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19 May 2008

Volume 92, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 92, 202101 (2008); http://dx.doi.org/10.1063/1.2927379 (3 pages)

Jasmin Aghassi, Matthias H. Hettler, and Gerd Schön
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Nitrogen-induced intermixing of InAsN quantum dots with the GaAs matrix

L. Ivanova, H. Eisele, A. Lenz, R. Timm, M. Dähne, O. Schumann, L. Geelhaar, and H. Riechert

Appl. Phys. Lett. 92, 203101 (2008); http://dx.doi.org/10.1063/1.2919053 (3 pages) | Cited 9 times

Online Publication Date: 19 May 2008

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We investigated the influence of nitrogen incorporation on the growth of InAsN/GaAs quantum dots (QDs) using cross-sectional scanning tunneling microscopy. Nitrogen exposure during InAs growth leads to a rather strong dissolution and the formation of extended almost spherical InGaAs QDs with a very low nitrogen content. Nitrogen atoms are instead observed in the surrounding GaAs matrix, and indium atoms are even found underneath the nominal base plane of the QDs. These effects are related to a rather low solubility of nitrogen within InAs, leading to high strain between indium-rich QDs and the surrounding nitrogen-rich matrix.
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81.05.Ea III-V semiconductors
87.64.Dz Scanning tunneling and atomic force microscopy
68.65.Hb Quantum dots (patterned in quantum wells)
64.75.Bc Solubility

Conformal Al2O3 dielectric layer deposited by atomic layer deposition for graphene-based nanoelectronics

Bongki Lee, Seong-Yong Park, Hyun-Chul Kim, KyeongJae Cho, Eric M. Vogel, Moon J. Kim, Robert M. Wallace, and Jiyoung Kim

Appl. Phys. Lett. 92, 203102 (2008); http://dx.doi.org/10.1063/1.2928228 (3 pages) | Cited 55 times

Online Publication Date: 20 May 2008

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We present a facile route which combines the functionalization of a highly oriented pyrolytic graphite surface with an atomic layer deposition (ALD) process to allow for conformal Al2O3 layers. While the trimethylaluminum (TMA)/H2O process caused selective deposition only along step edges, the TMA/O3 process began to provide nucleation sites on the basal planes of the surface. O3 pretreatment, immediately followed by the ALD process with TMA/O3 chemistry, formed Al2O3 layers without any preferential deposition at the step edges. This is attributed to functionalization of graphene by ozone treatment, imparting a hydrophilic character which is desirable for ALD deposition.
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81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
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Fabrication of graphene p-n-p junctions with contactless top gates

Gang Liu, Jairo Velasco, Jr., Wenzhong Bao, and Chun Ning Lau

Appl. Phys. Lett. 92, 203103 (2008); http://dx.doi.org/10.1063/1.2928234 (3 pages) | Cited 48 times

Online Publication Date: 20 May 2008

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We developed a multilevel lithography process to fabricate graphene p-n-p junctions with contactless, suspended top gates. This fabrication procedure minimizes damage or doping to the single atomic layer, which is only exposed to conventional resists and developers. The process does not require special equipment for depositing gate dielectrics or releasing sacrificial layers, and is compatible with annealing procedures that improve device mobility. Using this technique, we fabricate graphene devices with suspended local top gates, where the creation of high quality graphene p-n-p junctions is confirmed by transport data at zero and high magnetic fields.
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81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Cc Kinetics of defect formation and annealing

Focusing of surface phonon polaritons

A. J. Huber, B. Deutsch, L. Novotny, and R. Hillenbrand

Appl. Phys. Lett. 92, 203104 (2008); http://dx.doi.org/10.1063/1.2930681 (3 pages) | Cited 11 times

Online Publication Date: 20 May 2008

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Surface phonon polaritons (SPs) on crystal substrates have applications in microscopy, biosensing, and photonics. Here, we demonstrate focusing of SPs on a silicon carbide (SiC) crystal. A simple metal-film element is fabricated on the SiC sample in order to focus the surface waves. Pseudoheterodyne scanning near-field infrared microscopy is used to obtain amplitude and phase maps of the local fields verifying the enhanced amplitude in the focus. Simulations of this system are presented, based on a modified Huygens’ principle, which show good agreement with the experimental results.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.Ja Surface and interface dynamics and vibrations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
68.37.Uv Near-field scanning microscopy and spectroscopy

Edge-truncated cubic platinum nanoparticles as anode catalysts for direct methanol fuel cells

Y. G. Liu, S. L. Shi, X. Y. Xue, J. Y. Zhang, Y. G. Wang, and T. H. Wang

Appl. Phys. Lett. 92, 203105 (2008); http://dx.doi.org/10.1063/1.2928223 (3 pages) | Cited 2 times

Online Publication Date: 21 May 2008

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The edge-truncated cubic platinum nanoparticles (ECPs) are synthesized with the addition of silver ions. The nanoparticle is closed by 6 {100} facets and 12 {110} facets, confirmed from the transmission electron microscopy and cyclic voltammogram (CV) results. The current density increases up to a maximum of 1.05 mA cm−2 (Jf) during the forward sweep. A current density ratio value of 1.12 and the sharp initial current drop in the CV reveal that the tailored facets of the ECPs dominate the methanol oxidation behaviors. Our results show promising anode catalysts of truncated-edge cubic platinum nanoparticles for direct methanol fuel cells.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.47.Pm Phosphoric-acid fuel cells (PAFC); other fuel cells

Configuration control of quantum dot molecules by droplet epitaxy

K. A. Sablon, J. H. Lee, Zh. M. Wang, J. H. Shultz, and G. J. Salamo

Appl. Phys. Lett. 92, 203106 (2008); http://dx.doi.org/10.1063/1.2924308 (3 pages) | Cited 29 times

Online Publication Date: 21 May 2008

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We demonstrate that by changing the substrate temperature at which Ga droplets form and by varying the InAs deposition, we are able to control the configuration of quantum dots per GaAs mound. The size of the Ga droplets increases with increasing substrate temperature and resulting configurations show a very strong correlation with the size of initial GaAs islands. In distinction from previous reports, we attained two structures: quadmolecules and quantum rod pairs. Quadmolecules are elongated along the [011] crystallographic direction due to strain-driven processes and are directly formed at the edges of the GaAs mounds. On the other hand, quantum rod pairs formed along the [01−1] direction due to higher anisotropic diffusion.
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68.65.Hb Quantum dots (patterned in quantum wells)

Vacancy engineering by optimized laser irradiation in boron-implanted, preamorphized silicon substrate

D. X. M. Tan, K. L. Pey, K. K. Ong, B. Colombeau, C. M. Ng, S. H. Yeong, A. T. S. Wee, C. J. Liu, and X. C. Wang

Appl. Phys. Lett. 92, 203107 (2008); http://dx.doi.org/10.1063/1.2930687 (3 pages)

Online Publication Date: 21 May 2008

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In this letter, the effect of vacancies generated by preirradiated laser on dopant diffusion and activation in preamorphized silicon substrate has been studied. Laser-induced melting in silicon was used to generate excess vacancies near the maximum melt depth before silicon substrate amorphization and subsequent boron implantation. We demonstrate that by matching the preirradiated laser melt depth with the implant amorphize depth, it can effectively reduce the silicon self-interstitials released from the end-of-range defect band. The results show great suppression in boron transient enhanced diffusion and significant removal of end-of-range defects. This is attributed to the recombination of laser-generated excess vacancies with preamorphizing induced free silicon interstitials at the end-of-range region.
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61.72.jd Vacancies
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
61.72.uf Ge and Si
66.30.J- Diffusion of impurities
64.70.dj Melting of specific substances

Theoretical investigation of the relationships between magnetic circular dichroism signals and Gilbert damping coefficient in magnetic films

Jie Lu and Peng Yan

Appl. Phys. Lett. 92, 203108 (2008); http://dx.doi.org/10.1063/1.2920804 (3 pages)

Online Publication Date: 22 May 2008

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Inspired by the traditional ferromagnetic resonance (FMR) approach, the relationships between two kinds of magnetic circular dichroism signals and the Gilbert damping coefficient in magnetic films are theoretically investigated within linear response framework. These results may provide inspirations on potential experimental strategies to remeasure the Gilbert damping coefficient, which is traditionally obtained from FMR technique.
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75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Tunable electronic band structures of hydrogen-terminated ⟨112⟩ silicon nanowires

A. J. Lu, R. Q. Zhang, and S. T. Lee

Appl. Phys. Lett. 92, 203109 (2008); http://dx.doi.org/10.1063/1.2936088 (3 pages) | Cited 15 times

Online Publication Date: 22 May 2008

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The possibility of inducing indirect-to-direct band gap transition in silicon nanowires (SiNWs) by changing wire diameter is well known. Here, we show that for ⟨112⟩-oriented SiNWs indirect-to-direct band gap transition can be tuned simply by changing the wire cross-section shape or the cross-sectional aspect ratio of the (111) and (110) facets that enclose the wire, instead of changing the wire diameter. The cross-sectional aspect ratio must be smaller than 0.5 in order to maintain a direct band gap, indicating the important role of the (110) facet.
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73.21.Hb Quantum wires
73.22.-f Electronic structure of nanoscale materials and related systems
68.65.La Quantum wires (patterned in quantum wells)
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)

Residual strain in ZnO nanowires grown by catalyst-free chemical vapor deposition on GaN/sapphire (0001)

F. C. Tsao, J. Y. Chen, C. H. Kuo, G. C. Chi, C. J. Pan, P. J. Huang, C. J. Tun, B. J. Pong, T. H. Hsueh, C. Y. Chang, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 92, 203110 (2008); http://dx.doi.org/10.1063/1.2936090 (3 pages) | Cited 9 times

Online Publication Date: 22 May 2008

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ZnO nanowires were grown on 2-μm-thick GaN templates by chemical vapor deposition without employing any metal catalysts. The GaN template was deposited by metal-organic chemical vapor deposition on a c-plane sapphire substrate. The diameters of the resulting nanowires were in the range of 40–250 nm depending on growth time. The ZnO nanowires were vertically well aligned with uniform length, diameter, and distribution density as revealed by electron microscopy. X-ray diffraction spectra showed that ZnO grew in single c-axis orientation with the c axis normal to the GaN basal plane, indicating a heteroepitaxial relationship of (0002)ZnO‖(0002)GaN. The lattice constant of the c axis of the ZnO nanowires with diameter of 40 nm was 5.211 Å, which is larger than that of bulk ZnO (5.207 Å). The ZnO nanowires exhibit a residual tensile strain along the c axis, which decreases with increasing diameter.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
61.66.Fn Inorganic compounds

Miniaturization of photonic waveguides by the use of left-handed materials

Philippe Tassin, Xavier Sahyoun, and Irina Veretennicoff

Appl. Phys. Lett. 92, 203111 (2008); http://dx.doi.org/10.1063/1.2936299 (3 pages) | Cited 13 times

Online Publication Date: 22 May 2008

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We propose the use of a left-handed material in an optical waveguide structure to reduce its thickness well below the wavelength of light. We demonstrate that a layer of left-handed material, added to the cladding of a planar waveguide rather than to its core, allows for good light confinement in a subwavelength thin waveguide. We attribute the observed behavior to the change in phase evolution of electromagnetic waves in the guide. This technique can be used for the miniaturization of photonic integrated circuits.
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42.82.Et Waveguides, couplers, and arrays
42.70.-a Optical materials

Lithiated assemblies of metal chalcogenide nanowires

P. Murugan, Vijay Kumar, Yoshiyuki Kawazoe, and Norio Ota

Appl. Phys. Lett. 92, 203112 (2008); http://dx.doi.org/10.1063/1.2920437 (3 pages) | Cited 3 times

Online Publication Date: 22 May 2008

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We study hexagonal assemblies of M6X6 (M = Mo and W and X = S, Se, and Te) nanowires from first-principles calculations to understand their structural stability, electronic properties, and the effects of Li intercalation. It is shown that due to van der Waals interactions between the nanowires, the intercalation is achieved without a significant change in their atomic structure. With an increase in Li concentration, we predict a new phase for Li3Mo6S6 compound, in which the hexagonal assembly transforms to a monoclinic structure by a change in the orientation of nanowires. The LixMo6S6 assemblies are electrically conductive and can be potentially used as cathode materials in Li-ion batteries for nanoscale applications. The voltage of such a battery, calculated to be 1.7 V, can be manipulated such as by iodine doping without a significant change in the atomic structure.
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82.47.Aa Lithium-ion batteries
61.46.-w Structure of nanoscale materials
71.20.Ps Other inorganic compounds
73.63.-b Electronic transport in nanoscale materials and structures
71.15.-m Methods of electronic structure calculations

UV-induced surface electrical conductivity jump of polymer nanocomposites

Guang-Xin Chen, Masahiro Miyauchi, and Hiroshi Shimizu

Appl. Phys. Lett. 92, 203113 (2008); http://dx.doi.org/10.1063/1.2918442 (3 pages)

Online Publication Date: 23 May 2008

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A method of improving the electrical conductivity of polymer nanocomposites under UV irradiation was described. An anatase TiO2-grafted carbon nanotube could function as a conductive filler and a photocatalyst when it compounds with a poly(L-lactide) to produce a composite. After UV irradiation, the decomposition of the polymer only occurred on the surface of a poly(L-lactide)/TiO2 grafted carbon nanotube composite and not on bulk, resulting in an electrical conductivity jump as high as six orders of magnitude.
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73.25.+i Surface conductivity and carrier phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.50.Hp Processes caused by visible and UV light
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Low resistivity of Pt silicide nanowires measured using double-scanning-probe tunneling microscope

Do Kyung Lim, Osamu Kubo, Yoshitaka Shingaya, Tomonobu Nakayama, Young Heon Kim, Jeong Yong Lee, Masakazu Aono, Hangil Lee, Dohyun Lee, and Sehun Kim

Appl. Phys. Lett. 92, 203114 (2008); http://dx.doi.org/10.1063/1.2935329 (3 pages) | Cited 9 times

Online Publication Date: 23 May 2008

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We measure the resistivity of platinum-silicide nanowires (Pt2Si NWs) epitaxially formed on a Si(100) surface using double-scanning-probe tunneling microscope. Despite the large Schottky barrier height reported on a macroscopic Pt2Si/n-Si interface, leakage current through the substrate is observed in the resistance measurement, and is quantitatively estimated to be separated from the current through the nanowire. The measured resistivity of Pt2Si NWs is about half the reported resistivity of thick Pt2Si films, which could be due to additional conduction paths through surface or interface states on NWs.
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73.63.Nm Quantum wires
73.30.+y Surface double layers, Schottky barriers, and work functions
73.21.Hb Quantum wires
73.20.At Surface states, band structure, electron density of states

Mesoscale reverse stick-slip nanofriction behavior of vertically aligned multiwalled carbon nanotube superlattices

J. Lou, F. Ding, H. Lu, J. Goldman, Y. Sun, and B. I. Yakobson

Appl. Phys. Lett. 92, 203115 (2008); http://dx.doi.org/10.1063/1.2936866 (3 pages)

Online Publication Date: 23 May 2008

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Characteristics of sliding friction behaviors of vertically aligned multiwalled carbon nanotube (CNT) superlattices have been investigated in this letter. Friction force was measured using both regular atomic force microscopy (AFM) probe and colloidal AFM probe consisting of a 15 μm diameter borosilicate sphere attached to the end of regular cantilever. A distinct reverse stick-slip behavior was observed in the current study compared to the usual stick-slip behavior reported in literature. It was found that this reverse stick-slip behavior was primarily due to the combined effects of surface topology and elastic deformation of CNTs, which were verified by experiments and atomistic simulations.
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81.40.Pq Friction, lubrication, and wear
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.25.-g Mechanical properties of nanoscale systems
62.20.D- Elasticity
62.20.F- Deformation and plasticity
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Thermoelectric properties of aligned carbon nanotubes

Shamim M. Mirza and H. Grebel

Appl. Phys. Lett. 92, 203116 (2008); http://dx.doi.org/10.1063/1.2931084 (3 pages) | Cited 1 time

Online Publication Date: 23 May 2008

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We have investigated the thermoelectric (TE) properties of films composed of aligned and randomly dispersed n-type, p-type, and p-n junctions. The TE voltage that was developed across aligned films was larger than the voltage developed along their axis of symmetry by a factor of almost 3. The TE voltage that developed across aligned and parallel p-n junction was almost seven times larger then the voltage developed over randomly oriented p-type only films.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Pa Thermoelectric and thermomagnetic effects

Magnéli phases TinO2n−1 nanowires: Formation, optical, and transport properties

Wei-Qiang Han and Yan Zhang

Appl. Phys. Lett. 92, 203117 (2008); http://dx.doi.org/10.1063/1.2937152 (3 pages) | Cited 5 times

Online Publication Date: 23 May 2008

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We have prepared triclinic Ti8O15 nanowires and Ti4O7 quasi-one-dimensional fibers by heat-treating thick H2Ti3O7 nanowires under hydrogen atmospheres at 850 and 1050 °C, respectively. In contrast to wide-bandgap semiconducting tetragonal TiO2, both Ti8O15 and Ti4O7 exhibit high electrical conducting behavior at room temperature. The electrical conductivities of Ti8O15 and Ti4O7 are, respectively, 0.24 and 10.4 S/cm at 300 K, and 2.4×10−5 and 4×10−3 S/cm at 77 K. In both materials, the light absorption band covers the full visible-light spectrum region and extends into the near-infrared region.
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81.16.-c Methods of micro- and nanofabrication and processing
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)
78.40.Fy Semiconductors
78.30.Hv Other nonmetallic inorganics
78.67.Lt Quantum wires
73.63.Nm Quantum wires
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