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12 Mar 2007

Volume 90, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 113108 (2007); http://dx.doi.org/10.1063/1.2714186 (3 pages)

Samuel L. Mensah, Vijaya K. Kayastha, Ilia N. Ivanov, David B. Geohegan, and Yoke Khin Yap
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Undoped high mobility two-dimensional hole-channel GaAs/AlxGa1−xAs heterostructure field-effect transistors with atomic-layer-deposited dielectric

T. M. Lu, D. R. Luhman, K. Lai, D. C. Tsui, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 90, 112113 (2007); http://dx.doi.org/10.1063/1.2714094 (3 pages) | Cited 3 times

Online Publication Date: 16 March 2007

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The authors have fabricated undoped p-channel GaAs/AlxGa1−xAs heterostructure field-effect transistors with nearly ideal drain current-voltage characteristics, using atomic-layer-deposited Al2O3 as the dielectric, and measured their transport properties. At 0.3 K, the densities and mobilities of the two dimensional holes can be tuned up to 2.9×1011/cm2 and 6.4×105 cm2/V s, respectively. The variable density high mobility two-dimensional hole system provides a large parameter space for the study of two-dimensional physics.
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85.30.Tv Field effect devices

Electromigration-induced Kirkendall voids at the Cu/Cu3Sn interface in flip-chip Cu/Sn/Cu joints

C. Y. Liu, J. T. Chen, Y. C. Chuang, Lin Ke, and S. J. Wang

Appl. Phys. Lett. 90, 112114 (2007); http://dx.doi.org/10.1063/1.2714100 (3 pages) | Cited 14 times

Online Publication Date: 16 March 2007

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Polarity void formation has been observed at the Cu3Sn/Cu interfaces in current-stressed Cu/Sn/Cu flip-chip joints. Electromigration voids were observed at the Cu3Sn/Cu anode interface, but no voids were found at the Cu3Sn/Cu cathode interface. The backstress in the anode’s Cu trace line caused a vacancy backflow toward the Cu3Sn/Cu anode interface, which led to serious void formation. In the opposite Cu3Sn/Cu cathode interface, Cu atoms in the cathode’s Cu trace line electromigrated toward the Cu3Sn/Cu cathode interface, which alleviated or healed possible Kirkendall void formation due to the normal annealing process.
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66.30.Qa Electromigration
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.72.Qq Microscopic defects (voids, inclusions, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation
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High quality Fe3−δO4/InAs hybrid structure for electrical spin injection

Marhoun Ferhat and Kanji Yoh

Appl. Phys. Lett. 90, 112501 (2007); http://dx.doi.org/10.1063/1.2713784 (3 pages) | Cited 15 times

Online Publication Date: 14 March 2007

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Single crystalline Fe3−δO4 (0 ⩽ δ ⩽ 0.33) films have been epitaxially grown on InAs (001) substrates by molecular beam epitaxy using O2 as source of active oxygen. Under optimum growth conditions, in situ real time reflection high-energy electron diffraction patterns, along with ex situ atomic force microscopy, indicate that (001) Fe3−δO4 can be grown under step-flow-growth mode with a characteristic (math×math)R45 surface reconstruction. X-ray photoelectron spectroscopy demonstrates the possibility of obtaining iron oxides with compositions ranging from Fe3O4 to γ-Fe2O3. Measurements with a superconducting quantum interference device magnetometer at 300 K show good magnetic properties, suggesting that iron-based oxides may be promising for spintronic applications.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth
79.60.Dp Adsorbed layers and thin films
75.47.Pq Other materials

Exchange bias effect and enhanced magnetoresistance in La0.67Sr0.33MnO3/SrTiO3 superlattices

S. J. Zhu, J. Yuan, B. Y. Zhu, F. C. Zhang, B. Xu, L. X. Cao, X. G. Qiu, B. R. Zhao, and P. X. Zhang

Appl. Phys. Lett. 90, 112502 (2007); http://dx.doi.org/10.1063/1.2713175 (3 pages) | Cited 6 times

Online Publication Date: 15 March 2007

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The magnetization and electrical transport in the superlattices consisting of ferromagnetic La0.67Sr0.33MnO3 and nonmagnetic insulating SrTiO3 layers have been investigated. A significant displacement of the hysteresis loop along the field axis is observed when the sample is field-cooled through the blocking temperature TB. The strength of displacement, termed as exchange field HE, is found to exponentially decay with temperature. The magnetoresistance in field-cooling process is obviously enhanced compared to that in zero-field-cooling process. The existence of the disordered spin state at the interface is suggested to be the origin of such phenomena.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
73.40.-c Electronic transport in interface structures
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Magneto-optical and magnetotransport properties of heavily Mn-doped GaMnAs

Shinobu Ohya, Kenichi Ohno, and Masaaki Tanaka

Appl. Phys. Lett. 90, 112503 (2007); http://dx.doi.org/10.1063/1.2713176 (3 pages) | Cited 23 times

Online Publication Date: 15 March 2007

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The authors have studied the magneto-optical and magnetotrasnport properties of Ga1−xMnxAs thin films with high Mn concentrations (x = 12.2%–21.3%) grown by molecular-beam epitaxy. These heavily Mn-doped GaMnAs films were formed by decreasing the growth temperature to as low as 150–190 °C and by reducing the film thickness to 10 nm in order to prevent precipitation of hexagonal MnAs clusters. Magnetic circular dichroism and anomalous Hall effect measurements indicate that these GaMnAs films have the nature of intrinsic ferromagnetic semiconductors with high ferromagnetic transition temperature up to 170 K.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
73.61.Ey III-V semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Spin-transfer-induced magnetization switching in tunnel junctions with nanocurrent channels

Yisong Zhang, Zongzhi Zhang, Yaowen Liu, B. Ma, and Q. Y. Jin

Appl. Phys. Lett. 90, 112504 (2007); http://dx.doi.org/10.1063/1.2713143 (3 pages) | Cited 8 times

Online Publication Date: 16 March 2007

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Spin-transfer-induced magnetization switching processes are evidenced by the “snapshots” of magnetic configurations for junctions containing nanocurrent channels (NCCs). The switching behaviors are found to be closely related to the NCC size and its actual location. Both the switching time t and critical current density Jc decrease with the increase of NCC size. Faster switching and lower Jc are observed for NCC located in the center. This work suggests a reasonable design frame to efficiently manipulate the Jc reduction and fast switching in practical spin-transfer-switched devices.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
85.35.-p Nanoelectronic devices
85.70.-w Magnetic devices

Channel width effect on the spin-orbit interaction parameter in a two-dimensional electron gas

Jae Hyun Kwon, Hyun Cheol Koo, Joonyeon Chang, Suk-Hee Han, and Jonghwa Eom

Appl. Phys. Lett. 90, 112505 (2007); http://dx.doi.org/10.1063/1.2714993 (3 pages) | Cited 19 times

Online Publication Date: 16 March 2007

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The spin splitting energy obtained from the Shubnikov–de Haas oscillation increases with decreasing channel width (w) of the InAs-based heterostructure. Since the surface charge concentration depends only weakly on w, the channel width dependence of the spin splitting energy is attributed to variations in the spin-orbit interaction strength. The spin-orbit interaction parameter was found to be inversely proportional to math in the range of w = 2–64 μm. Our findings indicate that a strong spin-orbit interaction is induced in a narrow channel due to suppression of the spin precession length for a thin quantum well layer system.
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73.21.Fg Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.63.Hs Quantum wells
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.My Galvanomagnetic and other magnetotransport effects
85.75.Hh Spin polarized field effect transistors

FeCoSiN film with ordered FeCo nanoparticles embedded in a Si-rich matrix

Yan Liu, C. Y. Tan, Z. W. Liu, and C. K. Ong

Appl. Phys. Lett. 90, 112506 (2007); http://dx.doi.org/10.1063/1.2714280 (3 pages) | Cited 16 times

Online Publication Date: 16 March 2007

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FeCoSiN film consisting of ordered arrays of FeCo nanoparticles embedded in a Si-rich matrix was fabricated on silicon substrate by reactive rf magnetron sputtering. These nanoparticles have a face-centered cubic structure and a mean diameter of ∼ 7 nm. The FeCoSiN film has a very high resistivity of up to 1000 μΩ cm due to the breakup of the metal continuum into isolated metal nanoparticles. The static and dynamic magnetic properties of the film were also investigated. A saturation magnetization of 1.0 T, coercivity of less than 5 Oe in both easy and hard axes, and anisotropy field of 27 Oe were obtained. The microwave permeability measurement showed a permeability of around 400 at low frequency and a ferromagnetic resonance frequency of about 1.1 GHz.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
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Dielectric response of Sr doped CaCu3Ti4O12 ceramics

Wei Li, Robert W. Schwartz, Aiping Chen, and Jinsong Zhu

Appl. Phys. Lett. 90, 112901 (2007); http://dx.doi.org/10.1063/1.2713167 (3 pages) | Cited 15 times

Online Publication Date: 12 March 2007

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Ca1−xSrxCu3Ti4O12 (x = 0, 0.1, and 0.2) ceramics were fabricated and their dielectric properties were investigated. It was found that the dielectric constant significantly decreased with the increase of Sr content at low temperature region (<250 K) and remained almost unchanged at high temperature region (>250 K). Three sets of relaxation peaks were observed in electric modulus plots, which were considered to be associated with grains, domain boundaries, and grain boundaries, respectively. Through the analysis of the heights and calculated activation energies of the relaxation peaks, it is strongly believed that the suppressed dielectric constant is related to the change of domain boundaries with Sr doping.
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77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
61.72.Mm Grain and twin boundaries
61.72.up Other materials

Aging-induced dielectric relaxation in barium titanate ceramics

Mohamad M. Ahmad, Koji Yamada, Paul Meuffels, and Rainer Waser

Appl. Phys. Lett. 90, 112902 (2007); http://dx.doi.org/10.1063/1.2713178 (3 pages) | Cited 16 times

Online Publication Date: 12 March 2007

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In this letter the authors report on the aging effect on the phase transitions and dielectric properties of 1 mol % Mn-doped BaTiO3 ceramics. Aging the ceramics in the ferroelectric state stimulates a resistance for the orthorhombic-tetragonal and tetragonal-cubic phase transitions, which leads to stabilization of the tetragonal phase over a wider temperature range. The dielectric constant of the aged sample shows dispersion, associated with a dielectric loss relaxation peak near the 100 kHz frequency region, in contrast to the unaged one. The present results are discussed in light of the existing models for ferroelectric domain stabilization.
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77.22.Gm Dielectric loss and relaxation
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

Mechanism of leakage current reduction of tantalum oxide capacitors by titanium doping

W. S. Lau, T. S. Tan, Premila Babu, and Nathan P. Sandler

Appl. Phys. Lett. 90, 112903 (2007); http://dx.doi.org/10.1063/1.2710000 (3 pages) | Cited 15 times

Online Publication Date: 13 March 2007

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In this letter, the authors will point out that defect states related to oxygen vacancies in tantalum oxide capacitors can be suppressed by titanium doping, resulting in significant leakage current reduction. The theory is that titanium forms an acceptor which can move at high temperature and neutralize other donors. However, defect states which cannot be suppressed by titanium doping were detected. These are explained by H2O-related contamination occurring at low temperature (<400 °C) during the cooling down period.
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84.32.Tt Capacitors
85.40.Ry Impurity doping, diffusion and ion implantation technology

Correlation between the dynamics of polar nanoregions and temperature evolution of central peaks in Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 ferroelectric relaxors

Jae-Hyeon Ko, Do Han Kim, and Seiji Kojima

Appl. Phys. Lett. 90, 112904 (2007); http://dx.doi.org/10.1063/1.2713170 (3 pages) | Cited 17 times

Online Publication Date: 13 March 2007

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Acoustic properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 have been investigated in a wide temperature range. The sound velocity of acoustic phonons showed a deviation from its high-temperature linear behavior at the Burns temperature TB ∼ 730 K. Upon cooling, acoustic properties exhibited significant changes at about 550 K in polarization state and width of the central peak in addition to changes in frequency and damping of acoustic phonons. This finding suggests that, besides TB, another intermediate characteristic temperature exists in the evolution of relaxor dynamics, which might be related to the formation of long-lived polar nanoregions and associated local strain fields.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Relaxor behavior in the solid solution between dielectric Ba(Mg1/3Nb2/3)O3 and ferroelectric PbTiO3

Xifa Long and Zuo-Guang Ye

Appl. Phys. Lett. 90, 112905 (2007); http://dx.doi.org/10.1063/1.2713236 (3 pages) | Cited 16 times

Online Publication Date: 13 March 2007

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Relaxor behavior has been found in the solid solution between complex perovskite Ba(Mg1/3Nb2/3)O3 (BMN) and ferroelectric PbTiO3 (PT), 0.4BMN-0.6PT, prepared by solid state reactions. A strong dispersion of the maximum dielectric permittivity (ε′) appears around the temperature of Tm, which shifts towards higher temperatures with increasing frequency. The variation of Tm with frequency follows the Vogel-Fulcher relationship. The variation of 1/ε′ with temperature above Tm deviates from the Curie-Weiss law but satisfies a Lorentz-type function. The dielectric hysteresis loops are displayed at several temperatures which become slimmer at T>Tm. The remnant polarization gradually decreases with increasing temperature and persists up to above Tm.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization

Temperature scaling of dynamic hysteresis in soft lead zirconate titanate bulk ceramic

R. Yimnirun, R. Wongmaneerung, S. Wongsaenmai, A. Ngamjarurojana, S. Ananta, and Y. Laosiritaworn

Appl. Phys. Lett. 90, 112906 (2007); http://dx.doi.org/10.1063/1.2713336 (3 pages) | Cited 27 times

Online Publication Date: 13 March 2007

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The temperature scaling of the dynamic hysteresis was investigated in soft ferroelectric bulk ceramic. The power-law temperature scaling relations were obtained for hystersis area 〈A〉 and remnant polarization Pr, while the coercivity EC was found to scale linearly with temperature T. The three temperature scaling relations were also field dependent. At fixed field amplitude E0, the scaling relations take the forms of 〈A〉∝T−1.1024, Pr∝T−1.2322, and (EC0−EC)∝T. Furthermore, the product of Pr and EC also provides the same scaling law on the T dependence in comparison with 〈A〉.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Characteristics of (Pb,Sr)TiO3/ZrO2 structures on Si and SiON/Si substrates

Hung-Yao Chen, Jenn-Ming Wu, Hsin-Erh Huang, and Hui-Yun Bor

Appl. Phys. Lett. 90, 112907 (2007); http://dx.doi.org/10.1063/1.2712807 (3 pages) | Cited 12 times

Online Publication Date: 14 March 2007

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The ferroelectric (Pb,Sr)TiO3 (PST) thin film with ZrO2 insulating buffer on Si and SiON(3 nm)/Si substrates was fabricated by rf magnetron sputtering. ZrO2 demonstrates excellent insulating properties on either Si or SiON/Si substrates. The metal-ferroelectric-insulator-semiconductor structure shows low leakage currents and exhibits clockwise capacitance-voltage hysteresis loops which are due to the ferroelectric polarization of the PST films. The maximum memory windows of the hysteresis loops are 0.8 and 1.37 V, respectively for PST/ZrO2 films on Si and SiON/Si substrates. This is of potential as memory devices. The charge injection effect under large sweeping voltages is discussed.
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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
77.22.Ej Polarization and depolarization
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Dynamic hysteresis and scaling behavior of hard lead zirconate titanate bulk ceramics

R. Yimnirun, R. Wongmaneerung, S. Wongsaenmai, A. Ngamjarurojana, S. Ananta, and Y. Laosiritaworn

Appl. Phys. Lett. 90, 112908 (2007); http://dx.doi.org/10.1063/1.2713769 (3 pages) | Cited 24 times

Online Publication Date: 14 March 2007

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The scaling relation of ferroelectric hysteresis area 〈A〉 against frequency f and field amplitude E0 for the saturated loops of the hard lead zirconate titanate bulk ceramic takes the form of 〈A〉∝f−0.28E00.89, while that for the minor loops takes the form of 〈A〉∝f−0.43E03.19. In both cases, the scaling relations are similar to those of its soft counterpart. This indicates that the dynamic behaviors and scaling relations in bulk ceramics are mainly governed by the domain states and structures, while the distinct types of complex defects contribute mainly to the difference in the coercive field observed in hard and soft ceramics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis

High pressure bulk synthesis and characterization of the predicted multiferroic Bi(Fe1/2Cr1/2)O3

Matthew R. Suchomel, Chris I. Thomas, Mathieu Allix, Matthew J. Rosseinsky, Andrew M. Fogg, and Michael F. Thomas

Appl. Phys. Lett. 90, 112909 (2007); http://dx.doi.org/10.1063/1.2713757 (3 pages) | Cited 26 times

Online Publication Date: 15 March 2007

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Bi(Fe1/2Cr1/2)O3, a recently proposed candidate multiferroic perovskite, is prepared in a bulk form by high pressure solid-state synthesis. The material is isostructural with polar BiFeO3 but is paramagnetic at room temperature due to disorder of the Fe3+ and Cr3+ cations on the B site. Mössbauer and magnetization measurements show a transition to a cooperative magnetic state below 130 K.
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75.20.Ck Nonmetals
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Dependence of breakdown field on dielectric (interelectrode) thickness in base-metal electroded multilayer capacitors

Alexander D. Milliken, Andrew J. Bell, and James F. Scott

Appl. Phys. Lett. 90, 112910 (2007); http://dx.doi.org/10.1063/1.2713780 (3 pages) | Cited 8 times

Online Publication Date: 15 March 2007

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The authors have empirically determined the dependence of breakdown field EB versus dielectric thickness d (electrode separation) for a large number (4100) of BaTiO3-based multilayer capacitors with Ni base-metal electrodes. The data averaged over lateral area show for 6<d<22 μm that EB = const×d−n, where n = 0.50±0.06, a result compatible with macroscopic “thermal” dc breakdown mechanisms. More precisely, however, the results nearly perfectly fit a situation of breakdown occurring in connected defects from collision ionization resulting from field emission from the cathode.
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84.32.Tt Capacitors

Fluorine incorporation at HfO2/SiO2 interfaces in high-k metal-oxide-semiconductor gate stacks: Local electronic structure

Jeong-Hee Ha, Kang-ill Seo, Paul C. McIntyre, Krishna C. Sarawat, and Kyeongjae Cho

Appl. Phys. Lett. 90, 112911 (2007); http://dx.doi.org/10.1063/1.2712785 (3 pages) | Cited 12 times

Online Publication Date: 16 March 2007

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Effects of fluorine incorporation on the electrical properties of HfO2/SiO2 dielectric stacks are investigated through both ab initio simulations and electrical measurements. The results show that F ions are able to remove midgap states resulting from undercoordinated Hf ions at the HfO2/SiO2 interface. They also indicate that F incorporation increases the leakage current if an excessive amount of F ions are present in the dielectric, beyond that required to passivate the undercoordinated interfacial Hf ions. A possible way to maximize the benefits of F incorporation for high-k gate stack electrical characteristics is discussed.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states

Electrical properties of germanium/metal-oxide gate stacks with atomic layer deposition grown hafnium-dioxide and plasma-synthesized interface layers

Takuya Sugawara, Yasuhiro Oshima, Raghavasimhan Sreenivasan, and Paul C. McIntyre

Appl. Phys. Lett. 90, 112912 (2007); http://dx.doi.org/10.1063/1.2472197 (3 pages) | Cited 26 times

Online Publication Date: 16 March 2007

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The electrical properties of metal-oxide-semiconductor (MOS) capacitors composed of atomic-layer-deposited (ALD) hafnium-dioxide (HfO2) dielectrics and plasma-synthesized interface layers were investigated. MOS capacitor with oxynitride interface layer shows negative flatband voltage (Vfb) shift from the ideal value. Hafnium-alkylamide ALD process performed on a plasma nitrided silicon surface causes negative Vfb shift. Germanium MOS capacitors show additional negative Vfb shift (−0.5 V). X-ray photoelectron spectroscopy shows evidence of germanium diffusion into the HfO2 layer. Germanium MOS capacitor with tantalum-oxynitride (TaON) interface layer shows superior electrical properties. These results indicate that the selection of the interface layer strongly influences germanium MOS capacitor electrical properties.
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84.32.Tt Capacitors
85.30.Tv Field effect devices

Fabrication and material properties of submicrometer SrTiO3 films exfoliated using crystal ion slicing

Ryan M. Roth, Djordje Djukic, Yoo Seung Lee, Richard M. Osgood, Jr., Penelope A. Lewis, Sasha Bakhru, and Hassaram Bakhru

Appl. Phys. Lett. 90, 112913 (2007); http://dx.doi.org/10.1063/1.2711655 (3 pages) | Cited 3 times

Online Publication Date: 16 March 2007

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The crystal quality of submicrometer-thick SrTiO3 films that are formed by exfoliation from bulk crystals using deep implantation with H-ion beams is investigated. Nuclear reaction analysis and Rutherford backscattering/channeling are used to measure the implantation depth, crystal-lattice disruption, and surface damage prior to exfoliation. The surface profiles of the exfoliated films are examined with atomic force microscopy; the roughness is shown to be reducible to subnanometer levels with postexfoliation mechanical polishing.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.80.Jh Ion radiation effects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
77.55.-g Dielectric thin films

Probing intrinsic polarization properties in bismuth-layered ferroelectric films

Takayuki Watanabe, Hiroshi Funakubo, Minoru Osada, Hiroshi Uchida, Isao Okada, Brian J. Rodriguez, and Alexei Gruverman

Appl. Phys. Lett. 90, 112914 (2007); http://dx.doi.org/10.1063/1.2713858 (3 pages) | Cited 7 times

Online Publication Date: 16 March 2007

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The authors report on an approach to establish intrinsic polarization properties in bismuth-layered ferroelectric films by piezoelectric coefficient and soft-mode spectroscopy, as well as by a direct polarization–electric field hysteresis. In epitaxially grown (Bi4−xNdx)Ti3O12 (0 ⩽ x ⩽ 0.73) films, they show that these complementary characterizations can phenomenologically and thermodynamically represent the intrinsic polarization states in (Bi4−xNdx)Ti3O12 films, and the intrinsic Ps of 67 μC/cm2 is estimated for pure Bi4Ti3O12, superior to 50 μC/cm2 in bulk single crystal. Their results provide a pathway to draw full potential in ferroelectric thin films.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.65.Bn Piezoelectric and electrostrictive constants
77.80.Dj Domain structure; hysteresis
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Finite size effect in ZnO nanowires

Pai-Chun Chang, Chung-Jen Chien, Daniel Stichtenoth, Carsten Ronning, and Jia Grace Lu

Appl. Phys. Lett. 90, 113101 (2007); http://dx.doi.org/10.1063/1.2712507 (3 pages) | Cited 53 times

Online Publication Date: 12 March 2007

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To clarify the size effect in semiconductor nanowires with decreasing diameters but not yet reaching the quantum confinement region, single crystalline zinc oxide nanowires with diameters around 10 nm are synthesized. Electrical transport measurements of these thin nanowires show significant increase in conductivity accompanied by diminished gate modulation and reduced mobility. This phenomenon is a result of the enrichment of surface states owing to the increased surface-to-volume ratio. The enhanced surface effect is confirmed by the temperature dependent photoluminescence measurements and contributes to the “anomalous” blueshift. This study shows that surface states play a dominant role in the electrical and optical properties of quasi-one-dimensional materials.
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73.63.Nm Quantum wires
78.67.Lt Quantum wires
72.20.Fr Low-field transport and mobility; piezoresistance
78.55.Et II-VI semiconductors

Nanoelectromechanical switches based on carbon nanotubes for microwave and millimeter waves

M. Dragoman, A. Takacs, A. A. Muller, H. Hartnagel, R. Plana, K. Grenier, and D. Dubuc

Appl. Phys. Lett. 90, 113102 (2007); http://dx.doi.org/10.1063/1.2712774 (3 pages) | Cited 7 times

Online Publication Date: 12 March 2007

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In this letter the authors analyze two configurations of nanoelectromechanical switches, which are working in the microwave and millimeter wave frequency ranges. Metallic nanotubes vertically or horizontally positioned on a propagating high frequency planar waveguide disable or enable the electromagnetic field propagation, whether they are actuated or not by a dc electric field of a few volts. Although the dimensions of metallic nanotubes are very small in comparison with the planar waveguide dimensions and the operating wavelengths, these switches are very efficient and agile.
Show PACS
84.40.Az Waveguides, transmission lines, striplines
84.32.Dd Connectors, relays, and switches
81.07.De Nanotubes
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.35.Kt Nanotube devices

Tuning InAs quantum dots for high areal density and wideband emission

C. Y. Ngo, S. F. Yoon, W. J. Fan, and S. J. Chua

Appl. Phys. Lett. 90, 113103 (2007); http://dx.doi.org/10.1063/1.2713148 (3 pages) | Cited 16 times

Online Publication Date: 12 March 2007

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The authors report the effect of growth temperature and monolayer coverage on areal density and photoluminescence spectral width of InAs quantum dot (QD). Areal density and spectral width were found to be strongly dependent on growth temperature and monolayer coverage, respectively. Upon proper tuning, both high areal density and large photoluminescence spectral width were obtained. Areal density of 1.5×1011 cm−2 is four times higher than those previously reported, while spectral width of 136 nm is the broadest spectral width obtained without any forms of band gap engineering. These results will contribute to an improvement in the performance of QD superluminescent diode.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
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