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23 Jun 2008

Volume 92, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 92, 254102 (2008); http://dx.doi.org/10.1063/1.2945893 (3 pages)

M. Trinker, S. Groth, S. Haslinger, S. Manz, T. Betz, S. Schneider, I. Bar-Joseph, T. Schumm, and J. Schmiedmayer
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Large tunneling magnetoresistance in a field-effect transistor with a nanoscale ferromagnetic gate

J.-U. Bae, T.-Y. Lin, Y. Yoon, S. J. Kim, A. Imre, W. Porod, J. L. Reno, and J. P. Bird

Appl. Phys. Lett. 92, 253101 (2008); http://dx.doi.org/10.1063/1.2951901 (3 pages) | Cited 10 times

Online Publication Date: 23 June 2008

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We demonstrate large, and hysteretic, tunneling magnetoresistance (MR) in field-effect transistors (FETs), when their usual nonmagnetic gate is replaced with a nanoscale ferromagnet. Our analysis indicates that the enhanced MR in the tunneling regime results from the ability of the fringing magnetic fields, which emanate from the nanomagnet into the FET channel, to provide an additional modulation of the electrostatic barrier induced by the applied gate voltage. The ability of this device to detect changes in magnetization may eventually allow the implementation of reprogrammable devices for universal logic and memory applications.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Synthesis and electrical properties of TiSi2 nanocables

Chenxia Zou, Xinzheng Zhang, Guangyin Jing, Jingmin Zhang, Zhimin Liao, and Dapeng Yu

Appl. Phys. Lett. 92, 253102 (2008); http://dx.doi.org/10.1063/1.2948897 (3 pages) | Cited 5 times

Online Publication Date: 23 June 2008

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Uniform TiSi2 nanocables were synthesized on large substrates using a simple physical vapor deposition method. X-ray diffraction, scanning electron microscopy, and transmission electronic microscopy were employed to characterize the samples. It reveals that the as-grown TiSi2 nanocables are of high quality single crystal inside with thin amorphous SiO2 sheathing layer. Electrical properties of these core-shell structure nanowires are also presented. Insulativity of the outer layer and stable metallic characters of the inside single crystal TiSi2 were observed. Moreover, carrying capacity of current density is up to 1011 A/m2. The nanoscale structure and excellent electrical performance make the TiSi2 nanocables good candidate for electrical interconnection in potential nanodevices.
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81.16.-c Methods of micro- and nanofabrication and processing
73.63.-b Electronic transport in nanoscale materials and structures
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Polarization-dependent sensing of a self-assembled monolayer using biaxial nanohole arrays

F. Eftekhari, R. Gordon, J. Ferreira, A. G. Brolo, and D. Sinton

Appl. Phys. Lett. 92, 253103 (2008); http://dx.doi.org/10.1063/1.2949682 (3 pages) | Cited 16 times

Online Publication Date: 23 June 2008

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We demonstrate surface plasmon resonance (SPR) sensing based on the polarization-dependent extraordinary optical transmission through a biaxial nanohole array. The biaxial array has two periodicities in a single array that can be individually probed by varying polarization. Here, the SPR polarization-spectral dependence is demonstrated for the detection of a self-assembled monolayer for four sets of biaxial array periodicities. By monitoring the polarization dependence of transmission through the nanohole arrays with biaxial periodicity, surface-sensitive refractive index induced intensity variations may be separated from other effects such as absorption, scattering, and intensity fluctuations, while using a single wavelength source. Biaxial sensing is useful for ongoing microfluidic integration of nanohole SPR, where the light source is transmitted through a microfluidic channel.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Enhanced magnetic behavior in carbon encapsulated nickel nanotubules through a linear polymer template

Vidyadhar Singh, S. Ram, M. Ranot, Je-Geun Park, and V. Srinivas

Appl. Phys. Lett. 92, 253104 (2008); http://dx.doi.org/10.1063/1.2950323 (3 pages) | Cited 2 times

Online Publication Date: 25 June 2008

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Carbon encapsulated Ni nanotubules, synthesized by a simple chemical method with linear polymer templates, reveal a high saturation magnetization (Ms) close to bulk fcc-Ni value, with larger coercivity 140 Oe at 300 K. An improvement in basic ferromagnetic character is reflected in the remanent magnetization (Mr), which is enhanced to be Mr/Ms ∼ 0.3, intrinsic of strongly ferromagnetic pseudosingle domains. The TEM images consist of fcc-Ni of ∼ 350 nm long cylindrical tubules with an average 20 nm diameter. The sample has two Raman bands of 1350 cm−1 (D-band) and 1590 cm−1 (G-band) characterizing the presence of a graphitic carbon (disordered).
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75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
61.46.Fg Nanotubes

Effect of InGaN quantum dot size on the recombination process in light-emitting diodes

Il-Kyu Park, Min-Ki Kwon, Chu-Young Cho, Ja-Yeon Kim, Chang-Hee Cho, and Seong-Ju Park

Appl. Phys. Lett. 92, 253105 (2008); http://dx.doi.org/10.1063/1.2951607 (3 pages) | Cited 15 times

Online Publication Date: 25 June 2008

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The effect of InGaN quantum dot (QD) size on the performance of light-emitting diodes (LEDs) was investigated by varying the QD size from 1.32 to 2.81 nm. The electroluminescence peak of the LEDs containing small QDs (1.32 nm) was redshifted with increasing input current while that of large QDs (2.81 nm) was blueshifted up to 40 mA due to the screening effect of the piezoelectric field. The optical output power of LEDs fabricated with small QDs was much higher compared to those with large QDs. These results were attributed to a weaker piezoelectric field and enhanced quantum confinement in small QDs.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling

Enhanced field emission from hexagonal rhodium nanostructures

Bhaskar R. Sathe, Bhalchandra A. Kakade, Imtiaz S. Mulla, Vijayamohanan K. Pillai, Dattatray J. Late, Mahendra A. More, and Dilip S. Joag

Appl. Phys. Lett. 92, 253106 (2008); http://dx.doi.org/10.1063/1.2943657 (3 pages) | Cited 7 times

Online Publication Date: 25 June 2008

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Shape selective synthesis of nanostructured Rh hexagons has been demonstrated with the help of a modified chemical vapor deposition using rhodium acetate. An ultralow threshold field of 0.72 V/μm is observed to generate a field emission current density of 4×10−3 μA/cm2. The high enhancement factor (9325) indicates that the origin of electron emission is from nanostructured features. The smaller size of emitting area, excellent current density, and stability over a period of more than 3 h are promising characteristics for the development of electron sources.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Bc Nanocrystalline materials

Hysteretic magnetophotoluminescence in Mn ion implanted silicon rich oxide thin films

W. Pan, P. G. Kotula, M. S. Carroll, T. Monson, and Y. Q. Wang

Appl. Phys. Lett. 92, 253107 (2008); http://dx.doi.org/10.1063/1.2952277 (3 pages)

Online Publication Date: 25 June 2008

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We present our recent results of magnetophotoluminescence (PL) in Mn ion implanted silicon rich oxide thin films. A hysteretic behavior was observed when the PL peak intensity is plotted against the applied magnetic field. It disappeared when the measurement temperature was higher than 60 K. In a controlled thin film sample without Mn-ion implantation no hysteresis was observed down to the lowest temperature of 1.3 K. We propose that the origin of this hysteretic behavior is probably due to a ferromagnetic order in the Mn ion implanted thin films.
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78.20.Ls Magneto-optical effects
78.55.-m Photoluminescence, properties and materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.U- Doping and impurity implantation
75.50.Dd Nonmetallic ferromagnetic materials

Formation of nickel-based nanocrystal monolayers for nonvolatile memory applications

Yoo-Sung Jang, Jong-Hwan Yoon, and Robert G. Elliman

Appl. Phys. Lett. 92, 253108 (2008); http://dx.doi.org/10.1063/1.2952287 (3 pages) | Cited 14 times

Online Publication Date: 25 June 2008

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A simple method for fabricating metal silicide nanocrystal layers with narrow spatial distributions is demonstrated and shown to produce structures suitable for nonvolatile memory applications. The method is based on high-temperature annealing of a sandwich structure comprised of a thin metal (Ni) film sandwiched between two silicon-rich oxide (SiOx) layers and has the feature in which the size of the NCs can be controlled by varying the silicon concentrations in the SiOx layers or the initial nickel film thickness. The typical nanocrystal diameters and densities are 3.6 nm and 1.2×1012 cm−2, respectively. Capacitance-voltage (C-V) measurements on test structures with these characteristics are shown to have C-V characteristics suitable for nonvolatile memory applications, including a C-V memory window of 11.7 V for sweep voltages between −12 V and +12.
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81.07.Bc Nanocrystalline materials
84.30.Sk Pulse and digital circuits
81.40.Gh Other heat and thermomechanical treatments

Parametrically pumped ultrahigh Q electromechanical resonator

I. Mahboob and H. Yamaguchi

Appl. Phys. Lett. 92, 253109 (2008); http://dx.doi.org/10.1063/1.2949319 (3 pages) | Cited 7 times

Online Publication Date: 25 June 2008

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The spectral purity of an electromechanical resonance (quality factor Q) can be enhanced by more than one order of magnitude to ∼ 2.5×106 by parametrically exciting the fundamental mode via double frequency modulations to the spring constant mediated by the piezoelectric effect. We theoretically demonstrate that this Q enhancement is an intrinsic property of the parametric resonator by solving the equation of motion for this system. The Q enhancement demonstrated here results in smaller perturbations in the resonance ( ∼ 0.05 Hz) becoming visible which enables the charge sensitivity of the electromechanical oscillator to improve by a factor equal to the Q enhancement.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
77.65.Fs Electromechanical resonance; quartz resonators
84.30.Ng Oscillators, pulse generators, and function generators

Gigantic magneto-optical effects induced by (Fe/Co)-cosubstitution in titania nanosheets

Minoru Osada, Masayuki Itose, Yasuo Ebina, Kanta Ono, Shigenori Ueda, Keisuke Kobayashi, and Takayoshi Sasaki

Appl. Phys. Lett. 92, 253110 (2008); http://dx.doi.org/10.1063/1.2937094 (3 pages) | Cited 13 times

Online Publication Date: 25 June 2008

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Magneto-optical Faraday effect has been investigated for 3d-transition-metal-substituted titania nanosheets Ti1−xMxO2 (M = Fe,Co). In Ti0.8Co0.2O2 and Ti0.6Fe0.4O2 nanosheets, a strong magneto-optical response ( ∼ 104 deg/cm) appeared near the absorption edge at 260 nm. We find that tailoring magneto-optical properties could be achieved by (Fe/Co) cosubstitution and an optimally doped Ti0.75Fe0.1Co0.15O2 nanosheet exhibits a gigantic magneto-optical response ( ∼ 105 deg/cm) over the wide wavelength region (400–750 nm). By analyzing electronic structures from first-principle calculations, we have clarified that the d-d transitions are responsible for the gigantic signal in (Fe/Co)-cosubstituted nanosheets.
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78.20.Ls Magneto-optical effects
73.22.-f Electronic structure of nanoscale materials and related systems
75.50.Dd Nonmetallic ferromagnetic materials
71.15.-m Methods of electronic structure calculations

Surface plasmon on aluminum concentric rings arranged in a long-range periodic structure

Yi-Tsung Chang, Dah-Ching Tzuang, Yi-Ting Wu, Chi-Feng Chan, Yi-Han Ye, Ting-Hsiang Hung, Yu-Fan Chen, and Si-Chen Lee

Appl. Phys. Lett. 92, 253111 (2008); http://dx.doi.org/10.1063/1.2949743 (3 pages) | Cited 6 times

Online Publication Date: 25 June 2008

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The enhanced optical transmission through the annular aluminum metal with different number of concentric rings arranged in a long-range periodic structure on the silicon substrate is investigated. The measured transmission spectra demonstrate that the surface plasmon modes depend sensitively on the structural parameters of the metallic rings. The degenerate (1,0), (1,1), and (2,1) Al/Si surface plasmon modes are determined by the long periodicity of the structure. The localized modes in cavities with different length can be observed in this structure as well. These phenomena suggest that both surface plasmons and localized cavity modes are excited within super unit cell.
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78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.Er Solid metals and alloys

Ultraviolet photoluminescence from 6H silicon carbide nanoparticles

Andrea M. Rossi, Thomas E. Murphy, and Vytas Reipa

Appl. Phys. Lett. 92, 253112 (2008); http://dx.doi.org/10.1063/1.2950084 (3 pages) | Cited 20 times

Online Publication Date: 25 June 2008

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We report stable photoluminescence from 6H silicon carbide nanocrystals dispersed in three different solvents: water, hydrofluoric acid, and toluene. Transmission electron micrograph surveys reveal a size distribution that contains a significant fraction of monocrystal particles with diameters below 3 nm—small enough for quantum confinement to play a role in increasing the effective bandgap energy. The ultraviolet photoluminescence band observed at 3.5 eV in the colloidal solutions is consistent with quantum confinement estimates based on the effective mass model.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.20.Nr Semiconductor compounds
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Horizontally aligned Cu5Si polycrystalline nanorods on Si

Wei Wu, Qingkai Yu, Jiaming Zhang, Jie Lian, Gang Liang, Rodney C. Ewing, and Shin-Shem Pei

Appl. Phys. Lett. 92, 253113 (2008); http://dx.doi.org/10.1063/1.2952770 (3 pages) | Cited 1 time

Online Publication Date: 26 June 2008

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In this letter, we report a method for the growth of copper silicide (Cu5Si) nanorods with a horizontal alignment via chemical vapor deposition. The Cu5Si nanorods with an oxygen-rich shell grew in the [110] direction of Si on a (001) Si substrate. A growth model that explains the formation mechanism of the horizontally aligned, polycrystalline nanorods is proposed.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Tuning the torsional properties of carbon nanotube systems with axial prestress

Byeong-Woo Jeong, Jang-Keun Lim, and Susan B. Sinnott

Appl. Phys. Lett. 92, 253114 (2008); http://dx.doi.org/10.1063/1.2945665 (3 pages) | Cited 10 times

Online Publication Date: 26 June 2008

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The effects of tensile or compressive prestress on the torsional responses of carbon nanotubes are examined using classical molecular dynamics simulations. Prestressing the nanotubes is predicted to significantly change their critical torsional moment and stiffness. This is therefore an approach by which the torsional mechanical properties and oscillation frequencies of carbon nanotubes may be tuned. Importantly, the predicted changes in torsional stiffness are unique relative to conventional linear elastic materials and are indicative of nonlinear oscillations due to nonlinear mechanical effects.
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81.07.De Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
61.46.Fg Nanotubes
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations

Proton conduction in thin film yttrium-doped barium zirconate

Joon Hyung Shim, Turgut M. Gür, and Fritz B. Prinz

Appl. Phys. Lett. 92, 253115 (2008); http://dx.doi.org/10.1063/1.2947584 (3 pages) | Cited 12 times

Online Publication Date: 27 June 2008

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The proton conductivity of yttrium-doped barium zirconate (BYZ) films epitaxially grown on MgO(100) has been studied in the range of 140–290 °C as a function of film thickness (60–670 nm) in relation to their crystal and morphological structure at the nanoscale. Highly textured 60 nm BYZ film epitaxially grown on MgO(100) showed high ionic conductivity, close to its bulk value. In contrast, thicker polycrystalline samples with rougher surfaces, caused by grain boundary formation, exhibited lower conductivity.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
68.55.jd Thickness

Direct observation of local magnetic field generated by micromagnet

Shinji Watanabe, Susumu Sasaki, Shinya Sato, Naoki Isogai, and Yoshinori Matsumoto

Appl. Phys. Lett. 92, 253116 (2008); http://dx.doi.org/10.1063/1.2944144 (3 pages)

Online Publication Date: 27 June 2008

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Using standard nuclear magnetic resonance (NMR) technique and a well-fabricated sample, we have succeeded in directly observing local magnetic field generated by a micromagnet Ni45Fe55 (with thickness of 400 nm), which was sputtered on an Al layer of 20 nm thickness. Improved sensitivity of our NMR technique enabled us to clearly observe Al-NMR signals, which are confirmed to come from Al nuclei in the 20 nm layers. From the analysis of the Al-NMR spectra, the local magnetic field was found to be +0.17±0.02 (−0.20±0.01) T, the sign of which is consistent with the geometry that the external magnetic field was applied perpendicular (parallel) to the Al layer. The present study gives a potential key element toward realizing higher resolution in magnetic resonance imaging.
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76.60.Pc NMR imaging
75.50.Bb Fe and its alloys

Effects of local gas-flow field on synthesis of oxide nanowires during thermal oxidation

ChunHua Xu, XiangLong Yang, San-Qiang Shi, Yang Liu, Charles Surya, and ChungHo Woo

Appl. Phys. Lett. 92, 253117 (2008); http://dx.doi.org/10.1063/1.2940597 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2008

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Ω-shaped copper specimens are oxidized in wet air. The results show that totally no-wire structure, CuO whiskers, and the high density of well-aligned CuO nanowires can be formed simultaneously on the different positions of the specimen. A three-dimensional flow simulation results indicate that the direction of velocity vectors of local gas flow affects the alignment of nanowires during oxidation while the shear stress of flowing gas near the surface of a Ω-shaped specimen controls the density of nanowires.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Vb Quantum wires
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
68.65.La Quantum wires (patterned in quantum wells)

On the spectral response of quantum dot infrared photodetectors: Postgrowth annealing and polarization behaviors

B. Aslan, C. Y. Song, and H. C. Liu

Appl. Phys. Lett. 92, 253118 (2008); http://dx.doi.org/10.1063/1.2953083 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2008

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Effects of the postgrowth rapid thermal annealing on the device properties of a multilayer InAs/GaAs quantum dot infrared photodetector are investigated. Clear shift in the spectral photoresponse toward smaller energy region with increasing annealing temperatures is shown. Polarization behaviors of the photoresponse peaks are presented.
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78.66.Fd III-V semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
85.60.Gz Photodetectors (including infrared and CCD detectors)
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