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26 Feb 2007

Volume 90, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 093127 (2007); http://dx.doi.org/10.1063/1.2710743 (3 pages)

Y. Q. Li, J. X. Tang, H. Wang, J. A. Zapien, Y. Y. Shan, and S. T. Lee
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Experimental observation of oxygen-related defect state in pentacene thin films

V. Nádaždy, R. Durný, J. Puigdollers, C. Voz, S. Cheylan, and K. Gmucová

Appl. Phys. Lett. 90, 092112 (2007); http://dx.doi.org/10.1063/1.2710203 (3 pages) | Cited 23 times

Online Publication Date: 28 February 2007

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The authors report on a metastable defect observed in pentacene thin films. The defect, which is characterized by a hole trap at Ev+0.6 eV and attempt-to-escape frequency of 5×1012 s−1, can be reversibly created/removed under a negative/positive bias voltage applied to the aluminum/pentacene Schottky diode at room temperature in air. Annealing the sample in vacuum at 360 K removes the defect and prevents its creation by application of any bias voltage in vacuum. Considering recent calculations of defects in pentacene the authors assume that the defect is formed by replacing one of the hydrogen atoms by an oxygen atom (C22H13O).
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71.55.Ht Other nonmetals
73.61.Ph Polymers; organic compounds
73.40.Ns Metal-nonmetal contacts
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes

Fabrication of n-type nanotube transistors with large-work-function electrodes

Sunkyung Moon, Soon-Gul Lee, Woon Song, Joon Sung Lee, Nam Kim, Jinhee Kim, and Noejung Park

Appl. Phys. Lett. 90, 092113 (2007); http://dx.doi.org/10.1063/1.2709934 (3 pages) | Cited 7 times

Online Publication Date: 28 February 2007

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The authors found experimentally that carbon nanotube field-effect transistors (CNFETs) could exhibit n-type characteristics even though their electrodes consist of a large-work-function metal such as Co. To explain their result, which is contrary to the general belief that CNFETs with large-work-function electrodes always lead to p-type characteristics, ab initio electronic structure calculation for the metal-carbon nanotube junction was performed, which showed that the Fermi level alignment at the junction could sensitively depend on microscopic structures of the metal-carbon nanotube junction. This suggests that deposition method of electrodes as well as the metal type could be utilized to obtain n-type CNFETs.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Modification of transparent and conducting single wall carbon nanotube thin films via bromine functionalization

Giovanni Fanchini, Husnu Emrah Unalan, and Manish Chhowalla

Appl. Phys. Lett. 90, 092114 (2007); http://dx.doi.org/10.1063/1.2709903 (3 pages) | Cited 14 times

Online Publication Date: 1 March 2007

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The results of bromine doping of transparent and conducting single wall carbon nanotube (SWNT) thin films are described. Br profoundly effects the density of states (DOS) of SWNTs which leads to dramatic improvement in the electrical properties. The authors show that the role of the Br is not only in shifting the Fermi level but also in forming acceptor sites in metallic SWNTs. These modifications of the DOS through bromination lead to simultaneous increase in both the on/off ratio and mobility of thin film transistors. Furthermore, the transistor characteristics of Br-functionalized SWNTs are similar in air, inert atmosphere, and vacuum.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
61.72.up Other materials

Effects of nitrogen incorporation in InSb1−xNx grown using radio frequency plasma-assisted molecular beam epitaxy

H. T. Pham, S. F. Yoon, K. H. Tan, and D. Boning

Appl. Phys. Lett. 90, 092115 (2007); http://dx.doi.org/10.1063/1.2710751 (3 pages) | Cited 10 times

Online Publication Date: 1 March 2007

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InSb1−xNx was grown by radio frequency plasma-assisted molecular beam epitaxy. The effect of nitrogen plasma power (200–500 W) and growth temperature (330–420 °C) on nitrogen incorporation was investigated. A combined analysis involving x-ray diffraction, x-ray photoelectron spectroscopy, and secondary ion mass spectroscopy measurements indicates that the dominant nitrogen defect is interstitial N–Sb. Increasing the plasma power resulted in increase in the interstitial N–Sb amount rather than the substitutional NSb amount. For fixed plasma power, decreasing the growth temperature helped reduce the interstitial N–Sb defect. Under the experimental conditions, the average value of substitutional N is approximately 1.6%–2%.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.60.Dp Adsorbed layers and thin films
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Incorporation and drift of hydrogen at low temperatures in ZnO

Y. L. Wang, F. Ren, H. S. Kim, S. J. Pearton, and D. P. Norton

Appl. Phys. Lett. 90, 092116 (2007); http://dx.doi.org/10.1063/1.2711201 (3 pages) | Cited 5 times

Online Publication Date: 1 March 2007

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Hydrogen is found to diffuse rapidly into ZnO from either a molecular (D2) gas source or from a D2 plasma at temperatures in the range of 100–200 °C. In samples deuterated from a plasma excited at 13.56 MHz, the incorporated deuterium concentration is saturated at 6×1018 cm−3 throughout the entire 1.2 μm epi-ZnO thickness at 250 °C. This deuterium is stable against reverse bias application at 25 °C for 24 h. By sharp contrast, deuterium incorporated from exposure to D2 gas at 100 °C can be entirely removed by reverse (negative) bias application in a diode structure using a Pt contact on the n-type ZnO. These results are consistent with the state of the deuterium in the ZnO being a function of both the concentration and the flux during incorporation. At low concentrations, the deuterium is likely to be in a positively charged atomic form or bound in defects that are readily dissociated by an electric field, while at higher concentrations the deuterium may be in neutral states such as D2 or OH complexes.
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61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
73.40.Ns Metal-nonmetal contacts

Photovoltaic properties and exciplex emission of polyphenylenevinylene-based blend solar cells

Chunhong Yin, Thomas Kietzke, Dieter Neher, and Hans-Heinrich Hörhold

Appl. Phys. Lett. 90, 092117 (2007); http://dx.doi.org/10.1063/1.2710474 (3 pages) | Cited 38 times

Online Publication Date: 2 March 2007

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By studying the photoluminescence emission and photovoltaic properties of blends of polyphenylenevinylene (PPV)-based electron donating and accepting polymers, the authors observed a strict anticorrelation between relative exciplex emission in the solid state and photovoltaic efficiency of corresponding blend devices. Comparative studies on defined bilayer geometries showed that the overall shape of the current-voltage characteristics under illumination is independent of device geometry and layer thickness. Consequently, they conclude that the photocurrent in PPV-based blends is mainly determined by the efficiency to form free carriers rather than by free carrier recombination.
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84.60.Jt Photoelectric conversion
78.66.Qn Polymers; organic compounds

Mn-doped AlN nanowires with room temperature ferromagnetic ordering

Y. Yang, Q. Zhao, X. Z. Zhang, Z. G. Liu, C. X. Zou, B. Shen, and D. P. Yu

Appl. Phys. Lett. 90, 092118 (2007); http://dx.doi.org/10.1063/1.2475276 (3 pages) | Cited 12 times

Online Publication Date: 2 March 2007

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Mn-doped AlN nanowires were synthesized by in situ doping of Mn using a chemical vapor deposition method. Analyses of microstructure and chemical compositions indicate that the as-prepared samples were homogenously Mn-doped AlN nanowires. The low temperature photoluminescence, and magnetization as a function applied magnetic field of the Mn-doped AlN nanowires were investigated. A Curie temperature higher than 300 K was observed from the as-doped nanowires. The room temperature ferromagnetic properties of the synthesized Mn-doped AlN nanowires make it an excellent candidate for applications in future spintronic nanodevices.
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68.65.La Quantum wires (patterned in quantum wells)
75.50.Dd Nonmetallic ferromagnetic materials
75.75.-c Magnetic properties of nanostructures
61.72.uj III-V and II-VI semiconductors
78.67.Lt Quantum wires
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Temperature behavior of inhomogeneous Pt/GaN Schottky contacts

Ferdinando Iucolano, Fabrizio Roccaforte, Filippo Giannazzo, and Vito Raineri

Appl. Phys. Lett. 90, 092119 (2007); http://dx.doi.org/10.1063/1.2710770 (3 pages) | Cited 18 times

Online Publication Date: 2 March 2007

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In this letter, a correlation between the nanoscale localized electrical properties of the Pt/GaN Schottky barrier and the temperature behavior of macroscopic Schottky diodes is demonstrated. Although a significant improvement of the ideality factor of the diodes is achieved after annealing at 400 °C, local current-voltage measurements, performed with a biased tip of a conductive atomic force microscope, revealed the inhomogeneous nature of the barrier. Its nanoscale degree of homogeneity was quantitatively described by means of Tung’s model [Phys. Rev. B 45, 13509 (1992) ], allowing the authors to explain the temperature dependence of the electrical characteristics of the macroscopic diodes.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
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Aqueous microdrop manipulation and mixing using ferrofluid dynamics

Woo-Bin Song, Zhenwen Ding, Chulwoo Son, and Babak Ziaie

Appl. Phys. Lett. 90, 092501 (2007); http://dx.doi.org/10.1063/1.2709514 (3 pages) | Cited 9 times

Online Publication Date: 26 February 2007

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In this letter, the authors present a simple method to manipulate free microdroplets using ferrofluid dynamics. For droplet transport, a set of periodic lines of ferrofluid on top of a silicon wafer is created by a single strip magnet and dynamically changed by the rotation of a magnetic stirrer underneath it. It is demonstrated that the speed of droplet movement depends on the rotation speed of the magnetic stirrer as well as the size of the droplet. For better droplet mixing efficiency, a discontinuous pattern at the mixing spots is created by adding a smaller strip magnet to the above setup.
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47.65.Cb Magnetic fluids and ferrofluids
47.55.D- Drops and bubbles
47.51.+a Mixing
47.54.De Experimental aspects
47.61.Jd Multiphase flows
47.85.Np Fluidics

Magnetic characterization of CoFeB/MgO and CoFe/MgO interfaces

Ezana Negusse, A. Lussier, J. Dvorak, Y. U. Idzerda, S. R. Shinde, Y. Nagamine, S. Furukawa, K. Tsunekawa, and D. D. Djayaprawira

Appl. Phys. Lett. 90, 092502 (2007); http://dx.doi.org/10.1063/1.2709619 (3 pages) | Cited 8 times

Online Publication Date: 26 February 2007

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The use of CoFeB ferromagnetic electrodes in place of CoFe has been shown to significantly increase the tunneling magnetoresistance (TMR) of MgO based magnetic tunnel junctions (MTJs). By using soft x-ray scattering techniques, we show that the behavior of the magnetic moments located at the CoFe–MgO interface are drastically different from the rest of the CoFe film, whereas the magnetic response of the CoFeB–MgO interfacial moments is coherent with the film’s bulk. Our results support the view that the high TMR values observed in MgO based MTJs with CoFeB electrodes are due to the uniform magnetic response of the entire CoFeB electrode including the MgO interfacial moments.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Bb Fe and its alloys
78.70.Ck X-ray scattering

Collective spin modes in monodimensional magnonic crystals consisting of dipolarly coupled nanowires

G. Gubbiotti, S. Tacchi, G. Carlotti, N. Singh, S. Goolaup, A. O. Adeyeye, and M. Kostylev

Appl. Phys. Lett. 90, 092503 (2007); http://dx.doi.org/10.1063/1.2709909 (3 pages) | Cited 42 times

Online Publication Date: 26 February 2007

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Magnetization dynamics of dipolarly coupled nanowire arrays has been studied by Brillouin light scattering. Measurements performed in uniformly magnetized wires as a function of the transferred wave vector demonstrated the existence of several discrete collective modes, propagating through the structure with a periodic dispersion curve encompassing several Brillouin zones relative to the artificial spatial periodicity. This experimental evidence has been quantitatively explained by a theoretical model which permits the calculation of the dispersion relation for collective modes in patterned arrays through the numerical solution of an eigenvalue problem for an integral operator.
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75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Thermal effects on the critical current of spin torque switching in spin valve nanopillars

M. L. Schneider, M. R. Pufall, W. H. Rippard, S. E. Russek, and J. A. Katine

Appl. Phys. Lett. 90, 092504 (2007); http://dx.doi.org/10.1063/1.2709963 (3 pages) | Cited 11 times

Online Publication Date: 28 February 2007

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In spin valve nanopillars, temperature affects the spin torque reversal of the free magnetic layer. The authors compare values of zero temperature critical switching current Ic0 extrapolated from room temperature pulsed current switching measurements to those of quasistatic current sweeps at 5 K. The values extrapolated from the room temperature pulsed switching probability measurements are always less than or equal to those of the low temperature quasistatic measurements. Further, the room temperature device-to-device variations of the critical switching current are drastically reduced at low temperature, where the Ic0 agrees with theory. Finally, the authors find that Ic0 scales with the free layer volume, as expected.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials

Current-induced vortex-vortex switching in a nanopillar comprising two Co nano-rings

T. Yang, A. Hirohata, M. Hara, T. Kimura, and Y. Otani

Appl. Phys. Lett. 90, 092505 (2007); http://dx.doi.org/10.1063/1.2710185 (3 pages) | Cited 13 times

Online Publication Date: 28 February 2007

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The authors fabricated a current-perpendicular-to-plane pseudo-spin-valve nanopillar comprising a thick and a thin Co rings with deep submicron lateral sizes. The dc current can effectively induce the flux-closure vortex states in the rings with desired chiralities. Abrupt transitions between the vortex states are also realized by the dc current and detected with the giant magnetoresistance effect. Both Oersted field and spin-transfer torque are found important to the magnetic transitions, but the former is dominant. They can be designed to cooperate with each other in the vortex-to-vortex transitions by carefully setting the chirality of the vortex state in the thick Co ring.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.De Giant magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Reduction of ac transport and magnetization loss of a high-Tc superconducting tape by placing soft ferromagnetic materials at the edges

F. Gömöry, J. Šouc, M. Vojenčiak, A. K. M. Alamgir, Z. Han, and Ch. Gu

Appl. Phys. Lett. 90, 092506 (2007); http://dx.doi.org/10.1063/1.2710753 (3 pages) | Cited 10 times

Online Publication Date: 1 March 2007

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Reduction of dissipation at the transport of alternating current as well as when exposed to a time varying magnetic field has been observed in the tape from high-temperature superconductor Bi2Sr2Ca2Cu3O10 covered by a Ni sheath at the edges. The improvement of critical current can explain this achievement only in part. Analysis of experimental data shows that also a more favorable pattern of the magnetic flux penetration should take place.
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74.72.-h Cuprate superconductors
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties
74.25.Sv Critical currents
84.71.Mn Superconducting wires, fibers, and tapes

Magnetic properties and tunneling magnetoresistance effect in Fe–CdFeS granular films

K. W. Liu, J. Y. Zhang, D. Z. Shen, X. J. Wu, B. H. Li, B. S. Li, Y. M. Lu, and X. W Fan

Appl. Phys. Lett. 90, 092507 (2007); http://dx.doi.org/10.1063/1.2709892 (3 pages) | Cited 9 times

Online Publication Date: 2 March 2007

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Granular thin film samples composed of Fe clusters embedded in CdFeS were prepared with using low pressure metal organic chemical vapor deposition. Temperature dependence of the resistivity of the granular film follows well the relationship for the tunneling transport between the iron granules. A large negative magnetoresistance of about 2.2% at 0.1 T was observed at room temperature due to the presence of Fe clusters. The hysteresis behavior observed in the magnetoresistance corresponded exactly to those of the hysteresis loop in the magnetization measurement, which evidently showed the correlation between the magnetoresistance and global magnetization in the sample.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.50.Pp Magnetic semiconductors

Quantitative investigation of a terahertz artificial magnetic resonance using oblique angle spectroscopy

T. Driscoll, G. O. Andreev, D. N. Basov, S. Palit, Tong Ren, Jack Mock, Sang-Yeon Cho, Nan Marie Jokerst, and D. R. Smith

Appl. Phys. Lett. 90, 092508 (2007); http://dx.doi.org/10.1063/1.2679766 (3 pages) | Cited 13 times

Online Publication Date: 2 March 2007

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The authors present a spectroscopic analysis of a planar split-ring-resonator (SRR) medium at terahertz frequencies, quantitatively characterizing the associated magnetic resonance. Experimental quantification at terahertz and infrared frequencies of metamaterial optical constants has been primarily absent, largely due to the difficulty of collecting phase information at these frequencies. In this letter, the authors circumvent the need for phase information in the characterization by acquiring the power transmitted through the metamaterial at a series of oblique angles, and relating the multiangle data set to the effective permittivity and permeability through the Fresnel expressions. The resulting measurements reveal the expected resonant permeability of the SRR which exhibits a range of negative values, the minimum value being μ = −0.8 at 1.1 THz.
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78.70.Gq Microwave and radio-frequency interactions
42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

High performance hard magnetic NdFeB thick films for integration into micro-electro-mechanical systems

N. M. Dempsey, A. Walther, F. May, D. Givord, K. Khlopkov, and O. Gutfleisch

Appl. Phys. Lett. 90, 092509 (2007); http://dx.doi.org/10.1063/1.2710771 (3 pages) | Cited 33 times

Online Publication Date: 2 March 2007

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5 μm thick NdFeB films have been sputtered onto 100 mm Si substrates using high rate sputtering (18 μm/h). Films were deposited at ⩽ 500 °C and then annealed at 750 °C for 10 min. While films deposited at temperatures up to 450 °C have equiaxed grains, the size of which decreases with increasing deposition temperature, the films deposited at 500 °C have columnar grains. The out-of-plane remanent magnetization increases with deposition temperature, reaching a maximum value of 1.4 T, while the coercivity remains constant at about 1.6 T. The maximum energy product achieved (400 kJ/m3) is comparable to that of high-quality NdFeB sintered magnets.
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81.15.Cd Deposition by sputtering
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Highly tunable and temperature insensitive multilayer barium strontium titanate films

S. Zhong, S. P. Alpay, M. W. Cole, E. Ngo, S. Hirsch, and J. D. Demaree

Appl. Phys. Lett. 90, 092901 (2007); http://dx.doi.org/10.1063/1.2710005 (3 pages) | Cited 41 times

Online Publication Date: 27 February 2007

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Multilayered Ba1−xSrxTiO3 (BST) films were deposited on Pt coated Si substrates via metalorganic solution deposition. The multilayer heterostructures consisted of three distinct layers of ∼ 220 nm nominal thickness with compositions corresponding to BST 63/37, BST 78/22, and BST 88/12. At room temperature, the heterostructure has a small-signal dielectric permittivity of 360 with a dissipation factor of 0.012 and a dielectric tunability of 65% at 444 kV/cm. These properties exhibited minimal dispersion as a function of temperature ranging from 90 to −10 °C. These results are explained via a thermodynamic model that incorporates electrical, mechanical, and electromechanical interactions between BST layers.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
65.40.G- Other thermodynamical quantities
82.45.-h Electrochemistry and electrophoresis

Examination of flatband and threshold voltage tuning of HfO2/TiN field effect transistors by dielectric cap layers

S. Guha, V. K. Paruchuri, M. Copel, V. Narayanan, Y. Y. Wang, P. E. Batson, N. A. Bojarczuk, B. Linder, and B. Doris

Appl. Phys. Lett. 90, 092902 (2007); http://dx.doi.org/10.1063/1.2709642 (3 pages) | Cited 40 times

Online Publication Date: 1 March 2007

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The authors have examined the role of sub nanometer La2O3 and LaN cap layers interposed in Si/HfO2/TiN high-k gate dielectric stacks in tuning the flatband and threshold voltages of capacitors and transistors. High performance, band edge n metal oxide field effect transistors with channel lengths down to 60 nm may be fabricated without significant compromise in mobility, electrical thickness, and threshold voltage. They have carried out a microstructural evaluation of these stacks and correlated these results with the electrical behavior of the devices.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Ferroelectric and switching behavior of poly(vinylidene fluoride-trifluoroethylene) copolymer ultrathin films with polypyrrole interface

Haisheng Xu, Juhua Zhong, Xiaobing Liu, Jianhua Chen, and Dong Shen

Appl. Phys. Lett. 90, 092903 (2007); http://dx.doi.org/10.1063/1.2710477 (3 pages) | Cited 25 times

Online Publication Date: 1 March 2007

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Thin polypyrrole-poly(styrene sulfonate) acid film is employed as interface layers between both bottom and top metal electrodes of a ferroelectric polymer, poly(vinylidene fluoride-trifluoroethylene) copolymer capacitor. The sandwiched structure Titanium∕polypyrrole-poly(styrene sulfonate)∕poly(vinylidene fluoride-trifluoroethylene)∕polypyrrole-poly(styrene sulfonate)∕titanium shows prominent ferroelectric properties even as the thickness of P(VDF-TrFE) film is down to 500 Å. The coercive voltage as low as 2.6 V is obtained with a remanent polarization of 86 mC/m2 and a switching time of 30 μs. The cell remains good ferroelectric properties at 60 °C, which is the operating temperature for many electronics. Moreover, the sandwiched structure shows excellent data retention, after more than 1×107 of switching cycles, the remanent polarization remains as high as 69 mC/m2. The soft conductive polymer electrodes not only increase the crystallinity but also enhance the crystal dipole orientation comparing with the conventionally used metal electrodes.
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77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds
77.22.Ej Polarization and depolarization
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Phase structures and electrical properties of new lead-free (Na0.5K0.5)NbO3–(Bi0.5Na0.5)TiO3 ceramics

Ruzhong Zuo, Xusheng Fang, and Chun Ye

Appl. Phys. Lett. 90, 092904 (2007); http://dx.doi.org/10.1063/1.2710768 (3 pages) | Cited 100 times

Online Publication Date: 1 March 2007

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Highly dense (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 (NKN-BST) solid solution piezoelectric ceramics have been fabricated by ordinary sintering. All compositions show pure perovskite structures, showing room-temperature symmetries of orthorhombic at x ⩽ 0.02, of tetragonal at 0.03 ⩽ x ⩽ 0.09, of cubic at 0.09<x ⩽ 0.20, and of rhombohedral at x>0.20. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was identified in the composition range of 0.02<x<0.03. The materials near the MPB exhibit a strong compositional dependence, owning peak values of the planar electromechanical coupling factor kp ∼ 43%, the piezoelectric constant d33 ∼ 195 pC/N, and the Curie temperature of 375 °C comparable to that of commercial lead zinconate titanate ceramics. The results indicate that NKN-BST ceramic is a promising lead-free piezoelectric candidate material.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.65.Bn Piezoelectric and electrostrictive constants

Ferroelectric rods with adjustable dielectric tunability

Yue Zheng, C. H. Woo, Biao Wang, and Z. Y. Zhu

Appl. Phys. Lett. 90, 092905 (2007); http://dx.doi.org/10.1063/1.2709899 (3 pages) | Cited 5 times

Online Publication Date: 2 March 2007

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The polarization, dielectric constant, and tunability of a radial-loaded ferroelectric rod inside a highly pressurized polyethylene tube are calculated for both macro- and nanodimensions within a thermodynamic model. All studied properties, including the Curie temperature, are found to vary substantially by the applied load. The authors’ results indicate that many properties of the ferroelectric rod, including its tunability, can be optimized in this design by adjusting the applied pressure.
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77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)
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Room temperature fast synthesis of zinc oxide nanowires by inductive heating

Lei Luo, Brian D. Sosnowchik, and Liwei Lin

Appl. Phys. Lett. 90, 093101 (2007); http://dx.doi.org/10.1063/1.2709618 (3 pages) | Cited 20 times

Online Publication Date: 26 February 2007

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ZnO nanowires have been rapidly synthesized using inductive heating in a room temperature environment. Nanowires with random and aligned orientations were grown on silicon and 4H-SiC (0001) substrates in less than 5 min, respectively, using ZnO/graphite as the solid source powder. Scanning electron microscopy showed nanowire diameters of 20–120 nm and lengths up to 5 μm, and transmission electron microscopy verified the single-crystalline lattice of the nanowires. Electrical properties were studied by connecting a single ZnO nanowire in the field-effect transistor configuration. This demonstration further illustrates the feasibility of a simple and fast nanoscale synthesis using inductive heating for nanomaterial synthesis.
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81.05.Dz II-VI semiconductors
81.07.Vb Quantum wires
68.37.Lp Transmission electron microscopy (TEM)
73.63.Nm Quantum wires

Holographic three-dimensional polymeric photonic crystals operating in the 1550 nm window

Jiaqi Chen, Wei Jiang, Xiaonan Chen, Li Wang, Sasa Zhang, and Ray T. Chen

Appl. Phys. Lett. 90, 093102 (2007); http://dx.doi.org/10.1063/1.2709641 (3 pages) | Cited 13 times

Online Publication Date: 26 February 2007

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A polygonal prism based holographic fabrication method has been demonstrated for a three-dimensional face-centered-cubic-type submicron polymer photonic crystal using both positive and negative photoresists. Special fabrication treatments have been introduced to ensure the survivability of the fabricated large area ( ∼ 1 cm2) nanostructures. Scanning electron microscopy and diffraction results proved the good uniformity of the fabricated structures. With the proper design of the refraction prism the authors have achieved the required band gap for S+C bands (1460–1565 nm) in the [111] direction. The transmission and reflection spectra obtained by Fourier transform infrared spectroscopy are in good agreement with simulated band structure.
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42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
42.40.My Applications
42.86.+b Optical workshop techniques
81.16.Nd Micro- and nanolithography
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Growth competition during glancing angle deposition of nanorod honeycomb arrays

C. M. Zhou and D. Gall

Appl. Phys. Lett. 90, 093103 (2007); http://dx.doi.org/10.1063/1.2709929 (3 pages) | Cited 23 times

Online Publication Date: 26 February 2007

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Arrays of Ta nanorods were grown by glancing angle deposition (GLAD) onto honeycomb Cr nanodot patterns that were evaporated onto Si substrates through a self-assembled monolayer of SiO2 nanospheres. Statistical size analyses from arrays of rods with variable average length l and width w, with 210 nm ⩽ l ⩽ 650 nm and 109 nm ⩽ w ⩽ 304 nm, show that the distribution in w broadens with increasing l and decreasing w, but remains approximately constant with a fixed l/w ratio. This is attributed to an intercolumnar growth competition that exacerbates nanorod size fluctuations but scales with rod size. These results suggest that the overall nanostructure shapes during low-temperature GLAD are independent of material-specific length scales and are, therefore, completely controlled by the geometric shadowing.
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81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
61.46.-w Structure of nanoscale materials
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