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11 Jul 2005

Volume 87, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 024103 (2005); http://dx.doi.org/10.1063/1.1984098 (3 pages)

A. Dupuis, J. Léopoldès, D. G. Bucknall, and J. M. Yeomans
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Electrical initialization and manipulation of electron spins in an L-shaped strained n-InGaAs channel

Y. K. Kato, R. C. Myers, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 87, 022503 (2005); http://dx.doi.org/10.1063/1.1994930 (3 pages) | Cited 28 times

Online Publication Date: 6 July 2005

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An L-shaped strained n-InGaAs channel is used to polarize and subsequently rotate electron spins solely by means of electric fields. Precession of electrically excited spins in the absence of applied magnetic fields is directly observed by Kerr rotation microscopy. In addition, in-plane and out-of-plane components of the spin polarization in the channel are simultaneously imaged.
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78.20.Jq Electro-optical effects
72.25.Dc Spin polarized transport in semiconductors

Magnetoresistance sensor with an out-of-plane magnetized sensing layer

Sebastiaan van Dijken and J. M. D. Coey

Appl. Phys. Lett. 87, 022504 (2005); http://dx.doi.org/10.1063/1.1957111 (3 pages) | Cited 20 times

Online Publication Date: 7 July 2005

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A concept for a linear and reversible magnetoresistance sensor is demonstrated using a magnetic spin valve. The sensor is based on coherent rotation of an out-of-plane magnetized sensing layer in parallel-to-plane applied magnetic fields. For Pt/CoFe sensing layers, the sensor response depends critically on the perpendicular magnetic anisotropy of the CoFe film and, therefore, on its thickness tCoFe. Sensors with small tCoFe exhibit a high linearity up to applied fields of about 50 mT, but their magnetic field sensitivity is rather small. The sensitivity, however, increases with tCoFe and it reaches its maximum value just below the spin reorientation transition in the CoFe sensing layer.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
07.55.-w Magnetic instruments and components
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.30.Gw Magnetic anisotropy
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Magnetocapacitance effect in perovskite-superlattice based multiferroics

M. P. Singh, W. Prellier, Ch. Simon, and B. Raveau

Appl. Phys. Lett. 87, 022505 (2005); http://dx.doi.org/10.1063/1.1988979 (3 pages) | Cited 40 times

Online Publication Date: 7 July 2005

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We report the structural and magnetoelectrical properties of La0.7Ca0.3MnO3/BaTiO3 perovskite superlattices grown on (001)-oriented SrTiO3 by the pulsed laser deposition technique. Magnetic hysteresis loops, together with temperature dependent magnetic properties, exhibit well-defined coercivity and magnetic transition temperature (TC) ∼ 140 K. dc electrical studies of films show that the magnetoresistance (MR) is dependent on the BaTiO3 thickness, and negative MR as high as 30% at 100 K are observed. The ac electrical studies reveal that the impedance and capacitance in these films vary with the applied magnetic field due to the magnetoelectrical coupling in these structures—a key feature of multiferroics. A negative magnetocapacitance value in the film as high as 3% per tesla at 1 kHz and 100 K is demonstrated, opening the route for designing novel functional materials.
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75.50.Dd Nonmetallic ferromagnetic materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Lx Magnetic oxides
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Fg Pulsed laser ablation deposition
77.80.-e Ferroelectricity and antiferroelectricity

Ferromagnetism and metal-like transport in antiferromagnetic insulator heterostructures

P. Padhan, P. Murugavel, and W. Prellier

Appl. Phys. Lett. 87, 022506 (2005); http://dx.doi.org/10.1063/1.1992657 (3 pages) | Cited 2 times

Online Publication Date: 8 July 2005

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Strained Pr0.5Ca0.5MnO3/La0.5Ca0.5MnO3/Pr0.5Ca0.5MnO3 trilayers were grown on (001)‐SrTiO3 substrates using the pulsed-laser deposition technique. The coupling at the interfaces of several trilayers has been investigated from magnetization and electronic transport experiments. An increase of La0.5Ca0.5MnO3 layer thickness induces a magnetic ordering in the strain layers and at the interfaces, leading to ferromagnetic behavior and enhanced coercivity, while resistivity shows metal-like behaviors. These effects are not observed in the parent compounds, which are antiferromagnetic insulators, opening a path to induce artificially some novel properties.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Fg Pulsed laser ablation deposition

Nanopatterning of a thin ferromagnetic CoFe film by focused-ion-beam irradiation

D. McGrouther and J. N. Chapman

Appl. Phys. Lett. 87, 022507 (2005); http://dx.doi.org/10.1063/1.1992661 (3 pages) | Cited 19 times

Online Publication Date: 8 July 2005

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High-resolution magnetic patterning of a thin CoFe layer has been performed by irradiation using a focused-ion-beam system. Features <50 nm wide were formed reproducibly. The irradiated pattern comprised sets of alternating 3.0- and 1.0-μm-long magnetic wires, 100 nm wide. During magnetization reversal, the longer wires reversed at a lower field resulting in the formation of an ordered array of domains with density 10 μm−1 supporting antiparallel magnetization. The ability to create domains at predefined locations is important both for fundamental studies and technological applications.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Vb Quantum wires
75.60.Jk Magnetization reversal mechanisms
75.50.Bb Fe and its alloys
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
61.46.-w Structure of nanoscale materials
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.65.La Quantum wires (patterned in quantum wells)

Size dependence, nucleation, and phase transformation of FePt nanoparticles

Yi Ding and Sara A. Majetich

Appl. Phys. Lett. 87, 022508 (2005); http://dx.doi.org/10.1063/1.1993773 (3 pages) | Cited 19 times

Online Publication Date: 8 July 2005

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Monolayers of chemically prepared FePt nanoparticles were deposited on silicon nitride membrane windows, and annealed under different conditions. Hysteresis loops showed a bimodal distribution of switching fields. The size dependence determined from transmission electron microscopy was correlated with the magnetic switching field distribution, assuming that all particles above a threshold size d* had high anisotropy. This simplified model yielded a common value of d*, independent of the annealing conditions. The dependence of d* on the initial particle size indicated the importance of grain boundaries as nucleation sites, and supports the hypothesis that the fcc-to-fct phase transformation is kinetically limited.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
61.46.-w Structure of nanoscale materials
61.72.Mm Grain and twin boundaries
64.70.K- Solid-solid transitions
64.60.Q- Nucleation
68.37.Lp Transmission electron microscopy (TEM)
81.40.Gh Other heat and thermomechanical treatments

Perovskite manganite magnetic tunnel junctions with enhanced coercivity contrast

Y. Ishii, H. Yamada, H. Sato, H. Akoh, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 87, 022509 (2005); http://dx.doi.org/10.1063/1.1995955 (3 pages) | Cited 17 times

Online Publication Date: 8 July 2005

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We have fabricated (La,Sr)MnO3 (LSMO)-based magnetic tunnel junctions with Ru-doped LSMO (LSMRO) film used as one of the electrodes. The Ru doping enhances the coercivity of LSMO, resulting in a sharp steplike tunnel magnetoresistance (TMR) response with a high contrast in the coercive field (Hc) for magnetization reversal. Although the difference of the Hc between the top LSMRO and the bottom LSMO electrodes decreases with increasing the temperature, it is large enough to give a clear TMR response even at a relatively higher temperature region of around 200 K. By changing the dimensions of the top LSMRO electrode, the Hc is found to have no dependence on the geometric aspect variations of the top electrode but slightly on the junction area.
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75.50.Dd Nonmetallic ferromagnetic materials
72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
61.72.up Other materials
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Effects of post-deposition annealing in O2 on the electrical characteristics of LaAlO3 films on Si

L. Miotti, K. P. Bastos, C. Driemeier, V. Edon, M. C. Hugon, B. Agius, and I. J. R. Baumvol

Appl. Phys. Lett. 87, 022901 (2005); http://dx.doi.org/10.1063/1.1989447 (3 pages) | Cited 14 times

Online Publication Date: 5 July 2005

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LaAlO3 films were deposited on p-type Si(100) by sputtering from a LaAlO3 target. C×V characteristics were determined in nonannealed and O2-annealed capacitors having LaAlO3 films as dielectric and RuO2 as top electrode. Thermal annealing in O2 atmosphere reduced flat band voltage to acceptable values for advanced Si-based devices. math–math isotopic substitution was characterized by Rutherford backscattering spectrometry and nuclear resonant reaction profiling. Chemical analysis of the films was accomplished by x-ray photoelectron spectroscopy. The electrical improvements observed after thermal annealing in O2 were attributed to the incorporation of oxygen from the gas phase, possibly healing oxygen vacancies in the films and providing mobile oxygen to the interface.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.72.J- Point defects and defect clusters

Titanium-added praseodymium silicate high-k layers on Si(001)

T. Schroeder, G. Lupina, J. Dabrowski, A. Mane, Ch. Wenger, G. Lippert, and H.-J. Müssig

Appl. Phys. Lett. 87, 022902 (2005); http://dx.doi.org/10.1063/1.1978978 (3 pages) | Cited 33 times

Online Publication Date: 6 July 2005

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Titanium-added praseodymium silicate layers on Si(001) are promising high-k insulators for silicon-based nanoelectronic devices. Synchrotron radiation x-ray photoelectron spectroscopy was applied to study the effect of titanium additives on the praseodymium silicate/Si system. Nondestructive depth profiling by variation of the photon energy shows that thermal annealing activates the diffusion of deposited titanium into the praseodymium silicate. A homogeneous praseodymium titanium silicate layer is formed that shows high-quality electrical properties.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.61.Ng Insulators
66.30.J- Diffusion of impurities

Electron spin resonance investigation of oxygen-vacancy-related defects in BaTiO3 thin films

V. V. Laguta, A. M. Slipenyuk, I. P. Bykov, M. D. Glinchuk, M. Maglione, D. Michau, J. Rosa, and L. Jastrabik

Appl. Phys. Lett. 87, 022903 (2005); http://dx.doi.org/10.1063/1.1954900 (3 pages) | Cited 11 times

Online Publication Date: 7 July 2005

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The Ti3+ center, based on a regular Ti site perturbed by an oxygen vacancy (VO), is identified by electron spin resonance (ESR) in textured BaTiO3 films. The center shows tetragonal symmetry along cubic ⟨100⟩ axes with g-factors: g‖ = 1.997, g⊥ = 1.904. The spectrum of this defect disappeared after the film annealing at 700 °C in an O2 atmosphere. We describe the observed spectrum as Ti3+–VO couple defects or F+ center, which have never been observed in bulk BaTiO3. ESR is thus a unique tool to identify oxygen-vacancy-related defects, which have a large effect on the performance of ferroelectric films.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
77.80.-e Ferroelectricity and antiferroelectricity
81.40.Gh Other heat and thermomechanical treatments
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters

A giant pyroelectric effect of a rigid rod-like polymer, poly[(s)-(-)-2-propionic acid methyl isocyanate]

Atsushi Sugita, Yuhji Yamashira, and Shigeru Tasaka

Appl. Phys. Lett. 87, 022904 (2005); http://dx.doi.org/10.1063/1.1978981 (3 pages) | Cited 3 times

Online Publication Date: 7 July 2005

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Electric activity of a rigid rod-like polymer, poly[(s)-(-)-2-propionic acid methyl isocyanate] (Pc*IC), in a solid state is reported. A measurement of a displacement-field hysteresis loop reveals that Pc*IC chain systems possessed polarization for which the direction can be inversed by an external field. Remanent polarization and a coercive field were determined to be 16.4 mC/m2 and 15.7 MV/m, respectively, at 20 °C. The polymer also exhibited the excellent pyroelectricity. A pyroelectric coefficient of about 300 μmC/m2 K at 95 °C was one magnitude larger than those of other pyroelectric polymers and was almost comparable with those of some inorganic pyroelectric materials.
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77.84.Jd Polymers; organic compounds
77.70.+a Pyroelectric and electrocaloric effects
77.22.Ej Polarization and depolarization
72.80.Le Polymers; organic compounds (including organic semiconductors)

Rearrangement of ferroelectric domain structure induced by chemical etching

V. Ya. Shur, A. I. Lobov, A. G. Shur, S. Kurimura, Y. Nomura, K. Terabe, X. Y. Liu, and K. Kitamura

Appl. Phys. Lett. 87, 022905 (2005); http://dx.doi.org/10.1063/1.1993769 (3 pages) | Cited 17 times

Online Publication Date: 7 July 2005

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The rearrangement of the domain structure induced by chemical etching has been observed in periodically poled MgO-doped stoichiometric lithium tantalate single crystals. Topographic and piezoresponse scanning probe microscopy have been used for measuring the etching relief height and domain wall position after etching. The considerable shift of the domain wall during etching by pure hydrofluoric acid has been revealed by analysis of the experimental data. We have found that the wall motion proceeded after the termination of the etching procedure. We have shown that the whole consequence of the domain wall positions during etching is recorded in the etching relief height and can be extracted with high spatial and temporal resolution.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)

Characterization of highly (110)- and (111)-oriented Pb(Zr,Ti)O3 films on BaPbO3 electrode using Ru conducting barrier

Chun-Sheng Liang and Jenn-Ming Wu

Appl. Phys. Lett. 87, 022906 (2005); http://dx.doi.org/10.1063/1.1996850 (3 pages) | Cited 11 times

Online Publication Date: 8 July 2005

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Highly non-(001)-oriented Pb(Zr,Ti)O3 (PZT) films have been fabricated by rf-magnetron sputtering. The preferential (110)-oriented BaPbO3 (BPO) deposited on Ru buffer layer induces the growth of (110)-oriented PZT film. With the aid of self-organized growth of PZT, the orientation of the film deposited on random-oriented BPO/Pt(111)/Ru(002) is (111)-preferred. The insertion of Pt layer between BPO and Ru changes the orientation of PZT from (110) to (111) and prevents the oxygen diffusion. These non-(001)-oriented PZT films possess more superior ferroelectric, fatigue, and retention properties than those of (001)-oriented PZT films.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
77.80.-e Ferroelectricity and antiferroelectricity
81.15.Cd Deposition by sputtering

Electrode and grain-boundary effects on the conductivity of CaCu3Ti4O12

Lei Zhang

Appl. Phys. Lett. 87, 022907 (2005); http://dx.doi.org/10.1063/1.1993748 (3 pages) | Cited 41 times

Online Publication Date: 8 July 2005

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The ac conductivity of CaCu3Ti4O12 (CCTO) ceramics was studied in the temperature range 173<T<443 K. The dc conductivities containing the components of electrodes (σe) and grain boundaries (σgb) were measured, from which a thermal activation energies of ∼ 0.54 eV was inferred. Different behaviors of dielectric relaxations are responsible for the two contributing components.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
72.80.Sk Insulators
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.22.Gm Dielectric loss and relaxation
61.72.Mm Grain and twin boundaries
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GaAs on Si(111)—crystal shape and strain relaxation in nanoscale patterned growth

S. C. Lee, L. R. Dawson, S. R. J. Brueck, and Y.-B. Jiang

Appl. Phys. Lett. 87, 023101 (2005); http://dx.doi.org/10.1063/1.1984100 (3 pages) | Cited 2 times

Online Publication Date: 6 July 2005

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Nanoscale patterned growth of GaAs on Si(111) by molecular beam epitaxy is examined. A 355 nm period two-dimensional array of circular holes (diameter ∼ 200–250 nm) is fabricated into a 45-nm-thick SiO2 film on a Si(111) substrate by large-area interferometric lithography and dry etching. For 300 nm deposition, the GaAs epilayer selectively deposited within each hole on the patterned substrate is surrounded by {1math0}-type sidewalls perpendicular to Si(111), resulting in a hexagon-based prismatic pillar, without significant lateral overgrowth. At the initial stage of growth, twins parallel to Si(111) and an aperiodic mixture of cubic and hexagonal phases are observed but most of the GaAs pillars are terminated with a cubic phase region. Raman scattering reveals that the individual nanoscale GaAs pillars are completely strain relaxed.
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81.05.Ea III-V semiconductors
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Mm Grain and twin boundaries

Approach to nonphotoperturbed differential capacitance measurements: A front-wing cantilever

M. N. Chang, C. Y. Chen, W. J. Huang, and T. C. Cheng

Appl. Phys. Lett. 87, 023102 (2005); http://dx.doi.org/10.1063/1.1994949 (3 pages) | Cited 4 times

Online Publication Date: 6 July 2005

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We have developed a front-wing (FW) cantilever structure that can significantly suppress photoperturbation effects during scanning capacitance microscopy (SCM) and scanning capacitance spectroscopy (SCS) measurements. The FW cantilever provides an effective shadow area that fully covers the scan region, allowing us to synchronously obtain SCM images and the corresponding topographic images without photoperturbation problems. Nonphotoperturbed differential capacitance characteristics versus tip biases were also obtained for SCS by the use of these FW cantilevers. This means that nonphotoperturbed SCM and SCS measurements can be carried out during the typical SCM operations.
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07.79.-v Scanning probe microscopes and components
07.68.+m Photography, photographic instruments; xerography

Efficient field emission from α-Fe2O3 nanoflakes on an atomic force microscope tip

Y. W. Zhu, T. Yu, C. H. Sow, Y. J. Liu, A. T. S. Wee, X. J. Xu, C. T. Lim, and J. T. L. Thong

Appl. Phys. Lett. 87, 023103 (2005); http://dx.doi.org/10.1063/1.1991978 (3 pages) | Cited 46 times

Online Publication Date: 7 July 2005

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Aligned arrays of flake-shaped hematite (α-Fe2O3) nanostructure have been fabricated on an atomic force microscope (AFM) tip. They are created by simply heating an iron-coated AFM tip in ambience on a hot plate. These nanoflakes are characterized as α-Fe2O3 single crystalline structures with tip radii as small as several nanometers and are highly effective as electron field emitters. With a vacuum gap of about 150 μm, field emission measurements of α-Fe2O3 nanoflakes on AFM tips show a low turn-on voltage of about 400–600 V and a high current density of 1.6 A cm−2 under 900 V. Such high emission current density is attributed to the nanoscale sharp tips of the as-grown nanoflakes. Based on the Fowler–Nordheim theory, it is demonstrated the enhancement factor of α-Fe2O3 nanoflakes on AFM tips is comparable to that of carbon nanotubes. Our findings suggest that α-Fe2O3 nanoflakes are potentially useful as candidates for future electron field emission devices.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Hydrogen as origin of compressive intrinsic stress in hydrogenated amorphous silicon: The contribution of clustered forms

B. Pantchev, P. Danesh, and B. Schmidt

Appl. Phys. Lett. 87, 023104 (2005); http://dx.doi.org/10.1063/1.1999007 (3 pages) | Cited 2 times

Online Publication Date: 8 July 2005

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The role of hydrogen in hydrogenated amorphous silicon (a‐Si:H) has been studied from the viewpoint of its specific contribution to mechanical stress in the material. Hydrogen ion implantation has been used to increase the hydrogen concentration. In order to distinguish the effect of the changed hydrogen concentration∕bonding configuration from the accompanying implantation-induced defects, a‐Si:H samples with corresponding number of displacements have been studied, created using proper doses of silicon ion implantation. The experimental results have shown that it is the silicon-bonded hydrogen that essentially affects the stress, as the major contribution has its clustered bonding configuration.
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61.72.uf Ge and Si
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.50.Lt Crystal binding; cohesive energy

Enhanced thermoelectric performance in PbTe-based superlattice structures from reduction of lattice thermal conductivity

J. C. Caylor, K. Coonley, J. Stuart, T. Colpitts, and R. Venkatasubramanian

Appl. Phys. Lett. 87, 023105 (2005); http://dx.doi.org/10.1063/1.1992662 (3 pages) | Cited 46 times

Online Publication Date: 8 July 2005

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We have fabricated two-dimensional n-type PbTe/PbTe0.75Se0.25 structures using an evaporation process. In optimized films exhibiting a high-quality superlattice structure, a significant reduction in lattice thermal conductivity has been experimentally measured. The reduction would indicate enhanced thermoelectric device performance compared to standard PbTeSe alloys given that the electrical components, specifically, the Seebeck coefficient and electrical resistivity, were not observed to deteriorate from bulk values. The analysis of these films shows continuous layers with a true two-dimensional superlattice structure, as opposed to the PbTe/PbSe system that exhibits zero-dimensional structures from self-assembly. The room-temperature measurement of cross-plane figure-of-merit in a n-type PbTe/PbTe0.75Se0.25 device structure by the transient method has been combined with temperature-dependent measurements of in-plane resistivity and Seebeck coefficient to yield evidence of enhanced thermoelectric performance. The similarities and differences between the superlattice in the PbTe/PbTe0.75Se0.25 system and the Bi2Te3/Sb2Te3 material system are presented.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Hd Other semiconductors
73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.61.Le Other inorganic semiconductors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Ultrafast carrier dynamics in ZnO nanorods

Chi-Kuang Sun, Shih-Ze Sun, Kung-Hsuan Lin, Kenneth Yi-Jie Zhang, Hsiang-Lin Liu, Sai-Chang Liu, and Jih-Jen Wu

Appl. Phys. Lett. 87, 023106 (2005); http://dx.doi.org/10.1063/1.1989444 (3 pages) | Cited 19 times

Online Publication Date: 8 July 2005

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Free exciton and above-band-gap free carrier dynamics in ZnO nanorods have been investigated at room temperature with a femtosecond transient transmission measurement. Following the photoexcitation of above-band-gap free carriers, an extremely fast external thermalization time on the order of 200 fs can be observed. Under high excitation, hot phonon effects were found to delay the carrier cooling process. While the photoexcitation energy was tuned to match the free exciton transition, stable exciton formation can be uncovered while no evident exciton ionization process can be found unless the photoexcited exciton density exceeded the Mott density.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.-p Spectroscopy of solid state dynamics
78.40.Fy Semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.35.-y Excitons and related phenomena
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Ballistic thermal and electrical conductance measurements on individual multiwall carbon nanotubes

Elisabetta Brown, Ling Hao, John C. Gallop, and John C. Macfarlane

Appl. Phys. Lett. 87, 023107 (2005); http://dx.doi.org/10.1063/1.1993768 (3 pages) | Cited 26 times

Online Publication Date: 8 July 2005

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We report thermal measurements on individual carbon nanotubes using a temperature sensing scanned microscope probe. An arc-grown bundle of multiwalled nanotubes (MWNTs) is mechanically attached to a thermal probe. The heat flow down individual MWNTs is recorded as a function of the temperature difference across them. Simultaneous measurements of thermal and electrical conductance are recorded. The size of the conductance steps observed at room temperature and the correlation between electrical and thermal conductance steps are discussed and we present evidence for ballistic transport of both phonons and electrons in these tubes.
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73.23.Ad Ballistic transport
73.63.Fg Nanotubes
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
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Fabrication of field-effect transistor device with higher fullerene, C88

Takayuki Nagano, Hiroyuki Sugiyama, Eiji Kuwahara, Rie Watanabe, Haruka Kusai, Yoko Kashino, and Yoshihiro Kubozono

Appl. Phys. Lett. 87, 023501 (2005); http://dx.doi.org/10.1063/1.1994957 (3 pages) | Cited 6 times

Online Publication Date: 6 July 2005

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A fullerene field-effect transistor (FET) device has been fabricated with thin films of C88, and n-channel normally on depletion-type FET properties have been found in this FET device. The C88 FET exhibited a high mobility, μ, of 2.5×10−3 cm2 V−1 s−1 at 300 K, in fullerene FETs. The carrier transport showed a thermally activated hopping transport. The n-channel normally on FET properties and the hopping transport reflect the small mobility gap and low carrier concentration in the channel region of C88 thin films.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
73.61.Wp Fullerenes and related materials
72.20.Ee Mobility edges; hopping transport

Threshold voltage instability of amorphous silicon thin-film transistors under constant current stress

Shah M. Jahinuzzaman, Afrin Sultana, Kapil Sakariya, Peyman Servati, and Arokia Nathan

Appl. Phys. Lett. 87, 023502 (2005); http://dx.doi.org/10.1063/1.1993766 (3 pages) | Cited 27 times

Online Publication Date: 7 July 2005

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We investigate the time-dependent shift in the threshold voltage of amorphous silicon thin-film transistor stressed with constant drain current. We observe a nonsaturating power-law time dependence, which is in contrast to the conventional stretched exponential that saturates at prolonged stress time. The result is consistent with the carrier-induced defect creation model and corroborates the nonlinear dependence of the rate of defect creation on the band-tail carrier density.
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85.30.Tv Field effect devices

Improvement of current gain of C-doped GaAsSb-base heterojunction bipolar transistors by using an InAlP emitter

Yasuhiro Oda, Haruki Yokoyama, Kenji Kurishima, Takashi Kobayashi, Noriyuki Watanabe, and Masahiro Uchida

Appl. Phys. Lett. 87, 023503 (2005); http://dx.doi.org/10.1063/1.1995948 (2 pages) | Cited 10 times

Online Publication Date: 7 July 2005

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Large conduction band edge discontinuity (ΔEc) at the emitter/base interface in InP/GaAs0.51Sb0.49/InP heterojunction bipolar transistor (HBT) is one of the possible reasons that the recombination process in the emitter/base depletion region dominates the characteristics of this HBT. We fabricate an InAlP emitter/GaAs0.51Sb0.49base/InP collector HBT for reducing the ΔEc at the emitter/base interface. It is demonstrated that a HBT with an InAlP emitter shows a relatively lower recombination current than one with an InP emitter, resulting in the higher current gain. It is also found that the decrease of recombination current depends on the Al content of InAlP emitter. Additionally, the ideality factor of the emitter-base current is smallest at the Al content of 0.15 in the InAlP emitter. These results indicate that using an InAlP emitter is effective for improving the current gain of GaAsSb-base HBTs.
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85.30.Pq Bipolar transistors

Flexible semitransparent pentacene thin-film transistors with polymer dielectric layers and NiOx electrodes

Jiyoul Lee, D. K. Hwang, Jeong-M. Choi, Kimoon Lee, Jae Hoon Kim, Seongil Im, Ji Hoon Park, and Eugene Kim

Appl. Phys. Lett. 87, 023504 (2005); http://dx.doi.org/10.1063/1.1996839 (3 pages) | Cited 29 times

Online Publication Date: 8 July 2005

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We have fabricated the flexible semitransparent pentacene-based thin-film transistors (TFTs) with poly-4-vinylphenol (PVP) dielectric layers which were deposited by spin coating on a thermostable plastic substrate with a conductive film. For the source∕drain (S∕D) electrodes of our flexible pentacene TFTs both Au and semitransparent NiOx have been tested. It was found that NiOx was better matched to the pentacene channel for the S∕D contacts than Au. Our flexible pentacene TFTs with semitransparent NiOx contacts exhibited mobility of ∼ 0.24 cm2/V s higher than that achieved with Au contacts ( ∼ 0.14 cm2/V s) and also demonstrated a higher initial drain current.
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85.30.Tv Field effect devices
77.84.Jd Polymers; organic compounds
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