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21 May 2007

Volume 90, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 213501 (2007); http://dx.doi.org/10.1063/1.2742294 (3 pages)

Jong-Hyun Ahn, Hoon-Sik Kim, Etienne Menard, Keon Jae Lee, Zhengtao Zhu, Dae-Hyeong Kim, Ralph G. Nuzzo, John A. Rogers, Islamshah Amlani, Vadim Kushner, Shawn G. Thomas, and Terrisa Duenas
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Transmission through randomly arranged microcells of subwavelength holes on an aluminum film

Yi-Tsung Chang, Tzu-Hung Chuang, Chieh-Hung Yang, Ming-Wei Tsai, and Si-Chen Lee

Appl. Phys. Lett. 90, 213101 (2007); http://dx.doi.org/10.1063/1.2740175 (3 pages) | Cited 3 times

Online Publication Date: 21 May 2007

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This investigation presents an observation of enhanced optical transmission through an Al film that is perforated with microcells that are arranged in random structures. The dispersion relations of the Al/p-Si surface plasmon polariton in these structures with individual microcells with 3×3, 6×6, 9×9, 12×12, and 16×16 hole arrays of hexagonal were deduced. The transmission peak wavelength is determined from the spatial period of the microcell arrays. The random structure provides multicolor light transmission, which can be exploited in infrared wavelength-selective devices.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
61.66.Bi Elemental solids
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Magnetism in dodecanethiol-capped gold nanoparticles: Role of size and capping agent

P. Dutta, S. Pal, M. S. Seehra, M. Anand, and C. B. Roberts

Appl. Phys. Lett. 90, 213102 (2007); http://dx.doi.org/10.1063/1.2740577 (3 pages) | Cited 24 times

Online Publication Date: 21 May 2007

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In gold nanoparticles (Au NPs) capped with dodecanethiol (DT), the authors report the observation of superparamagnetic blocking temperature TB ≃ 50 K in D ≃ 5 nm NPs but only diamagnetism in 12 nm NPs. For T<TB = 50 K, the strong temperature dependence of coercivity Hc, saturation magnetization Ms, and exchange bias He (in the field-cooled sample) confirm the blocked state resembling ferromagnetism with Hc ≃ 250 Oe, He ≃ −40 Oe, and Ms ≃ 10−2 emu/g at 5 K. The observed electron magnetic resonance line shows expected shift, broadening, and reduced intensity below TB. A magnetic moment μ ≃ 0.006μB per Au atom attached to DT is determined using a model which yields Ms varying as 1/D, with its source being holes in the 5d band of Au produced by charge transfer from Au to S atoms in DT.
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75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.20.En Metals and alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

Antiadhesion considerations for UV nanoimprint lithography

F. A. Houle, C. T. Rettner, D. C. Miller, and R. Sooriyakumaran

Appl. Phys. Lett. 90, 213103 (2007); http://dx.doi.org/10.1063/1.2740578 (3 pages) | Cited 18 times

Online Publication Date: 21 May 2007

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Low surface energy fluorosilane layers are widely used as release coatings for quartz templates in UV nanoimprint lithography, yet they are generally found to degrade with use. It is found that these layers are chemically attacked when used with UV cured methacrylate and vinyl ether resists, as found previously for acrylate resists, leading to the conclusion that low reactivity and not low surface energy is of importance for effective release layers. It is shown that an ion-beam deposited diamondlike carbon release coating is a useful alternative, having both stability in a reactive environment and lower adhesion despite its higher surface energy.
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81.16.Nd Micro- and nanolithography
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.35.Md Surface thermodynamics, surface energies

Multiphonon Raman scattering in GaN nanowires

S. Dhara, Sharat Chandra, G. Mangamma, S. Kalavathi, P. Shankar, K. G. M. Nair, A. K. Tyagi, C. W. Hsu, C. C. Kuo, L. C. Chen, K. H. Chen, and K. K. Sriram

Appl. Phys. Lett. 90, 213104 (2007); http://dx.doi.org/10.1063/1.2741410 (3 pages) | Cited 12 times

Online Publication Date: 21 May 2007

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UV Raman scattering studies show longitudinal optical (LO) mode up to fourth order in wurtzite GaN nanowire system. Fröhlich interaction of electron with the long range electrostatic field of ionic bonded GaN gives rise to enhancement in LO phonon modes. Good crystalline quality, as indicated by the crystallographic as well as luminescence studies, is thought to be responsible for this significant observation. Calculated size dependence, incorporating size corrected dielectric constants, of electron-phonon interaction energy agrees well with measured values and also predict stronger interaction energy than that of the bulk for diameter below ∼ 3 nm.
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78.67.Lt Quantum wires
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
68.65.La Quantum wires (patterned in quantum wells)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
77.22.Ch Permittivity (dielectric function)

Suppression of InAs/GaAs quantum dot decomposition by the incorporation of a GaAsSb capping layer

J. M. Ulloa, I. W. D. Drouzas, P. M. Koenraad, D. J. Mowbray, M. J. Steer, H. Y. Liu, and M. Hopkinson

Appl. Phys. Lett. 90, 213105 (2007); http://dx.doi.org/10.1063/1.2741608 (3 pages) | Cited 29 times

Online Publication Date: 23 May 2007

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The influence of a GaAsSb capping layer on the structural properties of self-assembled InAs/GaAs quantum dots (QDs) is studied on the atomic scale by cross-sectional scanning tunneling microscopy. QDs capped with GaAs0.75Sb0.25 exhibit a full pyramidal shape and a height more than twice that of the typical GaAs-capped QDs, indicating that capping with GaAsSb suppresses dot decomposition. This behavior is most likely related to the reduced lattice mismatch between the dot and the capping layer.
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68.65.Hb Quantum dots (patterned in quantum wells)
64.75.-g Phase equilibria

Fabrication and enhanced magnetoresistance of SiO2-coated Fe3O4 nanosphere compact

Junfeng Wang, Jing Shi, Decheng Tian, Hong Deng, Yadong Li, Pengyun Song, and Chinping Chen

Appl. Phys. Lett. 90, 213106 (2007); http://dx.doi.org/10.1063/1.2741612 (3 pages) | Cited 14 times

Online Publication Date: 23 May 2007

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Magnetoresistance (MR) of a nanostructured material, monodisperse Fe3O4 nanospheres of about 200 nm coated with thin SiO2 and compactly cold pressed and sintered, has been investigated. A high MR, up to 10.8% at 1 T and 17% at 8 T, has been observed at 100 K. This enhanced MR is likely arising from the spin-polarized tunneling of conducting electrons through the insulating SiO2 boundaries. The decrease of the MR with the temperature increasing was attributed to the existence of the local spins in the grain boundaries. In addition, the MR ratio decreases with the SiO2 thickness increasing and sintering temperature decreasing. It suggests that the magnetic property of the insulating barrier is crucial for enhancing the low-field MR at a high temperature.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.Gk Colossal magnetoresistance
81.07.Bc Nanocrystalline materials
81.10.Fq Growth from melts; zone melting and refining
72.25.-b Spin polarized transport
73.40.Gk Tunneling

Electrodeposition of Pd nanoparticles on single-walled carbon nanotubes for flexible hydrogen sensors

Yugang Sun and H. Hau Wang

Appl. Phys. Lett. 90, 213107 (2007); http://dx.doi.org/10.1063/1.2742596 (3 pages) | Cited 35 times

Online Publication Date: 23 May 2007

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Single-walled carbon nanotubes on thin plastic substrates have been decorated with Pd nanoparticles through a simple electrochemical deposition process and have been used to fabricate high-performance hydrogen sensors with excellent mechanical flexibility. The typical flexible sensors exhibit sensitivity (i.e., the change of resistance) of ∼ 75% for 0.05% hydrogen in air and response time of ∼ 3 s for 1% hydrogen at room temperature. The performance of the as-fabricated devices keeps essentially unchanged even when they are bent to curving profile with bending radius of 7.5 mm and after they are operated for 2000 cycles of bending/relaxing.
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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
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution

Field emission patterns from multiwall carbon nanotubes with a cone-shaped tip

Yahachi Saito, Yuhki Tsujimoto, Akira Koshio, and Fumio Kokai

Appl. Phys. Lett. 90, 213108 (2007); http://dx.doi.org/10.1063/1.2742637 (3 pages) | Cited 11 times

Online Publication Date: 23 May 2007

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Electron emission from multiwall carbon nanotubes (CNTs) with a cone-shaped tip, on the apex of which five pentagons are present, has been studied by field emission microscopy (FEM). Two types of FEM patterns were observed: one is a well-defined “pentagon” pattern that is typically observed for ordinal multiwall CNTs though the number of pentagons is five in the case of cone-shaped CNTs, and the other is a “dim” pattern that is usually observed for single-wall CNTs. Appearance voltages of the respective patterns and transmission electron microscopy study of the cone-shaped CNTs suggest that the pentagon patterns originate from CNTs with apex radii larger than approximately 2 nm while the dim patterns originate from those with the smaller apex radii.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Fg Nanotubes

Effects of dye adsorption on the electron transport properties in ZnO-nanowire dye-sensitized solar cells

Jih-Jen Wu, Guan-Ren Chen, Hung-Hsien Yang, Chen-Hao Ku, and Jr-Yuan Lai

Appl. Phys. Lett. 90, 213109 (2007); http://dx.doi.org/10.1063/1.2742639 (3 pages) | Cited 73 times

Online Publication Date: 23 May 2007

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Mercurochrome and N3 dyes are employed to be the sensitizers in the ZnO-nanowire (NW) dye-sensitized solar cells (DSSCs). A lower fill factor is obtained in the N3-sensitized cell which results in comparable efficiencies in both ZnO-NW DSSCs although the N3 molecules possess a wider absorptive range for light harvesting. Electrochemical impedance spectroscopy and open-circuit photovoltage decay measurements are employed to investigate the electron transport properties in both ZnO-NW DSSCs. The results indicate that more abundant electron interfacial recombination occurs in the N3-sensitized ZnO-NW DSSC due to the higher surface trap density in the ZnO-NW photoanode after N3 dye adsorption.
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73.63.Nm Quantum wires
68.43.Mn Adsorption kinetics
84.60.Jt Photoelectric conversion
82.80.Fk Electrochemical methods
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Local quantum dot tuning on photonic crystal chips

Andrei Faraon, Dirk Englund, Ilya Fushman, Jelena Vučković, Nick Stoltz, and Pierre Petroff

Appl. Phys. Lett. 90, 213110 (2007); http://dx.doi.org/10.1063/1.2742789 (3 pages) | Cited 36 times

Online Publication Date: 23 May 2007

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Quantum networks based on InAs quantum dots embedded in photonic crystal devices rely on quantum dots being in resonance with each other and with the cavities they are embedded in. The authors developed a technique based on temperature tuning to spectrally align different quantum dots located on the same chip. The technique allows for up to 1.8 nm reversible on-chip quantum dot tuning.
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81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.70.Qs Photonic bandgap materials
78.67.Hc Quantum dots

Robust functionalization of amorphous cadmium sulfide films using z-lift amplitude modulated atomic force microscopy-assisted electrostatic nanolithography

Ivan Dolog, Robert R. Mallik, and Sergei F. Lyuksyutov

Appl. Phys. Lett. 90, 213111 (2007); http://dx.doi.org/10.1063/1.2742910 (3 pages) | Cited 3 times

Online Publication Date: 23 May 2007

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A robust technique, based on vertical (z-lift) manipulation of a negatively biased oscillating atomic force microscope cantilever, is developed which creates raised columnar nanostructures with high aspect ratios (up to 40 nm high/150 nm wide) on amorphous CdS thin films. The nanostructures’ height (8–40 nm) is proportional to z-lift of the tip and correlates with CdS film thickness. An in-house modified electric force microscopy is used to record the associated surface charge distribution which is found to be opposite to that of the tip.
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81.16.Nd Micro- and nanolithography
68.37.Ps Atomic force microscopy (AFM)
81.07.Bc Nanocrystalline materials

Raman scattering by thin film nanomosaic rutile TiO2

Carolyn Rubin Aita

Appl. Phys. Lett. 90, 213112 (2007); http://dx.doi.org/10.1063/1.2742914 (3 pages) | Cited 12 times

Online Publication Date: 23 May 2007

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Thin TiO2 films with rutile short-range atomic order grown at room temperature have a nanostructure of rectangular domains based on a faulted rutile structure. Raman scattering by nanomosaic rutile in single layer TiO2 and TiO2–Al2O3 nanolaminate films is reported here. In all architectures, the Eg phonon mode frequency is similar to bulk but the A1g mode frequency is significantly blueshifted. These results are different from published Raman scattering spectra of other nanocrystalline rutile TiO2. A model for nanomosaic rutile is presented in which TiO6 octahedra in the faulted regions are severely distorted with a lengthened equatorial Ti–O bond and a shortened apical Ti–O bond. The observed A1g mode blueshift is a consequence of the shortened apical bond.
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78.30.Hv Other nonmetallic inorganics
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Hk Nanocrystals
63.20.-e Phonons in crystal lattices
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.55.-a Thin film structure and morphology

In situ treatment of a scanning gate microscopy tip

A. E. Gildemeister, T. Ihn, M. Sigrist, K. Ensslin, D. C. Driscoll, and A. C. Gossard

Appl. Phys. Lett. 90, 213113 (2007); http://dx.doi.org/10.1063/1.2742314 (3 pages) | Cited 4 times

Online Publication Date: 24 May 2007

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In scanning gate microscopy, where the tip of a scanning force microscope is used as a movable gate to study electronic transport in nanostructures, the shape and magnitude of the tip-induced potential are important for the resolution and interpretation of the measurements. Contaminations picked up during topography scans may significantly alter this potential. The authors present an in situ high-field treatment of the tip that improves the tip-induced potential. A quantum dot was used to measure the tip-induced potential.
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07.79.Lh Atomic force microscopes

Continuous near-infrared-to-ultraviolet lasing from II-VI nanoribbons

J. A. Zapien, Y. K. Liu, Y. Y. Shan, H. Tang, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 90, 213114 (2007); http://dx.doi.org/10.1063/1.2736286 (3 pages) | Cited 11 times

Online Publication Date: 24 May 2007

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The authors show that II-VI nanoribbons are capable of room-temperature lasing covering the complete spectral range from near infrared (NIR) to ultraviolet (UV). This is accomplished by simply using nanoribbons of two ternary compositions, namely, CdSXSe1−X and ZnYCd1−YS. Under optical pumping, CdSXSe1−X nanoribbons lase from NIR (710 nm) to green (510 nm) as X changes from 0 to 1, while ZnYCd1−YS nanoribbons lase from green (510 nm) to UV (340 nm) as Y varies from 0 to 1. Furthermore, lasing control shows fine-tuning via composition changes that overlap thermally induced tuning. This demonstrates that II-VI materials can enable lasing at any selected wavelength between 710 and 340 nm with continuous tuning capabilities.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
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