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3 Aug 2009

Volume 95, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 95, 052901 (2009); http://dx.doi.org/10.1063/1.3190518 (3 pages)

Didit Yudistira, Sarah Benchabane, Davide Janner, and Valerio Pruneri
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Direct observation of the gas-surface interaction kinetics in nanowires through pulsed self-heating assisted conductometric measurements

J. D. Prades, R. Jimenez-Diaz, F. Hernandez-Ramirez, J. Pan, A. Romano-Rodriguez, S. Mathur, and J. R. Morante

Appl. Phys. Lett. 95, 053101 (2009); http://dx.doi.org/10.1063/1.3192358 (3 pages) | Cited 8 times

Online Publication Date: 4 August 2009

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Dynamics of gas-surface interactions determine the limits of the fastest response times of sensors based on metal oxides. Here, the kinetics of adsorption and desorption of gaseous molecules onto the surface of metal oxide nanowires was analyzed through pulsed self-heating assisted conductometric measurements. This approach overcomes gas diffusion, which is typical of conventional porous film based devices, and provides thermal response times fast enough to evaluate the fundamental gas-surface reactions kinetics. Experimental response and recovery times of individual SnO2 nanowires toward oxidizing and reducing gases obtained with the here-proposed methodology were related to the reaction barriers predicted by theoretical models and other experimental techniques.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
66.30.Pa Diffusion in nanoscale solids
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.43.Mn Adsorption kinetics
68.43.Nr Desorption kinetics

Surface relief grating formation on nano-objects

R. Barillé, P. Tajalli, S. Zielinska, E. Ortyl, S. Kucharski, and J. M. Nunzi

Appl. Phys. Lett. 95, 053102 (2009); http://dx.doi.org/10.1063/1.3192359 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2009

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We exploit the photoinduced migration effect in azopolymer thin films to induce surface relief patterning of nano-objects. Manipulation and precise control of the molecular order is achieved at the nanoscale. Interaction between a laser beam from an argon laser and the azopolymer nano-objects induces structures on the surface. The self-patterning process is observed to depend on the laser beam polarization.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.-b Surface treatments
42.62.-b Laser applications
42.70.Jk Polymers and organics
42.79.Dj Gratings

Nanostructured semiconductor heterojunctions from quantum dot layers

R. Könenkamp, A. Nadarajah, and Robert C. Word

Appl. Phys. Lett. 95, 053103 (2009); http://dx.doi.org/10.1063/1.3193531 (3 pages) | Cited 1 time

Online Publication Date: 4 August 2009

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We report the deposition of conformal thin layers of 10–50 nm thickness from II-VI quantum dot suspensions on ZnO nanowire substrates. Smooth polycrystalline films of high electronic quality can be obtained from CdSe quantum dots after annealing at moderate temperatures. The electronic properties are adequate for detector and solar cell applications. The growth and annealing temperatures permit deposition on light-weight and flexible substrates. Some elemental diffusion of Se across the CdSe/ZnO interface occurs in the film formation. A comparison with CdS/ZnO junctions indicates that the low Se diffusion rates are essential for efficient charge transfer.
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81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Transition from static to kinetic friction of metallic nanoparticles

Dirk Dietzel, Michael Feldmann, Harald Fuchs, Udo D. Schwarz, and André Schirmeisen

Appl. Phys. Lett. 95, 053104 (2009); http://dx.doi.org/10.1063/1.3193551 (3 pages) | Cited 8 times

Online Publication Date: 4 August 2009

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Nanometer scale metallic islands were manipulated on a graphite surface by placing the tip of an atomic force microscope on top of the particles. Above a certain lateral force threshold particle sliding is observed, which allows us to quantify the transition from static to kinetic friction. This transition shows hysteretic character in the force domain and is characterized by a constant ratio of kinetic versus static friction of one half.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Crucial role of doping dynamics on transport properties of Sb-doped SnO2 nanowires

Annop Klamchuen, Takeshi Yanagida, Kazuki Nagashima, Shu Seki, Keisuke Oka, Masateru Taniguchi, and Tomoji Kawai

Appl. Phys. Lett. 95, 053105 (2009); http://dx.doi.org/10.1063/1.3186080 (3 pages) | Cited 15 times

Online Publication Date: 4 August 2009

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Impurity doping on semiconductor nanowires grown by vapor-liquid-solid (VLS) mechanism remains an important challenge. Here we demonstrate the importance of doping dynamics to control the transport properties of Sb-doped SnO2 nanowires. Sb doping decreased the resistivity of SnO2 nanowires down to 10−3 Ω cm range, while there was the lower bound of resistivity even increasing further the dopant concentration from supplied source. We found that the doping limitation is related to the re-evaporation events of dopant through vapor-solid growth process rather than VLS process. Thus understanding the dopant incorporation dynamics is essential to control the transport properties of SnO2 nanowires by impurity doping.
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61.72.up Other materials
73.63.-b Electronic transport in nanoscale materials and structures
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Piezoelectric aluminum nitride nanoelectromechanical actuators

Nipun Sinha, Graham E. Wabiszewski, Rashed Mahameed, Valery V. Felmetsger, Shawn M. Tanner, Robert W. Carpick, and Gianluca Piazza

Appl. Phys. Lett. 95, 053106 (2009); http://dx.doi.org/10.1063/1.3194148 (3 pages) | Cited 15 times

Online Publication Date: 4 August 2009

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This letter reports the implementation of ultrathin (100 nm) aluminum nitride (AlN) piezoelectric layers for the fabrication of vertically deflecting nanoactuators. The films exhibit an average piezoelectric coefficient (d31 ∼ −1.9 pC/N), which is comparable to its microscale counterpart. This allows vertical deflections as large as 40 nm from 18 μm long and 350 nm thick multilayer cantilever bimorph beams with 2 V actuation. Furthermore, in-plane stress and stress gradients have been simultaneously controlled. The films exhibit leakage currents lower than 2 nA/cm2 at 1 V, and have an average relative dielectric constant of approximately 9.2 (as in thicker films). These material characteristics and actuation results make the AlN nanofilms ideal candidates for the realization of nanoelectromechanical switches for low power logic applications.
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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
77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
68.60.Bs Mechanical and acoustical properties

Enhanced infrared emission from colloidal HgTe nanocrystal quantum dots on silicon-on-insulator photonic crystals

Chunxia Wang, Jürgen Roither, Raimund Kirschschlager, Maksym V. Kovalenko, Moritz Brehm, Thomas Fromherz, Qiang Kan, Pingheng Tan, Jian Liu, Hongda Chen, and Wolfgang Heiss

Appl. Phys. Lett. 95, 053107 (2009); http://dx.doi.org/10.1063/1.3194151 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2009

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A two dimensional silicon-on-insulator based photonic crystal structure is used to enhance the emission from colloidal HgTe nanocrystal quantum dots embedded in a thin polymer film. The enhancement is resonant to the leaky eigenmodes of the photonic crystals due to coherent scattering effects. Transmittance and photoluminescence experiments are presented to map the leaky mode dispersion and the angle dependence of the emission enhancement factor, which reaches values up to 80 (650) for vertical (oblique) emission in the telecommunication wavelength range.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
82.70.Dd Colloids
42.70.Qs Photonic bandgap materials

Quantitative study of interior nanostructure in hollow zinc oxide particles on the basis of nondestructive x-ray nanotomography

Wenjie Li, Ning Wang, Jie Chen, Gang Liu, Zhiyun Pan, Yong Guan, Yunhao Yang, Wenquan Wu, Jinping Tian, Shiqiang Wei, Ziyu Wu, Yangchao Tian, and Lin Guo

Appl. Phys. Lett. 95, 053108 (2009); http://dx.doi.org/10.1063/1.3196250 (3 pages) | Cited 10 times

Online Publication Date: 4 August 2009

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The complicated three-dimensional interior structures of the polycrystalline hollow zinc oxide microspheres were clearly obtained by the nondestructive nanocomputed tomography (nano-CT) technique. The parameters such as diameter, volume, porosity, and surface area were calculated by the quantitative analysis of reconstructed data. Especially, three single selected particles with different typical structures were separated and compared. With these results, the distinction of the particles can be clearly understood in nanoscale. This study reveals that nano-CT is an effective and competent tool for investigating the three-dimensional interior structures of nanomaterials in the natural environment.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Yz X-ray microscopy
81.70.Tx Computed tomography

Modulation of alternating electric field inside photoexcited carbon nanotubes

Hong Zhang and Yoshiyuki Miyamoto

Appl. Phys. Lett. 95, 053109 (2009); http://dx.doi.org/10.1063/1.3196317 (3 pages) | Cited 5 times

Online Publication Date: 4 August 2009

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Modulation of an alternating electric field (E-field) inside semiconducting carbon nanotubes (CNTs) has been studied with polarization perpendicular to the tube axis. The real-time dynamics of the electron wave functions and atoms in the CNTs was investigated by applying first-principles time-dependent density functional theory. The E-field inside the CNTs was not screened completely and was actually enhanced depending on the frequency. The enhancement was due to the increasing amplitude of the oscillating electron cloud with the resonant frequency. This finding provides a clear insight into the optical response of CNTs and also of molecules encapsulated in CNTs.
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78.67.Ch Nanotubes
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Analysis of liquid mediated friction during alignment in large area UV imprint lithography

Seock Hwan Kang, Si Hwan Park, and Woo Il Lee

Appl. Phys. Lett. 95, 053110 (2009); http://dx.doi.org/10.1063/1.3190507 (3 pages)

Online Publication Date: 4 August 2009

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Stiction in large area imprint lithography was studied by a microtribological approach. As imprinting area is expanded, fine aligning movement can be hindered by the adhesion or in-plane friction between the mold and the substrate. In this study, an analytical model for stiction force in the alignment process was proposed and evaluated by measuring the friction force between two plates mediated by a thin liquid film. Experimental verification was conducted for various geometries and surface conditions. Analytic and experimental results demonstrated that the meniscus force induced from surface tension was the most critical parameter affecting stiction in an alignment process.
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85.40.Hp Lithography, masks and pattern transfer
62.10.+s Mechanical properties of liquids
68.35.Gy Mechanical properties; surface strains
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.16.Nd Micro- and nanolithography

Morphology, orientation relationship, and stability analysis of Cu2O nanoclusters on SrTiO3 (100)

Satyanarayana V. N. T. Kuchibhatla, S. Y. Hu, Z. Q. Yu, V. Shutthanandan, Y. L. Li, P. Nachimuthu, W. Jiang, S. Thevuthasan, C. H. Henager, Jr., and S. K. Sundaram

Appl. Phys. Lett. 95, 053111 (2009); http://dx.doi.org/10.1063/1.3193530 (3 pages) | Cited 2 times

Online Publication Date: 5 August 2009

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Reflection high energy electron diffraction, atomic force microscopy, and theoretical studies based on classical nucleation theory have been used to interpret the morphology, orientation relationship, and stability of Cu2O nanoclusters on SrTiO3 (100) (STO). We propose that the competing interfacial and elastic energies facilitate an in-plane rotation of the Cu2O clusters by 45° with respect to the STO substrate and stabilize Cu2O clusters on STO(100) with an orientation relationship of (001)Cu2O//(001)SrTiO3 and 〈100〉Cu2O//〈110〉SrTiO3. Our preliminary theoretical analysis also suggests that this particular orientation results in smaller critical nucleus sizes and lower nucleation barriers and also indicates a chemical potential (growth rate) dependence of the orientation relationship.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
68.35.Md Surface thermodynamics, surface energies
81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Focusing properties of microspheres containing multiconcentric metallic rings

Chin-Kai Chang, Chau-Shioung Yeh, Chih-Kung Lee, Ming-Wei Lai, Ji-Tian Yeh, and Jung-Ming Liu

Appl. Phys. Lett. 95, 053112 (2009); http://dx.doi.org/10.1063/1.3200243 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2009

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We fabricated multiconcentric metallic rings on a polystyrene microbead by using a focused ion beam. We found this type of structure possesses good focusing properties unlike planar multiconcentric metallic rings, which require varying the width of each ring. In addition, we found that we can change the shape of the bead by heating it, after which we then fabricated multiconcentric metallic rings around it. Our results showed that the focal distance of the structure as well as the size of the focal spot increased as the heating time increased. These kinds of structures have good potential for application to optical imaging and photolithography.
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42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics
42.86.+b Optical workshop techniques
73.22.Lp Collective excitations

Photoluminescence study of single ZnO nanostructures: Size effect

L. Feng, C. Cheng, B. D. Yao, N. Wang, and M. M. T. Loy

Appl. Phys. Lett. 95, 053113 (2009); http://dx.doi.org/10.1063/1.3200232 (3 pages) | Cited 9 times

Online Publication Date: 6 August 2009

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Spatially resolved photoluminescence (PL) investigations were carried out on ZnO single nanowires, tetrapods, and nanocrystals. The fractional intensity for bound exciton (BX) transitions was shown to be correlated with the size in all these ZnO nanostructures. This size dependency is attributed to the inhomogeneous density distribution of the defects as binding sites for BX in the ZnO nanostructures, in good agreement with a simple model calculation.
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78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.07.Vb Quantum wires
78.67.Lt Quantum wires
61.72.-y Defects and impurities in crystals; microstructure
73.22.Lp Collective excitations

Quintuple-layer epitaxy of thin films of topological insulator Bi2Se3

Guanhua Zhang, Huajun Qin, Jing Teng, Jiandong Guo, Qinlin Guo, Xi Dai, Zhong Fang, and Kehui Wu

Appl. Phys. Lett. 95, 053114 (2009); http://dx.doi.org/10.1063/1.3200237 (3 pages) | Cited 55 times

Online Publication Date: 6 August 2009

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Atomically smooth, single crystalline Bi2Se3 thin films were prepared on Si(111) by molecular beam epitaxy. Scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron emission spectroscopy, and Raman spectroscopy were used to characterize the stoichiometry and crystallinity of the film. The films grow in a self-organized quintuple layer by quintuple-layer mode, and atomically smooth films can be obtained, with controllable thickness down to one quintuple layer ( ∼ 1 nm).
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68.55.ag Semiconductors
68.55.jd Thickness
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.60.Dp Adsorbed layers and thin films
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors

Designing periodic arrays of metal nanoparticles for light-trapping applications in solar cells

S. Mokkapati, F. J. Beck, A. Polman, and K. R. Catchpole

Appl. Phys. Lett. 95, 053115 (2009); http://dx.doi.org/10.1063/1.3200948 (3 pages) | Cited 43 times

Online Publication Date: 7 August 2009

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We present criteria for optimizing the light-trapping efficiency of periodic arrays of metal nanoparticles for Si solar cell applications. The scattering cross section of the nanoparticles and the diffraction efficiency of the grating should be maximized in the long wavelength range. The grating pitch should be chosen to allow higher order diffraction modes for long wavelengths while maintaining the highest possible fill factor. These conditions place strong constraints on the optimal parameters (particle size of ∼ 200 nm and pitch of ∼ 400 nm) for periodic arrays of metal nanoparticles, in contrast to dielectric gratings, where a relatively wide range of periods and feature sizes can be used for efficient light trapping.
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84.60.Jt Photoelectric conversion
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Near-IR vibrational dynamics of periodic gold single and pair nanocuboids

Li Wang, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa, and Naoto Tamai

Appl. Phys. Lett. 95, 053116 (2009); http://dx.doi.org/10.1063/1.3202403 (3 pages) | Cited 4 times

Online Publication Date: 7 August 2009

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We examined vibrational dynamics of periodic gold single and pair nanocuboids with 9 nm separation at 400 nm excitation by near-IR transient absorption spectroscopy. The similar oscillation periods of coherent phonon vibration (77±1 ps) were observed for both nanocuboids while the damping of the pair was faster than that of the single. From the analysis of bleaching peak shift and finite-difference time-domain calculation, the lattice change in coherent phonon vibration was estimated to be ±1% for a quasiextensional and ±3% for an quasibreathing modes of a single nanocuboid.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.30.Er Solid metals and alloys
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