chun Zhang, and Y. R. Shen

Appl. Phys. Lett. 82, 3068 (2003); http://dx.doi.org/10.1063/1.1570937 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2003

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Sum-frequency vibrational spectroscopy was used to show that mechanical rubbing could induce domains of ferroelectric ordering in films of odd-numbered nylon. In each domain, the dipole groups of NH and CO were aligned perpendicular to the rubbing direction and parallel to the surface. © 2003 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
78.66.Qn Polymers; organic compounds
77.80.Dj Domain structure; hysteresis
78.30.Jw Organic compounds, polymers

Spatial inhomogeneity of imprint and switching behavior in ferroelectric capacitors

A. Gruverman, B. J. Rodriguez, A. I. Kingon, R. J. Nemanich, J. S. Cross, and M. Tsukada

Appl. Phys. Lett. 82, 3071 (2003); http://dx.doi.org/10.1063/1.1570942 (3 pages) | Cited 35 times

Online Publication Date: 29 April 2003

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Piezoresponse force microscopy has been used to perform nanoscale characterization of the spatial variations in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3-based capacitors on Pt electrodes. Mapping of polarization distribution in the poled capacitors as well as local d33–V loop measurements revealed a significant difference in imprint and switching behavior between the peripheral and inner parts of the capacitors. It has been found that the inner regions of the capacitors are negatively imprinted (with the preferential direction of the normal component of polarization upward) and tend to switch back after application of the positive poling voltage. On the other hand, switchable regions at the edge of the integrated capacitors generally exhibit more symmetric hysteresis behavior. Application of an ac switching voltage, contrary to what was expected, resulted in an increase of the negatively imprinted regions. The observed effect has been explained by incomplete or asymmetric switching due to the mechanical stress conditions existing in the central parts of the capacitors. © 2003 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena

Full-relativistic calculations of the SrTiO3 carrier effective masses and complex dielectric function

M. Marques, L. K. Teles, V. Anjos, L. M. R. Scolfaro, J. R. Leite, V. N. Freire, G. A. Farias, and E. F. da Silva

Appl. Phys. Lett. 82, 3074 (2003); http://dx.doi.org/10.1063/1.1570922 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2003

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We perform fully relativistic band-structure calculations for cubic SrTiO3, which are used to obtain carrier effective masses and the frequency behavior of its complex dielectric function ϵ(ω). The obtained values and anisotropy of the carrier effective masses are shown to be highly influenced by the relativistic contributions. In order to evaluate the static dielectric constant, the low-frequency behavior of ϵ(ω) is obtained by taking into account also the optical phonon contributions to the imaginary part of ϵ(ω), adopting a simplified classical oscillator dispersion model. It is found that the phonon contribution leads to about 240 times (at T = 85 K) the value of the bare electronic contribution to the dielectric constant. The calculated temperature dependence of the dielectric constant is shown to be consistent with that observed in bulk SrTiO3 static permittivity measurements. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.20.Ps Other inorganic compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
77.22.Ch Permittivity (dielectric function)
71.15.Rf Relativistic effects
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Transport properties of LaTiO3+x films and heterostructures

A. Schmehl, F. Lichtenberg, H. Bielefeldt, J. Mannhart, and D. G. Schlom

Appl. Phys. Lett. 82, 3077 (2003); http://dx.doi.org/10.1063/1.1572960 (3 pages) | Cited 26 times

Online Publication Date: 29 April 2003

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We report on the transport properties of LaTiO3+ε and LaTiO3.5 films. The LaTiO3+ε samples show metallic transport and several samples exhibit a hysteretic drop of resistance during cooldown at ∼ 240 K. The ferroelectric LaTiO3.5 samples, grown in capacitor structures, have nonlinear, diode-like and hysteretic V(I) characteristics. Two charge-controlled transport regimes are found, which can be utilized for switching the devices between two voltage states. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena
73.61.Le Other inorganic semiconductors
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Surface structures of a Co-doped anatase TiO2 (001) film investigated by scanning tunneling microscopy

J. S. Yang, D. H. Kim, S. D. Bu, T. W. Noh, S. H. Phark, Z. G. Khim, I. W. Lyo, and S.-J. Oh

Appl. Phys. Lett. 82, 3080 (2003); http://dx.doi.org/10.1063/1.1571983 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2003

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The surface structure of an anatase Ti0.94Co0.06O2 (001) film, grown epitaxially on a Nb-doped SrTiO3 (001) substrate, was investigated using in situ scanning tunneling microscopy. For the as-grown film, a (1×n) (n = 3, 4, 5, and 6) reconstructed surface was observed that shows (n−2) faint rows between adjacent bright rows. After annealing at 650 °C, nanoparticles appeared, mostly on the step edges. From the I–V curves measured by scanning tunneling spectroscopy, the tunneling gap of Co:TiO2 was estimated to be about 3.0 eV, consistent with the band gap (Eg = 3.2 eV) of pure anatase TiO2. However, on nanoparticles, the I–V curve showed a much smaller gap, suggesting that the particle must be different from TiO2. © 2003 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.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials

Quantum dot amplifiers with high output power and low noise

Tommy W. Berg and Jesper Mørk

Appl. Phys. Lett. 82, 3083 (2003); http://dx.doi.org/10.1063/1.1571226 (3 pages) | Cited 33 times

Online Publication Date: 29 April 2003

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Quantum dot semiconductor optical amplifiers have been theoretically investigated and are predicted to achieve high saturated output power, large gain, and low noise figure. We discuss the device dynamics and, in particular, show that the presence of highly inverted barrier states does not limit the performance of these devices. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes

Measuring electrical current during scanning probe oxidation

F. Pérez-Murano, C. Martín, N. Barniol, H. Kuramochi, H. Yokoyama, and J. A. Dagata

Appl. Phys. Lett. 82, 3086 (2003); http://dx.doi.org/10.1063/1.1572480 (3 pages) | Cited 23 times

Online Publication Date: 29 April 2003

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Electrical current is measured during scanning probe oxidation by performing force versus distance curves under the application of a positive sample voltage. It is shown how the time dependence of the current provides information about the kinetics of oxide growth under conditions in which the tip–surface distance is known unequivocally during current acquisition. Current measurements at finite tip–sample distance, in particular, unveil how the geometry of the meniscus influences its electrical conduction properties as well as the role of space charge at very small tip–sample distances. © 2003 American Institute of Physics.
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81.65.Mq Oxidation
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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