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15 Jan 2007

Volume 90, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 032108 (2007); http://dx.doi.org/10.1063/1.2431702 (3 pages)

D. Buca, B. Holländer, S. Feste, St. Lenk, H. Trinkaus, S. Mantl, R. Loo, and M. Caymax
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Enhanced luminescence from catalyst-free grown InP nanowires

M. Mattila, T. Hakkarainen, H. Lipsanen, H. Jiang, and E. I. Kauppinen

Appl. Phys. Lett. 90, 033101 (2007); http://dx.doi.org/10.1063/1.2431711 (3 pages) | Cited 17 times

Online Publication Date: 16 January 2007

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The surface effects in the optical properties of catalyst-free grown InP nanowires are investigated. Both as-grown nanowires and nanowires treated with hydrofluoric acid are studied using low- and room-temperature continuous-wave and time-resolved photoluminescence measurements and transmission electron microscopy. It is shown that the room-temperature photoluminescence intensity is increased by two orders of magnitude after the surface treatment, and that there is also a significant increase in the double-exponential photoluminescence decay time.
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78.67.Lt Quantum wires
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
68.65.La Quantum wires (patterned in quantum wells)
81.65.-b Surface treatments
68.37.Lp Transmission electron microscopy (TEM)

Sliding of zinc oxide nanowires on silicon substrate

A. V. Desai and M. A. Haque

Appl. Phys. Lett. 90, 033102 (2007); http://dx.doi.org/10.1063/1.2431712 (3 pages) | Cited 13 times

Online Publication Date: 16 January 2007

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Adhesion and friction forces between zinc oxide nanowires and silicon substrate were studied in situ inside a scanning electron microscope. A procedure for measuring these forces from the bending profiles of the nanowires was developed and the van der Waals and friction forces were found to be about 81.05 pN and 7.7 nN, respectively. The pronounced friction was explained using nanoscale adhesion-friction coupling mechanisms. Immediate implication of the findings is on the accuracy of nanomechanical characterization using bending experiments.
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68.65.La Quantum wires (patterned in quantum wells)
68.35.Np Adhesion
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Coulomb blockade and Kondo effect in a few-electron silicon/silicon-germanium quantum dot

Levente J. Klein, Donald E. Savage, and Mark A. Eriksson

Appl. Phys. Lett. 90, 033103 (2007); http://dx.doi.org/10.1063/1.2431760 (3 pages) | Cited 15 times

Online Publication Date: 16 January 2007

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Transport measurements at cryogenic temperatures through a few-electron top gated quantum dot fabricated in a silicon/silicon-germanium heterostructure are reported. Variations in gate voltage induce a transition from an isolated dot toward a dot strongly coupled to the leads. In addition to Coulomb blockade, when the dot is strongly coupled to the leads, the authors observe the appearance of a zero bias conductance peak due to the Kondo effect. The Kondo peak splits in a magnetic field, and the splitting scales linearly with the applied field. They also observe a transition from pure Coulomb blockade to peaks with a Fano line shape.
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73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
72.25.Dc Spin polarized transport in semiconductors

Low-temperature growth of ZnO nanorods in anodic aluminum oxide on Si substrate by atomic layer deposition

Ching-Jung Yang, Shun-Min Wang, Shih-Wei Liang, Yung-Huang Chang, Chih Chen, and Jia-Min Shieh

Appl. Phys. Lett. 90, 033104 (2007); http://dx.doi.org/10.1063/1.2431786 (3 pages) | Cited 19 times

Online Publication Date: 16 January 2007

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Low-temperature growth of self-organized ZnO nanorods on Si substrate is achieved using anodic aluminum oxide and atomic layer deposition at 250 °C without catalyst or seed layer. Photoluminescence spectrum indicates that the ZnO nanorod arrays exhibit a blue∕green luminescence at 480 nm. In addition, the nanorod arrays demonstrate excellent field-emission properties with a turn-on electric field of 6.5 V μm−1 and a threshold electric field of 9.8 V μm−1, which are attributed to the perfectly perpendicular alignment of ZnO nanorods to the Si substrate.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Et II-VI semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.16.Dn Self-assembly
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials

Complete suppression of large InAs island formation on GaAs by metal organic chemical vapor deposition with periodic AsH3 interruption

Youngsoo Lee, Eungjin Ahn, Jungsub Kim, Pilkyung Moon, Changjae Yang, Euijoon Yoon, Hyunjin Lim, and Hyeonsik Cheong

Appl. Phys. Lett. 90, 033105 (2007); http://dx.doi.org/10.1063/1.2432285 (3 pages) | Cited 9 times

Online Publication Date: 16 January 2007

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Self-assembled InAs quantum dots (QDs) on GaAs substrates were grown by metal organic chemical vapor deposition with periodic AsH3 interruption. In contrast to the conventional InAs QD growth method, AsH3 was interrupted periodically while TMIn was introduced into the reactor continuously. By interrupting AsH3 periodically, the growth surface is modulated between As-stabilized surface and In-stabilized one, resulting in complete suppression of relaxed large island formation and significant improvement in photoluminescence intensity. With further optimization of growth parameters, the authors obtained the emission at 1.32 μm and narrow linewidth of 32 meV at room temperature.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

AgInSe2 nanorods: A semiconducting material for saturable absorber

Hendry I. Elim, Wei Ji, Meng-Tack Ng, and Jagadese J. Vittal

Appl. Phys. Lett. 90, 033106 (2007); http://dx.doi.org/10.1063/1.2429030 (3 pages) | Cited 5 times

Online Publication Date: 16 January 2007

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AgInSe2 nanorods (NRs) with a diameter of 15 nm have been investigated for their nonlinear optical responses by using Z-scan and transient absorption techniques with femtosecond laser pulses of photon energy greater than the band gap. At excitation irradiance of 20 GW/cm2, AgInSe2 NRs reveal saturation in the nonlinear absorption and optical Kerr nonlinearity with a recovery time determined to be a few tens of picoseconds. Such large saturable absorption and Kerr nonlinearity exhibit a third-order susceptibility of 1.2×10−8 esu and a figure of merit of 0.04 esu cm s−1, making AgInSe2 NRs a promising candidate for saturable absorption devices.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Epitaxial growth of ZnO nanowall networks on GaN/sapphire substrates

Sang-Woo Kim, Hyun-Kyu Park, Min-Su Yi, Nae-Man Park, Jong-Hyurk Park, Sang-Hyeob Kim, Sung-Lyul Maeng, Chel-Jong Choi, and Seung-Eon Moon

Appl. Phys. Lett. 90, 033107 (2007); http://dx.doi.org/10.1063/1.2430918 (3 pages) | Cited 29 times

Online Publication Date: 17 January 2007

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Heteroepitaxy of vertically well-aligned ZnO nanowall networks with a honeycomblike pattern on GaN/c-Al2O3 substrates by the help of a Au catalyst was realized. The ZnO nanowall networks with wall thicknesses of 80–140 nm and an average height of about 2 μm were grown on a self-formed ZnO thin film during the growth on the GaN/c-Al2O3 substrates. It was found that both single-crystalline ZnO nanowalls and catalytic Au have an epitaxial relation to the GaN thin film in synchrotron x-ray scattering experiments. Hydrogen-sensing properties of the ZnO nanowall networks have also been investigated.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Size-dependent piezoelectricity in zinc oxide nanofilms from first-principles calculations

Chun Li, Wanlin Guo, Yong Kong, and Huajian Gao

Appl. Phys. Lett. 90, 033108 (2007); http://dx.doi.org/10.1063/1.2430686 (3 pages) | Cited 11 times

Online Publication Date: 17 January 2007

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The size dependence of the piezoelectricity in ZnO nanofilms is investigated using ab initio density-functional theory calculations. The effective piezoelectric constant of ZnO nanofilms increases monotonically with increasing film thickness in the nanoscale simulated in the present work, and surprisingly, exceeds that of the bulk ZnO when the thickness is greater than 2.4 nm. The enhancement over the bulk value reaches 11% when the film thickness is 2.9 nm.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Bn Piezoelectric and electrostrictive constants
61.46.-w Structure of nanoscale materials

Buckling characterization of vertical ZnO nanowires using nanoindentation

Liang-Wen Ji, Sheng-Joue Young, Te-Hua Fang, and Chien-Hung Liu

Appl. Phys. Lett. 90, 033109 (2007); http://dx.doi.org/10.1063/1.2431785 (3 pages) | Cited 26 times

Online Publication Date: 17 January 2007

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Nanomechanical characterization of vertical well-aligned single-crystal ZnO nanowires on ZnO:Ga/glass templates was performed by nanoindentation technique. The buckling loads were found to be 1465 and 215 μN for the ZnO nanowires of 100 and 30 nm diameters, respectively. Furthermore, the buckling energies for the ZnO nanowires of 100 and 30 nm diameters were 3.62×10−10 and 3.69×10−11 J, respectively. Based on the Euler buckling model, Young’s modulus of the individual ZnO nanowire has been derived from two possible modes in this work.
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68.65.La Quantum wires (patterned in quantum wells)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations

Inelastic buckling of carbon nanotubes

Q. Wang, W. H. Duan, K. M. Liew, and X. Q. He

Appl. Phys. Lett. 90, 033110 (2007); http://dx.doi.org/10.1063/1.2432235 (3 pages) | Cited 29 times

Online Publication Date: 17 January 2007

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A hybrid continuum mechanics and molecular mechanics model is developed in this letter to predict the critical strain of the inelastic buckling of armchair and zigzag carbon nanotubes (CNTS) with beamlike buckle shapes. The explicit analytical buckling results of the hybrid model are verified by molecular dynamics simulations via the MATERIALS STUDIO software package and by available research findings. The simplicity and effectiveness of the model make it possible to further predict and produce benchmark solutions for the size-dependent buckling results of CNTs. The hybrid model enables thorough understanding of the stability behavior of CNTs and is useful for their applications.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Through-wafer electroplated copper interconnect with ultrafine grains and high density of nanotwins

Luhua Xu, Pradeep Dixit, Jianmin Miao, John H. L. Pang, Xi Zhang, K. N. Tu, and Robert Preisser

Appl. Phys. Lett. 90, 033111 (2007); http://dx.doi.org/10.1063/1.2432284 (3 pages) | Cited 21 times

Online Publication Date: 17 January 2007

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High aspect ratio ( ∼ 15) and ultrafine pitch ( ∼ 35 μm) through-wafer copper interconnection columns were fabricated by aspect-ratio-dependent electroplating. By controlling the process parameters, ultrafine copper grains with nanoscale twins (twin lamellar width ∼ 20 nm) were obtained in the copper columns. Transmission electron microscope reveals that the density of these nanotwins depends on the location along the length of the columns. The highest twin density was achieved at the bottom of the column where the electroplating starts. The presence of higher density of the nanotwins yields significant higher hardness ( ∼ 2.4 GPa) than that with lower twin density ( ∼ 1.8 GPa). The electrical conductivity of the electroplated copper (2.2 μΩ cm) is retained comparable to the pure copper.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
73.61.At Metal and metallic alloys

Field emission of silicon nanowires grown on carbon cloth

Baoqing Zeng, Guangyong Xiong, Shuo Chen, Wenzhong Wang, D. Z. Wang, and Z. F. Ren

Appl. Phys. Lett. 90, 033112 (2007); http://dx.doi.org/10.1063/1.2428543 (3 pages) | Cited 17 times

Online Publication Date: 17 January 2007

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A low operating electric field has been achieved on silicon nanowires grown on carbon cloth. The silicon nanowires were grown on carbon cloth via the vapor-liquid-solid reaction using silane gas as the silicon source and gold as catalyst from the decomposition of hydrogen gold tetrachloride. An emission current density of 1 mA/cm2 was obtained at an operating electric field of 0.7 V/μm. Such low field is resulted from a high field enhancement factor of 6.1×104 due to the combined effects of the high intrinsic aspect ratio of silicon nanowires and the woven geometry of carbon cloth. Such results may lead silicon nanowire field emitters to practical applications in vacuum microelectronic devices including microwave devices.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.21.Hb Quantum wires

Design of plasmon cavities for solid-state cavity quantum electrodynamics applications

Yiyang Gong and Jelena Vučković

Appl. Phys. Lett. 90, 033113 (2007); http://dx.doi.org/10.1063/1.2431450 (3 pages) | Cited 21 times

Online Publication Date: 18 January 2007

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Research on photonic cavities with low mode volume and high quality factor garners much attention because of applications ranging from optoelectronics to cavity quantum electrodynamics (QED). The authors propose a cavity based on surface plasmon modes confined by metallic distributed Bragg reflectors. They analyze the structure with finite difference time domain simulations and obtain modes with quality factor of 1000 (including losses from metals at low temperatures), reduced mode volume relative to photonic crystal cavities, Purcell enhancements of hundreds, and even the capability of enabling cavity QED strong coupling.
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42.79.Bh Lenses, prisms and mirrors
12.20.Ds Specific calculations
42.79.Dj Gratings
42.70.Qs Photonic bandgap materials

Arrays of Ni nanowire/multiwalled carbon nanotube/amorphous carbon nanotube heterojunctions containing Schottky contacts

Jun Luo, Jing Zhu, Zhipeng Huang, and Lu Zhang

Appl. Phys. Lett. 90, 033114 (2007); http://dx.doi.org/10.1063/1.2404972 (3 pages) | Cited 5 times

Online Publication Date: 18 January 2007

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Ordered arrays of heterojunctions comprising Ni nanowires, multiwalled carbon nanotubes, and amorphous carbon nanotubes (a-CNTs) connected end to end were fabricated. The current-voltage (I-V) characteristics of the heterojunctions embedded in the arrays were measured by a conductive atomic force microscope. It was found that although the electrical signals of Schottky contacts in some heterojunctions were buried by those of the long a-CNT segments, Schottky contacts in the other heterojunctions played a central role and made the corresponding heterojunctions possess rectifying I-V characteristics. The quantitative analysis showed that the thermionic emission theory was applicable to Schottky contacts in one-dimensional heterojunctions.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ns Metal-nonmetal contacts

Defect-free twisted-nematic cells with low pretilt using chiral polyimide surfaces

Suk-Won Choi, Yoichi Takanishi, Ken Ishikawa, and Hideo Takezoe

Appl. Phys. Lett. 90, 033115 (2007); http://dx.doi.org/10.1063/1.2431047 (3 pages) | Cited 5 times

Online Publication Date: 19 January 2007

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The authors have demonstrated a technique for rodlike liquid crystal alignment using polyimide films with chiral carbons in the side chains. The authors succeeded in lifting degeneracy of two twisted configurations in the 90° twisted-nematic cells, even though the pretilt angle in the cell with rubbed polyimide (PI) surfaces is low (Θ ⩽ 1°). This phenomenon is due to chirality of molecular level on the PI surfaces, which is transferred to the bulk and acts as a kind of symmetry breaking powers.
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42.79.Kr Display devices, liquid-crystal devices

Conductivity of carbon nanotube polymer composites

James T. Wescott, Paul Kung, and Amitesh Maiti

Appl. Phys. Lett. 90, 033116 (2007); http://dx.doi.org/10.1063/1.2432237 (3 pages) | Cited 22 times

Online Publication Date: 19 January 2007

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Dissipative particle dynamics simulations were used to investigate methods of controlling the assembly of percolating networks of carbon nanotubes (CNTs) in thin films of block copolymer melts. For suitably chosen polymers the CNTs were found to spontaneously self-assemble into topologically interesting patterns. The mesoscale morphology was projected onto a finite-element grid and the electrical conductivity of the films computed. The conductivity displayed nonmonotonic behavior as a function of relative polymer fractions in the melt. Results are compared and contrasted with CNT dispersion in small-molecule fluids and mixtures.
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73.61.-r Electrical properties of specific thin films
73.63.-b Electronic transport in nanoscale materials and structures
72.10.-d Theory of electronic transport; scattering mechanisms
72.80.Tm Composite materials
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology

Uniformity enhancement of carbon nanofiber emitters via electrical discharge machining

Jong Girl Ok, Bo Hyun Kim, Woo Yong Sung, Chong Nam Chu, and Yong Hyup Kim

Appl. Phys. Lett. 90, 033117 (2007); http://dx.doi.org/10.1063/1.2432239 (3 pages) | Cited 8 times

Online Publication Date: 19 January 2007

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A very simple, clean, and effective method based on a reliable machining process called electrical discharge machining (EDM) was introduced in order to enhance the field emission uniformity of carbon nanofibers (CNFs). After an EDM post-treatment, the uniformity of the CNF emitters was clearly improved without contaminations, damages, or crystalline deteriorations of the CNFs. As a result, field emission uniformity was apparently enhanced at a low electric field range, promising that the method can be practical for applications requiring both large size and fine uniformity such as in a backlight unit.
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85.45.Db Field emitters and arrays, cold electron emitters

Dissipative force modulation Kelvin probe force microscopy applying doubled frequency ac bias voltage

Hikaru Nomura, Kenichiro Kawasaki, Takuma Chikamoto, Yan Jun Li, Yoshitaka Naitoh, Masami Kageshima, and Yasuhiro Sugawara

Appl. Phys. Lett. 90, 033118 (2007); http://dx.doi.org/10.1063/1.2432281 (3 pages) | Cited 1 time

Online Publication Date: 19 January 2007

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The authors propose a surface potential measurement technique using dissipative force modulation (DM) method with an ac bias voltage of doubled harmonic frequency (2ω) of the oscillating cantilever (2ωDM method). The effect of the stray capacitance between a cantilever and a sample on electrostatic force spectroscopy/Kelvin probe force microscopy measurement is almost completely removed in 2ωDM method, since the distance dependence of the modulated electrostatic force increases from 1/z to 1/z2. 2ωDM method has an advantage of high force sensitivity due to the high Q factor of the cantilever in vacuum. The authors demonstrate quantitative surface potential measurement by using dissipative tip-sample interactions.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
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