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7 Sep 2009

Volume 95, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 95, 083506 (2009); http://dx.doi.org/10.1063/1.3216851 (3 pages)

J. Z. Sun, M. C. Gaidis, E. J. O’Sullivan, E. A. Joseph, G. Hu, D. W. Abraham, J. J. Nowak, P. L. Trouilloud, Yu Lu, S. L. Brown, D. C. Worledge, and W. J. Gallagher

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Higher-order surface free energy in azimuthal nematic anchoring on nanopatterned grooves

Jin Seog Gwag, Jin Hyuk Kwon, Masahito Oh-e, Jun-ichi Niitsuma, Makoto Yoneya, and Hiroshi Yokoyama

Appl. Phys. Lett. 95, 103101 (2009); http://dx.doi.org/10.1063/1.3225556 (3 pages) | Cited 5 times

Online Publication Date: 8 September 2009

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The higher-order component in liquid crystal (LC) surface free energy beyond the Rapini–Papoular anchoring potential was examined for azimuthal anchoring by analyzing nematic LC alignment on nanogrooved surfaces treated by rubbing or photoalignment. We confirmed that the surface anchoring energy for large director deviations cannot be properly described with the Rapini–Papoular form and should include higher order contributions in a power series of sin2 ϕ, as ∑n = 12Wn sin2n ϕ, with ϕ being the azimuthal angular deviation. Based on the corrected Berreman’s theory, we obtained the anchoring ratio between the first and second order terms, W2/W1 ≈ −1/4, and the surface elastic constant, K24 ≈ −0.846K22, for 4-n-pentyl-4′-cyanobiphenyl.
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61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
68.03.Cd Surface tension and related phenomena
65.20.Jk Studies of thermodynamic properties of specific liquids
62.10.+s Mechanical properties of liquids
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Design and performance of a simple, room-temperature Ga2O3 nanowire gas sensor

S. P. Arnold, S. M. Prokes, F. K. Perkins, and M. E. Zaghloul

Appl. Phys. Lett. 95, 103102 (2009); http://dx.doi.org/10.1063/1.3223617 (3 pages) | Cited 10 times

Online Publication Date: 8 September 2009

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Ga2O3 nanowire gas sensors were fabricated using the vapor-liquid-solid method of nanowire growth over platinum interdigitated electrodes. While cheaply and easily fabricated, the sensors are capable of detecting various analytes at room temperature. As analyte is adsorbed onto the nanowire surfaces, a change in the device capacitance is measured. Fast recovery of the sensing devices, without the use of an external heat source, allows these devices to operate at low power. Capacitance is seen to increase following a Freundlich isotherm in response to increasing concentrations of analyte vapors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
81.16.-c Methods of micro- and nanofabrication and processing
68.43.Fg Adsorbate structure (binding sites, geometry)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Semiconductor behaviors of low loading multiwall carbon nanotube/poly(dimethylsiloxane) composites

C. H. Hu, C. H. Liu, L. Z. Chen, and S. S. Fan

Appl. Phys. Lett. 95, 103103 (2009); http://dx.doi.org/10.1063/1.3223777 (3 pages) | Cited 3 times

Online Publication Date: 8 September 2009

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We present a flexible electronic material fabricated by incorporating multiwall carbon nanotubes (MWNTs) into poly(dimethylsiloxane) rubber (0.35 wt % MWNT loading is most appropriate in our study). Resistance-temperature data for different composites (0.35–5 wt %) are analyzed within Coulomb gap variable range hopping model, which well explains the semiconductor behaviors in low MWNT loading composites. Field effect transistors fabricated using 0.35 wt % composite show a p-type behavior with a high effective mobility of 1.98 cm2 V s and linear transconductance 8.34×10−8 S at 2.5 V drain voltage. These results suggest an optional way of seeking for high-quality flexible electronic materials.
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81.05.Qk Reinforced polymers and polymer-based composites
81.07.De Nanotubes
85.30.Tv Field effect devices

Transparent self-assembled films of reduced graphene oxide platelets

Yanwu Zhu, Weiwei Cai, Richard D. Piner, Aruna Velamakanni, and Rodney S. Ruoff

Appl. Phys. Lett. 95, 103104 (2009); http://dx.doi.org/10.1063/1.3212862 (3 pages) | Cited 34 times

Online Publication Date: 8 September 2009

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Transparent conducting films have been fabricated in one step, combining self-assembly and chemical reduction of graphene oxide platelets dispersed in water. The films are of centimeter scale and their thickness can be controlled by the concentration of the graphene oxide suspension. The optical transmittance values at a wavelength of 550 nm were 87% and 96% for the films made from 1.5 and 0.5 mg/ml suspensions, respectively, and have sheet resistances of 11.3 and 31.7 kΩ/◻. Scanning and transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy were used to characterize the films.
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81.16.Dn Self-assembly
68.60.-p Physical properties of thin films, nonelectronic
79.60.Dp Adsorbed layers and thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators
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Direct near-field optical investigation of phase-change medium in blue-ray recordable and erasable disk

Jen-You Chu, Shen-Chuan Lo, Shu-Chen Chen, You-Chia Chang, and Juen-Kai Wang

Appl. Phys. Lett. 95, 103105 (2009); http://dx.doi.org/10.1063/1.3222901 (3 pages) | Cited 2 times

Online Publication Date: 9 September 2009

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The authors report a direct examination of recorded marks in blue-ray recordable and erasable disks with scattering-type scanning near-field optical microscopy. The optical contrasts of the crystalline and amorphous regions of the phase-change layer match with the prediction based on their optical constants. The determined spatial optical variation in the recorded marks reflects the intensity profile of the recording laser beam. The identified nanometer-sized optical features are shown to correspond to 10 nm-sized crystalline domains within the amorphous recorded marks. The revealed near-field signatures show a potential influence on the carrier-to-noise ratio of this optical storage medium.
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42.79.Vb Optical storage systems, optical disks

Origin of frequency-dependent line edge roughness: Monte Carlo and fast Fourier-transform studies

Akinori Saeki, Takahiro Kozawa, and Seiichi Tagawa

Appl. Phys. Lett. 95, 103106 (2009); http://dx.doi.org/10.1063/1.3225149 (3 pages) | Cited 1 time

Online Publication Date: 9 September 2009

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The low-frequency line edge roughness (LER) of a chemically amplified resist (CAR) has a marked effect on the quality of electrical circuits, especially those produced by sub-30-nm-scale fabrication by extreme ultraviolet lithography. We examined the origin of frequency-dependent LER by Monte Carlo and dissolution simulations of a positive-tone CAR subjected to electron beam lithography. The correlation between frequency components and LER is highlighted to clarify which component is dominant. We found that the resist process parameters, such as the exposure dose, the base quencher, and the development, cause low-frequency LER even in the absence of mesoscale resist roughness.
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85.40.Hp Lithography, masks and pattern transfer

Patterning concept for sculptured nanostructures with arbitrary periods

C. Patzig, J. Zajadacz, K. Zimmer, R. Fechner, C. Khare, and B. Rauschenbach

Appl. Phys. Lett. 95, 103107 (2009); http://dx.doi.org/10.1063/1.3222911 (3 pages) | Cited 3 times

Online Publication Date: 9 September 2009

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An approach to deposit sculptured nanostructures with arbitrary interstructure spacing is presented. Based on a combination of glancing angle deposition with a preceding two-step electron beam lithography substrate patterning, the concept allows the deposition of nanostructures on artificial seeds at any predetermined place on the substrate. Due to the glancing angle deposition principle, with the help of an appropriate substrate rotation during deposition, those structures can additionally be shaped into nearly arbitrary morphologies. To demonstrate the feasibility of the proposed method, separated sculptured nanostructures of silicon with interstructure spacings of (10–20) μm were assembled.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials

Tuning electronic and magnetic properties of graphene by surface modification

Jian Zhou, Miao Miao Wu, Xiao Zhou, and Qiang Sun

Appl. Phys. Lett. 95, 103108 (2009); http://dx.doi.org/10.1063/1.3225154 (3 pages) | Cited 44 times

Online Publication Date: 9 September 2009

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We have demonstrated that the electronic and magnetic properties of graphene sheet can be delicately tuned by surface modification. Applying an external electric field to a fully hydrogenated graphene sheet can unload hydrogen atoms on one side, while keeping the hydrogen atoms on the other side, thus forming a half-hydrogenated graphene sheet, where the unpaired electrons in the unsaturated C sites give rise to magnetic moments, coupled through extended p-p interactions. Furthermore, the electronic structure of the resulting half-hydrogenated graphene sheet can be further tuned by introducing F atoms on the other side, making a nonmagnetic semiconductor with a direct band gap.
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71.20.Tx Fullerenes and related materials; intercalation compounds
75.30.Cr Saturation moments and magnetic susceptibilities

Cutting and self-healing molecular wires studied by dynamic force microscopy

S. Kawai, S. Maier, Th. Glatzel, S. Koch, B. Such, L. Zimmerli, L.-A. Fendt, F. Diederich, and E. Meyer

Appl. Phys. Lett. 95, 103109 (2009); http://dx.doi.org/10.1063/1.3216057 (3 pages) | Cited 5 times

Online Publication Date: 9 September 2009

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Tip-induced deformations of meso-(4-cyanophenyl)-substituted Zn(II) porphyrin molecular wires self-assembled on KBr(001) were studied by frequency modulation dynamic force microscopy. Since the wires are weakly bonded to the KBr substrate and to the neighboring molecules, they can easily be cut by the scanning tip. We found that the damaged molecular wires self-healed at room temperature.
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85.65.+h Molecular electronic devices
84.32.Hh Inductors and coils; wiring
81.16.Dn Self-assembly

Scanning tunneling microscopy and spectroscopy of the phase change alloy Ge1Sb2Te4

D. Subramaniam, C. Pauly, M. Liebmann, M. Woda, P. Rausch, P. Merkelbach, M. Wuttig, and M. Morgenstern

Appl. Phys. Lett. 95, 103110 (2009); http://dx.doi.org/10.1063/1.3211991 (3 pages) | Cited 3 times

Online Publication Date: 9 September 2009

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Scanning tunneling microscopy and spectroscopy have been employed to reveal the evolution of the band gap and the Fermi level as a function of the annealing temperature for Ge1Sb2Te4, a promising material for phase change memory applications. The band gap decreases continuously from 0.65 eV in the amorphous phase via 0.3 eV in the metastable crystalline phase to zero gap in the stable crystalline phase. The Fermi level moves from the center of the gap in the amorphous phase close to the valence band within the crystalline phases. Moreover, the metastable phase has been imaged with atomic resolution, presumably showing the Te lattice at negative sample bias and the Ge/Sb/vacancy lattice at positive bias.
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73.22.-f Electronic structure of nanoscale materials and related systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.72.jd Vacancies
81.40.Gh Other heat and thermomechanical treatments

Piezoelectric nanoelectromechanical resonators based on aluminum nitride thin films

R. B. Karabalin, M. H. Matheny, X. L. Feng, E. Defaÿ, G. Le Rhun, C. Marcoux, S. Hentz, P. Andreucci, and M. L. Roukes

Appl. Phys. Lett. 95, 103111 (2009); http://dx.doi.org/10.1063/1.3216586 (3 pages) | Cited 26 times

Online Publication Date: 9 September 2009

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We demonstrate piezoelectrically actuated, electrically tunable nanomechanical resonators based on multilayers containing a 100-nm-thin aluminum nitride (AlN) layer. Efficient piezoelectric actuation of very high frequency fundamental flexural modes up to ∼ 80 MHz is demonstrated at room temperature. Thermomechanical fluctuations of AlN cantilevers measured by optical interferometry enable calibration of the transduction responsivity and displacement sensitivities of the resonators. Measurements and analyses show that the 100 nm AlN layer employed has an excellent piezoelectric coefficient, d31 = 2.4 pm/V. Doubly clamped AlN beams exhibit significant frequency tuning behavior with applied dc voltage.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.65.-j Piezoelectricity and electromechanical effects
77.55.-g Dielectric thin films
07.10.Cm Micromechanical devices and systems

Surface scattering effect on the electrical resistivity of single crystalline silver nanowires self-assembled on vicinal Si (001)

Qiaojian Huang, Carmen M. Lilley, and Matthias Bode

Appl. Phys. Lett. 95, 103112 (2009); http://dx.doi.org/10.1063/1.3216836 (3 pages) | Cited 10 times

Online Publication Date: 10 September 2009

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Fundamental questions as to the nature of electron surface scattering in nanoscale materials remain unanswered. In order to isolate the effects of surface scattering from grain boundary scattering, single crystalline trapezoidal silver (Ag) nanowires were self-assembled on vicinal silicon substrate. The well established kinetic theory to model electron surface scattering effects on the electrical resistivity of nanowires was extended to include trapezoidal geometries. The experimentally measured electrical resistivity for Ag nanowires was found to fit the theoretical resistivity for the case of electrons diffusely scattering from the nanowire surface.
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73.63.-b Electronic transport in nanoscale materials and structures
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Qm Scattering mechanisms and Kondo effect
79.20.-m Impact phenomena (including electron spectra and sputtering)
81.16.Dn Self-assembly

Electrode metal dependence of the rectifying performance for molecular devices: A density functional study

X. Q. Deng, J. C. Zhou, Z. H. Zhang, G. P. Tang, and M. Qiu

Appl. Phys. Lett. 95, 103113 (2009); http://dx.doi.org/10.1063/1.3205114 (3 pages) | Cited 28 times

Online Publication Date: 11 September 2009

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Carrying out theoretical calculations using the nonequilibrium Green’s function method combined with the density functional theory, the transport properties of the terphenyl molecule connected to the two Y (Y = Li, Al, or Au) metal electrodes are investigated. The results show that the electrode metals have a distinct influence on rectifying performance of such devices. For the Au electrode system, we can observe a best rectifying performance, next for the Al electrode system, and the rectifying effect can be nearly neglected for the Li electrode system. Our findings suggest that the rectifying characteristics are intimately related to electrode materials.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.10.-d Theory of electronic transport; scattering mechanisms

Rapid and reversible hydrogen sorption in Mg–Fe–Ti thin films

Beniamin Zahiri, Chris T. Harrower, Babak Shalchi Amirkhiz, and David Mitlin

Appl. Phys. Lett. 95, 103114 (2009); http://dx.doi.org/10.1063/1.3212734 (3 pages) | Cited 16 times

Online Publication Date: 11 September 2009

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This study focused on hydrogen sorption properties of 1.5 μm thick Mg–10 at. % Fe–10 Ti, Mg–15 at. % Fe–15 Ti, and Mg–20 at. % Fe–20 Ti films. We show that the alloys display remarkable sorption behavior: At 200 °C the films are capable of absorbing nearly 5 wt % hydrogen in seconds and desorbing in minutes. Furthermore this sorption behavior is stable over cycling. In the Mg–15 at. % Fe–15 Ti alloy there is no kinetic or capacity degradation even after 100 absorption/desorption cycles. Pressure–composition isotherm data for Mg–10 at. % Fe–10 Ti indicates that the sorption enhancement is due to improved kinetics rather than any altered thermodynamics. We envision these alloys as becoming the material of choice for a variety of sensing and storage applications.
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68.43.Nr Desorption kinetics
65.40.G- Other thermodynamical quantities
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