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2 Oct 2006

Volume 89, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 142101 (2006); http://dx.doi.org/10.1063/1.2358202 (3 pages)

H. C. Lin, P. D. Ye, Y. Xuan, G. Lu, A. Facchetti, and T. J. Marks
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Ultraviolet photoluminescence from 3C-SiC nanorods

Ligong Zhang, Weiyou Yang, Hua Jin, Zhuhong Zheng, Zhipeng Xie, Hezhuo Miao, and Linan An

Appl. Phys. Lett. 89, 143101 (2006); http://dx.doi.org/10.1063/1.2358313 (3 pages) | Cited 22 times

Online Publication Date: 2 October 2006

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An intensive sharp photoluminescence at 3.3 eV is observed from single-crystal 3C-SiC nanorods. Structural characterization reveals that the nanorods contain a fairly large amount of threefold stacking faults. We tentatively attribute the emission to these stalking faults, which structurally resemble 6H-SiC nano-layers of 1.5 nm embedded in a 3C-SiC matrix. The emission mechanism is discussed in terms of spontaneous polarization at the stacking faults.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
61.72.Nn Stacking faults and other planar or extended defects
61.46.Hk Nanocrystals

Space-charge-limited current in nanowires depleted by oxygen adsorption

Y. Gu and L. J. Lauhon

Appl. Phys. Lett. 89, 143102 (2006); http://dx.doi.org/10.1063/1.2358316 (3 pages) | Cited 26 times

Online Publication Date: 2 October 2006

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The effects of oxygen adsorption on the conductivity and carrier transport mechanisms in CdS nanowires were established through variable temperature electrical transport and photoconductivity measurements. n-type CdS nanowires were found to be significantly less conductive in the ambient air than in the vacuum due to electron depletion induced by adsorbed oxygen. The current-voltage characteristics of depleted nanowires exhibited a power law behavior consistent with space-charge-limited conduction in the presence of traps. Analysis of the voltage and temperature dependencies of the space-charge-limited current showed that the nanowire surface traps are exponentially distributed in energy with a characteristic depth of ∼ 0.28±0.04 eV.
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73.63.Nm Quantum wires
72.20.Ht High-field and nonlinear effects
72.40.+w Photoconduction and photovoltaic effects
68.43.Mn Adsorption kinetics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Characterizing the nanoacoustic superlattice in a phonon cavity using a piezoelectric single quantum well

Kung-Hsuan Lin, Chieh-Feng Chang, Chang-Chi Pan, Jen-Inn Chyi, Stacia Keller, Umesh Mishra, Steven P. DenBaars, and Chi-Kuang Sun

Appl. Phys. Lett. 89, 143103 (2006); http://dx.doi.org/10.1063/1.2358321 (3 pages) | Cited 4 times

Online Publication Date: 2 October 2006

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We have experimentally and theoretically investigated, both in the time domain and in the frequency domain, the characteristics of a nanoacoustic mirror, which is a 17-period 8 nm/8 nm Al0.7Ga0.3N/Al0.2Ga0.8N superlattice and its first phononic band gap frequency is centered at ∼ 280 GHz. By using a femtosecond optical pulse to excite and detect the nanoacoustic strain pulses with an In0.2Ga0.8N single quantum well, we directly measured the transient dynamics of the acoustic nanowaves inside a phonon cavity composed of the studied nanoacoustic mirror. The phase-resolved reflection transfer function of the phononic band gap superlattice and the properties of the nanophononic cavity have been experimentally obtained and investigated.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
62.65.+k Acoustical properties of solids
78.47.-p Spectroscopy of solid state dynamics
42.30.Lr Modulation and optical transfer functions

Electric-field-induced low temperature oxidation of tungsten nanowires

C. Nowak, R. Kirchheim, and G. Schmitz

Appl. Phys. Lett. 89, 143104 (2006); http://dx.doi.org/10.1063/1.2358203 (3 pages) | Cited 7 times

Online Publication Date: 3 October 2006

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Experiments on the room temperature oxidation of tip-shaped tungsten nanowires under an externally applied electric field are reported, yielding the controlled formation of tungsten oxide layers up to several tens of nanometers thick in the high field region at the tip of the nanowires. The initially very fast oxidation reaction is observed to virtually terminate at a field dependent state, defined by a critical field strength of 1.15(2)×109 V/m. Since electric fields of the order of 109 V/m are easily obtained, the observed effect may influence the chemical stability of nanoscaled systems significantly when used in ambient atmosphere.
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81.65.Mq Oxidation
68.37.Lp Transmission electron microscopy (TEM)
81.05.Bx Metals, semimetals, and alloys

Self-selected apex angle distribution in aluminum nitride and indium nitride nanotips

Surojit Chattopadhyay, Kuei-Hsien Chen, Shih-Chen Shi, Chien-Ting Wu, Cheng-Hsuan Chen, and Li-Chyong Chen

Appl. Phys. Lett. 89, 143105 (2006); http://dx.doi.org/10.1063/1.2358291 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2006

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A “step-edge” model has been proposed to explain the growth of solid nanotips of aluminum nitride (AlN) and indium nitride (InN) grown by thermal and metal organic chemical vapor depositions, respectively. The model predicts a set of apex angles that solid AlN and InN nanotips can have. A statistical distribution of the apex angle in InN nanotips indicates the discrete set of apex angles and its probability of nucleation.
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81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Highly ordered graphene for two dimensional electronics

J. Hass, R. Feng, T. Li, X. Li, Z. Zong, W. A. de Heer, P. N. First, E. H. Conrad, C. A. Jeffrey, and C. Berger

Appl. Phys. Lett. 89, 143106 (2006); http://dx.doi.org/10.1063/1.2358299 (3 pages) | Cited 118 times

Online Publication Date: 3 October 2006

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With expanding interest in graphene-based electronics, it is crucial that high quality graphene films be grown. Sublimation of Si from the 4H-SiC(0001) (Si-terminated) surface in ultrahigh vacuum is a demonstrated method to produce epitaxial graphene sheets on a semiconductor. In this letter the authors show that graphene grown from the SiC(000math) (C-terminated) surface are of higher quality than those previously grown on SiC(0001). Graphene grown on the C face can have structural domain sizes more than three times larger than those grown on the Si face while at the same time reducing SiC substrate disorder from sublimation by an order of magnitude.
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81.05.U- Carbon/carbon-based materials
64.70.Hz Solid-vapor transitions
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

High ionic conductivity in ultrathin nanocrystalline gadolinia-doped ceria films

Hong Huang, Turgut M. Gür, Yuji Saito, and Fritz Prinz

Appl. Phys. Lett. 89, 143107 (2006); http://dx.doi.org/10.1063/1.2358851 (3 pages) | Cited 30 times

Online Publication Date: 3 October 2006

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High ionic conductivities were observed in ultrathin nanocrystalline gadolinia-doped ceria (GDC) films with thicknesses comparable to the grain size (20–50 nm). Conductivities were determined to be effectively three to four orders of magnitude higher relative to those of thicker films (>500 nm). The distinct properties in ultrathin GDC films were attributed to the reduction of cross grain boundary resistance and the segregation of the Gd dopants in the vicinity of grain boundaries.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
73.61.Ng Insulators
61.72.Mm Grain and twin boundaries
68.60.Wm Other nonelectronic physical properties
64.75.-g Phase equilibria

Bend loss for channel plasmon polaritons

Valentyn S. Volkov, Sergey I. Bozhevolnyi, Eloise Devaux, and Thomas W. Ebbesen

Appl. Phys. Lett. 89, 143108 (2006); http://dx.doi.org/10.1063/1.2358953 (3 pages) | Cited 18 times

Online Publication Date: 3 October 2006

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Using near-field optical microscopy, the authors investigate propagation of channel plasmon polaritons excited in the wavelength range of 1425–1640 nm along smoothly bent and split V-shaped grooves milled in a gold film. We find that for 0.6-μm-wide and 1.1-μm-deep grooves bent with the smallest curvature radius of ≅ 0.83 μm, the double bend (for S bends) and splitting (for Y splitters) losses decrease for longer wavelengths approaching (in the wavelength range of 1600–1640 nm) the levels of ∼ 0 and 0.5 dB, respectively.
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78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Electrostatically actuated resonance of amorphous silicon microresonators in water

T. Adrega, V. Chu, and J. P. Conde

Appl. Phys. Lett. 89, 143109 (2006); http://dx.doi.org/10.1063/1.2358215 (3 pages) | Cited 9 times

Online Publication Date: 4 October 2006

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The resonance of electrostatically actuated amorphous silicon microbridges immersed in de-ionized water is characterized. It is shown that under correct actuation conditions resonance can be measured in water without electrolysis or electrode screening. The resonance frequency of these nonpassivated structures is also studied in air and under vacuum for microbridges with different lengths. When the operating medium is changed from vacuum to air, the resonance frequency decreases by 5% and the quality factor decreases from approximately 1000 to 100. Operation in de-ionized water produces a 60% shift in resonance frequency to lower values and the quality factor decreases to 10.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Electrical conductance and breakdown in individual CNx multiwalled nanotubes

Hilary J. Burch, Julia A. Davies, Elisabetta Brown, Ling Hao, Sonia Antoranz Contera, Nicole Grobert, and J. F. Ryan

Appl. Phys. Lett. 89, 143110 (2006); http://dx.doi.org/10.1063/1.2358308 (3 pages) | Cited 10 times

Online Publication Date: 4 October 2006

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Doping of carbon nanotubes with nitrogen during growth strongly modifies their electronic structure through n-type doping. This provides the possibility of producing nanotubes with high conductances, independent of tube chirality. To date, electrical measurements on individual nitrogen-doped multiwalled nanotubes (CNx MWNTs) have reported surprisingly low conductances ( ∼ 0.01G0). Here the authors present high conductance (1.0±0.3G0) measurements at low bias for individual CNx MWNTs. Conductance increases linearly with voltage at a rate of 0.7±0.2G0/V until the threshold for electrical breakdown is reached. Discrete current steps of 20±10 μA are then observed.
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73.63.Fg Nanotubes
61.46.Fg Nanotubes

Emission property of carbon nanotube with defects

Gu Wei

Appl. Phys. Lett. 89, 143111 (2006); http://dx.doi.org/10.1063/1.2358955 (3 pages) | Cited 9 times

Online Publication Date: 4 October 2006

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Based on the density of states obtained by theoretical calculation, electron transport mechanism of carbon nanotube is studied for field emission applications. This letter focuses on how Stone-Wales defect and vacancy-related defect affect carbon nanotube’s emission property. The influence is presented in the form of electron traces. The result shows that Stone-Wales defects reduce carbon nanotube’s emission current, while vacancy-related defects give rise to it. This phenomenon can be expressed by adding a defective effect coefficient kd into the classical Fowler-Nordheim formula. Detailed relationship between kd and defect type and number is also presented.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.Fg Nanotubes
61.46.Fg Nanotubes

Three-dimensional observation of nanoscopic precipitates in an aluminum alloy by microtomography with Fresnel zone plate optics

H. Toda, K. Uesugi, A. Takeuchi, K. Minami, M. Kobayashi, and T. Kobayashi

Appl. Phys. Lett. 89, 143112 (2006); http://dx.doi.org/10.1063/1.2359288 (3 pages) | Cited 14 times

Online Publication Date: 4 October 2006

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Microtomography combined with hard x-ray imaging microscopy has been employed to observe nanoscopic features in a material, which has, to date, only been done by the transmission electron microscopy (TEM). Here, the authors show a characteristic microstructure in an aluminum alloy, such as a slant gap between growing precipitates that impinge on each other due to the presence of a solute-depleted zone. Such observation is not possible by conventional projection microtomography even using the highest resolution available. It would appear that the present technique has a unique potential to observe nanoscopic features inside materials that are several orders of magnitude thicker than TEM specimens.
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61.72.-y Defects and impurities in crystals; microstructure
61.46.-w Structure of nanoscale materials
68.37.Yz X-ray microscopy
81.30.Mh Solid-phase precipitation

Confined optical modes and amplified spontaneous emission from a microtube cavity formed by vacuum assisted filtration

S. Balakrishnan, Y. Gun’ko, Yu. P. Rakovich, J. F. Donegan, T. S. Perova, and R. A. Moore

Appl. Phys. Lett. 89, 143113 (2006); http://dx.doi.org/10.1063/1.2356691 (3 pages) | Cited 2 times

Online Publication Date: 4 October 2006

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The authors demonstrate a new route to the fabrication of individual aluminosilicate microtubes that can act as micron-scale optical cylindrical resonators. The microtubes were prepared using a simple vacuum assisted wetting and filtration through a microchannel glass matrix. Microphotoluminescence spectra of the microtube cavity show sharp resonant modes with quality factors up to 3200. A strong reduction of the emission decay time at high excitation power confirms the occurrence of amplified spontaneous emission from a single microtube.
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42.79.-e Optical elements, devices, and systems

In situ investigation of the island nucleation of Ge on Si(001) using x-ray scattering methods

T. U. Schülli, M.-I. Richard, G. Renaud, V. Favre-Nicolin, E. Wintersberger, and G. Bauer

Appl. Phys. Lett. 89, 143114 (2006); http://dx.doi.org/10.1063/1.2358300 (3 pages) | Cited 15 times

Online Publication Date: 5 October 2006

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The growth of Ge on Si(001) is investigated in situ at 500 and 600 °C, combining grazing incidence diffraction, multiple wavelength anomalous diffraction, and small angle scattering. This allows probing simultaneously the island shape, strain state, composition, and the transition from wetting layer to island growth. At 500 °C no intermixing occurs. The wetting layer is found to decrease by one atomic layer at the onset of island nucleation. At 600 °C interdiffusion plays an important role in strain relaxation leading to a more stable wetting layer. Small angle scattering yields the island morphology and shows the transition from pyramids to multifacetted domes.
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81.05.Cy Elemental semiconductors
78.70.Ck X-ray scattering
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Fx Diffusion; interface formation

Rapid nanopatterning of a Zr-based metallic glass surface utilizing focused ion beam induced selective etching

Noritaka Kawasegi, Noboru Morita, Shigeru Yamada, Noboru Takano, Tatsuo Oyama, Kiwamu Ashida, Jun Taniguchi, Iwao Miyamoto, Sadao Momota, and Hitoshi Ofune

Appl. Phys. Lett. 89, 143115 (2006); http://dx.doi.org/10.1063/1.2360181 (3 pages) | Cited 4 times

Online Publication Date: 6 October 2006

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A simple and rapid method is proposed for nanoscale patterning on a metallic glass surface using focused ion beam irradiation followed by wet etching. It was found that the etch rate of a metallic glass surface irradiated with Ga+ ions could be drastically changed, and rapid patterning was possible with this method. Cross-sectional transmission electron microscopy observation reveals that the metallic glass substrate maintains an amorphous phase following irradiation. Etching enhancement was not observed for irradiation with Ar+ ions. The results indicate that enhancement of etching results from the presence of implanted Ga+ ions rather than a change in crystallography.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
61.80.Jh Ion radiation effects
61.72.up Other materials
61.43.Fs Glasses
68.37.Lp Transmission electron microscopy (TEM)

Determination of free carrier density and space charge layer variation in nanocrystalline In3+ doped tin oxides using Fourier transforminfrared spectroscopy

Christina Drake, Sameer Deshpande, and Sudipta Seal

Appl. Phys. Lett. 89, 143116 (2006); http://dx.doi.org/10.1063/1.2360185 (3 pages) | Cited 8 times

Online Publication Date: 6 October 2006

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A correlation between the surface reactions and the electrical response of doped nano-metal-oxide-semiconductors exposed to reducing gas is established using Fourier transform infrared (FTIR) spectroscopy. The effect of processing temperature on the microstructure evolution and the electronic conduction of the nanocrystalline In–SnO2 is presented. Variation in the charge carrier density is correlated to the solid/gas reaction of In–SnO2 in the nanodomain using the Drude-Zener theory including Spitzer and Fan’s [Phys. Rev. 99, 1893 (1955) ] correction to accommodate for the quantum effects. Higher gas sensitivity for nanocrystalline size less than twice the space charge layer thickness is observed using in situ FTIR.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Jp Dielectric breakdown and space-charge effects
72.20.-i Conductivity phenomena in semiconductors and insulators
78.30.Hv Other nonmetallic inorganics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.46.Hk Nanocrystals

Tip-enhanced fluorescence microscopy of high-density samples

Changan Xie, Chun Mu, Jonathan R. Cox, and Jordan M. Gerton

Appl. Phys. Lett. 89, 143117 (2006); http://dx.doi.org/10.1063/1.2358122 (3 pages) | Cited 2 times

Online Publication Date: 6 October 2006

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High-density samples of fluorescent quantum dots (QDs) were imaged using an apertureless near-field optical microscopy technique. QD fluorescence was modulated by oscillating a silicon atomic force microscope tip above an illuminated sample and a lock-in amplifier was used to suppress background from the excitation laser. Spatial resolution near 10 nm and a peak signal-to-noise ratio (SNR) of ∼ 60 were achieved. Individual QDs within high-density ensembles were still easily resolved (SNR>5) at a density of 14 QDs/μm2. These results have favorable implications for the eventual nanoscale imaging of viable biological systems, such as cellular membranes.
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07.79.Fc Near-field scanning optical microscopes
78.67.Hc Quantum dots
78.55.-m Photoluminescence, properties and materials

Detection of phospholipid-carbon nanotube translocation using fluorescence energy transfer

Sijie Lin, Gayatri Keskar, Yonnie Wu, Xi Wang, Andrew S. Mount, Stephen J. Klaine, Jessica M. Moore, Apparao M. Rao, and Pu Chun Ke

Appl. Phys. Lett. 89, 143118 (2006); http://dx.doi.org/10.1063/1.2360228 (3 pages) | Cited 18 times

Online Publication Date: 6 October 2006

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Single-walled carbon nanotubes (SWNTs) and lysophospholipids readily assemble into supramolecular complexes in aqueous solutions. Upon light excitation the fluorescence of rhodamine-labeled lysophospholipids was redshifted and quenched due to the optical absorption of the SWNTs. Utilizing fluorescence energy transfer, the authors detected the translocation and disassembly of SWNT complexes in MCF breast cancer cells. These lipid-coated SWNT complexes enable drugs to be delivered at an effective dose and their subsequent release to be monitored in real time.
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81.16.Dn Self-assembly
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.16.D- Membranes, bilayers, and vesicles
87.85.J- Biomaterials
87.17.-d Cell processes
87.15.M- Spectra of biomolecules

Effect of aggregation on thermal conduction in colloidal nanofluids

Ravi Prasher, William Evans, Paul Meakin, Jacob Fish, Patrick Phelan, and Pawel Keblinski

Appl. Phys. Lett. 89, 143119 (2006); http://dx.doi.org/10.1063/1.2360229 (3 pages) | Cited 100 times

Online Publication Date: 6 October 2006

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Using effective medium theory the authors demonstrate that the thermal conductivity of nanofluids can be significantly enhanced by the aggregation of nanoparticles into clusters. Predictions of the effective medium theory are in excellent agreement with detailed numerical calculation on model nanofluids involving fractal clusters and show the importance of cluster morphology on thermal conductivity enhancements.
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66.25.+g Thermal conduction in nonmetallic liquids
82.70.Dd Colloids

Electroluminescence mapping of CuGaSe2 solar cells by atomic force microscopy

Manuel J. Romero, C.-S. Jiang, J. Abushama, H. R. Moutinho, M. M. Al-Jassim, and R. Noufi

Appl. Phys. Lett. 89, 143120 (2006); http://dx.doi.org/10.1063/1.2360230 (3 pages) | Cited 4 times

Online Publication Date: 6 October 2006

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The authors report on the observation of electroluminescence (EL) in CuGaSe2 solar cells using tapping-mode atomic force microscopy based on tuning-fork sensors. Individually injected current pulses are seen during intermittent contact driven by an external bias applied to the conducting tip. It follows that EL can be stimulated when the solar cell is forward biased during the contact cycle. Local L-V characteristics show evidence for EL, with a threshold voltage of 3.0–3.7 V. Mapping of the photon emission suggests that grain boundaries effectively isolate grain interiors, which behave as individual light-emitting diodes.
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84.60.Jt Photoelectric conversion

Observation of numerous E2 mode phonon replicas in the room temperature photoluminescence spectra of ZnO nanowires: Evidence of strong deformation potential electron-phonon coupling

S. Ramanathan, S. Bandyopadhyay, L. K. Hussey, and M. Muñoz

Appl. Phys. Lett. 89, 143121 (2006); http://dx.doi.org/10.1063/1.2360255 (3 pages) | Cited 4 times

Online Publication Date: 6 October 2006

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See Also: RETRACTION

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The authors report the observation of numerous (>20) phonon replica peaks in the room temperature photoluminescence spectrum of ZnO nanowires embedded in 50 nm diameter pores of an anodic alumina film. The peaks are spaced in energy by ∼ 54 meV, which is the energy of a nonpolar phonon with symmetry E2 in ZnO. These peaks are possibly caused by resonant phonon-assisted decay of photoexcited electrons to an impurity band, followed by radiative recombination. These results suggest that even though ZnO is strongly polar, deformation potential coupling to a nonpolar phonon mode may be stronger than Fröhlich coupling to polar phonon modes.
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78.67.Lt Quantum wires
78.55.Et II-VI semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.38.-k Polarons and electron-phonon interactions
71.55.Gs II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High performance thin film bulk acoustic resonator covered with carbon nanotubes

M. Dragoman, A. Muller, D. Neculoiu, D. Vasilache, G. Konstantinidis, K. Grenier, D. Dubuc, L. Bary, R. Plana, and E. Flahaut

Appl. Phys. Lett. 89, 143122 (2006); http://dx.doi.org/10.1063/1.2358838 (3 pages) | Cited 2 times

Online Publication Date: 6 October 2006

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This letter presents experimental results concerning a thin film bulk acoustic wave resonator realized on a thin GaN membrane and covered with a thin film of double walled carbon nanotube mixture. The quality factor was measured before and after the coating of the resonator with the nanotube thin film. The quality factor has increased more than ten times when the resonator was coated with nanotubes, due to their high elasticity modulus and low density, which confers a much higher acoustic impedance of the resonator electrodes and thus confines much better the longitudinal acoustic standing waves inside the resonator.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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