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15 Mar 2010

Volume 96, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 111901 (2010); http://dx.doi.org/10.1063/1.3358107 (3 pages)

B. Rožič, S. Krause, H. Finkelmann, G. Cordoyiannis, and Z. Kutnjak
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Role of field-effect on c-Si surface passivation by ultrathin (2–20 nm) atomic layer deposited Al2O3

N. M. Terlinden, G. Dingemans, M. C. M van de Sanden, and W. M. M. Kessels

Appl. Phys. Lett. 96, 112101 (2010); http://dx.doi.org/10.1063/1.3334729 (3 pages) | Cited 17 times

Online Publication Date: 15 March 2010

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Al2O3 synthesized by plasma-assisted atomic layer deposition yields excellent surface passivation of crystalline silicon (c-Si) for films down to ∼ 5 nm in thickness. Optical second-harmonic generation was employed to distinguish between the influence of field-effect passivation and chemical passivation through the measurement of the electric field in the c-Si space-charge region. It is demonstrated that this electric field—and hence the negative fixed charge density—is virtually unaffected by the Al2O3 thickness between 2 and 20 nm indicating that a decrease in chemical passivation causes the reduced passivation performance for <5 nm thick Al2O3 films.
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81.65.Rv Passivation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Tunneling spectroscopy of electron subbands in thin silicon-on-insulator metal-oxide-semiconductor field-effect transistors

J. Noborisaka, K. Nishiguchi, H. Kageshima, Y. Ono, and A. Fujiwara

Appl. Phys. Lett. 96, 112102 (2010); http://dx.doi.org/10.1063/1.3360224 (3 pages) | Cited 2 times

Online Publication Date: 17 March 2010

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We report the tunneling spectroscopy of thin silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors with tunneling gate oxide. When electrons are injected into a thin SOI well, the gate-tunneling current shows kink structures originating from quantized energy levels in the SOI well. From the theoretical consideration of the energy levels and their density of states, the observed features can be ascribed to electron tunneling into the in-plane fourfold degenerate valley subbands. Furthermore, inhomogeneous peak broadening of the kink structures in the experiment is well explained by the SOI thickness variation.
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85.30.Tv Field effect devices

Electrical observation of a tunable band gap in bilayer graphene nanoribbons at room temperature

B. N. Szafranek, D. Schall, M. Otto, D. Neumaier, and H. Kurz

Appl. Phys. Lett. 96, 112103 (2010); http://dx.doi.org/10.1063/1.3364139 (3 pages) | Cited 23 times

Online Publication Date: 17 March 2010

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We investigate the transport properties of double-gated bilayer graphene nanoribbons at room temperature. The devices were fabricated using complementary metal-oxide semiconductor (CMOS)-compatible processes. By analyzing the dependence of the resistance at the charge neutrality point as a function of the electric field applied perpendicular to the graphene surface, we show that a band gap in the density of states opens, reaching an effective value of ∼ 50 meV. This demonstrates the potential of bilayer graphene as channel material for a field-effect transistor in a conventional CMOS environment.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.22.Pr Electronic structure of graphene
78.67.Wj Optical properties of graphene
72.80.Vp Electronic transport in graphene

AlGaAs/GaAs single electron transistor fabricated without modulation doping

A. M. See, O. Klochan, A. R. Hamilton, A. P. Micolich, M. Aagesen, and P. E. Lindelof

Appl. Phys. Lett. 96, 112104 (2010); http://dx.doi.org/10.1063/1.3358388 (3 pages) | Cited 7 times

Online Publication Date: 19 March 2010

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We have fabricated a quantum dot single electron transistor, based on AlGaAs/GaAs heterojunction without modulation doping, which exhibits clear and stable Coulomb blockade oscillations. The temperature dependence of the Coulomb blockade peak line shape is well described by standard Coulomb blockade theory in the quantum regime. Bias spectroscopy measurements have allowed us to directly extract the charging energy, and showed clear evidence of excited state transport, confirming that individual quantum states in the dot can be resolved.
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81.07.Ta Quantum dots
85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
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Temperature dependent nucleation and annihilation of individual magnetic vortices

G. Mihajlović, M. S. Patrick, J. E. Pearson, V. Novosad, S. D. Bader, M. Field, G. J. Sullivan, and A. Hoffmann

Appl. Phys. Lett. 96, 112501 (2010); http://dx.doi.org/10.1063/1.3360841 (3 pages) | Cited 6 times

Online Publication Date: 15 March 2010

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We studied the temperature dependence of the magnetization reversal in individual submicron permalloy disks with micro-Hall and bend-resistance magnetometry. The nucleation field exhibits a nonmonotonic dependence with positive and negative slopes at low and high temperatures, respectively, while the annihilation field monotonically decreases with increasing temperature, but with distinctly different slopes at low and high temperatures. Our analysis suggests that at low temperatures vortex nucleation and annihilation proceeds via thermal activation over an energy barrier, while at high temperatures they are governed by a temperature dependence of the saturation magnetization.
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75.60.Jk Magnetization reversal mechanisms
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys

Effects of annealing on the local structure of Fe and Co in CoFeB/MgO/CoFeB tunnel junctions: An extended x-ray-absorption fine structure study

Abdul K. Rumaiz, J. C. Woicik, W. G. Wang, Jean Jordan-Sweet, G. H. Jaffari, C. Ni, John Q. Xiao, and C. L. Chien

Appl. Phys. Lett. 96, 112502 (2010); http://dx.doi.org/10.1063/1.3364137 (3 pages) | Cited 6 times

Online Publication Date: 16 March 2010

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Extended x-ray-absorption fine structure (EXAFS) was used to study the evolution of the local structure of Fe and Co as a function of annealing time in CoFeB/MgO/CoFeB magnetic tunnel junctions. EXAFS indicates B depletion and crystallization of the CoFeB layers within a few seconds of the post growth high temperature anneal. The decrease in first-shell Debye–Waller factor and hence the increase in structural order during annealing explains the increase in tunnel magnetoresistance observed as a result of post deposition annealing.
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75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
61.72.Cc Kinetics of defect formation and annealing
78.70.Dm X-ray absorption spectra

Irreversibility of field-induced magnetostructural transition in NiCoMnSb shape memory alloy revealed by magnetization, transport and heat capacity studies

Ajaya K. Nayak, K. G. Suresh, and A. K. Nigam

Appl. Phys. Lett. 96, 112503 (2010); http://dx.doi.org/10.1063/1.3365181 (3 pages) | Cited 8 times

Online Publication Date: 17 March 2010

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The effects of magnetic field on the martensitic transition have been studied in Ni45Co5Mn38Sb12. We find a large field-induced irreversibility in this system, as revealed by the field dependence of resistivity, magnetization, and heat capacity data. At the critical temperature, the field-induced conversion of the martensitic to austenite phase is not reversible under any field variation. At this temperature any energy fluctuation induces nucleation and growth of the equilibrium austenite phase at the expense of the metastable martensitic phase and gets arrested. All these three measurements completely rule out the coexistence of austenite and martensitic phases in the irreversibility regime.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
64.70.K- Solid-solid transitions
62.20.fg Shape-memory effect; yield stress; superelasticity

Superparamagnetic and superspin glass behaviors in the martensitic state of Ni43.5Co6.5Mn39Sn11 magnetic shape memory alloy

D. Y. Cong, S. Roth, J. Liu, Q. Luo, M. Pötschke, C. Hürrich, and L. Schultz

Appl. Phys. Lett. 96, 112504 (2010); http://dx.doi.org/10.1063/1.3367721 (3 pages) | Cited 10 times

Online Publication Date: 17 March 2010

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The magnetic state of the low-temperature martensite in a Ni43.5Co6.5Mn39Sn11 magnetic shape memory alloy (MSMA) is disclosed. At temperatures (T) above a critical temperature Tf, the magnetization versus field [M(H)] curves display a sigmoid shape, show no magnetic hysteresis, and can be well fitted according to the Langevin model, confirming that the martensite shows superparamagnetic behavior at T>Tf. On the other hand, the observation of a memory effect during the stop-and-wait protocol and the analysis of dynamic magnetic properties probed by ac susceptibility measurements unequivocally corroborate the superspin glass behavior of interacting magnetic clusters at T<Tf. The present study provides significant insights into the magnetism of martensite in MSMAs.
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81.30.Kf Martensitic transformations
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
64.70.kd Metals and alloys
62.20.fg Shape-memory effect; yield stress; superelasticity

Electrode artifacts in low resistance organic spin valves

Alberto Riminucci, Mirko Prezioso, Patrizio Graziosi, and Carol Newby

Appl. Phys. Lett. 96, 112505 (2010); http://dx.doi.org/10.1063/1.3309599 (3 pages) | Cited 4 times

Online Publication Date: 17 March 2010

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Artifacts can originate from the inherent shortcomings of the cross bar configuration, when the resistance of the device is small compared to that of one of the electrodes. This is particularly relevant to the field of organic spintronics, in which at least one recent work overlooked this effect. We use a simplified one-dimensional resistor model and a full three-dimensional finite element method simulation to show that an increase in the resistance of one electrode appears as a decrease of the measured resistance. We found that the model agrees qualitatively but not quantitatively with observation.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
02.70.Dh Finite-element and Galerkin methods

In-plane reorientation of magnetization in epitaxial exchange biased Fe/MnPd bilayers

Qing-feng Zhan and Kannan M. Krishnan

Appl. Phys. Lett. 96, 112506 (2010); http://dx.doi.org/10.1063/1.3367705 (3 pages) | Cited 5 times

Online Publication Date: 18 March 2010

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We investigated the in-plane reorientation of magnetization in epitaxial Fe/MnPd bilayers. The samples with various thicknesses of MnPd and Fe layers present a conventional square and an unusual two-step exchange biased hysteresis loops at different temperature. The shape of the loops is reproduced using the coherent rotation model and including the relative orientation of the uniaxial anisotropy with respect to the exchange bias. The parallel and perpendicular uniaxial anisotropies in the ferromagnetic layer are linked to the aligned and the reoriented states, respectively. The magnetic reorientation between the aligned and the reoriented states, which is determined by the competition between the interface exchange coupling and the intrinsic uniaxial energies, is shown to be driven by the temperature, as well as the thickness of MnPd and Fe layers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Gw Magnetic anisotropy

Comparing magnetotransport and surface magnetic properties of half-metallic CrO2 films grown by low pressure and atmospheric pressure chemical vapor deposition

M. Pathak, X. Zhong, J. Wang, X. Zhang, T. M. Klein, P. LeClair, and A. Gupta

Appl. Phys. Lett. 96, 112507 (2010); http://dx.doi.org/10.1063/1.3367783 (3 pages)

Online Publication Date: 18 March 2010

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CrO2 films prepared by low pressure chemical vapor deposition (LPCVD) using Cr(CO)6 precursor have been investigated and compared with epitaxial half metallic CrO2 films prepared at atmospheric pressure (APCVD) using CrO3 precursor for their magnetotransport and surface magnetic properties. LPCVD films showed higher resistivity than APCVD epitaxial (100) CrO2 films prepared on (100) TiO2 substrates. Magnetoresistance of LPCVD films is comparable to that of APCVD films. X-ray magnetic circular dichroism suggests a reduced surface magnetic moment for LPCVD films. This reduced magnetic moment is attributed to antiferromagnetic alignment of the uncompensated Cr spins in the Cr2O3 surface layer.
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73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Rf Surface magnetism
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Epitaxial stabilization of ε-Fe2O3 (00l) thin films on SrTiO3 (111)

M. Gich, J. Gazquez, A. Roig, A. Crespi, J. Fontcuberta, J. C. Idrobo, S. J. Pennycook, M. Varela, V. Skumryev, and M. Varela

Appl. Phys. Lett. 96, 112508 (2010); http://dx.doi.org/10.1063/1.3360217 (3 pages) | Cited 2 times

Online Publication Date: 18 March 2010

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Thin films of the metastable and elusive ε-Fe2O3 have been epitaxially stabilized on SrTiO3 (111) substrates. The ε-Fe2O3 films present a (001) orientation perpendicular to the substrate and three in-plane domains measuring a few nanometers and showing atomically sharp interfaces. We argue that this domain structure, rather than the epitaxial-strain, plays an essential role in stabilizing the ε-Fe2O3 by minimizing the energy of (100) surfaces. The ε-Fe2O3 films show a large in-plane coercivity ∼ 8 kOe which combined with the magnetoelectric character claimed for this oxide may lead to novel applications in spintronics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.78.-n Magnetization dynamics
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.85.+t Magnetoelectric effects, multiferroics

Hot electron transport in magnetic tunnel transistors with an epitaxial MgO tunnel barrier

Taro Nagahama, Hidekazu Saito, and Shinji Yuasa

Appl. Phys. Lett. 96, 112509 (2010); http://dx.doi.org/10.1063/1.3360222 (3 pages) | Cited 3 times

Online Publication Date: 18 March 2010

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We fabricated fully epitaxial magnetic tunnel transistors (MTTs) consisting of a Fe(001)/MgO(001) emitter and a Fe(001) based on a n-GaAs(001) collector. We observed much higher transfer ratio (α) and magnetocurrent (MC) ratio than those of the previously reported MTTs that had an amorphous AlO barrier. These improvements are due to the coherent tunneling and single-crystalline base layer. In addition, a pronounced peak structure appeared in the emitter bias dependence of α, which might be attributed to the interface resonance states at the Fe(001)/GaAs(001) interface.
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85.70.-w Magnetic devices
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.Pq Bipolar transistors
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Spin wave mode transition induced by surface anisotropy and characteristic length in magnetic nanoparticles

Peiheng Zhou (周佩珩), Li Zhang (张丽), and Longjiang Deng (邓龙江)

Appl. Phys. Lett. 96, 112510 (2010); http://dx.doi.org/10.1063/1.3360882 (3 pages) | Cited 2 times

Online Publication Date: 18 March 2010

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In magnetic nanoparticles with cylindrical symmetry of the magnetization configurations, spin wave mode transition (SWMT) is predicted for the case of a surface anisotropy parallel to the uniform magnetization. Theoretical investigation has shown that a characteristic length can be determined to evaluate the spatial influence of the spin wave mode excited by surface anisotropy. This knowledge implies SWMT occurs as the particle size exceeds the corresponding characteristic length. An indirect experimental observation of the SWMT is also provided. These results can be utilized for ferromagnetic resonances control in magnetic devices.
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75.75.Jn Dynamics of magnetic nanoparticles
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Rf Surface magnetism

Correlated d0 ferromagnetism and photoluminescence in undoped ZnO nanowires

Guozhong Xing, Dandan Wang, Jiabao Yi, Lili Yang, Ming Gao, Mi He, Jinghai Yang, Jun Ding, Tze Chien Sum, and Tom Wu

Appl. Phys. Lett. 96, 112511 (2010); http://dx.doi.org/10.1063/1.3340930 (3 pages) | Cited 53 times

Online Publication Date: 19 March 2010

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We report the correlated d0 ferromagnetism and photoluminescence in undoped single-crystalline ZnO nanowires synthesized by using a vapor transport method. We systematically tune the oxygen deficiency in the ZnO nanowires from 4% to 20% by adjusting the growth conditions, i.e., selecting different catalyst (Au or Ag) and varying the growth temperature. Our study suggests that oxygen vacancies induce characteristic photoluminescence and significantly boost the room-temperature ferromagnetism. Such undoped ZnO nanowires with tunable magnetic and optical properties are promising to find applications in multifunctional spintronic and photonic nanodevices.
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78.55.Et II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.67.Uh Nanowires
81.07.Gf Nanowires
75.75.-c Magnetic properties of nanostructures
75.75.Cd Fabrication of magnetic nanostructures
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Physical and electrical characteristics of the high-k Ta2O5 (tantalum pentoxide) dielectric deposited on the polycrystalline silicon

Chyuan-Haur Kao, Hsiang Chen, Jing Sing Chiu, Kung Shao Chen, and Yu Tsung Pan

Appl. Phys. Lett. 96, 112901 (2010); http://dx.doi.org/10.1063/1.3334725 (3 pages) | Cited 8 times

Online Publication Date: 15 March 2010

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The high-k Ta2O5 films deposited on the polycrystalline silicon treated with different postrapid thermal annealing temperatures were formed as high-k interdielectrics. Physical and electrical characteristics of the Ta2O5 dielectrics were investigated with x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and electrical analysis. The annealing at 800 °C was found to be the optimal condition to reduce the defects and interface traps existed in the interface between the Ta2O5 dielectric and polysilicon to fabricate a well-crystallized film with higher breakdown field, lower leakage current and smaller charge trapping rate. This Ta2O5 dielectric shows promise for future generation of nonvolatile memory.
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77.55.-g Dielectric thin films
68.60.Wm Other nonelectronic physical properties
73.61.Ng Insulators
79.60.Dp Adsorbed layers and thin films
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments

Effects of postgate dielectric treatment on germanium-based metal-oxide-semiconductor device by supercritical fluid technology

Po-Tsun Liu, Chen-Shuo Huang, Yi-Ling Huang, Jing-Ru Lin, Szu-Lin Cheng, Yoshio Nishi, and S. M. Sze

Appl. Phys. Lett. 96, 112902 (2010); http://dx.doi.org/10.1063/1.3365177 (3 pages)

Online Publication Date: 17 March 2010

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Supercritical fluid (SCF) technology is employed at low temperature as a postgate dielectric treatment to improve gate SiO2/germanium (Ge) interface in a Ge-based metal-oxide-semiconductor (Ge-MOS) device. The SCF can transport the oxidant and penetrate the gate oxide layer for the oxidation of SiO2/Ge interface at 150 °C. A smooth interfacial GeO2 layer between gate SiO2 and Ge is thereby formed after SCF treatment, and the frequency dispersion of capacitance-voltage characteristics is also effectively alleviated. Furthermore, the electrical degradation of Ge-MOS after a postgate dielectric annealing at 450 °C can be restored to a extent similar to the initial state.
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85.30.-z Semiconductor devices
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing

Anisotropy of domain growth in epitaxial ferroelectric capacitors

D. Wu, I. Vrejoiu, M. Alexe, and A. Gruverman

Appl. Phys. Lett. 96, 112903 (2010); http://dx.doi.org/10.1063/1.3366724 (3 pages) | Cited 9 times

Online Publication Date: 17 March 2010

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Piezoresponse force microscopy (PFM) has been applied to investigate the switching kinetics in microscale epitaxial Pb(Zr,Ti)O3 capacitors. It is shown that transition from low to high field range brings about a qualitative change in domain growth kinetics, namely, laterally isotropic growth in the high fields as opposed to highly anisotropic growth in the low fields. It is suggested that anisotropy of domain growth can be attributed to orientational variations in the activation energy due to film microstructure. Fitting the switching kinetics using the Kolmogorov–Avrami–Ishibashi model shows excellent agreement with the PFM experimental data and yields the integer values of domain dimensionality.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors

Identification of the controlling parameter for the set-state resistance of a TiO2 resistive switching cell

Seul Ji Song, Kyung Min Kim, Gun Hwan Kim, Min Hwan Lee, Jun Yeong Seok, Ranju Jung, and Cheol Seong Hwang

Appl. Phys. Lett. 96, 112904 (2010); http://dx.doi.org/10.1063/1.3355415 (3 pages) | Cited 14 times

Online Publication Date: 18 March 2010

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This study examined the parameter controlling the set-state resistance (Rset) of a Pt/TiO2/Pt resistive switching (RS) cell in unipolar RS mode. Although the compliance current in the current-voltage sweep had some effect on the Rset, the uncontrolled flow of charge from the parametric analyzer prevented making an accurate estimation of the parameters. The current transient in pulse switching observed using a high-speed digital oscilloscope and physical modeling showed that the capacitive charge moves vigorously at the moment of on-switching, and Rset is governed by the level of migrating charge. The actual switching time was ⪡50 ns.
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73.40.Rw Metal-insulator-metal structures

Interfacial self cleaning during atomic layer deposition and annealing of HfO2 films on native (100)-GaAs substrates

Rahul Suri, Daniel J. Lichtenwalner, and Veena Misra

Appl. Phys. Lett. 96, 112905 (2010); http://dx.doi.org/10.1063/1.3357422 (3 pages) | Cited 12 times

Online Publication Date: 18 March 2010

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The reduction in native oxides on GaAs surface during atomic layer deposition (ALD) of HfO2 using tetrakis-dimethylamino-hafnium precursor was investigated using x-ray photoelectron spectroscopy. The role of the ALD growth temperature on the reaction between surface oxides and precursor was studied. Interfacial oxide reduction was found to be insignificant for ALD at 200 °C, while nearly complete for growth at 300 °C. During postdeposition annealing at 400 °C, any arsenic oxides present were found to decompose, resulting in an increase in the interfacial gallium oxides. Thus, control of the ALD process plays a large role in determining interface properties.
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81.65.Cf Surface cleaning, etching, patterning
77.55.D- High-permittivity gate dielectric films
61.72.Cc Kinetics of defect formation and annealing
79.60.Dp Adsorbed layers and thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators

Local measurements of Preisach density in polycrystalline ferroelectric capacitors using piezoresponse force spectroscopy

O. Ovchinnikov, S. Jesse, S. Guo, K. Seal, P. Bintachitt, I. Fujii, S. Trolier-McKinstry, and S. V. Kalinin

Appl. Phys. Lett. 96, 112906 (2010); http://dx.doi.org/10.1063/1.3360220 (3 pages) | Cited 4 times

Online Publication Date: 18 March 2010

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Polarization switching in polycrystalline ferroelectric capacitors is explored using piezoresponse force microscopy (PFM) based first-order reversal curve (FORC) measurements. The band excitation method facilitates decoupling the electromechanical responses from variations in surface elastic properties. A simulated annealing method is developed to estimate the Preisach densities from PFM FORC data. Microscopic and macroscopic Preisach densities are compared, illustrating good agreement between the two.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.65.-j Piezoelectricity and electromechanical effects

Frequency dependent electrical measurements of amorphous GeSbSe chalcogenide thin films

M. Mirsaneh, E. Furman, J. V. Ryan, M. T. Lanagan, and C. G. Pantano

Appl. Phys. Lett. 96, 112907 (2010); http://dx.doi.org/10.1063/1.3360225 (3 pages) | Cited 1 time

Online Publication Date: 18 March 2010

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A commercial bulk chalcogenide glass (Ge28Sb12Se60) was used as a source to fabricate amorphous thin films via thermal evaporation technique. At low frequencies (<1 MHz) impedance spectroscopy was performed to measure electrical properties. To measure ac conductivity at microwave frequencies, a split resonance cavity technique was applied for which a model based on parallel arrangement of substrate and film capacitors was developed. This model was used to extract tan δ and ac conductivity of the films. Microwave ac conductivity was correlated with the extrapolated low frequency conductivity data confirming applicability of the universal law commonly observed in amorphous semiconductors.
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73.61.Jc Amorphous semiconductors; glasses
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Strain-driven alignment of In nanocrystals on InGaAs quantum dot arrays and coupled plasmon-quantum dot emission

A. Urbańczyk, G. J. Hamhuis, and R. Nötzel

Appl. Phys. Lett. 96, 113101 (2010); http://dx.doi.org/10.1063/1.3358122 (3 pages) | Cited 9 times

Online Publication Date: 15 March 2010

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We report the alignment of In nanocrystals on top of linear InGaAs quantum dot (QD) arrays formed by self-organized anisotropic strain engineering on GaAs (100) by molecular beam epitaxy. The alignment is independent of a thin GaAs cap layer on the QDs revealing its origin is due to local strain recognition. This enables nanometer-scale precise lateral and vertical site registration between the QDs and the In nanocrystals and arrays in a single self-organizing formation process. The plasmon resonance of the In nanocrystals overlaps with the high-energy side of the QD emission leading to clear modification of the QD emission spectrum.
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73.21.La Quantum dots
68.55.ag Semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.07.Ta Quantum dots
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

A direct transfer of layer-area graphene

William Regan, Nasim Alem, Benjamín Alemán, Baisong Geng, Çağlar Girit, Lorenzo Maserati, Feng Wang, Michael Crommie, and A. Zettl

Appl. Phys. Lett. 96, 113102 (2010); http://dx.doi.org/10.1063/1.3337091 (3 pages) | Cited 32 times

Online Publication Date: 15 March 2010

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A facile method is reported for the direct (polymer-free) transfer of layer-area graphene from metal growth substrates to selected target substrates. The direct route, by avoiding several wet chemical steps and accompanying mechanical stresses and contamination common to all presently reported layer-area graphene transfer methods, enables fabrication of layer-area graphene devices with unprecedented quality. To demonstrate, we directly transfer layer-area graphene from Cu growth substrates to holey amorphous carbon transmission electron microscopy (TEM) grids, resulting in robust, clean, full-coverage graphene grids ideal for high resolution TEM.
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81.05.ue Graphene
68.65.Pq Graphene films

The gain effect in a magnetic plasmon waveguide

Shuming Wang, Zhihong Zhu, Jingxiao Cao, Tao Li, Hui Liu, Shining Zhu, and Xiang Zhang

Appl. Phys. Lett. 96, 113103 (2010); http://dx.doi.org/10.1063/1.3365179 (3 pages) | Cited 4 times

Online Publication Date: 16 March 2010

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Show Abstract
Loss is a crucial problem in plasmonic integrated optical circuits and metamaterials. The Er, Yb codoped gain material is introduced into a magnetic plasmon waveguide composed of a chain of nanosandwiches in order to solve the loss problem in such subwavelength waveguide. The magnetic plasmon mode and a higher order mode are chosen as the signal and pump light to enhance the radiation and pump efficiencies. The signal light propagating in the waveguide is investigated with different Er3+ doping concentration and signal decay time. It is shown that the gain effect cannot only compensate the loss but also is able to amplify the signal, when exceeding certain threshold values of doping concentration and signal decay time.
Show PACS
42.82.Et Waveguides, couplers, and arrays
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
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