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6 Aug 2007

Volume 91, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 063118 (2007); http://dx.doi.org/10.1063/1.2768861 (3 pages)

Douglas C. Meier, Steve Semancik, Bradley Button, Evgheni Strelcov, and Andrei Kolmakov
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Directed assembly of gold nanoparticle nanowires and networks for nanodevices

Xugang Xiong, Ahmed Busnaina, Selvapraba Selvarasah, Sivasubramanian Somu, Ming Wei, Joey Mead, Chia-Ling Chen, Juan Aceros, Prashanth Makaram, and Mehmet R. Dokmeci

Appl. Phys. Lett. 91, 063101 (2007); http://dx.doi.org/10.1063/1.2763967 (3 pages) | Cited 13 times

Online Publication Date: 6 August 2007

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Alternating electric field is used to assemble gold nanoparticle nanowires from liquid suspensions. The effects of electrode geometry and the dielectrophoresis force on the chaining and branching of nanowire formation are investigated. The nanowire assembly processes are modeled using finite element calculations, and the particle trajectories under the combined influence of dielectrophoresis force and viscous drag are simulated. Nanoparticle nanowires with 10 nm resolution are fabricated. The wires can be further oriented along an externally introduced flow. This work provides an approach towards rapid assembly and organization of ultrasmall nanoparticle networks.
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81.16.Dn Self-assembly
81.07.-b Nanoscale materials and structures: fabrication and characterization

Evolution of interfacial adhesion force in dynamic micromachines due to repetitive impact loading

M. A. Philippine, S. J. Timpe, and K. Komvopoulos

Appl. Phys. Lett. 91, 063102 (2007); http://dx.doi.org/10.1063/1.2764111 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2007

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A contact-mode surface micromachine was used to study the effect of repetitive impact loading on the evolution of the adhesion force at sidewall contact interfaces. Low and stable adhesion force was encountered during the initial stage of impact testing (run-in phase). A surface degradation phase occurred subsequently in which the adhesion force increased logarithmically with impact cycles. The experimental trend was used to derive a method for predicting micromachine failure due to excessive interfacial adhesion. High-magnification scanning electron microscopy did not reveal any modification of the surface topography even after 5.5×107 impact cycles, despite the significant enhancement of the adhesion force, attributed to the increase of the real contact area and the higher surface energy produced as a result of the removal of thin surface layers. The dominant surface degradation mechanisms are interpreted in the context of adhesion force measurements and microscopy images of the impacted surfaces.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
89.20.Kk Engineering

Synthesis of elongated Au nanoparticles in silica matrix by ion irradiation

Y. K. Mishra, F. Singh, D. K. Avasthi, J. C. Pivin, D. Malinovska, and E. Pippel

Appl. Phys. Lett. 91, 063103 (2007); http://dx.doi.org/10.1063/1.2764556 (3 pages) | Cited 26 times

Online Publication Date: 6 August 2007

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The present work reports the synthesis of elongated Au nanoparticles (NPs) parallel to each other, embedded in silica matrix. Au NPs in silica, prepared using rf magnetron sputtering, were irradiated by 120 MeV Au ions at different fluences to induce elongation. Optical absorption study of irradiated film showed a clear splitting of surface plasmon bands corresponding to transverse and longitudinal modes. Transmission electron microscopy investigations of pristine and irradiated samples revealed an elongation (aspect ratio of ∼ 3.5) in Au NPs occurred as a result of irradiation. The results are discussed in the framework of thermal spike model.
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81.16.-c Methods of micro- and nanofabrication and processing
61.80.Jh Ion radiation effects
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
68.60.Bs Mechanical and acoustical properties
78.66.-w Optical properties of specific thin films

Electrostatic characteristics of tether atoms in connecting organic molecules to the surface of silicon

Peiji Zhao and Dwight Woolard

Appl. Phys. Lett. 91, 063104 (2007); http://dx.doi.org/10.1063/1.2766670 (3 pages)

Online Publication Date: 6 August 2007

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In this letter, the authors analyze the electrostatic characteristics of the tether atoms connecting organic molecules onto silicon (100)-2×1 surfaces, which is a key factor in the design of molecular devices for information processing and biomolecular sensing. Design principles for silicon surfaces with required electrostatic functionality are presented.
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68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.-c Electronic transport in interface structures

Fine tuning of equilibrium distance of two-dimensional colloidal assembly under an alternating electric field

Yu Liu, Rong-Guo Xie, and Xiang-Yang Liu

Appl. Phys. Lett. 91, 063105 (2007); http://dx.doi.org/10.1063/1.2766838 (3 pages) | Cited 12 times

Online Publication Date: 6 August 2007

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The authors study the effect of temperature on two-dimensional (2D) colloidal assembly subjected to an alternating electric field (AEF). At high frequencies (>500 Hz), an increase in temperature leads to an increase in the upper cutoff frequency of the assembly, consistent with an electrohydrodynamic (EHD) mechanism. At low frequencies (<300 Hz), the authors observe a crossover frequency at which the behavior of the temperature dependence changes, suggesting a change in the origin of the EHD mechanism. By controlling the temperature and the AEF, the authors develop a method to finely tune the equilibrium distance of the 2D colloidal assembly over a wide range.
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82.70.Dd Colloids
47.57.J- Colloidal systems
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Room-temperature ferromagnetism in Fe-doped PbTiO3 nanocrystals

Zhaohui Ren, Gang Xu, Xiao Wei, Yong Liu, Xiaohong Hou, Piyi Du, Wenjian Weng, Ge Shen, and Gaorong Han

Appl. Phys. Lett. 91, 063106 (2007); http://dx.doi.org/10.1063/1.2766839 (3 pages) | Cited 22 times

Online Publication Date: 6 August 2007

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Room-temperature ferromagnetism has been observed in Fe-doped PbTiO3 nanocrystals. The magnetism of the nanocrystals develops from diamagnetism to ferromagnetism and the paramagnetism on increasing nominal Fe doping concentration from 0 to 4 mol %. Transmission electron microscope (TEM) and high-resolution TEM data indicate that Fe-doped PbTiO3 nanocrystals with the size of ∼ 100 nm are organized to form a planarlike self-assembly via oriented aggregation. These assembled nanostructures effectively improve room-temperature ferromagnetism of the sample. The exchange interaction of ferric ions via an electron trapped in a bridging oxygen vacancy (F center) is employed to explain the ferromagnetism of Fe-doped PbTiO3 nanocrystals.
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75.20.Ck Nonmetals
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Enhancement of polycrystalline silicon solar cells using ultrathin films of silicon nanoparticle

M. Stupca, M. Alsalhi, T. Al Saud, A. Almuhanna, and M. H. Nayfeh

Appl. Phys. Lett. 91, 063107 (2007); http://dx.doi.org/10.1063/1.2766958 (3 pages) | Cited 31 times

Online Publication Date: 6 August 2007

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Ultrathin films of highly monodispersed luminescent Si nanoparticles are directly integrated on polycrystalline Si solar cells. The authors monitor the open-circuit voltage and the short circuit current. The results demonstrate that films of 1 nm blue luminescent or 2.85 nm red luminescent Si nanoparticles produce large voltage enhancements with improved power performance of 60% in the UV/blue range. In the visible, the enhancements are ∼ 10% for the red and ∼ 3% for the blue particles. The results point to a significant role for charge resonant transport across the nanofilm and Schottky-like rectification at nanoparticle-metal interface.
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88.40.-j Solar energy
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.40.Ei Rectification

Extraordinary transmission through a silver film perforated with cross shaped hole arrays in a square lattice

Chia-Yi Chen, Ming-Wei Tsai, Tzu-Hung Chuang, Yi-Tsung Chang, and Si-Chen Lee

Appl. Phys. Lett. 91, 063108 (2007); http://dx.doi.org/10.1063/1.2767183 (3 pages) | Cited 25 times

Online Publication Date: 7 August 2007

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In this work, the transmission through cross shaped hole with different sizes but the same lattice constant was measured with the polarized light to investigate the variation of localized charge oscillation around the hole. The comparison between the transmission intensities through the similarly arranged periodic hole array with different hole shapes, i.e., cross, square, and rectangular, were also measured. The cross shaped hole gives rise to a larger transmission of light than those perforated with square or rectangular hole.
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78.66.Bz Metals and metallic alloys
42.70.Qs Photonic bandgap materials

Local modification of electronic structure of Si (111)-7×7 surfaces by forming molybdenum-encapsulating Si clusters

Noriyuki Uchida, Hiroshi Yahata, Toshihiko Kanayama, and Leonid Bolotov

Appl. Phys. Lett. 91, 063109 (2007); http://dx.doi.org/10.1063/1.2767205 (3 pages) | Cited 2 times

Online Publication Date: 7 August 2007

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Using scanning tunneling microscopy, the authors show that uniform-size Mo-encapsulating Si clusters, MoSin, were synthesized on Si (111)-7×7 surfaces by the reaction between SiH4 and Mo atoms deposited on the surface followed by thermal annealing at 600 °C. Comparing observed images with ab initio structure calculations indicates that n = 6. According to scanning tunneling spectroscopy measurements, the MoSin cluster has a semiconducting energy gap of approximately 0.3 eV, indicating that the metallic electronic state of the 7×7 surface can be locally modified by formation of the MoSin cluster.
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73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations

Vertically standing carbon nanotubes as charge storage nodes for an ultimately scaled nonvolatile memory application

Seong-Wan Ryu, Xing-Jiu Huang, and Yang-Kyu Choi

Appl. Phys. Lett. 91, 063110 (2007); http://dx.doi.org/10.1063/1.2767211 (3 pages) | Cited 7 times

Online Publication Date: 7 August 2007

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Vertically standing single-walled carbon nanotube (SSWCNT)-embedded transistors have been demonstrated for a flash memory application. The performance of the SSWCNT device was compared with a lying SWCNT (LSWCNT) device to verify the directional effect of immobilized SWCNTs. The SSWCNT device shows a better program/erase transient and a threefold enhanced retention characteristics over the LSWCNT device due to the high coupling ratio and the defect immunity based on the isolated distribution and vertical directionality nature of the SSWCNT.
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85.35.Kt Nanotube devices
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Nondestructive thickness measurement of biological layers at the nanoscale by simultaneous topography and capacitance imaging

Ignacio Casuso, Laura Fumagalli, Gabriel Gomila, and Esteve Padrós

Appl. Phys. Lett. 91, 063111 (2007); http://dx.doi.org/10.1063/1.2767979 (3 pages) | Cited 8 times

Online Publication Date: 7 August 2007

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Nanoscale capacitance images of purple membrane layers are obtained simultaneously to topography in a nondestructive manner by operating alternating current sensing atomic force microscopy in jumping mode. Capacitance images show excellent agreement with theoretical modeling and prove to be a noninvasive method for measuring the thickness of purple membrane layers beyond the single monolayer limit with nanoscale lateral spatial resolution. With the ability of spatially resolving the capacitance while preserving the sample from damaging, this technique can be applied for nanoscale thickness measurement of other biological layers and soft materials in general.
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87.64.Dz Scanning tunneling and atomic force microscopy
87.16.D- Membranes, bilayers, and vesicles

Giant elasticity of photopolymer nanowires

Sana Nakanishi, Satoru Shoji, Satoshi Kawata, and Hong-Bo Sun

Appl. Phys. Lett. 91, 063112 (2007); http://dx.doi.org/10.1063/1.2767995 (3 pages) | Cited 8 times

Online Publication Date: 7 August 2007

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Giant elasticity, reflected by a shear modulus three order smaller than seen in the bulk of the same materials, is found in polymer nanowires, which are prepared by two-photon polymerization into a shape of spring: geometry capable to magnify mechanical deformations. An approach intervening the competitive processes of dissolving and polymerization in the course of rinsing of written structures was proposed for continuously tuning the shear modulus and fixing them at desired level. These results not only reveal a characteristic of polymers when the material size enters into the regime of hundreds of nanometers but also indicate prospect polymer microelectromechanical system for biocompatible applications.
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61.46.-w Structure of nanoscale materials
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
42.70.Jk Polymers and organics

Implantation-induced nonequilibrium reaction between Zn ions of 60 keV and SiO2 target

H. Amekura, M. Yoshitake, O. A. Plaksin, N. Kishimoto, Ch. Buchal, and S. Mantl

Appl. Phys. Lett. 91, 063113 (2007); http://dx.doi.org/10.1063/1.2768004 (3 pages) | Cited 3 times

Online Publication Date: 7 August 2007

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Silica glass (SiO2) was implanted with 60 keV Zn+ ions to a fluence of 1.0×1017 ions/cm2, and the chemical states were investigated along the depth in as-implanted state by x-ray excited Auger electron spectroscopy and x-ray photoelectron spectroscopy. The metallic Zn and Zn2SiO4 phases were found to have, respectively, formed in the shallow and deep regions of the SiO2, whereas thermodynamics predicts the Zn phase only. Oxygen atoms in SiO2 are preferentially displaced to the deeper region because of the lighter mass. The excess oxygen in the deep region and athermal energy from the implantation drive the formation of Zn2SiO4.
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61.43.Fs Glasses
61.72.up Other materials
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Displacement currents in semiconductor quantum dots embedded dielectric media: A method for room temperature photon detection

P. V. V. Jayaweera, A. G. U. Perera, and K. Tennakone

Appl. Phys. Lett. 91, 063114 (2007); http://dx.doi.org/10.1063/1.2768305 (3 pages) | Cited 1 time

Online Publication Date: 7 August 2007

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It is shown that the high electronic polarizability of quantum dots can be utilized to devise photon detectors by embedding quantum dots in dielectric media to form capacitors. Modulated light generates displacement currents and an expression is obtained for responsivity in terms of the properties of the quantum dot, the dielectric, and the detector geometry. A model detector constituted of PbS quantum dots embedded in paraffin wax is devised to illustrate the principle, giving ∼ 0.6 A/W as an upper limit for the responsivity. As these systems sense only the variations of the light intensity, they could be operated at ambient temperature.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.Hc Quantum dots
85.60.Gz Photodetectors (including infrared and CCD detectors)
84.32.Tt Capacitors

Phase transformation and freestanding nanoparticles formation in lead zirconate titanate derived by sol-gel

Yasir Faheem and Khurram Saleem Joya

Appl. Phys. Lett. 91, 063115 (2007); http://dx.doi.org/10.1063/1.2768626 (3 pages) | Cited 2 times

Online Publication Date: 8 August 2007

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Generation of the freestanding lead zirconate titanate (PZT) nanoparticles and their phase transformation behavior is investigated in this research. PZT sol-gel precursor was dried at 250 °C and partially calcined at 450 °C for 30 min to decompose organics and bring down the free energy barrier for perovskite crystallization. Annealed at 550–600 °C, sol-gel PZT powder exhibited freestanding nanocrystalline morphology. The electron diffraction pattern obtained from nanoparticles confirmed their crystallinity and perovskite phase formation. The structural characteristics were evaluated by transmission electron microscope and x-ray diffraction techniques. The average PZT nanoparticle size of 20 nm was observed by transmission electron microscope and Scherrer’s method.
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64.70.K- Solid-solid transitions
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.40.Gh Other heat and thermomechanical treatments
81.16.-c Methods of micro- and nanofabrication and processing

First-principles study of magnetic properties in V-doped ZnO

Qian Wang, Qiang Sun, Puru Jena, Zheng Hu, R. Note, and Y. Kawazoe

Appl. Phys. Lett. 91, 063116 (2007); http://dx.doi.org/10.1063/1.2768628 (3 pages) | Cited 17 times

Online Publication Date: 8 August 2007

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A comprehensive theoretical study of electronic and magnetic properties of V-doped ZnO in bulk as well as (11math0) thin films has been performed using density functional theory. Vanadium atoms substituted at Zn sites show very little selectivity of site occupancy. More importantly, different geometries with ferromagnetic, ferrimagnetic, and antiferromagnetic configurations are found to be energetically nearly degenerate both in Zn1−xVxO bulk and subsurface layers of the thin film. On the other hand, V atoms couple ferromagnetically when they occupy surface sites of the thin film. The diverse magnetic behaviors in V-doped ZnO account for the many reported conflicting experimental results.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics
71.20.Nr Semiconductor compounds

On the enhancement of field emission performance of ultrananocrystalline diamond coated nanoemitters

Yu-Fen Tzeng, Yen-Chih Lee, Chi-Young Lee, I.-Nan Lin, and Hsin-Tien Chiu

Appl. Phys. Lett. 91, 063117 (2007); http://dx.doi.org/10.1063/1.2768880 (3 pages) | Cited 9 times

Online Publication Date: 8 August 2007

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Ultrananocrystalline diamond (UNCD) nanoemitters were synthesized by a microwave plasma enhanced chemical vapor deposition process using silicon nanowires (SiNWs) as the template. Preseeding markedly enhances the nucleation of diamond on the SiNW templates, resulting in UNCD grains of smaller size and uniform distribution, which leads to significantly improved electron field emission (EFE) properties. The EFE for UNCD nanoemitters can be turned on at (E0)UNCD-NE = 4.4 V/μm, achieving large EFE current density, (Je)UNCD-NE = 13.9 mA/cm2 at an applied field of 12 V/μm, which is comparable with that of carbon nanotubes, but with much better processing reliability.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
61.46.Hk Nanocrystals

Coupling nanowire chemiresistors with MEMS microhotplate gas sensing platforms

Douglas C. Meier, Steve Semancik, Bradley Button, Evgheni Strelcov, and Andrei Kolmakov

Appl. Phys. Lett. 91, 063118 (2007); http://dx.doi.org/10.1063/1.2768861 (3 pages) | Cited 26 times

Online Publication Date: 9 August 2007

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Recent advances in nanotechnology have yielded materials and structures that offer great potential for improving the sensitivity, selectivity, stability, and speed of next-generation chemical gas sensors. To fabricate practical devices, the “bottom-up” approach of producing nanoscale sensing elements must be integrated with the “top-down” methodology currently dominating microtechnology. In this letter, the authors illustrate this approach by coupling a single-crystal SnO2 nanowire sensing element with a microhotplate gas sensor platform. The sensing results obtained using this prototype sensor demonstrate encouraging performance aspects including reduced operating temperature, reduced power consumption, good stability, and enhanced sensitivity.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Formation of one-dimensional nanoparticle chains

Yu Chen and A. M. Goldman

Appl. Phys. Lett. 91, 063119 (2007); http://dx.doi.org/10.1063/1.2768891 (3 pages) | Cited 7 times

Online Publication Date: 9 August 2007

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The authors report an approach to forming one-dimensional chains of nanoparticles. It is a purely physical process and thus is free from both chemical contamination and residue side products. The size of the dots as well as the interdot spacing can be manipulated by adjusting the conditions of a postannealing process, changing the initial wire width, or using different substrates. Taking advantage of the capability for precise positioning using e-beam lithograpy, this method is a relatively simple route to fabricating one-dimensional nanoparticle chains with precise geometries.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
81.07.Ta Quantum dots
81.40.Gh Other heat and thermomechanical treatments

Magnetic trapping induced low temperature phase transition from fcc to fct in pulsed laser deposition of FePt:Al2O3 nanocomposite thin films

J. J. Lin, T. Zhang, P. Lee, S. V. Springham, T. L. Tan, R. S. Rawat, T. White, R. Ramanujan, and J. Guo

Appl. Phys. Lett. 91, 063120 (2007); http://dx.doi.org/10.1063/1.2768904 (3 pages) | Cited 4 times

Online Publication Date: 9 August 2007

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FePt:Al2O3 nanocomposite thin films have been synthesized by magnetic trapping assisted pulsed laser deposition. The annealing temperature required for phase transition from low Ku fcc-FePt to high Ku fct-FePt is lowered down from about 600 °C for conventional pulsed laser deposition (PLD) to 300 °C for magnetic trapping assisted PLD. For the sample annealed at 300 °C with fct phase FePt nanoparticles, the average nanoparticle size is estimated to be about 8.7±2.1 nm, and the magnetic properties are improved which makes it a potentially good candidate for possible applications in high density data storage.
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64.70.K- Solid-solid transitions
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.70.Ak Magnetic properties of monolayers and thin films

Surface plasmon leakage in its coupling with an InGaN/GaN quantum well through an Ohmic contact

Dong-Ming Yeh, Chi-Feng Huang, Yen-Cheng Lu, Cheng-Yen Chen, Tsung-Yi Tang, Jeng-Jie Huang, Kun-Ching Shen, Ying-Jay Yang, and C. C. Yang

Appl. Phys. Lett. 91, 063121 (2007); http://dx.doi.org/10.1063/1.2768913 (3 pages) | Cited 8 times

Online Publication Date: 9 August 2007

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The authors demonstrate the leakage of surface plasmon (SP) through the Ohmic contact of either p-type or n-type GaN layer in the coupling process between SP and an InGaN/GaN quantum well (QW). It is shown that the photoluminescence (PL) intensity is significantly reduced when an Ohmic contact is formed, in contrast to the case of significant PL enhancement when an insulating thin layer is applied between the doped semiconductor and metal. The observation implies that, in using the SP-QW coupling for enhancing emission in a light-emitting diode, the metals for Ohmic contact and SP generation must be isolated from each other. A thin dielectric interlayer in the region for SP-QW coupling is useful for avoiding the leakage of SP energy.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
78.67.De Quantum wells
73.40.Ns Metal-nonmetal contacts
78.55.Cr III-V semiconductors

Strain relaxation and stress-driven interdiffusion in InAs/InGaAs/InP nanowires

L. Nieto, J. R. R. Bortoleto, M. A. Cotta, R. Magalhães-Paniago, and H. R. Gutiérrez

Appl. Phys. Lett. 91, 063122 (2007); http://dx.doi.org/10.1063/1.2764446 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2007

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The authors have investigated strain relaxation in InAs/InGaAs/InP nanowires (NW’s). Transmission electron microscopy images show an additional stress field attributed to compositional modulation in the ternary layer, which disrupts NW formation and drives Ga interdiffusion into InAs, according to grazing incidence x-Ray diffraction under anomalous scattering conditions. The strain profile along the NW, however, is not significantly affected when interdiffusion is considered. Results show that the InAs NW energetic stability is preserved with the introduction of ternary buffer layer in the structure.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials

Spin-dependent transport in nanocomposites of Alq3 molecules and cobalt nanoparticles

Shinichi Tanabe, Shinji Miwa, Masaki Mizuguchi, Teruya Shinjo, Yoshishige Suzuki, and Masashi Shiraishi

Appl. Phys. Lett. 91, 063123 (2007); http://dx.doi.org/10.1063/1.2769748 (3 pages) | Cited 17 times

Online Publication Date: 9 August 2007

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The authors have observed magnetoresistance (MR) ratios of 12% and 0.1% at 4.2 and 290 K, respectively, in a nanocomposite in which Co nanoparticles are embedded in the fine molecular structure of a tris(8-hydroxyquinoline) aluminum (Alq3) matrix. Structural analyses, magnetization measurements, and conduction properties of the device reveal that the MR effect is induced by spin-dependent transport in the Alq3.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
72.25.Mk Spin transport through interfaces
72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Pq Other materials
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Making graphene visible

P. Blake, E. W. Hill, A. H. Castro Neto, K. S. Novoselov, D. Jiang, R. Yang, T. J. Booth, and A. K. Geim

Appl. Phys. Lett. 91, 063124 (2007); http://dx.doi.org/10.1063/1.2768624 (3 pages) | Cited 306 times

Online Publication Date: 10 August 2007

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Microfabrication of graphene devices used in many experimental studies currently relies on the fact that graphene crystallites can be visualized using optical microscopy if prepared on top of Si wafers with a certain thickness of SiO2. The authors study graphene’s visibility and show that it depends strongly on both thickness of SiO2 and light wavelength. They have found that by using monochromatic illumination, graphene can be isolated for any SiO2 thickness, albeit 300 nm (the current standard) and, especially, ≈ 100 nm are most suitable for its visual detection. By using a Fresnel-law-based model, they quantitatively describe the experimental data.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Visibility of graphene flakes on a dielectric substrate

D. S. L. Abergel, A. Russell, and Vladimir I. Fal’ko

Appl. Phys. Lett. 91, 063125 (2007); http://dx.doi.org/10.1063/1.2768625 (3 pages) | Cited 92 times

Online Publication Date: 10 August 2007

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The authors model the optical visibility of monolayer and bilayer graphene deposited on a SiO2/Si substrate or thermally annealed on the surface of SiC. Visibility is much stonger in reflection than in transmission, reaching the optimum conditions when the bare substrate transmits light resonantly. In the optical range of frequencies a bilayer is approximately twice as visible as a monolayer thereby making the two types of graphene distinguishable from each other.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.40.Fy Semiconductors
81.40.Gh Other heat and thermomechanical treatments
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