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20 Jul 2009

Volume 95, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 033502 (2009); http://dx.doi.org/10.1063/1.3178556 (3 pages)

Akihito Ikedo, Takahiro Kawashima, Takeshi Kawano, and Makoto Ishida
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Reduction of dislocation density in epitaxial GaN layers by overgrowth of defect-related etch pits

J. L. Weyher, H. Ashraf, and P. R. Hageman

Appl. Phys. Lett. 95, 031913 (2009); http://dx.doi.org/10.1063/1.3171928 (3 pages) | Cited 9 times

Online Publication Date: 22 July 2009

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GaN templates grown by the metal organic chemical vapor deposition method were etched in a defect-selective molten salts eutectic and were subsequently overgrown by a GaN layer using the hydride vapor phase epitaxy (HVPE) method. Optimized conditions of etching and of HVPE growth processes resulted in a significant reduction of the dislocations density (DD). Local areas virtually free of dislocations were obtained on ∼ 50% of the surface, while the average DD was reduced from 3×109 cm−2 in the template to about 2×107 cm−2 in the HVPE-grown GaN layer. A model has been developed to explain the mechanism of reduction of the DD during the overgrowth process. The model was confirmed by the photoetching of cleaved layers.
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68.55.ag Semiconductors
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.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.65.Cf Surface cleaning, etching, patterning

Observation of space-separated multiexciton generation in photocurrent of Au/por-Si/p-Si structure

O. M. Sreseli, O. S. El’tsina, L. V. Belyakov, and D. N. Goryachev

Appl. Phys. Lett. 95, 031914 (2009); http://dx.doi.org/10.1063/1.3186785 (3 pages) | Cited 3 times

Online Publication Date: 24 July 2009

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Photocurrent efficiency (ratio of the number of photogenerated carriers to the number of absorbed photons) of Au/por-Si/p-Si structure in a wide spectral range was investigated. The low-energy edge of nanoporous silicon (por-Si) sensibility was determined, and the enhancement in por-Si photocurrent efficiency was observed for incident photon energies above 3.5 eV. This threshold was demonstrated to exceed twice a bandgap of most nanocrystals in por-Si. Carrier tunneling among nanocrystals through thin oxide layers was shown as well. Efficiency enhancement is explained by space-separated double-exciton generation, when a high-energy photon absorbed in a nanocrystal results in two excitons in adjacent nanocrystals.
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73.63.Bd Nanocrystalline materials
73.50.Pz Photoconduction and photovoltaic effects
73.40.Ns Metal-nonmetal contacts
73.40.Gk Tunneling
61.43.Gt Powders, porous materials
71.35.-y Excitons and related phenomena
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On the 1/f noise of triple-gate field-effect transistors with high-k gate dielectric

N. Lukyanchikova, N. Garbar, V Kudina, A. Smolanka, S. Put, C. Claeys, and E. Simoen

Appl. Phys. Lett. 95, 032101 (2009); http://dx.doi.org/10.1063/1.3180703 (3 pages) | Cited 7 times

Online Publication Date: 20 July 2009

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The low-frequency noise of triple-gate fin field-effect transistors (finFETs) fabricated on silicon-on-insulator (SOI) substrates, with HfO2 or HfSiON gate stacks has been studied. In most cases, 1/fγ noise has been observed with γ<1 for low frequencies f. It is shown that this type of noise can be ascribed to number fluctuations and scales with the effective device area. Based on a simple tunneling model, the noise spectral density has been converted to an oxide trap density profile, exhibiting a decay in Not for larger distances from the Si–SiO2 interface. This stands in contrast with planar bulk devices with a similar high-k gate stack and seems to be typical for the fin processing used, irrespective of further process details, like the use of selective epitaxial growth, strained SOI or strain-inducing cap layers.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.70.+m Noise processes and phenomena
73.40.Gk Tunneling

Hole diffusion profile in a p-p+ silicon homojunction determined by terahertz and midinfrared spectroscopic ellipsometry

T. Hofmann, C. M. Herzinger, T. E. Tiwald, J. A. Woollam, and M. Schubert

Appl. Phys. Lett. 95, 032102 (2009); http://dx.doi.org/10.1063/1.3184567 (3 pages) | Cited 6 times

Online Publication Date: 20 July 2009

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Noninvasive optical measurement of hole diffusion profiles in p-p+ silicon homojunction is reported by ellipsometry in the terahertz (0.2–1.5 THz) and midinfrared (9–50 THz) spectral regions. In the terahertz region a surface-guided wave resonance with transverse-electrical polarization is observed at the boundary of the p-p+ homojunction, and which is found to be extremely sensitive to the low-doped p-type carrier concentration as well as to the hole diffusion profile within the p-p+ homojunction. Effective mass approximations allow determination of homojunction hole concentrations as p = 2.9×1015 cm−3, p+ = 5.6×1018 cm−3, and diffusion time constant Dt = 7.7×10−3 μm2, in agreement with previous electrical investigations.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
66.30.H- Self-diffusion and ionic conduction in nonmetals
72.80.Cw Elemental semiconductors

Probing microwave capacitance of self-assembled quantum dots

Guanglei Cheng, Jeremy Levy, and Gilberto Medeiros-Ribeiro

Appl. Phys. Lett. 95, 032103 (2009); http://dx.doi.org/10.1063/1.3184572 (3 pages)

Online Publication Date: 20 July 2009

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Self-assembled quantum dots have remarkable optical, electronic, and spintronic properties that make them leading candidates for quantum information technologies. Their characterization requires rapid and local determination of both charge and spin degrees of freedom. We present a way to probe the capacitance of small ensembles of quantum dots at microwave frequencies. The technique employs a capacitance sensor based on a microwave microstrip resonator with sensitivity ∼ 10−19 F/math, high enough to probe single electrons. The integration of this design in a scanning microscope will provide an important tool for investigating single charge and spin dynamics in self-assembled quantum dot systems.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.07.Mp Transducers
81.07.Ta Quantum dots
81.16.Dn Self-assembly
84.40.-x Radiowave and microwave (including millimeter wave) technology
84.40.Az Waveguides, transmission lines, striplines

Atomic migration in molten and crystalline Ge2Sb2Te5 under high electric field

Tae-Youl Yang, Il-Mok Park, Byoung-Joon Kim, and Young-Chang Joo

Appl. Phys. Lett. 95, 032104 (2009); http://dx.doi.org/10.1063/1.3184584 (3 pages) | Cited 18 times

Online Publication Date: 20 July 2009

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Atomic migration under an electric field, electromigration, in molten and crystalline Ge2Sb2Te5 was studied using a pulsed dc stress to an isolated line structure. Under a single pulse ( ∼ 10−3 s), Ge2Sb2Te5 was melted by Joule heating, and an electrostatic force-induced drift of Ge and Sb toward the cathode and Te toward the anode was observed. Effective charge numbers were calculated to be 0.28, 0.38, and −0.29 for Ge, Sb, and Te, respectively. Electromigration in the crystalline state was studied by applying a 10 MHz pulsed dc; constituent elements migrated toward the cathode, which suggests a hole wind-force operating in this phase.
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81.05.Bx Metals, semimetals, and alloys
82.45.Fk Electrodes
66.30.Qa Electromigration

Sn12Sb88 material for phase change memory

Feng Rao, Zhitang Song, Kun Ren, Xuelai Li, Liangcai Wu, Wei Xi, and Bo Liu

Appl. Phys. Lett. 95, 032105 (2009); http://dx.doi.org/10.1063/1.3184787 (3 pages) | Cited 17 times

Online Publication Date: 21 July 2009

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Phase change memory cell based on Sn12Sb88 film shows reversible phase change abilities between high and low resistance states. We calculate the resonance character of crystalline SnSb material, which proves that SnSb is a potential phase change candidate. Sn12Sb88 is the suitable composition that has faster crystallization speed, higher crystallization temperature, and larger crystallization activation energy but lower melting point than those of Ge2Sb2Te5 material. Hence, phase change memory cell using this composition is able to show quicker set operation speed, better data retention ability, and lower reset power consumption than those of the Ge2Sb2Te5 based cell.
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64.70.K- Solid-solid transitions
64.70.dj Melting of specific substances
68.55.A- Nucleation and growth

Analysis of point defects in AlN epilayers by cathodoluminescence spectroscopy

Barbara Bastek, Frank Bertram, Juergen Christen, Thomas Hempel, Armin Dadgar, and Alois Krost

Appl. Phys. Lett. 95, 032106 (2009); http://dx.doi.org/10.1063/1.3154518 (3 pages) | Cited 4 times

Online Publication Date: 21 July 2009

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We present a systematic cathodoluminescence study yielding a clear correlation between the different growth conditions and the appearance and strength of the characteristic luminescence fingerprints of the individual point defects in AlN. In particular, the incorporation of oxygen and the formation of oxygen-related and probably silicon-related DX centers as well as the native Al and N vacancies are still a problem. The thermal activation of the deep defect centers is investigated by temperature dependent cathodoluminescence spectroscopy.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.ag Semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.jd Vacancies

Band structure design and photocatalytic activity of In2O3/N–InNbO4 composite

Jun Lv, Tetsuya Kako, Zhigang Zou, and Jinhua Ye

Appl. Phys. Lett. 95, 032107 (2009); http://dx.doi.org/10.1063/1.3183507 (3 pages) | Cited 7 times

Online Publication Date: 21 July 2009

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In this study, the band structure of In2O3/N–InNbO4 composite was considered to be advantageous for the transportation and separation of photoexcited electron/hole pairs. This composite was synthesized and characterized by powder x-ray diffraction, UV-visible diffuse reflectance spectroscopy, transmission electron microscope, and x-ray photoelectrons spectroscopy. The photocatalytic experiments indicated the H2 evolution rate of In2O3/N–InNbO4 composite was 27.3 μmol h−1 g−1 under visible light irradiation (λ>420 nm), which was 18.6 times the rate of In2O3 and 2.3 times the rate of N–InNbO4.
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81.20.-n Methods of materials synthesis and materials processing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.40.-q Absorption and reflection spectra: visible and ultraviolet
79.60.-i Photoemission and photoelectron spectra
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.05.cp X-ray diffraction
82.50.-m Photochemistry
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Relationship between 4H-SiC/SiO2 transition layer thickness and mobility

T. L. Biggerstaff, C. L. Reynolds, Jr., T. Zheleva, A. Lelis, D. Habersat, S. Haney, S.-H. Ryu, A. Agarwal, and G. Duscher

Appl. Phys. Lett. 95, 032108 (2009); http://dx.doi.org/10.1063/1.3144272 (3 pages) | Cited 14 times

Online Publication Date: 22 July 2009

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The interfacial region between silicon carbide (SiC) and its native oxide contains a high density of interfacial traps, which is considered a major problem leading to a lower mobility that has hindered SiC metal oxide semiconductor field effect transistors from reaching their theoretical expectations. We investigate the microstructure and chemistry of the 4H-SiC/SiO2 interface due to variations in nitric oxide annealing and aluminum implantation using Z-contrast imaging and electron energy loss spectroscopy. A transition layer with a carbon to silicon ratio greater than 1 is consistently observed on the SiC side of the interface in each of these samples, and the width of this transition layer is found to be inversely related to the effective channel mobility measured on fabricated devices.
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73.20.-r Electron states at surfaces and interfaces
85.30.Tv Field effect devices
81.40.Gh Other heat and thermomechanical treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.ag Semiconductors
79.20.Uv Electron energy loss spectroscopy

Optical and magnetic properties of CuMnO2 epitaxial thin films with a delafossite-derivative structure

H. Hiraga, T. Fukumura, A. Ohtomo, T. Makino, A. Ohkubo, H. Kimura, and M. Kawasaki

Appl. Phys. Lett. 95, 032109 (2009); http://dx.doi.org/10.1063/1.3186790 (3 pages) | Cited 3 times

Online Publication Date: 22 July 2009

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A distorted delafossite CuMnO2, called crednerite, was formed into epitaxial thin films on MgAl2O4 (111) substrates by pulsed laser deposition method. X-ray diffraction revealed that the films had high crystalline quality with epitaxial relationship of CuMnO2 (001)//MgAl2O4 (111) and CuMnO2 [100]//MgAl2O4 〈11-2〉. The ultraviolet-visible optical response revealed a distinct absorption peak at 4.5 eV presumably with excitonic nature and broad peaks at 3.0 and 3.7 eV assignable to O 2p–Mn 3d charge transfer excitation. Small magnetic hysteresis with remanent magnetization of 0.04μB/Mn was observed below 20 K, representing canted antiferromagnetic spin ordering.
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78.66.-w Optical properties of specific thin films
75.50.Ee Antiferromagnetics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.40.Ha Other nonmetallic inorganics
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Aharonov–Bohm oscillations in a nanoscale dopant ring in silicon

T. C. G. Reusch, A. Fuhrer, M. Füchsle, B. Weber, and M. Y. Simmons

Appl. Phys. Lett. 95, 032110 (2009); http://dx.doi.org/10.1063/1.3186031 (3 pages) | Cited 1 time

Online Publication Date: 23 July 2009

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We have fabricated a nanoscale ring of phosphorus dopants in silicon using a scanning tunneling microscope to pattern a hydrogen resist layer. Low-temperature magnetotransport measurements reveal both aperiodic universal conductance fluctuations and periodic Aharonov–Bohm oscillations. From the ratio of the h/e and h/2e components of the Aharonov–Bohm oscillations, we estimate a phase coherence length of ≃ 100 nm at a temperature T = 100 mK. This is in agreement with previous results from weak localization measurements on low-dimensional dopant devices in silicon.
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61.72.uf Ge and Si
73.63.-b Electronic transport in nanoscale materials and structures
72.20.My Galvanomagnetic and other magnetotransport effects

Electroconductance in single-wall carbon nanotubes

Manu Jaiswal, C. S. Suchand Sangeeth, and Reghu Menon

Appl. Phys. Lett. 95, 032111 (2009); http://dx.doi.org/10.1063/1.3186082 (3 pages) | Cited 2 times

Online Publication Date: 24 July 2009

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A comparative study of the electric-field induced hopping transport probes the effective dimensionality (D) in bulk and ultrathin films of single-wall carbon nanotubes (SWNTs). The values of the scaling function exponents for the electroconductance are found to be consistent with that in three-dimensional and two-dimensional systems. The significant difference in threshold voltage in these two types of SWNTs is a consequence of the variation in the number of energetically favorable sites available for charge carriers to hop by using the energy from the field. Furthermore, a modification to the magnetotransport is observed under high electric-fields.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
73.63.Fg Nanotubes
73.61.Wp Fullerenes and related materials
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Magnetically controlled superconducting weak links

J. Van de Vondel, A. V. Silhanek, B. Raes, W. Gillijns, R. B. G. Kramer, V. V. Moshchalkov, J. Sautner, and V. Metlushko

Appl. Phys. Lett. 95, 032501 (2009); http://dx.doi.org/10.1063/1.3180492 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2009

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We have designed and characterized a magnetic template which can be switched between chains of parallel and antiparallel field distribution by applying an in-plane magnetic field. The parallel field profile creates highly mobile vortex channels in a superconducting film deposited on top, reproducing the behavior of a weak link as evidenced by the presence of Shapiro steps in the current-voltage characteristics under rf excitation. The Josephson coupling can be fully suppressed by changing the field distribution to the antiparallel state. As a result, a reversible ON/OFF switch for magnetically induced weak links has been demonstrated.
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85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.50.+r Tunneling phenomena; Josephson effects

Magneto-optical Kerr effect in perpendicularly magnetized Co/Pt films on two-dimensional colloidal crystals

Z. Liu, L. Shi, Z. Shi, X. H. Liu, J. Zi, S. M. Zhou, S. J. Wei, J. Li, X. Zhang, and Y. J. Xia

Appl. Phys. Lett. 95, 032502 (2009); http://dx.doi.org/10.1063/1.3182689 (3 pages) | Cited 9 times

Online Publication Date: 21 July 2009

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Magneto-optical Kerr effect and optical reflectance are measured in the visible region for perpendicularly magnetized Co/Pt films on self-assembly array of two-dimensional closely packed polystyrene spheres. Peaks and valleys are observed in the magneto-optical Kerr and the optical reflectance spectra and their positions scale with the sphere diameter. In explanation of the above scenario, not only the Mie optical scattering of single nanocaps but also the surface plasmon resonance should be considered. This work will facilitate development of magnetoplasmonic nanosensors.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
82.70.Dd Colloids
78.20.Ls Magneto-optical effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.05.Bx Metals, semimetals, and alloys

Anomalous Hall effect in quarternary Heusler-type Ni50Mn17Fe8Ga25 melt-spun ribbons

Zhiyong Zhu, Siu Wing Or, and Guangheng Wu

Appl. Phys. Lett. 95, 032503 (2009); http://dx.doi.org/10.1063/1.3176479 (3 pages) | Cited 4 times

Online Publication Date: 21 July 2009

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The anomalous Hall effect (AHE) in quarternary Heusler-type Ni50Mn17Fe8Ga25 melt-spun ribbons is investigated. Experimental correlation between saturated anomalous Hall resistivity (ρAMS) and longitudinal resistivity (ρxx) is achieved for the low-temperature martensitic phase and the high-temperature austenitic phase as ρAMS∞ρxxn = 4.2 and ρAMS∞ρxxn = 2.1, respectively. The unexpectedly large exponent of n = 4.2 in the martensitic phase is found to contradict the traditional theory of AHE with n = 1–2, but it can be explained by a side-jump model beyond the short-range limit as a result of the intermediate-range spin-dependent electron scattering by relatively large Mn-rich clusters instead. The restoration of the exponent back to a normal value of n = 2.1 in the austenitic phase is ascribed to the domination of the electron scattering by phonons, compared to that by the Mn-rich clusters, at elevated temperatures and with phonon softening in the transverse-acoustic TA2 mode.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
71.38.-k Polarons and electron-phonon interactions
81.30.Kf Martensitic transformations
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.kd Metals and alloys
75.50.Bb Fe and its alloys

Resistance of domain walls created by means of a magnetic force microscope in transversally magnetized epitaxial Fe wires

C. Hassel, S. Stienen, F. M. Römer, R. Meckenstock, G. Dumpich, and J. Lindner

Appl. Phys. Lett. 95, 032504 (2009); http://dx.doi.org/10.1063/1.3187219 (3 pages) | Cited 3 times

Online Publication Date: 22 July 2009

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Magnetic domain walls are created in a controllable way in transversally magnetized epitaxial Fe wires on GaAs(110) by approaching a magnetic force microscope (MFM) tip. The electrical resistance-change due to the addition of these domain walls is measured. The anisotropic magnetoresistance as well as the intrinsic domain wall resistance contribute to the resistance-change. The efficiency of this procedure is proven by MFM images, which are obtained subsequent to the domain wall creation at a larger sample-to-probe distance. The contribution of the anisotropic magnetoresistance is calculated using micromagnetic calculations, thus making it possible to quantify the intrinsic domain wall resistance.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Np Metals and alloys
81.05.Bx Metals, semimetals, and alloys
68.37.Rt Magnetic force microscopy (MFM)
73.61.At Metal and metallic alloys

Domain-wall depinning by controlling its configuration at notch

Sheng-Huang Huang and Chih-Huang Lai

Appl. Phys. Lett. 95, 032505 (2009); http://dx.doi.org/10.1063/1.3187530 (3 pages) | Cited 10 times

Online Publication Date: 22 July 2009

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We study current-induced magnetic domain wall (DW) motion in nanostripes with reduced dimensions in which transverse-type DWs are stable. Micromagnetic simulation reveals that the depinning probability of the DW strongly depends on the DW configuration when the DW approaches the notch. The spin torque energy does not only drive DW motion but contribute to the transformation of DW configurations between transverse- and antivortex-type when the current density is above a threshold value. When the DW changes from the transverse to antivortex state, it stores potential energy which helps it to depin from the notch.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
75.40.Mg Numerical simulation studies
75.50.Tt Fine-particle systems; nanocrystalline materials

Atomic-scale spectroscopic imaging of CoFeB/Mg–B–O/CoFeB magnetic tunnel junctions

J. J. Cha, J. C. Read, W. F. Egelhoff, Jr., P. Y. Huang, H. W. Tseng, Y. Li, R. A. Buhrman, and D. A. Muller

Appl. Phys. Lett. 95, 032506 (2009); http://dx.doi.org/10.1063/1.3184766 (3 pages) | Cited 23 times

Online Publication Date: 23 July 2009

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Atomic-scale electron spectroscopic imaging on sputtered magnetic tunnel junctions (MTJs) with a thin, <2 nm, MgO layer and B-alloyed electrodes reveals B diffusion into the MgO, resulting in a Mg–B–O tunnel barrier. This ∼ 2 nm thick interfacial layer forms due to oxidation of CoFeB during radio frequency sputtering of MgO and subsequent B diffusion into MgO during annealing. We measure a room-temperature tunneling magnetoresistance (TMR) of ∼ 200% in IrMn/CoFeB/Mg–B–O/CoFeB MTJs after annealing, demonstrating that thin Mg–B–O barriers can produce relatively high TMR.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
66.30.H- Self-diffusion and ionic conduction in nonmetals
75.47.Pq Other materials
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
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Internal fields in solid electrolytes due to interface effects

Bjoern Martin and Herbert Kliem

Appl. Phys. Lett. 95, 032901 (2009); http://dx.doi.org/10.1063/1.3184791 (3 pages) | Cited 5 times

Online Publication Date: 20 July 2009

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The space charge distribution and therefore the distribution of the internal potential in ion-conducting polymers can strongly be influenced by electrode effects. Due to image forces the electrodes attract mobile ions to the electrolyte/electrode interface. Simulations performed with a three-dimensional hopping model yield a charge accumulation of mobile ions at the electrodes as well as a depletion zone near this accumulation layer even without external applied field. The resulting potential shows a maximum in the middle of the sample. Measurements of the surface potential performed with a scanning Kelvin probe using polyethylene oxide confirm the model.
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66.30.hk Polymers
82.45.Fk Electrodes
77.22.Jp Dielectric breakdown and space-charge effects
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.45.Gj Electrolytes
73.25.+i Surface conductivity and carrier phenomena

Self-organized (Ba0.7,Sr0.3)TiO3 nanocomposite with improved figure of merit

B. Guigues, X. H. Zhu, J. Sobotka, N. Guiblin, E. Defaÿ, and B. Dkhil

Appl. Phys. Lett. 95, 032902 (2009); http://dx.doi.org/10.1063/1.3179523 (3 pages) | Cited 2 times

Online Publication Date: 20 July 2009

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Self-organized (Ba0.7,Sr0.3) TiO3 (BST) thin film nanocomposites with spherical inclusions have been fabricated. The composite structures were built up from initial amorphous BST films, thanks to an adequate thermal treatment. Microstructural and electrical analyses are reported as a function of crystallization ratio q. Our experimental results agree with recently developed models of composite materials. The main conclusion of the study is that high dielectric performances can be obtained with a half-crystallized material. For a 630 °C annealing temperature (q-ratio equal to 0.47), Vendik commutation quality factor reaches 1500, which is two times greater than a fully crystallized sample annealed at 700 °C.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.46.Hk Nanocrystals

Electronic transport through in situ grown ultrathin BaTiO3 films

Junsoo Shin, S. V. Kalinin, E. W. Plummer, and A. P. Baddorf

Appl. Phys. Lett. 95, 032903 (2009); http://dx.doi.org/10.1063/1.3186067 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2009

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Polarization-mediated transport properties of ultrathin (4 and 10 unit cells) fully strained polar BaTiO3 films are studied by scanning tunneling microscopy and spectroscopy. High quality BaTiO3 films are grown on SrRuO3/SrTiO3 by pulsed laser deposition and characterized in situ in ultrahigh vacuum. Previous structural measurements have shown that these films are polarized. Current-voltage curves exhibit features at ∼ ±2.5 V, which show hysteresis consistent with bias-induced polarization switching. The intensity and voltage of the features indicate a stochastic process. These features are not observed on nonpolarized SrTiO3 films grown and characterized similarly.
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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.Dj Domain structure; hysteresis
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Fg Pulsed laser ablation deposition
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization

Electric-field-induced phase transformation at a lead-free morphotropic phase boundary: Case study in a 93%(Bi0.5Na0.5)TiO3–7% BaTiO3 piezoelectric ceramic

John E. Daniels, Wook Jo, Jürgen Rödel, and Jacob L. Jones

Appl. Phys. Lett. 95, 032904 (2009); http://dx.doi.org/10.1063/1.3182679 (3 pages) | Cited 61 times

Online Publication Date: 21 July 2009

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The electric-field-induced strain in 93%(Bi0.5Na0.5)TiO3–7%BaTiO3 polycrystalline ceramic is shown to be the result of an electric-field-induced phase transformation from a pseudocubic to tetragonal symmetry. High-energy x-ray diffraction is used to illustrate the microstructural nature of the transformation. A combination of induced unit cell volumetric changes, domain texture, and anisotropic lattice strains are responsible for the observed macroscopic strain. This strain mechanism is not analogous to the high electric-field-induced strains observed in lead-based morphotropic phase boundary systems. Thus, systems which appear cubic under zero field should not be excluded from the search for lead-free piezoelectric compositions.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
64.70.K- Solid-solid transitions
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects

Improved thermal stability, interface, and electrical properties of HfO2 films prepared by pulsed laser deposition using in situ ionized nitrogen

Yi Wang, Hao Wang, Jun Zhang, Hanbin Wang, Cong Ye, Yong Jiang, and Qing Wang

Appl. Phys. Lett. 95, 032905 (2009); http://dx.doi.org/10.1063/1.3184577 (3 pages) | Cited 6 times

Online Publication Date: 21 July 2009

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Nitrogen is incorporated into thin HfO2 films by pulsed laser deposition using in situ ionized nitrogen. The improved thermal stability and interfacial microstructure are further confirmed by high-resolution transmission electron microscopy. The composition of the thin film is investigated by x-ray photoelectron spectroscopy and electron energy-loss spectroscopy. Electrical studies show a property permittivity of 27.7 and low leakage current density were achieved by incorporation of a small amount (about 1 at. %) of nitrogen. The dominant conduction mechanisms of the Pt/HfO2/p-Si structure are trap-assisted tunneling and Schottky emission at low electric field for the gate and substrate injection, respectively.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Ch Permittivity (dielectric function)
73.43.Jn Tunneling
81.15.Fg Pulsed laser ablation deposition
79.60.Dp Adsorbed layers and thin films
77.55.-g Dielectric thin films
79.20.Uv Electron energy loss spectroscopy

Molecular beam epitaxy of SrTiO3 with a growth window

Bharat Jalan, Pouya Moetakef, and Susanne Stemmer

Appl. Phys. Lett. 95, 032906 (2009); http://dx.doi.org/10.1063/1.3184767 (3 pages) | Cited 17 times

Online Publication Date: 23 July 2009

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Many complex oxides with only nonvolatile constituents do not have a wide growth window in conventional molecular beam epitaxy (MBE) approaches, which makes it difficult to obtain stoichiometric films. Here it is shown that a growth window in which the stoichiometry is self-regulating can be achieved for SrTiO3 films by using a hybrid MBE approach that uses a volatile metal-organic source for Ti, titanium tetra isopropoxide (TTIP). The growth window widens and shifts to higher TTIP/Sr flux ratios with increasing temperature, showing that it is related to the desorption of the volatile TTIP. We demonstrate stoichiometric, highly perfect, insulating SrTiO3 films. The approach can be adapted for the growth of other complex oxides that previously were believed to have no wide MBE growth window.
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68.55.aj Insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.43.Nr Desorption kinetics
61.66.Bi Elemental solids
61.66.Dk Alloys
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