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8 Oct 2007

Volume 91, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 91, 153101 (2007); http://dx.doi.org/10.1063/1.2793688 (3 pages)

B. J. Lee, K. Park, and Z. M. Zhang
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Energy pathways in nanoscale thermal radiation

B. J. Lee, K. Park, and Z. M. Zhang

Appl. Phys. Lett. 91, 153101 (2007); http://dx.doi.org/10.1063/1.2793688 (3 pages) | Cited 10 times

Online Publication Date: 8 October 2007

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We show in this letter that when nanoscale radiation between two parallel plates is considered, the Poynting vector is decoupled for each parallel wavevector component (β) due to the nature of thermal emission, as manifested by the fluctuation-dissipation theorem. The streamlines calculated by tracing the Poynting vector vividly demonstrate that the spectral radiative energy travels in infinite directions along curved lines. Depending on the β value, the energy pathway may exhibit considerable lateral shift. This letter elucidates the fundamental characteristics of nanoscale thermal radiation that is important for applications, such as near-field optical sensors and energy conversion devices.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Thermally induced capacitive effect of a nanoporous monel

Yu Qiao, Venkata K. Punyamurtula, and Aijie Han

Appl. Phys. Lett. 91, 153102 (2007); http://dx.doi.org/10.1063/1.2798245 (3 pages) | Cited 4 times

Online Publication Date: 8 October 2007

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As temperature changes, the equilibrium condition at a solid-liquid interface would be disrupted and the ion density varies, which, in turn, affects the interface potential. In the current study, this phenomenon is analyzed by using nanoporous monel electrodes. The experimental data show that, as the ion density is thermally adjusted, the capacitive effect leads to a significant thermal-to-electric energy conversion.
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84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
82.45.Fk Electrodes
82.45.Yz Nanostructured materials in electrochemistry

Nanopore in metal-dielectric sandwich for DNA position control

Stas Polonsky, Steve Rossnagel, and Gustavo Stolovitzky

Appl. Phys. Lett. 91, 153103 (2007); http://dx.doi.org/10.1063/1.2798247 (3 pages) | Cited 18 times

Online Publication Date: 8 October 2007

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We present the concept of a nanoelectromechanical device capable of controlling the position of DNA inside a nanopore with a single nucleotide accuracy. The device utilizes the interaction of discrete charges along the backbone of a DNA molecule with the electric field inside the nanopore. In analogy to solid state transistors in which a small voltage controls the current between two electrodes, a voltage strategically located inside the nanopore can control the translocation of a single DNA molecule between a cis and a trans reservoirs. We propose an immediate application of the device as a replacement of capillary electrophoresis in DNA sequencing.
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82.37.Rs Single molecule manipulation of proteins and other biological molecules
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.39.Pj Nucleic acids, DNA and RNA bases

Structural characterization and low temperature growth of ferromagnetic Bi–Cu codoped ZnO bicrystal nanowires

C. Xu, J. Chun, D. Kim, B. Chon, and T. Joo

Appl. Phys. Lett. 91, 153104 (2007); http://dx.doi.org/10.1063/1.2791005 (3 pages) | Cited 8 times

Online Publication Date: 8 October 2007

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Ferromagnetic Bi–Cu codoped ZnO nanowires were fabricated at temperatures as low as 300 °C via a vapor phase transport using the mixture of Zn, BiI3 and CuI powders. They are grown as a bicrystal, along the [01math2] direction, have a width of 40–150 nm, and a length of a few microns. The investigation of the growth mechanism proposes that the synergy of BiCu and iodine/iodide induces the formation of bicrystallinity. The photoluminescence measurement shows the cooperative effect of Bi and Cu ions. The ferromagnetism observed in this study is the result of the combined effect of structural defects, the substitution of Cu into Zn site along the c axis, and codoping of Bi.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires
75.50.Pp Magnetic semiconductors
78.55.Et II-VI semiconductors

Spin field effect transistor with a graphene channel

Y. G. Semenov, K. W. Kim, and J. M. Zavada

Appl. Phys. Lett. 91, 153105 (2007); http://dx.doi.org/10.1063/1.2798596 (3 pages) | Cited 36 times

Online Publication Date: 9 October 2007

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A spin field effect transistor (FET) is proposed by utilizing a graphene layer as the channel. Similar to the conventional spin FETs, the device involves spin injection and spin detection by ferromagnetic source and drain. Due to the negligible spin-orbit coupling in the carbon based materials, spin manipulation in the channel is achieved via electrical control of the electron exchange interaction with a ferromagnetic gate dielectric. Numerical estimates indicate the feasibility of the concept if the bias can induce a change in the exchange interaction energy of the order of meV. When nanoribbons are used for a finite channel width, those with armchair-type edges can maintain the device stability against the thermal dispersion.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Enhancing the optical properties of InAs quantum dots by an InAlAsSb overgrown layer

Pei-Chin Chiu, Wei-Sheng Liu, Meng-Jie Shiau, Jen-Inn Chyi, Wen-Yen Chen, Hsing-Szu Chang, and Tzu-Min Hsu

Appl. Phys. Lett. 91, 153106 (2007); http://dx.doi.org/10.1063/1.2798601 (3 pages) | Cited 5 times

Online Publication Date: 9 October 2007

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The optical properties of InAs quantum dots (QDs) with a GaAs, an InAlAs, or an InAlAsSb overgrown layer are studied. For the InAs QDs with an InAlAsSb overgrown layer, their room temperature photoluminescence intensity is enhanced by as much as 4.5-fold compared to that of the QDs with an InAlAs one while maintaining similar narrow linewidth (26 meV) and large ground-to first excited-state separation (103 meV). The increase in radiative efficiency of the InAs/InAlAsSb heterostructure is attributed to its better material quality due to the surfactant nature of Sb adatoms.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Study of inorganic fullerenes and carbon nanotubes by in situ Raman tribometry

L. Joly-Pottuz, J. M. Martin, M. Belin, F. Dassenoy, G. Montagnac, and B. Reynard

Appl. Phys. Lett. 91, 153107 (2007); http://dx.doi.org/10.1063/1.2790077 (3 pages) | Cited 7 times

Online Publication Date: 9 October 2007

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Nanoparticles such as inorganic fullerenes of metal dichalcogenides or carbon nanotubes have been recently used as lubricant additives and they present excellent tribological properties. Raman spectroscopy is a useful technique to follow modification of these two structures. We developed an original tribometer able to perform in situ Raman analyses during sliding steel on a sapphire flat. These analyses gave unique information on real-time structural changes of nanoparticles inside the contact area: inorganic fullerenes are tribologically active by a progressive exfoliation process and carbon nanotubes is changed to amorphous carbon. Lubrication mechanism of these particles are explained in the light of analytical results.
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81.05.ub Fullerenes and related materials
81.07.De Nanotubes
62.20.Qp Friction, tribology, and hardness
81.70.Fy Nondestructive testing: optical methods

Photon-induced formation of CdS nanocrystals in selected areas of polymer matrices

Athanassia Athanassiou, Roberto Cingolani, Elsa Tsiranidou, Costas Fotakis, Anna Maria Laera, Emanuela Piscopiello, and Leander Tapfer

Appl. Phys. Lett. 91, 153108 (2007); http://dx.doi.org/10.1063/1.2790484 (3 pages) | Cited 3 times

Online Publication Date: 10 October 2007

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We demonstrate light-induced formation of semiconductor quantum dots in TOPAS® polymer matrix with very high control of their size and their spatial localization. Irradiation with UV laser pulses of polymer films embedding Cd thiolate precursors results in the formation of cadmium sulfide nanocrystals well confined in the irradiation area, through a macroscopically nondestructive procedure for the host matrix. With increasing number of laser pulses, we accomplish the formation of nanoparticles with gradually increasing dimensions, resulting in the dynamic change of the spectra emitted by the formed nanocomposite areas. The findings are supported by x-ray diffraction and transmission electron microscopy measurements.
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61.82.Pv Polymers, organic compounds
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.07.Bc Nanocrystalline materials
81.16.Mk Laser-assisted deposition

Characterization of nanostructures during growth using a quartz monitor

A. B. Phillips and B. S. Shivaram

Appl. Phys. Lett. 91, 153109 (2007); http://dx.doi.org/10.1063/1.2798249 (3 pages) | Cited 3 times

Online Publication Date: 10 October 2007

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The quartz thickness monitor, a high Q mechanical device, is ubiquitous in thin film deposition applications. It provides information that is one dimensional—the average thickness of the film. In this letter, we describe a method where a related device, a surface acoustic wave resonator, employed as a gravimetric sensor has been used to ascertain the radius of freestanding spherical nanoparticles. Direct measurements of particle size through scanning electron microscopy confirm the validity of this method. Its success implies that use of high Q mechanical oscillators can be extended to extract the lateral extent of nanostructures during growth.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
84.30.Ng Oscillators, pulse generators, and function generators

Self-assembly of CdSe/ZnSe(001) quantum dot structures mediated by a tellurium cap layer

S. Mahapatra, K. Brunner, and C. Bougerol

Appl. Phys. Lett. 91, 153110 (2007); http://dx.doi.org/10.1063/1.2798251 (3 pages) | Cited 3 times

Online Publication Date: 10 October 2007

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Ensembles of CdSe/ZnSe quantum dots (QDs), with different self-assembled patterns, have been realized by depositing amorphous Te (a-Te) onto an epitaxial CdSe layer and subsequently desorbing it. During temperature ramp up for desorption, Te forms an epitaxially oriented polycrystalline layer along the grain boundaries of which, desorption initiates. Consequently, the underlying CdSe layer is first exposed in narrow trenches, within which QDs nucleate preferentially. The morphology of the polycrystalline Te layer, which strongly depends on the a-Te cap layer thickness, governs the spatial pattern of the QDs. By a variant technique, wherein a noncrystallizing amorphous layer is intentionally patterned before desorption, QDs might be positioned on predefined sites.
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81.07.Ta Quantum dots
81.05.Dz II-VI semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
68.43.Mn Adsorption kinetics
61.72.Mm Grain and twin boundaries

Gigahertz frequency flexible carbon nanotube transistors

N. Chimot, V. Derycke, M. F. Goffman, J. P. Bourgoin, H. Happy, and G. Dambrine

Appl. Phys. Lett. 91, 153111 (2007); http://dx.doi.org/10.1063/1.2798583 (3 pages) | Cited 21 times

Online Publication Date: 10 October 2007

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We investigate the high frequency performances of flexible field-effect transistors based on carbon nanotubes. A large density of mostly aligned carbon nanotubes deposited on a flexible substrate by dielectrophoresis serves as the channel. The transistors display a constant transconductance up to at least 6 GHz and a current gain cutoff frequency (fT) as high as 1 GHz at VDS = −700 mV. Bending tests show that the devices can withstand a high degree of flexion characterized by a constant transconductance for radius of curvature as small as 3.3 mm.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Structure and magnetism in VO2 nanorods

Jitae Park, In Hwan Oh, Eunmo Lee, Kyu Won Lee, Cheol Eui Lee, Kyung Song, and Youn-Joong Kim

Appl. Phys. Lett. 91, 153112 (2007); http://dx.doi.org/10.1063/1.2798587 (3 pages) | Cited 12 times

Online Publication Date: 10 October 2007

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The structural and magnetic properties in vanadium dioxide (VO2) nanorods prepared by the hydrothermal treatment are shown to be markedly different from the case of the bulk system. A peculiar mixed phase of an insulating monoclinic structure (M2) that is observed in the bulk systems under doping or stress and a rutile (R) structure was revealed and confirmed by transmission electron microscopy, x-ray diffraction, and electron spin resonance measurements. Besides, a broad transition from a high-temperature magnetic phase to a low-temperature one, with quite distinct magnetic correlation strengths, was observed.
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75.75.-c Magnetic properties of nanostructures
71.27.+a Strongly correlated electron systems; heavy fermions
61.46.-w Structure of nanoscale materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Controllable modification of transport properties of single-walled carbon nanotube field effect transistors with in situ Al decoration

Hyo-Suk Kim, Byoung-Kye Kim, Ju-Jin Kim, Jeong-O Lee, and Noejung Park

Appl. Phys. Lett. 91, 153113 (2007); http://dx.doi.org/10.1063/1.2798590 (3 pages) | Cited 11 times

Online Publication Date: 10 October 2007

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We use an in situ Al decoration technique to control the transport characteristics of single-walled carbon nanotube field effect transistors (SWNT-FETs). Al nanoparticle decoration in a high vacuum caused the devices to change from p-type to n-type FETs, and subsequent exposure to the ambient atmosphere induced a gradual recovery of p-type character. In comparison with the bare SWNT-FETs under high vacuum, the channel-open devices with decorated Al particles exhibited reduced current under ambient conditions. However, selective Al decoration only at the contact resulted in an improved p-type current in ambient air.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices

Highly parallel mix-and-match fabrication of nanopillar arrays integrated in microfluidic channels for long DNA molecule separation

J. Shi, A. P. Fang, L. Malaquin, A. Pépin, D. Decanini, J. L. Viovy, and Y. Chen

Appl. Phys. Lett. 91, 153114 (2007); http://dx.doi.org/10.1063/1.2793616 (3 pages) | Cited 15 times

Online Publication Date: 11 October 2007

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We report on a mix-and-match method based on a combination of soft UV nanoimprint lithography, contact optical lithography, and reactive-ion-etch techniques, which is applicable for high throughput manufacturing of nanostructure integrated microfluidic devices. We demonstrate the integration of high density and high aspect ratio nanopillars into microfluidic channels as electrophoresis sieving matrices. As a result, λ DNA and T4 DNA can be separated within a few minutes. By changing the pattern design, the device could be used for separation of other types of molecules.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.15.Tt Electrophoresis
47.61.-k Micro- and nano- scale flow phenomena

Nanolasers to enable data storage beyond 10 Tbit/in.2

Rabee Ikkawi, Nissim Amos, Alexander Krichevsky, Roman Chomko, Dmitri Litvinov, and Sakhrat Khizroev

Appl. Phys. Lett. 91, 153115 (2007); http://dx.doi.org/10.1063/1.2799239 (2 pages) | Cited 3 times

Online Publication Date: 11 October 2007

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A focused ion beam (FIB) fabricated nanolaser is demonstrated to be able to focus light with power of over 250 nW into a 30 nm spot. To fabricate a nanolaser, a 100 nm thick aluminum film was deposited on the emitting edge of a diode laser. FIB was used to etch various apertures into the film. The power was measured by a scanning near-field optical microscope in the near-field regime with a 10 nm separation between the probe and the air bearing surface of the nanolaser. Out of four different shapes under study, “C”-shape aperture was found to have the highest throughput.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.16.Nd Micro- and nanolithography
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Effects of compressive strains on electrical conductivities of a macroscale carbon nanotube block

Victor L. Pushparaj, Lijie Ci, Subbalakshmi Sreekala, Ashavani Kumar, Sai Kesapragada, Daniel Gall, Omkaram Nalamasu, Ajayan M. Pulickel, and Jonghwan Suhr

Appl. Phys. Lett. 91, 153116 (2007); http://dx.doi.org/10.1063/1.2798599 (3 pages) | Cited 17 times

Online Publication Date: 11 October 2007

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A macroscopic block ( ∼ 9 mm3) of aligned carbon nanotubes (CNTs) was grown by chemical vapor deposition and its simultaneous electrical conductivity and compressive strain responses were measured parallel and perpendicular to the CNT alignment. The block exhibits elastic moduli of 0.9 and 1.6 MPa for compressive strain of <20% in parallel and perpendicular configurations, respectively. The electrical conductivity increases with increasing compressive strain in both configurations. The reversible electrical conductivity and compressive strain responses of block is attributed to elastic bending of CNTs. These excellent properties of CNT block can be used in compressive strain sensing applications.
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73.63.Fg Nanotubes
62.25.-g Mechanical properties of nanoscale systems
61.46.Fg Nanotubes
81.40.Lm Deformation, plasticity, and creep
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations

SmCo5/Fe nanocomposites synthesized from reductive annealing of oxide nanoparticles

Yanglong Hou, Shouheng Sun, Chuanbing Rong, and J. Ping Liu

Appl. Phys. Lett. 91, 153117 (2007); http://dx.doi.org/10.1063/1.2799170 (3 pages) | Cited 17 times

Online Publication Date: 12 October 2007

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Hard magnetic nanocomposites SmCo5/Fex (x = 0–2.9) are synthesized by a simultaneous calcium reduction of Sm–Co–O and Fe3O4 nanoparticles. The composites consist of nanostructured SmCo5 and Fe with their average grain sizes at 29 and 8 nm, respectively. The magnetic properties of the composites can be tuned by controlling Fe composition. SmCo5/Fe1.5 shows an enhanced remanent magnetization at 56 emu/g (45 emu/g for SmCo5). The largest coercivity value of 11.6 kOe is achieved with SmCo5/Fe0.23. The synthesis represents a general process toward SmCo-based exchange-spring nanocomposites for high performance permanent magnet applications.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
75.50.Bb Fe and its alloys
81.40.Gh Other heat and thermomechanical treatments
75.50.Ww Permanent magnets
82.30.-b Specific chemical reactions; reaction mechanisms
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