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20 Apr 2009

Volume 94, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 161105 (2009); http://dx.doi.org/10.1063/1.3119666 (3 pages)

Artur R. Davoyan, Ilya V. Shadrivov, Andrey A. Sukhorukov, and Yuri S. Kivshar
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Stress field analysis to understand the breakdown characteristics of stacked high-k dielectrics

Byoung Hun Lee, Changyong Kang, Rino Choi, Hi-Deok Lee, and Gennadi Bersuker

Appl. Phys. Lett. 94, 162904 (2009); http://dx.doi.org/10.1063/1.3122924 (3 pages) | Cited 2 times

Online Publication Date: 23 April 2009

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The validity of the stress biases used in reliability studies of high-k dielectric is discussed by analyzing the stress biases used in previous works. For single layer dielectrics, stress biases near the time zero dielectric breakdown point have been used to reduce the test time. However, stacked dielectrics need a more careful approach to avoid overstress. We show that the majority of earlier work on the reliability of high-k dielectric used high electric field and those results may not be optimal for predicting intrinsic reliability characteristics. A simple guideline to avoid overstress is provided.
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77.22.Jp Dielectric breakdown and space-charge effects
77.55.-g Dielectric thin films

Growth of homoepitaxial SrTiO3 thin films by molecular-beam epitaxy

C. M. Brooks, L. Fitting Kourkoutis, T. Heeg, J. Schubert, D. A. Muller, and D. G. Schlom

Appl. Phys. Lett. 94, 162905 (2009); http://dx.doi.org/10.1063/1.3117365 (3 pages) | Cited 31 times

Online Publication Date: 24 April 2009

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We report the structural properties of homoepitaxial (100) SrTiO3 films grown by reactive molecular-beam epitaxy (MBE). The lattice spacing and x-ray diffraction (XRD) rocking curves of stoichiometric MBE-grown SrTiO3 films are indistinguishable from the underlying SrTiO3 substrates. Off-stoichiometry for both strontium-rich and strontium-poor compositions (i.e., Sr1+xTiO3+δ films with −0.2<x<0.2) results in lattice expansion with significant changes to the shuttered reflection high-energy electron diffraction oscillations, XRD, and film microstructure. The dependence of lattice spacing on nonstoichiometry is smaller for MBE-grown films than for homoepitaxial (100) Sr1+xTiO3+δ films prepared by pulsed-laser deposition or sputtering.
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68.55.jd Thickness
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Crystallographic dependence of loss in domain engineered relaxor-PT single crystals

Shujun Zhang, Nevin P. Sherlock, Richard J. Meyer, Jr., and Thomas R. Shrout

Appl. Phys. Lett. 94, 162906 (2009); http://dx.doi.org/10.1063/1.3125431 (3 pages) | Cited 24 times

Online Publication Date: 24 April 2009

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Domain engineered 〈001〉 oriented relaxor-PbTiO3 ferroelectric crystals exhibit high electromechanical properties and low mechanical Q values, analogous to “soft” piezoelectric ceramics. However, their characteristic low dielectric loss ( ≤ 0.5%) and strain-electric field hysteresis are reflective of “hard” piezoelectric materials. In this work, the electromechanical behavior of relaxor-PT crystals was investigated as a function of crystallographic orientations. It was found that the electrical and mechanical losses in crystals depends on the specific engineered domain configuration, with high Q observed for the 〈110〉 orientation. The high Q, together with high electromechanical coupling ( ∼ 0.9) for 〈110〉 oriented relaxor-PT crystals, make them promising candidates for resonant based high power transducer applications.
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77.80.Dj Domain structure; hysteresis
77.22.Gm Dielectric loss and relaxation
77.65.-j Piezoelectricity and electromechanical effects
61.50.-f Structure of bulk crystals

Effect of thermal annealing on charge exchange between oxygen interstitial defects within HfO2 and oxygen-deficient silicon centers within the SiO2/Si interface

J. L. Lauer, J. L. Shohet, and Y. Nishi

Appl. Phys. Lett. 94, 162907 (2009); http://dx.doi.org/10.1063/1.3122925 (3 pages) | Cited 8 times

Online Publication Date: 24 April 2009

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We compare the charging response of rapid thermally annealed (800 and 1000 °C) 4 nm thick HfO2 to as-deposited HfO2 on Si by measuring the surface potential of the HfO2 layers after vacuum ultraviolet (VUV) irradiation with 11.6 eV photons. From VUV spectroscopy, we determined all HfO2 layers show the presence of oxygen-interstitial defects (OIDs). The electronic states of OID in HfO2 line up in energy with oxygen-deficient Si centers within the SiO2 interfacial layer. This implies charge exchange between OIDs within HfO2 and the O-deficient silicon centers within the SiO2 interfacial layer are very important for controlling the radiation-induced trapped charge in HfO2 dielectric stacks.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.jj Interstitials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
78.40.-q Absorption and reflection spectra: visible and ultraviolet
77.55.-g Dielectric thin films

Dielectric properties and tunability of cubic pyrochlore Bi1.5MgNb1.5O7 thin films

S. W. Jiang, Y. R. Li, R. G. Li, N. D. Xiong, L. F. Tan, X. Z. Liu, and B. W. Tao

Appl. Phys. Lett. 94, 162908 (2009); http://dx.doi.org/10.1063/1.3126442 (3 pages) | Cited 4 times

Online Publication Date: 24 April 2009

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The Bi1.5MgNb1.5O7 thin films with cubic pyrochlore structure were prepared onto Pt-coated sapphire substrates by rf magnetron sputtering deposition from a stoichiometric target. Dielectric measurements indicated that the Bi1.5MgNb1.5O7 thin films exhibited low dielectric loss of ∼ 0.0018–0.004, medium dielectric constant of ∼ 86, and superior tunable dielectric properties at room temperature. A bias field of 1.6 MV/cm resulted in the maximum voltage tunability of 39%. A brief discussion is given on the enhanced tunability compared to Bi1.5ZnNb1.5O7 thin films. The low loss and superior tunability make Bi1.5MgNb1.5O7 thin films promising for potential tunable capacitor applications.
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77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
81.15.Cd Deposition by sputtering
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Synthesis parameter space of bismuth catalyzed germanium nanowires

Ying Xiang, Linyou Cao, Jordi Arbiol, Mark L. Brongersma, and Anna Fontcuberta i Morral

Appl. Phys. Lett. 94, 163101 (2009); http://dx.doi.org/10.1063/1.3116625 (3 pages) | Cited 5 times

Online Publication Date: 20 April 2009

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The synthesis parameter space of bismuth catalyzed germanium nanowires by chemical vapor deposition is determined. The process window for high aspect ratio nanowires is found to be extremely narrow. The optimal conditions are found to be 300 °C and 150 Torr gas pressure. For lower temperatures, the solubility of Ge in Bi is too low for the nucleation of Ge nanowires to occur. For higher temperatures, small Bi droplets tend to evaporate leading to an extreme reduction in the nanowire density. The extremely low process temperature makes Bi a good candidate for its growth on low cost and low thermal budget substrates such as plastics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Vb Quantum wires

Polarization-sensitive near-field investigation of photonic crystal microcavities

Silvia Vignolini, Francesca Intonti, Francesco Riboli, Diederik S. Wiersma, Laurent Balet, Lianhe H. Li, Marco Francardi, Annamaria Gerardino, Andrea Fiore, and Massimo Gurioli

Appl. Phys. Lett. 94, 163102 (2009); http://dx.doi.org/10.1063/1.3118578 (3 pages) | Cited 12 times

Online Publication Date: 20 April 2009

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We report on polarization sensitive imaging of two-dimensional photonic crystal microcavity modes. By using a near-field scanning optical microscope with a polarization sensitive setup, it is possible to selectively map, with a resolution beyond the diffraction limit, each electric field component in the plane of the sample. In addition, the simultaneous analysis of photoluminescence maps in different polarization channels allowed us to obtain important insight on near-field microscopy detection mechanism. Finite difference time domain simulations confirm the experimental results.
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42.70.Qs Photonic bandgap materials
02.70.Bf Finite-difference methods
78.55.-m Photoluminescence, properties and materials
07.79.-v Scanning probe microscopes and components

Investigation into the lateral junction growth of single asperity contact using static atomistic simulations

Yeau-Ren Jeng and Shin-Rung Peng

Appl. Phys. Lett. 94, 163103 (2009); http://dx.doi.org/10.1063/1.3122144 (3 pages) | Cited 3 times

Online Publication Date: 20 April 2009

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According to continuum mechanics theory, the metallic junctions formed between the contact asperities on two opposing surfaces increase in size until gross sliding occurs. Our atomistic simulations reveal that the onset of lateral junction growth is caused by the slips of the asperity atoms. Furthermore, it is shown that the presence of an adsorbed layer on the asperity surface delays the onset of lateral junction growth. The present simulation results are found to be consistent with the experimental results presented in the literature and provide a valuable interpretation of the lateral junction growth phenomenon from a nanoscale perspective.
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68.35.Gy Mechanical properties; surface strains
68.35.Np Adhesion
61.46.-w Structure of nanoscale materials
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Autonomously motile catalytic nanomotors by bubble propulsion

J. G. Gibbs and Y.-P. Zhao

Appl. Phys. Lett. 94, 163104 (2009); http://dx.doi.org/10.1063/1.3122346 (3 pages) | Cited 33 times

Online Publication Date: 20 April 2009

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A bubble propulsion model based on catalyzed hydrogen peroxide decomposition and momentum change via O2 bubbles detaching from the catalytic surface is proposed to explain the autonomous motion of catalytic nanomotors. The propelling force closely depends upon the surface tension of the liquid as well as the bulk concentration of hydrogen peroxide, and the model predictions are supported by the experimental data of Pt-coated spherical silica microbead motors.
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81.16.-c Methods of micro- and nanofabrication and processing
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.03.Cd Surface tension and related phenomena
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Self-assembly of densely packed and aligned bilayer ZnO nanorod arrays

L. Chow, O. Lupan, H. Heinrich, and G. Chai

Appl. Phys. Lett. 94, 163105 (2009); http://dx.doi.org/10.1063/1.3118583 (3 pages) | Cited 19 times

Online Publication Date: 21 April 2009

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We present a method of self-assembly of densely packed and aligned bilayer ZnO nanorod arrays in a hydrothermal synthesis process. The alkali hydrothermal environment first induced the growth of hydrotalcitelike zincowoodwardite plates, which provide a lattice-matched surface for the self-assembly of ZnO nanorod arrays. The high packing density of the ZnO nanorod arrays demonstrates efficient nucleation and growth processes of ZnO on the zincowoodwardite. The interfacial phenomena involved in the growth of ZnO and self-assembly are discussed. The two-dimensional arrays of ZnO nanorods may find future applications in nanoelectronics and nanophotonics.
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81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors

Si nanowire ion-sensitive field-effect transistors with a shared floating gate

Katsuhiko Nishiguchi, Nicolas Clement, Toru Yamaguchi, and Akira Fujiwara

Appl. Phys. Lett. 94, 163106 (2009); http://dx.doi.org/10.1063/1.3123002 (3 pages) | Cited 2 times

Online Publication Date: 21 April 2009

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Ion-sensitive field-effect transistors (ISFETs) arrayed in parallel were fabricated on a silicon-on-insulator substrate. Since the nanoscale wire channels of the ISFETs are bridged with a floating gate on which molecules are preferably immobilized, signals originating from charged materials only on the floating gate can appear and can therefore be distinguished from background noise, which leads to noise-robust sensing. Additionally, the nanoscale channels provide the ISFETs with single-electron-resolution charge sensitivity as well as a reduction in background noise induced in the wider channels used as electrical leads. These features promise the detection of a small number of molecules.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Single nanoparticle alignment by atomic force microscopy indentation

ChaeHo Shin, InSu Jeon, SeungHee Jeon, and Zheong G. Khim

Appl. Phys. Lett. 94, 163107 (2009); http://dx.doi.org/10.1063/1.3124661 (3 pages) | Cited 3 times

Online Publication Date: 22 April 2009

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Unavoidable bulge formation during an indentation process is a serious obstacle to trapping nanoparticles in dent holes or trenches. We found an easy method of removing polymethyl methacrylate (PMMA) bulges formed during atomic force microscopy indentation. The method allowed the creation of dent holes or trenches in PMMA without bulges, which, using capillary interaction, allowed us to place 40-nm-diameter Au particles at precise locations. Furthermore, we could adjust the gap distance ( ∼ 10 nm) between the nanoparticle and the bottom electrode. The method will be helpful in characterizing the nanoparticles and molecules and, ultimately, will help in the development of nanoparitcle- or molecule-attached devices.
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81.16.Ta Atom manipulation
81.07.Wx Nanopowders
68.03.-g Gas-liquid and vacuum-liquid interfaces
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness

Pseudo spin valves based on L10 (111)-oriented FePt fixed layers with tilted anisotropy

C. L. Zha, J. Persson, S. Bonetti, Y. Y. Fang, and Johan Åkerman

Appl. Phys. Lett. 94, 163108 (2009); http://dx.doi.org/10.1063/1.3123003 (3 pages) | Cited 16 times

Online Publication Date: 22 April 2009

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We demonstrate magnetoresistance (MR) in excess of 4% in FePt/CoFe/Cu/CoFe/NiFe pseudo spin valves based on L10 (111)-oriented FePt fixed layers with a 36° out-of-plane tilted magnetization. The high MR is achieved by increasing the spin polarization at the Cu interfaces, using thin CoFe, and optimizing the FePt growth and Cu interface quality using Ta and Ta/Pt underlayers. We observe well-separated switching of the FePt/CoFe fixed layer and the CoFe/NiFe free layer, suggesting that CoFe is rigidly exchange coupled to FePt and NiFe in the respective layers.
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75.47.De Giant magnetoresistance
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Electrical and magnetic interaction along a defective single-walled carbon nanotube channel

Yun-Hi Lee (이윤희) and Ji-Young Noh (노지영)

Appl. Phys. Lett. 94, 163109 (2009); http://dx.doi.org/10.1063/1.3116117 (3 pages)

Online Publication Date: 22 April 2009

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We study the electrical and magnetic interaction in a low conduction regime for laterally as-grown defective single-walled carbon nanotube channel as functions of bias and gate voltage, combined with direct current and magnetic phase image by current-atomic force microscopy and magnetic force microscopy. For the SWNT field effect transistor at very low bias direct imaging of the current flow on the 0.9 and 2 nm diameter single-walled nanotube (SWNT) devices revealed that locally conducting islands occur along the SWNT channel, and become an origin of electrical behavior in the stage of minimal conduction. In contrast, the homogenous magnetic interaction along the as-laterally-grown individual SWNT channel observed by magnetic force measurements suggest a hint that as-grown single SWNT channel may be a reliable candidate for use in magnetoelectronics, regardless of whether clean or defective SWNT.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Suspending single-wall carbon nanotube thin film infrared bolometers on microchannels

Rongtao Lu, Zhuangzhi Li, Guowei Xu, and Judy Z. Wu

Appl. Phys. Lett. 94, 163110 (2009); http://dx.doi.org/10.1063/1.3124651 (3 pages) | Cited 17 times

Online Publication Date: 23 April 2009

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Suspended single-wall carbon nanotube (SWCNT) thin film bolometers have been fabricated on microchannels patterned on Si substrates using electron-beam lithography. The much improved bolometric photoresponse is attributed to the reduced thermal link between SWCNT bolometer and substrate, which can be controlled by tuning the width and spacing of the microchannels. The detectivity D∗ up to 4.5×105 cm Hz1/2/W has been obtained at room temperature, which is at least five times better than that of the unsuspended counterpart and may be further improved via elimination of metallic SWCNTs and improvement of the charge and heat transport across the intertube junctions.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
85.35.Kt Nanotube devices
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Origins of nonzero multiple photon emission probability from single quantum dots embedded in photonic crystal nanocavities

Hsiang-Szu Chang, Wen-Yen Chen, Tzu-Min Hsu, Tung-Po Hsieh, Jen-Inn Chyi, and Wen-Hao Chang

Appl. Phys. Lett. 94, 163111 (2009); http://dx.doi.org/10.1063/1.3125222 (3 pages) | Cited 1 time

Online Publication Date: 23 April 2009

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This work explores the origins of nonzero multiphoton emission probability for quantum dots embedded in photonic crystal nanocavities using different excitation energies to inject excitons into either the GaAs barrier or the quantum-dot excited state. The detected multiphoton events are established to arise from both the recapture of excitons and background emissions from the wetting layer tail states. The exciton emission is analyzed using rate-equation calculations, which suggest that multiphoton emission is dominated by the recapture effect.
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78.67.Hc Quantum dots
42.70.Qs Photonic bandgap materials
71.35.-y Excitons and related phenomena

Infrared p-i-n photodiodes based on InAs quantum dots grown on 20 nm patterned GaAs

Azar Alizadeh, David Hays, Chris Keimel, Vicki H. Watkins, Ken R. Conway, Seth T. Taylor, Rosalyn Neander, Lauraine Denault, Christina deSouza, Igor Saveliev, Marina Blumin, Harry E. Ruda, Edit Braunstein, and Colin Jones

Appl. Phys. Lett. 94, 163112 (2009); http://dx.doi.org/10.1063/1.3111159 (3 pages) | Cited 4 times

Online Publication Date: 23 April 2009

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We report on selective area growth of InAs quantum dots on GaAs substrates patterned with a hexagonal array of 20 nm pores using block copolymer lithography. We discuss the mechanisms of growth, highlighting the variation in the resulting morphology as a function of nucleation enhancing AlGaAs layers. We also evaluate the optoelectronic performance of p-i-n photodiodes based on single layer nanopatterned grown InAs quantum dot devices. At low to moderate reverse biases, we observe room temperature photoresponse in both near- and mid-IR regimes. At high biases, we observe strong avalanche effects in the mid-IR range with a gain factor of ∼ 4000.
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85.60.Dw Photodiodes; phototransistors; photoresistors
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Rf Micro- and nanoscale pattern formation

Contact resistance in carbon nanostructure via interconnects

Wen Wu, Shoba Krishnan, Toshishige Yamada, Xuhui Sun, Patrick Wilhite, Raymond Wu, Ke Li, and Cary Y. Yang

Appl. Phys. Lett. 94, 163113 (2009); http://dx.doi.org/10.1063/1.3123164 (3 pages) | Cited 8 times

Online Publication Date: 23 April 2009

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We present an in-depth electrical characterization of contact resistance in carbon nanostructure via interconnects. Test structures designed and fabricated for via applications contain vertically aligned arrays of carbon nanofibers (CNFs) grown on a thin titanium film on silicon substrate and embedded in silicon dioxide. Current-voltage measurements are performed on single CNFs using atomic force microscope current-sensing technique. By analyzing the dependence of measured resistance on CNF diameter, we extract the CNF resistivity and the metal-CNF contact resistance.
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73.40.Cg Contact resistance, contact potential
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.63.-b Electronic transport in nanoscale materials and structures
73.40.Ns Metal-nonmetal contacts

Sharp emission from single InAs quantum dots grown on vicinal GaAs surfaces

U. Perinetti, N. Akopian, Yu. B. Samsonenko, A. D. Bouravleuv, G. E. Cirlin, and V. Zwiller

Appl. Phys. Lett. 94, 163114 (2009); http://dx.doi.org/10.1063/1.3125430 (3 pages) | Cited 4 times

Online Publication Date: 24 April 2009

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We report on optical studies of single InAs quantum dots grown on vicinal GaAs(001) surfaces. To ensure low quantum dot density and appropriate size, we deposit InAs layers 1.4 or 1.5 ML thick, thinner than the critical thickness for Stranski–Krastanov quantum dot formation. These dots show sharp and bright photoluminescence. Lifetime measurements reveal an exciton lifetime of 500 ps. Polarization measurements show an exciton fine structure splitting of 15 μeV and allow to identify the exciton and charged exciton transitions with linewidth as narrow as 23 μeV.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
71.35.Pq Charged excitons (trions)

A metallic graphene layer adsorbed with lithium

Chih-Kai Yang

Appl. Phys. Lett. 94, 163115 (2009); http://dx.doi.org/10.1063/1.3126008 (3 pages) | Cited 16 times

Online Publication Date: 24 April 2009

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We found, by density functional calculation, that lithium atoms can be bonded to a graphene layer alternately on both sides by distorting the relative positions of the carbon atoms in the honeycomb lattice. Compared to the recently synthesized graphane by hydrogenation in which each carbon is pulled out of the plane by hydrogen, the carbon is pushed off instead by the attached lithium. And, surprisingly, the counterintuitive structure is a conductor. This should give consequences to its application in lithium storage.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.15.Nc Total energy and cohesive energy calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Frequency dependent capacitance and plasmon excitations in a coherent parallel-plate capacitor

Jun Quan, Yabin Yu, and T. C. Au Yeung

Appl. Phys. Lett. 94, 163116 (2009); http://dx.doi.org/10.1063/1.3122927 (3 pages) | Cited 1 time

Online Publication Date: 24 April 2009

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We report the theoretical investigations of frequency-dependent capacitance in a coherent parallel-plate capacitor. It is found that the capacitance strongly depends on frequency and is complex at finite frequency. An interesting result is that in the frequency dependence of capacitance, a peak in the imaginary part of capacitance corresponds to the minimum of the real part and is related to a plasmonlike excitation, which is of damping and has a short lifetime. We also discussed the size effect of the capacitor and find that the capacitance approaches geometric capacitance when the distance between two plates of the capacitor is very large.
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84.32.Tt Capacitors

Unified theory of gas damping of flexible microcantilevers at low ambient pressures

Rahul A. Bidkar, Ryan C. Tung, Alina A. Alexeenko, Hartono Sumali, and Arvind Raman

Appl. Phys. Lett. 94, 163117 (2009); http://dx.doi.org/10.1063/1.3122933 (3 pages) | Cited 10 times

Online Publication Date: 24 April 2009

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Predicting the gas damping of microcantilevers oscillating in different vibration modes in unbounded gas at low pressures is relevant for increasing the sensitivity of microcantilever-based sensors. While existing free-molecular theories are valid only at very high Knudsen numbers, continuum models are valid only at very low Knudsen numbers. We solve the quasisteady Boltzmann equation and compute a closed-form fit for gas damping of rectangular microcantilevers that is valid over four orders of magnitude of Knudsen numbers spanning the free-molecular, the transition, and the low pressure slip flow regimes. Experiments are performed using silicon microcantilevers under controlled pressures to validate the theory.
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47.45.Gx Slip flows and accommodation
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Bimodal magnetic force microscopy: Separation of short and long range forces

Jason W. Li, Jason P. Cleveland, and Roger Proksch

Appl. Phys. Lett. 94, 163118 (2009); http://dx.doi.org/10.1063/1.3126521 (3 pages) | Cited 12 times

Online Publication Date: 24 April 2009

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An application of bimodal atomic force microscopy [ T. R. Rodriguez and R. Garcia, Appl. Phys. Lett. 84, 449 (2004) ] which allows simultaneous and separated imaging of both long range magnetic and shorter range topographical forces is described. This technique has a spatial resolution and a signal-to-noise ratio at least as good as other magnetic force microscopy techniques with the advantage of requiring only a single pass. Besides being an improvement on existing magnetic imaging techniques, the results also shed light on the fundamental contrast mechanisms in bimodal atomic force microscopy because the sign of the long range magnetic forces changes with the sample magnetization, but all the other sample properties such as elasticity and surface roughness remain the same. The results confirm the theoretical predictions of Rodriguez and Garcia.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.70.Rf Surface magnetism
68.37.Rt Magnetic force microscopy (MFM)
68.37.Ps Atomic force microscopy (AFM)

Role of defects in the anomalous photoconductivity in ZnO nanowires

A. Bera and D. Basak

Appl. Phys. Lett. 94, 163119 (2009); http://dx.doi.org/10.1063/1.3123167 (3 pages) | Cited 33 times

Online Publication Date: 24 April 2009

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The anomalous photocurrent decay in aqueous solution grown ZnO nanowires (NWs) under steady ultraviolet light illumination have been investigated. The photocurrent growth-decay measurements using the above-band and subband gap light excitation energies in the as-grown and annealed NWs show that while a VZn-related defect complex is formed by the surface adsorbed H2O molecules, a faster carrier trapping by the surface adsorbed O2 molecules and a slower carrier recombination at the defect, Zni cause the photocurrent decay under steady illumination supported by the results of the photocurrent spectra and photoluminescence measurements. The predicted mechanism has been explained through a model.
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72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing
71.20.Nr Semiconductor compounds
73.63.Nm Quantum wires
78.67.Lt Quantum wires
71.55.Gs II-VI semiconductors
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
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Measurement of polar C-plane and nonpolar A-plane InN/ZnO heterojunctions band offsets by x-ray photoelectron spectroscopy

A. L. Yang, H. P. Song, H. Y. Wei, X. L. Liu, J. Wang, X. Q. Lv, P. Jin, S. Y. Yang, Q. S. Zhu, and Z. G. Wang

Appl. Phys. Lett. 94, 163301 (2009); http://dx.doi.org/10.1063/1.3123814 (3 pages) | Cited 9 times

Online Publication Date: 20 April 2009

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The valence band offsets of the wurtzite polar C-plane and nonpolar A-plane InN/ZnO heterojunctions are directly determined by x-ray photoelectron spectroscopy to be 1.76±0.2 eV and 2.20±0.2 eV. The heterojunctions form in the type-I straddling configuration with a conduction band offsets of 0.84±0.2 eV and 0.40±0.2 eV. The difference of valence band offsets of them mainly attributes to the spontaneous polarization effect. Our results show important face dependence for InN/ZnO heterojunctions, and the valence band offset of A-plane heterojunction is more close to the “intrinsic” valence band offset.
Show PACS
73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures
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